对二甲苯液相催化氧化动力学(Ⅰ)反应机理和动力学模型

针对PX高温液相催化氧化过程的特点开发了一套气液固三相反应实验技术 ,进行了氧化过程的动力学实验研究 .根据自由基反应机理和Co Mn Br三元催化体系的作用机制对PX氧化过程进行了深入的剖析 ,分析了芳烃中甲基和醛基的各步氧化机理及其与催化剂循环之间的耦合作用 .在此基础上推导出关于反应物浓度的动力学模型 ,并根据实验数据计算出各动力学参数 .     

对二甲苯液相催化氧化动力学实验技术

对二甲苯(PX)高温液相催化氧化是一个复杂反应过程,动力学实验研究的难点在于3个方面,即反应条件的控制,反应浆料的取样与样品的分析测试。开发了一项新颖有效的气液固三相反应实验技术,较好地解决了上述难题。该实验技术为PX氧化动力学研究以及其它烃类的液相催化氧化过程的研究提供了可靠的实验手段。     

PX氧化反应动力学模型研究

建立了一套半连续的PX高温催化氧化反应动力学实验装置,并进行了相关的动力学研究。依据实验数据和机理分析,提出了反应组分抑制的动力学模型。     

对二甲苯二次氧化过程中液相反应的研究

通过半连续实验考察了对二甲苯(PX)二次氧化过程中的液相氧化,并对该过程进行了模拟计算。设计和进行了包含PX液相氧化、中断反应以及降温二次液相氧化三个阶段的实验;通过动力学实验测定和数据回归确定了基于芳烃氧化自由基链式反应机理的PX液相氧化动力学模型的参数;采用建立的PX液相氧化机理模型对PX分段氧化过程进行了预测。结果表明,对中断反应后的降温二次液相氧化间歇过程,采用第一阶段末期自由基浓度做初值时模型预测值与实验值符合良好;而假设自由基初值浓度为零时,PX液相氧化动力学模型对二次氧化的液相反应预测效果较差,其原因可能是中断降温后的氧化母液中存在过氧基团会使二次液相氧化反应极快地被再引发启动。     

“PX氧化反应特性及模型化”项目通过鉴定

为实现 PTA生产技术的国产化 ,从 1 998年7月开始 ,仪征化纤公司和浙江大学联合进行精对二甲苯 (PX)氧化反应特性及模型化的研究开发。把 PX制 PTA的氧化反应动力学和氧化过程技术开发确立为核心技术开发 ,经过两年多的研究 ,成功开发出一套新颖、可靠的 PX高温氧化动力学实验装置 ,较好地解决了实验装置的条件控制 ,取样方法 ,样品分析测试等 3个方面的技术难题 ,获得相应动力学方程的有关基础数据 ,开发了相应的动力学模型和软件。所得结果系统可靠 ,模型与工业化数据一致 ,达到国内领先水平 ,为仪征化纤公司 PTA生产装置安全、稳定…     

对二甲苯液相催化氧化动力学(Ⅲ)催化剂配比与浓度的影响

对二甲苯(PX)高温液相催化氧化过程采用Co-Mn-Br三元复合催化剂，对该催化体系的机理作了深入探讨，针对催化剂总浓度、溴浓度以及钴锰配比对主反应的影响规律进行了系统的动力学实验，获得了各步反应速率随催化剂浓度与配比的变化关系.研究发现，在实验所考察的温度与催化剂组成条件下该催化体系存在一最佳钴锰配比（1∶1），溴浓度和催化剂总浓度对反应速率都有显著的影响，其中以溴浓度最为敏感.     

PX二次氧化过程的探讨

以中国石化上海石油化工股份有限公司2#氧化装置的PX氧化工序为主要研究对象,探索了PX氧化装置进行二次氧化的可行性。从上海石化工艺特点、PX氧化工序扩容改造前后对比,以及目前运行状况等方面对PX氧化过程进行了综合的分析和评价。结合PX氧化反应动力学、气液传质等因素,最后给出了年产40万t/a二次氧化反应器的初步设计方案。研究结果为工业PTA生产装置的操作优化和改造提供了依据。     

粗对苯二甲酸的高温熟化动力学研究

针对粗对苯二甲酸高温熟化过程的特点,开发了一套气液固三相熟化动力学实验技术,进行了熟化过程的动力学实验研究,对粗对苯二甲酸的熟化过程机理进行了剖析和数学描述。在此基础上,提出了粗对苯二甲酸的熟化动力学模型,并根据实验数据计算出了各动力学参数。揭示了粗对苯二甲酸的熟化规律,为 PTA 技术的工业技改和设计提供了依据。     

环戊烯氧化反应宏观动力学模型

建立环戊烯氧化制戊二醛过程反应宏观动力学模型,并进行模型检验。结果表明,根据模型进行的模拟计算结果与实验结果符合较好,说明采用所确定的反应动力学模型及模型参数,进行环戊烯氧化反应过程的模拟计算和优化研究是可行。     

基于自由基反应机理的芳烃液相氧化动力学模型

基于自由基链式反应机理,概括性地提出了芳烃液相氧化的基元反应步骤。针对芳烃氧化的特点对动力学模型进行了简化处理,减少了模型参数。运用提出的建模方法,建立了3个氧化实例的动力学模型,包括对二甲苯(PX)氧化生产对苯二甲酸(TPA)、对甲基苯甲酸(p-TA)氧化生产TPA、乙苯(EB)氧化生产乙苯氢过氧化物(EBHP)。拟合回归结果表明,上述动力学模型对实验数据的拟合效果均较好,最大拟合偏差不大于10%;并且涉及链传递和链终止反应步骤的共用参数不随反应条件而改变。     

精对苯二甲酸生产工艺新进展

介绍了近年以对二甲苯（PX）和对苯二甲酸（PTA）为原料生产聚酯的基本情况,以及以PX为原料的液相空气氧化法与加氢精制法生产PTA的工艺.着重论述扩大PTA生产规模、开辟生产PX新技术路线的最新动态,以及新型催化剂和超临界技术的应用等.     

Catalytic oxidation of toluene and m-xylene by activated carbon fiber impregnated with transition metals

The catalytic oxidation of volatile organic compounds (VOCs) into mainly CO₂ and H₂O appears promising in the context of the abatement of atmospheric gaseous pollutants and is the subject of this paper. The catalytic oxidation of toluene and m-xylene was carried out in a tubular reactor on a phenolic resin based activated carbon fiber (ACF) impregnated with nitrates of Co, Cr, Ni, and Cu at the reaction temperatures below 300 °C. The extent of the removal (i.e. conversion) of toluene and m-xylene was examined through the breakthrough curves and was found to strongly depend on the types and loading of the metal precursors. The experimental results showed that the reaction rate was significantly affected by O₂ concentration below 3% (v/v). The performance of the ACFs impregnated with 5% (w/w) of Ni oxide was found to be superior to that of other metal oxides at reaction temperature between 170 and 290 °C. A surface kinetic mechanism for the catalytic oxidation of volatile organic compound was proposed and incorporated in a transport model developed to explain the experimental breakthrough data.     

Investigation of the oxidation of o-Xylene over a Vanadia/Titania catalyst by means of the TAP reactor

The oxidation of o-xylene over a commercial V₂O₅/TiO₂ (anatase) catalyst was studied in the TAP (Temporal Analysis of Products) reactor system. The transient method with high time resolution has led to new insights into the reaction mechanism. The selective oxidation is shown to consist of a sequence of steps, involving intermediates which desorb as o-toluolaldehyde and phtalide. The key reaction step in the non-selective oxidation is shown to be a decar-bonylation of a surface species, leading to a surface benzoate. The kinetics of the elementary steps in the reaction were derived from a quantitative analysis of the transient responses on o-xylene pulses.     

Selective oxidation of o-xylene to phthalic anhydride over vanadia/titania: A comparative study of integral and recycle reactor operation

Two vanadia/titania catalysts, containing 1 and 8 wt% vanadia on anatase, have been investigated for the selective oxidation of o-xylene to phthalic anhydride. In a comparative study, activity and selectivity in o-xylene oxidation were measured using an integral reactor and a reactor with external product recirculation, with the objective of studying the influence of backmixing in the latter on the reaction behaviour. Adsorbed surface species were investigated by means of in-situ diffuse reflectance FT-IR spectroscopy, using an environmental chamber which corresponds to an integral reactor. No difference in activity and selectivity in o-xylene oxidation was observed between the two catalysts. FT-IR studies showed adsorbed o-xylene, benzoate and a high concentration of phthalic anhydride on the surface of both catalysts. o-Xylene oxidation follows a sequential reaction path, with o-tolualdehyde as the first intermediate and phthalide, phthalic anhydride and maleic anhydride as sequential products. No evidence was found for a direct oxidation-path of o-xylene to phthalic anhydride. Total oxidation products CO and CO₂ are formed by direct oxidation of the o-xylene and by oxidation of the reaction products. Due to greatly reduced concentration and temperature gradients, the recycle reactor proved to be highly suitable for studying the extremely exothermic oxidation of o-xylene.     

Progress in the research and development of p-xylene liquid phase oxidation process

The process of p-xylene liquid phase oxidation to produce purified terephthalic acid (PTA) involves a series of liquid phase radical reactions, chemical absorption, reactive crystallization, and evaporation. A commercial PTA production flow sheet includes a number of unit operations, which construct a complex process system. In this paper, a review of research and development (R&D) works on PTA process carried out in Zhejiang University during recent years is introduced. The works cover the oxidation and crystallization kinetics, gas-liquid mass transfer and evaporation, reactor modeling, database development, novel reactor design, process modeling, simulation, and optimization. The author emphasizes the viewpoint through this case study that chemical reaction engineering should be developed to process system engineering to extend its scope, and particular attention should be paid on reactor and process modeling.     

A kinetic modeling study of self-ignition of low alkylbenzenes at engine-relevant conditions

The self-ignition of low alkylbenzenes at engine-relevant conditions has been studied with kinetic modeling. A previously developed chemical kinetic model for gasoline surrogate fuels [J.C.G. Andrae, R.A. Head, Combust Flame 156 (2009) 842-51] was extended with chemistry for ethylbenzene and m-xylene resulting in an overall model consisting of 150 species and 759 reactions. In model validation, comparisons were made between model predictions and experimental data of ignition delay times measured behind reflected shock waves, laminar burning velocities collected at elevated temperature and pressure and species profiles in a high-pressure single pulse shock tube. Generally good agreement was found and the model is sensitive to changes in mixture strength, pressure and temperature. Shock tube ignition delay modeling results for ethylbenzene and m-xylene also compare well to the ones for toluene. The rate controlling step for the ignition of ethylbenzene in the current mechanism is the reaction with ethylphenyl radical and oxygen. Ignition delay time for m-xylene was found to be very sensitive to reactions involving hydrogen atom abstraction from fuel by hydroxyl and oxygen and to branching reactions where methylbenzyl reacts with oxygen and hydroperoxide. The validated mechanism was used to study fuel chemistry effects when blending ethylbenzene with the paraffinic fuels iso-octane and n-heptane. A sensitivity- and flow path analysis showed that a higher consumption of hydroperoxide by ethylphenyl than expected from the contribution of neat ethylbenzene in a fuel mixture with iso-octane inhibits both iso-octane and ethylbenzene ignition. This can explain the observed increase in ignition delay time and octane number for fuel mixtures compared to neat fuels.     

Facile and not facile reactions for the production of maleic and phthalic anhydrides with vanadium mixed oxides based catalysts

Vanadium is a key element in the formulation of catalysts for the production of anhydrides by selective vapor oxidation with molecular oxygen. A study of the oxidations ofo-xylene,n-butane and benzene on V-P, V-Mo and V-Ti mixed oxides, the commercial catalysts for the synthesis of anhydrides, was carried out. The oxidation ofo-xylene on the three catalysts was the most facile reaction leading to high yields in phthalic anhydride; on the contrary in the oxidation ofn-butane only V-P mixed oxide was active and selective. V-P mixed oxide is active and selective in the oxidation of all the feedstocks and can be identified as the most polyfunctional catalyst. V-Mo is active and selective in botho-xylene and benzene oxidation and V-Ti only ino-xylene oxidation. Moreover the lesser selectivity in phthalic anhydride observed with V-P and V-Mo mixed oxides has been attributed to parallel oxidation reactions to the formation of phthalic anhydride, evidenced by a higher amount of phthalide.