PROCESS FOR REGENERATING SPENT HYDROFINING CATALYSTS

Abstract: Spent Hydrofining catalysts (e.g. comprising Co and Mo supported on alumina) are regenerated by contact with an aqueous solution of a heteropoly acid of general for­ mula H x (YM₁₂O₄₀) where Y is at least one element selected from phosphorus, silicon, titanium, germanium, arsenic, zirconium, thorium and cerium; M is at least one of Mo, W, Nb, and Ta, x is 3 when Y is pentavalent and 4 when Y is tetravalent. Thereafter, the catalyst is calcined to remove coke. The heteropoly acid removes from the spent catalyst metals (particularly V, Ni and Co) which are deposited dur­ ing hydrofining and reduce its efficacy, without substan­ tially affecting the support. The heteropoly acid solution may contain up to 50 wt. % (based on the heteropoly acid) of H₂O₂ to enhance the removal of vanadium. The spent catalyst may be pre-sulfided before contact with the heteropoly acid to enhance the removal of vanadium.

Description: "PROCESS FOR REGENERATING SPENT HYDROFIXING CATALYSTS" The present invention relates to a process for regenerating spent catalysts used in hydrofining operations, and more particularly, to a process for the regeneration of spent catalysts employed in hydro desuifurization and hydrodenitrogenation by a process which includes treatment with a heteropoly acid. In this specification, the Periodic Classification of the Elements is that devised by the Fisher Scientific Company, Catalogue No. 5-702-10 appearing in "The Condensed Chemical Dictionary". Edited by A. & E. Rose (Reinhold), 7th Edition. The abbreviation "HDSt' represents hydrodesulfurization, and "GO-FINING" is a trade name for thc hydrofining of heavier feedstocks such as gas oils. As is well-known, hydrodesulfurization of, e.g., petroleum fractions, is usually carried out employing an alumina catalyst support impregnated with Group VIB and VIII metals such as molybdenum and cobalt. While such catalysts are extremely useful in reducing sulfur content, the effectiveness of these catalysts is diminished during the course of processing as a result of two problems. First, carboy residues (coke) deposit on the surface of the catalyst, thereby reducing the effective surface area and pore size for catalytic activity. Second, heavy metals in the feedstock, such as nickel, and more importantly, vanadium, tend to poison the catalyst, again resulting in reduced catalytic activity. During the course of processing, the temperature is generally increased at a predetermined rate in order to compensate for the coking and poisoning effects. however, as the temperature is increased, a greater percentage of feedstock is cracked, thereby resulting in a decrease of desirable product. Further, the increase in processing temperature results in an increase in the deposition rate of carbon residues. Regeneration of spent catalysts has been th± subject of much investigation and, consequently, a number of approaches for regenerating hydrodesulfurization catalysts have been developed. In particular, acidic media, such as mineral acids, anhydrous HF, oxalic acid and other carboxylic acids and acidified amine solutions, and oxidizing media, such as hydrogen peroxide, have been employed. However, such methods either (1) result in removal of unacceptable amounts of catalytically active metals, e.g., cobalt and molybdcnuin, as well as some solubilization of the support material, e.g., alumina, or (2) do not regenerate a sufficiently highly degree of catalytic activity, so that catalytic activity of te regenerated catalyst is considerably inferior to that of fresh catalyst. A sulfurous atmosphera at a pressure of at least 0.10 atmospheres and at a temperature of between 400 and 825 C has also been employed to regenerate the spent metal catalyst; see U.S. Patent 4,014,815, issued March 29, 1977. The process is employed for a time sufficient for the selective formation of sulfides of carbon and vanadium, which sulfides are characterized by having a high volatility and solubility in the sulfurous atmosphere and are selectively removed from the catalyst at the temperature of the press. While the disclosed process is useful in regeneration of spent catalysts, it requires and/or involves highly corrosive conditions and formation of very specific volatile sulfide species. The temperatures required for vanadium removal at acceptable rates may damage the catalyst support. In accordance with the invention, spent catalyst which has been used in hydrofining of hydrocarbon feedstock is regenerated by contacting the spent catalyst with a solution of a heteropoly acid as defined below containing 0 to 50 wt.% hydrogen peroxide, based on the concentration of the heteropoly acid, with prior optional contaCt of the catalyst with a gaseous sulfur-containing reagent having or providing a partial pressure of sulfur of at least about 0.01 atmospheres at a temperature of up to 6500C. Heteropoly acide are defined by the following general formula Hx (YM12O40), where Y is at least one element selected from phosphorus, silicon, titanium, germanium, arsenic, zirconium, thorium and cerium; M is at least one element selected from molybdenum, tungsten, niobium and tantalum and x is 3 when Y is pentavalent (P, As) and x is 4 when Y is tetravalent (Si, Ti, Ge, Zr, Ce, Th). Up to one half of M may be replaced by at least one element selected from nickel, cobalt and vanadium. During recrystallization of a heteropoly acid, a hydrated species of the acid is usuaily obtained, as is well-known. The number of water molecules depends on the particular process of recrystallization of the heteropoly acid, and while typically ranging from about 5 to 50, is not critical. Examples of heteropoly acids useful in the practice of the invention include molybdophosphoric acid, 113(P'rio12040), molybdosilicic acid, H4(SiMol2040), tungstosilicic acid, H4(SiW12040), and tungstophosphoric acid, H3(PW12040) For Co-Mo/A1203 catalysts, a molybdenum-containing heteropoly acid is preferred, since it has been found that heteropoly acid treatment incorporates molybdenum in the A1203 support in a dispersed manner without phosphorus overloading. The addition of hydrogen peroxide to the heteropoly acid is found not to alter this result. An example of a heteropoly acid particularly useful in the practice of the invention is molybdophosphoric acid (}SA) having the general formula H3(PNo12040).nH2O, for example, H3(PMol2040).36H20. The process results in the extraction of from 60 to 100% vanadium, at least 90% nickel and about 50% cobalt, with essentially no loss of molybdenum and aluminum (from the alumina support) and with preservation of the structural integrity of the support. Extraction of metals is accompanied by partial removal of sulfur and by substantial increase in pore volume and surface area. Additional processing by doping the deijetallized catalyst with cobalt or nickel followed by calcination markedly promotes carbon decoking, further sulfur removal and additional increase in surface area and pore volume. Hydrofining activity and product selectivity of the regenerated spent catalyst is substantially the same as that of fresh catalyst. Regeneration of substantially complete catalytic activity in spent hydrodesulfurization catalysts is accomplished by contacting spent catalyst with a heteropoly acid under mild conditions of pH, temperature and agitation. Optionally, a solution of the heteropoly acid containing up to about 50 wt.% of hydrogen peroxide, based on the concentration of¯the acid, may be employed. Also optionally, the spent catalyst may be treated first with a gaseous sulfur-containing reagent. The hydrodesulfurization catalysts which may be treated in accordance with the invention include those supported catalysts having Group VIB or VIII metals, including nickel, cobalt, tungsten and molybdenum and combinations of these. The metals may be in elemental, oxide or sulfide form or any combination thereof. The support may be any refractory oxide or other inert support, including alumina. The spent catalyst may be pre-cleaned with an organic solvent to remove contaminating surface oils prior to or during treatment in accordance with the inven- tion. The organic solvent can vary over a wide range of hydrocarbons comprising aliphatics, aromatics, cycloparaf fins or mixtures of these, preferably boiling below about 250 C. Examples of suitable organic solvents include decane, benzene, toluene, xylene, cyclohexane, and tetralin. Cracked naphtha can also be used. The object of the so' ven. extraction process is to render the surface and the bulk of the catalyst roe accessible to the heteropoly acid solution, and theeby effect efficient removal of the contaminating metals, e.g., vanadium and nickel. The spent. catalyst is optionally sulfided with a sulfur-containing reagent having a partial pressure of sulfur of at least about O.01 atmospheres and preferably at least about 0.1 to 1 atmospheres at the processing tempera- ture given below. An example of a suitable sulfur-contain- ing reagent is H2S, either pure or diluted to no less than about 15% by an active gas such as hydrogen or an inert gas such as nitrogen or argon. The temperature of the sulfiding process ray be carried out at any temperature from ambient up to about 650 C and preferably about 3000 to 500 C, Aost preferably, the temperature should be at least about 425 C for sesqulsulfide (V2S3) formation. The sesquinsulfide forms more rapidly than VS4, which is formed at lower temperatures. The time of the presulfiding process preferably ranges from about 1 to 4 hours, with shorter times being associated with higher temperatures. For example, presulfiding spent HDS catalyst in H2S (neat) for 4 hours at 500 C results in substantially complete conversion of wanadiuni species such as V02+, VS4, VO SO to vanadium sulfide. The spent catalyst, whether presulfided or rot, is contacted with a heteropoly acid under rild conditions of pH, temperature and agitation, employing any of the contacting processes usually used in petroleum process ing, such as in a stationary phase or mildly agitated condition or in a plug flow reactor or any continuous moving concurrent or countercurrent liquid-solid bed reactor. The temperature of the process ranges between ambient to about 80 C and preferably about 300 to 600C to maintain the stability and concentration of the heteropoly anion. An aqueous solution of the heteropoly acid is employed. The concentration of heteropoly acid in aqueous solution preferably ranges from about 0.1 to 25 wt.% and more preferably about 0.2 to 6 wt.%. The concentration of the heteropoly acid is chosen on the basis of the loading of the toxic metal contaminants, with higher concentrations being associated with higher concentrations of contaminants. The pH of the solution ranges from about 1 to 3, and preferably about 1.5 to 2.5, to maintain the stability of the heteropoly acid in solution. The spent catalyst is contacted with the heteropoly acid for about 4 to 200 hours and preferably about 1W; to 50 hours, depending upon the amount of metals to be removed. The longer times are associated with higher concentrations of contaminants. In general, the reaction is substantially complete in about 10 to 24 hours, depending onthe catalyst particulate size and the vanadium species present. The heteropoly acid may be optionally replaced with fresh solution at suitable intervals, such as about 10 hours, to accelerate removal of the contaminating metals. An aqueous solution of a heteropoly acid with hydrogen peroxide is most preferably employed. The con "a' centration or the hydrogen peroxide in tne soLutLonlrange from about 1 to 50 wt.% and preferably 3 to 15 wt.% and most preferably about 15 wt.%, based on the amount of heteropoly acid. Conveniently, the volume ratio of heteropoly acid to hydrogen peroxide is about 100;1 v/v, employing prediluted hydrogen peroxide to form a solution having the final concentration given above. The concentrations of the heteropoly acid and hydrogen peroxide are chosen on the basis of the loading of the toxic metal contaminants, with higher concentrations being associated with higher concentrations of contaminants. The use of hydrogen peroxide in conjunction t heteropoly acid Is particularly efficacious in removing certain vanadium species which are largely unaffected by other processes. For example, the combina- tion of molybdophosphoric acid and hydrogen peroxide results in the oxidation of compounds containing vanadyl species (V02+) by a factor of three times as compared with molybdophosphoric acid treatment alone. Such vanac:yl species are generally formed on the catalyst during the course of the hydrodesulfurization process and their removal is important. The presence of at least about 1 wt.% H2O2 iflciy be necessary to achieve the effect, while greater than about 50 wt.% H202 provides little additional benefit. WIthout subscribing to any particular theory, it appears that the hydrogen peroxide provides several benefits. First, hydrogen peroxide apparently helps maintain the heteropoly acid in the highest oxidation state. Othenvise, vanadium species, in being oxidized from lower to higher states, would reduce the heteropoly acid, thus adversely affecting its extracting capabilities. Second, hydrogen peroxide apparently assists in oxidizing V4+ to V51, VO2+ to V205 and V2S3 td VOSO4, all of which higher oxidation species are more soluble and hence more retractable by the heteropoly acid. Use of the heteropoly acid/hydrogen peroxide solution also results in a significant increase in both rate and extent of carbon radical generation. While a three-fold increase in carbon radical density accompanies treatment with a heteropoly acid along, such as molybdophosphoric acid, addition of hydrogen peroxide leads to a higher carbon radical level at a faster rate. The increased carbon radical level apparently indicates breaking of the carbon 1,crust" on the catalyst surface, again facilitating extraction of contaminating metals. The method disclosed above results in the extraction of about 60 to 100% vanadium, at least about 90% nickel and about 50/0 cobalt, together with substantial increase in both surface area and pore volume of the catalyst. The alumina-based support remains essentially unchanged. This process also results in molybdenum loading on the support in a-well-dispersed manner without aggre- gation or cluster formation. Surprisingly, excess phosphorus loading is avoided by the process of the invention. Finally, the extraction of vanadium, nickel and cobalt results in a substantial reduction in sulfur build-up in the catalyst. While not subscribing to any particular theory, it appears that the reduction is due to removal of sulfur in the form of oxysulfides, oxysulfites or oxysulfates of the metals. As described above, the process results in substantial removal of metals which tend two poison the catalyst, with consequent removal of other contaminants such as sulfur and concommitant regeneration of catalytic activity. However, it has also been found thatone-time (lx) impregnation of the catalyst with a cobalt salt following treatment with the heteropoly acid, followed by calcination at modified temperatures of about 450"C or less in air, results in the substantial removal of carbon, as well as further removal of sulfur, together with a further increase in pore volume and surface area of the catalyst, and accordingly is preferred. Cobalt impregnation may be accomplished using water soluble cobalt salts, preferably sulfur-free water soluble cobalt salts, such as cobalt nitrate and cobalt acetate. Impregnation may be done by the well-knoam technique of incipient wetness, adsorption from solution or evaporation of the salt onto the catalyst. Because of ease of operation, incipient wetness technique is preferred. The calcination is carried out for about 2 to 15 hours, preferably about 3 to 6 hours, in an dxidizing atmosphere, such as air, in order to maintain support integrity and to facilitate coke removal. The cobalt salt is oxidized with cobalt oxide and carbon is oxidized to gaseous oxides of carbon. Moderate calcination temperatures reduce the risk of formation of localized hot spots, which would otherwise result in fracture of the catalyst support. However, higher temperatures may be employed by carefully employing the oxygen content of the atmosphere, as is well-known in the art. A second (2x) cobalt impregnation followed by a second calcination under the conditions given above result in essentially complete removal of carbon and sulfur from the catalyst, and accordingly is most preferred. Analogous nickel salts may alternatively be employed to impregnate nickel in HDS catalysts such as Ni-Mo/A1203 Catalysts regenerated by molybdophosphoric acid in accordance with the foregoing process were tested for their hydrodesulfurization activity in a flow reactor at temperatures of 310 , 325" and 350"C; pressure of 3.1 MPa and liquid hourly space velocity (LHSV) of about 5.9 to 6.0. It was found that after the first cobalt impregnation and calcination, the catalyst exhibited about 75% HDS activity as compared to fresh commercial Co-Mo/A1203 catalyst. After the second cobalt impregnation and calcination, the HDS activity was nearly 105%, as compared with the fresh commercial catalyst. It is likely that by calcining for longer periods of time with a single cobalt impregnation, the hydrodesulfurization activity of the regenerated catalyst can be equally enhance Metals such as nickel, cobalt, vanadium and the like solubilized by the heteropoly acid or heteropoly acid/hydrogen peroxide solution can be recovered by conventional solvent extraction, ion exchange or chelation technology. Metals so recovered can be used in the impregnation process (e.g., Co and Co-Mo/A1203 catalysts) or for the manufacture of fresh catalysts. In place of cobalt salts, nickel salts can also be used to aid in coke burning and to provide catalyst containing primarily Ni-?Io/A1203, which are suitable for hydrodenitrogenation reaction in addition to possessing HDS activity. EXAMPLES Example 1 - Treatment of Spent Catalyst with Molybdo- phosphoric Acid. Spent Co-No/A1203 catalysts, used for hydrodesulfurization of Cold Lake crude, was regenerated The spent catalyst was small pore size, about 30 to 50 A average, and loaded with 0.5 to 0.8% nickel and 5 to 8% vanadium. The spent catalyst was first pre-cleaned with' benzene or toluene for 5 to 50 hours. Following this procedure, the catalyst was dried at 1000C under reduced pressure. The spent catalyst was then treated under the following conditions with molybdophosphoric acid (EXA): A 50 g sample of the spent Co-Mo catalyst was contacted with 500 ml of a 0.4% freshly prepared aqueous solution of dodecamolybdophosphoric acid having the formula H3(PM012040).24H20 and a pH of 2.0 to 2.5. The flask was maintained at 40 to 60"C on a rotary shaker at a mixing rate of 150 rpm for 90 to 120 hours. The rate of vanadium extraction was monitored by determining the vanadium content spectrophotometrically in filtered samples at intervals of 24 hours of incubation. The process was terminated when about 80% of the vanadium had been extracted from the catalyst. The percent elemental compositions of spent catalyst and catalyst regenerated by MPA treatment, lx cobalt impregnation, lx calcination (Runs 68, 71, 73 and 74) and 2x cobalt impregnation, 2x calcination (Run 76) are summarized in Table I. Cobalt impregnation was done by incipient wetness technique, emplcying cobalt acetate; calcination was carried out at 450 C for 2 hours in air. Following treatment, 70 to 80% vanadium, 98% nickel and abou 5 cobalt were extracted from the catalyst. There was no change in M: or A1203 concentration. In all batches, the alumina support remained unchanged, as indicated by aluminum crystallite size (determine- by X-ray diffraction pattern). The amount of sulfur and cat carbon reduction in samples treated with MPA alone and in samples lx and 2x calcined after lx and 2 x cobalt impregnation, respectively, are summarized in Tables II and III, respectively. Sulfur was analyzed by method ASTM D-1552-64 and cat carbon by a modified version of method ASTM E 30-56 using a combustion tube of 30.5 cms length with inlet and outlet temperatures of 11000C and a centre temperature of 1200 C. (The same analysis methods were employed for other examples). The hydro desulfurization activity of fresh catalyst, spent catalyst and spent catalyst regenerated by MPA treatment followed by lx cobalt impregnation and lx calcination (Runs 68, 71, 73 and 74) and 2x cobalt impregnation and 2x calcination (Run 76) are summarized in Table IV. Catalyst activity was determined by conversion of dibenzothiophene (DBT) to bip'enyl, hydrogenated biphenyl and H2S. For Runs 68, 71, 73 and 74, the HDS activity of the regenerated catalyst approached that of the fresh catalyst at temperatures of 3100, 3250 and 35000. For Run 76, the HDS activity at these temperatures was at least 32 greater than that of the fresh catalyst. The increase in surface area (in2/g) and pore volume (cm3/g) of spent catalyst compared with regenerated catalyst after (1) MPA treatment alone; (2) tBA treatment followed by lx cobalt impregnation, lx calcination; and (3) MPA treatment followed by 2x cobalt impregnation, 2x calcination are summarized in Table V. TABLE I PERCENT ELEMENTAL COMPOSITION OF SPENT AND MOLYBDPHOSPHORIC ACID (MPA) TREATED SPENT Co-Mo/Al2O3 CATALYST Cat (1) (2) (2) (2) (2) (3) Sample Carbon SO4-S CoO MoO3 V2O5 NiO Al2O3 %Total Spent catalyst 11.20 9.34 3.45 8.25 11.50 0.77 54.00 98.54 Run 68 (4) 8.20 4.88 1.34 20.58 4.50 -- 56.00 95.52 Run 68 (4,5) 3.06 1.92 2.91 19.40 4.17 -- 68.00 99.46 Run 71 (4) 8.20 4.88 1.35 17.94 5.75 -- 56.00 94.12 Run 71 (4,5) 0.39 1.89 2.98 23.74 6.44 -- 68.00 104.94 Run 73 (4) 8.20 4.88 1.34 19.06 5.01 -- 56.00 94.51 Run 73 (4,5) 1.58 1.92 3.15 20.55 5.76 -- 68.00 103.94 Run 74 (4) 8.40 2.52 1.26 19.06 4.50 -- 58.00 94.00 Run 74 (4,5,6) 0.23 1.29 6.16 24.52 4.74 -- 67.00 103.94 (ave.) Run 76 (4) 8.60 1.82 1.70 22.60 2.88 -- 56.00 93.64 Run 76 (4,5) 3.64 0.72 2.50 27.90 2.91 -- 68.00 105.51 Run 76 (4-7) 0.46 0.66 5.20 28.50 3.60 -- 68.70 107.72 (ave.) (1) Assumed 50% total sulfur as sulfate. (2) By X-ray fluorescence spectrophotometry. (3) According to a modified version of method no. E-120 (4) MPa treated. (5) MPA treated 1x cobalt impregnated (cobalt content 2-4%) and 1x calcined. (6) MPA treated 1x cobalt impregnated (cobalt content 4.80%) and 1x calcined. (7) MPA treated 2x cobalt impregnated (cobalt content 4-5%) and 2x calcined. TABLE II PERCENT SUFLUR REMOVED MOLYBDOPHOSPHORIC ACID (MPA) TREATED SPENT Co-Mo/Al2O3 CATALYST Residual Sulfur Residual Sulfur After 1 x Cobalt After 2x Cobalt % Inital After MPA % Impregnation & % Impregnation & Reduc Sample Sulfur Treatment Reduction 1x Calcination Reduction 2x Calcination tion Spent catalyst 6.25 -- 0 -- -- -- - Spent catalyst 6.25 -- -- 4.05 36.0 -- - Run 68 6.25 3.25 48 1.29 80.0 -- - Run 71 6.25 3.25 48 1.66 74.0 -- - Run 73 6.25 3.25 48 1.29 80.0 -- - Run 74 4.17 1.69 59 1.86 80.0 -- - Run 76 4.17 1.27 70 1.49 88.0 -- -- TABLE III EFFECT OF TYPE OF MIXING AND COBALT DOPING ON CAT-CARBON REMOVAL FROM SPENT AND MOLYBDOPHOSPHORIC ACID (MPA) TREATED Co-Mo/Al2O3 CATALYST Initial % Residual % %Cat Carbon Sample Cat Carbon Treatment Cat Carbon Removed Spent catalyst 11.20 None -- 0 Spent catalyst 11.20 Calcined 7.4 33 Spent catalyst 11.20 1x Co Impregnated and 3.06 73 1x Calcined Run 68 (1) 11.20 MPA Treated 8.20 27 Run 68 (1) 11.20 MPA Treatedk 1x Co Impregnated 3.10 72 and 1x Calcined Run 71 (2) 11.20 MPA Treatedk 1x Co Impregnated 0.39 99 and 1x Calcined Run 73 (1) 11.20 MPA Treatedk 1x Co Impregnated 1.58 87 and 1x Calcined Run 74 (2) 11.20 MPA Treatedk 1x Co Impregnated 0.23 98 and 1x Calcined Run 76 (1) 11.20 MPA Treatedk 1x Co Impregnated 3.71 69 and 1x Calcined Run 76 (1) 11.20 MPA Treatedk 1x Co Impregnated 0.45 96 and 1x Calcined (1) Mixing by shaking; (2) Mixing in concurrently moving liquid-solid bed. TABLE IV HYDRODESULFURIZATION ACTIVITY OF FRESH, SPENT AND MOLYBDOPHOSPHORIC (MPA) TREATED Co-Mo/Al2O3 CATALYST Mole Percent DBT Conversion Sample 310 C. 325 C. 350 C. Fresh catalyst (commercial) 49 77 95 Spent catalyst (1,3) 10 23 44 Run 68 (2,3) 44 65 91 Run 72 (2,4) 29 55 81 Run 73 (2,3) 31 55 81 Run 74 (2,4,5) (ave.) 31 55 81 Average of Runs 68,72,73 & 4 34 58 85 % Activity of fresh catalyst 69 76 89 Run 76 (3,6) 54 84(7) 98 % Activity of frech catalyst 110 110 103 (1) Solvent extracted, 1 x co impregnated and 1 x calcined. (2) MPA created, 1x Co impregnated and 1x calcined. Cobalt content 2-47. (3) Mixing by ahaking. (4) Mixing in concurrently moving liquid-solid bed. (5) Cobalt content 4.80%. (6) MTA created, 2x Co impregnated and 2x calcined. Cobalt content 4-5%. (7) Estimated by extrapolation of 310 and 350 C data. TABLE V SURFACE AREA (SA) AND PORE VOLUME (PV) OF SPENT AND MOLYBDOPHOSPHORIC ACID (MPA) TREATED Co-Mo/Al2O3 CATALYST After Aftzer After Initial MPA Treatment 1x Impregnation 2xImpregnation S2A. P.V. S2A. P.V. & 1x Calcination & 2x Calcination Sample mê/g cm /g mê/g cm /g S.A. mê/h P.V. cm /g S.A.mê/g P.V.cm /g Spent catalyst 136 0.24 -- -- -- -- -- - Run 68 136 0.24 201 0.34 227 0.43 -- - Run 71 136 0.24 200 0.31 204 0.36 -- - Run 73 136 0.24 196 0.35 222 0.43 -- - Run 74 166 0.27 233 0.43 239 0.49 -- - Run 76 131 0.25 211 0.36 291 0.52 275 0.59 Example 2 - Treatment of Spent Catalyst w2 th Flolyhdo p]osphori c Acid Spent Co-Mo/Al2O3 catalyst, used for hydrodesulfurization of Cold Lake crude, was regenerated. The spent catalyst wa,s large pore size, about 100 to 150 2 average, and highly loaded with metals (6% nickel and 18% vanadium). The spent catalyst was first pre-cleaned with toluene for 48 hours. Following this procedure, the catalyst was dried at 1000C under reduced pressure. The spent catalyst was then treated under the following conditions with molybdopliosphoric acid (PA): A 20 g sample of the solvent-extracted, spent Co-Mo catalyst was suspended in 1000 ml of 0.4X freshly prepared aqueous solution of dodecamolybdophosphoric acid of the formula H3(PNo12O40).24H20 at a pH 0 0 of 2.0 to 2.5. The system was maintained at 40 to 60 C on a rotary shaker at a mixing rate of 100 to 120 rpm. Samples at various intervals were withdrawn and clarified by sedimentation. The clarified fluids were monitored by atomic absorption spectroscopy for the determination of vanadium and nickel concentrations. The percent elemental compositions of spent catalyst and catalyst regenerated by tSA treatment, and 2x cobalt impregnation and 2x calcination are preserved in Table VI. After 90 to 120 hours, 70 to 80% vanadium, 93X nickel, and about 40Z cobalt were extracted from the catalyst. There was no change in Mo or A1203 concentration. Cobalt impregnation was done by incipient wetness technique, employing cobalt nitrate; calcination was carried out at 4000C for 2 hours in air. The percent sulfur and cat carbon removed after 2x cobalt impregnation and 2x calcination are presented in Tables VII and VIII, respectively. The demetallized, 2x cobalt impregnated and 2x calcined material exhibited 84, 86 and 99% hydrodesulfurization activity of a fresh, small pore, low metals loaded Co-lIo catalyst at temperatures of 310 , 325 and 350 C, respectively, as shown in Table IX. Th2 increase in surface area (m2/g) and pore volume (cm3/g) of'spent catalyst compared with regenerated catalyst after MPA treatment followed by 2x cobalt impregnation, 2x calcination are summarized in Table X. The low surface area and pore volume values indicated for Run 81 are attributed to an increase in pellet density due to heavy carbon and metals loading and high attrition of the catalyst under process condi- tions. The low pore volume obtained after TEA treatment cobalt impregnation and calcination is probably due to loading the pores by t2A and cobalt. It should be. noted that calcining the catalyst after cobalt impregnation increased the surface area by 36%, TABLE VI PERCENT ELEMENTAL COMPOSITION OF SPENT AND MOLYBDOPHOSPHORIC ACID (MPA) TREATED SPENT Co-Mo/Al2O3 CATALYST (1) (2) (2) (2) (2) (3) Sample Cat Carbon SO4-S CoO MoO3 V2O5 NiO Al2O3 % Total Spent catalyst 20.16 19.28 1.14 5.70 38.36 6.45 21.72 112.81 Run 81 (4) 0.54 1.15 7.12 51.0 8.03 0.16 50.11 118.11 (1) Assumed 50% total sulfur as sulfate. (2) By X-ray fluorescence spectrophotometry. (3) According to modified method No.ASTM-E120 (4) MPA treated, 2x cobalt impregnated (cobalt content 4-5%) und 2x calcined. TABLE VII PERCENT SULFUR REMOVED FROM MOLYBDOPHOSPHORIC ACID (MPA) TREATED SPENT Co-Mo/Al2O3 CATALYST Residual Sulfur After Initial After MPA % 2 x Cobalt Impregnation % Sample Sulfur Treatment Reduction and 2 x Calcination Reduction Spent catalyst 6.25 -- 0 -- - Run 81 19.28 14.70 24 1.15 94 TABLE VIII EFFECT OF TYPE OF MIXING AND COBALT DOPING ON CAT-CARBON REMOVAL FROM SPENT AND MOLYBDOPHOSPHORIC ACID (MPA) TREATED Co-Mo /Al2O3 CATALYST Initial % Residual % % Cat Carbon Sample Cat Carbon Treatment Cat Carbon Removed Spent catalyst 20.16 None -- 0 Run 81 (1) 20.16 MTA Treated, 2 x Co 0.54 97 Impregnated and 2 x Calcined (1) (1) Mixing rate 100 rpm. TABLE IX 'HYDRODESULFURIZATI0N ACTIVITY OF FRESH, SPENT AND MOLYBDO PHOSPHORIC ACID (MPA) TREATED Co-Mo/A1203 CATALYST Mole Percent DBT Conversion Sample 310 C 325 C 350 C Fresh catalyst (commercial) 49 77 95 Run 81 (1,2) 41 66 94 7. ActivIty of Fresh Catalyst 84 86 99 (1) Mixing by shaking at 100 rpm. (2) MPA treated, 2x Co impregnated and 2x calcined. Cobalt content 4-5, TABLE X SURFACE AREA (SA) AND PORE VOLUME (PV) OF SPENT AND MOLYB DOPHOSPHORIC ACID (MPA) TREATED Co-Mo/Al2O3 CATALYST After 2x Impregnation Initial and 2x Calcination Sample S.A. mê/g P.V. cm /g S.A. mê/g P.V. cm /g Run 81 87 O.iL 118 0.07 Example 3 - Treatment of Spent Catalvsts with Heteropoly Acids The following heteropoly acids were investigated for their ability to extract vanadium and nickel deposited on Co-Mo HDS catalyst during process conditions: Four 1 g samples of solvent-cleaned, small pore size, spent Co-Mo HDS catalyst (as in Example 1) were placed in a 300 ml Erlenmeyer flask. To each flask was added 100 ml of a 0.4 g wt.% aqueous solution of the following heteropoly acids: dodecamolybdophosphoric acid, H3(PMo12O40).24H2O, dodecamoylbdosilicic acid, H4(SiMo12O40).24H2O, dodecantungstophosphoric acid, H3(PW12O40).24H2O, and dodecatungstosilicic acid, H4(SiW12O40).24H2O. The flasks containing the catalyst and the heteropoly acid ere maintained at 600C on a rotary shaker at a mixing rate of 100 rpm. At the end of 24 hours, the extracts were separated from the catalysts by decantation and passed through 0.2 / m size Millipore filters. The catalysts were resuspended in 100 ml quantities of fresh heteropoly acids and the flasks were maintained for an additional 24 hours under the same conditions described above At the end of the second 24-hour period, the extracts were separated from the catalysts by decantation and the catalysts were washed thoroughly with deionized distilled water and dried at lOO0C for 48 hours. The dried catalysts were stored under nitrogen until subsequent analysis. The second 24-hour period extracts were treated in the same manner as the first extracts. The pM values of the first and second 24-hour extracts were determined. The pH changes are summarized in Table XI. Vanadium, nickel, cobalt, molybdenum and aluminum concentrations in each of the filtered extracts were determined by atomic absorption spectroscopy. The percent metals extracted by each of the heteropoly acids from the spent CoZ o HDS catalyst are summarized in Table XII. TABLE XI pH CHANGES DURING FIRST AND SECOND 24 HOUR PERIOD OF HETEROPOLY ACID EXTRACTS OF SPENT Co-Mo HDS CATALYST pH at end of 1st Initial pH pH at end of 2nd Heteropoly Acid Initial pH 24 hr.extraction fresh acid 24 hr.extraction H3(PMo12O40).24H2O 2.32 2.92 2.32 2.78 H4(SiMo12O40).24H2O 2.20 3.20 2.20 2.86 H3(PW12O40).24H2O 2.30 3.30 2.30 3.16 H4(SiW12O40).24H2O 2.40 3.40 2.40 3.22 TABLE XII PERCENT METALS EXTRACTED BY HETEROPOLY ACID AFTER 48 HOURS FROM SPENT Co-Mo HDS CATALYST Heteropoly Acid V Ni Co Mo Al H3(PMo12O40).24H2O 80 80 40 0 0 H4(SiMo12O40).24H2O 89 90 50 0 0 H3(PW12O40).24H2O 63 90 50 0 0 H4(SiW12O40).24H2O 66 95 60 0 0 Example 4 - Results of Heteropoly Acid Treatment The surface area and pore volume of spent and treated catalysts (small pore) were determined as a function of heteropoly acid treatment. The results are given in Table XIII, below. TABLE XIII SURFACE AREA AND PORE VOLUME OF SOLVENT-EXTRACTED SPENT CATALYST, FOLLOWED BY HETEROPOLY ACID EXTRACTION Surface Area Pore Volume Heteropoly Acid Treatment mê/g cm /g Spent catalyst 166 0.212 H3(PMo12O40).24H2O 220 0.313 H4(SiMo12O40).24H2O 223 0.350 F(PW12040).24H2O 199 0.299 H4(SiW12040).24}320 217 0.306 Fresh catalyst 265 0.50 Table XIII clearly dgmonstrates that upon treatment with a heteropoly acid, both surface area and pore volume increase significantly. Example 5 - Hydrogen Peroxide Enhancement of Carbon Radical Generation. Samples of small pore Co-Mo/A1203 spent hydrotreating catalyst from the Amuay refinery used for hydrodesulfurization in Exxon's GO-FINING process were subjected to treatments of varying duration with dodecamolybdophosphoric acid (MPA) and with or without added hydrogen peroxide. When added, the amount of peroxide employed was 3 wt.% of the total MPA present. An aqueous solution of '1PA (0.4 wt.%) of pH 2.3 was employed. The carbon radical density per unit volume of catalyst was determined by paramagnetic resonance observations. Table XIV below set forth the relative carbon radical density, with the starting material assigned a value of unity. TABLE XIV RELATIVE CARBON RADICAL DENSITY MPA MPA + 3 wt. % H2O2 Time Radical Density Time Radical Density (hrs) (relative units) (hrs) (relative units) (hrs) (relative units) (hrs) (relative 'units) 0 1.0 0 1.0 4 4.8 2 7.2 20 6.0 4 10.0 28 5.4 6 9.8 50 7.5 20 16.3 72 6.6 28 18.4 Clearly, use of hydrogen peroxide in conjunction -with the heteropoly acid increased the carbon radical density. While not subscribing to any particular theory, the increased carbon radical density suggests that the carbon "crust" on the catalyst surface is more readily broken in the presence of the peroxide, thereby facilita ting more rapid extraction of contaminating metals by tPe heteropoly acid. Example 6 - Metals Removal Improved by Hvdroen Peroxide Addition. Magnetic resonance techniques were used to monitor levels of different vanadium species on spent hydrotreat ing catalysts. As shown in Table XV below, V2S3 species were very readily extracted by treatment with MPA alone. Other species, such as the surface species and VO- as sociated with A1203, were much less tractable. After treatment in the aqueous solution of heteropoly acid plus 3 wt.% H202 of Example 5, however, the concentration of the surface species was reduced to a small fraction of its total value and the concentration of the VOê species was also appreciably reduced. It should be noted that the reduction in surface species and V02-' species occurred in a much shorter time employing the heteropoly acid/hydrogen peroxide solution, as compared to hetero poly acid solution alone. TABLE XV AMOUNT OF VANADIUM REMOVED Vanadium Type Vanadium Surface VOê+ Sulfide Species Species Spent Large Pore Catalyst, Residuum Feed: -Before MPA Treatment 7 wt.% 5 wt.% - 1 wt.% -After MPA Treatment < 0.5 wt.% 3 wt.% 1 wt.% (90 hrs.) Spent Small Pore Catalyst, GO-FINING Feed -Before MPA+H2O2 Treatment -- 5 wt.% 1 wt.% -Aftre MPAüH2O2 Treatment -- < 1 wt.% 0.4 wt.% (26 hrs.) Examole 7 - Reduction of VOê+ Species with Hydrogen Peroxide Addition. The VOê+ species was found to be uneffected by treatment with aqueous solutions containing MPA alone. Upon addition of 3 wt.% H202 (based on ilPA), the follow ing extraction kinetics were observed, demonstrating significant extraction of VOê+ within about 20 hours, The anomalous result after six hours was found to be reproducible; no satisfactory explanation is known. TABLE XVI REDUCTION OF vo2+ Time, hrs. Relative Vo2 Intensity 0 84 2 78 4 74 6 108 20 38 26 45 Example 8 - Effect of Catalyst Size on Vanadium Extraction. A sample of solvent-extracted, spent Co-Mo/ A1203 catalyst was used to determine the effect of size on vanadium extraction with the heteropoly acid, molybdo phosphoric acid (MPA). The vanadium extraction was de termined employing (a) 1/16 inch extrudate and (b) 125 to 150 A m size powder with aqueous solutions of MPA alone and W2A + 15 wt.% H202 100:1 v/v. The amount of MPA in aqueous solution was 0.4 wt.%; the pH was 2.3. The extraction rates were determined in a continuous plug flow reactor maintained at 600C with a flow rate of 1 ml/min. Samples were collected at suitable intervals. The vanadium extracted was determined by atomic absorption spectrophotometry. The data on the percent vanadium ex tracted are summarized in Table XVII below. TABLE XVII PERCENT VANADIUM EXTRACTED Extraction Time, hours Catalyst Size Treatment 2 4 6 8 10 12 15 1/16 pellet MPA 5 10 15 18 23 26 30 1/16 pellet MPA + H202 15 30 41 51 57 62 66 125-150 + m MPA 10 16 21 25 29 33 38 125-150 4 m MPA + H202 23 36 44 55 62 70 81 It is clear from Table XVII that (1) MPA supplemented with hydrogen peroxide is much more effective in vanadium removal than MPA alone and (2) crushing the catalyst further increases the rate of vanadium removal. Example 9 - Effect of Hydrogen Peroxide Concentration on Rate of Vanadium Extraction. Toluene-extracted spent Co-No/Al203 catalyst was contacted with an aqueous solution of a heteropoly acid (MPA) alone and MPA supplemented with various concentraticnsof H202 in a continuous plug flow reactor maintained at 600C and a flow rate of 1 ml/min. The amount of MPA in aqueous solution was 0.4 wt.%; the ratio of MPA:peroxide was 100:1 v/v. Samples were collected at suitable intervals and vanadium concentration was determined by atomic absorption spectrophotometry. The data on the rate of vanadium extracted are summarized in Table XVIII. TABLE XVIII RATE OF VANADIUM EXTRACTED, g/ml/min. Extraction Time, hours Treatment 2 4 6 8 12 16 20 24 42 42 46 54 58 68 76 86 84 + 3% H2O2 50 60 70 78 100 120 142 140 MPA + 15 22 55 60 90 100 100 146 180 200 MPA + 30% H2O2 60 75 80 120 180 204 220 240 The data in Table XVIII demonstrate that addition of hydrogen peroxide to the heteropoly acid enhances both the rate and amount of vanadium removal. Example 10 - Effects of Hydrogen Peroxide Concentration on Percent of Vanadium Extracted. The experiment given in Example 9 was repeated, utilizing different concentrations of hydrogen peroxide with MPA. The data on the percent vanadium extracted are summarized in Table XIX below. TABLE SIX PERCENT VANADIUM EXTRACTED Extraction Time, hours Treatment 1 2 4 20 24 MPA 2 4 7.5 33 38 MPA -: 3% H202 5 10 16 44 49 MPA + 9% H2O2 7 12 22 59 63 MPA + 15% H2O2 10 23 43 73 80 Again, it is clear that addition of hydrogen peroxide to the heteropoly acid is much more effective in vanadium removal. Example 11 - Effect of TemPerature on Rate of Vanadium Extraction. Toluene-extracted spent Co-Mo/A1203 hydrode sulfurization catalyst was contacted with an aqueous solu tion of a heteropoly acid ('iPA, 0.4 wt.%) supplemented with 3 wt.% H202 100:1 v/v. The rate of extraction of vanadium in a continuous plug flow reactor at a flow rate of 1 ml/min was determined at 500, 600, and 700C Eluates were collected at suitable intervals and vanadium concentration in each fraction was determined by atomic absorption spectrophotometry. The influence of temperature on the rate of vanadium extraction is summarized in Table XX, below. TABLE XX RATE OF VANADIUM EXTRACTED, g/ml/min Extraction Time, hours Temperature C 2 4 6 8 10 12 14 16 18 20 24 50 17 20 32 37 40 44 46 48 50 50 50 60 104 132 150 144 132 114 102 92 87 80 76 70 150 182 202 200 188 180 172 164 154 144 128 From Table XX, it is clear that the increase in temperature facilitates the vanadium removal. However, at temperatures much higher than about 70 C, evaporation of solvent water also becomes significant. Therefore, tempera tures much above 80 C should be avoided. e 12 - Conversion of the Surface Vanadium Species to Vanadium Sulfide. Samples of small pore CoMo/Al2O3 spent hydro treating catalyst from the Ainuay refiner used for hvdro desulfurization in Exxon's GO-FINING process were subjected to treatments of varying temperatures and duration with substantially pure H2S gas at 1 atm. The results are tabulated in Table XXI below. Table XXI Temperature Time % V2S3 (Approx.) Spent catalyst - - 0 H2S Treatments: 400 C 4 hr. 50 500 C 4 hr. 80 500 C 1 hr. 40 600 C 1 hr. 65 The results show that a substantial portion of the surface vanadium species is converted to V2S3. This species is readily extractable with a heteropoly acid such as dodecamolybdophosphoric acid (MPA). Example 13 - Effect of Presulfiding on Vanadium Extraction. Solvent-extracted spent Co-Mo/Al2O3 was pre sulfided with a stream of 100% H2S (1 atm) at a flow rate of 10 liter/hr. at 5000C for four hours. The temperature was slow, raised from 30 to 90 C in 0.5 hr, from 90 C to 5000C in 1 hour and held at 500 C for 4 hours. After presulfiding, the catalyst was coqled to room temperature with a stream of 02-free, dry nitrogen The presulfided, spent catalyst was stored under nitrogen atmosphere until further use. The vanadium extraction with a heteropoly acid, molybdophosphoric acid (MPA), from a presulfided 1/16 inch extrudate was carried out in a continuous plug flow reactor at a flow rate of 1 ml/min and at a temperature of 60 C. Aqueous solutions of MPA alone and MPA + 15 wt.% H202 100:1 v/v were employed, The amount of MPA was 0.4 wt.%; the pH was 2.3. Samples were collected at suitable intervals and vanadium concentration was determined with atomic absorption spectrophotometry. The data on the percent vanadium extracted at various intervals are summarized in Table XXII below. TABLE XXII PERCENT OF VANADIUM EXTRACTED Extraction Time, hrs. Treatment 5 10 15 20 30 40 50 MPA 9 18 26 33 44 54 62 Presulfided+MPA 20 28 35 43 56 68 78 MPA + H2O2 42 53 60 64 72 77 83 Presulfided+MPA 45 54 62 70 82 90 97 + H2O2 From Table EXII, it is clear that incorporation of the presulfiding step is highly beneficial to the vanadium extraction. Combining presulfiding with the heteropoly acid/nydrogen peroxide extraction results in almost complete removal of vanadium. Example 14 - Effect of Presulfiding TemDerature on Vanadium Extraction. Two samples of solvent-extracted, 1/16 inch extrudates of spent Co-Mo/Al203 catalyst were presulfided at 400 C and at 500 C for 4 hours in a 100% H25 stream. The extraction with heteropoly acid (MPA) alone and supplemented with 15 wt.% H2O2 (as in Example 13) was carried out in a continuous plug flow reactor at 60 C with a flow rate of 1 ml/min. Samples were collected at suitable intervals and analyzed for vanadium with atomic absorption spectrophotometry. The data on the percent vanadium extracted are summarized in Table XXIII below. t I I T PERCENT VANADIUM EXTRACTED Extraction Time, hrs. Treatment Presulfide Extraction 2 4 5 7 10 15 18 20 25 30 -- MPA - - 9 - 18 26 -- 33 -- 44 400 C, 4 hrs MPA 4 11 - 16 21 30 33 -- 42 - -- MPA + H2O2 - -- 42 -- 53 60 -- 64 -- 72 400 C, 4 hrs MPA + H2O2 12 21 -- 40 48 58 63 -- 76 -500 C, 4 hrs MPA + H2O2 12 23 -- 40 53 72 80 -- 92 - Again, it is clear that presulfiding, particularly at higher temperatures, increases both the rate and extent of vanadium removal. Example 15 - Effect of Catalvst Particulate Size on Vanadium Extraction. The experiment given in Example 14 was reseated, except that the catalyst was crushed to give 20 to 40 mesh size particles. Presulfiding was carried out at 5000C for 4 hours. Extraction was with MPA and 15 wt.% H202 100:1 v/v. The data are summarized in Table XXIV below. TABLE XXIV PERCENT VANADIUM EXTRACTED Extraction Time, hrs. Treatment 3 5 10 15 20 25 30 35 40 Presulfided + MPA + ' H2O2 20 27 45 57 66 74 80 90 95 ExamDle 16 - Effect of Presulfidina Temperature on Vanadium Extraction from Crushed Catalvst. The experiment given in Example 15 was repeated, employing presulfiding temperatures of 5000C for 1 hour and 6000C for 1 hour. The data on the percent vanadium extracted are summarized in Table XXV below. TABLE XXV PERCENT VANADIUM EXTRACTED Extraction Time. hrs. Presulfide Treatment 2 4 5 8 10 12 16 500 C, 1 hr. 21 39 54 75 87 90 95 600 C, 1 hr. 29 54 65 77 87 92 97 These data suggest that presulfiding treatments of shorter duration are adequate to convert to an extractable sulfide. Example 17 - X-Rav Crystallite Size Measurement. Samples of small pore 1/16 inch extrudate and 20 to 40 mesh size particles of Co-Mo/A1203 spent hydrotreating catalyst used for hydrodesulfurization were subjected to treatments of varying temperatures and duration with a 100% H2S gas (1 atm) at a velocity of 10 liters/hr. The catalyst was cooled to room temperature under a stream of inert gas such as oxygen-free nitrogen or argon. The A1203 crystallite size was determined by X-ray diffraction. The results are summarized in Table XXVI below. TABLE XXVI Al2O3 Crystallite Size, A Spent Caalyst, solvent extracted 41 Fresulaided at 400 C-4 hrs 44 (pellet) Presulfided at 500 C-4 hrs 46 (pellet) Presulfided at 500 C-1 hr 43 (20-40 mesh) Persulfided at 600 C-1 hr 43 (20-40 mesh) From Table XXVI, it is clear that presulfiding the spent catalyst, whether 1/16 inch pellets or 20 to 40 mesh size particles, at the conditions listed does not substantially alter the Al2O3 crystallite size. This indicates that the structural integrity of the support is essentially preserved.

Claims: 1. A process for regenerating a spent hydrofining catalyst which comprises contacting the spent catalyst with an aqueous solution of a heteropoly acid having the general formula Hx(YM12040) where Y is at least one element selected from phosphorus, silicon, titanium, germanium, arsenic, zirconium, thorium and cerium; M is at least one element selected from molybdenum, tungsten, niobium and tantalum and x is 3 when Y is pentavalent and 4 when Y is tetravalent, which aqueous solution contains 0 to 50 wt. Z hydrogen pcroxide, based on the amount of heteropoly acid, with optional prior contact of the catalyst with a gaseous, sulfur-containing reagent having or providing a partial pressure of sulfur of at least 0.01 atmospheres at a temperature of up to 6500C, followed by impregnating the treated catalyst with a water-soluble cobalt or nickel salt, followed by calcination in air at maximum temperature of about 4500C. 2. The process of claim 1 in which Y is phcrphonls and M is molybdenum. 3. The process of claim 2 in which up to one-half of M is replaced by at least one element selected from nickel, cobalt and v nadiu- 4. The process of any one of claims 1 to 3 in which the spent catalyst is contacted with the heteropoly acid solution at a temperature between ambient and 80 C. 5. The process of any one of claims 1 to 4 in which the concentration of the heteropoly acid in solution is in the range of from 0.1 to 25 wt. % 6. The process of claim 5 in which the said solution has a pH in the range of from 1 to 3. 7. The process of any one of claims 1 to 6 in which the concentration of hydrogen peroxide is at least 1 wt. %. 8. The process of claim 7 2n which the concentration of hydrogen pcroxide is in the range of from 3 to 15 wt. %. 9. The process of any one of claim 1 to 8 in which the spent catalyst is contacted by the heteropoly acid/hydrogen peroxide solution for a period of time of from 4 to 200 hours. 10. The process of any one of claims 1 to 9 in which the said impregnation and calcination are repeated at least once. 11. The process of any one of claims 1 to 10 in which the hydrofining catalyst comprises a cobalt-molybdenum-loaded alumina support.

Inventors: MOHAN, RAAM RAMANUJA, SILBERNAGEL, BERNARD GEORGE, SINGHAL, GOPAL HARI
Applicants: EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1979
Main classification: C10G45
IPC codes: B01J23, C10G45