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کاربرد نوع شرط:
- جایگاه : پژوهشی
- مجله: Polyolefins Journal
- نوع مقاله: Journal Article
- کلمات کلیدی: Microstructure,Oil,Olefin,oligomerization,metallocene
- چکیده:
- چکیده انگلیسی: Herein a quenched-flow kinetic technique was applied to calculate the rate constants of 1-hexene and 1-octene oligomerization catalyzed by the Cp2ZrCl2 and Cp2HfCl2/MAO catalyst systems, and subsequently a mechanism for the higher α-olefin oligomerization reaction was proposed. The oligomerization results showed that Zr-based catalyst in the oligomerization of 1-octene had the highest activity of 17 in comparison to Hfbased one with an activity value of 15 g oligomer/(mmolCat.h)). According to the obtained results, increasing monomer length led to a shift in molecular weight and polydispersity index value (Mw/Mn) to lower values. Furthermore, the microstructure-viscosity relationship was followed by the calculation of branching ratio and short-chain branching percentage. The obtained results revealed that, the oligomers synthesized by the Cp2HfCl2 catalyst had lower short chain branching ratio value and short-chain branching percentages. According to the kinetic results, the initiation rate constant (ki) of Zr-based catalyst was higher than that of Hf-based catalyst, and the order of calculated propagation rate constants was Zr>Hf for both the 1-hexene and 1-octene-based oligomerizations.
- انتشار مقاله: 14-08-1399
- نویسندگان: Ahad Hanifpour,Mahdi Hashemzadeh Gargari,Mohammad Reza Rostami Darounkola,Zahra Kalantari,Naeimeh Bahri-Laleh
- مشاهده
- جایگاه : پژوهشی
- مجله: Polyolefins Journal
- نوع مقاله: Journal Article
- کلمات کلیدی: Ziegler-Natta catalysts,1-hexene polymerization,poly(α-olefin),tacticity
- چکیده:
- چکیده انگلیسی: The aim of this study was to examine the effect of catalyst doping on the performance of MgCl2. EtOH/TiCl4 catalyst system. In this regard, a series of undoped as well as FeCl3-doped catalysts was prepared and employed in 1-hexene polymerization. A modified catalyst containing 10 wt. % of FeCl3 dopant demonstrated the highest activity, with 32% activity increase compared to unmodified one, among the series. The GPC results showed a lower molecular weight as well as broader MWD for the poly1-hexenes obtained from FeCl3-doped catalyst. The distribution of active centers was analyzed using deconvolution of the MW profiles with using multiple Flory functions. It was demonstrated that the number of active sites increased by 10 wt. % FeCl3 doping, however, by more increasing the dopant amount to 15 wt.%, the number of active sites decreased. The 13C-NMR results indicated that, FeCl3 doping did not have a considerable effect on the polymer tacticity (with total tacticity of 53 %), however it increased by donor presence to the maximum value of 60 %.
- انتشار مقاله: 20-12-1395
- نویسندگان: Farshid Nouri-Ahangarani,Mehdi Nekoomanesh,Seyed Amin Mirmohammadi,Naeimeh Bahri-Laleh
- مشاهده
- جایگاه : پژوهشی
- مجله: Polyolefins Journal
- نوع مقاله: Journal Article
- کلمات کلیدی: Iran,Middle East,statistics,Olefin,petrochemical company,polyolefin,NPC
- چکیده:
- چکیده انگلیسی: Due to easy availability of cheaper raw material and increase in new applications, the use of polyolefins in various industries is becoming a major priority. The Middle East region, on account of its vast oil and gas reserves has, in the last decade or so, been developing many new petrochemical complexes with their expansion into colossal polyolefin production capacities. The predictions are that by 2020 the Middle East region will dominate the polyolefin industry as a whole. Furthermore, with proven oil reserves of about 21.7 thousand million tons (4th world ranking) and natural gas of 34.0 trillion cubic meters (1st world ranking), Iran’s petrochemical industry is supported by diverse and abundant feedstock reserves. In line with other polyolefin producers’ developments in the Middle East, Iran's National Petrochemical Company (NPC) has undergone massive structural and technological transformations in the last two decades in order to set up ambitious plans for further capacity increase and native technology developments. This article mainly focuses on Iran today’s position and its future plans in the polyolefins industry.
- انتشار مقاله: 26-02-1394
- نویسندگان: Naeimeh Bahri-Laleh,Mehdi Nekoomanesh-Haghighi,Samahe Sadjadi,Ali Pajouhan
- مشاهده
- جایگاه : پژوهشی
- مجله: Polyolefins Journal
- نوع مقاله: Journal Article
- کلمات کلیدی: Molecular Simulation,DFT,metallocene catalysts,Setereoselective polymerization,Isotactic polypropylene
- چکیده:
- چکیده انگلیسی: In this study we have tested the ability of a standard DFT computational protocol to reproduce the experimentally obtained stereoselectivity of 26 different C2-symmetric zirconocene catalysts active in propylene polymerization. The catalysts were chosen for their relevance in metallocene catalyzed polymerization of propylene. To this end, primary insertion of both si- and re-propylene enantiofaces into the Zr-CH2-CH(CH3)2 bond was considered to simulate the growing chains step. The energy difference between these two transition states, ΔEre-si, was taken as a measure of the stereoselectivity (pentad: mmmm%) of different catalysts. The results clearly indicated that there was a good agreement between ΔEre-si and the mmmm% values, so that greater ΔEre-si could correspond to higher mmmm%. A model was fitted to the experimentally obtained mmmm% against theoretical ΔEre-si. The coefficient of determination (R2) of the resultant plot was 0.9793, which indicated a good accuracy of the model. Finally, to quantify the steric role of the studied ligands in the observed stereoselectivity, the analysis of the buried volume (VBur) and of the steric maps was performed for two representative complexes. The images revealed that a greater asymmetric localization of the %VBur around the metal center led to a higher mmmm% in the resultant polymer.
- انتشار مقاله: 16-07-1393
- نویسندگان: Naeimeh bahri-Laleh,Laura Falivene,Luigi Cavallo
- مشاهده
- جایگاه : پژوهشی
- مجله: Polyolefins Journal
- نوع مقاله: Journal Article
- کلمات کلیدی: Ziegler-Natta,MgCl2,thermal dealcoholation,polyolefin,dynamic structure
- چکیده:
- چکیده انگلیسی: Primary MgCl2.3.3EtOH adduct (PCT1) was prepared by melt quenching method and then submitted into a programmed thermal dealcoholation project using a fluidized bed reactor. During thermal dealcoholation program, different MgCl2.nEtOH support samples with n= 3.0, 2.7, 2.4, and 2.1 were selected and named as PCT2 to PCT5, respectively. Structural analysis of the support samples showed a significant increase in the surface area, from 7.4 m2/g to 12.8 m2/g, together with the decrease in peaks height at 2θ≈ 8.9 and 9.7˚ by moving from PCT1 to PCT5. After characterization of support samples, final catalysts were prepared by reacting these samples with TiCl4 and examined in slurry phase propylene polymerization. Prepared catalysts showed similar stereospecifities but different activities in the polymerization experiments, so that, with proceeding dealcoholation from PCT1 to PCT2 catalyst activity was reached a maximum amount of 2.9 kgPP/g Cat.h, and then by further dealcoholation, from PCT2 to PCT5, catalyst activity decreased gradually. In the last section, effect of time interval between thermal dealcoholation and catalyst preparation, which is called storage time, on the crystal and morphological characteristics of the two of the best adduct samples, namely MgCl2.2.4EtOH and MgCl2.3.0EtOH, was studied, as well. Storage time greatly affected the characteristics of the adducts together with resulted catalysts, and the best catalyst activity was achieved for the ones prepared immediately after adduct preparation.
- انتشار مقاله: 15-02-1392
- نویسندگان: Najmeh Hadian,Shokoofeh Hakim,Mehdi Nekoomanesh-Haghighi,Naeimeh bahri-Laleh
- مشاهده
- جایگاه : پژوهشی
- مجله: Communications In Catalysis
- نوع مقاله: Journal Article
- کلمات کلیدی: LLDPE,modified support,FeCl3,Ziegler-Natta catalyst,1-hexene
- چکیده:
- چکیده انگلیسی: Effect of FeCl3 and FeCl3/SiCl4-doping on the performance of MgCl2(ethoxide type)/TiCl4/TEAL catalytic system was evaluated in the linear low density polyethylene (LLDPE) synthesis using 1-hexene as the comonomer. Results revealed that FeCl3/SiCl4 modified catalytic system has better performance in terms of catalyst activity and comonomer incorporation when compared with unmodified catalyst or the catalytic system in the presence of FeCl3 alone. In fact, the introduction of FeCl3 doper, in its optimum amount of 10 wt. %, together with SiCl4 induced better catalytic performance with 212 and 90 % increase in catalyst activity and 1-hexene incorporation, respectively. Copolymers characterization showed increased bulk density together with decreased crystallinity and Tm in the polymers from modified catalysts. Overall results showed that, new catalytic system represented in this work, is a good candidate for large scale LLDPE production with high comonomer amount.
- انتشار مقاله: 23-06-1396
- نویسندگان: Reza Bazvand,Naeimeh Bahri-Laleh,Mehdi Nekoomanesh,Hossein Abedini,Ahad Hanifpour
- مشاهده
- جایگاه : پژوهشی
- مجله: Communications In Catalysis
- نوع مقاله: Journal Article
- کلمات کلیدی: LLDPE,modified support,FeCl3,Ziegler-Natta catalyst,1-hexene
- چکیده:
- چکیده انگلیسی: Effect of FeCl3 and FeCl3/SiCl4-doping on the performance of MgCl2(ethoxide type)/TiCl4/TEAL catalytic system was evaluated in the linear low density polyethylene (LLDPE) synthesis using 1-hexene as the comonomer. Results revealed that FeCl3/SiCl4 modified catalytic system has better performance in terms of catalyst activity and comonomer incorporation when compared with unmodified catalyst or the catalytic system in the presence of FeCl3 alone. In fact, the introduction of FeCl3 doper, in its optimum amount of 10 wt. %, together with SiCl4 induced better catalytic performance with 212 and 90 % increase in catalyst activity and 1-hexene incorporation, respectively. Copolymers characterization showed increased bulk density together with decreased crystallinity and Tm in the polymers from modified catalysts. Overall results showed that, new catalytic system represented in this work, is a good candidate for large scale LLDPE production with high comonomer amount.
- انتشار مقاله: 23-06-1396
- نویسندگان: Reza Bazvand,Naeimeh Bahri-Laleh,Mehdi Nekoomanesh,Hossein Abedini,Ahad Hanifpour
- مشاهده