Catalysis
Mohammad Javad Sharifi; Alireza Fazlali; Seyed Hamed Mahdaviani; Davood soudbar
Abstract
The performance of the catalyst system [chromium(III)/pyrrole/co-catalyst/halide] on the trimerization of ethylene has been studied using the combined experimental and response surface method (RSM). The chromium(III) tris(2-ethylhexanoate) was synthesized and characterized by FTIR, 1HNMR and 13CNMR, ...
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The performance of the catalyst system [chromium(III)/pyrrole/co-catalyst/halide] on the trimerization of ethylene has been studied using the combined experimental and response surface method (RSM). The chromium(III) tris(2-ethylhexanoate) was synthesized and characterized by FTIR, 1HNMR and 13CNMR, to study chemical properties and identify molecular structures. The effect of four variables Al/Cr molar ratio, halide/Cr molar ratio, reaction temperature and catalyst dosage have been considered on catalyst activity, 1-hexene selectivity and polymer content. The central composite design (CCD) model with three main parameters in three response levels for each factor was applied to analyze the effects of the parameters. The comparative studies showed that carbon-tetra-chloride (CCl4) and tri-n-octyl-aluminum (TNOA) were the best candidates for this catalyst system, demonstrating high selectivity of 1-hexene formation, higher catalytic activity and lower polymer content. Based on the RSM results, the best trimerization condition for ethylene at 25 bar and 91.2°C was obtained at the catalytic system [Cr(2-EH)3/2,5-DMP/CCl4/TNOA] molar ratio of 1:6:10.8:201.5, which showed the activity of 105328 (g 1-C6/(g Cr.hr)), 99.21% selectivity for 1-hexene and no polymer was formed. The predicted process parameters were also verified by actual experiments at the optimized conditions.
Polyolefin blends
Somayeh Rafiei; Davood Soudbar; Minoo Sadri; Fatemeh Shafiei
Abstract
Thermoplastic vulcanizates (TPVs) were prepared based on polypropylene (PP) and polybutadiene rubber (PBR) at different PP/PBR compositions (70/30 and 60/40). PP-grafted-maleic anhydride (PP-g-MA) was introduced into the TPVs at different concentrations (10 and 20%). The compatibilizing effect of PP-g-MA ...
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Thermoplastic vulcanizates (TPVs) were prepared based on polypropylene (PP) and polybutadiene rubber (PBR) at different PP/PBR compositions (70/30 and 60/40). PP-grafted-maleic anhydride (PP-g-MA) was introduced into the TPVs at different concentrations (10 and 20%). The compatibilizing effect of PP-g-MA was demonstrated through cross-sectional morphology. PP-g-MA exhibited a suppressing impact on the coalescence of the rubber domains, leading to a finer and more uniform distribution of the PBR phase. Due to the higher rubber content, the compatibilizing effect was more pronounced for the 60/40 composition, which was on the averge of forming a co-continuous morphology. However, it was found that a higher PP-g-MA content is needed to effectively compatibilize the TPVs. Rheological results revealed opposing effects on the viscoelastic response of the system. However, the elastic response was intensified once higher content of PP-g-MA was used, suggesting its compatibilizing role. Dynamic mechanical analysis results proved the existence of opposing effects and revealed the profound compatibilizing effects of PP-g-MA, especially at higher content (20%). Izod impact strength exhibited moderate and notable enhancements in both TPV compositions by adding 10% and 20% of PP-g-MA, respectively, attributed to the highly increased compatibility of the PP/PBR TPVs, especially at higher levels of PP-g-MA content.
Olefin synthesis
Sajjad Bahrami Reyhan; Seyed Mahdi Alavi; Davood Soudbar
Abstract
Ethylene dimerization is a significant process among the other petrochemical processes due to the production of alpha olefins as the most widely used industrial intermediate. Titanium tetra butoxide/tetrahydrofuran/triethyl aluminum is the main homogeneous catalyst complex in this process. On the other ...
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Ethylene dimerization is a significant process among the other petrochemical processes due to the production of alpha olefins as the most widely used industrial intermediate. Titanium tetra butoxide/tetrahydrofuran/triethyl aluminum is the main homogeneous catalyst complex in this process. On the other hand, the formation of polymer or oligomerization side reactions are the salient obstacles in the ethylene dimerization process. The effect of various promoters from the group of halo hydrocarbons, along with different modifiers from the group of esters and silane compounds had been investigated to conquer the barriers mentioned above. The reaction conversion, selectivity, and polymer production were the remarkable parameters that were evaluated to study the components’ impacts. The results indicated that the addition of promoters through reaction with Triethyl aluminum (TEA) (co-catalyst) increased the reaction speed and thus increased the conversion of the reaction to 88.26% and reduced the reaction time to 60 min. Among the promoters, the reaction conversion and selectivity of dichloromethane were 88.26% and 78.45%, higher than that of dibromopropane (48.52% and 39.52%), but a higher amount of polymer was produced by dichloromethane. Moreover, Esters strongly decreased the catalyst activity, resulting in a decrease in the conversion to under 25%. On the other hand, silanes showed a significant effect on the control of the polymer chains in Ziegler-Natta homogeneous catalysts. Dicyclopentyldimethoxysilane (DCPDS) modifier brought about an increase of 1.5% in ethylene conversion and a 6% increase in the 1-butene selectivity. At the same time, the polymer formation also prevented a significant amount so the amount of polymer decreased to about 2.1 mg. DCPDS modifier performed better than the Cyclohexylmethyldimethoxysilane (CHMDS) donor.
