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CASCADE Hydrolytic Recovery and Conversion of Suberin in High Pressure Media

Periodic Reporting for period 1 - SUBLUBE (CASCADE Hydrolytic Recovery and Conversion of Suberin in High Pressure Media)

Reporting period: 2020-10-15 to 2022-10-14

Bioeconomy is a widely accepted strategy in order to mitigate the adverse effects of climate change while addressing economic, societal and ecological concerns. The SUBLUBE project has been conceived in support of the European Strategy of Bioeconomy, the State R&D Program Oriented to the Challenges of the Society of Spain (Programa Estatal de I+D+i Orientada a los Retos de la Sociedad), the RIS3 Castilla y Leon Regional Strategy and the Bioeconomy Institute of Universidad de Valladolid. It aims to contribute to these frameworks by developing green processes that would enable sustainable raw-material-to-product conversions. Specifically, SUBLUBE is envisioned to capture waste streams of the cork processing industry and upgrade the valuable component (suberin) into a useful biochemical (biolubricant). Cork is rich in natural biopolyesters in the form of suberinic acids which can be an alternative to mineral and vegetable oils as a biolubricant base. Conventional chemical pathways for suberin recovery involving alkali hydrolysis and alkali methanolysis reactions are organic solvent-intensive and requires arduous processing, and yet recovers suberin in minimal quantity. Herein, we propose the ultrafast supercritical hydrolysis in a continuous microreactor as a novel process to isolate suberin from cork in high yields, without the use of harsh chemicals and at a shorter reaction time than conventional approaches. Moreover, since supercritical water (SCW) as a low ionic reaction media will allow the hydrolysis of polysaccharides and lignin and will avoid the hydrolysis of biopolyesters, which will lead to the separation of suberin in its intact form. Suberin in its intact form would produce longer-chain structure enriched with multiple functional groups that are more suitable for biolubricant base synthesis in the subsequent processing. SUBLUBE is made possible by the integration of various disciplines such as materials and analytical chemistry, chemical process engineering, and cork chemistry.
From October 15, 2020October 14, 2022, I carried out experiments involving suberin recovery and characterization at the Bioeconomy Institute of Valladolid University, Valladolid, Spain under the supervision of Prof. Maria Jose Cocero, with a three-month secondment at the LAQV-REQUIMTE of the Universidade Nova de Lisboa, Caparica, Portugal. I have carried out the following works: (i) Isolation of suberin methyl esters by chemical conventional method; (ii) Recovery of intact suberin in a subero-lignin complex by supercritical hydrolysis in a continuous microreactor; (iii) Isolation of suberin from the subero-lignin complex by dioxane extraction; (iv) Subcritical hydrolysis of suberin in microwave, conventional batch and semicontinuous reactors (v) Extensive Characterization of suberin and its acid and methyl ester derivatives generated produced from the technologies mentioned in (i-iv) and (vi) Production of biolubricants from isolated suberin and suberinic acids.
perimental techniques, instrumental analyses and mathematical calculations. I spent the first three months understanding the conventional chemical pathway and the necessary methods for suberin characeterization. This way, I understood the clear advantage of ultrafast supercritical hydrolysis over the conventional chemical approach, which includes greater product yields and better product properties. I operated the ultrafast microrreactor and employed mathematical calculations to estimate the ion product values of water. I have recovered suberin intact in a subero-lignin complex and correlated the properties of the products with respect to the ion product values and reaction time. I have also developed the method to extract pristine suberin from the subero-lignin complex based on dioxane extraction. I also carried out subcritical hydrolysis in batch and semicontinuous reactors and compared the product composition in terms of cellulose, lignin and suberin yields to that of ultrafast hydrolysis products. I have characterized the subero-lignin complex (ultrafast supercritical hydrolysis product), the pristine suberin (isolated by dioxane extraction), suberin methyl esters (from alkaline methanolysis) and suberinic acids (from alkali hydrolysis) through a variety of techniques including surface micrography, thermal properties and structural functionalities. It was found that it is necessary to strike a balance between the combination of reaction time and ion product of water in order to avoid the formation of competing repolymerization reactions that would allow the liquefaction of cellulose and lignin to yield higher suberin amount. I have also developed a method to convert the suberinic acids into biolubricant base.
The results were discussed in detail in an academic article published in Green Chemistry ( I have also partcipated in several activities to disseminate the results and raise attention to the project such as the Science Week, European researcher`s night, #ElFuturoDELaUVa and Day International Of Women And Girls In Science.
The expected final results of the project is to provide an extensive knowledge and understanding of suberin characteristics and properties and the process conditions that would enable its recovery in intact form to facilitate its upconversion. The findings in this study will pave way towards a wider valorization of suberin due to availability and product development based on its derivatives and to expand the portfolio of ultrafast microreactors for more complex biomass valorization. This will open doors to more sustainable materials supply and waste recovery which could have economic contributions in the foreseeable future.