A combined acidification/PEO flocculation process to improve the lignin removal from the pre-hydrolysis liquor of kraft-based dissolving pulp production process

The presence of lignin impairs the utilization of the hemicelluloses dissolved in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process. In this paper, a novel process was developed by combining the acidification and poly ethylene oxide (PEO) flocculation concepts to improve the lignin removal. The results showed that the lignin removal was improved by the addition of PEO to the acidified PHL, particularly at a low pH of 1.5. The main mechanisms involved are the lignin/PEO complex formation and the bridging of the formed complexes. This hypothesis was supported by the turbidity, FTIR and particle size measurements. Interestingly, the hemicelluloses removal from the acidification/PEO flocculation was marginal, which would be beneficial for the down-stream ethanol production from the PHL. Additionally, a process flow diagram was proposed that incorporates this new concept into the existing configuration of kraft-based dissolving pulp production process.     

Recovery of lignocelluloses from pre-hydrolysis liquor in the lime kiln of kraft-based dissolving pulp production process by adsorption to lime mud

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.     

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. © 2012 American Institute of Chemical Engineers Biotechnol. Prog., 28: 998–1004, 2012     

Two stages of treatments for upgrading bleached softwood paper grade pulp to dissolving pulp for viscose production

To convert bleached softwood paper grade pulp into dissolving pulp for viscose application, two stages of treatments consisting of enzymatic treatment and alkaline peroxide treatment were investigated. It was found that high reactivity (about 80%) of pulp could be achieved by endoglucanases (EG)-rich industrial cellulase treatment, and the α-cellulose content as well as the viscosity of enzymatically treated pulp can be further adjusted by the alkaline peroxide treatment with certain dosages of NaOH and H₂O₂ to finally meet the quality requirements of dissolving pulp. The resulting pulp with 68.7% of reactivity, 92.1% of α-cellulose content, and 506.9 mL/g of pulp viscosity could be obtained after the two stages of treatments. The appropriate dosage of EG-rich cellulase was 300 IU/g bone dry pulp in the stage of enzymatic treatment, while the suitable dosages of NaOH and H₂O₂ were 9 wt% and 1 wt%, respectively, in the stage of alkaline peroxide treatment.     

Fruit softening in banana: correlation among stress-relaxation parameters, cell wall components and starch during ripening

Bananas, Musa (AAA group, Cavendish subgroup) 'Giant Cavendish', were ripened in a biotron at 25°C with ethylene during 4 days. Changes in mechanical properties of pulp were detected by a stress-relaxation technique. The decrease in T₀, the parameter for minimum stress-relaxation time, began between day 0.5 and 1, while the decrease in initial stress began between day 0 and 0.5, suggesting that the decrease in elasticity and viscosity of pulp is a crucial physical event of pulp softening. Cellulose and moisture contents were about 3 and 780 mg (g fresh weight)⁻¹, respectively, which were unchanged during ripening. The decrease in starch content of cell materials and in uronic acid content of the pectic polysaccharides of the cell walls began between day 0.5 and 1. As regards the sugar composition of the hemicellulose fraction, decreases in arabinose, mannose and galactose contents began between day 0 and 0.5. The results show that the partial decrease in hemicelluloses preceded the breakdown of starch and suggest that the coordinated degradation of pectic and hemicellulosic polysaccharides and starch is the main cause for the pulp softening process.     

Bleaching of soda pulp of fibres of Musa textilis nee (abaca) with peracetic acid

In this work, we studied the influence of operational variables in the bleaching of soda pulp of Musa textilis nee (abaca) [viz. temperature (55-85 degrees C), bleaching time (30-150 min) and peracetic acid concentration oven dry pulp (0.5-4.5%)] on the kappa number and viscosity of the bleached pulp, as well as on the breaking length, burst index and brightness of paper sheets made from it. For this purpose, we used a central composite factorial design in order to identify the optimum operating conditions. In this way equations relating the dependent variables to the operational variables of the bleaching process were derived. These equations reproduce the dependent variables with errors less than 12% for all, except the viscosity which was predicted with errors less than 18%. Obtaining bleached pulp with the highest possible viscosity (1519 ml/g), and paper sheets with the maximum possible breaking length (6547 m) and burst index (5.00 kN/g), entails using a temperature of 55 degrees C, a peracetic acid concentration of 4.5% and a bleaching time of 150 min. This provides a brightness of 79.90%, which is only 6.53% lower than the maximum possible value (85.48%).     

Nitrification, denitrification, and dechlorination in bleached kraft pulp mill wastewater

This study deals with combining the biologi cal removal of organic halogens with the removal of nitrogen from bleached kraft pulp mill wastewater in fluidized-bed reactors under nitrifying and denitrifying conditions. Untreated and biotreated bleached kraft pulp mill wastewaters had no detrimental effect on nitrification or denitrification. The nitrifying biofilm reactor, pregrown on synthetic inorganic feed with ammonia, removed without a lag phase adsorbable organic halogens [7.2 mg Cl (g biomass volatile solids)⁻¹day⁻¹] from bleached kraft pulp mill wastewater and selected chlorophenols from synthetic wastewater. Electron microscopical examination of the biofilm showed that bacteria, morphologically similar to the nitrifying species Nitrosomonas or Nitrobacter, and Nitrosospira were dominant. The denitrifying fluidized-bed reactor, pregrown on nitrate and methanol, denitrified without a lag phase bleached kraft pulp mill wastewater. Under denitrifying conditions, 35% of the total organic carbon content of untreated bleached kraft pulp mill waste water was removed. The reducing power delivered by untreated bleached kraft pulp mill wastewater for denitrification was 2 mmol electrons/mmol carbon mineralized. Dechlorination under denitrifying conditions was negligible. Received: 21 November 1996 / Received revision: 27 January 1997 / Accepted: 1 February 1997     

Biobleaching of wheat straw-rich soda pulp with alkalophilic laccase from gamma-proteobacterium JB: optimization of process parameters using response surface methodology

An alkalophilic laccase from gamma-proteobacterium JB was applied to wheat straw-rich soda pulp to check its bleaching potential by using response surface methodology based on central composite design. The design was employed by selecting laccase units, ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) concentration and pH as model factors. The results of second order factorial design experiments showed that all three independent variables had significant effect on brightness and kappa number of laccase-treated pulp. Optimum conditions for biobleaching of pulp with laccase preparation (specific activity, 65 nkat mg(-1) protein) were 20 nkat g(-1) of pulp, 2mM ABTS and pH 8.0 which enhanced brightness by 5.89% and reduced kappa number by 21.1% within 4h of incubation at 55 degrees C, without further alkaline extraction of pulp. Tear index (8%) and burst index (18%) also improved for laccase-treated pulp as compared to control raw pulp. Treatment of chemically (CEH1H2) bleached pulp with laccase showed significant effect on release of chromophores, hydrophobic and reducing compounds. Laccase-prebleaching of raw pulp reduced the use of hypochlorite by 10% to achieve brightness of resultant hand sheets similar to the fully chemically bleached pulp.     

Combination of steam explosion and laccase-mediator treatments prior to Eucalyptus globulus kraft pulping

The effect of a pretreatment consisting of steam explosion (SE) followed by a laccase mediator system (LMS) stage on Eucalyptus globulus kraft pulping has been evaluated and compared with fungal pretreatments. Pretreatment with SE and LMS was more efficient than pretreatments using Pycnoporus sanguineus and Trametes sp. I-62. Steam explosion not only improved the enzyme penetration into the wood chips and shortened the pulping process by 60%, but also extracted around 50% of the hemicelluloses which could be converted into value-added products. The optimal conditions for the LMS treatment were 3 h, 3 UA/g and 40 °C. Compared to SE, the SE/LMS treatment yielded an increase in delignification of 13.9% without affecting pulp properties, provided a similar screened kraft yield, and reduced consumption of chemical reagents Na₂S and NaOH by 11.5% and 6.3%, respectively. Therefore, SE/LMS is a promising pretreatment for converting the pulp mill into a forest bio-refinery.     

Preparation of superabsorbent cellulosic hydrogels

In this work, milled softwood (SW) bleached kraft fibers were crosslinked by esterification with poly(vinyl methyl ether-co-maleic acid) (PVMEMA) and polyethylene glycol (PEG). The effects of fiber length, crosslinking reaction time, and dosage of PVMEMA on water absorption and retention value (WAARV) for the crosslinked fibers were determined. The results show that as the softwood fiber length is mechanically decreased from 2.41 to 0.50 mm and employing a weight ratio of fiber to polymers equivalent to 1.00:1.28 the WAARV increased from 86.50 to 189.20 g/g. Analysis of the crosslinked fibers by SEM and light microscope indicated that the polymers and fibers form a crosslinked fibrous matrix. FT-IR spectroscopy was employed to detect the ester linkage between PVMEMA and PEG/SW kraft pulp fibers. The results suggested that the ester crosslinked pulps exhibit excellent water absorbent properties and have the potential of utilizing milled bleached SW kraft fibers, such as refiner dust or pulp fines, for novel water absorbent applications.     

Cross-sectional analysis of the polysaccharide composition in cellulosic fiber materials by enzymatic peeling/high-performance capillary zone electrophoresis

A combined enzymatic, chemical, and analytical approach was used to determine the cross-sectional carbohydrate composition in cellulosic fibers. The outer surface of cellulosic fibers was enzymatically removed layer-by-layer with precise quantitative control, and the monosaccharides in the peelings were subsequently analyzed by high-performance capillary electrophoresis (HPCE) after precolumn derivatization with a UV label. This method was applied to dissolving pulps and regenerated cellulose fibers, with special emphasis on the cross-sectional distribution of hemicelluloses. Commercially available enzyme solutions were used, resulting in a reproducible peeling. Significant differences were found in the hemicellulose distribution across the fiber of different dissolving pulps, dependent on both natural source (beech or spruce) and preparation process (acidic sulfite cook or prehydrolysis kraft cook). Among the dissolving pulps, beech prehydrolysis kraft pulp showed the highest enrichment of surface xylan. Similar, albeit smaller, differences were noticed between various regenerated fibers (viscose, viscose Modal, and Lyocell): a thin hemicellulose-rich outermost layer was found in all the regenerated fibers studied.     

Application of enzymes in producing bleached pulp from wheat straw

Crude enzymes produced by different strains were used in the production of bleached wheat straw pulp. Pre-treatment with enzymes from Penicillium A10 and Aspergillus L22 at a xylanase dosage of 4 IU/g prior to pulping decreased pulp kappa number by 6.29% and 12.07% respectively as compared to the control. High cellulase activity in crude enzymes has a negative influence on pulping. Xylanase pre-bleaching reduced chlorine charge by 20-30%, or increased final brightness by approximately 4-5% ISO, and improved the pulp strength properties. Xylanase could substitute for alkali extraction in CEH sequence, and be used for treating chemical-bleached pulp, which resulted in higher strength properties for bleached pulp. Modification of bleached pulp with enzymes of 3 IU/g (on xylanase) increased pulp brightness and breaking length by 3-6% ISO and 160-790 m respectively, and decreased post color number and beating degree of pulp by 29-36% and 2.5-5.5 degrees SR respectively, as compared to the original pulp.     

Biobleaching of banana fibre pulp using <Emphasis Type="Italic">Bacillus subtilis</Emphasis> C O1 xylanase produced from wheat bran under solid-state cultivation

A cellulase-free xylanase produced by Bacillus subtilis C 01 from wheat bran under solid-state cultivation was tested for its efficacy in biobleaching of raw banana fibre and banana pulp obtained through a mechanical pulping process. Banana pulp samples treated with crude xylanase (450 nkat g⁻¹ pulp) resulted in a 19.6% increase in the brightness as compared to untreated pulp. The presence of chromophores, hydrophobic compounds and an increased reducing sugar (10.79 mg g⁻¹ pulp) quantity in the bleached solution after enzymatic treatment indicated the removal of materials that were absorbed at 237 nm from the banana pulp.     

Isolation and characterisation of cellulose obtained by a two-stage treatment with organosolv and cyanamide activated hydrogen peroxide from wheat straw

Seven wheat straw cellulose preparations were isolated by a two-stage acidic organosolv treatment followed by cyanamide activated hydrogen peroxide bleaching. The effects of concentration of acetic and formic acids on the yield of cellulose and degradation of lignin and non-cellulose polysaccharides were investigated. Organic acids were more effective than alcohols on the degradation of lignin and hemicelluloses. Formic acid/acetic acid/water (30/60/10, v/v/v) system was found to be the most effective in delignification and removal of non-cellulose polysaccharides from the straw and did not have any undesirable effects on cellulose properties such as its intrinsic viscosity. In this case, the treatment removed 94.1% of the original lignin and 76.5% of the original hemicelluloses using 0.1% HCl as a catalyst at 85 °C for 4 h. Cyanamide activated hydrogen peroxide bleaching degraded substantial amounts of residual hemicelluloses and lignin, produced the cellulose samples having a relatively high purity. Under a best condition, a cellulose relatively free of lignin (0.7%) and with intrinsic viscosity of 393 ml g⁻¹ and favourable molar mass (213,940 g mol⁻¹) was obtained. Both unbleached and bleached cellulose preparations were further characterised by FT-IR and CP/MAS ¹³C NMR spectroscopy, and thermal stability.     

Characterization and biobleaching effect of hemicellulases produced by thermophilic fungi

The culture supernatant of Thermomyces lanuginosus strains MED 2D and MED 4B1 had high activities of xylanase with low inducible activities of -xylosidase. The crude xylanase was optimally active at 70 °C and at pH 6.0 to 6.5. Subsequently Eucalyptus kraft pulp was treated with MED 2D supernatant at 10 IU per gram pulp resulting in a 10.5% reduction in Kappa number. XECEDED-Refined bleached pulp resulted in handsheets with increased brightness compared to the control (X = xylanase treatment; E = alkaline extraction; C = Cl2 treatment; D = ClO2 treatment).     

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

Background

In 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.

Results

In 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.

Conclusions

This 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.

     

Behavior of different monocomponent endoglucanases on the accessibility and reactivity of dissolving-grade pulps for viscose process

Three different commercial monocomponent endoglucanases, with and without a cellulose-binding domain (CBD) and differences in their glycosidic hydrolysis mechanisms, were compared with respect to their ability to enhance the accessibility and reactivity of dissolving-grade pulps for viscose production. Hardwood (eucalyptus) and softwood (mixture of Norway spruce and Scots pine) commercial dried and never-dried bleached sulfite dissolving pulps were used for this purpose. The effects of the enzymatic treatments on pulps were studied by reactivity, according to Fock's method, and viscosity measurements, and recording of molecular weight distributions. Among the different assayed enzymes, endoglucanase with a CBD and an inverting hydrolysis mechanism was found to be the most effective in increasing the reactivity of both pulps. Simultaneously, the viscosity decreased, being more marked for softwood dissolving pulp. A narrower molecular weight distribution, with a great reduction in the amount of long-chain cellulose molecules was observed in both pulps, being more pronounced for softwood dissolving pulp. By contrast, endoglucanase without a CBD and a retaining hydrolysis mechanism showed a barley enhancement of the studied properties. The effects of the different endoglucanase treatments were more pronounced when never-dried dissolving pulps were used.     

Optimization of hydrogen peroxide in totally chlorine free bleaching of cellulose pulp from olive tree residues

The influence of the operating conditions used in the bleaching of olive wood trimmings pulp (viz. hydrogen peroxide concentration and time) on the yield, kappa index and viscosity of the resulting pulp and on strength-related properties of paper sheets was studied to determine the optimal bleaching conditions of this pulp. Hydrogen peroxide bleached pulps at different sequences (oxygen, ozone, chlorine dioxide and alkaline extractions) were compared. Hydrogen peroxide bleaching proved to be suitable for this pulp. Considerable improvements in viscosity were obtained with respect to other bleaching sequences such as oxygen, ozone and chlorine dioxide. Hydrogen peroxide bleaching decreased the kappa index 51.3% less than ozone bleaching, 25.0% less than chlorine dioxide (D) and 6.3% less combined chlorine dioxide-alkaline extraction (DE). To obtain kappa indices 50.9% and 37.9% lower than the index achieved by hydrogen peroxide, oxygen (LaO(p)) and ozone (LaO(LaZ)R) sequences respectively were needed. Lower-medium levels of hydrogen peroxide concentrations (1-3%) and high reaction times (210 min) proved to be suitable for bleaching of pulp olive trimming residues. This approach could be used on this residue to produce adequately bleached pulp.     

Pulp properties and their influence on enzymatic degradability

Endoglucanase treatment of pulp for the adjustment of viscosity and the increase in pulp reactivity is a promising step in the concept for the beneficial production of dissolving pulps from paper grade pulps. To promote the commercial applicability of these enzymes, the influence of pulp properties such as carbohydrate composition, pulp type and cellulose morphology on the enzymatic degradability of a pulp was examined. High contents of hemicelluloses and lignin were shown to impair the accessibility of the cellulose to the enzymes. Due to the elevated swelling capacity of cellulose II, conversion of the cellulose morphology from I to II upon alkaline treatments showed a large increasing effect on the cellulose accessibility, and enzymatic degradability. Reactivity measurements of softwood sulfite pulps after enzymatic degradation and acid-catalyzed hydrolysis, respectively, revealed elevated reactivity for the pulp after acid treatment. This is in contrast to effects of enzyme treatments reported for CCE treated kraft pulps.     

Fractionation of wheat straw by atmospheric acetic acid process

Fractionation of wheat straw was investigated using an atmospheric acetic acid process. Under the typical conditions of 90% (v/v) aqueous AcOH, 4% H(2)SO(4) (w/w, on straw), ratio of liquor to straw (L/S) 10 (v/w), pulping temperature 105 degrees C, and pulping time 3h, wheat straw was fractionated to pulp (cellulose), lignin and monosaccharides mainly from hemicellulose with yields of approximately 50%, 15% and 35%, respectively. Acetic acid pulp from the straw had an acceptable strength for paper and could be bleached to a high brightness over 85% with a short bleaching sequence. Acetic acid pulp was also a potential feedstock for fuels and chemicals. The acetic acid process separated pentose and hexose in wheat straw to a large extent. Most of the pentose (xylan) was dissolved, whereas the hexose (glucan) remained in the pulp. Approximately 30% of carbohydrates in wheat straw were hydrolyzed to monosaccharides during acetic acid pulping, of which xylose accounted for 70% and glucose for 12%. The acetic acid lignin from wheat straw showed relatively lower molecular weight and fusibility, which made the lignin a promising raw material for many products, such as adhesive and molded products.