Filter Aids & Media
Why filter aids are needed
Very fine solids — seed fines in crude oil, or spent bleaching earth after bleaching — quickly plug a plain filter, slowing or stopping flow. Filter aids solve this by forming a porous, permeable layer that traps the fines while letting oil pass, keeping the filter productive. They are used across the filtering stage and in refining wherever a solid must be separated from oil at high clarity.
Diatomaceous earth, perlite and cellulose
Diatomaceous earth (DE, kieselguhr) — fossilized diatom silica — is the classic filter aid, available in grades from fast (coarse) to fine (high clarity). Perlite, an expanded volcanic glass, is a lighter alternative. Cellulose fibres are used alone or blended, and are favored where mineral aids are unwanted. Each is chosen by the clarity needed and flow rate acceptable — finer aids give brighter oil but slower flow. Food-grade quality is essential for edible oil.
Pre-coat, body feed and filter cloths
Filter aids are used two ways. A pre-coat is deposited on the filter surface first, forming the initial permeable layer; body feed is dosed continuously into the oil so the building cake stays porous rather than blinding. In a plate filter press, filter cloths form the actual barrier, sometimes with a filter-aid pre-coat on top. Choosing aid grade, cloth and dosing to match the solids and clarity target is what keeps clarification running smoothly and the oil bottle-bright.
Disposal, food safety and choosing a grade
Spent filter aid leaves the process as an oily cake that must be handled and disposed of responsibly, much like spent bleaching earth; where the two are filtered together after refining, the combined cake is managed as one waste stream. Selecting the right aid grade is a balance familiar across filtration: a finer aid gives brighter oil but slower flow and more aid consumed, while a coarser aid flows fast but clarifies less. Because everything here contacts edible oil, only food-grade filter aids and cloths may be used, and suppliers should provide food-contact documentation. Matching aid, cloth and dosing to the specific solids load — seed fines in crude oil behave differently from fine spent earth — is what keeps a clarification step both productive and consistently bright.
Where it is used
Filtering · Refining (bleaching filtration)
Indicative reference
| Parameter | Typical |
|---|---|
| Common aids | diatomaceous earth, perlite, cellulose |
| Media | filter cloths (in filter press) |
| Use modes | pre-coat (thin layer on the cloth) + body feed (~0.1–0.5% of oil, dosed into the stream) |
| Grade trade-off | fine grade = clearer oil but slower flow |
| Requirement | food-grade quality |
FAQ
What is a filter aid?
A porous material (like diatomaceous earth or perlite) added to oil filtration to trap fine solids and keep the filter from blinding, maintaining flow and clarity.
What is diatomaceous earth used for in oil?
As a filter aid — its fine silica structure traps solids while letting oil pass. It clarifies crude oil and helps remove spent bleaching earth after refining.
What is the difference between pre-coat and body feed?
Pre-coat is the initial filter-aid layer laid on the filter surface; body feed is aid dosed continuously into the oil to keep the filter cake porous during the run.
Do filter aids need to be food-grade?
Yes — anything contacting edible oil must be food-grade and compliant with applicable food-safety rules.