CA1084893A - Rejuvenation process for catalyst carrier particles and for catalysts - Google Patents
Rejuvenation process for catalyst carrier particles and for catalystsInfo
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- CA1084893A CA1084893A CA253,004A CA253004A CA1084893A CA 1084893 A CA1084893 A CA 1084893A CA 253004 A CA253004 A CA 253004A CA 1084893 A CA1084893 A CA 1084893A
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Abstract
ABSTRACT OF THE DISCLOSURE
REJUVENATION PROCESS FOR CATALYST CARRIER
PARTICLES AND FOR CATALYSTS
A process for rejuvenating catalyst carrier particles comprising alumina, having pores plugged or fouled with metal sulfide contaminant as a result of hydrotreating a hydrocarbon feed containing organometallic compounds and sulfur-containing compounds using a catalyst for which the particles are the carrier for catalytic components, by the process steps including leaching with at least 5 weight percent aqueous nitric acid and oxidizing residual oxidizable matter from the leached particles by contacting them at a temperature below their sintering temperature with molecular oxygen. A
rejuvenated catalyst is prepared from the rejuvenated carrier particles by restoring the catalytic component by impregnating the leached carrier particles with a suitable solution of the catalytic component, or a precursor thereof, and calcining the resulting particles below their sintering temperature.
REJUVENATION PROCESS FOR CATALYST CARRIER
PARTICLES AND FOR CATALYSTS
A process for rejuvenating catalyst carrier particles comprising alumina, having pores plugged or fouled with metal sulfide contaminant as a result of hydrotreating a hydrocarbon feed containing organometallic compounds and sulfur-containing compounds using a catalyst for which the particles are the carrier for catalytic components, by the process steps including leaching with at least 5 weight percent aqueous nitric acid and oxidizing residual oxidizable matter from the leached particles by contacting them at a temperature below their sintering temperature with molecular oxygen. A
rejuvenated catalyst is prepared from the rejuvenated carrier particles by restoring the catalytic component by impregnating the leached carrier particles with a suitable solution of the catalytic component, or a precursor thereof, and calcining the resulting particles below their sintering temperature.
Description
108~893 B~CKGROUND_OF__HE_INVENTION
2 Fi_ld_of the_I_v_____n
3 This invention relates to a process for regenerating
4 dsactivated catalyst carrier particles. More particularly, it relates to rejuvenating a metal-sulfide-contaminated hydrocarbon-6 treating catalyst.
7 The dwindling of world petroleum reserves has made it 8 necessary to squeeze more and more refined products from every 9 barrel of crude oil. The heavy, high-boiling, metal- and sulfur-containing portion of crude oil which formerly was ~urned as low-11 grade fuel or used as a material for the construction of roads 12 must now also be catalytically hydrotre~ted for the recovery of 13 refined products. Because of the high-metal and sulfur content 14 of this material, hydrotreating catalyst lives frequently become unduly shortened because of the fouling of catalyst pores. ~he 16 problem is magnified because catalysts satisfactory for 17 hydrotreating require for their production the use of customized 18 carriers having relattively large surface areas and unique pore 19 diameter characteristics. Such carriers, in contrast to conven-tional materials, now represent a significant fraction of the 21 catalyst cost. Consequently, there is a need for an effective 22 process for the rejuvenation of these carriers that they may be 23 reused for the production of rejuvenated hydrotreating catalysts.
24 D---Ei~t----o----e---Ei--r-AEt Various methods have been disclosed for removing metal 26 sulfide contaminants from catalyst carrier particles. These 27 methods are reviewed in large part and a yet further method is 28 disclosed in U.S. Patent 3,791,989. In general, the object of 29 these methods is to achieve some improvement in a used catalyst 3~ by selectively dissolving contaminants present in the pores of 31 hydrogenation catalyst carrier particles. While a moderate 32 degree of success appears to be achieved from the use of these methods, the activities and catalyst lives of the resulting regenerated catalysts usually are inferior relative to those of the new catalysts.
It is an object of this invention to provïde a process L
for the regeneration of porous catalyst carriers comprising alumina and to produce rejuvenated catalysts from these rejuvenated carriers.
SUMMA:RY OF THE INVENTION
According to the present invention, a process for rejuvenating a catalyst comprising an effective amount of a catalytic component disposed on an alumina carrier, said catalytic component comprising a Group VI metal or compound thereof and a Group VIII metal or compound thereof, and said catalyst having pores which are plugged or fouled by metal sulfide contaminants as a result of use of said catalyst in hydrotreating a hydrocarbon feed which contains an organometallic compound and sulfur-contaminants, which comprises: leaching at least 50~ of said metal sulfide contaminants, calculated as metal, from said catalyst with aqueous nitric acid solution, ` 20 said solution having a nitric acid concentration in the rangefrom about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0C to the reflux temperature of said solution, and (b) effected by using for each gram of - said catalyst an amount of said solution in the range of 4-20 ml, said amount being in excess of the stoichiometric quantities required for said metal sulfide contaminant; oxidiz-ing residual oxidizable matter from said leached catalyst by contacting said catalyst with molecular oxygen at a temperature below the sintering temeprature of said catalyst.
In a yet further aspect of the present invention, a process is provided for rejuvenating a catalyst comprising an ~ - 3 -L~ .
- ~084893 effecti~e amount of a catalytic component disposed on a carrier selected from the group consisting of particles of alumina and of alumina-silica mixtures, the particles containing pores plugged or fouled by metal sulfide contaminants as a result of contact with a hydrocarbon feed containing organometallic compounds and sulfur-containing compounds under hydrotreating conditions, which comprises, in addition to the two steps described above for the rejuvenation of the catalyst carrier partïcles, the restoring of the effective amount of a catalytic component by impregnating the - 3a -: ~084893 1 leached particles vith at least one solution of the catalytic 2 component or a precursor thereof and calcining the resulting 3 impregnated particles at a temperature below their sintering 4 temperature.
In a yet further and preferred aspect of the present 6 invention, the catalytic component of the hydrotreating catalyst 7 comprises a Group VI metal or compound thereof and a Group VIII
8 metal or compound thereof.
In a preferred embodiment, the carrier particles of a 11 spent, select, high-activity hydrodesulfurization (HDS) catalyst 12 are first rejuvenated and then used for the preparation of a 13 rejuvenated select, high-activity HDS c~talyst. The spent 14 catalyst, which has not been treated other than to wash off residual hydrocarbons to give a free-flowing material, is used as 16 the feed for the process.
17 The spent catalyst and aqueous nitric acid are charged 18 to a suitable leaching vessel, which is resistant to the 19 corrosive action of nitric acid, for example a glass-lined or stainless-steel vessel. For each gram of the catalyst, about 5 21 ml of 12.5% weight aqueous nitric acid are charged to the vessel.
22 Vigorous exothermic leaching action ensues upon the contacting of 23 the spent catalyst with the nitric acid. Desirably the 24 temperature is maintained in the range 10-22C. Nitrogen oxides are produced and evolved as the leaching proceeds, and is 26 substantially complete for the removal of sulfide contaminants 27 after about 1 hour, when the evolution of nitrogen oxides more or 28 less ceases~ The leaching may be continued for 1-3 hours, 29 particularly where the metal contamination is severe.
In a typical leaching operation in vhich the HDS cata-31 lyst comprises porous alumina, cobalt, molybdenum and phosphorus 32 and the metal contaminants are sulfides of vanadium, nickel and 1 iron, all but about 6% of thc cobalt, about 15% of the vanadium 2 and about 12~ of the nickel (all calculated as metal) is removed 3 from the carrier particles, and only very little (less than 4 4 weight) of the alumina is leached from the particles. In addition, the acid leaching action removes about 75~0 of the 6 sulfur content and little or none of the carbon content of the 7 spent catalyst.
8 The leached carrier particles are next impregnated with 9 an aqueous solution containing sufficient cobalt in the form of cobalt nitrate and molybdenum in the form of phosphomolybdic acid 11 as reguired to reconstitute the cobalt and molybdenum (calculated 12 as the metals) catalytic components of the original fresh 13 catalyst. The impregnation is effected by conventional means, 14 for example imbibation of the impregnation solution by the carrier particles and evaporation of the water solvent and 16 loosely bound water.
17 Next the residual oxidizable matter, for example carbon 18 and sulfur contaminants, is removed from the leached and 19 impregnated carrier particles by contacting them with an inert gas, for example nitrogen, containing 1-5 volume percent of 21 molecular oxygen, while maintaining the particles at a tem-22 perature in the range 340-400C. This contacting is continued 23 until the major portion, if not all, of the carbon contaminant on 24 the carrier particles has been converted to CO2 and vented from the carrier particles. For practical purposes, the oxidation 26 with molecular oxygen results in the removal of all of the carbon 27 and sulfur contaminants. Surprisingly, the pore volume of the 28 resulting rejuvenated HDS catalyst is usually within experimental 29 limits of accuracy the same as that of the fresh catalyst, as is 30' likewise the average pore diameter. The surface area of the 31 rejuvenated catalyst is as large as, if not larger than, that of 32 the fresh catalyst, while the crush strength of the regenerated iO84893 1 catalyst is excellent.
2 Most surprising is the result noted that after an 3 initial break-in period on stream, the rejuvenated catalyst (see 4 FIG. 3) exhibits a markedly improved fouling rate relative to a fresh HDS catalyst.
7 FIG. 1 shows the removal of metal from a spent catalyst 8 carrier as a function of nitric acid strength.
9 F.IG. 2 shows the weight percent metals removal as a function of the amount of nitric acid used for leaching.
11 FIG. 3 shows a comparison under comparable conditions 12 of the performance of a fresh catalyst vs. the performance of a 13 rejuvenated catalyst.
Ca rier Mate___l_ 16 Porous particulate carrier materials comprising alumina 17 sized for use in a fixed-bed hydrotreating reactor and ordinarily 18 employed as carrier particles for hydrotreating (hydro-19 desulfurizing, hydrocracking, hydrodemetallation and hydrode-nitrification) catalysts are in general rejuvenated by the 21 present process and are contemplated for use as feeds herein.
22 The particle sizing usually varies in the diameter range from 0.5 23 to 10 mm and may be any suitable shape. Preferably the carrier 24 material is a mixture of silica and alumina in any proportions.
Still more preferably, the carrier material consists essentially 26 of alumina. This process is advantageously applied to particles 27 having a surface area of at least 50 mZ/gram and is especially 28 - advantageous when used to rejuvenate high-surface-area carriers 29 comprising alumina ordinarily used in the preparation of HDS
30' catalysts for use in hydrotreating sulfur-containing and metals-31 contaminated hydrocarbons. Such feeds routinely plug or foul the 32 pores and surfaces of the catalyst.
1 C_taly_i _C__p_n_n_ 2 The present process is preferably applied to spent 3 hydrotreating catalyst particles comprising Group VI and/or Group 4 VIII metals and a carrier material as described above. Effective amounts of the catalytic components of these catalysts vary, and 6 ordinarily are in the range, calculated as metal, from 1 to 25 7 weight percent of the composite catalyst. Other components, such 8 as promoters and stabilizers, may also be present in minor 9 amounts, for example phosphorus. Usually these catalysts are prepared using conventional solution impregnation methods. They 11 may also be prepared by gelation, cogelation, and the like 12 methods, of the carrier component wherein the catalytic 13 components are incorporated into the carrier at any convenient `;
14 time, for example during gelation, after gelation, after calcination of the carrier, and the like. Preferably the spent 16 catalysts used as feeds in the process have in their preparation 17 been subjected, either as the total composite or as the carrier 18 per se, to calcination at a temperature in the range 426-871C, 19 preferably 482-593C, prior to use. Such catalysts in general appear to suffer little or no loss of support material by 21 dissolution in the nitric acid leaching solution of the present 22 process. They also appear to suffer but a minor loss, if-any, of 23 crush strength as a result of the leaching.
24 Le _hin~_C_n_ltl__s A. A_id_C____nt_at_on 26 For the leaching of metal sulfide contaminants from 27 spent hydrotreating catalysts, a sufficiently concentrated 28 aqueous nitric acid solution must be used. Although the relative 29 ease of dissolution of metal sulfide contaminants varies depending upon a number of factors, including the specific metal, 31 the degree of pore plugqing and the like, a satisfactory concen-32 tration for the nitric acid is, in general, in the range 5 to 10 ~89~893 1 weight percent (e.g., about 0.8 to 1.7 molar). Preferably the 2 concentration of the nitric acid is in the range 10 to 17.5 3 weight percent (e.g., about 1.7 to 3 molar). Higher 4 concentrations may be used, but such use is relatively disadvan-tageous in terms of increasing dissolution of the carrier 6 particles and increasing loss of crush strength of the particles.
7 8ecause the leaching reaction is exothermic and gas is evolved, 8 the use of nitric acid having an excessive concentration is 9 disadvantageous for further reasons in that such use includes problems of temperature control and foam-up control. There 11 appears to be no redeeming counteradvantage to the foregoing 12 - disa~vantages in the use of n-itric acid having a concentration 13 above about 20 weight percent (e.g., about 3.4 molar).
14 ~. Tem~erature The temperature which should be used for the leaching 16 varies, depending upon factors such as the acid concentration 17 used, the particular carrier particles involved, and the degree 18 of the leaching. Usually the initial temperature should be lower 19 than the final temperature as a matter of convenience in controlling the more exothermic phase of the leaching and the 21 evolution of gaseous by-products. In general, a satisfactory 22 temperature is in the range 0C to the reflux temperature for the 23 leaching solution. The use of higher temperatures tends to 24 result in increased dissolution of the carrier particles themselves. Preferably a temperature in the range from about 26 10C to 30C is employed. More preferably a temperature in the 27 range 10-20C is employed.
28 Residual-Matter Oxid__ion 29 The oxidizable residual matter present OD the leached 30' carrier varies in composition, depending upon the prior service 31 of the spent catalyst. In general, the material appears to be 32 ~ainly carbonaceous matter, i.e., coke, sulfocàrbon solids, and ~84893 1 the like. It is readily oxidizable to gaseous products at a 2 temperature below the sintering temperature of the particles.
3 Usually the oxidation of this material is so exothermic that it 4 is desirably effected, at least in the initial stage, by using molecular oxygen diluted by an inert gas, for example nitrogen or 6 carbon dioxide, in order to avoid subjecting the leached carrier 7 particles to a temperature which exceeds their sintering 8 temperature. Otherwise, the particles tend to suffer a severe 9 loss in surface area and may suffer undesirable changes in the pore characteristics. Preferably the oxidizing of this residual 11 matter is effected in the main by contacting an oxidizing gas 12 comprising nitrogen containing from 1 to 5 volume percent of 13 molecular oxygen with the leached carrier particles, the 14 contactinq being at a temperature in the range from about 260C
to 540C, more preferably 340C to 400C. The oxidation is 1~ satisfactorily complete when the effluent gas contains little or 17 no carbon dioxide and/or sulfur oxide gas.
18 I_Preqn_t_Q_ 19 For the rejuvenation and/or reconstitution of the spent catalyst, the catalytic components removed by the leaching must 21 be restored, or if a new combination of catalytic components is 22 desired by impregnating the leached and partially rejuvenated 23 carrier with a suitable solution. While the impregnation is 24 desirably effected prior to completing the carrier rejuvenation by the oxidizing step, it may also be conveniently effected 26 afterwards. Routine impregnation methods are contemplated and 27 used in this step. The carrier particles are immersed in a 28 solution containing one or more of the desired catalytic 29 components or a suitable precursor thereof, and the absorbed 30' solvent, which is usually water but not necessarily so, is 31 evaporated from the leached carrier particles. The impregnation 32 may be achieved in a single-dunk-type operation with the _ 9 _ 108~893 1 catalytic components all present, or by the use of two or more 2 impregnating solutlons. The single-dun~ method is preferred.
3 That is, a single solution containing sufficient of the catalytic 4 components, for example cobalt nitrate and phosphomolybdic acid, is used to restore the metal contents of these components to that ~ of the fresh catalyst before use in a hydrotreating process.
7 Calci__t_on 8 Depending upon whether or not the fresh catalyst prior 9 to its use was desirably calcined, the _omposite resulting from the above-described impregnation step is also calcined.
11 Calcination, in any event, is carried out after any oxidizable 12 residue on the leached carrier is removed by an oxidation step.
13 Calcination is carried out at a temperature below the sintering 14 temperature of the particles, preferably at a temperature in the range 426C to 871C, and more preferably 482C to 593C.
17 The following examples are for the further illustration 18 -but not limitation of the present invention.
19 Exa_~
In this example the effect of nitric acid concentration 21 upon the leaching of metal sulfide contaminant and sulfur-22 containing contaminant is demonstrated in a series of runs using 23 water alone and by using a series of nitri~ acid concentrations 24 in which the acid and spent catalyst particles are contacted in a glass reactor. For each gram of the spent catalyst, 6.5 mls, an 26 excess, of nitric acid was used. Except for the acid 27 concentrations (see FIG. 1), the conditions employed in these 28 runs were as follows:
29 Temperature, C 10-21 Pressure Atmospheric 31 Time, hours 4 32 The spent catalyst used in these runs had been expended iO84893 .
1 in hydrodesulfurization service in which the hydrocarbon feed had 2 a high sulfur and a high metals content. The fresh catalyst 3 contained molybdenum and cobalt, calculated as metals, in the 4 weight percents 12 and 3, respectively. ~he spent catalyst contained vanadium, nickel, iron, carbon and sulfur in the weight 6 percents 5.4, 1.7, 0.2, 13.4 and 11.0, respectively. The metals 7 contents were determined using x-ray fluorescence (estimated 8 uncertainty ~10% of value) and the carbon and sulfur were 9 determined by combustion (estimated uncertainty ~5% of value).
The results of the runs are shown in FIG. 1. These data 11 establish that for effective removal of metal sulfide 12 contaminants (vanadium and nickel), for example removal of at 13 least 75 weight percent, a substantial nitric acid concentration 14 must be employed, that is, a concentration which is at least in the ran~e 0.8 to 1.7 molar, and preferably is in the range 1.7 to 16 3 molar. Th-ese data also establish that there is no apparent 17 advantage in the use of an acid concentration in excess of about 18 3.5 molar.
19 Exampl__2 In this example, the effect of the amount of nitric 21 acid used upon the removal of metal sulfide and sulfur from the 22 spent catalyst particles by leaching is demonstrated in a series 23 of runs. The conditions and spent catalyst used were as in 24 Example 1, except that the nitric acid used was 3 molar and the relative amounts of acid used were varied (see FIG. 2). These 26 data establish that provided at least sufficient acid is employed 27 for the effective ~for example at least 75X) removal of the metal 28 sulfide contaminants, there is no apparent advantage in the use 29 of a large excess of the acid for removal of metal sulfide 30! contaminants. In the case of the spent catalyst used in these 31 examples, a satisfactory amount is at least about S mls of acid 32 per gram of spent catalyst. These runs also suggest that the 1~84893 1 amount of acid desirably used per unit weight of the spent 2 catalyst varies depending in the main upon the relative amount of 3 the spent catalyst metal, sulfur impurity, and metal sulfide 4 impurity components present in the spent catalyst which are leached from the carrier particles.
6 In general, it appears from these examples that the use 7 per gram of spent catalyst of an amount of a suitable con-8 centrated nitric acid in the range from about 4 to 20 mls results 9 in an effective removal of metal sulfide contaminant from a spent hydrotreating catalyst. Preferably, when the acid concentration 11 is in the range 1 to 3 molar, and the amount of acid employed, in 12 general, should be in the range from about 4 to 10 mls per gram 13 of spent catalyst, more preferably 4 to 7 mls.
14 ExamPl__3 In this example the performance in hydrodesulfurization 16 service of a rejuvenated catalyst as herein was compared with the 17 performance of a fresh catalyst. The hydrocarbon feed was an 18 Iranian heavy atmospheric residuum containing about 2.7 weight 19 percent of sulfur and a high metals content. Within experimental limits for molybdenum and cobalt determination, the respective 21 catalysts contained the same amount of molybdenum and cobalt 22 catalytic components. In addition, the rejuvenated catalyst 23 prior to use contained about 0.8 weight percent of vanadium 24 (calculated as metal) and trace amounts of nickel, iron and sulfur.
26 The surface areas (BET nitrogen method~ for the fresh 27 catalyst and the rejuvenated catalyst were 164 and 187 m2/g, 28 respectively, and the densities were each 1.3 g/cc. The larger 29 surface area for the rejuvenated catalyst is attributable to the rejuvenation process, because the carrier particles employed were 31- the same for the fresh comparison catalyst and for the parent to 32 the rejuvenated catalyst. (The improvement in surface area, 1~84893 1 about 14~, of the rejuvenated catalyst over the fresh catalyst is 2 therefore an unexpected bonus.) 3 The process conditions in the comparative runs were:
4 Pressure, atmospheres 139 H2 feed, SCM/100 liters 177 6 LHSV 1.6 7 The results from the above-described comparative runs 8 are shown in ~IG. 3. These data establish that during an initial 9 break-in period of about 140 hours, both catalysts, the fresh ~10 catalyst and rejuvenated catalyst, exhibited for practical 11 purposes the same fouling rate. Thereafter, the fouling rate for 12 the rejuvenated catalyst was markedly superior to that of the 13 fresh catalyst, i.e., a negligible rate vs. a rate of about 14 0.08C per hour.
7 The dwindling of world petroleum reserves has made it 8 necessary to squeeze more and more refined products from every 9 barrel of crude oil. The heavy, high-boiling, metal- and sulfur-containing portion of crude oil which formerly was ~urned as low-11 grade fuel or used as a material for the construction of roads 12 must now also be catalytically hydrotre~ted for the recovery of 13 refined products. Because of the high-metal and sulfur content 14 of this material, hydrotreating catalyst lives frequently become unduly shortened because of the fouling of catalyst pores. ~he 16 problem is magnified because catalysts satisfactory for 17 hydrotreating require for their production the use of customized 18 carriers having relattively large surface areas and unique pore 19 diameter characteristics. Such carriers, in contrast to conven-tional materials, now represent a significant fraction of the 21 catalyst cost. Consequently, there is a need for an effective 22 process for the rejuvenation of these carriers that they may be 23 reused for the production of rejuvenated hydrotreating catalysts.
24 D---Ei~t----o----e---Ei--r-AEt Various methods have been disclosed for removing metal 26 sulfide contaminants from catalyst carrier particles. These 27 methods are reviewed in large part and a yet further method is 28 disclosed in U.S. Patent 3,791,989. In general, the object of 29 these methods is to achieve some improvement in a used catalyst 3~ by selectively dissolving contaminants present in the pores of 31 hydrogenation catalyst carrier particles. While a moderate 32 degree of success appears to be achieved from the use of these methods, the activities and catalyst lives of the resulting regenerated catalysts usually are inferior relative to those of the new catalysts.
It is an object of this invention to provïde a process L
for the regeneration of porous catalyst carriers comprising alumina and to produce rejuvenated catalysts from these rejuvenated carriers.
SUMMA:RY OF THE INVENTION
According to the present invention, a process for rejuvenating a catalyst comprising an effective amount of a catalytic component disposed on an alumina carrier, said catalytic component comprising a Group VI metal or compound thereof and a Group VIII metal or compound thereof, and said catalyst having pores which are plugged or fouled by metal sulfide contaminants as a result of use of said catalyst in hydrotreating a hydrocarbon feed which contains an organometallic compound and sulfur-contaminants, which comprises: leaching at least 50~ of said metal sulfide contaminants, calculated as metal, from said catalyst with aqueous nitric acid solution, ` 20 said solution having a nitric acid concentration in the rangefrom about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0C to the reflux temperature of said solution, and (b) effected by using for each gram of - said catalyst an amount of said solution in the range of 4-20 ml, said amount being in excess of the stoichiometric quantities required for said metal sulfide contaminant; oxidiz-ing residual oxidizable matter from said leached catalyst by contacting said catalyst with molecular oxygen at a temperature below the sintering temeprature of said catalyst.
In a yet further aspect of the present invention, a process is provided for rejuvenating a catalyst comprising an ~ - 3 -L~ .
- ~084893 effecti~e amount of a catalytic component disposed on a carrier selected from the group consisting of particles of alumina and of alumina-silica mixtures, the particles containing pores plugged or fouled by metal sulfide contaminants as a result of contact with a hydrocarbon feed containing organometallic compounds and sulfur-containing compounds under hydrotreating conditions, which comprises, in addition to the two steps described above for the rejuvenation of the catalyst carrier partïcles, the restoring of the effective amount of a catalytic component by impregnating the - 3a -: ~084893 1 leached particles vith at least one solution of the catalytic 2 component or a precursor thereof and calcining the resulting 3 impregnated particles at a temperature below their sintering 4 temperature.
In a yet further and preferred aspect of the present 6 invention, the catalytic component of the hydrotreating catalyst 7 comprises a Group VI metal or compound thereof and a Group VIII
8 metal or compound thereof.
In a preferred embodiment, the carrier particles of a 11 spent, select, high-activity hydrodesulfurization (HDS) catalyst 12 are first rejuvenated and then used for the preparation of a 13 rejuvenated select, high-activity HDS c~talyst. The spent 14 catalyst, which has not been treated other than to wash off residual hydrocarbons to give a free-flowing material, is used as 16 the feed for the process.
17 The spent catalyst and aqueous nitric acid are charged 18 to a suitable leaching vessel, which is resistant to the 19 corrosive action of nitric acid, for example a glass-lined or stainless-steel vessel. For each gram of the catalyst, about 5 21 ml of 12.5% weight aqueous nitric acid are charged to the vessel.
22 Vigorous exothermic leaching action ensues upon the contacting of 23 the spent catalyst with the nitric acid. Desirably the 24 temperature is maintained in the range 10-22C. Nitrogen oxides are produced and evolved as the leaching proceeds, and is 26 substantially complete for the removal of sulfide contaminants 27 after about 1 hour, when the evolution of nitrogen oxides more or 28 less ceases~ The leaching may be continued for 1-3 hours, 29 particularly where the metal contamination is severe.
In a typical leaching operation in vhich the HDS cata-31 lyst comprises porous alumina, cobalt, molybdenum and phosphorus 32 and the metal contaminants are sulfides of vanadium, nickel and 1 iron, all but about 6% of thc cobalt, about 15% of the vanadium 2 and about 12~ of the nickel (all calculated as metal) is removed 3 from the carrier particles, and only very little (less than 4 4 weight) of the alumina is leached from the particles. In addition, the acid leaching action removes about 75~0 of the 6 sulfur content and little or none of the carbon content of the 7 spent catalyst.
8 The leached carrier particles are next impregnated with 9 an aqueous solution containing sufficient cobalt in the form of cobalt nitrate and molybdenum in the form of phosphomolybdic acid 11 as reguired to reconstitute the cobalt and molybdenum (calculated 12 as the metals) catalytic components of the original fresh 13 catalyst. The impregnation is effected by conventional means, 14 for example imbibation of the impregnation solution by the carrier particles and evaporation of the water solvent and 16 loosely bound water.
17 Next the residual oxidizable matter, for example carbon 18 and sulfur contaminants, is removed from the leached and 19 impregnated carrier particles by contacting them with an inert gas, for example nitrogen, containing 1-5 volume percent of 21 molecular oxygen, while maintaining the particles at a tem-22 perature in the range 340-400C. This contacting is continued 23 until the major portion, if not all, of the carbon contaminant on 24 the carrier particles has been converted to CO2 and vented from the carrier particles. For practical purposes, the oxidation 26 with molecular oxygen results in the removal of all of the carbon 27 and sulfur contaminants. Surprisingly, the pore volume of the 28 resulting rejuvenated HDS catalyst is usually within experimental 29 limits of accuracy the same as that of the fresh catalyst, as is 30' likewise the average pore diameter. The surface area of the 31 rejuvenated catalyst is as large as, if not larger than, that of 32 the fresh catalyst, while the crush strength of the regenerated iO84893 1 catalyst is excellent.
2 Most surprising is the result noted that after an 3 initial break-in period on stream, the rejuvenated catalyst (see 4 FIG. 3) exhibits a markedly improved fouling rate relative to a fresh HDS catalyst.
7 FIG. 1 shows the removal of metal from a spent catalyst 8 carrier as a function of nitric acid strength.
9 F.IG. 2 shows the weight percent metals removal as a function of the amount of nitric acid used for leaching.
11 FIG. 3 shows a comparison under comparable conditions 12 of the performance of a fresh catalyst vs. the performance of a 13 rejuvenated catalyst.
Ca rier Mate___l_ 16 Porous particulate carrier materials comprising alumina 17 sized for use in a fixed-bed hydrotreating reactor and ordinarily 18 employed as carrier particles for hydrotreating (hydro-19 desulfurizing, hydrocracking, hydrodemetallation and hydrode-nitrification) catalysts are in general rejuvenated by the 21 present process and are contemplated for use as feeds herein.
22 The particle sizing usually varies in the diameter range from 0.5 23 to 10 mm and may be any suitable shape. Preferably the carrier 24 material is a mixture of silica and alumina in any proportions.
Still more preferably, the carrier material consists essentially 26 of alumina. This process is advantageously applied to particles 27 having a surface area of at least 50 mZ/gram and is especially 28 - advantageous when used to rejuvenate high-surface-area carriers 29 comprising alumina ordinarily used in the preparation of HDS
30' catalysts for use in hydrotreating sulfur-containing and metals-31 contaminated hydrocarbons. Such feeds routinely plug or foul the 32 pores and surfaces of the catalyst.
1 C_taly_i _C__p_n_n_ 2 The present process is preferably applied to spent 3 hydrotreating catalyst particles comprising Group VI and/or Group 4 VIII metals and a carrier material as described above. Effective amounts of the catalytic components of these catalysts vary, and 6 ordinarily are in the range, calculated as metal, from 1 to 25 7 weight percent of the composite catalyst. Other components, such 8 as promoters and stabilizers, may also be present in minor 9 amounts, for example phosphorus. Usually these catalysts are prepared using conventional solution impregnation methods. They 11 may also be prepared by gelation, cogelation, and the like 12 methods, of the carrier component wherein the catalytic 13 components are incorporated into the carrier at any convenient `;
14 time, for example during gelation, after gelation, after calcination of the carrier, and the like. Preferably the spent 16 catalysts used as feeds in the process have in their preparation 17 been subjected, either as the total composite or as the carrier 18 per se, to calcination at a temperature in the range 426-871C, 19 preferably 482-593C, prior to use. Such catalysts in general appear to suffer little or no loss of support material by 21 dissolution in the nitric acid leaching solution of the present 22 process. They also appear to suffer but a minor loss, if-any, of 23 crush strength as a result of the leaching.
24 Le _hin~_C_n_ltl__s A. A_id_C____nt_at_on 26 For the leaching of metal sulfide contaminants from 27 spent hydrotreating catalysts, a sufficiently concentrated 28 aqueous nitric acid solution must be used. Although the relative 29 ease of dissolution of metal sulfide contaminants varies depending upon a number of factors, including the specific metal, 31 the degree of pore plugqing and the like, a satisfactory concen-32 tration for the nitric acid is, in general, in the range 5 to 10 ~89~893 1 weight percent (e.g., about 0.8 to 1.7 molar). Preferably the 2 concentration of the nitric acid is in the range 10 to 17.5 3 weight percent (e.g., about 1.7 to 3 molar). Higher 4 concentrations may be used, but such use is relatively disadvan-tageous in terms of increasing dissolution of the carrier 6 particles and increasing loss of crush strength of the particles.
7 8ecause the leaching reaction is exothermic and gas is evolved, 8 the use of nitric acid having an excessive concentration is 9 disadvantageous for further reasons in that such use includes problems of temperature control and foam-up control. There 11 appears to be no redeeming counteradvantage to the foregoing 12 - disa~vantages in the use of n-itric acid having a concentration 13 above about 20 weight percent (e.g., about 3.4 molar).
14 ~. Tem~erature The temperature which should be used for the leaching 16 varies, depending upon factors such as the acid concentration 17 used, the particular carrier particles involved, and the degree 18 of the leaching. Usually the initial temperature should be lower 19 than the final temperature as a matter of convenience in controlling the more exothermic phase of the leaching and the 21 evolution of gaseous by-products. In general, a satisfactory 22 temperature is in the range 0C to the reflux temperature for the 23 leaching solution. The use of higher temperatures tends to 24 result in increased dissolution of the carrier particles themselves. Preferably a temperature in the range from about 26 10C to 30C is employed. More preferably a temperature in the 27 range 10-20C is employed.
28 Residual-Matter Oxid__ion 29 The oxidizable residual matter present OD the leached 30' carrier varies in composition, depending upon the prior service 31 of the spent catalyst. In general, the material appears to be 32 ~ainly carbonaceous matter, i.e., coke, sulfocàrbon solids, and ~84893 1 the like. It is readily oxidizable to gaseous products at a 2 temperature below the sintering temperature of the particles.
3 Usually the oxidation of this material is so exothermic that it 4 is desirably effected, at least in the initial stage, by using molecular oxygen diluted by an inert gas, for example nitrogen or 6 carbon dioxide, in order to avoid subjecting the leached carrier 7 particles to a temperature which exceeds their sintering 8 temperature. Otherwise, the particles tend to suffer a severe 9 loss in surface area and may suffer undesirable changes in the pore characteristics. Preferably the oxidizing of this residual 11 matter is effected in the main by contacting an oxidizing gas 12 comprising nitrogen containing from 1 to 5 volume percent of 13 molecular oxygen with the leached carrier particles, the 14 contactinq being at a temperature in the range from about 260C
to 540C, more preferably 340C to 400C. The oxidation is 1~ satisfactorily complete when the effluent gas contains little or 17 no carbon dioxide and/or sulfur oxide gas.
18 I_Preqn_t_Q_ 19 For the rejuvenation and/or reconstitution of the spent catalyst, the catalytic components removed by the leaching must 21 be restored, or if a new combination of catalytic components is 22 desired by impregnating the leached and partially rejuvenated 23 carrier with a suitable solution. While the impregnation is 24 desirably effected prior to completing the carrier rejuvenation by the oxidizing step, it may also be conveniently effected 26 afterwards. Routine impregnation methods are contemplated and 27 used in this step. The carrier particles are immersed in a 28 solution containing one or more of the desired catalytic 29 components or a suitable precursor thereof, and the absorbed 30' solvent, which is usually water but not necessarily so, is 31 evaporated from the leached carrier particles. The impregnation 32 may be achieved in a single-dunk-type operation with the _ 9 _ 108~893 1 catalytic components all present, or by the use of two or more 2 impregnating solutlons. The single-dun~ method is preferred.
3 That is, a single solution containing sufficient of the catalytic 4 components, for example cobalt nitrate and phosphomolybdic acid, is used to restore the metal contents of these components to that ~ of the fresh catalyst before use in a hydrotreating process.
7 Calci__t_on 8 Depending upon whether or not the fresh catalyst prior 9 to its use was desirably calcined, the _omposite resulting from the above-described impregnation step is also calcined.
11 Calcination, in any event, is carried out after any oxidizable 12 residue on the leached carrier is removed by an oxidation step.
13 Calcination is carried out at a temperature below the sintering 14 temperature of the particles, preferably at a temperature in the range 426C to 871C, and more preferably 482C to 593C.
17 The following examples are for the further illustration 18 -but not limitation of the present invention.
19 Exa_~
In this example the effect of nitric acid concentration 21 upon the leaching of metal sulfide contaminant and sulfur-22 containing contaminant is demonstrated in a series of runs using 23 water alone and by using a series of nitri~ acid concentrations 24 in which the acid and spent catalyst particles are contacted in a glass reactor. For each gram of the spent catalyst, 6.5 mls, an 26 excess, of nitric acid was used. Except for the acid 27 concentrations (see FIG. 1), the conditions employed in these 28 runs were as follows:
29 Temperature, C 10-21 Pressure Atmospheric 31 Time, hours 4 32 The spent catalyst used in these runs had been expended iO84893 .
1 in hydrodesulfurization service in which the hydrocarbon feed had 2 a high sulfur and a high metals content. The fresh catalyst 3 contained molybdenum and cobalt, calculated as metals, in the 4 weight percents 12 and 3, respectively. ~he spent catalyst contained vanadium, nickel, iron, carbon and sulfur in the weight 6 percents 5.4, 1.7, 0.2, 13.4 and 11.0, respectively. The metals 7 contents were determined using x-ray fluorescence (estimated 8 uncertainty ~10% of value) and the carbon and sulfur were 9 determined by combustion (estimated uncertainty ~5% of value).
The results of the runs are shown in FIG. 1. These data 11 establish that for effective removal of metal sulfide 12 contaminants (vanadium and nickel), for example removal of at 13 least 75 weight percent, a substantial nitric acid concentration 14 must be employed, that is, a concentration which is at least in the ran~e 0.8 to 1.7 molar, and preferably is in the range 1.7 to 16 3 molar. Th-ese data also establish that there is no apparent 17 advantage in the use of an acid concentration in excess of about 18 3.5 molar.
19 Exampl__2 In this example, the effect of the amount of nitric 21 acid used upon the removal of metal sulfide and sulfur from the 22 spent catalyst particles by leaching is demonstrated in a series 23 of runs. The conditions and spent catalyst used were as in 24 Example 1, except that the nitric acid used was 3 molar and the relative amounts of acid used were varied (see FIG. 2). These 26 data establish that provided at least sufficient acid is employed 27 for the effective ~for example at least 75X) removal of the metal 28 sulfide contaminants, there is no apparent advantage in the use 29 of a large excess of the acid for removal of metal sulfide 30! contaminants. In the case of the spent catalyst used in these 31 examples, a satisfactory amount is at least about S mls of acid 32 per gram of spent catalyst. These runs also suggest that the 1~84893 1 amount of acid desirably used per unit weight of the spent 2 catalyst varies depending in the main upon the relative amount of 3 the spent catalyst metal, sulfur impurity, and metal sulfide 4 impurity components present in the spent catalyst which are leached from the carrier particles.
6 In general, it appears from these examples that the use 7 per gram of spent catalyst of an amount of a suitable con-8 centrated nitric acid in the range from about 4 to 20 mls results 9 in an effective removal of metal sulfide contaminant from a spent hydrotreating catalyst. Preferably, when the acid concentration 11 is in the range 1 to 3 molar, and the amount of acid employed, in 12 general, should be in the range from about 4 to 10 mls per gram 13 of spent catalyst, more preferably 4 to 7 mls.
14 ExamPl__3 In this example the performance in hydrodesulfurization 16 service of a rejuvenated catalyst as herein was compared with the 17 performance of a fresh catalyst. The hydrocarbon feed was an 18 Iranian heavy atmospheric residuum containing about 2.7 weight 19 percent of sulfur and a high metals content. Within experimental limits for molybdenum and cobalt determination, the respective 21 catalysts contained the same amount of molybdenum and cobalt 22 catalytic components. In addition, the rejuvenated catalyst 23 prior to use contained about 0.8 weight percent of vanadium 24 (calculated as metal) and trace amounts of nickel, iron and sulfur.
26 The surface areas (BET nitrogen method~ for the fresh 27 catalyst and the rejuvenated catalyst were 164 and 187 m2/g, 28 respectively, and the densities were each 1.3 g/cc. The larger 29 surface area for the rejuvenated catalyst is attributable to the rejuvenation process, because the carrier particles employed were 31- the same for the fresh comparison catalyst and for the parent to 32 the rejuvenated catalyst. (The improvement in surface area, 1~84893 1 about 14~, of the rejuvenated catalyst over the fresh catalyst is 2 therefore an unexpected bonus.) 3 The process conditions in the comparative runs were:
4 Pressure, atmospheres 139 H2 feed, SCM/100 liters 177 6 LHSV 1.6 7 The results from the above-described comparative runs 8 are shown in ~IG. 3. These data establish that during an initial 9 break-in period of about 140 hours, both catalysts, the fresh ~10 catalyst and rejuvenated catalyst, exhibited for practical 11 purposes the same fouling rate. Thereafter, the fouling rate for 12 the rejuvenated catalyst was markedly superior to that of the 13 fresh catalyst, i.e., a negligible rate vs. a rate of about 14 0.08C per hour.
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for rejuvenating a catalyst comprising an effective amount of a catalytic component disposed on an alumina carrier, said catalytic component comprising a Group VI metal or compound thereof and a Group VIII metal or compound thereof, and said catalyst having pores which are plugged or fouled by metal sulfide contaminants as a result of use of said catalyst in hydrotreating a hydrocarbon feed which contains an organometallic compound and sulfur-contaminants, which comprises:
(1) leaching at least 50% of said metal sulfide con-taminants, calculated as metal, from said catalyst with aqueous nitric acid solution, said solution having a nitric acid concen-tration in the range from about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0°C to the reflux temperature of said solution, and (b) effected by using for each gram of said catalyst an amount of said solution in the range of 4-20 ml. said amount being in excess of the stoichiometric quantities required for said metal sulfide contaminant;
(2) oxidizing residual oxidixable matter from said leached catalyst by contacting said catalyst with molecular oxy-gen at a temperature below the sintering temperature of said catalyst.
(1) leaching at least 50% of said metal sulfide con-taminants, calculated as metal, from said catalyst with aqueous nitric acid solution, said solution having a nitric acid concen-tration in the range from about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0°C to the reflux temperature of said solution, and (b) effected by using for each gram of said catalyst an amount of said solution in the range of 4-20 ml. said amount being in excess of the stoichiometric quantities required for said metal sulfide contaminant;
(2) oxidizing residual oxidixable matter from said leached catalyst by contacting said catalyst with molecular oxy-gen at a temperature below the sintering temperature of said catalyst.
2. A process for rejuvenating a catalyst comprising a catalytic component disposed on a carrier, which carrier is selected from the group consisting of particles of alumina and of silica-alumina mixtures, said catalytic component comprising a Group VI metal or compound thereof and a Group VIII metal or compound thereof, said catalyst having pores which are plugged or fouled by metal sulfide contaminants as a result of using said catalyst for hydrotreating hydrocarbon feeds containing organometallic compounds and sulfur contaminants, which com-prises:
(1) leaching at least 50% of said metal sulfide contaminant, calculated as metal, from said catalyst with a solu-tion of aqueous nitric acid, said solution having a nitric acid concentration in the range from about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0°C to the reflux temperature of said solution, and (b) effected by using for each gram of said catalyst an amount of said solution in the range of 4-20 ml, said amount of solution being in excess of the stoichiometric quantities required for said sulfide contaminant;
(2) impregnating said leached catalyst with at least one solution of the catalytic component or precursor thereof to restore the catalytic components lost during said leaching;
(3) oxidizing residual oxidizable matter from said leached and impregnated catalyst by contacting said catalyst at a temperature below the catalyst sintering temperature with molecular oxygen; and (4) calcining the resulting impregnated catalyst after said catalyst has undergone the oxidizing step, at a temperature below the sintering temperature of said catalyst.
(1) leaching at least 50% of said metal sulfide contaminant, calculated as metal, from said catalyst with a solu-tion of aqueous nitric acid, said solution having a nitric acid concentration in the range from about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0°C to the reflux temperature of said solution, and (b) effected by using for each gram of said catalyst an amount of said solution in the range of 4-20 ml, said amount of solution being in excess of the stoichiometric quantities required for said sulfide contaminant;
(2) impregnating said leached catalyst with at least one solution of the catalytic component or precursor thereof to restore the catalytic components lost during said leaching;
(3) oxidizing residual oxidizable matter from said leached and impregnated catalyst by contacting said catalyst at a temperature below the catalyst sintering temperature with molecular oxygen; and (4) calcining the resulting impregnated catalyst after said catalyst has undergone the oxidizing step, at a temperature below the sintering temperature of said catalyst.
3. A process as in claim 2 further characterized in that at least 75% of said metal sulfide is leached.
4. A process as in claim 2 further characterized in that said catalyst is sized in the diameter range from 0.5 to 10 mm and has a surface area of at least 50 m2 per gram.
5. A process as in claim 2 further characterized in that the concentration of said nitric acid solution is in the range 1.7 to 3 molar.
6. A process as in claim 2 further characterized in that said leaching is carried out at a temperature in the range from about 10°C to 30°C.
7. A process as in claim 2 further characterized in that said oxidizing is carried out at a temperature in the range from about 260°C to the sintering temperature of said particles.
8. A process as in claim 2 further characterized in that said oxidizing is carried out at a temperature in the range from about 260°C to 540°C.
9. A process for rejuvenating a hydrotreating catalyst comprising a catalytic component of cobalt, molybdenum and phos-phorus disposed upon alumina having pores fouled or plugged with vanadium sulfide, which comprises:
(1) leaching said catalyst at a temperature in the range 10-22°C with aqueous nitric acid solution containing about 12.5 weight percent of said acid, thereby removing at least 75%
of said vanadium sulfide, a substantial portion of said cobalt and a minor portion of said molybdenum;
(2) restoring said catalytic component by impregn-ating said leached particles with a solution containing cobalt nitrate and phosphomolybdic acid;
(3) oxidizing residual oxidizable matter from said leached and impregnated particles by contacting said particles with an inert gas containing an amount of molecular oxygen gas in the range 1 to 5 volume percent, said contacting being at a temperature in the range 340° to 400°C; and (4) calcining the oxidized particles at a temperature in the range from about 426° to 871°C.
(1) leaching said catalyst at a temperature in the range 10-22°C with aqueous nitric acid solution containing about 12.5 weight percent of said acid, thereby removing at least 75%
of said vanadium sulfide, a substantial portion of said cobalt and a minor portion of said molybdenum;
(2) restoring said catalytic component by impregn-ating said leached particles with a solution containing cobalt nitrate and phosphomolybdic acid;
(3) oxidizing residual oxidizable matter from said leached and impregnated particles by contacting said particles with an inert gas containing an amount of molecular oxygen gas in the range 1 to 5 volume percent, said contacting being at a temperature in the range 340° to 400°C; and (4) calcining the oxidized particles at a temperature in the range from about 426° to 871°C.
10. A process as in claim 2 further characterized in that said restoring is carried out after said oxidizing.
11. A process for rejuvenating a catalyst comprising a catalytic component disposed on a carrier, which carrier is selected from the group consisting of particles of alumina and of silica-alumina mixtures, said catalytic component comprising a Group VI metal or compound thereof and a Group VIII metal or compound thereof, said catalyst having pores which are plugged or fouled by metal sulfide contaminants as a result of using said catalyst for hydrotreating hydrocarbon feeds containing organometallic compounds and sulfur contaminants, which com-prises:
(1) leaching at least 50% of said metal sulfide contaminant, calculated as metal, from said catalyst with a solution of aqueous nitric acid, said solution having a nitric acid concentration in the range from about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0°C to the reflux temperature of said solution, and (b) effected by using for each gram of said catalyst an amount of said solution in the range of 4-20 ml. said amount of solution being in excess of the stoichiometric quantities required for said sulfide contaminant;
(2) oxidizing residual oxidizable matter from said leached and impregnated catalyst by contacting said catalyst at a temperature below the catalyst sintering temperature with molecular oxygen;
(3) impregnating said leached catalyst with at least one solution of the catalytic component or precursor thereof to restore the catalytic components lost during said leaching;
and (4) calcining the resulting impregnated catalyst after said catalyst has undergone the oxidizing step, at a tem-perature below the sintering temperature of said catalyst.
(1) leaching at least 50% of said metal sulfide contaminant, calculated as metal, from said catalyst with a solution of aqueous nitric acid, said solution having a nitric acid concentration in the range from about 0.8-3 molar, said leaching being (a) carried out at a temperature in the range from 0°C to the reflux temperature of said solution, and (b) effected by using for each gram of said catalyst an amount of said solution in the range of 4-20 ml. said amount of solution being in excess of the stoichiometric quantities required for said sulfide contaminant;
(2) oxidizing residual oxidizable matter from said leached and impregnated catalyst by contacting said catalyst at a temperature below the catalyst sintering temperature with molecular oxygen;
(3) impregnating said leached catalyst with at least one solution of the catalytic component or precursor thereof to restore the catalytic components lost during said leaching;
and (4) calcining the resulting impregnated catalyst after said catalyst has undergone the oxidizing step, at a tem-perature below the sintering temperature of said catalyst.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US59111875A | 1975-06-27 | 1975-06-27 | |
| US591,118 | 1975-06-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1084893A true CA1084893A (en) | 1980-09-02 |
Family
ID=24365119
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA253,004A Expired CA1084893A (en) | 1975-06-27 | 1976-05-20 | Rejuvenation process for catalyst carrier particles and for catalysts |
Country Status (2)
| Country | Link |
|---|---|
| JP (1) | JPS5214593A (en) |
| CA (1) | CA1084893A (en) |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5635940B2 (en) * | 1973-05-22 | 1981-08-20 | ||
| JPS549995B2 (en) * | 1973-11-06 | 1979-04-28 |
-
1976
- 1976-05-20 CA CA253,004A patent/CA1084893A/en not_active Expired
- 1976-06-23 JP JP51074256A patent/JPS5214593A/en active Pending
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| Publication number | Publication date |
|---|---|
| JPS5214593A (en) | 1977-02-03 |
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