Avoiding over-cracking reactions in hydrocracking processes by means of desilication treatment of zeolites

DAVID TRUEBA; ROBERTO PALOS; GARCÍA, JUAN RAFAEL; FRANCISCO J. VELA; JAVIER EREÑA; ALAZNE GUTIÉRREZ

Milán

Simposio; 11th International Symposium on Catalysis in Multiphase Reactors & 10th International Symposium on Multifunctional Reactors; 2021

AIDIC-The Italian Association of Chemical Engineering

The utilization of zeolites as support for noble metals-based catalysts in hydrocracking is well known. However, these catalysts can lead to an overcracking of the feed [1], which results in a decrease of the yields of the lumps of interest, i.e., naphtha and diesel.A decrease on temperature or pressure can affect not only the cracking capacity of the system, but also the yields of naphtha and diesel, thus being a need of finding out an alternative way to reduce the over-cracking without reducing those yields. In this context, a modification of the catalysts employed appears as a feasible option. As the metal function of the catalyst promotes the hydrogenation function, modifying the support is a better path, which has been already tested by desilication in a process different to hydrocracking [2], observing a decrease on total acidity and a modification of the mesoporous structure. This procedure consists on immersing the zeolite in a NaOH aqueous solution 0.1 M, stirring at 25 ºC during 15 min. Then the suspensions are neutralized with HCl, exchanged with NH4Cl solutions and finally washed with deionized water, dried at 110 ºC during 16 h and calcined at 550 ºC for 4 h.The selection of n-hexadecane (n-C16) as a model compound of hydrocracking processes has some specific reasons: on one side, the products of its conversion are quite relatable to those obtained in the hydrocracking of vacuum gasoil; and on the other side, the application of a primary and secondary cracking analysis (PASCA) to n-C16 hydrocracking has been previously assessed [3]. This analysis is based on the idea that primary cracking leads to equal amounts of the products, while secondary cracking (that of primary cracking products) would result in larger amounts of compounds with less carbon atoms due to the cracking of the compounds with more carbon atoms. The ratio between the extension of primary and secondary cracking (mol of product molecules cracked with respect to the reactive molecules cracked, ASC/APC) can be applied to measure the overcracking of the model compound. This parameter is an effective index to quantify the over-cracking, as values over 0 indicate that the average number of carbon atoms is lower than 8, and values below zero are related to a higher number of carbon atoms in the products. Therefore, a decrease on this index is expected in the search of a minimization of the n-C16 over-cracking.