Porous, metal-containing carbonaceous material

Abstract: A porous, metal-containing carbonaceous material is disclosed which comprises a porous, carbonaceous body, and fine particles of a metal having an average particle size of 1 µm or less and dispersed in the carbonaceous body. The carbonaceous material may be obtained by a method including the steps of: (a) providing finely divided particles of a metal oxide having an average particle size of 1 µm or less; (b) mixing the particles with an organic substance to obtain a mixture; and (c) carbonizing the mixture in a non-oxidizing atmosphere to convert the organic substance into a porous carbonaceous body and to convert the metal oxide particles into elemental metal particles dispersed in the carbonaceous body.

Description: This invention relates to a method of producing a porous, metal-containing carbonaceous material. Porous carbonaceous materials such as activated carbon and carbon fibers are now used in a variety of fields as gas absorbents, water treatment materials, filters, catalysts, etc. Composite carbonaceous materials are also known in which metal compounds such as metal oxides deposit on inside surfaces of pores of carbonaceous bodies. Such a composite material is prepared by impregnating a carbonaceous body with a solution containing a metal oxide. US-A-4513096 discloses an active carbon catalyst which comprises a dispersion of at least one metal component selected from chromium, aluminum, manganese and tungsten components dispersed in a porous carbon matrix which also has elemental iron deposited on or, uniformly dispersed within, the matrix. Processes for preparing this catalyst are described which involve pyrolysis of an organic precursor compound in admixture with chromium, aluminum, manganese and/or tungsten component(s), whereafter the pyrolysis product is admixed with a precursor of iron which is subsequently reduced to elemental iron. The present invention is concerned to provide an improved method for producing a porous carbonaceous body in which is dispersed fine particles of an elemental metal. In accordance with the present invention there is provided a method of producing a porous, metal-containing carbonaceous material, comprising the steps of: (a) providing finely divided particles of a metal oxide having an average particle size of 1 µm or less, said particles each being coated with a layer of an anionic surfactant; (b) mixing said particles with an organic substance to obtain a mixture; and (c) carbonizing said mixture in a non-oxidising atmosphere to convert said organic substance into a porous carbonaceous body and to convert said metal oxide particles into elemental metal particles dispersed in said carbonaceous body. The present invention will now be described in detail below. In carrying out the method according to the present invention, first finely divided metal oxide with a particle size of 1 µm or less is mixed with an organic substance. The metal oxide is generally an oxide of one or more metals of Group Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb, VIa, VIIa or VIII of the Periodic Table. Of these, the use of a metal oxide capable of being easily converted into elemental metal upon being heated in the presence of a reducing agent such as hydrogen gas, carbon monoxide or carbon is desirable. Illustrative of suitable metal oxides are those of Ag, Cu, Ca, Mg, Ba, Zn, Al, Ga, Ti, Zr, Sn, V, Sb, Cr, Mo, Fe, Co, Ni and mixtures thereof. The metal oxide employed is determined according to the intended use of the carbonaceous material. It is preferred that the metal oxide have an average particle size of 30 nm (300 Å) or less. In order to obtain excellent homogeneity in the dispersion of the metal oxide in the organic substance, it is a feature of the present method that the metal oxide particles are each covered with a layer of an anionic surfactant, such as a monomolecular layer of a fatty acid metal salt. Such a super-fine metal oxide may be obtained by the method disclosed in Japanese Unexamined Patent Application (Tokkyo Kokai) Nos. 60-231,798, 62-83305 and 62-138,333. Any organic substance may be used for the purpose of the present invention as long as it can give a porous carbonaceous or carbon body upon heated in a non-oxidizing atmosphere. Illustrative of suitable organic substances are phenol resins, epoxy resins, urea resins, formalin resins, vinyl chloride resins, acrylic resins, styrene resins, polyamide resins, polyvinyl alcohol resins, polyethylene resins, polypropylene resins, petroleum pitch, coal tar pitch, asphalt, wood chips, pulp, coconut husk, rice hull, sugars, starch, coal particles and coke powder. In the case of an organic substance available as powder, such as pulp powder, coal powder, coke powder or thermosetting resin powder, it is advisable to mix the powder with the finely divided metal oxide in the presence of a binder and, if necessary, water, and to shape the resulting mixture into pellets, cylinders, sheets or any other desired forms. As the binder may be used, for example, sulfite pulp liquor, molasses, avicel, soft pitch, coal tar, carboxymethyl cellulose or polyvinyl alcohol. In the case of a thermally fusible organic substance, such as petroleum pitch, coal tar pitch or asphalt, it is advisable to mix the finely divided metal oxide with the molten organic substance with heating. The resulting mixture is preferably further heat treated to increase its softening point and is then shaped into pellets, fibers or any other desired form. The mixture of the finely divided metal oxide with the organic substance is carbonized at a temperature and for a period of time sufficient to convert the organic substance into a porous carbonaceous body and to covert the metal oxide into the elemental metal. The carbonization is generally performed at a temperature of 800-1000 °C. During the course of the carbonization, the organic substance is thermally decomposed to form a reducing gas such as hydrogen or carbon monoxide which serves to reduce the metal oxide into the elemental metal. The carbon produced also serves as a reducing agent. The carbonization is carried out in a non-oxidizing atmosphere such as in the atmosphere of nitrogen, carbon dioxide, a combustion gas or steam. As long as the organic substance is prevented from burning, a small amount of oxygen may be present in the atmosphere in which the carbonization is effected. As a result of the carbonization, there is obtained a porous, carbonaceous body of an open cellular structure having dispersed therein fine particles of a metal having an average particle size of 1 um or less. The content of the elemental metal is generally 5-60 % based on the total weight of the elemental metal and the carbonaceous body. As the particulate metal oxide used as a starting material has a surface layer of an anionic surfactant, the resulting elemental metal particles each have a carbon layer formed as a result of the carbonization of the anionic surfactant. The carbon layer has a multiplicity of cracks. The elemental metal particles coated with the carbon layer are homogeneously dispersed in the matrix of carbon derived from the organic substance. The porous, carbonaceous material according to the present invention may be formed into metal-containing activated carbon by heat treatment in steam. Because of the presence of super-fine elemental metal particles, the porous carbonaceous material according to the present invention has a high activity and lends itself to various applications, depending on the kind of the metal. For example, material containing a transition metal such as Fe, Cu or Co can be utilized as an oxygen absorbent when used in conjunction with a suitable electrolyte such as sodium chloride. Material of the present invention containing V, Ni, Mo or the like catalytic metal can be suitably used as a lipophilic catalyst for, for example, hydrogenation of an organic substance. When processed to form activated carbon, the material of the present invention is advantageously used as a gas absorbent for the treatment of a gas containing hydrogen chloride or sulfur dioxide. Porous material according to the present invention containing an electrically conductive metal such as Cu or Ag may be used as an electromagnetic interference shield material. When a ferromagnetic metal is used, the porous carbonaceous material can be used as a material having both electromagnetic interference shield property and a radio wave absorbing property. The following example will further illustrate the present invention. Example 1 Coal powder (100 parts by weight) having an particle size of 74 µm (200 mesh, Tyler) or finer was mixed with 50 parts by weight of ferric oxide powder (coated with monomolecular layer of potassium stearate, average particle size of about 50 Å) and 30 parts by weight of soft pitch (softening point: about 50 °C). The mixture was kneaded at 75 °C and cooled to obtain blocks. The blocks were heated to 850 °C at a rate of 10 °C/minute in a non-oxidizing atmosphere and maintained at that temperature for 30 minutes to obtain a carbonised product. After cooling in the atmosphere of nitrogen, the carbonized product was ground into particles. The chemical analysis revealed that the iron oxide was converted into metallic iron. The microscopic observation showed that the metallic iron particulate was homogeneously dispersed in the carbon matrix. The thus obtained metallic iron-containing carbon particles (100 parts by weight) was mixed with 30 parts by weight of an aqueous sodium chloride solution (concentration: 15 %) to obtain an oxygen absorbent. This absorbent (10 g) was placed in a 100 cc vessel and the vessel was sealed. After standing for 24 hours, the oxygen content in the vessel was measured. No oxygen was detected.

Claims: A method of producing a porous, metal-containing carbonaceous material, comprising the steps of: (a) providing finely divided particles of a metal oxide having an average particle size of 1 µm or less, said particles each being coated with a layer of an anionic surfactant; (b) mixing said particles with an organic substance to obtain a mixture; and (c) carbonizing said mixture in a non-oxidizing atmosphere to convert said organic substance into a porous carbonaceous body and to convert said metal oxide particles into elemental metal particles dispersed in said carbonaceous body. A method as claimed in claim 1, wherein said metal oxide is an oxide of one or more metals of Group Ib, IIa, IIb, IIIa, IIIb, IVa, IVb, Va, Vb, VIa, VIIa or VIII. A method as claimed in claim 2, wherein said metal oxide is an oxide of Ag, Cu, Ca, Mg, Ba, Zn, Al, Ga, Ti, Zr, Sn, V, Sb, Cr, Mo, Fe, Co Ni, or mixtures thereof. A method as claimed in any preceding claim, wherein said metal oxide has an average particle size of 30 nm (300 Å) or less. A method as claimed in any preceding claim, wherein said anionic surfactant layer is a monomolecular layer of a fatty acid metal salt. A method as claimed in any preceding claim, wherein said organic substance is at least one substance selected from phenol resins, epoxy resins, urea resins, formalin resins, vinyl chloride resins, acrylic resins, styrene resins, polyamide resins, polyvinyl alcohol resins, polyethylene resins, polypropylene resins, petroleum pitch, coal tar pitch, asphalt, wood chips, pulp, coconut husk, rice hull, sugars, starch, coal particles and coke powder. A method as claimed in any preceding claim, wherein said mixture is formed into a shaped body before step (c). A method as claimed in claim 7, wherein said shaped body is a pellet. A method as claimed in any preceding claim, wherein step (c) is performed at a temperature of 800-1000 °C. A method as claimed in any preceding claim, wherein step (c) is performed in the atmosphere of nitrogen, carbon dioxide, a combustion gas or steam. A method as claimed in any preceding claim, wherein said mixture has such a content of said metal oxide that the amount of said elemental metal is 5-60 % based on the total weight of said elemental metal and said carbonaceous body.

Inventors: TACHIBANA MASAO, TACHIBANA, MASAO
Applicants: SOMAR CORP, SOMAR CORPORATION
Application year: 1989
Main classification: C04B38
IPC codes: C04B35, B01J20, C01B31, C22C1, C04B38