In China, VOCs have been systematically controlled as a kind of pollutants, and a great deal of research and practice has been carried out on VOCs treatment technologies at home and abroad. VOCs treatment technology varied, in the application should be based on the actual situation of the factory to make a reasonable choice. Experts believe that the catalytic combustion technology due to low light-off temperature, a wide range of applications, no secondary pollution and other characteristics as the most promising VOCs processing technology.
One of the most promising technologies for catalytic combustion or VOCs treatment
Volatile organic compounds (VOCs) are one of the major pollutants of air pollution and can produce photochemical smog. They are also important precursors of PM2.5. VOCs treatment technology is divided into two major categories of recovery and destruction, in these treatment technologies, catalytic combustion technology due to low light-off temperature, a wide range of applications, no secondary pollution and other characteristics of the most promising application of technology. This article summarizes VOCs treatment technologies and highlights the progress of research on VOCs catalytic combustion.
0 Preface
Volatile organic compounds (VOCs) are organic compounds that have a saturated vapor pressure of more than 7OPa at room temperature and a boiling point of less than 260oC at atmospheric pressure. A wide range of VOCs, most of them have an irritating odor, can cause poisoning, carcinogenic effects, and VOCs is the formation of photochemical smog and atmospheric particulate matter PM an important source. As a big manufacturing country in our country, VOCs emissions have reached the top in the world. Among them, VOCs emitted by industrial production are in urgent need of treatment because of their high emission concentration, long duration, large number of pollutants and significant impact on the air quality in the region.
In order to effectively control the pollution of VOCs, the state has formulated a series of laws and regulations. The revised version of the Air Pollution Prevention and Control Law, which came into effect on January 1, 2016, will include VOCs for the first time in regulation. At the same time, VOCs will be included in the national development plan for the first time. In the 13th Five-Year Plan period, , Its total emissions fell more than 10%, estimated a total of more than 10 million tVOCs. At present, the areas with high VOCs emissions in our country are mainly those with economically and industrially advanced economy such as Beijing, Tianjin, the Yangtze River Delta and the Pearl River Delta. VOCs have gradually become the focus of air pollution control in these areas. Beijing took the lead in the collection of VOCs sewage charges, the fee is 20 yuan / kg, up to 40 yuan / kg. Up to now, sixteen provinces and cities such as Beijing, Shanghai, Hebei and Jiangsu have released the rules on collection of sewage charges for volatile organic compounds.
1 VOCs treatment technology
In China, VOCs have been systematically controlled as a kind of pollutant. A great deal of researches and practices have also been carried out on VOCs treatment technologies at home and abroad. The MEP also solicited and screened a batch of advanced technologies for VOCs pollution prevention and control and compiled (2016 National Advanced Pollution Prevention and Control Technology Directory (VOCs Prevention and Control)), its management technology can be divided into recovery and destruction.
1.1 Recycling Technology
Recycling technology is generally used to separate organic substances by physical methods such as changing temperature or pressure, including absorption, adsorption, condensation, membrane separation and the like. The recovered VOCs can be reused after simple purification, or concentratedly treated.
Absorption technology is the use of non-volatile organic solvents on the exhaust gas absorption, the VOCs dissolved in the solvent. The technology can be used when the organic waste gas flow is high and the concentration is high. However, the operation cost of recycling the absorbent is relatively high, which limits the development of the technology. Adsorption technology is the use of activated carbon, molecular sieve and other larvae L adsorption material will VOCs in the exhaust gas adsorbed on the adsorbent surface, so as to achieve the purpose of separation. Although adsorption technology is widely used, this technology is only suitable for low concentration VOCs. High concentration VOCs will lead to frequent regeneration of adsorbents, which not only increases the cost of exhaust gas treatment, but also risks of VOCs escaping during the regeneration process. Condensation technology refers to the system pressure is increased or the system temperature is reduced, the VOCs in the gas condenses into liquid, which will be removed. However, the condensation process needs low temperature and high pressure, which consumes a large amount of energy. However, the technology is not effective in purifying low-concentration and low-boiling VOCs. Membrane separation technology is the use of air and VOCs penetrating ability of different or rely on the membrane selectivity of the gas mixture of different molecules separated. Due to the high cost of permeation membranes, however, it is mainly used for the recovery of valuable organic compounds.
1.2 destruction of technology
Destruction technology is the use of microorganisms, heat or catalysts such as chemical or biochemical reactions of organic matter decomposition of non-polluting water, carbon dioxide and other non-toxic small molecule compounds, including biotechnology, thermal incineration, photocatalysis and catalytic combustion technology.
The essence of biotechnology is that microorganisms in the metabolism, the organic matter in the exhaust gas is decomposed into carbon dioxide and water, at the same time to provide their own energy. However, microorganisms are harsh on the living environment and the biochemical reaction rate is relatively low. Thermal incineration technology refers to the exhaust gas temperature rises to the ignition point and quickly burn VOCs into harmless gas. The method has the advantages of simple process and high processing efficiency. However, in the combustion process, the energy consumption is huge. At the same time, nitrogen oxides generated by high temperature and dioxin produced by incomplete combustion of organic matters can cause secondary pollution to the environment. Photocatalysis uses photocatalysts to decompose VOCs into water and carbon dioxide under light conditions. As the photocatalytic reaction is slow, less efficient, so the application is not wide. Catalytic combustion refers to the rapid oxidation of VOCs to water and carbon dioxide at the catalyst surface at temperatures below the ignition point. The technology is one of the most promising VOCs treatment technologies due to its low ignition temperature, wide range of application and no secondary pollution.
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