Three Adsorption and Desorption Technologies of Activated Carbon

pressure swing adsorption

Pressure swing adsorption (PSA) refers to the cyclic operation process in which the adsorption and desorption of the adsorbate are promoted under various pressure environments by periodically adjusting the system pressure in a constant temperature or no heat source state. Combining with the difference of operation mode, according to the difference between van der Waals forces, PSA can be divided into equilibrium adsorption type separated by ordinary activated carbon and speed separation type separated by special activated carbon molecular sieve. Most of the adsorption treatment processes are carried out under normal pressure conditions, and the desorption process is operated by reducing the operating pressure or vacuuming, and the greater the vacuum degree during the desorption process, the better the desorption. However, in the actual operation process, the high vacuum degree puts forward higher requirements on the performance of the adsorption equipment and the energy consumption during operation is relatively large. Combined with factors such as the treatment cost of VOCs and the adsorption effect, the industry usually sets the desorption pressure to 8-10kPa. Due to the high degree of automation, PSA technology can build a cyclic operation mode, but during the specific operation, continuous pressure and decompression are required, which requires high equipment performance and large energy consumption. It is usually used in the field of high-grade solvent recovery. middle.

Temperature swing adsorption

The operating mechanism of temperature swing adsorption (TSA) can be described as follows: the equilibrium adsorption capacity of the adsorbent is used to decrease with the increase of temperature to realize the adsorption under normal temperature conditions, and the process of reaching the preset desorption target after the temperature rises. The desorption process of activated carbon is endothermic, and the increase of temperature can obviously promote the desorption efficiency. If water vapor, hot gas and other media are used for desorption, the desorption temperature is generally controlled in the range of 100 to 200 °C. In the process of adsorption treatment of VOCs, if the adsorption capacity index is too high, and the adsorbate belongs to small molecular hydrocarbons and aromatic organics with a relatively low boiling point, water vapor desorption can be used for condensation recovery; if the adsorption capacity is too high Low, for example, the adsorption targets are VOCs such as toluene and dimethylacetamide. It is recommended to use other hot gases (hot air, hot N2, etc.) for purging for desorption. achieve recycling. RAMALINGAM and others applied TSA technology to analyze the recovery and utilization of three common indoor VOCs, acetone, dichloromethane and ethyl formate, and found that the optimal operating conditions for the thermal N2 regeneration of the above three types of VOCs are: T=170℃ , V=0.17m/s. Compared with pressure swing adsorption, temperature swing adsorption usually uses a fixed bed, which has higher adsorption efficiency, simple equipment and facilities, and a relatively mature process.

Electric swing adsorption

Electro-swing adsorption (ESA), which is mostly used in the field of gas purification and separation, is a new type of process that has just been developed in recent years, and its essence is temperature-swing adsorption. However, compared with traditional temperature swing adsorption, the desorption process of electric swing adsorption is realized by electrically heating the saturated adsorbent, and the heat formed by the Joule effect will significantly promote the release process of the adsorbate. The application of electrical swing adsorption in the field of VOCs treatment has the following advantages: 1. The heating system is simple in structure; 2. The energy can be directly transferred to the adsorbent to improve the utilization efficiency of energy; 3. The heating efficiency is high, which can significantly reduce the energy in the process of VOCs treatment. loss rate; ④ can independently control the gas flow rate and the rise rate of adsorbent temperature; ⑤ the direction of heat flow and mass flow are consistent, which can help to further improve the desorption efficiency; ⑥ low operating cost, compared with hot steam regeneration process, Power conversion desorption can save more than 50.0% of the cost; ⑦; excellent regeneration performance, foreign studies have found that after 12 cycles of power swing adsorption process, the adsorption capacity of the adsorbent still retains 97.0-100.0%.