Sodium hydroxide, also known as caustic soda (NaOH), is a highly versatile chemical that is used in a variety of industrial applications. In the maritime industry, caustic soda is commonly used in scrubbers as part of the exhaust gas cleaning process.

Scrubbers are installed on vessels to remove harmful pollutants, such as sulphur oxides (SOx), from the exhaust gas emissions produced by burning marine fuels, heavy fuel oil (HFO) in this case. Caustic soda is an essential component of the scrubber process, as it is used to neutralize the acidic sulphur oxides in the exhaust gas.

In the scrubber system, the exhaust gas is sprayed with a mixture of seawater and caustic soda, which reacts with the sulphur oxides to form a neutral compound that can be safely released into the atmosphere. This process is known as "scrubbing" or "desulphurization".

The use of caustic soda in scrubbers is critical for compliance with regulations such as the International Maritime Organization's (IMO) MARPOL Annex VI, which sets limits on sulphur emissions from ships. By using caustic soda in scrubbers, vessels can significantly reduce their emissions and avoid costly fines for non-compliance. Overall, caustic soda plays an important role in the maritime industry by helping to reduce harmful emissions and promote sustainability.