CS266960B1 - Method of treatment of waste hydrochloric acid - Google Patents

Abstract

Waste hydrochloric acid is pre-neutralized with calcium and/or magnesium carbonate and then neutralized with calcium hydroxide in the presence of a polyelectrolyte. The precipitated impurities are separated by sedimentation.

Description

The invention relates to the neutralization of waste hydrochloric acid produced during production

2-methyl-4-chlorophenoxyacetic acid:

2-Methyl-4-chlorophenoxyacetic acid is most often prepared by chlorination of 2-methylphenoxyacetic acid with chlorine gas or sodium hypochlorite. Chlorination with sodium hypochlorite in the presence of mineral acid and recovery of 2-methyl-4-chlorophenoxyacetic acid is described in AO 179 200. Mineral acid, most often hydrochloric acid, which is contaminated with phenoxyacetic acids such as 2-methylphenoxyacetic acid, 2-methyl- 4-chlorophenoxyacetic acid, 2-methyl-6-chlorophenoxyacetic acid, 2-methyl-4,6-dichlorophenoxyacetic acid, mineral salts, in particular sodium chloride, 2-methylphenol chloride derivatives. The pH of the waste acid is 0 to 2, because the precipitated 2-methyl-4-chlorophenoxyacetic acid is easily filterable therefrom.

There are problems in the use and processing of waste acid, due to the fact that it is almost saturated with inorganic salts and has a low concentration of mineral acids. It cannot be discharged as sewage, as water authorities only agree to discharge after neutralization to pH 6 to 8. The simplest neutralization is with lyes, especially NaOH or Ca (OH) _{2 <} A certain disadvantage here is a sharp change in the pH value in the vicinity equivalent point at pH 7, which can cause difficulties on an industrial scale.

The above drawbacks are alleviated by the method of treating waste hydrochloric acid from the production of 2-methyl-4-chlorophenoxyacetic acid, which consists in pre-neutralizing the waste hydrochloric acid with calcium and / or magnesium carbonate to a pH of 2 to 6.5 and done with calcium hydroxide in the presence of a polyelectrolyte. The polyelectrolyte is added to better coagulate the precipitated parts and accelerate their sedimentation.

An advantage of the process according to the invention is that relatively fasting raw materials, which are commonly found in nature, such as limestone or dolomite, are used for the pre-neutralization of hydrochloric acid. The advantage of these substances is that they are practically insoluble in water and that it is not possible to pass into the alkaline pH range with an excess of limestone or dolomite. Donated neutralization with calcium hydroxide is done if the resulting pH value is required to be close to 7 or above 7. The pH value after done-neutralization is determined by the relevant water authorities when discharged into watercourses. Sometimes the pH value after donation is determined by the extent to which contaminants, for example Fe, Mg, Zn cations and the like, are to be removed from the waste hydrochloric acid. Advantageously, the pre-neutralization of the waste hydrochloric acid can be done in the 2-methyl-4-chlorophenoxyacetic acid production and the neutralization can be done at the central neutralization station in the plant, after mixing the pre-neutralized waste hydrochloric acid with other effluents from other plants. Pre-neutralized hydrochloric acid is less corrosive and therefore the material from which the pipe is made is less demanding.

Example 1

Waste hydrochloric acid from the production of 2-methyl-4-chlorophenoxyacetic acid according to MS. AO 179 200 has the following composition:

hydrogen chloride 1.8% by weight

phenoxyacetic acid 4.1 g / l

Cl chlorine derivatives of 2-methylphenol

92.8 g / l

0.16 g / l

000 ml of waste hydrochloric acid were neutralized with limestone to pH 3.1. After separating the limestone, 0.2 ml of a 0.1% by weight aqueous polyelectrolyte gel (Magnaflor) was added to the reaction mixture. Then, with a 5.5% by weight suspension of Ca (OH) _{2, the} reaction mixture was neutralized to pH 7.2. The precipitated impurities were separated by sedimentation.

CS 266 960 Bl

Example 2

The procedure of Example 1 was followed, except that the waste hydrochloric acid was pre-neutralized to pH 4.3. Then, the reaction solution was mixed with the wastewater from the production CHZJD, so that the resulting solution was chemically contaminated water, which is currently formed in the CHZJD and which had the following composition:

pH value with ² " 2.9 1 600 mg / 1 Cl 1 025 mg / 1 ChSK (2 hours) Zn ²⁺ 865 12 mg O ₂ / l mg / 1 Al ³⁺ 15 mg / 1 Fe ³⁺ 9 mg / 1 Mg ²⁺ 48 mg / 1 To one liter of reaction 0 was added to the mixture

, 2 ml of 0.1% by weight of an aqueous polyelectrolyte gel (Magnoflor) and then 5.5% by weight of a suspension of Ca (OH) _? . The pH after neutralization 2 + 3+ 3+ 2+ cii was 7.6. The precipitated impurities, especially the hydrated oxides of Zn, Fe, Al, Mg, were separated by sedimentation.

Example 3

The procedure of Example 1 was followed, except that the waste hydrochloric acid was pre-neutralized with micronized magnesite to pH 6.4. The pH after doneutralization was 7.4. Precipitated impurities were removed by sedimentation.

The invention finds application in the neutralization of waste hydrochloric acid formed in the production of 2-methyl-4-chlorophenoxyacetic acid. Preferably, the waste hydrochloric acid can be pre-neutralized in the production of 2-methyl-4-chlorophenoxyacetic acid and the neutralization can be done at a central acid waste water neutralization station.

Claims (1)

OBJECT OF THE INVENTION Process for the treatment of waste hydrochloric acid from the production of 2-methyl-4-chlorophenoxyacetic acid contaminated with 2-methylphenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, 2-methyl-4,6-dichlorophenoxyacetic acid, 2-methylphenol, sodium chloride, alkali neutralization, consisting of pre-neutralization of the waste hydrochloric acid to a pH of 2 to 6.5 with calcium and / or magnesium carbonate, characterized in that the reaction mixture thus treated is neutralized with calcium hydroxide in the presence of a polyelectrolyte and the precipitated impurities are separated by sedimentation.