Australian Atomic Energy Commission Research Establishment Lucas Heights
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AAEC/E281 oo cs LU \ u LU AUSTRALIAN ATOMIC ENERGY COMMISSION RESEARCH ESTABLISHMENT LUCAS HEIGHTS A REVIEW OF FLUORINE CELLS AND FLUORINE PRODUCTION FACILITIES by R.J. RING D. ROYSTON September 1973 ISBN 0 642 99601 6 ERRATA A REVIEW OF FLUORINE CELLS AND FLUORINE PRODUCTION FACILITIES by R.J. Ring and D. Royston CONTENTS Table 6 ... (After Neumack) should read ... (After Neumark) Table If- ... (After Valkt) should read ... (After Vallet) Figure 23 ... Type USAEC ... should read ... Typical USAEC A REVIEW OF FLUORINE CELLS AND FLUORINE PRODUCTION FACILITIES by R.J. RING D. ROYSTON ABSTRACT The development of laboratory and industrial scale electrolytic cells used for the generation of fluorine is reviewed and the construction and operating characteristics of these cells are examined in detail. In addition, the associated facilities required for the supply and treatment of raw materials, treatment of product gases and disposal of waste materials are described. Safety practices adopted in the design and operation of equipment including personnel protection and first aid procedures are also outlined. CONTENTS Page INTRODUCTION 1 DEVELOPMENT OF LABORATORY FLUORINE CELLS 2 2.1 Low Temperature Cells 2 2.2 High Temperature Cells 3 2.3 Medium Temperature Cells 4 2.4 Other Electrolytes Used in Fluorine Cells 6 DEVELOPMENT OF INDUSTRIAL FLUORINE CELLS 7 3.1 High Temperature Cells 8 3.1.1 General features 8 3.1.2 Anode construction 9 3.1.3 Cathode construction 9 3.1.4 Tank and skirt construction 9 National Library of Australia card number and ISBN 0 642 99601 6 3.2 Medium Temperature Cells 10 3.2.1 General features 10 3.2.2 Anode construction 10 The following descriptors have been selected from the INIS Thesaurus 3.2.3 Cathode construction 18 to describe the subject content of this report for information retrieval purposes. For further details please refer to IAEA-INIS-12 (INIS: Manual for Indexing) 3.2.4 Cell tank construction 19 and IAEA-INIS-13 (INIS: Thesaurus) published in Vienna by the International 3.2.5 Skirt and diaphragm construction 22 Atomic Energy Agency. 3.2.6 Insulation and gasket materials 24 POLARISATION 25 ANODES; BIBLIOGRAPHIES; CARBON; CATHODES; CORROSION; DIRECT 4.1 Anode Polarisation 25 CURRENT; ELECTROLYTIC CELLS; ELECTROLYTES; FLUORINE; HIGH TEMPERATURE; HYDROFLUORIC ACID; IMPURITIES; INDUSTRIAL PLANTS; 4.1.1 Mechanism of fluorine generation 25 LABORATORY EQUIPMENT; LITHIUM FLUORIDES; MEDIUM TEMPERATURE; 4.1.2 Mechanism of anode polarisation 26 NICKEL; NONRADIOACTIVE WASTE DISPOSAL; PRODUCTION; REVIEWS; SAFETY; TEMPERATURE DEPENDENCE 4.1.3 Anode effect 27 4.1.4 Causes of anode polarisation 28 4.1.5 Methods of overcoming anode polarisation in 29 British cells 4.1.6 Methods of overcoming anode polarisation in 30 American cells 4.1.7 The influence of electrolyte purity on anode 34 behaviour 4.2 Cathode Polarisation 36 CONTENTS (Cont'd.) CONTENTS (Cont'd.) Page Table 4 Industrial Cells - Operating Characteristics OPERATING CHARACTERISTICS OF FLUORINE CELLS 37 Table 5 Industrial Cells - Construction Details 5.1 Bipolar Corrosion 37 Table 6 Corrosion of Cathode Materials in KF.HF Electrolyte at 250°C 5.2 Composition and Temperature of Electrolyte 37 (After Neumack 1947) 5.2.1 Corrosion 38 Table 7 Physical Properties of Carbon Anodes (After Karr 1946, Dykstra et. 5.2.2 Misting 38 al 1955 and Huber et al 1958). 5.2.3 Effect on anode polarisation 38 Table 8 Service Lives of Cell Tanks (After Dykstra et al. 1955) 5.3 Circulation of Electrolyte and the Accumulation of Sludge 39 Table 9 The Inter-Relationship between Design Features and Resulting 5.4 Anode to Cathode Separation and the Position of the Skirt 40 Malfunctions in Fluorine Generators (After Finley 1953) 5.5 Current Density 42 Table 10 Voltages Produced by Cathode Polarisation (After Schumb 1946) Table 11 Relationship betwen Air Permeability of Carbons and their Tendency INDUSTRIAL PRODUCTION OF FLUORINE 44 to Polarise (After Rudge 1966, 1971) 6.1 Hydrogen Fluoride Feed Systems 44 Table 12 Supply and Handling of Hydrogen Fluoride 6.1.1 Alarm systems 46 Table 13 Preparation of Electrolyte 6.2 Electrolyte Preparation 47 Table 14 Disposal of Fluorine and Hydrogen Fluoride 6.3 Treatment of Cell Off-gases 47 Table 15 Materials of Construction for Handling Fluorine - Oak Ridge Gaseous 6.4 Cell Handling and Cleaning Facilities 50 Diffusion Plant (After McGuffey et al 1962) 6.5 Storage and Tranportation of Fluorine 52 Table 16 Materials of Construction for handling Hydrofluoric Acid and Fluorine 6.6 Disposal of Fluorine and Hydrogen Fluoride 53 Portsmouth Gaseous Diffusion Plant (After Giffels and Valkt 1956a) 6.6.1 Fluorine disposal 53 Table 17 Recommended Materials for Handling Fluorine - Allied Chemical 55 6.6.2 Hydrogen fluoride disposal Corporation (After Neumark and Siegmund 1966, Siegmund 1967) 57 6.7 Equipment Design Table 18 Resistance of Materials to Hydrofluoric Acid and Hydrogen Fluoride 57 6.7.1 Materials of construction Vapour - Imperial Chemical Industries (After Imperial Chemical 58 6.7.2 Fabrication techniques Industries Ltd. 1971) 6.7.3 Procedures prior to plant operation 59 Table 19 Recommended Materials for Handling Hydrofluoric Acid (HF Content 6.8 Safety Practices and Equipment 60 > 60%) - Stauffer Chemical Co. (After Stauffer Chemical 6.8.1 Ventilation 61 Company 1964) 6.8.2 Protective clothing - handling of hydrogen fluoride 62 Table 20 Corrosion Resistance of Materials to Hydrofluoric Acid - Stauffer 6.8.3 Protective clothing - handling of fluorine 65 Chemical Co. (After Stauffer Chemical Company 1964) 6.8.4 First aid procedures 66 Table 21 Concentrations of Fluorine and Hydrogen Fluoride Allowed in a 7. ACKNOWLEDGEMENT 69 Working Environment (After Siegmund 1967) Table 22 Ventilation Rates - Oak Ridge and Portsmouth Gaseous Diffusion 8. REFERENCES 69 Plants (After Goodyear Atomic Corporation 1967b, Smiley and Brater 1956) Table 1 Early Laboratory Cells Table 2 Melting Points of Metal Fluorides (After Weast 1970) Table 3 Melting Points of Alkali Polyfluorides (°C) CONTENTS (Cont'd.) CONTENTS (Cont'd.) Figure 1 Flow Diagram of a Fluorine Generation Plant Figure 23 Packing Gland ~ Type USAEC Cell (After Huber et al. 1958) Figure 2 Phase Diagram of the Potassium Fluoride-Hydrogen Fluoride System Figure 24 Characteristic Cell Voltage Curves (After Ebel and Montillon (After Cady 1934) 1952) Figure 3 Low Temperature Cell of Moissan (1886) (After Cady et al. 1942) Figure 25 The Influence of Contact Angle (0) on Bubble Shape (After Figure 4 High Temperature Cell of Argo et il. (1919) (After Leech 1956) Rudge 1956) Figure 5 Medium Temperature Cell of Lebeau and Damiens (1925) (After Figure 26 Schematic Sketch of Electrolyte Flow (standard cell) (After Leech 1956) Ebel and Montillon, 1952) Figure 6 Medium Temperature Cell of Cady et al. (1942) (After Cady Figure 27 Improved Circulation and Reduced Electrode Spacing (modified et al. 1942) cell) (After Ebel and Montillon 1952) Figure 7 High Temperature Cell of Johns Hopkins University (After Burford Figure 28 Layout of Fluorine Plant (After Jacobson et al. 1955) et al. 1951). Figure 8 Method of Anode Support - Falkenhagen Cell (After Carter et al.1946), Figure 9 General Assembly of USAEC E-type Cell (After Kelly and Clark 1967a, 1968a) Figure 10 Half Section of USAEC E-type Cell (After Kelly and Clark 1967a, 1968a) Figure li Anode Connection - Leverkusen Cell (After Karr 1946) Figure 12 Anode Connection - USAEC C-type Ceil (After Vavalides et al 1958) Figure 13 Method of Anode Support - Hooker and Du Pont Cells (After Downing 1951a) Figure 14 Anode Connection - USAEC E-type Cell (After Cable et al. 1962). Figure 15 Anode Assembly - USAEC E-type Cell (After Kelly and Clark 1967a, 1968a) Figure 16 Section of the Allied Chemical Corporation Cell (After Neumark and Siegmund, 1966) Figure 17 Cathode Assembly - USAEC E-type Cell (After Kelly and Clark 1967a, 1968a) Figure 18 Tank Construction - Typical USAEC Cell (After Dykstra et al. 1958) Figure 19 Tank Construction - Leverkusen Cell (After Karr 1946) Figure 20 Cell Cover - Typical USAEC Cell (After Dykstra et al. 1958) Figure 21 Cooling System - Leverkusen Cell (After Karr 1946) Figure 22 Diaphragm Assembly - USAEC E-type Cell (After Kelly and Clark 1967a, 1968a) 1. INTRODUCTION Fluorine was named by Ampere in 1812 and isolated by Moissan in 1886 by the electrolysis of anhydrous hydrofluoric acid containing a small concen- tration of potassium fluoride, fluorine being liberated at the anode. 2HF > H2 + F2 The potassium fluoride rendered the covalent hydrogen fluoride conducting and it was this discovery that allowed the isolation of fluorine after many years of effort. Fluorine has been produced industrially for the last 30 years, mainly for the production of uranium hexafluoride in the nuclear industry and for propellants in space rockets. Smaller quantities are used for organic fluorochemicals, sulphur hexafluoride and other inorganic fluorides. This report surveys the development of fluorine cells on both a laboratory and industrial scale, in particular the design, construction and operating features of modern production cells are described in detail. In addition to the electrolytic cell, the production of fluorine requires equipment (see Figure 1) for the storage and vaporisation of hydrogen fluoride, preparation of electrolyte, treatment and compression of the off-gases, and the disposal, in emergencies, of fluorine and hydrofluoric acid. The design and operation of this equipment are also described as well as aspects of protective clothing, safety equipment and first aid procedures for use with fluorine and hydrogen fluoride. 2. DEVELOPMENT OF LABORATORY FLUORINE CELLS operation was not reported. In the period 1936-1942, a number of attempts were Electrolytic cells and associated techniques for the generation of made by ICI (Rudge 1941, 1949a, 1956, 1971) to develop a low temperature cell fluorine were developed on a laboratory scale for many years before increased which operated at room temperature with an electrolyte of KF.8HF.