Records with Subject: Reaction Engineering
Showing records 1 to 25 of 91. [First] Page: 1 2 3 4 Last
Thermochemical Conversion of Napier Grass for Production of Renewable Syngas
Mohamad Syazarudin Md Said, Wan Azlina Wan Abdul Karim Ghani, Tan Hong Boon, Siti Aslina Hussain, Denny Kok Sum Ng
December 9, 2019 (v1)
Keywords: energy crop, gasification, Napier grass, Renewable and Sustainable Energy, solid biofuel
Fuel resource diversification is a global effort to deviate from non-renewable fossil fuels. Biomass has been identified as an alternative solid biofuel source due to its desirable properties and carbon neutrality. As reported in the literature, biomass can positively contribute towards combating climate change while providing alleviation for energy security issue. As part of efforts to diversify biomass resources, this work intends to explore the potential of Napier grass, one type of energy crop, for the production of renewable syngas via gasification. This energy crop is originally from Africa, which is highly productive with low cost (40 tonnes per year per hectare). Limited studies were conducted to analyze the potential of such an energy crop as a fuel source, which is the subject of this work. In order to analyze the full potential of such energy crop, the physical and chemical characteristics of this biomass was first analyzed. To determine the productivity of syngas from this... [more]
A Theoretical and Experimental Study for Screening Inhibitors for Styrene Polymerization
Ali Darvishi, Mohammad Reza Rahimpour, Sona Raeissi
December 9, 2019 (v1)
Keywords: density functional theory, inhibitors, phenolic, polymerization, stable nitroxide radicals, styrene
Styrene is one of the most important monomers utilized in the synthesis of various polymers. Nevertheless, during distillation, storage, and transportation of ST, undesired polymer (i.e., UP) formation can take place. Thus, the control of undesired polymerization of styrene is a challenging issue facing industry. To tackle the mentioned issue, the antipolymer and antioxidant activity of stable nitroxide radicals (i.e., SNRs) and phenolics in styrene polymerization were studied by density functional theory (DFT) calculation and experimental approach. The electrophilicity index and growth percentage have been determined by DFT calculation and experimental approach, respectively. It is depicted that 2,6-di-tert-butyl-4-methoxyphenol (DTBMP) and 2,6-di-tert-butyl-4-methylphenol (BHT) from phenolics, and 4-hydroxy-2,2,6,6-tetramethyl piperidine 1-Oxyl (4-hydroxy-TEMPO) and 4-oxo-2,2,6,6-tetramethylpiperidine 1-Oxyl (4-oxo-TEMPO) from stable nitroxide radicals were the most effective inhibit... [more]
An Overview of Temperature Issues in Microwave-Assisted Pyrolysis
Mattia Bartoli, Marco Frediani, Cedric Briens, Franco Berruti, Luca Rosi
December 3, 2019 (v1)
Keywords: microwave, pyrolysis, temperature control
Microwave-assisted pyrolysis is a promising thermochemical technique to convert waste polymers and biomass into raw chemicals and fuels. However, this process involves several issues related to the interactions between materials and microwaves. Consequently, the control of temperature during microwave-assisted pyrolysis is a hard task both for measurement and uniformity during the overall pyrolytic run. In this review, we introduce some of the main theoretical aspects of the microwaves−materials interactions alongside the issues related to microwave pyrolytic processability of materials.
Numerical Investigation of Solid-Fueled Chemical Looping Combustion Process Utilizing Char for Carbon Capture
Xiaojia Wang, Xianli Liu, Yong Zhang, Bo Zhang, Baosheng Jin
November 24, 2019 (v1)
Keywords: bubbling fluidized bed, char, chemical looping combustion, fuel reactor, numerical simulation
The in-depth understanding of the gas−solid flow and reaction behaviors, and their coupling characteristics during the chemical looping combustion (CLC) process has the guiding significance for the operation and optimization of a chemical looping combustor. A three-dimensional numerical model is applied to investigate the char-fueled CLC characteristics in a fuel reactor for efficient CO2 separation and capture. Simulations are carried out in a bubbling fluidized bed fuel reactor with a height of 2.0 m and a diameter of 0.22 m. The initial bed height is 1.1 m, and hence the height−diameter ratio of the slumped bed is five. The oxygen carrier is prepared with 14 wt% of CuO on 86 wt% of inert Al2O3. In the process of mathematical modeling, a Eulerian-Eulerian two-fluid model is adopted for both of the gas and solid phases. Gas turbulence is modeled on the basis of a k−ε turbulent model. The reaction kinetics parameters are addressed based upon previous experimental investigations from li... [more]
Insights into Kinetics of Methane Hydrate Formation in the Presence of Surfactants
Jyoti Shanker Pandey, Yousef Jouljamal Daas, Nicolas von Solms
November 24, 2019 (v1)
Keywords: gas uptake, induction time, methane hydrate, rocking cell, sodium dodecyl sulfate
Sodium dodecyl sulfate (SDS) is a well-known surfactant, which can accelerate methane hydrate formation. In this work, methane hydrate formation kinetics were studied in the presence of SDS using a rocking cell apparatus in both temperature-ramping and isothermal modes. Ramping and isothermal experiments together suggest that SDS concentration plays a vital role in the formation kinetics of methane hydrate, both in terms of induction time and of final gas uptake. There is a trade-off between growth rate and gas uptake for the optimum SDS concentration, such that an increase in SDS concentration decreases the induction time but also decreases the gas storage capacity for a given volume. The experiments also confirm the potential use of the rocking cell for investigating hydrate promoters. It allows multiple systems to run in parallel at similar experimental temperature and pressure conditions, thus shortening the total experimentation time. Understanding methane hydrate formation and st... [more]
Improvement of Catalytic Activity of Platinum Nanoparticles Decorated Carbon Graphene Composite on Oxygen Electroreduction for Fuel Cells
Halima Begum, Young-Bae Kim
November 24, 2019 (v1)
Keywords: composite, Fuel Cells, graphene, oxygen reduction reaction, platinum carbon
High-performance platinum (Pt)-based catalyst development is crucially important for reducing high overpotential of sluggish oxygen reduction reaction (ORR) at Pt-based electrocatalysts, although the high cost and scarcity in nature of Pt are profoundly hampering the practical use of it in fuel cells. Thus, the enhancing activity of Pt-based electrocatalysts with minimal Pt-loading through alloy, core−shell or composite making has been implemented. This article deals with enhancing electrocatalytic activity on ORR of commercially available platinum/carbon (Pt/C) with graphene sheets through a simple composite making. The Pt/C with graphene sheets composite materials (denoted as Pt/Cx:G10−x) have been characterized by several instrumental measurements. It shows that the Pt nanoparticles (NPs) from the Pt/C have been transferred towards the π-conjugated systems of the graphene sheets with better monolayer dispersion. The optimized Pt/C8:G2 composite has higher specific surface area and b... [more]
Understanding the Lack of Reactivity of 2,4-Dihydroxybenzaldehyde Towards the Biginelli Adduct Using Density Functional Theory Molecular Modeling
Virginia Flores-Morales, Eduardo D. Ayala-Medrano, José García-Elías, Margarita L. Martínez-Fierro, Edgar Marquez, José Mora
October 26, 2019 (v1)
Keywords: density functional theory, dihydropyrimidinthione derivatives, intermediaries, mechanism reaction, one-pot reaction
The Biginelli reaction is a multicomponent reaction for obtaining dihydropyrimidinthiones quickly, with multiple substitution patterns. The reaction mechanism remains unclear. Three possible pathways proposed for the reaction are the iminium route, an enamine intermediate, and the Knoevenagel pathway. However, when thiourea was used, no theoretical calculations were reported. Thus, based on the literature, the iminium pathway was used to obtain evidence explaining the lack of reactivity of 2,4-dihydroxybenzaldehyde towards the Biginelli adduct, compared with 4-hydroxybenzaldehyde. This computational study, carried out using the B3LYP/6-31++G(d,p) level of theory, showed an increment of 150 kJ/mol in the activation energy of the slowest pathway, due to the presence of a hydroxyl group in position 2 (ortho) of the aromatic aldehyde, decreasing its reactivity. Natural bond orbital (NBO) calculations suggest that the determinant steps are simultaneous, i.e., the polarization of the carbony... [more]
On the Recovery of PLP-Molar Mass Distribution at High Laser Frequencies: A Simulation Study
Shaghayegh Hamzehlou, M. Ali Aboudzadeh, Yuri Reyes
October 26, 2019 (v1)
Keywords: degree of branching, n-butyl acrylate, PLP-SEC
Due to the inherent difficulties in determination of the degree of branching for polymers produced in pulsed laser polymerization (PLP) experiments, the behavior of the degree of branching and backbiting reaction in high laser frequency and relatively high reaction temperatures have not been well-established. Herein, through a simulation study, the validity of different explanations on the recovery of PLP-molar mass distribution at high laser frequencies is discussed. It is shown that the reduction of the backbiting reaction rate at high laser frequency, and consequent decrease in the degree of branching, is not a necessary condition for recovering the PLP-molar mass distribution. The findings of this work provide simulation support to a previous explanation about the possibility of using high laser frequency for reliable determination of the propagation rate coefficient for acrylic monomers.
Aqueous and Enzymatic Extraction of Oil and Protein from Almond Cake: A Comparative Study
Thaiza S. P. Souza, Fernanda F. G. Dias, Maria G. B. Koblitz, Juliana M. L. N. de M. Bell
September 23, 2019 (v1)
Keywords: almond cake, aqueous extraction, oil extraction, protein extraction, solubility
The almond cake is a protein- and oil-rich by-product of the mechanical expression of almond oil that has the potential to be used as a source of valuable proteins and lipids for food applications. The objectives of this study were to evaluate the individual and combined effects of solids-to-liquid ratio (SLR), reaction time, and enzyme use on oil and protein extraction yields from almond cake. A central composite rotatable design was employed to maximize the overall extractability and distribution of extracted components among the fractions generated by the aqueous (AEP) and enzyme-assisted aqueous extraction process (EAEP). Simultaneous extraction of oil and protein by the AEP was favored by the use of low SLR (1:12.82) and longer reaction times (2 h), where extraction yields of 48.2% and 70% were achieved, respectively. Increased use of enzyme (0.85%) in the EAEP resulted in higher oil (50%) and protein (75%) extraction yields in a shorter reaction time (1 h), compared with the AEP... [more]
Lanthanum Effect on Ni/Al2O3 as a Catalyst Applied in Steam Reforming of Glycerol for Hydrogen Production
Nuria Sánchez, José María Encinar, Sergio Nogales, Juan Félix González
September 23, 2019 (v1)
Keywords: biodiesel, Hydrogen, non-noble transition metals, Syngas, X-ray photoelectron spectroscopy
Nowadays, the massive production of biodiesel leads to a surplus of glycerol. Thus, new applications of this by-product are being developed. In this study, glycerol steam reforming was carried out with Ni catalysts supported on Al2O3 rings and La-modified Al2O3. The catalysts were characterized by N2 physical adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and thermogravimetry. Both catalysts were effective in glycerol steam reforming. However, Ni/Al2O3 activity decreased over reaction time. Ni/La2O3/Al2O3 showed the best stability during the reaction. In addition, the activity of the modified support, La2O3/Al2O3, was evaluated. The modification of the support lent catalytic properties to the solid. Some conditions such as catalyst arrangement (catalyst in the first or second reactor), space velocity, and reaction temperature were studied. The highest hydrogen production was obtained when half the amount of the catalyst was located in bot... [more]
Recent Novel Hybrid Pd−Fe3O4 Nanoparticles as Catalysts for Various C−C Coupling Reactions
Sanha Jang, Shamim Ahmed Hira, Dicky Annas, Sehwan Song, Mohammad Yusuf, Ji Chan Park, Sungkyun Park, Kang Hyun Park
September 13, 2019 (v1)
Keywords: C–C coupling reaction, heterogeneous catalyst, hybrid catalyst, Pd–Fe3O4 nanoparticles
The use of nanostructure materials as heterogeneous catalysts in the synthesis of organic compounds have been receiving more attention in the rapid developing area of nanotechnology. In this review, we mainly focused on our own work on the synthesis of hybrid palladium−iron oxide nanoparticles. We discuss the synthesis of Pd−Fe3O4—both morphology-controlled synthesis of Pd−Fe3O4 and transition metal-loaded Pd−Fe3O4—as well as its application in various C−C coupling reactions. In the case of rose-like Pd−Fe3O4 hybrid nanoparticles, thermal decomposition can be used instead of oxidants or reductants, and morphology can be easily controlled. We have developed a method for the synthesis of nanoparticles that is facile and eco-friendly. The catalyst was recyclable for up to five continual cycles without significant loss of catalytic activity and may provide a great platform as a catalyst for other organic reactions in the near future.
Kinetics of Arsenic Removal in Waste Acid by the Combination of CuSO4 and Zero-Valent Iron
Yunhao Xi, Yongguang Luo, Jingtian Zou, Jing Li, Tianqi Liao, Libo Zhang, Chen Wang, Xiteng Li, Guo Lin
September 5, 2019 (v1)
Keywords: arsenic, kinetic, waste acid, zero-valent iron
In this study, we investigated the kinetics of arsenic removal from waste acid by the combination of zero-valent iron (ZVI) and CuSO4. ZVI samples were characterized by X-ray diffraction and scanning electron microscopy before and after arsenic removal; the results showed that after the arsenic removal reaction, As2O3 and magnetite phases were detected on the surface of these samples. Kinetic studies were carried out under different reaction temperatures, with different CuSO4 concentrations, and with different iron to arsenic molar ratios (Fe/As). The kinetic data of the arsenic removal were fitted to different kinetic models. The fitting results showed that the arsenic removal process could be described by the shrinking core model, controlled by residual layer diffusion. The apparent activation energy of the reaction was 9.0628 kJ/mol, the reaction order with the CuSO4 concentrations was −0.12681, and the reaction order with the molar ratio of iron to arsenic (Fe/As) was 3.152.
Modeling of the Free Radical Copolymerization Kinetics of n-Butyl Acrylate, Methyl Methacrylate and 2-Ethylhexyl Acrylate Using PREDICI®
Javier A. Gómez-Reguera, Eduardo Vivaldo-Lima, Vida A. Gabriel, Marc A. Dubé
September 5, 2019 (v1)
Keywords: 2-ethylhexyl acrylate, methyl methacrylate, Modelling, n-butyl acrylate, polymerization kinetics
Kinetic modeling of the bulk free radical copolymerizations of n-butyl acrylate (BA) and 2-ethylhexyl acrylate (EHA); methyl methacrylate (MMA) and EHA; as well as BA, MMA and EHA was performed using the software PREDICI®. Predicted results of conversion versus time, composition versus conversion, and molecular weight development are compared against experimental data at different feed compositions. Diffusion-controlled effects and backbiting for BA were incorporated into the model as they proved to be significant in these polymerizations. The set of estimated global parameters allows one to assess the performance of these copolymerization systems over a wide range of monomer compositions.
The Effect of Various Nanofluids on Absorption Intensification of CO2/SO2 in a Single-Bubble Column
Soroush Karamian, Dariush Mowla, Feridun Esmaeilzadeh
September 5, 2019 (v1)
Keywords: absorption intensification, bubble column, mass transfer coefficient, nanofluids
Application of nanoparticles in aqueous base-fluids for intensification of absorption rate is an efficient method for absorption progress within the system incorporating bubble-liquid process. In this research, SO2 and CO2 were separately injected as single raising bubbles containing nanofluids to study the impact of nanoparticle effects on acidic gases absorption. In order to do this, comprehensive experimental studies were done. These works also tried to investigate the effect of different nanofluids such as water/Al2O3 or water/Fe2O3 or water/SiO2 on the absorption rate. The results showed that the absorption of CO2 and SO2 in nanofluids significantly increases up to 77 percent in comparison with base fluid. It was also observed that the type of gas molecules and nanoparticles determine the mechanism of mass transfer enhancement by nanofluids. Additionally, our findings indicated that the values of mass transfer coefficient of SO2 in water/Al2O3, water/Fe2O3 and water/SiO2 nanofluid... [more]
Separating Electronic from Steric Effects in Ethene/α-Olefin Copolymerization: A Case Study on Octahedral [ONNO] Zr-Catalysts
Francesco Zaccaria, Roberta Cipullo, Andrea Correa, Peter H. M. Budzelaar, Vincenzo Busico, Christian Ehm
August 15, 2019 (v1)
Keywords: DFT, electronic effects, insertion kinetics, olefin capture, olefin copolymerization, post-metallocene, reactivity ratios, salan catalysts
Four Cl/Me substituted [ONNO] Zr-catalysts have been tested in ethene/α-olefin polymerization. Replacing electron-donating methyl with isosteric but electron-withdrawing chlorine substituents results in a significant increase of comonomer incorporation. Exploration of steric and electronic properties of the ancillary ligand by DFT confirm that relative reactivity ratios are mainly determined by the electrophilicity of the metal center. Furthermore, quantitative DFT modeling of propagation barriers that determine polymerization kinetics reveals that electronic effects observed in these catalysts affect relative barriers for insertion and a capture-like transition state (TS).
Dynamic Modelling of Phosphorolytic Cleavage Catalyzed by Pyrimidine-Nucleoside Phosphorylase
Robert T. Giessmann, Niels Krausch, Felix Kaspar, Mariano Nicolas Cruz Bournazou, Anke Wagner, Peter Neubauer, Matthias Gimpel
August 15, 2019 (v1)
Keywords: Dynamic Modelling, enzymatic reaction, ODE model, process kinetics, pyrimidine-nucleoside phosphorylase, reversible reaction, spectroscopic assay
Pyrimidine-nucleoside phosphorylases (Py-NPases) have a significant potential to contribute to the economic and ecological production of modified nucleosides. These can be produced via pentose-1-phosphates, an interesting but mostly labile and expensive precursor. Thus far, no dynamic model exists for the production process of pentose-1-phosphates, which involves the equilibrium state of the Py-NPase catalyzed reversible reaction. Previously developed enzymological models are based on the understanding of the structural principles of the enzyme and focus on the description of initial rates only. The model generation is further complicated, as Py-NPases accept two substrates which they convert to two products. To create a well-balanced model from accurate experimental data, we utilized an improved high-throughput spectroscopic assay to monitor reactions over the whole time course until equilibrium was reached. We examined the conversion of deoxythymidine and phosphate to deoxyribose-1-p... [more]
Catalytic Effect of NaCl on the Improvement of the Physicochemical Structure of Coal-Based Activated Carbons for SO2 Adsorption
Dongdong Liu, Rui Su, Zhengkai Hao, Xiaoman Zhao, Boyin Jia, Liangjie Dong
August 7, 2019 (v1)
Keywords: activated carbons, catalytic activation, physicochemical structure, SO2 adsorption
The utilization of coal-based activated carbons focuses on improving the physicochemical structure for achieving high-capacity. Herein, the catalytic effect of NaCl (1 and 3 wt%) in the presence of oxygen functional groups on the improvement of the physicochemical structure of coal-based activated carbons is studied in this work. A large quantity of Na can be retained in 1NaJXO and 3NaJXO with the presence of oxygen functional groups to promote further its catalytic characteristics during pyrolysis, resulting in the disordered transformation of the carbon structure. In addition, the development of micropores is mainly affected by the distribution and movement of Na catalyst, whereas the growth of mesopores is mainly influenced by the evolution of oxygen functional groups. Then, the active sites of 3NaJXO-800 can no longer be consumed preferentially in the presence of Na catalyst during subsequent CO2 activation to facilitate the sustained disordered conversion of the microstructure and... [more]
Experimental Study on Spent FCC Catalysts for the Catalytic Cracking Process of Waste Tires
Chuansheng Wang, Xiaolong Tian, Baishun Zhao, Lin Zhu, Shaoming Li
August 7, 2019 (v1)
Keywords: catalytic cracking, chemical raw materials, spent FCC catalysts, sulfur-containing material conversion, used tires
Research on the synergistic high-value reuse of waste tires and used catalysts in spent fluid catalytic cracking (FCC) catalysts was carried out in this study to address the serious ecological and environmental problems caused by waste tires and spent FCC catalysts. The experiment, in which a spent FCC catalyst was applied to the catalytic cracking of waste tires, fully utilized the residual activity of the spent FCC catalyst and was compared with a waste tire pyrolysis experiment. The comparative experimental results indicated that the spent FCC catalyst could improve the cracking efficiency of waste tires, increase the output of light oil in pyrolysis products, and improve the quality of pyrolysis oil. It could also be used for the conversion of sulfur compounds during cracking. The content of 2-methyl-1-propylene in catalytic cracking gas was found to be up to 65.59%, so a new method for producing high-value chemical raw materials by the catalytic cracking of waste tires with spent... [more]
Highly Porous Graphitic Activated Carbons from Lignite via Microwave Pretreatment and Iron-Catalyzed Graphitization at Low-Temperature for Supercapacitor Electrode Materials
Dongdong Liu, Xiaoman Zhao, Rui Su, Zhengkai Hao, Boyin Jia, Song Li, Liangjie Dong
July 31, 2019 (v1)
Keywords: activated carbons, graphitization, high porosity, supercapacitor material
At present, the preparation of highly porous graphitic activated carbons (HPGACs) using the usual physical and chemical activation methods has met a bottleneck. In this study, HPGACs are directly synthesized from lignite at 900 °C. The whole process is completed by a microwave pretreatment, a graphitization conversion of the carbon framework at a low temperature using a small amount of FeCl3 (10−30 wt%), and a subsequent physical activation using CO2. Consequently, the dispersed and mobile iron species, in the absence of oxygen functional groups (removed during the microwave pretreatment), can greatly promote catalytic graphitization during pyrolysis, and, as an activating catalyst, can further facilitate the porosity development during activation. The as-obtained AC-2FeHLH-5-41.4(H) presents a low defect density, high purity, and specific surface area of 1852.43 m2 g−1, which is far greater than the AC-HLH-5-55.6(H) obtained solely by physical activation. AC-2FeHLH-5-41.4(H) as a supe... [more]
Nitroxide-Mediated Copolymerization of Itaconate Esters with Styrene
Sepehr Kardan, Omar Garcia Valdez, Adrien Métafiot, Milan Maric
July 29, 2019 (v1)
Keywords: copolymerization, itaconate esters, nitroxide mediated polymerization
Replacing petro-based materials with renewably sourced ones has clearly been applied to polymers, such as those derived from itaconic acid (IA) and its derivatives. Di-n-butyl itaconate (DBI) was (co)polymerized via nitroxide mediated polymerization (NMP) to impart elastomeric (rubber) properties. Homopolymerization of DBI by NMP was not possible, due to a stable adduct being formed. However, DBI/styrene (S) copolymerization by NMP at various initial molar feed compositions fDBI,0 was polymerizable at different reaction temperatures (70−110 °C) in 1,4 dioxane solution. DBI/S copolymerizations largely obeyed first order kinetics for initial DBI compositions of 10% to 80%. Number-average molecular weight (Mn) versus conversion for various DBI/S copolymerizations however showed significant deviations from the theoretical Mn as a result of chain transfer reactions (that are more likely to occur at high temperatures) and/or the poor reactivity of DBI via an NMP mechanism. In order to suppre... [more]
High-Temperature Permittivity and Microwave Pretreatment Characteristics of Nickel-Containing Sludge from Battery Production
Zhanyong Guo, Ping Guo, Guang Su, Demei Zhai, Fang Cheng, Fachuang Li
July 29, 2019 (v1)
Keywords: dielectric properties, microwave, nickel-containing sludge
Permittivity is a vitally important parameter for the description of the absorption and heating characteristics of materials under microwave irradiation. In this paper, the permittivity of nickel-containing sludge (NCS), which is created during battery production as a cheap secondary resource, was measured at temperatures from 20 °C to 600 °C at 2.45 GHz using the cavity perturbation method. In addition, the loss tangent (tanδ) and penetration depth (Dp) of microwaves into the material were calculated. The results of the permittivity study show that the dielectric constant (ε′) and dielectric loss factor (ε″) of the NCS increase with increasing temperature. The variations of the loss tangent (tanδ) and penetration depth (Dp) with the temperature can be divided into two parts at 200 °C. The effect of the initial moisture content on the dielectric properties of the material is notably greater than that of the temperature, which was confirmed by the heating curve. After microwave pretreat... [more]
Mechanism and Modelling of Reactive Crystallization Process of Lithium Carbonate
Shaolei Zhao, Jie Gao, Siyang Ma, Chao Li, Yiming Ma, Yang He, Junbo Gong, Fu Zhou, Bingyuan Zhang, Weiwei Tang
July 28, 2019 (v1)
Keywords: crystallization mechanisms, lithium carbonate, multi-response optimization, reactive crystallization, response surface methodology
The reactive crystallization of lithium carbonate (Li2CO3) from lithium sulfate (Li2SO4) and sodium carbonate (Na2CO3) solutions is a key process in harvesting solid lithium, whether from ores, brines, or clays. However, the process kinetics and mechanism remain poorly understood and the modelling of the reactive crystallization of Li2CO3 is not available. Hence, this work aims to determine the kinetics and mechanisms of the nucleation and growth of Li2CO3 reactive crystallization by induction time measurements and to model and optimize the crystallization process using response surface methodology. Induction time measurements were carried out as functions of initial supersaturation and temperature using a laser method. It was found that the primary nucleation mechanism of Li2CO3 varies with solution supersaturations, in which, expectedly, the heterogenous nucleation mechanism dominates at low supersaturations while the homogeneous nucleation mode governs at high supersaturations. The... [more]
Study on the Adsorption, Diffusion and Permeation Selectivity of Shale Gas in Organics
Zhouhua Wang, Yun Li, Huang Liu, Fanhua Zeng, Ping Guo, Wei Jiang
July 26, 2019 (v1)
Keywords: adsorption diffusion, kerogen, molecular simulation, permeation selectivity, shale gas
As kerogen is the main organic component in shale, the adsorption capacity, diffusion and permeability of the gas in kerogen plays an important role in shale gas production. Based on the molecular model of type II kerogen, an organic nanoporous structure was established. The Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods were used to study the adsorption and diffusion capacity of mixed gas systems with different mole ratios of CO₂ and CH₄ in the foregoing nanoporous structure, and gas adsorption, isosteric heats of adsorption and self-diffusion coefficient were obtained. The selective permeation of gas components in the organic pores was further studied. The results show that CO₂ and CH₄ present physical adsorption in the organic nanopores. The adsorption capacity of CO₂ is larger than that of CH₄ in organic pores, but the self-diffusion coefficient of CH₄ in mixed gas is larger than that of CO₂. Moreover, the self-diffusion coefficient in the horizontal directi... [more]
Nanostructure and Oxidation Reactivity of Nascent Soot Particles in Ethylene/Pentanol Flames
Yaoyao Ying, Chenxuan Xu, Dong Liu, Bo Jiang, Pengfei Wang, Wei Wang
July 26, 2019 (v1)
Keywords: ethylene/pentanol flame, nanostructure, nascent soot particles, oxidation reactivity
As byproducts of the combustion process of hydrocarbon fuels, soot particles are difficult to remove, and they can greatly harm human health and pollute the environment. Therefore, the formation and growth processes of the soot particles has become a study focus of researchers. In this paper, the nanostructure and oxidation reactivity of carbonaceous particles collected from ethylene inverse diffusion flames with or without the additions of three pentanol isomers (1-pentanol, 3-methyl-1-butanol, and 2-methyl-1-butanol) were investigated in detail. The nanostructure and oxidation characteristics of nascent soot particles were characterized using high resolution transmission electron microscopy (HRTEM), X-ray diffractometry (XRD) and thermogravimetric analysis (TGA). It was found that the nascent soot cluster of pure ethylene flame had a loose structure, while the additions of pentanol isomers made the soot agglomerates more compact and delayed the growth of graphitic structures. The pen... [more]
Desorption Kinetics and Mechanisms of CO₂ on Amine-Based Mesoporous Silica Materials
Yang Teng, Zhilin Liu, Gang Xu, Kai Zhang
July 26, 2019 (v1)
Keywords: amine modified MCM-41, Avrami’s fractional model, desorption kinetics, film diffusion, intraparticle diffusion, zero length column
Tetraethylenepentamine (TEPA)-based mesoporous MCM-41 is used as the adsorbent to determine the CO₂ desorption kinetics of amine-modified materials after adsorption. The experimental data of CO₂ desorption as a function of time are derived by zero-length column at different temperatures (35, 50, and 70 °C) and analyzed by Avrami’s fractional-order kinetic model. A new method is used to distinguish the physical desorption and chemical desorption performance of surface-modified mesoporous MCM-41. The activation energy Ea of CO₂ physical desorption and chemical desorption calculated from Arrhenius equation are 15.86 kJ/mol and 57.15 kJ/mol, respectively. Furthermore, intraparticle diffusion and Boyd’s film models are selected to investigate the mechanism of CO₂ desorption from MCM-41 and surface-modified MCM-41. For MCM-41, there are three rate-limiting steps during the desorption process. Film diffusion is more prominent for the CO₂ desorption rates at low temperatures, and pore diffusio... [more]
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