Abstract
Carbon dioxide solubility in non-aqueous and aqueous mixtures of methyldiethanolamine (MDEA) with monoethylene glycol (MEG) was studied due to the relevance of these solvents for the combined acid gas removal and hydrate control in natural gas treatment. Vapor-liquid equilibrium (VLE) measurements were conducted at temperatures from 303 K to 393 K and pressures up to 600 kPa. In the aqueous solvents, the effect of water content in carbon dioxide solubility was investigated. The absorption capacity of the aqueous solvents decreased with increasing glycol content and decreasing water content, at constant amine concentration. A comparison of the studied systems with concentrated aqueous MDEA was also performed. The non-aqueous solvents were studied in the whole composition range, from pure MDEA to pure MEG. The solubility of carbon dioxide increased with increasing amine content only up to 30–50 wt% MDEA-MEG, upon which it decreased. Water content determination and Nuclear Magnetic Resonance (NMR) analysis were used for the chemical characterization of the systems and explanation of the results. It was found that in the presence of MDEA, a chemical reaction occurs between carbon dioxide and MEG. A theory based on MEG autoprotolysis is proposed which is further supported by supplementary VLE data obtained in blends of MDEA and triethylene glycol.
Highlights
Primary downstream processes in natural gas production are the removal of acid gases, namely carbon dioxide (CO2) and hydrogen sulfide (H2S), and the removal of water in order to meet pipeline transportation specifications, gas quality specifications and environmental requirements
We further investigated our vapor-liquid equilibrium (VLE) results through Karl-Fischer titration, Nuclear Magnetic Resonance (NMR) spectroscopy, and comparison with MDEA – triethylene glycol (TEG) systems in order to understand the underlying phenomena and identify possible chemical reactions undergone during the absorption of CO2 into aqueous and non-aqueous MDEA-glycol blends
As we investigate several non-aqueous blends, it was decided to use Karl-Fischer titration for the quantification of the water present. Analysis was performed both before and after the VLE experiments for selected non-aqueous systems studied in this work
Summary
Primary downstream processes in natural gas production are the removal of acid gases, namely carbon dioxide (CO2) and hydrogen sulfide (H2S), and the removal of water in order to meet pipeline transportation specifications, gas quality specifications and environmental requirements. In offshore gas and oil wells, non-regenerative chemicals, called scavengers, are commonly used to control hydrogen sulfide content in natural gas. They are not ideal since their use imposes space, weight and disposal requirements which are not friendly for offshore/subsea application [2], and they cannot treat high H2S concentrations. Oil and gas fields experience reservoir souring, i.e. increase in sulfur content, due to EOR (Enhanced Oil Recovery) activities such as water injection [4]. Maintaining production and safe operation in increasingly sour fields is an important industrial challenge
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