Removal of trimethylamine acetaldehyde and ammonia gases using electron attachment reaction

Abstract

Experimental investigation on the application of electron attachment to the removal of dilute gaseous pollutants has been carried out using a corona-discharge deposition-type reactor. The high selectivity of electron attachment to electronegative gas molecules is utilized to effectively remove the impurity gases at ppm and even ppb concentration levels. The effects of several factors, namely, discharge current, inlet gas concentration, space velocity and coexisting O₂ or H₂O vapor on the individual removal efficiency of three kinds of gaseous pollutants, namely, trimethylamine ((CH₃)₃N), acetaldehyde (CH₃CHO) and ammonia (NH₃) have been investigated. The experimental results reveal that generally the higher the discharge current, the higher the removal efficiency, whereas the space velocity and inlet gas concentration yield the opposite effects. It has been found that the presence of O₂ enhances the removal efficiency of each impurity gas. The enhancement is experimentally shown to be attributable to the ozone reaction in the removal of (CH₃)₃N from O₂ -N₂ mixed gas. Water vapor also enhances the removal efficiency of (CH₃)₃N and CH₃CHO. Furthermore, the high selectivity of electron attachment to electronegative gas molecules is utilized to the simultaneous removal of dilute (CH₃)₃N-CH₃CHO, NH₃-CH₃CHO, SO₂- (CH₃)₃N, SO₂-CH₃CHO, NO₂ -CH₃CHO and CO₂-CH₃CHO from air in the single reactor in order to find out the effect of discharge current on their removal efficiency. Since undesirable reaction by-products are produced on the removal of SO₂- (CH₃)₃N from air, a two-reactor system has been proposed and shown to remove the binary pair with negligible reaction by-product. The experimental results show that generally the higher the discharge current, the higher the removal efficiency. Compared to single impurity removal, it has been shown that the presence of SO₂ enhances the removal efficiency but retards that of CH₃CHO in a single reactor, but some reaction by-products are generated. The problem can be avoided by using two independently operated reactors in series. In the case of coexisting of NO₂, it is noted that the lower the inlet NO₂ concentration, the lower the discharge current that still yields beneficial effect. At higher discharge currents, the retarding effect of CO₂ on CH₃CHO removal is obviously significant.