Glycerin

Basic Information

Chemical Name: Glycerin (also known as Glycerol or 1,2,3-Propanetriol)

CAS Registry Number: 56-81-5

Molecular Formula: C₃H₈O₃

Molecular Weight: 92.09 g/mol

Chemical Structure: A triol compound with a central propane backbone and three hydroxyl (-OH) groups, giving it strong hydrophilicity and reactivity.

Physical Properties

Appearance: Clear, colorless, viscous liquid with no visible turbidity; has a mild, sweet taste and no distinct odor.

Density: 1.261 g/cm³ at 20°C (higher than water, due to its polar hydroxyl groups).

Melting Point: 17.8°C (solidifies into a white, crystalline mass at temperatures below this; easily melts upon gentle heating).

Boiling Point: 290°C (decomposes slightly above this temperature if not under reduced pressure).

Viscosity: High viscosity (≈1490 mPa·s at 20°C); viscosity decreases with increasing temperature (e.g., ≈210 mPa·s at 50°C).

Solubility: Highly soluble in water (miscible in all proportions) and polar solvents (e.g., ethanol, propylene glycol); insoluble in non-polar solvents (e.g., oils, gasoline, benzene).

Hygroscopicity: Excellent moisture-absorbing ability—readily absorbs water vapor from the air, making it effective as a humectant.

Refractive Index: 1.4746 at 20°C (useful for purity testing in industrial quality control).

Chemical Properties

Stability: Chemically stable under normal storage and handling conditions (avoid extreme heat or strong oxidizing agents, which may cause decomposition).

Reactivity: The three hydroxyl groups enable reactions such as esterification (to form glycerides, e.g., in cosmetics or biodiesel), etherification, and dehydration (to produce acrolein under high heat).

Non-Toxicity: Generally recognized as safe (GRAS) by regulatory bodies like the U.S. FDA and EU EFSA; non-irritating to skin and mucous membranes at typical usage concentrations.

pH: Neutral to slightly alkaline (pH 6.0–8.0 for aqueous solutions, depending on purity).

Manufacturing Processes

Glycerin is primarily produced through three industrial routes:

Saponification of Fats/Oils: A traditional method where animal or vegetable fats are reacted with alkalis (e.g., sodium hydroxide) to produce soap—glycerin is a byproduct of this process.

Transesterification for Biodiesel: A major modern source—when vegetable oils or animal fats are converted to biodiesel (methyl/ethyl esters), glycerin is generated as a co-product (typically 10% by weight of biodiesel output).

Synthetic Production: From petrochemical feedstocks (e.g., propylene), via processes like epoxidation and hydrolysis—used to produce high-purity grades for specialized applications (e.g., pharmaceuticals).

Purity Grades

Commercial glycerin is available in several purity grades tailored to specific uses:

GradePurity LevelKey ApplicationsTechnical Grade≥95%Industrial uses (e.g., antifreeze, lubricants, plasticizers)Cosmetic Grade≥99.5%Personal care products (e.g., lotions, soaps, toothpaste)Food Grade≥99.7%Food additives (e.g., sweetener, humectant, solvent)Pharmaceutical Grade≥99.8%Pharmaceuticals (e.g., oral formulations, injectables, medical devices)

Key Characteristics & Advantages

Humectancy: Effectively retains moisture, preventing drying in products like cosmetics, food, and textiles.

Solvent Power: Acts as a non-toxic solvent for polar compounds (e.g., vitamins, fragrances, active pharmaceutical ingredients).

Plasticizing Ability: Softens and improves flexibility in polymers (e.g., cellulose, polyvinyl alcohol) and coatings.

Thermal Stability: Resists freezing (lowers the freezing point of aqueous solutions) and maintains viscosity over a wide temperature range.

Biodegradability: Breaks down into harmless byproducts (CO₂ and water) in the environment, aligning with sustainable practices.

Major Applications

1. Personal Care & Cosmetics

Humectant in lotions, creams, and moisturizers (prevents skin dryness).

Emollient in soaps, shampoos, and conditioners (improves skin/hair softness).

Solvent for fragrances, dyes, and active ingredients (e.g., in serums or sunscreens).

2. Food & Beverage

FDA-approved humectant (e.g., in baked goods, confectionery, and processed meats to retain moisture).

Low-calorie sweetener (≈60% the sweetness of sucrose) in diet foods, beverages, and oral care products.

Cryoprotectant (prevents ice crystal formation in frozen foods like ice cream).

3. Pharmaceuticals & Healthcare

Excipient in oral medications (syrups, tablets) as a binder, sweetener, or moisture stabilizer.

Component in injectable formulations (as a solvent or isotonic agent).

Lubricant for medical devices (e.g., syringes, catheters) and skin protectants (e.g., in burn ointments).

4. Industrial & Other Uses

Antifreeze and coolant (in automotive, HVAC, and industrial systems, often blended with water).

Lubricant for machinery and plastic processing.

Precursor in biodiesel production (as a co-product) and in the manufacture of explosives (e.g., nitroglycerin).

Packaging & Storage

Packaging: Available in food-grade HDPE drums (20 L, 200 L), IBC totes (1000 L), or bulk tankers for industrial use. Smaller quantities (e.g., 1 L bottles) are offered for laboratory or cosmetic formulation needs.

Storage:

Keep in a cool, dry, well-ventilated area away from direct sunlight and heat sources (to avoid viscosity changes or decomposition).

Seal containers tightly to prevent absorption of atmospheric moisture (which may dilute purity) and contamination.

Avoid contact with strong oxidizers (e.g., chlorine, peroxides) and incompatible materials (e.g., strong acids).

Glycerin’s versatility, non-toxicity, and favorable physical-chemical properties make it a critical ingredient across industries, from everyday consumer goods to high-precision pharmaceutical and industrial applications.