Equilibrium Conversion Research Articles

The quest for a better solvent for the direct hydration of cyclohexene: From molecular screening to process design

Cylcohexanol is an essential bulk chemical that can be produced via cyclohexene hydration, a liquid-liquid two-phase reaction that is limited by the low reaction rate and the equilibrium conversion. Adding an appropriate solvent is the most promising method to break through these limitations. However, in previous works the solvent was almost blindly selected without a global consideration. In this work, a rational multiscale method is proposed for the effective selection of an economical and sustainable solvent for the direct hydration of cyclohexene. At the molecular scale, liquid-liquid phase equilibrium was estimated using group contribution methods to rapidly screen the potential solvent candidates from a range of organics, based on the partition coefficient. At the reactor scale, the candidates were experimentally investigated to pick out the solvents that could significantly improve the conversion, without introducing side reactions or deactivating the catalyst. At the process scale, the total annual cost (TAC), CO2 emission, and other metrics were calculated to evaluate the eco-efficiency of all solvents. Using this multi-scale method, acetophenone was selected as an eco-efficient solvent from over 100 organics, resulting in the reduction of TAC by 8 % and CO2 emission by 17 % in the production process. Using acetophenone also led to the increase of cyclohexanol yield from 12.3 % to 27.6 % without the occurrence of side reactions and catalyst deactivation.

Kinetic Investigation for Chemical Depolymerization of Post-Consumer PET Waste Using Sodium Ethoxide

Reaction kinetics provides significant insights into the reaction rate and mechanism to control a chemical reaction. In the present work, the detailed kinetics of glycolytic depolymerization of post-consumer polyethylene terephthalate (PET) waste in the presence of sodium ethoxide (EtONa) was investigated. The glycolysis experiments were conducted in a batch reactor over a temperature range of 160 to 197 °C. The confirmation of the product, the bis(2-hydroxyethyl)terephthalate monomer, was carried out using nuclear magnetic resonance spectroscopy, high-performance liquid chromatography, differential scanning calorimetry, and X-ray diffraction techniques. Investigations on the influence of particle size and temperature showed that conversion increased with a decrease in particle size and increasing temperature. Equilibrium conversions were found at different temperatures, and a van ’t Hoff plot was used to confirm that the depolymerization reaction is endothermic. Gibbs’ free energy was used to calculate the ceiling temperature (TC = 156 °C). Three kinetic models were tested for their applicability. It was found that the EtONa-catalyzed glycolysis of PET follows a first-order reversible reaction kinetic model at higher temperatures (170–197 °C). However, a heterogeneous shrinking core mechanism was applicable in a lower temperature range (160–170 °C). The kinetic evaluation revealed that the PET glycolysis reaction consists of heterogeneous and homogeneous mechanisms depending upon the depolymerization stages at various temperatures.

High Internal Phase Pickering Emulsion Stabilized by Lipase-Coated ZIF-8 Nanoparticles towards Recyclable Biphasic Biocatalyst

High internal phase Pickering emulsion (Pickering HIPE) stabilized by enzyme-decorated metal-organic frameworks (MOFs) nanoparticles is developed for biphasic biocatalysts to enhance lipase catalysis and recycling. Specifically, enzyme decorated nanoparticles are prepared via ZIF-8 physisorption of a model lipase Candida antarctica Lipase B (CALB), named ZIF-8@CALB, to be both Pickering stabilizer and catalytic sites. An oil-in-water (o/w) Pickering HIPE with oil/water volume ratio of 3 could then be fabricated by homogenizing p-nitrophenyl palmitate (p-NPP) n-heptane solution into the ZIF-8@CALB aqueous dispersion. The biocatalytic hydrolysis of p-NPP is conducted by just standing the biphasic system at room temperature. The Pickering HIPE system achieves a product conversion of up to 48.9% within 0.5 h, whereas the p-NPP n-heptane solution system containing free CALB only achieves a stable product conversion of 6.8% for the same time. Moreover, the ZIF@CALB could be recovered by a simple centrifugation at 800 rpm, and then reused in the next cycle. The hydrolysis equilibrium conversion rate of p-NPP keeps over 40% for all 8 cycles, reflecting the high catalytic efficiency and recyclability of the Pickering HIPE. This study provides a new opportunity in designing Enzyme-MOFs-based Pickering interfacial biocatalyst for practical applications.

Hybrid Catalyst Coupling Zn Single Atoms and CuNx Clusters for Synergetic Catalytic Reduction of CO2

AbstractReverse water‐gas shift (RWGS) reaction is the initial and necessary step of CO2 hydrogenation to high value‐added products, and regulating the selectivity of CO is still a fundamental challenge. In the present study, an efficient catalyst (CuZnNx@C‐N) composed by Zn single atoms and Cu clusters stabilized by nitrogen sites is reported. It contains saturated four‐coordinate Zn‐N4 sites and low valence CuNx clusters. Monodisperse Zn induces the aggregation of pyridinic N to form Zn‐N4 and N4 structures, which show strong Lewis basicity and has strong adsorption for *CO2 and *COOH intermediates, but weak adsorption for *CO, thus greatly improves the CO2 conversion and CO selectivity. The catalyst calcined at 700 °C exhibits the highest CO2 conversion of 43.6% under atmospheric pressure, which is 18.33 times of Cu‐ZnO and close to the thermodynamic equilibrium conversion rate (49.9%) of CO2. In the catalytic process, CuNx not only adsorbs and activates H2, but also cooperates with the adjacent Zn‐N4 and N4 structures to jointly activate CO2 molecules and further promotes the hydrogenation of CO2. This synergistic mechanism will provide new insights for developing efficient hydrogenation catalysts.

Flexible NiRu Systems for CO2 Methanation: From Efficient Catalysts to Advanced Dual-Function Materials.

CO2 emissions in the atmosphere have been increasing rapidly in recent years, causing global warming. CO2 methanation reaction is deemed to be a way to combat these emissions by converting CO2 into synthetic natural gas, i.e., CH4. NiRu/CeAl and NiRu/CeZr both demonstrated favourable activity for CO2 methanation, with NiRu/CeAl approaching equilibrium conversion at 350 °C with 100% CH4 selectivity. Its stability under high space velocity (400 L·g-1·h-1) was also commendable. By adding an adsorbent, potassium, the CO2 adsorption capability of NiRu/CeAl was boosted, allowing it to function as a dual-function material (DFM) for integrated CO2 capture and utilisation, producing 0.264 mol of CH4/kg of sample from captured CO2. Furthermore, time-resolved operando DRIFTS-MS measurements were performed to gain insights into the process mechanism. The obtained results demonstrate that CO2 was captured on basic sites and was also dissociated on metallic sites in such a way that during the reduction step, methane was produced by two different pathways. This study reveals that by adding an adsorbent to the formulation of an effective NiRu methanation catalyst, advanced dual-function materials can be designed.

Zeolite Y hydrolyses methyl methacrylate to methacrylic acid in the gas phase

Poly(methyl methacrylate) (PMMA) depolymerizes to its monomer methyl methacrylate (MMA) below 400 °C but the accompanying byproducts have similar boiling points, which incurs excessive separation costs rendering the process economically challenging. Hydrolyzing MMA to methacrylic acid (MAA) is an economic alternative since its boiling point is 61 °C higher. Zeolites are among a class of heterogeneous catalyst with Brønsted acidity that protonate the ester carbonyl group in the much less common gas-phase route to acids. Here, for the first time, we report the hydrolysis kinetics of MMA to MAA in the gas phase over a Y/SiO2 zeolite with a 960 m2 g−1 surface area. MMA conversion in an 8 mm fixed bed reactor averaged 94 % above 200 °C and a yield of 85 %. Operating the reactor in excess water vapour shifts the equilibrium conversion towards the products. Surface reaction between adsorbed MMA and water is the rate controlling step. Heterogeneous supports control the hydrophobic properties, and thereby activity and stability. Introducing zeolites in the matrix of a silica gel facilitates access to all external zeolite active sites compared to spray-drying with Ludox where the SiO2 shell covers the external catalyst surface. Nuclear magnetic resonance spectroscopy with magic angle spinning (MAS NMR) and ultra-violet visible (UV–vis) detected Brønsted acidity. The reaction rate is first order in methacrylic acid and water and the equilibrium conversion is about 95 % above 200 °C. The apparent activation energy was 106 kJ mol−1.

Thermodynamics of the heterogeneous synthesis of polyoxymethylene dimethyl ethers from paraformaldehyde and dimethoxymethane in presence of methanol and water

Polyoxymethylene dimethyl ethers (PODEn) are promising diesel additives that can reduce the exhaust emission remarkably. Although the thermodynamic model has been proposed for the homogenous synthesis of PODEn, the thermodynamics of heterogeneous synthesis of PODEn from paraformaldehyde and dimethoxymethane is still a challenge because of the complicated characteristics of paraformaldehyde. In this work, a thermodynamic model containing solid paraformaldehyde and liquid dimethoxymethane, methanol and water was established. Experimental validation showed that this model was applicable in a wide range of reaction temperature and feeding composition. This thermodynamic model was then used to study the influence of the reaction temperature, feeding ratio, and addition of water/methanol on the equilibrium conversion. The different starting compositions from heterogeneous and homogenous reactants for the synthesis of PODEn were compared based on thermodynamic analysis, showing that using paraformaldehyde and dimethoxymethane as feedstock gave the highest CH2O conversion and PODE3-5 yield.

An Experimental Study of a Zeolite Membrane Reactor for Reverse Water Gas Shift.

Reverse water gas shift (RWGS) is attracting attention as one of the promising technologies for CO2 conversion. Selective removal of H2O from the reaction system can improve the CO2 conversion beyond the equilibrium conversion of RWGS in a conventional reactor. In this study, a conventional plug-flow reactor without membrane, and two types of RWGS membrane reactors using ZSM-5 membranes, were developed. The yield of CO without membrane (Case 1) was almost the same as the equilibrium conversion. A membrane reactor (Case 2) showed a CO yield 2-3% above that of a conventional reactor. From the results, the effectiveness of the dehydration membrane reactor for RWGS was verified. In addition, CO yield was further increased in the reactor made up of the combination of conventional reactor and membrane reactor (Case 3). For example, the CO yields in Cases 1, 2, and 3 at 560 K were 21.8, 24.9, and 29.0%, respectively. Although the CO yield increased in Case 2, a large amount of raw materials penetrated through the membrane to the permeation side, and was lost. In Case 3, H2 and CO2 permeation through the membrane were suppressed because of the existence of H2O, resulting in the prevention of the leakage of raw material, and contributing to the high CO yield.

CO2 Hydrogenation to Renewable Methane on Ni/Ru Modified ZSM-5 Zeolites: The Role of the Preparation Procedure

Mono- and bimetallic Ni- and Ru-modified micro-mesoporous ZSM-5 catalysts were prepared by wet impregnation. The influence of the Ni content, the addition of Ru and the sequence of the modification by two metals on the physicochemical properties of the catalysts were studied. They were characterized by X-ray powder diffraction (XRD), N2 physisorption, temperature-programmed reduction (TPR-TGA), TEM and XPS spectroscopy. Formation of finely dispersed nickel and/or ruthenium oxide species was observed on the external surface and in the pores of zeolite support. It was found that the peculiarity of the used zeolite structure and the modification procedure determine the type of formed metal oxides, their dispersion and reducibility. XPS study revealed that the surface became rich in nickel and poorer in ruthenium for bimetallic catalysts. Ni had higher dispersion in the presence of ruthenium, and TPR investigations also confirmed its facilitated reducibility. The studied catalysts were tested in CO2 hydrogenation to methane. 10Ni5RuZSM-5 material showed the highest activity and high selectivity for methane formation, reaching the equilibrium conversion and 100% selectivity at 400 °C. Stability and reusability of the latter catalyst show that it is appropriate for practical application.

High purity vanadium pentoxide preparation via gas phase oxidation of vanadium oxytrichloride in fluidized bed reactor

With the increasing demand for high purity vanadium pentoxide for manufacturing of all-vanadium redox flow batteries (VRFBs), production of high purity vanadium pentoxide by chlorination process is an efficient and clean approach. However, oxidation of vanadium oxytrichloride is the controlling step. In the present work, gaseous vanadium oxytrichloride oxidation and vanadium pentoxide deposition behavior on particle substrates in a fluidized bed reactor were investigated. Results showed that the thermodynamic equilibrium conversion of oxidation gradually decreased with increasing temperature above 400 °C, while the kinetic limitation was predominant at low temperatures. Subsequently, oxidation experiments were conducted to investigate the influences of parameters on the conversion efficiency. Under optimized reaction conditions, the conversion of vanadium oxytrichloride and the deposition rate of vanadium pentoxide could achieve 68.52 % and 0.48 g/(h·g), respectively. It was more preferable than previous works that the purity of deposited vanadium pentoxide products reached 99.99 wt%, while impurities that would greatly affect electrochemical performance of the VRFBs were undetectable. This novel method provides an efficient route for the preparation of high purity vanadium pentoxide along with the recycling of chlorine gas for the chlorination process, which would be a promising method for green and sustainable development of the vanadium industry.

Effect of hemicellulose extraction pretreatment on sulfonated corncob biochar for catalytic biodiesel production

In this work, waste corncob with high hemicellulose content was selected as the carbon source to investigate the effect of hemicellulose extraction on the prepared sulfonated biochar for biodiesel production. After hemicellulose extraction, the optimized sulfonated biochar with a maximum -SO3H density of 2.05 mmol/g was synthesized under 3 h of carbonization at 300 °C, then 2 h of sulfonation at 90 °C. For the esterification, the 98.5% oleic acid equilibrium conversion was achieved under optimized reaction parameters: a 12:1 molar ratio (methanol/oleic acid) and a 10 wt% catalyst dosage at 65 °C for 4 h. The catalyst still reached 70% conversion efficiency after 10 cycles, which proved that the hemicellulose extraction not only played a role in the rational utilization of biomass but also the significantly-improved catalyst lifetime was beneficial to the sustainable production of biodiesel.

Non thermal plasma assisted water-gas shift reactions under mild conditions: state of the art and a future perspective

The water gas shift (WGS) reaction is important for many industrial processes such as ammonia synthesis, oil refining and fuel cells. WGS reaction is exothermic and limited by kinetics and chemical equilibrium, and under conventional thermocatalytic conditions, the desired thermodynamic equilibrium conversion and sufficiently fast kinetics can rarely be achieved simultaneously. To address such limitations, non-thermal plasma (NTP) processes have been recently proposed to enhance the kinetics at low temperatures (via gas phase activation), and realising favourable thermodynamic conversion. Here, a critical review of the relevant state-of-the-art regarding NTP-assisted WGS reactions (including both catalytic and non-catalytic systems) is presented. In addition, it also evaluates the concept of reaction-separation integration using novel membrane reactors to improve WGS reaction by shifting reaction equilibrium to favour hydrogen production. Finally, the prospect regarding future research avenues in advancing the NTP-assisted WGS processes is shared.

Efficient Removal of Ammonia Nitrogen by an Electrochemical Process for Spent Caustic Wastewater Treatment

Spent caustic wastewater produced in a soda plant has a high concentration of ammonia nitrogen (NH4+-N). As excessive NH4+-N discharging into water bodies would cause eutrophication as well as destruction to the ecology balance, developing an efficient technology for NH4+-N removal from the spent caustic wastewater is imperative in the current society. In this study, an electrochemical process with graphene electrodes was designed for the NH4+-N removal in the spent caustic wastewater. The removal efficiency of the NH4+-N during the electrochemical process could reach 98.7% at 4 A in a short treatment time (within 120 s) with an acceptable energy consumption (6.1 kWh/m3-order). NO3− and NO2− were not detected during the electrochemical process. An insignificant amount of NH2Cl, NHCl2, and NCl3 produced in the treatment suggested that little of the NH4+-N reacted with chlorine, that is, chlorination played a negligible role in the NH4+-N removal. By electron equilibrium and nitrogen conversion analysis, we think that NH4+-N was primarily converted to NH2(ads) on the surface of a graphene electrode by one-electron transfer during the direct oxidation of the electrochemical process. Due to the high calcium ion (Ca2+) in the spent caustic wastewater, the electrode scale significantly increased to 1.4 g after treatment of 240 s at 4 A. By X-ray diffraction (XRD) analysis, the composition of the electrode scale is portlandite Ca(OH)2. Although the electrode scale was obvious during the electrochemical treatment, it could be alleviated by alternating the electrode polarity. As a result, the life and efficiency of the graphene electrode for NH4+-N removal could remain stable for a long time. These results suggest that the electrochemical process with a graphene electrode may provide a competitive technology for NH4+-N removal in spent caustic wastewater treatment.

Calculation of microwave heating temperature distribution based on SVD truncation

In mathematical models of microwave heating with infinite-dimensional characteristics, it is difficult to use traditional numerical methods to improve computational efficiency. In this work, we propose a fast and accurate method to calculate the temperature distribution of materials under microwave heating. First, we analysed the relationship between the choice of model order and the solution accuracy by downscaling the infinite-dimensional heat conduction partial differential equation (PDE) model into a finite-dimensional ordinary differential equation (ODE) model. Additionally, the effect of different boundary conditions on the global temperature distribution was analysed. Second, the equilibrium conversion matrix was calculated using the singular value decomposition (SVD) truncation method under homogeneous boundary conditions. Using this matrix, a lower-dimensional microwave heating ODE model was further obtained. Finally, the numerical simulation results showed that the root mean square error (RMSE) was only 0.07 and the maximum relative error was only −0.85%. The computation time of the equilibrium conversion matrix was 2.12 ∼ 3.00 ms, and the model calculation time was reduced by 97.78%. We compared the calculated temperature rise curves with those obtained using the conventional COMSOL model. The SVD truncation method achieved an efficient and accurate solution for the microwave heating model.

Modeling and Simulation of Water-Gas Shift Reactors with and without Membrane

The objective of this study is to investigate the usage of membrane reactor technology in the water-gas shift reaction. Furthermore an assessment of the optimum parameters for the maximum conversion of carbon monoxide was carried out. The water-gas shift reaction is a well-known step for upgrading carbon monoxide to carbon dioxide in the production of purified Hydrogen gas. More recently, a renewed interest in the water-gas reaction carried out in hydrogen selective membrane reactors has been observed, because of the growing use of polymeric electrolyte membrane fuel cells, that operate using high-purity hydrogen. Membrane reactors are viewed as an interesting technology in order to overcome the equilibrium conversion limitations in non-membrane reactors. Firstly, the modelling and simulation of the reactor without membrane was carried out, and the obtained results were validated against the experimental published results, then the membrane reactor was simulated by employing a Hydrogen-selective Palladium membrane. A one dimensional steady state model was developed; mass and heat balances were solved simultaneously using MATLAB software. It was found that the conversion of carbon monoxide reaches a maximum of 29% for the non-membrane reactor and 90% for the membrane reactor, which represents an improvement of 210%. It was found that the optimum operating condition for membrane reactor were temperatures of 740 K, pressure of 10 atm and a reactor length of 115 cm.

Optimized Semi-Interpenetrated p(HEMA)/PVP Hydrogels for Artistic Surface Cleaning

The synthesis of hydrogels that are based on poly-hydroxyethyl methacrylate, p(HEMA), network semi-interpenetrated with linear polyvinylpyrrolidone (PVP) was optimized in order to allow both a fast preparation and a high cleaning effectiveness of artistic surfaces. For this purpose, the synthesis parameters of the gel with PVP having a high molecular weight (1300 kDa) that were reported in the literature, were modified in terms of temperature, time, and crosslinker amount. In addition, the gel composition was modified by using PVP with different molecular weights, by changing the initiator and by adding maleic anhydride. The modified gels were characterized in terms of equilibrium water content (EWC), water uptake, conversion grade, and thermal properties by differential scanning calorimetry (DSC). The cleaning effectiveness of the gels was studied through the removal of copper salts from laboratory-stained specimens. Cleaning materials were characterized by electron paramagnetic resonance (EPR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, and inductively-coupled plasma-mass spectrometry (ICP-MS). Cleaning was assessed on marble specimens by color variation measurements. The gel synthesis is accelerated by using PVP 360 kDa. The addition of maleic anhydride in the p(HEMA)/PVP network allows the most effective removal of copper salt deposits from marble since it acts as a chelator towards copper ions.

Kinetics study of esterification reaction of acrylic acid with n-butanol

Homogeneous catalytic esterification reaction of acrylic acid and n-butanol was carried out in a batch reactor. The impacts of reaction temperatures on the esterification reaction of acrylic acid with n-butyl alcohol were investigated. Based on the findings of the experiments, the rate constants, equilibrium constant, activation energy, enthalpy, and entropy were determined. Reaction temperatures were varied from 50 °C to 70 °C at a constant catalyst loading 2 % and alcohol/acid molar ratio 1:1. Equilibrium conversion increases from 67.55 % to 77.81 % as the temperature increased from 50 to 70 °C. These results provide an approach to understand the significant effect of temperature on the esterification kinetics of acrylic acid and n-butanol.

Combining reverse water gas shift with gas fermentation for renewable liquid fuel synthesis

Recently in Cell Reports Physical Science , Li et al. reported that alkali carbonates catalyze selectively the reverse water gas shift (RWGS) reaction at equilibrium conversion. The resulting mixture of CO/CO 2 /H 2 was used in gas fermentation to produce ethanol, achieving a power-to-liquid fuel system with an overall efficiency of ∼50%. Recently in Cell Reports Physical Science , Li et al. reported that alkali carbonates catalyze selectively the reverse water gas shift (RWGS) reaction at equilibrium conversion. The resulting mixture of CO/CO 2 /H 2 was used in gas fermentation to produce ethanol, achieving a power-to-liquid fuel system with an overall efficiency of ∼50%.

Feasibility analysis of water gas shift reaction for the removal of trace CO in hydrogen

The thermodynamic simulation analysis of carbon monoxide water gas shift in rich hydrogen was researched by using the method of Gibbs free energy minimization with Aspen plus software. For the purpose of purifying trace amount of CO in hydrogen, two raw gas compositions, 1%CO–99%H2 and 1%CO–24%CO2–75%H2, were purposely selected, and the influences of water to gas molar ratio (1–7) and transformation temperature (40–280 °C) were investigated. The results showed similar variation law as compared with the water gas shift of a pure CO gas. When the transformation temperature increased, the chemical equilibrium shifted toward the reverse direction, resulting in decreased CO equilibrium conversion; when the water to gas molar ratio increased, the CO conversion increased. The results also showed that CO2 had great negative effects on CO conversion compared with H2. For the CO/H2 feed gas, it was concluded that it was possible to reduce the 1% CO content to 100 ppm at 120 °C with the use of the best low-temperature catalyst reported in literature. If we want to further reduce the trace amount of CO in hydrogen to 10 ppm, it is necessary to develop ultra-low temperature catalysts that are highly active below 70 °C.

Nanosheets-stacked Al2O3-flower anchoring Pt catalyst for intensified ethylene production from ethane dehydrogenation

Catalytic ethane dehydrogenation (CEDH) to ethylene is an important alternative to oil-based cracking processes due to the shale gas revolution, but the dominant Pt-based catalysts still suffer from fast deactivation, caused by coke formation and Pt sintering. Herein, we report a catalyst of nanosheets-stacked Al2O3-flower anchoring Pt species onto pentacoordinated Al (AlV) sites with a low Pt loading of only 0.07 wt%. This catalyst was prepared by a simple wet impregnation method without introducing any promoter, exhibiting a stable ethane conversion of 25–27 % (close to thermodynamic equilibrium conversion) with ethylene selectivity of 95–97 % within a single running of 300 h (590 °C, 33 vol% C2H6/N2, GHSVC2H6 of 2100 mL h−1 g−1), and moreover, a high TOF value of 6084 h−1 could be achieved. This work offers a promising CEDH catalyst, with both very high Pt dispersion (from appropriate amount of AlV sites) and intensified mass transfer (from nanosheet feature).