Development of a photocatalytic reaction system to gain raw materials from lignin derivatives

Wood biomass consists of cellulose (40-50%), lignin (16-33%), hemicelluloses (15-30%), and a variety of extractives (1-10%). After cellulose, lignin is the most abundant renewable carbon source on earth. More than 70 million tons of various types of lignin preparations are produced as waste material by the paper industry yearly. Moreover, lignin represents the only viable source to produce aromatic compounds as fossil fuel alternative.

Photocatalysis, belonging to the advanced oxidation processes (AOPs), is a potential new transformation technology for lignin derivatives to value added products such as phenol, benzene, toluene and xylene amongst others.

The goal of this work was to develop a photocatalytic reaction system which could effectively depolymerize lignin into value added chemicals such as phenolic derivatives or thermosets like phenolic resins and thus propose a processing concept for lignin conversion.

This work reports the synthesis of immobilized catalyst via the sol-gel route on porous glass support material. A comparative study is done regarding the morphology of the coatings, degradation rates, reaction rates, dissolved carbon (DC), formation of peaks and fluorescence of product peaks formed from the photocatalytic degradation of lignin sulfonate obtained from a local paper plant. Through simultaneous reaction-extraction pathways applying dialysis filtration and a highly porous polystyrene divinylbenzene adsorbent resin (HR-P) for the solid phase extraction (SPE), an attempt was made to isolate smaller molecules produced from the photocatalytic degradation of lignin sulfonate. Moreover a relatively high concentrationof lignin sulfonate (0.5g/L) was used for the experiments. Ultraviolet-visible (UV-Vis) spectroscopy revealed a faster degradation of the aliphatic moiety compared to the aromatic moiety which constitutes lignin. New peaks were observed from High performance liquid chromatography (HPLC) analysis and some of these peaks showed signals when studied under fluorescence detection. This suggested the production of new substances and fluorophores. The catalytic coatings were done through the sol- gel procedure and they could be used many times.