Effect of the Preparation Method on the Porosity of Amorphous Silica-Alumina to be Used in Hydrocracking Reactions

EFFECT OF THE PREPARATION METHOD ON THE POROSITY OF AMORPHOUS SILICA-ALUMINA TO BE USED IN HYDROCRACKING REACTIONS

Angélica L. Coconubo-Díaz^1A, Alexander Guzmán-Monsalve^2B, Luz M. Ballesteros-Rueda^1C

 

1: Centro de Investigaciones en Catálisis, Escuela de Ingeniería Química, Carrera 27 Calle 9 Universidad Industrial de Santander, Bucaramanga, Santander, Colombia

2: Km 7 Vía Piedecuesta, Instituto Colombiano del Petróleo, Piedecuesta, Santander, Colombia

e-mail: angelica.coconubo@gmail.com ^A, alexander.guzman@ecopetrol.com.co ^B, luzmabal@uis.edu.co ^C 

 

ABSTRACT

Catalyst for heavy oil and vacuum gas oil hydrocracking (HCK) require high pore diameter to treat the bulky molecules present in such kind of feedstocks,  in order to allow the access of large molecules into the active sites of the catalyst, avoiding diffusional limitations [1, 2]. Amorphous AluminoSilicates (ASAs) are widely used as catalyst support in the heavy oil refining industry because of its physico-chemical properties (acidity and large pore size) [1, 3, 4].  On the other hand, several authors have stated that the synthesis methods of ASAs impacts the textural properties such as surface area and pore size [4]. Particulary, in the sol-gel method, the control of the hydrolysis process and condensation is very important to obtain the desired gel [3, 5].

In the present study, bifunctional catalysts consisting of nickel-molybdenum (NiMo) supported on amorphous silica-alumina were prepared using two different sol-gel methods. It is well known that the characteristics of the obtained oxides depend on the sol-gel parameters such as precursor molecules, concentration, solvent type, temperature, amount of water and pH [6, 7]. The sol-gel methods used were: sol-gel using PolyEthylene Glycol (PEG) as an organic template [8], and sol-gel with gel skeletal reinforcement [9]. In the first method the amount of PEG was varied taking into account the amount of silica precursor used which, in this study, was TetraEthyl OrthoSilicate (TEOS); on the other hand, in the second method was varied the amount of TEOS used in the reinforcement solution (RS). In addition, in both methods the calcination were carried out at two different values of temperature, in order to compare its effect in the textural properties of the supports.  The supports (ASAs) and the NiMo catalysts were characterized by means of N₂-physisorption, X-ray diffraction, SEM-spectroscopy, and NH₃-adsorption; in order to determine their chemical and physical properties.

Amorphous silica-alumina prepared by the first method, showed both type of porosities: micro and mesopores, and it was found that surface area and mesoporosity area increased while the amount of PEG added increased as well. On the other hand, ASAs prepared by the second method showed only mesoporosity, meaning that RS helps avoiding the formation of micropores. Additionally, surface area, pore volumen and pore size, increased while increasing the TEOS amount in the RS.  Furthermore, it was found, that the calcination temperature affects the porosity of the material using both methods, since the surface area decreased when the highest calcination temperature was used likely ocurring by sinterization of the material.

Keywords: Hydrocracking, Amorphous Aluminosilicates, Ni-Mo Catalyst, Sol-Gel method, Polyethylene Glycol, Gel Skeletal Reinforcement, Vacuum Gas Oil.

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