Search

Utilization of lignin is among the most pressing problems for biorefineries that convert lignocellulosic biomass to fuels and chemicals. Recently "lignin-first" biomass fractionation has received increasing attention. In most biorefining concepts, carbohydrate portions of the biomass are separated, and their monomeric sugar components released, while the relatively chemically stable lignin rich byproduct remains underutilized. Conversely, in lignin-first processes, a one-pot fractionation and depolymerization is performed, leading to an oil rich in phenolic compounds and a cellulosic pulp. Usually, the pulp is considered as a fermentation feedstock to produce ethanol. Herein, the results of a study where various cellulosic pulps are tested for their potential to produce valuable products via pyrolysis processes, assessed via analytical pyrolysis (py-GC), are presented. Samples of herbaceous (switchgrass) and woody biomass (oak) were subjected to both an acid-catalyzed and a supported-metal-catalyzed reductive lignin-first depolymerization, and the pulps were compared. Fast pyrolysis of the pulps produced levoglucosan in yields of up to about 35 wt %. When normalized for the amount of biomass entering the entire process, performing the lignin-first reductive depolymerization resulted in 4.0–4.6 times the yield of levoglucosan than pyrolysis of raw biomass. Pulps derived from switchgrass were better feedstocks for levoglucosan production compared with pulps from oak, and pulps produced from metal-on-carbon catalyzed depolymerization produced more levoglucosan than those from acid-catalyzed depolymerization. Catalytic pyrolysis over HZSM-5 produced aromatic hydrocarbons from the pulps. In this case, the yields were similar from both feedstocks and catalyst types, suggesting that there is no advantage to lignin fractionation prior to zeolite-catalyzed catalytic pyrolysis for hydrocarbons. [ABSTRACT FROM AUTHOR]

[Display omitted] • Constructing N-doped carbon supported Co catalyst for lignin-first strategy. • Catalyst morphology, metal dispersion and N content were regulated by melamine dosage. • Pyridinic N enhanced lignin adsorption and decreased C–O bond disassociation energy. • Atom-cluster Co was loaded by the presence of pyridinic N in the carrier. • 40.62 wt% of monophenolics from lignin and 84.02 wt% of cellulose were obtained. The lignin-first strategy is a crucial approach for highly efficient depolymerization of lignin to produce aromatic monomers as the condensation of lignin occurred during the separating process which increased the difficulty in depolymerization. In this work, a cobalt atom clusters supported on nitrogen-doped carbon catalysts (Co/NC-15) was prepared by adjusting the dosage of melamine to control the morphology, structure, and pyridinic nitrogen content of the catalysts. DFT calculations based on lignin model showed that the doping of nitrogen increased the adsorption energy of the lignin on the supports and decreased the dissociation energy of C-O bonds. Under lignin first strategy, Co/NC-15 exhibited good ability to break C-O bonds at 220 °C of mild condition, in which 84.32 wt% of lignin in lignocellulosic biomass was converted into 40.62 wt% of aromatic monomers, while 84.02 wt% of cellulose was preserved. The atom clusters Co/NC-15 exhibited good catalytic activity to lignin depolymerization due to efficient cleavage of C-O bonds, and hence showed the promising prospect in potential industrial application. [ABSTRACT FROM AUTHOR]

The utilization of lignocellulosic biomass promotes the concept of sustainability and contribute to carbon neutrality. In contrast to traditional biomass pretreatment, lignin-first biomass pretreatment considers both the integrity of lignin and sugar production. There has been increasing interest in applying the concept of lignin-first biomass pretreatment to traditional pretreatment processes. Progress has been made in the field in the past three years or so. It is timely to offer a systematic analysis of the current state of lignin-first biomass pretreatment, and identify existing challenges and future trends in the field. Herein, we first present a brief introduction to biomass recalcitrance and pretreatment, followed by a discussion of lignin repolymerization/condensation during pretreatment and different strategies to stabilize lignin. Next, we focus on biomass pretreatments with active protection of the β-O-4 bonds in lignin. Ionic liquid (IL) pretreatment, deep eutectic solvent (DES) pretreatment, acidified organosolv pretreatment, and organic acid pretreatment are the main pretreatment technologies that have been studied with the active protection of the β-O-4 linkages. We emphasize the importance of retention of high β-O-4 content in valorizing lignin by depolymerization approach. Finally, we provide our perspectives on the challenges and opportunities in this field, in support of efforts to advance lignin-first biomass pretreatment. [Display omitted] • Lignin-first biomass pretreatment aims to maximize both sugar yield and β-O-4 bonds preservation. • Active protection of the β-O-4 bonds has been extended to several typical pretreatment processes. • Ionic liquids, deep eutectic solvents, organic solvents, and organic acids were discussed. • Mild pretreatment conditions and chemical stabilization of lignin were analyzed. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel pre-treatment strategy for LCB for 2G ethanol biorefinery. • Complete and effective utilization of all the components of lignocellulosic biomass. • Depolymerization of native lignin into phenolic monomers. • Reaction chemistry behind lignin valorisation. • Role of RCF biorefinery to achieve SDGs. Presently, the use of lignocellulosic biomass is mainly focused on creating pulp/paper, energy, sugars and bioethanol from the holocellulose component, leaving behind lignin to be discarded or burned as waste despite of its highest aromatic carbon and energy content (22–29 KJ/g). During the pulping process, lignin undergoes significant structural changes to yield technical lignin. For a circular bioeconomy, there is an urgent need to enhance the use of native lignin for generating more valuable products. Over the last few years, a new method called 'lignin-first', or 'reductive catalytic fractionation' (RCF), has been devised to achieve selective phenolic monomers under mild reaction conditions. This involves deconstructing lignin before capitalizing on carbohydrates. The objective of this study is to record the recent developments of the 'lignin-first' process. This review also underlines the contribution of RCF biorefinery towards achieving sustainable development goals (SDGs) and concludes with an overview of challenges and upcoming opportunities. [ABSTRACT FROM AUTHOR]

• High selective GVL solvent for biomass fractionation into C5, C6 sugars and lignin. • Formaldehyde co-solvent to hinder C C bonds formation and protect lignin and xylose. • Process flowsheeting, simulation and LCA of lignin-first multi-product biorefineries. • Up to 8.8% steam savings and 1.85 MW cogeneration via process-to-process integration. • High sustainable bio-based levulinic acid, furfural and lignin-aromatics production. This work presents solutions for the holistic utilization of lignocellulosic biomass based on the "lignin-first" concept. Biomass is fractionated by employing γ-Valerolactone (GVL) andformaldehyde solvents to effectively extract and protect the lignin and xylose ingredients. The process flowsheet of a large scale biomass fractionation technology – recently validated at laboratory scale by Shuai et al. (2016a) – has been developed and simulated to test and build performance in use of energy, water and materials. The biorefinery value chain further integrates chemistries for the production of platform chemicals and biofuels (furfural, levulinic acid and lignin-aromatics), while the C6 sugars fraction is partially converted into GVL to offset any solvent losses. Energy integration and techno-economic analyses revealed 38–60% steam savings, 2.5–3.1 MW power cogeneration potential and 10–15 Μ€ annual profitability for the overall multiple-product biorefinery. Finally, a cradle-to-gate LCA approach identified environmental hot-spots (e.g. the use of THF in hydrotreatment) and estimated up to 11.1 kg_CO2eq emissions per kg of end-product. [ABSTRACT FROM AUTHOR]