Mechanism and Kinetics of Methylating C6–C12 Methylbenzenes with Methanol and Dimethyl Ether in H-MFI Zeolites

ACS Catalysis ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 6444-6460 ◽  
Author(s):  
Mykela DeLuca ◽  
Pavlo Kravchenko ◽  
Alexander Hoffman ◽  
David Hibbitts
Keyword(s):  
Dimethyl Ether ◽  
Mechanism And Kinetics ◽  
Mfi Zeolites ◽  
Kinetics Of

Mechanism and Kinetics of Methylating C6–C12 Methylbenzenes with Methanol and DME in H-MFI Zeolites

2019 ◽  
Author(s):  
Mykela DeLuca ◽  
Pavlo Kravchenko ◽  
Alexander Hoffman ◽  
David Hibbitts
Keyword(s):  
Density Functional ◽  
Functional Theory ◽  
Co Catalysts ◽  
Aromatic Species ◽  
Mechanism And Kinetics ◽  
Methanol To Hydrocarbon ◽  
Methylating Agents ◽  
Mfi Zeolites ◽  
Kinetics Of ◽  
Adsorptive Properties

<p> This study uses periodic density functional theory (DFT) to determine the reaction mechanism and effects of reactant size for all 20 arene (C<sub>6</sub>–C<sub>12</sub>) methylation reactions using CH<sub>3</sub>OH and CH<sub>3</sub>OCH<sub>3</sub> as methylating agents in H-MFI zeolites. Reactant, product, and transition state structures were manually generated, optimized, and then systematically reoriented and reoptimized to sufficiently sample the potential energy surface and thus identify global minima and the most stable transition states which interconnect them. These systematic reorientations decreased energies by up to 50 kJ mol<sup>−1</sup>, demonstrating their necessity when analyzing reaction pathways or adsorptive properties of zeolites. Benzene-DME methylation occurs via sequential pathways, consistent with prior reports, but is limited by surface methylation which is stabilized by co-adsorbed benzene via novel cooperativity between the channels and intersections within MFI. These co-adsorbate assisted surface methylations generally prevail over unassisted routes. Calculated free energy barriers and reaction energies suggest that both the sequential and concerted methylation mechanisms can generally occur, depending on the methylating agent and methylbenzene being reacted—there is no consensus mechanism for these homologous reactions. Intrinsic methylation barriers for step-wise reactions of benzene to hexamethylbenzene remain between 75–137 kJ mol<sup>−1</sup> at conditions relevant to methanol-to-hydrocarbon (MTH) reactions where such arene species act as co-catalysts. Intrinsic methylation barriers are similar between CH<sub>3</sub>OH and CH<sub>3</sub>OCH<sub>3</sub> suggesting that both species are equally capable of interconverting between methylbenzene species. Additionally, these methylation barriers do not systematically increase as the number of methyl-substituents on the arene increases and the formation of higher methylated arenes is thermodynamically favorable. These barriers are significantly lower than those associated with alkene formation during the aromatic cycle, suggesting that aromatic species formed during MTH reactions either egress from the catalyst—depending on that zeolite’s pore structure—or become trapped as extensively-substituted C<sub>10</sub>–C<sub>12</sub> species which can either isomerize to form olefins or ultimately create polyaromatic species that deactivate MTH catalysts.</p>

Mechanism and Kinetics of Methylating C6–C12 Methylbenzenes with Methanol and DME in H-MFI Zeolites

2019 ◽  
Author(s):  
Mykela DeLuca ◽  
Pavlo Kravchenko ◽  
Alexander Hoffman ◽  
David Hibbitts
Keyword(s):  
Density Functional ◽  
Functional Theory ◽  
Co Catalysts ◽  
Aromatic Species ◽  
Mechanism And Kinetics ◽  
Methanol To Hydrocarbon ◽  
Methylating Agents ◽  
Mfi Zeolites ◽  
Kinetics Of ◽  
Adsorptive Properties

<p> This study uses periodic density functional theory (DFT) to determine the reaction mechanism and effects of reactant size for all 20 arene (C<sub>6</sub>–C<sub>12</sub>) methylation reactions using CH<sub>3</sub>OH and CH<sub>3</sub>OCH<sub>3</sub> as methylating agents in H-MFI zeolites. Reactant, product, and transition state structures were manually generated, optimized, and then systematically reoriented and reoptimized to sufficiently sample the potential energy surface and thus identify global minima and the most stable transition states which interconnect them. These systematic reorientations decreased energies by up to 50 kJ mol<sup>−1</sup>, demonstrating their necessity when analyzing reaction pathways or adsorptive properties of zeolites. Benzene-DME methylation occurs via sequential pathways, consistent with prior reports, but is limited by surface methylation which is stabilized by co-adsorbed benzene via novel cooperativity between the channels and intersections within MFI. These co-adsorbate assisted surface methylations generally prevail over unassisted routes. Calculated free energy barriers and reaction energies suggest that both the sequential and concerted methylation mechanisms can generally occur, depending on the methylating agent and methylbenzene being reacted—there is no consensus mechanism for these homologous reactions. Intrinsic methylation barriers for step-wise reactions of benzene to hexamethylbenzene remain between 75–137 kJ mol<sup>−1</sup> at conditions relevant to methanol-to-hydrocarbon (MTH) reactions where such arene species act as co-catalysts. Intrinsic methylation barriers are similar between CH<sub>3</sub>OH and CH<sub>3</sub>OCH<sub>3</sub> suggesting that both species are equally capable of interconverting between methylbenzene species. Additionally, these methylation barriers do not systematically increase as the number of methyl-substituents on the arene increases and the formation of higher methylated arenes is thermodynamically favorable. These barriers are significantly lower than those associated with alkene formation during the aromatic cycle, suggesting that aromatic species formed during MTH reactions either egress from the catalyst—depending on that zeolite’s pore structure—or become trapped as extensively-substituted C<sub>10</sub>–C<sub>12</sub> species which can either isomerize to form olefins or ultimately create polyaromatic species that deactivate MTH catalysts.</p>

An investigation into the mechanism and kinetics of dimethoxymethane carbonylation over FAU and MFI zeolites

2010 ◽  
Vol 274 (2) ◽  
pp. 150-162 ◽  
Author(s):  
Fuat E. Celik ◽  
Taejin Kim ◽  
Anton N. Mlinar ◽  
Alexis T. Bell
Keyword(s):  
Mechanism And Kinetics ◽  
Mfi Zeolites ◽  
Kinetics Of

Oil extraction from the sunflower seeds, mechanism and kinetics of the process

2020 ◽  
Vol 3 (1) ◽  
pp. 155-160
Author(s):  
Ye. M. Semenyshyn ◽  
◽  
V. M. Atamanyuk ◽  
O. Ya. Dobrovetska ◽  
T. I. Rymar ◽  
...  
Keyword(s):  
Oil Extraction ◽  
Sunflower Seeds ◽  
Mechanism And Kinetics ◽  
Kinetics Of

Studies on the Behavior Some Paints in Electro-insulating Fluid Based on Vegetable Esters

2018 ◽  
Vol 69 (5) ◽  
pp. 1139-1144
Author(s):  
Iosif Lingvay ◽  
Adriana Mariana Bors ◽  
Livia Carmen Ungureanu ◽  
Valerica Stanoi ◽  
Traian Rus
Keyword(s):  
Structural Changes ◽  
Oxidation Processes ◽  
High Oleic ◽  
Painting Materials ◽  
Insulating Paper ◽  
Different Types ◽  
Mechanism And Kinetics ◽  
Kinetics Of ◽  
Natural Ester

For the purpose of using three different types of painting materials for the inner protection of the transformer vats, their behavior was studied under actual conditions of operation in the transformer (thermal stress in electro-insulating fluid based on the natural ester in contact with copper for electro-technical use and electro-insulating paper). By comparing determination of the content in furans products (HPLC technique) and gases formed (by gas-chromatography) in the electro-insulating fluid (natural ester with high oleic content) thermally aged at 130 �C to 1000 hours in closed glass vessels, it have been found that the presence the investigated painting materials lead to a change in the mechanism and kinetics of the thermo-oxidation processes. These changes are supported by oxygen dissolved in oil, what leads to decrease both to gases formation CO2, CO, H2, CH4, C2H4 and C2H6) and furans products (5-HMF, 2-FOL, 2 -FAL and 2-ACF). The painting materials investigated during the heat treatment applied did not suffer any remarkable structural changes affecting their functionality in the electro-insulating fluid based on vegetable esters.

Mechanism and Kinetics of the Hydrogen Failure of Thermoelectric Materials during Water Electrolysis

2020 ◽  
Vol 2020 (10) ◽  
pp. 1102-1115
Author(s):  
M. A. Korzhuev ◽  
I. V. Katin ◽  
M. A. Kretova ◽  
E. S. Avilov
Keyword(s):  
Thermoelectric Materials ◽  
Water Electrolysis ◽  
Mechanism And Kinetics ◽  
Kinetics Of
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