Lignin as Renewable Raw Material Calvo-Flores, Francisco García; Dobado, José A.
ChemSusChem,
November 22, 2010, Letnik:
3, Številka:
11
Journal Article
Recenzirano
Lignin is by far the most abundant substance based on aromatic moieties in nature, and the largest contributor to soil organic matter. Millions of tonnes of several lignin preparations are produced ...by the paper industry every year, and a minimal amount of lignin is isolated by direct extraction of lignin from plants. Lignin is used either directly or chemically modified, as a binder, dispersant agent for pesticides, emulsifier, heavy metal sequestrant, or component for composites and copolymers. For value‐added applications of lignin to be improved, medium‐ and long‐term conversion technologies must be developed, especially for the preparation of low‐molecular‐weight compounds as an alternative to the petrochemical industry.
Join my network of LignIn! Lignin is by far the most abundant substance based on aromatic moieties in nature, and the largest contributor to soil organic matter. For value‐added applications of lignin to be improved, medium‐ and long‐term conversion technologies must be developed, especially for the preparation of low‐molecular‐weight compounds as an alternative to the petrochemical industry.
One of the highlights of green chemistry is the development of techniques and procedures with low environmental impact. In the last years, deep eutectic solvents (DES) have become an important ...alternative to conventional organic solvents. For a period ionic liquids have provoked remarkable interest, but they have been displaced by DES because they show easier preparation methods, lower prices, many of them are biodegradable and compatible with biological systems. In addition, they show adjustable physicochemical properties, high thermal stability, low volatility and are compatible with water. In this paper is reviewed the state of the art of the use of DES paying special attention to the role of reaction media in organic synthesis.
Deep eutectic solvents are an interesting alternative to conventional solvents, both as a reaction medium and for many processes and technologies used in chemistry and related sciences. They are easily prepared, versatile, many of them can be obtained from renewable sources and can be designed and adapted for specific processes. For all these reasons, they have been studied intensively in recent years and their interest is constantly growing. This paper reviews some of the most prominent applications and which are the fields of interest that may be a focus of applications in the near future.
Melatonin, a tryptophan-derived molecule, is endogenously generated in animal, plant, fungal and prokaryotic cells. Given its antioxidant properties, it is involved in a myriad of signaling functions ...associated with various aspects of plant growth and development. In higher plants, melatonin (Mel) interacts with plant regulators such as phytohormones, as well as reactive oxygen and nitrogen species including hydrogen peroxide (H2O2), nitric oxide (NO) and hydrogen sulfide (H2S). It shows great potential as a biotechnological tool to alleviate biotic and abiotic stress, to delay senescence and to conserve the sensory and nutritional quality of postharvest horticultural products which are of considerable economic importance worldwide. This review provides a comprehensive overview of the biochemistry of Mel, whose endogenous induction and exogenous application can play an important biotechnological role in enhancing the marketability and hence earnings from postharvest horticultural crops.
Many school systems across the globe turned to online education during the COVID-19 pandemic. This context differs significantly from the prepandemic situation in which massive open online courses ...attracted large numbers of voluntary learners who struggled with completion. Students who are provided online courses by their high schools also have their behavior determined by actions of their teachers and school system. We conducted experiments to improve participation in online learning before, during, and right after the COVID-19 outbreak, with 1,151 schools covering more than 45,000 students in their final years of high school in Ecuador. These experiments tested light-touch interventions at scale, motivated by behavioral science, and were carried out at three levels: that of the system, teacher, and student. We find the largest impacts come from intervening at the system level. A cheap, online learning management system for centralized monitoring increased participation by 0.21 SD and subject knowledge by 0.13 SD relative to decentralized management. Centralized management is particularly effective for underperforming schools. Teacher-level nudges in the form of benchmarking emails, encouragement messages, and administrative reminders did not improve student participation. There was no significant impact of encouragement messages to students, or in having them plan and team-up with peers. Small financial incentives in the form of lottery prizes for finishing lessons did increase study time, but was less cost-effective, and had no significant impact on knowledge. The results show the difficulty in incentivizing online learning at scale, and a key role for central monitoring.
To determine the fracture resistance of chairside computer-aided design and computer-aided manufacturing (CAD-CAM) zirconia surveyed crowns for a mandibular first molar without occlusal rest and with ...four different rest seat designs.
Seventy CAD-CAM zirconia 4Y-PSZ (IPS e.max ZirCAD MT for CEREC A1, C15, Ivoclar Vivadent) crowns (14 specimens/group) were designed and fabricated with a dental chairside CAD-CAM system (CEREC PrimeScan, and CEREC MCXL Dentsply Sirona). The restorations were divided into groups according to the following rest seat designs: (1) Surveyed crown without rest seat, (2) surveyed crowns with disto-occlusal rest seat, (3) surveyed crowns with disto-occlusal extended rest seat, (4) surveyed crowns with interproximal rest seat, and (5) continuous rest seat. Crowns were treated with a primer system (Monobond Plus, Ivoclar Vivadent) and cemented using resin luting cement (Multilink Automix, Ivoclar Vivadent) to resin-printed dies (Grey Resin V4, FormLabs). Subsequently, the crowns were subjected to 200,000 load cycles at 1 Hz with 20 N force and then loaded with a steel indenter until fracture. The test results were analyzed with one-way Analysis of Variance (ANOVA) and HSD Tukey post-Hoc test.
The mean fracture resistance of surveyed crowns without and with different rest seats was significantly different from each other. Surveyed crowns with no rest seat displayed the highest resistance (4238 N) followed by crowns with continuous rest seat (3601 N), crowns with disto-occlusal extended rest seat (3283 N), and crowns with disto-occlusal rest seat (3257 N). Crowns with interproximal rest seat displayed the lowest fracture resistance (2723 N).
Surveyed crowns without rest seats had a higher fracture resistance than crowns with rest seats Surveyed crowns with interproximal rest seats presented the lowest fracture resistance among all rest seat designs. Crowns with disto-occlusal rest seats, disto-occlusal extended rest seats, and continuous rest seats displayed similar fracture resistance.
The data obtained from field-based forest inventories, mainly basal area and stem density, are relevant for the analysis of aboveground biomass and forest fragmentation. Due to its persistently ...flooded ground, fieldwork in mangrove forests is time-consuming and complicated. Since mangroves are sensitive to the effects of climate change, selecting a reliable field method is of utmost importance. To this end, we analyzed 4 mangrove classes: Rhizophora mangle (RM), Laguncularia racemosa (LR), Avicennia germinans (AG), and AG shrub. We georeferenced and counted all mangrove stems within four 0.04 ha (20 × 20 m square). We analyzed data from 3 circular area plots and the plotless point-centered quarter method (PCQM) based on the original square plots. Depending on the mangrove class, PCQM overestimated basal area by up to 34% and stem density by 21%. The 3 circular plot surveys underestimated basal area from –1% to –29% and stem density from –3 to –25%. Based on the results, we suggest using a circular plot of 0.04 ha (r = 11.28 m) in less dense forests (RM and AG) and a circular plot of 0.015 ha (r = 6.9 m) with forest densities greater than 3,500 stems/ha (LR and AG shrub). The advantages of using the circular plot approach over PCQM are that mangrove inventories can be quantified quickly and do not require a minimum number of sampling points.
General anesthesia (GA) is a reversible drug-induced state of altered arousal required for more than 60,000 surgical procedures each day in the United States alone. Sedation and unconsciousness under ...GA are associated with stereotyped electrophysiological oscillations that are thought to reflect profound disruptions of activity in neuronal circuits that mediate awareness and cognition. Computational models make specific predictions about the role of the cortex and thalamus in these oscillations. In this paper, we provide in vivo evidence in rats that alpha oscillations (10–15 Hz) induced by the commonly used anesthetic drug propofol are synchronized between the thalamus and the medial prefrontal cortex. We also show that at deep levels of unconsciousness where movement ceases, coherent thalamocortical delta oscillations (1–5 Hz) develop, distinct from concurrent slow oscillations (0.1–1 Hz). The structure of these oscillations in both cortex and thalamus closely parallel those observed in the human electroencephalogram during propofol-induced unconsciousness. During emergence from GA, this synchronized activity dissipates in a sequence different from that observed during loss of consciousness. A possible explanation is that recovery from anesthesia-induced unconsciousness follows a “boot-up” sequence actively driven by ascending arousal centers. The involvement of medial prefrontal cortex suggests that when these oscillations (alpha, delta, slow) are observed in humans, self-awareness and internal consciousness would be impaired if not abolished. These studies advance our understanding of anesthesia-induced unconsciousness and altered arousal and further establish principled neurophysiological markers of these states.
Sustainable Chemistry Metrics Calvo-Flores, Francisco García
ChemSusChem,
01/2009, Letnik:
2, Številka:
10
Journal Article
Recenzirano
Green chemistry has developed mathematical parameters to describe the sustainability of chemical reactions and processes, in order to quantify their environmental impact. These parameters are related ...to mass and energy magnitudes, and enable analyses and numerical diagnoses of chemical reactions. The environmental impact factor (E factor), atom economy, and reaction mass efficiency have been the most influential metrics, and they are interconnected by mathematical equations. The ecodesign concept must also be considered for complex industrial syntheses, as a part of the sustainability of manufacturing processes. The aim of this Concept article is to identify the main parameters for evaluating undesirable environmental consequences.
Green machine: There are many parameters that attempt to quantify the sustainability of chemical reactions or methods. This Concept article evaluates and interconnects these parameters, and describes their suitability for assessing different parts of complex processes. Particular emphasis is placed on the necessity of integrating these metrics into everyday practice.
Emerging Pollutants Calvo-Flores, Francisco G; Isac-García, Joaquín; Dobado, José A
2018, 2017-12-18
eBook
An excellent, concise, and interdisciplinary overview of different classes of emerging pollutants arising, for example, from pharmaceuticals, pesticides, personal care products, and industrial ...chemicals and their impact on water, soil, and air. Following an introduction to chemical pollutants, with special attention focused on organic compounds and their properties, the book goes on to describe major emerging pollutants grouped according to their applications in different sectors of industrial or economic activity. For each type of compound, the chemical structure, main properties, and source are presented, along with their fate in the environment as pollutants, the latest analytical methods for detection, possible health or ecology consequences, as well as current regulatory laws. New developments, such as nanotechnology as a pollution source, are also included. The book closes with a chapter devoted to conclusions and future perspectives.
This work presents a novel approach to recover industrial waste heat and to integrate it into utilities, refrigeration, and electricity production through the incorporation of heat exchanger networks ...and thermal engines (steam Rankine cycle, organic Rankine cycle, and absorption refrigeration cycle). The solution approach is based on the iteration between metaheuristic–deterministic optimization strategies. Metaheuristic optimization is established through the MS Excel-VBA-Aspen Plus link to obtain accurate modeling results. Deterministic optimization is implemented in the GAMS platform, where the mathematical formulation is based on a superstructure that considers all of the energy interconnections between the heat exchanger network, utilities, and thermal engines. Furthermore, economic, environmental, and social targets are evaluated. A case study is presented to show the applicability of the proposed methodology. The operating conditions obtained are presented (working fluid flow rate, temperatures, pressures, and efficiencies) for each thermal engine. Furthermore, the results show an increase in the total annual profit by 148%.
PDF
