Optical Brightening Agent (Textile Industry)

NFX Nanofiltration Membrane 
Background 
Optical brightening agents are special dyes that absorb ultraviolet light and re‐emit light in the blue region, usually at 420‐470nm. This application is called the “whitening effect”, which is commonly used to enhance the appearance of certain colors without the damaging effects of bleaching. By increasing the amount of blue light reflected, yellow tones appear whiter. 
Membrane technology can be applied to capture and concentrate the optical brightening agent for reuse to lower the operating cost in textile and paper industries. Membrane technology provides a process of simultaneous concentrating and desalinating dye solution and thus obtaining concentrated dye with low salt content. 

Feed Solution, Membrane, & Operating Conditions 
An optical brightening agent was used to test the feasibility of using Synder’s NFX nanofiltration membrane to concentrate the dye for reuse.

 Feed Solution  
Material Optical Brightening Agent
Molecular Weight (Da) 430
Dye Manufacturer  JiNing XinHui Chemical Industry CO. LTD.
 Membrane  
Element  NFX-Spiral Element
Membrane Polyamide-TFC
 NF Standard Operating Parameters   
Pressure (PSI)  110 
Temperature (C) 20-25
Comparison between the concentrate (A), permeate (B) and feed solution (C) at the end of the experimeTest Results 
In a single batch process, the initial volume  was concentrated by a factor of 2 while achieving a rejection rate of greater than 99%.  The effectiveness of the NFX membrane in concentrating this dye is represented visually in a side-by side comparison (Picture 1), where the difference between permeate (B) and concentrate solution (A) is clear. The results of the filtration are summarized in table 2. 
Results  
Dye Rejection  >99%
Average Permeate Flux (GFD)  9.4
Overall salt rejection (final)   22.4%

Conclusions
The NFX membrane is very effective in concentrating the optical brightening agent. The average permeate flux is 9.4 GFD, while exhibiting a 49% decline over the entire batch process. Through a comparison of the conductivity of the permeate and concentrate, the salt species in the dye solution seems to pass through the NFX membrane easily. This low salt rejection is ideal to improve the quality of dye solution during the concentration process. Thus, the implementation of the NFX membrane can potentially reduce the capital costs associated with textile manufacturing and give plants an increased ability to meet discharge regulations.