Coconut Shell Versus Bituminous Coal Activated Carbon

By Ken Schaeffer and Robert Potwora

Activated carbon (AC) filter media is commonly used in point of use/point of entry (POU/POE) water applications. The type of raw materials used to produce AC has a major impact upon its characteristics. The two most common are coconut shell and bituminous coal.yongruida activated carbon

Coconut shell-based AC has the most micropores. Micropores are defined as pores less than 20-angstrom units (two nm) in diameter. AC produced from bituminous coal have fewer micropores, but more mesopores and macropores. Mesopores are between 20 and 500 angstrom units (two and 50nm); macropores exceed 500 angstrom units (50nm). See Table 1.

The scanning electron micrographs (SEM) shown in Figure 1 were taken at 1,000X magnification. At this magnification, the prevalence of the micropores can be seen in the coconut shell-based activated carbon.

Coconut shell-based Bituminous coal-based
Pore volume among different pore sizes is measured by nitrogen adsorptionand mercury intrusion. Nitrogen adsorption and mercury intrusion pore volume results can be plotted to obtain a pore volume distribution (Figure 2). The amount of micropores present in coconut shell-based AC is about 50 percent higher than bituminous coal-based activated carbon.

Figure 2. Pore volume distribution

The most common method used to distinguish micropore volume is the ASTM D 4607, standard Test Method for Determinaqtion of Iodine Number of Activated Carbon, ASTM International. Table 2 compares iodine numbers and other key properties between coconut shell- and bituminous coal-based AC.

Table 3. Benzene at 10 ppbcarbon pellets with free sample

Hrbons means they have much higher capacity to adsorb small molecules, such as volatile organic chemicals (VOC). Higher capacity means coconut shell-based activated carbon will last longer before it needs to be changed out.