Chlorinated VOC removal in the pharma sector

Methylene chloride, or dichloromethane (DCM), is a solvent with a wide variety of applications in sectors as varied as food and aviation. In the pharmaceutical industry, it is used to extract chemicals from plants or foods for medicines such as steroids, antibiotics and vitamins. However, it is toxic to human health, with the known potential to irritate the skin and damage the central nervous system. Therefore, air emissions containing DCM are subject to stringent controls, which vary between countries and industries. Activated carbon is a highly effective method for purifying air emissions of DCM, used either on its own or to ‘polish’ emissions that have already been treated through e.g. cryogenic condensation.

The problem

Our client, a medium-sized company, is one of many in Italy, which produces goods on behalf of major names in the pharma sector. It was commissioned to make three batches of a molecule for registration purposes, with a view to starting full-scale production at a later date.

The production process would result in air emissions from a reactor that would contain volatile organic compounds (VOCs) with smaller amounts of toluene and other compounds.

In Italy, plants starting production today are subject to very low DCM limits: at least under 20 mgC/m3, and sometimes as low as 5 mgC/m3. This legal limit did not apply in this case as it was just a trial run, but the client knew it needed to find a solution for the longer term and wanted to test this on beforehand.  

As the chlorinated VOC emissions would be emitted due to tank venting and depressurization, the flow rate would be very low: around 200 m3/h. The client had been told by other firms providing activated carbon filters that none were suitable for low flow rates due to the risk of channelling ­– when emissions find the easiest path through a filter, saturating some spots of the filter bed while leaving the remainder untouched.  

Therefore, the client believed its only option was cryogenic condensation, which involves lowering the temperature of emissions so that contaminants are turned into liquid droplets, which can then be treated.

This method is expensive and may not fully remove pollutants from emissions. The equipment is also complicated to install, so not suitable for a trial run.

The solution

The client first encountered DESOTEC at the Ecomondo trade fair in November 2019 in Italy and found, to its surprise, that we were able to offer a suitable filter for low flow rates: the AIRCON 2000 C.

This model is specifically designed to treat very low air flows and avoid channelling. Furthermore, it can handle concentration peaks, as is typical for emissions released when reactors are opened.

As DESOTEC’s filters are easy to install or remove, and are available on a daily rental basis, the client could try them out before making a long-term decision. Although the client did not need an immediate solution, it decided to take a proactive approach.

Within two weeks of this initial meeting, DESOTEC had carried out preliminary evaluations. Within one month, we had installed two AIRCON 2000 C filters at the plant, ready to start immediately.

The results

Production went ahead on the three trial batches, with the client monitoring emissions to evaluate the DESOTEC filters. It found that concentrations of DCM after treatment were well below 5 mgC/m3, at around 1 or 2 mgC/m3.

The company was delighted and is now ready to implement the DESOTEC system when they start full-scale manufacture of this product.

In discontinuous production processes such as this, activated carbon is a cost-effective solution: emissions simply pass through the filter, and contaminants are adsorbed if present. Cryogenic condensation, however, requires energy usage whether or not emissions contain pollutants, driving up costs.

DESOTEC filters could also be used to ‘polish’ emissions that have been treated cryogenically, before discharging the cleaned air harmlessly into the atmosphere.

The client is also pleased with how easy DESOTEC filters are to install or remove, allowing them to expand production quickly with no upfront investment required.

This offers them the flexibility to win new commissions from third-party clients, conduct trials and expand their business when needed.