What Is Glycerin?

It’s in our food, our moisturisers, our cars and even our rockets. We’re talking about glycerin, of course, and today we’re looking into its structure, how it’s made and even its role in dynamite.

Glycerin was discovered by Carl Wilhelm Scheele in 1783. Even then, it was immediately known for its characterising sweet taste. Scheele even referred to it as the “sweet principle of fat.”

This colourless compound goes by many different aliases, including glycerine and glycerol. While these names are virtually interchangeable, glycerol is sometimes used to refer to the pure chemical product, whereas glycerin can refer to the more impure commercial product.

Structure & Characteristics

Glycerin is a simple polyol compound, meaning that it contains multiple hydroxyl groups. Three hydroxyl groups, to be exact, are contained in glycerin’s structure. This also establishes it as trihydroxy.

Its structure means that it is extremely soluble in water which also characterises it as hygroscopic. This means it is able to attract and hold water molecules from the environment. In nature, glycerin is the backbone of fatty acid esters. Therefore, instead of three hydroxyl groups, three fatty acid molecules are attached.

Glycerin can be characterised by a few attributes. It is:

• Colourless
• Transparent
• Odourless
• Viscous
• Non-toxic
• Sweet-tasting
• Hygroscopic

These properties mean that it has a wide range of uses. In the food industry, it is largely used as a sweetener. Glycerin also behaves well as a humectant, which is a substance that is used to retain moisture. Therefore, it is commonly used in things like moisturisers.

As well as these, it is also used in pharmaceutical formulations, as an emollient and as a key ingredient in resins used to make protective coatings for automotive enamels.

Production of Glycerin

Prior to 1948, glycerin was obtained as a by-product from soaps that contained animal and vegetable fats. However, its production percentage began to increase in the later years as industries began synthesising it from propylene.

Natural Production of Glycerin

In nature, glycerin is generally derived from plant and animal sources, namely soybeans, palm and tallow. In these sources, it occurs as triglycerides. These are esters of glycerin.

When triglycerides undergo hydrolysis, they produce a fatty acid derivative. The esters in fatty acids can then be combined with lyre to make soap, where glycerin can be separated as a by-product. There are many processes that have been used in the natural production of glycerine. These include:

• High-pressure splitting of fatty acid esters
• Transesterification
• Obtaining glycerin as a by-product of biodiesel production

Disadvantages of Natural Production

The hydrolysis of triglycerides to get glycerin often results in a crude product of variable quality. Therefore, it is necessary for it to undergo purification which can be expensive.

Crude glycerin is purified using activated carbon, which removes organic impurities through chemical absorption. Alkali can then be used to remove any unreacted glycerin esters, and finally ion exchange is used to remove salts.

To obtain high purity glycerin, the product is put through a multi-step distillation process.

Synthetic Production of Glycerin

Producing glycerin synthetically can be done through various processes involving propylene. The most commonly used method is as follows:

1. Propylene undergoes chlorination to produce allyl chloride
2. Allyl chloride is oxidised with hypochlorite to produce dichlorohydrins
3. Dichlorohydrins react with a strong base to form epichlorohydrin
4. Epichlorohydrin is finally hydrolysed to produce glycerin

Dangers of Synthetic Production

Many people do tend to prefer glycerin that has been naturally obtained. This is because of the use of epichlorohydrin in the above process, which has been classified as a carcinogen and can be toxic to the human body. For this reason, glycerin that has been obtained from animal or vegetable oils and fats is safer to use than synthetic productions.

Glycerin Reactions

Although glycerin appears under guise in many everyday things, it is also used in more explosive reactions that surpass the everyday object.

Flaming Volcano

We’ve all seen, and maybe even made the papier-mâché and baking soda volcano in high school science class. However, there is a more adult-friendly version that glycerin plays a huge part in.

Start by crushing some potassium permanganate (KMnO₄) into a fine powder and arranging it into a volcano shape on a heat proof surface. Potassium permanganate is a crystalline solid with a purplish hue. In a variety of reactions, it behaves as a strong oxidising agent.

Once your potassium permanganate is in position, use a dropping pipette to slowly drip glycerin into the top of the heap. After a few seconds, the mixture will begin to smoke before bursting into purple-pink flames.

When these two substances meet, glycerin is oxidised with potassium permanganate in an exothermic reaction. The carbon contained in it gets oxidised into carbon dioxide while the hydrogen gets oxidised into water. Because of these chemical reactions, enough heat is generated to cause glycerin to evaporate. As this continues it eventually ignites, and the presence of potassium ions is what makes the flames purple.

This process is very similar to fuel being burned, except the oxygen comes from the potassium permanganate instead of the air.

Dynamite

Glycerin may be used in your favourite pudding, but it is also contained in some of the most powerful explosives known.

When you add glycerin to a concentrated mixture of nitric and sulphuric acid, it reacts to form nitroglycerin (C₃H₅(ONO₂)₃). This is the key ingredient used in dynamite, and joins nitrocellulose in propellants like rockets and missiles.

Nitroglycerin contains as much as 19% nitrogen and a sufficient supply of oxygen atoms. These atoms oxidise the carbon and hydrogen atoms while nitrogen is being liberated, leading to the powerful explosion associated with dynamite.

There are a range of applications that use glycerin. At ReAgent, we provide glycerin products for analytical, laboratory and general use, and supply them in sizes ranging from 500ml drums to 1,000L IBCs. Our glycerin is among the highest quality blends in the UK, so place your order today!