These arise from differences in chemical structure, stemming from differences in the production methods used. The pore size distribution patterns given below, may however clarify why certain carbon types are more appropriate than others in a given application. Powdered activated carbons Figure 7 provides pore size distributions for various powdered carbons. Peat, lignite, and coconut shell based carbons are all steam activated. Lignite based carbons are relatively mesoporous, featuring not only pores in the 1-4 nm radii range, but also larger mesopores which provide excellent accessibility.
Coconut shell based carbons are strictly microporous.
They are suitable when only low molecular weight material is to be removed. The presence of higher molecular weight material readily leads to plugging of the entrances to the micropores, severely reducing the practical performance. Chemically activated carbons are extremely porous, both in the micropore and mesopore ranges. However, compared to steam activated carbons, chemically activated carbons provide a pore surface which is less hydrophobic and more negatively charged. As a result, e.g. a high activity peat based carbon may perform similarly to a chemically activated carbon with a much higher pore volume.