DD257257A1 - PROCESS FOR CLEANING PYRIDINE - Google Patents

Abstract

The invention relates to a process for purifying pyridine for use in UV spectroscopy, which was obtained from smelt or coal tar. The pyridine produced in the usual way is purified by reciprocal acetylacetate distillation with acetic acid and water, dried and distilled.

Description

Characteristic of the known technical solutions

Pyridine, which was obtained from dry distillates of coal, contains a variety of trace impurities, which among other things, the use as a solvent for UV spectroscopy without additional expensive purification operations do not allow.

Thus, in Organikum (Berlin 1986, 16 th edition) it is recommended to purify the pyridine by successive drying with potassium hydroxide, distillation, treatment with phosphoric acid and repeated distillation. This method is characterized by protracted operation, in part with dangerous chemicals.

It is further known that by simple high-efficiency operations pyridine can be purified by salt formation with perchloric acid.

{Chem. Reports, 59, 1926, p. 448)

Due to their explosiveness, however, the resulting intermediates can only be handled with great dangers

Fabrics dar.

Also known is a multi-stage process, which is characterized essentially by a Selendioxidbehandlung. (Angew.

Chemistry, 68, 1956, p. 61)

In addition to a complicated technology, this method has the disadvantage of low yield and the risky work with highly toxic selenium compounds.

Object of the invention

The object of the invention is to separate organic compounds contained in pyridine as impurities by simple operations.

Explanation of the essence of the invention

It is an object of the present invention to remove predominantly sulfur-containing compounds contained in the carbonaceous pyridine and to deteriorate the permeability of pyridine to ultraviolet light by thermal separation processes.

According to the invention, by using the maximum azeotrope, pyridine / organic carboxylic acids are more readily volatilized.

Sulfur contaminants and by using the minimum azeotrope pyridine / water low volatilities impurities removed.

Subsequently, the product is dried in a known manner and the pyridine is finally distilled.

In this case, pyridine separated off in the customary manner from sulfur or tar products is mixed with the amount of concentrated acetic acid corresponding to the azeotrope composition and rectified. In the first fraction, a pyridine containing the majority of the impurities is obtained, which can be used to recover sulfur-containing components.

The second fraction contains only small amounts of impurities. It can be added back to the pyridine in the next batch.

It is now added so much water that the pyridine / acetic acid azeotrope is destroyed.

In the further distillation, a mixture of pure pyridine and water passes over according to the azeotrope composition. This azeotropic mixture is dried. The dried pyridine is finally rectified to give a pyridine distillate that meets the purity requirements for UV content and permeability.

embodiment

The invention will be explained in more detail in the following exemplary embodiments. '

Example 1:

900 ml of pyridine are mixed with 930 ml of glacial acetic acid in a distillation flask with attached packed column (1 m length, 28 mm diameter, 4 mm stainless steel coil) and steam divider and rectified at a reflux ratio of 1:10 and a reflux rate of 400 ml / h.

The pyridine used had the following quality parameters:

Water content: 0.10% sulfur content: 501 ppm UV spectrum, 1 cm layer thickness wavelength permeability nm , % - 305 0 310 27 330 50 340 95

The first 200 ml distillate (head temp 373-41 OK) was taken for work-up to obtain by-products.

The second 200 ml distillate (head temp 410K) was added to a subsequent batch.

After adding 1200 ml of water to the bottom, the water / pyridine azeotrope (725 ml), which was now passing at 367 K, was collected for further processing.

The following fraction 368-373K (200ml) contains essentially water and may be added in place of water in the next batch.

The then transferred fractions of 373-390.5 K (400 ml) should be discarded.

The 390.5-41OK boiling fractions (275ml) contain predominantly acetic acid and some pyridine. They are used in a new approach instead of acetic acid.

By renewed addition of water to the bottom of this distillation batch 360 ml of pyridine / water azeotrope are recovered.

The combined pyridine / water azeotropes (1 085ml) are added in a second equippable distillation equipment with 100ml of benzene and the water is discharged by distillation, wherein the separating out of the distillate benzene is added to the reflux. After no more water separated at the top of the column, the added benzene was distilled off and then the pyridine fractionated. In the boiling range 387-388K 600ml quality pyridine went over.

The distillate had the following characteristics:

Water content: 549 ppm sulfur content: 28 ppm Benz content: 1.0 ppm UV spectrum, 1 cm layer thickness Wavelength (nm) Permeability (%) 305 20 310 72 330 96 340, 99

This corresponds to the requirements for a pyridine for UV spectroscopy.

Example 2

Under the conditions mentioned in Example 1, a pyridine, pure, was used with the following analytical parameters.

Water content: 0.23% sulfur content: 1 500 ppm UV spectrum 1 cm layer thickness wavelength permeability nm % 305 1 310 3 330 13

340 45

The resulting UV-pure product has the following characteristics:

Water content: 370 ppm sulfur content: 10ppm UV spectrum 1 cm layer thickness wavelength permeability nm % 305 20 310 72 330 97 340 99

Claims (1)

Process for the purification of pyridine, characterized in that pyridine obtained from sulfur or coal tar is converted to a maximum azeotrope by addition of carboxylic acids, in particular acetic acid, the readily volatile impurities are removed by rectification, the carboxylic acid / pyridine azeotrope by addition of water in a Pyridine / water azeotrope is converted and distilled, the resulting pyridine / water mixture is dried, in particular by azeotropic distillation and finally rectified. Field of application of the invention The invention relates to a process for the purification of pyridine derived from carbonaceous and coking products used as a solvent for ultraviolet spectroscopic studies.