Determination of Hydrocarbon Adsorption on Solid CO2 and N2O in LOX at Ambient Pressure

Abstract

The enrichment of hydrocarbons represents a serious hazard for Air Separation Units (ASU), as several incidents have shown in the past. Regarding the potential hazard due to acetylene accumulation in Revex-plants, literature exists reporting a considerable acetylene amount adsorbed on solid CO2. Thus a potential risk was estimated due to hydrocarbon adsorption on solids in the liquid oxygen (LOX) bath of ASUs. Therefore, Linde Process Engineering and Contracting Division was interested in checking the literature results. With two model hydrocarbons, acetylene and propane, adsorption tests on solid CO2 and N2O in LOX at ambient pressure were performed. The loading was determined by evaporation of the liquid (“indirect determination” method) or the solid CO2/N2O (“direct determination” method) in a pressure vessel. The loading was consistent with the ratio concentration hydrocarbon/concentration CO2 or N2O and is expressed in Vppm (Volume parts per million). Propane exhibited a very small loading on CO2 as well as on N2O. In comparison with the alkane the alkine, acetylene, adsorbed much better on CO2 and N2O. Amounts of up to 700 Vppm acetylene on solid CO2 were found at 89.7 K. The loading depended on the way the solid was generated, but was not affected by the concentration of acetylene in the investigated range. However, the accumulation of acetylene by adsorption should not attain a dangerous amount in the LOX of ASUs.