Trace carbon monoxide and hydrogen conversion prior to cryogenic distillation of air

Abstract

Liquid Nitrogen is required in the semiconductor industry. This is generally produced by cryogenic distillation of air. However, trace levels of Carbon Monoxide and Hydrogen need to be removed from Nitrogen prior to its use in the semiconductor industry. This may be accomplished by catalytic conversion of trace Carbon Monoxide and Hydrogen to Carbon dioxide and Water, respectively. These impurities (Carbon dioxide and Water) are then removed by adsorption from air. The latest technology is to incorporate the catalytic conversion into adsorption based thermal swing pre-purification units, which are already used to remove Water and Carbon dioxide from air prior to its cryogenic distillation. Our experiments show that even though Hydrogen is converted to Water by a catalytic reaction, presence of Carbon dioxide in this stream significantly lowers the performance of the catalyst by as much as five-fold. Also, Hydrogen removal by the novel metal Pd catalyst does not follow a typical catalyst behavior but an adsorption breakthrough type behavior, i.e. for a constant inlet concentration the outlet concentration of Hydrogen breaks through at some time and then increases with time. On the other hand, Carbon monoxide conversion on a Hopcalite type catalyst follows typical catalyst behavior, i.e. for a constant inlet concentration the outlet concentration of Carbon monoxide is constant and does not change with time. Experimental data demonstrating these effects followed by a theoretical explanation are presented.