Possibility to use spent catalyst from fluid catalytic cracking process for geopolymer synthesis

Abstract

Fluid catalytic cracking catalyst residue (spent FCCC) is an inorganic by-product obtained from petrol refineries. It is made up mostly of SiO2 and Al2O3 (about 90 % of its chemical composition) and consists mainly of zeolite (faujasite) and amorphous aluminosilicate matrix. Due to the relatively low quantities of the spent FCCC produced worldwide (~160000 tons per year), landfilling is usually considered as the simplest and the most economical option for its disposal. This work assesses the possibility to use locally produced spent FCCC as starting material for alkali activated materials (geopolymers) synthesis. Geopolymers are class of alkali activated materials that are obtained by alkali activation of an aluminosilicate precursor. The main product of alkali activation reaction is amorphous aluminosilicate gel, “geopolymer” gel. Due to highly interconnected, three-dimensional structure of geopolymer gel, these materials can show high compressive strength and very good durability and can be regarded as an alternative to Portland cement in some applications. Synthesis of geopolymer binder based on spent FCCC was carried out by using sodium silicate solutions with different SiO2/Na2O ratios as alkaline activators. The alkali activation reaction was performed at 65 °C for 24 hours. Structural characterization of the synthesized geopolymer samples showed that alkali activation of the spent FCCC sample led to the conversion of the zeolitic phase (faujasite) to aluminosilicate geopolymer gel. It was found that, when SiO2/Na2O ratio of the activating solution was 1.25 - 1.50, compressive strength of the geopolymer mortars based on spent FCCC was higher than 70 MPa. These results indicated potential to use spent FCCC as precursor for geopolymer production.