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Chemical Engineering Science

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A kinetic modeling framework for the peroxide-initiated radical polymerization of styrene in the presence of rubber particles from recycled tires
Dimitrios Meimaroglou; Daniela Florez; Guo-Hua Hu;
Keywords:Styrene;Radical polymerization;Ground-tire rubber;Kinetic model;Method of moments;Peroxide
Abstracts:A novel modeling framework is presented for the peroxide-initiated radical polymerization of styrene, in the presence of ground-tire rubber particles. The model takes into account the previously observed effects of the rubber particles, and their highly-reactive additives, on the course of the polymerization. To this end, a generalized kinetic mechanism is proposed, on the basis of a typical styrene homopolymerization scheme, including also a series of additional chemical reactions that are implemented to describe the deviation of the system from the respective homopolymerization case when ground-tire rubber is present in the mixture. This deviation is mainly manifested through an accelerated peroxide decomposition and significant retardation and inhibition of the reaction and displays a non-linear dependence on the contents of rubber particles and initiator. The proposed model succeeds in predicting this behavior under different reaction conditions, while its generality makes it suitable for implementation in other similar grafting polymerization systems.
Synthesis of ZIF-67 derived Co-based catalytic membrane for highly efficient reduction of p-nitrophenol
Qingqing Chen; Hong Jiang; Rizhi Chen;
Keywords:Catalytic membrane;Metal organic frameworks;N-doped carbon;P-nitrophenol;Membrane reactor
Abstracts:It is significantly valuable to convert p-nitrophenol to p-aminophenol by catalysis. Herein, a novel [email protected]/CM catalytic membrane was synthesized, where ZIF-67 was first in-situ grown on the surface and in the pores of a ceramic membrane (CM) and then pyrolyzed to produce [email protected] carbon ([email protected]). The calcination temperature and Co2+ concentration significantly affect the microstructure of [email protected]/CM-X-Y (X represents the Co2+ molar concentration in methanol solution and Y represents the calcination temperature), and the corresponding catalytic properties for the p-nitrophenol reduction. The as-fabricated catalytic membrane [email protected]/CM-0.6–900 exhibits a superior catalytic activity, with a p-nitrophenol conversion of above 99% within 10 min, which is three times higher than that of [email protected]/CM-0.6–400. [email protected]/CM-0.6–900 also shows excellent reusability during five hydrogenation cycles. Abundant mesopores, high flux, many relatively isolated [email protected] particles with higher Co0 content, high N-pyrrolic content, and the protection function of CN are the reasons for the superior catalytic performance of [email protected]/CM-0.6–900.
Multiscale modelling of diffusion and enzymatic reaction in porous electrodes in Direct Electron Transfer mode
T.D. Le; D. Lasseux; L. Zhang; C. Carucci; S. Gounel; S. Bichon; F. Lorenzutti; A. Kuhn; T. Šafarik; N. Mano;
Keywords:Porous electrode;Direct Electron Transfer;Bilirubin Oxidase;Diffusion reaction;Volume averaging method
Abstracts:This work is dedicated to a multi-scale modelling of coupled diffusion and reaction in a porous micro-electrode operating in the Direct Electron Transfer mode. The pore-scale physico-electrochemical unsteady model is developed considering the oxygen reduction, catalyzed by an enzyme coating the pores of the electrode, coupled to the diffusion of oxygen and mass balance of enzymes. This model is formally upscaled to obtain an original closed unsteady macroscopic model operating at the electrode scale, together with the associated closure providing the effective diffusivity tensor. A validation of this model is carried out from a comparison with the solution of the initial 3D pore-scale governing equations considering the bilirubin oxydase as the catalyst. The relevance and accuracy of the macroscale model are proved allowing a considerable simulation speedup. It is further employed to successfully predict experimental voltammetry results obtained with porous gold electrodes functionnalized with a bilirubin oxidase mutant (BOD S362C). This model represents a breakthrough by providing an operational simple way of understanding and further optimizing porous electrodes functioning in DET mode.
Determination of mass transfer coefficients in high-pressure CO2-H2O flows in microcapillaries using a colorimetric method
T. Deleau; J-J. Letourneau; S. Camy; J. Aubin; F. Espitalier;
Keywords:Mass transfer;High-pressure;Microfluidics;Two-phase flow;Colorimetric method
Abstracts:This study presents a method for the experimental determination of the local volumetric mass transfer coefficient kLaL in a high-pressure two-phase flow of water ( H2O) and carbon dioxide ( CO2) in a micro-capillary using a colorimetric method. H2O and CO2 are fed continuously and co-axially injected at high-pressure (10 MPa) and moderate temperature (303 K) into a microcapillary. Under the flow conditions studied, a segmented flow of CO2 in H2O is formed. The CO2 dissolves into the H2O-rich phase, thereby reducing the pH to about 3.3, depending on the pressure and temperature. The pH of the H2O-rich phase is determined over the entire length of the capillary using a pH sensitive indicator coupled with high-speed imaging and analysis. The concentration of CO2 in the water-rich phase is deduced from this pH value using literature experimental data. The CO2 concentration data and the unit-cell model, which has been modified to account for high pressure conditions, have then been used to determine the volumetric mass transfer coefficient, kLaL, of CO2 into the liquid phase along the entire length of the microreactor. The experimentally derived kLaL ​​ranges between 1 and 13 s−1.
Comparison of models for predicting cleaning of viscoplastic soil layers by impinging coherent turbulent water jets
R.R. Fernandes; J.-H. Tsai; D.I. Wilson;
Keywords:Cleaning;Impinging jet;Modelling;Viscoplastic fluid;Viscous dissipation;Volume of fluid
Abstracts:Different approaches to model the cleaning of (i) very thin and (ii) thin soil layers by impinging water jets are compared to evaluate their predictive capabilities. Cleaning experiments were performed with coherent 2 mm and 3 mm diameter water jets (Re > 10,000) impinging on flat layers of an insoluble, viscoplastic petroleum jelly. The jelly exhibited creep below the yield stress and Herschel-Bulkley behaviour above it. A two-film shear-driven model for case (i) gave very poor predictive capability, partly due to the complex soil rheology. Case (ii) data were compared to modified versions of the phenomenological model of Fernandes and Wilson (2020), and a fully-coupled CFD model of the liquid and soil motion using the volume of fluid method. The modifications to the former did not improve its accuracy. The latter gave a good prediction of the initial cleaning behaviour for the case considered: the high computational cost precluded extensive testing.
Mixing characteristics and energy conversion in the coalescence process of the two droplets
Xiaoming Luo; Ke Xu; Wanrui Li; Xin Huang; Limin He;
Keywords:Coalescence;Internal mixing;Capillary pressure difference;Mixing mode;Interfacial tension ratio;Diameter ratio
Abstracts:In the case of fluid flow with a low Reynolds number, the internal fluid stratification can be easily observed after droplet coalescence, impeding rapid mixing of fluid. In this study, the capillary pressure difference is increased by adjusting the droplet size and the interfacial tension, so that a strong jet can be generated, resulting in a rapid mixing. Five distinct droplet mixing modes have been found. The phase diagram of the droplet mixing modes is obtained and the transition rule of the droplet mixing modes is established on this basis. A novel energy distribution model is employed to analyze the dependence between liquid bridge expansion and jet movement of two droplets. In addition, a criterion for evaluating the mixing efficiency of droplets is presented. The results presented in this paper provide a theoretical basis and practical guidance for realizing the efficient mixing of microfluids.
Dispersion phenomena of liquid droplet impacting on the single fiber with different wettabilities
Zhi-Hao Liu; Yan-Bin Li; Meng-Jun Su; Yong Luo; Guang-Wen Chu;
Keywords:Droplet dispersion;Single fiber;Surface wettability;CFD simulation;Dynamic contact angle
Abstracts:The impaction process of droplet on fiber (used as packing) including capture and dispersion is widely encountered in the multiphase reactors. Numerous studies have been conducted to illustrate the captured phenomena, while the phenomena and mechanism of dispersion are still unclear. In this work, the high-speed photography and computational fluid dynamics simulation were employed to investigate the dispersion phenomena of liquid droplet impacting on the single fiber with different wettabilities. Three flow patterns, named one-drop, one-film, and two-film dripping were observed from experimental results. Four contact angle models were implemented in the simulation. The gas–liquid interfacial area and energy utilization efficiency respectively increased from 1.85 to 3.38 times of initial area and from 1.97 % to 48.29 % when the contact angle increased from 45° to 155°. The results are of great significance to understand the dispersion phenomena as well as the enhanced dispersion efficiency of liquid in chemical reactors.
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