US2389713A

US2389713A - Conversion of hydrocarbons

Info

Publication number: US2389713A
Application number: US478240A
Authority: US
Inventors: Harold V Atwell
Original assignee: Texaco Inc
Current assignee: Texaco Inc
Priority date: 1943-03-06
Filing date: 1943-03-06
Publication date: 1945-11-27
Anticipated expiration: 1962-11-27

Description

Nov. 27, 1945. H. v. ATWELL 2,389,713.

CONVERSION OF HYDROCARBONS Filed March 6, 1943 CHARGING STOCKjj CRACKING THERMAL OR CATALYTIC FIQACTIONATE "I '31 it GASES RESIDUE 5A5 OIL k GASOLINE INTE RMED IATE FRACTION BENZENE/ I I I "1 I CATALYTIC CONVERSION I BENZENE EXCHANGE REA ION I i HYDROGEN/ L 'FRACTIONATE l 27' l 2 23 218 1'2 l l CQC. GASES l l TOLUENE) 29 I 1 CRACKING I MOTOR THERMAL GR CATALYTIC FUEL HAROLD y. ATWELL Patented Nov. 27, 1945 CONVERSION OF HYDROCARBONS Harold V. Atwell, Beacon, N. Y., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application March 6, 1943, Serial No. 478,240

Claims.

This invention relates to the treatment of hydrocarbons for the production of toluene as well as motor fuel rich in aromatics. The invention is directed to the production of products rich in the lower boiling aromatics and well adapted for use in blending to produce high anti-knock gasoline or motor fuel, more particularly aviation gasoline, while also producing high yields or high concentrations of toluene.

In accordance with the invention, petroleum stocks higher boiling than gasoline, such as gas oil, are subjected to either thermal or catalytic cracking for the production of lower boiling products, the cracked products are fractionated to obtain light motor fuel fractions, intermediate boiling fractions and higher boiling fractions, and the intermediate boiling fractions are subjected to conversion conditions adapted for the selective conversion to toluene.

In conducting the selective conversion into toluene, the intermediate fractions are subjected to conversion in the presence of benzene and in contact with a catalyst adapted to promote an exchange reaction between methyl groups resulting in the formation of toluene. In this conversion, higher boiling aromatic hydrocarbons comprising di-alkyl, tri-alkyl, or poly-alkyl aromatic hydrocarbons, or longer chain mono-alkyl hydrocarbons are converted to lower boiling alkyl aromatic hydrocarbons, and an exchange reaction occurs between benzene and higher boiling aromatic hydrocarbons to produce alkyl benzenes in the gasoline boiling range, particularly toluene. An important feature of this stepof the process involves the introduction of hydrogen to the conversion zone for the purpose of suppressing carbon formation.

By carrying on the exchange reaction between the methyl groups under conditions which are selective to the formation of toluene it is found that there is a consumption of benzene and disappearance of aromatic hydrocarbons in the higher boiling ranges, more particularly in the range above the boiling point of the xylenes. Consequently, since the presence of aromatics is deleterious in both thermal and catalytic cracking, the benzene exchange reaction step, conducted under conditions selective to the formation of toluene, serves to improve the characteristics of the higher boiling stocks for subsequent cracking. Accordingly, the invention contemplates the cracking of petroleum stocks, either thermally or catalytically, under conditions favorable to the production of a high yield of aromatic hydrocarbons, fractionating the cracked products to obtain an intermediate boiling fraction, subjecting this fraction comprising gas oil or kerosene constituents, as well as higher boiling gasoline constituents, to the exchange reaction with benzene under conditions selective to the production of toluene and finally cracking, either thermally or catalytically, the higher boiling components from the exchange reaction step which have been improved in quality for further cracking by reason of the disappearance of higher boiling aromatic hydrocarbons.

For the purpose of more fully describing the invention, reference is hadto the accompanying flow diagram, which illustrates diagrammatically a particular embodiment of the invention.

The charging stock is introduced through a line it! to a conversion step H wherein the oil is subjected to either thermal or catalytic cracking. The preferred charging stock is a, gas oil having an initial boiling point of about SOD-600 F. In the thermal cracking process, the gas oil is subjected to low pressure, high .temperature cracking conditions, such as pressures under p. s. i., preferably pressures below 50 lbs. or approximating atmospheric pressure and temperatures of the order of 900-1100 F. The conversion is carried on with high rate of cracking per pass such as 20-35%, as measured by conversion into gasoline, so as to produce gasoline constituents of high anti-knock quality and to produce a high yield of aromatic hydrocarbons. In the catalytic cracking process the gas oil is subjected to cracking in contact with any of the usual catalysts adapted for catalytic cracking. The synthetic silica-alumina cracking catalysts are recommended. The catalytic cracking is carried on under moderate superatmospheric pressures, preferably not over 50 p. s. i. and at temperatures of the order of 900-1000 F. to effect a total conversion of some 50-60% or a conversion into gasoline amounting to about 30-40%.

The cracked products are passed to a fractionating step I2 wherein they are fractionated to obtain a normally gaseousiraction withdrawn through line l3, a light gasoline fraction withdrawn through line M, an intermediate fraction withdrawn through line IS, a higher boiling condensate withdrawn through line I 6 and a residual fraction withdrawn through line H. The normally gaseous fraction is with advantage recycled to the cracking step I I, in which case the recycled fraction may consist of either the entire normally gaseous fraction, light fraction consisting essen tially of hydrogen and methane, or a higher boiling fraction consisting essentially of C3 and C4 hydrocarbons.

When carrying on thermal cracking in step II it is preferable to recycle a C3-C4 fraction to the thermal cracking zone which results in an increase in the production of aromatics. When conducting catalytic cracking in step H either lower boiling or higher boiling normally gaseous fractions may be recycled to the catalytic 'cracking zone but a light fraction including hydrogen is particularly beneficial when using a catalyst responsive to hydrogen, such as boria on alumina.

The lower boiling gasoline constituents passing through line I 4 are of high anti-knock character and are directed to the motor fuel tank IS.

The intermediate fraction withdrawn through line i5 is directed to a catalytic conversion step l9 wherein it is subjected to conversion conditions for the selective conversion to toluene. The boiling range of this fraction varies with the particular objects in view. From the standpoint of conversion to toluene it is considered preferable to employ a fraction having an initial boiling point of about 250-300" F. and an end point approximating 500-600 F. and from the standpoint of using up minimum proportions of motor fuel constituents in the conversion to toluene and yet obtain a high toluene yield, a fraction consisting essentially of constituents boiling between 300 F. and 550 F. is recommended. When it is desired to improve the quality of higher boiling hydrocarbons for subsequent cracking, as well as producing toluene and low boiling aromatic hydrocarbons, the end point of the intermediate fraction may be raised to a relatively high temperature such as 700-800 F.

The gas oil fraction in line 16 and the residual fraction in line I! may be withdrawn from the system. In some cases the removal of a separate gas oil out may be eliminated, particularly when withdrawing, through line l5, a wide boiling range fraction of such high end point as to include gas oil fractions.

The intermediate fraction, passed through line I5, is subjected to conversion conditions in step I9 for the selective conversion to toluene. In conducting this conversion, benzene, introduced through line 20, is-added to the intermediate boiling fraction and the mixture is subjected to conversion temperatures in contact with a catalyst adapted to catalyze reactions involving conversion from higher boiling into lower boiling hydrocarbons and adapted also to promote an exchange reaction between benzene and higher boiling aromatic hydrocarbons resulting in the selective formation of toluene.

The conversion in step I9 is carried on in the presence of catalysts capable of promoting a selective conversion to toluene. Certain synthetic silica-alumina catalysts are particularly adapted for catalyzing this selective conversion. These catalysts may be prepared by mixing gels of silica and alumina and of silica and alumina with zirconia or thoria. Another suitable catalyst is boria on alumina (B203 on A1203) which catalyst may be prepared by precipitating an aluminous oxide gel, mixing the gel with boric acid and heating. This catalyst is particularly adapted to catalyze the exchange reaction in the .presence of hydrogen. The reaction takes place at temperatures of the order of 900 to 1000 velocities of, for example, 0.5-5.0 v./v./hr. The reaction may be advantageously conducted under a rather wide range of pressure such as low pressures of the order of 50 to 200 p. s. i. up to higher F. with space pressures such as 400 to 1000 p. s. i., the higher pressures being especially desired for operations conducted with a considerable partial pressure of hydrogen. overall disappearance of higher boiling aromatics accompanied by a net production of toluene and consumption of benzene.

The products of conversion are passed to a fractionating step 2| wherein the products are fractionated to recover the toluene and other desired fractions. The fractionation may be so conducted as to obtain a light, normally gaseous fraction withdrawn through line 22, a heavier gaseous fraction withdrawn through line 23, a light gasoline fraction withdrawn through line 24, a toluene fraction withdrawn throu h line 25, a higher boiling gasoline fraction withdrawn through line 26, and a higher boiling fraction withdrawn through line 21. The light, gaseous fraction may consist essentially of hydrogen or of hydrogen and methane and this fraction may be recycled to the conversion step l9, together with extraneous hydrogen if desired, for the purpose of suppressing carbon formation in the conversion zone. The higher boiling gaseous fraction which may consist essentially of C3 and C4 hydrocarbons may be withdrawn from the system or may be added to the gases which are recycled to the cracking step II. The toluene fraction may be subjected to treatment with sulfuric acid to effect removal of any olefins present and may be given such further fractionation or solvent treatment as may be necessary in order to produce a toluene product of sufficient purity for nitration purposes. The high boiling motor fuel fraction, withdrawn through line 26, is rich in xylenes and this fraction is directed to the motor fuel tank 18 for blending to produce the desired motor fuel product and the low boiling fraction, withdrawn through line 24, is also directed to the blending tank l8.

In the reactions occurring in the conversion step I! there is a pronounced tendency toward the disappearance of aromatics in the fractions boiling above the xylenes with the result that the higher boiling fraction as withdrawn through line 21 is well adapted for recycling to the cracking step II for either thermal or catalytic cracking. Accordingly, the high boiling fraction or gas oil stock withdrawn through line 21 may be directed through line 28 to the conversion step II. In an alternative operation this heavy fraction may be directed to a conversion step 29. In the latter conversion step the high boiling fraction is subjected to further cracking, either thermal or catalytic, to effect an additional conversion into lower boiling products.

In a modification of the process, the fractionation may be so modified as to separate from the rest of the hydrocarbons boiling in the gasoline boiling range, in addition to the toluene fraction, a benzene fraction, and fractions comprising xylenes and ethyl benzene and these benzene, xylene and ethyl benzene fractions may be recycled to the catalytic conversion step l9. When it is desired to produce aviation gasoline, it is generally preferable to exclude the benzene fraction from the blending stocks going intothe aviation motor fuel and to recycle this benzene fraction to the conversion step IS, in which case the other fractions rich in aromatic hydrocarbons may be included in theblending stock for the aviation motor fuel. And'when the toluene not desired for nitration or other purposes the Under these conditions there is an toluene fraction may also be included in the motor fuel blend.

In an example of the invention a Mid-Continent gas oil having a boiling range of about 600-800 F. is subjected to deep cracking at a temperature of 1050 F. under 100 p. s. i. with a conversion into gas approximating 30%. The products are fractionated to separate a light gasoline cut from an intermediate out having a boiling range of from 300 to 600 F. and constituting about 20% of the gas oil charge. This intermediate cut is mixed with benzene at a ratio of 1:1 and subjected to catalytic conversion in contact with a synthetic silica-alumina catalyst at a temperature of 900 F. under 200 p. s. i. and with a space velocity of 1 v./v./hr. to effect selective conversion to toluene.

In a second example, a highly naphthenic gas oil from Mirando crude, having a boiling range of 550-700 F., is subjected to catalytic cracking, in contact with a synthetic silica-alumina catalyst, with an'extent of conversion sufficient to effect a gas yield of about 20%, a yield of 300 F. end point gasoline approximating 40% and a yield of an intermediate fraction boiling from 300 to 550 F. of about 25%. Two volumes of this intermediate fraction are mixed with one volume of benzene and the mixture is subjected to catalytic cracking at a temperature of 950 F. in contact with alumina on boria under 500 p. s. i. and with a hydrogen recycle approximating 3000 cu. ft. of hydrogen per barrel of .charge to the conversion zone to effect selective conversion to toluene.

In a third example, Miranda gas oil is subjected to catalytic cracking in contact with alumina on boria at a temperature of 1000 R, in the presence of hydrogen, under 400 p. s. i. and the intermediate cut boiling from 300 to 550 F. is subjected to selective conversion to toluene under conditions similar to those of the second example.

While I have described a particular embodiment of my invention for purposes of illustration, it should be understood that various modifications and adaptations th fwf 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 and aromatic motor fuels the process that comprises subjecting a higher boiling petroleum stock to cracking temperature under conditions to effect conversion into lower boiling hydrocarbons and extensive conversion into aromatic hydrocarbons, fractionating the resultant cracked products to obtain an intermediate fraction rich in aromatic hydrocarbons and comprising gas oil constituents and the higher boiling components of gasoline, adding benzene to said intermediate fraction and subjecting the mixture to catalytic conversion in contact with a synthetic silica-alumina catalyst to effect selective conversion to toluene accompanied with a net reduction in aromatics boiling above the xylenes, fractionating the resultant products of conversion to separate lighter fractions comprising toluene from higher boiling fractions comprising gas oil constituents of reduced aromaticity and subjecting said higher boiling fractions to further cracking to effect formation of lower boiling products.

2. In the manufacture of toluene and aromatic motor fuels the process that comprises subjecting a higher boiling hydrocarbon oil to cracking temperature in a cracking zone under conditions to effect conversion into lower boiling hydrocarbons and extensive conversion into aromatic hydrocarbons, fractionating the resultant cracked products to obtain an intermediate fraction rich in aromatic hydrocarbons and comprising gas oil constituents and the higher boiling components of gasoline, adding benzene to said intermediate fraction and subjecting the mixture to catalytic conversion in contact with a synthetic silicaalumina catalyst to effect selective conversion to toluene accompanied with a net reduction in aromatics boiling above the xylenes, fractionating the resultant products ofconversion to separate lighter fractions com-prising toluene from higher boiling fractions comprising gas oil constituents of reduced aromaticity and directing said higher boiling fractions to the aforesaid cracking zone.

3. In the manufacture of toluene and aromatic motor fuels the process that comprises subjecting a gas oil stock to cracking temperature in a crack-' ing zone under conditions to effect conversion into lower boiling hydrocarbons and extensive conversion into aromatic hydrocarbons, fractionating the resultant cracked products to separate an intermediate fraction from lower boiling and higher boiling fractions, adding benzene to said intermediate fraction and subjecting the mixture to catalytic conversion in contact with a synthetic silica-alumina catalyst to effect selective conversion to toluene and a net reduction in aromatics higher boiling than the xylenes, fractionating the resultant products of conversion to obtain fractions comprising normally gaseous hydrocarbons, toluene and motor fuel fractions and higher boiling fractions of reduced aromaticity, and directing said normally gaseous and higher boiling fractions to the aforesaid cracking zone.

4. In the manufacture of toluene and aromatic motor fuels theprocess that comprises subjecting a higher boiling hydrocarbon oil to cracking temperature in a cracking zone under conditions to effect conversion into lower boiling hydrocarbons and extensive conversion into aromatic hydrocarbons, fractionating the resultant cracked products to separate an intermediate fraction from lower boiling and higher boiling fractions, adding benzene to said intermediate fraction and subjecting the mixture to catalytic conversion in a conversion zone in contact with a boria-alumina catalyst in the presence of hydrogen to effect selective conversion to toluene and a net reduction in aromatic hydrocarbons higher boiling than the xylenes, fractionating the resultant products of conversion to obtain fractions comprising lighter normally gaseous constituents including hydrogen, a heavier normally gaseous fraction including C3 and C0 hydrocarbons, motor fuel and toluene fractions and a fraction higher boiling than the xylenes, recycling said lighter normally gaseous fraction to said conversion zone, directing the heavier normally gaseous fraction and said fraction higher boiling than the xylenes to the aforesaid cracking zone.

5. The process according to claim 2 in which the said higher boiling hydrocarbon oil and said higher boiling fractions comprising gas all constituents of reduced aromaticity are subjected to thermal cracking in said cracking zone.

6. The process according to claim 2 in which the said higher boiling hydrocarbon oil and said higher boiling fractions comprising gas oil constituents of reduced aromaticity are subjected to catalytic cracking in said cracking zone.

7. In the manufacture of toluene and aromatic motor fuels from petroleum stocks the process that comprises subjecting a higher boiling petroleum stock to cracking temperature to effect conversion into lower boiling hydrocarbons and extensive conversion into aromatic hydrocarbons, fractionating the resultant cracked products to obtain an intermediate fraction rich in aromatic hydrocarbons and having an initial boiling point of about 250-300" F. and an end point of about 500-600" F., adding benzene to said intermediate fraction and subjecting the mixture to conversion in contact with a snythetic silica-alumina catalyst under conditions to effect a concomitant conversion into lower boiling hydrocarbons and an exchange reaction between benzene and higher boiling homologs thereoffto produce a net consumption of benzene and selective formation of toluene with a net reduction in aromatic hydrocarbons higher boiling than the xylenes, fractionating the resultant products of conversion to obtain lower boiling fractions comprising aro-' matic hydrocarbons including toluene and a fraction higher boiling than the xylenes which contains constituents within the boiling range of gas oil and is of lower aromaticity than that of the corresponding fraction charged to said conversion step, and subjecting said fraction higher boiling than the xylenes to cracking to produce lower boiling hydrocarbons.

8. In the manufacture of toluene and aromatic motor fuels from petroleum stocks the process that comprises subjecting a higher boiling petroleum stock to cracking temperature in a cracking zone to effect conversion into lower boiling hydrocarbons and extensive conversion into aromatic hydrocarbons, fractionating the resultant cracked products to obtain an intermediate fraction rich in aromatic hydrocarbons and having an initial boiling point of about 250-300" F, and an end point of about 500-600 F., adding benzene to said intermediate fraction and subjecting the mixture to conversion in contact with a synthetic silica-alumina catalyst under conditions to effect a concomitant conversion into lower boiling hydrocarbons and an exchange reaction between benzene and higher boiling homologs thereof to produce a net consumption of benzene and selective formation of toluene with a net reduction in aromatic hydrocarbons higher boiling than the xylenes, fractionating the resultant products of higher boiling than the xylenes to the aforesaid cracking zone for conversion into lower boiling hydrocarbons.

9. In the manufacture of toluene and aromatic motor fuels from petroleum stocks the process that comprises subjecting a higher boiling petroleum stock to cracking temperature in a cracking zone to efl'ect conversion into lower boiling hydrocarbons and extensive conversion into aromatic hydrocarbons, fractionating the resultant cracked products to obtain an intermediate fraction rich in aromatic hydrocarbons and having an initial boiling point of about 250-300 F. and an end point of about DO-800 R, adding benzene to said intermediate fraction and subjecting the mixture to conversion in contact with a synthetic silicaalumina catalyst under conditions to eifect a concomitant conversion into lower boiling hydrocarbons and an exchange reaction between benzene and higher boiling homologs thereof to produce a net consumption of benzene and selective formation of toluene with a net reduction in arcmatic hydrocarbons higher boiling than the xylenes, fractionating the resultant products of conversion to obtain lower boiling fractions comprising aromatic hydrocarbons including, toluene and a fraction higher boiling than the xylenes which contains constituents within the boiling range of gas oil and is of lower aromaticity than that of the corresponding fraction charged to said conversion step, and directing said fraction higher boiling than the xylenes to the aforesaid cracking zone for conversion into lower boiling hydrocarbons.

10. In the manufacture of toluene and aromatic motor fuels the process that comprises subjecting higher boiling hydrocarbon oil to cracking temperature under conditions to effect conversion into lower boiling hydrocarbons and ex- 40 tensive conversion into aromatic hydrocarbons,

conversion to obtain lower boiling fractions comprising aromatic hydrocarbons including toluene and a fraction higher boiling than the xylenes which contains constituents within the boiling range of gas oil and is of lower aromaticity than that of the corresponding fraction charged to said conversion step, and directing said fraction fractionating the resultant cracked products to separate an intermediate fraction from lower boiling and higher boiling fractions, adding benzene to said intermediate fraction and subjecting the mixture, to catalytic conversion in a conversion zone in contact with a boria-alumina catalyst in the presence of hydrogen to effect selective conversion to toluene and a net reduction in aromatic hydrocarbons higher boiling than the xylenes, fractionating the resulting products of conversion to obtain fractions comprising normally gaseous constituents including hydrogen, toluene, and a higher boiling fraction comprising constituents higher boiling than xylenes, recycling said normally gaseous fraction to said conversion zone and subjecting said higher boiling fraction to cracking to effect formation of lower boiling hydrocarbons.

HAROLD V. A'I'WELL.