Effect of attapulgite pore size distribution on soybean oil bleaching

The pore size distribution and specific surface area of the attapulgite is a crucial parameter for the uptake of pigments of oil. Bleaching of the soybean oil with three attapulgites with different pore size distribution, which were assigned a, b, and c, respectively was investigated. The specific surface area and the pore size distribution of the attapulgites were characterized. The Freundlich isotherm analysis was used to evaluate the sorption capacity of the three attapulgite. Sample b gave the highest surface area and sample c the lowest. Sample b exhibited a wider pore distribution (8-65 angstrom) whereas samples a and c had more micropores smaller than 15 angstrom. Sample a, in contrast to samples b and c, was characterized by some larger pores (100-170 angstrom). The sorption capacity followed the sequence: attapulgite sample c > attapulgite sample a > attapulgite sample b. The sorption capacity was decided by the pore size distribution. The more pores with a distribution range 9-32 (i.e., close to the diameter of the pigments), the more pigments were removed. The attapulgite sample c, which had most pores (8-32 angstrom) was the best.