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To reveal the effect of torrefaction pretreatment on pyrolysis and gasification reactivity of biomass, corn cob was first subjected to torrefaction pretreatment in a fixed-bed reactor at various reaction temperatures. The pyrolysis reactivity, kinetics, and gasification reactivity of torrefied corn cob were systematically assessed by various methods, proving that torrefaction pretreatment has a substantial influence on the physicochemical properties of corn cobs. The O/C and H/C molar ratios of corn cobs considerably drop with the increasing torrefaction temperature, and their higher heat-ing value (HHV) and energy density rise as well. It is found that torrefaction improves the pyrolysis reactivity of corn cobs because hemicellulose degradation is more severe than cellulose degradation during torrefaction, resulting in an increase in the percentage of cellulose in torrefied corn cobs. However, the severe depolymerization, polycondensation, and carbonization reaction during torre-faction of corn cobs at 280–300 °C can lead to a significant decline in the pyrolysis reactivity of corn cobs. Torrefaction pretreatment increases the pyrolysis activation energy of corn cobs, in addition to decreasing the char gasification reactivity of corn cob. The average char gasification reactivity of corn cobs drops when torrefaction severity increases. The passivation of active sites on the char surface may cause condensation and carbonation reactions of corn cobs during torrefaction. These findings provide new sights into the reasonable design of efficient torrefaction methods for appli-cation prior to pyrolysis and gasification of biomass. [ABSTRACT FROM AUTHOR]

• Acid pretreatment achieved oriented pyrolysis of holocellulose into anhydrosugars. • Oriented pyrolysis of xylan at low temperature was achieved by HCl-demineralization. • 0.1%H 2 SO 4 -impregnation achieved oriented pyrolysis of cellulose at low temperature. • The reaction mechanism was elucidated by in-situ DRIFT combined with 2D-PCIS. Fast pyrolysis is a promising method to convert cellulose and hemicellulose into anhydrosugars, but the current method is energy intensive and provides poor yield and selectivity for anhydrosugars. The possibility of using mineral acid pretreatment to achieve oriented pyrolysis of cellulose and xylan at low temperature was explored in this study. The pyrolysis behaviors and mechanism of cellulose and xylan were investigated by pyrolysis–gas chromatography/mass spectrometry and in-situ diffuse reflectance infrared Fourier transform spectroscopy combined with two-dimensional perturbation correlation infrared spectroscopy. The results showed that H 2 SO 4 -impregnation and HCl-demineralization achieved the oriented pyrolysis of cellulose and xylan into anhydrosugars at 300 °C. The highest yields of levoglucosan and levoglucosenone (33.3 and 9.7%) were obtained from pyrolysis of 0.1%H 2 SO 4 -impregnated cellulose at 300 °C, while those of xylosan and 1,5-anhydro-4-deoxypent-1-en-3-ulose (19.4 and 8.4%) were produced from pyrolysis of HCl-demineralized xylan at 300 °C. It is inferred that H 2 SO 4 could promote the condensation of hydroxyls at C6 and C1 positions and the cleavage of glycosidic bonds to form levoglucosan. And AAEMs could inhibit the intra-molecular dehydration of C3 hydroxyl and C2 hydrogen atom of levoglucosan to form levoglucosenone. The demineralization of xylan could promote the cleavage of glycosidic bonds and dehydration reactions to form xylosan and 1,5-anhydro-4-deoxypent-1-en-3-ulose. These findings provide a simple method to achieve oriented pyrolysis of cellulose and xylan at low temperature. [ABSTRACT FROM AUTHOR]

• H 2 SO 4 loading can lower the pyrolysis temperature of biomass from 500 to 300 °C. • The formation of light oxygenates, permanent gases and char was suppressed. • 50–60 wt% biomass was converted into anhydrosugars and their dehydrated products. • The reaction pathways for pyrolysis of H 2 SO 4 -loaded biomass at 300 °C were proposed. Fast pyrolysis is a promising method for the production of liquid fuels and chemicals from lignocellulosic biomass. However, the catalytic effects of inherent alkali and alkaline earth metals and the high temperature used for the fast pyrolysis of biomass can drastically promote uncontrolled C-C/C-O bond cleavages and polycondensation reactions, resulting in the formation of considerable amounts of undesired light oxygenated organic compounds, permanent gases and char. Here, we demonstrate that H 2 SO 4 loading can lower the pyrolysis temperature of biomass from 500 to 300 °C with higher yield of platform chemicals. The pyrolysis of H 2 SO 4 -loaded biomass at 300 °C is capable of selectively breaking C-O bonds in polysaccharides and effectively suppressing the formation of light oxygenated organic compounds, permanent gases and char. Approximately 50–60 wt% biomass feedstocks are primarily converted into anhydrosugars (mainly levoglucosan and xylosan) and their dehydrated products (mainly levoglucosenone and furfural). It is inferred that H 2 SO 4 combined with the inherent alkali and alkaline earth metals (AAEM) in raw biomass can simultaneously inhibits the catalytic functions of AAEM and H 2 SO 4 for achieving oriented conversion of hemicellulose and cellulose at low temperature. This study provides a very simple, atom-economical and energy-efficient pyrolytic strategy for enhancing the production of platform chemicals from biomass. [ABSTRACT FROM AUTHOR]

To identify the roles of alkali/alkaline earth metals (AAEM) and reaction temperature during pyrolysis of hemicellulose, the effects of AAEM doping on the pyrolysis behaviors, kinetics, and product yields of xylan at different pyrolysis temperatures were assessed. The results demonstrated that the yields of anhydrosugars from pyrolysis of xylan were dependent on the AAEM cations and their doping concentrations. Demineralization achieved the directional conversion of xylan into xylosan at 300 °C. The doping of even 0.05 mmol/g AAEM significantly suppressed their formation. The yields of xylosan from pyrolysis of xylan doped with different AAEM cations decreased in the following order: Mg2+

• WO x -TiO 2 -Al 2 O 3 exhibits a catalytic capacity comparable to HZSM-5. • The Ti3+ in W-O-Ti bond can act as Lewis acid sites to bind to C-O bonds. • The increase in Lewis acid favors the deoxygenation reaction. • The coupling effect of WO x and Al 2 O 3 promotes the alkylation reactions of aromatics. Lignin catalytic pyrolysis for sustainable aromatic production is a promising approach for reducing the overwhelming dependence on fossil resources while mitigating CO 2 emissions. The key to achieving the efficient catalytic pyrolysis of lignin lies in the rational design of advanced catalysts with excellent deoxygenation capacity. In this study, we develop a novel mixed metal oxide (WO x -TiO 2 -Al 2 O 3) as efficient solid Lewis acid catalysts for the catalytic pyrolysis of lignin. We demonstrate that WO x -TiO 2 -Al 2 O 3 exhibits the best catalytic ability at a pyrolysis temperature of 600 °C with a catalyst-to-lignin weight ratio of 2. The yields of bio-oil and monocyclic aromatic hydrocarbons (benzene, toluene, and xylene) can respectively reach 30.2 wt% and 1.6 wt%, which is slightly lower than those of the commercial HZSM-5 catalyst (31.7 wt% and 1.9 wt%). We also prove that the M−O−M bonds formed between oxygenophilic metals can generate electron holes as the temperature increasing. Those holes may combine with C-O bonds of phenolic compounds to generate metal–oxygen–carbon (M−O−C) bonds, facilitating the deoxygenation of lignin-derived pyrolysis vapours. These findings may provide guidance for the design of novel solid Lewis acid catalysts for the direct deoxygenation of lignin for the preparation of aromatic compounds. [ABSTRACT FROM AUTHOR]

Lignocellulosic biomass is an abundantly available feedstock for the sustainable production of chemicals and materials. However, total conversion of three major components within biomass (hemicellulose, cellulose and lignin) into chemicals and materials via single hydrolysis or fast pyrolysis remains a challenge because of the heterogeneous structure and recalcitrant nature of biomass, which is especially evident for softwood. In order to address these challenges, with ethylene glycol as solvent and different acids (HCl, HClO 4 , H 2 SO 4 , H 3 PO 4 ,HCOOH, C 3 H 6 O 3 , or CH 3 COOH) as catalyst, an integrated process consisting of different acids-assisted organosolvolysis and subsequent fast pyrolysis was proposed for maximizing conversion of softwood into sugars (hemicellulosic and pyrolytic sugars) and ultrafine lignin. Mechanistic insight into acids-assisted organosolvolysis of recalcitrant pine indicated that, acid pKa and H+ concentrations were vital factors influencing the deconstruction of softwood into cellulose-rich fraction, hemicellulosic sugars and high purity ultrafine lignin. This considerably enhanced the heterolytic cleavage of cellulose into levoglucosan (LG) in subsequent fast pyrolysis. The highest LG yield of 44.45 wt% was realized by HCl due to its high pKa value and maximum H+ concentration. Total conversion efficiencies of strong acids-assisted integrated process were superior to those from medium strong and weak acids-assisted process with the highest total conversion efficiency of 61.61 wt% achieved by HClO 4 and that of HCl and H 2 SO 4 over 50.00 wt%. Moreover, prewashing feedstocks with HCl solution could effectively improve the total conversion efficiency as well as the purity and uniformity of ultrafine lignin. These findings help to provide an efficient process for maximizing the conversion efficiency of recalcitrant softwood for the production of sugars and ultrafine lignin. Image 1 [ABSTRACT FROM AUTHOR]

Hemicellulose is the most reactive component of biomass during torrefaction. Torrefied hemicellulose will be one of the most significant factors determining the reactivity of torrefied biomass during subsequent pyrolysis and CO 2 gasification. Xylan, as the representative for hemicellulose, was torrefied in a bench scale tubular reactor with varying torrefaction temperature and residence time. The results demonstrated that the pyrolysis and CO 2 gasification reactivity of xylan and its derived char was evidently reduced by torrefaction. As torrefaction temperature increased from 200 to 280 °C, the comprehensive pyrolysis index (CPI) of xylan decreased evidently from 16.14 to 2.72 10-4%/(min·°C2), while the average CO 2 gasification reactivity of biochar derived from xylan decreased from 9.11 to 7.33 min−1. These results could be attributed to that xylan proceeded devolatilization, polycondensation and carbonization reactions during torrefaction to form torrefied xylan with a condensed aromatic structure. The H/C or O/C ratio of torrefied xylan can be used as a structural indicator for quantitative evaluation of its torrefaction severity and resulting reactivity during pyrolysis and CO 2 gasification. These findings can provide useful information for identifying the effect of torrefaction on structure alterations of hemicellulose and resulting reactivity during pyrolysis and CO 2 gasification. • Quantitative structure-reactivity relationships of torrefied xylan were established. • The pyrolysis/gasification reactivity of xylan was reduced by torrefaction. • H/C ratio of xylan can be used for evaluation its pyrolysis/gasification reactivity. [ABSTRACT FROM AUTHOR]