Zengli Zhao

Effect of torrefaction on structure and fast pyrolysis behavior of corncobs

Pretreatment of corncobs using torrefaction was conducted in an auger reactor at 250-300 °C and residence times of 10-60 min. The torrefied corncobs were fast pyrolyzed in a bubbling fluidized bed reactor at 470 °C to obtain high-quality bio-oil. The heating value and pH of the bio-oil improved when the torrefaction as pretreatment was applied; however, increasing bio-oil yield penalties were observed with increasing torrefaction severity. Fourier transform infrared Spectroscopy (FTIR) and quantitative solid (13)C nuclear magnetic resonance spectrometry (NMR) analysis of torrefied corncobs showed that the devolatilization, crosslinking and charring of corncobs during torrefaction could be responsible for the bio-oil yield penalties. Gas chromatography-mass spectrometry (GC-MS) analysis showed that the acetic acid and furfural contents of the bio-oil decreased with torrefaction temperature or residence time. The results showed that torrefaction is an effective method of pretreatment for improving bio-oil quality if the crosslinking and charring of biomass can be restricted.

Effect of hydrothermal pretreatment on properties of bio-oil produced from fast pyrolysis of eucalyptus wood in a fluidized bed reactor

Eucalyptus wood powder was first subjected to hydrothermal pretreatment in a high-pressure reactor at 160-190°C, and subsequently fast pyrolyzed in a fluidized bed reactor at 500°C to obtain high quality bio-oil. This study focused on investigating effect of hydrothermal pretreatment on bio-oil properties. Hemicellulose and some metals were effectively removed from eucalyptus wood, while cellulose content was enhanced. No significant charring and carbonization of constituents was observed during hydrothermal pretreatment. Thus pretreated eucalyptus wood gave higher bio-oil yield than original eucalyptus wood. Chemical composition of bio-oil was examined by GC/MS and (13)C NMR analyses. Bio-oil produced from pretreated eucalyptus wood exhibited lower contents of ketones and acids, while much higher levoglucosan content than bio-oil produced from original eucalyptus wood, which would help to improve thermal stability of bio-oil and extract levoglucosan from bio-oil. Hydrothermal pretreatment also improved bio-oil fuel quality through lowering water content and enhancing heating value.

Comparison of the effect of wet and dry torrefaction on chemical structure and pyrolysis behavior of corncobs

Wet and dry torrefaction of corncobs was conducted in high-pressure reactor and tube-type reactor, respectively. Effect of wet and dry torrefaction on chemical structure and pyrolysis behavior of corncobs was compared. The results showed that hemicellulose could be effectively removed from corncobs by torrefaction. However, dry torrefaction caused severe degradation of cellulose and the cross-linking and charring of corncobs. X-ray diffraction analysis revealed that crystallinity degree of corncobs was evidently enhanced during wet torrefaction, but reduced during dry torrefaction as raising treatment temperature. In thermogravimetric analysis, wet torrefied corncobs produced less carbonaceous residues than raw corncobs, while dry torrefied corncobs gave much more residues owing to increased content of acid insoluble lignin. Pyrolysis-gas chromatography/mass spectroscopy analysis indicated that wet torrefaction significantly promoted levoglucosan yield owing to the removal of alkali metals. Therefore, wet torrefaction can be considered as a more effective pretreatment method for fast pyrolysis of biomass.

Maximum synergistic effect in the coupling conversion of bio-derived furans and methanol over ZSM-5 for enhancing aromatic production

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.

Obtaining fermentable sugars by dilute acid hydrolysis of hemicellulose and fast pyrolysis of cellulose

The objective of this study was to get fermentable sugars by dilute acid hydrolysis of hemicellulose and fast pyrolysis of cellulose from sugarcane bagasse. Hemicellulose could be easily hydrolyzed by dilute acid as sugars. The remained solid residue of acid hydrolysis was utilized to get levoglucosan by fast pyrolysis economically. Levoglucosan yield from crystalline cellulose could be as high as 61.47%. Dilute acid hydrolysis was also a promising pretreatment for levoglucosan production from lignocellulose. The dilute acid pretreated sugarcane bagasse resulted in higher levoglucosan yield (40.50%) in fast pyrolysis by micropyrolyzer, which was more effective than water washed (29.10%) and un-pretreated (12.84%). It was mainly ascribed to the effective removal of alkali and alkaline earth metals and the accumulation of crystalline cellulose. This strategy seems a promising route to achieve inexpensive fermentable sugars from lignocellulose for biorefinery.

The comparison of obtaining fermentable sugars from cellulose by enzymatic hydrolysis and fast pyrolysis

Sugars are one of intermediates in the biological and chemical conversion of biomass. The objective of this study was to make comparison of obtaining fermentable sugars by enzymatic hydrolysis and fast pyrolysis of ball milling pretreated cellulose. After ball milling pretreatment for 0-18h, with the accumulation of alkali and alkali earth metals (from 50.8 to 276.4ppm) and decrease of the crystalline structure (from 89.8% to 10.1%), the hydrolysis yields increased from 23.6% to 56.0% in enzymatic saccharification, while the yields of levoglucosan diminished from 61.5% to 45.6% gradually in fast pyrolysis. Both enzymatic saccharification and fast pyrolysis had unique attractive features and unfavorable limitations. The present research provided a concept for considering choices among the technologies and feedstocks currently available.

Overcoming biomass recalcitrance for enhancing sugar production from fast pyrolysis of biomass by microwave pretreatment in glycerol

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.

La1-xSrxFeO3 perovskites as oxygen carriers for the partial oxidation of methane to syngas

We prepared perovskite-type oxides La1-xSrxFeO3 (x = 0, 0.3, 0.5, 0.9) by a combustion method and used these as oxygen carriers for the partial oxidation of methane. X-ray diffration, scanning electron microscopy and H-2 temperature-programmed reduction techniques were used to characterize the samples. Their reduction and oxidation activities were investigated using a thermogravimetric analysis reactor and fixed-bed reaction equipment, respectively. The results showed that the lattice oxygen in La1-xSrxFeO3 was suitable for the partial oxidation of methane to produce syngas. Their capacity to provide oxygen was enhanced by the partial substitution of La3+ by Sr2+ and the synthesized materials have good regenerability. The optimal degree of Sr substitution was found to be x = 0.3-0.5 for La1-xSrxFeO3 with regard to reactivity, selectivity, and oxygen-donating ability. CH4 conversion was higher than 70%, and the n(H-2)/n(CO) ratio remained about 2:1 and no obvious decomposition of CH4 occurred

Comprehensive utilization of glycerol from sugarcane bagasse pretreatment to fermentation

In this study, the effects of glycerol pretreatment on subsequent glycerol fermentation and biomass fast pyrolysis were investigated. The liquid fraction from the pretreatment process was evaluated to be feasible for fermentation by Paenibacillus polymyxa and could be an economic substrate. The pretreated biomass was further utilized to obtain levoglucosan by fast pyrolysis. The pretreated sugarcane bagasse exhibited significantly higher levoglucosan yield (47.70%) than that of un-pretreated sample (11.25%). The promotion could likely be attributed to the effective removal of alkali and alkaline earth metals by glycerol pretreatment. This research developed an economically viable manufacturing paradigm to utilize glycerol comprehensively and enhance the formation of levoglucosan effectively from lignocellulose.

Perovskite-type LaFe1− xMnxO3 (x=0, 0.3, 0.5, 0.7, 1.0) oxygen carriers for chemical-looping steam methane reforming: Oxidation activity and resistance to carbon formation

The effects of Mn substitution of LaMnxFe1−xO3 (x=0, 0.3, 0.5, 0.7, 1.0) on the oxidation activity and resistance to carbon formation for chemical-looping steam methane reforming (CL-SMR) were investigated. The desired crystalline perovskite phases were formed by transferring from the orthorhombic structure of LaFeO3 to rhombohedral lattice of LaMnO3 as the degree of Mn-doping increased. Manganese ions have a mixed state of Mn3+ and Mn4+ in the LaFe1−xMnxO3, meanwhile inducing the states of highly mixed character of Fe2+, Fe3+ and Fe4+ in iron ions. Substitution of Mn for Fe with proper value not only increases the lattice oxygen, which is conducive to the partial oxidation of CH4 to produce syngas, but also enhances the lattice oxygen mobility from the bulk to the surface of the oxygen carrier particles. Judging from the points of the redox reactivity, resistance to carbon formation and hydrogen generation capacity, the optimal range of the degree of Mn substitution is x=0.3–0.5.