Valorization of rubberwood waste into porous carbon

Abstract

Rubberwood is one of the main Thailand goods exports. In each year, about 45,000 hectares of rubber tree are cut down, only about 30% of them is appropriated for furniture production while most of the rest is used as woodfuel. This research work focuses on the valorization of rubberwood waste into porous carbon and the optimization of carbonization process for the production of hierarchical porous carbon. Rubberwood wastes obtained from a rubberwood processing industry (in Thailand’s southern region) were treated with H3PO4 and subjected to two different carbonization methods. In the first method, the rubberwood was carbonized at 500°C for 1 h (PC-1step). The second method consisted of two steps of heat treatment, the rubberwood was pre-carbonized at 200°C for 15 min and subsequently carbonized at 500°C for 45 min (PC-2step). The physical properties of the porous carbon were investigated using thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, and N2 adsorption-desorption isotherm techniques. The porous carbons obtained from both carbonization methods have hierarchical porous structures comprising the naturally existing tubular macropores (diameter 4-20 μm) and the micropores (diameter 0.3-1 nm) generated during carbonization process. The PC-2step provides a specific surface area of 336.2 m2 g-1 and a pore volume of 0.093 cm3 g-1, which are almost twice those of the PC-1step. It is possible that the pre-carbonization at 200°C would allow a slow and gradual evaporation of moisture within the wood, thus preserving pore walls in the materials. The obtained hierarchical porous carbons can be used in many applications such as energy storage, waste water treatment, air purification and metal recovery.