Dissolving Pulp Production Research Articles

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.

Recycling cellulase towards industrial application of enzyme treatment on hardwood kraft-based dissolving pulp

Cost-effectiveness is vital for enzymatic treatment of dissolving pulp towards industrial application. The strategy of cellulase recycling with fresh cellulase addition was demonstrated in this work to activate the dissolving pulp, i.e. decreasing viscosity and increasing Fock reactivity. Results showed that 48.8–35.1% of cellulase activity can be recovered from the filtered liquor in five recycle rounds, which can be reused for enzymatic treatment of dissolving pulp. As a result, the recycling cellulase with addition fresh cellulase of 1mg/g led to the pulp of viscosity 470mL/g and Fock reactivity 80%, which is comparable with cellulase charge of 2mg/g. Other pulp properties such as alpha-cellulose, alkaline solubility and molecular weight distribution were also determined. Additionally, a zero-release of recycling cellulase treatment was proposed to integrate into the dissolving pulp production process.

Analysis of submerged membrane for a sludge-bed anaerobic membrane bioreactor treating prehydrolysis liquor

ABSTRACTAn analysis of foulants and the performance of membranes in innovative sludge-bed anaerobic membrane bioreactors (SB-AnMBRs) were evaluated at mesophilic (35°C for approx. 400 days) followed by thermophilic (55°C for approx. 400 days) temperatures while treating the prehydrolysis liquor (PHL) waste stream from a dissolving pulp production plant. The membrane fouling of SB-AnMBR was analyzed for 0.1, 0.15 and 0.2 m3/m2/d flux conditions. Physico-chemical analyses of the membrane showed that the combination of 5% citric acid, 0.5% NaOCl and 2% NaOH solutions was effective in achieving more than 80% recovery of membrane flux. Chemical characterization of foulants showed that proteins were more predominant in membrane fouling than carbohydrates. Sugars and lignin contribution were negligible as compared to proteins in the total organic carbon content of the foulant. Membrane fouling occurred through a biofilm-dominated process and organic fouling. Combination of cleaning chemicals which included 0.5% NaClO and 2% NaOH solutions was most effective in the removal of the organic foulants. SEM analysis showed the pictorial evolution of the impact of fouling on the pore openings and the effect of cleaning on the membrane surface.

Preparation of dissolving pulp from oil palm empty fruit bunch by prehydrolysis soda-anthraquinone cooking method

This study aimed to investigate the production of dissolving pulp (DP) from empty fruit bunch (EFB) of oil palm (Elaeis guineensis) as a non-wood material using a combination of prehydrolysis, soda-anthraquinone (AQ) cooking, and elementary chlorine-free (ECF) or totally chlorine-free (TCF) bleaching. Prehydrolysis was performed for 90–180 min at 150 °C. Subsequently, the prehydrolyzed EFB was subjected to several soda-AQ cooking conditions with active alkali (AA) dosages of 19, 20, and 21 % at 160 °C. The obtained pulps were bleached following ECF and TCF sequences with oxygen (O), chlorine dioxide (D0), extraction with peroxide (Ep), chlorine dioxide (D1), and peroxymonosulfuric acid (Psa) stages. The results showed that the optimal duration of the prehydrolysis was 180 min, while the best AA dosage of the soda-AQ cooking was 20 %. The determination of pulp qualities showed that ECF bleaching with the Psa–D0–Ep–D1 sequence reached 90.7 % ISO brightness, 8.5 cP viscosity, 98.6 % α-cellulose, and that TCF bleaching with the O–Psa–Ep–Psa–E sequence attained 81.6 % ISO brightness, 9.6 cP viscosity, and 95.9 % α-cellulose. The results indicated a promising potential of EFB for DP production.

Effect of Coagulating Agents on Lignin and Oligosaccharide Contents in Pre-Hydrolysis Liquor Obtained in the Production of Dissolving Pulp from Poplar Residual Slabs

Pre-hydrolysis is an important step in the poplar residual slab dissolving pulp production process, as it aids in removing as much hemicellulose as possible from the cellulose fibers. In the pre-hydrolysis process, a portion of lignin also dissolves, along with the hemicelluloses. The presence of lignin in prehydrolysis liquor (PHL) is detrimental to the separation of xylo-oligosaccharide from the prehydrolysis liquor. This study researched lignin removal from PHL with three coagulating agents, namely aluminum sulfate (alum), polyaluminum chloride (PAC), and polydiallyldimethyl ammonium chloride (pDADMAC). It was found that the removal of lignin increased as the dosage of the alum, PAC, and pDADMAC increased. Additionally, the highest retention of xylo-oligosaccharide in the PHL occurred at dosages of 120 mg/L for alum and 160 mg/L for PAC and pDADMAC. The contents of the other oligosaccharides in PHL fluctuated irregularly with increasing dosages of the alum, PAC, and pDADMAC.

Simultaneous bench scale production of dissolving grade pulp and valuable hemicelluloses from softwood kraft pulp by ionic liquid extraction

Ionic liquid extraction of wood pulp has been highlighted as a highly potential new process for dissolving pulp production. Coproduction with a polymeric hemicellulose fraction was demonstrated in bench scale from softwood kraft pulp using extraction with the ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc) and water. In total, the recovered pulp and hemicellulose fraction together yielded 95.5wt.% of the pulp input. The extracted pulp had a remarkably high purity with an R18-value of 97.8%. The hemicellulose fraction consisted of galactoglucomannan, arabinoxylan and some cellulose and was precipitated from the ionic liquid-water mixture. After hydroxypropylation of the hemicellulose fraction, films were prepared and barrier and strength properties were compared to films from other polysaccharides. Reduced oxygen and water vapor permeation and good strength properties were demonstrated when compared to corresponding films from hydroxypropylated xylan from cold caustic extraction. The films have potential for applications in food packaging and edible films.

Production of furfural from an industrial pre-hydrolysis liquor

Pre-Hydrolysis Liquor (PHL) produced from the prehydrolysis kraft-based (PHK) dissolving pulp production process can be considered as a potential source for the production of biomaterials and biochemicals. Several dissolved organics such as hemicelluloses, lignin and acetic acid can be recovered and converted to valuable products. Xylan/xylose, a 5-carbon sugar and the major component of the hardwood PHL can be utilized to produce furfural. Pretreatment is necessary to increase the furfural yield, mainly by removing lignin, facilitating processing and minimizing the side reactions. In this research, adsorption by activated carbon, ion exchange resin treatment, and concentration by membrane filtration were utilized as pretreatments of PHL for furfural production. It was found that a furfural yield of 57% was achieved from the PHL at 190°C, using sulfuric acid as a catalyst. An overall process, integrated into the existing PHK dissolving pulp production process, was proposed to produce furfural from the PHL which fits well to the Integrated Forest Biorefinery concept.

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.

A process to produce furfural and acetic acid from pre-hydrolysis liquor of kraft based dissolving pulp process

Pre-hydrolysis Liquor (PHL) is an aqueous stream containing dissolved organics, produced in the pre-hydrolysis kraft (PHK)-based dissolving pulp production process. Hemicelluloses (6wt.%) and acetic acid (1wt.%) present in the PHL can be used or recovered as valuable products, instead of being used as fuel for recovery boiler operation. In this work, hemicelluloses in the PHL were concentrated about 3 times by membrane nano-filtration (NF), while simultaneously separating acetic acid in permeate. NF permeate was subjected to reverse osmosis (RO) to obtain concentrated acetic acid which was subsequently extracted with tertiary amines and polar organic diluents. The concentrated sugars/hemicelluloses in the NF concentrate were converted to furfural using monophase and biphase reactor systems. Overall, a sequential bio-refining process to recover organics from PHL was developed.

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.

Preparation of Dissolving Pulp Made from Poplar Residual Slabs and Effect of Xylanase Post-treatment on Its Reactivity

The production of dissolving pulp from poplar wood residual slabs was investigated. The residual slab chips were initially prehydrolyzed and subsequently pulped by the kraft process; the resulting brownstock was bleached using a totally chlorine-free (TCF) sequence to full brightness. The pulp contained low pentosans and high α-cellulose content, and the pulp had high reactivity. Its hemicellulose content, reactivity, and degree of polymerization were within acceptable levels for a rayon-grade dissolving pulp. Thus, the residual slabs from poplar can be regarded as a viable raw material for dissolving pulp production. The reactivity of this dissolving pulp was drastically decreased after the xylanase post-treatment, which can slightly lower the pentosans levels. Simultaneously, the crystallinity index of the resulting pulp obviously decreased after xylanase post-treatment.

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.

Kinetics of furfural production from pre-hydrolysis liquor (PHL) of a kraft-based hardwood dissolving pulp production process

The kinetics of C-5 sugars (xylose/xylan) conversion to furfural in an industrial pre-hydrolysis liquor (PHL) in both acetic acid (HAc)-catalyzed system and sulfuric acid (H2SO4)-catalyzed system, were determined in a temperature range of 150–190 °C. The main reactions involved during the process included: 1) C-5 sugars consumption for furfural formation and side reactions; 2) furfural degradation. It was found that these reactions followed first order kinetics. A consecutive reaction model (from xylose to furfural, then to degradation products) fitted into the data obtained in the H2SO4-catalyzed system; while a consecutive/parallel model suited for the HAc-catalyzed system due to side reactions, which also consumed C-5 sugars. The activation energy for C-5 sugar disappearance, and the furfural degradation, was 151 kJ mol−1 and 115 kJ mol−1, respectively, in the HAc-catalyzed system.

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.