Adsorptive Separation Of CO₂ From Its Mixture With N₂ And CH₄

Greenhouse effect is one of the global environmnental problems. The main greenhouse gas is carbon dioxide, while the exhaust gas from power stations is the main sources of CO₂ emissions, so separation/capature of carbon dioxide has significant effect to the decreasing of greenhouse gases emission.In this paper, the first aim was to find an excellent adsorbent to separate CO₂ from its mixture. Firstly, triethanolamine （TEA）, N-Methyldiethanolamine （MDEA） and mixed amine with high boiling point and different concentration were selected to modify the surface of silica gel and activated carbon, which were researched by adsorption and desorption experiments for the mixtures of CO₂ and CH₄ respectively. The breakthrough curves、desorption curves, and the parameters of separation factors and purging ratios were obtained. In addition, 13X molecular sieve was researched by adsorption and desorption experiments for the mixtures of CO₂ and CH₄ respectively, whose breakthrough curves, desorption curves, and the parameters of separation factors and purging ratios were obtained.The compare and analysis for adsorption and desorption performances of different sorbents showed: when silica gel coating ratio 0.8 TEA, silica gel coating ratio 0.6 MDEA, silica gel coating Piperazine（PZ）/MDEA mole ratio（R=0.167）, their separation factors were optimal and were 10.09, 11.05 and 18.98 respectively. For activated carbon and it coating MDEA, their separation factors were very small. For the 13X molecular sieve, the separation factor was 6.24. The sorbent regeneration could be achieved by pressure reduction and back-purge at ambient temperature in short time and it’s capacity remains stable after many cycles of breakthrough and regeneration just as the liquid film, which proved the feasibility of the PSS process using this new sorbent. therefore, the silica gel coating PZ/MDEA with mole ratio（R=0.167）for separation of CO₂ and CH₄ was best.PSS process was tested for different process conditions. Cycle sequence including adsorptive pressure, the times for sorption, pressure equalization and the propriate purge gas velocity were determined. Continuous operation test demonstrated that the sorption property was stable, and the content of CO₂ in the column-top stream decreased to below 0.05% in 9 cycles and kept the level till the end of 200 pressure swing sorption （PSS） cycles. A 2-column process was used to verify the applicability of the pressure swing sorption technology using the amine-modified sorbent for the separation of CO₂/N₂ and CO₂/CH₄ and remained stable in long-time, which proves the industrial applicability of the new technology.