Showing papers by "Fang Chen published in 2018"

An “ideal lignin” facilitates full biomass utilization

Abstract: Lignin, a major component of lignocellulosic biomass, is crucial to plant growth and development but is a major impediment to efficient biomass utilization in various processes. Valorizing lignin is increasingly realized as being essential. However, rapid condensation of lignin during acidic extraction leads to the formation of recalcitrant condensed units that, along with similar units and structural heterogeneity in native lignin, drastically limits product yield and selectivity. Catechyl lignin (C-lignin), which is essentially a benzodioxane homopolymer without condensed units, might represent an ideal lignin for valorization, as it circumvents these issues. We discovered that C-lignin is highly acid-resistant. Hydrogenolysis of C-lignin resulted in the cleavage of all benzodioxane structures to produce catechyl-type monomers in near-quantitative yield with a selectivity of 90% to a single monomer.

Reductive Catalytic Fractionation of C-Lignin

Abstract: Lignin composed solely of caffeyl alcohol units, or C-lignin, was recently discovered in the seed coats of a number of vanilla orchid and cactus species. The caffeyl alcohol monomer polymerizes into a highly uniform benzodioxane backbone, making C-lignin a promising substrate for lignin valorization, where heterogeneity is a key challenge. In this study, we used reductive catalytic fractionation (RCF) on vanilla seeds to investigate the depolymerization of naturally grown C-lignin. To overcome challenges associated with the high extractive content and poor sugar retention in vanilla seeds, the ratio of monomer yield to total lignin yield was used to isolate the depolymerization efficiency of C-lignin from the extraction efficiency of lignin from seeds. This approach allowed us to compare extents of depolymerization across lignin types and biomass feedstocks. C-Lignin RCF generated extents of depolymerization akin to those of hardwoods, despite observing incomplete benzodioxane cleavage due to catalyst dea...

Beat Frequency Oscillation Analysis for Power Electronic Converters in DC Nanogrid Based on Crossed Frequency Output Impedance Matrix Model

Abstract: The interaction of power electronic converters in a microgrid can introduce system instability and power quality issues Existing investigations focus on interactions either in low-frequency regions, such as the constant power load, or in very high-frequency regions like electromagnetic interference However, interactions of power converters around their switching frequency range are not included In fact, the interaction of dc–dc converters with different switching frequencies can introduce beat frequency oscillation in certain cases Since additional frequency component (beat frequency) is generated, traditional impedance concept is no longer the tool for beat frequency oscillation analysis and new models need to be developed In this paper, a crossed frequency output impedance matrix model is proposed to describe the terminal characteristics of a dc–dc converter around its switching frequency range A high-frequency equivalent circuit model for the converter is then developed to predict the beat frequency oscillation in parallel and cascaded systems, which results from the interaction of power converters with different switching frequencies Finally, design guidelines are proposed to avoid potential beat frequency oscillation in a dc nanogrid Experimental results for both parallel and cascaded systems validate the accuracy and effectiveness of the proposed prediction method and design guidelines

Mesoporous zeolites for biofuel upgrading and glycerol conversion

Abstract: With the recent emphasis and development of sustainable chemistry, the conversion of biomass feedstocks into alternative fuels and fine chemicals over various heterogeneous catalysts has received much attention. In particular, owing to their uniform micropores, strong acidity, and stable and rigid frameworks, zeolites as catalysts or co-catalysts have exhibited excellent catalytic performances in many reactions, including hydrodesulfurization, Fischer-Tropsch synthesis, and hydrodeoxygenation. However, the relatively small sizes of the zeolite micropores strongly limit the conversion of bulky biomolecules. To overcome this issue, mesoporous zeolites with pores larger than those of biomolecules have been synthesized. As expected, these mesoporous zeolites have outperformed conventional zeolites with improved activities, better selectivities, and longer catalyst lives for the upgrading of pyrolysis oils, the transformation of lipids into biofuels, and the conversion of glycerol into acrolein and aromatic compounds. This review briefly summarizes recent works on the rational synthesis of mesoporous zeolites and their superior catalytic properties in biomass conversion.

Interface converter common mode voltage control

Abstract: Aspects of interface converter common mode (CM) voltage control are described. In one embodiment, a bi-directional alternating current (AC) to direct current (DC) interface converter system includes an AC-DC converter between an AC power system and an interface link and a DC-DC converter between a DC power system and the interface link. The AC-DC converter can include a bridge converter having power switches, such as field-insulated gate bipolar transistors (IGBTs) or another power semiconductor device. The system also includes a control loop that generates control signals for switching the power switches of the AC-DC converter, and a CM control loop that injects a CM control signal into the control loop. By injecting the CM control signal into the control loop, low-frequency ripple and asymmetry between positive and negative output voltages of the DC power system can be reduced.