Assessment of the Subsurface Environmental Fate of Amines Used by the Gas Industry

Abstract

Abstract Alkanolamines are commonly used by the natural gas industry to remove acid gases from the natural gas stream. At gas processing plants that use alkanolamines for acid gas removal (AGR), spills and the on-site management of wastes containing alkanolamines and their associated sludges have commonly resulted in subsurface contamination that is presently the focus of some environmental concern. Research has been conducted by the Energy & Environmental Research Center that examines the subsurface transport and fate of the most commonly used alkanolamines, namely, monoethanolamine (MEA), diiethanolamine (DEA), and methyldiethanolamine (MDEA), and process-derived sludge from AGR units that utilize each of those compounds. Experimental activities were conducted that can be grouped into three areas:qualitative, semiquantitative, and quantitative characterization of alkanolamine-derived sludges;investigations of the interactions of MEA, DEA, and MDEA with soils; andactivities investigating the biodegradability of MEA, DEA, MDEA, and associated sludges. Characterization of the sludges was performed using gas chromatography coupled with mass spectroscopy (GC-MS). In order to examine the potential effects of different soil types on subsurface transport and fate, investigations of interactions between alkanolamines and soil and of biodegradation of alkanolamines and process-derived sludges were performed using soils collected from Louisiana, New Mexico, and Alberta. These areas were selected to represent not only three unique soil types, but also to represent three regions of North America that produce an abundance of sour natural gas. The results of this research provide the natural gas industry with data and insights that will enable them to 1) significantly improve the assessment of subsurface alkanolamine-related contamination where it is known or suspected to occur and 2) make soundly based decisions concerning the remediation of that contamination. Introduction The natural gas industry commonly uses alkanolamines to remove hydrogen sulfide (H2S), carbon dioxide (CO2), and other acid gases from the natural gas in which they occur ("sour" gas if H2S is present). At sour gas processing plants, as at all plants that use alkanolamines for acid gas removal (AGR), unplanned releases and on-site management of wastes containing alkanolamines and process-derived thermal reaction products have commonly resulted in subsurface contamination that is presently the focus of some environmental concern in Canada. In the United States, there are at least 394 gas-sweetening facilities that use amine-based AGR units, and the production and processing of sour gas is expected to increase in the coming years. A few workers have reported toxicity associated with waste material generated by amine-based AGR units. Generally, adequate data exist to confirm the presence of alkanolamines and at least some of their thermal reaction and biodegradation products in soils and groundwater at the sites in question. However, analytical and other difficulties have typically prevented the nature and extent of alkanolamine-related contamination from being determined in detail at individual sites. At the same time, limited work has been done on the behavior of the chemical species in question in the subsurface; therefore, little is known about their subsurface transport and fate. This places the natural gas industry in the difficult position of having to effectively address a contamination issue that is neither well defined nor well understood. The results of this research program will enable the natural gas industry to significantly improve the assessment of subsurface alkanolamine-related contamination at sites where it is known or suspected to occur and make soundly based decisions concerning the remediation of that contamination. This program, which through directed research is specifically focused on monoethanolamine (MEA), diethanolamine (DEA), methyldiethanolam inc (MDEA), and process-derived wastes from AGR units that utilize each of those compounds, includes activities which can be grouped into three areas: P. 255^