Wet shale gas contains relatively high concentrations of heavier hydrocarbons. In industry, the cryogenic separation process is used to separate methane and heavier hydrocarbons for the downstream conversion. In this work, the feasibility of direct application of wet gas in the partial oxidation (POX) process was studied. Flat flame experiments of methane with addition of ethane and propane were conducted using a McKenna reactor. The results showed that the mole fractions of acetylene and CO increased by 15% and 25% when using wet gas as the feedstock. Four detailed chemical mechanisms were verified, and the Curran and modified GRI 3.0 mechanisms gave good predictions of the POX of wet gas. The modified GRI 3.0 was further used in the three-dimensional computational fluid dynamics (CFD) simulations of a 3-jet reactor at industrial conditions. The results showed that in the wet gas POX process a higher C2H2 yield was obtained, and the optimal equivalence ratio slightly increased from 4.0 to 4.07 and the optimal quenching position moved from 0.4 to 0.45 m compared with the methane POX process.

The partial oxidation (POX) of methane is one of the most important processes to produce acetylene and syngas. The reaction pathway analysis using a detailed chemical mechanism (modified GRI 3.0) showed that the exothermal oxidation and endothermic pyrolysis reactions were highly coupled in the original POX process, which limited the yield of acetylene. A new process that physically separated the heat supply and pyrolysis reactions was proposed to increase the acetylene yield. The maximum yield of acetylene was enhanced from 33% to 52% in the theoretical calculations assuming inert and instantaneous mixing. A jet-in-cross-flow (JICF) reactor was designed to realize this new process. The computational fluid dynamics (CFD) method coupled with the modified GRI 3.0 was applied to simulate the complex interaction between turbulent mixing and reactions. The results showed that a high acetylene yield of 41% could be obtained in the JICF reactor. The optimization of the reactor indicated that the optimum number of jets was 8, and the optimal mixing ratio was 0.566 for maximum acetylene yield. The maximum acetylene yield significantly decreased in a larger reactor, and mixing enhancement was the main way to further improve the acetylene yield.

ZIF-8 encapsulated Pt nanoparticles (NPs) were investigated for the hydrogenation of 3-methylcrotonaldehyde to prenol using the geometric effect. HR-TEM, HAADF-STEM, XRD, nitrogen adsorption isotherm characterization and size-selective reaction evaluation demonstrated that the Pt NPs were encapsulated in the inner space of ZIF-8. The Pt NPs in the Pt@ZIF-8 catalyst were surrounded by apertures with sizes commensurate with 3-methylcrotonaldehyde molecules. These narrow apertures forced the 3-methylcrotonaldehyde molecules to linearly approach the active sites. The CC bond in the middle of the 3-methylcrotonaldehyde molecule was prevented from interacting with the Pt active sites by the narrow apertures around the Pt NPs, while the CO bond at the tail-end was easily adsorbed and further hydrogenated to prenol. Using this geometric effect, the Pt@ZIF-8 catalyst exhibited a high selectivity to prenol (>84%) even at a high conversion (>90%).

•A significant synergistic effect was observed between CeO2 and TiO2 as supports.•The effects of compositions on the catalytic performance.•Lower apparent activation barriers for CO2 activation and methanol synthesis.Mixed oxides of CuCeOx, CuTiOx and CuCeTiOx were prepared and evaluated for methanol synthesis via the hydrogenation of CO2. A significant synergistic effect was observed between CeO2 and TiO2 as supports. The CuCeTiOx catalyst was about 4 and 260 times more active than CuTiOx and CuCeOx, respectively, in terms of turnover frequency (TOF) values. The effect of changing the amounts of CeO2, TiO2 and CuO on the catalytic performance of CuCeOx was also studied. With increasing content of CeO2, the CO2 conversion firstly increased and then decreased, with the CeO2/TiO2 weight ratio of 1 being optimal. An increase in the CuO content slightly enhanced the CO2 conversion due to the increase of metal surface area. Kinetic experiments showed that the apparent activation barriers were lower for CO2 activation and methanol synthesis over CuCeTiOx than other Cu-based catalysts.Download high-res image (71KB)Download full-size image

•SO42−/TiO2 catalysts highly active for PODEn synthesis were prepared.•Activity showed a volcano relationship with precursor solution concentration.•Spatial distribution of S strongly affected acid properties and catalyst activity.•Synergetic effect existed between Brønsted and Lewis sites for PODEn synthesis.•New catalytic mechanism was proposed based on Brønsted and Lewis acid sites.Polyoxymethylene dimethyl ethers (PODEn, CH3O(CH2O)nCH3, where n ≥ 1) are receiving much attention as ideal diesel fuel additives because they can significantly reduce the emission of smoke and engine exhaust during combustion. PODEn are synthesized over acid catalysts. In this work, highly efficient sulfate titania catalysts were prepared by impregnation for the synthesis of PODEn from dimethoxymethane (DMM) and paraformaldehyde (PF). XPS and XRF were used to determine the spatial distribution of S, and NH3-TPD and Pyridine-IR were used to measure acid properties. The concentration of the precursor solution had an important effect on the catalyst activity. The spatial distribution of S influenced the acid properties and catalyst activity. A catalytic mechanism based on Brønsted and Lewis acid sites was proposed, which explained the synergistic effect of Brønsted and Lewis acid sites in the reaction for the first time.Reaction mechanism for the synthesis of PODEn on Brønsted and Lewis acid sites.Download high-res image (67KB)Download full-size image

•Bubble column at elevated pressure was simulated with a CFD-PBM coupled model.•Both hindering effect and wake accelerating effect were included in drag correction.•Elevated pressure significantly enhanced bubble breakup and decreased bubble size.•CFD-PBM coupled model successfully predicted the significant effects of pressure.Bubble column reactors are often operated under elevated pressure. However, the significant effects of pressure are not well understood. This work aimed to simulate the bubble column operated at elevated pressure by computational fluid dynamics (CFD) coupled with the population balance model (PBM). The effect of the pressure on the bubble breakup was considered based on the mechanism of internal flow during bubble deformation and breakup. For the drag coefficient of bubble swarms, both the hindering effect of small bubbles and the wake accelerating effect of large bubbles were taken into account. Good predictions were obtained concerning the effect of the operating pressure on the gas holdup in both the homogeneous and heterogeneous regimes, especially the significant increase of the gas holdup and decrease of the bubble size at elevated pressure. These results showed that the CFD-PBM coupled model was promising for further simulation of the bubble column under complex operating conditions.Download high-res image (98KB)Download full-size image

•Simulate the industrial-scale gas quenching reactor of jet-in-cross-flow by CFD coupled detailed chemical mechanism.•Compare predicts of interaction of turbulence and reaction with PDF and EDC model.•Evaluate the effect of mass flow ratio on mixing and quenching performance.•Acetylene hydrogenation to ethylene is responsible for acetylene depletion.In the water quenching process for partial oxidation (POX) of nature gas to acetylene, the temperature of the product gas mixture directly decreases from about 1800 K to 360 K, thus the heat cannot be recovered. To overcome this problem, a new gas quenching process of jet-in-cross-flow (JICF) was proposed for the partial oxidation (POX) process to enhance the energy efficiency. The computational fluid dynamics (CFD) coupled with detailed chemistry was employed to simulate the mixing and quenching performance in an industrial-scale JICF reactor. Both the Probability Distribution Function (PDF) and Eddy Dissipation Concept (EDC) models were used to compute the chemical source term, and the PDF model predicted a higher acetylene loss. The uniform index (UI), temperature, species concentrations and acetylene loss were investigated during the quenching process. Using the PDF, the optimum main/jets flow mass ratio was determined as 2.59, at which the loss percent of acetylene was about 3 wt%. The simulation results show that the gas quenching process is very attractive because the heat can be effectively recovered after the quenching at a cost of slight loss of acetylene.

•CFD-PBM model was well validated in a bubble column with organic liquids.•Low liquid viscosity and surface tension enhanced bubble breakup but hindered coalescence.•Effect of temperature was well predicted with corresponding liquid properties.•Bubble breakup model was crucial for reliable predictions of CFD-PBM model.The CFD-PBM coupled model was validated in a bubble column with organic liquids under industrial conditions. Experimental data of the gas holdup, bubble size distribution and mass transfer rate were collected from the literature. The liquid viscosity and surface tension were two important parameters affecting the hydrodynamics. Low liquid viscosity and surface tension enhanced the bubble breakup but hindered the bubble coalescence. Compared with water, organic liquids led to a higher gas holdup, smaller bubble size and larger mass transfer rate. The elevated temperature decreased the liquid viscosity and surface tension. The effects of temperature on the hydrodynamic and gas-liquid mass transfer behaviors were well predicted using the corresponding liquid properties. The CFD-PBM coupled model gave good predictions because it quantitatively described the effect of liquid properties on the bubble size, interphase forces, turbulence parameters, and bubble breakup and coalescence behaviors. The simulations with different bubble breakup models showed that the accuracy of the bubble breakup model was crucial for reliable predictions of the CFD-PBM coupled model.

BaSO4 catalysts with different micromorphologies and crystal texture were prepared and used to investigate the structure–activity relationship in the dehydration reaction of lactic acid (LA) to acrylic acid (AA). SEM and N2 physisorption were used to study the micromorphology. XRD and photoluminescence spectra were employed to analyze the crystal texture of samples prepared with different methods and treatments. The results revealed that BaSO4 with smaller crystals and more defects had higher activity and selectivity to AA. It was likely that the crystal defects provided the active acid sites for dehydration of LA to AA, as evidenced by XPS and NH3-TPD measurements. Using ethanol as the solvent and ultrasound treatment during the preparation of BaSO4, imperfect small crystals with more defects were formed, which increased the AA selectivity to 78.8%.

AbstractBACKGROUNDBubble column reactors are widely used in chemical processes and wastewater processing. The relevant properties of surface tension play important roles in the hydrodynamics and bubble coalescence and breakup. However, the underlying mechanisms are complicated and need further research. In this work, the bubble behaviors were studied in a bubble column of 0.1 m i.d. with pure liquids of different surface tension and alcohol solutions varying in concentration and alcohol type.RESULTSThe bubble size and shape were measured by the photographic technique. The gas holdups of small bubbles and large bubbles were measured by dynamic gas disengagement (DGD) experiments. In the pure liquids, the bubble size decreased and the total gas holdup increased with decreasing liquid surface tension. In the alcohol solutions, the liquid surface tension was almost unchanged with a little addition of ethanol to pure water, but the bubble size decreased and the total gas holdup increased significantly. In the ethanol solutions, the gas holdup reached its maximum at a critical ethanol volumetric concentration of about 3%.CONCLUSIONSThe bubble behaviors in pure liquids and alcohol solutions were very different. The coalescence of small bubbles was inhibited more significantly in alcohol solutions than in pure liquids. The dynamic surface tension effect strongly affected the bubble behaviors in the alcohol solutions, and the predicted critical concentration based on this effect agreed well with the experimental value. © 2016 Society of Chemical Industry

•Partially decoupled process (PDP) is proposed for efficient conversion of C2H6.•Simulations are carried out by CFD coupled with detailed reaction mechanism.•PDP has a higher C2H2 + C2H4 yield than POX and steam cracking processes.•Ethane DPD is less sensitive to mixing and reactor scale-up than methane PDP.The ethane contained in wet shale gas is usually used to produce ethylene through the steam cracking process. In parallel, the partial oxidation (POX) of methane is the most important method to produce acetylene. In this paper, the feasibility of the POX process of ethane was first explored. The reaction pathway analysis showed that the exothermal oxidation and endothermic pyrolysis reactions were highly coupled, which limited the yield of C2 species (C2H2 + C2H4). To overcome this problem, a new process named partially decoupling process (PDP) was proposed to physically separate the heat supply and pyrolysis reactions in a jet-in-cross-flow (JICF) reactor. The computational fluid dynamics (CFD) coupled with a detailed reaction mechanism, the modified GRI 3.0, was applied to simulate the complex interaction between turbulent mixing and reactions. The results showed that a high combined yield of ethylene and acetylene (69%) could be obtained. The operating and reactor structural parameters were further optimized based on the CFD simulations. The maximum yield of C2 products was found less sensitive to the mixing in the ethane PDP than in the methane PDP, making it easier to scale up the reactor for the ethane PDP.Download high-res image (177KB)Download full-size image

Furfural is a promising renewable platform compound derived from lignocellulosic biomass that can be further converted to biofuels and biochemicals. The highly functionalized molecular structure of furfural makes it a desired raw material for the sustainable production of value-added chemicals containing oxygen atoms. The conversion of furfural to C4 and C5 chemicals by various catalytic processes is reviewed. The C5 chemicals are mainly produced through sequential steps of selective hydrogenation and/or hydrogenolysis, while most of the C4 chemicals are synthesized with selective oxidation as the first step. This review divides the chemical products from furfural into several groups according to their carbon numbers and synthesis routes, with emphasis on the catalysts and reaction mechanisms. The applications of these chemicals and their traditional production from fossil feedstocks have also been added as background information. Additionally, recent advances in the development of heterogeneous catalysts for furfural production are briefly reviewed.Keywords: C4 chemical; C5 chemical; catalyst; furfural; platform compound; reaction pathway

A two-step process was developed for the production of γ-butyrolactone (GBL) from furfural. Furfural was first oxidized using homogeneous acid catalysts under mild conditions in an aqueous/organic bi-phasic system to obtain 2(5H)-furanone, which was then selectively hydrogenated to GBL with a high yield over supported metal catalysts.

Polyoxymethylene dimethyl ethers (CH3–O–(CH2O)n–CH3, PODEn) are potential environmentally benign coal-based diesel fuel blending compounds. They are synthesized from dimethoxymethane (DMM) and paraformaldehyde (PF). Among the PODEn homologues, PODE3–4 have a good match with diesel as a fuel, while the undersized PODE1–2 and oversized PODEn>4 have unsuitable properties. This work studied the molecular size reforming of undersized PODE1–2 and oversized PODEn>4 by two different methods, namely, self-reforming and reacting with DMM over an acidic ion exchange resin. The molecular size reforming of PODE1–2 and PODEn>4 by self-reforming gave a high concentration of formaldehyde, which shifted the distribution to longer chain PODEn and formed solid PF. In contrast, PODE1–2 and PODEn>4 were mainly converted to PODE3–4 by the reaction with DMM and the high concentration of formaldehyde was also diminished. The equilibrium reorganized molecular size distribution of PODE1–2 and PODEn>4 followed the Schulz–Flory distribution. A proposed kinetic model described well the molecular size reforming pathways of PODE1–2 and PODEn>4. A methanol-to-PODEn close-loop process was proposed to enhance atom-economy by recycling the PODE1–2 and PODEn>4 streams.

meta-Xylylenediamine (m-XDA) is industrially produced by the hydrogenation of isophthalonitrile (IPN) using Raney® Ni/Co and basic additives. Compared with Raney® Ni/Co, the supported Ni/Co catalysts are safer and have better mechanical strength. This work aimed at studying the catalytic performance of the supported Ni–Co catalysts in hydrogenation of IPN to m-XDA. The active sites for the condensation side reactions were studied using Ni–Co catalysts supported on different oxides and with different loadings. It was found that the acid sites catalyzed the condensation reactions between intermediate imines and amines. Two types of acid sites existed on the supported Ni–Co catalysts, namely, the original acid sites of the support and new acid sites formed by Ni/Co aluminates. In addition to acid sites, the surface hydroxyl groups on the oxide supports also catalyzed the condensation reactions, but were not active for the hydrogenation reaction. By increasing the Ni–Co loading, the selectivity to m-XDA was significantly enhanced, which was attributed to the suppression of both acid sites and hydroxyl groups. Compared to the low-loading catalysts (5Ni–1.25Co/Al2O3 and 5Ni–1.25Co/SiO2), the high-loading catalysts (20Ni–5Co/Al2O3 and 20Ni–5Co/SiO2) increased the m-XDA selectivity from ∼45.5 to 99.9%.

The hydrogenation of Isophthalonitrile (IPN) to meta-xylylenediamine (m-XDA) is usually catalyzed by RANEY® or supported Ni based catalysts in the presence of a basic additive. The supported catalysts have better mechanical strength and are safer than RANEY® Ni catalysts. This work aimed to study the catalytic performance of γ-Al2O3 supported Ni and Ni–M (M = Fe, Co, Cu) bimetallic catalysts in IPN hydrogenation. The H2-TPR results revealed that the introduction of a second metal enhanced the reducibility of Ni catalyst. The Ni–M bimetallic catalysts also had different metal dispersion, electronic properties and adsorption strength. Among Fe, Co and Cu, Fe showed the best promoting effect, which was attributed to the strong N–metal bonding and weak H–metal adsorption strength, which enhanced the catalytic activity and m-XDA selectivity. The catalytic performance also strongly depended on the Ni–Fe mass ratio. For the γ-Al2O3 supported Ni and Ni–M catalysts with a low Ni loading of 5 wt%, the rate constant kr increased from 0.024 mol0.2 L−0.2 min−1 over 5Ni/Al2O3 to 0.033 mol0.2 L−0.2 min−1 over 5Ni–1.67Fe/Al2O3, meanwhile the m-XDA selectivity increased from 34.7% to 49.5%. Over the Ni–Fe bimetallic catalyst with high metal loading, 20Ni–5Fe/Al2O3, a very high m-XDA selectivity of 99.9% was obtained.

Molybdenum carbide (Mo2C and Ni/Mo2C) catalysts were compared with Pd/SiO2 for the hydrogenation of several diene molecules, 1,3-butadiene, 1,3- and 1,4-cyclohexadiene (CHD). Compared to Pd/SiO2, Mo2C showed similar hydrogenation rate for 1,3-butadiene and 1,3-CHD and even higher rate for 1,4-CHD, but with significant deactivation rate for 1,3-CHD hydrogenation. However, the hydrogenation activity of Mo2C could be completely regenerated by H2 treatment at 723 K for the three molecules. The Ni modified Mo2C catalysts retained similar activity for 1,3-butadiene hydrogenation with significantly enhanced selectivity for 1-butene production. The 1-butene selectivity increased with increasing Ni loading below 15 %. Among the Ni modified Mo2C catalysts, 8.6 % Ni/Mo2C showed the highest selectivity to 1-butene, which was even higher selectivity than that over Pd/SiO2. Compared to Pd/SiO2, both Mo2C and Ni/Mo2C showed combined advantages in hydrogenation activity and catalyst cost reduction, demonstrating the potential to use less expensive carbide catalysts to replace precious metals for hydrogenation reactions.

•Plant oil asphalt (POA) can be efficiently converted to transport fuel.•Alkali metal compounds affect pyrolysis rate, product yields and composition.•Maximum yield of pyrolytic oil (80 wt.%) is obtained with addition of chlorides.•Depth of cracking can be effectively controlled in vacuum catalytic pyrolysis.Plant oil asphalt (POA) is underutilized lipid-based biomass residue generated from the oleochemical industry. In this work, alkali metal compounds were used as catalysts for vacuum pyrolysis of POA. Their effects on the pyrolysis reaction rate, product yields and compositions were studied. The POA feed was characterized by proximate and ultimate analysis and inductively coupled plasma-mass spectrometry (ICP-MS). The pyrolytic oil was analyzed by gas chromatography–mass spectrometry (GC–MS), thermo-gravimetric analysis (TGA) and chromatography-simulated distillation analysis. The results showed that alkali metal compounds accelerated the pyrolysis reaction rate in the order of chlorides ≈ sulphates > hydroxides > carbonates > non-catalyst, and affected the yield of pyrolytic oil in the order of chlorides (80 wt.%) ≈ sulphates (77 wt.%) > non-catalyst (71 wt.%) > carbonates (68 wt.%) > hydroxides (55 wt.%). The quality of the pyrolytic oil was in the order of hydroxides > carbonates > non-catalyst ≈ chlorides ≈ sulphates.

Plant oil asphalt (POA) is a new concerned lipid-based residue biomass generated from the oleochemical industry. In this work, the pyrolysis kinetics of POA was studied by thermogravimetric analysis at heating rates of 7, 10, 20, and 30 K min–1 under a nitrogen atmosphere using the distributed activation energy model (DAEM). The kinetic parameters, including the activation energy E, distribution function of activation energy f(E), and pre-exponential factor k0, were obtained. The activation energy E ranged from 75 to 300 kJ mol–1, and the f(E) curve showed a broad peak around 155–200 kJ mol–1. The linear relationship between ln k0 and activation energy E indicated that there existed a kinetic compensation effect in pyrolysis of POA. A double-Gaussian DAEM was employed for simulation of POA pyrolysis by assuming POA as a mixture of two pseudo-components. In comparison to the single-Gaussian DAEM, the double-Gaussian DAEM was better to predict the pyrolysis behavior of POA. This work validated the applicability of the double-Gaussian DAEM to the lipid-based material POA.

The hydrogenation of isophthalonitrile (IPN) to meta-xylylenediamine (m-XDA) is usually catalyzed by the Raney or supported Ni based catalysts in the presence of basic additive. Although the supported catalysts are safer than the Raney Ni catalysts, they have lower selectivity to m-XDA. This work revealed that the acid sites of NiCo/Al2O3 were responsible for the condensation reactions between amines and imines, which were the dominant side reactions. Besides the original acid sites on γ-Al2O3, the loading of Ni–Co introduced new acid sites, which had a greater contribution to the condensation reactions. The K modification significantly enhanced the selectivity to m-XDA by reducing the two kinds of acid sites. Due to the formation mechanism of new acid sites and the K modification mechanism on these sites, both the K loading and K impregnation sequence affected the catalytic performance. When 3.0 wt% K was introduced to NiCo/Al2O3 by co-impregnation (3KNiCo/Al2O3), the catalyst acidity decreased by 82%, and the selectivity to m-XDA increased from 45.5% to 99.9%. The superiority of the optimized catalyst 3KNiCo/Al2O3 was also confirmed when no basic additive was used.

The selective dehydration–oxidation of glycerol to acrylic acid is a very attractive approach for glycerol utilization. In this work, we demonstrated an efficient two-bed system for this process. The dehydration catalyst was Cs2.5H0.5PW12O40 supported on Nb2O5 (CsPW-Nb), and the oxidation catalyst was vanadium–molybdenum mixed oxides supported on silicon carbide (VMo–SiC). The experimental results showed that the optimum reaction temperature and oxygen ratio for these two catalysts were very similar. This made the two-bed system simple and efficient. Compared with the single-bed system, the two-bed system with the dehydration catalyst and oxidation catalyst loaded separately was more favorable to avoid the overoxidation reaction of glycerol. A high yield of acrylic acid was achieved at optimized conditions in the two-bed system. The Brønsted acid sites on the dehydration catalysts were the active sites for acrolein formation. The byproducts produced on Lewis acid sites in the dehydration step and the water in the glycerol feed did not show negative effects on the acrolein oxidation reaction. Both the CsPW-Nb and VMo-SiC catalysts were stable for at least 70 h and had very good thermal stability at the coke burning temperature of 500 °C.

The selective hydrogenation of acetylene is usually a gas-phase reaction. In this work, a liquid phase was introduced as a selective solvent to improve the selectivity to ethylene by coupling absorption to the reaction. The catalyst was 0.01% Pd supported on a low surface area silica. N-methyl-2-pyrrolidone (NMP) was used as a selective solvent, and decane was used as a nonselective solvent for comparison. The liquid-phase hydrogenation was carried out in a stirred flat bottom flask operated in gas continuous and liquid batch mode, and the gas-phase hydrogenation was carried out in a fixed bed reactor. The selectivity to ethylene in the gas-phase hydrogenation was 50–70%. In contrast, the highest selectivity to ethylene in the NMP liquid-phase hydrogenation was increased to 96%, while in decane it had the same value as in the gas phase. In NMP, a low reaction temperature below 80 °C did not give a high selectivity to ethylene because the relatively high ethylene solubility in NMP led to deep hydrogenation and the high acetylene solubility caused more oligomerization. Good catalyst stability was obtained under the optimized conditions of a relatively low space velocity, H2:C2H2 ratio above 10, and reaction temperature above 80 °C. Significant deactivation also occurred in NMP under other conditions due to oligomerization.

Coker gas oil (CGO) is a poor-quality feedstock for fluidized bed catalytic cracking (FCC) or hydrocracking. The pretreatment of CGO, especially hydrotreating, can significantly improve the product quality and protect the catalyst. In this work, we studied the hydrodesulfurization (HDS) of CGO in a slurry reactor. All the experiments were carried out in an autoclave using a NiMo/Al2O3 catalyst at reaction temperature 340°C–400°C, pressure 6–10 MPa, and stirring speed 800 r·min−1, with hydrogen-to-oil ratio in the range of 500–1500. The effects of the operating parameters on the desulfurization ratio were investigated and discussed. A macro reaction kinetic model was established for the HDS of CGO in the slurry reactor.

In the noncatalytic partial oxidation process, autoignition of the heated premixed combustible gases is a major source of reactor damage, unstable operation, and even explosion accidents. The knowledge of the autoignition behavior is of great importance to risk assessment and loss prevention in the partial oxidation reactors. The large experimental effort could be reduced if a reliable modeling procedure is available to identify the safe operating conditions. In this work the reliability of the detailed kinetic modeling method was investigated by comparing the simulated results with the experimental data reported in the literatures. It was found that the USC II mechanism gave the best predictions on the ignition delay times for the methane/air mixtures with equivalence ratios of 3.33 and 6.67. This mechanism was used to extrapolate the ignition delay times in the industrial partial oxidation process. The effects of initial temperature and equivalence ratio on ignition delay times were also investigated. The species concentration profiles were analyzed to understand the underlying ignition chemistry. The sensitivity analysis was carried out for the identification of the main reactions affecting the autoignition process.

Gas–liquid mass-transfer behaviors in aqueous alcohol solutions were studied in an internal-loop airlift reactor of 5-m height and 0.28-m i.d. in the superficial gas velocity (Ug) range from 2.0 to 10.0 cm/s. Air and aqueous n-butanol solutions were used as the gas and liquid phases, respectively. It was found that the volumetric mass-transfer coefficient decreased with increasing n-butanol concentration (CA) below a critical CA value of 0.5 wt % and increased with increasing CA above this concentration. To confirm this result, further experiments were also carried out in a bubble column of 0.12-m i.d. at Ug = 6 cm/s, and similar results were obtained. Further analysis showed that the value of kla/αg was independent of the superficial gas velocity and equal to 0.21 1/s in the air–water system; however, it decreased with increasing CA up to 0.25 wt % in n-butanol solutions, and further addition of n-butanol had no effect on kla/αg. A critical CA value of 0.5 wt % was also found for the liquid-side mass-transfer coefficient (kl). Below this concentration, kl decreased with increasing CA, whereas above this concentration, further addition of n-butanol had no effect on kl.

Bubble columns are widely used in chemical and biochemical processes due to their excellent mass and heat transfer characteristics and simple construction. However, their fundamental hydrodynamic behaviors, which are essential for reactor scale-up and design, are still not fully understood. To develop design tools for engineering purposes, much research has been carried out in the area of computational fluid dynamics (CFD) modeling and simulation of gas-liquid flows. Due to the importance of the bubble behavior, the bubble size distribution must be considered in the CFD models. The population balance model (PBM) is an effective approach to predict the bubble size distribution, and great efforts have been made in recent years to couple the PBM into CFD simulations. This article gives a selective review of the modeling and simulation of bubble column reactors using CFD coupled with PBM. Bubble breakup and coalescence models due to different mechanisms are discussed. It is shown that the CFD-PBM coupled model with proper bubble breakup and coalescence models and interphase force formulations has the ability of predicting the complex hydrodynamics in different flow regimes and, thus, provides a unified description of both the homogeneous and heterogeneous regimes. Further study is needed to improve the models of bubble coalescence and breakup, turbulence modification in high gas holdup, and interphase forces of bubble swarms.

A novel multistage internal-loop airlift reactor was realized by using a novel interstage internal. In this reactor, a gas layer is formed below the internal and has important effects on the hydrodynamic behavior. The effects of the opening ratio of the internal for the gas and liquid channels and superficial gas and liquid velocities were experimentally studied in both cocurrent and countercurrent operations. The results show that the gas layer height increases with an increase in the superficial gas velocity for both cocurrent and countercurrent flows. With an increase in the superficial liquid velocity, the gas layer height decreases for cocurrent flow, but increases for countercurrent flow. The opening ratio of the internal for gas channels has a much more significant influence on the gas layer height than that for the liquid channel. A mathematical model for predictions of the gas layer height was proposed based on the balance between the pressure drops of the gas and liquid through the internal. A good agreement was obtained between the calculated and experimental data. This model can be used for the optimum design of the novel multistage internal-loop airlift reactor.

The partial oxidation of hydrocarbons is an important technical route to produce acetylene for chemical industry. The partial oxidation reactor is the key to high acetylene yields. This work is an experimental and numerical study on the use of a methane flame to produce acetylene. A lab scale partial oxidation reactor was used to produce ultra fuel-rich premixed jet flames. The axial temperature and species concentration profiles were measured for different equivalence ratios and preheating temperatures, and these were compared to numerical results from Computational Fluid Dynamics (CFD) simulations that used the Reynolds Averaged Navier-Stokes Probability Density Function (RANS-PDF) approach coupled with detailed chemical mechanisms. The Leeds 1.5, GRI 3.0 and San Diego mechanisms were used to investigate the effect of the detailed chemical mechanisms. The effects of equivalence ratio and preheating temperature on acetylene production were experimentally and numerically studied. The experimental validations indicated that the present numerical simulation provided reliable prediction on the partial oxidation of methane. Using this simulation method the optimal equivalence ratio for acetylene production was determined to be 3.6. Increasing preheating temperature improved acetylene production and shortened greatly the ignition delay time. So the increase of preheating temperature had to be limited to avoid uncontrolled ignition in the mixing chamber and the pyrolysis of methane in the preheater.

•PdNiPd(1 1 1) surface is more active for 1,3-butadiene hydrogenation than Pd(1 1 1).•EXAFS confirms the formation of bimetallic bonds in supported catalyst.•PdNi/γ-Al2O3 has higher hydrogenation activity than its monometallic counterparts.•PdNi/γ-Al2O3 gives ∼20% higher 1-butene selectivity than Pd/γ-Al2O3.•PdNi/γ-Al2O3 is a better catalyst for 1,3-butadiene removal.The selective hydrogenation of 1,3-butadiene serves as a means to purify the butene stream generated from cracking naphtha or gas oil. To identify selective hydrogenation catalysts, 1,3-butadiene was studied on single crystal Ni/Pd(1 1 1) bimetallic surfaces, utilizing density functional theory (DFT) calculations and temperature-programmed desorption (TPD). DFT calculations predicted that the Pd-terminated bimetallic surface should be more active and selective to produce 1-butene, which were verified experimentally using TPD. The promising results on model surfaces were extended to γ-Al2O3-supported catalysts using both batch and flow reactors. Extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) confirmed the formation of bimetallic nanoparticles. The PdNi bimetallic catalyst showed higher hydrogenation activity and 1-butene selectivity than the monometallic catalysts. The excellent correlation between model surfaces and supported catalysts demonstrates the feasibility of designing effective bimetallic catalysts for selective hydrogenation reactions.Download high-res image (63KB)Download full-size image

•Furanone is hydrogenated to GBL with a high yield over Pt-based bimetallic catalysts.•Ni-terminated bimetallic surface is the most active for furanone hydrogenation to GBL.•TOF of supported catalysts follows the trend of Pt-Ni > Pt-Co > Pt > Ni > Co.•Catalyst selectivity follows the trend of Pt-Ni > Ni > Pt-Co > Co > Pt.•Good correlation between model surfaces and supported catalysts is obtained.The selective hydrogenation of biomass-derived 2(5H)-furanone to γ-butyrolactone (GBL) was studied over Pt-Ni and Pt-Co bimetallic model surfaces and supported catalysts. The reactions of 2(5H)-furanone were investigated on Ni/Pt(1 1 1) and Co/Pt(1 1 1) bimetallic surfaces using temperature-programmed desorption (TPD), revealing that the Ni-terminated bimetallic Ni-Pt-Pt(1 1 1) surface was more active and selective to produce GBL. Parallel density functional theory (DFT) calculations also confirmed the higher hydrogenation activity on Ni-Pt-Pt(1 1 1) due to bimetallic effect. The promising results on model surfaces were extended to SiO2-supported catalysts. The hydrogenation activity in terms of the initial turnover frequency (TOF) followed the trend of Pt-Ni > Pt-Co > Pt > Ni > Co, where the TOF over Pt-Ni was almost twice higher than that over Pt. With the excellent correlation between model surfaces and supported catalysts, the Pt-Ni bimetallic catalyst was identified as a promising option for the selective hydrogenation of 2(5H)-furanone to GBL.Download high-res image (137KB)Download full-size image

•The feasibility of producing acrolein from crude glycerol was confirmed.•Among the impurities only the alkali metal ions caused catalyst deactivation.•A stable acrolein yield of 85% was obtained from desalted crude glycerol.•HPW/Cs-SBA catalyst showed good thermal stability and regeneration ability.The feasibility of producing acrolein from crude glycerol was studied by the dehydration reaction over H3PW12O40 (HPW) supported on Cs-modified SBA-15 (HPW/Cs-SBA). The influence of impurities in crude glycerol was investigated. Only the alkali metal ions caused catalyst deactivation and decreased the acrolein selectivity because they decreased the amount of catalytically effective medium Brønsted acid sites. This problem was solved by glycerol desalination, and a stable acrolein yield of 85% was obtained through 60 h of reaction, which was as good as that with pure glycerol. In addition, HPW/Cs-SBA showed good thermal stability and regeneration ability after the reaction with desalted crude glycerol.Download full-size image

•Pd–Ni is more selective for 1,3-butadiene hydrogenation to 1-butene than Pd.•Support nature does not affect 1,3-butadiene hydrogenation activity.•PdNi/γ-Al2O3 is most selective to 1-butene at low 1,3-butadiene conversions.•Support reducibility/oxide defect affect 1-butene selectivity.Our previous work showed that the Pd–Ni bimetallic catalyst had better hydrogenation activity and 1-butene selectivity in the selective hydrogenation of 1,3-butadiene. In the present work, the effect of oxide supports on the hydrogenation of 1,3-butadiene was studied over Pd–Ni bimetallic catalysts supported on γ-Al2O3, SiO2, CeO2, ZrO2 and TiO2. Transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) were used to characterize the particle size and the extent of Pd–Ni bimetallic bond formation, respectively. The support effect affected the bimetallic particle structure, but appeared to have no apparent influence in the hydrogenation activity. All the bimetallic catalysts showed ∼100% selectivity to butenes; however, the supports affected the 1-butene selectivity. PdNi/γ-Al2O3 showed the highest 1-butene selectivity of ∼80% at 1,3-butadiene conversions lower than 50% but decreased rapidly at higher conversion. The different performance of the supports in 1-butene selectivity might be attributed to strong metal-support interaction (SMSI), the oxygen defects and the geometric/electronic effect on the catalysts.

The pseudopotential in Shan and Chen-type multiphase models was investigated and modified based on a virial equation of state with newly proposed parameters. This modified pseudopotential was used in a lattice Boltzmann model and shown to be suitable for simulating sufficiently large gas–liquid density ratios with good numerical stability and only small spurious velocities. The spurious velocity was reduced by reducing the pseudo-sound speed by the use of suitable parameters. The multicomponent multiphase model based on this modified pseudopotential can be used in bubbly flow simulations. Bubble rise behavior was simulated using a 3D multicomponent and multiphase model with a high density ratio. The predicted terminal velocity and drag coefficient of a single bubble agreed well with those calculated from empirical correlations. The drag coefficient of bubbles in the homogenous regime decreased with increased gas holdup. A new relationship between the bubble drag coefficient and gas holdup in the homogenous regime was proposed.

The partial oxidation (POX) of natural gas to produce acetylene was studied using detailed chemistry simulation to determine the influences of adding H2, C2H6 and C3H8 to the CH4 feed. Four detailed chemistry mechanisms, codenamed GRI 3.0, GRI 486, Petersen, and Curran, for describing the POX of natural gas under fuel-rich conditions were evaluated by comparing calculated results with ignition delay time and homogeneous oxidation data. The Curran mechanism gave the best performance, and was further used to examine the influences brought about by changes in the natural gas composition due to the addition of H2, C2H6 and C3H8. The addition of H2, C2H6 and C3H8 reduced the consumption of natural gas per ton of acetylene produced, and would enhance the economy of the POX process and help use up excess H2, C2H6 and C3H8 from other processes in chemical plants. For natural gases that contain small amounts of higher hydrocarbons, the adding of H2, C2H6 and C3H8 significantly decreased the ignition delay time, and the residence time of the feed in the mixing zone has to be reduced when adding these species to avoid uncontrolled combustion.

The need for more complete removal of sulfur from fuels is due to the lower allowable sulfur content in gasoline and diesel, which is made difficult by the increased sulfur contents of crude oils. This work reports an experimental study on the hydrodesulfurization (HDS) of diesel in a slurry reactor. HDS of straight-run diesel using a NiMoS/Al2O3 catalyst was studied in a high-pressure autoclave for the following operating conditions: 4.8–23.1 wt% catalyst in the reactor, 320–360 °C, 3–5 MPa pressure, and 0.56–2.77 L/min hydrogen flow rate. It was found that the reaction rate was proportional to the catalyst amount and increased with temperature, pressure and hydrogen flow rate. The reaction kinetics for the HDS reaction in the slurry reactor was obtained. As compared with HDS in a fixed bed reactor, HDS in a slurry reactor is promising because of the uniform temperature profile, high catalyst efficiency, and online removal and addition of catalyst.

A core–shell structure of Pt@SnOx/SiO2 was developed for the selective hydrogenation of acrolein. This structure significantly promoted the synergetic effect between Pt and SnOx for the selective hydrogenation of the CO bond in the presence of the CC bond, and showed high activity and selectivity to allyl alcohol.

ZIF-8 encapsulated Pt nanoparticles (NPs) were investigated for the hydrogenation of 3-methylcrotonaldehyde to prenol using the geometric effect. HR-TEM, HAADF-STEM, XRD, nitrogen adsorption isotherm characterization and size-selective reaction evaluation demonstrated that the Pt NPs were encapsulated in the inner space of ZIF-8. The Pt NPs in the Pt@ZIF-8 catalyst were surrounded by apertures with sizes commensurate with 3-methylcrotonaldehyde molecules. These narrow apertures forced the 3-methylcrotonaldehyde molecules to linearly approach the active sites. The CC bond in the middle of the 3-methylcrotonaldehyde molecule was prevented from interacting with the Pt active sites by the narrow apertures around the Pt NPs, while the CO bond at the tail-end was easily adsorbed and further hydrogenated to prenol. Using this geometric effect, the Pt@ZIF-8 catalyst exhibited a high selectivity to prenol (>84%) even at a high conversion (>90%).