Glycerol (CAS 56-81-5): storage and disposal

Glycerol is a thick, clear liquid found neat on school and college shelves, in pharmacy and veterinary stock, and in histology and pathology labs as an ingredient of mounting media. It is not classified as hazardous on the sources we checked, though it remains a chemical waste that needs an accurate description. It ignites with strong oxidisers, notably permanganate, which is the pairing to watch.

CAS number: 56-81-5
Form: Liquid
Storage class: General
Usual EWC code: 16 05 09

What to do this week

Check the label is readable and write down the opened date if it is not already there.
Check it is stored as general stock and apart from the items listed under "Do not store with".
If you no longer need it, add it to your disposal list so it goes on the next collection.

Safe storage in a school or lab

A screw cap bottle is how glycerol arrives, and the thick liquid leaves a sticky residue on the thread and the shelf. Keep the cap clean and tight, because it absorbs moisture from the air. A dry, labelled store is right, dated on arrival and kept away from food grade supplies. Keep it clear of chromium trioxide, nitric acid, perchloric acid, potassium permanganate and sulfuric acid. Permanganate can ignite or explode with these materials, and chromium trioxide can ignite organic liquids on contact. Mounting media in a histology store belong with the bench reagents, not beside oxidising stock.

How to tell it has deteriorated

Moisture is how glycerol shows its age. It absorbs water from the air, so a bottle opened many times may run thinner than a fresh one, and a very old bottle often has a wet, sticky neck and a label spotted with drips. Mounting media made with it can go cloudy or grow mould, and jelly types can set or dry out around the cap. Sound stock is a clear, thick liquid with a clean thread. Crystals, mould or a sour smell are not expected on neat glycerol, and a bottle showing them is recorded as contaminated and left closed.

How it must be disposed of

By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a non-regulated or low hazard laboratory pack with compatible chemicals.

Waste code 16 05 09 covers laboratory chemicals not classified as hazardous on the sources we checked, and it travels with a waste transfer note. A hospital, pharmacy or pathology holder uses 18 01 07, and a veterinary practice uses 18 02 06. Mounting media take their description from the label, since they may hold other ingredients. Specialist collection is the only route. Even with a mild classification, slow moving glycerol must not go to a drain, a bin or a skip, and nobody should try to treat it first.

Waste codes and transport details for Glycerol
EWC code, laboratory chemicals	16 05 09
Human healthcare setting	18 01 07
Veterinary setting	18 02 06
Hazardous waste	No

The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.

Do not store with

Named chemicals to keep apart

Chromium trioxideChromium trioxide can ignite organic liquids on contact.
Nitric acidNitric acid reacts violently with organic solvents and can ignite them or build pressure in waste bottles.
Perchloric acidPerchloric acid forms explosive mixtures with organic material.
Potassium permanganatePermanganate can ignite or explode with these materials.
Sulfuric acidConcentrated sulfuric acid reacts violently with these materials.

Common quantities we collect

Usually held as: neat, mounting media.

Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.

Where it is commonly held

Questions

Pharmacy glycerol is not classified as hazardous. Can it go in the ordinary bin?

No. It is still a chemical waste and has to be described accurately under the Duty of Care. It goes by specialist collection with a waste transfer note, not into the bin.

Why is glycerol kept away from potassium permanganate?

Permanganate can ignite or explode with it, and glycerol ignites with strong oxidisers in general. Keep them on separate shelves, and never leave them to share a tray or a drip catcher.

How should glycerol mounting medium be described for collection?

By the label on the bottle. Mounting media can hold other ingredients, so give the product name as printed, the amount left and its condition, and say if it has gone cloudy or mouldy.

Our glycerol bottle now runs thinner than before. Is it still usable?

It has taken up water from the air, which is expected with repeated opening. Whether it suits your work is a lab decision. For storage, tighten the cap, keep the neck clean and date the bottle.