Continuous emulsion polymerization of vinyl acetate. Part I: Experimental studies

An interesting feature of commercial continuous emulsion polymerization reactors is the important phenomenon of sustained oscillations. Laboratory investigations of emulsion polymerization in a continuous stirred tank reactor (CSTR) have shown that the conversion, number of polymer particles and other related properties often oscillate widely with time. These oscillations can lead to emulsifier levels too small to adequately cover polymer particles resulting in excessive agglomeration and reactor fouling. Herein is reported an extensive experimental study of vinyl acetate emulsion polymerization in a CSTR. The effects of initiator and emulsifier concentrations, mean residence time and rate of agitation on the production rate and size distribution of polyvinyl acetate latices were investigated. Domains of reactor operation which give rise to sustained oscillations and massive agglomeration of the latex are mapped which give rise to sustained oscillations and massive agglomeration of the latex are mapped out. The effect of different start-up policies on reactor transients were also investigated.     

Continuous emulsion polymerisation of styrene and methyl acrylate

An investigation of continuous emulsion polymerisation kinetics was carried out using a series of three continuous stirred tank reactors (CSTR), and styrene and methyl acrylate as types of monomer with different solubilities in water. Steady-state conversion fluctuations reported in the literature could be suppressed by holding the feed rates constant. The results obtained are only partly in agreement with the theory proposed by Gershberg & Longfield, who combined the basic assumptions of the Smith-Ewart theory with steady-state CSTR kinetics. An explanation for the deviations from this theory is therefore suggested which takes into account the tendency of relatively water-soluble monomers to form particles from the homogeneous solution and to undergo so-called interparticle termination as a result of migration of radicals between the latex particles.     

Molecular weight distribution in low-density polyethylene polymerization; impact of scission mechanisms in the case of a tubular reactor

It has been shown that scission kinetics strongly affects the molecular weight distribution (MWD) of low-density polyethylene (ldPE) in a continuous stirred tank reactor (CSTR). The present paper focuses on the effects of different chemical scission mechanisms, linear and topological scission, as well as mechanical scission on MWD in batch and tubular reactors. In contrast to the CSTR, a batch reactor MWD does not show bimodalities or long tails. The tubular reactor was modeled as an industrially representative system with four initiator injection points and a proper ‘cocktail’ of different initiators. Calculated MWD was compared to one experimentally determined with SEC-MALLS for a commercial tubular product and fair agreement was found. Typically, these MWDs are broad, but not bimodal. Sensitivity studies were performed as to scission kinetics and the effect of chain transfer agent (CTA). Both batch and tubular reactor were observed to be less sensitive to scission kinetics than a CSTR. In addition, alternative CTA injection strategies (downstream positions) were tested. These showed interesting behavior leading to very broad and bimodal MWD. The model allows following the MWD broadening along the tube. We conclude that batch and tubular ldPE reactors lead to completely different MWD behavior than a CSTR and that it is possible to manipulate it to a great extent.     

黄贮玉米秸秆在全混流、竖向推流、折流板竖向推流反应器中的厌氧发酵特性

为提高厌氧发酵的效率和秸秆利用率,将玉米干秸秆经过物理生物联合预处理形成黄贮玉米秸秆。本研究通过实验考察了黄贮玉米秸秆在竖向推流反应器（vertical plug flow,VPF）、全混流反应器（continuous stirred tank reactor,CSTR）和由本文作者课题组首创的折流板竖向推流反应器（baffled vertical plug flow,BVPF）中的厌氧发酵产气性能。结果表明,VPF反应器在有机负荷率（organic loading rate,OLR）为0.5gVS/(L·d)时运行良好,但提高OLR会出现出料困难的问题。CSTR有搅拌装置,所以反应器能够快速达到产气平衡。在OLR为1gVS/(L·d)时,BVPF达到稳定所需时间比CSTR多7天,但最终趋于稳定时CSTR和BVPF反应器的单位挥发性固体（volatile solid,VS）的日产气量分别为390.9mL和382.4mL。在OLR为2gVS/(L·d)时,BVPF达到稳定所需时间仅比CSTR多2天,稳定时CSTR和BVPF反应器的单位VS日产气量分别为291.3mL和294.9mL。此外,3种反应器在运行阶段,pH和VFA/TIC值都能维持稳定。在提高OLR后,BVPF和CSTR能够达到新的平衡状态。本实验结果表明VPF反应器只能用于低OLR的情况;CSTR达到稳定状态所需的时间较短,但CSTR和BVPF在稳定运行时的产气效率基本持平。由于BVPF的耗能量、耗水量低,因此该类反应器有良好的商业应用前景。     

Emulsion polymerisation in continuous reactor systems

Continuous reactor systems find important applications in the production of sythetic polymer latexes and increased production rates are providing additional incentives for the development of new continuous systems. The fundamental factors that should be considered in the development of continuous processes are reviewed in this paper. Particular emphasis is placed on exploring the differences between batch and continuous reactors and why these difference can lead to different latex product, even if the same recipe is employed. These factors make the task of designing continuous reactor systems based on batch research and development very difficult and risky. Thus it is recommended that small-scale continuous reactors be employed early in a product/process development effort if that effort is likely to lead to a continuous commercial process. The published literature on continuous emulsion polymerization reactors has been reasonably active in the past ten years. Our understanding of the chemistry and reactor modelling has been advanced but a number of areas for fruitful research remains. Some of these problems are reviewed and directions for new efforts are suggested.     

The quasi-steady-state approximation in continuous stirred tank reactors

The Quasi-steady-state-approximation (QSSA) applied lo continuous stirred tank reactors (CSTR) is examined. The induction period is found to be somewhat longer and the error in the QSSA larger than for batch reactors. This error is usually insignificant except when CSTR conversions are low. An alternative approximation is proposed for this case. The errors in the QSSA are also illustrated for the well known cases of Enzyme and Free-Radical polymerization kinetics.     

Differentiation criteria study for continuous stirred tank reactor and plug flow reactor

All reactors in reality are not ideal plug flow reactor (PFR) or ideal continuous stirred tank reactor (CSTR). They are difficult to differentiate. This study was to investigate the reactor analysis of PFR and CSTR through tracer response curves, residence time distributions (RTD) and several hydraulic performance indexes. We set up the differentiated value of each index. The tracer response curve showed that our lab-scale CSTR was close to ideal CSTR and got 99.9% recovery. In the RTD curves, the results could significantly recognize the PFR nature of high rate pond (HRP). With hydraulic performance indexes study, every selected index demonstrated that the studied HRP was closer to PFR than the studied CSTR. Based on the lab-scale study results, this study established the cutting point between the PFR and CSTR in each index; we were looking through the different types of reactors in literature and we confirmed the criteria with all literature reactors with the “graphic method”. The method helped us to establish those important values to help us to differentiate the reactor types in practice and to understand the designs better.     

Emulsion copolymerization of vinyl esters in continuous reactors: Comparison between loop and continuous stirred tank reactors

The high solids emulsion copolymerization of vinyl acetate and veova 10 was studied in a continuous loop reactor and in a continuous stirred tank reactor (CSTR) in an attempt to elucidate the similarities and differences between these reactors. Reactions were carried out under comparable conditions, namely, similar macromixing and the same feed composition and space time. The behavior of both reactors was almost the same when the heat generation rate was low; otherwise, thermal runaway occurred in the CSTR whereas the loop reactor temperature was easily controlled. © 1995 John Wiley & Sons, Inc.     

Continuous tube-CSTR reactor system for emulsion polymerization kinetic studies

A plug-flow tubular reactor (PFT) was used to generate a latex feed stream for a CSTR. Measurements of monomer conversion, particle number, particle size distribution and molecular weight distribution in the effluent streams of both reactors were used to study transport of free radicals and chain transfer agents in the emulsion polymerization of styrene.     

Cellular automata modeling of continuous stirred tank reactors

The classical dynamical systems model of continuous stirred tank reactors (CSTR) in which a first order chemical reaction takes place is reformulated in terms of the stochastic cellular automata procedure developed in the works of Seyborg [2] and Neuforth [3], which is extended by including the feed flow of chemical reactants. We show that this cellular automata model is able to simulate the dilution rate and the mixing process in the CSTR, as well as the details of the heat removal due to the jacket. The cellular automata approach is expected to be of considerable applicability at any industrial scale and especially for any type of microchemical system.     

Polymerization reactor: The influence of “gel effect” in batch and continuous solution polymerization of methyl methacrylate

This article describes the influence of gel effect in the free radical polymerization of methyl methacrylate. A mathematical model has been developed which tries to predict the performance of batch and continuous polymerization reactors under dynamic and steady-state conditions. The influence of diffusion phenomena on the process kinetics (gel effect) is very important. The autoacceleration in the polymerization rate of the batch reactor and the mulitple steady state for the continuous stirred tank reactor (CSTR) are connected with the attainment of critical conditions in the system. Such a model is useful for the design of the reactor and the choice of the control system.     

Anionic polymerization of styrene: The search for an industrial process

Anionic polymerizations were carried out in the laboratory using a CSTR reactor design and conditions typical of current commercial mass polystyrene plants. Polystyrene having excellent color and polydispersity was produced. Polymer quality, styrene conversion, and molecular weight control were all linked to use of polymerization feed of consistently high purity and polymerization in the 90–110°C temperature range. The results of this study clearly show that high quality polystyrene can be made utilizing anionic polymerization chemistry in existing well mixed mass polystyrene reactors of the CSTR design. The key to the successful practice of this technology is the ability to produce consistently high purity polymerization feed.     

Process Intensification in the Production of Specialty Waterborne Polymers

Summary: The feasibility of obtaining specialty waterborne adhesives in a CSTR was investigated facing the possibility of replacing the traditional semi‐batch reactors, which are commonly used in their production by a more efficient system. The key aspects focused on this work were the safety of the process, the kinetic feasibility, and the quality of the products, having as a reference the adhesive performance of the polymers produced in the semi‐batch reactors. Simulations showed that the production of 280 tons per week could be safely carried out even using mean residence times as short as 10 min. From a kinetic point of view, it was found that under these conditions, reasonable high conversions could be achieved in the reactor, resulting on a high production per unit volume of reactor. Furthermore, the adhesive properties of the latex were analyzed, and a much higher shear resistance was found for the latexes produced in the continuous reactor, while peel resistance and tack were found to be very similar disregarding the type of reactor used.

Safe process conditions in a CSTR.     

羧基丁苯胶乳工业技术的工程开发

利用羧基丁苯胶乳中试和工业试验提出的聚合釜的放大规律和试验数据，以工业化为目标，分析了聚合釜的传热和脱气釜的放大问题，比较了２０ｍ３、３０ｍ３聚合釜放大的技术成熟性和两种结构不同的脱气釜的脱气性能。选择２台２０ｍ３聚合釜与２台５０ｍ３塔式脱气釜的匹配方案，完成了１万ｔ／ａ羧基丁苯胶乳生产装置的基础设计。经工业化生产后，证明该工业技术的工程开发是成功的，产品质量达到了工业试验产品的水平．     

Dynamic simulation and control of auto-refrigerated CSTR and tubular reactor for bulk styrene polymerization

Dynamic simulation and control of a two-stage continuous bulk styrene polymerization process is developed to predict the performance of auto-refrigerated CSTR and tubular reactors. The tubular reactor is subdivided into three temperature-control jacket zones. In this paper temperature control of auto-refrigerated continuous stirred tank reactor and tubular reactor are carried out, simultaneously. Two strategies are proposed for the control of tubular reactor. At the first strategy the controlled variable is jacket temperature and in the second strategy the controlled variable is the reactor temperature at the exit of each section. The set points for polymer grade transition are obtained using optimization of reactors temperatures via genetic algorithm (GA). Simulation results show that both of the control strategies are successful but second strategy has better performance in the control of polymer properties in the presence of disturbance and model mismatch.     

Glycerolysis of Fatty Acid Methyl Esters: 2. Simulation and Experiments in Continuous Reactors

The glycerolysis of methyl ester was investigated in flow reactors. This reaction represents a liquid two-phase reaction with changing reaction rates in a batch reactor. A semi-empirical model tested earlier with batch reactor data was used to simulate different continuous processes for this reaction. Among the processes simulated, a single continuous-flow stirred tank reactor (CSTR) without recycling was considered most appropriate for experimental implementation, although simulations showed that a faster reaction rate is possible with the application of a CSTR followed by a tubular reactor with certain associated residence times. The CSTR simulations were verified experimentally. A good agreement was found between the experimental data and simulation results.     

On the measurement of coal liquefaction kinetics

Coal liquefaction kinetic rate constants play an important role in the design and operation of liquefaction reactors. The objectives of this work are to present a comparative review of the measurement techniques which have appeared in the recent literature, and to analyse briefly some of the kinetic models used in the measurements of the rate constants. A mathematical technique to analyse multicomponent-multireaction kinetic schemes using the data obtained from autoclave (closed) and continuous stirred tank reactors (CSTR, open) is discussed.     

Mixing performance comparison of milliscale continuous high‐shear mixers

Mixing performance of two continuous flow millilitre‐scale reactors (volumes 9.5 mL and 2.5 mL) equipped with rotor‐stator mixers was studied. Cumulative residence time distributions (RTD) were determined experimentally using a step response method. Distributions were measured for both reactors by varying impeller speed and feed flow rate. The mixing effect was determined by measured RTDs. Computational fluid dynamics (CFD) were used to verify that the residence time distribution in the measurement outlet agreed with the outlet flow. The mixing power of both reactors was determined using a calorimetric method. The reactor inlet flow rate was found to affect mixing performance at 1–13 s residence times but the effect of impeller speed could not be noted. Both milliscale reactors are close to an ideal continuous stirred‐tank reactor (CSTR) at the studied impeller speed and flow rate ranges. The specific interfacial area was found to depend on the reactor inlet flow rate at constant impeller speed for the case of copper solvent extraction.

     

STEADY-STATE MODELLING OF A LATEX REACTOR TRAIN FOR THE PRODUCTION OF STYRENE-BUTADIENE RUBBER

A mathematical model is developed for the emulsion copolymerization of styrene and butadiene carried out in a continuous train of stirred tank reactors. The model predicts copolymer composition, conversion, molecular weight averages, and long chain branching frequencies, as well as the latex particle size distribution for all reactors in the train. It is capable of simulating closely the behaviour of industrial SBR processes.

Several simulation studies are performed. Topics investigated include: process operating modifications to improve productivity; the effect of chain transfer agent flow rate and number of reactors on the molecular weight development; the effect of process modifications on the development of the particle size distribution down the reactor train; and the effect of reactor design on particle generation rates.     

对连续搅拌反应釜的变量结构观察器线性反馈控制的开发(英文)

This paper deals with the design of an observer-based nonlinear control for continuous stirred tank reactors(CSTR).A variable structure observer is constructed to estimate the whole process state variables.This observer is basically the conventional Luenberger observer with an additional switching term used to guarantee the robustness against modeling errors.The observer is coupled with a nonlinear controller,designed based on input-output linearization for controlling the reactor temperature.The asymptotical stability of the closed-loop system is shown by the Lyapunov stability theorem.Finally,computer simulations are developed for showing the performance of the proposed approach.