| 1. |
- Abdelaziz, Omar Y., et al.
(author)
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Biological valorization of low molecular weight lignin
- 2016
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In: Biotechnology Advances. - : Elsevier BV. - 0734-9750. ; 34:8, s. 1318-1346
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Research review (peer-reviewed)abstract
- Lignin is a major component of lignocellulosic biomass and as such, it is processed in enormous amounts in the pulp and paper industry worldwide. In such industry it mainly serves the purpose of a fuel to provide process steam and electricity, and to a minor extent to provide low grade heat for external purposes. Also from other biorefinery concepts, including 2nd generation ethanol, increasing amounts of lignin will be generated. Other uses for lignin – apart from fuel production – are of increasing interest not least in these new biorefinery concepts. These new uses can broadly be divided into application of the polymer as such, native or modified, or the use of lignin as a feedstock for the production of chemicals. The present review focuses on the latter and in particular the advances in the biological routes for chemicals production from lignin. Such a biological route will likely involve an initial depolymerization, which is followed by biological conversion of the obtained smaller lignin fragments. The conversion can be either a short catalytic conversion into desired chemicals, or a longer metabolic conversion. In this review, we give a brief summary of sources of lignin, methods of depolymerization, biological pathways for conversion of the lignin monomers and the analytical tools necessary for characterizing and evaluating key lignin attributes.
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| 2. |
- Cunico, Larissa P., et al.
(author)
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Enhanced distribution kinetics in liquid-liquid extraction by CO2-expanded solvents
- 2020
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In: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446. ; 163
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Journal article (peer-reviewed)abstract
- Liquid-liquid extraction (LLE) is a useful extraction technique for highly complex samples, however, it suffers from being slow due to mass transfer limitations. Carbon dioxide expanded liquids (CXL) is a good replacement of traditional organic solvents for extraction, and for the first time, the use of CXL in LLE was evaluated. An equipment consisting of a high-pressure view cell with on-line gas chromatography analysis was built and validated, and thereafter used to obtain novel phase equilibria data of the CO2/n-octanol/water system. The system was connected on-line to HPLC to study the potential of CO2-expanded liquid-liquid extraction (CXLLE) of pharmaceutical contaminants in water. In comparison with traditional LLE performed under similar experimental conditions, the addition of CO2 as a viscosity-lowering entrainer significantly increased the speed of mass transfer. Changes in compound log D (octanol-water distribution ratio) values brought by the CO2 expansion also proved the possibility of selectivity-tuning in CXLLE.
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| 3. |
- Li, Kena, et al.
(author)
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Membrane separation of the base-catalyzed depolymerization of black liquor retentate for low-molecular-mass compound production
- 2019
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In: Membranes. - : MDPI AG. - 2077-0375. ; 9:8
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Journal article (peer-reviewed)abstract
- One way of valorizing the lignin waste stream from the pulp and paper industries is depolymerizing it into low-molecular-mass compounds (LMMC). However, a common problem in the depolymerization of Kraft lignin is the low yields of small aromatic molecules obtained. In the present work, the combination of the repeated depolymerization of lignin and the separation of LMMC from depolymerized lignin to upgrade them into value-added chemicals was studied. In so doing, we investigated the possibility of depolymerizing black liquor retentate (BLR). The base-catalyzed depolymerization of BLR was performed using a continuous flow reactor at 170–210 °C, with a 2 min residence time. The results obtained indicate that BLR can be depolymerized effectively under the experimental conditions. Depolymerized lignin LMMC can be successfully separated by a GR95PP membrane, and thus be protected from repolymerization. Through combining membrane filtration with base-catalyzed depolymerization, more than half of the lignin could be depolymerized into LMMC. Around 46 mg/g of lignin monomers (guaiacol, vanillin, acetovanillone, and acetosyringone), which can potentially be upgraded to high-valued chemicals, were produced. On the basis of our results, we suggest use of a recycling Kraft lignin depolymerization and filtration process for maximizing the production of LMMC under mild alkaline conditions.
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| 4. |
- Mitra, Mainak, et al.
(author)
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Highly enantioselective epoxidation of olefins by H 2 O 2 catalyzed by a non-heme Fe(ii) catalyst of a chiral tetradentate ligand
- 2019
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In: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 48:18, s. 6123-6131
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Journal article (peer-reviewed)abstract
- The chiral tetradentate N4-donor ligand, 1-methyl-2-({(S)-2-[(S)-1-(1-methylbenzimidazol-2-yl methyl)pyrrolidin-2-yl]pyrrolidin-1-yl}methyl) benzimidazole (S,S- PDBz L), based on a chiral dipyrrolidine backbone, has been synthesized and its corresponding Fe(ii) complex has been prepared and characterized. The X-ray structure of the complex reveals that the Fe(ii) ion is in a distorted octahedral coordination environment with two cis-oriented coordination sites occupied by (labile) triflate anions. The ability of the iron complex to catalyze asymmetric epoxidation reactions of olefins with H 2 O 2 was investigated, using 2-cyclohexen-1-one, 2-cyclopenten-1-one, cis-β-methylstyrene, isophorone, chalcones and tetralones as substrates. Different carboxylic acids were used as additives to enhance yields and enantioselectivities, and 2-ethylhexanoic acid was found to give the best results. The catalysis results indicate that the Fe(ii) complex is capable of effecting comparatively high enantioselectivities (>80%) in the epoxidation reactions.
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| 5. |
- Prothmann, Jens, et al.
(author)
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Ultra-high-performance supercritical fluid chromatography with quadrupole-time-of-flight mass spectrometry (UHPSFC/QTOF-MS) for analysis of lignin-derived monomeric compounds in processed lignin samples
- 2017
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In: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 409:30, s. 7049-7061
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Journal article (peer-reviewed)abstract
- The conversion of lignin to potentially high-value low molecular weight compounds often results in complex mixtures of monomeric and oligomeric compounds. In this study, a method for the quantitative and qualitative analysis of 40 lignin-derived compounds using ultra-high-performance supercritical fluid chromatography coupled to quadrupole-time-of-flight mass spectrometry (UHPSFC/QTOF-MS) has been developed. Seven different columns were explored for maximum selectivity. Makeup solvent composition and ion source settings were optimised using a D-optimal design of experiment (DoE). Differently processed lignin samples were analysed and used for the method validation. The new UHPSFC/QTOF-MS method showed good separation of the 40 compounds within only 6-min retention time, and out of these, 36 showed high ionisation efficiency in negative electrospray ionisation mode. [Figure not available: see fulltext.]
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| 6. |
- Sun, Mingzhe, et al.
(author)
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Comprehensive on-line two-dimensional liquid chromatography × supercritical fluid chromatography with trapping column-assisted modulation for depolymerised lignin analysis
- 2018
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In: Journal of Chromatography A. - : Elsevier BV. - 0021-9673. ; 1541, s. 21-30
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Journal article (peer-reviewed)abstract
- Lignin depolymerisation produces a large variety of low molecular weight phenolic compounds that can be upgraded to value-added chemicals. Detailed analysis of these complex depolymerisation mixtures is, however, hampered by the lack of resolving power of traditional analysis techniques. In this study, a novel online comprehensive two-dimensional reversed-phase liquid chromatography (RPLC) × supercritical fluid chromatography (SFC) method with trapping column interface was developed for the separation of phenolic compounds in depolymerised lignin samples. The trapping capacities of different trapping columns were evaluated. The influence of large volume water-containing injection on SFC performance was studied. The relation between peak capacity and first dimension flow rate and gradient was investigated. The optimized method was applied for the analysis of a depolymerised lignin sample. The RPLC × SFC system exhibited high degree of orthogonality. Compared with traditional loop based interface, trapping column interface can significantly shorten the analysis time and offer higher detectability, with the disadvantage of more severe undersampling in the first dimension.
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| 7. |
- Sun, Mingzhe, et al.
(author)
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Dynamic extraction coupled on-line to liquid chromatography with a parallel sampling interface—a proof of concept for monitoring extraction kinetics
- 2019
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In: Analytical and Bioanalytical Chemistry. - : Springer Science and Business Media LLC. - 1618-2642 .- 1618-2650. ; 411:16, s. 3675-3683
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Journal article (peer-reviewed)abstract
- 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.
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| 8. |
- Sun, Mingzhe, et al.
(author)
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Signal enhancement in supercritical fluid chromatography-diode-array detection with multiple injection
- 2019
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In: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 42:24, s. 3727-3737
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Journal article (peer-reviewed)abstract
- To circumvent the detrimental effects of large-volume injection with fixed-loop injector in modern supercritical fluid chromatography, the feasibility of performing multiple injection was investigated. By accumulating analytes from a certain number of continual small-volume injections, compounds can be concentrated on the column head, and this leads to signal enhancement compared with a single injection. The signal to noise enhancement of different compounds appeared to be associated with their retention on different stationary phases and with type of sample diluent. The diethylamine column gave the best signal to noise enhancement when acetonitrile was used as sample diluent and the 2-picolylamine column showed the best overall performance with water as the sample diluent. The advantage of multiple injection over one-time large-volume injection was proven with sulfanilamide, with both acetonitrile and water as sample diluents. The multiple injection approach exhibited comparable within- and between-day precision of retention time and peak area with those of single injections. The potential of the multiple injection approach was demonstrated in the analysis of sulfanilamide-spiked honey extract and diclofenac-spiked ground water sample. The limitations of this approach were also discussed.
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| 9. |
- Sun, Mingzhe
(author)
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Supercritical fluid chromatography and two-dimensional liquid chromatography : From new applications to technical innovations
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Lignin depolymerisation can be utilized to produce value-added aromatic compounds. One of the major challenges in lignin depolymerisation study is the development of effective analytical tools to unravel the huge complexity of the depolymerisation product mixture. Traditional gas chromatography (GC) and high- performance liquid chromatography (HPLC) methods applied for this purpose are often in lack of a high resolving power to separate the various components, which exist in a large number in samples of this type. This PhD work started with the development of a 6-minute fast supercritical fluid chromatography method for the analysis of lignin-derived phenols from alkaline cupric oxide oxidation, which demonstrated for the first time the potential of supercritical fluid chromatography in the lignin type phenol analysis. As a continuation of this work to enable analysis of more model compounds with structural elucidation, a supercritical fluid chromatography with quadrupole-time-of-flight mass spectrometry method was developed. Considering the complexity of processed lignin sample, a two-dimensional liquid chromatography × supercritical fluid chromatography system was constructed with trapping column assisted modulation. The system exhibited high degree of orthogonality. A trapping column interface also significantly shorten the run time with higher detectability of the compounds compared with a traditional loop based interface. Large volume and water injection in supercritical fluid chromatography often lead to poor separation and peak shape, due to strong solvent effect and viscous fingering. Multiple injection technique was investigated in this PhD study to enable the injection of relatively large volume to enhance the detectability. The signal-to-noise ratio enhancement was found to be strongly dependent on retention. Multiple injection provided better enhancement of signal-to-noise than one-time injection of large volume, with comparable repeatability and reproducibility. Water as sample diluent was investigated to study its effect on retention and peak shape. The influence of water in sample diluent varies with varying stationary phases, injection volumes and sample diluent water contents. The study proved that it can be advantageous to use sample diluent containing water, especially when polar stationary phases are used. Monitoring a complete dynamic extraction process is not possible with any set-up reported so far, but coupling extraction with chromatography with a parallel sampling interface can be a potential solution. As a proof of concept, an on-line pressurized hot water extraction-liquid chromatography system with parallel sampling was built imitating the two-dimensional chromatography philosophy. The system was used in a kinetic study of extraction of curcuminoids from turmeric. Compound-specific extraction curves were obtained and thermal degradation of curcumin could also be demonstrated.
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| 10. |
- Sun, Mingzhe, et al.
(author)
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Ultra-high performance supercritical fluid chromatography of lignin-derived phenols from alkaline cupric oxide oxidation
- 2016
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In: Journal of Separation Science. - : Wiley. - 1615-9306 .- 1615-9314. ; 39:16, s. 3123-3129
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Journal article (peer-reviewed)abstract
- Traditional chromatographic methods for the analysis of lignin-derived phenolic compounds in environmental samples are generally time consuming. In this work, an ultra-high performance supercritical fluid chromatography method with a diode array detector for the analysis of major lignin-derived phenolic compounds produced by alkaline cupric oxide oxidation was developed. In an analysis of a collection of 11 representative monomeric lignin phenolic compounds, all compounds were clearly separated within 6 min with excellent peak shapes, with a limit of detection of 0.5–2.5 μM, a limit of quantification of 2.5–5.0 μM, and a dynamic range of 5.0–2.0 mM (R2 > 0.997). The new ultra-high performance supercritical fluid chromatography method was also applied for the qualitative and quantitative analysis of lignin-derived phenolic compounds obtained upon alkaline cupric oxide oxidation of a commercial humic acid. Ten out of the previous eleven model compounds could be quantified in the oxidized humic acid sample. The high separation power and short analysis time obtained demonstrate for the first time that supercritical fluid chromatography is a fast and reliable technique for the analysis of lignin-derived phenols in complex environmental samples.
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