Hydrothermal conversion of glucose in multiscale batch processes. Analysis of the gas,liquid and solid residues

Hydrothermal conversion is an interesting process to transform (very) humid biomass into high energy vectors or valuable products in the liquid or solid state. In the supercritical domain, water becomes a solvent for organics as well as a reactant, and thus the cellulosic content is effectively hydrolyzed into glucose, largely considered as its model molecule.The kinetics of glucose decomposition during the heating step in the batch reactor were investigated through the analysis of glucose concentration. Glucose reacts totally before reaching the supercritical point of water. Among the operating parameters that influence supercritical water gasification, this paper presents only the effect of reaction temperature through gas composition, liquid carbon content and structure of the solid. Glucose gasification in a batch process (5 wt% glucose, 0.5 wt% catalyst, 600 °C, 25 MPa, 60 min) produced 1.5 mol of hydrogen per mol of glucose. The gas has energetic properties (H₂, CH₄, C₂H₆) while the liquid contains substances that could be used as platform molecules (5-HMF). The solid phase is composed of carbon (almost pure) in two distinct phases: spherical nanoparticles and an amorphous phase.     

Hydrogen-gas production with Citrobacter intermedim and Clostridium pasteurianum

Citrobacter intermedius and Clostridium pasteurianum were grown in 14-dm³ batch reactors on glucose and measured for biomass and H2 production. Gas production with C. intermedius was found to be growth related, whereas that with C. pasteurianum was entirely produced during the stationary phase of growth. The maximum yield and productivity of H₂ with C. intermedius was 60% H₂ or 1 mol of H₂ mol^?1 of glucose at a maximum of 3.7 mmol of H₂ h^?1 and 85% H₂ or 1.5 mol of Ha mol^?1 of glucose at a maximum of 9.0 mmol of H₂ h^?1 with C. pasteurianum. The overall H₂ productivity (QH₂) was 2.5 mmol of H₂ h^?1 g^?1 dry biomass for C. pasteurianum at a glucose concentration of 7.6 g dm^?3. As the glucose concentration was increased from 7.6 to 15.4 g dm^?3, up to 44% of the gas produced with C. pasteurianum was growth associated. The remainder of the gas was produced in the stationary phase. In this case the overall Ha productivity (QH₂) was 1.2 mmol of H₂ h^?1 g^?1 dry biomass. The comparative experiments indicate that maximum yields and rates of H₂ production were achieved with C. pasteurianum.     

Cultivation of spirulina maxima in an annular photochemical reactor

An 8-L annular photochemical reactor has been designed and built for the cultivation of micro- or semi-microalgae at the laboratory scale. It may be operated in batch or continuous mode and is controlled for pH, temperature, gas mixture ratio (CO₂ and air), flow rate, light intensity and also illumination type (daylight or plant growth light) and mode (continuous or intermittent). It behaves as a perfect mixed reactor for all concentrations of algal cells. The reactor was used for the cultivation of the blue-green alga Spirulina maxima in a synthetic medium in both batch and continuous operations. At the dilution rate of 0.24 day^?1, the optimal productivity was 0.91 g/L-day for biomass or 0.55 g/L-day for protein. This is equivalent to 14.5 g/m²-day for biomass or 8.7 g/m²-day for protein. The optimal productivity as well as the chemical composition of the algal biomass were comparable to results obtained from pilot plant studies and reported in the current literature.     

N2O‐Vermeidung bei der Behandlung hoch stickstoffreicher Abwässer

In comparison to a single‐stage deammonification system, large differences of N₂O emissions in double stage treatment with nitrification have been documented. Experiences are presented from pilot‐scale nitrification plants employing continuous feeding and clarification as well as sequencing‐batch reactor systems. During treatment of digestion centrate with high NH₄‐N concentrations, nitrous oxide gas was identified in reactors and exhaust gases. With similar NH₄ reduction, the results revealed an order of a magnitude lower N₂O emissions during wastewater treatment in a single‐stage deammonification system.     

Biomass gasification in supercritical water: Part 1. Effect of the nature of biomass

In this study, biomass feedstocks, including lignocellulosic materials and the tannery wastes, were gasified in supercritical water. Gasification experiments were performed in a batch autoclave at 500 °C. The amount of gases, the gas compositions and the amount of water soluble compounds from gasification were determined. The hydrogen yields ranging between 4.05 and 4.65 mol H₂/kg biomass have been obtained. The results showed that the yields and composition of gases depend also on the organic materials other than cellulose and lignin in lignocellulosic material. In addition to this, it was concluded that the kind of lignin may also have an effect on gasification products. In the case of tannery wastes, the type of tannen agent used in leather production considerably effected the gasification results.     

The removal of hydrogen sulfide with manganic sorbent in a high-temperature fluidized-bed reactor

The removal of hydrogen sulfide (H₂S) from simulated gas was carried out in a batch type fluidized-bed reactor using natural manganese ore (NMO), which consists of several metal oxides (MnO_x: 51.85%, FeO_y: 3.86%, CaO: 0.11%). The H₂S breakthrough curves were obtained by changing temperature, gas velocity, initial H₂S concentration, and aspect ratio. Moreover, the effects of the particle size and the particle-mixing fraction on H₂S removal were investigated in a binary system of different particle size. From this study, H₂S removal efficiency increased with increasing temperature but decreased with increasing excess gas velocity. The breakthrough time for H₂S decreased as the gas velocity increased, which leads to reducing gas-solid contacting due to gas bypassing in a fluidized bed reactor. Improvement of H₂S removal efficiency in continuous process can be expected from the results of the binary particle system with different size in a batch experiment. The NMO could be considered as a potential sorbent in H₂S removal.     

Co-gasification of woody biomass and coal with air and steam

The co-gasification of woody biomass and coal with air and steam was carried out in order to supply syngas for the synthesis of liquid fuels from the biomass with coal. The experiment was performed using a downdraft fixed bed gasifier at 1173 K. The effect of the feedstock with a varying content of woody biomass and coal on the co-gasification behavior was studied by varying the biomass ratio from 0 to 1; this ratio is the woody biomass content in the total feedstock on a carbon basis. The conversion to gas on a carbon basis increased with an increase in the biomass ratio, whereas the conversions to char and tar decreased. With an increase in the biomass ratio, the H₂ composition decreased and the CO₂ compositions increased. However, the CO composition was independent of the biomass ratio. A low biomass ratio led to the production of a gas favorable for methanol and hydrocarbon fuel synthesis, and a high biomass ratio led to the production of a gas favorable for DME synthesis. The synergy due to the mixture of woody biomass and coal might be observed in the extent of the water–gas shift reaction. The co-gasification conditions in the study provided a cold gas efficiency ranging from 65% to 85%.     

Hydrogen production from biomass: The behavior of impurities over a CO shift unit and a biodiesel scrubber used as a gas treatment stage

Most of the hydrogen produced is derived from fossil fuels. Bioenergy2020+ and TU Wien have been working on hydrogen production from biomass since 2009. A pilot plant for hydrogen production from lignocellulosic feedstock was installed onsite using a fluidized bed biomass gasifier in Güssing, Austria. In this work, the behavior of impurities over the gas conditioning stage was investigated. Stable CO conversion and hydration of sulfur components could be observed. Ammonia, benzene, toluene, xylene (BTX) and sulfur reduction could be measured after the biodiesel scrubber. The results show the possibility of using a commercial Fe/Cr-based CO shift catalyst in impurity-rich gas applications. In addition to hydrogen production, the gas treatment setup seems to also be a promising method for adjusting the H₂ to CO ratio for synthesis gas applications.     

Hydrothermal gasification of glucose using Raney nickel and homogeneous organometallic catalysts

Catalytic gasification of biomass to fuel gaseous in sub and super critical water is a promising method for production of sustainable energy. In this paper, a microreactor has been utilized to study the hydrothermal gasification of glucose in the presence of transition metal chelates consisting of nickel(II) acetylacetonate (Ni(acac)₂), cobalt(II) acetylacetonate (Co(acac)₂), iron(III) acetylacetonate (Fe(acac)₃) and Raney-nickel particles. The reaction temperature and pressure were 310–350 °C and 100–210 bar, respectively. Effects of addition of catalysts, reaction temperature, reaction time, glucose concentration and liquid water volume fraction on the amount of the generated gas as well as its composition were investigated. Results indicated that the presence of the organometallic compounds can slightly facilitate the rate of decomposition of glucose. This enhancement in reaction rate was more pronounced at higher concentrations of the feed (~ 0.65 M) compared with lower concentrations (~ 0.06 M). In contrast to these homogeneous catalysts, Raney-nickel catalyst improved the gas yield by a factor of 3 to 5. It has been observed that the amount of the produced gas almost doubles when the batch time increased from 3 to 30 min, while no significant change was observed from 30 to 60 min. Finally, remarks on optimization of the amount of added water into the reaction vessel are provided.     

Microbial treatment of sour gases for the removal and oxidation of hydrogen sulphide

It has been demonstrated that the bacterium Thiobacillus denitrificans may be readily cultured aerobically and anaerobically in batch and continuous cultures on hydrogen sulphide (H₂S) gas under sulphide-limiting conditions. Under these conditions sulphide concentrations in the culture medium were less than 1 μM resulting in very low concentrations of H₂S in the reactor outlet gas. The stoichiometries of both the aerobic and anaerobic reactions were determined and stable reactor operation demonstrated for up to five months. Maximum loading of the biomass was determined to be 5.4–7.6 mmoles H₂S/h-g biomass under anaerobic conditions and 15.1–20.9 mmoles H₂S/h-g biomass under aerobic conditions. Indicators of reactor upset were determined and recovery from upset demonstrated. Heterotrophic contamination was shown to have negligible effect on reactor performance with respect to hydrogen sulphide oxidation. In fact, growth of T. denitrificans in the presence of floc-forming heterotrophs produced a hydrogen sulphide active floc with excellent settling characteristics. A case study of the application of this technology to the removal and oxidation of H₂S from biogas is presented.     

Partial nitrification of sludge reject water using suspended and granular biomass

BACKGROUND: Partial nitrification–Anammox is a combined promising advanced biological process for the removal of nitrogen from wastewater, which allows important savings in energy consumption, sludge production, and organic carbon. Granular biomass appears to be an interesting alternative to conventional activated sludge, mainly because of its better settling properties. This study deals with the experimental results of a comparison between a conventional and a granular sequencing batch reactor (SBR) for the partial nitrification of reject water. RESULTS: After some days of operation, 30 days in the conventional SBR (system A) and 100 days in the granular SBR (system B), partial nitrification was achieved. Granular sludge showed much better settling properties than suspended biomass, with values of sludge volumetric index (SVI₁₀) of 130 mL g^?1 in system A and 38 mL g^?1 in system B. Consequently, the solids concentration within the granular reactor was three times higher than for the conventional system while the concentration of solids in the effluent was 10 times higher in the conventional SBR. Morphology, microstructure and microbial populations in both systems were also studied. CONCLUSION: A partial nitrification process was successfully achieved in both systems, obtaining an effluent with a NO₂^?‐N/NH₄⁺‐N ratio near 1, suitable for a following Anammox process. Granular biomass, mostly formed by round particles, showed better settling properties, leading to better sludge–effluent separation as well as higher biomass retention in the reactor. The granulation process does not affect bacterial populations, since they were the same in both systems. Copyright © 2011 Society of Chemical Industry     

Direct Biomass Fuel Cell (BMFC) with Anode/Catalyst Comprising a Nanocomposite of a Mesoporous n-Semiconductor Film and a Metal Thin Layer: A New Concept of Catalyst Design

Abstract  

We designed an efficient direct biomass fuel cell (BMFC) anode and prepared a nanocomposite [base electrode/mesoporous n-semiconductor (SC) thin film/metal thin layer]. A Pt thin layer was photodeposited onto a mesoporous 20-μm thick TiO₂ thin film having a roughness factor of 2000, which was coated on an F-doped tin oxide/glass base electrode (FTO). This anode/catalyst nanocomposite was efficient at decomposing aqueous solutions of glucose and other biomass-related compounds in combination with an O₂-reducing cathode the other side of which was exposed to ambient air. The nanocomposite exhibited sharp optimum conditions at the atomic ratio of Pt/Ti = 0.33 in the BMFC, generating high electrical power of 2 mW cm⁻² without any light irradiation or bias potential when using a 1 M glucose aqueous solution. This output power is 20 times as large as that generated by a mesoporous TiO₂ film anode under UV-light (18 mW cm⁻²) irradiation. At this ratio, the coated Pt specifically exhibited metallic luster, and its average Pt thickness on the mesoporous TiO₂ nanostructure was calculated to be 0.40 nm. The high BMFC activity was interpreted by the simultaneous Schottky-junction/Ohmic contact nature of the nanocomposite. Other biomass compounds such as sucrose, ethanol and polysaccharides were also effective as direct fuels for the BMFC. Immediately after soaking this composite anode without a cathode in a glucose aqueous solution, continuous evolution of H₂ bubbles was observed from the anode surface. The electrical power generation and H₂ production are easily changed by connecting and disconnecting a cathode, respectively. Based on a simple design and calculation, the present system with glucose fuel has the potential to construct a module stack of 2 kW m⁻³. Simultaneous material/energy circulation by using the BMFC with biomass and its waste fuel is proposed for application in future social systems.     

Oxidation of low concentrations of hydrogen sulphide: Process optimization and kinetic studies

Low concentrations (e.g. < 3) of H₂ S in natural gas can be selectively oxidized over an “granular Hydrodarco” activated carbon catalyst to elemental sulphur, water and a small fraction of by-product sulphur dioxide, SO₂. To optimize the H₂ S catalytic oxidation process, the process was conducted in the temperature range 125—200 °C, at pressures 230—3200 kPa, with the O/H₂ S ratio being varied from 1.05 to 1.20 and using different types of sour and acid gases as feed. The optimum temperature was determined to be approximately 175 °C for high H₂ S conversion and low SO₂ production with an O/H₂ S ratio 1.05 times the stoichiometric ratio. The life of the activated carbon catalyst has been extended by removing heavy hydrocarbons from the feed gas. The process has been performed at elevated pressures to increase H₂ S conversion, to maintain it for a longer period and to minimize SO₂ production. The process is not impeded by water vapour up to 10 mol% in the feed gas containing low concentrations of CO₂ (< 1.0). A decrease in H₂ S conversion and an increase in SO₂ production were obtained with an increase in water vapour in the feed gas containing a high percentage of CO₂. The process works well with “sour natural gas” containing approximately 1% H₂ S and with “acid gas” containing both H₂ S and CO₂. It gives somewhat higher H₂ S conversion and low SO₂ production with feed gas containing low concentrations of CO₂. A kinetics study to determine the rate-controlling step for the H₂ S catalytic oxidation reaction over “granular Hydrodarco” activated carbon has been conducted. It was concluded that either adsorption of O₂ or H₂ S from the bulk phase onto the catalyst surface is the rate-controlling step of the H₂ S catalytic oxidation reaction.     

Water Gas Shift in Microreactors at Elevated Pressure: Platinum-Based Catalyst Systems and Pressure Effects

A new lab-scale microstructured reactor was used for investigations on enhancing the H₂/CO ratio in synthesis gas from biomass feedstocks via the water gas shift reaction. A model mixture of carbon monoxide, carbon dioxide, water, and hydrogen was used to reproduce the typical synthesis gas composition from dry biomass gasification. Catalyst layers were prepared and characterized; a combined incipient wetness impregnation and sol–gel technology was applied. The catalytic activities of Pt/CeO₂ and Pt/CeO₂/Al₂O₃ films were determined at temperatures of 400–600 °C and pressures of up to 45 bars. Increased pressure leads to higher values of CO conversion and to increased formation of hydrocarbons (CH₄, C₂H₆, etc.) and coke. Methane is the main by-product, and coke formation was attributed to the catalytic activity of peripheral reactor components.     

H2 rich product gas by steam gasification of biomass with in situ CO2 absorption in a dual fluidized bed system of 8 MW fuel input

The steam gasification of solid biomass by means of the absorption enhanced reforming process (AER process) yields a high quality product gas with increased hydrogen content. The product gas can be used for a wide range of applications which covers the conventional combined heat and power production as well as the operation of fuel cells, the conversion into liquid fuels or the generation of synthetic natural gas and hydrogen. On the basis of a dual fluidized bed system, steam gasification of biomass is coupled with in situ CO₂ absorption to enhance the formation of hydrogen. The reactive bed material (limestone) used in the dual fluidized bed system realizes the continuous CO₂ removal by cyclic carbonation of CaO and calcination of CaCO₃. Biomass gasification with in situ CO₂ absorption has been substantially proven in pilot plant scale of 100 kW fuel input. The present paper outlines the basic principles of steam gasification combined with the AER process the investigations in reactive bed materials, and concentrates further on the first time application of the AER process on industrial scale. The first time application has been carried out within an experimental campaign at a combined heat and power plant of 8 MW fuel input. The results are outlined with regard to the process conditions and achieved product gas composition. Furthermore, the results are compared with standard steam gasification of biomass as well as with application of absorption enhanced reforming process at pilot plant scale.     

Pure H2 production through hollow fiber hydrogen‐selective MFI zeolite membranes using steam as sweep gas

Hollow fiber MFI zeolite membranes were modified by catalytic cracking deposition of methyldiethoxysilane to enhance their H₂/CO₂ separation performance and further used in high temperature water gas shift membrane reactor. Steam was used as the sweep gas in the MR for the production of pure H₂. Extensive investigations were conducted on MR performance by variations of temperature, feed pressure, sweep steam flow rate, and steam‐to‐CO ratio. CO conversion was obviously enhanced in the MR as compared with conventional packed‐bed reactor (PBR) due to the coupled effects of H₂ removal as well as counter‐diffusion of sweep steam. Significant increment in CO conversion for MR vs. PBR was obtained at relatively low temperature and steam‐to‐CO ratio. A high H₂ permeate purity of 98.2% could be achieved in the MR swept by steam. Moreover, the MR exhibited an excellent long‐term operating stability for 100 h in despite of the membrane quality. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3459–3469, 2015     

Statistical optimization of fermentation conditions for the improved production of poly-β-hydroxybutyrate from Bacillus subtilis

Poly-β-hydroxybutyrate (PHB) has been an effective biodegradable plastic obtained by microbial fermentation. Batch fermentation of Bacillus subtilis features an attractive system for the production of PHB. Identification of appropriate media components and cultivation conditions are extremely important for the optimal production of biomass and/or PHB production. Statistical media design was utilized for the optimization of different fermentation variables (glucose, peptone, sodium chloride, K₂HPO₄, KH₂PO₄, ammonium sulfate, ammonium chloride, sodium sulfate, temperature, inoculum size, and pH). The optimized media predicted the optimal dry cell weight of 7.54?g?L^?1 and PHB production of 77.2?mg?L^?1 at 1?g?L^?1 of peptone, 1.46?g?L^?1 sodium sulfate, and pH 6.8 in 24?h. Glucose utilization, batch growth, and PHB production kinetics of B. subtilis were determined experimentally. The effect of substrate inhibition on specific growth rate was also determined experimentally for B. subtilis. The values of kinetic and substrate inhibition parameters obtained from this study shall be utilized to develop a mathematical model for PHB production for further improving the production of PHB.     

Gasification of Microalgae Using Supercritical Water and the Potential of Effluent Recycling

The gasification of microalgae in supercritical water was investigated in this work. The product gas contained mainly H₂, CO₂, CH₄, and C₂H₆. Operation at high temperatures and lower biomass concentrations resulted in the highest carbon gasification efficiency and the lowest total organic carbon levels in the residual water. Due to its content of inorganic nutrients, the residual water was applied as cultivation medium for microalgae. However, algal growth in the untreated residual water was inhibited by the existence of potentially toxic substances evolved from gasification. Upon treatment by activated carbon filtration and ultraviolet light degradation, these substances were eliminated and cultivation in the residual water was possible. The major fraction of inorganic residues from gasification was recovered by means of water purging, increasing the potential of nutrient recycling for cultivation.     

Hydrodenitrogenation of Quinoline Over a Dispersed Molybdenium Catalyst Using in situ Hydrogen

Hydrodenitrogenation (HDN) of quinoline using a Mo-based dispersed catalyst was studied in a batch reactor using H₂ generated in situ via the water gas shift reaction. In situ H₂ was found to be more active for HDN than externally supplied H₂. Both water and H₂S have an effect on HDN.     

Performance of yttria-stabilized zirconia fuel cell using H2–CO2 gas system and CO–O2 gas system

This paper reports the performance of an yttria-stabilized zirconia fuel cell (YSZ) using five kinds of gas systems. The final target of this research is to establish the combined fuel cell systems which can produce a H₂ fuel and circulate CO₂ gas in the production process of electric power. A large electric power was measured in the H₂–O₂ gas system and the CO–O₂ gas system at 1073 K. The formation process of O²⁻ ions in the endothermic cathodic reaction (1/2O₂+2e⁻→O²⁻) controlled the cell performance in both the gas systems. The electric power of the H₂–CO₂ gas system, which allowed to change CO₂ gas into a CO fuel (H₂+CO₂→H₂O+CO) in the cathode, was 1/31–1/11 of the maximum electric power for the H₂–O₂ gas system. This result is related to the larger endothermic energy for the formation of O²⁻ ions from CO₂ molecules at the cathode (CO₂+2e⁻→CO+O²⁻) than from O₂ molecules. The CO–H₂O gas system and the H₂–H₂O gas system was expected to produce a H₂ fuel in the cathode (CO+H₂O→H₂+CO₂, H₂+H₂O→H₂+H₂O). Although relatively high OCV values (open circuit voltage) were measured in these gas systems, no electric power was measured. At this moment, it was difficult to apply H₂O vapor as an oxidant to the cathodic reaction in a YSZ fuel cell.