SRS Machine

Introduction of removal sulfate by nanofiltration

Nanofiltration (NF) membrane, with its molecules entrapped was around 80~1000 Da, is a special and very promising variety in the separating membranes. The surface of nanofiltration membrane separation layer is composed of polyelectrolyte and electrostatic interactions of ions, so they are certain to reject inorganic salt. The structure of nanofiltration membranes are composite film, that is the chemical composite of film surface chemical separation layer and the support layer are different.

TANGENT company provide composite nanofiltration membrane from the world's most famous membrane company, nanofiltration is a membrane screening process which is related to aperture size, the pressure difference of membrane on both sides is the driving force and the nanofiltration membrane is taken as the filter medium. under pressure, when the liquid flows through the membrane, nanofiltration hole many allow water and Cl - molecules through nanofiltration membrane surface and become Permeate liquid, other materials, greater than the surface membrane nanofiltration aperture, such as SO 2- , are trapped in the other side and become concentrated liquid, so as to realize the purpose of separation,purification and concentration of solution. With the popularity of ion-exchange membrane caustic soda technology, brine purity constraint of ion-exchange membrane caustic soda is more and more outstanding. Enrichment of sulfate ion in brine is an important factor affecting the present ion-exchange membrane economic benefit. The main reason for the generation of sulfate ion is from raw materials, which contain sulfate ion and after electrolytic brine dechlorination add Na 2 SO 3 . The change of sulfate ion is negligible with the out of cathode products and the brine loss. The mainly effect of sulfate ion to ion-exchange membrane caustic soda has following several aspects:

(1) the sulfate ion release oxygen at the anode, reduce anode current efficiency and the purity of chlorine gas.

(2)the melamine salt format with other material impacting the life of ion-exchange membrane.

(3) sulfate ion effect the content of sodium chloride in brine, when the sulfate ion content is too high, it will lead to a lot of salt crystallization in system, even

to the extent that the pipeline blockage or pump impeller.

Currently, the removal of sulfate ion method used in ion-exchange membrane caustic soda process are as follows: (1) the chemical precipitation method: adding barium chloride method, adding calcium chloride method, adding barium carbonate method; (2) membrane method and freezing method.

At present, most of the enterprise use chemical precipitation method to remove sodium sulfate by adding barium chloride, which is a highly toxic substance and is categorized as high-risk chemicals in the factory, it should be more careful in the process of use, because barium chloride is expensive and need adding quantity, so operating cost is too high. At the same time, method of adding barium chloride removing sodium sulfate is to add a new impurity removing other impurities, usually about 10% of barium chloride is not used and resulting in waste of barium chloride. Barium sulfate precipitation must ensure that the sulfate ion overdose, otherwise barium ion will exceed the standard. The Nanofiltration sulfate removal system by physical method, the new impurities (barium) can’t be brought into brine, moreover, sulfate ion concentration can also be controlled less than 5g/L. This can obviously increase the quality of brine, greatly

reduces the influence of ion-exchange membrane internal channel by barium ion and sulfate ion, to further improve the current efficiency of electrolytic, potentially prolong the service life of ion-exchange membrane. At the same time, it creates the conditions for the preparation of purity chlorine from the source. Nanofiltration sulfate removal system only needs one-time investment in equipment, low operation cost, no toxic and harmful substances, no pollution, easy to clean production, Contribute to the achievement of energy conservation and emission reduction, and it can improve the utilization rate of the brine compared with traditional sulfate removal process.


Removing sodium sulfate by nanofiltration membrane for 70kta caustic soda.

The removed sulfate brine


Component  Index

NaCl :  195± 10 g/L

Na 2 SO 4 :  ≤2.5g/L

Pressure : 0.25MPa(g)

Flow :  32±1m 3 /h

Connection condition :  Pipeline

The rich sodium sulfate brine

Component  Index

NaCl:  195± 10 g/L

Na 2 SO 4 :  70±10g/l

Pressure  0.25MPa(g)

Flow  ≤4.5m 3 /h

Connection condition:  Pipeline