Tubular Reactor System Research Articles

Production of C2−C4 Olefins with Fischer‐Tropsch‐Synthesis: The Effect of Cu Promoter Loading on an Fe−Cu−K/SiO2 Catalyst

AbstractIn this study we focus on the iron‐based catalyst to produce C2−C4 olefin hydrocarbons via the high‐temperature Fischer‐Tropsch synthesis. Promoters have a significant impact on catalyst stability, activity, and product selectivity. Therefore, we investigated the effect of the Cu promoter in an Fe−Cu−K/SiO2 catalyst. We compared the catalyst without Cu and 1, 2, 3, 4, and 5 wt % Cu loadings. The overall catalyst activity increased from 0 to 3 wt % Cu loading and started to decrease at 4 and 5 wt % Cu loadings. Although overall catalyst activity had an optimum with 3 and 4 wt % Cu loading, the Cu loading had a negligible effect on product selectivity. However, when compared to a non‐Cu promoted catalyst, the Cu addition increased the selectivity towards olefinic C2−C4 hydrocarbons. The Fischer‐Tropsch experiments were performed in a tubular reactor system at 300 °C, 21 bar and H2 : CO=2 at different feed volume flows, with hydrogen activation. According to the performed temperature‐programmed dynamic chemisorption analysis, the Cu promoter assisted the iron reduction, and the lower overall activity to 0–2 wt % Cu loading might relate to insufficient dissociated H surface species, rather than the availability of C from dissociated CO.

CO2 methanation over low-loaded Ni-M, Ru-M (M = Co, Mn) catalysts supported on CeO2 and SiC

The concentration of the major greenhouse gas CO2 is rapidly increasing in the atmosphere, leading to global warming and a range of environmental issues. An efficient circulation and utilization of CO2 is critical in the current environmental context. Methanation, an exothermic process, emerges as a critical strategy for effective CO2 utilization. On this front, there is a significant demand for rational design of catalysts that maintain high activity and methane selectivity over a wide temperature range (250–550 °C). The catalyst that can promise a consistent reaction even at 500 °C under an atmospheric pressure is thus obliged. The present study investigated bimetallic catalysts with SiC, which is known for its exceptional thermal conductivity, and CeO2, which is characterized by its CO₂ affinity, as base materials. We incorporated Ni-M and Ru-M (M = Co and Mn) as the active metals, each loaded at 2 %. Impressively, with merely 20 mg, the Ni-Co/SiC catalyst achieved a CO2 conversion rate of 77 % and CH₄ selectivity of 88 % at 500 °C, in a fixed-bed tubular reactor system with conditions of H2/CO2 = 4, a total flow rate of 70 ml min−1, and a steady GHSV of 12,000 h−1. Moreover, 2Ni-2Co/CeO2 catalyst demonstrated exceptional performance with a 76 % conversion of CO2 and a 83 % selectivity for CH4, all under identical conditions. The catalyst's durability was confirmed by a subsequent 40-hour stability test, which showed only a 3–5 % degradation. The developed catalysts were comprehensively characterized by BET/BJH, CO pulse chemisorption, H2-TPR, HAADF-STEM-EDS, SEM-EDS and XRD etc. to unveil their physicochemical and surface traits. It was found that Co and Mn, when integrated, effectively restrained the agglomeration of Ni and Ru particles, ensuring optimal metal dispersion on the support. In conclusion, our synthesized bimetallic catalysts shown a sustained catalytic capability, even in the high-temperature environment.

Study of norfloxacin degradation by advanced oxidation process using UV/TiO2/H2O2 in an annular reactor

Norfloxacin (NFX) residual was frequently found in domestic wastewater, sewage treatment plants, hospital wastewater, and surface water like lakes and rivers. This threatens the ecological balance of the environment. Moreover, normal biological treatment methods (including membrane bioreactor - MBR) are not feasible for the removal of NFX. In this study, the degradation of NFX through advanced oxidation processes (AOPs) utilising UV/TiO2 and H2O2 as reagents in a laboratory-scale tubular reactor system was conducted. The degradation reactions of NFX could be represented by the Langmuir-Hinshelwood kinetic model. The influence of factors, including TiO2and H2O2 concentrations, UV irradiation intensity, and hydrodynamic conditions (specifically, Reynolds number), on the apparent reaction rate constant (kapp) was evaluated. The results demonstrated that the advanced oxidation process employing the combined reagents of UV/TiO2/H2O2 under the following reaction conditions: TiO2 and H2O2concentrations of 0.2 g/l and 0.0492 mol/l, UV irradiation intensity of 225 W/m2, and Reynolds number of 6700, achieved an apparent degradation reaction rate constant for NFX of 0.052 min-1.

Constrained profile estimation for distributed parameter system in one dimension using orthogonal collocation

Several industrial processes fall under the category of Distributed parameter systems (DPS) which are represented as coupled partial differential equations (PDEs). Obtaining accurate and physically meaningful profile estimates of states despite only a limited number of spatially distributed measurements, is a pre-requisite for adequately controlling such systems. In this work, we propose an online constrained state profile estimation approach for DPS. The approach is based on reduced-dimension model represented by differential and algebraic equations (DAE) which in turn is developed by discretization of the PDEs along the spatial coordinate using the orthogonal collocation (OC) method. A profile prediction error based approach is proposed for systematically fixing the dimension of the OC model to be used. Further, to compensate for the inevitable model plant mismatch (MPM) arising in the process of the dimensionality reduction, additive zero mean Gaussian white noise processes are introduced in both state dynamics as well as measurement model. Statistics of these noises are obtained based on simulation based realizations of approximation errors at collocation points and measurement locations. To incorporate the identified correlation between the resulting state and measurement noises in the estimation method, we propose a constrained DAE-EKF (extended Kalman Filter) extension to deal with such correlations. The estimation approach also involves an appropriately formulated optimization based update step to ensure constraint satisfaction over the entire spatial profile leading to physically meaningful state profile estimates. The constrained profile estimator is also integrated with an online moving window based parameter estimation, which enables tracking of both time varying parameters and state profiles. The efficacy of the proposed approach is demonstrated by conducting stochastic simulation studies using two tubular reactor systems. The results show that the proposed constrained online state estimation approach is able to obtain accurate profile estimates at low computational cost, while ensuring that the profile estimates satisfy the given constraints.

Analysis of the Effectiveness Factor in a Fixed-Bed Tubular Reactor System: Catalytic Dehydrogenation of Cyclohexanol

The modeling and simulation of the catalytic dehydrogenation process of cyclohexanol in a fixed-bed catalytic reactor is presented, leading to finding the relationship between the effectiveness factor, the Thiele modulus, and the Weisz–Prater modulus of the catalyst particles with respect to their axial and radial position, for which the external conditions of concentration and temperature around each particle were previously obtained by applying the material and energy balances in the catalyst bed considering a two-dimensional pseudo-homogeneous model with radial diffusion. Subsequently, the material balances are established in terms of the molar flux density and conversion, the energy balance in terms of the heat flux density, Fick’s law, Fourier’s law, and the differential form of the effectiveness factor non-isothermal for each particle chosen based on the proposed meshing. The Thiele modulus calculated for most of the points is between 0.8 and 0.25, with a tendency towards the lower limit, and the theoretical values established as the limit for the Thiele modulus fluctuate between 0.4<Th<4. Therefore, the effectiveness factor analyzed is between 1 and 1/Th; this indicates that both the reaction speed as well as the diffusion speed within the particle have an influence on the intraparticle process, which is confirmed by the calculation of the Weisz–Prater modulus whose values are not <<1 nor >>1. The results obtained are subjected to a statistical test leading to analyzing whether there are significant differences both in the Thiele modulus, as well as in the effectiveness factor with respect to the radius and length of the reactor. It has been determined that there are no significant differences between the effectiveness factor with respect to the radius of the reactor; however, according to the analysis of variance, there are significant differences in the effectiveness factor with respect to length and, likewise, there are significant differences in the Thiele modulus and the Weisz–Prater modulus with respect to radius and length.

Studying of different supported metal catalysts for bio-JET production

Since 2011, the volume of passenger air transport grew nearly 7.5%/year, while freight air transport grew 3.6%/year regarding to the performed kilometers. The expansion of the aviation sector resulted increasing fuel consumption, too. The growing usage of fossil-based jet fuel results significant particle and carbon dioxide emissions, which causes remarkable environment pollution. This emission can only be reduced with using alternative jet fuels, especially those are originated from natural/waste fatty acid/-ester triglyceride sources. The aim of the experimental work was to compare industrially applied sulfide-state catalysts containing different transition metals from the aspect of catalytic conversion of mixtures of waste coconut oil and unrefined kerosene to produce jet fuel at various process parameters (temperature = 280–360 °C, liquid hourly space velocity = 1.0–3.0 h−1, pressure = 30 bar, hydrogen/hydrocarbon volume ratio = 600 Nm3/m3) in a continuous down-flow tubular reactor system. The obtained products contributes to decrease in particle and carbon dioxide emission of aircrafts due to their lower aromatic content. The smoke point of the products obtained at favorable process parameters was higher than 30 mm, while the requirement in ASTM D 1655 standard is minimum 25 mm.

Improved event-triggered control for a chemical tubular reactor with singular perturbations

This study proposes an improved event-triggered controller based on spatiotemporally sampled data for the temperature and concentration profiles of a chemical tubular reactor subject to singular perturbations. The resulting system contains not only the spatial location characteristics but also multiple-time-scale features, which results in problems in the system design. To reduce the network communication burden, a spatiotemporal data approach is employed, based on which an improved spatiotemporal-event-triggered mechanism is proposed. Furthermore, a point-control strategy is developed to reduce the system-control costs for limited actuators. Finally, some conditions that guarantee stability of the chemical tubular reactor system are given, and the simulation results are presented to demonstrate the validity and applicability of the proposed design.

Sensor Fault Accommodation for a Plug Flow Reactor using an M-Estimator

The presence of gross errors in the measurements can lead to biased state estimates when conventional Bayesian estimators are used. This can hamper the model-based monitoring and control schemes that rely on the accurate state estimates. In this work, we have developed a framework for robust estimation of the state profiles for Distributed parameter systems (DPSs), in the presence of biased measurements. The proposed approach uses an M-estimator to identify the faulty sensor. The sensor fault diagnosis is then used to augment the state estimator with an extra state that estimates the drifting sensor bias. The proposed approach has been applied to an Auto-Thermal tubular reactor system. The proposed scheme successfully isolates the biased temperature sensors and includes or removes additional bias states as and when required. The gross errors/biases are estimated and subsequently accommodated to provide accurate estimates of spatial profiles of reactor concentration and temperature.

Enhancing the amination reaction of 4-nitrochlorobenzene in a tubular reactor

In this work, a tubular reactor with a micromixer was introduced in attempt to enhance the amination reaction of 4-nitrochlorobenzene in terms of the process efficiency and safety. It was found that the reaction system containing a large excess of ammonia water can become homogeneous at high temperature. Thus, as both micromixing and the heat transfer performance were guaranteed, the set-up combining a micromixer and a microtube reactor enabled the reaction to exhibit homogeneous reaction characteristics, meeting the demands of efficiency and reliability. Furthermore, using a multi-channel sampling system connected behind the micromixer, the reaction kinetics were studied in a modified “stop flow” mode, which is adaptable for in-situ fast homogenization, high temperature, and high pressure. The reaction conditions were screened and a kinetic model was developed. Accordingly, we propose and verify a self-circulation strategy to reduce the burden of ammonia separation and recovery in a continuous tubular reactor system.

Design of Photobioreactors for Algal Biomass Growth

The present energy scenario of depleting sources of fossil fuel, increasing the cost of processed fuel and geopolitical policies have made it imperative that alternate energy sources and processes that reduce greenhouse gas emissions be identified. Biofuels from algae, in recent times, have emerged as a potential alternative to fossil fuels, as it can be easily produced, stored, and used as transportation fuels. Here, mathematical design models are developed for tubular, bubble column, and airlift photobioreactors to calculate their productivity for the growth of algal biomass. A modified Monod kinetic equation is used to estimate the specific growth rate of the biomass. The model equations are solved for tubular reactor systems and the estimated productivities are successfully validated against values available in published literature. It is found that the tubular reactor has productivity, around 2.1 g/L.day. The analysis is also done to identify the effect of light, nutrient, and carbon dioxide on overall productivity.

Kinetic Study Based on the Carbide Mechanism of a Co-Pt/γ-Al2O3 Fischer–Tropsch Catalyst Tested in a Laboratory-Scale Tubular Reactor

A Co-Pt/γ-Al2O3 catalyst was manufactured and tested for Fischer–Tropsch applications. Catalyst kinetic experiments were performed using a tubular fixed-bed reactor system. The operative conditions were varied between 478 and 503 K, 15 and 30 bar, H2/CO molar ratio 1.06 and 2.11 at a carbon monoxide conversion level of about 10%. Several kinetic models were derived, and a carbide mechanism model was chosen, taking into account an increasing value of termination energy for α-olefins with increasing carbon numbers. In order to assess catalyst suitability for the determination of reaction kinetics and comparability to similar Fischer–Tropsch Synthesis (FTS) applications, the catalyst was characterized with gas sorption analysis, temperature-programmed reduction (TPR), and X-ray diffraction (XRD) techniques. The kinetic model developed is capable of describing the intrinsic behavior of the catalyst correctly. It accounts for the main deviations from the typical Anderson-Schulz-Flory distribution for Fischer–Tropsch products, with calculated activation energies and adsorption enthalpies in line with values available from the literature. The model suitably predicts the formation rates of methane and ethylene, as well as of the other α-olefins. Furthermore, it properly estimates high molecular weight n-paraffin formation up to carbon number C80.

Effects of structural and concentration polarization on the efficiency of Pd membrane permeator

For the processes of extracting hydrogen from the mixed gas of fusion reactors, it is of benefit to find an efficient method for hydrogen isotopes recovery and cyclic utilization. To enhance the hydrogen extraction efficiency, the properties of hydrogen permeation under various operating conditions in the tubular Pd membrane reactor system have been first investigated using the computational fluid dynamics (CFD) and material diffusion model. The results show that the predominated factor for the hydrogen extraction efficiency of tubular Pd membrane reactor is the fluid field of permeation pipe, further the effects of flux velocity, membrane length and thickness on the extraction efficiency at different pressures, as well as the concentration polarization effect at different conditions have been evaluated. The results could be significant for improving the engineering design of a highly efficient extraction Pd reactor by greater aspect ratio reactor. In addition, this method can also be used to simulate isotope separation process in Pd membrane reactor.

Improvement of microalgae biomass productivity and subsequent biogas yield of hydrothermal gasification via optimization of illumination

This study examines the light factorial optimization of Chlorella vulgaris microalgae cultivation under different wavelengths and light intensities. RGB light-emitting diodes were applied on microtiter plate and lab scale stirred tank photobioreactors. One-way ANOVA and response surface methodology were adopted to investigate the effects on biomass productivity. The highest biomass productivity is found at 243.5 and 96.8 μmol photon m−2 s−1 in case of red and blue color intensities, respectively. Scaled-up fermentation in stirred tank photobioreactors shows that changing light intensity and aeration settings result in differing biomass productivity and composition. The effects of targeted cultivation are investigated on hydrothermal gasification (HTG) which is carried out in tubular reactor system at 550 °C, 30.0 MPa and average 120 s residence time. It is found that the fermentation of microalgae under optimized light factor levels results in higher H2 yield compared to unoptimized light intensity levels. Throughout the HTG process high H2 yield is achieved (4.38–9.34 mol kg−1) without using any catalyst, which indicates that the efficiency of downstream processing can be increased already at the cultivation stage.

High Yield Synthesis of Polystyrene Microspheres by Continuous Long Tubular Reactor and Their Application to Antiglare Film for High Resolution Displays

Uniform polystyrene (PS) microspheres are synthesized by dispersion polymerization in a continuous long tubular reactor (CLTR) system, whereas the batch reactor system yields ∼1.8 fold smaller PS microspheres because the CLTR system has higher conversion (∼92%) and more number of nuclei at early stage than the batch system (∼68 %) due to better heat transfer. The uniform PS microspheres can be synthesized in CLTR system with high conversion if the residence time (reaction time) in CLTR is longer than the saturation time of reaction (conversion). In addition, when we apply the PS microspheres to antiglare (AG) film for high resolution displays, the AG film exhibits good pencil hardness of 4 H under 200 g load and internal, external, and total haze of 12.50, 4.38, and 16.88, respectively.

Enzymatic Continuous Flow Synthesis of Thiol-Terminated Poly(δ-Valerolactone) and Block Copolymers.

Thiol-terminated poly(δ-valerolactone) is directly synthesized via enzymatic 6-mercapto-1-hexanol initiated ring-opening polymerization in both batch and microreactor. By using Candida antartica Lipase B immobilized tubular reactor, narrowly dispersed poly(δ-valerolactone) with higher thiol fidelity is more efficiently prepared in contrast to the batch reactor. Moreover, the integrated enzyme packed tubular reactor system is established to perform the chain extension experiments. Thiol-terminated poly(δ-valerolactone)-block-poly(ε-caprolactone) and poly(ε-caprolactone)-block-poly(δ-valerolactone) are easily prepared by modulating the monomer introduction sequence.

Numerical Computation for a Kind of Time Optimal Control Problem for the Tubular Reactor System

This paper is devoted to the study of numerical computation for a kind of time optimal control problem for the tubular reactor system. This kind of time optimal control problem is aimed at delaying the initiation time τ of the active control as late as possible, such that the state governed by this controlled system can reach the target set at a given ending time T. To compute the time optimal control problem, we firstly approximate the original problem by finite element method and get a new approximation time optimal control problem governed by ordinary differential equations. Then, through the control parameterization method and time-scaling transformation, the approximation problem becomes an optimal parameter selection problem. Finally, we use Sequential Quadratic Program algorithm to solve the optimal parameter selection problem. A numerical simulation is given for illustration.

Gas Phase Thermal Oxidation of Endosulfan and Formation of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans.

This paper investigates the thermal decomposition of technical endosulfan under oxidative conditions and the subsequent formation of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans (PCDD/F, dioxins), and their precursors. Both quantum chemical calculations and laboratory experiments were employed to investigate the pathways of oxidation of endosulfan. The laboratory scale apparatus used consists of a tubular reactor and product collection system and analysis train. The results report the effect of temperature (523-923 K) and O2 concentration on PCDD/F formation in a N2 bath gas at a residence time of 5 s. The decomposition of endosulfan produces two types of PCDD/F precursors, involving all chlorinated benzenes (CBz) and chlorinated phenols (CPh). Oxidation of endosulfan favors the formation of PCDF over PCDD. Octachlorodibenzofuran is the most abundant homologue group detected in all experiments. The maximum emission factor for PCDD/F was observed at 923 K and O2 content of 6% and corresponds to 64 ng TEQ-WHO2005 per mg of endosulfan and a total dioxin concentration of 1131 ng/mg of endosulfan.

Development of heterogeneous preparation with inulinase for tubular reactor systems

We developed highly stable heterogeneous preparations of inulinase immobilized on the ion-exchange matrixes and show that such preparations effectively split the chemically pure inulin and the inulin contained in plant extracts.The optimal conditions of hydrolysis are created for the migration of inulin solution from top to bottom (the downsteam flow) through the column filled by immobilized compounds extracted from Kluyveromyces marxianus and Helianthus tuberosus with the flow rate of 3mL/min. For the bottom-up migration of the inulin solution (i.e. the upstream flow) through the column the flow rate of 5mL/min was found to be the most optimal for the hydrolysis.When the extract of H. tuberosus was allowed to pass through the column filled by the immobilized plant inulinase from top to bottom with the flow rate of 5–10mL/min, the conditions for hydrolysis appear to be the most optimal. The conditions for hydrolysis were also found to be favourable for the bottom-up moving of the H. tuberosus extract through the column for the flow rate of 3–5mL/min.For the yeasts inulinase immobilized on VION KN-1 the most optimal flow rates of the H. tuberosus extract in the reactor were found to be similar for the following rates of inulin flow, viz. 3mL/min for the downstream flow and 5mL/min for the upstream flow.A theoretical description of the process of the inulin hydrolysis has been proposed and experimentally verified, which allows predicting the time of the full hydrolysis at different operating conditions with an error not exceeding 20%. It could be applied for the design of continuous reactors.

Oxidative dehydrogenation of propane over V$_{2}$O$_{5}$ and K$_{2}$O-V$_{2}$O$_{5}$ impregnated MgAl$_{2}$O$_{4}$ catalysts

V$_{2}$O$_{5}$ and K$_{2}$O-V$_{2}$O$_{5}$ impregnated MgAl$_{2}$O$_{4}$ catalysts were prepared and tested for the oxidative dehydrogenation of propane. The as-synthesized catalysts were characterized by using the XRD, BET, NH$_{3}$-TPD, TPR, and XPS methods. The catalytic tests were performed in a fixed bed tubular quartz reactor system between 450 and 550 $^{\circ}$C. It was observed that the conversion of propane increased but hydrocarbon selectivity decreased with increasing temperature over the V$_{2}$O$_{5}$/MgAl$_{2}$O$_{4}$ catalysts. The BET surface area values and surface acidities decreased upon potassium addition for the K-V$_{2}$O$_{5}$/MgAl$_{2}$O$_{4}$ catalysts, which resulted in a drastic drop in the conversion values obtained. The propylene and total hydrocarbon selectivities increased with increasing temperature.

Stabilizing model predictive control using parameter-dependent dynamic policy for nonlinear systems modeled with neural networks

A class of parameter-dependent dynamic control policies is explored for its use in a model predictive control (MPC) algorithm for a nonlinear system modeled with a feedforward neural network (NN). The NN-modeled system is expressed as a polytopic quasi-linear-parameter-varying (quasi-LPV) system over a region of the state-input space for a range of operating points, and the dynamics of the proposed policy, which are optimized off-line to enlarge the region of attraction, are allowed to depend on a time-varying parameter of the polytopic quasi-LPV system model such that the resulting control involves a continuous gain-scheduling that leads to reduced conservativeness. A complete MPC algorithm using the dynamic policy as the terminal policy ensures stabilization and improved control performance over a larger domain of attraction without a larger horizon length. Simulation examples with tank and tubular reactor systems illustrate the effective performance of the proposed approach in practical applications.