Recovery of slaughterhouse animal fatty wastewater sludge by conversion into fatty acid butyl esters by acid-catalyzed esterification

Two types of Animal Fatty Wastewater Sludges (AFWS 1 and 2) were analyzed and fully characterized to determine their suitability for conversion into biofuel. AFWS 1 was determined to be unsuitable as it contains 68.8 wt.% water and only 32.3 wt.% dry material, of which only around 80% is lipids to be converted. AFWS 2 has only 15.7 wt.% water and 84.3 wt.% dry material of which is assumed to 100% lipids as the protein and ash contents were determined to be negligible. The 4-dodecylbenzenesulfonic acid (DBSA) catalyzed esterification of AFWS with 1-butanol was performed in a novel batch reactor fitted with a drying chimney for the “in situ” removal of water and optimized using a non-conventional Doehlert surface response methodology. The optimized condition was found to be 1.66 mol equivalent of 1-butanol (with respect to total fatty acid chains), 10 wt.% of DBSA catalyst (with respect to AFWS) at 105 °C for 3 h. Fatty Acid Butyl Esters (FABEs) were isolated in good yields (95%+) as well as a blend of FABEs with 1-butanol (16%). The two potential biofuels were analyzed in comparison with current and analogous biofuels (FAME based biodiesel, and FABE products made from vegetable oils) and were found to exhibit high cetane numbers and flash point values.