Enhanced regeneration of spent FCC catalyst by using oxalic acid-sulfuric acid mixture under ultrasonic irradiation

Abstract

An effective method comprising the immersion in dilute sulfuric acid and the leaching in a mixture of sulfuric acid and oxalic acid under ultrasonic irradiation is provided to improve the removal effect of harmful metals in spent FCC catalyst without destroying the zeolite Y framework and the microstructure of spent catalyst particle. The influence of different experimental conditions on the regeneration effect of spent catalyst is studied by using SEM, EPMA-EDX, XRD, ICP, N2 adsorption, and particle size analysis techniques. The experimental results show that immersion in sulfuric acid can effectively restore blocked pores and increase the specific surface area of spent catalyst by 51.7% compared with the untreated spent catalyst, which is beneficial to the subsequent acid leaching. After leaching in a mixture of 0.5 mol/L oxalic acid and 2 wt.% sulfuric acid for 30 min at 70 °C with an ultrasonic power of 250 W, the regenerated catalyst with complete particle structure and zeolite Y framework is obtained with the removing rates of Fe, V, and Ni being 36.2, 43.8 and 30.1%, respectively, whereas Al loss is only 7.9%. Compared with conventional leaching, ultrasonic assisted leaching only needs 1/4 of the time to achieve much the same harmful metal removal effect and has superior advantages in retaining the integrity of particles.