Alkaline Pulping Process Research Articles

Alkaline Pulping of Red Meranti (Shorea selanica Blume)

The suitability for papermaking of red meranti (Shorea selanica Blume) wood for three alkaline pulping processes i.e soda, soda-anthraquinone (AQ), and kraft was studied. The fiber morphology and chemical properties were also examined. Cooks were made for 20% (as Na2O) activate alkali. The resulting pulp and paper properties were investigated. The basic density of red meranti was 0.42 g/cm3 and can be classified to be of medium density. The fibre proportion (67.14%) and fibre length (1.07 mm) of red meranti in this study were within the range of tropical hardwoods. The derived values for Runkel ratio, slender ratio, and flexibility coefficient were 0.54, 54.93, and 0.62, respectively. Furthermore, total extractives, lignin, and cellulose contents as well as solubility in 1% NaOH were 5.17%, 31.05%, 45.20%, and 26.02%, respectively. The alkaline pulps showed low kappa number (16~22) and reject level (0.5~1.5%) with the best results for screened yield (47.41%) being achieved in soda pulping. With regard to strength and optical properties of the paper hand-sheets, soda-AQ pulping showed the highest value in burst index (2.36 KPa m2/g), tear index (8.47 + 1.13 mNm2/g), and brightness (19.81%), whereas kraft pulping gave the best result in tensile index (28.39 Nm/g). The comparatively low values of yield and strength properties in kraft pulping might be due to overcooking in this experiment.

Promotive or suppressive effect of co-existing nucleophiles on lignin condensation in alkaline pulping processes

This study aimed to quantitatively examine how the addition of a strong or weak nucleophile (1.0 mol/L) to a soda cooking treatment (1.0 mol/L NaOH) at 150 °C affects the disappearance and condensation reactions of a simple phenolic lignin model compound, vanillyl alcohol (Va). All the observed phenomena could basically be attributed to the adduct formation of each reagent with the quinone methide intermediate derived from Va (QMVa) and the stabilization of the adduct. The adduct is irreversibly stabilized to be its conjugate base when the reagent was MeNH2 or Me2NH, resulting in the accumulation of the adduct and consequent consumption of QMVa without the reformation of Va from QMVa and condensation reactions of Va with QMVa. The adduct is not stabilized to be its conjugate base and reproduce QMVa when the reagent was Me3N, CO3 2¯, or SO4 2¯ (the sodium salt), resulting in the increased concentration of QMVa to promote the condensation reactions of Va with QMVa. These suppressive and promotive effects were more visible in the same treatment of Va with each nucleophile without the addition of NaOH, in which the concentration of hydroxide anion was low.

Revisiting the condensation reaction of lignin in alkaline pulping with quantitativity part III: predominant formation of α-β-type over α-5-type condensation product in soda cooking treatments of apocynol and creosol

Progress in the condensation of lignin is believed to interfere with delignification in alkaline pulping processes without any clear evidence, which motivated us to revisit it quantitatively. This study is the 3rd in the series which evaluates the condensation reactions of lignin in model systems of soda cooking processes using 4-(1-hydroxyethyl)-2-methoxyphenol (apocynol, Ap) and 2-methoxy-4-methylphenol (creosol, Cr). Ap was primarily converted to 2-methoxy-4-vinylphenol (vinylguaiacol, Vg) via the quinone methide intermediate to establish equilibrium before condensation reactions proceeded. Only the α-5-type condensation product between Ap and Cr (ApCr, 1-(4-hydroxy-3-methoxyphenyl)-1-(2-hydroxy-3-methoxy-5-methylphenyl)ethane) and the α-β-type condensation product between Ap and Vg or two molecules of Vg (ApVg, trans-1,3-bis(4-hydroxy-3-methoxyphenyl)but-1-ene) were identified without detecting any self-condensation products of Ap. The α-β-type condensation has not been well known and is an important finding of this study. The formation of ApVg was over 10 times faster than that of ApCr, which demonstrates that the α-β-type condensation is a major mode in soda cooking. However, because origins of α-β-type condensation substructures, such as C6-C2-type enol ethers, do not exist in native lignin, the results support our previous conclusion that the condensation reactions of lignin progress less frequently than previously believed.

Revisiting the condensation reaction of lignin in alkaline pulping with quantitativity. Part 2: evaluation of self-condensation of vanillyl alcohol compared with its condensation with creosol under soda cooking conditions

Condensation of lignin is believed to interfere with delignification in alkaline pulping processes. The lack of clear evidence motivated us to quantitatively revisit it. This article evaluates the self-condensation of 4-hydroxymethyl-2-methoxyphenol (vanillyl alcohol, Va) in the simplest model system using Va and 2-methoxy-4-methylphenol (creosol, Cr) under the same soda cooking conditions employed in our previous paper. Dimeric and trimeric self-condensation products of Va consisting of the α-5 bond (VaVa, 2-(4-hydroxy-3-methoxybenzyl)-4-hydroxymethyl-6-methoxyphenol), α-1 bond (VaVa’, bis(4-hydroxy-3-methoxyphenyl)methane), and α-5 & α-1 bonds (VaVaVa’, 2,4-bis(4-hydroxy-3-methoxy-benzyl)-6-methoxyphenol) were identified and quantified. The formation rate of VaVa from Va was suggested to be about twice of that of VaVa’, and to be similar to that of the condensation product between the α-carbon of Va and the aromatic C5-carbon of Cr (VaCr), which was identified in the first paper. Among all these detected condensation products, only VaVa that can be converted to the corresponding quinone methide (QM) readily underwent further condensation to be VaVaVa’ and others. Only the monomers (Va and Cr) possessing the small steric factors condense with electrophilic QM’s as nucleophiles. These results suggest that condensation of lignin in actual soda cooking processes, with steric factors much larger than the model system, progresses much less frequently than generally believed.

Fractionation of banana rachis using ionic liquids: Sustainability and selectivity of choline lactate

Lignocellulosic biomass is a valuable source of energy and raw materials. However, in order to unlock the full potential of this renewable source, it needs to be fractionated to separate its main components: cellulose, lignin and hemicellulose. Current extraction methods (Kraft, Organosolv) are very effective but are not entirely free of drawbacks, such as a high energy and water consumption and the use of potentially toxic chemicals. Ionic liquids (ILs) have been explored as a sustainable alternative for biomass treatment since they have shown selectivity during biomass fractionation. In this work, the ability of 6 ILs to selectively extract lignin from banana rachis was investigated, including choline lactate [Cho+][Lac-] which is acknowledged by its lack of toxicity, biodegradability and ease of synthesis from renewable resources. Recovered cellulose batches were characterised by X-ray diffraction and FT-IR spectroscopy and compared with cellulose from banana rachis obtained by traditional alkaline pulping process.

Taxonomic, physical and morphological characterization of four species of agave with potential for the production of cellulose fibers from the leaves

The aim of the study was to characterize taxonomic, physical, and morphologically distinct species agaváceas tequila, mezcal and pulque grown in different regions of Mexico. Four species were evaluated Agave lechuguilla Torr., Agave salmiana B. Otto ex Salm-Dick, both from the state of Hidalgo; Agave angustifolia Haw. From the state of Oaxaca and Agave tequilana Weber, Var. Azul, Jalisco. The work was divided into two phases: botanical phase and physical study. In the botanical phase classification and taxonomic characterization of phenological, ecological and ethnobotanical database was revised. In the physical phase size and leaf characteristics of the plant is characterized. We analyzed moisture, fiber granulometry and scanning electron microscopy to assess fiber morphologies. From the results of physical characterization and fiber lengths found, we concluded that there is high potential to produce cellulose pulp. The species A. angustifolia and A. tequilana were presented minor percentage of sizes <0.5 mm that could affect an alkaline pulping process. For the species A. tequilana 98.5% fibers <1 mm being the majority corresponding to the fraction 0.5-1.0 mm (84.3%) which corresponds to a size suitable for cellulosic pulp paper making was obtained. The species A. angustifolia showed 85.06% fibers <1 mm fraction between 0.5-1.0 mm majority (65.2%).

Revisiting the condensation reaction of lignin in alkaline pulping with quantitativity part I: the simplest condensation between vanillyl alcohol and creosol under soda cooking conditions

The condensation reaction of lignin is believed to interfere with delignification in alkaline pulping processes, without any clear evidence, which has motivated us to quantitatively revisit it. This paper is the first of a series, and hence we employed the simplest model system using 4-hydroxymethyl-2-methoxyphenol (vanillyl alcohol, Va) and 2-methoxy-4-methylphenol (creosol, Cr) under soda cooking conditions. The α-5-type condensation product between these compounds [VaCr, 2-(4-hydroxy-3-methoxybenzyl)-6-methoxy-4-methylphenol] was identified and quantified as exclusive. VaCr was yielded with a mole amount of 24%, 46%, 62%, or 72% based on that of disappearing Va at a reaction time of 120 min when the ratio of the initial concentration of Cr to that of Va was 1.0, 2.5, 5.0, or 7.5, respectively. These yields and an HPLC analysis of the reaction solution obtained by a treatment of Va as the sole compound under the same soda cooking conditions suggested the formation of self-condensation products of Va even in the treatments containing Cr. The obtained results comprehensively suggested that the self-condensation of Va progresses more readily than the condensation between Va and Cr. The factors behind this will be the topic of our next paper.

Ecofriendly wood adhesives from date palm fronds lignin for plywood

Utilization of lignin phenol glyoxal (LPG) resins was studied as a potential alternative for phenol formaldehyde (PF) resins. Lignin was extracted by alkaline pulping processes (kraft and soda) from date palm fronds (DPF) and was used as an alternative for phenol in LPG resins. The isolated lignin samples were characterized using complementary analyses that included Fourier transform infrared (FTIR) spectroscopy, 13C nuclear magnetic resonance (NMR) spectroscopy, thermal stability, thermogravi-metric analysis (TGA), and differential scanning calorimetry (DSC). Kraft lignin phenol glyoxal (KLPG) and soda lignin phenol glyoxal (SLPG) resins also were characterized in terms of solid content, viscosity, and gel time. Finally, physico-mechanical tests were performed on plywood panels that were treated with different molar ratios of LPG resins. The results revealed that 50% (w/w) KLPG resin resulted in higher tensile strength (65.3 MPa) than PF resin (58.57 MPa), which was potentially attributed to the higher amount of phenolic groups compared to soda lignin. Therefore, the substitution of DPF lignin in LPG resins enhanced the adhesive in terms of its chemical and mechanical properties, enabling it to produce a more environmentally friendly wood adhesive.

Contribution of the γ-hydroxy group to the β-O-4 bond cleavage of lignin model compounds in a basic system using tert-butoxide

The most common non-phenolic β-O-4-type lignin model compounds with or without the γ-hydroxymethyl group (C6-C3- or C6-C2-type, respectively) were treated in a 0.5 mol/L potassium tert-butoxide in DMSO solution at 30 °C to examine the effects of presence of the group. The β-O-4 bond of the C6-C3-type cleaved more rapidly than the C6-C2-type, indicating that the γ-hydroxy group contributes to the cleavage, in contrast to their reactions in alkaline pulping processes. Furthermore, the β-O-4 bond of the threo isomer of the C6-C3-type cleaved more rapidly than that of the erythro isomer. This result can be attributed to the fact that the erythro isomer has the hydrogen bond between a generated alkoxide and the other hydroxy group at its α- and γ-positions in its most-preferential conformer, interfering with the β-O-4 bond cleavage. It was also suggested in treatments of their methyl-etherified derivatives at the α- or γ-hydroxy group that the contribution of the γ-hydroxy group of the threo isomer is greater than that of the erythro isomer. Detailed examination of the distribution profile of reaction products supported this greater contribution of the γ-hydroxy group of the threo isomer.

Quantitative Correlation between the Chemical Structure and Reactivity of Lignin in Alkaline Pulping Processes

Quantitative Correlation between the Chemical Structure and Reactivity of Lignin in Alkaline Pulping Processes

Evaluation of lignins from side-streams generated in an olive tree pruning-based biorefinery: Bioethanol production and alkaline pulping

In modern lignocellulosic-based biorefineries, carbohydrates can be transformed into biofuels and pulp and paper, whereas lignin is burned to obtain energy. However, a part of lignin could be converted into value-added products including bio-based aromatic chemicals, as well as building blocks for materials. Then, a good knowledge of lignin is necessary to define its valorisation procedure. This study characterized different lignins from side-streams produced from olive tree pruning bioethanol production (lignins collected from steam explosion pretreatment with water or phosphoric acid as catalysts, followed by simultaneous saccharification and fermentation process) and alkaline pulping (lignins recovered from kraft and soda-AQ black liquors). Together with the chemical composition, the structure of lignins was investigated by FTIR, 13C NMR, and 2D NMR. Bioethanol lignins had clearly distinct characteristics compared to pulping lignins; a certain number of side-chain linkages (mostly alkyl–aryl ether and resinol) accompanied with lower phenolic hydroxyls content. Bioethanol lignins also showed a significant amount of carbohydrates, mainly glucose and protein impurities. By contrast, pulping lignins revealed xylose together with a dramatical reduction of side-chains (some resinol linkages survive) and thereby higher phenol content, indicating rather severe lignin degradation during alkaline pulping processes. All lignins showed a predominance of syringyl units.

INFLUÊNCIA DE LÍQUIDOS IÔNICOS NO TRATAMENTO DA PALHA DE MILHO PARA A PRODUÇÃO DE BIOETANOL

Este estudo propôs verificar a eficiência do tratamento da palha de milho com diferentes LIs no aumento do teor de açúcares fermentescíveis. Assim, inicialmente, foi realizado o processo de polpação alcalina da palha, sendo verificados teores de lignina de 8,30 % e 3,20 % e de holocelulose de 66,79 % e 95,26 % nas palhas bruta e polpada, respectivamente, além da síntese e caracterização dos LIs acetato de sec-butilamônio, lactato de sec-butilamônio, acetato de n-butilamônio e lactato de n-butilamônio. Posteriormente, foi realizado o tratamento das palhas bruta e polpada com os LIs e hidrólise enzimática, sendo verificada uma razão mássica de glicose de até 17,57% na palha polpada e tratada com o acetato de n-butilamônio, contra 3,98% na palha somente polpada e, um aumento de até 90,7% na razão mássica de açúcares fermentescíveis na palha tratada, em relação, a palha sem tratamento, sendo esta eficiência, maior, ao utilizar-se líquidos iônicos com o cátion n-butilamônio.

Exploring Ulex europaeus to Produce Nontoxic Binderless Fibreboard

Ulex europaeus is one of the most abundant and aggressively invasive plants on the world. Its fibres, which can be isolated using an alkaline pulping process, have been successfully thermo-pressed into high-density fibreboards without any type of binder. The influence of the bioorganic and crystalline components on the product was investigated using crystallographic, thermo-analytical, and mechanical techniques. Cellulose was predominantly an Iβ polymorph, more common in hardwood, but the composition of the material was typical of softwood. Both the crystallinity in the fibres and the average domain size of cellulose increased during thermo-pressing. Notwithstanding that the residual lignin was present in a small amount, this promoted the cohesion of fibres by improving hydrolysis and adhesion properties. The best overall properties were observed in the pressed products of 1030 ± 38 kg/m3, showing an elastic modulus of 4.31 ± 0.26 GPa, with a modulus of rupture of 26.5 ± 1.3 MPa. These results serve as the basis to transform the invasive species into a fully non-toxic added-value resource.

A biorefinery scheme to fractionate bamboo into high-grade dissolving pulp and ethanol

BackgroundBamboo is a highly abundant source of biomass which is underutilized despite having a chemical composition and fiber structure similar as wood. The main challenge for the industrial processing of bamboo is the high level of silica, which forms water-insoluble precipitates negetively affecting the process systems. A cost-competitive and eco-friendly scheme for the production of high-purity dissolving grade pulp from bamboo not only requires a process for silica removal, but also needs to fully utilize all of the materials dissolved in the process which includes lignin, and cellulosic and hemicellulosic sugars as well as the silica. Many investigations have been carried out to resolve the silica issue, but none of them has led to a commercial process. In this work, alkaline pretreatment of bamboo was conducted to extract silica prior to pulping process. The silica-free substrate was used to produce high-grade dissolving pulp. The dissolved silica, lignin, hemicellulosic sugars, and degraded cellulose in the spent liquors obtained from alkaline pretreatment and pulping process were recovered for providing high-value bio-based chemicals and fuel.ResultsAn integrated process which combines dissolving pulp production with the recovery of excellent sustainable biofuel and biochemical feedstocks is presented in this work. Pretreatment at 95 °C with 12% NaOH charge for 150 min extracted all the silica and about 30% of the hemicellulose from bamboo. After kraft pulping, xylanase treatment and cold caustic extraction, pulp with hemicellulose content of about 3.5% was obtained. This pulp, after bleaching, provided a cellulose acetate grade dissolving pulp with α-cellulose content higher than 97% and hemicellulose content less than 2%. The amount of silica and lignin that could be recovered from the process corresponded to 95 and 77.86% of the two components in the original chips, respectively. Enzymatic hydrolysis and fermentation of the concentrated and detoxified sugar mixture liquor showed that an ethanol recovery of 0.46 g/g sugar was achieved with 93.2% of hydrolyzed sugars being consumed. A mass balance of the overall process showed that 76.59 g of solids was recovered from 100 g (o.d.) of green bamboo.ConclusionsThe present work proposes an integrated biorefinery process that contains alkaline pre-extraction, kraft pulping, enzyme treatment and cold caustic extraction for the production of high-grade dissolving pulp and recovery of silica, lignin, and hemicellulose from bamboo. This process could alleviate the silica-associated challenges and provide feedstocks for bio-based products, thereby allowing the improvement and expansion of bamboo utilization in industrial processes.

Quality evaluation of dissolving pulp fabricated from banana plant stem and its potential for biorefinery

The study was conducted to evaluate the quality of dissolving pulp of Musa sapientum L. (banana) plant stem and its potential for biorefinery. Introduction of pre-hydrolysis prior to any alkaline pulping process helps to reduce the content of hemicellulose and consequently produce acceptably high content of cellulose pulp. Water pre-hydrolysis was done at 150°C for 90min. The amount of lignin, xylan and glucan in the extracted pre-hydrolysis liquor (PHL) was 1.6, 4.9 and 1.6%, respectively. Pulping of pre-extracted chips was done following soda-AQ, alkaline sulfite and kraft process. The ratio of chip to liquor was 1:7 for both pre-hydrolysis and pulping. The kraft pulping process with 20% active alkali and 25% sulfidity at 150°C for 90min showed the best result. The lowest kappa number was 26.2 with a considerable pulp yield of 32.7%. The pulp was bleached by acidic NaClO2 and the consistency was 10% based on air-dried pulp. The lowest amount of 7% NaClO2 was used for the bleaching sequence of D0ED1ED2. After D0ED1ED2 bleaching, the pulp showed that α-cellulose, brightness and ash were 91.9, 77.9 and 1.6% respectively. The viscosity was 19.9cP. Hence, there is a possibility to use banana plant stem as a raw material for dissolving grade pulp and other bioproducts.

Comparison of acid sulfite (AS)- and prehydrolysis kraft (PHK)-based dissolving pulps

The processability and quality of viscose are mainly influenced by the properties of dissolving pulps. Acid sulfite (AS) and prehydrolysis kraft (PHK) are the main commercial processes for the production of dissolving pulps. In this paper, the properties of dissolving pulps obtained from the AS and PHK processes, with respect to purity, molecular weight distribution (MWD), porosity, surface area, accessibility and reactivity, were comparatively evaluated. The results indicated that the PHK pulps had higher α-cellulose, lower S10/S18 content, and narrower MWD than the AS pulps, which can be ascribed to the different reaction mechanisms in the acid and alkaline pulping processes. The traditional parameters (S10/S18, α-cellulose and intrinsic viscosity) were insufficient to evaluate the pulp quality when comparing with dissolving pulps from different pulping processes. The Fock reactivity and the Chinese filterability tests were applied to evaluate their end-use properties in the rayon production process. The AS pulps had better accessibility than the PHK pulps (larger pore size and volume and thinner primary wall), supporting the conclusion that the AS samples exhibited higher reactivity that the PHK samples. The results from the Fock reactivity and Chinese filterability corresponded well.

Effect of type of aromatic nucleus in lignin on the rate of the β-O-4 bond cleavage during alkaline pulping process

Several C6–C3 and C6–C2-type dimeric non-phenolic β-O-4 lignin model compounds, whose aromatic nuclei consisting of the carbon skeleton and β-O-4 linkage are named the A- and B-rings, respectively, were treated under alkaline pulping conditions to examine whether or not the substitution of methoxyl group on the B-ring or of guaiacyl for syringyl A-ring accelerates the β-O-4 cleavage as a further study of our previous reports. It was suggested that either first or second substitution of methoxyl group on the B-ring accelerates the β-O-4 cleavage in both C6–C3 and C6–C2 compounds although the former compounds are more sensitive to the substitution than the latter, suggesting that the lack of the γ-hydroxymethyl group makes model compound insensitive to the substitution. It was confirmed that the substitution of guaiacyl for syringyl A-ring accelerates the β-O-4 cleavage in both C6–C3 and C6–C2 compounds with the degrees similar to each other regardless of the type of the B-ring. It was clarified that the leaving ability of the leaving B-ring phenoxides in the β-O-4 cleavage does not correlate well with the pK a values of the conjugate acids of the phenoxides, which is not in accordance with the common property of a nucleophilic substitution reaction.

Enhanced Hydrolysis of Hemicellulose in Corn Stalk by Alkali Pretreatment

Alkali hydrolysis was used as a method of decomposing hemicellulose in corn stalk in this paper. The effects of NaOH concentration, hydrolysis time and hydrolysis temperature in the pretreatment on the degradation of hemicellulose in corn stalk were investigated. In addition, the yields of reducing-sugar and alkali hydrolysis corn stalk were discussed. The experimental results showed that the process of alkali hydrolysis had positive effect on the removal of hemicellulose in corn stalk and the whole process almost finished in 3h. The maximum reducing-sugar yield was 7.2% by the pretreatment with 20% NaOH for 6 h at 90°C, and 6.6% under the condition of 15% NaOH for 3h at 90°C, which was slightly lower than the maximum reducing-sugar yield, but the alkali charge and hydrolysis time dramatically reduced. So it was clarified that the best pretreatment condition was 15% NaOH for 3h at 90°C, and also this method is easy to applied in the alkaline pulping process.

Quantitative Difference in the Rates of the β-O-4 Bond Cleavage between Lignin Model Compounds with and without γ-Hydroxymethyl Groups during the Alkaline Pulping Process

To examine the effect of the presence of γ-hydroxymethyl groups on the rate of the β-O-4 bond cleavage during the alkaline pulping process, the rates of the β-O-4 bond cleavage of non-phenolic lignin model compounds without a γ-hydroxymethyl group, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (G’G) and 2-(2,6-dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)ethanol (G’S), were compared with those of analogous model compounds with a γ-hydroxymethyl group, 2-(2-methoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (GG) and 2-(2,6-dimethoxyphenoxy)-1-(3,4-dimethoxyphenyl)propane-1,3-diol (GS), under alkaline pulping conditions. The disappearance of G’G or G’S was accompanied by the quantitative liberation of 2-methoxyphenol or 2,6-dimethoxyphenol, respectively, indicating that the disappearance resulted from the β-O-4 bond cleavage. The disappearance rate of G’G or G’S was in between those of the erythro and threo isomers of GG or GS, respectively. This result seems to be reasonably explained when the steric repulsions of the three staggered conformations are taken into consideration. The disappearance rate of G’G or G’S increased, but the increment became moderate with increasing hydroxide concentration.

Non-woody plants as raw materials for production of microfibrillated cellulose (MFC): A comparative study

The extraction of microfibrillated cellulose (MFC) from fibres of several non-woody plants (basts of flax, hemp, jute, leaves of sisal and abaca) has been explored. MFC was isolated using high pressure homogenization process at a pressure lower than 600bar. Fibres extracted from the plants by alkaline pulping process were first bleached and submitted to TEMPO-mediated oxidation to facilitate the fibrillation process. Evidence of the successful isolation of nanofibrils was given by FE-SEM observation revealing fibrils with a width in the 20 up to 50nm range, depending on the fibres origin. Particular attention was paid to characterize the ensuing MFC using different physical methods (DP, transparency degree, DRX) to enable a comparative analysis of the nanofibrils properties, and evaluate the ease of fibrillation. From this investigation, it seems that the fibres with the highest content in hemicelluloses led to the highest yield in MFC.