Browsing by Author "Vuorinen, Tapani, Prof., Aalto University, Department of Bioproducts and Biosystems, Finland"
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- Bromide-free TEMPO-mediated oxidation of cellulose by hypochlorite - fundamental and practical aspects
School of Chemical Technology | Doctoral dissertation (article-based)(2017) Pääkkönen, TimoTEMPO-mediated oxidation of pulp is a pretreatment procedure which is applied to produce TEMPO-oxidized cellulose nanofibers (TOCN). TOCN is proposed to be a raw material for many applications such as electro-optical films, microelectronics, gas-barrier films, cosmetics, flame-resistant materials and other high-tech applications. The drawback in the traditional procedure, which is effective enough for industrial purposes, is the use of bromide in high quantities. Thus, bromide is considered to be highly undesired in the waste water due to the environmental and corrosion concerns. This thesis focused on the development of an industrially feasible bromide-free TEMPO-mediated oxidation procedure of birch kraft pulp which can be applied with the production of the TOCN. TEMPO conversion to TEMPO+ is an underestimated and uncharted process step in the conventional TEMPO-oxidation processes. Here, two separate TEMPO activation steps were developed. TEMPO was activated with ClO2 or NaOCl in the closed vessel prior to the addition in the reactor. Then, the bromide-free TEMPO-mediated oxidations of bleached birch kraft pulp were conducted with the industrially feasible reaction rate. Finally, the oxidized pulps with the adequate carboxylate content were fluidized to TOCN, which is typically a transparent gel. Later, an effective alkali pretreatment of bleached birch kraft pulp was developed to enhance the reaction rate of bromide-free TEMPO-mediated oxidation of the pulp. The TEMPO-oxidation time of alkali treated birch pulp reduced drastically from few hours to half an hour when an adequate hypochlorite addition was used with TEMPO-oxidation. The reached carboxylate content of the TEMPO-oxidized pulp by a high hypochlorite addition was clearly higher with the alkali treated pulps than with the untreated pulps. Atomic force microscopy topography and rheological characterization was applied to study alkali treated TOCN gels as a function of decreased xylan content. An iodometric titration method was developed to monitor TEMPO+ content of catalyst and pulp solutions. This novel analytical method was applied with studying the reaction mechanisms and kinetics of TEMPO-mediated oxidation. The kinetics of the TEMPO conversion to TEMPO+ with Cl(+1) and Br(+1) was examined with the titration method. The importance of the separate TEMPO activation step was found to be an essential part of bromide-free TEMPO-oxidation. Once TEMPO is converted to TEMPO+, which can be conducted with Cl(+1), ClO2 or Br(+1), the reaction rate is dependent on the reaction rate with TEMPO+ and primary hydroxyls or reoxidation of the reduced catalyst (TEMPOH) to TEMPO+. The results of the thesis facilitates the development of industrially feasible TOCN production. - Catalyzed and non-catalyzed hypochlorous acid bleaching of kraft pulps
School of Chemical Technology | Doctoral dissertation (article-based)(2023) Isaza Ferro, EstefaniaPulp bleaching is an energy intensive process because removing residual lignin and HexA, while preserving carbohydrates, requires multistage bleaching sequences which operate at high temperatures and have long residence times. Hence, creating faster bleaching technologies could help to decrease the energy consumption of pulp industry. Catalytic pulp bleaching (Hcat) is a new technology that uses hypochlorous acid (HOCl) and a tertiary amine (DABCO or its derivatives) to selectively oxidize lignin and HexA. Indeed, fully bleached pulp can be obtained in just 1 h using catalytic a bleaching sequence (HcatZP). But there are still several incognitas regarding the efficiency of Hcat stage and its environmental impact. Furthermore, bleaching with HOCl has been discouraged in the past for quality and environmental concerns; even thought HOCl is produced in situ in chlorine dioxide bleaching (D), the most common bleaching stage nowadays. This dissertation tested several catalytic bleaching sequences and identified that the best position for Hcat is at the start of the bleaching sequence. Here, it is most efficient for delignification, and the produced organic halogen bound to the pulp (OX) can be degraded in posterior ozone (Z) and peroxide (P) bleaching stages, producing fully blechached pulps with industrially acceptable OX levels. Several DABCO derivated catalysts were tested in Hcat stage, with an alkyl substituted DABCO derivative called CEM DABCO being the most stable with HOCl while forming a highly active chloroamonium cation. In an attempt towards a catalytic D stage, CEM DABCO was used the reaction of HOCl with chlorite ions, which regenerates chlorine dioxide in-situ regeneration in D stage. CEM DABCO catalyzed the reaction and increased chlorine dioxide stability. However, further studies are required for achieving a catalytic D stage. The role of the catalyst on bleaching with HOCl was assessed in catalyzed (Hcat) and uncatalyzed (Hmild) bleaching by measuring their stoichiometry for lignin and HexA degradation, and their pulps and filtrates properties. The similar properties of the pulps, filtrates, and stoichiometric ratios (for lignin and HexA degradation) confirmed that the catalyst only increased the speed of reactions and did not modify their stoichiometries. Hence, the bleaching sequence without the catalyst HmildZP was tested producing fully bleached pulps with low levels of OX in the final pulp. The filtrates from Hmild stage were digested to european acceptable levels for liquid emissions from pulp mills. Overall, pulp bleaching with HOCl is a feasible alternative due to its efficiency, selectivity, and low cost (compared to chlorine dioxide) but its use is limited to low HOCl dosages at the start of bleaching sequences. - Characterisation of lignocellulose components by analytical pyrolysis gas chromatography mass spectrometry
School of Chemical Technology | Doctoral dissertation (article-based)(2017) Ohra-aho, TainaAnalytical pyrolysis combined with gas chromatography mass spectrometry (Py-GC/MS) is a technique that can be used for the analysis of lignocellulose materials in situ. Pyrolysis degradation products provide information concerning the nature and origin of the initial sample. The main aim of this thesis was to apply analytical pyrolysis for lignin and carbohydrate characterisation from various lignocellulosic plant materials. Isothermal pyrolysis was the main technique utilised. In addition, thermochemolysis, thermal desorption and fractionated pyrolysis were applied in order to provide better understanding of the changes observed in lignin structure and carbohydrate composition in various materials and processes. In pyrolysis, hardwood lignin is degraded to guaiacyl and syringyl type pyrolysis degradation products with similar side chain structures, whereas carbohydrates form stable anhydrosugars. Lignin degradation products can be used to define the lignin composition and S/G ratio of the wood feedstocks. However, Py-GC/MS cannot be recommended for the comparison of carbohydrate composition between different wood species. Information on lignin structure and quantity was obtained directly from pulps by Py-GC/MS. Decrease of oxygenated lignin pyrolysis products and increase of short side chain structures were associated with beta-ether bond cleavage. Decrease of the short side chain structures as a function of delignification was interpreted to indicate leaching of the lignin products formed in cooking, and thus enrichment of native lignin in the residual pulp lignin. Due to the more complex chemical structure of brewers spent grain than of wood, its lignin composition was characterised by Py-GC/MS and thermochemolysis. Thermochemolysis results demonstrated that Py-GC/MS leads to underestimation of native type syringyl structures and S/G ratios. In addition, thermochemolysis with TMAAc and TMAH reagents was applied as a means to differentiate between free fatty acids and esters, respectively. The results showed that thermochemolysis with alkaline TMAH can be used to determine total fatty acid contents from the aliphatic and aromatic esters. TMAAc can be used to distinguish between free acids and aliphatic esters, but not between aromatic esters and free acids. In addition a thermal desorption method was developed to provide information on the odorous volatile organic compounds released from lignin. The method is applicable to the comparison of different lignin samples below their thermal degradation temperatures. - Development of novel methods for production of cellulose-based materials
School of Chemical Technology | Doctoral dissertation (article-based)(2019) Khanjani, PegahModern technology requires sustainable solutions for future new applications. Different types of cellulose such as cellulose nanocrystals (CNCs) and microfibrillated cellulose (MFC) are of particular interest as renewable, highly functionalizable and widely available raw materials. In this thesis, various novel methods for the production of cellulose-based materials were explored. The main findings of this study can be divided into two parts: (i) introducing a method for assessing the reactivity of cellulose in chemical pulps and bacterial cellulose (BC) under mild conditions (RT and pH 9) (Paper I) and ii) investgating several approaches for the chemical functionalization of cellulose as an easy way to adjust the properties of the macromolecule for various purposes. Esterification of cellulose with long-chain aliphatic acid chloride is an effective technique for enhancing the hydrophobicity of cellulose, which can then be used as a coating (Paper II). Another crucial route of cellular functionalization is TEMPO-mediated oxidation, which forms carboxyl groups on the surface of MFC. Crosslinking of these carboxyl groups with metal ions under specific conditions leads to increased tensile strength of the cellulosic film (Paper III and IV). The results yield different approaches to the cellulose reactivity and to improve the water-resistance and tensile strength of the paper and Films, respectively, which may create many renewable options in various applications to replace fossil raw materials. - Fractionation of willow bark for combined production of extracts and fiber bundles
School of Chemical Technology | Doctoral dissertation (article-based)(2018) Dou, JinzeThis study investigates the coproduction of willow bark sclerenchyma fiber bundles and extracts in order to increase the potential added-value from short-rotation willow biomass. Willow is a fast growing biomass source that is grown mainly for heat and power generation, especially in the Northern Hemisphere on marginal lands. On afforested peatland, willow can be grown to prevent erosion and to remove excess nutrients from the soil. A few sporadic studies investigating useful bioactive phenolic compounds from willow bark have been conducted, but burning bark for energy purposes is prevalent. The novel introduced biorefinery concept aims to use 1) the bark fraction for the production of fibers and extractives and 2) the wood fraction is hydrolyzed for sugars and lignin recovered for chemical industry. The morphology and chemical constitution of the inner bark is characterized as the first step towards complete willow valorization. The distinguishing features of inner bark are its high ash and extractive content and bundles of relatively long and thick-walled sclerenchyma fibers. We discovered that picein, triandrin and catechin could be extracted at an approximate 14% overall yield rate from bark by hot water (20 min at 80 ºC). 2D–HSQC NMR spectroscopy and wet chemical analyses demonstrate that guaiacyl is the predominant unit in bark lignin over syringyl and p-hydroxyphenyl. Therefore, the bark lignin structure is the key for developing a novel strategy for separating fiber bundles by judiciously using a mild alkali treatment, followed by fabrication of a composite from the fiber bundle layer and polylactic acid (PLA). Effective routes for separating such fiber bundles require a much lower amount of energy and chemicals than does the separation of individual fibers by conventional methods. Moreover, the fiber bundles exhibited the best compatibility (fiber surface lignin up to 40%) with the matrix PLA compared to other reinforcements. This strategy expands novel composite applications of bark fiber bundles, indicating considerable promise for utilizing this otherwise burned bark material. Additionally, bark lignocellulose nanofibrils exhibit higher hydrophobic properties, and its films display higher tensile strength in comparison with wood, which again provides another example of the superior properties of the bark compared to the wood. This thesis carried out a general, integrative study regarding the morphological structural and chemical characterization of bark and wood, their fractionation, as well as a review of the literature in order to achieve full utilization of fibers and extractives from bark. Gaps in our current knowledge and potentially interesting research approaches are identified and discussed. - Phenomena-Based Modeling of Alkaline Pulping Processes
School of Chemical Technology | Doctoral dissertation (article-based)(2021) Fearon, OlesyaThis doctoral thesis focuses on developing a phenomena-based molecular-level model for kraft and other alkaline pulping processes by utilizing fundamental knowledge on reaction kinetics, thermodynamics and mass transfer. A major benefit from the fundamental approach applied is that the model is, in principle, valid regardless of the reaction environment. Modelling of the pulping process at molecular level provides a new way to examine the relative importance of various phenomena, the validity of theories and provide a platform for developing and testing new ideas. In comparison with experimental research, simulation can be a more cost-efficient way to study and rethink processes, to make them more efficient and environmentally friendly and to improve the quality products with minimal cost. The objective of this thesis work was to create a comprehensive pulping chemistry model, including carbohydrate degradation and delignification in kraft and other alkaline pulping processes. The work was divided into parts and problems were solved in turns. First, literature was reviewed with a target to find the necessary data on the reaction mechanisms and the kinetic parameters of the reactions involved. Secondly, the missing knowledge on the reaction kinetics of strong nucleophiles with non-phenolic lignin with α-carbonyl functionality was obtained experimentally through applying the dimeric model compound adlerone. Further, lignin and carbohydrates were modelled as monomeric pseudo-compounds with experimentally determined chemical characteristics. The macromolecular aspect of lignin was considered in lignin dissolution. The pulping model developed is formed of an extensive library of the reactions of hydroxyl and hydrogen sulfide ions with pseudo-lignin and carbohydrate structures. When simulating the pulping under given conditions, the outcome consists of time-dependent concentrations of the pseudo-structures and real chemical compounds. Additionally, some engineering parameters, such as kappa number, intrinsic viscosity and brightness, were included in the model that derives them from the chemical composition. Consequently, the model could be validated by analytical data as well as by engineering parameters values. The model prediction was compared against experimental results and demonstrated generally a good correlation. The Donnan effect included in the model was important for predicting the content of hexenuronic acid in the system correctly. Inclusion of thermodynamic and stereochemical aspect of lignin could possibly improve the model prediction further. - The properties and applications of long chain cellulose esters
School of Chemical Technology | Doctoral dissertation (article-based)(2020) Willberg-Keyriläinen, PiaEnvironmental awareness and growing concern about plastic waste and the depletion of non-renewable resources have boosted interest in bio-based polymers in recent years. Although the fraction of bio-based polymers in the global plastics market is still small, the demand and share of bio-based polymers is rapidly increasing. The aim of this dissertation was to prove that fully bio-based long chain cellulose esters have the potential to replace traditional oil-based plastics in selected applications. In this research, the long chain cellulose esters were synthesized with different side chain lengths (C6-C18) and the influence of side chain length on barrier, mechanical and thermal properties was demonstrated. In order to study the differences in pulp reactivity and properties of cellulose esters, the molar mass of commercial softwood dissolving pulp was decreased in a controlled manner by ozone-hydrogen peroxide treatment. This research proved that decreasing cellulose molar mass enabled the synthesis of long chain cellulose esters with better reaction efficiency than with the original cellulose. In addition, both the cellulose molar mass and the degree of substitution could be controlled. The resulting long chain cellulose esters formed transparent, flexible and heat sealable films with good water vapor barrier and mechanical properties. Cellulose esters formed smooth and homogeneous coatings with good adhesions when nanocellulose (CNF) films and virgin kraft papers were coated. The long chain cellulose ester coatings also significantly improved the moisture barrier properties of CNF film and kraft paper – these values decreased linearly as a function of ester chain length up to 50% from non-coated values. These coatings also significantly improved the surface smoothness of CNF films by decreasing nano-roughness. The long chain cellulose ester coatings made the material heat sealable and, in addition, the coatings had no antimicrobial activity, and only few microbes adhered to the surface of these films. These results demonstrate that long chain cellulose ester coatings have potential in future packaging applications where surface smoothness, heat sealability and good water vapor barrier properties are required. Injection molding of long chain cellulose esters and their blends was also studied and the mechanical properties were investigated. The results indicate that thermoplastic long chain cellulose esters are completely processable without any addition of a plasticizer, which is very unusual in the case of cellulose esters. This research proves that these materials have good potential to be used in injection molding applications. - Tertiary Amines in Catalytic Pulp Bleaching
School of Chemical Technology | Doctoral dissertation (article-based)(2019) Afsahi, GhazalehThe motif of the current study arises from the importance of the paper in Finland as one of the core industries. The latest released statistics reported by the Confederation of European Paper Industries (CEPI) confirms that Finland, by producing 28.5% of pulp production, possesses the second rank in terms of the production of pulp among all members of the CEPI. Pulp bleaching as one of the subcategories of the tremendous paper industries aim at producing high quality paper with three fundamental goals: the pulp maintains its color over the time; it does not revert color by exposing to the sunlight; and retains its strength. With these goals, sodium hypochlorite bleaching was initiated in the 18th century which was later replaced by chlorine in 1930s. Environmental concerns prompted this industry to opt the Elemental Chlorine Free (ECF) and the Totally Chlorine Free (TCF) bleaching processes, which alleviate the concerns about the release of organochlorine compounds. Nowadays, the ECF with chlorine dioxide is the dominant technology worldwide. Consequently, in this thesis we present a couple of catalysts which introduce a significant reduction in the retention time of the ECF bleaching processes and concurrently bring in a considerable decrease in the chemical consumption. In modern ECF hardwood pulp mills the bleaching sequences (A/D-EOP-D-P or D/A-EOP-D-P) initiate with a long, hot acidic stage which a primary target is to remove most of hexenuronic acid in the pulp. Therefore, active chlorine can be consumed from the traditional 40 kg/t to the level of 20-25 kg/t. The whole bleaching sequence lasts typically 4-5 h. The nucleophilic nature of hypochlorous acid formed in situ in chlorine dioxide bleaching leads to the secondary reactions of hexenuronic acid. Indeed, the nucleophilicity of hypochlorous acid could be enhanced through formation of a highly reactive, electrophilic quaternary chloroammonium cation in the presence of a tertiary amine. After discovering a catalyst, triethylenediamine that is both an industrially used and stable enough chemical, catalytic bleaching (Hcat), utilizing hypochlorite (H), triethylenediamine (DABCO) and its derivative N-carboxymethyltriethylenediamine (CM-DABCO), has the potential to improve the chemical and energetic efficiency of bleaching processes in chemical pulp mills, e.g., through reducing the reaction time of the bleaching processes. Indeed, this thesis studied to clarify if new kraft pulp bleaching sequences with not only Hcat as the first stage (HcatZP and HcatZ/DP) but also as an initial stage of chlorine dioxide (D) and an intermediate stage of Hcat (D0EHcatP) could provide fully bleached pulps. The bleaching sequences of the studied eucalyptus pulps include HcatZP, HcatZ/DP and D0EHcatP which attained a final brightness of 88, 89, and 88% ISO, respectively. In this thesis, it was shown that the HcatZP bleached pulps had low carbonyl group content. Interestingly it was shown that cellulose is not damaged at all in the ozone stage that typically depolymerizes cellulose. In the last part of the thesis, the efficiency and stability of the applied catalysts were studied which made the CM-DABCO as the supreme catalyst. Thus, it can already be claimed that production of almost fully bleached pulp with an exceptionally efficient system is feasible. Softwood pulp bleaching technology has not undertaken major developments in comparison with hardwood pulp bleaching during the last generation. The reason is the content of hexenuronic acid in softwood pulps is relatively low which makes the use of the long, hot acid treatment uneconomic. The catalytic bleaching offers here a solution which extracts hexenuronic acid very fast without depolymerizing cellulose.