JPH0553790B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION This invention relates to a method for recovering high yield and high purity quinoline from a coal tar fraction. Prior art In addition to quinoline, the quinoline-containing fraction obtained by distilling coal tar contains aromatic hydrocarbons such as methylnaphthalene and biphenyl, and nitrogen-containing heterocyclic compounds such as isoquinoline and indole, which have very similar boiling points. There are many organic compounds that have Therefore, even if this quinoline-containing fraction is subjected to precision distillation, methylnaphthalene and isoquinoline will be distilled out together with quinoline, making it impossible to recover quinoline with high purity. For this reason, conventionally, the middle oil fraction obtained by distilling coal tar was treated with sulfuric acid to extract quinoline as quinoline sulfate, washed with light oil to remove neutral components such as naphthalene, and then neutralized with ammonia. Crude quinoline is obtained by decomposition, which is then dehydrated and distilled to obtain quinoline. Alternatively, the coal tar distillate fraction is extracted with a buffered aqueous salt solution with a pH of about 0.5 to 3.0 to obtain an aqueous extract containing quinoline, isoquinoline, or both, which is neutralized with sodium hydroxide or ammonia. The tar base is converted back to its base form, and quinoline and isoquinolite are separated by distillation. (Japanese Patent Application Laid-Open No. 58-26825) However, the method of extracting quinoline with acid such as sulfuric acid or a buffered salt aqueous solution with a pH of approximately 0.5 to 3.0 not only requires a complicated process, but also involves the extraction of tar bases such as isoquinoline and indole other than quinoline. are also extracted together, so it is necessary to perform a very strict fractional distillation in the final distillation step. In addition, waste liquid such as acid and ammonia is generated, and waste liquid treatment is required. Problems to be Solved by the Invention The present invention provides a method for recovering quinoline from coal tar with high yield and high purity without requiring complicated steps. Means for Solving the Problems The method for recovering quinoline of the present invention involves adding diethylene glycol to a quinoline-containing fraction obtained by distilling coal tar and subjecting it to distillation to collect methylnaphthalenes at a temperature lower than the quinoline distillation temperature. Step 1 of distilling off by azeotroping with diethylene glycol to obtain a bottom oil in which the ratio of methylnaphthalenes to quinoline is 0.2 or less by weight; Step 2 of separating diethylene glycol from the bottom oil obtained in Step 1; and Step 3 of performing precision distillation of the column bottom oil obtained in Step 3 to recover quinoline as an overhead distillate. Step 4 may be performed in which the overhead distillate obtained in Step 3 is subjected to precision distillation again. Function/Effect According to the present invention, first, in step 1, diethylene glycol is added as an entrainer to a quinoline-containing fraction obtained by distilling coal tar, and then distilled. As a result, methylnaphthalenes, which have a boiling point close to that of quinoline, are distilled out from the top of the column as an azeotrope with diethylene glycol in a temperature range lower than the temperature at which quinoline is distilled off. This distillation is carried out under conditions such that a bottom oil having a weight ratio of methylnaphthalenes to quinoline of 0.2 or less is obtained. This bottom oil may continue to contain aromatic oils other than methylnaphthalene. In step 2, excess diethylene glycol added as an entrainer is separated from the bottom oil from which most of the methylnaphthalenes have been removed. This separation may be carried out by conventional means well known to those skilled in the art. For example, diethylene glycol can be extracted by adding a liquid (e.g., water) that dissolves diethylene glycol but does not easily dissolve quinoline.
Diethylene glycol can be almost completely separated and removed from the bottom oil. The bottom oil from which diethylene glycol has been separated is
In step 3, precision distillation is performed. Even if the column bottom oil still contains aromatic oils other than methylnaphthalene, high-purity quinoline can be recovered in high yield as a top oil product by precision distillation. Separate the quinoline concentrated fraction with
By further subjecting this fraction to precision distillation in step 4, even higher purity quinoline can be recovered. Distillation in this invention is carried out using a conventional distillation column at normal pressure or reduced pressure. In addition, the amount of diethylene glycol added to the quinoline-containing fraction from coal tar is 0.2~
5 times the weight is appropriate. Next, details of the present invention will be explained based on the drawings. FIG. 1 shows one embodiment of the present invention, in which diethylene glycol (L) is added to a quinoline-containing fraction (K) of a feedstock oil in a pipe 1 via a pipe 2, and a pipe to be described later. The diethylene glycol circulating from 13 is combined and introduced into the first distillation column 3 for distillation. Methylnaphthalene and diethylene glycol are
Since the distillate is azeotropically distilled from the top of the tower through pipe 4 at a temperature of 230°C or lower, reflux is applied from pipe 6 at a reflux ratio of 2 to 15. The azeotrope of methylnaphthalene and diethylene glycol distilled from pipe 4 through pipe 7 is
The mixture is introduced into a separation tank 8 and left to stand at room temperature to separate into methylnaphthalene and diethylene glycol, and the methylnaphthalene fraction is recovered from pipe 9. Diethylene glycol is circulated from the separation tank 8 to the pipe 1 via the pipe 10. The bottom oil of the first distillation column 3 contains almost no methylnaphthalene, so it contains quinoline and other substances.
It is a mixture with a boiling point of 65 or higher at 230℃. This tower bottom oil is introduced into a solvent recovery tank 11 through a pipe 5, and diethylene glycol is recovered by an appropriate method and recycled through a pipe 13 and a pipe 10 for reuse. The recovery of this diethylene glycol is
This can be carried out by a solvent extraction method using water as an extraction solvent according to a conventional method. For example, the amount of diethylene glycol contained in the bottom oil is 0.5 times or more by weight,
Preferably, 1 to 2 times the amount of water is used to separate the upper layer, an oil layer containing quinoline, and the lower layer, an aqueous layer containing diethylene glycol.
Diethylene glycol can be separated. The bottom oil separated from the solvent is charged to a second distillation column 14 via a line 12. From the top of the second distillation column 14, 240
It is distilled off through a pipe 15 at a temperature below 0.degree. C., and a fraction containing quinoline as a main component is distilled off through a pipe 17 while being refluxed at a reflux ratio of 5 to 15. In this second distillation, if the distillation temperature range is narrowed, highly pure quinoline can be obtained, but the quinoline remains in the bottom of the pot extracted from the pipe 16, resulting in a low yield. In addition, by widening the distillation temperature range,
If the quinoline fraction obtained at 245°C or lower is subjected to precision distillation again (not shown), even higher purity quinoline can be obtained at a higher yield.
Stepwise distillation is preferred. In addition, although the case of atmospheric pressure distillation was described above, it is also possible to perform vacuum distillation if necessary. Example 1 300 g of diethylene glycol was added to 600 g of a quinoline-containing fraction with the composition shown in Table 1 obtained by distilling coal tar, and the first distillation was carried out at a reflux ratio of 2 until the top temperature reached 230°C. , diethylene glycol and methylnaphthalene azeotrope 606.8g
I got it. The results are shown in Table 2.

【table】

[Table] As shown in Table 2, 97.8% of the methylnaphthalene in the raw material was
On the other hand, quinoline lost only 5.0%. Distillation was carried out under normal pressure using a precision distillation device packed in a heliback with approximately 50 theoretical plates. Undistilled diethylene glycol was removed from 293.2 g of bottom oil from this distillation column to obtain 235.9 g of bottom oil having the composition shown in Table 3. This column bottom oil was subjected to a second distillation using a helipack packed distillation apparatus with approximately 20 theoretical plates at a reflux ratio of 15, and the boiling point range
33.6g of fraction at 238-240°C was collected. The quinoline content in this fraction is 95.0% as shown in Table 3.
The recovery rate of quinoline from raw materials was 66.3%.

[Table] Example 2 In the second distillation operation in Example 1, the boiling point range
61.3 g of a fraction between 237 and 245°C was collected. The quinoline content in this fraction is 70.96 as shown in Table 4.
It was %. This was subjected to a third distillation at a reflux ratio of 15 using a helipack-packed precision distillation apparatus with approximately 45 theoretical plates to obtain 42.5 g of a fraction with a boiling point range of 238 to 240°C. The quinoline content in this fraction was 99.0% as shown in Table 4, and the quinoline recovery rate was 88.6%.

[Table] Comparative Example 1 500 g of the quinoline-containing fraction shown in Table 1 used in the Examples was distilled under normal pressure at a reflux ratio of 15 using a helipack packed precision distillation apparatus with approximately 50 theoretical plates. 30.5 g of a fraction with a boiling point range of 236-240°C was obtained. The quinoline content in this fraction was 49.47% as shown in Table 5, and the quinoline recovery rate was 36.8%.

[Table] Comparative Example 2 150 g of diethylene glycol was added to 600 g of the quinoline-containing fraction shown in Table 1 used in the example, and refluxed under normal pressure using a helipack packed precision distillation apparatus with approximately 50 theoretical plates. The first distillation was carried out at a ratio of 2 to 226° C., yielding 486.2 g of an azeotrope of diethylene glycol and methylnaphthalene. Undistilled diethylene glycol was removed from 263.8 g of bottom oil from this distillation apparatus to obtain 252.7 g of bottom oil having the composition shown in Table 6.

[Table] This column bottom oil was subjected to a second distillation under normal pressure at a reflux ratio of 15 using a helipack-packed precision distillation apparatus with approximately 20 theoretical plates.
63.39g was recovered. The quinoline content in this fraction was 68.40% as shown in Table 7. It was distilled into a third distillate at a reflux ratio of 15 under normal pressure using a helipack packed precision distillation apparatus with approximately 45 theoretical plates. Distilled and obtained 36.87g of distillate with a boiling point range of 238-240℃6
I got it. The quinoline content in this fraction is 98.00% as shown in Table 7, and the quinoline recovery rate is 75%.
It was hot.

[Table] Comparative Example 3 This example shows an example in which quinoline is recovered by the same process as in Example 2 using monoethylene glycol as an entrainer. Monoethylene glycol
Add 700g and use a helipack packed precision distillation device with approximately 50 theoretical plates to distill the mixture under normal pressure at a reflux ratio of 2.
The first distillation is carried out until the temperature reaches 192℃, and the azeotrope of methylnaphthalene of monoethylene glycol is extracted.
1032.8g was obtained. The results are shown in Table 8. Up to 97.6% of the methylnaphthalenes contained in the raw material were distilled out in the distillation up to the boiling point range of 192°C, while 8.0% of quinoline was lost. Undistilled monoethylene glycol was removed from 267.2 g of bottom oil from this distillation apparatus to obtain 207.3 g of bottom oil having the composition shown in Table 9. The ratio of methylnaphthalenes contained in this bottom oil to quinoline was 0.2 or less by weight.

【table】

[Table] This column bottom oil was subjected to a second distillation under normal pressure using a helipack-packed precision distillation apparatus with approximately 20 theoretical plates at a reflux ratio of 15, and a fraction with a boiling point range of 237 to 245°C was distilled.
63.41g was recovered. The quinoline content in this fraction was 68.51% as shown in Table 10. This was subjected to a third distillation at a reflux ratio of 15 under normal pressure using a helipack-packed precision distillation apparatus with about 50 theoretical plates, and 39.26 g of a fraction with a boiling point range of 238 to 240°C was recovered. The purity of quinoline in the fraction thus obtained was 10
As shown in the table, the quinoline recovery rate is 98.78% and 80.5
It was %.

[Table] As can be seen from the above results, when quinoline is recovered by the same process as the present invention using monoethylene glycol as an entrainer, methyl The amount of entrainer consumed for azeotroping naphthalene was about 2.5 times higher, and the purity and recovery rate of the recovered quinoline was low.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet showing one embodiment of the present invention. 1, 2, 4, 5, 6, 7, 9, 10, 12, 1
3, 15, 16, 17... Pipe line, 3... First distillation column, 8... Separation tank, 11... Solvent recovery tank, 14
...Second distillation column.

Claims (1)

[Claims] 1. Diethylene glycol is added to a quinoline-containing fraction obtained by distilling coal tar, and methylnaphthalenes are azeotropically distilled off with diethylene glycol at a temperature lower than the quinoline distillation temperature, Step 1 of obtaining a bottom oil with a weight ratio of methylnaphthalenes to quinoline of 0.2 or less; Step 2 of separating diethylene glycol from the bottom oil obtained in Step 1; and Step 2 of not containing diethylene glycol obtained in Step 2. A method for recovering quinoline, comprising step 3 of performing precision distillation of column bottom oil and recovering quinoline as a column top distillate. 2. The method for recovering quinoline according to claim 1, further comprising a step 4 of subjecting the column top product obtained in step 3 to precision distillation again.