US3271294A - Hydroisomerization process - Google Patents

Description

States This invention relates to a process for isomerizing and hydrogenating an olefin containing hydrocarbon stream thereby increasing the octane number of such a stream. Specifically, the invention relates to an improved process and a dual function catalyst for increasing the octane number, especially the motor octane number, of an olefinic hydrocarbon fraction, by passage over said catalyst comprising an acidic and hydrogenation component on a solid support.

In present refinery operations, certain streams boiling from 30-350F. and containing an appreciable concentration of olefins containing from 4 to 8 carbon atoms are obtained from catalytic cracking and thermal cracking operations. A common characteristic of these olefinic streams is that they have a fairly high research octane number, but the motor octane number is lower than that desirable in modern combustion engines. The research and motor octane numbers as used in this specification are determined by ASTM method D1656-59T (Research) and D357-59 (Motor). This difference between the research and motor octane number of a gasoline, commonly called the sensitivity, is becoming the limiting factor in refinery gasoline blending operations. Thus, any process for improving the motor octane of these olefinic naphthas and lowering the sensitivity will be economically advantageous and useful.

An object of this invention is the preparation of a catalyst suitable for the isomerization and saturation of olefins to isoparafiins. A specific object of this invention is a process wherein light olefinic naphthas are converted to saturated hydrocarbons having much higher motor octane numbers and, in some cases, higher re search octane numbers by passage over the catalyst described herein. Another specific object of this invention is to decrease the sensitivity of the gasoline and to increase the octane index. Thus, by this process, the sensitivity of the gasoline is decreased and the octane index is increased. By octane index is meant the weighted average of research and motor octane number and is a technique used by refiners to rate the road performance of a motor fuel. A still further specific object of this invention is the optimization of either the gasoline or middle distillate fraction depending upon operating conditions. Further objects will be apparent from a description of this invention hereinbelow.

It has been discovered that by using a solid dual function catalyst, that is, one containing an acidic component as well as a hydrogenating component, one can obtain the very desirable reactions of olefin isomerization to isoolefins with the subsequent saturation of these isoolefins to isoparafiins. The following table shows the research and motor octane numbers of some typical normal and isoolefins in the 30 to 200 F. range, both before and after hydrogenation.

atent It is apparent from the above data that hydrogenation of the normal olefins to parafiins lowers the research octane number, but has a variable effect on the motor octane number (reactions 1, 2 and 3). Processes have been proposed involving straight hydrogenation of catalytic and thermal naphthas to decrease the gasoline sensitivity. This, however, leads in many cases to a loss in octane number.

The above data shows that saturation of isoolefins to isoparaflins (reactions 4, 5 and 6) will increase the motor octane number markedly. The latter series of reactions is involved in the upgrading of olefinic naphthas over the dual function catalyst of the present invention.' That is, isoolefins, either from isomerization by the acidic support or present in the feed, are saturated by hydrogen exchange or hydrogenation. By analyses of the products from this reaction, it is inferred that other reactions beside isomerization and hydrogen exchange (or hydrogenation) take place. Polymerization, cracking of polymer, alkylation and aromatization are all believed to participate to some extent in the overall reaction scheme.

According to the process of this invention, alight naphtha boiling substantially in the range of 30 to 350 F. is passed over a reaction zone containing a catalyst containing an acidic and a hydrogenation component. Typical feeds which can be used in this process are ones which contain any significant amount of olefins. However, maximum improvement in octane number is obtained with streams containing a high proportion of olefins. Examples of such feeds are light catalytic naphtha, thermal naphtha (obtained from thermal cracking or visbreaking of heavy materials), fluid coker naphtha or, in general, any material containing at least 10% by volume of olefinic hydrocarbons, but preferably above 20%. The preferred feed for this process is an olefin containing stream boiling in the 30 to 200 F. range wherein the olefin content is from 50 to by volume. A preferred and specific catalyst for use in the process of this invention is one comprising a mixed salt of molybdenum oxide and cobalt oxide, commonly called cobalt molybdate, on a solid acidic support such as a silica-alumina. Another example of this type of dual function catalyst, nickel-sulfide on silica-alumina is given in my co-pending application Serial Number 234,009, filed even date herewith. In general, the hydrogenation component can be 3 composed of metals or salts of these metals selected from Groups VIB and VIII of the Periodic Chart appearing in the 6th edition of the Merck Index (1952).

Conditions under which the process of this invention can be carried out vary widely, that is, feed rates of 0.1 to 10 volumes of hydrocarbon per volume of catalyst per hour (v./v./hr.), pressures of 0 to 2000 p.s.i.g. hydrogen pressure, temperatures in the range of 250 to 1200 F., and from 100 to 5000 standard cubic feet of hydrogen per barrel of feed naphtha (s.c.f./b.). The preferred conditions in this process are 0.2 to 2 v./v./hr. naphtha feed rate, temperature of 400 to 900 F., 500 to 1000 p.s.i.g. hydrogen pressure, and about 2000 to 4500 standard cubic feet of hydrogen per barrel of naphtha feed. At temperatures of 350 to 500 F. optimization of middle distillates is the result, whereas at temperature-s of 500 to 800 optimum yields of materials boiling in the gasoline range are obtained.

Catalysts which are suitable for use in this process are those containing acidic sites plus a mild hydrogenating component. One example of such a catalyst as herein set forth before is a cobalt-molybdenum salt which has been deposited on silica alumina cracking catalyst (88% silica, 12% alumina) in an amount of from 1 to percent by weight in equal molar proportions (the molar proportions can vary somewhat, however), prepared under conditions set forth hereafter. Sulfided nickel on silica alumina, another example of a dual function catalyst suitable for use in this process, is described in my copending application Serial Number 234,009 mentioned heretofore. Other examples of mild hydrogenating components are molybdenum oxide, molybdenum. sulfide, iron sulfide, cob-alt sulfide and other salts of these metallic elements.

Suitable bases for impregnation are all of the well known catalytic cracking catalysts such as 88% silica- 1 2% alumina, 75% silica-% alumina, silica-magnesia, silica-alumina-thoria catalysts, silica gel phosphoric acid on kieselguhr, hydrogen fluoride activated alumina, acidic clay and all other solid acidic catalysts known in the art. The catalyst employed in this invention can be prepared in either of two ways. By one method, a compound of the mixed oxides CoMoO is suspended in water, preferably containing a mineral acid such as nitric acid, and mixed with the silica-alumina base,

An equally preferred method involves the impregnation of the silica-alumina base with soluble salts of cobalt and molybdenum followed by calcination to convert these salts to their oxides. Any of the impregnation methods known in the art can be used to prepare the cobalt molybdate catalyst, except that the silica-alumina sup port is substituted for the pure alumina support normally used.

In either case, the inorganic components are either dissolved -or suspended in sufiicient water to produce a thick slurry when mixed with the silicaaalumina base. The slurry is well mixed, dried in an oven slightly above the boiling point of water, that is, about 250 F. and pilled. The catalyst pills are then calcined for 1-20 hours at 500 to 1500 F.

The hydrocarbon product obtained according to this process is substantially a saturated one, most of the olefins (that is, butenes to octenes) being converted to isoparaffins. Other chemical processes which take place in this system are polymerization, alkylation, aromatization and cracking. These reactions are well known to occur over acidic type catalysts. These polymerization and alkylation processes lead to materials boiling outside of the gasoline range. Since gasoline is one of the most profitable products in the refinery, it is advantageous except in special situations to obtain as high a yield of gasoline as is possible. This can be accomplished in this invention by operating at the upper temperature limits of the process and the yield of material boiling in the gasoline range 15-430 F.) is proportional to the temperature used in the process. However, it may be desirable in some areas, such as Europe, to limit the production of gasoline fractions and optimize or maximize the yield of middle distillates (hydrocarbons boiling in the range 300 to 600 F.). This is accomplished by operating in the lower temperature limits of the process. The quality of the middle distillates thus produced is good, the product having a high cetane number and low pour point indicating applications either as home heating oil or diesel fuel.

The following examples will illustrate, but not limit the invention:

Example 1.22.5 grams of CoMoO were suspended in 300 cc. of water and then thoroughly mixed with 250 grams of 12% alumina, 88% silica cracking catalyst. The mixture was then heated to 150 'F., dried at 250 F., pilled, and calcined for 4 hours at 1200 F.

Example 2.-The catalyst prepared in Example 1 was placed in a flow reactor and 40 to 200 F. (boiling point range) light catalytic naphtha was passed over the catalyst under the conditions given below. A run using 88% silica-12% alumina alone is included to show the superiority of the products obtained with the present system. Also, typical results which one would obtain by nonselective hydrogenation of the naphtha are included to show the superiority of this process, which gives both sensitivity and octane level improvement.

Run Number 1 2 3 88% Silica, OOMOO4 on Pd on Catalyst l2 Silica- Charcoal Alumina Alumina 400 400 500 500 500 3, 200 3, 200 Batch Feed Yield, Percent of Feed:

13.1. 40-200 1? 52. 7 54. 8 102 13.1. 200 F.+ 32.0 36.4 0 O and lower 15. 3 8. 8 0 Inspections, i0-200 F.

Product:

FIA, Vol. Percent (Fluorescent Indicator Analyscs) Aromatics 4. 1 3.1 2. 9 3.6 Olefins 64. 7 32. 9 9.7 12. 6 saturates 32. 2 64.0 87. 4 83. 3 Blending Octane No.

(25 vol. Percent in a Synthetic Pool): 1

Rcsearch+3 cc. (of

tetraethyl ad) 94.0 97. 4 98. 6 93.4 Motor+3 cc (of tetraethyl lead) 80 87.2 93. 2 88. 2 A Octane Index 6. 0 9. 8 3. 6 Sensitivity 14 10. 2 5. 4 5. 2

1 Synthetic Pool: Consists of a blend of catalytic pentenes, alkylate gasoline and catalytic reformate and having a research octane number Ss)13 bstantially above 103 and a motor octane number substantially above It is evident from the examples set forth that this process will convert light olefinic naphthas into materials having much higher motor octane numbers than the feed, and in some cases, higher research octane numbers. Gasoline yield can be controlled by severity of operating conditions or alternately middle distillate yield can be maximized, if desired, depending upon refinery situations. In the above table, data are included using silica-alumina alone which is the acidic component of the catalyst or palladium on charcoal which would be an example of hydrogenation without isomerization. The process of this invention increases both research and motor octane number whereas the acidic silica-alumina catalyst does not lower the sensitivity appreciably. Palladium on charcoal, which is strictly a hydrogenation catalyst lowers the sensitivity somewhat, but there is very little increase in octane index.

Specifically, it should be noted that the motor blending octane number of the light catalytic naphtha was increased from 80 to 93.2 and the research blending octane number was increased several units also. The net result was an increase in octane index of 9.8 and a decrease in the sensitivity from 14 units to 5.4 units.

It is a further advantage of this particular invention that it can be practiced in units already existing for the isocracking or other processes which use a similar catalyst. The process, according to this invention, can be practiced simply by substituting this catalyst, altering the reactor conditions slightly and feeding a light olefinic naphtha rather than a heavy 250 F. material.

It is possible to prepare the catalyst in powder form, that is, omit the pilling operation. This powdered catalyst when suitably prepared as described herein, can be used in a fluidized operation to upgrade light olefinic naphthas. A catalyst of this type would be particularly suitable for use in an existing fluid hydroforming unit.

It is further evident that the operation can be carried out in two temperature stages, that is, one stage operating at a low temperature to promote the isomerization and hydrogenation reactions and a high temperature stage to crack the polymer formed in the first stage to isoparaffinic material boiling in the gasoline range.

These and other modifications falling Within the scope of this invention can be made without departing from the coverage of the appended claims.

What is claimed is:

1. A method for treating a naphtha feed containing at least percent by volume of olefinic materials wherein process conditions are optimized to produce as a principal product a middle distillate boiling in the range of 300 to 600 R, which comprises passing said naphtha feed over a hydrocracking catalyst base containing from 1 to 20 percent by Weight of C0MOO4 deposited thereon, the feed rate of said hydrocarbon being from 0.1 to 10 v./v./hr. at a hydrogen pressure of from 0 to 2000 p.s.i.g.

and a temperature of from 350 to 500 F., said treatment being conducted in the presence of from 100 to 5000 standard cubic feet of hydrogen per barrel of said naphtha feed.

2. A process for the conversion of a naphtha feed containing at least 20 percent by volume of olefins by an isomerization and hydrogen saturation reaction which comprises contacting said feed in a hydroisornerization zone with a catalyst comprising from 1 to 20 weight percent of CoMoO and 99 to weight percent of a silicaalumina base, said base containing a majority of silica, at a space velocity of from 0.1 to 10 volumes of said feed per volume of said catalyst per hour in the presence of from 100 to 5000 standard cubic feet of added hydrogen per barrel of said feed, maintaining in said hydroisomeriz'ation zone a hydrogen partial pressure of from 500 to 1000 p.s.i.g. and a temperature of from 500 to 800 F, and recovering as a principal product from said hydroisomerization zone a motor fuel fraction boiling in the range of 15 to 430 F. and having a higher octane num ber and a lower sensitivity than said feed.

References Cited by the Examiner UNITED STATES PATENTS 2,352,416 6/1944 Thomas et al. 208-134 2,695,866 11/1954 'MCGrath 208'-1-36 2,717,231 9/1955 Lutz et al. 208136 2,774,720 12/1956 Garbo 208134 2,960,460 11/1960 Ryer et al. 208134 3,074,893 1/1963 Elle-rt et al. 20 8136 3,132,092 5/1964 Vaell 208---l36 DELBERT E. GANTZ, Primary Examiner.

ALPHONSO D. SULLIVAN, Examiner.

H. DEVINE, Assistant Examiner.

Claims (1)

1. A METHOD FOR TREATING A NAPHTHA FEED CONTAINING AT LEAST 10 PERCENT BY VOLUME OF OLEFINIC MATERIALS WHEREIN PROCESS CONDITIONS ARE OPTIMIZED TO PRODUCE AS A PRINCIPAL PRODUCT A MIDDLE DISTILLATE BOILING IN THE RANGE OF 300* TO 600*F., WHICH COMPRISES PASSING SAID NAPHTHA FEED OVER A HYDROCRACKING CATALYST BASE CONTAINING FROM 1 TO 20 PERCENT BY WEIGHT OF COMOO4 DEPOSITED THEREON, THE FEED RATE OF SAID HYDROCARBON BEING FROM 0.1 TO 10 V./V./HR. AT A HYDROGEN PRESSURE OF FROM 0 TO 2000 P.S.I.G. AND A TEMPERATURE OF FROM 350* TO 500*F, SAID TREATMENT BEING CONDUCTED IN THE PRESENCE OF FROM 100 TO 5000 STANDAARD CUBIC FEET OF HYDROGEN PER BARREL OF SAID NAPHTHA FEED.