Distillation Separation of Hydrofluoric Acid using Salt Effect on Vapor–Liquid Equilibrium of Acid Mixture of Nitric Acid+Hydrofluoric Acid+Water system

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  • Yamamoto Hideki
    Department of Chemical Engineering, Faculty of Engineering, Kansai University
  • Yoneda Yuji
    Department of Chemical Engineering, Faculty of Engineering, Kansai University
  • Ono Tomohiro
    Department of Chemical Engineering, Faculty of Engineering, Kansai University
  • Hirano Masato
    Department of Chemical Engineering, Faculty of Engineering, Kansai University
  • Maeda Ryohei
    Department of Chemical Engineering, Faculty of Engineering, Kansai University

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  • 塩効果を利用したフッ酸–硝酸系混酸廃液からのフッ酸の蒸留分離
  • エン コウカ オ リヨウシタ フッサン ショウサンケイ コンサン ハイエキ カラノ フッサン ノ ジョウリュウ ブンリ
  • Distillation Separation of Hydrofluoric Acid using Salt Effect on Vapor–Liquid Equilibrium of Acid Mixture of Nitric Acid+Hydrofluoric Acid+Water system

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In the semiconductor manufacturing process, mixtures of hydrofruoric acid, nitric acid and other acids are often used as washing or etching solutions for silicon wafers. In our previous paper, the salt effect on vapor-liquid equilibrium of nitric acid-water systems was measured, and a distillation method for separation of nitric acid from acid mixture was been presented.<br>This study presents the distillation treatment of hydrofluoric acid with use of the salt effect on the vapor-liquid equilibrium for acid aqueous solutions and acid mixtures. The vapor–liquid equilibrium of hydrofluoric acid-salt systems (fluorite, potassium nitrate, cesium nitrate) was measured using apparatus made of PFE (perfluoro alkyl vinyl ether). Cesium nitrate showed a salting-out effect on the vapor–liquid equilibrium of the hydrofluoric acid-water system. Fluorite and potassium nitrate showed a salting-in effect on the hydrofluoric acid-water system. Separation of hydrofluoric acid from an acid mixture containing nitric acid and hydrofluoric acid was tested by the simple distillation treatment using the salt effect of cesium nitrate (45 wt%). Acid mixture of nitric acid (5.0 mol/dm3) and hydrofluoric acid (5.0 mol/dm3) was prepared as sample solution for distillation test. The concentration of nitric acid in the first distillate decreased from 5.0 mol/dm3 to 1.13 mol/dm3, and the concentration of hydrofluoric acid increased to 5.41 mol/dm3. This first distillate was further distilled without addition of salt. The concentrations of hydrofluoric acid and nitric acid in the second distillate were 7.21 mol/dm3 and 0.46 mol/dm3, respectively. It was thus found that the salt effect on vapor–liquid equilibrium of acid mixtures was effective for the recycling of acids from acid mixture wastes.

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