At a Glance

• Identity: Caustic soda = Sodium hydroxide = Lye = NaOH (identical compound)
• Global production: Over 70 million tonnes annually
• Molecular weight: 39.9971 g/mol
• Forms available: Flakes, pearls/beads, liquid solution (20-50%), micropowder
• Primary production: Chlor-alkali electrolysis process
• pH: Approximately 14 (highly alkaline)
• Main hazard: Highly corrosive to skin, eyes, and organic materials

There’s no actual difference. Caustic soda, which is the same chemical as sodium hydroxide and is also known as lye, is a strong alkaline inorganic compound. These three names—caustic soda, sodium hydroxide, and lye, all refer to the exact same chemical compound with the formula NaOH. It is important to recognize that the terms “caustic soda,” “sodium hydroxide” and “lye” all refer to the same chemical compound of NaOH. These terms are used interchangeably throughout the industry.

Yet confusion persists. People search “sodium hydroxide vs caustic soda” expecting to find differences in properties, applications, or safety profiles. The reality is simpler: different industries and regions simply prefer different names for the same chemical. Understanding where each name comes from and how this versatile compound functions across industries reveals why it ranks among the world’s most important industrial chemicals.

Why Three Names for One Chemical?

Caustic Soda:

• The term “caustic soda” originates from its highly corrosive nature, with “caustic” referring to its ability to break down organic materials and “soda” stemming from its historical production from soda ash (sodium carbonate)
• Preferred in industrial and commercial contexts
• Common in manufacturing, chemical processing, and bulk supply

Sodium Hydroxide:

• Sodium hydroxide is the chemical name of caustic soda and has been derived from its chemical structure
• Used in scientific, technical, and regulatory documentation
• Standard nomenclature in chemistry, safety data sheets, academic papers

Lye:

• Often referred to by its household name of “lye,” which literally means “wash stuff” in Old English, caustic soda has probably been used since the time of the ancient Babylonians and Egyptians
• Traditional name in soap-making and household applications
• Most familiar to consumers and artisans

Chemical Properties

Basic Physical Properties

Property	Value/Description
Chemical formula	NaOH
Molecular weight	39.9971 g/mol
Appearance	White solid (various forms)
Melting point	318°C (604°F)
Boiling point	1,388°C (2,530°F)
Solubility in water	Highly soluble (exothermic reaction)
pH (0.5% solution)	~13
pH (1% solution)	~14
Odor	Odorless

Key Chemical Characteristics

Hygroscopic Nature:

• It readily absorbs moisture and carbon dioxide from the air
• Must be stored in airtight containers
• Exposure to air causes gradual degradation and carbonation
• Weight increases as it absorbs atmospheric moisture

Exothermic Dissolution:

• Releases significant heat when dissolved in water
• Safety rule: Always add caustic soda to water, never water to caustic soda
• Rapid mixing can cause violent boiling and splashing
• Temperature can exceed 80°C during dissolution

Corrosive Action:

• Sodium hydroxide is a highly corrosive base and alkali that decomposes lipids and proteins at ambient temperatures, and may cause severe chemical burns at high concentrations
• Dissolves fats, oils, greases (saponification)
• Breaks down proteins
• Attacks glass slowly (etching over time)
• Corrodes aluminum, zinc, tin, and other amphoteric metals

Commercial Forms

Caustic soda is commercially available in several forms, each tailored to specific industrial or domestic applications

1. Caustic Soda Flakes

Characteristics:

• Caustic Soda Flakes are a kind of ionic salt composed of sodium ions Na+ and hydroxide ions OH- in the form of NaOH
• White, flat pieces with narrow thickness
• Typical purity: 98-99%
• Easy to measure and handle
• Lower dust generation than powder

Applications:

• Paper manufacturing (pulping and bleaching)
• Textile processing
• Chemical synthesis requiring precise dosing
• Water treatment facilities

2. Caustic Soda Pearls/Beads

Characteristics:

• Caustic soda pearls are spherical shaped. They are also named as soda grain and granulated caustic soda
• Uniform spherical shape
• Typical purity: 99%
• Free-flowing properties
• Easier automated dosing

Applications:

• Automated industrial systems
• Batch chemical processes
• Soap and detergent manufacturing
• Pharmaceutical production

3. Caustic Soda Liquid

Characteristics:

• Caustic soda liquid, or lye, is clear like water but has more viscosity. It could be made in different concentrations by evaporating water or by adding more water to a concentrated solution
• Common concentrations: 20%, 25%, 32%, 50%
• Clear, colorless appearance
• Higher viscosity than water
• Immediate usability (no dissolution needed)

Applications:

• Continuous process industries
• Water treatment (pH adjustment)
• Pulp and paper mills
• Food processing

Viscosity Considerations:

• The viscosity of sodium hydroxide solutions plays a direct role in its application as well as its storage
• 50% solution has viscosity ~78 mPa·s (vs. water at 1.0 mPa·s)
• Viscosity decreases with temperature increase
• Affects pumping requirements and mixing efficiency

Production: The Chlor-Alkali Process

Manufacturers produce sodium hydroxide as a co-product with chlorine and hydrogen through the electrolysis of brine, a salt solution (NaCl)

Three Cell Technologies:

1. Membrane Cell (Modern Standard):

• Uses ion-selective membrane
• Produces high-purity caustic soda
• Lower energy consumption
• Minimal environmental impact
• Most new facilities use this technology

2. Diaphragm Cell:

• Uses asbestos or polymer diaphragm
• Produces lower concentration (10-12%)
• Requires concentration step
• Being phased out in many regions

3. Mercury Cell (Largely Phased Out):

• Uses mercury cathode
• Environmental concerns about mercury
• Being replaced globally
• Still operates in some older facilities

Production Scale:

China is the only country in Asia with a considerable sodium hydroxide market, and it is one of the leading producers of this chemical

Top Global Producers:

• China (largest producer)
• United States
• Germany
• Oceania
• Middle East (growing capacity)

Annual Global Production:

• Sodium hydroxide is ranked in the top five in terms of the amount produced globally per year, at more than 70 million tonnes

Major Industrial Applications

Paper and Pulp Industry

Functions:

• Scouring: Removes natural fats, waxes, and oils from cotton. Bleaching: Assists in whitening fabrics before dyeing. pH control: Essential for dyeing processes to ensure color stability
• Delignification (breaking down lignin in wood)
• Brightening and bleaching pulp
• De-inking recycled paper
• pH adjustment in process water

Typical Usage:

• 40-60 kg per ton of pulp produced
• Usually applied as 10-20% solution
• Critical for kraft pulping process

Chemical Manufacturing

The largest single broad use of sodium hydroxide is in the manufacturing of other chemicals and end-products

Products Synthesized:

• Organic chemicals (phenolics, epoxides)
• Active pharmaceutical ingredients: Used in the synthesis of aspirin, anticoagulants, and lipid-lowering drugs
• Synthetic fibers (rayon, spandex)
• Plastics and polymers
• Dyes and pigments

Soap and Detergent Production

Saponification Process:

• Commonly known as lye, it has been used to make soap for centuries
• Reacts with fats and oils to produce soap
• When combined with oils or fats in the saponification process, the caustic soda compound is transformed during the reaction to make the soap safe to use
• Traditional cold-process soap requires precise NaOH calculations
• Industrial soap manufacturing uses continuous saponification

Detergent Applications:

• Neutralizing fatty acids
• pH adjustment in liquid detergents
• Processing surfactants
• Manufacturing builders and chelating agents

Water Treatment

Municipal Applications:

• By absorbing both water and carbon dioxide, caustic soda (sodium hydroxide, or NaOH) elevates the pH of water
• Neutralizing acidic water supplies
• pH adjustment in drinking water treatment
• Coagulation aid for impurity removal
• Regenerating ion exchange resins

Industrial Water Treatment:

• Boiler water pH control
• Cooling tower maintenance
• Wastewater neutralization
• Heavy metal precipitation

Textile Industry

The textile sector uses caustic soda at multiple stages of fabric processing

Processing Stages:

• Scouring: Removes natural fats, waxes, oils from raw cotton
• Mercerization: Strengthens cotton fiber, increases luster and dye uptake
• Bleaching: Assists whitening before dyeing
• pH Control: Maintains proper conditions for dyeing

Mercerization Benefits:

• Increases fiber strength by 20%
• Improves dye absorption
• Creates silk-like appearance
• Requires 18-28% NaOH concentration

Food Processing

Food uses of sodium hydroxide include washing or chemical peeling of fruits and vegetables, chocolate and cocoa processing, caramel coloring production, poultry scalding, soft drink processing, and thickening ice cream

Specific Applications:

Food Product	Purpose	Typical Process
Olives	Olive debittering: Used to remove oleuropein, the bitter component in olives	Lye curing
Pretzels	Creates the unique shiny crust and firm texture through a quick lye dip before baking	Dipping in dilute solution
Fruits/vegetables	Peeling fruits and vegetables: Especially potatoes, tomatoes, and peaches; softens outer layers for easier removal	Chemical peeling
Hominy	Processing corn	Nixtamalization
Asian noodles	Alkaline texture	Kansui water preparation

Food-Grade Standards:

• Must meet strict purity requirements
• Heavy metal limits enforced
• Controlled production environment
• Complete dissolution required (no residual flakes)

Petroleum Refining

Applications:

• Removing acidic impurities from crude oil
• Neutralizing sulfur compounds
• pH control in various refining processes
• Processing specialty petroleum products

Aluminum Production

Bayer Process:

• The chemical compound is also used to break down the sedimentary rock that aluminum is extracted from
• Dissolving aluminum oxide from bauxite ore
• Consuming ~1.5 tonnes NaOH per tonne alumina
• Creates aluminum production’s largest NaOH demand

Biodiesel Manufacturing

For the manufacture of biodiesel, sodium hydroxide is used as a catalyst for the transesterification of methanol and triglycerides. This only works with anhydrous sodium hydroxide, because combined with water the fat would turn into soap

Process Requirements:

• Anhydrous NaOH essential (moisture creates soap)
• Typical catalyst loading: 0.5-1.5% by weight
• Preferred over potassium hydroxide for cost reasons
• Enables conversion of vegetable oils to biodiesel

Safety Considerations

Health Hazards

Skin Contact:

• Causes severe chemical burns immediately
• Dissolves proteins and fats in skin tissue
• Painless initially (nerve endings destroyed)
• Penetrates deeply if not washed immediately

Eye Contact:

• Causes permanent blindness if untreated
• Corneal damage occurs within seconds
• Requires immediate copious water flushing
• Medical attention mandatory

Inhalation:

• Mist or dust irritates respiratory tract
• Can cause pulmonary edema at high concentrations
• Chronic exposure damages lung tissue
• Proper ventilation essential

Ingestion:

• Severe burns to mouth, throat, esophagus, stomach
• Can cause perforation of digestive tract
• DO NOT induce vomiting
• Immediate medical attention critical

Personal Protective Equipment (PPE)

Minimum Required:

• Chemical-resistant gloves (nitrile, neoprene, or rubber)
• Safety goggles or face shield
• Chemical-resistant apron or suit
• Closed-toe shoes (chemical-resistant boots for large quantities)
• Long sleeves and pants

For Large-Scale Operations:

• Full face shield over safety goggles
• Chemical-resistant overalls
• Respiratory protection if dust/mist generated
• Emergency eyewash stations within 10 seconds reach
• Safety showers accessible

Storage Requirements

Sodium hydroxide must be stored in airtight containers to preserve its normality as it will absorb water and carbon dioxide from the atmosphere

Container Materials (Compatible):

• Common materials that are compatible with sodium hydroxide and often utilized for NaOH storage include: polyethylene (HDPE, usual, XLPE, less common), carbon steel, polyvinyl chloride (PVC), stainless steel, and fiberglass reinforced plastic (FRP, with a resistant liner)

Storage Conditions:

• Caustic soda is a hazardous material, so it should be stored in a cool and dry place with a good ventilation system. Keep caustic soda away from sunlight, moisture, and reactive materials such as acids
• Temperature-controlled environment preferred
• Segregated from acids, oxidizers, reactive metals
• Clear labeling with hazard warnings
• Spill containment for liquid storage

Incompatible Materials:

• Aluminum (reacts violently)
• Zinc and tin (hydrogen gas generation)
• Glass (slowly etches)
• Organic materials (combustion risk)

First Aid Procedures

Skin Contact:

1. Remove contaminated clothing immediately
2. Flush with copious water for minimum 20 minutes
3. DO NOT attempt to neutralize with acid
4. Seek medical attention even if burn seems minor

Eye Contact:

1. Flush with water immediately for minimum 20 minutes
2. Hold eyelids open to ensure thorough rinsing
3. Remove contact lenses if possible during rinsing
4. Seek immediate emergency medical care

Inhalation:

1. Move to fresh air immediately
2. Keep warm and at rest
3. Administer oxygen if breathing difficult
4. Seek medical attention

Ingestion:

1. DO NOT induce vomiting
2. Rinse mouth with water (do not swallow)
3. Give water or milk to drink if conscious
4. Seek immediate emergency medical attention

Quality Specifications

Industrial Grade Standards

Caustic Soda Flakes (98% min):

Parameter	Specification
NaOH content	98.0% min
Na₂CO₃	0.5% max
NaCl	0.03% max
Fe₂O₃	0.005% max

Caustic Soda Liquid (50%):

Parameter	Specification
NaOH concentration	50% ± 0.5%
Na₂CO₃	0.5% max
NaCl	100 ppm max
Fe	5 ppm max

Food Grade (FCC) Standards

• Higher purity requirements
• Stricter heavy metal limits (As, Pb, Hg)
• Mercury: <1 ppm
• Lead: <2 ppm
• Arsenic: <3 ppm

Pharmaceutical Grade (USP/EP)

• Highest purity level
• Comprehensive impurity testing
• Batch-specific documentation
• Certified manufacturing facilities

Sourcing Industrial Caustic Soda

For manufacturers requiring sodium hydroxide across various grades and forms, partnering with suppliers who understand application requirements and provide consistent quality makes operational success possible. Elchemy’s technology-driven platform connects industrial buyers with verified suppliers of caustic soda meeting specifications from food-grade to technical grade.

Founded by engineers from IIT Bombay, IIT Delhi, and IIM Ahmedabad, Elchemy transforms chemical distribution through customer-centric technology. Whether you need caustic soda flakes for soap manufacturing, liquid solutions for water treatment, or pharmaceutical-grade material for drug synthesis, our platform addresses supply chain challenges through transparent sourcing from both Indian and global suppliers. We provide certificates of analysis, safety documentation, logistics support, and technical assistance that helps companies maintain reliable access to this essential industrial chemical.

Conclusion

The distinction between caustic soda and sodium hydroxide exists only in terminology, not in chemistry. Whether called sodium hydroxide in scientific contexts, caustic soda in industrial settings, or lye in household applications, NaOH remains one of the most important and versatile chemicals in modern industry. Its production exceeds 70 million tonnes annually because virtually every manufacturing sector depends on its unique properties: strong alkalinity, protein-dissolving capability, fat-saponification power, and acid-neutralizing function. Understanding that these three names represent identical chemistry helps avoid confusion while emphasizing the need for proper safety protocols regardless of which term appears on the label.