Coconut Shell Activated Carbon Prepared by Physical Activation
Activated carbon has extensive internal pore structure, high specific surface area, and is used in various fields such as chemical, pharmaceuticals, food processing, environmental protection. The main raw materials for the preparation of activated carbon are high-carbon materials such as coal, wood, nut shells. The methods of preparing activated carbon are mainly divided into physical activation method and chemical activation method. Physical activation method is to carbonize the raw material and then activate it with water vapor or carbon dioxide. The chemical activation method is to impregnate chemicals on activated carbon and the carbonization and activation are completed together.
The coconut shell activated carbon prepared by physical activation method has high hardness and good adsorption performance, and is widely used in gas adsorption, water treatment and chemical production. Under normal circumstances, coconut shell activated carbon has relatively developed micropores and high surface area, but its mesopores are not as developed as its micropores. How to prepare high-performance coconut shell activated carbon products by optimizing operating parameters is a long-term problem. And in the physical activation process, even if the quality of raw materials is guaranteed to be consistent, the adsorption characteristics and pore size distribution of activated carbon are greatly affected by various operation factors. The test below is to find the optimal activation temperature and time for coconut shell activated carbon prepared by physical activation.
First, place the carbonized coconut shell material samples in the upper part of reactor, connect the device, heat it up to 100 °C, and then introduce steam and keep the flow rate at 3 kg/h. Stop heating the samples after activation for different times (30 – 300 min) at temperatures ranging from 600 – 1000 °C. Stop feeding steam when the temperature is lower than 100 °C. Take the samples out when the temperatures drop to room temperatures. Dry the activated carbon at 120 °C for 12 h, then weigh, and calculate the yield of activated carbon, test the iodine number and the adsorption of phenol.
The influence of activation temperature
In order to study the influence of activation temperature on the yield and adsorption performance of the activated carbon, the activation time is kept constant at 120 min.
From the test results, the yield of activated carbon gradually decreases with the increase of activation temperature. After the activation temperature reaches 800 °C, the yield decreases rapidly, and drops to 4% at 1000 °C. This is because the reaction between carbon and steam is endothermic, and the reaction rate increases with the increase of temperature, the loss on ignition of activated carbon will increase. The iodine number and phenol adsorption both first increase with the increase of temperature, and then decrease after the temperature reaches 900 °C. So, within the test range, the activation temperature of coconut shell activated carbon prepared by steam activation method is preferably about 800 – 850 °C.
The influence of activation time
The temperature is fixed at 850 °C in order to test the influence of activation time. As steam activation is essentially carbon being oxidized, with the prolongation of activation time, the loss on ignition of activated carbon increases gradually, that is, the yield of activated carbon decreases with the increase of activation time. This decrease is faster in the initial stage. And after 120 min, the decrease is not very obvious, which indicates that the reaction between carbon and steam is not uniformly, but selectively carried out on the surface of carbon. It is generally believed that the oxidation reaction occurs only at positions such as edges of microcrystalline, defective positions that has a high affinity for the activating agent. Since the test is at the optimal activation temperature of 850 °C, the reaction is not very violent, and the change of yield is not very obvious with the prolongation of time.
The iodine number of activated carbon is the highest when the activation time is 120 min. And the highest phenol adsorption value is with 60 min activation time. If the activation time is too long and the activation is excessive, part of the pore structure will be greatly affected and the specific surface area will decrease, so the adsorption performance of activated carbon will decrease.