| 1. |
- Sewring, Tor, 1988, et al.
(author)
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Estimation of the deprotonation degree of phenolic groups on kraft lignin
- 2015
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In: NWBC 2015 - 6th Nordic Wood Biorefinery Conference. - : VTT Technical Research Centre of Finland. - 9789513883539 ; , s. 442-449
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Conference paper (peer-reviewed)abstract
- Lignin is an abundant biomaterial, with potential as raw material feed stock for production of solid- and liquid fuels as well as phenolic components and carbon fibres. Lignin may be separated from various process streams in an integrated pulp production and wood-based biorefinery. Separation of Kraft lignin from black liquor can be made by the LignoBoost technology; it starts with precipitation of lignin by acidification of the black liquor and consequently protonation of the phenolic groups on lignin, in equilibrium with the surrounding liquid. The protonation degree of phenolic groups on kraft lignin has been identified as a key-property in controlling the precipitation yield. It has been investigated if the protonation degree of lignin in a black liquor system can be modelled using a modified Poisson-Boltzmann cell model which has been combined with the Pitzer method. It was found that the model gave reasonable results. Furthermore, the model indicated that the protonation degree is strongly dependent on the pH and temperature of the black liquor, however, the molecular weight of lignin has a minor influence and at the high ionic strength in black liquor a small change in ionic strength has only a very small influence on the protonation. Additionally, the predicted deprotonation degrees were compared with previously measured precipitation degrees at industrially relevant conditions.
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| 2. |
- Sewring, Tor, 1988, et al.
(author)
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Predictions of Pair Interaction Potentials between Kraft Lignin Macromolecules in Black Liquors by Utilization of a Modified Poisson-Boltzmann Approach
- 2019
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In: Industrial & Engineering Chemistry Research. - : American Chemical Society. - 0888-5885 .- 1520-5045. ; 58:8, s. 3427-3439
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Journal article (peer-reviewed)abstract
- In this investigation, a modified Poisson-Boltzmann approach has been used to estimate the mean ion concentration distributions of ionic species present in black liquors around charged kraft lignin macromolecules at industrially relevant conditions. The distributions were utilized to predict the double layer repulsion and, further, predict the overall pair interaction potentials between two kraft lignin macromolecules or particles immersed in the black liquor electrolyte. The properties of softwood black liquors were used as input data to the model. The numerical results predicted the pair interaction potentials to remain repulsive up to salt concentrations of about 2.5 M at pOH 1. The critical coagulation concentration of salt was predicted to decrease as the pOH of the black liquor was increased. The predictions at 65 °C and moderate levels of pOH (3.5) and salt concentration (1.9 M) were found to be in good agreement with previous observations reported in the literature.
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| 3. |
- Zhu, Weizhen, 1985, et al.
(author)
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Equilibrium of lignin precipitation
- 2011
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In: 16th International Symposium on Wood, Fiber and Pulping Chemistry - Proceedings, ISWFPC, Tianjin; 8 June 2011 through 10 June 2011. ; 1, s. 195-199
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Conference paper (peer-reviewed)
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| 4. |
- Zhu, Weizhen, 1985
(author)
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Equilibrium of lignin precipitation: The effects of pH, temperature, ion strength and wood origins
- 2013
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Licentiate thesis (other academic/artistic)abstract
- The kraft process is the predominant method for producing pulp in Scandinavia. However, the material efficiency in modern kraft pulp mills for pulp production is only 40−55% and the final product consists mainly of cellulose. A novel process called “LignoBoost” has been introduced recently for extracting lignin from alkaline black liquor. The separated lignin can either be utilized as solid fuel or raw material of other value-added products such as carbon fibre or phenols, which is one step towards a combined pulp and biorefinery process. The LignoBoost process consists of four major steps: precipitation, filtration, re-dispersing and final washing. Whilst filtration and washing have already been investigated extensively, more knowledge needs to be gained of the precipitation step. In this work, lignin precipitation was performed by the acidification of black liquor at various process conditions, namely pH, temperature and ion strength, and the influences exerted by these parameters on the equilibrium of lignin precipitation were investigated. Carbohydrate analysis was performed on the precipitated solid and lignin-lean liquor, and the average molecular weight of the precipitated lignin was determined. The content of the functional groups (i.e. phenolic and methoxyl) in the precipitated lignin was analyzed and, finally, new parameters in a given model from a previous study for estimating the precipitation yield of lignin were provided and evaluated.The results show that the precipitation yield of lignin increases with decreasing pH and temperature and/or with increasing ion strength of the black liquor used. The concentration of carbohydrates in lignin decreases with decreasing pH or with increasing temperature, and that an increasing amount of lower molecular weight lignin is precipitated at a higher precipitation yield. Furthermore, it was found, for the experimental conditions chosen, that the precipitation pH has a much stronger influence than the temperature and the ion strength on the precipitation yield and the average molecular weight of the precipitated lignin. According to 1H and 13C NMR spectra analysis, the content of phenolic and methoxyl groups in the precipitated lignin increases with increasing precipitation yield.
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| 5. |
- Zhu, Weizhen, 1985, et al.
(author)
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Investigation and Characterization of Lignin Precipitation in the LignoBoost Process
- 2014
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In: Journal of Wood Chemistry and Technology. - : Informa UK Limited. - 1532-2319 .- 0277-3813. ; 34:2, s. 77-97
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Journal article (peer-reviewed)abstract
- Lignin of high purity can be separated from black liquor using the LignoBoost process, of which the overall efficiency is largely dependent on the precipitation yield of lignin, which depends on the properties of black liquor and process conditions. In this paper, the influences of process conditions on the precipitation yield of lignin from mixed hardwood/softwood black liquor were investigated. The Klason and standardUV method were used to determine lignin concentration. The chemical and structural properties of lignin were also analyzed. The results showed that the precipitation yield of lignin increased along with a decrease in pH and temperature, or with an increase in the ion strength of black liquor, and the yield was lower when mixed softwood/hardwood black liquor was used. It also showed that at a higher precipitation yield the precipitatedlignin had a lower average molecular weight but had higher methoxyl and phenolic hydroxyl content
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| 6. |
- Zhu, Weizhen, 1985, et al.
(author)
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Lignin separation from kraft black liquor by combined ultrafiltration and precipitation: a study of solubility of lignin with different molecular properties
- 2016
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In: Nordic Pulp and Paper Research Journal. - : Walter de Gruyter GmbH. - 2000-0669 .- 0283-2631. ; 31:2, s. 270-278
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Journal article (peer-reviewed)abstract
- Lignin from wood is by far the largest source of bio-based aromatic raw material. Today a vast amount of lignin is processes and incinerated in kraft pulp mills around the world. One possible option to utilize the energy surplus in a modern kraft pulp mill is to extract lignin from black liquor. Precipitation of lignin is one important step in an extraction process. This study investigates how the molecular size and functional groups of lignin influenced the precipitation yield. Cross-flow filtration was applied to fractionate lignin with different molecular weights from a black liquor, precipitation studies was made on the different fractions. The precipitated lignin was characterized by GPC, HPAEC-PAD and NMR analysis. The results show that it was possible to obtain a more homogenous lignin by fractionation using cross-flow filtration. It was found that the molecular properties of kraft lignin, i.e. molecular weight and functional groups, influenced the yield of lignin precipitation: at the same precipitation condition, lignin fraction with higher molecular weight has higher precipitation yield. Lignin fraction with lower molecular weight contains less amount of carbohydrates and methoxyl groups but higher amount of phenolic groups.
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| 7. |
- Zhu, Weizhen, 1985
(author)
-
Precipitation of Kraft Lignin: Yield and Equilibrium
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Kraft pulping is the dominant pulping process used in the world today. The material efficiency in modern kraft pulp mills is, however, only 40−55% and the final product consists mainly of cellulose. Recently, a novel process called “LignoBoost” has been introduced to separate lignin from kraft black liquor. The separated lignin can be utilized either as a solid fuel or as a raw material for the production of carbon fibres or chemicals. It makes it possible for a traditional pulp mill to become a combined biorefinery. There are four major steps in the LignoBoost process: precipitation of lignin, filtration of lignin, re-dispersion of the lignin suspension and, finally, washing of lignin. The filtration and washing steps have been investigated extensively already, so it is of interest to gain more knowledge regarding the precipitation of lignin. Two kraft black liquors were used in this work: a mixed hardwood/softwood black liquor and a softwood black liquor. Cross-flow filtration was used to fractionate lignin with a different molecular weight from the softwood black liquor. The precipitation of lignin was performed by acidifying the black liquor at various process conditions, namely pH, temperature and ionic strength of the black liquor. The influences exerted by these parameters on the precipitation yield of lignin were investigated. The molecular properties (average molecular weight and functional groups) of precipitated lignin, together with a carbohydrate analysis of the black liquor and precipitated lignin, were determined. Finally, the dissociation degree of the phenolic groups on the lignin molecules was estimated using the Poisson-Boltzmann cell model. The results show that the precipitation yield of lignin increases with decreasing pH and temperature and/or with increasing ionic strength of the black liquor. There is an increasing amount of lignin with a lower molecular weight that is precipitated at a higher yield. Within the same precipitation conditions, the lignin fraction with the highest molecular weight tends to have the highest yield. According to NMR analysis of lignin, the content of methoxyl groups decreases for softwood lignin but increases for mixed hardwood/softwood lignin at a higher yield, whereas the content of phenolic groups increases at a higher yield for both types of lignin. The content of carbohydrates decreases with increasing yield. In a highly electrolyte solution (such as black liquor), the dissociation degree of the phenolic groups on the lignin molecules is related to the alkalinity and temperature of the precipitation conditions, but less so to an increase in the ionic strength or the molecular weight of the lignin.
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| 8. |
- Zhu, Weizhen, 1985, et al.
(author)
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Precipitation of lignin from softwood black liquor: An investigation of the equilibrium and molecular properties of lignin
- 2015
-
In: BioResources. - : BioResources. - 1930-2126 .- 1930-2126. ; 10:1, s. 1696-1714
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Journal article (peer-reviewed)abstract
- Extracting lignin from black liquor is an attractive option in modern pulp mills as a unit process for a combined biorefinery. The lignin obtained can be utilized as solid fuel or other high-value added products. The precipitation equilibrium of kraft lignin from softwood black liquor was studied in this work. It was found that with decreasing pH and temperature, or increasing ion strength, the solid yield increases. Moreover, precipitated softwood kraft lignin has a higher molecular weight and contains lower amounts of carbohydrates and phenolic groups than lignin precipitated from mixed hardwood/softwood black liquor. The content of methoxyl groups in softwood kraft lignin was found to decrease with increasing precipitation yield. An empirical model for estimating the precipitation yield of lignin was proposed and evaluated.
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| 9. |
- Zhu, Weizhen, 1985, et al.
(author)
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The molecular properties and carbohydrate content of lignins precipitated from black liquor
- 2015
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In: Holzforschung. - : Walter de Gruyter GmbH. - 1437-434X .- 0018-3830. ; 69:2, s. 143-152
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Journal article (peer-reviewed)abstract
- Precipitation and utilization of lignin from black liquor (BL) offers many promising advantages to modern kraft pulp mills. A novel process, known as “LignoBoost”, has recently been introduced as a process for separating lignin from BL; it results in lignins with a low ash and high dry solid content. There is a lack of knowledge regarding the influences of process parameters on the behavior of lignin in the precipitation step. In this study, the yield of precipitated lignin and its average molecular weight (MWt) and carbohydrate content were the focus. Nuclear magnetic resonance (NMR) analysis showed that the lignin yield increased at lower pH and temperatures or when the ion strength of BL was elevated. High yield lignins contained more low MWt components and such lignins have more phenolic OH and methoxy groups. Xylan content of the lignins decreased with decreasing pH and increasing temperature, but glucomannan content was virtually unaffected by the conditions of precipitation.
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