Mercury Migration and Speciation Study during Monoethylene Glycol Regeneration Processes

Abstract

The partitioning of mercury from the distillation process used to regenerate water-laden monoethylene glycol (MEG) in the natural gas processing industry is a highly complicated process. The experiments detailed in this paper concerned the transfer and partitioning of mercury species in an unpressurized laboratory scale process at a distillation temperature of 170 °C. Experiments were conducted with both laboratory grade MEG solutions and industry based samples obtained from a natural gas processing facility. It was found that ionic mercury (Hg2+) was not stable in MEG samples taken from the natural gas processing facility due in part to the high pH (pH >8) and the various additives as well as the buildup of inorganic compounds within a recirculated industrial MEG sample. That is, Hg2+ can accumulate in the solid tar residue as a precipitated mass as well as decompose and partition out of the MEG solution as gas phase elemental mercury (Hg0). Significantly, it was found that approximately 50% of the spiked Hg2+ in an industry based sample is reduced and leaves as Hg0 during the MEG regeneration process, whereas only 10% leaves as Hg0 in laboratory based samples. The partition percentage is highly dependent on the salt and organic content present in the MEG solution. The results from these types of studies could potentially lead to more cost-effective mercury treatment technologies for natural gas processing industries as well as improve the understanding of how potential mercury contamination of recirculating MEG behaves during natural gas recovery processes.