High purity is a near-universal requirement throughout the specialty chemicals industry, essential for many of the applications we take for granted in our daily life. The purification process is often a significant portion of the manufacturing cost for many specialty chemicals, including organic semiconductors and pharmaceuticals. Reducing this manufacturing cost is a key step in the effort to efficiently produce the necessary materials for our modern world. This dissertation examines two key purification processes, thermal gradient sublimation and crystallization, in order to offer potential routes for process improvement. Thermal gradient sublimation is examined through the lens of organic semiconductors, which are often purified using this technique at the industrial scale. Interestingly, the sublimation process is limited by vapor phase transport and deposition, not solid phase mechanisms. A model for this process is developed, suggesting potential routes to efficient scale-up and separation improvements. This dissertation also proposes a new method for crystallization control, pressure-swing. In this approach, rapid changes in pressure are used to control solubility during the crystallization process. A model describing the changes in solubility due to these pressure changes is developed, and several process validation experiments are performed using pharmaceutical molecules as model systems. While these tests show an enhanced control of solubility, attempts to replicate experimental results obtained using traditional crystallization control are only partially successful when using the pressure-swing technique.