Glycerin is a byproduct of biodiesel production produced during the transesterification of fats and oils. This versatile compound, often undervalued, holds immense potential for creating value-added products. Through chemical/biochemical and thermochemical routes glycerin can be transformed into commodities like biopolymers, chemicals, and cosmetics, contributing to a sustainable circular economy.
Before learning about the value-added products, let us learn how glycerin is produced in the biofuel production process.
How Glycerin is Produced as a Byproduct in Biofuel Production
Glycerin is a natural byproduct created during the production of biodiesel. The process begins with transesterification, where fats or oils, such as vegetable oil or animal fat, react with alcohol, usually methanol, in the presence of a catalyst like sodium hydroxide or potassium hydroxide.
1. Mixing: Methanol and the catalyst are mixed to form methoxide.
2. Reaction: Methoxide is added to the fats or oils. This starts the transesterification reaction, where the triglycerides in the oil break down.
3. Separation: The reaction produces two products: biodiesel and crude glycerin. These separate naturally due to differences in density.
4. Purification: The crude glycerin contains impurities like water, soap, and alcohol. It is refined to remove these and produce purer glycerin.
This process not only generates clean-burning biodiesel but also creates glycerin, offering opportunities for further value creation. Here are the value-added products of glycerin that can increase the economic value of biofuel production.
Value-Added Products from Glycerin
Chemical/biochemical conversion of crude glycerol, a byproduct of biodiesel production, is a critical process that generates several valuable products. Each product has unique applications across various industries. Below is an in-depth discussion of how these products are produced and where they are used.
1,3-Propanediol (1,3-PDO)
Production:
1,3-Propanediol (1,3-PDO) is primarily produced through microbial fermentation using crude glycerol as the carbon source. Bacterial strains such as Clostridium butyricum and Klebsiella pneumoniae are commonly used. The process begins with the fermentation of glycerol under anaerobic conditions.
- The metabolic pathway involves the reduction of glycerol to 3-hydroxypropionaldehyde, which is then further reduced to 1,3-PDO.
- This bioconversion is optimized by controlling pH, temperature, and substrate concentration, ensuring high yield.
Applications:
- Polymer Industry: 1,3-PDO is a key monomer in the production of polytrimethylene terephthalate (PTT), a polymer used in textiles and carpets.
- Cosmetics and Personal Care: It serves as a humectant and solvent.
- Food Industry: Used as a flavouring agent and preservative.
Hydrogen Gas (H2)
Production:
Hydrogen gas is produced via glycerol reforming processes, including steam reforming and aqueous-phase reforming (APR).
- Steam Reforming: Involves reacting glycerol with steam at high temperatures (700–1000°C) in the presence of a catalyst, typically nickel-based.
- Aqueous Phase Reforming: Conducted at lower temperatures and pressures, using metal catalysts like platinum or palladium.
Applications:
- Energy Sector: Hydrogen is a clean energy carrier for fuel cells and hydrogen-powered vehicles.
- Chemical Industry: Used in ammonia synthesis and refining processes.
- Metal Industry: Employed in metal treatment and reduction processes.
Epichlorohydrin
Production:
Epichlorohydrin is synthesized from glycerol through a multi-step chemical process.
- Glycerol is chlorinated using hydrochloric acid to produce dichlorohydroxypropane.
- This intermediate undergoes dehydrochlorination in the presence of a base, such as sodium hydroxide, yielding epichlorohydrin.
Applications:
- Resins and Plastics: A primary raw material for producing epoxy resins.
- Pharmaceuticals: Used in synthesizing various drugs.
- Water Treatment: Employed in creating ion-exchange resins.
Monoglycerides and Diglycerides
Production:
These compounds are produced through the glycerolysis of fats or oils.
- Glycerol reacts with triglycerides (fats or oils) in the presence of a catalyst, typically an alkaline or enzymatic one.
- The reaction yields monoglycerides and diglycerides as intermediates, with the ratio controlled by process conditions.
Applications:
- Food Industry: Widely used as emulsifiers in bakery, dairy, and confectionery products.
- Pharmaceuticals: Serve as solubilizing agents in drug formulations.
- Cosmetics: Act as stabilizers and moisturizers in creams and lotions.
Glycerol Carbonate
Production:
Glycerol carbonate is synthesized through the reaction of glycerol with dimethyl carbonate or urea.
- In the dimethyl carbonate route, a transesterification reaction occurs, catalyzed by enzymes or chemical catalysts.
- In the urea route, glycerol reacts with urea at elevated temperatures with zinc oxide or other catalysts.
Applications:
- Polymers: Used as a precursor in polyurethane production.
- Solvents: Functions as a green solvent in paints and coatings.
- Pharmaceuticals: Acts as an intermediate in drug synthesis.
Acetins (Mono-, Di-, and Triacetins)
Production:
Acetins are produced through the acetylation of glycerol with acetic acid or acetic anhydride.
- The reaction is catalyzed by acidic or enzymatic catalysts, and reaction conditions are controlled to favour the formation of mono-, di-, or triacetin.
Applications:
- Food Industry: Triacetin is used as a flavour carrier and humectant.
- Pharmaceuticals: Acts as a solvent in drug formulations.
- Explosives: Triacetin serves as a plasticizer in nitroglycerin-based explosives.
Succinic Acid
Production:
Succinic acid can be produced through the fermentation of glycerol using specific microorganisms.
- Bacterial strains such as Actinobacillus succinogenes Anaerobiospirillum succiniciproducens, Mannheimia succiniciproducens, and engineered Escherichia coli or Corynebacterium glutamicum are used.
- Glycerol acts as a carbon source, and fermentation occurs under anaerobic conditions with optimized pH and nutrient availability.
Applications:
- Food Industry: Used as an acidity regulator and flavour enhancer.
- Pharmaceuticals: Functions as a precursor for drug synthesis.
- Bioplastics: A key component in the production of polybutylene succinate (PBS).
Biopolymers (PHA, PHB, and Acrylates)
Production:
Biopolymers are synthesized through microbial fermentation of glycerol under nitrogen- and phosphate-limited conditions.
- Polyhydroxyalkanoates (PHAs): Produced by bacterial strains like Halomonas sp. using glycerol as the carbon source.
- Polyhydroxybutyrate (PHB): Generated by strains such as Burkholderia cepacia with varying glycerol concentrations.
- Acrylates: Produced through chemical conversion involving esterification reactions.
Applications:
- Bioplastics: PHAs and PHBs are biodegradable plastics for packaging and medical devices.
- Coatings and Adhesives: Acrylates are used in paints and glues.
- Textiles: Biopolymers enhance fabric properties.
Propylene Glycol
Production:
Propylene glycol is synthesized by hydrogenating glycerol in the presence of metal catalysts such as copper or nickel.
- The process involves high-pressure hydrogenation, converting glycerol into propylene glycol and water.
Applications:
- Food Industry: Used as a humectant and flavour carrier.
- Pharmaceuticals: Functions as a solvent in syrups and topical formulations.
- Industrial Applications: Acts as an antifreeze agent and de-icer.
Apart from the glycerol based value-added products, glycerin is also used to reduce the high free fatty acid (FFA) content of feedstock for biodiesel production. Let us know more about this process.
Glycerolysis for Reducing High FFA Content in Biodiesel Feedstock: A Cost-Effective Solution
Glycerolysis is a promising method for addressing the challenges of high free fatty acid (FFA) content in biodiesel feedstocks. Using a heterogeneous base catalyst, such as calcium oxide (CaO), this process enhances the economic and environmental value of biodiesel production. Below are the key aspects of how glycerolysis improves feedstock and its benefits:
How Glycerolysis Works
- FFA Reduction: Glycerol reacts with free fatty acids to form glycerides (mono-, di-, and triglycerides).
- Catalyst Efficiency: CaO acts as a solid catalyst, reducing reaction time and simplifying separation.
- Optimal Conditions: Under 170°C, 40 minutes, and specific glycerol-to-oil ratios, FFA content drops below 3%.
Benefits of Glycerolysis
- Increases Feedstock Usability: Converts high-FFA oils into biodiesel-compatible materials.
- Reduces Production Costs: Allows the use of cheaper, non-edible oils without food-agriculture competition.
- Environmentally Friendly: Decreases waste and supports sustainable fuel alternatives.
- Simplifies Processing: Solid catalysts are easy to recover and reuse, lowering operational complexity.
- Shorter Reaction Time: Compared to acid-catalyzed processes, glycerolysis achieves results faster and at lower temperatures.
Applications in Biodiesel Production
- Improved Yield: High-quality feedstock ensures efficient biodiesel conversion.
- Adaptability: Effective for non-edible oils, expanding resource options for producers.
By reducing FFA in oil feedstocks, glycerolysis addresses a critical limitation of traditional biodiesel production. This innovative process enhances the feasibility of using high-FFA oils, supporting cost-effective, eco-friendly biodiesel production on a larger scale.
Industrial Potential of Glycerin: Opportunities for Biodiesel Producers
Thus, glycerol conversion opens up diverse opportunities across various industries. Its versatility allows biodiesel producers to explore new markets and enhance revenue streams. Here’s why glycerin is a game-changer:
- Industrial Versatility: From bioplastics to cosmetics, glycerin finds applications in polymers, personal care, and pharmaceuticals.
- Clean Energy Applications: Glycerin-based hydrogen gas and biofuels contribute to a greener energy sector.
- Sustainability: Using glycerin supports a circular economy by minimizing waste and maximizing resource utilization.
- Cost-Effective Feedstock: Reducing high FFA content in biodiesel feedstocks makes production more efficient and eco-friendly.
- Market Expansion: Purified glycerin can be sold to industries such as food, chemicals, and construction, increasing the market reach of biodiesel producers.
By utilizing crude or refined glycerin, biodiesel producers can diversify their offerings, enhance profitability, and support sustainable industrial practices. The future of biodiesel isn’t just fuel—it’s tapping into endless industrial potential.
Contact MAGTECH, the leading biodiesel plant manufacturer and glycerin purification solution provider to learn more. Get to know from industry experts with diverse experience how you can tap the potential market of Glycerol based Value-Added Products and flourish your biofuel business.
https://www.sciencedirect.com/science/article/abs/pii/S1364032120307875
https://www.sciencedirect.com/science/article/pii/S2215017X1500065X
