Investigation and Characterization of Lignin Precipitation in the LignoBoost Process

Lignin of high purity can be separated from black liquor using the LignoBoost process, of which the overall efficiency is largely dependent on the precipitation yield of lignin, which depends on the properties of black liquor and process conditions. In this paper, the influences of process conditions on the precipitation yield of lignin from mixed hardwood/softwood black liquor were investigated. The Klason and standard UV method were used to determine lignin concentration. The chemical and structural properties of lignin were also analyzed. The results showed that the precipitation yield of lignin increased along with a decrease in pH and temperature, or with an increase in the ion strength of black liquor, and the yield was lower when mixed softwood/hardwood black liquor was used. It also showed that at a higher precipitation yield the precipitated lignin had a lower average molecular weight but had higher methoxyl and phenolic hydroxyl content.     

Phenolic compounds from vacuum pyrolysis of wood wastes

Various softwood and hardwood bark residues, primary sludges and softwood sawdust residues were processed by vacuum pyrolysis in a laboratory scale batch reactor. The pyrolysis oil, water, charcoal, and gas were recovered and analyzed. The pyrolysis oils were analyzed in details for their content in phenolic compounds after derivatization to their acetyl derivatives. The influence of temperature, heating rate, feedstock bed thickness, particle size and feedstock water pretreatment on the yield of phenols was investigated. The highest yield of phenols was obtained when hardwood bark was soaked in water for 48 hours and pyrolyzed at a temperature of 450°C and a heating rate of 10°C/min. Pyrolysis performance was evaluated in terms of total phenolic yield and composition.     

Purification process for recovering hydroxy acids from soda black liquor

Black liquor, a side product of chemical pulping, contains hydroxy acids that have many potential applications, e.g., as polymer precursors. Currently there are no feasible separation processes available for recovery of hydroxy acids from such solutions. Neutralization is usually though to be a necessary pre-treatment, but it adds into chemical consumption and may impede the integration of the recovery process to a pulp mill. In this work, an experimental investigation of a new process concept for the recovery and purification of hydroxy acids from soda black liquor without neutralization is presented. The process consists of ultrafiltration, size-exclusion chromatography, ion-exchange, adsorption, and evaporation. Mixtures of hydroxy acids in high purity were produced from black liquor of soda pulping using the process. A reduction of 99% in lignin content of the organic acid fraction was achieved. In the chromatographic separation step, the recovery of sodium hydroxide was almost 100%. The average purities of hydroxy acids isolated from softwood and hardwood black liquors were 81% and 63% on mass basis, respectively.     

STEADY SHEAR FLOW PROPERTIES OF HIGH SOLIDS SOFTWOOD KRAFT BLACK LIQUORS: EFFECTS OF TEMPERATURE, SOLIDS CONCENTRATIONS, LIGNIN MOLECULAR WEIGHT AND SHEAR RATE

The steady shear flow properties of several softwood kraft black liquors (slash pine) from a two level, four variable factorially designed pulping experiment were determined for solids concentrations from 50% to 85%, temperatures from 40°C to 140°C and shear rates up to 10,000 s-1 by using Instron capillary and Haake coaxial cylinder rheometers. It was shown that the slip velocity at the wall of the capillary is insignificant and that a two capillary method can be used to determine the viscosity of the samples. At high solids, black liquor can exhibit non-Newtonian behavior dependent upon temperature, solids concentrations, solids composition and shear rate. In general, the liquors behave as pseudoplastic fluids. The exact level of viscosity at any given condition is dependent upon the solids composition which will vary from liquor-to-liquor. The flow behavior of the liquors was described using power-law, Cross and Carreau-Yasuda models. Superposition principles developed for polymer melts and concentrated polymer solutions were applied to obtain reduced correlations for viscosity behavior of the liquors. By using a suitable reference temperature, related to the glass transition temperature of black liquors, a generalized WLF type shift factor was obtained for the liquors used in this study and can be used to obtain a reduced plot of viscosity behavior of other black liquors.     

THE INFLUENCE OF COMPOSITION ON THE SWELLING OF KRAFT BLACK LIQUOR DURING PYROLYSIS

During the drying and pyrolysis phases of kraft black liquor combustion, significant swelling of individual liquor particles occurs. Swollen volumes can reach 20 to 30 times the original volume during combustion. The swelling process can affect the combustibility of black liquor and the amount of carryover in a recovery furnace.

The composition of black liquor was found to have a large influence on swelling. A combination of sugar acids and kraft lignin swelled to a larger extent than when either component was pyrolyzed separately. A 1:1 ratio of these two components resulted in maximum swelling for the various ratios tested. The molecular weight of kraft lignin had an effect on swollen volume with higher molecular weight fractions producing lower swelling chars.

Other components were found to reduce the swelling of black liquors. Extractives interfered with the swelling by appearing to change the deformable properties of the pyrolyzing material. Inorganic salts acted as a diluent.

Analysis of the surface characteristics of chars revealed that good swelling chars were composed of small bubbles 50 to 150 microns in diameter. Poor swelling liquors did not exhibit this phenomenon. The formation of bubbles was found to be initiated at 240°C, which closely corresponded to the thermal decomposition temperature of a sugar acid. Kraft lignin appeared to have a major influence on the fluid properties of the pyrolyzing particle. The composition of black liquor determines to a large extent surface forces present in black liquor; these forces are thought to be responsible for the extent to which kraft black liquors deform and swell during pyrolysis.     

Oxidation of Hardwood Kraft-Lignin to Phenolic Derivatives. Nitrobenzene and Copper Oxide as Oxidants

A hardwood kraft lignin (obtained by precipitating an industrial black liquor with a solution of calcium salt in alcohol) was oxidized in alkaline medium to obtain phenolic compounds (syringaldehyde, vanillin, syringic acid and vanillic acid). Nitrobenzene and copper (II) oxide were the oxidants employed. Influence of temperature, reaction time and oxidant concentration on yield and product distribution were studied. The results show that nitrobenzene is a more effective oxidant (15–18 % of aldehydes on kraft lignin) than copper (II) oxide (7–8 %). Product distribution showed the highest aldehyde selectivity for nitrobenzene, due to the presence of two additional oxidation products in the copper oxide oxidations. In the oxidation to aldehydes, the alcohol-calcium precipitated kraft lignin is a better raw material than other precipitated kraft lignin.     

Structural Changes in Lignin During Kraft Cooking Part 3. On the Structure of Dissolved Lignins

Two series of pine kraft lignins were prepared by a) normal kraft cooks to different pulp yield levels and precipitation of the lignins from the black liquors by acidification and b) by successive acidification of the black liquor obtained from a flow-through cook. All the lignins were extensively purified, subjected to elemental and methoxyl analysis and subsequently acetylated.

Quantitative ¹³C-NMR analysis was carried out on acetylated samples and the results were combined with the results of phenolic group determination by means of aminolysis and with elemental analysis data. The various acetylated lignins were also subjected to analysis by size exclusion chromatography.

All results are discussed with reference to known features of kraft cooking and of kraft lignins.     

Modified Kraft Pulping of Bagasse: Infrared Spectroscopy of Lignin

Abstract

The infrared spectroscopy of precipitated lignin from waste black liquors of bagasse pulping with kraft sulfite pulping process was investigated. Also the effect of anthraquinon and methanol addition in the soda, kraft and kraft-sulfite pulping liquor on the infrared specra of the precipitated lignin was studied. The presence of methanol in the pulping liquor causes an increase in the degradation as well as increase in the carboxylic group in the precipitated lignin. Also, the phenolic hydroxyl group in case of kraft lignin is higher than soda lignin. Presence of sulfite in the kraft-sulfite pulping liquor produces lignin hydroxyl groups.     

温度对二氧化碳酸析提取黑液中木质素的影响

以碱法制浆的松木黑液为原料,用二氧化碳酸化黑液提取其中的木质素,考察了反应温度(40~80℃)对酸析木质素产率及其无机盐和糖分等含量的影响,采用凝胶渗透色谱(GPC)、离子色谱仪(IC)、元素分析仪和热重分析仪(TG)对木质素产物进行结构表征。结果表明,温度升高不利于木质素析出,产率下降;但较高温度下制备的木质素中无机盐、糖分及硫含量低,纯度高;同时温度越高,木质素相对分子质量越大,甲氧基含量增大,但酚羟基含量减小。TG和DTG曲线显示,反应温度升高木质素最大失重速率增加,残余量减少。     

Liquid Lignin from the SLRPTM Process: The Effect of Processing Conditions and Black-Liquor Properties

CO₂ acidification of Kraft black liquors was performed at temperatures of 100–150°C and pressures of 5–8 bar in an investigation of the SLRP^TM process. At these conditions, a highly hydrated, lignin-rich liquid (vs. the usual solid) separated out to form a new phase. The solids content/ionic strength of the starting black liquor was found to be a key variable for controlling the bulk and molecular properties of the ?liquid-lignin” (LL) phase. For example, black liquors of lower ionic strengths (20% solids) produced LLs with lower ash contents and higher molecular weights, albeit in lower yields. In contrast, higher ionic strengths/solids content (40%) produced LLs in higher yields with higher aromatic and aliphatic hydroxyl contents. Temperature effects were significant only at the highest levels. The degree of hydration of the LL phase was found to be a useful measure of the water available for hydration of ionized/polarizable groups in lignin.     

Interactions of Optical Brightening Agents With High Yield Pulps

Abstract

The interactions of Optical Brightening Agents (OBA) with High Yield Pulp (HYP) fibers under two methods of OBA addition were evaluated on a softwood TMP and hardwood (aspen) HYP: OBA added to the peroxide bleach liquor (Method A), and OBA added conventionally at the wet end (Method B). The treated pulps were fractionated and OBA retention and efficiency in each fraction were determined. Adding OBA to the bleach liquor gave a higher OBA retention than adding OBA at the wet end; the hardwood HYP had a higher OBA brightening efficiency than the softwood TMP. The results are explained in terms of pulp morphology, lignin content, and process conditions (temperature and contact time). Adding OBA to the mechanical pulp also improved the brightness stability during the light-induced yellowing process.     

Chemical composition and physical properties of black liquors and their effects on liquor recovery operation in Brazilian pulp mills

Black liquor is the major by-product and fuel of pulp mills. In this work, effects of black liquor properties on its recovery unit operation are analyzed. Thus, an experimental methodology for characterizing the principal chemical and physical properties of eucalyptus Kraft and bamboo soda black liquors has been developed, including sample collections from six Brazilian mills. Based on results, eucalyptus and bamboo black liquors present higher contents of non-processing elements (NPEs), higher concentration and different molar mass of lignin than those reported by the pine Kraft black liquor. This leads to distinct rheological properties of these liquors. By comparing results obtained for the both liquors, the bamboo and the eucalyptus, the former has the lowest sulfur level, the highest silicon and lignin concentration and, consequently, the highest apparent viscosity.     

Sugars and Sugar Acids in Lignosulphonate Products

Abstract

The monosaccharide contents of solid lignosulphonate products from spent sulphite liquors were determined by capillary gas chromatography. The predominant monosaccharide was mannose in two softwood calcium bisulphite cases, and xylose in a hardwood calcium bisulphite case. Monosaccharide analysis before and after ultrafiltration of lignosulphonates showed that about 10–25% of the neutral sugars did not pass through the membranes, and presumably remained associated with the lignosulphonates. Chemical “de-sugaring” treatments removed all but traces of the monosaccharides; when hot aqueous sodium hydroxide was used for this purpose, the main products were 3-deoxy carboxylic acids derived from the hexoses.     

Thermochemical Conversion of Black Liquor in the Liquid Phase

Abstract

Black liquor from kraft pulping of pine wood was pressure heated (about 20 MPa) for 45 minutes at both 300 °c and 350 °c and in both the presence and absence of a reducing atmosphere. Variable amounts of organic-phase (40–64 % of the black liquor organics), water-soluble (14–70 %), and volatile (12–55 %) products were formed. The organic-phase product originates mainly from the lignin fraction of black liquor, whereas, during the treatments, the corresponding hydroxy acid fraction was primarily degraded into lower acid intermediates and volatile components. The effects of temperature and gas atmosphere (carbon monoxide, hydrogen or nitrogen) on the conversion of black liquor are discussed.     

Lowering Kraft Black Liquor Viscosity by Ultrafiltration

Abstract

High viscosity is a major factor limiting the percentage total dissolved solids (%TDS) to which kraft black liquor (KBL), a spent pulping liquor, can be concentrated before it is burned to recover its fuel value and its inorganic chemicals. The effect on black liquor viscosity of removing high molecular weight lignin by ultrafiltration of 16% and 24% TDS liquors was studied.

Viscosities of ultrafiltration permeates were reduced relative to feed black liquors. When a permeate was concentrated to higher %TDS levels, its viscosity decreased yet further relative to feed samples evaporated to similar solids levels. Retentate viscosity was very high relative to both feed and permeate.

Ultrafiltration was carried out at 75[ddot]C using polysulfone membranes in a plate-and-frame or hollow fiber system. Flux rates varied greatly depending upon the specific liquor used. Flux was enhanced by increased temperature and increased linear velocity. The membrane molecular weight cutoff (MWCO) typically used was 50,000; increasing MWCO to 100,000 or 200,000 did not enhance flux.     

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

Abstract

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).     

Solubility of sodium oxalate in kraft black liquors below 100°C

Precipitation of sodium salts from kraft black liquor leads to scale formation in the evaporation plants of kraft pulp mills. Sodium oxalate scaling is most prevalent in mills pulping tropical hardwoods such as eucalyptus and acacia, but it has also been found in the scales in high solids lines after the concentrators in mills pulping softwoods. There is very limited solubility data for sodium oxalate in black liquor, especially below 100°C. This study measures the solubility limit in four different black liquors from 14% to 47% dry solids between 50 and 90°C. The newly generated solubility data in black liquors enhance our understanding of sodium oxalate scale formation in low solids effects of the evaporation plant. An example of an application to a kraft pulp mill with sodium oxalate scaling in the seventh effect is given.     

蒸煮液的物理化学特征及在制浆过程中的行为 Ⅱ.木素对蒸煮液的表面张力的影响

通过加入木素自制黑液及取自一个连续等温蒸煮过程的黑液的数据比较,研究了木素对蒸煮液的表面张力的影响。结果显示,木素起着表面活性剂的作用使蒸煮液的表面张力降低。但木素对实际取得的黑液的表面张力的影响要大于人工自制的,其主要原因是前者还含有木材的其它成分,如半纤维素及脂肪酸。黑液表面张力的主要成分是Lifshitz-van der Waals引力 γLLW,其次是Lewis酸碱反应力γLAB。     

Optimization of beech wood pulping in catalyzed acetic acid media

Fagus sylvatica wood samples were treated in HCl‐catalyzed, acetic acid solutions. The effects of selected operational variables (catalyst concentration, reaction time and liquor to wood ratio) on pulp yield, composition of pulps and composition of pulping liquors were assessed using incomplete, second‐order, centred, factorial designs. Pulp composition was measured by the contents in cellulose, xylan and lignin. The concentrations of glucose, xylose and furfural in pulping liquors were also considered as experimental variables. Under selected conditions, pulps with 5.8% to 7.5% Klason lignin (kappa numbers in the range 25 to 33), 77.2% to 85.3% cellulose and 3.3% to 6.1% xylan were obtained at 45.8% to 50.0% pulp yield. The selected pulps showed good SCAN viscosity (723 to 814 mL/g) and alkaline resistances which were affected by the acetyl group content of samples (6.6 to 7.6 weight percent).     

Enzymatic Hydrolysis of Carboxymethylcellulose and Filter Paper by Immobilized Cellulases on Lignophenols

The cost of cellulase is a major factor limiting the enzymatic hydrolysis of cellulosic biomass. Thus, immobilization of cellulase would be an important advancement. Lignophenol is a lignin-based functional phenolic polymer synthesized from a lignocellulosic material and a phenol derivative at ambient temperature. Cellulase derived from Trichoderma reesei is easily immobilized by softwood and hardwood lignocresol simply by mixing to produce a water-insoluble lignophenol-cellulase complex. Enzymatic hydrolysis performances of cellulases immobilized on lignocresols are approximately 80–90% and 30–50% relative to that of free cellulase in the hydrolysis of carboxymethylcellulose (CMC) and filter paper, respectively. Cellulase was active enough even after adsorption on lignocresols. Limited physical contact between solid substrates and immobilized cellulase due to the presence of lignocresol seems to lead to lower enzymatic activity for solid substrates. Hardwood lignocresol-immobilized cellulase exhibits slightly higher activity than softwood lignocresol-immobilized cellulase when the same amount of cellulase is used per gram lignocresol. Although cellulase activity gradually decreases with recycling, sufficient enzymatic activity, at least for hydrolyzing soluble substrates, remains that it can be reused.