Catalysis
Jonas B Biagini; Joao Henrique Zimnoch dos Santos
Abstract
The determination of Ti+4 in Ziegler–Natta catalysts is highly relevant for industrial plants that use Ziegler–Natta (ZN) catalysts based on TiCl4 as a source of titanium. The catalyst preparation step requires analytical monitoring during the dilution process for the morphological effect ...
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The determination of Ti+4 in Ziegler–Natta catalysts is highly relevant for industrial plants that use Ziegler–Natta (ZN) catalysts based on TiCl4 as a source of titanium. The catalyst preparation step requires analytical monitoring during the dilution process for the morphological effect according to the relationship between the Ti+3 and Ti+4 concentrations in the polymerization process, which in turn depend on a variety of intended grades for different market applications. Spectrophotometry in the visible region was evaluated as a potential analytical technique for the quantification of Ti+4 in ZN catalysts. The present study proposes the use of an easily accessible, reliable and low-cost validated instrumental method for Ti+4 determination. Therefore, the technical details regarding sample preparation, instrumental analytical parameters and performance characteristics of the method were descriptively addressed. The quantitative evaluation of performance parameters (namely, specificity, linearity, detection and quantification limits, precision, accuracy and robustness) demonstrated successful results compared with the theoretical values of the studied reference sample. The precision of the method by visible spectrophotometry was estimated at 0.4% for the relative error, and the accuracy presented within an IC of 95% for the LOC ± 1.7 mmolTi/L for the average concentration of 339.5 mmolTi L-1 in reference to the Tyzor ® TnBT sample with a theoretical concentration of 337 mmol L-1 study solution from this work. The method was shown to be a supporting tool for quantitative Ti+4 species determination in the control of industrial processes.
Catalysis
Farabi Hossain; Md Enamul Hoque
Abstract
This mini-review addresses the burgeoning requirements for environmentally friendly processes in the polymer industry, focusing on recent progress in developing catalytic systems for sustainable olefin polymerization. Improvements in homogeneous and heterogeneous catalyst design have resulted in greater ...
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This mini-review addresses the burgeoning requirements for environmentally friendly processes in the polymer industry, focusing on recent progress in developing catalytic systems for sustainable olefin polymerization. Improvements in homogeneous and heterogeneous catalyst design have resulted in greater control over polymer properties (molecular weight, tacticity, comonomer incorporation). Particularly, Group 4 metallocene and post-metallocene catalysts have enjoyed high activity and a degree of control over polymer microstructure. Late transition metal catalysts (nickel and palladium complexes in particular) afford unique advantages in producing branched polyethylene and conducting polymerizations in polar solvents. Computational studies and novel support strategies have yielded improvements for heterogeneous Ziegler-Natta catalysts. Potential for reducing environmental impact through green catalysis approaches include enzyme-based systems, ionic liquids, and photoactivated catalysts. These catalytic advances have permitted previously unavailable control over polymer properties, including molecular weight distribution and functional group incorporation. Challenges remain regarding the stability of the catalysts, incorporation of comonomer, and economic feasibility. Future work focuses on new ligand design, extending the monomer scope to include renewable feeds tocks and improving the activation procedures. There is a critical need to integrate computational modeling, machine learning, and advanced characterization techniques to facilitate catalyst discovery and understanding of complex structure-property relationships. In general, this review demonstrates the ongoing development of olefin polymerization toward more sustainable practices and describes the important role of advanced catalytic systems in determining the future of the polymer industry).
Catalysis
Mohammad Javad Sharifi; Alireza Fazlali; Seyed Hamed Mahdaviani; Davood soudbar
Abstract
The performance of the catalyst system [chromium(III)/pyrrole/co-catalyst/halide] on the trimerization of ethylene has been studied using the combined experimental and response surface method (RSM). The chromium(III) tris(2-ethylhexanoate) was synthesized and characterized by FTIR, 1HNMR and 13CNMR, ...
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The performance of the catalyst system [chromium(III)/pyrrole/co-catalyst/halide] on the trimerization of ethylene has been studied using the combined experimental and response surface method (RSM). The chromium(III) tris(2-ethylhexanoate) was synthesized and characterized by FTIR, 1HNMR and 13CNMR, to study chemical properties and identify molecular structures. The effect of four variables Al/Cr molar ratio, halide/Cr molar ratio, reaction temperature and catalyst dosage have been considered on catalyst activity, 1-hexene selectivity and polymer content. The central composite design (CCD) model with three main parameters in three response levels for each factor was applied to analyze the effects of the parameters. The comparative studies showed that carbon-tetra-chloride (CCl4) and tri-n-octyl-aluminum (TNOA) were the best candidates for this catalyst system, demonstrating high selectivity of 1-hexene formation, higher catalytic activity and lower polymer content. Based on the RSM results, the best trimerization condition for ethylene at 25 bar and 91.2°C was obtained at the catalytic system [Cr(2-EH)3/2,5-DMP/CCl4/TNOA] molar ratio of 1:6:10.8:201.5, which showed the activity of 105328 (g 1-C6/(g Cr.hr)), 99.21% selectivity for 1-hexene and no polymer was formed. The predicted process parameters were also verified by actual experiments at the optimized conditions.
Catalysis
Tatiana B. Mikenas; A. V. Sholma; Vladimir A. Zakharov; Mikhail Matsko
Abstract
The paper presents data on the effect exerted by magnesium dichloride in Ziegler-Natta catalysts on the activity and molecular weight of polyethylene (PE) produced by ethylene polymerization in the absence or presence of hydrogen. It was found that ethylene polymerization in the absence of hydrogen over ...
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The paper presents data on the effect exerted by magnesium dichloride in Ziegler-Natta catalysts on the activity and molecular weight of polyethylene (PE) produced by ethylene polymerization in the absence or presence of hydrogen. It was found that ethylene polymerization in the absence of hydrogen over titanium-magnesium catalysts (TMCs) with different ratio of titanium chloride and magnesium dichloride (Ti/Mg = 0.5 and 0.07), oxidation state of titanium (TiCl3 or TiCl4) and structural characteristics of the catalysts leads to the formation of PE with a close molecular weight. At the same time, PE obtained over a δ-TiCl3 catalyst has a much (threefold) higher molecular weight. The introduction of hydrogen during polymerization for decreasing the molecular weight of PE is accompanied by a sharp drop in activity of the δ-TiCl3 catalyst, in distinction to the highly active supported TMC containing 3 wt. % Ti. Data about the effect of hydrogen content during polymerization on the molecular weight of PE were used to calculate the ratio of rate constants for polymer chain transfer with hydrogen (KtrH) and polymer chain propagation reaction (Кр). This value was close for TMCs of different composition containing magnesium dichloride. In the case of δ-TiCl3, the KtrH/Кр value was approximately two times lower compared to TMCs.
Catalysis
Kotohiro Nomura
Abstract
Certain cyclic olefin copolymers (COCs) are known as promising amorphous materials with high transparency in the UV-vis region, thermal and humidity resistance, low dielectric constant, low water absorption, and dimensional stability. This short review focuses on the synthesis of (new) cyclic olefin ...
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Certain cyclic olefin copolymers (COCs) are known as promising amorphous materials with high transparency in the UV-vis region, thermal and humidity resistance, low dielectric constant, low water absorption, and dimensional stability. This short review focuses on the synthesis of (new) cyclic olefin copolymers by designed (nonbridged) half-titanocene catalysts, which enabled to proceed synthesis of the amorphous polymers by ethylene/ propylene copolymerization not only with norbornene (NBE), and tetracyclododecene (TCD), but also with so called low strained cyclic olefins (cyclopentene, cyclohexene, cycloheptene, and cyclooctene). Their thermal properties (glass transition temperature, Tg values) are affected by structure of the cyclic olefin employed and the contents, whereas linear relationships between Tg values and the contents were observed in all cases.
Catalysis
Majedeh Maroofi; Gholam Hossein Zohuri; Saeid Ahmadjo; Navid Ramezanian
Abstract
A mono-nuclear catalyst of bis-imine cobalt (MC) was synthesized with using 2,6-dibenzhydryl-4-ethoxy phenyl as a ligand. The so huge ligand was prepared via the reaction of 2,6-dibenzhydryl-4-ethoxy phenyl)-N=(CH3)-C(CH3)=O with diacetyl with equal mole stoichiometry in presence of formic acid catalysis. ...
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A mono-nuclear catalyst of bis-imine cobalt (MC) was synthesized with using 2,6-dibenzhydryl-4-ethoxy phenyl as a ligand. The so huge ligand was prepared via the reaction of 2,6-dibenzhydryl-4-ethoxy phenyl)-N=(CH3)-C(CH3)=O with diacetyl with equal mole stoichiometry in presence of formic acid catalysis. The catalyst was synthesized via a reaction between the ligands and cobalt salt (CoCl2). The catalyst was used for polymerization of methyl methacrylate (MMA), (a polar monomer) in the presence of modified methylaluminoxane (MMAO). The highest polymerization activity (8.6 g PMMA/mmol cat. h) was obtained at [cocatalyst]/[catalyst]=1000:1 molar ratio and at room temperature reaction. For the prepared PMMA, Polymer with branching density of 263/1000C was obtained using 1H NMR technique calculation. The microstructure of one of the produced PMMA was as follow: 48% syndiotactic, 29% isotactic and 23% atactic. GPC analysis of the polymer showed a number average molecular weight of about 5.7 × 105 g/mol and a narrow molecular weight distribution of 1.57.
Catalysis
Hongfan Hu; Rongqing Ma; Chenxi Cui; Guoliang Mao; Shixuan Xin
Abstract
Due to the large ionic radius and high electro-positivity nature, rare earth metal complexes are difficult to stabilize and undergo pathways like ligand redistribution and intramolecular C-H activation. To solve such problems and retain reactive versatility, rare earth complexes supported by a variety ...
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Due to the large ionic radius and high electro-positivity nature, rare earth metal complexes are difficult to stabilize and undergo pathways like ligand redistribution and intramolecular C-H activation. To solve such problems and retain reactive versatility, rare earth complexes supported by a variety of tridentate PNP pincer ligands have been explored. Such complexes can serve as perfect precursors for preparing ultra-active rare earth species containing two metal-carbon bands, let alone Ln=N and Ln=P multiple bonds. In addition, the combined stability and activity of the cation rare earth mediates made them the best catalysts for the polymerization of olefins and other non-polar hydrocarbon monomers, especially conjugated dienes. The practical utilization of rare earth metal catalysts for new materials production have also extensively explored by experts from the academic and industries.
Catalysis
Kefeng Xie; Wei Hao; Shengyuan Xu; Jie Wang; Xiong Wang; Zhengang Han
Abstract
The substituents on cyclopentadienyl (Cp) can regulate the electronic effect and hindrance of the active center in the metallocene catalyst. This modification can greatly change the catalytic activity of the catalyst and affect some features of the polymer. In order to study the effect of alkyl substituents ...
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The substituents on cyclopentadienyl (Cp) can regulate the electronic effect and hindrance of the active center in the metallocene catalyst. This modification can greatly change the catalytic activity of the catalyst and affect some features of the polymer. In order to study the effect of alkyl substituents on Cp in the performance of a typical metallocene catalyst Cp2TiCl2 for ethylene polymerization, two types of catalyst active centers were designed, including non-bridge Cp2(R)TiCH3]+ and bridge [NCP2 (R)TiCH3]+ (R = H, Me, iPr). The effects of alkyl substituent steric hindrance were explored by density functional theory on the complex of catalyst active center with ethylene and the formation of transition state. The results showed that the increase of substituent steric hindrance was unfavorable to complex between ethylene monomer with catalyst active center. Moreover, the bigger alkyl substituent, the greater the activation energy of ethylene insertion into catalyst active center and the more difficult is ethylene polymerization. Therefore, the performance of metallocene catalysts could be regulated by the substituent on Cp.
Catalysis
Odilia Pérez-Camacho; Eduardo Cardozo-Villalba
Abstract
In this work, the interaction between a polystearylmethacrylate (Mn = 8,900 g mol-1, Xn = 26, Ð = 1.1) and modified methylaluminoxane 12 (MMAO-12) co-catalyst is studied using different spectroscopic methods. The effect of this oxygen-donor additive was measured by the changes in the bulk ...
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In this work, the interaction between a polystearylmethacrylate (Mn = 8,900 g mol-1, Xn = 26, Ð = 1.1) and modified methylaluminoxane 12 (MMAO-12) co-catalyst is studied using different spectroscopic methods. The effect of this oxygen-donor additive was measured by the changes in the bulk density of the raw polyethylene, which resulted increased respect to those obtained in blank reactions. A decrease in the activity was also observed as a penalty for the improvement of the bulk density, enhancing the possibility of reducing fouling. The coordination of the carbonyl oxygen groups of polystearylmethacrylate to aluminum (III) centers is confirmed by 1H-NMR and FTIR studies, and by a simple semi-empirical computational calculation. A method for obtaining a tri-component co-catalyst mixture is described using the methyl-bridging capacity of trimethylaluminum and its Lewis acidity to get the polystearylmethacrylate and MMAO-12 linked together. This robust adduct introduces a hierarchy over the PE chain growing, leading to higher bulk densities for PE beads (0.43 g cm-3) concerning blank reactions (0.26 g cm-3).
Catalysis
Nina V. Semikolenova; Valentina N. Panchenko; Mikhail A. Matsko; Vladimir A. Zakharov
Abstract
For preparation of highly active supported catalyst with bis(imino)pyridyl Fe(II) complexes (Fe1, Fe2) and N,N-α-diimine complex of Ni (Ni3), silica modified with alumina (SiO2 (Al)) was used as a support. Data on the possibility to regulate molecular weight (MW) and molecular weight distribution ...
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For preparation of highly active supported catalyst with bis(imino)pyridyl Fe(II) complexes (Fe1, Fe2) and N,N-α-diimine complex of Ni (Ni3), silica modified with alumina (SiO2 (Al)) was used as a support. Data on the possibility to regulate molecular weight (MW) and molecular weight distribution (MWD) of polyethylene (PE), produced over the supported catalyst Fe1/SiO2 (Al)+TIBA by variation of polymerization temperature and the addition of hydrogen and hexene-1, are obtained. The prepared PE samples were characterized by Mw values varied from 80 to 350 kg/mol and various MMD (Mw/Mn=4.6-11.7).By grafting on SiO2(Al) of two different iron bis(imino)pyridyl complexes, producing PE with diverse MW, bi-component catalyst was prepared. This catalyst generates linear PE with broad and bimodal MWD (Mw/Mn=33). Fixation on SiO2(Al) of α-diimine Ni(II) pre-catalyst (Ni3), yielding high molecular weight branched PE at the ethylene homopolymerization, and bis(imino)pyridyl Fe(II) complex (Fe2) that forms lower molecular weight linear PE, affords formation of a new bi-component catalyst. The catalyst produces PE with broad MWD and high content of branches concentrated in high molecular weight PE fraction.
Catalysis
Masayoshi Saito; Toshiya Uozumi; Masahide Murata; Takuo Kataoka; Riichiro Chujo
Abstract
Ziegler-Natta catalyst for propylene polymerization, which TiCl4 and di-alkyl phthalate were supported on MgCl2, was analyzed by solid state 13C NMR. It was confirmed that the spin-lattice relaxation time (“relaxation time” hereafter) of carbonyl group in phthalate was shortened with ...
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Ziegler-Natta catalyst for propylene polymerization, which TiCl4 and di-alkyl phthalate were supported on MgCl2, was analyzed by solid state 13C NMR. It was confirmed that the spin-lattice relaxation time (“relaxation time” hereafter) of carbonyl group in phthalate was shortened with increasing measurement temperature as a general manner because of the enhancing of molecular mobility at high temperature. The degree of the relaxation period reduction with temperature was influenced by the alkyl group size in phthalate molecule; the larger alkyl group showed a greater shorting of the relaxation period. A short relaxation time should suggest a weak interaction between the phthalate molecule and the MgCl2 support surface. The change in catalytic performance was discussed by the active site formation mechanism involving the phthalate removal step.
Catalysis
Zenghui Zhao; Tatiana Mikenas; Vladimir Aleksandrovich Zakharov; Marina Nikolaeva; Mikhail Matsko; Elena Bessudnova; Wei Wu
Abstract
The new highly active supported vanadium-magnesium catalyst (VMC) has been studied in α-olefin (1-butene, 1-hexene)/ ethylene copolymerization in the presence of hydrogen. Data on the effect of α-olefin/ethylene ratio in copolymerization on the content of branchings in copolymers, kinetic ...
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The new highly active supported vanadium-magnesium catalyst (VMC) has been studied in α-olefin (1-butene, 1-hexene)/ ethylene copolymerization in the presence of hydrogen. Data on the effect of α-olefin/ethylene ratio in copolymerization on the content of branchings in copolymers, kinetic profile, copolymer yield, molecular weight and molecular weight distribution of copolymers have been obtained. It was found that both α-olefins are effective chain transfer agents in the ethylene-α-olefins copolymerization. The copolymerization ability of VMC is much higher than that of the well known titanium-magnesium catalysts. It was found that the use of optimal conditions of ethylene/α-olefin polymerization on the VMC catalyst makes it possible to obtain copolymers with a high yield (10-16 kg gcat-1 cat for 2 h) the copolymers having broad and bimodal MWD. Data on the branchings distribution in copolymers prepared with VMC catalyst have been obtained via fractionation of copolymers on the fractions with narrow polydispersity (Mw/Mn ≈ 2). Quite a uniform distribution of branchings over fractions with different molecular weight was found in distinction to inhomogeneous distribution of branchings in copolymers produced over the well known supported titaniu-magnesium catalyst.
Catalysis
Alikhani Ali; Shokoufeh Hakim; Mehdi Nekoomanesh
Abstract
This study presents methods for treating a kind of nanoclay and investigates the effects of methylaluminoxane (MAO) exposure time and or dodecylamine (DDA) reflux time on in-situ polymerization of ethylene in the presence of nanoclay and examines the morphology and properties of the prepared polyethylene/clay ...
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This study presents methods for treating a kind of nanoclay and investigates the effects of methylaluminoxane (MAO) exposure time and or dodecylamine (DDA) reflux time on in-situ polymerization of ethylene in the presence of nanoclay and examines the morphology and properties of the prepared polyethylene/clay nanocomposites. The results revealed that by increasing MAO exposure time productivity decreased. Modification of nanoclay by NH3/MAO led to formation of exfoliated structures. In treatment with NH3/DDA, the change in reflux time resulted in different structures. SEM demonstrated that the morphology of the nanocomposites strongly depended on the modification method and treatment time. Dynamic mechanical analysis indicated that the elastic modulus of the nanocomposites increased by increasing MAO exposure time. The nanocomposites treated with different MAO exposure times showed similar thermal degradation behavior. The nanocomposite modified under the condition of 24 h DDA reflux time indicated the lowest thermal decomposition temperature due to poor dispersion of nanoclay in the synthesized nanocomposite. The nanocomposites modified by NH3/MAO had higher degree of crystallinity compared to those modified by NH3/DDA, which could be attributed to the difference in dispersion level of the modified clays. A relationship between the rheological properties, weight fraction and dispersion of modified nanoclay was observed. The findings showed that the modification condition had a significant influence on the morphology and properties of the synthesized nanocomposites.
Catalysis
Gholam-Reza Nejabat
Abstract
Since 1999, when Takuzo Aida proposed the preparation of high density polyethylene (HDPE) crystalline nanofibers through polymerization of ethylene by a Cp2 TiCl2 /MCM-41 catalyst, many researchers have published various papers on different aspects of the idea. The published researches show that the ...
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Since 1999, when Takuzo Aida proposed the preparation of high density polyethylene (HDPE) crystalline nanofibers through polymerization of ethylene by a Cp2 TiCl2 /MCM-41 catalyst, many researchers have published various papers on different aspects of the idea. The published researches show that the endeavors to polymerize other types of alpha olefins, especially propylene, to obtain polyolefins with crystalline nanofiberous morphology have not been successful and no one has reported such morphology for them. In the present article, a possible reason behind these observations is proposed. Comparing the direction of the growth of HDPE chains and isotactic polypropylene (iPP) helices to become appropriate for making polymer crystals shows that HDPE chains are able to form crystal unit cells without concerning upward or downward chain growth direction, while the growth direction of adjacent iPP chains might be responsible for unsuccessful synthesis of crystalline iPP nanofibers in confined channels of the mesoporous catalysts. iPP helices can crystallize beside each other only in the form of anticline isochiral helices.
Catalysis
Andrea M. Rimkus; Helmut G. Alt
Abstract
Eight different zirconium phenoxyimine complexes were synthesized, characterized and tested as catalysts for ethylene polymerization. The phenoxyimine compounds were prepared by condensation of substituted salicylaldehydes with aliphatic and aromatic amines, the substituted salicylaldehydes from ortho ...
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Eight different zirconium phenoxyimine complexes were synthesized, characterized and tested as catalysts for ethylene polymerization. The phenoxyimine compounds were prepared by condensation of substituted salicylaldehydes with aliphatic and aromatic amines, the substituted salicylaldehydes from ortho substituted phenols and paraformaldehyde. The introduction of iodo substituents was achieved either by iodination of the aldehyde component followed by condensation with amines or the iodination of the aldehyde after the condensation with amines or the iodination via condensation with iodo substituted amines. Deprotonation of the hydroxy function of phenoxyimine compounds and reaction with zirconium tetrachloride gave mononuclear bis(phenoxyimine) zirconium complexes in good yields. These complexes were activated with methylaluminoxane (MAO) and applied for ethylene polymerization. The performances of the various catalysts were compared and structure-property-relationships were discussed.
Catalysis
Liang Zhu; Xuelian He; Ruihua Cheng; Zhen Liu; Ning Zhao; Boping Liu
Abstract
SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide (Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg ...
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SiO2/MgCl2 (ethoxide type)/TiCl4 Ziegler-Natta catalysts for use in ethylene polymerization and ethylene/1-hexene copolymerization have been prepared using silica with a supported layer of magnesium ethoxide (Mg(OEt)2) as a catalyst precursor, followed by treating with TiCl4 at different Ti/Mg molar ratios, which showed significant effects on the active centers and pore structures of the catalysts. The formation amount of β-MgCl2 carrier increased to a maximum with increasing the Ti/Mg molar ratio from 1.50 to 2.25, and then decreased with the further increasing of Ti/Mg molar to 2.50. When the Ti/Mg molar ratio reached 2.25, the catalyst showed the best performance of polymerization, which could be attributed to the most active centers, high surface area and loose surface structure, mainly owing to the high conversion of Mg(OEt)2 to β-MgCl2. The polymers obtained showed medium and high molecular weight (Mw) with medium molecular weight distribution (MWD). In contrast to the conventional Mg(OEt)2-based ZN catalysts, the sphericity of particles was easy to control in this bi-supported catalyst. Furthermore, the prepared catalysts exhibited rather high activity, good copolymerization ability and hydrogen response.
Catalysis
Lei Cui; Ji-Xing Yang; Yan-Guo Li; Yue-Sheng Li
Abstract
Novel cyclic olefin polymers (COPs) derived from bulky cyclic olefins, tricyclodipentadiene (TCPD) and tricyclo[6.4.0.19,12]-tridec-10-ene (TTE), with high glass transition temperature (Tg), excellent thermal stability, and high transparency, have been synthesized by ring-opening metathesis polymerization ...
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Novel cyclic olefin polymers (COPs) derived from bulky cyclic olefins, tricyclodipentadiene (TCPD) and tricyclo[6.4.0.19,12]-tridec-10-ene (TTE), with high glass transition temperature (Tg), excellent thermal stability, and high transparency, have been synthesized by ring-opening metathesis polymerization (ROMP) and subsequent hydrogenation. ROMP of TCPD and TTE was carried out successfully without gel formation using a WCl6/i-Bu3Al/Et-OH/hexene catalyst system at room temperature. By changing the TCPD/TTE molar ratio, the optimized catalyst component ratio for the polymerization varied. Chemical structures of the unsaturated and hydrogenated polymers were characterized by 1H NMR technique. Thermal properties of these newly synthesized polymers were determined using TGA and DSC measurements. The degradation temperatures (Td) were all above 420°C in N2, indicating that all these copolymers had excellent thermal stability. After hydrogenation, Tg of ROMP polymers was decreased by 30-60°C. The Tg of h-pTCPD reached as high as about 230°C. The light transmittances of these polymer films were also analyzed using UV-Vis absorption spectroscopy. A high light transmittance of up to 92% was found by UV-Vis absorption spectra for these polymer films.
Catalysis
Ting Fu; Ruihua Cheng; Xuelian He; Zhen Liu; Zhou Tian; Boping Liu
Abstract
Vanadium-modified (SiO2/MgO/MgCl2)•TiClx Ziegler-Natta catalysts were prepared through co-impregnation of water-soluble magnesium and vanadium salts under different pH values. Several key factors such as pH value of co-impregnation solution during catalyst preparation, catalyst performances including ...
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Vanadium-modified (SiO2/MgO/MgCl2)•TiClx Ziegler-Natta catalysts were prepared through co-impregnation of water-soluble magnesium and vanadium salts under different pH values. Several key factors such as pH value of co-impregnation solution during catalyst preparation, catalyst performances including catalytic activity, ethylene/1-hexene copolymerization and hydrogen response were investigated. It is found that the components, structures and performance of the catalysts are obviously affected by changing the pH value (pH=5, 7 and 9) of co-impregnation solution. An appropriate pH value (pH=7) can maximize catalytic activity and hydrogen response, while lower pH value (pH=5) is beneficial to the 1-hexene incorporation. The GPC results show that the polymers obtained have high average molecular weight.
Catalysis
Leticia Pereira; Maria Marques
Abstract
Ethylene-norbornene copolymers were synthesized with a homogeneous catalyst system based on bis(imino) pyridine iron with the addition of diethyl zinc (DEZ) as alkyd transfer agent to promote immortal copolymerization. The addition of DEZ did not influence the catalytic activity in copolymerization with ...
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Ethylene-norbornene copolymers were synthesized with a homogeneous catalyst system based on bis(imino) pyridine iron with the addition of diethyl zinc (DEZ) as alkyd transfer agent to promote immortal copolymerization. The addition of DEZ did not influence the catalytic activity in copolymerization with 7.5 mmol of norbornene (NB), but in the reactions with 70 mmol, the comonomer promoted an increase of activity. We observed by thermal analysis that the norbornene inserted in the chains promoted an increase in thermal stability of the synthesized material with higher amounts of comonomer, since the temperature of initial degradation was much higher for these copolymers compared to polyethylene. In addition, for the copolymers with 7.5 mmol of norbornene, the DEZ served as alkyd transfer agent, as shown by the gel permeation chromatography analysis, leading to a decrease in both molar mass and polydispersity. The UV-Vis spectra showed that the diethyl zinc did not change the catalytically active center, but only acted as an alkyd transfer agent.
Catalysis
Hossein Bordbar; Ali Akbar Yousefi; Hossein Abedini
Abstract
Titanium (Ti) is the ninth most abundant element on earth. The titanium mineral ores are widely distributed in different parts of the world. The two main ores of titanium include rutile (TiO2) and ilmenite (FeO.TiO2). It is aimed to provide the readers with an insight to the main processes currently ...
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Titanium (Ti) is the ninth most abundant element on earth. The titanium mineral ores are widely distributed in different parts of the world. The two main ores of titanium include rutile (TiO2) and ilmenite (FeO.TiO2). It is aimed to provide the readers with an insight to the main processes currently employed to extract and recover titanium tetrachloride (TiCl4) from different titanium ores. Due to the crucial importance of TiCl4 catalyst in the synthesis and polymerization of polyolefins, the present work examines the literature and developments made in the processing of ilmenite and rutile ores for the extraction of TiCl4. The attention has been paid to the chlorination processes and the main parameters affecting the recovery of TiCl4. Different approaches developed to date are reviewed. Different processes, reaction mechanisms and conditions as well as the kinetic models developed for extraction and purification of TiCl4 in fluidized bed reactors are also reviewed. A literature survey on the combined fluidized bed reactor systems developed for achieving a high-grade synthetic rutile via selective chlorination of low-grade titanium ores having high metal oxides content such as magnesium oxide (MgO) and calcium oxide (CaO) is also reported. Different strategies adopted to avoid agglomeration process during the extraction process are discussed too.
Catalysis
Feng He; Peiyuan Li; Anyang Wu; Tao Xu; Zhisheng Fu; Liang Zhu; Zhiqiang Fan
Abstract
In this paper, a series of well-defined polyethylene-b-polytetrafluoroethylene diblock copolymers (PE–b– PTFEs) were prepared by a coupling reaction of hydroxyl-terminated polyethylene (PE–OH) and isocyanateterminated 1H,1H-perfluoro-1-tetradecanol (PFDO–NCO). PE–OH was ...
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In this paper, a series of well-defined polyethylene-b-polytetrafluoroethylene diblock copolymers (PE–b– PTFEs) were prepared by a coupling reaction of hydroxyl-terminated polyethylene (PE–OH) and isocyanateterminated 1H,1H-perfluoro-1-tetradecanol (PFDO–NCO). PE–OH was prepared by the coordination chain transfer polymerization using 2,6-bis[1-(2,6-diisopropylphenyl)imino ethyl] pyridine iron (II) dichloride /dry ethylaluminoxane/ZnEt2 as catalyst and subsequent in situ oxidation with oxygen. PFDO–NCO was synthesized through the condensation reaction of 1H,1H- perfluoro-1-tetradecanol (PFDO) with isophoronediisocyanate (IPDI). Subsequently, the thermal characterization and the application of these diblock copolymers were investigated. The relationship between the molecular structure and the properties was disclosed. The results indicated that the diblock copolymers were effective surface modification agents for linear low density polyethylene (LLDPE). After that the PE–b–PTFE being spin-coated onto the surface of LLDPE film, the film was dramatically turned into a superhydrophobic film with a water contact angle as high as 151.4º. This kind of film is potential to be used as selfcleaning, anti-icing and anticorrosion material.
Catalysis
Qiaoqiao Sun; Ruihua Cheng; Zhen Liu; Xuelian He; Ning Zhao; Boping Liu
Abstract
Chromium-vanadium (Cr-V) bimetallic catalysts are prepared by the introduction of vanadium into the Phillips catalyst which is one of the most significant industrial ethylene polymerization catalysts for tuning the Phillips catalyst performances and improving polyethylene properties. In the present work, ...
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Chromium-vanadium (Cr-V) bimetallic catalysts are prepared by the introduction of vanadium into the Phillips catalyst which is one of the most significant industrial ethylene polymerization catalysts for tuning the Phillips catalyst performances and improving polyethylene properties. In the present work, titanium species were introduced into the fluorine-modified chromium-vanadium bimetallic catalysts (Cr-V-F) and the prepared catalysts were systematically explored. The element content results of multi-component catalysts showed that a competitive inhibition interaction existed between chromium and vanadium, whereas chromium was more preferable to attach to the Ti-SiO2 than vanadium. In addition, ethylene homopolymerization and ethylene/1-hexene copolymerization were carried out and examined with different catalysts. The introduction of titanium into fluorine-modified bimetallic catalysts enhanced the molecular weight (MW) and broadened the molecular weight distribution (MWD) of polyethylene. The MW of the titanium- and fluorine-modified bimetallic catalysts (Cr-V-F/Ti) firstly rose up and then dropped down with the increasing of the Al/Cr molar ratio. The Cr-V-F/Ti catalysts showed slightly depressed hydrogen response and incorporation of 1-hexene. The short-chain branch distribution (SCBD) results, which were characterized by TREF/SSA, showed that the introduction of the titanium species increased the SCB content in low MW fractions and decreased the SCB content in the high Mw fractions of ethylene/1-hexene copolymers obtained from (Cr-V-F/3Ti)600 in contrast to that from (Cr-V-F)600.
Catalysis
Farshid Nouri-Ahangarani; Mehdi Nekoomanesh; Seyed Amin Mirmohammadi; Naeimeh Bahri-Laleh
Abstract
The aim of this study was to examine the effect of catalyst doping on the performance of MgCl2. EtOH/TiCl4 catalyst system. In this regard, a series of undoped as well as FeCl3-doped catalysts was prepared and employed in 1-hexene polymerization. A modified catalyst containing 10 wt. % of FeCl3 dopant ...
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The aim of this study was to examine the effect of catalyst doping on the performance of MgCl2. EtOH/TiCl4 catalyst system. In this regard, a series of undoped as well as FeCl3-doped catalysts was prepared and employed in 1-hexene polymerization. A modified catalyst containing 10 wt. % of FeCl3 dopant demonstrated the highest activity, with 32% activity increase compared to unmodified one, among the series. The GPC results showed a lower molecular weight as well as broader MWD for the poly1-hexenes obtained from FeCl3-doped catalyst. The distribution of active centers was analyzed using deconvolution of the MW profiles with using multiple Flory functions. It was demonstrated that the number of active sites increased by 10 wt. % FeCl3 doping, however, by more increasing the dopant amount to 15 wt.%, the number of active sites decreased. The 13C-NMR results indicated that, FeCl3 doping did not have a considerable effect on the polymer tacticity (with total tacticity of 53 %), however it increased by donor presence to the maximum value of 60 %.
Catalysis
He-Xin Zhang; Seung-Ri Lee; Dong-Ho Lee; Xue-Quan Zhang; Keun-Byoung Yoon
Abstract
Despite the great potential of graphene as a nanofiller, achieving homogeneous dispersion remains the key challenge for effectively reinforcing polyolefin (such as polyethylene (PE) and polypropylene (PP)) nanocomposites. Therefore, in this research, we report a facile combined in situ polymerization ...
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Despite the great potential of graphene as a nanofiller, achieving homogeneous dispersion remains the key challenge for effectively reinforcing polyolefin (such as polyethylene (PE) and polypropylene (PP)) nanocomposites. Therefore, in this research, we report a facile combined in situ polymerization and masterbatch method for fabricating PP/reduced graphene oxide (rGO) nanocomposites. In the polymerization stage, the synthesized catalyst exhibited a very high activity toward propylene polymerization, while the resultant PP/rGO with a very high isotactic index (I.I. = 99.3), broad molecular weight distribution (Mw/Mn = 14.9), and thermal stability was produced. After meltblending with commercial PP, a significantly increased modulus along with no observable change in tensile strength and elongation-at-break were achieved via the addition of a very small amount of rGO; these properties resulted from the suitable dispersion and good interface adhesion of the graphene sheet and PP matrix. Thus, this work provides a method for production of high performance PP.
Catalysis
Valentina Nikolaevna Panchenko; Ludmila Viktorovna Vorontsova; Vladimir Aleksandrovich Zakharov
Abstract
The interaction of the external donor (propyltrimethoxysilane - PTMS) with titanium-magnesium catalysts (TMCs) containing dibutylphthalate (DBP) as internal donor, which were prepared in different ways, was studied by chemical analysis and infrared diffuse reflectance spectroscopy (DRIFTS). The chemical ...
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The interaction of the external donor (propyltrimethoxysilane - PTMS) with titanium-magnesium catalysts (TMCs) containing dibutylphthalate (DBP) as internal donor, which were prepared in different ways, was studied by chemical analysis and infrared diffuse reflectance spectroscopy (DRIFTS). The chemical composition of the catalysts after their interaction with heptane solutions of PTMS, PTMS/AlEt3 or AlEt3 during 1h at 70°C showed that this interaction led to removal of both TiCl4 and DBP from the catalysts. The fractions of DBP and Ti extracted, as well as the amounts of PTMS and AlEt3 bound, depended on the method of synthesizing the catalysts. DRIFT spectroscopy data concerning the state of DBP in the catalysts, before and after treatment with heptane solutions of PTMS or PTMS/AlEt3 during 1h at 70°C, showed that PTMS could substitute both TiCl4 and DBP, while adsorbing on coordinatively unsaturated Ti and Mg ions in the catalyst. The presence of AlEt3 played a key role in the interaction of PTMS with the catalyst. Activity data for propylene polymerization showed that treatment of TMC catalysts with PTMS before polymerization led to a sharp activity decrease due to deactivation of active sites, while the interaction of the catalyst with PTMS in the presence of AlEt3 led only to a slight decrease of activity, probably due to deactivation of non-stereospecific active centers.
