Coimbra Chemistry Center

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Publications

Lignin extraction from waste pine sawdust using a biomass derived binary solvent system

Publication . Magalhães, Solange; Filipe, Alexandra; Melro, Elodie; Fernandes, Catarina; Vitorino, Carla; Alves, Luís; Romano, Anabela; Rasteiro, Maria G.; Medronho, Bruno; MDPI

Lignocellulosic biomass fractionation is typically performed using methods that are somehow harsh to the environment, such as in the case of kraft pulping. In recent years, the development of new sustainable and environmentally friendly alternatives has grown significantly. Among the developed systems, bio-based solvents emerge as promising alternatives for biomass processing. Therefore, in the present work, the bio-based and renewable chemicals, levulinic acid (LA) and formic acid (FA), were combined to fractionate lignocellulosic waste (i.e., maritime pine sawdust) and isolate lignin. Different parameters, such as LA:FA ratio, temperature, and extraction time, were optimized to boost the yield and purity of extracted lignin. The LA:FA ratio was found to be crucial regarding the superior lignin extraction from the waste biomass. Moreover, the increase in temperature and extraction time enhances the amount of extracted residue but compromises the lignin purity and reduces its molecular weight. The electron microscopy images revealed that biomass samples suffer significant structural and morphological changes, which further suggests the suitability of the newly developed bio-fractionation process. The same was concluded by the FTIR analysis, in which no remaining lignin was detected in the cellulose-rich fraction. Overall, the novel combination of bio-sourced FA and LA has shown to be a very promising system for lignin extraction with high purity from biomass waste, thus contributing to extend the opportunities of lignin manipulation and valorization into novel added-value biomaterials.

2021-03-30Journal article

Open Access

Levulinic acid-based “green” solvents for lignocellulose fractionation: on the superior extraction yield and selectivity toward lignin

Publication . Melro, Elodie; Riddell, Alexander; Bernin, Diana; Rosa Da Costa, Ana; Valente, Artur J. M.; Antunes, Filipe E.; Romano, Anabela; Norgren, Magnus; Medronho, Bruno

The high potential use of lignin in novel biomaterialsand chemicalsrepresents an important opportunity for the valorization of the mostabundant natural resource of aromatic molecules. From an environmentalperspective, it is highly desirable replacing the hazardous methodscurrently used to extract lignin from lignocellulosic biomass anddevelop more sustainable and environmentally friendly approaches.Therefore, in this work, levulinic acid (a "green" solventobtained from biomass) was successfully used, for the first time,to selectively extract high-quality lignin from pine wood sawdustresidues at 200 degrees C for 6 h (at atmospheric pressure). Moreover,the addition of catalytic concentrations of inorganic acids (i.e.,H2SO4 or HCl) was found to substantially reducethe temperature and reaction times needed (i.e., 140 degrees C, 2 h)for complete lignin extraction without compromising its purity. NMRdata suggests that condensed OH structures and acidic groups are presentin the lignin following extraction. Levulinic acid can be easily recycledand efficiently reused several times without affecting its performance.Furthermore, excellent solvent reusability and performance of extractionof other wood residues has been successfully demonstrated, thus makingthe developed levulinic acid-based procedure highly appealing andpromising to replace the traditional less sustainable methodologies.

2023Journal article

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Ethyl 7-Acetyl-8a-methyl-3-(1-phenyl-1H-tetrazol-5-yl)-1,4,4a,5,6,8a-hexahydro-7H-pyrano[2,3-c]pyridazine-1-carboxylate

Publication . Lopes, Susana M. M.; Lemos, Americo; Paixão, José A.; Pinho e Melo, Teresa M. V. D.

The Diels–Alder reaction of ethyl 3-(1-phenyl-1H-tetrazol-5-yl-1,2-diaza-1,3-butadiene-1-carboxylate with 2-acetyl-6-methyl-2,3-dihydro-4H-pyran (methyl vinyl ketone dimer) regioselectively afforded the corresponding 3-(tetrazol-5-yl)-hexahydro-7H-pyrano[2,3-c]pyridazine in quantitative yield. An X-ray crystal structure of this cycloadduct is reported.

2022-02-10Journal article

Open Access

Synthesis of Non-symmetrical Dispiro-1,2,4,5-Tetraoxanes and Dispiro-1,2,4-Trioxanes Catalyzed by Silica Sulfuric Acid

Publication . Amado, Patrícia; Frija, Luís M. T.; Coelho, Jaime A. S.; O’Neill, Paul M.; Cristiano, Maria De Lurdes

A novel protocol for the preparation of nonsymmetrical 1,2,4,5-tetraoxanes and 1,2,4-trioxanes, promoted by the heterogeneous silica sulfuric acid (SSA) catalyst, is reported. Different ketones react under mild conditions with gemdihydroperoxides or peroxysilyl alcohols/beta-hydroperoxy alcohols to generate the corresponding endoperoxides in good yields. Our mechanistic proposal, assisted by molecular orbital calculations, at the.B97XD/def2-TZVPP/PCM(DCM)// B3LYP/6-31G(d) level of theory, enhances the role of SSA in the cyclocondensation step. This novel procedure differs from previously reported methods by using readily available and inexpensive reagents, with recyclable properties, thereby establishing a valid alternative approach for the synthesis of new biologically active endoperoxides.

2021Journal article

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Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted process

Publication . Melro, Elodie; Duarte, Hugo; Antunes, Filipe E.; Valente, Artur J.M.; Romano, Anabela; Norgren, Magnus; Medronho, Bruno

Phenolic foams are typically produced from phenolic resins, using phenol and formaldehyde precursors. Therefore, common phenolic foams are non-sustainable, comprising growing environmental, health, and economic concerns. In this work, lignin extracted from pine wood residues using a "green" levulinic acid-based solvent, was used to partially substitute non-sustainable phenol. The novel engineered foams were systematically compared to foams composed of different types of commercially available technical lignins. Different features were analyzed, such as foam density, microstructure (electron microscopy), surface hydrophilicity (contact angle), chemical grafting (infrared spectroscopy) and mechanical and thermal features. Overall, it was observed that up to 30 wt% of phenol can be substituted by the new type of lignin, without compromising the foam properties. This work provides a new insights on the development of novel lignin-based foams as a very promising sustainable and renewable alternative to petrol-based counterparts.

2023-09Journal article

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