(296g) Multicontaminant Warm Gas Cleanup Sorbents for Coal and Biomass Derived Synthesis Gas

Gasification technologies convert coal, biomass and other heavy feedstocks into synthesis gas feed streams that can either be used as a fuel for highly efficient power generation cycles or converted into value-added chemicals and transportation fuels. However, coal-derived synthesis gas contains a myriad of contaminants (e.g. sulfur, halides, nitrogen, mercury and arsenic) that may be regulated in power plant emissions and act as poisons for the catalysts used in downstream chemical manufacturing processes. Since these heteroatom and trace metal contaminants can easily poison the Water Gas Shift (WGS) and Fischer-Tropsch (F-T) catalysts, inhibit their activity and change their product selectivity. In addition, the biomass feedstock will introduce a different spectrum of contaminants, including the vapors of alkali metals (such as sodium and potassium compounds) and their respective salts (e.g., KCl and NaCl), ammonia and phosphorous that could affect the performance of WGS and FT catalysts. Due to the complex nature of the synthesis gas (derived from both coal and biomass) and the molecular permutations by which these contaminants are present in the gas, it is difficult to formulate catalysts that are resistant to all of these contaminants without significant loss of activity. Therefore, the synthesis gas feed must be treated before it enters the FT and WGS systems to insure that the impurity levels in the incident gas are acceptable. The contaminant control technology must work at elevated temperatures, near or above the operating temperature of the FT and WGS systems (180-300^oC range), since the high temperature operation eliminates the need for the expensive heat exchangers (to cool the synthesis gas to the operating temperature of the clean-up system and then to re-heat it back to the operating temperature of the WGS and FT processes) and the gray water treatment problems associated with the large amounts of process condensate.

TDA Research, Inc. (TDA) has developed a low-cost, high capacity, sorbent that can remove trace contaminants including sulfur, halides, arsenic and mercury from both coal and biomass derived synthesis gas. The sorbent will reduce the concentration of all these contaminants to ppbv levels, providing optimum protection for the Fischer-Tropsch synthesis catalysts used to convert coal and biomass derived synthesis gas into liquid fuels. Unlike the commercially available trace metal adsorbents or sulfur polishing sorbents, our sorbent operates at elevated temperatures (500^oF). We carried out trace contaminant cleanup of simulated coal and biomass derived synthesis gas with our warm gas cleanup sorbent and our sorbent was able to achieve very high capacity for most of the trace contaminants. The performance results of our warm gas trace contaminant removal sorbent will be presented in the meeting.