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Chlor-alkali Plant: An Overview

Chlor-alkali is a process widely used to produce chlorine, caustic soda, and chlorine and sodium-based products such as sodium hypochlorite, chlorosulphonic acid, hydrochloric acid bleaching power, polyaluminium chloride, hydrogen gas, chlorinated paraffinetc at an industrial scale. The process uses sodium chloride solution (brine). The Chlor-alkali industry produces a range of chemicals by electrolysis of salt solutions, and currently, 95% of chlorine production worldwide is done by this industry. Chlorine is largely used in the synthesis of chlorinated organic compounds. Vinyl chloride monomer (VCM) for synthesising polyvinyl chloride (PVC) remains the main driver of the Chlor-alkali manufacturing segment. The primary consumers of caustic soda in India are textiles (21%), alumina (12%), inorganic chemicals (13%), pulp & paper (8%), soaps and detergents (7%). Caustic soda, or sodium hydroxide, represents a highly versatile chemical base that finds its way into the production of pulp, paper, and textiles, as a water treatment agent and soaps and detergents. The Chlor-alkali process plays a predominant role in the industry because its products are used in many major industrial chemical processes. However, Chlor-alkali plants are among the highest energy-consuming processes with pollutant emissions that seriously affect the environment. In this write-up, you will discover all legalities associated with setting up a Chlor-alkali unit and the requirements needed to start a business in the industry. First, let's understand the different applications areas of caustic soda and chlorine.



Production of metals and resource

Used in Alumina refining, propylene oxide, polycarbonate resin, epoxies, synthetic fibres, soaps, detergents, rayon and cellophane production

Pulp and paper industry

Caustic soda is used for pulping of wood chips. Chlorine and compounds are used in wood pulp bleaching in paper industry.

Petroleum and natural gas

Caustic soda is used as a drilling fluid.

Manufacture of organic chemicals

Chlorine is used for making ethylene dichloride, glycerin,glycols, chlorinated solvents and chlorinated methane.

Plastic industry

Used for making plastics, most notably polyvinyl chloride (PVC), used extensively in building and construction.


96 per cent of all pesticides are produced using chlorine

Industrial solvents

A variety of chlorinated compounds are used as industrial solvents, including the main ingredient used in dry cleaning.

Water treatment

Chlorine is used in 98 per cent of the water treatment plants in the world


85 per cent of all pharmaceuticals use chlorine

Other relevant applications

Domestic bleaches, flame-retardants, food additives, refrigerants, insulation, computer chip manufacturing and hospital disinfectants.

How is Caustic Soda produced

Caustic soda is produced industrially by the Chlor-alkali process, which constitutes the electrolysis of salt of sodium chloride. Here in this process, the term ‘chlor’ stands for the product Chlorine, and ‘alkali’ is for Sodium hydroxide. The reaction follows the following path.

  • A Chlor-alkali unit, during the production of caustic soda, yields chlorine and sodium hydroxide in nearly equal amounts, while hydrogen is released as a by-product.
  • The Membrane cell process for the Chlor-alkali Plant uses brine and a membrane cell with positive and negatively charged electrodes. The anode oxidises the chloride ion, which loses an electron to become free chlorine gas. The hydrogen ions are attracted at the cathode and produce hydrogen gas.
  • The semi-permeable membrane allows the sodium ions to collect into a second chamber, where they react with water to produce sodium hydroxide.

Waste Generation from the Chlor-alkali Plant

Chlor-alkali Units are categorised as a red category industry as this industry is highly energy intensive and generates various kinds of waste. This industrial sector is one of the 17 ‘Highly Polluting Industries. Such plants have different sections like NaOH, Cl2, SBP etc., that release toxic effluents. Additionally, fuel consumption is also on the higher side. The following is the waste generated from the Chlor-alkali Plants that will need proper management.

Solid wastes: These are waste generated from the diaphragm cell plants and the membrane cell plants. The major waste stream from the processes consists of brine mud, which is the sludge that is produced from brine purification. Sludge also contains various compounds, typically magnesium, calcium, iron, and other metal hydroxides. Solid wastes from mercury cell plants include spent graphite from decomposer cells and spent caustic filtration cartridges from the filtration of caustic soda solution. Mercury cell plants also produce some mercury in solid sludge waste.

Wastewater: During the Ion exchange process, wash water, cell wash water, brine purge etc., are released that must be properly treated.

Hazardous wastes: Chlorinated hydrocarbon waste from the purification step of the diaphragm cell process, spilled mercury from sumps and mercury cell wastewater are a few of the hazardous wastes generated from the Chlor-alkali plant.

Licences needed by the Chlor-alkali Plant

The following is the list of licences and approvals needed by a Chlor-alkali Unit from the central and state government.

Pollution NOC/ Consent Certificate

As the plant falls under the red category industries, it will need a Pollution NOC certificate from the respective State Pollution Control Board (SPCB) / Pollution Control Committee (PCC). The document required for the two stages i.e.consent to establish (CTE) and Consent to Operate (CTO) are

  • Correctly filled application form of the concerned SPCB
  • Signed undertaking
  • Site or layout plan with a roadmap 
  • Detailed project report
  • Details of the product manufacturing processes.
  • Proof of installed machinery, the capital cost of the land, building etc.
  • Water balance, water source and required quantity 
  • Land ownership documents
  • Industry registration documents
  • Consent fee (as applicable)
  • Any other document mentioned in the application

Environmental Clearance

The Chlor-alkali project will fall under Category ‘A’ of item 4(d) of the Schedule of Environment Impact Assessment (EIA) Notification, 2006 and requires appraisal at Central Level by Expert Appraisal Committee (EAC). The list of documents required by the project proponent at this stage includes

  • Detailed Project Description (project's name, location, proposed area breakup, water requirement, waste generation etc.)
  • Site/ Layout plan
  • Proof of installed machinery
  • Proof of Land Ownership
  • ID proof of Signatory
  • Quality test Report (if applicable)
  • Proof of mitigation options adopted
  • Proof of Electricity and water connection

Factory’s Licence

The Chlor-alkali Plant must register itself under the Factories Act of 1948. The standard documents needed for this licence are

  • Duly filled in the application form
  • Application Fees
  • Existing building plan
  • List of Partners or directors with their addresses.
  • NOC from other partners / Board Resolution under sections 2(n) and 7 of the Factories Act, 1948.
  • Proof of Occupier as Director/ Proprietor / Partner
  • Proof of sanctioned load of electricity.
  • Proof of occupancy.
  • Flow chart of the manufacturing process.
  • List of raw materials used in manufacturing.
  • List of machinery installed or any such other particulars as the Chief Inspector/Director may require.

Additional Licences and Authorisations required for setting up Chlor-alkali plant

  • Business Registration
  • ISI certification (Regional Office of the Bureau of Indian Standards (BIS))
  • MSME Registration (from the centralised online portal)
  • Fire NOC (from State Fire department)
  • Hazardous Waste Management Authorisation/ Membership of TSDF facility

Market Potential and Scope of the Chlor-alkali Manufacturing Units

Around 37 caustic soda units are spread across India with a total installed capacity of 3.20 MMT per annum, with the top 10 chlor-alkali plants producing about 60% of the entire output. Installed capacity for caustic soda and chlorine, which is co-produced, has grown at a CAGR of 7.8% between FY16 and FY20.

Many chlor-alkali plants are located together with PVC plants that use the gaseous Cl2. Globally, 40% of Cl2 from the chlor-alkali process is utilised in PVC production, whereas in India, it is 6.64%. India, however, is expected to show rapid growth in the caustic soda market due to increased industrialisation, urbanisation, and population and the increasing demand due to these factors.

 About 60% of the total new capacity in the last few years has been from western India, where the broader chemical industry is located. Overall, Gujarat accounts for about 55% of the total installed capacity for caustic soda.

Export Market: Although the industry's focus is primarily domestic, only 3-5% of total production is exported (mainly as flakes). But exports have been growing in the past few years. Much of it is destined for countries where the chemical industry is undeveloped. Caustic soda flakes are imported to make essential goods and textile processing. Most of the import is targeted to Africa, while some small quantities go to some South East Asian countries, such as Indonesia, Vietnam and Myanmar. In FY19, earnings from export were about 105 million USD.

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