UV-Vis Spectroscopy and Chemometrics for the Monitoring of Organosolv Pretreatments

Abstract

Lignocellulosic agricultural side products like wheat straw are widely seen as an important contribution to a sustainable future economy. However, the optimization of biorefinery processes, especially the pretreatment step, is crucial for an economically viable biorefinery. The monitoring of this pretreatment process in terms of delignification and the generation of the fermentation inhibitors acetic acid, furfural, and hydroxymethylfurfural (HMF) is essential in order to adapt the process parameters for a desired outcome and an economical operation. However, traditional wet chemistry methods are time-consuming and not suitable for on-line process monitoring. Therefore, UV-Vis spectroscopy in combination with partial least-squares regression was used for the determination of the concentrations of lignin, acetic acid, furfural, and HMF. Five different data blocks with increasing amounts of impurities were investigated to evaluate the influence of the inevitable impurities on the calibration models. Lignin showed a good prediction accuracy with 95% tolerance intervals between ±0.46 to ±1.6 mg/L for concentrations up to 30 mg/L. Also, the other components could be predicted with a sufficient accuracy for on-line process monitoring. A satisfactory calibration can be obtained with 10 to 20 reference samples valid at process temperatures between 160 • C and 180 • C.Lignin is a highly irregularly branched polyphenolic polyether, consisting of the primary monolignols, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol, which are connected via aromatic and aliphatic ether bonds [6]. Even by using only one type of raw material in a lignocellulosic biorefinery, the growth environment, harvesting method, and storage can increase the inherent biomass property of heterogeneity [7].The mentioned variability in the composition and structure of feedstocks poses one of the most significant challenges to the industrial-scale processing of lignocellulosic materials [6]. Therefore, in-situ process monitoring of the pretreatment and the lignin concentration is essential for an adaption of process parameters and a constant product quality. However, traditional wet chemistry methods are expensive and time-consuming, requiring several days for a full composition analysis, which is a timeframe clearly incompatible with on-line process monitoring [8].In addition to the lignin concentration, degradation products generated during the pretreatment process such as furfural, hydroxymethylfurfural (HMF), and acetic acid are of interest. The furans originate from the dehydration of hexose and pentose sugars, whereas the acetic acid originates from the cleavage of the acetyl substitutions from xylan, and both are of particular importance for the toxicity in yeasts [9][10][11]. A low concentration of these inhibitors is therefore favored for subsequent fermentation processes and needs to be monitored. These components can be measured by HPLC in a time frame of hours, which is inappropriate for on-line process monitoring [12].Therefore, spec...

Characterization and Antibacterial Properties of Autoclaved Carboxylated Wood Nanocellulose

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“…However, the UV− vis spectra revealed an absorbance maxima at 250 nm and not the typical peak at 277 nm for furfural detection. 37 Other typical compounds from carbohydrate degradation such as hydroxymethylfurfural and levulinic acid have absorbance maxima at 284 and 266 nm, respectively. 38 Note that the peak at 250 nm is also present in the nonautoclaved samples, but with minor intensity.…”

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