Preparation and characterization of spherical PP/PB alloys with MgCl2-supported Ziegler-Natta catalyst

Polypropylene（PP）/polybutene-1（PB） alloys within reactor were prepared by MgCl₂-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology.First,propylene homo-polymerizations were carried out to form isotactic polypropylene（iPP） particles containing active catalyst.Then,butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles.Finally,iPP/PB alloys with spherical shape and adjustable PB content were synthesized.The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed.The composition and physical properties of the PP alloys were characterized by FT-IR,¹³C-NMR,SEM,DSC and XRD.It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly（butene-co -propylene） random copolymers and poly（butene-block-propylene） block copolymers.SEM measurements verified that the PB phases with size in the range of 300-400 nm dispersed in the PP matrix uniformly.The incorporation of PB upon the PP matrix affects the properties of final products greatly.     

Preparation of polypropylene/clay nanocomposites by <Emphasis Type="Italic">in situ</Emphasis> polymerization with TiCl<Subscript>4</Subscript>/MgCl<Subscript>2</Subscript>/clay compound catalyst

TiCl₄/MgCl₂/clay compound catalyst was prepared by chemical reaction.Exfoliated polypropylene（PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst.Effects of polymerization temperature,polymerization time,propylene pressure,solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied.Under optimal conditions,activity of the nano-compound catalyst is about 88.3 kg/（mol Ti·h）.Isotacticity of PP obtained in the nanocomposites is in the range of 89%-99%,and its melting temperature is about 159℃.The weight-average molecular weight of PP can reach 6.7×10⁵ - 7.8×10⁵,and the molecular weight distribution is between 7.7 and 7.9.     

STUDIES ON THE KINETICS OF PROPYLENE POLYMERIZATION WITH THE COMPLEXTYPE TiCl_3 CATALYST

The active center concentration C_p, the rate constant k_p, and the activation energy of chain propagation E_p in the polymerization of propylene with complex-type TiCl_3-(C_2H_5)_2AlCl catalyst system were studied. The Mn was corrected by (?) value determined by GPC. The values thus obtained for C_p, k_p, and E_p at 50℃were 3.01 mol/mol Ti, 6.27 1/mol·sec, and 5.10 Kcal/mol respectively.The kinetic parameters were compared with those obtained from conventional TiCl_3·AlCl_2 catalyst, showing that the higher activity of the complex-type catalyst over the conventional catalyst is not only due to the higher C_p of the former, but to a greater extent due to the increase of the k_p value.     

Photopolymerization of Cyclohexene Oxide Initiated with Iron-arene Complex

Two iron-arene complex photoinitiators with different substituents in arene ligands were synthesized, their activities in initiating photopolymerization of cyclohexene oxide (CHO) were compared with that of IRGACURE 261, a commercialized photoinitiator from Ciba-Geigy. A higher activity was found when the arene ligand was substituted with a stronger electron donating group. For the system initiated by IRGACURE 261 the concentration of active centers in CHO polymerization was determined and it was found that the concentration is maximum at around 35℃. The post (dark) polymerization was significant, the polymerization yield decreased with the increase of irradiation temperature and increased with the increase of post polymerization temperature. The results are interpreted based on the mechanism proposed by Lohse, et al..     

Exploring Si/Mg composite supported Ziegler-Natta Ti-based catalysts for propylene polymerization

A series of(Si_O2/MgO/ID/MgCl_2)·TiClx Ziegler-Natta catalysts for propylene polymerization has been prepared with a new method. These catalysts were synthesized using soluble Mg-compounds as the Mg-source and the preparation progress was relatively simple. The catalyst could copy the spherical shape of the carrier very well. The propylene polymerization results showed that the catalyst revealed the best activity with 9,9-di(methoxymethyl)fluorene(BMMF) as internal donor at 50 °C with the optimal molar ratio Al/Ti = 5, which was much lower than what the industrial polypropylene catalyst used(at least molar ratio Al/Ti = 100), resulting in great cost saving. Additionally, the polymerization kinetics of the catalyst exhibited very stable property after achieving a relatively high value. These catalysts possessed rather high activity and good hydrogen response. The isotactic index(Ⅱ.) value of the PP products could be higher than 98% in the presence of both internal and external electron donors. Moreover, temperature rising elution fractionation method was used to understand the influence of donors and H2 on the properties of the PP products.     

Effects of pretreatment and reduction on the Co/Al2O3 catalyst for CO hydrogenation

The purpose of this study was to investigate the effect of preadsorbed CO at different temperatures, calcination temperatures, the combined influence of reduction temperature and time, and pretreatment using hydrogen or syngas as reduction agents on the F-T synthesis （FTS） activity and selectivity of Co/Al2O3 catalyst. The reactivity of the carbon species at higher preadsorption temperature with H2 in TPSR decreased, whereas the carbon-containing species showed higher reactivity over Co/Al2O3 catalyst with low calcination temperature. This agreed well with the order of catalytic activity for F-T synthesis on this catalyst. The catalytic activity of the catalyst varied with reduction temperature and time remarkably. CODEX optimization gave an optimum reduction temperature of 756 K and reduction time of 6.2 h and estimated C5＋ yield perfectly. The pretreatment of Co/Al2O3 catalyst with different reduction agents （hydrogen or syngas） showed important influences on the catalytic performance. A high CO conversion and C5＋ yield were obtained on the catalyst reduced by hydrogen, whereas methane selectivity on the catalyst reduced by syngas was much higher than that on the catalyst reduced by hydrogen.     

The Influence of Bridge Type on the Activity of Supported Metallocene Catalysts in Ethylene Polymerization简

Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride(Et(Ind)2 ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride(Me2 Si(Ind)2 ZrCl2) preactivated with methylaluminoxane(MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2 Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2 Si(Ind)2 ZrCl2 /MAO and Et(Ind)2 ZrCl2 /MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE.     

Propylene Polymerization Catalyzed by Bis(R_3-indenyl) Zirconium Dichloride/Aluminoxane──Synthesis of Metallocenes and Influence ofSolvent Polarity on Polymerization

Three unbridged metallocenes, bis(2,4,7-Me3-indenyl)zirconium dichloride(1) , bis(2-Me-4, 7-Et2-indenyl)zirconium dichloride (2) and bis (2, 4, 6-Me3-indenyl) zirconium dichloride (3) were synthesized. The effect of solvent polarity on propylene polymerization catalyzed by the metallocenes in the presence of methylaluminoxane(MAO) and triisobutylaluminum(TIBA) was investigated in the toluene/CH2Cl2 mixed solvent. Changing the solvent polarity was found to influence the catalytic activity, polymer molecular weight and stereospecificity of the catalysts. The changes in the position of the substituents on the ligand caused the different responses of the catalyst to the changes in solvent polarity. The isotactic stereosequence of polypropylene was found to increase with the increase in the polarity of the reaction medium.     

Regioselectivity Study on Propylene Polymerization Catalyzed by Neutral Salicyladiminato Pd（Ⅱ） Model Complex with DFT Method

Many attempts have been made to control the regioselectivity for olefin polymerization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacing a nitrogen atom in the Pd(Ⅱ) diimine catalyst with an oxygen atom from density functional theory method at the B3LYP/LANL2DZ level. The results show that the 1,2-insertion becomes a rival mechanism to the 2,1-insertion when the nitrogen atom is replaced by the oxygen atom leading to an asymmetric environment in the catalyst, and that the steric effect in the asymmetrical catalyst plays an important part in the polymerization. The insertion barrier from 2-O is much higher than that from 2-N. A pyramid transition state was characterized for the catalyst to convert 2-O back to 2-N through internal rotation. The propylene prefers to coordinate at the opposite side of O in the catalyst. This is the driving force for the internal rotation.The results are significant for isotactic and syndiotactic polymerization.     

Effects of Citric Acid Concentration and Activation Temperature on the Synthesis of Carbon Nanotubes

A series of Ni-La-Mg catalyst samples were prepared by citric acid complex method, and carbonnanotubes were synthesized by catalytic decomposition of CH4 on these catalysts. The effects of the citricacid concentration and the activation temperature on catalytic activity were investigated by CO adsorption,TEM and XRD techniques. The experimental results showed that the particle size of the catalysts preparedthrough gel auto-combustion varied with the concentration of citric acid. Therefore carbon nanotubes with different diameters were obtained correspondingly. The effect of activation temperature on the activity of catalyst was negligible from 500 to 700℃, but it became pronounced at lower or higher temperatures.     

Plasma Treatment of Ni Catalyst for Partial Oxidation of Methane

The 10%Ni/Al2O3 catalyst for partial oxidation of methane was treated by DBD (dielectric barrier discharge) plasma in a continuous system under atmospheric pressure and room temperature by flowing He. It was found that 10%Ni/Al2O3 catalyst treated by plasma presents a higher catalytic activity and an enhanced stability than the catalysts prepared without plasma treatment. The methane conversion over the catalyst treated by plasma is 3%-5% higher than the catalysts untreated by plasma. Moreover,the enhanced dispersion of the catalyst can be achieved by plasma treatment, which can improve the interaction between active species and supports, catalytic activity and the resistance to carbon deposition.     

STUDIES ON TiCI4/Mg (OEt)_2/EB SUPPORTED CATALYSTS FOR PROPYLENE POLYMERIZATION

The supported catalysts for propylene polymerization were prepared by milling Mg (OEt)_2 with EB (ethylbenzoate) and treating with TiCl_4 solution. When TiCl_4/(Mg(OEt)_2/EB) (mol.) ratio was increased, decrease in contents of-OEt and Ti of the catalysts was observed, while the content of EB increased. It is proved by analyses of IR, X-ray and XPS that during co-milling Mg(OEt)_2 with EB no reactions have taken place. But after treatment with TiCl_4 solution, Mg(OEt)_2 converts into MgCl_2 and EB coordinates on the resulting MgCl_2 carrier, a surface complex forms.The activity of catalysts,isotacticity and vicosimetric molecular weight of polypropylene increase with the decrease of the content of ethoxyl group. The kinetic curves of propene polymerization obtained with present catalysts system display decay curves. It is found from the triad tacticity calculated from the expanded spectra of methyl carbon region that, ethoxyl group in catalyst has an effect on the configuration of polymer chain.     

茂－茚锆金属络合物催化乙烯/1－己烯共聚和丙稀均聚研究

Complexes （R^1Cp）（R^2Ind）ZrCl2, the catalysts previously reported active for ethylene polymerization showed high activity in ethylene/1-hexene copolymerization and propylene polymerization in the presence of MAO. The content of 1-hexene in copolymers ranged from 1.2% to 3.2%. In propylene polymerization the complex 1 showed the highest activity, up to 1.2×10^6 g of polypropylene per mol of catalyst per hour. Based on the analysis of NMR spectral data, the relationships between complex structures and polymerization results were explored.     

Organocatalytic stereoselective cationic polymerization of vinyl ethers by employing a confined BrΦnsted acid as the catalyst

The properties of poly(vinyl ether)s(PVEs)are highly dependent on their tacticity,and the appealing thermoplastics features of isotactic PVEs have drawn considerable efforts to develop stereoselective cationic polymerization methods to access this class of polymers.However,reported methods that could achieve a high degree of tacticity control are limited to process employing metal-based Lewis acids,and with various limitations on catalyst loading,monomer scope,etc.Here,we introduce a metal-free stereoselective cationic polymerization of vinyl ethers by employing a class of chiral confined Br?nsted acids,imidodiphosphorimidates(IDPis),as the catalyst.This organocatalytic approach features its metal-free conditions,high efficiency,high stereoselectivity,single catalyst system,operation simplicity,etc.     

Recyclable Fenton-like catalyst based on zeolite Y supported ultrafine,highly-dispersed Fe2O3 nanoparticles for removal of organics under mild conditions

The active Fenton-like catalyst, obtained by highly dispersed Fe₂O₃ nanoparticles in size of 5 nm on the surface of zeolite Y, shows the excellent degradation efficiency to phenol higher than 90% under the mild conditions of room temperature and neutral solution, and the catalyst can be easily recovered with stable catalytic activity for 8 cycles.     

HIGHLY ACTIVE CATALYTIC STEREOSPECIFIC POLYMERIZATION OF STYRENE

A novel highly active catalyst of TiCl_4/MgCl_2--Al(C_2H_5), system (called SN-1 catalyst, in whichrare earth compound NdCl_3, is included) was used for studying stereospecific polymerization of styrenein benzene solution. Highly isotactic polystyrene was prepared with far better yield and higher cataly-tic efficiency than the results ever reported in literatures. The influences of concentration of mono-mer, catalyst, triethyaluminum as well as polymerization temperature on the catalytic efficiency, yield,tacticity and molecular weight of polystytene have been investigated.     

PREPARATION OF ULTRAFINE PARTICLE IRON-CARBONIDE CATALYST AND CHARACTERIZATION OF ITS CATALYTICAL BEHAVIOR

Studies on ultrafine particle catalyst have attracted many researchers' attention by its large surfacearea,higher activity and selectivity.Based on the mechanism of α-Fe and Fe_xC_y as the catalyticalactive species this paper reports for the first time the preparation method of Fe_3C ultrafine parti-cle catalyst,from highly dispersed amorphous Fe powder and free carbon.The Fe powder and free car-bon,prepared by laser pyrolysis technique,was then treated by washing and heating at high tempera-ture protected with N_2.The catalyst prepared under different experimental conditions wascharacterazed by means of XRD,electronic diffraction and TEM.It shows that the crystlline grain sizeis in a range of 1-4nm and composed of Fe_3C and α-Fe.It has been found that the ultrafine particleiron-carbonide catalyst exhibited much higher activity and selectivity to light olefins.At the standardatmosphere and 380℃ reaction temperature,the conversion of CO reached a maximum of 80%.     

混合外给电子体环己基甲基二甲氧基硅烷/二苯基二氯硅烷对丙烯聚合的影响

The effect CMMS (cyclohexylmethyl dimethoxysilane/DPCS (diphenyl dichloridesilane) as electron donor on the polymerization of propene was discussed. The solvent polymerization of propene was carried out in 60 ℃ at 1. 04×10⁵ Pa. It was found that the catalyst activity has gone up by 20 per cent when CMMS/DPCS=1/3 under the given condition . The concentration of active titanium center (C) was determined with kinetic-molecular weight method. It turns out that the active titanium centers do not increase by using mixedelectron donor CMMS/DPCS as compare with CMMS as electron donor but can increase Kp by 20% In addition,average-chain length can be achieved in five minutes with CMMS/DPCS.So polymer isotacticity index does not change with the time of polymerization.     

Effects of Temperature and Catalyst to Oil Weight Ratio on the Catalytic Conversion of Heavy Oil to Propylene Using ZSM-5 and USY Catalysts

It is useful for practical operation to study the rules of production of propylene by the catalytic conversion of heavy oil in FCC (fluid catalytic cracking). The effects of temperature and C/O ratio (catalyst to oil weight ratio) on the distribution of the product and the yield of propylene were investigated on a micro reactor unit with two model catalysts, namely ZSM-5/Al2O3 and USY/Al2O3, and Fushun vacuum gas oil (VGO) was used as the feedstock. The conversion of heavy oil over ZSM-5 catalyst can be comparable to that of USY catalyst at high temperature and high C/O ratio. The rate of conversion of heavy oil using the ZSM-5 equilibrium catalyst is lower compared with the USY equilibrium catalyst under the general FCC conditions and this can be attributed to the poor steam ability of the ZSM-5 equilibrium catalyst. The difference in pore topologies of USY and ZSM-5 is the reason why the principal products for the above two catalysts is different, namely gasoline and liquid petroleum gas (LPG), repspectively. So the LPG selectivity, especially the propylene selectivity, may decline if USY is added into the FCC catalyst for maximizing the production of propylene. Increasing the C/O ratio is the most economical method for the increase of LPG yield than the increase of the temperature of the two model catalysts, because the loss of light oil is less in the former case. There is an inverse correlation between HTC (hydrogen transfer coefficient) and the yield of propylene, and restricting the hydrogen transfer reaction is the more important measure in increasing the yield of propylene of the ZSM-5 catalyst. The ethylene yield of ZSM-5/Al2O3 is higher, but the gaseous side products with low value are not enhanced when ZSM-5 catalyst is used. Moreover, for LPG and the end products, dry gas and coke, their ranges of reaction conditions to which their yields are dependent are different, and that of end products is more severe than that of LPG. So it is clear that maximizing LPG and propylene and restricting dry gas and coke can be both achieved via increasing the severity of reaction conditions among the range of reaction conditions which LPG yield is sensitive to.     

THE BEHAVIOR OF HOMOGENEOUS IRON-BASED CATALYSTS BEARING PYRIDINE DIIMINE LIGANDS FOR ETHYLENE POLYMERIZATION*

The polymerization of ethylene by two iron-based catalysts, {[2,6-ArN=C(Me)_2C_5H_3N]FeCl_2} (Ar=2,6-C_6H_3-Me_21; 2,6-C_6Hv3 (i-Pr)v2 Ⅱ) has been investigated. Catalyst Ⅱ produces higher molecular weight polyethylene (PE) and broadenedpolydispersities relative to catalyst Ⅰ under analogous conditions and all polymers are linear. The kinetic profiles with ironcatalysts showed a smooth pattern during both rate build-up and rate lowering, which are different from the metallocenecatalysts. The polymerization activity increases with Al/Fe value and an optimum temperature range at 40～45℃ was observed. The molecular weight of PE decreases with the increase of Al/Fe ratio and rise of polymerization temperature.