Reusability of the catalyst and the amount of leached-sulfur estimated by CHNS
elemental analysis for 6 reaction cycles. The experiment was done under optimum
esterification condition: methanol-to-PFAD molar ratio ¼ 10:1; catalyst
amount ¼ 2.5 wt.% ICG(15)-SO3H; reaction temperature ¼ 75 C; reaction time ¼ 2 h.