Solvent and catalyst effect in the formic acid aided lignin-to-liquids

Research Progress on Lignin Depolymerization Strategies: A Review

As the only natural source of aromatic biopolymers, lignin can be converted into value-added chemicals and biofuels, showing great potential in realizing the development of green chemistry. At present, lignin is predominantly used for combustion to generate energy, and the real value of lignin is difficult to maximize. Accordingly, the depolymerization of lignin is of great significance for its high-value utilization. This review discusses the latest progress in the field of lignin depolymerization, including catalytic conversion systems using various thermochemical, chemocatalytic, photocatalytic, electrocatalytic, and biological depolymerization methods, as well as the involved reaction mechanisms and obtained products of various protocols, focusing on green and efficient lignin depolymerization strategies. In addition, the challenges faced by lignin depolymerization are also expounded, putting forward possible directions of developing lignin depolymerization strategies in the future.

Carbon-Based Nanocatalysts (CnCs) for Biomass Valorization and Hazardous Organics Remediation

The continuous increase of the demand in merchandise and fuels augments the need of modern approaches for the mass-production of renewable chemicals derived from abundant feedstocks, like biomass, as well as for the water and soil remediation pollution resulting from the anthropogenic discharge of organic compounds. Towards these directions and within the concept of circular (bio)economy, the development of efficient and sustainable catalytic processes is of paramount importance. Within this context, the design of novel catalysts play a key role, with carbon-based nanocatalysts (CnCs) representing one of the most promising class of materials. In this review, a wide range of CnCs utilized for biomass valorization towards valuable chemicals production, and for environmental remediation applications are summarized and discussed. Emphasis is given in particular on the catalytic production of 5-hydroxymethylfurfural (5-HMF) from cellulose or starch-rich food waste, the hydrogenolysis of lignin towards high bio-oil yields enriched predominately in alkyl and oxygenated phenolic monomers, the photocatalytic, sonocatalytic or sonophotocatalytic selective partial oxidation of 5-HMF to 2,5-diformylfuran (DFF) and the decomposition of organic pollutants in aqueous matrixes. The carbonaceous materials were utilized as stand-alone catalysts or as supports of (nano)metals are various types of activated micro/mesoporous carbons, graphene/graphite and the chemically modified counterparts like graphite oxide and reduced graphite oxide, carbon nanotubes, carbon quantum dots, graphitic carbon nitride, and fullerenes.

Ni12P5/P-N-C Derived from Natural Single-Celled Chlorella for Catalytic Depolymerization of Lignin into Monophenols

Lignin is exceptionally abundant in nature and is regarded as a renewable, cheap, and environmentally friendly resource for the manufacture of aromatic chemicals. A novel Ni₁₂P₅/P-N-C catalyst for catalytic hydrogenolysis of lignin was synthesized. The catalysts were prepared by simple impregnation and carbonization using the nonprecious metal Ni taken up by the cell wall of Chlorella in Ni(NO₃)₂ solution. There were only two steps in this process, making the whole process very simple, efficient, and economical. Ni₁₂P₅ was uniformly distributed in the catalyst. During the hydrogenolysis of lignin, after 4 h reaction at 270 °C, the yield of bio-oil reached 65.26%, the yield of monomer reached 9.60%, and the selectivity to alkylphenol reached 76.15%. The mixed solvent of ethanol/isopropanol (1:1, v/v) is used as the solvent for the hydrogenolysis of lignin, which not only had excellent hydrogen transferability but also improved the yield of bio-oil, inhibiting the generation of char. No external hydrogen was used, thus avoiding safety issues in hydrogen transport and storage.

Effective Depolymerization of Sodium Lignosulfonate over SO42−/TiO2 Catalyst

In this paper, liquefaction of sodium lignosulfonate (SL) over SO42−/TiO2 catalyst in methanol/glycerol was investigated. Effects of temperature, time, the ratio of methanol to glycerol and catalyst dosage were also studied. It was indicated that optimal reaction condition (the temperature of 160 °C, the time of 1 h, solvent ratio (methanol/glycerol) of 2:1, catalyst dosage of 5 wt % (based on lignin input)) was obtained after sets of experiments. The maximum yields of liquefaction (89.8%) and bio-oil (86.8%) were gained under the optimal reaction conditions. Bio-oil was analyzed by elemental analysis, FT-IR and gas chromatogram and mass spectrometry (GC/MS). It was shown that the functional groups of bio-oil were enriched and calorific value of bio-oil was increased. Finally, it can be seen from GC/MS analysis that the type of products included alcohols, ethers, phenols, ketones, esters and acids. Phenolic compounds mainly consisted of G (guaiacyl)-type phenols.