Pulping Black Liquor Research Articles

Complexation modelling and oxidation mechanism of organic pollutants in cotton pulp black liquor during iron salt precipitation and electrochemical treatment

Removal behavior of organic pollutants such as lignin in cotton pulp black liquor (CPBL) was investigated in precipitation followed by electrochemical oxidation (EO) using FeCl3, Fe2(SO4)3, FeCl2 and FeSO4 as precipitants, electrolyte and catalysts. Based on comparison of precipitation efficacy of iron salts, spectroscopic techniques, thermodynamic equilibrium calculations and molecular dynamics (MD) simulations were used to provide insight into the interaction between iron cations and lignin. The results showed that FeCl3 achieved the highest removal of chemical oxygen demand (COD, 76.05%), UV254 (69.21%) and lignin (78.28%). Iron cationic complexation with lignin was identified as the key mechanism in precipitation. Fe3+ was more active in binding to organic ligands mainly due to charge effect compared to Fe2+. The strong Fe−sulphate coordination affected the complexation with lignin. MD simulations showed the formation of inner sphere complexes of iron cations with deprotonated carboxyl and hydroxyl groups via bidentate and monodentate coordination. The removal efficiency of electrochemical oxidation (EO) as a post−treatment of the precipitation was dependent on iron salts. Removals of COD, UV254 and color can achieve 98.88%, 98.9% and 99.97% by FeCl3 precipitation and EO processes. The effluent reached the primary discharge standard specified in Integrated Wastewater Discharge Standard of China (GB8978−1996). FeCl3 demonstrated significant advantages in the removal of organic pollutants from cotton pulp black liquor in the combined process of precipitation and electrochemical treatment and may have practical application potential.

High-value utilization of bamboo pulp black liquor lignin: Preparation of silicon-carbide derived materials and its application

The black liquor of bamboo pulp contains a large amount of silicon, which makes it difficult to separate industrial lignin, thus hindering its high-value utilization. Herein, this paper dedicates to exploring the high-value use of silica-containing lignin. Tetraethyl silicate (TEOS) was added to the above silicon-containing lignin for crosslinking with the lignin to prevent disintegration during carbonization and provide an additional source of silica. The carbonization is carried out at 600 °C (LT-6), 900 °C (LT-9) and 1200 °C (LT-12), and the structural evolution of SiOxCy is innovatively analyzed. The results show that LT-9 is dominated by the SiO3C structure and has a specific surface area of 269 m2 g−1. The specific capacitance of LT-9 and LT-12 as supercapacitors electrodes is 78.6 F g−1 and 74.8 F g−1 at a current density of 1 A g−1, and remains 95 % and 91.7 % after 10,000 cycles. Moreover, LT-9 has a high yield of 54 %. In this work, silicon-containing lignin is exploratively prepared as a silicon-carbide-derived material. Furthermore, the potential relationship between different SiOxCy molecular structures and electrochemical performance is evaluated, which is instructive for the high-value utilization of black liquor in bamboo pulp.

Porous activated carbons derived from bamboo pulp black liquor for effective adsorption removal of tetracycline hydrochloride and malachite green from water.

As a kind of wastewater produced by papermaking industry, bamboo pulp black liquor (BPBL) discharged into water causes serious environmental problems. In this work, BPBL was successfully converted into porous carbon after activation with potassium hydroxide (KOH) through one-step carbonization, and adsorption properties of porous carbon derived from bamboo pulp black liquor (BLPC) for tetracycline hydrochloride (TCH) and malachite green (MG) were studied. The adsorption capacities of BLPC for TCH and MG are 1047 and 1277 mg/g, respectively, due to its large specific surface area of 1859.08 m2/g. Kinetics and isotherm data are well fitted to the pseudo-second-order rate model and Langmuir model, respectively. Adsorption experiments and characterizations reveal that the adsorption mechanism involved in TCH and MG adsorption on BLPC mainly depends on the synergistic effect of pore filling, H-bonding, π-π interactions and weak electrostatic interactions. In addition, BLPC shows excellent photothermal properties, and the adsorption capacity of TCH and MG on BLPC can reach 584 and 847 mg/g under the irradiation of near infrared lamp for 50 min, respectively. The synthesized BLPC with high adsorption efficiency, good recovery ability, improved adsorption under near-infrared irradiation can be a promising and effective adsorbent for TCH or MG or other pollutes.

Hydrodeoxygenation of guaiacol to bio-hydrocarbons over Ni catalyst supported on activated coconut carbon in alkaline condition

Pulping black liquor is a serious source of water pollution worldwide, which is very difficult to subsequently treat. Lignin is the main component of the black liquor and is the only natural aromatic recyclable resource, which is burnt as waste in the Kraft pulping industry. Designing an efficient lignin conversion catalyst that suitable for the strong alkaline environment of black liquor harbors tremendous carbon-neutral potential but still remains a scientific and technological challenge. In this work, the strong alkaline environment of black liquor was simulated, and low-cost pretreated Ni/AC catalysts were adopted to the hydrodeoxygenation (HDO) of a lignin model (guaiacol), and a breakthrough was achieved in the efficient transformation of lignin compound into hydrocarbons. By multitechniques, (e.g., FT-IR, XPS, Boehm titration, HRTEM), the relevance between introducing functional acid groups and the surface properties of catalysts was revealed. It is found that the increased acidic groups are responsible for the enhanced C(sp2)-O cleavage reactions, while improving the dispersion of Ni NPs and thus enhance the HDO efficiency. It is worth noting that better selectivity of benzene and lower hydrogen consumption are achieved on Ni/NOAC during the HDO process. Furthermore, the reaction routes of guaiacol on catalysts with different functional acid groups were proposed. This work provides guidance for efficient utilization of lignin in waste black liquor, and is of great significance to the development of sustainable carbon-neutral biorefinery and environmental protection.

Activated carbon induced hydrothermal carbonization for the treatment of cotton pulp black liquor

Powdered activated carbon (PAC) was introduced into hydrothermal carbonization (HTC) as a catalyst for treatment of cotton pulp black liquor (CPBL) in the present work. The influence of main operating parameters on treatment efficiency in hydrothermal carbonization catalyzed by PAC (PAC-HTC) and changes of PAC due to hydrochar formation on PAC surfaces were studied. Experimental results showed that high temperature and sufficient carbonization time were crucial for HTC of CPBL. The presence of PAC in HTC resulted in significant improvement for CPBL decontamination for 6 h of reaction at 300 °C. Removals of chemical oxygen demand (COD), UV254 and lignin reached 89.59%, 99.71% and 99.79%, respectively. PAC can not only adsorb small molecule organics, but also promote the decomposition and carbonation of biomass macromolecules such as lignin. PAC showed outstanding reusability in the PAC-HTC process, as organics adsorbed on the surface of PAC participated in HTC reactions to realize in-situ regeneration. The PAC-HTC process developed in this work may provide a new alternative for CPBL treatment.

Photoelectrocatalytic degradation of wastewater and simultaneous hydrogen production on copper nanorod-supported coal-based N-carbon dot composite nanocatalysts

Cotton pulp black liquor (CPBL) is a highly concentrated organic wastewater with complex composition, and its direct discharge is extremely harmful to the environment. As an important industrial raw material, hydrogen (H2) has a wide range of applications in many fields such as energy and chemicals. In the study, the composite catalyst N-CDs/Cu NRs was prepared in two steps: firstly, coal-based nitrogen-doped carbon dots (N-CDs) were prepared by the ammonia hydrothermal cutting method using Xinjiang Wucaiwan coal as the carbon source; secondly, N-CDs were loaded onto the surface of copper nanorods (Cu NRs; prepared by a liquid-phase reduction) by a hydrothermal method. While characterizing the structure of the material, the performance of photoelectrocatalytic (PEC) degradation of CPBL and H2 production using N-CDs/Cu NRs was investigated: this PEC double reaction takes place in an H-type photoreactor, where the anode degrades CPBL and the cathode produces H2. The chemical oxygen demand removal rate (RTCODCr) of CPBL reached 94.33% and the yield of H2 reached 272.0 mmol in 60 min of reaction. The GC–MS results showed that all aldehydes, phenols, acids, amines, ethers, and most alkanes, ketones and esters in CPBL could be degraded after 60 min.

Comparison of precipitation behavior of color biopolymer in cotton pulp black liquor with metal chlorides

Cotton pulp black liquor (CPBL) is high alkaline wastewater generated in the production of cotton pulp dreg. The recovery of resource and water is of great practical significance for sustainable development of viscose fiber industry. In this work, precipitation of color biopolymer such as lignin in CPBL was investigated using CaCl2, MgCl2, AlCl3 and FeCl3 as precipitants. The main influencing factors, solid/liquid separation performances, the characteristics of precipitates, and interactions between metal ions and organic compounds were studied. The removal of lignin was found in the order: FeCl3 (89.73%) > AlCl3 (83.96%) > CaCl2 (49.39%) > MgCl2 (42.15%). Removals of organic matter with molecular weight greater than 100 kDa by FeCl3, AlCl3, CaCl2 and MgCl2 precipitation were 94.27%, 93.77%, 74.54% and 76.02%, respectively. The mechanism of biopolymer removal by precipitation was identified as the complexation between high valence metal cations and negatively charged hydroxyl or carboxyl groups. In addition, metal hydroxides or carbonates would form in situ in the native pH condition and may participate in the removal of lignin by adsorption or enmeshment.

Industrial lignins: the potential for efficient removal of Cr(VI) from wastewater.

Cr(VI), a serious threat to human health, widely exists in the effluents of various industrial processes. In this paper, the potential of industrial lignin for efficient removal of Cr(VI) from wastewater was systematically investigated, including pulping black liquor lignin (BLN), enzymolysis lignin (ELN), and SPORL pretreatment spent liquor (FS). The structure characterizations of three lignins were investigated by thermogravimetry (TG), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) surface area measurement, scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). Among these three lignins, BLN showed the highest adsorption amount of Cr(VI) and good selectivity in wastewater simulation. According to the Langmuir model, the calculated maximum adsorption amount of Cr(VI) on ELN, BLN, and FS was 801.57, 864.30, and 642.26 mg g-1, respectively. The adsorption of Cr(VI) by industrial lignins was a chemisorption process, during which Cr(VI) was reduced to low-toxic Cr(III). This paper provided a promising application for the effective utilization of industrial lignins.

Preparation and characterization of high-performance activated carbon from papermaking black-liquor at low temperature

The crude commercial Indulin C kraft lignin (InCL) isolated from pulping black-liquor was used to producing the high-value activated carbon (InCL-AC) with excellent performance. High yields (52.46 %) of InCL-AC with high BET surface area were produced from low cost and unpurified kraft lignin at low temperature (350 °C) using the cheap and environmental-friendly activation agent H3PO4. InCL-AC with higher BET surface areas and larger pore volume than the lignin-based ACs obtained from other commercial lignins, such as Indulin AT (InATL), alkali lignin (AlkL), and Norlig 11D (LS). The adsorption processes of InCL-AC followed the pseudo-second order kinetics with maximum MB adsorption monolayer capacity of 508 mg/g. This approach supplied a potential and effective solution of increasing profit and reducing carbon emissions in pulp production, which is very promising in terms of technical, economic, and environmental feasibilities to transform waste biomass into sustainable feedstocks.

Spray atomization simulation of bamboo kraft black liquor with high solid content at splash-plate nozzle

Increasing the solids content of pulping black liquor burned in a furnace is a development trend of the alkali recovery system in the pulp and paper industry. However, the viscosity of kraft black liquor increases exponentially with an increase in solids content, especially in the case of non-wood pulping black liquor, such as bamboo. This brings great difficulties to the pulping system and atomization of black liquor at the splash-plate nozzle, which is a complete atomization unit constituted of a splash nozzle and a splash plate. To obtain instructive results for industry, a simulation of the atomization process was made using Fluent software for the bamboo kraft black liquor with solids contents of 70 wt% and 80 wt%, which flowed through splash nozzles with the diameter of 22 or 20 mm. The studies were conducted on the distribution of flow field in the nozzle and atomization region through changing the injection pressure and nozzle diameter. The variation of atomization characteristic parameters, such as liquid film thickness, and breakup length, were elucidated. The results reveal the relationship between spray atomization with injection pressure and nozzle diameter, which provides a theoretical basis for improving the concentration of black liquor entering alkali recovery in the future.

A low capital method for silicon interference in bamboo kraft pulping alkaline recovery system

The problem posed by the silicon interference in bamboo pulp black liquor has been troubling bamboo pulp mills as well as hindering the development of non-wood pulp mills. Silica is separated from bamboo pulp black liquor by acid precipitation, accompanied by the sediment of lignin, which is disadvantageous to alkali recovery system. The amount of carboxylate increases through the oxidation of lignin, and the solubility of lignin increases. So the lignin precipitation and the removal of silica can be quantified by the combination of acidification and light oxidation. For solving the problem, we separate the silicon in the black liquor through oxygen oxidation and carbon dioxide acidification without affecting the stability of the alkali recovery system. TG, combustion calorific value and visible light absorption are tested after oxidation and acidification. Finally, by comparing with the mature pulp black liquid alkali recovery system, it is concluded that when taking economic capital into consideration, oxidizing to pH 12.45(at 80 °C) and acidifying to pH 10 (at 50 °C) are suitable for our goal. In this case, the silicon removal rate reaches 76.41 wt%; the amount of separated lignin is 17.58 wt% and the calorific value loss of black liquor reaches 26.47%.

Novel silicon‐contained lignin‐based carbon fibers derived from bamboo pulping black liquor with improved electrochemical performance for supercapacitors

AbstractCarbon fibers (CFs) are a promising candidate as electrode materials for flexible supercapacitors given its light weight and moderate cost. In this study, the lignin used was partially separated from kraft bamboo pulping black liquor and the higher molecular weight fraction, unavoidably contains a small amount of silicon compounds, so named silicon‐contained lignin. Novel CFs were prepared using commercial polyacrylonitrile (PAN) and the lignin by electrospinning and further carbonization. Even in the presence of silicon compounds, the fibrous morphology of precursor fibers was significantly good, and the CFs with uniform fiber diameter and high specific surface area up to 182 m2/g were obtained with an increase in silicon‐contained lignin. The CFs fabricated from silicon‐contained lignin and commercial PAN had higher specific capacitance (22.20 mF/cm2at 10 mA/cm2) and superb cycling stability (94.21%) than that from silicon‐free lignin or pure PAN separately.

Thermal degradation of lignins fractionated by gradient acid precipitation

The pyrolysis behavior of lignin fractions fractionated by gradient acid precipitation from poplar kraft pulping black liquor was investigated by pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). The results revealed that the molecular weight of lignin had no distinct effect on the categories of pyrolysis products, while had an obvious effect on the relative content of products. At 500 °C, pyrolysis of LpH6 produced the highest relative contents of guaiacol-type (G-type) and syringol-type (S-type) compounds (44.41 % and 36.12 %, respectively), and high molecular weight lignin favored the generation of syringol and guaiacol. As pyrolysis temperature rose to 650 °C, relative contents of phenol-type (H-type) and catechol-type (C-type) compounds (20.92 % and 10.76 %, respectively) derived from LpH4 pyrolysis were the highest. Demethoxylation and dehydroxylation were promoted at high temperature, resulting in an increase in the relative content of aromatic hydrocarbons. Pyrolysis of kraft lignin (KL) produced the highest relative content of H-type compounds (43.24 %) at 800 °C. The research could give some contribution to the design of pyrolytic parameters for production of specific aromatic compounds from fractionated lignin.

Magnetic composite Ca(OH)2/Fe3O4 for highly efficient flocculation in papermaking black liquor without pH neutralization

Industrially, lignin in pulp liquor not only obstructed the realization of value-added products, but also threatened the aquatic ecosystem. A magnetic composite Ca(OH)2/Fe3O4, combining the eco-friendliness of Ca-based flocculants with the convenience of magnetic flocculation, was simply compounded to efficiently flocculate lignin from papermaking black liquor. Morphologic and structural features of the flocculant before and after flocculation were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), vibrating sample magnetometer (VSM) and X-ray photoelectron spectroscopy (XPS). The flocculant Ca(OH)2/Fe3O4 presented mesoporous and core-shell structure, which acted directly in the sodium lignin aqueous solution without pH neutralization, maintaining high lignin removal between 91% and 95%. Ca(OH)2/Fe3O4 showed a wider salts (0–1 mol/L NaCl) and pH (9–12.5) tolerance. In actual pulp black liquor, Ca(OH)2/Fe3O4 exhibited high removal of 90.16% and 85.93% for lignin and chemical oxygen demand (COD), respectively. The flocculation performance of Ca(OH)2/Fe3O4 outdistanced that of the traditional flocculant polyacrylamide (PAM). It displayed magnetically separable with a good reusability. The removal of lignin could attain 90.54% even after 6 cycles. Charge neutralization, micro-bridging, destabilization and sedimentation were involved in the process of lignin flocculation. Consequently, Ca(OH)2/Fe3O4 presented huge potential in papermaking black liquor treatment.

Maximizing yield of liquid-lignin from membrane filtration retentate of kraft black liquor

Removal of lignin from kraft pulping black liquor has the potential to increase pulp production, and at the same time lignin can serve as raw material for renewable fuels. There are well-known challenges associated with the outtake of lignin from kraft black liquor. Examples of such challenges are acid consumption and effects on the Na/S balance in the pulp mill, which can be decreased by a new process concept combining membrane filtration and liquid-lignin separation. In this study, we investigated the yield of liquid-lignin in separation from kraft black liquor retentate, specifically concerning how it was influenced by the presence of xylose and galactoglucomannan. For example, the liquid lignin yield after carbon dioxide separation decreased from 89.3 % to 85.2 % and 86.1 % with the addition of 20 g/L xylose and galactoglucomannan, respectively. The results showed that the yield of liquid-lignin decreased with an increasing amount of sugar added. Similarly to previous research, our results showed an improvement of liquid-lignin yield associated with a decrease in the content of sugars in cases of heat treatment prior to separation.We suggest a new explanation for the interaction between lignin and hemicellulose, namely that the interactions occur at a molecular level, with lignin in solution, and that these interactions possibly involve the formation of covalent lignin-carbohydrate bonds. This makes the lignin more polar and less prone to form a liquid-lignin phase.

Ni/MnO2 doping pulping lignin-based porous carbon as supercapacitors electrode materials

Lignin extracted from pulping black liquor as carbon source, C4H6O4Ni·4H2O as acatalyst and KMnO4 as dopant, a lignin-based porous carbon material (PC-Ni/MnO2) co-doped with Ni and MnO2 was prepared and used in electrode materials for supercapacitors. During the high-temperature carbonization process, part of amorphous carbon generates a multi-layer graphene structure, causing the PC-Ni/MnO2 to has a high degree of graphitization. Meanwhile, KMnO4 gradually decomposes and reacts with C to produce MnO2. The lignin-based porous carbon material has a higher pseudocapacitance, the specific capacitance of PC-Ni/MnO2 can reach 267.34 F g−1 at a current density of 0.1 A g−1. After 5 000 cycles charge and discharge test, the specific capacitance retention rate kept 83.6% at a current density of 1 A g−1, showing good rate performance and electrochemical stability. A symmetrical supercapacitor prepared by PC-Ni/MnO2 as electrodes, its energy density can reach 28 Wh·kg−1 as the power density of the capacitor is 360 W kg−1. And the supercapacitor also exhibited good cyclic stability with 86.3% retention of initial capacitance after 5000 cycles at 1.0 A g−1. When two such supercapacitors in series, a LED lamp can be light. These induct that the doping of Ni and MnO2 can improve the capacitance characteristics, showing that the biomass porous carbon has great practical application value.

In situ synthesis of “brick and mortar”-type lignin-derived carbon/TiO2 composite with a remarkable photocatalytic performance

Alkali lignin (AL), an industrial waste from pulping black liquor, is mainly applied as a low-grade combustible energy source. Design and preparation of high value-added materials with AL is still a challenge. In this work, we firstly introduced ammonium group into AL and prepared quaternized alkali lignin (QAL) for improving the solubility in acidic aqueous solution. Then a facile sol–gel and carbonization process was developed to fabricate lignin-derived carbon/TiO2 (LC/TiO2) composite photocatalyst using QAL as the carbon precursor. The microstructural characteristics and optical property of the LC/TiO2 composite were systematically characterized. Composite exhibited a “brick (TiO2 nanoparticles) and mortar (LC)”-type construction, and TiO2 nanoparticles were coated with LC. The introduction of LC endowed TiO2 with extended photoabsorption region and enhanced separation of photo-generated charge carriers. LC/TiO2 obtained at a carbonization temperature of 650°C presented the highest photocatalytic activity for the degradation of organic dye, which was about 3.4 times that of bare TiO2. Moreover, LC/TiO2 also presented good recyclability. This facile strategy not only offers great opportunities for the high value-added application of industrial lignin, but also promotes the practical application of TiO2 photocatalyst.

A novel catalyst prepared from black liquor for biodiesel conversion: An optimization study

This paper reports a new approach for high-value conversion of black liquor into biochar to catalyse the transesterification for biodiesel conversion using waste fry oil (WFO). The central composite design (CCD) and response surface methodology (RSM) were employed to optimize the biodiesel preparation using the catalyst prepared from the paper pulp black liquor precipitated biochar. The transesterification reaction is catalysed by oxidative functional groups (enolic) on the surface of biochar. The effect of alkaline loading in biochar, carbonization temperature, the methanol to oil ratio and the catalyst loading were systematically investigated. The optimal biodiesel conversion conditions were achieved as the following: 27wt% (alkaline loading in biochar), 585 °C (carbonization temperature), 7 (methanol to oil ratio) and 5.5 wt% (catalyst loading), with the biodiesel yield of 95%.

Coupling of alkaline precipitation and alkali-activated hydrogen peroxide oxidation for reuse of cotton pulp black liquor

The cotton pulp black liquor (CPBL) is high alkalinity wastewater generated in the production of cotton pulp dreg. In the present work, CPBL was treated by a coupling process of alkaline precipitation and alkali-activated hydrogen peroxide (H2O2) oxidation to remove colorants, so that the water and alkali can be reused in cotton linters cooking for cleaner production of cotton pulp dreg. The influence of main operating parameters of alkaline precipitation and alkali-activated H2O2 oxidation was investigated. The reactive oxygen species (ROS) tests in alkali-activated H2O2 combined with analyses of degradation products were conducted to explore the possible reaction mechanism. Experimental results showed that alkaline precipitation was more effective compared to traditional acid precipitation. The removal efficiencies of COD, UV254 and color were 30.83%, 40.69% and 65.21%, when 13 g L−1 CaCl2 was added. Removal efficiencies of UV254 of 30.22% and color of 80.78% can be achieved for the alkali-activated H2O2 process (H2O2 dosage of 30 mmol L−1, 2 h reaction time, and temperature 60 °C). Consequently, total removals of UV254, lignin and color were 61.4%, 67.8% and 92.79% in the integrated process. The quality of the effluent after treatment satisfied requirements of recycling for cotton pulp dreg production. It was found that superoxide radical (O2−·) was the dominant ROS and hydroxyl ion (OH−) was mainly responsible for activation of H2O2 in the oxidation process.

Partial Replacement of Coarse Aggregate with Coconut shell and using Pulp Black Liquor as Admixture

Partial Replacement of Coarse Aggregate with Coconut shell and using Pulp Black Liquor as Admixture