Steam explosion is a well-known process to pretreat lignocellulosic biomass in order to enhance sugar yields in enzymatic hydrolysis, but pretreatment conditions have to be optimized individually for each material. In this study, we investigated how the results of a pretreatment optimization procedure are influenced by the chosen reaction conditions in the enzymatic hydrolysis. Beechwood was pretreated by steam explosion and the resulting biomass was subjected to enzymatic hydrolysis at glucan loadings of 1% and 5% employing either washed solids or the whole pretreatment slurry. For enzymatic hydrolysis in both reaction modes at a glucan loading of 1%, the glucose yields markedly increased with increasing severity and with increasing pretreatment temperature at identical severities and maximal values were reached at a pretreatment temperature of 230 °C. However, the optimal severity was 5.0 for washed solids enzymatic hydrolysis, but only 4.75 for whole slurry enzymatic hydrolysis. When the glucan loading was increased to 5%, glucose yields hardly increased for pretreatment temperatures between 210 and 230 °C at a given severity, and a pretreatment temperature of 220 °C was sufficient under these conditions. Consequently, it is important to precisely choose the desired conditions of the enzymatic hydrolysis reaction, when aiming to optimize the pretreatment conditions for a certain biomass.

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Biomass pretreatment is a mandatory step for the biochemical conversion of lignocellulose to chemicals. During pretreatment, soluble compounds are released into the prehydrolyzate that inhibit the enzymatic hydrolysis step. In this work, we investigated how the reaction conditions in steam explosion pretreatment of beechwood (severity: 3.0–5.25; temperature: 160–230 °C) influence the resulting amounts of different inhibitors. Furthermore, we quantified the extent of enzyme inhibition during enzymatic hydrolysis of Avicel in the presence of the prehydrolyzates. The amounts of phenolics, HMF, acetic acid and formic acid increased with increasing pretreatment severities and maximal quantities of 21.6, 8.3, 43.7 and 10.9 mg/gbeechwood, respectively, were measured at the highest severity. In contrast, the furfural concentration peaked at a temperature of 200 °C and a severity of 4.75. The presence of the prehydrolyzates in enzymatic hydrolysis of Avicel lowered the glucose yields by 5–26%. Mainly, the amount of phenolics and xylose and xylooligomers contributed to the reduced yield. As the maximal amounts of these two inhibitors can be found at different conditions, a wide range of pretreatment severities led to severely inhibiting prehydrolyzates. This study may provide guidelines when choosing optimal pretreatment conditions for whole slurry enzymatic hydrolysis.

2,3-Dinitrotoluene (2,3-DNT) thermal decomposition and its products were studied. Main attention was paid on the initial stage of decomposition, because the degradation of even a few percent of high energetic compound may cause significant hazard. Partial decomposition of 2,3-DNT was performed conditioning at the temperature range of 457-568 K. Impurities production at the initial stage of decomposition was determined by the analysis of melting enthalpy decrease with cryometric method. Mean self-aggregation number of the initial substance was defined and determined to estimate the molecular mass of products of 2,3-DNT thermal conditioning. MALDI TOF method was used for independent molecular mass verification. 2,3-DNT is thermally stable substance. Heating of its sample from the ambient temperature to 486 K with the heating rate of 2 K min -1 does not cause thermal decomposition. Very good reproducibility of melting process performed on the same sample was obtained. Only prolonged conditioning at raised temperature leads to initial substance loss. Two competitive reactions, aggregation and decomposition, were run during 2,3-DNT thermal conditioning. Heating with low heating rate leads to products with higher molecular masses. Two different results prove that: MALDI TOF analysis and the melting enthalpy decrease which is higher than the increase in impurities content determined with cryometric method. Mass spectrum of the thermally conditioned 2,3-DNT samples includes strong signals with (among others) following m/z values: 551, 687, 1062, 1137, 1211. Formed macromolecular compounds were stable until the temperature of 500 K.