The high nitrogen content in wood waste containing urea formaldehyde from furniture industry hampers its utilization as a clean fuel. Herein, microwave-assisted organosolv pretreatment of wood waste using glycerol as solvent was conducted in a commercial microwave reactor with varying temperature of 120–240 °C for reducing nitrogen content. The elemental analysis shows that up to 88.1 % of nitrogen and 92.9 % of alkali and alkaline earth metals in wood waste can be removed by microwave-assisted glycerolysis. The solid nuclear magnetic resonance spectrometry analysis illustrate that the urea–formaldehyde resin, lignin and hemicellulose fractions in wood waste can also be simultaneously reduced by pretreatment. Raw and pretreated wood waste was subsequently fast pyrolyzed in a semi-batch pyroprobe reactor. The experimental results demonstrate that the relative content of levoglucosan in pyrolysis vapors was significantly enhanced by pretreatment, whereas the relative content of nitrogen-containing compounds was reduced obviously. These findings provide a simple and efficient pretreatment method for reducing the formation of nitrogenous compounds during fast pyrolysis of nitrogen-rich wood waste.

Fast pyrolysis is a potential alternative route to obtain fermentable anhydrosugar (levoglucosan) from biomass. However, the low yield of anhydrosugar from biomass fast pyrolysis hampers its rapid development. Microwave-assisted organosolvolysis could be an effective pretreatment method prior to fast pyrolysis of biomass for addressing this challenge. Here, in order to examine the feedstock flexibility of microwave-assisted organosolv pretreatment on anhydrosugar production from different agricultural and forest residues, three kinds of representative agricultural and forest residues, pine, eucalyptus, and straw, were selected as feedstocks in this study. Pretreatment of them using microwave-assisted glycerolysis was performed in an atmospheric microwave reactor. The pretreated agricultural and forest residues was subsequently fast pyrolyzed in a commercial micropyrolysis reactor. The results demonstrated that microwave-assisted glycerolysis is a versatile and feedstock flexible pretreatment method prior to biomass fast pyrolysis for enhancing anhydrosugar production. The highest yield of levoglucosan (59.4%) was reached by fast pyrolysis of eucalyptus pretreated at 150 W for 20 min. The yield was boosted by 13.5 times compared to that obtained from fast pyrolysis of raw eucalyptus.Keywords: Anhydrosugar; Fast pyrolysis; Feedstock flexibility; Microwave; Organosolv pretreatment

A hydrothermal treatment experiment of eucalyptus wood was carried out in a high-pressure batch reactor at temperatures between 160 and 190 °C. The effect on chemical structure and pyrolysis behavior of eucalyptus wood as a result of hydrothermal treatment was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric (TG) analysis, and pyrolysis gas chromatography mass spectroscopy (Py-GC/MS). From FTIR analysis, it was observed that hydrothermal treatment could effectively remove acetyl groups from eucalyptus wood. XRD analysis showed that crystallinity degree of eucalyptus wood was enhanced by hydrothermal treatment due to the degradation of hemicellulose and amorphous cellulose, and crystalline size of cellulose became larger owing to the removal of small crystallites. TG analysis suggested that no significant carbonization and cross-linking of chemical components in eucalyptus wood occurred during hydrothermal treatment, and the thermal stability of eucalyptus wood was enhanced. Compared to raw eucalyptus wood, hydrothermally treated eucalyptus wood gave much higher levoglucosan yields but lower yields of reactive compounds including ketones, aldehydes, and organic acids in the Py-GC/MS experiment. This implied that hydrothermal treatment had positive impacts on biomass pyrolysis product distribution and could improve chemical composition of bio-oil produced from fast pyrolysis.

Levoglucosan, mainly derived from cellulose fast pyrolysis, is a versatile precursor to fuels, pharmaceuticals, and other value-added chemicals. However, biomass fast pyrolysis produces a very low amount of levoglucosan when compared to the theoretical yield based on cellulose fraction. Microwave pretreatment of biomass in glycerol is a potential pretreatment method prior to fast pyrolysis for enhancing levoglucosan yield since it can achieve the rapid heating and specific molecular activations for promoting the delignification and demineralization of biomass. In order to examine the validity of the pretreatment method, pretreatment of corncob in glycerol was conducted in a microwave reactor under ambient pressure. The pretreated corncobs were subsequently fast pyrolyzed in a semi-batch pyroprobe reactor. The experimental results show that microwave pretreatment in glycerol can serve as an effective pretreatment method for improving the sugar yield. The levoglucosan yield from fast pyrolysis of corncob pretreated at 150 W for 18 min was about 189 times higher than that of raw corncob. It was mainly ascribed to the effective removal of alkali and alkaline earth metals during microwave pretreatment of corncob in glycerol. In addition, the selective removal of lignin and hemicellulose fractions of corncob during pretreatment also plays positive roles in enhancing the levoglucosan yield.

To understand the effect of torrefaction severity on structure changes of hemicellulose, cellulose, lignin and their subsequent catalytic fast pyrolysis (CFP) behavior, torrefaction of lignin, hemicellulose, and cellulose was performed in a tubular reactor with different reaction temperatures (210–300 °C) and residence times (20–60 min). The experimental results show that the rank order of thermal stability during torrefaction was cellulose > lignin > hemicellulose. The torrefied hemicelulose, cellulose, and lignin were subsequently catalytic-fast-pyrolyzed over HZSM-5 in a semi-batch pyroprobe reactor. The effects of the torrefaction temperature and residence time on aromatic yields and selectivity from CFP of torrefied hemicellulose, cellulose, and lignin were investigated. The experimental results showed that torrefaction can cause the reduction in the aromatic yield and increase in benzene, toluene, and xylenes (BTX) selectivity from CFP of torrefied hemicellulose and lignin. It has little impact on CFP of torrefied cellulose. The results can be explained by Fourier transform infrared (FTIR) spectroscopy and 13C cross-polarization magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) analysis of torrefied hemicellulose, cellulose, and lignin. The rank order of structure change during torrefaction was hemicellulose > lignin > cellulose. The devolatilization and polycondensation of hemicellulose and lignin during torrefaction could be mainly responsible for the yield penalties of aromatic production from CFP of torrefied hemicellulose and lignin.

We firstly propose the coupling conversion of bio-derived furans and methanol over ZSM-5 for enhancing aromatic production. The coupling conversion of bio-derived furans and methanol was conducted in a continuous fixed bed reactor. 2-Methylfuran (MF) was used as a probe molecule to identify the possible reaction pathways. The effects of the methanol to MF molar ratio, reaction temperature and weight hourly space velocity (WHSV) on the product distribution from the coupling conversion of MF and methanol were investigated. The experimental results showed that the aromatic yield from the coupling conversion of MF and methanol is about 5.2 times higher than that of the catalytic fast pyrolysis of only MF. In addition, it can also enhance the yield of olefins, the selectivity of xylenes and reduce coke formation. These results indicate that there is a significant synergistic effect between MF and methanol. The synergistic effect could be attributed to the methanol-to-olefins reactions, the Diels–Alder reactions of furans with olefins, and the alkylation reaction of benzene/toluene with methanol occurring during the coupling conversion of MF and methanol. The reaction conditions for maximizing the synergistic effect were a methanol to MF molar ratio of 2 at 550 °C. Moreover, the comparative study of the coupling conversion of different bio-derived furans (MF, 2,5-dimethylfuran (DMF), furfural (FF) and furfuryl alcohol (FA)) and methanol were also considered in this study. The coupling conversion of DMF and methanol exhibited maximum yields of aromatics, olefins and a minimum yield of coke, suggesting that DMF is the best candidate of bio-derived furans for aromatic production in the coupling conversion of bio-derived furans and methanol.

•Product distributions from CFP were significantly affected by crystal size of ZSM-5.•ZSM-5 with crystal size of 200 nm exhibited maximum yield of aromatics.•Hemicellulose, cellulose and lignin play very different roles in CFP of biomass.To determine the effect of crystal sizes of ZSM-5 and feedstock species on aromatic yield and selectivity from catalytic fast pyrolysis of biomass, catalytic fast pyrolysis (CFP) of different feedstock species (cellulose, hemicellulose, lignin, pine, corncob and straw) over ZSM-5 with varying crystal size (2 μm, 200 nm and 50 nm) was conducted in a Pyroprobe pyrolyzer (5200, CDS Analytical). The experimental results show that ZSM-5 with crystal size of 200 nm exhibited the maximum aromatic yield and minimum BTX selectivity. The results could be attributed to its highest micropore surface area, amount of weak acid and maximum Brønsted to Lewis acid sites ratio (B/L ratio). Cellulose, hemicellulose and lignin play very different roles in catalytic fast pyrolysis of biomass. Cellulose exhibited the maximum aromatic yield of 38.4% and minimum non-condensable gas yield of 18.4%. Lignin showed the highest coke yield of 68.6% and lowest aromatic yield of 10.2%. And hemicellulose displayed the lowest coke yield of 29.4% and highest yield of non-condensable gas of 39.1%.

Two-staged biomass pyrolysis process consisting of torrefaction and subsequent fast pyrolysis is proposed to obtain high quality bio-oil. The purpose of this study is to evaluate the effect of torrefaction temperature on yield, composition, and physical properties of the liquid of torrefaction and bio-oil. Torrefaction of pine was conducted on an auger reactor at 240–320 °C with a residence time of 40 min to produce liquid of torrefaction and torrefied pine. Then, the torrefied pine was fast pyrolyzed in a bubbling fluidized bed reactor at 520 °C to produce bio-oil. Torrefied pine was characterized by chemical composition analysis and Fourier transform infrared (FTIR) spectroscopy. The liquid of torrefaction was determined by gas chromatography (GC); bio-oil was characterized by gas chromatography mass spectroscopy (GC-MS) and 13C nuclear magnetic resonance spectrometry (NMR). The experimental results show that water content in liquid of torrefaction and water and acetic acid content in bio-oil decreased with elevated torrefaction temperature, while the yield of liquid of torrefaction, aromaticity, higher heating value, and density of bio-oil increased. However, the yield of total liquid (sum of liquid of torrefaction and bio-oil) decreased significantly with elevated torrefaction temperature because of the cross-linking and carbonization of torrefied pine.

Torrefaction experiments of sprucewood and bagasse were performed in an auger reactor at 260 °C, 280 °C, and 300 °C. The chemical composition and pyrolysis behavior of the resulting torrefied biomass were examined in detail. A number of water and lightweight organic compounds were removed from biomass through torrefaction treatment. Chemical component analysis showed that more acid insoluble fibers were formed in torrefied bagasses obtained at 280 and 300 °C, which suggested cross-linking and carbonization of carbohydrates probably took place in bagasse torrefaction. FTIR (Fourier transform infrared) analysis indicated that thermal decomposition of carbohydrate (mainly hemicellulose) predominated over lignin decomposition and the cross-linking of cellulose in torrefaction. XRD analysis revealed that the degradation of amorphous hemicellulose and amorphous regions of cellulose resulted in increases of crystallinity of torrefied biomass obtained below 300 °C. Thermogravimetric analysis revealed that the decomposition of cellulose in torrefied biomass was accelerated by torrefaction treatment. Py-GC/MS analysis exhibited that the yields of acetic acid and other lightweight compounds were lower in pyrolysis of torrefied sprucewood obtained at 300 °C and all torrefied bagasses than those in raw biomass pyrolysis, while the yields of levoglucosan in torrefied biomass pyrolysis were obviously higher. This implied that more stable pyrolysis oil with higher content of levoglucosan could be obtained from torrefied biomass.

The low temperature pyrolysis characteristics of major components of biomass were investigated using thermogravimetric analysis (TGA) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). The results obtained by TGA show that the thermal stability of major components of biomass was in descending order of cellulose > lignin > hemicellulose. The main pyrolysis temperature range of hemicellulose is at 210–320°C, whereas those of cellulose and lignin are 310–390°C and 200–550°C, respectively. The Py-GC/MS was used for studying the effects of temperature on low temperature pyrolysis products of major components of biomass, which had different contribution to the volatiles. The degradation of hemicellulose generates acetic acid, 1-hydroxy-propanone, and 1-hydroxy-2-butanone. The high yield of levoglucosan and anhydro-cellobise is from pyrolysis of cellulose. Guaiacol is associated with degradation of the lignin.