The selection and operation of low temperature catalytic
combustion catalyst of Organic exhaust gas (VOC)
Volatile organic compounds, known as Voc, including aldehyde, ketone, acid, ester, alkanes, benzene
series and its derivatives, etc. Voc is one of the most common pollutants in Petroleum, chemical industry
and light industry, such as in the production of pharmacy, printing, painting, shoes, toys and other
industries. It will be poisonous and seriously danger to people’s life if exposed to the envious of
contaminants for a long time. There are two methods to remove Voc: 1. destructive methods, such as direct combustion, catalytic
combustion, Bio-film process etc.; 2. non-destructive methods （recycling methods), such as adsorption, condensation and membrane separation,
etc. We always adopt burning method because of the longest research history and it’s mature technology.
Direct combustion (temperature higher than 800 ℃, and often open fires) is suitable for processing
the gas with small volume and high concentration of pollutants. This method is to be eliminated because
of its high energy consumption with high operation temperature and may produce the secondary pollution,
such as Box.
Catalytic combustion method is suitable for processing the gas with big volume and low concentration of
pollutants. It is also called low temperature catalytic combustion due to its operating temperature is much
lower than the direct method (generally at 300-500 ℃, without flame).
The catalyst is the main components in the low temperature catalytic combustion. It can be classified as
noble metal catalyst (platinum, palladium, gold, iridium, etc.) and non-noble metal catalysts.
Due to the processing capacity ( life, activity etc) of noble metal catalyst is better than non noble one,
more than 80% Voc catalysts in the market are adopted to use noble metal catalysts.
The following introduce the selection and operation of noble metal catalysts for low temperature catalytic
combustion.
1. Selection
1.1 Selection of activity:
The activity of Noble metal catalysts for low temperature catalytic combustion is relevant to the activity of
noble metal, its components and contents. The activity components of the catalyst are palladium ,
platinum, or the combination of the two metals in the current market. The content is about 0.05%-0.3%.
The catalyst activity is proportional to the content of active component. It can be usually described as
waste gas conversion rate, space velocity or initial ignition temperature. If to select catalyst with high
activity, the price must be higher with high metal content. If the catalyst activity content is 0.05%, the
activity can be guaranteed with the operating temperature 300 ℃, the space velocity not more than
10000h-1, the max exhaust gas conversion rate will be 90%.
1.2 Selection of technical specification
In the market, there two kinds of Noble metal catalysts for low temperature catalytic combustion, one is
noble metal catalyst particles, using γ-Al2O3 as catalyst carrier, the content of metal is usually 0.05%-0.1%,
size Ф3--Ф6, crushing strength 60N, resistance drop can reach more than 30000pa with flow rate 3m/s and
1m loading height, in this condition, we can adopt noble metal catalyst particles when the gas pressure is
high.
Another one is noble metal catalyst which using cordierite honeycomb as carrier, the content of metal is
about 0.05%-0.3%, common size: 100×100×50、100×100×100、50×50×50、49×49×49、150×150×50，
hole density 8-32/cm2 ,the hole density is larger, the activity will be better. When the catalyst’s hole density
is 32/cm2 , its resistance drop can reach more than 1000Pa with flow rate 3m/s and 1m loading height.
We usually adopt honeycomb noble metal catalyst when the gas pressure is low.
2. Operation
The correct and standard operation is the most important to assure catalyst activity and service life.
The operation of Noble metal catalysts for low temperature catalytic combustion is generally followed
the instruction provided by the manufacture, but must be attention:
2.1 It must adopt fresh air to preheat the catalyst before processing, in order to stimulate its initial
activity. It is forbidden to use the waste gas and the process is not allowed before the catalyst preheated.
2.2 It must use fresh air to cool down and stop the machine, exhaust gas is forbidden.
2.3 The inlet temperature of the catalyst bed must be stabilized, or the catalyst will be cracked.
2.4 Judging the catalyst activity decay can be used before and after the reaction temperature is serious
attenuation or the catalytic bed outlet concentration is too high to judge the magnitude of increase.