Characteristics of hydrogen separation from the gas mixture by using the multi-stage inorganic membrane

Abstract

The separation characteristics of hydrogen from the gas mixture were investigated by using a single and multi-stage inorganic membrane. Numerical simulation for three-stage gas separation system was conducted to predict the optimal operating conditions for the multi-stage gas separation. Three palladium impregnated porous membranes were prepared by using the sol-gel, hydrolysis, and soaking and vapor deposition(SVD) techniques. The gas flow through pores of prepared porous membranes was achieved dominantly by the Knudsen flow. The ideal hydrogen separation factors were above the Knudsen limit only at low pressure difference and high temperature due to the surface flow. But, at high pressure difference regime, the poiseuille flow took part in the gas transport through pores of the prepared membrane. The hydrogen separation factors for the gas mixture were increased with increasing the pressure difference and temperature. However, they reached to the maximum because of the poiseuille flow. As the membrane was used repeatedly, the separation performance of prepared membranes was decayed and the real hydrogen separation factors for $H_2/N_2$ and $H_2/CO_2$ were dropped from 1.9 to 1.5 and from 2.1 to 1.8, respectively. For the $H_2/N_2/CH_4/CO_2$ mixture, the separation factors showed a maximum value with increasing the pressure difference. By two-stage gas separation without recycle stream, the hydrogen gas separation factor from nitrogen was increased about 40 % than that for a single stage. The separation factors predicted by the numerical simulation for $H_2/N_2$ and $H_2/CO_2$ mixture were in good agreement with the experimental results. By the numerical simulation for three-stage separation, it was clear that the proposed three-stage separation system with the recycle stream could increase the hydrogen separation factor for $H_2/N_2$ mixture from 1.8 to 3.65 when using three membrane all of which have same permeability and the ideal separation factor near to ...