| 1. |
- Belkheiri, Tallal, 1985, et al.
(author)
-
Effect of pH on Kraft Lignin Depolymerisation in Subcritical Water
- 2016
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:6, s. 4916-4924
-
Journal article (peer-reviewed)abstract
- Softwood kraft lignin was depolymerized using subcritical water (623 K and 25 MPa) in a continuous small pilot unit. ZrO2 and K2CO3 were used as catalysts, and phenol was used as capping agent to suppress repolymerization. The effect of pH was investigated by adding KOH in five steps to the feed. The yield of water-soluble organics increased with pH. The yield of bio-oil was also influenced by the pH and varied between 28 and 32 wt %. The char yield on the zirconia catalyst showed a minimum at pH 8.1. The yield of suspended solids was low at pH below 8.1 but increased at higher pH values. The oxygen content in the bio-oil was only 15 wt %, compared to about 26 wt % in the kraft lignin.
|
|
| 2. |
- Belkheiri, Tallal, 1985, et al.
(author)
-
Hydrothermal liquefaction of kraft lignin in sub-critical water: the influence of the sodium and potassium fraction
- 2018
-
In: Biomass Conversion and Biorefinery. - : Springer Science and Business Media LLC. - 2190-6815 .- 2190-6823. ; 8:3, s. 585-595
-
Journal article (peer-reviewed)abstract
- As a part of developing a hydrothermal liquefaction (HTL) process to valorise lignin, it is important to consider integration possibilities with existing infrastructures in order to obtain an overall positive economic impact. One obvious example is to integrate the HTL process with the kraft pulp mill: transport and storage costs is reduced, the temperature levels on process streams can be matched (energy integration) and the recovery/use of alkali can be made efficient. In this study, softwood kraft lignin was depolymerised using sub-critical water (623 K; 25 MPa) in a continuous, small pilot unit with a flow rate of 2 kg/h. ZrO2, K2CO3/KOH and Na2CO3/NaOH were used as catalytic system, and phenol as the capping agent. The influence of the ratio between sodium and potassium in the feed on the yield and composition of the product stream was investigated. The results showed that bio-oil, water-soluble organics (WSO) and char yields were not remarkably influenced by shifting the catalytic system from potassium to sodium. Moreover, the yields of most phenolic compounds did not change significantly when the sodium fraction was varied in the feed. The amounts of suspended solids in the bio-oil produced showed, however, a diminishing trend, (decrease from 10.8 to 3.8%) when the sodium fraction was increased in the feed, whilst the opposite trend was observed for the heavy oil, which increased from 24.6 to 37.6%.
|
|
| 3. |
- Belkheiri, Tallal, 1985, et al.
(author)
-
Hydrothermal Liquefaction of Kraft Lignin in Subcritical Water: Influence of Phenol as Capping Agent
- 2018
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:5, s. 5923-5932
-
Journal article (peer-reviewed)abstract
- The depolymerization of LignoBoost Kraft lignin in subcritical water, i.e. hydrothermal liquefaction (HTL), was investigated using ZrO 2 , K 2 CO 3 , and KOH as catalysts in a fixed-bed reactor with recirculation. Focus was placed on the effect exerted by the concentration of the phenol in suppressing repolymerization, which is responsible for forming char. Feeds with various concentrations of phenol (2-10%) were investigated, and the results showed that phenol partially prevents repolymerization even at low concentrations. The bio-oil yield of (61.0 ± 2.7) % was fairly stable when the concentration of phenol was varied. In the case of the formation of char on the catalyst, the char yield revealed a weakly decreasing trend (14.6-12.3%) when the amount of phenol in the feed was increased. The results also showed that the phenolic monomers that are alkylated, such as o-/p-cresols, increased significantly with increasing concentrations of phenol, while aromatic compounds, based on a guaiacol ring structure, showed decreasing trends.
|
|
| 4. |
- Lyckeskog, Huyen, 1985, et al.
(author)
-
Storage Stability of Bio-oils Derived from the Catalytic Conversion of Softwood Kraft Lignin in Subcritical Water
- 2016
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:4, s. 3097-3106
-
Journal article (peer-reviewed)abstract
- The stability of lignin-derived bio-oil obtained from a continuous process [base (K2CO3)-catalyzed, using phenol as a capping agent] under subcritical conditions of water (25 MPa, 290-370 degrees C) was investigated. The lignin-derived bio-oil obtained was stored at ambient temperature for 2 years. Our results show that the base concentration in the feed solution affects the stability of this lignin-derived bio-oil during its long-term storage. It was found that, at low base concentrations (i.e., 0.4%-1.0%), the yields of all lignin-derived bio-oil fractions were relatively stable. At high base concentrations (i.e., 1.6%-2.2%), however, the yield of high-molecular-weight (high-Mw) structures increased and that of low-molecular-weight (low-Mw) structures decreased after storage. This indicated that the low-Mw materials had been polymerized to form high-Mw materials. In addition, it was found that the yield of gas chromatography-mass spectrometry (GC-MS)-identified compounds (excluding phenol) in this lignin-derived bio-oil decreased from 15% to 11%. This is probably due to the presence of solids in these lignin derived bio-oils, which promotes the catalytic polymerization reactions, suggesting that it is beneficial to remove the solids from this lignin-derived bio-oil in order to enhance its stability. Compared to the results obtained from bio-oil derived from biomass pyrolysis, our results show that bio-oil derived from the conversion of lignin in subcritical water has better chemical stability during long-term storage.
|
|
| 5. |
- Mattsson, Cecilia, 1970, et al.
(author)
-
About structural changes of lignin during kraft cooking and the kinetics of delignification
- 2017
-
In: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 71:7-8, s. 545-553
-
Journal article (peer-reviewed)abstract
- Wood meal was submitted to kraft cooking in a small-scale flow-through reactor and the structural changes of lignin have been investigated. The rate determining steps in kraft cooking were in focus. Based on two-dimensional nuclear magnetic resonance (2D-NMR) measurements on lignin fractions extracted at different cooking times from the black liquor, it was observed that the main lignin reactions occur within 10-20 min and thus the kinetics of the chemical reaction cannot be the rate-determining step. On the other hand, the molecular weight (MW) of lignin is shifted towards larger fragments in the course of cooking time but the MW decreases with increasing ionic strength. Obviously, the kinetics of the delignification are strongly dependent on solubility and/or mass transport at the cell wall level. At chip size level, the mass transport of cooking chemicals into the wood chip may influence the overall kinetics in the initial part of the cooking. At longer cooking times the concentration of chemicals becomes sufficiently high in the wood chips, and the delignification is progressively governed by solubility and/or mass transport of lignin molecules occurring at the cell wall level.
|
|
| 6. |
- Mattsson, Cecilia, 1970, et al.
(author)
-
Subcritical water de-polymerization of Kraft lignin: A process for future biorefineries. Structural characterization of bio-oil and solids
- 2015
-
In: NWBC 2015 - 6th Nordic Wood Biorefinery Conference. ; , s. 112-119
-
Conference paper (peer-reviewed)abstract
- A 2D-NMR analysis was carried out on fractionated bio-oil in order to investigate the result of the subcritical water base catalysed de-polymerization of LignoBoost Kraft lignin (350 °C, 25 MPa). It was confirmed that the signals from aliphatic lignin inter-unit linkages, i.e. ß-O-4’, ß-ß’, ß-1’ and ß-5’, had disappeared in all bio-oil fractions (light oil, heavy oil and suspended solids). This means that both aliphatic carbon-oxygen (C-O) and carbon-carbon (C-C) bonds in LignoBoost Kraft lignin have been broken and an effective de-polymerization has occurred. However, re-polymerization to higher molecular weight (Mw) fractions take place simultaneously. These higher Mw fractions (heavy oil and suspended solids) were found to be re-polymerized macromolecules (Mw distribution 5.4 kDa and 19.5 kDa resp.) with new structural networks based on guaiacol/disubstituted aromatic ethers and polyaromatic hydrocarbon structures tightly bound together. In this work it has been demonstrated that the subcritical water de-polymerization process of LignoBoost Kraft lignin does function; an effective de-oxygenation of LignoBoost Kraft lignin takes place, generating a bio-oil with a low content of atomic oxygen (15 wt.%) suitable for further processing at fossil-based oil refineries.
|
|
| 7. |
- Mattsson, Cecilia, 1970, et al.
(author)
-
Using 2D NMR to characterize the structure of the low and high molecular weight fractions of bio-oil obtained from LignoBoost (TM) kraft lignin depolymerized in subcritical water
- 2016
-
In: Biomass and Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 95, s. 364-377
-
Journal article (peer-reviewed)abstract
- In this work a multilevel analysis approach have been used for characterization of LignoBoostTM kraft lignin and bio-oil produced from LignoBoostTM kraft lignin using a process based on subcritical water (350 degrees C, 25 MPa). LignoBoostTM kraft lignin and the different fractions of the bio-oil (light oil, heavy oil and suspended solids) was characterized with high field NMR (18.8 T, 2D(13)C, H-1-HSQC NMR and C-13-NMR), GPC, GC-MS and elemental composition to improve understanding of the subcritical process. By using high resolution 2D HSQC NMR it was possible determine the chemical structures both on low and high molecular weight fractions of the bio-oil. It was confirmed that the signals from the aliphatic lignin inter-unit linkages, i.e. beta-O-4', beta-beta', beta-1' and beta-5', had disappeared from all of the bio-oil fractions studied. This means that both the aliphatic carbon-oxygen (C-O) and to some extent carbon-carbon (C-C) bonds in LignoBoostTM kraft lignin have been cleaved and an effective depolymerization has occurred. However, re-polymerization into higher molecular weight (Mw) fractions takes place simultaneously. These higher Mw fractions (heavy oil and suspended solids) were found to be re-polymerized macromolecules, with new structural networks based on guaiacol/disubstituted aromatic ethers and polyaromatic hydrocarbon structures bound tightly together. (C) 2016 Elsevier Ltd. All rights reserved.
|
|
| 8. |
- Nguyen Lyckeskog, Huyen, 1985, et al.
(author)
-
Accelerated aging of bio-oil from lignin conversion in subcritical water
- 2017
-
In: Tappi Journal. - : TAPPI. - 0734-1415. ; 16:3, s. 123-141
-
Journal article (other academic/artistic)abstract
- Accelerated aging of bio-oil derived from lignin was investigated at different aging temperatures (50 degrees C and 80 degrees C) and times (1 hour, 1 day, 1 week, and 1 month). The bio-oil used was produced by the hydrothermal liquefaction of kraft lignin, using phenol as the capping agent, and base (potassium carbonate and potassium hydroxide) and zirconium dioxide as the catalytic system in subcritical water. Elemental composition, molecular weight (by using gel permeation chromatography), and chemical composition (by using gas chromatography-mass spectrometry and 2D nuclear magnetic resonance [18.8 T, DMSO-d(6)]) of the bio-oil were measured to gain better understanding of the changes that occurred after being subjected to an accelerated aging process. The lignin-derived hydrothermal liquefaction bio-oil was quite stable compared with biomass-pyrolysis bio-oil. The yield of the low molecular weight fraction (light oil) decreased from 64.1% to 58.1% and that of tetrahydrofuran insoluble fraction increased from 16.5% to 22.2% after aging at 80 degrees C for 1 month. Phenol and phenolic dimers (Ar-CH2-Ar) had high reactivity compared with other aromatic substituents (i.e., methoxyl and aldehyde groups); these may participate in the polymerization/condensation reactions in the hydrothermal liquefaction bio-oil during accelerated aging. Moreover, the 2D heteronuclear single quantum coherence nuclear magnetic resonance spectra of the high molecular weight fraction (heavy oil) in the aged raw oil in the aromatic region showed that the structure of this fraction was a combination of phenol-alkyl patterns, and the guaiacol cross-peaks of Ar-2, Ar-5, and Ar-6 after aging indicate that a new polymer was formed during the aging process. Application: Pulp mill personnel can use this information when considering technology to extract lignin from black liquor and process it further into bio-oil.
|
|
| 9. |
- Nguyen Lyckeskog, Huyen, 1985, et al.
(author)
-
Storage stability of bio-oils derived from the catatytic conversion of kraft lignin in subcritical water
- 2016
-
In: European Biomass Conference and Exhibition Proceedings. - 2282-5819. ; 2016:24thEUBCE, s. 1107-1110
-
Conference paper (peer-reviewed)abstract
- In the efforts of replacing fossil raw material with renewable resources, most attention has been on carbohydrates (e.g. 2nd generation ethanol). However, during the last period of time the interest in lignin has raised due to its aromatic nature and that it now has started to be more abundant. The conversion of lignin in subcritical water into smaller aromatic units is a promising process because of the relatively mild operating temperatures, which allows the aromatic structures to be retained. In this work, we have investigated the storage stability of lignin-derived bio-oil obtained from the continuous process at subcritical conditions of water (25 MPa, 350oC). The bio-oil was stored at an ambient temperature for 1–2 years. The changes in water concentration (Karl Fischer measurement), chemical composition (GC-MS and elemental analysis) and molecular weight (GPC analysis) of bio-oils were evaluated before and after the storage. The bio-oil was fractionated into: light oil (a low Mw fraction), heavy oil and solids (the high Mw fractions) and all three fractions were analyzed in order to obtain a better understanding about the stability of monomeric as well as oligomeric structures.
|
|
| 10. |
- Nguyen Lyckeskog, Huyen, 1985, et al.
(author)
-
Thermal stability of low and high Mw fractions of bio-oil derived from lignin conversion in subcritical water
- 2017
-
In: Biomass Conversion and Biorefinery. - : Springer Science and Business Media LLC. - 2190-6815 .- 2190-6823. ; 7:4, s. 401-414
-
Journal article (peer-reviewed)abstract
- The thermal stability of bio-oil influences its application in industry and is, therefore, a very important factor that must be taken into consideration. In this study, the stability of low and high molecular weight (Mw) fractions of bio-oil obtained from the hydrothermal liquefaction (HTL) of lignin in subcritical water was studied at an elevated temperature (80 °C) for a period of 1 h, 1 day and 1 week. The changes in molecular weight (gel permeation chromatography (GPC)) and chemical composition (gas chromatography–mass spectrometry (GC–MS) and 2D heteronuclear single quantum correlation (HSQC) NMR (18.8 T, DMSO-d6)) of low and high Mw fractions of the HTL bio-oil (i.e. light oil (LO) and heavy oil (HO)) were evaluated before and after ageing. It was found that only a slight formation of high Mw insoluble structures was obtained during ageing at elevated temperature for 1 week: 0.5% for the LO and 3.1% for the HO. These higher Mw moieties might be formed from different polymerisation/condensation reactions of the reactive compounds (i.e. anisoles, guaiacols, phenols, methylene (–CH2–) groups in phenolic dimers and xanthene). The high Mw insolubles in both the LO and the HO were analysed for structural composition using 2D HSQC NMR to obtain a better understanding of the changes in the composition of bio-oil fractions during the accelerated ageing process. In addition, a chemical shift database in DMSO-d6 was analysed for a subset of phenolic model compounds to simplify the interpretation of the 2D HSQC NMR spectra.
|
|
