GB2076808A - Purification of naphthoquinone - Google Patents

Abstract

Crude naphthoquinone containing polycondensation products and resinous matters of naphthoquinone derivatives, obtained by the oxidation of naphthalene is purified by preparing a solution of said crude naphthoquinone in an aromatic hydrocarbon solvent selected from benzene, toluene, xylene and cumene, concentrating said solution at a concentration of about 40 to 60 wt.% and cooling said supersaturated solution to a temperature higher than 35 DEG C to crystallize only naphthoquinone and inhibit the crystallization of said polycondensation product and resinous matters of naphthoquinone derivatives.

Description

SPECIFICATION Process for purifying naphthoquinone BACKGROUND OF THE INVENTION The present invention relates to a process for purifying naphthoquinone obtained by an oxidation of naphthalene, by an extraction followed by a crystallization.

Naphthoquinone (1 ,4-naphthoquinone referring to as NQ otherwise specified) has been produced by an oxidation of naphthalene such as a catalytic liquid phase oxidation of naphthalene and a catalytic vapor phase oxidation of naphthalene which are described in USP 4,202,828. In these processes, polycondensed products and resinous matters of 1 ,4-naphthoquinone and 1 ,2-naphthoquinone have been also produced as by-products to contaminate naphthoquinone. It has not been easy to purify naphthoquinone.

In the conventional catalytic vapor phase oxidation of naphthalene, the reaction mixture gas obtained by the oxidation of naphthalene (containing naphthoquinone, phthalic anhydride, maleic anhydride, and naphthalene) is washed with water, if necessary, after condensing phthalic anhydride in a condenser, so as to collect the products of naphthoquinone, phthalic anhydride and maleic anhydride 1 and naphthoquinone is separated from water soluble matters such as phthalic acid and maleic acid by the conventional process to obtain a crude naphthoquinone in an industrial process. The resulting crude naphthoquinone contains impurities of phthalic acid, benzoic acid maleic acid and polycondensed products of naphthoquinone.

It has been known to purify such crude naphthoquinone by a recrystallization from a solvent such : as acetic acid or nonpolar solvents of petroleum ether and ligroin. When acetic acid is used, there is difficulty in a recovery of the solvent because of corrosive and water soluble properties of acetic acid.

When petroleum ether is used, solubility of naphthoquinone is low.

On the other hand, it has been known that aromatic hydrocarbon solvents such as benzene, toluene and xylene are solvents having high solubility of naphthoquinone, however, polycondensation products and resinous matters of 1 ,4-naphthoquinone and 1 ,2-naphthoquinone as by-products produced together with naphthoquinone are also highly soluble in the aromatic hydrocarbon solvents and could not be easily separated by a recrystallization because of a cocrystallization of these polycondensation products and resinous matters and naphthoquinone.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a process for purifying naphthoquinone to separate naphthoquinone from by-products of polycondensation products and resinous matters of 1,4naphthoquinone and 1 ,2-naphthoquinone so as to give high purity of naphthoquinone.

It is another object of the present invention to provide a process for purifying naphthoquinone from a crude naphthoquinone which contains by-products of polycondensation products and resinous matters of 1 ,4-naphthoquinone and 1 ,2-naphthoquinone by a crystallization of naphthoquinone under a condition solubilizing these polycondensation products and resinous matters.

The foregoing and other objects of the present invention have been attained by providing a process for purifying naphthoquinone obtained by an oxidation of naphthalene, by an extraction or a dissolution followed by a crystallization or recrystallization which comprises preparing a solution of said crude naphthoquinone containing polycondensation products and resinous matters of naphthoquinone derivatives in an aromatic hydrocarbon solvent selected from the group consisting of benzene toluene, zylene and cumene, concentrating said solution at a concentration of about 40 to 60 wt. % and cooling said supersaturated solution under preventing excess cooling to be lower than 350C to crystallize only naphthoquinone under inhibiting a crystallization of said polycondensation product and resinous matters of naphthoquinone derivatives.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graph showing a relation of purities of crystallized naphthoquinone and concentration of naphthoquinone in solutions: Figure 2 is a graph showing a relation of purities of crystallized naphthoquinone and times required for cooling a solution of a crude naphthoquinone from 800C to 400C; and Figure 3 is a graph showing a relation of purities of crystallized naphthoquinone and cooled temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Conditions for selectively crystallizing naphthoquinone from an aromatic hydrocarbon solvent have been studied to find the fact that naphthoquinone having high purity can be obtained by controlling a concentration of a solution of a crude naphthoquinone, a crystallization temperature and a cooling rate. The present invention has been attained by the finding.

A crude naphthoquinone used as the source in the process of the present invention is produced by an oxidation of naphthalene. The oxidation of naphthalene is usually carried out by a catalytic vapor phase oxidation though it can be also carried out by a catalytic liquid phase oxidation. The reaction mixture gas formed by a catalytic vapor phase reaction of naphthalene contains mainly naphthoquinone and phthalic anhydride. Naphthoquinone can be separated by the following conventional processes.

(1) A process for treating an aqueous slurry of naphthoquinone and phthalic acid obtained by washing the reaction mixture gas with an aromatic hydrocarbon solvent which is immiscible to water such as orthoxylene to extract naphthoquinone so as to separate naphthoquinone from phthalic acid.

(2) A process for dissolving completely phthalic acid into water and separating a crystallized naphthoquinone by a filtration; and (3) A process for converting phthalic acid into a monosalt of phthalic acid by an addition of a base to dissolve the monosalt into water and separating crystallized naphthoquinone by a filtration etc.

The resulting crude naphthoquinone is obtained in a form of solution of a crude naphthoquinone in an aromatic hydrocarbon solvent or in a form of powder. Such crude naphthoquinone can be used in the process of the present invention. The crude naphthoquinone contains polycondensation products and resinous matters of 1,4-naphthoquinone and 1,2-naphthoquinone and has a purity of about 85 to 95%.

The organic solvent used for the process of the present invention is an aromatic hydrocarbon solvent such as benzene, toluene, xylene, cumene. In general, an azeotropic point of xylene is relatively high and a vapor pressure of xylene is relatively high in the recovery of the solvent. Xylene includes oxylene, m-xylene and p-xylene or mixed xylene. It is preferable to use orthoxylene.

The process of the present invention will be carried out by the following process. The solution of naphthoquinone obtained by dissolving the crude naphthoquinone in an aromatic hydrocarbon solvent such as orthoxylene or by water-washing and separating naphthoquinone by an extraction, is usually concentrated to be a concentration of about 40 to 60% by weight based on the solution under maintaining a temperature for dissolving the crude naphthoquinone such as 70 to 900C and then, the concentrated solution is cooled at a cooling rate of less than about 800 C/hour preferably less than about 400C/hourto a temperature of higher than 35 C to crystallize only naphthoquinone and the resulting slurry of crystallized naphthoquinone is treated by a conventional separating method of mechanical method of a filtration or a centrifugal separation or a natural sedimentation to separate naphthoquinone, if necessary washing the resulting cake with a solvent, and the product is dried to obtain a pure naphthoquinone.

The filtrate can be recycled. The filtrate can be also mixed with the other solution of naphthoquinone and the Diels-Alder reaction adduct is obtained by reacting the mixture with butadiene and is oxidized with air in an aqueous solution of a base to obtain anthraquinone.

The solution of crude naphthoquinone can be washed with an alkaline aqueous solution such as a solution of sodium hydrogen-carbonate to separate alkaiine water soluble impurities before the crystallization, so as to obtain naphthoquinone having higher purity.

A concentration of the solution of naphthoquinone is in a range of about 40 to 60% preferably about 45 to 55%. The effect of the concentration of the solution of naphthoquinone is shown in Figure 1. Figure 1 is a graph showing the relation of purities of the crystallized naphthoquinone and concentrations thereof in the case of the cooling of the solution of naphthoquinone (purity of 91.4%) from 800C to 400C at a cooling rate of 200 C/hour. As shown in Figure 1 , when the concentration is lower than 40%, the purity of naphthoquinone is remarkably lowered and the yield of naphthoquinone is lowered. When the concentration is higher than about 60%, the fluidity of the slurry resulted by the cooling is low and the caking of the naphthoquinone is easily caused. These are disadvantageous.

The cooling rate is usually lower than 800C/hour preferably lower than 400 C/hour but higher than about 5 C/hour. Figure 2 shows the effect of the cooling rate to the purity of the crystallized naphthoquinone. Figure 2 is a graph showing relation of cooling times and purities of the crystallized naphthoquinone given in the cooling of 50% solution of a crude naphthoquinone (purity of 91.4%) in orthoxylene from 800C to 400C at a constant cooling rate. In Figure 2, the lowering of the purity of the crystallized naphthoquinone is found in the case of higher than 400C/hour especially higher than 800C/hour of the cooling rate. On the other hand, when the cooling rate is remarkably high as 4800C/hour, the crystals are fine to cause difficulty of filtering or to cause severe scaling.In order to obtain naphthoquinone having a purity of about 99%, it is preferable to cool it for longer than about 2 hours at a cooling rate of less than about 200 C/hour.

The low cooling rate is preferable for the crystal growth but it is not preferable for an industrial purpose. The cooling rate is preferably higher than about 50C hour especially higher than 7"C/hour.

The final cooling temperature should be about 350C or higher preferably higher than about 400C and lower than about 600C. Figure 3 shows the effect of the final cooling temperature to the purity of the crystallized naphthoquinone. Figure 3 is a graph showing the relation of final cooling temperatures and purities of crystallized naphthoquinone obtained by cooling 50% solution of a crude naphthoquinone (purity of 91.4%) in orthoxylene from 800C to the final cooling temperature at a cooling rate of 200C/hour. In Figure 3, the purity of crystallized naphthoquinone is remarkably low at a temperature of lower than about 350C, and the yield of naphthoquinone is too low at higher than 600C as the industrial process.

The process of the present invention can be a batch system or a continuous system. The batch system is remarkably advantageous in view of the temperature control.

As described in detail, in accordance with the purification of the present invention, a crude naphthoquinone is crystallized or recrystallized from a solution of an aromatic hydrocarbon solvent having high solubility of naphthoquinone such as xylene to obtain a purified naphthoquinone having high purity such as about 99% from the crude naphthoquinone (for example, purity of about 90%).

The industrial value is remarkably high.

The present invention is based on the special phenomenon that naphthoquinone is crystallized without crystallizing polycondensation products and resinous matters of 1,4-naphthoquinone and 1,2naphthoquinone from the special solvent under a special condition, because of synergistic effect of naphthoquinone and the polycondensation products and the resinous matters thereof at high concentration in the solvent at the specific temperature.

The crystallization of naphthoquinone is resulted in the supersaturated condition.

The present invention will be illustrated by certain examples and references which are provided for purposes of illustration only and are not intended to be limiting the invention.

EXAMPLE 1 An aqueous slurry of naphthoquinone and phthalic acid was obtained by washing a reaction mixture gas obtained by a catalytic vapor phase oxidation of naphthalene with water, to collect them and naphthoquinone was extracted from the aqueous slurry with orthoxylene at 850C to separate a solution of naphthoquinone in orthoxylene (22% of naphthoquinone). The solution was concentrated in vacuum at 80"C to obtain 50% solution of naphthoquinone. The purity of naphthoquinone in the solution was 91.4%. 4,500 Wt. part of the solution was cooled with stirring at an average cooling rate of 200 C/hour from 800C to 400 C, The resulting slurry of crystallized naphthoquinone was filtered to obtain a cake.The filtered cake was dried to obtain naphthoquinone having a purity of 97.1% at an yield of 74%.

The filtered cake obtained by the same method was washed with a same volume of orthoxylene and dried to obtain a purified naphthoquinone having a purity of 99.2% at an yield of 54%.

EXAMPLE 2 In accordance with the process of Example 1, except varying a concentration of the solution of the crude naphthoquinone, an average cooling rate and a final cooling temperature as shown in Table 1 and washing the resulting cake with the same volume of orthoxylene, each purification was carried out. The results are shown in Table 1.

TABLE 1

Run No. 1 2 3 4 5 6 7 Concentration of NO (%) 60 40 50 50 50 50 50 Amount of NQ solution (part) 4,500 4,500 4,500 4,500 4,500 4,500 4,500 Final cooling temperature (oC) 40 40 40 40 40 60 50 Cooling rate ("C/hour) 20 20 40 10 7 20 20 YieldofNQ(%) 55 48 54 54 53 45 50 Purity of NQ ( /0) 99.2 98.6 98.9 99.2 99.2 99.9 99.4 TABLE 1 (Continued)

Run No. Ref Ref. Ref.

Concentration of NO ( /n) 30 30 50 Amount of NQ solution (part) 4,500 4,500 4,500 Final cooling temperature ( C) 40 40 20 1 20 Cooling rate ( C/hour) 20 80 20 20 Yield of NQ ( /0) 35 52 61 35 61 Purity of NQ ( /0) 97.2 97.8 96.8 Note: NQ: naphthoquinone EXAMPLE 3 In accordance with the process of Example 1, toluene, benzene or cumene was used instead of orthoxylene, each purification was carried out to obtain each purified naphtoquinone having a purity of higher than 99%.

Claims (9)

1. In a process for purifying naphthoquinone obtained by an oxidation of naphthalene, by an extraction or a dissolution followed by a crystallization or recrystallization, an improvement characterized by preparing a solution of said crude naphthoquinone containing polycondensation products and resinous matters of naphthoquinone derivatives in an aromatic hydrocarbon solvent selected from the group consisting of benzene, toluene, xylene and cumene, concentrating said solution at a concentration of about 40 to 60 wt.% and cooling said supersaturated solution under preventing excess cooling to be lower than 350C to crystallize only naphthoquinone under inhibiting a crystallization of said polycondensation product and resinous matters of naphthoquinone derivatives.

2. The process according to Claim 1 wherein said concentration of said crude naphthoquinone is in a range of about 45 to 55 wt.%.

3. The process according to Claim 1 wherein said temperature in the cooling is in a range of about 40 to 600C.

4. The process according to Claim 1 wherein said cooling is carried out at a cooling rate of lower than about 800C/hour.

5. The process according to Claim 1 wherein said cooling is carried out at a cooling rate of lower than about 4O0C/hour.

6. The process according to Claim 1 wherein said aromatic hydrocarbon solvent is xylene.

7. The process according to Claim 6 wherein said xylene is orthoxylene.

8. The process according to Claim 1 wherein said supersaturated solution of said crude naphthoquinone containing naphthoquinone oligomers and other derivatives is xylene at a concentration of about 40 to 60 wt.% is prepared by concentrating said extracted solution in vacuum at a temperature for maintaining a solution and said supersaturated solution is cooled to be higher than 350C to crystallize only naphthoquinone under inhibiting a crystallization of said naphthoquinone polycondensed products and other derivatives thereof.

9. A process according to claim 1 substantially as herein described with reference to any one of the Examples.