Traditional Fixed-bed Reactor Research Articles

A combined experimental and modeling study of Microwave-assisted methane dehydroaromatization process

The challenges in direct methane conversion to higher-value chemicals include rapid catalyst deactivation and comparatively low single-pass conversion. The most important step in direct methane conversion is the activation of strong C–H bonds. In this paper, we integrated microwave irradiation with heterogeneous catalysis to enable a higher methane conversion to C2 and aromatics at low temperature. The results showed that the methane conversion can reach 18% at 550 °C under microwave irradiation, while a temperature higher than 800 °C was required to achieve the same level of methane conversion in a traditional fixed-bed reactor. The microwave irradiation may facilitate this heterogeneous catalysis process both thermally and non-thermally. Thermal effect, as known as “hot spots”, can be characterized experimentally. The results indicated the “hot spot” temperature can reach as high as 800 °C while the bulk temperature stayed at 550 °C. However, the non-thermal effect is difficult to characterize due to the limitations of existing in-situ instrumentations. Finite-element modeling can be a powerful engineering tool to simulate and understand complex physic fields. The simulation results show that between spherical catalyst particles the electric field on the catalyst bed was at a level of 104 V/m and the non-uniform electric field distribution on the catalyst bed. Under this level of external electric field, methane activation on the catalyst surface was possible. These field distributions can explain the non-thermal effects of microwave-assisted catalytic chemical reactions, supported by the observation of benzene hydrogenolysis side reaction. With the thermal and non-thermal effects from microwave irradiation, microwave-assisted heterogeneous catalytic process can be an attractive solution to activate stable feedstock molecules and can be applied to direct methane conversion process.

Novel insight into composite packing of copper modified adsorbents for synergistically capturing H2S&HCl in low-temperature anaerobic environment

• Simultaneous removal of HCl&H 2 S in low-temperature anaerobic condition was designed. • Mixed packing adsorbents achieved the optimal and synchronous capture of HCl&H 2 S. • HCl led to the formation of flower-like nanosheets and reduced sulfate production. • The effects of adsorption parameters on simultaneous HCl@H 2 S removal were studied. Trace amount of acid gas components in industrial gas is the main cause of air pollution, which greatly restricts the sustainable utilization of industrial coal gas resources. However, there is still a blank in the research of selective deep removal of H 2 S&HCl under low temperature anaerobic conditions. In this work, simultaneous desulfurization and dechlorination performance were investigated using the combined two copper based porous adsorbents under low-temperature anaerobic conditions in a traditional fixed bed reactor. The breakthrough curves of simultaneous desulfurization and dechlorination over single or composite adsorbents were respectively explored, and the results showed that the composite packing indicated the optimal adsorption efficiencies. The maximum chlorination rate and sulfurization rate of the adsorbents Cu@Na and Cu@ASC were 0.787 and 0.6, respectively. Among the adsorption process, the presence of HCl leads to the distribution of copper sulfide products in the form of flower-like nanosheets and partly inhibited the formation of sulfate. In addition, the effects of different adsorption conditions such as reaction temperature, mass ratio, humidity and CO 2 concentration on simultaneous desulfurization and dechlorination were also studied. The experimental results illustrate that the composite packing of these two porous materials has the opportunity to achieve the selective separation of multi-component trace acid gas from low temperature industrial gas.

Split feed strategy for low-permselective membrane reactors: A simulation study for enhancing CO2 methanation

A non-isothermal membrane reactor (MR) was simulated to study the production of methane through CO2 hydrogenation. The reaction kinetics of a commercial catalyst and the extrapolated properties of a steam-selective sodalite (SOD) membrane were considered. A traditional fixed-bed reactor (TR) was also simulated and its performance compared with that obtained with a MR in the temperature and pressure range of 250−410 °C and 1−7 atm, respectively. The results indicate that at higher temperatures the SOD membrane removes not only water but also a significant amount of reactants from the reaction medium. It was demonstrated that this can be solved splitting the feed between both chambers (retentate and permeate), reducing the reactants loss due to a lower driving force. However, the methane permeation through the SOD membrane limits the process performance. The simulation of an ideal MR (i.e. membrane with infinite selectivity to water), with the perspective of assessing its potential, allowed reaching a conversion of 89.5 % (at 390 °C and 1 atm), being able not only to improve the catalytic bed conversion of a TR in the same conditions (82.7 %), but also to surpass the chemical equilibrium conversion (85.4 %), showing that the full potential of the MR technology for this application still depends on the development of adequate membranes.

Tuning Selectivity in Catalytic Conversion of CO 2 by One-Atom-Switching of Au 9 and Au 8 Pd 1 Catalysts

The optimization of catalysts for CO2 hydrogenation that is carried out in a traditional fixed-bed reactor predominantly focuses on pursuing various nanoparticles at the nanoscale. Much less is kno...

CO2 Hydrogenation to Ethanol over Cu@Na-Beta

Summary Here, we report a high-performance catalyst Cu@Na-Beta, prepared via a unique method to embed 2∼5 nm Cu nanoparticles in crystalline particles of Na-Beta zeolite, for CO2 hydrogenation to ethanol as the only organic product in a traditional fixed-bed reactor. The ethanol yield in a single pass can reach ∼14% at 300°C, ∼12,000 mL·gcat−1·h−1, and 2.1 MPa, corresponding to a space-time yield of ∼398 mg·gcat−1·h−1. The key step of the reaction is considered as the rapid bonding of CO2∗ with surface methyl species at step sites of Cu nanoparticles to CH3COO∗ that converts to ethanol in following hydrogenation steps. The points of the catalyst seemed to be that the irregular copper nanoparticles stuck in zeolitic frameworks offer high density of step sites and the intimate surrounding of zeolitic frameworks strongly constrain the CO2 reactions at the copper surface and block by-products, such as methanol, formic acid, and acetyl acid.

Hydrogen production by silica membrane reactor during dehydrogenation of methylcyclohexane: CFD analysis

A comprehensive computational fluid dynamic model has been developed using COMSOL Multiphysics 5.4 software to predict the behavior of a membrane reactor in dehydrogenation of methylcyclohexane for hydrogen production. A reliable reaction kinetic of dehydrogenation reaction and a permeation mechanism of hydrogen through silica membrane have been used in computational fluid dynamic modeling. For performance comparison, an equivalent traditional fixed bed reactor without hydrogen removal has been also modeled. After model validation, it has been used to evaluate the operating parameters effect on the performance of both the silica membrane reactor and the equivalent traditional reactor as well. The operating temperature ranged between 473 and 553 K, pressure between 1 and 2.5 bar, sweep factor from ˜6.22 to 25 and feed flow rate from 1 to 5 × 10−6 mol/s. The membrane reactor performed better than the equivalent traditional reactor, achieving as best result complete methylcyclohexane conversion and 96% hydrogen recovery.

Effects of the Limestone Particle Size on the Sulfation Reactivity at Low SO2 Concentrations Using a LC-TGA.

Limestone particle size has a crucial influence on SO2 capture efficiency, however there are few studies on the sulfation reactivity, which covers a broad range of particle sizes at low SO2 concentrations. In this paper, a large-capacity thermogravimetric analyzer (LC-TGA) was developed to obtain the sulfur removal reaction rate under a wide range of particle sizes (3 μm–600 μm) and SO2 concentrations (250 ppm–2000 ppm), and then compared with the results of a traditional fixed bed reactor and a commercial TGA. The experimental results showed that the LC-TGA can well eliminate the external mass transfer and obtain a better measurement performance. Both the final conversion and the reaction rate reduced with the decreasing of SO2 concentration, but ultrafine limestone particles still showed the good sulfation reactivity even at 250 ppm SO2. An empirical sulfation model was established based on the experimental results, which can well predict the sulfation process of different limestone particle sizes at low SO2 concentrations. The model parameters have a strong negative correlation against the particle size, and the fit of the reaction order of SO2 was found to be about 0.6. The model form is very simple to incorporate it into available fluidized bed combustion models to predict SO2 emission.

Particle-resolved simulation of packed beds by non-body conforming locally refined orthogonal hexahedral mesh

Abstract The traditional fixed-bed reactor design is usually not suitable for the low tube-to-particle diameter ratios (N = D/d

Oxidative dehydrogenation of ethane to ethylene over phase-pure M1 MoVNbTeOx catalysts in a micro-channel reactor

Due to its excellent heat transfer ability, the micro-channel reactor with coated phase-pure M1 catalysts can achieve reactor productivity nearly 5 times higher than that of a traditional fixed-bed reactor under the same reaction conditions in oxidative dehydrogenation of ethane (ODHE).

Studies on water–gas-shift enhanced by adsorption and membrane permeation

A new sorption enhanced membrane reactor (SEMR), consisting of a packed adsorbent-catalyst bed (10% CuO/CeO2 catalyst and a hydrotalcite-derived Mg–Al mixed oxide) around a tubular Pd/Ag hollow fibre membrane, has been proposed to obtain high purity H2 and simultaneous capture of CO2 during the water gas shift reaction. For comparison purposes, catalytic activity tests were carried out at atmospheric pressure and operating temperatures between 100°C and 550°C in three different catalytic reactors: (1) a fixed-bed reactor (FBR), (2) a sorption enhanced reactor (SER) and (2) a new SEMR. In all cases, the feed mixture Ar/CO/H2O ratio was 11/1/0.75 with a space velocity of 22L/gh. The performance of the FBR was used as a reference to compare with the results obtained from the SER and SEMR. The H2 yield at 350°C using the SER was 80%, which is 33% higher than that obtained in the traditional FBR and 18% higher than the corresponding thermodynamic equilibrium. However, due to the high CO/H2O ratio (R>1), undesirable side-reactions such as C deposition become important at temperatures higher than 400°C. A similar behaviour was observed using the SEMR, however in this case, a high purity COx free H2 production was obtained. This preliminary study shows relevant data obtained using a SER and the new SEMR, which allows for the better understanding and design of multifunctional catalytic reactors.

Dry reforming of methane using Pd-based membrane reactors fabricated from different substrates

In this study, performance and feasibility of a hollow fibre membrane reactor (HFMR), consisting of a packed catalyst bed around a Pd coated Al2O3 hollow fibre membrane, has been studied and compared with both conventional Pd based tubular membrane reactor (TMR) fabricated from a stainless steel substrate and traditional fixed-bed reactor (FBR). The ceramic based HFMR presents several advantages over MRs such as the deposition of ultra thin Pd membranes and the possibility to scale up the whole multifunctional process by module configuration. The results obtained at 450°C during the methane dry reforming (MDR) reaction showed that, although CH4 conversion using the HFMR was almost the same as that of a catalytic TMR, the amount of Pd employed for the Pd layer deposition in the HFMR was fifteen times less than that in TMR. Moreover, the CH4 conversion using the HFMR was 72% higher than that in a traditional FBR and 34% higher than thermodynamic equilibrium. Also, a high purity COX-free H2 production (10.5ml/mgh) was achieved at 525°C using a sweep gas of 100ml/min in the lumen side of the HFMR.

New catalytic reactors prepared from symmetric and asymmetric ceramic hollow fibres

In this study, asymmetric and symmetric Al2O3 hollow fibres were employed as a support of a 10% CuO/CeO2 catalyst in the development of an asymmetric hollow fibre reactor (AHFR) and a symmetric hollow fibre reactor (SHFR), respectively. The 10% CuO/CeO2 catalyst was successfully deposited in both Al2O3 hollow fibre substrates by the sol–gel Pechini method. The impregnated fibres were characterized by Ar permeability, Hg porosimetry, X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution optical microscopy. The water gas shift (WGS) reaction was chosen as a sample reaction to compare the performances of both AHFR and SHFR with a traditional fixed bed reactor (FBR). The catalytic activity tests in the FBR were carried out using the powder ground from either the asymmetric or symmetric Al2O3 hollow fibre impregnated with 10% CuO/CeO2. Two different configurations, “dead-end” and “open-end”, were studied in the AHFR and SHFR. The experimental results show that, despite the differences observed between the AHFR and SHFR, both reactors offer important advantages over conventional FBRs including high catalytic activity along with a better selectivity.

Asymmetric ceramic hollow fibres applied in heterogeneous catalytic gas phase reactions

The present work provides a summary of the state of the art of using asymmetric ceramic hollow fibres as substrates for inorganic dense membranes and/or catalysts, in the development of new hollow fibre reactors for heterogeneous catalytic gas phase reactions. Three different hollow fibre reactor designs were studied; a hollow fibre membrane reactor (HFMR), a catalytic hollow fibre micro-reactor (CHFMR) and a catalytic hollow fibre membrane micro-reactor (CHFMMR). The performance of the HFMR, CHFMR and CHFMMR in different reactions such as methanol steam reforming (MSR), dry reforming of methane (DRM) and water gas shift (WGS) was compared with that of a traditional fixed-bed reactor configuration. A Pd-based membrane (thickness of approximately 5μm) was deposited on the outer surface of the asymmetric ceramic hollow fibres using an electroless plating technique, in the development of both the HFMR and CHFMMR. The Pd-based membranes showed high H2 permeability (10.7≤PH2≤14.1 L m−2 s−1 atm−1/2 at T=450°C and ΔP=1bar) and infinite H2 selectivity under the different reaction conditions studied. The catalyst was deposited on the walls of finger-like region of the asymmetric ceramic hollow fibres by the sol–gel Pechini method, in the development of the CHFMR and CHFMMR. The CHFMMR, which showed a performance 2.5 times higher than that in a traditional fixed-bed reactor, is proposed as a key step in the intensification of heterogeneous catalytic gas phase processes by integration of membrane-reactor and micro-reactor technologies.

Hydrogen enrichment and separation from synthesis gas by the use of a membrane reactor

One of the objectives of the CHRISGAS project was to study innovative gas separation and gas upgrading systems that have not been developed sufficiently yet to be tested at a demonstration scale within the time frame of the project, but which show some attractive merits and features for further development. In this framework CIEMAT studied, at bench scale, hydrogen enrichment and separation from syngas by the use of membranes and membrane catalytic reactors. In this paper results about hydrogen separation from synthesis gas by means of selective membranes are presented. Studies dealt with the evaluation of permeation and selectivity to hydrogen of prepared and pre-commercial Pd-based membranes. Whereas prepared membranes turned out to be non-selective, due to discontinuities of the palladium layer, studies conducted with the pre-commercial membrane showed that by means of a membrane reactor it is possible to completely separate hydrogen from the other gas components and produce pure hydrogen as a permeate stream, even in the case of complex reaction system (H2/CO/CO2/H2O) under WGS conditions gas mixtures. The advantages of using a water-gas shift membrane reactor (MR) over a traditional fixed bed reactor (TR) have also been studied. The experimental device included the pre-commercial Pd-based membrane and a commercial high temperature Fe–Cr-based, WGS catalyst, which was packed in the annulus between the membrane and the reactor outer shell. Results show that in the MR concept, removal of H2 from the reaction side has a positive effect on WGS reaction, reaching higher CO conversion than in a traditional packed bed reactor at a given temperature. On increasing pressure on the reaction side permeation is enhanced and hence carbon monoxide conversion increases.

Modeling of CO 2-selective water gas shift membrane reactor for fuel cell

Water gas shift (WGS) reaction is critical to hydrogen purification for fuel cells. Being reversible and exothermic, the WGS reaction in the traditional fixed bed reactor is not efficient. Using a CO 2-selective membrane reactor shifts the reaction towards the product side, which enhances the conversion of CO and increases the purity of the H 2 product at a high pressure. The simultaneous reaction and transport process in the countercurrent WGS membrane reactor was simulated by using a one-dimensional non-isothermal model, and the effect of several system parameters including CO 2/H 2 selectivity, CO 2 permeability, and sweep-to-feed molar flow rate ratio were investigated. The synthesis gases from both autothermal reforming and steam reforming were used as the feed gas, while heated air was used as the sweep gas. A published WGS reaction rate expression with the commercial Cu/ZnO catalyst was incorporated into the model. The modeling results show that a CO concentration of less than 10 ppm, a H 2 recovery of greater than 97%, and a H 2 concentration of greater than 54% (on the dry basis) are achievable from autothermal reforming syngas. If steam reforming syngas is used as the feed gas, H 2 concentration can be as high as 99.64% (on the dry basis).

Preparation and Characterization of TiO2-Coated Optical-Fiber in a Photo Reactor

An optical-fiber photo reactor (OFPR) was designed and assembled to provide uniform light distribution inside the reactor, which spread light energy more efficiently than a traditional fixed-bed reactor. TiO2 films were coated on optical fibers using the dip-coating method. Titania solutions were prepared through the thermal hydrolysis of titanium butoxide, commercial Hombikat XXS100 solution, and Degussa P25 suspension for comparison. The thicknesses of the films ranged from 60 to 600 nm after calcination at 500℃, and the sizes of the nanocrystals in the TiO2 films were 15-25 nm, as estimated from SEM micrographs. Anatase phase was found from the XRD patterns in all the TiO2 films. The profilemeter and ASTM D3359 adhesion test results showed that uniform TiO2 films were formed with strong adhesion using the thermal hydrolysis and Hombikat XXS100 solutions, while those coated with P25-suspension exhibited poor adhesion on a glass surface. The contact angle of the water decreased to almost zero within 30 minutes under UV-light irradiation and then recovered to the initial contact angle in darkness, implying super hydrophilicity and perfection of the TiO2 films. Ammonia was photocatalytically decomposed in the OFPR under artificial light irradiation, indicating good photocatalytic reactivity of the TiO2-coated fibers.

Methanol synthesis from CO2 using a silicone rubber/ceramic composite membrane reactor

A one-dimensional isothermal pseudo-homogeneous parallel flow model was developed for the methanol synthesis from CO2 in a silicone rubber/ceramic composite membrane reactor. The fourth-order Runge–Kutta method was adopted to simulate the process behaviors in the membrane reactor. How those parameters affect the reaction behaviors in the membrane reactor, such as Damköhler number Da, pressure ratio pr, reaction temperature T, membrane separation factor α, membrane permeation parameter Φ, as well as the non-uniform parameter of membrane permeation L1, were discussed in detail. Parts of the theoretical results were tested and verified; the experimental results showed that the conversion of the main reaction in the membrane reactor increased by 22% against traditional fixed bed reactor, and the optimal non-uniform parameter of membrane permeation rate, L1,opt, does exist.

Preparation, characterization and application of a catalytic NaA membrane for CH 4/CO 2 reforming to syngas

The NaA and La 2NiO 4/NaA composite membranes were prepared by means of in situ hydrothermal synthesis. The structure, morphology, separation performance, as well as chemical state and surface composition of a La 2NiO 4/NaA composite membrane were investigated by means of techniques, such as XRD, SEM-EDX, GC, TPD, XPS, and XAES. When the membrane was applied in a membrane reactor for CH 4/CO 2 reforming, CH 4 and CO 2 conversions, and CO and H 2 selectivities were significantly higher than the values observed over a traditional fixed-bed reactor. We studied the effects of the flow rate of sweeping N 2, gas hour space velocity (GHSV), and reaction temperature on the conversions of CH 4 and CO 2. The carbon deposited on the surface of membrane was studied by means of the TPO–MS technique.

An analysis of the performance of membrane reactors for the water–gas shift reaction using gas feed mixtures

The water–gas shift (WGS) reaction in membrane reactors has been widely studied by several authors. From these works, the increase of the CO conversion above the equilibrium values appears to be possible when hydrogen is removed through the membrane. However, to date, this feasibility has been verified mostly when feeding pure reagents to the reactor, although in an industrial context the feed normally contains several other compounds. The objective of this work has been to analyse the effect of the feed composition on the membrane reactor efficiency in order to determine the best conditions in terms of CO conversion. At this purpose, experimental tests with mixtures of different compositions have been carried out in three different systems of reaction: (1) traditional fixed-bed reactor; (2) membrane reactor with mesoporous ceramic membrane; (3) membrane reactor with palladium membrane. The experiments included permeation (for the membrane reactors) and reaction tests. The experimental results obtained with the various systems of reaction have been compared. A mathematical model has been also formulated for the different type of reactors used in order to verify the experimental results obtained. From the work carried out it can be concluded that by using the palladium membrane reactor it is possible to overcome the equilibrium conversion. Moreover, a complete conversion has been achieved for one of the mixtures fed to the reactor.

00/00093 Slurry phase Fischer-Tropsch synthesis process development

Fischer-Tropsch synthesis can convert a variety of synthesis gas mixtures produced from both coal and natural gas to obtain hydrocarbons, which can be further processed to manufacture automotive fuels. As the Fischer-Tropsch reaction is highly exothermic, a slurry phase reactor offers a significant advantage over the traditional fixed bed reactor for heat management. Since 1992, Air Products and DOE have been developing the slurry phase Fischer-Tropsch synthesis process with help of a number of industrial partners. This paper discusses the evolution of the technology through four pilot plant campaigns conducted at DOE`s Alternative Fuels Development Unit in LaPorte, Texas. Key issues such as catalyst-wax separation, reactor productivity improvements, reactor temperature control, and in-situ activation are addressed.