Methods for treating hydrocarbon streams containing mercaptan compounds

1. A method for treating hydrocarbon streams containing mercaptan compounds comprising the steps of:

contacting a first, light hydrocarbon stream comprising mercaptan compounds with a first alkaline caustic solution to remove the mercaptan compounds from the first hydrocarbon stream and generate a second alkaline caustic solution comprising mercaptan compounds; wherein the light hydrocarbon stream comprises greater than about 80 mass-% C 3 hydrocarbons, or greater than about 80 mass-% C 4 hydrocarbons, or greater than about 80 mass-% C 3 and C 4 hydrocarbons;

oxidizing the mercaptan compounds in the second alkaline caustic solution to generate a third alkaline solution comprising a first concentration of disulfide compounds;

separating a portion of the disulfide compounds in the third alkaline solution to form a fourth alkaline caustic solution comprising a second concentration of disulfide compounds, wherein the first concentration of disulfide compounds is greater than the second concentration of disulfide compounds; and

contacting the fourth alkaline solution with a second, heavy hydrocarbon stream comprising greater than about 80 mass-% naphtha compounds and further comprising mercaptan compounds to remove the mercaptan compounds from the second hydrocarbon stream, remove the disulfide compounds from the fourth alkaline caustic solution, and generate the first alkaline caustic solution.

2. The method of claim 1 , wherein contacting with the first alkaline solution comprises contacting with a solution comprising a sodium hydroxide solution.

3. The method of claim 1 , wherein oxidizing the mercaptan compounds comprises contacting the mercaptan compounds with an oxidizing catalyst and oxygen.

4. The method of claim 1 , wherein the separating the portion of the disulfide compounds in the third alkaline solution to form a fourth alkaline caustic solution comprising a second concentration of disulfide compounds, comprises a physical phase separation process.

5. The method of claim 1 , wherein generating the third alkaline solution comprises generating an alkaline solution comprising a disulfide concentration of about 200 wt. ppm or less.

6. The method of claim 1 , wherein generating the fourth alkaline solution comprises generating an alkaline solution comprising a disulfide concentration of less than about 5 wt. ppm.

7. A method for treating hydrocarbon streams containing mercaptan compounds comprising the steps of:

contacting a first, light hydrocarbon stream comprising mercaptan compounds with a first alkaline caustic solution to remove the mercaptan compounds from the first hydrocarbon stream and generate a second alkaline caustic solution comprising mercaptan compounds; wherein the light hydrocarbon stream comprises greater than about 80 mass-% C 3 hydrocarbons, or greater than about 80 mass-% C 4 hydrocarbons;

contacting a second, light hydrocarbon stream comprising greater than about 80 mass-% C 4 hydrocarbons and further comprising mercaptan compounds with a third alkaline caustic solution to remove the mercaptan compounds from the second hydrocarbon stream and generate a fourth alkaline caustic solution comprising mercaptan compounds;

combining the second and the fourth alkaline caustic solutions to form a fifth alkaline caustic solution comprising mercaptan compounds;

oxidizing the mercaptan compounds in the fifth alkaline caustic solution to generate a sixth alkaline solution comprising a first concentration of disulfide compounds;

separating a portion of the disulfide compounds in the sixth alkaline solution to form a seventh alkaline caustic solution comprising a second concentration of disulfide compounds, wherein the first concentration of disulfide compounds is greater than the second concentration of disulfide compounds;

contacting the seventh alkaline solution with a third, heavy hydrocarbon stream comprising greater than about 80 mass-% naphtha compounds and further comprising mercaptan compounds to remove the mercaptan compounds from the third hydrocarbon stream, remove the disulfide compounds from the seventh alkaline caustic solution, and generate an eighth alkaline caustic solution; and

separating the eighth alkaline caustic solution into the first alkaline caustic solution and an additional portion of the second alkaline caustic solution.

8. The method of claim 7 , wherein contacting with the first alkaline solution comprises contacting with a solution comprising a sodium hydroxide solution.

9. The method of claim 7 , wherein oxidizing the mercaptan compounds comprises contacting the mercaptan compounds with an oxidizing catalyst and oxygen.

10. The method of claim 7 , wherein separating the portion of the disulfide compounds in the sixth alkaline solution to form a seventh alkaline caustic solution comprises a physical phase separation process.

11. The method of claim 7 , wherein generating the sixth alkaline solution comprises generating an alkaline solution comprising a disulfide concentration of about 200 wt. ppm or less.

12. The method of claim 7 , wherein generating the seventh alkaline solution comprises generating an alkaline solution comprising a disulfide concentration of less than about 5 wt. ppm.

13. A method for treating hydrocarbon streams containing mercaptan compounds comprising the steps of:

contacting a first, light hydrocarbon stream comprising greater than about 80 mass-% C 3 hydrocarbons mercaptan compounds with a first alkaline caustic solution comprising sodium hydroxide to remove the mercaptan compounds from the first hydrocarbon stream and generate a second alkaline caustic solution comprising mercaptan compounds;

contacting a second, light hydrocarbon stream comprising C 4 hydrocarbons and mercaptan compounds with a third alkaline caustic solution comprising sodium hydroxide to remove the mercaptan compounds from the second hydrocarbon stream and generate a fourth alkaline caustic solution comprising mercaptan compounds;

combining the second and the fourth alkaline caustic solutions to from a fifth alkaline caustic solution comprising mercaptan compounds;

oxidizing the mercaptan compounds in the fifth alkaline caustic solution by contacting the fifth alkaline caustic solution with an oxidizing catalyst comprising a metal phthalocyanine derivate and oxygen to generate a sixth alkaline solution comprising a first concentration of disulfide compounds;

separating a portion of the disulfide compounds in the sixth alkaline solution using a physical phase separation process to form a seventh alkaline caustic solution comprising a second concentration of disulfide compounds, wherein the first concentration of disulfide compounds is greater than the second concentration of disulfide compounds;

contacting the seventh alkaline solution with a third, heavy hydrocarbon stream comprising naphtha hydrocarbons and mercaptan compounds to remove the mercaptan compounds from the third hydrocarbon stream, remove the disulfide compounds from the seventh alkaline caustic solution, and generate an eighth alkaline caustic solution;

further contacting the third hydrocarbon stream with a dilute alkaline caustic solution to remove further mercaptan compounds from the third hydrocarbon stream; and

separating the eighth alkaline caustic solution into the first alkaline caustic solution and an additional portion of the second alkaline caustic solution.