CA1071612A - Hydrocarbon cracking catalyst - Google Patents

Abstract

Abstract of the Disclosure A process for preparing a zeolite containing hydro_ carbon cracking catalyst characterized by exceptionally high catalytic activity and superior coke selectivity, containing relatively small amounts of rare earths, by combining a zeolite prepared by a combination of thermal stabilization, de-alumination and rare earth ion exchange into a suitable matrix.

Description

Background of the In~rention The use of zeolite promoted cracking catalysts is well known. U.S. Patent 3,140,249 to Plank et al.
is typical of the early patents in this area. These patents generally disclose the use of a faujasitic type zeolite having a silica to alumina ratio of about 3 to 6 that has exchanged therein a fairly substantial quantity of rare earth oxides, distended in a matrix such a~
silica, silica-alumina, silica-zirconia, alumina, etc.
The preferred catalyst comprise the rare earth exchange faujasitic zeolites in a silica-alumina matrix.
Continuing efforts have been made to improve these catalysts by making them more stable, more resistant to high temperature and more economical. One of the recurring problems is the use of the relatively rare and quite costly rare earth salts in t~e preparation of these catalysts. The process of the instant application prepares a stable active zeolite containing catalyst that minimizing ~he amount of rare earth contained therein.
0 Brief Description of the Invention .
I have found that an exceptionally stable and active ~catalyst can be prepared by suspending a faujasitlc type zeolite with a silica to alumina ratio of greater than 7 to 20 in a suitable matrix. The zeolite is present as about 5 to 50 percent, preferably about 10 to 30 percent of the composite and contains less than 10 percent of rare earth.
Detailed Description of the Invention -The first step in our process is the preparation of the zeolite having a silica to alumina ratio of greater than 7 to ahout 20. The method for preparing the zeolite is not part of this invention it is disclosed in United States ~ 2 -, J

Patent 3,595,611 to McDaniel et al issued July 27, 1971.
Briefly the process comprises treatlng a faujasitic type zeolite that hasbeen subjected to an ion exchange to reduce the Na2O content to less than 4%, followed by calcin-ation at a temperature in excess of 1200F. for a period of about 0.1 hours. This stabilized faujasite is then treated with a dilute mineral acid to remove a portion o~ the alumina and shift the silica to alumina ratio from about 3.5 to 6 to greater than 7 to about 20.
The critically important features of -this process are the preparation of the stabilized zeolite by the com-bination of ion exchange and calcination steps followed by the acid treatment to remove a portion of the alumina. The product recovered from this treatment is a zeolite having a high degree of stability and relatively low ion exchange capacity.
The next step of the process is incorporation of the rare earth or other cations into the partially de-aluminated zeolite by ion exchange. This is accomplished by conventional ion exchange techniques. Because of the low ion exchange capacity the amount of rare earth or other ions in the zeolite is relatively low, generally in the order of 1 to 10 percent dry weight.
Crac~ing catalysts normally contain rare earths exchanged into the zeolite. However, other cations such as magnesium also give satisfactory results.
Thus, in accordance with the present teachinys a method is provided for the preparation of stable crystalline zeolite which comprises exchanging a sodium Type ~ zeolite which has a silica to alumina ratio of about 3.5 to 6 with an ammonium salt to reduce the Na2O content to less than ~ - 3 -Ir~ , ~ i percent by weight. The zeolite is then exchanged with a solution of rare earth ions -to proviae a rare earth oxide content of about O . 5 to 4 percent by weight. The zeolite is then washed to remove excess salts and heated to a temperature of about 700 to 1600F. The zeolite is then contacted with a dilute solution of a mineral acid to remove alumina therefrom and to increase the silica to alumina ratio in the range of about 7 to 2~ and subsequently exchanging the zeolite ~ith a solution of metal ions selected from the group consisting of rare earth and magnesium ions ~o impart a concentration of metal îons of from a~out l to lO percent by weight.
In the next step of the preferred process of the invention the zeolite in the rare earth or other cation form is distended into an inorganic oxide matrix. In manner the zeolite crystals are suspended in and distributed ~, 30 ~ . ~

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~hroughout the matrixO The catalyst-matrix suspension can be readily prepared by dispersing the æeolite in the rate earth form in a suitable siliceous sol a~d gelling the sol by various means. In addition, the zeolite may be dispersed in a cogel of silica and an oxide of a second metal.
Examples of suitable cogels include silica-alumina, silica~
magnesia, silica-zirconia9 silica-titania, as well as tertiary combinations such as silica-alumina-zirconia, silica-alumina-magnesia, silica~magnesia-zirconia, etc.
T&e preferred cogels include silica-alumina and silica~
magnesia, with silica-alumina being particularly preferred~
In addition, the matrix may contain a considerable amount of clay that is normally added to the sodium silicate solution prior to forming the cogel with alumina~ magnesia;
etc.
These gels and cogel will generally comprise a major portion of silica and a minor portion of the other oxide or vxides.
The silica content of the siliceous gel or cogel matrix will generally be in the range of 55-100 weight percent, preferably ; 20 60~90 weight percent with the other metals in the range of 5-45 weight percent, preferably 10-40 weight percentO
If clay is added as a component of the matrix it is only present in the amount of 10 to 70 percent.
The qilica-alumina hydrogels can be produced by any number of known methodsO For example, a hydrous precipitate of silica can be prepared by mixing the solution of sodium silicate with an acid such as sulfuric acid or with carbon dioxide to produce a slurry having a pH below 9~ usually below 7. A solution of an alumlnum salt such as aluminum sulfate~ for example~ i,4 then added and the pH of the mixture is ad~usted to above 4 by the addition of an alkaline material such as ammonia in order to precipitate the alumina.

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As pointed out above, in addition it is contemplated that the matrix can comprise natural or synthetic clays such as kaolin type clays, montmorillonite, bentonite, halloysite, etc.
The zeolite-matrix compositions are prepared by intimately admixing the aforesaid described zeolite with the siliceous hydrogelS clay or mixtures thereof and thereafter obtaining a composite product comprising the zeolite component uniformly distributed throughout and suspended in the inorganic oxide matrix.
The zeolite component of the catalyst is normally present in the amount of about 5 to 50 percent, preferably about 10 to 30 percent.
My invention is illustrated by the following specific but nonlimiting examples~
Example 1 The zeolite described in U.S0 Patent 3,595,611 and designated PCY was prepared by treating a faujasite having a silica to alumina ratio of about 3.5 to 5 with a ;
combination of ammonium ion exchange and metal ion exchangeO
The zeolite was first exchanged with an ammonium salt solution to reduce the Na20 content to about 2.5 to 3.5 percent. The zeolite was then filtered and the cake returned to the solution of a salt contaiDing rare earth or other cations sufficient to provide 0.5 to 15 percent rare earth o~ide or the equivalent amount of other cations to the ~eolite. The product was then filtered, washed free of e~cess salt and heated at a temperature of about 700 to 1600Fo The product was then cooled and exchanged with - 30 an ammonium salt solution to reduce the Na20 content to - less than 1 percentO

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A 100 gram sample of this zeolite was treated with a dilute (0.1) normal solution of nitric acid a~ a temperature of 30Co for a period nf 4 hoursD The zeolite was filtered and again treated with nitric acid. A total of 0.75 moles of nitric acid was used in this treatment. The zeolite was then recovered, washed free of dissolved salts and dried. The analysis of the zeolite in weight percent was as follows: Na20 less than 0.2; SiO2 B3.2; A1203 12.6;
rare earth oxides lo 5.
The zeolite was prepared as a catalyst component by dry mixing the zeolite with a semi-synthetic commercial cracking catalyst having a low activity. The semi-synthetic catalyst contained 60 percent silica-alumina and 40 percent clay. The physical blend of the two components was formed into pills and the catalytic activity was determined using a microactivity tes~. In this test the samples to be tested are placed in a reactor and heated to a temperature of 900F. in the presence of a WeSt Texas Gas Uil Feed. The catalyst oil ratio was 5.88 and the weight hourly space velocity was 16. In this run the catalyst prepared to contain 10% of our novel zeolite, designated catalyst Cg was compared with a semi-synthetic catalyst that contalned no zeolite designated catalyst B
and with a catalyst containing 10% of the ultra stable fau~asite designated catalyst Ao The data collected in the series of runs is set out in the table below.

TABLE I

Catalyst B _ C_ Conversion volume percent 29.08 46.82 61.54 H2 weight percent 0.0540.045 0-059 Cl weight percent 0.0990.092 0.146 C2 weight percent 0.1040.060 0,211 C3 volume percent 0.360.44 0.88 C4 volume percent 7.709.34 11.7 C5 ~ gasoline volume 21.9038.64 52.16 percent Coke weight percent 1.361.14 1.42 It is apparent from a review of this data that the catalyst of the instant application has a good conversion and a high conversion to gasoline with a small conversion to coke. This result was achieved even though the catalyst contained only 0.1~ rare earth oxide.
Example 2 A run was completed in which the amount of rare earth oxide in the zeolite was increased by an additional rare earth exchange A ~o~al of 25 grams of the zeolite described in Example 1 was exchanged with a rare earth chloride solution containing 10 grams of rare earth chlorlde (asRE 23) per 100 ml. using ratios of zeolite to rare earth to water of 1 to 1 to 10. The exchange was carried out for 30 mlnutes at a temperature of about 90C. The zeollte was wasned free of dissolved salts and dried. The analysls of the zeolite ln weight percent was as follows:
Na2O - O.1; rare earth oxide 7.1; alumina - 10.2;
silica - 82.6. A physical blend of 10~ of the zeolite and 90% of the low activity commercial semi-synthetic ` cracking catalyst was prepared and pills were foxmed from this mixture. The microactivity of this ca~alyst (designated Catalyst D) was compared with the catalyst designated A of Example 1. The results of this comparison are set out in the table below.

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Table II

Catalyst A D
Conversion volume percent 46.82 71.93 H2-weight percent 0 045 0.052 Cl weight percent 0.092 0.243 C2 weight percent 0.060 0.260 C3 volume percent 0.44 1.22 C4 volume percent 9.34 12.72 C + gasoline volume 38.64 60.56 5 percent Coke weight percent 1.14 1.89 3.~7~

It is apparent from review of these data that there is a substantial improvement in conversion and a substantial improvement in gasoline recovery when the amount of rare earth in the zeolite is increased.
Example 3 In this example the product of Example 1 was given an additional exchange with a mag~esium chloride solution.
A total of 25 grams of the zeolite was exchanged with a magnesium chloride solution containing 10 grams of mag~esium chloride per 100 ml. The zeolite to magnesium chloride to water ratios were 1:1:10. The zeolite was washed free of excess salt and dried. The analysis of the zeolite in weight perc~nt was as follows: Na2O - 1.0;
RE2O3 - 1.5; A1203 - 10.4; SiO2 - 87; MgO - 1Ø A
catalyst was prepared from this zeolite by physically blending `10% of the zeolite and 90% of a low activity commercial semi-synthetic cracking catalyst. The mixture was formed into pills and the microactivity test was carried out under the same conditions as in Example 1.
The product of this run was identified as catalyst E
and was compared with the catalyst A of Example 1.
The data collected in this run is set out in the table below.

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Table III
Catalyst A E
Conversion volume percent46.82 71.68 H2 weight percent 0.045 0.062 Cl weight percent 0O092 0.195 C2 weight percent 0.060 0.253 C3 volume percent 0.44 1.27 C4 volume percent 9.34 12.76 C5 ~ gasoline volume percent 38.64 60.43 Coke weight percent 1.14 1.39 It is apparent from the data that a catalyst containing as little as 0.1% magnesium gives excellent conversions.

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Claims (8)

WHAT IS CLAIMED IS:

1. A method for preparing a stable crystalline zeolite which comprises:
a. exchanging a sodium Type Y zeolite having a silica to alumina ratio of about 3.5 to 6 with an ammonium salt to reduce the Na2O content thereof to less than 4 percent by weight;
b. exchanging said zeolite with a solution of rare earth ions to provide a rare earth oxide content of about 0.5 to 4 percent by weight;
c. washing said zeolite to remove excess salts;
d. heating said zeolite to a temperature of about 700 to 1600°F;
e. contacting said zeolite with a dilute solution of a mineral acid to remove alumina there-from and thereby increase the silica to alumina ratio to a range of about 7 to 20; and f. exchanging the zeolite of step e. with a solution of metal ions selected from the group consisting of rare earth and magnesium ions to impart a concentration of metal ions of from about 1 to 10 percent by weight.

2. The method of Claim 1 wherein the zeolite of step d. is exchanged with ammonium ions to reduce the Na2O content to less that 1 percent by weight.

3. The method of Claim 1 wherein the Na2O content of the zeolite is reduced to from about 2.5 to 3.5 percent by weight during the exchange of step a.

4. The method of Claim 1 wherein said dilute acid solution is dilute nitric acid.

5. A catalyst composition which comprises the zeolite prepared by the method of Claim lin an amount of from about 5 to 50 percent by weight admixed with an inorganic oxide matrix.

6. The catalyst composition of Claim 5 wherein said inorganic oxide matrix is selected from the group comprising clay, silica, alumina and silica-alumina hydrogel.

7. A method for catalytically cracking hydrocarbons which comprises contacting hydrocarbons with the catalyst prepared by the method of Claim 1 under catalytic cracking conditions, and recovering cracked hydrocarbons of lower molecular weight.

8. The zeolite prepared by the method of Claim 1.