US3759821A - Catalytic process for upgrading cracked gasolines - Google Patents

Abstract

A PROCESS IS DISCLOSED FOR UPGRADING CATALYTICALLY CRACKED GASOLINE WHICH INVOLVES FRACTIONATING A CATALYTICALLY CRACKED GASOLINE INTO A C6- OVERHEAD AND A C7+ BOTTOM FRACTION AND CONTACTING THE C7+ BOTTOM FRACTION WITH A ZSM-5 TYPE ZEOLITE. THE LIQUID PRODUCT OBTAINED FROM CONTACTING THE C7+ BOTTOM FRACTION WITH THE ZSM-5 TYPE ZEOLITE IS THEREAFTER BLENDED WITH THE ORIGINAL C6- FRACTION TO GIVE A FINAL GASOLINE OF INCREASED OCTANE NUMBER. THE REACTION CAN BE CARRIED OUT IN THE ABSENCE OF HYDROGEN AND IN THE ABSENCE OF A HYDROGENATION/DEHYDROGENATION COMPONENT ON THE ZEOLITES.

Description

tlnitedstat Patent 3,759,821 CATALYTIC PROCESS FOR UPGRADING CRACKED GASOLINES James A. Brennan, Cherry Hill, William E. Garwood, Haddonfield, and Harold C. Myers, Woodhury, N.J., assignors to Mobil Oil Corporation No Drawing. Filed Mar. 29, 1971, Ser. No. 129,212

Int. Cl. Clilg 35/06 U.S. Cl. 208-93 6 Claims ABSTRACT OF THE DISCLOSURE A process is disclosed for upgrading catalytically cracked gasoline which involves fractionating a catalytically cracked gasoline into a C3 overhead and a C bottom fraction and contacting the 0 bottom fraction with a ZSM-5 type zeolite. The liquid product obtained from contacting the (37+ bottom fraction with the ZSM-S type zeolite is thereafter blended with the original 0 fraction to give a final gasoline of increased octane number. The reaction can be carried out in the absence of hydrogen and in the absence of a hydrogenation/dehydrogenation component on the zeolites.

DESCRIPTION OF THE INVENTION There have been many processes known in the art which have been designed for the purpose of upgrading the octane number of gasoline and the patent and technical literature abounds with discussions of various processes. 0

One fundamental problem which is faced in all processes for upgrading octane number is that the increase in octane number is invariably at the expense of yields of total liquid product so that the art has continuously strived to obtain a process which would give an increase in octane number at the least expense of loss of yield. Typical processes for increasing octane number have been so-called reforming processes wherein a naphtha is contacted with a conventional reforming catalyst usually of the platinum type. During the past decade there has been developed processes utilizing crystalline aluminosilicate zeolites for upgrading the octane number of various petroleum fractions and usually process of this type have been employed in combination with a conventional reforming operation, Le. a reforming operation is carried out to a certain severity and the reformed product is thereafter contacted with a crystalline aluminosilicate zeolite usually having a pore size of about 5 angstrom units, either under cracking and/or hydrocracking conditions.

The novel process of this invention is also concerned with improving the octane number of gasolines, but it is not directed towards increasing the octane number of a reformate. It is concerned with increasing octane numbers of catalytically cracked gasoline as opposed to increasing the octane number of either a naphtha or reformate.

As can well be appreciated with the recent emphasis on environmental control and the desirability of either eliminating or lowering the amount of lead which is usually present as an additive in gasoline, a process which will increase the octane number of gasoline so as to either eliminate or minimize the amount of lead which is necessary to raise it to a still higher octane is, indeed, desirable.

i The instant invention is predicated upon the discovery that the octane number of a catalytically cracked gasoline can be further increased by treatment of a selective fraction thereof with a crystalline aluminosilicate identified as a ZSM5 type.

It is to be immediately understood that it is absolutely material inthe novel process of this invention that the catalytically cracked gasoline be fractionated into a C fraction and 210 fraction and only the C fraction conice tacted under conversion conditions with the ZSM-S type zeolite. For reasons which are not completely understood, it has been found that if the entire catalytically cracked gasoline (without being fractionated) is subjected to contact with the same ZSM-S type zeolites, no increase in octane number will occur. If, however, the teachings of this invention are carried out, a rather significant increase in octane number occurs at the expense of a rather low loss of yield.

As has heretofore been stated, the process of this invention involves fractionating a catalytically cracked gasoline into a C overhead and 0 bottom fraction. This is usually accomplished at 180 F. although the novel process of this invention is applicable to cuts ranging from 160 to 200 F.

The C bottom fraction is then contacted with a crystalline aluminosilicate of the ZSM-S type and said contact is found to be effective in the absence of added hydrogen and in the absence of a hydrogenation/dehydrogenation component. The liquid product obtained from contact with said ZSM-S catalyst is thereafter blended back to the C overhead so as to produce a product having an increased octane number.

The catalytically cracked gasoline which is fractionated into the C to 0 fractions in accordance with the teachings of this invention is not narrowly critical and any commercial catalytically cracked gasoline is operable whether the gasoline be prepared by processes involving use of amorphous catalysts such as silica alumina or whether it had been prepared by cracking gas oil with crystalline aluminosilicate zeolites or whether it had been prepared by a catalyst comprising a mixture of an amorphous and crystalline material, i.e. a crystalline aluminosilicate in a matrix. It is also to be understood that the catalytically cracked gasoline is also intended to include gasoline which has been prepared by various commercial hydrocracking processes.

As has heretofore been stated, the novel process of this invention utilizes crystalline aluminosilicates of the ZSM-5 type.

ZSM-S type zeolites include not only ZSM-S but also ZSM-8 zeolites. ZSM-5 materials are disclosed and claimed in copend-ing application Ser. No. 865,472, filed Oct. 10, 1969, now Pat. No. 3,702,886 and ZSM-S is disclosed and claimed in copending application Ser. No. 865,- 418, filed Oct. 10, 1969, now abandoned.

The family of ZSM-5 type compositions has the characteristic X-ray diffraction pattern set forth in Table 1, hereinbelow. ZSM-S compositions can also be identified, in terms of mole ratios of oxides as follows:

0.9:i:0.2M 2 0 1W; 0 325- Y OgIZHz 0 wherein M is a cation, n is the valence of said cation, W is selected from the group consisting of aluminum and gallium, Y is selected from the group consisting of silicon and germanium, and z is from 0 to 40. In a preferred synthesized form, the zeolite has a formula, in terms ofmole ratios of oxides, as follows:

0.9:l:0.2M O A1 0 :5-100 SlOzIZHaO and M is selected from the group consisting of a mixture of alkali metal cations, especially sodium, and tetraalkylammonium cations, the alkyl groups of which preferably contain 25 carbon atoms.

In a preferred embodiment of ZSM-5, W is aluminum, Y is silicon and the silica/alumina mole ratio is. at least 10 and ranges up to about 60.

Members of the family of ZSM-5 zeolites possess a definite distinguishing crystalline structure whose X-ray dififraction pattern shows the following significant lines:

These values as well as all other X-ray data were determined by standard techniques. The radiation was the K- alpha doublet of copper, and a scintillation counter spectrometer with a strip chart pen recorder was used. The peak heights, I, and the positions as a function of 2 times theta, where theta is the Bragg angle, were read from the spectrometer chart. From these the relative intensities, 100 UK, where I is the intensity of the strongest line or peak, and d (obs.), the interplanar spacing in A, corresponding to the recorded lines, were calculated. In Table 1 the relative intensities are given in terms of the symbol S= strong, M=medium, MS=medium strong, MW=medium weak and VS=very strong. It should be understood that this X-ray difiraction pattern is characteristic of all the species of the ZSM-S compositions. Ion exchange of the sodium ion with cations reveals substantially the same pattern with some minor shifts in interplanar spacing and variation in relative intensity. Other minor variations can occur depending on the silicon to aluminum ratio of the particular sample, as well as if it has been subjected to thermal treatment. Various cation exchanged forms of ZSM- have been prepared. X-ray powder diffraction patterns of several of these forms are set forth below. The ZSM-5 forms set forth below are all aluminosilicates.

TABLE 2 X-RAY DIFFRACTION ZSM-5 POWDER 1N CAlION EXCHANGED FORMS, d SPACINGS OBSERVED As made HCl N 6.01 CaCla RE Cl: .AgNOs 4.61 4. 62 4. 62 4. 61 4. 63 4. 62 4.46 4.46 4.46 4.36 4. 37 4. 37 4. 36 4. 37 4. 37 4.26. 4. 27 4. 27 4. 26 4. 27 4. 27 4.08. 4. 09 4. 09 4. 09 4. 09 4.00. 4. 91 4. 01 4. 00 4. 01 4. 01 3.84. 3. 85 3. 85 3. 85 3. 86 3. 86 3.82. 3. 82 3. 82 3. 82 3. 83 3. 82 3.75. 3. 75 3. 75 3. 76 3. 76 3. 75 3.72- 3. 72 3. 72 3. 72 3. 72 3. 72 3.64. 3. 65 3. 65 3. 65 3. 65 3. 65 3. 60 3. 6O 3. 60 3. 61 3. 60 3.48 3. 49 3. 49 3. 48 3. 49 3. 49 3.44 3. 45 3. 45 3. 44 3. 45 3. 45 3.3 3. 35 3. 36 3. 35 3. 35 3. 35 3. 31 3. 32 3. 31 3. 32 a. s2

As made H01 N 2101 021012 RECls AgNO;;

Zeohte ZSM-S can be sultably prepared by preparing a solution containing water, tetrapropyl ammonium hydroxide, and the elements of sodium oxide an oxide of aluminum or gallium and an oxide of silica, and having a composition, in terms of mole ratios of oxides, falling within the following ranges:

wherein R is propyl, W is aluminum and Y is silicon. This mixture is maintained at reaction conditions until the crystals of the zeolite are formed. Thereafter the catalysts are separated from the liquid and recovered. Typical reaction conditions consist of a temperature of from about 75 C. to 175 C. for a period of about six hours to 60 days. A more preferred temperature range is from about to C. with the amount of time at a temperature in such range being from about 12 hours to 20 days. 1

The digestion of the gel particles is carried out until crystals form. The solid product is separated from the reaction medium, as by cooling the whole to room temperature, filtering and water washing.

ZSM-S is preferably formed as an aluminosilicate. The composition can be prepared utilizing materials which supply the elements of the appropriate oxide. Such com-.

positions include, for an aluminosilicate, sodium aluminate, alumina, sodium silicate, silica hydrosol, silica gel, silicic acid, sodium hydroxide and tetrapropylammonium hydroxide. It will be understood that each oxide component utilized in the reaction mixture for preparing a member of the ZSM-S family can be supplied by one or more initial reactants and they can be mixed together in any order. For example, sodium oxide can be supplied by an aqueous solution of'sodium hydroxide, or by an aqueous solution of sodium silicate; tetrapropylammonium cation can be supplied by the bromide salt. The reaction mixture can be prepared either batchwise or continuously. Crystal size and crystallization time of the ZSM-S composition will vary with the nature of the reaction mixture employed. ZSM-8 can also be identified, in terms of mole ratios of oxides, as follows:

0.9;l;0.2M 2 masons-100 SiOzzzIhO wherein M is at least one cation, in is the valence thereof and z is from to 40. In a preferred synthesized form,

the zeolite has a formula, in terms of mole ratios of oxides, as follows:

0.9i0.2M 2 o AlrOmlO-GO siommo and M is selected from the group consisting of a mixture of alkali metal cations, especially sodium, and tetraethylammonium cations.

ZSM-8 possesses a definite distinguishing crystalline structure having the following X-ray diffraction pattern:

TAB LE 4 Zeolite ZSM- S can be suitably prepared by reacting a water solution containing either tetraethylammonium hydroxide or tetraethylammonium bromide together with the elements of sodium oxide, aluminum oxide, and an oxide of silica. The operable relative proportions of the various ingredients have not beenfully determined and it is to be immediately understood that not any and all proportions of reactants will operate to produce the desired zeolite. In' fact, completely diiferent zeolites can be prepared utilizing the same starting materials depending upon their relative concentration and reaction conditions as is set forth in US. 3,308,069. In general, however, it has been found that when tetraethylammonium hydroxide is employed, ZSM-S can be prepared from said hydroxide, sodium oxide," aluminum oxide, silica and water by re- 0 acting said materials in such proportions that the form ing solution has a composition in terms of mole ratios of oxides falling within the following range SiO /Al O --from about 10 to about 200 Na O/tetraethylammonium hydroxide-from about 0.05

Tetraethylammonium hydroxide/SiO from about 0.08

H O/tetraethyIammonium hydroxide-4mm about to about 200 Thereafter, the crystals are separated from the liquid and recovered. Typical reaction conditions consist of maintaining the foregoing reaction mixture at a temperature of from about C. to 175 C. for a period of time of from about six hours to 60 days. A more preferred temperature range is from about to C. with the amount of time at a temperature in such range being from about 12 hours to 8 days.

The ZSM5 type zeolites used in the instant invention usually have the original cations associated therewith replaced by a wide variety of other cations according to techniques well known in the art. Typical replacing cations would include hydrogen, ammonium and metal cations in cluding mixtures of the same. Of the replacing cations, particular preference is given to cations of hydrogen, ammonium, rare earth, and mixtures: thereof.

Typical ion exchange techniques would be to contact the particular zeolite with a salt of the desired replacing cation or cations. Although a wide variety of salts can be employed, particular preference is given to chlorides, nitrates and sulfates.

Representative ion exchange techniques are disclosed in a wide variety of patents including US. Pats. 3,140,249; 3,140,251; and 3,140,253.

Following contact with the salt solution of the desired replacing cation, the zeolites may be washed with water and dried at a temperature ranging from 150 F. to about 600 F. and thereafter heated in air or other inert gas at temperatures ranging from about 500 F. to 1500 F. for periods of time ranging from 1 to 48 hours or more.

It is also possible to treat the zeolite with steam at elevated temperatures ranging from 800 F. to 1600" F. and preferably 1000 F. and 1500 E, if such is desired. The treatment may be accomplishedin atmospheres consisting partially or entirely of steam.

A similar treatment can be accomplished at lower temperatures and elevated pressures, e.g. 350-700 F. at 10 to about 200 atmospheres.

One embodiment of this invention resides in the use of a porous matrix together with the ZSM-S type zeolite previously described. The ZSM5 type zeolite can be combined, dispersed or otherwise intimately admixed with a porous matrix in such proportions that the resulting product contains from 1% to 95% by weight, and preferably from 50 to 80% by weight, of the zeolite in the final composite.

The term porous matrix includes inorganic compositions with which the aluminosilicates can be combined, dispersed or otherwise intimately admixed wherein the matrix may be active or inactive. It is to be understood that the porosity of the compositions employed as a matrix can either be inherent in the particular material or it can be introduced by mechanical or chemical means. Representative matrices which can be employed include metals and alloys thereof, sintered metals and sintered glass, asbestos, silicon carbide aggregates, pumice, firebrick, diatomaceous earths, and inorganic oxides. Inorganic compositions especially those of a siliceous nature are preferred. Of these matrices, inorganic oxides such as clay, chemically treated clay, silica, silica-alumina, etc., are particularly preferred because of their superior porosity, attrition resistance, and stability.

The compositing of the aluminosilicate with an inorganic oxide can be achieved by several methods wherein the aluminosilicates are reduced to a particle size less than 7 40 microns, preferably less than 10 microns, and intimately admixed with an inorganic oxide while the latter is in a hydrous state such as in the form of hydrosol, hydrogel, wet gelatinous precipitate, or in a dried state, or a mixture thereof. Thus, finely divided aluminosilicates can be mixed directly with a siliceous gel formed by hydrolyzing a basic solution of alkali metal silicate with an acid such as hydrochloric, sulfuric, acetic, etc. The mixing of the three components can be accomplished in any desired manner, such as in a ball mill or other types of mills. The aluminosilicates also may be dispersed in a hydrosol obtained by reacting an alkali metal silicate With an acid or alkaline coagulant. The hydrosol is then permitted to set in mass to a hydrogel which is thereafter dried and broken into pieces of desired shape or dried by conventional spray drying techniques or dispersed through a nozzle into a bath of oil or other water-immiscible suspending medium to obtain spheroidally shaped bead particles of catalyst such as described in US. Pat. 2,384,946. The aluminosilicate siliceous gel thus obtained is washed free of soluble salts and thereafter dried and/or calcined as desired.

In a like manner, the aluminosilicates may be incorporated with an aluminiferous oxide. Such gels and hydrous oxides are well known in the art and may be prepared, for example by adding ammonium hydroxide, ammonium carbonate, etc., to a salt of aluminum, such aluminum chloride, aluminum sulfate, aluminum nitrate, etc., in an amount suflicient to form aluminum hydroxide which, upon drying is converted to alumina. The aluminosilicate may be incorporated with the aluminiferous oxide While the latter is in the form of hydrosol, hydrogel, or wet gelatinous precipitate or hydrous oxide, or in the dried state.

The catalytically active inorganic oxide matrix may also consist of a plural gel comprising a predominant amount of silica with one or more metals or oxides thereof selected from Groups I-B, II, III, IV, V, VI, VII and VIII of the Priodic Table. Particular preference is given to plural gels or silica with meta oxides of Groups II-A, III and We of the Periodic Table, especially wherein the metal oxide is rare earth oxide, magnesia, alumina, zirconia, titania, beryllia, thoria, or combination thereof. The preparation of plural gels is well known and generally involves either separate precipitation or coprecipitation techniques, in which a suitable salt of the metal oxide is added to an alkali metal silicate and an acid or base, as required, is added to precipitate the corresponding oxide. The silica content of the siliceous gel matrix contemplated herein is generally within the range of 55 to 100 weight percent with the metal oxide content ranging from to 45 percent.

The inorganic oxide may also consist of raw clay or a clay mineral which has been treated with an acid medium to render it active. The aluminosilicate can be incorporated into the clay simply by blending the two and fashioning the mixture into desired shapes. Suitable clays include attapulgite and kaolin.

The novel process of this invention is carried out simply by contacting said C7+ fraction of a catalytically cracked gasoline with a ZSM-S type zeolite at a temperature from about 400 to 800 F. The reaction can take place at atmospheric pressure and in the absence of added hydrogen.

It is to be immediately understood, however, that although the invention has been described with reference to the fact that it is not necessary to use a hydrogenation/ dehydrogenation component nor is it necessary to carry out the reaction in the presence of added hydrogen, nevertheless, both these features can be employed if such is desired. It might very well be, for example, that the presence of a hydrogenation component might have a beneficial efiect on the catalyst in that it might be able to even further add to its stability by hydrogenating coke preformers as is Well known in the art. It is to be understood, however, that the preferred embodiment of this invention resides in operating in the absence of hydrogen and in the absence of a hydrogenation component.

When a hydrogenation/dehydrogenation component is used it can be any hydrogenation component conventionally known in the art. These components can include metals, oxides, and sulfides of metals of the Periodic Table which fall in Group VIB including chromium, molybdenum, tungsten and the like; Group II-B including zinc cadmium, Group VII-B including manganese and rhenium and Group VIII including cobalt, nickel, platinum, palladium, ruthenium, rhodium, and the like, and combinations of metals, sulfides and oxides of metals of Group VIB and VIII, such as nickel-tungsten-sulfide, cobalt oxide-molybdenum oxide and the like.

Thus, the processing conditions envisioned in the opera tion of an instant process have temperatures ranging from 400 to 800 F., pressure ranging from 01,000 lbs. p.s.i.g., hydrogen to hydrocarbon ratios are from 0-20 and LHSV from 0.01-50. Preferred operating conditions are temperatures from 500 to 700, 500 p.s.i.g. pressure, absence of hydrogen, and LHSV of from 1 to 20.

The following examples will now illustrate the best mode contemplated for carrying out this invention.

EXAMPLE 1 A catalytically cracked gasoline was obtained from a commercial fluid cracking operation. It was then fractionated into a C fraction and a C7+ fraction in a conventional 25 plate distillation column. Properties of the charge and the two fractions were as follows:

IBP, 180 180 F.* Charge F. (Cr) 1*) Weight percent 100 31. 1 68.9 Volume percent 100 36. 7 63. 3 Gravity, API 53. 7 41.2 Gravity, specific 0. 7640 0.8193 Research octane, 0 m1. TEL 92.2 1 97 90. 7

1 Estimate.

EXAMPLES 2-4 Example Temperature, F. (average) 550 602 703 LHSV 1.3 1.0 1.3 Liquid product, weight percent.-. 99. 6 99. 6 98. 8 Gravity, API 40. 8 40.7 41. 0 Gravity, specific 0.8212 0.8217 0. 8203 Volume, percent 99.3 99. 3 98. 6 Research octane, 0 ml. TEL 90.1 91.8 93.2 Dry gas (Ci-Ca), wt. percent 0. 4 0.4 0. 9

From the above it can be seen that Examples 3 and 4 resulted in increasing the octane number from 90.7 to as high as 93.2 at a loss to dry gas of less than 0.9 weight percent.

EXAMPLES 5-6- Examples 5 and 6 will illustrate that octane improvement will not be realized if the entire gasoline charge (not fractionated) is contacted with the ZSM-5 zeolite.

In these examples the charge was that set forth in Example 1 and all conditions were otherwise the same as used in Examples 3 and 4.

The results are shown in the following table.

Example Charge 5 6 Temperature, F. (average) 598 703 LHSV 1. 1 0. 9 Liquid product, weight percent. 100 97. 1 97. 2 Gravity, AP 53. 7 50. 8 49. 9 Gravity, specific 7640 7762 7800 Volume, percent 100 95. 6 95. 2 Research octane, 0 m1. TEL 92. 2 91. 9 92. 3 Dry gas (C -C3), weight percent 1.3 1.3

From the above it can be seen that no octane improvement resulted and that loss to dry gas was over one weight percent.

EXAMPLES 7-8 Example Untreated gasoline 7 8 Volume, percent 100 99. 6 99.1 Research octane, 0 ml. TEL 92. 2 93. 1 93. 9

What is claimed is: 1. A process for upgrading catalytically cracked gasoline which comprises fractionating said catalytically cracked gasoline into two fractions which are a C3- and C7+ fraction, contacting said 0 fraction under conversion conditions with a crystalline zeolite having an X-ray dilfraction pattern as set forth in Table 1 and blending the liquid product obtained from said conversion with said C fraction to obtain a gasoline having an enhanced octane number.

2. The process of claim 1 wherein the zeolitic material is ZSM-S.

3. The process of claim 1 wherein the zeolitic material is ZSM-8.

4. The process of claim 1 wherein the zeolitic material has a hydrogenationldehydrogenation component associated therewith.

5. The process of claim 2 wherein the ZSM-5 has been base exchanged with ammonium or hydrogen cations.

6. The process of claim 3 wherein the ZSM-8 has been base exchanged with ammonium or hydrogen ions.

References Cited UNITED STATES PATENTS 2,890,997 6/ 1959 Hirschler 20893 3,044,950 7/1962 Swartz 20893 3,574,092 4/ 1971 Mitsche 208-138 3,438,887 4/1969 Morris et al. 208-87 3,016,344 1/1962 Kirsch 208-93 3,247,099 4/1966 Oleck et a1. 208138 3,644,200 2/1972 Young 208138 HERBERT LEVINE, Primary Examiner US. Cl. X.R.

2081 3 8, Dig. 2

32 3 I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,759, September 18, 1973 James A. Brennan, William E. Garwood inventofls) d Harold C. Myers It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column line L under column heading "RECl "1.15" should be -3.l5--.

Column 4, line "estslysts' should be --crysta.ls--.

Column 7, line 38 "Priodic" should be --Periodic-.'

Signed and sealed this 14th day of June 1971;.

(SEAL) Attest:

EDWARD T LFLETCHER, JR. 0 MARSHALL DANN Attesting Officer. Commissioner of Patents