ZnO nanoparticle catalysts for use in transesterification and esterification reactions and method of making
A method of forming a product from an oil feedstock, such as a biodiesel product, and a heterogeneous catalyst system used to form said product is disclosed. This catalyst system, which has a high tolerance for the presence of water and free fatty acids (FFA) in the oil feedstock, may simultaneously catalyze both the esterification of FAA and the transesterification of triglycerides present in the oil feedstock. The catalyst system is comprised of a mixture of zinc oxide and a second metal oxide. The zinc oxide includes a mixture of amorphous zinc oxide and zinc oxide nanocrystals, the zinc nanocrystals having a mean grain size between about 20 and 80 nanometers with at least one of the nanocrystals including a mesopore having a diameter of about 5 to 15 nanometers. Preferably, the second metal oxide is a lanthanum oxide, the lanthanum oxide being selected as one from the group of La 2 CO 5 , LaOOH, and combinations or mixtures thereof.
1. A method of forming a product by heterogeneous catalysis, the method comprising:
contacting a feedstock comprising a triglyceride and a free fatty acid with an alcohol in the presence of a heterogeneous catalyst, the catalyst comprising a mixture of zinc oxide nanocrystals and lanthanum oxide, the zinc oxide nanocrystals having a mean grain size between about 20 and 80 nanometers with at least one of the nanocrystals including a mesopore having a diameter of about 5 to 15 nanometers;
wherein both the catalyzed transesterification of the triglyceride and the catalyzed esterification of the free fatty acid occur to form the respective corresponding alcoholic esters of the triglyceride and the free fatty acid.
2. The method of claim 1 , wherein the concentration of the free fatty acid in the feedstock is greater than about 0.5 wt. %.
3. The method of claim 1 , wherein the feedstock further comprises water in a concentration that is greater than about 1 wt. %.
4. The method of claim 1 , wherein the lanthanum oxide is selected from the group consisting of La 2 CO 5 , LaOOH, and combinations or mixtures thereof.
5. The method of claim 1 , wherein the mixture of zinc and lanthanum oxides includes a combination of oxides having a Zn:La bulk molar ratio between about 9.0:1.0 and 1.0:1.0.
6. The method of claim 2 , wherein the free fatty acid concentration is greater than about 4 wt. %.
7. The method of claim 3 , wherein the water concentration is greater than about 3 wt. %.
8. The method of claim 1 , wherein the corresponding alcoholic ester of the free fatty acids has a greater than about 90% yield.
9. The method of claim 8 , wherein the greater than about 90% yield is obtained after a period of time in which the amorphous zinc oxide and second metal oxide of the catalyst system partially leach into the reaction mixture;
wherein the leaching of the amorphous zinc oxide and second metal oxide into the reaction mixture exposes the surface of the zinc nanocrystals in the catalyst system to the reaction mixture.
10. The method of claim 1 , wherein the alcohol to feedstock molar ratio is greater than about 28.
11. The method of claim 1 , wherein the feedstock is selected from the group consisting of waste cooking oil, unrefined soybean oil, unrefined palm oil, food-grade soybean oil, and combinations or mixtures thereof.
12. The method of claim 1 , wherein the catalyst further comprises amorphous zinc oxide.