VOCs in industrial processes. What mitigation strategy?

Volatile Organic Compounds (VOCs ) and odors can be generated by various industrial processes. Identifying potential sources of VOC emissions from these processes is essential to developing effective mitigation strategies.

Among the substances used in industry, solvents in particular emit VOCs. They are used in the composition of products that will be consumed as raw materials or supplies in an industrial process, e.g. paint, ink, varnish, paint strippers, maintenance products, cleaning products, phytosanitary products, cosmetics, etc.

All industrial sectors use solvents that emit VOCs in their various process operations. For example:

• Clean and sanitize surfaces and products: floors, equipment, clothing…
• Degreasing metal and plastic parts …
• Dissolve and strip glue and paint residues…
• Diluting a product: inks used by printers, paints used by painters, but also agricultural products…
• Extract, separate, synthesize and purify chemical compounds

We’d like to take you on a tour of VOC minimization practices in industrial processes.

General VOC reduction practices in industrial processes

To mitigate the presence of VOCs in an industrial process, here are some common practices in the industrial sector

• Install a VOC extraction system at source and a treatment system. For example, extraction hoods and an activated carbon adsorption filter can be used to minimize the dispersion of VOCs in the ambient air.
• Substitute products containing VOCs with alternative substances with lower VOC content, when the industrial process allows. To do this, it is first necessary to identify and assess the specific sources of VOCs on the industrial site.
• Optimize industrial processes to minimize VOC emissions (adjust production parameters, optimize operating conditions, etc.).
• Regularly check industrial equipment for VOC leaks.
• Ensure that waste management practices reduce VOC emissions. This may involve using closed containers, recycling solvents and disposing of waste properly.
• Set up an air quality monitoring system to detect VOC concentrations (e.g. electronic nose).
• Ensure that theindustrial installation complies with the standards and limits imposed by VOC emission regulations.
• Raising staff awareness of the risks associated with VOCs.
• By adopting these best practices, companies can help to reduce VOC emissions, control industrial odours and improve indoor air quality, benefiting both workers’ health and the environment.

By adopting these practices, manufacturers will emit fewer VOCs and improve ambient air quality, which will benefit both the health and safety of workers and the environment.

VOCs emitted by certain industrial processes

Here are a few industrial processes that can produce VOCs and odors, and the associated mitigation strategies.

What VOCs are emitted in industrial printing processes, and what are the mitigation strategies?

VOCs emitted by the gravure printing process

This printing process for very large runs of catalog periodicals, or for mass-produced cardboard packaging (e.g. cigarette packaging, confectionery, liquids, etc.) uses toluene as a solvent. It is an aromatic VOC included in ink formulations or used to dilute inks. Over 95% of toluene used in the print production process ends up in ambient air; and less than 5% of toluene used ends up in paper fibers (ANESM 2012). Packaging gravure tends to use solvents that emit oxygenated VOCs (ester, alcohol, ketone).

In addition, VOCs are emitted at the output of printing and drying processes: effluents containing VOCs, solvent recovered for reuse or sale, VOCs emitted by the process or the solvent recovery system.

VOC mitigation strategy for gravure printing

The use of a retention ink which reduces the speed of film formation compared with toluene inks. VOC emissions are then concentrated in the drying unit, where they are captured and treated.

VOCs emitted by the offset printing process

This printing process is used for large runs of books, magazines and catalogs. At the start of the printing process, VOCs are released by inks, fount solution (containing isopropanol) and additives. Duringprinting, a diffuse emission of isopropanol occurs. Drying the print emits the highest proportion of VOCs. In addition, the ink in the print may slightly release VOCs. At the end of the printing process, when the plates and cylinders are cleaned, the solvents used emit very small quantities of VOCs (aliphatic, cyclic and/or naphthenic hydrocarbons (white spirit, naphtha, etc.).

VOC mitigation strategy in offset printing

Source capture at the furnace and treatment of VOC-laden off-gases is the first preventive measure.

Adding glycol ethers (1% to 5%) to the fount solution can halve the proportion of isopropanol (from 10% to 5%), and thus reduce VOC emissions from the plant by up to 40%. However, glycol ethers are VOCs, some of which are toxic.

Volatile solvents can also be partially or totally substituted in products used to clean equipment and supplies.

VOCs emitted by the flexographic printing process

Flexography is a relief printing process using a flexible photopolymer plate on a rotary press. This process works like a continuous inking unit and can be used to print flexible packaging (corrugated or flat cardboard, plastic films, advertising bags), adhesive labels, metal packaging, etc. The solvents used in flexography that emit VOCs are alcohols, acetates and glycol ethers.

VOC mitigation strategy for flexo printing

The use of water-based inks (may contain between 5 and 20% solvent) or UV inks (need to change presses). Remaining solvents should be captured at source and treated with activated carbon.

VOCs emitted by letterpress printing

Letterpress is a printing process that consists of printing the raised characters that make up a text onto paper. Letterpress printing is used for documents with print runs of between 20,000 and 30,000 copies: leaflets, flyers, administrative documents. VOCs emitted by solvents and thinners include hydrocarbons (turpentine, toluene, xylene, etc.), chlorinated compounds and ethyl alcohol.

Letterpress VOC mitigation strategy

The use of low-VOC inks, theinstallation of a source capture and filtrationsystem , and the management of VOC-emitting printing waste are all part of the mitigation strategies for the letterpress printing process.

VOCs emitted in screen printing

Silk-screen printing, an ink-impregnated textile screen printing process, can print on paper, cardboard, fabric, wood, metal, plastic, etc., each time using an appropriate ink. The graphics industry (advertising, signage, fine arts, etc.), electronics (printed circuits) and floor and wall coverings are the main users. The VOCs emitted by screen printing are diverse: aromatic VOCs (trimethylbenzene, toluene, xylene), alicyclic VOCs (cyclohexane), oxygenated VOCs (alcohols, ketones, esters). They are due to theevaporation of the solvent contained in the ink (up to 65%), in cleaning products.

VOC mitigation strategy for screen printing

The use of water-based inks and ink removers with low VOC emissions (e.g. soy methyl ester) reduces emissions. Capturing VOCs at source during screen and ink preparation, printing, transfer and drying, and screen cleaning is essential. Storage of VOC-emitting waste in ventilated garbage cans completes the VOC mitigation system.

What VOCs are emitted in industrial coating processes, and what are the mitigation strategies?

VOCs emitted in automotive paint processes

In automotive production, the paint application process includes several steps that emit VOCs. The “primary” layers are applied by electrophoresis. Subsequent coats of primer (solvent content 37-60%), base (75%), lacquer (60-70%) or varnish (60%) are usually applied by spraying, followed by cleaning and drying. The VOCs emitted at each stage by the solvents contained in different coatings are: white spirit (a group of aliphatic hydrocarbons), isopropanol, benzyl alcohol, ethanol and acetone.

VOC mitigation strategy for coating processes in automotive production

Gaseous effluent treatment by capturing VOCs at source and filtering them, in particular using activated carbon, forms the basis of prevention. The use of coating application techniques that reduce solvent consumption during spraying and cleaning operations, the organization of production to reduce solvent consumption and recovery, the choice of waterborne or powder paints, and the use of solvent-free cleaning products in the case of waterborne paints are all mitigation strategies in this sector.

VOCs emitted by other industrial coating processes (excluding automotive manufacturing)

These are the VOCs emitted by paint, lacquer and varnish applications on plastic, metal, textiles, ceramics, glass… Products containing solvents (30 to 80%) are used for: cleaning the substrate, applying the coating, drying.

• VOCs emitted by solvents used in metal coating include: butyl acetate and xylene (for thinning); methyl ethyl ketone, acetone, toluene (for cleaning), and also benzene, formaldehyde…
• On plastics, coating and cleaning operations emit VOCs such as butyl acetate, xylene, methyl isobutyl ketone, isobutanol and formaldehyde.
• On textiles, the VOCs emitted are methyl ethyl ketone, toluene and perchloroethylene.
• On other substrates, the main VOCs emitted are butyl acetate and xylene.

VOC mitigation strategy for industrial coating processes

Apart from source capture and treatment of VOCs as the main mitigation measure, source reduction of VOCs is a complementary strategy. This means using spraying techniques that reduce VOC emissions, using products that contain fewer VOCs (high-solids, water-based or powder paints), and using cleaning techniques that consume less solvent.

VOCs emitted in the bodywork sector

These are VOCs emitted during the application of paint and varnish to bodywork to be refinished and repainted, and by cleaning products. These are mainly aromatic and aliphatic hydrocarbon VOCs, and oxygenated VOCs (alcohols, ketones, esters).

VOC mitigation strategy for bodywork refinishing

Capture at source in paint booths, then treatment before external discharge to comply with emission limit values based on the surface area of the workshop and the quantity of solvent used, remains the main mitigation measure. The use of spraying techniques that reduce paint consumption and therefore VOC emissions, the use of products with lower VOC emissions (high-solids paint, waterborne paint or varnish, UV varnish), and cleaning techniques that reduce VOC emissions are the most common mitigation strategies in the bodywork sector.

What VOCs are emitted in the manufacture of paints, varnishes, inks and adhesives, and what are the mitigation strategies?

The formulation components of these substances are prepared and stored in liquid form from powdered materials and solvents. The components are then dispensed in the required doses and mixed to form the finished product. Around 200 VOCs can be used as solvents in this industrial sector. For paint, varnish and ink manufacturing processes, the VOCs emitted include aliphatic and aromatic hydrocarbons, xylene, toluene, dichloromethane, esters and alcohols. For glue and gelatin production processes, the main VOCs are methyl ethyl ketone, ethyl acetate and hydrocarbons.

VOC mitigation strategy for the manufacture of paints, varnishes, inks and adhesives

The first measure is the capture at source and treatment of VOC-laden off-gases. For example, the use of mobile activated carbon filters is highly adaptable to variations in production conditions. VOC emission mitigation strategies involve the use of substitute products with low solvent content (waterborne or high-solids products), or solvent-free products. For cleaning products, manufacturers can replace organic solvents with aqueous solutions of sodium hydroxide and potassium hydroxide, heated to 80° but requiring treatment of the wash water.

What VOCs are emitted in adhesive coating production processes, and what are the mitigation strategies?

VOCs enter an adhesive coating process via the solvent-based glues that will coat the surface of this coating, and via the thinners used. VOC emissions are high during drying. The main distinctions are

• acrylic glues for making adhesives (tapes, labels, etc.), gluing floor and wall coverings, applying PVC sheeting to wood panels, etc.
• vinyl glues used to bond PVC parts in the automotive industry (windshields, etc.), the building industry (drainpipes, etc.) and the construction industry.
• polyurethane adhesives for the packaging, textile and footwear industries
• neoprene adhesives for the automotive, footwear and construction industries.

Industrial adhesive coating processes mainly emit the following VOCs: methyl ethyl ketone, dimethyl ethyl ketone, butyl acetate, ethyl acetate, ethyl benzene, toluene, xylene.

VOC mitigation strategy in adhesive coating manufacturing

In the drying process, VOC emissions are captured at source and then filtered by activated carbon, significantly reducing atmospheric emissions. Other VOC mitigation techniques are identical to those used in glue manufacture, as described above.

What VOCs are emitted in pharmaceutical manufacturing processes, and what are the mitigation strategies?

Industrial processes range from the production of the active pharmaceutical ingredient (raw material) to the production of a pharmaceutical form (tablet, capsule, ointment, syrup, spray, etc.). Many operations in pharmaceutical manufacturing processes involve solvents and lead to the emission of VOCs: loading a mixer, filling effluent storage tanks, injecting sterile air into pipes to eliminate the product before cleaning, transferring solvent from tanker trucks into storage drums, sampling for quality control… The pharmaceutical industry uses some fifty solvents that emit VOCs. These include a dozen specific CMR-classified VOCs: dioxane, chloroform, dimethylformamide, dichloroethane, methylene chloride, perchloroethylene, dimethylamine, diglyme and triglyme.

VOC mitigation strategy in drug manufacturing

Each operation using solvents and emitting VOCs requires source capture and treatment. Often the process used is adsorption on activated carbon alongside thermal oxidation. Minimizing VOC emissions involves isolating sources and drying in closed circuits to reduce fugitive emissions, cleaning closed equipment and recirculating process purges where possible to avoid direct VOC emissions through openings. The substitution of solvents is more delicate, as they are chosen for their physicochemical characteristics which contribute to the process. On a case-by-case basis, the manufacturer can substitute the solvent used for the operation with a solvent emitting less toxic VOCs.

What VOCs are emitted in mechanical engineering processes, and what are the mitigation strategies?

These mainly involve cleaning metal surfaces before or after machining to remove grease, cutting fluids, oils and solid particles. The aim is either to prepare for the next operation, or to improve the appearance of the surface. Cleaning can combine solvent-based chemical action, mechanical action (ultrasound, spraying, manual or mechanical agitation), and a certain level of temperature to increase chemical efficiency. Rinsing and drying often follow. The VOCs traditionally emitted in this type of operation are: halogenated VOCs (perchloroethylene, dichloromethane, trichloroethylene), hydrocarbon VOCs, oxygenated VOCs (acetone, ethanol, isopropanol, glycol ethers, glycol esters, methyl ethyl ketone).

VOC mitigation strategy for the mechanical engineering industry

VOCs are captured at source and recovered by activated carbon filtration as a priority. Solvent substitution by detergents (with additives that emit fewer VOCs), detergents containing surfactants and bacteria (biogenic VOC emissions), agrosolvents, thermal stripping, laser or cold plasma processes (nuclear and aeronautical industries), ice or dry ice blasting (specific applications), CO ₂ ( currently being industrialized).

What VOCs are emitted in foundry processes, and what are the mitigation strategies?

Casting involves pouring molten metal into a mold to produce a metal part. The mold can be made using the sand-to-green process (sand + clay + carbon) or a chemical setting process (sand + resin). The use of chemical binders results in the production of various VOCs during mixing, molding and core-making, storage, casting and cooling. The main VOCs emitted during the industrial process are: volatile organic carbon, aromatic hydrocarbon VOCs: benzene, ethylbenzene, toluene, xylene (BTEX), oxygenated VOCs including aldehydes (formaldehyde, acrolein, acetaldehyde), phenol, alcohol, esters.

VOC mitigation strategy for the foundry industry

The first strategy is to capture emissions at source using extractor hoods, and treat them at the various stages of the process. To reduce emissions at source, the use of graphite in the green sand process reduces volatile carbon. As for the chemical setting process, the trend is towards the use of resins with fewer VOC-emitting components.