APPLICATION OF THE SHRINKING CORE MODEL TO THE KINETICS OF ZINC OXIDE DESULFURIZATION

The kinetics of H2S 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 H2S 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 H2S at the controlled stages were discussed.

Shell and shrinking core kinetics model of Mg-based hydrogen storage alloys

The kinetics equation of the Mg-based hydrogen storage alloys (Mg-Ni-MO) was established by the shell and shrinking core model. The total coefficients of the kinetics equation of the hydrogen absorption and desorption process with shell diffusion as the controlling step were determined by semi-empirical and semi-theoretical methods, and the apparent activation energy of the hydrogen absorption process was obtained. The calculation results can well accord with the experimental data, and can well forecast the hydrogen storage capacity and absorption rate at different times. By using the kinetics equation, the effects of temperature and pressure on the hydrogen storage process can also be well understood. The kinetics equation is helpful for the design of the hydrogen storage container.

Kinetics of zinc sulfide concentrate direct leaching in pilot plant scale and development of semi-empirical model

The direct leaching kinetics of an iron-poor zinc sulfide concentrate in the tubular reactor was examined.All tests werecarried out in the pilot plant.To allow the execution of hydrostatic pressure condition,the slurry with ferrous sulfate and sulfuric acidsolution was filled into a vertical tube(9m in height)and air was blown from the bottom of the reactor.The effects of initial acidconcentration,temperature,particle size,initial zinc sulfate concentration,pulp density and the concentration of Fe on the leachingkinetics were investigated.Results of the kinetic analysis indicate that direct leaching of zinc sulfide concentrate follows shrinkingcore model(SCM).This process was controlled by a chemical reaction with the apparent activation energy of49.7kJ/mol.Furthermore,a semi-empirical equation is obtained,showing that the order of the iron,sulfuric acid and zinc sulfate concentrationsand particle radius are0.982,0.189,-0.097and-0.992,respectively.Analysis of the unreacted and reacted sulfide particles bySEM-EDS shows that insensitive agitation in the reactor causes detachment of the sulfur layer from the particles surface in lowerthan60%Zn conversion and lixiviant in the face with sphalerite particles.

Optimization of process parameters and kinetic modelling for leaching of copper from oxidized copper ore in nitric acid solutions

The leaching behavior of Tunceli malachite mineral was investigated in nitric acid solutions by two steps to evaluate the effect of various experimental parameters.In the first step,the optimal conditions for the leaching process were determined,while in the second step,a kinetic evaluation for the process was performed.In the optimization experiments,the concentration of nitric acid,temperature,stirring speed,and solid-to-liquid ratio were selected as the independent variables,and the central composite design method(CCD)was applied to the experimental data.At the end of the experiments,the optimal values for the concentration of nitric acid,temperature,solid-to-liquid ratio and stirring speed were determined to be 0.5 mol/L,50℃,0.004 g/m L and 500 r/min,respectively.Under the optimal conditions,the leaching rate was found to be 99%for 120 min of reaction time.In the kinetic evaluation tests,the effects of the concentration of nitric acid,temperature,stirring speed,solid-to-liquid ratio and particle size on the leaching rate of copper from malachite were investigated.In these tests,it was determined that the leaching rate increased with the increase in the temperature,acid concentration and stirring speed,and with the decrease in the particle size and solid-to-liquid ratio.In consequence of the kinetic analysis,it was observed that the leaching kinetics followed the mixed kinetic model,and a mathematical model for the leaching process was introduced.The activation energy for this process was calculated to be 36.23 k J/mol.

乙二胺盐酸盐与氢氧化钙反应动力学

在双氨基硅烷偶联剂的工业生产过程中会产生大量的乙二胺盐酸盐副产物,该副产物通过与氢氧化钙进行中和反应得到无水乙二胺,可实现乙二胺的循环利用。利用电导率法建立乙二胺盐酸盐转化率和电导率的关系,考察了液固比、盐浓度、温度等因素对乙二胺盐酸盐转化率的影响,并确定了最优工艺条件。实验结果表明,乙二胺盐酸盐的转化率随着液固比及乙二胺盐酸盐浓度的增大而降低。基于缩芯模型,建立乙二胺盐酸盐和氢氧化钙的动力学方程。根据实验数据求出反应过程的活化能,发现乙二胺盐酸盐和氢氧化钙的中和反应主要受内部扩散控制。动力学模型为Kt=1-3(1-x)^(2/3)+2(1-x),活化能为30.89 kJ/mol。该研究为从乙二胺盐酸盐副产物提取无水乙二胺提供了实验依据。

Mass transfer process of peanut protein extracted by bis(2-ethylhexyl)sodium sulfosuccinate reverse micelles

The liquid-liquid extraction method using reverse micelles can simultaneously extract lipid and protein of oilseeds,which have become increasingly popular in recent years.However,there are few studies on mass transfer processes and models,which are helpful to better control the extraction process of oils and proteins.In this paper,mass transfer process of peanut protein extracted by bis(2-ethylhexyl)sodium sulfosuccinate(AOT)/isooctane reverse micelles was investigated.The effects of stirring speed(0,70,140,and 210 r/min),temperature of extraction(30,35,40,45,and 50℃),peanut flour particle size(0.355,0.450,0.600,and 0.900 mm)and solidliquid ratio(0.010,0.0125,0.015,0.0175,and 0.020 g/mL)on extraction rate were examined.The results showed that extraction rate increased with temperature rising,particle size reduction as well as solid-liquid ratio increase respectively,while little effect of stirring speed(P>0.05)was observed.The apparent activation energy of extraction process was calculated as 10.02 kJ/mol and Arrhenius constant(A)was 1.91 by Arrhenius equation.There was a linear relationship between reaction rate constant and the square of the inverse of initial particle radius(1/r_(0)^(2))(P<0.05).This phenomenon and this shrinking core model were anastomosed.In brief,the extraction process was controlled by the diffusion of protein from the virgin zone interface of particle through the reacted zone and it was in line with the first order reaction.Mass transfer kinetics of peanut protein extracted by reverse micelles was established and it was verified by experimental results.The results provide an important theoretical guidance for industrial production of peanut protein separation and purification.

Establishment and verification of a shrinking core model for dilute acid hydrolysis of lignocellulose

The kinetics oflignocellulose hydrolysis under the conditions of high temperature and dilute acid （mass fraction 0.05%） was investigated in this paper. By studying the reducing sugar concentration versus reaction tempera ture （170℃-220℃） and reaction time （150-1800 s） during the hydrolysis process of five kinds of crop straw （rice, wheat, cotton, rape and corn）, the shrinking core model was established, and the differential equation of the model and its analytical solution were obtained. With a numerical calculation method, the kinetic equation was estimated, and the degradation of reducing sugar obeyed firstorder kinetics was obtained. The calculated results from the equations agreed well with the original experimental data. The calculation by the model showed that the reducing sugar concentration increases as the size of the particles decrease, and the uniform particles increase.

Li_4Ti_5O_(12)的合成及对Li^+的离子交换动力学

用溶胶-凝胶法合成出Li4Ti5O12,对其进行了酸改性,制得锂离子筛IE-H.测定了IE-H对Li+、Na+的饱和交换容量和pH滴定曲线等离子交换性能,并对其进行了X射线衍射分析,同时采用中断接触法判断该离子交换反应的控制机理,用缩核模型描述离子筛IE-H交换Li+的动力学.结果表明,合成出的Li4Ti5O12和锂离子筛IE-H均为尖晶石结构;用不同浓度HNO3溶液处理Li4Ti5O12时,Li+的抽出率为19.6%-81.5%,Ti4+的抽出率在4.2%以下;锂离子筛IE-H对Li+的饱和交换容量较高,达到5.95mmol·g-1,离子筛IE-H交换Li+的控制步骤是颗粒扩散控制(PDC),得到了25℃,Li+浓度为20.0mmol·L-1和5.0mmol·L-1时锂离子筛交换Li+的动力学方程和颗粒扩散系数.

湿法浸出粘土矿中钒的动力学

为了提高湿法浸出粘土矿中钒的综合浸出效率,并对湿法浸出粘土矿中钒提供理论依据,从动力学角度分析整个浸出过程。考察温度、液固比、硫酸质量分数和搅拌速率对浸出过程的影响。研究结果表明:在80℃、液固比为4?1以及硫酸质量分数为20%时,浸取8h,粘土矿中钒的浸出率可达到92.3%。经正交实验和动力学推导,得到描述浸出过程的经验方程,粘土矿湿法浸出钒的动力学模型为收缩核动力学模型,浸出表观活化能为11.611kJ/mol,该模型表明浸出过程中的控制步骤是决定于固膜扩散速率。提高温度、液固比和硫酸质量分数,均可加速钒的浸出速度,提高钒的浸出率。

钛酸锌高温煤气脱硫剂再生行为的研究

在热天平装置上研究了再生反应温度、反应气体中氧气体积分数、脱硫剂颗粒粒径对钛酸锌高温煤气脱硫剂再生行为的影响。实验结果表明,较高的反应温度和氧气体积分数,较小的颗粒粒径有利于提高脱硫剂的再生反应速率。由于二次反应的影响,脱硫剂再生过程中有硫酸盐生成,提高反应温度或降低反应气体的氧气体积分数可以减少硫酸盐的生成。利用收缩核模型对其动力学行为进行了分析,结果表明,脱硫剂的再生过程存在动力学控制步骤的转移。脱硫剂再生转化率较低(<65%)时,再生过程主要受化学反应控制;再生转化率较高(>75%)时,再生过程主要受颗粒内扩散控制。表观化学反应速率常数的指前因子为8.01×10-2m/s,活化能为19.11 kJ/mol;有效扩散系数的指前因子为3.12×10-4m2/s,扩散活化能为48.84 kJ/mol。

磷石膏还原分解过程中CaS的产生机理分析

在N2气氛下,利用热重分析仪和管式炉,研究了不同粒径还原剂高硫煤条件下磷石膏分解过程中CaS的产生机理.结果表明:在1 000～1 150℃的范围内,CaS主要是由磷石膏中的CaSO4与高硫煤气化产生的CO反应产生.在CaSO4分解过程中CaS与CaO的生成反应存在明显的平行竞争现象.CaS的产生机理可以通过缩芯模型进行合理解释.对磷石膏分解的固相及气相产物进行的物性分析表明,不同粒径高硫煤对CaS生成量的影响主要是通过控制煤粉气化过程及后续反应来实现的.

超声波辅助硫化镍矿氧化浸出动力学

选用过硫酸盐+银盐作氧化剂,在超声波作用下对硫化镍矿进行直接氧化浸出,研究搅拌速率、过硫酸钠浓度、浸出温度、银盐浓度及粒度对镍浸出率的影响规律,探讨氧化浸出反应机理。结果表明:在一定范围内,在超声波作用下搅拌速率或者粒度的变化对镍浸出率影响不显著;镍浸出率随Na2S2O8浓度的增大以及温度的升高而增加,但是当温度高于70℃后,浸出率的增加不明显;在浸出过程中起主导作用的是S2O82-,少量银盐的存在对浸出反应有促进作用。通过对该体系浸出过程动力学参数的考察,发现其符合缩核模型,过程总体反应速率受界面化学反应控制,表观活化能为39.67kJ/mol,建立了浸出过程的宏观动力学方程。

典型农业生物质催化气化反应动力学特性研究

以CaO、MgO和Fe_2O_3为催化剂,用程序升温热重法对典型农业生物质催化气化特性及反应动力学进行了研究。利用均相反应模型和缩核反应模型对转化率与温度的关系进行了拟和计算,得到了谷壳样在4种不同二氧化碳气化条件下热解阶段及焦炭气化阶段的活化能和指数前因子。结果表明,在820～1000℃区间内,添加CaO的谷壳样表观活化能比谷壳的大;而添加MgO和Fe_2O_3的谷壳样表观活化能与谷壳的相比,分别下降了32.6%和17.9%以上,可以看出3种催化剂催化活性大小顺序为MgO>Fe_2O_3>CaO,活化能区间范围为15.25～123.74kJ/ mol。研究表明在低温区间(热解阶段),反应机理更趋向于均相反应模型,而在高温区间(气化阶段),反应机理更趋向于缩核反应模型。最后给出了谷壳在热解阶段及焦炭气化阶段的反应动力学方程。

湿法炼锌废渣中硫脲浸出银的动力学

探讨了从湿法炼锌废渣中用硫脲浸出回收银的浸出反应动力学 ,从这种难浸的含银炼锌废渣中用硫脲浸出回收银 ,浸出反应是一种典型的氧化还原反应并可充分进行。同时 ,通过动力学推导得出 ,从湿法炼锌废渣中用硫脲浸出银的反应动力学模型为收缩核动力学模型 ,同时计算出浸出活化能为 13.2 6kJ/mol。该模型反映了浸出过程中控制整个反应速率的决定步骤是固膜扩散速率 。

氘化锂粉末与O_2,CO_2和水汽的反应动力学研究

研究了28℃下,氘化锂粉末与O2,CO2和水汽的反应动力学。结果表明,氘化锂与O2,CO2的反应很微弱,而与水汽的反应速率相对要大得多。室温下氘化锂与水汽的反应可用收缩未反应芯模型来描述,界面化学反应为二级反应,反应速率常数为0 281kPa-1·min-1。

一氧化碳还原热解硫酸镁制备高纯氧化镁

利用菱镁矿和工业纯硫酸制备七水硫酸镁,进一步脱水得到无水硫酸镁。以无水硫酸镁和CO气体为原料,经高温煅烧制备高纯氧化镁,考察硫酸镁粒径、CO气体流量、煅烧温度和煅烧时间对硫酸镁转化率的影响。通过单因素实验确定的最佳工艺条件为:粒径51.8μm,CO气体流量30 mL/min,煅烧温度800℃,煅烧时间2.0 h。样品氧化镁经X射线衍射和扫描电镜表征,纯度达到99%,其平均粒径为40nm,单分子表面为多孔蓬松状。经实验和动力学推导得到描述热解过程的经验方程,CO气体还原热解硫酸镁的动力学模型为收缩核动力学模型,热解表观活化能为234.055 kJ/mol,该模型表明热解过程中的控制步骤决定于氧化还原速率。

焦炭溶损反应动力学及其模型研究

利用未反应核收缩模型对高炉焦炭与CO2的反应动力学进行了研究,建立了以可测参数(R)表达的焦炭与CO2的反应动力学关系式。并对反应速率常数和有效扩散系数、表观反应活化能和有效扩散活化能及反应过程中各步骤阻力进行了分析。结果表明,(1)焦炭与CO2的反应符合未反应核收缩模型。(2)反应的表观活化能Ea=124.5 kJ/mol,有效扩散活化能ED=642.4 kJ/mol;界面化学反应的阻力随反应温度升高而增加;残余灰层内的内扩散传质阻力相对比例随温度升高而下降。(3)焦炭溶损反应在低温区主要受内扩散控制,随着温度升高,反应由外扩散、化学反应和内扩散三步控制;当进入高温区,反应进行一段时间后主要受内扩散控制。

磷酸分解磷矿石的动力学

采用间歇反应器，在反应温度６０８０℃，磷酸浓度２０４０％Ｐ２Ｏ５，磷矿粒径０．１３８０．７ｍｍ，搅拌速度５００转／分的条件下，研究了磷酸分解上蒜磷矿的酸解反应动力学。研究表明，在上述条件下，该过程的速率控制步骤为氢离子通过Ｃａ（Ｈ２ＰＯ４）２的固态膜向反应界面的扩散。并建立了酸解过程的动力学模型，该模型在α＝０．０５上显著。表观活化能Ｅａ＝１０．０８ｋＪ·ｍｏｌ－１。

LiNi_(0.05)Mn_(1.95)O_4的合成及对Li^+的离子交换动力学

用溶胶-凝胶法合成出尖晶石结构的LiNi0.05Mn1.95O4,用0.5mol·L-1过硫酸铵对其进行改型,制得锂离子筛LiNiMn-H。LiNiMn-H对Li+的饱和交换容量达5.2mmol·g-1。用缩核模型(Shrinking-Core Model)处理该离子交换的反应动力学数据得到LiNiMn-H吸附Li+时离子交换反应的控制步骤是颗粒扩散控制(PDC),同时得到了该实验条件下锂离子筛LiNiMn-H吸附Li+的动力学方程和颗粒扩散系数De。

煤在燃烧过程中灰层有效扩散系数的实验研究与应用

搭建了大颗粒热重实验台,通过测量焦炭反应速率得出有效扩散系数的变化规律.将有效扩散系数的实验拟合表达式应用于整体层燃模型,得到改进的层燃模型,并对改进前后层燃模型的预测结果与实炉测量结果进行了比较.结果表明:不同煤种的有效扩散系数均随着反应的进行而减小,且与灰层厚度之间符合指数关系;煤种和温度是有效扩散系数的重要影响因素,无烟煤的初始有效扩散系数比烟煤的小,有效扩散系数的下降速率比烟煤快;反应温度高于灰熔点时会引起烧结现象,使有效扩散系数减小;考虑灰层生长对有效扩散系数影响的模型可以更准确地预测床层燃烧的气体产物分布和燃烧速率.