Many refineries add a small dose of citric acid before bleaching. Far from incidental, this practice has a clear technical purpose and works in synergy with activated bleaching earth. This guide explains why citric acid pretreatment improves bleaching results.
The Problem of Non-Hydratable Phospholipids
Some phospholipids form complexes with calcium and magnesium that do not hydrate during water degumming. These non-hydratable phospholipids (NHP) survive into the bleaching step and consume adsorbent capacity. Citric acid helps break these metal complexes.
How Citric Acid Works
Citric acid chelates calcium and magnesium ions, converting non-hydratable phospholipids into a hydratable form and freeing trace metals. This makes both the phospholipids and the metals far easier for the bleaching earth to adsorb.
The Combined Effect
With citric acid pretreatment, the bleaching earth spends less of its capacity fighting NHP and metals, leaving more capacity for colour removal. The result is better colour at the same dosage, or the same colour at lower dosage.
Dosage and Sequence
Citric acid is typically dosed as a dilute solution into the oil before or at the start of bleaching, at small levels (often around 0.05–0.1%). The exact dose and contact are tuned to the oil and the metal/phospholipid load.
Maximising the Benefit
The synergy is greatest when paired with a high-quality, high-surface-area earth. Bleach Master's strong adsorption capacity takes full advantage of the cleaner, citric-acid-conditioned oil.
Frequently Asked Questions
Why add citric acid before bleaching?
Citric acid chelates calcium and magnesium, converting non-hydratable phospholipids into a removable form and freeing trace metals. This lets the bleaching earth focus its capacity on colour removal.
How much citric acid is used?
Typically a small dose, often around 0.05–0.1% as a dilute solution, added before or at the start of bleaching. The exact level is tuned to the oil's metal and phospholipid load.
Does citric acid reduce bleaching earth consumption?
Indirectly, yes. By removing NHP and metals, it frees the earth's capacity for colour bodies, allowing better colour at the same dosage or the same colour at lower dosage.
Does this work with any bleaching earth?
The synergy applies broadly, but it delivers the most benefit when paired with a high-surface-area, high-activity earth that can capitalise on the cleaner conditioned oil.
Need Activated Bleaching Earth for Your Refinery?
Contact Umiya Minerals for product samples, technical data sheets, and bulk pricing. We supply pan-India from Bhuj, Gujarat.