| 1. |
- Aminzadeh, Selda, 1984, et al.
(författare)
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Membrane filtration of kraft lignin: Structural charactristics and antioxidant activity of the low-molecular-weight fraction
- 2018
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Ingår i: Industrial Crops and Products. - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 112, s. 200-209
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Tidskriftsartikel (refereegranskat)abstract
- Lignin, which is the second most abundant biomass component and has carbon-rich phenolic content, is a promising renewable raw material for multiple applications, such as carbon fibers, adhesives, and emulsifiers. To use lignin efficiently, it is important to ensure its purity and homogeneity. As a result, the separation of lignin into fractions with high purity and narrow molecular-weight distributions is likely a prerequisite for several applications. Ultrafiltration using ceramic membranes has many advantages, including enabling direct lignin extraction from Kraft pulp cooking liquors without pH and temperature adjustment. One challenge with membrane filtration using such a system is the potential for reduced membrane performance over time, which is associated with fouling. In this study, LignoBoost Kraft lignin was fractionated using a ceramic membrane with a molecular weight cut-off of 1 kDa. The separation behavior during ultrafiltration fractionation was investigated and the antioxidant properties of the recovered low-molecular-weight (low-MW) lignin samples were evaluated. Using this model system, the permeate fluxes were unstable during the 100 h of membrane operation. However, a decrease in the average MW in the permeate over time was observed. The shift in MW was most pronounced for virgin membranes, while a more stable MW distribution was evident for membranes subjected to multiple cleaning cycles. According to 2D NMR analysis, low-MW lignin that was recovered after 100 h of operation, consisted of smaller lignin fragments, such as dimers and oligomers, with a high content of methoxy-groups. This was confirmed using the size exclusion chromatography method, which indicated an weigh average molecular weight in the range of 450–500 Da. 31P NMR spectroscopy showed that, despite the lower total content of phenolic OH groups, the low-MW sample had a higher proportion of non-condensed phenolic OH groups. The results of the antioxidant tests demonstrated the strong potential of lignin and its low-MW fraction as a natural antioxidant, particularly for lipid-containing systems. The low-MW lignin fraction showed better antioxidant activity than the non-fractionated LignoBoost lignin in the kinetic oxygen radical absorbance capacity (ORAC) test and demonstrated three-fold stronger inhibition of the substrate (fluorescein) than the reference antioxidant Trolox (a water-soluble derivative of vitamin E).
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| 2. |
- Arandia, Kenneth Gacutno, 1990, et al.
(författare)
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Fouling characteristics of microcrystalline cellulose during cross-flow microfiltration: Insights from fluid dynamic gauging and molecular dynamics simulations
- 2023
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Ingår i: Journal of Membrane Science. - : Elsevier BV. - 1873-3123 .- 0376-7388. ; 669
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Tidskriftsartikel (refereegranskat)abstract
- The fouling behaviour of microcrystalline cellulose (MCC) particles on polyethersulfone (PES) membranes was investigated using fluid dynamic gauging (FDG) and molecular dynamics (MD) simulations. Experimental cross-flow microfiltration (MF) of a dilute MCC suspension at 400 mbar transmembrane pressure using 0.45 μm PES membranes revealed an estimated fouling layer thickness of 616 ± 5 μm for both fouled and re-fouled membranes at an applied shear stress of 37 ± 2 Pa. A decline in pure water flux was observed after each membrane cleaning and flushing procedure, indicating that highly resilient layers were formed close to the membrane surface. A possible explanation for the formation of resilient cellulose layers was obtained through MD simulations of the free energy profiles, which predicted deep energy minima at close interparticle separations of the cellulose–cellulose and cellulose–PES systems. The consequence of this energy minima is that attractive and repulsive forces are in balance at a specific distance between the particles, suggesting high binding energy at close interparticle distances. This implies that a certain force is needed to remove the layer or redisperse the cellulose particles. MD simulations also suggested that contributions made by repulsive hydration forces negatively influenced the adsorption of cellulose particles onto the PES membrane. These results highlight how experimental FDG measurements, when complemented with MD simulations, can provide insights into the fouling behaviour of an organic model material during cross-flow filtration.
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| 3. |
- Arandia, Kenneth Gacutno, 1990, et al.
(författare)
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Monitoring Membrane Fouling Using Fluid Dynamic Gauging: Influence of Feed Characteristics and Operating Conditions
- 2023
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Ingår i: Membranes. - 2077-0375. ; 13:10
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies on membrane fouling have made considerable progress in reducing its adverse effects. However, a lack of comprehensive studies focusing on the underlying fouling mechanisms remains. This work aims to address a part of this gap by investigating the influence of feed suspension chemistry and operating conditions on the fouling characteristics of microcrystalline cellulose. Fluid dynamic gauging (FDG) was employed to monitor the properties of fouling layers under varied conditions. FDG results revealed that the cohesive strength of fouling layers increased in the direction towards the membrane, which can be associated with the higher compressive pressures exerted on foulants deposited near the surface. At lower pHs and higher ionic strengths, reduced electrostatic repulsions between particles likely resulted in particle agglomeration, leading to the formation of thicker cakes. In addition, thicker cake layers were also observed at higher feed concentrations, higher operating transmembrane pressures, and longer filtration times. The cross-flow velocity influenced the resilience of fouling layers significantly, resulting in thinner yet stronger cake layers in the transition and turbulent flow regimes. These findings regarding the influence of feed characteristics and operating conditions on the fouling behavior can be beneficial in developing effective antifouling strategies in membrane separation processes.
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| 4. |
- Durruty, Julie, 1988, et al.
(författare)
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Filtration properties of kraft lignin : The influence of xylan and precipitation conditions
- 2017
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Ingår i: Nordic Pulp & Paper Research Journal. - : AB Svensk Papperstidning. - 0283-2631 .- 2000-0669. ; 32:4, s. 508-526
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Tidskriftsartikel (refereegranskat)abstract
- LignoBoost lignin powder was dissolved together with xylan and re-precipitated. The influence of the (i) precipitation temperature, (ii) rate of acidification and (iii) final pH of the slurries on the resulting material and its filtration properties was investigated. In the case of slow acidification, larger agglomerates were obtained for slurries with higher precipitation temperatures as well as with higher ionic strengths. Fast acidification led to a more heterogeneous formation of particles, having a broader particle size distribution, compared to slow acidification. Chemical analysis of different layers of the filter cakes formed revealed that xylan was distributed evenly on the solid lignin, reinforcing the hypothesis that xylan is sorbed onto the lignin agglomerates when precipitated together with lignin. Furthermore, the resulting lignin-xylan mixtures were found to be more difficult to filter in the case of a higher final pH of the slurry (pH 4), close to the pKa values of the carboxylic acid groups of xylan, compared to lower pH values (pH 1-3). This is likely the result of an increase in electrostatic repulsive interactions between the particles/agglomerates at higher pH: a locally more porous solid structure is formed, leading to a larger solid/liquid surface area during filtration.
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| 5. |
- Durruty, Julie, 1988, et al.
(författare)
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Local and average filtration properties of kraft softwood lignin
- 2015
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Ingår i: Nordic Pulp and Paper Research Journal. - 2000-0669 .- 0283-2631. ; 30:1, s. 132-140
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Tidskriftsartikel (refereegranskat)abstract
- The extraction of lignin from black liquor is of interest in order to increase the overall material yield when producing paper pulp by the kraft process. The extracted lignin can be used either as a solid biofuel or a potential alternative raw material to fossil oil for the production of various green chemicals and high valuable products such as carbon fibres. The LignoBoost process is a new approach in which the kraft lignin extracted reaches a high level of purity. In this study, the local and average dead-end filtration properties during dewatering of a softwood lignin extracted from black liquor using the LignoBoost process were investigated; the material was also characterized. It was found that the investigated lignin was an easy to filter material that formed weakly compressible filter cakes in the solid compressive pressure range of 0.03 to 1.5 MPa. The concentration of the lignin slurry did not influence the filtration properties; the resulting cakes final heights were in the industrial size range. Moreover, the two different filter media used yielded similar results. Semi-empirical relationships were fitted successfully to the experimental local data and a good estimation of the average filtration properties was also obtained using the relationships fitted parameters. This indicates a good agreement between the local and average experimental data.
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| 6. |
- Durruty, Julie, 1988, et al.
(författare)
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Local filtration properties of Kraft lignin : The influence of residual xylan
- 2017
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Ingår i: Separation and Purification Technology. - : Elsevier B.V.. - 1383-5866 .- 1873-3794. ; 179, s. 455-466
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Tidskriftsartikel (refereegranskat)abstract
- The influence of lignin and xylan interactions on the filtration properties of precipitated LignoBoost lignin was investigated. LignoBoost lignin was (i) suspended in acid water with xylan added and (ii) dissolved together with xylan and then re-precipitated. The resulting lignin-xylan mixtures were more difficult to filter than the original LignoBoost lignin, although the formed filter cake was also found more porous in the case of re-precipitated solids. Furthermore, the pressure dependency of the filtration properties was shown to increase after the addition of xylan. One possible explanation based on the findings presented in this paper is that xylan is sorbed at the surface of the lignin agglomerates: it increases the contact area between solid and liquid, thus making the particle structure more porous. The influence of ionic strength was also investigated through the addition of sodium sulphate: it was found that increasing the ionic strength of the slurries made the solids easier to separate, possibly due to a decrease in electrostatic repulsive interactions between the solids and the formation of a denser solid structure.
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| 7. |
- Durruty, Julie, 1988, et al.
(författare)
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Local filtration properties of kraft lignin : influence of ligning-carbohydrate complex
- 2015
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Ingår i: 6th Nordic Wood Biorefinery Conference, NWBC 2015. - : VTT Technical Research Centre of Finland. - 9789513883539 ; , s. 301-308
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Konferensbidrag (refereegranskat)abstract
- The influence of lignin and xylan interactions on the filtration properties of precipitated LignoBoost lignin is investigated. LignoBoost lignin was dissolved together with added xylan and then re-precipitated. The resulting lignin-xylan suspension was more difficult to filter than the original LignoBoost lignin, although the mix also formed more porous filter cakes. One of the possible explanations suggested by the findings presented in this paper is that xylan is sorbed at the surface of the lignin agglomerates, increasing the contact area between solid and liquid and making the particles local structure more porous.
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| 8. |
- Helander, Mikael, et al.
(författare)
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Parameters Affecting the Cross-flow Filtration of Dissolved LignoBoost Kraft Lignin
- 2015
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Ingår i: Journal of wood chemistry and technology. - : Taylor & Francis Group. - 0277-3813 .- 1532-2319. ; 36:1, s. 1-8
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- In the kraft pulping process, the lignin-containing by-product kraft black liquor is currently combusted as an energy source. LignoBoost is a technique that extracts lignin from kraft black liquor, resulting in a lignin-lean black liquor, which is returned to the process, and an extracted kraft lignin. To facilitate the use of the extracted kraft lignin in high-value applications, it can be refined via fractionation to produce a more homogeneous starting raw material. Hence, the aim of this study is to investigate the behavior of dissolved softwood kraft lignin during cross-flow filtration. The effects of the lignin concentration, pH, and ionic strength on the fractionation of the dissolved lignin during cross-flow filtration are investigated. The results indicate that large amounts of low-molecular-weight kraft lignin can be produced from solutions having a low lignin concentration. Furthermore, the effects of pH and ionic strength on the fractionation of low-molecular-weight lignin are identified within the studied ranges.
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| 9. |
- Jørgensen, Mads Koustrup, et al.
(författare)
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Quantifying charge effects on fouling layer strength and (ir)removability during cross-flow microfiltration
- 2021
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Ingår i: Membranes. - : MDPI AG. - 2077-0375. ; 11:1, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Fouling of membranes is still an important limiting factor in the application of membrane technology. Therefore, there is still a need for an in-depth understanding of which parameters affect the (ir)removability of fouling layers, as well as the mechanisms behind fouling. In this study, fluid dynamic gauging (FDG) was used to investigate the influence of charge effects between negatively charged foulant particles and cations on cake cohesive strength. Fouling cakes’ thicknesses and cohesive strengths were estimated during membrane operations, where microfiltration (MF) membranes were fouled in a feed-and-bleed cross-flow filtration system with low and highly negatively charged polystyrene-polyacrylic acid core-shell particles. In addition, an added procedure to determine the irremovability of cakes using FDG was also proposed. Comparing layers formed in the presence and absence of calcium ions revealed that layers formed without calcium ions had significantly lower cohesive strength than layers formed in the presence of calcium ions, which is explained by the bridging effect between negatively charged particles and calcium ions. Results also confirmed more cohesive cakes formed by high negative charge particles in the presence of calcium compared to lower negative charge particles. Hence, it was demonstrated that FDG can be used to assess the cohesive strength ((ir)removability) of cake layers, and to study how cake cohesive strength depends on foulant surface charge and ionic composition of the solution.
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| 10. |
- Kinnarinen, Teemu, et al.
(författare)
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Local properties of filter cakes formed from pH-adjusted bauxite residue slurries
- 2018
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Ingår i: Separation and Purification Technology. - : Elsevier BV. - 1873-3794 .- 1383-5866. ; 194, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Solid-liquid separation of bauxite residue is a topical issue in the alumina industry, not least due to the great quantity and problematic properties of this highly alkaline residue. The objective of this contribution is to provide deeper knowledge about the solid–liquid separation of pH-adjusted (pH 11) bauxite residue by investigating the local filtration properties of filter cakes produced with a piston press. Two bauxite residue samples having different particle size distribution were investigated. Measured local data of the hydrostatic pressure and solidosity was used together with flow rate data to calculate local specific filtration resistance as well as compressibility data. For the investigated pressure range (0.2–2 MPa) it was found that the residue formed slightly/moderately compressible filter cakes with a specific cake resistance between 5·1011 to 1.5·1012 m/kg. The sodium recovery and final cake solidosity were strongly dependent on the applied pressure, but only to a minor extent on the particle size reduction obtained by the applied mechanical treatment. The filter cakes formed from the mechanically treated samples did, however, display a somewhat higher pressure dependence for the local specific filtration resistance compared to the non-ground samples.
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