## 4 Results and Discussion
The comparison of the coalescence performance for the filter media coated using three commercial solutions from NanoX is presented in Figure 4:3 The differences between them are very pronounced. The EC1206 coalescing filter operates in a very similar way to unmodified material; however, the dP values are higher, and the upper limit of the dP sensor was exceeded after twelve hours. Moreover, the stepwise increase of the pressure drop caused by the flow interruption was not eliminated. This issue was significantly reduced for both oleophobic coatings, EC5028 and EC5029. In the case of material coated by the EC5029, a very fast increase of the pressure drop was observed, reaching the maximum measurable value in 5 h (see Figure 10). Although for this material the efficiency was the highest, the filter was blocked by the oil, which was probably kept on the upstream part of the filter. During the breaks of the system operation, an additional amount of oil was probably pushed out from the porous material driven by the capillary forces, which caused an additional increase in the dP. The filter modified using the EC5028 performed the best. The dP jumps were significantly reduced when the element was saturated with the oil. In addition, the efficiency did not decrease at the end of the test, which was observed for the unmodified material. The results of the oil mist separation experiment for PDMS-coated media are presented in Figure 4:4 Very similar profiles of the pressure drop versus time were obtained for all three concentrations; however, the lowest terminal dP value and the smallest variations for the saturated element were observed for the modification carried out using the 0.2% concentration of the polymer in the hexane. Figure 4:5 The fractional efficiency for the unmodified filtration material at the end of the experiment (i.e., when the filter structure was saturated with the oil). Based on the test results for flat media, the EC5028 and PDMS 0.2% modifications were selected for further testing in the form of the pleated cartridge filter. The selection criteria were as follows: a stable performance over a time of experiment and a minimal pressure drift when saturated. The additional layer of thickness \(\sim\)3 mm made of polyester wrapped on the pleats was fitted on the outlet as a protection of the gas stream from re-entrainment. Although the flow rate was recalculated to obtain the same superficial velocity through the filtration material, a different geometry and the presence of the afore-mentioned drain layer were responsible for the observed slightly higher values of the pressure drop for the pleated cartridge when compared to the flat material (Figures 9 and 12). The presence  
Figure 4:6 Experimental results for the filters modified with the PDMS. Figure 4:7 Experimental results for the filters modified using commercial coatings from NanoX. of a drain layer helped to reduce the amount of re-entrained droplets in the unmodified element; however, this negative phenomenon was not fully eliminated (Figure 13). In the case of coalescer modified with the PDMS, no droplet carryover in the purified gas was observed, hence the separation efficiency of the saturated element was not reduced (this negative effect was not observed for the test of flat material either, where no drain layer was included). A pronounced difference in operation was obtained for the EC5028 modification on the pleated cartridge when compared to flat media. The separation efficiency was very high, but due to a different geometry, the material was more extensively blocked on the inlet with the oil accumulated between adjacent pleats. This is a possible reason why a fast increase of the dP above the 10 kPa was observed for the EC5028 coating on the cartridge filter (Figure 12). The best-performing filtration material obtained for PDMS-coated fiberglass from a 0.2% solution was also verified in a much longer experimental program in which a single element was used five times.