Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Spectroscopic analysis of hot-water- and dilute-acid-extracted hardwood and softwood chips
Graphical abstract
Introduction
The manufacture of novel, high-value products from lignocellulosics has been considered as a solution to facilitate an evolutionary shift within the conventional forest industry towards a more competitive business model and more efficient utilization of raw materials [1], [2]. This viewpoint has led to a transformation that includes implementing different biorefinery units into existing pulp and paper mills and evolution of integrated forest biorefineries (IFBRs) [3]. In modern IFBRs, the target is to extract carbohydrates, extractives, lignin, and other materials from biomass and convert them into value-added products, simultaneously minimizing the production of waste. Within this context, biomass pretreatment technologies (physical, chemical, or biochemical methods) mainly applied to recover hemicelluloses-derived carbohydrates from wood prior to pulping have been considered a crucial step [4].
The most common chemical pretreatments utilized for recovering particularly hemicelluloses-derived carbohydrates are performed either with pressurized hot water or diluted mineral acid [4], [5], [6], [7], [8]. By hot-water extraction, the main aim is usually to produce hydrolysates, especially containing oligo- and polysaccharides, whereas the pretreatments conducted with diluted acid typically result in the intensive formation of monosaccharides [9]. However, in addition to carbohydrates, other wood components (i.e., lignin and extractives) as well as all their degradation products (e.g., aliphatic acids and furanoic compounds) are also incorporated to hydrolysates.
The pretreatment processes have a profound effect on the chemical composition of wood and the subsequent delignification behavior of the pretreated feedstocks [10], [11]. In order to maintain the quality of the produced chemical pulp, the detailed effects of conducted pretreatments on wood composition must be understood. Within this framework, reliable and rapid methods for measuring the residual, structural, chemical components constituting cell walls of the pretreated wood material are highly appreciated. Conventional wet chemical analyses are accurate, but they have limitations, especially with regard to the amount of material required to confirm the analysis and overall time-consuming processes [12]. However, several spectroscopic analysis methods, such as Fourier transform infrared (FTIR) [13], [14], [15], [16], near infrared (NIR) [[17], [18], [19], [20]], and attenuated total reflectance (ATR) [21], [22], [23] infrared spectroscopy, have been proposed for providing a solution to the above mentioned problems; they comprise low-cost instrumentation and generally require very little sample preparation.
In this study, hot-water- and dilute-acid-extracted silver/white birch (Betula pendula/B. pubescens) and Scots pine (Pinus sylvestris) wood materials were investigated by ATR spectroscopy, especially keeping in mind their potential utilization for biorefineries. The main aim was to clarify if essential effects of varying pretreatments conditions on the original wood materials could be easily detected by this method.
Section snippets
Raw materials
Industrial silver/white birch (Betula pendula/B. pubescens) and Scots pine (Pinus sylvestris) chips were used in the laboratory-scale pretreatments with hot-water and diluted sulfuric acid. The used chips were laboratory-screened according to SCAN-CM 40:94 [24], and chips having knots, bark residues, and other visible impurities were manually removed. The maximum thickness of the used chips was 7 mm, maximum width 13 mm, and minimum width 7 mm.
Pretreatments
Laboratory-scale pretreatment experiments of screened
Raw materials for pretreatment experiments
Chemical composition of the feedstock materials used for the hot-water and acidic pretreatment experiments is presented in Table 1. As expected, the two wood species differed from each other, especially in the contents of hemicellulose moieties and lignin, showing characteristic differences commonly described in the literature [34]; birch contains more xylose but less galactose, mannose, and lignin than pine.
Pretreatments
Yields of wood residues after pretreatments are presented in Table 2. In general, with
Conclusions
Effects of hot-water and dilute acid pretreatments on chemical composition of hardwood and softwood were investigated by attenuated total reflectance (ATR) infrared spectroscopy. Spectral data were compared to the corresponding chemical composition data determined by conventional wood chemistry analyses for evaluating the suitability of ATR spectroscopy for describing the phenomena taking place during such pretreatments. Results clearly indicated that this rapid and simple spectral method could
Acknowledgement
Financial support from the Maj and Tor Nessling Foundation (number 201700063) (Joni Lehto) is gratefully acknowledged.
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