Near-infrared spectroscopy (NIRS) in conjunction with multivariate calibration have proved to be adequate techniques to predict water content as well as methanol concentration in a industrial multicomponent mixture. The calibration models were developed using real industrial complex samples of water, methanol, and several other components in variable but lower concentrations such as sulfonic acids, acetone, and methyl cyanide. These samples come from industrial distillation of hydrated methanol. Prior to the establishment of the two calibration models, wavelength selection, original spectral data compression by means of the principal components analysis technique, and preprocessing optimization were performed. Calibration was modeled according to partial least squares (PLS) regression which was developed using the mean centering and the leave-one-out cross validation (LOOCV) method for the optimization of the principal components (PC) number. Both models were developed in the 5369−5153 cm −1 spectral region. Karl Fischer titration and gas chromatography were used as reference methods for water and methanol quantification, respectively. The suitability of the models was evaluated through the calculation of the standard error of calibration and standard error of prediction. For the water content determination the variance scaling pretreatment was applied with 12 PLS factors, the calibration and prediction errors being 2.56% and 1.76% respectively. As for the methanol concentration variance scaling was applied in conjunction with Savitzky−Golay's second order derivative with six PLS factors. In this case the calibration and prediction errors were 0.42% and 0.90%, respectively.

The production of xylooligosaccharides (XOS) by acid hydrolysis using an alkaline extraction filtrate from the bleached kraft pulp of Eucalyptus globulus is a rapid and effective process. The reaction kinetics knowledge is, however, extremely important to optimize the experimental conditions that maximize XOS production and limit the formation of xylose (unwanted product). In this work, a pseudo-homogeneous model of irreversible first-order reactions is proposed, considering the sequential degradation of fast-reacting xylan into high-and lowmolecular-weight oligomers, followed by their conversion to xylose. A kinetic parameter estimation based on the Arrhenius equation was performed, considering the temperature and acid concentration effects. The kinetic model presented good fittings to the experimental results (R 2 mostly between 0.97 and 0.99), proving its suitability to describe xylan hydrolysis over time. The mapping of XOS maximum yields as a function of pH, temperature, and time was also represented, allowing fast prediction for other operating conditions.

Xylooligosaccharides (XOS) are oligomers with recognized and important prebiotic properties, whose consumption is associated with several health benefits, including a positive impact on the immune system. In this work, XOS were produced through a green process of enzymatic hydrolysis performed directly on an intermediate product from a pulp and paper industry, Eucalyptus bleached kraft pulp. Focusing on an industrial, sustainable and more economical application, two goals were defined and validated: (i) no pretreatment of the substrate and (ii) the replacement of the commonly used buffer solution as reaction medium for only water. The influence of the most relevant operating conditions on the production of XOS as well as the respective yields obtained were very similar when using either buffer or water as the reaction medium. For the use of water, although the solution pH decreases during the enzymatic reaction, this change did not affect the production of XOS. For the optimized conditions, 80 °C and 100 U/g pulp, a maximum yield of 31.4 ± 2.6% per total xylan in the pulp was obtained, resulting in more than 50 kg of XOS per ton of pulp. The correspondent hydrolysate was mainly composed by xylobiose (66%) and xylotriose (29%), oligomers with the highest prebiotic effect.