The effects of poisoning materials on catalytic activity and isospecificity of the supported Ziegler-Natta catalyst were investigated.A minor amount of simple structure of Lewis base,i.e.,methanol,acetone,ethyl acetat...The effects of poisoning materials on catalytic activity and isospecificity of the supported Ziegler-Natta catalyst were investigated.A minor amount of simple structure of Lewis base,i.e.,methanol,acetone,ethyl acetate,was introduced into the catalyst slurry for partial poisoning catalytic active centers.It was found that the variations in deactivation power were in the order of methanol>acetone>ethyl acetate.The kinetic investigation via stopped-flow polymerization showed that poisoning compounds cau...展开更多
A comprehensive mechanism for propylene polymerization was proposed by considering the effects of main impurities in the material on propylene polymerization. According to the proposed mechanism, Monte Carlo simulatio...A comprehensive mechanism for propylene polymerization was proposed by considering the effects of main impurities in the material on propylene polymerization. According to the proposed mechanism, Monte Carlo simulation was employed to investigate the polymerization kinetics in order to determine the effects of the main impurities on the polymerization. Significant influences of the main impurities on the rate, number-average degree and controlling capability of hydrogen of the polymerization were analyzed.展开更多
The estimation of the amount of reactive impurities in a loop reactor is of strategic importance to the propylene polymerization industry. It is essential to investigate the level of impurities in order to develop rel...The estimation of the amount of reactive impurities in a loop reactor is of strategic importance to the propylene polymerization industry. It is essential to investigate the level of impurities in order to develop reliable monitoring and control strategies. This paper described one approach based on generation function technique with the following two steps. First, a new mechanism for propylene polymerization was proposed by considering the effects of the reactive impurities in the material on the propylene polymerization. Second, a series of equations of population balance for the propylene polymerization in loop reactors were established based on the proposed mechanism. Accordingly, the equations were transformed into the mathematic matrix through the generation function technique to investigate the effects of the reactive impurities on the propylene polymerization. Significant effects of the reactive impurities were analyzed through computational simulation. The results show that the concentration of active centre on catalysts and the polymerization conversion both decrease with the increase of the initial concentration of any reactive impurity; hydrogen concentration decreases with the increase of the initial concentration of ethylene or butylenes, whereas, it increases with the increase of the initial concentration of propadiene; the simulated weight average molecular weight and the molecular weight distribution index of polymer resins both increase with the increase of the initial concentration of ethylene or butylenes. They decrease with the increase of the initial concentration of propadiene.展开更多
A two-phase dynamic model,describing gas phase propylene polymerization in a fluidized bed reactor,was used to explore the dynamic behavior and process control of the polypropylene production rate and reactor temperat...A two-phase dynamic model,describing gas phase propylene polymerization in a fluidized bed reactor,was used to explore the dynamic behavior and process control of the polypropylene production rate and reactor temperature.The open loop analysis revealed the nonlinear behavior of the polypropylene fluidized bed reactor,justifying the use of an advanced control algorithm for efficient control of the process variables.In this case,a centralized model predictive control(MPC) technique was implemented to control the polypropylene production rate and reactor temperature by manipulating the catalyst feed rate and cooling water flow rate respectively.The corresponding MPC controller was able to track changes in the setpoint smoothly for the reactor temperature and production rate while the setpoint tracking of the conventional proportional-integral(PI) controller was oscillatory with overshoots and obvious interaction between the reactor temperature and production rate loops.The MPC was able to produce controller moves which not only were well within the specified input constraints for both control variables,but also non-aggressive and sufficiently smooth for practical implementations.Furthermore,the closed loop dynamic simulations indicated that the speed of rejecting the process disturbances for the MPC controller were also acceptable for both controlled variables.展开更多
A novel mathematical model for single particle slurry propylene polymerization using heterogeneous Ziegler-Natta catalysts has been developed to describe the kinetic behavior,the molecular weight distribution,the mono...A novel mathematical model for single particle slurry propylene polymerization using heterogeneous Ziegler-Natta catalysts has been developed to describe the kinetic behavior,the molecular weight distribution,the monomer concentration,the degree of polymerization,the polydispersity index(PDI),etc.This model provides a more valid mathematical description by accounting for the monomer diffusion phenomena at two levels as multi- grain model counts,and obtains results that are more applicable to the conditions existing in most polymerizations of industrial interest.Considering that some models on the mesoscale phenomena are so complex that some existing modeling aspects have to be simplified or even neglected to make the model convenient for use in interesting engi- neering studies,it is very important to put some effort into determining what sort of numerical analysis works best for these problems.For this reason,special attention is paid to these studies to explore an efficient algorithm using adaptive grid-point spacing in a finite-difference technique to figure out more practical mass transport models and convection-diffusion models efficiently.The reasonable outcomes,as well as the significant computation time sav- ing,have been achieved,thereby displaying the advantage of this calculation method.展开更多
A series of electron donors,including 1,1-cyclopentanecarboxylic acid diethyl ester (CPCADEE),1,1cyclopentanedimethanol acetic diester (CPDMAD),1,1-biethoxymethyl pentane (BEMP),2,2-diethyl diethylmalonate (DEDEM)and ...A series of electron donors,including 1,1-cyclopentanecarboxylic acid diethyl ester (CPCADEE),1,1cyclopentanedimethanol acetic diester (CPDMAD),1,1-biethoxymethyl pentane (BEMP),2,2-diethyl diethylmalonate (DEDEM)and 2,2-diethyl-1,3-propanediol acetic diester (DEPDADE),were synthesized by diethyl malonate (DEM).The purities and structures of the above products were characterized by gas chromatography (GC) and gas chromatography-mass spectrometer (GC-MS),respectively.Furthermore,the possible optimal three-dimensional structures of these donors were simulated by means of Gaussian 03 and Chem 3D.Then these electron donors were coordinated with tetrachloro titanium (TiCl 4) and chloride magnesium (MgCl 2)to obtain the catalysts for the polymerization of propylene.The catalytic activities and properties of polypropylene are greatly improved by adding external donor(ED) when CPCADEE or DEPDADE is used as internal donor(ID).However,when BEMP was used as ID,the highest catalytic activity is obtained without adding ED,which can reduce production costs and simplify catalytic synthesis.The experiments indicate that BEMP has the shortest distance of oxygen atoms and the highest electronegativity.展开更多
This article presents a detailed structural study of a new spherical Mg Cl2-supported Ti Cl4 Ziegler-Natta catalyst for isotactic propylene polymerization, and researches on the relationship between catalyst structure...This article presents a detailed structural study of a new spherical Mg Cl2-supported Ti Cl4 Ziegler-Natta catalyst for isotactic propylene polymerization, and researches on the relationship between catalyst structure and polymer properties. The spherical support with the chemical composition of CH3CH2 OMg OCH(CH2Cl)2 has been synthesized from a new dispersion system and is used as the supporting material to prepare Ziegler-Natta catalyst. The XRD analysis indicates that the catalyst is fully activated with δ-Mg Cl2 in the active catalyst. The far-IR spectrometric results confirm again the presence of δ-Mg Cl2 in the active catalyst. Textural property of the active catalyst exhibits high surface area coupled with high porosity. The high activity in propylene polymerization is mainly ascribed to the full activation and the porous structure of the catalyst. Scanning electron microscopy/energy dispersive spectrometer mapping results indicate a uniform titanium distribution throughout the catalyst particles. Particle size analysis shows that the catalyst has a narrow particle size distribution. The perfect spherical shape, uniform titanium distribution and narrow particle size distribution of the catalyst confirm the advantage of polymer particles production with less fines. The solid state 13 C NMR and mid-IR spectroscopic analyses indicate that there exists strong complexation between diisobutyl phthalate and Mg Cl2, which leads to the high isotacticity of polypropylene.展开更多
Two unbridged metallocene catalysts, bis(2,4,7-trimethylindenyl)zirconium dichloride (met-I) and bis(2,4,6-trimethylindenyl)zirconium dichloride (met-II), which are different in the position of substituents on the six...Two unbridged metallocene catalysts, bis(2,4,7-trimethylindenyl)zirconium dichloride (met-I) and bis(2,4,6-trimethylindenyl)zirconium dichloride (met-II), which are different in the position of substituents on the six-membered ring of the indenyl ligands were synthesized. The effect of substituents in the two metallocenes on the propylene polymerization was studied in the presence of methylaluminoxane (MAO) and triisobutylaluminium (TIBA). From the analysis of microstructure determined by C-13-NMR, it was demonstrated that the polymers produced by met-II have higher [mmmm] isotactic sequences than that of met-I. Using a mechanism based on model statistical analysis, it was found that chain-end model was dominant for met-I. However, met-II obeys the concurrent two-sites model during polymerization, which can be attributed to the existence of 'racemic-like' conformer in its system.展开更多
A novel highly active C-s-symmetric metallocene catalyst namely: meso-dimethylsilylbis (2,4,6-trimethyl-1 -indenyl)zirconium dichloride is presented. The effect of polymerization temperature (0-70 degrees C) on the ca...A novel highly active C-s-symmetric metallocene catalyst namely: meso-dimethylsilylbis (2,4,6-trimethyl-1 -indenyl)zirconium dichloride is presented. The effect of polymerization temperature (0-70 degrees C) on the catalyst performance for propylene polymerization has been investigated. This catalyst shows very high activity at 50 degrees C which is higher than the activity of the racemic analogue, and the resulted polypropylene is amorphous in nature with isotactic pentad content [mmmm] of 12 %.展开更多
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 s...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.展开更多
Many attempts have been made to control the regioselectivity for olefin poly- merization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacin...Many attempts have been made to control the regioselectivity for olefin poly- merization 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.展开更多
The effects of adding Al(i-C_4H_9)_3 (TBA) to rac-Me2Si(Ind)2ZrCl2/ MAO catalyzed propylene-1-octene copolymerization were studied. At TBA /MAO (Al/AI mole ratio) of about 0.6, the polymerization activity was found to...The effects of adding Al(i-C_4H_9)_3 (TBA) to rac-Me2Si(Ind)2ZrCl2/ MAO catalyzed propylene-1-octene copolymerization were studied. At TBA /MAO (Al/AI mole ratio) of about 0.6, the polymerization activity was found to be much higher than the system without TBA. Increases of polymer molecular weight and 1-octene content from addition of TBA were also observed.展开更多
In the preparation of catalyst for propylene polymerization, the Mg(OEt) 2 support was activated with ethanol/CO 2 system followed by solidification, and treated with TiCl 4 in the presence of ethylbenzoate as an inte...In the preparation of catalyst for propylene polymerization, the Mg(OEt) 2 support was activated with ethanol/CO 2 system followed by solidification, and treated with TiCl 4 in the presence of ethylbenzoate as an internal donor(ID). The chemical compositions of the activated support and the prepared catalyst were examined in detail. During the dissolution of Mg(OEt) 2 support in ethanol medium with CO 2 bubbling, the structure of support changed to magnesium hydrocarbyl carbonate, (CH 3CH 2O) 2- x Mg(O (C O) OCH 2CH 3) x ( x = 1,2). The content of carbonated CO 2 in the activated support was dependent on the heat treatment in the solidification of support. In the preparation procedure of polymerization catalyst, the activated support was treated with TiCl 4 so that the structure of support was converted to MgCl 2 with the incorporation of ID. The polymerization behavior of the pre-pared catalyst was also studied in the presence of phenyltriethoxysilane as an external donor.展开更多
The bond breaking and forming in chemical reactions is a typical rare event,which is one of the difficult problems in molecular dynamics simulations.Numerous enhanced sampling methods have been developed to extend the...The bond breaking and forming in chemical reactions is a typical rare event,which is one of the difficult problems in molecular dynamics simulations.Numerous enhanced sampling methods have been developed to extend the time scale covered by molecular simulations.However,the difficulties of obtaining appropriate collective variables from complicated reaction pathways and a controlled sampling over the desired phase space remain as challenges.Herein,we use MetaITS,which combines metadynamics and integrated tempered sampling,to increase the sampling efficiency for chemical reactions.Metadynamics with collective variables obtained by harmonic linear discriminant analysis can efficiently decrease the main energy barrier of chemical reaction.Meanwhile,integrated tempered sampling can enhance the exploration of other degrees of freedom.In this study,we applied the MetaITS method to two transition-metal-catalyzed organic reactions with complicated reaction coordinates.We simulated here a zirconocene-catalyzed propylene polymerization to investigate the regioselectivity and temperature effects.We also studied a Sharpless epoxidation reaction,for which both chiral products are observed through simulation.展开更多
Transformation of living ring-opening metathesis polymerization into coordination polymerization by converting the titanacyclobutane group attached to a polynorbornene chain into titanocene alkoxide has been used for ...Transformation of living ring-opening metathesis polymerization into coordination polymerization by converting the titanacyclobutane group attached to a polynorbornene chain into titanocene alkoxide has been used for the synthesis of polynorbornene-poly(ethylene-co-propylene) block copolymer. Preliminary characterizations of the copolymerization products by solvent extraction and C-13 NMR spectrum are reported.展开更多
Ansa-Cyclohexyl-bis(4,5,6,7-tertrahydro-l-indenyl) zirconium dichloride (5) was used as catalyst for propylene and ethylene polymerization together with methyl aluminoxane (MAO) as the cocatalyst. Isotactic poly...Ansa-Cyclohexyl-bis(4,5,6,7-tertrahydro-l-indenyl) zirconium dichloride (5) was used as catalyst for propylene and ethylene polymerization together with methyl aluminoxane (MAO) as the cocatalyst. Isotactic polypropylene (PP) was obtained with the highest activity of 6.37× 107g PP (molZr)^-1h^-1. The mesomeso (mmmmm) pentads sequence content of PP was determined by 13C NMR spectroscopy. The dependence of the microstructure on the reaction temperature and the AI/Zr molar ratio was examined and the catalytic activity of complex 5 was compared with that of the similar ansa-zirconocene 3. The high activity of the new zirconocene 5 for propylene isospectic polymerization at high temperature (60℃) is the result of its unique bridged-group structure. Complex 5/MAO displays also high catalytic activity of 0.46× 10^6 to 9.87× 10^6g PE(molZr)^-h^-in the homo-polymerization of ethylene, The visometric molecular weight of PE ranges from 0.97×10^4 to 11.16×10^4 g.mol^- under the given conditions.^13C NMR spectroscopy analysis proves the PE to be linear polyethylene (LPE).展开更多
A L463^5 Box-Behnken design was used for developing a model to predict and optimize the molecular weight (Mw ) of polypropylene (PP) ; a second-order polynomial regression equation was derived to predict responses...A L463^5 Box-Behnken design was used for developing a model to predict and optimize the molecular weight (Mw ) of polypropylene (PP) ; a second-order polynomial regression equation was derived to predict responses. The significance of variables and their interactions were tested by means of the ANOVA with 95% confidence limits; the standardized effects were investigated by Pareto chart, the optimum values of the selected variables were obtained by analyzing the response surface contour plots. The optimized Mw value of 1. 217 × 10^5 g/mol was very close to the industrial value ( ( 1.22 ±0. 004) ×10^6 g/tool) at the optimum values.展开更多
A series of C1-symmetric ethylene-bridged ansa-(3-R-cyclopentadienyl)(fluorenyl) metallocene complexes(Zr: 1-5;Hf: 6) have been synthesized, characterized and investigated as catalyst precursors for the high temperatu...A series of C1-symmetric ethylene-bridged ansa-(3-R-cyclopentadienyl)(fluorenyl) metallocene complexes(Zr: 1-5;Hf: 6) have been synthesized, characterized and investigated as catalyst precursors for the high temperature ethylene polymerization. Using methylaluminoxane(MAO) as the cocatalyst, zirconium complexes 1-5 bearing a bulky substituent on the 3-position of the cyclopendienyl ring showed high catalytic activities up to 1.48×10^(7) g PE·mol_(Zr)^(-1)·h^(-1) toward the polymerization of ethylene and afforded polyethylenes with high molecular weights(1.49×10^(5)-6.31×10^(5) g/mol), meanwhile exhibting great thermal stability at high temperatures up to 120 ℃ together with a long catalytic life time up to 2 h. By adopting low Al/Zr ratios, such as 125, polyethylenes with ultra high molecular weights up to 2.86×106 g/mol were obtained. It is worthy of noting that zirconium complexes 1-4 bearing a substituent with an aryl pendant showed temperature-dependent activities, which increased rapidly with the increase of polymerization temperature, thus weak interaction of the pendent aryl group with the cationic active center is proposed to account for the very low activities displayed at low temperatures. In contrast to zirconocene complexes 1-5, hafnocene complex 6 only displayed very low catalytic activities toward the polymerization of ethylene and afforded polyethylenes with molecular weights ten times smaller than those obtained by zirconocene complexes 1-5. Zirconocene complexes 1-5 were also able to catalyse the polymerization of propylene at high temperatures, but only afforded waxes with low molecular weights.展开更多
基金The authors gratefully acknowledge the Thailand Research Fund(TRF)Royal Golden Jubilee program for the financial support.
文摘The effects of poisoning materials on catalytic activity and isospecificity of the supported Ziegler-Natta catalyst were investigated.A minor amount of simple structure of Lewis base,i.e.,methanol,acetone,ethyl acetate,was introduced into the catalyst slurry for partial poisoning catalytic active centers.It was found that the variations in deactivation power were in the order of methanol>acetone>ethyl acetate.The kinetic investigation via stopped-flow polymerization showed that poisoning compounds cau...
基金Supported by the National Natural Science Foundation of China (No.20406016) and Fujian Petrochemical Company ofSINOPEC (No. MS/FJ-08-JS-15-2005-01).
文摘A comprehensive mechanism for propylene polymerization was proposed by considering the effects of main impurities in the material on propylene polymerization. According to the proposed mechanism, Monte Carlo simulation was employed to investigate the polymerization kinetics in order to determine the effects of the main impurities on the polymerization. Significant influences of the main impurities on the rate, number-average degree and controlling capability of hydrogen of the polymerization were analyzed.
基金This work was financially supported by the National Natural Science Foundation of China (No. 20406016)Fujian Petrochemical Company of SINOPEC (No. MS/FJ-08-JS-15-2005-01)
文摘The estimation of the amount of reactive impurities in a loop reactor is of strategic importance to the propylene polymerization industry. It is essential to investigate the level of impurities in order to develop reliable monitoring and control strategies. This paper described one approach based on generation function technique with the following two steps. First, a new mechanism for propylene polymerization was proposed by considering the effects of the reactive impurities in the material on the propylene polymerization. Second, a series of equations of population balance for the propylene polymerization in loop reactors were established based on the proposed mechanism. Accordingly, the equations were transformed into the mathematic matrix through the generation function technique to investigate the effects of the reactive impurities on the propylene polymerization. Significant effects of the reactive impurities were analyzed through computational simulation. The results show that the concentration of active centre on catalysts and the polymerization conversion both decrease with the increase of the initial concentration of any reactive impurity; hydrogen concentration decreases with the increase of the initial concentration of ethylene or butylenes, whereas, it increases with the increase of the initial concentration of propadiene; the simulated weight average molecular weight and the molecular weight distribution index of polymer resins both increase with the increase of the initial concentration of ethylene or butylenes. They decrease with the increase of the initial concentration of propadiene.
基金Supported by the Research Grants of the Research Council of Malaya
文摘A two-phase dynamic model,describing gas phase propylene polymerization in a fluidized bed reactor,was used to explore the dynamic behavior and process control of the polypropylene production rate and reactor temperature.The open loop analysis revealed the nonlinear behavior of the polypropylene fluidized bed reactor,justifying the use of an advanced control algorithm for efficient control of the process variables.In this case,a centralized model predictive control(MPC) technique was implemented to control the polypropylene production rate and reactor temperature by manipulating the catalyst feed rate and cooling water flow rate respectively.The corresponding MPC controller was able to track changes in the setpoint smoothly for the reactor temperature and production rate while the setpoint tracking of the conventional proportional-integral(PI) controller was oscillatory with overshoots and obvious interaction between the reactor temperature and production rate loops.The MPC was able to produce controller moves which not only were well within the specified input constraints for both control variables,but also non-aggressive and sufficiently smooth for practical implementations.Furthermore,the closed loop dynamic simulations indicated that the speed of rejecting the process disturbances for the MPC controller were also acceptable for both controlled variables.
基金Supported by the National High Technology Development Program of China (No.2006AA05Z226), Natural Science Foundation of Zhejiang Province (No.Y105370), National HI-TECH Industrialization Program of China (No.2004-2080), and Science Fund for Distinguished Young Scholars of Zhejiang University (No. 111000-581645).
文摘A novel mathematical model for single particle slurry propylene polymerization using heterogeneous Ziegler-Natta catalysts has been developed to describe the kinetic behavior,the molecular weight distribution,the monomer concentration,the degree of polymerization,the polydispersity index(PDI),etc.This model provides a more valid mathematical description by accounting for the monomer diffusion phenomena at two levels as multi- grain model counts,and obtains results that are more applicable to the conditions existing in most polymerizations of industrial interest.Considering that some models on the mesoscale phenomena are so complex that some existing modeling aspects have to be simplified or even neglected to make the model convenient for use in interesting engi- neering studies,it is very important to put some effort into determining what sort of numerical analysis works best for these problems.For this reason,special attention is paid to these studies to explore an efficient algorithm using adaptive grid-point spacing in a finite-difference technique to figure out more practical mass transport models and convection-diffusion models efficiently.The reasonable outcomes,as well as the significant computation time sav- ing,have been achieved,thereby displaying the advantage of this calculation method.
基金Supported by National Natural Science Foundation of China (No. 20476080)Tianjin Natural Science Foundation (No. 07JCYBJC00600)
文摘A series of electron donors,including 1,1-cyclopentanecarboxylic acid diethyl ester (CPCADEE),1,1cyclopentanedimethanol acetic diester (CPDMAD),1,1-biethoxymethyl pentane (BEMP),2,2-diethyl diethylmalonate (DEDEM)and 2,2-diethyl-1,3-propanediol acetic diester (DEPDADE),were synthesized by diethyl malonate (DEM).The purities and structures of the above products were characterized by gas chromatography (GC) and gas chromatography-mass spectrometer (GC-MS),respectively.Furthermore,the possible optimal three-dimensional structures of these donors were simulated by means of Gaussian 03 and Chem 3D.Then these electron donors were coordinated with tetrachloro titanium (TiCl 4) and chloride magnesium (MgCl 2)to obtain the catalysts for the polymerization of propylene.The catalytic activities and properties of polypropylene are greatly improved by adding external donor(ED) when CPCADEE or DEPDADE is used as internal donor(ID).However,when BEMP was used as ID,the highest catalytic activity is obtained without adding ED,which can reduce production costs and simplify catalytic synthesis.The experiments indicate that BEMP has the shortest distance of oxygen atoms and the highest electronegativity.
基金the Sinopec Beijing Research Institute of Chemical Industry for its financial support (No. 5-12ZS0419, 5-10ZS0245, 5-12ZS0270)
文摘This article presents a detailed structural study of a new spherical Mg Cl2-supported Ti Cl4 Ziegler-Natta catalyst for isotactic propylene polymerization, and researches on the relationship between catalyst structure and polymer properties. The spherical support with the chemical composition of CH3CH2 OMg OCH(CH2Cl)2 has been synthesized from a new dispersion system and is used as the supporting material to prepare Ziegler-Natta catalyst. The XRD analysis indicates that the catalyst is fully activated with δ-Mg Cl2 in the active catalyst. The far-IR spectrometric results confirm again the presence of δ-Mg Cl2 in the active catalyst. Textural property of the active catalyst exhibits high surface area coupled with high porosity. The high activity in propylene polymerization is mainly ascribed to the full activation and the porous structure of the catalyst. Scanning electron microscopy/energy dispersive spectrometer mapping results indicate a uniform titanium distribution throughout the catalyst particles. Particle size analysis shows that the catalyst has a narrow particle size distribution. The perfect spherical shape, uniform titanium distribution and narrow particle size distribution of the catalyst confirm the advantage of polymer particles production with less fines. The solid state 13 C NMR and mid-IR spectroscopic analyses indicate that there exists strong complexation between diisobutyl phthalate and Mg Cl2, which leads to the high isotacticity of polypropylene.
基金This project was supported by the National Natural Science Foundation of China and the Petrochemical Incorporation of China (Grant number: 29734144).
文摘Two unbridged metallocene catalysts, bis(2,4,7-trimethylindenyl)zirconium dichloride (met-I) and bis(2,4,6-trimethylindenyl)zirconium dichloride (met-II), which are different in the position of substituents on the six-membered ring of the indenyl ligands were synthesized. The effect of substituents in the two metallocenes on the propylene polymerization was studied in the presence of methylaluminoxane (MAO) and triisobutylaluminium (TIBA). From the analysis of microstructure determined by C-13-NMR, it was demonstrated that the polymers produced by met-II have higher [mmmm] isotactic sequences than that of met-I. Using a mechanism based on model statistical analysis, it was found that chain-end model was dominant for met-I. However, met-II obeys the concurrent two-sites model during polymerization, which can be attributed to the existence of 'racemic-like' conformer in its system.
文摘A novel highly active C-s-symmetric metallocene catalyst namely: meso-dimethylsilylbis (2,4,6-trimethyl-1 -indenyl)zirconium dichloride is presented. The effect of polymerization temperature (0-70 degrees C) on the catalyst performance for propylene polymerization has been investigated. This catalyst shows very high activity at 50 degrees C which is higher than the activity of the racemic analogue, and the resulted polypropylene is amorphous in nature with isotactic pentad content [mmmm] of 12 %.
基金National Natural Science Foundation of China and SINOPEC(No.29734144).
文摘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.
基金This work was supported by the Natural Science Foundation of Heilongjiang Province (No. B0313) and Research Foundation of China University of Mining and Technology
文摘Many attempts have been made to control the regioselectivity for olefin poly- merization 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.
文摘The effects of adding Al(i-C_4H_9)_3 (TBA) to rac-Me2Si(Ind)2ZrCl2/ MAO catalyzed propylene-1-octene copolymerization were studied. At TBA /MAO (Al/AI mole ratio) of about 0.6, the polymerization activity was found to be much higher than the system without TBA. Increases of polymer molecular weight and 1-octene content from addition of TBA were also observed.
文摘In the preparation of catalyst for propylene polymerization, the Mg(OEt) 2 support was activated with ethanol/CO 2 system followed by solidification, and treated with TiCl 4 in the presence of ethylbenzoate as an internal donor(ID). The chemical compositions of the activated support and the prepared catalyst were examined in detail. During the dissolution of Mg(OEt) 2 support in ethanol medium with CO 2 bubbling, the structure of support changed to magnesium hydrocarbyl carbonate, (CH 3CH 2O) 2- x Mg(O (C O) OCH 2CH 3) x ( x = 1,2). The content of carbonated CO 2 in the activated support was dependent on the heat treatment in the solidification of support. In the preparation procedure of polymerization catalyst, the activated support was treated with TiCl 4 so that the structure of support was converted to MgCl 2 with the incorporation of ID. The polymerization behavior of the pre-pared catalyst was also studied in the presence of phenyltriethoxysilane as an external donor.
基金supported by National Natural Science Foundation of China(grant nos.21927901,21821004,and 21873007 to Y.Q.G.,grant no.21933004 to Y.D.W.,grant nos.22273061 and 22003042 to Y.I.Y.)the Key-Area Research and Development Program of Guangdong Province(grant no.2020B0101350001 to Y.D.W.).
文摘The bond breaking and forming in chemical reactions is a typical rare event,which is one of the difficult problems in molecular dynamics simulations.Numerous enhanced sampling methods have been developed to extend the time scale covered by molecular simulations.However,the difficulties of obtaining appropriate collective variables from complicated reaction pathways and a controlled sampling over the desired phase space remain as challenges.Herein,we use MetaITS,which combines metadynamics and integrated tempered sampling,to increase the sampling efficiency for chemical reactions.Metadynamics with collective variables obtained by harmonic linear discriminant analysis can efficiently decrease the main energy barrier of chemical reaction.Meanwhile,integrated tempered sampling can enhance the exploration of other degrees of freedom.In this study,we applied the MetaITS method to two transition-metal-catalyzed organic reactions with complicated reaction coordinates.We simulated here a zirconocene-catalyzed propylene polymerization to investigate the regioselectivity and temperature effects.We also studied a Sharpless epoxidation reaction,for which both chiral products are observed through simulation.
文摘Transformation of living ring-opening metathesis polymerization into coordination polymerization by converting the titanacyclobutane group attached to a polynorbornene chain into titanocene alkoxide has been used for the synthesis of polynorbornene-poly(ethylene-co-propylene) block copolymer. Preliminary characterizations of the copolymerization products by solvent extraction and C-13 NMR spectrum are reported.
基金the National Natural Science Foundation of China(20374043)SINOPEC(X501025)
文摘Ansa-Cyclohexyl-bis(4,5,6,7-tertrahydro-l-indenyl) zirconium dichloride (5) was used as catalyst for propylene and ethylene polymerization together with methyl aluminoxane (MAO) as the cocatalyst. Isotactic polypropylene (PP) was obtained with the highest activity of 6.37× 107g PP (molZr)^-1h^-1. The mesomeso (mmmmm) pentads sequence content of PP was determined by 13C NMR spectroscopy. The dependence of the microstructure on the reaction temperature and the AI/Zr molar ratio was examined and the catalytic activity of complex 5 was compared with that of the similar ansa-zirconocene 3. The high activity of the new zirconocene 5 for propylene isospectic polymerization at high temperature (60℃) is the result of its unique bridged-group structure. Complex 5/MAO displays also high catalytic activity of 0.46× 10^6 to 9.87× 10^6g PE(molZr)^-h^-in the homo-polymerization of ethylene, The visometric molecular weight of PE ranges from 0.97×10^4 to 11.16×10^4 g.mol^- under the given conditions.^13C NMR spectroscopy analysis proves the PE to be linear polyethylene (LPE).
基金Supported by the R&D Program of Catalyst Company,SINOPEC(G8101-11-ZS-0016*)
文摘A L463^5 Box-Behnken design was used for developing a model to predict and optimize the molecular weight (Mw ) of polypropylene (PP) ; a second-order polynomial regression equation was derived to predict responses. The significance of variables and their interactions were tested by means of the ANOVA with 95% confidence limits; the standardized effects were investigated by Pareto chart, the optimum values of the selected variables were obtained by analyzing the response surface contour plots. The optimized Mw value of 1. 217 × 10^5 g/mol was very close to the industrial value ( ( 1.22 ±0. 004) ×10^6 g/tool) at the optimum values.
基金financially supported by the National Natural Science Foundation of China (No.21274041)。
文摘A series of C1-symmetric ethylene-bridged ansa-(3-R-cyclopentadienyl)(fluorenyl) metallocene complexes(Zr: 1-5;Hf: 6) have been synthesized, characterized and investigated as catalyst precursors for the high temperature ethylene polymerization. Using methylaluminoxane(MAO) as the cocatalyst, zirconium complexes 1-5 bearing a bulky substituent on the 3-position of the cyclopendienyl ring showed high catalytic activities up to 1.48×10^(7) g PE·mol_(Zr)^(-1)·h^(-1) toward the polymerization of ethylene and afforded polyethylenes with high molecular weights(1.49×10^(5)-6.31×10^(5) g/mol), meanwhile exhibting great thermal stability at high temperatures up to 120 ℃ together with a long catalytic life time up to 2 h. By adopting low Al/Zr ratios, such as 125, polyethylenes with ultra high molecular weights up to 2.86×106 g/mol were obtained. It is worthy of noting that zirconium complexes 1-4 bearing a substituent with an aryl pendant showed temperature-dependent activities, which increased rapidly with the increase of polymerization temperature, thus weak interaction of the pendent aryl group with the cationic active center is proposed to account for the very low activities displayed at low temperatures. In contrast to zirconocene complexes 1-5, hafnocene complex 6 only displayed very low catalytic activities toward the polymerization of ethylene and afforded polyethylenes with molecular weights ten times smaller than those obtained by zirconocene complexes 1-5. Zirconocene complexes 1-5 were also able to catalyse the polymerization of propylene at high temperatures, but only afforded waxes with low molecular weights.