Measurement and modeling of mercury solubility in methanol, glycols, and N-methyldiethanolamine

Abstract

Vapor–liquid–liquid equilibria were investigated in the five organic liquids, namely, methanol, monoethylene glycol (MEG), diethylene glycol (DEG), triethylene glycol (TEG), and N-methyldiethanolamine (MDEA) with elemental mercury (Hg) under atmospheric pressure at 298 to 333 K. All samples were prepared in a nitrogen atmosphere, and the Hg mole fraction in the organic liquid phase was determined with a total Hg analyzer based on cold-vapor absorption spectroscopy. The Hg mole fractions were in the ranges from 8.31 × 10-8 to 3.23 × 10-7 in methanol, 5.65 × 10-8 to 1.27 × 10-7 in MEG, 1.59 × 10-7 to 3.82 × 10-7 in DEG, 2.73 × 10-7 to 6.34 × 10-7 in TEG, and 1.80 × 10-7 to 3.61 × 10-7 in MDEA, and the temperature dependences followed the van’t Hoff equation were. The following ranking in terms of the Hg mole fraction was determined: TEG > DEG ? MDEA > methanol > MEG, on the basis of three isotherms measured in the experimental temperature range. For MEG, DEG, and TEG, the ratio of the Hg mole fraction was apparently related to the number of constituent atoms, excepting hydroxy groups and hydrogen atoms, of the solvent molecule. Similar estimates were made for MDEA and for C6–8, and C10 aliphatic hydrocarbons. A previously proposed thermodynamic model was applied to the experimental data to calculate the Hg solubility in the organic liquid phase. This model was based on the Peng–Robinson equation of state under the assumption that the Hg phase remains an immiscible liquid. The mole fractions of the organic liquid phase were well correlated. This model is expected to be useful for understanding Hg behavior in dehydration and gas sweetening processes in the oil and gas industry.