Combined sorbent catalyst media for destruction of halogenated VOCs

Several chromium modified zeolites have been developed and tested for their ability to physisorb chlorinated VOCs (CVOCs) at ambient and then catalytically destroy them at elevated temperatures (ca. 300 degrees C). These dual function materials, which act as both sorbents and catalysts, are believed to be the key to implementing a new energy efficient process for the destruction of low concentration level CVOC streams. Data showing catalytic activity, sorptivity and other physical properties for Y and ZSM-5 zeolites based media are presented. A chromium exchanged ZSM-5 (Cr-ZSM-5) medium which showed superior performance catalytically (> 95% TCE and MeCl(2) destruction at 300 degrees C) and adequate sorption capacity (0.074 g TCE/g sorbent, 0.064 g MeCl(2)/g sorbent at 23 degrees C in the presence of humid air) was chosen for subsequent dual function tests. These tests showed that ambient temperature fixed bed sorption of CVOCs followed by periodic heating of the upper portion of the bed to catalytic temperatures (ca. 35 degrees C) with slow temperature ramping of the lower portion to desorb trapped CVOCs, produced a highly energy efficient cyclic process for their destruction. A Cr-ZSM-5 bed, which alternately stored and then destroyed CVOC from a humid 110 ppm TCE stream at a space velocity of 2400 h(-1), was shown to operate over a 1460 min cycle which required heating for only 7% of the time.