US2399780A - Manufacture of aromatic hydrocarbons - Google Patents

Description

May 7, 1946.

G. B. ARNOLD 2,399,780

MANUFACTURE OF AROMATIC HYDROCARBONS Filed July 9, 1942 CATALYTIC CONVERSION BENZENE EXCHANGE REACTION MOTOR FUEL t 1 |9- l3 FRACTIONATE |5- HIGHER XYLENE BENZENE BOILING FRACTION R i TOLUENE g I BENZENE 2.0 i

CATALYTIC CONVERSION (BENZENE EXCHANGE REACTION).

GEORGE B. ARNOLD 11v VENTOR HIS A TTORNE Y Patented May 7, 1946 MANUFACTURE OF ABOMATIC HYDBOCABBONS George B. Arnold, Beacon, N. 2., aaaignor to The Texas Company, New York, N. Y., a corporation of Delaware Application July 9, 1942, Serial No. 450,253 .6 Claims. (c1. 260-668) This invention relates to the treatment of hydrocarbons, particularly petroleum hydrocarbons for the production of highly aromatic motor fuels as well as toluene.

The invention relates to a process in which higher boiling aromatic hydrocarbons in the presence of benzene and in contact with a suitable catalyst are subjected to a conversion involving an exchange reaction between benzene and higher boiling aromatic hydrocarbons to form lower bolling aromatic hydrocarbons within the gasoline boiling range including toluene. In accordance with the invention petroleum stocks containing aromatic hydrocarbons are subjected to catalytic conversion in the presence of benzene, the products of conversion are fractionated to separate the lower boiling products from a higher boiling traction and such higher boiling fraction is subjected either to a second catalytic conversion operation in the presence of benzene or is subjected to cracking or conversion to produce lower boiling products adapted for the exchange reaction operation.

The invention will be understood by reference to the accompanying flow. diagram which represents diagrammatically a particular embodiment of the invention.

The charging stock comprising a gasoline or naphtha stock is introduced through a line 9 together with benzene, admitted through line III, to' a catalytic conversion step I l. The charging stock is preferably a naphtha stock containing aromatic hydrocarbons and having an initial boiling point of about 250-310 F. and 'an end point of 400 F.-500 F. Since the amount of aromatic hydrocarbons in the naphtha fractions of most crude petroleums is quite low the charging stock will generally be a product from a previous conversion process such as naphtha stocks produced by thermal or catalytic or reformed or aromatized naphtha stocks. A very suitable stock may comprise the higher boiling products produced in the so-called hydroforming process in which a straight run gasoline stock is subjected'to conversion temperatures of about 900 lit-1000 F. in contact with an aromatizing catalyst such as molybdena-alumina and chrome-alumina while in the presence of hydrogen and under 'superatmospheric pressures such as 200-400 p. s. i.

In the catalytic conversion step II the mixture of benzene and higher boiling stock is raised to a conversion temperature of the order of 800 F.- 1000 F. in contact with a catalyst adapted to promote conversion into lower boiling hydrocarbons and promote an exchange reaction between benzene and higher boiling homologs thereof to form lower boiling hydrocarbons in the gasoline boiling range. In the conversion operation higher boiling aromatic hydrocarbons consisting essentially of dlalkyl, trialkyl or polyalkyi aromatics or longer chain monoalkyl hydrocarbons are converted to lower boiling hydrocarbons boiling within the gasoline boiling range and an exchange reaction occurs between benzene and higher boiling aromatic hydrocarbons to produce alkyl benzenes in the gasoline boiling range including toluene.

Certain synthetic silica-alumina and aluminum-containing catalysts serve the function of catalyzing the conversion into lower boiling hydrocarbons as well as the exchange reaction between benzene and higher boiling homologs thereof to selectively produce toluene. A synthetic silica-alumina catalyst is recommended as a superior catalyst for accomplishing this two-fold purpose. This catalyst may be prepared by precipitating a mixed gel of silica and alumina and may contain additional reactive agents such as zirconia and thoria. The catalyst should be substantially free from alkali metal. Metallic fluorides such as aluminum magnesium and chromium fluorides dispersed on adsorptive carriers or inorganic gels such as silica and silica alumina gels are also adapted to function as catalysts for this two-fold purpose. Such catalysts are disclosed in the pending applications of Preston L. Veltman and Arthur R. Goldsby, Serial No. 311,- 942, filed December 30, 1939, and Preston L. Veltman, Serial No. 311,943, filed December 30, 1939, and Serial No. 379,483, filed February 18, 1941. Another suitable catalyst comprises aluminum phosphate having dispersed thereon a solid metallic fluoride such as aluminum fluoride, magnesium fluoride and chromium fluoride as disclosed in the pending application of Preston L. Veltman, Serial No. 313,759, filed January 13, 1940, now Patent 2,301,913. The pending applications referred to contain detailed disclosures of these catalysts and reference may be had thereto for detailed descriptions of the catalysts and the methods of preparing them. The catalysts employed in my invention may be in the form of stationary or moving beds of pulverulent or pelleted metal through which the hydrocarbon vapors are passed or in a powdered or finely divided form used as a-slurry or in suspension as in the so-called fluid type of catalytic cracking operation.

The mixture charged to the catalytic conversion and benzene exchange reaction step ii may be composed of about 0.2-8.0 volumes of benzene to 1 volume of naphtha stock. The mixture is subjected to temperatures of the order of 800 F.-

1000 F. at space velocities of the order of 0.1 up to 5.0 to 10, the space velocity being defined as the liquid volume per hour per space volume of catalyst. For the production of toluene there appears to be no advantage in the use of temperaturesabove 1000 F. at space velocities of about 1 but when merely a motor fuel product is desired temperatures above 1000 F.may be employed. The operation may be conducted under a wide range of pressure such as relatively low pressures of the order to 50200 p. s. 1. up to higher pressures such as 400-600 p. s. i. or even higher pressures. In the reactions occurring in the presence of the catalyst higher boiling hydrocarbons are converted into lower boiling hydrocarbons, polyalkyl aromatic hydrocarbons being converted to lower boiling aromatic hydrocarbons and an exchange reaction takes place between the benzene and certain of the aromatic hydrocarbons, particularly aromatics of intermediate boiling range such as the xylenes, to effect the formation of lower boiling aromatics in the gasoline boiling range including toluene. When directing the operation specifically for the production of toluene the operation is characterized by an overall disappearance of higher boiling aromatics and by a net conversion to toluene and consumption of benzene.

The reaction products pass through line l2 to a fractionating step [3 wherein the products are fractionated to obtain the fractions desired.

Thus the products may be fractionated to obtain a benzene cut withdrawn through line H, a toluene out withdrawn through line I5, an intermediate boiling range cut withdrawn through line I6 and a higher boiling fraction withdrawn through line II. when it is desired to recover toluene it is advantageous to recycle the benzene cut through line it to the conversion step Ii and to pass the fractions boiling above toluene to the subsequent conversion operation. When making a motor fuel cut, which may be withdrawn through line is, such cut may include the benzene and toluene fractions or if desired the benzene fractions may be separately recovered and recycled to the conversion step ll.

The fractions higher boiling than the motor fuel cut withdrawn through line l9, or higher boiling than the toluene cut withdrawn through line 15, are directed through lines It and II to a catalytic conversion step 20. In this step the higher boiling fractions from the preceding benzene exchange reaction step are subjected to a catalytic conversion either with or without benzene. When operating with benzene, makup benzene may be directed through line 2| to the conversion step 20 and benzene from the fractionating step ii may, if desired, be passed through a branch line 22 for introduction to the catalytic cracking step 20. In this operation a mixture of benzene and higher boiling fractions are subjected to conversion conditions similar to those described for the conversion step I l to eflect conversion into lower boiling hydrocarbons and produce an exchange reaction between benzene and higher boiling alkyl aromatics. By carrying on the benzene exchange reaction in two stages higher conversions to lower boiling aromatic hydrocarbons including toluene may be produced than can be accomplished in a single stage. The reaction products may be passed through a line 23 to the fractionating step II for fractionation together with the products from the conversion step I I.

When operating without added benzene in the conversion step 20 the operation is preferably carried on in the presence of a catalyst adapted to promote conversion into lower boiling hydrocarbons and particularly into aromatic hydrocarbons adapted for the benzene exchange reaction. Aluminum fluoride, magnesium fluoride and chromium fluoride may be mentioned as catalysts which are particularly adapted for use in step 20, since these catalysts have the peculiar property of promoting a selective conversion to benzene and thus serve to provide benzene for the conversion step II. The operation is preferably conducted at temperatures of the order of 900 F.-1100 F., under superatmospheric pressures, such as -400 p. s. i.

In an alternative operation in accordance with the invention the fractionation is so conducted in the fractionating step I3 as to separate a fraction of intermediate boiling range, including particularly the xylenes, from the higher boiling products and to recycle this intermediate fraction, as withdrawn through line l6, through the line 2| to the conversion step ii, while directing the higher boiling products withdrawn through line H to the conversion step 20. In this operation it is advantageous to subject the higher boiling fraction which is directed to the conversion step 20 to catalytic cracking in the absence of added benzene under conditions favorable for the conversion of the higher boiling hydrocarbons into lower boiling hydrocarbons, particularly aromatic hydrocarbons. The use of the fluoride catalysts, which have been mentioned as promoting a selective conversion to benzene, is highly advantageous in this operation in view of the relatively large yields of benzene produced. The recycling of the intermediate fraction containing xylenes to the benzene exchange reaction step ii is particularly advantageous because the xylenes are more eflective in the exchange reaction with benzene to produce toluene than higher boiling aromatics, since the :wlenes by reacting molecule for molecule with benzene produce two molecules of toluene while the higher boiling aromatics react molecule for molecule with benzene to give one molecule of toluene.

While I have described a particular embodiment of my invention for purposes of illustration, it should be understood that various modifications and adaptations thereof which will be obvious to one skilled in the art, may be made within the spirit of the invention as set forth in the appended claims.

I claim:

1. In the manufacture of toluene the process that comprises subjecting a mixture of benzene and hydrocarbon 011 containing aromatic hydrocarbons higher boiling than toluene to catalytic conversion in a conversion zone to effect conversion into lower boiling hydrocarbons and produce an exchange reaction between benzene and higher boiling homologs thereof to thereby consume benzene and effect selective conversion to toluene, fractionating the resultant products of conversion to sepa te lower boilin fractions cluding toluene from higher boiling fractions, subjectingsuch higher boiling fractions to catalytic cracking in a second conversion zone in contact with a metallic fluoride catalyst to effect selective conversion to benzene, fractionating resultant cracked products of the latter con- !6 version to obtain a benzene fraction and recyaaoavso 3 cling said benzene fraction to the first mentioned catalytic conversion zone.

2. In the manufacture of toluene the process that comprises subjecting a mixture of benzene and hydrocarbon oil containing aromatic hydrocarbons higher boiling than toluene to eatalytic conversion in a conversion zone to effect conversion into lower boiling hydrocarbons and produce an exchange reaction between benzene and higher boiling homologg thereof to thereby consume benzene and effect selective conversion to toluene, fractionating the resultant products of conversion to obtain fractions comprising benzene, toluene, xylene fractions and a higher boiling fraction containing aromatic hydrocarbons, subjecting said higher boiling fraction to catalytic cracking in a second conversion zone in contact with a metallic fluoride catalyst to effect conversion into lower boiling aromatic hydrocarbons comprising benzene and xylenes, fractionating the resultant product of conversion from the latter conversion operation and recycling benzene and xylene fractions to the first mentioned catalytic conversion zone.

3. In the manufacture of toluene the process that comprises subjecting a mixture of benzene and hydrocarbon oil containing aromatic hydrocarbons higher boiling than toluene to eatalytic conversion in a conversion zone to effect conversion into lower boiling hydrocarbons and produce an exchange reaction between benzene and higher boiling homologs thereof to thereby consume benzene and effect selective conversion to toluene, directing the resultant'products of conversion to a fractionating zone wherein fractionation takes place to separate fractions comprising benzene, toluene, and higher boiling hydrocarbons, directing the higher boiling hydrocarbon fraction to a second conversion zone wherein the hydrocarbons are subjected to eatlvtie cracking in contact with 'a metallic fluoride catalyst to effect conversion into lower boilin hydrocarbons, directing the resultant products of conversion to said fractionating zone and recycling the benzene fraction to the first mentioned conversion zone.

4. In the manufacture of toluene the process that comprises subjecting a mixture of benzene and hydrocarbon oil containing aromatic hydrocarbons higher boiling than toluene to eatalytic conversion in a conversion zone to effect conversion into lower boiling hydrocarbons and produce an exchange reaction between benzene and higher boiling hcmologs thereof to thereby consume benzene and effect selective conversion to toluene, directing the resultant products of conversion to a fractionating zone wherein the products are fractionated to separate fractions comprising benzene, toluene, xylene and higher boiling hydrocarbons. directing the higher boiling hydrocarbons to a second conversion zone wherein the hydrocarbons are subiected to catalytic cracking in contact with a metallic fluoride to effectconversionto lower boiling hydrocarbons, directing the resultant products of conversion to said fractionating zone and recycling the benzene and xylene fractions to the first mentioned conversion zone.

' 5. In the manufacture of toluene the process that comprises subjecting a mixture of benzene and petroleum naphtha containing aro-' matic hydrocarbons to conversion in a conversion zone in contact with a catalyst comprising a synthetic composite of precipitated silica and alumina at a temperature of the order of 800l000 F. to thereby effect conversion into lower boiling hydrocarbons and effect an exchange reaction between benzene and higher boiling homolog thereof to produce a net con-.

sumption of benzene and a selective formation of toluene with a net reduction in aromatichydrocarbons higher boiling than the xylenes, fractionating the resultant products of conversion in a fractionating zone to separate fractions comprising benzene, toluene and xylenes from higher boiling hydrocarbons, directing said higher boiling hydrocarbons to a second conversion zone wherein the hydrocarbons are subjected to conversion temperature in contact with a cracking catalyst to effect conversion into lower boiling hydrocarbons, directing the resultant products of conversion from the latter conversion zone to said fractionating zone and recycling the benzene fraction to the first-mentioned conversion zone.

6. In the manufactureof toluene the process that comprises subjecting a mixture of benzene and petroleum naphtha containing aromatic hydrocarbons to conversion in a conversion zone in contact with a catalyst comprising a synthetic composite of precipitated silica and alumina at a temperature of the order of 800-1000 F. to thereby eflect conversion into lower boiling h8- drocarbon and eifect an exchange reaction between benzene and higher boiling homologs thereof to produce a net consumption of benzene and a selective formation of toluene with a net reduction in aromatic hydrocarbons higher boiling than the xylenes, fractionating the resultant products of conversion in a fractionating zone to separate benzene, toluene and xylene fractions from higher boiling hydrocarbons, directing said higher boiling hydrocarbons to a second conversion zone wherein the hydrocarbons are subjected to conversion temperature in contact with a cracking catalyst to effect conversion into lower boiling hydrocarbons, directing the resultant products of conversion from the latter conversion zone to said fractionating zone and cycling the benzene and xylene fractions to the first-mentioned conversion zone.

GEORGE B. ARNOLD.

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