Basic knowledge of cellulose filtration aid products

In the cellulose filtration operation, in order to reduce the filtration resistance, increase the filtration rate or obtain a highly clarified filtrate, an auxiliary powdery substance is added, which is called cellulose filtration aid products.

Cellulose filtration aid products are auxiliary materials used to reduce filter cake resistance or filter media resistance. Usually some hard powdery or fibrous solids. Filter aids are only used in filtration operations for the purpose of obtaining a clean filtrate. There are two types of filter cakes formed by filtration: one type has considerable rigidity, and the structure does not change with the increase of operating pressure, which is called incompressible filter cake; the other type of filter cake has a structure that changes with the increase of operating pressure, resulting in filter cake. The filtrate flow channel in the filtrate shrinks, and the flow resistance of the filtrate increases sharply, which is called compressible filter cake.

For compressible filter cakes, adding cellulose filtration aid products can increase its rigidity and prevent the increase of filtration resistance. When filtering the suspension containing viscous fine particles, a dense filter cake layer is often formed. Adding filter aids can change the filter cake structure and reduce the filter cake resistance. How to use the filter aid: one is to mix the filter aid with the suspension to be filtered in a certain proportion, and then filter together; the other is to prepare a suspension containing only the filter aid, filter first, and filter it on the filter medium. A precoat is formed before the slurry is filtered. The filter aid pre-coating can withstand certain pressure without deformation, and can prevent the filter cloth from increasing resistance due to clogging.

Commonly used cellulose filtration aid products include diatomite, perlite, cellulose, asbestos, graphite powder, sawdust, magnesium oxide, gypsum, activated carbon, acid clay, etc. Diatomite has a large specific surface area, can adsorb colloidal substances, and form a filter cake with a high porosity. It is the most widely used filter aid. Paper pulp is mostly used as a precoat to prevent early clogging of the filter cloth.