Synder NDX for Dye Desalting & Dye Concentration Applications

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The manufacturing of dyes in the textile industry requires the use of high concentrations of salts, such as NaCl. However, the removal of these salts is necessary in the preparation and purification of the final dye product. In such cases, dye desalting and concentration using nanofiltration is an effective means of improving dye strength, purity, and value. The concentration capacity of nanofiltration membranes also plays an important role in textile wastewater treatment by increasing both product recovery and reuse. In this case study, the performance of Synder’s new NDX membrane was evaluated in a dye desalting and concentration application.


Synder NDX 2540 elements were tested at 120psi and at a feed flow rate of 4gpm at 25°C. The simulated feed stream was comprised of 3wt% Reactive Red 195 dye and 5wt% NaCl. Testing was performed through 6x volume concentration factor (VCF). Reactive Red 195 and Na+ rejection, as well as permeate flux, were measured throughout the duration of testing.


Dye rejection of NDX was consistent at >99.9% for all tested concentration factors. Sodium rejection was observed to increase slightly over the duration of testing but remained less than 22% by the end of the study. Permeate flux declined by from an initial average of 26GFD to 17GFD at 6x VCF under constant pressure.

NDX-for-Dye-Desalting-&-Dye-Concentrationmap Figure 1. Flux and rejection performance of Synder NDX according to VCF.


In a feed stream comprised of 3% dye and 5% NaCl, NDX exhibits consistently high dye rejection and high salt passage rates through 6x VCF. Despite a high concentration of dissolved solids, NDX demonstrates solid flux performance under relatively low operating pressures. These results indicate that the Synder NDX membrane is well-suited for dye concentration and desalting applications in the textile industry.