US2398074A - Process for manufacturing toluene - Google Patents

Description

enemas 9, 1946 .umrso s'ra'ras mm iorrrca mocass roa MANUFACTURING TOLUENE 1 David a. Brandt, Westileld, 1s. 1., alsignor to Cities Service Oil Company, New York, N. Y., a corporation oi Pennsylvania- Application March 19, 1942, Serial No. 435,219

1 Glaim. The'present invention relates toan improved process for the manufacture of toluene and more Dflrticularly to the manufacture of nitration grade toluene from petroleum Many attempts have been made to manufacture technical benzene. toluene and other aromatic hydrocarbons from petroleum stocks,-b'ut for the most part such processes have not been of commercial importance because oi various difficulties encountered. On the other hand, petroleum stocks, such as gas oil, have been successfully converted into products containing substantial percentages of aromatic hydrocarbons, portions of which are recovered along with other constituents boiling within the usual gasoline range and used for motor fuel.

It is understood that some attempts have been made to manufacture toluene from selected petroleum stocks such as those recovered in the extraction of crude oils. or fractions; with such agents as liquid sulphur dioxide. It is also noted in the literature that toluene, along with benzene, has been produced in certain processes applied to the cracking of kerosene. For example, Kanep (Chem. Abs. 1935, vol.29. p. 5640) pyrolized various kerosene fractions at 700 6., obtaining from about 12% to 21% oi aromatic hydrocarbons. He found that the percentage of aromatic hydrocar- 260-368) ent invention comprises in general the steps of vfirst producing a particularv petroleum stock which may be directly converted into a product containing a high percentage of toluene. This stock is made in accordance with'the features of the present invention by starting with a gas oil. kerosene or othersuitable petroleum distillate, which maybe largely parail'lnic. the stock being passed in a confined stream or restrictedcrosssection through a pipe still furnace and cracked therein at a temperature of about 980 F. This cracking is preferably completed in the pipe still furnace, but may be completed to the desired extent by passing the high-temperature partially converted products from the furnace into an enlarged reaction chamber where aconsiderable time reaction is allowed for the cracking to take place. At the point where the desired reaction has been completed, the products are immediately and instantly cooled to a temperature be,

low that of further reaction, such, for example.

bons decreased as the boiling range of the kerosene rraction'increased, and that in general the proportion of 1-- he formed was greater than that of toluene.

So far as mown, the manufacture oi nitration grade toluene from petroleum has not been accomplished, at least on a pra'chcai or commercial.

scale. One of the cultles encountered, in addition to the fact that relatively low percentages of toluene were produced, is that of recovering nitration grade toluene from the light materlals of similar boiling point which are proggiced alongwith benzene and other hydrocarns. The primary object of the present invention therefore isrto overcome the dificulties which have been encountered in previous attpts to.

manufacture toluene from petroleum and at the same time provide a commercial process in which relatively high percentages of toluene are obtained in conversion operations.

Another object of the present invention is to provide an improved process for the manufacture of nitration grade toluene in which the hydrocarbon constituents of the toluene may be readily separated as a nitration grade product.

Accordingly, the improved process of the presas to a temperature from 600 to 700 F. The resulting vapor products are then subjected to a series of iractionating operations to' segregate out a distillate boiling within the range or from about 250 to 500 1''.

This distillate having the characteristics described hereinafter, is thereupon subjected to a particular type of conversion operation for converting it into a product containing a substantial proportion of toluene. by p ssing it in a conflned stream of restricted cross section through a heating zone in which it is vaporized and superheated to a temperature of from 800 to 1200 F.. and then digested in an enlarged reaction zone, either with or without contactwlth a catalyst. The resulting products which will be comprised of toluene and high boiling constituents boiling above that of toluene, as well as lower boiling hystock for the process is introduced into the apparatus at a pressure of from 200 to 500 lbs. per

6. The resulting highly heated products are conducted from the pipe still furnace through a transfer line l0 and introduced into the upper portion of a vertical reaction chamber l2, where the products are permitted to react for a time sunlcient to convert the charging stock into a final product containing a maximum of condensable constituents boilingbelow about 500 F. The reaction products reaching the bottom of the chamber I2 are withdrawn through a line l4 and suddenly reduced in temperature by the introduction of a relatively cool fluid such as water through a valved line l5. This cooling operation is preferably suflicient to reduce the temperature of the cracked products to about 700 F.. at which temperature they are introduced along with the cooling medium into the lower portion of a vapor separating and scrubbing chamber l6 mounted below the reaction chamber l2. The high boiling constituents are separated out in the bottom of the chamber it while the vapors are passed up around bafiles therein, and are scrubbed with a regulated proportion of high boiling distillate introduced into the up er part of the chamber 16 through a valved line H. Some of the distillate introduced through the line I! is vaporized but the unvaporized portion together with the high boiling liquid constituents collected in the bottom of the chamber l6 are withdrawn as fuel oil through a valved line ii. The vapor remaining uncondensed in the chamber l6, together with vaporized distillate, are discharged through a vapor line 20 at a temperature of from 600 to 700 F. and introduced into the lower portion of a fractionating tower 22.

The purpose of the fractionating tower 22 is to separat from the vapor constituents the highboiling hydrocarbons distilling at temperatures above about 500 F. The resulting distillate is preferably used as a recycle stock in the process and therefore withdrawn through a line 24 and forced by means of a pump therein into the line 2 to comprise av portion of the charging stock for th pipe still furnace 8. A portion of the stock in the line 24 may be conducted into the line H and used to scrub the vapors in i6. The vapors separated out in the tower 22 are conducted overhead through a vapor line 26, condensed in a condenser therein, and the resulting condensate and uncondensed constituents conducted into a I 30 and forced by means of a pump therein (preferably controlled from a float in chamber 26), through a valved line 32 into the tower 22, to control the fractionation therein, and through a valved line 34 into a stabilizer tower 86.

The pressure maintained in the receiver 28 should be at least about 200 lbs. per square inch,

. so that most of the C4 hydrocarbons will be condensed and not discharged from the receiver with the gas. The pressures in the tower 22 and chambers l2 and I! will be correspondingly higher, at least suflicient to cause the regular flow of vapors through the apparatus.

The condensable product recovered in the receiver 26 and conducted into the stabilizer II through the valved line 24 will include hydrocarbons boiling up to about 500 F. The cracking operation carried out in the pipe still furnace 8 and chamber I2 is preferably controlled, so that the gas oil charging stock, on a once through basis, is converted into a condensable product containing approximately 65% of constituents boiling below about 500 F., such constituents being largely unsaturated olefinic and aromatic hydrocarbons and substantially free of paraflinic hydrocarbons having more than 5 carbon atoms.

The stabilizer 36 is preferabl operated at a pressur of about 300 lbs. per square inch, to produce a stable distillate at the bottom of the stabilizer which contains only the desired proportion of C4 hydrocarbons, and which is substantially free of C: and lower hydrocarbons. The overhead vapors from this stabilizer, comprising substantially all of the lower hydrocarbons than C4, and the undesired C4, are conducted through a vapor line 36, subjected to condensation in a condenser therein, and the resulting products passed into a receiver 40, which may be used merely for the separation of suflicient condensate to be used as reflux for the control of the stabilizer 36. This reflux is passed from the receiver 40 through a line 42 and a pump therein into the tower 36. Theexcess of light materials taken overhead from th stabilizer 36 is discharged from line 42 or through a pressure valve controlled vapor line from the receiver 40.

The stabilized'distillate produced in the stabilizer 36 is conducted through a valved line 44 and passed into a fractionating tower 46 operated at a lower pressure than that maintained in the stabilizer 36. The stabilized distillate is fractionated in the tower 46 to take overhead a light gasoline fraction and leave a bottoms prodnot having a boiling range of from about 250- 500 F. The light gasoline is taken overhead in vapor form, condensed and collected in a receiver, from which a portion of the condensate may be returned to the upper part of the tower 46, while the light gasoline product is withdrawn to storage for blending purposes.

The bottoms product withdrawn from the tower 46, and which should be substantially free of parafllnic hydrocarbons is conducted through a line 48 and forced by mean of a pump therein at a pressure of about 500 pounds per square inch through heating coils mounted in a pipe still furnace 60. The stock passed through this pipe still furnace is preferably heated to a temperature sufllcient to vaporize the stock and superheat the vapors to a temperature of from 800 to 0 F., after which the vapor products are passed through a transfer line 62 into a catalyst chamber 64 in which the vapors pass in intimate contact with a catalyst adapted to convert the constituents of th vapors under cyclization and alkylation conditions into a product containing a maximum proportion of toluene. Activated carbon is a suitable catalytic material and it may be deposited on any suitable refractory material supported in chamber 64. Other catalysts such as the oxides of vanadium, chromium, manganese ,or cobalt, zinc chloride and other may be used. The catalytic action may be eil'ected in various other ways, as, for example, by suspending the activated carbon or other catalyst in finely divided form in a stream or body oi" high-temperature vapors as they are discharged from the furnace 50 through the line 52. Activated carbon containing of a metal oxide or chloride is also suitable.

In most instances the high-temperature products passing through the chamber 5.4 are actually raised in temperature by the catalytic action, and care should be taken to prevent a temperature rise above approximately 1060 F. The pressure in the chamber 54 should be from about 225 lbs. to about 350 lbs. per square inch.

The high temperature conversion products produced in the catalyst chamber 54 are conducted therefrom into a line 56 and instantly chilled to a low temperature of approximately 600 F., by the introduction of a relatively cool fluid, preferably water, through a valved line 57. The resulting relatively cool mixtur passes into a baffled separating and scrubbing chamber 58 in straw oil.

The absorber or'absorption tower 68 is operated under temperature and pressure conditions,

preferably a pressure of about 250 lbs. per quare inch, adapted to liberate all possible normally gaseou hydrocarbons of C3 and lower, while recovering the C4 and higher hydrocarbons. The unabsorbed gases in the absorber 68 are discharged fromthe top of the absorber through a pressure valve controlled line 89 as shown. The absorption medium used in the tower 68 may be any suitable high boiling absorption oil, such as The absorption medium is preferably separable from toluene by distillation and is preferably used in sufllcient quantity to prevent es.

cape of any toluene with the overhead gases. Back pressure is preferably maintained from the tower 58 through apparatus elements 65, 62, 58, 54 and 50. although considerable pressure drops through these elements may be obtained by the which any high boiling materials are separated as liquid and withdrawn through a valved line 59 at the bottom of the chamber. The vapors separated out in the chamber 58, containing the desired toluene and being substantially free of paraflinic hydrocarbons are passed upwardly through the chamber in contact with a high boiling distillate scrubbing oil introduced into the upper part of the chamber from a valved line 60. The oil introduced through the line 60 may be hot,

or introduced in mall quantity. and not use to reduce the temperature of the vapor much below pha e. The condensate produced in the. tower i withdrawn through a valved line 63 and forced by means of a pump therein into. the line 48 leading to the pipe still furnace 50. A- portion of this distillate from the bottom of the towe 62 may be used in the top of the scrubber 58 by conducting a regulated portion thereof through the line 60. The distillate in the line 63 is hi hlv unsaturated and contain a considerable oropor- 1 tion of aromatic hy r ca on a d is therefore very suitable as stock for the furn ce 5" and the reactions carried out in the chamber 54.

The toluene and other constituents remaining in vapor form in the fractionatin tower 62 are conducted overhead through a vapor line 64. sub. iected to condensing conditions in a. condenser therein. and the resulting condensate anduncondensed gases conducted into a'recelver and water separator 65. The water separat d out in the receiver is withdrawn throu h a valved line from the bottom thereof. while the condensate and uncondensed gases are conducte through a line 66 into an absorber 68.- A portion of the condensate separated out in the receiver is withdrawn through a valved line 61 and introduced into the upper part of the fractionating tower 62 to control the fractionation therein.

use of the. control valves provided. A higher pressure may be-used in 88 than in 62 by pumping the materials in line 56 into the absorber 88.

The mixture of absorption medium and distillate collected in the base of the absorber 68. including the toluene and constituents boiling within the range of light gasoline as well as lower boiling normally gaseous hydrocarbons, is conducted through a line 10 and forced by means of a pump therein into a stabilizer tower 12 in which the mixture is stabilized to eliminate overhead any propane and lower hy'drocarbonsas well as excess C4 hydrocarbons not desirable in the light gasoline fraction from the standpoint of vapor pressure. The vapor fraction taken overhead from the tower 12 is conducted through avapor line 14', and a condenser therein, and the mixed products are collected in a receiver 15 from which the gases are discharged through a pressure valve controlled line while the Condensate is withdrawn through a valve controlled line IS. A portion of this condensate is introduced into the top of the stabilizer 12 for controlling fractionation as indicated.

The stabilized mixture collected in the base of the tower I2 including the absorption medium. toluene and li ht gasoline. is conducted through a valved line 11 at substantially reduced pressure into a still 18 in which the toluene and light gasoline product is vaporized and separated from the absorption medium which ma include all possible constituents boiling above the boilin point of toluene under the conditions. Such constituents for example may include hydrocarbons boiling in thehigher boiling range portion of gasoline, in fact gasoline range material boiling above toluene may be used as absorption-media. The vaporized materials including the toluene are conducted from the still I8 through a vapor line 80 into a fractionating tower 82. while the absorption medium is withdrawn from the still 18 through a line 84 and forced by means of a pump therein through a cooler 86 mounted in the line. and then into the upper portion of the absorption tower 58. Excess material in lin 84 over that required in 68 may be used as gasoline blend-' ing stock or sent to the furnace 50.

The fractionation carried out in the tower 82 is preferably conducted in such a manner that the light gasolineboiling range materials boiling below the boiling point of toluene are taken overhead while the toluene is held back in the tower. The vapors from the tower 82 are conducted resulting product is collected in a receiver 90,

the overhead product introduced through a valve controlled line 94.

The toluene product produced in the operation and which may include some constituents of substantially the same boiling point is withdrawn from the tower 82 through a valved line 96. The relatively pure toluene withdrawn through the line 96 will be almost entirely free of paraflinic hydrocarbons which normally cause considerable trouble in the fractionation of toluene made from coal. The product, however, may contain small percentages of unsaturated oleflnic type hydrocarbons having about the same boiling point as toluene, and these may be effectively removed by contacting the toluene product (in a well-known manner not shown) with sulfuric acid of from 64 to 66'B. gravity containing from 0.5 to approximately 1% of nitric acid. The product is preferably refractionated after acid treatment, and such refractionation ma be effected in the presence of a selective solvent or carrier agent. Toluene to be used for nitration purposes should be free of unsaturated olefinic type hydrocarbons, have a boiling point of about 110 C., with an initial not below 108.5 C., and distilling completely at a temperature below 111 C, For certain purposes the toluene fraction removed through the line 98 may be used directly,

preferably after acid treatment.

The charging stock for the pipe still furnace 50, as stated above, should be substantially free of parafllnic hydrocarbons. It preferably comprises a mixture of unsaturated oleflnic and aromatic hydrocarbons of which about20% are aromatics, although the proportion may run as high as 35%. While this stock may possibly be secured from other sources than by the method of production described above, no present source of such material is known. The charging stock for pipe still furnace 50 therefore is preferably made in the manner described above. The light gasoline in the tower 46 may be conveniently used for blending with straight run gasoline or other suitable heavy gasoline stock, as for example that from still 18.

From the foregoing description of the improved process of the present invention, it will be readily apparent that certain modifications may be made therein without departing from the spirit and scope of the invention as defined in the claim.

Having described the invention in its preferred form, what is claimed as new is:

A process for the manufacture of toluene, which comprises passing a hydrocarbon charging stock in a confined stream of restricted cross-section through a conversion zone and therein subjecting it to non-catalytic cracking conditions at a temperature in the neighborhood of 1000 F. for a sufilcient time to produce substantially a maximum of condensable constituents boiling below a temperature of about 500 F. which is substantially free of paraflin hydrocarbons having more than five carbon atoms to the molecule, quenching the resulting high temperature conversion products and fractionating the same to recover the constituents boiling between about 250 and 500 F. as a separate fraction consisting essentially of oleflnes and aromatic hydrocarbons, passing this separate fraction through a separate heating and conversion zone maintained at a pressure of from 225 to 350 lbs. per square inch and subjecting the fraction to conversion condi tions at a temperature in the neighborhood of v 1000 F. for a suihcient time to convert said frac-

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