Numerical simulation of micro-mixing in gas–liquid and solid–liquid stirred tanks with the coupled CFD-E-model

The coupled CFD-E-model for multiphase micro-mixing was developed,and used to predict the micro-mixing effects on the parallel competing chemical reactions in semi-batch gas–liquid and solid–liquid stirred tanks.Based on the multiphase macro-flow field,the key parameters of the micro-mixing E-model were obtained with solving the Reynolds-averaged transport equations of mixture fraction and its variance at low computational costs.Compared with experimental data,the multiphase numerical method shows the satisfactory predicting ability.For the gas–liquid system,the segregated reaction zone is mainly near the feed point,and shrinks to the exit of feed-pipe when the feed position is closer to the impeller.Besides,surface feed requires more time to completely exhaust the added H+solution than that of impeller region feed at the same operating condition.For the solid–liquid system,when the solid suspension cloud is formed at high solid holdups,the flow velocity in the clear liquid layer above the cloud is notably reduced and the reactions proceed slowly in this almost stagnant zone.Therefore,the segregation index in this case is larger than that in the dilute solid–liquid system.

Polycrystalline ZSM-5 Aggregates Induced by Seed and Catalytic Performance in Methanol to Hydrocarbon

Synthesis of ZSM-5 zeolite typically utilizes small molecule polyamines or quaternary ammonium salts as organic structure guiding agent(OSDA).By contrast,the OSDA-free hydrothermal synthesis system eliminates the use of organic templates and the subsequent calcination procedure.This not only reduces the cost of synthesis,but also prevents environmental pollution from the combustion of organic templates,representing an eco-friendly approach.Despite this,literature suggests that even so-called template-free synthesis systems often involve trace amount of organic substances like alcohol.In the present work,a calcined commercial ZSM-5 zeolite was served as seed,with sodium aluminate as aluminum source and silica sol as silicon source,ensuring an entirely template-free synthesis system.Polycrystalline ZSM-5 aggregates consisted of rod-like nanocrystals were successfully prepared in the completely OSDA-free system.Effects of the Si/Al ratio in ZSM-5 seed,dosage and crystallization conditions such as crystallization temperature and crystallization time on ZSM-5 synthesis were investigated.The results show that a highly crystallinity ZSM-5 aggregate consisting of primary nano-sized crystals less than 100 nm is produced from a gel precursor with 5.6%(in mass)seed after hydrothermal treatment for 48 h.Furthermore,the Si/Al ratio in ZSM-5 seed has little effect on the topological structure and pore structure of the synthesized samples.However,the seeds with a low Si/Al ratio facilitate faster crystallization of zeolite and enhance the acidity,especially the strong acid centers,of the catalyst.The catalytic performance of the synthesized polycrystalline ZSM-5 was evaluated during dehydration of methanol and compared with a commercial reference ZSM-5r.The results exhibit that as compared with the reference catalyst,the fabricated sample has a longer catalytic lifetime(16 h vs 8 h)attributed to its hierarchical pores derived from the loosely packed primary nanoparticles.Additionally,the prepared polycrystalline catalyst also exhibits a higher aromatics selectivity(28.1%-29.8%vs 26.5%).

Pd^(0)-O v-Ce^(3+) Interfacial Sites with Charge Redistribution for Enhanced Hydrogenation of Methyl Oleate to Methyl Stearate

Improving the efficiency of metal/reducible metal oxide interfacial sites for hydrogenation reactions of unsaturated groups(e.g.,C=C and C=O)is a promising yet challenging endeavor.In our study,we developed a Pd/CeO_(2) catalyst by enhancing the oxygen vacancy(O V)concentration in CeO_(2) through high-temperature treatment.This process led to the formation of an interface structure ideal for supporting the hydrogenation of methyl oleate to methyl stearate.Specifi cally,metal Pd^(0) atoms bonded to the O V in defective CeO_(2) formed Pd^(0)-O v-Ce^(3+)interfacial sites,enabling strong electron transfer from CeO_(2) to Pd.The interfacial sites exhibit a synergistic adsorption eff ect on the reaction substrate.Pd^(0) sites promote the adsorption and activation of C=C bonds,while O V preferably adsorbs C=O bonds,mitigating competition with C=C bonds for Pd^(0) adsorption sites.This synergy ensures rapid C=C bond activation and accelerates the attack of active H*species on the semi-hydrogenated intermediate.As a result,our Pd/CeO_(2)-500 catalyst,enriched with Pd^(0)-O v-Ce^(3+)interfacial sites,dem-onstrated excellent hydrogenation activity at just 30℃.The catalyst achieved a Cis-C18:1 conversion rate of 99.8% and a methyl stearate formation rate of 5.7 mol/(h·g metal).This work revealed the interfacial sites for enhanced hydrogenation reactions and provided ideas for designing highly active hydrogenation catalysts.

Diesel molecular composition and blending modeling based on SUBEM framework

Diesel molecular compositional model has important application for diesel quality prediction,blending,and molecular-level process model development.In this paper,different types of diesel molecular compositional and blending models were constructed based on the SU-BEM framework.More than 1500 representative molecules were selected to form the molecular structure library.The probability density functions(PDFs)combination was determined by experimental data and experience.A quadratic optimization strategy combining genetic algorithm with local optimization algorithm was adopted to improve the accuracy of the compositional model.The model results show good agreement with the experimental data.The diesel blending model was constructed at the molecular-level based on the above diesel compositional models.The properties of the blending model accord with the experimental regulations.It is proved that the compositional models and blending model constructed have high accuracy and strong prediction capability,and are applicable to the industrial process.

Study on Reaction Types and Environment in Different Regions of Diesel Deep Hydrodesulfurization Reactor

In this work,the influence of reaction conditions on hydrocarbon distribution and product quality was tested to obtain the rule of variation with different residence time.A semi-experience and semi-mechanism dynamics model was established and modified.Based on the simulation results,the hydrogenation reactor is divided into five regions:the upper two regions are mainly saturated with most of tri-cyclic and bi-cyclic aromatics,and 90%of nitrides are converted,while all simple sulfide and some 4,6-DMDBT compounds undergo transformation reactions.In the lower three regions,the reaction rate of HDS and HDN slows down,while the rate of monocyclic aromatic saturation increases.The HDS,HDN and HDA rates of the optimized catalyst grading scheme are significantly increased.

Reaction Process of Heavy Hydrocarbons Hydrogenation in Ebullated Bed

The properties and structural changes of unconverted oil(UCO)obtained from ebullated bed hydrogenation at different residue conversion rates were analyzed to clarify the reaction process of heavy components.Meanwhile,the processing routes of UCO,delayed coking,and solvent deasphalting,were investigated.The results showed that with the increase of conversion,the impurity removal rate increased;meanwhile the contents of sulfur and metal in UCO decreased,while the contents of nitrogen and residual carbon increased,and the colloidal stability of UCO became worse.The structural parameters of UCO indicated that the change in molecular structure of heavy oil mainly covered the opening of cycloalkanes ring,hydrogenation saturation of aromatic rings and dealkylation reaction during hydrogenation in the ebullated bed;the aromatic structure was basically unchanged at high conversion,and was mainly due to the ring opening of cycloalkanes and the fracture reaction of alkyl side chains.The coking route of UCO showed that low sulfur petroleum coke with different grades could be prepared by adjusting the conversion in ebullated bed to produce UCOs with different properties.The coke generating coefficient and sulfur transfer coefficient in UCO coking process were higher than those in residue coking.The properties of deasphalted oil(DAO)of UCO were significantly improved and could be used as FCC or hydrocracking feedstock.The DAO yield of UCO feedstock at high conversion was higher,and its sulfur content was lower and CCR value was higher.

Acetic acid-and furfural-based adaptive evolution of Saccharomyces cerevisiae strains for improving stress tolerance and lignocellulosic ethanol production

Acetic acid and furfural are known as prevalent inhibitors deriving from pretreatment during lignocellulosic ethanol production.They negatively impact cell growth,glucose uptake and ethanol biosynthesis of Saccharomyces cerevisiae strains.Development of industrial S.cerevisiae strains with high tolerance towards these inhibitors is thus critical for efficient lignocellulosic ethanol production.In this study,the acetic acid or furfural tolerance of different S.cerevisiae strains could be significantly enhanced after adaptive evolution via serial cultivation for 40 generations under stress conditions.The acetic acid-based adaptive strain SPSC01-TA9 produced 30.5 g·L^(-1)ethanol with a yield of 0.46 g·g^(-1)in the presence of 9 g·L^(-1)acetic acid,while the acetic acid/furfural-based adaptive strain SPSC01-TAF94 produced more ethanol of 36.2 g·L^(-1)with increased yield up to 0.49 g·g^(-1)in the presence of both 9 g·L^(-1)acetic acid and 4 g·L^(-1)furfural.Significant improvements were also observed during non-detoxified corn stover hydrolysate culture by SPSC01-TAF94,which achieved ethanol production and yield of 29.1 g·L^(-1)and 0.49 g·g^(-1),respectively,the growth and fermentation efficiency of acetic acid/furfural-based adaptive strain in hydrolysate was 95%higher than those of wildtype strains,indicating the acetic acid-and furfural-based adaptive evolution strategy could be an effective approach for improving lignocellulosic ethanol production.The adapted strains developed in this study with enhanced tolerance against acetic acid and furfural could be potentially contribute to economically feasible and sustainable lignocellulosic biorefinery.

Oil droplet movement and micro-flow characteristics during interaction process between gas bubble and oil droplet in flotation

Flotation is an efficient pre-treatment technology for oily water.In this work,the interaction process between the moving oil droplet and the gas bubble was studied by high-speed camera and Bassset-Boussinesq-Oseen(BBO)theoretical model,and the experimental and simulation results of the oil droplet trajectory were compared.Moreover,the micro-particle image velocimetry system was utilized to observe the flow inside and outside of the moving oil droplet.The results show that the BBO model with the mobile bubble’s surface can reflect the velocity change trend of the oil droplet during the interaction process between the moving oil droplet and the gas bubble,but there are some significant differences between the experimental and simulation results.While the oil droplet is moving on the bubble’s surface,the velocity of the area near the contact point of oil droplet–gas bubble is less than that of the other areas inside the oil droplet.Meanwhile,the flow of water above the oil drop is more biased towards the gas bubble.

Acidity Evaluation of Industrially Dealuminated Y Zeolite via Methylcyclohexane Transformation

The catalytic transformation of methylcyclohexane as an accepted probe reaction to evaluate zeolitic acidity(concentration,strength,and accessibility)is employed to study the acidity and the reactivity of three commercial dealuminated Y zeolites(DAY)with different Si/Al ratios and meso/microporosities,with their properties analyzed by N_(2) adsorption/desorption,pyridine-IR,and hydroxyl-IR spectroscopy technologies.The global activity(conversion)is largely dependent on the concentration of the acid sites,and the activity of the protonic sites in terms of turnover frequency(TOF)reflects the accessibility of acid sites.The products of aromatics and isomers,and the yield of cracking products increase with the increase of concentration of strong protonic sites in zeolite micropores.Moreover,the decrease of aromatics with the reduction of the concentration of acid sites and the diffusion length within DAY zeolites are observed due to the decrease of the secondary reaction.For the same reason,it results in the increasing of C_(7)products and alkenes/alkanes ratios in the cracking products.The high i-C_(4)product selectivity is a unique reflection of the high percentage of very strong acid sites,which is characterized by the hydroxyl-IR band at 3600 cm^(-1).

Propane dehydro-aromatization reaction over PtFe@S-1 coupling with Zn/ZSM-5 tandem catalysts: the role of Zn species

Unraveling the structure-activity relationship and improving the catalytic performance is paramount in propane dehydro-aromatization reactions. Herein, a tandem catalyst with high propane dehydro-aromatization reaction performance was prepared via coupling the PtFe@S-1 with Zn/ZSM-5 zeolites (PtFe@S-1&1.0Zn/ZSM-5), which exhibits high dehydrogenation activity, aromatics selectivity (~60% at ~78% propane conversion), and stability. The addition of zinc inhibits the cleavage of C_(6)^(=) intermediates on ZSM-5 and promotes the aromatization pathway by weakening zeolite acid strength, significantly improving the selectivity to aromatics. This understanding of the structure-activity relationship in propane dehydro-aromatization reaction helps develop future high-performance catalysts.