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Avelino Corma - One of the best experts on this subject based on the ideXlab platform.
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One-pot co-crystallization of beta and pentasil nanozeolites for the direct conversion of a heavy reformate fraction into xylenes
Applied Catalysis A: General, 2019Co-Authors: Vicente J. Margarit, M. Teresa Portilla, M. Teresa Navarro, Raed Abudawoud, Ibrahim M. Al-zahrani, Sohel Shaikh, Cristina Martínez, Avelino CormaAbstract:Abstract Upgrading of the heavy reformate fraction (HR), containing mainly C9+ aromatics, is usually performed by Dealkylation or by transalkylation with added benzene and/or toluene to obtain the more valuable xylenes. However, when the costs related to the use of benzene and toluene are considered, the one-step Dealkylation/transalkylation of the C9+ alkylaromatics to xylenes becomes economically attractive. Thus, in a first step, ethylmethylbenzenes (EMB) will have to be dealkylated to toluene, which will then react with the trimethylbenzenes (TMB) present in the HR feed to produce xylenes by transalkylation. Medium pore zeolites will favor Dealkylation, whereas large pore zeolites will be more adequate for carrying out the transalkylation reaction. In this work, we present the one-pot synthesis of beta-pentasil aggregates with tunable ratios of the large pore beta to the medium pore component. We show that the close proximity of the beta and pentasil nanocrystals obtained by one-pot co-crystallization synthesis, results in a highly efficient catalyst for the consecutive Dealkylation/transalkylation process. The bifunctional catalyst based on the co-crystallized aggregate is more active and selective to xylenes than a catalyst based on a physical mixture of equivalent beta and pentasil nanozeolites synthesized following an analogous procedure. The small crystallite sizes of the co-crystallized zeolites provide the additional advantage of a lower deactivation rate as compared to a reference benchmark catalyst. Results are shown on both, model molecules and industrial HR feed.
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a rational design of alkyl aromatics Dealkylation transalkylation catalysts using c8 and c9 alkyl aromatics as reactants
Journal of Catalysis, 2004Co-Authors: Jose M Serra, Emmanuelle Guillon, Avelino CormaAbstract:A catalyst has been designed to optimize the Dealkylation of ethyl and propyl aromatics while producing the transalkylation of tri- and tetramethylbenzene with toluene in order to maximize xylenes and benzene when processing heavy reformate. Conversion of model ethyl-aromatics under realistic transalkylation conditions has been studied over two reference catalysts and seven different acid zeolites including topologies with channel systems containing 10 MR, 12 MR, and 10 + 12 MR. Catalytic testing was accomplished by means of a high-throughput reactor system. It has been found that zeolite structure has a direct influence on the ethyl Dealkylation/transalkylation activity, increasing the ethylbenzene conversion and Dealkylation selectivity when decreasing the zeolite pore volume. Moreover, Re/IM-5 and, specially, Re/ZSM-5 zeolites show an excellent Dealkylation activity. Ethylbenzene undergoes different bimolecular reactions giving as primary products either benzene and diethylbenzene or toluene and ethyltoluene, each reaction involving a different biphenylic intermediate and the selectivity toward each mechanism is directly influenced by the zeolite pore size and geometry.
Martin Elsner - One of the best experts on this subject based on the ideXlab platform.
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cytochrome p450 catalyzed Dealkylation of atrazine by rhodococcus sp strain ni86 21 involves hydrogen atom transfer rather than single electron transfer
Dalton Transactions, 2014Co-Authors: Armin H Meyer, Agnieszka Dybaladefratyka, Peter J Alaimo, Inacrist Geronimo, Ariana D Sanchez, Christopher J Cramer, Martin ElsnerAbstract:Cytochrome P450 enzymes are responsible for a multitude of natural transformation reactions. For oxidative N-Dealkylation, single electron (SET) and hydrogen atom abstraction (HAT) have been debated as underlying mechanisms. Combined evidence from (i) product distribution and (ii) isotope effects indicate that HAT, rather than SET, initiates N-Dealkylation of atrazine to desethyl- and desisopropylatrazine by the microorganism Rhodococcus sp. strain NI86/21. (i) Product analysis revealed a non-selective oxidation at both the αC and βC-atom of the alkyl chain, which is expected for a radical reaction, but not SET. (ii) Normal 13C and 15N as well as pronounced 2H isotope effects (ecarbon: −4.0‰ ± 0.2‰; enitrogen: −1.4‰ ± 0.3‰, KIEH: 3.6 ± 0.8) agree qualitatively with calculated values for HAT, whereas inverse 13C and 15N isotope effects are predicted for SET. Analogous results are observed with the Fe(IV)O model system [5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-iron(III)-chloride + NaIO4], but not with permanganate. These results emphasize the relevance of the HAT mechanism for N-Dealkylation by P450.
Agnieszka Dybaladefratyka - One of the best experts on this subject based on the ideXlab platform.
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cytochrome p450 catalyzed Dealkylation of atrazine by rhodococcus sp strain ni86 21 involves hydrogen atom transfer rather than single electron transfer
Dalton Transactions, 2014Co-Authors: Armin H Meyer, Agnieszka Dybaladefratyka, Peter J Alaimo, Inacrist Geronimo, Ariana D Sanchez, Christopher J Cramer, Martin ElsnerAbstract:Cytochrome P450 enzymes are responsible for a multitude of natural transformation reactions. For oxidative N-Dealkylation, single electron (SET) and hydrogen atom abstraction (HAT) have been debated as underlying mechanisms. Combined evidence from (i) product distribution and (ii) isotope effects indicate that HAT, rather than SET, initiates N-Dealkylation of atrazine to desethyl- and desisopropylatrazine by the microorganism Rhodococcus sp. strain NI86/21. (i) Product analysis revealed a non-selective oxidation at both the αC and βC-atom of the alkyl chain, which is expected for a radical reaction, but not SET. (ii) Normal 13C and 15N as well as pronounced 2H isotope effects (ecarbon: −4.0‰ ± 0.2‰; enitrogen: −1.4‰ ± 0.3‰, KIEH: 3.6 ± 0.8) agree qualitatively with calculated values for HAT, whereas inverse 13C and 15N isotope effects are predicted for SET. Analogous results are observed with the Fe(IV)O model system [5,10,15,20-tetrakis(pentafluorophenyl)porphyrin-iron(III)-chloride + NaIO4], but not with permanganate. These results emphasize the relevance of the HAT mechanism for N-Dealkylation by P450.
Jeffrey P Jones - One of the best experts on this subject based on the ideXlab platform.
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evidence for two different active oxygen species in cytochrome p450 bm3 mediated sulfoxidation and n Dealkylation reactions
Journal of the American Chemical Society, 2002Co-Authors: Trent J Volz, Denise A Rock, Jeffrey P JonesAbstract:Herein, we report the results from two experiments that are consistent with sulfoxidation and N-Dealkylation involving two different enzyme substrate complexes and thus two different active oxygen species that do not interchange. The first experiment involves the use of a mutant that may increase the amount of the hydroperoxy-iron species (FeIIIO2H).1 This mutant increases the amount of sulfoxidation relative to the amount of N-Dealkylation by 4-fold. In a second experiment, deuterium substitution on the N-methyl groups of substrate does not result in an increase in sulfoxidation. This later result is consistent with N-Dealkylation and sulfoxidation being mediated by two different active oxygen species. While the data indicate two active oxygen species, they do not distinguish between the different possibilities for the active oxygen species.
Syed A. Ali - One of the best experts on this subject based on the ideXlab platform.
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kinetics of Dealkylation transalkylation of c9 alkyl aromatics over zeolites of different structures
Chemical Engineering Research & Design, 2013Co-Authors: Syed A. Ali, Kehinde E. Ogunronbi, S AlkhattafAbstract:Abstract Dealkylation of methylethylbenzenes as well as the conversion of mixtures trimethylbenzenes (TMBs) and methylethylbenzenes (MEBs) over medium- and large-pore zeolites with different topologies and acid-site concentrations were investigated in a fluidized-bed reactor. MEB conversion, its Dealkylation selectivity and transalkylation selectivity were profoundly influenced by the topology of the zeolites. Zeolite beta shows a highest MEB conversion (70–80%) while ZSM-5 exhibited very high Dealkylation selectivity. The results of kinetic study indicate that MEB conversion is influenced by zeolite type and by SiO 2 /Al 2 O 3 ratio. The extent of TMB and MEB conversions over different zeolites as well as xylene yields indicate that while ZSM-5 could substantially convert MEBs (mainly by Dealkylation), it could not effectively catalyze TMB conversion. On the other hand, the conversions of MEBs as well as TMBs were quite high over mordenite and zeolite beta, resulting in much higher xylene yields. These results indicate that while the Dealkylation of MEBs is a necessary condition, it is not a sufficient condition to obtain higher xylene yield. Kinetic modeling results show that the transalkylation reaction was significantly faster than the disproportionation reaction indicating that the transfer of methyl group from TMB to toluene is a preferred route under the reaction conditions studied.
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Kinetics of Dealkylation–transalkylation of C9 alkyl-aromatics over zeolites of different structures
Chemical Engineering Research and Design, 2013Co-Authors: Syed A. Ali, Kehinde E. Ogunronbi, Sulaiman S. Al-khattafAbstract:Abstract Dealkylation of methylethylbenzenes as well as the conversion of mixtures trimethylbenzenes (TMBs) and methylethylbenzenes (MEBs) over medium- and large-pore zeolites with different topologies and acid-site concentrations were investigated in a fluidized-bed reactor. MEB conversion, its Dealkylation selectivity and transalkylation selectivity were profoundly influenced by the topology of the zeolites. Zeolite beta shows a highest MEB conversion (70–80%) while ZSM-5 exhibited very high Dealkylation selectivity. The results of kinetic study indicate that MEB conversion is influenced by zeolite type and by SiO 2 /Al 2 O 3 ratio. The extent of TMB and MEB conversions over different zeolites as well as xylene yields indicate that while ZSM-5 could substantially convert MEBs (mainly by Dealkylation), it could not effectively catalyze TMB conversion. On the other hand, the conversions of MEBs as well as TMBs were quite high over mordenite and zeolite beta, resulting in much higher xylene yields. These results indicate that while the Dealkylation of MEBs is a necessary condition, it is not a sufficient condition to obtain higher xylene yield. Kinetic modeling results show that the transalkylation reaction was significantly faster than the disproportionation reaction indicating that the transfer of methyl group from TMB to toluene is a preferred route under the reaction conditions studied.
