Aqueous phase reforming of lignin-rich hydrothermal liquefaction by-products: A study on catalyst deactivation

The water fraction derived from the hydrothermal liquefaction of a lignin-rich feedstock was subjected to aqueous phase reforming to produce hydrogen. Deactivation of the catalyst was observed, and it was ascribed to fouling phenomena caused by phenolic oligomers. Simple aromatics like guaiacol and phenol, as well as inorganics, were proved not to be the cause of the deactivation thanks to the use of a multi-component synthetic mixture. The influence of using activated carbon as a pretreatment was studied, leading to a strong improvement of the performance when it was carried out at high temperature. The extent of deactivation was assessed using aqueous phase reforming of glycolic acid as a model reaction test. The results were found to be correlated with the surface area of the catalyst. A thermal regeneration in inert conditions was evaluated as a mode of catalyst regeneration. While the textural properties were partially recovered, the performance of the catalyst only slightly improved. A spectroscopic analysis of the solids in the aqueous solution was carried out, highlighting the structural similarities between their nature and the lignin residue. The results obtained in this study helped to enlarge the knowledge on the aqueous phase reforming of real complex mixtures, looking at indicators of paramount importance for a possible industrial application such as the stability of the catalyst.