Glycerine — Frequently Asked Questions

Use refined glycerine made to a pharmacopoeia monograph, normally USP or Ph. Eur. at 99.5% or higher. These grades are water-white and nearly odourless, and they are tested for diethylene glycol and ethylene glycol, which matters for anything applied to skin or put in the mouth. Technical glycerine can have a similar assay, but it is made to a producer specification rather than a monograph and is intended for industrial uses such as resins, inks and antifreeze.

MONG means matter organic non-glycerol: fatty acids, soaps, esters and other organic impurities. It is usually calculated as 100 minus the glycerol, water and ash percentages. High MONG raises refining losses, fouls distillation equipment and can cause foaming, so refiners set a maximum and value the crude against it. Crude from well-run fat splitting tends to have low MONG, while poorly processed biodiesel crude can be much higher than the usual 1–5%.

Both are refined grades, and the difference is mainly water content. The 99.7% grade suits moisture-sensitive uses such as some polyurethane systems and pharmaceutical processes, and it leaves a little more margin if the product picks up water in storage. For most cosmetic, food and general uses, 99.5% is sufficient. Because glycerine is hygroscopic, poor storage can take either grade below its assay, so the specification only helps if the tank stays dry.

Glycerine absorbs moisture from the air. Each time a tank breathes during filling, emptying or temperature changes, it draws in humid air, and the glycerine slowly dilutes. Over weeks, a refined grade can fall out of specification. A nitrogen blanket or a desiccant breather keeps the headspace dry. Keep drums and IBCs tightly closed, and reseal part-used containers straight away.

Only in a few applications. Crude glycerine contains water, catalyst salts, MONG and possibly methanol, which make it unsuitable for most formulated products. It is used as feedstock for refiners, in anaerobic digestion for biogas and in some chemical processes, and in animal feed only where regulations and the specific grade allow. For resins, personal care or food, it has to be refined to technical or pharmacopoeial grade first.

Ask for an origin declaration with the quotation that states whether the grade is vegetable, animal or synthetic and, where relevant, which oils it comes from. Glycerine from different origins can pass the same monograph tests, so the certificate of analysis alone does not show origin. If your market needs kosher, halal or sustainable palm evidence, ask for the certificate and its scope for the refining site. Check that each certificate names the grade you are buying.