US2416990A - Production of styrene - Google Patents

Description

March 4, 1947. M- H. GORIN ETALQ 2,416,990

PRODUCTION OF STYRENE Filed June 12, 1944 P/POPYZEM BENZENE ALMA TIOIV 5 1e ZONE M SEPARA T/ON ZONE SEPAEA T1 ON ZONE .S'TYRENE 7v mRAGE Manuel H G'orl'rz Everett Gar-1'12 I v IIVWNTOBS y M 61407?) A TTORW Y Patented Mar. 4, 1947 i V 2 415 990 UNITED STATES PATENT OFFICE PRODUCTION OF STYRENE Manuel H. Gorin and Everett Gorln, Dallas, Tex.,

- assignors, by mesne assignments, to Socony- Vacuum Oil Company, Incorporated, New York,

N. Y., a corporation of New York Application June 12, 1944, Serial No. 539,972 3 Claims. (Cl. 260-669) This invention relates to the production of stynot obtained to separate isopropyl benzene from rene. More particularly, the invention is conunconverted benzene and propylene which are cerned with an improved process of producing styrecycled to the alkylation zone, (c) passing the rene from benzene and propylene, which process isopropyl benzene to a mixing zone wherein it is is adaptable for commercial scale operation. 5 admixed with a-methyl styrene, (d) subjecting It is well known that styrene can be produced the mixture formed to pyrolysis to form styrene; directly by the pyrolysis of isopropyl benzene. (e) fractionating the product mixture to separate However, a major drawback of the reaction has benzene-propylene, styrene, u-methyl styrene and been the presence of side reactions by virtue of unreacted isopropyl benzenev (,f) returning the which a substantial proportion of the isopropyl benzene and propylene to the alkylation zone of benzene is converted to undesirable end products the process, (g) recycling the a-methyl styrene with a consequent reduction in the yield of styand the unreacted isopropyl benzene to said migrrene. The principal side reactions which take ing zone wherein they are admixed 'with addi- 'place are (1) the conversion of isopropyl bentional isopropyl benzene derived from the alfor use one. commercial scale. the subsequent pyrolysis of the mixture formed, The present invention has for its prime o je t the formation of u-methyl styrene is practically the provision of a method of pyrolyzing isopropyl completely suppressed, and (i) recovering the stybenzene whereby greatly improved yields of styrene formed,

rene, over those-heretofore reported, are obtained. A prominent feature of our invention resides in Another object of the invention is to provide our discovery that by introducing into the pyrola method of pyrolyzing isopr yl n n W er ysis zone a reaction mixture comprising isopropyl by the conditions of the reaction are so selected benzene and a-methyl styrene in such proporand adjusted that substantially none of the isotions that the mo] ratio of a-methyl styrene to propyl benzene is lost through conversion to aisopropyl benzene is approximately 0.63 to 1, the methyl styrene, i. e., the e-methyl styrene-formside reaction which produces a-methyl styrene is g d reaction S practically pp es practically completely suppressed, while the yield Another object is to provide a method of proof styrene is accordingly increased. By carrying du ine tyr ne from benz ne and pr pylene as out the pyrolysis in this way yields of styrene starting materials. amounting to at least '76 percent of theoretical Another object is to provide a method of manon the basis of isopropyl benzene decomposed in llfacturing y e from e ne and propylene any one pass through the pyrolysis zone may be which method utilizes in combination an alkylaattained. Furthermore, the benzene and pro.- tion step and a pyrolysis step whereby benzene pylene formed by the dealkylation side reaction and propylene formed in the pyrolysis step are 40 in the pyrolysis step are recovered in our process yield of styrene over that'obtainable by use of are reacted to reform isopropyl benzene which is the pyrolysis step alone. subsequently sent to the pyrolysis step and ulti- Still another object is to provide a continuous mately converted to styrene. Since the amounts pr s f r m n r n styr ne from nzene of propylene and benzene recovered and returned and propylene which is adaptable for use on a to the process in the manner just described is apcommercial scale. proximately 7 percent of the isopropyl benzene Other objects and advantages of our invention decomposed, the conversion of isopropyl benzene will be appa t f o th f l w ng des r pt n to styrene is approximately 82 percent of theothereof and the appended claims. retical on the basis of isopropyl benzene decom- Broadly stated, our inventioncomprises a conposed in the pyrolysis. Also, since by the proctinuous process for the production of styrene from ess of our invention provision is made for the rebenzene and propylene which involves the folturn of unreacted isopropyl benzene to the pylowing steps: (a) reacting benzeneand propylene rolysis zone (between 30 and 70 per cent of the in an alkylation zone, (b) fractionating the prodisopropyl benzene is decomposed in a single pass) and its ultimate conversion to styrene. a yield of approximately 82 percent of theoretical on the basis of total isopropyl benzene charged to the pyrolysis zone Such a. yield of styrene cannot be obtained by the use of prior art methods of pyrolyzing isopropyl benzene in so far as we are aware.

The alkylation of benzene with propylene is -well known and this step of our invention may be carried out employing any of the methods heretofore proposed. Thus it has been disclosed that the reaction may be effected in the presence of such catalytic agents as sulphuric acid, hydrofluoric acid and metallic salts of the Friedel- Crafts type. Also, .certain bleaching earths, kaolins and similar silicates, treated with acids, have been employed as contact catalysts for this reaction. The particular reaction conditions to be employed, such as temperature, pressure, and residence or contact time vary considerably depending upon the particular catalytic agent utilized.

A particularly suitable catalyst for carrying out the alkylation step of our process is our specially prepared silica-alumina" contact catalyst. The preparation of this catalyst is disclosed in detail and claimed in our co-pending application, Serial Number 460,654, filed October 3, 1942. As disclosed in the co-pending application the silica alumina catalyst may be prepared as follows. A silica gel is prepared from a dilute solution of sodium silicate by precipitation with a hydrochloric acid. The gel is washed free of chloride ion and alumina is precipitated on the surface of the gel by contacting the gel with 0.2 N aluminum sulphate solution at 90 C. for two hours. The catalyst is then washed free of sulphate ion and dried at 125 C. for 48 hours.

Employing a silica-alumina" catalyst prepared in the manner above described we have obtained conversions of propylene to alkylate amounting to 95 percent of theoretical, or better, the alkylate product comprising approximately 90 percent by weight of the desired mono-isopropyl benzene. We have found that best results are obtained when the reaction is conducted in the liquid phase. The particular advantage of this type of operation over vapor phase operation is that of longer catalyst life. The length of catalyst life is, of course, an important consideration from the standpoint of commercial operation.

To conduct the alkylation reaction in the liquid phase in the presence of our silica-alumina catalyst it is generally desirable to dissolve propylene in benzene to form a reaction mixture having a benzene-propylene mol ratio of about 6 to 1, or higher. The mixture may then be pumped into the reaction chamber under pressure and brought into contact with the suitably divided solid catalyst. Liquid space velocities of from about to about 30 cc./cc. of catalyst per hour have been found to give excellent zene. Operating temperatures of from 150 C. to 350 C. have been found satisfactory, the preferred range being from 175 C. to 225 C. Pressures of from 50 to '70 atmospheres should be employed to maintain the reactants in the liquid phase at these temperatures.

From the alkylation step of our process the product mixture is withdrawn, cooled and fractionated. Benzene and propylene, recovered by .the fractionation, are recycled to the alkylation zone. The small amount of diisopropyl benzene separated from the product mixture is withdrawn is obtained by our process.

' be such that from 30 to 70 yields of isopropyl benfrom the process, while the desired isopropyl benzene product is directed to admixture with a-methyl styrene in the manner which is described herebelow in connection with the appended drawing. The amounts of isopropyl benzene and u-methyl styrene going into admixture are carefully regulated so that a reaction mixture having the desired composition of 0.63 mole of a-methyl styrene per mole of isopropyl benzene is formed. This mixture is passed to a, preheating chamber wherein it is vaporized and heated to a temperature approaching that which is suflicient to pyrolyze isopropyl benzene, for example; from 300 C. to 500 C. The vaporized mixture just prior to entering the pyrolysis reactor is admixed with about 3, times its volume of diluent steam or nitrogen. The diluent vapor should be preheated suflicient to supply the necessary heat of pyrolysis. A typical gaseous mixture made up in this way comprises, for example, approximately 18 parts isopropyl benzene, 11 parts a-methyl styrene and '72 parts of steam.

In the pyrolysis zone a reaction mixture of the above defined composition is passed through a metal tube, or tubes, lined with a ceramic material or graphite, preferably the former. Where ceramic lined tubes are employed the heat of reaction is preferably supplied by superheating the diluent vapor to a temperature sufliciently high to furnish the heat of pyrolysis. Where graphite-lined reaction tubes are employed the heat of pyrolysis may be supplied either by externally heating the reaction tubes, or pre+ heating the diluent vapor. The temperature of the vaporous mixture in the pyrolysis zone should be from 600 C. to 800 0. Generally, pyrolysis is conducted at about atmospheric pressure, though pressures up to 5 atmospheres may be used. The time of contact for the pyrolysis should percent of the isopropyl benzene in the feed to the pyrolysis zone is decomposed at the operating temperature employed. For example, at 700 C. the contact time should be no longer than 3 seconds, and preferably about 2 seconds. Longer heating times have been found to induce cracking and undesirable tar formation, which occasionally results in a clogging of the reaction tubes. The reacted mixture is withdrawn from the pyrolysis zone into an eflicient cooling apparatus wherein it is rapidly cooled sufflciently to condense the normally liquid components thereof.

The uncondensed condensed components of the product mixture and fractionated to separate propylene, which is returned to the alkylation step. Light gases, comprising mostly methane and with small amounts of ethylene, are withdrawn from the process. Where a gas such as nitrogen has been employed as the diluent vapor for the pyrolysis reaction, separation .and recovery of the unconverted propylene reactant is not considered economically feasible. However, if the diluent vapor is steam, recovery of the propylene can be readily accomplished.

The condensed portion of the produce mixture is fractionated to separate benzene, styrene, unconverted isopropyl benzene and a-methyl styrene. The benzene is returned to the alkylation step, while the unconverted isopropyl benzene and the a-methyl styrene are recycled to admixture with isopropyl benzene, deriving from the alkylation step, and subsequently returned to the pyportion is separated from the a-naoo'o rolysis step. Since under ployed, a-methyl styrene is material in the recycle stream.

For the purpose of more clearly illustrating the Referring to the drawing, benzene and propylene are admitted to the pre-alkylation mixing perature level of from 150 C. to 350 C. Since the reaction is exothermic in character, the rethe required heat. A pressure of from-40 to 70 atmospheres will be requiredfor liquid phase operation at these temperatures when employpump to force the' reactionzone.

by way of lines 8,

' highto vaporize the 6 to "prepyrolysis mixing zone l8. Here the isopropyl benzene is brought into is described herebelow. The

amount of isopropyl benzene admitted tothe mixperalture in the zone I 8 is maintained sumciently low a decomposition of the isopropyl benzene pyrolysis zone.

70 percent of passing through the peratures are employed.

Upon with cooled, and the various components separated by fractional distillation.

Light gases such as Example Streams of benzene and mitted to a pre-alkylation a reaction mixture in which propylene were admixing zone to form the propylene is substantially completely dissolved in the benzene, the mol ratio of propylene to benzene in the mixture formed being approximately 1 to '7. The mixture was withdrawn from the mixing zone and delivered under pressure into an alkylation reactor wherein it was passed over a silica-alumina catalyst at a liquid space velocity of 18 cc./cc. of catalyst per hour. The temperature of the reaction zone was maintained at approximately 210 C. and the pressure at about 50 atmospheres. The charge of reaction mixture to the alkylator consisted of 52,600 grams of benzene, and 4050 grams of propylene.

The product derived from the alkylation reactor was cooled and fractionated. From the fractionation, 9380 grams of mono-isopropyl benzene and 1101.6 grams of diisopropyl benzene were recovered. This combined alkylate product represents a 95% of theoretical conversion of the propylene charged of which 89 percent by weight constituted the desired mono-alkylate product.

The isopropyl benzene recovered from the separation zone was sent to a prepyrolysis mixing zone wherein it was commingled with a stream of a-methyl styrene to produce a homogeneous mixture which comprised approximately .63 mol of a-methyl styrene per mol of isopropyl benzene. The mixture was heated in this zone to a temperature of about 400 C. A stream of this vaporous mixture was brought a stream of superheated steam, which served as r a diluent and heat supplying medium, at the entrance of the pyrolysis zone. The flow in each of the streams was regulated so that a mixture having a ratio of approximately 3 volumes of steam to 1 volume of reaction mixture was formed. The combined stream in the pyrolysis reactor attained a temperature of about 700 C. for 2.3 seconds. The eflluent stream from the reactor was immediately cooled in a water cooled apparatus. The gaseous portion of the product mixture was fractionated to remove light gases. The condensed portion upon fractionation yielded 2600 grams of styrene. 5420 grams of isopropyl benzene, 1'19 grams of benzene and 106 grams of propylene. f the 5500 grams of u-methyl styrene introduced to the prepyrolysls" mixing step of the process, a total of 5415 grams were recovered from the fractionation of the pyrolysis product. 407 grams of tar were obtained from the distillation of the pyrolysis product.

From the foregoing example it may be seen that from the 9380 grams of isopropyl benzene, obtained by the consumption of 3853 grams of propylene and 6300 grams of benzene in the alkylation step, which were subsequently charged to the pyrolysis step, 5420 grams were available for recycle to the pyrolysis step, 285'grams were available as propylene and benzene for recycle to-the alkylation step, and the balance 3675 grams were consumed. Of the isopropyl benzene converted to product not available directly for reuse in the process, 2600 grams or 81.7% of theoretical were converted to the desired styrene product.

It will thus be understood by those skilled in the art that by operating our process in a continuous manner as described in-connection with the drawing, whereby the benzene, propylene and isopropyl benzene, recovered in the fractionation of the pyrolysis product, are recycled and utilized by the process to produce additional styrene, the actual yield of styrene which may be obtained by our process is in the order of 80 to 85 percent.

As pointed out at the outset of this specification and indicated by the example, the a-methyl into contact with styrene content of the reaction mixture charged to the pyrolysis step is practically completely. recoverable in our process and may be conveniently recycled to the pyrolysis zone. This feature of our process affords a distinct advantage from the standpoint of continuous operation, since no provision for stance from the process system is required. Thus. small losses of a-methyl styrene from the process system, due to incomplete recovery of this material in the fractionation of the pyrolysis product, may be replenished by temporarily decreasing the proportion of a-methyl styrene in the reaction mixture to allow additional a-methyl styrene to form in the pyrolysis.

While we have indicated that the mixture charged to the pyrolysis zone should contain about 0.63 mole of a-methyl styrene per mole of isopropyl benzene for optimum yield ofstyrene, it is realized that exact control of the composition of this mixture is diflicult to obtain and it should be understood that such control is not necessary to obtain substantially the full benefit of our invention. Thus, so long as a ratio of from about 0.60 to about 0.65 mole of a-methyl styrene to one mole of isopropyl benzene is maintained in the pyrolysis mixture the benefit of our invention will be obtained, and such operation is considered as coming within the scope of our invention.

The foregoing disclosed the general and broad character of the invention and the example is sufiiciently indicative of its value from a commercial standpoint. However, it should be understood that the invention is not limited in scope to the specific conditions and catalyst described or the experimental data given, but rather only as indicated in the appended claims.

We claim:

1. A process of manufacturing styrene comprising the steps of (1) reacting a mixture of benzene and propylene in an alkylation zone to form isopropyl benzene, (2) fractionating the product obtained to separate isopropyl benzene therefrom, (3) mixing the isopropyl benzene derived from step 2 with a-methyl styrene and additional isopropyl benzene obtained in the manner hereinafter defined to form a mixture having a ratio of 1- mol of isopropyl benzene to between .60 and .65 mol of a-methyl styrene, (4) diluting the mixture formed with from 2 to 5 times its volume of an inert diluent gas, (5)

subjecting the diluted mixture obtained in step-3 to reaction in a pyrolysis zone at a temperature of from 600 C. to 800 C. and at a pressure of from 1 to 5 atmospheres to form styrene, (6) subjecting the product obtained in step 5 to fractional distillation to separate benzene, propylene, isopropyl benzene and a-methyl styrene therefrom, ('7) returning the benzene and propylene obtained in step 6 to step 1, (8) returning the isopropyl benzene obtained in-step 6 to step 3 as the additional isopropyl benzene in step 3, (9) returning the a-methyl styrene from step 6 to step 3 as at least the major portion of the a-methyl styrene in step 3, and (10) recovering the styrene formed in step 5.

2. A process for producing styrene comprising as principal steps, subjecting a mixture of benzene and propylene to reaction in an alkylation zone to form isopropyl benzene, fractionating the product obtained from said alkylating zone to separate benzene, propylene and isopropyl ben-, zene, returning the benzene and the addition or removal of this subspecification has described and propylene to the alkylation zone, mixing the isopropyl benzene with an inert diluent gas, a-methyl styrene, and additional isopropyl benzene obtained in the manner which a-methyl styrene is recycled to the pyhereinafter defined, subjecting the mixture thus Y formed to pyrolysis in a ceramic lined reactorto form styrene, fractionating the product-obtained from said pyrolysis zone to separate propylene, benzene, styrene, isopropyl benzene and a-methyl styrene, returning the propylene and benzene thus obtained to the alkylation zone, returning the separated isopropyl benzene to the mixing step as the additional isopropyl benzene in said 1 mixing step, returning the separated a-methyl styrene to the mixing step in said mixing step, controlling the proportions of isopropyl benzene and d-methyl styrene being as the a-methyl styrene rolysis zone along with unreacted isopropyl benzene for the purpose of suppressmg said undepyrolysis so that the mol ratio of a-methyl styrene to isopropyl benzene in said mixture is from .60 to .65 whereby the side reaction which forms a-methyl styrene in said pyrolysis is substantially completely suppressed.

MANUEL H. GORIN. EVERETT GORIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,198,185 Stanley et al Apr. 23, 1940 2,143,493 Stanley et a]. Jan. 10, 1939

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