Progress toward Biomass and Coal-Derived Syngas Warm Cleanup: Proof-of-Concept Process Demonstration of Multicontaminant Removal for Biomass Application

Systems comprising multiple sorbent and catalytic beds have been developed for the warm cleanup of coal- and biomass-derived syngas. Tailored specifically for biomass application, the process described here consists of six primary unit operations: (1) a Na2CO3 bed for HCl removal, (2) two regenerable ZnO beds in parallel for bulk H2S removal, (3) a ZnO bed for H2S polishing, (4) a NiCu/SBA-16 sorbent for trace metal (e.g., AsH3) removal, (5) a steam reforming catalyst bed for tars and light hydrocarbon reformation and NH3 decomposition, and (6) a Cu-based LT-WGS catalyst bed. Simulated biomass-derived syngas containing possible inorganic contaminants (H2S, AsH3, HCl, and NH3) and hydrocarbons (methane, ethylene, benzene, and naphthalene) was used to demonstrate process effectiveness. The efficiency of the process was demonstrated for a period of 175 h, during which time no signs of deactivation were observed. However, postrun analysis revealed that small levels of sulfur slipped through the sorbent bed train to the two downstream catalytic beds. Future improvements will be made to the trace metal polishing sorbent to ensure complete inorganic contaminant removal (to low parts per billion level) prior to the catalytic steps. However, dual regenerating ZnO beds were effective for continuous removal for the vast majority of the sulfur present in the feed gas. The process was effective for complete AsH3 and HCl removal. The steam reforming catalyst completely reformed all the hydrocarbons present in the feed (methane, ethylene, benzene, and naphthalene) to additional syngas. However, postrun evaluation, under kinetically controlled conditions, indicates some deactivation of the steam reforming catalyst occurred. Spent catalyst characterization suggests this can be attributed, in part, to coke formation, likely due to the presence of benzene and/or naphthalene in the feed. Future adaptation of this technology may require dual, regenerable steam reformers. The process and materials described in this report hold promise for the warm cleanup of a variety of contaminant species within warm syngas.