Method for recovering platinum group element

Abstract

Provided is a method for recovering a platinum group element from a solution containing a platinum group element, the method using a capture agent to induce adsorption of the platinum group element by the capture agent. In this method, the platinum group element is adsorbed by a capture agent such that at least 50 mol% of the platinum group element adsorbed by the capture agent is in the form of a platinum group element complex in an oxidized state, and the platinum group element is thereby recovered.

Description

Method for recovering platinum group elements

[0001] The present invention relates to a method for recovering platinum group elements from a solution containing platinum group elements.

[0002] Nitrile rubber (acrylonitrile-butadiene copolymer rubber) has traditionally been used as a material for automotive rubber parts such as hoses and tubes, taking advantage of its oil resistance, mechanical properties, chemical resistance, etc., and hydrogenated nitrile rubber (hydrogenated acrylonitrile-butadiene copolymer rubber), which is made by hydrogenating the carbon-carbon double bonds in the polymer main chain of nitrile rubber, has even better heat resistance and is therefore used for rubber parts such as belts, hoses, and diaphragms.

[0003] Such hydrogenated nitrile rubber is produced, for example, by the following production process: emulsion polymerization of a monomer mixture containing an α,β-ethylenically unsaturated nitrile monomer and a conjugated diene monomer, coagulation and drying of the nitrile rubber latex obtained by emulsion polymerization, and then dissolving the nitrile rubber obtained by coagulation and drying in a water-soluble organic solvent to obtain a water-soluble organic solvent solution of nitrile rubber, to which a platinum group element-containing catalyst is added as a hydrogenation catalyst, followed by hydrogenation.

[0004] On the other hand, the hydrogenated nitrile rubber produced by such a production method uses a platinum group element-containing catalyst as a hydrogenation catalyst, and from the viewpoint of suppressing coloration of the hydrogenated nitrile rubber finally obtained, removal of the platinum group element-containing catalyst has been studied in order to reduce the content of the platinum group element-containing catalyst contained in the hydrogenated nitrile rubber.

[0005] As a technique for recovering such platinum group element-containing catalysts, for example, Patent Document 1 discloses a method in which a complexing agent is added to a reaction mixture of a hydrogenation reaction carried out in the presence of a platinum group element-containing catalyst supported on a carrier, the complexing agent complexes the platinum group element-containing catalyst that has been released from the carrier and is contained in the reaction mixture, the resulting complex is re-supported on a carrier, and the carrier is then removed from the reaction mixture.

[0006] Japanese Patent Application Laid-Open No. 2004-26998

[0007] On the other hand, because the platinum group elements contained in platinum group element-containing catalysts are expensive, there has been a demand in recent years for their recovery and reuse. In response to this demand, the inventors conducted research and found that while the technology of Patent Document 1 can remove platinum group element-containing catalysts from solutions of the platinum group element-containing catalysts at a relatively high removal rate, the amount of platinum group elements that can be recovered is small. Therefore, improvements are desired in terms of the recovery and reuse of platinum group elements. The present invention has been made in light of this situation, and aims to provide a method for recovering platinum group elements that can recover platinum group elements with high efficiency.

[0008] As a result of intensive research conducted by the present inventors to achieve the above-mentioned object, they have found that the above-mentioned problems can be solved by using a scavenger to adsorb a platinum group element onto the scavenger, and recovering the platinum group element from a solution containing the platinum group element, so that the proportion of the platinum group element adsorbed onto the scavenger in the form of an oxidized platinum group element complex is at least a predetermined value, thereby recovering the platinum group element, and have thus completed the present invention.

[0009] That is, according to the present invention, there is provided a method for recovering platinum group elements from a solution containing the platinum group elements by using a scavenger to adsorb the platinum group elements onto the scavenger, in which the platinum group elements are recovered by adsorbing the platinum group elements onto the scavenger in a state in which the proportion of the platinum group elements adsorbed onto the scavenger in the form of an oxidized platinum group element complex is 50% or more by mole.

[0010] In the method for recovering platinum group elements of the present invention, it is preferable to recover platinum group elements by adsorbing the platinum group elements onto the scavenger in a state in which the proportion of platinum group elements adsorbed onto the scavenger in the form of platinum group element complexes in an oxidation state of 2 or more is 50% by mole or more. In the method for recovering platinum group elements of the present invention, it is preferable to recover platinum group elements in the presence of a complexing agent represented by the following general formula (1): ｎ H ｍ N ｐ O ｑ X ｒ(1) (In the above general formula (1), X is an element other than C, H, N, or O, n = 1 to 13, m = 1 to 18, p = 0 to 4, q = 0 to 4, r = 0 to 4, and at least one of p and q is 1 or greater.) In the method for recovering platinum group elements of the present invention, it is preferable that the complexing agent is an ammonium salt, an amine, or an imine. In the method for recovering platinum group elements of the present invention, it is preferable that the solution containing a platinum group element is a solution containing a platinum group element and a polymer. In the method for recovering platinum group elements of the present invention, it is preferable that the solution containing a platinum group element is a solution containing hydrogenated nitrile rubber and a platinum group element derived from a platinum group element-containing catalyst. In the method for recovering platinum group elements of the present invention, it is preferable that recovery of the platinum group element contained in the solution containing platinum group elements by adsorption to the scavenger is started in a state in which the solution containing platinum group elements is simultaneously contacted with a non-metal-oxidizing agent, a complexing agent, and a scavenger. In the method for recovering platinum group elements of the present invention, it is preferable to simultaneously contact a solution containing platinum group elements with a non-metal-oxidizing agent and a complexing agent, and pass the solution containing 50% or more mol of oxidized platinum group element complexes through a column packed with a scavenger to adsorb the platinum group elements to the scavenger. In the method for recovering platinum group elements of the present invention, it is preferable that the non-metal-oxidizing agent is hydrogen peroxide, air, or oxygen. In the method for recovering platinum group elements of the present invention, it is preferable that the scavenger is surface-treated silica.

[0011] According to the present invention, it is possible to provide a method for recovering platinum group elements that can recover platinum group elements with high efficiency.

[0012] The method for recovering platinum group elements of the present invention is a method for recovering platinum group elements from a solution containing the platinum group elements by using a scavenger to adsorb the platinum group elements onto the scavenger, and recovering the platinum group elements by adsorbing the platinum group elements onto the scavenger in a state in which the proportion of the platinum group elements adsorbed in the form of an oxidized platinum group element complex is 50% or more by mole.

[0013] <Platinum Group Elements> First, the platinum group elements to be recovered in the recovery method of the present invention will be described. In the recovery method of the present invention, the platinum group elements to be recovered may be those contained in a solution containing a platinum group element. Examples of such a solution containing a platinum group element include platinum group elements contained in a solution containing a platinum group element and a polymer. More specifically, examples include platinum group elements derived from platinum group element-containing catalysts used to obtain hydrogenated conjugated diene rubbers such as hydrogenated nitrile rubber by hydrogenating carbon-carbon double bonds contained in conjugated diene rubbers such as nitrile rubber. That is, examples include platinum group elements derived from platinum group element-containing catalysts contained in a solution of hydrogenated conjugated diene rubbers such as hydrogenated nitrile rubber. The hydrogenation reaction of nitrile rubber will be used as an example of the hydrogenation reaction of such conjugated diene rubber and will be described below.

[0014] Examples of nitrile rubbers include copolymers obtained by copolymerizing a monomer mixture containing at least an α,β-ethylenically unsaturated nitrile monomer and a conjugated diene monomer. The α,β-ethylenically unsaturated nitrile monomer is not particularly limited as long as it is an α,β-ethylenically unsaturated compound having a nitrile group, and examples include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile. Examples of conjugated diene monomers include conjugated diene monomers having 4 to 6 carbon atoms, such as 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and chloroprene.

[0015] The content of α,β-ethylenically unsaturated nitrile monomer units in the nitrile rubber is preferably 5 to 60% by weight, more preferably 10 to 50% by weight, and even more preferably 15 to 50% by weight, based on the total monomer units. Also, the content of conjugated diene monomer units (including the hydrogenated portion by hydrogenation reaction) in the nitrile rubber is preferably 40 to 95% by weight, more preferably 50 to 90% by weight, and even more preferably 50 to 85% by weight, based on the total monomer units.

[0016] The nitrile rubber may be a copolymer of an α,β-ethylenically unsaturated nitrile monomer and a conjugated diene monomer, and other monomers copolymerizable therewith. Examples of such other copolymerizable monomers include α,β-ethylenically unsaturated monocarboxylic acid monomers such as acrylic acid and methacrylic acid; α,β-ethylenically unsaturated polycarboxylic acid monomers; α,β-ethylenically unsaturated monocarboxylic acid ester monomers such as methyl acrylate, ethyl acrylate, and n-butyl acrylate; α,β-ethylenically unsaturated dicarboxylic acid monoester monomers such as mono-n-butyl maleate and mono-n-butyl fumarate; ethylene; α-olefin monomers, aromatic vinyl monomers; fluorine-containing vinyl monomers; and copolymerizable antioxidants.

[0017] The hydrogenation reaction of nitrile rubber is usually carried out using a platinum group element-containing catalyst. The hydrogenation reaction of nitrile rubber can be carried out on the latex of nitrile rubber obtained by emulsion polymerization in the latex state, or the latex of nitrile rubber obtained by emulsion polymerization is coagulated and dried to obtain solid nitrile rubber, and the obtained nitrile rubber is dissolved in an organic solvent to carry out the hydrogenation reaction in the state of a polymer solution. Among these, from the viewpoint of catalytic activity, it is preferable to dissolve the obtained nitrile rubber in a water-soluble organic solvent to carry out the hydrogenation reaction in the state of a polymer solution.

[0018] The coagulation and drying of the nitrile rubber latex may be carried out by a known method, but it is preferable to provide a treatment step in which the crumbs obtained by coagulation are brought into contact with a basic aqueous solution, thereby modifying the nitrile rubber obtained so that the pH of the polymer solution measured by dissolving the nitrile rubber in tetrahydrofuran (THF) exceeds 7. The pH of the polymer solution measured by dissolving the nitrile rubber in THF and adding several wt % of water to the THF is preferably in the range of 7.2 to 12, more preferably 7.5 to 11.5, and most preferably 8 to 11. This contact treatment of the crumbs with a basic aqueous solution makes it possible to rapidly proceed with solution-based hydrogenation (hydrogenation carried out by dissolving the crumbs in an organic solvent).

[0019] The concentration of the nitrile rubber in the polymer solution during the hydrogenation reaction is preferably 1 to 70% by weight, more preferably 1 to 40% by weight, and particularly preferably 2 to 20% by weight. Examples of organic solvents include ketones such as acetone, methyl ethyl ketone, diethyl ketone, and methyl isopropyl ketone; ethers such as tetrahydrofuran and dioxane; esters such as ethyl acetate; aldehydes such as dimethylformamide; aromatic compounds such as toluene, chlorobenzene, and monochlorobenzene; and halogenated aliphatic compounds. Among these organic solvents, ketones are preferably used, and acetone is particularly preferably used.

[0020] When carrying out the hydrogenation reaction, a platinum group element-containing catalyst is used as the hydrogenation catalyst. The platinum group element-containing catalyst is not particularly limited as long as it is a catalyst containing a platinum group element, i.e., ruthenium, rhodium, palladium, osmium, iridium, or platinum, but from the viewpoint of catalytic activity and easy availability, a palladium compound or a rhodium compound is preferred, and a palladium compound is more preferred. Furthermore, two or more platinum group element compounds may be used in combination, but in this case, it is also preferred that the palladium compound be the main catalyst component.

[0021] The palladium compound used is usually a divalent or tetravalent palladium compound, which is in the form of a salt or a complex salt.

[0022] Examples of palladium compounds include palladium acetate, palladium cyanide, palladium fluoride, palladium chloride, palladium bromide, palladium iodide, palladium nitrate, palladium sulfate, palladium oxide, palladium hydroxide, dichloro(cyclooctadiene)palladium, dichloro(norbornadiene)palladium, dichlorobis(triphenylphosphine)palladium, sodium tetrachloropalladate, ammonium hexachloropalladate, and potassium tetracyanopalladate.

[0023] Among these palladium compounds, palladium acetate, palladium nitrate, palladium sulfate, palladium chloride, sodium tetrachloropalladate, and ammonium hexachloropalladate are preferred, and palladium acetate, palladium nitrate, and palladium chloride are more preferred.

[0024] Examples of rhodium compounds include rhodium chloride, rhodium bromide, rhodium iodide, rhodium nitrate, rhodium sulfate, rhodium acetate, rhodium formate, rhodium propionate, rhodium butyrate, rhodium valerate, rhodium naphthenate, rhodium acetylacetonate, rhodium oxide, and rhodium trihydroxide.

[0025] As the platinum group element-containing catalyst, the above-mentioned palladium compound or rhodium compound may be used as it is, or the above-mentioned catalyst component such as the palladium compound or rhodium compound may be supported on a carrier and used as a supported catalyst.

[0026] The carrier for forming the supported catalyst may be any carrier generally used as a carrier for metal catalysts, but specifically, inorganic compounds containing carbon, silicon, aluminum, magnesium, etc. are preferred. Among these, from the viewpoint of further increasing the adsorption efficiency of catalyst components such as palladium compounds and rhodium compounds, the carrier should have the characteristics of an average particle diameter of 1 μm to 500 μm and a specific surface area of ​​200 to 2000 m. ２ It is preferable to use one having a molecular weight of 1 / g.

[0027] Such a carrier is appropriately selected from known catalyst carriers such as activated carbon, activated clay, talc, clay, alumina gel, silica, diatomaceous earth, and synthetic zeolite. Methods for supporting the catalyst component on the carrier include, for example, impregnation, coating, spraying, and precipitation. The amount of the catalyst component supported is typically 0.5 to 80% by weight, preferably 1 to 50% by weight, and more preferably 2 to 30% by weight, of the catalyst component relative to the total weight of the catalyst and carrier. The carrier supporting the catalyst component can be shaped into, for example, a sphere, a cylinder, a polygonal pillar, a honeycomb, or other shape, depending on the type of reactor and the reaction format.

[0028] Furthermore, when a salt of a platinum group element such as a palladium compound or a rhodium compound is used as a platinum group element-containing catalyst without being supported on a carrier, it is preferable to use a stabilizer in combination to stabilize these compounds. By making the stabilizer present in a medium in which a platinum group element-containing catalyst such as a palladium compound or a rhodium compound is dissolved or dispersed, nitrile rubber can be hydrogenated at a high hydrogenation rate. A complexed platinum group element-containing catalyst may also be used.

[0029] Examples of such stabilizers include polymers of vinyl compounds having polar groups in their side chains, such as polyvinylpyrrolidone, polyvinyl alcohol, polyvinyl acetal, and polyalkyl vinyl ether; metal salts of polyacrylic acid, such as sodium polyacrylate and potassium polyacrylate; polyethers, such as polyethylene oxide, polypropylene oxide, and ethylene oxide-propylene oxide copolymer; cellulose derivatives, such as carboxymethyl cellulose and hydroxypropyl cellulose; and natural polymers, such as gelatin and albumin. Among these, polymers of vinyl compounds having polar groups in their side chains or polyethers are preferred. Among polymers of vinyl compounds having polar groups in their side chains, polyvinylpyrrolidone and polyalkyl vinyl ethers are preferred, and polymethyl vinyl ether is more preferred. Examples of complexing ligands include triphenylphosphine and the like.

[0030] In addition, a reducing agent may be used in combination during the hydrogenation reaction. Examples of the reducing agent include hydrazines such as hydrazine, hydrazine hydrate, hydrazine acetate, hydrazine sulfate, and hydrazine hydrochloride, and compounds that liberate hydrazine.

[0031] The temperature of the hydrogenation reaction is usually 0 to 200° C., preferably 5 to 150° C., and more preferably 10 to 100° C. By setting the temperature of the hydrogenation reaction within the above range, it is possible to achieve a sufficient reaction rate while suppressing side reactions.

[0032] The hydrogen pressure during the hydrogenation reaction is usually 0.1 to 20 MPa, preferably 0.1 to 15 MPa, and more preferably 0.1 to 10 MPa. The reaction time is not particularly limited, but is usually 30 minutes to 50 hours. It is preferable to first replace the hydrogen gas in the reaction system with an inert gas such as nitrogen, and then further replace it with hydrogen before pressurizing.

[0033] When a supported catalyst is used as the platinum group element-containing catalyst, the supported catalyst can be separated by filtration, centrifugation, or the like to obtain a water-soluble organic solvent solution of hydrogenated nitrile rubber.

[0034] <Method for recovering platinum group elements> Next, the method for recovering platinum group elements of the present invention will be described. The method for recovering platinum group elements of the present invention is a method for recovering platinum group elements from a solution containing platinum group elements by using a scavenger and allowing the scavenger to adsorb the platinum group elements.

[0035] Examples of solutions containing a platinum group element include a solution of a hydrogenated conjugated diene rubber such as the above-mentioned hydrogenated nitrile rubber, and when the solution containing a platinum group element is a solution of a hydrogenated conjugated diene rubber such as the above-mentioned hydrogenated nitrile rubber, examples include a solution containing a platinum group element derived from a platinum group element-containing catalyst. When the solution containing a platinum group element is a solution of a hydrogenated conjugated diene rubber such as the above-mentioned hydrogenated nitrile rubber, and a supported catalyst is used as the platinum group element-containing catalyst, the supported catalyst may be separated by filtration or centrifugation, and the solution obtained may be subjected to the method for recovering a platinum group element of the present invention, or the solution in which the supported catalyst remains may be subjected to the method for recovering a platinum group element of the present invention without separation.

[0036] In the method for recovering platinum group elements of the present invention, a scavenger is used to recover platinum group elements by contacting the scavenger with a solution containing the platinum group elements and allowing the scavenger to adsorb the platinum group elements. The platinum group elements are recovered by adsorbing the platinum group elements onto the scavenger in a state where the proportion of the platinum group elements adsorbed on the scavenger in the form of oxidized platinum group element complexes is 50% or more by mole. More specifically, the scavenger with the platinum group elements adsorbed in this state is set to a state where the proportion of the platinum group elements adsorbed on the scavenger in the form of oxidized platinum group element complexes is 50% or more by mole, and the scavenger with the platinum group elements adsorbed in this state is separated from the solution containing the platinum group elements. According to the present invention, by adopting such a configuration, platinum group elements can be recovered with high efficiency. That is, the amount of platinum group elements captured by the scavenger can be increased (the capture rate can be increased), thereby increasing the reuse rate.

[0037] In the recovery method of the present invention, a scavenger is used to adsorb the platinum group elements contained in a solution containing the platinum group elements onto the scavenger, and the present inventors have conducted extensive research focusing on the state of the platinum group elements adsorbed onto the scavenger. Specifically, the present inventors have conducted extensive research focusing on the state of the platinum group elements adsorbed onto the scavenger and have found that the states of the platinum group elements adsorbed onto the scavenger, particularly the oxidation state, are not necessarily uniform, and further, by setting the proportion of platinum group elements adsorbed onto the scavenger in the form of oxidized platinum group element complexes to 50 mol % or more and recovering the scavenger in such a state, it is possible to increase the amount of platinum group elements captured by the scavenger (to increase the capture rate), thereby achieving a high recovery rate.

[0038] In the recovery method of the present invention, the platinum group elements may be recovered by adsorbing them onto a scavenger when the proportion of the platinum group elements adsorbed in the form of oxidized platinum group element complexes is 50 mol % or more, but it is desirable to recover the platinum group elements by adsorbing them onto a scavenger when the proportion of the platinum group elements adsorbed in the form of oxidized platinum group element complexes is preferably 60 mol % or more, more preferably 65 mol % or more, and even more preferably 68 mol % or more. The upper limit of the platinum group elements adsorbed in the form of oxidized platinum group element complexes is not particularly limited, but is preferably 99 mol % or less.

[0039] In the recovery method of the present invention, the platinum group elements may be recovered by adsorbing them onto a scavenger when the proportion of the platinum group elements adsorbed in the form of an oxidized platinum group element complex is 50% or more by mole, but from the viewpoint of increasing the amount of platinum group elements captured by the scavenger, it is desirable to recover the platinum group elements by adsorbing them onto a scavenger when the proportion of the platinum group elements adsorbed in the form of a platinum group element complex in an oxidation state of divalent or higher is 50% or more by mole. The proportion of the platinum group elements adsorbed in the form of a platinum group element complex in an oxidation state of divalent or higher is preferably 60 mol % or more, more preferably 65 mol % or more, and even more preferably 68 mol % or more, and although there is no particular upper limit, it is preferably 99 mol % or less.

[0040] The proportion of platinum group elements adsorbed in the form of platinum group element complexes in an oxidized state, or the proportion of platinum group elements adsorbed in the form of platinum group element complexes in an oxidation state of divalent or higher, can be determined, for example, by performing XAFS measurement to measure the valence ratio of the platinum group elements, as described in the Examples below.

[0041] In the recovery method of the present invention, a scavenger is brought into contact with a solution containing a platinum group element to adsorb the platinum group element onto the scavenger, and it is believed that the proportion of oxidized platinum group element complexes (and the proportion of platinum group element complexes in an oxidation state of divalent or higher) in the platinum group elements adsorbed by the scavenger and the proportion of oxidized platinum group element complexes (and the proportion of platinum group element complexes in an oxidation state of divalent or higher) in the solution containing the platinum group element will be close in value. In other words, the capture ability of the scavenger for platinum group elements is nearly the same regardless of the state of the platinum group element, i.e., whether or not an oxidized platinum group element complex (and a platinum group element complex in an oxidation state of divalent or higher) is formed. Therefore, it is believed that the above proportion in the platinum group element adsorbed by the scavenger and the above proportion in the solution containing the platinum group element will be close in value. Therefore, in the recovery method of the present invention, it is preferable to increase the proportion of oxidized platinum group element complexes (and the proportion of divalent or higher oxidation state platinum group element complexes) in the platinum group elements contained in the solution containing platinum group elements to within the above range and adsorb them onto the capture agent.

[0042] In the recovery method of the present invention, examples of platinum group elements include ruthenium, rhodium, palladium, osmium, iridium, and platinum, and among these, palladium and rhodium are preferred, with palladium being more preferred.

[0043] In the recovery method of the present invention, the platinum group element may be recovered by adsorbing the platinum group element onto a scavenger when the proportion of the platinum group element adsorbed in the form of an oxidized platinum group element complex is 50% or more by mole. Specific methods for this purpose are not particularly limited. For example, preferred methods include contacting a solution containing a platinum group element with a non-metal-oxidizing agent, a complexing agent, and a scavenger simultaneously, and then initiating recovery of the platinum group element contained in the solution by adsorption onto the scavenger; or contacting a solution containing a platinum group element with a non-metal-oxidizing agent and a complexing agent simultaneously, then contacting the solution with a scavenger, and initiating recovery of the platinum group element contained in the solution by adsorption onto the scavenger.

[0044] More specifically, it is preferable to start the process of recovering the platinum group elements contained in the solution containing platinum group elements by simultaneously causing a non-metal-oxidizing agent and a complexing agent and / or a scavenger to be present in the solution, and then heating the reaction solution in this state to preferably 35 to 150°C, more preferably 40 to 140°C. That is, it is preferable to start the process of recovering the platinum group elements in the solution containing platinum group elements in the simultaneous presence of a non-metal-oxidizing agent and a complexing agent (i.e., by heating to the above-mentioned temperature). In this case, from the viewpoint of further enhancing the effects of the present invention, it is more preferable to simultaneously cause a scavenger to be present in addition to a non-metal-oxidizing agent and a complexing agent, and then heating the solution in this state to the above-mentioned temperature to start the process of recovering the platinum group elements contained in the solution containing platinum group elements.

[0045] By starting the recovery process of a platinum group element in the simultaneous presence of a metal-free oxidizing agent and a complexing agent and / or a scavenger, the oxidation reaction of the platinum group element contained in the solution containing the platinum group element can be more appropriately progressed, thereby appropriately increasing the proportion of platinum group elements contained in the solution containing the platinum group element that are in the form of oxidized platinum group element complexes, and ultimately making it possible to preferably increase the proportion of platinum group elements adsorbed in the form of oxidized platinum group element complexes to 50% by mole or more of the platinum group elements adsorbed on the scavenger. In particular, according to the findings of the present inventors, if a recovery process is initiated in the absence of either a non-metal-oxidizing agent or a complexing agent, the proportion of platinum group elements in the form of oxidized platinum group element complexes contained in the solution containing platinum group elements tends not to increase effectively even as the recovery process progresses. However, by initiating a recovery process for platinum group elements in the simultaneous presence of a non-metal-oxidizing agent, a complexing agent and / or a scavenger, the proportion of platinum group elements in the form of oxidized platinum group element complexes contained in the solution containing platinum group elements can be appropriately increased as the recovery process progresses.

[0046] The scavenger may be present simultaneously at the start of the platinum group element recovery process, or may be incorporated into the reaction system by adding it to the reaction system after the start of the platinum group element recovery process, etc. Alternatively, the platinum group element recovery process may be started in a state in which the non-metal-oxidizing agent and the complexing agent are simultaneously present in a platinum group element-containing solution, and the reaction results in a solution in which the proportion of oxidized platinum group element complexes is 50% or more by mole, and this solution is passed through a column packed with the scavenger, and the platinum group elements are adsorbed onto the scavenger when the proportion of platinum group element adsorbed in the form of oxidized platinum group element complexes is 50% or more by mole, thereby recovering the platinum group elements.

[0047] The metal-free oxidizing agent is not particularly limited as long as it acts as an oxidizing agent and does not contain a metal, and examples thereof include iodine; peroxides such as hydrogen peroxide, peracetic acid, and perbenzoic acid; air; and oxygen; and among these, hydrogen peroxide, air, and oxygen are preferred.

[0048] When air or oxygen is used as the metal-non-oxidizing agent, it may be introduced by continuously blowing it into a solution containing a platinum group element under atmospheric pressure, or a method of pressurizing it under predetermined pressurized conditions may be employed. In this case, the pressurized condition is preferably 0.2 to 10 MPa, more preferably 0.4 to 8 MPa, even more preferably 0.5 to 5 MPa, and particularly preferably 0.7 to 2.5 MPa. Furthermore, when oxygen is used, it may be used in a state mixed with an inert gas such as nitrogen. In this case, the oxygen concentration is preferably 0.2 to 90 vol%, more preferably 0.4 to 70 vol%, even more preferably 1 to 50 vol%, and particularly preferably 2 to 12 vol%.

[0049] Furthermore, when a peroxide such as hydrogen peroxide is used as the non-metal-oxidizing agent, the amount of the peroxide such as hydrogen peroxide used is preferably 0.5 to 200 molar times, more preferably 1 to 150 molar times, even more preferably 2 to 100 molar times, and particularly preferably 5 to 50 molar times, relative to the molar amount of the platinum group elements contained in the solution containing the platinum group elements. At least a portion of the total amount of the non-metal-oxidizing agent used in the recovery treatment may be present at the start of the recovery treatment of the platinum group elements, or may be additionally added after the start of the recovery treatment of the platinum group elements.

[0050] The complexing agent is not particularly limited as long as it has a complexing ability for a platinum group element and can form a complex in an oxidized state, but a complexing agent represented by the following general formula (1) is preferred. ｎ H ｍ N ｐ O ｑ X ｒ (1) (In the above general formula (1), X is an element other than C, H, N, and O, n = 1 to 13, m = 1 to 18, p = 0 to 4, q = 0 to 4, r = 0 to 4, and at least one of p and q is 1 or greater.)

[0051] In the general formula (1), examples of X include S, P, and halogen, and among these, S is preferred. Furthermore, n is 1 to 13, preferably 2 to 12, and more preferably 3 to 12, m is 1 to 18, preferably 2 to 18, and more preferably 4 to 18, p is 0 to 4, and preferably 0 to 2, q is 0 to 4, and preferably 0 to 2, and r is 0 to 4, and preferably 0 to 1.

[0052] Examples of compounds represented by the general formula (1) include organic ammonium salts such as ammonium acetate, amines such as ethylenediamine and triethylenetetramine, oximes such as dimethylglyoxime, imines such as bipyridine and phenanthroline, ketones such as acetylacetone and carbamide, glycine, thiourea, 1-methylpiperazine, etc. Among these, organic ammonium salts, amines, and imines are preferred, and ammonium acetate, triethylenetetramine, and phenanthroline are suitable.

[0053] In addition to the compound represented by the general formula (1), inorganic ammonium salts can also be used as complexing agents. That is, both organic and inorganic ammonium salts can be used. Examples of inorganic ammonium salts include ammonium halides, and preferred examples of ammonium halides include ammonium bromide and ammonium chloride.

[0054] The amount of complexing agent used is preferably 1 to 200 molar times, more preferably 2 to 150 molar times, even more preferably 3 to 100 molar times, and particularly preferably 20 to 80 molar times, relative to the molar amount of platinum group elements contained in the solution containing platinum group elements. By using an amount of complexing agent within the above range, platinum group elements can be recovered with higher efficiency. Note that it is sufficient for at least a portion of the total amount of complexing agent to be used in the recovery process to be present at the start of the platinum group element recovery process, and additional addition may be made after the start of the platinum group element recovery process. However, from the perspective of recovering platinum group elements with higher efficiency, it is desirable for the entire amount to be used in the recovery process to be present at the start of the platinum group element recovery process.

[0055] The scavenger may be any material capable of capturing or adsorbing platinum group elements, and is not particularly limited thereto, but examples thereof include resins, silica, and carbon black. From the viewpoint of capturing or adsorbing ability, silica is preferred, and surface-treated silica is particularly preferred. Examples of surface-treated silica include thiol-modified silica, silanol-modified silica, amine-modified silica, thiourea-modified silica, phosphate-modified silica, and carbamate-modified silica. Of these, thiol-modified silica, silanol-modified silica, and amine-modified silica are preferred.

[0056] The amount of scavenger used is preferably 1 to 500 times, more preferably 2 to 300 times, even more preferably 5 to 100 times, and particularly preferably 35 to 65 times the weight of the platinum group elements contained in the solution containing platinum group elements. By using an amount of scavenger within the above range, it is possible to recover platinum group elements with higher efficiency. Note that it is sufficient for at least a portion of the total amount of scavenger used in the recovery process to be present at the start of the platinum group element recovery process, and additional addition may be made after the start of the platinum group element recovery process. However, from the perspective of recovering platinum group elements with higher efficiency, it is desirable for the entire amount to be used in the recovery process to be present at the start of the platinum group element recovery process.

[0057] In the recovery method of the present invention, the recovery treatment time is not particularly limited, but is preferably 1 to 96 hours, more preferably 2 to 48 hours, and even more preferably 4 to 24 hours. By setting the recovery treatment time within the above range, platinum group elements can be recovered more efficiently and with a high recovery rate.

[0058] In the recovery method of the present invention, the recovery process for platinum group elements is initiated in the simultaneous presence of a non-metal-oxidizing agent, a complexing agent, and a scavenger, and after the recovery process is completed, the solution after the recovery process is filtered or the like to recover (filter off) the scavenger with the platinum group element adsorbed thereon. This allows the platinum group element to be recovered in a state where it is adsorbed to the scavenger, by separating it from the solution after the recovery process.

[0059] According to the recovery method of the present invention, the platinum group elements are recovered by adsorbing them onto a scavenger when the proportion of platinum group elements adsorbed in the form of oxidized platinum group element complexes is 50% or more by mole. This allows the platinum group elements to be recovered at a high recovery rate, thereby enabling the platinum group elements to be reused at a high rate and suitably reused. Furthermore, since the recovery method of the present invention allows the platinum group elements to be recovered at a high recovery rate, it is possible to increase the removal rate of the platinum group elements from a solution containing the platinum group elements. Therefore, for example, by subjecting a solution containing a polymer, more specifically a solution of a hydrogenated conjugated diene rubber such as hydrogenated nitrile rubber, as the solution containing the platinum group elements to the recovery treatment of the present invention, it is possible to obtain a hydrogenated conjugated diene rubber (polymer) such as hydrogenated nitrile rubber with a reduced platinum group element content. In particular, in hydrogenated conjugated diene rubbers (polymers) such as hydrogenated nitrile rubber, by reducing the content of platinum group elements, it is possible to effectively suppress coloration due to platinum group elements while improving mechanical strength such as tensile strength.

[0060] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following, "parts" are by weight unless otherwise specified. The methods for testing or evaluating physical properties and characteristics are as follows.

[0061] <Iodine Value> The iodine value of the hydrogenated nitrile rubber was measured in accordance with JIS K6235.

[0062] <Mooney Viscosity> The Mooney viscosity (polymer Mooney viscosity) of the hydrogenated nitrile rubber was measured at 100°C in accordance with JIS K6300.

[0063] <Palladium Content> The palladium content was determined by atomic absorption spectrometry. The atomic absorption spectrometer used for the measurement was a ZA-3000 manufactured by Hitachi High-Tech Science Corporation, and the furnace method and flame method were used as appropriate.

[0064] <Measurement of the ratio of palladium valence> The dried scavenger was attached to a substrate such as a metal plate and subjected to XAFS (SPring-8 BL14B2) measurement. The valence was confirmed from the measurement results, and the ratio of each valence of palladium adsorbed to the scavenger was calculated by fitting. The measurement was performed using a Pd K-edge of 24,155-24,715 eV, a fluorescence yield method, Si(311), and a scan time of 32 min / sample.

[0065] Preparation Example 1 (Preparation of Hydrogenated Nitrile Rubber Solution 1) In a reactor, 0.2 parts of sodium carbonate was dissolved in 200 parts of ion-exchanged water, and 2.3 parts of fatty acid potassium soap (potassium salt of fatty acid) was added thereto to prepare an aqueous soap solution. Then, 38 parts of acrylonitrile and 0.45 parts of t-dodecyl mercaptan (molecular weight modifier) ​​were charged to this aqueous soap solution, in this order, and the gas inside was replaced with nitrogen three times. Then, 62 parts of 1,3-butadiene was charged. Next, the reactor was kept at 5°C, and 0.1 parts of cumene hydroperoxide (polymerization initiator), a reducing agent, and appropriate amounts of a chelating agent were charged to initiate the polymerization reaction. Then, when the polymerization conversion rate reached 80%, 0.05 parts of a 1 wt% aqueous solution of hydroquinone (polymerization terminator) and 0.05 parts of N-isopropylhydroxylamine (polymerization terminator) were added to terminate the polymerization reaction, 0.4 parts of an alkylated phenol compound was added, and residual monomers were removed using a rotary evaporator with water at a temperature of 60°C, thereby obtaining a nitrile rubber latex (solid content concentration: approximately 25 wt%). The pH of the obtained latex was 9.6.

[0066] Next, the nitrile rubber latex obtained above was added to an aqueous solution of aluminum sulfate in an amount equivalent to 3% by weight of the nitrile rubber content in the latex obtained above, and the mixture was stirred to coagulate the latex, which was then washed with water and an alkaline aqueous solution while being filtered off, and then vacuum dried for 12 hours at 60° C. to obtain solid nitrile rubber. The solid nitrile rubber obtained was then dissolved in acetone to a concentration of 14% by weight, which was placed in an autoclave, and a silica-supported palladium catalyst (a catalyst in which palladium metal is supported on silica) was added in an amount of 500 ppm by weight in terms of palladium metal relative to the nitrile rubber, followed by hydrogenation reaction at a hydrogen pressure of 3.0 MPa.

[0067] After completion of the hydrogenation reaction, the reaction system was cooled to room temperature, and the hydrogen in the system was replaced with nitrogen. Then, the solution of hydrogenated nitrile rubber obtained by the hydrogenation reaction was filtered to recover the silica-supported palladium catalyst, and the obtained filtrate was designated as hydrogenated nitrile rubber solution 1 as a sample to be subjected to catalyst recovery treatment.

[0068] A portion of the obtained hydrogenated nitrile rubber solution 1 was collected and poured into 10 times the amount of water to precipitate a polymer, and the obtained polymer was dried in a vacuum dryer for 24 hours to obtain solid hydrogenated nitrile rubber. The composition of the hydrogenated nitrile rubber was 36% by weight of acrylonitrile units and 74% by weight of butadiene units (including saturated portions), with an iodine value of 8 and a polymer Mooney viscosity [ML1+4, 100°C] of 63. The amount of palladium metal in the obtained solid hydrogenated nitrile rubber was measured by atomic absorption spectrometry, and the amount of palladium metal was found to be 250 ppm by weight. From this result, it can be said that the amount of palladium metal in hydrogenated nitrile rubber solution 1 was 250 ppm by weight.

[0069] Preparation Example 2 (Preparation of Hydrogenated Nitrile Rubber Solution 2) Except for changing the amount of the silica-supported palladium catalyst used to 400 ppm by weight in terms of palladium metal, polymerization and hydrogenation reaction were carried out in the same manner as in Preparation Example 1. Then, the solution of hydrogenated nitrile rubber obtained by the hydrogenation reaction was filtered to recover the silica-supported palladium catalyst, and the obtained filtrate was designated as hydrogenated nitrile rubber solution 2 as a sample to be subjected to catalyst recovery treatment.

[0070] A portion of the obtained hydrogenated nitrile rubber solution 2 was sampled and measured in the same manner as in Example 1, and the composition of the hydrogenated nitrile rubber was 36% by weight of acrylonitrile units and 74% by weight of butadiene units (including saturated portions), the iodine value was 9, and the polymer Mooney viscosity [ML1+4, 100°C] was 62. The amount of palladium metal in the obtained solid hydrogenated nitrile rubber was measured by atomic absorption spectrometry, and the amount of palladium metal was 190 ppm by weight. From this result, it can be said that the amount of palladium metal in hydrogenated nitrile rubber solution 2 was 190 ppm by weight.

[0071] Preparation Example 3 (Preparation of Hydrogenated Nitrile Rubber Solution 3) Except for changing the amount of the silica-supported palladium catalyst used to 330 ppm by weight in terms of palladium metal, polymerization and hydrogenation reaction were carried out in the same manner as in Preparation Example 1. Then, the solution of hydrogenated nitrile rubber obtained by the hydrogenation reaction was filtered to recover the silica-supported palladium catalyst, and the obtained filtrate was used as hydrogenated nitrile rubber solution 3 as a sample to be subjected to catalyst recovery treatment.

[0072] A portion of the obtained hydrogenated nitrile rubber solution 3 was sampled and measured in the same manner as in Example 1, and the composition of the hydrogenated nitrile rubber was 36% by weight of acrylonitrile units and 74% by weight of butadiene units (including saturated portions), the iodine value was 12, and the polymer Mooney viscosity [ML1+4, 100°C] was 59. The amount of palladium metal in the obtained solid hydrogenated nitrile rubber was measured by atomic absorption spectrometry, and the amount of palladium metal was 160 ppm by weight. From this result, it can be said that the amount of palladium metal in hydrogenated nitrile rubber solution 3 was 160 ppm by weight.

[0073] Preparation Example 4 (Preparation of Hydrogenated Nitrile Rubber Solution 4) Polymerization was carried out in the same manner as in Production Example 1 to obtain a latex of nitrile rubber. The obtained latex of nitrile rubber was then coagulated, washed with water, and dried in the same manner as in Example 1 to obtain solid nitrile rubber, which was then dissolved in acetone to obtain an acetone solution of nitrile rubber with a nitrile rubber concentration of 15% by weight.

[0074] Next, in a separate reactor, 1 part of palladium acetate, 3 parts of polymethyl vinyl ether, and 3 parts of hydrazine (10 wt % aqueous solution) were mixed with 800 parts of acetone to obtain a solution of palladium acetate catalyst.

[0075] Next, the palladium acetate catalyst solution prepared above was added to the acetone solution of nitrile rubber obtained above in an amount such that the amount of palladium metal was 250 ppm by weight relative to the nitrile rubber, and this was placed in an autoclave equipped with a stirrer, and nitrogen gas was passed through for 10 minutes to remove dissolved oxygen. Next, the system was purged twice with hydrogen gas, and then pressurized with 5 MPa of hydrogen, and the contents were heated to 50°C and stirred for 6 hours to carry out a hydrogenation reaction, thereby obtaining an acetone solution of hydrogenated nitrile rubber. The obtained acetone solution of hydrogenated nitrile rubber was designated hydrogenated nitrile rubber solution 4 as a sample to be subjected to catalyst recovery treatment.

[0076] A portion of the obtained hydrogenated nitrile rubber solution 4 was sampled and measured in the same manner as in Example 1, and the composition of the hydrogenated nitrile rubber was 36% by weight of acrylonitrile units and 74% by weight of butadiene units (including saturated portions), the iodine value was 7.4, and the polymer Mooney viscosity [ML1+4, 100°C] was 65. The amount of palladium metal in the obtained solid hydrogenated nitrile rubber was measured by atomic absorption spectrometry, and the amount of palladium metal was 250 ppm by weight. From this result, it can be said that the amount of palladium metal in hydrogenated nitrile rubber solution 4 was 250 ppm by weight.

[0077] Preparation Example 5 (Preparation of Hydrogenated Nitrile Rubber Solution 5) In a reactor, 0.2 parts of sodium carbonate was dissolved in 200 parts of ion-exchanged water, and 2.25 parts of fatty acid potassium soap (potassium salt of fatty acid) was added thereto to prepare an aqueous soap solution. Then, 13 parts of acrylonitrile, 49 parts of n-butyl acrylate, and 0.45 parts of t-dodecyl mercaptan (molecular weight modifier) ​​were charged to this aqueous soap solution, and the internal gas was replaced with nitrogen three times, followed by charging 21 parts of 1,3-butadiene. Next, the reactor was kept at 5°C, and 0.1 parts of cumene hydroperoxide (polymerization initiator), a reducing agent, and appropriate amounts of a chelating agent were charged to initiate the polymerization reaction. When the reaction conversion rate reached 60%, 8 parts of acrylonitrile and 9 parts of 1,3-butadiene were added, and when the polymerization conversion rate reached 85%, 0.05 parts of a 10 wt% aqueous solution of hydroquinone (polymerization terminator) and 0.05 parts of N-isopropylhydroxylamine (polymerization terminator) were added to terminate the polymerization reaction, and 0.45 parts of an alkylated phenol compound was added. Residual monomers were then removed using a rotary evaporator at a water temperature of 60°C to obtain a nitrile rubber latex (solids concentration: approximately 25 wt%). The pH of the obtained latex was 10.1.

[0078] Next, the nitrile rubber latex obtained above was added to an aqueous solution of aluminum sulfate in an amount equivalent to 3% by weight of the nitrile rubber content of the latex obtained above, and the mixture was stirred to coagulate the latex, which was then washed with water and an alkaline aqueous solution and filtered, and then vacuum dried for 12 hours at 60° C. to obtain solid nitrile rubber. The solid nitrile rubber obtained was then dissolved in acetone to a concentration of 12% by weight, which was placed in an autoclave, and a silica-supported palladium catalyst (a catalyst in which palladium metal is supported on silica) was added in an amount of 500 ppm by weight in terms of palladium metal relative to the nitrile rubber, followed by a hydrogenation reaction at a hydrogen pressure of 3.0 MPa.

[0079] After completion of the hydrogenation reaction, the reaction system was cooled to room temperature, and the hydrogen in the system was replaced with nitrogen. Then, the solution of hydrogenated nitrile rubber obtained by the hydrogenation reaction was filtered to recover the silica-supported palladium catalyst, and the obtained filtrate was designated as hydrogenated nitrile rubber solution 5 as a sample to be subjected to catalyst recovery treatment.

[0080] A portion of the obtained hydrogenated nitrile rubber solution 5 was sampled and measured in the same manner as in Example 1, and the composition of the hydrogenated nitrile rubber was 19% by weight of acrylonitrile units, 38% by weight of butadiene units (including saturated portions), and 43% by weight of n-butyl acrylate units, the iodine value was 10.9, and the polymer Mooney viscosity [ML1+4, 100°C] was 43. The amount of palladium metal in the obtained solid hydrogenated nitrile rubber was measured by atomic absorption spectrometry, and the amount of palladium metal was 250 ppm by weight. From this result, it can be said that the amount of palladium metal in hydrogenated nitrile rubber solution 5 was 250 ppm by weight.

[0081] Example 1 The hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1 was placed in a pressure-resistant vessel equipped with a stirrer, and thiol-modified silica (trade name "SH SILICA", manufactured by Fuji Silysia Chemical Ltd.; the same applies hereinafter) serving as a scavenger was added to this solution in an amount 50 times by weight relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1. Next, triethylenetetramine (hereinafter referred to as "TETA" as appropriate) serving as a complexing agent was added to this solution in an amount 60 times by molar ratio relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1. Next, the mixture was pressurized to 1 MPa with 7% by volume of oxygen, and then heated to 55°C, and stirred at 55°C for 24 hours while continuing to pressurize with oxygen. After completion of the reaction, the thiol-modified silica was recovered from the reaction mixture by filtration, thereby performing a catalyst recovery process. The obtained filtrate was poured into 10 times the amount of water to precipitate a rubber component. The obtained rubber component was removed and vacuum-dried in a vacuum dryer for 24 hours to obtain a hydrogenated nitrile rubber. The amount of palladium metal in the obtained hydrogenated nitrile rubber was 70 ppm by weight. The thiol-modified silica recovered by filtration was washed with acetone to remove any adhering rubber components, and then dried. A portion of the dried thiol-modified silica was then subjected to XAFS measurement according to the method described above to determine the weight percentage of palladium in an oxidation state of 2 or higher in the palladium recovered by the thiol-modified silica. The results are shown in Table 1. A portion of the dried thiol-modified silica was also subjected to wet decomposition to obtain a measurement solution, and the amount of palladium metal captured and recovered by the thiol-modified silica as a scavenger was measured by atomic absorption spectrometry, which was 155 ppm by weight per hydrogenated nitrile rubber.

[0082] Then, the catalyst removal rate and catalyst recovery rate were calculated according to the following formulas from the amount of palladium metal in the hydrogenated nitrile rubber before the catalyst recovery treatment (250 ppm by weight), the amount of palladium metal in the hydrogenated nitrile rubber after the catalyst recovery treatment (70 ppm by weight), and the amount of palladium metal captured and recovered by the scavenger (thiol-modified silica) (155 ppm by weight). The results are shown in Table 1. Catalyst removal rate (%) = {(amount of palladium metal in hydrogenated nitrile rubber before the catalyst recovery treatment - amount of palladium metal in hydrogenated nitrile rubber after the catalyst recovery treatment) / amount of palladium metal in hydrogenated nitrile rubber before the catalyst recovery treatment} x 100 Catalyst recovery rate (%) = (amount of palladium metal captured and recovered by the scavenger (thiol-modified silica) / amount of palladium metal in hydrogenated nitrile rubber before the catalyst recovery treatment) x 100

[0083] Example 2 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 2 obtained in Preparation Example 2 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, silanol-modified silica was used in place of thiol-modified silica in the amount shown in Table 1, the amount of triethylenetetramine used was the amount shown in Table 1, 8% by volume of oxygen was used instead of 7% by volume of oxygen, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 67 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 112 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0084] Example 3 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 2 obtained in Preparation Example 2 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, amine-modified silica (trade name "NH SILICA", manufactured by Fuji Silysia Chemical Ltd.; the same applies hereinafter) was used in place of thiol-modified silica in the amount shown in Table 1, triethylenetetramine was used in the amount shown in Table 1, 7% by volume oxygen was not used but instead hydrogen peroxide was used in an amount 15 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 2, stirring was carried out at 55°C for 3 hours, and then hydrogen peroxide was further added in an amount 15 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 2, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 44 ppm by weight. The recovered silanol-modified silica was also subjected to XAFS measurement in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more valences. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 130 ppm by weight per weight of the hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0085] Example 4 A catalyst recovery treatment was carried out in the same manner as in Example 3, except that the amount of triethylenetetramine used was changed to the amount shown in Table 1, the amount of aqueous hydrogen peroxide added was changed to 0.12 times the amount of palladium metal contained in hydrogenated nitrile rubber solution 2 in terms of a molar ratio, and after adding 0.12 times the amount of aqueous hydrogen peroxide, the solution was heated to 55°C, and stirred at 55°C for 6 hours while continuously adding aqueous hydrogen peroxide every minute in an amount in terms of a molar ratio of 0.12 times the amount of palladium metal contained in hydrogenated nitrile rubber solution 2. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 48 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 132 ppm by weight based on the weight of the hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate calculated from these results are shown in Table 1.

[0086] Example 5 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 3 obtained in Preparation Example 3 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, amine-modified silica was used in place of thiol-modified silica in the amount shown in Table 1, ammonium bromide was used in place of triethylenetetramine in the amount shown in Table 1, 7% by volume oxygen was not used but instead hydrogen peroxide water was used in an amount 30 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 3, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 20 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 115 ppm by weight based on the weight of the hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0087] Example 6 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that ammonium chloride was used in place of triethylenetetramine in the amount shown in Table 1, that 7% by volume oxygen was not used but instead hydrogen peroxide water was used in an amount 15 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 1, and that the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 25 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 206 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0088] Example 7 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 2 obtained in Preparation Example 2 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, phenanthroline was used instead of triethylenetetramine in the amount shown in Table 1, 7% by volume oxygen was not used but instead hydrogen peroxide water was used in an amount 10 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 2, stirring was carried out at 55°C for 3 hours, and then hydrogen peroxide water was further added in an amount 10 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 2, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 65 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 130 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1. In Example 7, the catalyst removal rate and catalyst recovery rate showed different values ​​due to the influence of measurement error, but they were determined to be approximately the same values ​​(the same applies to Examples 8, 9, 11, and 12).

[0089] Example 8 Catalyst recovery treatment was carried out in the same manner as in Example 4, except that phenanthroline was used in place of triethylenetetramine in the amount shown in Table 1, and silanol-modified silica was used in place of amine-modified silica in the amount shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 59 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 138 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0090] Example 9 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 2 obtained in Preparation Example 2 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, phenanthroline was used instead of triethylenetetramine in the amount shown in Table 1, 7% by volume of oxygen was supplied by continuously blowing it in at normal pressure in an open system instead of supplying it under a pressurized condition of 1 MPa, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 42 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 152 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0091] Example 10 A catalyst recovery treatment was carried out in the same manner as in Example 5, except that phenanthroline was used in place of ammonium bromide in the amount shown in Table 1, the amount of hydrogen peroxide used was the amount shown in Table 1, and thiol-modified silica was used in place of amine-modified silica in the amount shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 39 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 120 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0092] Example 11 A catalyst recovery treatment was carried out in the same manner as in Example 5, except that ammonium acetate was used in the amount shown in Table 1 instead of ammonium bromide, the amount of hydrogen peroxide solution used was the amount shown in Table 1, silanol-modified silica was used in the amount shown in Table 1 instead of amine-modified silica, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 53 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 113 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0093] Example 12 A catalyst recovery treatment was carried out in the same manner as in Example 1, except that silanol-modified silica was used in place of thiol-modified silica in the amount shown in Table 1, ammonium acetate was used in place of triethylenetetramine in the amount shown in Table 1, 7% by volume oxygen was not used but instead hydrogen peroxide water was used in a molar ratio 15 times the amount of palladium metal contained in hydrogenated nitrile rubber solution 1, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 83 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 174 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0094] Example 13 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 4 obtained in Preparation Example 4 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, ammonium chloride was used in the amount shown in Table 1 instead of triethylenetetramine, and 8% by volume of oxygen was used instead of 7% by volume of oxygen. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 55 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight proportion of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was 132 ppm by weight per hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0095] Example 14 Catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 5 obtained in Preparation Example 5 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, ammonium chloride was used instead of triethylenetetramine in the amount shown in Table 1, 7% by volume oxygen was not used but instead hydrogen peroxide water was used in an amount 10 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 5, stirring was carried out at 55°C for 3 hours, and then hydrogen peroxide water was further added in an amount 10 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 5, and the reaction time was set to the time shown in Table 1. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 43 ppm by weight. Furthermore, XAFS measurement was carried out on the recovered silanol-modified silica in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 180 ppm by weight based on the weight of the hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate calculated from these results are shown in Table 1.

[0096] Example 15 A catalyst recovery treatment was carried out in the same manner as in Example 1, except that hydrogenated nitrile rubber solution 2 obtained in Preparation Example 2 was used instead of hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1, thiol-modified silica was not added as a scavenger, ammonium acetate was used instead of triethylenetetramine in the amount shown in Table 1, 7% by volume oxygen was not used but instead aqueous hydrogen peroxide was used in an amount 10 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 2, stirring was carried out for 3 hours at 55°C, and then additional aqueous hydrogen peroxide was added in an amount 10 times the molar ratio of the amount of palladium metal contained in hydrogenated nitrile rubber solution 2, and the reaction time was set to the time shown in Table 1. Thereafter, the hydrogenated nitrile rubber solution that had been subjected to the catalyst recovery treatment was passed through a column packed with a thiourea-modified ion exchange resin (scavenger). Then, using the solution obtained after passing the liquid through, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 45 ppm by weight. The thiourea-modified ion exchange resin in the column was subjected to XAFS measurement in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more valences. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the thiourea-modified ion exchange resin was measured in the same manner as in Example 1, and was found to be 124 ppm by weight per weight of hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0097] Comparative Example 1 The hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1 was charged into a pressure-resistant vessel equipped with a stirrer, and triethylenetetramine as a complexing agent was added to this solution in an amount 10 times by molar ratio relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1. Next, hydrogen peroxide was added in an amount 20 times by molar ratio relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1. Next, the solution was heated to 55°C and stirred at 55°C for 5 hours, after which thiol-modified silica as a scavenger was added in an amount 50 times by weight relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1, and stirring was continued at 55°C for another 2 hours. After completion of the reaction, the thiol-modified silica was recovered from the reaction mixture by filtration, thereby carrying out a catalyst recovery process. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 112 ppm by weight. The recovered silanol-modified silica was subjected to XAFS measurement in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more valences. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 75 ppm by weight per weight of the hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0098] Comparative Example 2 The hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1 was charged into a pressure-resistant vessel equipped with a stirrer, and thiol-modified silica as a scavenger was added to this solution in an amount 50 times by weight relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1. Next, dimethylglyoxime as a complexing agent was added to this solution in an amount 40 times by molar ratio relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1. Next, hydrogen peroxide was added in an amount 20 times by molar ratio relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1, and the solution was heated to 55°C and stirred at 55°C for 6 hours. After completion of the reaction, the thiol-modified silica was recovered from the reaction mixture by filtration, thereby carrying out a catalyst recovery process. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 237 ppm by weight. The recovered silanol-modified silica was subjected to XAFS measurement in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more valences. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 12 ppm by weight per weight of hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0099] Comparative Example 3: The hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1 was placed in a pressure-resistant vessel equipped with a stirrer, and 7% by volume of oxygen was introduced into the solution at normal pressure in an open system. The solution was then heated to 55°C, and stirring was continued at 55°C for 3 hours while continuing to blow in oxygen. After 3 hours of stirring, ammonium bromide was added in an amount 40 times the molar ratio of the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1, and stirring was continued for another 3 hours at 55°C while continuing to blow in oxygen. Next, silanol-modified silica was added to the solution in an amount 50 times the weight ratio of the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1, and stirring was continued for another 2 hours at 55°C while continuing to pressurize with oxygen. After completion of the reaction, the silanol-modified silica was recovered from the reaction mixture by filtration, thereby carrying out a catalyst recovery process. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the resulting hydrogenated nitrile rubber was 172 ppm by weight. The recovered silanol-modified silica was subjected to XAFS measurement in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more valences. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 15 ppm by weight per weight of hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0100] Comparative Example 4 The hydrogenated nitrile rubber solution 1 obtained in Preparation Example 1 was placed in a pressure-resistant vessel equipped with a stirrer, and hydrogen peroxide was added in an amount 20 times by molar ratio relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1, followed by stirring at 55°C for 3 hours. After stirring for 3 hours, ammonia water was added in an amount 30 times by molar ratio relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1, and the mixture was stirred for an additional 2 hours at 55°C. Next, silanol-modified silica was added to this solution in an amount 50 times by weight relative to the amount of palladium metal contained in the hydrogenated nitrile rubber solution 1, followed by stirring for an additional 2 hours at 55°C. After completion of the reaction, the silanol-modified silica was recovered from the reaction mixture by filtration, thereby carrying out a catalyst recovery process. Then, hydrogenated nitrile rubber was obtained in the same manner as in Example 1, and the amount of palladium metal in the obtained hydrogenated nitrile rubber was 90 ppm by weight. The recovered silanol-modified silica was subjected to XAFS measurement in the same manner as in Example 1 to determine the weight percentage of palladium in an oxidation state of 2 or more valences. The results are shown in Table 1. Furthermore, the amount of palladium metal captured and recovered by the silanol-modified silica was measured in the same manner as in Example 1, and was found to be 12 ppm by weight per weight of hydrogenated nitrile rubber. The catalyst removal rate and catalyst recovery rate determined from these results are shown in Table 1.

[0101] In Table 1, the amount of oxidizing agent used is a molar multiple of the amount of palladium contained in the hydrogenated nitrile rubber solution, or indicates the oxygen injection conditions, the amount of complexing agent used is a molar multiple of the amount of palladium contained in the hydrogenated nitrile rubber solution, and the amount of scavenger used is a weight multiple of the amount of palladium contained in the hydrogenated nitrile rubber solution. Also, Table 1 shows the proportion of platinum group elements adsorbed in the form of platinum group element complexes in an oxidation state of divalent or higher, but the proportions of platinum group elements adsorbed in the form of platinum group element complexes in an oxidized state, including a monovalent oxidation state, were also similar values.

[0102] As shown in Table 1, when the platinum group elements were recovered by adsorbing them onto a scavenger in a state where the proportion of the platinum group elements adsorbed onto the scavenger in the form of an oxidized platinum group element complex (the proportion of the platinum group elements adsorbed in the form of a platinum group element complex in an oxidation state of divalent or higher) was 50% by mole or more, the capture rate by the scavenger was high, making it possible to recover the platinum group elements at a high recovery rate, and furthermore, the removal rate of the platinum group elements from the hydrogenated nitrile rubber solution was also high (Examples 1 to 15). On the other hand, when the platinum group elements were recovered by adsorbing them onto a scavenger in a state where the proportion of the platinum group elements adsorbed onto the scavenger in the form of an oxidized platinum group element complex (the proportion of the platinum group elements adsorbed in the form of a platinum group element complex in an oxidation state of divalent or higher) was less than 50% by mole, the capture rate by the scavenger was low, and the recovery of the platinum group elements was low (Comparative Examples 1 to 4).

Claims

1. A method for recovering platinum group elements from a solution containing platinum group elements by using a scavenging agent to adsorb the platinum group elements onto the scavenging agent, A method for recovering platinum group elements, wherein the platinum group elements adsorbed onto the scavenger are recovered by adsorbing them onto the scavenger in a state where the proportion of platinum group elements adsorbed in the form of oxidized platinum group element complexes is 50% or more of the platinum group elements adsorbed onto the scavenger.

2. A method for recovering platinum group elements according to claim 1, wherein the platinum group elements are adsorbed onto a scavenger, and the proportion of platinum group elements adsorbed in the form of platinum group element complexes in an oxidized state of 2 or higher is 50% mole or more, and the platinum group elements are recovered by adsorbing the platinum group elements onto the scavenger.

3. A method for recovering platinum group elements according to claim 1 or 2, wherein the platinum group elements are recovered in the presence of a complexing agent represented by the following general formula (1). C ｎ H ｍ N ｐ O ｑ X ｒ (1) (In the above general formula (1), X is an element other than C, H, N, and O, with n = 1 to 13, m = 1 to 18, p = 0 to 4, q = 0 to 4, and r = 0 to 4, and at least one of p and q is 1 or greater.)

4. The method for recovering platinum group elements according to claim 3, wherein the complexing agent is an ammonium salt, an amine, or an imine.

5. The method for recovering platinum group elements according to claim 1 or 2, wherein the solution containing the platinum group elements is a solution containing platinum group elements and a polymer.

6. The method for recovering platinum group elements according to claim 5, wherein the solution containing the platinum group elements is a solution containing hydrogenated nitrile rubber and platinum group elements derived from a platinum group element-containing catalyst.

7. A method for recovering platinum group elements according to claim 1 or 2, wherein a metal-free oxidizing agent, a complexing agent, and a scavenging agent are simultaneously brought into contact with a solution containing platinum group elements, and the recovery of platinum group elements contained in the solution by adsorption onto the scavenging agent is initiated.

8. A method for recovering platinum group elements according to claim 1 or 2, characterized in that a metal-free oxidizing agent and a complexing agent are simultaneously brought into contact with a solution containing platinum group elements, and the solution, in which the proportion of oxidized platinum group element complexes is 50% molar or more, is passed through a column packed with a scavenging agent, thereby adsorbing the platinum group elements onto the scavenging agent.

9. The method for recovering platinum group elements according to claim 7, wherein the metal-non-oxidizing agent is hydrogen peroxide, air, or oxygen.

10. The method for recovering platinum group elements according to claim 1 or 2, wherein the scavenging agent is surface-treated silica.