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In this work, a comprehensive process simulation was developed to study and predict the pyrolysis of linear low-density polyethylene (LLDPE) in a fluidized bed reactor (FBR). The comprehensive simulation operated at 600 and 700 °C to investigate the pyrolytic oil and wax yields. These products were chosen as they mimic fuel range products available as a renewable fuel and energy source. The results showed that the oil yield decreased from 600 to 700 °C. This is because of an increase in the polyolefin polymer matrix’s vibration leading to an increase in temperature and absorbed thermal energy. In addition, there is a higher gas yield produced and negligible wax formation at 700 °C, which is beneficial in controlling accrued plastic waste (PW), of which polyethylene (PE) represents a vast proportion of via thermo-chemical conversion (TCC) technologies. The detailed process simulation was compared with experimental data under the same technology and operating conditions, and it was found that less than 10% discrepancy was observed between the two sets of data, suggesting a good validation between the two studies. Further studies showed that the diesel fuel lumped hydrocarbon (HC) range (C10-C19) was between 40 and 63% in the pyrolysis oil yield obtained. Moreover, the temperature profiles and fluidized bed distributor parameters were compared and investigated. The current simulation has proven that it can successfully predict the pyrolysis of LLDPE in an FBR.

The selective deoxygenation of palm oil to produce green diesel has been investigated over Ni catalysts supported on ZrO2 (Ni/Zr) and CeO2–ZrO2 (Ni/CeZr) supports. The modification of the support with CeO2 acted to improve the Ni dispersion and oxygen lability of the catalyst, while reducing the overall surface acidity. The Ni/CeZr catalyst exhibited higher triglyceride (TG) conversion and yield for the desirable C15–C18 hydrocarbons, as well as improved stability compared to the unmodified Ni/Zr catalyst, with TG conversion and C15–C18 yield remaining above 85% and 80% respectively during 20 h of continuous operation at 300 oC. The high C17 yields also revealed the dominance of the deCOx (decarbonylation/decarboxylation) pathway. A fully comprehensive process simulation model has been developed to validate the experimental findings in this study, and a very good validation with the experimental data has been demonstrated. The model was then further utilised to investigate the effects of temperature, H2 partial pressure, H2/oil feed ratio and LHSV. The model predicted that maximum triglyceride conversion was attainable at reaction conditions of 300 °C temperature, 30 bar H2 partial pressure, H2/oil of 1000 cm3/cm3 feed ratio and 1.2 h−1 LHSV., MAG and NDC gratefully acknowledge that this researched was co-financed by Greece and the European Union (European Social Fund-ESF) through the Operational Programme “Human Resources Development, Education and Lifelong Learning” (MIS-5050170). KP and SA acknowledge the financial support from the Abu Dhabi Department of Education and Knowledge through the grant AARE-2019-233 and the support from Khalifa University through the grant RC2-2018-024. VS acknowledges the ICTS ELECMI-LMA for offering access to their instruments and expertise.

Climate change, the greenhouse effect and fossil fuel extraction have gained a growing interest in research and industrial circles to provide alternative chemicals and fuel synthesis technologies. Carbon dioxide (CO2) hydrogenation to value-added chemicals using hydrogen (H-2) from renewable power (solar, wind) offers a unique solution. From this aspect this review describes the various products, namely methane (C-1), methanol, ethanol, dimethyl ether (DME) and hydrocarbons (HCs) originating via CO2 hydrogenation reaction. In addition, conventional reactor units for the CO2 hydrogenation process are explained, as well as different types of microreactors with key pathways to determine catalyst activity and selectivity of the value-added chemicals. Finally, limitations between conventional units and microreactors and future directions for CO2 hydrogenation are detailed and discussed. The benefits of such set-ups in providing platforms that could be utilized in the future for major scale-up and industrial operation are also emphasized.

In response to the growing trend of greenhouse gas emissions from the production and use of conventional fuels, COx free hydrogen generation is introduced as an alternative and efficient energy carrier. Due to hydrogen's storage challenges, is more efficient to be produced on-site by other chemical compounds for fuel cell applications. This work outlines the production of hydrogen (H2) from ammonia (NH3) and hydrous hydrazine (N2H4·H2O) catalytic decomposition. Both substances are giving nitrogen (N2) as a by-product, which is not toxic. Moreover, heterogeneous catalysts that were studied through the years are presented. Lastly, a reactoristic view of the ammonia decomposition is provided with different reactors such as catalytic membrane reactors (CMRs), fixed-bed reactors (FBRs) and micro-reactors (MRs) for the evaluation of their performance.

The need to replace fossil fuels with sustainable alternatives has been a critical issue in recent years. Hydrogen fuel is a promising alternative to fossil fuels because of its wide availability and high energy density. For the very first time, novel microreactor configurations for the formic acid decomposition have been studied using computational modeling methodologies. The decomposition of formic acid using a commercial 5 wt % Pd/C catalyst, under mild conditions, has been assessed in packed bed, coated wall, and membrane microreactors. Computational fluid dynamics (CFD) was utilized to develop the comprehensive heterogeneous microreactor models. The CFD modeling study begins with the development of a packed bed microreactor to validate the experimental work, subsequently followed by the theoretical development of novel microreactor configurations to perform further studies. Previous work using CFD modeling had predicted that the deactivation of the Pd/C catalyst was due to the production of the poisoning species CO during the reaction. The novel membrane microreactor facilitates the continuous removal of CO during the reaction, therefore prolonging the lifetime of the catalyst and enhancing the formic acid conversion by approximately 40% when compared to the other microreactor configurations. For all microreactors studied, the formic acid conversion increases as the temperature increases, and the liquid flow rate decreases. Further studies revealed that all microreactor configurations had negligible internal and external pore diffusion resistances. The detailed models developed in this work have provided an interesting insight into the intensification of the formic acid decomposition reaction over a Pd/C catalyst.

With fossil fuel being the major source of energy, CO2 emission levels need to be reduced to a minimal amount namely from anthropogenic sources. Energy consumption is expected to rise by 48% in the next 30 years, and global warming is becoming an alarming issue which needs to be addressed on a thorough technical basis. Nonetheless, exploring CO2 capture using membrane contactor technology has shown great potential to be applied and utilised by industry to deal with post- and pre-combustion of CO2. A systematic review of the literature has been conducted to analyse and assess CO2 removal using membrane contactors for capturing techniques in industrial processes. The review began with a total of 2650 papers, which were obtained from three major databases, and then were excluded down to a final number of 525 papers following a defined set of criteria. The results showed that the use of hollow fibre membranes have demonstrated popularity, as well as the use of amine solvents for CO2 removal. This current systematic review in CO2 removal and capture is an important milestone in the synthesis of up to date research with the potential to serve as a benchmark databank for further research in similar areas of work. This study provides the first systematic enquiry in the evidence to research further sustainable methods to capture and separate CO2.

Ni-based catalysts supported on sol-gel prepared Pr-doped CeO2 with varied porosity and nanostructure were tested for the CO2 methanation reaction. It was found that the use of ethylene glycol in the absence of H2O during a modified Pechini synthesis led to a metal oxide support with larger pore size and volume, which was conducive toward the deposition of medium-sized Ni nanoparticles confined into the nanoporous structure. The high Ni dispersion and availability of surface defects and basic sites acted to greatly improve the catalyst’s activity. CFD simulations were used to theoretically predict the catalytic performance given the reactor geometry, whereas COMSOL and ASPEN software were employed to design the models. Both modelling approaches (CFD and process simulation) showed a good validation with the experimental results and therefore confirm their ability for applications related to the prediction of the CO2 methanation behaviour., AIT, NDC and MAG acknowledge support of this work by the project “Development of new innovative low carbon energy technologies to improve excellence in the Region of Western Macedonia” (MIS 5047197), which is implemented under the Action “Reinforcement of the Research and Innovation Infrastructure” funded by the Operational Program "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014–2020) and co-financed by Greece and the European Union (European Regional Development Fund). AGSH, AAD and KP acknowledge support from Khalifa University through the grant RC2–2018-024. Additional partial support has been provided by the Abu Dhabi Award for Research Excellence (AARE) 2019 through project AARE19–233. VS acknowledges the ICTS ELECMI-LMA for offering access to their instruments and expertise.

The use of hydrogen as a renewable fuel has attracted great attention in recent years. The decomposition of formic acid under mild conditions was investigated using a 2%Pd6Zn4 catalyst in a batch reactor. The results showed that the conversion of formic acid increases with reaction temperature and with the formic acid concentration. A process-simulation model was developed to predict the decomposition of formic acid using 2%Pd6Zn4 in a batch reactor. The model demonstrated very good validation with the experimental work. Further comparisons between the 2%Pd6Zn4 catalyst and a commercial Pd/C catalyst were carried out. It was found that the 2%Pd6Zn4 demonstrated significantly higher conversions when compared with the commercial catalyst., The authors thank London South Bank University; School of Engineering for the PhD fund that supports the work of Sanaa Hafeez.

Carbon dioxide (CO2) is one of the major atmospheric greenhouse gases (GHG). The continuous increase of CO2 concentration and its long atmospheric lifetime may cause long-term negative effects on the climate. It is important to develop technologies to capture and minimize those emissions into the atmosphere. The objective of this work is to design and study theoretically and experimentally a numbering-up/scale-out membrane microreactor in order to be used as a capture system. The main aim of the work is to obtain an even flow distribution at each plate of the reactor. Nearly uniform flow distribution was achieved at each layer of the numbering-up microreactor according to the carried-out CFD models. The maximum difference between the average velocities was less than 6% for both gas and liquid flows. To obtain better flow distribution into the microreactor, the radius of the inlet/outlet tube was optimized. Results from CFD and experimental simulations do not match, and slightly maldistribution in achieved in the experimental system due to phase breakthrough and imperfections on the fabrication of the plates. Moreover, comparing the single channel microreactor to the scale-out microreactor, the latter showed poorer performance on CO2 removal while expecting the reactors to have similar performance. By installing inserts with different channel widths, the experimental results were identical to the original case.

A computational fluid dynamics (CFD) model was derived and validated in order to investigate the hydrodeoxygenation reaction of 4-propylguaiacol, which is a lignin-derived compound present in bio-oil. A 2-D packed bed microreactor was simulated using a pre-sulphided NiMo/Al2O3 solid catalyst in isothermal operation. A pseudo-homogeneous model was first created to validate the experimental results from the literature. Various operational parameters were investigated and validated with experimental data, such as temperature, pressure and liquid flow rate, and it was found that the CFD findings were in very good agreement with the results from the literature. The model was then upgraded to that of a detailed multiphase configuration, and phenomena such as internal and external mass transfer limitations were investigated, as well as reactant concentrations on the rate of 4-propylguaiacol. Both models were in agreement with the experimental data, and therefore confirm their ability for applications related to the prediction of the behaviour of bio-oil compound hydrodeoxygenation.

For the first time, a fully comprehensive heterogeneous computational fluid dynamic (CFD) model has been developed to predict the selective catalytic deoxygenation of palm oil to produce green diesel over an Ni/ZrO2 catalyst. The modelling results were compared to experimental data, and a very good validation was obtained. It was found that for the Ni/ZrO2 catalyst, the paraffin conversion increased with temperature, reaching a maximum value (&gt, 95%) at 300 °C. However, temperatures greater than 300 °C resulted in a loss of conversion due to the fact of catalyst deactivation. In addition, at longer times, the model predicted that the catalyst activity would decline faster at temperatures higher than 250 °C. The CFD model was able to predict this deactivation by relating the catalytic activity with the reaction temperature.

The use of hydrogen as a renewable fuel has gained increasing attention in recent years due to its abundance and efficiency. The decomposition of formic acid for hydrogen production under mild conditions of 30 °C has been investigated using a 5 wt.% Pd/C catalyst and a fixed bed microreactor. Furthermore, a comprehensive heterogeneous computational fluid dynamic (CFD) model has been developed to validate the experimental data. The results showed a very good agreement between the CFD studies and experimental work. Catalyst reusability studies have shown that after 10 reactivation processes, the activity of the catalyst can be restored to offer the same level of activity as the fresh sample of the catalyst. The CFD model was able to simulate the catalyst deactivation based on the production of the poisoning species CO, and a sound validation was obtained with the experimental data. Further studies demonstrated that the conversion of formic acid enhances with increasing temperature and decreasing liquid flow rate. Moreover, the CFD model established that the reaction system was devoid of any internal and external mass transfer limitations. The model developed can be used to successfully predict the decomposition of formic acid in microreactors for potential fuel cell applications.

The demand for energy is continuously increasing worldwide. This places a constant strain on the production and availability of fossil fuels on which most current energy sources are based. Thus, alternative sources of energy (non-fossil based) are urgently needed to produce liquid fuels. However, conventional technologies and reactors used for these alternative processes have been associated with low mass and heat transfer rates, long reaction times and extreme temperatures and pressures. To address these limitations, microreactors have been developed and utilised over the past decade, and have been proven to increase product yields and reduce residence time and product selectivity when compared to conventional reactors. This paper provides an in-depth review of the liquid fuel production routes over the last decade, and highlights the advantages of microreactors that have been successfully employed to overcome some of the issues faced with conventional bulk reactors.

Population growth has led to higher consumption of fossil fuel, and subsequently to a major increase of greenhouse gases emissions to the atmosphere, thus inducing global warming. Fossil fuel supplies are depleting, and the price of these fuels is increasing. Moreover, there are concerns about related emissions of toxic pollutants such as sulphur dioxide and aromatic hydrocarbons. Here, we review alternative fuel technologies. We focus on how membrane reactors improve the existing production processes of renewable fuels. Advantages and environmental benefits of membrane reactors are compared to the conventional techniques. Membrane reactors have been applied successfully to improve biodiesel, hydrogen and Fischer–Tropsch synthesis. Membranes help the conversion of products, whilst shifting the equilibrium of the reaction and reducing undesired by-products. Membrane reactors also overcome immiscibility issues that hinder conventional reactor processes. Overall, membrane reactors reduce cost and energy needed for the treatment of wastewater from fuel production. Funding text The authors would like to thank London South Bank University, School of Engineering, for the PhD funding support.

In this communication, we discuss various production methods as potential venues targeted towards alternative fuel generation. These will revolve around the Fischer–Tropsch (FT) process and biodiesel and hydrogen generation techniques. The implementation of membrane reactors in the production of fuels will be shown and discussed; and their advantages will be detailed. The main routes of hydrogen production are also detailed, which include autothermal reforming and biological process. This was done to compare the main advantages of various techniques for the production of hydrogen, as it is noted to be the most desired utility fuel that can serve various purposes. The application of membranes also facilitates an increase in the conversion of desired products while shifting the equilibrium of the reaction and reducing undesired by-products. Membrane reactors also overcome immiscibility issues that hinder conventional reactor processes. Membrane reactors are also demonstrated to reduce the difficulty in separating and purifying impurities, as they couple separation and reaction in one process. This shows drastic economic and energy requirement reductions in the amount of wastewater treatment associated with conventional fuel production reactor. Emphasis is also paid to catalytic membranes used for the production of biodiesel, which can also remove glycerol from the product line as an added advantage.

Industrial solid waste management encompasses a vital part of developed and developing countries strategies alike. It manages waste generated from vital industries and governs the hazardous waste generated as a major component of integrated waste management strategies. This article reviews the practices that govern the management approaches utilized in the developed world for industrial spent catalysts. It critically assesses the current situation of waste management within the developing world region focusing on the industrial waste component, in a novel attempt to crucially develop a strategy for a way forward based on best practices and future directions with major European industries. The review also draws parallels with European countries to compare their practices with those of the State of Kuwait, which rely solely on landfilling for the management of its industrial waste. Spent catalysts recovery methods are discussed at length covering conventional methods of valuable metals and chemicals recovery (e.g., hydrometallurgical, solid–liquid and liquid–liquid extraction) as well as biological recovery methods. A major gap exists within regulations that govern the practice of managing industrial waste in Kuwait, where it is essential to start regulating industries that generate spent catalysts inview of encouraging the establishment of valorization industries for metal and chemical recovery. This will also create a sustainable practice within state borders, and can reduce the environmental impact of landfilling such waste in Kuwait. Industrial solid waste management encompasses a vital part of developed and developing countries strategies alike. It manages waste generated from vital industries and governs the hazardous waste generated as a major component of integrated waste management strategies. This article reviews the practices that govern the management approaches utilized in the developed world for industrial spent catalysts. It critically assesses the current situation of waste management within the developing world region focusing on the industrial waste component, in a novel attempt to crucially develop a strategy for a way forward based on best practices and future directions with major European industries. The review also draws parallels with European countries to compare their practices with those of the State of Kuwait, which rely solely on landfilling for the management of its industrial waste. Spent catalysts recovery methods are discussed at length covering conventional methods of valuable metals and chemicals recovery (e.g., hydrometallurgical, solid-liquid and liquid-liquid extraction) as well as biological recovery methods. A major gap exists within regulations that govern the practice of managing industrial waste in Kuwait, where it is essential to start regulating industries that generate spent catalysts in-view of encouraging the establishment of valorization industries for metal and chemical recovery. This will also create a sustainable practice within state borders, and can reduce the environmental impact of landfilling such waste in Kuwait.