Effect of membrane on yield of equilibrium reaction - case I: H2S reversible arrow H-2+1/xS(x) with membrane of Knudsen diffusion characteristics

Using mathematical model and experimental method, the thermal and non-catal ytic decomposition of hydrogen sulfide in membrane reactor with porous memb rane of Knudsen diffusion characteristics was investigated. It was found that in terms of the yield, the membrane reactor can have its merit over the reactor without membrane in the case where inverse of space velocity 1/S-v is larger than some critical value, and there is a maximum v alue of specific yield SY defined as the ratio of yield for the membrane re actor to that for the reactor without membrane, SYmax when almost all the r eactant permeates through the membrane. Lower a product of permeance PH2 an d the ratio of membrane area to reactor volume 1/h, P-H2/h and higher press ure in the main chamber p(R) is favorable to obtain higher SYmax and the av erage concentration of H-2 in the permeate. But the reactor length needed t o permeate almost all the reactant increases. There might exist optimum PH2 /h from the viewpoint of cost. Using membrane reactor integrated with ZrO2- SiO2 composite membrane, the reaction was carried out under the following c onditions: T = 973 and 1023 K, p(R) = 0.11 and 0.20 MPa, pressure in the pe rmeate chamber of 5 kPa and 1/S-v = 21-77 s. With the experimental conditio n, T = 1023 K, p(R) = 0.11 MPa and 1/S-v = 77 s, SY was 0.35 in maximum. Th e experimental results were compared with the results of the mathematical a nalysis. The agreement between both the results is found rather good at a l ower reacting temperature, but not so good at a higher reacting temperature . (C) 1999 Elsevier Science B.V. All rights reserved.