Investigating Lignin-Derived Monomers and Oligomers in Low-Molecular-Weight Fractions Separated from Depolymerized Black Liquor Retentate by Membrane Filtration

Base-catalyzed depolymerization of black liquor retentate (BLR) from the kraft pulping process, followed by ultrafiltration, has been suggested as a means of obtaining low-molecular-weight (LMW) compounds. The chemical complexity of BLR, which consists of a mixture of softwood and hardwood lignin that has undergone several kinds of treatment, leads to a complex mixture of LMW compounds, making the separation of components for the formation of value-added chemicals more difficult. Identifying the phenolic compounds in the LMW fractions obtained under different depolymerization conditions is essential for the upgrading process. In this study, a state-of-the-art nontargeted analysis method using ultra-high-performance supercritical fluid chromatography coupled to high-resolution multiple-stage tandem mass spectrometry (UHPSFC/HRMSⁿ) combined with a Kendrick mass defect-based classification model was applied to analyze the monomers and oligomers in the LMW fractions separated from BLR samples depolymerized at 170–210 °C. The most common phenolic compound types were dimers, followed by monomers. A second round of depolymerization yielded low amounts of monomers and dimers, while a high number of trimers were formed, thought to be the result of repolymerization.     

Correction of inner-filter effect in fluorescence excitation-emission matrix spectrometry using Raman scatter

Fluorescence excitation-emission matrix (EEM) spectroscopy is a useful tool for interpretation of fluorescence information from natural water samples. One of the major problems with this technique is the inner-filter effect (IFE), i.e. absorption of light at both the excitation and emission wavelengths. The common solutions are to either dilute the sample or apply some form of mathematical correction, most often based on the measured absorbance of the sample. Since dilution is not always possible, e.g. in on-line or in situ EEM recordings, and corrections based on absorbance are hampered primarily by the use of a separate absorbance instrument, neither of these solutions is optimal. In this work, we propose a mathematical correction procedure based on the intensity of Raman scatter from water. This procedure was found to reduce the error after correction by up to 50% in comparison with two absorbance correction procedures. Furthermore, it does not require the use of a separate absorbance measurement, and it is applicable to on-line and in situ EEM recordings, where the IFE would otherwise cause problems.     

O-O bond cleavage in dinuclear peroxo complexes of iron porphyrins: a quantum chemical study

To gain insight into the mechanisms of O2 activation and cleavage in metalloenzymes, biomimetic metal complexes have been constructed and experimentally characterized. One such model complex is the dinuclear peroxo complex of iron porphyrins observed at low temperature in a non-coordinating solvent. The present theoretical study examines the O-O bond cleavage in these complexes, experimentally observed to occur either at increased temperature or when a strongly coordinating base is added. Using hybrid density functional theory, it is shown that the O-O bond cleavage always occurs in a state where two low-spin irons (S = +/-1/2) are antiferromagnetically coupled to a diamagnetic state. This state is the ground state when the strong base is present and forms an axial ligand to the free iron positions. In contrast, without the axial ligands, the ground state of the dinuclear peroxo complex has two high-spin irons (S = +/-5/2) coupled antiferromagnetically. Thus, the activation barrier for O-O bond cleavage is higher without the base because it includes also the promotion energy from the ground state to the reacting state. It is further found that this excitation energy, going from 10 unpaired electrons in the high-spin case to 2 in the low-spin case, is unusually difficult to determine accurately from density functional theory because it is extremely sensitive to the amount of exact exchange included in the functional.     

Large eddy simulation of compressible channel flow

Astract The present study is a contribution to the analysis of wall-bounded compressible flows, including a special focus on wall modeling for compressible turbulent boundary layer in a plane channel. large eddy simulation (LES) of fully developed isothermal channel flows at Re = 3,000 and Re = 4,880 with a sufficient mesh refinement at the wall are carried out in the Mach number range 0.3 ≤ M ≤ 3 for two different source term formulations: first the classical extension of the incompressible configuration by Coleman et al. (J. Fluid Mech. 305:159–183, 1995), second a formulation presently derived to model both streamwise pressure drop and streamwise internal energy loss in a spatially developed compressible channel flow. It is shown that the second formulation is consistent with the spatial problem and yields a much stronger cooling effect at the wall than the classical formulation. Based on the present LES data bank, compressibility and low Reynolds number effects are analysed in terms of coherent structure and statistics. A study of the universality of the structure of the turbulence in non-hypersonic compressible boundary layers (M≤5) is performed in reference to Bradshaw (Annu. Rev. Fluid. Mech. 9:33–54, 1977). An improvement of the van Driest transformation is proposed; it accounts for both density and viscosity changes in the wall layer. Consistently, a new integral wall scaling (y ^c+) which accounts for strong temperature gradients at the wall is developed for the present non-adiabatic compressible flow. The modification of the strong Reynolds analogy proposed by Huang et al. (J. Fluid Mech. 305:185–218, 1995) to model the correlation between velocity and temperature for non-adiabatic wall layers is assessed on the basis of a Crocco–Busemann relation specific to channel flow. The key role of the mixing turbulent Prandtl number Pr _m is pointed out. Results show very good agreement for both source formulations although each of them involve a very different amount of energy transfer at the wall. The present work was performed within the framework of the French–German research initiative “large eddy simulation of complex flows’ (UR 507). The computing resources were provided by IDRIS-France. The authors gratefully acknowledge the financial support from the Centre National de la Recherche Scientifique (CNRS), the Centre d’été Mathématique de Recherche Avancée en Calcul Scientifique (CEMRACS) and the Direction Générale de l’Armement (DGA/D4S).     

Dynamic extraction coupled on-line to liquid chromatography with a parallel sampling interface—a proof of concept for monitoring extraction kinetics

On-line hyphenation of extraction with chromatography has been explored in several different types of combinations. However, monitoring the complete process of a dynamic, continuous-flow extraction is not possible with any hyphenated system reported so far. The current work demonstrates that this challenging task can be effectively fulfilled by using a parallel sampling interface, which mimics the concept of comprehensive two-dimensional chromatography. In this study, pressurised hot water extraction was coupled on-line with ultra-high-performance liquid chromatography. The set-up was utilised in a kinetic study of dynamic pressurised hot water extraction of curcuminoids from turmeric powder. Compound-specific extraction curves were obtained, which clearly indicated the rate-limiting factors of the extraction processes under different conditions. Additionally, thermal degradation of curcumin during the extraction could also be demonstrated in some of the extractions.

     

Determination of phase transitions in binary systems of mesogenic compounds by optical absorption spectroscopy

The use is described of absorption spectroscopy for determining phase transitions in the mesogenic compound cholesteryl myristate (CM) and in binary mixtures of terephthalbis-butyl-aniline (TBBA) and cholesteryl myristate. The temperature dependence of the optical densities in the visible region at phase transitions is reported. The transition temperatures obtained with this method are in good agreement with the results obtained with other methods.     

Experimental approach of co-firing and anaerobic fermentation of biomass and coal, and their thermochemical properties

This article studied two sorts of biomass (corn and beech sawdust) and two varieties of coal (bituminous coal and lignite), which can produce energy using two different technologies: co-firing and anaerobic fermentation in pilot installations, in order to determine the future perspectives of those materials for large scale applications. By thermal analysis, the thermochemical characteristics of biomass (corn and beech sawdust) and of coal (bituminous coal from Jiu Valley and lignite from Oltenia basin) were determined. The co-firing tests have been achieved at a ratio of 15?% biomass, the rest being coal. At biomass?Ccoal co-firing, the SO₂, NO_x, CO, CO₂ and fly ash concentrations in the flue gases is lower than the burning of fossil fuels. In the anaerobic fermentation of biomass, the maximum concentration of methane inside the produced biogas was 50?C55?% by volume in the beech sawdust batch and 67?C68?% by volume in the corn batch.     

Poly[[tetraaquadi‐μ4‐glutarato‐μ2‐terephthalato‐dineodymium(III)] heptadecahydrate]

The title compound, [Nd₂(C₅H₆O₄)₂(C₈H₄O₄)(H₂O)₄]·17H₂O, obtained via hydrothermal reaction of Nd₂O₃ with glutaric acid and terephthalic acid, assembles as a three‐dimensional open framework with ten‐coordinate Nd–O polyhedra. The asymmetric part of the unit cell contains half a glutarate anion, a quarter of a terephthalate dianion, half an Nd^III cation, one coordinated water molecule and 4.25 solvent water molecules. Each [NdO₁₀] coordination polyhedron is comprised of six O atoms originating from four glutarate anions, two others from a terephthalate carboxylate group, which coordinates in a bidentate fashion, and two from water molecules. The Nd—O distances range from 2.4184 (18) to 2.7463 (18) Å. The coordination polyhedra are interconnected by the glutarate anions, extending as a two‐dimensional layer throughout the bc plane. Individual two‐dimensional layers are interlinked via terephthalate anions along the a axis. This arrangement results in rectangular‐shaped cavities with interstices of approximately 3.5 × 6 × 6.5 Å (approximately 140 ų), which are occupied by water molecules. The Nd^III cations, terephthalate anions, glutarate anions and one of the interstitial water molecules are located on special crystallographic positions. The Nd–terephthalate–Nd units are located across twofold rotation axes parallel to [100], with the Nd^III cations located directly on these axes. In addition, the terephthalate anion is bisected by a crystallographic mirror plane perpendicular to that axis, thus creating an inversion centre in the middle of the aromatic ring. The glutarate ligand is bisected by a crystallographic mirror plane perpendicular to (001). One of the solvent water molecules lies on a site of 2/m symmetry, and the symmetry‐imposed disorder of its H atoms extends to the H atoms of the other four solvent water molecules, which are disordered over two equally occupied and mutually exclusive sets of positions.     

Measuring the relative efficiency of the food and drink industry in the chosen EU countries using the data envelopment analysis with missing data

Central European Journal of Operations Research - The food and drink industry is one of the leading manufacturing sectors in the economies of many EU countries. However, when compared to other...