Study On CO₂Absorption And Regeneration Characteristics In Piperazine And Its Derivatives

Green House Gas Effect has become a global climate issue in recent years. Anthropogenic greenhouse gas emission due to human activities is believed to be the major cause of global warming. Carbon capture and storage technologies are believed to be one of the most important keys to global warming. Separating CO2from mixed gas (such as flue gas, landfill gas, etc.) emitted into atmosphere by absorption into alkanolamine solutions is a relatively economic and effective CO2capture technology.This thesis deeply studied properties of carbon dioxide absorption and regeneration in conventional MDEA+DEA, and novel piperazine and its derivative solutions. CO2equilibrium solubility, continuous regeneration capabilities and other properties were studied under different temperature and pressures. The results indicated:CO2equilibrium solubility in alkanolamine solutions decreased with temperature rise, and increased with CO2partial pressure increases. For MDEA+DEA solutions, equilibrium solubility was sensitive to pressure increases when CO2partial pressure was below200kPa, and higher equilibrium solubility could be achieved under operating temperature of313K. While under higher pressures, higher temperature (323K) could promote molecular diffusion in concentrated solutions, thus leading to higher equilibrium solubility. For PZ and HEP, equilibrium solubility under313K and323K was close when CO2partial pressure was above400kPa. Equilibrium solubility increased with pressure increase, and under the same temperature and pressure, the higher the concentration of the solution, the higher the equilibrium solubility.Overall reaction time decreased with temperature rise, and with pressure increase, overall reaction time first increased and then decreased. Overall reaction time was maximized under CO2partial pressure of200kPa for MDEA+DEA solutions, while300kPa for PZ and HEP.Under pressure above150kPa, CO2equilibrium solubility in alkanolamine solutions decreased as5M2-PE>2.5M PZ+2.5M2-PE>5M PZ>2.5M PZ+2.5M HEP>5M HEP>2.5M PZ+2.5M1,4-DHEP>45%MDEA+5%DEA>5M1,4-DHEP. CO2equilibrium solubility decreased with increasing number of substitution groups for PZ derivatives.After7times of regenerations, absorption capacity of regenerated MDEA+DEA solution was74.54%of that of fresh solution, and pH was76.5%. The best regeneration temperature was378K for PZ solutions, and under this temperature, absorption capacity of regenerated PZ solution after10times of regenerations decreased to90.24%of fresh solution, and pH only decreased by8.0%. For HEP, the best regeneration temperature was383K. Under such temperature, absorption capacity of regenerated solution after10times of regenerations decreased to82.81%of fresh solution, and pH decreased by15.2%, from12.5to10.6. The ration of absorption capacity of regenerated solutions to fresh solutions of all alkanolamine solutions decreased as PZ90.67%> PZ+HEP87.18%> PZ+1,4-DHEP> HEP82.81%>1,4-DHEP78.90%> MDEA+DEA74.54%> PZ+2-PE73.45%>2-PE61.60%. PZ, HEP and their mixture solutions as well as PZ and1,4-DHEP mixed solutions had better continuous regeneration capabilities.HEP could be used singly or with PZ in CO2absorption, to keep PZ’s advantages of fast reaction, low regeneration cost and resistance to temperature and erosion, and to overcome the disadvantage of low solubility in water.