Amplification of Periodic Temperature Disturbances in a Packed‐Bed Reactor: CO Oxidation over a CuO/Al2O3 Catalyst

Amplification of periodic variations of input temperature in a product‐inhibited reaction — CO oxidation over CuO‐γ‐Al₂O₃ — was investigated experimentally in an insulated packed‐bed reactor. At steady state the temperature profile was elongated compared with that of a reactant‐inhibited CO oxidation over Pt/Al₂O₃, studied elsewhere. Under periodic operation, amplitudes of the resulting travelling temperature waves, monitored downstream from the reaction front, were amplified to a greater extent than those in the reactant‐inhibited CO oxidation over Pt/Al₂O₃. The magnitude of the amplification depended on the perturbation frequency and showed resonance behaviour. The magnitude decreased monotonically with increasing perturbation amplitude.     

Selective Hydrogenation of Acetylene in an Ethylene Stream in an Adiabatic Reactor

In earlier studies the behavior of single catalyst pellets of Pd on alumina has been investigated for the reaction of acetylene in an ethylene stream with hydrogen. Particle runaway, temperature over‐ and undershoots and chemically induced temperature oscillations have been observed. After that, the steady state and dynamic behavior of an adiabatic packed bed reactor has been studied experimentally. Temperature profiles of both the gas and solid phase as well as local temperature differences between the two phases were measured. Also here the temperature in the reaction zone exhibited oscillatory behavior. On addition of CO, the oscillations disappeared and the selectivity improved. For a given set of operating conditions, there existed a relatively small range of CO contents with good selectivity and satisfactory conversion. This range depends strongly on the inlet temperature. The dynamic response of the reactor to changes in the CO content showed a considerable wrong‐way behavior. This high sensitivity to fluctuations in the CO content, found for our experimental reactor, indicates a probable cause for a thermal runaway in industrial practice. Recommendations for a stable reactor operation are given.     

Fischer‐Tropsch Synthesis: Modeling and Performance Study for Fe‐HZSM5 Bifunctional Catalyst

A water‐cooled fixed bed Fischer‐Tropsch reactor packed with Fe‐HZSM5 catalyst has been modeled in two dimensions (radial and axial) using the intrinsic reaction rates previously developed at RIPI. The reactor is used for production of high‐octane gasoline from synthesis gas. The Fischer‐Tropsch synthesis reactor was a shell and tube type with high pressure boiling water circulating on the shell side. By the use of a two‐dimensional model, the effects of some important operating parameters such as cooling temperature, H₂/CO ratio in syngas and reactor tube diameter on the performance capability of the reactor were investigated. Based on these results, the optimum operating conditions and the tube specification were determined. The model has been used to estimate the optimum operating conditions for the pilot plant to be operated in RIPI.     

BEHAVIOUR OF AN ADIABATIC PACKED BED REACTOR PART 1: EXPERIMENTAL STUDY

The steady state and dynamic behaviour of an adiabatic packed bed reactor for the selective hydrogenation of ethyne and ethene mixtures was studied experimentally. Different methods to achieve adiabatic conditions on a laboratory scale were tested. Temperature profiles of both the gas and solid phase as well as local temperature differences between the two phases were measured. For hydrogenation in the absence of carbon monoxide the selectivity was always poor. Also, in that case, the temperature in the reaction zone exhibited oscillatory behaviour. On addition of CO, the oscillations disappeared and the selectivity improved. For a given set of operating conditions there existed a relatively small range of CO contents with good selectivity and satisfactory conversion. This range depends strongly on the inlet temperature. The dynamic response of the reactor to changes in the CO content showed a considerable wrong-way behaviour. This high sensitivity to fluctuations in the CO content, found for our experimental reactor, indicates a probable cause for a thermal runaway in industrial practice.     

Pure H2 production through hollow fiber hydrogen‐selective MFI zeolite membranes using steam as sweep gas

Hollow fiber MFI zeolite membranes were modified by catalytic cracking deposition of methyldiethoxysilane to enhance their H₂/CO₂ separation performance and further used in high temperature water gas shift membrane reactor. Steam was used as the sweep gas in the MR for the production of pure H₂. Extensive investigations were conducted on MR performance by variations of temperature, feed pressure, sweep steam flow rate, and steam‐to‐CO ratio. CO conversion was obviously enhanced in the MR as compared with conventional packed‐bed reactor (PBR) due to the coupled effects of H₂ removal as well as counter‐diffusion of sweep steam. Significant increment in CO conversion for MR vs. PBR was obtained at relatively low temperature and steam‐to‐CO ratio. A high H₂ permeate purity of 98.2% could be achieved in the MR swept by steam. Moreover, the MR exhibited an excellent long‐term operating stability for 100 h in despite of the membrane quality. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3459–3469, 2015     

Study of Unsteady‐State Operation of Methanation by Modeling and Simulation

Methanation of CO under unsteady‐state operation conditions was studied systematically based on a simplified mathematical model for an integral reactor using steady‐state kinetics available in the literature. The inlet composition of CO and H₂ was changed stepwise and the step response of the system was monitored in order to study the dynamic behavior of the reactor. Furthermore, periodic changes were applied with different cycling times. It was observed that the time average reaction rate could not be improved by cycling the feed composition. Moreover, the reactor appears to be self‐stabilizing, since the amplitude at the outlet is reduced, leading to a steady state for high cycling frequencies. The results allow conclusions on principles to design a methanation reactor for unsteady‐state operation. However, it also becomes obvious that unsteady‐state kinetics is mandatory in order to describe the experimental results obtained under dynamic conditions.     

Modeling of transient heterogeneous two-dimensional catalytic packed bed reactor

A two-dimensional transient catalytic packed bed model, incorporating all transport parameters and resistances, along with boundary conditions based on a catalytic single pellet has been developed. Thermal conduction through the solid phase is included in the model. The overall steady state reactor performances of packed bed reactor using a model proposed in this study are compared with those from different models which are often used for a packed bed reactor. The model presented is very useful in the presence of internal temperature and concentration gradients in the catalyst pellets. The dynamic behavior in feed temperature change is examined during ethane hydrogenolysis. A transient thermal runaway is observed by feed temperature decrease. The sensitivities of the computation to each physical parameter and the effects of some simplifying assumptions in the model are also analyzed. The magnitude and position of hot spot in catalytic packed bed reactor are relatively sensitive to thermal parameters and characteristic parameters of a catalyst pellet.     

CO2 reduction with Zn particles in a packed‐bed reactor

A two‐step solar thermochemical cycle for splitting CO₂ with Zn/ZnO redox reactions is considered, consisting of: (1) the endothermic dissociation of ZnO with concentrated solar radiation as the heat source and (2) the non‐solar, exothermic, reduction of CO₂ to CO by oxidizing Zn to ZnO; the latter is recycled to the first step. The second step of the cycle is investigated using a packed‐bed reactor where micron‐sized Zn particles were immobilized in mixtures with submicron‐sized ZnO particles. Experimental runs were performed for Zn mass fractions in the range 67–100 wt % and CO₂ concentration in the range 25–100%, yielding Zn‐to‐ZnO conversions up to 71% because of sintering prevention, as corroborated by SEM analysis. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

ESTIMATION OF KINETIC PARAMETERS FOR ELEMENTARY SURFACE PROCESSES FROM INTEGRAL REACTOR DATA. CO OXIDATION OVER Pt/ Al2O3

A novel method has been developed which can be used for kinetic parameter estimation from laboratory reactor data. It is based on discrete modeling and variational techniques applied to an integral reactor packed with supported catalyst pellets. This new method, similar to the McCabe-Thiele method in distillation column design, has been used to determine kinetic parameters of adsorption, desorption and surface reaction steps for CO oxidation over Pt/ AI₂ O₃catalysts at 500° C and atmospheric pressure. The results clearly indicate the importance of the coverage dependency of CO desorption activation energy in the steady state kinetics of CO oxidation. The good agreement of the results with those on single crystal Pt surfaces indicates no significant metal-support interactions for the Pt/ Al₂O₃ system during CO oxidation     

Thermodynamic Analysis for Quantifying Fuel Cell Grade H2 Production by Methanol Steam Reforming

Steam reforming of methanol in fixed‐bed and hybrid reactors, namely, traditional fixed‐bed reactor (FBR1), fixed‐bed reactor with H₂‐selective membrane (FBR2), and fixed‐bed reactor with CO₂ adsorption (FBR3) is thermodynamically analyzed. The performance of these reactors is compared in terms of quality and quantity of H₂ production for fuel cell application. In FBR2 and FBR3, the contents of undesired products CO, CH₄, and carbon are highly reduced.     

Application of chitosan‐entrapped β‐galactosidase in a packed‐bed reactor system

The model enzyme β‐galactosidase was entrapped in chitosan gel beads and tested for hydrolytic activity and its potential for application in a packed‐bed reactor. The chitosan beads had an enzyme entrapment efficiency of 59% and retained 56% of the enzyme activity of the free enzyme. The Michaelis constant (K_m) was 0.0086 and 0.011 μmol/mL for the free and immobilized enzymes, respectively. The maximum velocity of the reaction (V_max) was 285.7 and 55.25 μmol mL^?1 min^?1 for the free and immobilized enzymes, respectively. In pH stability tests, the immobilized enzyme exhibited a greater range of pH stability and shifted to include a more acidic pH optimum, compared to that of the free enzyme. A 2.54 × 16.51‐cm tubular reactor was constructed to hold 300 mL of chitosan‐immobilized enzyme. A full‐factorial test design was implemented to test the effect of substrate flow (20 and 100 mL/min), concentration (0.0015 and 0.003M), and repeated use of the test bed on efficiency of the system. Parameters were analyzed using repeated‐measures analysis of variance. Flow (p < 0.05) and concentration (p < 0.05) significantly affected substrate conversion, as did the interaction progressing from Run 1 to Run 2 on a bed (p < 0.05). Reactor stability tests indicated that the packed‐bed reactor continued to convert substrate for more than 12 h with a minimal reduction in conversion efficiency. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1294–1299, 2004     

Enhanced Conversion in the Direct Synthesis of Diethyl Carbonate from Ethanol and CO2 by Process Intensification

To overcome the low equilibrium conversion in the direct synthesis of diethyl carbonate from ethanol and CO₂ under moderate reaction conditions, the reaction was conducted in a membrane reactor packed with pelletized Cu‐Ni:3‐1 supported on activated carbon. A SiO₂/γ‐Al₂O₃ commercial membrane and zeolite A membranes synthesized on commercial Al₂O₃ supports were evaluated in the membrane reactor. Although characterization of the membranes by X‐ray diffraction confirmed the presence of a zeolite A layer on the supports, gas permeation and permselectivity tests of ethanol and water evidenced some defects of the synthesized membranes. An increase in conversion with respect to a conventional packed‐bed reactor was observed in the membrane reactors prepared on Al₂O₃, but equilibrium conversion was not attained. However, with the commercial membrane, the ethanol conversion was higher than the equilibrium conversion.     

CFD analysis of low temperature water gas shift reactor

In the design of water gas shift reactors, the performance of catalysts is not known a priori and hence having a general kinetic expression will be of much help. Computational Fluid Dynamic study was carried out to investigate the performance of a packed bed reactor for different feed compositions using five commonly used types of macro kinetic models. User Defined Functions were developed for the reaction rate to predict the CO conversion in the reactor. The effects of temperature and time factor on CO conversion were studied. The Langmuir-Hinshelwood model gave the best prediction for H₂ rich mixtures. The Temkin model was better for higher CO concentrations, whereas the other models gave large deviations for the fixed bed reactor.     

A continuous esterification of malonic acid with citronellol using packed bed reactor: Investigation of parameter and kinetics study

A continuous packed bed immobilized lipase reactor was used in the synthesis of citronellyl malonate. Biocatalyst Candida rugosa lipases which were immobilized on Amberlite MB-1 support were employed to synthesize citronellyl malonate. Investigations on the effect of different citronellol and malonic acid concentration and feed flow rate on the conversion were being conducted. Full conversion of acid to product was achieved at high concentration of citronellol (50 mmol/L) and reached a steady state after 180 min of reaction time. Maximum conversion of acid was found at a ratio of 1:3 acids to alcohol concentration. An inhibition effect was observed when a high concentration of malonic acid was used in the system. A higher feed flow rate into the packed bed reactor system had increased the conversion to 90%. An investigation on the kinetics was conducted and an ordered bi bi mechanism with dead end complex of malonic acid was found to fit the initial rate data.     

Multidimensional modeling of a microfibrous entrapped cobalt catalyst Fischer‐Tropsch reactor bed

Thermal management of highly exothermic Fischer‐Tropsch synthesis (FTS) has been a challenging bottleneck limiting the radial dimension of the packed‐bed (PB) reactor tube to 1.5 in. ID. A computational demonstration of a novel microfibrous entrapped cobalt catalyst (MFECC) in mitigating hot spot formation has been evaluated. Specifically, a two‐dimensional (2‐D) model was developed in COMSOL^®, validated with experimental data and subsequently employed to demonstrate scale‐up of the FTS bed from 0.59 to 4 in. ID. Significant hot spot of 102.39 K in PB was reduced to 9.4 K in MFECC bed under gas phase at 528.15 K and 2 MPa. Improvement in heat transfer within the MFECC bed facilitates higher productivities at low space velocities (≥1000 h^?1) corresponding to high CO conversion (≥90%). Additionally, the MFECC reactor provides an eightfold increase in the reactor ID at hot spots ≤ 30 K with CO% conversions ≥ 90%. This model was developed for a typical FTS cobalt‐based catalyst where CO₂ production is negligible. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1723–1731, 2018     

Optimal operation of a membrane reactor network

In this contribution, the operation of a membrane reactor network (MRN) for the oxidative coupling of methane is optimized. Therefore, three reactors, a fixed bed reactor (FBR) and two packed bed‐membrane reactors, are modeled. For the (CPBMR), a two‐dimensional (2‐D) model is presented. This model incorporates radial diffusion and thermal conduction. In addition, two 10 cm long cooling segments for the CPBMR are implemented based on the idea of a fixed cooling temperature positioned outside the reactor shell. The model is discretized using a newly developed 2‐D orthogonal collocation on finite elements with a combination of Hermite for the radial and Lagrangian polynomials for the axial coordinate. Membrane thickness, feed compositions, temperatures at the inlet and for the cooling, diameters, and the amount of inert packing in the reactors are considered as decision variables. The optimization results in C₂ yields of up to 40% with a selectivity in C₂ products of more than 60%. The MRN consisting of an additional packed‐bed membrane reactor with an alternative feeding policy and a FBR shows a lower yield than the individual CPBMR. © 2013 American Institute of Chemical Engineers AIChE J, 60: 170–180, 2014     

Disk-shaped packed bed micro-reactor for butane-to-syngas processing

A novel disk-shaped packed bed micro-reactor containing Rh/ceria/zirconia nanoparticles is investigated with respect to catalytic butane-to-syngas processing at moderate temperatures of 550 °C. The main goal of this study is the development of an efficient butane processor which can be integrated into a micro solid oxide fuel cell system due to its small size, easily packaged geometry in layered microdevices, high compactness, low pressure drop, and low reaction temperature. It is shown that Rh/ceria/zirconia has an excellent long-term stability and achieves very high C₄H₁₀ conversion and syngas selectivity, considering the relatively low operating temperature. The yields of H₂ and CO can be increased up to 71% and 57%, respectively, by optimizing operational parameters such as the C/O ratio and the total inlet flow rate. The introduced disk-shaped packed bed reactor shows significant advantages in catalytic behavior, at a 6.5 times lower pressure drop compared to an equivalent tubular packed bed reactor. This increased catalytic performance is pursued extensively by investigating possible reaction pathways in three regions of the radial-flow reactor, leading to the significant discovery of a threefold pathway of syngas production on a single catalyst. To this end, it is shown that the excellent selectivities to H₂ and CO for high flow rates are due to the combination of partial oxidation, steam reforming, and dry reforming of C₄H₁₀, indicating one direct and two indirect reaction paths.     

Upgrading of Simulated Syngas by Using a Nanoporous Silica Membrane Reactor

The permeance properties of a nanoporous silica membrane were first evaluated in a laboratory‐scale porous silica membrane reactor (MR). The results indicated that CO, CO₂, and N₂ inhibited H₂ permeation. Increased H₂ permeability and selectivity were obtained when gas was transferred from the lumen side to the shell side. This was therefore selected as a suitable permeation direction. On this basis, upgrading of simulated syngas was experimentally investigated as a function of temperature (150 – 300 °C), feed pressure (up to 0.4 MPa), and gas hourly space velocity (GHSV), by using a nanoporous silica MR in the presence of a Cu/ZnO/Al₂O₃ catalyst. The CO conversion obtained with the MR was significantly higher than that with a packed‐bed reactor (PBR) and broke the thermodynamic equilibrium of a PBR at 275 – 300 °C and a GHSV of 2665 h^–1. The use of a low GHSV and high feed pressure improved the CO conversion and led to the recovery of more H₂.     

Influence of TiO2‐Layer Thickness of Spray‐Coated Glass Beads on Their Photocatalytic Performance

TiO₂ is a suitable catalyst for potential photocatalytic processes, e.g., in wastewater treatment. For a technical realization of such processes, the application of immobilized TiO₂ in a continuous process would be desirable. However, since UV radiation has a limited penetration depth into a packed bed of pure TiO₂, supporting it on UV‐transparent glass beads offers the possibility to implement continuous photocatalytic processes in a fixed‐bed reactor. Considering this fact, glass beads were coated with TiO₂ powder in a fluidized‐bed reactor. The coated glass beads with varying TiO₂ layer thickness were tested in the photocatalytic degradation of methylene blue, and the influence of an addition of methyl cellulose during the coating process on the photocatalytic performance was investigated.