A Comparison of Bituminous Coal-Based and Coconut Shell-Based Activated Carbon for Removal of Trace Hazardous Air Pollutants in Landfill Gas

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A Comparison of Bituminous Coal-Based and Coconut Shell-Based Activated Carbon for Removal of Trace Hazardous Air Pollutants in Landfill Gas

Original Article, C49
Athappan A, L. Sattler M.
Journal. Civil Eng. Urban. 3(6):331-337. 2013

ABSTRACT:This study explored adsorption as a method of controlling hazardous air pollutant emissions from landfill gas (LFG). In particular, the study compared bituminous coal-based (BPL) and coconut shell-based (OVC) activated carbons as adsorbents for the hazardous landfill gas constituents para-, ortho-, and meta-xylene; ethylbenzene; and methyl ethyl ketone (MEK). Experiments were designed to replicate typical field usage conditions, using ambient temperature and relative humidity values, and testing the carbon as is, without pretreatment to remove moisture.  BPL and OVC carbons from Calgon Carbon were tested in vials, with initial headspace concentrations ranging from 2130 to 5020 ppmv (86 to 120 mg/m3). Pollutant concentration remaining in the headspace at equilibrium was measured using an SRI 8610 gas chromatograph with flame ionization detector. Tests were conducted at 45-70% relative humidity and room temperature. Adsorption curve fits of Langmuir and Freundlich isotherms (LI and FI) were determined for each compound and each type of activated carbon. For MEK, BPL and OVC adsorption capacities were similar for all concentrations. For ethylbenzene and the xylene isomers, however, OVC coconut shell-based carbon had a higher adsorption capacity at lower concentrations, but BPL coal-based carbon had a higher capacity at higher concentrations. This is likely due to the greater external surface area for OVC carbon, and the greater internal surface area for BPL carbon. For both carbons, at low concentrations adsorption capacity was highest for ethylbenzene, at intermediate concentrations highest for para-xylene, and at high concentrations highest for ortho-xylene. For ethylbenzene and MEK, the Freundlich isotherm fit the data better; for the xylenes, the Langmuir isotherm generally fit the data better. Manufacturer isotherms, developed for ideal conditions, predicted significantly higher maximum adsorption capacities than those determined in this research. Both bituminous coal-based and coconut shell-based activated carbons showed promise for removing hazardous air pollutants from landfill gas, for different concentration levels.
Keywords:Adsorption, Landfill Gas, Hazardous Air Pollutants, Xylene, Ethylbenzene, MEK

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