Conclusions
The production of ethyl ester from CPO, a high wt.% FFA feedstock, under microwave assistance has been investigated. It has been found that microwave irradiation facilitates the synthesis of ethyl ester from triglycerides within a few minutes. In addition, feedstocks with a high-FFA content cannot be transesterified by a transesterificationprocesswithanalkalinecatalyst.Thisisbecause alkaline catalysts react with the FFA to form soap, which prevents the separation of the glycerol and ethyl ester. A two-step esterification and transesterification process has thus been developed to convert the high-FFA oils into ethyl ester. The first step (acid-catalyzed esterification) reduces the FFA content of the oil from 7.5wt.% to less than 2 wt.%. The alkaline-catalyzed transesterification process then converts the products from the first step to ethyl esters and glycerol. For the studied esterification process, the amountofFFAwasreducedfrom7.5 wt.%toaround1.4wt.%under optimum conditions of a molar ratio of FFA to ethanol of 1:24, 4% wt./wt. H2SO4/FFA as catalyst, a reaction time of 1 h, and a microwave power of 70W. This two-step transesterification process
Fig. 4. GC–MS chromatogram of ethyl esters (the esterification process involved a 1:24 M ratio of FFA to ethanol, 4% wt./wt. H2SO4/FFA, a reaction time of 1h, and a microwavepowerof70 W;thetransesterificationprocessinvolveda1:4 MratioofCPOtoethanol,1.5%wt./wt.KOH/CPO,areaction timeof5min,and amicrowavepowerof 70 W).
Table 3 Properties of ethyl ester in comparison with those of methyl ester standards.
Properties Unit Test method This work
ASTM D6751-02* Acid value mg KOH/g ASTM D664 0.33 0.80 max Ash content wt.% ASTM D874 0.0066 0.02 max Cloud point C ASTM D2500 8 3 to 12 Copper corrosion No. ASTM D130 1 3 max Density at 15C kg/m3 ASTM D4052 879.8 870–900 Distillation 95% C ASTM D86 337 360 max Ester content wt.% EN 14103 97.4 – Flash point C ASTM D93 160 130 min Pour point C ASTM D97 6 15 to 10 Viscosity at 40 C mm 2/s ASTM D445 5.57 1.9–6.0 Water content wt.% ASTM D6304 0.03 0.03 max
* Standard for methyl ester (adopting ASTM D6751-02 for the methyl ester to the ethyl ester) [16].
K. Suppalakpanya et al./Fuel 89 (2010) 2140–2144 2143
yielded 80 wt.% CPO ethyl ester; its ester content was 97.4 wt.% and its fuel properties were within the limits prescribed by American standards for methyl ester.