超临界甲苯中聚苯乙烯的降解研究

随着塑料使用量的大增,废旧塑料如聚苯乙烯的回收利用问题已经引起广泛关注。苯类物质是聚苯乙烯的优良溶剂,在超临界条件下其优异的传质、传热性能使聚苯乙烯快速降解。在高压反应釜中,反应温度350~390℃下以甲苯为超临界溶剂考察了聚苯乙烯(PS)的降解特性,分析了温度、原料配比和催化剂对聚苯乙烯降解过程的影响,结果表明温度对降解过程影响最大,是影响苯乙烯收率的最主要的因素,反应温度达到360℃时聚苯乙烯几乎完全降解。     

聚苯乙烯超临界催化降解

以氧化钡为催化剂分别在超临界甲苯和正己烷的介质中考察了聚苯乙烯(PS)的降解过程,结果表明甲苯的效果优于正己烷.在超临界甲苯介质中考察了反应温度和原料配比对聚苯乙烯转化率、苯乙烯收率和产物分布的影响,并确定了聚苯乙烯在超临界甲苯中催化降解的适宜工艺条件为:反应温度340℃,反应时间30 min,甲苯和PS质量比为15.0.     

聚苯乙烯在超临界甲苯中的可视降解及动力学

采用微型可视反应器考察了在超临界甲苯中聚苯乙烯降解的相变过程. 随温度升高聚苯乙烯在甲苯中迅速溶解,体系在略高于甲苯临界点处气液两相界面消失,且伴随着临界乳光现象,随后反应体系呈均相. 考察了聚苯乙烯超临界降解和热降解的反应特性,结果表明,聚苯乙烯超临界降解转化率明显高于热降解转化率;聚苯乙烯超临界降解初期分子量迅速降低的同时转化率也快速上升,而聚苯乙烯热降解初期分子量迅速降低过程中转化率很低. 由于聚苯乙烯在超临界甲苯中降解是均相反应,显著降低了反应体系的密度和粘度,改善了传递效果,因此超临界降解速率明显提高. 聚苯乙烯降解反应为一级反应,在温度为330~370℃时热降解活化能为186.1 kJ/mol,超临界体系改善了降解环境,活化能明显降低,为143.5 kJ/mol.     

废旧聚苯乙烯塑料的催化热解研究进展

随着塑料消费量的不断升级,大量的废弃塑料对生态环境造成了严重的负面影响。与传统的塑料回收技术相比,采用催化热解的方法从废旧塑料中回收利用高附加值的热解油是一种环保的、可持续发展的技术。在热塑性塑料中,聚苯乙烯产量位居第4,伴随塑料的消费产生了大量堆积,通过催化热解对废旧聚苯乙烯进行回收利用,产生了较大的环境和经济效益。对废旧聚苯乙烯的催化热解进行研究,主要分析比较了催化热解过程中影响苯乙烯单体收率及产物组成的各种因素,包括反应温度、反应升温速率、反应停留时间、催化剂类型、反应器类型、溶剂等。最后,对废旧聚苯乙烯的可回收利用前景进行了展望。     

聚苯乙烯高温快速热解制备苯乙烯的研究

将聚苯乙烯(PS)溶于甲苯以雾化方式进料,在管式反应器中借助高温短停留时间快速热解制取苯乙烯,探讨了热解温度、停留时间、热解气氛、喷嘴口径等反应条件对热解的影响。结果表明,随停留时间增加,油相和苯乙烯收率总体呈上升趋势;苯乙烯收率随热解温度升高呈先增加后下降趋势,890 ℃时苯乙烯收率最大达到36.67 %;热解气主要为甲烷、乙烯和丙烯,其收率随停留时间和热解温度增加而增加;引入水蒸气可以减少反应结炭;喷嘴口径明显影响油相和苯乙烯收率。     

PP／RPS反应性共混研究

用IR及DSC研究了（侧基含有过氧键的聚苯乙烯）与PP之间的反应,考察了反应温度、苯乙烯单体等对共混过程的影响。结果表明：RPS/PP共混体系中,PP降解严重,而PP/RPS/Rt（苯乙烯）共混体系可有效地抑制降解,反应生成的PP-g-PS对PP/PS合金具有增容作用,提高了合金的力学性能。     

聚对苯二甲酸丁二醇酯在超临界甲醇中降解机理的研究

在高压间歇无搅拌反应器中研究了聚对苯二甲酸丁二醇酯(PBT)在高温甲醇溶液中的降解行为,通过对降解产物的各种定性和定量的分析,提出了超临界甲醇降解PBT的机理为在甲醇的作用下聚合物分子链的随机断裂和酯交换反应双重作用下发生的降解反应,建立了降解-反应模型.PBT在甲醇溶液中的降解可分为超临界区、非超临界区和中间过渡区三个区域.通过分子量测定考察了PBT在不同的区域中降解规律.在非临界区PBT在溶剂中处于溶胀状态,其数均分子量Mn下降缓慢,解聚程度低;在过渡区PBT的溶解性能提高,聚合物大分子发生断裂,降解速率加快;在超临界区,Mn随反应的进行而迅速下降,聚合物很快完全降解.在超临界区中PBT可实现完全降解,其主要产物为单体对苯二甲酸二甲酯(DMT)和丁二醇(BG),它们的收率可分别可达98.1%和72.3%.     

红外光谱法对苯乙烯共聚物的鉴别

聚苯乙烯以其价格低廉,综合性能良好得到广泛的应用,但由于聚苯乙烯抗冲击强度低、脆性大、耐试剂性能差等,限制了其应用。为了改善聚苯乙烯的综合性能,常用其他单体或树脂和苯乙烯共聚进行改性,然而不同类型苯乙烯共聚物的结构、性能、价格差别很大,为了更好的了解鉴定不同类型的苯乙烯共聚物,文章通过红外光谱法,对比几种常见的苯乙烯共聚物红外光谱图特征峰的差异,可以明显区分各种苯乙烯共聚物。     

乳液法聚苯乙烯纳米微球的制备

采用十二烷基硫酸钠为乳化剂、过硫酸盐为引发剂、苯乙烯为单体,在低水油比的条件下,采用乳液聚合方法合成了聚苯乙烯纳米微球,探讨了乳化剂用量、乳化时间、反应温度、引发剂用量和反应时间对单体转化率及产物分子量的影响.结果表明:在低水油比条件下,反应参数对苯乙烯的转化率和聚苯乙烯的分子量具有一定的影响.在最优条件下苯乙烯的转化率达到98%、聚苯乙烯的分子量达到32万.激光粒度分布测试结果显示,所得产物为单分散纳米微球.     

在超临界水中聚苯乙烯泡沫的降解

本文研究了聚苯乙烯泡沫在超临界水中的降解反应。考查了反应时间、温度和添加剂对降解反应的影响。实验结果显示,超临界水能将聚苯乙烯泡沫降解为油状产物。在反应的前30min内,分子量降低了约98％;提高温度对反应时间短的和/或无添加剂的配方有明显的促降解作用;添加剂用量在5％左右时,可得到更大的效率/成本比。     

Degradation of polystyrene in supercritical n-Hexane

Degradation of polystyrene was carried out in supercritical n-hexane under reaction temperature ranging from 330 °C to 390 °C, pressure ranging from 30 bar to 70 bar and reaction duration of 90 min. The conversion of polystyrene increased with rising temperature and pressure. The degradation performance was influenced by the temperature rather than applied pressure. Polystyrene rapidly degraded in 30 min after reaching a prescribed temperature ranging from 350 °C to 390 °C. At a prescribed temperature of 390 °C, the degree of degradation was higher than 90%. The degradation reaction was examined experimentally at a relatively low temperature of 330 °C. The degradation of polystyrene by using supercritical n-hexane has been found to be more effective compared to general pyrolysis (thermal degradation). Among the selectivity of liquid products, that of a single aromatic ring group like styrene at 390 °C increased up to 65% in 90 min. It was found from the analysis by a gel permeation Chromatograph (GPC), that high molecular-weight compounds decreased but oligomers increased with rising temperature.     

Thermal decomposition of polystyrene in supercritical methanol

The degradation of polystyrene (PS) in supercritical methanol was carried out under reaction temperatures ranging from 340 to 420°C and pressures of 10–30 MPa. The selectivity of liquid products was investigated at various reaction conditions. As the reaction proceeded, the selectivity of styrene monomer, dimer, 1,3-diphenyl propane, and 1,3-diphenyl butane had a declining tendency, whereas that of the rest (i.e., toluene, ethyl benzene, isopropyl benzene, and 3-phenyl propanol, etc.) had an inclining tendency. The sequences of decomposition reaction could be reasoned by analyzing the variation of selectivity of liquid products. The kinetic behavior of PS in supercritical methanol had been investigated. The degradation processes of PS in such supercritical fluids could be formulated by the first-order kinetic law at the initial stage of reaction. The activation energy for the degradation in supercritical methanol was evaluated to be 117.2 kJ/mol and it was also compared with the activation energies for depolymerization in other supercritical fluids and that for thermal pyrolysis. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

交联聚苯乙烯微球负载N-羟基邻苯二甲酰亚胺催化剂对甲苯和环己醇氧化的催化性能

通过分子设计,以交联聚苯乙烯(CPS)微球为基质,制备了固载化的N-羟基邻苯二甲酰亚胺(NHPI)催化剂. 先将CPS微球氯甲基化,制得氯甲基化微球CMCPS,再使微球表面的氯甲基与偏苯三酸酐(TMA)分子中的羧基酯化反应,将邻苯二甲酸酐(PA)键合到聚合物微球表面,获得键合邻苯二甲酸酐的微球CPS-PA,使之与盐酸羟胺反应,制备固载NHPI的微球CPS-NHPI,固载量达2.25 mmol/g,并对其进行表征. 将CPS-NHPI分别用于分子氧氧化甲苯和环己醇过程,考察微球的催化活性,分析其催化氧化机理. 结果表明,以三乙胺为缚酸剂,采用极性溶剂N,N-二甲基乙酰胺,在110℃下CMCPS表面的氯甲基与TMA可顺利反应. 适宜条件下CMCPS氯甲基的转化率可达73%. CPS-NHPI-Co(OAc)2催化体系对分子氧氧化甲苯和环己醇的催化活性良好,为自由基链反应机理.     

Copolymerization of ethylene with vinyl acetate. II. Effect of solvent on polymer yield and molecular weight

In the free-radical solution copolymerization of ethylene and vinyl acetate, polymer yield and molecular weight were found to vary considerably with the solvent used. Solvents were toluene, benzene, hexane, heptane, and cyclohexane. Molecular weights were highest in benzene and lowest in toluene and were readily explained by different solvent chain-transfer constants. Polymer yields were highest in aliphatic solvents and lowest in aromatic solvents including benzene. This was attributed to different types of interactions of the solvents with radical species. The saturated aliphatic solvents undergo hydrogen abstraction reactions, but these give reactive alkyl radicals which reinitiate polymer growth. Toluene also undergoes hydrogen abstraction reactions, but the resultant benzyl radical is resonance stabilized and does not readily reinitiate polymerization. Benzene does not undergo hydrogen abstraction reactions. The low yields are attributed to complex formation. A consideration of kinetic theory indicates that complex formation with both initiator and growing polymer radicals is involved. Differences in viscosity, ethylene solubility, and initiator half-life in the different solvents, as well as induced decomposition of the initiator, were not determining factors.     

Coal liquefaction using supercritical toluene–tetralin mixture in a semi-continuous reactor

Liquefaction of Banpoo coal and Mae Moh coal using supercritical toluene–tetralin mixture was performed in a semi-continuous apparatus at a temperature ranging from 370 to 490 °C and under pressures up to 12.2 MPa. The addition of tetralin to toluene increased the coal conversion and the liquid yield by the stabilization of radical fragments and inhibition of radical recombination. The effect of solvent pre-swelling treatment and catalyst impregnation on conversion and liquid yield was also examined. The combination effects of catalyst and swelling enhanced conversion and the liquid yield of sub-bituminous coal. The yield of coal liquid at the condition of 490 °C and 10 MPa with toluene–tetralin reached a maximum 45 wt.% (in daf coal) with THF as the swelling agent and ZnCl₂ as the catalyst. The coal residue, after extraction, maintained most of its heating value and had a lower sulfur content.     

超/亚临界CO2中邻甲酚羧基化合成邻甲基水杨酸

在超/亚临界CO2中合成邻甲基水杨酸,对探索其绿色合成和CO2的资源化利用有重要意义。本实验以邻甲酚为原料,考察了无水K2CO3、无水Na2CO3等催化剂的活性,选取催化效果最好的无水K2CO3在超/亚临界CO2中一步法直接催化合成邻甲基水杨酸。在反应时间1～6 h、催化剂相对投加量nK2CO3/nO-Cresol为0.05～1.25、反应温度130～270 ℃、反应压力4～14 MPa的条件下对邻甲酚在超/亚临界CO2中的羧基化反应进行了研究。结果表明：邻甲酚的转化率与产物收率随反应时间的延长均出现先增加的趋势,不同的是转化率最后趋于稳定,产物收率则略有减少;邻甲酚的转化率与产物收率随催化剂相对投加量的增加先快速增加然后趋缓,随反应温度、反应压力的增加先增加后减少。较佳的实验条件为：反应时间3 h、催化剂相对投加量0.5、反应温度190 ℃、反应压力8 MPa,此时,邻甲酚转化率可达19.7%,邻甲基水杨酸收率可达17.5%。此外,提出了超/亚临界CO2中邻甲酚羧基化反应可能存在的机理。     

Gold-Catalyzed Aerobic Oxidation of Benzyl Alcohol: Effect of Gold Particle Size on Activity and Selectivity in Different Solvents

The effect of the size of gold particles deposited on CeO₂ and TiO₂ supports on their catalytic behavior in the aerobic oxidation of benzyl alcohol in different solvents (mesitylene, toluene, and supercritical carbon dioxide) has been investigated. The size of supported gold particles deposited via a colloidal route was in the range 1.3–11.3 nm, as determined by means of EXAFS and HAADF-STEM measurements. The catalytic performance of the supported gold catalysts in the different solvents revealed a significant effect of the gold particle size. Optimal activity was observed for catalysts with medium particle size (ca. 6.9 nm) whereas smaller and bigger particles showed inferior activity. Identical trends for the activity–particle size relationship were found using Au/CeO₂ and Au/TiO₂ for the reaction at atmospheric pressure in conventional solvents (mesitylene, toluene) as well as under supercritical conditions (scCO₂). Selectivity to benzaldehyde was only weakly affected by the gold particle size and mainly depended on reaction conditions. In supercritical CO₂ (scCO₂) selectivity was higher than in the conventional solvents under atmospheric pressure. All catalysts tested with particle sizes ranging from 1.3 to 11.3 nm showed excellent selectivity of 99% or higher under supercritical conditions.     

Enantioselective hydrogenation of ethyl pyruvate in supercritical fluids

The enantioselective hydrogenation of ethyl pyruvate to (R)-ethyl lactate has been studied using gases under supercritical conditions as solvents. The catalyst was a 5 wt% Pt/alumina modified with cinchonidine. In supercritical ethane the reaction time could be reduced by a factor of 3.5 compared to toluene under similar conditions, without any loss in enantioselectivity. A further advantage of ethane is that the enantioselectivity remains high even at high catalyst/reactant ratio, which is interesting in view of a possible application of a continuous fixed-bed reactor for this reaction. A strong catalyst deactivation was observed in supercritical CO₂, which is due to the reduction of CO₂ on Pt as indicated by FTIR.     

超临界乙醇体系中苯酚催化加氢的降解规律

目前,液化的生物油与石油粗油成分接近,通常环类化合物含量高,如煤焦油中酚及其衍生物含量占40%以上,急需加氢升级技术。超临界乙醇（243.1℃,6.38MPa）温度、压力条件低,具有良好的传质性能,且为绿色、可再生溶剂。在超临界乙醇体系下的催化加氢是一种油升级有效方式。本文以苯酚为生物油中环类化合物典型模型,在300～400℃、Pt/C催化剂下,探讨超临界乙醇体系下苯酚催化加氢过程。研究分析了超临界乙醇中温度、氢气压力和反应时间对苯酚催化加氢降解规律的影响,并建立了能很好地描述过程中苯酚转化率的动力学模型（R2 = 0.989）。实验表明：该体系下的苯酚催化加氢降解反应的级数为二级,反应的活化能为51.7kJ/mol;尽管升高温度和氢气压力均能提高苯酚的转化率,但温度对转化率的影响更为显著。本研究将为更好地控制反应过程和提高超临界乙醇体系中苯酚的转化率提供参考。     

金属卟啉催化空气氧化甲苯制取苯甲醛及苯甲醇的新工艺

在少量简单金属钴卟啉的催化下,无需外加溶剂及反应引发剂,甲苯可由空气直接选择性液相催化成为苯甲醛及苯甲醇。反应结果表明反应时间、反应温度、压力、催化剂用量及空气流量等工艺参数的变化对反应都有影响。在165℃、0．8MPa、3．4ppm及40L／h空气流量的最佳反应条件下,甲苯的转化率可以达到8．7％,同时醛醇选择性可以达到近60％。同传统空气氧化甲苯制取苯甲醛体系相比,此催化体系工艺条件简单、清洁无污染,产品质量好。研究结果表明,金属卟啉存在下的催化空气氧化甲苯制取苯甲醛及苯甲醇的反应经历了一个由金属卟啉引发的自由基反应历程。