Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Reexamination Certificate
1994-11-21
2001-10-30
Hendrickson, Stuart L. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
C423S44500R
Reexamination Certificate
active
06310000
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the manufacture, from a bituminous coal or bituminous material, of a carbonaceous char which catalyzes the rapid decomposition of hydrogen peroxide in aqueous solutions.
BACKGROUND OF THE INVENTION
Carbons which are capable of functioning as catalysts per se are well known. For example, as early as 1867 Calvert observed that the presence of charcoal enhanced a variety of oxidation reactions, including the oxidation of hydrogen sulfide, phosphine, and various organics. In those instances where carbon has been observed to affect such reactions, it has functioned as a true catalyst, i.e. it affects only the rate of a given reaction but is not itself changed by the reaction to any significant degree. It is also known that carbon chars prepared from nitrogen-rich starting materials are much more effective in catalyzing certain reactions than those prepared from nitrogen-poor feedstocks. Also, enhanced catalytic properties can be imparted to high-temperature chars prepared from nitrogen-poor starting materials by simply exposing such chars to nitrogen-containing compounds such as ammonia at high temperatures. High-temperature chars are those prepared at temperatures greater than 700° C. while low-temperature chars are prepared at temperatures less than 700° C. A number of investigators have prepared catalytically-active chars by the simple calcination or calcination-activation of low- or high-temperature chars prepared from nitrogen-rich materials such as polyacylonitrile and polyamide.
More recently, the oxidation of high-temperature chars prepared from nitrogen-poor feedstocks prior to or during exposure to nitrogen-containing compounds has been explored. Similarly, the oxidation of a low-temperature char prepared from nitrogen-rich feedstocks such as polyacrylonitrile has been evaluated.
However, all of the prior art processes for preparing carbons which are catalytically active per se have certain disadvantages which limit their overall utility and practicality. For example, some use nitrogen-rich starting materials such as polyacrylonitrile or polyamide. Such materials are expensive and have been found to generate large amounts of cyanide and other toxic gases upon carbonization. Those that use chars derived from nitrogen-poor starting materials invariably also use high-temperature chars, such as activated carbons, which require further processing. Since such materials are fairly inert chemically, the use of extensive and aggressive chemical post-treatments is usually required to effect significant changes in their catalytic capabilities. The use of high-temperature chars is, therefore, inevitably more expensive than the direct use of the raw materials from which they are derived. Additionally, such processes involve the use of large amounts of toxic and/or hazardous reagents such as nitric acid, sulfuric acid, ammonia, or toluene diisocyanate, and the generation of significant amounts of toxic and/or hazardous byproducts such as sulfur dioxide, nitric oxide, and cyanide.
Accordingly, it is the object of the present invention to provide an improved process for the manufacture of a catalytically-active carbon wherein the carbon catalyst is is prepared directly from an inexpensive and abundant nitrogen-poor starting material such as a bituminous coal or a bituminous material. It is further the object of the present invention to limit the use of agents responsible for imparting catalytic activity to the carbon by performing the essential treatments during the low temperature transition of the starting material to the final product. These treatments include oxidation of the low temperature char, preferably by inexpensive, abundant, and relatively non-toxic oxidants. The oxidized, low-temperature char is then contacted with small amounts of an inexpensive, abundant, and relatively non-toxic nitrogen-containing compound in combination with sucrose or fructose prior to and/or during the initial exposure of the oxidized char to temperatures greater than 700° C. By this method, carbon materials with high catalytic activity per se for a variety of chemical reactions can be manufactured relatively inexpensively and conveniently, with minimal departure from conventional processes for the manufacture of high-temperature carbon chars such as activated carbons and coke.
SUMMARY OF THE INVENTION
The present invention comprises a process for the manufacture of a carbon having significant catalytic properties per se wherein the carbon catalyst is prepared directly from an inexpensive and abundant nitrogen-poor feedstock such as a bituminous coal or a bituminous material such as those derived from higher or lower rank bitumens and coals and ligno-cellulose materials by various chemical treatments. Examples of higher rank coals include anthracite and semi-anthracite coals while examples of lower rank coals include peat, lignite, and subbituminous coal. Examples of the chemical treatments of these feedstocks include alkali metal treatment of the high rank materials and zinc chloride or phosphoric acid treatment of the low rank materials. These types of treatments can also be applied to ligno-cellulose materials.
In the preferred embodiment of the invention, the feedstock material is pulverized, mixed if necessary with a small amount of a suitable binder such as pitch, briquetted or otherwise formed, and sized. The sized material is then extensively oxidized with an inexpensive, abundant, and relatively non-toxic oxidant such as air at temperatures; less than 700° C., preferably less than 400° C. The oxidation is continued until additional gains in the catalytic activity of the final product are no longer desired. The oxidation is well beyond that required to remove the coking properties of typical bituminous coals, and produces a highly oxidized low-temperature carbonaceous char. Other convenient means of oxidation can also be used to effect the low-temperature oxidation and carbonization of the starting material.
The oxidized low-temperature char is then contacted with small amounts of an inexpensive, abundant, and relatively non-toxic nitrogen-containing compound such as urea in combination with sucrose or fructose prior to and/or during the initial exposure of the highly oxidized char to temperatures greater than 700° C. The amount of nitrogen-containing compound used is typically small, preferably less than 5% by weight of the oxidized low-temperature char or such that additional gains in the catalytic activity of the final product are no longer evident. The amounts of sucrose or fructose used are also typically small. Effective amounts can be as little as about one-half by weight of that amount of applied nitrogen-containing compound although higher levels may prove to be more effective. It has been found that the sucrose or fructose may be conveniently applied to the oxidized low-temperature char by means of an aqueous solution. When applied in this manner, the solution solute concentration should be adjusted such that the solution viscosity is low enough to provide for uniform distribution within the structure of the oxidized char while still providing for a relatively high loading on the oxidized char.
The initial exposure of the oxidized low-temperature char to temperatures equal to or above 700° C. is carried out while maintaining contact of the char with both the nitrogen-containing compound and the sucrose or fructose. Such thermal treatment is commonly referred to as “calcination”. This calcination or heating to high temperatures, is preferably conducted under an atmosphere that is inert except for the gases and vapors attributable to the char and/or the nitrogen-containing compound and/or the sucrose and/or the fructose. The heating rate and temperatures are selected such that additional gains in the catalytic activity of the final product are no longer evident. The resultant high-temperature char may then be activated to the desired density and yield at temperatures above 700° C., preferably above 900° C., in stea
Hayden Richard A.
Matviya Thomas M.
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