JPH0420412B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for refining naphthalene, which is generally referred to as 95% naphthalene, containing benzothiophene recovered from naphthalene oil, middle oil, etc. obtained by distilling coal tar. <Prior Art> Naphthalene is an important substance as a raw material for medicines, dyes, phthalic anhydride, anthraquinone, and the like. Methods for recovering naphthalene from naphthalene oil and medium oil obtained by distilling coal tar include methods of precipitating crystals by natural cooling or forced cooling and centrifugal separation, and methods using only distillation, but the mainstream method is the distillation method. (December 1973, pages 76-77 of "Aromatic and Tar Industry Handbook" published by the Japan Aromatic Industry Association). However, the naphthalene obtained usually has a purity of about 95% and is generally referred to as 95% naphthalene. 95%
Naphthalene contains various impurities such as trace amounts of neutral components such as methylnaphthalene, basic components such as quinoline, acidic components such as phenol derivatives, and sulfur compounds such as benzothiophene. As a method to remove these impurities and produce purified naphthalene, the hydrogenation method
119856, JP 54-144349), methanol recrystallization method (JP 47-47020), impurity removal method by adding anhydrous aluminum chloride (JP 47-47021), fractional crystallization and white clay Combined treatment method (Japanese Patent Publication No. 47-47023), oxalic acid addition method (Japanese Patent Publication No. 53-144557), acetic anhydride addition method (Japanese Patent Publication No. 60-3051), metal or metal oxide catalyst addition method (Japanese Patent Application Laid-open No. 54-81247, Japanese Patent Application Laid-Open No. 53-147048), etc. are known. Among the conventional methods mentioned above, the hydrogenation method that is carried out on an industrial scale requires the addition of a step for removing ethylbenzene, which is a decomposition product of tetralin and benzothiophene, which are produced by hydrogenating a part of naphthalene. Product yield decreases. Similarly, with the fractional crystallization method, the removal of benzothiophene, a sulfur compound, is insufficient, so when low-sulfur products are required, it is necessary to add a deflow step, and naphthalene is lost along with the fractionated mother liquor, resulting in a loss of product quality. Retention decreases. The impurity removal method by adding anhydrous aluminum chloride polymerizes or decomposes impurities to obtain purified naphthalene, but the desulfurization rate is not necessarily good (koks i Khimiya No. 10 No. 39).
40 [1977]), a method of treatment in the presence of acetyl chloride has recently been proposed (Chem.
lnd 1985, pp. 338-339), but has the drawback of high cost. Other conventional methods also have problems in equipment corrosion resistance, product yield, and sulfur compound removal rate, and are not fully satisfactory. In particular, it is difficult to almost completely remove the sulfur compounds contained in 95% naphthalene, and it also requires multiple steps and the installation of complex equipment, which has the disadvantage of being expensive without large-scale production. <Problems to be Solved> The present invention eliminates the drawbacks of the impurity removal method by adding anhydrous aluminum chloride, and provides a method for economically producing purified naphthalene with a high desulfurization rate and high purity. <Details of the invention> As a result of various studies and examinations of the reasons why the desulfurization rate does not improve in the naphthalene purification method by adding anhydrous aluminum chloride, the present inventors found that a part of the benzothiophene contained in 95% naphthalene is hydrogenated. The boiling point of this dihydrobenzothiophene (220-222°C) is close to the boiling point of naphthalene (218°C), so it cannot be separated by distillation, leading to a decrease in the desulfurization rate. In addition, it was determined that naphthalene was partially hydrogenated and converted to tetralin, which remained in naphthalene during distillation and caused a decrease in purity.Due to anhydrous aluminum chloride treatment, a portion of naphthalene was converted to tetralin. It has been found that the conversion to
1979-pages 1210 to 1215) is a previously unknown fact that is produced by desulfurization reactions with fundamentally different reaction systems. Furthermore, it is a completely unknown fact that benzothiophene is partially converted to dihydrobenzothiophene by anhydrous aluminum chloride treatment. Therefore, as a result of further intensive research into the removal of dihydrobenzothiophene, we found that naphthalene and dihydrobenzothiophene cannot be separated by normal pressure distillation, which is carried out in ordinary naphthalene refining, because there is almost no difference in boiling point. They discovered that they can be separated by twisting, and arrived at this invention. That is, this invention is a naphthalene desulfurization method in which naphthalene containing benzothiophene as an impurity is treated with anhydrous aluminum chloride, then anhydrous aluminum chloride is extracted using an aqueous hydrochloric acid solution, and then distilled. This is a method for producing purified naphthalene, which is characterized by recovering the naphthalene as a fraction and separating dihydrobenzothiophene as a residue. Although it has not been quantitatively clarified how the specific volatility of naphthalene and dihydrobenzothiophene changes with distillation pressure (therefore, distillation temperature), naphthalene and dihydrobenzothiophene are used industrially. The conditions for separation are a distillation pressure of 500
mmHg or less, using a distillation column with 20 or more theoretical plates,
A rough guideline is a reflux ratio of 1 or more. Note that this condition is a value experimentally determined by the inventors. Treat naphthalene with anhydrous aluminum chloride,
If aluminum chloride is extracted with hydrochloric acid or the like and then distilled under the above conditions, it will contain almost no sulfur (0.01
% or less) purified naphthalene is obtained. However, this purified naphthalene contains approximately 0.2 to 0.5 tetralin.
If it is necessary to obtain purified naphthalene with a purity of 99.8% or higher, tetralin is separated by distillation under normal pressure or reduced pressure, and then dihydrobenzothiophene is separated. The reason why benzothiophene and naphthalene are hydrogenated by anhydrous aluminum chloride treatment is not clear, but it is thought that hydrogen generated when naphthalene is partially polymerized with anhydrous aluminum chloride is the cause. The amount of anhydrous aluminum chloride added is 0.01 to 5.0 times, preferably 0.25 to 2.0 times, in molar ratio to the total sulfur content in naphthalene. Reaction temperature is 50-120
℃ is appropriate; if the reaction temperature is low, it will take time to dissolve anhydrous aluminum chloride, and if the reaction temperature is high, polymerization or lightening will occur due to side reactions. A sufficient reaction time is about 15 minutes after dissolving the anhydrous aluminum chloride. Even including the dissolution time, 60 minutes is sufficient. Anhydrous aluminum chloride may be removed by a known method using water or an aqueous solution such as hydrochloric acid and sulfuric acid. <Example> 2109 g of 95% naphthalene (purity 96.4%) containing 2.4% benzothiophene (total sulfur approximately 0.57%) was
The mixture was heated to .degree. C., 51.3 g of anhydrous aluminum chloride was added, and the mixture was treated for 2 hours with stirring. and concentration 5
After extracting and separating aluminum chloride by adding 210 g of 10% hydrochloric acid, the mixture was further washed with 105 g of 10% sodium hydroxide to recover 2100 g of an oil layer. This oil was divided into three parts, and 700 g of it was distilled at atmospheric pressure at a reflux ratio of 5 using a distillation column with 50 theoretical plates and a diameter of 15 mm.
27.7g as pre-distillate, as naphthalene fraction
633.7g was collected (conventional method). In addition, 700g of the remaining 1400g was distilled under reduced pressure (200mmHg) at a reflux ratio of 5 using the same distillation column, resulting in 26.4g as a pre-distillate and 637.2g as a naphthalene fraction.
g (Example 1). Using the same distillation column, the last 700 g was distilled at normal pressure with a reflux ratio of 50 for the pre-distillate, and under reduced pressure (200 mmHg) with a reflux ratio of 5 for the naphthalene fraction, resulting in 27.7 g as the pre-distillate and 27.7 g as the naphthalene fraction. 638.6g was obtained (Example 2). The composition of each fraction obtained was measured by gas chromatography. The results are shown in Table 1. The total sulfur in each fraction was measured by combustion-coulometric titration using a trace sulfur analyzer manufactured by Mitsubishi Chemical Industries, Ltd.

[Table] As shown in Table 1, purified naphthalene with extremely low sulfur content can be obtained by treating it with anhydrous aluminum chloride and then distilling it under reduced pressure. Furthermore, by removing tetralin in the pre-distillate, it is possible to obtain purified naphthalene with a purity of 99.9%. Purified naphthalene of high purity was obtained.

Claims (1)

[Scope of Claims] 1. A naphthalene desulfurization method in which naphthalene containing benzothiophene as an impurity is treated with anhydrous aluminum chloride, and then the anhydrous aluminum chloride is extracted using an aqueous hydrochloric acid solution and then distilled,
A method for producing purified naphthalene, which comprises performing distillation under reduced pressure, recovering naphthalene as a fraction, and separating dihydrobenzothiophene as a residue. 2. The method for producing purified naphthalene according to claim 1, wherein the vacuum distillation is carried out using a distillation column having 20 or more theoretical plates, a reflux ratio of 1 or more, and a pressure of 500 mmHg or less. 3. The method for producing purified naphthalene according to claims 1 and 2, characterized in that tetralin is distilled off as a pre-distillate under normal pressure to reduced pressure and then distilled under reduced pressure.