Polyol Synthesis from Crude Glycerol
In our previous technical articles, it was mentioned about the production of bio-polyol from vegetable oils, which is used in the polyurethane sector. (If you want to read it, you can visit http://www.evocopolymers.com/blog-detail/synthesis-of-bio-polyol-from-vegetable-oils/ ). Vegetable oils used in the polyurethane industry are also used in the cosmetics and food industry. For this reason, it is thought that the use of vegetable oils in the polyurethane sector will have negative effects on prices. In order to prevent the price increase, alternative raw materials that can be used instead of vegetable oils were sought, and as a result, studies were conducted on the use of crude glycerol, which is released as a by-product in the biodiesel industry [1, 2].
Glycerol has wide application areas in food, medicine, cosmetics, tobacco, polyurethane and many industries and approximately 10% crude glycerol is released as a by-product in the biodiesel production process [1, 2, 3]. However crude glycerol contains various impurities such as water, soap, free fatty acids, fatty acid methyl esters, methanol and catalyst. For this reason, high cost purification processes are required in crude glycerol in order to be used in industries such as pharmaceuticals and cosmetics. On the contrary, crude glycerol can be used directly in the polyurethane sector without purification [2, 4, 5].
In the polyurethane industry, crude glycerol is used as an initiator in the production of polyether polyols used to obtain flexible, semi-flexible and rigid foams, as a solvent in the production of bio-polyols and as a crosslinker in polyol systems. The production of the polyether polyol is accomplished by the addition of suitable solvents and crude glycerol under the preferred reaction temperature and time, usually in the presence of a catalyst [1, 2, 4]. At the same time, the polyglycerol obtained after polymerization of crude glycerol is reacted with castor oil in the next step to obtain bio-based polyols [6]. Polyglycerol has been successfully applied in the rigid polyurethane industry due to its high crosslink density [7]. Recently, studies have been carried out to use crude glycerol as a solvent in the production of bio-polyols through the liquefaction of biomass. The liquefaction process usually takes place during the filtration, neutralization and oxidation processes of glycerol in the presence of homogeneous acid and base catalysts [2, 5]. In these studies, it was concluded that the impurities in crude glycerol improved some properties of polyurethanes compared to polyurethanes produced using bio-polyol synthesized from purified glycerol in polyurethanes produced using bio-polyol synthesized from crude glycerol as an advantage [5]. Examples of improved properties are the increase in thermal stability as a result of the decrease in the thermal conductivity coefficient, the increase in the compressive strength with the increase of the crosslink density and the improvement of some mechanical properties [1, 6].
Crude glycerol, which is released as a by-product in the petrochemical industry, can be used as a raw material in the polyol and bio-polyol production in the polyurethane industry without requiring cost purification processes. For this reason, it provides positive benefits to the sectors both ecologically and economically.
REFERENCES
[1] Hejna, A., Kirpluks, M., Kosmela, P., Cabulis, U., Haponiuk, J., Piszczyk, L., “The influence of crude glycerol and castor oil-based polyol on thestructure and performance of rigid polyurethane-polyisocyanurate foams”, Industrial Crops and Products, Volume 95 , Pages 113–125, 2017.
[2] Luo, X., Hu., S., Zhang, X., Li, Yebo., “Thermochemical conversion of crude glycerol to biopolyols for the production of polyurethane foams”, Bioresource Technology, Volume 139, Pages 323–329, 2013.
[3] Ningaraju, C., Yatish, K. V., & Sakar, M., "Simultaneous refining of biodiesel-derived crude glycerol and synthesis of value-added powdered catalysts for biodiesel production: A green chemistry approach for sustainable biodiesel industries." Journal of Cleaner Production (2022): 132448.
[4] Cui, S., Liu, Z., Li, Y., “Bio-polyols synthesized from crude glycerol and applications on polyurethane wood adhesives”, Industrial Crops & Products, Volume 108, Pages 798–805, 2017.
[5] Jasiūnas, L., McKenna, S. T., "Mechanical, thermal properties and stability of rigid polyurethane foams produced with crude-glycerol derived biomass biopolyols.", Journal of Polymers and the Environment 28.5 (2020): 1378-1389.
[6] Hejna, A., Kosmela, P., Kirpluks, M., Cabulis, U., Klein, M., Haponiuk, J., "Structure, mechanical, thermal and fire behavior assessments of environmentally friendly crude glycerol-based rigid polyisocyanurate foams." Journal of Polymers and the Environment 26.5 (2018): 1854-1868.
[7] Hejna, A., Kosmela, P., Klein, M., Formela, K., Kopczyńska, M., Haponiuk, J., & Piszczyk, Ł., "Two-step conversion of crude glycerol generated by biodiesel production into biopolyols: Synthesis, structural and physical chemical characterization." Journal of Polymers and the Environment 26.8 (2018): 3334-3344.
Authors: Beste TATLISES Date: September 2022
