A team led by researchers at the University of Cordoba (Spain) have used a CaO alkaline heterogeneous catalyst to produce what they call a “second-generation biodiesel” blend composed of 2:1 molar mixture of conventional fatty acid methyl esters (FAME, or regular biodiesel) and monoglyceride (MG). The process integrates glycerol—the conventional by-product of the transesterification process used to produce FAME—as MG.
The resulting blend exhibits properties similar to conventional biodiesel, while reducing waste and improving conversion. As reported in their paper in the journal Fuel, the FAME/MG blend they produced using the CaO alkaline heterogeneous catalyst was similar to such blends produced by more expensive lipases.
Biodiesel is produced from vegetable oils or animal fats via a transesterification reaction with a short chain alcohol and a basic catalyst such as sodium or potassium methoxide. Regardless of the specifics of a given conventional transesterification process, the researchers note, in all cases, glycerol is collected as a byproduct.
The generation of glycerol not only represents a notable performance loss in the process, it is also creating an enormous waste problem.
Thus, the transformation of waste glycerol into oxygen-containing branched compounds … is currently being considered as an interesting solution to provide an outlet for increasing glycerol stocks.
… In this respect, several oxygenated compounds, obtained by glycerol transformation by etherification, esterification and acetalisation, have been assessed as additives or additional components for biodiesel formulation. The addition of these compounds has not only improved the low-temperature properties of biodiesel (i.e., pour point and cold filter plugging point) and viscosity, but also they did not impair any other important biodiesel analyzed quality parameters.
… another target of great interest currently is the production, in only one reaction, of new biofuels that integrate the glycerol as a derivative product, miscible with the fatty acid methyl or ethyl esters (FAME or FAEE) obtained in a unique transesterification process. … This methodology avoids the glycerol separation before its transformation and, in a similar way as previously obtained with derivatives of glycerol, these biofuels not only prevent the waste generation of waste, but also increase the yield of the process, always higher than nominal 10%, by incorporating some glycerol derivatives into the reaction products.
… In general, these techniques are based on the use of various lipases, where instead of using methanol, the lipase-catalyzed synthesis of FAME can also be performed using alternative alcohol donors such as methyl or ethyl (alkyl) acetate or dimethyl carbonate. … However, the current existing limitations to use industrial lipases are mainly associated with their high costs, so that in order to achieve a further increase in the viability and competitiveness [with] respect to the enzymatic process, the present study aims to achieve the partial transesterification reaction, through the kinetic control of the chemical reaction, the obtain the same results previously described in stereoselective enzymatic processes. Thus, this research aims to get the same kind of biodiesel by using CaO like alkaline heterogeneous catalyst as an alternative to the more expensive lipases.—Calero et al.
|Representative scheme of the production of the FAME/MG blend using CaO. Calero et al. Click to enlarge.|
In their study, the researchers found that the CaO catalyst was very suitable for the partial transesterification of triglycerides, despite the lower catalytic activity compared to conventional full transesterification catalysts such as NaOH or KOH (resulting in the production of three FAME and one glycerol molecules).
If used for conventional biodiesel, CaO needs to be operated at higher pressures and temperatures; however the team obtained the new biodiesel blend with CaO at atmospheric pressure; 6:1 molar ratio of methanol to oil; 7% CaO loading; and 65 °C reaction temperature.
The CaO catalyst maintained sustained activity after being repeatedly used for 20 cycles.
In this way, under the optimized experimental conditions, the partial transesterification reaction was achieved through the kinetic control of the chemical reaction to obtain the same results previously described in stereoselective enzymatic processes. Thus, the same type of biodiesel that integrates glycerol is obtained by using CaO, instead of the more expensive lipases.—Calero et al.
Juan Calero, Diego Luna, Enrique D. Sancho, Carlos Luna, Felipa M. Bautista, Antonio A. Romero, Alejandro Posadillo, Cristóbal Verdugo (2014) “Development of a new biodiesel that integrates glycerol, by using CaO as heterogeneous catalyst, in the partial methanolysis of sunflower oil,” Fuel, Volume 122, Pages 94-102, doi: 10.1016/j.fuel.2014.01.033