(747b) Modified Li2ZrO3 Sorbents for Selective CO2 Removal From Biomass-Derived Syngas

In the thermochemical process of converting biomass to synthetic fuels via gasification and catalytic conversion of syngas, excess carbon dioxide must be removed before the fuel synthesis reactor. Studies have shown that CO₂ removal is expensive with the estimated capital cost of an amine-based scrubbing system accounting for 20% of the total plant cost and an even larger share of the energy cost. In the thermochemical biomass to ethanol process, about 25 tons of CO₂ must be removed per hour requiring 130 mmBtu/h of process heat primarily provided by burning raw syngas resulting in decreased ethanol yield. Solid-phase sorbents can remove CO₂ with potentially much smaller energy and yield. Depending on the sorbent used, CO₂ removal can be done at relatively low or high temperature locations within a given process depending on the overall thermal balance of the plant. The use of solid phase sorbents requires a feasible unit operation where the process gas can contact the sorbent at the required temperature and residence time for removal and within the pressure drop constraints of the process. The sorbent must be separated from the gas efficiently to minimize replacement costs and possibly to prevent damage to downstream equipment. Solid-phase sorbents for the removal of CO₂ were investigated using a N₂/CO₂ gas stream at a CO₂ concentration similar to that found in a biomass gasification process (10-15 vol%). A mixture of lithium zirconate, potassium carbonate and sodium carbonate was used in these tests. As a sorbent support may be required for solid-phase sorbents to be viable, removal rates for various supports will be presented. We will also report the results of testing the sorbent with typical syngas compositions and process conditions using a micro-activity test system .