Hydroxylation and hexanoylation of epoxidized waste cooking oil and epoxidized waste cooking oil methyl esters: Process optimization and physico-chemical characterization

Abstract

A novel process for the synthesis of biodegradable bio-lubricant basestocks from epoxidized waste cooking oil (WCO) and waste cooking oil fatty acid methyl ester (WCOFAME) was proposed. The synthesis process involves two steps, during the first step, epoxidized WCO, WCOFAME were hydroxylated (ring opening) in the presence of alcohol followed by functionalization of anhydride groups into resultant hydroxyl group. Hydroxylation of epoxidized WCO and WCOFAME was carried out with various alcohols such as methanol, 2-Propanol, 1-Butanol and 2-Ethyl hexanol (2-EH) in presence of homogeneous (sulfuric acid) and heterogeneous (ion exchange resin (IR-120)) acid catalysts. During the hydroxylation reaction, two different approaches (sequential addition and pre-mix addition) were attempted in adding the reactants (catalyst, alcohol) to epoxides. Both the approaches were studied thoroughly and concluded that outcomes of the pre-mix addition were best in terms of product conversion (99.5%), reaction time (30 min and 15 min) than the sequential addition. Similarly, hexanoylation was carried out in the presence of hexanoic anhydride; cationic ion exchange resin (Amberlyst-15) was used as a strong acidic catalyst (3 wt.%). After each reaction, products were identified and confirmed by oxirane analysis (titrimetric technique) and spectral analysis (FTIR, 13C NMR). Significant physico-chemical properties (pour point, thermo-oxidative stability, rheology, tribology and biodegradability) of the hydroxylated and hexanoylated WCO, WCOFAME was found to be −14.93 ℃, −28.45 ℃, −13.97 ℃, and −27.15 ℃ after the structural modifications and the biodegradability of the prepared bio-lubricant basestocks contributed 93.6% and 90.8% for hexanoylated WCO, WCOFAME.