Rapid expansion of supercritical solution with solid cosolvent (RESS-SC) process: Formation of 2-aminobenzoic acid nanoparticle

A high solubility in supercritical fluid is desired for performing rapid expansion of supercritical solutions (RESS) to produce particles. Unfortunately, extremely low solubility of polar compounds in supercritical CO2 makes RESS unviable for commercial applications. Liquid cosolvents can improve the solubility, but are unsuitable due to the dissolution of particles in expansion chamber. This work uses a solid cosolvent, menthol, for 2-aminobenzoic acid (ABA) solubilization in CO2. ABA solubility is increased from 57 to 6600 μmol/mol at 236 bar and 50 °C by using menthol-saturated CO2. The other drawback of the conventional RESS process is the size of the particles obtained which is mostly in the micron range, due to growth by agglomeration in expansion chamber. In rapid expansion of supercritical solution with solid cosolvent (RESS-SC) process, solid cosolvent hinders the particle growth resulting in small nanoparticles. For example, RESS-SC process produced ∼80 nm size ABA particles, which is significantly smaller than ∼610 nm size particles obtained from RESS process. Menthol is easily removed from ABA nanoparticles by sublimation (lyophilization). DSC, XRD and SEM analyses are used to characterize the particles.