1,721,006 research outputs found
Impact of water plasticization on dialcohol cellulose fibres melt processing-structure-properties relationship
Get PDFCellulose and its derivatives are considered sustainable alternatives to non-biodegradable fossil-based plastics. Chemically modified cellulose fibres to dialcohol cellulose (DAC) fibres demonstrated a melt processing window between the glass transition and degradation temperatures which enabled their extrusion by using only water as a temporary plasticizer. With the aim of supporting an industrial upscale of DAC fibres, this study investigates the processing design and the feasibility of melt processing, minimizing the moisture. Melt processes-structure-properties relationships were studied by varying the sequence of primary and secondary melt processes, i.e., extrusion and injection moulding, and by changing the moisture content. The effect of moisture and processing design on the fibre structural properties, such as molecular weight, crystallinity, fibre morphology and fibre suspensions rheology, was assessed. Then, the thermomechanical behaviour of the 3D-shaped DAC injected materials was correlated with DAC fibres structural features obtained by the different processing design and moisture content. Our results identified the injection moulding as a milder process for achieving the preparation of 3D-shaped material with enhanced mechanical properties. Moreover, we disclosed the relevance of controlled moisture in the extrusion process for enabling a secondary shaping directly after compounding and the possibility of 3D-shaping DAC fibres after a rehydration step
Galactoglucomannan recovery from softwood spent sulfite liquor: Challenges, process design and techno-economic evaluations
Get PDFIn the production of pulp and paper, water-soluble components, such as hemicellulose, monosaccharides, and lignin, are released and accumulate in the process water. The process water is usually concentrated and incinerated for heat generation and the recovery of pulping chemicals, such as in the Kraft and sulfite processes. The growing trend toward a more sustainable forest industry has increased the interest in the biorefinery concept. The utilization of wasted wood components, such as hemicelluloses and lignin, as raw materials for the development of specialty chemicals and biofuels is essential for continued growth of the forest industry.The aim of the work that is described in this thesis was to separate and purify hemicellulose (galactoglucomannan (GGM)) from softwood-based spent sulfite liquor (SSL). To this end, various separation techniques were investigated, of which membrane filtration, antisolvent precipitation, and adsorption were primarily used. The SSL in these studies was diluted and therefore needed to be concentrated before any further treatment. The concentration was performed using ultrafiltration (UF), and the purity was increased using diafiltration (DF). In the first UF study, 3 hydrophobic polysulfone (PS) membranes were used to achieve this goal. The 50-kDa UF membrane performed best in terms of low fouling, high flux, and retention of the products. Although the membrane fouling was among the lowest for the 50-kDa UF membrane, the fouling remained high. To reduce the fouling, two prefiltration methods were investigated—microfiltration (MF) and dead-end filtration (DEF)—of which DEF was the most appropriate method, given the low loss of products, which was negligible. DEF required the use of diatomaceous earth as a filter aid, which could have a negative influence on the pulp-mill, in case of membrane failure. For this reason, the membrane material was changed from PS to regenerated cellulose (RC), which is hydrophilic, at the UF stage. The results showed that the RC membranes were far superior to the PS membranes, with higher fluxes and less fouling. Also, the retention of lignin was lower using the RC membranes, which led to higher separation between the GGM and lignin. The best-performing RC membrane (RC70PP) was incorporated into on-site pilot equipment, in which the operating conditions from the lab-scale equipment were scaled up. The pilot had worse performance than the lab-scale setup, perhaps due to the higher Reynolds number and shear rates in the latter, as revealed by computational fluid dynamics. The pilot studies also showed that a 1-hour alkaline cleaning step was sufficient to remove foulants and maintain a stable flux. The separation of GGM and lignin using membrane filtration was not possible, likely due to the narrow difference in molecular weights between them and the formation of a gel layer or cake on the membrane surface that made the separation difficult. The separation was instead achieved with antisolvent precipitation and adsorption. For the antisolvent precipitation, this step was performed after the UF step to reduce the required amount of antisolvents, whereas for the adsorption, it was included as a pretreatment step prior to the UF to determine the influence of the lignin content on the UF step. Separation was possible using both methods, with antisolvent precipitation giving a separation degree of 76% using acetone as the antisolvent, versus 60% for adsorption, which corresponded to an 85% removal rate of the lignin. Finally, a techno-economic evaluation was conducted on various predetermined process configurations, showing that the combination of UF and adsorption (as the post-treatment step) was the most cost-efficient process that also fulfilled the design criteria
Influence of pre-filtration on membrane performance during isolation of lignin-carbohydrate-complexes from spent sulfite liquor
No full textGalactoglucomannan recovery from softwood spent sulfite liquor: Challenges, process design and techno-economic evaluations [Elektronisk resurs]
No full textIn the production of pulp and paper, water-soluble components, such as hemicellulose, monosaccharides, and lignin, are released and accumulate in the process water. The process water is usually concentrated and incinerated for heat generation and the recovery of pulping chemicals, such as in the Kraft and sulfite processes. The growing trend toward a more sustainable forest industry has increased the interest in the biorefinery concept. The utilization of wasted wood components, such as hemicelluloses and lignin, as raw materials for the development of specialty chemicals and biofuels is essential for continued growth of the forest industry. The aim of the work that is described in this thesis was to separate and purify hemicellulose (galactoglucomannan (GGM)) from softwood-based spent sulfite liquor (SSL). To this end, various separation techniques were investigated, of which membrane filtration, antisolvent precipitation, and adsorption were primarily used. The SSL in these studies was diluted and therefore needed to be concentrated before any further treatment. The concentration was performed using ultrafiltration (UF), and the purity was increased using diafiltration (DF). In the first UF study, 3 hydrophobic polysulfone (PS) membranes were used to achieve this goal. The 50-kDa UF membrane performed best in terms of low fouling, high flux, and retention of the products. Although the membrane fouling was among the lowest for the 50-kDa UF membrane, the fouling remained high. To reduce the fouling, two prefiltration methods were investigated—microfiltration (MF) and dead-end filtration (DEF)—of which DEF was the most appropriate method, given the low loss of products, which was negligible. DEF required the use of diatomaceous earth as a filter aid, which could have a negative influence on the pulp-mill, in case of membrane failure. For this reason, the membrane material was changed from PS to regenerated cellulose (RC), which is hydrophilic, at the UF stage. The results showed that the RC membranes were far superior to the PS membranes, with higher fluxes and less fouling. Also, the retention of lignin was lower using the RC membranes, which led to higher separation between the GGM and lignin. The best-performing RC membrane (RC70PP) was incorporated into on-site pilot equipment, in which the operating conditions from the lab-scale equipment were scaled up. The pilot had worse performance than the lab-scale setup, perhaps due to the higher Reynolds number and shear rates in the latter, as revealed by computational fluid dynamics. The pilot studies also showed that a 1-hour alkaline cleaning step was sufficient to remove foulants and maintain a stable flux. The separation of GGM and lignin using membrane filtration was not possible, likely due to the narrow difference in molecular weights between them and the formation of a gel layer or cake on the membrane surface that made the separation difficult. The separation was instead achieved with antisolvent precipitation and adsorption. For the antisolvent precipitation, this step was performed after the UF step to reduce the required amount of antisolvents, whereas for the adsorption, it was included as a pretreatment step prior to the UF to determine the influence of the lignin content on the UF step. Separation was possible using both methods, with antisolvent precipitation giving a separation degree of 76% using acetone as the antisolvent, versus 60% for adsorption, which corresponded to an 85% removal rate of the lignin. Finally, a techno-economic evaluation was conducted on various predetermined process configurations, showing that the combination of UF and adsorption (as the post-treatment step) was the most cost-efficient process that also fulfilled the design criteria
From waste to high-value products: Impact of galactoglucomannan purity on selected hydrogel properties
No full textHydrogels are a hydrophilic network of polymers (usually cross-linked polysaccharides) that are natural or synthetic. Applications of hydrogels are many in the biomedical field. Because of the high water absorption (10 to 200 grams of water per gram of hydrogel), hydrogels have a high degree of flexibility similar to natural human tissue. Human cells can be incorporated into the hydrogel, which in turn can be used to repair damaged tissue. An option is to incorporate drugs in the gels to treat a damaged area by a sustained-release drug-delivery system. Other uses have been in the production of bio-sensors, as absorbent in, e.g. diapers or in the production of contact lenses.Hemicelluloses (in this work galactoglucomannan (GGM)) are a promising renewable raw material for the production of hydrogels. Given their high abundance (constituting up to 25% of the wood cell walls) and current lack of use (usually incinerated together with other biopolymers in the pulp and paper industry), makes this work valuable from an economical and industrial point-of-view.In this work, we examine the possibility to produce hydrogels from GGM extracted from sodium-based spent-sulfite-liquor using a combination of membrane filtration and anti-solvent precipitation. The impact of GGM purity or the addition of lignosulfonates to the cross-linking reaction mixture (in-direct effect of the downstream processing, which affect the overall process economy) on the mechanical, thermal and chemical properties of the hydrogel have been examined and evaluated
Techno-economic evaluation for the process optimization of galactoglucomannan and lignin recovery by ultrafiltration
No full textGalactoglucomannans (GGM) can be used as a precursor for the production of surfactants, plastics, hydrogels etc. However, separation of galactoglucomannan (GGM) from lignin and lignin-carbohydrate-complexes using membrane filtration is difficult. Precipitation of GGM with anti-solvents is an approach that has been previously studied. A membrane filtration step prior to precipitation is economically beneficial to decrease anti-solvent requirements with increasing concentration of GGM. However, previous studies have shown that membrane fouling is a problem that can have a large impact on the life-time of the membranes but also the overall yield of the products.The raw material used in this study was a sodium-based spent-sulfite-liquor (SSL) provided by Domsjö Fabriker (Örnsköldsvik, Sweden) and is the outtake after the first pulping step of softwood (60 % Picea abies and 40 % Pinus sylvestris). The SSL was concentrated with a 50 kDa polysulfone membrane (hydrophobic) and four regenerative cellulose membranes (30, 20, 10 and 5 kDa) (hydrophilic) to a volume reduction of 90 %. The resulting retentate was analyzed for the composition and the product yields were calculated. Membrane data, such as, flux, trans-membrane pressure, cross-flow velocity and degree of fouling were used together with the GGM yields in a techno-economic evaluation to find a cost-efficient process for the separation and purification of GGM and lignin from SSL
From lab-scale to on-site pilot trials for the recovery of hemicellulose by ultrafiltration: Experimental and theoretical evaluations
No full textSpent sulfite liquor (SSL) is a byproduct of the sulfite pulping process of wood. SSL usually contains monosugars and lignosulfonates, which are fermented to produce ethanol and dried to generate lignosulfonate salts. However, the SSL that was used in this work was derived from the first step of a 2-step sulfite pulping process of softwood under mild pulping conditions in the first stage of cooking. The resulting SSL contained polymeric hemicelluloses, which are not used today but have many potential applications. The up-concentration of this SSL had been performed on a lab scale by ultrafiltration. However, the pilot-scale ultrafiltration of hemicellulose-rich sodium-based SSL has not been reported. In this study, the operating conditions for the lab-scale concentration of hemicellulose-rich, sodium-based SSL were examined in a pilot-scale membrane filtration unit. The permeate flux and retention of products were lower in the pilot equipment compared with the lab-scale setup, perhaps related to the lower Reynolds number and shear rate in the former, as indicated by simulations of computational fluid dynamics. The pilot equipment also ran at a higher volume reduction compared with the lab-scale system, which could explain the difference in flux and retention. The effects of fouling and cleaning were also determined, wherein an alkaline cleaning step (pH 11) for 1 h was sufficient to remove foulants and maintain a stable average flux of 88 L/m2h and the nonchanging retention of products
Influence of dielectric constant on the separation of O-acetyl-galactoglucomannan and lignin-carbohydrate-complexes during anti-solvent precipitation of ultra-filtrated spent-sulfite liquor
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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