Micro-Macro Kinetic Perspective and Enhancement Mechanism of Carbon Separation Via the Hydrate Method in the Thf-Co2-Ch4 System

Abstract

The hydrate method is expected to achieve safe and low-energy capture of higher concentrations of CO2 in shale gas or biogas, contributing to a reduction in CO2 emissions and an increase in CH4 gas utilization efficiency. In this study, we investigated the possibility of separating CO2-CH4 gas mixtures via the hydrate method at lower pressures (3 MPa) using 5.56 mol% THF as a promoter. The multiscale thermodynamic variability and kinetic properties of CO2, CH4, CO2-CH4 and THF mixed hydrates were compared with DSC and Raman spectroscopy in the temperature range of 278.95-284.95 K. The experimental results demonstrate that the enhanced competition for CH4 gas within the small cage of hydrate formed at higher temperatures results in a hydrate growth pattern close to that of the pure CH4-THF hydrate system, leading to a maximum gas capture of 43.59 ± 0.48 mmol/mol and CO2 recovery of 81.6%, as well as the best separation factor of 2.31 ± 0.38 at 282.95 K. Furthermore, the enhancement effect of different concentrations (500-3000 ppm) of L-phenylalanine and L-leucine on the separation efficiency at 282.95 K was compared, and the CO2 recovery increased to nearly 84%. Moreover, the separation factor under the amino acid system was largest in the presence of 1000 ppm L-phenylalanine at 0.97 ± 0.16, lower than that of the pure THF system, indicating that the capture ability of hydrate to CH4 gas is greatly enhanced by amino acids, which is expected to provide higher concentrations of CO2-enriched gas in future studies of multistage separation of CO2-CH4 mixtures due to enhancement of the CO2 capture separation efficiency.

Keywords: CO2-CH4 separation, hydrate, Tetrahydrofuran, Amino acids, Raman spectroscopy