Separation of supercritical fluid mixtures with a membrane process

Asymmetric polyamide Kapton R membrane was made by casting a solution of 18wt % polyamic acid and 5wt% phenanthrene in dimethylacetainide at 70゚C with a four-minutes evaporation time. Usine thismembrane, a separation factor alpha_<ethanol/CO2>，8.7 was obtained at 373k and 15mpa 6.5 at 423k and 15mpa for the experimemt involving theseparation of gaseous mixtures of co_2 and ethanol with a concentration ratio of 15Its value at 373k is 1.3 times higher than at 423k, and increases with total pressure，while the separation factor at 423k remains constant with pressure.The activation energies ofpermeability were 2.6 kj/mol for ethanol and 7.1 kj/mol for supercritical co_2 These values are verysmall compared to those of 48 kj/mol for ethanol and 25 kj/mol for co_2 with the symmetric超critical fluid permeation experiment might be the best method to determinepermeation mechanism whether pore flow model or solution-diffusion modelfrom the measurement of activation energy of permeation.From the data obtaineda calculation was carried out to determine the required membrane area for 90% recovery of ethanolfrom mixtures with an initial concentration of 1 mol% and a feed rate of 36 mol/h. This area is 0.82m^2 for separations conducted at 10 MPa and 373 K and 0.28 m^2 at 15 MPa and 373 K. and threequarters of operating energy of pressurization might be saved. Therefore过程整合与membrane recovery could save operating energy about 3/4 and the size ofthe main compressor will be reduced to 1/4 theoretically。

Asymmetric polyamide Kapton^R membrane was made by casting a solution of 18 wt% polyamic acid and 5 wt% phenanthrene in dimethylacetainide at 70ﾟC with a four-minutes evaporation time. Usine this membrane, a separation factor alpha_<ethanol/CO2>, 8.7 was obtained at 373 K and 15 MPa and 6.5 at 423 K and 15 MPa for the experimemt involving the separation of gaseous mixtures Of CO_2 and ethanol with a concentration ratio of 15 : 1. Its value at 373 K is 1.3 times higher than at 423 K, and increases with total pressure, while the separation factor at 423 K remains constant with pressure.The activation energies of permeability were 2.6 kj/mol for ethanol and 7.1 kj/mol for supercritical CO_2・These values are very small compared to those of 48 kj/mol for ethanol and 25 kj/mol for CO_2 with the symmetric polyamide membrane. Supercritical fluid permeation experiment might be the best method to determine the permeation mechanism whether pore flow model or solution-diffusion model, from the measurement of activation energy of permeation.From the data obtained, a calculation was carried out to determine the required membrane area for 90% recovery of ethanol from mixtures with an initial concentration of 1 mol% and a feed rate of 36 mol/h. This area is 0.82 m^2 for separations conducted at 10 MPa and 373 K and 0.28 m^2 at 15 MPa and 373 K. And three quarters of operating energy of pressurization might be saved. Therefore, the process integrated with membrane recovery could save operating energy about 3/4 and the size of the main compressor will be reduced to 1/4 theoretically.