Osmotic distillation process for concentrating a liquid containing sodium chloride

Patent metadata

Field	Value
Publication number	US-2018186665-A1
Application number	US-201615740174-A
Country	US
Kind code	A1
Filing date	Jun 29, 2016
Priority date	Jul 1, 2015
Publication date	Jul 5, 2018
Grant date	—

Abstract

Described is an osmotic distillation process for concentrating a liquid containing sodium chloride, and in particular a treatment process for used reaction water containing sodium chloride from the production of polymers.

First claim

1 .- 17 . (canceled)

18 . An osmotic distillation process for concentrating an aqueous liquid containing sodium chloride, where the liquid has a concentration of up to 20% by weight of sodium chloride, preferably from 2 to 18% by weight of sodium chloride, which comprises at least the following steps,
a) optionally prepurification of the liquid to remove organic secondary constituents, in particular down to a total content of the organic secondary constituents of 20 ppm, b) introduction of the purified liquid into a first zone as evaporation zone which is separated from a diffusion zone adjoining this first zone by a hydrophobic first membrane which is permeable to water vapor, c) diffusion of water vapor from the liquid containing sodium chloride through the membrane into the diffusion zone, d) further diffusion of water vapor from the diffusion zone through a second hydrophobic membrane which is permeable to water vapor into a stripping zone adjoining the diffusion zone and absorption of the water vapor in a draw solution which is continuously replaced in the stripping zone.

19 . The process as claimed in claim 18 , wherein a concentrated alkaline metal hydroxide solution, in particular concentrated sodium hydroxide solution, preferably having a concentration of alkaline metal hydroxide, particularly preferably of NaOH, of from 10% by weight to 50% by weight, preferably from 15% by weight to 35% by weight, particularly preferably from 20% by weight to 33% by weight, is used as draw solution.

20 . The process as claimed in claim 18 , wherein the diffusion zone has drainage for discharging liquid and condensate, in particular laden with interfering anions, particularly preferably with chloride anions, or of any liquid passing through the membranes and into the diffusion zone or draw solution is discharged from the diffusion zone.

21 . The process as claimed in claim 18 , wherein the aqueous liquid containing sodium chloride is production wastewater from a process for preparing polymers, in particular for preparing polycarbonate or polyurethane intermediates.

22 . The process as claimed in claim 18 , wherein the first membrane and the second membrane are, independently of one another, based on a hydrophobic polymer, in particular on polypropylene and/or polytetrafluoroethylene (PTFE).

23 . The process as claimed in claim 18 , wherein the different zones: evaporation zone, diffusion zone, stripping zone are maintained independently of one another at atmospheric pressure or reduced pressure, in particular at a pressure of from 10 to 600 mbar.

24 . The process as claimed in claim 18 , wherein the different zones: evaporation zone, diffusion zone, stripping zone are, independently of one another, maintained at a temperature of from 10 to 80° C., particularly preferably from 20 to 60° C.

25 . The process as claimed in claim 24 , wherein the temperature in the evaporation zone is greater than in the adjoining zones, namely the diffusion zone and the stripping zone.

26 . The process as claimed in claim 18 , wherein the liquid containing sodium chloride in the evaporation zone and the draw solution in the stripping zone are conveyed in countercurrent relative to one another past the respective membranes.

27 . The process as claimed in claim 18 , wherein the aqueous liquid containing sodium chloride has turbulent flow in the region of the evaporation zone.

28 . The process as claimed in claim 18 , wherein the internals which are contacted by the process liquids in the zones: evaporation zone, diffusion zone, stripping zone have been joined to one another by means of fusion bonding, in particular by frictional welding or laser welding, particularly preferably by frictional welding, in particular without use of adhesives or bonding agents.

29 . The process as claimed in claim 18 , wherein the draw solution is alkaline metal hydroxide solution and is taken from a coupled electrolysis process for the electrolysis of alkaline metal chloride and, after uptake of water vapor in the stripping zone (1), is introduced into a coupled chemical production process, in particular for preparing polymers.

30 . The process as claimed in claim 18 , wherein the aqueous liquid containing sodium chloride is taken from a coupled chemical production process, in particular a process for preparing polymers, and, after having been concentrated in the evaporation zone, is introduced into a coupled electrolysis process for the electrolysis of alkaline metal chloride.

31 . The process as claimed in claim 18 , wherein the process steps b), c) and d) are carried out in a plurality of stages, with at least one further combination of evaporation zone, diffusion zone, stripping zone being employed.

32 . The process as claimed in claim 18 , wherein the liquid exiting from the first evaporation zone in a first arrangement made up of evaporation zone, diffusion zone, stripping zone is again subjected to process steps b) and c) in at least one downstream further arrange ent made up of evaporation zone, diffusion zone, stripping zone and the diluted draw solution exiting from a second stripping zone in at least one downstream arrangement made up of evaporation zone, diffusion zone, stripping zone is used for carrying out step d) in the first arrangement made up of evaporation zone, diffusion zone, stripping zone.

33 . The process as claimed in claim 32 , wherein the concentrated aqueous liquid containing sodium chloride exiting from the evaporation zone of the first osmotic distillation arrangement is subjected to heat exchange in order to set the operating temperature before introduction into a subsequent further osmotic distillation arrangement.

34 . The process as claimed in claim 32 , wherein the draw solution exiting from the stripping zone of the first osmotic distillation arrangement is subjected to heat exchange in order to set the operating temperature before introduction into a subsequent further osmotic distillation arrangement.

Assignees

• Covestro Deutschland Ag

Inventors

• Bulan Andreas
• Schiesser Yuliya
• Weber Rainer

Classifications

• B01D2311/04

  Specific process operations in the feed stream; Feed pretreatment · CPC title

• C02F2101/12

  Halogens or halogen-containing compounds · CPC title

• C02F2103/38

  Polymers · CPC title

• B01D2313/32

  Intermediate chambers · CPC title

• C02F1/447 Primary

  by membrane distillation (distillation and evaporation without the use of membranes C02F1/04) · CPC title