Advances in adsorption and recovery technologies for volatile organic compounds (VOCs)

Volatile organic compounds (VOCs) not only have strong toxicity, but also are important precursors and participants affecting regional air pollution in China. Therefore, the control of VOCs has received more and more attention. Adsorption is currently the most widely used and most mature method for recovering VOCs. The common adsorbent, adsorbent regeneration technology, adsorption equipment, main adsorption technology and adsorption-related combination treatment technology are introduced. The problems and development trends of adsorption recovery technology in the treatment of VOCs are discussed.

In recent years, large-scale smog weather has occurred in many parts of China, and the problem of regional atmospheric composite pollution characterized by ozone, fine particulate matter (PM:) and acid rain has become increasingly prominent. As an important precursor of ozone and secondary organic particles, Volatile Organic Compounds (VOCs) play an extremely important role in the atmospheric chemical reaction process. At the same time, most VOCs are highly irritating and toxic. If benzene is listed as the first class of carcinogens, n-hexane, heptane and octane affect the human central nervous system.

In May 2010, the General Office of the State Council officially proposed the requirements for strengthening the prevention and control of VOCs pollution at the national level for the first time. VOCs, SO, NO and particulate matter were listed together as key pollutants for improving the quality of the atmospheric environment. China's first comprehensive air pollution prevention and control plan issued at the end of December 2012, the “Twelfth Five-Year Plan for Air Pollution Prevention and Control in Key Areas” requires the improvement of VOCs emission project construction requirements, the implementation of key industry governance, and the improvement of VOCs pollution prevention and control system.

The use of alternative products, improved processes and equipment replacement in the production process is the preferred measure to reduce the generation and emission of VOCs. However, for some processes and production, the road to cleaner production is still very long. In a short period of time, the end-control technology is still An indispensable means. At present, the governance technologies of VOCs mainly include recycling and destruction methods. Whether it is environmentally friendly or economically, recycling is a VOCs governance technology that deserves to be promoted.

VOCs recycling technology includes adsorption, condensation, absorption, membrane separation, etc. Among them, the adsorption method is simple, wide in application range and high in purification efficiency. It is a traditional VOCs treatment technology and is the most widely used treatment technology. Xi Jinjun and others found that the adsorption technology has the highest market share (38%) in China by investigating a large number of industrial VOCs processing technology projects. In the case of suitable VOCs, adsorption technology is an economical and clean production concept. Therefore, it is widely used at home and abroad.

1. Adsorption treatment technology

The adsorption method is a method for adsorbing and purifying pollutants in exhaust gas by using various solid adsorbents. Generally, adsorption is divided into physical adsorption and chemical adsorption, and the purification of VOCs is mainly carried out by physical adsorption. The adsorption method is suitable for treating low-concentration and high-volume organic waste gas, and is mainly used for adsorbing and recovering fat and aromatic hydrocarbons, most chlorine-containing solvents, common alcohols, some ketones and esters. The key technologies of the adsorption method are the determination of adsorbents, adsorption equipment and processes, regeneration media, post-treatment processes, and the like.

1.1 commonly used adsorbents

At present, the adsorbents commonly used in the purification of VOCs are inorganic and organic adsorbents. The inorganic adsorbents are mainly used, mainly activated carbon (including granular activated carbon, honeycomb activated carbon and activated carbon fiber), molecular sieve (including granular molecular sieve, molecular sieve molding). Bulk honeycomb and molecular sieve coating materials), zeolite, granular silica gel, activated alumina, porous clay ore, etc., and organic adsorbents mainly refer to high polymer adsorption resins.

The most inorganic inorganic adsorbent is activated carbon. Compared with granular activated carbon, honeycomb activated carbon has the advantage of low bed resistance. At present, the adsorbent for treating high-volume and low-concentration VOCs in China is mainly composed of honeycomb activated carbon. Activated carbon fiber has the advantages of large specific surface area, abundant micropores and uniform distribution, fast adsorption and desorption rate, high adsorption efficiency and easy regeneration. Activated carbon materials have very good adsorption capacity for non-polar substances such as organic solvents; on the contrary, for polar substances such as water, the adsorption is poor, so it is possible to regenerate with water vapor conveniently.

The main components of zeolite and molecular sieve are all aluminosilicates, which have good thermal stability and are safe to regenerate when using hot gas flow. Different types of molecular sieves have different adsorption effects on VOCs, so the molecular sieve can be chemically modified and modified to improve the removal effect of VOCs.