阅读说明：本技术 含盐生产用水的后处理和再使用方法 (Post-treatment and reuse method of salt-containing production water ) 是由 Y·席塞尔 K·维纳 A·布兰 于 2019-02-11 设计创作，主要内容包括：描述了用于来自化学生产工艺的含有至少4重量%浓度的碱金属氯化物作为盐以及有机或无机和有机杂质的含盐生产用水的后处理和用于通过盐的预纯化和浓缩、结晶和纯化的组合的盐的再使用的方法,以及任选随后盐在电解中用于生产基础化学品的使用。(A method for the post-treatment of salt-containing process water from a chemical production process containing an alkali metal chloride as salt and organic or inorganic and organic impurities in a concentration of at least 4 wt.% and the reuse of the salt for the combined purification and concentration, crystallization and purification by pre-purification of the salt and optionally the subsequent use of the salt in electrolysis for the production of basic chemicals is described.)

1. Method for the post-treatment and reuse of brine process water (1a, 1b, 1c) from a production process (Ia, Ib, Ic), in particular from a chemical production process, said brine process water (1a, 1b, 1c) containing an alkali metal chloride, preferably sodium chloride, as salt in a concentration of at least 4 wt. -%, and organic or inorganic and organic impurities, wherein

a) The process water (1a, 1b, 1c) is first subjected to an oxidation and/or adsorptive purification (IIa, IIb, IIc) to remove organic impurities, wherein one or more adsorbents selected from the group consisting of activated carbon, adsorbent resins and zeolites are used as preferred adsorbents,

b) optionally producing a preconcentrated purified process water (4) from the purified process water (2a, 2b, 2c, 2d) by removing water (3), in particular to remove water to a concentration of alkali chloride in the process water of not more than 26% by weight, preferably by means of one or more of the following methods, as required: high pressure reverse osmosis, electrodialysis, evaporation, membrane distillation or vaporization,

c) optionally introducing a partial amount (6) of the purified process water (2a, 2b, 2c, 2d; 4) from step a) or b) having a salt concentration of 4 to 26% by weight, preferably 7 to 26% by weight, into a brine circuit (29) of chlor-alkali electrolysis (VIII),

d) the process water (2a, 2b, 2c, 2d; 4) from step a) or optionally from step b) or the remaining amount of process water optionally left by step c) is further concentrated by removing water (V)

e) And crystallizing (VI) an alkali chloride

f) (VII) is separated and purified from the mother liquor as solid alkali chloride, preferably by means of washing, so that the solid alkali chloride (13), when analyzed after dissolution in deionized purified water at a concentration of 300 g/l, has a TOC content of not more than 1mg/l,

g) introducing the solid purified alkali chloride (13) from step f) into a brine stream (28) of chlor-alkali electrolysis (VIII),

h) the product obtained from alkali chloride electrolysis (VIII) after steps g) and optionally c): chlorine (30), alkali metal hydroxide (31), preferably sodium hydroxide, and optionally hydrogen are recycled to the production process (Ia, Ib, Ic) as required.

2. The method according to claim 1, characterized in that the optional oxidative purification (IIa, IIb, IIc) in step a) to remove organic impurities is carried out by treatment with ozone at an initial pH in the process water (1a, 1b, 1c) set to at least 1 and a temperature of at least 35 ℃, preferably at least 50 ℃, and the amount of ozone is preferably not more than 2 g of ozone per liter of process water (1a, 1b, 1 c).

3. Method according to claim 1 or 2, characterized in that in step a) the oxidative purification (IIc) of organic impurities of the process water (1a, 1b, 1c) is carried out by means of an electrochemical reaction at the diamond electrode, preferably at the boron-doped diamond electrode, optionally in addition to or only in addition to a further oxidative purification.

4. The process according to any one of claims 1 to 3, characterized in that the purification of the organic impurities in step a) is carried out to a residual impurity content of not more than 5mg/l TOC.

5. The process according to any one of claims 1 to 4, characterized in that the concentration of salts, in particular alkali metal chlorides, in the process water (1a, 1b, 1c) before step a) is at least 6 wt. -%, preferably at least 8 wt. -%, particularly preferably at least 12 wt. -%.

6. The process according to any of claims 1 to 5, characterized in that the water (3) obtained in the preconcentration in optional step b) is reused for diluting an alkali metal hydroxide solution (33; 34), preferably a sodium hydroxide solution, for the production process (Ia, Ib, Ic), in particular for the preparation process of polycarbonate (Ia), polycarbonate precursor (Ib) or MDA (Ic).

7. The process according to any of claims 1 to 6, characterized in that the water (17, 18, 19, 23) obtained in the concentration and crystallization in steps d) and e) is reused for diluting an alkali metal hydroxide solution (33), preferably a sodium hydroxide solution, for the production process (Ia, Ib, Ic), in particular for the preparation process of polycarbonate, polycarbonate precursor or MDA.

8. The process according to any one of claims 1 to 7, characterized in that the solid alkali chloride (13) obtained in the crystallization (VI) in step f) is washed, preferably counter-current washed, with deionized water (16) and/or with a purified alkali chloride solution (7) to achieve purification before reuse.

9. The method according to any one of claims 1 to 8, characterized in that the production process (Ia, Ib, Ic) from which the process water (1a, 1b, 1c) is obtained is a process for the preparation of polycarbonate or a polycarbonate precursor, in particular diphenyl carbonate, or an isocyanate, in particular diphenylmethane diisocyanate or methylenebis (aniline) (MDA).

10. The process according to any one of claims 1 to 9, characterized in that the water removed and obtained in the optional pre-concentration according to step b) and/or the concentration according to step d) or e) is used for the optional washing of the solid salt (13) in step f).

11. The process according to any one of claims 1 to 10, characterized in that a purified alkali metal chloride solution from the substream (7) of the process water which has been purified in step a) or from the substream of the purified process water which has been concentrated in step b) is used for the washing (VII) in step f).

12. The process according to any one of claims 1 to 11, characterized in that the alkali chloride solution obtained by dissolving the purified alkali chloride salt in the water removed and obtained in the performance of step b) and/or d) is used for washing (VII) in step f).

13. The process according to any one of claims 1 to 12, characterized in that the mother liquor which has been separated from the alkali metal chloride (13) in step f) is divided into two streams and one larger stream is recycled to the concentration according to step d) and the other smaller substream (12) is discarded, the substream (12) making up no more than 5% by weight of the separated mother liquor.

14. The process according to any one of claims 1 to 13, characterized in that 5 to 20 parts by weight of washing liquid are used for the optional washing of the solid alkali chloride in step f), based on 100 parts by weight of separated alkali chloride.

15. The process according to any one of claims 1 to 14, characterized in that the organic impurity is a compound selected from: aniline, MDA and their precursor compounds: formaldehyde, methanol, phenol; or is selected from: bisphenol a, phenol and benzene derivatives with different alkyl substituents and halogenated aromatic compounds, preferably those selected from the group consisting of butylphenol, isopropylphenol, chlorophenol and bromophenol and aliphatic amines and ammonium salts thereof, in particular trimethylamine, butylamine, dimethylbenzylamine, ethylpiperidine and quaternary ammonium salts thereof.

16. The process according to any one of claims 1 to 15, characterized in that the inorganic impurities are compounds selected from: cations and anions of the metals Ca, Mg, Fe, Al, Si, B, Sc, Ba, Ti, Cr, Mn, Ni and Ru, in particular selected from: cl^-、F^-、Br^-、SiO₄ ^2-、SO₄ ^2-A salt of the anion combination of (1).

Example (b):

general description of the working Water aftertreatment and concentration from various sources

The work-up and concentration of the process water can be carried out by evaporation and crystallization of the various prepurified process waters, either alone or together, according to the flow diagram as depicted in fig. 1.

Figure 1 schematically shows the process of the invention wherein process water from different sources (MDA, SPC and DPC production) is concentrated by evaporation and crystallization.

In the case of SPC production (Ia), process water 1a is formed and first hydrochloric acid (HCl) is used to reach a pH of less than 8 and then (IIa) is prepurified with activated carbon. Prepurified stream 2a may optionally be preconcentrated (III) to form stream 4 and then introduced into mixed process water 5 or may be introduced directly (2d) into mixed process water 5.

In the case of DPC production (Ib), process water 1b is formed and likewise hydrochloric acid (HCl) is used to reach a pH of less than 8, and then prepurified with activated carbon (IIb) and introduced as stream 2b into the mixed process water 5.

In the case of MDA production (Ic), process water 1c is formed and brought to the appropriate pH value also using hydrochloric acid (HCl), and then oxidatively prepurified (IIc) is introduced as stream 2c into the mixed process water 5.

A substream 6 may be extracted from the mixed process water 5 and fed to the brine loop of electrolysis VIII. A further sub-stream 7 may optionally be fed to the solid/liquid separator VII for salt washing. The remaining mixed process water may then be introduced as feed stream 8 into heat exchanger IV and preheated therein.

Preference is given to using the hot distillate 18 or 17 from the evaporation stage V (stream 18) or the crystallization VI (stream 17) for this purpose. In the subsequent evaporation stage V and crystallization stage VI, water is extracted by evaporation as distillate 17 or 18 to form brine streams 9 and 10. The amount of water evaporated depends on the concentration of impurities in feed stream 8. Typically more than 95% of the water can be extracted from the feed stream 8. Evaporation and crystallization in a single unit (not shown) may also be used, depending on the size of feed stream 8.

The evaporated water is compressed by means of a compressor and used for heating evaporation (stage V) or crystallization (stage VI) (mechanical vapor compression; not shown here). However, as an alternative, in the case of a multistage process, it can be fed directly to the next stage of a multistage evaporation or crystallization apparatus to effect heating (not shown here). The condensate 17 or 18 (distillate) formed from the steam is used to preheat the feed stream 8 in heat exchanger IV. Since the prepurification of the feed stream 8 results in a TOC content of the distillate 17 or 18 of less than 5mg/l, it can be used after feed preheating in processes requiring a specific purity, such as chlor-alkali membrane electrolysis VIII (stream 21).

Evaporation and crystallization of VI formed a mixture 11 of solid salts and mother liquor with NaCl saturation. The mother liquor contains most of the organic and inorganic impurities. Thus, a portion of the mother liquor remaining after crystallization (stream 12, purge) is withdrawn from crystallization stage VI together with most of the impurities present therein and discarded.

A portion of the mother liquor 14 is separated from the mixture 11 in separator VII and recycled to the crystallization step VI.

The solid salt with the remaining adhering mother liquor is washed in stage VII with distillate (substream 20) as wash water and obtained as clean salt 13. It is particularly advantageous to carry out a countercurrent washing with the distillate (stream 20) in stage VII: a particularly pure stream 20 is used for the second washing step of the solid salt. In this second washing step in stage VII, stream 20 carries away residual impurities from the surface of the solid salt. The loaded wash water was collected and used for the primary wash step in stage VII. Here it displaces the remaining adhering mother liquor and carries away additional further impurities. Since the wash water also becomes loaded with salt, it is recycled after the washing in stage VII to the crystals VI as loaded wash water 15 as well.

Alternatively, the washing or counter-current washing of the salts in stage VII can also be carried out using fresh water, preferably demineralized or deionized water (stream 16), instead of distillate 20.

As the water becomes loaded with salt in the wash or counter current wash in stage VII, as shown in fig. 1, prepurified process water (stream 7) may also optionally be used. Since this already contains salt, the loss of crystalline salt in the wash is lower.

The use of a salt solution with an electrolytic input concentration (stream 27) is particularly advantageous, since in this case little crystalline salt is dissolved.

The amount of the washing liquid was 10 parts by weight based on 100 parts by weight of the alkali metal chloride which had been separated out.

Due to crystallization and counter current washing, the resulting salt is provided in the purity required for CA electrolysis of VIII. In saturated solutions, the TOC value is preferably less than or equal to 5 mg/l.

Especially since a portion of the salt is withdrawn with the mother liquor (stream 12) and discarded, a portion of the amount of salt must be added as make-up (stream 24) to provide sufficient chlorine for processes Ia-Ic from CA electrolysis (step VIII). The amount of salt from the evaporation/crystallization step (stream 13) and this make-up 24 are fed as stream 25 to the CA electrolysis VIII. Depending on the requirements of electrolysis VIII, it may be necessary to introduce fresh water (stream 26) to make the starting solution 28 for electrolysis VIII.

To meet the water requirements of CA electrolysis, a portion 6 of the prepurified process water may instead be fed directly to electrolysis VIII. The salt demand is met by the crystalline salt 13 and the salt 24 introduced from the outside. The stream is mixed with dilute brine 29 to give a brine concentration with about 300 g/l NaCl. The TOC content of the mixture must not exceed 5 mg/l.

The chlorine gas 30 formed in the electrolysis is used for the production processes SPC, DPC and MDI (chlorine gas input streams 37a, 37b, 37 c). The sodium hydroxide 31 formed is likewise used here. The need beyond the sodium hydroxide formed is provided by the introduction of external sodium hydroxide 32, if necessary.

Since the total sodium hydroxide stream 33 is typically used as the dilution feed stream 36a, 36b, 36c in the production processes Ia, Ib and Ic, a dilute caustic solution (streams 34, 35) can be made using the sub-stream 23 from the distillate 19 and the permeate 3 from the pre-concentration. The excess water 22 may be used for other purposes in the production process.