MATHEMATICAL MODELING OF NON-CATALYTIC LIQUID-SOLID REACTION AND ITS SOLUTION BY ORTHOGONAL COLLOCATION

The mathematical model of non-catalytic liquid-solid diffusion reactions discussed in this paper can be applied to quite different cases. The models in the literature such as unreacted shrinking core model, two stage model and homogeneous model can be considered as special cases of the above model which has been derived for leaching vanadium from steel slag with sodium carbonate and]or sodium bicarbonate solution reacting with two components in the slag simultaneously. The vanadium leaching reaction is inhibited by the solid product formed during the reaction. The power law equation can be used to represent the kinetic experimental data of leaching reaction. The model equations have been solved by orthogonal collocation and semi-implicit Runge-Kutta method. The parameters of the model have been estimated by the complex method. The calculated results based on this model is in good agreement with experimental data.     

Application of the shrinking core model to the kinetics of zinc oxide desulfurization

The kinetics of H_2S removal by zinc oxide desulfurizer was studied through thermogravimetricanalysis.The experimental results show that desulfurization rate was controlled,at high temperatureand low conversion,by the chemical reaction rate,and at low temperature and high conversion by thegrain diffusion rate.The reaction is first order with respect to H_2S concentration in the differentcontrolled stages.The kinetic behavior can be modeled through the employment of the shrinking coremodel.The values of the model parameters were determined.The variation tendencies with temperatureand concentration of H_2S at the controlled stages were discussed.     

Useful experimental technique for the study of heterogeneous reactions

The heterogeneous CaO/SO₂ reaction has been thoroughly investigated by developing a series of new experimental techniques including the TGA reactor, the volulmetric reactor and the entrained flow reactor. The heterogeneous system is designed in such a way that most of the gas film and pore diffusion resistances are reduced. The modelling of each step related to the reaction is discussed while the chemical reaction and product layer diffusion are emphasized as the main influences on the SO₂removal. The unchanging size shrinking core model is used to describe the reaction progress with a two stage assumption which has been confirmed in the TGA reactor: first, a very fast surface reaction, followed by a product layer diffusion controlled reaction. It was found from the experiments that the SO₂-partial pressure aat the very beginning is very important for a high removal efficiency during the initial reaction period.     

The electrochemical reduction of VO2 in acidic solution at high overpotentials

An investigation has been carried out to attempt to understand the unusually low apparent symmetry factor observed during the reduction of V(5) at higher overpotentials at carbon electrodes (typically <0.13, or >460 mV decade⁻¹). This reaction is of interest because it occurs in vanadium redox-flow batteries (VRBs) during discharge. Polarisation curves were measured using a rotating disk electrode (RDE). The reaction was not solution mass transport controlled, was pH independent (ca from 0 to 1), and the observed Tafel slope was unaffected by V(5) concentration over a range from 0.031 to 280 mM. Electrode double layer capacitance measurements were also carried out in sulphuric acid with and without vanadium. These tests showed that the presence of V(5) caused a suppression of the normal carbon surface quinone pseudocapacitance, as well as the appearance of two new pseudocapacitance peaks, one around 0.175-0.2 V and the other around 0.675-0.725 V versus SCE. The observed results do not appear consistent with a precipitated film causing diffusion limitations or causing IR drop. A model is developed to try to explain the data, which involves electron transfer through an adsorbed layer of vanadium.     

T302锌锰系脱硫剂脱除H_2S在的宏观动力学

用热重法研究了T302锌锰系脱硫剂脱除H_2S的宏观动力学行为.实验表明,该过程对H_2S为一级反应.在200～400℃的温度范围,反应初期为表面反应控制,中后期转移为颗粒扩散控制.宏观动力学行为可用等效粒子模型来描述.表面反应及固体扩散活化能分别为11.842、20.865kJ/mol.对反应存在最佳温度及固体扩散活化能大于表面反应活化能进行了讨论.     

界面聚合制备复合膜过程的数学模型

基于高分子物理化学、质量传递和相分离成膜理论,研究在复合膜制备过程中采用界面聚合反应成膜的机理,建立了非稳态条件下反应．扩散联合控制的数学模型;通过有针对性地简化,该模型可适用于反应控制和扩散控制。模型中无量纲参数有明确的物理意义,较好地反映了界面聚合反应成膜过程的机理。无量纲化处理使模型解析解形式更为简单、实用,模型与实验数据吻合良好,且优于现有模型。通过模拟计算,可得出单体(A组分)浓度、膜的厚度、膜厚增长率随时间的变化关系,并可考察聚合反应速率常数、单体(A组分)在复合层中的扩散系数、单体初始浓度等参数对成膜过程的影响．理论结果可用于指导界面聚合反应成膜实践。     

T305脱硫剂脱除H2S反应宏观动力学行为

用热重法研究了T305氧化锌脱硫剂脱除H₂S反应的宏观动力学。研究表明,脱硫反应动力学行为可用等效粒子模型猫迷。给出了该模型的各参数估值,分析了孔扩散、粒子内扩散及烧结对反应行为的影响。     

D815树脂吸附钒的性能及动力学研究

实验研究了钒溶液在D815树脂上的吸附行为,并从热力学和动力学两个方面对吸附过程进行了分析.结果表明:在温度为30℃,pH为2.20,五氧化二钒初始浓度为15.0g/L条件下,树脂的饱和吸附容量达到最大值520 mg/g;在钒溶液流速为0.1 mL·min(-1)·g(-1)条件下,吸附经过2h左右达到穿透点,50 h...     

Cure kinetics of epoxy resin used for advanced composites

The cure kinetics of an epoxy resin used for the preparation of advanced polymeric composite structures was studied by isothermal differential scanning calorimetry (DSC). A series of isothermal DSC runs provided information about the kinetics of cure over a wide temperature range. According to the heat evolution behavior during the curing process, several influencing factors of isothermal curing reactions were evaluated. The results showed that the isothermal kinetic reaction of this epoxy resin followed an autocatalytic kinetic mechanism. In the latter reaction stage, the curing reaction became controlled mainly by diffusion. Cure rate was then modeled using a modified Kamal autocatalytic model that accounts for the shift from a chemically controlled reaction to a diffusion‐controlled reaction. The model parameters were determined by a nonlinear multiple regression method. Copyright © 2004 Society of Chemical Industry     

Removal of Metanil Yellow from its Aqueous Solution by Fly Ash and Activated Carbon Produced from Different Sources

Abstract

The present study has been undertaken to observe the relative efficiency of removal of metanil yellow from its aqueous solution by using different adsorbents like fly ash and activated carbon produced from different sources i.e. coconut shell, mehagani saw dust, and rice husk. It has also been observed that the rate of adsorption is highly dependent on contact time, adsorbent dose, pH, and initial concentration of the dyestuff. Rate of removal has been observed to increase with increasing contact time and adsorbent dose but with decreasing initial concentration. Higher removal has been observed generally in acidic range. Adsorptions by the adsorbents under investigation follow the Freundlich and Langmuir isotherm models where Freundlich and Langmuir constants have also been determined at different temperatures. Isotherms have been used to obtain the thermodynamic parameters like free energy, enthalpy and entropy of adsorption. Kinetic studies showed that all the adsorbents follow first order adsorption rate model with respect to the dye solution concentration. Various kinetic parameters such as first order adsorption rate constant, mass‐transfer co‐efficient, pore‐diffusion constant, and activation energy of adsorption were evaluated to establish the mechanism. Adsorption processes were found to be endothermic, spontaneous, and pore‐diffusion controlled for all the adsorbents. Among the adsorbents used in this study, activated carbon produced from mehagani saw dust has been found to be the most effective, which remove almost 100% metanil yellow from its 1000 ppm aqueous solution.     

Modeling methyl methacrylate free radical polymerization: Reaction in hydrophilic nanopores

In previous work, we developed a simplified model for the diffusion controlled bulk polymerization of methyl methacrylate and extended the model to capture the reaction under nanoconfinement. The calorimetric conversion versus time data in bulk and in silanized hydrophobic nanopores was well captured by the model. Here we further extend the model to capture the reaction in native hydrophilic controlled pore glass (CPG) nanopores accounting for catalysis by surface silanol groups. The ability of the model to describe experimental data is tested. In order to fit the data, the parameters describing monomer and active chain diffusion differ from that in hydrophobic pores.     

A two-dimensional model of second order rapid reactions in turbulent tubular reactors

Previous studies of second order rapid reactions in turbulent tubular reactors have been analyzed in terms of a one-dimensional model. Deviations between theory and experiment have been interpreted in terms of diffusion limited reaction rates. In this paper the experimental results are re-analyzed in terms of a two-dimensional model leading to the conclusion that mixing and entrance region effects are responsible for the deviations between the experimental results and one-dimensional theory. A new upper bound for the Damköhler number associated with diffusion controlled reaction rates is suggested.     

微波作用下二硫代氨基甲酸盐脱除重质原油中的镍钒

研究了微波强化作用下二硫代氨基甲酸盐NS系列化合物对新疆重质原油的脱镍钒效果.合成了具有—CSS—配位基团的NS系列化合物,该系列产物分子结构中—CSS—配位基团,可以与原油中的镍和钒发生配位反应形成水溶性化合物从而从原油中脱除.对于原油脱镍钒效果为NS3 >NS2 >NS4 >NS1,在微波强化作用下NS3脱镍钒剂对原油脱镍钒的实验表明,NS3加入量为200mg/L,微波时间为3min,微波功率为700W,反应温度为90℃和反应时间为20min的条件下,原油中镍和钒的脱除率分别为79.8%和82.4%,微波强化作用后原油的脱镍钒效率增加.     

二维颗粒反应的分数维模型

本文将分数维理论引入颗粒与流体的非均相反应系统,提出不规则颗粒二维反应的分数维模型.在假稳态条件下,对不规则颗粒的核收缩反应方程求得解析解.结果表明,当反应受膜扩散控制、灰层扩散控制和化学反应控制时,颗粒的分数维越高,反应总速率越快;而在膜扩散控制阶段,分数维对相对反应时间没有影响.     

Evaluation of Transport Phenomena for Removing Vanadium from Petrochemical Industry Solid Waste

Transport phenomena are investigated which are involved in the electrokinetic remediation process used for removing vanadium from deactivated catalysts from oil catalytic cracking that are currently allotted to cement plants and class-I landfills. Variables such as the concentration of electrolyte, electric potential, and applied electric current were evaluated in order to determine the effects produced by electroosmosis, diffusion, hydraulic gradient, and electromigration on the removal of vanadium from the catalyst. It was observed that migration is the most relevant phenomenon in the remediation tests, and for the best remediation condition, the migratory flow accounted for about 87 % of the vanadium removal.     

V、Mo修饰SBA-15分子筛结构与催化性质的DFT计算预测

采用密度泛函方法,计算了介空分子筛SBA-15及V和Mo原子修饰后分子筛的几何参数及红外光谱,与实测值比较,确定了分子筛的合理模型。通过分析模型化合物的前线分子轨道,推测了V和Mo原子修饰前后分子筛表面的酸碱中心及氧化还原性质。最后,由计算得到分子筛表面VO4和MoO5基团的Mayer键级推测,当此类催化剂参与酸碱和氧化还原反应时,基团上的三种化学键(MO─Si、M─OSi和MO)中,MO─Si键最容易断裂打开,参加化学反应。     

Removal of Hexavalent Chromium from Aqueous Solutions by Sodium Dodecyl Sulfate Stabilized Nano Zero-Valent Iron: A Kinetics,Equilibrium, Thermodynamics Study

Sodium dodecyl sulfate stable nanoscale zero-valent iron (SDS-nZVI) was synthesized by the sodium borohydride reduction method, characterized with SEM and XRD. SDS-nZVI was used for the removal of Cr (VI) from aqueous solutions at different conditions in a batch process. XRD analysis indicated the presence of iron oxide and iron-chromium hydroxide coprecipitation on the surface of SDS-nZVI after reaction some time. The reaction kinetics, mechanism, isotherms, and thermodynamics for Cr (VI) removal of aqueous solution via SDS-nZVI were investigated. The pseudo-second-order model was relatively suitable for describing the reaction process. Intraparticle diffusion model was used to analysis the mechanism, the results indicated that there were two processes (bulk diffusion and surface diffusion) controlling the reaction rate, while only one was rate limiting in any particular time range. The fitted Temkin and D-R model satisfactorily explanted the experimental data in the range of 303–343 K. The maximum removal capacity of SDS-nZVI for Cr (VI) was obtained for 336.7 mg g^?1 at 303 K. The overall removal process was endothermic. These results demonstrated that SDS-nZVI could potentially be used as an effective material for environmental remediation.     

Kinetics of polyvinyl butyral (PVB) synthesis reaction catalyzed by deep eutectic solvent

In this work, the kinetics of the polyvinyl butyral (PVB) synthesis reaction catalyzed by the deep eutectic solvents (DESs) at the low-temperature stage was studied to control the particle size of PVB resin and optimize its synthesis process. The effects of stirring speed, the concentration of polyvinyl alcohol (PVA), catalyst dosage, and temperature on the synthesis reaction of PVB were investigated. The data obtained from kinetic experiments at 283.15–298.15 K were fitted with the shrinking core models, and the results showed that the model controlled by internal diffusion fitted well with the experimental data. The internal diffusion coefficient, D_A, of n-butanal in the product layer was further calculated by the obtained model parameters, and it was applied to predict the synthesis reaction of PVB at different concentrations of n-butanal. The results indicated that the shrinking core model controlled by internal diffusion is suitable to describe the kinetics of the PVB synthesis reaction. DES played a dual role in catalysis and dispersion in the synthesis of PVB, and it was a green catalyst with good potential for PVB industrial applications.     

钒铬还原渣碱浸提钒工艺及其动力学

采用常压下空气氧化-碱浸工艺,对钒冶炼的钒铬还原渣进行提钒. 通过正交实验考察了碱浓度、浸出温度、液固比对钒浸出率的影响,研究了钒的浸出动力学. 结果表明,最佳条件为碱浓度100 g/L、浸出温度100℃、液固比4 mL/g、浸出时间1 h. 该条件下钒浸出率最高达98%. 钒的浸出过程符合核收缩模型,受扩散步骤控制,表观活化能为11.04 kJ/mol.