US2383072A - Producing toluene - Google Patents

Description

Patented AugaZl,

Alexl G. oblaa, einen, 1u., signor to standard gli Company, Chicago, Ill., a corporation of diana Application December 12, 1.940, Serial No.l 369,843

` (ci. 26o-ses) 7 Claims.

'I'his invention relates to a process of producing toluene from petroleum hydrocarbons. An object f the invention is to produce both toluene and high knock rating motor fuelsimultaneous` ly-with the aid of catalysts without the destruction of large amounts-of' the petroleumhydrocarbons such as occurs in the case of high tem- Referring to the drawing, heavy naphtha is chargedby line I0 to heater Il wherein it is vaporized and heated to a high conversion tem- I perature and conducted by transfer line I2 to reaction chamber I3 where it fundergoes conver- Vsion in the presence of a catalyst. `The naphtha perature pyrolysis for the production of toluene from petroleum. Other and more detailed objects will be shown in the description of the invention.

In the manufacture of benzene and toluene from petroleum by high temperature pyrolysis. for example, at temperatures of the order of 1400 F. to 1600 F., a large proportion of the paran hydrocarbons is degraded to coke ,and permanent gases. Yields of aromatic distillates and particularly toluene are relatively low. .I have now discovered that bythe use of catalysts at moderate temperatures within the cracking range, I may obtain substantial yields of toluene from petroleum naphtha accompanied by relaemployed in my process may suitably be either `straight run or cracked petroleum naphtha, preferably the former.

I prefer to employ a heavy naphtha having an initial boiling point of about 200 to 300 F. and-a iinal boiling point of about 450 F.- Somewhat heavier naphthas may be employed, however, including a material commonly classed as kerosene and a light gas oil having iinal boiling -points as high as 600 to 650 F. Parailinic and olenic naphthas may be employed though somewhatA better yields of toluene are obtained from the more aromatic or naphthenic types of naphtha.

' able catalyst for eiecting conversion or reformnve1y 4lime degradation ofthe naphtha into gas and carbon.

\ 4 Myprocessinvolves treating petroleum naph-` tha in two successive steps under specific conditions of catalyst treatment and separation of intermediate products.- In the rst step of vmy process the petroleum naphtha is treated under aromatizing conditions in the presence of ahydrogenation-dehydrogenation catalyst at elevated temperature whereby the aromatic hydrocarbon content of the naphtha is greatly increased, partly by cyclization of parailinic and/or l oleilnic hydrocarbons and partly las a result of dehydrogenation of naphthenic hydrocarbons. Toluene is separated from the products and higher boiling aromatic hydrocarbons are subjected to a second high temperature catalytic treatment with a cracking or hydrocarbon splitting catalyst whereby certain of the higher boiling aromatic hydrocarbons are decomposed to produce additional toluene.- Other aromaticvhydro- .carbons not decomposed or decomposable in the second stage of the process are separated and employed as highknock rating motor fuel, high solvency naphtha suitable for lacquer andpaint solvents, etc.

The process will b'readily understood by relferring to the drawing Fwhich accompanies this spectdcation and is a part thereof. 'I'he draw- I ing shows diagrammatically ka. layout for a plant to produce toluene and high knock rating mo r fuel from petroleum naphtha in accordance t my invention.

plate I4.

ing of theV naphtha. The ycatalyst which is a porous, granular mass, is supported on perforated Catalysts of the `hydrogenatingde hydrogenating type are preferred, including the difllcultly reducible oxides such as vanadium,A chromium and molybdenum oxides and oxides of other metals in the left columns of groups V and VI. It is preferred to employ these oxides supported on a suitable base, particularly granular alumina or magnesia. Activated alumina, magnesiteor bauxite activated by acid, treating may be employed as a base. The amount of hydrogenating-dehydrogenating metal oxide 4supported on the aluminafor example, may be of the order of 5 to 25%.

Hydrogen may be employed in the reactor I3, the hydrogen being introduced, for example, by line I5, and passed through the'furnace with they naphtha. 'I'he amount of hydrogen may suitably equal the volume of hydrocarbon vapors undergoing treatment or it may exceed that volume by as much as 2 to 5 vfold. When employing hydrogen, it is desirable to maintainr the pres-- sure 'in reactor I3 within the range of 50 pounds to 600 pounds, preferably about to 250 pounds per square inch.. The rate of contacting the oil vapors with the catalyst in I3 may suitably be about 0.2 to 5.0 volumes of liquid hydrocarbon per gross volume of catalyst per hour. The rate will depend partly on temperature, partly on the character of thefstock and the activityA of the catalyst. A temperature in reaction chamber I3 of fthe order 4of 900 to 1050 F. is satisfactory.

vapors leaving reactor I3 pass by line I6 to fractionator I1 where they are fractionated 4several streams as indicated by the drawoff lines into I8, I 9 and 20 and vapor line 2|. In the operation, the reflux in tower I1 is trapped out at different levels and the highest boiling fraction is withdrawn at the base of the fractionator by drawoff line 22. The fraction withdrawn at line I9 is further fractionated in side fractionator 23 where lighter materials are taken overhead and returned by line 24 to main fractionator I1. A side cut boiling above about 115 C., containing principally xylenes and heavier aromatic hydrocarbons, is withdrawn by line 25 and employed in the blending' of motor fuel or as a high solvency is withdrawn by line 20 and is fractionated infractionator 21 from which a toluene cut is With-v drawn by side drawoff line 28. A higher boiling fraction, containing in part xylenes and toluene, is withdrawn from fractionator 21 via bottom drawoft line 29. This bottom fraction serves as part of the reflux in fractionator 23. Lighter materials -in 21 are driven off from the toluene and returned to the main fractionator I1 by line 30.

Vapors from tower .I1 are conducted by line 2| to condenser 3I and receiver 32 where fixed gases are separated and the light naphtha, which is a W boiling light condensateis withdrawn by line 33. This stock may be combined with the heavier naphtha in line 25 to Vproduce a motor fuel which is withdrawn by line 34.

i Stock which contains aromatics boiling within the range of from about 146 C. to about 210 C. is trapped out at I8 from tower I1 and is conducted by line 35 to line 26 where it is combined with the bottoms from tower 23 and charged by pump 36 to coll 31- in heater 38 from which the hot oil vapors are conducted by line 33 to catalyst chamber 40. Different conversion conditions and different catalysts vare employed in chamber 40 from those employed in reactor I3. In chamber 40 the principal reaction is one of carbon to carbon bond rupture rather than-dehydrogenation and ring formation, typical of the catalyst and conditions the range of 950 to 1200 F. and thepredominant reaction appears to be a splitting or dealkylationtion by alkylation of the lighter alkyl aromatics in reactor 40 and hence the xylenes, toluene and benzene are preferably removed from the feed passing to reactor 40'. A stock having an initial' boiling point of about 146 to 150 C. is suitable and this stock may be obtained by proper regu-,-

v lation of fractionatlng conditions in tower I1 and side fractionator 23. .'I'hus, referring to tower 23 the xylene may constitute a large proportion of the naphtha in line 25, which isemployed` for y in I3. In 40 the temperature is preferably within 50 motor fuel or high solvency naphtha. A heavier fraction withdrawn from tower I1 by line 35 and/or from fractionator `23 by line 26 may contain a large amount of alkyl substituted toluene in which alkyl groups of 2 or more carbon atoms are present. Ethyl toluene having a boiling point of about 158. C. is characteristic of this material. Tower 40 yis filled with porous, granular catalyst of the conversion or splitting type such as active silica, the alumina-silica complexes, acid treated clays, acid treated bentonite, etc. Super Filtrol is an example of the latter type of catalyst. Silica gel impregnated with small amounts of magnesia, alumina, or with small amounts of alumina and zirconia may also be used supported on porous plate 4 I. Thevvapors pass downward through the catalyst bed in reactor 40 and escape by line 42 leading to fractionator 43.

Two side streams may be withdrawn from fractionator 43; the lower stream by line 44 has an initial boiling point of about 150 C. or higher and is suitable for blending with light naphtha from 32 making a motor ,fuel of high knock rating which 'leaves the system by line 34 previously described. A part of this stream may be recycled to furnace 38 by line 45 is desired. A toluene fraction is taken from tower 43 by line 41 leading to side fractionator 48 where lighter fractions are eliminated as overhead and relatively pure toluene -is withdrawn by side drawoii" line 49. A higher boiling fraction may be withdrawn from fractionator 48 by line 50 leading to line 44. Alternatively, this heavy fraction may be returned to the tower 43 for reuxing therein. The toluene removed by line 49 may be combined With the toluene in line 28 and discharged from the system by line 5I.

Vapors from fractionatcr 43 are led by line 52 to condenser 53 and receiver 54 where the gases are separated and a light naphtha having a boiling range of about 30 to 110 C. may be led by line 55 into admixture with the stocks from lines 25 and 33 to motor fuel line 34.

Residual fractions containing relatively high side fractions in tower I1 may be conducted in regular manner previously described without substantial change. By this system of operation substituted toluene compounds boiling above 150 C. are conducted by line 35 and pump 36 back to heater 38 where they are reprocessed until com' pletely converted into toluene.

As pointed out hereinabove, the conditions employed in reaction tower 40 are generally more,

stringent than those employed in reaction chamber'l3. Contact rates represented by space velocities of about 0.2 to 2 volumes `of oil charged per hour perapparent volume of catalyst are characteristic. 950 to 1050u F. and the pressure about atmospheric to 50 pounds per square inch. The -prin cipal reaction occurring in reactor 40 is dealkylation of alkyl side chains on the aromatic nucleus. 'I'he amount of toluene produced in the .-operation of reactor 40 is, therefore, primarily dependent on the amount of polyalkylated benzene available in the process. In general. with average feed stocks,

such vagMid-lContinent' and East Texas naphtha The preferred temperature is about" asesora side fractionator 48 as a'result of the-dealkylal tion of heavier substituted' aromatic hydrocarbons in reactor 40, thus making the total yield of toluene about 30%, based on the heavy naphtha charged to heater I I.

It is believed that the reaction occurring in reactor I3 is largely one ofdehydrogenation and aromatization. High aromatic compounds may be converted into aromatics by the former reaction and straight chain paraln compounds are also converted to aromatics by cyclization.` Hydrogen exerts a beneficial eiect upon the catalyst, increasing the catalyst life and maintaining activity. lHydrogen for the process may be obtained' partially or ,entirely from the spent gases discharged from separator'1 32 where it'occurs in admixture with xedhydrocarbon gases.

When the catalysts in reactors I3 and 40 become spent they may be restored to substantially their original activity by oxidizing oil the carbonaceous material with air vor mixtures of air with flue gas or other inert gas after purging the reactors of hydrocarbon vapors. Purge lines and catalyst regeneration lines are not shown on the drawing.

Although I have described my invention with respect to afspecic apparatus for carrying out the process, I do` not intend that it be limited except as described in the following claims.

I claim: i

1. The process of making toluene from vpetroleum riaphtha which comprises initially subjecting .said naphtha to catalytic conversion inthe presence of hydrogen and a hydrogenating-dehydrogenating catalyst under aromatizing conditions of ltemperature and pressure whereby said 2. The processv of claim `1 wherein a xylene fraction is combined with a fraction lighter than toluene to produce a motor' fuel of high knock rating.

3. The process of producing toluene from petroleum naphtha which comprises subjecting said naphtha to the action of a solid hydrogenatingf dehydrogenating catalyst ofthe metal oxide type 4in the presence of hydrogen at a' temperature within the range of 900fto 1100 F; and a space velocity of about 0.2 to 5`volumes per hour per volu-me of catalyst whereby aromatic hydrocarbons are produced, fractionating said aromatic hydrocarbons and separatingl therefrom a toluene fraction, a xylene fraction and Ia fraction boiling between about 145 C. and 210 C., subjecting said last-mentioned fraction to the action of a porous,

solid cracking catalyst at a pressure of about 0 to 50 pounds per square inch gage, a temperaturewithin the range of 950 to 1150 F. and space velocity of about .2 to 2 volumes per hour per volurrie of catalyst, thereby converting a substantial amount of heavier aromatic hydrocarbons into toluene, and recovering said toluene 'from' the conversion products by fractionation.'

4. The process of claim 3 wherein the hot converslonproducts obtained from said cracking catalyst are conducted without condensation directly to the fractionation step following said hydrogenation-dehydrogenation catalyst treatment and fractionated therein to recover toluene.

5. 'I'he process of claim 3 wherein the said hy- "drogenation-dehydrogenation catalystis an oxide i I of a metal of the left columns of groups V and VI of the periodic system. v

6. The process of cla-im 3 wherein the hydrocarbon cracking catalyst is a compound compris-v I ing essentially activated silica.

7. .'Ikhe process of producing toluene from paraiin hydrocarbons which`compri`ses subjecting a paralnlc petroleum naphtha to cyclization in the presence of hydrogen and a dehydrogenating catalyst at a cyclization temperature of about 900 to 1050 F., thereby converting a substantial portion of the parailln hydrocarbon into toluene and other aromatic hydrocarbons, separating from the aronaphtha is Asubstantially converted into a mixture r' of aromatic hydrocarbons containing to1uene,` xylene and heavier aromatics, frationating said hydrocarbons and removing therefrom a toluene fraction and a fraction heavierth'an xylene boilmatic hydrocarbon products a toluene fraction, a xylene` fraction' and a heavy fraction substantially all boiling above the boiling point of xylene,

subjecting said heavy fraction to the action of a porous, solid, cracking catalyst at a pressure of aboutO to 5 0 pounds per square inch gage and a temperature of about 950 to 1150 F., thereby converting heavy aromatic'hydrocarbons into lower square inch gage,` whereby additional toluene is v produced and separating said additional from the conversion products.

toluene boiling aromatic hydrocarbons including toluene,

and recovering the desired toluene from the products of said conversion.

ALEX G.. oBLAD.

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