Usage Methods and Environmental Considerations of Cyclohexylamine in Leather Tanning Processes

Introduction

Cyclohexylamine (CHA), also known as 1-cyclohexylamine or cyclohexanamine, is an organic compound with the molecular formula C6H11NH2. It is a colorless liquid with a strong amine odor and is widely used in various industrial applications, including leather tanning. The leather tanning industry has been utilizing CHA for its unique properties that enhance the quality and durability of leather products. This article aims to provide a comprehensive overview of the usage methods and environmental considerations of cyclohexylamine in leather tanning processes. We will delve into the product parameters, application techniques, environmental impacts, and regulatory guidelines, supported by relevant literature from both domestic and international sources.

Product Parameters of Cyclohexylamine

Physical and Chemical Properties

Property	Value
Molecular Formula	C6H11NH2
Molecular Weight	101.16 g/mol
Appearance	Colorless liquid
Odor	Strong amine odor
Boiling Point	134-136°C
Melting Point	-28°C
Density	0.86 g/cm³ at 20°C
Solubility in Water	20 g/100 mL at 20°C
pH (1% solution)	11.5
Flash Point	47°C
Autoignition Temperature	450°C
Viscosity	1.3 cP at 20°C

Safety and Handling

Hazard	Description
Flammability	Highly flammable; keep away from heat, sparks, and open flames.
Toxicity	Inhalation can cause irritation to the respiratory system. Skin contact can cause burns. Eye contact can cause severe irritation and damage.
Environmental Impact	Can be harmful to aquatic life if released into water bodies.
Storage Conditions	Store in a cool, well-ventilated area. Keep container tightly closed.
Personal Protective Equipment (PPE)	Use gloves, goggles, and a respirator when handling.

Usage Methods in Leather Tanning

Pre-Tanning Stage

In the pre-tanning stage, cyclohexylamine is often used to adjust the pH of the hide or skin. This step is crucial for ensuring that the subsequent chemical treatments are effective. The pH adjustment helps in the removal of non-fibrous proteins and other impurities from the raw hide.

Step-by-Step Process:

1. Preparation of Solution: Dissolve cyclohexylamine in water to create a 1-2% solution.
2. Application: Immerse the hides in the solution for 1-2 hours.
3. Rinsing: Rinse the hides thoroughly with water to remove excess CHA.

Tanning Stage

During the tanning process, cyclohexylamine acts as a pH buffer and a catalyst for the tanning agents. It helps in the uniform distribution of tanning agents, such as chromium salts, throughout the hide, resulting in a more consistent and durable leather product.

Step-by-Step Process:

1. Preparation of Tanning Bath: Mix the tanning agent (e.g., chromium sulfate) with water and add the required amount of cyclohexylamine to adjust the pH to the desired level (usually around 3.5-4.0).
2. Soaking: Soak the hides in the tanning bath for 8-12 hours.
3. Draining and Drying: Drain the hides and allow them to dry naturally or in a controlled environment.

Post-Tanning Stage

In the post-tanning stage, cyclohexylamine can be used to neutralize any residual acidity and to improve the softness and suppleness of the leather. This step is essential for enhancing the final quality of the leather product.

Step-by-Step Process:

1. Neutralization: Prepare a 1-2% solution of cyclohexylamine and immerse the tanned hides for 30-60 minutes.
2. Softening: Add a softening agent (e.g., lanolin) to the solution to further enhance the leather’s flexibility.
3. Final Rinsing and Drying: Rinse the hides thoroughly and allow them to dry completely.

Environmental Considerations

Wastewater Management

The use of cyclohexylamine in leather tanning generates wastewater that contains high levels of organic compounds and other pollutants. Proper management of this wastewater is crucial to prevent environmental contamination.

Treatment Methods:

1. Physical Treatment: Sedimentation and filtration to remove solid particles.
2. Chemical Treatment: Neutralization of pH using acids or bases.
3. Biological Treatment: Aerobic or anaerobic digestion to break down organic compounds.
4. Advanced Oxidation Processes (AOPs): Use of ozone, hydrogen peroxide, or UV light to degrade persistent pollutants.

Air Emissions

The use of cyclohexylamine can result in the release of volatile organic compounds (VOCs) into the air, which can have adverse effects on human health and the environment. Effective ventilation systems and emission control technologies are necessary to minimize these emissions.

Control Measures:

1. Enclosure and Ventilation: Enclose the tanning areas and use exhaust fans to vent VOCs outside.
2. Adsorption: Use activated carbon or other adsorbents to capture VOCs.
3. Incineration: Burn off VOCs in a controlled incinerator.

Soil Contamination

Improper disposal of tanning waste can lead to soil contamination, affecting plant growth and soil microorganisms. Regular soil testing and remediation measures are essential to mitigate these risks.

Remediation Techniques:

1. Phytoremediation: Use of plants to absorb and degrade contaminants.
2. Chemical Remediation: Application of chemicals to neutralize or precipitate contaminants.
3. Bioremediation: Use of microorganisms to break down contaminants.

Regulatory Guidelines

International Regulations

1. REACH (Registration, Evaluation, Authorization and Restriction of Chemicals): The European Union’s REACH regulation requires manufacturers and importers to register cyclohexylamine and provide safety data sheets (SDS) for its use.
2. OSHA (Occupational Safety and Health Administration): In the United States, OSHA sets permissible exposure limits (PELs) for cyclohexylamine to protect workers’ health.
3. GHS (Globally Harmonized System of Classification and Labelling of Chemicals): The GHS provides a standardized framework for classifying and labeling chemicals, including cyclohexylamine, to ensure safe handling and transport.

Domestic Regulations

1. China’s Environmental Protection Law: Requires tanneries to implement pollution control measures and comply with national discharge standards.
2. India’s Environment (Protection) Act: Mandates the use of best available technologies (BAT) to minimize environmental impact and ensures compliance with effluent discharge norms.
3. Brazil’s National Environmental Council (CONAMA): Sets standards for the treatment and disposal of industrial waste, including tanning waste.

Case Studies

Case Study 1: Environmental Impact Assessment in India

A study conducted by the Central Pollution Control Board (CPCB) in India evaluated the environmental impact of cyclohexylamine in leather tanning. The study found that the implementation of advanced wastewater treatment methods, such as AOPs, significantly reduced the concentration of organic pollutants in the effluent. Additionally, the use of bioremediation techniques helped in the degradation of residual contaminants in the soil.

Case Study 2: Occupational Health and Safety in the United States

The National Institute for Occupational Safety and Health (NIOSH) conducted a study on the occupational health and safety of workers in tanneries using cyclohexylamine. The study recommended the use of personal protective equipment (PPE) and the installation of local exhaust ventilation systems to reduce worker exposure to VOCs. The implementation of these measures resulted in a significant decrease in reported cases of respiratory and skin irritation among workers.

Conclusion

Cyclohexylamine plays a vital role in the leather tanning industry, contributing to the production of high-quality and durable leather products. However, its use also poses significant environmental and health challenges. By adhering to proper usage methods, implementing effective waste management practices, and complying with regulatory guidelines, the leather tanning industry can minimize the negative impacts of cyclohexylamine and ensure sustainable operations.

References

1. European Chemicals Agency (ECHA). (2021). REACH Regulation. Retrieved from https://echa.europa.eu/reach
2. Occupational Safety and Health Administration (OSHA). (2021). Permissible Exposure Limits (PELs). Retrieved from https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9992
3. United Nations Economic Commission for Europe (UNECE). (2021). Globally Harmonized System of Classification and Labelling of Chemicals (GHS). Retrieved from https://www.unece.org/trans/main/danger/publi/ghs/ghs_welcome_e.html
4. Central Pollution Control Board (CPCB). (2020). Environmental Impact Assessment of Leather Tanning Industries. New Delhi: CPCB.
5. National Institute for Occupational Safety and Health (NIOSH). (2019). Occupational Health and Safety in Tanneries Using Cyclohexylamine. Cincinnati, OH: NIOSH.
6. Zhang, L., & Wang, X. (2018). Advanced Wastewater Treatment Technologies in Leather Tanning. Journal of Environmental Science and Technology, 12(3), 456-468.
7. Mishra, S., & Singh, R. (2017). Bioremediation of Tanning Waste Contaminated Soil. Journal of Environmental Management, 201, 123-134.
8. Conselho Nacional do Meio Ambiente (CONAMA). (2021). Resolução CONAMA No. 430. Brasília: CONAMA.