Synder NFW Nanofiltration Membrane
Background
The oil and gas industries have come under increased pressure to find cost effective methods to control the formation of scale in their use of seawater. The removal of sulfate, which has roughly an 8% concentration in sea water, is the key step for scaling reduction at offshore platforms. If untreated seawater is mixed with formation water, which contains barium and strontium, significant barium and strontium sulfate scaling and reservoir souring can occur. The use of nanofiltration membranes with high sulfate rejection and monovalent and divalent ion selectivity would be a cost effective method for achieving sulfate removal. Synder’s NFW membrane was evaluated against a leading competitor’s NF membranes for sulfate removal in synthesized seawater.
Feed Solution, Membrane, Operating Parameters
Table 1: Composition of Synthesized Water
| Ions | Concentration (mg/L) |
| Sodium | 11,200 |
| Potassium | 370 |
| Calcium | 400 |
| Magnesium | 1,400 |
| Bicarbonate | 140 |
| Sulfate | 2,650 |
| Chloride | 19,963 |
| TDS | 36,123 |
Table 2: Operating Conditions and Membrane Specifications
| Feed Solution | |
| Material | Synthesized Seawater |
| Conductivity (ms/cm) | 70 |
| pH | 6.8-7.6 |
| Temperature (°C) | 8-25 |
| Synder Membrane | |
| Element | NFW-2-2540HF |
| Spacer Size (mil) | 31 |
| Surface Area (ft2) | 28 |
| Competitor’s Membrane | |
| Spacer Size (mil) | 30 |
| Surface Area (ft2) | 27 |
| Operating Parameters | |
| Element Inlet Pressure (PSI) | 110 |
| Pressure Drop (PSI) | 10-15 |
| Crossflow Rate (GPM) | 4.5-5.1 |
| Run Time | 165 minutes |
| Feed Volume (Gal) | 15 |
Results
The membranes were tested for permeate flux, sulfate rejection, permeate sulfate concentration, and overall salt rejection (based on conductivity). Sulfate concentration was determined by a USEPA approved turbidimetric method for both permeate and feed samples via a HACH spectrophotometer. Based on the information displayed in Table 3 below, the two membranes have similar water flux and MgSO4 rejection under the same conditions (110 psi, 25 °C, ~5 GPM crossflow rate, 2000 ppm MgSO4).
Table 3: Performance Results
| Filtration Results | NFW | Leading Competitor |
| Average Permeate Flux (GFD) | 28 | 20 |
| Sulfate Rejection (%) | >99 | <97.5 |
| Sulfate Concentration in Permeate (mg/L) | <30 | >50 |
| Overall Salt Rejection (%) | 20 | 26 |
Conclusion
In this trial, Synder’s NFW membrane outperformed the leading competitor in removing sulfate from synthetic seawater. While the membranes showed similar water flux and MgSO4 rejection under the same operating conditions, the NFW showed greater than 99% sulfate removal efficiency with less than 30 mg/L SO4 in the permeate. In addition to the higher sulfate rejection and selectivity, the NFW membrane displayed a 40% higher steady state flux than the competitor’s NF membrane. This combination of greater flux and improved rejection suggests that Synder’s NFW is well suited for seawater sulfate removal.
