Preparing method of a phenolic oligomer antioxidant
A method for preparing a phenolic oligomer antioxidant with a very small residual content of butylated hydroxytoluene (BHT) is provided. Specifically, the method for preparing the phenolic oligomer antioxidant relates to a method which is capable of a BHT-free phenolic oligomer antioxidant or a phenolic oligomer antioxidant containing a trace amount of residual BHT by removing the precursor of BHT as much as possible by performing the concentration under the reduced pressure while injecting an inert gas to an intermediate product and/or removing BHT by performing the concentration under the reduced pressure while injecting an inert gas to the final product.
1. A method for preparing a phenolic oligomer antioxidant, which comprises:
(a) reacting p-cresol with dicyclopentadiene (DCPD) in the presence of a boron fluoride catalyst;
(b) removing residual p-cresol to 500 ppm or less by concentrating a product of (a) under reduced pressure;
(c) reacting a product of (b) with isobutene in the presence of an acid; and
(d) obtaining a phenolic oligomer antioxidant with a residual content of butylated hydroxytoluene (BHT) of 500 ppm or less by concentrating a product of (c) under the reduced pressure,
wherein one or more of steps (b) and (d) are performed while injecting an inert gas through a gas line having one of a sparger type tip and tube type tip with a gas hourly space velocity (GHSV) of the inert gas for the concentration of the product of step (a) or (c) respectively is 0.6-30 L/hr per 1 kg of the product of step (a) or (c) respectively.
2. The method for preparing the phenolic oligomer antioxidant according to claim 1 , wherein the acid in (c) is one or more selected from sulfuric acid, p-toluenesulfonic acid, and methanesulfonic acid.
3. The method for preparing the phenolic oligomer antioxidant according to claim 1 , wherein, in (d), the temperature for the concentration of the product of step (c) is 170-250° C.
4. The method for preparing the phenolic oligomer antioxidant according to claim 1 , wherein, in (d), the pressure for the concentration of the product of step (c) is 100 mmHg or lower.
5. The method for preparing the phenolic oligomer antioxidant according to claim 1 , wherein in step (d) the GHSV of the inert gas for the concentration of the product of step (c) is 0.6-30 L/hr per 1 kg of the product of step (c).
6. The method for preparing the phenolic oligomer antioxidant according to claim 1 , wherein, (b) is performed while injecting the inert gas to the product of (a).
7. The method for preparing a phenolic oligomer antioxidant according to claim 6 , wherein, in (b), the temperature for the concentration of the product of step (a) is 170-250° C.
8. The method for preparing the phenolic oligomer antioxidant according to claim 6 , wherein, in (b), the pressure for the concentration of the product of step (a) is 100 mmHg or lower.
9. The method for preparing a phenolic oligomer antioxidant according to claim 6 , wherein in step (b) GHSV of the inert gas for the concentration of the product of step (a) is 0.6-30 L/hr per 1 kg of the product of step (a).
10. The method for preparing a phenolic oligomer antioxidant according to claim 1 wherein
in step (b) the GHSV of the inert gas for the concentration of the product of step (a) is 0.6-30 L/hr per 1 kg of the product of step (a), and
in step (d) the GHSV of the inert gas for the concentration of the product of step (c) is 0.6-30 L/hr per 1 kg of the product of step (c).