A dehydration membrane reactor towards highly efficient LPG synthesis via CO₂ hydrogenation

In recent years, CO₂ hydrogenation has garnered increasing attention as a promising avenue towards the conversion of captured CO₂ to valuable liquid chemicals, including CH₃OH, CH₃OCH₃, and liquified petroleum gas (LPG). However, chemical conversion of CO₂ has proven to be immensely challenging, resulting in low CO₂ conversion (< 35 %) and product yields (< 15 %). H₂O, unavoidably evolved during CO₂ hydrogenation, imposes both thermodynamic and kinetic penalties on CO₂ hydrogenation reactions via adsorption on catalyst active sites and promotion of undesirable reaction pathways. In this work, to greatly facilitate direct conversion of CO₂ to LPG over a bifunctional Cu/Zn/Zr on Al₂O₃ (CZZA)/Pd-β-zeolite catalyst, a dehydration membrane reactor (MR) featuring a H₂O-conducting Na⁺-gated nanochannel membrane was studied. Before the incorporation of the Na⁺-gated membrane, the CZZA/Pd-β-zeolite was unable to produce LPG at 280–310 °C and 14 bar, and the CO₂ conversion was limited to < 35 %. In stark contrast, the MR exhibited CO₂ conversion and LPG yield of 72.1 % and 51.7 %, respectively. The operating conditions of the MR were systematically investigated to determine the maximum achievable performance resulting in CO₂ conversion and LPG yield as high as 90.2 % and 60.5 %, respectively. Furthermore, the LPG space–time yield (STY) at the optimized conditions was near that of the best-performing traditional reactors (TRs) in the literature but at 3 times and 8 times increased CO₂ conversion and time factor (W/F), respectively. The MR in this work demonstrates the synergistic efficacy of combined H₂O removal and CH₃OH consumption towards highly efficient hydrogenation of CO₂ for LPG production.