Auswahl der wissenschaftlichen Literatur zum Thema „Methylchlorosilanes synthesis“

CuCl and Cu are active phases for CH3Cl cracking, a side reaction of the methylchlorosilanes direct synthesis. In the presence of black carbon simulating coke, CuCl is reduced leading to Cu, inactive for the direct synthesis, and chlorinated coke.

Pendant la synthèse de Müller-Rochow, le silicium (Si) et le chlorure de méthyle (CH3Cl) réagissent pour former des méthylchlorosilanes (MCS) en présence d'un précurseur de cuivre et de promoteurs Zn et Sn. Le CH3Cl peut subir des réactions de craquage qui entraînent la formation de composés carbonés (coke) perturbant le fonctionnement des réacteurs industriels, ce qui entraîne une perte de production. L'objectif de cette thèse était d'étudier le craquage du CH3Cl et la formation de coke pendant l'étape d'activation de la synthèse des MCS et de trouver des solutions industrielles pour prévenir la formation de coke. Le chlorure de cuivre, généralement utilisé comme précurseur, peut soit former Cu3Si, actif pour la synthèse des MCS, soit être réduit en Cu, qui s'est révélé inactif pour la synthèse des MCS mais actif pour le craquage du CH3Cl. Dans ce travail, cette réaction secondaire est corrélée avec la formation de Cu(0), qui se produit dès le début de la synthèse des MCS et est favorisée par les promoteurs Zn et Sn. Cependant, il a été démontré que la cinétique de formation de Cu(0) est plus rapide que celle de Cu3Si, même en l'absence de promoteurs. Par conséquent, il est impossible d'éviter la formation de Cu(0) qui pourrait contribuer au craquage du CH3Cl. Une approche pour réduire la formation de coke a été de diminuer l'acidité en ajoutant des métaux alcalins : KCl et CsCl. Cela a donné des résultats favorables : il a été possible de réduire le taux de production de coke en diminuant la quantité de phase cristalline Cu(0) formée. Certaines explications ont été proposées<br>During the Müller-Rochow synthesis, Si and CH3Cl reacts to form methylchlorosilanes (MCS) in presence of a copper precursor, Zn and Sn promoters. CH3Cl can suffer from cracking reactions which results in the formation of carbonaceous compounds (coke) that disturbs the operation of industrial reactors, leading to a production loss. The purpose of this thesis was to study the CH3Cl cracking and the formation of coke during the activation step of the MCS synthesis and to find industrial solutions to prevent coke formation. Copper chloride which is generally used as precursor can either form Cu3Si, active for the MCS synthesis or be reduced into Cu(0) that was found to be inactive for the MCS synthesis but active for the CH3Cl cracking. In this work, this side reaction is correlated with Cu(0) formation which occurs from the beginning of the MCS synthesis and is enhanced by Zn and Sn promoters. However, Cu(0) formation kinetic was shown to be faster than Cu3Si even in the absence of promoters. Therefore, it is impossible to avoid Cu(0) formation which could contribute to CH3Cl cracking. An approach to reduce coke formation was to lower the acidity by adding alkali metals: KCl and CsCl. This provided favorable outcomes: it was possible to lower the coke production rate due to the reduction of the amount of Cu(0) crystalline phase formation. Some explanations were proposed

No presente trabalho foi realizado um estudo de alguns aspectos da reação de obtenção de dimetildiclorosilano a partir da reação entre silícios grau químico (SiGQ) ou de elevada pureza (99,999%) e cloreto de metila catalisada por cobre e promotores em reator de leito fluidizado. Foram estudados os efeitos da temperatura sobre o processo de ativação e sobre a reação com o fim de obter um valor aproximado da energia aparente de ativação para cada uma dessas etapas; o efeito do tamanho médio das partículas de silício e do catalisador sobre os parâmetros de desempenho da reação e o de contaminantes usuais do SiGQ, a saber Ca, Fe e Al, sobre silício de elevada pureza (99,999%). Uma discussão sobre o efeito de compensação característico da reação direta foi realizada sendo proposta uma explicação da origem desse efeito, que aparentemente se deve ao caracter anisotrópico da reação, e uma explicação complementar com relação ao papel dos promotores na reação. Os resultados mostraram que a energia aparente de ativação obtida por meio dos experimentos realizados neste estudo encontram-se em valores próximos ao normalmente encontrado na literatura. Aparentemente existe uma variação da seletividade com a variação do tamanho de partícula tanto do silício quanto do catalisador, que se deve ao grau de cobertura da superfície do silício pelo catalisador. Observou-se ainda que os parâmetros de desempenho se correlacionam melhor com a área geométrica do que com a área específica medida pelo método de adsorsão de N2 (BET). Os elementos Ca, Al e Fe, na forma que foram adicionados, mostraram algum efeito sobre os parâmetros de desempenho da reação, porém verificou-se que o efeito das impurezas é maior se estas estiverem presentes originalmente no silício.<br>Some important aspects of dimethyldichlorosilane direct synthesis from methyl chloride and both chemical grade silicon and high purity silicon (99.999%) catalyzed by copper and promoters in a fluidized bed reactor was studied. The effects of temperature on the activation process and on the reaction were studied to obtain an estimate of the apparent activation energy for each process step. The influence of average particle diameter of silicon and of catalyst and the effect of Ca, Al and Fe additions in the catalyst system were also evaluated. A discussion about the so-called isokinetic compensation behavior which is observed in the direct synthesis is presented. The proposed explanation about the origin of this phenomena is based on the anisotropic character of the reaction. A complementary explanation about the mechanism of promoters action was also proposed. The obtained values of apparent activation energies are within the range reported in the literature. Selectivity and activity showed some variation with both catalyst and silicon particle sizes. This behavior was explained in terms of silicon particle coverage by the catalyst system. The performance parameters show better correlation with the geometric area measured by laser diffraction than with the BET area obtained by N2 adsorption. The promoters Ca, Fe and Al have shown effect over the reaction, however these effects were more proeminent if they are originally present in silicon structure.