氯乙烯悬浮聚合pH值的调节与应用研究

为改善氯乙烯悬浮聚合过程体系的pH值，本文对聚合体系pH值的控制与调节进行了研究，取得了一些规律性的小试数据．为扩试和生产试验提供了依据。     

丁二烯—苯乙烯乳液聚合中硫醇的分子量调节作用

研究了硫醇的种类,用量及加入方式对反应速率、分子量及分子量分布的影响,结果表明,除叔四、八碳硫醇使反应速度降低外,其它均无影响;叔十二碳硫醇是较为理想的分子量调节剂,改变其用量可以适当调整分子量;增量法是实现高转化率、控制分子量、保证产品质量的有效措施。     

调节镍系顺丁橡胶分子量的研究

研究了改变聚合工艺条件及加入分子量调节剂D、C对顺丁橡胶分子量的调节作用，结果表明：Ni-Al-B体系中改变聚合工艺条件不能大幅度调节顺丁橡胶的分子量，加入分子量调节剂D可以大幅度调节顺丁橡胶的分子量；加入分子量调节剂C可以降低顺丁橡胶的分子量。     

丁—苯乳聚中不同引发体系的反应速度

本文以短周期(≤10小时)高转化(70±2％)E-SBR-1500的合成为目标,在对比不同氧化—还原引发剂聚合活性的基础上,研究了氯化剂/还原剂配比、电解质、乳化剂、硫醇和聚合温度对聚合速度的影响,为确定合成配方和加料方式提供了基础数据。     

复合调节体系对合成SBS微观结构及反应速率的影响

通过活性阴离子聚合手段,以正丁基锂为引发剂、环己烷为溶剂,合成苯乙烯-丁二烯-苯乙烯三元嵌段共聚物(SBS).分别研究了单一调节剂四氢呋喃(THF)、复合调节体系四甲基乙烯基二胺(TMEDA)与THF、二乙二醇二甲醚(2G)与THF对SBS微观结构的影响.结果表明,在聚合温度为60℃,苯乙烯(St)与丁二烯(Bd)质量...     

苯乙烯装置聚合物的产生与预防研究

针对抚顺石化公司石油二厂苯乙烯装置生产过程中出现的苯乙烯聚合问题,结合苯乙烯独特的分子结构和化学性质,分析了工业生产过程中极易发生聚合的原因。当苯乙烯分子发生聚合时,产生的反应热能促使苯乙烯形成新的自由基,进而引发新的聚合反应。提出了在苯乙烯生产过程中尽量降低单体苯乙烯存在温度,减少在单一设备中的停留时间,提高原料乙苯纯度,苯乙烯在精馏单元加入DNBP阻聚剂和在苯乙烯贮存容器内加入TBC阻聚剂等有效防止苯乙烯聚合的措施,大大降低了苯乙烯聚合物,促进了苯乙烯装置平稳生产和长周期运行,进而提高苯乙烯装置经济效益。     

羧基丁腈胶乳在20m~3釜的工业放大研究

主要考察了羧基丁腈胶乳在工业放大中引发剂的用量及其加入方式、反应前期温度、搅拌转速等因素对聚合过程及胶乳稳定性的影响。结果表明 :在 2 0m3 釜上引发剂的使用量仅为小试的5 0 %～ 60 % ,且引发剂量减少及加入时间延长 ,使聚合稳定性增加 ,设备操作周期延长 ;反应初期温度以1 5± 2℃为宜 ;反应转化率 <70 % ,搅拌器采用 1 0 0r/min转速 ,转化率≥ 70 % ,搅拌器采用 75r/min转速 ,可有效减少胶乳的凝胶量 ,提高胶乳质量。     

羧基丁腈胶乳在20m^3釜的工业放大研究

主要考察了羧基丁腈胶乳在工业放大中引发剂的用量及其加入方式、反应前期温度、搅拌转速等因素对聚合过程及胶乳稳定性的影响.结果表明在20m3釜上引发剂的使用量仅为小试的50%～60%,且引发剂量减少及加入时间延长,使聚合稳定性增加,设备操作周期延长;反应初期温度以15±2℃为宜;反应转化率＜70%,搅拌器采用100r/min转速,转化率≥70%,搅拌器采用75r/min转速,可有效减少胶乳的凝胶量,提高胶乳质量.     

WCl6—Al（i—Bu）2Cl催化丁二烯—苯乙烯共聚合：丁苯共聚物的结构组…

对丁苯共聚物的＾１Ｈ－ＮＭＲ谱图进行了归属，并建立了计算其４种结构单元含量的方程式。当Ａｌ（ｉ－Ｂｕ）２Ｃｌ／ＷＣｌ６＝６（摩尔比）时，苯乙烯单元含量最低，丁二烯单元含量最高；Ｂｄ单元含量随Ｂｄ／Ｓｔ值的增加而提高，总的Ｓｔ单元含量随Ｂｄ／Ｓｔ值的增加而降低；聚合时间对单元含量的影响与Ｂｄ／Ｓｔ值的影响相似；提高聚合温度，Ｓｔ单元含量降低。用微分法求得转化率低于１０％时Ｓｔ的竞聚率为４．７０，Ｂｄ     

丙烯腈连续水相沉淀聚合过程的在线研究

在模拟工业流程的连续小试装置上进行了丙烯腈和醋酸乙烯酯的水相沉淀共聚合在线研究.考察了连续小试装置的操作特征等.通过聚合体系pH值和聚合温度实时反馈控制技术,即时分析聚合过程特征,发现体系pH值是最敏感的操作参数,而且响应灵敏和精确,能及时提供一些非稳定聚合状态的信息.     

Chain transfer behavior of fractionated commercial mercaptans in emulsion polymerization of styrene

The chain transfer behavior of fractionated commercial tertiary mercaptans was investigated in batch and semicontinuous emulsion polymerization of styrene over the entire monomer conversion range. Four mercaptans were obtained by fractionation, which contained 9, 11, 12, and 13 carbons, respectively. The effect of the mercaptans was evaluated in terms of the consumption rates of the monomer and the chain transfer agents, the number average degree of polymerization, DP_n, and the polydispersity index, I, of the polymer. The batch experiments showed that the chain transfer efficiency decreases with increasing carbon number, which is due primarily to a lower diffusion rate of the chain transfer agent to the reaction sites (growing latex particles) through the aqueous phase. The partitioning ratio of the chain transfer agents between the aqueous phase and the monomer droplets also contributes, to a lesser extent, to the efficiency. The number average degree of polymerization and the polydispersity index are primarily controlled by the ratio of the mercaptan consumption rate over that of the monomer. In order to obtain a polymer with a constant DP_n and a narrow I, this ratio should be as close to unity as possible, as is the case for C₁₁. Otherwise, too high a ratio causes a severe increase in DP_n at the end of polymerization, and too low a ratio leads in the opposite direction. The semicontinuous experiments confirmed the batch results. © 1994 John Wiley & Sons, Inc.     

Regulation of molecular weight of styrene–butadiene rubber. III. Choice of regulator from the homologous series of aliphatic mercaptans

The regulating efficiency of four aliphatic mercaptans was studied in emulsion copolymerization of butadiene with styrene, at +5°C. with the use of the redox system, diisopropylbenzene hydroperoxide–complexed ferrous iron–sodium formaldehyde sulfoxylate as an initiator and the sodium soap of disproportionated rosin as an emulsifier. The apparent transfer constants C of tertiary mercaptans decreased logarithmically with increasing length of molecule. This tendency is connected with the analogous dependency of solubilities of these compounds in water. The mercaptans did not affect the rate of polymerization. The value of C is independent of the amount of regulator used. With the value of C, the amount of regulator, and the conversion known, it is possible to predict the molecular weight of the polymers, except for the region of poor regulation, where the deteriorative influence of termination and crosslinking reactions takes place. The apparent transfer constant of tertiary dodecyl mercaptan decreased with increasing rate of polymerization. After elimination of diffuse processes, the value of the actual relative transfer constant was calculated. The tertiary dodecyl mercaptan has been selected as the most convenient molecular weight regulator for emulsion copolymerization of butadiene with styrene of all compounds studied for the system mentioned.     

Modification of emulsion polymerizations with microemulsions of mercaptans

Microemulsions of dodecyl and higher mercaptans are easily prepared with common surfactants and alkanol cosurfactants readily available in the emulsion polymerization industry. The reactivity of the microemulsified heavy mercaptan is greatly enhanced when properly prepared and charged. The regulating index of tert-hexadecyl mercaptan for a styrene–butadiene copolymerization (SBR) can be increased from 0.3 for the control to over 10 for the microemulsified modifier. Several ways of varying the reactivity of the modifier over a considerable range are presented. This article also presents solutions to some of the problems that arise in the preparation and use of the microemulsions. Applications of microemulsified mercaptans to modification of standard emulsion polymerizations are included. This method of enhancing the reactivity of modifiers is more practical than the preagitation technique previously reported.¹     

Molecular weight distribution of polystyrene and of butadiene–styrene copolymers prepared in emulsion systems

Polystyrene and butadiene–styrene copolymers (SBR) were prepared in emulsion systems with a homologous series of commercial mercaptan modifiers. The molecular weight distribution (MWD) of the sets of polymers changed in a consistant manner when the regulating index of the mercaptan was relatively low. However the shape of the MWD curves appeared distorted in comparsion to theoretical curves when the modifier depleted rapidly and when divinylbenzene was present in the system. The divergence from the theoretical curve is attributed to a higher degree of branching in the high molecular weight fractions. Differences in MWD of SBR made with n- and tert- dodecyl mercaptans was marked. Notable differences were also found for SBR 1500 samples from the industry at random, but only slight differences were seen in a set of SBR 1503 samples. This study shows how the MWD of polymers prepared in emulsions can be varied simply by use of modifiers with different regulating indexes.     

The reversibility of the adsorption of methane–methyl mercaptan mixtures in nanoporous carbon

The results of extensive molecular dynamics simulations and theoretical considerations of the adsorption of methane–methyl mercaptan mixtures in slit-shaped carbon nanopores are presented. We observe significant mobility of both methane and mercaptan molecules within the pore volume, between pores, and between adsorbed and gas phases for a wide range of temperatures and pressures. Although mercaptans adsorb preferentially relative to methane, the process remains reversible, provided non-oxidizing conditions are maintained. A mercaptan/methane ratio of the order of 200 ppm in the adsorbed phase is sufficient for the gas phase to have a mercaptan concentration above the human threshold for detection. The reversibility of the adsorption process and low concentration of mercaptans makes it unlikely that these would be harmful for adsorbed natural gas storage systems.     

Modification of butadiene–acrylonitrile and styrene–acrylonitrile copolymerizations in emulsion systems

Modification of acrylonitrile in copolymerizations with butadiene and with styrene in hot and cold emulsion recipes has been studied. Series of primary, secondary, and tertiary mercaptans in addition to several miscellaneous modifiers were tested. Kinetically the rate data for the monomer pairs containing acrylonitrile better fit first-order plots than the curves obtained for an ideal emulsion polymerization. In this study all modifier depletions in nitrile systems were plotted as log mercaptan versus log conversion and the slope of the curve was taken as the transfer constant. Normal mercaptans were inefficient modifiers in nitrile systems as determined in polymerization and depletion experiments. Secondary mercaptans, 2-nonyl, 2-decyl, and mixtures in this molecular weight range, were promising modifiers for low temperature (5°C.) nitrile systems. 2-Nonyl mercaptan gave enhanced modification by incremental addition of the modifier indicating this procedure could be used to advantage in preparing nitrile rubbers. The series of tertiary mercaptans from C₁₃ to C₇ showed an improvement in modification of low temperature nitrile systems as the molecular weight decreased. A plot of the data on a molar basis shows that the optimum modifier falls in the C₉–C₈ range. The optimum transfer constant for the most efficient modification of 70/30 and of 80/20 butadiene–acrylonitrile polymerizations at 5°C. terminated at 60% conversion is 2. Depletion data show that the transfer constant for a mercaptan decreases as the nitrile content in mixtures with butadiene increases. The properties of the vulcanizates of the 70/30 and 80/20 butadiene–acrylonitrile polymers prepared in the presence of low molecular weight mercaptans were equivalent to or better than those of the controls. These data show that nitrile polymers could be modified with a lower molecule weight mercaptan with no loss of properties but with a considerable saving in amount of modifier. Mercaptans are essential for the initiation of butadiene–acrylonitrile in the presence of persulfate at 50°C. For the hot nitrile rubber preparations, the series of mercaptan from t-C₁₀ to t-C₇ are efficient modifiers. However, the heptyl and octyl mercaptans are retarders, and the t-C₉ and t-C₁₀ are the preferred modifiers for efficiency and unretarded polymerization. The modification with a series of mercaptans ranging from t-C_13.2 to t-C₈ of 75/25 styreneacrylonitrile at 50°C. in presence of persulfate–bisulfite showed a consistent behavior. The transfer constant decreased in a regular manner as the molecular weight of the mercaptan increased, and for the series of tertiary modifiers the t-C₁₀ mercaptan was the most efficient as judged by a melt flow test.     

丙烯腈与丙烯酸乙酯乳液共聚合及其表征

用氧化还原引发体系在低温下研究了丙烯腈与丙烯酸乙酯的乳液共聚合。考察了聚合温度、乳化剂浓度和分子量调节剂浓度对聚合的影响 ,结果表明 ,随温度升高 ,乳化剂浓度增大 ,单体转化率和分子量增大 ,乳液更稳定 ;链转移剂十二烷基硫醇浓度增加 ,分子量显著降低 ,转化率有所降低 ,表明十二烷基硫醇在调节分子量的同时也起着缓聚剂的作用。用激光粒径分析仪考察了 2 0℃时聚合过程中乳胶粒子大小的变化 ,发现聚合过程的成核和增长均在胶束中进行的。用凝胶渗透色谱法研究了十二烷基硫醇对聚合物分子量的影响 ,发现聚合时加入分子量调节剂 ,活性链寿命较短并呈单峰分布 :聚合时不加入分子量调节剂 ,活性链寿命较长并呈双峰分布。 DSC结果表明 ,随聚合体系中软单体含量增加 ,共聚物的玻璃化温度降低。     

Base‐free catalytic aerobic oxidation of mercaptans for gasoline sweetening over HTLcs‐derived CuZnAl catalyst

An aerobic oxidative removal of mercaptans from gasoline in the absence of liquid base has been demonstrated for gasoline sweetening over CuZnAl catalyst. This process could proceed at large WHSV of gasoline (50–70 h^?1) with >95% mercaptan conversion at 150°C (or 300°C) using an O₂/S molar ratio of 20–40. At 150°C, dimerization of mercaptans occurred dominantly to form their disulfides. At 300°C, deep oxidation of the mercaptans to SO₂ was the dominant process in the first tens of hours, but it decreased then with prolonged time on stream and meanwhile the dimerization increased. The spent catalyst could be restored to its fresh activity level only through a calcination treatment in air. This process was also demonstrated to be effective and efficient for sweetening of a real cracking gasoline. © 2009 American Institute of Chemical Engineers AIChE J, 2009