(748d) Oxidative Conversion of Lignin to Value Added Products Using Oxygen and Hydrogen Peroxide

One of the most significant challenges in the 21^st century is the development of a sustainable global economy. This calls for development of processes and technologies that allow sustainable production of materials from renewable natural resources. Kraft lignin is one such resource with annual production of 45 million metric tons/year from pulp and paper mills. Biorefinery lignin, the solid stream of biomass after enzymatic hydrolysis is another huge energy and carbon reserve. Lignin valorisation can be performed using oxidation strategy to produce value added products. The aim of this work is to deepen the fundamental understanding of factors governing the oxidative conversion processes using biorefinery and kraft lignin to further integrate into current pulp and paper industry. Vanillin with a market value of (approx.) $13,000/ton is one of the main value-added products obtained from alkaline oxidation of lignin. However, the current challenge of this process is to selectivity control and improve vanillin yield. In this study, softwood Lignoboost kraft lignin, (LBoost) and enzymatic hydrolysis (H-lignin) were used as starting materials to perform bench scale oxidations with oxygen and peroxide. Vanillin (V) was obtained as the main product along with vanillic acid (VA), and carboxylic acids such as formic and oxalic acids. In the oxidation with O₂, H-lignin provided 2.85% w/w of V, and 2.25% of VA compared to LBoost with 1.84% of V and 1.25% of VA per phenolic OH (mmol/g). The higher yield of H-lignin (5.1% w/w against LBoost - 3.09% w/w) is due to its structural characteristics close to native lignin. The concentration profiles of V and VA, the variation of O₂ partial pressure in the reactive medium and the variation of temperature with H₂O₂ oxidation were also investigated. It was also observed that oxygen partial pressure was the critical parameter determining vanillin yield reaching optimum yields at lower pressures & increased vanillin oxidation rate at higher pressures. The results obtained provide a further understanding on factors affecting phenolic aldehyde yield which paves a way to selectively improve vanillin yield. These results also show a potential to develop a lignin valorization pathway integrating with current pulp and paper manufacturing processes, thereby making a sustainable bio-refinery.