Delignification Pretreatment Research Articles

Effect of delignification pretreatment and furfurylation on practical properties of alder wood (Alnus spp.)

Partial delignification of alder wood specimens was performed with alkaline sulfite and peracetic acid (PAA) methods, and subsequently the delignified samples were saturated with furfuryl alcohol, as an eco-friendly chemical. The aim of delignification before furfurylation was to facilitate the penetration of furfuryl alcohol into the cell wall, in order to overcome the weak mechanical properties and hydrophilicity of alder wood as a fast growing species. The results showed that alkaline delignification removed a lower percentage of lignin despite more significant mass loss as compared to peracetic acid delignification method, which indicates more carbohydrates degradation in alkaline delignification. Infrared spectroscopy also confirmed more retention of carbohydrates in the sample delignified with peracetic acid. The polymerization of furfuryl alcohol in the cell cavities decreased the access of water molecules to the hydroxyl groups of the cell wall, increased the contact angle, and decreasing surface wettability. This effect was more noticeable in the PAA-delignified samples. Mechanical tests revealed that the delignified samples with peracetic acid had higher mechanical strength and modulus, compared to the alkaline sulfite delignified samples. This was attributable to the maintenance of carbohydrates during the delignification process.

Optimized Furfural Production Using the Acid Catalytic Conversion of Xylan Liquor from Organosolv-Fractionated Rice Husk

This study determined the optimal production of furfural (FuR) from liquid hydrolysate xylan liquor obtained through a two-stage pretreatment process using NaOH for de-ashing and EtOH for the delignification of raw rice husk (RH). The de-ashing pretreatment was conducted at 150 °C, with 6.0% (w/v) NaOH and a reaction time of 40 min. The optimal conditions for delignification pretreatment, performed using an organosolv fractionation method with EtOH, were a reaction temperature of 150 °C, 60% (v/v) EtOH, 0.25% (w/v) H2SO4, and a reaction time of 90 min. Through a two-stage pretreatment process, a liquid hydrolysate in the form of xylan liquor was obtained, which was subjected to an acid catalytic conversion process to produce FuR. The process conditions were varied, with reaction temperatures of 130–170 °C, H2SO4 catalyst concentrations of 1.0–3.0 wt.%, and reaction times of 0–90 min. The Response Surface Methodology tool was used to identify the optimal FuR yield from xylan liquor. Ultimately, the optimal process conditions for the acid catalytic conversion were found to be a substrate-to-catalyst ratio of 2:8, a reaction temperature of 168.9 °C, a catalyst concentration of 1.9 wt.%, and a reaction time of 41.24 min, achieving an FuR yield of 67.31%.

PHYSICO-CHEMICAL AND ELECTROCHEMICAL DELIGNIFICATION AS A PRETREATMENT OF LIGNOCELLULOSIC BIOMASS FOR DIFFERENT APPLICATIONS: A MINI-REVIEW

In recent years, the applications of lignocellulosic biomass (LCB) have substantially increased due to its versatility in different areas of study and interest. Therefore, it is evident that the delignification pretreatment of LCB is fundamental to assure the viability and commercial quality of the final product for different industrial uses. The efficiency of delignification, the obtainment of the desired products, and the required quality depend mainly on the type of pretreatment and the method used. This paper presents a state-of-the-art overview of physical, chemical, organic, biological, hybrid (combination of two or more pretreatments), and other novel pretreatments for the delignification of different lignocellulosic biomass. Additionally, the conditions necessary for the application of the pretreatments, the effect of the variables involved, and the advantages and disadvantages of each method are discussed. Finally, advances in the development of sustainable methods are discussed.

Pretreatment of Camellia oleifera shell by ethanolamine-based solvents for selective delignification and enhanced enzymatic saccharification

Fruit shell biomass is an agricultural waste that could be valorised into various value-added chemicals. However, the intertwined structure between lignin and holocellulose limits free sugar generation for further fermentation, requiring efficient pretreatment for selective delignification. We pretreated Camellia oleifera shell by ethanolamine-based solvents (binary deep eutectic solvents and single ethanolamine or its derivatives), and compared pretreatment effectiveness of these solvents. Single ethanolamine was the best among ethanolamine-based solvents, indicating the unnecessity of deep eutectic solvent synthesis. Furthermore, structural characterization confirms that ethanolamine could effectively deconstruct Camellia oleifera shell with the highest delignification (76.46%) and sugar yields (83.73% for glucose and 66.87% for xylose) at 130 °C for 3 h. Additionally, correlation analysis suggests that alkalinity and proton dissociation capacity together determined the delignification capacity of ethanolamine. Our findings serve a potential solution to valorise the waste fruit shell lignocellulose resources.

The Effect of Ultrasonication and Delignification Treatment on the Sugar Released Value of Wood

The objective of these research was to study the impact of ultrasonication and delignification pretreatments in several wood species on their easiness for enzymatic hydrolysis, having the potential to be developed as the feedstocks for bioethanol production. Four different wood species from three botanical gardens in Indonesia have been selected, i.e., Gymnostoma sumatranum, Firmiana malayana, Pterocarpus indicus, and Alstonia scholaris, due to their higher sugar released values than a fast-grown tree, Sengon (Paraserianthes falcataria), when all were directly enzymatically hydrolyzed without pretreatment. The sugar released values after ultrasonication and enzymatic hydrolysis were between 3 – 5.5 mg/100 mg wood meal. When delignification pretreatment was performed, the sugar released values were higher than those with ultrasonication, ranging between 4 – 10.2 mg/100 mg wood meal. All the sugar released values after pretreatment were higher than those without pretreatment. Gymnostoma sumatranum was selected as the most potential wood species in this study due to its consistency among the species producing highest sugar released across different treatments. The SEM results showed that there was no significant changes in the morphological structure of the untreated fiber before and after enzymatic saccharification since it still had a complex structure due to the high lignin content. However, after the delignification treatment, the surface morphology of the fiber showed a decrease in the number of pits of the fiber, the surface residual of pits were reduced, parallel lines were more clearly visible, and the fiber structure was damaged with more small holes presented. The surface morphology of the fiber from the wood powder having delignification pretreatment supports the sugar released values which shows that the these values were higher than other treatments due to more recalcitrant substances were degraded, making it was easier for enzymes to break down cellulose. After ultrasonication, the SEM result showed less disrupted cell wall compared to after delignification which confirmed the higher sugar released data with delignification.

Flame retardant effect of lignin/carbon nanohorns/potassium carbonate composite flame retardant on fir pretreated under different methods

Fir wood is widely used in construction, however its thermal degradability and flammability pose significant challenges to its safe use. In this work, we used a new carbonaceous nanomaterial called single-walled carbon nanohorns (SWCNHs), in combination with lignin and potassium carbonate to prepare a composite flame retardant and investigated the effect of different pretreatments on the flame retardant effect of fir wood. After delignification pretreatment and vacuum impregnation of fir wood with the flame retardant, the pk1-HRR and the pk2-HRR decreased by 37.59 % and 25.07 %, THP decreased by 55.71 %, TSP decreased by 59.81 %, COP significantly decreased by 74.02 %, char residual weight increased by 14.11 % compared with new wood (NW), and LOI reached 28.8 %. And the composite flame retardant forms a char layer during burning, which acts as a protective layer. This provides new insights into the application of SWCNHs in wood flame retardancy.

Investigating the potential of avocado seeds for bioethanol production: A study on boiled water delignification pretreatment

The increasing need for alternative fuels to replace fossil fuels has made bioethanol a promising option. Although numerous sources of sugar generation and agricultural wastes can be converted into ethanol, Avocado Seeds (AS) are particularly attractive as raw materials due to their abundance, high carbohydrate content, and lack of interactions with the food chain. Therefore, this study investigated the potential of AS for bioethanol production using several steps, including boiled water delignification pretreatment, catalytic hydrolysis, and fermentation with Saccharomyces cerevisiae. The delignification pretreatment of AS involved soaking in 4% (w/v) sodium hydroxide liquor for 24 hours. Then the mixture was heated to 80°C and stirred slowly for 2.5 hours and after that washing with boiled water at 100 oC for 1.5 hours and screening the mixture. Subsequently, catalytic hydrolysis and fermentation were carried out using two different concentrations of Saccharomyces cerevisiae as yeast, namely 10% (w/v) and 15% (w/v). Qualitative sample analysis was conducted using scanning electron microscopy (SEM) to observe the effect of delignification pretreatment, while FTIR analysis using Thermo Scientific Nicolet iS50 was used to test for glucose functional groups. Quantitative analysis was performed using gas chromatography 7890b mass spectrophotometry 5977A, Agilent DBVRX to determine hydrolysate fermentation. The results revealed that the highest ethanol yield was achieved through fermentation with 15% (w/v) yeast and 40% (v/v) catalyst, resulting in an ethanol yield of 83.755% of the theoretical maximum.

Chemomechanical pretreatment for efficient delignification and saccharification of corn stover biomass

The development of multifunctional pretreatments for effective and economical fractionation of lignocellulosic biomass (LCB), while targeting entirely lignocellulose-oriented valorization can pave the cutting-edge innovation in biorefinery. Herein, a promising high-solid chemomechanical pretreatment (CMP) based on ball milling (BM) coupled with ethylenediamine (EDA) pretreatment was designed to maximize the output of corn stover (CS) biomass under the mild temperature (≤120 °C) and active stabilization. The synergistic effects of EDA/BM configuration brought about desirable characteristics that eventually intensify delignification and saccharification at the expense of less solvent load and energy consumption up to 3.0 MJ kg−1 compare with EDA pretreatment (7.3 MJ kg−1). Importantly, CMP generated aminated and uncondensed lignin up to 85 % at 400 rpm for 1 h, with a high content of β-O-4 linkages (44.7/100Ar), which render it competently suitable for valorization into nitrogen-containing aromatic chemicals and lignin-based fluorescent materials. CMP led to 97 % conversion of glucan, and 94 % of xylan in 72 h at enzymatic loading of 1 and 0.5 %w. w-1 of Cellic CTec3 and xylanase, respectively. This lignin-first and entirely lignocellulose-oriented pretreatment could overcome the hampering of solid-state conversion and contribute to the sustainable LCB-based economy.

Low-temperature highly selective water delignification based on geopolymer materials

Delignification pretreatment is the main source of high cost and high pollution in biomass processing. This paper reports on a simple cheap geopolymers-based highly selective and efficient pretreatment process for delignification under low-temperature water-cooking without discharging black liquor. The geopolymer with a SiO2/Al2O3 ratio of 4.4 showed the largest number of acidic sites and highest catalytic activity. Under mild reaction conditions (mGeopolymer/mFiber = 1/4, 90 min and 90 °C), the delignification rates of woody (eucalyptus) and herbaceous (bagasse) biomass increased by up to 38.90% and 62.20%, respectively. Moreover, the low-alkali black liquor produced by the new water delignification process facilitates subsequent water treatment, eliminating the need for alkali recovery. This study confirms the immense application prospects of geopolymers for the highly selective delignification of most biomass fibre. This study will develop a low-temperature water-cooking process for the delignification of papermaking or biomass processing without wastewater discharge.

Enhancement of Enzymatic Hydrolysis of Sugarcane Bagasse by the Combination of Delignification Pretreatment and Polysorbate 80

Delignification pretreatment with alkali under various conditions (25–160 °C for 1–12 h) or sodium chlorite at 75 °C for 4 h was applied to improve the enzymatic digestibility of sugarcane bagasse by removing hemicellulose and lignin. Compared with the elimination of hemicellulose, delignification contributed more in achieving a higher glucose yield. In addition, the characterization of untreated and pretreated sugarcane bagasse was conducted to determine the influence of hemicellulose and lignin degradation on subsequent enzymatic digestibility. Furthermore, Polysorbate 80 was added to reduce the enzyme loading, shorten the hydrolysis time, and enhance the efficiency of enzymatic hydrolysis, suggesting that the glucose yield of 92.2% was obtained with enzyme loading of 5 FPU/g substrate. However, the increased yield of glucose with Polysorbate 80 occurred with an increased lignin content and a reduction of enzyme loading, and the yield decreased sharply as the hydrolysis time was prolonged from 6 h to 24 h.

Efficient delignification of sugarcane bagasse by Fenton oxidation coupled with ultrasound-assisted NaOH for biotransformation from Agaricus sinodeliciosus var. Chaidam

Sugarcane bagasse (SCB), a widely available lignocellulosic by-product, could be potentially used in macrofungal bioconversion for high-value bioactive compounds. For macrofungus with poor lignin degradation capacity, its recalcitrant lignin structure blocked the release of fermentable sugars for cell growth. Herein, the main objective was to construct an effective delignification pretreatment strategy for SCB biotransformation and synthesis of bioactive substances by Agaricus sinodeliciosus var. Chaidam. Different pretreatments including chemical (alkali and Fenton oxidation) and ultrasound methods were used to intensify the delignification process. Physico-chemical characteristics of native and pretreated SCB were examined via XRD, XPS, FT-IR and 13C ssNMR to characterize crystallinity index, surface lignin and chemical structure. Lignocellulose-degrading enzymes were also used to assess the ability of the macrofungus to degrade SCB. By comparing morphological structure, chemical composition and fermentation characteristics, a suitable multiple sequential pretreatment method was finally identified. Our findings revealed that Fenton-ultrasound-alkali pre-treatment has an optimum delignification effect on SCB with never-uncovered excellent ability to detoxify harmful substances produced by Fenton oxidation. Under this pretreatment condition, the cellulose content was increased by 106.45%, whereas hemicelluloses and lignin were decreased by 48.34% and 74.15%, respectively. The macrofungal growth, intracellular polysaccharides, total phenols and terpenoids formation were 2.4, 1.46, 1.36 and 1.66 times higher than those of the untreated, respectively. Fermentation kinetic results showed outstanding fit and prediction of macrofungal growth and enzymatic activity secretion on above pretreated SCB. This study shed light on developing a novel pretreatment strategy for low-cost SCB lignocellulose transformation into high-value products.

A combination of deep eutectic solvent and ethanol pretreatment for synergistic delignification and enhanced enzymatic hydrolysis for biorefinary process

A novel pretreatment system containing deep eutectic solvents and ethanol (DES-E) for synergistic carbohydrate conversion and delignification was reported in this study. The DES-E pretreatment resulted in an enhanced glucose yield compared to individual DES and ethanol pretreatment for the three tested biomass, including Broussonetia papyrifera, corn stover and pine. To further explore the delignification mechanism, the solubilized lignin and residual lignin from Broussonetia papyrifera was recovered and extracted, then thoroughly characterized. The highest total OH content was found in the DES-E solubilized lignin, which could be used as antioxidant. The presence of ethanol in pretreatment liquor could protect the β-O-4 substructure from breakage and reduce lignin condensation, which favors the subsequent enzymatic hydrolysis. Comparable glucose yield and delignification performance was achieved by recycled DES. DES-E pretreatment offers a promising method for lignin isolation and cellulose digestibility improvement simultaneously.

Valorization of Lower Grade Resin, Bark, and Fruit of Styrax Sumatrana

Styrax sumatrana or the kemenyan tree grows in North Sumatera, Indonesia, and its resin is commonly utilized by the local community. Other parts of kemenyan, such as barks and fruits contain valuable compounds that can be extracted to produce high-value bioproducts. This study examined the effect of different resin grades on the physical parameters and cinnamic acid content, delignification pre-treatment period of kemenyan barks with Phanerocahete chrysosporium on the amount of extracted saponin from the barks, and different fruit ripeness on the composition of the fruits. This study showed that grade IV, V and VI resin contain 21.78 to 24.89% cinnamic acid. The isolated cinnamic acid had a purity of 90.9 to 94.3%. Pre-treatments of kemenyan barks were able to degrade 15% of the lignin after 21 days of incubation with Phanerochaete chrysosporium. and increased the amount of extracted saponin up to 7.5-fold higher compared to the non-pre-treated barks. Ripe kemenyan fruits had a higher protein (4.27-10.23%) and crude fat (0.91-7.36%) content as compared to the unripe fruits. Fatty acid composition of the crude fat had been determined and primarily consists of linoleic acid (31.71-42.33%) and palmitic acid (30.44-30.82%) for both ripe and unripe fruits.

Evaluation of volatile fatty acids (VFAs) production in thermophilic and mesophilic anaerobic digestion of oil palm empty fruit bunch (OPEFB)

Palm oil is one of the leading global commodities, and Indonesia is one of the largest palm oil producers in the world. One of the solid wastes generated from oil palm industrial activities is oil palm empty fruit bunches (OPEFB). The annual accumulation of OPEFB in Indonesia is 126,317.54 tons/year, and it increases with increasing palm oil production. The cellulosic content of OPEFB is a potential substrate for anaerobic digestion to produce volatile fatty acids (VFAs). This study used chemical pretreatment (NaOH 8% w/V) for OPEFB delignification before the anaerobic digestion for VFAs production. Digested cow manure (DCM) was used as the inoculum. Process optimization of producing VFAs is challenging because VFAs act as intermediate products in the metabolic pathway of anaerobic digestion. In general, the temperature can affect the activity of hydrolytic and acidogenic facultative microorganisms. It increases the hydrolysis rate of organic polymers to more soluble forms and improves the performance of anaerobic reactors for the formation of VFAs. This study examines the effect of temperature on the anaerobic digestion process of OPEFB for VFAs production in a batch reactor. The temperature varied in mesophilic (29 °C) and thermophilic (55 °C) conditions. This study showed that anaerobic digestion in the thermophilic conditions produces almost thrice VFAs compared to the mesophilic process. The highest accumulation of VFAs in both reactors occurred on the seventh day, i.e., 3311.57 ± 89 mg.L−1 at ORP -163 ± 16 mV in the thermophilic reactor and 1307 ± 42 mg.L−1 at ORP -224 ± 32 mV in the mesophilic reactor. Acetic acid was the dominant VFA in each reactor. The VFA production in thermophilic reactor (RT) reached 59% of the stoichiometric potential. Although the thermophilic condition improves the VFA yield compared to the mesophilic condition, further study is still needed to increase the VFA production from OPEFB.

Biogas Production from Coffee Pulp and Chicken Feathers Using Liquid- and Solid-State Anaerobic Digestions

Agricultural waste, particularly lignocellulose, has been used in the second generation of biogas. Coffee pulp and chicken feathers can be developed as biogas raw materials because of their suitability as a biogas substrate. This study investigates the effect of the percentage of total solids (TS), carbon to nitrogen ratio (C/N, g/g), and delignification pretreatment on biogas production from coffee pulp and chicken feathers, and aims to compose kinetics using the modified Gompertz model. The results show that adjusting the percentage of TS at low-level speeds up the degradation process, which increases chemical oxygen demand (COD) reduction and biogas production. COD reduction and biogas production increase optimally at the 25 (g/g) C/N ratio. Pretreatment delignification aids microorganisms in substrate decomposition, resulting in faster COD reduction and biogas conversion. The 25% TS and 25 (g/g) C/N ratio with the delignification process achieved the best biogas production, with biogas production of 10,438.04 mL. The Gompertz method shows that the difference in TS percentage can influence biogas production. Moreover, the method shows that biogas production is higher with the delignification process than without it.

Effect of Oxidation Time on the Properties of Cellulose Nanocrystals Prepared from Balsa and Kapok Fibers Using Ammonium Persulfate.

This study aimed to evaluate the effect of ammonium persulfate’s (APS) oxidation time on the characteristics of the cellulose nanocrystals (CNCs) of balsa and kapok fibers after delignification pretreatment with sodium chlorite/acetic acid. This two-step method is important for increasing the zeta potential value and achieving higher thermal stability. The fibers were partially delignified using acidified sodium chlorite for four cycles, followed by APS oxidation at 60 °C for 8, 12, and 16 h. The isolated CNCs with a rod-like structure showed an average diameter in the range of 5.5–12.6 nm and an aspect ratio of 14.7–28.2. Increasing the reaction time resulted in a gradual reduction in the CNC dimensions. The higher surface charge of the balsa and kapok CNCs was observed at a longer oxidation time. The CNCs prepared from kapok had the highest colloid stability after oxidation for 16 h (−62.27 mV). The CNCs with higher crystallinity had longer oxidation times. Thermogravimetric analysis revealed that the CNCs with a higher thermal stability had longer oxidation times. All of the parameters were influenced by the oxidation time. This study indicates that APS oxidation for 8–16 h can produce CNCs from delignified balsa and kapok with satisfactory zeta potential values and thermal stabilities.

Improvement of saccharide yield from wood by simultaneous enzymatic delignification and saccharification using a ligninolytic enzyme and cellulase

White-rot fungi are thought to hold promise for development of a delignification pretreatment process for wood biorefinery that is less energy-consuming than current processes. However, the reaction must take place over weeks and consumes non-neglectable amounts of saccharides. To establish a biological process for wood biorefinery would first require establishment of an enzymatic approach to delignification. Such an approach has the potential to lower costs and reduce saccharide loss. Here, we attempted enzymatic delignification reactions using manganese peroxidases (MnP), a lignin-degrading enzyme, under several reaction conditions. The delignification rate from beech wood meal (particle size <45μm) of up to 11.0% in 48h was reached in a MnP reaction supplemented with multiple co-oxidants, glucose, glucose oxidase (GOD) and commercial cellulase. An additional 48-h reaction using fresh MnP/co-oxidants increased the delignification rate to 14.2%. Simultaneous enzymatic delignification and saccharification, which occurs without a need for glucose supplementation, successfully improved the glucose yield to 160% of the reaction without MnP. Development of a more accurate imitation of the mechanisms of delignification that occurs in white-rot fungi has the potential to improve the monosaccharide yield resulting from simultaneous delignification and saccharification.

Assessment of the papermaking potential of processed Miscanthus × giganteus stalks using alkaline pre-treatment and hydrodynamic cavitation for delignification

One way of satisfying increased market demand and simultaneously achieving a reduced environmental load in the industrial paper production is the use of fibrous agricultural residues. The aims of this study were i) to investigate the effect of alkaline – hydrodynamic cavitation (HC) pre-treatments on the delignification of Miscanthus × giganteus stalks (MGS) and ii) establishing the suitability of MGS as feedstock and their exploitation in pulp and paper manufacturing. It was demonstrated that the proposed treatment is an efficient delignification method for the non-wood fiber sources, such as miscanthus. A significant outcome of this work was the observation that HC treatment preserved the fibres lengths and surface quality of raw MGS, but at the same time increased the amount of kinked and curled fibers present in cavitated miscanthus fibers. The average miscanthus fiber length was found to be relatively short at 0.45 (±0.28) mm, while the slenderness ratio, the flexibility coefficient and Runkel ratio values were calculated to be 28.13, 38.16 and 1.62, respectively. The estimated physical properties of MGS pulp hand-sheets were 24.88 (±3.09) N m g−1 as the tensile index, 0.92 (±0.06) kPa m2 g−1 as the burst index and 4.0 (±0.37) mN m2 g−1 as the tear index. Overall the current work demonstrated effective use of hydrodynamic cavitation for improving the processing in pulp and paper manufacturing.

Assessing the potential of lignocellulosic energy crops as an alternative resource for bioethanol production using ultrasound assisted dilute acid pretreatment

Abstract Nowadays, more research is directed towards the development of sustainable and eco-friendly technology for the bioethanol production using lignocellulosic biomass to address the global energy requirement. The present study was focused on evaluating the chemical composition and bioethanol production potential of four different lignocellulosic biomass viz., Typha angustifolia, Saccharum arundinaceum, Arundo donax, and Ipomoea carnea. The study exploits the application of ultrasound (US) assisted dilute acid pretreatment for delignification of lignocellulosic biomass. The compositional analysis of biomasses, before and after pretreatment, showed that lignin structure was degraded and more cellulose was exposed for enzymatic saccharification. During enzymatic hydrolysis, Saccharum arundinaceum yielded the highest value of 309.75 ± 3.98 mg/g for total reducing sugar (TRS) among all the biomasses. Typha angustifolia yielded a higher percentage of ethanol of 81.91 ± 8.17% when compared to other biomasses. After the pretreatment, the changes in the morphological features, functional groups, and cellulose crystallinity were examined using various characterization techniques. The variations in peak intensity of functional groups in FTIR and decrease in crystallinity index in XRD indicate that cellulose content was increased with a decrease in lignin content due to the synergistic effect of dilute acid and cavitational effect of US shock waves. Among the lignocellulosic biomass examined, Typha angustifolia resulted a maximum bioethanol production of 5.12 ± 0.87% (w/v) during fermentation. The outputs of the present study showed that the four lignocellulosic perennial energy crops could be utilized as a potential feedstock for the production of bioethanol.

Combining acid-based deep eutectic solvents and microwave irradiation for improved chestnut shell waste valorization

Key features of the deep eutectic solvent-microwave assisted simultaneous extraction of polyphenols and delignification pretreatment of chestnut shell waste are presented.