Solid base catalyzed depolymerization of lignin into low molecular weight products

Abstract

For the biorefinery concept to become commercially viable, it is essential to add value to lignin which is the only naturally available aromatic polymer. A one-pot depolymerization of lignin into reactive substituted phenolic compounds (platform chemicals and octane enhancers) with low molecular weight is of paramount importance and for that, the development of an environmentally benign method is necessary. Herein we report the depolymerization of high molecular weight lignin (60 000 Da) over various recyclable solid base catalysts at 250 °C over 1 h. Under these conditions, most of the zeolitic catalysts (NaX, NaY, NaP) showed very high yields of low molecular weight products compared to other catalysts (MgO, CaO, HT, HAP). But in particular, over NaX the maximum yield (51%) of low molecular weight products was achieved. Identification and quantification of products was done by GC, GC-MS, HPLC, LC-MS, CHNS, NMR and FT-IR techniques. The revelation of retention of most of the functional groups on products present in lignin was confirmed by FT-IR studies. It is observed that the efficiencies of catalysts were dependent on pH, the cation, the type and concentration of basic sites, etc. A unique study on the product adsorption capacities on solids was done and it is recognized that as the strength of basic sites increases, adsorption enhances.