•Proposed a new method to numerically study the solidification of a droplet.•Developed a novel numerical method to capture the shrinkage of the droplet correctly.•Provided a deep insight into the details of mass transfer during this process.•Revealed several factors influencing this process from micro-scale point of view.The removal of organic solvent plays an important role in the fabrication of polymer spheres by emulsion-based solvent evaporation technique. Mathematical model describing the mass transfer of fluorobenzene (FB) inside the O/W emulsion droplet, from the droplet to the continuous phase and from the continuous phase to the atmosphere to produce millimeter-sized polystyrene (PS) spheres was established. A novel approach based on finite volume method was developed to numerically solve the mathematical equations concerning the shrinkage of the solidifying droplet. Using this method, the variations of the droplet size and the concentration field inside the droplet were captured. The details of the solidification process which cannot be obtained using experimental methods were revealed. Several factors influencing the curing rate and mass transfer process, such as droplet number, initial droplet diameter, initial concentration and addition of FB in the continuous phase, were investigated in detail. The simulation results indicated that changing the initial concentration or changing the initial diameter of the droplet to tune the solidified particle size were essentially the same considering their effects on the details of the solidification process. When adding FB in the continuous phase to reduce the curing rate and concentration gradient, dispersing the added FB into droplets with the same diameter to that of the PS/FB droplet to be solidified has the most significant effect.

•Developed color-gradient LBM method with successful simulation of Janus droplet formation in microchannel.•Demonstrated the mechanism of Janus droplet formation mode with the Capillary number.•Investigated the dynamic behavior of dispersed thread in the droplet forming process.•Revealed the evolution behavior of each part of dispersed thread.A ternary lattice Boltzmann method based on the color-gradient model was successfully established to numerically investigate the Janus droplet formation in a Y-junction microfluidic device. We first validated the model by comparing the simulation results of contact relationship of mono-dispersed droplets with the theoretical solutions, and then studied Janus droplet formation and the breakup dynamics in Y-junction numerically. The results showed that the Janus droplet size obeys a scaling law during the formation. The dynamic behavior of dispersed thread, including the thread tip and minimum width of thread, revealed that the breakup of the thread is a self-thinning process. The evolution of the minimum width of dispersed thread is dominated by evolution time in a power law relationship. The deep investigation of each dispersed thread indicated that the dynamic behavior of each thread is identical before the final pinch-off in the formation process.

•An effectiveness factor model based on microkinetics derived semi-analytically.•A hybrid scheme for multiscale modeling of microchannel methane reformer.•Accurate information of the reactor, washcoat and catalyst scales retained.•Over 10-fold speed-up obtained compared to a full model.This paper proposes a methodology for efficient multiscale modeling and simulation of washcoated microchannel reactor by the use of an effectiveness factor submodel. The methodology is demonstrated in the context of modeling a microchannel methane reformer for miniaturized gas-to-liquids (GTL) application. The effectiveness factor submodel is derived specifically for a detailed multi-step reforming kinetics using the data provided by 2D CFD simulations with simplified reactor geometry and fully resolved washcoat. The generalized Thiele modulus approach is exploited to facilitate simple explicit estimations of the effectiveness factors of CH4 and H2O. The root mean squared error of the predictions is shown to be 0.015. On this basis, a hybrid model is formed including the CFD model of the reactor, 1D reaction-diffusion equations of the washcoat and the effectiveness factor submodel as the interface in-between. The hybrid model can accurately reproduce gas phase and intra-washcoat profiles of gas species and surface reaction intermediates for various washcoat properties along with time savings of more than an order of magnitude. The results also show that the reformer’s performance is sensitive to washcoat diffusion resistance.

Effect of reduction and carburization pretreatment on iron catalyst for CO hydrogenation to light olefins was investigated. The bulk structure and surface composition of the catalysts during pretreatment were characterized by means of X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS) and high-resolution transmission electron microscopy(HRTEM). The results indicated that phase transformation of iron phases involved α-Fe2O3→Fe3O4→α-Fe both in the bulk and on the surface layers in hydrogen atmosphere. However, α-Fe2O3 was firstly transformed to Fe3C and then to Fe5C2 in CO atmosphere, while in syngas atmosphere directly to Fe5C2. As carburization pretreatment time was prolonged, the degree of carburization on the surface increased, and the increase degree of iron catalyst carburization in CO pretreatment was stronger than that in syngas pretreatment. It inferred that surface carbon species was more easily formed in syngas pretreatment instead of iron carbide in CO pretreatment. After hydrogen pretreatment, when the catalyst was reduced to a mixture of magnetite and metallic iron, the selectivity to light olefins was relatively low. Under the joint effects of the active sites from surface iron carbide and surface carbon layers blocking the active sites, longer CO pretreatment time resulted in higher methane selectivity and less light olefins. The selectivity to methane on H2-pretreated catalyst was lower than that of CO-pretreated catalyst.

•A multiscale reactor model of integrated microchannel methane reformer•Reformer's operation window delineated for various options of miniaturized GTL•Recycled fuel reduces GHG emission at the price of poorer operability.•Combined reforming improves CO productivity and suppresses GHG emission.•Better operability and GHG emission using more diffusible reforming catalystMiniaturized gas-to-liquids (GTL) process utilizes remote, distributed natural gas reserves to produce liquid synfuels. The demand for cost-down to enable smaller production scales requires carefully evaluating different process alternatives involving gas recycles and feedstock variations. We develop a multiscale reactor model combining CFD, microkinetics and reliable effectiveness factor correlations to simulate a microchannel methane reformer producing syngas under conditions relevant for miniaturized GTL. The reformer's operation is evaluated for various fuels and feedstock compositions. It is shown that the attainable production scale is 30,000 h− 1 regardless of fuel. Recycling the Fischer-Tropsch (F-T) tail gas can reduce the reformer's greenhouse gases (GHG) emission by ~ 18% at the cost of a narrower operation window under high fuel-to-reforming gas ratios. Use of reforming feedstock containing 25 vol% CO2 increases the maximum CO productivity by 30% and reduces the GHG emission by 6–17%, while the operability is unaffected. To improve the reformers' operability when fueled by F-T tail gas, 5% 1-μm transport pores is introduced into the reforming catalyst, which drastically extends the operation window and reduces the GHG emission, thus broadening the attainable scale of production to over 40,000 h− 1.

Chemical Percolation Devolatilization (CPD) theory was applied to investigate the devolatilization performance of asphalt. On the basis of the original CPD model, algebraic approaches for two chemical structure parameters (i.e., initial intact bridge and char bridge fractions) were modified with the consideration of the structure features of asphalt sample. The 13C NMR analysis data of the sample were adopted to determine the modified chemical structure parameters, while kinetic parameters were fitted based on the data of thermogravimetric analysis. Two sub-models, i.e., the distillation model and the cross-linking model, were found to be indispensable for describing asphalt devolatilization. As a result, the model predictions revealed the evolution of bridge variables during devolatilization, which helped to interpret the reaction procedures in detail. Further discussion was made to theoretically predict the yields of products at different heating rates, and the results indicated that an increasing heating rate did benefit the yield of the total volatiles from the asphalt sample.

•Steam methane reforming in a micro-channel reactor at high pressure was studied.•Ni catalyst plates showed good performance of catalyst activity and stability.•Contact time was the key point to make full use of Ni catalyst activity.•High hydrogen productivity was realized at ultrahigh GHSV and elevated pressure.Hydrogen has drawn much attention as both a kind of clean and efficient energy and an important chemical material. Among numerous production method, steaming methane reforming (SMR) accounts for most of the hydrogen production over the world. In this work, we investigated the behavior of Ni catalyst and performance of micro-channel reactor at high pressure for SMR process. The influences of various temperature, steam-to-methane ratio, GHSV at high pressure varied from 0.5 MPa to 2.0 MPa were studied in details. Even when the process was conducted at 240,000 h−1, the methane conversion could still approach to the thermodynamics limitation at 900 °C and 2.0 MPa, which confirmed that micro-channel reactor with coated catalyst is not only feasible but high efficient for SMR process. Besides, we realized the hydrogen productivity of about 0.1 m3/h in a single channel at 2.0 MPa, namely 1.95 × 104 m3/(m3 h) space time productivity.Download high-res image (126KB)Download full-size image

•Presented a state-of-the-art review on plasma assisted chemical processes and reactors.•Illustrated the principles of thermal and non-thermal plasmas and their applications in reaction engineering.•Proposed the key issues for R&D activities in relation to plasma intensified processes.Plasma assisted chemical processes and reactors have drawn more and more attention in academic research and industrial applications. On one hand, plasmas change the fluid properties at atomic/molecular scale. On the other hand, the mutual contact between plasmas and the substances are alternated at meso-scale, bringing up unique features of transport phenomena and reactions in such chemical reactors. This short review aims to introduce some fundamental and practical aspects of thermal and non-thermal plasmas with their broad applications in chemical reaction engineering.

This work aims to understand the gasification performance of municipal solid waste (MSW) by means of thermodynamic analysis. Thermodynamic analysis is based on the assumption that the gasification reactions take place at the thermodynamic equilibrium condition, without regard to the reactor and process characteristics. First, model components of MSW including food, green wastes, paper, textiles, rubber, chlorine-free plastic, and polyvinyl chloride were chosen as the feedstock of a steam gasification process, with the steam temperature ranging from 973 K to 2273 K and the steam-to-MSW ratio (STMR) ranging from 1 to 5. It was found that the effect of the STMR on the gasification performance was almost the same as that of the steam temperature. All the differences among the seven types of MSW were caused by the variation of their compositions. Next, the gasification of actual MSW was analyzed using this thermodynamic equilibrium model. It was possible to count the inorganic components of actual MSW as silicon dioxide or aluminum oxide for the purpose of simplification, due to the fact that the inorganic components mainly affected the reactor temperature. A detailed comparison was made of the composition of the gaseous products obtained using steam, hydrogen, and air gasifying agents to provide basic knowledge regarding the appropriate choice of gasifying agent in MSW treatment upon demand.

•Introduced an integrated detailed kinetic mechanism for acetylene decomposition at high temperature.•Revealed the general requirements in preserving acetylene during quenching processes.•Discussed the co-production of acetylene and ethylene and energy re-utilization of chemical quenching method.•Proposed a detailed propane-quenching optimization for pilot-plant acetylene production by plasma coal pyrolysis.Quenching of acetylene-rich gas at high temperature is an essential step in most acetylene production processes. Different from traditional physical quenching methods (e.g., water spray), chemical quenching has the advantage of reusing the gas heat content and producing co-products while preventing acetylene from decomposing. In this work, a detailed kinetic mechanism was proposed to theoretically describe and reveal the chemical quenching process. Reactions of small hydrocarbons, PAHs growth and soot formation were taken into consideration to build the model, which was validated by reported data. Afterwards, an ideal PFR model was used to investigate the effects of different operating conditions, including temperature after quenching, quenching time, and quenching media. Furthermore, the proposed model was used to optimize the chemical quenching operation for a pilot-plant acetylene production process based on thermal plasma technique. The results showed that chemical quenching could effectively realize both energy re-utilization and ethylene co-production, while maintaining a satisfactory yield of acetylene.

•Washcoat-resolved CFD model and microkinetics for heterogeneous catalysis.•Considerable mass transport limitation in catalytic washcoat demonstrated.•Marked dependence of reactor performance on washcoat thickness and pore diameter.•Optimal washcoat thickness around 75 μm for 10% Ni catalyst.The effect of washcoat properties is theoretically investigated for steam methane reforming (SMR) in a plate microchannel reactor. Transport phenomena and reaction within the catalytic washcoat and in the bulk gas phase are modeled using a two-dimensional, comprehensive CFD model with fully resolved catalytic washcoat, coupled with detailed chemistry for SMR over Ni catalyst. Simulation results show that the process is governed by internal mass transfer and reaction, therefore the reactor performance depends markedly on the washcoat structure and dimension. Increasing pore size of the washcoat leads to improved heat coupling, which lowers the hotspot temperature and reduces axial temperature gradients. In the meantime, the role of porosity remains trivial. Further, using a thicker washcoat carrying a greater loading of catalyst can considerably increase the reactor throughput within washcoat thickness of 75 μm, at the expense of certain loss of the catalyst productivity. Optimized washcoat properties would rely on the catalyst activity, price and specific process demands.

Thermal plasma technique is proposed as a potential approach to pyrolyze asphaltenes to useful chemicals at ultrahigh temperature. Thermal plasma pyrolysis experiments show that acetylene is the major gaseous product with concentration up to 45 wt.%, together with some hydrogen and methane as well as the solids residue as by-products. To predict such a millisecond process, a particle-scale heat transfer model coupled with a modified competition kinetic model has been proposed, in which the heat exchange between the plasma gas and the particles as well as the heat transfer inside the particles are taken into account. Typical results indicate that the pyrolysis temperature would remarkably increase the heating rate. The heating rate would exceed 107 K/s at 2000 K in H2 thermal plasma and the devolatilization process would complete in 0.4 ms for 50 μm asphaltene particles, H2 thermal plasma provides better heating exchange efficiency between the plasma and particles than He, N2 or Ar. Linear relationship is found between the heating rate and the devolatilization time under bi-logarithm coordinates at a certain temperature, regardless of the plasma gas compositions and pulverized sub-millimeter particle size, which gives powerful guidance for process optimization of the asphaltene pyrolysis.

A high rate fabrication of a thin film complex consisting of cubic-SiC nanocrystals, amorphous silicon and graphite was realized using an atmospheric pressure thermal plasma enhanced chemical vapor deposition (APTPECVD) process with SiCl4 and C2H2 as the silicon source and carbon source, respectively. The morphology, crystal structure and surface chemical composition of the products were characterized. The APTPECVD SiC nanocrystals have average diameters between 18 and 30 nm. A room temperature red region photoluminescence (PL) property originated from the quantum confinement effect of these SiC nanocrystals was observed under UV wavelength excitation. Moreover, pure SiC nanocrystals with a red region PL property can be obtained after a simple post-treatment, including calcining and etching processes. These red photoluminescent SiC nanocrystals can be utilized as biomarkers in bioimaging and drug delivery.

Graphene nanosheets (GNs) are successfully deposited via a radio frequency (RF) induction thermal plasma pyrolysis process using methane as the precursor. Products are characterized by X-ray powder diffractometer (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy and BET measurements. The results illustrate that those few-layer GNs with the number of layer at about 5 and the size at 200–500 nm are deposited. The H2 atmosphere in the RF induction thermal plasma is the key factor to fabricate the few-layer GNs. The direct conversion of CH4 to few-layer GNs through RF thermal plasma process suggests that the technique is simple, easy to operate, and is suitable for mass production of few-layer GNs in a continuous and scalable process.

Phase-pure M1 MoVNbTeOx catalyst plates have been prepared on a metal–ceramic complex substrate by a dip-coating method. At a temperature of 420 °C and atmospheric pressure, the performance of the M1-PVA catalyst plate in a micro-channel reactor approached an ethane conversion of ~60% and an ethylene selectivity of ~85% with a high catalyst productivity of 0.64 kgC2H4 kgcat−1 h−1. Due to the excellent heat transfer ability, it is demonstrated that the micro-channel reactor can achieve the same reactor productivity as a traditional fixed-bed reactor within only 20% of its volume. XRD, SEM and ICP characterization indicated that the M1-PVA catalyst plate has a high stability in the micro-channel system.

This work applied coal tar as a potential kind of feedstock in thermal plasma pyrolysis process, by which effective transforming from coal tar to acetylene could be realized in milliseconds. A kilowatt level lab-scale plasma pyrolysis device for coal tar pyrolysis was established. Experiments with three typical coal tars were carried out to investigate the influences of operating parameters on the feedstock conversion and the yields of total light gas and acetylene. The results show that low-temperature coal tar has the best pyrolysis performance, with the highest light gas yield exceeding 70 % and acetylene yield of 45 % when using Ar plasma. Considering both conversion and energy efficiency, 6.0 × 104 kJ/kg is regarded as the most appropriate specific energy input for coal tar in Ar/H2 plasma, which promises a conversion of 65 %. Further discussion was made that coal tar has better pyrolysis properties than coals.

Nanocrystalline silicon is a promising alternative for the conventional crystalline silicon materials in the photovoltaic industry because of its better photostability and easy fabrication. However, the low deposition rates of conventional nanocrystalline silicon fabrication processes have hampered its application in industry. Thermal plasma has been used to successfully realize the high rate deposition of nanocrystalline silicon in this work. Optical emission spectroscopy (OES) diagnostic and thermodynamic equilibrium calculation are carried out to better understand the mechanism of deposition reactions and the effect of SiCl4 input rate on the nanocrystalline silicon deposition rate and product properties. Emission lines of atomic silicon, atomic hydrogen and atomic argon are observed. The results show that the amount of silicon related species in the gas phase is the main factor affecting the deposition process, which has a linear relationship with nanocrystalline silicon deposition rate, grain size and crystalline fraction at the high H2 dilution ratio of the deposition system.

This work used thermal plasma to enhance the deposition process of SiC nanocrystals, with SiCl4 and CH4 as the Si source and C source, respectively. Thin films containing SiC nanocrystals, a-Si and graphite were deposited on the substrates. The morphology and crystalline structure of the samples were characterized by various techniques, including SEM, TEM, and XRD. SiC nanocrystals were observed being covered by carbon films and embedded in the network formed by graphite and a-Si. The effect of SiCl4 input rate on the deposition process and product properties was studied in detail, combining characterization techniques and optical emission spectroscopy (OES) diagnostic results. Based on the OES diagnostic of the plasma zone, the concentrations of atomic Si and C in the gas phase are concluded to be the main factors affecting the deposition process. Finally, a simple deposition mechanism is deduced based on the experimental results, which indicates the formation of SiC nanocrystals through the assembly of atomic species in the plasma.

We prepared paclitaxel-loaded disulfide-crosslinked human serum albumin nanoparticles (PTX-HSA-NPs) in a microfluidic platform. The entire process includes four steps, i.e., a pretreatment step to partially reduce albumin, a mixing and co-precipitation step, a reaction step, and a dialysis step. Two important factors dominate the successful preparation of stable PTX-HSA-NPs: one is the choice of the anti-solvent in the co-precipitation step, and the other is the reaction time in the reaction step. We demonstrated that the drug-loaded nanoparticles are stable against dilution by the inter-albumin disulfide bonds, but still have a quick drug release profile in the intracellular-mimicking reduction environment. Through cell studies, we showed that the albumin nanoparticle carriers are safe and characterized the cell toxicity of the paclitaxel-loaded nanoparticles with cell lines of human breast cancer cells (MCF-7).

•Investigated coal devolatilization under slow, fast and plasma pyrolysis conditions.•Explained the enhanced yield of light gases in the fast pyrolysis experiments.•Discussed the relationship among the slow, fast and plasma pyrolysis processes.•Revealed the significant effect of heating rate on carbon conversion to light gases.•Established a mechanism model for improving the proposed coal rank selection method.Experiments were carried out in a drop tube furnace and a lab-scale plasma reactor to investigate the effects of coal properties, particle ultimate temperature and heating rate (i.e., 10−1 to 101 K/s for slow pyrolysis, 102 to 104 K/s for fast pyrolysis and 104 to 106 K/s for rapid plasma pyrolysis processes) on coal devolatilization performances. The results revealed that fast pyrolysis of coal would greatly increase the yield of light gases compared to slow pyrolysis process. The increased yield of light gases strongly depended on the coal rank and mainly came from the secondary tar cracking reactions. The comparisons of slow pyrolysis, fast pyrolysis and rapid plasma pyrolysis processes indicated that the major effect of the increased heating rate was to raise the carbon conversion to light gases and then greatly increase the yields of gaseous hydrocarbons correspondingly. In addition, fast pyrolysis behaved much closer to plasma pyrolysis for the coals with the volatile matter content higher than 37%. Therefore, understanding on the fast pyrolysis in a drop tube furnace could help to provide a simple, quick method for preliminary selection of coal rank for plasma pyrolysis process. Finally, a comprehensive single-particle heat transfer mechanism model was established to further discover the effect of heating rate on coal devolatilization and to improve the accuracy of the proposed coal rank selection method.

We have presented a self-cross-link strategy to fabricate HSA nanoparticles using a desolvation method. The nanoparticles were stabilized by intermolecular disulfide bonds while still dissolvable in reducing media. The fabrication process does not involve any toxic chemicals and hence the nanoparticles may be useful as a drug carrier.

Hydrogenated nanocrystalline silicon (nc-Si:H) is a promising alternative for crystalline silicon (c-Si) in the photovoltaic industry. We proposed an atmospheric pressure thermal plasma enhanced CVD (APTPECVD) process for high rate deposition of nc-Si:H on silicon and glass substrates using SiCl4 as the deposition precursor. The deposition rate under typical operating conditions could reach 9.78 nm s−1, and the deposited nc-Si:H film thickness could reach 17.6 μm. The grain diameter and crystalline fraction of the deposition product were characterized using SEM, TEM, Raman spectroscopy and XRD. The photoluminescence performance at room temperature was discovered.

The bimetallic Ni–Fe catalysts used in CO total-methanation reaction were prepared by the impregnation method on γ-Al2O3 support for the production of substitute natural gas (SNG). The catalysts were characterized by N2 physisorption measurements, field-emission scanning electron microscopy (FE-SEM), and H2 temperature-programmed reduction (H2-TPR). The methanation performance under the industrial total-methanation conditions (0.1–3.0 MPa, H2/CO = 3.0–3.1) was studied in detail using Ni–Fe/γ-Al2O3 as a heterogeneous catalyst. The results showed that the addition of Fe to the catalyst can effectively improve the catalytic activity of Ni/γ-Al2O3, while the high activity of bimetallic Ni–Fe catalyst was attributed to the quality of Ni–Fe alloy in the catalyst in terms of the experimental results of H2-TPR. The sample with appropriate Ni/Fe molar ratio of about 3 exhibited the highest CO conversion (near 100% at 225–550 °C) and the highest CH4 selectivity (over 99% at 300–450 °C) under the reaction pressure of 3.0 MPa. Furthermore, based on the systematic study of catalyst components, MgO in the catalyst can increase the reduction temperature of nickel oxide on the support. The silicon species as an impurity in the support play a negative role in the catalytic activity, especially for the CH4 selectivity.Graphical abstractThe bimetallic Ni–Fe catalysts used in CO total-methanation reaction were prepared by the impregnation method on γ-Al2O3 support for the production of substitute natural gas (SNG). The methanation performance under the industrial total-methanation conditions (0.1–3.0 MPa, H2/CO = 3.0–3.1) was studied in detail using Ni–Fe/γ-Al2O3 as a heterogeneous catalyst. The results showed that the addition of Fe to the catalyst can effectively improve the catalytic activity of Ni/γ-Al2O3, while the high activity of bimetallic Ni–Fe catalyst was attributed to the quality of Ni–Fe alloy in the catalyst in terms of the experimental results of H2-TPR.Highlights► Bimetallic Ni–Fe catalysts were prepared for total-methanation process, showing excellent catalytic performance. ► High activity of Ni–Fe catalysts was attributed to the quality of Ni–Fe alloy. ► Silicon content in catalyst support as an impurity played a negative role in CH4 selectivity.

Cold atmospheric plasma is considered to be a promising approach for decontamination purposes, e.g. dyeing water decoloration. In order to better understand the complex mechanism of the plasma physics coupled with the plasma chemistry involved in the interaction of the polluted water with the discharge plasma, a novel approach was proposed to study the in situ oxidation process between the plasma and liquid phase in two dielectric barrier discharge (DBD) plasma reactors with different bottom shape (concave vs. plane), by using the planar laser induced fluorescence technique to visualize the process dynamics. Rhodamine B was employed as the tracer dye, which was gradually decomposed by the combined effect of the chemically active radicals (OH, O, H2O2, etc.) as well as the intense UV radiation in the DBD plasma process. The results showed that the DBD plasma filaments induced certain fluctuation on the Rhodamine B liquid layer, which accordingly intensified the mass transfer to a large extent thus accelerated the oxidation process. The comparison of the measured concentration fields in the two DBD plasma reactors illustrated that the DBD reactor #1 with concave bottom showed higher oxidation efficiency than the DBD reactor #2 with plane bottom. Additionally, the experiments demonstrated that the oxidation efficiency in the DBD plasma water treatment was much better than that in the reactor with pure oxidation by ozone gas, which can be further improved by injecting the additional oxygen gas bubbles into the liquid phase in the plasma reactor.

Liquid hydrocarbons including n-hexane, cyclohexane and toluene are pyrolyzed in H2/Ar plasma to investigate the effects of feedstock properties and key operating conditions (e.g., the feedstock specific input power and residence time) on the reaction performance. The experiments verify that the non-aromatic hydrocarbons show better chemical reactivity than partially aromatic substances. Meanwhile, the straight-chain alkanes and cycloalkanes have better yields of ethylene during the pyrolysis. The results also demonstrate that the pyrolysis reactions are almost completed within the first 0.8 ms in Ar/H2 plasma independent of the feed substances (i.e., liquid hydrocarbons), where the increased feedstock specific input power enhances the reactant conversions and correspondingly raises the yields of acetylene. At a feedstock specific input power of 4.7 × 104 kJ/kg, the n-hexane conversion is over 90 % and the yield of acetylene reaches 70 %. In addition, when using n-hexane as the feedstock, very little coke is formed during the course of reaction. Comprehensive comparisons of the current experiments with the data reported in the literature are made to point out the key influencing factors, i.e., the effective mass ratio of C/H (RC/H) in the gaseous phase and the quench temperature. Both two factors would need to be enhanced in order to get a better performance. Finally, the improvements on the specific energy requirement of this process are discussed.

Three Ni-based catalysts, namely Ni/ZrO2/Al2O3, Ni/La–Ca/Al2O3 and Ni0.5Mg2.5AlO9 catalysts were prepared, tested and characterized for steam reforming of methane (SRM), especially at high space velocities. Experimental results demonstrated that Ni0.5Mg2.5AlO9 catalysts showed excellent catalytic activity, e.g., the high reaction performance (i.e., activity and stability) at a very short residence time of 20 ms. For the accompanied water gas shift (WGS) reaction with the SRM at the steam to methane ratio of 3:1, the overall hydrogen yield depended on both the CH4 conversion and the CO2 selectivity. The results showed that CO2 selectivity had opposite trend compared with CH4 conversion in such a short-contact process. Catalyst characterizations by XRD, SEM-EDS, TEM and TGA suggested that the good performance of nickel catalysts was closely related with the good dispersion of the active component. The nano-sized nickel particles in strong interaction with the supports would lead to the good dispersion, thereafter having a slight tendency to sintering, and then to coking.

A comprehensive study on the catalytic performance of Ni catalyst to implement millisecond steam reforming of methane (SRM) reaction in micro-channel reactors was conducted in this work. A new method to manufacture the metal–ceramics complex substrate as catalyst support was presented, that is, a layer of nano-particles, α-Al2O3, was thermally sprayed on a metallic substrate, usually FeCrAlloy. Ni or Rh catalyst was then impregnated on the substrate, forming firm and active catalyst coatings. The fall-off rate of the catalyst can be neglected after the plates experienced the high-temperature SRM reaction, showing the reliability in long-term use and the excellent catalytic performance for SRM reaction in micro-channel reactors. In comparison with the expensive Rh catalyst, Ni also showed wonderful performance to catalyze the SRM reaction in micro-reactors within milliseconds. Using the appropriate reactor design, CH4 conversion reached above 90% when the residence time was as short as 32 ms for catalyst loading of 6.8 g/m2. When the residence time was longer than 100 ms, CH4 conversion was above 98%. Besides, catalyst deactivation was not detected for 500 h on stream with S/C ratio of 3.0, and for 12 h with S/C of 1.0 as well. Extensive characterizations on these Ni catalyst plates using XRD, SEM, TEM and XPS demonstrated that Ni catalysts prepared in this work did not show any sign of deactivation after being used in the micro-channel system under high-temperature operation.

The catalyst deactivation of rhodium-coated foam monolith with CO2 and/or H2O addition was investigated both experimentally and numerically to understand the means to improve the durability of the rhodium catalyst applied for catalytic partial oxidation of methane (CPOM). The results showed that the addition of He, CO2, and/or H2O could all improve the catalyst stability mainly due to the reduced hot-spot temperature in the oxidation zone for the reason of either the dilution effect or the simultaneously endothermic reaction of CO2/steam reforming. In particular, the catalyst stability can be greatly enhanced even at a low C/O ratio (i.e., carbon/oxygen ratio in atom of 0.85) with the addition of CO2 or H2O. Under the same conditions, high CH4 conversion (e.g., 0.8−0.85) can be achieved. The H2 yield can be adjusted by the added quantities of CO2 and/or H2O, which would allow the conventional pure CPOM process to be flexible to tune the composition of its product gas. These experimental results improved the understanding of how to modulate the CPOM process to achieve different reactor performances with the corresponding catalyst stability. Furthermore, CFD simulation with detailed chemistry was carried out. The model predictions had good agreement with the experimental results using the modified kinetics of the CO2 adsorption reaction, which was mostly not addressed when simulating a pure CPOM process in the literature for the little effect of CO2.

Considering the inevitable high energy input to implement the CO2 reforming of methane under high-temperature operation using conventional catalysis method, the low temperature conversion of CO2 and methane in the coaxial dielectric barrier discharge (DBD) plasma reactor was investigated in this work. Steam was introduced to enhance the CO2 reforming of methane with synergetic catalysis effect by cold plasma and catalyst. The experimental results showed that a certain percent of steam could promote the conversion of both CH4 and CO2. Meanwhile, the carbon deposition was evidently reduced compared with the dry reforming of methane. With the increase of steam input, the steam reforming occurred predominantly. As a result, the hydrogen volume percentage in the product gases increased. In this way, the products with different H2/CO ratio could be achieved by changing the mole ratio of CH4/CO2/H2O at the reactor inlet. In particular, when the mole ratio of H2O/CH4 increased to almost 3 corresponding to the pure steam reforming process, the conversion of CH4 reached almost 0.95 and the selectivity to H2 was almost 0.99 at 773K.Highlights► Steam enhanced CO2 reforming of CH4 with synergetic catalysis by cold plasma and catalyst. ► Doubled space velocity under same power input with reduced carbon deposition. ► Adjustable composition of product gases by changing the mole ratio of CH4/CO2/H2O. ► Excellent reactor performance at low temperature for plasma assisted steam reforming.

Drug nanocrystal has become an important technology for poorly water-soluble drug delivery, and it is highly desirable to understand their formation mechanism and structure evolution pathway. Here we used curcumin as the model drug and studied in detail its nanoprecipitate structure evolution from a micromixer. Curcumin initially precipitated out as amorphous nanospheres, and then went through amorphous aggregation before transforming into needle-shaped crystals. The results clearly show a nonclassical crystallization pathway for curcumin nanoprecipitation.

Coal pyrolysis to acetylene in thermal plasma provides a direct route to make chemicals from coal resources, where the rapid heating and release of volatile matters in coal particles play the dominant role in the overall reactor performance. A mechanism model incorporating the heat conduction in solid materials, diffusion of released volatile gases, and reactions was proposed for a deep understanding of the heat transport inside a coal particle under extreme environmental conditions such as high temperatures greater than 2000 K and milliseconds of reaction time. The two competing rates model, known as the Kobayashi model, was applied to describe the devolatilization kinetics, which was verified by comparing the predicted yield of volatiles with the experimental data in the literature. Thermal balance between coal particles and the hot carrier gas was established, and the four influencing factors including the heating rate, particle size, reactants flow ratio, and heat of devolatilization were paid attention when analyzing the heating profile inside the particles and the yield of volatiles. The results showed that the inherent resistance due to the volatiles released from coal particles seriously impeded the thermal energy transportation from heating gas to the particle. This led to a weakened heating rate, i.e., a long heating up time, and thereafter a low yield of volatiles, especially when the particle size was large (e.g., >40 μm). Meanwhile, the heat conduction inside the coal particle also imposed additional resistance to reduce the heat transportation rate from heating gas to the particle, especially when the particle size was larger than 80 μm. The predicted yield of volatiles considering the mechanism of the two resistances agreed reasonably with the reported experimental data under different operating conditions but was smaller than that which could be obtained when neither resistance is considered. It can be concluded that the proposed heat transport mechanism inside coal particles works well in understanding the coal pyrolysis process at ultrahigh temperatures.

The gas–solid flows in a two-dimensional downer of 10 m in height and 0.10 m in width were simulated using a CFD–DEM method, where the motion of particles was modeled by discrete element method (DEM) and the gas flow was described by Navier–Stokes equations. The simulations revealed a rich variety of developing flow structures in the downer under different operating conditions. The two-phase flow development can be clearly characterized by the micro-scale particle distributions in the downer. Near the inlet, the particle distribution is dominated by the distributor design. Then, the particles disperse in the column, forming a homogeneous transit region. After that clusters start to form and modulate the gas–solid flow field till the fully-developed state. The particle-scale simulation disclosed that the clusters are composed of loosely collected particles, and these particles have the same flow direction as the bulk flow so that no particle backmixing can be observed. As the particles in the downer have the tendency to maintain the inertia, the capability of lateral transfer of particles is relatively weak, which was illustrated by tracking the movement of the single particles and clusters. The simulations of the inlet effect on the hydrodynamics in the downer showed that the gas–solid flow structure and the mixing behavior are sensitive to the inlet design. An inappropriate design or operation would probably cause the undesired flow phenomena such as the wide distribution of residence times. The time-averaged hydrodynamics based on the transient simulations showed good agreement with the experimental findings in the literature. The simulation based on the CFD–DEM coupled approach provides a theoretical way to comprehensively understand the physics at micro- to macro-scales in the co-currently downward gas–solid flows.The gas–solid flows in a two–dimensional downer were simulated using a CFD–DEM method, which provides a theoretical way to deeply understand the physics at micro– to macro–scales. The flow structures were comprehensively disclosed and the time-averaged hydrodynamics showed good agreement with the experimental findings in the literature.

micro-reactor has drawn more and more attention in recent years due to the process intensification on basic transport phenomena in micro-channels, which would often lead to the improved reactor performance. Steam reforming of methane (SRM) in micro-reactor has great potential to realize a low-cost, compact process for hydrogen production via an evident shortening of reaction time from seconds to milliseconds. This work focuses on the detailed modeling and simulation of a micro-reactor design for SRM reaction with the integration of a micro-channel for Rh-catalyzed endothermic reaction, a micro-channel for Pt-catalyzed exothermic reaction and a wall in between with Rh or Pt-catalyst coated layer. The elementary reaction kinetics for SRM process is adopted in the CFD model, while the combustion channel is described by global reaction kinetics. The model predictions were quantitatively validated by the experimental data in the literature. For the extremely fast reactions in both channels, the simulations indicated the significance of the heat conduction ability of the reactor wall as well as the interplay between the exothermic and endothermic reactions (e.g., the flow rate ratio of fuel gas to reforming gas). The characteristic width of 0.5 mm is considered to be a suitable channel size to balance the trade-off between the heat transfer behavior in micro-channels and the easy fabrication of micro-channels.

Dry reforming of CH4 with CO2 to produce syngas was investigated in a plasma reactor without catalysts at atmospheric pressure. The reactants passed through the plasma zone and reacted in milliseconds with high conversions and selectivity due to the localized high temperature. The results showed that both conversions and selectivity were higher when using a DC arc discharge than using a pulsed DC arc. Increasing the input energy density promoted the conversions of reactants. At an input power of 204 W, the conversions of CO2 and CH4 reached 99.3 and 99.6%, respectively, and the selectivity to products was almost 100%, where the molar ratio of CO2/CH4 was 1 with the reactants flow rate of 100 ml/min. Very little coke was formed during the course of reaction. Key parameters such as the pulse frequency, the input power and the total feed flow rate were studied to find the optimum operating condition.

Numerical simulation of fully developed hydrodynamics of a riser and a downer was carried out using an Eulerian–Lagrangian model, where the particles are modeled by the discrete element method (DEM) and the gas by the Navier–Stokes equations. Periodic flow domain with two side walls was adopted to simulate the fully developed dynamics in a 2D channel of 10 cm in width. All the simulations were carried out under the same superficial gas velocity and solids holdup in the domain, starting with a homogenous state for both gas and solids, and followed by the evolution of the dynamics to the heterogeneous state with distinct clustering in the riser and the downer. In the riser, particle clusters move slowly, tending to suspend along the wall or to flow downwards, which causes wide residence time distribution of the particles. In the downer, clusters still exist, but they have faster velocities than the discrete particles. Loosely collected particles in the clusters move in the same direction as the bulk flow, resulting in plug flow in the downer. The residence time distribution (RTD) of solids was computed by tracking the displacements of all particles in the flow direction. The results show a rather wide RTD for the solids in the riser but a sharp peak RTD in the downer, much in agreement with the experimental findings in the literature. The ensemble average of transient dynamics also shows reasonable profiles of solids volume fraction and solids velocity, and their dependence on particle density.

A novel droplet-based approach for the mixing intensification was proposed in this study, where mixing occurred inside hanging droplets out of a micro-channel. Two miscible liquid streams were first confined into the same micro-channel but remained unmixed until the outlet by controlling flow conditions. When the segregated streams flowed out of the micro-channel, droplets would form spontaneously in the open-air environment. Thus, the simultaneous mixing would be activated by the inherent chaotic advection within each droplet. Meanwhile, the external disturbance could be conveniently applied on the droplets to enhance the inner chaotic flows for a better mixing performance. Planar laser-induced fluorescence (PLIF) technique was employed to visualize the dynamic mixing behavior in each droplet. The results showed that a rich variety of mixing performance at different time scales could be achieved under well-controlled conditions. Additionally, the application of this approach for mixing intensification was demonstrated by the preparation of curcumin nano-particles (i.e., nano-drugs) in the antisolvent precipitation process. High quality products with spherical shape and narrow size distribution could be well obtained, and the initial concentration of the curcumin solution played a dominant role in the average particle size.

This paper gives an overview of the recent development of modeling and simulation of chemically reacting flows in gas–solid catalytic and non-catalytic processes. General methodology has been focused on the Eulerian–Lagrangian description of particulate flows, where the particles behave as the catalysts or the reactant materials. For the strong interaction between the transport phenomena (i.e., momentum, heat and mass transfer) and the chemical reactions at the particle scale, a cross-scale modeling approach, i.e., CFD–DEM or CFD–DPM, is established for describing a wide variety of complex reacting flows in multiphase reactors. Representative processes, including fluid catalytic cracking (FCC), catalytic conversion of syngas to methane, and coal pyrolysis to acetylene in thermal plasma, are chosen as case studies to demonstrate the unique advantages of the theoretical scheme based on the integrated particle-scale information with clear physical meanings. This type of modeling approach provides a solid basis for understanding the multiphase reacting flow problems in general.

A two-dimensional reactor model incorporating hydrodynamics, mass balance, energy balance, and a 4-lump/14-lump kinetic model was established to simulate the riser and downer based fluid catalytic cracking (FCC) processes. The kinetic parameters of the 4-lump kinetic model were re-evaluated from the originally published experimental data for a more reliable description of the FCC process. The 14-lump kinetic model based on a molecular description of cracking and hydrogen transfer reactions was to include more details about the feedstock composition, reaction mechanisms, and the products distribution for a better understanding on the reactor performance for FCC process. This comprehensive model captured the key characteristics of the gas−solid reacting flows in the riser and downer, i.e., the uniformity of flow structures, the distinct backmixing behavior in the riser and downer, and the momentum and energy balances during the complex FCC reactions. The model predictions were first validated against industrial data from several literature sources and found to agree with each other reasonably well. Then, the simulations were carried out to fully understand the different reactor performances of riser and downer in the application of FCC refining processes. It can be concluded that the downer benefits from its advantages of the plug-flow nature and uniform flow structures, tending to have more products in the middle distillates, e.g., gasoline and light olefins, especially under high-severity operations. Better control of the reaction extent for increased selectivity to desired intermediate products would allow the use of downer reactors for the larger-scale practical applications in the FCC process, together with the valuable byproduction of light olefins.

The synergetic effect of commercial catalyst Ni/Al2O3 with the low-temperature plasma created by a dielectric barrier discharge (DBD) for the dry reforming of methane was investigated in a coaxial DBD reactor. Three different contact modes of prereduced catalyst with plasma were studied to determine the interaction of plasma and catalyst, especially their synergetic effect. When the catalyst was placed at the end of the discharge zone or absolutely separated with the discharge zone, there was no synergetic effect or much worse effect than only using plasma or only using catalyst. However, when the catalyst was fully filled in the annular discharge gap, the synergetic effect was achieved. In addition, with the increase of temperature, the synergetic effect appeared to be evident from 673 K. The experiments also demonstrated that the unreduced catalyst filled in the annular discharge gap can be in-situ reduced during the reaction at around 673 K by the assistance of the in-situ plasma. However, the synergetic effect was lower and the carbon deposition on the catalyst was higher than that with the prereduced catalyst.

The catalyst deactivation behavior of rhodium-coated foam monolith was systematically investigated in order to understand the means to improve the durability of the rhodium catalyst applied for catalytic partial oxidation of methane (CPOM). The overall CPOM reactions on the foam structured catalyst have been acknowledged to take place first in an oxidation zone and thereafter in a reforming zone. Severe metal sintering near the entrance of the structured catalyst (i.e., in the oxidation zone) was identified to be responsible for the observed deactivation of rhodium catalyst in the course of a 1000 h time-on-stream test under quasi-adiabatic conditions. Further analyses on the deactivation process indicated that the reaction pathway in the oxidation zone near the entrance can be summarized by a mixed mechanism, that is, two oxidation reactions and one reforming reaction, where H2 is the indirect product of steam reforming of the unreacted CH4. Detailed studies on the dependence of the catalyst stability on the operating conditions and the catalyst designs showed that adding an inert gas to the reactant gases, increasing the metal loading and/or decreasing the pore size of the foam-structured catalyst in the oxidation zone, can improve the catalyst stability, while the catalyst modifications in the reforming zone has little effect on the overall behavior of the catalyst stability.

Low temperature conversion of CH4 and CO2 was investigated in a coaxial dielectric barrier discharge reactor at ambient pressure. Main parameters, including the input power, the residence time, the discharge gap, the molar ratio of the feed gases and the multi-stage ionization design were evaluated to understand the ways to improve the conversion of greenhouse gases and reduce the output of by-products. At certain input power, the conversion of CH4 and CO2 can reach 0.797 and 0.527, respectively, when the molar ratio of CH4/CO2 is one. When this ratio was low to 1:5, the conversion of CH4 was promoted to 0.843 and the selectivity to CO and H2 was almost 100%. The multi-stage ionization favored the conversion of CO2, which would also be an efficient design to promote the selectivity to the main products such as CO and H2 and suppress the selectivity to the by-products.

Downer reactor, in which gas and solids move downward co-currently, has unique features such as the plug-flow reactor performance and relatively uniform flow structure compared to other gas–solids fluidized bed reactors, e.g., bubbling bed, turbulent bed and riser. Downer is therefore acknowledged as a novel multiphase flow reactor with great potential in high-severity operated processes, such as the high temperature, ultra-short contact time reactions with the intermediates as the desired products. Typical process developments in industry have directed to (1) the new-generation refinery process for cracking of heavier feedstock to gasoline and light olefins (e.g., propylene) as by-products; and (2) coal pyrolysis in hydrogen plasma which opens up a direct means for producing acetylene, i.e., a new route to synthesize chemicals from a clean coal utilization process. This paper is to give a comprehensive review on the development of fundamental researches on downer reactors as well as the particular industrial demonstrations for the fluid catalytic cracking (FCC) of heavy oils and coal pyrolysis in thermal plasma.This paper is to give a comprehensive review on the development of fundamental researches on downer reactors as well as the particular industrial demonstrations for the fluid catalytic cracking (FCC) of heavy oils and the coal pyrolysis in the thermal plasma.

A coupled high-density downer-to-riser (DtoR) reactor is proposed for the controlled reaction pathway in the fluid catalytic cracking (FCC) process with the desired products distribution, e.g., clean gasoline with less olefin content. Hydrodynamics in such a reactor coupling system is studied using a compressive model that considers the pressure balances around all the sub-units in the prototype. The continuity closure condition is used to determine the material balance of the solid particles flowing in the circulating fluidized bed system. The model predictions have good agreement with the experimental data in rather wide operating conditions, e.g., when the solids circulation rate goes to more than 400 kg/m2 s. The effects of the solids inventory, the superficial gas velocity, the particle diameter and density, the inside diameter of risers, and the fractional opening of the control valve for the solids flow on the operation of the DtoR system, are investigated and discussed in detail. It is demonstrated that the model offers appropriate guidance for the design and the operation of the coupled circulating fluidized bed system.Hydrodynamics in a coupled high-density downer-to-riser (DtoR) reactor is studied using a compressive model that considers the pressure balances around all the sub-units in the prototype with the material balance of the solid particles. The proposed model could offer appropriate guidance for the design and the operation of the coupled circulating fluidized bed system.

The jet flow mixers in which fluids are mixed in the confined millimeter-sized channels were further studied to better understand the fast liquid mixing process and the means to intensify the mixing performance. Four mixer designs with different modifications on the local configuration for adjusted contact mode between liquids were investigated by visualizing the mixing processes using planar laser-induced fluorescence (PLIF) technique. A large amount of experiments with various operating conditions were carried out for all the four designs. The common feature in all the cases was that the two liquids can be mixed well in milliseconds, where the momentum ratio between the bulk and the jet flows played a significant role in the mixing performance. The results also demonstrated that the contact mode between the two liquids had a great effect on the mixing performance. By dividing the side-jet liquid stream into several smaller aperture-jets, the mixing process can be clearly improved, which can be attributed to the increased contact area and the higher velocity difference between the two liquids.

A discrete element method (DEM)-computational fluid dynamics (CFD) two-way coupling method was employed to simulate the hydrodynamics in a two-dimensional spouted bed with draft plates. The motion of particles was modeled by the DEM and the gas flow was modeled by the Navier-Stokes equation. The interactions between gas and particles were considered using a twoway coupling method. The motion of particles in the spouted bed with complex geometry was solved by combining DEM and boundary element method (BEM). The minimal spouted velocity was obtained by the BEMDEM-CFD simulation and the variation of the flow pattern in the bed with different superficial gas velocity was studied. The relationship between the pressure drop of the spouted bed and the superficial gas velocity was achieved from the simulations. The radial profile of the averaged vertical velocities of particles and the profile of the averaged void fraction in the spout and the annulus were statistically analyzed. The flow characteristics of the gas-solid system in the two-dimensional spouted bed were clearly described by the simulation results.

Milliseconds process to produce hydrogen by steam methane reforming (SMR) reaction, based on Ni catalyst rather than noble catalyst such as Pd, Rh or Ru, in micro-channel reactors has been paid more and more attentions in recent years. This work aimed to further improve the catalytic performance of nickel-based catalyst by the introduction of additives, i.e., MgO and FeO, prepared by impregnation method on the micro-channels made of metal-ceramic complex substrate. The prepared catalysts were tested in the same micro-channel reactor by switching the catalyst plates. The results showed that among the tested catalysts Ni-Mg catalyst had the highest activity, especially under harsh conditions, i.e., at high space velocity and/or low reaction temperature. Moreover, the catalyst activity and selectivity were stable during the 12 h on stream test even when the ratio of steam to carbon (S/C) was as low as 1.0. The addition of MgO promoted the active Ni species to have a good dispersion on the substrate, leading to a better catalytic performance for SMR reaction.SMR catalytic performance of nickel-based catalyst in micro-channel reactor has been improved by the introduction of extra additives. MgO favors the increase of methane conversion and Ni-Fe alloy favors the increase of CO2 selectivity.Download full-size image

Using thermal plasma for coal pyrolysis to acetylene provides a direct route to make chemicals from coal resources, where the temperature field in the reactor plays a dominant role in the performance of coal devolatilization. A comprehensive computational fluid dynamics with discrete phase model (CFD-DPM) has been established to describe the rapid coal pyrolysis process in a reactor under ultra-high temperatures. The simulations based on this model helped to understand the complex gas–particle reaction behavior in the millisecond process of coal pyrolysis. The particle-scale physics such as the heat conduction inside solid materials, diffusion of released volatile gases, coal devolatilization, and tar cracking reactions were incorporated. The improved chemical percolation devolatilization (CPD) model was applied to describe the devolatilization behavior of rapidly heated coal based on the physical and chemical transformations of the coal structure. This model was proved to be qualified for describing the complex gas–particle reaction behavior with milliseconds residence time by the operation experience of a 5-MW plasma reactor. Then the simulations revealed the fact that the particle heating and devolatilization are strongly affected by the grade of the temperature and the residence time of coal particles in the high temperature zone(s). Highly concentrated energy input in the reactor may not intensify the reactor performance. As a potential solution, multi-stage heating design would provide more flexibilities to effectively adjust the devolatilization performances under the same energy input.Highlights► A cross-scale CFD model incorporating particle-scale physics and improved CPD model. ► Theoretical analysis of coal devolatilization with experimental validation. ► Particle heating: strongly affected by temperature field and residence time. ► Multi-stage heating design: more flexible to adjust the pyrolysis performance.

CFD simulation with detailed chemistry was conducted to understand the catalytic partial oxidation of methane (CPOM) on rhodium-coated foam monolith. For the underlying process occurred extremely fast with large gradients of temperature and species concentrations at the inlet, special attention must be paid to the appropriate treatment on computational geometry and corresponding boundary conditions for the simulation. Discussions were made carefully on this proposed issue in geometry modeling that the reliable predictions can be authentically obtained by adopting the same geometry as the experiments from the viewpoint of physics in order to fully consider the heat conduction/diffusion at the reactor inlet. The right model system was sufficiently validated by both the conceptual analysis and the experimental results. The reactor performance of CPOM process was thereafter studied by numerically revealing the effects of wall heat conduction, the channel diameter and the catalytic surface area on the profiles of temperature and species concentrations. The results showed that the maximum wall temperature, which was crucial for the catalyst stability, could be significantly reduced by increasing the thermal conductivity of the wall, and/or the channel diameter, and/or the catalytic surface area, but accompanied with a slight drop of the methane conversion. This deficiency can be retrieved by decreasing the atom feed ratio of C/O and/or elongating the catalytic bed. These results pointed out the necessity of facilitating the foam material, the channel diameter and the catalytic surface area with the operating conditions in order to achieve the best performance of the CPOM process in the millisecond reactor.

•A detailed kinetic model for C2H2 decomposition and soot formation is established.•Two key operating parameters of quenching are studied in detail and optimized.•Effects of H2 on C2H4 formation and C2H2 condensation during quenching are discussed.•A comprehensive understanding of the pilot plant experimental data is achieved.A detailed chemical kinetic mechanism based on the Appel-Bockhorn-Frenklach (ABF) model was established to describe acetylene decomposition, ethylene formation, and soot formation during quenching in coal pyrolysis to acetylene process. The predictions agreed well with the reported acetylene pyrolysis experimental data. Numerical simulations were then performed to deeply understand the reaction behaviors during quenching of coal pyrolysis in thermal plasma, and to optimize the quenching design for better heat recovery. Two key operating parameters of quenching, i.e., the temperature after quenching and the quenching rate, were studied in detail and optimized after the kinetics were validated. The simulation results also proved that hydrogen can promote the formation of ethylene and inhibit the condensation of acetylene during quenching. In particular, in-depth discussion of acetylene decomposition and ethylene formation using this detailed kinetic mechanism combined with thermodynamic method provided a comprehensive understanding of the thermodynamics and kinetics interpreting pilot plant experimental data.

In the present work, a k1–ε1–k2–k12 two-fluid model based on the kinetic theory of granular flow (KTGF) was employed to predict the flow behavior of gas and solids in downers, where the particles of small size as 70 μm in diameter apparently interact with the gas turbulence. The turbulence energy interaction between gas and solids was described by different k12 transport equations, while the particle dissipation by the large-scale gas turbulent motion was taken into account through a drift velocity. Johnson–Jackson boundary condition was adopted to describe the influence of the wall on the hydrodynamics. The simulation results by current CFD model were compared with the experimental data and simulation results reported by Cheng et al. (1999. Chem. Eng. Sci. 54, 2019) and Zhang and Zhu (1999. Chem. Eng. Sci. 54, 5461). Good agreement was obtained based on the PDE-type k12 transport equation. The results demonstrated that the proposed model could provide good physical understanding on the hydrodynamics of gas–solid multiphase flow in downers. Using the current model, the mechanism for formation and disappearance of the dense-ring flow structure and the scale-up characteristics of downers were discussed.Highlights► We use a k1–ε1–k2–k12 two-fluid model to revisit the hydrodynamics in downers well. ► Particles of small size as 70 μm apparently interact with the gas turbulence. ► Formation and disappearance of the dense-ring flow structure were predicted well. ► Scale-up characteristics of downers were discussed based on the validated model.

The CFD–DEM coupled approach was used to simulate the complex gas–solid reacting flows in fluid catalytic cracking (FCC) processes accommodated in riser or downer reactors. Considering the solid catalyzed gas-phase reactions, the model particularly incorporated the descriptions for heat transfer behaviors between particles and between gas and particles, the instantaneous catalyst deactivation, and the lumped kinetics in the gas phase for FCC process, together with the governing equations for the hydrodynamics. The distinct advantage of the present approach is that the catalyst activity can be calculated in time by tracking the history of the particle movement with the occurrence of heat transfer and chemical reactions. The simulation results captured the major features of FCC process very well either in riser or in downer, which had reasonable agreement with the experimental data in the literature. The reduced selectivity to the desired intermediate products in risers, especially under high catalyst-to-oil ratios, can be clearly understood from the simulated backmixing behavior of solid catalysts and the deactivation of catalysts at different locations in the reactor, which caused the non-ideal reaction progress inside the reactor space. It can be concluded that this type of modeling approach forms a solid basis for the cross-scale modeling of general multi-phase catalytic reacting flows.

The reactive mixing process in a stirred tank has drawn much attention due to the complex interplay between the hydrodynamics and the chemical kinetics. However, there is still a lack of effective measurement techniques to explore the detailed information. To quantify the reactive mixing process, a novel reactive planar laser-induced fluorescence (reactive-PLIF) technique was developed to visualize how the two liquids mixed and reacted with each other. The main principle was to capture the process characterized by the fluorescence signal of the tracer dye (i.e., Rhodamine B), which varied in time and space because of being oxidized by the oxidant (i.e., the hydroxyl radical OH) generated between Fe2+ and H2O2 (i.e., a Fenton reaction). The behaviors were recorded by a high-speed digital camera and quantitatively analyzed. The influences of the impeller rotation speed, the impeller position and the liquid properties on the processes were evaluated. The relationship between the reactive mixing and the physical mixing can be determined by the results from the (reactive-)PLIF measurements. This novel technique enabled the convenient measurement of liquid mixing process with reactions at a low cost.

We have presented a self-cross-link strategy to fabricate HSA nanoparticles using a desolvation method. The nanoparticles were stabilized by intermolecular disulfide bonds while still dissolvable in reducing media. The fabrication process does not involve any toxic chemicals and hence the nanoparticles may be useful as a drug carrier.

Phase-pure M1 MoVNbTeOx catalyst plates have been prepared on a metal–ceramic complex substrate by a dip-coating method. At a temperature of 420 °C and atmospheric pressure, the performance of the M1-PVA catalyst plate in a micro-channel reactor approached an ethane conversion of ~60% and an ethylene selectivity of ~85% with a high catalyst productivity of 0.64 kgC2H4 kgcat−1 h−1. Due to the excellent heat transfer ability, it is demonstrated that the micro-channel reactor can achieve the same reactor productivity as a traditional fixed-bed reactor within only 20% of its volume. XRD, SEM and ICP characterization indicated that the M1-PVA catalyst plate has a high stability in the micro-channel system.

A high rate fabrication of a thin film complex consisting of cubic-SiC nanocrystals, amorphous silicon and graphite was realized using an atmospheric pressure thermal plasma enhanced chemical vapor deposition (APTPECVD) process with SiCl4 and C2H2 as the silicon source and carbon source, respectively. The morphology, crystal structure and surface chemical composition of the products were characterized. The APTPECVD SiC nanocrystals have average diameters between 18 and 30 nm. A room temperature red region photoluminescence (PL) property originated from the quantum confinement effect of these SiC nanocrystals was observed under UV wavelength excitation. Moreover, pure SiC nanocrystals with a red region PL property can be obtained after a simple post-treatment, including calcining and etching processes. These red photoluminescent SiC nanocrystals can be utilized as biomarkers in bioimaging and drug delivery.