Browsing by Author "Relvas, F."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Green chemistry and biorefineries: common future?Publication . Carvalho, V.; Relvas, F.; Lopes, André; Morais, Ana Rita C.; Silva, Sara P. Magalhães da; Mata, Ana C.; Roseiro, Luisa B.; Lukasik, Rafal M.Green Chemistry and Biorefinery concepts are two approaches helping to develop new and more sustainable processes.The implementation of both methodologies impels to fossil-independent future with bioeconomy based on natural feedstock like biowaste and industrial by-products. The development of technologies for valorisation of these resources is a key role of society in the creation of sustainable and more environmentally friendly future. Shortly after the Rio Declaration on Environment and Development, Anastas and Warner presented 12 Principles of Green Chemistry but more a decade before Trevor Kletz in his Jubilee lecture entitled “What you don’t have, can’t leak” draw the frames in which scientific and industrial work should be performed. This basis of green chemistry created a fundament for further development and implementation of Anastas and Warner principles of green chemistry. One of these frames is integration of green chemistry principles in the biorefinery concept. The biorefinery is an industrial facility (or network of facilities) that cover an extensive range of combined technologies aiming to full sustainable transformation of biomass into their building blocks with the concomitant production of biofuels, energy, chemicals and materials, preferably of value added products. One of the principles of green chemistry is the use of more sustainable solvents. Some examples of them are ionic liquids (ILs) and supercritical fluids (scF). This work will demonstrate the successful examples of lignocellulosic biomass valorisation using green solvents answering the question regarding the feasibility of future biorefineries made in a greener manner.
- Kinetic modeling of hemicellulose-derived biomass hydrolysis under high pressure CO2–H2O mixture technologyPublication . Relvas, F.; Morais, Ana Rita C.; Lukasik, Rafal M.This work is focused on the development of kinetic models of hydrolysis of hemicellulose-derived wheat straw under high-pressure CO2.H2O technology. The experiments were performed at fixed temperature (180.C), varying pressure from 0 (water-only reaction), 20, 35 to 50 bar of initial CO2 pressure and reaction times varied from 0 to 45 min. The three accurate kinetic models allowed to describe the effect of reaction conditions mainly hitherto not studied CO2 pressure and reaction time on the concentration of intermediate compounds such as xylose and arabinose in both oligomer and monomer form as well as final compounds e.g. acetic acid, furfural and other degradation products. Modeling demonstrated that addition of CO2 plays an important role in kinetics study of hemicellulose fraction hydrolysis being the fastest step the polysaccharides f hydrolysis into sugars in oligomer form. Even negligible amount of CO2 (20 bar of initial pressure) improves the initial kinetic constant of aforementioned reaction by almost 40% in comparison to water-only process. Depletion of oligosaccharides ' concentration and counterbalanced production of monomer sugars were found for longer reaction times, achieving maximum faster for CO2 assisted than CO2 free processes. Moreover, the increase of initial CO2 pressure demonstrated to be highly efficient in enhancement of the kinetic constants of all reactions occurring in the liquors. The developed models demonstrated a good fitting to the experimental data albeit the complex composition of raw material as well as the multistep analytical process.
- Selective hydrolysis of wheat straw hemicellulose using high-pressure CO2 as catalystPublication . Relvas, F.; Morais, Ana Rita C.; Lukasik, Rafal M.The processing of wheat straw using high-pressure CO2–H2O technology was studied with the objective to evaluate the effect of CO2 as catalyst on the hydrothermal production of hemicellulose-derived sugars either as oligomers or as monomers. Also, the reduction of the crystallinity of the cellulose-rich fraction was assessed. Over a range of reaction conditions (0 to 50 bar of initial CO2 pressure and 0 to 45 minutes of holding time, at T ¼ 180 C), the addition of CO2 to water-based processes led to the in situ formation of carbonic acid, which allowed us to obtain a higher dissolution of wheat straw hemicellulose. Furthermore, this approach led to a xylo-oligosaccharide (XOS) rich fraction, yielding 79.6 g of XOS per 100 g of the initial xylan content (at 50 bar of initial CO2 pressure and 12 min of residence time) while the water-only process gave only 70.8 g of XOS per 100 g of initial xylan content. Furthermore, for higher pressures of CO2, a decrease in oligosaccharide content was found and was counterbalanced by production of monomer sugars, achieving a maximum of 5.7 g L1 at the severest condition.