Preparation of combined oleophobic fibre filters with pore size gradients and their high-efficiency removal of oil mist droplets

Pore size is a key factor that influences the removal of oil mist droplets by a coalescence filter. However, the influence of the pore size distribution among different filter layers on filtration performance has not been thoroughly explored. In this work, a method for preparing glass fibre filtration media with a specific structure as well as good oleophobic properties and mechanical strength was developed by combining the wet-spinning method and immersive modification. The prepared single-layer media were combined in various three-layer structures with increasing pore size gradient, decreasing pore size gradient and uniform pore size distribution. The trends in the pressure drop and droplet penetration ratio of the resulting combined filters over time were analysed systematically. The results demonstrated that in the combined filter, the first layer material had a significant influence on the filtration process and steady-state performance. Throughout filtration, the pressure drop of the filter with a decreasing pore size gradient had layering characteristics, which was conducive to capturing droplets within different particle size intervals in different stages and thereby relieving the operational pressure on different layers. Hence, the filter with a decreasing pore size gradient had a relatively low steady-state pressure drop and the best comprehensive filtration performance for submicron droplets. However, the filter with an increasing pore size gradient had the highest separation efficiency for submicron droplets and its concentration of steady-state downstream droplets was 19% lower than that in the filter composed of three layers of minimum pore size materials. The proposed mechanism by which the filter with the increasing pore size gradient improved the coalescence filtration efficiency for submicron droplets was based on capillary theory.

Automated summary

Pore size is crucial for oil mist droplet removal by coalescence filter, but the influence of pore size distribution on filtration performance is not well explored. This study developed a method to prepare glass fiber filtration media with specific structure, oleophobic properties, and mechanical strength. The combined filters with increasing, decreasing, and uniform pore size distribution were analyzed for pressure drop and droplet penetration ratio. The filter with decreasing pore size gradient had the lowest steady-state pressure drop, best filtration performance for submicron droplets, and layering characteristics. The filter with increasing pore size gradient had the highest separation efficiency and lower downstream droplet concentration based on capillary theory.