正己烷裂解反应自由基模型的理论研究

采用量子化学法研究了模型化合物正己烷裂解过程,并计算其动力学参数。依据自由基理论,建立由216个基元反应组成的正己烷裂解反应自由基模型,用CBS-QB3法计算链引发和终止反应动力学参数,用MPW1B95/6-311+G(2d,2p)法计算链增长反应动力学参数。根据动力学参数计算结果,忽略相对不重要的反应,将模型简化为160个基元反应。模拟计算表明,在相同的裂解条件下,简化模型模拟结果与完整模型模拟结果一致,各组分相差不大于0.1%wt;建立的动力学模型对主要产物收率预测较好,与实验值相差小于0.7%wt,可正确地预测正己烷裂解产物的组成和各组分含量沿反应管长度的分布,为进一步研究复杂的烃裂解过程提供了基础。     

智能化基元反应动力学数据库的建立

本文建立的智能化动力学数据库，用户不但能检索到化学家已经测定的大量的基元反应的动力学数据，还能进行未知反应动力数学的理论估算，从而提供更多有实用价值的基元反应的动力学参数数值，使人们对复杂反应过程实现计算机模拟的可能性更大。     

基于简化模型的T型微反应器设计

分析T型微反应器内流体混合程度和反应产物收率的常用方法:是建立计算流体动态模型,也就是CFD模型,可是这种模型不适用于微反应器的优化设计,因为利用CFD模型进行优化计算需要的大量的计算时间。本研究开发了一个描述T型微反应器流体流动状态的简化模型,通过假设边界条件和假设扩散系数的设定来计算微反应器内反应产物收率。其中假设边界条件用来描述强混合效果在反应通道入口处的流动状态,假设扩散系数用来描述混合效果在流动路径上的变化。本研究依据此简化模型,确立了一种优化设计方法:,用来设计具有最优尺寸的T型微反应器。优化问题的目标函数是最大反应产物收率,优化约束包括反应通道尺寸约束和操作压力约束。在求解过程中,首先建立尺寸约束边界条件下的CFD模型,然后依据CFD模型计算结果:,求解简化模型中的未知参数。将建好的简化模型作为优化问题的等式约束,最后求出最优的T型微反应器。简化模型和优化设计方法:的有效性通过一个快速平行串联反应在微反应器中的反应过程来验证。简化模型的优化设计结果:和CFD模型验证结果:高度一致。     

间歇反应过程仿真模型的研究

该文在用机理法建立缩合反应动力学模型的基础上,建立了间歇反应过程的动态仿真模型,并采用欧拉法对全混釜反应器进行物料、热量衡算及相平衡计算。在相平衡计算中引入定容闪蒸算法,利用“双层法”确定相平衡方程中的参数,既保证了计算的准确性和稳定性,又符合动态模拟快速的要求,取得了较好的仿真效果。     

Gsp气化炉建模与动态模拟

为了能够更好的模拟Gsp煤气化炉,建立了新的气化炉模型。Gsp煤气化炉内部反应较为复杂,温度、压力较高难以模拟,为了对气化炉建立数学模型并且对生产工艺进行动态模拟,通过对煤气化炉装置物料流动方式的分析,结合煤气化反应的动力学、物料衡算和能量衡算,简化反应过程的次要因素,最终用通用化工动态流程模拟优化软件平台建立了气化炉反应器的串联全混流模型,并且选用四阶龙格-库塔法进行求解计算。反应器动态模拟的数值结果与实测值相比较,发现通过优化计算的结果可以把误差控制在1%以内,证明建立的数学模型能够很好地模拟工艺流程,为模拟Gsp煤气化炉提供了一种新的思路。     

化学动力学过程模拟软件的开发

采用Borland C Builder 6.0可视化编程环境和基于面向对象的C 语言开发动力学模拟软件。该软件中对微分方程组的求解采用四阶龙格-库塔法。该软件适用于模拟各种化学动力学过程,用户可以根据不同情况设置复杂反应的任意步骤及其基元反应、相应反应速率常数及各物种的初始浓度和反应时间等。软件根据用户设定的参数自动计算出参与反应过程中各物种的浓度变化,同时提供Excel输出功能和绘图功能,可以直观地看到反应的动力学曲线。该软件不需要其他应用软件支持,可以在Windows 98/Me/2000/XP/2003下直接运行。程序涉及到的算法,需要较复杂的数据结构,程序采用C 语言提供的标准模板库,简化了程序设计并提高了运行效率。该软件模拟了一个包含平行-连串反应的化学动力学过程,运行速度较快,并得到精确的计算结果。     

面向人臂三角形动作基元的拟人臂运动学

对拟人臂的运动规划问题进行了研究.通过引入动作基元的概念,将动作基元空间作为连接任务空间与关节空间的桥梁,构建了一个"关节空间-动作基元空间-任务空间"的三级运动规划框架.这种规划方式既保证了对拟人臂运动过程的控制,又简化了复杂操作任务的运动规划.在抽象的动作基元基础之上提出了一个具体的人臂三角形模型,用以描述拟人臂的运动状态.通过引入拟人臂工作平面的概念,利用坐标变换与几何分析相结合的方法详细推导并建立了人臂三角形空间与任务空间和关节空间之间的正逆运动学,为基于人臂三角形的动作基元设计奠定了基础.最后通过仿真算例验证了运动学算法的有效性与可行性.     

短停留时间下的神华上湾煤直接液化恒温阶段反应动力学研究

以中国神华煤制油化工有限公司上海研究院0.01 t/d神华煤直接液化工艺连续装置实验数据为基础,建立适合神华煤直接液化反应恒温阶段在短停留时间下的集总动力学模型,模型在保证液化反应升温阶段和恒温阶段是一个连续整体的前提下,使用BFGS变尺度法优化计算得到了恒温阶段模型参数。结果表明,液化反应在短停留时间时的恒温阶段动力学模型预测的组分收率的计算值与实验值平均相对偏差、平均绝对偏差分别为5.23%、0.90%,吻合良好,该模型可以较好地反映神华煤直接液化恒温阶段在短停留时间的反应过程。     

超声电机定子的动力学特性仿真

将行波超声电机的两相振动简化为两自由度系统,建立了基于模态假定的动力学方程,基于机电类比建立定子系统的传递函数技导纳表达式,通过有限元计算及实验测量确定模型参数,在此基础上建立了定子动力学模型的仿真模型结果表明该模型可用于进行定子的参数化设计及性能的预测。     

圆形截面T型微反应器的优化设计

对圆形截面T型微反应器进行优化设计,可以增强反应器内流体混合程度,进而提高反应产物收率。和矩形截面微反应器相比,圆形截面的微反应器内部压力各向均衡,有利于克服操作压力提高对微反应器壁面承压的影响。本研究开发了一个描述圆形截面T型微反应器流体流动状态的简化模型,通过层叠式假设边界条件描述反应通道入口处的强混合流动状态,进而计算微反应器内反应产物收率。依据此简化模型,本研究应用改进型模拟退火算法,用来设计具有最优反应器半径和最优入口管径中心差的的T型微反应器。优化问题的目标函数是最大反应产物收率,优化约束包括反应通道半径约束和操作压力约束。本研究利用gPROMS和Matlab的混合编程,利用改进型模拟退火算法,实现优化算法和简化模型的求解。优化求解的有效性通过一个平行串联反应在微反应器中的反应过程来验证,求解结果和CFD模型验证结果比较一致。     

用计算奇异值摄动方法简化复杂化学反应动力学模型

介绍了用于简化化学反应动力模型的计算奇异值摄动方法(CSP),给出了其基本思想与具体计算方法,然后用该方法来对一氧化碳／氢气在空气中燃烧的化学反应、激波管中甲烷的点火燃烧反应实例进行了简化。从计算结果看,CSP方法是一种比较有效的化学反应模型简化方法,用该方法简化得出的简化模型不仅减少了微分求解的组分数目,而且保持了较高的计算精度,能有效提高计算效率,具有较强的工程实际价值。     

REACTKIN—a program for modelling the chemical reactions in electrolytes solutions

In this paper, REACTKIN, the new computer program for modelling the kinetics of complex homogeneous chemical reactions in electrolyte and non-electrolyte solutions has been presented. This program makes possible the creation of a model of a reaction in the convenient form of a graph as well as simulating the course of a reaction on the basis of the model created. REACTKIN allows the determination of the rate constants of elementary reactions using experimental kinetic data concerning the influence of the ionic strength of the solution. The program REACTKIN can be of importance in the studies of multi-step chemical reactions in electrolyte solutions as well as in chemistry education.     

Reaction analysis and visualization of ReaxFF molecular dynamics simulations

ReaxFF MD (Reactive Force Field Molecular Dynamics) is a promising method for investigating complex chemical reactions in relatively larger scale molecular systems. The existing analysis tools for ReaxFF MD lack the capability of capturing chemical reactions directly by analyzing the simulation trajectory, which is critical in exploring reaction mechanisms. This paper presents the algorithms, implementation strategies, features, and applications of VARxMD, a tool for Visualization and Analysis of Reactive Molecular Dynamics. VARxMD is dedicated to detailed chemical reaction analysis and visualization from the trajectories obtained in ReaxFF MD simulations. The interrelationships among the atoms, bonds, fragments, species and reactions are analyzed directly from the three-dimensional (3D) coordinates and bond orders of the atoms in a trajectory, which are accomplished by determination of atomic connectivity for recognizing connected molecular fragments, perception of bond types in the connected fragments for molecules or radicals, indexing of all these molecules or radicals (chemical species) based on their 3D coordinates and recognition of bond breaking or forming in the chemical species for reactions. Consequently, detailed chemical reactions taking place between two sampled frames can be generated automatically. VARxMD is the first tool specialized for reaction analysis and visualization in ReaxFF MD simulations. Applications of VARxMD in ReaxFF MD simulations of coal and HDPE (high-density polyethylene) pyrolysis show that VARxMD provides the capabilities in exploring the reaction mechanism in large systems with complex chemical reactions involved that are difficult to access manually.     

Model complexity reduction of chemical reaction networks using mixed-integer quadratic programming

The model complexity reduction problem of large chemical reaction networks under isobaric and isothermal conditions is considered. With a given detailed kinetic mechanism and measured data of the key species over a finite time horizon, the complexity reduction is formulated in the form of a mixed-integer quadratic optimization problem where the objective function is derived from the parametric sensitivity matrix. The proposed method sequentially eliminates reactions from the mechanism and simultaneously tunes the remaining parameters until the pre-specified tolerance limit in the species concentration space is reached. The computational efficiency and numerical stability of the optimization are improved by a pre-reduction step followed by suitable scaling and initial conditioning of the Hessian involved. The proposed complexity reduction method is illustrated using three well-known case studies taken from reaction kinetics literature.     

Numerical study of a stochastic particle method for homogeneous gas-phase reactions

In this paper, we study a stochastic particle system that describes homogeneous gas-phase reactions of a number of chemical species. First, we introduce the system as a Markov jump process and discuss how relevant physical quantities are represented in terms of appropriate random variables. Then, we show how various deterministic equations, used in the literature, are derived from the stochastic system in the limit when the number of particles goes to infinity. Finally, we apply the corresponding stochastic algorithm to a toy problem, a simple formal reaction mechanism, and a real combustion problem. This problem is given by the isothermal combustion of a homogeneous mixture of heptane and air modelled by a detailed reaction mechanism with 107 chemical species and 808 reversible reactions. Heptane as described in this chemical mechanism serves as model-fuel for different types of internal combustion engines. In particular, we study the order of convergence with respect to the number of simulation particles, and illustrate the limitations of the method.     

Visualization methods in analysis of detailed chemical kinetics modelling

Sensitivity analysis, principal component analysis of the sensitivity matrix, and rate-of-production analysis are useful tools in interpreting detailed chemical kinetics calculations. This paper deals with the practical use and communication of the sensitivity analysis and the related methods are discussed. Some limitations of sensitivity analysis, originating from the mathematical concept (e.g. first-order or brute force methods) or from the software-specific implementation of the method, are discussed. As supplementary tools to the current methods, three novel visual tools for analysis of detailed chemical kinetics mechanisms are introduced: (a) scaled sensitivity analysis which is especially suited for studying initiation reactions where the span of reaction rates is high; (b) automated generation of reaction pathway plots which provides an immediate graphical illustration of the chemical processes occurring; (c) explorative (or chemometric) analysis of accumulated rate of progress matrices which assist in the identification of reaction subsets. The application of these tools are demonstrated by analysing NOx enhanced oxidation of methane at 700-1200 K.     

Thermodynamic Structure of Nonlinear Macrokinetics in Reaction-Diffusion Systems

Affinity picture — new for transport phenomena — and the traditional Onsagerian picture are shown to constitute two equivalent representations for kinetics of chemical reactions and transfer processes. Two competing directions in elementary chemical or transport steps are analyzed. Nonequilibrium systems are described by equations of nonlinear kinetics of Marcelin-Kohnstamm-de Donder type that contain terms exponential with respect to the Planck potentials and temperature reciprocal. Simultaneously these equations are analytical expressions characterizing the transport of the substance or energy through the energy barrier. We regard kinetics of this sort as potential representations of a generalized law of mass action that includes the effect of transfer phenomena and external fields. We also consider physical consequences of these kinetics closely and far from equilibrium, and show how diverse processes can be described. In these developments we point out the significance of nonlinear symmetries and generalized affinity. Correspondence with the Onsager's theory is shown in the vicinity of thermodynamic equilibrium. Yet, the theory shows that far from equilibrium the rates of transport processes and chemical reactions cannot be determined uniquely in terms of their affinities because these rates depend on all state coordinates of the system.