Membrane Separation and Pore Diffusion of Organic Molecules Adsorbed on Controlled-porous Acidic Ceramics

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With the aim of membrane separation of benzene(b.p. 80.1 C) and cyclohexane(b.p. 80.7 C), their permeation coefficients (Q) were betermined for a controlled-porous glass membrane (cornig, No.7930): (1) Whenever substrates were fed singly or in the mixed state (1:1 mole ratio), permeabiity of benzene was higher than that of cyclohexane (measured temperature range, 30-70 C). (2)As the tempearture was elevated, the permeability of benzene was raised, while cyclohexane showed little temperature dependence. Based on this contrasted temperature dependence, it is concluded that the surgace-flow mechanism is predominant for the permeation of benzene, whereas the surface-flow and kundsen-flow mechanisms are in competition for that of cyclohexane.(3) When the membrane surface was modified with silver ions, q of benzene was reduced to one-half its initial value, ahile q of cyclohaxane scarcely changed. Thus the permiability was selectively controlled by the attractive interaction between denzene pi-electrons and the silver ion. With the pulsed field-gradient nmr method, self-diffusion constants (d) Were measured for both benzene and cyclohexane molecules absorbed in the pores of glass membranes: by the surface modification with silver ions. d of benzene was lowered, which is consistent with the tendency observed for Q. By virtue of the stronger interaction between benzene and the surface, a higher surface concentration is expectable for benzene than for cyclohexane. Hence the results of Q(benzene) > Q(cyclohexanre) would be ascribed to the effectiveness of surface flow of benzene nuder the condition of membrane separation.