How greenhouse gas vanishes into thin air
Sustainability and climate protection | Laughing gas, or nitrous oxide, sounds anything but dangerous, but it is much more harmful to the climate than CO2. So thyssenkrupp developed a process to remove it almost entirely from emissions from industrial plants.
CO2 is considered to be the gas which is the primary cause of climate change and global warming. However, there are many other gases which are in fact considerably more harmful in direct comparison. For example, a metric ton of nitrous oxide is over 265 times more harmful to the climate than a ton of CO2. The substance with the chemical formula N2O does actually occur naturally in the earth’s atmosphere, but only in very small quantities. But as nitrous oxide now occurs in concentrated, man-made form, it is having similar effects to other greenhouse gases. It forms a layer which is impermeable to thermal radiation and prevents the heat reflected by the earth from escaping into space. This slowly contributes to the warming of the atmosphere, particularly as nitrous oxide remains there for around 120 years on average, before it is broken down again.
Nitrous oxide is created in large quantities during the manufacture of nitric acid, which is an important basic material in the production of fertilizer. Year after year almost 500,000 tons of nitrous oxide are created here – which corresponds to approx. 130 million tons of CO2. So with the right process it is possible to eliminate a lot of harmful gas, particularly as – in contrast with CO2 – nitrous oxide is relatively easy to split into its harmless components, nitrogen and oxygen. thyssenkrupp Industrial Solutions already developed just such a process, EnviNOx®, years ago.
enviNOx: waste gas is turned into clean air
“The waste gas is simply passed over a special catalyst, with the aid of which the N2O is broken down into its component parts,” explains Meinhard Schwefer, Principal Chemist at thyssenkrupp Industrial Solutions. This is made possible by zeolite catalysts (aluminum silicates), which have been activated in a special way with iron ions. “With them, the nitrous oxide can be largely broken down, including under industrial conditions,” says Schwefer. In addition, EnviNOx® also eliminates the toxic NOx nitrogen oxides contained in the waste gas – completely! In fact, if a reducing agent such as ammonia is added during the catalytic process, it converts the NOx into water and nitrogen.
You don’t have to rebuild your production plant if you want to use EnviNOx®. For example, the waste gas purification system can be integrated very simply at the end of the nitric acid production process. A relatively small step for the plant operator, but a big step for climate protection. The 30 or so EnviNOx® systems from thyssenkrupp Industrial Solutions which are now in operation worldwide ensure that around 20,000 tons of NOx nitrogen oxides and approximately 56,000 tons of nitrous oxide are converted each year.
Nitrous oxide vanishes into thin air
There is a long story behind the development of the process. When Meinhard Schwefer and his team started to develop the process in 2000, very few people were interested in the greenhouse gas N2O. Other researchers had already discovered the interactions of aluminum silicates and iron ions with nitrous oxide. Schwefer: “But they had not recognized the industrial potential.” And nor did they have the interdisciplinary knowledge needed to develop a process.
The chemists and engineers at thyssenkrupp Industrial Solutions conducted tests in the laboratory and in real waste gas, to discover under which conditions the catalysts worked best, i.e. most effectively. This development process lasted several years. “To be successful, you have to be prepared to go into a lot of detail and you need plenty of staying power,” says Schwefel. The first installation was then sold in 2006. The EU declared the process to be a “Best Available Technique” in 2008, recommending it to the operators and builders of nitric acid plants. Now around 15 percent of the nitric acid plants worldwide are equipped with the solution from thyssenkrupp Industrial Solutions. In this way EnviNOx® eliminates the equivalent of almost 15 million tons of CO2 equivalents per year.
Industrial plant for the production of nitric acid: The EnviNOx® process breaks down up to 99 percent of the nitrous oxide created in the process. © thyssenkrupp