Production of solubilized carbohydrates from lignocellulosic biomass using solvent liquefaction

Solvent liquefaction using polar aprotic solvents is a promising approach for production of solubilized carbohydrates as biofuel precursor from lignocellulosic biomass. However, many technical challenges preclude its application at commercial scale. This research focuses on improving upon these challenges with bench-scale studies on liquefaction of cellulose and hardwood biomass in a variety of polar aprotic solvents. Cellulose conversion was studied in a variety of polar aprotic solvents at hot, pressurized conditions, including 1,4-Dioxane, ethyl acetate, tetrahydrofuran (THF), methyl iso-butyl ketone (MIBK), acetone, acetonitrile, and γ-valerolactone (GVL). Maximum yield of depolymerized carbohydrate and products of carbohydrate dehydration from cellulose, called solubilized products, was 72 to 98% at 350 oC within 8-16 min of reaction. The most prevalent solubilized carbohydrate product was levoglucosan and it was produced with yields reaching 41% and 34% in acetonitrile and GVL, respectively. Levoglucosan yields increased with increasing polar solubility parameter of the solvent. This behavior of solvents could be attributed to reduction of apparent activation energy of cellulose depolymerization in higher polarity solvents. Recovery of solvents in all cases was high. The effectiveness of a wide range of polar aprotic solvents, including1,4-Dioxane, ethyl acetate, THF, MIBK, acetone, acetonitrile, and GVL, in depolymerizing cellulose into solubilized carbohydrates in the presence of dilute acid catalyst. While yields of solubilized carbohydrates strongly depended on the polar solubility parameters of solvents, the use of dilute acid catalyst substantially removed differences in the yields for various polar aprotic solvents. The equalized solubilized carbohydrate yields among the polar aprotic solvents were 83-97%. Levoglucosan and solubilized carbohydrates yields in 1,4-Dioxane, THF, and acetone approached that of GVL, along with completely solubilizing cellulose within 1-7 min. The low polarity, low boiling point solvents showed high stability and competitive yields of the anhydrosugar compared to high polarity and high boiling solvent such as GVL due to low initial rates of levoglucosan degradation. The ease of separation of low polarity, low-boiling solvents offers them as attractive media for solubilized carbohydrates production when used in presence of acid catalyst. Use of 1,4-Dioxane to depolymerize cellulose for production of solubilized carbohydrates was explored. The low boiling point of this low polarity solvent offers inexpensive and simple separation compared to higher boiling point solvents like GVL, which has been previously investigated for acid-catalyzed depolymerization of cellulose. In this work, several key reaction parameters including reaction temperature, acid catalyst concentration, and content of co-solvent water in 1,4-Dioxane were studied for their impact on enhancing sugar production from cellulose. Yield of levoglucosan, the major anhydrosugar product of cellulose depolymerization, was maximized at 71% by operating at high temperature, short reaction time, low acid concentration and low mass loading of cellulose. Use of water as a co-solvent improved cellulose solubilization and promoted solubilized carbohydrates production at low temperature and high mass loading. This behavior of acid-catalyzed co-solvent system could potentially enable processing of cellulose at high solid loadings and milder conditions thus increasing its applicability at large scale. In this work, a novel two-step liquefaction process was developed for bench-scale production of solubilized, fermentable carbohydrates from hardwood biomass in a mixture of THF, water and dilute sulfuric acid. THF facilitates solubilization of lignin and hemicellulose in the biomass in presence of dilute acid catalyst resulting in 61% lignin extraction and 64% xylose recovery in a mild pretreatment step. The pretreatment loosens up the structure of biomass by delignification and produces a cellulose-rich hardwood, which could be readily solubilized at low temperature in a subsequent solvent liquefaction step using THF/water/acid mixture. The combined pretreatment and solvent liquefaction process produced 60% glucose yield and 89% xylose yields based on initial amounts of glucan and xylan in untreated biomass. Additionally, volumetric productivity of sugars was four orders of magnitude larger than conventional enzymatic hydrolysis. This process, not only achieves comparable sugar yields and significantly enhanced sugar productivity compared to biological processes and state-of-the-art solvent liquefaction techniques, but it also offers prospects for overcoming economic and sustainability barriers of cellulosic ethanol production by using THF which is relatively low-cost and low toxicity, derivable from biomass, and readily separable from sugar solution due to its low boiling point

Sustainable Materials: Production Methods and End-of-life Strategies

All three natural polymers of biomass and the monomer platforms derived from them present multiple avenues to develop products from specialty to bulk markets, which could serve as entry points into the industry for bio based sustainable materials. However, several roadblocks still exist in the pathway of technology development of these materials due to challenges related to cost-competitiveness, scalability, performance and sustainability. This review outlines these major technical challenges as four key checkpoints (cost-competitive, scalability, sustainability, performance) to be addressed for successful market entry of a new sustainable material

Production of sugars from lignocellulosic biomass via biochemical and thermochemical routes

Sugars are precursors to the majority of the world’s biofuels. Most of these come from sugar and starch crops, such as sugarcane and corn grain. Lignocellulosic sugars, although more challenging to extract from biomass, represent a large, untapped, opportunity. In response to the increasing attention to renewable energy, fuels, and chemicals, we review and compare two strategies for extracting sugars from lignocellulosic biomass: biochemical and thermochemical processing. Biochemical processing based on enzymatic hydrolysis has high sugar yield but is relatively slow. Thermochemical processing, which includes fast pyrolysis and solvent liquefaction, offers increased throughput and operability at the expense of low sugar yields

Production of solubilized carbohydrates from lignocellulosic biomass using solvent liquefaction

Solvent liquefaction using polar aprotic solvents is a promising approach for production of solubilized carbohydrates as biofuel precursor from lignocellulosic biomass. However, many technical challenges preclude its application at commercial scale. This research focuses on improving upon these challenges with bench-scale studies on liquefaction of cellulose and hardwood biomass in a variety of polar aprotic solvents. Cellulose conversion was studied in a variety of polar aprotic solvents at hot, pressurized conditions, including 1,4-Dioxane, ethyl acetate, tetrahydrofuran (THF), methyl iso-butyl ketone (MIBK), acetone, acetonitrile, and γ-valerolactone (GVL). Maximum yield of depolymerized carbohydrate and products of carbohydrate dehydration from cellulose, called solubilized products, was 72 to 98% at 350 oC within 8-16 min of reaction. The most prevalent solubilized carbohydrate product was levoglucosan and it was produced with yields reaching 41% and 34% in acetonitrile and GVL, respectively. Levoglucosan yields increased with increasing polar solubility parameter of the solvent. This behavior of solvents could be attributed to reduction of apparent activation energy of cellulose depolymerization in higher polarity solvents. Recovery of solvents in all cases was high. The effectiveness of a wide range of polar aprotic solvents, including1,4-Dioxane, ethyl acetate, THF, MIBK, acetone, acetonitrile, and GVL, in depolymerizing cellulose into solubilized carbohydrates in the presence of dilute acid catalyst. While yields of solubilized carbohydrates strongly depended on the polar solubility parameters of solvents, the use of dilute acid catalyst substantially removed differences in the yields for various polar aprotic solvents. The equalized solubilized carbohydrate yields among the polar aprotic solvents were 83-97%. Levoglucosan and solubilized carbohydrates yields in 1,4-Dioxane, THF, and acetone approached that of GVL, along with completely solubilizing cellulose within 1-7 min. The low polarity, low boiling point solvents showed high stability and competitive yields of the anhydrosugar compared to high polarity and high boiling solvent such as GVL due to low initial rates of levoglucosan degradation. The ease of separation of low polarity, low-boiling solvents offers them as attractive media for solubilized carbohydrates production when used in presence of acid catalyst. Use of 1,4-Dioxane to depolymerize cellulose for production of solubilized carbohydrates was explored. The low boiling point of this low polarity solvent offers inexpensive and simple separation compared to higher boiling point solvents like GVL, which has been previously investigated for acid-catalyzed depolymerization of cellulose. In this work, several key reaction parameters including reaction temperature, acid catalyst concentration, and content of co-solvent water in 1,4-Dioxane were studied for their impact on enhancing sugar production from cellulose. Yield of levoglucosan, the major anhydrosugar product of cellulose depolymerization, was maximized at 71% by operating at high temperature, short reaction time, low acid concentration and low mass loading of cellulose. Use of water as a co-solvent improved cellulose solubilization and promoted solubilized carbohydrates production at low temperature and high mass loading. This behavior of acid-catalyzed co-solvent system could potentially enable processing of cellulose at high solid loadings and milder conditions thus increasing its applicability at large scale. In this work, a novel two-step liquefaction process was developed for bench-scale production of solubilized, fermentable carbohydrates from hardwood biomass in a mixture of THF, water and dilute sulfuric acid. THF facilitates solubilization of lignin and hemicellulose in the biomass in presence of dilute acid catalyst resulting in 61% lignin extraction and 64% xylose recovery in a mild pretreatment step. The pretreatment loosens up the structure of biomass by delignification and produces a cellulose-rich hardwood, which could be readily solubilized at low temperature in a subsequent solvent liquefaction step using THF/water/acid mixture. The combined pretreatment and solvent liquefaction process produced 60% glucose yield and 89% xylose yields based on initial amounts of glucan and xylan in untreated biomass. Additionally, volumetric productivity of sugars was four orders of magnitude larger than conventional enzymatic hydrolysis. This process, not only achieves comparable sugar yields and significantly enhanced sugar productivity compared to biological processes and state-of-the-art solvent liquefaction techniques, but it also offers prospects for overcoming economic and sustainability barriers of cellulosic ethanol production by using THF which is relatively low-cost and low toxicity, derivable from biomass, and readily separable from sugar solution due to its low boiling point.</p

Factors Influencing Cellulosic Sugar Production during Acid-Catalyzed Solvent Liquefaction in 1,4-dioxane

This work explores the use of 1,4-dioxane to depolymerize cellulose into solubilized carbohydrates. This low boiling point solvent offers inexpensive and simple separation compared to higher boiling point solvents such as Y-valerolactone previously considered for acid-catalyzed depolymerization of cellulose. In the present study, several key reaction parameters, including reaction temperature, catalyst concentration, and water content, were studied as major factors influencing sugar production from cellulose. A maximum yield of 51% for levoglucosan, the major product of cellulose depolymerization, was achieved at higher temperature, shorter reaction time and lower acid concentration in the ranges tested for these parameters. Addition of water as co-solvent enhanced solubilization of cellulose and increased solubilized carbohydrate production, which could potentially enable processing of cellulose at high feedstock loadings and milder operating conditions.This document is the unedited Authors version of a Submitted Work that was subsequently accepted for publication in ACS Sustainable Chemistry & Engineering, copyright American Chemical Society after peer review. To access the final edited and published work see DOI: 10.1021/acssuschemeng.9b05108. Posted with permission.</p

The effect of moisture on hydrocarbon-based solvent liquefaction of pine, cellulose and lignin

In this paper we examined the effect of moisture on the solvent liquefaction of loblolly pine, cellulose, and lignin in tetralin at 280 °C and pressures ranging from 15 to 70 bar. Solvent liquefaction experiments were conducted in a quasi-batch reactor capable of continuous pressure control and external vapor condensation. Moisture was varied by the controlled addition of de-ionized water. Control over the system pressure subsequently impacted the removal of water vapor from the reactor. Liquid yield decreased by 25, 21, and 35 wt%, for pine, cellulose, and lignin, respectively, when moisture content was increased from 1 to 50 wt% at 42 bar. Humins were observed in the solid residue from liquefaction of wet cellulose. Wet lignin yielded a substantial amount of solid residue compared to dry lignin with a corresponding decrease in total phenolic monomer production. It was concluded that the ionic dissociation of water was an important factor in loss of liquid yield in the presence of water. Although water was less than 20 wt% of the solvent loading in these experiments, it strongly influenced the liquefaction of biomass and biomass components.This is a manuscript of an article published as Haverly, Martin R., Arpa Ghosh, and Robert C. Brown. "The effect of moisture on hydrocarbon-based solvent liquefaction of pine, cellulose and lignin." Journal of Analytical and Applied Pyrolysis (2019): 104758. DOI: 10.1016/j.jaap.2019.104758. Posted with permission.</p

Tetrahydrofuran-based two-step solvent liquefaction process for production of lignocellulosic sugars

Large-scale production of biofuels and chemicals will require cost-effective, sustainable, and rapid deconstruction of waste biomass into its constituent sugars. Here, we introduce a novel two-step liquefaction process for producing fermentable sugars from hardwood biomass using a mixture of tetrahydrofuran (THF), water and dilute sulfuric acid. THF promotes acid-catalyzed solubilization of lignin and hemicellulose in biomass achieving 61% lignin extraction and 64% xylose recovery in a mild pretreatment step. The pretreatment opens the structure of biomass through delignification and produces a cellulose-rich biomass, which is readily solubilized at low temperature giving 65% total sugar yields in a subsequent liquefaction process employing the same solvent mixture. This process achieves competitive sugar yields at high volumetric productivity compared to conventional saccharification methods. THF, which can be derived from renewable resources, has several benefits as solvent including ease of recovery from the sugar solution and relatively low toxicity and cost.This article is published as Ghosh, Arpa, Martin Haverly, Jake Lindstrom, Patrick A. Johnston, and Robert C. Brown. "Tetrahydrofuran-based two-step solvent liquefaction process for production of lignocellulosic sugars." Reaction Chemistry & Engineering 5, no. 9 (2020): 1694-1707. DOI: 10.1039/D0RE00192A. Posted with permission.</p