Effect of Ultrasound on Lignocellulosic Biomass as a Pretreatment for Biorefinery and Biofuel Applications

The conversion of lignocellulosic biomass for biofuels and biorefinery applications is limited due to the cost of pretreatment to separate or access the biomass’s three main usable components, cellulose, hemicellulose, and lignin. After pretreatment, each component may be utilized via chemical conversion, hydrolysis, and/or fermentation. In this review we aim first, to identify the current status-quo of knowledge of the parametric effects of ultrasound, second, to evaluate the potential of ultrasound as a pretreatment and fractionation method of lignocellulose, and last, to identify the challenges that this technology faces. Ultrasound produces chemical and physical effects which were both found to augment the pretreatment of lignocellulose via delignification and surface erosion. The magnitudes of these effects are altered when the ultrasonic field is influenced by parameters such as solvent, ultrasonic frequency, and reactor geometry and type. Therefore, the implementation of ultrasound for the pretreatment of lignocellulose must consider the variation of ultrasonic influences to capitalize on the key effects of ultrasound. Currently the literature is dominated by low frequency ultrasonic treatment, coupled with alkaline solutions. High frequency ultrasound, oxidizing solutions, and use of combined alternative augmentation techniques show promise for the reduction of energy consumed and synergistic enhancement of ultrasonic treatment. Furthermore, feedstock characteristics, reactor configuration, kinetics, and the ultrasonic environment should be considered

Kinetic Modeling Study of the Effect of Iron on Ignition and Combustion of <i>n</i>‑Heptane in Counter-flow Diffusion Flames

A kinetic modeling study of the effect of iron on the ignition and combustion characteristics of diesel, modeled as <i>n</i>-heptane, in compression ignition engines was carried out using CHEMKIN PRO. The ignition was simulated using the SENKIN code, and combustion was modeled using the OPPDIF code. The kinetic models incorporated <i>n</i>-heptane mechanisms involving 159 species and 1540 reactions and iron reaction mechanisms of 7 iron species and 46 reactions. It was found that small amounts of iron in the fuel significantly reduced the ignition delay time. The ignition delay time decreased with an increasing iron concentration. A reaction pathway analysis showed that the ignition was promoted as a result of an early injection of the OH radicals. It was also showed that the addition of iron increased the peak flame temperature of <i>n</i>-heptane in the counter-flow diffusion flame and reduced the maximum mole fractions of H and O in the peak flame region as a result of the catalytic recombination cycles involving FeO, Fe­(OH)₂, and FeOH. The reaction rates of H + O₂ ⇔ O + OH and CO + OH ⇔ CO₂ + H in the peak flame region were found to increase, which is considered to be responsible for the increased peak flame temperature

Rational Design of ZnFe₂O₄/In₂O₃ Nanoheterostructures: Efficient Photocatalyst for Gaseous 1,2-Dichlorobenzene Degradation and Mechanistic Insight

Novel ZnFe₂O₄/In₂O₃ hybrid nanoheterostructures with enhanced visible-light catalytic performance were fabricated by assembling ZnFe₂O₄ nanoparticles on the surface of monodispersed In₂O₃ nanospheres, and their photocatalytic performances were evaluated via the degradation of gaseous 1,2-dichlorobenzene (<i>o</i>-DCB). The catalytic activity of the resulting heterostructures for degradation of <i>o</i>-DCB was higher than that of either pure In₂O₃ or ZnFe₂O₄. The enhanced activity was mainly ascribed to the enhanced visible-light harvesting ability, efficient spatial separation, and prolonged lifetimes of photogenerated charges. Meanwhile, the main reaction intermediates including <i>o</i>-benzoquinone type species, phenolate species, formates, acetates, and maleates were verified with <i>in situ</i> FTIR spectroscopy. Additionally, a tentative catalytic reaction mechanism and the generation pathway of ^•OH over the ZnFe₂O₄/In₂O₃ nanohetero­structures were postulated. The present work provides some significative information for the eradication of harmful chlorinated volatile organic compounds and is expected to benefit the development of In₂O₃-based hybrid heterostructures

Insight into the Mechanism of Selective Catalytic Reduction of NO_<i>x</i> by Propene over the Cu/Ti_0.7Zr_0.3O₂ Catalyst by Fourier Transform Infrared Spectroscopy and Density Functional Theory Calculations

The mechanism of selective catalytic reduction of NO_<i>x</i> by propene (C₃H₆-SCR) over the Cu/Ti_0.7Zr_0.3O₂ catalyst was studied by <i>in situ</i> Fourier transform infrared (FTIR) spectroscopy and density functional theory (DFT) calculations. Especially, the formation and transformation of cyanide (−CN species) during the reaction was discussed. According to FTIR results, the excellent performance of the Cu/Ti_0.7Zr_0.3O₂ catalyst in C₃H₆-SCR was attributed to the coexistence of two parallel pathways to produce N₂ by the isocyanate (−NCO species) and −CN species intermediates. Besides the hydrolysis of the −NCO species, the reaction between the −CN species and nitrates and/or NO₂ was also a crucial pathway for the NO reduction. On the basis of the DFT calculations on the energy of possible intermediates and transition states at the B3LYP/6-311 G (d, p) level of theory, the reaction channel of −CN species in the SCR reaction was identified and the role of −CN species as a crucial intermediate to generate N₂ was also confirmed from the thermodynamics view. In combination of the FTIR and DFT results, a modified mechanism with two parallel pathways to produce N₂ by the reaction of −NCO and −CN species over the Cu/Ti_0.7Zr_0.3O₂ catalyst was proposed

Rates of maltose production by BAM3 with G4, G5 and G6 substrates.

<p>The rates of maltose production from 5 mM G4, G5 or G6, were quantified by GC-MS.</p

Model for control of starch breakdown by maltotriose and DPE1.

<p><b>A:</b> Key enzyme reactions (BAM3 and DPE1) in the model. <b>B:</b> Schematic diagram of starch breakdown controlled by maltotriose (G3) and DPE1. The rate at which glucose (G) is exported from the chloroplast determines the stromal concentration of G and hence the G3 concentration. High [G] and hence high [G3] concentration inhibits BAM3 and therefore slows the rate of starch breakdown.</p

Inhibition of <i>Arabidopsis</i> chloroplast β-amylase BAM3 by maltotriose suggests a mechanism for the control of transitory leaf starch mobilisation

<div><p>Starch breakdown in leaves at night is tightly matched to the duration of the dark period, but the mechanism by which this regulation is achieved is unknown. In <i>Arabidopsis</i> chloroplasts, β-amylase BAM3 hydrolyses transitory starch, producing maltose and residual maltotriose. The aim of the current research was to investigate the regulatory and kinetic properties of BAM3. The BAM3 protein was expressed in <i>Escherichia coli</i> and first assayed using a model substrate. Enzyme activity was stimulated by treatment with dithiothreitol and was increased 40% by 2–10 μM Ca²⁺ but did not require Mg²⁺. In order to investigate substrate specificity and possible regulatory effects of glucans, we developed a GC-MS method to assay reaction products. BAM3 readily hydrolysed maltohexaose with a K_m of 1.7 mM and K_cat of 4300 s^-1 but activity was 3.4-fold lower with maltopentaose and was negligible with maltotetraose. With maltohexaose or amylopectin as substrates and using [UL-¹³C₁₂]maltose in an isotopic dilution method, we discovered that BAM3 activity is inhibited by maltotriose at physiological (mM) concentrations, but not by maltose. In contrast, the extracellular β-amylase of barley is only weakly inhibited by maltotriose. Our results may explain the impaired starch breakdown in maltotriose-accumulating mutants such as <i>dpe1</i> which lacks the chloroplast disproportionating enzyme (DPE1) metabolising maltotriose to glucose. We hypothesise that the rate of starch breakdown in leaves can be regulated by inhibition of BAM3 by maltotriose, the concentration of which is determined by DPE, which is in turn influenced by the stromal concentration of glucose. Since the plastid glucose transporter pGlcT catalyses facilitated diffusion between stroma and cytosol, changes in consumption of glucose in the cytosol are expected to lead to concomitant changes in plastid glucose and maltotriose, and hence compensatory changes in BAM3 activity.</p></div

Comparison of BAM3 kinetic parameters using G5 and G6 as substrates.

<p>BAM3 kinetic parameters were measured using G5 (<b>A</b>) and G6 (<b>B</b>) as substrate. Michaelis-Menten and kinetic data were generated using the Sigma-enzyme kinetic program.</p

Comparison of BAM3 kinetic parameters using G5 and G6 substrates.

<p>Comparison of BAM3 kinetic parameters using G5 and G6 substrates.</p

Inhibitory effect of maltotriose on BAM3.

<p>Maltotriose (G3) was added to the assay mix at the concentrations shown and maltose as the reaction product was detected by GC-MS. <b>A:</b> BAM3 acting on amylopectin (AP) as substrate, <b>B:</b> Barley BAM acting on AP, <b>C:</b> BAM3 acting on G6, <b>D:</b> Barley BAM acting on G6. Each value is the mean of three independent replicates (+/- SE) and significant differences determined by the Student’s <i>t</i>-test are shown (* P > 0.1; ** P > 0.05; *** P > 0.01).</p