Value Addition of Spent Catalyst

Abstract

Catalysis is one of the 12 principles of the green chemistry in which catalyst is used to change the rate of chemical reaction and a ect the reaction environment favorably. But the catalyst activity may decrease to very low levels and further regeneration may not be economically feasible. Hence the spent catalysts are eventually discarded as solid wastes. Present study is aimed at exploring an e ective method to utilize exhausted petroleum catalyst discarded in large volume from petroleum re ning industries. Silica and alu- mina are the major components of selected spent catalyst. Considering the quality and quantity of the available exhausted catalyst, an attempt to use this as raw mate- rial for synthesis of zeolite is explored. Also, its probable application as support for making heterogeneous catalyst is explored. Conversion of spent catalyst into NaA(4A) zeolite was carried out by hydrother- mal synthesis comprising of two primary steps: i) Extraction of silica followed by gel formation and ii) Hydrothermal synthesis at elevated temperature and time. Ex- traction of silica was studied under di erent conditions like use of spent catalyst i) with and without grinding and ii) varying parameters like gel conditions like ageing and stirring and iii)parameters like time and temperature of hydrothermal synthesis. Synthesized samples were characterized using various techniques like ICP-OES, X-ray di raction, FTIR for composition of material, identi cation of crystalline phases and crystallinity, formation of zeolites, respectively. Water adsorption property of selected samples showed lower adsorption compared to reference samples. This was due to the impurity phases present in the sample con rmed from XRD data. Ion exchange properties of synthesized 4A were also evaluated for the removal of heavy metals like cadmium (Cd), copper (Cu) and lead (Pb) from water under static conditions. Suitability of spent catalyst as a support for making zincoxide and indiumoxide cat- alyst was studied and their catalytic performance for liquid phase benzylation was evaluated. Around 93% crystallinity is obtained for 4A synthesized with ground spent cata- lyst and the lowering in crystallinity is attributed to the unconverted spent catalyst. Substantial calcium exchange capacity was observed (5.14 meqCaCO3/g)indicating its possible use in detergent applications. Ion exchange capacity of synthesized 4A for the removal of heavy metals like cadmium (Cd), copper (Cu) and lead (Pb) from water was found to be quite efficient.The binding property of the spent catalyst to use it as support in heterogeneous catalyst was found to be poor which needs to be improved.