Volatile Organic Compounds VOCs Adsorption Recovery Technology Progress

Abstract: Volatile organic compounds (VOCs) are not only highly toxic, but also are important precursors and participating substances that affect the regional air pollution in China. Therefore, the control of VOCs is receiving more and more attention. Adsorption method is currently the most widely used, most technologically mature method of recovering VOCs. The commonly used adsorbents, adsorbent regeneration technology, adsorption equipment, main adsorption processes and adsorption-related treatment technologies were introduced. The problems and trends in the treatment of VOCs were discussed.

In recent years, a large area of ​​haze has appeared on many occasions in many parts of China. The problem of regional air pollution characterized by ozone, fine particulate matter (PM) and acid rain has become increasingly prominent. Volatile Organic Compounds (VOCs), as important precursors to ozone and secondary organic particulates, play an extremely important role in atmospheric chemical reactions. At the same time, most VOCs are highly irritating and toxic. If benzene is classified as a first carcinogen, n-hexane, heptane and octane affect the central nervous system in humans.

In May 2010, for the first time, the General Office of the State Council formally put forward requirements for strengthening prevention and control of VOCs at the national level. VOCs, SO and NO, together with particulate matter, are listed as priority pollutants that improve the quality of the atmospheric environment. The 12th Five-Year Plan for Prevention and Control of Air Pollution in Key Areas of China's First Integrated Air Pollution Prevention and Control Plan issued at the end of December 2012 requires that the construction of VOCs emission-type projects be enhanced and key industries should be managed to improve the VOCs pollution prevention and control system.

Alternatives, improvements and equipment changes are the preferred measures to reduce the generation and emission of VOCs in the production process. However, for some processes and production, cleaner production is still going a long way and the end-of-pipe control technology is still An indispensable means. The current VOCs treatment technologies include recovery and destruction laws. Whether from the environmental protection or economic point of view, recovery methods are worth promoting VOCs governance technology.

VOCs recovery technology includes adsorption, condensation, absorption, membrane separation, adsorption equipment which is simple, wide range of applications, purification and high efficiency, is a traditional VOCs treatment technology, but also the most widely used treatment technology. Xi Jinying et al. Through the investigation of a large number of industrial VOCs processing engineering projects, the adsorption technology has the highest market share in China (38%). In the case of VOCs recovery, adsorption technology is an economical and clean production concept. Therefore, it is widely used at home and abroad.

1 adsorption method of governance technology

Adsorption method is the use of a variety of solid adsorbent exhaust emissions of pollutants in the adsorption purification method. Usually adsorption is divided into two types of physical adsorption and chemical adsorption, and VOCs exhaust purification mainly physical adsorption method. Adsorption method suitable for processing low concentration, high volume of organic waste gas, mainly for the adsorption of fat and aromatic hydrocarbons, most of the chlorine-containing solvents, alcohols, some ketones and esters. Adsorption of the key technologies are adsorbent, adsorption equipment and processes, regeneration medium, after-treatment process to determine.

1.1 commonly used adsorbent

At present, the commonly used adsorbents in the purification of VOCs are inorganic and organic adsorbents, inorganic adsorbents are the most commonly used, mainly activated carbon (including granular activated carbon, honeycomb activated carbon and activated carbon fiber), molecular sieve (including molecular sieve, molecular sieve Body honeycomb and molecular sieve coating material), zeolite, granular silica, activated alumina, porous clay ore, organic adsorbent mainly refers to the polymer adsorbent resin.

The most representative inorganic adsorbent is activated carbon. Compared with granular activated carbon, honeycomb activated carbon has the advantages of small bed resistance. At present, our country to deal with high-volume, low concentration of VOCs adsorbent to honeycomb activated carbon-based. Activated carbon fiber has a large surface area, rich pores and uniform distribution, absorption and desorption rate, adsorption efficiency, easy regeneration and so on. Activated carbon materials have very good adsorption capacity for non-polar substances, such as organic solvents; on the contrary, polar substances, such as water, adsorb poorly, so it is easy to regenerate with steam.

The main components of zeolites and molecular sieves are all aluminosilicates, which have good thermal stability and are safe to regenerate using hot gas streams. Different types of molecular sieves have different adsorption effects on VOCs, so the removal of VOCs can be improved by chemical modification and modification of molecular sieves.

1.2 adsorbent regeneration

In the VOCs treatment commonly used adsorbent regeneration methods are low pressure steam replacement regeneration, hot air purge regeneration and decompression or vacuum desorption regeneration. Low-pressure steam replacement regeneration, hot air purge regeneration suitable for the desorption of low boiling point low-molecular hydrocarbons and aromatic organic compounds.

At present, some new energy-saving adsorbent regeneration technologies have also been developed, such as microwave desorption, electric joule desorption, solvent replacement, ultrasonic regeneration and the like. These new desorption techniques have good energy-saving effect and high efficiency, but are still in the research stage at present, and they have less practical application.

1.3 common adsorption device

In organic waste gas treatment, the industry commonly used adsorption equipment fixed bed, moving bed, fluidized bed and zeolite honeycomb wheel adsorption device, the most classic, commonly used fixed bed. Zeolite honeycomb rotor adsorption device is a relatively new rotary adsorption system developed in the field of organic waste gas purification, also called rotor adsorber. Exhaust gases can be passed radially or axially through a sorbent-loaded rotor and passed through most of the rotating bed. Rotor adsorber has the advantages of small size, easy operation, low pressure drop, can be a large flow of exhaust gas treatment to a low concentration of purified gas, while the desorbed gas is high concentration and low flow, the general enrichment ratio up 1O ~ 15 times.

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