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U.S. Department of Energy (DOE) National Energy Technology Laboratory (NETL) on-site researchers have been examining and developing a novel solvent for precombustion capture that has the potential for improved performance and lower costs compared to Selexol? and Rectisol�. In Subtask 2.5, the Energy & Environmental Research Center (EERC) conducted actual comparison tests on actual coal-derived syngas of a PEGDME (polyethylene glycol dimethyl ether) Selexol-type solvent and three other solvents provided by NETL. One was a new hybrid PEG?PDMS (poly[dimethylsiloxane]) solvent engineered by NETL. In addition, two commercially available chemicals that are projected to have good CO2 capture abilities were also selected for testing on actual coal-derived syngas. These tests were conducted in the EERC high-pressure fluid-bed gasifier (HPFBG) system utilizing an existing gas-sweetening absorption system (GSAS) to test the solvents. <
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The four solvents tested were Solvent 1 ? AGR II from Coastal Chemical Co., LLC, NETL Solvent 2 ? XG-3229 Bis(methoxytriethyleneoxypropyl)hexamethyltrisiloxane, as manufactured by Gelast, Inc.
Solvent 3 ? CASSH-1 (diethyl sebacate), procured from Sigma Aldrich
and Solvent 4 ? TBP (tributyl phosphate), purchased from ThermoFisher Scientific. The solvents were all tested at a consistent syngas flow and composition at approximately 50 bar to make direct comparisons easier
two solvent flow rates which would bracket 90% CO2 capture
and, temperatures of 10�, 25�, 40�, and 55�C to determine the effects of temperature on CO2 uptake and CO2 to H2 selectivity. <
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Figure E-1 shows the results for CO2 uptake and selectivity for the various solvents. These data show that the CO2 uptake for the Selexol-type solvent for the PEG-PDMS-3 and CASHH-1 solvents at higher operating temperatures around 40�C was better than the Selexol-type solvent was able to achieve at the lower operating temperature of 10�C. Selectivity of CO2 over H2 was at least as good as Selexol for the PEG-PDMS-3 solvent and even better than Selexol for the CASSH-1 solvent. The TBP solvent also displayed good CO2 uptake
however, CO2/H2 selectivity was worse than for the Selexol-type solvent. Operation of precombustion CO2 solvents at temperatures above ambient can provide a 2% process efficiency improvement along with a significant capital cost reduction since refrigeration and solvent dehydration equipment is not required. The excellent results from these tests warrant further longer-duration testing with one or both superior NETL-provided solvents to determine if longer-term exposure to any coal-derived syngas trace species may have an adverse impact on solvent performance. <
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This project was funded through the EERC?DOE Joint Program on Research and Development for Fossil Energy-Related Resources Cooperative Agreement No. DE-FE0024233.<
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