Comparison of the adsorbent performance between rice hull ash and rice hull silica gel according to their structural differences

The microstructures of rice hull ash (RHA) and rice hull silica (RHS) were studied to understand its adsorption for free fatty acids (FFA) of degummed soybean oil. RHAs such as RHA300, RHA500, RHA700 and RHA900 were produced by heating rice hulls at temperatures of 300, 500, 700 and 900 °C, respectively. RHS500 was formed by alkali extraction of amorphous silica from RHA500. Heating temperature affects the pore development of RHAs, resulting in elongated large pores, as evident from the SEM data. A characteristic feature of amorphous material is shown in the XRD patterns of RHAs and RHS500 except RHA900. Although RHA500 has much lower surface area and pore volume compared to RHS500, it showed similar effectiveness in reducing FFA content of degummed soybean oil. It might be ascribed by higher macroporosity of RHA500 compared with RHS500, which was shown in the results of N2 adsorption.