CRACKING CATALYST AND USE THEREOF WITH SULPHUR-CONTAINING FEEDS

Abstract: A cracking catalyst composition co-impregnated with rare earth oxide and with either chromium, manganese, cobalt, nickel or platinum group metals. Such catalyst com­ positions, when used in catalytic cracking processes, result in significant reductions of sulfur content in the coke produced thereby, in turn significantly reducing sulfur oxide (SO x ) emission in the regeneration stack gases.

Description: This invention relates to a cracking catalyst and to its use in cracking sulphur-containing hydrocarbon feedstocks to reduce the emission of sulfur oxides (SOx) in the regenerator stack gases. In the regenerator of a catalytic cracking unit coke is burned off the catalyst to restore catalyst activity. The sulfur in the coke is converted to S02 and S03 (SOx), the emission of which into the atmosphere must be minimized. There has now been discovered a cracking catalyst composition co-impregnated with a combination of a rare earth oxide and with either chromium, manganese, cobalt, nickel or platinum group metals (Ru, Rh, Pd, Os, Ir and Pt). The starting composition is preferably a commercially manufactured material containing REY or REX crystalline aluminosilicate in a suitable matrix, such as the catalyst described in U.S. Specification 3,556,988. The new cracking catalyst can be employed in fluidized or moving bed catalytic cracking units well known to the art and their use therein results in lowering of the sulfur content in the coke deposits produced on the catalyst material and thus of the S02 and S03 (SOx) content of the regenerator flue gas. According to the invention, therefore, a cracking catalyst, comprising a composite of a rare earth exchanged crystalline aluminosilicate and a matrix wnich composite contains impregnated rare earth oxide in an amount between l and 10 weight percent of its exchange capacity, is characterized by further containing, co-impregnated with said rare earth oxides between 0.05 and 5 weight percent (expressed as oxide) of chranium, manganese, cobalt or nickel, or between 0.1 and 200 pp of a platinum group metal. The platinum group metal is preferably platinum itself, and is usually present in an amount between 0.5 and 10 ppm, while the amount of the chromium, manganese, cobalt or nickel is usually between 0.1 and 2 weight percent (expressed as oxide). As for the balance of the composition, the amount of impregnated rare earth oxide is preferably between 1 and 5 weight percent of said exchange capacity, the crystalline aluminosilicate is preferably zeolite Y, and the matrix in a favoured embodiment comprises silica, clay and zirconia. Suitable crystalline aluminosilicates, and their matrixing, are described in U.S. Specifications 3,140,249 and 3,140,253. Representative crystalline aluminosilicates suitable for the present invention include those natural and synthetic crystalline aluminosilicates having uniform pores of a diameter preferably between about 3 and 15 Angstrom units. Such crystalline aluminosilicates include zeolite A (U.S. Patent 2,882,243), zeolite X (U.S. Patent 2,882,244), zeolite Y (U.S. Patent 3,130,007), zeolite ZK-5 (U.S. Patent 3,247,195), zeolite ZK-4 (U.S. Patent 3,314,752) zeolite ZSM-5 (U.S. Patent 3,702,886), zeolite ZSM-11 (U.S. Patent 3,709,979) and zeolite ZSM-12 (U.S. Patent 3,832,449), synthetic mordenite, dealuminized synthetic mordenite merely to name a few, as well as naturally occurring zeolites including chabazite, faujasite, mordenite, and the like. Crystalline aluminosilicates having pore diameters between about 3 and 5 Angstrom units may be suitable for shape selective conversion catalysis, while crystalline aluminosilicates having pore diameter between about 6 and 15 Angstrom units are preferred by hydrocarbon conversion such as catalytic cracking and the like. Preferred crystalline aluminosilicates include the synthetic faujasite zeolites X and Y, with particular preference being accorded zeolite Y. High catalytic activity may be imparted to the zeolite by base exchanging alkali metal aluminosilicate partlcles - either before or after dispersion thereof in the matrix - with a base-exchange solution containing ions selected from the group consisting of cations of elements of Groups IB-VIl of the Periodic Table, hydrogen, and hydrogen precursors, including mixtures thereof with one another, in addition to rare earth exchange. hydrogen precursors such as ammonia and ammonium salts, typically undergo, upon heating degradation to hydrogen cations in contact with aluminosilicates. Suitable methods of base exchange are described in the aforenoted U.S. Patents 3,140,249 and 3,140,253. Where an alkali metal aluminosilicate is employed initially, it is essential to base exchange either the aluminosilicate particles before or after compositing with the matrix to reduce the sodium content of the final product to less than about 4% by weight and preferably less than 1% by weight. The sodium content of the final composite is essentially less than 1% by weight. Such compositions provide high catalytic activity when zeolite Y or zeolite X is the crystalline aluminosilicate component. A wide variety of rare earth compounds can be employed with facility as a source of rare earth ion or impregnant. Operable compounds include rare earth chlorides, bromides, iodides, carbonates, bicarbonates, sulfates, sulfides, thiocyanates, peroxysulfates, acetates, benzoates, citrates, nitrates, formates, propionates, butylrates, valerates, lactates, malanates, oxalates, palmitates, hydroxides, tartrates, and the like. The only limitation on the particular rare earth metal salt or salts employed is that it be sufficiently soluble in the fluid medium in which it is used to give the necessary rare earth ion transfer. The preferred rare earth salts are the chlorides, nitrates and sulfates. Representative of the rare earth metals are cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysoprosium, holmium, erbium, thulium, scandium, yttrium, and lutecium. The rare earth metal salts employed can either be the salt of a single rare earth metal or mixtures of rare earth metals, such as rare earth chlorides or didymium chlorides. As hereinafter referred to, a rare earth chloride solution is a mixture of rare earth chlorides consisting essentially of the chlorides of lanthanum, cerium, neodymium and praseodymium with minor amounts of samarium, gadolinium and yttrium. Rare earth chloride solutions are commercially available and the ones specifically referred to in the examples contain the chlorides of the rare earth mixture having the relative composition cerium (as CeO2) 48% by weight, lanthanum (as La203) 24% by weight, praseodymium (as Pr6011) 5% by weight, neodymium (as Nd203) 17% by weight, samarium (as Sm203) 3% by weight, gadolinium (as Gd203) 2% by weight, and other rare earth oxides 0.8% by weight. Didymium chloride is also a mixture of rare earth chlorides but having a lower cerium content. It consists of the following rare earths determined as oxides: lanthanum 45-56% by weight, cerium 1-2% by weight, praseodymium 9-10% by weight, neodymium 32-33% by weight, samarium 5-7% by weight, gadolinium 3-4% by weight, yttrium 0.4% by weight, and other rare earths 1-2% by weight. It is to be understood that other mixtures of rare earth are also applicable for the preparation of the novel compositions of this invention, although lanthanum, neodymium, praseodymium, samarium and gadolinium as well as mixtures of rare earth cations containing a predominant amount of one or more of the above cations are preferred since these metals provide optimum activity for hydrocarbon conversion, including catalytic cracking. The base catalyst used in one preferred embodiment of the invention contains 10% REY in a silica-clay-zirconia matrix. It was found, in accord with the invention, that when a base catalyst is co-impregnated with a combination of rare earth oxide and with either Cr203, MnO, CoO or NiO, the sulfur content in coke produced during cracking is reduced about 35-40%. The term "co-impregnated" is defined as impregnation of the rare earth and metals concurrently and not consecutively onto the base matrIa1. In order to more fully illustrate the nature of the invention and the manner of practicing same, the following nonlimitative examples are offered. Examples 1-10 The base catalyst (Example 1) used in these studies was a commercially manufactured catalyst containing 10% REY in a matrix consisting of 57% SiO2 2% ZrO2 andi% Al203 that had been post exch-;ed with rare earth chloride and contained 2.2 wt percent t±. The method of manufacture has been detailed in Patent 3,556,988. The base catalyst was impregnated with a solution containing both rare earth chloride and an additional metal salt. The impregnation was performed with a volume of solution just sufficient to fill the catalyst pores. The rare earth chloride (RECl3*6H2O) had a rare earth distribution of 24% La203, 48% CeO2, 5K Pr6011, 17% Md2O3, 3% Sm203, 2% Gd203, 0.2% Y203 and 0.8% other oxides. The catalysts prepared, the impregnating salts and relevant analysis are given in Table 1. After impregnation, each catalyst was dried in air for 16 hours at 25O0F. Each catalyst was subsequently steam-treated for 4 hours at 1400F with 100e,/ steam at 0 psig in a fluidized bed. The steamed catalysts were used to crack a high-sulfur gas oi;, the properties of which are given in Table 2, in a fixed fluidized bed at 9200F, 3 C/O, 8.3 WHSV. The product distributions obtained are given in Table 3. The percent sulfur in coke was determined by oxidizing the coke-containing spent catalyst in a stream of oxygen at about 11000F and passing the effluent gas through a 3% solution of hydrogen peroxide in water, thus converting S02 to S03 and absorbing all of the SO3. The sulfate so formed was titrated as sulfuric acid with Standard base (NaOH). TABLE 1 Ex. No. Metals Impregnated Salts for Impregantion RE2O3, % wt. Metal or Metal Oxide Content 1 Base - - 2.2 0 2 RE2O3, Cr2O3 RECl3#6H2O Cr(NO3)3#6H2O 3.4 0.28% Cr2O3 3 RE2O3, MnO RECl3#6H2O MnCl2#4H2O 3.4 0.28% MnO 4 RE2O3, Pd RECl3#6H2O Pd(NO3)2 3.6 0.02% Pd 5 RE2O3, Pt RECl3#6H2O Pt(NH3)4Cl2 3.1 0.5 ppm Pt 6 RE2O3, Pt RECl3#6H2O Pt(NH3)4Cl2 3.1 2 ppm Pt 7 RE2O3, MgO RECl3#6H2O Mg(NO3)2#6H2O 3.6 0.42% MgO 8 RE2O3, CoO RECl3#6H2O Co(NO3)2#6H2O 3.6 0.02% CoO 9 RE2O3, NiO RECl3#6H2O Ni(NO3)2#6H2O 3.4 0.125% NiO 10 RE2O3 RECl3#6H2O 3.5 0 TABLE 2 High-Sulfur Gas Oil Gravity, API 23.4 Sulfur, % Wt. 2.08 Nitrogen, % Wt. 0.10 Basic N, % Wt. 0.035 Conradson Carbon, Wt. % 0.28 Hydrogen, % Wt. 12.1 MW 332 Aniline Point, F 161 Bromine No. 6.0 R.I. at 70 C 1.4900 Sp. Grav., 60 F 0.9172 Paraffins, % Wt. 21.3 Naphthenes, % Wt. 27.8 Aromatics, % Wt. 50.9 CA 17.3 TABLE 3 Example No. 1 2 3 4 5 6 7 8 9 10 RE2O3 RE2O3, RE2O3, RE2O3, RE2O3, RE2O3, RE2O3, RE2O3, RE2O3. Impregnated Metals (Base) Cr2O3 MnO Pd 0.5 2 ppm MgO CoO NiO ppm Pt Pt Conversion, % Vol 69.2 68.4 68.4 64.3 67.0 68.9 62.2 65.9 61.4 68.9 C5+ Casoline, % Vol 58.3 59.6 57.4 55.6 55.4 56.6 56.0 58.7 50.6 39.2 Total C4'M, % Vol 11.5 11.5 9.6 9.7 12.5 13.0 9.3 9.5 8.3 12.7 Dry Gan, % Wt 6.8 6.0 5.4 5.6 6.4 6.3 5.2 5.5 6.0 6.4 Coke, % Wt 3.5 3.1 2.9 3.9 3.9 3.5 2.5 3.1 5.0 3.2 Hydrogen, % Wt 0.08 0.03 0.03 0.22 0.05 0.05 0.04 0.03 0.70 0.03 H2S, % Wt 0.76 0.77 0.78 0.79 0.77 0.78 0.73 0.73 0.78 0.70 % S in Coke (S/C X100) 3.9 1.8 1.9 2.5 2.3 2.5 2.0 2.4 2.1 2.8 Comparison of Example 1 with Example 2 shows that a substantial reduction of S in coke is obtained with a combination of Cr203 and rare earth. Thus, SOx emissions substantial increase in gasoline yield. In the case of xs (Example 3) or CoO (Example 8) combined with rare earth, reduction of SOx emissions are 60 and 45% respectively witch little or no loss of gasoline yield. However, in both cases, catalyst stability is moderately reduced, as evidenced by the lower conversion after steaming. The combination of platinum group metals with rare earth shows a substantial reduction of S in coke (Examples 4, 5, 6 vs Example 1). The use of such catalysts in combination with complete CO combustion regeneration in an FCC unit would result in both lower S in coke and lower Coke yields and there are substantially lower SOx emissions. Less desirable effects are observed for other metals. Thus, MgO (Example 7) reduces the S in coke, but this effect is accompanied by loss of stability. Nickel oxide (Example 9) also reduces S in coke, but substantially increases both hydrogen and coke yields. It is to be noted that in all cases in which the S in coke is reduced, the H2S yield shows no increase, indicating that the S not incorporated in the coke remains in liquid products, probably the heavy cycle oil.

Claims: WHAT WE CLAIM IS: 1. A cracking. catalyst, comprising a composite of a rare earth exchanged crystalline aluminosilicate and a matrix which composite contains impregnated rare earth oxide in an amount between 1 and 10 weight percent of its exchange capacity, characterized by further containing, co-impregnated with said rare earth oxide, between 0.05 and 5 weight percent (expressed as oxide) of chromium, manganese, cobalt or nickel, or between 0.1 and 200 ppm of a platinum group metal. 2. A catalyst according to Claim 1 wherein the platinum group metal is platinum itself. 3. A catalyst according to Claim 1 wherein the amount of chromium, manganese, cobalt or nickel is between 0.1 and 2 weight percent (expressed as oxide). 4. A catalyst according to Claim 1 or Claim 2 wherein the amount of platinum group metal is between 0.5 and 10 ppm. 5. A catalyst according to any preceding claim wherein the amount of impregnated rare earth oxide is between 1 and 5 weight percent of said exchange capacity. 6; A catalyst according to any preceding claim wherein said crystalline aluminosilicate is zeolite Y. 7. A catalyst according to any preceding claim wherein said matrix comprises silica, clay and zirconia. 8. A process for cracking a sulphur-containing hydrocarbon feedstock which comprises contacting the same under cracking conditions with a catalyst in accordance with any of Claims 1 to 7.

Inventors: CHESTER, ARTHUR WARREN, MCVEIGH, HARRY ALLEN, STOVER, WILLIAM ALBERT
Applicants: MOBIL OIL CORPORATION
Application year: 1979
Main classification: C10G11
IPC codes: C10G11, B01J29