A novel reforming method for hydrogen production from biomass steam gasification

In this work, an experimental study of biomass gasification in different operation conditions has been carried out in an updraft gasifier combined with a porous ceramic reformer. The effects of gasifier temperature, steam to biomass ratio (S/B), and reforming temperature on the gas characteristic parameters were investigated with and without porous ceramic filled in reformer. The results indicated that considerable synergistics effects were observed as the porous ceramic was filled in reformer leading to an increase in the hydrogen production. With the increasing gasifier temperature varying from 800 to 950 °C, hydrogen yield increased from 49.97 to 79.91 g H₂/kg biomass. Steam/biomass ratio of 2.05 seemed to be optimal in all steam-gasification runs. The effect of reforming temperature for water-soluble tar produced in porous ceramic reforming was also investigated, and it was found that the conversion ratio of total organic carbon (TOC) contents is between 71.08% and 75.74%.     

Perovskite modified catalysts with improved coke resistance for steam reforming of glycerol to renewable hydrogen fuel

Catalytic steam reforming of renewable feedstock to renewable energy or chemicals always goes with intense coking activities that produce carbonaceous products leading to low performance and eventual catalyst deactivation. Supported metal catalyst such as Ni/Al₂O₃ is known to catalysed gasification and decomposition of biomass feedstock largely for renewable fuel production with promising results. Catalyst deactivation from high carbon deposition, agglomeration and phase transformations resulting to rapid deactivation are some of the issues identified with the use of the catalyst. In this work, improvement on the coke resistance and catalytic properties of Ni/Al₂O₃ catalyst is sought via the use of a thermally stable and coke-resistant perovskite La_0.75Sr_0.25Cr_0.5Mn_0.5O_3-δ (LSCM) as catalyst promoter/modifier and involving Zirconia-doped Ceria (Ce-Zr) as alternative support in steam reforming of pure and by-product glycerol. The stabilizing influence of the LSCM on the Ni catalyst has improved stability against agents of deactivation with a consequent significant improvement of catalytic activity of Ni/Al₂O₃ in H₂ production and robust suppression of carbon deposition. Particularly, the synergy between the LSCM promoter and alternative Ce_0.75Zr_0.25O₂ support enhanced the basic and redox properties known for Ce_0.75Zr_0.25O₂ support in contrast to the week acid centres in γ-Al₂O₃ support which further improved nickel stability, catalyst–support interaction with a resultant high catalytic activity and robust coke suppression as a result of enhanced oxygen mobility. There is correlation between the product distribution, nature of coke deposited and reforming temperature as well as type of support and structural modification. Hence, integration of a robust perovskite material as a catalyst promoter and choice of support could be tailored in design and development of robust catalyst systems to improve the performance of supported metal catalysts, particularly the suppression of carbon deposition for hydrocarbon and biomass conversion to renewable fuel or chemicals.     

Experimental study on cyclone air gasification of wood powder

In this paper, effects of the equivalence ratio (ER) and the secondary air on the gasification system were studied. The results indicate that as the ER varies in the range of 0.20–0.26, the low heating value (LHV) of the producer gas is in the range of 3.64–5.76 MJ/Nm³, the carbon conversion is 55%–67% and the cold gas efficiency of the gasification system is 33%–47%. In contrast to the gasification without the secondary air, air staged process is a gasification method capable of increasing the LHV of the producer gas from 4.63 to 5.67 MJ/Nm³, the carbon conversion from 65.5% to 81.2%, and the cold gas efficiency of the gasifier from 42.5% to 56.87%, while the tar content of the producer gas decreases from 13.96 to 5.6 g/Nm³. There exists an optimum ratio of the secondary air.     

Influence of supports on catalytic behavior of nickel catalysts in carbon dioxide reforming of toluene as a model compound of tar from biomass gasification

A series of supported Ni catalysts including Ni/MgO, Ni/γ-Al2O3, Ni/α-Al2O3, Ni/SiO2 and Ni/ZrO2 was tested in CO2 reforming of toluene as a model compound of tar from biomass gasification in a fluidized bed reactor, and characterized by the means of temperature programmed reduction with hydrogen (H2-TPR), XRD, TEM and temperature programmed oxidation (TPO). Combining the characterization results with the performance tests, the activity of catalyst greatly depended on Ni particles size, and the stability was affected by the coke composition. Both of them (Ni particle size and coke composition) were closely related to the interaction between nickel and support which would determine the chemical environment where Ni inhabited. The best catalytic performance was observed on Ni/MgO due to the strong interaction between NiO and MgO via the formation of Ni-Mg-O solid solution, and the highest dispersion of Ni particle in the basic environment.     

Absorptive removal of biomass tar using water and oily materials

Water is the most common choice of absorption medium selected in many gasification systems. Because of poor solubility of tar in water, hydrophobic absorbents (diesel fuel, biodiesel fuel, vegetable oil, and engine oil) were studied on their absorption efficiency of biomass tar and compared with water. The results showed that only 31.8% of gravimetric tar was removed by the water scrubber, whereas the highest removal of gravimetric tar was obtained by a vegetable oil scrubber with a removal efficiency of 60.4%. When focusing on light PAH tar removal, the absorption efficiency can be ranked in the following order; diesel fuel > vegetable oil > biodiesel fuel > engine oil > water. On the other hand, an increase in gravimetric tar was observed for diesel fuel and biodiesel fuel scrubbers because of their easy evaporation. Therefore, the vegetable oil is recommended as the best absorbent to be used in gasification systems.     

Advances in thermochemical conversion of woody biomass to energy,fuels and chemicals

Biomass has been recognised as a promising resource for future energy and fuels. The biomass, originated from plants, is renewable and application of its derived energy and fuels is close to carbon-neutral by considering that the growing plants absorb CO₂ for photosynthesis. However, the complex physical structure and chemical composition of the biomass significantly hinder its conversion to gaseous and liquid fuels.This paper reviews recent advances in biomass thermochemical conversion technologies for energy, liquid fuels and chemicals. Combustion process produces heat or heat and power from the biomass through oxidation reactions; however, this is a mature technology and has been successfully applied in industry. Therefore, this review will focus on the remaining three thermochemical processes, namely biomass pyrolysis, biomass thermal liquefaction and biomass gasification. For biomass pyrolysis, biomass pretreatment and application of catalysts can simplify the bio-oil composition and retain high yield. In biomass liquefaction, application of appropriate solvents and catalysts improves the liquid product quality and yield. Gaseous product from biomass gasification is relatively simple and can be further processed for useful products. Dual fluidised bed (DFB) gasification technology using steam as gasification agent provides an opportunity for achieving high hydrogen content and CO₂ capture with application of appropriate catalytic bed materials. In addition, multi-staged gasification technology, and integrated biomass pyrolysis and gasification as well as gasification for poly-generation have attracted increasing attention.     

Steam–air fluidized bed gasification of distillers grains: Effects of steam to biomass ratio,equivalence ratio and gasification temperature

In this study, thermochemical biomass gasification was performed on a bench-scale fluidized-bed gasifier with steam and air as fluidizing and oxidizing agents. Distillers grains, a non-fermentable byproduct of ethanol production, were used as the biomass feedstock for the gasification. The goal was to investigate the effects of furnace temperature, steam to biomass ratio and equivalence ratio on gas composition, carbon conversion efficiency and energy conversion efficiency of the product gas. The experiments were conducted using a 3 × 3 × 3 full factorial design with temperatures of 650, 750 and 850 °C, steam to biomass ratios of 0, 7.30 and 14.29 and equivalence ratios of 0.07, 0.15 and 0.29. Gasification temperature was found to be the most influential factor. Increasing the temperature resulted in increases in hydrogen and methane contents, carbon conversion and energy efficiencies. Increasing equivalence ratio decreased the hydrogen content but increased carbon conversion and energy efficiencies. The steam to biomass ratio was optimal in the intermediate levels for maximal carbon conversion and energy efficiencies.     

Influence of operation conditions and additives on the development of producer gas and tar reduction in air gasification of construction woody wastes using a two-stage gasifier

Air gasification was conducted with fractions of construction woody wastes in a two-stage gasifier, consisting of a fluidized bed zone and a tar cracking zone. The aim of this work is to investigate the influence of reaction conditions and additives on the composition of producer gas and tar content in producer gas.A producer gas obtained with activated carbon of 540 g at an ER of 0.26 was mainly composed of H₂ (25 vol.%), CO (22 vol.%) and CH₄ (5 vol.%). Regarding tar removal efficiency, activated carbon was better than olivine. The tar removal rate with virgin activated carbon reached up to 80%. The reuse of spent activated carbon caused an efficiency loss in tar removal to some extent. Overall, it seems that the strong need for intensive downstream tar removal measurements can be removed with the use of a two-stage gasifier and the application of activated carbon.     

Effects of the reforming reagents and fuel species on tar reforming reaction

In this study, using wood chips and polyethylene (PE) as fuels, the effects of air and/or steam as reagents on the tar reforming were clarified quantitatively with a simulated gasifier/reformer apparatus of a two-staged gasification process. The results show that when only steam or air was supplied into the reformer, the tar residual rate (defined as the ratio of the tar amount in the reformed gas to the tar amount in the pyrolysis gas) and the carbon particulate concentration in both reformed gases produced from pyrolysis gases of wood chips and PE decreased with the increase of the steam ratio (H₂O/C, 0–1.0) or the air ratio (ER, 0–0.30). Supplying steam into the reformer to suppress carbon particulate formation for PE pyrolysis gas is more effective than for wood chips pyrolysis gas. Comparing with the results of steam only reforming, the effect of air supply on reduction of the tar residual rate was more significant, while that on suppression of carbon particulate formation was smaller.     

Pyrolytic characteristics of biomass acid hydrolysis residue rich in lignin

Pyrolytic characteristics of acid hydrolysis residue (AHR) of corncob and pinewood (CAHR, WAHR) were investigated using a thermo-gravimetric analyzer (TGA) and a self-designed pyrolysis apparatus. Gasification reactivity of CAHR char was then examined using TGA and X-ray diffractometer. Result of TGA showed that thermal degradation curves of AHR descended smoothly along with temperature increasing from 150 °C to 850 °C, while a “sharp mass loss stage” for original biomass feedstock (OBF) was observed. Char yield from AHR (42.64-30.35 wt.%) was found to be much greater than that from OBF (26.4-19.15 wt.%). In addition, gasification reactivity of CAHR char was lower than that of corncob char, and there was big difference in micro-crystallite structure. It was also found that CAHR char reactivity decreased with pyrolysis temperature, but increased with pyrolysis heating rate and gasification temperature at 850-950 °C. Furthermore, CAHR char reactivity performed better under steam atmosphere than under CO₂ atmosphere.     

Alumina/silica supported K2CO3 as a catalyst for biodiesel synthesis from sunflower oil

The new type of catalyst for fatty acid methyl esters (FAME or biodiesel) synthesis with K₂CO₃ as active component on alumina/silica support was synthesized using sol–gel method. Corresponding catalyst (xerogel) was prepared by 12 h drying the wet gel in air at 300 °C, 600 °C or 1000 °C at atmospheric pressure. The catalysts activity in the methanolysis of sunflower oil was compared to the activity of the pure K₂CO₃. The effects of various reaction variables on the yield of FAME were investigated. It was found that the temperature of 120 °C and methanol to oil molar ratio of 15:1, are optimal conditions for FAME synthesis with synthesized catalyst. Repeated use of same amount of catalyst indicated that effect of potassium leaching obviously existed leading to decrease of catalyst activity.     

基于钙基催化剂的生物质焦油催化裂解试验

生物质气化技术是生物质高值利用的重要技术之一，然而却存在副产品焦油难以处理的问题。为了解决生物质气化过程中副产品焦油的问题，以钙基催化剂为床料，在流化床反应器内开展焦油催化裂解试验。结果表明，钙基催化剂对焦油裂解具有很好的催化作用，可显著提高焦油裂解效率；流化床的操作条件对生物质焦油的催化裂解过程产生了重要影响，即操作温度越高，焦油裂解效率也越高，加入适当比例的水蒸气可以提高焦油裂解效率，且能增大产品气的产量。研究结果显示，添加钙基催化剂后，理想的操作温度为850℃，水蒸气与焦油质量比例为5∶1。研究结果为焦油的再利用相关研究提供了参考。     

Hydrogen production by sorption-enhanced steam reforming of glycerol

Catalytic steam reforming of glycerol for H₂ production has been evaluated experimentally in a continuous flow fixed-bed reactor. The experiments were carried out under atmospheric pressure within a temperature range of 400–700 °C. A commercial Ni-based catalyst and a dolomite sorbent were used for the steam reforming reactions and in situ CO₂ removal. The product gases were measured by on-line gas analysers. The results show that H₂ productivity is greatly increased with increasing temperature and the formation of methane by-product becomes negligible above 500 °C. The results suggest an optimal temperature of ∼500 °C for the glycerol steam reforming with in situ CO₂ removal using calcined dolomite as the sorbent, at which the CO₂ breakthrough time is longest and the H₂ purity is highest. The shrinking core model and the 1D-diffusion model describe well the CO₂ removal under the conditions of this work.     

Catalytic hydrolysis of lignocellulosic biomass into 5-hydroxymethylfurfural in ionic liquid

Production of 5-hydroxymethylfurfural (HMF) from cellulose catalyzed by solid acids and metal chlorides was studied in the 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) under microwave irradiation. Among the applied catalysts, the use of CrCl₃/LiCl resulted in the highest yield of HMF. The effects of catalyst dosage (mole ratio of catalyst to glucose units in the feedstock) and reaction temperature on HMF yields were investigated to obtain optimal process conditions. With the 1:1 mol ratio of catalyst to glucose unit, the HMF yield reached 62.3% at 160 °C for 10 min. Untreated wheat straw was also investigated as feedstock to produce HMF for the practical use of raw biomass, in which the HMF yield was comparable to that from pure cellulose. After the extraction of HMF, [BMIM]Cl and CrCl₃/LiCl could be reused and exhibited no activity loss after three successive runs.     

Fractionation of wheat and barley straw to access high-molecular-mass hemicelluloses prior to ethanol production

The cost efficiency of the biorefining process can be improved by extracting high-molecular-mass hemicelluloses from lignocellulosic biomass prior to ethanol production. These hemicelluloses can be used in several high-value-added applications and are likely to be important raw materials in the future. In this study, steam pretreatment in an alkaline environment was used to pretreat the lignocellulosic biomass for ethanol production and, at the same time, extract arabinoxylan with a high-molecular-mass. It was shown that 30% of the arabinoxylan in barley straw could be extracted with high-molecular-mass, without dissolving the cellulose. The cellulose in the solid fraction could then be hydrolysed with cellulase enzymes giving a cellulose conversion of about 80–90% after 72 h. For wheat straw, more than 40% of the arabinoxylan could be extracted with high-molecular-mass and the cellulose conversion of the solid residue after 72 h was about 70–85%. The high cellulose conversion of the pretreated wheat and barley straw shows that they can be used for ethanol production without further treatment. It is therefore concluded that it is possible to extract high-molecular-mass arabinoxylan simultaneously with the pretreatment of biomass for ethanol production in a single steam pretreatment step.     

An experimental study on biomass air-steam gasification in a fluidized bed

The characteristics of biomass air-steam gasification in a fluidized bed are studied in this paper. A series of experiments have been performed to investigate the effects of reactor temperature, steam to biomass ratio (S/B), equivalence ratio (ER) and biomass particle size on gas composition, gas yield, steam decomposition, low heating value (LHV) and carbon conversion efficiency. Over the ranges of the experimental conditions used, the fuel gas yield varied between 1.43 and 2.57 Nm3/kg biomass and the LHV of the fuel gas was between 6741 and 9143 kJ/Nm3. The results showed that higher temperature contributed to more hydrogen production, but too high a temperature lowered gas heating value. The LHV of fuel gas decreased with ER. Compared with biomass air gasification, the introduction of steam improved gas quality. However, excessive steam would lower gasification temperature and so degrade fuel gas quality. It was also shown that a smaller particle was more favorable for higher gas LHV and yield.     

Preliminary investigation on the production of fuels and bio-char from Chlamydomonas reinhardtii biomass residue after bio-hydrogen production

The aim of this work was to investigate the potential conversion of Chlamydomonas reinhardtii biomass harvested after hydrogen production. The spent algal biomass was converted into nitrogen-rich bio-char, biodiesel and pyrolysis oil (bio-oil). The yield of lipids (algal oil), obtained by solvent extraction, was 15 ± 2% w/w_dry-biomass. This oil was converted into biodiesel with a 8.7 ± 1% w/w_dry-biomass yield. The extraction residue was pyrolysed in a fixed bed reactor at 350 °C obtaining bio-char as the principal fraction (44 ± 1% w/w_dry-biomass) and 28 ± 2% w/w_dry-biomass of bio-oil. Pyrolysis fractions were characterized by elemental analysis, while the chemical composition of bio-oil was fully characterized by GC-MS, using various derivatization techniques. Energy outputs resulting from this approach were distributed in hydrogen (40%), biodiesel (12%) and pyrolysis fractions (48%), whereas bio-char was the largest fraction in terms of mass.     

Fed-batch fermentation of Tuber melanosporum for the hyperproduction of mycelia and bioactive Tuber polysaccharides

For the first time, a fed-batch fermentation process of Tuber melanosporum was developed for the efficient production of bioactive mycelia and Tuber polysaccharides. Each 1.67 g/L of peptone and 8.33 g/L of yeast extract were added on day 3, 6, and 9, respectively, and sucrose was fed to maintain its concentration around 35–5 g/L when its residual level decreased to 10–5 g/L. Then, the maximal biomass, the production of extracellular polysaccharides (EPS) and intracellular polysaccharides (IPS) reached 53.72 ± 2.57 g DW/L, 7.09 ± 0.62 and 4.43 ± 0.21 g/L, respectively. Compared with the batch culture conducted in the enriched medium, the biomass, the production of EPS and IPS were enhanced by 55.8%, 222.3% and 103.2%, respectively. Not only the cell density but also the production of EPS and IPS were the highest ever reported in truffle fermentation, and the biomass was also the highest as ever reported in mushroom fermentation.     

Effects of CO2 concentration on growth of filamentous algae and Littorella uniflora in a Danish softwater lake

An experiment was conducted from May to November in Lake Hampen, Denmark, to study the effect of higher CO₂ concentration on the biomass of filamentous algae. Three enclosures (1.5 m diameter) were enriched with free CO₂ to ∼10 times atmospheric equilibrium (∼170 μM) and three enclosures were kept at atmospheric equilibrium (∼17 μM). The isoetid Littorella uniflora dominated the vegetation in the enclosures. Low concentrations of nitrate and phosphate in the water were observed, especially in the summer months. During the summer, a high biomass of filamentous algae (dominated by Zygnema sp.) developed in both types of enclosures (18–58 g dry wt. m⁻² in July and August), but the biomass of algae was significantly higher (1.9–38 times) in the CO₂ enriched enclosures than in enclosures with low CO₂ concentration. L. uniflora biomass, especially leaf biomass, also showed a significant positive response to increased CO₂ concentration (75.0 ± 10.4 and 133.3 ± 42.5 g dry wt. m⁻² at low and high CO₂ concentrations, respectively) even though the massive filamentous algal growth decreased the light intensity. Both filamentous algae (in August) and L. uniflora showed lower tissue concentrations of N and P at high CO₂ concentration.