Kraft-based Dissolving Pulp Production 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.

Optimization of Lignin Recovery from the Pre-Hydrolysate of Kraft-Based Dissolving Pulp Production Processes

A pre-hydrolysate is an aqueous stream obtained during the production of hardwood kraft dissolving pulp. It is rich in sugars and contains dissolved organic matters. The purpose of this study is to investigate the optimization of lignin recovery from wood pre-hydrolysates and to characterize the extracted lignin. The optimal conditions for lignin extraction have been determined to be (a) a filtration temperature of 40 °C, (b) a sulfuric acid concentration of 8.5 kg·m−3, and (c) a coagulation time of 180 min. Using these conditions, high filtration rates have been obtained and the extracted lignin has a low content of impurities (8.3%), a low molecular weight (1270 Da), and a very low polydispersity (Mw/Mn = 1.22). Compared to kraft lignin, the pre-hydrolysate lignin has a much lower molecular weight and could be a potential candidate for niche applications. A high lignin recovery rate is possible (52% of the total lignin content in the pre-hydrolysate).

Highly efficient lignin removal from the waste liquor of chemical pulping with an integrated polyaluminium chloride-assisted acidification/activated carbon adsorption process

To separate and utilize the saccharides from the waste liquor is an essential subject with significant economic and environmental benefits for wood bio-refinery of pre-hydrolysis kraft-based dissolving pulp production processing. However, the presence of lignin-derived substances makes this application still a quite challenging problem. In this paper, a novel process is proposed by integrating the polyaluminium chloride (PAC) -assisted acidification and activated carbon adsorption concepts to enhance the lignin removal from the premixed liquor of prehydrolysate and black liquor. The results show that 95.4% of acid-insoluble lignin (from 23.8 to 1.1 g/L) was removed by PAC-assisted acidification at a mild acidification of pH to 6.0 with the condition assisted by PAC concentration of 300 mg/L. This can dramatically reduce the acid consumption compared to traditional acidification when pH around 3.0 was required during the acidification of waste liquor to obtain higher lignin removal. After the removal of acid-insoluble lignin, 70.2% of acid-soluble lignin (from 10.4 to 3.1 g/L) can be removed by the treatment of optimized adsorption of activated carbon. Meanwhile, it was found that the presence of acid-insoluble lignin would deposit and block the pore structure on the activated carbon, thus affecting the further adsorption of acid-soluble lignin on the activated carbon. When the concentration of acid-insoluble lignin was over 1.5 g/L, this negative effect became very obvious, which was confirmed by the analysis of specific surface area and the observation of scanning electron microscope. This is an important, if not major, finding that will offer valuable reference on the optimization of acid soluble lignin removal by adsorption treatment in the future.

Selective removal of soluble lignin from pre-hydrolysis liquor of bamboo willow dissolving pulp

The selective removal of lignin can be a profitable value-added utilization for the pre-hydrolysis liquor (PHL) produced during kraft-based dissolving pulp production. In this work, the soluble lignin was removed from PHL using CaCl2, Al2(SO4)3, cationic polyacrylamide (CPAM), and a CPAM/Al2(SO4)3 dual-system treatment. The results of zeta potential recording revealed that 8.86% of soluble lignin was removed by CaCl2 treatment through charge neutralization and adsorption, and 13.1% soluble lignin was removed by CPAM through charge neutralization and flocculation bridging. The optimal dosages of CaCl2, CPAM, Al2(SO4)3, and CPAM/Al2(SO4)3 dual-system treatments were 2.0 wt%, 30 ppm, 300 ppm, and 60/300 ppm respectively, at which the soluble lignin removals were 8.09%, 9.24%, 18.3%, and 25.0%, respectively. Additionally, the total sugar loss by the CPAM/Al2(SO4)3 dual-system treatment was higher than that by other individual systems; however, the soluble lignin selective removal by the CaCl2 treatment was the highest, at over 80%.

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.

Recycling immobilized laccase for lignin removal from prehydrolysis liquor of kraft-based dissolving pulp

Laccase treatment of prehydrolysis liquor (PHL) produced in a kraft-based dissolving pulp production may allow for purification of its hemicelluloses. In this work, a magnetic support of magnetic silica particle (Fe3O4/SiO2) was synthesized to immobilize laccase from Trametes versicolor. The laccase treatment led to increases in the molecular weight of lignin, which facilitated its removal from PHL. The results showed that laccase activity remained at 65% after seven successive recycle runs. The combination of 10 wt.% fresh immobilized laccase and 90 wt.% recycled immobilized laccase at the overall dosage of 1 U/mL led to 34% lignin removal, irrespective of the recycling runs. The laccase treatment caused 13 wt.% sugar losses from PHL. Based on the results, a process for removing lignin from PHL was proposed based on the application and recovery of an immobilized laccase system.

Wet oxidation of activated carbon for enhanced adsorptive removal of lignin from the prehydrolysis liquor of kraft-based dissolving pulp production in an integrated forest biorefinery

Prehydrolysis is a key step for the production of kraft-based dissolving pulp. The pre-hydrolysis liquor mainly contains hemicellulosic components. Lignin can also be released into the pre-hydrolysis liquor, which hinders the purification and utilization of these hemicellulosic components. In this work, wet oxidation of activated carbon with nitric acid was employed to enhance the adsorptive removal of lignin from the pre-hydrolysis liquor. Under mild oxidation conditions (2% nitric acid solution), the oxidization of activated carbon resulted in significant enhancement of lignin removal. Adsorption isotherms showed that the specific surface area and the amount of carboxyl groups were affected by the oxidation treatment. The selective removal of lignin fitted well with the pseudo-second order kinetics model.

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.

Fractionation and characterization of saccharides and lignin components in wood prehydrolysis liquor from dissolving pulp production

Saccharides and lignin components in prehydrolysis liquor (PHL) from kraft-based dissolving pulp production was characterized after being fractionated using membrane filtration. The results showed that the membrane filtration provided a method for organics fractionation with considerable recovery rate, but exhibited some disadvantages. Besides the limited ability in purifying oligosaccharides (OS) due to the overlaps of molecular weight distribution with lignin components, the membrane filtration could not improve the homogeneity of OS as indicated by the analysis of chemical compositions and the degree of polymerization (DP), which may be ascribed to the linear conformation of OS. The characterization of lignin components indicated a great potential for polymer industry because of the remarkable content of phenolic hydroxyl groups (PhOH), especially for low molecular weight (LMW) fraction. It was concluded the organics in PHL provided streams of value-added chemicals. However, the practical significance thereof can be realized and maximized only when they are successfully and completely fractionated.

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.

Modeling laccase-induced lignin removal in prehydrolysis liquor from kraft-based dissolving pulp production

Laccase treatment is a promising approach to remove lignin from prehydrolysis liquor (PHL) for value added utilization of hemicellulose rich waste streams. Modeling the lignin removal process is of practical interest for prediction and control of laccase treatment of PHL. The present study focused on the lignin removal through variation of laccase charge and treatment time. Results showed that the lignin removal may be divided into two phases, i.e. a fast initial phase followed by a second slow phase. A kinetic model based on the experimental results was developed, which can be used to predict the lignin removal of PHL during the laccase treatment.

Production of furfural from waste aqueous hemicellulose solution of hardwood over ZSM-5 zeolite

This study aimed to produce furfural from waste aqueous hemicellulose solution of a hardwood kraft-based dissolving pulp production processing in a green method. The maximum furfural yield of 82.4% and the xylose conversion of 96.8% were achieved at 463K, 1.0g ZSM-5, 1.05g NaCl and organic solvent-to-aqueous phase ratio of 30:15 (V/V) for 3h. The furfural yield was just 51.5% when the same concentration of pure xylose solution was used. Under the optimized condition, furfural yield was still up to 67.1% even after the fifth reused of catalyst. Catalyst recycling study showed that ZSM-5 has a certain stability and can be efficiently reused.

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.

Recovery of Acetic Acid from Prehydrolysis Liquor of Kraft Hardwood Dissolving Pulp using Ion-exchange Resin

The growing demand for rayon and cellulosic products has resulted in the conversion of a number of kraft pulp mills into dissolving pulp mills in recent years. In fact, kraft-based dissolving pulp production fits well into the concept of an integrated forest biorefinery, in particular, the utilization of dissolved organics in the pre-hydrolysis liquor (PHL) for bio-materials and bio-energy purposes. In this study, the recovery of acetic acid, the second major component in the PHL of the kraft-based hardwood dissolving pulp production process, was investigated using amine-based resin adsorption. Activated carbon (AC) adsorption was adopted as the first step to remove the lignin, and six AC samples were evaluated for this purpose. Among them, CR325 W-Ultra Powder AC showed the best result and removed about 90% of lignin with a minimal loss of hemicellulosic sugars and acetic acid from PHL at a ratio of 1:20 (AC:PHL). Subsequently, the adsorption of acetic acid from AC-treated PHL (TPHL) was studied on tertiary and quaternary amine-based resins. The tertiary amine resin demonstrated better adsorption efficiency. Desorption of the adsorbed acetic acid from the amine resin using sodium hydroxide solution was also studied, and the results showed that 66 to 84% acetic acid desorption occurred using a 4% NaOH solution.

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.