Investigation of the Chemistry of Oxygen Delignification of Low Kappa Softwood Kraft Pulp using an Organic/Inorganic Chemical Selectivity System

Abstract

Oxygen delignification (OD) of low kappa softwood kraft pulp was examined in two steps without inter‐stage washing as part of an overall program to evaluate the efficiency of a selectivity enhancement system consisting of phenol and magnesium sulfate. Black liquor carryover in the reaction system did not substantially affect delignification and the selectivity of these OD reactions. The residual lignins from both the original pulp and oxygen‐delignified pulp with and without the phenol/MgSO₄ selectivity enhancement system were prepared and characterized using NMR spectroscopy. The effluent lignins after oxygen delignification were also prepared and characterized. The lignin characterizations provided the basis for the rationalization of the selectivity observed. A significant finding of this study was that the phenol/MgSO₄ system in the oxygen delignification reaction appeared to hinder phenolic guaiacyl unit condensation. It also appeared to enrich the levels of p‐hydroxyphenyls in the residual lignin.     

Effect of xylanase on ozone bleaching kinetics and properties of Eucalyptus kraft pulp

Environmental pressure has led the pulp and paper industry to develop new technologies in order to reduce or suppress the presence of various pollutants in effluents from bleaching plants. One of the choices for this purpose is enzyme‐based biotechnology. This study deals with the effect of using a xylanase‐based enzymatic pretreatment, in a TCF (Totally Chlorine Free) sequence, on the properties of the resulting paper pulps. The hexenuronic acid content in the pulp and the physical properties of the paper were also studied. The performance of the xylanase was analysed through kinetic studies on ozone bleaching. The enzymatic pretreatment results in easier bleaching and delignification of the pulp, causing a bleach‐boosting effect. The decreased consumption of reagent is related to a decreased content of hexenuronic groups. The physical properties of the treated pulp are similar to those of untreated pulps. Cellulose degradation, delignification and chromophores' removal show first‐order kinetics. Enzyme pretreatment leads to differences between the kinetic constants of cellulose degradation and chromophores' removal, due to an increased accessibility to bleaching agents. The xylanase treatment leads to a lower floor kappa number (IK_∞) during the ozone stage. Copyright © 2003 Society of Chemical Industry     

Soda Pulping of Hardwoods Catalyzed by Anthraquinone and Methyl Substituted Anthraquinones

Abstract

Black liquor gasification (BLG) as well as the recovery of lignin and other organic compounds from pulping black liquor would be aided if an efficient sulfur‐free pulping process could be developed. This has provided new impetus for research on soda pulping with redox catalysts instead of sodium sulfide that is presently used in the kraft process. Soda/anthraquinone (AQ) pulping afforded white birch (Betula papyrifera) and sugar maple (Acer saccharum) pulps with equal if not superior strength to kraft pulps. However, the delignification rate was significantly lower for soda/AQ pulping. When AQ was replaced by 2‐methylanthraquinone (2‐MAQ) a delignification rate only slightly lower than that of kraft pulping was obtained at the same effective alkali (EA). At a kappa number of ～20, a soda/2‐MAQ pulp was produced from sugar maple at a higher yield (1.2% on chips) than for a kraft pulp. 2‐MAQ was synthesized, as a powder, at 75% yield using an AlCl₃–mediated Friedel‐Crafts reaction that is one of the methods used for commercial production of AQ.     

The effect of mixing on the generation of alkaline peroxymonosulfate

Alkaline peroxymonosulfate (PMS) has been successfully used in the laboratory for bleaching kraft pulp. Used in conjunction with oxygen, the addition of 1.0% PMS to an oxygen delignification system can increase delignification from 49% to 73% without reducing pulp strength. One promising method of achieving this is the catalytic oxidation of sodium sulfite with oxygen. Laboratory generation of PMS is readily achieved, but typically at low yields and low concentrations. Here we investigate the mixing‐sensitivity of its generation under semi‐batch reaction conditions using a number of laboratory mixers. Our primary focus was on the energy dissipation in the reaction zone and its effect on PMS yield and concentration. By managing the chemical contacting strategy and increasing energy dissipation in the reaction zone we were able to generate PMS at higher yields and concentrations than previously reported.     

Xylanase effects on pulp delignification

Xylanase effects on softwood pulp delignification were investigated experimentally and using mathematical models. The effect of xylanase molecular size on pulp delignification was investigated. As xylanase molecular weight decreased from 67 kDaltons to 20 kDaltons, lignin removal from pulp increased from 30 wt% to 48 wt%, respectively. The rate of xylanase-aided pulp delignification was studied using a batch system. The rate-data was fitted to a mathematical model of the batch system that enabled estimation of process parameters including xylanase and lignin effective diffusivities, lignin mass transport coefficient, and effective particle diameter for mass transport. Parameter values thus obtained were used to simulate the semi-batch delignification process, which predicted 84.6% of lignin available to UGA xylanase (MW=39,000 Daltons) would be removed in 2.5 h.     

XYLANASE EFFECTS ON PULP DELIGNIFICATION

Xylanase effects on softwood pulp delignification were investigated experimentally and using mathematical models. The effect of xylanase molecular size on pulp delignification was investigated. As xylanase molecular weight decreased from 67 kDaltons to 20 kDaltons, lignin removal from pulp increased from 30 wt% to 48 wt%, respectively. The rate of xylanase-aided pulp delignification was studied using a batch system. The rate-data was fitted to a mathematical model of the batch system that enabled estimation of process parameters including xylanase and lignin effective diffusivities, lignin mass transport coefficient, and effective particle diameter for mass transport. Parameter values thus obtained were used to simulate the semi-batch delignification process, which predicted 84.6% of lignin available to UGA xylanase (MW=39,000 Daltons) would be removed in 2.5 h.     

麦草亚铵法氧脱木素浆的短流程漂白

对麦草亚铵法氧脱木素浆进行了P、HP和HQP漂白对比研究,结果表明:在过氧化氢单段漂白时,Na2SiO3的适宜用量为0.4%,在所选过氧化氢用量、NaOH用量、温度和时间的四因素三水平方差分析漂白工艺中,影响纸浆白度的主要因素为NaOH用量;而采用HP和HQP漂白时,漂白浆的白度分别达到78.1%(ISO)和81.9%(ISO),可见采用螯合处理的效果明显。     

Factors affecting the optimal performance of a high-yield pulping operation

Process models based on data from close to one hundred pilot scale pulping runs are used to investigate strategies for operating a chemimechanical pulp mill. Optimal values for a total of 55 process and pulp quality variables have been calculated by applying a genetic algorithm search to a fuzzy model of the overall system. This model consists of over 90 distinct empirical relationships. Results indicate that pulp quality is maintained at minimal fibre and energy costs when the chemical pretreatment is conducted at moderately low temperature using a high SO₂ concentration producing both high sulphonation and high yield simultaneously. Subsequent refining should involve applying at least 65% of the total energy in the primary stage. The pulp quality obtained is comparable to that of a CTMP pulp but with the added benefit of higher freeness.     

麦草亚铵法氧脱木素浆蒽醌强化次氯酸盐漂白

对麦草亚铵法氧脱木素浆进行蒽醌强化的次氯酸盐漂白工艺的研究,结果表明:在所选四因素三水平漂白工艺中,影响纸浆白度和卡伯值的主要因素是用氯量,当用氯量为7%时,纸浆白度为71.1%ISO;另外,在50℃和80℃的条件下,对麦草亚铵法氧脱木素浆分别进行添加氨基磺酸和蒽醌的漂白研究,发现次氯酸盐漂白时添加蒽醌比添加氨基磺酸的漂白效果好,不仅漂白浆的白度和黏度均得到提高,而且脱木素能力也显示加强。     

Selective Degradation of Lignin Polymer by Chlorine Dioxide During Chemical Pulp Delignification in Flow Through Reactor

The delignification of pulp in a conventional batch reactor provides convenient conditions for inutile secondary reactions in which ClO₂ reacts with oxidized aromatic units of lignin. In this study the flow-through reactor was applied to minimize secondary reactions. The obtained results showed that the removal of oxidized lignin from the reaction zone significantly enhanced the ClO₂ reaction toward non-oxidized units of lignin. Application of an organic solvent-water solution, bleaching liquor, significantly increased the removal of oxidized lignin and decreased considerably the secondary reactions. Although this technique considerably improved ClO₂ effective efficiency, large amounts of chlorate formation decreased the overall effect of improved ClO₂ global efficiency.     

Alkaline sulfite/anthraquinone pretreatment followed by disk refining of Pinus radiata and Pinus caribaea wood chips for biochemical ethanol production

BACKGROUND: Alkaline sulfite/anthraquinone (ASA) cooking of Pinus radiata and Pinus caribaea wood chips followed by disk refining was used as a pretreatment for the production of low lignified and high fibrillated pulps. The pulps produced with different delignification degrees and refined at different energy inputs (250, 750 and 1600 Wh) were saccharified with cellulases and fermented to ethanol with Saccharomyces cerevisiae using separated hydrolysis and fermentation (SHF) or semi‐simultaneous saccharification and fermentation (SSSF) processes. RESULTS: Delignification of ASA pulps was between 25% and 50%, with low glucans losses. Pulp yield was from 70 to 78% for pulps of P. radiata and 60% for the pulp of P. caribaea. Pulps obtained after refining were evaluated in assays of enzymatic hydrolysis. Glucans‐to‐glucose conversion varied from 20 to 70%, depending on the degree of delignification and fibrillation of the pulps. The best ASA pulp of P. radiata was used in SHF and SSSF experiments of ethanol production. Such experiments produced maximum ethanol concentration of 20 g L^?1, which represented roughly 90% of glucose conversion and an estimated amount of 260 L ethanol ton^?1 wood. P. caribaea pulp also presented good performance in the enzymatic hydrolysis and fermentation but, due to the low amount of cellulose present, only 140 L ethanol would be obtained from each ton of wood. CONCLUSION: ASA cooking followed by disk refining was shown to be an efficient pretreatment process, which generated a low lignified and high‐fibrillated substrate that allowed the production of ethanol from the softwoods with high conversion yields. Copyright © 2012 Society of Chemical Industry     

Development of Mathematical Models for Describing Organosolv Pulping Kinetics of Fungally Pretreated Wood Samples

Abstract

Eucalyptus grandis wood samples decayed by white- and brown-rot fungi were cooked at 180°C for 5 to 100 min with methanol/water (78:22 v/v) containing 25 mM of CaCl₂ and 25 mM MgSO₄. Mathematical models for describing organosolv pulping kinetics of the fungally pretreated samples were developed to estimate delignification constants, and also rate constants for xylan and wood mass solubilization. These models had high R² values and were able to predict pulp yield, as well as lignin and xylan contents during the process at 99% confidence level. Delignification of undecayed control samples had a rate constant of 2.0 × 10^?2 min^?1 for the bulk phase. Most decayed samples presented delignification constants higher than those of the control. Some decayed samples exhibited an additional delignification phase at the beginning of the process, which was characterized by a low solubilization rate. These samples required insertion of an additional term in the model to represent this phase.     

Investigation of Laccase/N-Hydroxybenzotriazole Delignification of Kraft Pulp

Abstract

N-hydroxybenzotriazole, a mediator for laccase delignification of kraft pulps, was shown to be unstable under the biobleaching conditions. The treatment of N-hydroxybenzotriazole either with laccase alone or in the presence of kraft pulp yielded benzotriazole. The reductive conversion of N-hydroxybenzotriazole to benzotriazole was found to occur rapidly in the presence of pulp. Furthermore, benzotriazole was found to be inactive as a mediator for laccase catalyzed delignification of kraft pulps. Hence, the overall conversion of N-hydroxybenzotriazole to benzotriazole is detrimental towards the bio-delignification process.     

NAEM—ASAM制浆过程中木素和碳水化合物的溶出规律

研究了中性碱土金属盐（NAEM）催化的碱性亚硫酸钠溶液中添加蒽醌和甲醇（ASAM）法制浆的机理，结果表明，NAEM＋ASAM法蒸煮对木素具有良好的选择性，从而改善了碳水化合物的稳定性，成浆具有高的半纤维素保留率。     

Characterization of kraft pulp delignification using sodium dithionite as bleaching agent

Abstract

The delignification of kraft pulp with sodium dithionite was studied to remove lignin content in the pulp. The sodium dithionite dissolves the chromophoric groups and residual lignin present in the pulp. The increase in dosage of sodium dithionite and reaction temperature of delignification has positive effect on kappa reduction of pulp. X ray diffraction was used to determine the crystallinity index of bleached pulp. The crystallinity increased from 83.3% for unbleached pulp to 86.7% after delignification. Fourier transform infrared spectroscopy shows the reduction in hydrogen bonding in bleached pulp and also the conversion of cellulose I to cellulose II. FT-Raman spectra shows that the fluorescence observed in the spectra of unbleached pulp reduced significantly in comparison to the spectra of bleached pulp resulting in removal of residual lignin and chromophoric groups present in the pulp. Scanning electron imaging shows the smoothening of fiber surface after bleaching. The delignification reaction followed first-order kinetics and activation energy is 33.57kJ/mol.     

KINETICS OF AQUEOUS ETHYLENEDIAMINE-ETHANOL-ANTHRAQUINONE DELIGNIFICATION PROCESS

A new organosolv pulping method has been investigated. Delignification can be carried out by digesting the lignocellulosic material in an aqueous solution of ethylenediamine (EDA) and ethanol (EtOH) in combination with catalytic amounts of anthraquinone (AQ). This aqueous EDA-EtOH-AQ pulping is found to be highly selective in delignification and is flexible to softwoods. Bulk delignification was found to take place according to a pair of first-order mechanisms, like aqueous ethanol pulping. In the initial phase of delignification more than 50% lignin is removed, while the rest is extracted in the second slower step. The rate constants for each step are of the same order of magnitude and higher than those obtained in ethanol pulping. This indicated that overall delignification is faster when compared to aqueous ethanol pulping. The Arrhenius activation energy for the initial step was found to be 6.4 kcal/mole. The high selectivity in the detignification during the EDA-EtOH—AQ process is observed at all levels of delignification and shows at least an 18—20% increase in yield when compared with ethanol pulping.     

Exergy as a tool for measuring process intensification in chemical engineering

Exergy is defined as the maximum shaft work that can be done in a process to bring the system into equilibrium with the environment. Thus, exergy analyses are the first step to understand where the weak points of processes are. It considers intrinsically the quality of energy: when energy loses its quality, exergy is destroyed. In addition, optimization of processes aiming at the minimization of exergy destruction can be done as a function of the topology and physical characteristics of the system, such as finite dimensions, shapes, materials, finite speeds, and finite‐time intervals of operation, establishing a direct relationship between exergy and process intensification. However, the emphasis on exergy in chemical engineering is still very poor compared with other fields, in spite of being one of the areas in which more exergy is destroyed due to reaction and separation . This paper gives an overview of the current application of exergy analyses in chemical engineering, showing the main fields in which exergy studies are performed and focusing the attention on two critical points of action: separation technologies (distillation and membrane technology) and CO₂ capture. New research trends in chemical engineering using exergy as a tool for process intensification are highlighted. © 2013 Society of Chemical Industry     

Integrating laccase–mediator treatment into an industrial‐type sequence for totally chlorine‐free bleaching of eucalypt kraft pulp

Enzymatic delignification using the high‐redox potential thermostable laccase from the fungus Pycnoporus cinnabarinus and a chemical mediator (1‐hydroxybenzotriazole) was investigated to improve totally chlorine‐free (TCF) bleaching of Eucalyptus globulus kraft pulps. Different points of incorporation of the enzyme treatment into an industrial‐type bleaching sequence (consisting of double oxygen, chelation and peroxide stages) were investigated in pressurized laboratory reactors. The best final pulp properties were obtained using an O? O? L? Q? PoP sequence, where a laccase–mediator stage (L) was incorporated between double oxygen and chelation. The worse results, when the enzymatic and chelation treatments were combined in a unique stage, seemed related to partial inhibition of laccase‐mediator activity by the chelator. The new TCF sequence including the laccase stage permitted to improve eucalypt pulp delignification to values around kappa 5 (hexenuronic acid contribution over 50%) compared to kappa 7 using only TCF chemical reagents. In a similar way, the final brightness obtained, over 91% ISO, was 3–4 points higher than that obtained in the chemical sequences. Although technical and economic issues are to be solved, the results obtained show the feasibility of integrating a laccase–mediator treatment into a TCF sequence for bleaching eucalypt kraft pulp. Copyright © 2006 Society of Chemical Industry     

SO2-Ethanol-Water (SEW) Pulping: II. Kinetics for Spruce,Beech, and Wheat Straw

Abstract

SO₂-ethanol-water (SEW) delignification kinetics for spruce, beech, and wheat straw are presented. All these species produce pulps using SEW cooking liquor and follow first order delignification kinetics at similar bulk delignification rates. However, residual delignification is much slower for beech than for spruce.

The hemicelluloses retention (135°C) and cellulose degradation kinetics are also characterized for beech SEW pulping. Xylan and glucomannan are removed from the pulp following first-order kinetics with a higher rate constant for xylan. Cellulose is retained in the fibers until kappa number 9, after which it starts to dissolve in the liquor. The yield also drops significantly in the region of kappa numbers 9–7.

Cellulose degradation is followed by intrinsic viscosity measurements and is found to be zero order in cellulose. The rates are higher at 135 and 145°C for beech SEW pulping than for spruce.     

Near-Infrared Spectroscopy and Chemometric Analysis for Determining Oxygen Delignification Yield

Abstract

Oxygen delignification studies were carried out using a softwood kraft pulp under varying reaction temperatures (80–140°C) and alkaline charges (1–12%). Near-infrared (NIR) spectroscopy combined with chemometric methods was employed to analyze oxygen delignification pulp yields, which were compared to gravimetric analysis. Principal component analysis (PCA) of the NIR spectra data was performed and a partial least-square (PLS) regression model was developed to predict the pulp yield of oxygen delignified pulps based on the NIR spectra data. PCA analysis indicated that 99.1% of total variances of NIR spectra data in the range of 1100–2266 nm could be expressed by three principle components. A PLS1 model based on the NIR spectra data had good predictive ability and appeared to be an effective tool for pulp yield prediction for the oxygen delignification process.