Modification of the(SiO_2/MgO/MgCl_2)·TiCl_x Ziegler-Natta Polyethylene Catalysts Using the Third Metal Elements

Various(SiO_2/MgO/MgCl_2)·Ti Clx Ziegler-Natta catalysts modified by the third metal elements were synthesized by the co-impregnation of water-soluble magnesium and the third metal salts. Several key factors including the electronegativity of the third metal elements, catalyst performances in ethylene homo-polymerization, ethylene/1-hexene copolymerization and hydrogen response were systematically investigated. Both the catalyst performance and the polymer properties are influenced by the introduction of the third metal elements. Compared with the unmodified(SiO_2/MgO/MgCl_2)·Ti Clx Ziegler-Natta catalyst, activity and 1-hexene incorporation are enhanced by the introduction of zirconium, vanadium, aluminum and chromium, while deteriorated by the addition of ferrum, nickel, molybdenum and tungsten. Correlations of the catalyst activities and 1-hexene incorporation ability with the electronegativity of the third metal elements are discovered. It is found that the lower electronegativity of the third metal elements leads to the catalyst with higher activity and higher α-olefin co-polymerization ability. The polyethylene produced by a nickel modified catalyst showed broad molecular weight distribution(MWD) and the lowest average molecular weight(MW), while by using a ferrum modified catalyst, the resulting polyethylene had the highest MW, reaching the ultra-high MW area. Vanadium and chromium modified catalysts demonstrated the best hydrogen response.     

EFFECTS OF EXTERNAL DONOR ON ACTIVE CENTER DISTRIBUTION OF SUPPORTED ZIEGLER-NATTA CATALYST

The composition distribution (CD) and microisotacticity distribution (ID) of propene/1-hexene copolymer synthesized by MgCl_2/DIBP/TiCl_4 (DIBP: diisobutyl phthalate) weredetermined by fractionating the copolymers according to crystallinity and characterizingthe fractions by ~(13)CNMR. The effects of two alkoxysilane donors, triethoxyphenylsilane(PTES) and dimethoxydi-tert-butylsilane (TBMS), on CD and ID of the copolymrs werecompared. Three main parts in the CD diagram of each copolymer were distinguished,which were correlated to active center distribution (ACD) based on three groupe of dif-ferent active centers. By studying the changes in 1-hexene content, microisotacticity andreactivity ratio product of three typical fractions, the effects of external donor on ACDwere better elucidated. It was found that TBMS shows much stronger effects on ACD thanPTES. In the former system, most fractions were produced on active centers with relativelylower r_1r_2, higher reactivity to 1-hexene, and higher stereospecificity as compared to thesystem without external donor. It is concluded that the observed very extensive changesin ACD are mainly resulted by the formation of new types of active centers, possibly bycoordination of external donor to certain positions on the catalyst.     

METATHESIS OF 1-HEXENE OVER MOLYBDENUM AND TUNGSTEN CATALYSTS IMMOBILIZED ON POLYMERS

Molybdenum and tungsten components in catalysts Bu_4N〔Mo(CO)_5Cl〕-EtAlCl_2andWCl_6-Bu_4Sn were immobilized respectively on polymers.The influence of immobilization ofthe soluble catalysts on their catalytic behavior in the metathesis of 1—hexene was investi-gated.It has been found that polystyrene is a good supporting material among all thepolymers tested.The immobilized catalysts have higher stability and better selectivity incomparison with their homogeneous equivalents.The metathesis yield of 1-hexene is in-creased by fourfold with WCl_6immobilized on polystyrene.The reason for the increase ofstability of the immobilized catalyst is discussed.     

Copolymerization of ethylene and 1-hexene with TiCl4/MgCl2 catalysts modified by 2,6-diisopropylphenol

A supported TiCl4/MgCl2 catalyst without internal electron donor (O-cat) was prepared firstly. Then it was modified by 2,6-diisopropylphenol to make a novel modified catalyst (M-cat). These two catalysts were used to catalyze ethylene/1-hexene copolymerization and 1-hexene homopolymerization. The influence of cocatalyst and hydrogen on the catalytic behavior of these two catalysts was investigated. In ethylene/1-hexene copolymerization, the introduction of 2,6-iPr2C6H3O-groups did not deactivate the supported TiCl4/MgCl2 catalyst. Although the 1-hexene incorporation in ethylene/1-hexene copolymer prepared by M-cat was lower than that prepared by O-cat, the composition distribution of the former was narrower than that of the latter. Methylaluminoxane (MAO) was a more effective activator for M-cat than triisobutyl-aluminium (TIBA). MAO led to higher yield and more uniform chain structure. In 1-hexene homopolymerization, the presence of 2,6-iPr2C6H3O-groups lowered the propagation rate constants. Two types of active centers with a chemically bonded 2,6-iPr2C6H3O-group were proposed to explain the observed phenomena in M-cat.     

Ti-Si composite oxide-supported cobalt catalysts for CO2 hydrogenation

In the present work, different silica-based supported cobalt (Co) catalysts were synthesized and used for CO2 hydrogenation for methanation. Different supports, such as SSP, MCM-41, TiSSP and TiMCM were used to prepare Co catalysts with 20 wt% Co loading. The supports and catalysts were characterized by means of N2 physisorption, XRD, SEM/EDX, XPS, TPR and CO chemisorption. It is found that after calcination of catalysts, Ti is present in the form of anatase. The introduction of Ti plays important roles in the properties of Co catalysts by:(i) facilitating the reduction of Co oxides species which are strongly interacted with support, (ii) preventing the formation of silicate compounds, and (iii) inhibiting the RWGS reaction. Based on CO2 hydrogenation, the CoTiMCM catalyst exhibites the highest activity and stability.     

Carbon layer-coated ordered mesoporous silica supported Co-based catalysts for higher alcohol synthesis: The role of carbon source

Surface chemical properties of supports have an important influence on active sites and their catalytic behavio r.Here,we fabricated a series of cobalt-based catalysts supported by carbon layer-coated ordered mesoporous silica(OMS) composites for higher alcohol synthesis(HAS).The carbon layers were derived from different sources and uniformly coated on the porous surface of OMS.Combined with the characterization results of carbonized catalysts,it is demonstrated that the carbon layer-coated supports significantly enhanced the metal dispersion and increased the ratio of Co2+ to Co0 sites,which further increased the CO conversion and alcohols selectivity.Moreover,it is found that the catalytic activity changed in line with the amount of defects and surface oxygenic groups of carbon layers,which re sulted from the different carbon sources.The highest space time yield of C2+OH was 27.5 mmol gcat-1h-1)obtained by the catalyst coated with glucose-derived carbon layer.But the carbon source is not the key factor influencing the distribution of Co-Co2+ dual sites and shows little effect on selectivity in HAS.These results may guide for further design of carbon supported catalysts.     

DEPENDENCE OF THE DISTRIBUTION OF ACTIVE CENTERS ON MONOMER IN SUPPORTED ZIEGLER-NATTA CATALYSTS

Distribution of active centers(ACD)of ethylene or 1-hexene homopolymerization and ethylene-1-hexene copolymerization with a MgCl_2/TiCl_4 type Z-N catalyst were studied by deconvolution of the polymer molecular weight distribution into multiple Flory components.Each Flory component is thought to be formed by a certain type of active center. ACD of ethylene-1-hexene copolymer with very low 1-hexene incorporation was compared with that of ethylene homopolymer to see the effect of introducingα-olefin on eth...     

Excellent complete conversion activity for methane and CO of Pd/TiOz-Zro.sA10.5O1.75 catalyst used in lean-bum natural gas vehicles

Palladium catalysts are supported on TiO2, ZrO2, A12O3, Zro.sAlo.501.75 and TiO2-Zro.sAlo.501.75 prepared by co-precipitation method, re- spectively. Catalytic activities for methane and CO oxidation are evaluated in a gas mixture that simulated the exhaust from lean-burn natural gas vehicles （NGVs）. Pd/TiO2-Zro.sAlo.501.75 performs the best catalytic activity among the tested five catalysts. For CH4, the light-off temperature （Tso） is 254 ℃, and the complete conversion temperature （Tgo） is 280 ℃; for CO, Tso is 84 ℃, and Tgo was 96 ℃. Various techniques, including N2 adsorption-desorption, X-ray diffraction （XRD）, H2-temperature-programmed reduction （H2-TPR）, X-ray photoelec- tron spectroscopy （XPS）, and scanning electron microscopy （SEM） are employed to characterize the effect of supports on the physicochemical properties of prepared catalysts. N2 adsorption-desorption and SEM show that TiO2-Zro.5Al0.501.75 expresses uniform nano-particles and large meso-pore diameters of 26 nm. H2-TPR and XRD indicate that PdO is well dispersed on the supports and strongly interacted with each other. The results of XPS show that the electron density around PdO and the proportion of active oxygen on TiO2-Zro.sAl0.501.75 are maxima among the five supports.     

Excellent complete conversion activity for methane and CO of Pd/TiO_2-Zr_(0.5)Al_(0.5)O_(1.75) catalyst used in lean-burn natural gas vehicles

Palladium catalysts are supported on TiO2, ZrO2, Al2O3, Zr0.5Al0.5O1.75 and TiO2-Zr0.5Al0.5O1.75 prepared by co-precipitation method, respectively. Catalytic activities for methane and CO oxidation are evaluated in a gas mixture that simulated the exhaust from lean-burn natural gas vehicles(NGVs). Pd/TiO2-Zr0.5Al0.5O1.75 performs the best catalytic activity among the tested five catalysts. For CH4, the light-off temperature(T50) is 254℃, and the complete conversion temperature(T90) is 280℃; for CO, T50 is 84℃, and T90 was 96℃. Various techniques, including N2adsorption-desorption, X-ray diffraction(XRD), H2-temperature-programmed reduction(H2-TPR), X-ray photoelectron spectroscopy(XPS), and scanning electron microscopy(SEM) are employed to characterize the effect of supports on the physicochemical properties of prepared catalysts. N2adsorption-desorption and SEM show that TiO2-Zr0.5Al0.5O1.75 expresses uniform nano-particles and large meso-pore diameters of 26 nm. H2-TPR and XRD indicate that PdO is well dispersed on the supports and strongly interacted with each other. The results of XPS show that the electron density around PdO and the proportion of active oxygen on TiO2-Zr0.5Al0.5O1.75 are maxima among the five supports.     

Microstructure characterization of short-chain branching polyethylene with differential scanning calorimetry and successive selfnucleation/annealing thermal fractionation

A series of the copolymers of ethylene with 1-hexene(M1–M9) synthesized by metallocene catalyst Et[Ind]2ZrCl2/MAO was studied by differential scanning calorimetry and successive self-nucleation and annealing(SSA) thermal fractionation. The distribution of methylene sequence length(MSL) in the different copolymers was determined using the SSA method. The comonomer contents of samples M4 and M5 are 2.04 mol% and 2.78 mol%, respectively. Both M4 and M5 have low comonomer content and their MSL distribution profiles exhibit a monotonous increase trend with their MSL. The longest MSL of M5 is 167, and its corresponding molar percent is 43.95%, which is higher than that of M4. Moreover, the melting temperature(Tm) of M5 is also higher than that of M4. The comonomer contents of samples M7, M8, and M9 are 8.73 mol%, 14.18 mol% and 15.05 mol%, respectively. M7, M8, and M9 have high comonomer contents, and their MSL distribution profiles display unimodality. M7 has a lower peak value of 33 and a narrow MSL distribution, resulting in a Tm lower than that of M8 and M9. The MSL and its distribution are also key points that influence the melting behavior of copolymers. Sometimes, MSL and its distribution of copolymers have a greater impact on it than the total comonomer contents, which is different from traditional views.     

CO吸附原位红外光谱结合分子模拟计算研究FCC汽油加氢脱硫催化剂的选择性

以脱硫选择性不同的2组催化裂化汽油加氢脱硫催化剂为研究对象, 采用CO吸附原位红外光谱表征了2组催化剂的活性相特征, 并通过分子模拟计算方法比较了助剂Co加入前后噻吩和1-己烯在催化剂表面的电荷分布、吸附能及其加氢反应的活化能等, 探讨了助剂Co的加入对选择性加氢脱硫催化剂脱硫选择性的作用机理. 结果表明, 加氢脱硫催化剂CoMoS活性相的增加有利于提高催化剂的加氢脱硫/加氢降烯烃(HDS/HYD)选择性. 与1-己烯加氢位相比, Co的加入显著提高了噻吩分子加氢位的缺电子性, 噻吩在催化剂表面的吸附度增强, 显著降低噻吩加氢反应的能垒, 从而使噻吩加氢反应更易进行. 这也表明CoMoS为高HDS活性、高HDS/HYD选择性的活性相.     

Preparation of rhodium–phyllosilicate catalysts without leaching in liquid-phase 1-hexene hydrogenation

Rhodium catalysts have been prepared on palygorskite and montmorillonite (clay) supports by reduction with hydrogen (1 atmosphere) at room temperature of a cationic organometallic rhodium compound anchored to the support. The activity of these catalysts for the hydrogenation of liquid-phase 1-hexene remains constant with increase of prehydrogenation time and with re-use for several runs. No rhodium leaching is observed.     

羟基磷灰石负载HRh(CO)(TPPTS)3催化1-己烯氢甲酰化反应高选择性和特殊的异构化功能

采用浸渍法制备了以羟基磷灰石(HAP)载型水溶性铑络合物HRh(CO)(TPPTS)3/HAP催化剂(TPPTS=三苯基膦三间磺酸钠), 采用傅里叶变换红外光谱(FTIR)、 固体核磁共振波谱(31P CP-MAS NMR)、 扫描电子显微镜(SEM)、 电感耦合等离子发射光谱(ICP-OES)和比表面积测定(BET)等对催化剂进行了表征. 该催化剂在催化1-己烯氢甲酰化反应中表现出高活性和高选择性, 在优化条件下获得了100%的醛选择性和高转化频率(TOF=2465 h-1). 该催化剂还对1-己烯、 2-己烯和3-己烯表现出特殊的异构化功能. 该催化剂制备方法简单, 通过简单离心分离可以循环使用. 对HAP负载HRh(CO)(TPPTS)3的原理以及催化剂对烯烃异构化的机理进行了探讨.     

New processes for the selective production of 1-octene

Linear α-olefins, especially 1-hexene and 1-octene, are key components for the production of LLDPE and the demand for 1-hexene and 1-octene increased enormously in recent years. To meet this demand several processes were developed in the last decade to produce 1-hexene and 1-octene selectively. Here we review the new processes for 1-octene production based on homogeneous catalysts.Sasol's coal-based high temperature Fischer–Tropsch technology produces an Anderson–Schulz–Flory distribution of hydrocarbons with high α-olefin content and the desired alkenes, including 1-heptene and 1-octene, are separated by distillation. In this case, as in the SHOP process, 1-octene constitutes only a minor part of the total yield.Nowadays other technologies are being applied or considered for on-purpose 1-octene production: hydroformylation of 1-heptene, the telomerization of 1,3-butadiene, and ethene tetramerization.1-Heptene can be converted in three steps to 1-octene: (1) hydroformylation of 1-heptene to octanal, (2) hydrogenation of octanal to 1-octanol, and (3) dehydration of 1-octanol to 1-octene. This process was commercialized by Sasol.Dow commercialized a process based on butadiene. Telomerization of butadiene with methanol in the presence of a palladium catalyst yields 1-methoxy-2,7-octadiene, which is fully hydrogenated to 1-methoxyoctane in the next step. Subsequent cracking of 1-methoxyoctane gives 1-octene and methanol for recycle. Recently highly active and stable phosphine based systems were reported that show particularly good performance for the industrially attractive feedstock, the C₄ cut of the paraffin cracker.1-Hexene can be obtained by ethene trimerization by a family of catalysts based mainly on Cr. High selectivity to 1-hexene can be achieved thanks the propensity of the chromium based catalyst to form 7-membered ring metallacycles. Sasol has found catalyst systems that allow the formation of a 9-membered metallacycle in large proportion relative to 7-membered ring formation, yielding 1-octene.     

Ethylene/1-Hexene Copolymerization with Modified Ziegler-Natta Catalyst

Siloxane compounds were treated with the compounds containing internal donors, such as aromatic ester, phosphate, or 1,3-diether compounds, and the resulting intermediates were further reacted with TiCl₄ to form the modified Ziegler-Natta catalysts for ethylene/1-hexene(E-H) copolymerization. Using the modified Ziegler-Natta catalysts, the effect of the internal donors and the molar ratio of alcohol to magnesium on the catalyst performance was investigated by the orthogonal experiments. The synthetic method of the catalysts was also optimized by choosing the proper way to mix the internal donors. The branch degree, sequence structure, molecular weight, and molecular weight distribution of the copolymer products were determined by Fourier transform infrared spectroscopy(FTIR), carbon-13 nuclear magnetic resonance(¹³C NMR) spectrometry and gel permeation chromatography(GPC). Under the optimum conditions, the catalytic system with tetraethyl orthosilicate and 2,2-dimethoxypropane as the internal donors exhibited the best performance with an activity of 926.74 g copolymer/(g Cat·h^-1). The branch degree, 1-hexene content, and molecular weight distribution of the resulting copolymers reached up to 40 branches/1000C, 5.99% and 5.8, respectively.     

Studies of Intermolecular Heterogeneity Distribution in Ethylene/1-hexene Copolymers Using DSC Method

The investigation of the intermolecular composition distribution of an ethylene/1-hexene copolymers using DSC method has been carried out. The known methods: step crystallization (SC) and successive self-nucleation/annealing (SSA) have been adapted for this purpose, and particularly, the optimal condition of the process have been chosen to enable the best fractional crystallization of the copolymer. The method has been applied for fractionation of two ethylene/1-hexenecopolymers synthesized with supported vanadium and zirconocene catalysts and having similar concentrations of 1-hexene. Although metallocene catalysts are known from their more homogeneous structure of active sites in comparison to multi-site Ziegler–Natta catalysts, the copolymers obtained over both catalytic systems gave DSC curves resolved into several peaks but with different melting points. Using the Thomson–Gibbs equation, comparable average lamellar thickness of the separated peaks has been calculated. The amounts of copolymer fraction with defined lamellar thickness have been determined. It was obtained that the copolymer produced from the metallocene system contains a thinner and more homogeneous lamella thickness than that obtained with Ziegler–Natta vanadium catalyst supported on the same carrier. This revised version was published online in August 2006 with corrections to the Cover Date.