| Preventing anthropogenic climate change by reducing emissions of C02 is a critical issue worldwide. Carbon capture and storage (CCS) technology is considered to be a promising means of addressing the CO2 emission problem.Among the CCS technologies, the most mature technology for C02 capture is chemical absorption process. However, the large energy demand of the process is the major obstacle to the application in large scale commercial plants.To reduce the energy demand, a new class of CO2 absorbents, the CO2 phase change absorbent (CPCA), was proposed at 2009 and immediately received much attention during the last 4-5years. The absorbents become two phases after C02 absorption, the C02-lean phase recycles back to the absorber without regeneration and only the C02-rich phase goes to the stripper for the thermal regeneration. The volume of absorbent for regeneration is decreased which potentially reducing the process energy demand. However, the CPCA suffers several issues. For example, the details of the absorbents were missed or the given amines were expensive; the phase change mechanism of CPCA should be clearly verified; the process of using CPCA should be proposed.To overcome these issues, in this thesis, we propose a series of CPCAs induced by salting-out effect and cosolvent effect for C02 capture, and develop membrane flash process to intensify the desorption process for high-viscous lower phase of CPC As.Firstly, as the reaction of MEA and CO2 would generate ionic species,based on phase separation would be happened induced by salting-out effect,the CPCAs composed of MEA + 1-propanol/2-propanol/tert-butanol + H2O were deveolped. For 30wt% MEA+1-propanol+H2O, the upper phase was alcohol-rich phase and the lower phase was C02-rich phase, the lower phase's maximum C02 loading was 4.47mol/kg, the viscosity was 77.00mpa s. The absorption rate of CPCAs was higher. The maximum value of cyclic capacity was 2.59 mol C02/kg which was 62% higher than that of 30wt% MEA.Secondly, based on salting-out effect, the organic solvents were introduced into amine + H2O absorbents to develop CPCAs. In order to further investigate the phase change mechanism, the amine hydrochloride was using to replace the formed salts and established amine hydrochloride+organic solvents+H20 two-phase system. The effects of organic solvents and salts on the phase-separation ability of the studied system were discussed. As a result,the concentration of organic solvents between 50?70%, the organic solvents with small polar and small dielectric constant, high concentration of salts can lead a strong ability of phase separation. According to these achievements, we propose and optimized a series of CPCAs induced by salting-out effect which composed of amine+organic solvents+H2O.Thirdly, for amine which cannot compose CPCAs, we consider amine as cosolvent, and propose a universal method to develop CPCAs induced by cosolvent effect. The MDEA+1 -butanol/1 -pentanol/1 -hexanol+H20 were screened as CPCAs. For 30wt% MDEA+1-butanol+H20, the absorption rate of CPCAs was higher. The maximum value of cyclic capacity is 2.48mol CO2/kg which was 75.9% higher than that of 30wt% MDEA.Finally, a novel mass transfer intensified approach for desorption of CPCAs' lower phase with high viscosity using membrane flash process was presented. The process can increase mass transfer area and mass transfer driving force. For CPCAs composed of MDEA+1-butanol+H20, under the optimal conditions, the resident time was only several seconds, CO2 desorption ratio is as high as 91.98%. Based on above study, the process for using CPCAs was presented.In conclusion, in this thesis, we propose a series of CPCAs induced by salting-out effect and cosolvent effect for CO2 capture, and develop membrane flash process to intensify the desorption process for high-viscous lower phase of CPCAs. It laid the foundations for CPCAs application and provided a feasible means to reduce energy consumption for CO2 capture. |
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