Reverse osmosis composite membranes for boron removal

Abstract

Improved methods for reducing boron concentration in seawater or brackish water, while simultaneously maintaining or improving the salt rejection of membrane and flow performance of polyamide reverse osmosis (RO) membranes include contacting the water with a composite membrane comprising moieties derived from an aromatic sulfonyl halide, a heteroaromatic sulfonyl halide, a sulfinyl halide; a sulfenyl halide; a sulfuryl halide; a phosphoryl halide; a phosphonyl halide; a phosphinyl halide; a thiophosphoryl halide; a thiophosphonyl halide, an isocyanate, a urea, a cyanate, an aromatic carbonyl halide, an epoxide or a mixture thereof.

Description

BACKGROUND[0001]Reverse osmosis (RO) membrane desalination uses membrane technology to transform seawater and brackish water into fresh water for drinking, irrigation, and industrial applications. Such processes require substantially less energy than do thermal desalination processes such as multi-stage flash, and so, reverse osmosis membrane technology is increasingly used to produce fresh water from seawater or brackish water.[0002]Reverse osmosis is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure. This is the reverse of an osmosis process, which is the natural movement of solvent from an area of low solute concentration, through a membrane, to an area of high solute concentration when no external pressure is applied. The membrane here is semipermeable, meaning it allows the passage of solvent but not of solute. The membranes used for reve...

AI Technical Summary

Problems solved by technology

However, the RO process has not been very effective in the removal of neutral contaminants such as boron despite its capacity to efficiently remove up to 99.7% of ionic species.

Excess boron also harmful to plant growth; deleterious effects include massive leaf damages, premature ripening, and reduced crop yields.

Thus, boric acid is significantly smaller than hydrated sodium (3.58 Å) and chloride (3.32 Å) ions, making the removal of boron significantly more difficult than sodium chloride salt.

As a result, it is difficult for a RO membrane desalination process to achieve an average boron rejection over 90%, which is typically required to produce a permeate that meets the requirements of the many applications.

Although these additional treatment steps lead to reduced boron concentration, they increase costs substantially.

However, even with these membranes, it has been difficult for a single-pass full-scale RO process to reduce the boron level to below 0.5 mg / L, while achieving required system recovery, unless an additional treatment step is employed.