Activation treatment is an important stage in the preparation of activated carbon. There are two ways of activation: physical activation and chemical activation. In physical activation, the raw material is often carbonized first, and then carbon dioxide or steam is introduced at a certain temperature. This method has long activation time, high temperature and high energy consumption. Chemical activation is a preparation method of carbonization and activation at the same time, which simplifies the operation and saves time and energy. It is a widely used activation treatment method at present.
Potassium hydroxide activation method is an activation method developed from the 1970s. As an activator, potassium hydroxide mainly inhibits the formation of tar and improves the reaction yield. In addition, it mainly uses potassium hydroxide, potassium oxide and potassium carbonate to etch part of the carbon in the raw material and generate porous carbon after washing.
Next, through the activation process with anthracite as raw material and KOH as chemical activator, the relationship between temperature and ignition loss rate is obtained through thermal analysis experiment, and the activation process of KOH as chemical activator is discussed.
After the coal is roughly crushed by jaw crusher, the granular coal is finely ground by ball mill, and the pulverized coal is sieved through 200 mesh to obtain raw material 1. Weigh 145g of raw material 1 pulverized coal, add 10ml of hydrochloric acid (36.5%), 10ml of hydrofluoric acid (73%), 20ml of perchloric acid (37%) and 50ml of water, stir evenly and soak at room temperature for 24h.
Wash the above raw materials with a suction filtration device until the pH value is 6, and then place them in an electric blast drying box to dry thousands of water. This is raw material 2.
Weigh 10g of dried pulverized coal, add 10ml of potassium hydroxide solution (10%), stir it into a paste, put it in a watch glass, place it in an electric blast drying oven and keep it warm at 105C for 30min. This is raw material 3.
Take a little of raw material 1, take inert gas nitrogen as protective gas, and conduct thermal analysis at a heating rate of 15C / min.
Take a little of raw material 2, take nitrogen as protective gas, and conduct thermal analysis when the heating rate is 15C / min. Take a small amount of raw material 3, take nitrogen as the protective gas, and conduct thermal analysis when the heating rate is 15C / min.
The loss on ignition curve of acid treated raw coal powder is quite different from that of raw coal powder without acid treatment: before 600C, the loss on ignition rate of acid treated raw coal powder is only 1.2%, while the loss on ignition rate of acid treated raw coal powder has reached 28%, which is mainly due to the formation of the following molecular model after soaking coal powder in perchloric acid: coohz2cho 49 (hc104) 1.4 (H2O) 3.8 in the activation process, when the temperature rises above 200C, perchloric acid erodes part of the carbon and makes it lose weight.
When the temperature rises from thermal analysis to 350 ~ 550c, the sample quality basically remains unchanged, and the exothermic peak can be seen from DSC. At this time, the activator potassium hydroxide (melting point: 360C) has been molten, and KOH begins to decompose: 2koh-k2o + H2O
At the same time, the hydrogen atoms in the coal tar are replaced by KOH atoms to form a network structure, which prevents the formation of cross-linking between the above raw materials.
As the temperature continues to rise to 600C, alkali metal compounds (such as K2O and k2003) begin to react with carbon, so that carbon is released in the form of oxide, and alkali metal potassium is formed. The passage of potassium between the planes of graphite microcrystals produces etching on the unexposed surface, so as to increase the microporous structure, change the aromatic plane structure and electronic distribution in the microcrystals, and improve the performance of activated carbon.
From the comparison of heat flux curves, it can be seen that there is a strong absorption peak at nearly 700C, which may be the change caused by the heat absorption of an activation reaction, and the DTG also reaches the extreme value at this time. Therefore, when making activated carbon with KOH as activator, the holding time at 700C may have a certain impact on the adsorption performance and pore structure of activated carbon.
The actual loss on ignition rate of the mixture of activator and raw pulverized coal is quite different from the curve obtained by theoretical calculation (assuming that KOH has no effect on raw pulverized coal):
After 600C, the actual weight loss rate is much larger than calculated due to the chemical reaction between K2O, k20o3 and carbon. The reason is that alkali metal oxides (such as K2O and K2CO3) begin to react with carbon, so that carbon is released in the form of oxide.
When the temperature is greater than 800C, on the one hand, it will increase the loss on ignition rate and low product yield. On the other hand, it may lead to the collapse of microporous structure after excessive carbon loss on ignition, resulting in the unsatisfactory pore size distribution of activated carbon. Therefore, the appropriate activation temperature is between 750 ~ 800C. According to the activation characteristics of KOH, activated carbon samples with excellent properties can be developed by different activation processes.
This is how to explain the activation treatment of potassium hydroxide through experiments. Of course, protective measures should be taken during the experiment. Personal safety is very important. For more information, please visit cncprobuild.com Com consultation!