Conventional Packed-bed Reactor Research Articles

Zeolite Membrane-Based Low-Temperature Dehydrogenation of a Liquid Organic Hydrogen Carrier: A Key Step in the Development of a Hydrogen Economy.

Methylcyclohexane (MCH) dehydrogenation is an equilibrium-limited reaction that requires high temperatures (>300°C) for complete conversion. However, high-temperature operation can degrade catalytic activity and produce unwanted side products. Thus, a hybrid zeolite membrane (Z) is prepared on the inner surface of a tubular support and used it as a wall in a membrane reactor (MR) configuration. Pt/C catalysts is packed diluted with quartz sand inside the Z-coated tube and applied the MR for MCH dehydrogenation at low temperatures (190-250°C). Z showed a remarkable H2-permselectivity in the presence of both toluene and MCH, yielding separation factors over 350. The Z-based MR achieved higher MCH conversion (75.3%±0.8% at 220°C) than the conventional packed-bed reactor (56.4%±0.3%) and the equilibrium state (53.2%), owing to the selective removal of H2 through Z. In summary, the hybrid zeolite MR enhances MCH dehydrogenation at low temperatures by overcoming thermodynamic limitations and improves the catalytic performance and product selectivity of the reaction.

Is monolithic configuration superior to random packing in a fixed bed reactor for CLC like processes?

In light of the geometric deficiencies and diffusion constraints of conventional packed-bed reactors, the potential application of monolithic configurations in fixed-bed reactors was explored using the structure-resolved CFD approach. This work delves into how geometric features of fixed beds influence flow patterns and related transport phenomena. To assess the performance of mass transfer and heterogeneous reactions in different configurations, we conducted simulations of fixed-bed chemical looping combustion (CLC) processes, in which a simplified model of non-catalytic gas-solid reactions is implemented to reduce the computational costs. Our findings highlight the importance of face contact between reaction tube and the monolithic structure, which effectively eliminates the inherent wall effects of random packing and enhances the radial heat conduction. More uniform geometry in the monolithic configuration naturally suppresses violent interstitial channeling flow in the random packing. Notably, the honeycomb configuration demonstrates an exceptionally low pressure drop, about two orders of magnitude smaller than that of the Raschig ring packing, and the designable monolithic configurations offers the potential to further reduce the pressure drop with enlarged voidage. Open-cell foams exhibit excellent convective and radial heat transport properties, promote homogeneous flow fields, and demonstrate superior performance in conjugate transport and heterogeneous reactions.

Experimental investigation of a packed bed membrane reactor for the direct conversion of CO2 to dimethyl ether

In this study, the performance of a packed bed membrane reactor (PBMR) based on carbon molecular sieve membranes for the one-step CO2 conversion to dimethyl ether (DME) is experimentally compared to that of a conventional packed bed reactor (PBR) using a CuO-ZnO-Al2O3/HZSM-5 bifunctional catalyst. The PBMR outperforms the PBR in most of the experimental conditions. The benefits were greater at lower GHSV (i.e., conditions that approach thermodynamic equilibrium and water formation is more severe), with both XCO2 and YDME improvements of +35–40 % and +16–27 %, respectively. Larger sweep gas-to-feed (SW) ratios increase the extent of water removal (ca. 80 % at SW=5), and thus the performance of the PBMR. Nevertheless, alongside the removal of water, a considerably amount of all products are removed as well, leading to a greater improvement in the CO yield (+122 %) than the DME yield (+66 %). Higher temperatures selectively improve the rWGS reaction, leading to a lower YDME with respect to the PBR at 260 °C, due to the significant loss of methanol. Furthermore, larger transmembrane pressures (∆P) were not beneficial for the performance of the PBMR due to the excess reactant loss (i.e., 98–99 % at ∆P = 3 bar). Finally, the reactor models developed in our previous studies accurately describe the performance of both the PBR and PBMR in the range of tested conditions. This result is of high relevance, since the reactor models could be used for further optimization studies and to simulate conditions which were not explored experimentally.

Design and optimization of a crossflow tube reactor system for hydrogen production by combining ethanol steam reforming and water gas shift reaction

Crossflow tube reactors with crossflow configuration are considered a special design for hydrogen production via ethanol steam reforming with less catalyst than conventional packed bed reactors. However, the results showed that crossflow tube reactors would produce an elevated concentration of carbon monoxide, which has a detrimental effect on further applications of the product gas from steam reforming, such as hydrogen purification. This drawback can be diminished by integrating a water gas shift reaction unit into the steam reformer. This study's combined system is numerically investigated for hydrogen production and enrichment. The results show that low reaction temperatures are favorable for hydrogen production. The steam/ethanol (S/E) ratio of 3 is optimal for hydrogen production and CO reduction in the system combined with ethanol steam reforming and water gas shift reaction. Both variations in the catalytic tube diameter and the catalyst thickness positively affect hydrogen production. However, the effect of the tube diameter is higher than that of the catalyst thickness. This study also uses a parametric sweep associated with the evolutionary computation of bound optimization by quadratic approximation (BOBYQA) method to optimize the system’s tube arrangement. The optimized system intensifies H2 yield by 1.05 times and improves CO reduction by 37.71% compared to ethanol steam reforming alone.

Production of linear alpha olefin 1-octene through 1-octanol dehydration in packed-bed membrane reactors with large mesoporous membranes (PMRL) for remarkable improvement in 1-octanol conversion and 1-octene yield

In this study, we report a packed-bed membrane reactor with large mesoporous membranes (PMRL) as a solution to remarkable improvement in 1-octanol conversion and 1-octene yield of 1-octanol dehydration. Compared to the conventional packed-bed reactors (PR), 1-octanol conversion and 1-octanol yield of the PMRL increased by up to 21.3% and 16.4% in the temperature range of 340 °C–380 °C. The PMRL has simultaneously advantages of packed-bed reactors and membrane reactors. As the PMRL is equipped with large mesoporous membranes under a catalyst bed in the existing packed-bed reactors to achieve conversion enhancement like membrane reactors, the PMRL can be operated under ambient pressure without autogenous pressure in spite of the absence of a retentate side and sweeping gas which should be needed in the existing packed-bed membrane reactor equipped with dense, microporous, and mesoporous membranes because of autogenous pressure. Therefore, the PMRL can be easily applied to any existing packed-bed reactors for dehydration or dehydrogenation reaction regardless of types of heterogeneous catalysts, because the catalysts can be easily loaded on the membranes in the PMRL without the retentate side and sweeping gas.

Ethylene Production from Oxidative Coupling of Methane in Solid Oxide Electrochemical Cells

The oxidative coupling of methane (OCM) to ethylene is a potentially more economical and environmentally benign approach for ethylene production compared to conventional high temperature thermal cracking of natural gas. The OCM reaction is typically conducted in packed bed flow reactors under thermal conditions in the presence of a heterogeneous catalyst. However, due to the intrinsic thermodynamic and kinetic constraints, the existing catalytic systems operated in packed bed reactors have not yet met the techno-economic requirements for the commercialization of this process. As an alternative, membrane reactors that selectively conduct the oxygen ions (O2-) could potentially offer significantly higher methane conversion and C2 product selectivity compared to conventional packed bed reactors. The lower partial pressure of oxygen and the distinct nature of oxygen species available for methane oxidation in the membrane reactor could effectively suppress the kinetics of the chemical transformations leading to the combustion products. In this context, solid oxide electrochemical cells (SOEC), specifically based on oxygen ion conducting membranes, are excellent platforms for conducting the OCM reaction. Here we demonstrate the development of novel SOECs integrated with a series of advanced OCM catalysts to achieve highly efficient ethylene production.

A three-dimensional conjugate heat transfer model for methanol synthesis in a modular millireactor

In this work, a modular millireactor (MMR) is designed and modeled using the computational fluid dynamics (CFD) tool OpenFOAM. First, the method is validated against a conventional packed bed reactor (PBR) model (1D) with Aspen Plus. Next, the method is applied to study the effects of pressure (2–6 MPa) and temperature (483–533 K) on the performance of the MMR. Conjugate heat transfer (CHT) CFD results for the MMR are compared against a corresponding PBR at isothermal conditions. For the MMR, the methanol yield is shown to vary between 9–23 % within the studied parameter range. Overall, the MMR outperforms the PBR at conditions studied in this work. The maximum difference in methanol yield between MMR and the PBR is noted to be a factor of 1.71 at 533 K and 5 MPa. Such a large discrepancy advocates the usage of 3D CHT/CFD.

Methanol steam reforming over PdZn/ZnAl2O4/Al2O3 in a catalytic membrane reactor: An experimental and modelling study

A catalytic membrane reactor equipped with Pd–Ag metallic membranes and loaded with PdZn/ZnAl 2 O 4 /Al 2 O 3 catalytic pellets was tested for the methanol steam reforming reaction (S/C = 1) aimed at producing a pure hydrogen stream for PEM fuel cell feeding. The catalyst was prepared in two steps. First, commercial γ-Al 2 O 3 pellets were impregnated with ZnCl 2 and calcined at 700 °C to obtain a ZnAl 2 O 4 shell, and subsequently impregnated with PdCl 2 and reduced at 600 °C to obtain PdZn alloy nanoparticles. The catalyst was tested both in a conventional packed bed reactor and in a catalytic membrane reactor. A 3D CFD non-isothermal model with mass transfer limitations was developed and validated with experimental data. The reactions of methanol steam reforming, reverse water-gas shift and methanation were modeled under different pressure, temperature and feed load values. The model was used to study and simulate the CMR under different operation conditions. • PdZn/ZnAl 2 O 4 /Al 2 O 3 catalytic pellets designed for the methanol steam reforming. • Kinetic analysis in catalytic packed bed reactor and catalytic membrane reactor. • 3D CFD non-isothermal model with mass transfer limitations developed and validated. • Catalytic membrane reactor simulated under different operation conditions.

High purity, self-sustained, pressurized hydrogen production from ammonia in a catalytic membrane reactor

The combination of catalytic decomposition of ammonia and in situ separation of hydrogen holds great promise for the use of ammonia as a clean energy carrier. However, finding the optimal catalyst – membrane pair and operation conditions have proved challenging. Here, we demonstrate that cobalt-based catalysts for ammonia decomposition can be efficiently used together with a Pd-Au based membrane to produce high purity hydrogen at elevated pressure. Compared to a conventional packed bed reactor, the membrane reactor offers several operational advantages that result in energetic and economic benefits. The robustness and durability of the combined system has been demonstrated for>1000 h on stream, yielding a very pure hydrogen stream (>99.97 % H2) and recovery (>90 %). When considering the required hydrogen compression for storage/utilization and environmental issues, the combined system offers the additional advantage of production of hydrogen at moderate pressures along with full ammonia conversion. Altogether, our results demonstrate the possibility of deploying high pressure (350 bar) hydrogen generators from ammonia with H2 efficiencies of circa 75% without any external energy input and/or derived CO2 emissions.

Catalytic reduction of in-flow aqueous Cr(vi) using a slurry of activated carbon fiber-supported Ni nanoparticles in a coiled flow inverter

CFI technology is utilized for the in-flow reduction of Cr(vi) using formic acid as the reducing agent and an aqueous dispersion of Ni/ACF, as an alternative to the conventional packed bed reactors.

Assessment of CO2 capture efficiency in packed bed versus 3D-printed monolith reactors for SEWGS using CFD modeling

Sorption Enhanced Water-Gas Shift (SEWGS) couples the water gas-shift reaction with CO2 adsorption on potassium-promoted hydrotalcite (K-HTC) sorbent material for hydrogen production and CO2 capture. Here, computational fluid dynamics (CFD) models are developed to simulate the adsorption step in SEWGS considering both packed bed and monolith reactors. The goal of this research is increasing SEWGS productivity by using 3D-printed structured bed reactors, as opposed to conventional packed bed reactors, due to the well-known advantages of monoliths, such as less mass transfer limitations and lower pressure drops. The paper presents numerical modeling and simulation work supported by experimental validation in order to compare packed bed and monolith reactors with respect to SEWGS performance. The packed bed multiscale CFD model is validated using breakthrough experimental data. A bench-scale CFD structured bed model is developed and validated based on breakthrough measurements performed by TNO using 3D-printed K-HTC monolith structures. Furthermore, geometry effects on mass transfer efficiency are investigated through CFD modeling for the bench-scale reactor. A scale-up of the monolith model to pilot-scale allows for a proper comparison with the packed bed technology. Monolith reactor model breakthrough predictions show there is a considerable increase in mass transfer rate over the packed bed reactor for the adsorption step in SEWGS, demonstrating promising potential towards enhancing the carbon capture technology.

Membrane Reactor for Methanol Synthesis Using Si-Rich LTA Zeolite Membrane.

We successfully demonstrated the effect of a membrane reactor for methanol synthesis to improve one-pass CO2 conversion. An Si-rich LTA membrane for dehydration from a methanol synthesis reaction field was synthesized by the seed-assisted hydrothermal synthesis method. The H2O permselective performance of the membrane showed 1.5 × 10−6 mol m−2 s−1 Pa−1 as H2O permeance and around 2000 as selectivity of H2O/MeOH at 473 K. From the results of membrane reactor tests, the CO2 conversion of the membrane reactor was higher than that of the conventional packed-bed reactor under the all of experimental conditions. Especially, at 4 MPa of reaction pressure, the conversion using the membrane reactor was around 60%. In the case of using a packed-bed reactor, the conversion was 20% under the same conditions. In addition, the calculated and experimental conversion were in good agreement in both the case of the membrane reactor and packed-bed reactor.

Polymer-Ceramic Composite Membranes for Water Removal in Membrane Reactors.

Methanol can be obtained through CO2 hydrogenation in a membrane reactor with higher yield or lower pressure than in a conventional packed bed reactor. In this study, we explore a new kind of membrane with the potential suitability for such membrane reactors. Silicone–ceramic composite membranes are synthetized and characterized for their capability to selectively remove water from a mixture containing hydrogen, CO2, and water at temperatures typical for methanol synthesis. We show that this membrane can achieve selective permeation of water under such harsh conditions, and thus is an alternative candidate for use in membrane reactors for processes where water is one of the products and the yield is limited by thermodynamic equilibrium.

Comparative techno-economic analysis for steam methane reforming in a sorption-enhanced membrane reactor: Simultaneous H2 production and CO2 capture

Hydrogen (H2) is currently receiving significant attention as a sustainable energy carrier. Steam methane reforming (SMR) accounts for approximately 50% of H2 production methods worldwide. However, SMR is concern because of the prodigious carbon dioxide (CO2) emissions that have resulted in a global climate emergency. CO2 emissions remain, although some efforts have been made in a membrane reactor (MR) coupled with membranes to improve the H2 yield. A sorption-enhanced membrane reactor (SEMR) has been proposed as a next-generation process for simultaneous H2 production and CO2 capture. In this study, the thermodynamic and economic evaluation of SEMR were implemented using a process simulation, an itemized cost estimation, a sensitivity analysis (SA), and an uncertainty analysis (UA). The thermodynamic analysis results revealed that unit H2 production costs of 4.53, 1.98, and 3.04 $ kgH2−1 were obtained at 773 K for a conventional packed-bed reactor (PBR), a MR, and a SEMR, respectively. The SA results identified PSA as the most critical economic parameter for a unit H2 production cost for a PBR, whereas natural gas is determined to be the most influential parameter for a MR and a SEMR. The UA results from a Monte-Carlo simulation provided a broad range of unit H2 production costs, with 4.26–5.44 $ kgH2−1 for a PBR, 1.61–2.94 $ kgH2−1 for a MR, and 2.83–4.19 $ kgH2−1 for an SEMR. This indicates that using a SEMR for next-generation H2 production and CO2 capture is beneficial.

H2 production via ammonia decomposition in a catalytic membrane reactor

The membrane reactor is proposed in this work as a system with high potential to efficiently recover the hydrogen (H2) stored in ammonia (NH3), which has been recently proposed as an alternative for H2 storage. With this technology, NH3 decomposition and high-purity H2 separation are simultaneously performed within the same unit, and high H2 separation efficiency is achieved at lower temperature compared to conventional systems, leading to energetic and economic benefits. NH3 decomposition was experimentally performed in a Pd-based membrane reactor over a Ru-based catalyst and the performance of the conventional packed bed reactor were used as benchmark for a comparison. The results demonstrate that the introduction of a membrane in a conventional reactor enhances its performance and allows to achieve conversion higher than the thermodynamic equilibrium conversion for sufficiently high temperatures. For temperatures from and above 425 °C, full NH3 conversion was achieved and more than 86% of H2 fed to the system as ammonia was recovered with a purity of 99.998%. The application of vacuum at the membrane permeate side leads to higher H2 recovery and NH3 conversions beyond thermodynamic restrictions. On the other hand, the reactor feed flow rate and operating pressure have not shown major impacts on NH3 conversion.

Thermal Assessment of a Micro Fibrous Fischer Tropsch Fixed Bed Reactor Using Computational Fluid Dynamics

A two-dimensional (2D) Computational Fluid Dynamics (CFD) scale-up model of the Fischer Tropsch reactor was developed to thermally compare the Microfibrous-Entrapped-Cobalt-Catalyst (MFECC) and the conventional Packed Bed Reactor (PBR). The model implements an advanced predictive detailed kinetic model to study the effect of a thermal runaway on C5+ hydrocarbon product selectivity. Results demonstrate the superior capability of the MFECC bed in mitigating hotspot formation due to its ultra-high thermal conductivity. Furthermore, a process intensification study for radial scale-up of the reactor bed from 15 mm internal diameter (ID) to 102 mm ID demonstrated that large tube diameters in PBR lead to temperature runaway >200 K corresponding to >90% CO conversion at 100% methane selectivity, which is highly undesirable. While the MFECC bed hotspot temperature corresponded to <10 K at >30% CO conversion, attributing to significantly high thermal conductivity of the MFECC bed. Moreover, a noticeable improvement in C5+ hydrocarbon selectivity >70% was observed in the MFECC bed in contrast to a significantly low number for the PBR (<5%).

Investigation of the benefits of diabatic microreactors for process intensification of the water-gas shift reaction within the steam reforming process

Currently, the steam reforming process is the largest industrial source of hydrogen. Improving its efficiency can help to reduce associated carbon emissions and hydrogen production costs. Intensifying the water-gas shift reaction using microreactors with integrated cooling is one way of achieving this. In this study, a 2-D computational model of one of these microreactors is developed, validated with experimental data, and then used to demonstrate how microreactors can enhance the conversion of the water-gas shift reaction beyond what can be achieved using conventional packed bed reactors. These results are then generalized into a full system model of the steam reforming process to demonstrate how microreactors can reduce hydrogen production costs. The results suggest that microreactors can significantly reduce the required reactor volume and catalyst loading for the water-gas shift reaction and can similarly reduce the hydrogen production costs associated with the steam reforming process.

Modeling and simulation of a reactive separation system for carbon capture and utilization in biogas streams

An effective energy storage approach, such as Power-to-Gas, is essential to provide the grid with a steady supply of power generated by renewable sources. In a Power-to-Gas concept, excess renewable energy is stored in the form of H2 which, in turn, can react with CO2 from sources such as biogas to be converted into CH4 and generate Renewable Natural Gas (RNG). Methanation however, is an exothermic and equilibrium-limited reaction which suffers from poor heat management when carried-out in conventional packed-bed reactors. Additionally, unreacted H2 mixed with CH4 has to be removed before the RNG is injected into the pipeline. To improve the methanation of biogas, two commercial high temperature reactive separation systems have been studied numerically in this work: (i) an extractor/distributor membrane reactor employing a carbon molecular sieve membrane; (ii) a distributor membrane reactor using a palladium membrane. Both configurations have been shown to considerably reduce the content of CO2 and H2 in the resulting RNG and, hence, the post-processing efforts needed as compared to a packed-bed reactor operating under the same conditions.

A carbon molecular sieve membrane-based reactive separation process for pre-combustion CO2 capture

We discuss here a hybrid system combining a membrane reactor (MR) and an adsorptive reactor (AR), with the MR's reject stream serving as the AR's feed. We apply this system for the water gas shift (WGS) reaction for H2 generation and simultaneous CO2 capture in the context of the Integrated Gas Combined Cycle (IGCC) process for power generation from coal and biomass. This MR-AR system attains a high conversion exceeding equilibrium, produces a pure H2 product for power generation, and delivers a high-pressure CO2 stream ready for sequestration. Specifically, in our study we use carbon molecular sieve membranes (CMSMs) and a commercial sour-shift WGS catalyst. Lab experiments were carried-out to determine the membrane characteristics, and the MR performance under IGCC-relevant conditions, i.e., for temperatures up to 250 °C and pressures up to 25 bar, employing a model coal gasifier syngas. The CMSM and the catalyst have displayed robust and stable performance during a long-term run (~750 h of syngas exposure). We evaluated the MR-AR system in multi-cycle runs and it has demonstrated superior performance to that of a conventional packed-bed reactor, producing a high-purity H2 product directly useable in a turbine for power generation. We conclude from the study, that the CMSM-based MR-AR system is a good candidate technology for environmentally-benign power generation. We are currently constructing a pilot-scale system for field demonstration of the technology.

Feasibility of reactive distillation for methanol synthesis

The performance of reactive distillation (RD) for methanol synthesis from syngas in terms of reactant conversions and methanol productivity was studied in this simulation work. An inert, high boiling solvent (tetraglyme) was used to maintain sufficient liquid load in the column under the reaction conditions. A fully reactive column with four reactive stages was considered and the results were compared with a conventional packed bed reactor (PBR) and a slurry reactor (SR). Six different syngas feed compositions were considered by varying the proportions of CO, CO2 and H2. A power law kinetic model for methanol synthesis on conventional Cu-ZnO-Al2O3 catalyst was used to simulate the RD and the SR, and a Langmuir-Hinshelwood-Hougen-Watson (LHHW) model was employed in the PBR for the same type of catalyst. Despite the high pressure (50 atm) used in the RD column, the presence of non-condensables allowed for separation and also removed the necessity for a reboiler. The performance of the RD was found to be comparable with the SR. Though the PBR gave higher methanol productivities due to the absence of a separate liquid phase, it exhibited lower conversions than the SR and RD for syngas rich in CO2.