Innovation Spotlight
EnviCat® N2O
Catalysts against the
climate killer nitrous oxide
Issue: Fall 2012
The catalyst EnviCat®1 N2O in the innovative EnviNOx®2 process
removes large amounts of the hazardous greenhouse gas
Melting ice in the Antarctic, devastating droughts in Africa, violent storms and rainfall in
Germany: the signs of climate change can no longer be ignored. Most people are aware that
carbon dioxide is a major contributor to the greenhouse effect – but know hardly anything
about other climate gases. Nitrous oxide, for example, is the third most damaging climate
gas after methane and is responsible for about six percent of anthropogenic climate effects.
One unit of nitrous oxide is about 300 times more climate-damaging than the same amount
of CO2. Nitrous oxide results mainly from the industrial production of nitric acid that is used
in fertilizer manufacture and other processes. The novel EnviNOx process was developed by
Uhde to remove the dangerous climate killer and other nitrogen­oxides from the waste gas of
industrial plants and convert it to the harmless substances nitrogen, oxygen and water. The
catalyst EnviCat N2O from Clariant plays the key role in this process.
Nitrous oxide – commonly known as happy gas or laughing gas – actually sounds like a
completely harmless substance. For humans, the gas with the slightly sweetish odor and
consisting of the elements nitrogen and oxygen (chemical formula: N2O) is in fact benign
when handled correctly. For example, it is used to foam whipped cream. If inhaled, it can
bring about a spasmodic inclination to laugh and a condition resembling drunkenness. It was
formerly used as an anesthetic for this reason. Nitrous oxide occurs naturally in the earth’s
atmosphere, but only at harmless trace levels.
1 Trademark of Clariant registered in many countries
2 Trademark of ThyssenKrupp Uhde GmbH
EnviCat® N2O | Innovation Spotlight
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Clariant International Ltd
Business Unit Catalysis & Energy
Lenbachplatz 6
80333 München
Germany
www.clariant.com
www.innovation.clariant.com
www.catalysis-energy.clariant.com
In higher concentrations, however­, it is extremely harmful for our climate because of its
about 25 times greater longevity in the earth’s atmosphere than CO2. The main human activities that produce nitrous oxide are agriculture, incineration of refuse and sewage sludge,
burning of fossil fuels and nitric acid production.
Nitrous oxide – by-product of nitric acid production
Nitric acid is an important chemical feedstock. It is used primarily in fertilizer and nylon
production­, the photographic industry, precious metal separation and explosives manufacture. About seven kilograms of nitrous oxide are generated as a by-product per metric ton of
nitric acid produced. An estimated 400,000 metric tons of nitrous oxide are therefore emitted
every year by nitric acid plants worldwide. Since nitrous oxide is about 300 times more
harmful than CO2, this has the same atmospheric pollution impact as 120 million metric tons
of carbon dioxide – equivalent to the emissions from about 50 million cars, the total number
at present on the road in Germany and the Netherlands. For several years, the legislator has
therefore been imposing strict limits on nitrous gas emissions; exhaust gas must now contain
not more than 400 ppm (parts per million) N2O.
»To ensure compliance with these limits, ThyssenKrupp Uhde GmbH with its decadeslong technology competence in the field of nitric acid plants and Clariant with its globally
acknowledged expertise in developing and manufacturing catalysts have jointly developed
the catalyst EnviCat N2O for the EnviNOx process,« explains Dr. Thorsten Bauer, Group Vice
President Sales/Key Account Management Catalysis and Energy at Clariant. »This process
removes nearly all of the nitrous oxide from the tail gas of nitric acid plants.« Moreover, it
also renders innocuous other nitrogen oxides (often called NOx) that represent a considerable pollution threat for man and the environment. The nitrous oxide is converted in two
stages: in the first stage, the nitrous oxide is decomposed to oxygen and nitrogen with the
aid of the catalyst EnviCat N2O. In the second stage, the nitrogen oxides are mixed with
ammonia to produce harmless nitrogen and water.
The Clariant catalyst EnviCat N2O
used in the EnviNOx process removes almost
completely the nitrous oxides and other nitrogen oxides in the tail gas of nitric acid plants.
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Catalyst against the climate killer
»At the heart of the process,« says Dr. Roderik Althoff, Product Manager Zeolites at Clariant,
»is the highly active catalyst EnviCat N2O consisting of porous, crystalline zeolites.« Zeolites
are a group of minerals containing mainly aluminum, silicon and oxygen. »In EnviCat N2O,
we have dispersed iron into the crystal lattice of the zeolites by means of an ion exchange
process.« Like all catalysts, EnviCat N2O takes part in the chemical reaction without itself
being used up. In the EnviNOx reactor, the nitrous oxide is passed through the catalyst
bed at temperatures between 300 to 500 degrees Celsius depending on the application.
The nitrous oxide molecules attach to the iron cations and temporarily bind firmly to them
because of the strong chemical bonds. The technical term for this process is chemisorption.
The nature of the catalyst determines the degree of this chemisorption. On the one hand, it
must be strong enough for oxygen and nitrogen atoms to separate and form new bonds with
further oxygen atoms, but on the other hand it must not be so strong as to prevent the new
molecules leaving the catalyst and block further reactions. In this way, harmless nitrogen
and water are formed.
»Purification of the tail gas by the EnviNOx process can be placed at the end of nitric acid
production without difficulties and without impacting the manufacturing process,« explains
Dr. Dirk Köster, Head of Design and Project Management Department, Hydrogen and
Nitrates Division of the engineering and construction company ThyssenKrupp Uhde in
Dortmund, Germany. »This is a great advantage for manufacturers, because it means they don’t
have to modify the process cycles.« This solution also allows continuous monitoring of tail
gas purification by public authorities. After a service life of several years, the catalyst can then
undergo safe and eco-friendly disposal. The first tail gas purification system with EnviNOx
was installed in Austria in 2003. The process was widely adopted in the following years;
to date 20 of these plants have been installed around the world. Every year, the EnviNOx
process purifies climate-damaging nitrous oxide emissions equivalent to an output of more
than twelve million metric tons of carbon dioxide, comparable to the emissions of more than
four million passenger cars. If all nitric acid plants were equipped with EnviNOx, this figure
could be increased more than tenfold.
One unit of nitrous oxide is about 300
times more harmful than the same amount of
CO2. It is generated primarly in the production
of nitric acid used as agricultural fertilizer, but
also by road traffic.
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Chemistry
Explained
How nitrous oxide harms the climate and atmosphere
Anthropogenic nitrous oxide emissions amount to about ten million metric tons annually.
Each year, the concentration of nitrous oxide in the atmosphere increases by 0.2 to 0.3
percent. Nitrous oxide emissions are harmful in two respects: they worsen the greenhouse
effect and increase the hole in the ozone layer.
Animation with sound available at:
www.innovation.clariant.com
Nitrous oxide influences the greenhouse effect in a similar way to carbon dioxide: it reflects
the heat radiated by the earth’s surface which otherwise would escape into space. This
causes the atmosphere to heat up like in a greenhouse. Nitrous oxide rises into the
stratosphere, reaching altitudes of more than ten kilometers. It then remains there for an
average 114 years before it is broken down again. One unit of nitrous oxide is therefore about
300 times more harmful than the same amount of CO2. With a proportion of six percent,
nitrous oxide contributes considerably to anthropogenic climate change. After carbon
dioxide and methane, it is the third most harmful climate gas.
Nitrous oxide also enlarges the hole in the ozone layer because it breaks down ozone under
the influence of UV light. The hole in the ozone layer is a large area over the Antarctic where
the atmosphere’s natural ozone layer has thinned out. The protective function of this layer
in filtering out harmful UV radiation is therefore no longer assured in this region. Until they
were prohibited in the 1990s, chlorofluorocarbons (CFCs) were the main destroyers of the
ozone layer. A study by American scientists* has shown that nitrous oxide is now destroying the ozone layer more aggressively than any other substance.
*Nitrous Oxide (N2O): The Dominant Ozone-Depleting Substance Emitted in the 21st Century, Science, 2009,
Vol. 326 no. 5949, pp. 123–125.
Nitrous oxide emissions increase the
greenhouse effect and damage the natural
ozone layer.
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Chemistry explained
Greenhouse gas
Source
Potential
(with reference to
100 years)
Lifetime
Animation with sound available at:
www.innovation.clariant.com
Carbon dioxide
(CO2)
Burning of biomass (forest /
fire clearance) and fossil energy
sources (coal, crude oil, natural
gas), external respiration, high
exchange through CO2 circulation
1**
4 years
Methane
(CH4)
Rice cultivation, cattle breeding,
waste water treatment plants, refuse dumps, coal mining (mine gas,
methane), natural gas and crude
oil production
25**
12 years**
Nitrous oxide
(N2O)
Nitrogen fertilizer in agriculture,
burning of biomass, cattle breeding, certain industrial processes
(e.g. fertilizer or nylon production)
298**
114 years**
Chlorofluoro­
carbons
CFCs
Group of different compounds,
refrigerants in cooling systems,
filling gas in foams, propellants
in spray cans, between 1989
and 2000 prohibited in various
industrialized countries, since
2010 also in developing countries.
<14,400**
45–1,700 years**
**IPCC Fourth Assessment Report: Climate Change 2007; Working Group I, The Physical Science Basis.
Informative Links
www.catalysis-energy.clariant.com
www.ipcc.ch
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