CS244317B1 - Process for treating waste hydrochloric acid from the production of 2-methyl-4-chloro-phenoxyacetic acid - Google Patents

Abstract

Process for the treatment of waste hydrochloric acid from the production of 2-methyl-4-chlorophenoxyacetic acid, which is characterized in that the waste hydrochloric acid is pre-neutralized to a pH of 2 to 5, and compounds which form near the value of pH 7 buffer. The process can be used to neutralize the effluent from the production of 2-methyl-4-chlorophenoxyacetic acid, which is used as a herbicide, before it is discharged to the sewer.

Description

3 4 244317

BACKGROUND OF THE INVENTION The present invention relates to the neutralization of waste hydrochloric acid resulting from the production of 2-methyl-4-chlorophenoxyacetic acid. Often, 2-methyl-4-chlorophenoxyacetic acid prepares chlorination of 2-methyl-phenoxyacetic acid with chlorine gas or sodium hypochlorite. Chlorination with sodium hypochlorite in the presence of mineral acid to obtain 2-methyl-4-chlorophenoxyacetic acid from the reaction mixture by precipitating it in excess mineral acid of the description is AO no. an acid, most commonly 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, especially sodium chloride, chloro derivatives of 2-methylphenol. The pH of the waste acid is 0 to 2, with the result that the precipitated 2-methyl-4-chlorophenoxyacetic acid is easily filterable.

In the use and treatment of waste acid problems, since it is so saturated with inorganic salts and low mineral acid concentrations. As waste cannot be discharged into the sewage system, since the water management authorities only agree to discharge after neutralization of pH 6 to 8. The simplest neutralization is with lye, especially NaOH or Ca (OH) 2, which is described in Ing. Truchlík, CSc. Improve MCPA, No. P-61-21, VÚAgTBratislava (3980). An undesirable disadvantage is the slight change in pH close to an equivalence point at pH 7, which can induce difficulties in industrial scale.

The aforementioned drawbacks are alleviated by the treatment of the hydrochloric acid waste from the production of 2-methyl-4-chlorophenoxyacetic acid, characterized in that the hydrochloric acid containing impurities such as phenoxyacetic acids is predominantly 2-methylphenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, 2-methyl-4,6-dichlorophenoxyacetic acid, mineral salts, especially sodium chloride, chloro derivatives of 2-methylphenol, pre-alkaline with calcium hydroxide or carbonate and / or magnesium hydroxide or magnesium carbonate at a concentration of 0.1 to 99.5 wt. The pH is 2 to 5.

With increasing pH, the reaction rate of neutralization with carbonate is reduced. The reaction mixture is then neutralized to a pH of 6 to 8 with aqueous sodium bicarbonate at a concentration of 0.1 to 30% by weight. or sodium hydroxide concentration of 0.1 to 45 wt. or a calcium hydroxide slurry containing 0.1 to 35 percent by weight calcium hydroxide.

To pre-neutralize the waste hydrochloric acid, the spent calcium carbonate resulting from the absorption of carbon dioxide from the off-gas after chlorination of the fumarate is used in a calcium hydroxide suspension. An advantage of the process according to the invention is that pre-neutralizing hydrochloric acid is used in the preparation of fastening chemicals such as lime or limestone, possibly dolomite. In the neutralization process, it is preferred that the reaction mixture is virtually impossible to get into the alkaline pH range when it contains excess Ca 2+ ions in the solution. Indication of the desired pH value is given by the white haze of the reaction mixture and is simple and easy to observe. In the pH range 6 to 8, the reaction medium under these conditions has the character of a buffer. Pre-neutralization can be obtained from the reaction mixture by phenoxyacetic acids which are used! e.g. as herbicides. If the calcium carbonates are present in the solution after partial neutralization, sodium carbonate may advantageously be used for the neutralization, if sodium or calcium hydroxide is used in the solution after partial neutralization of the magnesium salt. Pre-neutralization may be avoided by the absorption of CO 2 and Cl 2 after the chlorination of the furoal which is waste. Example 1 100 ml of waste hydrochloric acid by filtration of 2-methyl-4-chlorophenoxyacetic acid with a content of IlCl of 21.9 g / l, 108.5 g / l Cl and 3.9 g / l of phenoxyacetic acids0.19 g / l of chloro derivatives 2 -methylphenol was neutralized with limestone at a pH of 3.1. Excess limestone was filtered off and 10 ml of the mixture was neutralized with 1% (w / w) Na2CO3 solution. The dependence of the amount of solution added from the pH in Table 1 is:

Claims (2)

2443X7 Volume (ml) 1% (w / w) Na2CO3 pH value Note 0 3 4 5 6 7 89 10 11 3 4.5 6 turbidity 66 6.3 white turbidity 6.6 7.2 7.5 8 Example 2 Example 1 was followed with the difference that calcium hydroxide of about 5% (w / w) suspension and pH after pre-neutralization were 3.4 for pre-neutralization. To 100 mL of pre-neutralized acid, 30 mL of 1% (w / w) Na 2 CO 3 solution was added. The resulting pH was 6.0. EXAMPLE 3 The procedure of Example 1 was followed, with the difference that the pre-neutralization was 4.3 and the pH was pre-neutralized. The resulting mixture was neutralized with 4 ml of a 1% (w / w) NaOH solution to pH 6. Example 4 Example 1 was followed with the difference that magnesium carbonate was used for the pre-neutralization and the pH was 3.9. ml of Ca (OH) 2 suspension. The pH of the poneutralization was 6.2. EXAMPLE 5 Example 1 was followed with the difference that dolomite was used for the pre-neutralization and the pH after pre-neutralization was 4.4 and the mixture was neutralized with the object 1. Preparation of the waste hydrochloric acid 2). methyl 4-chlorophenoxyacetic acid contaminated with phenoxyacetic acids such as 2-methylphenoxyacetic acid, 2-methyl-4-chlorophenoxyacetic acid, 2-methyl-4,6-dichlorophenoxyacetic acid, 2-methyl-6-chlorophenoxyacetic acid, chloro derivatives 2-methylphenol, sodium chloride, neutralizing with alkali, characterized in that the waste hydrochloric acid is pre-neutralized to a pH of 2 to 5 with calcium carbonate or calcium hydroxide and / or magnesium hydroxide or magnesium carbonate at a concentration of 0.1 to 99.5% wt. and thus 25 ml of 1% (w / w) Na2CO3. PHbola 6. EXAMPLE 6 Example 1 was followed with the difference that the CaCO3 waste formed during the capture of CO2 and Cl2 residues from chlorination of the fural by chlorine gas was used. After pre-neutralization, the reaction mixture was rated 3.9. 3 ml of 1% Na2CO3 (% w / w) were used for neutralization. The pH after the neutralization was 6.1. EXAMPLE 7 Example 5 was followed with the difference that 1.2 ml of 22% (w / w) Na2CO3 was used for the neutralization. The resulting pH was 6.4. EXAMPLE 8 Example 4 was followed with the difference that 0.5 g of about 30% Ca (OH) 2 suspension was used to be neutralized. The pH after neutralization was 6.9. The invention can be used to produce 2-methyl-4-chlorophenoxyacetic acids to neutralize the resulting hydrochloric acid waste. Neutralization to a pH of 6 to 8 is a condition of the water authorities without which it is not possible to discharge the hydrochloric acid wastewater into the wastewater. The resulting reaction mixture is neutralized to a pH of 6-8 with an aqueous solution of sodium carbonate at a concentration of 0.1 to 30% by weight. or sodium hydroxide concentration of 0.1 to 45% by weight. or a calcium hydroxide suspension containing 0.1 to 35 wt. calcium hydroxide. 2. Process according to claim 1, characterized in that calcium carbonate resulting from the absorption of carbon dioxide and chlorine from the off-gas, chlorination of the fural in a slurry of calcium hydroxide hydroxide is used to pre-neutralize the hydrochloric acid.