4. The sources of Air Emission in Leather
Air emissions in leather production can be toxic and may contain odorous substances. For example, sulphides, ammonia, organic solvents, and other particulates. Emissions of those toxic substances may reach levels requiring ventilation of the workplace.
- Leather dust from mechanical operations and powdered dyestuffs can also require special ventilation arrangements.
- Sulphides, thioles, and organic solvents: Odour tend to be generated by these substances. Odour from putrefaction may constitute a major problem.
- Organic solvents: They are used as carriers in the formulation of the finish and they are also used in commercial finishing products (e.g. lacquers).
The main problem with organic solvent-based coating agents is the emission of volatile organic compounds (VOCs), which are released during and after the coating process. The emission of organic solvents are currently regulated by laws in different areas of the world. Therefore, leather coating activities must comply with those laws. Furthermore, solvents which are used in a coating process are assumed to be emitted unless they have been recovered. All these risks compounded by high fire hazards making finishing departments possibly the most potentially harmful to workers’ health.
Indeed untreated organic solvent emissions from the finishing process can vary between 100 and 3500 mg/m
3 in conventional processes. About 50% of measurable emissions arise from spray-finishing machines, 50% from dryers. Fugitive emissions to the air and solvents in wastes represent the rest of solvent consumption. (Source: UNIDO- The FSLM 2019)
The main parameters important to understand the convenience of the single organic solvent-based finishing agents are the:
- Type of organic solvent used with regard to toxicity and the recycling options;
- Efficiency of abatement in all processes where organic solvents can be released;
- Ratio of recycling or reuse of the organic solvent.
(Source: UNIDO- The FSLM 2019)VOC releases from leather during storage are estimated as 10% of the applied organic solvents that remain in the leather; and about 60% of the amount emitted in the drying tunnel. The rest is emitted during storage. Ideally, VOC free finishing systems should be based on renewable resources.