Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Reexamination Certificate
2000-03-02
2001-05-08
Hendrickson, Stuart L. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
C428S402000
Reexamination Certificate
active
06228803
ABSTRACT:
BACKGROUND OF THE INVENTION
Activated carbon has found use in various applications such as air and water purification, hydrocarbon adsorption in automotive evaporative emission control and cold start hydrocarbon adsorption, etc. While microporous structure carbon (pore diameter less than 20 angstroms and BET surface area of 1000-3000 m
2
/g) are suitable for many applications such as gas phase adsorption e.g. light hydrocarbons and H
2
S, some applications require larger size of pores in the carbon for optimum adsorption and/or catalytic activity. For example, removal of larger molecular size pollutants such as humine, protein, etc. in liquid phase, in addition to conventional gaseous pollutants, such as hydrocarbons, or certain kinds of pesticides require specific surface properties and poresize distributions. When catalytic or chemical reaction is limited by mass and heat transfer, larger size of pores in the carbon is preferred. Also, mesoporosity in the carbon is sometimes required for adequate catalyst loading and dispersion.
Activated carbon monoliths, whether in the form of a coating on a substrate, or a shaped structure of activated carbon, have found use in various applications especially where durability and low pressure drop is required, such as some chemical reactions using strong acidic or basic solvents or other corrosive media.
Metal catalysts have been used to make activated carbon supported catalysts, as have been disclosed in U.S. Pat. No. 5,488,023. However, up to this time, there has not been a method of making activated carbon that having tailored properties, porosity, for example, for some gas and liquid phase, as well as catalytic applications.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided mesoporous carbon and a method of making mesoporous carbon that involves forming a mixture of a high carbon-yielding carbon precursor that when carbonized yields greater than about 40% carbon on a cured basis, and an additive that can be catalyst metal and/or low carbon-yielding carbon precursor that when carbonized yields no greater than about 40% by weight carbon on a cured basis. When a catalyst metal is used, the amount of catalyst metal after the subsequent carbonization step is no greater than about 1 wt. % based on the carbon. The mixture is cured, and the carbon precursors are carbonized and activated to produce mesoporous activated carbon.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to making mesoporous activated carbon by combining a high carbon-yielding carbon precursor, low carbon-yielding additive and/or catalyst metal compound followed by curing, carbonizing and finally activating the carbon by heat-treatment in activating agents such as steam and carbon dioxide, etc. When a catalyst metal compound is used, the amount of catalyst metal delivered is no greater than about 1% by weight based on the carbon that is present after the carbonization step.
According to this invention, by mesoporous carbon is meant that at least about 50%, and more typically about 60% to 90% of the total pore volume is in the range of 20 to 500 angstroms and no more than 25 percent pore volume is in the range of large pores (>500 angstroms).
By carbon precursor is meant a synthetic polymeric carbon-containing substance that converts to continuous structure carbon on heating. A carbon precursor is preferred over activated carbon particles because as a result of curing, carbonizing and activating, the carbon atoms are arranged in a continuous uninterrupted structure of random three-dimensional graphitic platelets.
By high-yielding carbon precursor is meant that on curing, the precursor yields greater than about 40% of the cured resin is converted to carbon on carbonization. For purposes of this invention, an especially useful high-yielding carbon precursor is a synthetic polymeric carbon precursor, e.g. a synthetic resin in the form of a solution or low viscosity liquid at ambient temperatures or capable of being liquefied by heating or other means. Synthetic polymeric carbon precursors include any liquid or liquefiable carbonaceous substances. Examples of useful carbon precursors include thermosetting resins and some thermoplastic resins.
Low viscosity carbon precursors (e.g., thermosetting resins) are preferred for coating applications because their low viscosity allows greater penetration into the substrate. Typical resin viscosity ranges from about 50 to 100 cp. Any high carbon yield resin can be used. Phenolic and furan resins are the most suitable. Phenolic resins are most preferred due to their low viscosity, high carbon yield, high degree of cross-linking upon curing relative to other precursors, and low cost. Suitable phenolic resins are resole resin such as 43250 polyophen resin, and 43290 from Occidental Chemical Corporation, and Durite resole resin from Borden Chemical Company. One especially suitable furan liquid resin is Furcab-LP from QO Chemicals Inc.
The carbon precursor can include a single high carbon-yielding precursor material, or a mixture of two or more such precursor materials. Optionally, already-made activated carbon can be added to liquid carbon precursor to adjust the viscosity of the precursor for forming or shaping into structures.
To obtain carbon of desired porosity, a catalyst metal and/or low carbon-yielding carbon precursor is included with the high-carbon-yielding carbon precursor.
The low carbon-yielding carbon precursor is that which when carbonized has a carbon yield of no greater than about 40% on a cured basis. Some especially useful low carbon-yielding carbon precursors are cross linking additives are glycerine, melamine formaldehyde, epoxy, and/or polyvinyl alcohol. One advantage of using the low carbon-yielding carbon precursor alone without the catalyst metal is that the step of removing the catalyst metal in cases where a catalyst metal is not desired in the final product, is eliminated.
When metal catalysts are present in the carbon matrix, topographical effects of surface etching, channeling and etch pitting are induced by each individual metal additive during activation, depending on their own physical and chemical properties, carbon structures, and reaction conditions. To selectively generate desirable mesoporous activated carbon, these three actions are coordinated to provide desired pore size. Channeling and pitting provide a chance to produce pores, and surface etching provides a chance for pore enlargement.
The metal catalyst suitable can be alkali, alkaline earth, transition, and/or noble metal. Advantageously, the catalyst metals are Pt, Pd, Rh, Ag, Au, Fe, Re, Sn, Nb, V, Zn, Pb, Ge, As, Se, Co, Cr, Ni, Mn, Cu, Li, Mg, Ba, Mo, Ru, Os, Ir, Ca, Y or combinations of these. Preferred metals are Pt, Co, Ni, and/or Fe, especially Fe in the +3 oxidation state; with Co being especially preferred. The metal catalyst is preferably in the form of a precursor or compound e.g. organic or inorganic salt of a catalyst metal, which decomposes to the catalyst metal or catalyst metal oxide on heating, such as sulfates, nitrates, etc. A metal compound, preferably finely dispersed, is preferred to the elemental form because metal powder tends to form larger grains of graphitic regions instead of the favored opposite effect. Examples of compounds are oxides, chlorides, (except alkali or alkaline earths) nitrates, carbonates, sulphates, complex ammonium salts, etc. Organometallic compounds of the appropriate type metals can be used with or without low carbon-yielding carbon precursor. For example, acetates such as cobalt acetate, and/or acetylacetonates such as cobalt, platinum, and/or iron acetylacetonate are especially suited. While not wishing to be bound by theory, it is believed that the bulky organic structure introduced to the resin is thermally set after curing to the matrix and may help form more porosity when these structures are removed during carbonization. Therefore, more catalysts are exposed to the surface for additional pore size engineering during activation step.
Gadkaree Kishor P.
Hickman David L.
Peng Y. Lisa
Tao Tinghong
Corning Incorporated
Gheorghiu Anca C.
Hendrickson Stuart L.
Herzfeld L. Rita
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