Integrated membrane gas separation process for the valorisation of H2 and CO2 to biomethane
Luigi Marsico, Adele Brunetti, Enrico Catizzone, Massimo Migliori, Giuseppe Barbieri
Abstract
In this work, we focused on a membrane gas separation system aimed at enhancing the efficiency of a process for CO 2 valorisation into synthetic methane production via hydrogenation of a biogas stream. This system is designed for separating and recycling unreacted CO 2 and H 2 downstream of a methanation reactor. The inlet stream of the membrane separation system consists of unconverted CO 2 and H 2 , apart from the CH 4 from biogas and that produced by CO 2 conversion. The membrane separation is analysed by using performance maps based a 1D mathematical model, already developed and validated, considering the selectivity and permeance properties of a polyimide membrane. The outcomes of the membrane system, constituted by two steps operated at 20 bar, show that the proposed integrated process allows a quantitative CO 2 conversion into methane. The integration of the multi-step membrane process leads to a final retentate stream suitable for direct injection into the gas grid with CH 4 ≥ 97.5% molar, and CO 2 and H 2 within the targets of Italian regulation, CH 4 yields up to 0.987 confirmed a nearly complete CO 2 valorisation into CH 4 and a near-zero emissions process.