Search Results (34)

This review outlines a comprehensive methodology for the research and development of heterogeneous catalytic technologies (R&D_HeCaTe). Emphasis is placed on the fundamental interactions between reactants, solvents, and heterogeneous catalysts—specifically the roles of catalytic centers and support materials (e.g., functional groups) in modulating activation energies and stabilizing catalytic functionality. Particular attention is given to catalyst deactivation mechanisms and potential regeneration strategies. The application of molecular modeling and chemical engineering analyses, including reaction kinetics, thermal effects, and mass and heat transport phenomena, is identified as essential for R&D_HeCaTe. Reactor configuration is discussed in relation to key physicochemical parameters such as molecular diffusivity, reaction exothermicity, operating temperature and pressure, and the phase and “aggressiveness” of the reaction system. Suitable reactor types—such as suspension reactors, fixed-bed reactors, and flow microreactors—are evaluated accordingly. Economic and environmental considerations are also addressed, with a focus on the complexity of reactions, selectivity versus conversion trade-offs, catalyst disposal, and separation challenges. To illustrate the breadth and applicability of the proposed framework, representative industrial processes are discussed, including ammonia synthesis, fluid catalytic cracking, methanol production, alkyl tert-butyl ethers, and aniline. Full article

The conventional urea-based process for hydrazine hydrate production faces challenges including low product yield and high energy consumption. To overcome these limitations, we propose an innovative integrated approach combining jet reactor technology with membrane separation, further enhanced through heat network optimization. Through process simulation and sensitivity analysis, the following optimal distillation parameters were identified: nine theoretical stages, feed entry at the fifth stage, a reflux ratio of 0.6, and a distillate flow rate of 354 kg/h. Systematic optimization of the heat exchanger network (HEN) using pinch technology achieved substantial energy savings, reducing hot utility consumption by 66.8% (to 1317 MJ/h) and cold utility usage by 62.7% (to 1503 MJ/h). The redesigned HEN prioritized temperature-cascaded heat recovery, enabling 67% energy recuperation from exothermic reaction streams. Operational costs decreased by 12%, underscoring the economic viability of coupling process intensification with thermal integration. This work establishes a sustainable framework for hydrazine hydrate synthesis, balancing industrial feasibility with reduced environmental impact in chemical manufacturing. Full article

Hydrogen prereduction of two manganese ores fines was investigated under varied operating conditions in a fluidized bed. The manganese ores used in this study are the Zambian ore and the South African Nchwaneng ore from the Kalahari region. The samples were milled and sized before they were characterized with regard to sphericity, Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) chemical analyses, X-ray diffraction (XRD) analyses and Scanning Electrons Microscope (SEM) analyses. Prereduction experiments were conducted in a laboratory scale fluidized bed with the parameters of interest being minimum fluidization velocity, terminal velocity, elutriation, average bed voidage, residence time, temperature, intrinsic ore properties and cohesive adhesion. Experiments for the determination of fluidization velocity and terminal velocity were conducted at both ambient temperature and elevated temperature ($500 °$C, $550 °$C, $600 °$C, $700 °$C, $800 °$C and $900 °$C), and for varied sample masses (100 g, 300 g and 700 g) and varied particle-size ranges (200–$300 \mathrm{\mu }$m, 300–$425 \mathrm{\mu }$m, 425–$500 \mathrm{\mu }$m and 500–$600 \mathrm{\mu }$m). The experimentally observed minimum fluidization velocities for particles size groupings of [+106–$200 \mathrm{\mu }$m], [+200–$300 \mathrm{\mu }$m], [+300–$425 \mathrm{\mu }$m], [+425–$500 \mathrm{\mu }$m] and [+500–$600 \mathrm{\mu }$m] as well as the mix (20 wt% of each) was comparable with the theoretical minimum fluidization velocity. The fluidized bed was heated to a desired temperature at a rate of $10 °$C/min under argon whilst logging the pressure drop across the bed with increasing temperature. The convectional cooling during the introduction of cold hydrogen as well as the net energy of endothermic and exothermic chemical reactions were observed to result in a temperature drop in the order of 100 to $250 °$C. Thermal mineral transformation under argon was observed to yield iron manganese oxide in the order of 15 to 30 wt/wt%. Prereduction was conducted using hydrogen gas at a desired temperature and terminal velocity. Reduction extent was observed to increase with the increasing temperature and residence time. Increasing reduction temperature beyond $700 °$C was not observed to improve reduction, whereas longer residence time (of up to 40 min) was observed to favor the formation of iron manganese oxide, iron manganese and manganosite. For hydrogen prereduction experiment conducted at $900 °$C, the reactor was observed to be brittle after the experiment. Cohesive adhesion was observed to be more pronounced at $900 °$C. Full article

This critical review evaluates chemical looping combustion using a syngas derived from gasified biomass (BMD Syngas). It is anticipated that establishing such a process will open new opportunities for CO₂ sequestration and the use of highly concentrated CO₂ in the manufacturing and synthesis of fuels from entirely renewable feedstocks. This review focuses on the process conducted through using two interconnected fluidized bed units: a nickel oxide reduction unit (an endothermic Fuel Reactor) and a nickel oxidation unit (an exothermic Air Reactor). In this respect, a high-performance OC (HPOC) with Ni on a γ-Al₂O₃ fluidizable support (20wt% Ni, 1wt% Co, 5wt% La/γ-Al₂O₃) was developed at the CREC (Chemical Reactor Engineering Centre) of the University of Western Ontario, Canada. The HPOC was studied in a CREC Riser Simulator. The benefits of this mini-fluidized unit are that it can be operated at 2–40 s reaction times, 550–650 °C temperatures, 1.3–2.5 H₂/CO ratios, and 0.5–1 biomass/syngas stoichiometric ratios, mimicking the conditions of industrial-scale CLC units. When using a syngas derived from biomass and the HPOC under these operating conditions, 90% CO, 92% H₂, and 88% CH4 conversions, together with a 91% CO₂ yield, were obtained. These results allowed the prediction of a 1.84–3.0 wt% ($g_{O_2}/g_{{OC}_{}}$) oxygen transport capacity, with a 40–70% nickel oxide conversion. The experimental data acquired with the CREC Riser Simulator permitted the development of realistic kinetic models. The resulting kinetics were used in combination with Computational Particle Fluid Dynamics (CPFD) to demonstrate the operability of a large-scale industrial syngas CLC process in a downer fuel unit. In addition, these CPFD simulations were employed to corroborate that high CO₂ yields are achievable in 12–15 m length downer fuel units. Full article

The chemical looping reforming of methane using an SrFeO₃ oxygen carrier to produce synthesis gas from solar energy was experimentally investigated and validated. High-temperature solar heat was used to provide the reaction enthalpy, and therefore the methane feedstock was entirely dedicated to producing syngas. The two-step isothermal process encompassed partial perovskite reduction with methane (partial oxidation of CH₄) and exothermic oxidation of SrFeO_3-δ with CO₂ or H₂O splitting under the same operating temperature. The oxygen carrier material was shaped in the form of a reticulated porous foam structure for enhancing heat and mass transfer, and it was cycled in a solar-heated tubular reactor under different operating parameters (temperature: 950–1050 °C, methane mole fraction: 5–30%, and type of oxidant gas: H₂O vs. CO₂). This study aimed to assess the fuel production capacity of the two-step process and to demonstrate the potential of using strontium ferrite perovskite during solar cycling for the first time. The maximum H₂ and CO production rates during CH₄-induced reduction were 70 and 25 mL/min at 1000 °C and 15% CH₄ mole fraction. The increase in both the cycle temperature and the methane mole fraction promoted the reduction step, thereby enhancing syngas yields up to 569 mL/g during reduction at 1000 °C under 30% CH₄ (778 mL/g including both cycle steps), and thus outperforming the performance of the benchmark ceria material. In contrast, the oxidation step was not significantly affected by the experimental conditions and the material’s redox performance was weakly dependent on the nature of the oxidizing gas. The syngas yield remained above 200 mL/g during the oxidation step either with H₂O or CO₂. Twelve successive redox cycles with stable patterns in the syngas production yields validated material stability. Combining concentrated solar energy and chemical looping reforming was shown to be a promising and sustainable pathway toward carbon-neutral solar fuels. Full article

The chemical-looping reforming (CLR) of methane for hydrogen production employs a solid oxygen carrier (OC) and combines endothermic and exothermic stages, allowing for potential autothermal operation. This study conducted a thermodynamic analysis using Gibbs free energy minimization and energy balances to assess the behavior of WO₃, MnWO₄, and NiWO₄ as OCs in the CLR process. The effects of CH₄:OC ratios and reactor temperatures on equilibrium composition and the energy performance were examined. The results demonstrated that elevated reduction temperatures promote OC conversion and the formation of more reduced solid products. Molar ratios above stoichiometric prevent carbon formation, whereas stoichiometric ratios result in higher H₂ yield, achieving 98% at 1000 °C. However, these conditions do not support autothermal operation, which requires CH₄:OC molar ratios above stoichiometric. Additionally, lower oxidation temperatures are preferred regardless of the OC, due to the lower heat needed to preheat the air, which has a greater effect on the net heat. For the reduction temperature, its effect depends on the type of OC analyzed. The maximum H₂ yield obtained under autothermal operation was 88% for the three OCs, at 875 °C for MnWO₄ and 775 °C for both WO₃ and NiWO₄. Full article

Tetroxane derivatives are interesting drugs for antileishmaniasis and antimalaric treatments. The gas-phase thermal decomposition of 3,6,-dimethyl-1,2,4,5-tetroxane (DMT) and 3,3,6,6,-tetramethyl-1,2,4,5-tetroxane (acetone diperoxide (ACDP)) was studied at 493–543 K by direct gas chromatography by means of a flow reactor. The reaction is produced in the injector chamber at different temperatures. The resulting kinetics Arrhenius equations were calculated for both tetroxanes. Including the parent compound of the series 1,2,4,5-tetroxane (formaldehyde diperoxide (FDP)), the activation energy and frequency factors decrease linearly with the number of methyl groups. The reaction mechanisms of ACDP and 3,6,6-trimethyl-1,2,4,5-tetroxane (TMT) decomposition have been studied by means of the DFT method with the BHANDHLYP functional. Our calculations confirm that the concerted mechanism should be discarded and that only the stepwise mechanism occurs. The critical points of the singlet and triplet state potential energy surfaces (S- and T-PES) of the thermolysis reaction of both compounds have been determined. The calculated activation energies of the different steps vary linearly with the number of methyl groups of the methyl-tetroxanes series. The mechanism for the S-PES leads to a diradical O···O open structure, which leads to a C···O dissociation in the second step and the production of the first acetaldehyde/acetone molecule. This last one yields a second C···O dissociation, producing O₂ and another acetone/acetaldehyde molecule. The O₂ molecule is in the singlet state. A quasi-parallel mechanism for the T-PES from the open diradical to products is also found. Most of the critical points of both PES are linear with the number of methyl groups. Reaction in the triplet state is much more exothermic than the singlet state mechanism. Transitions from the singlet ground state, S₀ and low-lying singlet states S_1–3, to the low-lying triplet excited states, T_1–4, (chemical excitation) in the family of methyl tetroxanes are also studied at the CASSCF/CASPT2 level. Two possible mechanisms are possible here: (i) from S₀ to T₃ by strong spin orbit coupling (SOC) and subsequent fast internal conversion to the excited T₁ state and (ii) from S₀ to S₂ from internal conversion and subsequent S₂ to T₁ by SOC. From these experimental and theoretical results, the additivity effect of the methyl groups in the thermolysis reaction of the methyl tetroxane derivatives is clearly highlighted. This information will have a great impact for controlling these processes in the laboratory and chemical industries. Full article

As one of the main industrial segments of the current geoeconomics scenario, agro-industrial activities generate excessive amounts of waste. The gasification of such waste using supercritical water (SCWG) has the potential to convert the waste and generate products with high added value, hydrogen being the product of greatest interest. Within this context, this article presents studies on the SCWG processes of lignocellulosic residues from cotton, rice, and mustard husks. The Gibbs energy minimization (minG) and entropy maximization (maxS) approaches were applied to evaluate the processes conditioned in isothermal and adiabatic reactors, respectively. The thermodynamic and phase equilibria were written as a nonlinear programming problem using the Peng–Robinson state solution for the prediction of fugacity coefficients. As an optimization tool, TeS (Thermodynamic Equilibrium Simulation) software v.10 was used with the help of the trust-constr algorithm to search for the optimal point. The simulated results were validated with experimental data presenting surface coefficients greater than 0.99, validating the use of the proposed modeling to evaluate reaction systems of interest. It was found that increases in temperature and amounts of biomass in the process feed tend to maximize hydrogen formation. In addition to these variables, the H₂/CO ratio is of interest considering that these processes can be directed toward the production of synthesis gas (syngas). The results indicated that the selected processes can be directed to the production of synthesis gas, including the production of chemicals such as methanol, dimethyl ether, and ammonia. Using an entropy maximization approach, it was possible to verify the thermal behavior of reaction systems. The maxS results indicated that the selected processes have a predominantly exothermic character. The initial temperature and biomass composition had predominant effects on the equilibrium temperature of the system. In summary, this work applied advanced optimization and modeling methodologies to validate the feasibility of SCWG processes in producing hydrogen and other valuable chemicals from agro-industrial waste. Full article

The sintering of iron ammonia synthesis catalysts (nanocrystalline iron promoted with: Al₂O₃, CaO and K₂O) was studied under a hydrogen atmosphere, in a temperature range of 773 to 973 K to obtain stationary states. The catalysts were characterized by measuring the nitriding reaction rate under an ammonia atmosphere at 748 K to obtain steady states and the measurement of specific surface area. Chemical processes were conducted in a tubular differential reactor enabling thermogravimetric measurements and the chemical composition analysis of a gas phase under conditions allowing experiments to be carried out in the kinetic region of chemical reactions. An extended model of the active surface of the iron ammonia synthesis catalyst was presented, taking into account the influence of the gas phase composition and process temperature. The surface of iron nanocrystallites was wetted using promoters in an exothermic process associated with the formation of the surface Fe^s-O- bond and the change in the surface energy of iron nanocrystallites. Promoters formed on the surface of iron nanocrystallites with different structures of chemisorbed dipoles, depending on the composition of the gas phase. The occupied sites stabilized the structure, and the free sites were active sites in the process of adsorption of chemical reagents and in sintering. Based on the bonding energy of the promoter oxides and the difference in surface energy between the covered and uncovered surfaces, the wetting abilities of promoters, which can be arranged according to the order K₂O > Fe₃O₄ > Al₂O₃ > CaO, were estimated. By increasing the temperature in the endothermic sintering process, the degree of surface coverage with dipoles of promoters decreased, and thus the catalyst underwent sintering. The size distribution of nanocrystallites did not change with decreasing temperature. Only the equilibrium between the glass phase and the surface of iron nanocrystallites was then established. Full article

Reactor temperature manipulation to increase product yields of chemical reactions is a known technique used in many industrial processes. In the case of exothermic chemical reactions, the well-known Le Chatelier’s principle predicts that a decrease in temperature will displace the chemical reaction toward the formation of products by increasing the value of the equilibrium constant. The reverse is true for endothermic reactions. Reactor temperature manipulation in an industrial system, however, affects the values of many variables, including physical properties, transport parameters, reaction kinetic parameters, etc. In the case of reactive absorption, some variables change with increasing temperatures due to solute absorption, while others change in such a way that the solute absorption rate decreases. For example, temperature drop increases product formation for exothermic reactions but reduces the value of transport parameters, leading to decreasing interfacial concentrations and absorption rates. Therefore, temperature manipulation strategies must be designed carefully to achieve the process goals. In this work, we theoretically study the use of temperature as a tool to increase CO₂ absorption by solvents in a semi-batch reactor. A computer code has been developed and validated using reported experimental data. Calculated results demonstrate an increase in absorbed CO₂ of more than 28% with respect to the highest temperature used. Despite high agitation and high gas flow rate, the system is mass transfer controlled at short times, becoming kinetically controlled as time increases. An operating strategy to decrease cooling energy costs is also proposed. This study reveals that reactor temperature manipulation can be an effective process to improve CO₂ absorption by solvents in two-phase semi-batch reactors. Full article

Redox materials have been investigated for various thermochemical processing applications including solar fuel production (hydrogen, syngas), ammonia synthesis, thermochemical energy storage, and air separation/oxygen pumping, while involving concentrated solar energy as the high-temperature process heat source for solid–gas reactions. Accordingly, these materials can be processed in two-step redox cycles for thermochemical fuel production from H₂O and CO₂ splitting. In such cycles, the metal oxide is first thermally reduced when heated under concentrated solar energy. Then, the reduced material is re-oxidized with either H₂O or CO₂ to produce H₂ or CO. The mixture forms syngas that can be used for the synthesis of various hydrocarbon fuels. An alternative process involves redox systems of metal oxides/nitrides for ammonia synthesis from N₂ and H₂O based on chemical looping cycles. A metal nitride reacts with steam to form ammonia and the corresponding metal oxide. The latter is then recycled in a nitridation reaction with N₂ and a reducer. In another process, redox systems can be processed in reversible endothermal/exothermal reactions for solar thermochemical energy storage at high temperature. The reduction corresponds to the heat charge while the reverse oxidation with air leads to the heat discharge for supplying process heat to a downstream process. Similar reversible redox reactions can finally be used for oxygen separation from air, which results in separate flows of O₂ and N₂ that can be both valorized, or thermochemical oxygen pumping to absorb residual oxygen. This review deals with the different redox materials involving stoichiometric or non-stoichiometric materials applied to solar fuel production (H₂, syngas, ammonia), thermochemical energy storage, and thermochemical air separation or gas purification. The most relevant chemical looping reactions and the best performing materials acting as the oxygen carriers are identified and described, as well as the chemical reactors suitable for solar energy absorption, conversion, and storage. Full article

Thermochemical heat storage is an important solar-heat-storage technology with a high temperature and high energy density, which has attracted increasing attention and research in recent years. The mono-metallic redox pair Co₃O₄/CoO realizes heat storage and exothermic process through a reversible redox reaction. Its basic principle is to store energy by heat absorption through a reduction reaction during high-irradiation hours (high temperature) and then release heat through an exothermic-oxidation reaction during low-irradiation hours (low temperature). This paper presents the design of a cobalt-oxide honeycomb structure, which is extruded from pure Co₃O₄, a porous media with a high heat-storage density and a high conversion rate. Based on the experimental data, a three-dimensional axisymmetric multi-physics numerical model was developed to simulate the flow, heat transfer, mass transfer, and chemical reaction in the thermochemical heat-storage reactor. Unlike the previous treatment approach of equating chemical reactions with surface reactions, the model in this paper considers the consumption and generation of solids and the diffusion and transfer of oxygen in the porous medium during the reaction process, which brings the simulation results closer to the real values. Finally, the influence of the physical parameters of the honeycomb-structured body on the storage and exothermic process is explored in a wide range. The simulation results show that the physical-parameter settings and structural design of the cobalt-oxide honeycomb structure used in this paper are reasonable, and are conducive to improving its charging/discharging performance. Full article

The methanation process is discussed as one way to chemically store renewable energy in a future energy system. An important criterion for its application is the availability of compact, low-cost reactor concepts with high conversion rates for decentralized use where the renewable energy is produced. Current research focuses on the maximization of the methane yield through improved temperature control of the exothermic reaction, which attempts to avoid both kinetic and thermodynamic limitations. In this context, traditional manufacturing methods limit the design options of the reactor and thus the temperature control possibilities. The use of additive manufacturing methods removes this restriction and creates new freedom in the design process. This paper formulates the requirements for a novel methanation reactor and presents their implementation to a highly innovative reactor concept called ‘ADDmeth’. By using a conical reaction channel expanding from Ø 8 to 32 mm, three twisted, expanding heat pipes (Ø 8 mm in evaporation zone, Ø 12 mm in condenser zone) and a lattice structure for feed gas preheating and mechanical stabilization of the reactor, the design explicitly exploits the advantages of additive manufacturing. The reactor is very compact with a specific mass of 0.36 kg/kW and has a high share of functional volume of 52%. The reactor development was accompanied by tensile tests of additively manufactured samples with the used material 1.4404 (316 L), strength calculations for stability verification and feasibility studies on the printability of fine structures. Ultimate tensile strengths of up to 750 N/mm² (at room temperature) and sufficiently high safety factors of the pressure-loaded structures against yielding were determined. Finally, the paper presents the manufactured bench-scale reactor ADDmeth1 and its implementation. Full article

This paper presents an adaptive control scheme to face the challenge of rejecting input and output disturbances. The research is put on a layer of the design and start-up of chemical plants. The emphasis is on handling disturbances appearing in a narrow band of frequencies, which illustrates standard forms of disturbances in the alluded kind of systems. The controller is made up of a central RS structure that stabilizes the closed-loop plant. A second layer boosts the control law performance by adding the Youla–Kucera (YK) filter or Q parametrization and taking advantage of the internal model principle (IMP). This practice aids in modeling unknown disturbances with online control adjustment. We probe the resultant compensator for three non-isothermal continuous stirred tank reactors connected in series. The plant should conduct a first-order exothermic reaction consuming reactant A, while an isothermal operation stays and the outlet concentration is close to its nominal value. The primary concerns are open-loop instability and steady-state multiplicity in the plant’s first unit. The control objective is to reject input and output disturbances in a band of frequencies of $0.0002\mathrm{Hz}$ to $0.007\mathrm{Hz}$, whether there are variants or not in time. We test the controller with input signals depicting both variations in the auxiliary services and abrupt changes. We then compare the executions of the resultant control law with a model-based predictive control (MPC). We find comparable responses to multiple disturbances. However, the adaptive control offers an effortless control input. We also conclude that the adaptive controller responds well to reference changes, while the MPC fails due to input constraints. Full article

Chemical looping combustion is one novel technology for controlling CO${}_2$ emission with a low energy cost. Due to a lack of understanding of the detailed and micro behavior of the CLC process, especially for a three dimensional structure, numerical simulations are carried out in this work. The configuration is built according to the experimental unit and gaseous fuel is used in this work. A two-fluid model considering heterogeneous reactions is established, and the flow behaviour and reaction characteristics are obtained. The temperature in the air reactor increases with height owing to the exothermic reaction of the xidation of the oxygen carrier, while the temperature in the fuel reactor decreases with height due to the endothermic reaction. The oxidation level of the oxygen carrier is obtained by simulation, which is hard for measurement, and the difference between the inlet and outlet is 0.065. The influences of the operating temperature and injection rate of fuel are presented to understand the performance of the system. The highest fuel conversion rate reaches 0.92 under high operating temperature. The numerical results are helpful for acquiring insight on the flow and reactive behaviour of CLC reactors. Full article