Electrolyzers voltage/current density

Fused sodium chloride is electrolyzed at hath temperature varying between 565 to 600°C at a cell voltage of 5.7 to 7 V and the cell current varying from 25 to 35 kA. The cathode current density is mostly about 9.8 kA/m. Often calcium chloride is added to sodium chloride in the cell bath to lower its melting point. Calcium is largely removed from sodium by filtration at about 110°C. Other electrolyte compositions have heen used in which calcium is partially or fully replaced. The cell feed must he free of sulfate and other impurities. 

A steel electrolyzer. 1.2 L in capacity, with nickel anodes and steel cathodes was used. Area of anodes 750 cm2. Lining material of the cell was PTFE. The initial concentration of the trialkylphosphane oxide in HF was 15%. Working conditions current density 20-50mA cm-2, voltage 5.2-5.6 V, temperature of electrolyte 10-20 C, temperature of the reflux condenser — 20 to —25 C. As the level of the electrolyte in the electrolyzer fell, the necessary amount of HF was added. The liquid perfluorinated products collected at the bottom of the electrolyzer and were periodically removed. The MF dissolved in the product was removed by the passage of (dry) air, and the residue was distilled. 

A. A dilute Na2S04 solution is to be electrolyzed with a pair of smooth Pt electrodes at a current density of 100 A An2 and a current of 0.100 A. The products are H2(g) and Oz(g) at 1.00 bar. Calculate the required voltage if the cell resistance is 2.00 il and there is no concentration polarization. What would your answer be if the Pt electrodes were replaced by Au electrodes ... 

An electrolyzer with a capacity up to 500 cu ni. per hour consists of 100 chambers, is 12 m long, 2.6 m wide and 5 m high. At a current load of 7500 A the electrodes operate with a current density of 25 to 30 A/sq. dm. When a 26—27 % solution of KOH is used as electrolyte at a temperature of 75 to 80 °C, the voltage across one compartment will be approximately 2.2 V and across the entire electrolyzer 350 V the power input will then be 2600 kw the power consumption necessary to produce 1 cu. in of hydrogen will range from 5.3 to 5.4 kw-hr. The hydrogen produced is 90.0% pure and the oxygen 99.5— 90.8% pure. 

When the operation started, the iron tank and the individual boxes were filled with saturated solution of sodium (or potassium) chloride while solid salt was put into the stoneware cylinders. The level of electrolyte in tho anode boxes was always somewhat higher than in the tank. During electrolysis the temperature was kept at 85 °C by steam heating steam entered the heating element of the tank through piping H. The voltage across the electrolyzer was 3.5 to 4.0 V. The total current load was about 2500 A which corresponded to a current density of some 2 A/sq. dm. 

An electrolyzer of the above type was loaded with a current of 4000 amperes corresponding to the current density of roughly 5 A/sq dm at the anode. The voltage across the bath was 3.2 to 3.8 V at a temperature 45—(50 °C Current efficiency attained 90 per cent while the content of sodium hydroxide in the caustic solution reached about 120 grams per litre. 

Earlier types of electrolyzers worked with a current of 2200 A the current density at the anode was 4.7 A/sq. dm and the voltage across the bath 3.7 to 4.2 V while the temperature of the electrolyte was 60 °C. The sodium hydroxide content in the caustic solution produced was about 120 grams per litre and the remaining sodium chloride amounted to some 180 grams per litre. Current efficiency was between 92 and 94 per cent. 

In the modem type of electrolyzers the electrodes are set closer together approximately 14—20 mm apart. The cathodes are corrugated and the anodes are shaped according to the corrugations. In this way it was possible to raise current density to some 15 A/sq. dm. In order to achieve the highest possible current efficiency a part of the electrolyte is continually removed from the electrolyzer, resaturated with sodium chloride and returned to the bath. The voltage across the electrolyzer amounts to 3.5 to 3.8 V. Electrolyzers for 12 000 to 24 000 A have been constructed for which less floor space was needed. These modem electrolyzers require 230 to 240 kw-hr. of direct, current and 153 kg of NaCl to produce 100 kg of 100 per cent Bodium hydroxide. 

The Hargreaves-Bird electrolyzer was loaded with 2600 A, current density on the surface of the diaphragm 2 A/sq. dm and voltage 3.6 to 4.0 V. 150 to 170 grams of sodium carbonate per one litre catholyte was obtained while currents efficiency was between 80 to 85 per cent. The temperature was maintained at about 80 °C. 

According to available references this electrolyzer was designed for a load of 2000 A, the current density on the anode being about 8 A/sq. dm. The voltage across the electrolyzer was 2.8 to 3.5 V at 80 to 90 °C. Current efficiency waB... 

Electrolysis is performed at a room temperature at a current density of about 0.5 A/sq. dm. and a voltage across the electrolyzer of 2 V. If the amount... 

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