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Lignin has been produced in large quantities in the pulp manufacturing process; however, its valorization has been challenging. The production of lignin polymers has shown pathways to produce water soluble products to be used as flocculants and dispersants. However, these lignin-based polymers may interact with each other and form large flocs that could reduce their efficiency in interacting with other colloidal particles. This study aims at evaluating the self-assembly of kraft lignin-acrylamide polymers in aqueous environments under different salt concentrations. The sedimentation studies using a vertical scan analyzer showed that a higher molecular weight lignin polymer had a higher tendency for sedimentation than a lower molecular weight one. Quartz crystal microbalance with dissipation (QCM-D) was used for studying the self-assembly behavior of lignin polymers with different molecular weights. The results suggested that lignin polymer with the higher molecular weight of 96,992 g/mol had a higher tendency to self-assemble by forming a loose floc as compared to that with a lower molecular weight. Also, salt disrupted the self-assembly of lignin polymers greatly. [ABSTRACT FROM AUTHOR]

The spent liquor, SL, of neutral sulphite semi chemical pulping process contains lignosulfonate and hemicelluloses, but it is currently treated in the wastewater treatment of the process. This treatment decomposes the lignosulfonate. However, lignosulfonate can be extracted for a better use, but the extraction process is not an easy task. The main objective of this work was to extract lignosulfonate from SL via treating the SL with surfactant. The results showed that the acidification of SL to pH 1.8 caused 6% lignosulfonate, 53% hemicelluloses, and 7% COD removals from SL. Acidification followed by dodecyltrimethylammonium chloride, DTAC, treatment of SL at the optimal conditions of 22 °C, 1.8 pH and 10 mg/g of DTAC/SL yielded 40% lignosulfonate, 78% hemicelluloses, and 25% COD removals. Model solutions were prepared via dissolving commercial lignosulfonate and xylan in solutions or purifying SL via membrane dialysis in order to investigate the impact of SL components, i.e. hemicelluloses and residual cooking chemicals, on the isolation of lignosulfonate from SL. The model analyses confirmed that the presence of impurities, i.e. residual cooking salts, significantly affected the isolation of lignosulfonate from the SL, but the presence of hemicellulose had a minor effect in extracting lignosulfonate from SL via DTAC treatment. In addition, the elemental analysis confirmed that DTAC and lignosulfonate had a ratio of 0.584 mol/mol in precipitates. [ABSTRACT FROM AUTHOR]

The pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process is currently sent to the recovery boiler and incinerated. However, PHL contains about 5-8% lignocelluloses that can be utilized in the production of value-added chemicals. In this study, a process for producing xylitol from hemicelluloses in PHL is developed. This process involves several acidification, neutralization, adsorption (along with reactivation) and evaporation stages. The mass balance indicates that 533kg/h xylitol (with 99% purity), 187kg/h lignin, 806kg/h basic ferric acetate, and 1600 kg/h gypsum can be produced from 41,670 kg/h PHL. The energy balance shows that the evaporators are the largest consumers of energy, while the reactivation kiln, acidification, neutralization, and precipitation processes generate some heat. Overall, 41% conversion of xylose to xylitol is achieved. [ABSTRACT FROM AUTHOR]

Abstract: A process for removing inhibitors from pre-hydrolysis liquor (PHL) of a kraft-based dissolving pulp production process by adsorption and flocculation, and the characteristics of this process were studied. In this process, industrially produced PHL was treated with unmodified and oxidized activated carbon as an absorbent and polydiallyldimethylammonium chloride (PDADMAC) as a flocculant. The overall removal of lignin and furfural in the developed process was 83.3% and 100%, respectively, while that of hemicelluloses was 32.7%. These results confirmed that the developed process can remove inhibitors from PHL prior to producing value-added products, e.g. ethanol and xylitol via fermentation. [Copyright &y& Elsevier]

Abstract: Dissolved lignocelluloses from the pre-hydrolysis liquor (PHL) of kraft-based dissolving pulp production process were recovered by adsorption to lime mud produced in the causticizing plant of the kraft process. The adsorption of lignocelluloses was a fast process, and could be completed within one hour. The addition of polydiallyldimethylammonium chloride (PDADMAC) significantly increased the amounts of adsorbed lignin and hemicelluloses, which more than doubled at the PDADMAC dosage of 0.1% (based on the weight of PHL). The measured heating values of the adsorbed lignocelluloses indicate that adsorption of lignocelluloses to lime mud may result in the energy saving of the lime kiln. The process proposed in this study could also be adapted to decrease inhibitor concentrations (lignin and acetic acid) if the dissolved hemicelluloses in the PHL were used to produce value-added products, e.g., ethanol, xylitol, based on the fermentation process. [Copyright &y& Elsevier]

Abstract: In this work, the flocculation concept was employed to recover the dissolved lignocellulosic materials of industrially produced pre-hydrolysis liquor (PHL) using two different molecular weights of chitosan. The analysis revealed the maximum turbidity of 1000NTU or 1900NTU via adding 2.2mg/g low molecular weight (LMW) or 1.7mg/g high molecular weight (HMW) chitosan to the PHL, respectively. Also, the maximum furfural removal of 55% or 50% was obtained by adding 0.7mg/g or 0.5mg/g LMW or HMW chitosan to the PHL, respectively. The maximum recovery of oligomeric sugars was 20% or 25% by adding 1.5 or 0.5mg/g LMW or HMW chitosan, while that of lignin was 40% or 35% by applying 2.2mg/g or 1.7mg/g LMW or HMW chitosan to the PHL, respectively. The removal of monomeric sugars and acetic acid was rather limited. The particle size and nitrogen analyses were also hired to characterize the properties of the formed complexes. [Copyright &y& Elsevier]

Abstract: Hemicelluloses in industrially produced pre-hydrolysis liquor (PHL) were precipitated with ethanol. These PHL-derived hemicelluloses (PHL-EH) and a commercial, pure birch wood xylan sample (powder form) (BWX) were bleached using chlorine dioxide (D0 and D1) and hydrogen peroxide (Ep) in the D0EpD1 sequence, and the chemical compositions, molecular weights and charge densities of the treated samples were assessed. When applied to high-yield pulp (HYP) at 50mg/g, 26 and 20mg/g of the bleached PHL-EH and BWX, respectively, were adsorbed without significantly affecting paper properties. These results suggest that semi-bleached hemicelluloses could be used to increase the basis weight of paper products. Furthermore, an integrated process was proposed that converts the kraft-based dissolving pulp production process into a biorefinery unit with dissolving pulp, bleached hemicelluloses and lignin as main products. [Copyright &y& Elsevier]

Abstract: In this paper, we proposed a new modification for an ethanol-based pulping process, which would consist of the pre-hydrolysis (pre-extraction) of wood chips for removing hemicelluloses; the ethanol extraction of pre-hydrolyzed wood chips for removing lignin; and the post purification of cellulose, leading to the production of pure cellulose. We also experimentally evaluated the separation of hemicelluloses from the pre-hydrolysis liquor (PHL) obtained from a pulp mill. To remove lignin from the PHL, it was acidified to a pH of 2, which resulted in 47% lignin precipitation. The lignin separation from the acidified PHL was further improved via adding polyethylene oxide and poly aluminum chloride or adding ethyl acetate. To recover the hemicelluloses from the acidified PHL, ethanol was added to the acidified PHL with a volumetric ratio of 4 to 1. The isolated lignin and hemicelluloses were characterized by a Fourier transform infrared spectroscopy (FTIR) and a gas permeation chromatography (GPC). [ABSTRACT FROM AUTHOR]

• The properties of technical lignin produced commercially were compared. • The challenges, opportunities, and future directions of lignin valorization were discussed. • Currently, products derived from technical lignin include adhesives, resins, and plasticizers. • The purity, molecular weight, and solubility affect the valorization strategies of technical lignin. Currently, the majority of chemicals are derived from petroleum-based feedstocks. In recent years, the valorization of lignin as feedstock for the production of alternative chemicals has attracted tremendous attention. Despite the renewed interest in the development of valorized lignin, few lignin-based chemicals have been produced at industrial scales and still, most of the lignin is used as an energy source. This review paper intends to discuss the technical obstacles and challenges in converting lignin moieties into value-added products effectively. Alternative modification routes have been discussed to produce lignin-based materials, while these routes strongly rely on the chemical structure of lignin. The propose of this review is to provide insight into the crucial role of the commercial lignin extraction processes on the properties of generated technical lignin and ultimately on its potential in reacting with other chemicals for inducing valorized lignin-derived materials for altered applications. Existing strategies for the functionalization of technical lignin are also summarized. The challenges, opportunities, and future direction regarding the biorefining of technical lignin are reviewed. [ABSTRACT FROM AUTHOR]

Abstract In this work, fly ash (FA) and polydiallyldimethylammonium chloride (PDADMAC) were utilized to treat the spent liquor (SL) of thermomechanical pulping (TMP) process in an effort to remove its lignocelluloses. The incorporation of PDADMAC into the system reduced the dosage of FA required for achieving acceptable lignocellulose removals. The maximum lignocellulose removals of 81%, 78%, 56%, 53% and 97% were achieved for lignin, hemicellulose, COD, BOD, and turbidity via treating SL with 100 g/L of FA at 25 °C for 60 min and subsequently treating with 100 mg/L of PDADMAC at 25 °C for 30 min, respectively. Comparing the two-step processes, FA pretreatment with PDADMAC post treatment was more effective than the two step process of PDADMAC pretreatment and FA post treatment. In this case, the FA pretreatment generated metal-organic complexes, and the addition of PDADMAC facilitated the formation of large flocs that could be separated from the system readily. A one stage process of combined PDADMAC and FA was less effective than the two-stage process of FA and PDADMAC treatments in removing lignocelluloses from SL. Graphical abstract Image 1 Highlights • Spent liquor of mechanical pulping process contains lignocelluloses. • Fly ash and cationic polymer were used for treating spent liquor. • A two-step treatment of fly ash and cationic polymer was very effective. • A one step treatment of fly ash or cationic polymer was not as effective. [ABSTRACT FROM AUTHOR]

In this work, pulp mill wastewater was treated with a novel polymer flocculant, which was synthesized through polymerizing (2-methacryloyloxyethyl) trimethyl ammonium chloride (DMC) and xylan. Xylan-DMC polymer removed 94.5% of turbidity, 61.7% of chemical oxygen demand (COD), 45.0% of lignin, 65.7% of sugar and 73.5% of biological oxygen demand (BOD) from the wastewater at the polymer concentration of 500 mg/L. The flocculation mechanism was fundamentally assessed with determining hydrodynamic size and chord length of flocs in the wastewater at different dosages of xylan-DMC polymer in the system. By adding polymers, the number of flocs with a small chord length (10–50 μm) decreased, while that with a large chord length (150–300 μm) increased, indicating the small particles agglomerated via bridging induced by the polymer. The sedimentation of formed flocs was quantitatively investigated by a vertical scan analyzer and the results depicted that the flocs could settle readily from the system. [ABSTRACT FROM AUTHOR]

Currently, the dissolved lignocelluloses in the spent liquor (SL) of a thermomechanical pulping process are treated in wastewater treatment systems and thus they are wasted. In this work, polydiallyldimethylammonium chloride (PDADMAC), with different molecular weights, was used for flocculating lignocelluloses of SL and thus isolating them from SL. Results showed that the maximum removals were 38% via treating SL with 100 mg/L of PDADMAC (with 1045 kg/mol molecular weight) at 25 °C for 30 min. The focused beam reflectance measurement of the flocculation process revealed that the chord length of the flocs with the maximum square weighted counts was increased from 70 to 100 μm and also their maximum square weighted counts was increased from 5 to 25 μm 2 /s. The flocs contained 60.71–74.41 wt% PDADMAC, the balance of lignocelluloses and the heating value of 24–25 MJ/kg. The high molecular PDADMAC generated flocs with more organics and a higher heating value. [ABSTRACT FROM AUTHOR]

In the present study, biomass based fly ash was used to remove lignocellulose from the spent liquor (SL) of a thermomechanical pulping process. The effect of independent parameters, e.g. time, temperature and dosage, on the performance of fly ash in treating SL was studied using an optimal design of response surface methodology. Under the optimal conditions (time 160 min, temperature 40 °C and fly ash dosage of 150 g/L), the removals of turbidity, COD and lignin were 75.1%, 61.3% and 63.5%, respectively. Furthermore, the sedimentation and drainability of fly ash/SL systems were investigated to separate fly ash from SL after the treatment. The sedimentation analysis showed that fly ash would not be settled from the system fast, but sedimentation was improved at a higher temperature of 60 °C than 30 °C. Interestingly, the drainability analysis showed that fly ash could be separated from the SL by filtration. Increasing the fly ash dosage from 120 g/L to 180 g/L reduced the average filtrate rate from 95 mL/min to 25 mL/min, and it was improved from 35 mL/min to 75 mL/min with the temperature increasing from 25 °C to 75 °C. Agitation intensity did not affect the filtration performance, but it increased the solid content of the filtrate from 0.30 wt.% to 0.35 wt.%. [ABSTRACT FROM AUTHOR]

Kraft lignin is currently combusted in the pulping process to produce heat. It can be extracted from the process and converted to value-added products, but its limited water solubility hampers its end use applications. The main objective of this study was to investigate the carboxymethylation of hardwood kraft lignin to produce an anionic water soluble product. The results showed that the optimal conditions for carboxymethylation were 1.5 M NaOH concentration, 3 mol/mol sodium chloroacetate (SCA)/lignin ratio, 40 °C, 4 h and 16.7 g/L lignin concentration. The produced lignin had a charge density and carboxylate group of 1.8 meq/g and 1.68 mmol/g, respectively. The carboxymethylated lignin was further characterized using thermogravimetric analyzer (TGA), Fourier Transform Infrared (FTIR) spectrophotometer, Nuclear magnetic resonance spectroscopy (H NMR) and elemental analyses. Moreover, the application of carboxymethylated lignin as a dispersant for a clay suspension was successfully analyzed by means of a photometric dispersion analyzer. [ABSTRACT FROM AUTHOR]

Hemicelluloses and lignin present in the spent liquor (SL) of neutral sulfite semichemical (NSSC) pulping process can potentially be converted into value-added products such as furfural, hydroxymethylfurfural, levulinic acid, phenols and adhesives. However, the direct conversion of hemicelluloses and lignin of SL into value-added products is uneconomical due to the dilute nature of the SL. To have a feasible downstream process for utilizing lignocelluloses of SL, the lignocelluloses should initially be separated from the SL. In this study, an adsorption process (via applying activated carbon) was considered for isolating the dissolved lignin and hemicelluloses from the SL of an NSSC pulping process. Under the optimal conditions of pH, SL/AC weight ratio, time and temperature of 5.7, 30, 360 min and 30 °C, the maximum lignin and hemicellulose adsorptions were 0.33 and 0.25 g/g on AC. The chemical oxygen demand (COD) and turbidity of the SL were decreased by 11% and 39%, respectively, as a result of lignocellulose adsorption on AC. Also, the incineration behavior of the SL-treated AC was studied with a thermo-gravimetric analysis (TGA). [Copyright &y& Elsevier]

Abstract: Hemicelluloses are the main organics dissolved in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process. In this study, two methods were employed to isolate the hemicelluloses from industrial PHL samples. The results showed that the hemicelluloses, precipitated in ethanol after an acidification step (Method 2), had a very high brightness (83% ISO) and low lignin content (0.44%) compared with the hemicelluloses obtained by the direct precipitation in ethanol without the acidification (Method 1), which had a brightness of 17.2% ISO and a lignin content of 5.67%. Furthermore, the hemicelluloses isolated via Method 2 were rendered cationic by using glycidyltrimethylammonium chloride (GTMAC), and the process parameters for the cationization reaction were studied, including the water content, reaction temperature and time, molar ratio of GTMAC/hemicelluloses, and the sodium hydroxide dosage. The optimized conditions for the cationic modification were 35% water content, 5% sodium hydroxide (both based on the mass of hemicelluloses), 1 (mol) GTMAC/hemicelluloses ratio, 65 °C, and 4 h reaction time. Finally, the cationic hemicelluloses were characterized and compared with unmodified hemicelluloses using the FT-IR and NMR analyses. [Copyright &y& Elsevier]

• PDADMAC was used as flocculant for lignosulfonate of pulping spent liquor. • The molecular weight of PDADMAC substantially affected the flocculation process. • Floc formation and sedimentation were studied in stirring and non-stirring systems. • The impact of salt and sugar on floc formation was studied. • The results showed promising approach for developing a cleaner pulping process. Lignosulfonate is a major component of the spent liquor of the sulfite pulping process. Flocculation has been used worldwide for isolating colloidal substances from solutions and thus can be adapted for separating lignosulfonate from the spent liquor. The adaptation of flocculation process would generate lignosulfonate-based flocs with a potential use as a value-added product and reduce the concentration of lignosulfonate in the spent liquor implying that this process can facilitate spent liquor's treatment operation. To evaluate the performance of this flocculation process, the interaction of lignosulfonate with polydiallyldimethylammonium chloride (PDADMAC) having various molecular weights was fundamentally studied in simulated systems under stirring and non-stirring environments. Focused beam reflectance measurement (FBRM) and vertical scan analyzer confirmed the fast kinetics of floc formation. A correlation was observed between the flocculation index of complexes and the molecular weight of PDADMAC. Increasing the PDADMAC's molecular weight led to the production of more flocs with larger sizes in the stirred system. However, larger flocs were weaker than smaller ones. Sedimentation analysis proved that the higher molecular weight PDADMAC generated more flocs with looser structures, but these flocs settled faster than the flocs produced by PDADMAC with smaller sizes. The results confirmed that the non-stirred system was more sensitive than stirring one to the dosage of PDADMAC. The flocculation efficiency was improved in the presence of salt while no change in the flocculation process was observed in the presence of sugar. The outcomes of this study suggest a promising alternative to isolate lignosulfoante from the spent liquor. [ABSTRACT FROM AUTHOR]

Currently, lignin is mainly produced in pulping processes, but it is considered as an under-utilized chemical since it is being mainly used as a fuel source. Lignin contains many hydroxyl groups that can participate in chemical reactions to produce value-added products. Flocculants, adsorbents, and dispersants have a wide range of applications in industry, but they are mainly oil-based chemicals and expensive. This paper reviews the pathways to produce water soluble lignin-based flocculants, adsorbents, and dispersants. It provides information on the recent progress in the possible use of these lignin-based flocculants, adsorbents, and dispersants. It also critically discusses the advantages and disadvantages of various approaches to produce such products. The challenges present in the production of lignin-based flocculants, adsorbents, and dispersants and possible scenarios to overcome these challenges for commercial use of these products in industry are discussed. [ABSTRACT FROM AUTHOR]