US2861958A - Process of preparing a silica-aluminaplatinum catalyst - Google Patents

Description

United States Patent p PROCESS OF PREPARING A SILICA-ALUMINA- PLATINUM CATALYST No Drawing. Application March 30, 1954 Serial No. 419,931

5 Claims. (Cl. 252-455) This invention relates to supported platinum catalysts. In one specific aspect, it relates to gasoline reforming catalysts. In another specific aspect, it relates to gasoline reforming processes employing these catalysts. In still another specific aspect, it relates to methods of preparing reforming catalysts.

In'the production of motor fuels, it has been found that certain classes of hydrocarbons have higher octane ratings than others. Accordingly, the overall octane rating of a motor fuel would be increased by any treatment which increases the content of these high-octane constituents. By way of illustration, gasoline is made up of hydrocarbons having about 4 to 11 carbon atoms and classified broadly as aromatic, naphthenic, olefinic, paratfinic, and isoparafiinic. The octane numbers of the pure hydrocarbons are a function of their molecular size and chemical nature. In general, it is understood that isoparaifins and aromatics have high octane ratings, naphthenes and mono-olefins intermediate ratings and normal paraffins low ratings. Di-olefins, because of their instability, cannot be tolerated. Thus, in order to produce a gasoline having high anti-knock qualities, it is desirable to have the highest possible content of aromatics and isoparafiins.

Unfortunately, the hydrocarbon cracking reactions by which petroleum distillates are formed do not permit close control over the aromatic content of the distillates so produced. The cracked products can be upgraded (octans-wise) by distillation, but the yield is lowered by the amount of low-octane constituents removed. It is known that straight run naphthas and cracked distillates can be upgraded by catalytic treatments which convert the lowoctane compounds to high-octane compounds. This process of upgrading gasolines is referred to as catalytic reforming. The reforming reactions, generally, are dehydrogenation, dehydrocyclization, and isomerization. By these reactions straight chain hydrocarbons are converted to branched hydrocarbons, certain naphthenic constituents are converted to cyclohexanes from which aromatics are formed by dehydrogenation. The entire field of catalytic reforming is rather complex and difiicult to interpret but the results are significant.

Efficient reforming of motor fuels requires that there occur a small amount of cracking in order that any heavier-than-gasoline components (distilling above about 400 F.) be cracked to yield lower boiling constituents, which may be subsequently upgraded. It is desirable that reforming reactions be effected with a minimum of 2,861,958 Patented Nov. 25, 1958 gas formation and coke deposition since the former reduces the yield and the latter may impair the efliciency of the catalyst. Reforming processes are normally carried out in the presence of hydrogen in order to maintain the gas formation and coke deposition at a minimum. Since hydrogen is formed by the reforming reactions, it is not usually necessary to add extraneous hydrogen to the system except at the start-up.

The prior art has disclosed a number of catalysts as being suitable for reforming gasoline fractions. Among these are platinum or palladium supported on a base which exhibits cracking activity, examples of which are silica-alumina, silica-alumina-zirconia, or silica-magnesia. In the case of silica-alumina bases, the prior art teaches that the alumina content must be 5% or greater in order for the base to have the requisite cracking activity. One type of commercial reforming catalyst is prepared by impregnating a composite silica-alumina base (12% l 15% alumina) with a platinum compound, which is subsequently reduced to metallic platinum. In view of the relatively high cost of producing a composite silicaalumina cracking component base, it is desirable to find a catalyst which does not require the use of this type of base. This unfavorable cost factor is made worse by the fact that impregnation techniques are complicated and success is not always assured.

Another type of reforming catalyst is prepared by impregnating an alumina base with a platinum compound, which is subsequently converted to metallic platinum.

Silica gel alone has no cracking activity and has never been used as a base for reforming catalysts. This is unfortunate since granular silica gel is simple to make, while alumina and the composite bases require more extensive procedures. Silica gel is a comparatively low-cost base and a reforming catalyst prepared therefrom would be much cheaper than conventional catalysts.

In accordance with the present invention, it is now possible to prepare an efficient reforming catalyst on a silica gel base.

It is therefore an object of this invention to provide a superior petroleum reforming catalyst. It is another object to provide a method for preparing a reforming catalyst on a silica gel base. It is still another object to provide a process for reforming petroleum fractions. Other objects and advantages of the present invention will be apparent to those skilled in the art from the following detailed description and the appended claims.

The novel catalyst of the present invention comprises a silica gel base supporting the requisite amount of platinum and a very small amount of alumina deposited on the silica gel simultaneously with the platinum. The catalyst is prepared by impregnating silica gel with an aqueous solution containing aluminum and chloroplatinate ions, drying the impregnated silica gel, and converting the aluminum and platinum constituents to metallic platinum and alumina.

It has been discovered that silica gel impregnated with about 0.05-5 wt. percent of platinum and about 0.01-LO wt. percent alumina from aqueous solutions of aluminum chloroplatinate, postulated as Al (PtCl or mixed aqueous solutions of an aluminum salt and chloroplatinic acid tremely porous structure. the -scientific literature and is described in the patent literature-as early as U. 5. Patent No. 1,297,724 of jaiuminum chloroplatinate. 'impregnated with the aluminum chloroplatinate solution,

yields,upon reduction, a catalyst which has the desired reforming characteristics of the conventional platinum trations.

The silica gel useful in the present invention is a prepared form of amorphous silicon dioxide having an ex- It is extensively described in Walter'A. Patrick. It maybe prepared by mixing predetermined amounts of a-mineral acid, e. g. sulfuric acid,

and asoluble silicate, e. .g. sodium silicate, allowing the resulting mixture to set to a jelly-like hydrogel,

washing the hydrogel to remove soluble salts and drying the washed material. The dried material may be crushed and screened :to the desired particle size. It is usually given an activation treatment, which comprises heating the dried material to a temperature slightly in excess of the temperature at which the finished material is to be used. Silica gel is .a well-known article of commerce and is {widely used as a desiccant, a carrier for other catalytic agents and as a filler in paints and varnishes. The material prepared in .the described manner is in the form'of hard, rugged, irregularly shaped granules. These maybe used as the base for preparing the catalyst of the present invention or they may be formed into shapes as desired. 7 Dried silica gel is an excellent adsorbent and can be readily impregnated with aqueous solutions.

Platinum on silica .gel catalysts have been prepared heretofore by impregnating silica gel with chloro-platinic acid. These catalysts are used for sulfur dioxide oxidation. However, they have no value as hydrocarbon reforming catalysts and are not to be confused with the catalysts of thepresent invention which also contain very small amounts of alumina and are prepared by different methods.

In one embodiment of the present invention the'silica gel base is impregnated with aluminum chloroplatinate. This compound is the aluminum salt of chloroplatinic acid and may be formed by obvious chemical reactions.

-A convenient method'is to add a relatively pure hydrous alumina in excess to an aqueous solution of chloroplatinic acid. The solution dissolves alumina'to give a yellow '-.-solutior 1.contain.ing the undissolved excess of alumina,

which is removed by filtration to give a clearsolution of The silica gel base is then using-any convenient impregnation technique. The concentration of aluminum chloroplatinate in the impregnating solution is adjusted to give the desired platinum .contentto the finished catalyst when the silica gel has been saturated to the extent obtained by the specific procedure.

the-empirical formula for aluminum chloroplatinate is -Al (-PtC l this formula dictates that the alumina content of a catalyst prepared by the above method be approximately one-fifth the platinum content. Thus, if thezplatinum content is 0.5 weight percent, the alumina content is about 0.1 Weight percent. In practice, the alumina content from aluminum chloroplatinate pre- ..pared by the above procedure is somewhat higher, as

much as three or four times the stoichiometric. This slight excess of alumina is not of any consequence and does not appear to have any detrimental eifect on the catalyst. However, as will be indicated later, reducing the alumina content below the stoichiometric quantity has a decidedly adverse effect.

Thus, pure aluminum 4- chloroplatinate may be used as the impreguant or the more easily prepared but somewhat less pure material prepared as indicated above may be used.

In addition to aluminum chloroplatinate, other solutions containing aluminum and chloroplatinate ions may be employed to impregnate the silica gel with alumina and platinum simultaneously. Mixed solutions of an aluminum salt and chloroplatinic acid are entirely satisfactory.

In a specific embodiment of the present invention the impregnant comprises a mixed solution of aluminum chloride and chloroplatinic acid. This mixed solution permits greater flexibility of control over the alumina content or the ratio of platinum to alumina in the final catalyst, by varying the quantity of aluminum chloride in the mixed solution. In some instances, this method may be preferred to other methods.

The aluminum and chloroplatinate ion containing impregnating solutions maybe applied to the silica gel base by spraying agiven quantity ofbjase with'suflicientI-s'olution to give the desired platinum and alumina content to the finished catalyst. When the spray technique is used, the concentration of the aluminum and chloroplatinate ions in the solution should -be such that the gel is brought to the stage of incipient wetness. This insures uniform dispersion of the platinum throughout the base. The impregnated base is dried and the aluminum and chloro platinate constituents are converted to alumina and plan num by known methods.

As an alternative to the spray technique, the silica gel base maybe immersed in the impregnating solution until it becomes-saturated, following -which,i t is drained to remove excess liquid and dried and reduced. =In using this method, .it is necessary to take into consideration the unexplainedphenomenon that silica gel appears to repel the chloroplatinate ions so that there is -a selective adsorption of water from these impregnating solutions, re-

suiting in an increase in concentration of chloroplatinate method is to pass a stream of heated-air or gas througha bed of the impregnated gel. Thedriedi'gelis-reduced with hydrogen in a manner to give a silica geliimpregnated with'the small amounts of platinum and alumina. A1- ternatively, the hydrogen reduction may be substituted by thermal decomposition .or other convenient means of converting the aluminum'and chloroplatinate constituents to alumina and metallic platinum.

The present'invention will be further illustrated-by the following non-limiting examples:

EXAMPLE 1 Three series, designated as Series A, B, and C, ofsupported platinum catalysts were prepared. Series A and C comprise five catalysts containing approximately 0.05, 0.10 0.20, 0.40 and 0.80 weight percent platinum. Series B comprises three catalysts containing approximately 0.15, 0.30, and 0.60 weight percent platinum. The catalysts of each series were prepared by the same general methods as indicated hereafter:

Series A-Chloroplatinic acid on silica-aluminagranules Series B --Chloro platinic acid on silica gel Series C-Aluminum chloroplatinate on silica gel The silica alumina base contained approximately llij percent alumina and was prepared by impregnating assists washed silica hydrogen with aluminum nitrate and drying of m. /g. and was similar to the bases used in commercial catalysts.

Series A The catalysts of Series A were prepared by soaking the silica-alumina base in a solution of chloroplatinic acid of suitable concentration for eight days at approximately 180 F., using a closed container to prevent evaporation of liquid. The concentrations of the platinum solutions were selected to give the desired platinum content in the finished catalyst, as determined by the adsorption characteristics of this base. At the end of the impregnation pe riod, the jars were cooled, the excess liquid was drained off and the impregnated granules were washed three times with distilled water to remove soluble platinum. Following this, the granules were dried in an oven for 48 hours at 230 F. and then heated to about 450 F. for about 1% hours in a stream of dry oxygen-free nitrogen. The dried material was reduced for two hours at 450 F. in a stream of dry, oxygen-free hydrogen. The reduced catalysts were finally cooled to ambient temperatures in a hydrogen stream.

Series B The catalysts of Series B were prepared by impregnating a commercial grade of silica gel identified as The Davison Chemical Corporations Grade 40 silica gel. The properties of this material are indicated hereafter:

SiO (dry basis) 99.60% min. Water soluble 0.50% max. Density 40-45 lbs. per cu. ft.

An 8-12 mesh fraction of this silica gel was heated for four hours at 1200 F. following Which it was cooled and sprayed with the predetermined amount of chloroplatinic acid solution to give the desired platinum content in the finished catalyst. The thus impregnated material was dried and reduced in the manner described for Series A.

Series C The catalysts of Series C were prepared by the same method of impregnation of the same silica gel base described for those of the Series B, but using the aluminum chloroplatinate impregnating solution of this invention. This solution was prepared by dissolving freshly precipitated hydrous alumina in a solution of chloroplatinic acid. Drying and reduction of the catalysts were carried out in the same manner employed for the catalysts of Series A and B.

The catalysts of the foregoing series were prepared under very carefully controlled conditions to insure that, apart from fundamental dilferences, the procedures followed were as nearly identical as possible. All of the catalysts were analyzed for total platinum to facilitate comparison between the catalysts at the same platinum level.

The activities of the catalysts in each series were examined by the methylcyclopentane (hereinafter designated as' MCP) method. In carrying out this test, a mixture of MCP and hydrogen was passed over 50 m1. of 8-12 mesh catalyst in a tubular reactor at a temperature of 860 F. and a pressure of 500 lbs/sq. in. The hydrogen to hydrocarbon ratio was 6 to 1, and the liquid hourly space velocity was 2.25. Isomerization-dehydrogenation reactions result in the conversion of MCP to benzene. The activity of each catalyst was measured by the yield of benzene obtained during the second hour of the test. Gases from the reactor were passed through a water trap at 32 F. and thence through a Dry Ice trap. The benzene content of the liquid product was determined by examination with a Beckman spectrophotometer. Losses comprised uncondensible gases. The results of these tests appear in the following table.

TAB LE 1 Weight percent Yield Weight by MCP Test Catalyst No. percent Platinum Liquid Benzene Product v The MCP activities of Series C catalysts, prepared by the method of this invention, increased with increased 'platinum content, the yield of benzene reaching a value of 11.9% at about 0.7% platinum. These activities were somewhat lower than those of Series A catalysts (extended chloroplatinic acid impregnation of a silica-alumina base at 180 F.). However, the yields of liquid product attained with Series C catalysts were superior in most in stances to those with Series A catalysts.

Series B catalysts (chloroplatinic acid-silica gel) all showed very low activities in striking contrast to the activities of the catalysts prepared according to the present invention, which contain only a few hundredths of a per cent more alumina.

EXAMPLE 2 ASTM distillation: F.

Over-point 178 10% 212 50% 255 319 330 Endpoint 350 API Gravity 60 F.: 56-57. CPR-Research Octane No. 54-57.

in a tubular reactor over a bed of 75 ml. of 8-12 mesh catalyst, which had been activated at 900 F. for one hour. The inlet temperature was 930 F. and the pressure 500 lbs./ sq. in. The hydrogen to hydrocarbon ratio was 12.6 to 1 and the liquid hourly space velocity 3.0.

The activity and stability of each catalyst was assessed by considering the Research Octane numbers of the, reformates' produced after 72 and 200 hours. A catalyst is regarded as good if, under the above conditions, the octane number of the reformate after 72 hours is 88 or greater, and the decrease in octane number between 72 and200 hours does not excess about, 2.5 units. The following. table illustrates the results of these tests:

accrues scribed in Example 2. A mixture of hydrogen and the East Texas Naphtha o f Example 2'was passed in a tubu- TABLE 2 CFR-RO No. at 4 lb. Volume API Gravity Weight R. V'; P. Percent 60 F. Catalyst Percent Yield at Platinum 88.0

72 hr. 200 hr. Decrease CFR-RO 72 hr. 200 hr.

Series A:

Only four of the seven catalysts tested metthe 88.0

octane requirement at 72 hours, and/or a decrease of, less than 2.5 units after 200 hours. These were Numbers 4 and 5 of Series A, chloroplatinic acid-silica-alurnina base, and Numbers 4 and 5 of Series C prepared by the present invention. Although Series C CatalystNo. 3 did not produce an 88 octane reformate, the increase in octane rating of the feed from 56-57 to 81-82 is indicative of its substantial reforming ability. To determine the yield-octane lar reactor over 75. ml. of 8t1'2mesh eatalyst which had been activated for two hours at 1000-F. The inlet temperature was 940 F., and the pressure 500 lbs/sq. in. The liquid hourly space velocity was 3.0 andthe hydrogen to hydrocarbon ratio 10.0 to 1. CFR Research Octane Numbers and API Gravities of the reformates were measured after 72 and 200 hours on stream. Volm pe cent. yield w s dete m ned at CFR-RO No. 89.5-

The following table presents the results of these tests.

relationship in cases where an octane of 88 was closely approximated but not attained, the yield which would be expected at 88 was estimated by applying a correction factor.

Table 2 indicates that the octane number of the reformate after 200 hours increases as the platinum content of Series A and Series C catalyst is increased. The table further shows that Series A and Series C catalysts containing approximately the same weight percent platinum produce reformates after 200 hours of approximately the same octane rating. The optimum platinum content of both catalysts appears to be about 0.40.5 weight percent. It is also evident from Table 2 that the yield from Series C catalysts, which contain, less than 1 weight percent alumina on the silica gel support, are as good as the yields attainable With Series A catalysts, the silica-alumina base of whicheontains 15.5 weight percent alumina.

The API gravity measurements of the reformates prepared with the catalystsof this invention after 72 and 200 hours are fairly constant. This indicates that the novelcatalyst is quite stable after 200 hours on stream.

EXAMPLE 3v platinum contents of Catalyst B were made to closely approximate those of Catalyst Ref mi g s Qadi p'ns re si la it? e e espace velocity is defined as the volume of oil These data clearly indicate that catalysts prepared either by impregnation of a silica gel base with aluminum chloroplatinate or with a solution containing aluminum chloride and chloroplatinic acid are entirely satisfactory reforming catalysts. They both produce high yields of high octane reformates, and are both highly stable catalysts.

In addition to aluminum chloroplatinate and a mixed solution containing aluminurnchloride and chloroplatinic acid, other solutions containing aluminum ions and ehlorep i te io may b employed to im ate the s l ca l ordi to th i ven ien- A a p act a matter, certa al mi um sa t o h r than um m ehleri emay be c mbine i h h e p a d t term a sat sfactor mp e natin t n. e l m num nitrate. The choiceof aluminum salts, however, is necessarily restricted to those. which do not contain ions which will poison the final catalyst or reduce its initial activity. Acceptable aluminum salts are those whose anions will be removed from the catalyst during hydrogen reduction or calcination as the case may be.

The reforming process employing the catalyst prepared in accordance with the present invention will be effected at a temperature of about 600 to about 1000 F., at a pressure of about 1000 p: s. i. and at a liquid hourly space velocity of about0.5-l0. The liquid hourly per hour per volume of catalyst in the reaction zone. Sufiicient ydrogen will usually be pr duced in th r mi g re action to furnish thehydrogen required in the process, and therefore it is usually unnecessary tointroduce extraneous hydrogen except at'the "start up. In order to assure a sufficient hydrogen atmosphere in the reaction Zone'after start up, hydrogen produced is usually refi l/5 15 51.- Tlle hydrogen present in the reaction zone will be within the. range of trom 'about0.5 to about 15 mols of hydrogen per mol of hydrocarbon. The exact ternperature, pressure, space velocity and hydrogen to hydrocarbon ratio used in any given operation will depend upon the particular gasoline fraction being treated and the products desired.

I claim:

1. A method for preparing a silica gel base catalyst suitable for reforming gasoline fractions which comprises impregnating silica gel with an aqueous solution of aluminum chloroplatinate in amount suflicient to incorporate in said gel about 005 5.0 weight percent platinum and 0.011.0 weight percent alumina, drying the impregnated gel, and converting the adsorbed platinum compound to alumina and metallic platinum.

2. A method for preparing a silica gel base catalyst suitable for reforming gasoline fractions Which comprises activating silica gel at a temperature above that at which reformingis carried out, impregnating the activated gel with an aqueous solution of aluminum chloroplatinate in amount sufficient to incorporate in said gel about 0.055.0 weight percent platinum and 0.011.0 weight percent alumina, drying the impregnated gel, and converting the adsorbed platinum compound to alumina and metallic platinum.

3. A method according to claim 2 wherein the catalyst is thermally activated following conversion of the adsorbed constitutents.

4. A method for preparing a silica gel base catalyst suitable for reforming gasoline fractions which comprises heating silica gel at a temperature of about 1200 F. for a period of about 4 hours and thereby activating said gel, impregnating the activated gel with an aqueous solution of aluminum chloroplatinate in amount sufficient to incorporate in said gel about 0.055.0 weight percent platinum and 0.011.0 weight percent alumina, drying the impregnated gel, and converting the adsorbed platinum compound to alumina and metallic platinum.

5. A method for preparing a silica gel base catalyst suitable for reforming gasoline fractions which comprises heating silica gel granules having a particle size of about 812 mesh at a temperature of about 1200 F. for a period of about 4 hours and thereby activating said gel, impregnating the activated gel with an aqueous solution of aluminum chloroplatinate in amount sufiicient to incorporate in said gel about 0.05-5.0 Weight percent platinum and 0.01-1.0 weight percent alumina, drying the impregnated gel, and reducing the dried gel in an atmosphere of hydrogen.

References Cited in the file of this patent UNITED STATES PATENTS 2,005,412 Connolly et al. June 18, 1935 2,437,532 Huffman et al. Mar. 9, 1948 2,452,198 Kennedy et al. Oct. 26, 1948 2,470,142 Chapman et al. May 17, 1949 2,550,531 Ciapetta Apr. 24, 1951 2,589,189 Ciapetta et al. Mar. 11, 1952 2,635,123 Kennedy Apr. 14, 1953 2,662,861 Riblett et al. Dec. 15, 1953 2,663,620 Haensel Dec. 22, 1953

Claims (1)

1. A METHOD FOR PREPARING A SILICA GEL BASE CATALYST SUITABLE FOR REFORMING GASOLINE FRACTIONS WHICH COMPRISES NUM CHLOROPLATINATE IN AMOUNT SUFFICIENT TO INCORPORATE IN SAID GEL ABOUT 0.05-5.0 WEIGHT PERCENT PLATINUM AND 0.01-1.0 WEIGHT PERCENT ALUMINA, DRYING THE IMPREGNATED GEL, AND CONVERTING THE ADSORBED PLATINUM COMPOUND TO ALUMINUM AND METALLIC PLATINUM.