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- Cork Liquefaction for Polyurethane Foam ProdutionPublication . Esteves, Bruno; Dulyanska, Yuliya; Costa, Catarina; Vicente, Jose; Domingos, Idalina; Pereira, Helena; Lemos, Luis; Cruz-Lopes, LuísaCork is one of the most important forest products in Portugal. The cork processing industry is highly resource-efficient, with the only residue, cork powder, which is too minor in quantity for agglomerate production. This work studied the usage of cork powder for the production of added-value products via polyol liquefaction. Liquefactions were performed in a reactor using a mixture of polyethylene glycol (PEG 400) and glycerol as solvents, which were catalyzed by the addition of sulphuric acid. Several cork-to-solvent ratios, reaction temperatures, and reaction times were tested. Polyurethane foams were prepared by combining polyol mixtures with a catalyst, surfactant, blowing agent, and polymeric isocyanate. Mechanical tests of the produced foams were conducted, and compressive modulus of elasticity and compressive stress at 10% deformation were determined. The results show that the best conditions for obtaining high liquefaction yields are as follows: 160 ºC for 1 h; glycerol-to-PEG 400 ratio of 1:9; cork-to-solvent ratio of 1:6; and 3% H2SO4 catalyst addition. The Fourier Transform Infrared (FTIR) spectra indicated that the lignocellulosic fractions of the cork were more selectively dissolved during acidified polyol liquefaction than the suberin. With liquefied cork powder using these optimized conditions, it is possible to produce polyurethane foams with desired properties.
- Influence of Chemical Composition on Heating Value of Biomass: A Review and Bibliometric AnalysisPublication . Esteves, Bruno; Sen, Umut; Pereira, HelenaAbstract: Biomass has become an increasingly important resource for energy generation. The influence of the chemical composition on the heating value of biomass has not been a thoroughly studied subject, as shown by a bibliometric analysis. It is well known that the heating value of lignin is significantly higher (23.26–25.58 MJ/kg) than that of polysaccharides (18.6 MJ/kg), while extractives often have HHVs over 30 MJ/kg, depending on their oxidation levels. Therefore, the proportions of the chemical components in biomass determine its HHV. Softwoods generally have higher HHVs than hardwoods due to their higher contents of lignin and lipophilic resin. Ashes are incombustible, and a high ash content leads to a lower HHV in biomass. Several models have been proposed to correlate the heating values and chemical compounds of biomass, but the most accurate models are based on the lignin from extracted samples, while good correlations between lignin and extractives have also been reported. No good correlations have been obtained with polysaccharide compounds.
- Quality assessment of heat-treated wood by NIR spectroscopyPublication . Esteves, Bruno; Pereira, HelenaNIR spectroscopy was tested for predicting the properties of heat treated wood using pine (Pinus pinaster) and eucalypt (Eucalyptus globulus) woods with two types of treatment: in oven and in a steam autoclave. Mass loss, equilibrium moisture content, dimensional stability, MOE, bending strength, colour CIELAB parameters and extrac- tives content were determined. NIR spectra were obtained using a fibre probe on the radial surface of the samples. NIR models for mass loss showed very high coefficients of determination ( R2 ) for cross validation ranging from 96– 98%. The models obtained for wood properties were in gen- eral good with coefficients of determination ranging from 78–95% for equilibrium moisture content, 53–78% for di- mensional stability, 47–89% for MOE, 75–77% for bending strength and 84–99%, 52–96% and 66–98% for colour pa- rameters L, a∗ and b∗, respectively. R2 of the models for extractive content varied between 41.9–79.8% for pine and between 35.3–82.2% for eucalypt wood. NIR spectroscopy showed a good potential for quality control and characteri- zation of heat treated woods.
- Optimizing Douglas-fir bark liquefaction in mixtures of glycerol and polyethylene glycol and KOHPublication . Esteves, Bruno; Cruz-Lopes, Luísa; Ferreira, José; Domingos, Idalina; Nunes, Lina; Pereira, HelenaThe outer bark of Douglas-fir (Pseudotsuga menziesii) has a significant amount of cork tissue that may be an important source of chemicals derived from its natural polymers, suberin, cellulose, hemicelluloses and lignin. The present work focuses on the polyalcohol liquefaction of Douglas-fir bark with glycerol and polyethylene glycol (PEG) in order to obtain a liquid that can be further processed to other chemicals and products. The results show that Pseudotsuga bark can be liquefied in a significant percentage in presence of alkali. The best liquefaction yield was obtained with 6% KOH as agents. Although the use of a cosolvent is favorable, good liquefaction yields can also be obtained by glycerol alone. Lower temperatures are favorable as they lead to acceptable liquefaction yields. FTIR-ATR studies showed that all the structural compounds of the bark were attacked and depolymerized. The process tested has a high potential for generation of value-added products from liquefied Douglas-fir bark.
- Chemical characterization, bioactive and fuel properties of waste cork and phloem fractions from Quercus cerris L. barkPublication . Sen, Ali; Miranda, Isabel; Esteves, Bruno; Pereira, HelenaWaste biomass composed of cork-rich and phloem-rich granules obtained from the fractioning of Quercus cerris L. bark were characterized for bulk density, chemical composition, bio-active components, ash composition, and higher heating value. Bulk density of the fractions relate to their cork content and deceases with smaller particle size due to a cork enrichment in the finer particles. The bulk density may therefore be used as an indicator of suberin content of waste cork and phloem fractions. Waste cork fractions are rich sources of lipophilic and polar extracts while waste phloem fractions contain high amount of polar extracts. The polar extracts of both biomass fractions showed very high antioxidant capacities with IC50 values between 2.5 and 7.3 μg extract mL-1 for cork fractions and 5.8 and 11.7 μg extract mL-1 for phloem fractions. Higher heating values in waste cork fractions increase with decreasing particle size and ranged between 20 and 22 MJ kg-1. A biorefinery scheme was developed for the valorization of the waste cork and phloem fractions based on their physical, chemical, bioactive, and higher heating values
- Heat-treated wood as chromium adsorption materialPublication . Esteves, Bruno; Cruz-Lopes, Luísa; Figueirinha, Artur; de Lemos, Luis Teixeira; Ferreira, José; Pereira, Helena; Domingos, IdalinaHeavy metals adsorption with lignocellulosic materials has been heavily researched in the last years. Since heat activation has been used with good results to increase the adsorption capacity of some materials, heat-treated wood might be a better adsorbent. This hypothesis is the basis of the present study. The adsorption tests were made with powdered pine wood, heat-treated at 190–210 °C. All the heat-treated samples showed a significantly higher adsorption compared to untreated wood. The maximum adsorption was obtained at pH 3 for heat-treated wood at 210 °C. The kinetics of the adsorption process fitted a pseudo-second-order reaction (R2 0.990–0.996). Adsorption fitted well both the Langmuir and the Freundlich model, but the Freundlich model presented higher R2 (0.988–0.998). The qmax values estimated by the Langmuir plotting were in the range 15.6–19.4 mg/g and the n values from Freundlich isotherms between 1.87 and 2.39. Heat-treated wood was a better adsorption material than untreated wood for chromium adsorption. This can be a good application for the sawdust produced by the processing of heat-treated wood at primary and secondary wood processing mills or for the recycling of heat-treated wood at the end of product life.
- Life Cycle Assessment of Maritime Pine Wood: A Portuguese Case StudyPublication . Ferreira, José; Jones, Dennis; Esteves, Bruno; Cruz-Lopes, Luisa; Pereira, Helena; Domingos, IdalinaLife Cycle Assessment has become one of the most recognized and internationally accepted method for examining the environmental performance of forest products and processes. The main aim of this study was to evaluate the potential environmental impact associated with different commercial outputs of maritime pine wood (round, industrial, and residual) produced in the Portuguese forest under natural regeneration. Identifying the hotspots in the life cycle (cradle-to-gate) of each sort of maritime pine was another objective of the study. SimaPro software was used for this study, whilst the CML-IA (baseline) method was chosen to assess the environmental impacts. The study showed that round wood presented the highest values in all impact categories and industrial wood presented the lowest values except in photochemical oxidation where residual wood was the best co-product when economic allocation is chosen. The major hot spots appeared to be the felling and hauling processes due to fossil fuel combustion in the chainsaw and forwarder, respectively. The co-product that should be more environmentally friendly considerably depends on the allocation procedure chosen.
- Pyrolysis and Extraction of Bark in a Biorefineries Context: A Critical ReviewPublication . Sen, Umut; Esteves, Bruno; Pereira, HelenaAbstract: Bark-based biorefineries are estimated to become a trending topic in the coming years, particularly with their adsorbent applications and antioxidant production. While the potential benefits of bark-based biorefineries are well-recognized, it is not known how to develop a bark-based biorefinery considering different unit operations and the potential end products. The characterization and screening of different barks for chemical composition is the initial step in biorefinery development, along with the selection of the relevant conversion processes. This state-of-the-art review provides background knowledge on the pyrolysis and extraction studies of bark as the key conversion operations. The results of recent (2010–2022) bark pyrolysis and extraction studies were critically analyzed for process conditions, product properties, and product yields, as well as a discussion of energy-saving possibilities. A biorefinery scheme was proposed based on these data. The current knowledge gaps were identified and future directions were evaluated, which include the production of charcoals, platform chemicals, and extract profiling for specific applications. The results indicate that barks are particularly rich in hydrophilic extractives with potential antioxidant properties and pyrolysis operations, resulting in functional chars that may be used in value-added applications as adsorbent materials. A biorefinery scheme allows for the production of platform chemicals, antioxidant extracts and biochars from barks while contributing to the reduction of waste and environmental pollution.
- Insights into the combustion behavior of cork and phloem: effect of chemical components and biomass morphologyPublication . Sen, Ali Umut; Esteves, Bruno; Lemos, Francisco; Pereira, HelenaThermochemical analysis, wet-chemical analysis, and scanning electron microscopy observations were performed on granulated cork samples of Quercus cerris and Beaucarnea recurvata and on Q. cerris and Betula pendula phloems. The results show that the combustion behavior depends both on the chemical composition and the morphology of the bark fractions. The ignition temperature relies on the chemical composition while the combustion rate depends on the morphology and particle size. Ash and suberin contents are positively correlated with ignition and burnout temperatures of cork which vary between 255 and 290 °C, and 500 and 600 °C, respectively. Suberin delays the char oxidation reaction in cork. The average activation energies of cork and phloem are 31.1 and 21.2 kJ mol−1 in the first and second stages of combustion respectively.
- Removal of Antibiotics by Biochars: A Critical ReviewPublication . Sen, Umut; Esteves, Bruno; Aguiar, Terencio; Pereira, HelenaAntibiotics are pharmaceuticals that are used to treat bacterial infections in humans and animals, and they are also used as growth promoters in livestock production. These activities lead to an alarming accumulation of antibiotics in aquatic environments, resulting in selection pressure for antibiotic resistance. Given that it is impractical to completely avoid the use of antibiotics, addressing the removal of antibiotics from the environment has become an important challenge. Adsorption methods and adsorbents have received particular attention because adsorption is highly efficient in the removal of low-concentration chemicals. Among the different adsorbents, biochars have shown promise for antibiotic removal, owing to their low cost and efficiency as well as their potential for modification to further increase their adsorption capacity. This review attempts to analyze the surface properties and ash contents of different biochars and to critically discuss the knowledge gaps in antibiotic adsorption. A total of 184 articles on antibiotic properties, adsorption of antibiotics, and biochar properties were reviewed, with a focus on the last 12 years. Antibiotic adsorption by pristine biochars and modified biochars was critically reviewed. Recommendations are provided for the adsorption of different antibiotic classes by biochars.