26/06/2019
A new process scheme for 100% chemical recycling of polyurethanes Lukasz Pazdur, Christophe Vande Velde, Pieter Billen
Polyurethanes – problems and challenges Facts: - One of the most relevant polymer - 6 th most used plastic - The world production 18 milion tons per year Problems: - High resistance to biodegadation - Environmental issue with landfjlling - Physical recycling applied only to thermoplastic PURs Challenges: - Chemical recycling - Thermal recycling (pyrolysis) 3
Success story of polyurethanes (PURs) - Condensation polymers - Synthesized from polyols and isocyanates - Wide diversity of polyols and isocyanates numerous difgerent polymers tunable properties - Classifjcation of PURs: Foams Flexible (mattresses) Rigid (buildings isolation) CASEs ( C oatings, A dhesives, S ealants, E lastomers) 4
Recycling of PUR - Mechanical recycling Only 1% of total amount of produced PURs Not applicable for PURs foams - Thermal recycling High temperature required (at least 250 °C) Inert atmosphere required Complex mixture Not yet industrially applied - Chemical recycling Recovery of polyols only Lack of circular process 5
Chemical recycling - Hydrolysis - Glycolysis - Aminolysis - Phosphorolysis 6
First attempt for chemical recycling Challenges: - Complete recovery (both polyols and isocyanates) - Circular approach Problems: - High number of products (and side-products) - Diffjculties with separation - Diffjculties with analysis 7
First attempt for chemical recycling 8
New process scheme 9
Model synthesis and chemical recycling - Control synthesis (full track of functional group formation) - Easier analysis - Screening of side products formation - Infmuence of molecular size on hydrolysis / glycolysis 10
Model synthesis Selected isocyanates: Selected alcohols: 11
Model synthesis: - Synthesis of simple urethane (carbamate) bond: - Synthesis of dicarbamates By means of diol By means of diisocyanates - Synthesis of polyurethanes 12
Reactivity of isocyanates - infmuence of catalyst Infmuence of catalyst 120 100 80 Conversion [%] Tin 2- hexanoate 60 Sulfuric acid Without catalyst 40 20 0 0 20 40 60 80 100 120 140 160 180 200 Time [min] 13
Cleavage of urethane bond - Alcoholysis - Hydrolysis (base- and acid catalyzed) 14
Results Cleavage Model molecule Condition Results Alcoholysis Tin 2-ethyl No (with hexanoate alcoholysis MeOH) NaOH 90 % of MPhC 10 % of Aniline NaOH + 5 % of H 2 O MPhC 95 % of Aniline Hydrolysis Acidic No (H 2 SO 4 ) hydrolysis Alkali 98 % of (NaOH) Aniline Alkali 99 % of (NaOH) Aniline * MW = 2500 – 3000 D * Alkali 94 % of (NaOH) Aniline 15
Conclusions - Alkali cleavage more effjcient than acidic cleavage - The more sterically hindered molecule, the more diffjcult cleavage Higher temperature required Longer time Presence of co-solvent - Pre-study regarding the thermal decomposition Small amount of isocyanates obtained Up to now only on lab scale, lack of industrialization 16
Further actions A comprehensive “toolbox” will be generated, to be used for: - The recycling of polyurethanes - Analysis of the difgerent products - Screening of possible side- products 17
Bibliography • Molero C, Ramos MJ, et al ( 2010 ). WIT T ransaction on Ecology and the Environment 140:69-78 • A European Strategy for Plastics in a Circular Economy ( 2018 ). COM/2018/028 fjnal • Behrendt G, Naber BW ( 2009 ). J Univ Chem T echnol Metallurgy 44(1):3-23 • Simon D, Borreguero AM et al ( 2015 ) The Handbook of Environmental Chemistry. Vol. 32, Springer, 229-260 • Wu CH, Chang CY et al ( 2003 ). Polym Degrad Stabil 80(1):103-111 • Nikje MMA, Mohammadi FHA ( 2009 ). Polimery/Polymers 54(7-8):541- 545 • Herlinger H ( 2007 ) Structure and reactivity of isocyanate. Stuttgart • Dai Z, Hatano B, et al ( 2002 ). Polym Degrad Stabil 76(2): 179-184 • Shi Y, Zhan X at el ( 2009 ). Chem React Eng T echnol 25:88 • Bauer G ( 1996 ) Recycling of polyurethanes. Munchen: Hanser Publications, 518-537 • Molero C, de Lucas A, et al ( 2009 ). J Mater Cycles waste Manage 11(2):130-132 • Simon D, Garcia MT ( 2013 ). Polym Degrad Stabil 98(1):144-149 • Modesti M ( 1996 ) Recycling of Polyurethane Polymers. Vol. 13, T economic Publishing CO., USA. 18
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