链烷烃热裂解过程结构动力学模型与模拟

根据作者提出的结构-反应活性关系预测出链烷烃裂解时主要基元反应的动力学参数。以乙烷十丙烷混合裂解为例,就不同的反应网络进行了对比分析,提出了反应个数尽可能少而又能全面、真实反映裂解过程的反应网络。用Gear法模拟求解了由此建立的C_4单烃及其混合烃裂解的结构动力学模型,模型预测的产物分布与文献发表的中试数据吻合很好。     

石油烃热裂解反应速率常数估算方法的研究进展

石油烃热裂解反应动力学模型是工业裂解炉的核心技术之一。建立具有广泛适用性的石油烃热裂解自由基机理模型，需要获得构建该模型反应网络中各个基元反应的反应速率常数，综述了包括线性自由能关系、估算活化能的非线性方程、反应速率和分子特征量关系以及部分依赖实验确定反应速率的4类文献中报道过的估算反应速率常数的方法，并结合石油烃热裂解反应机理模型的需求，认为裂解机理模型中的反应可根据分类的不同，选取其中合适的方法进行反应速率常数的估算。     

1-丁烯热裂解自由基反应模型的建立及验证

基于自由基链式反应机理,将Materials Studio(MS)模拟和Aspen Plus模拟计算相结合研究了1-丁烯热裂解自由基反应机理,运用MS软件对1-丁烯的结构进行优化、分析,建立了初步的、可能发生的12个自由基反应网络和2个可能反应路径;对1-丁烯可能发生的热裂解自由基反应进行模拟计算,得到1-丁烯裂解自由基反应相关动力学参数如活化能(Ea)及速率常数(k)等;用Aspen模拟软件建立裂解反应器模拟实验过程,预测1-丁烯热裂解自由基反应产物分布情况。结果表明,1-丁烯热裂解自由基反应机理模型与一维热裂解工艺模型软件模拟1-丁烯热裂解的主要产物的种类一致,预测的产物分布也吻合,1-丁烯热裂解的主要目的产物是丁二烯、丙烯及少许乙烯,与已有的实验结论相符。     

聚烯烃与其裂解产物返回共裂解的研究

以聚烯烃塑料为裂解原料,在间歇反应釜中进行轻度热裂解,加热速率3—5℃/min,温度400℃,停留时间0—80 min;制取液相石油烃。为克服热裂解过程中的传热不均匀,提高热裂解产物轻质馏分的含量,进行了部分热裂解产物返回作为原料与聚烯烃塑料进行共裂解的实验探究,并对其裂解气相产物进行了气相色谱分析,液相产物进行了红外光谱、核磁共振氢谱表征以及GC-MS定量分析。结果表明:在400℃进行共裂解,液相产物平均收率约为90%,所得液相石油烃C数分布广,主要组分为链烷烃,其中直链烷烃所占比例44.03%。在聚烯烃塑料轻度裂解过程中部分热裂解产物返回共裂解,有利于裂解过程的传热,促进所得石油烃的轻质化且裂解过程中不会发生结焦反应。但共裂解液相产物中离心沉积物增多,主要组成为链烷烃,可作为裂解原料再次进行利用。     

煤快速裂解过程脂肪烃的组成及生成机制

研究煤快速裂解过程脂肪烃的组成与生成行为是优化煤炭分级热解气化工艺的关键。本研究借助快速裂解仪联用气相色谱-飞行时间质谱考察了一种淄博烟煤的快速裂解行为,深入分析了裂解产物脂肪烃的组成,进而依据实验结果推测了产物生成机理。结果显示快速裂解过程共有60种脂肪烃类化合物生成,主要包括直链烷烃、支链烷烃、直链烯烃、支链烯烃以及少量环烷烃、取代环烷烃、环烯烃以及二烯烃和炔烃。脂肪烃类碳数分布于C_3-C_(16)之间,并且主要以C_(10)以下为主。由于快速裂解的热流密度较大,使得煤中芳环外侧链同时发生多处断键反应。裂解一次产物进一步发生取代、加成和环化等二次反应是裂解产物中低碳烯烃、支链和环烷烃类生成的主要原因。此外,C_(13)脂肪烃含量较高表明原煤中含有大量26个碳的烷基侧链。     

基于结构导向集总的FCC汽油催化裂解分子尺度动力学模型

利用结构导向集总模型构造烃分子和编制反应网络,并结合Monte Carlo模拟方法,建立了催化裂化（FCC）汽油催化裂解反应的分子尺度动力学模型。结构导向集总模型选用7个分子结构片段表示催化汽油中的分子,生成2000个共计92种烃类分子代表催化汽油原料组成。模型选取催化汽油中含量较多的11种单体烃作为模型化合物研究其催化裂解反应行为,并以此为依据制定反应规则,求取模型所需反应速率常数。模拟结果表明,应用结构导向集总模型和Monte Carlo模拟方法进行催化裂解分子尺度动力学建模是可行的,能对多种反应产物的产率进行预测。模拟值和实验结果符合良好,相对误差基本在10%以内。模型对延长反应时间后的产品收率有一定的预测能力。     

石脑油组成结构对乙烯收率的影响

就石脑油组成中直链烷烃含量、异构烷烃含量、环烷烃含量、烷烃正异比等因素与其蒸汽热裂解乙烯收率的关系进行粗略分析.并根据理论分析与实验、生产经验,结合最小二乘法的数学分析方法,在大量试验数据的基础上初步拟合了一些经验方程.这些方程可作为判断石脑油裂解性能优劣和预测石脑油乙烯收率的粗略工具.     

金属盐和油层矿物存在下的稠油水热裂解反应动力学

根据金属盐和油层矿物存在下的稠油水热裂解反应实验结果,建立包括气体、饱和烃、芳香烃、胶质和沥青质在内的五集总动力学模型,并求取模型中的反应速率常数和活化能.计算结果表明,胶质作为主要反应中心,是气体、芳香烃和饱和烃等轻组分含量增长的主要来源.沥青质主要转化成胶质,裂化产物较少.实验数据与计算结果较吻合,所提出的五集总动力学模型可用来描述金属盐和油层矿物存在下的稠油水热裂解反应规律.     

高压DSC对烃类燃料安定性的研究

热氧化和热裂解过程中沉积物的生成是影响燃料安定性的重要因素。燃料发生氧化反应的温度越高,其抗氧化性能越好;温度是影响裂解沉积量的主要因素,随着温度的升高沉积量迅速增加。本文利用高压DSC对各种燃料烃(正构烷烃、环烷烃、烷基芳烃和双环烃)的安定性进行了研究。结果表明,在氧化反应中,环己烷的抗氧化性能最好,抗氧化性能最差的是四氢萘和正丁苯;在裂解反应中,四氢萘发生裂解反应的温度最高,其次是环烷烃J、P-10、正构烷烃、十氢萘,裂解温度最低的为正丁苯。     

D4/APAEDMS本体开环共聚反应机理及调控基元反应

Monte Carlo方法首次用来揭示八甲基环四硅氧烷（D₄）与N-β-氨乙基-γ-氨丙基甲基二甲氧基硅烷（APAEDMS）的本体开环共聚反应机理的关键调控基元反应.基于已提出的该体系本体共聚反应机理,并兼顾模拟精度与计算经济性,Monte Carlo模拟模型采用自由体积理论简化扩散效应并与本征反应动力学方程耦合.其中,本征动力学速率常数通过模拟主要共聚基元反应得到.基于优化的动力学速率常数通过模拟从分子水平上揭示：D₄/APAEDMS本体共聚机理为一伴有逐步特征的阴离子连锁聚合.其中,链引发及其逆反应对D₄/APAEDMS的本体共聚反应没有直接调控作用,而链缩合及其逆反应是本体系反应机理不同于纯活性阴离子聚合或逐步聚合反应机理的关键原因.     

Dehydrogenation kinetic model of heavy paraffins

Based on the dehydrogenation mechanism of heavy paraffins under industrial conditions, the intrinsic reaction kinetic model and catalyst deactivation model were established considering the influence of side reactions with different carbon‐number heavy paraffins. Based on the experimental data of dehydrogenation reactions with different carbon‐number paraffins in an axial continuous‐flow isothermal fixed‐bed microreactor, Powell optimization method was used to estimate the model parameters. The results show that there is a liner relationship between the activation energies and pre‐exponential factors of homologous reactions and carbon number of paraffins. A correlation model about the deactivation rate constants under different conditions was established. The validation of kinetic model showed that the model could be used to predict detailed product distribution with different feedstocks under different reaction conditions. © 2017 American Institute of Chemical Engineers AIChE J, 2017     

Hydrocracking of Fischer‐Tropsch waxes: Kinetic modeling via LHHW approach

A lumped kinetic model to describe the hydrocracking of complex mixtures of paraffins, such as Fischer‐Tropsch waxes, has been developed. A Langmuir‐Hinshelwood‐Hougen‐Watson approach has been followed, accounting for physisorption by means of the Langmuir isotherm. Finally, a complete form of the rate expression is used, thus introducing the equilibrium constants for dehydrogenation and protonation elementary steps. To minimize the number of model parameters, the kinetic and thermodynamic constants are defined as functions of the chain length. Vapor–liquid equilibrium is calculated along the reactor, and the hydrocarbons concentrations are described by means of fugacity. The model provides quite a good fitting of experimental results and is able to predict the effects of the operating conditions (temperature, pressure, H₂/wax ratio, and WHSV). Outstandingly, the estimated values and trends of the kinetic and thermodynamic constants (activation energies, Langmuir adsorption constants, etc.) are in line with their physical meaning. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Transient microkinetic modelling of n-heptane catalytic cracking over H-USY zeolite

A microkinetic model for the catalytic cracking of n-heptane is proposed comprising a set of significant elementary steps which generate a complex reaction network. This approach constitutes a compromise between fundamental and lumped models since the reaction scheme is detailed to the carbon atom level by considering separately olefins, paraffins and adsorbed carbenium ions with the same carbon atom number. Elementary rate constants are estimated through expressions relating species reactivity with their carbon atom number. Fitting the model against experimental data over a large parameter space was performed using a micro-genetic algorithm with binary encoding and logarithmic distribution. The advantage of this approach is that it allows modelling the reaction network without supposition of rate determining steps. The model predicts very well the observed transient activity for n-heptane cracking over H-USY zeolite at and in general, it reasonably predicts the experimental trends for the products distribution.     

MODELING OF GAS OIL CATALYTIC CRACKING IN A FIXED BED REACTOR USING A FIVE-LUMP KINETIC MODEL

A five-lump kinetic model had been developed for modeling of gas oil catalytic cracking. The experiments were carried out in a standard fixed bed micro-activity test (MAT) reactor. Distribution of the cracking product components was determined as a function of temperature. The sequential step optimization method was used to estimate the kinetic constants. A MAT reactor nonisothermal and the unsteady-state model was proposed. The overall heat of the reactions was established from the macroscopic difference of the products' and the reactants' enthalpies. The influence of the feedstock and the reactor temperature was discussed. The reactor and the kinetic models were validated using the experimental MAT results. Simulation results were in good agreement with the experimental data.     

基于精细自由基反应机理的丙烷裂解炉炉管CFD模拟(英文)

In the radiant section of cracking furnace, the thermal cracking process is highly coupled with turbulent flow, heat transfer and mass transfer. In this paper, a three-dimensional simulation of propane pyrolysis reactor tube is performed based on a detailed kinetic radical cracking scheme, combined with a comprehensive rigorous computational fluid dynamics（CFD） model. The eddy-dissipation-concept（EDC） model is introduced to deal with turbulence-chemistry interaction of cracking gas, especially for the multi-step radical kinetics. Considering the high aspect ratio and severe gradient phenomenon, numerical strategies such as grid resolution and refinement, stepping method and relaxation technique at different levels are employed to accelerate convergence. Large scale of radial nonuniformity in the vicinity of the tube wall is investigated. Spatial distributions of each radical reaction rate are first studied, and made it possible to identify the dominant elementary reactions. Additionally, a series of operating conditions including the feedstock feed rate, wall temperature profile and heat flux profile towards the reactor tubes are investigated. The obtained results can be used as scientific guide for further technical retrofit and operation optimization aiming at high conversion and selectivity of pyrolysis process.     

CONSISTENCY OF THE TEN-LUMP KINETIC MODEL FOR CRACKING: STUDY IN A LABORATORY REACTOR AND USE FOR SIMULATION OF AN FCCU

The kinetic constants corresponding to the ten-lump kinetic model have been determined by carrying out the cracking of three different feeds in a laboratory reactor under experimental conditions (temperature, contact time, C/O ratio) similar to those of industrial FCC units and using a commercial catalyst. The kinetic constants are independent of the feed composition, which is evidence of the consistency of the ten-lump kinetic model. The kinetic constants determined have been used in the simulation of an FCC unit operated following two strategies (maximization of the yield of gasoline and mean distillates), and in both cases it has been proven that the results of the simulation are in agreement with those of the industrial plant.     

KINETICS OF GRAFTING IN SOLUTION POLYMERIZATION

A mechanistic kinetic model, which includes several elementary reactions occurring simultaneously, is developed for the kinetics of grafting in solution polymerization. This model allows prediction of the rate of polymerization and grafting efficiency under various reaction conditions. It also permits evaluation of grafting reaction rate constants. Experimental data available in the literature are used to test the model. Very good agreement is observed between the data and model predictions.     

A new generic approach for the modeling of fluid catalytic cracking (FCC) riser reactor

A new kinetic model for the fluid catalytic cracking (FCC) riser is developed. An elementary reaction scheme, for the FCC, based on cracking of a large number of lumps in the form of narrow boiling pseudocomponents is proposed. The kinetic parameters are estimated using a semi-empirical approach based on normal probability distribution. The correlation proposed for the kinetic parameters’ estimation contains four parameters that depend on the feed characteristics, catalyst activity, and coke forming tendency of the feed. This approach eliminates the need of determining a large number of rate constants required for conventional lumped models. The model seems to be more versatile than existing models and opens up a new dimension for making generic models suitable for the analysis and control studies of FCC units. The model also incorporates catalyst deactivation and two-phase flow in the riser reactor. Predictions of the model compare well with the yield pattern of industrial scale plant data reported in literature.     

Simplified Free‐Radical Reaction Kinetics for p‐Xylene Oxidation to Terephthalic Acid

The kinetic models based on complex free‐radical mechanisms always involve lots of parameters, which result in model overparameterization. In this work, on the basis of free‐radical reaction mechanisms, a simplified kinetics for liquid‐phase catalytic oxidation of p‐xylene (PX) to terephthalic acid (TPA) was developed. By assuming that different peroxy radicals have equivalent reactivity, all the initiation rate constants are identical, and the differences in the rates of termination between various peroxy radicals are neglected, the kinetic model is simplified to include only six parameters that are to be determined by experiment. The kinetic model established in this paper was shown to have satisfactory precision in predicting the concentration profiles. The kinetic model proposed is even simpler than the first ‐ order kinetic model because the rate constants concerning chain propagation and termination are independent of temperature within the range investigated.