Sometimes during a synthetic organic reaction workup, small particulate matter clogs an attempted filtration. This situation is called filter ‘blinding’. The cause of this blinding may be the major component itself or some small particulate solid or sticky impurity. Filter papers clog more readily than filter cloths and filter cloths differ from each other depending upon the material of their construction. When filter paper clogs in developing the small-scale laboratory procedure, filter pads cut from the filter cloth material used in your pilot plant or plant should be tested. Perhaps what you are seeing using filter paper in the lab will be more manageable at scale but you need to confirm this.
If the blinding of the filter is attributable to impurities and not the major compound of interest, a first filtration of the solution before crystallization is induced can remove a useful amount of the material that is blocking your main filtration. This ‘sparkling’ filtration can use a thin layer of a filter aid even include charcoal.
To overcome the most difficult problems filter aids (Celite®, Hyflo®, kieselgur) are added to the hot mixture before the main product has precipitated, the solution is stirred vigorously, and then slowly cooled to bring out the main product onto the inert solid. The filter aid and product are collected together and the majority of the dissolved byproducts, co-products, and processing chemicals may be carried away with the filtrate. The product can be dissolved off the filter-aid and the workup of the product, now in solution, continued.