烟用改性聚丙烯滤材结构与性能研究 第Ⅰ报 EVA/PP共混物流变性的研究

采用孟山都加工性能测试仪研究了EVA/P共混物的流变性能。发现在所研究的温度剪切速率范围内,EVA/PP共混物的粘度随着EVA含量的增加而增加;共混物粘度对温度的依赖关系服从Arrhenius方程,即:η_a=A exp(E/RT);在较高的切变速率及温度范围内,共混物的粘度可用公式lgη_a =w_1lgη_a~1+w_2lgη_a~2来估算,理论估算值与实验值相当吻合。     

2-(1-环己烯基)环己酮合成反应的动力学

研究了环己酮在NJ1固体酸催化剂作用下合成2-(1-环己烯基)环己酮的反应规律,考察了反应温度、催化剂用量和移走反应生成的水对反应的影响,由实验数据按照二级连串反应拟合估算了动力学参数,建立了由环己酮合成2-(1-环己烯基)环己酮的主、副反应动力学模型,模型计算值与实验值拟合良好。     

ZSM—5沸石催化剂上甲苯／乙醇烷基化反应活性稳定性的初步预测

在其它反应条件不变的前提下,通过调变空速的方法,测出催化剂的稳空速点。稳空速点的测定,不但可以确定最佳空速条件,而且可做为初步预测反应活性稳定性的一种尝试。提出了催化剂的活性中心有效利用率η的概念。利用η的大小,可作为初步预测反应活性稳定性的另一种尝试。     

费托催化剂η-Fe2C(011)上CH4形成及C－C耦合机理研究

Fe_2C是低温Fe基费托催化剂的主要活性相,研究其上费托反应机理具有十分重要的意义。从原子尺度上通过密度泛函理论(DFT)计算研究了Fe_2C稳定晶相η-Fe_2C的(011)表面上甲烷形成和C—C耦合的反应机理。计算结果表明,η-Fe_2C(011)表面上甲烷形成的有效能垒为1.03 eV,其低于CH_i+CH_j耦合反应的有效能垒(1.52～2.98 eV),且最可能的C—C耦合反应路径为C+CH_3。进一步比较研究了η-Fe_2C(011)表面与其他Fe基费托催化剂表面之间的CH_4和C_(2+)选择性差异,发现选择性高度敏感于Fe基催化剂的表面与体相结构,其中η-Fe_2C(011)表面具有较高的甲烷选择性。     

烃类转化催化剂以及碳纤维载体孔结构表征参数的测定

在害功能扩散他装置上, 用定压稳态法, 以CH₄、N₂为扩散气体, 在实验条件下测得了天然气蒸汽转化催化剂及碳纤维载体的孔结构表征参数曲节因子。在常压及30～500 ℃范围内, 催化剂的曲节因子τ值为1.8~3.5;碳纤维载体的τ值为(5~9)×10^-3～(5~9)×10^-4。由本实验数据计算得到催化剂的有效因子是:C119-02(η)=0.165，Z107(η)=0.207，Z110y(η)=0.208,川Ⅲ型(η)=0.215，C10(η)=0.223，CN-18(η)=0.299。文中对所得结果进行了简要分析。碳纤维载体中所进行的扩散接近对流扩散状态, 表明它是一种理想的催化剂载体。     

用熔体的零切粘度和熔融指数研究聚丙烯的分子量分布

本文采用自制落球粘度计测定了用高效催化剂和化学降解两种方法生产的常用纤维级聚丙烯的零切粘度η_0,并与熔融指数仪测得的熔融指数MI值相结合求得聚丙烯分子量分布指数α值。研究表明,本法测得的η_0与熔体流变仪测得的η_0基本相符。本文还探讨了影响η_0测试的诸因素,在正确操作情况下,测试误差可小于5%。本仪器简单、价廉,在聚丙烯生产厂可推广使用作为指导生产工艺的依据。     

均匀设计在PCT合成工艺研究中的应用

采用均匀设计的方法,对聚对苯二甲酸1,4-环己烷二甲酯(PCT)熔融缩聚反应工艺条件进行了系统研究。以原料1,4-环己烷二甲醇(CHDM)与精对苯二甲酸(PTA)的物质的量之比n、熔融缩聚反应温度T、熔融缩聚反应时间t和催化剂浓度ccat为变量,以合成的PCT特性黏度[η]为指标,按照4因素7水平的均匀设计方案安排实验,根据实验结果拟合得到了各工艺参数与[η]之间的关系方程式,由该方程式得到了PCT熔融缩聚反应最优工艺条件:n为1.9,T为305.3℃;t为120 min;ccat为1 400μmol/mol PTA。在该最优工艺条件下,预测的[η]值为0.83 dL/g,与实际实验的验证结果相吻合。最后,基于最优工艺条件,讨论了各个工艺参数的变化对[η]的影响。结果发现,在实验考查范围内,随n和T的增加,[η]先升高后降低;随t的增加,[η]先快速升高而后其升高趋势逐渐变缓;[η]随ccat的增加呈线性增长的趋势。     

mPEG-b-PCL的酶催化反应挤出制备及其结构研究

以小型双螺杆挤出机为反应容器,以脂肪酶Novozyme-435为催化剂,采用反应挤出工艺,研究了甲氧基聚乙二醇(mPEG)引发ε-己内酯的开环聚合反应,制得甲氧基聚乙二醇-b-聚ε-己内酯(mPEG-b-PCL),考察了ε-己内酯单体转化率(η),mPEG的引发效率(η_(mPEG)),水对聚合反应的影响。结果表明:由核磁共振氢谱分析确定聚合产物为mPEG-b-PCL;在反应温度90℃条件下,反应时间为120,240,360 min时,η分别为82.01%,89.76%,92.61%,η_(mPEG)分别为28.17%,40.13%,35.31%,即η_(mPEG)先增加后降低;PCL链段的水解是η_(mPEG)降低的主要原因。     

球形催化剂颗粒内气体扩散及其有效因子

研究了三元催化器处理天然气汽车尾气过程中球形催化剂颗粒内的尾气扩散系数、浓度分布以及催化剂有效因子(η)等影响因素.结果表明,适当增大催化剂颗粒的平均孔半径或增大分子的平均自由程,可使扩散系数在整个催化剂颗粒内均保持较高的值.随Thiele模数(Φs)值的减小,催化剂颗粒内的相对浓度分布更为均匀,且呈整体增大的趋势,有...     

对苯二甲酸精制钯炭催化剂内扩散及有效因子的研究

在高压间歇反应釜研究了对苯二甲酸中杂质对羧基苯甲醛（4-CBA）在不同粒径的钯炭催化剂上进行加氢反应的特性。结果表明,催化剂粒径对4-CBA的加氢反应影响较大,催化剂的粒径减小,有效因子增大,反应速率增大,反应为内扩散控制。在反应温度150 ℃和240 ℃条件下,测定了钯炭催化剂内扩散有效因子,估算4-CBA在钯炭催化剂内的有效扩散系数Deff和催化剂的曲折因子,并提出了钯炭催化剂开发的改进方向。     

Effectiveness factor of a catalyst pellet in a trickle bed reactor: Limiting reactant in the gas phase

The influence of both internal and external wettings on the effectiveness factor of a partially wetted catalyst pellet in a trickle-bed reactor when the limiting reactant is in the gas phase is analyzed.A new parameter, not considered up to now, measuring the gas-liquid interfacial area inside and on the pellet surface, is introduced to study different forms of wetting.The reaction in the dry zone is also taken into account and its influence on the effectiveness factor for both the pores mouth and pores end dry is studied.An approximate analytical expression for the effectiveness factor, giving close results to the numerical solution, is proposed.     

Effectiveness factor approximations for multiple steady states in porous catalysts

The effectiveness factor is formally determined by solving a two-point boundary value problem, often numerically. To enhance the computational efficiency in simulations of large-scale reactor systems with porous catalysts, a simple approximation formula for the effectiveness factor is often used. For some reaction rate functions, however, the effectiveness factor as a function of Thiele modulus can show multiple values or sharp changes for a small change in the modulus. In this case, single-valued approximations of the effectiveness factor may give rise to large errors. Based on the two well-known asymptotes of the effectiveness factor for small and large Thiele moduli, we proposed equations for the approximation of the effectiveness factor for up to three multiple steady states and two catalyst geometries of an infinite slab and a sphere. The proposed equations were demonstrated to be useful in estimating the effectiveness factor, particularly for the stable steady states, and also in quickly estimating the Thiele modulus range where multiple effectiveness factors should be searched.     

Effectiveness factors for non-uniform catalytic activity of a spherical pellet

The effectiveness factor for catalysts with non-uniform activity of different intrinsic activity profiles was derived as functions of a modified Weisz modulus and a modified Thiele modulus. The modified moduluses were chosen so as to take into consideration the different diffusion lengths in catalysts with non-uniform activity.     

Effect of internal diffusion on the apparent stability of nonuniformly distributed biocatalysts

Theoretical analysis was carried out for the stability of enzymes with pseudo first order kinetics immobilized in three different structures. The stabilities with respect to time and temperature were in the order of core-structured, uniform and shell-structured immobilization methods in contrast to the effectiveness factor order of shell-structured, uniform and core-structured. The shell-structured immobilized enzyme was much more efficient in terms of effectivensss factor than the uniform type, but there was not much difference between time stabilities of the two systems. The core-structured system had the lowest effectiveness factor among the three, but it showed improved stability compared with the two especially when initial Thiele modulus was high.     

乙酸甲酯水解催化精馏过程催化剂包内的传质模型(Ⅱ)效率因子的测定与计算

建立了能较客观反映流体在催化剂包内流动状况的循环式间歇恒温反应装置 ,测定了不同催化剂包尺寸和不同液体喷淋密度下的乙酸甲酯水解宏观动力学和表观速率常数 ,估算了催化剂包内径向有效扩散系数约为 9× 10 ^-8m² ·s^-1。应用本文 (Ⅰ )报的传质模型计算了催化剂包效率因子 ,与实验结果吻合较好 ,其平均偏差为 3 2 % ,最大偏差为 13 7%。     

Overall effectiveness factor of heterogeneous-homogeneous chain reactions with one limited species in a catalytic slurry reactor

The analysis of the overall effectiveness factor for the reaction system involving heterogeneous-homogeneous chain reactions at low concentration of one species is studied. A more general theoretical analysis for estimating the overall effectiveness factor of reaction systems which can be a heterogeneous-homogeneous chain reaction system at low concentration of one species in a slurry reactor is presented, incorporating all the transport parameters. The concepts of overall effectiveness factors for reactions have been extended from the traditional heterogeneous reaction system to the heterogeneous-homogeneous chain reaction system. The effects of reaction mechanism and kinetic models on the overall effectiveness factor are also proposed. Comparisons of the overall effectiveness factor for a slurry reactor with or without considering the reaction mechanism are also obtained.     

Catalyst particle shapes and pore structure engineering for hydrodesulfurization and hydrodenitrogenation reactions

Catalyst particle shapes and pore structure engineering are crucial for alleviating internal diffusion limitations in the hydrodesulfurization (HDS)/hydrodenitrogenation (HDN) of gas oil. The effects of catalyst particle shapes (sphere, cylinder, trilobe, and tetralobe) and pore structures (pore diameter and porosity) on HDS/HDN performance at the particle scale are investigated via mathematical modeling. The relationship between particle shape and effectiveness factor is first established, and the specific surface areas of different catalyst particles show a positive correlation with the average HDS/HDN reaction rates. The catalyst particle shapes primarily alter the average HDS/HDN reaction rate to adjust the HDS/HDN effectiveness factor. An optimal average HDS/HDN reaction rate exists as the catalyst pore diameter and porosity increase, and this optimum value indicates a tradeoff between diffusion and reaction. In contrast to catalyst particle shapes, the catalyst pore diameter and the porosity of catalyst particles primarily alter the surface HDS/HDN reaction rate to adjust the HDS/HDN effectiveness factor. This study provides insights into the engineering of catalyst particle shapes and pore structures for improving HDS/HDN catalyst particle efficiency.     

Effectiveness factors for immobilized-enzyme reactions

The effect of intraparticle diffusion in artificial membranes on the kinetic behavior of immobilized enzymes has been considered theoretically in terms of an effectiveness factor. When the immobilized enxymes obey a Michaelis-Menten relationship, an approximate equation is proposed for the effectiveness factor. For a substrate inhibited enzymatic reaction, the effectiveness factor may exceed unity and display multiple steady-state behavior. Thus, the over-all rate of reaction in the artificial membrane is faster in this case than that when the substrate concentration in the interior is at the same as that at the exterior surface. In the case of a product inhibited enzymatic reaction, the effectiveness factor is always less than that which corresponds to a Michaelis-Menten relationship.     

Effectiveness factor under cyclic operation of a reactor

Results are reported on the influence of intraparticle diffusion on the measured rate of reaction under a condition where the feed composition is changing periodically. The specific application is to cyclic operation of an ammonia synthesis reactor. The effectiveness factor calculated relative to the steady-state kinetic rates for the time-average feed condition for fine particles was higher than the comparable steady-state effectiveness factor as a result of the rate improvement due to cycling. The effectiveness factor calculated relative to the time-average rate of reaction under cyclic operation for the fine particles was much less than unity and similar numerically to the steady-state effectiveness factor. The cycling effectiveness factor by either definition varied with cycling conditions because of the complex interaction of cycling parameters.