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Co-gasification of biomass and coal in large-scale, Integrated Gasification Combined Cycle (IGCC) plants increases the efficiency and reduces the environmental impact of making synthesis gas ("syngas") that can be used in Coal-Biomass-to-Liquids (CBTL) processes for producing transportation fuels. However, the water-gas shift (WGS) and Fischer-Tropsch synthesis (FTS) catalysts used in these processes may be poisoned by multiple contaminants found in coal-biomass derived syngas; sulfur species, trace toxic metals, halides, nitrogen species, the vapors of alkali metals and their salts (e.g., KCl and NaCl), ammonia, and phosphorous. Thus, it is essential to develop a fundamental understanding of poisoning/inhibition mechanisms before investing in the development of any costly mitigation technologies. We therefore investigated the impact of potential contaminants (H{sub 2}S, NH{sub 3}, HCN, AsH{sub 3}, PH{sub 3}, HCl, NaCl, KCl, AS{sub 3}, NH{sub 4}NO{sub 3}, NH{sub 4}OH, KNO{sub 3}, HBr, HF, and HNO{sub 3}) on the performance and lifetime of commercially available and generic (prepared in-house) WGS and FT catalysts; ferrochrome-based high-temperature WGS catalyst (HT-WGS, Shiftmax 120â¢, SÃ¼d-Chemie), low-temperature Cu/ZnO-based WGS catalyst (LT-WGS, Shiftmax 230â¢, SÃ¼d-Chemie), and iron- and cobalt-based Fischer-Trospch synthesis catalysts (Fe-FT & Co-FT, UK-CAER). In this project, TDA Research, Inc. collaborated with a team at the University of Kentucky Center for Applied Energy Research (UK-CAER) led by Dr. Burt Davis. We first conducted a detailed thermodynamic analysis. The three primary mechanisms whereby the contaminants may deactivate the catalyst are condensation, deposition, and reaction. AsH{sub 3}, PH{sub 3}, H{sub 2}S, HCl, NH{sub 3} and HCN were found to have a major impact on the Fe-FT catalyst by producing reaction products, while NaCl, KCl and PH{sub 3} produce trace amounts of deposition products. The impact of the contaminants on the activity, selectivity, and deactivation rates (lifetime) of the catalysts was determined in bench-scale tests. Most of the contaminants appeared to adsorb onto (or react with) the HT- and LT-WGS catalysts were they were co-fed with the syngas: ï· 4.5 ppmv AsH{sub 3} or 1 ppmv PH{sub 3} in the syngas impacted the selectivity and CO conversion of both catalysts; ï· H{sub 2}S slowly degraded both WGS catalysts; - A binary mixture of H{sub 2}S (60 ppmv) and NH{sub 3} (38 ppmv) impacted the activity of the LT-WGS catalyst, but not the HT-WGS catalyst ï· Moderate levels of NH{sub 3} (100 ppmv) or HCN (10 ppmv) had no impact ï· NaCl or KCl had essentially no effect on the HT-WGS catalyst, but the activity of the LT-WGS catalyst decreased very slowly Long-term experiments on the Co-FT catalyst at 260 and 270 Â°C showed that all of the contaminants impacted it to some extent with the exception of NaCl and HF. Irrespective of its source (e.g., NH{sub 3}, KNO{sub 3}, or HNO{sub 3}), ammonia suppressed the activity of the Co-FT catalyst to a moderate degree. There was essentially no impact the Fe-FT catalyst when up to 100 ppmw halide compounds (NaCl and KCl), or up to 40 ppmw alkali bicarbonates (NaHCO{sub 3} and KHCO{sub 3}). After testing, BET analysis showed that the surface areas, and pore volumes and diameters of both WGS catalysts decreased during both single and binary H2S and NH3 tests, which was attributed to sintering and pore filling by the impurities. The HT-WGS catalyst was evaluated with XRD after testing in syngas that contained 1 ppmv PH{sub 3}, or 2 ppmv H{sub 2}S, or both H{sub 2}S (60 ppmv) and NH{sub 3} (38 ppmv). The peaks became sharper during testing, which was indicative of crystal growth and sintering, but no new phases were detected. After LT-WGS tests (3-33 ppmv NH{sub 3} and/or 0-88 ppmv H{sub 2}S) there were a few new phases that appeared, including sulfides. The fresh Fe-FT catalyst was nanocrystalline and amorphous. ICP-AA spectroscopy and other methods (e.g., chromatography) were used to analyze for Fe, Cu, S, K, Na, P, As, Cl, C, H, and N on both the fresh and tested catalysts. The HT-WGS catalyst displayed higher concentrations of impurities from H{sub 2}S, NaCl, PH{sub 3}, KCl, and AsH{sub 3} on its surface, but no measurable increases in the concentrations of N, H, and C. The LT-WGS catalyst also contained higher concentrations of impurities from H{sub 2}S, NaCl, NH{sub 3}+H{sub 2}S, and AsH{sub 3}, but no measurable increase in N, H, P, and C. The WGS catalysts exposed to the alkali contaminants (i.e., Na{sup +}, K{sup +} and Cl{sup -}) showed much higher levels of these metals since they were mixed directly with the catalyst. The Fe-FT catalyst tested in 40 ppmw NaHCO{sub 3} or KHCO{sub 3} had 300-400 ppmw Na{sup +} or K{sup +} while testing in KCl resulted in 800 and 111 ppmw K{sup +} or Cl{sup -}, but these small amounts had no impact. A techno-economic trade-off analysis was carried out that evaluated the cost of cleaning up the syngas versus the added costs of premature catalyst replacement due to poisoning. Using the experimentally determined rates of catalyst deactivation, we estimated catalyst lifetimes to identify the critical deactivation rates that would require a syngas cleanup system to protect the catalysts. We found that in most cases a cleanup system would be economically justified. This project enabled us to determine the sensitivity of the WGS and FT catalysts used in CBTL processes to the contaminants in coal-biomass derived syngas, provided information on their service lifetimes, and will enable DOE and FTS technology developers to assess the risk of catalyst deactivation if these contaminants slip through syngas clean-up systems. We developed a fundamental understanding of the catalyst degradation mechanisms, which can help guide follow-on research on potential catalyst improvements and/or process modifications needed to reduce the capital and operating expenses of producing drop-in liquid fuels in CBTL plants. The commercialization of CBTL technologies depends on the development of syngas clean-up systems that can virtually eliminate these contaminants from syngas to protect the catalysts from deactivation

Impact of Contaminants Present in Coal-Biomass Derived Synthesis Gas on Water-gas Shift and Fischer-Tropsch Synthesis Catalysts