US3116232A - Process for upgrading cracked gasoline fractions - Google Patents

Description

Dec. 1963 M. NAGER EI'AL PROCESS FOR UPGRADING CRACKED GASOLINE FRACTIONS Filed D60. 1. 1961 FRAOTIOIATOR coom COHPRESSOR IIYDROISOIERIZATIOI ZINE FIG. I

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IIIDROISOIEIIZED IIYDROGEIATED DEBUTAIIZED REFORIATE a 2 l .0 lo a: a: S. 2:

THEIR ATTORNEY 00TAIE IIIIIEI, F-l-0 United States Patent O 3,116,232 PROCESS FOR UPGRADING CRACKED GASOLINE FRACTIONS Maxwell Nager, Pasadena, John Ward Jenkins, La Porte,

This invention relates to a process for upgrading cracked gasoline fractions and particularly to the up grading of cracked naphtha by a special hydrogenating treatment followed by catalytic reforming.

Catalytic reforming is a well known and widely used process for upgrading hydrocarbon fractions boiling in the motor gasoline or naphtha boiling range to increase their octane number. In catalytic reforming, a naphtha fraction is contacted at elevated temperatures and pressures together with hydrogen or hydrogen enriched process gas in the presence of solid catalytic materials under conditions such that there is no net consumption of hydrogen and ordinarily there is a net production of hydrogen in the process. The main reactions leading to improvement in octane number are the dehydrogenation and dehydroisomerization of naphthcnes, dehydrocyclization of parallins to aromatic hydrocarbons and the hydrocraeking of low octane normal parallins. Minor reactions which also occur are the isomerization of normal parafiins, and some condcnsations.

Catalytic reforming operations are ordinarily carried out at temperatures of 850--l000' F. and a pressure in the range of about 50 to 1000 pounds per square inch.-

Catalysts for the reforming process comprise a hydrogenationdchydrogcnation component on a suitable carrier such as alumina. Particularly suitable reforming catalysts comprise a small amount, e.g., 0.l-2% of a noble metal, e.g., Pt, Pd, and Rh, supported on a carrier such as alumina, alumina-silica composites, and the like, and frequently promoted with small amounts, e.g., 0.l-3% of chlorine and/or fluorine. Platinum on halogenated alumina is a highly effective and widely used catalyst. However, the older so-callcd hydroforming catalysts such as compounds of such elements as molybdenum, chromium, cobalt and the like supported on a base, e.g., by weight molybdenum on alumina, are also suitable rcforming catalysts. Catalytic reforming processes are described in the Oil and GasJournal," 59, No. 14, April 3, 1961, pages 142-150.

Catalytic reforming is usually applied to naphtha fractions, i.c., those having a boiling range of about l85 to 420' F., since these fractions are more susceptible to octane improvement because of their rich naphthene content. Straight-run naphthas are a highly desired feed for' upgrading by catalytic reforming because of their high naphthene content, usually about 40% or more, and because of their low octane number. Cracked naphthas such as are obtained from the thermal or catalytic cracking of hydrocarbon oils boiling above the gasoline boiling' rangc, are also suitable for upgrading by the catalytic reforming process. In general, the catalytic cracked n'aphthe. is less suited to' catalytic reforming than straight-run or thermal cracked'naphtha because of its "already relatively high'oet'ane number and aromatic content.

The'naphtha feed to a catalytic reforming'process is usually subjected to a pretreatment such as hydrodesulfurization to remove sulfur and nitrogen compounds. In the case of cracked naphtha, olefins in'the cracked stream are saturated by hydrogenation to the corresponding parafilns in addition to the removal of sulfur compounds. The catalyst employed in the hydrodesulfurlzation process is generally cobalt molybdenum on alumina, which may or may not be'stabilized by a minor percent of silica.

3,116,232 Patented Dec. 31, 1963 "ice These hydrogenation catalysts are widely available commercially. Under the hydrogenation conditions, the naphtha is little affected other than the removal of sulfur and nitrogen and/or saturation of olefins as the case may be.

It has now been found, however, that a cracked naphtha can be greatly improved as a catalytic reforming feed by subjecting the naphtha to a catalytic hydroisomerization process rather than to a conventional hydrodcsulfurization process. The invention therefore, is a process for upgrading cracked naphtha wherein the naphtha is passed at an elevated temperature and pressure together with a hydrogen-containing gas over a hydroisomerization catalyst and the hydroisomerized naphtha is then passed at an elevated temperature and pressure over a reforming catalyst at catalytic reforming conditions.

In the hydroisomerization process, the cracked naphtha undergoes a substantial change in composition. In addition to desulfurization and denitrilication, a synthesis of ring compounds is observed. This is unexpected for while it is known to convert normal or lightly branched olefins to the corresponding isoparailins by means of an olefin hydroisomerization catalyst, the improvement in the quantity of cyclic compounds has not been observed heretofore. Hydroisomerization of the normal or lightly branched olefins to highly branched isoparaflins is disclosed in copending application Serial No. 39,818, filed- June 30, 1960, by Joost C. Platteeuw and Johannes l-l. Choufoer.

Various olefin hydroisomerization catalysts can be used within the general and broad scope of the process of the present invention. These catalysts may be defined as comprising a hydrogenation component which is associated with a solid acid-acting support. The hydrogenation component should have a relatively weak hydrogenation activity. One of the main functions of the hydrogenation component is to promote the hydrogenation ofhighly unsaturated compounds, such as diolefins which are present in the feed or are formed as an intermediate reaction product, which would tend to deposit on the catalyst as a polymerization product. Rapid deactivation of the isomerization function of the catalyst is prevented in this manner and at the same time, through hydrogenation of diolefins to monoolefins which can then take part in the isomerization reaction, a higher yield of branched hydrocarbons is obtained. The use of a component with too strong a hydrogenation action, such as nickel, will result in hydrogenation of the monoolefins before the isomerization component has been able to perform its action.

Highly suitable catalysts comprise a solid acid isomerization catalyst containing a sulfide of one or more of the metals of the left-hand column of group V1 (chromium, molybdenum, tungsten) and/or a sulfide of one or more of the metals of group Vlll (iron, cobalt, nickel) of the periodic table. By solid acid isomerization catalysts it is meant those which when absorbing butter yellow and other weaker basic indicators, show a color change of these indicators, indicating the transition to the acid form. Suitable acid isomerization catalysts for the dual function catalyst of the invention are compounds of silica and alumina, such as silica-alumina cracking catalyst, compounds of silica and zircoium dioxide, compounds of boron trioxide and alumina, compounds of boron trioxide and silica, compounds of alumina and halogen, such as alumina and chlorine and the like. A catalyst consisting of silica-alumina compounds, in partieular those having a silica content of at least 60% by weight and an alumina content of about by weight are preferred. Nickel sulfide and/or cobalt sulfide deposited or distended on silica-alumina are particularly preferred olefin hydroisomerization catalysts.

j The amount of metal sulfide applied to the acid isomerization catalyst can vary within wide limits and is generally in the range from about 0.5-15% by weight based on the total catalyst. Thus, for example, a catalyst containing silica and alumina, and having a silica content of at least 60% by weight (based on the total catalyst) and to which is applied 1 to by weight of nickel sulfide (based on the total catalyst) is an excellent catalyst for use in the process of the invention. The metal sulfide can be applied to the acid isomerization catalyst, for instance silica-alumina cracking catalyst, by any suitable method known per se. For example, the metal sulfide can be applied by impregnating the acid catalyst with a solution of a salt of the corresponding metal, for in stance nickel nitrate followed by drying, calcining and finally sulfiding with hydrogen sulfide or a gas containing hydrogen sulfide.

The olefinic gasoline fractions to be upgraded by the process of the invention are obtained from the catalytic or thermal cracking of hydrocarbon oils boiling above the gasoline boiling range. While it is required that the cracked fraction employed as feed in the process of the invention include at least components boiling within the naphtha boiling range, i.e., boiling in the range from about 185 to 420' F., and preferably about 200 to 390 F., it is generally preferred to use full boiling range cracked gasoline as feed.

The inclusion of light cracked fractions with heavy cracked naphtha as feed has important advantages even though the light fractions are not desired as reforming feed and must be separated from the hydroisomerized naphtha. In the hydroisomerization reaction, light olefins and particularly the normal or lightly branched olefins are converted into isoparaflins. 'Ihus, the olefin content of the light fraction is reduced which is important from the standpoint of air pollution, and the sensitivity (Re search Method octane-Motor Method octane) is reduced without excessive loss of Research Method octane.

Moreover, in the hydroisomerization of cracked naphtha, light boiling hydrocarbons, usually referred to as light-ends," are formed as a result of hydrocracking reactions and/or conversion of olefins to lower boiling isoparaffins. Such light ends are generally unsuitable as a reforming feed. On the other hand, in the hydroisomerization of light cracked gasoline, some heavy ends" are formed which can be suitably reformed. Therefore, it is better to effect separation of light gasoline fractions from naphtha fractions after rather than before the hydroisomerization reaction.

Hydroisomerization of the olefins in the cracked gasoline fraction is an exothermic reaction and consequently, a large increase in temperature results from the heat of reaction which is liberated. The increase in temperature can be sufficient to promote hydrocracking, which is also an exothermic reaction, and thus lead to so-called runaway hydrocracking. Thus, excessive temperature increases in the reaction zone can result in loss in yield, increased carbonaceous deposits on the catalyst, and possible harm to the catalyst itself. Although, any suitable conventional method of preventing excessive temperature increases in the reaction zone can be employed, such as subdivision of the catalyst into a number of separate beds connected in series with cooling of the reaction mixture between the beds, or by recycling liquid product, it is generally desired to admix with the olefinic hydroisomerization feed a staright-run naphtha fraction as disclosed in copcnding application, Serial No. 136,795 by Marius 't Hart, filed September 8, 1961. The straight-run naphtha fraction, which is a desired reforming feed fraction, is substantially unaffected in the hydroisomerization process except for desulfurlzation and denitrlficatlon.

The hydroisomerization conversion is carried out in the presence of hydrogen at elevated pressure, preferably at a total pressure not exceeding 1500 p.s.l.g., for instance, in the range of from 150 to 1200 p.s.i.g., and particularly from about 300 to 900 p.s.i.g. -The hydrogen partial pressure can vary within wide limits and is preferably from 50 to of the total pressure. It is not necessary to employ pure hydrogen since hydrogen-containing gases such as hydrogen enriched gases formed in the subsequent reforming step or in the reforming of other hydrocarbon oils are also suitable.

The olefinic cracked fraction is converted at an elevated temperature in the range of from 400 to 900 F. and preferably from 500 to 750 F.

The liquid hourly space velocity of the olefinic cracked fraction to be hydroisomerized is generally in the range of from 0.5 to 20 barrels of liquid hydrocarbons per hour per barrel of catalyst, although lower or higher velocities may also be used.

In the hydroisomerization zone, a substantial portion of the non-cyclic hydrocarbons, primarily the olefin hydrocarbons, are converted into the cyclic compounds, such as naphthenes and/or aromatics. This increase in concentration of cyclic compounds markedly improves the recovered naphtha as a reforming feed stock. Thus, when the hydroisomerized naphtha is subjected to a catalytic reforming process, such as with a reforming catalyst and reforming conditions as mentioned hereinbefore, a higher yield of reformate for a given octane is obtained com pared to that obtained from a cracked naphtha which has been hydrotrcated in a conventional manner.

The process of the invention will now be illustrated with reference to the drawing wherein FIGURE 1 shows a preferred embodiment and FIGURE 2 shows an advantage obtained by the invention.

Referring to FIGURE 1, a C /3Q0 F. cracked gasoline supplied through line 1 is mixed with a straight-run 200/390' F. fraction from line 2 and heated in furnace 3. Hydrogen-containing gas which has been heated in the same or a separate furnace is supplied through line 4, and is mixed with the hydrocarbon feed in line 5. The mixture of hydrogen and hydrocarbon is passed to reaction zone 6 containing a suitable hydroisomerization catalyst such as nickel sulfide or cobalt sulfide deposited on silica-alumina cracking catalyst. Effluent from the reaction zone is cooled and partially condensed in cooler 7 and is passed to gas/liquid separator 8. Hydrogen-containing gases are withdrawn from the separator via line 9 for recycle to reaction zone 6.

Liquid hydriosomerizate is withdrawn from separator 8 through line 10 and passed to fractionation zone 11 wherein a light fraction boiling below about F. and preferably below about 200 F. is separated and removed overhead through line 12. The light fraction can be worked up as desired, such as by fractionation to recover the butanes, particularly isobutane, with the C 185 F. fraction being sent to motor gasoline blending. A 185 F.+, preferably 200 F.+ naphtha fraction is withdrawn from the fractionation z'onc through line 13 and is heated in furnace 14. The heated naphtha is mixed with hot hydrogen-containing gas from line 15 and the mixture, at the desired reforming temperature, is passed to reforming zone containing a suitable reforming catalyst, such as a commercial platinum/halogen/alumina catalyst designated as R-8 and supplied by Universal Oil Products Company.

Effluent from the reforming zone is cooled and partially condensed in cooler 17 and is passed to gas/liquid separator. 18. Hydrogemcontaining gases are withdrawn from separator 18 through line 19 and at least a part is recycled to the reforming zone. All or a part of the excess gas is supplied via line 20 as make-up to the hydroisomcrization zone or is withdrawn for other use via line 21. Liquid reformate withdrawn from separator 18 via line 22 is worked up in any suitably desired manner, usually such as stabilization to remove light boiling normally gaseous hydrocarbons and to recover a C lreformatc product. If desired, the ieformate product can be sent to motor gasoline blending as a separate component or can be blended with the light hydroisomerizate fraction.

EXAMPLE I The starting material was a wide boiling range (120/365 F.) hydrocarbon fraction comprising on a volume basis approximately 40% light catalytically cracked gasoline, 35% second-cut cracked gasoline (a mix-ture of catalytic and thermal cracked naphtha, predominantly catalytic cracked naphtha), and 25% straightrun naphtha. Properties of the starting material are given below in Table I.

For comparative results, separate portions of the starting material were subjected to a conventional hydrogenation process and a hydroisomerization process. The hydrogenation catalyst used was a commercially available catalyst comprising cobalt molybdenum on alumina (i4.7% w. Mo0 2.8% Co,O,/Ai;0;). The hydroisomerization catalyst was sulfided nickel w.) distended on silica alumina cracking catalyst (approximately 25% N 0,, 75% SiO Operating conditions and typical results for a series of runs are given in Table II.

Table II COMPARISON OF HYDROGENA'IION AND UYDROISOMERIZATION 11ydrogo- Ilydrolsomnation erization Operating Conditions:

Tern F 008 040 113K l 1. 4 Pressure, pat; 7 750 Productive Y elds, percent v.:

C; and lighter 0.3 [(1. 0. 2 l. 4 o. 2 O. 2 (Zr-182 F 24. 6 25.0 182 F.+ 77. 1 75. 4 Product Properties:

API Gravity at 60 F 8i. 7 80. 8 0. 002 0. 005 0 2 11. 2 12. 9

1 1 0 1 Paraiiins 09 98 38. 1 33. t 34. 0 88. 3 25.0 27.0 D]. tDi N sphzhontbsuufimd 2. 0 0. 4

s reon w. var

thi no 168 is"! 181 184 I6 107 105 233 232 272 274 207 802 837 840 96 851 864 E 1 409 445 It can be seen from the hydrocarbon type analysis for each product that the hydroisomerized naphtha has an appreciably higher cyclic content and reduced paraffin content compared to the hydrogenated naphtha. This result is attributed at least in part to the cyciiz ation of olefins in the cracked naphtha.

EXAMPLE II A straight-run naphtha platformer feed was hydroisomerized over nickel sulfide on silica alumina at 675 F., 750 p.s.i.g., and 1.3 LHSV. Analysis of the C product is compared to that of the straight-run naphtha feed in Table 111.

Table III ANALYSIS OF IIYDROISOMERIZATION FEED AND PRODUCT Feed Product saturates 42. 9 43. 2 i2. 0 43. 1 13.0 12. 4 1.5 1.3

EXAMPLE Ill The superiority of hydroisomerized cracked naphtha as a reforming feed is indicated by comparative experiments wherein hydrogenated naphtha and hydroisomerized naphtha are separately reformed over a dehydrogenation catalyst. Each naphtha feed was a composite sample from a series of comparative runs which were described in Example I.

The catalyst used was a commercially available reforming catalyst comprising 0.75% w. Pt, 0.35% w. Cl, 0.35% F/Al O The reforming reaction was carried out at 400 p.s.i.g., 2 LHSV, and a Pi /oil molar ratio of 10-11. Temperature was varied to provide a range of severities. The results of these experiments are shown in FIGURE 2 of the drawing which gives the yield-octane relationship for each reformed naphtha. By referring to the drawing, it is clearly seen that when reformed to the same octane rating, the yield obtained from hydroisomerized naphtha is significantly higher than the yield obtained from hydrogenated naphtha.

We claim as our invention:

1. A process for upgrading a cracked gasoline into high octane motor fuel which comprises contacting said cracked gasoline with hydrogen at hydroisomerization condition: in the presence of a hydroisomerization catalyst comprising a sulfide of a metal selected from the group consisting of chromium, molybdenum, tungsten, iron cobalt nickel, and mixtures thereof associated with an acid-acting support, separating the hydroisomerization effluent intc a naphtha fraction and a light fraction boiling belo the naphtha boiling range, contacting the naphtha frac tion with hydrogen at reforming conditions in the presence of a reforming catalyst, and recovering a liquid reformat: of high octane number.

2. A process according to claim 1 wherein the cracker gasoline is obtained from the catalytic cracking of hy drocarbon oil boiling above the gasoline boiling range 3. A process according to claim 1 wherein the crackec gasoline is obtained from the thermal cracking of hydrocarbon oils boiling above the gasoline boiling range.

4. A process for upgrading a cracked gasoline into high octane motor fuel which comprises mixing a cracked gasoline boiling in the range from about C to about 420 F. with a straight-run naphtha, contacting the mixture with hydrogen at hydroisomerization conditions in the presence of a hydroisomerization catalyst comprising a sulfide of a metal selected from the group consisting of chromium, molybdenum, tungsten, iron, cobalt, nickel, and mixtures thereof associated with an acid-acting support, separating the hydroisomerization effluent into a naphtha fraction and a light fraction boiling below the naphtha boiling range, contacting the naphtha fraction with hydrogen at reforming conditions in the presence of a reforming catalyst, and recovering a liquid reformate of high octane number.

5. A process for upgrading a cracked gasoline into high octane motor fuel which comprises contacting said gasoline with hydrogen at hydroisomerization conditions in the presence of a hydroisomerization catalyst comprising a sulfide of a metal selected from the group consisting of chromium, molybdenum, tungsten, iron cobalt, nickel, and mixtures thereof associated with an acid-acting support separating hydroisomerization liquid etlluent into a light fraction boiling below about 185 F. and a naphtha fraction boiling above about 185' F., contacting the naphtha fraction with hydrogen at reforming conditions in the presence of a reforming catalyst, and recovering liquid reformate of high octane number.

6. A process according to claim 5 wherein the liquid reformate is stabilized and blended with the light isomerizate fraction.

7. A process for upgrading a cracked gasoline into high octane motor fuel which comprises contacting said gasoline with hydrogen at hydroisomerization conditions in the presence of a hydroisomerization catalyst comprising nickel sulfide deposited on active silica-alumina cracking catalyst, separating hydroisomerization efiluent into a light fraction boiling below about 185 F. and a naphtha f raction boiling above about 185 F., contacting the naphtha fraction together with hydrogen at reforming conditions in the presence of a platinum reforming catalyst, and recovering a liquid reformate of high octane number.

8. A process according to claim 7 wherein a straightrun naphtha fraction is mixed with the cracked gasoline and the mixture is hydroisomerized.

9. A process for upgrading a cracked gasoline into high octane motor fuel which comprises mixing a cracked gasoline boiling in the range from C to about 390' F. with a straight-run naphtha boiling from about 200' F.

to 390 F., contacting the mixture with hydrogen at hydroisomerization conditions in the presence of a hydroisomerization catalyst comprising nickel sulfide deposited on active silica-alumina cracking catalyst separating hydroisomerization efiluent into a light fraction boiling below about 200 F. and a naphtha fraction boiling above about 200 F., contacting the naphtha fraction together with hydrogen at reforming conditions in the presence of a platinum reforming catalyst, and recovering a liquid reformate of high octane number.

10. A process for upgrading a cracked gasoline into high octane motor fuel which comprises separating said cracked gasoline into a light fraction and a naphtha fraction contacting said naphtha fraction with hydrogen at hydroisomerization conditions in the presence of a hydroisomerization catalyst comprising a sulfide of a metal selected from the group consisting of chromium, molybdenum, tungsten, iron, cobalt, nickel, and mixtures thereof associated with an acid-acting support, recovering a hydroisomerized naphtha fraction, and contacting the hydroisomerized naphtha together with hydrogen at reforming conditions in the presence of a reforming catalyst.

11. A process according to claim 10 wherein a straightrun naphtha is mixed with the cracked naphtha and the mixed naphtha is hydroisomerized.

12. A process for upgrading a cracked gasoline fraction into high octane motor fuel which comprises contacting a cracked naphtha fraction with hydrogen at hydroisomerization conditions in the presence of a hydroisomerization catalyst comprising a sulfide of a metal selected from the group consisting of chromium molybdenum, tungsten, iron, cobalt, nickel, and mixtures thereof associated with an acid-acting support, recovering a hydroisomerized naphtha, and contacting the hydroisomerized naphtha fraction with hydrogen at reforming conditions in the presence of a reforming catalyst, and recovering a liquid reformate of high octane number.

13. A process according to claim 1 wherein the hydroisomerization catalyst is cobalt sulfide deposited on active silica-alumina cracking catalyst.

14. A process according to claim 1 wherein the hydroisomerization catalyst is nickel sulfide deposited on active silica-alumina cracking catalyst.

References Cited in the file of this patent UNITED STATES PATENTS 2,740,751 Haensel et al. Apr. 3, 1956 2,913,393 Sarno Nov. 17, 1959 2,944,006 Scott July 5, 1960 3,008,895 Hansford et al. Nov. 14, 1961

Claims (1)

1. A PROCESS FOR UPGRADING A CRACKED GASOLINE INTO HIGH OCTANE MOTOR FUEL WHICH COMPRISES CONTACTING SAID CRACKED GASOLINE WITH HYDROGEN AT HYDROISOMERIZATION CONDITIONS IN THE PRESENCE OF A HYDROISOMERIZATION CATALYST COMPRISING A SULFIDE OF A METAL SELECTED FROM THE GROUP CONSISTING OF CHROMIUM, MOLYBDENUM, TUNGSTEN, IRON COBALT, NICKEL, AND MIXTURES THEREOF ASSOCIATED WITH AN ACID-ACTING SUPPORT, SEPARATING THE HYDROISOMERIZATION EFFLUENT INTO A NAPHTHA FRACTION AND A LIGHT FRACTION BOILING BELOW THE NAPHTHA BOILING RANGE, CONTACTING THE NAPHTHA FRACTION WITH HYDROGEN AT REFORMING CONDITIONS IN THE PRESENCE OF A REFORMING CATALYST, AND RECOVERING A LIQUID REFORMATE OF HIGH OCTANE NUMBER.

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