Degree Of Delignification Research Articles

Associating cooking additives with sodium hydroxide to pretreat bamboo residues for improving the enzymatic saccharification and monosaccharides production

Cooking additive pulping technique is used in kraft mill to increase delignification degree and pulp yield. In this work, cooking additives were firstly applied in the sodium hydroxide pretreatment for improving the bioconversion of bamboo residues to monosaccharides. Meanwhile, steam explosion and sulfuric acid pretreatments were also carried out on the sample to compare their impacts on monosaccharides production. Results indicated that associating anthraquinone with sodium hydroxide pretreatment showed the best performance in improving the original carbohydrates recovery, delignification, enzymatic saccharification, and monosaccharides production. After consecutive pretreatment and enzymatic saccharification process, 347.49g, 307.48g, 142.93g, and 87.15g of monosaccharides were released from 1000g dry bamboo residues pretreated by sodium hydroxide associating with anthraquinone, sodium hydroxide, steam explosion and sulfuric acid, respectively. The results suggested that associating cooking additive with sodium hydroxide is an effective pretreatment for bamboo residues to enhance enzymatic saccharification for monosaccharides production.

Ethanol organosolv pretreatment of softwood (Picea abies) and sugarcane bagasse for biofuel and biorefinery applications

Ethanol derived from biomass has the potential to be a renewable transportation fuel that can replace gasoline. This work was carried out to establish an optimized ethanol organosolv pretreatment of Norway spruce (Picea abies) for bioethanol production (63 wt% EtOH, pH ~3.5 in aqueous phase, 170–240 °C, 90 min) utilizing hydrolytic enzymes in the saccharification step. To test the generality of the method, a series of ethanol organosolv pretreatments were also performed on sugarcane bagasse (50 wt% EtOH, pH ~3.5 in aqueous phase, 155–210 °C, 90–120 min). The degree of delignification increased with increasing temperature during pretreatment, and the fastest increase was observed with sugarcane bagasse. The pretreatments were carried out in a batch mode. The maximum degree of delignification of ~65 % was reached at ~235 °C for Norway spruce, while sugarcane bagasse reached ~80 % at ~210 °C. Cellulose was subjected to degradation (5–10 % points) at these temperatures. Subsequent enzymatic hydrolysis (30 FPU/g cellulose, 32 pNPGU/g cellulose, 50 °C, 48 h) of ethanol organosolv-pretreated biomass achieved complete conversion for both raw materials at the highest degrees of delignification.

Supercritical carbon dioxide combined with 1-butyl-3-methylimidazolium acetate and ethanol for the pretreatment and enzymatic hydrolysis of sugarcane bagasse

The use of green solvents for the partial delignification of milled sugarcane bagasse (1mm particle size) and for the enhancement of its susceptibility to enzymatic hydrolysis was demonstrated. The experiments were carried out for 2h using 40g of supercritical carbon dioxide combined with 1-butyl-3-methylimidazolium acetate and 15.8g of ethanol. The effects of temperature (110–180°C), pressure (195–250bar) and IL-to-bagasse mass ratio (0:1–1:1) were investigated through a factorial design in which the response variables were the extent of delignification and both anhydroglucose and anhydroxylose contents in the pretreated materials. The highest delignification degree (41%) led to the best substrate for hydrolysis, giving a 70.7wt% glucose yield after 12h using 5wt% and Cellic CTec2® (Novozymes) at 10mgg−1 total solids. Hence, excellent substrates for hydrolysis were produced with a minimal IL requirement, which could be recovered by ethanol washing for its downstream processing and reuse.

Chemical composition and kraft pulping potential of 12 eucalypt species

Eucalypts are among the most important short-rotation hardwoods, planted worldwide for the pulp and paper industry. Even though the genus comprises over 700 species, only about a dozen species are used for pulping purposes, therefore, showing the potential for diversification. Six-year-old eucalypt trees from 12 species (Eucalyptus botryoides, Eucalyptus camaldulensis, Eucalyptus globulus, Eucalyptus grandis, Corymbia maculata, Eucalyptus ovata, Eucalyptus propinqua, Eucalyptus resinifera, Eucalyptus rudis, Eucalyptus saligna, Eucalyptus sideroxylon, and Eucalyptus viminalis) were analyzed for chemical composition, fiber morphological, pulping and handsheet paper properties to determine their kraft pulping suitability. The 12 species showed substantial differences regarding extractives (6.1–18.9%), lignin (21.6–30.8%) and holocellulose content (55.4–70.1%). The high inter-species variation in chemical composition produced pulps with different yields (between 38.9 and 49.8%) and degree of delignification (kappa number between 11.6 and 24.2). The combination of these results with the morphological and handsheet properties suggests that E. globulus, E. ovata, E. grandis,E. saligna and E. botryoides have the best overall characteristics for kraft pulping.

Reactive organosolv lignin extraction from wheat straw: Influence of Lewis acid catalysts on structural and chemical properties of lignins

Lewis acids have been studied as catalysts in the organosolv treatment of wheat straw. Fractionation of the lignocellulosic biomass and fragmentation of lignin have been performed in aqueous ethanol in the presence of FeCl2, CuCl2, FeCl3, Ga(OTf)3, ZrOCl2 or Sc(OTf)3. The lignins were characterised in terms of molecular weight, βO4 linkage content and chemical functions through size exclusion chromatography; thioacidolysis; 31P and 13C NMR spectroscopies. The degree of delignification and the yield of Klason lignin increased with the hardness of the Lewis acid. About half of the delignification products were water-soluble monomers and oligomers. The nature of the Lewis acid influenced also the characteristics of the precipitated lignins. The molecular mass, the amount of OH groups and of aliphatic CO bonds decreased as cation hardness increased.

The influence of magnesium oxide charge on kappa number after oxygen delignification of softwood acid sulfite pulp

A laboratory study has been carried out on the utilization of magnesium oxide (MgO) as alkali in an oxygen delignification stage after acid sulfite pulping of softwood. The first objective was to reconfirm results from previous researchers to better understand the process mechanism concerning optimum MgO charge with respect to kappa number reduction. The second objective was to determine if for example the ionic strength could be an important variable in such a stage. It was found that the MgO charge should not be too high as this resulted in reduced degree of delignification which was unexpected. The results also suggested that the ionic strength in the liquor could be an important parameter in the oxygen delignification stage and that it should not be too high. Thus, ionic strength effects seemed to be present already at 0.02 mol/l which is below the normal ion concentration in a pulp mill. The results indicated that there are at least two chemical activities that are competing in an MgO based oxygen delignification stage. The alkalinity is one and a higher alkalinity improves the degree of delignification. The other seemed to be the ionic strength and if this is too high the degree of delignification will go down.

Evaluation of alkaline deconstruction processes for Brazilian new generation of eucalypt clones

Wood utilization for pulp and paper and biorefinery applications requires some kind of mechanical and/or physical–chemical pretreatment. Among the chemical treatments the alkaline ones are the most used worldwide, although acid and solvent treatments have also being used. This paper deals with eucalypt wood deconstruction with alkaline processes including soda-AQ, soda-AQ-O2, soda-O2, and kraft. The kraft process is largely used by the pulp industry and is evaluated here only to serve as a reference. The behavior of the four eucalypt clones selected in chapter 2 were investigated when submitted to the aforementioned processes regarding their screened yield, chemical demands and pulp quality at different kappa number levels (15, 35, 50, and 70). The two most promising processes (kraft and soda-AQ) were chosen for producing pulps (kappa 15 and 20) which were studied in depth (content of carbohydrates, uronic acid, hexenuronic acid, polysaccharide molecular weight, residual lignin structure, etc.), as well as their respective black liquors (heating value, solid content, elemental analysis, and lignin structure). The main findings of this work were: (1) the wood of the four different hybrid eucalypt clones behave similarly in the various alkaline deconstruction treatments; (2) the soda-AQ and Kraft were considered the most suitable processes for producing pulp on the basis of yield, chemical demands and pulp fiber integrity; (3) the soda-AQ process can potentially replace the kraft for a high degree of wood delignification (kappa number 15); (4) the alkaline processes using oxygen (soda-AQ-O2 and soda-O2) are more suitable for wood deconstruction aimed at biofuels; and (5) the soda-AQ process resulted black liquor of more suitable burning characteristics than the kraft.

Characterization of dissolved lignins from acetic acid Lignofibre (LGF) organosolv pulping and discussion of its delignification mechanisms

Abstract Birch chips were cooked by means of the Lignofibre (LGF) organosolv process in acetic acid (AA) and phosphinic acid (H3PO2) at 150°C. The delignification rate and structure of the dissolved lignin was followed as a function of time. The degree of delignification increased steadily up to 88% during the 120 min treatment time. The dissolved lignins were precipitated from the spent liquor (SL) by water addition, washed, and purified for the analyses. Elemental analysis, 31P nuclear magnetic resonance (NMR), heteronuclear single-quantum coherence (HSQC) NMR, pyrolysis-gas chromatography/mass spectrometry (GC/MS), and gel permeation chromatography (GPC) were applied for the structural elucidation. It was found that the cleavage of the β-aryl ether linkages is the main reaction leading to delignification, accompanied by the formation of free phenolic hydroxyl groups and reduction in the content of aliphatic hydroxyl groups. The structure of the dissolved lignin remained the same after the drastic changes at the early stages of cooking (up to 30 min cooking time), indicating that secondary reactions (e.g., condensation) do not take place to a significant extent. H3PO2 probably enhances the acidolysis reaction via an ester derivative that both boosts the cleavage reaction and prevents the formation of the carbocation intermediate that induces condensation. Homolytic cleavage reactions may take place parallel to the acidolytic reactions.

Wood quality effect on kraft pulping performance

The aim of this study was to evaluate the wood quality in the kraft pulping performance under two different pulping conditions at two delignification degrees based on results for the yield, brightness, viscosity, and k/ kappa corrected index. Eucalyptus wood (A, B, and C) was analyzed about their physicochemical properties (basic and apparent density, insoluble and soluble lignin content, extractive content, ash and insoluble ash in hydrochloric acid) and used for pulp production by modified kraft cooking, using two different pulping conditions: Condition I (PI) 16.5% effective alkali, 30% sulfidity, and 155o of cooking temperature; and Condition II (PII) 17.5% effective alkali, 32% sulfidity,and 147oC cooking temperature. Both conditions were performed to kappa number 15.5 ± 0.5 and 18.0 ± 0.5. The following pulping parameters and pulp properties produced were evaluated: H factor, screened yield, viscosity, brightness, hexenuronic acid content, and the k/kappa corrected index. The A wood, which had lower extractives and lignin content in its constitution, as well as lower basic and apparent density when compared with B and C woods, showed good results for cooking parameters, especially the pulp produced at PII condition at kappa number 18.0 ± 0.5.Also, the A wood showed higher screened yield, brightness, and viscosity comparing to the other pulps produced. Those pulps produced with higher kappa number have lower k/kappa corrected index.

Morphological, mechanical, and optical properties of cypress papers

Abstract The pulping properties of cypress species are not known and the present paper aims to filling this gap. Namely, Cupressus lusitanica Mill., C. sempervirens L. and C. arizonica Greene have been submitted to kraft pulping and the pulp properties are compared with those of Pinus pinaster Aiton. and P. sylvestris Watereri as references. Schopper Riegler degree, density, Bekk’s smoothness, tensile index, tear index, burst index, stretch, dry zero-span strength, wet zero-span strength, brightness, opacity and light scattering coefficient have been tested. The pulp yields and delignification degrees of cypress woods were lower than those of the pine references. Fibre length, width and coarseness were statistically different between pines and cypress species and C. sempervirens pulps have corresponding data close to those of pine species. Cypress pulps can be refined much faster than pine pulps. The papers sheets of cypress fibres have, in general, lower mechanical performance than those of pine fibres. Papers from C. arizonica and C. lusitanica are similar and C. sempervirens has intermediate properties being between the other cypress and pine species. However, cypress fibres are relatively short, flexible and collapsible and can be refined with low energy demand, and thus could be incorporated into papers resulting in products with better light scattering and smoothness.

Effect of Kraft Cooking Conditions on the Chemical Composition of the Surface and Bulk of Spruce Fibers

By varying cooking temperature, alkali charge, ionic strength, and cooking time in Kraft pulping of spruce chips, pulps ranging between kappa numbers 20–80 were obtained. The unbleached Kraft pulp fibers were subjected to mechanical peeling in order to separate the surface material from the bulk of the fibers and the carbohydrate composition and lignin content of the two fractions were analyzed. As expected, the lignin and xylan contents were higher on the fiber surface than in the fiber wall. The percentage of xylan on the fiber surface was fairly constant, independent of different pulping conditions or degree of delignification. The lignin proportion on the fiber surface gradually decreased with decreasing kappa number. At a given kappa number, pulping at a higher temperature resulted in less lignin on the fiber surface, probably because of the higher solubility of lignin at higher temperature. Cooking at lower alkali charge also resulted in lower lignin content on the fiber surface at a given kappa number. In this case, there was more time available for degradation of the surface lignin since the lower alkali charge resulted in longer cooking time needed to reach a certain kappa number.

Impact of Hot-Water Extraction on Acetone-Water Oxygen Delignification of Paulownia Spp. and Lignin Recovery

A hardwood-based biorefinery process starting with hot-water extraction (HWE) is recommended in order to remove most of the hemicelluloses/xylans before further processing. HWE may be followed by delignification in acetone/water in the presence of oxygen (AWO) for the production of cellulose and lignin. In this study, the HWE-AWO sequence was evaluated for its effectiveness at removing lignin from the fast-growing species Paulownia tomentosa (PT) and Paulownia elongata (PE), in comparison with the reference species, sugar maple (Acer saccharum, SM). HWE might lead to a remarkable increase in lignin accessibility, and as a result, a greater AWO delignification degree was observed for extracted PT, PE, and SM than for unextracted ones. Organosolv lignin was recovered from the spent liquor of AWO delignification of PT with/without prior HWE and characterized to evaluate the benefits of HWE on the lignin structure and purity. The lignin recovered from the spent liquor of HWE-AWO sequence is of higher purity and lighter color than that recovered from the AWO spent liquor. These properties along with low sulfur content are desirable for lignin high-value applications.

Pulp obtaining from miscathus stems

The process of obtaining of neutral sulfite pulp from the stems of Miscanthus giganteus was studied. The dependence of physical-mechanical parameters of the obtained pulp on the concentration of sulfur dioxide, temperature and pulping time is shown. It was established that the temperature increase from 160 to 180 oC and pulping time from 60 to 120 minutes leads to the improvement of physical-mechanical properties of pulp. The kinetic characteristics of the process of delignification of the Miscanthus stems were defined. It was established that the investigated process of delignification is described by the kinetic equation of the second order. It is shown that the increase in the concentration of sulfur dioxide in the pulping liquor from 20 to 40 g/l leads to the decrease in the activation energy of the specified process from 70.1 to 58,5 kJ/mol. The selectivity indexes of lignin removal (selectivity, degree of removal of carbohydrates, delignification degree) by the neutral sulfite method of delignification of Miscanthus giganteus were determined. The pulp, obtained from the stems of Miscanthus giganteus using the neutral sulfite method has the high physical-mechanical properties and can be used for the production of various types of paper and cardboard.

Comparison of MEA/AQ, soda and soda/AQ pulping of wheat and rye straw

MEA (monoethanolamine)/AQ pulping of wheat and rye straw and bleaching of the produced pulps were investigated. The delignification behaviour of wheat and rye straw using varying MEA/water and liquor/straw ratios was studied. Furthermore, the impacts of mono-, di-, tri-ethanolamine/water mixtures and addition of KOH to the cooking liquor were monitored. The best results were achieved with a MEA/water ratio of 50/50 at a liquor/straw ratio between 3:1 and 4:1. The use of the mixture of mono-, di-, tri-ethanolamine instead of MEA only was not effective for straw pulping. The effect of adding KOH to the MEA pulping liquor was negligible. The results of MEA pulping of both straw species were compared with results for production and bleaching of soda and soda/AQ reference pulps. At similar degree of delignification, the MEA pulps showed 10% higher yield (based on straw), which demonstrates the unusually high selectivity of MEA in straw pulping. The MEA straw pulps showed fairly low brightness and were more difficult to bleach than the corresponding soda pulps. Nevertheless, it is possible to bleach MEA pulps to more than 80% ISO brightness, applying an ECF bleaching sequences (O-Q-OP-DQ-P). With regard to bleachability, yield and strength properties the rye straw pulp sample performed much better than wheat straw pulp sample.

Dissolving pulp production from sugar cane bagasse

The main goal of this study was characterizing the sugar cane bagasse two main fractions: pith and depithed bagasse, and evaluating the potential of the depithed for production of dissolving grade pulps. The depithed bagasse was chemically characterized and converted into brown pulp of two different extents of delignification degrees (kappa 16.9 and 9.2) by the pre-hydrolysis soda process, which consists of bagasse treatment with hot water (15min at 180°C) followed by conventional soda pulping. The resulting pulps were fully bleached by the O-D-(EP)-D-P sequence and evaluated for their main dissolving pulp characteristics. The contents of cellulose, hemicelluloses and lignin in the pith and depithed bagasse varied significantly. For example, the lignin S:G:H of the pith and depithed bagasse were 1.0:1.6:1.8 and 1.0:2.1:2.0, respectively. The pre-hydrolysis pretreatment terminated at pH 3.4 and removed 29% of the depithed bagasse weight. The pre-hydrolysis soda process improves the xylan removal but decreases pulp yield. The bleached pulps showed similar glucans (∼95%), xylans (∼5.0%), ash (∼0.4%), silica (∼0.15%) and α-cellulose content (∼92%) regardless of kappa number. The low viscosity values and the high ash and silica contents limit the uses of the bagasse pulps for certain dissolving grades applications, but it is useful for production of viscose rayon and CMC derivatives after some demineralization. The elucidation of the pith lignin S:G:H ratio and the production of high yield (35.1%) dissolving pulp from depithed bagasse fraction without bleaching cost penalties are the main novelties of this paper.

Preliminary Study on Organosolv Pulping of Acacia Hybrid

Abstract An attempt was made on pulp production from the fast growing plant, Acacia hybrid to determine the total yield, screened yield, Kappa number, and fibre morphology of organosolv Acacia hybrid pulp. Uniform-sized chips were taken to undergo pulping in a digester with five different concentrations of ethanol, 50%, 60%, 70%, 80% and 90% (v/v) with 1 M of sodium hydroxide as catalyst. All chips were digested in a temperature-controlled digester with constant amount of water added and temperature of 185 o C with the duration of three hours cooking time and correspond pressure 1.1-1.2 MPa. It was observed that increasing of ethanol concentration has led to pulp yield increment and decreased in the degree of delignification at the same time. This study was aimed to focus on the effect of the varied concentration of organic solvent towards the pulp yield and its relationship with Kappa number and pulp yield.Key Words: organosolv pulping, ethanol, sodium hydroxide, Acacia hybrid, pulp yield

Improvement of kraft pulp bleaching by treatments with laccase, urea, and refining

Abstract Unbleached Eucalyptus kraft pulps were treated by three methods and the bleaching effects have been evaluated. The treatments were performed by a laccase-mediator system (LMS), refining (R), and urea (U) alone and in combination of these methods. The bleached pulps were characterized in terms of κ number, hexenuronic acid content, brightness, and viscosity. In addition, the lignin-carbohydrate complexes (LCCs) were fractionated and characterized with regard to the fractionation yield, lignin content, and carbohydrate composition. Moreover, the 1H nuclear magnetic resonance spectra were recorded and the thioacidolysis-gas chromatography and thioacidolysis-size exclusion chromatography analyses were performed. The LMS treatment resulted mainly in a slightly better delignification as manifested by a κ number (K no.) reduction of 0.8 units. The effects of the U treatment included delignification (1.4 κ units), hexenuronic acid removal (3 μmol g-1), and improved pulp brightness (3.4 ISO units). The R treatment darkened the pulp (3 ISO units), whereas the bleaching of the R-pulp by subsequent LMS or U treatment enhanced the brightness (0.5 unit more) or delignification (0.3 unit more). The residual lignin in the pulp samples was present mainly as xylan-lignin. The Klason lignin content from the xylan-lignin fraction decreased as the degree of delignification increased. The pulp darkening followed by the R treatment was interpreted as the result of the formation of condensed lignin structures, but these condensed lignins were substantially removed by the subsequent LMS or U treatment.

Delignification of deciduous wood under the action of hydrogen peroxide and ozone

Kinetic curves of the dependence of ozone specific absorption (Q r, sp ) upon the ozonation of aspen wood pretreated with solutions of hydrogen peroxide of various concentrations (from 5 × 10−4 to 2 × 10−1 mol/L) are obtained. The water content in the samples being 56 ± 3%. The initial rate of ozone absorption and total ozone consumption (Q inlet) are determined. Wood samples are investigated by IR and UV diffuse reflection spectroscopy. Based on the kinetics and spectral data, it is concluded that pretreating wood with a H2O2 solution allows the degree of delignification (DD) to be increased at a constant Q inlet value. The DD is maximal at $$ C_{H_2 O_2 } = 5 \times 10^{ - 3} $$ mol/L and is 88% in contrast to a sample ozonated without H2O2 (DD = 85%). The role of pretreatment with hydrogen peroxide and the subsequent action of the O3/H2O2 system in the process of delignification of wood is analyzed.

Kinetic Modeling and Mechanisms of Acid-Catalyzed Delignification of Sugarcane Bagasse by Aqueous Acetic Acid

Organosolv pretreatment of lignocellulose pertains to a biomass fractionation process to obtain cellulosic pulp, high-purity lignin, and hemicellulosic syrup. In the present work, sugarcane bagasse was delignified by aqueous acetic acid (AcH) under atmospheric pressure with addition of sulfuric acid (SA) as a catalyst. Based on the multilayered structure of plant cell wall and the inhibitive effect of dissolved lignin on delignification rate, a novel pseudo-homogeneous kinetic model was proposed by introducing the concept of “potential degree of delignification (dD)” into the model. It was found that delignification rate was a first-order reaction with respect to SA concentration, while AcH concentration showed a high reaction order to delignification rate. The activation energy for delignification was determined to be 64.41 kJ/mol. The relationships of kinetic constants and dD with reaction temperature, AcH, and SA concentrations were determined according to experimental data. Mechanism analysis indicated that cleavage of α-aryl ethers bonds were mainly responsible for the formation of lignin fragments. AcH concentration affected the solubility parameter (δ value) of AcH solution and the ability to form hydrogen bonds with lignin fragments. Therefore, the driving force for solubilizing lignin fragments increased with AcH concentration, and thus AcH concentration had a very significant influence on delignification rate.

Molecular Mass Distribution of Lignin from the Alkaline Pulping of Hardwood, Softwood, and Wheat Straw

The behavior of lignin during kraft (hardwood, softwood, and wheat straw) and soda-AQ (wheat straw) pulping was studied, mainly in terms of delignification degree and molecular mass distribution (MMD). In the initial delignification phase (at 140°C for 15–60 min), a prominent part of the dissolved softwood kraft lignin (18–25 g/L, MM mostly > 3,000 Da) was found in the liquid phase of chip cavities, rather than in the external bulk black liquor (5–7 g/L, MM mostly < 3,000 Da). The maximum weight average MM values ( w) of the soluble lignin under conventional cooking conditions were detected for the kraft softwood (4,100 Da), and kraft birch (3,400 Da) when the degree of delignification was 65–75%, corresponding to a residual lignin content of 5–10%. The maximum w of the dissolved wheat straw kraft (5,050 Da) and soda-AQ (5,900 Da) lignins was clearly higher than that of wood-based kraft lignins (2,950–4, 100 Da).