GB2151604A - Production of carbon black - Google Patents

Abstract

This disclosure relates to an improved furnace process for producing carbon blacks by the incomplete combustion of hydrocarbonaceous feedstock by varying the process described in U.S. Reissue Patent No. 28974 by carrying out the injection of a portion of the liquid hydrocarbon feedstock into the combustion gas stream as solid streams substantially radially at a location where the combustion gas stream has not attained maximum velocity whereby the resultant blacks have increased CDBP values and have properties which impart improved hysteresis to rubber formulations in which the blacks are incorporated.

Description

SPECIFICATION Production of carbon black This invention relates to the production of furnace blacks having many important applications.

These include use as fillers, pigments, and reinforcing agents in rubber and in plastics.

The furnace process for preparing carbon blacks involves a cracking and/or incomplete combustion of a hydrocarbon feedstock such as natural gas or cycle stock in an enclosed conversion zone at temperatures above 1256"K (1800"F) to produce carbon black. The carbon black entrained in the gases emanating from the conversion zone is then cooled and collected by any suitable means commonly used in the industry. It has, however, been desirable, although difficult, to produce furnace blacks of similar properties capable of imparting improved hysteretic properties to rubber formulations.

Accordingly, the primary object of this invention is to provide a process for preparing carbon blacks which are characterised by having properties indicative of improved hysteresis capabilities and having lower tinting strengths and higher values for crushed DBP (CDBP).

A further object of the invention is to provide a method for controlling the values of the tinting strength and CDBP of carbon blacks.

It has been found that the above objects may be achieved by modifying a modular or staged process for producing carbon black of the type disclosed and claimed in U.S. Reissue Patent No. 28,974. The staged process consists of an initially prepared primary (first-stage) combustion zone wherein a stream of hot gaseous combustion products is formed; a second or transition zone wherein a liquid hydrocarbon feedstock in the form of solid streams (coherent jets) is injected substantially transversely from the outer or inner periphery of the combustion gas stream into the pre-formed stream of hot gases; and a third zone (the reaction zone) wherein the carbon black formation occurs prior to termination of the reaction by quenching.

In processes of the aforementioned type where feedstock is injected from the outer periphery of the combustion gas stream, there is a possibility for combustion gases to pass through the system without having been utilized. This will occur, for example, when the hydrocarbon feedstock does not completely fill the area through which the combustion gases are flowing, thereby permitting unused heat in the form of combustion gases to escape. There is a greater tendency for this to occur as the size of the reactor is increased. To prevent this uneconomic loss of combustion gases, it is disclosed in U.S. Patent No. 3,922,335 to inject additional feedstock into the interior region of the combustion gas stream where the feedstock injected from the outer periphery of the transition zone would not reach.The patent describes the use of a suitable device such as a probe through which the additional liquid hydrocarbon feedstock would be injected into the core of the combustion gas stream in a substantially transverse manner, and in a direction from the center or core of the combustion gas stream outwardly toward the wall of the reactor. By so doing, it is shown that the combustion gases will be thoroughly utilized for the intended purposes of shearing atomizing, and dispersing the oil droplets. The injection of feedstock into the interior region of the combustion gas stream occurs in the same plane as that from which the feedstock is injected from the outer periphery of the transition zone toward the interior of the combustion gas stream. The process described in U.S.

3,922,335 is shown to provide exceptionally high throughput and high yields, and to have the ability to produce high quality carbon blacks.

There are instances, however, where it is desired to produce carbon blacks in a manner similar to both of the above processes but to produce blacks having different properties. In particular, it may be desirable to produce carbon blacks having reduced tinting strength and increased CDBP, which are indicators of increased rebound and better hysteretic properties.

The modification of the present modular or staged process which makes possible the preparation of the blacks having improved hysteresis involves carrying out the injection of a portion of the liquid hydrocarbon feedstock into the combustion gas stream as solid streams substantially radially at a location where the combustion gas stream has not attained maximum velocity.

Accordingly, therefore, the present invention provides a modular process for producing furnace carbon blacks wherein a fuel and an oxidant are reacted in a first zone so as to provide a stream of hot primary combustion gases possessing sufficient energy to convert a carbon blackyielding liquid hydrocarbon feedstock to carbon black, and wherein in a second zone liquid hydrocarbon feedstock is peripherally injected, in the form of a plurality of solid streams (coherent jets), into the stream of gaseous combustion products at a location where the combustion gas stream has reached maximum velocity in a direction substantially transverse to the direction of flow of the stream of combustion gases and under sufficient pressure to achieve the degree of penetration required for proper shearing and mixing of the feedstock and wherein a third zone the feedstock is decomposed and converted into carbon black prior to termination of the carbon forming reaction by quenching, and then cooling, separating and recovering the resultant carbon black, characterised in that a sufficient portion of the total amount of liquid hydrocarbon feedstock is introduced in the form of a plurality of solid streams, substantially radially into the combustion gas stream from the periphery thereof prior to the point at which the stream of combustion gases reaches maximum velocity. to thereby produce carbon blacks having increased CDBP values.

The feedstock may be injected from the outer or inner periphery of the combustion gas stream substantially radially into the lower velocity combustion gas stream.

It is preferred, however, to inject the solid streams of feedstock into the lower velocity combustion gas stream from the inner periphery thereof radially outwardly into the combustion gas stream. In the present staged process. maximum velocity of the combustion gas stream is reached at approximately the mid-point of the transition zone. Thus, for example, when the injection is being made through a probe, the modification can be carried out by retracting the probe into the first or primary combustion zone so that the feed stock, injected radially, whether inwardly or outwardly, enters a combustion gas stream having a lower velocity. The actual point or plane where the feedstock is injected into the lower velocity combustion gas stream in a radial direction may be varied considerably depending upon the specific grade or type of carbon black desired.It is believed that the radially inward or outward injection of the solid streams of liquid feedstock into a lower velocity combustion gas stream results in the formation of coarser size oil droplets which appear to be associated with increased CDBP values.

In the preparation of the hot combustion gases employed in preparing the blacks of the present invention, there are reacted in a suitable combustion chamber a liquid or gaseous fuel and a suitable oxidant stream such as air, oxygen, mixtures of air and oxygen or the like.

Among the fuels suitable for use in reacting with the oxidant stream in the combustion chamber to generate the hot combustion gases are included any of the readily combustible gas, vapor or liquid streams such as hydrogen, carbon monoxide, methane, acetylene. alcohols, and kerosene.

It is generally preferred, however, to utilize fuels having a high content of carbon-containing components and, in particular, hydrocarbons. For example, streams rich in methane such as natural gas and modified or enriched natural gas are excellent fuels as well as other streams containing high amounts of hydrocarbons such as various hydrocarbon gases and liquids and refinery by-products including ethane, propane, butane, and pentane fractions, fuel oils and the like. As referred to herein, the primary combustion represents the amount of oxidant used in the first stage of the modular process relative to the amount of oxidant theoretically required for the complete combustion of the first stage hydrocarbon to form carbon dioxide and water. In this manner, there is generated a stream of hot combustion gases flowing at a high linear velocity.It has furthermore been found that a pressure differential between the combustion chamber and the reaction chamber of at least 1.0 p.s.i. (6.9 kPa) and preferably of about 1.5 p.s.i. (10.3 kPa) to 10 p.s.i. (69 kPa), is desirable. Under these conditions, there is produced a stream of gaseous combustion products possessing sufficient kinetic energy to atomize a carbon blackyielding liquid hydrocarbonaceous feedstock sufficiently well to produce the desired carbon black products.The resultant combustion gas stream emanating from the primary combustion zone attains a temperature of at least about 2400"F. (1316"C), with the most preferable temperatures being at least above about 3000"F. (1649"C.). The hot combustion gases are propelled in a downstream direction at a high linear velocity which is accelerated by introducing the combustion gases into an enclosed transition stage of smaller diameter which may, if desired, be tapered or restricted such as by means of a conventional venturi throat.

In the present process a portion of the liquid feedstock is injected in the form of a plurality of solid streams from the inner or outer periphery of the combustion gas stream in a substantially radially outward or inward direction into the combustion gases at a point in the process where the combustion gas stream has not yet reached maximum velocity i.e., approximately the midpoint of the transition zone. The remainder of the liquid feedstock is injected in the form of a plurality of solid streams substantially radially at approximately the mid-point of the transition zone into the combustion gases from the outer or inner periphery of the combustion gas stream, with preference for injection from the outer periphery.By means of this technique for injecting the feedstock, the levels of tinting strength and CDBP of the carbon blacks produced are altered in a direction favoring improved hysteresis.

In the second stage of the process, the combustion gases are flowing at high velocity and there exists a gas kinetic head of at least about 1.0 p.s.i. (6.9 kPa). The portion of liquid carbon black-yielding hydrocarbon feedstock which is injected in the form of solid streams into the combustion gases in the transition or second zone, must be injected under sufficient pressure to achieve proper penetration thereby insuring a high rate of mixing and shearing of the hot combustion gases and the liquid hydrocarbon feedstock. The liquid feedstock is injected substantially transversely from the outer or inner periphery of the stream of hot combustion gases in the form of a plurality of solid streams (coherent jets) which penetrate well into the interior region, or core, of the stream of combustion gases.

Suitable for use herein as hydrocarbon feedstocks which are readily volatilizable under the conditions of the reaction are unsaturated hydrocarbons such as acetylene; olefins such as ethylene, propylene and butylene; aromatics such as benzene, toluene and xylene; certain saturated hydrocarbons; and volatilized hydrocarbons such as kerosene, naphthalenes, terpenes, ethylene tars, aromatic cycle stocks and the like.

The third stage of the modular process is a reaction zone which will permit sufficient residence time for the carbon black forming reaction to occur prior to termination of the reaction by quenching. The residence time in each instance depends upon the particular conditions of the process and the particular black desired.

Subsequent to the carbon black forming reaction having proceeded for the desired period of time, the reaction is terminated by spraying thereon a quench liquid, such as water, using at least one set of spray nozzles. The hot effluent gases containing the carbon black products suspended therein are then passed downstream where the steps of cooling, separating and collecting the carbon black are carried out in conventional manner. For example, the separation of the carbon black from the gas stream is readily accomplished by conventional means such as a precipitator, cyclone separator, bag filter, or combinations thereof.

When practicing the present invention, the amounts of feedstock injected into the primary combustion zone and at the point where the combustion gases have reached maximum velocity are any amounts of proportions which result in the process yielding carbon blacks having increased CDBP values. Furthermore, the blacks will impart improved hysteretic properties to rubber composition containing the blacks. It is preferred to inject an amount of from about 20 to about 80% of the liquid feedstock as solid streams in the primary combustion zone, with the remaining amount of the feedstock being injected as solid streams at approximately the point in the transition zone where the combustion gas stream has reached maximum velocity.In a particularly preferred embodiment, an amount of from about 40 to about 60% of the feedstock is injected in the primary combustion zone, with the remaining amount of the feedstock being injected at approximately the point in the transition zone where the combustion gas stream has reached maximum velocity.

The following testing procedures are used in evaluating the analytical and physical properties of the blacks produced by the present invention.

IODINE ADSORPTION NUMBER This is determined in accordance with ASTM D-1510-70.

TINT STRENGTH The tint strength of a carbon black sample is determined relative to an industry tint reference black in accordance with ASTM D3265-76a.

DIBUTYL PHTHA LA TE (DBP) ABSORPTION NUMBER The DBP absorption number of a carbon black is determined in accordance with ASTM D 2414-76. The results reported indicate whether or not the carbon black is in fluffy or pellet form.

CRUSHED DBP ABSORPTION NUMBER (CDBP) A carbon black pellet is subjected to a crushing type action and the structure is then measured in accordance with ASTM D-3493-79.

MODULUS AND TENSILE These physical properties are determined in accordance with the procedures described in ASTM D-412. In brief, the modulus measurement relates to the pounds per square inch pull observed when a sample of vulcanized rubber is stretched to 300% of its original length. The tensile measurement is a determination of the number of pounds per square inch pull required to rupture or break a sample of vulcanized rubber in a tension test.

EXTRUSION SHRINKAGE This is determined in accordance with ASTM D-2230-37 (Method B).

REBOUND This is determined in accordance with the procedure set forth in ASTM D-1054.

The invention will be more readily understood by reference to the following examples. There are, of course, many other forms of this invention which will become obvious to one skilled in the art, once the invention has been fully disclosed, and it will accordingly be recognized that these examples are given for the purpose of illustration only, and are not to be construed as limiting the scope of this invention in any way.

EXAMPLE 1 In this example there is employed a suitable reaction apparatus provided with means for supplying combustion gas-producing reactants, i.e., a fuel and an oxidant, either as separate streams or as precombusted gaseous reaction products to the primary combustion zone, and also means for supplying the carbon black-yielding hydrocarbonaceous feedstock which are movable so as to permit the adjustment of the location of the radially inward or outward injection of feedstock into the combustion gas stream prior to the point where maximum velocity is attained. The apparatus may be constructed of any suitable material such as metal and either provided with refractory insulation or surrounded by cooling means such as a recirculating liquid which is preferably water.Additionally, the reaction apparatus is equipped with temperature and pressure recording means, means for quenching the carbon black-forming reaction such as spray nozzles, means for cooling the carbon black product and means for separating and recovering the carbon black from other undesired by-products. In carrying out the present example, any suitable burner may be utilized in the primary or first stage combustion in which a primary combustion of 150% may be obtained.The first stage combustion gases having a 150% primary combustion, are formed by charging into the combustion zone of the apparatus air preheated to a temperature of 1200"F. (922'K.) at a rate of 475 k.s.c.f.h. (3.736 m3/sec), and natural gas at a rate of 32.6 k.s.c.f.h. (0.256 m3/sec) thereby generating a stream of hot combustion gases flowing in a downstream direction at a high linear velocity. The rapidly flowing stream of combustion gases passes into a second or transition zone which is of smaller cross-sectional diameter in order to increase the linear velocity of the stream of combustion gases. A suitable liquid hydrocarbonaceous feedstock is then introduced substantially transversely into the resultant stream of hot combustion gases.The feedstock is injected in the form of solid streams both from the outer periphery radially inwardly toward the core of the combustion gases through 1 2 unobstructed orifices each of which has a size of 0.059 inch (1.50 mm), and from the inner periphery radially outwardly into the combustion gas stream through 6 unobstructed orifices each of which has a size of 0.059 inch (1.50 mm). Accordingly, in this run one-third (1 /3) of the feedstock is injected from the inner periphery outwardly, with the remaining two-thirds (2/3) being injected inwardly from the outer periphery of the combustion gas stream.The total feedstock injection occurs in the same plane, namely at approximately the mid-point of the transition zone, at a combined rate of 968 g.p.h. (1.02 1 /sec), and under conditions sufficient to assure a proper degree of penetration into the combustion gas stream so that coke formation in the reactor will not occur. The transition zone of the apparatus has a diameter of 1 2.4 inches (315 mm) and a length of 11 inches (279 mm).

The reactor section has a diameter of 18 inches (457 mm) and a length of 9 feet (2.74 m), prior to quenching the reaction.

The reaction is carried out such that the overall combustion of the process is 26.1 %, or 3.83 equivalence ratio, and the water quench for terminating the reaction is located at a point 9 feet downstream of the location of feedstock injection. The analytical and performance characteristics of this black are reported in Table I. Moreover, this black is utilized herein as a control for Example No. 2 since the feedstock was totally introduced at the mid-point of the transition zone where maximum velocity of the combustion gas stream was reached.

EXAMPLE 2 The procedure of Example 1 is followed using the same apparatus. The main difference in this example from that of Example 1 involves altering the location at which the injection of liquid hydrocarbon feedstock in the form of solid streams from the inner periphery radially outwardly into the combustion gas stream is carried out. In this run the partial injection of liquid feedstock from the inner periphery occurs at a location where the combustion gas stream has not yet attained maximum velocity, i.e., prior to approximately the mid-point of the transition zone.

More specifically, combustion air, preheated to 1200"F. (922'K.) is introduced into the primary combustion zone at a rate of 475 k.s.c.f.h. (3.736 m3/sec) and natural gas is introduced at a rate of 19.8 k.s.c.f.h. (0.156 m3/sec) in order to provide a primary or first stage combustion fire having a 247% primary combustion. In this run, the total rate at which liquid hydrocarbon feedstock is injected into the combustion gas stream is 978 g.p.h. (1.03 1 /sec). Here, as in Example 1, the liquid feedstock is injected in the form of solid streams (coherent jets) from the outer periphery and from the inner periphery of the combustion gas stream. More precisely, 50% of the feestock is injected at approximately the mid-point of the transition zone through 3 unobstructed orifices each of which has a size of 0.110 inch (2.74 mm) from the outer periphery radially inwardly into the combustion gas stream. The remaining 50% of the liquid feedstock is injected as solid streams from the inner periphery of the combustion gas stream in a radially outward direction into the combustion gas stream through 3 unobstructed orifices each of which has a size of 0.11 3 inch (2.87 mm). However, the liquid feedstock injection from the inner periphery in this run is carried out at a location which is 1 8 inches (457 mm) upstream from the plane where maximum velocity of the combustion gas stream is reached, namely at approximately the mid-point of the transition zone.The resultant combustion gas stream passes into the reaction zone where the carbon black forming reaction is quenched with water at a point located 9 feet (2.74 m) downstream of the plane where maximum velocity of the combustion gas stream is reached, i.e., approximately the mid-point of the transition zone. The overall percent combustion of the run is 27.8%. The analytical and physical properties of this black are reported in Table I.

Example No. 1 2 Iodine No., mgI2/g black 89 82 Tinting Strength, % 112 99 DBP Absorption, pellets, cc/lOOg 134 129 CDBP (24M4), cc/lOOg 103 105 The suitability of the blacks of the present invention as low-hysteretic reinforcing agents for rubber compositions is clearly shown in the following Table II. In evaluating the blacks, the rubber formulations are readily prepared by conventional methods. For example, the rubber and the carbon black are intimately admixed together on a conventional mixing machine of the type normally used for mixing rubber or plastics such as a Banbury mixer and/or roll mill in order to insure satisfactory dispersion. The rubber formulations are compounded according to standard industry formulations for a natural rubber or synthetic rubber-containing formulation.The resulting vulcanizates are cured for the time specified in determining the particular physical property. In evaluating the performance of the carbon blacks of the present invention, the following formulation is utilized wherein the quantities are specified in parts by weight. The rubber formulation specifically used herein is the Synthetic Rubber Recipe of ASTM-D-3191-79 and is characterized as follows:: Ingredient Amount Polymer (SBR 1500/23.5% styrene, 76.5% butadiene) ing Zinc Oxide 3 1 Sulfur 175 Stearic Acid N-tert-butyl-2 benzotbiazole aul fenam ide 1 Carbon Black so In the following Table II there are demonstrated the advantageous and unexpected results achieved by the use of the carbon black products described hereinabove as additives in rubber formulations. It will, of course, be apparent that the examples, while being illustrative of the present invention, should not be construed as limiting or restrictive in any way.

TABLE II Physical Properties of Synthetic Rubber Vulcanizates Carbon Black Sample Ex. l* Ex. 2* 300% Modulus, 35 min., psi + 590 + 305 I a' I N (MPa) (+4.068) (+2.103) 300% Modulus, 50 min., psi + 670 + 335 N N N N (MPa) (+4.621) (+2.310) Tensile, 50 min., psi + 295 + 55 N N N U (MPa) (+2.034) (+0.379) Extrusion Shrinkage, % 89 89 Rebound, 60 min, % -3.9 -1.4 *The data are given relative to IRB No. 5.

A review of the data presented above reveals that blacks produced by the present process exhibit the desired properties. When incorporated into the rubber formulations, there is a significant improvement in the rebound property which is an indicator or a rubber vulcanisate having improved hysteresis.

Claims (6)

1. A modular process for producing furnace carbon blacks wherein a fuel and an oxidant are reacted in a first zone so as to provide a stream of hot primary combustion gases possessing sufficient energy to convert a carbon black-yielding liquid hydrocarbon feedstock to carbon black, and wherein in a second zone liquid hydrocarbon feedstock is peripherally injected, in the form of a plurality of solid streams (coherent jets), into the stream of gaseous combustion products at a location where the combustion gas stream has reached maximum velocity in a direction substantially transverse to the direction of flow of the stream of combustion gases and under sufficient pressure to achieve the degree of penetration required for proper shearing and mixing of the feedstock, and wherein in a third zone the feedstock is decomposed and converted into carbon black prior to termination of the carbon forming reaction by quenching, and then cooling, separating and recovering the resultant carbon black, characterised in that a sufficient portion of the total amount of liquid hydrocarbon feedstock is introduced in the form of a plurality of solid streams substantially radially into the combustion gas stream from the periphery thereof prior to the point at which the stream of combustion gases reaches maximum velocity, to thereby produce carbon blacks having increased CDBP values.

2. A process as defined in claim 1 wherein an amount of from 20 to 80% of the total amount of liquid feedstock is injected into the combustion gas stream prior to the location where maximum velocity of the combustion gas stream is reached, with the remainder being added at approximately the point where the combustion gas stream has reached maximum velocity.

3. A process as defined in claim 1 or 2 wherein an amount of from 40 to 60% of the total amount of liquid feedstock is injected into the combustion gas stream prior to the location where maximum velocity of the combustion gas stream is reached, with the remainder being added at approximately the point where the combustion gas stream has reached velocity.

4. A process as defined in claim 1, 2 or 3 wherein the liquid hydrocarbon feedstock which is injected into the stream of combustion gases prior to the point at which the stream of combustion gases has reached maximum velocity is injected in a substantially transverse direction outwardly from the inner periphery of the combustion gas stream.

5. A process as defined in claim 1, 2, 3, or 4 wherein the liquid hydrocarbon feedstock which is injected into the combustion gas stream at approximately the point where maximum velocity is reached is injected in a substantially transverse direction inwardly from the outer periphery of the combustion gas stream.

6. A process for producing furnace carbon blacks substantially as described herein with reference to Example 2.