CO2 separation is one of the most important roles in CO2 mitigation target as many human production activities (e.g., cement, iron and steel, and biogas productions) cause CO2 emissions. The solvent-based absorption is the most mature technology for CO2 separation, where different solvents capture CO2 either in chemical or physical absorptions. However, different solvents used in the process always suffer from various problems. For example, the high energy penalty for solvent regeneration, the high solvent loss caused by high volatility and the solvent degradation, and the equipment corrosion are the major concerns of chemical solvent. For the physical solvents, the co-absorption of components other than CO2 reduces the solvent selectivity and increases the operation complexity. Therefore, deeper knowledge about the developed process and new solvent development are the two major ways of overcoming the above-mentioned problems. The goal of this work was to perform systematic studies on both conventional process and novel solvent system(s) for CO2 separation. The CO2 separation with MEA-based process was selected in the field of the conventional approach to capture CO2 from the industrial flues gases. The MEA solvent concentration was identified first, and the effect of three selected parameters, i.e., CO2 concentration, gas flow rate, and CO2 removal rate on capital cost, operational cost, and annual total cost, was evaluated to reduce the energy demand and process cost. 20% MEA solvent is identified as the optimal concentration. According to the parameter study, the CO2 concentration shows the most significant effect, followed by the gas flow rate, and the CO2 removal rate causes the smallest effect. When varying the selected parameters, CAPEX has a greater change in percentage value than OPEX; however, OPEX was the most important one to the total cost owing to its larger absolute value (approximately 3 times of CAPEX). For the solvent development, a conventional polyamine PEHA was selected as it exhibits high thermal stability, low toxicity, and low vapor pressure. Lab testing indicates the 20 wt.% PEHA solution has the best CO2 absorption performance. By using the real bio-syngas from a pilot-scale fixed bed gasifier, the gases other than CO2 (i.e., CO, H2, CH4) were not absorbed in PEHA to any significant extent even at relatively high pressure, and their presence did not affect the CO2 absorption capacity significantly. 20 wt.% PEHA aqueous solvent is a promising chemical solvent for separating CO2 from bio-syngas. For the newly developed novel solvent, ionic liquid (IL) has drawn significant attention as a substitute of conventional solvents due to its superior properties, such as negligible vapor pressure, high thermal stability, and tunable structure. Among many studied ILs, the superbase IL named 1, 8-diazabicyclo-[5,4,0]undec-7-ene imidazole ([HDBU][IM]) shows a very promising CO2 absorption capacity (4.41 mol-CO2/kg-IL), while the high viscosity is a critical issue to cope with. Herein, adding cosolvent was selected as the method to mild the viscosity problem and maintain a high level of CO2 absorption capacity. The dimethyl ethers of polyethylene glycol (DEPG) was selected as the cosolvent of superbase-derived IL [HDBU][IM], and the optimal mass ratio (IL: cosolvent) was identified at 2:1. The temperature effect was studied, showing the high CO2 absorption capacity is favored with low temperature. The effect of gases (CH4, N2) presented in the inlet gas other than CO2 was positive in terms of CO2 selectivity. The thermodynamic modeling agreed well (ARD < 2.37%) with the experimental results. The [HDBU][IM]-DEPG binary system is a promising candidate for separating CO2 from CH4 and N2, and more research will be conducted in the future.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-84244 |
| Date | January 2021 |
| Creators | Wang, Nan |
| Publisher | Luleå tekniska universitet, Energivetenskap |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf, application/pdf |
| Rights | info:eu-repo/semantics/openAccess, info:eu-repo/semantics/openAccess |
| Relation | Licentiate thesis / Luleå University of Technology… → 31 dec 1996, 0280-8242 |
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