Life cycle assessment and techno-economic analysis of wood-based biorefineries for cellulosic ethanol production.

Poplar is widely used in the paper industry and accompanied by abundant branches waste, which is potential feedstock for bioethanol production. Acid-chlorite pretreatment can selectively remove lignin, thereby significantly increasing enzymatic efficiency. Moreover, lignin residues valorization via gasification-syngas fermentation can achieve higher fuel yield. Herein, environmental and economic aspects were conducted to assess technological routes, which guides further process optimization. Life cycle assessment results show that wood-based biorefineries especially coupling scenarios have significant advantages in reducing global warming potential in contrast to fossil-based automotive fuels. Normalization results indicate that acidification potential surpasses other indicators as the primary impact category. In terms of economic feasibility, coupling scenarios present better investment prospects. Bioethanol yield is the most critical factor affecting market competitiveness. Minimum ethanol selling price below ethanol international market price is promising with higher-levels technology. Further work should be focused on technological breakthrough, consumable reduction or replacement.

Product regulation and catalyst deactivation during ex-situ catalytic fast pyrolysis of biomass over Nickel-Molybdenum bimetallic modified micro-mesoporous zeolites and clays.

Ni-Mo bimetallic modified micro-mesoporous zeolite catalysts were prepared and employed in the process of ex-situ catalytic fast pyrolysis (CFP) of poplar to produce liquid fuel. Clay catalysts were incorporated to further improve the products quality. The mass yield of monocyclic aromatic hydrocarbons (MAHs) increased under the catalysis of composite catalysts AZM and NiMo/AZM. HAP&Zeolite dual catalyst system reduced coke yield of NiMo/AZM to 5.01 wt%. Through real-time monitoring of gas products, the catalytic performance of zeolites began to decrease after the ratio of biomass and catalyst was more than 1. A series of characterization results futher demonstrated that AZM and NiMo/AZM possessed more stable catalytic ability and higher catalytic activity during the whole CFP process. N2 adsorption-desorption measurement and Raman characterization illustrated the formation and structure of coke, catalyst deactivation and the protective mechanism of mesopores on micropores.

Surfactant assisted microwave irradiation pretreatment of corncob: Effect on hydrogen production capacity, energy consumption and physiochemical structure.

The combination pretreatment strategy is an effective way to intensify photo-fermentative biohydrogen production (PFHP) process. In this study, the synergistic effects of microwave irradiation and surfactants on the hydrogen production performance, energy analysis and structural characteristics was evaluated. Results revealed that hydrogen production performance was improved after microwave irradiation pretreatment (MIP) and surfactants assisted microwave irradiation pretreatment (SMIP). SMIP group had a higher cumulative hydrogen yield (CHY) of 367.87 ± 6.481 mL compared with control group (223.26 ± 4.329 mL) and MIP group (303.66 ± 3.366 mL), which was an increase of 36.01% and 64.77%, respectively. Energy evaluation analysis showed that the energy ratio of SMIP (0.49) was higher than that of MIP (0.37) in the PFHP system, therefore, SMIP can save more energy. After SMIP, the corncob lignocellulose structure was greatly damaged, which was verified by SEM, FTIR, XRD and XPS analyses.

Evaluation on nitrogen conversion during biomass torrefaction and its blend co-combustion with coal.

In this work, biomass torrefaction was combined with coal co-combustion to illustrate the differences in biomass performance and the mechanisms of migration and transformation of nitrogen over the entire course of thermal treatments. XPS analysis illustrated that torrefaction in CO2 suppressed the conversion of pyrrole-N (N-5) to quaternary-N (N-Q), whereas the trend for an O2 atmosphere moved in the opposite direction. During co-combustion, the impact on NO emission reduction shifted from positive to negative as the pretreatment temperature was raised, which is closely related to the six elementary reactions involving the intermediacy of NCO and NH, as well as to heterogeneous reduction of NO with char. In addition, torrefaction in a N2/O2 atmosphere at a lower temperature of 250 °C improved the properties of biomass and achieved the lowest NO emission during co-combustion, which provides the supporting theory needed for using effluent in power plants as a torrefaction medium.

Regulation mechanism of three key parameters on catalytic characterization of molybdenum modified bimetallic micro-mesoporous catalysts during catalytic fast pyrolysis of enzymatic hydrolysis lignin.

Novel preparation of molybdenum modified bimetallic micro-mesoporous catalyst was proposed innovatively to conduct catalytic fast pyrolysis of enzymatic hydrolysis lignin. The optimal catalytic characterization of the prepared catalyst was attributed to appropriate porous structure, the interaction between zeolite support and metal species, and the synergetic and stable mechanism of bimetallic active sites. With the incorporation of metal species into micro-mesoporous catalyst, the distribution of active sites experienced a regulation, which contributed to MAHs production and cracking of oxygen-containing substances. NiMo/AZM catalyst exhibited the most obvious coke inhibition effect (8.47 wt% of mass yield) and converted more high-ordered graphite carbon to low-ordered one, so as to make it easier to remove and prolong the catalyst lifetime, and obtained the highest mass yield of MAHs (13.15 wt%) as well as the minimum selectivity of bulky oxygenates (3.82%), which was the joint contribution of three key parameters.

Catalytic fast pyrolysis of enzymatic hydrolysis lignin over Lewis-acid catalyst niobium pentoxide and mechanism study.

Lewis-acid catalyst Nb2O5 is first applied in catalytic fast pyrolysis (CFP) of enzymatic hydrolysis lignin (EHL) to produce aromatic hydrocarbons (AHs) that can be used as alternative liquid fuels. The catalyst exhibits a good talent to convert lignin into AHs with quite little polycyclic aromatic hydrocarbons (PAHs) formation. The yield of AHs reaches 11.2 wt% and monocyclic aromatic hydrocarbons (MAHs) takes up 94% under the optimized condition (Catalyst to Lignin ratio 9:1, 650 °C). No coke is generated during the reactions. The reaction sequence is proposed and verified by model compound reactions. Furthermore, DFT calculations are performed to understand the mechanisms of limitation of PAHs or char/coke formation and the efficient deoxygenation ability over catalyst. Nb2O5 with Lewis acid sites is proved to be a promising catalyst for the production of AHs from lignin. This work provides a new idea on choice of catalysts for CFP of lignin in future.

Investigation of ash deposition dynamic process in an industrial biomass CFB boiler burning high alkali and chlorine fuel.

Biomass direct combustion for power generation is used widely in China. The circulating fluidized bed (CFB) boiler has a lower combustion temperature and a wide fuel adaptability, which is suitable for biomass combustion. The dynamic process of ash deposition in a CFB boiler is different from that in a grate furnace because it has a lower combustion temperature and a higher flue gas flow. In this work, the dynamic process of ash deposition on a superheater in a 50 MW biomass CFB boiler was studied by a deposit sampling system at different deposition times. Multiple deposit samples with different deposition times were observed and analysed to obtain an indication of deposit changes with time to understand the entire deposit build-up process. This study differs from previous studies on ash deposition and the deposition process could be identified as occurring in three stages: (1) initial deposition, (2) KCI deposition and (3) capturing of fly ash particles. In the first stage, the temperature gradient near the superheater led to the deposition of fine particles smaller than 2 µm from the flue gas through thermophoretic deposition. In the second stage, the surface became rough, which led to an increase in gas-phase KCl condensation rate and the formation of a dense and continuous KCl layer after the initial deposition. In the third stage, KCI provided a sticky layer to capture larger particles in the flue gas. Thus, more large particles were captured in the flue gas and the KCl continued to condense. As the surface temperature was increased, the condensation rate of the gas-phase KCl decreased. The higher surface temperature enhanced KCI melting and captured more fly ash particles, which led to a rapid build-up of ash deposits on the heating surfaces.

Release and transformation mechanisms of trace elements during biomass combustion.

The release and transformation mechanisms of trace elements (TEs) during biomass combustion and the environmental impact of TEs in biomass ash were evaluated in this study. Three types of biomass were selected as fuels, with a type of bituminous coal used as a comparison. The quantitative contents and chemical fractions of the TEs in the fuels, ash and char obtained after combustion and pyrolysis were analyzed. The results indicated that during the biomass combustion, the amounts of TEs released were ordered as follows: As > Cd, Pb, Zn > Cu. The TEs in the different chemical fractions both in the fuels and the solid products were shown to be in the forms of different specific compounds, and the transformation of each TE was discussed in depth. Cd, Cu and Zn were found to be released in higher quantities during pyrolysis than combustion and the reason may be that more nonvolatile TE oxides but less volatile TEs chlorides were formed during combustion. The assessment of the environmental impact of the TEs in biomass ash indicated that the environmental risks of Zn and Cu in biomass ash are higher than those in coal ash.

Investigating the correlation of biomass recalcitrance with pyrolysis oil using poplar as the feedstock.

Pyrolysis of five poplar samples with differing degrees of recalcitrance was performed; the correlations between the poplar enzymatic hydrolysis glucose yields and the physicochemical properties of pyrolysis product were investigated in this study. Sugar release of five poplar samples varied from 48.1 to 112.3 mg/g for glucose, and 12.0 to 32.4 mg/g for xylose. The yield of pyrolysis products was calculated and the molecular weight distribution of pyrolysis oils was measured by GPC, ranging from 268 to 289 g/mol for its weight-average molecular weight. GC-MS analysis of the bio-oil exhibited a strong correlation between biomass recalcitrance and guaiacyl-type structures in bio-oils. The correlation between biomass recalcitrance and the ratio of syringyl-to-guaiacyl-type-related structures was also assessed. The results from quantitative 31P NMR indicated some correlation between biomass recalcitrance and the guaiacyl hydroxyl groups in bio-oils. These results illustrate correlations and differences between converting biomass to biofuels via the biological and thermal platform.

Insights into agglomeration and separation of fly-ash particles in a sound wave field.

The efficiency of fine particle removal by using traditional devices is relatively low. Acoustic agglomeration is an effective pretreatment method that agglomerates particles before they enter a particulate control device so that they can be easily removed. The movements of particles exposed in a sound wave field were captured using a high-speed camera in this study. Agglomeration and separation of two particles were directly observed. Photographs were analyzed frame by frame to obtain motion information. A model was constructed, and COMSOL Multiphysics software was employed to simulate their relative motions. The simulation results matched the experimental results well. The conditions under which an aggregate consisting of two particles will be separated by a sound wave were calculated. The calculated results revealed that a non-breakable region exists: when sizes of primary particles are within this region, agglomerates will not be separated into smaller particles, but outside this region, agglomerates can be separated. The observation of particle motion deepens understanding of acoustic agglomeration and separation processes taking place in the agglomeration chamber. The calculation of separation of agglomerates can guide enhancement of acoustic agglomeration processes.

Catalytic fast pyrolysis of lignin to produce aromatic hydrocarbons: optimal conditions and reaction mechanism.

Catalytic fast pyrolysis of lignin with zeolite catalysts is a promising method to produce aromatic hydrocarbons. In this paper, alkali lignin was used as a model compound to pyrolyze with HZSM-5 (silica to alumina ratio, SAR = 23), HZSM-5(50), HZSM-5(80), HY and Hß. Non-condensable vapours and condensable fractions were determined and quantified by GC/FID and GC/MS respectively. 7.63 wt% of aromatic hydrocarbons and 3.34 wt% of C1-C4 alkanes and alkenes were acquired. The effects of catalysts and pyrolysis parameters were studied in this work. Different reaction pathways were compared and discussed by combining density functional theory (DFT) calculations. Cyclization reactions to form aromatic hydrocarbons were thought to be the main reaction pathway, while direct demethylation, demethoxylation and dehydration reactions were the secondary reaction pathway to convert phenolic lignin monomers to non-oxygenated aromatic hydrocarbons.

Simulation of nitrogen transformation in pressurized oxy-fuel combustion of pulverized coal.

Chemical kinetic modeling was applied to simulate N transformation in the pressurized oxy-fuel combustion process of pulverized coal. Modeling accuracy was validated by experimental data at different operation pressures. The key reaction paths from fuel-N to different N products were revealed by analyzing the rate of production. NO formation was synergistically affected by six elementary reactions, in which NCO and other intermediate species were involved. The reactions among N, NH, NH2, and NO were the key paths of N2 formation. After pressurizing the combustion system, NO and N2 contents decreased and increased, respectively. High operation pressure inhibited the diffusion of NO from the internal to the external part of char. This condition prolonged the residence time of NO inside the char, triggered a typical heterogeneous reaction between gaseous NO and unburned char, and reduced the conversion from fuel-N to NO. Moreover, modeling was performed to predict NO x emission in pressurized oxy-fuel combustion as a function of various operating parameters, including temperature and excess air and recycling ratios. This study may provide guidance for reducing NO x emissions and improving combustion efficiency in oxy-fuel combustion, and it can serve as a reference for industrial applications that involve pulverized coal combustion.

Spontaneous Cooling Absorption of CO2 by a Polymeric Ionic Liquid for Direct Air Capture.

A polymeric ionic liquid (PIL), with quaternary ammonium ions attached to the polymer matrix, displays CO2 affinity controlled by moisture. This finding led to the development of moisture swing absorption (MSA) for direct air capture of CO2. This work aims to elucidate the role of water in MSA. For some humidity range, CO2 absorption is an endothermic process associated with concurrent dehydration of the sorbent. The thermodynamic behavior of water indicates a decreased hydrophilicity of the PIL as the mobile anion transforms from CO32- to HCO3- during CO2 absorption. The decrease in hydrophilicity drives water out of the PIL, carrying heat away. The mechanism is elucidated by molecular modeling based on density functional theory. The finding of spontaneous cooling during absorption and its mechanism in the PIL opens new possibilities for designing an air capture sorbent with a strong CO2 affinity but low absorption heat.

Controllable synthesis of hierarchical MnOx/TiO2 composite nanofibers for complete oxidation of low-concentration acetone.

A novel hierarchical MnOx/TiO2 composite nanofiber was fabricated by combining the electrospinning technique and hydrothermal growth method. The synthesized nanomaterial, which comprised primary TiO2 nanofibers and secondary MnOx nanoneedles, was further investigated for complete catalytic oxidation of volatile organic compounds for the first time, and this presented high-oxidation performance on low-concentration acetone. The morphological, structural, physicochemical characterization, and catalytic performance analyses demonstrated that the highest catalytic activity was achieved from the obtained MnOx/TiO2 nanofiber catalyst with 30wt.% manganese loading. This finding can be ascribed to the synergistic effect of the specific hierarchical nanofibrous morphology, the abundant surface-adsorbed oxygen, the superior redox property, and the sufficient specific surface.

Effects of torrefaction on hemicellulose structural characteristics and pyrolysis behaviors.

The effects of torrefaction on hemicellulose characteristics and its pyrolysis behaviors were studied in detail. The oxygen content decreased significantly after torrefaction, leading to the increase of high heating value. Two-dimensional perturbation correlation analysis based on diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was performed to characterize the structural evolutions. It was found the dehydration of hydroxyls and the dissociation of branches were the main reactions at low torrefaction temperature. When the temperature further increased, the depolymerization of hemicellulose and the fragmentation of monosaccharide residues occurred. The distributed activation energy model with double Gaussian functions based on reaction-order model was used to investigate the pyrolysis kinetics. The results showed that torrefaction enhanced the activation energy for degradation reactions while lowered that for condensation reactions, and increased the devolatilization contribution of condensation reactions. Besides, torrefaction decreased the yields of typical pyrolytic products, such as acids, furans, alicyclic ketones and so on.

Investigation of hybrid plasma-catalytic removal of acetone over CuO/γ-Al2O3 catalysts using response surface method.

In this work, plasma-catalytic removal of low concentrations of acetone over CuO/γ-Al2O3 catalysts was carried out in a cylindrical dielectric barrier discharge (DBD) reactor. The combination of plasma and the CuO/γ-Al2O3 catalysts significantly enhanced the removal efficiency of acetone compared to the plasma process using the pure γ-Al2O3 support, with the 5.0 wt% CuO/γ-Al2O3 catalyst exhibiting the best acetone removal efficiency of 67.9%. Catalyst characterization was carried out to understand the effect the catalyst properties had on the activity of the CuO/γ-Al2O3 catalysts in the plasma-catalytic reaction. The results indicated that the formation of surface oxygen species on the surface of the catalysts was crucial for the oxidation of acetone in the plasma-catalytic reaction. The effects that various operating parameters (discharge power, flow rate and initial concentration of acetone) and the interactions between these parameters had on the performance of the plasma-catalytic removal of acetone over the 5.0 wt% CuO/γ-Al2O3 catalyst were investigated using central composite design (CCD). The significance of the independent variables and their interactions were evaluated by means of the Analysis of Variance (ANOVA). The results showed that the gas flow rate was the most significant factor affecting the removal efficiency of acetone, whilst the initial concentration of acetone played the most important role in determining the energy efficiency of the plasma-catalytic process.

A novel method of microwave heating mixed liquid-assisted regeneration of V2O5-WO3/TiO2 commercial SCR catalysts.

An experimental study on the regeneration of deactivated SCR catalysts was carried out using a microwave-assisted method containing three steps of washing with mixed liquid of ethanol and water, impregnating, and drying. After the regeneration treatment, NO conversion at 320 °C increased from 39 to 90% and vanadium content increased by 62.2%, which were much higher than those regenerated by the traditional method. The more impregnated vanadium was due to the fact that the rapid evaporation of mixed liquid inside the catalyst channels led to the enlargement of surface areas by creating more pores on the catalysts. Meanwhile, with the increasing concentrations of ethanol, the heating rate of the mixed liquid increased, and the volume after complete evaporation of the mixed liquid was gradually reduced. Since higher heating rate and lager volume after the liquid evaporation could help to create more pores, therefore, when the volume ratio of ethanol/mixed solution was 20%, the catalyst obtained the maximum specific surface area, which significantly increased to ca. 123% compared with the deactivated catalyst. In addition, the catalyst dried by microwave exhibited better catalytic activity than that dried in conventional oven. Therefore, this method showed great potential in industrial applications.

Pyrolysis behaviors of four lignin polymers isolated from the same pine wood.

Four lignin polymers, alkali lignin (AL), klason lignin (KL), organosolv lignin (OL), and milled wood lignin (MWL), were isolated from the same pine wood. Structural characterization by FTIR and (13)C NMR indicated that the four lignins have different structural features. Their pyrolysis behaviors were analyzed by TG-FTIR and Py-GC/MS. Thermally unstable ether bonds and side branches were well-preserved in AL and MWL, but were broken in OL and KL. Pyrolysis of AL and KL produce more phenols at low temperature by the breakage of ether bonds. AL and KL show lower activation energies in the main degradation stage, quantified by a distribution activation energy model with two linearly combined Gaussian functions. The evolution behaviors of typical gaseous products, CH4, CO2, and CO, were analyzed, and insights about the correlation between chemical structure and pyrolysis behavior were obtained.

[Spectroscopic Diagnosis of Two-Dimensional Distribution of OH Radicals in Wire-Plate Pulsed Corona Discharge Reactor].

Pulsed corona discharge in atmosphere has been widely regarded as an efficient flue gas treatment technology for the generation of active radical species, such as the OH radicals. The spatial distribution of OH radicals generated by pulsed corona discharge plays an important role in decomposing pollutants. The two-dimensional (2-D) distribution of OH radicals of positive wire--plate pulsed corona discharge was detected using laser-induced fluorescence (LIF). The influence of relative humidity (RH) and oxygen concentration on the 2-D distribution of OH radicals were investigated. The results indicated that the 2-D distribution of OH radicals was characterized by a fan-shaped distribution from the wire electrode to plate electrode, and both the maximum values of vertical length and horizontal width of the fan area was less than 1 cm. The 2-D distribution area of OH radicals increased significantly with increasing the RH and the optimum condition was 65% RH. The optimal level of the oxygen concentration for the 2-D distribution area of OH radicals was 2%. The process of OH radical generation and 2-D distribution area of OH radicals were significantly interfered when the oxygen concentration was larger than 15%. The total quenching rate coefficients for different RH values and oxygen concentration in this study were used to calculate the fluorescence yield of OH radical. The fluorescence yield, which is the ratio between the emission rate (Einstein coefficient) and the sum of the emission rate and quenching rate, was used to normalize the 2-D distribution area of OH radicals. The fluorescence yield of OH radical decreased with increasing the RH and oxygen concentration linearly and rapidly. It was also found that compared with the RH, the influence of the oxygen concentration had more notable effect on the fluorescence yield of OH radical and 2-D distribution area of OH radicals.

Experimental study of NO2 reduction in N2/Ar and O2/Ar mixtures by pulsed corona discharge.

Non-thermal plasma technology has been regarded as a promising alternative technology for NOx removal. The understanding of NO2 reduction characteristics is extremely important since NO2 reduction could lower the total NO oxidation rate in the plasma atmosphere. In this study, NO2 reduction was experimentally investigated using a non-thermal plasma reactor driven by a pulsed power supply for different simulated gas compositions and operating parameters. The NO2 reduction was promoted by increasing the specific energy density (SED), and the highest conversion rates were 33.7%, 42.1% and 25.7% for Ar, N2/Ar and O2/Ar, respectively. For a given SED, the NO2 conversion rate had the order N2/Ar>Ar>O2/Ar. The highest energy yield of 3.31g/kWh was obtained in N2/Ar plasma and decreased with increasing SED; the same trends were also found in the other two gas compositions. The conversion rate decreased with increasing initial NO2 concentration. Furthermore, the presence of N2 or O2 led to different reaction pathways for NO2 conversion due to the formation of different dominating reactive radicals.