DROP DISPERSION IN SUSPENSION POLYMERIZATION

Four models, two based on laminar shear and two based on turbulent flow, are proposed to describe drop dispersion in non-coalescing systems. The models predict the largest surviving drop size _dmax as a function of geometry, speed and physical property variables.

Laboratory data including suspension polymerization runs support the boundary layer laminar shear model for drops larger than approximately 200 microns. Smaller drops support a turbulence model.

The boundary layer shear model was confirmed in scale-up suspension polymerization runs aimed at producing 1000 micron maximum bead sizes. Five approximately geometrically similar polymerizers were used, varying in size from 7.5 to 15000 liters.     

悬浮聚合用HAP／SDBS无机分散体系的作用机理

研究了ＨＡＰ粉末的沉降特性与生成过程，考察了ＨＡＰ粉末和不同表面活性剂配合在苯乙烯单体分散液中的吸附特性，同时研究了ＨＡＰ粉末复合不同表面活性剂的无机分散体系用于苯乙烯单体悬浮聚合时的聚合稳定性。对ＨＡＰ／ＳＤＢＳ无机分散体系用于悬浮聚合时的分散作用机理进行了探讨。简化了用于苯乙烯悬浮聚合用ＨＡＰ的制备方法：取消缓冲体系，缩短陈化时间，室温制备。且制备的分散剂用于聚合时为常量的１／５。     

悬浮、乳液和分散聚合:工艺的考察(续)

<正> 乳液聚合过程描述在经典的乳液聚合中,单体是不溶(或微溶)于聚合介质的,但在表面活性剂(乳化剂或皂)的帮助下,单体被乳化于其冲,与悬浮聚合不一样,引发剂在是溶解在介质中的,而不是溶解于单体。在这些条件下,根据催化剂的性质和     

非水分散聚合

本文综述了非水分散聚合体系的组成、表征、理论研究（如稳定机理、聚合机理、反应动力学）及实际应用等方面的情况。     

无挡板悬浮聚合搅拌釜的粘釜规律

在φ300mm的有机玻璃釜中,用聚苯乙烯颗粒(PS)和粘胶建立了釜内流动条件对粘釜影响的冷模实验方法。研究了无挡板条件下搅拌釜内粘垢的产生及其分布规律,发现在相同搅拌功率下,各种搅拌桨叶对粘釜量的影响从低到高依次为双叶推进式桨、双叶45°斜桨、三叶后掠式桨、双叶60°斜桨、双叶平桨及六叶透平式桨,纵向分布随流型有所不同。并讨论了搅拌桨安装方式及搅拌转速对粘釜规律的影响。     

悬浮聚合反应的数学模型

以苯乙烯悬浮聚合反应为例,从机理分析出发,建立了聚合过程的动态模型,其中通过引入若干个动态校正系数,较充分地考虑了凝胶效应的影响,根据实验结果,对部分参数进行了辨识,提高了模型的精度,并适用整个反应过程,为先进控制规律的研究提供了必要基础.     

有挡板悬浮聚合搅拌釜的粘釜规律

在有机玻璃釜中,以冷模方法研究挡板条件对粘釜量及其分布的影响。发现挡板系数在0.1相似文献   

聚氨酯-聚丙烯酸树脂乳液聚合过程研究

本文讨论了在聚氨酯水分散体中进行丙烯酸酯共聚物乳液聚合过程。研究表明：聚氨酯水分散体起着种子乳液的作用,发生了核－壳到乳液聚合过程。     

GAS DISPERSION AND SOLID SUSPENSION IN A THREE-PHASE STIRRED TANK WITH MULTIPLE IMPELLERS

Despite much research on gas-liquid-solid systems and their widespread application in industry, gas dispersion with solid suspension in multistage stirred reactors equipped with multiple impellers has received little attention. We report here the critical just-suspension impeller speed for different concentrations of solid particles, gas holdup, and shaft power in a vessel of 0.48 m diameter with four baffles and dished base. Five agitator configurations, each with three impellers mounted on a single shaft, have been used in the experiments. Two novel impeller designs were used, a deep hollow blade (semi-ellipse) disc turbine (HEDT) and four-wide-blade hydrofoil impellers. The hydrofoils were used in both up-pumping (WH_U) and down-pumping (WH_D) modes. Glass beads of 50 ∼ 150 μm diameter and density 2500 kg · m^-3 were suspended at solid volumetric concentrations of 1.5, 3, 6, 9, and 15%. Results show that these suspended solids have little effect on the relative power demand. Agitators using the HEDT radial dispersing impeller at the bottom have a higher relative power demand (RPD = P_G/P_U) than those with WH_D or WH_U as the lowest one. For all impeller combinations there is little or no effect on gas holdup with increasing solid concentrations. Of the five different impeller combinations, those with an axial flow bottom impeller have significantly higher just-suspension agitation speeds and power consumption, so mounting the hydrofoil impeller at the bottom is not the optimal configuration for particle suspension. Of these impeller combinations, at a given gas flow rate the arrangement of HEDT + 2WH_U has the highest relative power demand, gas holdup, and power input for both the suspension of settling particles and gas dispersion.     

GAS DISPERSION AND SOLID SUSPENSION IN A THREE-PHASE STIRRED TANK WITH MULTIPLE IMPELLERS

Despite much research on gas-liquid-solid systems and their widespread application in industry, gas dispersion with solid suspension in multistage stirred reactors equipped with multiple impellers has received little attention. We report here the critical just-suspension impeller speed for different concentrations of solid particles, gas holdup, and shaft power in a vessel of 0.48 m diameter with four baffles and dished base. Five agitator configurations, each with three impellers mounted on a single shaft, have been used in the experiments. Two novel impeller designs were used, a deep hollow blade (semi-ellipse) disc turbine (HEDT) and four-wide-blade hydrofoil impellers. The hydrofoils were used in both up-pumping (WH_U) and down-pumping (WH_D) modes. Glass beads of 50 ～ 150 μm diameter and density 2500 kg · m^?3 were suspended at solid volumetric concentrations of 1.5, 3, 6, 9, and 15%. Results show that these suspended solids have little effect on the relative power demand. Agitators using the HEDT radial dispersing impeller at the bottom have a higher relative power demand (RPD = P_G/P_U) than those with WH_D or WH_U as the lowest one. For all impeller combinations there is little or no effect on gas holdup with increasing solid concentrations. Of the five different impeller combinations, those with an axial flow bottom impeller have significantly higher just-suspension agitation speeds and power consumption, so mounting the hydrofoil impeller at the bottom is not the optimal configuration for particle suspension. Of these impeller combinations, at a given gas flow rate the arrangement of HEDT + 2WH_U has the highest relative power demand, gas holdup, and power input for both the suspension of settling particles and gas dispersion.     

在无机分散剂存在下苯乙烯悬浮聚合宏观成粒的特征

以苯乙烯悬浮聚合为体系,考察羟基磷酸钙(HAP)或HAP与聚乙烯醇(PVA)复合为分散剂体系时,各种因素如分散剂浓度、油水比、搅拌速度等与瞬时液滴大小及分布之间的关系,并分析讨论瞬时液滴分散、合并的过程特征.结果表明,悬浮苯乙烯液滴聚合宏观成粒的特征与分散剂的分散机理无关,仅体现液滴分散、合并的过程特点.当采用分批加分散剂时,实验观察到瞬时液滴大小分布呈由单峰过渡到双峰,再发展成单峰分布的特征,从而找出了以分批加分散剂方式制备窄分布聚合物颗粒的理论依据.     

MACROPROCESS OF PARTICLE FORMATION IN SUSPENSION POLYMERIZATION OF STYRENE WITH INORGANIC STABILIZER SYSTEM

The macroprocess of particle formation from suspension droplets of styrene in a pdymerizationsystem was investigated.Inorganic hydroxyapatite or its mixture with polyvinyl alcohol as thepolymerization system was used.Those items such as the effects of the Weight fraction of dispersed-phase,the amount of the inorganic stabilizer and the agitation speed on the breakup and coalescence of thetransient dispersed drops etc.Were examined.Results showd that the dynamic behavior of the transi-ent polymer droplets changed in the presence of the suspension stabilizer during the reaction.     

二氧化钛悬浮液分散性研究

应用粒度仪和电子显微镜研究了二氧化钛的分散性、浆料的稳定性及二氧化钛在聚酯切片中的形状。结果表明：二氧化钛的分散性与分散介质及电解质有关;聚酯切片中的凝结粒子通常是由二氧化钛粒子无规则的团聚而成。     

水相沉淀聚合法合成聚丙烯腈的工艺研究

采用高转化率水相沉淀聚合实验方法,对ＡＮ（丙烯腈）／ＶＡｃ（醋酸乙烯酯）／ＳＳＳ（苯乙烯磺酸钠）三元共聚物进行了研究,重点考察了聚合温度,氧化剂／还原剂比例,反应ｐＨ值等工艺条件对聚合转化率、分子量、共聚物组成的影响,并确定了合适的聚合工艺条件。     

KINETIC STUDIES ON SUSPENSION POLYMERIZATION OF VINYL CHLORIDE

A kinetic model dC/dt=a βC~(1/3)for suspension polymerization of vinyl chloride was developed.Kineticstudies on such polymerization were carried out in a stainless steel tube reactor in the presence of high-,medium-,or low-activity initiators at different concentrations,and at temperatures ranging from 50 to 62~C.Twenty-six sets of kinetic data were obtained under different conditions.According to these experimentalresults,the acceleration behavior of vinyl chloride polymerization was discussed in detail.It is proposed thatthe auto-acceleration effect is due to the decrease of the termination rate constnat in the polymer-rich phaseand to the increase of initiator concentration owing to volume contraction during polymerization with aninitiator of lower activity.All plots of dC/dt against C are nonlinear during the two-phase stage,while dC/dtversus C~(2/2)curves show much better linearity up to 60—70% conversion.The proposed model can beused to explain satisfactorily why the reaction order of initiators is between 0.5 and 1.0.     

海泡石陶瓷料浆稳定性的研究

通过Zeta电位、沉降实验、粘度等测试表征不同分散剂对海泡石陶瓷料浆稳定性的影响。研究表明:阴离子活性剂十六烷基苯磺酸钠对固相浓度增大、粒径小的海泡石料浆的分散稳定性效果较好,且在pH=11,浓度为0.8wt%时达到最佳,其分散稳定作用的实质是增强了微粒间的静电排斥作用和空间位阻排斥作用,并减弱了范德华吸引作用。海泡石对SDBS的吸附曲线是Langmuir单分子层吸附模型。     

碳化硅浓悬浮体的分散特性和流变性研究

通过对碳化硅粉体在有机单体介质中的Zeta电位，分散剂用量和浓悬浮体的粘度等的测试及其沉降试验，详细研究了粒径分布较宽的碳化硅粉体（0.2-250μm)的胶体分散特性，沉降行为以及浓悬浮体的流变行为。结果表明，选用适量的分散剂四甲基氢氧化铵可使SiC颗粒的Zeta电位绝对值提高近20mV，调整浆料pH至11．9附近可制备出固相体积分数高达70％的SiC浓悬浮体。该浓悬浮体中粗细SiC颗粒间能达到一稳定的分数，悬浮粒子不会产生明显地沉降，其流变行为符合Quemada模型。     

悬浮聚合反应制备高相对分子质量PAN

通过悬浮聚合反应,合成了高相对分子质量的聚丙烯腈（ＰＡＮ）。研究了引发剂质量分数、反应温度、悬浮剂质量分数,单体配比等实验条件对聚合反应的影响以及悬浮聚合反应的动力学,对高相对分子质量聚丙烯腈溶液的流变性能作了初步研究。     

关于氯乙烯悬浮聚合反应的机理及其动力学

本文作者认为乙烯悬浮聚合反应的机理是:PVC 及其大分子自由基不溶解于单体,但能被单体溶胀成为粘胶体,沉析出的处于粘胶体中孤立状态的大分子自由基很难有彼此相遇形成双基链终止(偶合或歧化)的机会,因此 PVC 大分子自由基与粘胶体中的单体发生的链转移反应便成为其唯一的或起主导作用的链终止过程。通过链转移反应,在大分子自由基链终止的同时,形成了单体自由基,后者仍可与粘胶体中的单体发生链的引发、增长及转移等过程。另一方面,由于初级自由基、单体自由基、大分子自由基及单体等的极性与空间位阻作用的影响,使得聚合形成的 PVC 大分子为自由单体首尾相接的链节结构。本文作者按照上述机理进行了一系列高转化率的氯乙烯悬浮聚合反应动力学方程的推导,所推导的动力学方程经过科学实验和生产实践数据的反复验证,证明其是符合客观实际的。