Magnesium chloride supported high-mileage catalysts for olefin polymerization. I. Chemical composition and oxidation states of titanium

The chemical composition of a MgCl₂-supported, high-mileage catalyst has been determined at every stage of its preparation. Ball milling of MgCl₂ with ethyl benzoate (EB) resulted in the incorporation of 95% of the EB present to give MgCl₂·EB_0.15. A mild reaction with a half-mole equivalent of p-cresol (PC) at 50°C for 1 h resulted in near quantitative retention of p-cresol by the support. The composition is now approximately MgCl₂·EB_0.15P?_0.5. Addition of an amount of AlEt₃ corresponding to half-mole equivalent of p-cresol liberated one mole of ethane per mole of p-cresol, thus signaling quantitative reaction between the two components. The support contains on the average one ethyl group per Al. Further reaction with TiCl₄ resulted in the incorporation of titanium of approximately 8, 38, and 54% in the oxidation states of +2, +3, and +4, respectively. The ratio of Al to Ti in the catalyst lies in the range of 0.5–1.0. Only 19% of all the Ti⁺³ species in the catalyst can be observed by electron paramagnetic resonance (EPR); these are attributable to isolated Ti⁺³ complexes. The remaining EPR silent Ti⁺³ species are believed to be bridged to another Ti⁺³ by Cl ligands. The total Cl content is equal to the sum of 2 × Mg + 3 × Al + 3.5 × Ti. Most of the p-cresol moiety apparently disappeared from the support, leaving much of ethyl benzoate in the catalyst. Activation with AlEt₃/methyl-p-toluate complex reduces 90% of the Ti⁺⁴ in the catalyst to lower oxidation states. The ester apparently moderates the alkylating power of AlEt₃ to avoid excessive formation of divalent titanium sites. There appears to be a constant fraction of 1/4–1/5 of the titanium which is isolated and the remainder is in bridged clusters independent of the oxidation states of titanium.     

Comparative characterization of MgCl2/ethyl benzoate/TiCl4 and MgCl2/2,2,6,6 tetramethylpiperidine/TiCl4 Ziegler-Natta precatalysts

In this article we present the results of the preparation and characterization of two Ziegler–Natta precatalysts: MgCl₂/Ethyl benzoate (EB)/TiCl₄ and MgCl₂/2,2,6,6 tetramethylpiperidine (TMPiP)/TiCl₄ by means of FTIR, X-ray diffraction, SEM, BET surface area measurements, and other techniques applied at different steps of their preparation procedures. The precatalysts were prepared by impregnating with TiCl₄ a given amount of MgCl₂, which was previously ball-milled with the electron donor chosen. Prior to impregnation, the ball-milled material presented different surface compounds depending on the electron donor used: [(MgCl₂)₂] · 2EB, MgCl₂ · EB, or a salt of the amine. The solid milled with EB is more homogeneous than the one milled with the TMPiP. Titanium is better retained in the solid milled with EB. This precatalyst has better morphological properties and larger BET surface area. By means of FTIR, we found evidences that an adequate surface structure for the formation of stereospecific sites in MgCl₂/TMPiP/TiCl₄ was formed. © 1994 John Wiley & Sons, Inc.     

Superactive and stereospecific catalysts. III. Definitive identification of active sites by electron paramagnetic resonance

Superactive Ziegler–Natta catalysts have been prepared from a soluble MgCl₂·2-ethyl hexanol adduct in the presence of organic esters through reactions with TiCl₄ and activated with AlEt₃/phenyltriethoxy-silane. Electron paramagnetic spectra (EPR) were used to elucidate the nature and amount of those Ti⁺³ ions not bridged to another Ti⁺³ ion; the chlorine bridged Ti⁺³ ions are EPR silent. The EPR spectra were attributed to two rhombic Ti⁺³ sites with principal values for the g-tensors (1.967, 1.949, 1.915; and 1.979, 1.935, 1.887). The total amount of the EPR species, obtained by double integration of the EPR spectra, is in close agreement with the concentration of isospecific catalytic sites determined by radiotagging. This suggests that the nonspecific sites are EPR silent. When o-phthalic ester was present during the catalyst synthesis, there appears an EPR signal at the free electron g-value. This signal was attributed to a Ti⁺³ phthalate species with resonance stabilization and spin delocalization; it is absent in the catalysts made in the presence of monoesters such as ethyl benzoate. The effects of monomer, O₂, H₂O, and I₂ on the EPR spectra were investigated. The changes in the EPR spectral intensity and the total Ti⁺³ ions, the latter determined by redox titrations during a polymerization or catalyst aging, are described. The results were extensively compared with those observed for supported Ziegler–Natta catalyst prepared with crystalline MgCl₂.     

Adsorption of TiCl4 and electron donor on defective MgCl2 surfaces and propylene polymerization over Ziegler-Natta catalyst: A DFT study

The formations of defective MgCl₂ surfaces, and subsequent adsorption of Ti species and electron donor, as well as propylene polymerization over the Ziegler-Natta catalyst have been investigated using density functional theory (DFT) method. Twelve possible support models of regular and defective MgCl₂ (110) and (100) surfaces were built. The individual adsorptions of titanium chlorides as mononuclear or dinuclear, and ethyl benzoate (EB) as electron donor, on these models were evaluated. The analysis of energies presented the cases of EB adsorption were generally more stable than titanium chlorides on both surfaces. Thus, EB as internal electron donor mainly prevented TiCl₄ from coordinating on the MgCl₂ surfaces where mostly non-stereospecific active sites could be formed. Exceptionally, A5 the site model with terminal Cl-vacancy on the MgCl₂ support, presented stronger adsorption of TiCl₄ than that of EB on (110) surface. Since the TiCl₄ and ethyl benzoate (EB) would compete to adsorb on the support surface, it seems reasonable to assume that TiCl₄ might predominately occupy this site, which can act as the most plausible active site for propylene polymerization. The first insertion of propylene monomer into the A5 active site model showed that it exhibited good regioselectivity but poor stereospecificity in the absence of electron donor.     

The activation of MgCl2-supported ziegler-natta catalysts: A structural investigation

A mathematical procedure for the investigation of the lattice disorder by stacking faults in polycrystalline solids has been used in studying samples of MgCl₂ activated by ball milling for various times in the presence of TiCl₄. These samples have been investigated by X-ray diffraction and by measurements of surface area, crystallite dimensions, Ti content after washing and catalytic activity in the polymerization of ethylene.A good relationship has been confirmed between activation time and activity; furthermore, the structural variations introduced by ball milling are mainly associated with rotational disorder of the Cl-Mg-Cl triple layers. Nevertheless, the analysis by X-ray diffraction is not unequivocal about the relationships between structure and activity: other significant parameters, such as the surface area and the porosity, are probably very important.     

Kinetics of polymerization of 1-octene with Mgcl2-supported Ticl4 catalysts

A number of TiCl₄ catalysts supported on MgCl₂ which was activated by the recrystallization method using different alcohols were prepared with ethyl benzoate or dibutyl phthalate as the internal electron donor. All the catalysts were characterized by BET, x-ray diffraction, and hydrolysis–GC analysis. Kinetics of polymerization of 1-octene was studied with three of the above catalysts (having different internal electron donors) activated by AlEt₃. The rate of polymerization increased linearly with increasing temperature, and catalyst and monomer concentrations. From the Arrhenius plot, the overall activation energies of polymerization were determined and the dependence of rate on the AlEt₃ concentration could be explained by the Langmuir-Hinshelwood mechanism. ¹³C-NMR was used to study the effect of internal electron donors on the % isotacticity of poly(1-octene). The catalytic activities of all the catalysts were compared in 1-octene polymerization. © 1994 John Wiley & Sons, Inc.     

Superactive and stereospecific catalysts. I. Structures and productivity

Two series of catalysts were made, one from MgCl₂–A solution containing MgCl₂, EH (2-ethylhexanol), and EB (ethyl benzoate) dissolved in decane and another from MgCl₂–B solution containing MgCl₂, EH, and phthalic anhydride which reacted to form the corresponding phthalic ester. Reactions of these solutions with TiCl₄ with or without another ester produced a family of eight catalysts. They form two groups, one having monoesters as modifiers, and the other containing diesters as modifiers. The surface area, pore volume, x-diffractions, polymerization activity, and catalytic stereospecificity of these catalysts have been compared. The diester catalysts differ from the monoester catalysts in every respect. By comparison the corresponding member of the diester catalysts have half as much Ti per Mg, more than 10 times the pore volume, more than a 100-fold the surface area, about 50% more productivity, and greatly increased steroespecificity.     

Stereoregularity and regioregularity of active centers in propene polymerization

The relation between stereoregularity of active centers on a MgCl₂/TiCl₄ catalyst and functions of inside donor (ID) and outside donor (OD) was investigated in the case of ethyl benzoate (EB)/methyl p-toluate (MPT) as an ID/OD pair. The results indicate that stereregularity depends merely on the amount of MPT supported on the catalyst. On the other hand, regioregularity of active centers was investigated with a MgCl₂/TiCl₄/dioctyl phthalate(DOP)-Et₃Al/diphenyldimethoxysilane(DPDMS) catalyst system. Regio-irregular inserted units were detected only in end groups of PP. It indicates that regio-irregular insertion leads to dormant centers with respect to propene insertion, though such centers are active for hydrogen transfer.     

Vapor synthesis of high-activity catalysts for olefin polymerization

Vaporization of MgCl₂ and other metal halides results in monomeric gas-phase species. Cocondensation of these species with organic diluents such as heptane yields highly activated solids which are precursors to MgCl₂ supported “high-mileage” catalysts for olefin polymerization. These catalysts, prepared by treatment with TiCl₄ followed by standard activation with aluminum alkyls display high activity for ethylene and propylene polymerization. MgCl₂ can also be evaporated into neat TiCl₄ to give a related catalyst. The concentration of MgCl₂ in the diluent affects catalyst properties as does the nature of the diluent. TiCl₃, 3TiCl₃ · AlCl₃, VCl₃ and other metal halides are subject to similar activation.     

Magnesium-chloride-supported high-mileage catalysts for olefin polymerization. III. Electron paramagnetic resonance studies

Electron paramagnetic resonance (EPR) was used to study a MgCl₂-supported, high-mileage olefin polymerization catalyst. Anhydrous Toho MgCl₂ was the starting material. Treatment with HCl at an elevated temperature, ethyl benzoate by ball-milling, p-cresol, AlEt₃, and TiCl₄produced a catalyst that contained a single EPR observable Ti⁺³ species A, which was strongly attached to the catalyst surface, had a D_3h symmetry, and no other Ti⁺³ ion in an immediately adjacent site. Species A constitutes only 20% of all the trivalent titaniums; the remainder is EPR-silent and may be attributed to those Ti⁺³ ions that have adjacent sites occupied by one or more Ti⁺³ ions. Activation with preformed AlEt₃/methyl-p-toluate complexes produced a single Ti⁺³ species (C) with rhombic symmetry and displaying ²⁷Al superhyperfin splitting which has attributes for a stereospecific active site. This species is unstable under polymerization conditions and is transformed to another species with axial symmetry and solubilization. Both processes could lead to catalyst deactivation and loss of stereospecificity. Catalysts activated by AlEt₃ and methyl-p-toluate separately in various sequential orders produced a multitude of EPR-observable Ti⁺³ species with varying degrees of motional freedom deemed detrimental to stereospecific polymerization of α-olefins.     

State of various stereoregulating electron-donating compounds in titanium-magnesium catalysts for propylene polymerization: A diffuse reflectance IR spectroscopic study

Propylene polymerization on TiCl₄/donor/MgCl₂ (donor = ethyl benzoate, dibutyl phthalate, diisobutyl phthalate, diethyl 2,3-diisopropylsuccinate) supported catalysts is considered. The states of the donors in the catalysts have been investigated by diffuse reflectance IR spectroscopy. Data characterizing the distribution of the donors and the active component (TiCl₄) on the support surface have been obtained. Molecular weight distribution data for polypropylene are presented. The molecular weight distribution of polypropylene depends on the location of the donor and TiCl₄ molecules.     

Effect of catalyst aging on catalyst activity and stereospecificity for MgCl2/ethyl benzoate or dioctyl phthalate/TiCl4-triethylaluminium for propene polymerization

The aging of the MgCl₂/dioctyl phthalate (DOP) or ethyl benzoate (EB)/TiCl₄ catalyst was studied. Because of the strong complexation of DOP with the catalyst, only a small fraction of DOP was extracted by cocatalyst triethylaluminium (TEA) during aging, resulting in converting some highly isospecific sites into aspecific ones. No change of the overall number of sites was detected. EB, on the other hand, could be readily removed by TEA, resulting in a large increase in aspecific sites. Clustering of those sites facilitated catalyst deactivation.     

Catalyseurs Ziegler-Natta supportés sur MgCl2 pour la polymérisation stéréorégulée du propène. III. Systèmes catalytiques à hautes performances comprenant un solide ternaire: MgCl2, ester aromatique,TiCl4

An examination of the precatalyst which contains three compounds (MgCl₂–TiCl₄-aromatic ester) uncovered numberous properties that apparently are common to all precatalysts and have already been observed in the simpler systems: a continous decrease in the polymerization rate during polymerization, characterized by a deactivation index that does not depend on the precatalyst but only on the cocatalyst; isotacTiClty control by the [AI]/[aromatic ester] ratio in the cocatalytic solution; and fast and reversible control of kinetics and tacTiClty by the same ratio. The precatalyst prepared by impregnation of the aromatic ester in MgCl₂ or MgCl₂–TiCl₄ presents moderate or no improvement when compared with the simpler MgCl₂–TiCl₄ catalysts. The yellow precatalyst prepared by milling MgCl₂ with the aromatic ester and impregnating with TiCl₄ are the only products that provide high activity and isotactic index above 95% simultaneously, as revealed by the patent literature. Interpretation of the role played by the electron donor, based on infrared studies, are proposed: in the precatalyst it controls fixation of TiCl₄ on MgCl₂; in the cocatalytic solution it regulates the isospecificity of the active site by contact with the alkylaluminium-aromatic ester complex and slows polymerization. Free electron donor gradually poisons the active centers.     

Probing the Coordinative Unsaturation and Local Environment of Ti3+ Sites in an Activated High‐Yield Ziegler–Natta Catalyst

The typical activation of a fourth generation Ziegler–Natta catalyst TiCl₄/MgCl₂/phthalate with triethyl aluminum generates Ti³⁺ centers that are investigated by multi‐frequency continuous wave and pulse EPR methods. Two families of isolated, molecule‐like Ti³⁺ species have been identified. A comparison of the experimentally derived g tensors and ^35,37Cl hyperfine and nuclear‐quadrupole tensors with DFT‐computed values suggests that the dominant EPR‐active Ti³⁺ species is located on MgCl₂(110) surfaces (or equivalent MgCl₂ terminations with tetra‐coordinated Mg). O₂ reactivity tests show that a fraction of these Ti sites is chemically accessible, an important result in view of the search for the true catalyst active site in olefin polymerization.     

Density Functional Calculations for Electronic and Steric Effects of Ethyl Benzoate on Various Ti Species in MgCl2-Supported Ziegler-Natta Catalysts

Possible coadsorption states of Ti mononuclear species and ethyl benzoate (EB) and their interaction on MgCl₂ (110) and (100) surfaces were investigated with periodic density functional calculations in order to obtain the microscopic understanding about how EB affects the steric and electronic natures of the Ti species. EB was unlikely to be attached to the TiCl₄ species on both the MgCl₂ (110) and (100) surfaces. The coadsorption of EB at Mg²⁺ ions near the Ti species was as favorable as the separate adsorption, which implied the random placement of these adsorbants in the final catalyst. The charge redistributions upon coadsorption among the Ti species, EB and the support were found to be dependent on the surface structures: the electron density of the Ti speceies was rather decreased by the coadsorption on the (100) surface, while that of the Ti species was enhanced due to the support-mediated electron transfer from EB on the (110) surface. It was suggested that the presence of EB close to the Ti species should generate donor-related active sites selectively on the (110) surface.     

Copolymerization of ethylene and 1-butene with highly active TI/MG bimetallic catalysts. Effect of partial activation by Alet2Cl

Copolymerization of ethylene and 1-butene were performed using the catalyst system TiCl₃ · 1/3 AlCl₃/MgCl₂/THF with or without partial activation by AlEt₂Cl. The catalyst and the copolymers were characterized by IR spectroscopy. The experimental results reveal that partial activation strongly affects the catalytic sensitivity toward 1-butene and obviously leads to a two-step polymerization rate profile.     

Ethylene/1-hexene copolymerization with TiCl4/MgCl2/AlCl3 catalyst in the presence of hydrogen

A TiCl₄/AlCl₃/MgCl₂ (Cat-B) catalyst containing 5.2 wt.% Al was prepared by the reaction of TiCl₄ with ethanol adduct of AlCl₃/MgCl₂ mixture. A TiCl₄/MgCl₂ catalyst (Cat-A) without doped AlCl₃ was also prepared by the same method. Ethylene-1-hexene copolymerization catalyzed by Cat-B in the presence of hydrogen showed slightly higher efficiency and higher 1-hexene incorporation than Cat-A. Comonomer incorporation was markedly increased when the cocatalyst AlEt₃ was replaced by Al(i-Bu)₃. Adding Ph₂Si(OMe)₂ as external donor in the catalyst system caused decrease in polymerization activity and 1-hexene incorporation. Each copolymer sample was fractionated into three fractions: n-heptane insoluble fraction (fraction A), n-heptane soluble and n-hexane insoluble fraction (fraction B) and n-hexane soluble fraction (fraction C). In most cases the amount of intermediate fraction (fraction B) was smaller than the other fractions and did not increase as the total 1-hexene content increase, indicating the presence of two classes of copolymer fractions with greatly different comonomer content and clear bimodality of the copolymer composition distribution. Doping AlCl₃ in the catalyst, changing cocatalyst and adding external donor mainly changed the weight ratio of fraction A to fraction C, but exerted little influences on their composition. According to the sequence distribution data of the fractions, doping AlCl₃ in the catalyst resulted in slight decrease of product of reactivity ratios (r₁r₂) in both fraction A and fraction C.     

球磨时间对浆态床CO甲烷化Ni-Al_2O_3催化剂性能的影响

结合行星式球磨机,采用低温固相法制备Ni-Al_2O_3催化剂,考察了球磨时间对Ni-Al_2O_3催化剂晶相结构(XRD)、还原特征(H2-TPR)、孔道结构(BET)、粒径分布(PSD)、表面形貌(SEM)和浆态床CO甲烷化性能的影响.结果表明,球磨时间为60 min,催化剂(CT-60)平均粒径最小,为141 nm;比表面积最大,为329 m2/g.随球磨时间延长,Ni-Al_2O_3催化剂的甲烷化性能(CO转化率、CH_4选择性和CH_4收率)均先增加后减少.其中,球磨时间为60 min制备的催化剂(CT-60)甲烷化性能最佳,其CO转化率、CH_4选择性和CH_4收率分别达87.9%、8 6.8%和74.3%.结合催化剂表征可知,CT-60优异的性能与其具有较小的颗粒尺寸(141 nm)和较大的比表面积(329 m2·g-1)有很大的关联.即,催化剂颗粒尺寸越小,比表面积越大,其性能越好.     

Fourier transform infrared spectra of three titanium tetrachloride-ethyl benzoate complexes. Assignment based on five isotopic homologues and extension of the ethyl benzoate force field

FTIR spectra (200–1750 cm⁻¹) are given for (TiCl₄EB)₂, (TiCl₄)₂EB and TiCl₄EB₂, where EB is ethyl benzoate. A full assignment is given for (TiCl₄EB)₂ based on extension of an ethyl benzoate force field and four isotopically labelled complexes with ¹⁸Ocarbonyl-EB, d₅-EB, Ed₅-B and d₅-Ed₅-B. There is no evidence for bidentate complexation or complexation through the ether oxygen in any of the complexes. A strong coupling between the αCO stretching vibration and the ethyl group deformations can make simplified interpretations of differences between spectra misleading.     

Ionization of MgCl2 during the formation of α-olefin polymeryzation catalyst

The examination of the reaction between [MgCl₂(THF)₂], TiCl₄₍₃₎, AlCl₃, AlEt₃, AlEt₂Cl and the synthesis and isolation of compounds as crystals and resolution of their structure by the X-ray method were the subject of our study. It was expected that these investigations would help to understand the behaviour of MgCl₂ towards the transition metal and furnish useful relationships to the structure of catalyst active center and to the polymerization mechanism in TiCl₄₍₃₎/MgCl₂/AlEt₃ system. Our studies have revealed that the main difference between the first and higher generations of Ziegler-Natta catalysts is only the number of active centers.