Removal of arsine from synthesis gas using a copper on carbon adsorbent

A variety of supported metal and metal oxide adsorbents were evaluated for removal of arsine (AsH(3)) from synthesis gas (syngas), a mixture primarily of carbon monoxide and hydrogen. A copper(II) oxide (CuO)/carbon adsorbent was judged to be most promising and examined more thoroughly. Exposure of the CuO/carbon adsorbent to syngas at 750 psig resulted in only a modest increase in bed temperature. No evidence that the adsorbent acted as a methanol synthesis catalyst or promoted other syngas chemistry was observed. It was found, however, that even at modest temperatures (30-40 degrees C) some reduction to metallic copper (Cu) occurred. The exothermic reduction of CuO presented a significant operational concern, and use of the adsorbent required a controlled reduction to Cucarbon prior to exposure to syngas. The arsine affinity of CuO/carbon was very high with a minimum capacity of 3.0 wt % arsenic for a syngas feed containing 420 ppbv. The reduced adsorbent, Cu/carbon, was less effective for AsH(3) removal, and at 30 degrees C its capacity was 1.74 wt %. Operation at 140 degrees C resulted in more effective AsH(3) removal with a minimum arsenic capacity of 4.31 wt % for a feed gas containing 737 ppbv AsH(3). The kinetic limitation for AsH(3) adsorption at near ambient temperature is likely the result of slow migration of arsenic from the copper surface. At 140 degrees C arsenic migration is fast enough to provide a clean copper surface for adsorption. The Cu/carbon adsorbent was slightly less effective for phosphine removal than for AsH(3). The sulfur-containing contaminants thiophene, carbonyl sulfide, and carbon disulfide were only partially removed from a syngas feed, and the adsorbent had almost no affinity for methyl chloride.