Progress in the catalyst for ethylene/α-olefin copolymerization at high temperature

Ethylene/α-olefin copolymers are one of the most widely-used polyolefin materials. With the continuous improvement of polyolefin catalysts, high-performance polyolefin materials were synthesized by adjusting the chain microstructure, changing the comonomer type and comonomer insertion amount, among which the ethylene/α-olefin random copolymer elastomer (POE) and olefin block copolymer elastomer (OBC) are the most famous and well accepted by the market. The excellent properties of POE and OBC first depend on their polymer chain microstructure. The chain microstructure of polyolefins is fundamentally determined by the catalysts, polymerization conditions, comonomer feed policies, and reaction engineering. High-performance ethylene/α-olefin copolymer elastomers are currently prepared by high-temperature solution polymerization process, which needs to be carried out at a temperature above the melting point of the polymer and is beneficial to speed up the polymerization reaction rate and control the polyolefin chain microstructure. However, the high-temperature solution polymerization process launched more stringent requirements for the olefin coordination polymerization catalyst. Systematic reports on catalysts for high-temperature solution copolymerization of ethylene and α-olefins are lacking. In this review, we screened some catalysts suitable for the controllable copolymerization and high-temperature solution copolymerization of ethylene/α-olefin based on the catalyst's heat resistance, copolymerization activity, comonomer insertion ability, molecular weight, and distribution of the copolymer, including traditional Z–N catalysts, metallocene catalysts, and post-metallocene catalysts. And the future development of catalysts for high-temperature solution copolymerization of olefins, catalysts for precise control of polyolefin chain microstructures, and catalysts for olefin copolymerization with polar monomers at high temperature are envisaged.     

Self-assembled heterogeneous late transition–metal catalysts for ethylene polymerization; New approach to simple preparation of iron and nickel complexes immobilized in clay mineral interlayer

To develop heterogeneous catalysts for ethylene polymerization, bis(imino)pyridineiron(III), α-diiminenickel(II), and iminopyridinenickel(II) complexes were immobilized in the clay mineral (montmorillonite, fluorotetrasilicic mica or saponite) interlayers by a one-pot preparation method. In this method, the Fe^3 +- and Ni^2 +-exchanged clay minerals as an acid catalyst promoted the ligand formation from a ketone derivative and an aniline derivative, and then the formed ligand simultaneously coordinated to the metal ions located in the clay mineral interlayer. The obtained heterogeneous catalysts showed 100–3,000 g-PE g-cat^− 1 h^− 1 as activities for the ethylene polymerization/oligomerization.     

Epoxidation of ethylene over AgNaCl catalysts

Epoxidation of ethylene over sodium chloride-doped and granular sodium chloride-supported silver catalysts was performed at atmospheric pressure using conventional flow reactors. Although the stationary activity was somewhat low, each type of catalyst has shown high selectivity, 84–87%, under an ethylene-rich atmosphere. The selectivity was almost independent of reaction temperature, contact time, and catalyst composition. The total reaction rate rose exponentially with temperature until an apparent activation energy of 75.3 kJ mol⁻¹ was obtained. Under oxygen-rich atmospheres, marked drops in activity were observed. In exposing the deactivated catalysts to a stream of hydrogen, carbon dioxide was desorbed. The strongly enhanced adsorption of carbon dioxide promoted the formation of silver chloride. Silver particles on the granular sodium chloride were homogeneously dispersed and ~200 nm in size. In addition, the crystallite size of silver was 43–50 nm, which was not altered after the reaction or even after heating at 673 K in oxygen gas. In a pulse reaction using an ethylene-rich gas mixture, acetaldehydes other than ethylene oxide were formed, and, as the catalyst surface had been oxidized by irreversible adsorption of oxygen, the formation of carbon dioxide was promoted and that of acetaldehyde decreased.     

Rheological,thermal and crystallisation properties of ethylene,propylene and α-olefin copolymers. I Rheological properties

Abstract

A series of random ethylene, propylene/1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene copolymers, ethylene and propylene homopolymers were prepared and investigated. The rheological properties (steady state and dynamic shear viscosity, creep compliance and plateau modulus), of copolymer samples with different co-unit content and molecular masses were determined and compared with the properties of homopolymers. The effects of the length of counit and the comonomer content were investigated. The copolymers exhibited similar rheological properties to the homopolymer but they have a lower shear viscosity, normal viscosity, higher steady state creep compliance and smaller plateau modulus values. The effect of comonomer content was evaluated on the bases of free volume theory.     

Triple crystallization behavior of fractionated ethylene/α-olefin copolymers of different catalyst type

Non-isothermal crystallization processes in fractions of Ziegler-Natta (ZN) and single site (SS) based ethylene/1-butene and ethylene/1-hexene copolymers have been studied by differential scanning calorimetry (DSC). Fractionation of used copolymers was done according to molar mass (MM) and composition (comonomer content). It was observed in DSC scans that for fractions with high MM (larger than 10 kg/mol) in addition to the main high-temperature crystallization peak (HTCP), a very-low temperature crystallization peak (VLTCP) is present at temperatures in between 60–75 °C. Such peak is absent for the first fractions having very-low MM. The partial crystallinity and peak temperatures, obtained from VLTCP, increase with MM and level off at MM around 60–100 kg/mol. It was found that the crystallinity as related to the area of the VLTCP is catalyst type dependent, and is higher for the SS catalyst compared to the ZN. Peak temperature of VLTCP linearly decreases with increasing comonomer content at fixed MM while the partial crystallinity practically does not change with comonomer content.     

Novel heterogeneous zinc triflate catalysts for the rearrangement of α-pinene oxide

New solid acid catalysts based on silica‐supported zinc triflate have been prepared for use in the rearrangement of α-pinene oxide to campholenic aldehyde. These catalysts exhibit considerable activity and can be recycled without loss of selectivity towards the aldehyde. The selectivity towards the aldehyde can be increased to 80% (at 50% conversion) when the reaction is performed at 25°C using hexagonal mesoporous silica (HMS₂₄) as the catalyst support. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sol–gel immobilized aryl iodides for the catalytic oxidative α-tosyloxylation of ketones

New hybrid silica materials M1–M4, derived from mono and bis-silylated aryl iodides, have been prepared via sol–gel processes, either by the hydrolytic polycondensation of a bis-silylated monomer or by the co-gelification of a monosilylated precursor with tetraethylorthosilicate. They have been fully characterized by elemental analysis, ¹³C and ²⁹Si CP-MAS solid state NMR, IR, TGA, and nitrogen-sorption measurements. These organosilicas have been successfully applied as supported catalysts in the α-tosyloxylation of aliphatic ketones in the presence of m-chloroperbenzoic acid (m-CPBA) as an oxidant, with the corresponding α-tosyloxyketones obtained in moderate to good isolated yields. The recyclability of the supported catalysts by a simple filtration has also been investigated.     

Evaluation of Fe- and Cr-containing clinoptilolite catalysts for the production of camphene from α-pinene

The catalytic properties of the Cr³⁺- and Fe³⁺-loaded clinoptilolites were screened in the liquid-phase isomerization of α-pinene and the major products were found to be camphene and limonene. Selectivity to camphene was superior for the 0.7Fe-CL catalyst than those observed for the Raw-CL and 0.4Cr-CL catalyst. Over raw clinoptilolite, the proportion of limonene and other isomers reached ～65% while it was ～15% with 0.7Fe-CL and ～56% with 0.4Cr-CL. The results also show that the selectivity to camphene increases with increasing reaction time reaching up to about ～72% at 428 K over 0.7Fe-CL catalyst.     

Hydrogenation of α-enaminoketones with cobalt phosphine-modified catalysts

The synthesis of α-enamines and hydrogenation of these compounds were studied using cobalt-modified complexes. Cobalt complexes were characterized by ¹H, ¹³C and ³¹P NMR, elemental analysis and IR spectroscopy. Furthermore, the molecular structures of complexes C1–C2 and C4–C5 have been determined by single-crystal X-ray diffraction. All cobalt complexes investigated were active catalysts for the hydrogenation reaction. The best catalytic activity was obtained with an ortho-substituent in the phosphine ligand. Noteworthy, the reduction was chemoselective over the double bond.     

Hydrogen effect on the molecular weight distribution of polymers obtained by polymerization of ethylene and α-olefins over supported titanium-magnesium catalysts

Comparative data on the molecular weight distribution of polymers obtained by polymerization of ethylene, propylene and 1-hexene, and copolymerization of ethylene with α-olefins over the titanium-magnesium catalysts (TMC) in the absence and presence of hydrogen are presented. In contrast to the ethylene polymerization, in the cases of propylene and 1-hexene polymerization and copolymerization of ethylene with α-olefins, the hydrogen addition is characterized by noticeable narrowing of the molecular weight distribution (MWD) due to lower contribution of the MWD component with high molecular weight. This result is an evidence of the increased reactivity of TMC active sites producing high molecular weight poly-α-olefins and copolymers of ethylene with α-olefins in the chain transfer reaction with hydrogen. It is suggested that the increased reactivity of these sites in the transfer reaction with hydrogen appears after the 2,1-addition of α-olefin to the growing polymer chain.     

Highly efficient supported AlCl3-based cationic catalysts to produce polyα-olefin oil base stocks

The main aim of this research is to decrease the amount of AlCl₃ content that is very corrosive and hazardous in the catalytic system, required for the α-olefin oligomerization without substantial change of final oil features. This was successfully achieved by supporting AlCl₃ on different carriers. More precisely, a series of supported bimetallic catalysts was synthesized by immobilization of AlCl₃ and TiCl₄ onto Al₂O₃, SiO₂, and mixed supports, that is, Al₂O₃/FeCl₃ and SiO₂/FeCl₃. It was found that silica and alumina-based catalysts had higher catalytic activities compared to support free AlCl₃; however, this enhancement for silica-based supports was more significant. According to gel permeation chromatography (GPC) results, the use of single supports, that is, Al₂O₃ and SiO₂, increased oligomer's molecular weight, while the application of mixed supports resulted in the decrease of molecular weight of the oligomers. Viscosity characteristics of the synthesized oligomers have also been studied at two different temperatures of 40 and 100°C (KV⁴⁰ and KV¹⁰⁰). The viscosity index (VI) values, derived from KV⁴⁰ and KV¹⁰⁰, of the prepared oligomers were in the range of 126–145. The molecular weight and termination mechanisms of the oligomers were studied by ¹H-NMR spectroscopy. The obtained results disclosed that the employed reaction conditions led to the production of oligomer chains with various structures including vinylidene (Vd), and di and three-substituted vinylene (2Vn, 3Vn) structures.     

Selective synthesis of α-olefins on Fe-Zn Fischer-Tropsch catalysts

Fe/Zn oxides promoted with K and Cu selectively produce -olefins at typical Fischer-Tropsch synthesis conditions (2/1 H₂/CO, 1 MPa, and 270°C). The simultaneous presence of K and Cu introduces a synergistic activity enhancement while maintaining the high olefin selectivity obtained by alkali promotion. Structural and morphological differences in Fe-Zn oxides prepared from ammonium glycolate complexes or precipitated from nitrate solutions have only a small influence on catalytic properties. Catalyst behavior is strongly influenced by synergistic promoter effects (Cu, K) and by the controlled in situ conversion of iron oxide precursors to carbides.     

Biphasic synthesis of α-Tetralone using nickel complex catalysts

Organic-water interfacial autoxidation of tetralin was investigated using surface-active ligand complexes of transition metals (Cr, Ni, Mn, and Co) as catalysts, tetralin as the substrate and organic phase, and dodecyl sodium sulfate as an emulsifier. The major products formed under the experimental conditions of 60°C and 1 atm were α-tetralone and α-tetralol, and the highest selectivity of 71 % to the desired product a-tetralone was achieved with nickel-tetraethylenepentamine complex. The optimum ligand to catalyst ratio was established to be 2:1 for the improved reaction rate and phase separation. The organic-water phase volume ratio around which the maximum reaction rate was attained was 2:1. The reaction order with respect to oxygen shifted from first to zero as its partial pressure increased, and the reaction order with respect to nickel catalyst concentration varied from 1.7 to 1, and subsequently to with further increases in the metal concentration.     

Novel rhenium‐based catalysts for dehydrocondensation of methane with CO/CO2 towards ethylene and benzene

A new family of rhenium‐based catalysts bearing HZSM‐5 zeolite exhibits remarkable performances for the catalytic dehydrocondensation of methane with CO/CO₂ towards ethylene, benzene, and naphthalene in high selectivity of above 90% at 1–3 atm and 973–1023 K. In contrast to Mo/HZSM‐5 catalysts, the EXAFS and TG/DTA/Mass studies reveal that the metallic Re on HZSM‐5 zeolite is a catalytically active and stable phase for the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Copolymerization of ethylene with α-olefins over supported titanium–magnesium catalysts. II. Comonomer as a chain transfer agent

The data on the effect of comonomer (propylene and 1-hexene) on molecular weight (M_w), molecular weight distribution (MWD), and content of terminal double bonds were obtained for ethylene/α-olefin copolymers produced over a supported titanium–magnesium catalyst (TMC) upon polymerization in the absence of hydrogen. The experimental data on the effect of comonomer concentration on M_w of polymers were used to calculate the ratios between the effective rate constants of chain transfer with monomer and the propagation rate constant. It was shown that the effective rate constant of chain transfer with monomers increases in the row of monomers: ethylene < 1-hexene < propylene. Meanwhile, the data on the effect of copolymers on content of terminal double bonds of various types demonstrate that different reactions of chain transfer with comonomer may simultaneously occur during copolymerization. It results in simultaneous formation of terminal vinylidene and trans-vinylene bonds. Therefore, the calculated rate constants of chain transfer with comonomer are complex values, which include the rate constants of chain transfer with comonomer occurring via different mechanisms. The data on MWD, short chain branching (SCB) and terminal double bonds content of different types were obtained by molecular weight fractionation of copolymers followed by the analysis of narrow fractions. The analysis of the data on MWDs of SCB and terminal double bonds shows that active sites of the TMC are considerably heterogeneous with respect to the rates of different chain transfer reactions with monomers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

SO4–ZrO2 catalysts for the esterification of benzoic acid to methylbenzoate

SO₄–ZrO₂ catalysts, prepared by varying the conditions of oxide preparation and H₂SO₄ impregnation, have been characterized by means of different techniques (XRD, BET, Hammett–Bertolacini technique, XPS). The esterification of benzoic acid to methylbenzoate has been used to test the different catalysts and their catalytic performance has been discussed in the light of their bulk and surface properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of Pd loading and precursor on the catalytic performance of Pd/WO3–ZrO2 catalysts for selective oxidation of ethylene

The structure and properties of Pd/WO₃–ZrO₂ (W/Zr = 0.2) catalysts with different Pd loadings and precursors were investigated. The results indicate that Pd/WO₃–ZrO₂ prepared from a PdCl₂ precursor was optimum for high activity and selectivity. Moreover, ethylene conversion increased with the Pd loading. The structure and nature of the catalysts were characterized using X-ray diffraction, BET N₂ adsorption, H₂ temperature-programmed reduction and H₂ pulse adsorption techniques. The results reveal that the higher catalytic performance of Pd/WO₃–ZrO₂ prepared from PdCl₂ could be related to the formation of polytungstate species and the existence of well-dispersed Pd particles.     

Performance and mechanism of the separation of C8 α-olefin from F-T synthesis products using novel Ag-DES

As an attractive alternative technology for the separation of long chain olefin and paraffin, a novel silver-based deep eutectic solvent (Ag-DES) was prepared and utilized for 1-octene/n-octane separations. Comprehensive reactive extraction separation experiments were performed to highlight the Ag-DES concentration and operating temperature discriminations using compounds with different ratio of 1-octene/n-octane. The novel Ag-DES showed optimal separation performance regarding 1-octene/n-octane and possessed the highest levels separation selectivity in the range 3.57–16.11 with excellent circulation stability in our best knowledge. Furthermore, FT-Raman measurements and quantum chemistry calculation were performed to elucidate the interaction mechanism of Ag-DES in the separation of 1-octene and n-octane, which revealed that both chemical complexation and strong physical attraction existed in the complex of Ag-DES and 1-octene rather than n-octane. A practical process was proposed for the separation of olefin and paraffin, which indicates that an advanced separation technology could largely reduce the energy consumption. This study lends important insight for the development of Ag-DES reactive extraction separation process for the energy-efficient long chain α-olefins purification from F-T synthesis products.