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Neither the routes through which humin byproducts are formed, nor their molecular structure have yet been unequivocally established. A better understanding of the formation and physicochemical properties of humins, however, would aid in making biomass conversion processes more efficient. Here, an extensive multiple-technique-based study of the formation, molecular structure, and morphology of humins is presented as a function of sugar feed, the presence of additives (e.g., 1,2,4-trihydroxybenzene), and the applied processing conditions. Elemental analyses indicate that humins are formed through a dehydration pathway, with humin formation and levulinic acid yields strongly depending on the processing parameters. The addition of implied intermediates to the feedstocks showed that furan and phenol compounds formed during the acid-catalyzed dehydration of sugars are indeed included in the humin structure. IR spectra, sheared sum projections of solid-state 2DPASS (13) C NMR spectra, and pyrolysis GC-MS data indicate that humins consist of a furan-rich polymer network containing different oxygen functional groups. The structure is furthermore found to strongly depend on the type of feedstock. A model for the molecular structure of humins is proposed based on the data presented.

Levulinic acid (LA), accessible by the acid catalyzed degradation of biomass, is potentially a very versatile green intermediate chemical for the synthesis of various (bulk) chemicals for applications like fuel additives, polymers, and resin precursors. We report here a kinetic study on one of the key steps in the conversion of biomass to levulinic acid, i.e. the reaction of 5-hydroxymethylfurfural (HMF) to levulinic acid. The kinetic experiments were performed in a temperature window of 98-181 uC, acid concentrations between 0.05-1 M, and initial HMF concentrations between 0.1 and 1 M. The highest LA yield was 94% (mol/mol), obtained at an initial HMF concentration of 0.1 M and a sulfuric acid concentration of 1 M. The yield at full HMF conversion is independent of the temperature. An empirical rate expression for the main reaction as well as the side reaction to undesired humins was developed using the power law approach. Agreement between experimental and model data is good. The rate expressions were applied to gain insights into optimum process conditions for batch processing.

A variety of interesting bulk chemicals is accessible by the acid-catalyzed hydrolysis of cellulose. An interesting example is levulinic acid, a versatile precursor for fuel additives, polymers, and resins. A detailed kinetic study on the acid-catalyzed hydrolysis of cellulose to levulinic acid is reported in this paper. The kinetic experiments were performed in a temperature window of 150-200°C, sulfuric acid concentrations between 0.05 and 1 M, and initial cellulose intakes between 1.7 and 14 wt %. The highest yield of levulinic was 60 mol %, obtained at a temperature of 150°C, an initial cellulose intake of 1.7 wt %, and a sulfuric acid concentration of 1 M. A full kinetic model covering a broad range of reaction conditions was developed using the power-law approach. Agreement between the experimental data and the kinetic model is good. The kinetic expressions were used to gain insights into the optimum process conditions for the conversion of cellulose to levulinic acid in continuous-reactor configurations. The model predicts that the highest obtainable levulinic acid yield in continuous-reactor configurations is about 76 mol %, which was obtained when using reactors with a large extent of backmixing.

Fast pyrolysis oils from lignocellulosic biomass are promising second-generation biofuels. Unfortunately, the application range for such oils is limited because of the high acidity (pH∼2.5) and the presence of oxygen in a variety of chemical functionalities, and upgrading of the oils is required for most applications. Herein, we report an experimental study on the upgrading of fast pyrolysis oil by catalytic hydrotreatment. A variety of heterogeneous noble-metal catalysts were tested for this purpose (Ru/C, Ru/TiO 2 , Ru/Al 2 O 3 , Pt/C, and Pd/C), and the results were compared to those obtained with typical hydrotreatment catalysts (sulfided NiMo/ Al 2 O 3 and CoMo/Al 2 O 3 ). The reactions were carried out at temperatures of 250 and 350 °C and pressures of 100 and 200 bar. The Ru/C catalyst was found to be superior to the classical hydrotreating catalysts with respect to oil yield (up to 60 wt %) and deoxygenation level (up to 90 wt %). The upgraded products were less acidic and contained less water than the original fast pyrolysis oil. The HHV was about 40 MJ/kg, which is about twice the value of pyrolysis oil. Analyses of the products by 1 H NMR spectroscopy and 2D GC showed that the upgraded pyrolysis oil had lower contents of organic acids, aldehydes, ketones, and ethers than the feed, whereas the amounts of phenolics, aromatics, and alkanes were considerably higher.

Renewable nylon: 5‐Hydroxymethylfurfural (HMF), which can be obtained from renewable resources such as D‐fructose, was converted into caprolactone with very good overall selectivity in only three steps. The new route involves two hydrogenation steps to obtain 1,6‐hexanediol, which was oxidatively cyclized to caprolactone, and then converted into caprolactam.

BACKGROUND: Biomass is the only renewable feedstock containing carbon, and therefore the only alternative to fossil-derived crude oil derivatives. However, the main problems concerning the application of biomass for biofuels and bio-based chemicals are related to transport and handling, the limited scale of the conversion process and the competition with the food industry. To overcome such problems, an integral processing route for the conversion of (non-feed) biomass (residues) to transportation fuels is proposed. It includes a pretreatment process by fast pyrolysis, followed by upgrading to produce a crude-oil-like product, and finally co-refining in traditional refineries.

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