Biomass Model Compounds Research Articles

Char Formation Mechanism in Supercritical Water Gasification Process: A Study of Model Compounds

Char is one of the undesirable products in the supercritical water gasification of biomass, causing a reduction in carbon gasification efficiency. 5-HMF (5-hydroxymethylfurfural) is believed to be an intermediate in the char formation pathway. In this Article, the rate of formation of char particles obtained from experiments using glucose (a biomass model compound) was compared to that from experiments using 5-HMF (Chuntanapum and Matsumura, 2009). The glucose experiments were conducted in a temperature range of 300−400 °C, at 25 MPa, and for a residence time up to 70 s. The initial concentration of glucose was varied from 1.5 to 3 wt % (i.e., 0.083 to 0.167 M). Glucose was found to produce char particles 2 orders of magnitude faster than 5-HMF feedstock. The copresence of the other glucose decomposition products is thought to cause the difference in the char formation mechanism (i.e., the side reaction between 5-HMF and the other decomposition products) from that of 5-HMF alone. FT-IR and Raman spectroscopy of the solid products was carried out.

Hydrogen production by biomass gasification in supercritical water using concentrated solar energy: System development and proof of concept

A novel system of hydrogen production by biomass gasification in supercritical water using concentrated solar energy has been constructed, installed and tested at the State Key Laboratory of Multiphase Flow in Power Engineering (SKLMF). The “proof of concept” tests for solar-thermal gasification of biomass in supercritical water (SCW) were successfully carried out. Biomass model compounds (glucose) and real biomass (corn meal, wheat stalk) were gasified continuously with the novel system to produce hydrogen-rich gas. The effect of direct normal solar irradiation (DNI) and catalyst on gasification of biomass was also investigated. The results showed that the maximal gasification efficiency (the mass of product gas/the mass of feedstock) in excess of 110% were reached, hydrogen fraction in the gas product also approached to 50%. The experimental results confirmed the feasibility of the system and the advantage of the process, which supports future work to address the technical issues and develop the technology of solar-thermal hydrogen production by gasification of biomass in supercritical water.

Hydrogen production by catalytic near-critical water gasification and steam reforming of glucose

Near-critical water gasification (NCWG) and steam reforming (SR) were investigated for the production of hydrogen from a biomass model compound (glucose) using fixed bed tubular reactor. Ruthenium/carbon and nickel/yttria stabilized zirconia (YSZ) were utilized to enhance the reaction rates of the two processes for NCWG and SR, respectively. NCWG experiments were performed at 200 bar and 360–450 °C, while SR experiments were conducted at 500–800 °C and atmospheric pressure. Although in both cases complete carbon gasification is achieved, gas composition, hydrogen selectivity and overall energy efficiency show strong dependencies on the type of process itself and the associated operating conditions. It is shown that operating the reforming reaction of glucose at high pressures and low temperatures (NCWG) results in a significant amount of methane and trace amounts of carbon monoxide. In contrast, gasification of glucose at atmospheric pressures and high temperatures (SR) leads to a methane-free gas stream that contains few percents of carbon monoxide. Considering energy recovery and neglecting the heat losses, the maximum cold gas efficiency of the NCWG and SR reached 78% and 91%, respectively. The features of the two catalytic reaction processes are discussed in terms of the experiments and process simulations.

Efficient generation of hydrogen from biomass without carbon monoxide at room temperature – Formaldehyde to hydrogen catalyzed by Ag nanocrystals

In this paper, we present a new route for hydrogen generation from biomass at room temperature without any carbon monoxide over nano-metal-catalysts. It has been found that the Ag nanocrystals are highly efficient and stable catalysts for the CO-free hydrogen production from formaldehyde (HCHO), a model compound of biomass, at room temperature and at atmospheric pressure. By optimizing the structure and component of catalysts, reaction parameters such as temperature, catalyst amounts, oxygen, formaldehyde concentrations, and NaOH concentrations, the hydrogen generation rate has been maintained for hours without any decay. Furthermore, the apparent activation energy of the Ag catalyzed hydrogen production reaction is determined to be 11.8 kJ mol −1, which was much lower than that of the literature results (65 kJ mol −1) without catalyst. Because of its high hydrogen generation rate, hydrogen generation efficiency, lower activation energy, and the low cost, we speculate that this novel Ag catalyst based hydrogen generation reaction should be a promising candidate for providing hydrogen in PEMFCs at room temperature.

Brines in supercritical biomass gasification: 1. Salt extraction by salts and the influence on glucose conversion

The hydrothermal gasification of wet biomass is a promising process to use biomass residues of high water content to produce burnable gases. Here “green” biomass can be converted without prior drying. Recently important improvements are accomplished, but still challenges in view of the technical application exists. One of the most important challenges is the handling of salts as natural ingredients of biomass. In this study, salts forming a second salt-rich aqueous phase (hydrothermal brine) are used to catch other salts, to avoid plugging of the reactor by formation of solids. The sodium salts studied, were successfully captured by the hydrothermal brine, which also influences the conversion of glucose as model compound for biomass.

Hydrogen Production by Catalytic Steam Reforming of Model Compounds of Biomass Fast Pyrolysis Oil

AbstractA Ni/MgO-La2O3-Al2O3 catalyst with Ni as active component, Al2O3 as support, MgO and La2O3 as additives was prepared and its catalytic activity was evaluated in the process of hydrogen production from catalytic steam reforming of bio-oil. In the catalytic evaluation, some typical components present in bio-oil such as acetic acid, butanol, furfural, cyclopentanone and m-cresol were mixed following a certain proportion as model compounds. Reaction parameters like temperature, steam to carbon molar ratio and liquid hourly space velocity were studied with hydrogen yield as index. The optimal reaction conditions were obtained as follows: temperature 750-850 °C, steam to carbon molar ratio 5-9, liquid hourly space velocity 1.5-2.5 h-1. The maximum hydrogen yield was 88.14%. The carbon deposits were formed on the catalyst surface but its content decreased as reaction temperature increased in the bio-oil steam reforming process.

Subcritical Water Reaction Behavior of D‐Glucose as a Model Compound for Biomass Using Two Different Continuous‐Flow Reactor Configurations

AbstractRecently, cellulosic materials have been considered as a useful resource for the recovery of valuable chemicals and liquid fuels, etc. Cellulose is a homopolymer of D‐glucose, which is often used as a model compound for biomass. Reactions of D‐glucose in subcritical water as the reaction solvent were conducted using a single‐flow‐type reactor (S1) and an admixture‐type reactor with feed and preheated‐water flow (S2) at temperatures from 200 to 240 °C, pressures from 15 to 20 MPa, residence times from 40 to 120 s, and initial feed concentrations of 1.5–10 wt %. D‐Glucose was converted into aldehydes, organic acids and furans, with mainly organic acids obtained at 240 °C. D‐Glucose decomposition using reactors S1 and S2 revealed that the conversion rate of D‐glucose was promoted more using S2 than by S1. The yield of furans with S1 was higher than with S2, while the yield of organic acids from S1 was lower than that from S2.

Conversion of biomass model compound under hydrothermal conditions using batch reactor

Supercritical water has been focused on as an environmentally attractive reaction media where organic materials can be decomposed into smaller molecules. The reaction behavior of lignin model compound was studied in near- and supercritical water with a batch type reactor. Catechol was used as a model compound for aromatic rings in lignin. The reaction was carried out at temperatures of 643–693 K at various pressures under an argon atmosphere. The chemical species in the aqueous products were identified by gas chromatography mass spectrometry (GCMS) and quantified using high performance liquid chromatography (HPLC). The effect of pressure and reaction time on the conversion process of catechol was presented. The main products from the conversion of catechol was phenol and the value of global rate constant for catechol conversion ( k) is 3.0 × 10 −4–11.0 × 10 −4 min −1.

Catalytic gasification of biomass model compound in near-critical water

Catalytic gasification of biomass in sub- and supercritical water is a promising process for the production of fuel gaseous. In this paper, a batch microreactor has been utilized to study the near-critical water gasification of glucose in the presence of supported and unsupported metal catalysts consisting of Raney-nickel, Raney-cobalt, Raney-copper, carbon-supported ruthenium, and alumina-supported ruthenium. The reaction temperature and pressure were 340–380 °C and 150–250 bar, respectively. Effects of reaction temperature, reaction time, and catalyst loading on the amount of the generated gas as well as its composition were investigated. Results indicated that within our operating conditions, the conversion of glucose was sensitive to temperature but varying the catalyst loading in the range of 30–100 wt% did not significantly affect the conversion, implying that the experiments were mainly conducted at saturated amounts of catalyst. The following catalytic activities for the decomposition of glucose have been observed: Raney-nickel 4200 > Raney-nickel 3202 > ruthenium on alumina and ruthenium on carbon > Raney-copper > Raney-cobalt. However, the relatively small difference in the gas yields obtained by Raney-copper catalyzed reaction and those of Raney-nickel and ruthenium suggested this relatively inexpensive spongy structure of copper metal could be very useful for gasification of biomass in subcritical water environments.

Photocatalytic Hydrogen Production from Aqueous Solutions of Alcohol as Model Compounds of Biomass Using Visible Light-Responsive TiO2 Thin Films

Visible light-responsive TiO2 (Vis-TiO2) thin films were prepared by a radio frequency magnetron sputtering deposition method. The photoelectrochemical performance was improved by adding various kinds and concentrations of alcohol, i.e., model compounds of biomass, to water. The separate evolution of pure H2 was observed to proceed efficiently on these Vis-TiO2 thin films under visible light irradiation by using an aqueous solution of methanol.

Catalytic effects of potassium on lignin steam gasification with γ-Al2O3 as a bed material

The effects of potassium on the reactivity of biomass-char steam gasification with the presence of a porous material were investigated by using a thermogravimetric reactor with high-heating rates. Lignin was employed as a char-rich biomass model compound. The potassium carbonate (K2CO3) was added to lignin and a mixture of lignin and γ-Al2O3 porous particles by means of aqueous impregnation. The effects of K2CO3 and γ-Al2O3 addition on pyrol- ysis of lignin and steam gasification of lignin-derived char were evaluated in terms of lignin conversion and the gaseous products. Results showed that K2CO3 slightly increased the steam gasification rate of lignin-derived char, but it did not influence the conversion in both the pyrolysis and steam gasification steps. In addition, tar was reduced by adding K2CO3 because of the increment of carbon conversion to gas product. The presence of γ-Al2O3 was found to induce the lower reactivity of resulting char after pyrolysis, reducing the gasification rate and conversion. A significant im- provement in gasification conversion was observed with the presence of both K2CO3 and γ-Al2O3. Especially, almost complete gasification was achieved at a reaction temperature of 1,073 K.

Hydrothermal conversion of carbohydrate biomass into formic acid at mild temperatures

The production of formic acid or formate salts by hydrothermal oxidation of glucose, a model compound of carbohydrate biomass, was investigated in the presence and absence of alkali using a batch reactor with H2O2 oxidant. Results showed that glucose was converted into formate salts with an excellent yield of 75% at a mild temperature of 250 °C in the presence of alkali. The results should be helpful to facilitate studies for developing a new green process for the conversion of carbohydrate biomass into formic acid, which can be a potential intermediate for fuels, as well as other value-added products.

Production of lactic acid from glucose by alkaline hydrothermal reaction

In this paper, alkaline hydrothermal conversion of glucose, a model compound of carbohydrate biomass, into lactic acid was discussed. Results showed that both NaOH and Ca(OH)2, can promote the formation of lactic acid in a hydrothermal reaction of glucose. In the case of the addition of NaOH, lactic acid was obtained with a yield of 27% based on a starting carbon mass of glucose at 300 °C for 60 s with a NaOH concentration of 2.5 M. In the case of the addition of Ca(OH)2, the highest yield of lactic acid is 20%, which occurred at 300 °C for 60 s with a Ca(OH)2 concentration of 0.32 M. The formation mechanisms of lactic acid from glucose were also discussed according to intermediate products identified, to examine if lactic acid is also formed via the aldose having one and two carbon atoms besides via the aldose having three carbon atoms. Result showed that lactic acid may be generated via formaldehyde, glycolaldehyde besides via the aldose having three carbon atoms in hydrothermal reaction which all formed by the reverse aldol condensation of hexoses.

Hydrogen production from co-gasification of coal and biomass in supercritical water by continuous flow thermal-catalytic reaction system

Hydrogen is a clean energy carrier. Converting abundant coal sources and green biomass energy into hydrogen effectively and without any pollution promotes environmental protection. The co-gasification performance of coal and a model compound of biomass, carboxymethylcellulose (CMC) in supercritical water (SCW), were investigated experimentally. The influences of temperature, pressure and concentration on hydrogen production from co-gasification of coal and CMC in SCW under the given conditions (20–25 MPa, 650°C, 15–30 s) are discussed in detail. The experimental results show that H2, CO2 and CH4 are the main gas products, and the molar fraction of hydrogen reaches in excess of 60%. The higher pressure and higher CMC content facilitate hydrogen production; production is decreased remarkably given a longer residence time.

EFFECT OF HEATING RATE OF BIOMASS FEEDSTOCK ON CARBON GASIFICATION EFFICIENCY IN SUPERCRITICAL WATER GASIFICATION

ABSTRACT The effect of feedstock heating rate on the efficiency of gasification of a biomass in supercritical water was investigated using a continuous bench-scale reactor. A glucose solution (biomass model compound) and a cabbage slurry were gasified in supercritical water at various heating rates in a preheater. The results show that in the range of 10–30 K/s, carbon gasification efficiency improved as the heating rate increased.

Subcritical and Supercritical Water Gasification of Cellulose, Starch, Glucose, and Biomass Waste

The subcritical and supercritical water gasification of cellulose, starch, and glucose as representative biomass model compounds and biomass in the form of Cassava waste has been investigated in a heated batch reactor. Cellulose and starch are two polysaccharides which have identical chemical compositions based on the monomer glucose but which have different chemical structures and physical properties. The influence of temperature in the subcritical and supercritical regimes of water were examined in relation to the yield of the product gases, oil, char, and water. For the model compounds and the Cassava waste, the main gases produced were carbon dioxide, carbon monoxide, hydrogen, methane, and other hydrocarbons, and there was significant production of oil and char. There were, however, distinct differences between the yields of the different products and the trends in relation to temperature. Cellulose produced a higher yield of char, carbon monoxide, and C1−C4 hydrocarbons compared to starch and glucos...

Effect of Water Density on the Gasification of Lignin with Magnesium Oxide Supported Nickel Catalysts in Supercritical Water

Gasification of lignin biomass model compounds was examined in the presence of magnesium oxide supported nickel catalysts (Ni/MgO) in sub- and supercritical water from 523 to 673 K. The main gas products were methane, carbon dioxide, and hydrogen. The amount of gases produced increased with an increase in nickel loading on magnesium oxide. The highest total gas yield in a carbon basis was 78% with 20 wt % Ni/MgO catalyst at 673 K and 0.3 g/cm3 water density. In this system, the metal and support of Ni/MgO probably play different roles in gasification that MgO decomposed lignin to reactive intermediates and nickel promoted reaction between intermediates and water to form gases. The yield of methane and carbon dioxide increased with increasing water density but then decreased and leveled out to constant values, which indicates that water density affected the reaction kinetics.

Composition of Products from the Supercritical Water Gasification of Glucose: A Model Biomass Compound

Glucose, as a representative biomass model compound, was gasified under supercritical water conditions in a batch reactor. The influences of temperature in the subcritical and supercritical regimes of water, oxidant concentration, glucose concentration, and residence time were examined in relation to the yield and composition of the product gases and oils. The product gases were analyzed by packed-column gas chromatography, and the oils were extracted using solid-phase extraction and analyzed by coupled gas chromatography/mass spectrometry. The main gases produced were carbon dioxide, carbon monoxide, methane, and hydrogen, and there was significant production of oil and char. As the temperature was increased, there was an increase in the yield of gas; similarly, gas yield also increased as the concentration of the oxidant, hydrogen peroxide, was increased. The influence of residence time on the yield of products was small, with a slight decrease in oil yield and an increase in char yield. The oils were composed of a range of oxygenated compounds, including cyclopentanone, methoxybenzene, acetic acid, furfural, acetophenone, phenol, benzoic acid, and their alkylated derivatives. A reaction mechanism is proposed that describes a possible reaction route for the formation of the characteristic compounds found in the oils.

Hydrogen production by biomass gasification in supercritical water: A parametric study

Hydrogen production by biomass gasification in supercritical water is a promising technology for utilizing high moisture content biomass, but reactor plugging is a critical problem when feedstocks with high biomass content are gasified. The objective of this paper is to prevent the plugging problem by studying the effects of the various parameters on biomass gasification in supercritical water. These parameters include pressure, temperature, residence time, reactor geometrical configuration, reactor types, heating rate, reactor wall properties, biomass types, biomass particle size, catalysts and solution concentration. Biomass model compounds (glucose, cellulose) and real biomass are used in this work. All the biomasses have been successfully gasified and the product gas is composed of hydrogen, carbon dioxide, methane, carbon monoxide and a small amount of ethane and ethylene. The results show that the gas yield of biomass gasification in supercritical water is sensitive to some of the parameters and the ways of reducing reactor plugging are obtained.

Effect of Chemical Property of Waste Biomass on Air-Steam Gasification

Air-steam gasification of waste biomass was performed using a downdraft-fixed gasifier at atmospheric pressure and 1173K. The effect of a chemical property of waste biomass feedstock on the product distribution and product gas composition was statistically investigated. Twelve types of waste biomass and three types of model compounds of woody biomass were employed as feedstock. Gas, water soluble compound, water insoluble-acetone soluble compound, acetone insoluble compound, and char were obtained as products. Regardless of the variety of feedstock, the volatile matter content was the factor affecting the distribution to gas and product gas composition. The distribution to gas, i.e., the conversion to gas on a carbon basis, increased from 52.8 to 97.9C-mol% with an increase in the volatile matter content in the feedstock. The distributions to the water soluble compound, water insoluble-acetone soluble compound, and acetone insoluble compound were independent of the chemical property, and would be affected by the nitrogen and ash contents in the feedstock. The main product gas was H2 (20-35mol%), CO (15-30mol%), CO2 (20-35mol%), and CH4 (5-10mol%). When the volatile matter content was more than 70wt%, the molar ratio of H2 to CO in the product gas (H2/CO) decreased with an increase in the volatile matter content, while the molar ratio of H2 to CO2 (H2/CO2) was approximately unity and independent of the chemical property.In waste biomass with a volatile matter content of 70-80wt%, syngas with the desired H2/CO ratio for methanol synthesis was obtained. In waste biomass with a volatile matter content of more than 80wt%, syngas with the desired H2/CO ratio for dimethyl ether (DME) synthesis was obtained.