|Full Name||:||Teguh Kurniawan|
|Thesis Title||:||Cost-effective Catalyst Derived from Natural Zeolites through Ball Milling and Recrystallization Method for Hydrocarbon Conversion|
|Major Field||:||Chemical Engineering|
|Date of Degree||:||December 2017|
Natural zeolites are plentiful and inexpensive natural minerals, which have had wide applications in agriculture, aquaculture, soil adjustment, building materials, water purification, and wastewater treatment. However, the utilization of natural zeolites for catalysis purposes is limited due to low crystallinity and poor textural properties. In the present work, we investigate methods to synthesize catalysts from low-cost natural zeolites through facile methods, i.e. sequential milling-recrystallization, and sequential milling-recrystallization-dealumination. These catalysts were used in dimethyl ether to olefins conversion and n-butane isomerization.
We fabricated hierarchical mordenite nanoparticles from the low-cost natural mordenite through high-energy ball milling followed by hydrothermal recrystallization method. The as-received natural zeolites showed mordenite with impurity phases and low total surface area (ca. 133 m2/g) as indicated by X-ray diffraction study and nitrogen physisorption analysis, respectively. The as-received natural zeolites were milled by high-energy ball milling attritor to obtain nanoparticles within the size of 20-160 nm, which were confirmed by dynamic light scattering, field emission scanning electron microscopy, and transmission electron microscopy technique. The X-ray diffraction study revealed that crystallinity of the milled zeolites had decreased significantly. The crystallinity of mordenite nanoparticles was recovered after recrystallization of the milled sample in the hydrothermal basic silicate solution. The nitrogen physisorption study showed that the textural properties of recrystallized mordenite nanoparticles were improved with total surface area was ca. 240 m2/g and external surface area was ca. 150 m2/g, a 6-fold increase from the parent. The hierarchical pore system was observed in the recrystallized mordenite as the mesopore volume increased to 0.36 mL/g from only 0.04 mL/g in the as-received natural zeolites.
A high conversion of dimethyl ether was obtained over the recrystallized mordenite (99.7%) and milled natural mordenite (54.1%) as compared to the parent (1.2%). Moreover, the milling only and the sequential milling-recrystallization processes improved selectivity toward olefins and prolonged catalyst lifetime. The reduced particles size combined with the hierarchical porosity and acidity effectively enhanced catalysts activity and selectivity to olefins. The samples were further tested for n-butane isomerization. The isobutane selectivity over nanoparticles mordenite fabricated by the sequential milling-recrystallization increased to 28% as compared to 11% on the parent mordenite. Moreover, the recrystallized mordenite nanoparticles showed better catalyst stability as compared to the microparticles parent sample. Finally, dealumination procedures were applied to the recrystallized mordenite nanoparticles. The total surface area of dealuminated nanoparticle sample increased to ca. 354 m2/g. The nanoparticles mordenite obtained by the sequential milling-recrystallization-dealumination exhibited the highest selectivity of ca. 58% to isobutane and less deactivation rate in the n-butane isomerization.