TVOC, VOC, VOCs gas detection + Solution

VOCs TVOC、VOC、VOCS Gas detection + Solution

Introduce

• VOCs Volatile organic compounds (Volatile Organic Compounds) English abbreviations , It refers to that the saturated vapor pressure at room temperature is greater than 70.91Pa, The boiling point under normal pressure is less than 260℃ Organic compounds .

• From the perspective of environmental monitoring , Refers to the general name of non methane total hydrocarbons detected by hydrogen flame ion detector , Mainly including alkanes 、 Aromatics 、 Alkenes 、 Halogenated hydrocarbons 、 esters 、 aldehyde 、 Ketones and other organic compounds .

• The key point here is ：VOC and VOCs It's actually the same kind of substance , Volatile organic compounds (Volatile Organic Compounds) English abbreviations , Because volatile organic compounds generally have more than one component , therefore VOCs More accurate . also , In the process of daily communication , People are used to s Omit , As a result, some friends are confused VOC and VOCs.

• TVOC yes Total Volatile Organic Compounds Abbreviation , Total volatile organic compounds . World health organization (WHO,1989) Yes TVOC Is defined as ： The melting point is lower than room temperature , The boiling point range is 50～260℃ Between volatile organic compounds

Next is VOCs Main characteristics of gas 、 Sources and hazards 、 Legal basis for testing 、 toxicity VOCs The detection range of , as well as VOCs Analyze and summarize the solutions of gas detection .

One 、VOCs The basic characteristics of

1.1VOCs The definition of

VOCs Academic definition of ： It refers to the normal state （20℃,101.3kPa）, The vapor pressure is 0.1mmHg（13.3Pa） The above boiling point is 260℃(500℉) The following organic chemicals .

2.VOCs Characteristics of

● All contain carbon , Also contains H、O、N、P、S And halogen and other non-metallic elements .

● Low melting point , Easy to break down , volatile , Can participate in atmospheric photochemical reaction , In the sun Produce photochemical smoke .

● At room temperature , Most of them are colorless liquids , With pungent or special smell .

● Most of them are insoluble or insoluble in water , Soluble in organic solvents .

● There are millions of species , Most of them are flammable and explosive , Some are poisonous and even highly toxic .

● The relative vapor density is heavier than air .

3.VOCs The classification of

VOCs According to its chemical structure , Can be divided into ： Hydrocarbons （ alkane 、 Olefins and aromatics ）、 Ketones 、 esters 、 alcohols 、 Phenols 、 aldehyde 、 amine 、 nitrile （ Cyanogen ） Class etc. .

Two 、VOCs Source and harm of

common VOCs Type and composition

species	composition
Aliphatic hydrocarbon	methane 、 Ethane 、 propane 、 Cyclohexane 、 Methyl cyclopentane 、 hexane 、2- Methyl pentane 、2- Methyl hexane
Aromatic hydrocarbons	benzene 、 toluene 、 Ethylbenzene 、 Xylene 、 N-propyl benzene 、 styrene 、1,2,4- Trimethylbenzene
Halogenated compounds	Chlorofluoromethane 、 Dichloromethane 、 Chloroform 、 carbon tetrachloride 、1,1,1- Trichloroethane 、 Trichloroethylene 、 Tetrachloroethane 、 Chlorobenzene 、1,4- Dichlorobenzene
phenol 、 ether 、 Epoxy compounds	Cresol 、 phenol 、 Ether 、 ethylene oxide 、 Propylene oxide
ketone 、 aldehyde 、 alcohol 、 Polyol	acetone 、 Butanone 、 Cyclohexanone 、 formaldehyde 、 acetaldehyde 、 methanol 、 Isobutanol
nitrile 、 Amine compounds	Acrylonitrile 、 Dimethylformamide
acid 、 Ester compounds	acetic acid 、 Ethyl acetate 、 Butyl acetate
PAHs	naphthalene 、 Fei 、 Benzopyrene
Other	Methyl bromide 、 Chlorofluorocarbons 、 Chlorofluorocarbons

2.1 VOCs The source of the

VOCs The study of emission sources and pollutant emissions is to control the atmosphere VOCs The essence of , and VOCs Gases come from a wide range of sources . Typical VOCs Emission sources can be divided into anthropogenic emission sources （ Including fixed source and mobile source ） And natural emission sources （ Including biogenic and abiotic sources ） Two types of , Among them, man-made emission sources are the main , It is mostly the production process of petrochemical related industries 、 Product consumption behavior and vehicle exhaust cause .

Summarize through analysis ,VOCs It mainly comes from the following aspects ：

（1） Process tail gas discharged from petrochemical plants , Such as oil refining process , Petrochemical oxidation process , Petrochemical tank production process ;

（2） oil 、 coal 、 There may be a large amount of gas in the process of exploitation, storage and transportation VOCs Gas generation ;

（3） coal 、 oil 、 Petroleum products 、 Natural gas 、 Wood 、 Incomplete combustion products of tobacco burning , Smoke generated during waste incineration , Incomplete combustion hydrocarbon substances contained in the tail gas emitted by motor vehicles ;

（4） Interior decoration 、 Decoration materials such as paint 、 Painting and its solvents 、 Wood preservatives 、 coating 、 Plywood can release benzene at room temperature 、 toluene 、 formaldehyde 、 Phenols 、 Xylene 、 Formaldehyde and other volatile organic substances ;

（5） Cosmetics used in daily life , Organic pesticides 、 Deodorant 、 disinfectant 、 preservatives 、 Phenols can be produced during the processing and use of various detergents 、 Ethers 、 Volatile organic substances such as polycyclic aromatic hydrocarbons ;

（6） Various synthetic materials 、 Organic adhesives and other organic products will oxidize and crack at high temperature , It can produce some low molecular organic pollutants ;

（7） starch 、 fat 、 protein 、 cellulose 、 Some organic pollutants are produced during the oxidation and decomposition of sugars .

2.2 VOCs Hazards of

VOCs There are many kinds , Its harm to human health and living environment mainly reflects the following aspects ：

（1） majority VOCs With pungent smell or odor , It can cause people's sensory unhappiness , Seriously reduce people's quality of life . Malodorous gas refers to all gaseous substances that stimulate olfactory organs and cause people's unhappiness .

（2）VOCs The ingredients are complex , It has special smell and penetration 、 Volatile and fat soluble properties , It can cause many discomfort symptoms in the human body . It is also toxic 、 Irritant, teratogenic and carcinogenic effects , Especially benzene 、 toluene 、 Xylene and formaldehyde are the most harmful to human health , Long term exposure can cause anemia and leukemia . in addition ,VOCs Gas can also cause respiratory tract 、 renal 、 lung 、 liver 、 The nervous system 、 Diseases of digestive system and hematopoietic system . With VOCs The increase in concentration , Nausea occurs in the human body 、 Have a headache 、 tic 、 Coma and other symptoms .

（3）VOCs Most of them have photochemical reactivity , In the sun ,VOCs Will interact with the atmosphere NOx There's a chemical reaction , Form secondary pollutants （ Such as ： Ozone, etc ） Or intermediates with strong chemical activity （ Such as ： Free radicals, etc ）, Thus increasing the surface concentration of smoke and ozone , It will be life-threatening to people , At the same time, it will also endanger the growth of crops , Even lead to the death of crops . Smoke caused by photochemical reaction , In addition to reducing visibility , Ozone produced 、 Peroxyacetyl nitrate （PAN）、 Benzoyl peroxide nitrate （PBN）、 Aldehydes and other substances can stimulate human eyes and respiratory system , Endanger people's health , London 、 Photochemical smog pollution events have occurred in Tokyo and other cities .

（4） some VOCs Flammable , Such as benzene 、 toluene 、 acetone 、 Dimethylamine and thiohydrocarbon , If electrostatic sparks or other ignition sources are encountered when the emission concentration of these substances is high , It is easy to cause fire . In recent years, due to VOCs Fire and explosion accidents occur from time to time , Especially in petrochemical enterprises .

（5） part VOCs It can destroy the ozone layer , Such as chlorofluorocarbons . When it receives ultraviolet radiation from the sun , Can produce photochemical reactions , Produce chlorine atoms , So as to catalyze the destruction of ozone in the ozone layer . The reduction of ozone and the destruction of the ozone layer increase the amount of ultraviolet radiation reaching the ground . Ultraviolet rays are harmful to human skin 、 It is harmful to eyes and immune system .

3、 ... and 、 Scope of application

VOCs TVOC、VOC、VOCS The gas detection system solution is suitable for school scientific research 、 Building construction 、 Fire alarm 、 Sewage treatment 、 Industrial gas process control 、 Boiler Room 、 Waste treatment plant 、 Tunnel construction 、 petroleum pipeline 、 Gas station 、 Maintenance of underground gas pipeline 、 Indoor air quality testing 、 Safety protection in dangerous places 、 Aerospace 、 Military equipment monitoring, etc .
Through the above introduction, we can know ,VOC The impact on human body and environment is very huge , The environmental protection department produces VOC Industrial waste gas enterprises are also strictly regulated , In the past two years, the two sessions have successively mentioned various practical methods and measures to win the battle against environmental pollution , These have once again confirmed the important impact of the environment on the development of the whole society , This has also led to a number of sensors focusing on the detection of such gases .

Used in the market VOC Sensors are mainly divided into semiconductor and PID Type sensor （ Photoionization detector ）.

** Semiconductor type VOC sensor ：** When there is detected gas in the ambient air, the conductivity of the sensor changes , The higher the concentration of the gas , The higher the conductivity of the sensor . This change in conductivity can be converted into an output signal corresponding to the gas concentration by using a simple circuit . P-toluene 、 benzene 、 Formaldehyde and other organic gases have high sensitivity , Fast response and recovery time , Small size, good stability and other characteristics .

PID type VOC sensor ： It is composed of ultraviolet light source and air chamber . The principle of ultraviolet luminescence is the same as that of fluorescent tubes , But the frequency is high , High energy . After the measured gas reaches the gas chamber , The ultraviolet light emitted by the ultraviolet lamp ionizes to produce a charge flow , The gas concentration is positively correlated with the size of the charge flow , The gas concentration can be measured by measuring the charge flow .

PID Can detect most VOC, Except for low molecular weight hydrocarbons . Each of these VOC There is a photon energy , When there is direct light on VOC Upper time , Break it down into ions , This is the ionization potential or IP. If it is greater than IP The photon energy of interacts with the sample gas ,VOC Is ionized （ That is, it is detected ）.

PID Excellent sensitivity , Large dynamic range , Low... Can be measured under the background of higher inorganic gas concentration ppb Of VOC concentration . It has high sensitivity and high resolution , Small volume , High test stability , Strong anti-interference ability , It is mainly used outdoors VOC Gas pollution detection , Widely applicable to portable 、 Fixed gas detector , And various needs VOC Occasions and equipment for gas detection .

Four 、 Selection considerations

Specific products need to be analyzed and selected before use , The five most important points ：

One 、 Choose the appropriate detection principle ;

Two 、 Select the appropriate range ;

3、 ... and 、 Try to buy directly from the manufacturer ;

Four 、 Choose a famous brand ;

5、 ... and 、 Consult more manufacturers and compare more .