The mixing effect on the free radical MMA solution polymerization

Mathematical models of reactors for the polymerization of methylmethacrylate (MMA) have been developed and analyzed to elucidate reactor dynamics and to determine conditions for improved operation. The effects of mixing and heat transfer in an MMA polymerization reactor system have been explored by the development of an imperfect mixing model. To model imperfect mixing in polymerization, a reactor configuration using two tanks in parallel was used. Bifurcation diagrams developed using numerical analysis of the model have been drawn with two variable parameters, an exchange ratio, σ, and a volume ratio, κ. We use feed and coolant temperatures as bifurcation parameters. If variable parameters are small, the lower solution branch of the steady state solutions is quite different from that of a simple model that assumes perfect macro-mixing as bifurcation parameters change. If σ increases (κ=0.1, σ=1.0), the shape of a steady state solution curve differs significantly from that of a simple model as the feed temperature decreases.     

The effect of particle size distribution on the olefin polymer reactor dynamics

Mass and energy balances in a reactor have been derived to study the effect of particle size distribution (PSD) for each reaction mechanism on the reactor dynamics. It was observed that the PSD affects both bed height and particle volume. A feasible region for reactor operation has been calculated by using physical constraints. In a nonisothermal polymerization system, the reactor temperature does not change appreciably as catalyst injection rate increases. A unique steady state solution is found in a gas-phase continuous stirred-bed propylene polymerization reactor. The eigenvalues of the system of equations indicate that the steady state is unstable. A comparison with published data allows the observation that the actual reactor dynamics may be readily explained by using only the PSD derived from a simple reaction mechanism.     

A numerical bifurcation analysis of nonlinear oscillations in crystallization processes

The main aim of this work is the theoretical prediction and analysis of the nonlinear behavior of crystallization processes. As a first step towards the theoretical analysis a fairly simple population balance model including fines dissolution and classified product removal has been considered. By means of numerical bifurcation and stability analysis, regions in the parameter space of the operating conditions and the physical properties with periodic behavior have been predicted. Due to the simplicity of the underlying model the results are only of qualitative nature. Future work will focus on a quantitative prediction of the nonlinear behavior with more detailed models and an experimental verification.     

溶液法聚乙烯工艺反应前移、后移现象分析

抚顺石化公司乙烯化工厂聚乙烯装置所用的催化剂是由钛和钒为基础的齐格勒钛-钒催化剂.催化剂的注入量以及助、主催化剂的比例直接影响到反应的前移和后移,不仅造成了催化剂的消耗增加,而且直接影响到产品的质量.反应前移和后移的调整对于聚合反应至关重要.     

纳米硅基氧化物改性有机玻璃的制备及表征

以甲基丙烯酸甲(MMA),内米级硅基氧化物（nSiO)等为原料，使用特殊的工艺和新开发的助剂，采用原位加成聚合，制备了PMMA／nSiO复合材料。复合材料的冲击性能提高超过40％，维卡热变形温度提高15℃以上，可见光透过度88．1％，下降很少。     

Dynamics and stability of ethylene polymerization in multizone circulating reactors

Multizone circulating bed reactors (MZCR) have the exclusive characteristics of producing polymers of different molecular weights in a single particle. Traditional fluidized bed reactors, on the other hand, can produce only one kind of molecular weight with relatively narrow distribution. A dynamic model for the MZCR is used to illustrate the basic dynamic behavior of the new reactor design used for polyethylene production. The model is used to study the copolymerization of ethylene with butene. Several parameter sensitivity analyses are performed to show the computer-simulated time responses for reactor temperature, number-average molecular weight, weight-average molecular weight, catalyst feed rate and the monomer/comonomer concentration along the reactor length. At certain operating conditions dynamic instability is observed and the results for the effect of cooling water temperature, catalyst feed rate, monomer and comonomer initial feed concentration on the reactor temperature and polymer molecular weight reveal that the system is very sensitive to disturbances in the heat exchanger coolant temperature. Also, at some operating conditions, the reactor temperature oscillates above the polymer melting temperature. Temperature runaway above polymer softening point is a serious problem which may cause polymer melting and hence reactor shutdown. The oscillatory behavior of the reactor temperature necessitates a suitable temperature control scheme to be installed.     

高分子量聚甲基丙烯酸甲酯合成研究

聚甲基丙烯酸甲酯（PMMA）用途之一是作为HJ－73导弹续航药的包复层。为满足生产的需要，我们以悬浮聚合工艺进行了高分子量PMMA的合成研究。原材料（规格）配比MMA（工业级）100分散剂（自制）0．6～1．2（以干基计）引发剂（化学统）0．1～0．5水适量在装有高速搅拌器、温度计的白钢反应器中，投入分散剂和水，搅拌、分散1．sh，再投入溶有引发剂的MMA，按照一定的升温曲线，控制反应温度反应3h离心、洗涤、干燥、过筛。MMA的纯度影响着聚合反应的进程和聚合物的性质。经分析测定，MMA中的杂质有二甲醇、丙酮、异丁酸甲酯、a一羟…     

The use of particle swarm optimization for dynamical analysis in chemical processes

Particle swarm optimization is employed here to evaluate the parametric regions where different dynamic phenomena (periodic oscillations, double-period oscillations, chaos) can be expected in dynamic models. The proposed algorithm comprises two fundamental steps: the rough evaluation of regions where the desired solutions can be found and solution refining. The refining step allows the search for unstable solutions that may coexist with the other stable attractors. No preliminary bifurcation analysis is required. Simulations performed for distinct dynamic models show that the proposed algorithm is indeed able to locate different dynamic phenomena in the parameter space and that the algorithm may be of help for those interested in increasing the speed of more traditional dynamic bifurcation analysis.     

搪瓷反应釜内加装蛇管的改造

针对搪瓷反应釜冷却物料效果不佳的问题 ,在釜内加装冷却蛇管 ,改造后该釜使用效果较好     

Dynamics analysis of an age distribution model of oscillating yeast cultures

The ability of an age-population balance model to capture experimentally observed oscillatory dynamics of continuous cultures of budding yeast was investigated through numerical simulations. Experiments with continuous yeast cultures have shown that several oscillatory modes can occur at the same operating condition, and that the mode attained depends on the start-up conditions. Numerical simulations of the model did reveal the existence of several stable periodic solutions. However, each occurred over a different range of dilution rates. Experiments also have shown that the steady state in continuous yeast cultures is stable, even under conditions that allow oscillatory dynamics. The stability of the steady state of the age population balance model under conditions that allow oscillatory dynamics was not resolved. The Jacobian matrix at the steady state is highly ill conditioned, with some eigenvalues very close to the imaginary axis. Using different integration routines to solve the model gave different results with regard to the stability of the steady state, one solver finding the steady state to be stable, another finding the steady state to be unstable.     

Bifurcation analysis of two continuous bioreactors operated in series with recycle

In this paper, bifurcation analysis has been carried out for two continuous bioreactors operated in series with recycle from the second reactor. The existence of multiplicity of steady states is analyzed by considering Contois growth kinetics in the process model. It was observed that there exist two possible steady states of which one is trivial (wash out condition). Stability analysis is carried out to determine the stability of these steady states and it was observed that both these steady states are unstable in nature. Bifurcation analysis has been carried out for substrate and biomass concentration with dilution rate as the bifurcation parameter. Effect of recycle ratio, substrate separation factor and biomass separation factor is studied and analyzed. It was observed that Hopf bifurcation occurs at a dilution rate of 1.0208 with purely imaginary Eigen values which showed that sustained oscillatory behavior exists in the substrate concentration of the second reactor. The significance of different bifurcation points and the operating conditions by considering biomass and substrate concentrations in each reactor is studied and it was observed that the bioreactors need to be operated at intermediate dilution rates to obtain improved conversion and yield.     

Linear stability analysis of two monomer systems of frontal polymerization

Frontal polymerization is a method of manufacturing polymer via a self-propagating reaction wave. A mathematical model that describes both free-radical binary frontal polymerization and frontal copolymerization is presented. Linear stability of polymerization waves in the two monomer systems is studied. Parameters that are responsible for the loss of stability are identified, and stability boundaries in the parameter space are obtained.     

PWM电压型逆变器的数学模型分析

介绍了PWM波的生成原理 ,建立了基于PWM交 直 交电压型逆变器的动态数学模型 ,利用它分析了电压型PWM逆变器正常工作时的 8种基本开关模式 ,考虑了影响逆变器工作的各种因素 ,为优化PWM逆变器的研究奠定了理论基础     

苯乙烯—甲基丙烯酸稳定超浓乳液的制备及聚合

本文用一步法制得了稳定的苯乙烯一甲基丙烯酸超浓乳液。探讨了乳化剂浓度,乳化剂的类型,乳化剂的复配,单体体积分数及甲基丙烯酸含量对超浓度乳液稳定性的影响。初步探讨了体积分数,乳化剂浓度对超浓度乳液聚合过程及最终胶乳粒子的影响。     

等离子体表面改性法改善有机玻璃抗静电性能的研究

简述了有机玻璃产生静电的原因以及消除静电危害的方法,重点讨论了等离子体表面改性法改善材料抗静电性能的机理以及影响抗静电改性效果的工艺因素,并简要阐述了等离子体改性法改善材料抗静电性能的原因。     

Recent advances in polymer reaction engineering: Modeling and control of polymer properties

Complex reaction kinetics and mechanisms, physical changes and transport effects, non-ideal mixing, and strong process nonlinearity characterize polymerization processes. Polymer reaction engineering is a discipline that deals with various problems concerning the fundamental nature of chemical and physical phenomena in polymerization processes. Mathematical modeling is a powerful tool for the development of process understanding and advanced reactor technology in the polymer industry. This review discusses recent developments in modeling techniques for the calculation of polymer properties including molecular weight distribution, copolymer composition distribution, sequence length distribution and long chain branching. The application of process models to the design of model-based reactor optimizations and controls is also discussed with some examples. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

The bifurcation behavior of a polyurethane continuous stirred tank reactor

In this work the open-loop nonlinear bifurcation analysis of a continuous stirred tank reactor where polyurethane polymerization reactions take place is carried out. The effect of potential manipulated, disturbance and design variables on the reactor nonlinear behavior is addressed. Moreover, the impact of cascade feedback control on the steady-state multiplicity pattern is also discussed. It is shown that cascade control introduces new nonlinearity patterns increasing closed-loop sensitivity.     

Petroleum allocation at PETROBRAS: Mathematical model and a solution algorithm

Petroleum allocation is an important link for the integration of petroleum supply chain at PETROBRAS as it is responsible for refining the strategic supply planning information to be used at the operation levels. In this work we describe how mathematical programming is being used to solve the petroleum allocation problem and we show the effectiveness of a local search method by optimization to solve real industrial problems. We propose a mixed-integer linear programming formulation of the problem that relies on a time/space discretization network. As the model cannot be solved for the industrial size instances of the problem, and not even a feasible solution can be found after 15 days of computation, we implement an algorithm based on a heuristic to find a feasible solution and on a local search procedure based on optimization to improve it. Using this algorithm, solutions are found for all the case studies within 10% of optimality in less than 5 h.     

CFD analysis of air distribution in fluidised bed equipment

The unique features of the fluidised bed—excellent mixing capacity and high heat and mass transfer rates—are highly dependent on the quality of fluidisation resulting from the bubble characteristics of the fluidising gas, which to a large extent depend on the distributor design. In order to understand the fluidisation hydrodynamics of a fluidised bed operation, it is essential to assess how airflow is distributed through the equipment. This paper reports on the use of Computational Fluid Dynamics (CFD) as a numerical tool to enlarge this understanding. CFD simulations were performed for a Glatt GPCG-1 fluidised bed coater in which stainless steel woven wire mesh distributors are used as the standard distributor plates. Firstly, an experiment was set up in which the permeability and the inertial resistance of the investigated distributors were determined. Using these inputs, two types of boundary conditions, available in the CFD software Fluent, to model a porous medium such as a distributor, were compared. Furthermore, the CFD simulations were verified in the lab-scale fluidised bed unit using air mass flow rate, pressure drop and inner wall temperature recordings. As an unequal airflow inside the plenum of the GPCG-1 was found to occur, CFD was used as a design tool to investigate reactor configuration changes in order to obtain a more homogeneous airflow towards the distributor.