US2904607A - Alkylation of aromatics - Google Patents

Description

ALKYLATION OF AROMATICS William Judson Mattox and William Floyd Arey, Jr.,

Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Application January 29, 1957, Serial No. 636,909 6 Claims. (Cl. 260-671) The present invention relates to the production of alkyl aromatic compounds by reacting aromatic and olefinic hydrocarbons. More particularly, the present invention relates to a process for the production of alkyl aromatic hydrocarbon compounds of high anti-knock value, which are of suitable boiling range for use as motor fuels. Still more particularly, the present invention relates to a novel catalytic composition peculiarly adapted to produce high yields of alkylated aromatics.

Processes for the cracking of gas oil and similar petroleum fractions to gasoline result in the production of normally gaseous hydrocarbons such as ethylene, propylene, the butylenes and higher. Appreciable quantities of naphtha fraction product are also olefinic, and have relatively high octane values. However, with the increasing development of high compression engines, these fuels are not satisfactory from an anti-detonation viewpoint.

Alkylated aromatics boiling in the naphtha range are known to be capable, when added to naphthas boiling in the gasoline fraction, of imparting a high degree of anti-knock capability. Various methods for the production of alkylated aromatics by combining olefinic or similar unsaturated material, either from products of a conventional thermal or catalytic cracking process or from other sources, with aromatic compounds such as benzene or its homologues, have been proposed.

The prior art processes in general employ an acidic catalyst. The alkylating agent is most frequently an alkyl halide, an alcohol, or an alkene; the essential requirement is that the alkylating agent be capable of inter acting with the catalyst to produce a carbonium ion. The catalyst is a powerful electrophilic reagent, in the Lewis sense, such as AlC1 FeCl SbCl BF ZnCl TiCl HF, H2804, H3PO4, SiO Al O P205 and the like. These reactions are generally carried out at low temperatures and in particular when a Friedel-Crafts catalyst is employed, in the presence of a hydrogen halide such as HCl.

The prior art processes carried out with acidic catalysts are open to many objections. Beside the corrosive nature of the catalyst, the catalyst consumption is high as are regeneration costs, and yields of alkylate boiling in the gasoline range are low, and complicated separations and recycle of feed are required. Furthermore, these catalysts tend to polymerize the olefinic reagents and thus minimize available starting materials. 7

It is an object of the present invention to provide a highly eflicient process for the production of alkyl aromatic compounds.

It is a still further object of this invention to employ a non-acidic catalyst for alkylating aromatics with olefins which provides optimum yields of alkylated aromatics boiling within the naphtha boiling range and minimizes the formation of higher boiling compositions.

Other and further objects and advantages of the present invention will become more clear hereinafter.

nited States Patent 0 2,904,607; Fatented Sept. 15, 1959 It has now been found that aromatic may be particularly readily alkylated with olefins by contacting the reagents at moderately elevated temperatures with a crystalline alumino-silicate catalyst having pore openings adequate to admit freely the individual aromatic and olefinic molecule, and which catalysts have a basic rather than the hitherto desired acidic reaction. The pore opening will therefore be about 6 to 15 Angstroms. Too large an opening, however, does not permit the high activity because of the concomitant decrease in available surface area.

Alumino-silicates of high alkylation activity may be prepared by mixing and heating sodium aluminate and sodium silicate, preferably metasilicate, under carefully controlled conditions to produce a crystalline product which is subsequently dehydrated under condition to preserve the crystalline structure. The sodium content of the crystalline aluminosilicate may be replaced by effecting ion exchange with an appropriate metal salt such as a group II, 111 or IV metal. The metal ion influences the size of the pore openings, as does the ratio of the reagents and the reaction conditions.

In accordance with the present invention, the alkylation catalyst is prepared from a sodium silicate having a high ratio of soda to silica. The ratio is at least 0.8/1, and may be as high as 2/1. Preferably, however, the ratio is 1/ 1, and the desired reagent is sodium metasilicate. Water glass or sodium silicates having lower Na O/siO ratios do not form the adsorbent crystals unless subjected to extended heat soaking or crystallization periods.

The composition of the sodium aluminate is less critical than that of the sodium silicate. Sodium aluminates having any ratio of soda to alumina in the range of 1/1 to 3/1 may be employed; however, a sodium aluminate having a high ratio of soda to alumina is preferred, and a sodium aluminate having the ratio 1.5/1 Na O/Al O is particularly desirable. The amounts of sodium silicate solution and sodium aluminate solutions are such that the ratio of silica to alumina in the final mixture is at least 3/1 and preferably about 4/ 1l0/1. The method of mixing the sodium metasilicate and sodium aluminate solutions must be carried out in a manner allowing formation of a precipitate having a uniform composition. A preferred method is to add the sodium aluminate to the sodium metasilicate at ambient temperatures using rapid and efficient agitation to make a homogeneous paste. Thereafter the mixture is heated to about 180-215 F. for a period as long as 200 hours or more to ensure crystallization in the crystal form necessary to adsorb aromatic molecules. It has been found that the heat soaking period is essential to produce the desired product, which has a pore opening of about 13 Angstroms.

The process of preparing the catalyst may be more clearly understood when read in conjunction with Figure 1, which is a diagrammatic representation of a preferred method of manufacturing the large pore material. Turning now to that figure, a solution of sodium metasilicate is prepared in vessel 2 and of sodium aluminate in vessel 4. The concentration of the silicate may be in the range of about 30-300 grams of SiO per liter, preferably in the range of about 200 grams per liter. The solution of aluminate has a concentration in the range of 40400 grams A1 0 per liter, preferably about 200-300 grams per liter. The amounts of metasilicate and aluminate solutions employed are such that the ratio of silica to alumina in the final mixture is in the range of 3/ 1-10/ 1. A ratio of about 4/ l-8/ 1 is particularly desirable.

Sodium aluminate solution comprising 5-25 A1 0 is passed via line 1 into a mixing zone 5 where it is contacted with a sodium silicate solution comprising -25% SiO as solid, introduced through line 3. The mixing zone is preferably maintained at ambient temperatures. Mixing should be rapid and efiicient, e.g., the impeller zone of a centrifugal pump. The relative amounts of silicate and aluminate introduced to the mixing zone is about 3.5/1 ratio SiO /Al O The resulting mixture, or slurry, is then fed via line 7 through a heat exchanger 9 which is maintained at about 180 F. to 250 F. or higher. The heat exchanger may comprise water, or superheated steam, or high boiling organic materials, or heated fluid solids, at controlled temperature. During the time of passage through the heated zone, the slurry undergoes crystallization to give the desired adsorbent structure. The flow rate of the material through line 7 is adjusted so that the time interval spent in the heated zone 9 is sulficient to complete crystal formation. At about 210 F., this is about 3 to 24 hours; at higher temperatures, shorter times are required, while at lower temperatures, somewhat longer time is required. The effluent crystalline product is then taken via line 11 to a filter and subsequent finishing operations. If desired, a portion of the efiluent stream from the heated zone may be recycled via line 13 by a pump (not shown) to slurry line 7 to serve as seed material and possibly catalyst for the crystallization process.

The precipitated sodium-aluminosilicate, after the heatsoaking period, is withdrawn through line 11, passed to filtration and water-washing zone 17, and then dried and activated in calcination zone 15. Activation temperature may be in the range of 4001000 F., preferably about 700900 F.

The process of manufacture may be modified in various ways, providing the critical features of the high ratio of Na O/SiO in the sodium silicate and of the high ratio of SiO /Al O and the heat soaking period are maintained. Thus, it may be desirable to base-exchange the recovered zeolite with another ion, such as calcium, to form a calcium sodium alumino-silicate. This baseexchange modifies the size of the pore openings. Where this is done, the filter cake of sodium alumino-silicate may be base-exchanged with a solution of a calcium salt or other salt solutions before drying, though this is not essential. The crystalline precipitate of sodium alumino-silicate may be dried, activated by heating to about 700 to 900 F. and used as such, or if desired, the dried alumino-silicate may be base-exchanged with a salt solution.

The exchange reaction may be carried out in several stages if desired using a column contacting technique, countercurrent flow, or other known methods of carrying out base exchange reactions. If desired, very dilute solutions of calcium salt, for example 0.01 to 0.1 molar, may be employed for the base exchange reaction; however, it is preferred to use more concentrated solutions, for example, in the range of about 0.5 to 3.0 molar. A solution of calcium chloride having a concentration in the range of about 5 to 20 percent by weight is particularly preferred.

Base exchanging may be carried out by treating the wet precipitate in the filter with a salt solution, or by reslurrying the precipitate in a salt solution. Besides sodium, other alkali aluminates and metasilicates such as potassium, lithium and the like may be employed. Similarly, other water soluble salts may be employed in the base exchange reaction in place of calcium salts. For example, salts of potassium, lithium, strontium, magnesium, zinc, cadmium, and the like may be employed. Magnesium is particularly desirable.

The alkylation reaction is carried out in equipment of conventional type, one arrangement of which is illustrated in Figure 2. An aromatic, such as benzene or an aromatic concentrate is fed through line 2 along with .a gaseous olefin to a reactor 6 packed with the aluminosilicate catalyst and maintained at a temperature within the approximate range of 300 to 850 F., preferably 400 to 750 F., and at a pressure which may vary up to about 1000 p.s.i.g. The reaction product is passed through line 8 to gas separator 10 for recovery of unconverted olefins which are recycled via 12 to the alkylation reactor. Liquid product from this separator is transferred to a distillation column 16 for separation of unconverted aromatics, mono-alkyl aromatics, and any poly-alkyl aromatics formed. The unconverted aromatics fraction is recycled via 18 to the alkylation reactor while the mono-alkylated'aromatics are recovered as product. Poly-alkyl aromatics, such as the di-alkyl aromatics, will be recycled to the alkylation reaction if the yield of mono-alkyl aromatics is to be maximized, since these more highly alkylated products react with benzene in the presence of the alumino-silicate catalyst to form additional quantities of the mono-alkyl aromatic. One of the distinct advantages, therefore, to the use of the alumino-silicate catalyst is the formation, under normal operating conditions, of a high proportion of the mono-alkyl derivative. If, however, it is desired to maximize poly-alkyl aromatics production, the monoalkyl aromatic may be recycled to the reactor along with the unconverted aromatic while the poly-alkyl aromatics are recovered as product. When producing monoalkyl benzenes, the aromatic/ olefin mol ratio will preferably be about 1/1 to 10/1. If poly-alkyl aromatics are desired, the ratio is preferably about 0.5/1 or less.

In addition to the advantages already mentioned for the alumino-silicate catalyst, the adaptability of this catalytic material to various modes of contacting is outstanding in comparison with previously known catalysts. For example, the alumino-sil-icate may be used in fixedbed or moving-bed reactors, as pellets or various shaped forms, as a fluidized powder, or as a powder dispersed or suspended in the liquid hydrocarbon or in some suitable fluid. Further, the alumino-silicate not only is characterized by long life but is completely restored in activity after prolonged use by simple oxidation treatments with air or other oxygen-containing gas. The usual high catalyst losses and/or expense resulting from reworking of conventional acid type catalysts is avoided.

The process of the present invention may be further illustrated by the following example.

A crystalline sodium alumino-silicate having a pore opening of about 13 Angstroms, and prepared in a manner similar to that described heretofore was employed as an aromatic alkylation catalyst. The sodium aluminosilicate was prepared in aqueous medium at a final pH of 1012, and even after drying and calcining at 850 F. an aqueous suspension showed a pH .of 10-11, indicating the basic nature of this catalyst.

EXAMPLE 1 Alkylation of benzene with propylene sodium alumina-silicate catalysts [Temp-400 F.; pressure-atm.; CuHG/CaHo mo1ratio1.5/1]

Test N0 1 2 Alumino-Silicate Catalyst:

Pore Opening, A Composition Reaction Product:

Isopropylbenzene, Vol. percent Polyisopropylbenzene, Vol. percenL.

Alkylate: Isopropylbenzene, Vol. percent Polyisopropylbenzene, Vol. percent" These data show clearly that it is not enough to employ a zeolite for the alkylation catalyst, but a zeolite having pore openings large enough to admit the reactants. A 4 Angstrom pore opening is too small for this purpose and thus no product was obtained. On the other hand, with the 13 Angstrom pore openings, 83% of the alkylation product that was obtained was mono-alkyl aromatic. To produce alkylated product containing this high a percentage of cumene with phosphoric activated-kieselguhr catalyst (900 p.s.i., and 525 F.) requires a benzene to propylene mol ratio of 4/ l and a correspondingly high recycle of benzene.

EXAMPLE 2 A 500 gram sample of the 13 Angstrom pore diameter sodium zeolite was slurried in a liter of water and 1500 cc. of magnesium chloride solution added. The base exchange operation was repeated twice with fresh 12% magnesium chloride solution each time. The wet pellets were dried in an oven at 250 F. and calcined for 4 hours at 850 F. This material when analyzed showed that about 76% of the original soda content was replaced with magnesia.

The magnesium zeolite thus formed was tested for alkylation activity by contacting with propylene and toluene mixtures at 850 F. at atmospheric pressure. Feed rates were about 0.64 v./v./hr. for the toluene and about 5 mol propylene per mol of toluene feed. The results were as follows:

Liquid product, C 4- Mol percent toluene 69.3 Mol percent C C C aromatics 17.7

These data show that the magnesium form of this zeolite is also an active alkylating agent for aromatics with olefins.

Not only may aromatics be alkylated in accordance with the present invention, but also isoparaflins and alicyclic compounds. Thus, isobutane and isopentane may be alkylated with propylene or isobutylene.

It is also advantageous to employ these 13 Angstrom pore alumino-silicates for concentrating aromatics or isoparaifins from hydrocarbon streams. For example, the alumino-silicate may be used to concentrate the aromatic reactant from such materials as straight run, thermal or catalytic naphthas in which the aromatic content is usually quite low, and hence these streams could not normally be used as alkylation feeds. Aromatics for the alkylation can similarly be adsorbed from hydroformates or aromatized naphthas. Olefinic reactants may likewise be concentrated from a variety of feed sources.

What is claimed is:

1. A process for alkylating an aromatic hydrocarbon with an olefin which comprises contacting the same in the presence of a crystalline metallic alumino-silicate having a uniform pore opening of about 6 to 15 Angstrom units at a temperature of from about 300 to 850 F.

2. An improved process for alkylating aromatic hydrocarbons with olefins which comprises passing an olefinic stream to an alkylation zone, contacting said reactants with a crystalline metallic alumino-silicate having uniform pore openings of 13 Angstroms at about 400 to 750 F., and recovering good yields of alkylated aromatics from said zone.

3. An improved process for preparing a high octane motor fuel which comprises passing an aromatic hydrocarbon having from C to C carbon atoms and a low boiling olefin to an alkylation zone, contacting said mixture at a temperature of from about 400 to 750 F., with a metallic crystalline alumino-silicate catalyst having uniform pore openings of 13 Angstroms, forming a reaction product comprising monoalkylated and poly-alkylated aromatics, separating a high octane gasoline comprising substantial amounts of monoalkylated aromatics, and recycling poly-alkylated aromatics to said alkylation zone.

4. The process of claim 3 wherein said catalyst is a sodium alumino-silicate.

5. The process of claim 3 wherein said catalyst is a magnesium alumino-silicate.

6. The process of claim 3 wherein said aromatics are concentrated from a dilute aromatics comprising stream by contacting said stream with said alumino-silicates.

References Cited in the file of this patent UNITED STATES PATENTS 1,728,732 Jaeger Sept. 17, 1929 2,197,862 Hyman Apr. 23, 1940 2,253,285 Connolly Aug. 19, 1941 2,294,779 Hyman 'Sept. 1, 1942 2,317,803 Reeves et al Apr. 27, 1943 2,698,305 Plank et a1. Dec. 28, 1954

Claims (1)

1. A PROCESS FOR ALKYLATING AN AROMATIC HYDROCARBON WITH AN OLEFIN WHICH COMPRISE CONTACTING THE SAME IN THE PRESENCE OF A CRYSTALLINE METALLIC ALUMINO-SILICATE HAVING A UNIFORM PORE OPENING OF ABOUT 6 TO 15 ANGSTROM UNITS AT A TEMPERATURE OF FROM ABOUT 300* TO 850*F.

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