الملخص الإنجليزي
Energy demand increases annually, with fossil fuels being the primary source, leading to significant environmental concerns. Thus, clean energy from renewable resources like biogas, containing methane and carbon dioxide, must be utilized either exclusively or in conjunction with fossil fuels to reduce the environmental impacts of energy production systems. Biogas should be upgraded to biomethane by removing acid gases to fulfill the world's energy demand. In this study, a deep eutectic solvent (DES) was used as an absorbent in the biogas upgrading process, replacing conventional amine-solvent due to its features that overcome drawbacks of amine solvents of high energy consumption, high capital cost, high vapor pressure, and toxicity. 2 A deep eutectic solvent (DES) comprised of imidazole and monoethanolamide (Im-MEA) of molar ratio (1:4), was investigated for removing CO2, and N2 from raw biogas. The solubility of CH4, CO2, and N2 was studied in the DES within the pressure range of 4 to 18 bar with intervals of 4 bar and a temperature range of 35 to 55 ºC. The highest gas loadings obtained in Im:MEA (1:4) Im:MEA was 0.672 (mole CO2/mole DES), 0.154 (mole CH4/mole DES), and 0.134 (mole N /mole DES) at 18 bar and 35 ºC. From the solubility data obtained for all biogas constituents (CH4, CO2, and N2), it was observed that the solubility is directly proportional to pressure and inversely proportional to temperature. The solubility of CO2, CH4, and N2 was verified by calculating the Henry’s law constant. The calculated value of Henry’s law constant for CO2 at 35 ºC was 6.58 MPa Im:MEA, which is less than the reported value of 11.6 MPa for ChCl/Urea system at the same temperature. The findings vii revealed that the Im:MEA (1:4) system has better absorption capacity for all biogas constituents compared to most examined DES ChCl/Urea. In addition, three thermodynamic properties of dissolution enthalpy, dissolution Gibbs free energy, and dissolution entropy at standard conditions were also investigated. The findings showed that the heat of absorption of CO2-Im:MEA (1:4) was much less than that of conventional amine solvent, and the interactions of absorbent and constituent of biogas were highly ordered. The Biogas upgrading process was simulated in Aspen Plus. Aqueous amine solvent of 30% MEA based configuration was considered the base case for performance comparison with the proposed configuration using Im:MEA (1:4) DES. Process evaluation revealed that using Im:MEA (1:4) DES reduced the amount of solvent requirement by 32% compared to the amine-based process for the same objectives of high purity and recovery of biomethane. In addition, the proposed case showed an improvement in energy efficiency. While the process efficiency in terms of environmental reliability is in favor of the Im:MEA (1:4) DES case, where it achieved a higher capture rate (99%) and lower emissions (1.41 kg CO2/kmol). The economic evaluation indicated that the Im:MEA (1:4) based case resulted in total capital, operational, and total annualized cost savings of 33.24%, 17.72%, and 50.38%, respectively, compared to the MEA-based process. Utilizing the proposed DES as an absorbent can lower the total cost of the biomethane value chain and potentially effectively replace conventional solvents.
