Lignin Conversion Processes Research Articles

Heterogeneous Catalyzed Thermochemical Conversion of Lignin Model Compounds: An Overview.

Thermochemical lignin conversion processes can be described as complex reaction networks involving not only de-polymerization and re-polymerization reactions, but also chemical transformations of the depolymerized mono-, di-, and oligomeric compounds. They typically result in a product mixture consisting of a gaseous, liquid (i.e., mono-, di-, and oligomeric products), and solid phase. Consequently, researchers have developed a common strategy to simplify this issue by replacing lignin with simpler, but still representative, lignin model compounds. This strategy is typically applied to the elucidation of reaction mechanisms and the exploration of novel lignin conversion approaches. In this review, we present a general overview of the latest advances in the principal thermochemical processes applied for the conversion of lignin model compounds using heterogeneous catalysts. This review focuses on the most representative lignin conversion methods, i.e., reductive, oxidative, pyrolytic, and hydrolytic processes. An additional subchapter on the reforming of pyrolysis oil model compounds has also been included. Special attention will be given to those research papers using "green" reactants (i.e., H2 or renewable hydrogen donor molecules in reductive processes or air/O2 in oxidative processes) and solvents, although less environmentally friendly chemicals will be also considered. Moreover, the scope of the review is limited to those most representative lignin model compounds and to those reaction products that are typically targeted in lignin valorization.

Recent progress in the thermal and catalytic conversion of lignin

The issues over increases in energy demand and environmental pollution attributed to excessive use of fossil fuel have been the driving forces of the exploration for eco-friendly resource. Lignocellulosic biomass consisting of carbohydrates and lignin can be a renewable feedstock for replacing fossil fuels in the future because it is a plentiful and carbon neutral material. Especially, lignin, cross-linked phenolic polymers, is a topic of interest owing to its abundant production from pulp/paper industries as well as lignocellulose based biorefinery. The large potential of platform chemicals and biofuels from lignin has opened up an extensive range of opportunities to develop thermal and catalytic conversion technology. Over a few decades, several lignin conversion processes including catalytic pyrolysis, catalytic depolymerization, and catalytic oxidation have been developed to improve target products yields and to suppress side reactions. More recently, lignin-first approaches which maintain carbohydrates intact by selective extraction of lignin as valuable phenolics from whole biomass has been suggested. This review introduces recent ten years progress on thermal and catalytic conversion technology in terms of process type, catalyst development, and target products. This review is expected to offer an influential information for future research into the thermal and catalytic conversion of lignin as well as lignocellulosic feedstock.

High-Performance Magnetic Activated Carbon from Solid Waste from Lignin Conversion Processes. 2. Their Use as NiMo Catalyst Supports for Lignin Conversion

Lignin conversion processes produce carbon-rich residues [Oregui-Bengoechea et al. J. Anal. Appl. Pyrolysis 2015, 113, 713−722; Zakzeski et al. Chem. Rev. 2010, 110, 3552–3599] that can be converted into valuable materials such as magnetic activated carbons (MACs). Such lignin-derived MACs can be further used as functional substrates for hydrotreating NiMo catalysts. In this work, we studied the activity of different NiMo-MACs for the catalytic conversion of lignin in a formic acid/ethanol media (lignin-to-liquid, LtL, process). Two KOH-activated LtL hydrochars from eucalyptus (MACE) and Norwegian spruce (MACS) lignins were used as catalyst supports. In addition, the activity of the resulting NiMo-MACs, namely, C-MACE and C-MACS, was compared with a NiMo catalyst supported on a commercial activated carbon (AC). At reaction conditions of 340 °C and 6 h, the best result was obtained for the NiMo-MACS with a yield of 72.2 wt % of oil and 21.1 wt % of organic solids. At 300 °C and 10 h, both NiMo-MAC catalysts displayed higher hydrodeoxygenation (HDO) activities than their commercial counterpart, yielding considerably higher oil yields. The higher HDO activities are tentatively assigned to the formation of NiFe species on the catalytic surfaces of the NiMo-MAC catalysts. In addition, the magnetism exhibited by the C-MACS made it easy to recover the catalyst. However, a considerable loss of activity was observed upon recycling due to a chemical modification of the catalyst surface.

Correction to “High-Performance Magnetic Activated Carbon from Solid Waste from Lignin Conversion Processes. 1. Their Use As Adsorbents for CO2”

Correction to “High-Performance Magnetic Activated Carbon from Solid Waste from Lignin Conversion Processes. 1. Their Use As Adsorbents for CO₂”

WITHDRAWN: High-performance magnetic activated carbon from solid waste from lignin conversion processes. Part I: Their use as adsorbents for CO2

WITHDRAWN: High-performance magnetic activated carbon from solid waste from lignin conversion processes. Part I: Their use as adsorbents for CO2

High-Performance Magnetic Activated Carbon from Solid Waste from Lignin Conversion Processes. 1. Their Use As Adsorbents for CO2

Lignin is naturally abundant and a renewable precursor with the potential to be used in the production of both chemicals and materials. As many lignin conversion processes suffer from a significant production of solid wastes in the form of hydrochars, this study focused on transforming hydrochars into magnetic activated carbons (MAC). The hydrochars were produced via hydrothermal treatment of lignins together with formic acid. The activation of the hydrochars was performed chemically with KOH with a focus on the optimization of the MACs as adsorbents for CO2. MACs are potentially relevant to carbon capture and storage (CCS) and gas purification processes. In general, the MACs had high specific surface areas (up to 2875 m2/g), high specific pore volumes, and CO2 adsorption capacities of up to 6.0 mmol/g (1 atm, 0 °C). The textual properties of the MACs depended on the temperature of the activation. MACs activated at a temperature of 700 °C had very high ultramicropore volumes, which are relevant for potent...

Cu–Mo doped zeolite ZSM-5 catalyzed conversion of lignin to alkyl phenols with high selectivity

Challenging issues of lignin conversion processes including char formation, lower degree of depolymerization and lower product yield with no selectivity are worked out in this study.

Hydrothermal production of formic and acetic acids from syringol

The production of formic and acetic acids (or salts) by hydrothermal oxidation of syringol, a model compound for lignin, was investigated using a batch reactor. Results show that the highest yields of formic and acetic acids were, respectively, 59.6% and 11.3% at the reaction condition of 0.5 mol/L NaOH, 120% H2O2 supply and 280 °C. These results will inform studies aiming to develop more environmental friendly lignin conversion processes by obtaining products beyond a CO2 end product.