DD204912A1 - METHOD FOR OBTAINING RECYCLABLE COMPOUNDS FROM FORMAT-CONTAINED ALKALINE WASTEWATERS - Google Patents

Abstract

The invention relates to a process for the purification of formate-containing, alkaline effluents incurred in the production of Azoxybenzenen from nitrobenzene and methanolic Alkalihydroxidloesungen and has next to the recovery of usable substances to the target. Depending on the nature of the workup and the conditions, it is possible to isolate formic acid, alkali metal formate or alkali metal salt mixtures. To obtain formic acid, the wastewater is acidified and the formic acid is isolated by a suitable separation process such as distillation or extraction. Alkali formate is obtained by neutralization of the alkali lye contained in the wastewater with formic acid and the like. Removal of residual water. Alkali-formate containing salt mixtures, which are useful, for example, as silierungshilfsmittel be obtained by neutralization of the effluents with a mineral acid, evaporation and drying.

Description

Title of the invention:

Purification of formate-containing, alkaline wastewaters to give recoverable compounds

Field of application of the invention;

The invention can be used in the chemical industry in the preparation of tiitro compounds and methanoic alkali hydroxide solutions of azoxy compounds.

Characteristic of the known solutions *. In the production of azoxy compounds from ITitrobenzen and methanolic lye liquors accumulate concentrated effluents, which formiate substantially alkali metal hydroxide and alkali. contain »... These .. wastewater, are a burden for treatment plants. On the other hand, especially Alkaliformiat is economically of interest · Sine special processing method has not been described *

Object of the invention:

The aim of the invention is to purify alkaline, formate-containing wastewaters obtained in the production of azoxy compounds from IT nitrobenzene and methanolic alkali metal hydroxide while simultaneously recovering the formate contained therein as a lifting product in usable form. The IT benefit. of the .. procedure is based on. a discharge _; of wastewater treatment plants and of "the recovery of alkali or» formic acid *

Explanation of the essence of the invention:

The production of azoxy compounds from kitrobenzene and methanolic lye produces concentrated effluents containing approx. 30 % alkali hydroxide and 20 - 30 % alkali *

Mf '. 9 * νΗ

- 2 ~ L · * J%) L · JQ O

These concentrations represent a high wastewater load.

The invention is based on the idea of permitting a wastewater treatment in which the formate contained is isolated in a disposable form. According to the invention, the solution of problem 3ε succeeds according to the given conditions by releasing formic acid either from the formate, which is then converted to conventional Paths is isolated by distillation and extraction, or the alkali metal hydroxide is neutralized with formic acid and the formate by evaporation of the solution wins »The extraction of formic acid is carried out for example with methyl ethyl ketone. The separation of extractant and formic acid is then carried out by distillation, wherein the solvent is recycled to the extraction stage. The isolation of the formic acid can also be carried out in a manner known per se by vacuum distillation or by azeotropic distillation using a suitable _c hleppmittels. For example, benzene or n-heptane can be used. The concentration of the depositing of formic acid depends on the composition of the wastewater, the concentration of the acid used for neutralization, type of S _c hleppmittels and the conditions of the release. However, the work-up and concentration of the expelled formic acid is not the subject of the present invention. "Reference is made to the known technical solutions"

Bine another way of using the formate is in a further variant of the method according to the invention in that the alkali metal hydroxide contained in the process waste water is neutralized with a mineral acid and the salt mixture is isolated by evaporating the solution. The neutralization should be carried out at temperatures as low as possible in order to avoid losses of alkali formate. "

- 3 - £ JO £ Ό Q D

Good results were obtained with hydrochloric acid at 25 ^° C. "The salt mixture can be used, for example, as an auxiliary for silage for feed." For the purposes in question, the nature and composition of the salts or salt mixture obtained is usually sufficient. Optionally, the quality can be improved by washing with a suitable solvent, removing extractables and possibly preventing discoloration, so that the solution of the present wastewater problem can not be so easily and beneficially practiced. The process according to the invention Yri.rd illustrated by the following examples, wherein the yield data refer to the percentage of formate or formic acid recovered from the wastewater (the content was determined in each case by titration with KMnCK):

1, isolation of sodium formate

31? 5 g of waste water are neutralized with formic acid at 25 ^° C. »The concentration of formic acid is of no importance for the reaction. The solution is evaporated to dryness in vacuo

200 ⁰ C dried. ² ^

Yield: $ 6.7 g

Content of UaHOO ₂ : 90 % (= 78.3 % of Th *)

2. Isolation of Salzgeraischen

2 * 1 31 "5 g wastewater is neutralized with 50% sulfuric acid at 25 ± ger ⁰ O · The solution is concentrated to dryness in vacuo and the residue dried at 200 ⁰ C, yield: 17.3 g amount of NaHCO _2: 21 , 2 % (= 58.7 % of th.)

2 »2 31 95 g of wastewater are neutralized with concentrated hydrochloric acid * The solution is concentrated to dryness in vacuo and the residue is concentrated at 200 ^° C.»

2)

dries "

Yield: 16.8 g

Content of UaHCO ₂ : 31 % (= 82.5 % of theory )

3. Isolation of formic acid

3 · 1 473 g of waste water are acidified to pH 1 with 50% sulfuric acid »The solution is vacuum distilled to give 452 g of an aqueous formic acid» The content of HCOOH is 7.5 % C = a yield of 53 % d _e Th.)

3 »2 473 g of wastewater are acidified to a pH of 1 with 50% sulfuric acid. The reaction mixture is subjected to azeotropic distillation with n-heptane as entraining agent. 430 g of a 7% formic acid are present C = a yield of 47.5 % of theory . Thj

3 x 3 473 g of wastewater are treated with 50% H ₂ SO. acidified to a pH of 1 · The solution is extracted in Kutscherst EUDEL perforator with methyl ethyl ketone * The extract is separated by rectification, yield an.HCOOH: 25 g (= 39.2% of th _e.). ,

Bs was a process waste water containing 27.5% HaOH and 22.7% IaHCO ₂ .

The described drying is not absolutely necessary in practice. In the examples, it was described to make the results comparable to su »

The experiments were not optimized ₉ so that more concentrated solutions and higher yields can be expected when using more suitable extraction or trailing agents *

Claims (1)

C interest claims A process for recovering useful compounds from formate-containing, alkaline waste waters, characterized in that the alkali hydroxide contained in the wastewater is neutralized with an acid and the resulting salt mixture is isolated or the acid is acidified with an acid and the formic acid liberated from the formates is isolated * Process according to item 1, characterized in that the alkali hydroxide is neutralized with formic acid «