The present invention provides a process for preparing 2,3,3,3-tetrafluoropropene from 1,1,1,2,3-pentachloropropane and/or 1,1,2,2,3-pentachloropropane, comprising the following steps: (a) catalytic reaction of 1,1,1,2,3-pentachloropropane and/or 1,1,2,2,3-pentachloropropane with HF into a reaction mixture comprising HCl, 2-chloro-3,3,3-trifluoropropene, 2,3,3,3-tetrafluoropropene, unreacted HF, and optionally 1,1,1,2,2-pentafluoropropane; (b) separating the reaction mixture into a first stream comprising HCl and 2,3,3,3-tetrafluoropropene and a second stream comprising HF, 2-chloro-3,3,3-trifluoropropene and optionally 1,1,1,2,2-pentafluoropropane; (c) catalytic reaction of the second stream into a reaction mixture comprising 2,3,3,3-tetrafluoropropene, HCl, unreacted 2-chloro-3,3,3-trifluoropropene, unreacted HF and optionally 1,1,1,2,2-pentafluoropropane and (d) feeding the reaction mixture of step (c) directly without separation to step (a).

An azeotropic or quasi-azeotropic composition including hydrogen fluoride, Z-3,3,3-trifluoro-1-chloropropene and one or more (hydro)halocarbon compounds including 1 to 3 carbon atoms. The (hydro) halocarbon compounds are preferably selected among tetrachlorofluoropropanes, trichlorodifluoropropanes, dichlorotrifluoropropanes, chlorotetrafluoropropanes, pentafluoropropanes, dichlorodifluoropropenes, chlorotrifluoropropenes and tetrafluoropropenes. A process for producing a main (hydro)halocarbon compound, including the formation of a mixture of compounds including hydrogen fluoride, Z-3,3,3-trifluoro-1-chloropropene and one or more other (hydro)halocarbon compounds, distillation of this mixture making it possible to collect, firstly, an azeotropic composition, and, secondly, at least one of the compounds of the mixture.

A method for complex treatment of phosphogypsum comprising crushing of phosphogypsum and its washing with a solution of sulphuric acid, concentration 2-15%, and stirring at 50-80 C., wherein the resultant mixture is separated into a liquid fraction and a sediment containing mostly calcium sulphate, which is characterized in that metals are precipitated from the liquid fraction, mainly lanthanides, phosphates and sulphates of metals soluble in diluted sulphuric acid, and the sediment containing mostly calcium sulphate is converted in the presence of ammonia liquor and carbon dioxide to ammonium sulphate and calcium carbonate, wherein filtered and dried sediment of calcium carbonate is dissolved in a 15-30% solution of nitric acid while stirring continuously, and then the resultant CO.sub.2 is recirculated and used in the conversion of the first phase of the sediment, and the resultant mixture is separated into a solution of calcium nitrate with dissolved metals and a sediment of fluorides and silicates with metal precipitate.

The invention relates to a method and a device for producing diluted hydrofluoric acid using an electrode arrangement (1), which has an anode chamber (2) with an anode (4) and a cathode chamber (6) with a cathode (8), which are separated from one another by an anion exchange membrane (10), wherein in the methodpure water is guided through the anode chamber (2), pure water, which includes at least one electrolyte which forms fluoride ions (F), is guided through the cathode chamber (6), and an electrical voltage is applied between the anode (4) and the cathode (8) such that the fluoride ions (F) are moved through the anion exchange membrane (10) into the anode chamber (2), and an electrical current flows.

An azeotropic or quasi-azeotropic composition including hydrogen fluoride, 3,3,3-trifluoro-2-chloropropene and one or more (hydro)halogen-carbon compounds including between 1 and 3 carbon atoms. Also an azeotropic or quasi-azeotropic composition including hydrogen fluoride, 3,3,3-trifluoro-2-chloropropene, and one or more compounds selected from among 1,3,3,3-tetrafluoropropene, 1,1,1,2,2-pentafluoropropane, 2,3,3,3-tetrafluoropropene, 3,3,3-trifluoropropene, E-3,3,3-trifluoro-1-chloropropene, trifluoropropyne, 1,1,3,3-pentafluoropropane, 1,1,1,3,3-pentafluoropropane, 1,1,1,3,3-pentafluoropropene, 1,1,1,2,3-pentafluoropropene and 2-chloro,1,1,1,2-1 tetrafluoropropane.

The present invention relates to a high purity synthetic fluorite (CaF.sub.2). The present invention further relates to a process and an apparatus for preparing said high purity synthetic fluorite (CaF.sub.2), classified as acid grade, starting from fluorosilicic acid H.sub.2SiF.sub.6 (FSA) and calcium carbonate (CaCO.sub.3). Finally, the present invention relates to the use of said high purity synthetic fluorite (CaF.sub.2) in the industrial production of hydrofluoric acid.

A composition is provided including aqueous hydrogen fluoride; and a cross-linked copolymer comprising acrylamide units cross-linked with an acrylic acid salt. The cross-linked polymer has an average liquid aqueous hydrogen fluoride absorption capacity of less than 40 grams aqueous hydrogen fluoride per gram of cross-linked polymer.

An organic binder system is mixed with molding material for sand casting in the metals industry. The organic binder system has three parts, the first two of which are conventional and are used in the cold box or no bake process. The third part, which is combined with the first two parts at the time of use, contains at least an alkyl silicate and, optionally, a bipodal aminosilane. In some embodiments, an amount of hydrofluoric acid is included in one or both of the first two parts. Use of the organic binder system provides improved tensile strength in the mold, especially in high relative humidity.

A method for separating halocarbons and, in particular, a method for separating (Z)-1-chloro-3,3,3-trifluoropropene (HCFO-1233zd(Z), or simply 1233zd(Z)) and 1-chloro-1,3,3,3-tetrafluoropropane (HCFC-244fa, or simply 244fa) via distillation by adding a third component, hydrogen fluoride (HF), forming a binary azeotrope of 1233zd(Z) and HF. The binary 1233zd(Z)/HF azeotrope may then be recovered from the distillation column as an overhead stream which includes only a relatively minor amount of 244fa, while the 244fa may be recovered from the distillation column as a bottoms stream which includes only relatively minor amounts of 1233zd(Z) and HF.

Embodiments of the invention provide a method for atomic layer etching (ALE) of a substrate. According to one embodiment, the method includes providing a substrate, and exposing the substrate to hydrogen fluoride (HF) gas and a boron-containing gas to etch the substrate. According to another embodiment, the method includes providing a substrate containing a metal oxide film, exposing the substrate to HF gas to form a fluorinated surface layer on the metal oxide film, and exposing the substrate to a boron-containing gas to remove the fluorinated surface layer from the metal oxide film. The exposures may be repeated at least once to further etch the metal oxide film.