ZnO nanoparticle catalysts for use in biodiesel production and method of making

A heterogeneous catalyst system comprising:

• zinc oxide nanocrystals, the zinc oxide nanocrystals having a mean grain size between about 20 and 80 nanometers with at least one of the nanocrystals having a crystal face that includes a mesopore having a diameter of about 5 to 15 nanometers;
• and
• a second metal oxide, the second metal oxide being a lanthanum oxide;
• wherein the combination of the zinc oxide nanocrystals and the second metal oxide is capable of catalyzing both a transesterification reaction of a triglyceride with an alcohol and a esterification reaction of a free fatty acid with an alcohol.

A method of preparing a heterogeneous catalyst system, the method comprising:

• combining in a predetermined ratio, a Zn salt and a second metal salt, to form a first aqueous solution mixing the first aqueous solution with an aqueous urea solution to form a mixed solution;
• agitating and heating the mixed solution until a substantial amount of solid precipitate forms in the mixed solution;
• continuing to heat the mixed solution until the solution becomes a firm solid;
• drying the firm solid at a temperature greater than about 100° C. for a period of time of at least about 1 hour;
• and
• calcining the solid at an elevated temperature for a predetermined length of time to obtain a heterogeneous catalyst system comprising:
• 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 having a crystal face that includes a mesopore having a diameter of about 5 to 15 nanometers;
• and
• a lanthanum oxide,
• wherein the combination of the zinc oxide mixture and the lanthanum oxide exhibits a Zn:La bulk molar ratio between about 9.0:1.0 and 1.0:1.0 and having a first surface site and a second surface site, the first surface site capable of catalyzing a transesterification reaction of triglyceride with an alcohol and the second surface site capable of catalyzing a esterification reaction of a fatty acid with an alcohol.

A method comprising the steps of:

• providing a heterogeneous catalyst system, the catalyst system comprising:
• 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 having a crystal face that includes a mesopore having a diameter of about 5 to 15 nanometers;
• and a lanthanum oxide,
• wherein the combination of the zinc oxide mixture and the lanthanum oxide exhibits a Zn:La bulk molar ratio between about 9.0:1.0 and 1.0:1.0 and having a first surface site and a second surface site, the first surface site capable of catalyzing a transesterification reaction of triglyceride with an alcohol and the second surface site capable of catalyzing a esterification reaction of a fatty acid with an alcohol;
• placing a feedstock and an alcohol in contact with the catalyst system to form a reaction mixture, the feedstock including triglycerides, free fatty acids in a concentration that is greater than about 0.5 wt. % and water in a concentration that is greater than about 1 wt. %;
• heating the reaction mixture;
• and
• allowing the catalyzed transesterification of the triglycerides and the catalyzed esterification of the free fatty acids to simultaneously occur for a predetermined amount of time to form the respective corresponding alcoholic esters of the triglycerides and the free fatty acids.