The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are generally obtained from cellulose and hemicellulose fractions of biomass via the acid-catalyzed dehydration of their relative C6-C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.

Recent catalytic routes for the preparation and the upgrading of biomass derived furfural and 5-hydroxymethylfurfural

https://pubs.rsc.org/en/content/articlepdf/2019/CY/C9CY00415G

Novozym 435: the “perfect” lipase immobilized biocatalyst?

Lipases are the industrially important biocatalysts, which are envisioned to have tremendous applications in the manufacture of a wide range of products. Their unique properties such as better stability, selectivity and substrate specificity position them as the most expansively used industrial enzymes. The research on production and applications of lipases is ever growing and there exists a need to have a latest review on the research findings of lipases. The present review aims at giving the latest and broadest overall picture of research and development on lipases by including the current studies and progressions not only in the diverse industrial application fields of lipases, but also with regard to its structure, classification and sources. Also, a special emphasis has been made on the aspects such as process optimization, modeling, and design that are very critical for further scale-up and industrial implementation. The detailed tabulations provided in each section, which are prepared by the exhaustive review of current literature covering the various aspects of lipase including its production and applications along with example case studies, will serve as the comprehensive source of current advancements in lipase research. This review will be very useful for the researchers from both industry as well as academia in promoting lipolysis as the most promising approaches to intensified, greener and sustainable processes. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:5-28, 2018.

Recent advances on sources and industrial applications of lipases

In electric vehicle (EV) inverter systems, direct-current-link capacitors, which are bulky, heavy, and susceptible to degradation from self heating, can become a critical obstacle to high power density. This paper presents a comprehensive method for the analysis and comparative evaluation of dc-link capacitor applications to minimize the volume, mass, and capacitance. Models of equivalent series resistance that are valid over a range of frequency and operating temperature are derived and experimentally validated. The root-mean-square values and frequency spectra of the capacitor current are analyzed with respect to three modulation strategies and various operating conditions over practical ranges of load power factor and modulation index in EV drive systems. The modeling and analysis also consider the self-heating process and resulting core temperature of the dc-link capacitors, which impacts their lifetimes. Based on an 80-kW permanent-magnet (PM) motor drive system, the application of electrolytic capacitors and film capacitors has been evaluated by both simulation and experimental tests. The inverter power density is improved from 2.99 kW/L to 13.3 kW/L, without sacrificing the system performance in terms of power loss, core temperature, and lifetime.

http://web.mit.edu/parmstr/www/pubs/TVT.2012.2206082.pdf

Analysis and Evaluation of DC-Link Capacitors for High-Power-Density Electric Vehicle Drive Systems

Solar-to-chemical energy conversion via heterogeneous photocatalysis is one of the sustainable approaches to tackle the growing environmental and energy challenges. Among various promising photocatalytic materials, plasmonic-driven photocatalysts feature prominent solar-driven surface plasmon resonance (SPR). Non-noble plasmonic metals (NNPMs)-based photocatalysts have been identified as a unique alternative to noble metal-based ones due to their advantages like earth-abundance, cost-effectiveness, and large-scale application capability. This review comprehensively summarizes the most recent advances in the synthesis, characterization, and properties of NNPMs-based photocatalysts. After introducing the fundamental principles of SPR, the attributes and functionalities of NNPMs in governing surface/interfacial photocatalytic processes are presented. Next, the utilization of NNPMs-based photocatalytic materials for the removal of pollutants, water splitting, CO2 reduction, and organic transformations is discussed. The review concludes with current challenges and perspectives in advancing the NNPMs-based photocatalysts, which are timely and important to plasmon-based photocatalysis, a truly interdisciplinary field across materials science, chemistry, and physics.

Non-Noble Plasmonic Metal-Based Photocatalysts.

Modified efficient perturb and observe maximum power point tracking technique for grid-tied PV system

This paper presents a new symmetrical single-phase nine-level dc–ac converter for the applications of distributed generation systems. The proposed multilevel inverter (MLI) utilizes four independent dc sources to generate the nine output voltage levels considering a reduced number of switching devices. The proposed inverter consists of main and auxiliary circuits. The main circuit is a single H-bridge circuit, which is responsible for output voltage polarity. The auxiliary circuit consists of a special combination of switching devices, which are used to synthesize the multilevel output voltage. The merits of the proposed MLI are: increased output voltage levels at reduced number of switching devices, low switching loss, low total harmonic distortion, low dv/dt stress on the switches, and hence, low ratings of the switching devices, and low cost. The effectiveness of the proposed MLI and its pulsewidth modulation switching pattern has been verified experimentally by using a laboratory prototype controlled by DSPACE-1103.

Advanced Single-Phase Nine-Level Converter for the Integration of Multiterminal DC Supplies

This paper presents the line loss minimum condition in isolated substations and same substation multiple loop distribution systems by using the unified power flow controller (UPFC). In each case, the mathematical model is presented and the line loss minimum conditions are obtained based on the line parameters of the distribution feeders. Since multiple loop distribution system is fed from same substation, the line loss minimization can be achieved by compensating the summation of the line reactance voltage drop. In an isolated substation loop distribution system, the line loss minimization can be achieved by compensating the summation of the line reactance voltage drop in addition to the voltage difference of the substations. Realization of both cases can be achieved if the loop current is eliminated from the loop system. The series compensation technique applied by the UPFC is used to eliminate the loop current from the loop distribution system and hence minimize the total line loss. The effectiveness of the proposed control schemes of the UPFC have been verified experimentally.

Line Loss Minimization in Isolated Substations and Multiple Loop Distribution Systems Using the UPFC

5-Hydroxymethylfurfural (HMF), an important biobased platform chemical, can be potentially oxidized to several products that can serve as versatile building blocks for polymers. 5-Hydroxymethyl-2-furan carboxylic acid (HMFCA) is formed by incomplete oxidation of HMF but the reaction often suffers from substrate inhibition and overoxidation to other products. In this study, resting cells of Gluconobacteroxydans DSM 50049 were shown to oxidize HMF quantitatively to HMFCA with exquisite selectivity. Complete conversion of 31.5 g L -1
 crude HMF to HMFCA was achieved within 6 h under pH-controlled conditions. Initial productivity of 10 g L -1
 h -1
 was reduced to 2 g L -1
 h -1
 toward the end of the reaction. Thereafter, additional HMF added to the reaction mixture (12 g L -1
 ) was converted up to 94% within 17 h with 100% selectivity resulting in final HMFCA concentration of 44.6 g L -1
 and yield of 6.2 g g -1
 cell dry weight. Recovery of HMFCA from the reaction could be achieved by adsorption to anion exchange resins Amberlite IRA-400 (Cl -
 form) and Ambersep 900 (OH -
 form), the former showing higher binding (169 mg/g resin) and product recovery. Alternatively, liquid-liquid extraction with ethyl acetate provided a facile separation technique for the recovery of pure HMFCA.

Mahmoud A. Sayed

Papers

Non-Noble Plasmonic Metal-Based Photocatalysts.

Modified efficient perturb and observe maximum power point tracking technique for grid-tied PV system

Advanced Single-Phase Nine-Level Converter for the Integration of Multiterminal DC Supplies

Line Loss Minimization in Isolated Substations and Multiple Loop Distribution Systems Using the UPFC

Selective Oxidation of 5-Hydroxymethylfurfural to 5-Hydroxymethyl-2-furancarboxylic Acid Using Gluconobacter oxydans