Comparison of Activity of Ziegler-Natta Catalysts Prepared by Recrystallization and Chemical Reaction Methods towards Polymerization of Ethylene

In the present study, Ziegler-Natta catalysts were prepared on supports that were synthesized via two different methods. The first method (method A) is called the recrystallization method, which employed MgCl2 as a precursor. The second method (method B) is called chemical reaction method, which employed Mg(OEt)2 as a precursor. The catalysts were characterized by XRD, TGA, ESR and nitrogen physisorption. BET specific surface areas of catalyst A and B were 123.1 and 142.2 m2/g, respectively. Polymerization of ethylene was carried out over the catalyst and triethylaluminium. The catalyst prepared by method A exhibited higher activity than that prepared by method B. However, the properties of polymer obtained from both catalysts were similar. The results from XRD and TGA analyses confirmed that Mg(OEt)2 was converted to MgCl2

Investigation of Alkoxysilanes in the Presence of Hydrogen with Ziegler-Natta Catalysts in Ethylene Polymerization

Effect of hydrogen and alkoxysilanes as external donor were investigated using two commercial Ziegler-Natta catalysts (TiCl4/MgCl2•nEtOH and TiCl4/phthalate type/MgCl2) in ethylene polymerization. These catalysts were analyzed by EDX, FTIR and XRD measurements. Furthermore, catalytic activity was tested. According to the results, when alkoxysilane was introduced into the system, catalytic activity reduced. Compared these two alkoxysilanes, cyclohexylmethyldimethoxysilane (CHMDMS) can decrease activity more than dimethoxydimethylsilane (DMDMS) did. This was because CHMDMS has more bulky hydrocarbon groups than DMDMS. This led to restrict the direction of monomer insertion to active sites. In addition, when hydrogen was added into the system, CHMDMS is more sensitive to hydrogen than DMDMS. However, CHMDMS showed lower hydrogen response than DMDMS with increased hydrogen concentration. This was owing to its hydrogen sensitivity. Among the two catalysts, catalyst having internal donor can decrease sensitivity of catalyst activity in the system with hydrogen. The obtained polymers were further characterized by DSC and GPC.Effect of hydrogen and alkoxysilanes as external donor were investigated using two commercial Ziegler-Natta catalysts (TiCl4/MgCl2•nEtOH and TiCl4/phthalate type/MgCl2) in ethylene polymerization. These catalysts were analyzed by EDX, FTIR and XRD measurements. Furthermore, catalytic activity was tested. According to the results, when alkoxysilane was introduced into the system, catalytic activity reduced. Compared these two alkoxysilanes, cyclohexylmethyldimethoxysilane (CHMDMS) can decrease activity more than dimethoxydimethylsilane (DMDMS) did. This was because CHMDMS has more bulky hydrocarbon groups than DMDMS. This led to restrict the direction of monomer insertion to active sites. In addition, when hydrogen was added into the system, CHMDMS is more sensitive to hydrogen than DMDMS. However, CHMDMS showed lower hydrogen response than DMDMS with increased hydrogen concentration. This was owing to its hydrogen sensitivity. Among the two catalysts, catalyst having internal donor can decrease sensitivity of catalyst activity in the system with hydrogen. The obtained polymers were further characterized by DSC and GPC

A Comparative Study of AlCl 3

Ethylene homopolymerization over TiCl4/MgCl2/THF catalysts modified with different metal halide additives (AlCl3 and FeCl2) with and without hydrogen was investigated based on catalytic activity and polymer properties. Lewis acid modification can improve activity because it can remove the remaining THF in the final catalyst, which can poison the catalyst active sites via the ring-opening of THF that was confirmed by XRD measurements. Moreover, the activity enhancement was due to the formation of acidic sites by modifying the catalysts with Lewis acids. Thus, FeCl2 doped catalyst (Fe-THF) exhibited the highest activity followed by AlCl3 doped catalyst (Al-THF) and undoped catalyst (None-THF). In H2/C2H4 molar ratio of 0.08, Fe-THF showed a better hydrogen response than Al-THF due to more titanium cluster distribution. Fe-THF is considered to have more clustered Ti species than Al-THF. As a consequence, it led us to obtain more possible chances to precede chain transfer reaction by hydrogen. The molecular weight, melting temperature, and crystallinity of obtained polymers were investigated by GPC and DSC measurement, respectively

Facile Investigation of Ti3+ State in Ti-based Ziegler-Natta Catalyst with A Combination of Cocatalysts Using Electron Spin Resonance (ESR)

This study aims to investigate the influences of a combination of cocatalysts including triethylaluminum (TEA) and tri-n-octylaluminum (TnOA) for activation of a commercial Ti-based Ziegler-Natta catalyst during ethylene polymerization and ethylene/1-hexene copolymerization on the change in Ti3+ during polymerization. Thus, electron spin resonance (ESR) technique was performed to monitor the change in Ti3+ depending on the catalyst activation by a single and combination of cocatalyst. It revealed that the amount of Ti3+ played a crucial role on both ethylene polymerization and ethylene/1-hexene copolymerization. For ethylene polymerization, the activation with TEA apparently resulted in the highest catalytic activity. The activation with TEA+TnOA combination exhibited a moderate activity, whereas TnOA activation gave the lowest activity. In case of ethylene/1-hexene copolymerization, it revealed that the presence of 1-hexene decreased activity. The effect of different cocatalysts tended to be similar to the one in the absence of 1-hexene. The decrease of temperature from 80 to 70 °C in ethylene/1-hexene copolymerization tended to lower catalytic activity for TnOA and TEA+TnOA, whereas only slight effect was observed for TEA system. The effect of different cocatalyst activation on the change of Ti3+ state of catalyst was elucidated by ESR measurement. It appeared that the activation of catalyst with TEA+TnOA combination essentially inhibited the reduction of Ti3+ to Ti2+ leading to lower activity.  Furthermore, the polymer properties such as morphology and crystallinity can be altered by different cocatalysts. Copyright © 2020 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Metathesis of Ethylene and Trans-2-Butene over MgO Admixed WO3/SiO2 Catalysts

The performances of MgO admixed WO3/SiO2 catalysts were investigated in the cross metathesis of ethylene and 2-butene to propylene at 450oC atmospheric pressure. Compared to the WO3/SiO2 + silica gel, the conversion of 2-butene and the propylene selectivity were much higher on all the WO3/SiO2 + MgO catalysts. An increased propylene yield corresponded to the decrease in 1-butene and cis-2-butene by products. The results in this study also suggest suitable method to prepare highly stable MgO catalysts in order to maximize the propylene yield

Ethylene/1-Hexene Copolymerization over Different Phases Titania-Supported Zirconocene Catalysts

Ethylene/1-hexene copolymerization was performed over titania-supported zirconocene/dMMAO catalysts. Effects of titania having different phases on the catalytic activity and polymer properties were investigated. It was found that anatase titania exhibited the highest catalytic activity, and afforded copolymer with high 1-hexene incorporation among other titanias. According to TGA result, the stronger interaction between dMMAO and titania for anatase phase led to the highest catalytic activity, because the stronger interaction between cocatalyst and support would prevent the leaching of cocatalyst. Additionally, based on EDX mapping, a good dispersion of dMMAO over support surface is another reason for an increase in the catalytic activity. SEM analysis indicated that no significant change in polymer morphology was found for all supported catalysts. The incorporation of 1-hexene determined by 13C NMR suggested that titania which possessed high amount of [Al]dMMAO over support surface showed high ability to incorporate 1-hexene. The random copolymers were produced in all systems

Computational Study of Reactive and Coke-Resistant Catalysts for the Dry Reforming Reaction of Methane

The dry reforming reaction of methane (DRR) is one of the solutions utilized to deal with the global warming via the catalyzed reaction of the main greenhouse gas: carbon dioxide (COv2) with methane (CHv4), to produce the syngas of carbon monoxide (CO) and hydrogen (Hv2). Although it is a promising process, catalyst deactivation via coking shortens the life of catalysts and increases the cost of catalyst regeneration/replacement, both of which are important concerns. Hence, the search for catalysts of high activity and coke-resistance is the main goal. In this work, we feature a two-step procedure comprising the analysis and design of active and coke-resistant Ni-based DRR catalysts by employing computational techniques. These techniques include density functional theory (DFT) coupled to the ratings concept developed as a catalysts screening tool. The approach aims to investigate reaction and coking schemes prior to the setup of design criteria for such catalysts. The ratings concept is introduced as a screening tool to identify active and stable DRR catalysts via the interpretation of stability and reactivity ratings (RT-S and RT-R). The concept was then extended for practical applications, where reliable predictions of coke formation and removal rates are demonstrated. Such predictions emerge from the interpretation of experimental apparent activation energy values of Pt and Rh supported catalysts. The predicted trend of coking agrees well with the trend of coke deposition measured via temperature-programmed hydrogenation and temperature-programmed oxidation of these catalysts. Furthermore, optimal operating conditions are determined. Four strategies are proposed based on four types of DRR catalysts. In addition, the surface transformation entailing the interchange between Ni metallic, oxide and carbide during the DRR is studied since the control over these transformations is proposed to be the key factor for tuning the performance of DRR catalysts. Ternary contour plots are used for determining reactive and coke-resistant surface compositions. It is concluded that the surface composition for coke-resistant Ni-based DRR catalysts should consist of less than 10 % carbide and at least 75 % metallic. Finally, the design procedure and criteria for high performance DRR catalysts are discussed, where the control synthesis towards the Ni(111) as the dominant surface together with the control of surface transformation from metallic to carbide is proposed to be the main key

Effect of Cobalt Precursors on Properties of Co/CoAl2O4 Catalysts Synthesized by Solvothermal Method

In the present study, different cobalt precursors, such as cobalt acetylacetonate (CoAA), cobalt acetate (CoAC), cobalt nitrate (CoN) and cobalt chloride (CoCL), were employed to synthesize the cobalt on cobalt-aluminate catalysts by the solvothermal process. The calcined samples were characterized by means of N2 physisorption, XRD, SEM/EDX, TEM and TPR. The CO hydrogenation under methanation condition was performed to measure the activity and product distribution. It revealed that the CoN sample exhibited the highest activity due to high reducibility and large crystallite size having fewer interactions. The similar trend was observed for the CoAC and CoAA samples. However, the CoCL sample had the lowest activity, but highest selectivity to C2-C4 products. This was likely attributed to the different form of cobalt oxide species obtained from CoCl2 as seen from XRD

The Characteristics of Green Calcium Oxide Derived from Aquatic Materials

AbstractThermogravimetric Analysis of three aquatic materials, i.e. cuttlebone, mussel shell and oyster shell, and other physicochemical characteristics were investigated. The highest decomposition rates of aquatic materials under two surrounding gases, i.e. oxygen and nitrogen, exhibited no significant difference for cuttlebone (3.6×10-5-4.8×10-5 mg s-1 mginitial-1 at heating rate 5°C/min and 11.8 ×10-5 -12.5×10-5 mg s-1 mginitial-1 at heating rate 15°C/min) and mussel shell (3.4×10-5- 5.2×10-5 mg s-1 mginitial-1 at heating rate 5°C/min and 11.9×10-5 – 12.4×10-5 mg s-1 mginitial-1 at heating rate 15°C/min), while oyster shell provided the higher decomposition rate under nitrogen surrounding gas (7.6×10-4 mg s-1 mginitial-1 at heat rate 5°C/min and 21.53×10-4 mg s-1 mginitial-1 at heating rate 15°C/min). This is probably because of the difference in their starting crystalline structures, i.e. aragonite (cuttlebone and mussel shell) and calcite (oyster shell). The cubic calcium oxides were prepared by calcination of three aquatic materials under oxygen and nitrogen surrounding gases at 5°C/min ramping to 850°C for 2hours. All resulting calcium oxides obtained from oxygen atmosphere provided only cubic crystalline phases and the adsorption-desorption isotherms (IUPAC Type III), whereas the calcinations under nitrogen surrounding gas gave a presence of calcium hydroxide crystalline or hydroxyl- contaminate existing with cubic calcium oxide that influences on the strength and the number of carbon dioxide adsorption sites. The specific surface area of all resulting calcium oxides ranged from 0.1 – 1.5 m2/g and the average pore diameter was found in the range of 40-60nm. The the number of basic sites belonging to CaO derived from Oyster shell or Cuttlebone were improved while firing under oxygen atmosphere. The suitable firing condition is at the low heating rate to develop porous materials