Glycerol vs. Glycerin: What’s the Difference?

The use of glycerol and glycerin is widespread across the world in consumer goods production, and consumers often use both terms interchangeably. Still, are they the same, and, if not, what is the difference between glycerin and glycerol?

Glycerol is the pure form of the chemical compound. We find it directly in the triglycerides of fats and oils. Glycerin is the byproduct of producing fatty acid, fatty ester, or soap and contains 95 percent glycerol. Glycerol and glycerin share the same chemical compound, C3H8O3.

Read on to discover precisely what makes the two compounds different. You will learn their commercial uses and how prevalent glycerol and glycerin are in everyday products. At the end of the article, I have provided a few definitions that should aid your understanding of this topic.

Glycerol and Glycerin: Similar but not the Same 

Glycerol and glycerin are, to the layman, the same, and many use the terms interchangeably. However, while they appear to be the same, they are not since there are subtle differences.

In this section, we will endeavor to tease out exactly how glycerol and glycerin differ. 

What Is Glycerol?

Glycerol is a simple trihydroxy sugar alcohol that at room temperature is syrupy. It has no odor, no color, and is sweet to the taste. It is non-toxic in low concentrations and hygroscopic (source).  

Glycerol refers to the pure form and is a triol compound. Chemists find it in the triglycerides of oils and fats. The chemical compound of glycerol is 1,2,3,-propanetriol, CH2 OH-CHOH-CH2OH, and C3H8O3. 

There are three distinct processes and feedstock used to produce glycerol (source): 

  1. Using propylene synthesis through the hydrolysis of fatty acids. 
  2. Through transesterification of fatty acids and oils.
  3. Fermentation: as a byproduct of fermentation sugar with ethanol.

The hydrolysis, saponification, or transesterification of triglycerides produces glycerol and ester, a fatty acid derivative. The triglycerides in plants and animal sources are where you will find glycerol.

What Is Glycerin?

Glycerin has the same properties as glycerol. It is hygroscopic, virtually colorless, with diuretic and laxative osmotic effects. As a chemical compound, glycerin is a trihydroxy sugar alcohol.

Glycerin shares the chemical compound 1,2,3,-propanetriol, CH2 OH-CHOH-CH2OH, and C3H8O3 with glycerol, but glycerin is less pure; transesterification of oleochemicals (fats and oils) produces glycerin — glycerol is in the esters of fats and oils.

Glycerin is a byproduct of the hydrolyzation of fats and oils, which yields fatty acids or soaps (source).  Glycerin is also a byproduct of propylene, obtained through the process of cracking petroleum hydrocarbons.

The oleochemical industry uses glycerin as the commercial term when purity doesn’t necessarily count. It is important to note that pure glycerin is really pure glycerol.

There are two types of glycerin: natural and synthetic. Also, there are three methods used to obtain glycerin (natural and synthetic) from these processes.

One is the hydrolysis of oil — oil placed under high temperatures and pressure, producing fatty acids and sweetwater. The sweetwater contains 10 to 20 percent glycerol.

Another is the transesterification of oil combined with methanol. This method yields methyl acids and glycerin with a high glycerol content — also used to produce glycerol.

Last, saponification of oil or fat using caustic soda forming lye and lye soap. The soap contains 4–20 percent glycerol. 

However, not all glycerin is natural. The industry makes synthetic glycerin from propylene via epichlorohydrin (a petrochemical). The production of synthetic glycerin has begun to fade away, and most of the glycerin used today is the natural form.

To Summarize

Glycerol refers to the pure substance found directly in the triglycerides of fats and oils. It is a trihydroxy sugar alcohol.

Glycerin refers to the byproduct of producing fatty acid, fatty ester, or soap (from oils or fats) and is a trihydroxy sugar alcohol.

Both glycerol and glycerin are almost entirely non-toxic.

The Discovery of Glycerin and Glycerol

Nobel, Alfred, Plate, Coins, Medal, Portrait, Embossing
Image by IsaacFryxelius via Pixabay

The history leading to the discovery of glycerol and glycerin is a shared one. 

Glycerol was discovered in 1779 by K.W. Scheele, a Swedish scientist. While working on olive oil and lead monoxide saponification, he accidentally discovered a sweet byproduct of the reaction, which he named the sweet principle of fat” (source).

In 1886, Berthelot and Lucea’s work broke down glycerin’s molecular structure to C3H8O3,  three oxygen, and three hydrogen atoms.

During the early 1900s, the French investigator M.E. Chevreul discovered a new way to make fatty acids by adding alkali to fats and oils. The byproduct of this process was glycerin. 

It was Chevreul that unlocked the full potential of glycerin through his discovery of a new way to make fatty acids — fats treated with an alkali — and renamed Scheele’s “sweet principle of fat glycerin.

Prior to 1867, glycerol had yet proven to impact economic or commercial interests until Alfred Nobel was able to stabilize, transport, and handle trinitroglycerin — nitro glyceryl trinitrate, GTN.

The chemical formula 1,2,3-trinitroxypropane is the main explosive ingredient in dynamite. 

Alfred Nobel pushed glycerol into economic and commercial importance. Thanks to him, glycerol blasted its way through natural structures, making mining more efficient. Glycerol paved the way for the building of numerous infrastructure projects (source).

The Many Uses of Glycerol and Glycerin

As discussed above, glycerol and glycerin have many commercial applications across many industries; occasionally, the two may be interchangeable based solely on the product.

For instance, some products require a pure form while others do not.

Glycerol

As a hygroscopic compound, pure glycerol has many applications in both the food and cosmetic industry. 

Glycerol is a humectant, a solvent, a sweetener, a filler in pre-packaged foods, particularly low-fat versions, and a thickener for liqueurs. 

When mixed with water, glycerol is a preservative for a few types of plant leaves and, though not thoroughly tested, may also preserve foods.

Glycerol does not crystallize or foment and resists high temperatures, making it perfect for distilling, unlike other sugars. Vineyards often use glycerol in wine.

Glycerin

Glycerin is also hygroscopic and used to produce urethane foams, alkyd resin, drugs (especially for the gut), foods, tobacco, toothpaste, and cosmetics. For instance, it keeps soaps and lotions from drying out.

When exposed to freezing temperatures, glycerin supercools rather than crystallizing. When mixed with water, glycerin will resist freezing, and it was a perfect ingredient in automobile antifreeze. However, ethylene glycol has replaced it.

However, glycerin-water and glycerin-alcohol solutions are in use for various refrigeration systems and to quick-freeze food.

Another use of glycerin is in soldering fluxes, cement, textiles, and waxes. Due to glycerin’s properties, it makes an excellent solvent.

The food industry also uses glycerin as an emulsifier due to its virtually non-toxic nature.  Glycerin is an ingredient in food packaging (think bread wrappers) and in cans as a lining.

Glycerin produced from oleochemicals plays a role in making detergents, surfactants, soaps, paint, varnish, lubricant, copolymers, and pharmaceutical aids (source).

Glycerin, or specifically nitroglycerin, is a life-saving drug by equalizing oxygen and blood flow to the heart (source).

The Six Classes of Glycerin

Glycerin’s use in food and pharmaceuticals prompted the United States to assign classes and grades to glycerin — not necessary for glycerol as found in its pure form.

Each class of glycerin specifies the grade to use for various commercial purposes. The grades are as follows.

United States Pharmacopeia (USP) glycerin is clear, nearly colorless. Its use requires it to be of high purity with the taste and odor suitable for pharmaceutical and food use. The glycerol content in an aqueous solution must be 95 percent or higher.

Chemically Pure Glycerin (CP Glycerin) should be equivalent in quality to USP glycerin. However, CP Glycerin does not have any requirements, specifications, or standards required of USP glycerin.

Food Grade Glycerin in the United States must meet requirements outlined by the Committee on Food Protection of the National Research Council in the Food Chemicals Codex. The requirements for food-grade glycerin are very close to those of USP glycerin. 

High Gravity Glycerin is a designation in the United States. It refers to a commercial grade of glycerin that is virtually clear and conforms with Federal Specification 0-G-49IC. 

In the United States, Dynamite Glycerin must meet all High Gravity grade specifications other than color, which can’t be darker than the Federal Color Standards.

Saponification Crude (88%) and Soap Lye Crude (80%) are generic terms used in the United States to designate the different grades of crude glycerin recovered from triglycerides. The percentages indicate the content of glycerol. 

  • Saponification Crude is the sweetwater from the hydrolysis of fat.
  • Soap lye crude is leftover from spent lye after concentration in a desalting evaporator.

Glossary of Terms

TermDefinition
EsterA chemical compound derived from an acid 
FeedstockRaw material supplying an industrial process
HydrolysisAny chemical reaction where a water molecule ruptures one or more chemical bonds
HygroscopicThe ability to attract moisture from the surrounding air
NomenclatureThe system for naming things within a profession or field
Osmosis Movement of water through a living cell to a concentration with a higher solute equalizing both sides of the cell.
SaponificationA process that involves the conversion of fat, oil, or lipids, into soap and alcohol by the action of heat and aqueous alkali
TransesterificationA process whereby fat or oil will react with alcohol forming esters and glycerol
TriglycerideAn ester derived from glycerol and three fatty acids
Glossary of Terms

If you enjoy learning about subjects that cross-reference each other, read our article on dilation vs. dilatation. You may wish to further your knowledge of the food industry by reading “Food Types: Understanding the Various Food Groups.”

Glycerine and Glycerol in Hand Sanitizers

Hand sanitizers are one product used every day by most of the world’s population. Most of us probably overuse hand sanitizers and fear drying out our hands.

Isopropyl alcohol serves as the main ingredient in hand sanitizers, which efficiently kills germs but will dry out your skin. Commercial hand sanitizers contain either glycerin or aloe vera, both humectants, to combat the alcohol’s drying nature (source).

There are many recipes online if you happen to be someone who enjoys whipping up hand sanitizer at home.

Glycerol and Glycerin as an Energy Source

Biodiesel is an alternative fuel used in diesel engines. As a renewable source of energy, it has many environmental benefits. No matter the process producing the biodiesel, glycerol is a necessary byproduct.

Through the manufacture of biodiesel, there will be an excess of glycerol. 

There is ongoing research into how to use this overabundance of glycerol. The main idea of the investigation is its use as a source of renewable energy.

For instance, for direct combustion, mixed with animal dung and burned, or mixed with other fuels. 

Can I Use Glycerin Instead of Glycerol?

To answer this question, one must take into consideration what you are using it for. You wouldn’t want to put antifreeze on your face! Most of the glycerin you find for sale will not be pure glycerol.

As such, the labels read glycerin mixed with water or other chemicals. 

Essentially, you are using glycerol because glycerin contains 95 percent glycerol. Therefore, it boils down to what you are making if it requires pure glycerol.  

Glycerin is for sale in stores and online, but you will want to use the USP grade of glycerin. Be sure to carefully read the label for the proper use and possible side effects before using it. The following section will discuss side effects.

Possible Side Effects of Glycerol and Glycerin

While glycerol is an essential additive to food and cosmetics, one needs to be careful with products containing it.

Negative

Pure glycerol may cause the eyes, nose, lungs, and skin to become mildly irritated due to the way it decimates (dries out) moist tissue.

When ingested, vegetable glycerin can cause headaches, nausea, vomiting, excessive thirst, and dizziness. As sugar alcohol, your body cannot absorb it entirely, so you may develop gas and diarrhea if you drink it or eat it.

Positive

However, there are pleasant side-effects from using products containing glycerol and glycerin. 

Think about all the products that need to retain moisture, such as lotions, creams, silver polish, and makeup. 

Without glycerin or glycerol, they would become dry. Lotions moisturize (hydrate) your skin but also enable your skin to retain moisture.

What Is Vegetable Glycerin?

Coconut, Oil, Cosmetic, Cream, Lotion, Natural, Beauty
Image by Mohamed_Hassan via Pixabay

As we have discussed glycerin and glycerol in-depth, I will refrain from repeating information we’ve already covered and focus solely on what vegetable glycerin is.

Vegetable glycerin is not different from glycerin but is a variant form of glycerin derived solely from plant oils, such as coconut, palm, and soy, and is thus well-suited to a vegan or vegetarian lifestyle (source). 

Vegetable glycerin is moderately sweet and presents as a syrupy liquid. This article was written for strategiesforparents.com

Like glycerol and glycerin, it has many uses and is very popular as an ingredient in cosmetics (cruelty-free), food products, and the pharmaceutical industry. 

Final Thoughts

Teasing out how glycerol and glycerin differ is not an easy task. While the differences are barely distinguishable, they are there. They have a shared history and molecular formula (C3H8O3). 

Glycerin and glycerol are hygroscopic, basically non-toxic, colorless, with a sweet taste making them perfect ingredients for the cosmetic, food, and pharmaceutical industries.

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