Patent GB-848364-A (GB)
Title: Process and device for the production of lead tetraethyl
IPC: C25B3/13
Filed: 1958-06-11
Abstract: 848,364. Lead tetra ethyl made electrolytically. ZIEGLER, K. June 11, 1958 [June 12, 1957], No. 18693/58. Class 41 In a process for making lead tetraethyl by electrolysis of aluminium triethyl in the presence of sodium fluoride or similar electrolyte using a lead anode, the anolyte is separated from the catholyte by a diaphragm, and the anolyte consists of a mixture of NaAl(C 2 H 5 ) 4  and NaFAI(C z H s )3 preferably in chemically equivalent amounts. The conductivity of the mixture is increased by adding NaF.2Al(C 2 H 5 ) 3 . The temperature of the electrolysis is maintained at about 70 C., by continuously drawing off both the catholytes an anolyte, through a cooler, regenerating and recycling the electrolytes NaA](C 2 H 5 ) 4  is made by mixing Al(C 2 H 5 ) 3  at 125C. with sodium, and separating the deposited aluminium from the melt. The sodium aluminium triethyl fluoride compounds are made by mixing sodium fluoride with the aluminium alkyl at 120C. using the proportions required. All these compounds are auto-combustible and their preparation and subsequent electrolysis is effected in an inert atmosphere. The anolyte mixture is fed into a storage chamber A Fig. 3, and the catholyte which may be the same mixture or NaF2Al(C 2 H 5 ) 3  alone, is fed into a chamber K. The electrolytes are fed into separate compartments of the electrolytic cell E, provided with a diaphragm D preferably of fine pore filter paper or glass fibre. The cell consists of electrode end plates, separated from the diaphragm by frames of an insulating material e.g. synthetic resins, or wood impregnated with polyethylene or paraffin wax, and having inlets and outlets, the whole clamped together like a pressure filter. The electrodes may be metal plates, lead for the anode, iron, copper, or brass for the cathode, but preferably the cathode consists of obliquely mounted wires, adjacent which is mounted a movable frame of insulated stripping wires which scrape off the aluminium powder deposited on the cathode. Alternatively a jet of electrolyte with or without glass balls may be used, or by reversing the current. A voltage of preferably 2 to 5 volts is applied at a current density of 5 to 10 amps. dm<SP>2</SP>. The electrolytes flow continuously at about 4 litres per minute, the anolyte flowing to a vessel A<SP>1</SP> from which it is pumped to the storage vessel A. The catholyte which is maintained at a slightly higher level than the anolyte in the cell E, passes through a separating chamber B where the aluminium deposit is removed before recycling , to the chamber K. The used anolyte is freed from lead tetra ethyl by extraction with controlled amounts of a solvent, preferably iso octane, used in several extractions with cooling, and in last stages, by centrifuging. Final traces of lead may be removed by adding aluminium powder. The anolyte residue consists of NaF. 2 A<SP>1</SP> (C 2 H  5 ) 3 substantially free from lead, and may be used as catholyte. The catholyte is mixed with some aluminium tri-ethyl and may then be used as anolyte. The separated aluminium may be converted to aluminium triethyl, by treatment under pressure first with hydrogen and then with ethylene, and must be free of aluminium hydride. In modifications of the process, (a) a part of the anolyte is continuously treated for recovery of a part of the lead tetra ethyl content, and replaced by a part of the regenerated catholyte, (b) two diaphragms are used in the cell, the space between them forming a chamber through which a slow stream of an electrolyte flows to remove any lead compound seeping through the diaphragms. Specifications 770,707, 779,874, 794,359, 814,609 and 836,792 are referred to.