Process for the recovery of sodium sulfate

Patent metadata

Field	Value
Publication number	US-10414667-B2
Application number	US-201615748528-A
Country	US
Kind code	B2
Filing date	Jun 1, 2016
Priority date	Jul 28, 2015
Publication date	Sep 17, 2019
Grant date	Sep 17, 2019

Abstract

A process for the recovery of sodium sulfate from water, in particular from water deriving from a silica manufacturing process.

First claim

The invention claimed is:

1. A process for the recovery of Na 2 SO 4 from a water stream, said process comprising the steps of:
providing heat to a water stream W 0 in a heat-exchanger, wherein water stream W 0 comprises Na 2 SO 4 , by means of a flow of hot gas, said hot gas discharged from a drying apparatus, to obtain water stream W i at a temperature T i ;
feeding the water stream W i comprising Na 2 SO 4 at a concentration C i into a membrane distillation unit having a feed side and a permeate side separated by at least one membrane, wherein the water stream W i is fed into the feed side of the membrane distillation unit at a temperature T i greater than the temperature T p at the permeate side of the membrane distillation unit to obtain a water stream W f containing Na 2 SO 4 at a concentration C f >C i ; and
optionally separating solid Na 2 SO 4 from water stream W f .

2. The process of claim 1 further comprising the steps of:
reacting sodium silicate and sulfuric acid in an aqueous liquid medium to obtain a suspension of precipitated silica;
separating from the aqueous liquid medium and optionally washing the precipitated silica to provide wet precipitated silica and a water stream W 0 containing Na 2 SO 4 ; and
drying the wet precipitated silica in a drying apparatus, said apparatus discharging a flow of hot gas.

3. The process of claim 1 , wherein the amount of heat provided to water stream W i in the heat-exchanger is such that the temperature differential T i −T p in the membrane distillation unit is at least 5° C.

4. The process of claim 1 , wherein
water stream W 0 comprises Na 2 SO 4 and at least one of suspended silica, dissolved silica, Ca ions and Mg ions; and wherein the process further comprises treating said water stream W 0 to reduce the amount of at least one of suspended silica, dissolved silica, Ca ions and Mg ions contained in said water stream W 0 before the step of providing heat to water stream W 0 in a heat-exchanger.

5. The process of claim 1 , further comprising the step of: increasing the concentration of Na 2 SO 4 in water stream W 0 by means of nanofiltration or reverse osmosis before the step of providing heat to water stream W 0 in a heat-exchanger.

6. The process of claim 1 , further comprising the steps of:
separating water stream W f into a first water stream W f1 and a second water stream W f2 ;
joining said water stream W f1 with water stream W 0 ; and
optionally separating solid Na 2 SO 4 from water stream W f2 .

7. The process of claim 1 , wherein Na 2 SO 4 is recovered as a solid.

8. The process of claim 7 further comprising the step of increasing the concentration of Na 2 SO 4 in water stream W f before separating solid Na 2 SO 4 from said water stream.

9. The process of claim 1 , wherein the membrane distillation unit is selected from the group consisting of a direct-contact membrane distillation unit, an air gap membrane distillation, a vacuum membrane distillation unit and a vacuum multi-effect membrane distillation unit.

10. The process of claim 1 , wherein the drying apparatus is a spray dryer.

11. The process of claim 1 , wherein concentration C i is comprised between 2.0 wt % and 15.0 wt %.

12. The process of claim 1 , wherein concentration C f is 25.0 wt % to 32.0 wt %.

13. A process for the preparation of precipitated silica said process comprising the steps of:
obtaining precipitated silica in a water reaction medium;
generating a water stream W 0 comprising Na 2 SO 4 by separation of wet precipitated silica from the reaction medium and optionally washing;
drying the wet precipitated silica in a drying apparatus discharging a flow of hot gas;
recovering Na 2 SO 4 from water stream W 0 by means of the Na 2 SO 4 recovery process as claimed in claim 1 .

14. The process of claim 13 wherein precipitated silica is obtained by reaction of an alkaline silicate solution with an acid.

15. A system for carrying out the process of claim 13 said system comprising a reactor for the manufacture of precipitated silica, a unit for the filtration and optional washing of precipitated silica, a spray drying apparatus, a heat exchanger and a membrane distillation unit.

16. The process of claim 3 , wherein the amount of heat provided to water stream W i in the heat-exchanger is such that the temperature differential T i −T p in the membrane distillation unit is of at least 10° C.

17. The process of claim 14 , wherein precipitated silica is obtained by reaction of sodium silicate with sulfuric acid.

Assignees

• Rhodia Operations

Inventors

• Horbez Dominique
• Drioli Enrico

Classifications

• Y02W10/37

  using solar energy · CPC title

• C01D5/18

  Dehydration {(C01D5/145 takes precedence)} · CPC title

• B01D2311/2642

  Aggregation, sedimentation, flocculation, precipitation or coagulation · CPC title

• C01D5/16

  Purification {(C01D5/145 takes precedence)} · CPC title

• B01D2311/04

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