DD243268A1 - METHOD FOR REMOVING CONTAMINATION FROM PROCESS WAIVERS - Google Patents

Abstract

The invention relates to the removal of low concentrations of cyanides and / or sulfides and optionally ammonia from Prozeßabwaessern incurred in the recovery of n-alkanes from hydrocarbon mixtures. The separation takes place, optionally after prior rectifying separation of the ammonia, by treatment with air at elevated pressures and temperatures.

Description

Field of application of the invention

The invention relates to a process for the removal of sulfide- and cyanide-containing impurities from process effluents incurred in the recovery of n-alkanes from hydrocarbon mixtures.

Characteristic of the known technical solutions

Methods for removing sulfide and cyanide contaminants from process effluents are widely described in the patent literature. Thus, the destruction of the cyanide contained in coking plant effluents following the work-up by distillation by time-consuming biological treatment of ammonia-poor process wastewater (DE-OS 3006070).

Other ways to remove hydrogen cyanide and / or its salts are used in wastewater technology in the form of precipitation, oxidation or electrolysis.

In recent years, the detoxification of cyanide-containing wastewater by treatment at elevated pressures and temperatures has been reported several times. For example, DD-PS 109365 describes a process for detoxifying cyanide-containing solutions. At temperatures of 473 to 523 K and pressures of 0.4 to 15.0 MPa complete conversion of the cyanides in formate is achieved. The process results in corrosion problems due to the formation of formate.

In DD-WP 216229 a process for the removal of impurities from process wastewater is described, in which in the first process stage, a rectification of the circled process waste water with the addition of sodium hydroxide solution for separating the ammonia and in the second process stage, the process wastewater from the bottom of the rectification of Pressure hydrolysis is subjected at elevated temperatures.

Although this method allows the hydrolysis of the cyanides contained in the process effluents, sulfides are not degraded under these conditions. To eliminate the sulfides, a further process stage is required.

DD-WP 118598 proposes the processing of sulphide-containing wastewater with the aid of carbon dioxide. With this method, an additional, sewage polluting substance is introduced into the process.

DD-PS 120186 and DE-AS 2207902 describe processes for the oxidative detoxification of sulphidic process wastewaters by means of NaOCl or H ₂ O ₂ . The application of both methods is associated with the formation of a new polluting substance in the case of using NaOCl and economically very expensive. Furthermore, the methods have the disadvantage that the removal of impurities from ammonia-containing process wastewater due to the formation of nitrous gases is not possible. By AG Smith, Ridding process waters and caustics solutions of sulfids; Oil Gas Journal 54, No. 62,95 (1956), a process for the removal of sulfides with air at elevated temperatures and pressures is described. The possibility of simultaneously removing cyanides and sulfides under the chosen conditions is not mentioned.

Object of the invention

The aim of the invention is a process for the removal of impurities from process wastewaters containing cyanides and / or sulfides in low concentrations and resulting in the recovery of n-alkanes from hydrocarbon mixtures.

Explanation of the essence of the invention

The object was to develop a process for the removal of impurities from process wastewaters, in particular from ammoniacal wastewaters containing cyanides and / or sulfides in low concentrations.

The process to be developed should require as little energy as possible and guarantee minimal ammonia loss when cleaning ammoniacal wastewater.

According to the invention, this object is achieved in that the alkaline wastewater, optionally after prior rectifying separation of the ammonia, are treated with air at elevated temperatures and pressures.

Preferably, the oxidation of the complex pollutant mixture is carried out with air at temperatures of 408 to 673K, at pressures of 0.4 to 1.5 MPa and loads of 50 to 500 parts by volume of air per part by volume process wastewater and hour. While the removal of complex cyanides begins in pure form only at pressures above 4MPa and temperatures greater than 473K, this takes place in pollutant mixtures already at 0.4MPa and 408K.

The resulting from the sulfides polysulfides are removed by filtering from the wastewater and can be used for example for the production of sulfuric acid.

In the removal of impurities from ammoniacal process wastewater is carried out in a preceding process stage, a rectification of the wastewater with the addition of sodium hydroxide solution.

embodiments example 1

The alkaline process effluent (pH 9 to 11) with a cyanide content of 64mg CN ~ / I is at pressures of 0.4 to 1.0 MPa, a temperature of 408K and a load of 50 volumes of air per volume of waste water and hour ten hours in a reactor treated. The following results were obtained: Parameter ME Experiment no.

1 2

Pressure MPa 0.4 0.6 1.0

CN "content mg / l <5 <3 <1

Example 2

The alkaline process effluent (pH 9 to 11) with a cyanide content of 64mg CN ~ / I is treated at a pressure of 0.4 MPa, temperature of 408 to 473 K and a load of 50 volumes of air per volume of waste water and hour for ten hours in a reactor , The following results were obtained: Parameter ME Experiment no.

12

Temperature K 408 443

CN "content mg / l <5 S 4 <4

Example 3

The alkaline process effluent (pH 9 to 11) with a sulfide content of 42 g / l is at pressures of 0.4 to 1.0 MPa, a temperature of 408 K and a load of 50 parts by volume of air per part by volume of waste water and ten hours in a reactor treated.

The following results were achieved:

Parameter ME Experiment no. ......

1 2

Pressure MPa 0.4 1.0

Sulfide content after

the treatment g / i 29.3 14.1

Example 4

The ammoniacal process wastewater with a NH ₄ HS content of 50 g / l and a content of free or complexed cyanides of 65 mg / l and 580 mg / l was at a pressure of 0.3 MPa and a temperature of 343 K with the addition of sodium hydroxide solution rectified. By this measure, a waste water containing 42 mg / l NaHS, 64 mg / l NaCN, 550 mg / l Na ₃ Fe (CN) ₆ and small residual amounts of ammonia was obtained.

The alkaline process effluent was treated at a pressure of 0.4 MPa, a temperature of 408 K, a load of volumes of air per volume of wastewater and hour over a period of six hours. The following results were achieved:

Impurities Concentration and degree of degradation of impurities

before treatment after

free cyanide 64mg / L ¹¹ 100% complexed cyanide 550 mg / l ¹¹ 100% sulfide 42 g / l 0.9 g / l 97% 1 n. N. = Undetectable

Claims (2)

Invention claim: 1. A process for the removal of impurities from process effluents, which consist of cyanides and / or sulfides in low concentrations and in the recovery of n-alkanes from hydrocarbon mixtures and which may also contain ammonia, characterized in that the alkaline waste water, optionally after prior rectifying separation of the ammonia, be treated with air at elevated pressures and temperatures. 2. The method according to item!, Characterized in that the oxidation of the impurities contained in the process effluents at pressures of 0.4 to 1.5 MPa, at temperatures of 408 to 673 K and at loads of 50 to parts by volume of air per volume of wastewater and hour he follows.