Patent ID: 6433221
Filing Date: 2002-08-13
Classification: C07C,Y02P

Abstract:
A method of treating a reaction mixture produced by direct oxidation of cyclohexane to adipic acid, the reaction mixture comprising cyclohexane, adipic acid, a monobasic acid solvent having only primary and/or secondary hydrogen atoms, optionally water, and a metal ion catalyst, the method being characterized by steps of:(a) removing greater than 95% of the cyclohexane; (b) removing a major part of the adipic acid; (c) removing greater than 95% of the monobasic acid solvent by distillation, during which a protic solvent is added continuously or intermittently to provide a first single liquid phase, the first single liquid phase being homogeneous and solids-free, the protic solvent containing no carboxylic or mineral acid groups and having a normalized solvent polarity parameter EN in the range of 0.9 to 1.0; (d) adding to the first single liquid phase, a dipolar aprotic solvent and, if needed, additional protic solvent, in such quantities so as to provide a second single liquid phase that is homogeneous and solids-free at a desired first temperature, the dipolar aprotic solvent having a normalized solvent polarity parameter EN in the range of 0.2 to 0.4; (e) causing formation of two liquid phases, a solids-free protic liquid phase containing greater than 95% of the metal ion catalyst, and a solids-free aprotic liquid phase containing at least the majority of products and by-products of the reaction mixture by a process selected from a group consisting of lowering the first temperature to a second temperature, adding additional protic solvent, adding an apolar aprotic solvent having a EN value in the range of 0.0 to 0. 1, and a combination thereof; and (f) separating the solids-free protic liquid phase containing the catalyst from the solids-free aprotic liquid phase; wherein EN is defined by equation (1) EN=ET&af;(solvent)-ET&af;(TMS)ET&af;(water)-ET&af;(TMS)=ET&af;(solvent)-30.732.4(1)using water and tetramethylsilane as extreme reference solvents, such that ET (solvent) is the ET value corresponding to the solvent under consideration, ET (TMS) is the ET value corresponding to tetramethylsilane, and ET (water) is the ET value corresponding to water, and wherein ET is defined by equation (2) ET/(kcalÂ·molâˆ’1)=hÂ·cÂ·vÂ·NA=2.859Ã—10âˆ’3Â·v/cmâˆ’1â€ƒâ€ƒ(2) in which v is the wavenumber (cmâˆ’1) of the photon which produces the electronic excitation, h is Plank's constant, c is the velocity of light, and NA is Avogadro's Number, ET being based either directly on the transition energy for the longest wavelength solvatochromic absorption band of pyridinium-N-phenoxide betaine dye in the solvent under consideration, or indirectly by the use of the more lipophilic penta-tert-butyl-substituted pyridinium-N-phenoxide betaine dye in the solvent under consideration.