Sodium Hydroxide: Membrane vs. Diaphragm Grade
A sodium hydroxide is a chemical that has long been used in the manufacture of cleaners and soaps. It’s also an essential component of many other products, like papermaking and a variety of industrial food processes.
Generally, this scary-sounding ingredient is not harmful to you or your skin. However, it’s important to know about the process behind its use and how to safely handle it.
Advantages of the Membrane Cell Method
The membrane cell method produces chlorine and sodium hydroxide from the electrolysis of brine. This is a safe and energy-efficient process that addresses the safety concerns of older methods.
The membrane consists of a polymer that only allows positive ions to pass through. This means that only the sodium ions in the solution will pass through and not the chloride ions.
However, the membrane is also susceptible to contaminant ions such as Mg2+ and Ca2+ in the brine, which can shorten the useful lifetime of the membrane20–22.
Another advantage of the membrane cell method is that it requires less power than the diaphragm or mercury cells. This is a significant advantage because it saves money on the electric power required to run the plant.
Advantages of the Diaphragm Cell Method
Chlorine is produced from salt water in an electrolytic cell divided into two compartments by a membrane or diaphragm. The anode compartment contains a positively charged anode, and the cathode compartment contains a negatively charged cathode.
Sodium ions enter the anode and are oxidized to produce chlorine gas. At the same time, hydroxide ions are produced, and they too give up electrons to produce hydrogen gas.
This results in a buildup of the concentration of hydrogen and hydroxide ions around the cathode. The hydrogen ions flow through the diaphragm, which is permeable to brine, into a totally separate compartment, known as the decomposer or denuder.
The decomposer produces a solution of sodium hydroxide, which is usually around 50% concentration. This is often concentrated to a higher concentration by evaporation using steam and then sold in the form of Caustic soda.
Advantages of the Membrane Grade Method
Sodium hydroxide or caustic soda is a commonly used chemical in many industries. It is commonly found in the refining of bauxite ore to aluminum, pH regulation, chemical synthesis reactions, electroplating, and etching. It is also used in paper manufacturing, rayon and cellophane production, soaps, detergents, lubricants, drain cleaners, oven cleaners, and heavy-duty degreasers.
Despite the wide variety of uses for sodium hydroxide, it is hazardous to workers. It can burn the eyes, skin, and inner membranes.
The National Institute for Occupational Safety and Health (NIOSH) says that employers and workers should use a hierarchy of controls to keep people from getting exposed. They also encourage users to read the chemical label and the safety data sheet for any chemicals they work with.
Sodium hydroxide should be stored in airtight containers to avoid water and CO2 adsorption. These substances can cause a reduction in its purity. Alternatively, the container can be coated with an effective corrosion barrier. Tanks made of 1.9 specific gravity polyethylene, or XLPE, are recommended for the storage of caustic solutions.
Advantages of Diaphragm Grade Caustic Soda
Sodium hydroxide (naoh, also known as caustic soda) is one of the most important chemicals produced worldwide. It is used as a raw material in a wide variety of industries, including soap and detergent production, rubber reclaiming, petroleum manufacturing, rayon manufacture, and the pulp and paper industry.
It is a white solid that melts at 318 °C without decomposing and has a boiling point of 1,388 °C. It is available in flakes, granules, pellets, and as prepared solutions at different concentrations.
Caustic soda is a by-product of chlorine production and ranks third in tonnage produced. It is also used in the production of radii, paper, explosives, dyes, and petroleum products.