Bio Glycol refers to glycol compounds derived from renewable, biological sources rather than traditional fossil fuels. These eco-friendly alternatives are gaining attraction across industries due to their sustainability and reduced carbon footprint.
Types of Bio Glycols
Here are some common bio-based glycols and their uses:
Type Description Applications
Bio Monoethylene Glycol (Bio-MEG) Made from agricultural feedstock; purity ≥99.5% PET resins, textiles, packaging films, antifreeze, adhesives
Bio Diethylene Glycol (Bio-DEG) Solvent with humectant properties Plasticizers, polyester resins, polyurethanes, printing inks, brake fluids
Bio Triethylene Glycol (Bio-TEG) Highly hygroscopic; used for moisture removal Natural gas dehydration, vinyl plasticizers, air sanitizers
Advantages of Bio Glycols
• Sustainability: Derived from renewable resources like sugarcane molasses or wood.
• Environmental Benefits: Lower carbon emissions and reduced reliance on petroleum.
• Drop-in Compatibility: Can replace fossil-based glycols without altering existing production processes.
Production Insights
• Bio-MEG are made using certified wood, offering CO₂-neutral solutions for industries like automotive, textiles, and packaging.
• Bio propylene Glycol is produced via catalytic hydrogenation of glycerine sourced from biodiesel production.
Bio Glycol Production from Biomass
One of the most promising methods for producing bio-based MEG is through catalytic hydrogenation of biomass, such as corncob or wood-derived sugars.
Key Steps in the Process:
1. Biomass Pre-treatment
o Biomass (e.g., corncob, sugarcane bagasse) is cleaned and ground.
o Hydrolysis is performed to break down cellulose into glucose.
What Is Hydrolysis of Cellulose?
Cellulose is a complex carbohydrate made of long chains of glucose units. Hydrolysis is the chemical process that breaks these chains into individual glucose molecules.
Types of Hydrolysis:
1. Acid Hydrolysis
o Uses dilute or concentrated acids (e.g., sulfuric acid).
o High temperature and pressure.
o Fast but can produce unwanted by-products like furfural.
2. Enzymatic Hydrolysis
o Uses cellulase enzymes.
o Milder conditions (pH ~5, temp ~50°C).
o More selective and environmentally friendly.
Reaction Overview
The general reaction for cellulose hydrolysis:
(C6H10O5)n+nH2O→nC6H12O6
Where:
• (C6H10O5)n = Cellulose
• C6H12O6 = Glucose
Why It Matters for Bio Glycol
Once glucose is obtained:
• It can be hydrogenated into glycol compounds like MEG and propylene glycol.
• This forms the backbone of bio-based chemical production, replacing fossil-derived ethylene.
2. Catalytic Hydrogenation
• Glucose is converted into glycol compounds using a binary catalyst system.
• Hydrogen gas is introduced under controlled pressure and temperature.
Hydrogenation is a chemical reaction where hydrogen (H₂) is added to a molecule in the presence of a catalyst. In this case, glucose is hydrogenated to produce polyols—compounds with multiple hydroxyl (-OH) groups.
Reaction Pathway
The simplified reaction looks like this:
C6H12O6+H2→C2H6O2+C3H8O2+others ( in presence of catalyst)
Where:
• C₆H₁₂O₆ = Glucose
• C₂H₆O₂ = Ethylene glycol (EG)
• C₃H₈O₂ = Propylene glycol (PG)
Catalysts Used
Common catalysts include:
• Nickel-based catalysts (e.g., Raney Nickel)
• Copper-chromite
• Ruthenium or platinum on carbon (for higher selectivity)
These catalysts help break the glucose ring and rearrange carbon atoms to form smaller glycol molecules.
Reaction Conditions
• Temperature: 180–250°C
• Pressure: 50–150 bar of H₂
• Solvent: Often water or alcohol
• Time: Several hours depending on setup
Products Formed
Product Use Case
Ethylene Glycol (EG) Antifreeze, PET plastics
Propylene Glycol (PG) Cosmetics, food additives
Glycerol Pharmaceuticals, soaps
Sorbitol Sweeteners, surfactants
Sustainability Angle
This process allows for renewable glucose (from cellulose or starch) to replace petrochemical ethylene, making it a cornerstone of green chemistry.
3. Separation and Purification
• The resulting mixture contains MEG and other glycols.
Separation and Purification of MEG and Other Glycols
Initial Filtration
• Removes solid catalyst residues and unreacted biomass.
• Typically involves centrifugation or membrane filtration.
Evaporation / Flash Distillation
• Removes excess water from the reaction mixture.
• Uses vacuum evaporation to avoid thermal degradation of glycols.
Fractional Distillation
• Core step for separating MEG, DEG, and TEG based on boiling points.
Compound Boiling Point (°C)
MEG ~197
DEG ~245
TEG ~285
• MEG is distilled first, followed by DEG and TEG.
• Requires high-efficiency distillation columns with multiple trays or packing.
Purification
• Final polishing to remove trace impurities:
o Activated carbon for color and odor removal.
o Ion exchange resins to eliminate ionic contaminants.
o Vacuum distillation for ultra-pure grades.
Cooling and Storage
• Glycols are cooled and stored in inert conditions to prevent oxidation or moisture uptake.
Purity Grades
Glycol Industrial Purity High Purity (USP/Pharma)
MEG >99.5% >99.9%
DEG >99% —
TEG >98% —
PG >99.5% >99.9%
Using bio-derived glucose and green separation techniques (like membrane distillation or low-energy vacuum systems) enhances the environmental profile of MEG production.
Fractional Distillation: Isolating MEG by Boiling Point
Fractional distillation separates compounds based on their boiling points. In a glycol mixture, MEG has the lowest boiling point, making it the first to be distilled off.
Key Steps:
• The mixture is heated in a distillation column.
• Vapors rise and condense at different heights based on boiling points.
• MEG (~197°C) is collected first, followed by DEG (~245°C) and TEG (~285°C).
Equipment:
• Packed or tray columns for high separation efficiency.
• Reboilers and condensers to maintain temperature gradients.
• Often operated under vacuum to reduce thermal stress.
Filtration: Removing Solids and Impurities
Filtration is used before distillation to remove:
• Catalyst particles (e.g., nickel or copper residues)
• Unreacted biomass
• Charred organics or insoluble impurities
Techniques:
• Centrifugation for bulk solids.
• Membrane filtration for fine particulates.
• Activated carbon or ion exchange resins for trace contaminants.
Result: High-Purity MEG
After filtration and fractional distillation:
• MEG is typically >99.5% pure for industrial use.
• Further purification (e.g., vacuum distillation) can yield >99.9% purity for pharmaceutical or food-grade applications.
4. Optimization Techniques
• Response Surface Methodology (RSM) and Design of Experiments (DOE) are used to fine-tune parameters like:
1. Catalyst-to-feedstock ratio
2. Hydrogen pressure
3. Reaction temperature
In one study, optimized conditions yielded 70.2 wt.% MEG from corncob biomass, with properties aligning with ASTM standards.
Other Information (Insights) about BIO-GLYCOLs.
Petroleum based ethylene is oxidized to obtain ethylene oxide, followed by hydration of the ethylene oxide to produce EG. Reaction pathway for fossil fuel derived EG may be relatively simpler but it is a finite resource and notorious for greenhouse gas emission.
The increasing awareness for sustainable development and security of raw material has prompted scientific community to explore innovative paths for production of EG from renewable sources. Synthesizing bio-EG not only reduce supply chain dependence on the depleting petroleum, it also potentially decreases carbon footprint.
Plant biomass are widely available at low cost and does not compete with food chain. The valorisation of plant residues made up of cellulose, hemicellulose and lignin received considerable attention in the past decades. Both cellulose and hemicellulose are composed of long chains of sugar. Upon breaking down this complex sugar through cleavage of the C-O and C-C bonds, the shorter carbon chain can be further processed via biological or catalytic hydrogenation pathways.
In biological path, microorganisms, such as yeast, bacteria and mold, are used to convert the carbon-rich intermediates into ethanol. The biochemical process proceeds slowly at low temperature. Subsequently, ethanol is dehydrated in the presence of phosphoric or activated alumina catalyst to form bio-ethylene. Bio-ethylene then goes through similar production process for typical petroleum-based ethylene glycol. Corn starch, sugarcane, and wheat starch are the major feedstock for global bio-ethanol production. This technology is demonstrated in Brazil, India and Taiwan. A commercial scale bio-based EG plant with capacity of 500 kilo tonnes per annum is operated by JBF Industries, which known to be a supplier for Coca-Cola’s plant-based packaging.
While in catalytic conversion pathway, the smaller carbon compound from decomposition of carbohydrate undergoes retro-aldol and hydrogenation steps. The catalytic hydrogenolysis replaces the multi-steps sugar fermentation to bio-EG route with a simpler two steps process. However, the intricate reaction pathways of EG synthesis via catalytic transformation from cellulosic material results in co-production of homologous series of glycol by-product, namely 1,2-propanediol (PDO), 1,2-butanediol (BDO), glycerol and sorbitol. Nevertheless, high EG yield can be acquired by tuning the catalyst system and reaction conditions. In 2017, catalyst specialist Haldor Topsoe partnered with Braskem to prove a new sugar to biochemical technology in a demonstration plant. Depolymerization of sugar was accomplished via pyrolysis, followed by catalytic hydrogenation of the C1-C3 oxygenates, namely glycolaldehyde, glyoxal, acetol and pyruvaldehyde . Avantium commissioned a 10 tonnes per annum plant in 2020 to validate its proprietary Ray Technology™. The sugar-to-EG technology aims to be cost competitive for industrial scale deployment.
Recent years have shown shifting attention from pure cellulose to lignocellulosic biomass for studies on hydrolytic conversion for biobased EG. Using cellulose as starting material is not cost effective considering the tedious pre-treatment methodologies involving acids, bases, and other chemicals. However, raw biomass is a complex polymer having varying constituents dependent on genetics and climate conditions. Cellulose coexists with lignin, ash, and inorganic impurities in plant residues. Therefore, dissecting the composition of biomass and its impacts on polyol yield and catalyst activity are vital for large scale production of biobased EG. Probing deeper into performance of various catalysts system, researchers took initiatives to examine the stability of the catalysts over repeated runs under harsh hydrothermal reaction and severe pH conditions. Wang et al (2013) reported that EG yield obtained with combination of WO3/AC and Ni/AC catalysts drops sharply from 53% to 8% after four cycles. Despite the good product yield, the drastic deterioration of catalytic activity renders the catalyst unfeasible for scaling-up. Hence, extending the lifespan of catalyst is a pivotal step to make the catalytic conversion procedure economically attractive for industrial application.
Among the by-product generated from polysaccharides feedstock, 1,2-PDO and 1,2-BDO are known to have remarkably close boiling point with EG. For manufacture of polyester fibres and PET resins, stringent specification of high purity EG (i.e. above 99.9%) is necessary. High theoretical stages and massive reboiler duty are required for separation of these compounds using traditional distillation column. Besides, EG is susceptible to polymerization to form undesirable by-product at higher reboiler temperature condition, which is required to overcome the huge pressure drop due to height of column internals [25]. Posing more challenge to the removal of impurities, mixture of EG and BDO forms azeotrope with EG molar concentration of 48–52%. Equimolar loss of EG is expected during separation of BDO using conventional distillation columns [26]. In the quest to uncover the most efficient separation method, researchers have studied the application of multi-effect distillation, azeotropic distillation, reaction-assisted separation, melt crystallization and adsorption for bio-based EG purification.
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