Tubular Flow Reactor Research Articles

Characterization of particles generated by non-catalytic methane pyrolysis in a tubular flow reactor

Characterization of particles generated by non-catalytic methane pyrolysis in a tubular flow reactor

An Analytical Model for Electrochemical Tubular Flow Reactors

This paper introduces the first analytical model designed for tubular electrochemical flow reactor, enabling a detailed examination of how reactor geometry and material selection impact performance. The model revealed that certain conditions, such as high electrode resistance relative to charge transfer, electrolyte, and separator resistance, can lead to uneven current distributions and reduced electrode utilization. The model highlights a critical electrode radius, dependent on reactor geometry and material properties, that minimizes the Area Specific Resistance (ASR) while minimizing reactor size. Additionally, it was found that the ASR increases with reactor length, but this effect can be mitigated by using highly conductive electrodes, thus allowing for enhanced power output. These insights provide a foundation for future research and the development of more efficient tubular reactor designs.

Fe(III)-incorporated UiO-66(Zr)–NH2 frameworks: Microwave-assisted scalable production and their enhanced photo-Fenton degradation catalytic activities

In this work, the photocatalytic feasibility of UiO-66(Zr)–NH2 was tuned by combining a scalable producing approach and incorporating Fe3+. Different contents of Fe3+ were effectively incorporated into the UiO-66(Zr)–NH2 frameworks utilizing a microwave-assisted continuous flow tubular reactor within 10 min. It was observed that with increasing the Fe3+ content from 0.5 to 1.0, 2.0 and 3.0 M %, the production rate diminished from ∼ 1.72 to 1.65, 1.55, and 1.46 g/h, respectively. The hybrid Fe@UiO-66-NH2 (Fe@UON) showed enhanced light absorption and charge carrier separation efficiency owing to the newly formed heterostructures, Zr-O-Fe linkages, and –H2N:→ Fe3+ chelating. The optimal Fe@UON catalyst achieved the highest photo-Fenton degradation efficiency of ∼ 96 % towards tetracycline (TC) under energy-saving visible LED light (VLEL) conditions. The photodegradation was predominantly governed by the photo-induced species of ·O2–, h+, and •OH and facilitated by the Fe3+/Fe2+ cycles. At the same time, LC/MS analyses detailedly revealed the reaction pathways for the degradation. After several consecutive tests, the constructed hybrid Fe@UiO-66-NH2 catalysts maintained good catalytic durability, and there was an insignificant Fe leak to the environment. The findings showed that hybrid Fe3+@UiO-66(Zr)–NH2 derived from energy-effective, environmental and scalable methods could be a good material for treating antibiotic-polluted effluents.

Synthesis of bentonite-supported Ni, La, and Ca catalysts for hydrogen production through steam reforming of acetic acid

In this study, the production of hydrogen-rich gas through the steam reforming of acetic acid using bentonite-supported catalysts was investigated. Bentonite was treated by washing and calcination. Bentonite-supported Ni, Ca, La, Ni–La, and Ni–Ca catalysts with different active metal loadings of 10 and 30 wt% were synthesized using the wet impregnation method. The catalysts were characterized using XRD, XRF, SEM, EDS, BET, FT-IR, NH3-TPD, and Raman. The activity tests of the catalysts were carried out in a continuous flow tubular reactor at various temperatures (500, 600, 700, and 800 °C). Product gas composition was determined by gas chromatography (μ-GC). The effect of bentonite treatment, active metal type, and bimetallic combinations (Ni/Bent, Ni/Bent*, La/Bent, Ca/Bent, Ni–La/Bent, and Ni–Ca/Bent) were studied. The highest hydrogen yield obtained without a catalyst was 8.61% at 700 °C. This yield increased to 74.5% at 600 °C with 30 wt% Ni–La/Bentonite, and to 42.6% with 30 wt% Ni/Bentonite catalysts, respectively. The experimental results show that bentonite has a suitable catalytic activity on its own and is a promising support material for the steam reforming of acetic acid.

Synthesis, characterization, and performance evaluation of unsupported tetrametallic CoMoMnAl and CoMoZnAl catalysts for selective hydrodesulfurization (HDS)

New formulations of unsupported tetrametallic catalysts derived from layered double hydroxides (LDH) compounds were synthesized by a constant pH coprecipitation method, characterized, and evaluated in the selective hydrodesulfurization (HDS) of thiophene in the presence of cyclohexene. The layered double hydroxides were prepared using terephthalate (C8H8O2)2- as the interlayer anion with nominal aluminum molar fraction of 0.5, and nominal cobalt to MII (M = Zn or Mn) ratios of 0.2, 0.4 and 0.6. Molybdenum introduction in the LDH precursor was accomplished by an ion exchange process using the heptamolybdate anion. The calcined Mn samples showed a higher surface area than those obtained from Zn. The sulfidation was carried out in situ with a heating ramp up to 673 K and the catalysts were evaluated in a tubular flow reactor. The catalytic evaluation of Zn and Mn-based materials for simultaneous thiophene HDS and cyclohexene hydrogenation (HYD) was conducted at 573 K and 20 bar. The results show that the Zn-based unsupported catalysts synthesized here exhibited higher selectivity for the HDS reaction than an industrial one.

On the role of hydrogen inhibition in gas-phase methane pyrolysis for carbon capture and hydrogen production in a tubular flow reactor

The thermal pyrolysis of methane enables economically competitive hydrogen production without direct CO2 emissions. Although several mechanisms for the process have already been proposed, especially the inhibitory effect of hydrogen as well as the process operation at increased pressure have not yet been fully clarified. In this context, the present work investigates the influence of hydrogen and argon as inert gas on product composition, methane conversion, and hydrogen selectivity as a function of temperature (1000 °C to 1600 °C), residence time (1 s to 7 s), molar dilution ratio (1:1–4:1), and pressure (1 bar to 4 bar) in a high-temperature reactor. Within the scope of this work, total differences in CH4 conversion of up to 50 % could be observed at equal process parameters between an argon and hydrogen dilution, underlining the potential impact of diluents on the overall process. Moreover, increasing the pressure from 1 bar to 4 bar reduces the formation of byproducts significantly for both H2 and Ar as diluent, however, with different mechanistic characteristics. The most remarkable difference is the formation of propylene that exclusively takes place in argon-diluted reaction gas mixtures. This occurrence persists unabated, even under elevated pressures and temperatures reaching as high as 1600 °C. We ascribe this phenomenon to the interaction of methyl and ethyl radicals, establishing it as an impasse to further reactions leading to the formation of solid products. Herewith, the study provides novel insights from a reaction engineering perspective as well as from a process development perspective and clarifies the role of the dilution gases hydrogen and argon on the methane pyrolysis reaction.

Predicting Long-Time-Scale Kinetics under Variable Experimental Conditions with Kinetica.jl.

Predicting the degradation processes of molecules over long time scales is a key aspect of industrial materials design. However, it is made computationally challenging by the need to construct large networks of chemical reactions that are relevant to the experimental conditions that kinetic models must mirror, with every reaction requiring accurate kinetic data. Here, we showcase Kinetica.jl, a new software package for constructing large-scale chemical reaction networks in a fully automated fashion by exploring chemical reaction space with a kinetics-driven algorithm; coupled to efficient machine-learning models of activation energies for sampled elementary reactions, we show how this approach readily enables generation and kinetic characterization of networks containing ∼103 chemical species and ≃104-105 reactions. Symbolic-numeric modeling of the generated reaction networks is used to allow for flexible, efficient computation of kinetic profiles under experimentally realizable conditions such as continuously variable temperature regimes, enabling direct connection between bottom-up reaction networks and experimental observations. Highly efficient propagation of long-time-scale kinetic profiles is required for automated reaction network refinement and is enabled here by a new discrete kinetic approximation. The resulting Kinetica.jl simulation package therefore enables automated generation, characterization, and long-time-scale modeling of complex chemical reaction systems. We demonstrate this for hydrocarbon pyrolysis simulated over time scales of seconds, using transient temperature profiles representing those of tubular flow reactor experiments.

A multipass catalytic reactor insert for continuous hydrogen generation from methylcyclohexane

Herein we describe a multipass Catalytic Static Mixer (CSM) for implementation in on-demand hydrogen generation. The insert is a 3D printed metal scaffold with a catalyst coating containing a multitude of channels and a hollow core for a heater rod. This next generation of CSMs offers higher throughput and increased residence times for applications involving liquid-gas or gas only flow. We have implemented this CSM as an insert in a continuous flow tubular reactor for the dehydrogenation of Liquid Organic Hydrogen Carriers (LOHCs). The catalyst coating is comprised of 5 wt.% Pt/Al2O3 and is used for the dehydrogenation of methylcyclohexane (MCH) to generate hydrogen gas as the model system. This experimental study investigates the thermal profiles of the reactor and validates the potential of the CSM technology in hydrogen generation from LOHCs.

Liquid‐Liquid‐Gas Triphasic Hydrogenation of Bicarbonate to Formate in a Continuous Flow Tubular Reactor

AbstractMultiphasic reaction of bicarbonate hydrogenation to form formate using homogeneous Ru PNP pincer catalyst in a continuous flow tubular reactor is reported. The reaction system consists of three phases. Catalyst is dissolved in toluene while potassium bicarbonate is dissolved in water. The significance of efficient mixing among the organic phase, aqueous phase and gaseous hydrogen to improve hydrogenation reaction by using different inert packing materials is studied by operando visualization and also quantitatively discussed. The bicarbonate conversion of up to 67% is achieved after optimization of important reaction and reactor parameters. The designed reactor setup comprised of effective recycling system that recycles the catalyst with >99% activity.

Numerical and experimental evaluation of the hydrodynamics in a tubular swirling flow reactor and its comparison with the mixing regime of a stirred dark fermenter

This work aims to the computational fluid dynamics study and experimental evaluation of a homemade tubular swirling flow reactor and its comparison with a classical CSTR typically used in dark fermentation, considering a single phase.

A solvent-selection strategy for the hydrogenation reaction inside a tubular-flow reactor through a statistical approach

Solvent selection is crucial for optimizing reaction outcomes of various reactions.

Understanding of gas-phase methane pyrolysis towards hydrogen and solid carbon with detailed kinetic simulations and experiments

Methane (CH4) pyrolysis is studied in a tubular flow reactor for the production of hydrogen and solid carbon by combining kinetic modelling, numerical simulation and experiments in a high-temperature flow reactor. Operating conditions are varied such as temperature in the range of 1273–1873 K, hydrogen addition to the feed with a molar H2:CH4 ratio between 0 and 4, and residence time in the range of 3–7 s. Elementary-step reaction mechanisms consisting of pyrolysis and carbon coupling reactions among C1, C2, aromatic and polycyclic aromatic hydrocarbon species are used in the numerical simulations of the species profiles in flow direction. A thermodynamic analysis is performed to acquire the boundary conditions for operation as well to estimate probable by-products (C2H2, C2H4, C2H6, C6H6, C16H10 etc.) over the temperature range. Gas-phase kinetic modelling is performed revealing that CH4 conversion starts at temperatures above 1273 K. Higher temperatures increase CH4 conversion and H2 yield peaking at 1573 K. The cooling temperature gradient downstream of the hot zone in the reactor causes reverse reactions in gas-phase suppressing CH4 conversion. H2 addition to the feed is found to be a crucial parameter for controlling the by-product formation. In the experimental study, a solid carbon yield of 84 % is achieved while gaseous by-products remain less than 1 mol-% at 1673 K, H2:CH4 ratio of 2, and residence time of 5 s. Gas-phase reactions are found to be coupled to surface reactions at higher temperatures.

Chromatography assisted in-vitro refolding and purification of recombinant peptibody: Recombinant Romiplostim a case study

In-vitro protein refolding is one of the key rate-limiting unit operations in manufacturing of fusion proteins such as peptibodies expressed using E. coli. Dilution-assisted refolding is the most commonly used industrial practice to achieve the soluble, native functional form of the recombinant protein from the inclusion bodies. This study is focused on developing a chromatography-assisted in-vitro refolding platform to produce the biologically active, native form of recombinant peptibody. Recombinant Romiplostim was selected as a model protein for the study. A plug flow tubular reactor was connected in series with capture step affinity chromatography to achieve simultaneous in-vitro refolding and capture step purification of recombinant Romiplostim. Effect of various critical process parameters like fold dilution, temperature, residence time, and Cysteine: DTT ratio was studied using a central composite based design of experiment strategy to achieve a maximum refolding yield of selected peptibody. Under optimum refolding conditions, the maximum refolding yield of 57.0 ± 1.5 % and a purity of over 79.73 ± 3.4 % were achieved at 25-fold dilution, 15 °C temperature, 6 h residence time with 6 mM and 10 mM of cysteine and DTT, respectively. The formation of native peptibody structure was examined using various orthogonal analytical tools to study the protein's primary, secondary, and tertiary structure. The amino acid sequence for the disulfide-linked peptide was mapped using collision-induced dissociation (CID) to confirm the formation of interchain disulfide bonds between Cys7-Cys7 and Cys10-Cys10 similarly for intra-chain disulfide bonds between Cys42-Cys102, and Cys148-Cys206. The developed protocol here is a valuable tool to identify high-yield scalable refolding conditions for multi-domain proteins involving inter-domain disulfide bonds.

Performance evaluation of a new continuous flow tubular electrochemical reactor with ceramic membrane for the treatment of wastewater

Performance evaluation of a new continuous flow tubular electrochemical reactor with ceramic membrane for the treatment of wastewater

Autocatalytic flow chemistry

Autocatalysis is a crucial process of nonequilibrium self-organization in nature and is assumed to play a role in the origin of life. The essential dynamical phenomena of an autocatalytic reaction network are bistability and the development of propagating front when combined with diffusion. The presence of bulk fluid motion may widen the range of emerging behavior in those systems. Many aspects of the dynamics of autocatalytic reactions in a continuous flow have already been studied, especially the shape and dynamics of the chemical front and the influence of the chemical reactions on hydrodynamic instabilities. This paper aims to provide experimental evidence of bistability and related dynamical phenomena, such as excitability and oscillations in autocatalytic reactions performed in a tubular flow reactor, where the flow is laminar and advection is the dominating transport process. We show that the linear residence time ramp may result in the simultaneous appearance of different dynamic states along the length of the pipe. Therefore, long tubular reactors offer a unique opportunity to quickly explore the dynamics of reaction networks. These findings enhance our understanding of nonlinear flow chemistry and its role in natural pattern formation.

Supercritical water gasification of chicken manure continuously supplied into the reactor

The article presents the research results of the chicken manure gasification in supercritical water. The experiments were carried out using a tubular flow reactor at a pressure of 25 MPa, a temperature gradient along its vertical axis (390–600 °C from top to bottom), and a chicken manure flow rate of 6.9–9.6 g/min, including experiments with the addition of NaOH (2.4 wt%). Data were obtained on the yield and composition of carbonized residues, volatile and liquid products, as well as the content of toxic substances (phenols, N-containing aromatics, and polyaromatic hydrocarbons (PAHs)) and mineral components in effluent collected at the reactor outlet. It is shown that an increase in the residence time of reagents in the high-temperature region of the reactor (HTR) improves the gasification efficiency. Using gas chromatography – mass spectrometry, it was revealed that phenol, pyridine, pyrazine, pyrrole, aniline, indole, quinoline, and their alkyl derivatives predominate in the composition of water-soluble products. The total content of phenols in effluent decreases from 1.3 to 1.1 g/dm3 when increasing the residence time of reagents in HTR, and does not depend on adding NaOH while the total content of N-containing aromatics decreases from 1.0 to 0.7 g/dm3 when adding NaOH. The content of PAHs, which is dominated by naphthalene, increases from 0.5 to 2.1 mg/dm3 in effluent when increasing the residence time of reagents in HTR. According to capillary electrophoresis data, increasing the residence time in HTR and adding NaOH result in increase of the content of NH4+ ions in effluent from 9.8 to 10.9 g/dm3.

A continuous flow mode with a scalable tubular reactor for the green preparation of stable alkali lignin nanoparticles assisted by ultrasound

Lignin nanoparticles (LNPs) have become a hot topic recently because of their improved physicochemical properties and the excellent integration into various industrial sectors compared to lignin. However, the green large-scale production of stable LNPs severely restricts the high-value applications of LNPs. In this work, a simple and potentially scalable continuous-flow mode setup with a tubular flow reactor was designed for the green preparation of stable alkali LNPs assisted by ultrasound. When the flow rates of lignin solution and nitric acid solution were 8.00 mL/min and 2.67 mL/min respectively, and the length of the tube was 5.5 m, the average residence time of mixed solution was 62.2 s in the tubular reactor. Spheroid nanoparticles with an average size of 97.2 nm were obtained under this optimized condition. Furthermore, the results showed a better control of the mixing compared to the batch process, resulting in a homogeneous distribution of smaller particle sizes thus improving stability and UV-blocking properties. This is attributed to the better mixing and excellent mass transfer characteristics in the tube, which provides favorable conditions for the full contact and uniform dispersion of the mixed solution. More importantly, continuous flow mode makes it possible to prepare LNPs with excellent physicochemical properties on a large scale, which will bring great opportunities for the industrial production and application of LNPs.

Enhanced scale-up performance on residence time distribution by integrated microcapillaries with high size uniformity

Continuous tubular flow reactors are widely used by virtue of their simple structures, controllable reaction conditions, enhanced heat and mass transfer, etc. Microreactors present specific microscale characteristics including laminar flow, reduced diffusion path, enhanced mixing degree and high surface area to volume ratio. Microcapillary reactors combined the advantages of continuous processing and microscale reactions. However, the scale-up of microreactions is still a very challenging task for the loss of enhanced transport characteristics in microscale. Residence time distribution (RTD) is a vital research method to investigate the flow behaviors of microreactors. Microcapillary films (MCFs) containing several parallel microcapillaries provide a strategy to multiplex the microreactions. Nevertheless, the low size uniformity of microcapillaries in MCF strips hinders their application in microreactions. We carried out Computational Fluid Dynamic (CFD) simulations with experimental RTD validation to investigate the effects of dimension, convection and diffusion on RTD and the relationship between the RTD diversity and the size uniformity of microcapillaries under fixed velocities and volumetric flow rates. MCFs with high size uniformity were manufactured by liquid-assisted extrusion, and the coefficient of variance of the mean residence times of the microcapillaries in the MCF strip was only 2.8%. Neutralization reaction also showed the consistence of reaction performances among microcapillaries. With the enhanced scale-up performance on RTD and microreactions, MCFs are expected to have broad applications in large-scale microreactions in chemical engineering industry.

Ammonia thermal decomposition on quartz and stainless steel walls

Ammonia has been proposed as a promising solution for hydrogen carriers as well as clean fuels. However, the reaction kinetics is still not robust in many engineering applications, where the deviation is mainly caused by the surface reactions of ammonia on the wall. To examine the ammonia surface reaction on engineering materials, in the present study, the thermal decomposition of ammonia is systematically investigated in uniformly heated quartz/SUS304 tubular flow reactors with the prescribed heating length. A decrease in the inner diameter of the quartz tubular reactor leads to an increase in the ammonia thermal decomposition rate, showing that the thermal decomposition reaction occurs even on quartz surfaces, which is usually believed to be inert. The thermal decomposition on the SUS304 reactor surface starts from as low as 700 K, indicating it is much more reactive than the quartz surface. One-step surface reaction models of ammonia for quartz/SUS304 surfaces are proposed, with which the reaction rates are estimated based on the experimental data. The inner surface of the SUS304 tubular reactor after the thermal decomposition experiments is examined by X-ray photoelectron spectroscopy. The formation of iron nitride on SUS304, which in turn facilitates ammonia thermal decomposition, reveals the positive feedback between ammonia decomposition and nitriding. Moreover, the present one-step surface reaction on stainless steel has been validated by measuring ammonia distributions in the preheat zone of NH3/O2/N2 premixed flame impinging on a stainless steel plate through a two-photon absorption laser-induced fluorescence (TALIF) technique.

Catalytic multi-step continuous-flow processes for scalable transformation of eugenol into potential fragrances

Catalytic multi-step processes were optimized and developed under continuous-flow conditions, to transform eugenol into potential new fragrances. One approach consisted in the direct catalytic conversion of eugenyl acetate into the corresponding cyclic carbonate, through a two-step protocol that utilizes two different tubular flow reactors for Mn(V)-catalysed epoxidation, using imidazole as co-catalyst and hydrogen peroxide as the oxidant, followed by the epoxide carboxylation with carbon dioxide, catalysed by a binary ZnBr2/TBAB catalytic system. With this methodology, a productivity of 7.68 g product per day was obtained. The other approach is an efficient hydroformylation/acetalization sequential process, which operates through a multi-stage flow system consisting of a tubular reactor for the Rh(I)/xantphos-catalysed hydroformylation, coupled in series with a K10 packed bed reactor for the aldehyde acetalization step. This pioneering strategy allowed obtaining 94 % chemoselectivity for acetal formation and 96 % regioselectivity for the linear product, resulting in a process productivity of 10.02 g product per day.