Palm Acid Oil: Uses, Specifications and Buying Tips
Palm acid oil (PAO) is a by-product of chemically refining palm oil. The soapstock removed during alkali neutralisation is split with acid to recover the fatty acids, giving an oil with more than 50% free fatty acids. It is used in laundry soap, oleochemicals, biodiesel and animal feed fats such as calcium soaps.
This guide explains how palm acid oil is made, how it compares with PFAD and other acid oils, where it is used, and which specifications decide its value.
How palm acid oil is made
Crude palm oil is refined either physically or chemically. In chemical refining, caustic soda is added to neutralise the free fatty acids, which form soaps. These soaps, along with some entrained neutral oil, separate out as soapstock. Treating the soapstock with sulphuric acid splits the soaps back into fatty acids, and the oily layer that rises is acid oil.
InfoSAWIT describes PAO as a by-product of the alkali refining of palm oil with a free fatty acid content above 50%, good neutral oil yield and moisture of just 2% to 3%. The same process applied to soybean, rice bran, sunflower or cottonseed oil gives soya acid oil, rice bran acid oil and so on.
Palm acid oil vs PFAD and other acid oils
| Material | How it is produced | Typical FFA | Main uses |
|---|---|---|---|
| Palm acid oil (PAO) | Acid splitting of soapstock from chemical refining | Above 50% | Soap, oleochemicals, biodiesel, calcium soaps for feed |
| Palm fatty acid distillate (PFAD) | Distilled off during physical refining | About 82% | Feed, laundry soap, oleochemicals, biodiesel |
| Palm sludge oil (PSO) | Recovered from mill effluent | Up to 80% | Soap, boiler fuel, low-grade biodiesel feedstock |
| Soya, rice bran, sunflower acid oils | Same soapstock route as PAO | Varies by source | Soap, biodiesel, feed, oleochemicals |
PFAD composition from IChemE (81.7% FFA, 14.4% glycerides plus vitamin E, sterols and squalene). PSO figures from the Malaysian Palm Oil Board.
The source oil changes the fatty acid profile. Palm-based acid oils are rich in palmitic acid and are more saturated, so they have a lower iodine value than soybean or sunflower acid oils. That makes palm acid oil firmer and better suited to hard laundry soap, while the more unsaturated acid oils suit softer soaps and some oleochemical routes.
Uses of palm acid oil
Laundry soap and detergents
The traditional outlet. Acid oil is saponified with caustic soda to make laundry bars and soap noodles. InfoSAWIT notes that palm acid oil’s fatty acid content improves soap hardness and cleaning performance in industrial formulations.
Oleochemicals
Acid oil can be split and distilled into fatty acids, which then become esters, fatty alcohols and other intermediates for lubricants, surfactants and cosmetics. Glycerine is recovered along the way.
Biodiesel
High-FFA feedstocks cannot go straight into the standard alkaline biodiesel process, because the free acids form soap and cut yield. Industry practice is to first lower FFA, either by acid esterification or by glycerolysis. One process note states that acid oil must be brought below about 3% FFA before standard biodiesel manufacture, and that soya, cottonseed and rice bran acid oils are among the main biodiesel raw materials in India.
Animal feed fats
PAO is used to make calcium soaps, a rumen-protected fat for dairy cattle, and as an energy source in compound feed. Feed use needs tighter control of impurities and oxidation.
Specifications that set the value of acid oil
Neshiel supplies acid oil from rice bran, soybean, palm, sunflower and mixed sources. Its standard acid oil specification is shown below; palm acid oil will show a lower iodine value because palm oil is more saturated.
| Parameter | Neshiel typical value | Why it matters |
|---|---|---|
| Free fatty acid (FFA) | 50% to 70% (55% typical) | Decides the processing route and yield |
| Total fatty matter (TFM) | 98% | Soap makers effectively pay for TFM |
| Moisture | 1% | Water is dead weight and promotes hydrolysis |
| Unsaponifiable matter (USM) | 3% | Does not form soap; lowers soap quality |
| Saponification value | 190 | Sets caustic soda requirement |
| Acid value | 110 | Direct measure of free acidity |
| Iodine value | 118 (lower for palm) | Indicates unsaturation, soap hardness and oxidation risk |
For soap making, TFM and USM matter most. For biodiesel, FFA, moisture and impurities decide pre-treatment cost. For feed, ask for oxidation and contaminant data as well.
Testing acid oil on arrival
Acid oil is a variable material, so testing every tanker is standard practice. The core checks are:
- FFA by titration with alkali, reported as oleic or palmitic acid, using a standard method such as AOCS Ca 5a-40.
- Moisture by Karl Fischer titration or a hot-plate loss test.
- MIU, the trade term for moisture, impurities and unsaponifiables together. Many contracts set a single MIU limit and deduct for the excess.
- TFM, which soap makers use to calculate how much soap the lot will yield.
- Colour and odour, which flag oxidised or contaminated material.
Keep a retained sample from every delivery, sealed and labelled, until the lot has been used. It settles disputes quickly if a batch of soap or biodiesel goes off-spec.
Buying palm acid oil in bulk
- Specify the source oil (palm, soya, rice bran or mixed). Profiles differ enough to change soap hardness and process yield.
- Contract on FFA, TFM, moisture and USM, with a price adjustment for lots outside limits.
- Draw samples from the tanker at loading and on arrival, and test both.
- Store in clean, dry tanks. Moisture and heat raise FFA further and darken the oil.
- Check the supplier’s track record on consistency, not just the price per tonne.
Neshiel supplies acid oil in tanker loads of about 25,000 kg. For a deeper supplier checklist, read our guide on how to choose a reliable acid oil supplier.
Need palm, soya or rice bran acid oil in tanker loads? Contact Neshiel for specifications and pricing, or visit our acid oil supply page.
Frequently asked questions
What is palm acid oil used for?
Laundry soap, oleochemicals such as fatty acids and esters, biodiesel after FFA reduction, and calcium soaps and energy fats for animal feed.
What is the difference between palm acid oil and PFAD?
PAO comes from acid-splitting soapstock in chemical refining and has above 50% FFA. PFAD is distilled off in physical refining and has around 82% FFA.
Can palm acid oil be used for biodiesel?
Yes, but its free fatty acids must first be reduced, typically below about 3%, by esterification or glycerolysis before standard biodiesel processing.
What does TFM mean in acid oil?
Total fatty matter: the share of the oil that is fatty acids or glycerides, which is what turns into soap.
