| 1. |
- Abdelaziz, Omar, et al.
(författare)
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Continuous catalytic depolymerisation and conversion of industrial kraft lignin into low-molecular-weight aromatics
- 2018
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Ingår i: Biomass Conversion and Biorefinery. - : Springer Science and Business Media LLC. - 2190-6823 .- 2190-6815. ; 8:2, s. 455-470
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Tidskriftsartikel (refereegranskat)abstract
- Base-catalysed depolymerisation of lignin using sodium hydroxide has been shown to be an effective approach towards exploiting industrial (technical) lignins within the pulp and paper industry. In the present work, a pine kraft lignin (Indulin AT) which is precipitated from black liquor of linerboard-grade pulp was depolymerised via base catalysis to produce low-molecular-mass aromatics without any organic solvent/capping agent in a continuous-flow reactor setup for the first time. The catalytic conversion of lignin was performed/screened at temperatures varying from 170 to 250 °C, using NaOH/lignin weight ratio ≈ 1 with 5 wt% lignin solids loadings for residence times of 1, 2 and 4 min, respectively, with comprehensive characterisation of substrate and produced reaction mixtures. The products were characterised using size exclusion chromatography (SEC), nuclear magnetic resonance spectroscopy (NMR) and supercritical fluid chromatography-diode array detector-tandem mass spectrometry (SFC-MS). The optimum operating conditions for such depolymerisation appeared to be at 240 °C and 30 h−1, yielding the highest concentration of low-molecular-weight phenolics below the coking point. It was also found that the depolymerised lignin products exhibited better chemical stability during long-term storage at lower temperatures (~ 4 °C).
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| 2. |
- Almqvist, Henrik, et al.
(författare)
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Muconic Acid Production Using Engineered Pseudomonas putida KT2440 and a Guaiacol-Rich Fraction Derived from Kraft Lignin
- 2021
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 9:24, s. 8097-8106
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Tidskriftsartikel (refereegranskat)abstract
- Industrial lignin such as kraft lignin is an abundant feedstock for renewable chemicals and materials. In this study, a process was developed for depolymerization of kraft lignin followed by an upgrading separation step and further bioconversion of the obtained monoaromatic compounds to muconic acid. First, industrial kraft lignin, Indulin AT, was processed into a guaiacol-rich stream using base-catalyzed depolymerization. This stream was subsequently upgraded using liquid-liquid extraction and evaporation to yield a more concentrated and less inhibitory stream, adapted for bioconversion. Finally, guaiacol was quantitatively converted to muconic acid through bioconversion using an engineered Pseudomonas putida strain containing cytochrome P450 and ferredoxin reductase for guaiacol assimilation and deletion of the native catBC genes for muconic acid production. Isomerization of muconic acid in a fermentation medium depending on pH was also studied.
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| 3. |
- Li, Kena
(författare)
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Base-catalyzed depolymerization of kraft lignin for valuable chemical production
- 2021. - Media-Tryck
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lignin is one of the three predominant biopolymers that make up plants together with cellulose and hemicellulose, and it is the only plant component that is based on aromatic units. The industrial kraft pulping process generates large amounts of lignin, which is currently used to generate heat for the process. The subject of this thesis is the valorization of kraft lignin into valuable chemicals. The work started with the depolymerization of kraft lignin, followed by studies on efficient separation processes to obtain low-molecular-weight (LMW) compounds. Finally, the microbial conversion of lignin-derived monomers for the production of fine chemicals was investigated.A lab-scale continuous-flow reactor system was developed for the depolymerization of two different Kraft lignin samples: Indulin AT and black liquor retentate (BLR) using NaOH as the only catalyst. The depolymerization experiments were performed under mild conditions at temperatures less than 250 °C and residence times less than 4 min. The effect of the depolymerization temperature, residence time, NaOH concentration, and the lignin substrate loading on depolymerization was studied. Depolymerization of Indulin AT and BLR resulted in a mixture of lower molecular weight compounds. Temperature was found to be an important factor in the depolymerization of lignin, and the main phenolic compounds obtained after depolymerization were guaiacol and vanillin. An ultrafiltration GR95PP membrane with a cut-off of 2 kDa was used in membrane filtration studies. The combination of base-catalyzed depolymerization and membrane filtration was investigated in an attempt to obtain more lignin-derived LMW compounds without severe repolymerization. Ultrafiltration of the depolymerized BLR sample removed 60% of the LMW compounds. A separation process starting with membrane filtration followed by acid precipitation and low-temperature evaporation under vacuum is suggested to obtain pure guaiacol from the depolymerized lignin samples. Concentrated vanillin and other monomers were also separated and collected. Finally, bioconversion of guaiacol using an engineered strain of Pseudomonas putida KT2440 was studied. The strain had been modified for guaiacol consumption with a cytochrome P450 enzyme and ferredoxin reductase and also modified to produce muconic acid by deletion of the downstream enzymes encoded by catBC. Both pure and kraft lignin-derived guaiacol was quantitatively converted into muconic acid, which is a promising precursor to adipic acid or terephthalic acid used in the production of nylon-6,6 or bio-plastics e.g bio-PET.
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| 4. |
- Li, Kena, et al.
(författare)
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Investigating lignin-derived monomers and oligomers in low-molecular-weight fractions separated from depolymerized black liquor retentate by membrane filtration
- 2021
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Ingår i: Molecules. - : MDPI AG. - 1420-3049. ; 26:10
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Li, Kena, et al.
(författare)
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Maximizing yield of liquid-lignin from membrane filtration retentate of kraft black liquor
- 2021
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Ingår i: Industrial Crops and Products. - : Elsevier BV. - 0926-6690. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- Removal of lignin from kraft pulping black liquor has the potential to increase pulp production, and at the same time lignin can serve as raw material for renewable fuels. There are well-known challenges associated with the outtake of lignin from kraft black liquor. Examples of such challenges are acid consumption and effects on the Na/S balance in the pulp mill, which can be decreased by a new process concept combining membrane filtration and liquid-lignin separation. In this study, we investigated the yield of liquid-lignin in separation from kraft black liquor retentate, specifically concerning how it was influenced by the presence of xylose and galactoglucomannan. For example, the liquid lignin yield after carbon dioxide separation decreased from 89.3 % to 85.2 % and 86.1 % with the addition of 20 g/L xylose and galactoglucomannan, respectively. The results showed that the yield of liquid-lignin decreased with an increasing amount of sugar added. Similarly to previous research, our results showed an improvement of liquid-lignin yield associated with a decrease in the content of sugars in cases of heat treatment prior to separation. We suggest a new explanation for the interaction between lignin and hemicellulose, namely that the interactions occur at a molecular level, with lignin in solution, and that these interactions possibly involve the formation of covalent lignin-carbohydrate bonds. This makes the lignin more polar and less prone to form a liquid-lignin phase.
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| 6. |
- Li, Kena, et al.
(författare)
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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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Ingår i: Membranes. - : MDPI AG. - 2077-0375. ; 9:8
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Tidskriftsartikel (refereegranskat)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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| 7. |
- Li, Kena, et al.
(författare)
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Three-step conversion of Indulin AT to muconic acid under mild conditions
- 2021
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Ingår i: Biomass and Bioenergy. - : Elsevier BV. - 0961-9534. ; 153
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Tidskriftsartikel (refereegranskat)abstract
- The conversion of technical lignin into valuable chemicals is important for the complete utilization of lignocellulose. The kraft process dominates the pulp industry, and large amounts of kraft lignin are produced worldwide. However, the complexity of lignin limits its valorization. In this study, a kraft lignin, Indulin AT, was depolymerized under base conditions, and the effects of substrate loading, NaOH concentration, temperature, and hydrogen peroxide on depolymerization were investigated. The production of aromatic monomers is favored by a continuous flow process, even with a very short reaction time (2 min vs. 30 min in a batch reactor). Higher temperature and NaOH concentration led to a higher degree of depolymerization, and thus more guaiacol and vanillin. A guaiacol yield of 5.1% was obtained after depolymerization of 5 wt% of lignin and 2 wt% of NaOH at 200 °C with a residence time of 2 min. When taking the whole operation, including the cost and depolymerization efficiency, into consideration, the concentration, lignin loading of 4 wt% of lignin, NaOH concentration of 2 wt%, and the temperature of 210 °C were chosen as the optimal conditions for the production of a guaiacol-rich fraction. The permeate obtained by ultrafiltration of the depolymerized Indulin AT sample contained a higher amount of guaiacol, which was quantitatively converted to muconic acid using an engineered strain of Pseudomonas putida KT2440. The three-step process in this work involves base-catalyzed depolymerization, ultrafiltration, and biological conversion represent an efficient approach to convert Indulin AT lignin into muconic acid.
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| 8. |
- Prothmann, Jens, et al.
(författare)
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Non-targeted analysis strategy for the identification of phenolic compounds in complex technical lignin samples
- 2020
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Ingår i: ChemSusChem. - : Wiley. - 1864-564X .- 1864-5631. ; 13:17, s. 4605-4612
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Tidskriftsartikel (refereegranskat)abstract
- Lignin is the second most abundant biopolymer in nature and a promising renewable resource for aromatic chemicals. For the understanding of different lignin isolation and conversion processes, the identification of phenolic compounds is of importance. However, due to the vast number of possible chemical transformations, the prediction of produced phenolic structures is challenging, and a non-targeted analysis method is therefore needed. In this study, we present a non-targeted analysis method for the identification of phenolic compounds using ultra-high-performance supercritical fluid chromatography/high-resolution multiple stage tandem mass spectrometry combined with a Kendrick mass defect-based classification model. The method was applied to a Lignoboost Kraft lignin (LKL), a sodium Lignosulphonate lignin (SLS) and a depolymerised Kraft lignin (DKL) sample. In total, 260 tentative phenolic compounds were identified in the LKL sample, 50 in the SLS sample and 77 in the DKL sample.
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