US2396144A

US2396144A - Aromatic hydrocarbon alkylation

Info

Publication number: US2396144A
Application number: US464287A
Authority: US
Inventors: Anderson John; Edwin F Bullard; Sumner H Mcallister
Original assignee: Shell Development Co
Current assignee: Shell Development Co
Priority date: 1942-11-02
Filing date: 1942-11-02
Publication date: 1946-03-05
Anticipated expiration: 1963-03-05

Description

March 5, r1946. J. ANDERSON ET Al.

AROMATIC HYDROCARBON AL-{YLATION Filed NOV. 2, 1942 `Patented Mar. 5, 1946 HYDROCARBON ALKYLATION John Anderson, Berkeley, Edwin F. Bullard, Oakland, and Sumner H. McAllister, Lafayette, Calif., aasignors to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application November 2, 1942, Serial No. 484,2-87

(Cl. 26o-671) y Claims. This invention relates tothe alkylation of aro- Amatic hydrocarbons in the presence of sulfuric acid. It deals with a new and more economical method of carrying out such alkylations whereby the life of the catalyst acid and the yield and quality of the product may be increased.

It is well known that aromatic' hydrocarbons such as benzene, toluene. naphthalene and the like may be reacted in the presence of sulfuric acid with a wide variety of alkylating agents to produce the corresponding alkylated aromatic hydrocarbons. In the reaction methods previously used, however, the life of the catalyst acid has been undesirably short. For this reason the industry has turned to other more expensive catalysts requiring less desirable vapor phase methods of operation. An important object of the present invention is to reduce the cost of alkylating aromatic hydrocarbons by increasing the effective life of sulfuric acid catalysts in the reaction. Another object is to improve liquid phase methods of reacting aromatic hydrocarbons with alkylating agents in the presence of sulfuric acid. A further object is to increase the yield of desirable alkylation products obtainable by such reactions. Still another object is to produce aromatic alkylation products having superior properties, particularly as regards their motor fuel characteristics by means of sulfuric acid alkylation catalysts. Other objects and advantages oi the process of the invention will be apparent from the following description.

The aromatic hydrocarbons available for alkylation on a commercial scale all contain thiophene and other sulfur compounds. vThese sulfur compounds such as thiophene are known to be alkylatable under much the same conditions as are aromatic hydrocarbons. It would therefore be expected that they should not interfere with the alkylation process in any way. It has been found, however, that very small amounts ofV thiophene or the like in the aromatic hydrocarbon to be reacted can materially reduce the life of sulfuric acid alkylation catalysts and can reduce the yield of the alkylation products. Based upon this discovery, a processl has been devised for more economically alkylating aromatic hydrocarbons in the presence of sulfuricL alkylation is employed lin this pretreatment step. Thus, for example, in alkylating benzene with an "oleilne such as propylene, sulfuric acid of to concentration has been foundto be an esv pecially effective catalyst while for the pretreatment of the benzene used. with such acid, it is preferable to employ sulfuric acid of at least but preferably below concentration, since anhydrous acid has been found to cause undesirable sulfonation leading to emulsion formation and other difficulties. A ratio of acid to benzene above 1 to 10 by volume should be used and ratios of about 0.16:l to 025:1 are preferred although higher ratios may be used. The acid and benzene may be intimately contacted by agitation in a mixer l, of the drawing, or other vessel or by counter-current flow in a tower which may or may not contain packing to promote intimate mixing, or in any other suitable manner. A contact time of sulfuric acid with benzene of at least 3 minutes and more preferably 4 to 6 minutes or longer is desirable. Contact in a plurality of treatment stages is advantageous in reducing the amount of acid required for treatment of a given volume of aromatic hydrocarbon. For example, goodresults have been obtained by treating benzene with a total of 25 pounds of 98% sulfuric acid per barrel of benzene, the acid being added in four equal portions with 15 to 30 minutes agitation, followed by settling and decantation, in settler 2 of the drawing, in each case. The separated acid may be re-used for treatment of further benzene,'only the last treatment being with fresh acid. Instead of batch treatment, continuous methods of treating may be employed. A temperature between 10 and 40 C., preferably about 15 to 25 C., is maintained during the acid treatment. After the acid treatment the aromatic hydrocar- 0 bon ls preferably washed with water andv a base acid. For the purpose of illustrating the combination ofsteps characteristic of the process ln one of its preferred forms, the attached'drawing shows. diagrammatically, a typical process flow. While the method ofoperation which will be best in any given case will depend upon .the particular aromatic hydrocarbon or hydrocarbons used, it is preferred to react the aromatic hydrocarbon involved with concentrated sulfuric acid prior to contacting the hydrocarbon with the alkylation acid catalyst. Most preferably sulfuric acid of higher concentration than that-used for such as aqueous caustic soda,l calcium hydroxide or the like in units 4 and 5, respectively, of the drawing, before being used in the alkylation step ofy the invention carried out in alkylation unit 6.

The alkylation of the acidl treated aromatic hydrocarbon is preferably carried out in the presence of sulfuric acid under conditions at which all the reactants are in the liquid phase, using a substantial stoichiometric excess of the aromatic hydrocarbon based upon the amount of alkylating agent employed. It has already been suggested that in alkylating benzene with an olefine, for example. an excess of benzene over oleflne should beused in order to suppress the formation of higher alkylation products of the benzene. Such an excess of benzene is not sufficient, however, for most efficient reaction in the presence of'sulfuric acid, and it has been found desirable to use a feed containing at least four and more preferably five to ten or more mols of the aromatic hydrocarbon being alkylated per mol of olefine or equivalent alkylating agent in the process oi' the invention. With alkylating agents such. for example, as di-isopropyl ether or di-isopropyl sulfate, etc., capable of introducing two alkyl groups per mol of alkylating agent used, the proportions of aromatic hydrocarbon in the feed are preferably doubled so that most advantageously between ten and twenty mols of benzene are used per m01 oi dialkyl alkylating agent. In this way not only are undesirable side reactions such as the formation of polyalkylated products substantially eliminated, but also the effective life of the sulfuric acid in the process and the yield and quality of the mono-alkylated products are unexpectedly increased. The excess aromatic hydrocarbon in the `feed may advantageously comprise unreacted aromatic hydrocarbon-recovered from the reaction product and recycled to the alkylation.

As previously pointed out, sulfuric acid of about 80 to 90% concentration is the preferred catalyst for the alkylation step of the process. Most advantageously the sulfuric acid is maintained at a concentration of about 85 to 88% and a temperature of about 40 to 50 C. The acid concentration may be maintained within the desired range by replacing with stronger acid a part of the used acid phase obtained by stratifying the reacted emulsion in settler 1 of the drawing prior to return of the acid to the reactor by line 8.

At least 10 minutes contact time between acid and hydrocarbon should be allowed for the alkylation and more advantageously about to 30 minutes contact time should be provided` since it has been found that under otherwise analogous conditions the effective lifejof the sulfuric acid alkylation catalyst could be increased about 33%' by increasing the contact time from 10 to 20 minutes when alkylatlng benzene with propylene.

The reactants and catalyst acid may be agitated together in any suitable type of apparatus. v

' desired concentration of acid in the system. By

this method of operation the alkylation may be effected in the presence of even higher proportions of aromatic hydrocarbon to alkylating agent than are present in the feed. Thus, by controlling the rate of feed with relation to the 'rate of recirculation of emulsied reaction mixture so that the feed is admlxed with 10 to 2D or more volumes of reacted hydrocarbon in emulsified form, the alkylation may be effected in the presence. of about to 100 or more mols of aromatic hydrocarbon per mol of alkylatlng agent without making it necessary to correspondingiy increase the volume of reacted hydrocarbon which must be distilled for recovery of the product. To the same end, the alkylation may be carried out in two or more alkylation units to each of which -a part of the alkylating agent is fed, while the entire feed of aromatic hydrOoarbon to bev alkylated is fed to one unit only and the aromatic hydrocarbon feed for the other units comprises the hydrocarbon layer from the separator of the preceding alkylation unit in the series.

An important feature of the process of the invention in its preferred form comprises recycling atleast a part of the unreacted hydrocarbon recoveredl from the alkylation product in still I5, by lines I8 and I1 to the previously described acid pretreatment step instead of to the alkylation reaction by lines I8 and I8. This method of operation has been found to give improved results in respect to the quality of product and life of the catalyst acid in spite of the fact that the thus returned aromatic hydrocarbons have not only been previously treated under the same conditions for a period apparently entirely sufficient to complete all the desired changes but also have been further treated with sulfuric acid at a higher temperature in the alkylation stage of the process. It is quite unexpected, therefore, to find that further treatment of the excess unreacted aromatic hydrocarbon gives improved results. It may be that undesirable components which are not removed by the initial treatment of the aromatic feed and which build up in the system as the excess hydrocarbon is continuously recycled are modified under the alkylation conditions so that they are removed by the subsequent treatment. Regardless of the mechanism whereby the improvement is achieved, it has been found that the advantages of this procedure may be obtained without retreatment of the entire amount of the recycled aromatic hydrocarbon. At least about 20%. however, of such hydrocarbon should be treated and more preferably about 25% to 50% or more is returned to the treating stage of the process. Most advantageously, the aromatic hydrocarbon thus returned for treatment with sulfuric acid of higher concentration than the sulfuric acid used as the alkylationy catalyst is first reacted with caustic soda or other suitable base in unit I9 of the drawing. This treatment with a base will be hereinafter referred to as hydrolysis treatment because it is known that one of the results usually accomplished thereby is the hydrolysis of esters, such as sulfuric acid esters for example, which may be present. However, it will be understood that other reactions may take place instead of or in addition to the hydrolysis of sulfuric acid esters and that such other reactions may be just as, or more, important in bringing about the observed improvement which results from this step in the process. The expression hydrolysis will therefore be used to refer to any high temperature treatment with an aqueous, and preferably alkaline, medium, in which sulfur compounds are removed from the hydrocarbon phase of the reacted alkylation mixture or a component or components thereof, regardless of the nature of the reaction or reactions involved.

While the hydrolysis treatment may be variedv somewhat according to the nature of the aromatic hydrocarbon being alkylated and alkylating agent or agents used, etc., the preferred procedure comprises reaction with a dilute solution of sodium, calcium or ammonium hydroxide, although other strong bases such as other alkali metal hydroxides or Quaternary ammonium bases, etc., may be' used. The treatment is carried out at an elevated temperature in excess of 100 C., preferably under superatmospheric vat least minutes is desirable and times of about to 30 minutes are preferred.

The hydrolysis treatment may be applied to the entire hydrocarbon layer from the separator of the alkylation -unit which layer may be supplied to hydrolyzer I9 by lines 20 and I4, particularly whenrelatively pure reactants are being used for the alkylation, in which case the hydrocarbon layer will consist almost entirely of benzene and cumene.V However, when substantial amounts of lower boiling hydrocarbons are present in the mixture as when benzene is being alkylated with the propylene of a propylene-propane fraction of cracking products. for example, the presence of the propane during hydrolysis at the preferred high temperatures of about 150 C. may make it necessary to use fairly expensive pressure` resistant units for the treatment of the entire hydrocarbon layer from the separator. This cost may be reduced by removing the lower boiling hydrocarbons responsible for the generation of excessive pressures during or before the hy drolysis. Thus, for example, the basic solution to be employed in the hydrolysis may be added to the hydrocarbon layer from the alkylation separator 'I and the mixture may be fed to a stripping column II in which propane and/or other undesirable lower boiling hydrocarbons are separated by line I2. The presence of the base during this separation minimizes corrosion difficulties and the bottom product is a mixture of benzene and alkylation products with aqueous base which is fed by lines I3 and Il to the hydrolysis unit. Alternatively, the fractionation may be carried out in the presence of the aqueous basic solution so that the unreacted aromatic hydrocarbon is separated from the alkylation product at the same time that the hydrolysis is being effected. If necessary the unreacted aromatic hydrocarbon and/or alkylated product may be separately subjected to hydrolysis under the previously described'conditions. In some cases, of course, it may even be feasible to omit the hydrolysis treatment of the unreacted aromatic hydrocarbon and feed the mixture directly to still I5 by lines 20, III and 2| or lines I3, I4 and 2|. However, it is preferred to submit such hydrocarbon to the `treatment with alkali, most preferably along with the alkylation product. In any case the unreacted aromatic hydrocarbon is` recycled to the alkylation unit by line I1 or line I 8 for further reaction, most preferably after being again treated with sulfuric acid along with or separately from thel fresh aromatic feed as previously described. y

The following examples illustrate the advantages of the process as applied to the production of cumene by alkylating benzene with propylene. Analogous improvements may be obtained, however, when alkylating other aromatic hydrocarbons with the same or other alkylating agents in the presence of sulfuric acid.

Benzene containing 1.2% of thiophene was continuously treated by passing a stream into a mixer which fed emulsion of benzene and sulfuric acid to a separator from which the separated acid returned to the mixer so that the benzene was contacted with a fixed amount of acid. Using sulfuric acid of 98% concentration at 20 C., a contact time of 10 minutes and equal volumes of acid and hydrocarbon in the mixer, the sulfur content, of the total benzene was reduced to a total of 0.067% after 27.6 volumes had been treated per volume of acid. The acid at the end of the run was still active and the amount of benzene which could have been successfully treated therewith could have been considerably increased, particularly by carrying out the treatment in two or more stages. The loss in weight of the benzene was between 1.5 and 3.0%, of

. which 1.2% could be attributed to the removal of thiophene.

The alkylation step of the process was carried out in turbo mixer type of reactor arranged so that the hydrocarbon feed contacted a circulating stream of emulsified reaction mixture, a part of which was continuously withdrawn to a separator from which separated catalyst acid was continuously returned to the reactor. The feed was a mixture of benzene and a puried propanepropylene fraction substantially free from sulfurcontaining compounds, the proportions of benzene and propane-propylene fraction being such that the mol ratio of benzene to oleflne in the feed was 5 to 1. The other operating conditions maintained during alkylation were as follows:

Sulfuric acid catalyst concentration:

88.0 wt. per cent charging strength v79.2 wt. per cent dropping strength Feed composition: Benzene, 74.4 wt. per cent Propylene, 8.0 wt. percent Propane, 17.6 wt.'per cent Acid to hydrocarbon volume ratio. 1: 1

`Contact time, 20 minutes Temperature, 40 C.

Under these conditions, the following results were obtained with puriiled benzene:

Weight per cent cumene based on propylene fed 278 Per cent of reaction product boiling Volumes of cumene produced per volume of sulfuric acid used 16.6

Partially depropanized hydrocarbon product of the following composition was hydrolyzed with 20% by weight of caustic soda of 5% concentration using a temperature of C. for 10 minutes:

`Per cent by weight l Propane 2.8 Benzene 70.4 Cumene 26.8 Sulfur 0.088

The hydrolyzed product contained 0.026% sulfur.

that in the benzene for recycling being .0.03% and that in the remaining cumene fraction beingy acid treating'the initial benzene. The sulfuric acid catalyst life was only about two volumes of cumene per volume of acid or of the order of one-eighth of that obtained by the process of the invention. At the same time the yield of cumene, based on the propylene fed, was only 238% and the products boiling between 100 and 154 C. were only 88% 0f the total. Without hydrolysis treatment of the hydrocarbon layer from the alkylation the yield and quality of the product were materially reduced and extensive cracking and corrosion were encountered during depropanization in a pressure still. Substitution I v the molar ratio of benzene to propylene at the' point of introduction of the feed is below about 50:1, likewise reduces the yield and quality of the product. Experiments made using 86% sulfuric acid at 50 C. showed that the life of the catalyst was reduced from l2 to 9 volumes of cumene per volume of acid by reducing the average time of contact from 20 to 10 minutes.

It will thus be evident that the process of the invention offers many advantages, particularly in regard to economy and efficiency, compared with prior methods of alkylating aromatic hydrocarbons in the presence of sulfuric acid catalysts. The increased catalyst life and quality of product resulting from the new procedure of ilrst reacting the aromatic hydrocarbon feed in the absence.

of alkylating agents with sulfuric acid of higher concentration and at a lower temperature than used in the alkylation, especially when employed in connection with a like treatment of the recycled excess unreacted aromatic hydrocarbon, most preferably recycled aromatic hydrocarbon ethers, alcohols and esters such as di-ethyl, methyl-ethyl, methyl-isopropyl, di-normal propyl, ethyl-isopropyland the like ethers, ethyl and higher primary alcohols may be used. Either inorganic or organic esters such as halides, sulfates, phosphates. borates, formates, acetates and the like may be employed as alkylating agents. The alkylating agent may beused in a pure or substantially pure former asmixtures of one or more alkylating agents with or without other materials which do not interfere with lthe desired reaction.

Instead ofpure sulfuric acid as the catalyst, such acid containing suitable addition agents to modify or improve the reaction 4or sulfuric acid admixed with other alkylation catalysts may be employed. Sulfuric acid which has been employed for the alkylation of isoparafilns, for example, is a suitable catalyst for the process.

The invention is capable of modification not only with respect to the reactants which may be used but also in regard to the operating arrangements and conditions. Thus, while continuous methods -of reaction have been emphasized. intermittent or batch procedures are also suitable. Furthermore. instead of returning the hydrolyzed and/or acid treated recycled aromatic hydrocarbon to the same alkylation reactor it may be fed to a different alkylation unit in which the same or-*some other alkylating agent is used.

Also, the acidvtreatment of the recycled aromatic hydrocarbonmay be carried out separately from,

which has been subjected to hydrolysis, are of outstanding importance.

The new process may be applied to the alkylation of vnot only benzene but also a wide variety` of other aromatic hydrocarbons, although when used for the production of motor fuels or motor fuel components volatility considerations make it more advantageous to use lower boiling aroy matic hydrocarbons, particularly benzene and toluene. Where such considerations are of lesser importance higher boiling compounds .may be employed. Thus ethylbenzene, the xylenes, pro-A ene, normal butylenes, the amylenes or mixtures of one or more such oleflnes. Instead of the oleilnes, polymers thereof may be used. Not only may ethers. alcohols and esters corresponding to instead of together with, the treatment. if any, of the feed. Still other changes may be made without departing from the invention, which isl not limited to the details of operation disclosed lnor by lany theory proposed in explanation of the improved results obtained.

We claim as our invention: 1. .A process of producing cumene which comprises treating benzene with sulfuric acid of 95% lthe ratio of 3 to 10 mols of benzene per mol of Vpropylene and feeding the mixture into a circulating stream of an emulsion of benzene-containing hydrocarbon and sulfuric acid of to 90% lconcentration at a temperature of about 40 to 50 C. so as to maintain at the point of contact of said feed and emulsion amolar 'ratio of ben,

zene to oleflne of atleast 50 to 1 and a volume ratio of acid phase to vhydrocarbon phase between 0."Iv to 1 and 1.3 to 1, withdrawing and separating reacted emulsion after an average time of contact of at least 10 minutes, returning atleast a part of the acid phase from said withdrawn emulsion to the reaction, subjecting separated hydrocarbon containing excess unreacted benzene to a hydrolysis treatment with 10% to 50% by volume of an aqueous solution of a strong base of 2% to 10% concentration at between 100 C. and 180 C. for at least 5 minutes, returning at least a part of the thus treated benzene to the treatment with to 99% sulfuric acid and recovering the cumene produced.

2. A process of producing cumene which comprises treatins benzene with sulfuric acid of 95% to 99% concentration at 15 to 25 C. for at least 3 minutes in the absence of alkylating agents, reacting the treated benzene with propylene in the liquid phase in the presence of sulfuric acid of 80% to 90% concentration at a temperature of about 40 to 50 C. while maintaining a substanthe foregoing oleilnes be employed, but also other 75 tial molar excess of benzene over Aoleilne in the acted mixture into an acid phase and a reactedA hydrocarbon phase, returning vat least a part of the acid phase to the reaction, subjecting the reacted hydrocarbon containing cumene and excess unreacted benzene to a hydrolysis treatment with to 50% by volume of an aqueous solution of a strong base of 2% to 10% concentration at between 100 C. and 180 C. for at least 5 minutes, returning at least a part of the thus treated benzene to the treatment with 95% to 99% sulfuric acid and recovering the cumene produced.

3. A process of producing cumene which comprises treating benzene with sulfuric acid of 95% to 99% concentration at 15 to 25 C. for at least 3 minutes in the absence of alkylating agents, reacting a substantial molecular excess of the treated benzene with propylene in the presence of sulfuric acid under alkylating conditions, subjecting the reaction product to a hydrolysis treatment with a sodium hydroxide solution of 2% to 10% concentration at between 100 and 180 C. for at least 5 minutes and returning at least a part of the excess unreacted benzene to the treatment with 95% -to 99% sulfuric acid.

4. In a process of producing cumene by Ireact ing a substantial stoichiometric excess of benzene with an isopropylating agent in the presence of sulfuric acid of 80% to 90% concentration under alkylating conditions the improvement which comprises subjecting hydrocarbon products from said reaction comprising cumene and excess unreacted benzene froxnsaid reaction to a hydrolysis treatment with an aqueous basic solution at a Itemperature above 100 C., separating treated benzene from said hydrocarbon products, treating at least a part of the thus treated benzene with sulfuric acid of higher concentration than that used in said alkylation but below 100% strength in the absence .of alkylating agents and returning the treated benzene for further reaction with isopropylating agent.

5. In a process of producing cumene by reacting a substantial stiochiometric excess of benzene with an isopropylating agent in the presence of sulfuric acid of 80% to 90% concentration under allwlating conditions the 4improvement which comprises subjecting'hydrocarbon products from said reaction comprising cumene and unreacted benzene to a hydrolysis treatment with an aqueous solution of a base of 2% to 10% concentrawith an aqueous base at a temperature above 100 C., recovering said cumene, and returning at least -a part of the treated unreacted benzene for further reactionwith isopropylating agent.

7. A process of producing an alkylated aromatic hydrocarbon which comprises feeding an aromatic hydrocarbon and an oleflne in the .pro-

portion of5 to 10 mois of aromatic hydrocarbon per mol of oleiine into an emulsion of hydrocarbon containingy said aromatic hydrocarbon and sulfuric acid at 40 to 50 C. while maintaining in the reaction mixture a volumetric ratio of acid to hydrocarbon of between 0.7 to 1 and 1.3 to 1 and a molar ratio of aromatic hYdrocarbon to alkylating agent of at least 50 to 1,withdrawing and separating reacted emulsion after an average ltime of contact of acidand hydrocarbon of at least 20 minutes, subjecting hydrocarbon products from said reaction comprising alkylated aromatic hydrocarbon to a hydrolysis treatment with an aqueous base at a temperature above 100 C., recovering the thus treated alkylated aromatic hydrocarbon. and returning at least a part of the treated unreacted aromatic hydrocarbon for further reaction with the olefin.

8. In a process of producing an alkylated aromatic hydrocarbon by reacting a substantial stoichiometric excess of an aromatic hydrocarbon and an alkylating agent in the presence of sulfuric acid of at least 80% concentration under comprises subjecting the hydrocarbon products from said reaction comprising alkylated aromatic hydrocarbon to a hydrolysis treatment with an aqueous base at a temperature above 100 C., recovering the thus treated alkylated aromatic hydrocarbon, and returning at least a part :of the treated unreacted aromatic hydrocarbon for further reaction with alkylating agent.

9. In a process of producing an alkylated arcmatic hydrocarbon by reacting a substantial stoichiometric excess of an aromatic hydrocarbonand an alkylating agent in the presence of su1,

furie acid of at least 80% concentration under alkylating conditions, the improvement which comprises subjecting excess unreacted aromatic hydrocarbons from said reaction to a hydrolysis tion for at least 5 minutes at between 100 and 180 C. and returning at least a part of the thus treated benzene for further reaction with iso-- treatment with an aqueous basic solution at a temperature above 100 C. and returning at least a partof the hydrolyzed aromatic'hydrocarbon for further reaction with alkylating agent.

l0.' y In a process of producing an alkylated aromatic hydrocarbon by reacting a substantial stoichiometric excess of an aromatic hydrocarbon and an alkylating agent in the presence of sul-v furic acid of at least concentration under alkylating conditions, the improvement `which comprises subjecting excess unreacted aromaticY hydrocarbons from said reaction to a least 50 vto 1, withdrawing and separating reacted emulsion after an average time of contact ,0f acid and hydrocarbon of at least 20 minutes, subjecting hydrocarbon products` from said reaction comprising cumene to a hydrolysis treatment treatment with an aqueous basicv solution at a temperature above C. and treating at least a part of the thus hydrolyzed aromatic hydrocarbone with sulfuric acid'of higher concentration than that used in said alkylation but below JOHN ANDERSON.

EDWIN r. BULLARD. summa H. manzana.