Lignin Recovery Research Articles

Production of volatile fatty acids concomitant with phosphorus removal and lignin recovery by co-fermentation of waste activated sludge and black liquor

Waste activated sludge (WAS) and black liquor (BL) are the stubborn solid waste and wastewater in the industry that need high investment and operational costs for treatment. In this study, co-fermentation of WAS and BL was performed following a novel process for the production of volatile fatty acids (VFAs) concomitant with phosphorus removal and lignin recovery. BL offers alkaline liquor for WAS pretreatment, and the organic carbon in BL can be used for fermentation. The results showed that the semi-continuous fermentation test at pH 10 and the addition of 800 mg/L of Mg2+ were the optimal conditions for the production of VFAs (approximately 15,000 mg/L) and P removal (≈94%). Additionally, Mg2+ was suited to remove P due to the weak adsorption of Mg2+ by BL under alkaline conditions. Moreover, the composition of VFAs was affected by the pH, for example, high ratios of acetate and propionate were obtained under conditions of high and low pH, respectively. The dominant functional bacteria of Alkalibacterium, Propionibacterium, Proteiniphilum, and Tessaracoccus were found through the analysis of microbial diversity to be responsible for the production of VFAs. The bioconversion of small molecular lignin was also demonstrated through the characterization analyses. Co-fermentation was suggested as an economic and eco-friendly strategy for the treatment and resource utilization of WAS and BL via the overall assessment of the technical process.

Fractionation of Lignin Streams Using Tangential Flow Filtration

Lignin fractionation helps its valorization process and yields high-quality and -value products. In this study, cascading tangential flow filtration (TFF) was employed for the fractionation of lignin molecules. The lignin-rich stream was obtained from the pretreatment process of corn stover using alkali (NaOH) and cholinium lysinate ([Ch][Lys]) as the catalyst. The effect of TFF (microfiltration, ultrafiltration, and nanofiltration) on lignin molecular weight, sugar distribution, viscosity, and lignin functional groups was investigated. In general, the study concluded that the average molecular weight (MW) and polydispersity of the permeate stream decreased with the reduction of the membrane pore size. TFF was effective in separating the low-MW lignin (200–350 Da) from the aqueous stream. Approximately 2% of monomeric lignin and 10–20% of low-molecular-weight lignin were recovered from NaOH- and [Ch][Lys]-extracted streams. Techno-economic analysis (TEA) results show that a high percentage of the low-MW lignin extraction can be achieved via a cascade TFF membrane operating at high transmembrane pressures (TMPs) and cross membrane velocities. Additionally, a high initial concentration of lignin in the liquid stream plays a critical role in the lignin product yield and recovery cost.

The Use of Lignin for Environmental Protection: An Overview of Recent Literature

Reducing environmental pollution is a particularly important issue, intensively studied nationally and internationally, as evidenced by the large number of scientific papers published on this topic. Literature studies show that reducing environmental pollution means not only reducing the amount of air / water / soil pollutants but also finding ways to recover waste from industrial activities that will reduce the problems of environmental pollution due to their storage.The materials resulting from the gasification processes of cellulose waste, as well as the materials obtained with the help of cellulose extracted from cellulose waste, were tested in the adsorption processes of some polluting species and the results demonstrated the efficiency of these materials for reducing the environmental pollution. The use of lignin as an adsorbent for the removal of pollutants (organic dyes or metal ions) from industrial wastewater can be considered a viable alternative, which can be a solution to both the problem of lignin recovery and the reduction of pollutant content in industrial wastewater.

Low-Molecular-Weight Lignin Recovery with Nanofiltration in the Kraft Pulping Process.

Kraft lignin is an underutilized resource from the pulp and paper industry with the potential of being a key raw material for renewable fuels and chemicals. The separation of high-molecular-weight lignin from black liquor by ultrafiltration has been widely investigated, while the permeate containing low-molecular-weight lignin has received little attention. Nanofiltration can concentrate the low-molecular-weight lignin. This work, therefore, evaluates nanofiltration for the separation and concentration of low-molecular-weight lignin from the ultrafiltration permeate. For this study, eight flat polymeric sheet membranes and one polymeric hollow fiber membrane, with molecular weight cut-offs ranging from 100 to 2000 Da, were tested. A parametric study was conducted at 50 °C, 2.5–35 bar, and crossflow velocity of 0.3–0.5 m/s. At a transmembrane pressure of 35 bar, the best performing membranes were NF090801, with 90% lignin retention and 37 L/m2·h, and SelRO MPF-36, with 84% lignin retention and 72 L/m2·h. The other membranes showed either very high lignin retention with a very low flux or a high flux with retention lower than 80%. Concentration studies were performed with the two selected membranes at conditions (A) 50 °C and 35 bar and (B) 70 °C and 15 bar. The NF090801 membrane had the highest flux and lignin retention during the concentration studies. Overall, it was shown that the nanofiltration process is able to produce a concentrated lignin fraction, which can be either used to produce valuable chemicals or used to make lignin oil.

Development and comparison of membrane separation schemes for byproduct recovery from Egyptian rice straw black liquor

BackgroundRecovery of valuable ingredients from black liquor could lead to an environmentally and economically sound bioethanol production technology. In this work, two schemes comprising hybrid membrane systems incorporating ultrafiltration (UF) and nanofiltration (NF) are developed for the recovery of lignin, silica rich and cellulose/hemicellulose hydrolysates byproducts from alkaline pretreated rice straw.MethodsThe first scheme (I) comprises UF, NF and thermal vapor compression (TVC), while, the second scheme (II) includes UF, 2 stages of NF and 2 TVC units. Further treatments are suggested to produce solid byproducts with an economic value. Furthermore, material balance of the two schemes based on 1000 m3/d of black liquor and the main design features and comparative direct cost indicators of the main adopted units were deduced using WT Cost II© software.ResultsResults revealed that about (80–90%) yield of recovered byproducts from both schemes with equivalent amounts of 9.5, 5.5 and 18.5 ton/d of lignin, silica rich and cellulose/hemicellulose hydrolysates dry products, respectively. Moreover, reusable water recovery approaches 26% and 70% for schemes (I) and (II), respectively.ConclusionsFurther, the wastewater generated from scheme (II) is 2.9 times folds scheme (I) which improves the environmental impact of the former. Preliminary cost indicators revealed that both schemes have almost the same total direct capital cost.

Optimization by Response Surface Methodology of Ethanosolv Lignin Recovery from Coconut Fiber, Oil Palm Mesocarp Fiber, and Sugarcane Bagasse

Optimization by Response Surface Methodology of Ethanosolv Lignin Recovery from Coconut Fiber, Oil Palm Mesocarp Fiber, and Sugarcane Bagasse

Characterization of Eucalyptus Lignin Fractionation from a MIBK-Based Solvothermal Process

In this study, the effects of sulfuric acid on cellulose yield, lignin removal, and lignin recovery in solvothermal fractionation of eucalyptus (EC) were studied. An acid concentration of 0.04 M sulfuric acid (H2SO4), temperature of 180 °C and residence time of 30 min resulted in maximum lignin removal from the solid phase, at 87.7 %. Lignin recovery in the organic phase under optimum conditions was 84.6 %. It should be noted that H2SO4 was the best catalyst in the optimal solvothermal process, and it increased the cellulose yield to 95.2 % in the solid phase. Additionally, the physicochemical and structural properties of the extracted lignin were analyzed using FTIR, TGA, elemental analysis, GPC, and Py-GCMS methods. Thermal degradation analysis showed that recovered lignin is primarily composed of syringyl, guaiacyl and p-hydroxyphenyl units cross-linked by C–C, inter-unit α-O-4, β-O-4 linkages. The weight average molecular weight (Mw) analysis of recovered lignin demonstrated a low molecular weight for recovered lignin (2.19 g/mol). However, the main phenolic derivatives in the extracted lignin obtained from EC were S-units (i.e., syringol, 4-methylsyringol, 4-vinylsyringol). In addition, G-units (4-vinylguaiacol, 4-methylguaiacol, phenol, 2-methylphenol, and 4-methylphenol) were obtained after release from H-units. Py-GCMS analysis showed the predominance of G-units (32.8 %) over S-units (57.4 %). This work demonstrated the potential of fractionated lignin in the production of valuable chemicals in biorefineries.
 HIGHLIGHTS
 
 Eucalyptus was fractionated with solvothermal process with different conditions
 The maximum lignin removal of 87.7 % was achieved in the presence of catalyst of 0.04 M
 Organosolv fractionation enabled an extensive and selective delignification
 The structural changes of lignin were characterized comprehensively
 
 GRAPHICAL ABSTRACT

Influence of alkali and alkaline earth metals on the hydrothermal liquefaction of lignocellulosic model compounds

The alkali and alkaline earth metals (AAEMs) in biomass have a certain influence on its thermochemical conversion process. In order to study the influence of water-soluble AAEMs on hydrothermal liquefaction (HTL) to produce bio-oil, the metal chlorides of K, Na, Ca and Mg were used as additives, and glucose, xylan and lignin were typical lignocellulosic biomass to conduct HTL experiments. The results showed that AAEMs increased the yield of bio-oil from glucose and xylan by 42.1% and 23.8%, respectively, and the catalytic effect of alkaline earth metals was stronger. However, the addition of mixed metal chloride reduced the bio-oil yield and energy recovery of lignin. AAEMs provided more H+ and OH− active radicals in the aqueous phase, which intensified the esterification reaction and decarbonylation reaction, and promoted the diversification of substances. Meanwhile, AAEMs improved the Higher heating value and energy recovery rate of bio-oil, and Mg promoted the reduction reaction, the calorific value of bio-oil was increased by 7.4, 1.5 and 2.5%, respectively.

Alpha-, Beta- and Gamma-Cellulose Quantification and Two-Stage Concentrated-Dilute Acid Lignin Recovery from Three Rice Husks: Lignin Characterization and Depolymerization

Alpha-, Beta- and Gamma-Cellulose Quantification and Two-Stage Concentrated-Dilute Acid Lignin Recovery from Three Rice Husks: Lignin Characterization and Depolymerization

Organosolv pretreatment of oat husk using oxalic acid as an alternative organic acid and its potential applications in biorefinery

AbstractIn this study, ethanol organosolv treatment of oat husk and the potential effects of phosphoric acid and oxalic acid as alternatives to sulfuric acid were investigated. These acids were determined as effective as sulfuric acid to obtain high quality lignin and glucan and they can be used instead of sulfuric acid in solvent acidification. To determine the purity and recovery of both lignin and glucan, the effects of initial substrate amount, solid-to-liquid ratio, and amount of washing solutions were also examined using a one-factor-at-a-time strategy. Reducing the amount of washing solutions (water, solvent, or both) negatively affected lignin recovery, but it did not affect glucan recovery. The optimum conditions for pretreatment of the oat husk at higher glucan recovery were obtained with 50% aqueous ethanol acidified with oxalic acid at 210 °C for 90 min and solid-to-liquid ratio of 1:2. In the mixture of evaporated glucan-rich and hemicellulose-rich fractions obtained through the optimized condition, 4.62 g/L biomass containing 10.27% protein was produced by the cultivation of Aspergillus oryzae. The fractions obtained from organosolv treatment can be used to obtain value-added products such as biomass production, and thus contributing to a sustainable economy by integrating lignocellulosic substrate residues into the biorefinery.

Application of a recombinant GH10 endoxylanase from Thermoascus aurantiacus for xylooligosaccharide production from sugarcane bagasse and probiotic bacterial growth

Xylooligosaccharides (XOs) are a promising class of prebiotics capable of selectively stimulating the growth of the beneficial intestinal microbiota against intestinal pathogens. They can be obtained from xylan present in residual lignocellulosic material from agriculture. Thus, in this study we produced XOs by extracting xylan from sugarcane bagasse and hydrolyzing it using the GH10 xylanase from Thermoascus aurantiacus expressed by Pichia pastoris. An alkaline method to extract xylan is described, which resulted in 83.40% of xylan recovery and low amounts of cellulose and lignin. The enzymatic hydrolysate exhibited a mixture of XOs containing mainly xylobiose, xylotriose and xylotetraose. These oligosaccharides stimulated the growth of Lactobacillus casei, L. rhamnosus, L. fermentum and L. bulgaricus strains, which were able to produce organic acids, especially acetic acid. These findings demonstrate the possibility to redirect crop by-products to produce XOs and their use as a supplement to stimulate the growth of probiotic strains.

The Effect of the Kraft Pulping Process, Wood Species, and pH on Lignin Recovery from Black Liquor

Lignin has shown a great potential to produce fuels, value-added chemicals, and functional materials due to its high-energy density and intrinsic aromatic-based structure. Yet, the lignin precipitation of different biomasses needs investigation because most of the work has been performed on softwood and much less is known about hardwoods. In fact, the lignin from these two wooden biomasses vary in composition and pulping performance, which can reflect on lignin precipitation. Therefore, the present study investigated the precipitation and composition of 40 distinct kraft lignins obtained from pine, acacia, sweetgum, and eucalyptus black liquors. Two lignin fractions were precipitated at different pHs, according to known industrial lignin separation practices (pH = 9.5 and 2.5) from black liquors taken at different levels of pulping. Overall, lignin recovery increased with increasing lignin concentration in the black liquor, i.e., higher amounts of lignin were obtained at higher levels of delignification. In addition, pine lignins showed superior yields than the hardwoods and were around five times purer. Among the hardwoods, lignin recovery increased with the S–G ratio of the native lignin, and eucalyptus showed the best performance by achieving the highest yields and purities. Finally, the present work compared the lignin recovery yield and the purity of softwood and different hardwood lignins in a systematic way, which will increase awareness of this underutilized green material and could potentially increase the interest in establishing new lignin plants across the globe.

Physical and Chemical Properties of Acacia mangium Lignin Isolated from Pulp Mill Byproduct for Potential Application in Wood Composites.

The efficient isolation process and understanding of lignin properties are essential to determine key features and insights for more effective lignin valorization as a renewable feedstock for the production of bio-based chemicals including wood adhesives. This study successfully used dilute acid precipitation to recover lignin from black liquor (BL) through a single-step and ethanol-fractionated-step, with a lignin recovery of ~35% and ~16%, respectively. The physical characteristics of lignin, i.e., its morphological structure, were evaluated by scanning electron microscopy (SEM). The chemical properties of the isolated lignin were characterized using comprehensive analytical techniques such as chemical composition, solubility test, morphological structure, Fourier-transform infrared spectroscopy (FTIR), 1H and 13C Nuclear Magnetic Resonance (NMR), elucidation structure by pyrolysis-gas chromatography-mass spectroscopy (Py-GCMS), and gel permeation chromatography (GPC). The fingerprint analysis by FTIR detected the unique peaks corresponding to lignin, such as C=C and C-O in aromatic rings, but no significant differences in the fingerprint result between both lignin. The 1H and 13C NMR showed unique signals related to functional groups in lignin molecules such as methoxy, aromatic protons, aldehyde, and carboxylic acid. The lower insoluble acid content of lignin derived from fractionated-step (69.94%) than single-step (77.45%) correlated to lignin yield, total phenolic content, solubility, thermal stability, and molecular distribution. It contradicted the syringyl/guaiacyl (S/G) units’ ratio where ethanol fractionation slightly increased syringyl unit content, increasing the S/G ratio. Hence, the fractionation step affected more rupture and pores on the lignin morphological surface than the ethanol-fractionated step. The interrelationships between these chemical and physicochemical as well as different isolation methods were investigated. The results obtained could enhance the wider industrial application of lignin in manufacturing wood-based composites with improved properties and lower environmental impact.

Green mechano-chemical processing of lignocellulosic biomass for lignin recovery

Lignin extraction from biomass is heavily dependent on chemical processes that are harmful to the environment and the quality of the recovered lignin. Ionic liquid solvents are some of the latest solutions in green processing; however, their implementation for lignin recovery is limited by their high cost, typically high loadings requirements, and long processing times. To overcome these issues, in this study, high loadings of mixed hardwood flour (MHF) were processed with 1-butyl-3-methylimidazolium chloride (BmimCl) in a batch mixer. The rheological behaviour of the biomass and ionic liquid mixture was studied. The mixture had a high complex viscosity (approx. 107 Pa s) at low shear rates and displayed pronounced shear thinning behavior at 50 wt% MHF loading. A 22 factorial design was also implemented to study the effects of MHF solid loading amount and residence time on lignin extraction yield. A maximum yield of 36.6% was obtained at the maximum solid loading amount and residence time (50 wt% and 45 min, respectively). The extracted lignin samples were also characterized in comparison with commercial Kraft lignin and lignosulfonate. The novelty of this study is the successful lignin extraction at high solid loadings and shorter residence times compared to previous biomass pre-treatments with ionic liquids that employs low solid loading and long processing times.

One-pot production of 5-hydroxymethylfurfural and simultaneous lignin recovery from non-food lignocellulosic wastes using cost-effective ionic liquids

One-pot production of 5-hydroxymethylfurfural and simultaneous lignin recovery from non-food lignocellulosic wastes using cost-effective ionic liquids

Organosolv and ionosolv processes for autohydrolyzed poplar fractionation: Lignin recovery and characterization

Biomass fractionation plays a major role in the search for competitive biorefineries, where the isolation and recovery of the three woody fractions is key. In this sense, we have used autohydrolyzed hemicellulose-free poplar as feedstock to compare two fractionation processes, organosolv and ionosolv, oriented to lignin recovery. The recovered lignins were then characterize by different techniques (NMR, GPC, TGA). Both treatments were tested at different temperatures to analyze temperature influence on lignin recovery and properties. The highest lignin recovery was obtained with the ionosolv process at 135 °C, reaching a solid yield of ~70%. Lignin characterization showed differences between both treatments. Lignins enriched in C-O linkages and G units were recovered with the organosolv process, where increasing temperature led to highly depolymerized lignins. However, lignins with higher C-C linkages and S units contents were obtained with the ionosolv process, producing more thermically stable lignins. In addition, increasing temperature caused lignin repolymerization when employing ionic liquids as solvents. Therefore, this work outlines the most important differences between ionosolv and organosolv processes for biomass fractionation, focusing on lignin recovery and its properties, which is the first step in order to valorize all biomass fractions.

Ultrafiltration process for lignin-lean black liquor treatment at different acid conditions

ABSTRACT Black liquor treatment by acid precipitation produces two main streams: the high purity precipitated lignin and the lignin-lean black liquor (a diluted lignin solution). Here, we evaluated the ultrafiltration process for lignin recovery from lignin-lean black liquor at different pH values (9.0, 9.5 and 10.0). The ultrafiltration process was able to retain 83 ± 0.5% of lignin from the lignin-lean black liquor at pH 9.0. The permeate flux increased with the decrease in pH value (steady state flux of 5.3 ± 0.0 L h−1m−2 at pH 9.0). Cake formation was the main fouling occurrence during lignin-lean black liquor filtrations. The weight average molecular weight of the lignin-lean black liquor decreased from 1866 to 1208 Da after the ultrafiltration process. The pH value did not significantly influence the molecular weight of permeate stream. Permeate samples presented lower hydroxyl content and higher syringyl(S):guaiacyl(G) ratios than feed samples. Thus, the ultrafiltration process was able to concentrate lignin from the lignin-lean black liquor and to produce a permeate with a narrow molecular weight distribution. The precipitation at more acid conditions is suggested to improve permeate flux lignin retention from lignin-lean black liquor.

Recovery of organic acids from pre-treated Kraft black liquor using ultrafiltration and liquid-liquid extraction

Kraft black liquor (BL) is a toxic residue from paper manufacture that can be revalorized to obtain high value-added products. In this study, different integrated processes, consisting of a pre-treatment (lignin recovery [LR] or partial wet oxidation [PWO]) followed by ultrafiltration (UF) and liquid–liquid extraction (LLE), have been evaluated in order to recover short-chain organic acids (OA) from BL.After the UF step, a partial purification of OA was observed. Thus, the COD fraction attributable to OA increase 26.0%, 36.6% and 11.3% for untreated BL, BL after lignin recovery (LRBL) and partially oxidised BL (WOBL), respectively.The final LLE step was optimised analysing different combinations of extractants (trioctylamine, trioctylphosphine oxide and tributylphosphate), diluents (n-hexane and heptane) and temperatures (25, 40 and 55 °C), concluding that the most suitable solvent was 30% trioctylamine in heptane (v/v) at 40 °C, in which 76% of the OA mass was recovered in LRBL, 72% in BL and 68% in WOBL.The pre-treatment of BL improved the final recovery yield of OAs, increasing from 24.7% to 28.1% and 29.4% through PWO and LR, respectively. Therefore, LR was considered the most suitable pre-treatment due to its lower operating cost, widespread use, and greater recovery of OA.

Effect of Alkali and 1,4-Butanediol Contents on the Extraction of Lignin and Lignin-Based Activated Carbon.

In the process of lignin extraction by the organic solvent method, the amount of alkali and the content of 1,4-butanediol are important conditions that affect lignin yield. The effects of alkali and alcohol contents on lignin recovery, removal rate, and structure were studied. In this reaction system, the removal rate of lignin increased with the increase of alkali content but decreased with the increase of alcohol content. Fourier transform infrared (FT-IR) analysis showed that the phenol hydroxyl group and the ether bond in lignin had different trends in different alkali and 1,4-butanediol environments, and four different infrared parameters in lignin had an obvious linear relationship. Gel permeation chromatography (GPC) results showed that high alkali content and high 1,4-butanediol content could lead to the fragmentation of lignin. In addition, lignin extracted from alkali-quantity factor series was selected to prepare activated carbon, CaCl2 was selected as the activator, and its effects were studied. Results showed that in the process of extracting lignin, on the one hand, NaOH content affects the functional groups of activated carbon by affecting the aromatic structure of lignin; on the other hand, the NaOH content affects the graphitization degree and specific surface area of activated carbon by affecting the removal rate and the molecular weight of lignin.

High purity softwood lignin obtained by an eco-friendly organosolv process

Organosolv processes provide access to less degraded and higher purity lignins. However, these are rarely applied to softwood species with high lignin contents and complex condensed structures. We are presenting here the results of an optimized organosolv process, allowing for a high extraction yield of organosolv lignin from black spruce (Picea mariana), while preserving a good solid cellulose recovery. Optimized conditions are 70% ethanol liquor with a ratio of 1:10 (wood:liquor) and 5% FeCl3·6H2O as catalyst, treated in a Parr reactor for 90 min at 180 °C. The cellulosic pulp was then extracted with pure ethanol to recover the 2nd lignin. This 2nd lignin was darker in colour and denser than the 1st lignin obtained by precipitation from residual liquor. The other lignin properties were almost identical. The total lignin recovery averaged at 74% (with a purity of 97%), the highest result for lignin recovery from softwoods published so far.