Direct valorisation of bio-glycerol to acrylic acid: Experimental comparison of membrane and conventional reactors

This study demonstrates the proof-of-principle of using a membrane reactor to enhance acrylic acid production via oxidative dehydration of glycerol. The performance of the membrane reactor was compared with that of a conventional packed-bed reactor in terms of key reaction parameters. The dehydration reaction was carried out over the HZSM-5 (SAR-200) catalyst, followed by oxidation over the Ortho-MoVO catalyst. A design of experiments and optimisation strategy was applied to maximise acrylic acid selectivity by varying temperature, oxygen-to-glycerol molar ratio, gas hourly space velocity (GSHV), and feed-to-membrane ratio. Testing was carried out using up to 30 g of catalysts (diluted with an additional 120 g of solid inert). The membrane reactor outperforms the conventional packed-bed reactor, achieving a maximum acrylic acid selectivity of 58.7% under optimised conditions (280 °C, 1935 h−1 GHSV, 14:1 oxygen-to-glycerol ratio, and 50:50 feed-to-membrane ratio). The superior performance of the membrane reactor is attributed to controlled oxygen distribution via the membrane, which locally maintains a lower oxygen partial pressure, in line with first-order kinetics, resulting in improved net acrylic acid selectivity, with an increase of 10% compared to a packed-bed reactor. The major by-products are acetic acid, formic acid and COx. Overall, this study demonstrates the potential of the intensified membrane reactor for manufacturing of value-added chemicals and its applicability to future industrial processes.