Modified Retrograde Crystallization Process for Separation of Binary Solid Mixtures Exploiting the Crossover Region of Supercritical Carbon Dioxide

Abstract

A modified retrograde crystallization process with the circulation of supercritical carbon dioxide has been designed and tested for the separation of a mixture containing two solids. The apparatus consists of an extractor and a crystallizer, which are kept at different temperatures but at a fixed pressure within the crossover region. The metastable zone within the crossover region of the ternary system is first determined. Separation experiments are then conducted under various conditions with the crystallizer temperatures within or slightly above the metastable zone. The benzoic acid/1,10-decanediol/CO 2 system with a wide crossover region represents an ideal example of the modified process, and the results show that it is possible to obtain essentially pure products of both components (>97 wt %) from a 50/50 wt % mixture of benzoic acid and 1,10-decanediol. The average recovery is 49.3% for benzoic acid and 85.8% for 1,10-decanediol. The other system of 2,3-/2,6-dimethylnaphthalene/CO 2 with a narrow crossover region is then analyzed to demonstrate the possibility for the separation of organic isomers, and the results show that the modified process can produce the 2,6-dimethylnaphthalene of almost 100 wt % purity with a recovery of 37.1% starting from a mixture of 50/50 wt % isomers.

Two New Thermodynamic Constraints for a Solid/Supercritical Fluid System

“…In addition, it is useful for the evaluation of the efficiency of the retrograde crystallization process in a multi-component mixture because wider ranges of the crossover regions result in more efficient processes [1,3,6,8] and vice-versa. One such example is the separation of solid isomers from SCFs, where the retrograde crystallization process is not efficient and non-selective since the crossover pressures of the constituent binaries are very close to each other, which results in a narrow crossover region.…”

“…This phenomenon and its significance in separation technology have been explored by Chimowitz and Pennisi [4]. Schaeffer et al [5], Johnston et al [6], Kelly and Chimowitz [7] and Tai et al [8]. Esmaeilzadeh, and Goodarznia [9] also undertook some experimental research on this region.…”

A Mathematically Simplified Solid–Solid–Liquid Ternary Phase Diagram with Tie-Lines for Early Process Development Validated by Chiral Resolution of Racemic Ibuprofen

“…Single solvents such as ethanol and ethyl acetate (EA), and the positive azeotrope of ethanol-EA were used for this research. The positive azeotrope was included because it comprises simple organic solvents, and it is easily recyclable by simple distillation owing to its lower boiling point than any one of each of its solvent component. , Ionic liquids and deep eutectic solvents were not being considered due to the requirement of solvent swapping by water or other solvents for drying. , Using supercritical fluid as the solvent medium was also out of the scope of this research since the solvent phase can only be removed by depressurization instead of filtration. , Liquid–liquid phase separation (LLPS) occurring within the solid–solid–liquid ternary phase diagram for any particular system is not under our consideration as well …”

“…13,14 Using supercritical fluid as the solvent medium was also out of the scope of this research since the solvent phase can only be removed by depressurization instead of filtration. 15,16 Liquid− liquid phase separation (LLPS) occurring within the solid− solid−liquid ternary phase diagram for any particular system is not under our consideration as well. 17…”