Continuous emulsion polymerization of styrene in a single Couette–Taylor vortex flow reactor

The effect of the geometrical and operational parameters on the mixing characteristics of a Couette–Taylor vortex flow reactor (CTVFR) were investigated and were correlated with the same parameters by using the tank‐in‐series model. Continuous emulsion polymerization of styrene was conducted at 50°C in a CTVFR to clarify the effects on kinetic behavior and reactor performance of operational parameters such as rotational speed of inner cylinder (Taylor number), reactor mean residence time, and emulsifier and initiator concentrations in the feed streams. It was found that steady‐state monomer conversion and particle number could be freely varied only by varying the Taylor number. In order to explain the observed kinetic behavior of this polymerization system, a mathematical model was developed by combining the empirical correlation of the mixing characteristics of a CTVFR and a previously proposed kinetic model for the continuous emulsion polymerization of styrene in continuous stirred tank reactors connected in series (CSTRs). On the basis of these experimental results, it was concluded that a CTVFR is suitable for the first reactor (prereactor) of a continuous emulsion polymerization reactor system. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1931–1942, 2001     

Continuous emulsion polymerization of vinyl acetate. I. Operation in a single continuous stirred tank reactor using sodium lauryl sulfate as emulsifier

Continuous emulsion polymerizations of vinyl acetate were carried out at 50 °C in a single continuous stirred‐tank reactor using sodium lauryl sulfate as emulsifier and potassium persulfate as initiator. It was found that (1) the so‐called limit cycles could take place in monomer conversion, the number of polymer particles and the molecular weight of polymers produced under certain operating conditions, (2) the time‐average steady‐state monomer conversion was proportional to the 0.31 power of the emulsifier concentration in the feed, to the 0.50 power of the initiator concentration, to the ?1.0 power of the monomer concentration, and to the 0.90 power of the mean residence time, and (3) the time‐average steady‐state number of polymer particles produced was proportional to the 2.1 power of the emulsifier concentration in the feed, to the ?0.80 power of the initiator concentration, to the 0 power of the monomer concentration, and to the ?0.92 power of mean residence time. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2748–2754, 2002     

Optimization of polymer synthesis through distributed control of polymerization conditions

An optimal control methodology is applied to the goal of lowering polydispersity while increasing conversion in polymerization reactions. An illustration using initiator, heat, and monomer flux control profiles for free‐radical polymerization of styrene in a plug flow reactor is provided and compared with available experimental data. The design calculations use a kinetic model that includes the gel effect. The reactor designs show that distributed initiator, heat, and monomer fluxes along the length of the reactor lower the polydispersity of the styrene polymers and increase conversion for a given reaction time. The monomer flux maintains a nearly constant monomer concentration in the reactor. The initiator and heat fluxes are highly correlated. The temperature rises as a result the heat flux; but the initiator flux results in a lower initiator concentration relative to the initiator cofeed case. At a reaction time of 120 min, a conversion of 44% and a polydispersity of 1.73 have been achieved. The theoretical designs, although not proven to be globally optimal, are of high quality. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2922–2928, 2002     

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.     

Effect of multiple feeds on a termination-free polymerization in continuous stirred tank reactors

The effect of monomer and initiator feeds to each of a series of continuous stirred tank reactors (CSTR) on the molecular weight distributions, average molecular weight, polymer production rate, and initiator and monomer conversions is studied for the termination-free polymerization system. For initiator feed concentrations less than 0.001 mole/liter, the distribution becomes narrower as the polymer progresses from reactor 1 to reactor 3. But for concentrations of initiator of 0.01 mole/liter, the distribution may be broadened from reactor 1 to reactor 3. The broadening of the distribution results in the production of a lower molecular weight polymer.     

Effects of carboxylic additives on the polymerization characteristics of nylon‐6 reactors with diffusional water removal

The effects of carboxylic acid on the polymerization characteristics of nylon‐6 were investigated in reactor models that consist of a continuous‐flow stirred tank reactor (CSTR) and a tubular reactor with a diffusional water‐removal system, which are connected in series. Mathematical models for the CSTR and the tubular reactor were established and solved by numerical methods. In the CSTR, with an increase of the feed acetic acid content, the monomer conversion, and the molecular weights are increased. In the tubular reactor, the acid behaves like a catalyst and a modifier at the same time in the polymerization of nylon 6. The effects of the feed acetic acid content and the diffusional water removal on the zeroth, first, and second moments and the polydispersity index of the polymer were investigated. The polydispersity index is greatly affected by the feed content of carboxylic acid in the CSTR, but it finally approaches to values of ～ 2 in the tubular reactor. The diffusional water removal is found to have little effect on the polydispersity index of the polymer. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1226–1237, 2001     

Continuous inverse microemulsion polymerization

The inverse microemulsion polymerization of 2‐methacryloyl oxyethyl trimethyl ammonium chloride (MADQUAT) in a continuous stirred tank reactor is investigated. The effect of removing the oxygen from the feed tank, initiator concentration, aqueous phase volume/emulsifier volume ratio, and residence time on the monomer conversion, particle size, and molecular weight was investigated. The removal of the oxygen allowed high conversions with moderate amounts of initiator to be obtained. In general, the process did not present oscillations. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1341–1348, 1999     

Simulation and optimization of the continuous tower process for styrene polymerization

The continuous tower process, a popular industrial process for the manufacture of polystyrene, was simulated and optimized. A kinetic model for the thermal polymerization of styrene, which takes into account the Trommsdorff effect and the volume change accompanying the reaction, was developed. This was used to formulate model equations for the continuous flow stirred tank reactor (CSTR) and plug flow reactor (several sections) in the tower process. The model can predict monomer conversion, number‐ and weight‐average molecular weights, polydispersity index (PDI), and temperature at various locations in the unit, under specified operating conditions. Multiobjective optimization of this process was also carried out, for which an adaptation of a genetic algorithm (GA) was used. The two objectives were maximization of the final monomer conversion and minimization of the PDI of the product. The conversion in the CSTR was constrained to lie within a desired range, and polymer having a specified value of the number‐average molecular weight was to be produced. The optimal solution was a unique point (no Pareto sets were obtained). The optimal solutions indicated that the tower process is operated under near‐optimal conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 775–788, 2004     

Computational Fluid Dynamics Study of a Styrene Polymerization Reactor

The computational fluid dynamics (CFD) approach was adopted to simulate benzoyl peroxide (BPO)‐initiated styrene polymerization in a laboratory‐scale continuous stirred‐tank reactor (CSTR). The CFD results revealed the effects of non‐homogeneity and the short‐circuiting of the unreacted styrene and initiator on the reactor performance. The study also investigated the effects of the impeller speed and the residence time on the conversion and the flow behavior of the system. The CFD simulation showed that intense mixing remained confined to a small region near the impeller. With increasing impeller speed, it was found that the perfectly mixed region near the impeller expanded, thus reducing non‐homogeneity. Different contours were generated and exhibited the effect of the mixing parameters on the propagation rate and styrene conversion. The monomer and initiator conversions predicted with the CFD model were compared to those obtained with a CSTR model. The CFD model accounts for the non‐ideality behavior of the polymerization reactor, and hence conversion predictions are more realistic.     

Free radical solution oligomerization of styrene in a continuous-stirred tank reactor train

For free radical oligomerization of styrene, a scheme for calculating the molecular weight distribution and conversion in a continuous-stirred tank reactor (CSTR) train is developed, which also allows the calculation of molecular weight distribution (MWD) for batch reaction. Calculations show that under conventional or near dead-end condition: (1) increasing initial initiator concentration, reaction time and reaction temperature, and decreasing initial monomer concentration cause P?_n and P?_w to decrease and MWD to narrow; (2) increasing initial initiator concentration, reaction time and reaction temperature, and increasing monomer concentration cause monomer conversion to increase; (3) a single CSTR gives a lower rate of oligomer production, but a narrower MWD than does a batch reactor.     

一种连续流反应器内射流耦合搅拌流的混合特性

连续式搅拌反应器采用连续化工艺，可以保证生产过程的连续性，相较于传统反应器而言，连续式反应器内流场更复杂，进料口射流对于流场的影响较为明显。对传统的双层搅拌桨结构的微波反应釜进行连续化改造，基于计算流体力学CFD(Computational Fluid Dynamics)方法对不同射流方案下反应器内醇油混合液的流动及混合特性进行了数值模拟，得到反应器内混合液的流动特性和混合时间特征。结果表明：射流通过直接影响射流区的流场和改变反应器内的循环涡流位置间接影响全局流动；射流方向对于反应器内流型影响更大，逆时针射流时反应器内的速度梯度大，流体之间的剪切作用更强，混合性能最佳，相较于传统的间歇式搅拌反应器，混合时间缩短了33%。     

A numerical study on the effects of acidic catalyst on the polymerization of nylon-6

The effects of acetic acid on the polymerization characteristics of nylon-6 are investigated in a reactor model that consists of a continuous flow stirred tank reactor (CSTR) and a tubular reactor connected in series. Mathematical models for the CSTR and the tubular reactor have been established and solved by numerical methods. In the CSTR, the monomer conversion and the molecular weights are increased as the feed acetic acid concentration is increased. In the tubular reactor, the acid acts as both a catalyst and a modifier for the polymerization reaction. The effects of the feed acetic acid content on the zeroth, first and second moments and the polydispersity index of the polymer have been discussed.     

Highly efficient reversible addition–fragmentation chain‐transfer polymerization in ethanol/water via flow chemistry

Utilization of a flow reactor under high pressure allows highly efficient polymer synthesis via reversible addition–fragmentation chain‐transfer (RAFT ) polymerization in an aqueous system. Compared with the batch reaction, the flow reactor allows the RAFT polymerization to be performed in a high‐efficiency manner at the same temperature. The adjustable pressure of the system allows further elevation of the reaction temperature and hence faster polymerization. Other reaction parameters, such as flow rate and initiator concentration, were also well studied to tune the monomer conversion and the molar mass dispersity (?) of the obtained polymers. Gel permeation chromatography, nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopies (FTIR) were utilized to monitor the polymerization process. With the initiator concentration of 0.15 mmol L^?1, polymerization of poly(ethylene glycol) methyl ether methacrylate with monomer conversion of 52% at 100 °C under 73 bar can be achieved within 40 min with narrow molar mass dispersity (D) ? (<1.25). The strategy developed here provides a method to produce well‐defined polymers via RAFT polymerization with high efficiency in a continuous manner. © 2017 Society of Chemical Industry     

The dynamics of the continuous emulsion polymerization of methylmethacrylate

Experimental data on the dynamics of the continuous emulsion polymerization of methylmethacrylate are presented. Techniques for on-line reaction monitoring and digital data acquisition as reported previously are used to generate dynamic data on the monomer conversion and free emulsifier concentration. Data are reported confirming the existence of multiple steady states and limit cycles in the CSTR (continuous stirred tank reactor) emulsion polymerization of methylmethacrylate. Data are also reported suggesting the presence of steady states in the absence of micelles in the reactor. The possible causes of these phenomena, and the conditions under which they occur are discussed.     

Particle size distribution control in emulsion polymerization

Effects of the operating policies—the initial initiator amount; the initial emulsifier amount; the monomer addition mode: batch or semibatch; and the monomer addition rate under “monomer‐starved conditions” for the control of particle size distribution (PSD)—were studied through a model that simulates batch and semibatch reactor operations in conventional emulsion polymerization. The population balance model incorporates both the nucleation stage and the growth stage. The full PSDs were reported, which have normally been omitted in earlier studies. It was shown through simulations that the broadness of the distributions, both initial (obtained after the end of nucleation) and final (after complete conversion of monomer), can be controlled by the initial initiator amount and the emulsifier amount. The higher initiator amounts and the lower emulsifier amounts favor narrower initial and final distributions. The shape of the initial PSDs and the trends in the average size and range were preserved with subsequent addition of monomer in the batch or in the semibatch mode, although the final PSD was always considerably narrower than that of the initial PSD. The addition of monomer in the semibatch mode gave narrower distribution compared to that of the batch mode, and also, lower monomer addition rates gave narrower distributions (larger average sizes), which was a new result. It was further shown through simulations that, under monomer‐starved conditions, the reaction rate closely matched the monomer feed rate. These conclusions are explained (1) qualitatively—the shorter the length of the nucleation stage and the larger the length of the growth stage (provided the number of particles remains the same), the narrower is the distribution; and (2) mathematically—in terms of the “self‐sharpening” effect. Experimental evidence in favor of the self‐sharpening effect was given by analyzing the experimental particle size distributions in detail. The practical significance of this work was proposed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2884–2902, 2004     

Semicontinuous emulsion polymerization of vinyl acetate: Effect of ethoxylation degree of nonionic emulsifiers

Poly(vinyl acetate) latices were prepared in the presence of an ammonium persulfate initiator, 10–50 mol of an ethoxylated nonylphenol nonionic emulsifier, and a poly(vinyl alcohol) colloid stabilizer by applying semicontinuous emulsion polymerization (delayed monomer and initiator addition process) in a laboratory scale similar to industrial practice. Two approaches were applied: the molar concentration of the nonionic emulsifier was kept constant and the weight ratios in the polymerization recipe varied or the weight ratios were kept constant. The effects of the change in the ethoxylation degree of the emulsifier to the final latex viscosity, average polymer molecular weight, polymer grafting degree, surface tension of the latex, and the surface free energy of the dried films were investigated. It was determined that the resultant latex viscosity decreases and the viscosity‐average polymer molecular weight increases with increase of the nonionic emulsifier ethoxylation degree. The increase of the ethoxylation degree does not seriously affect the surface tension of the resultant latex or the surface free energy of the dried poly(vinyl acetate) films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 844–851, 2002     

CLOSED-LOOP CONTROL OF A SEEDED CONTINUOUS EMULSION POLYMERIZATION REACTOR SYSTEM

A reactor configuration for continuous emulsion polymerization is proposed consisting of a plug flow reactor followed by a train of CSTR's. Monomer conversion is controlled by manipulating the quantity of water and monomer which are allowed to bypass the plug flow reactor and enter the first CSTR directly. A multivariate pole-placement adaptive controller is used to implement the controls. Simulation results indicate good control of both conversion and particle size. Open-loop experimental results indicate the effectiveness of the plug flow reactor for eliminating the oscillations sometimes found in CSTR emulsion polymerization.     

Removal of Arsenic from Wastewaters by Airlift Electrocoagulation. Part 2: Continuous Reactor Experiments

Abstract

Arsenic removal from wastewater is a key problem for copper smelters. Conventional methods either prove to be complicated, expensive, or not sufficiently effective. This work shows the results of electrocoagulation (EC) in aqueous solutions containing arsenic in a newly designed and constructed cylindrical continuous airlift reactor. The residence time distribution measurements showed that the reactor behaved as an ideal continuous stirred tank reactor (CSTR) with perfect mixing. Ten EC experiments were carried out in the continuous airlift reactor with sacrificial iron electrodes. The variables were: initial As(V) concentration, liquid flow rate, and electric current density. The results showed that the airlift EC process could reduce an initial As concentration from 1000 mg L^?1 to 220 mg L^?1 – corresponding to a reduction of 78%. In addition, a 100 mg L^?1 solution was reduced by 88%. The Fe-to-As (mol/mol) ratio, when EC was working properly, was in the range of 1.3–1.5, which is very promising for the future development of the reactor. The arsenic removal is proportional with the electric current, the electric charge and the CSTR residence time. On the other hand, when the flow rate is increased, the arsenic removal decreases.     

Modeling and experimental studies of emulsion copolymerization systems. III. Acrylics

Using a previously published model and continuing the series of papers started with styrenic copolymers, predictions for evolution of conversion and average particle diameter in batch experiments are compared against experimental data for four emulsion copolymerizations involving at least one acrylic monomer: (1) methyl methacrylate/butyl acrylate, (2) methyl methacrylate/butadiene, (3) methyl methacrylate–vinyl acetate, and (4) butyl acrylate/vinyl acetate. For each system a fraction of factorial experiments were run covering simultaneous variations in five variables: initiator [I] and surfactant [E] concentrations, water to monomer ratio (W/M), monomer composition, and temperature. Data fitting is performed to represent the experimental data as several parameters are not available from independent experimental sources. The model is able to explain the effects of simultaneous changes in emulsifier concentration, initiator concentration, and water to monomer ratio on conversion and average particle size histories, although in some cases only qualitatively. An assessment of the degree in which a general emulsion copolymerization model is useful for practical applications is made. Physical insight is also gained by observing the trends of adjusted parameters with temperature and copolymer composition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1320–1338, 2002; DOI 10.1002/app.10003     

Semibatch emulsion copolymerization of butyl acrylate and glycidyl methacrylate: Effect of operating variables

Semibatch emulsion copolymerization was carried out to prepare poly(butyl acrylate‐co‐glycidyl methacrylate) latexes at 75°C, using potassium persulfate as an initiator, sodium dodecylbenzene sulfonate as an emulsifier and sodium bicarbonate as a buffer. The reaction was conducted in three stages; a further stage (called the steady stage, 2 h) was added to the traditionally stages (i.e., feed and seed stages) to improve considerably the monomer conversion. The monomer conversion and particle size distribution were studied by gravimetric and laser light scattering methods, respectively. The effects of variables such as agitation speed, emulsifier concentration, initiator concentration, feeding rate and comonomers ratio were fully investigated based on the monomer conversion‐time profiles and the particle size distribution to find the optimized copolymerization conditions. Increasing the agitation speed had a negative effect on the monomer conversion, but reduced coagulation of polymer particles. Monomer conversion could be improved by increasing the initiator or emulsifier contents. Feeding rate increased the polymer particle size sharply; however, it showed no significant effect on conversion. The final conversions were as high as 97–99% and they were recognized to be independent of the comonomers ratios employed. Morphological studies by scanning electron microscopy showed nano‐sized isolated particles which were partially aggregated. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010