Albano Matilde, Madeira Luís M, Miguel Carlos V
Department of Chemical Engineering, Faculty of Engineering, University of Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal.
Fraunhofer Portugal AWAM-Research Center for Smart Agriculture and Water Management, Régia Douro Park-Parque de Ciência e Tecnologia, 5000-033 Vila Real, Portugal.
Membranes (Basel). 2023 Jun 29;13(7):630. doi: 10.3390/membranes13070630.
Biogas is a valuable renewable energy source that can help mitigate greenhouse emissions. The dry reforming of methane (DRM) offers an alternative hydrogen production route with the advantage of using two main greenhouse gases, CO and CH. However, its real application is limited mainly due to catalyst deactivation by coke formation and the reverse water gas shift (RWGS) reaction that can occur in parallel. Additionally, the typical dry reforming temperature range is 700-950 °C, often leading to catalyst sintering. A low-temperature DRM process could be in principle achieved using a membrane reactor (MR) to shift the dry reforming equilibrium forward and inhibit the RWGS reaction. In this work, biogas reforming was investigated through the simulation of MRs with thin (3.4 µm) and thick (50 µm) Pd-Ag membranes. The effects of the feed temperature (from 450 to 550 °C), pressure (in the range of 2-20 bar), and biogas composition (CH/CO molar ratios from 1/1 to 7/3) were studied for the thin membrane through the calculation and comparison of several process indicators, namely CH and CO conversions, H yield, H/CO ratio and H recovery. Estimation of the CO-inhibiting effect on the H molar flux through the membrane was assessed for a thick membrane. Simulations for a thin Pd-Ag MR show that (i) CO and CH conversions and H yield increase with the feed temperature; (ii) H yield and average rate of coke formation increase for higher pressures; and (iii) increasing CH/CO feed molar ratio leads to higher H/CO ratios, but lower H yields. Moreover, simulations for a thick Pd-Ag MR showed that the average H molar flux decreases due to the CO inhibiting effect (. 15%) in the temperature range considered. In conclusion, this work showed that for the considered simulation conditions, the use of an MR leads to the inhibition of the RWGS reaction and improves H yield, but coke formation and CO inhibition on H permeation may pose limitations on its practical feasibility, for which proper strategies must be explored.
沼气是一种宝贵的可再生能源，有助于减少温室气体排放。甲烷干重整（DRM）提供了一种替代制氢途径，其优点是利用两种主要温室气体CO和CH₄。然而，其实际应用受到限制，主要原因是焦炭形成导致催化剂失活以及可能同时发生的逆水煤气变换（RWGS）反应。此外，典型的干重整温度范围是700-950℃，这常常导致催化剂烧结。原则上，使用膜反应器（MR）来使干重整平衡正向移动并抑制RWGS反应，可以实现低温DRM工艺。在这项工作中，通过模拟具有薄（3.4μm）和厚（50μm）Pd-Ag膜的膜反应器来研究沼气重整。通过计算和比较几个工艺指标，即CH₄和CO转化率、H₂产率、H₂/CO比和H₂回收率，研究了进料温度（450至550℃）、压力（2至20巴范围内）和沼气组成（CH₄/CO摩尔比从1/1至7/3）对薄钯银膜的影响。评估了厚膜中CO对通过膜的H₂摩尔通量的抑制作用。对薄Pd-Ag膜反应器的模拟表明：（i）CO和CH₄转化率以及H₂产率随进料温度升高而增加；（ii）较高压力下H₂产率和焦炭平均生成速率增加；（iii）进料CH₄/CO摩尔比增加导致H₂/CO比升高，但H₂产率降低。此外，对厚Pd-Ag膜反应器的模拟表明，在所考虑的温度范围内，由于CO的抑制作用（＞15%），平均H₂摩尔通量降低。总之，这项工作表明，在所考虑的模拟条件下，使用膜反应器可抑制RWGS反应并提高H₂产率，但焦炭形成和CO对H₂渗透的抑制作用可能对其实际可行性构成限制，对此必须探索适当的策略。
