Lignin Solvolysis Research Articles

Pentaethylphenol (Not 2,6-di-tert-butyl-4-ethylphenol) verified as the primary product of guaiacol ethanol alkylation reaction

Guaiacol ethanol alkylation (GEA), a model reaction of lignin solvolysis, has been intensively investigated. However, the product identification with gas chromatograph-mass spectrometer (GC-MS) was wrong due to the defect of the GC-MS databases. In this work, the main product was isolated with a flash chromatography technique and analyzed with 1H NMR and was identified as ethyl fully substituted phenol (or pentaethylphenol), which is contrary to the reported 2,6-di-tert-butyl-4-ethylphenol in previous literature. The NMR analysis of the entire product mixture further confirms that the product only contains ethyl substituted molecules, with no existence of isopropyl or tert-butyl substituted products. The byproducts, including ethyl partially substituted phenols, i.e., tetraethylphenol and triethylphenol, ethyl partially substituted guaiacol, 2-ethoxyphenol, and pentaethylbenzene, were also speculated based on the MS spectra. These findings rectify a long-standing error in product identification and may offer critical insights for mechanism investigations.

Nonreductive Fast Lignin Solvolysis in Flow-Through Reactors for the Sustainable Production of BTEX Aromatics from Corn Stover

Nonreductive Fast Lignin Solvolysis in Flow-Through Reactors for the Sustainable Production of BTEX Aromatics from Corn Stover

Ethanolysis of enzymatic hydrolysis lignin with Ni catalysts on different supports: The roles of catalytic sites

Catalytic lignin solvolysis (CLS) holds promise for efficient lignin utilization, yielding small molecules with minimal or no char formation. However, the role of different active sites of catalyst in CLS are rarely discussed. Here, Ni catalysts on different supports, i.e., SiO2, Al2O3, MgO, and ZrO2, were prepared with the aim of manipulating the relative importance of metal and acid-base functionalities to investigate the role of different active sites in the enzymatic hydrolysis of lignin (EHL) ethanolysis. The main ether linkage, i.e., β-O-4, in EHL is cleaved without the participation of a catalyst. Metal sites suppress repolymerization through hydrogenating active intermediates, while acid and base sites facilitate the conversion of phenolic monomers into complex alkylated and etherified products and also promote repolymerization reactions. Among the catalysts, Ni/SiO2 demonstrated the highest hydrogenation activity and yielded the most monomers (24.7 wt %) at 280 °C for 6 h under 2 MPa H2 in ethanol. These findings shed light on the catalytic mechanisms in CLS, offering valuable insights for future catalyst design.

Enhanced lignin-first valorization of biomass for producing monophenols over Ru/C cooperated with H2WO4

Herein, using Ru/C and H2WO4 as the catalysts, native lignin in biomass was efficiently depolymerized into monophenols following the lignin-first strategy at mild conditions. Upon the co-presence of Ru/C and H2WO4, birch lignin afforded monophenols in 40.4 wt% yield at 200 °C, which was 2.5 times that upon Ru/C and 7.5 times that upon H2WO4. 4-Propylsyringol and 4-propylguaiacol were two major products with a combined selectivity of 73%. 2D HSQC NMR of liquid product reveals that β-O-4 bonds in the soluble lignin fragments had been thoroughly disrupted. H2WO4 dissolving at high temperatures promoted the solvolysis of lignin from the biomass matrix, and Ru/C enhanced the following reductive depolymerization. The solid catalysts can be readily recovered for reuse at room temperature after the hydrolysis of carbohydrates, and the catalysts exhibited high activity after four recycles.

LEO and LiMO Fuels: Structural and Rheological Characterization of Solvolytically Fractionated Lignin Dispersed in Alcohols

The mild thermal solvolysis of lignin in alcohols is a promising technology for obtaining carbon-neutral fuels. Incorporating lignin in ethanol and methanol leads to a rise in volumetric energy density in concentrated dispersions. The deployment of these fuels and their concentrated formulations depends on their structural and rheological properties. Here, we investigate mildly depolymerized Protobind 1000 lignin dispersed in ethanol (LEO) and methanol (LiMO) at different percentages of solids. Small-angle X-ray scattering (SAXS) data of diluted and concentrated LEO and LiMO dispersions show that, in these formulations, lignin exists in two states: individual lignin coil structures and their aggregates. The lignin coil structures are a few nanometers in size (3–5 nm) in both solvents. Direct observation of the lignin coil structures was achieved by cryo-TEM images and supports the findings of the SAXS measurements. The radius of gyration of the lignin coil structures in dilute dispersions increases with increasing lignin content, while in concentrated dispersions, the opposite trend is observed. It is hypothesized that in the concentrated regime, the lignin structures are more compressed by adjacent coils, resulting in the formation of a network-like arrangement. Furthermore, the aggregates of lignin coil structures can be detected by SAXS in the concentrated dispersions as they exhibit an upturn at low Q. Rheology measurements also indicate the presence of very fragile aggregate networks. The concentrated dispersions exhibit shear-thinning behavior in the shear rate range of 10–3–100 s–1 and Newtonian behavior at higher shear rates (100–103 s–1). Moreover, the viscosities at high shear for ethanol and methanol samples are almost identical at the same solid percentages despite having slightly different water contents, suggesting that the interactions between lignin and the solvents do not determine the rheological behavior but rather the formation of the network structures formed by coils. Such polymeric networks are responsible for the stability of the dispersions at high solid percentages, while at low solid loads, the Brownian motion is sufficient to maintain the nanometer-sized lignin coils in the solvent.

Evaluation of environmental and economic hotspots and value creation in multi-product lignocellulosic biorefinery

This paper presents systematic analysis of value creation chains and their economic and environmental hotspots within a multi-product biorefinery with the primary goal to promote sustainable biorefining. Lignocellulosic biorefinery producing ethanol, crude lignin oil (CLO) and electricity was analysed. The methodology involves transformation of technological model into an input-output one with the use of matrix notation for the analysis of economic and environmental attributes along value chains. The results show that the accumulation of biomass through energy supply grows by a factor of 1.2 for ethanol and electricity, and by 1.4 for CLO value chains, of which solid recovery, lignin solvolysis and biomass pretreatment are responsible for the most significant growth indicating the necessity for energy optimization of those steps. The analysis reveals a superfluous role of infrastructure in pretreatment and lignin drying processes. Of infrastructural costs related to the equipment required for the pretreatment step, wastewater treatment (WWT) facility is responsible for 58%, and of the costs of lignin drying, the combined heat and power plant is responsible for 56%. WWT determines 75% of infrastructural GHG emissions attributable to pretreatment, and 57% of those related to lignin drying. This points at an advantage of a biorefinery concept involving the removal of lignin fraction before the valorization of carbohydrates. Another hotspot, the lignin solvolysis technology, shows environmental and economic advantages of its further optimization in terms of production costs and GHG emissions. The proposed method is helpful for analyzing economic and environmental hotspots in new biorefinery concepts and integration pathways.

Machine learning based analysis of reaction phenomena in catalytic lignin depolymerization

Heterogeneously catalyzed lignin solvolysis opens the possibility of transforming low value biomass into high value, useful aromatic chemicals, however, its reaction behavior is poorly understood due to the many possible interactions between reaction parameters. In this study, a novel predictive model for bio-oil yield, char yield and reaction time is developed using Random Forest (RF) regression method using data available from the literature to study the impact of surface properties of the catalyst and the weight averaged molecular weight of the lignin (Mw) used in the reaction. The models achieved a coefficient of determination (R2) score of 0.9062, 0.9428 and 0.8327, respectively, and feature importance for each case was explained and tied to studies that provide a mechanistic explanation for the performance of the model. Surface properties and lignin Mw showed no importance to the prediction of bio-oil yield and average pore diameter contributed 3% of feature importance to reaction time.

Effect of Reaction Conditions on Catalytic and Noncatalytic Lignin Solvolysis in Water Media Investigated for a 5 L Reactor.

The high content of oxygen in the lignin polymer and the prevalence of phenolic functional groups make the conversion of lignin to fuels and value-added products with well-defined chemical properties challenging. The lignin-to-liquid process using a water/formic acid reaction medium has been shown to convert the lignin polymer to monomers with a molecular weight range of 300–600 Da. The bio-oil comprises a complex mixture of monomeric phenols, aromatics, and aliphatic hydrocarbons with a high H/C and low O/C ratio. This study investigates the effect of the stirring rate, level of loading, and catalyst at 305 and 350 °C in a 5 L pilot scale reactor. The oil yields are found to be highest for experiments conducted using the maximum stirring rate, maximum level of loading, and Ru/Al2O3 catalyst with yields of more than 69 wt % on lignin intake. Goethite as a catalyst does not show good conversion efficiency at either reaction temperatures. The carbon recovery is highest for products produced at 305 °C. Furthermore, results from solid phase extraction on a DSC-CN solid phase show that 65–92 wt % the bio-oils can be recovered as fractions separated based on polarity.

Stirred and non-stirred lignin solvolysis with formic acid in aqueous and ethanolic solvent systems at different levels of loading in a 5-L reactor

Lignin polymer is biologically and chemically stable and requires highly vigorous conditions for de-polymerization, and subsequent stabilization of the monomeric conversion products to prevent re-polymerization and char production. The Lignin-to-Liquid (LtL) process is a solvolytic conversion of lignin with formic acid. Formic acid has been shown to both catalyze the de-polymerization and supply hydrogen that stabilizes the de-polymerization products. In this paper, lignin from Eucalyptus wood was used as the feedstock, and the LtL-process was performed in both aqueous and ethanolic solvent systems. The experimental variables were different levels of loading in the reactor, stirred and non-stirred conditions, and different reaction temperatures. The bio-oil consisted mostly of phenolic compounds, and the bio-oil yields differed with type of the solvent used, level of loading in the reactor, stirring condition, and operating temperature. More than 55 wt.% of the lignin was recovered as bio-oil at 320 °C at stirred conditions when the reactor was loaded at high level. Overall, the ethanolic solvent together with maximum level of loading in the reactor under stirred condition resulted in the highest bio-oil yield. Elemental balance data for bio-oil and char yields and the molecular composition of the bio-oils were also investigated using, respectively, elemental analysis and GC-MS. Finally, principal component analysis was used as well to systematically explore the relationship between the bio-oil and char yields and the reaction conditions.

Microwave-Assisted Catalytic Solvolysis of Lignin to Phenols: Kinetics and Product Characterization.

Lignin, a major component of lignocellulosic biomass, is a valuable source of phenolic and aromatic compounds. It is, therefore, vital to develop strategies to selectively deconstruct lignin to valuable chemicals. This study focuses on the kinetics of depolymerization of lignin and the production of phenols via a microwave-assisted catalytic process at mild conditions of 80 °C in dimethyl sulfoxide/water medium. Four different catalysts used in this study, viz., Fe2O3, LaFeO3, ZrO2, and zeolite-Y hydrogen (ZYH), were characterized for structure, specific surface area, and surface morphology. The molecular weight reduction of lignin and the evolution of phenolic monomers and oligomers were monitored using various techniques, and the rate constants of lignin degradation in the presence of different catalysts were determined using a continuous distribution kinetics model, assuming scission of the lignin macromolecule at any random position. The rate constants (min–1) followed the trend: ZYH (26 × 10–4) ≈ LaFeO3 (25 × 10–4) > ZrO2 (22 × 10–4) > Fe2O3 ≈ no catalyst (16 × 10–4). Vanillic acid (15 mg g–1) and methyl phenol (17 mg g–1) were the major phenolics obtained with LaFeO3, whereas coniferaldehyde (13 mg g–1) was the major phenolic compound with Fe2O3. Vanillin was produced at ca. 11 mg g–1 with both Fe2O3 and ZYH. LaFeO3 is shown to be a promising catalyst for both molecular weight reduction of lignin and the production of monomeric phenols, whereas the use of Fe2O3 results in the formation of only phenols, possibly via specific end-chain depolymerization. The selectivities of the monomeric phenols were higher with these two catalysts, whereas with ZYH and ZrO2, the selectivities of the oligomers were better. The reusability of the catalysts and the effect of catalyst loading on kinetics of lignin depolymerization were also evaluated.

Kinetic Studies of Lignin Solvolysis and Reduction by Reductive Catalytic Fractionation Decoupled in Flow-Through Reactors

Reductive catalytic fractionation (RCF) is an effective active-stabilization strategy to selectively extract and depolymerize lignin into aromatic monomers. Here, the kinetics of RCF were investigated by using flow-through reactors to decouple the two limiting mechanistic steps, namely lignin solvolysis and reduction. When operating in a solvolysis-limited regime, apparent energy barriers of 63 ± 1 and 64 ± 2 kJ mol–1 were measured for the solvent mediated lignin extraction of poplar using particle diameters of 0.5 < d < 1 mm and 0.075 < d < 0.25 mm, respectively. In contrast, when using mechanically stirred batch reactors, apparent barriers of 32 ± 1 and 39 ± 3 kJ mol–1 were measured for particle diameters of 0.5 < d < 1 mm and 0.075 < d < 0.25 mm, respectively. The difference of activation barriers between flow and batch reactors indicated that lignin extraction under typical RCF conditions in a 100 mL batch reactor stirred at 700 rpm was mass-transfer limited. In the reduction-limited regime, cleavage ...

Experimental and Kinetic Study on Lignin Depolymerization in Water/Formic Acid System.

Microwave-assisted depolymerization of black-liquor lignin in formic acid was studied, concentrating on the yield of liquid fractions as bio-oil 1 (mainly aromatic monomers) and bio-oil 2 (mainly aromatic oligomers) and the distribution of the specific compositions. Bio-oil 1 (9.69%) and bio-oil 2 (54.39%) achieved their maximum yields under 160 °C with the reaction time of 30 min. The chemical compositions of bio-oil 1 and bio-oil 2 were respectively identified by means of Gas Chromatography-Mass Spectrometer (GC-MS) and Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Ethanone, 1-(4-hydroxy-3-methoxyphenyl) and Ethanone, 1-(4-hydrox-3,5-dimethoxyphenyl) were evidenced to be the two prominent compounds in bio-oil 1. Production of aromatic oligomers with the molecular weight of 328, 342, 358, 378, 394, 424 and 454 identified by MALDI-TOF MS was substantially tuned with the reaction temperature. A two-separate-stage kinetic model was proposed to describe the acidic solvolysis of lignin assisted by microwave heating, where the first stage is dominated by the depolyerization of lignin to monomers and oligomers with the activation energy of 40.27 kJ·mol−1, and the second stage with the activation energy of 49.18 kJ·mol−1 is mainly ascribed to the repolymerization of first-stage produced compounds.

Noncatalytic Direct Liquefaction of Biorefinery Lignin by Ethanol

There is a growing interest in lignin valorization to biofuels and chemicals. Here, we propose a novel and simple noncatalytic process to directly liquefy lignin rich solid residual from second generation bioethanol production by solvolysis with ethanol. Through an extensive parameter study in batch autoclaves assessing the effects of varying reaction temperature, reaction time, and solvent:lignin ratio, it is shown that hydrothermally pretreated enzymatic hydrolysis lignin solvolysis in supercritical ethanol can produce a heptane soluble bio-oil without the need for exhaustive deoxygenation. The process does not require addition of catalyst or a reducing agent such as hydrogen. The process is advantageously carried out with a low reaction period (<1 h) and with a reduced amount of solvent to lignin feedstock (ethanol:lignin (w/w) ratio of 2:1) which is a previously unexplored domain for lignin solvolysis. The resulting bio-oil product is mainly a mixture of di- and monomeric lignin species where the orig...

Catalytic Oxidation of Lignin in Solvent Systems for Production of Renewable Chemicals: A Review.

Lignin as the most abundant source of aromatic chemicals in nature has attracted a great deal of attention in both academia and industry. Solvolysis is one of the promising methods to convert lignin to a number of petroleum-based aromatic chemicals. The process involving the depolymerization of the lignin macromolecule and repolymerization of fragments is complicated influenced by heating methods, reaction conditions, presence of a catalyst and solvent systems. Recently, numerous investigations attempted unveiling the inherent mechanism of this process in order to promote the production of valuable aromatics. Oxidative solvolysis of lignin can produce a number of the functionalized monomeric or oligomeric chemicals. A number of research groups should be greatly appreciated with regard to their contributions on the following two concerns: (1) the cracking mechanism of inter-unit linkages during the oxidative solvolysis of lignin; and (2) the development of novel catalysts for oxidative solvolysis of lignin and their performance. Investigations on lignin oxidative solvolysis are extensively overviewed in this work, concerning the above issues and the way-forward for lignin refinery.

Analysis of the effect of temperature and reaction time on yields, compositions and oil quality in catalytic and non-catalytic lignin solvolysis in a formic acid/water media using experimental design

The catalytic solvolysis of Norway spruce (Picea abies L.) lignin in a formic acid/water media was explored at different temperatures and reaction times (283–397°C and 21–700min, respectively). Non-catalyzed experiments were compared with the effect of three different type of bifunctional catalysts (Pd/Al2O3, Rh/Al2O3 and Ru/Al2O3) and a solid Lewis acid (γ–Al2O3). We demonstrated that surface response methodology (RSM) and principal component analysis (PCA) were an adequate tool to: (i) evaluate the effect of the catalysts, temperature and reaction time in the oil yield, oil quality (H/C and O/C ratios, and Mw) and composition of the oil, (ii) establish the differences and/or similarities between the three bifunctional catalyst and (iii) to determine the role of the noble metal and the alumina support in the reaction system. In addition, the most active catalysts, Ru/Al2O3, and the optimum reaction conditions were determined (i.e. 340°C and 6h).

Solvent consumption in non-catalytic alcohol solvolysis of biorefinery lignin

Identified solvent reaction routes in alcohol solvolysis of lignin where lignin-oil incorporation through covalent bonding is the only desired reaction.

Synergetic Effects of Alcohol/Water Mixing on the Catalytic Reductive Fractionation of Poplar Wood

One of the foremost challenges in lignocellulose conversion encompasses the integration of effective lignin valorization in current carbohydrate-oriented biorefinery schemes. Catalytic reductive fractionation (CRF) of lignocellulose offers a technology to simultaneously produce lignin-derived platform chemicals and a carbohydrate-enriched pulp via the combined action of lignin solvolysis and metal-catalyzed hydrogenolysis. Herein, the solvent (composition) plays a crucial role. In this contribution, we study the influence of alcohol/water mixtures by processing poplar sawdust in varying MeOH/water and EtOH/water blends. The results show particular effects that strongly depend on the applied water concentration. Low water concentrations enhance the removal of lignin from the biomass, while the majority of the carbohydrates are left untouched (scenario A). Contrarily, high water concentrations favor the solubilization of both hemicellulose and lignin, resulting in a more pure cellulosic residue (scenario B)...

The effect of solvent and input material pretreatment on product yield and composition of bio-oils from lignin solvolysis

Solvolytic conversion of lignin from wood with formic acid as a hydrogen donor can provide a renewable source of aromatic compounds, especially phenols. In this paper, lignin or lignin-enriched fractions from Norway spruce and white birch are compared with regard to yields of bio-oil in solvolytic conversion. Water as a green solvent is also compared to ethanol as the reaction medium, and the yields and composition of the produced oils are presented. Maximum yields by weight are inversely connected to the oxygen content of the feedstock, showing that pure lignins give the highest yields while carbohydrate-containing feedstocks undergo more deoxygenation and thus give lower yields. The overall composition of the bio-oils produced is quite stable and independent of the feedstock type and pretreatment, though some difference in the quantitative distribution of the individual components is observed. The use of water or ethanol as reaction media has a significant impact on the bio-oil yields and composition due to the alkylation of the aromatic rings by the ethyl group from the solvent.

Catalytic solvolysis of lignin with the modified HUSYs in formic acid assisted by microwave heating

Microwave-assisted catalytic solvolysis of lignin in formic acid was studied concerning the addition of HUSY catalysts modified by oxalic acid. Characteristics of the modified catalysts were examined by XRD, NH3-TPD and BET. The highest yield of liquid product was achieved as 88.28wt% (aromatic monomer fraction as bio-oil 1 of 15.36% and oligomer fraction as bio-oil 2 of 67.52%) with the addition of HUSY modified by 0.2mol/L oxalic acid (HUSY-0.2M). The production of aromatic monomers in bio-oil 1 identified by GC/MS was enhanced with the addition of HUSY catalysts regardless of acidic treatment, and achieved the maximum value for HUSY-0.2M experiment. Aromatic oligomers with molecular weight of 328, 342, 358, 378, 394, 424 and 454 were characterized by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) analysis. Formation of almost all identified oligomers was promoted with catalytic experiments with HUSYs except that of 328, extent of which is significantly determined by the pore size, Si/Al ratio and acidic site distribution of the modified catalysts.

Mechanism on microwave-assisted acidic solvolysis of black-liquor lignin.

Microwave-assisted degradation of black-liquor lignin with formic acid was studied, concerning the product yield and distribution of phenolic compounds against reaction temperature (110-180°C) and reaction time (5-90 min). The liquid product consisting of bio-oil 1 and bio-oil 2, achieved the maxima yield of 64.08% at 160°C and 30 min (bio-oil 1: 9.69% and bio-oil 2: 54.39%). The chemical information of bio-oil 1 and bio-oil 2 were respectively identified by means of Gas Chromatography-Mass Spectrometer (GC-MS) and Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), while the solid residue was analyzed by Gel Permeation Chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR). A possible mechanism was proposed for the microwave-assisted acidic solvolysis of lignin, specifying the kinetic relationship among the primary cracking of lignin, repolymerization of the oligomers and formation of solid residue.