Glycerol

 

Glycerol
aka Glycerine, propanetriol

Chemical formula	C3H5(OH)3
OTP appearance	colorless liquid
Index of refraction	1.473
Molar Mass(g/mol)	92.09
Density(g/cc)	1.Fname261
Melting Point(°C)	17.8
Boiling Point(°C)	290
NFPA 704	1 1 0
Thermal Decomposition	glycerol 200°C acrolein

Glycerol (aka glycerine or propane 1,2,3-triol) is an alcohol. It is used as a dermatologically neutral base for many products, including cosmetics and ointments.

Uses

Primary

• Feedstock for hand sanitizer
• Feedstock for nitroglycerin and dimercaprol (WHO LEM)

Secondary

• Pharmacopia: laxative (rectally applied)

Production

Extraction

via lead (II) oxide

Olive oil (primarily glyceryl tri-oleate) combined with lead (II) oxide and water, and boiled, gives lead oleate and glycerol

2 C₃H₅(C₁₈H₃₃O₂)₃ + 3 PbO + 3 H₂O

{

→

boil}

3 Pb(C₁₈H₃₃O₂)₂ + 2 C₃H₅(OH)₃

via transesterification

Materials

• 800g of water-free triglycerides
• 8g of fresh calcium oxide
• 60g g of 99.5% ethanol

Process

1. (If necessary) Warm the triglyceride mixture until it is liquid
2. Combine the alkali with the alcohol
3. Slowly mix the alkali solution into the triglyceride
4. Allow it to stand, keeping warm if necessary

   Check: it should separate into two layers

   NB The bottom layer is the (crude) glycerol, the top layer the ethyl esters

5. Separate the crude glycerol from the ethyl esters

Recovering the FFAs

1. Filter the ethyl esters
2. Add distilled water to the ethyl esters
3. Distil at 90°C to extract the ethanol
4. Distil at 110°C to remove excess water
5. The remainder is FFAs. They can be converted to soap via sodium hydroxide or potassium hydroxide

Further purification

1. Bubble Carbon dioxide through the crude glycerol, precipitating the calcium compounds.
2. Filter the crude glycerol
3. The filtered crude glycerol contains three impurities: water, ethanol, and dissolved adulterants

   NB Glycerol does not form azeotropes with water or ethanol

4. Distil the ethanol from the crude glycerol at 90°C
5. Evaporate the crude glycerol at 110°C to remove the water
6. Vacuum distil the glycerol to extract the pure glycerol
7. Discard the residue

Vacuum distillation

Because the decomposition point of glycerol (200) is below its boiling point(290), it cannot be normally distilled. However, the boiling point drops with the ambient pressure, so if the pressure is lowered, so is the boiling point, and thus the boiling point can fall below the decompisition point and distillation can be performed.

See Also

• Methods of Preparation of Fatty Acids and Their Derivatives: Laboratory Exercises, by List, Gary R.