Fractionation and concentration of kraft black liquor lignin with ultrafiltration

Kraft black liquor lignin is a biofuel that is separated from the cellulose during kraft pulping. Improved technology and energy integration in paper mills have led to an energy surplus at many mills. It is therefore of great interest to extract the lignin from the pulp mill and sell it as fuel to replace fossil fuel in other furnaces. The fractionation of kraft black liquor with a total dry matter content of about 15 wt% has been studied using ultrafiltration. The flux for three polymeric membranes with different cut-offs was investigated as well as their retention of lignin and other process specific substances. The retention of lignin for the three membranes with cut-offs of 4,8 and 20 kDa was 80%, 67% and 45%, respectively. The retention of sulphur and sodium was zero for all three membranes. The purity of the final lignin fuel is of importances as the ash content preferably should be as low as possible. The flux and retention during concentration and diafiltration of the black liquor were therefore studied. The dialfiltration operation was conducted in batch and semicontinuous mode. The lignin purity was 36% in the original kraft black liquor and 78% after semi-continuous dialfiltration.     

Processing of black liquors by UF/NF ceramic membranes

This study deals with the treatment of black liquor from wood pulping by means of membranes. UF/NFmembranes with a skin layer of TiO₂ and ZrO₂ have been applied to recover water and to concentrate the residual effluent. Three different membranes with molecular weight cut-off of 1, 5 and 15 kDa have been checked. The membranes have been tested either in single stage operation or in cascade. Total dissolved solids, organic matter, organic to mineral matter ratio and ash have been determined. In addition, chemical oxygen demand (COD) retention was calculated by measuring in the feed solution as well as in the permeate and in the concentrated solution. During the concentration step the steady state was reached after a few minutes running. There was not significant change in the permeate flow until the volume was reduced at half. Only the 15,000 Da membrane showed continuous permeate flow declining. Regardless the membrane used, dry matter, organic matter and COD analyses showed that the retention of organic substances fell in the range of 60-70%, depending on the conditions selected.     

Thermal studies on kraft black liquor

Kraft black liquor and lignin from the same batch were subjected to thermal analysis (DTA and TGA) under an inert atmosphere and also in an oxidising atmosphere to simulate conditions which might be encountered in the recovery furnace. Gasification studies were carried out by rapidly heating the sample under helium. Results showed that the thermal decomposition of black liquor can be divided into four characteristic steps: drying up to 200°C, pyrolysis between 200 and 550°C, inorganic sodium salt formation between 550 and 800°C and salt fusion between 800 and 1000°C. Gases evolved during gasification of black liquor are rich in flammable compounds while those from the lignin sample are rich in CO₂.     

Waste kraft black liquors as raw material for the production of nitrogeneous humic fertilizers by an oxidation-ammoniation process

The total acidity of humic materials obtained by oxidation of kraft black liquors was previously found to have a very important effect on the results of their ammoniation process (which yields nitrogenous humic fertilizers). This paper deals with a further study of the ammoniation process of two humic materials (with 20 and 60 ml NaOH 0.1 N/g of sample of total acidity) by using liquid NH₄OH. The influence of four independent variables (NH₄OH concentration, reaction temperature, NH₄OH/humic material ratio and reaction time) on the reaction yield, total and ammoniacal nitrogen content of the fertilizers was studied. A 2⁴ factorial design was followed to carry out the experiments. Four models equations, which establish a quantitative relation between the independent and the dependent variables, for each kind of humic material, were found as a result of this work.     

Ultrafiltration of industrial waste liquors from the manufacture of soy protein concentrates

Protein‐containing waste liquors from the manufacture of soy protein concentrates were processed by ultrafiltration to recover soluble protein using three different membranes (with molecular weight cut‐offs of 10, 30 and 50 kDa). Operating at 20 °C under reversible conditions, the experimental data of the normalized permeate flux (NPF) obtained at various transmembrane pressures were well described by a model reported in the literature. For each membrane and transmembrane pressure, the values of the parameters involved in the model were calculated. Operating at selected transmembrane pressures, protein rejections of 0.705, 0.747 and 0.637 were determined for the 10, 30 and 50 kDa membranes, respectively. Operation with the 10 kDa membrane at temperatures in the range 30–50 °C and operation with the 30 or 50 kDa membranes at 40 or 50 °C resulted in hysteresis. Copyright © 2006 Society of Chemical Industry     

Treatability of kraft spent liquor by microfiltration and andultrafiltration

The application of membrane technology on black liquor from pulp mills has been greatly limited due to the high temperature, high pH value and high suspended solid (SS) concentration of the black liquor, although many researchers have made a great effort. Attention has been paid to the inorganic membrane in this paper because it has the advantages of resistance to acid and alkali, a long life span, etc. The aim of this work was to study the feasibility of black liquor treatment by various organic OF and inorganic MF membranes. Based on the batch experiments with 200 kPa transmembrane and a temperature of 30C, the results showed that approximately 80% lignin retention was achieved with MF membranes and 90% lignin retention with OF membranes. The COD reduction in the permeation mainly resulted from lignin rejection. Both MF and OF membranes could reject silica and their efficiencies were all over 80%. The observed total filtration resistance was evaluated for the intrinsic resistance (R_pp), adsorption (R_a), pore plugging (R_pp), and concentration polarization (R_cp), using a series resistance model based on the pure water flux. The concentration polarization dominated the process for the inorganic membranes. However, the distributions of the filtration resistance for the organic membrane depended on the materials characteristics and the pore sizes. By a 40-day continuous experiment with a crossflow velocity of 2.3 m/s and transmembrane pressure of 200 kPa, the flux ofthe 0.2 μ inorganic MF membrane was 2001/m²h flux at 32°C after operation for 374 h, and 4001/m²h at 63°C for 625 h. During the operation process, no cleaning was carried out and the smooth operation period was more than 40 days. The experimental results highlighted the treatment of black liquor by membrane separation.     

Process performance in lignin separation from softwood black liquor by membrane filtration

Black liquor is a side-stream in the production of kraft pulp. The extraction of lignin and hemicelluloses from black liquor would reduce the load on the recovery boiler and give valuable by-products. Lignin was separated from black liquor by membrane filtration, using one ceramic and three polymeric nanofiltration membranes, with molecular weight cut-offs in the range of 200 Da to 1 kDa. Ultrafiltration was tested as a form of pretreatment prior to nanofiltration to separate hemicelluloses from lignin. The use of ultrafiltration prior to nanofiltration increased the flux drastically in the nanofiltration step with three of the membranes. The ceramic membrane exhibited a higher flux and lower lignin retention than the polymeric membranes. The two membranes with a molecular weight cut-off of 1 kDa were found to have the best performance in parametric studies, and were therefore used in concentration studies. The results were used for a preliminary economic evaluation of the process. These calculations showed that the most cost-effective alternative for the extraction of lignin was with the polymeric 1 kDa membrane without pretreatment, and that the production cost for a lignin solution with a concentration of 230 g L⁻¹ would be 46 € per ton of lignin.     

高压法三聚氰胺装置超滤系统的应用

介绍了高压法三聚氰胺装置中超滤系统的工艺特点,对其在应用中所存在的有关问题进行了分析,并介绍了所实行的相应的处理措施,这些措施有利于超滤系统的稳定运行.     

超滤法回收造纸黑液中木质素的研究

探讨采用超滤技术回收黑液中木质素过程的规律 ,给出了透过通量与超滤时间、超滤压力差、黑液溶质质量浓度的关系 ,考察了用表面活性剂改善膜表面抗污染的效果、黑液溶质质量浓度和操作压力差对木质素截留率的影响 ,并讨论了超滤过程的内在机理。实验结果表明超滤方法能有效回收黑液中的木质素     

Hydropyrolysis of kraft hardwood and softwood black liquor

The hydropyrolysis of hardwood and softwood derived black liquor was studied to develop material balance data and to investigate the potential yield of phenolic oils that might be obtained as chemical by-products of a kraft pulp mill. Hydropyrolysis reactions on softwood liquors were found to be more efficient in char formation than those on hardwood liquors. The yield of extractible phenolic oils was low, around 20–30 percent of black liquor organics, but the yields of simple phenols determined by gas chromatography were found to be even lower at 1–5 percent on black liquor organics.     

Ultrafiltration purification of waters contaminated with bifunctional reactive dyes

The problem with the removal of textile dyes from waste waters is an important issue both from an ecological and technological point of view. Besides well known conventional methods, membrane techniques of separation are used more and more nowadays. The successful application of such a process depends on membrane type, process conditions and the behavior of the membrane under these conditions. Process effectivity can be improved by using both conventional and membrane processes.     

离子交换除盐水处理系统中废液的利用

本文研究了利用离子交换除盐水处理系统再生废酸碱液．作氯－钠离子交换法的再生剂使用的原理、方法及其降碱软化工艺特性。     

预水解强度对相思木硫酸盐法制浆黑液性质的影响

经水热预水解技术处理木质纤维素,木片的主要成分发生变化,对后续的化学制浆性能及制浆黑液性质带来影响。本实验采用不同预水解强度（P因子）处理相思木片,并对其硫酸盐制浆行为和黑液性质进行分析。研究结果表明,随着P因子的增大,粗浆得率和细浆得率逐渐降低;浆料的卡伯值逐渐升高。当P因子＜200时,水解后木片的黑液固形物含量由空白组的138.48 g/L升高到162.86 g/L;木素含量由58.57 g/L升高到72.68 g/L;残碱量由4.37 g/L迅速降低到2.07 g/L。当200＜P因子＜600时,黑液固形物含量由162.86 g/L降低到142.71 g/L;黑液中木素含量由72.41 g/L降低到59.16 g/L;残碱量由2.07 g/L降低到1.26 g/L。当P因子＞600时,黑液中固形物含量由142.71 g/L升高到156.95 g/L;木素含量由59.16 g/L升高到62.16 g/L;残碱量由1.26 g/L升高到1.37 g/L。不同条件下,黑液中无机物含量变化不大;黑液固形物的热值由对照组的13.71 MJ/kg提高到14.63~15.09 MJ/kg。     

Kraft black liquor recovery in a fluidized bed: Part I — A review

The Tomlinson recovery boiler has been the mainstay of the kraft pulping industry for over fifty years. It is clear, however, that the main drawbacks to this process are the large capital costs of new plant and the smelt-water explosion hazard. This paper examines some of the fundamental scientific information which supports the concept of fluid bed gasification as an alternative to the Tomlinson boiler. It is shown that a knowledge of thermodynamics is useful but insufficient to completely understand the behaviour of the inorganic sulfur species during pyrolysis and gasification of kraft black liquor. Recent key experimental investigations at McGill have demonstrated that solid state reduction of sodium sulfate to sodium sulfide is feasible.     

Fabrication of B4C ultrafiltration membranes on SiC supports

The fabrication of B₄C ultrafiltration membranes is described. Firstly, a semi-dilute B₄C slurry was environmentally-friendly prepared by aqueous colloidal processing, optimizing its dispersion by sonication, and used to deposit B₄C membranes onto SiC macro-porous supports by dip-coating. Secondly, the resulting green membranes were characterised microstructurally by scanning electron microscopy (SEM), and pressureless sintered within the intermediate sintering regime. Thirdly, the sintered membranes were calcined in air to clean them from possible free carbon in the smallest pores, with the optimal calcination conditions having been identified by thermogravimetry coupled with mass spectrometry. Next, the calcined, sintered membranes were characterised microstructurally by SEM, tested mechanically against scratching, and characterised texturally by capillary flow porometry, thus identifying the optimal among them. Lastly, as a complement to the fabrication study, the filtration permeability of the optimal membrane was evaluated using deionized water. This work thus paves the way towards the fabrication of ceramic membranes based on B₄C, lighter and potentially more durable than others, for filtration applications.     

PP编织布与牛皮纸复合工艺易出现缺陷及改进措施

总结了PP编织布与牛皮纸复合工艺中易出现问题 ,并对其原因进行了简要分析 ,提出了切实可行的防止和改进措施     

Flux decline during ultrafiltration of kraft black liquor using different flow modules: a comparative study

Ultrafiltration of black liquor was studied in three different modules, namely, radial cross flow, rectangular cross flow and stirred cell over a wide range of operating conditions. Effects of different cut-off membranes on the permeate flux and observed rejection were also studied in the stirred cell module. Effects of operating conditions, e.g. pressure difference, Reynolds number and feed concentration on the permeate flux and observed rejection were also investigated. Such comparative study may be useful to select a suitable module, membrane and a set of optimum operating conditions to achieve a desired quantity and quality of permeate flux. A comparative analysis of flux decline for different modules is also presented using a simple resistance-in-series model.     

Application of ion-exclusion chromatography to alkaline pulping liquors; separation of hydroxy carboxylic acids from inorganic solids

Hydroxy carboxylic acids were separated from inorganic solids on a pilot-plant scale by using columns containing a strongly acidic polystyrene cation exchange resin with bed volumes of about 1000 and 200 dm³. The liquor samples were obtained from soda–anthraquinone pulping of pine wood and they were first acidified with sulfuric acid to precipitate most of the lignin and to liberate the hydroxy acids. Under appropriate conditions, using warm water (65°C) as eluent, the liquor sample could be resolved into two distinct fractions consisting mainly of hydroxy acids and sodium sulfate, respectively. This separation method seems promising as a complementary technique in connection with the recovery of aliphatic carboxylic acids from kraft black liquors, although further studies are required to optimize the conditions.     

膜分离技术在造纸废液中应用研究进展

综述了超滤、电渗析、纳滤等膜分离技术在造纸行业中的应用现状     

Ultrafiltration behaviors of pectin-containing solution extracted from citrus peel on a ZrO<Subscript>2</Subscript> ceramic membrane pilot unit

Ultrafiltration experiments on a solution of pectin, hesperidin, and other mixtures extracted from citrus peels have been performed on a 500 l/min pilot scale crossflow ceramic membrane unit. A 30,000 molecular weight cut-off (MWCO) zirconia (ZrO₂) ceramic membrane with a total effective flow area of 0.5 m² was used in the process. The permeate flux for pure water and hesperidin showed linear relationship with transmembrane pressure (ΔP), but the flux for pectin solutions showed a curvilinear relationship with ΔP and represented a rapid increase with increasing ΔP before leveling-off. Similar behavior was observed by adding different amounts of hesperidin to these pectin solutions, but with much lower permeate flows. The formation of gel layers on the membrane surface is mainly responsible for the lower permeate fluxes. In addition, the permeate flux decrease faster at higher ΔP, since higher ΔP brought bigger flux at lower pectin concentration. Compared with the more than 90% retention rate of macromolecular pectin, pigment and other component have less than 20% retention rate. So, the decolorization, the separation and purification of pectin preparations could be achieved simultaneously through ultrafiltration with a ceramic membrane.