ABSTRACT
Nanosized zeolite Y is used in various applications from catalysis in petroleum refining to nanofillers in water treatment membranes. Ball milling is a potential and fast technique to decrease the particle size of zeolite Y to the nano range. However, this technique is associated with a significant loss of crystallinity. Therefore, in this study, we investigate the effect of adding biodegradable and recyclable cellulose nanofibrils (CNFs) to zeolite Y in a wet ball milling approach. CNFs are added to shield the zeolite Y particles from harsh milling conditions due to their high surface area, mechanical strength, and water gel-like format. Different zeolite Y to CNFs ratios were studied and compared to optimize the ball milling process. The results showed that the optimal zeolite Y to CNFs ratio is 1:1 to produce a median particle size diameter of 100 nm and crystallinity index of 32%. The size reduction process provided accessibility to the zeolite pores and as a result increased their adsorption capacity. The adsorption capacity of ball-milled particles for methylene blue increased to 29.26 mg/g compared to 10.66 mg/g of the pristine Zeolite. These results demonstrate the potential of using CNF in protecting zeolite Y particles and possibly other micro particles during ball milling.
ABSTRACT
In this work, a hydrocracking catalyst, nano zeolite Y-NiO-WO3 is reshaped into nanofibrous form. This novel composite fiber show good mechanical strength together with a uniform elemental distribution for both the acidic and hydrogenation components as confirmed through scanning transmission electron microscopy. The catalyst is tested for n-heptane hydrocracking in a continuous flow fixed-bed reactor at reaction temperatures of 350 °C and 400 °C with a time on stream of 180 minutes. The fibers produced from nano zeolite-Y show superior performance with a total conversion of 98.81 wt% and 96.8 wt% at 350 °C and 400 °C respectively. In addition, a low amount of coke (0.40 wt% and 1.05 wt% at 350 °C and 400 °C respectively) was formed with the nano zeolite Y fibers. This superior performance is related to the enhanced accessibility due to the nanofiber shape where the non-woven mesh/network of catalytic fibers prevents the agglomeration of the nanoparticles. Agglomeration is a major cause of hindered accessibility of the reactants to the catalyst active sites. The zeolite particle size, and the shape of the fibrous catalyst, together with its mesoporous character (as confirmed through BET analysis) enhances diffusion and improves accessibility for the reactants to react on the catalytic active sites as proven by the high total n-heptane conversions and high hexane and iso hexane selectivity for n-heptane hydrocracking.
