Influence of Microwave Heating on Chemical Properties of Liquefied Lignocellulosic Residues

Alternatives for Chemical and Biochemical Lignin Valorization: Hot Topics from a Bibliometric Analysis of the Research Published During the 2000–2016 Period

A complete bibliometric analysis of the Scopus database was performed to identify the research trends related to lignin valorization from 2000 to 2016. The results from this analysis revealed an exponentially increasing number of publications and a high relevance of interdisciplinary collaboration. The simultaneous valorization of the three main components of lignocellulosic biomass (cellulose, hemicellulose, and lignin) has been revealed as a key aspect and optimal pretreatment is required for the subsequent lignin valorization. Research covers the determination of the lignin structure, isolation, and characterization; depolymerization by thermal and thermochemical methods; chemical, biochemical and biological conversion of depolymerized lignin; and lignin applications. Most methods for lignin depolymerization are focused on the selective cleavage of the β-O-4 linkage. Although many depolymerization methods have been developed, depolymerization with sodium hydroxide is the dominant process at industrial scale. Oxidative conversion of lignin is the most used method for the chemical lignin upgrading. Lignin uses can be classified according to its structure into lignin-derived aromatic compounds, lignin-derived carbon materials and lignin-derived polymeric materials. There are many advances in all approaches, but lignin-derived polymeric materials appear as a promising option.

Microwave-Driven Sugar Beet Pulp Liquefaction in Polyhydric Alcohols

Liquefaction of sugar beet pulp (SBP) was carried out using microwave irradiation as the heating source, ethylene glycol/glycerol at a ratio of 80/20 (w/w) as the liquefaction solvent and sulfuric acid as the catalyst at 160 °C. The effects of different liquefaction conditions, including two particle size ranges of SBP, liquefying solvent-to-SBP solids (LS/S) ratio and reaction time on the liquefaction yield, viscosity of the liquefaction products, chemical characteristics and morphology of residues were studied using viscometry, Fourier transform infrared (FTIR), X-ray diffraction (XRD), scanning electronic microscopy (SEM). The efficiency of liquefaction of SBP was found to depend on its particle size of SBP raw material and the LS/S ratio. The smaller SBP particles improved liquefaction efficiency and reduced the amount of solvent required. The crystallinity index of liquefaction residues indicated that crystalline cellulose was no longer the rate limiting factor of liquefaction process when the particle size of SBP was small (75–177 μm). A rugged and deformed surface of the liquefaction residue (observed through SEM) indicated that severe damage in the native fiber structure occurred during the liquefaction.

Mechanical and Thermal Properties of Polyurethane Foams from Liquefied Sugar Beet Pulp

Polyurethane (PU) foams were prepared from microwave liquefied sugar beet pulp (LSBP) and polymethylene polyphenyl isocyanate (PAPI) by using a one-step method. The [NCO]/[OH] ratio was increased from 0.6 to 1.2, and the effect of this ratio on the mechanical, thermal and microstructural properties of the LSBP–PU foams was studied. The allophanate, isocyanurate and free isocyanate were detected in all the foams. The thermal degradation of these foams in air occurred in two main stages; the first one occurred at 200–350 °C and the second one occurred at 300–400 °C. The Tg of the foams increased when the [NCO]/[OH] ratio increased up to 0.9 above which it decreased. As the [NCO]/[OH] ratio increased, the less regular structure and broken cell shape (observed through SEM) indicated that severe damage in structural stability and mechanical properties of LSBP–PU foams occurred. The cellular structure of the foams could be controlled by controlling the gelling and blowing reactions through the control of NCO]/[OH] ratio.

Protocol: A simple protocol for quantitative analysis of bio-oils through gas- chromatography/mass spectrometry

A new and simple protocol for quantitative analysis of bio-oils using gas-chromatography/mass spectrometry is suggested. Compounds were identified via their mass spectra, and then unavailable response factors were calculated with respect to diphenyl as the internal standard using a modified method previously suggested for gas chromatography with flame ionization detection. This new protocol was applied to the characterization of bio-oils obtained from the pyrolysis of woods of different sources or using different pyrolysis procedures. This protocol allowed evaluation of the yields of products from poplar pyrolysis (among 50% and 99%), while a reduced amounts of products were identified from the pyrolysis of cellulose (between 46% and 58%). The main product was always acetic acid, but it was formed in very large yields from poplar while lower yields were obtained from cellulose.