J.
R. M C G U F F E Y
RUDOLPH PALUZELLE
W. E . M U L D R E W
HANDLING GASEOUS FLUORINE IN INDUSTRY Presents problems no greater than other reactive or toxic chemicals
f immediate practical interest to anyone making or using elemental fluorine are the design and fabrication of handling equipment, materials of construction, and safe operating procedures. Although commercial production of elemental fluorine for the open market, primarily by General Chemical Division, Allied Chemical Corp., is now only about 1000 tons annually, additional handling equipment refhemenu and reduction of the psychological resistance to fluorine can bwst elemental fluorine use dramatically. The most promising use is in liquid rocket fuels, as an oxidizer. Fluorine in combination, of course, has made outstanding advances in refrigerants, aerosol propellants,
0
PRODUCTION BACKGROUND
Beginning in 1955, l&EC published o series of articles describing various ospects of the MXX)-ompere electrolytic cell developed to produce fluorine ot the Oak Ridge Goseous DiffusionPlant: Multiple Cell Fluorine Plant 47, 878 119551. Improved Medium Temperature Fluorine Cell 47, 883-7 119551. High Capacity long-life Fluorine Cell 50, 178 11958). A 25-Pound per Hour Fluorine Plant 50, 181 119581. An Improved Commercial Fluorine Cell 52,46A (July 19611. In addition to these articles, the Market Report of the Month in May 1961 (p. 23Al discussed fluorine. Another excellent reference, not published in I&EC, but of interest
to readers i s Manufacture of Uronium Hexafluoride, A/Conf. 15-P/52A, 2nd United Nations Conf. Peaceful Uses of Atomic
Energy, U.S.A. 46
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
fluorocarbon resins, and in reactive intermediates for unusual commercial scale organic syntheses. Millions of pounds of elemental fluorine have been produced, distributed, and stored at the Oak Ridge Gaseous Diffusion Plant. During 17 years of industrial experience, not a single disabling or lost-time injury has occurred in handling this highly reactive. elemmt. Damage to facilities and equipment has been limited to minor fires, usually at flanged joints. Extreme precautions were taken in all areas when the original fluorine pilot plant was constructed by Union Carbide at Oak Ridge in 1943. After several yean, less expensive designs and materials were introduced and operating practices in the large plant were modified without relaxing safety or efficiency. The reader interested in production of elemental fluorine at Oak Ridge can follow the development of these facilities in Industrial and Engineering Chemistry over a period of six years. This article will begin with the manufactured fluorine. Design Pmcticos
Rejaration for Use. Fluorine gas, discharged from the electrolytic cell at a pressure of 0 0.072 p.s.i.g., is collected in a common header. The header is oversize to permit collection and removal of electrolyte m i s t which is carried bver by the gas stream from the cells. Remaining electrolyte is then removed by passing the gas through porous Monel tubes in a filter unit. Early experience indicated that flanged joints should be avoided, but later it was found that by using calcium fluorideimpregnated Teflon gaskets, flanges can be safely installed in the low pressure portion of the system. Because a relatively high voltage is applied to the terminal cells in the series arrangement, qlectrically
*
.
insulated flanged joints are needed between the cells and collection header. The fluorine is comprmed from 0 to 2.5 p.s.i.g. in one of two five-stage centrifugal compressors. It contains 10 to 12% by volume of hydrogen fluoride as a contaminant, but this is reduced to 3% in a condenser operated at -110' F. Total fluorine production is measured in a total-flow orifice downstream from this condenser. In this low pressure, ambient temperature portion of the system, carbon steel pipe and fittings and Monei gate valves are used. At pressures below 2.5 p.s.i.g., special precautions such as series valving, valve extensions,or barricades are not required. Prior to use in a direct fluorination proceas, part of the fluorine is piped to a Monel heat exchanger and heated to 600' F. Reaction temperature of the direct fluorinationoperationisabove 1000'F. Then to consume unreacted fluorine, the gas is passed into a second reaction chamber which contains an excess of the material being fluorinated. During last year, the average concentration of fluorine in the vent gas released to the atmosphere has been only 2 p.p.m.
Building Vdilation. The facilities are housed in one building along with numerous other chemical operations, and precautionary techniques are carefully observed so that there is rarely more than 2 p.p.m. of fluorine in the air. Normal air change for industrial environments is provided (6 to 10 changes per hour), but for an emergency one air change per minute is provided. Ventilation blowers discharge to a 68-foot stack, vented high above adjac
