Parametric analysis and potential prediction of membrane processes for hydrogen production and pre-combustion CO2 capture

Abstract

This study primarily discusses the recommended membrane properties and potential usages of membrane systems for hydrogen purification and pre-combustion CO2 capture. Single-stage and two-stage systems for CO2 selective membranes (CSMs) and H2 selective membranes (HSMs) are investigated. To achieve the different goals for hydrogen purification, determining the possible operating range for different membrane systems is urgently required. It is found that CSMs are more appropriate for high purity H2 acquisition and that HSMs are more advantageous in terms of economic cost and H2 recovery over a relatively low purity range. The two-stage CSM has higher H2 recovery than the single-stage CSM membrane process. Although HSM is less competitive than CSM when extremely high product purity and high recovery are required, the hydrogen purity could be increased to more than 99.99% by increasing the HSM selectivity. Additionally, the recovery and purity analysis are restricted by the mass balance of the membrane system. Especially for HSM systems, a boundary that prevents the acquisition of high purity H2 is observed, and because of this boundary, two-stage HSM is unsuitable for stable operation over a low selectivity range. Additionally, for a two-stage CSM system, a cost-based optimization procedure is calculated and analyzed. With fixed membrane permeability, along with the product purity, the minimum cost selectivity is found. The moderation and cooperation between selectivity and permeability will reach a minimum cost for the unit product with different product purities. When the membrane permeance is 59.5 GPU and CO2/H2 selectivity is 63.5, the two-stage CSM system will acquire ultra-high purity (99.999%) hydrogen with a 99% hydrogen recovery, and under the optimum conditions, the CO2 purity is above 98.5%. Therefore, the increase in permeability requires an appropriate improvement of selectivity to reach the optimized conditions, which will reduce the hydrogen purification cost for integrated gasification combined cycle (IGCC) syngas. Moreover, the membrane selectivity must be enhanced during the development of gas separation membranes.