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.     

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.     

聚苯乙烯的超临界降解及其相关降解机理

介绍了超临界流体在聚苯乙烯降解中的应用及其相关的降解机理,分析了超临界流体降解聚苯乙烯的优缺点,指出超临界流体降解聚苯乙烯是一种全新的方法,具有广阔的发展前景。     

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。     

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。     

气相甲苯光催化降解反应动力学及机理

以紫外光为光源,锐钛矿型TiO2为催化剂,研究了气相甲苯光催化降解过程,并探讨了降解机理. 结果表明,甲苯光催化降解过程符合一级反应动力学方程,甲苯初始浓度越高,反应速率常数越小. 甲苯光催化降解的主要中间产物为己烷和苯. 在紫外光和TiO2作用下,甲苯经脱甲基反应生成苯和甲基,甲基可与甲苯分解产生的3-戊烯炔生成2,4-己二烯,经加氢转化为己烷.     

甲苯的复合氧化反应动力学及其降解的研究

在停止流动光谱仪反应器中研究了污水中的甲苯在3种氧化剂H2O2、O3和O3/H2O2、温度298K及pH=3~11时的氧化反应动力学及其降解过程。实验结果表明,甲苯在H2O2中氧化速率很慢,在O3中的氧化速率较快,当两种强氧化剂H2O2与O3耦合,构成高级氧化过程(AOP),甲苯的氧化速率最快。随着pH值增加,甲苯在O3和O3/H2O2中的氧化速率进一步加快。通过理论分析,初步探讨了有机污染物降解过程的机理;通过对实验数据的回归分析,获得了反应动力学常数。     

聚苯乙烯在空气中热降解的化学动力学研究

研究了聚苯乙烯在空气中的热降解化学动力学机理。实验结果显示,聚苯乙烯在空气中热降解存在两个失重阶段:第一阶段,温度范围从250.59℃开始至397.41℃,在此范围内,大约有85%的聚苯乙烯发生了分解;第二阶段为397.41～515.29℃,大约有15%的聚苯乙烯发生分解。动力学计算拟合结果表明,聚苯乙烯的主要失重阶段(第一阶段)的热解符合二级化学反应方程,其平均表观活化能Ea值为166.19kJ/mol,lnA值为32.15。     

甲苯的光催化降解及其动力学研究

进行了以自制锐钛型Fe3+-TiO2催化降解甲苯的研究,在自制的光催化反应器中,室温下以40 W白炽灯为光源,分析了TiO2的掺Fe3+量、催化剂投放量、甲苯初始浓度和溶液初始pH等因素的影响.结果表明:自制锐钛型Fe3+-TiO2能较有效地催化降解甲苯.在pH为2,TiO2掺Fe3+量为5％(物质的量分数)、催化剂投放量为2.0 g/L时对1.2 g/L甲苯的去除率在5h内可达60％以上.甲苯的降解过程表现为一级反应,表观反应速率常数k为0.0666 h-1,反应可用Langmuir-Hinshelwood动力学方程描述.     

Phase behavior and kinetics of polystyrene degradation in supercritical toluene

The phase behavior of polystyrene (PS) degradation in toluene was investigated in a visual high‐pressure reactor. The system of PS and toluene was heated from room temperature and atmospheric pressure to 350°C and 5.0 MPa. It was observed that during this process, PS dissolved quickly, and then, the system appeared to be a homogeneous phase, and PS degradation occurred in this system. With another high‐pressure batch reactor, PS degradation was studied in the temperature range 275–360°C and the pressure ranges 4.5–10.5 MPa. The drop‐in molecular weights in the temperature ranges and the amount of PS converted into volatile products were observed. Moreover, the effects of the temperature, pressure, and ratio of toluene to PS on the rate of PS degradation are discussed. The kinetic studies showed that the rate of PS degradation in supercritical toluene increased substantially because the degradation occurred in a homogeneous phase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetic study on the first stage during thermal degradation of polystyrene

The kinetic parameters of the first stage of polystyrene degradation have been investigated to elucidate the reaction mechanisms using the flow reactor system. The decrease in molecular weight of polystyrene was recorded at minute intervals over the temperature range 310°–390°C. Generally, the first and second stages were observed by thermogravimetric analysis (t.g.a.), however in the early stage of the degradation volatile yields of at least 5% occurred. Therefore, using t.g.a. analysis it is difficult to detect this earlier stage. It became evident that the first stage in the earlier part of the reaction could be detected by g.p.c. analysis. We have observed the hidden kinetic parameters of the nature of the first stage of the polystyrene degradation. The results indicate that the main chains were degraded randomly with the small quantitative volatile groups in the first stage and the rates of decrease in molecular weight in the first stage against reaction temperatures were evaluated as log k_s = 12.0 ? 41300/RT.     

Kinetic model for noncatalytic supercritical water gasification of cellulose and lignin

This article reports the first kinetics model for Supercritical Water Gasification (SCWG) that describes the formation and interconversion of individual gaseous species. The model comprises 11 reactions, and it uses a lumping scheme to handle the large number of intermediate compounds. We determined numerical values for the rate constants in the model by fitting it to experimental data previously reported for SCWG of cellulose and lignin. We validated the model by showing that it accurately predicts gas yields at biomass loadings and water densities not used in the parameter estimation. Sensitivity analysis and reaction rate analysis indicate that steam‐reforming and water–gas shift are the main sources of H₂ in SCWG, and intermediate species are the main sources of CO, CO₂, and CH₄. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

超临界流体在聚苯乙烯制备中的应用

综述了超临界流体在聚苯乙烯(PS)制备中的应用。超临界流体分级能方便地通过调节温度和压力对溶解度进行控制。获得相对分子质量分布较窄的PS级分;采用超临界流体可以连续稳定地制备纯度高和粒径分布均匀的微细PS;运用超临界溶液快速膨胀技术制得了微粒形态良好、粒径分布较窄的微米级PS微粒;采用超临界气体制备的微孔发泡PS复合材料具有较高的机械强度和性价比;PS超临界流体脱挥分具有能耗低、传质效率高的特点,而且不会引起聚合物的降解;使用超临界流体制备PS复合材料成为人们关注的研究热点。     

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     

Synthesis of montmorillonite/polystyrene nanocomposites in supercritical carbon dioxide

Monomer styrene and initiator N,N′‐azobis(isobutyronitrile) were impregnated into montmorillonite (MMT) galleries using supercritical CO₂ at 35°C and 12.0 MPa, after thermal polymerization of monomer at 65°C, resulting in MMT/polystyrene nanocomposites. The morphology and structure of the products were characterized by FTIR, powder X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The results indicate that MMT is dispersed in the composite with intercalated and exfoliated structures, enhancing the thermal stability of nanocomposites. Changing the soaking time and the content of MMT in the supercritical solution during the impregnating process can control the exfoliated extent of MMT. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1194–1197, 2004     

Preparation of polystyrene/montmorillonite nanocomposites in supercritical carbon dioxide

The preparation of polystyrene (PS)/montmorillonite (MMT) composites in supercritical carbon dioxide (SC? CO₂) was studied. Lipophilic organically modified MMT can be produced through an ion‐exchange reaction between native hydrophilic MMT and an intercalating agent (alkyl ammonium). PS/clay composites were prepared by free‐radical precipitation polymerization of styrene containing dispersed clay. X‐ray diffraction and transmission electron microscopy indicated that intercalation of MMT was achieved. PS/clay composites have a higher thermal decomposition temperature and lower glass‐transition temperature than pure PS. The IR spectrum analysis showed that the solvent of SC? CO₂ did not change the structures of the PS molecules, but there were some chemical interactions between the PS and the clay in the composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 22–28, 2005     

High‐pressure viscosity of polystyrene solutions in toluene + carbon dioxide binary mixtures

High‐pressure viscosity of polystyrene (M_w = 50,000, M_w/M_n ≤ 1.06) solutions in toluene and in mixtures of toluene + carbon dioxide was measured using a falling cylinder‐type viscometer at 320, 340, and 360 K, and up to 35 MPa. Solutions with polystyrene concentrations of 3, 5, and 7 wt % were investigated. Carbon dioxide levels in the range from 0 to 14.7 wt % were evaluated. Viscosity was observed to vary linearly with pressure at the temperatures and polymer concentrations investigated. Viscosity of the polymer solutions decreased as the concentration of carbon dioxide in the mixture was increased. The largest viscosity reduction was observed at the lowest temperature and at the highest concentration of polymer. The viscosity of the solutions was correlated with the solution density for different compositions. It was found that solutions of the same density have different viscosities, depending upon the carbon dioxide concentration in the mixture. The solutions with the higher carbon dioxide content display the lower viscosities at a given density. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 306–315, 2000     

Regeneration of nanoporous crystalline syndiotactic polystyrene by supercritical CO2

Guest desorption procedures for s‐PS clathrate samples, leading to formation and regeneration of the nanoporous δ phase, are compared. An extraction procedure, based on supercritical carbon dioxide, allows an easy and fast recovery of the guest molecules operating under relatively mild conditions (90–200 bar, 40°C) and generates a completely empty δ form, also starting from the most stable s‐PS clathrate forms. In agreement with a previously proposed crystal structure of the nanoporous δ form, X‐ray diffraction patterns of δ form powders obtained by this procedure do not show the peak, which is reduced but still apparent in samples extracted with previous procedures based on boiling solvents. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2077–2082, 1999     

合成制药废水生物降解动力学模型研究

应用Monod、Tessier和Moser模型,对菌株XZ(Bacillus)降解合成制药废水的试验数据进行非线性回归分析。结果表明:3种模型均可以用于模拟XZ降解制药废水过程中的生物量增长及污染物基质的降解;其中Moser模型对数据的拟合度最好;应用Monod模型得到的动力学参数qmax和Ksq分别为0.105 h-1和1 846.3 mg/L,证明XZ具有对该制药废水的高降解性和高适应性。动力学参数可以推算降解极限浓度Smin与产率系数YT和YN,进而用于制药废水生物处理反应器的优化和设计。