Progress 07/01/04 to 06/30/06
Outputs
C-FAR 2005 External. Surface area is a major property of activated carbon (AC) affecting its capacity for removal of most pollutants from air and water streams. Surface areas of AC prepared from corn fiber samples ranged from 300 to 920 m2/g with yields ranging from 23 to 10 wt% (dry basis), respectively. A corn fiber-derived AC (CFAC) with surface area of 410 m2/g was selected for testing. Methyl ethyl ketone (MEK) and toluene were selected as representative organic pollutants in air, and trichloroethylene (TCE) was selected as representative organic pollutant in water. On a surface area basis, the capacity of the CFAC for removal of MEK and toluene was comparable to two commercial ACs with surface areas ranging from 950 to 1,500 m2/g. The CFAC was more effective, on a surface area basis, for removal than the 950 m2/g coal-based AC and had a slightly lower capacity than the 1500 m2/g wood-based AC. Additional experiments were performed to evaluate the heating value of
the flammable off-gases generated during the on-site manufacturing of CFAC which could provide a source of energy to fire boilers for the production of steam in an ethanol plant. The heating value of the off-gases was about 7,900 Btu/lb (dry basis) which is comparable to the heating values of lignite and subbituminous coals. These results indicate that corn fiber is a suitable bio-based feed stock for producing AC. In addition, CFAC can be used as an effective adsorbent in various air and water pollution control processes and could compete with commercially available ACs as long as its adsorption surface area can be made equivalent to commercially available ACs. Although a high surface area activated carbon is desirable for some environmental applications, there are many applications, such as removal of mercury from coal combustion flue gases, where a lower surface area AC (<500 m2/g) is adequate. A low-cost CFAC can potentially compete with commercial ACs in this type of application.
An economic analysis performed in 2002 revealed that that the selling price of a 300-500 m2/g CFAC could be substantially lower than the price of many commercial carbons.
Impacts
The use of corn fiber for activated carbon production has several advantages to the corn ethanol industry. First, it could create another market for a low valued co-product and reduce the amount of low valued distillers dried grains (DDG) and corn gluten feed being produced by today's ethanol plants. These products compete directly with corn as an animal feed, to the detriment of the corn producer. Secondly, by using the corn fiber as a feedstock for another co-product (AC), the remaining animal feed becomes higher in protein and a source of feed for swine and poultry. This helps to expand the market base for DDG and corn gluten feed. The average selling price of AC carbon ranges from $500 to about $ 2,000 per ton. An ethanol plant processing 1 million tons of corn per year produces about 200,000 tons of dry corn fiber. At a 15-20% yield of activated carbon and an estimated price of $500 per ton, the total projected sale from activated carbon for this plant would be $15
to $20 million per year.
Publications
- A summary of the results obtained in this project was published in the summer 2006 issue of our C-FAR Connection newsletter. A manuscript is also being prepared for presentation at National American Chemical Society and for publication in Industrial and Engineering Chemistry.
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Progress 01/01/05 to 12/31/05
Outputs
C-FAR 2005 External. A microbalance adsorption apparatus was used to measure the gas-phase adsorption isotherms of a corn activated carbon (AC) at 25 C. The adsorption isotherms of the corn AC sample were similar for both MEK and toluene vapors. This suggests that differences in physical properties of organic vapors had little or no effect on their adsorption capacities. Second, the isotherms demonstrated a monotonic and almost linear increase with increasing vapor pressure, with 50% of the total organic adsorption capacity consumed at the first data point. This indicates that the corn AC sample is highly microporous and, therefore, will have significant adsorption capacities at lower pressures. Third, it was found that corn AC adsorbed much less vapors than other industrial activated carbons, such as an activated carbon fiber cloth and a granular commercial AC. At first glance, this suggested the corn AC sample was inferior to commonly used activated carbons which
could limit its use in vapor-phase environmental applications. However, when isotherms were recalculated on the basis of adsorption surface areas of AC samples, it was found that the adsorption capacity of all adsorbents were equivalent. This suggests that the low adsorption capacities for the corn AC sample were due only to its low adsorption surface area compared with the commercial AC tested. In other words, the corn AC could definitely compete with common activated carbons as long as its adsorption surface area can be made equivalent to commercially available ACs. Work is in progress to increase the adsorption surface area of corn AC to make them more competitive with commonly used activated carbons. Liquid-phase adsorption tests will be performed during winter and spring 2006.
Impacts
A comparison of the adsorption isotherms of a corn AC sample and two commercial activated carbons for MEK and toluene revealed that corn AC could definitely compete with commercial activated carbons as long as its adsorption surface area can be made equivalent to those of the commercially available ACs. Although a high surface area activated carbon is desirable for some environmental applications, there are many applications, such as removal of mercury from coal combustion flue gases, that a high surface area AC (>500 m2/g) is not needed. A low-cost corn AC can potentially compete with commercial ACs in this type of application. Work is in progress to evaluate the liquid-phase adsorption capacities of corn ACs. Theses result will also help identify potential markets for corn AC.
Publications
- No publications reported this period
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Progress 07/01/04 to 12/31/04
Outputs
C-FAR 2005 External. Several experiments were performed to collect gaseous and liquid products during thermo-chemical conversion of corn fiber to activated carbon. These experiments were performed to evaluate the heating value of the off gases. The flammable off-gases created by an on-site production of activated carbon could provide a source of energy to a fired boiler for the production of steam to use in producing ethanol. The composition and the heating value of the gaseous products were obtained and those of the liquid products are being determined. During the remaining project period, representative samples from a 300-pound batch of the activated carbon (AC) prepared from corn fiber in 2001 will be used as the starting material for producing additional activated carbons. This AC has a surface area of about 350 m2/g. Bench-scale studies will also be performed to produce two activated carbon samples with surface areas of 550 and 700 m2/g. Absorption capacities of
these ACs for removal of volatile organic compounds from air and trace pollutants from water streams will be measured. Samples in granular form will also be prepared by using conventional methods to prepare granular products. These results will be compared with data previously obtained with several commercially- activated carbons and will serve as a basis for evaluating potential markets for AC made from corn fiber byproduct. Furthermore, several activated carbon distribution companies will be contacted to discuss issues related to the potential size of markets and the expected selling price of the corn ACs based on their properties.
Impacts
The use of corn fiber for activated carbon production has several advantages to the corn ethanol industry. First, it could create another market for a low-valued coproduct and reduce the amount of low-valued distiller's dried grains (DDG) and corn gluten feed being produced by current ethanol plants. These products compete directly with corn to the detriment of the corn producer. Secondly, by using the corn fiber as a feedstock for another coproduct (activated carbon), the remaining animal feed becomes higher in protein and a source of feed for swine and poultry. This helps to expand the market base for DDG and corn gluten feed. Thirdly, the flammable off-gases created by the on-site production of activated carbon could provide a source of energy to fired boiler for the production of steam to use in producing ethanol.
Publications
- No publications reported this period
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