US2391818A - Process for manufacturing alkyl benzene hydrocarbons - Google Patents

Description

Patented Dec. 25, 1945 UNITED STATES PATENT OFFICE PROCESS FOR MANUFACTURING ALKYL BENZENE HYDROCARBONS David G. Brandt, Westfield, N. J assignor to Cities Service Oil Company, New York, N. Y., a corporation of Pennsylvania Application March 15, 1943, Serial No. 479,204

4 Claims.

mixture by burning or oxidizing the carbon contacting the tube wall as well as portions of the hydrocarbon mixture.

high temperatures adapted for the substantially complete cracking of hydrocarbons to' gas and carbon. In one of the conversion processes in which benzene hydrocarbons are produced, the

oil is cracked at a temperatureof about 1000 F. in a pipe coilheater and then discharged into an enlarged reaction chamber. In this operation a considerable amount of carbon is formed in the coil and in the chamber, and-numerous diillculties have arisen because of formation of deposits in the coil and the rapid accumulation of carbon in the chamber. I

The primary object of the present invention,

therefore, is to provide an improved process for,

the production of alkyl benzene hydrocarbons in which a relatively high percentage conversion to such compounds is obtained, particularly to compounds in which the alkyl more carbon atoms.

A further object of the invention is to provide improved process by which the conversion operation may be carried outwithout interference by the carbon formed in the reaction.

In general, the improved process of the present groups include two or invention includes the steps of heating the oil stock to be converted to a temperature in the neighborhood of 1100 I". under conditions adapted to produce a maximum of unsaturated olefin hydrocarbons and a minimum of free carbon, and

thereafter passing the high temperature mixture through a tubular reaction zone in which the temperature is raised 200 to 300 F., this operation being carried out in a tubular converter comprising an outer steel casing and a spaced inner tube of porous refractory through which the hydrocarbon products flow. The final conversion .of the heated products in the tubular converter is effected by introducing highly heated air of about 1100 F. into the outer steel casing and diffusing it through the porous refractory tube, and thereby preventing the deposit of. car- Other features and advantages of the improved process of the present invention will be apparent to those skilled in the art from the following detailed description of the invention taken in connection with the accompanying drawing which forms apart of this application. 7

Inthe drawing:

Fig. 1 is an elevational flow diagram of an apparatus particularly adapted for carrying out the improved process. I Fig.2 is an enlarged longitudinal sectional view' of a portion of the tubular converter showing the construction and arrangement of a preferred form of converter tube particularly adapted for carrying out the improved process of the present invention, but with a modified arrangement for supplying air and steam.

Fig. 3 is a cross-sectional view of the improved converter shown in Fig. 1, showing the modified arrangement for supplying air and steam to the tubular converter as in Fig. 2.

7 Referring to Fig. 1 of. the drawing, the oil stock to be converted; which'may be any one of the distillate stocks used in commercial oil cracking operations, is introduced into the apparatus through a line it which discharges the stock info the upper portion of a main fractionatlng tower I! in which the stock is used as a cooling and refluxing medium to hold back similar material for f recycling. The feed stock, together with such reflux material, flows from the bottom of the tower l2- through a line H which includes apump for forcing the oil at a pressure. of from 400 lbs. to

600 lbs. per square inch, through a series of heat- T ing coils mounted in a pipe still heater ii. The oil enters the heater i6 throughapreheater coil I! and passes through coils I8 and II which are preferably arranged for separate firing so that any desired temperature gradient and final temperature of about 1100 F. may be maintained to produce a maximum of unsaturated or olefinic hydrocarbons and a minimum of coke deposit or I carbon formation in the heating coils.

The tubes of the pipe still heater [8 are preferably of'the usual diameter of from two to five inches, commonly used in cracking furnaces. The cracked. products discharged from the coils 20 are conducted through a transfer line 22 into -a tubular converter which may be of any suitable length and which may be constructed as a single long tube or as a tube bank in which indiban in the tube, and heating the hydrocarbon vidu l s tubes are connected y return bends as shown in Pig. 1. The outlet end of the tubular converter extends into the side of a quenching and reflux chamber 24, as shown in Fig. 1.

The tubular converter 24, the structure of which is shown more in detail in Fig. 2, preferably comprises an outer steel casin 22, a relatively thick annular refractory insulation on the inside of the casing 22, and a spaced porous refractory tube or tubes 32 spaced from the inside wall of the insulation 30, so as to provide a series of annular spaces to be supplied with air or steam, as pointed out hereinafter. The porous refractory tube is preferably made up 'of a series of connected hollow tile members having annular socket or expansion joint projections 34 which rest in the insulation 20 and serve to provide and establish the space between the insulation 22 and the body of the tile members comprising the porous refractory tube 22. Highly heated air is supplied to the space or spaces around the refractory tube 82 through lines 24 which extend through the steel casing 24 and the refractory insulation 30. Steam may be supplied directly to the space around the tube 22, or indirectly through the lines by means of valved connections 22.

The steam and air connections for the tubular converter 24, as shown in Fig. l, are arranged slightly different from the showing in Figs. 2 and 3. In Fig. 1, air is supplied to the apparatus through a line 42, including a compressor which forces the air at a pressure in excess of the vapor pressure in the tube 22 through an air heater 42 in which the air is raised to the desired temperature, for example, a temperature of about 1100? R, the air being conducted from the heater to a sections of the converter 24 and avoid localised overheating. The hydrocarbon reactions taking place in the converter 24 are exothermic in character, and in the formation of alkylated benzene hydrocarbons will produce considerable free carbon. The exothermic reactions may be further controlled by the introduction of steam in regulated quantities through the valved lines 42 and 52, or through lines 22 in the form of arrangement shown in Fig. 3. This steam may be used for diluting the air introduced through the lines 2| or for replacing the use of air in certain portions of the converter in order to maintain the pressure differential between the outside and inside of the tube 23. The proportions of air and steam may be further regulated in a view of temperature changes resulting from carbon oxidation by the water-sas reaction.

The tube 22 may have an inside diameter of from 5" to 8" and may vary from '75 feet to 300 feet in length, or longer, the dimensions being chosen so as to give a very short reaction time transfer and distributer line 44 from which air a may be distributed to the various sections of the tubular converter 24 through the connecting valved branch lines 24. Steam may be supplied to the heater 42 from a steam supply line 42- which'connects into the line 40. and steam from the line 44 may also be distributed to all or a portion 'of the converter 24 through .valved branch lines 42. The lower section or length of the converter 24 may be supplied with steam from a line II having valved branch lines 42. The return bends of the converter 24 are constructed like the showing in Fig. 2.

The highly unsaturated oleflnic mixture entering the inlet of the converter 24 from the transfer line 22, passes through the porous refractory tube 22 and is directly heated and raised in temperature by the heat developed from the air admitted to the space around the tube 22 and,

diffused therethrough. The air pressure around the tube 22 is maintained above the pressure inside the tube 22, which is preferably about 400 lbs. per square v inch, so that air is diffused through substantially the entire area of the tube, and thereby produces an enveloping zone in which the carbon formed in the reaction is burned or oxidized, and in which portions of the hydrocarbons. are also oxidized or burned. The

air and steam is admitted to the various portions.

or sections of the converter 24 at such a rate as to produce and maintain any desired temperature gradient throughout the converter and drive of! or oxidize any. carbon which may approach the inner surface of the tube 22. a v

In carrying out the operations in the converter 24, the high temperature air delivered through the line 44 may contain a regulated proportion of steam admitted to the line 40, so as to control the amount of oxidation effected along the various which will not be so long as to cause decomposition of the side chains of alkylated benzenes. The converter 24 is suitable for carrying out high temperature high pressure conversions that could not be effected in externally heated metal tubular heaters. The end of the converter 24 projects into the chamber 28, and the products discharged therefrom are quickly cooled with water or other suitable cooling liquid sprayed into the products from a spray head I4 which surrounds the outlet end of the converter in the chamber 22.

The products in the chamber 28 are cooled to a rather low temperature and thoroughly washed with heavy oils, the resulting condensate, carbon slurry, and wash liquid being withdrawn from the bottom of 'the chamber 22 through a valved line it. A portion of this withdrawn oil is recirculated through a line 52 which terminates in a spray head in the upper portion of the cham- 4 ber as shown. The excess of the heavyo'il, in-

- flux. A portion of the condensate and charging the chamber 26.

stock reaching the bottom of the tower l2 may be withdrawn through a line 42 and forced by means of a pump therein into the upper portion' of the chamber 28 where it flows down over baffies provided therein, as shown. If desired, a portion of this distillate stock may be introduced into the line it through a valved branch line 44 .to aid in the cooling and washing of the conversion products in the chamber below the baffies. The proportion of oil withdrawn from the tower l2 through the line 22 is preferably controlled so that practically all is .revaporized in maybe controlled by the valves in lines it and 40.

The fractionation carried out in the tower I2 is directed mainly to the separation overhead of all desirable aromatic hydrocarbons, particularly the aliwlated benzene hydrocarbons, some of which may be of relatively high boiling point.

The cut temperature on the tower I 2, for example, may be from 400' to 500 F., the vapors The pressure in converter 24.

portion of this product is preferably used as reflux in the top of the tower I2 and may be supplied thereto through 'a' line 18 containing a pump, as shown. The product produced in the conversion operation is withdrawn from the apparatus through the valved line 16 and 'sent to suitable ,fractionating apparatus, not shown, for separation of the various alkylated benzene derivatives, and the production of high aromatic high compression motor fuels if desired.

The Ca, Ca and C4 hydrocarbons recovered in the gas recovery apparatus or from the fractionators handling the final product withdrawn through the line 16, maybe returned to the conversion apparatus by a supply line so which leads directly to the coils of the pipe still heaterlG. These returned hydrocarbons may be both paramnic and olefinic, and the ones returned will depend on the market or' other uses for various materials such as butane, isobutane, the butenes, propane, propene, ethane, and ethylene. Any of such hydrocarbons from an outside source may be used. It has been found that the introduction of C3 and other-light hydrocarbons increases the production'of aromatic hydrocarbons. The process may be operated as a oncethrough process by introducing all of the stock through the line 80, including hydrocarbon gases.

In Fig. 3, the converter 24 is shown in cross sectional view with a slightly modified arrange ment of the lines for supplying air and steam. Each of the three sections of the converter 24 are shown with the air distribution lines 38 connected directly into a main air supply line82 which corresponds to the line 44 in Fig. 1.v In Fig. 3 the steam is distributed to the lines 36 through valved distributor lines 38 from a main steam supply line 84. The line 84, is used in place of lines 46 and 50 in Fig. 1 and provides a simplified means for supplying steam toall of the sections or lengths of the converter. It is to be understood that the arrangement shown burning carbon and gases along the inside wall or the tube 32. The oxygen in the air reacts' with or bums hydrogen in the vapor stream to produce water, and burns the free carbonto form carbon monoxide. Some air is 7 preferably supplied throughout the len th of the converter 24 even though in some sections in the converter it may be necessary to supply some steam to prevent a runaway temperature condition caused by the exothermic reactions taking place, for example, in the firstsection of the converter. In fact, the air heated in the heater 42 may be diluted to a substantial extent with steam but not sufilcient to interfere with the attainment of the high temperatures in'the initial stages of the operation. The steam introduced through lines 48, 52 or through lines 38 (Figs. 2 and 3), will be a relatively low temperature, depending on the pressure, so that it will have a very substantial cooling eflect when introduced into the tube 32 from the space between the tube 32 and the refractory insulation 30.' Y

The improved process of the present invention may be illustrated in connection with the conversion of a paraflinic gas-oil stock which is introduced into the apparatus either through the line I 0 or the line 80, until the apparatus is'on stream, when, of course, the stock "would be fed through the line l0 into the tower l2, unless a once-through operation is desired; In either case the gas-oil stock is supplied at a pressure of about vapors conducted through the line 22. The

- is quickly cooled as it enters the chamber. 28. The reactions effected in the converter appear-l" stream of vapors passed into the converter 24 is rapidly raised to a temperature of approximately 1350 F. and subjected to conversion for a period of approximately eleven seconds, at a pressure of about 400 lbs. per square inch, after which it to be a combination of polymerization, cyclization, alkylation, isomerization and dehydrogenation reactions, which lead to the production of in Fig. 3 may be used in apparatus of'Fig. 1, and a that steam may be supplied to the central section of the converter 24, although for simplicity inthe showing, this is not indicated in Fig. 1.

The operation carried out in the converter 24 involves a relatively close control of the pressure around the tube 32, so that it always equals or exceeds the pressure of the hydrocarbon vapors in the tube. Furthermore-air or oxygen or other combustion supporting gas, at a temperature of about 1100 F. aids in controlling the temperature in the converter since no heat is lost in raising the temperature of the air from atmospheric temperature to 1100 F. This reduces the air required by about 20%, and also reduces vapor consumption in tube 32. The entering vapors, convarious cyclic and aromatic hydrocarbons, particularly relatively high boiling benzene hydrocarbons containing one or more side chains of from 2 to 6 carbon atoms. Some dialkyl benzene derivatives are formed and some alkylated. benzenes having relatively long branched side chains, all of which as far as known have high antiknock values. Practically all of these hydrocarbons are recovered overhead from the tower l2 and subiected to fractionation in fractionating equipment, not shown. The toluene content or the overhead mixture recovered from tower l2 may be fractionated, for example, to produce various relatively pure fractions, such for example as a relatively pure fraction of toluene which may be treated with sulfuric acid or extracted with a selective solvent in the usual way and refractionated to 'produce nitration grade toluene. Side chain aromatic hydrocarbons. such as toluene, the xylenes, ethylbenzene, n-propylbenzene, isopropylbenzene, and other related compounds, have very high critical compression ratios. Therefore, the aromatic production withdrawn through the I line It may be used for the manufacture of aromatic motor fuels, or certain fractions thereof may be used for increasing the critical compression ratio of other motor fuels.

The process of the present invention may be varied in some respects, as for example by converting individual oleflns, such as heptene or octene in th converter 24, but such materials are relatively expensive, and it is preferred to operate on relatively inexpensive stocks, such as gas-oil, kerosene, naphtha and similar materials alone or with hydrocarbon gases. The process may be carried out on a combination of stocks comprising liquid hydrocarbons introduced through the line it, and normally gaseous hydrocarbons of the type referred to above, introduced through the line 00. A residual stock may be used by inserting a residuum separator between colls II and 20. Different stocks may require different temperatures and diflerent perations for the furnace II,

The converter 24 may be operated at any selected prasure from atmospheric to 400 lbs. and above, and at high temperatures which could not be used in pipe still heaters with metal tubes. Modifications of the type referred to, as well as others coming within the scope of the invention, are intended to be covered by the accompanying claims.

Having thus described the invention, what is claimedasnew is: r

1. In a process for manufacturing side chain benzene hydrocarbons in which a petroleum oil distillate stock low in aromatic hydrocarbons is cracked at a temperature of about 1100' F. in a cracking zone to produce a vapor mixture consisting largely of unsaturated olefinic hydrocarbons, the improvement which comprises passing the vapor mixture directly from the cracking tune into avtubular porous refractory converter through which the vapor mixture passes as a stream and is heated rapidly by an annular envelop of burning carbon, hydrogen andvhydrocarbons produced by separately heating air to a high temperature and diffusing it while in a highly heated condition through the wall of said tubular converter around the stream of vapors passing therethru, said vapor mixture being heated in said converter to a temperature of from 1350"to 1450" 1". for a matter of seconds, whereby hydrocarbons of said vapor mixture are converted .to side chain benzenehydrocarbons and controlling the final temperature attained by said vapor mixture in said converter by diffusing team through the porous wall th m a process for manufacturing side chain benzene hydrocarbons as defined by claim 1 in which the air is supplied to said converter at a temperature of approximately 1100 F.

3. In a process for the production oi aromatic hydrocarbons and aromatic, type motor fuels from petroleum stocks, the improvement which comprises superheating the vapors of the petroleum stock to a high temperature of about 1100 F., passing the superheated vapors into a tubular conversion zone in which the vapor mixture is further heated and raised in temperature to about l350-1450 F. by an annular envelop or burning carbon, hydrogen and, hydrocarbons which envelop i produced by diifusing highly heated air through the wall of said tubular conversion zone around the stream 01' vapors therein, and controlling the final temperature attained by the vapor mixture by diffusing steam through the wall of said tubular conversion zone.

4. In a process for manufacturing aromatic hydrocarbons from petroleum oii stocks, the improvementwhich comprises passing a mixture of the petroleum 011 stock to be converted with a substantial proportion of hydrocarbon gases into and through a pipe still turnace in which the mixture is vaporized and the vapors cracked at temperature of about 1100. F., passing the man temperature products from the pipe still heater into and through a tubular conversion zone in which the products are heated to a temperature of irom about 1350' to 1450' I". by supplying a combustion supporting gas at high temperature to the outer surface of the stream in said conversion zone whereby portions of the stream are burned and deposition of carbon in the conversion zone is prevented, controlling the temperature attained by the products by admixing steam with said combustion supporting gas. passing the products from said conversion zone into a chamber and rapidly cooling them to a temperature of from 600 to 700 F., and passing the vapors from said chamber into a fractionating tower i'or therecovery of the desired aromatic hydrocarbons.

DAVID G. BRANDT.

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