| 1. |
- Belkheiri, Tallal, 1985, et al.
(författare)
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Effect of pH on Kraft Lignin Depolymerisation in Subcritical Water
- 2016
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 30:6, s. 4916-4924
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Tidskriftsartikel (refereegranskat)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.
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| 2. |
- Belkheiri, Tallal, 1985, et al.
(författare)
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Hydrothermal liquefaction of kraft lignin in sub-critical water: the influence of the sodium and potassium fraction
- 2018
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Ingår i: Biomass Conversion and Biorefinery. - : Springer Science and Business Media LLC. - 2190-6815 .- 2190-6823. ; 8:3, s. 585-595
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Tidskriftsartikel (refereegranskat)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%.
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| 3. |
- Belkheiri, Tallal, 1985, et al.
(författare)
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Hydrothermal Liquefaction of Kraft Lignin in Subcritical Water: Influence of Phenol as Capping Agent
- 2018
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Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 32:5, s. 5923-5932
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Tidskriftsartikel (refereegranskat)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.
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| 4. |
- Bengtsson, Andreas, et al.
(författare)
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Improved yield of carbon fibres from cellulose and kraft lignin
- 2018
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 72:12, s. 1007-1016
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Tidskriftsartikel (refereegranskat)abstract
- To meet the demand for carbon-fibre-reinforced composites in lightweight applications, cost-efficient processing and new raw materials are sought for. Cellulose and kraft lignin are each interesting renewables for this purpose due to their high availability. The molecular order of cellulose is an excellent property, as is the high carbon content of lignin. By co-processing cellulose and lignin, the advantages of these macromolecules are synergistic for producing carbon fibre (CF) of commercial grade in high yields. CFs were prepared from precursor fibres (PFs) made from 70:30 blends of softwood kraft lignin (SW-KL) and cellulose by dry-jet wet spinning with the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([EMIm][OAc]) as a solvent. In focus was the impact of the molecular mass of lignin and the type of cellulose source on the CF yield and properties, while membrane-filtrated kraft lignin and cellulose from dissolving kraft pulp and fully bleached paper-grade SW-KP (kraft pulp) served as sources. Under the investigated conditions, the yield increased from around 22% for CF from neat cellulose to about 40% in the presence of lignin, irrespective of the type of SW-KL. The yield increment was also higher relative to the theoretical one for CF made from blends (69%) compared to those made from neat celluloses (48-51%). No difference in the mechanical properties of the produced CF was observed.
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| 5. |
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| 6. |
- Bengtsson, Jenny, et al.
(författare)
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Identifying breach mechanism during air-gap spinning of lignin–cellulose ionic-liquid solutions
- 2019
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Ingår i: Journal of Applied Polymer Science. - : John Wiley and Sons Inc.. - 0021-8995 .- 1097-4628.
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Tidskriftsartikel (refereegranskat)abstract
- To be able to produce highly oriented and strong fibers from polymer solutions, a high elongational rate during the fiber-forming process is necessary. In the air-gap spinning process, a high elongational rate is realized by employing a high draw ratio, the ratio between take-up and extrusion velocity. Air-gap spinning of lignin–cellulose ionic-liquid solutions renders fibers that are promising to use as carbon fiber precursors. To further improve their mechanical properties, the polymer orientation should be maximized. However, achieving high draw ratios is limited by spinning instabilities that occur at high elongational rates. The aim of this experimental study is to understand the link between solution properties and the critical draw ratio during air-gap spinning. A maximum critical draw ratio with respect to temperature is found. Two mechanisms that limit the critical draw ratio are proposed, cohesive breach and draw resonance, the latter identified from high-speed videos. The two mechanisms clearly correlate with different temperature regions. The results from this work are not only of value for future work within the studied system but also for the design of air-gap spinning processes in general.
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| 7. |
- Bengtsson, Jenny, 1990, et al.
(författare)
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Mass transport and yield during spinning of lignin-cellulose carbon fiber precursors
- 2019
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 73:5, s. 509-516
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Tidskriftsartikel (refereegranskat)abstract
- Lignin, a substance considered as a residue in biomass and ethanol production, has been identified as a renewable resource suitable for making inexpensive carbon fibers (CFs), which would widen the range of possible applications for light-weight CFs reinforced composites. Wet spinning of lignin-cellulose ionic liquid solutions is a promising method for producing lignin-based CFs precursors. However, wet-spinning solutions containing lignin pose technical challenges that have to be solved to enable industrialization. One of these issues is that a part of the lignin leaches into the coagulation liquid, which reduces yield and might complicate solvent recovery. In this work, the mass transport during coagulation is studied in depth using a model system and trends are confirmed with spinning trials. It was discovered that during coagulation, efflux of ionic liquid is not hindered by lignin concentration in solution and the formed cellulose network will enclose soluble lignin. Consequently, a high total concentration of lignin and cellulose in solution is advantageous to maximize yield. This work provides a fundamental understanding on mass transport during coagulation of lignin-cellulose solutions, crucial information when designing new solution-based fiber forming processes.
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| 8. |
- Dang, Binh, 1980, et al.
(författare)
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Carbohydrate content of black liquor and precipitated lignin at different ionic strengths in flow-through kraft cooking
- 2018
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 72:7, s. 539-547
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Tidskriftsartikel (refereegranskat)abstract
- The influence of sodium ion concentration [Na+] on the dissolution of carbohydrates in black liquor (BL) during flow-through kraft cooking of Scots pine wood meal (Pinus sylvestris) was studied. Fractions of BL were collected at different times and the carbohydrate content of the various fractions was analysed. Lignin was precipitated from the BL by lowering the pH, and the carbohydrate content of the precipitated lignins (Lprec) was also examined. The molecular weight distribution (MWD) of the Lprecsamples was analysed. Xylose (Xyl) was found to be the most predominant sugar in BL aside from arabinose (Ara) and galactose (Gal), while the amounts of these sugars decreased with increasing levels of [Na+] in the cooking liquor. The minor amounts of mannose (Man) found in BL was not influenced by the [Na+]. The effects of NaCl and Na2CO3on the carbohydrate dissolution were similar, but slightly lower concentrations of Ara and Xyl were found in the case of NaCl application. All of the Lprecsamples contained some carbohydrate residues, the contents of which increased with increasing cooking time and decreased with higher [Na+]. It can be concluded that arabinoglucuronoxylan (AGX) along with arabinogalactans (AG) and arabinan, are covalently linked to lignin. The glucose (Glc) residue detected in Lprecmay originate from 1,3-β-glucan linked to lignin.
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| 9. |
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| 10. |
- Dernegård, Henric C O, 1981, et al.
(författare)
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Characterization of a dusting lime kiln - A mill study
- 2017
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Ingår i: PEERS Conference 2017: Maximizing Success Through Innovation. ; 2017-November, s. 488-500
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Konferensbidrag (refereegranskat)abstract
- © 2017 TAPPI Press. All rights reserved. The white liquor preparation is one of the main purposes of the recovery cycle in a kraft pulp mill and the lime kiln, being the single unit operation handling bulk solid materials, poses particular challenges in the recovery cycle. In this study, the influence of a dusting lime kiln on the preparation of white liquor was studied. The investigation showed that the dusting lime kiln produced a burned lime with a substantial fraction of fines at the expense of the fraction of granules, whereas a clear lime kiln had virtually no fines and more granules instead. Burned lime from both dusting and clear periods were collected and separated into fines and granules. The different fractions were slaked and causticized in a synthetic green liquor. The study found that the fines always delivered a lower effective alkali in the resulting white liquor, and that the particle sizes of the lime mud were always larger than those originating from the granules, implying that the fines were sintered harder. The industrial consequence is that a dusting lime kiln increases the load on the kiln because the yield of effective alkali is lower; it also introduces a greater dead load into the liquor cycle.
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