Method for producing butene polymer

1. A method for producing a butene polymer, comprising:

performing polymerization reaction by contacting a raw material component comprising 20% by mass or more of isobutene with a Lewis acid catalyst;

adding a butene oligomer to the reaction solution of the polymerization reaction;

water-washing the reaction solution supplemented with the butene oligomer to obtain the solution to be treated containing the reaction product and the butene oligomer; and

subjecting the solution to be treated containing a reaction product of the polymerization reaction and a butene oligomer added to the reaction product to distillation treatment to obtain the butene polymer, wherein

an amount of the butene oligomer added is 25 parts by mass or larger with respect to 100 parts by mass of the reaction product.

2. The method according to claim 1 , wherein the butene oligomer is a mixture of a dimer to a pentamer of butene.

3. The method according to claim 1 , wherein the Lewis acid catalyst is aluminum chloride, alkyl aluminum dichloride or a boron trifluoride complex.

4. The method according to claim 3 , wherein

the boron trifluoride complex is a complex of boron trifluoride and a complexing agent, and

the complexing agent is a primary alcohol.

5. The method according to claim 1 , wherein each of contents of moisture, a sulfur-containing compound and an oxygen-containing compound in the raw material component in the polymerization is 100 ppm by mass or smaller.

6. The method according to claim 1 , further comprising, before the polymerization, adjusting each of the contents of moisture, a sulfur-containing compound and an oxygen-containing compound in the raw material component to 100 ppm by mass or smaller by contacting the raw material component with a solid treatment agent.

7. The method according to claim 1 , wherein the amount of the butene oligomer added is 65 parts by mass or larger with respect to 100 parts by mass of the reaction product.

8. The method according to claim 1 , wherein a content of 1,3-butadiene in the raw material component in the polymerization is 1000 ppm by mass or smaller.

9. The method according to claim 1 , wherein

the distillation comprises subjecting the solution to be treated to distillation treatment to obtain the butene polymer and an oligomer component comprising the butene oligomer, and

the oligomer component is recycled for addition to the reaction product.

10. The method according to claim 1 , wherein the raw material component comprises a dilution of isobutene with a saturated hydrocarbon.

11. The method according to claim 1 , wherein the raw material component comprises a mixture of hydrocarbons having 4 carbon atoms formed by naphtha cracking.

12. The method according to claim 1 , wherein the raw material component comprises a mixture of hydrocarbons having 4 carbon atoms obtained by first fluid catalytic cracking of contacting a heavy oil with a fluid catalytic cracking catalyst on the conditions that a reaction zone exit temperature is 400° C. or higher and lower than 550° C., a catalyst/oil ratio is 2.0 to 15.0 in terms of a mass ratio, and a residence time of hydrocarbons in the reaction zone is 1.0 to 10.0 seconds.

13. The method according to claim 1 , wherein the raw material component comprises a mixture of hydrocarbons having 4 carbon atoms obtained by second fluid catalytic cracking of contacting a heavy oil with a catalyst containing 12 to 24% by mass of shape-selective zeolite on the conditions that a reaction zone exit temperature is 580 to 630° C., a catalyst/oil ratio is 15 to 40 in terms of a mass ratio, and a residence time of hydrocarbons in the reaction zone is 0.1 to 1.0 seconds.