Kraft Black Liquor Research Articles

Analysis of aliphatic and phenolic compounds present in industrial black liquors using HPLC-DAD and IC-MS/MS methods.

Carboxylic acids and aromatic compounds are essential building blocks and starting materials for the production of a wide range of fine chemicals and materials. Their recovery from kraft black liquor, an industrial effluent from pulp and paper mills, is a promising way to produce alternative bio-based chemicals. Reliable methods are needed to identify and quantify the molecules of interest in complex mixtures such as black liquors. First, an HPLC-DAD-based method was developed for the determination of aliphatic acids and phenolic compounds. It allowed the separation of 31 aliphatic and phenolic compounds. The method was applied to the identification of aliphatic and phenolic compounds in industrial black liquors. Then, an IC-MS/MS method was developed to confirm the identification and quantification of organic compounds in black liquor samples. 22 compounds were detected and identified by MS/MS detection. According to both methods, the major aliphatic acids in softwood kraft black liquor are formic acid (9.8g/L), acetic acid (7.1g/L), lactic acid (5.2g/L), glycolic acid (4.7g/L), 2-hydroxybutyric acid (2.3g/L), and oxalic acid (1.3g/L). Phenolic compounds were detected at very low levels (total concentration 1.4g/L). This study demonstrates the value of a multi-technique strategy for the identification and quantification of organic compounds in complex matrices such as black liquor.

Urea coated with cellulose acetate-lignin composite presents lower loss by ammonia volatilization

Urea is one of the main nitrogen sources used in plant nutrition. During its management, due to chemical, physical, and biological processes, part of N is volatilized in ammonia form, and negatively impacts the environment. When protected with renewable and biodegradable materials, such as lignin (Lig) and cellulose acetate (Ac), urea can reduce ammonia losses. Therefore, this work aimed to develop Lig and Ac composites to cover urea in order to reduce N-urea loss. The lignin was obtained by the acid precipitation of commercial kraft black liquor, corresponding to a 3-6 pH range. Film-forming solutions (Fs) were produced by combining Lig (0.3, 0.6, 0.9, and 1.2 %, w/w, based on Ac), and Ac (2 %, w/w, based on urea). In addition, two reference treatments were included: urea without coating (U) and urea coated only with Ac. In order to obtain the the coatings, the granules were placed in a dish-type granulator, equipped with shovels, sprayed with the Fs, kept in rotation (125 rpm), and dried under hot air flow (~100 ºC). Ammonia volatilization was evaluated in a static capture system (24 h), with 2% boric acid, followed by titration with sulfuric acid (0.005 mol/L). The results revealed that the granules with Ac coating, without and with Lig, reduced volatilization. For the coating without Lig, there was a U reduction of 33.2%. For the coating with Lig, the combination of Ac, 2%, and Lig, 0.9%, was the most effective, compared to urea without coating. The mean reduction in volatilization for this formulation was 58.4%. According to the visual and SEM image evaluations, the coating system developed was satisfactory and presented a thin and uniform layer. Satisfactory adhesion of the films was also observed, both with and without Lig, in the granule surfaces.

Tuning the antioxidant and antibacterial properties of lignin by physicochemical modification during sequential acid precipitation from Kraft black liquor

Turning lignin from black liquor waste into value-added bioactive agents is one of the possible routes for improving the sustainability and profitability of lignocellulosic industry. However, due to chemical and structural variability of lignin, it is necessary to isolate specific lignin fractions from black liquor with the purpose to achieve samples with unique chemical and structural characteristics and therefore, specific biological activities. In this study, poplar lignin fractions isolated from Kraft black liquor by sequential acid precipitation at pH´s 7.5, 5 and 2.5 (denoted as P-7.5, P-5 and P-2.5) were characterized according to their physicochemical, antioxidant and antibacterial properties. In general, lignin fractions displayed a wide elimination of lateral chains (aryl-β ether and C–C) and, therefore a high phenolic content and low molecular weight, as the pH sequential precipitation was decreased from 7.5 to 2.5. Moreover, thermal analysis revealed that the P-7.5 lignin fraction showed higher thermal stability than P-2.5 and P-5. In terms of antioxidant activity, the P-7.5 lignin fraction, with a higher S/G ratio and a less oxidized structure compared to P-5 and P-2.5, exhibited higher antioxidant activity. In addition, lower antibacterial effect was observed for all lignin fractions against Escherichia coli compared to that obtained against Staphylococcus aureus. Among them, the P-2.5 and P-5 fractions, with higher phenolic content and lower molecular weight values than P-7.5, showed a greater antibacterial effect against S. aureus.

Bioconversion of carboxylic acids derived from Kraft black liquor into lipids by Yarrowia lipolytica

Annually, around 1.3 billion metric tonnes of Kraft black liquor (KBL) are generated, commonly managed through evaporation before combustion, which contributes to environmental concerns. Therefore, implementing a comprehensive strategy for producing high-value-added compounds is essential for enhancing sustainability and resource efficiency in industrial processes. This study evaluated lignin recovery and single-cell oil (SCO) generation by the oleaginous yeast Yarrowia lipolytica employing KBL as a renewable feedstock, analysing the impact of C/N ratio, nitrogen source, and flask cultivation with cell recycling. Initially, KBL underwent acid precipitation to partially purify the stream and recover a valuable product such as lignin. The resultant liquid fraction of KBL after lignin recovery (LRKBL) exhibited a 21% viscosity reduction and a 65% decrease in chemical oxygen demand. The stream rich in carboxylic acids (5.9 ± 0.3 g/L acetic acid and 1.8 ± 0.2 g/L propionic acid) was used as the Y. lipolytica cultivation substrate. In the fermentation stage, the optimal C/N ratio for cell growth and biolipid accumulation was found to be 20, with a biomass yield (YX/S) of 0.56 ± 0.03 g/g and a lipid yield (YL/S) of 0.21 ± 0.01 g/g. The synergistic effect of organic and inorganic nitrogen sources significantly enhanced lipid production, achieving a concentration of 1.52 ± 0.06 g/L. Implementing a sequencing batch culture approach markedly increased lipid content from 38 ± 1% in the initial culture cycle to 52 ± 1% after four cycles, resulting in a twofold increase in lipid concentration. The SCO lipid profile under optimal conditions contained mainly oleic, linoleic, palmitic and stearic acids, making it suitable to produce biodiesel. Therefore, this integrated strategy offers a potential solution for waste management and biofuel production.

Pilot-scale nanofiltration and techno-economic evaluation of lignin recovery from kraft black liquor

This pilot-scale study investigates the possibility of using nanofiltration after ultrafiltration to improve lignin recovery from kraft black liquor in a pulp mill. The nanofiltration step can increase overall lignin recovery and provide a clean permeate that could be used in the smelt dissolving tank to produce green liquor. Nanofiltration of kraft black liquor ultrafiltration permeate was performed under two operating conditions: (A) 50 °C at 25 bar, and (B) 70 °C at 15 bar, which led to a lignin retention of 82% and 75%, respectively. Experimental data from condition A were used in a techno-economic analysis where four scenarios were evaluated: (1) a reference scenario, without lignin separation; (2) a scenario in which the ultrafiltration permeate was returned to the evaporators; (3) a scenario including ultrafiltration and nanofiltration, where the nanofiltration permeate was sent to the smelt dissolving tank; and (4) a scenario including ultrafiltration and nanofiltration, where the nanofiltration retentate was sent to the evaporators and the nanofiltration permeate to the smelt dissolving tank. The reduced energy consumption of the evaporators in scenario 4 resulted in an increase in sold electrical power of 19.4 GWh/y, giving a pay-back time on the investment in the nanofiltration plant of 2.2 years.

Effects of partial lignin extraction on rheological characteristics and combustion performance of high solids bamboo kraft black liquor

Abstract This study investigates the impact of lignin extraction on the rheological and combustion properties of high-solids bamboo kraft black liquor (BKBL), focusing on viscosity reduction and silicon interference mitigation. Lignin was extracted from BKBL using CO2 acid precipitation. The effects on viscosity, silicon content, calorific value, and Volumetric Isothermal Expansivity (VIE) were systematically analyzed. Extracting 25 % of lignin reduced the apparent viscosity of BKBL and achieved a 33 % desilication rate. However, this extraction also led to a proportional decrease in calorific value and VIE, with a 15 % extraction resulting in approximately 11 % and 13 % reductions, respectively. An extraction rate of 15–25 % is recommended to balance viscosity reduction and silicon removal with minimal impact on boiler combustion efficiency. This study provides practical insights into optimizing lignin extraction from BKBL, offering significant operational, economic, and environmental benefits for the bamboo kraft pulping industry.

Intermetallic TiFe particles generation within porous monolithic carbon materials arising from paper mill waste and their cooperative hydrogen storage properties

A new materials composed of TiFe particles stabilized onto a carbon support is described. The carbon support is derived from a waste from the paper industry called Kraft Black liquor. The particles are generated through an impregnation/reduction process of a mixture of titanium ethoxide and iron nitrate followed by a thermal treatment. The generated particles have been investigated through XPS, XRD and SEM analysis as well as tested for hydrogen storage. The hydrogen storage at 25 °C leads to a capacity of up to 0.5 wt% while at 150 °C, free of the carbon absorption, leads to a capacity of 0.2 wt% without any prior activation process.

From waste to resource: Transforming Kraft black liquor into sustainable porous carbon fillers for radome applications

The study addresses environmental and commercial challenges posed by weak black liquor (WBL) generated through the Kraft process in the paper industry. WBL, a toxic waste, annually reaches a staggering 1.3 billion tonnes globally. Currently, it is either incinerated for energy production or subjected to costly and complex chemical treatments to extract valuable compounds. Despite efforts to develop a scalable value-added material, the existing methods are inefficient in fully reusing WBL. Here, we report a simple chemical synthesis process that reuses 100 % of WBL without generating any waste materials; even salts recovered during the process might be reintegrated into the industry as chemical byproducts. Furthermore, given the simplicity and efficiency of the proposed synthesis methodology to transform WBL into a novel and sustainable porous carbon material, the carbon Kraft (CK). The process can also be scaled by using the right synthesis proportions and within a circular economy. CK exhibited desirable characteristics with a renewable content of 65 wt%, including a turbostratic graphitic-like structure (48.8 % graphitized), carbon content of 85 wt%, large specific surface area of 234.0 m2∙g−1, nanoporosity of 0.13 cm3∙g−1, and density of 1.92 g∙(cm3)-1. Moreover, CK showed electrical and thermal insulating characteristics, essential for use as fillers for elastomeric composite in electromagnetic transparent radome structures used to protect antennas and radars of unmanned aerial vehicles (UAV) from harsh environmental effects. Radomes were designed through the electromagnetic impedance match theory of half-wavelength calculations over specific frequencies of 1.3, 10, 15, 20, and 30 GHz. Results showed excellent transmission loss between −0.41 and −1.48 dB, representing 90.8 % and 70.5 % of transmittance, respectively.

Macroporous lignin adsorbents: A bio-sourced tool kit to defuse the Cr(VI) threat in wastewater

Amino-functionalised (triethylenetetramine) macroporous lignin monoliths were produced by curing an emulsion template containing untreated kraft black liquor with oxirane-crosslinkers. These lignin-based adsorbents were tested for the removal of Cr(VI) from water and synthetic waste water. A one-pot rout for their production is presented and their chemical and physical nature was investigated. Produced monoliths were tested in static and continuous adsorption experiments and chromium removal from water and synthetic wastewater was quantified via UV–vis spectroscopy. The nitrogen content of functionalised lignin monoliths reached up to 5.1 wt%, leading to adsorption capacities of up to 897 mg/g at pH = 2, as compared to non-functionalised lignin monoliths with a maximum adsorption capacity of 117 mg/g. The adsorption capacity of lignin monoliths produced is amongst the highest of bio-based materials presented in the literature.

Bi-functional and bi-metallic catalytic solvo-hydrothermal liquefaction for upgrading hydrocarbon of phenol-rich oil from kraft black liquor lignin

This study primarily aimed to enhance the hydrocarbon of a solvo-hydrothermal liquefaction (S-HTL) process initially extracting phenolic-rich oil. To catalyze the current process, HZSM-5 zeolite with its modifications were applied to S-HTL. Ni2P was first introduced to zeolite forming bifunctional catalyst and further coating it with either Co, Mo, or Zn to create bimetallic catalyst. The analysis showed that the zeolite structure did not change after the modifications. The acid sites on the catalyst were found to be principally responsible for the hydrodeoxygenation upgrading the oil yield, biomass conversion, and hydrocarbon generation. Catalytic HTL also produced compounds not detected in non-catalytic S-HTL which appeared to be largely promoted by the catalyst with Ni2P. Additionally, oil output, biomass conversion, and hydrocarbon yield were all substantially increased by catalyst (supplemented by Mo) about 20 %, 5 %, and 15 %, respectively. Moreover, Mo-supplemented catalyst with pre-treatment could be used for 5 more cycles with insignificant oil conversion reduction. Overall, the study synthesized bi-functional and bi-metallic catalysts and applied it to S-HTL improving the yield of generated oil and increasing hydrocarbon production.

Catalytic Upgrading of a Mixed Hydroxy Acid Feedstock Derived from Kraft Black Liquor.

Lignocellulosic feedstocks are widely studied for sustainable liquid fuel and chemical production. The pulp and paper industry generates large amounts of kraft black liquor (BL) from which a high volume of hydroxy acids (HAs) can be separated for further catalytic processing. Here, we explore the catalytic upgrading of HAs, including the conversion of (1) a model HA, gluconic acid; (2) a model mixture of HAs, and (3) a real mixture of HAs derived from kraft BL on M/Nb2O5 (M = Pd, Pt, Rh, and Ru). The hydrodeoxygenation of model gluconic acid reveals that "volatile" carboxylic acids (mainly C2 and C3), levulinic acid, and cyclic esters are significant products over all the catalysts, with Pd/Nb2O5 showing superior activity and selectivity toward valuable intermediates. The model mixture of HAs shows a wide range of reactivity over the supported metal catalyst, with the product selectivity strongly correlating to reaction temperature. Utilizing a 0.25% Pd/Nb2O5 catalyst, a real mixture of HAs derived from kraft BL is successfully dehydroxylated to produce a mixture rich in C3-C8 carboxylic acids that may be amenable for further upgrading, e.g., catalytically to ketones with high carbon chain lengths. Despite the feedstock complexity, we selectively cleaved the C-OH bonds of HAs, while successfully preserving most of the -COOH groups and minimizing C-C and C=O bond scission reactions under the operating conditions tested. The BL-derived HA stream is thus proposed to be a suitable platform for producing mixed carboxylic acid products from an overoxygenated byproduct feed.

Response surface methodology to optimize membrane cleaning in nanofiltration of kraft black liquor

Better understanding of membrane fouling and cleaning can help implementation of membrane filtration processes in the pulp and paper industry. The aim of this study was to optimize membrane cleaning in the nanofiltration of kraft black liquor ultrafiltered permeate for the recovery of lignin. This work wants to assess whether the cleaning process removes the main foulants; as well as the economic viability of the optimized cleaning compared to a standard cleaning in a nanofiltration membrane plant on industrial scale.The optimization of membrane cleaning was investigated using the response surface methodology. The factors studied were time, temperature, and cleaning agent (Ultrasil 110) concentration, and flux recovery was used to evaluate the success of cleaning. Experiments were performed on laboratory scale where flat-sheet polymeric membranes were fouled with kraft black liquor ultrafiltered permeate and cleaned using various combinations of the three factors.The model developed predicted a flux recovery of 88 % when cleaning was performed for 60 min with a solution of 0.8 wt% Ultrasil 110 at 40 °C. The flux recovery measured experimentally with these cleaning parameters was 80 %. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy analysis confirmed that the optimized cleaning removed the main foulants from the membrane surface. Moreover, increasing the cleaning agent concentration or the cleaning temperature did not always lead to a higher flux recovery. The techno-economic evaluation revealed that 16 % of the cleaning costs could be saved by optimizing the cleaning process.

Optimization of lignin precipitation from black liquor using organic acids and its valorization by preparing lignin nanoparticles

This work focuses on the precipitation of lignin from kraft black liquor (BL) along with its valorization into lignin nanoparticles (LNP). Two organic acids namely, acetic acid, and lactic acid were used for the precipitation of lignin as an alternative to sulfuric acid. An optimization study was carried out to determine the effect of three key variables, namely acid type, temperature, and pH, on the isolation yield and purity of lignin. The study showed that all factors primarily influenced the lignin yield, while the purity of precipitated lignin varied only around 1 % between minimum to maximum purity. Further, the acid precipitation method was selected for the preparation of LNP. The study aimed to observe the effect of pH, lignin concentration, and surfactant concentration over the properties of the prepared nanoparticles. The results showed that a smaller nanoparticle size and maximization of phenolic content was achieved with a lignin concentration of 35 mg/mL, a surfactant concentration of 10 % (w/w lignin), and a pH of 5. Additionally, the antibacterial activity of LNPs against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa bacteria was evaluated. The results showed only minor activity against Staphylococcus aureus. Overall, the study demonstrates the potential method for precipitation and valorization of lignin through the production of LNP with desirable properties.

Nanoarchitectonics of lignin-sepiolite bionanocomposite foams for application in environmental remediation

Innovative bionanocomposite foams based on precipitated Kraft lignin (Lig) and Kraft black liquor (BL) loaded with sepiolite (Sep) were prepared. BL/Sep bionanocomposites were synthesized by emulsion templating and Lig/Sep bionanocomposites were prepared by freeze-drying, resulting in stable and rigid foams. BL/Sep bionanocomposites displayed a closed cell structure, a specific area between 19 and 35 m2/g and macropores of varying sizes. The porosity in this technique is achieved by the mechanical agitation of the emulsion. On the other hand, freeze-dried Lig/Sep bionanocomposites showed open cell morphology with surface areas ranging from 1 to 4 m2/g and uniform macropores due to the ice-templating process. The presence of sepiolite in both types of bionanocomposite foams improved their stiffness, with Young's moduli ranging from 0.21 to 9.6 MPa. The capacity of the foams to adsorb metals, drugs and dyes was evaluated and it was found that the synthesized bionanocomposite foams exhibiting similar adsorption capacities as that reported for lignin. Sepiolite significantly improved the adsorption of Cu(II), Cd(II), acetaminophen (ACT), and methylene blue (MB) in BL/Sep bionanocomposites. Meanwhile, the Lig/Sep bionanocomposites demonstrated superior adsorption capacities for the Cr(VI) anion and aromatic ring compounds, including ACT and MB. In this respect, these lignin-sepiolite foams can be considered as promising materials for the removal of pollutants in aqueous solution.

Repurposing Kraft black Liquor as Reductant for Enhanced Lithium-Ion Battery Leaching.

The economic advantages of H2SO4 make it the acid of choice for the hydrometallurgical treatment of waste lithium-ion batteries (LIBs). However, to facilitate the full dissolution of the higher valency metal oxides present in the cathode black mass, a suitable reducing agent is required. Herein, the application of industrial black liquor (BL) obtained from the Kraft pulping for papermaking is investigated as a renewable reducing agent for the enhanced leaching of transition metals from LIB powder with H2SO4. The addition of acidified BL to H2SO4 significantly improved the leaching efficiency for a range of LIB cathode chemistries, with the strongest effect observed for manganese-rich active material. Focusing on NMC111 (LiMnxCoyNizO2) material, a linear correlation between the BL concentration and the leaching yield of Mn was obtained, with the best overall leaching efficiencies being achieved for 2.0 mol L-1 H2SO4 and 50 vol % of BL at 353 K. A quasi-total degradation of oxygenated and aromatic groups from the BL during NMC111 dissolution was observed after leaching, suggesting that these chemical groups are essential for LIB reduction. Finally, the leached transition metals could be easily recovered by pH adjustment and oxalic acid addition, closing the resource loop and fostering resource efficiency.

Odour reduction of kraft lignin by wet oxidation

This study assesses wet oxidation of partially concentrated Kraft black liquor (40% dry matter) as a method for odour reduction of the lignin obtained from it by acid precipitation. To this end, and for the first time ever, the effects of wet oxidation temperature (120–150 ºC) and pressure (10–50 bar) on the odour profile of both the black liquor and the acid precipitated lignin were analysed. 2-methoxyphenol, dimethyl disulphide and dimethyl trisulphide were the main responsible compounds of the black liquor odour and, in the case of the precipitated lignin, aldehydes and organic acids also contributed. The most odourless lignin was the one precipitated from Kraft black liquor oxidised at the most severe conditions tested (150 °C and 50 bar for 2 h). However, these also caused a reduction in the lignin yield, as well as significant compositional and appearance changes, thus limiting its use in certain fields.

Lignin extraction from kraft black liquor and its conversion to phenol-rich oil by hydrothermal liquefaction process

This study exploited lignin from black liquor as feedstock in the hydrothermal liquefaction process. The operation conditions such as temperature, operation time, and solvent ratio (by adding ethanol) were explored, with temperature identified as the most significant parameter. The optimum condition generating the highest oil yield (58.9 %) was found at an operating temperature, time, and solvent ratio of 275 °C, 30 min, and 1:1 water-to-ethanol ratio, respectively. The extracted oil was further characterized, revealing phenolic-rich oil containing about 83.4 % phenol, which was dominated by guaiacol. The lignin-to-oil conversion was initiated by thermochemical degradation comprising a series of multiple chemical reactions. The overall process reduced sulfur, nitrogen, and oxygen content linked to reaction instability, favoring solid char yield. The resulting higher heating value of the extracted phenol-rich oil was about 27.8 kJ/g, almost twice that of the raw black liquor only having 14.1 kJ/g.

Carbon black structural effect within kraft black liquor-based poly(HIPE): enhanced hydrogen storage and electro-capacitive properties

A biopolymer derived from Kraft Black Liquor was successfully incorporated with three types of carbon black, each varying in their characteristics. The resulting carbon materials demonstrate promising performance in energy storage applications.

Flexing with lignin: lignin-based elastomers synthesised from untreated kraft black liquor.

The synthesis and characterisation of a lignin-based elastomer system using lignin-epoxy-resins is presented. Untreated kraft black liquor was used to synthesise glycidyl lignin or black liquor-based epoxy resin (BLER), following a published procedure. A flexible, elastomeric thermoset was produced by cross-linking BLER with succinic anhydride (SA). The produced material was characterised in respect to its chemical, thermal, mechanical and swelling characteristics. In addition, vertical burning tests were performed. The obtained lignin-based elastomeric thermoset had a tensile strength of 1.0 ± 0.20 MPa and elastic moduli of 1.6 ± 1.4 and 0.44 ± 0.35 MPa at 5% and 50% elongation, respectively. A maximum elongation of 151 ± 49% was found.

Ether Bond Formation in Waste Biomass–Derived, Value-Added Technical Hardwood Kraft Lignin Using Glycolic Acid

Ether bond formation in technical hardwood kraft lignin (THKL) by crosslinking using glycolic acid was investigated for bio-adhesive applications. Industrial hardwood kraft black liquor was used to extract the THKL utilized by acidification. Chemical and thermal properties of the THKL with and without crosslinking were analyzed by Fourier transform infrared (FTIR) spectroscopy, solid-state 13C cross-polarization/magic angle spinning nuclear magnetic resonance (13C CP/MAS NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). FTIR results revealed a new peak corresponding to the ether bond and hemiacetal formation due to crosslinking at 1075 cm-1 and 1324 cm-1. 13C CP/MAS NMR spectra revealed the presence of a higher number of ether bonds due to the reduced aromatic and aliphatic hydroxyl groups in THKL and new bonds formed at 62-64 ppm and 168-191 ppm due to crosslinking. XPS results revealed that new bonds were formed between glycolic acid and THKL, leading to increased atomic oxygen percentage and carbon–oxygen bonds in crosslinked THKL detected by peak intensity changes at 287.7 and 288.8 related to O–C–O and O–C=O. Also, the oxygen content increased from 14.88% to 31.76% due to bond formation. GPC confirmed a higher molecular weight and broader molecular-weight distribution of THKL. DSC and TGA curves of crosslinked THKL revealed exothermic behavior, high thermal stability, and low thermal degradation rate. Owing to a significant amount of kraft black liquor being generated by wood pulp industries and attractive chemical properties of THKL, THKL demonstrates promise as a raw material to produce green, sustainable bio-adhesives via the crosslinking of its different hydroxyl groups using glycolic acid.