Abstract: To provide a solvent composition capable of removing soils such as dusts and oils attached to the surface of an article made of an acrylic resin or an article coated with an acrylic resin, without damaging it. An azeotrope-like solvent composition comprising from 38 to 41 mass % of (2,2,2-trifluoroethoxy)-1,1,2,2-tetrafluoroethane and from 59 to 62 mass % of perfluorohexane. A mixed solvent composition comprising from 30 to 60 mass % of (2,2,2-trifluoroethoxy)-1,1,2,2-tetrafluoroethane and from 40 to 70 mass % of perfluorohexane.

Abstract: To provide a solvent composition capable of removing soils such as dusts and oils attached to the surface of an article made of an acrylic resin or an article coated with an acrylic resin, without damaging it. An azeotrope-like solvent composition comprising from 38 to 41 mass % of (2,2,2-trifluoroethoxy)-1,1,2,2-tetrafluoroethane and from 59 to 62 mass % of perfluorohexane. A mixed solvent composition comprising from 30 to 60 mass % of (2,2,2-trifluoroethoxy)-1,1,2,2-tetrafluoroethane and from 40 to 70 mass % of perfluorohexane.

Abstract: A process for preparing hydrogen fluoride, which comprises (i) reacting calcium fluoride with sulfuric acid to produce a gypsum and a gas containing hydrogen fluoride, (ii) separating hydrogen fluoride from said gas containing hydrogen fluoride, (iii) absorbing said hydrogen fluoride-separated gas with water to obtain an aqueous solution containing hydrogen fluoride and silicofluoric acid, (iv) reacting calcium carbonate with said aqueous solution to obtain a suspension containing silicic acid and calcium fluoride, (v) adding an alkaline substance to said suspension to make pH at least 8, thereby stabilizing the silicic acid as a colloidal solution, (vi) separating a calcium fluoride solid and the colloidal solution of silicic acid from said suspension, and (vii) recycling the separated calcium fluoride as a starting calcium fluoride.