WFU Biofuels

Wake Forest students, faculty, staff and associates making and testing vegetable-oil based fuels.

Tuesday, November 29, 2005

Sugar Catalyzed Reaction

Recently there has been a lot of buzz by a Japanese group’s solid acid catalyst made from sugar (Nature, vol. 438, p 178, 2005). They reported converting FFA’s to the ethyl esters. This catalysis is special because it is hydrophobic and consists of sheets of fused rings with covalently attached SO3H groups.

Our group decided to make some and see how well it works. Making the catalysis was easy. We took 2 g of sucrose and heated at 400C for 15 hours under nitrogen. The remaining 0.5 g (loss of mass is due to dehydration of the sugars) was ground and heated to 150C in concentrated H2SO4 for 15 hours under nitrogen. After washing and drying, the yield was 0.61g (about a 30% mass return from the starting amount of sucrose)

From reading (Ind. Eng. Chem. Res. 2005, 44, 5353-5363) about solid acid catalyst we saw where most reactions were using 1 to 5% catalyst by weight. Also the WVO we are using is not tremendously high in FFA based on some initial titrations. So the rational for using this catalysis was to convert any FFA’s to the methyl ester in a fashion that would make the subsequent base step much easier. We also wanted to see if this reaction could also be used to convert the oil over to the FAME. This would mean using a large excess of MeOH. Here were the conditions:

12 g WVO
12 g MeOH (100% by weight, large excess to try to push oil over to ester)
0.6 g Cat (5% by weight or about 40 g/L)
Heat at 75 C for 12hours (again long reaction time for the oil to convert)

After heating, the reaction was filtered and the catalyst was washed with 20 mL THF and 20 mL hexanes. Solvent was removed by rotary evaporation. The pale yellow oil was centrifuged for 15 min yielding a small pellet of glycerin. So workup is very easy.

The small amount of glycerin instantly indicated that the most of the oil did NOT convert over to the ester as wished. Using 13C NMR and comparing to authentic samples we could see that the major component was oil with a small (~10% to 15%) amount of FAME. Actually more FAME than I expected so maybe some of the FFA’s were converted over? So it looks like it worked so far.

I suppose the real test will be the behavior of the “pretreated” oil under base conditions? If the FFA’s were indeed converted over to the methyl ester then the base step should be much easier to process. So next is to setup a base catalyzed reaction and see how it behaves.


At 2:20 PM, Blogger Asa Gray said...

Excellent bean-o! I'll be interested to hear how the base catalyzed part goes. Too bad about it not taking oil to fame after the FFAs were gone. That would have been excellent. Any way to stick bases on sugars?


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