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Pyrolysis-assisted catalytic hydrogenolysis over Pd/C in anisole (phenyl methyl ether) at relatively high temperatures (>300 °C) can convert softwood lignin into aromatic monomers in >60 mol% yield (based on lignin aromatic rings). In this process, lignin is pyrolytically degraded to soluble intermediates prior to catalytic conversion, therefore the pyrolysis stage plays an important role in determining the yield and monomer composition. In this study, pyrolysis-assisted hydrogenolysis of coniferyl alcohol, which is a major pyrolysis product, and milled wood lignin isolated from Japanese cedar was investigated in various solvents, including water, methanol, toluene, hexane, and anisole, to clarify the solvent effects. The effects of the solvent on undesired side reactions were also explored. The results show that anisole is the best solvent for aromatic monomer production, but hexane is the best solvent for phenol production via demethoxylation. These findings provide insights that will facilitate the development of efficient methods for monomer production from lignin.

Monoacylglycerols (MAGs) are typical impurities in biodiesel (fatty acid methyl esters, FAMEs) and are often the cause of solid precipitation because of their high melting points. In this study, the liquidus temperature of biodiesel, below which solidification of biodiesel components can occur, was measured by differential scanning calorimetry or visual observation, and was predicted by thermodynamic models. First, the solubility limit of MAGs, defined as the total MAG content above which MAGs can solidify before FAMEs, was found to be about 0.25 wt% for coconut methyl esters and about 0.5 wt% for palm methyl esters and rapeseed methyl esters. For biodiesel containing MAGs above the solubility limit, the compound formation (CF) model showed good agreement with the experimentally determined liquidus temperatures. This thermodynamic model assumed different types of MAGs solidifying simultaneously while forming molecular compounds. However, within the range of the total MAG content of actual biodiesel (typically less than 0.7 wt%), the number of fitting parameters in the CF model was excessive. This led to the use of a simplified version of the CF model with only one parameter, which still fitted the experimental results well. One parameter value was determined for biodiesel from one feedstock, allowing the liquidus temperature of biodiesel from a known feedstock to be predicted based only on the total MAG content, even for biodiesel containing diacylglycerols in addition to MAGs.

Monoacylglycerol (MAG), diacylglycerol (DAG), and triacylglycerol (TAG) are impurities in biodiesel and a major cause of precipitation. Understanding the behavior of such acylglycerols is essential for predicting biodiesel cold flow properties (CFPs). The previous study on MAG/MAG binary mixtures shows that they tend to solidify by forming molecular compounds. In contrast, TAG/TAG mixtures, which have been studied extensively, are commonly eutectic or monotectic systems, in which each component solidifies separately. The present study focuses on binary mixtures of DAG/DAG and different acylglycerol pairs (MAG/DAG, TAG/MAG, and DAG/TAG), and determination of their solid–liquid phase behavior by differential scanning calorimetry. These mixtures are found to behave as eutectic or monotectic systems with no sign of compound formation. As DAG and TAG have lower contents than MAG in biodiesel and they are unlikely to form molecular compounds with MAG, it is suggested that DAG and TAG have little effect on the biodiesel CFPs. Practical Applications: Biodiesel has attracted much interest because its blending with conventional fossil diesel has become more standard with biofuel mandates. From an energy perspective, the solid–liquid phase behavior of acylglycerols will contribute to building prediction models for biodiesel CFPs.

The thermal reactivities of cellulose and hemicellulose are significantly different in cell walls when compared with isolated components and differ in Japanese cedar (softwood) and Japanese beech (hardwood). Uronic acid bound to xylan promotes the thermal degradation of cellulose and hemicellulose, and its effect is different depending on the form of free acid (acting as an acid catalyst) or metal uronate (acting as a base catalyst). We evaluated the location of uronic acid in the cell wall by identifying the components affected by demineralization in pyrolysis of cedar and beech wood. The thermal reactivities of xylan and glucomannan in beech were changed by demineralization, but in cedar, glucomannan and cellulose reactivities were changed. Therefore, the location of uronic acid in the cell wall was established and differed between cedar and beech; close to glucomannan and xylan in beech, but close to glucomannan and cellulose in cedar. Such information is important for understanding the ultrastructure and pyrolysis behavior of softwood and hardwood cell walls.

Fatty acid methyl esters, which are used as biodiesel, can be produced by methyl esterification of fatty acids in supercritical methanol. However, in a reverse reaction, methyl esters are hydrolyzed to regenerate fatty acids due to the presence of water, which is produced by the esterification reaction, making it difficult to reduce the fatty acid content sufficiently. In this study, oleic acid was treated in supercritical methanol at 310 °C/20 MPa with a flow-type reactor by adding methyl formate to improve the yield of methyl ester. As a result, adding methyl formate improved the methyl ester yield approximately from 90 to 95 wt% compared with the treatment using methanol only. Methyl formate was hydrolyzed instead of fatty acid methyl esters, producing formic acid and methanol. Formic acid can be decomposed into gases such as H₂ and CO₂ by thermal decomposition in supercritical methanol. As these reactions consume water, removing it from the reaction system, the reaction equilibrium was considered to be shifted in the direction to improve the methyl ester yield.

Hydrogen bond donor solvents such as aromatic solvents inhibit the secondary degradation of cellulose-derived primary pyrolysis products. In a previous study, we found that the formation of solid carbonized products was completely inhibited during cellulose pyrolysis in aromatic solvents, with 5-hydroxymethylfurfural (5-HMF) recovered in certain yields instead. This indicated that 5-HMF is an intermediate in cellulose carbonization. To confirm this hypothesis, the thermal reactivity of 5-HMF was investigated. At 280 °C, pure 5-HMF polymerized into a hard glassy substance through OH group elimination, but further conversion was slow. When pyrolyzed in the presence of glycerol, a model of coexisting primary pyrolysis products from cellulose, a coupling reaction proceeded. Reactions characteristic of cellulose carbonization then occurred, including the formation of acidic groups and benzene-type structures in the solid products. These results confirmed the above hypothesis. The molecular mechanism of cellulose carbonization is discussed, focusing on the crystalline nature.

The topochemistry of Japanese beech (Fagus crenata) wood delignification was evaluated in this study following a supercritical methanol treatment (270 °C, 27 MPa). Ultraviolet microscopic analysis of the insoluble residue revealed that the lignin in the secondary wall was easily decomposed and removed because of the preferential cleavage of ether-type linkages. In contrast, the middle lamella lignin was initially resistant to supercritical methanol but eventually decomposed and was removed. In addition, UV-absorbing secondary products formed selectively inside the parenchyma cells. Results from the supercritical methanol treatment of demineralized beech wood indicated that inorganic substances in the lumen of parenchyma affected the formation of these secondary products, thus leading to an overestimation of the residual lignin. Therefore, the topochemistry of delignification was more precisely evaluated when using demineralized beech wood.

The formation of precipitates in biodiesel (comprising fatty acid methyl esters [FAMEs] obtained from plant oils) can lead to the clogging of fuel filters. Such precipitates are often caused by the solidification of acylglycerols (monoacylglycerols [MAGs], diacylglycerols [DAGs], and triacylglycerols [TAGs]) that have higher melting points than FAMEs. Based on our prior study on the solidification behavior of MAG/FAME binary mixtures, the present work investigated the behavior of various DAGs and TAGs combined with FAMEs. Differential scanning calorimetry was used to clarify the effects of acylglycerols on the cold-flow properties of biodiesel. When DAGs and TAGs were added to FAMEs, the liquidus temperatures (above which the mixtures were completely liquid) increased steeply even at low concentrations. This same behavior was observed previously in trials with MAGs, indicating that all acylglycerols readily precipitate in combination with FAMEs. However, thermodynamic analyses established that the reasons for such precipitation were different for different compounds. MAGs precipitates because they contain two hydroxyl groups and therefore have a low affinity for FAMEs. In contrast, TAGs precipitates as a result of their high enthalpies of fusion (which in turn are caused by high molecular weights), while both factors affect the precipitation of DAGs. A non-solid-solution thermodynamic model that assumes a eutectic system was found to accurately predict the liquidus temperatures of binary and multicomponent mixtures containing various acylglycerols with FAMEs.

Various Ni and Ni-Sn catalysts supported on TiO2 were prepared and the catalytic activities were evaluated for ethanol formation from aqueous acetic acid. Although catalytic activities of the Ni/TiO2 catalysts were limited, the addition of Sn improved the activity dramatically, and the optimum Ni/Sn ratio was approximately 1:1 (w/w). SnO2, the precursor of Sn, could not be reduced into metal Sn in pure form but did reduce into Ni-Sn alloys in the presence of NiO, the precursor of Ni. Analyses with XRD and SEM-EDS revealed that the Ni-Sn alloys were homogeneously dispersed on the TiO2 surface. Furthermore, IR analysis indicated that the Ti atoms in the catalyst act as a Lewis acid, which coordinates to the oxygen atoms of acetic acid, enhancing the attack of hydrogens activated on neighboring Ni-Sn alloys. Based on these results, Ni-Sn/TiO2 is proposed as an effective hydrogenation catalyst for converting aqueous acetic acid into ethanol.

Biomass-based ethanol or acetic acid can be produced by fermentation of saccharides following wood hydrolysis. Both high saccharide yield and concentration are essential for achieving an efficient hydrolysis process. However, there can be a trade-off between yield and concentration during semi-flow, hot-compressed water treatment, a candidate for wood hydrolysis. This trade-off is because the fast water flow rate is necessary for high saccharide yields, but the large amount of water dilutes the produced hydrolysate. In this study, we mixed octyl acetate, which is a water-immiscible solvent, during hot-compressed water treatment of beech wood. By adding octyl acetate, a high flow rate was achieved without increasing the water flow rate, and the saccharide concentration was thus improved, while suppressing the decrease in saccharide yield. Furthermore, lignin-derived oligomers, which have inhibitory effects on fermentation, were removed from hydrolysate because they can dissolve in octyl acetate. We performed acetic acid fermentation using the obtained hydrolysate and found that the fermentability was markedly improved compared with the hydrolysate obtained without octyl acetate.