CRACKING PROCESS AND CATALYST

Abstract: A catalyst suitable as an additive catalyst for fluid catalytic cracking is made by depositing 0.1 % to 2 % of Ga on ZSM-5 zeolite in (alkyl)ammonium form from a solution with pH in the range 1.5 to 3.5.

Description: CRACKING PROCESS AND CATALYST The present invention relates to fluid catalytic cracking of hydrocarbons, and to a catalyst suitable for use in such a process. Fluid catalytic cracking (FCC) is a well-known process for the conversion of higher boiling hydrocarbons into more valuable lower 5 boiling fractions, in particular gasoline. Various catalysts have been used for this process including catalysts based on various types of zeolite. The conventional cracking catalysts give relatively good yields of the desirable gasoline fraction. However, the quality of the 10 gasoline as measured by its octane number tends to be poor. There is a demand for gasoline fractions produced by catalytic cracking to have improved octane numbers. There are two octane number measurements which can be made on gasoline. One is Research Octane Number (or RON). The other is 15 Motor Octane Number (MON). In Europe in particular there is pressure to keep MON at a high value, but there is less pressure on maximizing RON. Any technique which enables the MON to be increased without an excessive fall in the amount of gasoline is particularly /c'.luable. 20 EP 259 155A proposes to improve the quality of gasoline produced by fluid catalytic cracking by using two catalysts. A conventional cracking catalyst based for example on zeolite X or Y is used together with a relatively smaller amount of an additive catalyst which is based on a zeolite, e.g. ZSM-5, differing from 25 that used in the conventional catalyst. The presence of such an additive improves the quality of the gasoline. There is a price to be paid. The gasoline yield, i.e. the proportion of the cracked product in the gasoline boiling range is decreased. There is thus a need to improve gasoline yields using additive catalysts, while still obtaining improved gasoline quality. EP 259 155A contains a brief reference, without supporting experimental evidence, to the possibility of introducing certain elements, including gallium, on to the additive catalyst so as to increase more feed to aromatics so as to improve the quality of the gasoline. We have now found that by selecting the correct quantity of gallium to be added to ZSM-5 zeolite catalyst and by adding it in a specific way increased amounts of gasoline are obtained with good octane performance. According to the present invention a process for making a catalyst suitable for use as an additive catalyst for _he fluid catalytic cracking of hydrocarbons comprises depositing on zeolite ZSM-5, which zeolite is in the (alkyl)ammonium form, a quantity of gallium in the range 0.1% to 2% by weight based on the weight of ZSM-5, from a solution with a pH in the range 1.5 to 3.5. According to another aspect of the present invention a process for cracking a hydrocarbon feed to give gasoline in the presence of a fluidized bed of a catalyst based on ZSM-5 zeolite, is characterised in that gallium has been deposited on the ZSM-5 zeolite, which zeolite is in (alkyl)ammonium form, from a solution of gallium ions with a pH in the range 1.5 to 3.5 in an amount in the range 0.1 to 2% by weight based on the weight of ZSM-5. The present invention is particularly suitable for use in a catalytic cracking process using two zeolite catalysts with a major amount of a first (or main) catalyst based on a zeolite and a minor amount of a second (or additive) catalyst based on ZSM-5 catalyst. Preferably, the additive catalyst is present in an amount which is 0.5 to 20% by weight of the total catalyst. In zeolite-based catalysts for fluid catalytic cracking the zeolite usually only forms part of the total catalyst partic --. which contains an amorphous matrix, e.g. alumina, and clay binders in addition to the zeolite. The ZSM-5 zeolite may for example form from 5 to 60% by weight of the catalyst particle. The production of zeolite-based catalysts for use in fluid catalytic cracking is carried out on a large scale commercially. It is not therefore necessary to give detailed information on catalyst preparation techniques or desired particle sizes. It is desirable to introduce gallium on to the ZSM-5 prior to binding the ZSM-5 with any matrix, alumina or clay. ZSM-5 is usually supplied in the hydrogen form. Before deposition of the gallium the ZSM-5 zeolite is converted to the (alkyl)ammonium form. By "(alkyl) mmonium" it is meant throughout this specification to be the ammonium ion itself and derivatives of the ammonium ion resulting from the substitution of hydrogen atoms by alkyl groups. Where the ZSM-5 zeolite is supplied in say the acid form it may be converted to the (alkyl)ammonium form by heating in an aqueous solution containing (alkyl)ammonium ions. Thus where it is desired to exchange the ZSM-5 with ammonium ions, the ZSM-5 may be refluxed with an aqueous solution of an ammonium salt, e.g. ammonium nitrate. The solution is preferably a relatively concentrated one containing a 1.5 to 2M solution of the ammonium salt (assuming that the salt has sufficient solubility). It may be desirable to adjust the pH to provide an alkaline solution by the addition of an (alkyl)ammonium hydroxide. The (alkyl)ammonium exchanged ZSM-5 is preferably washed with large quantities of water to remove unexchanged material, and then dried, for example at temperatures in the range 100-150°C. Suitable techniques for introducing the gallium are doping or impregnation from an aqueous or organic gallium solution. However it is undesirable to deposit the gallium from excessively acid solutions and thus the solution used must have a pH in the range 1.5 to 3.5, preferably not below 2. The quantity of gallium introduced on to the ZSM-5 is in the range 0.1 to 2.0% based on the weight of ZSM-5, preferably 0.3 to 1.0%. Aqueous solutions of gallium nitrate may be used to deposit the gallium. Such solutions have an acid pH, e.g. about 2.3. After deposition of the gallium the resulting product is dried, for example at temperatures in the range 100-150*C. The invention will now be described with reference to the following experiments, in which experiments identified by numbers are examples of the invention and experiments identified by letters are comparative tests which are not according to the invention. The general techniques set out below were used in the experiments. Steam Deactivation: Prior to evaluation catalyst samples were deactivated in a fluidised bed steamer at 816"C for 5 hours under 100% steam. (In a commercial cracking reactor the catalyst charge will consist of a mixture of relatively old catalyst and a small quantity of fresh catalyst. The steam deactivation step is carried out to produce a material for testing which will be comparable with the catalyst mixture used commercially). Performance Evaluation: Catalysts were evaluated for performance using a modified version of the ASTM MAT (microactivity test). This test has been described in the public literature (FCC Catalyst Selection, G D L Carter and G McElhiney, Hydrocarbon Processing Sept 1989). By repeating the test at different catalyst/oil ratios between 3 and 6 data was collected over a range of conversion levels. Plots of yield versus conversion for components of the mass balance were interpolated at 67% conversion to give a yield structure suitable for comparing catalyst εelectivities. Octane values were obtained from a GC octane correlation developed following the method of Anderson Sharkey and Walsh (J Inst pet vol March 1972) specifically for catalytically cracked gasoline. Examples 1-4 Zeolite ZSM-5 in the hydrogen form (500g) was refluxed for 2 hours in aqueous 2M ammonium nitrate solution (5 litres) whose pH had been adjusted to pH 9.0 with cone, aqueous ammonia. The resulting ammonium-exchanged zeolite was then filtered off and washed with distilled water (20 litres) and dried at 120*C. A gallium nitrate stock solution with a gallium concentration of 0.05g/ml was prepared by dissolving gallium nitrate in distilled water. This solution had a pH of 2.3. A solution for impregnating the ZSM-5 zeolite was prepared by diluting the stock solution with distilled water. The ZSM-5 zeolite (250 mg) was impregnated with the diluted solution (200 ml). The degree of dilution is selected to give the desired amount of gallium on the zeolite (as indicated in Table 1). The resulting paste was dried at 120*C for 17 hours. The ZSM-5 was then bound into catalyst particles by a commercially established procedure. The ZSM-5 catalyst particles were mixed with a commercial catalytic cracking base catalyst to give 5% by weight of the ZSM-5 catalyst in the total catalyst. The resulting mixtures were tested using the steam deactivators and performance evaluator procedures described earlier. The results are shown in Table 1. TABLE 1 In the above table DG is dry gas (methane, C ) LPG is liquefied petroleum gases (propane, butane) CCS is cracked catalytic spirit (gasoline) LCO is light cycle oil, and HCO is heavy cycle oil. Comparative Test A A comparative test was carried out as in Examples 3-6, except that no additive catalyst containing ZSM-5 was used. The results are shown in Table 2. Comparative Test B This is a comparative test not according to the invention. An experiment was carried out'as in Examples 1-4 except that the additive catalyst was prepared from ZSM-5 in the hydrogen form which had not been subjected to any further treatment before being incorporated in the additive catalyst. Comparative Test C A comparative test was carried out as in Examples 1-4 except that the pH of the gallium nitrate stock solution was adjusted to 1 by the addition of nitric acid. The results are shown in Table 2. Comparative Test D A comparative test was carried out as in Examples 1-4 except that the ZSM-5 was not converted from the hydrogen form to the ammonium form before the gallium was deposited. The results are shown in Table 2. TABLE 2 A comparison of the results for Tests A and B shows the l eduction in gasoline yield and increase in quality obtained using ar. additive catalysts. A comparison of the results for Test B and those shown in Table 1 for Examples 1-4 shows the increased gasoline yield obtained when the additive catalyst contains gallium, while still remaining an improved gasoline quality. A comparison of the results for Test B and Test A shows that the use of a gallium-containing additive catalyst not prepared in accordance with the invention gives no increase in gasoline yield compared with an additive catalyst which does not contain gallittm. The presence of gallium is not in itself sufficient to give good results. A comparison of the results for Test C with those ' for Example 2, both of which use 0.5% gallium, shows the higher gasoline yields obtained when gallium is deposited by the method of the invention. A comparison of the results for Test B (using an additive catalyst which does not contain Ga) with the results for Examples 1-4 shows that incorporating Ga in accordance with the invention gives an increased gasoline yield. There is a decrease in octane number, but the decrease in the MON is relatively small and is smaller than the decrease in RON. As explained earlier in a significant part of the world market the need to obtain a high MON is more important than the need to obtain a high RON.

Claims: Claims : 1. A process for making a catalyst suitable for use as an additive catalyst for the fluid catalytic cracking of hydrocarbons which comprises depositing on zeolite ZSM-5, which zeolite is in the (alkyl)ammonium form, a quantity of gallium in the range 0.1% to 2% by weight based on the weight of ZSM-5, from a solution with a pH in the range 1.5 to 3.5. 2. A process according to Claim 1 wherein the gallium is deposited on the ZSM-5 before binding the ZSM-5 into a catalyst particle. 3. A process according to either of Claims 1 or 2 wherein the quantity of gallium deposited on the ZSM-5 is in the range 0.3 to 1% by weight of the ZSM-5. 4. A catalyst suitable for use as an additive catalyst in the fluid catalytic cracking of hydrocarbons which contains 5 to 60% by weight of ZSM-5 on which gallium has been deposited by a process according to any one of Claims 1 to 3. 5. A process for cracking a hydrocarbon feed to give gasoline in the presence of a fluidised bed of a catalyst based on ZSM-5 zeolite, is characterised in that gallium has been deposited on the ZSM-5 zeolite in (alkyl)ammonium form from a solution of gallium ions with a pH in the range 1.5 to 3.5 in an amount in the range 0.1% to 2% by weight based on weight of ZSM-5. 6. A process according to Claim 5 wherein the catalyst based on ZSM-5 zeolite on which gallium has been deposited is an additive catalyst used in a minor amount together with a major amount of a main cracking catalyst. 7. A process according to Claim 6 wherein the additive catalyst is present in an amount which is 0.5% to 20% by weight of total catalyst.

Inventors: AITCHISON DAVID WILLIAM, GELSTHORPE MICHAEL ROBERT, SHARP CHRISTOPHER, WEEKS SIMON ANTHONY, AITCHISON, DAVID, WILLIAM, GELSTHORPE, MICHAEL, ROBERT, SHARP, CHRISTOPHER, WEEKS, SIMON, ANTHONY
Applicants: BRITISH PETROLEUM CO PLC, THE BRITISH PETROLEUM COMPANY PLC
Application year: 1991
Main classification: C10G11
IPC codes: B01J29, C10G11