Functionalization of MWCNT by -S[O.sub.3]H and -COOH Groups and Their Application as Solid Acidic: Catalysts for Esterification of Waste Chicken Fat

In the present research, the esterification of waste chicken fat (WCF) by two different homogeneous and heterogeneous catalysts has been studied. Sulfonate and carboxylate functionalized multiwall carbon nanotubes (MWCNT-S[O.sub.3]H, MWCNT-COOH) were applied as useful heterogeneous acidic catalysts during esterification of WCF. According to the experimental results, sulfonate-modified MWCNT showed more effective catalytic activity than did carboxylate-modified MWCNT. It was found that free fatty acid (FFA) of WCF in the single stage esterification of WCF had decreased down to less than 1% in the presence of 25% MWCNT-S[O.sub.3]H catalyst (according to the amount of FFA), reactor temperature of 90[degrees]C with contact time of 3 h, and methanol/FFA molar ratio of 30:1.Key words: waste chicken fat, biodiesel, MWCNT-S[O.sub.3]H, MWCNT-COOH, esterification, transesterification