Hopefully for industrial it's the 3 cells.
Mercury Cell - Sodium dissolves in mercury forming an amalgam. The amalgam flows out of the cell where it does not react with water or chlorine. Continues flowing until it reaches the decomposer where it is reacted with water. Here the amalgam decomposes (sodium is released) to form mercury, hydrogen and sodium hydroxide. Mercury-contaminated sludge is separated from the amalgam and the mercury recycled in the cell. The remainder is reacted with sodium sulfide. Some of the mercury which was leftover forms mercury (I) sulfide which is disposed of by adding it to cement, setting it in bricks and using these as landfill. Sodium hydroxide produced is pure as it was reacted with water which contained no chloride. 50% sodium hydroxide solution formed as well as the dry form.
Diaphragm Cell - Two electrolyte solutions are separated by a diaphragm made out of asbestos. Both compartments contain saturated brine. As electrolysis proceeds, chlorine ions are reduced at the anode and water is reduced at the cathode, forming hydrogen which is used in the hydrogenation of vegetable oil. The cathode compartment increasing becomes alkaline and is periodically removed. Sodium ions migrate from the anode compartment through the diaphragm and to the cathode compartment to neutralise the charge of the hydroxide ions formed. The diaphragm also allows for some diffusion of hydroxide and chloride ions. The solution formed at the anode compartment is a mixture of sodium hydroxide and sodium chloride which is further purified through crystallization of sodium chloride. About 50% sodium hydroxide formed as well as 2% sodium chloride.
Membrane Cell - Two electrolyte solutions are separated by a cation exchange teflon membrane which only allows the movement of sodium ions across and prevents hydroxide ions from moving through. Newly developed membranes allow the electrodes to be very close to each other on opposite ends of the membrane. This increases the efficiency of the cell and thus reduces costs. In comparison to the other cells, it produces sodium hydroxide in a cheap and efficient manner (less energy consumption) and is environmentally friendly.
Have not even talked about environmental issues, advantages and disadvantages or improvements (partitions particularly)
Would be easy 6-7 marks.