GB1576720A

GB1576720A - Catalytic cracking with reduced emission of noxious gases

Info

Publication number: GB1576720A
Application number: GB52791/76A
Authority: GB
Original assignee: Standard Oil Co
Current assignee: Standard Oil Co
Priority date: 1975-12-19
Filing date: 1976-12-17
Publication date: 1980-10-15
Also published as: FR2335581B1; CA1110567A; AU2068176A; FR2335581A1; BE849637A; AU499575B2

Description

(54) CATALYTIC CRACKING WITH REDUCED EMISSION OF NOXIOUS GASES (71) We, STANDARD OIL COMPANY, a corporation organised and existing under the laws of the State of Indiana, United States of America, of 200 East Randolph Drive, Chicago, Illinois, 60601, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a cyclic, fluidized catalytic cracking process which is suitable for use with sulfur-containing hydrocarbon feedstocks and which involves a marked diminution in the emission of sulfur oxides in the regenerator stack gases.

Cracking catalyst which has become relatively inactive due to deposition of carbonaceous deposits, commonly called "coke", during the cracking of hydrocarbons in the reaction zone is continuously withdrawn from the reaction zone. Such spent catalyst from the reaction zone is passed to a stripping zone where strippable carbonaceous deposits, namely hydrocarbons, are stripped from the catalyst which in turn is passed to a regeneration zone where the activity of the catalyst is restored by removing the non-strippable carbonaceous deposits by burning the coke in oxygen-containing gas to form carbon monoxide and carbon dioxide. Hot regenerated catalyst is then continuously returned to the reactor to repeat the cycle.

In catalytic cracking, a problem arises from the incomplete combustion of carbon monoxide to carbon dioxide in the regeneration zone, leaving a significant amount of carbon monoxide in the regeneration zone flue gases. Apart from the undesirability of discharge of carbon monoxide to the atmosphere, carbon monoxide and residual oxygen in the regeneration zone flue gases tend to react and thereby to cause burning in ducts and flues in the plant and damage to such structures by heating at excessive temperatures.

Further, when high-sulfur feedstocks, that is, petroleum hydrocarbon fractions containing organic sulfur compounds, are charged to a fluid-type catalytic cracking unit, the coke deposited on the catalyst contains sulfur. During regeneration of the coked, deactivated catalyst, the coke is burned from the catalyst surfaces; and, in this combustion process, the sulfur present is converted to sulfur dioxide, together with a minor proportion of sulfur trioxide, and thus included in the regeneration zone flue gas effluent stream. When cracking a high-sulfur feedstock, emissions of sulfur oxides are often in the range of about 1200 parts per million.

Pollution control standards have been developed for the emission of carbon monoxide and particulate matter and are expected to be considered soon for other emissions, such as the sulfur oxides, particularly sulfur dioxide. Consequently, much attention is being devoted to reducing the level of emissions of various combustion products and particulates from regeneration zone effluent streams associated with petroleum cracking units. It is necessary that the method chosen for reducing such emissions should be effective without lowering the activity and selectivity of the cracking catalyst. It is likewise necessary that the method chosen should not replace one form of undesirable emission with another problem, for example, an increase in particulate emission or operating costs. In view of these considerations, a highly desirable approach to a reduction in the emission of sulfur oxides from petroleum cracking units lies in the use of a cracking catalyst which is modified to minimize emissions of sulfur oxides, while maintaining catalyst activity, stability, and resistance to attrition, under conventional cracking conditions in either existing or new cracking units.

Although metals are generally avoided in cracking catalysts and it is considered problematical to crack metal-containing stocks in the presence of a cracking catalyst, South African Patent No. 7924/72 and its later issued counterpart, U.S. Patent No. 3,909,392, discussed in greater detail below, disclose the use in conjunction with cracking catalysts of combustion catalysts or promoters within the regeneration zone, which includes a metallic bar, mesh network, or screen in combustion zone; and fluidizable metal compounds, particularly powdered oxides of transition group metal, for example, ferric oxide, manganese dioxide, and rare earth oxides, which are added to the catalyst charge or confined within the regenerator vessel. Belgian Patent No.826,266 discloses a method very similar to that of U.S.

Patent No.3,909392, which involves a catalytic cracking catalyst in physical association with a carbon monoxide-oxidation promoting catalyst of a metal having an atomic number of at least 20 and mentions metals from Groups IB, IIB, and III to VIII of the Periodic Table of the elements, in particular platinum, palladium, rhodium, molybdenum, tungsten, copper, chromium, nickel, manganese, cobalt, vanadium, iron, cerium, ytterbium, or uranium as useful oxidation promoters. Further, U.S. Patent No. 3,808,121 discloses the regeneration of a cracking catalyst in the presence of a carbon monoxide oxidation catalyst which is retained in the regeneration zone.

Netherlands Patent Application No.7,412,423 discloses that a cracking catalyst containing less than 100 parts per million, calculated as metal, based on total catalyst, of at least one metal component consisting of a metal from Period 5 or 6 of Group VIII of the Periodic Chart, rhenium, or a compound thereof, showed particularly spectacular reductions in the carbon monoxide content in flue gases from catalytic cracking catalysts. This latter patent also discloses a molecular sieve-type cracking catalyst which is prepared in the sodium form, ion-exchanged with ammonium ions, and then impregnated with rare earth metals.

With regard to sulfur oxide emissions, although various methods for processing flue gas have been devised, for example, washing or scrubbing, chemical absorption, neutralization, and chemical reaction or conversion, all such methods for the removal of sulfur oxides require extensive and expensive auxiliary equipment, thus increasing both operating and capital costs. An approach set forth in U.S. Patent No. 3,699,037 contemplates the addition of at least a stoichiometric amount of a calcium or magnesium compound to the cracking cycle in relation to the amount of sulfur deposition on the catalyst. This added material is intended to react with sulfur oxides and then, being in a finely subdivided condition, exit from the cracking cycle as particulate matter in the regeneration zone flue gas stream. Continued addition of such material obviously increases operating costs. Similarly, U.S. Patents Nos.

3,030,300, and 3,030,314 disclose a catalytic cracking process which involves adding continuously to a moving bed cracking process cycle one or more compounds of boron, alkali metals and alkaline earth metals, so as thereby provided catalyst particles which have increased resistance against impact breakage and surface abrasion and which comprise a siliceous catalyst particle having a microporous, catalytically active core which is provided with an adherent, protective coating of a glaze comprising silica and one or more compounds of boron, alkali metals or alkaline earth metals, or any mixture thereof.

U.S. Patent No. 3,835,031 discloses a cyclic, fluidized catalytic cracking process which provides reduced emissions of sulfur oxides in the regenerator stack gases. The method is operated with a catalyst which comprises a molecular sieve in a silica-alumina matrix and which is impregnated with one or more Group IIA metal oxides. U.S. Patents Nos.

3,388,077; 3,409,390; and 3,849,343 disclose a method of effecting the conversion of a noxious waste gas stream containing carbon monoxide and sulfur oxides, which comprises contacting the stream with a catalytic composite of a porous refractory carrier material, a catalytically active metallic component, for example a platinum group metal, and at least one alkaline earth component chosen from the group consisting of calcium, barium, and strontium.

According to one embodiment of the present invention there is provided in a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing from 0.2 to 6 weight percent sulfur as organic sulfur compounds wherein (i) said feedstock is subjected to cracking in a reaction zone with fluidized particles of a molecular sieve-type cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable sulfur-containing carbonaceous deposits from the stripped catalyst particles with an oxygen containing gas; and (iv) regenerated catalyst particles are separared from regeneration zone effluent and recycled to the reaction zone, a method for reducing emissions of sulfur oxides in the regeneration zone effluent has stream which comprises: (a) adding fluidizable particles, other than said molecular sieve-type cracking catalyst, which contain a metallic reactant, to the cracking catalyst during the fluid catalytic cracking process to produce a mixture of particles which contains from 10 to 99.9975 weight percent of molecular sieve-type cracking catalyst, wherein the metallic reactant consists of at least one free or combined metallic element consisting of magnesium calcium, strontium or barium, and wherein the amount of said metallic reactant in the mixture of particle is sufficient to effect the absorption of at least 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (b) cracking said feedstock at a temperature within the range of from 850" to 1 ,2000F, inclusive; (c) stripping volatile deposits from the mixture of particles, which is separated from the reaction zone, with a stripping gas which contains steam at a temperature of from 950" to 1,200"F, wherein the weight ratio of steam to said cracking catalyst is from 0.0005 to 0.025; (d) regenerating said stripped mixture of particles at a temperature of from 1,050 to 1,450"F; (e) absorbing with the mixture of particles at least 50% of the sulur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (f) conveying the mixture of particles containing said absorbed sulfur oxides from the regeneration zone to the reaction zone; (g) withdrawing an effluent gas stream, from the regeneration zone containing molecular oxygen and having a low concentration- of sulfur oxides; and (h) withdrawing substantially all of said absorbed sulfur oxides as a sulfur-containing gas from the reaction and/or stripping zone.

In another embodiment of the present invention there is provided in a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing from 0.2 to 6 weight percent sulfur as organic sulfur compounds, wherein (i) said feedstock is subjected to cracking in a reaction zone with fluidized particles of a molecular sieve-type cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable sulfur-containing carbonaceous deposits from the stripped catalyst particles with an oxygen containing gas; and (iv) regenerated catalyst particles are separated from regeneration zone effluent and recycled to the reaction zone, a method for reducing emissions of sulfur oxides in the regeneration zone effluent gas stream which comprises: (a) incorporating into said catalyst particles at least one metal in elemental or combined form consisting of magnesium, calcium, strontium, or barium or any mixture thereof, by separately introducing at least one compound of said metal or metals into the process cycle, wherein said metal is incorporated in sufficient amount to effect the absorption of at least 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (b) cracking said feedstock at a temperature within the range of from 850" to 1,200"F inclusive; (c) stripping volatile deposits from the deactivated catalyst at a temperature of from 850" to 1,2000F with a stripping gas which contains steam, wherein the ratio of steam to said cracking catalyst is from 0.0005 to 0.025; (d) regenerating said stripped deactivated catalyst at a temperature of from 1,050 to 1,450"F; (e) absorbing with the catalyst particles containing said metal at least 50neo of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (f) conveying the catalyst particles containing said absorbed sulfur oxides from the regeneration zone to the reaction zone; (g) withdrawing an effluent gas stream from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides; and (h) withdrawing substantially all of said absorbed sulfur oxides as a sulfur-containing gas from the reaction and/or stripping zone.

In a preferred embodiment, the molecular sieve-type catalyst comprises a cracking catalyst matrix containing crystalline aluminosilicate distributed throughout said matrix. A compound of the metal or metals of the metallic reactant may be introduced into the process cycle.

The metallic reactant may be incorporated into the molecular sieve-type cracking catalyst, amorphous cracking catalyst or substantially inert solid. Such incorporation can be achieved either before or after the particular substrate is introduced into the cracking process cycle.

Conditions are employed in the cracking process cycle in one embodiment which are such that a stable metal- and sulfur-containing compound forms in the solid particles in the regeneration zone and a sulfur-containing gas is withdrawn from the stripping zone.

In the development of catalysts for the reduction of emissions of sulfur oxides in the flue gases from the regeneration zone of a fluid cracking operation, it is important that such catalysts should exhibit not only the capability initially to perform the specified function but also that they should have the capability to perform satisfactorily for prolonged periods of time. Thus, in the development of such catalysts, attention must be directed to the activity and stability characteristics of the catalysts. Activity in this regard is a measure of a catalyst's ability to reduce the emissions of sulfur oxides in the regeneration zone flue gases at a specified severity level, where the severity level means the conditions used, that is, the temperature, pressure, contact time, etc. The stability of a catalyst is a measure of the ability of the catalyst to maintain the activity characteristics over a specified period of time. Stability refers to the rate of change with time of the activity parameters, with a smaller rate implying a more stable catalyst. The stability should be such that the activity characteristics can be retained during prolonged periods of operation.

These key features are more easily attainable by introducing an effective agent for producing reduced sulfur oxide emissions, in this invention the metallic reactant, into the cracking process cycle and incorporating it into the solid particles in situ, rather than by compositing it with the molecular sieve-type cracking catalyst during manufacture of such cracking catalyst. Introducing the metallic reactant into the cracking process cycle as opposed to compositing it with the molecular sieve-type cracking catalyst during cracking catalyst preparation has been found to result in a greater reduction in sulfur oxide emissions in the regeneration zone flue gases. Adding the metallic reactant to the cracking process cycle is also advantageous in that a larger degree of control is maintained over any potential deleterious effect of the metallic reactant on the cracking reaction as the rate and/or amount of such metallic reactant introduced into the cracking cycle can be varied. Also, such metallic reactant previously composited with the cracking process cycle can be lost as fines during attrition of the cracking catalyst. Adding the metallic reactant to the cracking process cycle and incorporating it into the solid particles in situ allows for maintenance of a desired amount of metallic reactant on the outside or accessible portions of the cracking catalyst.

The improvement of this invention comprises introducing a material containing a metal of the metallic reactant into the cracking process cycle and incorporating the metallic reactant into the solid particles within the cracking process cycle; employing a stripping gas which contains steam; regenerating the stripped, deactivated cracking catalyst at regeneration temperatures in the range where the metal- and sulfur-containing compound in the solid particles is stable; and supplying sufficient oxygen to the regeneration zone in the oxygencontaining regeneration gas stream for flue gases containing molecular oxygen to be withdrawn from the regeneration zone.

The hydrocarbon feedstock for use in the process contains from 0.2 to 6 weight percent of sulfur in the form of organic sulfur compounds. Advantageously, the feedstock contains from about 0.5 to about 5 weight percent sulfur and more advantageously from about 1 to about 4 weight percent sulfur, wherein the sulfur is present in the form of organic sulfur compounds.

The cracking catalyst matrix of the molecular sieve-type cracking catalyst is preferably a combination of at least two materials selected from the group consisting of silica, alumina, thoria, and boria, and more preferably is silica-alumina. This cracking catalyst matrix preferably contains from about 10 to about 65, more preferably from about 25 to about 60 weight percent of alumina; preferably from about 35 to about 90, more preferably from about 35 to about 70 weight percent of silica; and preferably from about 0.5 to about 50, more preferably from about 5 to about 50 weight percent of crystalline aluminosilicate. The molecular sieve-type cracking catalyst makes up preferably from about 10 to about 99.9975, more preferably from about 30 to about 99.99, and most preferably from about 90 to 99.9 weight percent of the solid particles.

The metallic reactant consists of at least one free or combined metallic element which is selected from magnesium, calcium. strontium and barium. Consequently, the metallic reactant may be selected from magnesium. calcium, strontium and barium, their compounds and mixtures thereof. More preferably. the metallic reactant is selected from magnesium and calcium.

The oxide or oxides of the metallic element or elements of the metallic reactant are believed to be primarily responsible for the absorption of sulfur oxides in the regeneration zone. Consequently. it is advantageous to introduce the metallic element or elements of the metallic reactant into the catalytic cracking process cycle in the form of the oxide or oxides. It is sufficient. however. for the practice of this process that one or more suitable metallic elements should be chosen for use as the metallic reactant and introduced into the process cycle. The metallic element or elements of the metallic reactant are activated for the absorption of sulfur oxides in the regeneration zone as a consequence of the process steps of this invention. The activation is believed to involve either a partial or a substantially complete conversion of the metal or metals of the metallic reactant to the corresponding oxide or oxides. This activation is substantially unaffected by the precise manner in which such metallic element or elements may be chemically combined when initially introduced into the process cycle.

The metallic reactant is present in sufficient average amount in the regeneration zone to absorb a major proportion of the sulfur oxides produced by the burning of sulfur-containing carbonaceous deposits therein. At least about 50%, and advantageously more than about 80% of the sulfur oxides produced by such burning are absorbed by the metallic reactant in the regeneration zone. As a result, the concentration of sulfur oxides in the regeneration zone effluent gas stream from this novel process can be maintained at less than about 600-1000 parts per million by volume (ppmv), advantageously at less than about 600 ppmv, and more advantageously at less than about 400 ppmv.

The amount of metallic reactant employed, calculated as the metal or metals, is preferably in the range of from about 25 parts per million to about 7 weight percent, more preferably in the range of from about 0.01 weight percent to about 5 weight percent, and most preferably in the range of from about 0.1 weight percent to about 0.5 weight percent of the solid particles.

Certain individual solids in the solid particles of the method of this invention may contain an amount of the metallic reactant which is greater than the average amount thereof in the solid particles, provided that such certain individual solids are admixed with other individual solids in the solid particles containing a smaller amount of the metallic reactant such that the solid particles contain the above-mentioned average levels of the metallic reactant.

The stripped deactivated catalyst is regenerated at regeneration temperatures in the range where a stable metal- and sulfur-containing compound is formed in the solid particles from the metal in the metallic reactant and sulfur oxide. The regeneration temperature are in the range of from 1,050"F. to 1,4500F., and more preferably in the range of from about 1,1800F.

to about 1,350"F. The hydrocarbon feedstock is cracked at reaction temperatures in the range where the metal- and sulfur-containing compound in the solid particles reacts to form a sulfide of the metal in the metallic reactant. The cracking reaction temperature is in the range of from 850"F. to 1,200"F., and more preferably in the range of from about 870"F. to about 1,100"F. In one embodiment, the strippable deposits are stripped from the deactivated cracking catalyst with a steam-containing gas and at stripping temperatures in the range where the sulfide of the metal in the metallic reactant reacts with water to form hydrogen sulfide gas. The stripping temperatures are in the range of from 850"F. to 1,200"F., and more preferably in the range of from about 870 F. to about 1,000"F. The weight ratio of steamto-molecular sieve-type cracking catalyst being supplied to the stripping zone is in the range of from 0.0005 to 0.025, and more preferably in the range of from about 0.0015 to about 0.0125. The regeneration zone flue gases preferably contain at least 0.01 volume percent and more preferably at least 0.5 volume percent of oxygen in order for the desired reduction of emissions of noxious gas to be achieved.

In one embodiment of this invention, the material containing a metal of the metallic reactant is an oil- or water-soluble or -dispersible compound and the metallic reactant is incorporated into the molecular sieve-type cracking catalyst. In such case, the metallic reactant is incorporated into either the crystalline aluminosilicate or the matrix in the molecular sieve-type cracking catalyst. In this embodiment of this invention, the solid particles may additionally comprise at least one component selected from solids which are substantially inert to the cracking of hydrocarbon feedstock and an amorphous cracking catalyst; and the metallic reactant is incorporated into such component. In this embodiment, the compound which is introduced into the catalytic cracking process cycle, which comprises the cracking reaction zone, the stripping zone and the regeneration zone is preferably a metal salt. Examples include metal diketonates and metal carboxylates having from 1 to 20 carbon atoms. More preferably, such compound is magnesium acetylacetonate.

In another embodiment of this invention, the material containing a metal of the metallic reactant is the metallic reactant in powder form, for example magnesium oxide. In still another embodiment, such material is a composite of the metallic reactant supported on either an amorphous cracking catalyst or a solid which is substantially inert to the cracking reaction.

The cracking catalyst and metallic reactant of the method of this invention serve separate and essential functions. The cracking catalyst serves to catalyse the cracking reaction, while the metallic reactant is substantially inert toward the cracking reaction and has little, if any, adverse effect on the catalytic conversion operation under the conditions employed. With regard to the reduction of sulfur oxides in the regeneration zone flue gas, the solid particles adsorb sulfur oxides in the regeneration zone. The molecular sieve-type cracking catalyst itself often serves as an adsorbent for sulfur oxides. The metallic reactant reacts with the adsorbed sulfur oxides to form a metal- and sulfur-containing compound, in particular, metal sulfates, and specifically alkaline earth sulfates, in the solid particles. Provided that such metal- and sulfur-containing compound is stable under the operating conditions in the regeneration zone, it will be carried on the surfaces of the solid particles to the reaction zone and stripping zone where it is reduced and separated as a sulfur-containing gas, in particular, as hydrogen sulfide.

It is understood that the activity in reducing the emission of sulfur oxides in the regeneration zone flue gases may vary from metal to metal in the classes of those which may serve as a metal in the metallic reactant. Similarly, many of the specific metals which may serve as a metal in the metallic reactant do not necessarily yield equivalent results when compared with other specific metals which may be used in the metallic reactant or when utilized under varying conditions.

The solid particles used in the method of this invention are finely divided and have, for example, an average particle size in the range of from about 20 microns or less to about 150 microns, such that they are in a form suitable for fluidization. Suitable cracking catalyst matrices include those containing silica and/or alumina. Other refractory metal oxides may be employed. limited only by their ability to be effectively regenerated under the chosen conditions. Admixtures of clay-extended aluminas may also be employed. Preferred catalysts include combinations of silica and alumina, admixed with "molecular sieves", also known as zeolites or crystalline aluminosilicates. Suitable cracking catalysts contain a sufficient amount of crystalline aluminosilicates materially to increase the cracking activity of the catalyst, limited only by their ability to be effectively regenerated under the chosen conditions. The crystalline aluminosilicates usually have silica-to-alumina mole ratios of at least about 2: 1, for instance from about 2:1 to 12: 1, preferably from about 4:1 to about 6:1. Cracking catalysts with silica bases having a large proportion of silica, for example, from about 35 to about 90 weight percent silica, and from about 10 to about 65 weight percent alumina are suitable.

Such catalysts may be prepared by any suitable method, such as milling, cogelling, and the like, subject only to provision of the finished catalyst in a physical form capable of fluidization.

Suitable "molecular sieves" include both naturally occurring and synthetic aluminosilicate materials such as faujasite, chabazite, X-type and Y-type aluminosilicate materials, and ultrastable, large-pore crystalline aluminosilicate materials. When admixed with, for example, silica-alumina to provide a petroleum cracking catalyst. the molecular sieve content of the fresh finished catalyst particles is suitably within the range of from about 0.5 to about 50 weight percent, desirably from about 5 to about 50. An equilibrium "molecular sieve" cracking catalyst may contain as little as about 1 weight percent of crystalline material. The crystalline aluminosilicates are usually available or made in sodium form; the sodium component is then usually reduced to as small an amount as possible, generally less than about 0.30 weight percent, through ion-exchange with hydrogen ions, hydrogen-precursors such as ammonium ions, or polyvalent metal ions, including calcium, strontium. barium, following dense catalyst bed is not employed for cracking. In a typical case where riser cracking is employed for the conversion of a gas oil, the throughput ratio, or volume ratio of total feed to fresh feed, may vary from about 1:1 to 3:1. The conversion level may vary from about 40 to about 100 weight percent, and advantageously is maintained above about 60 weight percent, for example, between about 60 and 90 weight percent. By conversion is meant the percentage reduction by weight of hydrocarbons boiling above about 430"F. at atmospheric pressure resulting from the formation of lighter materials or coke. The weight ratio of total cracking catalyst-to-oil in the riser reactor may vary within the range of from about 2 to about 20, inclusive, in order that the fluidized dispersion will have a density within the range of from about 1 to about 20 pounds per cubic foot, inclusive. Desirably, the catalyst-to-oil ratio is maintained within the range of from about 3 to about 20, inclusive preferably from about 3 to about 7. The fluidizing velocity in the riser reactor may range from about 10 to about 100 feet per second. The riser reactor generally has a ratio of length-toaverage diameter of about 25:1. For the production of a typical naphtha product, the bottom section mixing temperature within the riser reactor is advantageously maintained at from about 1,000"F. to about 1,100"F, for vaporisation of the oil feed, and so that the top section exit temperature will be about 950"F. For cracking residues and synthetic fuels, substantially higher temperatures are necessary. Under these conditions, including provision for a rapid separation of spent catalyst from effluent oil vapour, a very short period of contact between the catalyst and oil will be established. Contact time within the riser reactor will generally be within the range of from about 1 to about 15 seconds, and preferably within the range of from about 3 to about 10 seconds. Short contact times are preferred because most of the hydrocarbon cracking occurs during the initial increment of contact time, and undesirable secondary reactions are then avoided. This is especially important if higher product yield and selectivity, including lesser coke production, are to be realized.

A short contact time between catalyst particles and oil vapours may be achieved by various means. For example, catalysts may be injected at one or more points along the length of a lower, or bottom, section of the riser. Similarly, oil feed may be injected at all the points along the length of the lower section of the riser reactor, and a different injection point may be employed for fresh and recycle feed streams. The lower section of the riser reactor may, for this purpose, include up to about 80 percent of the total riser length in order to provide extremely short effective contact times inducive to optimum conversion of petroleum feeds.

Where a dense catalyst bed is employed, provision may also be made for injection of catalyst particles and/or oil feed directly into the dense-bed zone.

While the conversion conditions set forth above are directed to the production of gasoline as fuel for spark-ignition internal combustion engines, the processing scheme may be suitably varied to permit maximum production of heavier hydrocarbon products such as jet fuel, diesel fuel, heating oil and chemicals, in particular, olefins and aromatics.

In the catalytic process, some non-volatile carbonaceous material, or "coke", is deposited on the catalyst particles. Coke comprises highly condensed aromatic hydrocarbons which generally contain a minor amount of hydrogen, say from about 4 to about 10 weight percent.

When the hydrocarbon feedstock contains organic sulfur compounds, the coke also contains sulfur. As coke builds up on the catalyst, the activity of the catalyst for cracking and the selectivity of the catalyst for producing gasoline blending stocks diminishes. The catalyst particles may recover a major proportion of their original capabilities by removal of most of the coke therefrom in a suitable regeneration process.

The spent catalyst from the petroleum conversion reactor is stripped prior to entering the regenerator. The stripping vessel for use in a fluidized bed catalytic cracking unit may suitably be maintained essentially at conversion reactor temperature and is of from 850 to 1,200"F.

and desirably will be maintained above about 870"F. Steam is a preferred stripping gas, although steam-containing nitrogen or other steam-containing inert or flue gas, may also be employed. The stripping gas is introduced at a pressure which is generally at least about 10, preferably about 35 pounds per square inch gauge, suitable to effect substantially complete removal of volatile compounds from the spent conversion catalyst.

The method of this invention can be employed with any conventional cracking catalyst regeneration scheme but is advantageously employed with a regeneration system involving at least one dense-bed and at least one dilute-phase zone. Stripped spent catalyst particles may enter the dense-bed section of the regenerator vessel through suitable lines evolving from the stripping vessel. Entry may be from the bottom or from the side, desirably near the top of the dense-bed fluidized zone. Entry may also be from the top of the regenerator where catalyst has first been contacted with substantially spent regeneration gas in a restricted dilute-phase zone.

Catalyst regeneration is accomplished by burning the coke deposits from the catalyst surface with a molecular oxygen-containing gas, such as air. Many regeneration techniques are practised commercially whereby a significant restoration of catalyst activity is achieved in response to the degree of coke removal. As coke is progressively removed from the catalyst, removal of the remaining coke becomes most difficult and, in practice, an intermediate level of restored catalyst activity is accepted as an economic compromise.

The burning of coke deposits from the catalyst requires a large volume of oxygen or air.

Although the disclosed invention is not to be limited thereby, it is believed that the oxidation of coke may be characterized in a simplified manner as the oxidation of carbon and represented by the following chemical equations:

Reactions (a) and (b) both occur under typical catalyst regeneration conditions wherein the catalyst temperature may range from about 1050 to about 1450"F., and are exemplary of gas-solid chemical interactions when regenerating catalyst at temperatures within this range.

The effect of any increase in temperature is reflected in an increased rate of combustion of carbon and a more complete removal of carbon, or coke, from the catalyst particles. As the increased rate of combustion is accompanied by an increased evolution of heat, whenever sufficient free or molecular oxygen is present, the gas-phase reaction (c) may occur. This latter reaction is initiated and propagated by free radicals and can be catalysed.

The burning of sulfur-containing coke deposits from the catalyst also results in the formation of sulfur oxides; and, although the disclosed invention is not to be limited thereby, this burning may be represented by the following chemical equations:

(d)S (in coke) + O2 g S03 eS O2 + 1/2 O2 SO3 Reactions (d) and (e) also occur under typical cracking catalyst regeneration conditions.

While reaction (d) is fast, reaction (e) is relatively slow. Reaction (e) can be catalysed by any catalyst which catalyses reaction (c) above. Molecular sieves adsorb sulfur oxides, and therefore reaction (e) can occur on the cracking catalyst in the solid particles of the method of this invention. Other components of the solid particles can also adsorb sulfur oxides. The resulting sulfur trioxide can then react with a suitable metal, or more particularly an oxide of the metal in the metallic reactant, to form a stable metal sulfate in the solid particles. When the solid particles are separated from the regeneration zone flue gases, the metal sulfate in the solid particles is circulated to the reaction zone. Thus, the sulfur is rendered unavailable for exit as gaseous sulfur oxides in the regeneration zone flue gas.

The sulfate remains on the solid particles as they pass to the cracking reaction zone and, in the reducing atmosphere therein, is converted to the sulfide of the metal in the metallic reactant and possibly to hydrogen sulfide. Upon stripping with a stream-containing stripping gas in the stripping zone, the sulfur is converted to hydrogen sulfide and exits in the stripping zone effluent stream. The metallic reactant is thereby regenerated and made available again for reaction with sulfur oxides in the next pass through the regeneration zone. Hydrogen sulfide can then be recovered with the cracking products from the stripping zone, separated and converted to elemental sulfur in conventional facilities.

Although the disclosed invention is not to be limited thereby, it is believed that these reactions can be summarized as follows: Regenerator Reactor Stripper

These reactions are made possible through the use of both the molecular sieve-type cracking catalyst and the metallic reactant of the method of this invention. The high cracking activity normally present in the molecular sieve catalyst remains substantially unaffected by the presence of the metallic reactant so that the anticipated conversion of feedstock and yield of cracked products are realized together with the diminution of emission of sulfur oxides.

The metallic reactant can be in a finely divided form, such as a powder, separate from the molecular sieve-type cracking catalyst or any other support. In such case, the metallic reactant is a powder which is separately introduced into the catalytic cracking process cycle and admixed with the molecular sieve-type cracking catalyst in situ in the catalytic cracking process cycle, but not before the molecular sieve-type cracking catalyst is introduced into the cracking process cycle. Generally, such powdered metallic reactant is advantageous in that a powder is easy to charge to, and to handle in, a fluidized catalytic cracking process system.

The particle size of the powder should be chosen so as to avoid segregation of the particles at the fluidizing velocities. Desirably, the particles in such powder are not so minute that problems occur such as excessive emission with the gases from the bed as entrained particulate matter; however, filters, cyclones, precipitators, and the like are usually employed in conjunction with fluidized catalytic cracking operations to recover most of the entrained particulate matter and to return it to the system so as to abate losses. The powder should be sufficiently strong for excessive attrition and degradation of the sized powder to be avoided.

Frequently, the average particle size of the powdered metallic reactant is from about 0.5 to 1 to 100 microns, preferably less than about 50 microns, in diameter. It has been noted that microsized particles, that is, having an average particle size of less than about 1 micron, for instance, from about 0.01 to 0.5 micron, may tend to form aggregates of larger size which may beneficially be emploted in the process of this invention. Illustrative of powdered metallic reactants which may be employed in this invention are magnesium oxide and calcium oxide, dolomite and Trimex (trade mark), manufactured by Trimex Corporation and described in U.S. Patent 3,630,696.

Alternatively, the metallic reactant can be incorporated onto a suitable support other than the molecular sieve-type cracking catalyst, outside the cracking process cycle, and the composite is then introduced into the cracking process cycle where it becomes a part of the solid particles. Such support can be an amorphous cracking catalyst or a solid which is substantially inert to the cracking reaction and can, for example, be ceramic in nature. In such a case, the supported metallic reactant is then admixed with the molecular sieve-type cracking catalyst within the cracking process cycle, but not before the molecular sieve-type cracking catalyst is introduced into the cracking process cycle. Desirably, the support used is porous and frequently has a surface area, including the area of the pores on the surface, of at least about 10, preferably at least about 50, square meters per gram. Illustrative of the supports are silica, alumina, silica-alumina and the like. The metallic reactant may be incorporated into such substrate by ion exchange, impregnation or other means, e.g. by contacting the substrate or a component thereof with a solution or solutions of a compound or compounds of the metal of the metallic reactant in an appropriate amount necessary to provide the desired concentration of the metallic reactant within the scope of the invention. The metallic reactant may be combined with such substrate either in any step during the preparation of the substrate or after the substrate has been prepared. One method of incorporation is to ion-exchange the substrate. Also useful is the ion-exchanging of siliceous solids or clays with a solution or solutions of a compound or compounds of the metallic element or elements of metallic reactant. Suitable compounds for this purpose include the metalhalides, preferably chlorides, nitrates, amine halides, oxides, sulfates, phosphates and other water-soluble inorganic salts; and also the metal carboxylates of from 1 to 5 carbon atoms, and alcoholates.

Alternatively, the metallic reactant can be incorporated into the molecular sieve-type cracking catalyst, or a portion thereof, in the solid particles of the method of this invention, or in the catalytic cracking process cycle, but not before the molecular sieve-type cracking catalyst has been introduced into the cracking process cycle. In such a case, the metallic reactant is introduced into the cracking catalyst during the cracking cycle; care should be taken in choice of the method of introduction so that the cracking activity and selectivity of the cracking catalyst are not adversely affected.

In any of the above cases, the precise manner in which the metal or metals of the metallic reactant are incorporated into the molecular sieve-type cracking catalyst, amorphous cracking catalyst, or substantially inert substrate is not known with absolute certainty. The metals may enter into a complex combination with the carrier material and other components of the solid particles of this invention. Therefore, it is understood that the use of the terms "metallic reactant" and "incorporated" into the substrate connotes that the metals of such component exist within the carrier material in a combined form and/or in the elemental state.

Impregnation may be practised in any way which will not destroy the structure of the substrate. The metallic reactant may be impregnated onto the molecular sieve-type cracking catalyst only within the cracking process cycle or into a support inert to the hydrocarbon cracking or amorphous cracking catalyst either within or outside the cracking process cycle.

Impregnation differs from the ion-exchange. Impregnation results in greater deposition and a primarily physical association on the surface of the substrate, while the ion-exchange results in a primarily chemical association and a greater diffusion and therefore less surface deposition. In impregnation, the metal is deposited and no significant ion-exchange occurs between the metal and the substrate. In impregnating the substrate, the metal or metals in the metallic reactant can be present in, or as, a water-soluble or organic solvent-soluble or -dispersible compound or compounds in an amount or amounts sufficient to contain the quantity of metal or metals desired on the substrate, and the substrate is contacted therewith. The composite may be dried to remove the solvent, leaving the metallic reactant deposited on the substrate.

Preferably, water-soluble nitrate salts are employed in the impregnating solution since residue from the thermal decomposition of the nitrate salts is relatively innocuous to the activity of the hydrocarbon cracking catalyst. The halogen and sulfate salts of the metal to be impregnated may also be employed; however, since the by-products resulting from thermal decomposition of such salts may be deleterious to the activity of the hydrocarbon cracking catalyst, these salts are most often employed when depositing the metallic reactant on substrates which are substantially inert to the cracking reaction and which do not significantly adversely affect the hydrocarbon cracking reaction.

Another method of physically depositing the metallic reactant on a substrate, particularly porous substrates such as crystalline aluminosilicates, is adsorption of a fluid decomposable compound or compounds of the metal or metals of the metallic reactant on the substrate, followed by thermal or chemical decomposition of the compound or compounds. The substrate may be activated by heating to remove any adsorbed water and then contacted with a fluid decomposable compound or compounds of the metal or metals of the metallic reactant, thereby adsorbing the compound or compounds onto the substrate. Typical of such compounds are the metal alkyls, volatile metal halides and the like. The adsorbed compound or compounds may then be reduced thermally or chemically to their active state, thus leaving uniformly dispersed on the substrate an active metallic reactant. Thermal reduction may be effected, for example, in the regeneration vessel during the regeneration process.

It is also advantageous to introduce a compound or compounds of the metal or metals in the metallic reactant into the cracking process cycle and to incorporate it in situ in the substrate.

Such compound or compounds may be introduced in oil- or water-soluble or -dispersible form, and in the solid, liquid or gaseous state, at any stage of the cracking process cycle so that wide distribution in the solid particles is achieved. For example, such compound or compounds may be admixed either with the feedstock or with fluidizing gas in reaction zone, with the regeneration gas, torch oil or water in the regeneration zone, or with the stripping gas in the stripping zone, or may be introduced as a separate stream. Suitable compounds for in situ incorporation include metal salts. Examples include metal diketonates and metal carboxylates having from 1 to 20 carbon atoms. A specific example is magnesium acetylacetonate.

Preferred embodiments of the method of this invention involve operation in conjunction with the regeneration scheme of U.S. Patent No. 3,909,392. U.S. Patent No. 3,909,392 is directed to an improved catalytic cracking process, including an improved process for the regeneration of catalysts employed in the fluid catalytic conversion of hydrocarbon feedstocks wherein the catalyst is deactivated by the deposition of coke on the catalytic surfaces.

The process enables the coke level on regenerated catalyst to be maintained at an extremely low level while simultaneously maintaining a favourable heat balance in the conversion unit and providing a flue gas stream having an extremely low carbon monoxide content. Heat from the combustion of carbon monoxide is absorbed by the regenerated catalyst and provides part of the process heat required in the hydrocarbon conversion zone. In one embodiment of the process of U.S. Patent No. 3,909,392, the combustion of carbon monoxide to carbon dioxide is carried substantially to completion within the regeneration vessel in a relatively dilute secondary catalyst regeneration zone, advantageously at a temperature within the range of from 1200"F. to 15000F. inclusive, desirably between about 1250C and 1450"F. The temperature of the secondary zone may be about 50 or 100 F. higher than that of the first regeneration zone. Partially regenerated catalyst from a relatively dense primary catalyst regeneration zone can be controllably flowed through the secondary zone in an amount and at a rate sufficient to absorb substantially all of the heat released by the combustion occurring in the secondary zone. Although most of the coke is burned from the catalyst in the primary zone, additional coke is burned from the partially regenerated catalyst while present in the secondary zone, and catalyst substantially free of coke may be recovered for recycle to the hydrocarbon conversion level.

In a second embodiment of the process of U.S. Patent No. 3,909,392, substantially all of the combustion, including both the oxidation of coke or carbon on the catalyst and the oxidation of carbon monoxide, occurs within a single, relatively dense phase regeneration zone in respect to the proper control of, principally, the regeneration temperature and gas velocity.

Similarly, when the process of the present invention is operated in embodiments involving the regeneration scheme of U.S. Patent No. 3,909,392, the major amount of heat liberated from the combustion of carbon monoxide in the regeneration zone is absorbed by the solid particles of this invention which include the cracking catalyst, and provides part of the heat required in the cracking zone. Beneficially, in such embodiments, the process of the present invention enables considerable coke and carbon monoxide to be combusted in the densephase zone. if one is present, wherein a substantially increased amount of solid particles is present, as compared with the dilute-phase zone, if one is present, to disperse the heat evolved therefrom. As the proportion of combustion occurring in the dense-phase zone is increased, the evolution of heat in the dilute-phase zone is substantially reduced, and, hence, the need to provide rapid turnover of solid particles in the dilute-phase zone to absorb the evolved heat is reduced or eliminated.

In such embodiments, the process includes the use of the solid particles of this invention which comprise molecular sieve-type cracking catalyst and the metallic reactant of this method, in a system which supports substantially complete combustion of carbon monoxide.

The low catalyst coke levels achieved are less than about 0.2 weight percent, preferably less than about 0.05 weight percent. This process can result in flue gas having carbon monoxide levels of less than about 0.2 volume percent, for example about 500 to 1000 parts per million, and as low as from 0 to about 500 parts per million. The process also includes provision for the recovery of evolved heat by transfer directly to the solid particles within the regeneration vessel.

In such embodiments, the fluidizing gas in the dense zone of the regenerator may have a velocity, for example, in the range of from about 0.2 to about 4 feet per second, desirably about 0.5 to 3 feet per second. The regeneration gas serving to fluidize the dense-bed contains free or molecular oxygen, and the oxygen is preferably charged to the regenerator in an amount somewhat in excess of that required for complete combustion of coke (carbon and hydrogen) to carbon dioxide and steam. The amount of oxygen in excess of that required for complete combustion of the coke may vary from about 0.1 to about 25 or more percent of the theoretical stoichiometric oxygen requirement for complete combustion of the coke, but, advantageously, need not be greater than about 10 percent. For example, when air is employed as the regeneration gas, a 10 percent excess of air provides only about 2 volume percent oxygen in the effluent spent gas stream. Advantageously, the concentration of molecular or free oxygen and carbon monoxide at any point within the regenerator is maintained outside of the explosive range under those conditions, and, preferably, the concentration of carbon monoxide is below the explosive range under those conditions, to eliminate any risk of detonation.

The regeneration gas, in addition to free or molecular oxygen, may contain inert, or diluent, gas such as nitrogen, steam, etc., recycle gas from the regenerator effluent, and the like. Frequently, the oxygen concentration of the regeneration gas at the inlet to the regenerator is from about 2 to 30 volume percent, preferably about 5 to 25 volume percent.

Since air is conveniently employed as a source of oxygen, a major proportion of the inert gas may be nitrogen. The inert gas may serve to dissipate excessive heat from the combustion of coke from the catalyst. A source of hot, inert gas is the effluent from the regenerator, and a proportion of this gas may be recycled to the regenerator and, for instance, combined with sufficient incoming air or other oxygen-containing gas, including essentially pure oxygen, to provide the desired oxygen content. Thus, the recycle gas may be employed in direct heat-exchange to increase the temperature of the regeneration gas to provide even further heat economies in the system.

Solid particles within the dilute-phase may be partially carried into the separation zone, usually comprising cyclone separators in a plurality of stages, from which solid particles can be returned directly through dip-legs to the dense-bed zone, and spent regeneration and combustion gases are collected in a plenum and finally discharged for suitable recovery of the heat energy contained therein. Recovery processes for heat from flue gases include steam generation, spent catalyst stripping, indirect heat exchange with various refinery streams such as feed to the particular conversion process, and employment in various drying or evaporation arrangements.

Reference is now made to the accompanying drawings, in which: Figures 1 and 2 are elevations partly in section, of embodiments of apparatus suitable for catalyst regeneration according to embodiments of the process of this invention involving the regeneration scheme of U.S. Patent No. 3,909,392.

Such embodiments may be employed beneficially in many existing petroleum hydrocarbon cracking process units, particularly fluid catalytic cracking units having a variety of spatial arrangements of cracking, stripping and regeneration sections thereof.

Figure 1 is illustrative of one such embodiment of this invention employing bottom entry of stripped, spent catalyst passing from a cracking reactor (not shown) to the illustrated regenerator. Solid particles containing spent catalyst, impregnated with a metallic reactant from a stripping zone associated with the catalyst exit from the reactor, enter from the bottom of regeneration vessel 1. The solid particles flow upwardly through inlet lines 2 and 3 and discharge into the dense bed through discharge heads 4 and 5, respectively. The dense-phase bed is maintained within the lower section 6 of the regenerator vessel 1 and extends upwardly to the phase interface 7. Solid particles within the dense-phase bed are fluidized by the flow of combustion air through a line 8, valve 9 and line 10 to an air ring 11. Substantially balanced air flow patterns through the regeneration zone may be achieved by the use of additional air rings (not shown), as required. Combustion with air of coke contained on the spent catalyst is initiated within the dense-phase bed. Higher temperatures may be achieved by temporarily burning a stream of torch oil, for example a decanted oil, within the bed. Torch oil may be added by passage through a line 12, valve 13 and line 14 which terminates in a nozzle located above the air ring 11. Fluidizing air velocities continuously carry some of the solid particles upwardly into the dilute-phase zone which occupies the upper section 15 of the regenerator vessel, that is, the section above the phase interface 7. Combustion of coke continues in the dilute-phase zone and the largely spent combustion gas together with entrained solid particles is withdrawn into first-stage cyclone separators 20 and 21. Most of the solid particles are separated in the first-stage cyclones and discharged downwardly through dip-legs 22 and 23 into the dense-phase zone. Gases and remaining solid particles are passed through interstage cyclone lines 24 and 25 to second-stage cyclone separators 26 and 27 where substantially all of the remaining solid particles are separated and passed downwardly through dip-legs 28 and 29 into the dense-phase bed. Substantially spent combustion gas then passes through lines 30 and 31 into a plenum 32 and is finally discharged from the regenerator vessel through a line 33. This effluent may be suitably heat-exchanged (not shown) with refinery stream or for the production of process steam. Solid particles containing regenerated catalyst from the dense bed are withdrawn through standpipes 34 and 35, fitted with collector heads 36 and 37, respectively, for return to the cracking reactor.

Although the supply of combustion air normally provides an excess the dense bed are withdrawn through standpipes 134 and 135, fitted with collector heads 136 and 137, respectively, for return to the catalytic cracking reactor.

As described for the embodiment of Figure 1, carbon monoxide burns in the dilute-phase providing a high temperature zone throughout much of the dilute-phase zone and particularly at approximately the location indicated by X. Control of regeneration temperature within the dilute-phase zone is effected largely through absorption of heat by the mass of solid particles carried upwardly by the rising combustion gas stream. Temperatures in the vicinity of the plenum, cyclone and connecting lines may, as required, be reduced with steam fed through a line 150, valve 151 and line 152 to a steam ring 153, which surrounds the plenum 132. Water spray means (not shown) may similarly be employed.

In another, particularly preferred embodiment of this invention, the apparatus shown in Figure 2 is employed with a significant change in operating parameters as compared with the above-described embodiment. In this embodiment, gas velocity and solid particles input are adjusted so that essentially complete combustion of coke and carbon monoxide is completed within the dense phase and the heat is dispersed throughout the bed.

When the system is operated according to either of the embodiments described above with reference to Figures 1 and 2, the recovery of the heat released by the essentially complete combustion of coke and carbon monoxide is by absorption in solid particles in both phases, and return of the solid particles to the dense-phase serves also to secure maintenance of the suitably high temperature within the dense-phase zone. The returned solid particles may carry with them additional heat to serve to raise the temperature of the dense-phase zone to a value which favours the removal of additional increments of coke deposits thereon, so that the combustion of the final increments of coke becomes substantially complete. When the system is operated so that essentially all combustion is completed within the dense catalyst phase, the heat is dispersed throughout the phase as it is absorbed by the fluidized solid particles and final increments of coke are combusted. Accordingly, in all embodiments, solid particles containing the regenerated catalyst passing from the regenerator back to the cracking reactor suitably contain from about 0.01 to about 0.10 weight percent, desirably from 0.01 to 0.05 weight percent, and preferably from about 0.01 to about 0.03 weight percent of carbon or coke on catalyst, and can be withdrawn from the regenerator at an advantageous temperature for use in the cracking reactor.

An outstanding advantage of this invention lies in providing a regenerated catalyst generally possessing enhanced activity and selectivity characteristics more closely approaching those of fresh conversion catalyst, particularly for use in conversions effected at very short contact times in riser reactors. The cracking activity of sieve-containing catalysts and their selectivity for converting hydrocarbon feeds to desired products are both dramatically affected in a favourable direction by the increased elimination of residual carbon or coke on the catalyst during regeneration. The low coke level on the regenerated catalyst is especially preferred with fluid cracking catalysts containing catalytically active, crystalline aluminosilicates. Accordingly, higher yields of desirable conversion products may be achieved.

In those cracking processes using a lower dense phase zone and an upper dilute phase zone in the regeneration zone, the oxidation of the carbon monoxide to carbon dioxide may be accomplished to a major extent, often at least about 60 percent, and frequently about 65 to 95 percent or more, to completion in the dense phase of the regenerator. The oxidation of carbon monoxide to carbon dioxide in the dense phase provides heat to aid in sustaining the combustion of the coke deposits from the fluid catalyst. Furthermore, with a substantial proportion of the carbon monoxide being oxidized in the dense phase, a lesser amount of carbon monoxide is present for combustion in the upper phase of the fluid catalyst in the regenerator, and thus "afterburning" and high temperatures due to uncontrolled excessive carbon monoxide combustion in the upper portion of the regenerator, which may deleteriously affect materials employed to construct the reactor, the waste gas flue and the collectors for any particulate materials in the waste gas, for example, cyclones, and which may impair catalyst activity, may be substantially reduced or avoided.

Solid particles containing the regenerated catalyst particles having unusually low residual coke contents are recovered from the dense phase and passed substantially at the dense-bed temperature through a standpipe to the cracking reactor for contacting with fresh hydrocarbon feed or a mixture thereof with recycle hydrocarbon fractions. Since the oxidation of the carbon monoxide evolved from the combustion of the coke deposits on the catalyst may occur to a major extent in the dense-phase and, in the preferred embodiments, essentially completely occurs in the dense phase, the regenerated catalyst can be returned to the cracking reactor at a much higher temperature as well as at a higher activity than in heretofore conventional operations.

A major benefit from the process of U.S. Patent No. 3,909,392 relates to the unusually low carbon monoxide content in the effluent gas stream from the regenerator which may be obtained. Whereas flue gas from the conventional regeneration of cracking catalysts usually contains from about 6 to about 10 percent carbon monoxide, a similar amount of carbon dioxide and very little oxygen, the carbon monoxide content of the flue gas from this novel regeneration process may be maintained at less than about 0.2 volume percent, for example, about 500 to 1000 parts per million by volume (ppmv) Advantageously, the content is even lower, for example, within the range of from 0 to about 500 ppmv. This low concentration of carbon monoxide in the flue-gas stream permits the direct release of effluent gases to the atmosphere while meeting ambient air quality standards. If required, any remaining carbon monoxide may suitably be burned in the exhaust from the regenerator flue gas stack. This advantage of the invention of U.S. Patent No. 3,909,392 additionally permits the elimination of capital expenditures otherwise required for the installation of carbon monoxide boilers and associated turbine-type devices or other means for the partial recovery of energy produced by the subsequent oxidation of the carbon monoxide while still meeting the existing standards for ambient air quality for carbon monoxide emissions.

The method of U.S. Patent No 3,909,392 provides additional benefits. Such benefits relate to the problem of after-burning and heat balance. A major problem often encountered and sought to be avoided in the practice, particularly, of fluid catalyst regeneration is the phenomenon known as "afterburning", described, for example, in Hengstebeck, Petroleum Processing McGraw-Hill Book Co., 1959, at pages 160 and 175, and discussed in Oil and Gas Journal, Volume 53 (No. 3), 1955, at pages 93-94. This term is descriptive of the further combustion of carbon monoxide to carbon dioxide, as represented by reaction (c) above, which is highly exothermic. Afterburning has been vigorously avoided in catalyst regeneration processes because it was felt it could lead to very high temperatures which might damage equipment and cause permanent deactivation of cracking catalyst particles. Many fluid catalyst regenerator operations have experienced afterburning, and a very substantial body of art has developed around numerous means for controlling regeneration techniques so as to avoid afterburning. More recently, it has been sought to raise regenerator temperatures for various reasons; elaborate arrangements have also been developed for the control of regenerator temperatures at the point of incipient afterburning by suitable means for the control of the oxygen supply to the regenerator vessel as set forth, for example, in U.S.

Patents Nos. 3,161,583 and 3,206,393, as well as in U.S. Patent No. 3,513,087. In typical contemporary practice, accordingly, with the avoidance of afterburning, the flue gas from catalyst regenerators usually contains very little oxygen and a substantial quantity of carbon monoxide and carbon dioxide in nearly equimolar amounts.

Further combustion of carbon monoxide to carbon dioxide is an attractive source of heat energy because reaction (c) is highly exothermic. Afterburning can proceed at temperatures above about 1100 F., and liberates approximately 4350 BTU per pound of carbon monoxide oxidized. This typically represents about one-fourth of the total heat evolution relizable by the combustion of coke. The combustion of carbon monoxide can be performed controllably in a separate zone or a carbon monoxide boiler, after the separation of effluent gas from catalyst, as described in, for example, U.S. Patent No. 2,753,925, with the released heat energy being employed in various refinery operations such as the generation of high-pressure steam. Other uses of such heat energy have been described in U.S. Patents No.s 3,012,962 and 3,137,133 (turbine drive) and U.S. Patent No. 3,363,993 (preheating of petroleum feedstock). Such heat recovery processes require separate and elaborate equipment but do serve to minimize the discharge of carbon monoxide into the atmosphere as a component of effluent gases, and hence, serve to avoid a potentially serious pollution hazard.

Moreover, silica-alumina catalysts, employed conventionally for many years in various processes for the cracking of petroleum hydrocarbons, are not particularly sensitive to the level of residual coke on catalyst provided that the coke level is not greater than about 0.5 weight percent. However, silica-alumina catalysts have been largely supplanted by catalysts additionally incorporating a crystalline aluminosilicate component and known as zeolites or "molecular sieves". The molecular sieve-containing catalysts are much more sensitive to the residual coke level, being greatly affected both with regard to catalyst activity and to catalyst selectivity for the conversion of feed to the desired product or products. Due to the difficulties encountered in conventional catalyst regeneration techniques for the removal of the last increments of residual carbon. the practical coke level usually corresponds to a residual coke content on regenerated catalyst within the range of from about 0.2 to about 0.3 weight percent.

Since enhanced activity and selectivity are achievable with sieve-type cracking catalysts at low coke levels, an attractive incentive is provided for discovering a means for reducing residual coke levels still further. Coke levels below about 0.05 weight percent are greatly desired but usually cannot be achieved by commercially practicable means. Considerations such as larger regeneration vessels, a greater catalyst inventory, greater heat losses, and the like. all serve to discourage the attainment of such ideal equilibrium catalyst activity levels.

Many fluid cracking units are operated on the "heat balance" principle, depending upon combustion of coke for the evolution of heat required in the process. Such units, however, have not been able fully to utilize the benefits of the cracking catalysts, particularly zeolite catalysts, which can especially be achieved in a riser reactor where contact times between catalysts and oil vapours may be extremely short. The type of operation which affords a high conversion coupled with a high selectivity, favours a low ratio of catalyst-to-oil in the riser reactor which leads to less coke being available to generate heat by combustion in the regenerator. Accordingly, an external heat source such as a feed preheat furnace, may frequently be added to increase the temperature of the catalyst or, alternatively, the unit may be operated at a lower temperature of fresh feed. Such undesirable features may be avoided or minimized by the process of U.S. Patent No. 3,909,392 which permits efficient recovery of additional heat by the solid particles for transfer to the riser reactor. The heat of combustion of coke in conventional operations is about 12,000 BTU per pound. The process of U.S.

Patent No.3,909,392 may increase available heat by combustion of the coke to about 17,000 or more BTU's per pound. This higher heat of combustion tends to raise the regenerator temperature, lower the level of coke on the regenerated catalyst, and lower the circulation rate of solid particles while providing improved yields at a given conversion level.

The invention is further illustrated by the following Examples. In the Examples, Examples 1 to 3 describe the preparation of cracking catalysts which carry a metallic reactant and which may be used in the method of this invention. Examples 4 to 10 are bench scale tests which show the utility of various metallic reactants in the method of this invention whilst Example 11 and 12 are full-scale tests in a commercial catalytic cracking unit. Example 11 is in a control experiment and Example 12 is an embodiment of the method of this invention.

EXAMPLE I Ten grams of a solution of 6.9 grams of a lubricating oil additive which contained 9.2 weight percent of magnesium, distributed as magnesium hydroxide, magnesium carbonate and magnesium polypropyl benzene sulfonate, dissolved in 33.1 grams of catalytic light cycle oil, were cracked in a bench scale cracking unit having a fluidized bed of 220 grams of an equilibrium, commercially available cracking catalyst which contained 2.5 weight percent of molecular sieve and about 0.6 weight percent of sodium and had been withdrawn from a commercial fluid catalytic cracking unit and then calcined. The cycle oil was cracked at 700"F for 4 minutes. After purging the catalyst bed with nitrogen for 10 minutes at 12500F., the catalyst bed was cooled to 700"F., and the cracking-purging-regeneration cycle was repeated until the magnesium, zinc, and phosphorus contents of the catalyst reached the levels of 1100, 703, and 59 parts per million, respectively. The zinc and phosphorus were inherently present.

EXAMPLE 2 The procedure of Example 1 was repeated, except that the cracking-purging-regeneration cycle was repeated with a 10 g solution containing 6.5 g of the oil and 3.5 g of a lube oil additive containing 1.6 wt. % Zn, 1.3 wt. % P, and 4.6 wt. % Mg until the magnesium, zinc, and phosphorus contents of the catalyst reached 2400, 1200 and 1097 parts per million, respectively.

EXAMPLE 3 The procedure of Example 2 was repeated, except that an equilibrium, commercially available cracking catalyst which contained 3.3 weight percent of molecular sieve in a silica-alumina matrix and had also been withdrawn from a commercial fluid catalytic cracking unit and calcined was employed. and the cracking-purging-regeneration cycle was repeated until the magnesium. zinc, and phosphorus contents of the catalyst reached 4600, 304, and 1,136 parts per million, respectively.

EXAMPLES 4-8 A bench-scale laboratory regeneration unit was used to test the potency of a number of impregnated catalysts for providing reduced emissions of sulfur dioxide in regeneration zone flue gases. A synthetic flue gas comprising 1,500 parts per million of sulfur dioxide in a mixture of 4 volume percent of each of oxygen and water vapour in nitrogen was passed through a fixed fluidized bed of the molecular sieve-type cracking catalyst impregnated with a metal. which was maintained in a glass regenerator surrounded by a furnace to provide the desired regeneration temperature of 1.250 F. The temperature of the catalyst was measured by thermocouples. A cyclone was used to separate entrained catalyst from the gas existing from the regenerator and to return the catalyst to the catalyst bed. The time during which the regenerator was operated under a given set of conditions ranged from about 40 to about 90 minutes in order to allow sufficient time to establish the oxidation state of the metal on the catalyst in an actual fluid catalytic cracking unit operation.

The sulfur dioxide content of the gas exiting from the regenerator was analysed continu ously with an ultraviolet analyser. The amount of sulfur dioxide removed from the regeneration zone flue gas was determined as the difference between the sulfur dioxide contents of the fresh synthetic gas mixture and of the gas exiting from the regenerator. The volume percentages of sulfur dioxide removed from the regeneration zone flue gas are shown as a function of elapsed time after beginning the experiment in Table 1 below. The volume percentage removed decreased with time as the catalyst surface became saturated.

Example 4 was a comparative test using a flow rate of the synthetic flue gas mixture of 1084 milliliters per minute and the unimpregnated equilibrium catalyst used in Examples 1 and 2, while Examples 5 and 6 involved the impregnated catalyst produced in Examples 1 and 2, TABLE l Example Volume Percent of Sulfur Dioxide Removed Time 4 5 6 7 8 0-10 78-63 85-82 92-91 36-24 60-49 10-20 63-43 82-78 91-89 24-16 49-29 20-30 43-32 78-74 89-88 16-14 39-33 30-40 32-27 74-70 88-87 14-13 33-30 respectively, and flow rates for the synthetic flue gas mixture of 989 and 1,014 milliliters per minutes, respectively. Example 7 was a comparative test using the unimpregnated catalyst used in Example 3 and a flow rate of the synthetic flue gas mixture of 891 milliliters per minute. Example 8 involved the impregnated catalyst produced in Example 3 and a flow rate of the synthetic flue gas mixture of 992 milliliters per minute. The flow rates were measured at 60"F.

EXAMPLES 9-10 In Example 9, the procedure of Examples 4-8 was repeated, except that a synthetic flue gas mixture comprising 4 volume percent of each of carbon monoxide, oxygen and water vapour in nitrogen was passed at a rate of about 1,000 milliliters per minute (measured at 600F) through a fluidized bed of a mixture of powdered magnesium oxide having a particle size of 5 microns and finer and an unimpregnated, calcined, equilibrium, commercially available, molecular sieve-type cracking catalyst containing 5.3 weight percent of hydrogen and rare earth ion-exchanged, Y-type crystalline aluminosilicate and silica-alumina, which contained 30 weight percent of alumina, instead of the impregnated catalaysts. The mixture contained 0.3 weight percent of magnesium oxide and about 70 volume percent of carbon monoxide was converted to carbon dioxide. In Example 10, the unimpregnated catalyst used in Example 9, was used in the absence of magnesium oxide, under otherwise identical conditions, and 58 volume percent of carbon monoxide was converted to carbon dioxide.

EXAMPLES 11-12 In Example 11, a gas oil feed having a sulfur content of 1.67 weight percent was cracked in a commercial fluid catalytic cracking unit having a riser reactor. Conventional regeneration was employed. A commercial, equilibrium molecular sieve-type cracking catalyst containing 2.5 weight percent of molecular sieve and about 0.6 weight percent of sodium was used. In Example 12, a second gas oil feed having a sulfur content of 1.68 weight percent was cracked in the same commercial unit using the same regeneration scheme and the same cracking catalyst, but, additionally. the catalyst was impregnated with magnesium and zinc. The magnesium and zinc were deposited on the catalyst by introducing into the reaction zone small concentrations of magnesium sulfonate and zinc dialkyldithiophosphate in the form of lubricating oil additive in the feedstock. After several hours of addition in this manner, levels of magnesium of 0.3 weight percent and of zinc of 0.1 weight percent built up on the cracking catalyst. The operating conditions and composition of the regeneration zone flue gases are shown in Table 2. below.

TABLE 2 Example 11 12 Cracking conditions: Cracking temperature, "F 974 970 Total Feed Rate, barrels/day 49,200 46,800 Throughput ratio 1.07 1.25 Catalyst circulation rate, tons/min. 29.1 26.4 Catalyst-to-oil weight ratio 5.3 5.2 Stripping conditions: Stripping temperature, "F. 970 965 Steam Ibs./ton catalyst 8.6 9.4 Regeneration conditions: Dense bed temperature, "F. 1270 1305 Combustion air rate, Ibs./hr. 412,000 487,000 Composition of regeneration zone effluent gas: CO2, mole percent 13.0 14.0 CO, mole percent 5.0 5.6 2 mole percent 0.5 2.0 Sulfur dioxide, ppmv 580 60 WHAT WE CLAIM IS: 1. In a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing from 0.2 to 6 weight percent sulfur as organic sulfur compounds wherein (i) said feedstock is subjected to cracking in a reaction zone with fluidized particles of a molecular sieve-type cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable sulfurcontaining carbonaceous deposits from the stripped catalyst particles with an oxygen containing gas; and (iv) regenerated catalyst particles are separated from regeneration zone effluent and recycled to the reaction zone, a method for reducing emissions.of sulfur oxides in the regeneration zone effluent gas stream which comprises: (a) adding fluidizable particles, other than said molecular-sieve type cracking catalyst, which contain a metallic reactant, to the cracking catalyst during the fluid catalytic cracking process to produce a mixture of particles which contains from 10 to 99.9975 weight percent of molecular sieve-type cracking catalyst, wherein the metallic reactant consists of at least one free or combined metallic element consisting of magnesium calcium, strontium or barium, and wherein the amount of said metallic reactant in the mixture of particle is sufficient to effect the absorption of at least 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (b) cracking said feedstock at a temperature within the range of from 850" to 1,2000F, inclusive; (c) stripping volatile deposits from the mixture of particles, which is separated from the reaction zone, with a stripping gas which contains steam at a temperature of from 850" to 1,200"F, wherein the weight ratio of steam to said cracking catalyst is from 0.0005 to 0.025; (d) regenerating said stripped mixture of particles at a temperature of from 1,050 to 1,450"F; (e) absorbing with the mixture of particles at least 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (f) conveying the mixture of particles containing said absorbed sulfur oxides from the regeneration zone to the reaction zone; (g) withdrawing an effluent gas stream from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides; and (h) withdrawing substantially all of said absorbed sulfur oxides as a sulfur-containing gas from the reaction and/or stripping zone.

2. A method as claimed in claim 1, wherein said metallic reactant consists of at least one free or combined metallic element consisting of magnesium or calcium, or any mixture thereof.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

TABLE 2 Example 11 12 Cracking conditions: Cracking temperature, "F 974 970 Total Feed Rate, barrels/day 49,200 46,800 Throughput ratio 1.07 1.25 Catalyst circulation rate, tons/min. 29.1 26.4 Catalyst-to-oil weight ratio 5.3 5.2 Stripping conditions: Stripping temperature, "F. 970 965 Steam Ibs./ton catalyst 8.6 9.4 Regeneration conditions: Dense bed temperature, "F. 1270 1305 Combustion air rate, Ibs./hr. 412,000 487,000 Composition of regeneration zone effluent gas: CO2, mole percent 13.0 14.0 CO, mole percent 5.0 5.6 2 mole percent 0.5 2.0 Sulfur dioxide, ppmv 580 60 WHAT WE CLAIM IS: 1. In a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing from 0.2 to 6 weight percent sulfur as organic sulfur compounds wherein (i) said feedstock is subjected to cracking in a reaction zone with fluidized particles of a molecular sieve-type cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable sulfurcontaining carbonaceous deposits from the stripped catalyst particles with an oxygen containing gas; and (iv) regenerated catalyst particles are separated from regeneration zone effluent and recycled to the reaction zone, a method for reducing emissions.of sulfur oxides in the regeneration zone effluent gas stream which comprises: (a) adding fluidizable particles, other than said molecular-sieve type cracking catalyst, which contain a metallic reactant, to the cracking catalyst during the fluid catalytic cracking process to produce a mixture of particles which contains from 10 to 99.9975 weight percent of molecular sieve-type cracking catalyst, wherein the metallic reactant consists of at least one free or combined metallic element consisting of magnesium calcium, strontium or barium, and wherein the amount of said metallic reactant in the mixture of particle is sufficient to effect the absorption of at least 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (b) cracking said feedstock at a temperature within the range of from 850" to 1,2000F, inclusive; (c) stripping volatile deposits from the mixture of particles, which is separated from the reaction zone, with a stripping gas which contains steam at a temperature of from 850" to 1,200"F, wherein the weight ratio of steam to said cracking catalyst is from 0.0005 to 0.025; (d) regenerating said stripped mixture of particles at a temperature of from 1,050 to 1,450"F; (e) absorbing with the mixture of particles at least 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (f) conveying the mixture of particles containing said absorbed sulfur oxides from the regeneration zone to the reaction zone; (g) withdrawing an effluent gas stream from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides; and (h) withdrawing substantially all of said absorbed sulfur oxides as a sulfur-containing gas from the reaction and/or stripping zone.
2. A method as claimed in claim 1, wherein said metallic reactant consists of at least one free or combined metallic element consisting of magnesium or calcium, or any mixture thereof.
3. A method as claimed in claim 1 or 2, wherein the amount of said metallic reactant,

calculated as the metal, is from 0.1 to 0.5 weight percent of said mixture of particles.
4. A method as claimed in any of claims 1 to 3, wherein said fluidizable particles which contain a metallic reactant comprise a supported metallic reactant in which the support consists of at least one amorphous cracking catalyst and/or solid which is substantially inert to the cracking reaction, or any mixture thereof.
5. A method as claimed in claim 4, wherein said support consists of silica, alumina, thoria, a boria, or any mixture thereof.
6. A method as claimed in any of claims 1 to 5, wherein said particles of molecular sieve-type cracking catalyst comprise from 90 to 99.9 weight percent of the mixture of particles.
7. A method as claimed in any of claims 1 to 6, wherein the ratio of steam to said cracking catalyst is from 0.0015 to 0.0125.
8. A method as claimed in any of claims 1 to 7, wherein the regeneration zone effluent gas stream contains at least 0.01 volume percent of molecular oxygen.
9. A method as claimed in any of claims 1 to 8, wherein the regeneration zone effluent gas stream contains less than 600 ppmv of sulfur oxides.
10. A method as claimed in any of claims 1 to 3 or 6 to 9, wherein the feedstock has a sulfur content in the range of from 1 to 4 weight percent inclusive.
11. A method as claimed in any of claims 1 to 10 wherein said fluidizable particles which contain a metallic reactant are particles of magnesium oxide.
12. In a process for the cyclic, fluidized, catalytic cracking of a hydrocarbon feedstock containing from 0.2 to 6 weight percent sulfur as organic sulfur compounds, wherein (i) said feedstock is subjected to cracking in a reaction zone with fluidized particles of a molecular sieve-type cracking catalyst; (ii) catalyst particles, which are deactivated by sulfur-containing carbonaceous deposits, are separated from reaction zone effluent and conveyed to a stripping zone wherein volatile deposits are removed from said deactivated catalyst by contact with a stripping gas; (iii) stripped catalyst particles are separated from stripping zone effluent and conveyed to a regeneration zone and regenerated by burning the non-strippable sulfurcontaining carbonaceous deposits from the stripped catalyst particles with an oxygen containing gas; and (iv) regenerated catalyst particles are separated from regeneration zone effluent and recycled to the reaction zone, a method for reducing emissions of sulfur oxides in the regeneration zone effluent gas stream which comprises: (a) incorporating into said catalyst particles at least one metal in elemental or combined form consisting of magnesium, calcium, strontium, or barium or any mixture thereof, by separately introducing at least one compound of said metal or metals into the process cycle, wherein said metal is incorporated in sufficient amount to effect the absorption of at least 50No of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (b) cracking said feedstock at a temperature within the range of from 850" to 1,200"F inclusive; (c) stripping volatile deposits from the deactivated catalyst at a temperature of from 850" to 1.2000F with a stripping gas which contains steam. wherein the ratio of steam to said cracking catalyst is from 0.0005 to 0.025; (d) regenerating said stripped deactivated catalyst at a temperature of from 1,050 to 1.450"F; (e) absorbing with the catalyst particles containing said metal at least 50% of the sulfur oxides produced by said burning of sulfur-containing carbonaceous deposits in the regeneration zone; (f) conveying the catalyst particles containing said absorbed sulfur oxides from the regeneration zone to the reaction zone; (g) withdrawing an effluent gas stream from the regeneration zone containing molecular oxygen and having a low concentration of sulfur oxides; and (h) withdrawing substantially all of said absorbed sulfur oxides as a sulfur-containing gas from the reaction and/or stripping zone.
13. A method as claimed in claim 12, wherein said metal consists of magnesium or calcium, or any mixture thereof.
14. A method as claimed in claim 12 or 13. wherein from 0.1 to 0.5 weight percent of said metal is incorporated into the catalyst particles.
15. A method as claimed in any of claims 12 to 14. wherein said metal compound is a metal salt.
16. A method as claimed in any of claims 12 to 15. wherein said metal compound consists of at least one metal diketonate and/or metal carboxylate having from 1 to 20 carbon atoms, or any mixture thereof.
17. A method as claimed in any of claims 12 to 16. wherein said metal compound is magnesium acetylacetonate.
18. A method as claimed in any of claims 12 to 17, wherein the ratio of steam to said cracking catalyst is from 0.0015 to 0.0125.
19. A method as claimed in any of claims 12 to 18 wherein the regeneration zone effluent gas stream contains at least 0.01 volume percent of molecular oxygen.
20. A method as claimed in any of claims 12 to 19 wherein the regeneration zone effluent gas stream contains less than 600 ppmv of sulfur oxides.
21. A method as claimed in any of claims 12 to 20 wherein the feedstock has a sulfur content in the range of from 1 to 4 weight percent.
22. A method as claimed in claim 1, substantially as herein described with reference to the accompanying drawing and/or Example 12.