| 其他摘要 | Abstract
Currently available fresh water is very scarce in global surface and groundwater.
Seawater desalination, collection and wastewater reuse are the only way to solve the
shortage of water resources. Membrane processes desalination technology has been
widely used in many fields and expanding, which has been widely applied process
including nanofiltration (NF) and reverse osmosis (RO), electrodialysis (ED), and
other technologies. Aiming at the deficiency of membrane technologies in water
desalination process, such as desalinating high salt and easily scaling water will arise
the problem of membrane fouling. This study not only from the aspects of technology,
put forward a new process: NF and ED combination (namely Fracsis) for ion
separation and recombinant, but also did a further research about the principle of ion
separation: preparing the functional membrane to improve the ion separation
performance of electrodialysis. First, the NF membrane can effectively separate
almost the bivalent ions into the condensed solution, then put the desalinated and
concentrated solution into the different chambers of ED. Under the electric field, the
ions of cations and anions were moving towards the opposite direction, so as to obtain
high salt solubility, improving the water recovery. After that, in the process of
preparation of ion exchange membrane, the traditional method for preparing
nanofiltration membrane, layer-by-layer self-assembly was used to modified
commercial anion exchange membrane surface, preparing the different layers of
polyelectrolyte membrane, to improve the ion selectivity of anion exchange
membrane. The following conclusions were got through this paper study:
(1) In Fracsis process, the NFS membrane obtained a high rejection for Ca
2+
, all
were above 98% in three pH systems, effective separation for bivalents. In ED
metathesis experiment, bivalent ions recombined with monovalent ions obtaining high
solubility salts. The water recovery rate after ED is higher than the theoretical value
no fouling in RO system, reached 80% in pH = 4 system. And through the theoretical calculation, the Fracsis system can reach the highest in the theoretical value of 98.5%.
The energy consumption of Fracsis system had carried on a simple calculation. The
energy consumption of the batch operation system was 4.2 to 4.8 RMB/m
3
. The
energy consumption is expected to further reduce through optimizing operation
parameters, expand the scale, installation of energy recovery device. Fracsis system
have prominent advantages for improving water recovery, reduce the sludge
production and the processing costs, which is expected to be applied to the synthesis
of organic or inorganic salt and the enrichment process.
(2) This research used simple and flexible method of layer-by-layer self-assembly
to modify the anion exchange membrane surface, prepared one kind of thin-film
composite anion exchange membrane with high ion selectivity for Cl
-
and SO 4
2-
. The
ion selectivity of base membrane was 1.0, and the increased with the layers number.
When modified by 5.5 layers, the selectivity was better than the commercial ACS
membrane with the value of 4.5.
Another hand, the modified anion exchange membranes were also evaluated by the
performance of separated organic acids. In the ED experiment, with the increase of
coating layers, the water contents and membrane resistance were gradually increasing,
but both lower than the ACS membrane. A trend was obviously observed that doping
graphene would reduce the membrane resistance. Layer-by-layer methods can
regulate the surface charge density of the membrane and the dense layer, thus
providing a simple and controllable preparation method to achieve the separation of
the ions, organic acids.
Due to the polyelectrolytes both were dissolved into water phase, making the
method as one kind of green environmental technology to modify the membrane
surface. This kind of TFC-AEM with monovalent ion selective separation for
monovalent and organic can be used in environmental protection, chemical industry,
separation and other fields. |
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