Comparison of Filtration Properties and Air Flow Characteristics of Membranes and Fibrous Depth Filters for Their Application in Air Purification

Providing particulate-free air is a major challenge not only in the chemical industry but garnered attention during the worldwide Covid-19 pandemic last year. Filter materials are frequently used for the separation of particles from air. The choice and assembly of the filter material is critical and must be done carefully to ensure high filtration efficiencies and low pressure drops. In this work, the air flow and filtration characteristics of commonly applied depth filter materials are examined and compared with those of a membrane.

The airflow characteristics through a fibrous coarse polyester (porosity 98%, fiber diameter 25µm) and fiberglass depth filters (porosity 94%, fiber diameter 4 µm) was examined. These different filters are commonly used in ventilation systems. Filtration efficiencies were examined using spherical polystyrene latex nanoparticles (0.5 and 1 µm) as well as with potassium chloride particles. Experiments were conducted to measure the filtration efficiency and pressure drop across the different filter media at a constant face velocity of 0.07 m/s. This data was then compared to model data using single fiber efficiency models. The aerosol experiments were then expanded to include Solecta PVDF 400 membranes (porosity 46%, pore diameter 45 nm), which are commonly used in microfiltration for the removal of bacteria, fungi, fats, and microorganisms. Pressure drops and filtration efficiencies of the fibrous filters were examined and expected results regarding these parameters were found.

The glass fiber filter gives higher filtration efficiencies than the coarse material but having a higher-pressure loss. An underestimation of filtration efficiency between model data and experimental data especially for the polyester filter were found and attributed to, for example, electrostatic effects in the synthetic media. These effects from coulomb or dipole forces that can appear in synthetic media but are not covered yet by the model applied here.

The membrane was shown to have a much higher filtration efficiency than the fibrous depth filters providing very clean air but also having a significantly higher pressure drop. This research indicated different behavior of these materials. Due to the complementary advantages of both material types such as high filtration efficiency of the membrane and low pressure drop of depth materials a combination of these materials could be a promising approach for further analysis.