59. Thakur, Ranjit; Gupta, Ram B., Rapid expansion of supercritical solution with solid cosolvent (RESS-SC) process: Formation of 2-aminobenzoic acid nanoparticle, Journal of Supercritical Fluids (2006), 37, 307-315.

Abstract

A high soly. in supercrit. fluid is desired for performing rapid expansion of supercrit. solns. (RESS) to produce particles. Unfortunately, extremely low soly. of polar compds. in supercrit. CO2 makes RESS unviable for com. applications. Liq. cosolvents can improve the soly., but are unsuitable due to the dissoln. of particles in expansion chamber. This work uses a solid cosolvent, menthol, for 2-aminobenzoic acid (ABA) solubilization in CO2. ABA soly. is increased from 57-6600 mmol/mol at 236 bar and 50° by using menthol-satd. 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 supercrit. soln. with solid cosolvent (RESS-SC) process, solid cosolvent hinders the particle growth resulting in small nanoparticles. For example, RESS-SC process produced .apprx.80 nm size ABA particles, which is significantly smaller than .apprx.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.

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