Biomass In Supercritical Water Research Articles

Reaction engineering for process intensification of supercritical water biomass refining

Status reports from public and private organizations make a roadmap for achieving a bioeconomy for society. Biobased industries, based on renewable materials and energy, are still in development to supporting a decentralized production that can be an alternative to the well-supported centralized petrochemical production plants. The use of pressurized water has been proposed as an environmentally compatible process to integrate the depolymerization–reaction–separation of the biomass supported processes. Supercritical water is emerging as a solvent and reaction medium capable of providing selective processes while significantly reducing the reaction time, leading to the possibility of developing compact equipment for the use in biomass decentralized production plants. The main ways of biomass upgrading in a hydrothermal medium are reviewed in this work: hydrolysis, fractionation, gasification and reaction. In the last years, a significant progress was achieved in obtaining of added value products from biomass by hydrothermal technologies. However, some challenges must still be overcome before a sustainable and efficient decentralized production is achieved.

Hydrothermal processing of fermentation residues in a continuous multistage rig – Operational challenges for liquefaction, salt separation, and catalytic gasification

Fermentation residues are a waste stream of biomethane production containing substantial amounts of organic matter, and thus representing a primary energy source which is mostly unused. For the first time this feedstock was tested for catalytic gasification in supercritical water (T ≥ 374 °C, p ≥ 22 MPa) for methane production. The processing steps include hydrothermal liquefaction, salt separation, as well as catalytic gasification over a ruthenium catalyst in supercritical water.In continuous experiments at a feed rate of 1 kg h−1 a partial liquefaction and carbonization of some of the solids was observed. Significant amounts of heavy tars were formed. Around 50% of the feed carbon remained in the rig. Furthermore, a homogeneous coke was formed, presumably originating from condensed tars. The mineralization of sulfur and its separation in the salt separator was insufficient, because most of the sulfur was still organically bound after liquefaction.Desalination was observed at a salt separator set point temperature of 450 °C and 28 MPa; however, some of the salts could not be withdrawn as a concentrated brine. At 430 °C no salt separation took place. Higher temperatures in the salt separator were found to promote tar and coke formation, resulting in conflicting process requirements for efficient biomass liquefaction and desalination. In the salt separator effluent, solid crystals identified as struvite (magnesium ammonium phosphate) were found. This is the first report of struvite formation from a supercritical water biomass conversion process and represents an important finding for producing a fertilizer from the separated salt brine.

Supercritical Water Biomass Gasification Process As a Successful Solution to Valorize Wine Distillery Wastewaters

The biomass is the whole organic matter of vegetable or animal origin. This material can be valorized in various ways: it can be used by manufacturers (lumber, paper, and biochemistry); it can be used as energy (heat, electricity, and fuel); and it can be used as food or in cosmetics. Various processes are nowadays used to valorize biomass. This work deals with the potentialities of the biomass gasification in supercritical water. The objective is to demonstrate the potentiality of this process to treat some aqueous waste from distillery to obtain a syngas with a high hydrogen yield. The bioresources of this study come from some agricultural alcohol (beet, sugar cane, and cereal) and wine-producing distilleries. Experiments have been carried out at different conversion severities, using a 100 mL batch reactor, during 0–60 min, at a pressure of 25 MPa and at temperatures between 400 and 500 °C. Complete product analyses will be presented. Particularly detailed gas analyses have been performed. The sodium a...

Characterization of a Spent Ru/C Catalyst after Gasification of Biomass in Supercritical Water

Carbon-supported ruthenium catalysts promote the gasification of aqueous organic feed with high efficiency to synthetic natural gas in supercritical water. Ruthenium metal was recently identified as the catalytically active species. [1] Occasionally deactivation is observed. To understand the deactivation, the fresh and several spent catalyst samples were investigated by RBS, ERDA, and XPS. The data revealed a massive reduction of the ruthenium concentration in toto and especially of the surface concentration. Of importance is the almost complete disappearance of the spectral features in the valance band region. Coverage of the ruthenium clusters e.g. with a thin 'carbonaceous' layer, i.e. a kind of fouling, or structural modifications of the ruthenium clusters might be the origin. Additionally, leaching of ruthenium might contribute, but is not considered a major effect, because ruthenium was never found in the liquid effluent of the reactor. The influence of additionally detected corrosion products (Ni, Cr, Fe, Ti) from the stainless steel and the titanium alloy walls seems to be small. No evidence for a deactivation by sulphur could be found.

Corrigendum: Towards Understanding the Catalytic Reforming of Biomass in Supercritical Water

In this Communication, a reaction mechanism for the gasification of ethanol in supercritical water on a carbon-supported ruthenium catalyst was proposed based on the observed oscillations in product gas flow and composition (see page 6436). The authors have now become aware of an artifact in their experimental set-up, which made them realize that the published interpretation is not sufficiently supported by their experimental data. Experiments that clarify the cause for the observed oscillations concerning the product gas are described in detail in the Supporting Information available for this Corrigendum. These experiments were performed by Marian Dreher in the authors’ research group, who made them also aware of the artifact. He was co-supervised by Jörg Wambach. The authors thank both colleagues for their valuable contribution. The authors wish to emphasize that all the information on the electronic state of the catalyst under hydrothermal and supercritical conditions, obtained from the XANES study, remains unaffected by this mistake.

Supercritical Gasification of Biomass: Thermodynamics Analysis with Gibbs Free Energy Minimization

Gasification of biomass in supercritical water is a successful technology for hydrogen production especially by using wet biomass. The whole process, from feeding to purification of hydrogen, consists of a lot of equipment, such as pumps, heat exchangers, heaters, reactors, etc. Because the main reactions take place in the gasification reactor, the gasifier is the most important equipment of the process. In this article, a thermodynamic model, including chemical equilibrium in the reactor that is based on Gibbs free energy minimization, is developed to estimate equilibrium composition for gasification of biomass in supercritical water for hydrogen production. For this analysis, we use three types of equations of state, including Peng-Robinson, statistical associating fluid theory equation of state, and a new equation of state. We consider glucose as a model of real biomass. The results of each equation of state are compared with the experimental data. The predicted results show good agreement with the experimental data and it shows that the product gases consist of hydrogen and carbon dioxide more often and methane and carbon monoxide less often. Finally, effects of temperature, pressure, and feedstock concentration are investigated on amount of hydrogen production.

Investigation of thermochemical conversion of biomass in supercritical water using a batch reactor

This study focused on gasification of biomass and a biomass model compound. Data are presented that show the presence of supercritical water enhances gasification efficiency, as it participates as both a solvent and a reactant. It is established that biomass gasification efficiencies are in the same range for all types of biomass. The thermodynamic changes of state are functions of elemental composition, not biomass species. The oxidation state of carbon atom of biomass is a key variable in determining the changes in enthalpy during both conventional combustion and supercritical water gasification. The oxidation state of the feed (together with the reaction conditions that influence the degree to which water participates as a reactant) also determines the vapor product composition.Decomposition reactions to vapor products are rapid and complete at high temperature (⩾550°C), catalytic mediation is not required. Temperature and residence time are important operating parameters for SCW gasification. Less important are the pressure of gasification (in the range of 40–67MPa) and the presence of catalyst. The vapor yield, gas composition, the carbon and hydrogen balance of SCW gasification are functions of gasification temperature, residence time and biomass load (concentration).

Hydrothermal gasification of olive mill wastewater as a biomass source in supercritical water

In this study, the hydrothermal gasification of biomass in supercritical water is investigated. The work is of peculiar value since a real biomass, olive mill wastewater (OMW), is used instead of model biomass compounds. OMW is a by-product obtained during olive oil production, which has a complex nature characterized by a high content of organic compounds and polyphenols. The high content of organics makes OMW a desirable biomass candidate as an energy source. The hydrothermal gasification experiments for OMW were conducted with five different reaction temperatures (400, 450, 500, 550 and 600 °C) and five different reaction times (30, 60, 90, 120 and 150 s), under a pressure of 25 MPa. The gaseous products are mainly composed of hydrogen, carbon dioxide, carbon monoxide and C 1–C 4 hydrocarbons, such as methane, ethane, propane and propylene. Maximum amount of the gas product obtained is 7.71 mL per mL OMW at a reaction temperature of 550 °C, with a reaction time of 30 s. The gas product composition is 9.23% for hydrogen, 34.84% for methane, 4.04% for ethane, 0.84% for propane, 0.83% for propylene, 49.34% for carbon dioxide, and 0.88% for minor components such as n-butane, i-butane, 1-butene, i-butene, t-2-butene, 1,3-butadiene and nitrogen at this reaction conditions.

Energetic analysis of gasification of aqueous biomass in supercritical water

Abstract The aim of this work is to investigate the field of gasification of aqueous biomass in supercritical water. In order to achieve this analysis, a mathematical model (based on thermodynamical equilibrium assumption) is built. This model allows not only the computation of the solid, liquid and gas phases produced in a process composed of a gasification reactor and a separator unit, but also the computation of the energy requirements or yields in these specific units. The composition of these three phases is computed in terms of fractions of CH 4 , H 2 , H 2 O, CO, CO 2 , H 2 S, NH 3 , C 6 H 5 OH, CH 3 COOH, CH 3 CHO, C (s) and minerals. The model also predicts the lower heating value of the gas leaving the process. The main problem that is encountered in the derivation of this mathematical model is the estimation of the activities of the chemical species present in the mixture as well as the enthalpy of this mixture. In this work, these evaluations are performed using Peng–Robinson equation of state. Results of the model are presented in the frame of gasification of vinasse, which is an aqueous residue from the alcohol production industry. It is shown that some specific conditions exist where it is not necessary to yield energy to the reactor to convert the incoming biomass into a gas for which the lower heating value can reach 5 MJ/kg with a gasification efficiency of 85%.

Towards Understanding the Catalytic Reforming of Biomass in Supercritical Water

A critical point: The function of a working ruthenium catalyst during the reforming of ethanol in supercritical water was studied in situ using X-ray absorption spectroscopy (see picture). The reforming of ethanol over a supported ruthenium catalyst in sub- and supercritical water is suggested to proceed by the same mechanism as steam reforming at low pressures.

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.

Supercritical water for environmental technologies

AbstractOVERVIEW: Supercritical water is a great medium in which to perform chemical reactions and to develop processes. Due to its unique thermo‐physico‐chemical properties, supercritical water is able to play the role of solvent of organic compounds and/or to react with them. These specific properties have been used since the 1990s to develop new technologies dedicated to the environment and energy.IMPACT: Supercritical water based technologies are innovative and efficient processes having a strong impact on society, the environment and the economy, and is termed a sustainable technology.APPLICATIONS: Three main applications for supercritical water technology are under development: (i) supercritical water oxidation (SCWO); (ii) supercritical water biomass gasification (SCBG); and (iii) hydrolysis of polymers in supercritical water (HPSCW) for composites/plastics recycling. In this paper some fundamentals of supercritical water are first presented to introduce the above three major developments. Then these technologies are reviewed in terms of their present and future industrial development and their impact on the environment and on energy production. Copyright © 2010 Society of Chemical Industry

Gasification of aqueous biomass in supercritical water: A thermodynamic equilibrium analysis

The aim of this work is to give insights into the gasification of aqueous biomass in supercritical water. More precisely, a mathematical model based on the thermodynamical equilibrium assumption is derived in this study. This model allows the computation of the solid, liquid and gas phases produced in a process composed of a gasification reactor and a separator. The composition of these three phases is computed in terms of fractions of CH 4, H 2, H 2O, CO, CO 2, H 2S, NH 3, C 6H 5OH, CH 3COOH, CH 3CHO, C (s) and minerals. In the reactor, this composition is computed according to the derivation of balance equations on atoms and to the derivation of equations translating chemical equilibrium between species. Because of the specific conditions prevailing in this device (above the critical point of pure water), the computation of the activity of chemical species in the reacting media is performed using Peng–Robinson equation of state. The modelling of the separator is performed using mass balances as well as equations translating physical equilibrium of species between liquid and gaseous phases. The numerical predictions of this mathematical model are compared to experimental results obtained in the case of gasification of methanol and glucose in supercritical water. The gasification of sewage sludge is also investigated in this study.

Hydrogen production and performance of nickel based catalysts synthesized using supercritical fluids for the gasification of biomass

A method for synthesizing carbon nanotube/fiber and aluminosilicate supported Ni catalysts using supercritical methanol is suggested. This one-pot synthesis method allows the metal precursor (nickel acetylacetonate) to reduce directly onto the surface of the carbon structure without the pretreatment of surface functional groups. The synthesized catalysts are confirmed to be active in the gasification of biomass in supercritical water—specifically for the production of hydrogen-rich gases. Although the synthesized catalysts can produce similar hydrogen yields (∼8mmol H2/g biomass) compared to two commercially available aluminosilicate supported Ni catalysts, the gas product ratio for producing hydrogen over methane for the synthesized catalysts was 3.5mol H2/mol CH4 compared to 1.3mol H2/mol CH4 for the commercial catalysts under the same conditions.

Economic analysis of sewage sludge gasification in supercritical water for hydrogen production

Abstract Supercritical water gasification (SCWG) is a process that is currently being developed for the gasification of biomass in supercritical water. The process principle is to make use of the changes of specific physical and chemical properties of water above the critical point. These properties allow for a nearly complete conversion of biomass into energy-rich fuel gases, namely hydrogen, methane, and carbon dioxide. The present article deals with the economic analysis of SCWG with sewage sludge as feedstock. SCWG is aimed at generating hydrogen as secondary fuel and, in addition, at serving as a method for disposing of bio-based sewage sludge waste. Based on the results of this economic analysis, the competitiveness of the process can be assessed in comparison to conventional technologies of hydrogen production. The costs of hydrogen production and revenues obtained from the disposal of sewage sludge are determined using the method of the total annual revenue requirement. Under the assumptions made, carrying charges have by far the largest share in the revenue requirement. In contrast, fuel costs are comparably small. It is found that supercritical gasification may well be competitive due to the revenues associated with the disposal of sewage sludge as a waste product. To study the influence of the assumptions made in the economic analysis on the final results, a sensitivity analysis is made.

Current and Foreseeable Applications of Supercritical Water for Energy and the Environment

It is crucial to develop economical and energy-efficient processes for the sustainable transformation of biomass into fuels and chemicals. In this context, supercritical water biomass valorization (SCBV) processes are an alternative way to produce biogas, biofuels, and valuable chemicals. Supercritical water technology has seen much progress over the last fifteen years and an industrial application has merged: the supercritical water oxidation of wastes. The evolution from lab-scale to pilot-scale facilities has provided data on reaction mechanisms, kinetics, modeling, and reactor technology as well as an important know-how, which can now be exploited to use the reactivity in supercritical water to transform biomass into gases (CO, H(2), CO(2), CH(4), and N(2)) or into liquids (liquid fuel and valuable chemicals) with the supercritical water biomass gasification and liquefaction processes, respectively. This Review highlights the potential of SCBV processes to transform biomass into gas and liquid energy sources and highlights the developments that are still necessary to push this technology onto the market.

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.

Exergetic efficiency and options for improving sewage sludge gasification in supercritical water

The present article deals with an exergy analysis of a process under development for the gasification of biomass in supercritical water (supercritical water gasification, SCWG). This process is aimed at generating hydrogen out of the biogenic feedstock sewage sludge. The principle of the process is based on making use of the modifications of specific physical and chemical properties of water above the critical point (T=374°C, p=221 bar). These properties allow for a nearly complete conversion of the organic substance contained in the feed material into energy-rich fuel gases, containing hydrogen, carbon dioxide and methane. Based on a steady-state model of the process, exergy flow rates are calculated for all components and a detailed exergy analysis is performed. From the exergetic variables, options to improve the individual plant components as well as the overall plant are derived. The components with the highest proportion of exergy destruction in the complete process are identified and possibilities of improving them and the complete system in order to increase the overall efficiency are demonstrated. The combustion chamber necessary for heat supply is found to be the component with the highest proportion of exergy destruction of the complete plant. Moreover, the components of air preheater, reactor contribute significantly to the exergy destruction of the complete system. Copyright © 2006 John Wiley & Sons, Ltd.

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.

Influence of Process Variables on Gasification of Corn Silage in Supercritical Water

Gasification of 5 wt % (DOM) corn silage in supercritical water was investigated in a continuous flow reactor. The influence of pressure, temperature, and residence time on the gas yield was determined. Changing the pressure in the range 250−400 bar did not alter the gas yield. The temperature was varied from 300 to 700 °C. At higher temperature, the conversion of biomass in supercritical water was completed. At lower temperature, the biomass is partly converted, and the gas yield is decreased. Residence time variations from 0.6 to 10 min revealed for each investigated temperature that with longer residence time, gas yield increased until a maximum was reached. Gas composition changed with residence time and temperature. At higher temperature, more hydrogen, methane, and ethane were obtained. The gas yield can be modeled in the studied conditions by assuming a zero-order kinetic.