Methods of refining natural oils, and methods of producing fuel compositions

1. A method of refining a natural oil comprising:

providing a feedstock comprising a natural oil;

reacting the feedstock in the presence of a metathesis catalyst to form a metathesized product comprising olefins, esters and residual metathesis catalyst;

treating the residual metathesis catalyst in the metathesis product with an isomerisation suppression agent comprising nitric acid to passivate at least a portion of the residual metathesis catalyst;

separating the olefins in the metathesized product from the esters in the metathesized product; and

transesterifying the esters in the presence of an alcohol to form a transesterified product.

2. The method of claim 1 wherein the natural oil is selected from the group consisting of canola oil, rapeseed oil, coconut oil, corn oil, cottonseed oil, olive oil, palm oil, peanut oil, safflower oil, sesame oil, soybean oil, sunflower oil, linseed oil, palm kernel oil, tung oil, jatropha oil, mustard oil, camelina oil, pennycress oil, hemp oil, algal oil, castor oil, lard, tallow, poultry fat, yellow grease, fish oil, tall oils, and combinations thereof.

3. The method of claim 1 wherein the residual metathesis catalyst comprises ruthenium.

4. The method of claim 1 wherein the nitric acid is selected from the group consisting of anhydrous nitric acid, fuming nitric acid, concentrated nitric acid, solid hydrates of nitric acid, solutions of nitric acid, and combinations thereof.

5. The method of claim 1 , further comprising hydrogenating the olefins to form a fuel composition that comprises (a) a jet fuel composition having a carbon number distribution between 5 and 16 or (b) a diesel fuel composition having a carbon number distribution between 8 and 25.

6. The method of claim 1 further comprising oligomerizing the olefins to form a material selected from the group consisting of poly-alpha-olefins, poly-internal-olefins, mineral oil replacements, biodiesel, and combinations thereof.

7. The method of claim 1 , further comprising: separating glycerin from the transesterified product through a liquid-liquid separation; washing the transesterified product with water after separating the glycerin to further remove the glycerin; and drying the transesterified product after the washing to separate the water from the transesterified product.

8. The method of claim 7 further comprising distilling the transesterified product to separate a specialty chemical selected from the group consisting of an ester of 9-decenoic acid, an ester of 9-undecenoic acid, an ester of 9-dodecenoic acid, and combinations thereof.

9. The method of claim 8 further comprising hydrolyzing the specialty chemical, thereby forming an acid selected from the group consisting of: 9-decenoic acid, 9-undecenoic acid, 9-dodecenonic acid, and combinations thereof.

10. The method of claim 1 further comprising reacting the transesterified product with itself to form a dimer.

11. The method of claim 1 wherein the reacting comprises self-metathesis of the natural oil.

12. The method of claim 1 wherein the feedstock further comprises a low-molecular weight-olefin and wherein the reacting comprises cross-metathesis between the natural oil and the low-molecular-weight olefin.

13. The method of claim 12 wherein the low-molecular-weight olefin comprises a material selected from the group consisting of ethylene, propylene, 1-butene, 2-butene, and combinations thereof.

14. The method of claim 12 wherein the low-molecular-weight olefin comprises at least one branched olefin having a carbon number between 4 and 10.

15. A method of producing a fuel composition comprising:

providing a feedstock comprising a natural oil;

reacting the feedstock in the presence of a metathesis catalyst to form a metathesized product comprising olefins, esters and residual metathesis catalyst;

treating the residual metathesis catalyst in the metathesis product with an isomerization souppression agent comprising nitric acid to passivate at least a portion of the residual metatheisis catalyst;

separating the olefins in the metathesized product from the esters in the metathesized product; and

hydrogenating the olefins to form a fuel composition.

16. The method of claim 15 further comprising flash-separating a light end stream from the metathesized product prior to separating the olefins from the esters, wherein the light end stream comprises a majority of hydrocarbons with carbon numbers 2 to 4.

17. The method of claim 15 further comprising separating a light end stream from the olefins prior to hydrogenating the olefins, wherein the light end stream comprises a majority of hydrocarbons with carbon numbers of 3 to 8.

18. The method of claim 15 further comprising separating a C 18+ heavy end stream from the olefins prior to hydrogenating the olefins, wherein the heavy end stream comprises a majority of hydrocarbons with carbon numbers of at least 18.

19. The method of claim 15 further comprising separating a C 18+ heavy end stream from the fuel composition, wherein the heavy end stream comprises a majority of hydrocarbons with carbon numbers of at least 18.

20. The method of claim 15 further comprising isomerizing the fuel composition, wherein a fraction of normal-paraffin compounds in the fuel composition are isomerized into iso-paraffin compounds.

21. The method of claim 15 wherein the reacting comprises self-metathesis of the natural oil.

22. The method of claim 15 wherein the feedstock further comprises a low-molecular-weight olefin and wherein the reacting comprises cross-metathesis between the natural oil and the low-molecular-weight olefin.