US2404104A - Method of producing ethyl benzene - Google Patents

Description

July 16, 1946.

R. M. sHEPARDsoN 2,494,104

METHOD 0F PRODUCING ETHYL BENZENE XYLENES OUTLET @5A/2EME R. M. SHEPARDSON METHOD oF4 PRODUGING mma.A BENZENE Filed Dec. 1l, 1942 July 16, 1946.

2 Sheets-Sheet 2 Patented July 16, 1946 METHOD OF PRODUCING ETHYL BEN ZENE Robert M. Shepardson, Madison, N. J., assgnor to Standard Oil Development Company, a corporation of Delaware Application December 11, 1942, Serial No. 468,612

2 Claims. (Cl. 26o-66S) The present invention relates to improvements in the art of processing hydrocarbon cils and, more particularly, it relates to the production of substituted aromatics, such as ethyl benzene styrene, by dehydrogenation of cyclo parailns.

In the prior application o'f the present inventor and another, Serial No. 429,012, filed January 3l, 1942, entitled Production of aromatics, there is described and claimed a process for producing styrene from a petroleum distillate derived from a naphthenic crude, the said distillate boiling within the range of about 26S-275 F., by subjecting the latter fraction to catalytic dehydrogenation, extracting the products of catalytic dehydrogenation with a selective solvent, fractionating the extract to obtain substantially pure ethyl benzene, subjecting the ethyl benzene to a dehydrogenation treatment and then recovering substantially pure styrene from the products of this last dehydrogenation by controlled distillation. The styrene thus obtained finds uses, among others, in the production of products such as synthetic resins, but is particularly suitable as one of the raw materials used in the production of synthetic rubber er rubber substitutes.

According to my present invention, which constitutes an improvement over the invention described in the aforesaid application, I rst subject an ethyl cyclohexane fraction to solvent extraction to remove xylenes and thereafter dehydrogenate the ethylcyclohexane to form ethylbenzene which can then be dehydrogenated to form styrene.

In the production of styrene by dehydrogenation of ethylbenzene, it is important that the ethylbenzene be quite pure. The presence of xylenes greatly reduces the amount of ethylbenzene converted to styrene, for which reason I wish to keep the quantity of xylenes present in the ethylbenzene below Although the ethylcyclohexane fraction or cut, which boils within the range of 260275 F., boils below the xylenes, boiling points of the latter in the pure state being in the range of 281-291 F., it has been found that the xylenes boil below their true boiling point in admixture with parailins and naphthenes, as a result of which appreciable quantities of xylenes are found in the narrow ethylcyclohexane cut of 26d-275 F. boiling range. Although the xylenes do not interfere in the dehydrogenation of ethylcyclohexane to ethylbenzene, it is not practical to separate metaand para-xylenes from ethylbenzene after the latter has been produced, and I have found that it improves the "rocess to remove the xylenes from the ethylcyclohexane but by solvent extraction before the latter is dehydrogenated to ethylbenzene.

The main object of the present invention, therefore, is to prepare a charging stock for the production of ethylbenzene from cycloparans which is substantially free of aromatics, such as xylene.

A more specific object of my present invention is to remove by solvent extraction from an ethylcyclohexane fraction the isomeric Xylenes prior to the dehydrogenation of the ethylcyclohexane to form ethylbenzene, so that following the dehydrogenation it will not be necessary to separate the ethylbenzene from metaand para-xylenes, this separation being extremely difcult.

Other and further objects of my invention will appear from the following more detailed description and claims.

In the accompanying drawings, Figs. I and I-A, I have shown a flow plan which illustratesV a preferred method of carrying my invention into practical effect.

Referring in detail to the drawings, a charging oil comprising a highly naphthenic petroleum fraction boiling within the range of from about 260-275 F. is introduced into the system thru line l, and thence pumped by pump 3 into a solvent extraction Zone 5 where it is contacted with a solvent which has a selective solvent power for aromatics. the said solvent being discharged into the top .of extraction tower 5 thru line I0. Within the tower an extract phase and a raffinate phase are formed. In the specific example I am illustrating, the solvent extraction is a liquidliquid phase, that is to say,.both the solvent which may be, for example, SO2, and the oil are in liquid phase. Better results may be obtained by heating the oil to vaporize the same and contacting the vapors with a high boiling solvent,

' such as phenol, furfural and resorcinol. However,

these details of solvent extracting a naphthene and/ or parafnic mixture containing naphthenes, paraiins, and aromatics are well known to the industry and numerous solvents suitable for this purpose are disclosed in the prior art. Later on in the present description I have given a full description of methods of solvent extracting aromatics from non-benzenoid hydrocarbons, and the methods later described in detail or similar methods may be used in the operation taking place.

A railinate phase containing the naphthenes and paranins of the charging oil is Withdrawn through line I2, while an extract phase is withdrawn through line I4. The extract phase, as stated, will contain the various isomers of xylene, and to recover and separate these and other aromatics from the solvent they are discharged into a stripping tower I6 where they are stripped with indirect steam or by other means. The xylenes are withdrawn from the stripper thru line 2|, are cooled in 22, thence discharged thru line 24 into a receiving drum 3U. 'I'he disposition of the xylenes does not form per se the real gist of this present invention, but in passing, it may be said that these Xylenes may be reacted with benzene in the presence of aluminum chloride to cause a formation of toluene by interaction between benzene molecules and the xylene molecules resulting in the transfer of a methyl group from the xylene molecule to the benzene molecule. The solvent freed of its aromatics and other hydro-carbon content may be withdrawn through line 25, passed through a cooler and recycled to line IG for further use in the process, extracting further quantities of aromatics from the charging oil. The separated xylenes are withdrawn through line 32.

Referring back to thesolvent extraction zone, the rafnite phase withdrawn through line I2 is discharged into a stripping zone 59 where it is treated with indirect steam discharged into said zone through line 52 in order to strip and remove solvent from the hydrocarbons. The solvent is withdrawn through line 64 and recycled via cooler St and line "It to line Il leading to the solvent extraction Zone 5. The hydrocarbons are recovered from stripping tower 50 through line 60 and thence .discharged into a red coil 65 where they are heated to a temperature of 60G-1190" F., depending upon the catalyst employed, thence withdrawn through line 6l and discharged into a reactor I0 containing catalyst C. The catalyst may be a IV,

V, VI, or VII group metal, metal sulfide or oxr ide, or mixtures of two or more, such as nickel sulfide and tungsten sulfide, and the catalyst itself may have the physical form of pills, pellets, extruded shapes, granules, lumps, and the like. The catalyst may be deposited on a suitable support such as activated alumina, magnesia, carbon. or even silica, or may be of the unsupported type. Catalysts which have been found satisfactory are chromium sesquioxide supported on activated alumina, the amount of the chromium oxide being 540% by weight, the balance being theY alumina, molybdenumoxide, say -l2% by weight supported on activated alumina, platinum, say 5% by weight, on activated carbon or a mixture of nickel sulde and tungsten suliide without a support.

It is preferable in my process to discharge hydrogen into line 60 from line 80 where it mixes with the hydrocarbons and passes with them through furnace @5 and then into the reaction zone, the amount of hydrogen being from 200G-8000 cu. ft. per barrel of cold oil fed. With hydrogen recirculation, the reactor will be maintained under superatmospheric pressure of 100-l000#, whereas without hydrogen recirculation, substantially atmospheric `operation is preferable. The feed rate of the hydrocarbon to the reaction zone is from 0.1-10 volumes of hydrocarbon per volume of catalyst per hour on a cold oil basis. The temperature prevailing within the reaction Zone will vary from 600 to 1000 F., depending upon the catalyst employed. With the platinum catalyst or a mixture of nickel sulfide and tungsten suliide, low temperatures of 60G-900 F. are preferred whereas temperatures of 90o-1000" F. are generally needed with chromium oxide or molybdenum oxide on alumina. Also, in the case of the former two catalysts, it is preferable to add heat to the reactor while dehydrogenation is in progress to maintain a constant temperature, this being accomplished by ring small diameter, say 1 to 6 inch, tubes or maintaining these tubes in ay high temperature salt bath, these small tubes containing the catalyst. With the latter two catalysts, however, a constant temperature is not required through the reaction zone, and the heat of reaction can be supplied as sensible heat in the charge stock, temperature decreasing through the reaction zone in this case. In the low temperature operation with catalysts consisting of platinum on charcoal or nickel sulde plus tungsten sulfide, regeneration of the catalyst by burning with air is not required, but this will be required frequently, say after 2-24 hours of operation, when the higher temperatures above 900 F. are employed. Under the conditions stated, the ethylcyclohexane undergoes dehydrogenation to form ethylbenzene.

The reaction products are withdrawn from reactor 'Iil through line I I8 and are discharged into a separation drum IZB where gaseous and liquid products may be separated. The gaseous products which will contain substantial quantities of free hydrogen and small quantities of low molecular weight hydrocarbons, such as methane, ethane and propane, are removed from separating means I2@ through line I2 I and recycled by means of booster compressor 8I in line 80 to line E!) to provide the hydrogen-containing gas required in the reaction chamber. Part of the hydrogen-containing gas is withdrawn through the hydrogen outlet indicated on the drawing. The reaction is preferably conducted under conditions such that there is no overall net consumption of free hydrogen.

The liquid product is removed from separating means 20 through line |22. This liquid product will contain substantial amounts of ethylbenzene together with non-aromatic hydrocarbons and possibly smaller amounts of other aromatics. All of the dimethylcyclohexanes except cis 1,2 dimethylcyclohexane which would dehydrogenate to orthoxylene have been excluded from the ethylcyclohexane fraction charged to dehydrogenation by choosing a fraction with a boiling range of 26o-275 F. The boiling points of the various dimethylcyclohexanes, ethylcyclohexane and the corresponding aromatics are tabulated below:

Analyses obtained on the ethylcyclohexane fractions of 260-275 F. boiling range from naphthenic crudes generally do not show the presence of appreciable quantitiesof cis 1,2 dimethylcyclohexane in which case the dehydrogenated product would not contain appreciable ortho-xylene. However, in some cases the cis 1,2 dimethylcyclohexane has been found in which case ortho-xylene would be found in the dehydrogenated product. In addition, if the dehydrogenation reaction is carried out at temperatures above 900 F., some thermal decomposition and Vpolymerization generally occurs with the result that benzene, toluene, and a very small quantity of aromatics boiling above xylenes are produced.

If the liquid-liquid extraction method is to be employed, the liquid products removed from separating means |20 thru line |22 are first introduced into` the upper portion of a conventional solvent extraction tower |21, as shown in Fig. |-A, adapted for countercurrent iiow of liquids. A modification of my invention involves fractionating the product from line |22 to recover a 250 to 300 F. fraction and sending this only to the solvent treater |21.

Prior to being introduced into extraction tower |21, the liquid products are mixed with several volumes of a solvent supplied thru line |20 which is capable of making a separation between aromatics and non-aromatics. Many different solvents of this type are known. Thus, liquid sulfur dioxide used at low temperatures, say below F., during the extraction is chosen as illustrative herein. The mixture of liquid sulfur dioxide and the liquid products of dehydrogenation are caused to flow in tower |21 countercurrent to a nonaromatic hydrocarbon diluent which is introduced into the bottom of tower |21 thru a line |29. This non-aromatic hydrocarbon diluent should have a boiling range substantially different from that of liquid sulfur dioxide and the hydrocarbons in the liquid products. Examples of a `lower boiling diluent are pentane and isopentane. Examples of a higher boiling diluent are a paraffinic heavy naphtha and a light kerosene.

The primary function of the non-aromatic hydrocarbon diluent is what may be called dilution displacement. rIVhis may be explained as follows:

Although parailns and naphthenes are practically insoluble in liquid SO2 at temperatures below 0 F., a mixture of liquid SO2 and aromatics will dissolve an appreciable quantity of non-aromatic hydrocarbons, the total hydrocarbon present in the extract being composed of possibly of non-aromatic and 80% of aromatic hydrocarbons. Some of these non-aromatic hydrocarbons will boil in the same range as the ethylbenzene and therefore cannot be separated therefrom by fractionation. By countercurrently washing the mixture of liquid sulfur dioxide and hydrocarbons with a relatively large amount of a non-aromatic hydrocarbon having a boiling range widely different from the ethylbenzene, the non-aromatic hydrocarbons originally associated with the ethylbenzene are displaced by the non-aromatic washing agent of widely different boiling range. Having essentially replaced the non-aromatic hydrocarbons originally associated with the mixture which boils in the same range as the ethylbenzene with non-aromatics having a much different boiling range, it is then possible to separate the nonaromatics from the ethylbenzene by fractionation.

The volume of non-aromatic hydrocarbon diluent with which the mixture of liquid sulfur dioxide and dehydrogenated hydrocarbons is washed should be at least suflicient to efect a substantial dilution displacement and may be from 50 to 150% or more of the volume of said mixture. The volume of non-aromatic diluent should not, however, be so great as to displace the liquid sulfur dioxide from the mixture.

A raffinate phase which will consist chiefly of non-aromatic hydrocarbon diluent, non-aromatic hydrocarbons from the original feed and some liquid sulfur dioxide is removed from tower |21 thru line I 30. This mixture may be distilled to recover the SO2 and the diluent (in apparatus not shown) for further use in the process. An extract phase which will consist chiefly of aromatic hydrocarbons, liquid sulfur dioxide and some non-aromatic hydrocarbon diluent is removed from tower |21 thru line |3| and introduced into stripping means |32 in which the sulfur dioxide is stripped out and removed thru n n d 6 line |33. The sulfur dioxide is recycled after cooling to line |28 and reused.

'Ihe raw ethylbenzene is substantially freed of other aromatics such as the various isomers of xylene as follows: It is withdrawn from stripper 32 thru pipe |34, thence passed thru a heater |35, then passed via line |36 into a fractionating tower |31 from the bottom of which orthoxylene is withdrawn thru line |39 while purified ethylbenzene is withdrawn thru line |40a, thence condensed in cooling coil |11 and thence conducted thru pipe |18 to ethylbenzene storage drum |19.

If the vapor-liquid extraction method is to be used, and this method is generally preferred, the liquid products removed from separating means |20 thru line |22 are passed directly thru valved line |40 and a heating means |4| into a tower 42 adapted for countercurrent flow 'of liquid and vapor and provided with a plurality of plates |43. When this method is used, valve |3|a is closed and valve |55a, is open. Prior to their introduction into tower 42, the liquid products are heated in heating means |4| to a temperature at which they are substantially completely vaporized. A high boiling selective solvent which remains in liquid phase at the temperature at which the liquid products are vaporized, is introduced into the upper portion of the tower thru a line |44. Suitable examples of this type of selective solvent are phenol, resorcinol and furfural. A rafnate substantially free from selective solvent is removed in vapor phase from the top of tower |42 thru line |45, is passed thru a cooling and condensing means |46 and is then collected in'a tank |41. A ,portion of the condensed rainate may be recycled to the top of the tower thru line |48 to act as reflux. The remainder of the raffinate is removed from tank |41 thru line |48-a.

A liquid extract phase, which consists essentially of selective solvent and aromatics, is removed from the bottom of tower |42 thru line |49 and introduced into a stripping means |50 provided with a heating coil which vaporizes the ethylbenzene. A portion of the extract phase may be continuously circulated thru the bottom of tower |42 and a heating means |5| by means of pump |52. Unvaporized selective solvent is removed from the bottom of stripping means |50 thru line |53 and may be recycled thru line |44 to the upper portion of tower |42'. Ethylbenzene of substantially pure form or at least substantially pure and free of xylenes, except some ortho-xylene, is recovered thru line |54 and discharged into heater |55 and thence into fractionator |31 where it is fractionated to recover pure ethylbenzene as previously explained.

The ethylbenzene fraction collected in tank |19 which may have been obtained by either one of the two methods of solvent extraction described above is removed from tank |19 thru line by means of pump |6| and forced thru line |62 into a heating means |63. The heated ethylbenzene fraction passes thence thru line |64 into a reaction chamber |65 wherein it is subjected to dehydrogenation to convert the ethylbenzene to styrene. The dehydrogenation of the ethylbenzene may be eifected either by a thermal, non-catalytic reaction or by a catalytic reaction.

If the dehydrogenation of the ethylbenzene is to be a thermal reaction, chamber |65 is maintained at a temperature between 1200 and 1500 F. and under atmospheric or subatmospheric p resrof liquid ethylbenzene per volume of reaction space per hour in order toobtain a very short time of Contact.

If the dehydrogenation of the ethylbenzene is to be catalytic, a suitable catalyst C is placed in reaction chamber |65 and the temperature is somewhat lower, say between 1000 and 1300 F. The feed rate may be of the order of 0.1 to 10 volumes of liquid ethylbenzene per volume of Ycatalyst per hour depending upon the nature of the catalyst used. The pressure may be atmospheric or below atmospheric and diluents such as steam or inert gas may be used. The other conditions may be essentially the same as in the thermal type of dehydrogenation. A good catalyst for use in reaction chamber |65 is that described in the application of Kenneth K. Kearby, Serial No. 430,873, led February 14, 1942, which consists of Parts by weight MgO 50 to 95 FezOa 3 to 49 KzO 0.5 to 10 CuO 0.5 t 20 with the preferred composition being:

Parts byweight MgO '72.4 FezOa 18.4 KzO 4.6 CuO 4.6

Whichever type of dehydrogenation is carried out in reaction chamber |65, the products of reaction are removed therefrom thru line |61, passed thru a coolin-g means |68 and thence into a separating means |69. cluding hydrogen, which may be recycled to reactor of the dehydrogenation are removed from separating means |69 thru line |10. Liquid products of the dehydrogenation are removed from separating means |69 thru line |1|, thence passed thru heating means |12 and introduced into tower |13 which is the first of a series of distillation towers for the separation of styrene from ethylbenzene and other products which may be associated with it. From the rst tower |13 benzene and toluene are taken overhead thru line |14. The bottoms are passed into a second tower |15 from which ethylbenzene is taken overhead thru line |16 and after passing thru a cooling means |11, may be returned to tank |19. The bottoms from tower |15 are passed thru line |86 into a third tower |80 from which the desired styrene is taken overhead thru line |3| and after being cooled in cooling means |82, is collected in tank |83. The bottoms from tower |80, which will consist essentially of polymerized fractions, are removed thru line |84. The distillation in towers |13, |15 and |19 is preferably conducted under vacuum or in the presence of steam in order to permit reduced temperatures. It is also desirable to introduce a small quantity of an inhibitor Gaseous products, in-Y into the upper portion of each tower to inhibit the polymerization of the styrene.

In the operation of the process, it will be understood that many variations may be made in the operating details without departing from the spirit and scope of the invention. For example, the reactions in reaction chambers 10 and |65 may be conducted in the presence of finely divided catalysts suspended in the vapors to be treated instead of in the presence of rigidly arranged stationary catalysts as illustrated in the drawings. From time to time when the catalysts C and C require regeneration to restore their activity, this may be accomplished in any suitable manner as, for example, by shutting off the flow of hydrocarbon vapors and passing hot, inert gases containing regulated quantities of air or oxygen thru the catalyst mass to remove the carbonaceous contaminants by combustion. It will be understood that if the catalyst is used in iinely divided, suspended form, regeneration cannot be in situ as would be the case when the catalyst is used in stationary form but must be effected outside the reaction chambers. The method of regeneration, however, will be essentially the same in both cases.y

I claim:

l. A process of producing ethyl benzene which comprises solvent treating, with a liquid solvent having preferential solvent power for aromatics, a petroleum oil fraction boiling in the range from 260 F. to 275 F. and containing ethyl cyclohexane with xylenes but substantially free from dimethyl cyclohexanes that boil below260 F. to remove the xylenes, thereafter converting' into ethyl benzene the ethyl cyclohexane in the solvent-treated fraction, freed of the xylenes, by'

dehydrogenation under superatmospheric pressure at a temperature of from about 600 to 1100 F. with added hydrogen in the presence of a catalyst containing a component selected from the class consisting of metals, oxides, and sulfides of metallic elements in groups IV, V, VI, and VIII of the periodic system, and recovering the ethyl benzene product.

2. A process of producing ethyl benzene which comprises solvent treating, with a liquid solvent having a preferential solvent power for aromatics, a petroleum oil fraction boiling in the range from 260 F. to 275 F., and containing ethyl cyclohexane with xylenes but substantially free from dimethyl cyclohexanes that boil below 260 F. to remove the xylenes, thereafter converting into ethyl benzene the ethyl cyclohexane in the solvent-treated fraction, freed of the xylenes, by dehydrogenating the ethyl cyclohexane in said solvent-treated fraction under superatmosphericpressure of to 1000 pounds persquare inch at. a temperature of from about 600 F. to 1100 F.

with added hydrogen in an amount of 2000 to 8000 cubic feet per barrel of the solvent-treated fraction on a cold feed basis in the presence of acatalyst containing a component selected from the class consisting of metals, oxides, and suldes of metallic elements in groups IV, V, VI, and VIII of the periodic system, the feed rate of the solventtreated fraction into contact with the catalyst being 0.1 to 10 volumes of oil per volume of catalyst per hour on a cold oil basis, and recovering the ethyl benzene product formed in the dehydrogenation.

ROBERT M. SHEPARDSON.

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