Purifying PU manufacturing emissions by eliminating isocyanates

Polyurethane (PU) is a highly versatile substance valued for its application in the automotive, home insulation, mattress, textile and shoe-making sectors among many others across Europe. However, PU is derived from compounds that have the potential to harm human health and the environment if released into the air. These include isocyanates and tetrahydrofuran. DESOTEC supplies industries across Europe with mobile activated carbon filters that can purify air flows from PU manufacturing, enabling them to keep well within legal limits.

The problem

The most well-known usage of PU is as a hard or flexible foam, which has insulating, thermal, sealing and acoustic properties.

However, the base material includes isocyanates, such as toluene diisocyanate (TDI) and methylene diphenyl diisocyanate (MDI). These toxic compounds are harmful to human health and the environment.

Another type of PU material is used to make synthetic fibres and elastics, including Spandex. This PU is derived from tetrahydrofuran (THF), a solvent.

There are several ways in which these various contaminants can be released into the environment if not filtered out.

Firstly, during the production of foam, an gas stream is blown into the liquid product. This results in emissions with high flow rate but low concentration of contaminants.

Secondly, during the storage of the raw materials in liquid form. The tanks vent gases, which contain MDI and TDI.

Thirdly, during the creation of thermoplastics at high pressure and high temperature in a reactor. The depressurisation of the reactor can cause emissions containing contaminants.

Finally, when PU is injected into moulds, for example to create car seats and mattress cores. Residues are left on the moulds, which must then be cleaned with solvents. This also creates polluting emissions.

All these applications require different solutions.

The solution

DESOTEC works with several plants using PU, helping analyse their problems and find viable solutions.

One company that uses a reactor to create thermoplastics suffered a failure in their existing filtering system. Within one week, DESOTEC was able to supply a mobile alternative as a back-up: the AIRCON HC.

This is essentially a silo filled with activated carbon, capable of handling a low flow rate with high concentrations of contaminants.

It has now become the plant’s long-term filter solution.

Another firm makes PU foam, discharging a high flow rate with low concentrations of MDI and TDI.

DESOTEC worked with the company to find a solution that could handle this flow rate. It installed two parallel AIRCON V-XL filters, which together can treat a flow rate of 110 000 m³ per hour.

In all cases, DESOTEC filters are provided on a rental basis, so companies do not need to make a major up-front investment.

When the filters are saturated, DESOTEC exchanges them and transports the spent filters off-site, so clients do not need to handle the spent carbon themselves.

The result

Isocyanates have a very high boiling point and a large molecular structure, making them highly adsorbable by carbon. Therefore, DESOTEC filters have proven to be highly effective.

All companies producing PU have found that DESOTEC full-service filtration solutions remove more than 99% of pollutants from their emissions – well within the legal limits set by authorities.

Filters are available in a range of sizes, meaning they can be suitable for even small-scale emissions that companies might not have previously considered.

DESOTEC helps clients analyse their daily or weekly results until they find the right level of carbon for their application.