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 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 is 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 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 maintains locally less oxygen partial pressure in line with first-order kinetics, resulting in improved net acrylic acid selectivity by 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 process for added value chemical and their route towards future industrial applications.