Sorption of sulfolane and diisopropanolamine by soils, clays and aquifer materials

The natural gas sweetening chemicals, sulfolane and diisopropanolamine (DIPA), are highly water soluble and have leached into the ground water from landfills and spills at some sour gas processing plant sites in western Canada. This paper reports on the results of batch equilibration studies designed to evaluate sulfolane and DIPA sorption parameters, which are of relevance to modeling fate and behavior of these compounds in the saturated zone. The sorbents included aquifer materials from three plant sites, reference montmorillonite and kaolinite, and six soils of various clay and organic matter contents. The DIPA sorption isotherms were curvilinear, the slope decreasing with increasing concentration. DIPA adsorption by montmorillonite decreased as the solution concentration of K2SO4 increased, consistent with a cation-exchange reaction. A decrease in pH from 8.3 to 6.8 produced a slight increase in DIPA adsorption by montmorillonite. X-ray analysis of DIPA-saturated montmorillonite showed that DIPA enters the interlayer space of the mineral. The sulfolane sorption isotherms were linear and sulfolane sorption by the aquifer materials was very low (Kd<1 l/kg), whereas DIPA uptake was somewhat higher (Kd<4 l/kg). Both compounds were sorbed more by clay minerals than by organic matter and cation exchange capacity was a reasonable predictor of the sorption of sulfolane and DIPA by soils and aquifer materials with low contents of organic C (<1 g/100 g). DIPA desorption from montmorillonite was low relative to adsorption, and some hysteresis was found for some aquifer materials in the desorption of DIPA. Based on estimates of retardation, sulfolane was predicted to move farther than DIPA under the conditions at plant sites.