Monolithic Reactor Research Articles

Comparison among monolithic and randomly packed reactors for the methanol-to-propylene process

A comparison among the monolithic and randomly packed reactors for the methanol conversion to propylene (MTP) process has been presented in this work by modeling and simulation based on adiabatic heterogeneous reactor models including the interactions of mass and heat transfer and chemical reactions between the gas and catalyst phases and inside the catalyst phase. Simulation results showed that the monolithic catalyst intensifies significantly the methanol conversion efficiency and the propylene selectivity, compared with the randomly packed catalyst pellets. The monolithic reactor can achieve a propylene selectivity high up to 88% with a methanol conversion of 95% at a space time of 7gcatalysthmolMeOH-1, but the random one does 82% with 80% at 27. For a complete methanol conversion, the monolithic catalyst amount is five times less than the random pellet catalyst in an adiabatic reactor. Furthermore, the higher cell density and thinner wall of the monolith produce the higher methanol conversion and propylene selectivity.

Modeling of diffusion and reaction in monolithic catalysts for the methanol-to-propylene process

The present paper gives an insight into the methanol conversion to propylene (MTP) performance in a monolith reactor by means of a two-dimensional adiabatic heterogeneous reactor model accounting for interfacial and intra-particle gradients. Interactions of mass and heat transfer and chemical reactions were taken into account within monolith channels and inside the channel walls. Concentration and temperature profiles in both radial and axial direction were calculated for a multiple-stage monolithic reactor simulating the MTP process with special focus to influence of monolith channel geometries on selectivity of propylene. Calculated results showed that the total yield of light C2–C4 olefins can be achieved high up to 71%, with that of propylene up to 49% by a selected monolith structure of 400 cells per square inch with a 0.2mm catalytic wall thickness. Thus, the monolithic catalyst with high cell density and thin walls is recommended for the MTP process.

Using the three-way catalyst monolith reactor for reducing exhaust emissions

The monolith reactor was developed for the cleaning of exhaust gases from combustion processes, both in cars and large power plants. Nowadays, monolith reactors are increasingly being used, developed, evaluated in automotive and stationary emission control reactors such as power plants and new reactor applications such as chemical and refining processes, catalytic combustion, ozone abatement, and others. Monolith catalysts, mainstays in gas-phase automotive and environmental process applications, have found new potential in replacing three-phase slurry reactors for the production of specialty chemicals, especially when their advantages are fully utilized in recirculation loop approaches. This paper gives a general overview about monolith reactors’ benefits, fabrication, characteristics, and typical use in automotive industry. Several commercial product applications and new developments for use of monolith reactors in automotive, stationary, and chemical industry have been discussed. Different types of monolith reactor systems manufacturing, modeling, and application areas are specified with their advantages and disadvantages. Some experimental studies have been attached to compare monolith reactor types with conventional reactors.

Particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen: Construction and performance for oxidative coupling of methane

A novel particle/metal-based monolithic catalysts dual-bed reactor with beds-interspace supplementary oxygen is constructed comprising of the upper-layer 5 wt%Na2WO4-2 wt%Mn/SiO2 particle catalyst and the under-layer 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3/FeCrAl metal-based monolithic catalyst as well as a side tube in the interspaces of two layers for supplementing O2. The reaction performance of oxidative coupling of methane (OCM) in the dual-bed reactor system is evaluated. The effects of the reaction parameters such as feed CH4/O2 ratio, reaction temperature and side tube feed O2 flowrate on the catalytic performance are investigated. The results indicate that the suggested mode of dual-bed reactor exhibits an excellent performance for OCM. CH4 conversion of 33.2%, C2H4 selectivity of 46.5% and C2 yield of 22.5% could be obtained, which have been increased by 6.4%, 4.1% and 5.5%, respectively, as compared with 5 wt%Na2WO4-2 wt%Mn/SiO2 particle catalyst in a single-bed reactor and increased by 10.7%, 31.9% and 17.7%, respectively, as compared with 3 wt%Ce-5 wt%Na2WO4-2 wt%Mn/SBA-15/Al2O3/FeCrAl metal-based monolithic catalyst in a single-bed reactor. The effective promotion of OCM performance in the reactor would supply a valuable reference for the industrialization of OCM process.

Preparation and characterization of TiO2-based plasma-sprayed coatings for NOx abatement

To minimize the formation of environmentally hazardous emissions, the catalytic reduction of NO by CO at metal oxide surfaces deposited by plasma spray technology on a Fe–Cr alloy support was studied. The paper outlines an experiment performed on a bench-scale reactor, describes the preparation of a catalytic monolithic reactor, the operating conditions as well as the properties of new-type catalytic coatings. As noted earlier in [1], the catalytic coatings containing an active component CuO effectively reduce the content of CO in the exhaust gas by over 90%. To enhance the NOx reduction by CO on the catalyst, TiO2 as a promoter and Ni powder as a catalyst were additionally incorporated in the initial mixture for catalytic coating formation. The structural and functional properties of the active layer – substrate system were analysed by methods of scanning electron microscopy (SEM), BET surface area, thermal analysis (DSC-TG), X-ray diffraction (XRD) and determination of roughness parameters. All the obtained coatings showed a good density, thermal stability and physical strength. However, irregularly agglomerated metal oxide layers had been formed in some places. The most active catalytic coating of Ni–Cu/TiO2–Al2O3 type showed an 80–90% removal for both NO and CO (CO/NO=3) in the oxidizing gas mixture.

Multidimensional nano-HPLC coupled with tandem mass spectrometry for analyzing biotinylated proteins

Multidimensional high-performance liquid chromatography (HPLC) is a key method in shotgun proteomics approaches for analyzing highly complex protein mixtures by complementary chromatographic separation principles. Here, we describe an integrated 3D-nano-HPLC/nano-electrospray ionization quadrupole time-of-flight mass spectrometry system that allows an enzymatic digestion of proteins followed by an enrichment and subsequent separation of the created peptide mixtures. The online 3D-nano-HPLC system is composed of a monolithic trypsin reactor in the first dimension, a monolithic affinity column with immobilized monomeric avidin in the second dimension, and a reversed phase C18 HPLC-Chip in the third dimension that is coupled to a nano-ESI-Q-TOF mass spectrometer. The 3D-LC/MS setup is exemplified for the identification of biotinylated proteins from a simple protein mixture. Additionally, we describe an online 2D-nano-HPLC/nano-ESI-LTQ-Orbitrap-MS/MS setup for the enrichment, separation, and identification of cross-linked, biotinylated species from chemical cross-linking of cytochrome c and a calmodulin/peptide complex using a novel trifunctional cross-linker with two amine-reactive groups and a biotin label.

HKUST-1 MOF: A matrix to synthesize CuO and CuO–CeO2 nanoparticle catalysts for CO oxidation

The oxidation of carbon monoxide using the metal organic framework (MOF) HKUST-1 is studied. Catalytic results and characterizations by XRD, TEM, H2-TPR, SEM and LRS show that HKUST-1 itself is not effective in CO oxidation, but is activated in the reaction atmosphere segregating active 5–15nm CuO particles upon the collapse of the MOF structure. Furthermore, the microporous structure of HKUST-1 is effective to disperse Ce precursors which, upon activation, allow the synthesis of a mixture of CuO and CeO2 nanoparticles in intimate contact. These nanoparticles present a very high activity in CO oxidation. It is shown that this synthesis route employing HKUST-1 as a matrix is useful to immobilize CuO–Ce2O nanoparticles in a monolithic reactor, while keeping a high catalytic activity.

Degradation of anionic and cationic surfactants in a monolithic swirl-flow photoreactor

The photocatalytic oxidations of anionic, dodecylbenzene sulfonate (DBS), and cationic, cetylpyridinium chloride (CPC) surfactants were studied in a swirl-flow monolithic reactor. The degradation kinetics in aqueous TiO2 suspensions was investigated as a function of catalyst loading, light intensity, initial surfactant concentration, dissolved oxygen concentration, and pH. A systematic analysis of rates at various loadings of TiO2 was carried out to distinguish “kinetic” and “transport” limited regimes for the photocatalytic degradation of DBS and CPC in TiO2 suspensions. The optimal catalyst loading of DBS and CPC in TiO2 suspensions were determined to be 0.75 and 1.5gL−1, respectively, at a neutral pH. A small increase in oxidation rates was observed with an increase in initial concentration of the surfactant and partial pressure of the oxygen in the system. The rates as a function of initial surfactant concentration and partial pressures of oxygen were determined using a Langmuir–Hinshelwood model. The photocatalytic oxidation of DBS and CPC showed an opposite pH dependence. Removal of DBS was efficient in acidic condition while CPC showed efficacy at basic pH. The adsorption of surfactants onto TiO2 surfaces as a function of pH was studied to explain the influence of pH on the oxidation rates. The subsequent decreases in TOC levels of surfactant during oxidation were found to be more efficient at a neutral pH than acidic or basic pH.

Sulfur removal in monolithic three-phase reactors: Model and simulation

Monolith three-phase reactors are candidate reactors for implementing the catalytic process of sulfur removal from gasoil because of the good mass transfer characteristics, low pressure drop, high geometric surface area and low axial dispersion and backmixing. An integrated approach which links momentum, mass and enthalpy transport processes in a monolith three-phase reactor under high-pressure gasoil sulfur removal conditions was proposed in this work. The two-scale, non-isothermal, unsteady-state model developed was used to analyze the effects of the catalyst loading, pressure, temperature, superficial liquid and gas velocity, reactants/products concentration on the performance of the monolith three-phase reactor. The value of the simulated behavior of the monolith reactor was discussed in the light of a sensitivity analysis of the model outputs with regard to the mass transfer parameters. The sulfur removal performance of the upflow configuration of the monolith three-phase reactor was compared with the performance of a usual trickle bed reactor operated at the same liquid space velocity based on the mass of catalyst.

ChemInform Abstract: Monolithic Catalysts and Reactors: High Precision with Low Energy Consumption

AbstractReview: 217 refs.

Towards the simulation of the catalytic monolith converter using discrete channel-scale models

Over the past twenty years, several computer models for structured catalytic reactors such as the monolith converter have been developed with various levels of complexity and accuracy. Despite the availability of faster and faster computers, no reports have been made yet on the successful simulation of transport phenomena in every channel of a monolith catalytic converter by means of a full three-dimensional discrete model. The purpose of this work is to show the potential of such a model, based on the lattice Boltzmann method (LBM), for simulating fluid flow in an elliptical shaped honeycomb monolith reactor comprising a total of 7539 parallel channels. This example of industrial relevance will serve to evidence the progress made in computer modeling in recent years, but also to bring up aspects that need to be further improved, such as the use of LBM to simulate efficiently turbulent flow and heat and mass transfer in this type of structured catalytic reactors.

Resolving a Challenge in the Modeling of Hydrogen Production Using Steam Reforming of Methane in Monolith Reactors Using CFD Methods

Reaction modeling of SMR (Steam Methane Reforming) process inside monolith reactors using two approaches were investigated and compared with each other. In the first approach, the reactions were assumed to take place exactly on the wall surfaces, while in the second approach they considered inside a thin thickness near the walls. Experiments of SMR were carried out in a lab-scale monolith reactor. A single-channel was considered and CFD model were developed for each of aforementioned approaches. Comparisons between modeling results and experimental data showed that the first approach (surface model) gives better results. Performing reactions are difficult and expensive, CFD simulations are considered as numerical experiments in many cases. It was concluded that obtained results from CFD analysis gives precise guidelines for further studies on optimization of SMR monolithic reactor performance.

Modeling and Simulation of Phthalic Anhydride Production in a Structured Metallic Monolith Reactor

Monolith are blocks consisting of large number of straight and parallel channels. Recently usage of metallic monolith for catalytic reactions are reported. These metallic monoliths provide excellent heat transfer properties which can effectively be utilized for highly exothermic reactions in catalytic packed bed reactor. We have developed a model for multi-tubular reactor of phthalic anhydride production utilizing these structured metallic monolith. The developed model on simulation reveals minimization of hot spot formation and hence substantial reduction of run-away conditions within the reactor. It has also been shown that usage of these novel monolth can increase the productivity of plant manifold.

Experimental and Theoretical Investigation of Controlling Regimes during Lean Oxidation of Methane and Propylene on Pt/Al2O3 Monolithic Reactors

The performance of a catalytic reactor is bounded by the kinetic regime at low temperature (or before light-off) and the mass-transfer-controlled regime at high temperature. Pore diffusion may also be significant at intermediate temperature. We utilize the recently developed criteria (Joshi, S. Y.; Harold, M. P.; Balakotaiah, V. Chem. Eng. Sci.2010, 65, 1729–1747) to characterize the controlling regimes during lean oxidation of CH4 and C3H6 in Pt/Al2O3 monolithic reactors. First, we determine the global kinetics of lean oxidation of CH4 and C3H6 in a Pt/Al2O3 monolithic catalyst. We also present a method for estimation of the effective diffusivity of the limiting reactant and the external mass-transfer coefficient under reacting conditions. Further, we characterize the relative contributions of chemical kinetics, washcoat diffusion, and external mass transfer as a function of the various catalyst design and operating parameters. The analysis reveals that methane oxidation is kinetically controlled over a wide range of temperatures (350–600 °C) whereas propylene oxidation has a more classical transition between the kinetic and mass-transfer-controlled regimes. We use the bench-scale results to analyze the impact of various design and operating variables on transitions between the controlling regimes.

Heat and mass transfer in automotive catalysts—The influence of turbulent velocity fluctuations

Monolithic reactors employed in automotive exhaust gas aftertreatment typically operate under fluctuating flow conditions. These fluctuations in the volumetric flow rate through the catalyst are caused by engine pulsations and the upstream exhaust gas turbulence.In the current work, the effects of the turbulent-to-laminar transition on the conversion of pollutants under mass-transfer limited operation of a monolithic reactor are investigated using numerical simulations. The most notable effect of the turbulence is an introduction of temporal fluctuations to the observed conversion at the outlet. These fluctuations are attributed to variations in the axial velocity (and thus the retention time) in the channel.A simplistic model for a single monolith channel in a tanks-in-series framework is suggested that captures this effect of the upstream turbulence on the dimensionless heat and mass transfer numbers in automotive catalysts. The model can be used to resolve the transient variations of the heat and mass transfer when the upstream turbulent characteristics are known. The effects of such variations on the catalytic conversion are likely to be most pronounced for reactions with negative-order kinetics when operating close to ignition or extinction.

CFD modeling of hydrogen production using steam reforming of methane in monolith reactors: Surface or volume-base reaction model?

In the present work, two approaches for reaction modeling in monolith reactors were taken into account and compared to each other. In the first approach, the reactions are assumed to take place on the wall surfaces, while penetration and reaction of chemical species inside a thin layer near the walls are of essential concern in the second approach. Experiments of Steam Methane Reforming (SMR) were carried out in a Bench-scale monolith reactor. A single-channel was considered and two axi-symmetric CFD models were developed for modeling. General kinetic models for SMR and Water–Gas-Shift (WGS) reaction rates based on Langmuir–Hinshelwood type were employed. Comparisons between modeling results and experimental data showed that despite its ease of implementation, the first approach (surface reactions) exhibits better results both in generality and accuracy. It was realized that uncertainties in obtaining the effective diffusion coefficients in the volumetric approach may cause a variation up to 16% in the prediction of reaction conversion.

A monolithic lipase reactor for biodiesel production by transesterification of triacylglycerides into fatty acid methyl esters.

An enzymatic reactor with lipase immobilized on a monolithic polymer support has been prepared and used to catalyze the transesterification of triacylglycerides into the fatty acid methyl esters commonly used for biodiesel. A design of experiments procedure was used to optimize the monolithic reactor with variables including control of the surface polarity of the monolith via variations in the length of the hydrocarbon chain in alkyl methacrylate monomer, time of grafting of 1-vinyl-4,4-dimethylazlactone used to activate the monolith, and time used for the immobilization of porcine lipase. Optimal conditions involved the use of a poly(stearyl methacrylate-co-ethylene dimethacrylate) monolith, grafted first with vinylazlactone, then treated with lipase for 2 h to carry out the immobilization of the enzyme. Best conditions for the transesterification of glyceryl tributyrate included a temperature of 37°C and a 10 min residence time of the substrate in the bioreactor. The reactor did not lose its activity even after pumping through it a solution of substrate equaling 1,000 reactor volumes. This enzymatic reactor was also used for the transesterification of triacylglycerides from soybean oil to fatty acid methyl esters thus demonstrating the ability of the reactor to produce biodiesel.

Oxidation reaction kinetics for the steam-iron process in support of hydrogen production

A hydrogen generation research program is focused on solar-driven hydrogen production by means of reactive metal water splitting. In order to dissociate water molecules at significantly reduced thermal energies as well as providing a practical means for efficient hydrogen and oxygen separation, an intermediary reactive material is introduced to realize water splitting in the form of an oxidation reaction. Elemental iron is used as the reactive material in the process commonly referred to as the steam-iron process. In order to exploit the unique characteristics of highly reactive materials and ultimately achieve the potential efficiency gains at the solar reactor scale, a monolithic laboratory-scale reactor has been designed to explore the fundamental kinetic rates during the iron oxidation reaction at temperatures ranging from about 650 to 900 K. Results show hydrogen production rates on the order of 1E-8 g/cm 2 s. Micro-Raman spectroscopy is used to access information on the exact iron oxide phase produced, and high resolution SEM and electron dispersion spectroscopy (EDS) are used to assess the oxide morphology and further quantify the oxide state, including spatial distributions.

Scaling up of continuous-flow, microwave-assisted, organic reactions by varying the size of Pd-functionalized catalytic monoliths

A product-scalable, catalytically mediated flow system has been developed to perform Suzuki–Miyaura reactions under a microwave heating regime, in which the volumetric throughput of a Pd-supported silica monolith can be used to increase the quantity of the product without changing the optimal operating conditions. Two silica monoliths (both 3 cm long), with comparable pore diameters and surface areas, were fabricated with diameters of 3.2 and 6.4 mm to give volumetric capacities of 0.205 and 0.790 mL, respectively. The two monoliths were functionalized with a loading of 4.5 wt % Pd and then sealed in heat-shrinkable Teflon® tubing to form a monolithic flow reactor. The Pd-supported silica monolith flow reactor was then placed into the microwave cavity and connected to an HPLC pump and a backpressure regulator to minimize the formation of gas bubbles. The flow rate and microwave power were varied to optimize the reactant contact time and temperature, respectively. Under optimal reaction conditions the quantity of product could be increased from 31 mg per hour to 340 mg per hour simply by changing the volumetric capacity of the monolith.

Numerical Investigation of Radiation Effects in Monolithic Catalytic Combustion Reactors

In modeling catalytic combustion in a monolithic catalytic converter, it is generally assumed that the gas within the individual monolith channels does not interfere with thermal radiation. To date, no quantitative study has been undertaken to validate this assumption. Past studies for carbon monoxide combustion also appear to indicate that the emissivity of the washcoat has little effect on the thermal radiation field. In order to investigate these two issues, methane-air combustion on platinum is modeled inside a single channel of a monolith using a detailed surface reaction mechanism comprised of 24 reactions between 19 species. Radiation transport is modeled using the Discrete Ordinates Method and a gray formulation. Planck-mean absorption coefficients of the gases, calculated from the HITEMP and HITRAN databases, are used to investigate participating medium effects. All calculations were performed using the commercial CFD code, CFD-ACE+™, supplemented by user-subroutines for calculating the radiative properties of the gas mixture. Results show that the conversion percentages and temperature distributions are unaltered by the inclusion of participating medium radiation effects, verifying the commonly held belief, stated earlier. However, in strong contrast with carbon monoxide combustion, the emissivity of the washcoat was found to significantly affect flammability limits in the case of methane combustion—the flame being hotter and more stable for smaller values of emissivity.