Title Slide
Electrolysis of Brine in the Diaphragm
Cell and the Chlor-Alkali Industry
Chemistry Presentation
Overview
• • Chlor-alkali industry produces chlorine (Cl₂),
hydrogen (H₂), and sodium hydroxide (NaOH).
• • One method used is the diaphragm cell
electrolysis of brine.
• • This presentation explains:
• – Chemical processes in the diaphragm cell
• – Economic advantages of this method
• – Industrial importance of halogens
• – Environmental impacts of the chlor-alkali
Electrolysis of Brine – Basic
Principle
• • Brine = concentrated sodium chloride (NaCl)
solution.
• • Electricity is passed through the solution to
drive a non-spontaneous reaction.
• • Products formed:
• – Chlorine gas (Cl₂)
• – Hydrogen gas (H₂)
• – Sodium hydroxide (NaOH)
• • A diaphragm separates the anode and
Structure of the Diaphragm Cell
• • Contains two electrodes: anode (+) and
cathode (−).
• • A porous diaphragm (traditionally asbestos)
separates the compartments.
• • The diaphragm allows ions to pass but
prevents mixing of gases.
• • Prevents chlorine from reacting with sodium
hydroxide.
Chemical Reactions in the Cell
• Anode Reaction (Oxidation):
• 2Cl⁻ → Cl₂(g) + 2e⁻
• Cathode Reaction (Reduction):
• 2H₂O + 2e⁻ → H₂(g) + 2OH⁻
• Overall Reaction:
• 2NaCl + 2H₂O → Cl₂ + H₂ + 2NaOH
Role of the Diaphragm
• • Allows Na⁺ ions to move from the anode
compartment to the cathode.
• • Prevents chlorine gas from mixing with
hydrogen gas (explosion risk).
• • Prevents chlorine from reacting with sodium
hydroxide.
• • Ensures safer and more efficient separation
of products.
Economic Advantages of the
Diaphragm Cell
• • Lower capital cost compared with mercury
and membrane cells.
• • Existing plants may already be fully
amortized.
• • Lower brine purity requirements reduce
purification costs.
• • Can operate using lower-quality salt sources.
Operational and Production
Advantages
• • Modern polymer diaphragms can last 3–5
years.
• • Lower maintenance and replacement costs.
• • Hydrogen produced can be recovered and
sold or used as fuel.
• • In regions with low electricity costs, overall
production can remain economical.
Physiological Effects of Chlorine
Exposure
• • Chlorine gas is highly toxic and a strong
respiratory irritant.
• • Low exposure (1–10 ppm): eye irritation,
coughing, sore throat.
• • Moderate to high exposure (>30 ppm): chest
pain, breathing difficulty, vomiting.
• • Extremely high exposure (>400 ppm): can be
fatal within minutes.
• • Chronic exposure may lead to asthma or
long-term lung damage.
Industrial Importance of Halogens
• • Halogens: fluorine, chlorine, bromine,
iodine.
• • Chlorine used in water purification, PVC
plastics, and disinfectants.
• • Fluorine used in Teflon, refrigerants, and
uranium processing.
• • Bromine used in flame retardants and
photographic chemicals.
• • Iodine used in medicines, antiseptics, and
nutrition supplements.
Environmental Impact of the
Chlor-Alkali Industry
• • High energy consumption during
electrolysis.
• • Older mercury cells caused mercury
pollution.
• • Diaphragm cells historically used asbestos
materials.
• • Possible emissions of chlorine and
chlorinated compounds.
• • Contamination of soil and groundwater at
some legacy sites.
Industry Improvements and Future
Solutions
• • Transition toward membrane cell
technology.
• • Membrane cells are more energy-efficient
and produce fewer pollutants.
• • Phase-out of mercury-cell plants in many
regions.
• • New technologies such as
oxygen-depolarized cathodes reduce energy
demand.
• • Continued focus on sustainable chemical
Conclusion
• • Electrolysis of brine is a key industrial
process producing chlorine, hydrogen, and
sodium hydroxide.
• • Diaphragm cells provide economic
advantages in some regions.
• • Halogens are vital in many industrial and
medical applications.
• • Environmental challenges remain, but
technological improvements are reducing
impacts.