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 °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 Cu/carbon 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 °C its capacity was 1.74 wt %. Operation at 140 °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 °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.