Patent Publication Number: US-3876754-A

Title: Preparation of chlorine pentafluoride

Description:
United States Patent H91 Pursley l l PREPARATION OF CHLORINF.  
 PENTAFLUORIDE [75l Inventor: John A. Parsley. Northridge. Calif.  
 [73] Assignee: North American Rockwell Corporation [22] Filed: June 9. I964 I&#39;ll] Appl. No.: 374.886  
 [52l U.S. Cl 423/466; l49/l [51] Int. Cl. (01h 7/24: C(llb 9/08 I58] Field of Search 33/205; 423/466 5m References Cited UNITED STATES PATENTS 2982.620 5/l96l Beattie et al 23/205 3.134.633 5/1964 Lawton et al 23/205 X OTHER PUBLICATIONS Stacey et al.. Advances in Fluorine Chemistry. Vol. 4. Butterworths lne.. Washington, DC. 1965. pp. 240 to 242. Smith, Science, Vol. l4], pp. I039 to I040 (Sept. 11. I963).  
 Prinmry klruminer- Leland A. Sebastian Attorney. Agent, or FirmRobert M. Sperry 145i Apr. 8, 1975 EXEMPLARY CLAIM l. A process for producing chlorine pentafluoride comprising the steps of continuously passing fluorine as one reactant and at least one member of the group consisting of chlorine. chlorine monofluoride and chlorine trifluoride as another reactant into a reaction chamber adjacent the lower end of the chamber. maintaining the temperature and pressure in the reac tion chamber sufficiently high to effect reaction between said reactants to form gaseous chlorine pentafluoride in a mixture with gaseous fluorine; continu ously passing said mixture from the reaction chamber at a place adjacent the upper end of the chamber into a condensing chamber at a place adjacent the upper end of the condensing chamber; maintaining the temperature in said condensing chamber sulficiently low to effect condensation of chlorine pentafluoride from said mixture; withdrawing condensed chlorine pentafluoride from said condensing chamber. and continuously recirculating the uncondensed gas from the condensing chamber at a place remote from the upper end of the condensing chamber to said reaction chamber at a place adjacent the lower end of the reaction chamber.  
 5 Claims, 1 Drawing Figure PATENTEDAPR&#39; 81975 3 6 U 5 m 8 5 v.2: 4 w o mom: m 2 I 2 w J 6 3 O 6 6 6 6 m J 3 J u $565 a? m 625% 3 ATTORNEY PREPARATION OF CHLORINE PENTAFLUORIDE This invention relates to process and apparatus of industrial plant size for production ofchlorine pentafluoride (ClF,-.) by reaction of fluorine with at least one member of the group consisting of chlorine. chlorine monofluoride (ClF) and chlorine trifluoride (ClF This invention is an improvement on the invention which is disclosed in patent application. Ser. No. 3l3.4l0, filed Sept. 30. 1963 now U.S. Pat. No. 3.756.780, by Donald Pilipovich et al.. for the synthesis of chlorine pentafluoride As mentioned in that patent application. chlorine pentafluoride is an extremely high energy oxidizer ofgreater oxidizing potential than chlorine trifluoride which finds utility as an oxidizer for rocket propellant fuels. The boiling point of chlorine pentafluoride is about -l4C.  
  The fluorine and the chlorine-fluorides for the chemical reactions of this invention are highly reactive with all organic compounds and with many inorganic compounds including glass and water with which they are violently reactive. Stainless steel is resistant to reaction with the fluorine and chlorine-fluoride chemicals involved in the process of this invention; however. items of plant equipment having moving parts and employing lubricants and elastomer seals are objectionable.  
  it is a general object of this invention to provide process and apparatus for continuous type production of chlorine pentafluoride. operable at high pressures without mechanical compression.  
  The apparatus of this invention includes a reaction chamber and a condensing chamber. the chambers being inter-connected at their upper ends for flow of gas from the reaction chamber to the condensing chamber with the pressures in the chambers being substantially the same. Fluorine as one reactant and chlorine and (or) chlorine fluoride as another reactant are continuously passed into the lower end of the reaction chamber. The temperature and pressure in the reaction chamber are maintained sufficiently high to effect formation of chlorine pentafluoride as a gas. The gaseous mixture in the reaction chamber. which comprises fluorine and chlorine pentafluoride. passes to the condensing chamber. The temperature in the condensing chamber is maintained sufficiently low to effect condensation of the chlorine pentafluoride from the mixture. The condensed chlorine pentafluoride settles to the bottom of the condensing chamber from where it is withdrawn. The uncondensed gas (primarily fluorine) is continuously recycled from the condensing chamber to the lower end of the reaction chamber. There is no significant pressure drop from one chamber to the other.  
  The motion of gases in the cyclical system of this invention. i.e., upward in the reaction chamber and downward in the condensing chamber, occurs through convection as a result of the differences of density of the gases in the respective chambers and the action of gravity. In the process of this invention. such convection is thermally produced. For the gases to ascend in the reaction chamber and descend in the condensing chamber, the static head of gas in the reaction chamber is less than that of the gas in the condensing chamber. In the case where the chambers are of the same height. to induce convection it is needed only that the average density in the reaction chamber exceed that in the condensing chamber. This is accomplished in the system of this invention by maintaining the temperature in the condensing chamber low enough to condense the fluorides and by maintaining the temperature in the reaction chamber high enough to effect reaction.  
  The chemical reactions involved in this invention are represented by the following equations:  
  As is explained in the aforementioned patent application. Ser. No. 313.410. an increase in pressure will cause an increase in yield of chlorine pentafluoride for each of the above equations. whereby pressures of 20.000 psi. for example. would result in a more facile production ofchlorine pentafluoride than L000 psi. for example. From an economical standpoint. it is desir able to employ conventional equipment rather than special heavy duty equipment. Balancing the factor of cost of equipment for a small plant against increase in yield due to increase in pressures. equipment designed to handle reactions occurring up to about 2.000 psi provides satisfactory results. A practical minimum for plant production is a pressure of about 500 psi.  
  As is set forth in the aforesaid patent application. complete fluorination of chlorine and (or) chlorinefluorides to form chlorine pentafluoride is accomplished by heating the fluorine and the chlorine&#39; containing reactant to a temperature of from about 100 to 400C (preferably from 100 to 280C) and by compressing the reactants to at least about l00 psi. preferably to at least 330 psi. At temperatures significantly above about 400C severe corrosion of the reaction vessels. (e.g.. stainless steel. Monel metal) occurs and the passive fluoride films on the reaction vessels and flow lines either decompose or volatilize to present fresh metal for corrosion.  
  The yield of the pentafluoride. based on the chlorine or chlorine-containing reactants is increased by using an excess of fluorine. When the reactants are fluorine and chlorine. the mono. tri. and penta fluorides are formed; when the reactants are fluorine and the monofluoride. the tri and the penta fluorides are formed. and when the reactants are fluorine and the trifluoride. the pentafluoride is formed. The use of about twice the stoichiometric quantity of fluorine for full fluorination to the pentafluoride provides improved yields; but if the excess of fluorine be substantially increased then the reaction time decreases because of increased volume and consequent flow rate through the reactor, wherefore the yield decreases.  
  lnert gases. e.g.. nitrogen and helium, do not affect the qualitative aspects of the reactions of this inven&#39; tion; however. inasmuch as the process of this invention is cyclical and continuous. inert gases should be avoided. otherwise they would accumulate in the system and thereby substantially decrease the concentra tions of the reactants. Purging of such noncondensible inerts may be effected through a vent at in line 75.  
  Impurity traces of water or other oxygen containing compounds in the reactants cause formation of FClO C10 and FClO as contaminants. Impurities of organic compounds result in fluorinated carbon compounds which would require periodic removal from the system.  
  The invention is hereinafter illustrated by description with reference to the accompanying drawing. the single FIGURE of which is a schematic representation of a pilot plant for continuous cyclical flow operations involving chemical reactions of fluorine and chlorine to produce chlorine pentafluoride.  
  ln the drawing. reference numerals l and 12 designate a reaction chamber and a condensing chamber. respectively. arranged side by side. The reaction chamber H) is defined by a tall cylinder [4 encircled by a full-length jacket l5. Adjacent its lower end. the cylinder [2 has an inlet 16 for admitting the reactants. gase ous fluorine and gaseous chlorine. and for admitting recycled uncondensed gas from the condensing chamber. Adjacent its upper end. cylinder 12 has an outlet [8 for flow of the product mixture from the reaction chamber. the mixture usually consisting essentially of fluorine. chlorine. trifluoridc and chlorine pentafluoride.  
  The jacket 15 serves to maintain the temperature in the reaction chamber sufficiently high. correlative to the pressure in the chamber. to effect reaction between the chlorine and the fluorine to form chlorine pentafluoride. The chemical reactions which occur in the retro tion chamber are exothermic. For a reaction chamber of relatively large size the jacket l5 is designed to remove heat from the chamber. For the illustrated pilot plant the jacket [5 is designed to permit operation at various temperatures. More particularly. the jacket [5 contains a heat-transfer fluid. cg. dowtherm. An immersion heater Z0 is positioned in the lower end portion of the jacket. and a water-cooled reflux condenser 21 is connected to the upper end of the jacket casing. For maintaining a predetermined temperature. the jacket is pressurized with an inert gas. e.g.. nitrogen. to develop aa pressure in the jacket at which the boiling point of the heat-transfer fluid will be about equal to the temperature at which it is desired that the reaction chamber be maintained. If for the case of a small plant having a reaction chamber of relatively large radiating surface area per unit volume. it may be necessary to continually add heat through energizing the heater 20. The condenser 21 serves to counteract the effect of too high a rate of heat addition by refluxing the vapor of the heat-transfer fluid.  
  The condensing chamber 12 is defined by a tall cylinder 23 encircled by a full-length jacket 24. The cylinder 23 has an inlet 25 adjacent its upperend. A flow line 26 connects the inlet 25 to the outlet [8 of the reaction chamber and thereby effects transfer of the gaseous product mixture from the reaction chamber to the condensing chamber. The jacket 24 serves to maintain the temperature in the condensing chamber sufficiently low. correlative to the pressure in the chamber. to condense the fluorides from the gaseous product mixture. The uncondensed gas (primarily fluorine) is withdrawn from the condensing Cham her by way of tube 28. Such fluorine outlet tube 28 has an open end 29 remote from the upper end of the condensing chamber and the tube extends upwardly from the lower end wall of the cylinder 23. A baffle 30 is spaced slightly above the opening 29 of the fluorine outlet tube 28 to deflect condensate from entering the tube. The condensed fluorides pass from the condensing chamber via flow line 32 having a valve 33 and leading to a storage tank 34 from where the fluorides may be passed to a fractionation system (not shown) for separating the pentafluoride from the 4 trifluoride. In a large scale plant the trifluoride is returned to the reaction chamber.  
  The jacket 24 for the illustrated pilot plant is provided with a conventional refrigerative system permitting use of various temperatures. A tank 37 containing a suitable heat-transfer fluid. e.g.. trichloroethylene. is connected by flow lines 38 and 39 to the jacket 24, and a pump 40 recirculates the heat-transfer fluid through the jacket 24 and the tank 37. For cooling the heattransfer fluid. there is a cylinder 42 of liquid nitrogen connected by flow line 43 to a coiled tube 44 in the tank 37. the coiled tube 44 being vented at its downstream end 45. A thermostatic valve 46 controls the amount of nitrogen which is passed through the coiled tube 44. For operating pressures in the reaction and condensing chambers of the order of about 4.000 psi. the condensing chamber may be designed for mere atmospheric cooling.  
  For supplying pressurized fluorine gas to the reaction chamber. the illustrated pilot plant includes a simple system having no pumps nor compressors. From a commercial cylinder of fluorine gas at 49 the gas passes by a line 50. equipped with a valve 5|. to a condenser 53 which includes a Dewar flask 54 adapted to contain liquid nitrogen. When practically all of the fluorine gas from the cylinder 49 is condensed into the condenser 53. the valve 5| is closed. The liquid nitrogen is then removed from the Dewar flask 54 allowing the condensed fluorine in the condenser 53 to warm to atmospheric temperature for transfer to a surge tank 56 via flow line 57 which is controlled by a valve 58. By Continually transferring fluorine from the condenser 53 to the surge tank. the pressure in the surge tank is maintained greater than that at which it has been elected to conduct the chemical reactions in the reaction chamber 10. From the surge tank 56 the pressurized fluorine gas passes through line 60, containing a constant pres sure-regulating valve 61, to a flow line 63 which is connected at its downstream end to the inlet 16 of the reaction chamber 10.  
  For supplying the chlorine constituent for the chlorine pentafluoride to be produced. the illustrated pilot plant uses chlorine from a commercial cylinder 66. A positive displacement pump 67 in a flow line 68 delivers liquid chlorine at a predetermined flow rate from the cylinder 66 to a tube 70 having a restrictor 7! between its ends. A heater 72 at the upstream side of the restrictor serves to vaporize the chlorine in the tube 70. Just downstream of the restrictor. the tube 70 has an inlet 74 to which a flow line 75 is connected for admitting uncondensed gas (primarily fluorine) from the exhaust tube 28 in the condensing chamber 12. A throttle valve 76 in a flow line 75 controls the rate of fluorine gas which is continuously recycled from the condensing chamber to the reaction chamber. The fluorine being recycled reacts with the chlorine gas in the tube 70 forming chlorine monofluoride and chlorine trifluoride. Inasmuch as the fluorinations which occur in the tube 70 are exothermic. there is a water jacket 78 around the downstream end portion of the tube 70 to permit control of the temperature of the contents of the tube which pass via line 79 to the inlet line 63 for the reaction chamber.  
  The use of reaction tube 70 and the pre-reaction of chlorine and fluorine to form chlorine monofluorine and chlorine trifluoride in reaction tube 70 is the discovery of Frederick D. Raniere and Curtis A. Younts and is disclosed and claimed in copending application Ser. No. 575,101, filed Aug. 1966.  
  The following table sets forth particulars of operating conditions for examples of the practice of this inven- 6 at a place adjacent the upper end of the condensing chamber; maintaining the temperature in said condensing chamber sufficiently low to effect condensation of chlorine pentai&#39;luoride from said mixture; withdrawing tion using a pilot plant as illustrated and in which the 5 condensed chlorine pentafluoridc from said condenscylinders 14 and 23 are of 3 inches and 2 inches, re ing chamber. and continuously recirculatingthe unconspectively. schedule 40 pipe 5 feet 3 inches long. and densed gas from the condensing chamber at a place rethe interconnecting tube is V: OD X 0.065 inch wall mote from the upper end ofthe condensing chamber to thickness:  
 Example No 1 3 3 Pressure in reaction chamber in psig. I020 l270 M90 Temp. in reaction chamber in l-I 495 485 400 Temp in condensing chamber in F. I00 -l00 -|00 Liquid chlorine supplied by pump 67. 34) 36 I00 c.c/hr. Rate of flow of recycled uncondenscd gas through S0 flow line 74. in ml/min and calculated at i500 psh 212F. Time of run in consecutive hours 53 N 87 Yield oi (lF in mol percent 25 4t 40 For the operating conditions of Example No, 3 in the said reaction chamber at a place adjacent the lower end above table. it has been calculated that the mo] ratio of of the reaction chamber. fluorine to chlorine is about 9: l. wherefore the amount 2. The process of claim I in which pressurized fluoof fluorine used (calculated on a basis of Hill percent rine gas is made available as said one reactant by the fluorination to ClF -J is slightly less than twice that steps of warming condensed fluorine to convert the needed. The process ofthis invention is operable under s me to gas under a pressure greater than that in the conditions where the ratio of fluorine atoms to chlorine id reaction h h atoms fed into the reaction chamber is in the range f 3a 3 The process of claim I in which the reaction chamfrom a ut ii to lll&#39; fl ilh ,13 l in her is at a temperature ol&#39;l rom l00C to 400C and the one end a ratio providing but slight excess of fluorine prcssurc in the reaction chamber is between 100 psi for full fluorination of the chlorine. and at the other d goon hIeiI cnd ofthe range a ratio providing substantial excess flu- 4 T process f li i hi h h macho h (&#34;inc y which ll wluld hc ucmmllciil m 35 her is at a temperature offrom 100C to 280C and the Pracmc lnvcmllmpressure in the reaction chamber is between 330 psi to Operable conditions for the process of this invention 5m i further include maintaining a differential between the 5 A cyChc-I process f Pmducihg h i mfl temperature in the reaction chamber and the tempcraoride by reaction between fluorine as one reactant and in thc Chilmhcr fmm 40 at least one member ofthe group consisting ofchlorine. ZOOOF m chlorine monofluoride and chlorine trifluoride as anlt will be understood that it is intended to cover all other mncuum thc [mu-E cumprising the steps of Changes mmlificitlms cximplcs maintaining the temperature and pressure in a reaction vcntion herein shown for the purpose olthis disclosure, Chamber sufficiently high m cffcct rennin&#34; between which fi dcPanres fmm Spill 5 said reactants to form gaseous chlorine pcntafluoride in m of the a mixture with gaseous fluorine; maintaining the tent- I I I I I I I perature in a condensing chamber sufficiently low to Huvmg dcscnhul the clmmcd effect condensation of chlorine pentafluoride from said mixture; passing said reactants into said reaction cham- Proccss for pmduclng chlmmu f her at a place adjacent the lower end of the reaction comprising the steps of continuously passing fluorine as Chamhcr; permitting mid mixture to flwv by thermal madam l m lcastfmc mumhcr &#34;h gmup convection from a place adjacent the upper end of the sistlng of chlorine. chlorine monolluoridc and chlorine mucmm chamber mm Said mndcnsing chamber at u trifluortde as another reactant into a react on chamber place adjwcm he upper end Hf the wndcnsing Charm mljuccm the lower cndll h chamber, f 55 her; withdrawing condensed chlorine pentafluoride and lircssurc &#34;V rcdctm Chamber from said condensing chamber, and permitting the unficlgmly l l: to i f l r l&#34; rcuilmmg condensed gas to flow from the condensing chamber at i e l f Q I l l f a place remote from the upper end of the condensing glseuus &#34;ommuuusly plwng chamber to said reaction chamber at a place adjacent ture from the reaction chamber at a place ad acent the he luwcr end 0f the rcnctinn t:hambm,  
 upper end of the chamber into a condensing chamber