Alkaline Peroxide Mechanical Pulp Research Articles

STUDY ON THE RHEOLOGICAL PROPERTIES OF FAST-GROWING EUCALYPTUS

To study the effect of retention and drainage aidson the fast-growing eucalyptus bleached kraft pulp (EBKP) suspensions, different concentrations of cationic polyacrylamide (CPAM)and cationic starch were dosed with EBKP suspensions and their effects on rheological properties were studied. Theshear yield stress (τy)of softwoodbleached kraft pulp(SBKP)and poplar alkaline peroxide mechanical pulp (PAPMP) were comparedandevaluated for their potential applications. The results show that in the steady-state shear condition, the τyof EBKP is proportional to the pulp mass concentration (Cm),corresponding to the exponential relation . SBKP had the highest τyvalues, followed by EBKP and PAPMP. Adding CPAM and cationic starch to EBKP suspensions at low to moderate doses increased the τy, butonce thelevels reached a certain point, the τyvalues began to deteriorate. This research is crucial to achieve optimally and stabilize the downstream manufacturing process in papermaking.

Study of a Novel Biorefining Method for Obtaining 2-Furaldehyde, Acetic Acid and Pulp from Birch Wood

Necessity for reduction of greenhouse gases emissions, the growing demand for improvement of biorefinery technologies and the development of new biorefining concepts, oblige us as a society, mainly scientists, to develop novel biorefinery approaches. The aim of this research was to comprehensively characterize lignocellulosic biomass that was obtained after 2-furaldehyde production, in terms of further valorization of this resource. This research shows that birch wood chips can be used in the new biorefinery processing chain for production of 2-furaldehyde, acetic acid and subsequent cellulose pulp obtaining, using thermomechanical and alkaline peroxide mechanical pulping process. In addition, obtained lignocellulosic residue was also characterized. Unique bench-scale reactor system was used to obtain a lignocellulosic material without pentoses and with maximum preservation of cellulose fiber for further use. Studies on the deacetylation and dehydration of birch wood hemicelluloses of pentose monosaccharides to 2-furaldehyde and acetic acid using orthophosphoric acid as a catalyst were carried out. Results showed that depending on the used pretreatment conditions the 2-furaldehyde yield was from 0.04 to 10.84 % o.d.m., the acetic acid yield was from 0.51 to 6.50 % o.d.m. and the lignocellulose residue yield was from 68.13 to 98.07 % o.d.m. with minimal content of admixtures. In addition, experimentally the optimal 2-furaldehyde production conditions regarding to purity and usability of cellulose in leftover of lignocellulosic material were developed. Best results in terms of both 2-furaldehyde yield and purity of residual lignocellulose were obtained in experiment where catalyst concentration was 70%, catalyst amount 4 wt.%, reaction temperature 175 °C and treatment time 60 min. By performing alkaline peroxide mechanical pulping of the relevant LC residue, it was possible to obtain pulp with tensile index comparable to standard printing paper, indicating that it is possible to perform stepwise 2-furaldehyde production with subsequent pulping to obtain various value added products.

Thermomechanical and Alkaline Peroxide Mechanical Pulping of Lignocellulose Residue Obtained from the 2-Furaldehyde Production Process.

The necessity for the reduction in greenhouse gas emissions, the growing demand for the improvement of biorefinery technologies, and the development of new biorefining concepts oblige us as a society, and particularly us, as scientists, to develop novel biorefinery approaches. The purpose of this study is to thoroughly evaluate the leftover lignocellulosic (LC) biomass obtained after the manufacture of 2-furaldehyde, with the intention of further valorizing this resource. This study demonstrates that by using thermomechanical and alkaline peroxide mechanical pulping techniques, birch wood chips can be used in the new biorefinery processing chain for the production of 2-furaraldehyde, acetic acid, and cellulose pulp. In addition, the obtained lignocellulosic residue is also characterized. To produce a lignocellulosic material without pentoses and with the greatest amount of cellulose fiber preserved for future use, a novel bench-scale reactor technology is used. Studies were conducted utilizing orthophosphoric acid as a catalyst to deacetylate and dehydrate pentose monosaccharides found in birch wood, converting them to 2-furaldehyde and acetic acid. The results showed that, with the least amount of admixtures, the yields of the initial feedstock’s oven-dried mass (o.d.m.) of 2-furaldehyde, acetic acid, and lignocellulose residue ranged from 0.04 to 10.84%, 0.51 to 6.50%, and 68.13 to 98.07%, respectively, depending on the pretreatment conditions utilized. The ideal 2-furaldehyde production conditions with reference to the purity and usability of cellulose in residual lignocellulosic material were also discovered through experimental testing. The experiment that produced the best results in terms of 2-furaldehyde yield and purity of residual lignocellulose used a catalyst concentration of 70%, a catalyst quantity of 4%, a reaction temperature of 175 °C, and a treatment period of 60 min. It was possible to create pulp with a tensile index similar to standard printing paper by mechanically pulping the necessary LC residue with alkaline peroxide, proving that stepwise 2-furaldehyde production may be carried out with subsequent pulping to provide a variety of value-added goods.

Impact of continuous electrochemical degradation of eucalyptus alkaline peroxide mechanical pulping wastewater

Levels of pollutants in pulp and papermaking wastewater are an important issue for environmental protection. High concentrations of contaminants can seriously affect the environment if they are not processed. Therefore, treating paper wastewater is a necessary option for governments to select appropriate treatment methods to remove the multi-component pollutants. In this study, the impact of continuous electro-degradation of eucalyptus alkaline peroxide mechanical pulping wastewater was studied. An electrolytic treatment method performed at a low voltage was used. Through the electrolysis method, the wastewater chemical oxygen demand was decreased by 98%, and color-generating groups were nearly all destroyed. During the electrolysis process, the pH value of wastewater continuously decreased and finally reached 2.5. Lowering the pH of the waste solution will help increase the electrolysis efficiency of the wastewater. A total of 5.8 g of alkali was obtained. The wastewater precipitation before and after electrolysis was analyzed by X-ray photoelectron, Fourier transform infrared, and energy-dispersive X-ray spectroscopies.

Furnishing autohydrolyzed poplar weakly alkaline P-RC APMP to make lightweight coated base paper

This work investigated the effects of autohydrolysis pretreatment severity on poplar (Populus tomentosa Carr.) woodchips used to make a type of high-yield pulp (HYP) known as preconditioning followed by refiner chemical treatment, alkaline peroxide mechanical pulp (P-RC APMP). It also investigated the ratios for partial-ly replacing sodium hydroxide (NaOH) with magnesium oxide (MgO) in the high-consistency (HC) retention stage of the P-RC APMP process on the obtained HYP’s properties. The results show that the pretreatment severity of autohydrolysis at combined hydrolysis factor (CHF) = 10.77 and the 50 wt% ratio for partially substituting NaOH with MgO were the optimum conditions for making light-weight coated (LWC) base paper. Compared to the conventional P-RC APMP, the optimized P-RC APMP had similar bulk and higher tensile, burst, and tear indices, as well as opacity, but a slightly lower ISO brightness. When the optimized P-RC APMP and commercial softwood bleached sulfate pulp (SBKP) were blended to make LWC base paper, the most favorable pulp furnish was comprised of 50% optimized P-RC APMP and 50% commercial SBKP. The obtained LWC base paper handsheet had better bulk, and its other properties could also meet the require-ments of LWC base paper.

Characterization of Birch Wood Residue after 2-Furaldehyde Obtaining, for Further Integration in Biorefinery Processing.

Latvia is a large manufacturer of plywood in Eastern Europe, with an annual production of 250,000 m3. In Latvia’s climatic conditions, birch (Betula pendula) is the main tree species that is mainly used for plywood production. A significant part of the processed wood makes up residues like veneer shorts, cores, and cut-offs (up to 30%), which have a high potential for value-added products. The aim of this research was to comprehensively characterize lignocellulosic (LC) biomass that was obtained after 2-furaldehyde production in terms of further valorization of this resource. The polymeric cellulose-enriched material can be used in the new biorefinery concept for the production of 2-furaldehyde, acetic acid, cellulose pulp, thermomechanical (TMP) and an alkaline peroxide mechanical (APMP) pulping process. In addition, we experimentally developed the best 2-furaldehyde production conditions to optimize the purity and usability of cellulose in the leftovers of the LC material. The best experimental results in terms of both 2-furaldehyde yield and the purity of residual lignocellulose were obtained if the catalyst concentration was 70%, the catalyst amount was 4 wt.%, the reaction temperature was 175 °C,and the treatment time was 60 min. After process optimization with DesignExpert11, we concluded that the best conditions for maximal glucose content (as cellulose fibers) was a catalyst concentration of 85%, a catalyst amount of 5 wt.%, a temperature of 164 °C, and a treatment time of 52 min.

H2O2 bleaching in mixed triploid poplar and acacia woodchips high-yield pulping process with substitution of 50 wt% NaOH by MgO and its kinetics study

In the present work, the H2O2 bleaching with the substitution of 50 wt% NaOH by MgO as the alkali source in the high-consistency (HC) retention stage of mixed triploid poplar (Populus tomentosa Carr.) and acacia (Acacia confusa Merr.) woodchips P-RC APMP (preconditioning followed by refiner chemical treatment, alkaline peroxide mechanical pulp) was conducted. Meanwhile, the related bleaching reaction kinetics was well established. The obtained high-yield pulp presented a higher bleaching yield, improved bulk, favorable brightness and physical properties in comparison with the obtained pulp using 100 % NaOH as the alkali source. Most importantly, the chemical oxygen demand (COD) of the bleaching effluent was greatly decreased. The established bleaching kinetic equation is as following: dwdt=K[H2O2]3.63[NaOH]1.08[MgO]0.57[Na2SiO3]0.05w−1.89K= A·e–E/RT where the activation energy E =57.2 kJ/mol. It demonstrates that the bleaching reaction rate greatly depends on the concentration of primary bleaching reagents. The magnitude of the dependent extent is [H2O2] > [NaOH] > [MgO] > [Na2SiO3]. The rapid rise of the pulp brightness increment occurred in the first 35 min in the bleaching reaction.

Carboxymethylation of polysaccharide isolated from Alkaline Peroxide Mechanical Pulping (APMP) waste liquor and its bioactivity

In recent years, the biological activity of polysaccharides and their derivatives has been widely studied. However, in addition to the natural polysaccharides directly extracted from plants and animals, there are rich polysaccharides in the pulping waste liquor that have not been fully utilized. The extracted polysaccharide from eucalyptus Alkaline Peroxide Mechanical Pulping (APMP) waste liquor was used as a raw material. For the production of carboxymethyl polysaccharide, the effects of temperature (T), the amount of alkali (NaOH) and the amount of etherifying agent (ClCH2COOH) on the degree of substitution (DS) were investigated, the optimal preparation conditions are: reaction time 2 h, temperature 75 °C, and the molar ratio of polysaccharide, NaOH and ClCH2COOH is 1:1:2, the highest DS is 1.47; FT-IR, NMR and GPC were used to characterize the structure and Molecular weight, the results show that the polysaccharide of APMP waste liquor is rich in xylan, and it was proved that the carboxymethyl substitution was successful and the positions of the substituent group were determined. The characterization and biological activity research of xylan polysaccharide (XP) and carboxymethyl xylan polysaccharide (CMXP), such as antioxidation, moisture absorption/retention, bacteriostatic action and cytotoxicity were discussed. CMXP shows better effects compared with XP.

Extraction of allelochemicals from poplar alkaline peroxide mechanical pulping effluents and their allelopathic effects on Microcystis aeruginosa

In this study, allelochemicals were extracted from pulping effluents rather than from the raw material of plants. Herein, five organic solvents (ethyl acetate (EAC), methyl tert-butyl ether (MTBE), dichloromethane (DCM), carbon tetrachloride (CTC), and petroleum (PE)) were applied to separately extracting the allelochemicals from alkaline peroxide mechanical pulp (APMP) effluents. The results from the algal density, inhibition ratio, and optical density of 446 nm (OD446nm) concluded that the extractives from the APMP effluents can act as effective allelochemicals and showed noticeable allelopathic inhibition effects on Microcystis aeruginosa growth. The results indicated that organic solvent extraction could be a practical approach to isolate the allelochemicals from the APMP effluents, which would broaden the potential application of the APMP effluents in the production of antimicrobial agents and other value-added materials.

Preparation of high oil absorption microfiber cryogels by mechanical method

Poplar alkaline peroxide mechanical pulp (APMP) was used as plant fiber raw material, and it was graded according to the lignin content. The graded raw materials were used to prepare lignin-containing microfibers (LCMFs) by micro-grinding, and then, the lignin-containing microfiber cryogels (LCMF-cryogels) were prepared by vacuum freeze-drying. The particle size distribution, micromorphology and dispersion stability of LCMFs were characterized by laser diffraction particle size analyzer, transmission electron microscopy and Zeta potentiometer. Then, the crystalline structure, pore structure, surface morphology and adsorption properties of LCMF-cryogels were analyzed. In addition, LCMF-cryogels were compared with the microfiber cryogels (MF-cryogels) which use commercial eucalyptus chemical bleaching pulp as raw material. It was proved that using poplar APMP as raw material to prepare cryogels is more advantageous. The results showed that the lower the lignin content in plant materials, the better the oil adsorption ability of cryogels. This is because the binding effect of lignin on the fiber is reduced, which makes the fibrillation of the fiber easier by external mechanical action. The maximum adsorption capacity of LCMF-cryogel for methyl silicone oil is 215 g/g, while that of MF-cryogel prepared from commercial eucalyptus chemical bleaching pulp is 102.5 g/g. The analysis of the properties of raw fiber and the gel pores shows that the change in the fiber morphology caused by different pulping methods has important influence on the development of LCMF-cryogels by mechanical refining. Poplar APMP is more suitable for preparing fiber-based cryogels oil-absorbing materials than commercial eucalyptus chemical bleaching pulp.

A survey of biomass from Aspergillus niger S13 treatment of APMP pulping effluent in the applications of animal feed

With the development of the paper industry, the problem of alkaline peroxide mechanical pulp (APMP) pulping effluent treatment is based on major issues. Currently, using APMP pulping effluent to prepare animal feedstuff is a research hotspot. The Aspergillus niger S13 aerobic fermentation was followed by a post-coagulation/flocculation process for the treatment of APMP pulping effluent. As the by-product, the biomass from the A. niger S13 aerobic fermentation process was assessed as a potential feedstuff. The nutrient contents and heavy metal contaminants of the prepared feedstuff were analyzed and compared with other feedstuff or bio-production from the literature. The toxicity of the prepared feedstuff was also assessed through Sprague-Dawley rat experiments. The research found that the prepared feedstuff was a nontoxic and safe nutritious material. It is worth noting that the prepared feedstuff also exhibited other attractive properties, such as the presence of miscellaneous and benign enzymes and lignin, which is very beneficial to the diet efficiency of animals. This study provides a facile and sustainable approach to harvest versatile and available feedstuff from APMP pulping effluents.

Prediction of strength properties of poplar alkaline peroxide mechanical pulp using near infrared spectroscopy and multivariate calibration

Application of near infrared (NIR) spectroscopy to pulp and paper research is almost based on chemical pulping, but little research has been directed toward the use of NIR to mechanical pulping. Compared with chemical pulp, mechanical pulp exhibits certain attractive qualities such as high pulping yield, sufficient opacity and bulk. However, because non-cellulose components (hemicelluloses and lignin) are preserved largely in the produced fibre, mechanical pulping process emerges easily production problem, such as inefficient chemical impregnation and unstable pulp properties. Therefore, it is necessary to explore a rapid measurement technique suitable for pulping process control. This study investigated the feasibility of NIR to predict rapidly the strength properties of mechanical pulp. Alkaline peroxide mechanical pulp (APMP), using poplar as raw material, was produced at pilot plant scale, different type of mechanical compressive pre-treatment and different pulping degree were implemented to increase variability in the obtained pulp samples. NIR spectra were collected from the rough and smooth surface of pulp handsheets to develop calibration models for tensile, burst, and tear index. Calibration statistics results indicated that rough surface spectra could provide more accurate and robust calibrations compared with smooth surface spectra. Additionally, spectral signal correction was proved to be a critical step for NIR calibration optimization. Based on spectra collected with multiplicative scatter correction and derivatives pre-processing, excellent NIR prediction performance was obtained with the root mean square error of 1.776 Nm g−1 for tensile index, 0.108 kPam2 g−1 for burst index and 0.116 mNm2 g−1 for tear index, the RPD values greater than 2.0 satisfying quantitative analysis.

Effects of Hot Water Pre-Extraction on Energy Consumption and Brightness of Bamboo Alkaline Peroxide Mechanical Pulp

The main purpose of this paper was to investigate the effects of hot water pre-extraction (HWP) on the refining energy consumption and the brightness of bamboo alkaline peroxide mechanical pulp (APMP). It was found that compared with un-extraction, the refining energy consumption dropped by about one-third after HWP. The reduction of energy consumption was proved through enhancing the channel of water and chemicals into inferior fiber based on the surface characterization of bamboo. Scanning electron microscope (SEM) images showed that the HWP made the fibers' structure loose and porous. Both pore volume and specific surface area were increased significantly after HWP, by 260.00% and 1804.76%, respectively. A decrease in pulp brightness was mainly due to the formation of new chromophore groups during the HWP process. The results of 13C nuclear magnetic resonance spectroscopy (13C-NMR) illustrated that some structures of milled wood lignin (MWL), such as guaiacyl, etherificated guaiacyl, and aromatic units, were increased during the HWP process. However, some lignin-links units of α-O-4, β-O-4, and some carbohydrate structures such as xylan, α- and β-glucose, and β-and β-mannose in lignin-carbohydrate complex (LCC) were evidently degraded. Additionally, most of the lignin and LCC were degraded under the simulative conditions of HWP bamboo. Furthermore, the analysis of UV spectrophotometry indicated that HWP was conductive to the generation of chromophore groups such as conjugated carbonyl, catechol, and o-benzoquinone.

Shapes Control of Bi2WO6 Nano-Structures as Photo-Fenton Catalysts for Pulping Wastewater Treatment

Bi2WO6 assembled by flower-like microspheres and nanosheets were controllably synthesized through a one-step hydrothermal approach. Multiple technologies, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectrum (UV–Vis), were carried out to characterize the as-synthesized samples. The photocatalytic efficiency of Bi2WO6 synthesized with a series of temperature and pH values shows different morphologies and photocatalytic properties. The photocatalyst (Bi2WO6) synthesized at 220 °C and pH of 7 exhibited the best photocatalytic performance, with the methylene blue (MB) degradation approaching 91.6% after reaction time of 60 min. Free radical capture experiments indicate that •OH is the primary reactive species in the methylene blue (MB) degradation reaction, h+ and •O2− contribute negligible influence, while the addition of H2O2 significantly improves the photocatalytic activity of Bi2WO6. Biodegraded poplar preconditioning refiner chemical alkaline peroxide mechanical pulp wastewater (PPW) was treated over Bi2WO6 under UV light (Bi2WO6/UV/H2O2); chemical oxygen demand (CODCr) and color degradation rate were 85.8% and 92.0%, respectively. These results show that Bi2WO6 semiconductors can be introduced as an efficient and stable photocatalyst for industry wastewater treatment.

Pollutant characteristics from wastewater of poplar pre-conditioning refiner chemical alkaline peroxide mechanical pulping pretreated with Phanerochaete chrysosporium

The compositions of the organic pollutants of chemi-mechanical pulping wastewater were studied using Fourier transform infrared spectra and gas chromatography-mass spectrometry. The chemical oxygen demand (COD) was approximately 18110 mg/L, and the ratio of biological oxygen demand to COD (BOD5/COD) was approximately 0.17, due to low biodegradability. In this study, Phanerochaete chrysosporium was selected and the changes in bacterial culture time required to transform pulping wastewater and the metabolites present before and after pretreatment in the wastewater were identified. A decline in the components of the pulping wastewater was observed. Initially, 43 kinds of organic compounds were detected in the raw water. After 3 days of treatment, only 21 organic compounds were detected. Then, 7 days later, the organic pollutants in the waste amounted to only 7 organic compounds. Through the analysis of analysis of P-RC APMP pulping wastewater and that treated by Phanerochaete chrysosporium using GC-MS, the relative content of organic acids was 12.4%, in which phenylpropionic acid had the highest concentration of 11.3%. So, in the culture medium, phenylpropionic acid as the single carbon source can be completely degraded within 96 h.

Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp via TEMPO-Mediated Oxidation and Homogenization

In this study, a poplar high-yield pulp [preconditioning refiner alkaline peroxide mechanical pulp (P-RC APMP)] was used to produce lignin-containing cellulose nanofibril (LCCNF) dispersions throug...

Valorization of Alkaline Peroxide Mechanical Pulp by Metal Chloride-Assisted Hydrotropic Pretreatment for Enzymatic Saccharification and Cellulose Nanofibrillation.

Developing economical and sustainable fractionation technology of lignocellulose cell walls is the key to reaping the full benefits of lignocellulosic biomass. This study evaluated the potential of metal chloride-assisted p-toluenesulfonic acid (p-TsOH) hydrolysis at low temperatures and under acid concentration for the co-production of sugars and lignocellulosic nanofibrils (LCNF). The results indicated that three metal chlorides obviously facilitated lignin solubilization, thereby enhancing the enzymatic hydrolysis efficiency and subsequent cellulose nanofibrillation. The CuCl2-assisted hydrotropic pretreatment was most suitable for delignification, resulting in a relatively higher enzymatic hydrolysis efficiency of 53.2%. It was observed that the higher residual lignin absorbed on the fiber surface, which exerted inhibitory effects on the enzymatic hydrolysis, while the lower lignin content substrates resulted in less entangled LCNF with thinner diameters. The metal chloride-assisted rapid and low-temperature fractionation process has a significant potential in achieving the energy-efficient and cost-effective valorization of lignocellulosic biomass.

N-Doped Carbon Aerogels Obtained from APMP Fiber Aerogels Saturated with Rhodamine Dye and Their Application as Supercapacitor Electrodes

We developed an efficient and environmentally friendly strategy for synthesizing an N-doped carbon aerogel by the carbonization of an alkaline peroxide mechanical pulp (APMP) fiber aerogel saturated with rhodamine B (RB) dyes. The APMP aerogel was prepared via cellulose extraction, sol-gel, and freeze drying. The resulting aerogel had a high adsorption capacity (250 mg g−1) and a fast adsorption rate (within 30 s) towards RB dyes. The saturated aerogel was used as a starting material for further carbonization to prepare N-doped carbon aerogels. SEM studies showed that the 3D network structure of the APMP aerogels was well preserved after RB adsorption and carbonization. The prepared carbon aerogel exhibited a graphitized structure, and N (2.15%) was doped at pyridinic N and pyrrolic N sites in the 3D carbon network. The specific capacitance of the N-doped carbon aerogel reached 185 F g−1 at a current density of 1 A g−1, which is higher than carbon aerogels (155 F g−1).

Surface Characterization of Plasma-treated Eucalyptus Alkaline Peroxide Mechanical Pulp using Electronic Spectroscopy Chemical Analysis and Atomic Force Microscopy

Eucalyptus alkaline peroxide mechanical pulp (APMP) fibers were modified by a low-temperature plasma (LTP) treatment within an air and oxygen mixture. An atomic force microscope (AFM) and electronic spectroscopy chemical analysis (ESCA) were used to analyze the morphological and chemical information of eucalyptus APMP fibers. According to the AFM results, LTP treatment etched the fibers’ surface, allowing for the removal of hydrophobic substances from the surface. According to the ESCA, the oxygen to carbon ratio of the APMP fiber surface increased from 50.08% to 55.47%, and the C1 peak area decreased from 8.89% to 8.45% after a LTP treatment. All of these results indicate that a LTP treatment can modify the APMP fibers and reduce the contents of lignin and extractives, thus exposing more carbohydrate.

Correlation between pyrolysis behaviors of the components and the overall pyrolysates from pulping spent liquor

The pyrolysis behaviors of the three major organic components of eucalyptus alkaline peroxide mechanical pulping (APMP) spent liquor including alkali lignin (AL), lignin-carbohydrate complexes (LCC), and polysaccharide (PLS) were studied with emphasis on the effect and contributions of components on the overall pyrolysates of APMP spent liquor solid (ASLS). Profound differences on product properties from each component pyrolysis were illustrated. The results indicated that the bio-oil during ASLS pyrolysis was mainly attributed to AL, while the bio-gas and char were mostly affected by PLS. Small molecule hydrocarbons released during ASLS pyrolysis mainly came from AL and LCC, and CO and CO2 mainly produced from PLS. As for bio-oils, AL generated the largest proportion of monomeric phenols and aromatic hydrocarbons (AHs), while PLS and LCC mainly contributed to the production of ketones, furans and acids. The correlation shown here is of interest for further studies on pulping spent liquor grading utilization.