Method for separating and purifying 2,6-dimethylnaphthalene
A method for separating and purifying 2,6-dimethylnaphthalene, is provided in which 2,6-dimethylnaphthalene of high purity is obtained from a mixture of dimethylnaphthalene isomers with a high yield, by means of a combined process of column melt crystallization and sweating operation.
1. A method for separating and purifying 2,6-dimethylnaphthalene, comprising the steps of:
1) performing melt crystallization to produce 2,6-dimethylnaphthalene crystals using a column melt crystallization process of adding a mixture of dimethylnaphthalene (DMN) isomers containing 2,6-dimethylnaphthalene to a column crystallization apparatus, melting the mixture in the apparatus, and then cooling a molten liquid of the mixture;
2) forming 2,6-dimethylnaphthalene crystal layers by separating the 2,6-dimethylnaphthalene crystals produced in Step 1) from the mother liquor by vacuum suction filtration;
3) performing a sweating operation of partially melting the impurities contained on the surfaces of the 2,6-dimethylnaphthalene crystal layers formed in Step 2) and between the 2,6-dimethylnaphthalene crystal layers, while suction filtering the impurities; and
4) melting the 2,6-dimethylnaphthalene crystals after the sweating operation, and separating and recovering 2,6-dimethylnaphthalene.
2. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein the cooling temperature in the column melt crystallization process of Step 1) is in the range of 0 to 65° C. in accordance with the composition of the raw material.
3. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein the cooling rate in the column melt crystallization process of Step 1) is in the range of 0.1 to 1° C./min.
4. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein the vacuum suction in Step 2) is performed by vacuum suction filtration at 50 to 300 torr.
5. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein the heating rate in the sweating operation of Step 3) is in the range of 0.1 to 1° C./min.
6. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein the heating temperature in the sweating operation of Step 3) is in the range of 60 to 100° C.
7. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein the mixture of dimethylnaphthalene isomers contains 20 to 80% by weight of 2,6-dimethylnaphthalene.
8. The method for separating and purifying 2,6-dimethylnaphthalene as as set forth in claim 1 , wherein crystal seeds are introduced in Step 1).
9. The method for separating and purifying of 2,6-dimethylnaphthalene as set forth in claim 8 , wherein the amount of the crystal seeds to be introduced is such that the weight ratio of the crystal seeds/the mixture of dimethylnaphthalene isomers is 1/10000 to 1/100.
10. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein ethanol is added in Step 1) as a solvent.
11. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 10 , wherein the ratio of solvents is such that the mixture of dimethylnaphthalene isomers:ethanol=1:0.5 to 1:5.
12. The method for separating and purifying 2,6-dimethylnaphthalene as set forth in claim 1 , wherein the Steps 1) and 2) are repeated twice or more.