Para-directed aromatic reactions over shape-selective molecular sieve zeolite catalysts

Chen, N. Y.; Kaeding, Warren W.; Dwyer, Francis G.

doi:10.1021/ja00516a065

Cited by 366 publications

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“…Como já comentado, o tratamento ácido nesta amostra, nas condições praticadas, não permitiu a troca iônica substancial dos íons Na + da zeólita pelos íons H + do É interessante observar da Figura 6 que a proporção de ortoxileno nos produtos, é bastante próxima ao equilíbrio no início da reação, e diminui consideravelmente com o tempo. Este comportamento indica possivelmente a participação de dois efeitos atuando simultaneamente; um relacionado com a propriedade de seletividade de forma no interior dos poros da mordenita, a qual favoreceria a formação do intermediário difenilmetano participante da formação do para-xileno, intermediário esse de menor tamanho que aquele que conduz à formação do isômero orto-xileno [18][19][20] . O outro efeito diz respeito ao número de sítios ativos presentes no interior dos poros e na superfície externa dos cristais da mordenita, nos quais ocorre o processo de isomerização do para-xileno ao meta-e ortoxileno.…”

Section: Figura 5 Conversão De Tolueno Sobre Zeólitas H-mor Desalumiunclassified

Desproporcionamento de tolueno sobre zeólitas tipo mordenita <FONT FACE=Symbol>-</FONT> atividade e seletividade na obtenção de xilenos

Escobar¹,

Batista²,

Urquieta‐González³

2000

Quím. Nova

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Recebido em 8/1/99; aceito em 16/12/99 TOLUENE DISPROPORTIONATION ON MORDENITE TYPE ZEOLITES -ACTIVITY AND SELECTIVITY IN THE XYLENES OBTENTION. A sodium mordenite zeolite (Na-MOR) was synthesized and modified by dealumination with chloridric acid solution (H-MOR). X-Ray Diffraction (XRD), Inductive Coupled Plasm (ICP) and Scanning Electron Micrograph (SEM) techniqueswere used for sample characterization. The zeolite catalytic behavior was evaluated through toluene disproportionation at 435°C. It was verified that mordenites were very selective for the disproportionation reaction and the samples with higher aluminum content showed larger initial activity, however, these samples showed too a higher deactivation velocity due to a blockage of the unidimensional porous system of the zeolite by coke deposits. The selectivity to xylene isomers was practically not influenced by the Si/Al ratio and changed with the time on stream, due to coke formation. Transition state shape selectivity inside the mordenite pores is also discussed.Keywords: toluene disproportionation; xylenes; mordenite zeolite. ARTIGO INTRODUÇÃOAs zeólitas, aluminossilicatos cristalinos, são materiais de grande aplicação em diversos processos químicos industriais, como trocadores iônicos, adsorventes e catalisadores 1 . Como catalisadores, as suas propriedades são consequência das suas características físicas e químicas: diâmetro de poros bem definidos na faixa entre 3 a 20Å, alta área específica, propriedades de troca iônica, capacidade de adsorção, alta estabilidade tér-mica e acentuada atividade catalítica. Na estrutura cristalina das zeólitas, os átomos de alumínio e silício coordenam-se de forma tetraédrica com átomos de oxigênio e, por essa razão, gera-se em torno do átomo de alumínio uma carga negativa a qual é contrabalançada por cátions extra-estruturais de diferentes tipos ou valências. Os cátions sódio e potássio são os mais frequentemente utilizados durante a síntese de zeólitas e, para obtenção da forma cataliticamente ativa, utilizada em processos com catálise ácida, esses cátions são intercambiados direta ou indiretamente por prótons, originando sítios de Brönsted, responsáveis pelas propriedades ácidas das zeólitas.Em catálise ácida, as zeólitas têm mostrado excelente potencial em diversas reações de transformação de hidrocarbonetos, tais como alquilação, isomerização e craqueamento, sendo por este fato amplamente utilizadas na indústria química e petroquímica 2,3 . A mordenita, uma zeólita com uma relação Si/Al de síntese igual a 5, tem apresentado uma crescente utilização em diversos processos de refino de petróleo e na obtenção de intermediários petroquímicos 4 . Essa zeólita tem mostrado vantagens como catalisador devido às características intrínsecas das zeólitas, acima comentadas, e à propriedade de seletividade de forma, a qual está associada as dimensões do seu sistema poroso, formado por canais de 7,0 x 6,5 Å 5 . No entanto, em consequência do seu sistema poroso unidimensional, a mordenita é particularmente suscetível a desati...

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Section: Figura 5 Conversão De Tolueno Sobre Zeólitas H-mor Desalumiunclassified

Desproporcionamento de tolueno sobre zeólitas tipo mordenita <FONT FACE=Symbol>-</FONT> atividade e seletividade na obtenção de xilenos

Escobar¹,

Batista²,

Urquieta‐González³

2000

Quím. Nova

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“…Among the zeolites, the acidic ones such as zeolite X and Y [4][5][6][7], zeolite b [8,9], mordenite [10] and ZSM-5 [11][12][13][14][15][16][17] are widely used catalysts for alkylation reaction. The deposition of an active catalyst can be conventionally done by coating the ceramic foam support by slurry of catalytic material containing a binder to ensure adhesion of the layer [18][19][20].…”

Section: Introductionmentioning

confidence: 99%

Kinetic modeling and study of H-ZSM-5 coated silicon carbide ceramic foam in toluene methylation to produce xylene

et al. 2017

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This work deals with the toluene alkylation reaction with methanol catalyzed by commercial H-ZSM-5 coated over SiC foam. The main product is xylene which is a well-known building block of many petrochemicals. The foam has been purchased and H-ZSM-5 was coated on it by dip-coating method. The coated foam was used as a catalyst block to study the reaction of toluene with methanol. The effect of variation of different reaction parameters such as reaction temperature, mole ratio of reactants, W/ F ratio, partial pressure, feed rate, number of ceramic block coated with catalyst was investigated. Effect of regeneration of the catalyst has also been studied. In addition, comparison of conversion with pellet and coated one was also studied to confirm the usefulness of ceramic foam as catalyst support to get the best conversion to xylene production.

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“…The shape selective conversion of xylenes over ZSM-5 has been investigated in detail by several workers [1][2][3][4][5][6][7][8][9][10][11][12]. Modifications of ZSM-5 by various compounds have been employed to enhance p-xylene selectivity from xylene transformation process [13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

“…Furthermore, the zeolite pretreatment or modification was found to further boost the zeolite shape selectivity [3][4][5][6]24]. For example, it is well known that p-xylene is 1000 to 10000 times faster in diffusion than both m and o xylems [11,24,25].…”

Section: Introductionmentioning

confidence: 99%

Enhancing p -xylene selectivity during m -xylene transformation using mildly pre-coked ZSM-5 catalyst

Al-Khattaf

2007

Chemical Engineering and Processing - Process Intensification

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In the present work, the transformation of m-xylene was studied over fresh and pre-coked H-ZSM-5 catalyst in a riser simulator over the temperature range of 350-500 o C.Significant differences were observed in both the activity and product selectivity pattern for the two forms of the catalyst.While, the fresh catalyst generally gave higher m-xylene conversion, the pre-coked catalyst produced higher Isomerization/Disproportionation (I/D) and Para/ Ortho xylene (P/O) ratios .For both forms of the catalyst, m-xylene conversion was found to increase with both reaction temperature and reaction time (0-15 s). A maximum conversion of 30.8% was achieved at 500 o C for a reaction time of 15 s using the fresh catalyst. The corresponding value for the pre-coked catalyst was 24.6%. P/O and I/D ratios as high as 2.5 and 10 respectively were observed with the pre-coked catalyst. It was also observed that the P/O and I/D ratios decreased with increasing temperature for both catalyst and that the difference between these ratios for the two catalysts is more pronounced between 400 and 450 o C than at higher temperatures. Kinetic modeling of the m-xylene transformation over the pre-coked catalyst yielded a lower activation energy for p-xylene formation compared to the fresh catalyst. And an activation energy of 17.5 kcal/mol for the of m-xylene dispropotionation was obtained for the precoked catalyst compared to 7.82 kcal/mol for the fresh catalyst. These values are indicative of the restriction posed on disproportionation by the pre-coked catalyst as reflected by higher I/D ratios.

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Para-directed aromatic reactions over shape-selective molecular sieve zeolite catalysts

Cited by 366 publications

References 0 publications

Desproporcionamento de tolueno sobre zeólitas tipo mordenita <FONT FACE=Symbol>-</FONT> atividade e seletividade na obtenção de xilenos

Desproporcionamento de tolueno sobre zeólitas tipo mordenita <FONT FACE=Symbol>-</FONT> atividade e seletividade na obtenção de xilenos

Kinetic modeling and study of H-ZSM-5 coated silicon carbide ceramic foam in toluene methylation to produce xylene

Enhancing p -xylene selectivity during m -xylene transformation using mildly pre-coked ZSM-5 catalyst

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