Organosolv Delignification Research Articles

Alcoholysis-induced changes in cell wall surfaces: Structural insights for the effective delignification of lignocellulosic biomass

Alcoholysis (organosolv delignification)-induced changes in cell wall surfaces were investigated to verify whether structural assessments are required for effective delignification. Softwood blocks of Cryptomeria japonica were subjected to alcoholysis at 100–150 °C, which gradually decreased their lignin content. Scanning electron microscopy revealed the emergence of amorphous mesh structures on the intercellular side and their transformation into spherical particles with increasing temperature. In addition, warty layers changed from uneven structures into spherical particles on the lumen side of tracheids. These particles produced in cell walls under harsh alcoholysis conditions, damaging the cell wall layers on both sides. Confocal laser scanning microscopy identified that they were mainly lignin eluted by alcoholysis. Alcoholysis at 130 °C providing the largest specific surface area showed intermediate stages of growth into spherical particles but allowed complete delignification when combined with NaClO2 bleaching. Therefore, the role of the spherical particles, which has so far been debatable, was clarified as causing damage rather than a bleaching accelerant. Focusing only on compositional changes while ignoring structural ones leads to the incorrect identification of optimal conditions that remove lignin but damage the cell walls. Our findings demonstrate that structural considerations are required for effective and noninvasive delignification.

Organosolv delignification of rice straw cellulose fiber for functional food packaging

Organosolv delignification of rice straw cellulose fiber for functional food packaging

An integrated olive stone biorefinery based on a two-step fractionation strategy

Olive stones (OS) constitute a waste lignocellulosic material produced by the olive oil industry in great amounts, that currently is only used as a low-value energy source for industrial or domestic boilers. Having in view its full valorization, this work proposes and validates an integrated strategy aiming to obtain three different streams of sugars / lignin-derived compounds. Dilute acid hydrolysis was used to obtain a xylose-rich hydroysate that was chemically converted into furfural with a 48.7 % yield. The resulting acid-pretreated solid biomass that consisted mainly of lignin and cellulose, was subjected to a catalyzed ethanol-based organosolv delignification. Temperature, time, and sulphuric acid concentration were optimized in order to recover added-value lignin products and digestible cellulose.

Organosolv delignification of birch wood (Betula pendula): DMSO/water pulping optimization

Abstract Improving the quality of cellulose semi-finished products for subsequent chemical processing in combination with the “green” concept is an important technical challenge. The article investigated a number of organic solvents as a delignifying agent. It has been shown that DMSO usage is the most efficient organosolv way to obtain cellulose from birch wood (B. pendula). The influence of the concentration of the organic solvent in the cooking liquid, the concentration of the acid catalyst, the duration and temperature of the process has been studied. The conditions for maximum process desirability at which the highest yield of cellulosic semi-finished product (CSP) and degree of delignification were as follows: 2 h treatment time at 156 °C, DMSO/water 75–95% solvent system with solid to liquid ratio of 1:10. At a concentration of DMSO in the cooking liquor of 85–90%, the degree of wood delignification was about 95%. The mechanical properties of the experimental DMSO pulp were similar to those of kraft pulp. DMSO lignin was characterized by Pyr-GC/MS. More than 65% of monomer fragments of phenolic compounds were S-unit derivatives. The results show that organosolv delignification with DMSO/Water can be proposed as an eco-friendly alternative process to the kraft pulping.

Mild Organosolv Delignification of Residual Aspen Bark after Extractives Isolation as a Step in Biorefinery Processing Schemes.

European aspen (Populus tremula (L.) (Salicaceae)) bark is a promising raw material in multi-step biorefinery schemes due to its wide availability and higher content of secondary metabolites in comparison to stem wood biomass. The main objective of this study was to investigate the major cell wall component-enriched fractions that were obtained from aspen bark residue after extractives isolation, primarily focusing on integration of separated lignin fractions and cellulose-enriched bark residue into complex valorization pathways. The “lignin first” biorefinery approach was applied using mild organosolv delignification. The varying solvent systems and process conditions for optimal delignification of residual aspen bark biomass were studied using a response surface methodology approach. The conditions for maximum process desirability at which the highest amount of lignin-enriched fraction was separated were as follows: 20-h treatment time at 117 °C, butanol/water 4:1 (v/v) solvent system with solid to liquid ratio of 1 to 10. At optimal separation conditions, lignin-enriched fraction exhibited a higher content of β–O–4 linkages vs. C–C linkages content in its structure as well as a high amount of hydroxyl groups, being attractive for its further valorization. At the same time, the content of glucose in products of cellulose-enriched residue hydrolysis was 52.1%, increased from 10.3% in untreated aspen bark. This indicates that this fraction is a promising raw material for obtaining cellulose and fermentable glucose. These results show that mild organosolv delignification of extracted tree bark can be proposed as a novel biorefinery approach for isolation of renewable value-added products with various application potentials.

Formic Acid-Based Organosolv Delignification of Sugarcane Bagasse for Efficient Enzymatic Saccharification

Formic Acid-Based Organosolv Delignification of Sugarcane Bagasse for Efficient Enzymatic Saccharification

Integral valorisation of walnut shells based on a three-step sequential delignification

Walnut kernels represent no more than 50–60% of the total weight of the fruit, so the sum of walnut shells generated every year is immense. Nonetheless, these shells could be further valorised for the extraction of their main constituents following a biorefinery scheme. Hence, the objective of this work was an integral valorisation of walnut shells, which involved a sequential organosolv delignification (200 °C, 90 min, 70/30 v/v EtOH/H2O, LSR 6:1) and several posterior non-isothermal hydrothermal treatments (180, 195 and 210 °C, LSR 8:1). Moreover, the spent solids after the aforementioned treatments were evaluated as possible sources of cellulose nanocrystals. The results showed that the sequential organosolv delignifications presented relative lignin yields up to 60%, which leaded to lignins that just differed on their molecular weight distributions. The hydrothermal treatments were efficient for the removal of still present hemicelluloses (14.7–71.8%), and permitted a successful cellulose nanocrystal obtaining whereas the spent solid from the delignification stages did not. Thus, this study presented an innovative strategy for the integral valorisation of walnut shells.

Fractionation of Eucalyptus regnans wood: properties of the soluble products and reactivity of the treated solids

Eucalyptus regnans wood samples were treated with water under diverse conditions, in order to obtain soluble hemicellulose-derived products. The composition of the liquid phase from the treatment leading to the best results was characterized in depth using a combination of spectrophotometric, spectrometric and chromatographic methods; and the susceptibility of the treated solids to further fractionation by organosolv delignification was assessed in additional experiments. The chemical and physicochemical properties of the resulting lignin were determined, and the suitability of the delignified solids as substrates for the one-pot manufacture of ethyl levulinate was evaluated on a quantitative basis.

Life Cycle Assessment of various biorefinery approaches for the valorisation of almond shells

In the near future, sustainable and efficient biorefineries would be essential for the production of commodity chemicals and high-added value compounds. Therefore, in this work, six scenarios differing on the delignification steps and cellulose conversion routes were assessed via Life Cycle Assessment methodology in order to study the environmental impacts derived from the conversion of an abundant agricultural residue (almond shells) into high added-value products and select the most suitable one for large-scale valorisation. The assessments were conducted employing experimental results and processing them by SimaPro software. The main conclusion achieved suggested that the enzymatic hydrolysis of the solid from any delignification step entailed the highest environmental impacts and had the highest relative contribution in all the studied impact categories with a maximum of 74%, which was ascribed to Scenario 5. It was also concluded that the organosolv delignification process affected overall more negatively than the alkaline treatment having bigger impacts especially in abiotic depletion (ADP) and photochemical oxidation (POP) categories. Finally, it can be stated that the best route for valorising the almond shell in a biorefinery facility is composed of autohydrolysis (common for every scenario), alkaline delignification, bleaching and acid hydrolysis steps for the obtaining of oligosaccharides, lignin and nanocrystals as products.

Steam explosion pretreatment improves acetic acid organosolv delignification of oil palm mesocarp fibers and sugarcane bagasse

Steam explosion can be used to pretreat lignocellulosic materials to decrease energy and chemical consumption during pulping to obtain environmentally friendly lignin and to improve lignin yield without changing its structure. The objective of this study was to evaluate the extraction of lignin from oil palm mesocarp fibers and sugarcane bagasse using steam explosion pretreatment followed by acetosolv. The biomasses were pretreated at 168 °C for a reaction time of 10 min. Steam explosion combined with acetosolv at lower severities was also carried out. Steam explosion followed by acetosolv increased the lignin yield by approximately 15% and 17% in oil palm mesocarp fibers and sugarcane bagasse, respectively. In addition, steam explosion decreased the reaction time of acetosolv four-fold while maintaining the lignin yield from sugarcane bagasse. Similar results were not obtained for oil palm mesocarp. High-purity and high-quality lignins were obtained using steam explosion pretreatment with structural characteristics similar to raw ones. Sugarcane bagasse lignin seems to be a better option for application in material science due its higher lignin yield and higher thermal stability. Our findings demonstrate that steam explosion is efficient for improving lignin yield and/or decreasing pulping severity.

Development of Pretreatment Strategies for the Fractionation of Hazelnut Shells in the Scope of Biorefinery

Hazelnut shells are an important waste from the hazelnut processing industry that could be valorized in a multi-product biorefinery. Individual or combined pretreatments may be integrated in processes enabling the integral fractionation of biomass. In this study, fractionation methods based on alkaline, alkaline-organosolv, organosolv, or acid-catalyzed organosolv treatments were applied to raw or autohydrolyzed hazelnut shells. A comparative analysis of results confirmed that the highest lignin removal was achieved with the acid-catalyzed organosolv delignification, which also allowed limited cellulose losses. When this treatment was applied to raw hazelnut shells, 65.3% of the lignin was removed, valuable hemicellulose-derived products were obtained, and the cellulose content of the processed solids increased up to 54%. Autohydrolysis of hazelnut shells resulted in the partial solubilization of hemicelluloses (mainly in the form of soluble oligosaccharides). Consecutive stages of autohydrolysis and acid-catalyzed organosolv delignification resulted in 47.9% lignin removal, yielding solids of increased cellulose content (55.4%) and very low content of residual hemicelluloses. The suitability of selected delignified and autohydrolyzed-delignified hazelnut shells as substrates for enzymatic hydrolysis was assessed in additional experiments. The most susceptible substrates (from acid-catalyzed organosolv treatments) reached 74.2% cellulose conversion into glucose, with a concentration of 28.52 g glucose/L.

Hydrothermal treatments of walnut shells: A potential pretreatment for subsequent product obtaining

Walnuts are nowadays widely consumed. Since the edible part of walnuts does not account more than 50–60% of their total weight, the total amount of shells produced annually is huge. However, as walnut shells are part of lignocellulosic biomass, they could be valorised via a biorefinery approach in order to extract their diverse constituents. For this reason, the aim of this work was to valorise walnut shells by a biorefinery scheme. The latest involved multiple microwave assisted and conventional hydrothermal treatments for the subsequent valorisation of oligosaccharides. Then, an organosolv delignification of the solid that permitted the maximum oligosaccharide yield was performed, in order to isolate the lignin. Finally, it was treated for cellulose nanocrystal obtaining. The results showed, on the one hand, that the hydrothermal treatments leaded to xyloligossacharide-rich liquors (1–17 g/L). On the other hand, the organosolv delignification resulted into the extraction of a highly pure lignin (93.6%) and a weight average molecular weight of 7000 Da. Moreover, the solid from the delignification treatment was suitable for a successful nanocrystal production. The extracted fractions could be employed in many applications and could be considered renewable precursors for new materials and chemicals. Hence, the proposed biorefinery scheme would allow an integral valorisation of currently undervalued walnut shells.

One-step synthesis of biomass-based sulfonated carbon catalyst by direct carbonization-sulfonation for organosolv delignification

Biomass-based sulfonated carbon catalyst (SCC) was prepared from corncob via direct sulfuric acid carbonization-sulfonation treatment. Central composite design was used to evaluate temperature and time for optimizing SCC yield and sulfonic acid (SO3H) density. The SO3H groups were successfully introduced to the SCC as evidenced by FTIR and sulfur analysis. Numerical optimization results showed that 100 °C and 5.78 h are the optimal conditions for maximizing yield (61.24%) and SO3H density (1.1408 mmol/g). The highest ethanol organosolv lignin (EOL) yield of 63.56% with a substrate yield of 39.08% was achieved at 20% SCC loading in the ethanol organosolv delignification of lignocellulosic biomass. The FTIR spectra of the isolated lignin revealed typical features of G-lignin, indicating that no drastic changes took place in the lignin structure during the process. This study developed a simple one-step preparation method of SCC, which was successfully used as a catalyst in an organosolv delignification of biomass.

Comparative Study on Pretreatment Processes for Different Utilization Purposes of Switchgrass.

Switchgrass (Panicum virgatum, L., Poaceae) with the advantages of high cellulose yield, and high growth even under low input and poor soil quality, has been identified as a promising candidate for production of low-cost biofuels, papermaking, and nanocellulose. In this study, 12 chemical pretreatments on a laboratory scale were compared for different utilization purposes of switchgrass. It was found that the pretreated switchgrass with sodium hydroxide showed considerable potential for providing mixed sugars for fermentation with 11.10% of residual lignin, 53.85% of residual cellulose, and 22.06% of residual hemicellulose. The pretreatment with 2.00% (v/v) nitric acid was the best method to remove 78.37% of hemicellulose and 39.82% of lignin under a low temperature (125 °C, 30 min), which can be used in the production of nanocellulose. Besides, a completely randomized design analysis of switchgrass pretreatments provided the alternative ethanol organosolv delignification of switchgrass for the papermaking industry with a high residual cellulose of 58.56%. Finally, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR) were carried out to confirm the changes in functional groups, crystallinity, and thermal behavior of the three materials, respectively, from the optimal pretreatments.

Prehydrolysis and organosolv delignification process for the recovery of hemicellulose and lignin from beech wood

Beechwood was fractionated using a two-stage process approach followed by enzymatic hydrolysis of the obtained pulp. Where most of the xylan was recovered by the prehydrolysis in the first stage, while the most lignin was recovered in the subsequent organosolv delignification. Close to 85.8 wt% of the original xylan was recovered (prehydrolysis: 150 °C, 90 min, and 20 mM H2SO4) compared to 8.9 wt% of the original xylan in case of organosolv, without the prehydrolysis stage (organosolv: 150 °C, 70 min, 50% w/w aqueous ethanol, and 20 mM H2SO4). Low severity prehydrolysis was found to enhance the lignin yield by organosolv delignification (the maximum lignin yield obtained was 82.7 wt% of the original lignin), which implies that the lignin recondensation was reduced during the prehydrolysis. Prehydrolysis substantially improved the enzymatic cellulose digestibility from 56.74 g/L, after organosolv without prehydrolysis to 86.75 g/L.

Sorption properties of organosolv lignin towards methylene blue

Involvement of secondary raw materials such as plant wastes and by-products of plant materials processing for solving problems of environmental pollution is considered as a promising direction by scientists in many countries of the world. The purpose of the paper is to study the structure and sorption properties of lignin as a by-product of organosolv delignification of wheat straw. In this work lignin precipitated from the spent cooking solution after oxidative-organosolv delignification of wheat straw was used as the raw material. Different methods of analysis were used to study the structure and properties of the obtained lignin, including gravimetric, spectroscopy, and microscopy. The sorption capacity of the material with respect to methylene blue was studied using model solutions and a spectrophotometric method to determine dye concentrations.Investigation of the sample by the method of infrared spectroscopy and scanning electron microscopy showed that organosolv lignin is a highly dispersed material with particles of various shapes and sizes, and contains a small number of polysaccharides, the total pore volume of such material is 0.431 cm3. The sorption capacity of lignin towards methylene blue was investigated as a function of the pH of the dye aqueous solution, its initial concentration, and the duration of the process. It is shown that the sorption capacity is largely depends on the pH of the medium and increases with a change in pH from 3 to 6. However, a further increase in pH does not change the specified indicator. This dependence of the sorption capacity is related to the property of the surface of the plant material to change the charge from positive in acidic medium to negative in neutral and alkaline, due to the presence of oxygen-containing functional groups (mainly phenolic and aliphatic hydroxyls), which are easy can be protonated and deprotonated. The absorption kinetics of the dye is quite fast and the sorption equilibrium is reached within the first 120 min of contact. Pseudo-first and pseudo-second order models and intraparticle diffusion were used to study the sorption kinetics. Compared to the kinetic model of pseudo-first order (R2 = 0,985) and intraparticle diffusion (R2 = 0,856), the kinetic model of pseudo-second order (R2 = 0,999) better describes the kinetics of sorption and indicates that fixation of the dye on the surface of the material takes place with the involvement of different mechanisms. To study the adsorption equilibrium in the sorption of methylene blue, model solutions with initial dye concentrations of 30 to 500 mg/l were used. It was found that at an initial concentration of methylene blue in a solution below 100 mg/l, the sorption capacity increases linearly with increasing initial concentrations. Then the increase in the sorption capacity is slower. The maximum sorption capacity is 44.7 mg/g. In the case of the adsorption isotherm, the Langmuir equation (R2 = 0.996) is more suitable than the Freundlich equation (R2 = 0.955) to describe the absorption process of the cationic dye and indicates that the adsorption is a monolayer.In general, it was shown that organosolv lignin from wheat straw with sorption capacity slightly exceeds oreganoslv lignin from other plant raw materials. Creating new, inexpensive and effective materials is an urgent task for scientists. Developing new resource-saving technologies to solve the problem of environmental pollution is a priority for chemical technology and ecology worldwide. This is especially important for Ukraine, as efficient processing of agricultural plant waste with the use of environmentally friendly technologies will help to meet the needs of many industries and improve the environment. It is promising for further to study the structure of organosolv lignin to determine the content of various functional groups and to determine the possibility of its use for absorption heavy metal ions from aqueous solutions.

Comparative study of biorefinery processes for the valorization of fast-growing Paulownia wood

In this work, valorization of Paulownia wood (PW) was proposed following several process configurations for biofuels and value-added compounds production. Firstly, autohydrolysis and ethanol-organosolv strategies were assessed separately for the fractionation of PW to enhance the enzymatic digestibility of cellulose. A third strategy focused on a sequential process (autohydrolysis and organosolv) was explored. Two temperatures were selected for the first stage of the combined process. High concentration of oligosaccharides (26.29 g/L) and high concentration of degradation products (17.21 g/L) were obtained at 210 and 230 °C, respectively. The solids obtained from both pretreatments were subjected to organosolv delignification (200 °C, 3 h and 50% ethanol) achieving delignification of 58 and 30% for the autohydrolyzed biomass at 210 °C and 230 °C, respectively. The combined process resulted in susceptible biomass able to produce 64 g/L of ethanol. Therefore, the strategies explored in this work open the possibility to build a refinery around Paulownia wood.

OxiOrganosolv: A novel acid free oxidative organosolv fractionation for lignocellulose fine sugar streams

The valorization of lignocellulosic biomass towards the production of value-added products requires an efficient pretreatment/fractionation step. In this work we present a novel, acid-free, mildly oxidative organosolv delignification process -OxiOrganosolv- which employs oxygen gas to depolymerize and remove lignin. The results demonstrate that the OxiOrganosolv process achieved lignin removal as high as 97% in a single stage, with a variety of solvents; it was also efficient in delignifying both beechwood (hardwood) and pine (softwood), a task in which organosolv pretreatments have failed in the past. Minimal amounts of sugar degradation products were detected, while cellulose recovery was ~100% in the solid pulp. Enzymatic hydrolysis of pulps showed >80 wt% cellulose conversion to glucose. Overall, the OxiOrganosolv pretreatment has significant advantages, including high delignification efficiency of hardwood and softwood biomass, absence of acid homogeneous catalysis and all corresponding challenges involved, and close to zero losses of sugars to degradation products.

Use of biomass for a development of nanocellulose-based biodegradable flexible thin film thermoelectric material

In this work, we used solar energy converted via photosynthesis into chemical energy of the biomass of the fast-growing perennial herb Miscanthus × giganteus for the manufacture of nanocellulose (NC) films, which are biodegradable alternative to common petroleum-based polymer substrates used in flexible electronics. To create the NC substrates, we applied an environmentally friendly method of organosolv delignification of plant raw materials carried out at a low temperature and in a relatively short time. Then by means of the low-temperature cheap and scalable method Successive Ionic Layer Adsorption and Reaction (SILAR) we deposited copper iodide (CuI) film of 0.72 µm thickness on both sides of the 12 µm thick NC substrate, and thus obtained light-weight and flexible biodegradable nontoxic thermoelectric material CuI/NC. Crystal structure, morphology, chemical composition, and optical, electrical and thermoelectric properties of the CuI/NC have been researched. Studies have shown that nanostructured p-type semiconductor CuI film in the CuI/NC TE material is quite dense and completely covers the NC surface. It has typical optical direct band gap ≈ 3.0 eV, is single-phase γ-CuI with crystallite sizes in the 19–25 nm range, with moderate dislocation density of (1.6–2.8) × 1015 lines/m2, and tolerable microstrains ε of (4–9) × 10−3 a.u. The determined value of the Seebeck coefficient S is ~228 μV K−1, at that, S is constant in the temperature range 290–335 K. Together with the thermoelectric power factor ≈ 36 μW·m−1·K−2it is favorable for the use of CuI/NC as new thermoelectric material for an in-plane design of biodegradable flexible thin film thermoelectric generator (TEG). At temperature gradient of 50 K, the single p-CuI thermoelectric leg made from CuI/NC strip of 3 cm long and 0.5 cm wide generates open circuit voltage 8.4 mV, short circuit current 0.7 µA and maximum output power 1.5 nW. It corresponds to the output power density 10 µW/m2, and thus confirms the suitability of CuI/NC to obtain electricity by the harvesting the waste environmental heat.

The effect of using different acids to catalyze the prehydrolysis stage on the organosolv delignification of beech wood in two-stage process

In this study, beech wood was fractionated in lab scale rector by one-stage and two-stage processes. The two-stage processes of the prehydrolysis with no catalyst (only water) and catalyst (sulfuric, phosphoric, oxalic acids), and the subsequent effect on the organosolv process were studied. A one-stage organosolv delignification of beech wood (control experiment) was conducted at 155 °C for 160 min in 1:1 ethanol/water mixture with 100 mM sulfuric acid, while the two-stage processes were conducted starting from the uncatalyzed and catalyzed (20–200 mM) prehydrolysis of beech wood at 175 °C for 60 min. The results indicate that sulfuric acid enhanced the removal of xylan from beech wood during the prehydrolysis stage. Moreover, the effectiveness of the delignification of beech wood using a one-stage process is more than the two-stage, as well as the enzymatic digestibility of the pulp, which was better than those of the two-stage processes. However, the enzymatic digestibility results of the pulp obtained after sulfuric acid catalyzed prehydrolysis followed by organosolv delignification shown better results than the other two-stage processes. Additionally, high klason content, low sugar content, low Mw, and high phenolic hydroxyl groups of lignin was recovered by a one-stage organosolv delignification.