Patent GB-685230-A (GB)
Title: Improvements in or relating to a continuous process of manufacturing lead tetra-alkyl compounds
Inventor: RODEKOHR HOWARD MARVIN
IPC: C07F7/24
Filed: 1950-06-30
Abstract: <PICT:0685230/IV (b)/1> <PICT:0685230/IV (b)/2> Lead tetra-alkyl is prepared by the continuous reaction of an active form of lead and an alkylating agent comprising one or more esters of inorganic acids having the desired alkyl group attached to the negative radical, wherein the active form of lead is introduced into an ascending stream of the alkylating agent under reaction conditions such that said alkylating agent is liquid at the reaction temperature and pressure used, the lead is suspended in said stream by the initial velocity of the stream, the terminal velocity of the stream is not greater than the initial velocity, and separating the resulting lead tetra-alkyl from the reaction products.  By "active form of lead" is meant lead halides, lead or lead containing materials which are active as the result of the state of aggregation and/or nature of the surface of the particles.  The reaction vessel may be a vertically elongated reaction vessel and the reactants are introduced into the lower end of the vessel, the velocity of the ascending stream of alkylating agent throughout the length of the vessel being not greater than the initial velocity.  The velocity of the alkylating agent may be decreased during its upward travel.  The initial velocity of said stream may be in excess of 0.10 feet per second and the terminal velocity may be in excess of 0.03 feet per second.  The reaction may be carried out at a temperature from 40 DEG  to 150 DEG C. and preferably from 70 DEG  to 120 DEG  C.  The reaction pressure may be from 70 to 250 lbs. per sq. inch.  The reaction product may be separated into liquids and solids, and the lead tetra-alkyl is washed from the solids with a liquid solvent, e.g. the liquid alkylating agent.  The separation may be effected by settling, and the liquid solvent is flowed upwardly through the solids at a velocity of less than 0.03 to 0.06 feet per second. Lead chloride, lead powders formed by grinding, chipping or other methods which form non-oxidized chemically clean surfaces, or lead formed by the reaction of lead bearing materials with alkylating agents during the formation of lead tetra-alkyl, e.g. from the reaction of sodium-lead alloy and ethyl chloride, may be used in the present process.  Suitable alkylating agents referred to are alkyl chlorides, bromides and iodides, and the alkyl sulphates. The preferred alkylating agent is ethyl chloride. Lead tetraalkyls which may be prepared are lead tetraethyl and dimethyldiethyl lead.  The apparatus in Fig. 1 comprises a reactor 10 in which liquid ethyl chloride introduced through line 11 passes upwardly through the reactor and reacts with sodium-lead alloy (in a molten form, e.g. as a spray, or in a comminuted state) introduced through line 12.  The conical shape of reactor 10 provides a liquid velocity gradient decreasing upwardly.  Heat released during the reaction vaporizes ethyl chloride which leaves the reactor through line 13 and is condensed and collected at 14 and 15 respectively. Hydrocarbons formed during the reaction are vented at 16.  The velocity of the liquid in the reactor brings the solids to the top and are swept out through line 17, which is separated from line 12 by baffle 18, into the settler extractor 20 through the valve 19.  The settler extractor comprises a settler 21 and an extractor 22, and an ascending stream of a solvent, e.g. ethyl chloride, introduced at 23 washes the solids collected in 22.  Ethyl chloride is also introduced into the extractor by means of line 25 from the drier 55 and by means of line 24 from the collector 15.  Ethyl chloride and lead tetra-ethyl vaporized as the result of the pressure drop through valve 19 are taken off through line 27 and condensed at 28.  Solids from the extractor 22 are removed by conveyer 29, and the ethyl chloride is removed therefrom with the drier 55 and is condensed at 28.  The effluent containing lead tetra-ethyl is discharged through line 30 and is split into two portions, one being returned to the reactor 10 and the other passing through line 31 to the heated stills 32 and 35. Volatile matter from the stills is condensed and returned to the extractor.  Crude lead tetra-ethyl is then subjected to an oxidizing treatment with a gas, e.g. air, in tower 41, and then a washing treatment in tower 51.  In Fig. II, the apparatus for the distillation and subsequent steps is omitted.  The alloy of sodium and lead is introduced through line 71 and the ethyl chloride is introduced through line 72 into the reactor 70.  Vaporized ethyl chloride and lead tetra-ethyl are condensed at 74 and are returned to the reactor.  Hydrocarbons are vented at 76.  The effluent from the reactor passes through line 79, which is protected from line 71 by baffle 78, into the separating unit 80.  The primary separation is effected in 81, and the solids collected in the inclined wall chamber 82 are then removed through valve 83 to the rotary filter 94.  Ethyl chloride is introduced through line 96 to wash the solids rotated on drum 95, and the liquid returns to the reactor.  Solids are removed by conveyer 99.  The liquid stream from the separating unit is discharged through line 90 and a portion of this liquid is returned to the reactor through line 92.