Ecoat Paint: UF Permeate Recovery

Synder UF Membranes 
Background
Cathodic paint is used in electrocoating processes to create a corrosion resistant film on the exterior of metal products.  These products are submerged in paint baths and painted via electrophoretic deposition.  After painting, products are submerged in rinse tanks, causing overflow into the paint baths.  It is essential to combat paint dilution and maintain stable paint concentration, otherwise coating and corrosion resistance may be compromised.  Ultrafiltration membranes are the industry standard for both concentrating cathodic paint and generating water for the initial rinse stages.  UF membranes should pass less than 0.3% solids for an acceptable concentration, sufficiently clean permeate, and effective pretreatment for Nanofiltration or Reverse Osmosis systems.  Synder’s V4, V5, and V6 PVDF UF membranes were tested for their performance in concentrating and recovering cathodic paint. The experiment was conducted on a single cell cross-flow filtration unit with a micro-pump.  The paint tested was supplied directly from the manufacturer.

Feed Solution, Membrane, Operation Condition 

 Feed Solution  
Material Cathodic Paint  
Dry mass (wt/wt) 12.8% 
 Membrane  
 Type V4, V5, V6 
 MWCO 70, 200, 500 kDa 
 Material PVDF with Surface Treatment 
 Operating Parameters  
 Inlet Pressure (PSI) 60 
 Temperature (°C) 19-27 
 Crossflow Rate (GPM) 0.9 

Results
The dry mass in the permeate from the UF membranes is listed in Figure 1. The results show that both the V4 and V5 membranes passed less than 0.3% dry mass, which meets industry standards.  The average flux of the V5 and V6 was approximately 18 GFD while the flux of the V4 was approximately 16 GFD. Based on the small amount of dry paint mass in the permeate, both the V4 and V5 membranes are suitable for cathodic paint recovery.

Percentage Dry Mass in Permeate
Figure 1: Percentage Dry Mass in Permeate
Permeate samples from the V4, V5, V6 membranes, and feed