In this work, the treatment of highly saline wastewaters simulating the effluent of the SCWG process was investigated for the first time using a combined process of electrocoagulation (EC) and electrochemical oxidation (EO) in a single set-up. First, EC with different metal electrodes (e.g. Fe, Al, SS) as anode was applied to synthetic wastewater and the effect of operating parameters, such as current density, electrolysis time and pH, on the process performance was systematically studied. Experimental design, statistical analysis and model optimization were carried out to determine the optimum experimental conditions that maximize the removal of lead ions while minimizing energy consumption. According to the results, EC was very effective in the removal of Pb2+ as 93 % was achieved under specific conditions (10 mA/cm2, 9 min, pH 10), while the energy consumption was relatively low at 0.88 kWh/m3 of treated wastewater. Furthermore, this work provides a performance evaluation of the integrated EC/EO process for the treatment of synthetic or real SCWG brines. EC/EO with two electrode pairs (Fe/Fe and BDD/SS) connected in parallel can achieve complete Pb2+ removal at high flow rates (175 ml/ min), corresponding to short electrolysis times (9 min), when treating a synthetic SCWG brine, and also performs very well under realistic conditions. In the case of real industrial wastewater, high removal rates of organic and inorganic substances; i.e., approx. 60 % PhOH, 40 % TOC, 75 % Pb2+, 75 % Ni2+, can be achieved after 132 min of electrolysis with 64 mA/cm2, which demonstrates the very high efficiency of the EC/EO.

A novel reactor concept for supercritical water gasification was developed where cold biomass is mixed with supercritical water for heating. This approach enhanced the gasification efficiency and reduced solid deposition. Following proof of concept over 100 h, a parametric study was conducted, varying biomass type, dry matter content (1.3-8.2 wt %), temperature (550-700 °C), pressure (240-300 bar), potassium addition (0-3750 ppm), and residence time (0-42 s). Results showed that biomass type, pressure, and potassium addition had a minimal impact on the process. Higher biomass concentration reduced carbon efficiency (CE) but maintained levels around 80%. Increasing the residence time at the reaction temperature significantly improved CE up to 8 s at 650 °C (τ = 0 s, CE = 27%; τ = 8 s, CE = 72%), beyond which gains plateaued. Temperature strongly influenced CE (T = 550 °C, CE = 58%; T = 700 °C, CE = 91%) and gas composition, with higher temperatures reducing organic carbon and tar formation but increasing methane (T = 550 °C, 9.5 vol % CH4; T = 700 °C, 15.9 vol % CH4) and C2+ (T = 550 °C, 2.3 vol % C2+; T = 700 °C, 5.1 vol % C2+) contents. Deviations in gas composition from equilibrium calculations, conducted with ASPEN HYSYS, suggest insufficient steam reforming, potentially addressable with a nickel catalyst. An empirical multilinear regression model was developed, accurately predicting outcomes for studied biomasses and reducing experimental effort for process optimization. Overall, the study demonstrates the reactor concept's superior performance and provides a strong foundation for further developing and optimizing supercritical water gasification processes that could potentially be applied to other feedstocks.

The integration of "biomass gasification with supercritical water ", "steam reforming of hydrocarbons", and "water-gas shift reaction" is a promising process concept for the conversion of moist biomass to "green hydrogen". This process concept was investigated in this work, considering ethanol as a biomass model compound. The gasification of ethanol with supercritical water can be accurately simulated, allowing a very good prediction of the gaseous product that will undergo steam reforming. A multidisciplinary study is presented, in which a comprehensive kinetic model for steam reforming of the gasification product gas was developed and validated with experimental data and then employed in a simulation of the whole process chain. Finally, a techno-economic and sensitivity analysis was applied. In the kinetic model, the high steam content overshadowed the influence of other substances in the sites balance on the catalyst surface, except for methane. After investigating the effect of ethanol concentration and feed flow rate, and considering the technical constraints imposed by the high organic matter content and the availability of actual waste biomass, the optimal values of the ethanol concentration and feed flow rate were 50 t h(-1) and 15 wt % ethanol, reaching a hydrogen break-even price of 6.8 $ kg(H2) (-1). The sensitivity analysis identified the ethanol price as the primary cost driver. Exploring waste biomass feedstocks, such as sewage sludge, demonstrated potential break-even prices as low as 0-1.8 $ kg(H2)( -1), which can compete with conventional technologies.

Soil and groundwater contaminated with heavy metals pose a threat to animals and humans. The use of plants by phytoremediation can help to free the soil and groundwater from the pollutants, but these plants will then become contaminated themselves. The aim of the present work is the energetic utilization of contaminated biomass and the separation of contaminants e.g. heavy metals. This is achieved by gasification of the contaminated biomass under conditions of supercritical water in a continuous laboratory plant. The separation of heavy metal contaminants like zinc, manganese or iron by process-integrated salt separation is necessary to avoid secondary contamination. Reed Canary Grass, Napier Grass and grapevine plants were gasified. Plant type had no effect on gasification efficiency or heavy metal removal. A mean carbon gasification efficiency of 58.3 % was achieved. In all cases, the reactor effluent was free of heavy metal contamination. The general ability to separate salts and heavy metals by salt separation was demonstrated (up to 35 % of heavy metal species detected in the salt brine). The separation is strongly dependent on the preheating temperature (increase in separation of salts when increasing preheating temperature from 460 to 550 C) and needs to be further improved to avoid the formation of solid deposits in the reaction system. Excessive solid deposition, consisting of coke, salts and corrosion products, limited the experimental duration.

It is important to know the limitations of the supercritical water gasification (SCWG) in terms of behavior of different biomasses, especially when determining whether SCWG is a suitable conversion process for a certain biomass. Ten different biomasses (eight different plant species, of which two were grown in two different sites) were processed to evaluate this aspect. Moist and dry, woody and grassy biomasses were gasified in the same experimental setup under similar conditions. Only small differences could be seen in the gasification experiments. The carbon gasification efficiency was 60.3 ± 5.1 %, the gas compositions were very similar. Solid deposits formed in all experiments in the same temperature zone of the reactor containing coke, salt building elements and heavy metals, sometimes leading to plugging. Nevertheless, an experimental duration of 6 h could be achieved for the dry biomasses. The experiment with the moist biomass Reed Canary Grass was ended early due to plugging of the feed tubing which is due to the different size reduction procedure for moist biomasses resulting in bigger biomass particles. This emphasizes the importance of sufficient size reduction prior to the experiment. Potassium addition as a homogeneous catalyst, in form of potassium hydroxide, has proven to be beneficial regarding gasification efficiency, but poses a threat regarding plugging due to salt deposits in the system.

The formation of solid deposits in the process of supercritical water gasification (SCWG) is one of the main problems hindering the commercial application of the process. Seven experiments were conducted with the grass Reed Canary Grass with different preheating temperatures, but all ended early due to the formation of solid deposits (maximum operation of 3.8 h). The position of solid deposits in the lab plant changed with the variation in the temperature profile. Since the formation of solid deposits consisting of salts, coke, and corrosion products is a severe issue that needs to be resolved in order to enable long-time operation, inner temperature measurements were conducted to determine the temperature range that corresponds with the zone of solid formation. The temperature range was found to be 400 to 440 °C. Wherever this temperature was first reached solid deposits occurred in the system that led to blockage of the flow. Additional to the influence of the temperature, the influence of the flow direction (up-flow or down-flow) on the operation of the continuous SCWG plant was examined. If salts are not separated from the system sufficiently, up-flow reactors should be avoided because they amplify the accumulation of solid deposits leading to a shortened operation time. The heating concept coupled with the salt separation needs to be redesigned in order to separate the salts before entering the gasification reactors. Outside of the determined temperature zone no deposition was visible. Thus, even though the gasification efficiency was low it could be shown that the operation was limited to the deposits forming in the heating section and not by incomplete gasification in the reactor where T > 600 °C.

For the first time, syngas fermentation was operated continuously with total cell retention and process pressures up to 4 barg in long-term runs of up to 3000 hours. Throughout this time, the process was stable. The measured data have shown that hydrogen uptake and ethanol space-time yield are highest at a slightly reduced pH of 5.7 compared to pH 5.9. Even lower pH values lead to higher acetic acid to ethanol product ratios, while C2 space-time yields remain constant. Increasing the hydrogen partial pressure to 1.52 bar resulted in a significant increase in hydrogen uptake rate and ethanol formation. An ethanol space-time yield of 10mmolL-1h-1 was short-term achieved, being the highest space-time yield measured to date for the wild type of C. ljungdahlii. Hydrogen uptake above a theoretical equilibrium concentration of 1.2mmolH2L-1 is significantly reduced, indicating an inhibition of an enzymatic reaction.

A continuous process for producing hydrogen from the gasification of ethanol with supercritical water (SCWG) is investigated, which involves a fixed bed steam methane reforming (SMR) reactor downstream of the SCWG reactor. Increasing temperature and decreasing space velocity in the SMR reactor resulted in increased hydrogen concentration and methane conversion. The catalyst activity was more affected at low than high pressures, presumably due to the kinetics of the SMR reaction. The significant increase in total hydrogen yield based on ethanol in the feed showed the importance of installing the reformer after gasification. The excessive steam from the SCWG reactor helped to prevent

Supercritical water gasification (SCWG) is a process in which biomass reacts with supercritical water to produce H2 and CH4-rich gas. The water-to-biomass ratio is a crucial variable in SCWG that affects the energy efficiency of the process. Despite the clear concept, systematic studies on water consumption during the formation of gaseous products are lacking. This study aims to determine the water consumption in SCWG of organic feedstock. Ethanol was used as an organic model compound since mass balances of complex biomasses like lignocelluloses are often incomplete due to the formation of solid deposits. The ethanol concentration ranged from 1.2 to 72 wt %, and complete gasification was achieved in all cases. Water consumption decreased with an increase in ethanol concentration due to enhanced methanation reactions with increasing organics. Stoichiometric calculations and ASPEN HYSYS simulations confirmed the experimental results, showing equilibrium gas compositions in the reaction system.

The influence of process water recycling during the Supercritical Water Gasification (SCWG) of dry biomasses was investigated. Dry biomass has to be diluted with water to a dry matter content of approximately 10 wt.% to gasify it in the process of supercritical water gasification. The treatment of wastewater in the SCWG process is cost intensive due to organic contaminants; therefore, the recycling of the process effluent is attractive. Salt separation is needed to avoid accumulation of salts in the effluents, since salts enhance corrosion rates and might cause blocking of the flow when the effluent is recycled. The grass Reed Canary Grass and grapevines were gasified. The recycling of the process effluent did not influence the composition of the product gas. In both cases the carbon efficiency decreased by 4% when wastewater was used to dilute the biomass. An increase in organic carbon and potassium in the reactor effluent was observed after gasification of the biomass with recycled process effluent. The addition of potassium hydroxide to the feed as a homogenous catalyst needs to be closely monitored and adjusted according to the potassium content of the reactor effluent. Insufficient salt separation proved to be an issue regarding formation of solid deposits in the reaction system.

The gasification of biomass with supercritical water, also known as SCWG, is a sustainable method of hydrogen production. The process produces a mixture of hydrogen, carbon oxides, and hydrocarbons. Upgrading this mixture through steam or dry re-forming of hydrocarbons to create synthesis gas and then extra hydrogen is a viable way to increase hydrogen production from biomass. This literature review discusses combining these two processes and recent experimental work on catalytic SCWG of biomass and its model compounds and steam/dry reforming of produced hydrocarbons. It focuses on catalysts used in these processes and their key criteria, such as activity, selectivity towards hydrogen and methane, and ability to inhibit carbon formation and deposition. A new criterion is proposed to evaluate catalyst performance in biomass SCWG and the need for further upgrading via reforming, based on the ratio of hydrogen bound in hydrocarbons to total hydrogen produced during SCWG. The review concludes that most catalysts used in biomass SCWG trap a large proportion of hydrogen in hydrocarbons, necessitating further processing of the product stream.

Synthesis gas fermentation with anaerobic microorganisms such as Clostridium ljungdahlii enables highly selective conversion of substrate gases such as CO, CO2, and H-2 to high value intermediates like organic acids and alcohols. By using a biomass retention system with the aid of cross-flow ultrafiltration in an external circuit for biomass retention at a CSTR, we have succeeded in retaining the biocatalyst in the reactor and in increasing the cell density by more than 160% and the space-time yield of C-2 products by 46%. In addition, we found that the use of a cell retention system promoted ethanol formation and decreased the acetic acid to ethanol product ratio. Low partial pressures of CO in the exhaust gas were found to promote hydrogen uptake and ethanol formation. The space-time yield of ethanol, 8.71 mmol L-1 h(-1), is the highest yield measured to date with an unmodified strain of C. ljungdahlii.

The energetic assessment of biomass conversion processes is important for evaluating their application potential. Process energy efficiency is often evaluated based on simulation results for processes under idealized conditions. The present work uses data from a laboratory plant to perform an evaluation of the supercritical water gasification (SCWG). For this purpose, experiments were conducted with two types of feedstock, Reed Canary Grass and ethanol. Under the present lab-plant configuration, a cold gas efficiency of up to 79% could be reached, which is comparable to the gasification of biomass in fluidized-bed gasifiers or entrained-flow gasifiers. Based on the obtained data on the produced substances and their distribution, a scale up to pilot plant size was conducted. A model was derived from the available data to energetically assess different SCWG plant sizes based on real laboratory results. This model can be transferred to other feedstocks and other process designs to approximate the optimal size for the used biomass feedstock. The importance of heat recuperation in this process is described in detail based on pilot-scale data.

Phytoremediation is an emerging concept for contaminated soil restoration via the use of resilient plants that can absorb soil contaminants. The harvested contaminated biomass can be thermochemically converted to energy carriers/chemicals, linking soil decontamination with biomass-to-energy and aligning with circular economy principles. Two thermochemical conversion steps of contaminated biomass, both used for contaminated biomass treatment/exploitation, are considered: Supercritical Water Gasification and Fast Pyrolysis. For the former, the vast majority of contaminants are transferred into liquid and gaseous effluents, and thus the application of purification steps is necessary prior to further processing. In Fast Pyrolysis, contaminants are mainly retained in the solid phase, but a part appears in the liquid phase due to fine solids entrainment. Contaminants include heavy metals, particulate matter, and hydrogen sulfide. The purified streams allow the in-process re-use of water for the Super Critical Water Gasification, the sulfur-free catalytic conversion of the fuel-rich gaseous stream of the same process into liquid fuels and recovery of an exploitable bio-oil rich stream from the Fast Pyrolysis. Considering the fundamental importance of purification/decontamination to exploit the aforementioned streams in an integrated context, a review of available such technologies is conducted, and options are shortlisted. Technologies of choice include polymeric-based membrane gas absorption for desulfurization, electrooxidation/electrocoagulation for the liquid product of Supercritical Water Gasification and microfiltration via ceramic membranes for fine solids removal from the Fast Pyrolysis bio-oil. Challenges, risks, and suitable strategies to implement these options in the context of biomass-to-energy conversion are discussed and recommendations are made.

Chemie Ingenieur TechnikVolume 94, Issue 9 p. 1252-1252 Vortrag Methods of reaction and reactor engineering to adjust product ratios and increase efficiency of syngas fermentation with Clostridium ljungdahlii L. Perret, Corresponding Author L. Perret lukas.perret@kit.edu Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanyCorrespondence: L. Perret (lukas.perret@kit.edu), Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanySearch for more papers by this authorN. Boukis, N. Boukis Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanySearch for more papers by this authorJ. Sauer, J. Sauer Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanySearch for more papers by this author L. Perret, Corresponding Author L. Perret lukas.perret@kit.edu Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanyCorrespondence: L. Perret (lukas.perret@kit.edu), Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanySearch for more papers by this authorN. Boukis, N. Boukis Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanySearch for more papers by this authorJ. Sauer, J. Sauer Karlsruhe Institute of Technology (KIT), Institute of Catalysis Research and Technology (IKFT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, GermanySearch for more papers by this author First published: 25 August 2022 https://doi.org/10.1002/cite.202255034AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume94, Issue9Special Issue: (Bio)Process Engineering – a Key to Sustainable Development: ProcessNet and DECHEMA-BioTechNet Jahrestagungen 2022 together with 13th ESBES SymposiumSeptember 2022Pages 1252-1252 RelatedInformation

Gasification of organic matter under the conditions of supercritical water (T > 374 °C, p > 221 bar) is an allothermal, continuous flow process suitable to convert materials with high moisture content (<20 wt.% dry matter) into a combustible gas. The gasification of organic matter with water as a solvent offers several benefits, particularly the omission of an energy-intensive drying process. The reactions are fast, and mean residence times inside the reactor are consequently low (less than 5 min). However, there are still various challenges to be met. The combination of high temperature and pressure and the low concentration of organic matter require a robust process design. Additionally, the low value of the feed and the product predestinate the process for decentralized applications, which is a challenge for the economics of an application. The present contribution summarizes the experience gained during more than 10 years of operation of the first dedicated pilot plant for supercritical water gasification of biomass. The emphasis lies on highlighting the challenges in process design. In addition to some fundamental results gained from comparable laboratory plants, selected experimental results of the pilot plant “VERENA” (acronym for the German expression “experimental facility for the energetic exploitation of agricultural matter”) are presented.

Microalgae are among the most promising sources of sustainable, carbon-neutral biofuels for the future. They are already being used as feedstock for producing biogas, biodiesel, bioethanol and kerosene, but the associated production methods consume a great deal of energy and are rather costly. Dr. Nikolaos Boukis from the Karlsruhe Institute of Technology (KIT) is working on the development of a sophisticated, thermochemical process with an energy balance that promises to improve the situation.

Chemie Ingenieur TechnikVolume 92, Issue 9 p. 1226-1226 Poster Mikroorganismen unter Druck – Einblicke in die Synthesegasfermentation bei erhöhtem Prozessdruck I. K. Stoll, Corresponding Author I. K. Stoll ina.stoll@kit.edu Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandCorrespondence: I. K. Stoll (ina.stoll@kit.edu), Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandSearch for more papers by this authorN. Boukis, N. Boukis Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandSearch for more papers by this authorJ. Sauer, J. Sauer Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandSearch for more papers by this author I. K. Stoll, Corresponding Author I. K. Stoll ina.stoll@kit.edu Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandCorrespondence: I. K. Stoll (ina.stoll@kit.edu), Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandSearch for more papers by this authorN. Boukis, N. Boukis Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandSearch for more papers by this authorJ. Sauer, J. Sauer Karlsruher Institut für Technologie (KIT), Institut für Katalyseforschung und -technologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, DeutschlandSearch for more papers by this author First published: 28 August 2020 https://doi.org/10.1002/cite.202055321AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume92, Issue9Special Issue: 10. ProcessNet-Jahrestagung und 34. DECHEMA-Jahrestagung der Biotechnologen 2020: Processes for FutureSeptember 2020Pages 1226-1226 RelatedInformation