Green Catalytic Approach for the Synthesis of Platform Chemicals from Palm Tree Lignin

Abstract

Lignin is the second most abundant naturally occurring macromolecule found in plant cell-wall, vascular components and woody stems. It is the largest renewable source of aromatic biopolymer. However, lignin is recalcitrant to be broken down by most chemicals. This is because of its complicated heterogeneous molecular structure. However, lignin depolymerization has huge potentials for the synthesis of a number of useful chemicals, perfumes and pharmaceuticals and toiletries. The oxidation products of lignin are important precursors for pulp/paper and food industries, synthetic thin films. Vanillin, veratryl aldehyde and para-benzoquinone are the oxidation products of lignin. These chemicals are the precursors of optically active alcohol, ketone, violuric acid and benzaldehyde. However, the oxidation of biolignin has been remaining a challenging task. Green catalytic approaches might be an interesting solution for the selective depolymerization of lignin into various platform chemicals. Metal oxide/silica supported nanoporous gold has received strong attention as green catalyst for the transformation of various natural polymers. Mesoporous metal oxide/silica provide enlarged surfaces for the breakdown of C-C, C-H and C-OH bonds. This paper has reviewed various green catalytic approaches for the control depolymerization of biolignin into platform chemicals.

Alkaline Partial Wet Oxidation of Lignin for the Production of Carboxylic Acids

“…It is estimated that 70 million tons of lignin is annually produced worldwide from the pulp and paper industry alone [5,7]. Lignin is also the largest renewable source of biopolymers [9]. However, unlike cellulose and hemicellulose, lignin has received limited attention and its potential has been underutilized with regard to valorization [6,10].…”

“…However, unlike cellulose and hemicellulose, lignin has received limited attention and its potential has been underutilized with regard to valorization [6,10]. The main reason for the limited interest is that, unlike cellulose and hemicellulose which are easily convertible fractions of wood, the heterogeneous and cross-linked structure of the lignin molecule complicates its controlled depolymerization into single chemicals [3,9]. Nevertheless, it is clear that lignin holds promise as a significant resource for the production of a wide range of renewable chemicals, due to its high energy content, its aromatic structure, the presence of highly reactive groups, and the fact that it will be generated in large quantities as second-generation biorefineries are deployed [10].…”

Microwave Assisted Degradation of Lignin to Monolignols

“…It has a major application in food industry and perfumery along with the sources of various pharmaceutical products. For example, monolignols like vanillin have a broader scope in the synthesis of numerous pharmaceutical ingredients [5].…”