Hygroscopic vs. Deliquescent Chemicals: Differences, Examples & Storage Tips

Moisture absorption is an important consideration in chemical storage because it can affect a substance's weight, concentration, physical properties, stability, and performance. Understanding how chemicals interact with humidity helps businesses select appropriate packaging, storage conditions, and handling procedures.

Hygroscopic chemicals absorb water vapor from the surrounding air, whereas deliquescent chemicals absorb enough moisture to dissolve and form an aqueous solution under suitable conditions. Deliquescence is a specific form of moisture absorption, meaning that deliquescent substances are hygroscopic, but not all hygroscopic substances are deliquescent.

Common examples include glycerol and silica gel, which interact with moisture in different ways, as well as calcium chloride, sodium hydroxide, and potassium hydroxide, which can exhibit deliquescent behavior under suitable environmental conditions.

At Aseschem, understanding the moisture-related properties of chemical raw materials is an important consideration when evaluating their suitability for industrial applications. This guide explains the difference between hygroscopic and deliquescent chemicals, their examples, and the best practices for storing moisture-sensitive materials.

What Are Hygroscopic Chemicals?

Hygroscopic chemicals are substances that absorb moisture from the surrounding atmosphere. Their ability to take up water depends on factors such as relative humidity, temperature, chemical composition, and exposure time.

When hygroscopic materials absorb moisture, their physical properties may change. Depending on the substance, these changes can include increased mass, stickiness, caking, altered flow characteristics, or changes in concentration.

For example, a hygroscopic powder may become difficult to pour or weigh accurately after absorbing moisture. A moisture-sensitive liquid may also absorb water, changing its concentration and potentially affecting its suitability for a particular industrial process.

It is important to note that hygroscopicity describes the tendency to absorb moisture; it does not mean that a substance will always remain solid or that it cannot dissolve in water.

Examples of Hygroscopic Materials

• Glycerol: A hygroscopic liquid that absorbs moisture from the air and is used in pharmaceutical, cosmetic, and personal-care formulations.

• Silica gel: A porous material used as a desiccant to capture moisture through adsorption on its surface and within its pore structure.

• Concentrated sulfuric acid: A substance with a strong affinity for water that can absorb atmospheric moisture and become diluted.

These examples have different chemical and physical properties. Their moisture uptake, storage requirements, and handling precautions should be assessed individually.

Why Is Hygroscopicity Important?

Moisture absorption can create practical challenges in industrial manufacturing and quality control. It may change the mass of a material, influence the accuracy of weighing and dosing, affect powder flow, or alter the concentration of a solution.

For this reason, businesses handling hygroscopic raw materials should follow the manufacturer's storage recommendations, use suitable packaging, and minimize unnecessary exposure to humid air.

What Are Deliquescent Chemicals?

Deliquescent chemicals are substances that absorb water vapor from the atmosphere until the absorbed water dissolves the material, forming an aqueous solution. This behavior occurs when the surrounding relative humidity reaches or exceeds the substance's deliquescence threshold at the relevant temperature.

Unlike a hygroscopic solid that may simply gain moisture or become sticky, a deliquescent solid can gradually lose its original solid form and become liquid as moisture accumulates.

The process depends on the substance's properties and the environmental conditions. Deliquescence does not necessarily mean that the chemical has decomposed or undergone an unwanted chemical reaction; it can be a physical process involving water absorption and dissolution.

Examples of Deliquescent Chemicals

• Calcium chloride: A moisture-absorbing salt used in applications such as dehumidification and moisture control. Under suitable humidity conditions, it can absorb enough water to form a solution.

• Sodium hydroxide: A strongly alkaline chemical that absorbs moisture and can deliquesce when environmental conditions permit sufficient water uptake.

• Potassium hydroxide: A hygroscopic, strongly alkaline substance that can absorb atmospheric moisture and form a solution through deliquescence.

These chemicals require careful storage and handling. Their packaging must be compatible with the chemical, and exposure to atmospheric moisture should be minimized.

For sodium hydroxide and potassium hydroxide, additional precautions are essential because both are corrosive. Always consult the relevant safety data sheet (SDS) before handling, transferring, or storing these materials.

Hygroscopic vs. Deliquescent Chemicals: Key Differences

The main difference between hygroscopic and deliquescent chemicals is the extent of moisture absorption and its effect on the material's physical state. Hygroscopic substances absorb water from the air, while deliquescent substances absorb sufficient water to dissolve and form a solution under suitable conditions.

 

Key takeaway: All deliquescent substances are hygroscopic, but not all hygroscopic substances are deliquescent. Whether a substance deliquesces depends on its properties and the surrounding conditions.

Hygroscopic Chemicals Examples: How They Behave

Different hygroscopic substances absorb and interact with water in different ways. Understanding these differences is important when selecting materials for manufacturing, formulation, laboratory work, and storage.

1. Glycerol

Glycerol is a hygroscopic liquid that absorbs moisture from the surrounding air. Its water content can change depending on exposure and environmental conditions. This property is relevant when controlling the composition of formulations used in cosmetics, personal care, and pharmaceutical applications.

2. Silica Gel

Silica gel is a porous adsorbent commonly used as a desiccant in packaging and storage applications. It captures water molecules on its internal surfaces and helps reduce moisture levels in an enclosed environment.

Although silica gel is often discussed alongside hygroscopic materials, adsorption is the more precise description of how it captures moisture. It should not be confused with salts that absorb water until they dissolve.

3. Concentrated Sulfuric Acid

Concentrated sulfuric acid has a strong affinity for water and absorbs atmospheric moisture. This can change its concentration and may affect its suitability for processes that require a specified chemical composition.

Sulfuric acid is highly corrosive and requires appropriate chemical-resistant containers, protective equipment, and handling procedures. Follow the product-specific SDS and applicable safety requirements.

Examples of Deliquescent Chemicals and Their Uses

Deliquescent chemicals are used in a range of industrial applications, but their tendency to absorb atmospheric moisture can affect storage, weighing, and processing.

1. Calcium Chloride

Calcium chloride is used in moisture-control products and in industrial applications such as dust suppression and de-icing. Its moisture absorption can be useful in these applications, but unwanted water uptake can also change its physical form and mass during storage.

2. Sodium Hydroxide

Sodium hydroxide is used in applications such as chemical manufacturing, pH adjustment, and cleaning formulations. Because it absorbs moisture and is highly corrosive, it should be stored in compatible, tightly closed containers under the conditions specified by the supplier.

3. Potassium Hydroxide

Potassium hydroxide is used in applications including chemical synthesis, alkaline formulations, and certain battery-related processes. Its moisture absorption can affect weighing and composition, making appropriate packaging and moisture control important.

The same chemical can behave differently depending on temperature, relative humidity, physical form, and exposure duration. Industrial users should therefore consult product specifications rather than rely solely on general descriptions of a chemical's properties.

How Humidity and Temperature Affect Moisture Absorption

Relative humidity is an important factor in determining how a chemical interacts with atmospheric moisture. As humidity changes, the tendency of a material to absorb water may also change.

A useful concept for understanding deliquescence is deliquescence relative humidity (DRH). This is the relative humidity threshold at which a substance can absorb enough atmospheric water to dissolve and form a solution at a specified temperature.

When the surrounding relative humidity exceeds the relevant DRH, a deliquescent substance may begin to absorb moisture and form a solution. Below that threshold, it may remain solid under the same conditions, although other moisture-related changes can still occur.

Temperature also influences moisture uptake and the conditions under which deliquescence occurs. The relationship is substance-specific, so a single humidity or temperature limit should not be applied to every chemical.

For industrial storage, the practical approach is to:

• Follow the storage temperature and humidity requirements stated by the manufacturer.

• Keep containers closed when materials are not being dispensed.

• Minimize exposure to humid air during weighing, sampling, and transfer.

• Use appropriate humidity monitoring where required by the material's specification or quality system.

• Review product-specific stability, packaging, and handling requirements before setting storage limits.

Storage Tips for Hygroscopic and Deliquescent Chemicals

Proper storage helps protect moisture-sensitive chemicals from unwanted changes and supports consistent product quality. The specific controls depend on the chemical, its physical form, its intended use, and its hazards.

1. Use Tightly Closed, Compatible Containers

Store chemicals in containers that are chemically compatible with the substance and suitable for limiting moisture ingress. Ensure that lids, closures, seals, and liners are appropriate for the material.

For corrosive substances such as sodium hydroxide, potassium hydroxide, and sulfuric acid, container compatibility is especially important.

2. Maintain Suitable Storage Conditions

Keep moisture-sensitive chemicals in the temperature and humidity conditions recommended by the manufacturer. If a substance requires a controlled environment, monitor the relevant parameters and maintain records where required by the applicable quality procedures.

Avoid placing containers in locations exposed to rain, condensation, or repeated temperature fluctuations.

3. Minimize Exposure During Handling

Open containers only when necessary. Close them promptly after dispensing and avoid leaving powders or liquids exposed to ambient air for extended periods.

Where appropriate, divide materials into suitable working quantities to reduce repeated opening of the main storage container. Any repackaging should preserve traceability and comply with the relevant safety and quality requirements.

4. Use Clean and Dry Handling Equipment

Moisture introduced through wet scoops, contaminated transfer equipment, or improperly dried containers can affect moisture-sensitive materials.

Use clean, dry, chemically compatible tools and follow the required procedures for sampling, weighing, and transfer. Avoid returning unused material to the original container if doing so could introduce contamination or moisture.

5. Select Packaging Based on the Chemical

Packaging requirements depend on the chemical's moisture sensitivity, corrosivity, physical form, and transport conditions. A moisture barrier may be important for some materials, while compatibility and corrosion resistance may be the primary concern for others.

Consult the supplier's packaging specifications and safety documentation before choosing a container or liner.

6. Follow the Safety Data Sheet

An SDS provides important information about hazards, safe handling, storage, incompatibilities, and emergency measures. It should be reviewed alongside the product specification and any applicable site-specific procedures.

If a chemical has absorbed moisture unexpectedly, do not assume that it remains suitable for use. Assess it according to the relevant quality procedures and seek technical guidance from the supplier when necessary.

Why Hygroscopic and Deliquescent Properties Matter in Industrial Applications?

Moisture sensitivity can influence raw-material handling, production efficiency, and final product quality across several industries.

1. Pharmaceuticals

Moisture uptake can affect the mass, flow, stability, or performance of certain pharmaceutical ingredients. Suitable packaging and environmental controls may be required to maintain specified material properties.

2. Cosmetics and Personal Care

Ingredients that absorb atmospheric moisture can influence formulation consistency and water content. Understanding these properties helps formulators maintain control over raw materials and finished products.

3. Chemical Manufacturing

Moisture absorption may affect reaction conditions, concentrations, dosing accuracy, and process consistency. Identifying moisture-sensitive materials early can help businesses establish appropriate handling and storage procedures.

4. Laboratories and Quality Control

Moisture uptake can influence weighing accuracy and the composition of analytical samples. Where a method requires a defined water content, laboratories should follow the prescribed preparation, storage, and measurement procedures.

Across these applications, the appropriate controls depend on the actual chemical and its intended use. At Aseschem, understanding the requirements associated with chemical raw materials helps support informed product selection and storage decisions.

How to Choose and Store Moisture-Sensitive Chemical Raw Materials

Businesses purchasing hygroscopic or deliquescent chemicals should evaluate more than the chemical name alone. A material's grade, specification, packaging, and storage requirements can all influence its suitability for an application.

Before procurement, consider the following:

• Product specifications: Verify the required grade, purity, concentration, and relevant quality parameters.

• Moisture sensitivity: Determine whether moisture uptake can affect the material's intended use or specified properties.

• Packaging compatibility: Confirm that the supplied container and closure are appropriate for the chemical and the expected storage conditions.

• Storage requirements: Review the manufacturer's recommendations for temperature, humidity, and container closure.

• Safety documentation: Obtain and review the current SDS and applicable technical documentation.

• Supplier guidance: Ask for product-specific advice when storage duration, transport conditions, or moisture exposure may affect suitability.

These checks help procurement and technical teams make informed decisions and reduce avoidable handling or quality issues.

Conclusion

The difference between hygroscopic and deliquescent chemicals lies in how much moisture they absorb and what happens as a result. Hygroscopic substances absorb water vapor from the atmosphere, while deliquescent substances absorb sufficient moisture to dissolve and form an aqueous solution under suitable conditions.

Examples such as glycerol, silica gel, calcium chloride, sodium hydroxide, and potassium hydroxide illustrate why moisture-related properties must be evaluated individually. Relative humidity, temperature, packaging, and exposure time can all influence material behavior.

For businesses handling chemical raw materials, appropriate storage, compatible packaging, controlled exposure, and adherence to product specifications are essential considerations. Aseschem emphasizes the importance of understanding chemical properties when evaluating raw materials for industrial use.

Always consult the relevant product specification and safety data sheet for chemical-specific storage and handling instructions.

Frequently Asked Questions

1. What is the difference between hygroscopic and deliquescent chemicals?

Hygroscopic chemicals absorb water vapor from the surrounding air. Deliquescent chemicals absorb enough moisture to dissolve and form an aqueous solution under suitable environmental conditions. Deliquescent substances are therefore a specific type of hygroscopic substance.

2. What are some examples of hygroscopic chemicals?

Glycerol and concentrated sulfuric acid absorb moisture from the atmosphere. Silica gel is also used to capture moisture as a desiccant, primarily through adsorption. These materials have different properties and moisture-uptake mechanisms.

3. What are common examples of deliquescent chemicals?

Calcium chloride, sodium hydroxide, and potassium hydroxide can exhibit deliquescent behavior under suitable humidity and temperature conditions. Their handling and storage requirements should be determined from the relevant product documentation.

4. How should hygroscopic chemicals be stored?

Store hygroscopic chemicals in tightly closed, chemically compatible containers under the temperature and humidity conditions recommended by the manufacturer. Minimize exposure to ambient air, use clean and dry handling equipment, and follow the relevant SDS.

5. Why is moisture control important for hygroscopic materials?

Moisture absorption can change a material's mass, concentration, consistency, flow properties, or suitability for an industrial process. Controlling exposure helps maintain the material's specified characteristics and supports accurate weighing and dosing.

6. Why do deliquescent chemicals turn into liquid?

Deliquescent chemicals absorb atmospheric water until the absorbed moisture dissolves the substance and forms an aqueous solution. This occurs when environmental conditions permit sufficient water uptake, typically when relative humidity reaches the substance's deliquescence threshold.

7. What is deliquescence relative humidity (DRH)?

Deliquescence relative humidity is the relative humidity at which a substance can absorb enough water vapor to dissolve and form a solution at a specified temperature. The threshold differs between substances and can vary with temperature.

8. Can hygroscopic and deliquescent chemicals be stored together?

There is no universal rule that all such chemicals can or cannot be stored together. Storage decisions must consider chemical compatibility, hazards, packaging, environmental requirements, and applicable segregation rules. Follow the SDS and the site's chemical-storage procedures.

9. What happens if a moisture-sensitive chemical absorbs too much water?

Depending on the substance, excess moisture may cause clumping, caking, changes in concentration, altered flow properties, or deliquescence. If the material no longer meets its specification, assess it using the applicable quality procedures before use.

10. What is the difference between hygroscopic and hydrophobic materials?

Hygroscopic materials tend to absorb moisture from the air, while hydrophobic materials tend to repel water or resist wetting. The terms describe different interactions with water and should not be used interchangeably.