Catalyst – solid sorbent – or support therefor: product or process – Solid sorbent – Free carbon containing
Reexamination Certificate
1997-04-11
2003-03-25
Hendrickson, Stuart L. (Department: 1754)
Catalyst, solid sorbent, or support therefor: product or process
Solid sorbent
Free carbon containing
C502S433000
Reexamination Certificate
active
06537947
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Activated carbons are high porosity, high surface area materials used in industry for purification and chemical recovery operations as well as environmental remediation. Toxic metal contamination of various water sources is a significant problem in many parts of the United States. Activated carbons, which can be produced from a number of precursor materials including coal, wood and agricultural wastes, are now being actively utilized for remediation of this problem. Carbon production is an expanding industry in the United States, with a present production rate of over 300 million pounds a year and a growth rate of over 5% annually. The present invention relates to the development of specifically modified carbons from low-density agricultural waste products that possess enhanced adsorption properties with regard to the uptake of metal ions.
2. Description of the Prior Art
The production of carbon, in the form of charcoal, is an age-old art. Carbon, when produced by non-oxidative pyrolysis, is a relatively inactive material possessing a surface area limited to several square meters per gram. In order to enhance its activity, a number of protocols have been developed. These include chemical treatment of the carbonaceous material with various salts or acids prior to pyrolysis, or a reaction of the already pyrolyzed product with high temperature carbon dioxide or steam. Activated carbon is able to preferentially adsorb organic compounds and non-polar materials from either liquid or gaseous media. This property has been attributed to its possession of a form which conveys the desirable physical properties of high porosity and large surface area.
Usmani et al., in their paper entitled “Preparation and Liquid-Phase Characterization of Granular Activated-Carbon from Rice Husk”, [
Bioresource Technology,
48, (1994), pp.31-35] teach a process for the preparation of granular activated carbons from both high- and low-ash rice husks by the use of zinc chloride in the dual functions of an activating agent and a binder.
Morgan et al., in a publication entitled “Binders and Base Materials for Active Carbon”, [
Industrial and Engineering Chemistry
, Vol. 38, No. 2, (1946), pp.219-227] disclose that various glucose carbohydrates differ markedly as materials for activated carbons; with dextrose behaving as a binder, cellulose as a base material, and starch having properties intermediate to either.
Arida et al., in “Production of High Quality Adsorbent Charcoal from Phil. Woods II. Granulated Activated Carbon”, [
Philippine Journal of Science
, Vol. 121, No.1, pp.31-52], disclose the formation of good quality granulated activated carbons from coconut coir and ipil-ipil when utilizing molasses as a binder.
In Release No. 0483.95 from the Office of Communications, United States Department of Agriculture, (1995), it is disclosed that granular activated carbons effective in the removal of metals may be created from agricultural wastes such as sugarcane bagasse as well as the ground hulls of soybean, cottonseed and rice. The process disclosed utilized black strap molasses as a binding agent and includes the steps of creating charcoal from briquettes in an oxygen-free furnace at over 480° C. and subsequent roasting in the presence of steam at 700° C. to create enhanced surface area.
Rivera-Utrilla et al., in a paper entitled “Effect of Carbon-Oxygen and Carbon-Nitrogen Surface Complexes on the Adsorption of Cations by Activated Carbons”, [
Adsorption Science & Technology
, (1986), 3, pp.293-302] details adsorption studies of Na
+
, Cs
+
, Ag
+
, Sr
2+
and Co
2+
utilizing carbons prepared from almond shells that had been activated with CO
2
at 850° C. for 8 hours and oxidized with air at 300° C. for 45 hours.
Molina-Sabio et al. in their paper entitled “Modification in Porous Texture and Oxygen Surface Groups of Activated Carbons by Oxidation”, [
Characterization of Porous Solids
II, Rodriguez-Reinoso et al. (edit.), 1991, Elsevier Science Publishers B. V., Amsterdam] disclose that while oxidation treatment of fruit pits by either air or chemical means (HNO
3
or H
2
O
2
) does not substantially modify the microporosity of the carbon structures created, the chemical nature of the carbon surface is changed considerably. No projected uses for these carbons are set forth.
Periasamy et al., in an article entitled “Process Development for Removal and Recovery of Cadmium from Wastewater by a Low-Cost Adsorbent: Adsorption Rates and Equilibrium Studies”,
Ind. Eng. Chem. Res.,
33, pp.317-320, (1994), show that at a concentration of 0.7 g/L, activated carbon produced from peanut hulls was able to achieve an almost quantitative removal of Cd(II) present at a concentration of 20 mg/L in an aqueous solution at a pH range of 3.5-9.5.
Moreno-Castilla et al., in an article entitled “Activated Carbon Surface Modifications by Nitric Acid, Hydrogen Peroxide, and Ammonium Peroxydisulfate Treatments” (
Langmuir,
1995, 11, pp.4386-4392), disclose the principle that acidic oxygen surface complexes are formed on activated carbons as a result of their treatment with either gas or solution phase oxidizing agents; and that inclusion of these complexes effect changes in the behavior of activated carbons when used either as adsorbents or catalysts.
While various methodologies for the creation of activated carbons exist, there remains a need for the creation of alternate viable and cost-effective products possessing enhanced adsorption characteristics.
SUMMARY OF THE INVENTION
We have now developed a novel process, which when carried out within specific operational parameters, effects the creation of activated carbons from low-density lignocellulosic agricultural waste possessing enhanced activity for the adsorption of metal ions. This method involves activation with either carbon dioxide or steam followed by atmospheric oxidation. It has now been discovered that the utilization of a relatively low temperature atmospheric oxidation step in conjunction with carbon dioxide or steam activation of the low-density agricultural waste carbon produces metallic binding oxygen functions in the mesopore and macropore regions of the carbon. Carbons produced by this process show metal adsorption capacities greater than that possessed by existing commercial carbons.
In accordance with this discovery, it is an object of the invention to provide a means for the creation of high quality metals-adsorbing carbons.
Another object is to provide activated carbon materials having high metal-adsorbing capacity.
Other objects and advantages of the invention will become readily apparent from the ensuing description.
DETAILED DESCRIPTION OF THE INVENTION
The present invention involves the creation of activated carbons from low-density lignocellulosic agricultural wastes, which possess enhanced adsorption ability with regard to metal cations. The carbon source for the activated carbons of the present invention may be any lignocellulosic material of plant origin having a combined cellulose and hemicellulose content greater than or equal to fifty percent (dry weight) and possessing a bulk density of less than 0.5 grams per cubic centimeter when measured for particles possessing a size range of 10 to 20 U.S. mesh. Exemplary materials include soybean hulls, rice hulls, cottonseed hulls, rice straw, wheat straw, oat straw, barley straw, sugarcane bagasse, corn cobs and peanut shells; with soybean hulls, peanut shells, rice straw and sugarcane bagasse being preferred.
According to the present invention, should a granular carbon product be desired, the low-density agricultural waste may optionally first be formed into pellets, briquettes, or extrudates by combination with a binder such as molasses, coal tar, or wood tar, before their conversion into a char. Relative ratios of the agricultural waste:binder may range from about 1:1 to about 6:1 (w/w), with a range of about 2:1 to about 4:1 being preferred. These formed precursor prod
Johns Mitchell M.
Marshall Wayne E.
Toles Christopher A.
Fado John D.
Hendrickson Stuart L.
Lipovsky Joseph A.
The United States of America as represented by the Secretary of
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