The effect of additives (piperazine, MEA) on the absorption of carbon dioxide into aqueous alkanolamine solutions were determined. A wetted-sphere absorption apparatus was used to measure the absorptionrate. The base-catalyzed hydration mechanism was used to interpret the kinetic data of aqueous solutions of MDEA. And the zwitterion deprotonation mechanism was used to interpret the kinetic data of aqueous solutions of AMP.
The rate of absorption of $CO_2$ into aqueous solutions of alkanolamine and mixtures of alkanolamine and additives were measured using a wetted-sphere absorber. The radius of sphere was 0.0327 m in this study. The flow rate of aqueous solutions of alkanolamine and mixtures of alkanolamine and additives was varied between $8.3\times10^{-7}-3.3\times10^{-6}m^3/s$ to make stable film on the sphere surface. The system temperature was controlled within ±O.5℃ of the set point temperature. The total pressure of system was about 1 atm. The liquid feed enters at the bottom of sphere and passes through the inside of tube. The liquid runs down along the sphere suface and outside of tube, making smooth film. The distance between the bottom of sphere and liquid level of the receiver was controlled by liquid level controller to reduce the exit effect. The $CO_2$ feed flows to purge the absorption chamber and the tubing, and fills them with $CO_2$. Then $CO_2$ turned off, and the gas filled in the long tubing started to flow into the absorption chamber. The gas flow rate into absorption chamber from the tubing was measured to find absorption rate.
The reaction kinetics of $CO_2$ with aqueous MDEA and piperazine added aqueous MDEA solutions were investigated. The apparent reaction rate constant increases with increasing MDEA concentration without pjperazine. But the apparent reaction rate censtant decreases with increasing MDEA concentration with piperazine. The apparent reaction rate constant significantly increases with increasing piperazine concentration. The highly concentrated MDEA solution needs more piperazine to activate reaction rate. The activation of reaction rate depends on the mole ratio of pjperazine and MDEA.
The absorption of $CO_2$ into aqueous mixtures of AMP and piperazine was investigated. The absorption rates of $CO_2$ into aqueous solutions of AMP in the range of 0.55-3.35 kmo]/m3 were measured at 303 and 313K. The zwitterion deprotonation mechanism was used to interpret the kinetic data of aqueous solutions of AMP. The absorption rates of aqueous mixtures of AMP and piperazine were measured. Piperazine was added 0.058, 0.115 and 0.233 kmo1/m3 for each AMP solutions. The apparent reaction rate constants increased with the addition of piperarine. The reaction rate of $CO_2$ with aqueous solutions of AMP increased with the addition of piperazine due to the contribution of the zwitterion deprotonation and the direct reaction of piperazine with $CO_2$. The zwitterion deprotonation constants of all the bases($H_2O, OH and amines) presented in liquid and the direct reaction rate constant of piperazine were obtained.
The absorption of $CO_2$ into aqueous mixtures of AMP and MEA was investigated. The absorption rates of $CO_2$ into aqueous solutions of AMP in the range of 0.55-3.35 kmo1/m3 were measured at 303 and 313K. MEA was added 0.08 and 0.16 kmol/m3 for each AMP solutions.The apparent reaction rate constants also increased with the addition of MEA. The reaction rate of $CO_2$ with aqueous solutions of AMP increased with the addition of MEA due to the contribution of the zwitterion deprotonation and the direct reaction of MEA with $CO_2$. The zwitterion deprotonation constants of all the bases($H_2O, OH and amines) presented in liquid and the direct reaction rate constant of MEA were obtained.
It is shown that the small addition of additives(piperazine, MEA)can promote the reaction rate of MDEA and AMP. The apparent reaction rate constants correlated with the proposed model in this study agreed well with the measured values.
