First, the concept
- Common expressions
HC: total hydrocarbons, including alkanes, olefins, aromatics (alkynes seem to be rarely considered)
NMHC: Non-methane total hydrocarbons, total hydrocarbons excluding methane.
TOG: Total organic gas, including total hydrocarbons, and also non-hydrocarbon organics.
NMOG: Non-methane organic gas, TOG minus methane.
1) VOC is a volatile organic compound
The definition of VOC is divided into two categories. One is the definition of VOC in the general sense, which only explains what volatile organic compounds are or under what conditions. The other is the definition in the sense of environmental protection. It is the active type of volatile organic compounds, that is, the types of volatile organic compounds that can cause harm. We usually refer to the definition in the World Health Organization.
The World Health Organization (WHO, 1989) defines total volatile organic compounds (TVOC) as the general term for volatile organic compounds with a melting point below room temperature and a boiling point between 50 and 260 ° C.
The definition of the VOC content in the national standard “Limits of Hazardous Substances in Interior Decoration Materials for Interior Wall Coatings” is: “The total volatile content in the paint minus the moisture content is the volatile organic compound content in the paint.”
The US ASTM D3960-98 standard defines VOC: any organic compound that can participate in atmospheric photochemical reactions.
US Federal Environmental Protection Agency (EPA) definition: Volatile organic compounds are any carbon compounds that participate in atmospheric photochemical reactions except CO, CO2, H2CO3, metal carbides, metal carbonates and ammonium carbonate.
Emission Standards for Air Pollutants in the Refining and Petrochemical Industries DB11 / 447-2007 Definition: A collective term for all organic compounds with vapor pressures greater than or equal to 0.01 kPa at 20 ° C or corresponding volatility under specific applicable conditions
Indoor air quality standard GB / T18883-2002 Total volatile organic compounds are defined as: Sampling with Tenax GC or TenaxTA, analysis with non-polar chromatography column (polarity index less than <= 3), retention time in n-hexane and n-hexadecane Among volatile organic compounds.
2) Definition of total non-methane hydrocarbons
Non-methane total hydrocarbons (NMHC) refer to hydrocarbons other than methane, among which are mainly (C2 to C8). (Some data also refer to C2-C12). The NMHC measured under specified conditions is the total amount of hydrocarbons other than methane that has a significant response to the gas chromatographic hydrogen flame ionization detector, in carbon. Non-methane total hydrocarbons mainly include alkane, olefin, aromatic hydrocarbon and oxygen-containing hydrocarbon.
Hydrocarbon substances usually exist in liquid or solid state except for methylation to gas under normal conditions, and have different vapor pressures depending on the difference in the size and structure of their molecular divisions. Therefore, as non-methane total hydrocarbons as atmospheric pollutants, actual The above refers to hydrocarbons with C2-C12.
- Analysis method of VOC
Air and Exhaust Gas Monitoring and Analysis Methods (4) “Solid Adsorption Thermal Desorption Gas Chromatography-Mass Spectrometry” or “Sampling Tank Sampling Gas Chromatography-Mass Spectrometry”
Refer to Civil Building Engineering Indoor Environmental Pollution Control Specification GB 50325-2001 Appendix E: Determination of Total Volatile Organic Compounds (TVOC) in Indoor Air Non-methane Total Hydrocarbons (NMHC)
Air and Exhaust Gas Monitoring and Analysis Methods (IV) “Methods for the Determination of Total Hydrocarbons and Non-methane Total Hydrocarbons” “Methods for the Determination of Total Hydrocarbons and Non-methane Total Hydrocarbons” “Determination of Non-methane Hydrocarbons by Gas Chromatography”
Determination of non-methane total hydrocarbons in exhaust gas from stationary pollution sources, gas chromatography HJ / T38-1999, both analytical methods have different emphasis. The commonly used method of VOC is adsorbent adsorption. Because of the selectivity of adsorbents, there is no one. It is suitable for all VOCs, and the tenax selected in Appendix E of GB 50325-2001 has a wider adsorption range and stronger adsorption capacity.
Another method of VOC is to directly use tank sampling, in the laboratory using cold trap condensation-rapid heating analysis, sample injection, this method can theoretically achieve non-destructive sampling, and has higher requirements on instruments and equipment.
- Analysis method of non-methane total hydrocarbons
Non-methane total hydrocarbons generally use direct injection, and the total hydrocarbons are then reduced by methane to obtain the results. However, the third method in gas and waste gas monitoring and analysis method (4), “Determination of non-methane hydrocarbons by gas chromatography,” is also performed by adsorption. Adsorbent-analysis, and then converted to total non-methane hydrocarbons.