US2427800A - Catalytic reforming of mixed gasolines - Google Patents

Description

Sept. 23, 1947. W. J. MATTox CATALYTIQ REFORMING OF MIXED'GASOLINES Filed March s1, 1945 Patented Sept. 23, 1947 CATALY'I'IC REFORMING MIXED GASOLINES William J. Mattox, La Grange, Ill., assigner to Universal Oil Products Company, Chicago, Ill., a corporation of Delaware Application March 31, 1945, Serial No. 585,999

This invention relates to the catalytic reforming of gasoline fractions and is more particularly concerned with the reforming of a mixture of specific fractions of straight run gasoline and thermally cracked gasoline under selective conditions of operation.

In the past, considerable work has been done on the reforming of gasoline fractions primarily y to improve their antiknock properties by the dehydrogenation of naphthene hydrocarbons contained therein to aromatics and the dehydrocyclization of paraiinic hydrocarbons to aromatic hydrocarbons. Generally, in ythis known operation, the naphtha fractions are subjected to contact with a reforming catalyst at temperatures within the range of from 400 C. to 600 C. and under pressures ranging from atmospheric to approXimatelyZO atmospheres. Naphtha fractions have also been reformed in an operation commonly called hydroforming inlwhich the naphtha is converted in the presence of hydrogen under conditions of temperature and pressure similar to those given above.

One of the chief difficulties of the previously described processes which has hampered the commercialization of these processes is that after relatively short periods of operation the catalyst tends to lose activity as a result ofdeposition of carbonaceous materials thereon- When this occurs it becomes necessary to reactivate the catalyst by removing the carbonaceous materials from the catalyst either by combustion or some other means, Since the catalysts usually employed for the reforming operation are somewhat thermophobic it is necessary to regulate the temperature rise obtained in the catalyst Zone by employing a regenerating gas composed of inert gas such as nitrogen and small amounts of oxygen. This regeneration operation entails the use of large and expensive equipment such as compressors, combustion gas generators, and so forth, which increases to a considerable extent the capital cost of the operation and decreases the commercial attractiveness of the process.

Further, the necessity of frequent regeneration prevents the operation from being truly continuous and forces the adoption of complicated schemes employing a plurality of reaction zones with staggered reaction cycles to provide a pseudo continuous operation. Here, again, the adoption of these complicated schemes increases the capital cost of the equipment.

It is a particular object of the present invention to provide a catalytic reforming process in Which the cafabfst may be employed for periods 1 Claim. (Cl. 196--50) in excess of about 10-15 days without the necessity of regeneration. This long on-stream time makes it possible to dispense with the need of auxiliary equipment for the regeneration of the catalyst as an integral part of the process.

In a broad aspect the present invention provides a process for catalytically reforming gasoline fractions which comprises subjecting a mixture of a straight run gasoline fraction and a thermally cracked gasoline fraction, the former fraction comprising at least by volume of said mixture and the latter fraction consisting primarily of hydrocarbons boiling above C., to the action of a reforming catalyst in the presence of hydrogen in the mol ratio of from about 0.5 mol to about 15 mols of hydrogen per mol of hydrocarbon at a temperature Within the range of from about 400 C. to about 600 C. and under a pressure in excess of about 30 atmospheres and correlating the conditions of operation and the proportions of the straight run gasoline fraction and cracked gasoline fraction to effect the reforming operation with no net consumption of hydrogen. One of the essential features of the present invention is the fact that the operation is carried out with no net consumption of hydrogen, The primary factors in maintaining this hydrogen balance within the process are the particular composition of the hydrocarbon feed and the operating conditions employed. In a thermally cracked gasoline, a greater proportion of the olenic hydrocarbons are found in the lower boiling fraction, that is, a fraction boiling below approximately 120 C. If these olefinic hydrocarbons are present in the portion of the feed being processed the amount of hydrogen required in the operation will be lmaterially increased, thereby disrupting the balance between the hydrogen required for saturation reactions and that produced in situ by dehydrogenation reactions and effect a net hydrogen consumption in the process. Therefore, to maintain a continuous operation it would be necessary to continuously supply hydrogen from some extraneous source which would result in a substantial increase in the cost of the operation and destroy its commercial utility. If, however, selected fractions of the cracked gasoline are employed, that is, those containing hydrocarbons boiling above 120 C. the percentage of olens present is much lower. These fractions contain substantial quantities of naphthenic hydrocarbons which upon dehydrogenation form aromatic hydrocarbons and thereby provide a source of hydrogen. This hydrogen production is sufficient to furnish at least a portion of the hydrogen consumed in the hydrogenation of hydrocarbon fragments produced by decomposition reactions. By a careful selection of the fractions of straight run and cracked gasolines employed and the proportions thereof, all the hydrogen needed for these hydrogenation reactions can be produced in situ thus preventing carbon deposition, and dispensing with the necessity of maintaining an extraneous supply of hydrogen. Therefore, ideal charging stocks for the process comprise straight run and cracked gasoline fractions having a high concentration of naphthenes which upon dehydrogenation to the corresponding aromatics produce substantial quantities of hydrogen.

However, in considering the boiling range of the straight run gasoline fraction to be employed, it is usually advantageous to include the lower boiling fractions thereof since the hydrocarbons contained therein provide a potential source of hydrogen.

As will be noted by studying the examples presented hereinafter in this specification, the operating conditions of temperature, pressure, and so forth, and the boiling ranges and proportions of the straight run gasoline and cracked gasoline fractions are selected so that nal gasoline blend including the reformed product and the material originally removed from the gasoline prior to processing has a bromine number substantially the same as that of a blend of the original straight run and cracked gasolines, that is within about 5 to 8 numbers thereof.

The catalyst which may be employed in the process of the present invention comprises compounds of the elements in the left-hand columns of groups V and VI of the periodic table and in particular the oxides or suldes of such elements as vanadium, chromium, molybdenum and tungsten, either alone or in admixture with one another. A particularly good combination comprises a mixture of the oxides of chromium and molybdenum. While these compounds may be employed alone it is preferable that they be used in conjunction with refractory supporting materials such as alumina, particularly activated alumina of commerce, silica, silica-alumina cornposites, magnesium oxide, zinc oxide, zirconium oxide, titanium oxide, thorium oxide, acid-treated clays such as acid-treated montmorillonite or bentonite, and similar supporting materials.

The above catalyst may be prepared by various methods. For example, the solid particles of the refractory material such as activated alumina may be impregnated with solutions of soluble compounds of one or more of the various elements named above, the impregnated material being subsequently dried and calcined. The catalysts may also be prepared by precipitation of a supporting material such as alumina in the presence of a dissolved compound of, for example, chromium or molybdenum followed by evaporation of the solution and by drying and further heating of the residue to develop the catalytic properties of the composite. Suitable catalyst may also be prepared by co-precipitation of the supporting materials and the activating compound or compounds and the subsequent drying and calcining of the precipitate. Another and particularly applicable method of catalyst preparation comprises the impregnation of freshly precipitated gels of the supporting materials such as alumina or silica with at least one of the compounds furnishing the highly catalytic component of the final catalyst followed by 'drying 4 and calcining of the impregnated gel. If a metal oxide is the desired catalytic component, it may be obtained by impregnation of the dry suppo1't' ing material, or the gel respectively, with a decomposable compound of the particular metal employed which produces an oxide upon calcination. The concentration of the catalytic compound in the nal composite catalyst will vary depending upon the specific supporting materials and active compounds employed.

The various features of the present invention will be more clearly pointed out in the description of the attached drawing which illustrates in conventional side elevation one type of apparatus in which the process of the present invention may be performed. However, since this drawing is merely for illustrative purposes the following description with reference to this drawing is not intended to unduly limit the scope of the invention.

A thermally cracked gasoline is introduced through line I containing valve 2 into pump 3 which discharges through line 4 containing valve 5 into fractionator 6 wherein the lighter materials are separated from the higher boiling materials leaving a bottoms fraction having an initial boiling point of about 120 C. A straight run gasoline is introduced through line 9 containing valve I0 and is mixed in line 9 with the bottoms fraction withdrawn from fractionator 6 through line 'I containing valve 8, The mixture is directed into pump I I which discharges through line I2 containing valve I3 through heat exchanger I4 into heating coil I5. The particular proportions of straight run gasoline and the higher boiling portion of the cracked gasoline may vary some what depending upon types of gasoline and the conditions of temperature and pressure employed in reactor I8, but under no circumstances will the amount of cracked gasoline be greater than about 50% by volume of the mixture. The proportions will be regulated so that no hydrogen consumption results in the operation. The mixed charge is passed through heating coil I5, disposed within heater 'II, wherein it is heated to a temperature within the range of from about 400 C. to about 600 C., and is introduced through line I5 containing valve I'I into reactor I8 wherein it is commingled with hydrogen or a hydrogen containing gas obtained as hereinafter set forth.

Reactor I8 comprises a large cylindrical vessel containing therein solid particles of catalyst in fixed bed relationship to the incoming reactants. The catalyst may be employed in large granules of varying size or may be of uniform size and shape such as pellets and extruded pieces. 'I'he reaction zone I8 is maintained at a temperature within the range of from 400 to about 600 C. and under a pressure in excess of about 30 atmospheres. The hydrogen concentration within the reaction zone is regulated so that the mol ratio of hydrogen to hydrocarbon is within the range of about 0.521 to 15:1. The hydrocarbon charge rate to the reactor is such that a liquid hourly space velocity within the range of about 0.1 to about 10 volumes of hydrocarbon charge per volume of catalyst and a mass velocity of the hydrocarbons in excess of 5 milligrams per square centimeter per second are maintained.

Although the present description is limited to an operation in which the catalyst is employed in a fixed bed relationship to the incoming reactants the operation may be conducted in various other ways. For example, the reactants may be introduced into the lower section of a reaction zone containing finely divided catalyst and the reactants passed upwardly at a rate suiicient to maintain the catalyst mass in a fluidized condition, In this Inode of operation the reaction products may be removed from the upper portion of the reaction zone and passed through cyclone separators wherein any entrained catalyst is removed and thereafter into a fractionator wherein the desired products are separated. The entrained catalyst removed in the cyclone separator may be returned to the reaction zone.

Another method of operation consists of passing the hydrocarbon reactants and hydrogen either countercurrently or concurrently through a dense moving mass of catalyst, the catalyst being continuously recycled to the reaction zone and the reaction products continuously removed from the reacting system.

Still another method of operation comprises adding nely divided catalyst to the hydrocarbon charge mixing hydrogen or hydrogen containing gases with the charge, passing the entire mixture, wherein the catalyst is being maintained in suspension, through a heating zone maintained under the desired conditions of temperature and pressure, separating the catalyst from the hydrocarbon in a separating and fractionating zone and recycling the catalyst to the reaction zone.

The products from reactor I8 are withdrawn through line I9 containing valve 2U and are passed through heat exchanger i4 and line 2I containing valve 22 into cooler 23 wherein the temperature of the reaction products is substantially reduced. The cooled reaction products leave cooler 23 through line 24, valve 25 and are introduced into receiver 26 wherein the light gases rich in hydrogen are separated from the reaction products. Receiver 26 is maintained at slightly less pressure than reactor I8. The gases separated from receiver 26 are withdrawn through line 21, valve 28 into the suction of compressor 29 which discharges through line 30, valve 3I into heating coil 32 disposed within heater 1I. The hydrogen-containing gas may be heated to about the same temperature to which the hydrocarbon charge is heated, or it may be heated to a temperature somewhat higher than that of the hydrocarbon charge, and is introduced to reactor I8 through line 33 containing valve 34. The liquid products from receiver 26 are directed through line 35 containing a pressure reducing valve 35 into receiver 31 which is maintained at a pressure substantially lower than that of receiver 26. In receiver 31 additional separation of the light gases from the liquid hydrocarbons is effected, the light gases being removed through line 38 containing valve 39 and directed intoabsorber 12 wherein small amounts of gasoline entrained in the gases are recovered.

A portion of the liquid hydrocarbons withdrawn from receiver 31 through line 4D is directed through line 50 and valve 5I to the suction side of pump 52 whichdischarges through line 53 containing valve 54 into line 2I thereby effecting the recirculation of liquid hydrocarbons to receiver 25. The recirculation of a portion of the liquid hydrocarbons to this receiver provides an additional solvent for the light hydrocarbon gases in the reaction products from reactor I8, thereby effecting a more complete concentration of the hydrogen in the gases leaving receiver 26 through line 21 and preventing the light hydrocarbon gases from accumulating in the recycle gas stream. The remaining portion of the liquid products withdrawn through line 40 is directed through valve 4I into heat exchanger 13 wherein the temperature is raised slightly and the heated material passed through line 14 containing valve 15 into receiver 42. light gases is removed from the liquid products in receiver I42 and withdrawn through line 64 containing valve 65 into line 38 wherein the gases are admixed with the gases from receiver 31 and the mixture is introduced into absorber 12 to recover any entrained gasoline contained therein.

The liquid product from receiver 42 is withdrawn through line 43 containing valve 44 and commingled with the light hydrocarbons separated from the `thermally cracked gasoline in fractionator 6, the latter hydrocarbons passing through line 56 containing valve 61 into pump 68 which discharges through line E9 containing valve 1U into line 43. The mixture is directed through line 43 into stabilizer 45 wherein stabilization is effected to produce the desired vapor pressure in the final product. Butane from an external source may be added to the hydrocarbons in stabilizer 45 if necessary to produce the desired vapor pressure. The nal gasoline productr is withdrawn from stabilizer 45 through line 46 containing valve 41. The light gases are withdrawn through line 48 containing valve 49 and may be cooled and collected as the product of the reaction or may be used or withdrawn as fuel.

The lean oil employed in absorber 1.2 is introduced through line 59 containing valve B into pump 5I which discharges through line 62 containing valve 53 into the upper portion of the absorber. The rich oil containing gasoline absorbed therein, is withdrawn through line 51, valve 58 to any suitable recovery system. The unabsorbed gases are removed through line 55 containing valve 56 and may be cooled and collected as a product of the reaction or passed directly to the fuel system. The initial charge of hydrogen is introduced in the system through line 13' containing valve 14. Hydrogen is introduced from an external source only during the initial starting of the operation since the process when conducted in accordance with the present invention produces sufcient hydrogen to maintain a balance during the remaining period of the operation.

If desired, the use of extraneous hydrogen may be avoided entirely. The plant may be pressured with a suitable gaseous hydrocarbon fraction such as a methane-containing fraction from natural gas or a hydrocarbon gas fraction derived from a thermal or catalytic cracking operation. A substantiallyv saturated hydrocarbon fraction containing substantial quantities of cyclohexane or alkyl cyclohexanes, preferably a fraction of this character derived from a straight run gasoline, is mixed with theV gas and passed through the reaction zone under mild conditions to eiect dehydrogenation of the naphthenes to corresponding aromatics without substantial decomposition or carbon deposition. This treatment of the naphthenic fraction is continued for a suflicient time to obtain a quantity of hydrogen adequate to supply the initial charge of hydrogen for the reforming treatment. The hydrogen thus produced is separated and recycled to the reaction Zone which, upon production of the hydrogen in adequate quantity, can then be employed to effect the catalytic reforming of the mixture of straight run and thermally cracked gasoline fractions.

An additional quantity of EXAMPLE I A 37.4 ASTM octane number straight run naphtha was reformed in admixture with Various portions of a 65.3 ASTM octane number cracked distillate over an alumina-chromium oxide catalyst. The operating conditions in these tests were maintained as follows:

Temperature C 500 Pressure atmospheres-- 68 Liquid hourly space velocity 4 Hydrogen to hydrocarbon mol ratio 4:1

Forv comparative purposes an initial run was made on a mixture containing the total cracked distillate with an equal volume of straight run and in test 6 a straight run gasoline only was reformed and blended with the untreated cracked distillate. The data obtained in this series of tests are summarized in Table I.

INSPECTION OF THE BLENDED GASOLINES Base Product charge,

Octane number, A. S. T. M. motor method. 73. 4 58. 4 +1 ce. TEL 80. 7 68. 5 +3 ce. TEL 84. 7 75. 6 Research octane number- 80. 4 63. 2 l ce. TE S7. 6 73. 0 +3 ce. TEL 91. 6 so. 1 Bromine number 33 Initial boiling point. 1

1 hase charge-50: 50 blend of original full boiling range cracked and straight run gasolinas.

Table I Test No 1 2 3 4 5 6 Cracked Naphtha:

Vol. per cent removed 12.4 23. 3 .4 49. 9 100 I. B. P. of the remaining fraction, C Total 46 75 100 125 0 Vol. per cent reformed 100 81.6 76. 7 65. 6 50.1 0 Cracked Gasoline, vol. per cent in chg 43. 8 34. 4 32.8 25. 1 0 St. Run, Vol. per cent in chg 50 50 50 50 50 100 Bromine No. of blend 31 Recovery:

Liquid, vol. per cent 89. 8 91.0 92. 7 91. o 94. 2 91. o Liquid, Wt. per cent 87. 8 89Y 0 90. 8 90.2 92. s so. 3 Gas, Uneond. wt. per cent. 11.0 9, 2 9. 8 7, 7 10. 2 Hydrogen Balance 1 0. 065 -0. 094 -0. 028 +0. 037 +0.190 Overall Liq. Yield, Product and original fraction removed,

Vol. per cent 89- S 91.6 03. 5 91.9 95.6 95. 5 Analysis:

Motor Method clear 70. 5 68.0 69. 6 65. 8 66. 3 63. 8 Motor Method-H ce. TEL 2 79. 3 77. 9 77.8 76.8 76. 9 72. 8 Motor Method-F3 cc. TEL A 85.1 S3. 1 83.7 82. 5 8l. 7 79. 7 Research Method clear 75. 6 73.7 75.1 73.0 73.3 70, 7 Research Method-H cc. TEL 81. 1 81.0 82. 5 80.5 80.8 78. 7 Research Method+3 cc. TEL 89.1 87.1 88. 7 87. 9 87.1 84. 9 Reid Vapor Pressure 9. 9 6. 9 e. 9 5. 6 7. 2 5. 1 Bromine Number 4 1l 17 22 27 37 Engler Distillation:

I. B. P 99 101 103 103 10S 115 129 135 134 138 145 152 173 234 282 318 l 358 B77 407 1.2 0.3 54.1 0. 7624 l Moles Hz per mole naphtha feed. -l- Denotes hydrogen production; denotes hydrogen consumption.

2 Tetra Ethyl Lead.

EXAMPLE II A mixture of a straight run gasoline and the 300 to 400 F. fraction of a thermally cracked gasoline Was reformed under the following conditions:

Catalyst Alumina-chromium oxide Temperature 520 C. Pressure 1000 lbs/sq. in. gauge Hydrogen recycle-- 4 moles/mole of hydrocarbon Mixture composition:

Straight run. vol. percent 73.6 (i300-400 F.) thermally cracked gasoline, vol. percent 26.4

The yields and comparison of the product with the base charge are shown in Table II.

Table II Yield of liquid product,V (Reformed product -|.-initial300 F. fraction of thermally cracked gasoline) 90.4 Hz produced, cu. ftJbbl. of straight run 47.5

It will be noted that though an appreciable improvement in the antiknock properties is obtained in the operation, the bromine number of the final blend is the same as that of the 50/50 blend of the original straight run and cracked gasoline.

In the runs shown in Tables I and II, the operations Were continued for a period of 15 days with no substantial carbon deposition on the catalyst. The properties of the product remained substantially constant throughout the operation.

I claim as my invention:

A catalytic reforming process which comprises subjecting a mixture of a straight-run gasoline fraction and a thermally cracked gasoline fraction, the former fraction comprising at least 50 percent of the total mixture and the latter fraction consisting primarily of hydrocarbons boiling above C., to the action of a reforming catalyst disposed Within a reaction zone in the presence of hydrogen in a mol ratio of about 0.5 mols 9 to about 15 mois of hydrogen per m01 of hydrocarbon at a temperature within the range of about 400 C. to about 600 C. under a pressure in excess of about 30 atmospheres, introducing the cooled reaction products into a first separating zone and therein separating a gaseous mixture rich in hydrogen from liquid hydrocarbons, recycling said gaseous mixture to the reaction zone, introducing the liquid hydrocarbons from said rst separating zone into a second separating zone maintained at a substantially lower pressure than said first separating zone and therein effecting further separation of gases containing hydrogen from liquid hydrocarbons, withdrawing a portion of the liquid hydrocarbons from said second separating zone and recycling said portion to the rst separating zone, withdrawing the remaining portion of liquid hydrocarbons from said second separating zone, heating said remaining portion and introducing the 20 Number heated hydrocarbons into a. third separating zone wherein light gases are separated from the liq- 10 uid hydrocarbons, introducing the light gases from said second and third separating Zones into an absorber wherein small amounts of gasoline hydrocarbons entrained in said light gases are recovered and stabilizing the liquid hydrocarbons Withdrawn from said third separating zone.

WILLIAM J. MA'I'I'OX.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,335,717 Welty, Jr., et al. Nov. 30, 1943 2,400,363 Meier May 14, 1946 FOREIGN PATENTS Country Date 420,235 Great Britain Nov. 28, 1934 423,001 Great Britain Jan, 23, 1935

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