Experimental and Theoretical Study of Diphenoxylate Solubility in Supercritical CO 2

ABSTRACT This study investigated the solubility of diphenoxylate in supercritical CO 2 with and without methanol as a cosolvent (2 and 4 mol%) at pressures of 170–410 bar and temperatures of 308–348 K. In pure supercritical CO 2 , solubility ranged from 0.21 × 10 −4 to 2.25 × 10 −4 , whereas methanol increased solubility to 1.08 × 10 −4 –5.47 × 10 −4 (2 mol%) and 1.42 × 10 −4 –8.06 × 10 −4 (4 mol%). The maximum solubility was obtained at 410 bar and 348 K with 4 mol% methanol, representing a 3.58‐fold enhancement over pure CO 2 . Semiempirical models and the Peng–Robinson equation of state successfully correlated solubility data, with the Garlapati (ii) and Jouyban models providing the best performance for binary and ternary systems, respectively.

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