Agricultural biomass residues represent an abundant and underutilized resource for the production of biogenic silica. However, the combined influence of feedstock chemistry, combustion conditions, and alkali and alkaline earth metal (AAEM) content on silica quality remains insufficiently understood. This study investigated the effects of ash chemistry, citric-acid pretreatment, combustion temperature (400–700°C), and residence time (1–4 h) on biogenic silica production from cassava peel, yam peel, coconut husk, corncob, and cornhusk. Silica quality was evaluated using elemental composition, specific surface area (S BET ), pore volume (PV), slagging indices, principal component analysis (PCA), Pearson correlation analysis, response surface methodology (RSM), and FactSage thermodynamic modeling. PCA identified SiO₂ content, S BET , PV, combustion temperature, and AAEM oxides as the principal variables contributing to variability in silica quality. PC1 and PC2 explained 28.4% and 14.2% of the total variance, respectively, distinguishing silica-rich systems from AAEM-rich ash compositions associated with increased slagging propensity. Citric acid pretreatment substantially increased silica contents from 20.01 to 38.62 wt.% in cassava peel, 26.70 to 45.22 wt.% in yam peel, 11.53 to 44.57 wt.% in coconut husk, 20.82 to 49.53 wt.% in corncob, and 39.94 to 70.74 wt.% in cornhusk. Corresponding reductions in alkali concentrations lowered slagging indices and delayed liquid-phase formation. Pearson correlation and RSM analyzes showed that combustion temperature was the dominant factor affecting silica textural properties. Response surface optimization identified an optimal combustion window of approximately 550–650°C and around 2 h residence time, providing the most favorable balance between silica purity, specific surface area, and pore volume preservation. These findings provide predictive guidelines for producing high-value biogenic silica from underutilized biomass residues while mitigating slagging.

Der Beitrag analysiert die wachsende Bedeutung biogener Abfälle und Reststoffe als zentrale Ressource im Transformationsprozess hin zu einer klimaneutralen Kreislaufwirtschaft. Angesichts des weiterhin hohen Ressourcenverbrauchs und der begrenzten Flächen- sowie Biomassepotenziale wird deutlich, dass die Abfallwirtschaft eine Schlüsselrolle bei der Umsetzung nationaler Klimaziele bis 2045 spielen kann und auch muss. Sie zählt seit Jahrzehnten zu den erfolgreichsten Sektoren bei der Reduktion von Treibhausgasemissionen und stellt essenzielle Sekundärrohstoffe und -energieträger bereit. Im Fokus steht die stofflich-energetische Verwertung biogener Abfälle und Reststoffe als Beitrag zur Bioökonomie und als Quelle „grünen“ Kohlenstoffs u. a. für Industrieprozesse. Nachhaltigkeit, Effizienz und Systemintegration sind hierbei zentrale Anforderungen. Der Artikel betont die Notwendigkeit von Kaskaden- und Koppelnutzungskonzepten sowie von Technologien, die negative Emissionen ermöglichen. Die 2025 eingestellte Nationale Biomassestrategie (NABIS) und die geplante Integration ihrer Inhalte in die Bioökonomiestrategie verdeutlichen den politischen Neuorientierungsbedarf im Umgang mit Biomasse in Deutschland. Für die Abfall- und Kreislaufwirtschaft ergeben sich daraus neue Aufgabenfelder: die Erschließung ungenutzter biogener Potenziale, die Optimierung von Stoffströmen und die Verzahnung mit der Energie- und Industriepolitik. Damit kann die Branche auch weiterhin wesentlich zur Defossilisierung und Ressourceneffizienz einer zirkulären Bioökonomie beitragen.

The selective catalytic reaction with ammonia has become established to reduce NOx emissions during combustion in gas engines. Catalyst application and the introduction of the reducing agent represent a major challenge, especially for small engines. In this work, the aging phenomena of a commercial VWT catalyst after 17 months of operation of a 70-kWel biogas gasoline engine are quantitatively determined. Using spatially resolved CFD it can be shown that these have no influence on the activity properties of the compact application.

Zur Reduzierung der NOx‐Emissionen bei der Verbrennung im Gasmotor hat sich die selektive katalytische Reaktion mit Ammoniak durchgesetzt. Insbesondere für kleine Motoren stellt die Katalysatorapplikation und die Einbringung des Reduktionsmittels eine große Herausforderung dar. In dieser Arbeit werden experimentell die Alterungserscheinungen eines kommerziellen VWT‐Katalysators nach 17‐monatigem Betrieb eines 70‐kWel Biogas‐Ottomotors quantitativ ermittelt. Mittels ortsaufgelöster CFD kann gezeigt werden, dass diese keinen Einfluss auf die Aktivitätseigenschaften der Kompaktapplikation zeigen.

The recycling of catalysts has emerged as a key solution to address environmental pollution and the scarcity of natural resources. This dynamic is further reinforced by the growing industrial demand for catalysts and the urgent need to transition to more sustainable production methods. In the context of chemical transformations, the direct reuse of recycled catalysts for chemical applications in particular represents an elegant route towards greener syntheses. In this article, we review recent advancements in the recycling of homogeneous and heterogeneous catalysts since 2020, emphasizing the utilization of waste-derived catalysts for chemical reactions. In particular, we consider three primary sources of waste: electronic waste, spent lithium-ion batteries, and industrial wastewater. For each of these waste streams, different extraction methods are explored for their effectiveness in obtaining catalysts suitable for a broad spectrum of chemical reactions. These presented studies emphasize the potential of recycled catalysts to contribute to a sustainable and waste-efficient future.

The synthesis and characterization of sol-gel-derived cornhusk support for low-temperature catalytic methane combustion (LTCMC) were investigated in this study. The prepared cornhusk support was impregnated with palladium and cerium oxide (Pd/CeO2) via the classical incipient wetness method. The resulting catalyst was characterized using various techniques, including X-ray diffraction (XRD), N2 physisorption (BET), transmission electron microscopy (TEM), and hydrogen temperature-programmed reduction (H2-TPR). The catalytic performance of the Pd/CeO2/CHSiO2 catalyst was evaluated for methane combustion in the temperature range of 150–600 °C using a temperature-controlled catalytic flow reactor, and its performance was compared with a commercial catalyst. The results showed that the Pd/CeO2 dispersed on SiO2 from the cornhusk ash support (Pd/CeO2/CHSiO2) catalyst exhibited excellent catalytic activity for methane combustion, with a conversion of 50% at 394 °C compared with 593 °C for the commercial silica catalyst (Pd/CeO2/commercial). Moreover, the Pd/CeO2/CHSiO2 catalyst displayed better catalytic stability after 10 h on stream, with a 7% marginal loss in catalytic activity compared with 11% recorded for the Pd/CeO2/commercial catalyst. The N2 physisorption and H2-TPR results indicated that the cornhusk SiO2 support possessed a higher surface area and strong reducibility than the synthesized commercial catalyst, contributing to the enhanced catalytic activity of the Pd/CeO2/SiO2 catalyst. Overall, the SiO2 generated from cornhusk ash exhibited promising potential as a low-cost and environmentally friendly support for LTCMC catalysts.

In view of the tremendous emissions of toxic gases and particulate matter (PM) by low-power firewood-fueled fireplaces, there is an urgent need for effective measures to lower emissions to keep this renewable and economical source for private home heating available in the future. For this purpose, an advanced combustion air control system was developed and tested on a commercial fireplace (HKD7, Bunner GmbH, Eggenfelden, Germany), complemented with a commercial oxidation catalyst (EmTechEngineering GmbH, Leipzig, Germany) placed in the post-combustion zone. Combustion air stream control of the wood-log charge combustion was realized by five different control algorithms to describe all situations of combustion properly. These control algorithms are based on the signals of commercial sensors representing catalyst temperature (thermocouple), residual oxygen concentration (LSU 4.9, Bosch GmbH, Gerlingen, Germany) and CO/HC-content in the exhaust (LH-sensor, Lamtec Mess- und Regeltechnik für Feuerungen GmbH & Co. KG, Walldorf (Germany)). The actual flows of the combustion air streams, as calculated for the primary and secondary combustion zone, are adjusted by motor-driven shutters and commercial air mass flow sensors (HFM7, Bosch GmbH, Gerlingen, Germany) in separate feedback control loops. For the first time, the residual CO/HC-content (CO, methane, formaldehyde, etc.) in the flue gas is in-situ monitored with a long-term stable AuPt/YSZ/Pt mixed potential high-temperature gas sensor, which allows continuous estimation of the flue gas quality with an accuracy of about ±10%. This parameter is not only an essential input for advanced combustion air stream control but also provides monitoring of the actual combustion quality and logging of this value over a whole heating period. By many firing experiments in the laboratory and by field tests over four months, it could be demonstrated that with this long-term stable and advanced automated firing system, depression of the gaseous emissions by about 90% related to manually operated fireplaces without catalyst could be achieved. In addition, preliminary investigations at a firing appliance complemented by an electrostatic precipitator yielded PM emission depression between 70% and 90%, depending on the firewood load.

The quality of wood combustion processes can be effectively improved by achieving the automated control of the combustion air feed. For this purpose, continuous flue gas analysis using in situ sensors is essential. Besides the successfully introduced monitoring of the combustion temperature and the residual oxygen concentration, in this study, in addition, a planar gas sensor is suggested that utilizes the thermoelectric principle to measure the exothermic heat generated by the oxidation of unburnt reducing exhaust gas components such as carbon monoxide (CO) and hydrocarbons (CxHy). The robust design made of high-temperature stable materials is tailored to the needs of flue gas analysis and offers numerous optimization options. Sensor signals are compared to flue gas analysis data from FTIR measurements during wood log batch firing. In general, impressive correlations between both data were found. Discrepancies occur during the cold start combustion phase. They can be attributed to changes in the ambient conditions around the sensor housing.

Porous silica was synthesized from cornhusk using the sol–gel polymeric route and compared with ash obtained from the direct combustion process under laboratory conditions. The unmodified ash from the direct combustion process was dissolved in NaOH for 1 h to form sodium silicate, which was subsequently hydrolyzed with citric acid to yield a silica xerogel. The obtained xerogel was characterized using inductively coupled plasma–optical emission spectrometry (ICP-OES), Fourier transforms infrared (FTIR) spectroscopy, X-ray diffraction (XRD), simultaneous thermal analysis (STA), gas sorption techniques to determine their elemental constituents, functional groups, crystalline phases, thermal stability, and porosity, respectively. The results showed that the synthesized silica xerogel exhibited porous network structures with a high-specific surface area and mesopore volume of 384 m 2 /g and 0.35 cm 3 /g, respectively. The pore size distribution revealed a complete transformation of the pore network structures of the unmodified ash from a monomodal to a bimodal pore system, with micro- and mesopore peaks centered around 1.5 and 3.8 nm, respectively. The ICP-OES results showed that the silica content significantly increased from 52.93 to 91.96 wt.% db after the sol–gel treatment. XRD diffraction confirmed the amorphicity of the silica particles obtained from the sol–gel extraction method. In addition, the STA data showed that the silica xerogel has high thermal stability compared to the unmodified ash, as the latter exhibited poor thermal stability and low textural properties. The high surface area and narrow pore cavity size distribution of the porous silica xerogel make it an ideal substrate for catalysts and an excellent template for growing other nanoparticles within the pores.

Catalysts can reduce emissions from biomass combustion systems. Efficient use in small-scale applications is challenging due to the variations of temperature, fluid flow, and flue gas composition. An analytical procedure was defined and evaluated with three commercial catalysts to realize efficient integration. The characterization included activity measurements at three facilities: a model gas analysis device, a laboratory-scale combustion system, and a wood log stove. The results demonstrate the possibilities of model gas analysis to define a scope of application and also the need for catalyst characterization under real operation conditions to determine the performance and stability of the final process. Temperature and gas hourly space velocity are the two main parameters influencing catalyst activity.

Firewood plays an important role in the transition towards more environment-friendly heating. However, most installed wood stoves are outdated and demonstrate low efficiency and high emissions. New regulations force users to upgrade or replace their units. Diverse retrofit devices have been developed and tested, but none satisfy the required performance indicators alone and there is a lack of research on their combined operation. We studied the single and combined performance of three technologies (catalytic oxidation, heat recovery and ESP) using a fractional factorial experimental design. The experimental units were two single-room wood stoves equipped with an exhaust fan. The exhaust fan operation pulled down the efficiency by 7–10%. The ESP dropped the PM by 40–46% and reduced the efficiency by 2–3%. The heat exchanger fan increased PM emissions by 38–57%, while efficiency improved by 19–36%. The catalyst reduced the PM by 9–38% while the CO decreased by 31–56%. The combination of the exhaust and heat exchanger fans decreased the PM about 18% and increased the efficiency 26%, while the combination of the ESP and catalyst accomplished a 67% PM reduction.

During the combustion of biogenic residues particulate matter, nitrogen oxides, chlorine and sulphur compounds as well as dioxins and furans occur in elevated concentrations depending on the respective fuel composition. Corresponding abatement technology is only available for the power plant sector and cannot be used economically on small biomass plants. Therefore an exhaust gas purification procedure was developed and tested which can be used economically in decentral biomass plants. The core of the exhaust aftertreatment process is a fabric filter with catalytically active filter bags which enables a combined reduction of dust and nitrogen oxides. An additional precoating of the fabric filter also removes acidic exhaust gas components such as SO2 and HCl. Experiments were conducted on pilot and field scale. Significant reduction of particle emissions, nitrogen oxides and chlorine compounds could be achieved. Further optimization of the quantities of reducing agent and precoat material supplied is necessary in order to improve the performance of the exhaust gas cleaning process.

Bioenergy represents the largest share of renewable energies in Germany and globally. In the German electricity sector, it provides energy in a predictable and flexible, as well as a market-oriented, way. In the areas of heat supply, as well as in the transport sector, there are no established sensible alternatives or supplements to bioenergy. A significant increase in global biomass production is considered unrealistic. The preservation of the producing ecosystems requires an orientation of bioenergy technologies towards sustainability requirements. The aim must therefore be to increase the efficiency of utilisation. There is great potential for optimisation in the comprehensive integration of bioenergy into the future energy system and in the emerging bioeconomy. Optimised cascade utilisation, the use of residual materials and the improved coupled production of material, and energetically usable products in one process are important guidelines for the further development of bioenergy technologies. In the bioeconomy, bioenergy plays the role of an integrated and emission-free provision of process energy. The achievement of negative emissions is also seen as a long-term development option. Prospects for the future are, however, naturally associated with a high degree of uncertainty.

AbstractDie bei der Verbrennung von Biogas freiwerdenden Schademissionen unterliegen gesetzlichen Grenzwerten. Um diese einhalten zu können, bedarf es einer Abgasnachbehandlung mittels Oxidationskatalysator. Im Laufe der Zeit kommt es durch Alterung des Katalysators zu abnehmenden Umsätzen der Schadstoffe. Bereits nach nur 1,5 Jahren Betriebszeit ist daher die Einhaltung des Formaldehydgrenzwertes nicht mehr sicher möglich. Als Ursache konnte hauptsächlich die Ablagerung von anorganischen Verbindungen (Ölaschen) identifiziert werden. Hierdurch werden aktive Zentren blockiert und Poren verstopft.

The emissions released during the burning of biogas are subject to legal limits. In order to comply with these limits, exhaust aftertreatment is required by oxidation catalyst. Over time, decreasing pollutant conversion occur due to aging of the catalyst. Therefore, after only 1.5 years working time, compliance with the formaldehyde limit is no longer possible with certainty. The main reason is the deposition of inorganic compounds called oil ashes. These flue gas components from biogas engines block the catalytic active species and plugs pores.

Chemie Ingenieur TechnikVolume 92, Issue 5 p. 666-666 VorschauFree Access Vorschau: Chem. Ing. Tech. 6/2020 First published: 23 April 2020 https://doi.org/10.1002/cite.202070506AboutPDF 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, Issue5Special Issue: ReaktionstechnikMay 2020Pages 666-666 RelatedInformation

The utilization of various solid biofuels in combustion plants often requires the application of secondary emission reduction measures in order to meet legal requirements. Since common multi-stage exhaust cleaning methods are too expensive for the application in decentral biomass combustion, new approaches have to be investigated which can be applied economically in small- and medium-sized plants. The combined removal of particulate and gaseous emissions in one unit can save investment and operation costs. In this context, a method for simultaneous reduction of particulate matter (PM) and nitrogen oxides (NO X ) was developed and tested. The investigations focused on the alignment of the system components and the determination of optimal operating parameters for use in decentralized biomass furnaces. Experiments with wood chips and different non-woody biomass pellets at a 120-kW pilot plant showed significant reduction of PM and NO X . There is still a need for optimization with regard to the NH 3 slip and the degree of particle separation.