An alternate approach to the determination of rate parameters in copolymerization

A new method which proposes the use of a steady state CSTR is presented for the determination of rate parameters in a copolymerization system. The approach does not limit the conversion levels in the reactor and allows precise estimation of reactivity ratios. In the presence of gel effect, the suggested approach additionally reveals the cumulative variations of termination rate processes with extent of conversion. Such an a priori method which enables estimation of rate parameters in the high conversion region has not been available in the literature previously. The method proposed is illustrated using copolymerization of styrene–methyl methacrylate as a model system.     

Blocking and copolymer heterogeneity in anionic copolymerization in industrial reactors

An analysis is given of the effect of reactor design on the variation of composition and extent of blocking in anionic copolymerization. Batch, pipeline, continuous stirred tank (CSTR), and recycle reactors are contrasted. Specifically, alkyl lithium-polymerized butadiene–styrene and alkyl sodium-polymerized p-methylstyrene–styrene are contrasted to the products of copolymerization of the same monomers by free-radical mechanism. It is shown for both systems that considerably more extensive blocking occurs in a batch reactor when the anionic polymerization mechanism is used. The free-radical copolymers, unlike the anionic copolymers, exhibit compositional heterogeneity in a batch reactor. Carrying out the polymerization reaction in a pipeline reactor gives results equivalent to the batch reactor if there is plug flow. However, if a parabolic profile exists in the reactor, there will be significantly increased compositional drift in the copolymer product and a broadened molecular weight distribution, with little effect on blocking. Recycle reactors, including the recirculating loop variety, seem effective in decreasing blocking. The extent of blocking may be considerably decreased in a wellmixed continuous stirred tank reactor. However, poor mixing will greatly increase both the extent of blocking and the compositional heterogeneity of the product.     

Increased Reactor Performance versus Reactor Safety Aspects in Acrylate Copolymerization

The aim of reducing cycle times of semibatch‐polymerization processes requires systematic investigations of the kinetics, careful adjustment of the desired polymer properties, proper thermal reactor design and reliable reactor safety assessment [1]. As a concrete example, a semibatch‐copolymerization was carefully examined with respect to four different aspects. Thermo‐kinetics of the reaction were investigated with isoperibolic reaction calorimetry and GC. In order to obtain reliable values for the overall heat transfer coefficient of the production scale reactor, cooling experiments were carried out with solvent and final copolymer solution as reactor content. For consistent reactor safety assessment additional investigations are necessary including case studies of breakdown incidences. These simulations were performed with a mathematical model based on the GC data and experimental vapor pressure curves. As a result of these calculations, a reduction of reaction time from 10 to 6 hours was possible. To convert into practice, it must be ensured that even in this shortened time a product of the same quality is produced.     

Kinetic study of olefin polymerization with a supported metallocene catalyst. II. Ethylene/1‐hexene copolymerization in gas phase

A kinetic study of ethylene/1‐hexene copolymerization is conducted with a supported metallocene catalyst in a gas‐phase reactor. The investigation into the kinetics of ethylene/1‐hexene copolymerization includes the effects of operational parameters such as the reaction temperature, pressure, and comonomer concentration. The large variations in gas‐phase composition using only an initial charge of 1‐hexene are illustrated by experiment. To remedy this, the ability to control the comonomer composition of 1‐hexene online for the entire duration of the reaction is demonstrated. Online perturbation techniques are implemented to determine key kinetic parameters such as the activation energies for propagation and catalyst deactivation. From pressure perturbation results, a reaction rate order close to 1 is obtained for ethylene in the presence of 1‐hexene. Finally, all the parameters obtained from the study are compared to those determined from ethylene–propylene (E–P) copolymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1096–1119, 2001     

多相光化学反应器的辐射能传递模型

以双通量模型为基础模拟多相光化学反应器中的辐射能传递行为 ,考虑透过光催化剂颗粒的光子总数修正了双通量模型 ,采用比较简单的模型说明了多相光化学反应器内量纲 1光辐射能分布和光催化剂的量纲 1吸收光子总数分布 ,举例讨论了半导体超细粉末二氧化钛为光催化剂的气固相光化学反应器在不同光催化剂粒径、不同反应器厚度条件下反应器内量纲 1光辐射能分布和光催化剂的量纲 1吸收光子总数分布     

Minimum end time policies for batchwise radical chain polymerization. Part VI: The initiator addition policies for copolymerization with constant copolymer composition control

For batchwise radical chain solution copolymerization, the minimum end time problem with constant copolymer composition control is studied by considering the initiator concentration (or feed rate) and temperature as two control variables. During copolymerization, the more rapidly depleting monomer is continuously fed to the reactor to maintain the comonomer ratio constant. The volume variation due to contraction during copolymerization, in addition to monomer and solvent feeding, is also considered. It is found that the optimal initiator addition policy is to make the rate of initiation (2fk_dIV) constant. The volume factor V is for taking account of volume variation. For the isothermal case, the number of moles of initiator in the reactor should remain constant. Experimental verification for acrylonitrile and styrene isothermal copolymerization with the proposed stepwise feeding of the more rapidly depleting monomer to simulate the optimal continuous monomer feeding policy shows that the present method is applicable.     

Intensification of Deep Hydrodesulfurization Through a Two-stage Combination of Monolith and Trickle Bed Reactors

Deep hydrodesulfurization (HDS) is an important process to produce high quality liquid fuels with ultra-low sul-fur. Process intensification for deep HDS could be implemented by developing new active c...     

Bulk copolymerization of styrene-acrylic esters: Some analysis and design considerations

A common framework for the analysis of styrene-acrylic ester systems has been developed by analyzing the pertinent kinetic information. This is shown to lead to a well defined strategy for the design of copolymerization reactors especially in the industrially relevant high conversion region. The existence of stable steady states and its influence on the system parameters has been illustrated for the case of a continuous stirred tank reactor (CSTR). A novel strategy of a CSTR operated with a recycle is proposed. This is shown to lead to an operation in the unique steady state with the added advantage of a high conversion and uniform copolymer composition. This would seem to be the first such analysis in the high conversion region.     

PROPAGATION OF REACTION FRONTS IN NONCATALYTIC NONISOTHERMAL GAS-SOLID FIXED BED REACTORS

This paper is devoted to the analysis of reaction fronts, in a noncatalytic nonisothermal gas-solid fixed bed reactor. A novel technique to obtain analytical approximate solutions by means of simple functions is presented. These analytical approximate solutions can be used to investigate the effect of various parameters in the reactor performance without resorting to numerical analysis. In addition, for adiabatic conditions and/or fast kinetics, the relationship between dependent variables can be investigated analytically. The technique is illustrated by analyzing the oxidation of ZnS in a fixed-bed reactor.     

Solution copolymerization of methyl methacrylate and alkyl methacrylates in a continuous stirred tank reactor(CSTR)

Continuous solution copolymerization of methyl methacrylate with ethyl methacrylate or n-butyl methacrylate was carried out in a continuous stirred tank reactor. Solvent and initiator used were toluene and benzoyl peroxide, respectively. Reaction volume was 1.2 litters, residence time 3 hours and polymerization temperature 80°C. The copolymerization conversions were analyzed by UV spectrophotometry and confirmed by measuring the solid weights of copolymers obtained after evaporating solvent. The copolymerization of methyl methacrylate and alkyl methacrylates followed the second order kinetics. The simulated conversions and copolymerization rates were compared with the experimental results. The average time to reach dynamic steady-state was three and half times of the residence time.     

Spheripol工艺生产高抗冲聚丙烯

介绍了Spheripol工艺生产高抗冲聚丙烯产品的方法,采用两步复合工艺生产嵌段聚丙烯,第1步采用环管反应器进行丙烯液相均聚反应,第2步采用流化床反应器进行丙烯均聚物与乙烯单体气相共聚反应,即在气相反应器中,利用来自环管反应器中的均聚物的残余活性,加入乙烯和补充的丙烯及氢气实现乙-丙共聚,共聚物的生成使最终产品的抗冲性能大大提高,尤其是低温下的抗冲性能。     

Kinetic study of olefin polymerization with a supported metallocene catalyst. I. Ethylene/propylene copolymerization in gas phase

A kinetic study of ethylene homopolymerization and copolymerization is conducted with a supported metallocene catalyst in a gas‐phase reactor. An experimental procedure is developed that minimizes the effect of impurities in the reactor and simultaneously yields consistent and reproducible reaction‐rate data. The effects of operational parameters such as reaction temperature, pressure, and comonomer concentration on the kinetics of both homopolymerization and copolymerization are investigated. Online perturbation techniques are implemented to determine key kinetic parameters such as the activation energies for ethylene propagation and catalyst deactivation. A reaction‐rate order close to 2 is obtained for ethylene homopolymerization from pressure perturbations, while near to first‐order dependency is observed in the presence of propylene. To quantify the effects of the operational parameters, a one‐site kinetic model for homopolymerization and a two‐site kinetic model for copolymerization are proposed. The necessary kinetic parameters in the model are estimated using the POLYRED™ package. The resulting kinetic model represents the kinetic data over a wide range of conditions for this supported metallocene catalyst. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 81–114, 2001     

Complex-radical terpolymerization of styrene, maleic anhydride, and N-vinyl pyrrolidone via γ-ray radiation: Synthesis, characterization, and micellization

Radical terpolymerization of donor–acceptor monomers, i.e. styrene (St), maleic anhydride (MA) and N-vinyl pyrrolidone (NVP) were carried out in methyl ethyl ketone(MEK) under γ-ray radiation at room temperature. Constants of copolymerization, complex formation, and some kinetic parameters for the monomer systems were studied by UV, ¹H NMR, Kelen-Tüdöş and Fineman-Ross methods, respectively. Obtained results show that terpolymerization proceeded mainly through ‘complex’ mechanisms in the state of near-binary copolymerization of StMA and MANVP complexes. The homo-polymerization of St and NVP and the copolymerization between St and NVP could hardly be occurred. The possible reason is the effect of protection from radiation by styrene with its aryl-ring structure and/or the much larger reactivity of the complex copolymerization between the donor–acceptor monomers. The terpolymer self-assembles into micelles in aqueous solution. Polymeric micelles, composed of chains of St–MA and MA–NVP with equal molar ratio, displayed narrow size distribution of about 120 nm. The critical association concentration of micelles was determined to be around 3 mg/L.     

Flame-resistant cotton textiles by a continuous photocuring process

A continuous process for the photoinitiated copolymerization of vinyl phosphonate oligomer (MW 0.5–1.0 kg) and N-methylolacrylamide from aqueous solutions with cotton printcloth and a sateen fabric was investigated. The free radical reactions, initiated on the cellulose molecules by exposure of the padded cotton fabric to UV radiation gave a flame-resistant (DOC FF 3-71 test) textile product. The effects of several variables on the efficiency of oligomer and monomer conversion to polymer add-on were determined, with maximum efficiencies being 75–85%. Variables were fabric speed through the reactor (0.006–0.039 m/sec), light transmission through Pyrex or quartz windows in the tunnel, four sets of interchangeable tri-power UV lamps having different spectral distributions and relative intensities, and heat buildup within the reactor. Selected samples of these modified cotton fabrics were evaluated for flame resistance, some textile properties, and elemental phosphorus and nitrogen analysis. Copolymer and phosphorus distribution within and between the cotton fibers were illustrated by transmission electron microscopy and by energy dispersive x-ray analysis.     

PE氯化原位接枝丙烯酸-2-羟基乙酯及丙烯酸丁酯制备热塑性弹性体的工业化及性能

PE氯化原位接枝丙烯酸-2-羟基乙酯(CPE-cg-HEA)及丙烯酸丁酯(CPE-cg-BA)均具有优良综合物理力学性能。本文主要讨论CPE-cg-HEA及CPE-cg-BA工业化制备过程。在2m3搅拌反应釜中进行固相氯化原位接枝反应,在PE氯化同时进行接枝反应,最终将丙烯酸-2-羟乙酯及丙烯酸丁酯(HEA、BA)分别接枝到骨架聚合物氯化聚乙烯(CPE)上。对产物物理力学性能进行了测试,并分别与实验室制备的接枝物和商品CPE性能进行了比较。实验结果表明了接枝共聚物工业化的可行性,与CPE相比具有更好的综合性能。     

San bulk copolymerization: Some new insights in kinetics and microstructure

A comprehensive study of the kinetics of the industrially important system of free radical bulk copolymerization of styrene and acrylonitrile, both at low and high conversions, is presented. The influence of gel effect on the kinetics, molecular weight distribution, cumulative composition distribution and the sequence length distribution of the SAN copolymer is examined. The study provides a fresh insight into the polymer structure and the influence of gel effect on the reactor behaviour.     

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.     

MASS TRANSFER EFFECTS IN LIQUEFACTION OF COAL BY SRC-II PROCESS PART II STUDY OF BUBBLE COLUMN REACTORS

The effects of hydrogen mass transfer resistance in large-scale SRC-II bubble column reactors (BCR), over large ranges of process variables, are studied. Due to the interactive effects of mass transfer resistance and gas hold up, the hydrogen consumption or liquid yield in a BCR has a maximum with respect to the specific mixing power. Under normal SRC-II process conditions a superficial gas velocity of about 0.01 m/s represents the optimum with respect to the hydrogen consumption or liquid yield. In general, the product quality requirement rather than the rate of hydrogen consumption determines the minimum specific mixing power requirement. Increase in hydrogen partial pressure can be used to reduce the level of mixing power required to maintain the desired product quality. Interrelations between mass transfer and gas hold effects and the variations in hydrogen concentration in slurry over large ranges of process conditions are also illustrated. This work provides some bases for the selection of reactor dimensions and process conditions for an SRC-II bubble column reactor (BCR).     

MASS TRANSFER EFFECTS IN LIQUEFACTION OF COAL BY SRC-II PROCESS PART II STUDY OF BUBBLE COLUMN REACTORS

The effects of hydrogen mass transfer resistance in large-scale SRC-II bubble column reactors (BCR), over large ranges of process variables, are studied. Due to the interactive effects of mass transfer resistance and gas hold up, the hydrogen consumption or liquid yield in a BCR has a maximum with respect to the specific mixing power. Under normal SRC-II process conditions a superficial gas velocity of about 0.01 m/s represents the optimum with respect to the hydrogen consumption or liquid yield. In general, the product quality requirement rather than the rate of hydrogen consumption determines the minimum specific mixing power requirement. Increase in hydrogen partial pressure can be used to reduce the level of mixing power required to maintain the desired product quality. Interrelations between mass transfer and gas hold effects and the variations in hydrogen concentration in slurry over large ranges of process conditions are also illustrated. This work provides some bases for the selection of reactor dimensions and process conditions for an SRC-II bubble column reactor (BCR).     

Effect of comonomer composition on the controlled free-radical copolymerization of styrene and maleic anhydride by reversible addition-fragmentation chain transfer (RAFT)

Controlled free-radical copolymerization of styrene and maleic anhydride was performed in 1,4-dioxane or tetrahydrofurane solution at 60 °C using the RAFT technique. The effect of monomer feed ratio on copolymerization kinetics and on control over molar mass distribution was examined. It was shown that polymerization was faster and quality of control was poorer when the proportion of maleic anhydride in the monomer feed was larger. These features were assigned to a decrease in the chain transfer constant of the polymeric RAFT agent, most probably due to an increase in the apparent rate constant of propagation with the proportion of maleic anhydride.