Modelling and simulation of a single slit micro packed bed reactor for methanol synthesis

A mathematical model for a single slit packed microstructured reactor-heat exchanger in the synthesis of methanol from syngas was developed. The model constitutes a simplified 3D-pseudo homogeneous approach for a reaction slit with integrated pillar geometry. Literature kinetic rate expressions for methanol synthesis over commercial Cu/ZnO/support type catalysts were applied at 80 bar total pressure, temperature range of 473-558 K, and syngas composition of H$_{2}$/CO/CO$_{2}$/N$_{2}$:65/25/ 5/5 mol%. The model is found capable of predicting experimental CO conversion data with acceptable accuracy. Superior thermal stability of the microchannel upon variation of different parameters such as contact time, feed gas temperature and reaction temperature were shown. The simulation results also reveal that the microchannel reactor can operate free of performance loss due to concentrations field that may arise from overlaid temperature fields. Simulations have also been used to calculate the rapid temperature transients at the inlet. The agreement between simulation results and experimental data signifies the applicability of the developed model for further design and performance optimization of microstructured reactors for methanol synthesis and other exothermic processes

What should be recycled: An integrated model for product recycling desirability

This research was focused on developing a new scientific approach for prioritising recycling of end-of-life products in a circular economy. To date, product complexity based on the mixture of materials has been used as a predictor of what gets recycled. While the separation of materials that make up a product has been modelled as a measure of product complexity, this does not taken into account the benefits and considerations in recycling products. In this paper, a new agenda and approach to prioritise the recycling of products was developed based on a recycling desirability index. The material mixing complexity measure was inverted into a simplicity index and then extended by modelling the security index for the mix of materials and the technological readiness level of recycling technologies. The extended model is proposed as an integrated measure of the desirability of recycling end-of-life products. From this analysis, an apparent recycling desirability boundary, enabling products to be prioritised for recycling, was developed. This model and analysis can be used as an information source in developing policies and product recycling priorities

Sustainable Sewage Sludge Management: From Current Practices to Emerging Nutrient Recovery Technologies

Nutrient recovery from secondary resources, such as wastewater, has received increasing attention in recent years. Nutrient cycle sustainability and recycling approaches are important measures under development and considerations. This paper aims to present an overview of routes and technologies for nutrient recovery from sewage sludge and measures for improving their sustainability. First, current routes for nutrient recovery from sewage sludge are briefly reviewed. Next, an overview of commercial nutrient recovery technologies, projects, and emerging techniques around the world with the key factors for a successful phosphorus recovery technology is presented. Finally, a proposal for improving the sustainability of these practices is presented. It is concluded that the gap between demand and supply can be a major driver for the shift from ‘removal and treat’ to ‘recovery and reuse’. Moreover, there is not, and will never be, a one-size-fits-all solution. Future strategies and roadmaps need to be adapted to the local economy and geographical context more than ever

Sustainable Sewage Sludge Management: From Current Practices to Emerging Nutrient Recovery Technologies

Nutrient recovery from secondary resources, such as wastewater, has received increasing attention in recent years. Nutrient cycle sustainability and recycling approaches are important measures under development and considerations. This paper aims to present an overview of routes and technologies for nutrient recovery from sewage sludge and measures for improving their sustainability. First, current routes for nutrient recovery from sewage sludge are briefly reviewed. Next, an overview of commercial nutrient recovery technologies, projects, and emerging techniques around the world with the key factors for a successful phosphorus recovery technology is presented. Finally, a proposal for improving the sustainability of these practices is presented. It is concluded that the gap between demand and supply can be a major driver for the shift from ‘removal and treat’ to ‘recovery and reuse’. Moreover, there is not, and will never be, a one-size-fits-all solution. Future strategies and roadmaps need to be adapted to the local economy and geographical context more than ever

Pd/CeO2 catalysts as powder in a fixed-bed reactor and as coating in a stacked foil microreactor for the methanol synthesis

Pd/CeO2 as a catalyst for methanol synthesis has been studied in a microreactor consisting of 14 structured foils in a fixed-bed laboratory reactor. Methanol synthesis was carried out at 80 bar and 300 °C with a syngas composition of H2/CO/CO2/N2 = 65/25/5/5. It was found that Pd/CeO2 as a foil coating was more active than the Pd/CeO2 powder catalyst on a Pd/CeO2 mass basis, both initially and after stabilization. In order to understand the Pd/CeO2 catalyst properties, both as a coating on the structured foils and as nanoparticles, techniques such as TEM, SEM, XRD and chemisorption were employed to characterize the catalysts before and after reaction experiments. The activity of the Pd/CeO2 foil coating is substantially better than the Pd/CeO2 powder despite significantly higher Pd dispersion of the Pd/CeO2 powder. This is ascribed to the Pd nanoparticles of the powder catalyst being partly covered by the ceria upon preparation and reduction. This prevents the accessibility of Pd to the gaseous reactants. A higher number of active sites are initially present in both catalysts, leading to high initial activity for methane as well as methanol formation. This may be explained by good interfacial contact between Pd and CeO2 created during preparation and reduction to form sites that are gradually lost under reaction conditions by a combination of sintering/agglomeration and enhanced coverage of the Pd by ceria layers.acceptedVersio