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.     

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.

     

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     

Application of hemicelluloses precipitated via ethanol treatment of pre-hydrolysis liquor in high-yield pulp

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 (D(0) and D(1)) and hydrogen peroxide (Ep) in the D(0)EpD(1) sequence, and the chemical compositions, molecular weights and charge densities of the treated samples were assessed. When applied to high-yield pulp (HYP) at 50 mg/g, 26 and 20 mg/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.     

PDADMAC as a flocculant for lignosulfonate of NSSC pulping process

The spent liquor (SL) of neutral sulfite semi‐chemical (NSSC) pulping process contains about 8 wt% lignocelluloses that can be extracted and used in the production of value‐added materials. In this work, a flocculation process followed by centrifugation was considered for isolating lignosulfonate and hemicelluloses from SL. It was observed that, by adding 20 mg/g of polydiallyldimethylammuniom chloride (PDADMAC) with 100,000–200,000 g/mol molecular weight to SL, 45% of lignosulfonate and 39% of hemicelluloses were removed at 30°C. The lignocellulose removal was more efficient for the dual flocculation system of low and high molecular weights PDADMAC than for individual PDADMAC systems. Overall, 49% of lignosulfonate, 47% of hemicelluloses and 97% of turbidity were removed from SL from the dual system when 10 mg/g low molecular weight PDADMAC and 10 mg/g high molecular weight PDADMAC were added to the SL at 30°C, subsequently. The thermogravimetric analysis (TGA) of generated flocs showed that all samples had similar thermal behaviour and 13–16 wt% of flocs remained as ash after burning at 700°C in nitrogen. As the flocs are made of lignocellulosic materials and they are thermally stable, they could be used as fillers in paper board production. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:686–691, 2016     

Flexible biorefinery for producing fermentation sugars, lignin and pulp from corn stover

A new biorefining process is presented that embodies green processing and sustainable development. In the spirit of a true biorefinery, the objective is to convert agricultural residues and other biomass feedstocks into value-added products such as fuel ethanol, dissolving pulp, and lignin for resin production. The continuous biomass fractionation process yields a liquid stream rich in hemicellulosic sugars, a lignin-rich liquid stream, and a solid cellulose stream. This paper generally discusses potential applications of the three streams and specifically provides results on the evaluation of the cellulose stream from corn stover as a source of fermentation sugars and specialty pulp. Enzymatic hydrolysis of this relatively pure cellulose stream requires significantly lower enzyme loadings because of minimal enzyme deactivation from nonspecific binding to lignin. A correlation was shown to exist between lignin removal efficiency and enzymatic digestibility. The cellulose produced was also demonstrated to be a suitable replacement for hardwood pulp, especially in the top ply of a linerboard. Also, the relatively pure nature of the cellulose renders it suitable as raw material for making dissolving pulp. This pulping approach has significantly smaller environmental footprint compared to the industry-standard kraft process because no sulfur- or chlorine-containing compounds are used. Although this option needs some minimal post-processing, it produces a higher value commodity than ethanol and, unlike ethanol, does not need extensive processing such as hydrolysis or fermentation. Potential use of low-molecular weight lignin as a raw material for wood adhesive production is discussed as well as its use as cement and feed binder. As a baseline application the hemicellulosic sugars captured in the hydrolyzate liquor can be used to produce ethanol, but potential utilization of xylose for xylitol fermentation is also feasible. Markets and values of these applications are juxtaposed with market penetration and saturation.     

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.     

Changes in the structural composition of hardwood kraft pulp during bleaching

The possibility of using xylanase preparations for hydrolyzing hemicelluloses in a non-bleached kraft pulp in order to facilitate its bleaching was studied. The effects of enzymatic preparations of fungal and bacterial origins were examined, and the optimal conditions for xylanase activity were determined. UV spectroscopy demonstrated that the treatment of kraft pulp with enzymatic preparations containing xylanase facilitated the subsequent removal of lignin and increased the brightness by 5%. The effect of enzymatic treatment was retained in the case of peroxide bleaching. The enzymatic preparations studied are promising for the development of chlorine-free pulp bleaching technologies.     

Chlorine-free extraction of cellulose from rice husk and whisker isolation

This work reports the isolation of cellulose whiskers from rice husk (RH) by means of an environmental friendly process for cellulose extraction and bleaching. The multistep process begins with the removal of pectin, cutin, waxes and other extractives from rice husk, then an alkaline treatment for the removal of hemicelluloses and lignin, and a two-step bleaching with hydrogen peroxide/tetra-acetylethylenediamine (TAED), followed by a mixture of acetic and nitric acids, for further delignification of the cellulose pulp. The techniques of infrared absorption spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), modulated differential scanning calorimetry (MDSC) and X-ray diffraction (XRD) showed that the overall process is adequate to obtain cellulose with high purity and crystallinity. This cellulose was submitted to sulfuric acid hydrolysis with the aim to isolate the whiskers. They showed the typical elongated rod-like aspect as revealed by transmission electron microscopy (TEM) and atomic force microscopy (AFM).     

Repeated batch process for biological treatment of black liquor using brown-rot basidiomycete <Emphasis Type="Italic">Fomitopsis</Emphasis> sp. IMER2

A repeated batch operation is developed for the treatment of alkaline pulp black liquor, through a process of biological acidification precipitation of lignin using brown rot fungus Fomitopsis sp. IMER2. The results showed that COD and color removal of black liquor was dependent on the biomass concentration, pH decrease and initial COD. Based on these results, the repeated batch process was successfully carried out 12 times over 36 days in an air bubble column bioreactor. The average reduction of COD and color was approximately 40% and 70%, respectively.     

Effect of alkaline and autohydrolysis processes on the purity of obtained hemicelluloses from corn stalks

A study of the potential of autohydrolysis and alkaline extraction processes from corn stalks was performed for high purity hemicellulose extraction. The influence of process parameters on the purity of obtained hemicelluloses was analyzed. An experimental design was developed for the autohydrolysis treatments to determine the optimal conditions to solubilize the hemicelluloses with lowest content in contaminants. On the other hand, alkaline extraction, including raw material pretreatment (dewaxing and delignification step) was carried out analyzing the effectiveness of this processes for maximum pure hemicellulose recovery. The maximum yield (54% of the raw material hemicelluloses) and the best physicochemical properties (highest hemicellulose content free of lignin) were obtained with these pretreatments in alkaline extraction. Moreover, the effect of lignin removal by sulfuric acid from the autohydrolysis liquors before hemicellulose precipitation was studied. This purification step has allowed to obtain lignin-free autohydrolysis hemicellulose but with the presence of sulfur as predominant contaminant.     

Change in composition of structural components of leaf cellulose sulfate during fermentation bleaching by xylanases

The possibility of the use of xylanase preparations for hydrolysing hemicelluloses in a non-bleached kraft pulp in order to facilitate its bleaching was studied. The effects of enzymatic preparations of the fungal and bacterial origins were examined, and the optimal conditions for xylanase activity were determined. UV spectroscopy demonstrated that the treatment of kraft pulp with the enzymatic preparations containing xylanase facilitated the subsequent removal of lignin and increased the brightness by 5%. The effect of enzymatic treatment was retained in the case of peroxide bleaching. The enzymatic preparations studied are promising for the development of chlorine-free pulp bleaching technologies.     

Routes to Potential Bioproducts from Lignocellulosic Biomass Lignin and Hemicelluloses

An essential feature of proposed fermentation-based lignocellulose to biofuel conversion processes will be the co-production of higher value chemicals from lignin and hemicellulose components. Over the years, many routes for chemical conversion of lignin and hemicelluloses have been developed by the pulp and paper industry and we propose that some of these can be applied for bioproducts manufacturing. For lignin products, thermochemical, chemical pulping, and bleaching methods for production of polymeric and monomeric chemicals are reviewed. We conclude that peroxyacid chemistry for phenol and ring-opened products looks most interesting. For hemicellulose products, preextraction of hemicelluloses from woody biomass is important and influences the mixture of solubilized material obtained. Furfural, xylitol, acetic acid, and lactic acid are possible targets for commercialization, and the latter can be further converted to acrylic acid. Pre-extraction of hemicelluloses can be integrated into most biomass-to-biofuel conversion processes.     

Relationship between Fungal Biomass Production and the Brightening of Hardwood Kraft Pulp by Coriolus versicolor

The white-rot fungus Coriolus versicolor increased the brightness of hardwood kraft pulp by two mechanisms depending on the concentration of available nitrogen. In low-nitrogen conditions, the brightening process was a chemical effect mediated by the fungus, associated with the removal of residual lignin in the pulp; kappa number was used as an indicator of lignin concentration. A five-day treatment in low-nitrogen conditions increased the brightness of hardwood kraft pulp from 36.2 to 54.5%, with a corresponding decrease in kappa number from 12.0 to 8.5, equivalent to a reduction in the lignin concentration from ca. 2.0% (wt/wt) to ca. 1.4% (wt/wt). Under these conditions, we concluded that the brightening of the pulp was a secondary metabolic event initiated after the depletion of available nitrogen. This method of brightening has been described as bleaching or biobleaching. By contrast, in high-nitrogen conditions, the brightening was a physical effect associated with the dilution of the dark pulp fibers by the relatively high levels of brighter fungal mycelium produced. Since this method of brightening was not evidently associated with lignin removal, it cannot be described as bleaching. In pulp samples brightened in high-nitrogen conditions, as brightness increased, there was a corresponding increase in kappa number. This observation was explained by the consumption of potassium permanganate by the fungal mycelium, which interfered with kappa number determinations at high fungal biomass levels.     

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.     

Bioremediation of paper and pulp mill effluents

Pulp and paper mill effluents pollute water, air and soil, causing a major threat to the environment. Several methods have been attempted by various researchers throughout the world for the removal of colour from pulp and paper mill effluents. The biological colour removal process uses several classes of microorganisms--bacteria, algae and fungi--to degrade the polymeric lignin derived chromophoric material. White rot fungi such as Phanerochaete chrysosporium, Corius versicolor, Trametes versicolor etc., are efficient in decolourizing paper and pulp mill effluents. Gliocladium virens, a saprophytic soil fungus decolourised paper and pulp mill effluents by 42% due to the production of hemicellulase, lignin peroxidase, manganese peroxidase and laccase.     

The effects of hemicelluloses and lignin removal on water uptake behavior of hemp fibers

This study investigated the individual influences of hemicelluloses and lignin removal on the water uptake behavior of hemp fibers. Hemp fibers with different content of either hemicelluloses or lignin were obtained by chemical treatment with 17.5% sodium hydroxide or 0.7% sodium chlorite. Various tests (capillary rise method, moisture sorption, water retention power) were applied to evaluate the change in water uptake of modified hemp fibers. The obtained results show that when the content of either hemicelluloses or lignin is reduced progressively by chemical treatment, the capillary properties of hemp fibers are improved, i.e. capillary rise height of modified fibers is increased up to 2.7 times in relation to unmodified fibers. Furthermore, hemicelluloses removal increases the moisture sorption and decreases the water retention values of hemp fibers, while lignin removal decreases the moisture sorption and increases the water retention ability of hemp fibers.     

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.     

Investigation of lignin-carbohydrate complexes in kraft pulps by selective enzymatic treatments

The occurrence of covalent bonds between residual lignin and polysaccharides in birch and pine kraft pulps was investigated by specific enzymatic treatments. Pure enzymes degrading cellulose, xylan and mannan were used both separately and in combination. Comparison of the molar masses of polysaccharides and lignin in the orginal pulps and in the residual pulps after enzymatic treatments showed that residual lignin in birch kraft pulp is linked at least to xylan. A minor portion may also be linked to cellulose. In pine kraft pulp some of the residual lignin appears to be linked to cellulose, glucomannan and xylan. The linkages between lignin and cellulose and hemicelluloses may be either native or formed during pulp processing. The results also provided new information on the synergistic action of cellulose- and hemicellulose-degrading enzymes on pulp fibres. The synergism appears to be mainly due to the structure of the pulp fibres, with different layers of cellulose sheets, hemicelluloses and lignin. On the other hand the results also provided information about fibre structure. The degradation of xylan clearly enhanced the action of enzymes on cellulose, suggesting that xylan partially covers the cellulose. A similar phenomenon was not observed in the simultaneous hydrolysis of glucomannan and cellulose. However, the results suggest that glucomannan does interact with cellulose, possibly by non-covalent linkages. Received: 8 July 1998 / Received revision: 7 October 1998 / Accepted: 11 October 1998     

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.