Patent Application
20070270609
Hereinafter, the present invention will be described in detail with reference to Examples.
The process for producing 2,6-naphthalenedicarboxylic acid comprises the steps of dissolving 2,6-dimethylnaphthalene in a solvent; producing 2,6-naphthalenedicarboxylic acid by oxidizing the dissolution product; crystallizing the produced 2,6-naphthalenedicarboxylic acid; and separating the crystallized 2,6-naphthalenedicarboxylic acid.
According to
The oxidation reaction is performed in the presence of catalyst. The catalyst used in the process of oxidizing 2,6-dimethylnaphthalene to 2,6-naphthalenedicarboxylic acid may be a complex catalyst system comprising transition metal catalyst components such as cobalt or manganese, and a bromine component in combination. The compound of cobalt component may be exemplified by cobalt acetate, cobalt naphthalate and cobalt carbonate, and the amount of the cobalt component compound may be, as expressed as a weight ratio of cobalt atoms to 2,6-dimethylnaphthalene, 0.02 to 0.15, preferably 0.04 to 0.12, and more preferably 0.06 to 0.1. The compound of manganese component may be exemplified by manganese acetate, manganese naphthalate, manganese carbonate and manganese bromide, and the weight ratio of manganese atoms to cobalt atoms may be 0.05 to 1.0, and preferably 0.15 to 0.4. The transition metal catalysts, namely, cobalt and manganese, can be used individually or in combination, but the total amount of the transition metal-catalysts is, as expressed as a weight ratio of the components containing cobalt and manganese atoms to 2,6-dimethylnaphthalene, is 0.03 to 0.25, and preferably 0.05 to 0.2. This amount of catalyst is determined in relation to the amount of impurities produced. Specifically, when the amount of the transition metal catalysts is less than 0.03, conversion of 2,6-formylnaphthoic acid, which corresponds to an intermediate of the oxidation reaction, is difficult, and the yield of the desired final product is reduced. On the other hand, when the amount of the transition metal catalysts exceeds 0.25, the transition metal may form a complex with trimellitic acid that is present as an impurity, thus lowering the purity of 2,6-naphthalenedicarboxylic acid. The catalyst comprising a bromine component, which is to be combined with the transition metal catalysts, may be at least one selected from the group consisting of manganese bromide, cobalt bromide, sodium bromide, ammonium bromide and tetrabromoethane. The amount of the bromine component catalyst may be 0.8 to 2.0, and preferably 1.0 to 1.5, as the weight ratio of bromine atoms to cobalt atoms. When the amount of the bromine component is less than 0.8, the amounts of the transition metal complex and of 2,6-naphthalenedicarboxylic acid are increased. On the other hand, when the amount exceeds 2.0, the amount of the transition metal complex decreases, but the amount of the bromine compound increases, and thus the amount of colored impurities also increases. Such increase in impurities may lead to an increase in the throughput of the purification process.
The 2,6-naphthalenedicarboxylic acid produced by the oxidation reaction is crystallized in a crystallization bath 12. In the crystallization bath 12, a solid phase 2,6-naphthalenedicarboxylic acid is produced from the oxidation product, in the form of solids with a uniform size at normal pressure and at a temperature of 100 to 120° C. The crystallization bath 12 contains crystallized 2,6-naphthalenedicarboxylic acid as well as the reaction mother liquor containing organic materials and the catalyst. In order to separate 2,6-naphthalenedicarboxylic acid from the reaction mother liquor, the product from the crystallization bath 12 is transported to the solid-liquid separation apparatus 13, where the product is separated into solid components and liquid components. The solid-liquid separation apparatus 13 may be a known apparatus for separating solids from liquids by means of filtration, centrifugation or settling.
2,6-naphthalenedicarboxylic acid, which is a solid component separated from the solid-liquid separation apparatus 13, is transported to a solids reservoir 14 for storing the final product, and the reaction mother liquor containing various organic materials and catalyst is transported to a liquid reservoir 15. The liquid reservoir 15 is connected to the reactant preparation bath 10 so that a portion of the mother liquor may be recycled to the reactant preparation bath 10.
The process for production of 2,6-naphthalenedicarboxylic acid described above comprises an oxidation process. The oxidation process is meant by a process of oxidizing 2,6-dimethylnaphthalene, and this process is carried out by introducing a catalyst and oxygen-containing air. The oxygen-containing air should be discharged after the oxidation process, and the oxygen content in the gas being discharged should be limited to a certain range. When the oxygen concentration in the gas being discharged after the oxidation reaction exceeds 10%, there is a risk of explosion due to the acetic acid that is used as the solvent. Therefore, it is necessary to control the oxygen concentration in the gas being discharged, and accordingly, it is advantageous that a diluent gas is introduced together with oxygen to the oxidation process. This diluent gas may be introduced to the oxidation process through a recycling process. Furthermore, the mother liquor discharged from the crystallization process contains the transition metal catalyst used in the oxidation reaction. The transition metal catalyst in the mother liquor may be recovered through a separate process. However, such a separate process requires an additional increase in the production costs, and may bring a disadvantageous effect in the aspect that the entire production process should be performed in a continuous mode. Thus, in the process for production of 2,6-naphthalenedicarboxylic acid of the invention, the diluent gas used in the oxidation process and the mother liquor discharged from the crystallization process are recycled.
According to
Oxygen-containing air and the diluent gas containing nitrogen or carbon dioxide are introduced to the oxidation reactor 11 for the oxidation process, through an air inlet 161 and a gas inlet 162, respectively. The amounts of the gases introduced can be adjusted by an air flow meter 16 such that the pressure inside the reactor, that is, the pressure inside the oxidation reactor 11, is maintained at 15 to 30 kg/cm2 as described above. Any residual gas remaining in the oxidation reactor 11 after the oxidation process is transported to a discharge flow meter 17 through an outlet 171. The discharge flow meter discharges some of the gas out of the system, while recycling the remaining portion of the gas to the oxidation reactor 11 via the air flow meter 16. The control of the amount discharged and the amount recycled is determined in accordance with the oxygen concentration in the discharged gas. For example, the amount of oxygen in the discharged gas should be maintained to be less than 10% based on the total gas weight. Therefore, when the amount of the discharged gas is measured to be close to 10%, the ratio of recycling may be increased. When the ratio of recycling is increased, the oxygen content in the gas discharged through the outlet 171 can be reduced. On the other hand, a portion of the bromine component used as catalyst can be discharged through the discharged gas. If needed, the amount of the bromine component may be measured, and the measured amount can be used to control the amount of the bromine component to be introduced as catalyst.
As shown in
The method for production according to the invention allows production of 2,6-naphthalenedicarboxylic acid having a high purity of 99.3%, preferably of 99.9%, by controlling the recycling ratio of the discharged gas or the recycling ratio of the mother liquor.
Now, specific examples for producing 2,6-naphthalenedicarboxylic acid according to the method of the invention will be described in the following.
A titanium reactor having a capacity of 300 L, which is equipped with a cooler, a heater and a stirrer, was charged with reactants and catalyst, and an oxidation reaction was performed. The oxidation reactor was set to a temperature of 200° C. and a pressure of 20 kg/cm2, and the stirrer was rotated at 700 rpm to disperse the reactant gases. During the reaction, air was introduced in an amount of about 35.7 moles per mole of 2,6-dimethylnaphthalene until the initial amount of the gas being recycled was secured, and was introduced in an amount of 22 moles per mole of 2,6-dimethylnaphthalene after the system was stabilized. As a diluent gas, nitrogen was introduced in an amount of 1.8 moles per mole of 2,6-dimethylnaphthalene, and after stabilization, the amount of the discharged gas to be recycled was adjusted such that the oxygen content in the discharged gas was 4 to 6% by weight. After the steps of oxidation reaction followed by crystallization and solid-liquid separation, the final product was obtained, and the final product was purged with BSTFA in a nitrogen environment and then subjected to analysis by gas chromatography. The amount of the mother liquor recycled during the production was adjusted to 10% by weight.
The amount of 2,6-dimethylnaphthalene used, the amount of acetic acid and the amount of catalyst are presented in Table 1, while the yield of the final product and the content of impurities are presented in Table 2.
2,6-naphtheledicarboxylic acid was produced under the same conditions as in Example 1, except that the amounts of acetic acid and catalyst as well as the amount of the mother liquor that are recycled were varied. The compounds used for the reaction and the resulting products are presented in Table 1 and Table 2, respectively.
The production was carried out under the same conditions as in Example 1, except that the discharged gas was not recycled in Comparative Example 1, while the oxygen content in the discharged gas was adjusted to 4 to 6% by weight, but the amount of the mother liquor being recycled was adjusted to the amount given in Table 1 in Comparative Example 2. The compounds used for the reaction and the resulting products are presented in Table 1 and Table 2, respectively.
According to Table 2, when the recycling ratio of the mother liquor is 5 to 20% by weight based on the mass of acetic acid introduced, the product can be obtained with high yield. When the reaction mother liquor is recycled in an excess amount as in Comparative Example 1, the purity and yield of the product are lowered. On the other hand, when the amount of the mother liquor being recycled is excessively small as in Comparative Example 2, the effect of recycling the mother liquor is hardly expected. Thus, it can be seen that when the oxidation reaction is carried out continuously, with the amount of the mother liquor being recycled being adjusted to 5 to 20% by weight based on the solvent, 2,6-naphthalenedicarboxylic acid of high purity and high chromaticity can be obtained. It was found that the effect of the amount of the discharged gas on the purity and yield was substantially negligible. However, the amount of gas being recycled may be related to the stability and economic aspects of the entire process.
The invention provides a method for producing 2,6-naphthalenedicarboxylic acid with stability and reduced production costs by controlling during the oxidation process so that a portion of the diluent gas being discharged is recycled. The method also allows production of 2,6-naphthalenedicarboxylic acid of high purity and high chromaticity by recycling a portion of the mother liquor.
This invention has been described above in connection with Examples. The suggested Examples are intended for illustrative purposes only, and any person having ordinary skill in the pertinent art will be able to have various modifications and equivalent arrangements of the suggested Examples within the technical spirit of the invention. It is to be understood that the invention is not limited to the suggested Examples, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2006-0045544 | May 2006 | KR | national |
