Energy saving manufacture of foam component isocyanate

Gas is key

Polyurethane foam is found in mattresses and upholstery, insulates refrigerators and buildings, and makes for particularly lightweight vehicle parts. It is a versatile material that ensures greater comfort and helps save energy. The components can also be produced in an environmentally responsible way – thanks to innovative processes from Covestro.
At its Dormagen site in Germany, Covestro needs 80 percent less solvent and 60 percent less energy to produce isocyanates.

Chemist Otto Bayer was actually trying to find a new way to produce textile fibers when instead, over 75 years ago, he invented a completely new type of plastic – polyurethanes. This material has become part and parcel of many everyday life products based on coatings, adhesives as well as flexible and rigid foams.

Polyurethanes are primarily produced from two chemical substances – isocyanates and polyols. Covestro ranks among the leading manufacturers of these two components. The company also considers itself a pioneer in improving the manufacture of these raw materials, making it easier, more cost-effective and eco-friendly. Researchers and process engineers are continuously working on improvements, often in collaboration with external partners.

60 percent less energy

Gas-phase technology is one of the success stories in isocyanate production. Among other things, it requires far less energy than liquid-based processes. It is used to produce isocyanates such as toluene diisocyanate (TDI), which is needed for flexible polyurethane foam. The key to this breakthrough is that two chemicals – toluene diamine (TDA) and phosgene – react in a gaseous state rather than as liquids in the final production step.

As a result, 80 percent less solvent and 60 percent less energy are needed. What’s more, annual carbon dioxide emissions for a typical large-scale plant (with a production capacity of 250,000 metric tons of TDI) are 60,000 metric tons lower than with the conventional process.

In addition to this, gas-phase technology helps increase the TDI yield, because the reaction takes place much faster and there are fewer secondary reactions. Also, 40 percent less phosgene is required per kilogram of TDI. And the benefits don’t end there. The fact that plants can be smaller makes them less expensive, with 20 percent lower investment costs than for a conventional production facility.

Use in industrial-scale plants

Covestro has been using this process at an industrial-scale plant at its site in Shanghai, China since 2011. It is also in use at a new plant in Dormagen, Germany, which was commissioned in late 2014. Covestro is just as innovative when it comes to manufacturing the isocyanate methylene diphenyl diisocyanate (MDI), the component for rigid foam. This requires the chemical aniline, from which the direct MDI precursor methylene diphenyl diamine (MDA) is obtained. In conventional (isothermal) aniline manufacture (from nitrobenzene and hydrogen gas), the heat generated is removed by carrier oils.

However, Covestro has developed an alternative that is far more ecologically compatible and efficient. This adiabatic process does not involve any heat exchange with the surroundings. Instead, the reaction heat is dissipated directly with the flow of aniline gas.

Among other things, this means the process requires a quarter less energy than the conventional one. The aniline produced in this way is also purer. Covestro is already using this technology at an MDI plant in Shanghai with an annual capacity of 350,000 metric tons.