Process Intensification of Living Cationic Polymerization of Isobutylene by a Flow Reaction System

Increasing the reaction temperature of the living cationic polymerization of isobutylene is crucial for industrial production due to the cost of refrigeration. The reaction temperature increase was achieved with an accelerated reaction rate using a flow reaction system. The polymerization conditions, including the flow reactor design, were based on the results of kinetic studies. Utilizing a milli‐scale flow reactor, polyisobutylene, which has a narrow molecular weight distribution, was obtained within a considerably short residence time at a high temperature. Furthermore, it was confirmed that the value of M_w/M_n correlates with the product of the Reynolds number and the angle of collision.     

Polymerization of olefins through heterogeneous catalysis. XVII. Experimental study and model interpretation of some aspects of olefin polymerization over a TiCl4/MgCl2 catalyst

Using a high-activity MgCl₂-supported TiCl₄ catalyst, kinetic studies of ethylene and propylene polymerization are conducted in a semi-batch gas phase stirred-bed reactor system. Based on the experimental observations obtained from this study and others in the literature, simple kinetic mechanisms are proposed to explain the data. This model considers both the site formation from the interaction of catalyst and cocatalyst as well as the participation of monomers during site activation. By using this model together with parameters estimated from various sources, some aspects of kinetic behavior have been successfully predicted. These include the rate enhancement introduced by α-olefins, the effect of the Al/Ti ratio on kinetic features such as catalyst activity and decay rate, as well as the different reaction orders observed for various monomers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1037–1052, 1997     

Polymerization of butadiene with tii4-Al(i-Bu)3 catalyst: Part I: Kinetic study

A kinetic study on the polymerization of butadiene in toluene with TiI₄-Al(i-Bu)₃ catalyst has been carried out in a batch reactor. The effects of catalyst concentration, Al/Ti ratio, initial monomer concentration and temperature on the polymerization rate and the molecular weight distribution were investigated. It was found that the rate of propagation which is first order with respect to monomer concentration is a function of Al/Ti ratio, having a maximum rate at a ratio of 1.5 and decreasing rapidly as ratio increases. The number of active sites which is directly proportional to the concentration of Til₄, is the prime determinant of the molecular weight of the polymer, yet the growth of the living polymer molecules is regulated by the chain transfer reaction to aluminum alkyls. The termination reaction was found significant only at Al/Ti ratio where the catalyst is most reactive.     

Kinetics of 2,2,6,6‐Tetramethylpiperidine Oxidation over Sn2+ on Ion Exchange Resin

The oxidation of 2,2,6,6‐tetramethylpiperidine (TEMP) over Sn²⁺ on ion exchange resin is carried out in a batch reactor. The influence of the reactant concentrations, reaction temperature and catalyst amount is investigated. Within the temperature range studied, 303–323 K, the reaction follows the second order kinetic equation ‐r_TEMP = kC_TEMPC_H2O2, with reaction rate constant k = 2.2 × 10⁷exp (‐51200/RT) L/mol h. We propose a reaction mechanism different from that for catalyzation by tungstate. The catalyst likely forms complexes with hydroxyl radicals, keeping their concentration steady. At the same time, the catalyst also decreases the decomposition of hydrogen peroxide caused by high temperatures and the reactant 2,2,6,6‐tetramethylpiperidine itself.     

Poly(1‐octene) synthesis using high performance supported titanium catalysts

Poly(1‐octene) was synthesized by polymerization of 1‐octene using high performance MgCl₂‐supported TiCl₄ in combination with triethyl aluminum (TEAl) as cocatalyst in n‐hexane for 2 h. Two catalysts, C₁ (diester catalyst) having di‐isobutyl phthalate as internal donor and C₂ (monoester catalyst) having ethyl benzoate as internal donor were utilized for the atmospheric polymerizations to evaluate the influence of structurally different internal donors on the productivity, rate of polymerization and molecular weight profiles. The kinetic profile assessed in terms of variation of reaction parameters like temperature, cocatalyst to catalyst molar ratio and monomer concentration was found to be dependent on them. From these kinetic analyses, optimize conditions for polymerizations of 1‐octene using diester as well as monoester catalyst were elucidated. The difference in the performance of diester and monoester catalyst system can be explained in terms of stability of active titanium species and chain transfer process. NMR spectroscopy of synthesized poly(1‐octene) indicate predominantly isotactic nature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Geometrically Constrained Polymerization of Styrene Over Heterogeneous Catalyst Layer in Silica Nanotube Reactors

Styrene has been polymerized to syndiotactic polystyrene (sPS) over a layer of heterogeneous Cp*Ti(OCH₃)₃/MAO catalyst immobilized onto the surfaces of silica nanotube reactor (SNTR) arrays of 60–200 nm in diameter. The polymer produced in the SNTR arrays has been found to have the molecular weights much larger than the polymers synthesized by a liquid slurry polymerization over silica-supported catalysts. A dynamic reactor model that consists of diffusion and reaction terms has been derived and solved to quantify the kinetics of styrene polymerization in a single nanotube reactor. The two-site kinetic model applied to the silica nanotube reactor model shows that the experimentally observed high polymer molecular weight can be fitted if the chain transfer rate constants for monomer and β-hydride elimination are reduced significantly. The simulation results suggest that the presence of dense crystalline sPS nanofibrils filling the nanotubes constrain the molecular movements of polymer chain ends in the proximity of catalyst sites to limit the chain transfer reactions. POLYM. ENG. SCI., 60:700–709, 2020. © 2020 Society of Plastics Engineers     

Steam reforming of methanol over a CuO/ZnO/Al2O3 catalyst, part I: Kinetic modelling

A kinetic study of the methanol steam reforming reaction was performed over a commercial CuO/ZnO/Al₂O₃ catalyst (Süd-Chemie, G66 MR), in the temperature range of 200–300 °C. The reactions considered in this work were methanol steam reforming (MSR) and reverse water gas shift (rWGS). Several MSR kinetic rate models developed by different authors were compared and the one was determined that best fitted the experimental data. A kinetic Langmuir–Hinshelwood model was proposed based on the work by Peppley et al. (1999a) . The kinetic expressions that presented the best fit were used to simulate the packed bed reactor with a one-dimensional model. A good agreement between the mathematical model and the experimental data was observed.     

Enantioselective Hydrogenation of Ethyl Benzoylformate,from Mechanism and Kinetics to Continuous Reactor Technology

The enantioselective hydrogenation of ethyl benzoylformate over (?)-cinchonidine (CD)-modified Pt/Al₂O₃ catalyst in semi-batch and continuous fixed bed reactors was studied as a function of the modifier concentration and reaction temperature. The kinetic results from the semibatch reactor showed a higher enantioselectivity and lower initial rate as the amount of modifier was increased. The results from the fixed bed reactor demonstrates that continuous enantioselective hydrogenation is possible and that continuous feeding of (?)-CD is needed to maintain a high steady-state enantioselectivity.     

Enantioselective Hydrogenation of Ethyl Benzoylformate,from Mechanism and Kinetics to Continuous Reactor Technology

The enantioselective hydrogenation of ethyl benzoylformate over (−)-cinchonidine (CD)-modified Pt/Al₂O₃ catalyst in semi-batch and continuous fixed bed reactors was studied as a function of the modifier concentration and reaction temperature. The kinetic results from the semibatch reactor showed a higher enantioselectivity and lower initial rate as the amount of modifier was increased. The results from the fixed bed reactor demonstrates that continuous enantioselective hydrogenation is possible and that continuous feeding of (−)-CD is needed to maintain a high steady-state enantioselectivity.

     

Synthesis of polyacrylonitrile via reverse atom transfer radial polymerization (ATRP) initiated by diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate,FeCl3, and triphenylphosphine

The reverse atom transfer radical polymerization (RATRP) technique using FeCl₃/triphenyl‐phosphine (PPh₃) complex as a catalyst was applied to the living radical polymerization of acrylonitrile (AN). A hexa‐substituted ethane thermal iniferter, diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS), was first used as the initiator in this iron‐based RATRP initiation system. A FeCl₃ to PPh₃ ratio of 1:3 not only gives the best control of molecular weight and its distribution but also provides a rather rapid reaction rate. The rate of polymerization increases with increasing the polymerization temperature and the apparent activation energy was calculated to be 54.9 kJ mol^?1. Because the polymers obtained were end‐functionalized by chlorine atoms, they were used as macro‐initiators to proceed the chain extension polymerization in the presence of an FeCl₂/PPh₃ catalyst system via a conventional ATRP process. Copyright © 2005 Society of Chemical Industry     

Late Transition Metal Catalyst Based on Cobalt for Polymerization of Ethylene

The late transition metal catalyst of [2,6-diacethylpyridinebis(2,6-diisopropylphenylimine)]cobalt(II) dichloride was prepared under controlled conditions and used for polymerization of ethylene. Methylaluminoxane (MAO) and triisobuthylaluminum (TIBA) were used as a cocatalyst and a scavenger, respectively. The highest activity of the catalyst was obtained at about 30°C; the activity decreased with increasing temperature. At polymerization temperatures higher than 50°C not only was a sharp decrease in the activity observed but also low molecular weight polyethylene product that was oily in appearance was obtained. The polymerization activity increased with increasing both of the monomer pressure and [MAO]:[Co] ratio. However, fouling of the reactor was strongly increased with increasing both of the monomer pressure and the amount of MAO used for the homogeneous polymerization. Hydrogen was used as the chain transfer. The activity of the catalyst and the viscosity average molecular weight (M_v) of the polymer obtained were not sensitive to hydrogen concentration. However, the viscosity average molecular weight of the polymer decreased with the monomer pressure. The (M_v), the melting point, and the crystallinity of the resulting polymer at the monomer pressure of 1 bar and polymerization temperature of 20°C were 1.2 × 10⁵, 133°C, and 67%, respectively. Heterogeneous polymerization of ethylene using the catalyst and the MAO/SiO₂ improved morphology of the resulting polymer; however, the activity of the catalyst was also decreased. Fouling of the reactor was eliminated using the supported catalyst system.     

Comparison of Mechanistic Models for the Catalytic Oxidation of Trichloroethylene over Cr/Al2O3 and Al‐Cr/Porous Glass Catalysts

In this study the catalytic oxidation of trichloroethylene was investigated in a fixed bed tubular reactor system that consisted of a 50 cm long and 3 cm inner diameter quartz glass tube packed with the catalyst. The Cr/Al₂O₃ catalyst (Cat. I) contains 3.8 w/o Cr and the Al‐Cr/porous glass catalysts (Cat. II) contain in one set 5.5 w/o Al and 9.6 w/o Cr and in the other set 6.2 w/o Al and 11.7 w/o Cr. The two types of catalysts were prepared by impregnation procedure. A number of kinetic rate expressions were evaluated for their ability to fit the experimental data to the integral reactor equation using SimuSolv packet program. The temperature influence on the reaction rate constants and the adsorption equilibrium constants were correlated simultaneously using Arrhenius and van't Hoff equations, respectively. The kinetic rate expression, based on Rideal‐Eley type model, describes well the integral conversion data for Cat. I while Langmuir‐Hinshelwood/Hougen‐Watson type model describes well the integral conversion data for Cat. II over the range of conditions investigated.     

Low-pressure polymerization of ethylene. II

This paper presents the kinetic study of polymerization of ethylene with VOCl₃ and aluminum alkyls such as Et₃Al and Et₂AlCl. The effect of various parameters like the [Al]/[V] ratio, catalyst concentration, reaction time, temperature, solvents, and additives on rate of the reaction, yield, and molecular weight is reported. Each of these parameters has a remarkable effect on the yield and the rate of polymerization for both catalyst systems. Triethylamine is found to increase the catalyst efficiency and the rate. It is also observed that aliphatic hydrocarbons acted as a better polymerization medium than did the aromatic ones.     

Synthesis of polyacrylonitrile via reverse atom transfer radical polymerization initiated by 1,1,2,2‐tetraphenyl‐1,2‐ethanediol/FeCl3/triphenylphosphine

FeCl₃ coordinated by triphenylphosphine was first used as the catalyst in the 1,1,2,2‐tetraphenyl‐1,2‐ethanediol‐initiated reverse atom transfer radical polymerization of acrylonitrile. A FeCl₃/triphenylphosphine ratio of 0.5 not only gave the best control of the molecular weight and its distribution but also provided a rather rapid reaction rate. The rate of polymerization increased with increasing polymerization temperature, and the apparent activation energy was calculated to be 62.4 kJ/mol. When FeCl₃ was replaced with CuCl₂, the reverse atom transfer radical polymerization of acrylonitrile did not show prominent living characteristics. To demonstrate the active nature of the polymer chain end, the polymers were used as macroinitiators to advance the chain‐extension polymerization in the presence of a CuCl/2,2′‐bipyridine catalyst system via a conventional atom transfer radical polymerization process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 4041–4045, 2007     

无机/有机复合载体负载TiCl_3/(n-BuCp)_2ZrCl_2复合催化剂用于宽峰聚乙烯的制备

采用溶胶-凝胶法,将苯乙烯-丙烯酸(PSA)共聚物包覆在以硅胶/MgCl2为载体的TiCl3催化剂上,负载(n-BuCp)2ZrCl2后制得Ziegler-Natta/茂金属复合催化剂。实验在同一反应釜中进行两段反应模拟双釜串联聚合工艺。在第一段反应中制备高分子量高支化度的乙烯/1-己烯共聚物,在第二段反应中,制备低分子量低支化度的聚合物。淤浆聚合结果表明,所得聚乙烯的熔融流动比(MI21.6/MI2.16)较宽,达到79,分子量分布达到18.6。两段反应得到的聚乙烯共混物的结晶度和熔融温度介于第一段、第二段单独反应时所得产物的结晶度和熔融温度之间,且DSC曲线具有单一的熔融峰,说明该两段反应法制备的聚乙烯共混物具有良好的共结晶行为。动力学研究同时表明,苯乙烯-丙烯酸共聚物的引入,使得催化剂的活性缓慢释放,活性持续时间明显长于负载于无机载体的催化剂,有利于灵活地调节各段反应的停留时间。     

Kinetics and mechanism of ethylene homopolymerization and copolymerization reactions with heterogeneous Ti-based Ziegler–Natta catalysts

A detailed kinetic analysis of ethylene homopolymerization reactions and its copolymerization reactions with 1-hexene with a supported Ti-based Ziegler–Natta catalyst (reactions in the absence and the presence of hydrogen) shows a number of distinct kinetic features which are interpreted as a manifestation of multi-site catalysis; the catalyst contains several types of polymerization centers which differ in stability and formation rates, the molecular weight of polymers they produce, and in their response to the presence of α-olefins and hydrogen. All these effects require introduction of a special kinetic mechanism which postulates an unusually low activity of growing polymer chains containing one ethylene unit, the Ti–C₂H₅ group, in the ethylene insertion reaction into the Ti–C bond. This peculiarity of the Ti–C₂H₅ group, which is probably caused by its β-agostic stabilization, predicts two kinetic/chemical features of ethylene polymerization reactions which have not been described yet, the deuterium effect on the homopolymer structure and the activation effect of α-olefins on chain initiation. Both effects were confirmed experimentally. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cumene Hydroperoxide Hydrogenation on a Pd/Al2O3 Catalyst in a Trickle Bed Reactor – Kinetics of Hydrogenation and Deactivation

Liquid‐phase hydrogenation using a Pd/Al₂O₃ catalyst provides a potential technique for the reduction of cumene hydroperoxide (CHP) to α‐cumyl alcohol (CA). In this paper, CHP hydrogenation was carried out in a cocurrent downflow trickle‐bed reactor over a wide range of reaction conditions to study the reaction and deactivation kinetics. The proposed intrinsic rate expression for CHP hydrogenation is based on an Eley‐Rideal mechanism that accounts for an irreversible surface reaction between the absorbed CHP with nonabsorbed hydrogen molecules. During CHP hydrogenation, an exponential decay in activity of the Pd/Al₂O₃ catalyst and the presence of residual activity were observed. A kinetic deactivation model with residual activity was developed. Based on reaction and deactivation kinetics, catalyst deactivation was attributed to oxidation of the catalyst surface by CHP. The presence of residual activity was due to the partial reduction of oxidized catalyst surface by hydrogen.     

Kinetic study of CO hydrogenation over co-precipitated iron–nickel catalyst

The kinetic of the Fischer–Tropsch synthesis over a Fe–Ni/Al₂O₃ catalyst was investigated in a fixed bed micro reactor. Experimental conditions were varied as follow: reaction pressure 2–10 bar, H₂/CO feed ratio of 2/1 and space velocity of 96–450 cm³(STP)/h/gram_catalyst at the temperature range 523–573 K. On the basis of carbide-enol mechanism and Langmuir–Hinshelwood–Hougen–Watson (LHHW) type rate equations, seventeen kinetic expressions for CO consumption were tested and interaction between adsorption HCO and dissociated adsorption hydrogen as the controlling step gave the most plausible kinetic model. The activation energy was 46.5 kJ/mole for optimal kinetic model.     

Emulsion polymerization of tetrafluoroethylene: effects of reaction conditions on the polymerization rate and polymer molecular weight

The emulsion polymerization of tetrafluoroethylene (TFE) was carried out in a semibatch reactor using a chemical initiator (ammonium persulfate) and a fluorinated surfactant (FC-143). The effects of the reaction condition were investigated though the polymerization rate, molecular weight of polytetrafluoroethylene (PTFE), and stability of the dispersion. The emulsion polymerization of TFE was different from conventional emulsion polymerization. The polymerization rate was suppressed when the polymer particles were significantly coagulated. The polymerization rate increased with operating temperature, surfactant concentration, and agitation speed, due to the enhanced stability of the polymer particles. However, once the parameter value was reached, the rate decreased due to the coagulation of the particles. Stable PTFE dispersion particles were obtained when the surfactant concentration was in the range between 3.48 × 10⁻³ and 32.48 × 10⁻³ mol/liter, which is below critical micelle concentration (CMC). The molecular weight of the PTFE obtained was a function of the surfactant and initiator concentrations, and the polymerization temperature. The molecular weight increased as each parameter decreased. This is against the phenomena observed in a conventional emulsion polymerization. A stable PTFE dispersion polymer having a high molecular weight was obtained by optimizing the reaction conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 777–793, 1999