In general , the VFD will be used to overcome the pressure drop across filter with its age and the differential pressure will be maintained by adjusting the exhaust dampers though pressure transmitter.
you can consider to use nutch filter,ANFD and Nauta drier.etc, provided if we know the process details like initial moisture, solvents, particle size etc.
I think , you have to use 0.01micron filter if the air comes to direct contact with product like jetmill.Preferably u can use the ss316 pipe after this filter.