Pervaporation Separation Of The Experimental Study Of The Low Concentration Of Ethanol / Water Solution

Pervaporation is a new technology of membrane separation for the separation of liquid mixtures, which based on the membrane's different selectivity towards the various components in the mixture. It has special advantage in the use of the separation of homogeneous mixtures such as azeotropic, closing-boiling and isomeric mixtures, which are difficult or impossible to separate by conventional methods, and will also be widely used in the separation of dilute alcohol aqueous solution.In this paper, a plat polydimethysiloxane (PDMS) composite membrane was prepared by-coating thin PDMS active layer on an organophilic polymer porous membrane which is singled out to act as supporting layer. The PDMS composite membranes have moderate selectivity towards ethanol, stable permeate flux and separation factor.The experiment of the separation of ethanol from dilute ethanol aqueous solution with the PDMS composite membranes was carried out. The effects of the operating conditions, temperature and feed concentration were studied. It is concluded that the temperature improved both the total flux and separation factor. An increase of the feed concentration results in an increase of the permeability and a decrease of selectivity. The permeating flux conformed to Arrenhenius equation: J = J₀ exp(-E_p/ RT).The mass transfer process in the PDMS composite membrane under different operating conditions has been researched to analyze the impacts of operation conditions, such as the temperature and the rate of flow, over mass transfer coefficient, and study the performance of the membrane modules being unlike in structure. The results showed that the increase of temperature and rate of flow have promoted the mass transfer coefficient. The structure of module has important influence on the mass transfer coefficient, and should be considered in the design of the module. The liquid film mass transfer coefficient is obvious greater than the diffusive mass transfer coefficient in membrane, so that the liquid film mass transfer resistance is not the governing factor of mass transfer in this experiment.The process of swelling of a dense PDMS membrane in ethanol aqueous solution were investigated to examine the changing of swelling ratios with the change of temperature, concentration and time. Results are demonstrated that the swelling ratios of PDMS membrane increased quickly within initial time, the temperature power-up has accelerated the swelling of membrane, and promoted the swelling ratios obviously in solution of high concentration. The swelling ratios assume the linearity relation basically with the concentration of the solution in the range inner examining. The distribution coefficients increased with the increasing of temperature, but decreased with the increasing of concentration of the solution. Just as the total flux and separation factor in pervaporation. So that it can be concluded that the properties of the membrane in swelling were just reflecting the performance in pervaporation.