Analysis for Trace Hydrocarbon Contaminants in Oxygen Reboilers

Abstract

As part of an air separation plant safety program, a study was undertaken to determine the amount and identity of the hydrocarbons heavier than ethane occurring in the reboilers of these plants, with the initial phase of the study being directed at a group of plants using Trane-core reboilers and having capacities in excess of 100 tons per day of oxygen. For a number of years acetylene and total hydrocarbons have been monitored on a routine basis, but little attention has been given to hydrocarbons containing more than two carbon atoms, except in specific locations known to have atmospheric hydrocarbon contamination. Since it was known that the higher hydrocarbons occurred in rather low concentrations—usually less than 1 ppm—a procedure had to be developed to provide accurate analyses in this range. Consequently, a technique was developed in which contaminants from a relatively large volume of vaporized LOX were concentrated in a cooled adsorbent column prior to chromatographic analysis. The procedure used was based on those described by Brenner and Ettre [¹], Eggertsen and Nelsen [²] and Gaulin et al. [³], who used cooled adsorption columns to concentrate contaminants from gases prior to chromatographic analysis. The procedure described here provides a simple, sensitive and relatively rapid method for the analysis of oxygen for C₂ to C₆ hydrocarbon contamination. The analyses have been extended to lower concentration levels than have been previously described, A further increase in sensitivity might be realized using a hydrogen flame ionization detector in place of the thermal conductivity detector.