| 1. |
- Ahlbom, Anders, 1993, et al.
(författare)
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On the hydrothermal depolymerisation of kraft lignin using glycerol as a capping agent
- 2023
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 77:3, s. 159-169
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Tidskriftsartikel (refereegranskat)abstract
- Depolymerisation of kraft lignin under hydrothermal conditions was investigated at short residence times (1–12 min) with glycerol being used as a capping agent. The weight average molecular weight (M w) of the products decreased within the first minute of residence time, with the inter-unit ether linkages breaking accordingly. Furthermore, the M w of the product fractions decreased at increasing residence times, while the char yield increased. Short residence times thus appear to be beneficial for mitigating the formation of char. Also, addition of NaOH reduced the yield of char. Although the addition of glycerol caused a decrease in the M w of the products, it seemed to increase the yield of char and therefore might not be a suitable capping agent for kraft lignin depolymerisation.
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| 2. |
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| 3. |
- Ahlbom, Anders, 1993, et al.
(författare)
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Towards understanding kraft lignin depolymerisation under hydrothermal conditions
- 2021
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 76:1, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- Kraft lignin depolymerisation using hydrothermal liquefaction suffers from the formation of char, resulting in a decreased product yield as well as causing operational problems. While this may be mitigated by the addition of capping agents such as phenol and isopropanol, other reaction parameters, for example reaction time and temperature, are also important for the product yields. In this work, the effect of short reaction times on the hydrothermal liquefaction of kraft lignin in an alkaline water and isopropanol mixture was investigated at 1-12 min and 290 °C. The results show that there were swift initial reactions: the major ether bonds in the lignin were broken within the first minute of reaction, and the molecular weight of all product fractions was halved at the very least. Longer reaction times, however, do not cause as pronounced structural changes as the initial reaction, indicating that a recalcitrant carbon-carbon skeleton remained in the products. Nevertheless, the yields of both char and monomers increased slowly with increasing reaction time. The swift initial depolymerising reactions were therefore followed by slower repolymerisation as well as a slow formation of monomers and dimers, which calls for careful tuning of the reaction time.
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| 4. |
- Ahlbom, Anders, 1993, et al.
(författare)
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Using guaiacol as a capping agent in the hydrothermal depolymerisation of kraft lignin
- 2023
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 38:4, s. 619-631
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Tidskriftsartikel (refereegranskat)abstract
- The depolymerisation of softwood kraft lignin was investigated, under hydrothermal conditions at 290 °C and 250 bar, with guaiacol in the reactor feed to evaluate its impact on the formation of char and on the molecular weights of the products. The effect of residence time was investigated in the time span 1-12 min. Lignin is depolymerised during the process and guaiacol is both formed and consumed during the reaction, with clearly noticeable changes as early as in the first minute of reaction. Although the addition of guaiacol in the reactor feed causes a reduction in the weight average molecular weight of the products, the yield of char increases. Longer residence times result in repolymerisation of the reaction products as well as a further increase in the yield of monoaromatic components and char.
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| 5. |
- Ahlbom, Anders, 1993, et al.
(författare)
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Using Isopropanol as a Capping Agent in the Hydrothermal Liquefaction of Kraft Lignin in Near-Critical Water
- 2021
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Ingår i: Energies. - : MDPI AG. - 1996-1073 .- 1996-1073. ; 14:4
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Tidskriftsartikel (refereegranskat)abstract
- In this study, Kraft lignin was depolymerised by hydrothermal liquefaction in near-critical water (290-335 degrees C, 250 bar) using Na2CO3 as an alkaline catalyst. Isopropanol was used as a co-solvent with the objective of investigating its capping effect and capability of reducing char formation. The resulting product, which was a mixture of an aqueous liquid, containing water-soluble organic compounds, and char, had a lower sulphur content than the Kraft lignin. Two-dimensional nuclear magnetic resonance studies of the organic precipitates of the aqueous phase and the char indicated that the major lignin bonds were broken. The high molar masses of the char and the water-soluble organics, nevertheless, indicate extensive repolymerisation of the organic constituents once they have been depolymerised from the lignin. With increasing temperature, the yield of char increased, although its molar mass decreased. The addition of isopropanol increased the yield of the water-soluble organic products and decreased the yield of the char as well as the molar masses of the products, which is indicative of a capping effect.
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| 6. |
- Belkheiri, Tallal, 1985, et al.
(författare)
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Kraft Lignin Depolymerization in Near-Critical Water: Effect of Changing Co-Solvent
- 2014
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 48:9-10, s. 813-818
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Tidskriftsartikel (refereegranskat)abstract
- As part of developing a process to valorize lignin in a pulp mill with lignin separation, the depolymerisation of lignin to valuable chemicals was investigated in near-critical water. This was done by using methanol as co-solvent and hydrogen donor, phenol to suppress repolymerization (e.g. formation of char), and ZrO2 as a heterogeneous catalyst, with potassium carbonate as a co-catalyst. The reaction was carried out in a continuous flow fixed-bed reactor (500 cm(3)), at 280-350 degrees C and 25MPa. An important aspect is to suppress char formation. Therefore, the char formation was studied by using different concentrations of methanol and phenol. The char yield varied between 14% and 26%. When using methanol as the only co-solvent, the char yield decreased with increasing methanol concentration. Adding phenol resulted in a further decrease. The reactor outlet consisted mainly of two liquid phases, an aqueous and an oil phase, mixed together. The chemical analysis of the aqueous phase showed the presence of mainly phenolic compounds, for instance guaiacol, catechol, phenol and cresol.
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| 7. |
- Giorni, Fausto, et al.
(författare)
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Phase equilibrium of the system supercritical carbon dioxide-lemon essential oil: New experimental data and thermodynamic modelling
- 2012
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446. ; 70, s. 8-16
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Tidskriftsartikel (refereegranskat)abstract
- New experimental phase equilibrium data on the system supercritical CO 2 -lemon oil are provided at 50°C and 70°C, for pressures in the range 8.6-10.1 MPa and 9.7-13.5 MPa, respectively. Additional phase equilibrium data on the binary sub-system CO 2 -limonene are also provided. The measurements were carried out in a double-chamber isothermal apparatus of 340 cm 3 . Both the mass fraction of CO 2 in the two phases and in the overall system was measured. The composition of the two phases on CO 2 -free basis was also measured. A thermodynamic model based on the Peng-Robinson equation of state was developed in order to represent the behaviour of the system supercritical CO 2 -lemon oil. The model uses only regression parameters calculated from binary sub-systems, thus being predictive with respect to the multicomponent mixture. A good representation of the phase equilibrium data is obtained with the proposed thermodynamic model.
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| 8. |
- Lyckeskog, Huyen, 1985, et al.
(författare)
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Catalytic depolymerisation and conversion of Kraft lignin into liquid products using near-critical water
- 2014
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446. ; 86, s. 67-75
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Tidskriftsartikel (refereegranskat)abstract
- A high-pressure pilot plant was developed to study the conversion of LignoBoost Kraft lignin into bio-oil and chemicals in near-critical water (350◦C, 25 MPa). The conversion takes place in a continuous fixed-bed catalytic reactor (500 cm3) filled with ZrO2 pellets. Lignin (mass fraction of approximately 5.5%) is dispersed in an aqueous solution containing K2CO3(from 0.4% to 2.2%) and phenol (approximately 4.1%).The feed flow rate is 1 kg/h (reactor residence time 11 min) and the reaction mixture is recirculated internally at a rate of approximately 10 kg/h. The products consist of an aqueous phase, containing phenolic chemicals, and a bio-oil, showing an increased heat value (32 MJ/kg) with respect to the lignin feed. The 1-ring aromatic compounds produced in the process are mainly anisoles, alkylphenols, guaiacols and catechols: their overall yield increases from 17% to 27% (dry lignin basis) as K2CO3 is increased.
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| 9. |
- Lyckeskog, Huyen, 1985, et al.
(författare)
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The effect of temperature on the catalytic conversion of Kraft lignin using near-critical water
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 170, s. 196-203
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Tidskriftsartikel (refereegranskat)abstract
- The catalytic conversion of suspended LignoBoost Kraft lignin was performed in near-critical water using ZrO2/K2CO3 as the catalytic system and phenol as the co-solvent and char suppressing agent. The reaction temperature was varied from 290 to 370 degrees C and its effect on the process was investigated in a continuous flow (1 kg/h). The yields of water-soluble organics (WSO), bio-oil and char (dry lignin basis) were in the ranges of 5-11%, 69-87% and 16-22%, respectively. The bio-oil, being partially deoxygenated, exhibited higher carbon content and heat value, but lower sulphur content than lignin. The main 1-ring aromatics (in WSO and diethylether-soluble bio-oil) were anisoles, alkylphenols, catechols and guaiacols. The results show that increasing temperature increases the yield of 1-ring aromatics remarkably, while it increases the formation of char moderately. An increase in the yields of anisoles, alkylphenols and catechols, together with a decrease in the yield of guaiacols, was also observed.
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| 10. |
- Maschietti, Marco, 1974, et al.
(författare)
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Supercritical carbon dioxide separation of fish oil ethyl esters by means of a continuous countercurrent process with an internal reflux
- 2014
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446. ; 86, s. 76-84
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Tidskriftsartikel (refereegranskat)abstract
- The continuous countercurrent fractionation of fish oil ethyl esters using supercritical carbon dioxide is studied, modelling a process with internal reflux generated by a thermal gradient at the top stage. A methodology for process design is proposed and applied to determine the relationships between the temperature at the top stage (T-1), the number of theoretical stages (N), and the solvent to feed ratio (S IF), with the aim of providing a quantitative comparison with the external reflux process. The internal reflux process is viable and, for stated process specifications (mass fraction and recovery of C20 + C22 ethyl esters of 95%), provides comparable or better results than the external reflux process. For example, operating at 13.3 MPa and 50 degrees C, and keeping T-1 in the range (66-70) degrees C, the specifications are attained with N and S/F in the range 16-30 and 88-120, respectively. (C) 2013 Elsevier B.V. All rights reserved.
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