Guoqiang Wei

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.

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.

Chemical-looping gasification of biomass in a 10 kWth interconnected fluidized bed reactor using Fe2O3/Al2O3 oxygen carrier

Abstract The aim of this research is to design and operate a 10 kW hot chemical-looping gasification (CLG) unit using Fe 2 O 3 /Al 2 O 3 as an oxygen carrier and saw dust as a fuel. The effect of the operation temperature on gas composition in the air reactor and the fuel reactor, and the carbon conversion of biomass to CO 2 and CO in the fuel reactor have been experimentally studied. A total 60 h run has been obtained with the same batch of oxygen carrier of iron oxide supported with alumina. The results show that CO and H 2 concentrations are increased with increasing temperature in the fuel reactor. It is also found that with increasing fuel reactor temperature, both the amount of residual char in the fuel reactor and CO 2 concentration of the exit gas from the air reactor are degreased. Carbon conversion rate and gasification efficiency are increased by increasing temperature and H 2 production at 870°C reaches the highest rate. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and BET-surface area tests have been used to characterize fresh and reacted oxygen carrier particles. The results display that the oxygen carrier activity is not declined and the specific surface area of the oxygen carrier particles is not decreased significantly.

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.

Preparation of double perovskite-type oxide LaSrFeCoO6 for chemical looping steam methane reforming to produce syngas and hydrogen

Double-perovskite type oxide LaSrFeCoO6 was used as oxygen carrier for chemical looping steam methane reforming (CL-SMR) due to its unique structure and reactivity. Solid-phase, amorphous alloy, sol-gel and micro-emulsion methods were used to prepare the LaSrFeCoO6 samples, and the as-prepared samples were characterized by means of X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H-2-TPR), X-ray photoelectron spectroscopy (XPS), Brunauer-Emmett-Teller (BET) surface area. Results showed that the samples made by the four different methods exhibited pure crystalline perovskite structure. The ordered double perovskite LaSrFeCoO6 was regarded as a regular arrangement of alternating FeO6 and CoO6 corner-shared octahedra, with La and Sr cations occupying the voids in between the octahedral. Because the La3+ and Sr2+ ions in A-site did not take part in reaction, the TPR patterns showed the reductive properties of the B-site metals. The reduction peaks at low temperature revealed the reduction of adsorbed oxygen on surface and combined with the reduction of Co3+ to Co2+ and to Co-0, while the reduction of Fe3+ to Fe2+ and the partial reduction of Fe2+ to Fe-0 occurred at higher temperatures. From the point of view of the oxygen-donation ability, resistance to carbon formation, as well as hydrogen generation capacity, the sample made by micro-emulsion method exhibited the best reactivity. Its redox reactivity was very stable in ten successive cycles without deactivation. Compared to the single perovskite-type oxides LaFeO3 and LaCoO3, the double perovskite LaSrFeCoO6 exhibited better syngas and hydrogen generation capacity.

CaO/MgO modified perovskite type oxides for chemical-looping steam reforming of methane

Abstract Chemical-looping steam methane reforming (CL-SMR) is a novel method proposed on the base of chemical looping combustion (CLC) technology. In the CL-SMR scheme, methane is partially oxidized to syngas (H2/CO=2.0) by the lattice oxygen in reformer reactor in the absence of gaseous oxidant, and then the reduced oxygen carrier is oxidized by steam to produce hydrogen in steam reactor. The use of perovskite type oxide LaFeO3 as an oxygen carrier in CL-SMR was studied. While the basicity of CaO/MgO modified oxygen carriers, LaFeO3-CaO and LaFeO3-MgO, were also synthesized aiming to increase specific surface area, thermostability, and resistance to coke formation. The synthesized oxides were characterized by X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), Brunauer-Emmett-Teller (BET) surface area and X-ray photoelectron spectroscopy (XPS). Three oxygen carriers exhibited high active and selective for syngas production from methane, and maintained perovskite type over cyclic redox operations. The LF-CaO sample is the best candidate for the CL-SMR of the three samples judging from the reactivity, selectivity, and resistance to carbon formation. It showed good regenerability during 5 redox reactions.

Biomass pyrolysis/gasification using three dimensional ordered macroporous (3DOM) Fe2O3 as an oxygen carrier

Polystyrene spheres were prepared by soap free emulsion polymerization method, then three dimensional ordered macroporous (3DOM) oxides Fe2O3 were successfully prepared after impregnation and calcination using nitrates as raw materials and citric acid as complexing agent. The samples were characterized by the techniques of scanning electron microscopy (SEM), X-ray diffraction (XRD), BET and mercury porosimetry. Pyrolysis and gasification of biomass with Fe2O3 as oxygen carriers in helium atmosphere were carried out in a thermogravimetric analyzer coupled with mass spectrometry (TG-MS). The possibility of 3DOM Fe2O3 functioning as gasification agent in biomass gasification substituted for pure oxygen, oxygen-enriched air or steam were investigated. Furthermore, a comparison experiment was carried out by using analytically pure Fe2O3 to analysis the high-performance of 3DOM Fe2O3. The characterization results showed that 3DOM Fe2O3 presented 3DOM morphology and the tiers were arranged alternatively and connected through three-dimensional pore structures. 3DOM Fe2O3 prepared was pure Fe2O3 and no other impurity phases existed when contrast with the XRD pattern of analytically pure Fe2O3, TG-MS results showed that Fe2O3 contributed to biomass gasification in high temperature stage. When used 3DOM Fe2O3 as oxygen carrier, the maximum weight loss and maximum weight loss rate raised 7.1% and 0.29%/min in the gasification stage, respectively, meanwhile two generation peaks of CO, CO2, and CH4 appeared in the MS curves.

Highly abrasion resistant thermally fused olivine as in-situ catalysts for tar reduction in a circulating fluidized bed biomass gasifier

Olivine synthesized by wetness impregnation (WI) and thermal fusion (TF) methods were investigated as in-situ catalysts to reduce the tar content during air-blown biomass gasification in a circulating fluidized bed (CFB). The results showed that the tar content decreases with the increase of reaction temperature. Raw-olivine reduced tar content by 40.6% compared to non-active bed material (silica sand) experiments; after calcination, the catalytic activities of olivine catalysts were further improved due to the migration of Fe from olivine grain to the surface. 1100-WI-olivine could reduce the tar content by up to 81.5% compared with that of raw-olivine because of the existence of Fe2O3, NiO and NiO-MgO. For 1400-TF-olivine, due to the formation of NiFe2O4, the tar content decreased to 0.77 g/Nm3, an 82.9% reduction compared to raw-olivine. Moreover, the TF-olivine had a stronger anti-attrition performance and was more suitable for using in a circulating fluidized bed.