Catalytic dehydration of glycerol to acrolein has the potential to valorise the glut of crude glycerol issuing from biodiesel production. This reaction requires catalysts with appropriate acidity, and intensive research activities have been focused on the application of families of catalysts including zeolites, heteropolyacids, mixed metal oxides and (oxo)-pyrophosphates, as their acidic properties are well-known. Nevertheless, their deactivation by coking remains the main obstacle in the way of large-scale industrial applications. Considering this important issue, various technologies have been proposed for regenerating the catalysts. This review shows that a well-balanced combination of an appropriate catalytic system together with an adapted regeneration process could put large-scale industrial applications within reach.

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The dehydration reaction of glycerol to acrolein is catalyzed by acid catalysts. These catalysts tend to suffer from the formation of carbonaceous species on their surface (coking), which leads to substantial degradation of their performances (deactivation). To regenerate the as-deactivated catalysts, various techniques have been proposed so far, such as the co-feeding of oxygen, continuous regeneration by using a moving catalytic bed, or alternating between reaction and regeneration. Herein, we study the regeneration of supported heteropolyacid catalysts. We show that the support has a strong impact on the thermal stability of the active phase. In particular, zirconia has been found to stabilize silicotungstic acid, thus enabling the nondestructive regeneration of the catalyst. Furthermore, the addition of steam to the regeneration feed has a positive impact by hindering the degradation reaction by equilibrium displacement. The catalysts are further used in a periodic reaction/regeneration process, whereby the possibility of maintaining long-term catalytic performances is evidenced.

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