From industrial black liquor to pure phenolic compounds: A combination of catalytic conversion with ionic liquids extraction

Abstract

The conversion, in a sustainable way, of paper industry wastes such as black liquor into value-added molecules is still challenging. Herein, a direct catalytic conversion of black liquor into an aqueous solution has been achieved at moderate temperature and pressure (<250°C, 2MPa). For this purpose, a multimetallic catalyst (Pd0.5/Ni1Cu1-Mg30AlOx) has been synthesized and fully characterized. In presence of this material, a carbon-based conversion of 12wt.% has been obtained. The final liquid is composed of value-added phenolic compounds (i.e., guaiacol, creosol…) and the reaction can be afforded up to five cycles without deactivation. The green chemistry concept consists of extracting these compounds without the use of volatile solvent and in safe operating conditions. For these reasons, the use of hydrophobic ionic liquids for the liquid–liquid extraction of these phenols has been investigated. The influences of the side chains of symmetric and asymmetric imidazolium-NTf2 as well as operational conditions (stirring rate and temperature) have been studied. As a result, [C1C6Im][NTf2] has been found to be efficient in one-step total extraction phenolic components contained in the solution issued from the catalytic conversion of black liquor. This study showed that the catalytic hydropyrolysis of black liquor could be considered as an alternative source of phenolic compounds to conventional fossil resources.