Effect of ash content on activated carbon
There are many parameters of activated carbon, ash content has a great influence on the performance of activated carbon except the parameters like Iodine value. The effects of ash content on the preparation, pore structure, and electrochemical properties of activated carbon were discussed in the following.
Effect of ash content on the production process of activated carbon
Ash refers to the inorganic part of activated carbon, which mainly including K2O, Na2O, CaO, MgO, Fe2O3, Al2O3, P2O5, SO3, Cl- and other components. The basic principle of activation is that the activator reacts with carbon atoms and consumes carbon atoms to form volatile gases, thus developing pore structures. In the whole activation process, the ash hardly has a beneficial effect, and the ash in the raw material will all be transferred to the activated carbon, reducing the fixed carbon content and affecting the adsorption performance of the activated carbon.
Effect of ash content on the pore structure of activated carbon
The existence of ash in activated carbon blocked some pores, and the removal of ash can form some new pores, especially micropores. When water vapor is used as an activator, if the ash content of raw material is high, the activated carbon will have larger pores, more medium and large pores, lower specific surface area. The preparation process of activated carbon is generally divided into three stages: the opening stage, producing a large number of micropores; In the reaming stage, a large number of mesopores are produced. In the stage of creating new holes, large holes and new micro holes are generated.
Effect of ash content on electrochemical properties of activated carbon
Ash content is an important reason for the poor electrochemical performance and low stability of supercapacitors. Ash will promote the diffusion of ions from the double electric layer to the solution. It accelerates the collapse of the double electric layer, increase the leakage current and self-discharge, and reduce the stability of the double electric layer. The existence of ash will reduce the capacitance value and rate characteristics of supercapacitive activated carbon. The surface hydrophilicity of low ash activated carbon is stronger than that of high ash activated carbon, which can promote the formation of double electric layer.
https://www.naturecarbon.com/coconut-shell-activated-carbon/activated-charcoal-for-edlc.html
The choice of deash time of activated carbon
One of the important ways to improve the quality of activated carbon is to choose the right time for effective deep deash of activated carbon. Activated carbon deash mainly in three stages: early, middle and late. Early deash refers to deash the raw material before production of activated carbon, but the amount of treatment is large. Medium deash will complicate the preparation process of activated carbon, so it is rarely adopted. Late deash is after the completion of activated carbon, which it is also widely adopted. In summary, the choice of deash timing should be taken the characteristics of raw materials themselves, preparation process and the application of activated carbon and other aspects of consideration into consideration.
In the process of production activated carbon, the existence of ash will lead to the increase of activator needed, the time will be prolonged, and accordingly the temperature will become higher. Ash will hinder the contact between activator and carbon atom, inhibit the activation, and affect the development and change of pores.
To obtain ultra-pure activated carbon, it is necessary to consider many factors, such as raw material, preparation technology and application, together with choosing the appropriate time and method of deash. Under the premise of ensuring full activation, if you want to save the amount of activator and get large pore size activated carbon, early deash can be considered. When the ash content of raw materials is low and difficult to remove, and the activated carbon with small pore size is desired, late deash can be considered.
