CS205775B1 - Method of purifiing the refuse waters containing the phenols - Google Patents

Description

Process for purification of waste waters containing phenols

BACKGROUND OF THE INVENTION The present invention relates to a process for the purification of phenolic-containing effluents and the recovery of phenols from industrial effluents by extraction with 2-methylpentanone-4, or mixtures thereof with n-butyl acetate, using a vibration motion.

Liquid extraction is often used to obtain monohydric and dibasic phenols from the wastewater of the fuel, metallurgical and chemical industries. Extraction waters are then further purified to achieve the desired degree of purity before being discharged into public watercourses. Either aromatic hydrocarbons, in particular benzene or n-butyl acetate, are commonly used for extraction. The waste water is brought into countercurrent contact with the solvent either in a cascade of mixers and settlers, in sieve tray columns or with rotating stirrers or discs.

A disadvantage of aromatic hydrocarbons is that their extraction capacity is relatively low and therefore solvent consumption is high. Therefore, the dimensions of the extractor and the consumption of substances and energy for solvent recovery are also large. The disadvantage of n-butyl acetate is, in particular, that it decomposes partially in contact with phenolic waters, especially at elevated temperatures during the distillation of the solvent, and thus losses occur.

The disadvantage of contacting the phenolic waters with the solvents in the sieve tray columns is that this type of contact is poorly effective, the contact area per unit volume of the device is small. This deficiency is countered by the dispersion of phases by rotary agitators in the cascades of the mixers and settlers and in the mixed columns. However, the disadvantage of rotary dispersion is that drops of very uneven size are formed. In particular, a significant proportion of fine drops is produced,

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Recently, it has been proposed to use 2-methylpentanone-4 (methylisobutylketone, MIBK), which has a more favorable phenol solubility than n-butyl acetate and which does not undergo mechanical decomposition in contact with phenol waters. However, since this solvent has a considerable ability to dissolve tarry substances, the difficulty in using a rotary motion to contact the solvent with phenolic water increases.

Surprisingly, the drawbacks of the prior art have been remedied by the method of the present invention and the apparatus. SUMMARY OF THE INVENTION The present invention provides a process for recovering phenols from wastewater by intensive countercurrent contact with 2-methylpenitanone-4 (MIBK) or a mixture thereof with n-butyl acetate containing at least 50 wt% MIBK by means of a vibration motion the solvent breaks down into drops while the phenolic water remains continuous. The ratio of solvent flow rate to phenolic water is 1: 8 to 1:16. The amplitude of the vibration motion is 0.15 to 0.35 cm, the frequency is 1.0 to 5 Hz.

The process of the invention at the same time removes two major drawbacks of the prior art: Loss of solvent by decomposition in contact with phenolic water and formation of emulsions preventing high volume performance and at the same time high extraction efficiency. The use of a vibration motion to disperse the solvent of the droplet makes it possible to evenly distribute the energy supplied to the liquid over the entire volume of the extractor. At the same time, by controlling the amplitude and frequency of the vibration movement, the droplet size can be reliably controlled. The resulting dispersion therefore has a suitable mean droplet size for maximum extraction efficiency and a narrow droplet size distribution around this mean size, so that neither emulsions nor coarse fractions are formed. This also ensures a high volume output of the extractor. The vibrational movement also minimally disrupts the countercurrent phase flow, which again contributes to high extraction efficiency. The use of a mixture of MIBK and n-butyl acetate eliminates the disadvantageous properties of each of the two solvents used alone. By diluting the n-butyl acetate with MIBK, its decomposition in contact with phenolic water and thus the chemical losses of the solvent are largely suppressed. Conversely, the presence of n-butyl acetate in MIBK reduces the solubility of tarry substances and thus the tendency to form emulsions. This also reduces the neutral oil content of the crude phenolic mixture obtained after distilling off the solvent, thereby facilitating the further purification process of the obtained phenols.

In the past, vibration movement has been applied in several types of devices for countercurrently intermittently soluble liquids (USP 2,011,186; DP 1 066 543; CSP 139 895;

CSP 132 022). Vibration extractors according to CS 139395 and CS 132 022 have proved to be the most suitable for carrying out the phenol extraction process according to the invention. The following examples show the results of the extraction according to the invention obtained on a pilot plant according to CS 132 132.

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Example 1

Phenol water from a brown coal gas pressurized gas plant containing 5600 mg / l of monobasic phenols was countercurrently contacted with a solvent containing 85 wt% MIBK, 11 wt% n-butyl acetate and 0.05 wt% monobasic phenols in a vibration extraction vial. floors with an inner diameter of 15 cm and a height of the active part of 4 m. The ratio of the volumetric flow rates of solvent and phenol water was 1:10. In the column were placed 38 perforated trays, which performed a vibration movement with an amplitude of 0.25 cm and a frequency of 4.5 Hz. On each floor there were 246 circular openings 0 0.3 cm for dispersing the solvent and 3 circular openings with a diameter of 3.3 cm for the passage of phenolic water. The specific volumetric flow rate of phenol water was 60 m / m h, the concentration of monohydric phenols in the phenolized water was 35 mg / l.

- Example 2

Phenolic water from a coal-fired coking plant containing 1371 mg / l of monobasic phenols was countercurrently contacted with a solvent containing 77 wt% MIBK, 21 wt% n-butyl acetate and 0.3 g / l of monobasic phenols. using the same equipment as in Example 1. The ratio of the volumetric flow rates of solvent and phenol water was 1:12. The vibration amplitude was 0.25 cm, frequency 1.42 Hz. The specific volumetric flow rate of phenol water was 60 ra / m h, the concentration of monohydric phenols in the de-phenolized water was 22 mg / l.

Claims (1)

SUBJECT OF THE INVENTION A process for the purification of phenol-containing waste water, wherein the phenol-containing water is brought into intensive countercurrent contact with a solvent of 2-methylpentanonero-4, optionally containing up to 50% by weight of n-butyl acetate, at a solvent to phenol water ratio of 1: 8 to 1:16 characterized in that the two phases are brought into contact with each other by means of a vibrational movement with an amplitude of 0.15 to 0.35 cm and a frequency of 1.0 to 5.0 Hz.