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This paper presents a comparative assessment of several novel synthetic natural gas fixed-bed reactor designs and configurations. The four reactor concepts presented in the paper use the Sabatier reaction between carbon dioxide and hydrogen to produce methane. Due to the exothermic nature of the reaction and its pressure sensitivity, this study emphasizes the ability and potential of the reactor configurations to provide effective cooling, and minimize heat gain and pressure drops, so that the maximum methane yield and carbon dioxide conversion can be achieved. Out of four reactor designs, Concept 1 follows a conventional cylindrical fixed-bed reactor design; however, the bed is separated horizontally to promote inter-cooling. Concept 2 separates the bed into 2 segments vertically to facilitate cooling along the length of the reactor. Concept 3 follows a horizontal configuration in which the catalyst beds are separated into rectangular prisms. The different configurations of Concepts 1 to 3 were designed by varying the reactor dimensions and the number of catalyst beds. Most notably, Concept 4 using a unique helical design provides more effective cooling to the catalyst bed by increasing the surface area and decreasing the diameter of the reactor channel. However, the volumetric flow of this specific reactor model is significantly reduced. Furthermore, the inlet conditions of 200 °C and 30 bar help achieve a CH 4 yield of approximately 85 % when considering Concept 1. [ABSTRACT FROM AUTHOR]

• Reactor and heat exchanger network are integrated considering the catalyst deactivation. • Relations among reactor parameters, energy consumption, and unit product cost are determined. • The variation of key parameters and product cost along with catalyst activity is illustrated. • The proposed method can target the optimal catalyst service life and catalyst weight. • The proposed method is efficient and provides detailed data without complex calculations. A systematic method is proposed for targeting the optimal catalyst service life, considering the catalyst deactivation and coupling integration of HEN and reactor. Relations among the reactor's conversion, inlet/outlet temperature, energy consumption, average product cost, and catalyst activity are determined based on the catalyst deactivation kinetics, energy balance, and the migration of the composite curves. The Reactor-HEN coupling diagram is constructed to illustrate the variation curves of these indexes with catalyst activity/catalyst regeneration activity and target the optimal regeneration activity. The optimal catalyst service time is further determined considering the catalyst deactivation dynamics. A practical process with benzene hydrogenation to cyclohexene is studied. The optimal regeneration activity of the Ru-Zn-B/ZrO 2 catalyst is determined to be 0.42, and the optimal service life is 1.32 y. The proposed method is efficient, and the results can guide the design and operation of the production processes. [ABSTRACT FROM AUTHOR]

In this study, we experimentally investigated the effects of geometrical parameters (such as the reactor length ( L ) and the inner diameter ( D R )), the step height ( r in − r R ) , the Reynolds number (Re), and the equivalence ratio ( φ )) of the inlet mixture on the behavior of the rich fuel methane–oxygen flames in non-adiabatic cylindrical meso-scale reactors with the backward facing step. During the experiments, seven different flame regimes were observed. These flame regimes were the blow-out, marginal, stationary (stable), RERI, stationary (stable)-flashback, RERI-flashback, and flashback, respectively. Also, the results showed that the length and diameter of reactors could strongly affect flame dynamics, especially the borders among the observed flame regimes in the meso-scale reactors. As a result, it was demonstrated that the reactor length and diameter obviously influenced the traveling speed and frequency of RERI flame regime. Also, it was shown that decreasing the step height from 1.4 mm to 0.4 mm suppressed RERI flame regime in the meso-scale reactors. Moreover, in the certain ranges of the equivalence ratio, increasing the Reynolds number decreased the flame presence range in the meso-scale reactors. Finally, it was concluded that RERI flame regime is a prevalent operational regime for applications in which an almost uniform temperature pattern on the outer surface of lengthy meso-scale reactors is required. However, it was shown that this privilege was not valid as compared to the temperature distribution patterns caused by the stationary flame regimes in the small length reactors. [ABSTRACT FROM AUTHOR]

Abstract: Reactive distillation (RD) can be advantageously used to improve the selectivity of the desired product in the multi-reaction system. Process synthesis and design of RD systems to attain the desired selectivity is a challenging task. Our previous work in this field (e.g. Amte et al., 2011, 2012) was restricted to fully reactive RD models and their networks. In this work, we examine the potential of a hybrid reactive distillation column, with both reactive and non-reactive sections, through an example of a single reactant complex reaction scheme (e.g. van de Vusse reaction) in which reactant is intermediate boiling. An algorithm for conceptual design of such columns is presented. It is based on the boundary value method (BVM) that utilizes the concept of operation leaves of rectifying and stripping sections; the overlap of which indicates the potential feasible split. Based on the desired selectivity, we determine the locus of reactive stage compositions in the RD column. Its intersections with the non-reactive stage composition lines (SCL) allow rapid screening of feasible designs of hybrid reactive distillation (HRD) columns. The approach generates multiple designs and allows one to compare them in terms of energy and catalyst requirement. The proposed method is applicable to single reactant single-feed hybrid columns, and because of its graphical representation, it cannot be directly used for systems with a large number of components. More work is therefore necessary to extend this approach to the multi-reactant double-feed hybrid configurations. [Copyright &y& Elsevier]

Abstract: Reactive distillation (RD) can be advantageously used to improve selectivity of the desired product in a multi-reaction system. Because of the complexity in vapor liquid equilibrium and reaction kinetics, the design methodology is not straightforward and one has to adopt conceptual design and synthesis methods to arrive at the appropriate RD configuration. This paper is continuation of our earlier work (), aimed at extending the concept of attainable region to a larger family of reactors that includes different reactive distillation units. In this work, we incorporate multistage reactive rectification and reactive stripping models with total reflux and total reboil, respectively. We further define the respective vectors, which justify the need of the corresponding units in the RD network. The van de Vusse schemes with both non-azeotropic and azeotropic vapor−liquid equilibria are considered and the attainable regions are constructed. Explanation is provided based on the visualization of selectivity lines in the composition space. In all the cases studied here, the feasible region is significantly broader than the one realized for the network of only conventional reactors. [Copyright &y& Elsevier]

Abstract: A photoreactor comprising a bundle of TiO2-coated quartz tubes was studied by varying its tube wall thickness and tube configuration as well as introducing a mesoporous SiO2 intermediate layer between the TiO2 coating and quartz tube. The bundled tube photoreactor (BTP) performance was assessed based on tube light propagation and photocatalytic degradation rate of ethylene. Increasing the tube wall thickness improved the tube light propagation and the degradation rate of ethylene. An array of eight 6-mm tubes was found to be the best BTP configuration in this work. The findings from varying the tube configuration suggested an effectively illuminated surface area as a second important parameter to consider when comparing different BTP performances. Introducing a mesoporous SiO2 intermediate layer with a thickness between 210 and 400nm between the TiO2 coating and quartz tube improved not only the tube light propagation but also the ethylene photocatalytic degradation rate by up to 70%. This improvement was attributed to controlled light refraction from the quartz tube, which can be achieved under the conditions of frustrated total internal reflection. [Copyright &y& Elsevier]

Abstract: A stochastic model representing annular flow in a tubular reactor is proposed. Numerical simulation was utilized to generate sample paths fitting the residence time distributions (RTD) of the system. The model was constructed from basic diffusion equations with the additional consideration of random effects disturbing the system, thus yielding a stochastic partial differential equation. The stochastic model is simulated using the Euler–Maruyama procedure. Experimental data from three tubular polymerization reactors were well fitted by the model. The model encompassed the two deterministic parameters, mean residence time and Peclet number, as well as three stochastic parameters: stochastic relevance (b), updated time (ΔT) and the seed that begins the Wiener process. The satisfactory results indicate that the model constitutes an important step toward comprehending the complex fluid dynamics of tubular flow systems. [Copyright &y& Elsevier]

Abstract: Using concentrated solar energy as the source of high-temperature process heat, a two-step CO2 splitting thermochemical cycle based on Zn/ZnO redox reactions is applied to produce renewable fuels. The solar thermochemical cycle consists of (1) the solar endothermic dissociation of ZnO to Zn and O2; (2) the non-solar exothermic reduction of CO2 with Zn to CO and ZnO; the latter is recycled to the 1st solar step. The second step of the cycle is experimentally investigated in a hot-wall quartz aerosol flow reactor, designed for quenching of Zn(g), formation of Zn nanoparticles, and in-situ oxidation with CO2. The effects of varying the reactants stoichiometry, reaction temperatures, and inlet flow temperatures for radial and annular flows were investigated. Chemical conversions of Zn to ZnO of up to 88% were obtained for a residence time of 3s. For all of the experiments, the reactions primarily occurred heterogeneously on the reaction zone surfaces, outside the aerosol jet flow. [Copyright &y& Elsevier]

Abstract: An optical fibre reactor with 30 hexagonal-shaped channels distributed within the optical fibre structure was investigated as a gas-phase photocatalytic reactor. TiO2 photocatalyst, with SiO2 sol acting as a binder, was coated on the channel walls at a thickness of 1.5μm. Effective light propagation lengths of 3.4 and 4.9cm were observed for incidental angles of 81.5° and 87.1°, respectively. The TiO2-coated channelled optical fibre reactor (COFR) was assessed for the photocatalytic degradation of gas-phase ethylene. The photocatalytic reaction rate of ethylene degradation was linear with respect to the incident photons. The reaction rate order for the incident photons was determined to be 0.93. Despite a longer effective light propagation length for an incidental angle of 87.1°, the quantum yield was independent of the incidental angle. The independence of the quantum yield on the incident photons and the angle of light incidence was attributed to the COFR design, where the propagating light was wholly confined within the reactor and, in turn, more effectively utilised by the TiO2. [Copyright &y& Elsevier]

[Display omitted] • A systematic method is proposed for synthesizing and optimizing the reaction-separation system. • The flexibility index is introduced to evaluate the operational flexibility of distillation sequences. • The effluent of reactor at different conditions is calculated based on Gibbs free energy. • Procedure is proposed to adjust design variables and guarantee the operational flexibility. • The optimization of two cases results in the production costs decreased by 26.19% and 38.6%. A methodology is presented to integrate reactor and distillation sequences and identify the optimal one with sufficient operational flexibility. The minimum Gibbs free energy principle and non-key component matrix are used to identify the composition of reactor's product and all distillation sequences. For distillation columns, key parameters are calculated based on Fenske-Underwood-Gilliland method, and the design variables, such as diameter and plate spacing, are identified to guarantee operational flexibility. The procedure is proposed for identifying the optimal distillation sequence with sufficient flexibility and minimum total annualized cost. For the studied styrene production process, the optimal sequence is identified from 14 possible sequences; its cost for producing unit product decreases by 26.19%, and the reactor's optimal inlet temperature is 930 K. For the ethylbenzene production process, the cost of unit product decreases by 38.6%, and the optimal byproduct recycling ratio is 1. [ABSTRACT FROM AUTHOR]

Advanced control is used to avoid large temperature offsets for a batch copolymerization gas phase reactor. A nonlinear state-space model is developed to represent the reactor behavior in terms of mass and energy balances. A growth model describes the gas phase copolymerization and includes an activation–deactivation model for the catalyst. The control system includes three manipulated inputs, three controlled outputs and two measurements, temperature and pressure. The strategy combines nonlinear control laws where states are either estimated by extended Kalman filtering or predicted from the kinetic model. This advanced control has been implemented with success on an industrial reactor. [Copyright &y& Elsevier]

Abstract: This paper focuses on struvite crystallization in controlled supersaturation. Struvite can be used as a slow-release fertilizer. Crystallization experiments were conducted using supersaturated solutions. The secondary focus of this paper is the design of a struvite recovery system in fed-batch-controlled supersaturation mode. The design and commissioning of fed-batch struvite crystallization included the determination of operating supersaturation of struvite crystallization, suitable seed materials and the composition of feed solution. Determination of operating supersaturation of struvite crystallization was conducted by two steps including thermodynamic simulation using gPROMS 2 [2] gPROMS process simulation software, Process System Enterprise, London, UK. (process simulation software) along with a set of batch experiments. Investigation of suitable seed materials was also conducted using set of batch experiments. Two types of seed materials including quartz sand and struvite seeds were used in the investigation of seed materials. Composition of feed solution included the investigation of struvite solution chemistry using PHREEQC 3 [3] US Geological Survey, Hydrologic Analysis Software Support Program, 437 National Centre, Reston VA 20192, E-mail: h2osoft@usgs.gov. thermodynamic modeling package. Based on the previously investigated design approach, struvite crystallization in fed-batch system was conducted using a 44-L of reactor with 15-L of initial reactant volume. [Copyright &y& Elsevier]

Abstract: We consider the flow of a thin liquid film over a spinning disc in the presence of an electric field. This is imposed by applying a potential between the disc and an electrode above the film. The integral method and lubrication theory are used to derive a coupled set of evolution equations for the film thickness, radial and azimuthal flow rates and the surface charge density. These equations are parameterized by a modified Weber number, a modified Masuda number, dimensionless conductivities and a dimensionless electrode separation. We focus on the limit of large liquid conductivity and explore the influence of the applied electric field on the film dynamics via numerical simulations. The effects of spatially and temporally varying electric fields and electrode geometry on the formation of waves are also examined. Our results indicate that increasing the intensity of the electric field or decreasing the electrode separation exerts a destabilizing effect, leading to the formation of interfacial waves of larger amplitude. Spatial and temporal variations of the electric field also lead to complex film dynamics which, beyond a certain threshold of the relevant parameter values, give rise to sustained formation of waves over a large fraction of the spinning disc. These results suggest that electric fields have the potential to enhance the degree of wave-induced process intensification. [Copyright &y& Elsevier]

Abstract: Ebullated bed reactors are suitable for deeply converting heavy feedstocks such as residues. In this study, a dynamic reactor model is developed taking into account hydrodynamics, catalytic and thermal kinetics. First, a validation of the hydrodynamic model is performed on a bench scale reactor using a radioactive tracer test for residence time distribution measurements under industrial conditions. In a second step, the complete dynamic model including kinetics is validated on the same reactor for various operating conditions. The model gives good predictions of conversions and yields. An improvement is required to assess this model for a larger range of operating conditions. [Copyright &y& Elsevier]

Abstract: A highly active Ag/alumina catalyst for continuous reduction of NO to nitrogen with n-octane under lean conditions was prepared. It was observed in the reactor set-up experiments for optimization of the converter, that surface generated gas phase species are crucial for obtaining high conversion. EPR and matrix isolated FTIR studies at low temperature (10–18K) were performed for identification of the radicals. Experimental data, observed at steady state conditions in the temperature range 300–550°C, was used to produce an artificial neural network model of the catalytic converter with four catalyst beds. [Copyright &y& Elsevier]

In suspension polymerisation it is sometimes necessary to add material to the reactor after the reaction has started. When that happens, the new material and existing drops can remain segregated for significant amounts of time. Hashim and Brooks (Chem. Eng. Sci. 57 (2002) 3703) showed that the viscosity of drops affects both their sizes and their rates of coalescence. In the work reported here, further clarification of the drop mixing process is achieved by using pairs of stabilised dispersions. Solutions of polystyrene (PS) in styrene formed the dispersed phase and the tracer die technique was used to determine the extent of drop mixing. Drop mixing rate increased when the polymer content of all the drops increased from 0 to 5 wt% but further increases in polymer content lead to a reduction in mixing rate. Drop viscosity affected the mixing rate both directly and indirectly, because viscosity affected drop size and that influenced the drop-mixing rate. With increased polymer content, the larger drops made little contribution to the mixing. Experimental results were compared with the prediction of a model developed previously by Alvarez et al. (Chem. Eng. Sci. 49(1) (1994) 99). The model is consistent with the initial coalescence rates that were deduced from the experimental measurements. Drops containing 0 wt% PS mixed more quickly with drops containing 5 wt% PS than with drops containing 10 wt% PS. In those cases, the initial drop size distribution was relatively wide but, gradually, became narrower (the larger drops disappeared). With no polymer in the dispersed phase, the mixing of pre-dispersed drops was slower than the mixing that occurred when a batch of non-dispersed material was added to a stabilised dispersion (i.e. batch mixing). But, with 10 wt% of polymer in the dispersed phase, the mixing rate of two stabilised dispersions was similar to the batch mixing rate (even though the added polymer solution was not initially protected by the stabiliser). Mixing of two stabilised dispersions, with drops containing different amounts of PS, indicated that drop viscosity influences the mixing rate more than the difference in drop sizes. [Copyright &y& Elsevier]

Electrochemical regeneration of NADH was performed in a new type of reactors: membrane electrochemical reactor (MER). The principle of these reactors is to confine the catalyst near the electrode thanks to a dialysis membrane (D-MER) and an ultrafiltration membrane (UF-MER). Several experimental conditions have been tested in the case of the synthesis of cyclohexanol from cyclohexanone. The best results (100% in 70 h) obtained in recycling mode with a rhodium complex as electrochemical mediator showed the potentiality of UF-MER as a process coupling a catalytic system and an electrochemical reaction. [Copyright &y& Elsevier]

Multifunctional autothermal reactors are a novel concept in process integration and intensification. They can be implemented as a countercurrent or reverse-flow reactor. A promising field of application is the coupling of endothermic and exothermic reactions. Methane steam reforming coupled with methane combustion is considered as a particular example. Several novel reactor configurations with co- and countercurrent flow in the reaction zone will be discussed by numerical simulation and an example for experimental verification will be presented. [Copyright &y& Elsevier]

Different dynamic operating behaviors of a continuous ethanol fermenter evidenced from bifurcation analysis and exhibited in a two-parameter continuation diagram (feed substrate concentration (S f) vs dilution rate parameter (D)). [Display omitted] • The dynamic behavior of a continuous fermentor was predicted by bifurcation theory. • The combination of arc-length continuation method and Heaviside function is detailed. • An oscillatory envelope of state variables was exhibited at a wide parameters range. • Bifurcation diagrams reveal the suitable conditions for continuous fermentation. The oscillatory behavior of a continuous ethanol fermentor, in the high feed sugar concentration region (200 g/L), is analyzed using the bifurcation theory. The mathematical model was solved using the arc-length continuation method including a refinement algorithm based on the Heaviside step function technique. Experimental data for ethanol production using Zymomonas mobillis were fitted to a phenomenological model based on the concept of dynamic specific growth rate and inhibition. Thus, a through connection is defined between model parameters and oscillatory behavior. Our approach shows the rich static and dynamic bifurcation topology of the continuous fermentation reactor, which includes Fold, Hopf, Bautin, and Cusp bifurcations. The four-dimensional model shows that intricate oscillations can occur and that the periodic attractors of the system can have thoughtful consequences on reactor performance. In fact, it is evidenced that, in some conditions, periodic/bifurcation behavior presents higher ethanol productivity than the corresponding steady-state. Bifurcation analysis provides insight into the possible operation conditions and their impact on conversion and productivity of the fermentation process. [ABSTRACT FROM AUTHOR]