Efficient removal of aerosol oil-mists using superoleophobic filters

Aerosol oil mists are generated from a number of processes such as friction, vibration, high speed gas transmission, and lubrication. Aerosol oil mists have been found to pose several problems including clogging, corrosion, wear, machinery contamination, and increased energy consumption. Therefore, elimination of aerosol oil-mists or even a selected gas type is a prerequisite for dehumidification, compressed air production, respirators, clean room filters, and engine crankcase ventilation. These have several applications in engineering, medicine, aerospace, pharmaceuticals, and energy production.

Most aerosol-mist filters are normally based on coalescence mechanism where oil droplets are captured by continuous clogging. Therefore, oil droplets are easily captured when their size is larger as compared to the filter pore sizes. It would then imply that filters with smaller pore sizes have higher filtration efficiency for small oil mists. Unfortunately, reducing the pore sizes generally leads to increased air-flow resistance. This reduces air flow speed and increases energy consumption for gas transport. In addition, oil droplets accumulated in small-pore-filters are blown off into the downstream flow, therefore, injuring the filtration efficiency.

Most of the conventional oil-mists filters are majorly based on fibrous materials reference to their small pore size, large surface area, ease of functionalization, excellent flexibility, and mass production capability. Researchers have continuously devoted their efforts in enhancing the filtration efficiency of these filters for oil-mists smaller than 1 µm without necessarily increasing energy consumption. Unfortunately, the filters have been found to have insufficient efficiency for filtering small oil mists. Researchers have then tried to adopt thicker filter mats in a bid to raise the filtration efficiency. Unfortunately, this has increased air-flow resistance and consequently, the cost of energy.

Researchers led by Dr Hongxia Wang from Deakin University in Australia in collaboration with scientists at China University of Petroleum-Beijing demonstrated for the first time that superoleophobic surfaces could significantly improve the filtration performance of small oil-mists. They prepared a superoleophobic surface through a wet chemical coating process implementing perfluoroakyl acrylic copolymer as a material. Their research work is published in journal, Journal of Materials Chemistry A.

The research team used a commercial glass fiber filter as model. After treatment with perfluoroalkyl acrylic copolymer, the filter recorded considerably improved oil-mists filtration efficiency.

Dr Wang highlighted that superoleophobic treatment had a significant effect on improving the filtration efficiency. For a filter thickness of about 1.12mm, they recorded a filtration efficiency for small aerosol oil-mists of approximately 96-99%. The pressure drop was however increased by only 6%, but the downstream oil mist content was reduced by over 85%.  For larger oil mists, the proposed filter had approximately 100% filtration efficiency, and the downstream oil content was close to zero.

The researchers then proposed bounce-collide-drain mechanism to explain the improved filtration performance. This novel concept would be important for the development of high efficiency, low energy consumption gas-liquid coalescing filters.

Professor Tong Lin from Deakin University indicates that this is a breakthrough work. Previously, people used nanofibers to improve oil mist filtration efficiency. Superwettability surface engineering will shed a new light to solve this long standing problem.