Separation of benzene and cyclohexane mixtures using an NaY-type zeolite membrane

An NaY-type zeolite membrane was formed on the outer surface of a 1.7-mm I.D. porous α-Al2O3 support tube using a hydrothermal synthesis. NaY-type zeolite powder was also prepared by the same procedure. The permeation and separation characteristics of single-component benzene (B) and cyclohexane (C), as well as an approximately equimolar mixture thereof, were investigated using the membrane at permeation temperatures of 358–413K. For the single-component systems, C permeated through the membrane faster than B, and the permeances to B and C increased with increase in permeation temperature in the ranges (0.6–3.0)×10−7 and (2.3–6.4)×10−7 mol m−2 sec−1 Pa−1, respectively. When the mixture was fed, however, B permeated faster than C, and the separation factor was dependent on the partial pressures on both the feed and permeate sides. The B/C separation factor reached 107 at a permeation temperature of 373K. The amounts of B and C, which were adsorbed to the NaY-type zeolite powder, were also determined at this temperature. The composition in the gas phase was maintained at approximately an equimolar ratio for the two components, and the total pressure of B and C was maintained at the pressures used for the permeation tests in the present study. The adsorption of B was approximately nine times that of C. Thus the B/C adsorption selectivity on the feed-side surface of the membrane was not the major factor for the high B/C separation factors.