CHLORINE PRODUCTION / NaOH STREAM

PROCESS INFORMATION
Electrolysis of brines with chlorine production at the anode and hydrogen together with sodium or potassium hydroxide at the cathode.

Two types of cells: diaphragm
mercury

Diaphragm Cell

The diaphragm cells contain a porous asbestos diaphragm to separate the anode from the cathode. This allows ions to pass through by electrical migration but reduces diffusion of products.

Anodes are graphite or Titanium (DSA).
Cathodes are made from steel wire.

Overall reaction:
Nacl + H2O - NaOH + 1/2 H2 + 1/2 Cl2

If OH* reach the anode hypochlorites are formed with subsequent loss of chlorine.

The following occurs:
2OH* - H2O + 1/2 O2 + 2E

The oxygen will attack the graphite and chlorinated HC are entrained in chlorine gas.

Mercury Cell

In a mercury cell, brine is partly decomposed in the electrolyzer between a graphite anode and a moving mercury cathode forming chlorine gas at the anode and sodium amalgam (NaHg) at the cathode.

The amalgam flows to the decomposer box where it becomes the anode to a short circuited iron or graphite cathode in an electrolyte of sodium hydroxide solution.

Purified water is fed to the decomposer; hydrogen is formed and NaOH concentration increases. Hg is formed and recycled to the electrolyzer.

Reactions:
electrolyzer 2Na Cl + Hg - Cl2 + 2Na(Hg)

decomposer 2Na(Hg) + 2H2O - 2NaOH + H2 + Hg

NaOH Stream

Often NaOH is concentrated from 50% or lower strength up to 70%. This operation is carried in a high vacuum (120 MMHg ABS) concentrator. Vacuum is generated by jet system with water intercoolers.

NaOH is entrained by the jet system up to 2000 mg/Nm³.

PROBLEMS TO SOLVE
Filters are installed before jet system to collect NaOH mists which mix with the water of intercondenser and create water pollution problem.

DESIGN SOLUTION
 HTP Panel filter of SS316 casing with PTFE Teflon fibre

 Candle Filters Type F2 with SS316 structure and PTFE Teflon fibre

IMAGES
	FLOW DIAGRAM - DIAPHRAGM CELL FLOW DIAGRAM - MERCURY CELL

Other Applications
ASPHALT CHLORINE PRODUCTION - WET CHLORINE CHLORINE PRODUCTION / DRY CHLORINE CHLORINE PRODUCTION / HYDROGEN STREAM COMPRESSED GAS / AIR DETERGENT SULPHONATION / AFTER THE SULPHONATION REACTOR DETERGENT SULPHONATION / BEFORE THE SULPHONATION REACTOR DETERGENT SULPHONATION / HOW ‘STAR’ CANDLES EFFICIENTLY HANDLED HIGH MIST LOADS, SAVING ENERGY AND COST HYDROCHLORIC ACID NITRIC ACID / INLET AIR AND NH3 FILTERS,NITRIC ACID / INLET AIR AND NH3 FILTERS NITRIC ACID / PLATINUM CATALYST OR PALLADIUM DUST RECOVERY NITROGEN FERTILISERS / AMMONIUM NITRATE – NEUTRALISER & EVAPORATOR NITROGEN FERTILISERS / AMMONIUM NITRATE – PRILLING TOWER NITROGEN FERTILISERS / AMMONIUM NITRATE PRILLING TOWER – SELECTIVE FILTRATION OF ONLY MOST HEAVILY CONTAMINATED AIR NITROGEN FERTILISERS / UREA – PRILLING TOWER NITROGEN FERTILISERS / UREA –EVAPORATOR NITROGEN FERTILISERS / UREA PRILLING TOWER DEMISTERS & COALESCERS FOR LOW PRESSURE LOSS FILTRATION AND CONCURRENT NH3 ABSORBTION. NON-FERROUS METALS PRODUCTION - Process Tanks OIL REFINING - FCC Fractionator and Pipestill PHOSPHATE FERTILISER PRODUCTION - P2O5 Separation from Phosphate Slurry PHOSPHATE FERTILISER PRODUCTION - Reactor Tanks PHOSPHORIC ACID / P2O5 FILTRATION SYSTEMS PHOSPHORIC ACID / WAGON LOADING - FUGITIVE EMISSIONS CONTROL PVC / VINYL COATING - Direct heated oven / Indirect heated oven +lacquer / chlorinated additives PVC / VINYL COATING - Indirect heated oven and no lacquer or chlorinated additives SO3 / OLEUM TANK VENTS SULPHURIC ACID / ACID CONCENTRATOR SULPHURIC ACID / ACID DISTRIBUTION SULPHURIC ACID / CROSS FLOW STRIPPER SULPHURIC ACID / DRYING TOWER SULPHURIC ACID / FINAL ABSORBTION TOWER IN SPENT ACID PLANTS SULPHURIC ACID / FINAL ABSORBTION TOWER OR SINGLE ABSORBTION TOWER SULPHURIC ACID / HEAT RECOVERY DESIGN PLANT INTERMEDIATE ABSORBTION TOWER SULPHURIC ACID / INTERMEDIATE ABSORBTION TOWER SULPHURIC ACID / Mercury Removal Tower SULPHURIC ACID / OLEUM UPSTREAM OF INTERMEDIATE ABSORBTION TOWER OR FINAL ABSORBTION TOWER OR SINGLE ABSORBTION TOWER SULPHURIC ACID PLANT SO2 TAIL GAS / NH3 / SO2 TAIL GAS SCRUBBING TOWER