Search results for "NEWA"
showing 10 items of 2491 documents
Activity of a Heterogeneous Catalyst in Deep Eutectic Solvents: The Case of Carbohydrate Conversion into 5-Hydroxymethylfurfural
2019
Obtaining industrially relevant products from renewable resources and developing processes under the light of sustainable chemistry is a prominent endeavor of present-day chemical research. In this context, herein we investigated the dehydration of fructose and sucrose in deep eutectic solvents promoted by the ion-exchange resin Amberlyst 15 as heterogeneous catalyst. We optimized the reaction conditions in terms of temperature, catalyst loading, and initial amount of substrate. Then, we looked at the effect of structural variations in the solvent components on the reaction outcome. Under the best experimental conditions, we obtained very good yields of 78% at 60 °C and 69% at 80 °C for fru…
Undecylenic acid: A tunable bio-based synthon for materials applications
2016
International audience; An undecylenic acid-based monoglyceride prepared from glycidol and undecylenic acid is used as suitable and tunable synthon for polymerization applications. Epoxidation and acrylation reactions lead to photopolymerizable monomers while transesterification with dimethyl carbonate, metathesis and aminolysis reactions provide access to polyhydroxyurethane-based materials. The successive intermediates were synthesized according to a green chemistry approach implicating solvent-less and catalyzed reactions, and were at each step fully characterized by infrared, 1H and 13C{1H} NMR spectroscopy, elemental analysis and mass spectrometry. Analyses of the resulting polymer mat…
Examples of xylochemistry: colorants and polymers
2017
Against the backdrop of modern sustainable chemistry and valorization of biomass for chemical raw materials, the syntheses of indigo dyes and polyamides as representatives of two classes of everyday chemical products based on xylochemicals are described. Wood-derived starting materials were transformed into functional materials using the principles of green chemistry to expand the scope of products gained from renewable resources. The indigo dyes were synthesized in a short, straightforward sequence starting from vanillin. Two polyamides, representatives of an important class of polymers, were obtained from 4-propylcyclohexanol, which is one of the longest known (and most abundant) hydrogen…
An E-Factor Minimized Protocol for a Sustainable and Efficient Heck Reaction in Flow
2014
A highly sustainable and waste-minimized protocol for Heck coupling has been defined. Optimal conditions have been defined by exploiting a heterogeneous catalyst based on supported ionic liquid-like phases featuring high Pd loading (10 wt %) and by optimizing its efficiency in a recoverable green reaction medium (acetonitrile/water azeotrope). Pure products 4a–l and 6a–h have been isolated chromatography-free in high yields (74–99%) and with extremely low environmental factor (E-factor) values (2.3–5.0). With the application of flow technology, the selected heterogeneous base and Pd catalyst have been fully recovered and reused, and minimum palladium leaching allowed for isolation of the fi…
GRID STABILITY IMPROVEMENT BY RES-BASED GENERATORS AND BATTERY ENERGY STORAGE SYSTEMS IN SMALL ISLANDS
2021
The integration of Renewable Energy Sources (RES) with power electronics interface to the grid, without the back-up of rotating inertia, endangers frequency stability. This issue becomes particularly critical in isolated power systems, like those of small islands not supplied by the main grid, in the case of high shares of production from unpredictable renewables such as photovoltaic and wind sources. Consequently, to preserve the security and the reliability of these systems, it is necessary to adopt new frequency adjustments mechanisms. In this context, the thesis investigates the transition toward an economically and technically feasible generating system based on RES, to achieve specifi…
Decoupled Control Scheme of Grid-Connected Split-Source Inverters
2017
During the last few years, single-stage power conversion systems has undergone a fast evolution to replace the conventional two-stage architecture, which includes a front-end dc-dc boost converter (BC) and an output voltage source inverter (VSI) [1]. This evolution has grown up to improve the overall system performance in terms of reducing its size, weight, and complexity. Most of these single-stage topologies and their different modulation schemes have been reviewed in [1]. Among these different single-stage options, the split-source inverter (SSI), shown in Figure 1, has been recently proposed in [2] as a single-stage dc-ac power converter topology to overcome some demerits in the other s…
Design of Photovoltaic System for Rural Electrification in Rwanda
2017
Master's thesis Renewable Energy ENE500 - University of Agder 2017 In this century of accelerated development in various domains, some African countries are still facing a challenge of lack of power due to its scarce in some places, where by the main source of power (generation of electricity) is hydro since thermal and fuel are still on a small scale. This problem results in less productivity and economic decline of some countries like Rwanda which is among African countries that are at a very high speed in development, the grid lines from distant places are stack and they are few compared to the need of electricity in all corners of the country, especially in rural areas whereby each hous…
Load mismatch of grid-connected photovoltaic systems: Review of the effects and analysis in an urban context
2013
Abstract The mismatch between generated and consumed electricity is a relevant topic of the energy and economic assessment of photovoltaic (PV) systems. Due to the load mismatch some amount of PV electricity may be exported to the grid because the electrical demand is temporarily lower than production, whereas a consumption, which is higher than production and/or that does not match the available PV generation, will require to be supplemented by the public grid electricity. The presence of the load mismatch can cause the effect of disadvantageously purchasing electricity from the grid and/or squandering the unexploited PV energy. If only a very small part of the PV generation is used to sup…
Renewable Energy Sources in the Baltic States and New Business Approach of the Sector
2021
Renewable energy sources (RES) are efficient in meeting the demand for clean and affordable energy. The need for RES is undeniable and has many advantages but there are also some challenges that need to be taken into consideration and adapted to the energy system. One of the challenges is RES volatility and its impact on electricity prices and power system operation. Europe is trending to power system decentralisation through the involvement of local authorities, active consumers and citizens in the system operation. This article provides main information about the energy sector of Latvia and RES in the Baltic countries. It proposes a methodology for the complex analysis of correlation and …
Are local food chains more sustainable than global food chains? Considerations for assessment
2016
© 2016 by the authors; licensee MDPI, Basel, Switzerland. This paper summarizes the main findings of the GLAMUR project which starts with an apparently simple question: is "local" more sustainable than "global"? Sustainability assessment is framed within a post-normal science perspective, advocating the integration of public deliberation and scientific research. The assessment spans 39 local, intermediate and global supply chain case studies across different commodities and countries. Assessment criteria cover environmental, economic, social, health and ethical sustainability dimensions. A closer view of the food system demonstrates a highly dynamic local-global continuum where actors, whil…