Sampling And Stability of Mercaptans: Comparison Between Bags, Canisters and Sorbent Tubes

Abstract

In this study the influence of sampling and storage of samples was studied focusing on a number of mercaptans. First the influence of the sampling material on the composition of the sampled gas was studied and secondly the stability of the mercaptans in the different sampling materials is followed over time. Stainless steel, Teflon and deactivated stainless steel were tested as inlet material for a Nalofane bag. These were compared with sampling using both stainless steel or Silonite treated canisters. As a last sampling strategy, active sampling on sorbent tubes was considered. The tests indicate the composition during sampling can be changed in presence of untreated stainless steel as this gives rise to the formation of disulfides. Furthermore, the stability over time of the mercaptans after sampling is very limited for the sorbent tubes with great loss of certain mercaptans over a very short period of time (>2 hours). Also in bags the stability is rather limited and the best stability can be obtained using canisters. So for sampling of mercaptans, Silonite or equivalent canisters are the most suitable way to transport the sample to the laboratory. In the lab, the samples should be analysed as quick as possible after sorbing them on tube or by an appropriate direct sampling system.