Kraft-based Dissolving Pulp Production Process Research Articles

Xylanase-assisted adsorption process for high purity sugar stream development from hydrolysis liquor of kraft-based dissolving pulp production process

This paper proposed a novel xylanase-assisted activated carbon process to produce a high-purity sugar stream from pre-hydrolysis liquid (PHL) of the kraft-based dissolving pulp production process. The results showed that the enzymatic hydrolysis could effectively improve the lignin removal and sugar purity at pH 5 and 50 °C. It was observed that the cleavage of lignin-carbohydrate complex (LCC) by enzyme led to more sugar and soluble lignin production in PHL. The main mechanisms involved are the reduced pore clog due to the lignin converted from colloidal to dissolved state at higher pH, lower sugar loss obtained by the reduction of polymerization degree of poly-sugars in PHL and also the removal of the lignin disconnected from the LCC. FTIR NMR, particle size, BET, and SEM analyses confirmed that the induced soluble lignin could be adsorbed by activated carbon effectively without blocking its pores, which improved the selectivity and productivity of activated carbon for removing lignin and generating higher purity sugar stream (97.5 wt. %). Based on the promising results and simplicity of the proposed operations, the introduced process may be attractive to the industry for generating high-purity sugars at an industrial scale.

A Novel and Effective Recyclable BiOCl/BiOBr Photocatalysis for Lignin Removal from Pre-Hydrolysis Liquor.

The presence of lignin hampers the utilization of hemicelluloses in the pre-hydrolysis liquor (PHL) from the kraft-based dissolving pulp production process. In this paper, a novel process for removing lignin from PHL was proposed by effectively recycling catalysts of BiOCl/BiOBr. During the whole process, BiOCl and BiOBr were not only adsorbents for removing lignin, but also photocatalysts for degrading lignin. The results showed that BiOCl and BiOBr treatments caused 36.3% and 33.9% lignin removal, respectively, at the optimized conditions, and the losses of hemicellulose-derived saccharides (HDS) were both 0.1%. The catalysts could be regenerated by simple photocatalytic treatment and obtain considerable CO and CO2. After 15 h of illumination, 49.9 μmol CO and 553.0 μmol CO2 were produced by BiOCl, and 38.7 μmol CO and 484.3 μmol CO2 were produced by BiOBr. Therefore, both BiOCl and BiOBr exhibit excellent adsorption and photocatalytic properties for lignin removal from pre-hydrolysis.

A process for purifying xylosugars of pre-hydrolysis liquor from kraft-based dissolving pulp production process

BackgroundIn the kraft-based dissolving pulp production process, pre-hydrolysis liquor (PHL) is produced, which contains hemicelluloses, lignin, furfural and acetic acid. PHL is currently burned in the recovery boiler of the kraft pulping process, but it can be utilized for the generation of high-valued products, such as xylitol and xylanase, via fermentation processes. However, some PHL constituents, e.g., furfural and lignin, are contaminants for fermentation processes and they must be eliminated for production of value-added products.ResultsIn this work, a process is introduced for removing contaminants of PHL. Ca(OH)2 treatment is the first step of this process, which removed 41.2% of lignin and negligible amount of sugars. In this step, a notable increase in the concentration of acetic acid was achieved (ranging from 6.2 to 11.7 g/L). In the second step, the implementation of adsorption using activated carbon (AC) at 1 wt% dosage led to additional 32% lignin and 5.9% xylosugar removals. In addition, laccase assisted activated carbon treatment led to further removal of lignin via accelerating lignin polymerization and adsorption on AC (i.e., removal from PHL). Overall, 90.7% of lignin, 100% of furfural, 5.7% of xylose, and 12% of xylan were removed from PHL, while the concentration of acetic acid became twofolds in the PHL.ConclusionsThis study reports an attractive process for purifying sugars and acetic acid of PHL. This process may be implemented for producing sugar-based value-added products from PHL. It also discusses the mechanism of Ca(OH)2 treatment, AC adsorption and laccase assisted activated carbon treatment for lignin removal.

Synthesizing Magnetic Support for Laccase Immobilization for the Purification of Pre-hydrolysis Liquor

Laccase immobilization is a promising method for the purification of pre-hydrolysis liquor (PHL) for large-scale applications based on recyclability and reusability. In this work, magnetic supports made of Fe3O4/SiO2 were synthesized by a sol-gel method and coated with silica. Then, glutaraldehyde was used as a linker between the support and laccase for immobilization. The immobilized laccase was evaluated by purifying the PHL from a kraft-based dissolving pulp production process. The results showed that the optimal immobilization conditions were a molar TEOS/Fe3O4 ratio of 0.6, glutaraldehyde concentration of 6%, laccase concentration of 0.4 mL/mg, and time of 3 h, which led to 71% laccase immobilization. The concentration of total sugar in the PHL increased from 71% to 75%, while the lignin content decreased from 15% to 10% after the immobilized laccase treatment. The separation advantage of the magnetic support enhanced the utility of the laccase.

Acidification of prehydrolysis liquor and spent liquor of neutral sulfite semichemical pulping process

Acidification has been commercialized for producing kraft lignin from black liquor of kraft pulping process. This work intended to evaluate the effectiveness of acidification in extracting lignocelluloses from the spent liquor of neutral sulfite semichemical pulping (NSSC) process and from prehydrolysis liquor (PHL) of kraft-based dissolving pulp production process. The results showed that the NSSC and PHL spent liquors had some lignin-carbohydrate complexes (LCC), and that the square weighted counts of particles with a chord length of 50–150μm in the spent liquors were significantly increased as pH dropped to 1.5. Interestingly, the acidification reduced the lignosulfonate/lignin content of NSSC and PHL by 13% or 20%, while dropped their oligosugars content by 75% and 38%, respectively. On a dry basis, the precipitates had more carbon, hydrogen and a high heating value of 18–22MJ/kg, but less oxygen, than spent liquors. The precipitates of PHL could be used as fuel.

Improvement of Furfural Production from Concentrated PreHydrolysis Liquor (PHL) of a Kraft-Based Hardwood Dissolving Pulp Production Process

Hemicelluloses present in the prehydrolysis liquor (PHL) of the hardwood kraft-based dissolving pulp production process can be utilized in the production of furfural, which is an important renewable, non-petroleum-based platform chemical. A lower furfural yield was observed from the concentrated sugars in PHL in acetic-acid-catalyzed systems. The reaction rate of sugar consumption and furfural destruction in PHL was higher than those of model xylan and xylose systems, which may be due to the side-reactions of lignin with sugars and carbonization of oligomeric sugars. In order to minimize these side-reactions, a steam-stripping method of generated furfural was adopted. The results showed that the method was effective in increasing the furfural yield (41.5%) from the concentrated PHL.

Cationic Hemicellulose As a Product of Dissolving Pulp Based Biorefinery

In the present technology practiced, hemicelluloses dissolved in the prehydrolysis liquor (PHL) of the kraft-based dissolving pulp production process is mixed with black liquor and incinerated in the kraft mill. In this study, solvent precipitation was used for isolating lignin and hemicelluloses from PHL. The results showed that acetone was a more effective and selective solvent than ethanol to isolate hemicelluloses. Furthermore, the cationization of hemicelluloses with glycidyl-trimethylammonium chloride resulted in cationic hemicelluloses with the charge density of 2.3 meq/g and molecular weight of 6330 g/mol. Based on these results, an integrated dissolving pulp-based biorefining process was proposed that would produce dissolving pulp and cationic hemicellulose as main products.

Purification of Hemicelluloses in Pre-Hydrolysis Liquor of Kraft-Based Dissolving Pulp Production Process Using Activated Carbon and Ion-Exchange Resin Adsorption Followed by Nanofiltration

Purification of Hemicelluloses in Pre-Hydrolysis Liquor of Kraft-Based Dissolving Pulp Production Process Using Activated Carbon and Ion-Exchange Resin Adsorption Followed by Nanofiltration

Lignin removal enhancement from prehydrolysis liquor of kraft-based dissolving pulp production by laccase-induced polymerization.

Lignin removal is essential for value-added utilization of hemicelluloses and acetic acid present in the prehydrolysis liquor (PHL) of a kraft-based hardwood dissolving pulp production. In this paper, a novel process concept, consisting of laccase-induced lignin polymerization, followed by filtration/flocculation, was developed to enhance the lignin removal. The results showed that the lignin removal increased from 11% to 46-61% at laccase concentration of 1-4 U mL(-1). The GPC results showed that the molecular weight of the lignin from the laccase treated PHL was increased by 160% in comparison with the original one. The subsequent flocculation using singular Poly-DADMAC system or dual polymer system of Poly-DADMAC/CPAM can further remove 10-15% lignin. The concentrations of hemicelluloses and acetic acid were negligibly affected during the laccase treatment, while flocculation caused 12-15% of total sugar loss. Additionally, the process incorporates this new concept into the kraft-based dissolving pulp production process was proposed.

Simulation analysis of producing xylitol from hemicelluloses of pre-hydrolysis liquor

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 1600kg/h gypsum can be produced from 41,670kg/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.

A process for enhancing the accessibility and reactivity of hardwood kraft-based dissolving pulp for viscose rayon production by cellulase treatment

The commercial pre-hydrolysis kraft-based dissolving pulp production process can be a typical example for the demonstration/implementation of the integrated forest biorefinery concept. In this study, the concept of cellulase treatment of this dissolving pulp for enhancement of accessibility/reactivity in terms of viscose rayon production was demonstrated. The cellulase treatment resulted in the formation of additional openings/surface areas in the fiber structure via the possible action of "etching". As a result, the pore volume of pulp fibers increased, which led to the increase in the accessibility to xanthation, and thus Fock reactivity. Results showed that the cellulase treatment was effective in increasing the Fock reactivity, at a cellulase dosage of 2u/g (based on the dry weight of pulp), the Fock reactivity increased from 47.67% to 79.9%. The adoption of cellulase treatment to hardwood kraft-based dissolving pulp can provide an efficient approach for enhancing its performance in the commercial viscose-rayon process.

Using Neutral Sulfite Semichemical Pulp to Adsorb Lignocelluloses from Prehydrolysis Liquor of the Kraft-based Dissolving Pulp Process

The effective use of prehydrolysis liquor (PHL), from the kraft-based dissolving pulp production process, may fit into the concept of integrated forest biorefinery (IFBR). The dissolved organics in the PHL include hemicelluloses, lignin, acetic acid, furfural and extractives. Adsorption of hemicelluloses and lignin onto the neutral sulphite semichemical (NSSC) pulp fibres may be a potential method of utilizing the dissolved organics in the PHL. The principal goal of this work was to study the adsorption of lignocelluloses of PHL onto the NSSC pulp fibres. In addition to the typical process variables, the effect of using polymers, such as coagulant and flocculant, on increasing the adsorption, was investigated. The effects of time and temperature were examined. It was shown that adsorption reached its maximum almost in 1 h. Also, it was demonstrated that a higher temperature improved the adsorption. Furthermore, the use of cationic polymers, such as polydiallyl dimethyl ammonium chloride (PDADMAC), a coagulant (Nalkat 2020) and flocculant (Ultimer 1470), could enhance the adsorption of lignocelluloses from PHL onto NSSC pulp fibres. The maximum lignin and hemicelluloses adsorption was 160 mg/g and 320 mg/g onto pulp (58% and 22% removal from PHL), respectively. It is concluded that lignocelluloses of the PHL can be adsorbed onto NSSC pulp fibres so as to work as papermaking additives; and typical polymers, such as coagulant and flocculant, can be used to enhance the lignocelluloses adsorption. Keywords: Adsorption, Lignocelluloses, Lignin, Hemicelluloses, Coagulant, Flocculant, NSSC pulp, Pre-hydrolysis liquor, Biorefinery.

Structural Characterization of Pre-hydrolysis Liquor Lignin and Its Comparison with Other Technical Lignins

The kraft-based dissolving pulp production process can be a model for the forest biorefinery concept. The objective of this study is to characterize the dissolved lignin present in the pre-hydrolysis liquor (PHL) to facilitate its subsequent use following the forest biorefinery concept. In this work, lignin was isolated from PHL by acidification using dilute H2SO4, followed by purification through dissolution in a dioxane solution (9:1) and re-precipitation with diethyl ether. The characteristics of PHL lignin were compared with those of the dioxane lignin, acetic acid (AA) lignin and ethanosolv (EL) lignin isolated from the same mixed hardwood (maple, poplar and birch wood chips, in a ratio of 7:2:1), which is the raw material used for dissolving pulp production. The obtained lignin samples were characterized by UV, FTIR, 1H-NMR spectroscopy, molecular weight determination, elemental and methoxyl analyses. The results showed that the absorptivity of dioxane lignin at 276 nm was 10.0 l g-1cm-1, while that of PHL lignin was 17.2 l g-1cm-1. The presence of condensed structures in the PHL lignin was also observed in the FTIR spectrum (strong bands at 870 and 890 cm-1), which was also present in the AA and EL lignins. The lignin isolated from PHL had a lower molecular weight and methoxyl group per C9 unit, in comparison with other lignin samples. 1H-NMR analysis indicated a significant increase in the phenolic hydroxyl content in the PHL lignin, caused by cleavage of aryl-ether bonds during the prehydrolysis. Keywords: PHL lignin, Dissolving pulp, Kraft pulping, Characteristics, Phenolic hydroxyl group, Molecular weight, Methoxyl group.

Recovery of acetic acid from pre-hydrolysis liquor of hardwood kraft-based dissolving pulp production process by reactive extraction with triisooctylamine

Acetic acid was one of the main compositions of the pre-hydrolysis liquor (PHL), which was recovered by reactive extraction with triisooctylamine (TIOA) diluted with decanol. Dilution of TIOA played an important role in extracting acetic acid from the PHL. The recovery of acetic acid from the PHL by TIOA was increased from 10.34% to 66.60% with the dilution of TIOA to 20% by decanol at the HAc to TIOA molar ratio of 1, consequently, the equilibrium distribution coefficient KD increased. The effects of time, temperature and pH on the extraction process were also studied. The extraction process was very fast. The acetic acid extraction decreased from 65.13% to 57.34% with the rise of temperature to 50°C from 20°C. A higher pH increased the dissociation of acetic acid, as a result, decreased acetic acid extraction. The hemicelluloses in the PHL were unaffected on the extraction process of acetic acid.

Viscosity of Prehydrolysis Liquor of a Hardwood Kraft-Based Dissolving Pulp Production Process

In this study, experimental viscosity results of hardwood prehydrolysis liquor (PHL) from the kraft-based dissolving pulp production process were obtained and used to develop empirical models describing the effect of temperature, solid content, the interaction between solute and solvent, and the concentration of lignin and hemicelluloses. The concentration, molar mass, and molecular weight of lignin and polysaccharide of PHL, all are the factors that affect the rheological behavior of the PHL. The results showed that, on the one side, Zaman and Fricke’s model gave better fitting when the viscosity is lower, on the other hand, a much better fitting of the Moosavifar’s model could be obtained by taking interaction between solute and solvent, solids content, concentration of lignin and hemicelluloses into account when the viscosity is higher, because of the interaction between solute lignin/hemicelluloses and solvent water, and the aggregation of lignin with itself, hemicelluloses with itself, and lignin with hemicelluloses. Consequently, using two different correlations in covering different viscosity value regions (η > 2 mPa s or η < 2 mPa s) of PHL led to better fitting of the data than those using just one single correlation.

Furfural formation from the pre-hydrolysis liquor of a hardwood kraft-based dissolving pulp production process

This study aimed to produce furfural from the PHL. Results showed best furfural yield of 32.8% and the furfural selectivity of 37.7% in the monophase system (170°C, 100min), while they were 60.1% and 69.8%, respectively in the biphase system. The lower furfural selectivity in the monophase system was explained by more side reactions, such as fragmentation, condensation reactions, resinification and others. Model compounds such as: xylose, furfural, syringaldehyde, were used to confirm/identify these side reactions. The addition of dilute sulfuric acid/acetic acid in the system under the same conditions decreased the recovery of furfural. The addition of syringaldehyde into the PHL also led to a decrease in the furfural yield, supporting the conclusion that lignin structures in the PHL may also be involved in the side reactions, thus decreasing the furfural yield.

Acid Hydrolysis of Prehydrolysis Liquor Produced from the Kraft-Based Dissolving Pulp Production Process

Acid hydrolysis is an essential step in converting polysaccharides to monosaccharides for the production of fuels and chemicals. The prehydrolysis liquor (PHL) from the kraft-based dissolving pulp production process contains mainly oligosugars with a minor amount of monosugars. In this study, the influence of process conditions, including the sulfuric acid concentration, temperature, and time on the PHL hydrolysis was thoroughly investigated in order to get maximum monosugar concentration with minimal degradation of sugars. The maximum monosugar concentration was obtained at 130 °C for 20 min when the hydrolysis was carried out with 1.78% H2SO4. A high acid concentration (3.33%) increased furfural formation and decreased the monosugar concentration. Acetic acid is generated from the acetyl groups bound to the dissolved hemicelluloses, resulting in a significant increase in the acetic acid concentration in the PHL.

A combined process of activated carbon adsorption, ion exchange resin treatment and membrane concentration for recovery of dissolved organics in pre-hydrolysis liquor of the kraft-based dissolving pulp production process

To recover dissolved organics in pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process, a new combined process concept of sequential steps of activated carbon adsorption, ion exchange resin treatment, and membrane concentration, was proposed. The removal of lignin in the PHL was achieved in the activated carbon adsorption step, which also facilitates the subsequent operations, such as the membrane filtration and ion exchange resin treatment. The ion exchange resin treatment resulted in the removal/concentration of acetic acid, which opens the door for acetic acid recovery. The membrane filtration is to recover/concentrate the dissolved sugars. The combined process resulted in the production of PHL-based concentrate with relatively high concentration of hemicellulosic sugars, i.e., 22.13%.

A process for isolating lignin of pre-hydrolysis liquor of kraft pulping process based on surfactant and calcium oxide treatments

Hemicelluloses present in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process can potentially be converted into value-added products such as ethanol and xylitol. However, the lignin present in the PHL is an inhibitor of fermentation processes, and thus should be isolated from the PHL prior to fermentation. In this study, a new process was proposed for isolating the lignin of PHL by overliming and surfactant treatment. The fundamentals associated with the interactions of lignin, surfactants and calcium hydroxide were discussed. In the experimental part of this work, three different cationic surfactants were applied to industrially produced PHL, and the most effective one, dodecyltrimethyl ammonium chloride (DTAC), was selected for further analysis. The optimum dosage of 0.3% DTAC/PHL was identified via turbidity and particle size analyses. Additionally, overliming via CaO treatment resulted in removing 36.1% lignin and 23% hemicelluloses. Overliming followed by the DTAC treatment was more effective than the DTAC treatment followed by overliming in removing lignin. In the former, the maximum removals of 43.6% lignin and 27% hemicelluloses were obtained. The formation of lignocelluloses/surfactant complexes was confirmed by means of a Fourier transform infrared spectroscopy (FTIR) and thermo gravimetric analyzer (TGA).

An integrated process for removing the inhibitors of the prehydrolysis liquor of kraft‐based dissolving pulp process via cationic polymer treatment

The prehydrolysis liquor (PHL) of the kraft-based dissolving pulp production process contains various amounts of hemicelluloses that can be utilized in the production of value-added products. In this work, a new process was proposed for removing the inhibitors of PHL via employing a flocculation concept to facilitate the utilization of hemicelluloses. Lignin, lignocelluloses/cationic polymer complexes, and possibly ethanol are the main products of this process. This process has been experimentally evaluated with an industrially produced PHL and cationic polymers. The results showed that 16% of lignin, 19% of acetic acid, 43% of furfural, and insignificant amount of sugars were removed from PHL via pretreating PHL with acid and lime at pH 7. Furthermore, by adding 0.4-0.5 mg g(-1) polydiallyldimethylammonium chloride (PDADMAC) or chitosan to the pretreated PHL, 12-14% acetic acid, 40-50% furfural, 5-6% monomeric sugars, and 25% oligomeric sugars were removed from the PHL. The complexes made from these components may be applied as organic fillers in various industries. Alternatively, by adding 1.2 or 1.4 mg g(-1) PDADMAC or chitosan to the pretreated PHL, 30 or 35% of lignin was removed, respectively, which induced complexes that could be used as a fuel source. The composition of the complexes formed was also determined in this work.