Processing Of Lignocellulosic Biomass Research Articles

Structural optimization of biohydrogen production: Impact of pretreatments on volatile fatty acids and biogas parameters

The present study aims to describe an innovative approach that enables the system to achieve high yielding for biohydrogen (bio-H2) production using xylose as a by-product of lignocellulosic biomass processing. A hybrid optimization technique, structural modelling, desirability analysis, and genetic algorithm could determine the optimum input factors to maximize useful biogas parameters, especially bio-H2 and CH4. As found, the input factors (pretreatment, digestion time and biogas relative pressure) and volatile fatty acids (acetic acid, propionic acid and butyric acid) had significantly impacted the biogas parameters and desirability score. The pretreatment factor had the most directly effect on bio-H2 and CH4 production among the factors, and the digestion time had the most indirectly effect. The optimization method showed that the best pretreatment was acidic pretreatment, digestion time > 20 h, biogas relative pressure in a range of 300–800 mbar, acetic acid in a range of 90–200 mg/L, propionic acid in a range of 20–150 mg/L, and butyric acid in a range of 250–420 mg/L. These values caused to produce H2 > 10.2 mmol/L, CH4 > 3.9 mmol/L, N2 < 15.3 mmol/L, CO2 < 19.5 mmol/L, total biogas > 0.31 L, produced biogas > 0.10 L, and accumulated biogas > 0.41 L.

Reductive Catalytic Fractionation of Lignocellulosic Biomass: A New Promising Method of its Integrated Processing

The review discusses the results of recent studies in the promising field of integrated processing of lignocellulosic biomass – the reductive catalytic fractionation (RCF). The effect of catalysts, cocatalysts, solvents, hydrogen sources and features of lignocellulosic feedstock on the selectivity of monomeric products formation from lignin is considered. RCF processes are performed mostly with the heterogeneous catalysts, which allow implementing the reductive depolymerization of lignin to obtain low-molecular compounds and preserve carbohydrate components of biomass. Among the studied catalysts based on platinum group metals and transition metals, the highest activity is observed for the catalysts containing Pd, Pt, Ru and Ni. Features of the metal also affect the composition of the resulting products. Thus, ruthenium catalysts make it possible to obtain 4-propylguaiacol as the main product, while Ni and Pd – 4-propanolguaiacol. Mo-containing catalysts, owing to their lower hydrogenating activity, can be used to obtain monolignols or their etherified derivatives with the preservation of carbohydrate components of lignocellulosic biomass. However, most efficient in RCF processes are the bifunctional catalysts, which have both the acidic and metallic active sites. Acidic sites promote the cleavage of the ether β-O-4 bonds, whereas metallic sites – the reduction of the formed intermediate compounds. An important aspect of choosing the appropriate catalysts for RCF process is the possibility of their repeated application. The use of a ferromagnetic catalyst or a catalyst basket allows separating the catalyst from the products.

H2O2 in Liquid Fractions of Hydrothermally Pretreated Biomasses: Implications of Lytic Polysaccharide Monooxygenases

Lytic polysaccharide monooxygenases (LPMOs) are important players in enzyme-aided valorization of lignocellulose. However, the recently discovered dependency of LPMO catalysis on H2O2 along with H2O2-caused inactivation of the enzyme calls for an in-depth understanding of the levels and the dynamics of H2O2 in various streams of the processing of lignocellulosic biomass. Using an LPMO-based sensitive detection, we assessed the dynamics of H2O2 in the liquid fractions (LFs) of hydrothermally pretreated wheat straw (agricultural residue), birch (hardwood), and pine (softwood). Upon contact with air, H2O2 was formed in the LFs of all biomasses. The initially high rate of H2O2 formation decayed with the half-life around 1–2 h to a low but stable plateau value. The rates of H2O2 formation were much higher than the rates of its accumulation, suggesting that H2O2 is an intermediate in aerobic oxidation of the compounds in LFs. Although the general traits were similar, LFs of different biomasses had different rates of H2O2 formation and accumulation. LFs of different biomasses also differed by their effect on the enzymatic degradation of cellulose. Compositional analyses revealed a number of different compounds that were formed and disappeared upon aerobic oxidation of LFs.

Vessel- and ray-specific monolignol biosynthesis as an approach to engineer fiber-hypolignification and enhanced saccharification in poplar.

Lignin is one of the main factors determining recalcitrance to processing of lignocellulosic biomass towards bio-based materials and fuels. Consequently, wood of plants engineered for low lignin content is typically more amenable to processing. However, lignin-modified plants often exhibit collapsed vessels and associated growth defects. Vessel-specific reintroduction of lignin biosynthesis in dwarfed low-lignin cinnamoyl-CoA reductase1 (ccr1) Arabidopsis mutants using the ProSNBE:AtCCR1 construct overcame the yield penalty while maintaining high saccharification yields, and showed that monolignols can be transported between the different xylem cells acting as 'good neighbors' in Arabidopsis. Here, we translated this research into the bio-energy crop poplar. By expressing ProSNBE:AtCCR1 into CRISPR/Cas9-generated ccr2 poplars, we aimed for vessel-specific lignin biosynthesis to: (i) achieve growth restoration while maintaining high saccharification yields; and (ii) study the existence of 'good neighbors' in poplar wood. Analyzing the resulting ccr2 ProSNBE:AtCCR1 poplars showed that vessels and rays act as good neighbors for lignification in poplar. If sufficient monolignols are produced by these cells, monolignols migrate over multiple cell layers, resulting in a restoration of the lignin amount to wild-type levels. If the supply of monolignols is limited, the monolignols are incorporated into the cell walls of the vessels and rays producing them and their adjoining cells resulting in fiber hypolignification. One such fiber-hypolignified line had 18% less lignin and, despite its small yield penalty, had an increase of up to 71% in sugar release on a plant base upon saccharification.

Catalytic Activity of Char Obtained from Fast Pyrolysis in Esterification Reactions

In this study different pathways for obtaining activated carbon with catalytical activity were analysed. Industrially fast pyrolysis is an efficient way of lignocellulosic biomass processing, since in this process various important high value chemicals are obtained. Biochar is obtained as the by-product in fast pyrolysis process from which activated carbon can be acquired with further chemical activation. Different methods for chemical activation of biochar were tested with the obtained activated charcoals being used as a catalyst in esterification reactions to evaluate their potential use as a heterogenic catalyst. Highest catalytical activity was observed when biochar was pre-treated with sulfuric acid at 80 °C for 24 hours. The obtained activated charcoal could be used as a catalyst for up to five times with no noticeable decrease in catalytic activity.

Multicriteria Definition of Small-Scale Biorefineries Based on a Statistical Classification

Biorefineries have many possible designs and therefore, present varied benefits in regards to sustainable development. Evaluating these biorefineries is central for the domain, and, as small-scale biorefineries (SSB) are commonly opposed to the large ones, specifying the concept of scale of a biorefinery is essential as well. However, there is no consensual definition of the “scale”, and the meaning of the term changes with the context. This paper presents a methodology to specify the concept of scale by grouping various biorefineries processing lignocellulosic biomass according to factors related to feedstock, process, economy and mobility of the facility, without any predetermined pattern. Data from 15 operational biorefineries are analyzed using a multivariate analysis combined with a hierarchical clustering. The classification obtained categorizes biorefineries into four design classes: smallest, small, hybrid and large scale. Small-scale biorefineries are characterized by a small investment cost (less than 2 M€), a low processing capacity (less than 100 t/day) and a low process complexity, while the end-products’ added value is variable. The mobility of the plants is a sufficient, but not necessary, criterion to have a small-scale biorefinery. Finally, the designs of the investigated biorefineries can be explained by two main trade-offs: one between the mobility and the processing capacity-investment cost, and the other between the process complexity and the added value.

Characterization of a new bifunctional endo-1,4-\u03b2-xylanase/esterase found in the rumen metagenome

Metagenomic data mining of the Nellore cattle rumen microbiota identified a new bifunctional enzyme, endo-1,4-β-xylanase/esterase, which was subsequently overexpressed in E. coli BL21 (DE3). This enzyme was stable at pH intervals of 5 to 6.5 and temperatures between 30 and 45 °C, and under the test conditions, it had a Vmax of 30.959 ± 2.334 µmol/min/mg, Km of 3.6 ± 0.6 mM and kcat of 2.323 ± 175 s−1. Additionally, the results showed that the enzyme is tolerant to NaCl and organic solvents and therefore is suitable for industrial environments. Xylanases are widely applicable, and the synergistic activity of endo-1,4-β-xylanase/esterase in a single molecule will improve the degradation efficiency of heteroxylans via the creation of xylanase binding sites. Therefore, this new molecule has the potential for use in lignocellulosic biomass processing and as an animal feed food additive and could improve xylooligosaccharide production efficiency.

Biochar in water and wastewater treatment - a sustainability assessment

• Biochar from ligno-cellulosics is explored for wastewater treatment. • Technologies to promote commercialization of sustainability are discussed. • Current trends in biochars identified to evaluate sustainability considerations. • Existing gaps and recommendations for future studies are discussed. Innovation of sustainable materials that are efficient, economic, environmentally friendly, and socially acceptable for real-scale environmental applications is currently a trend in the scientific community. Recently, biochar as one of the main pyrogenic products from thermo-chemical process of ligno-cellulosic biomass has been widely studied to deal with water pollutants and wastewaters. Thus, there is an urgent need for the assessment of developed technologies to promote commercialization of the most sustainable technologies in order to identify the existing technical gaps. This review aims to identify current trends in the literature in order to evaluate the technology against sustainability considerations, emphasizing on the recently published reviews as well as the highly cited papers. The existing gaps and recommendations for future studies are discussed.

Ionic liquids in the pretreatment of lignocellulosic biomass

The pretreatment is a key step in the processing of lignocellulosic biomass for its transformation into chemicals and materials of biorenewable origin. Ionic liquids, with their characteristic set of unique properties, have the potential to be the basis of novel pretreatment processes with higher effectiveness and improved sustainability as compared to the current state-of-the-art processes. In this opinion paper, the author provides a perspective on possible processing strategies for this pretreatment with ionic liquids, identifying different advantages as well as challenges to be overcome.

Solubility assessment of lignin monomeric compounds and organosolv lignin in deep eutectic solvents using in situ Fourier-transform infrared spectroscopy

Over the last years, the depletion of fossil resources allied with the growing energy demands and the increasing environmental pollution turned imperative the search for alternative renewable resources. Lignocellulosic biomass has been recognized as an excellent alternative feedstock due to its availability, renewability and low cost. Lignin, one of three major components of lignocellulosic biomass, arises as a by-product from the bio-ethanol production and the pulp and paper industry with high abundance of polyaromatic chemical structures. Yet, in spite of being the major aromatic resource of the bio-based economy with potential to obtain a wide variety of chemicals, only 2 % is being processed. In this sense, this works aims at shedding some light on the solubility of lignin monomeric compounds in presence of deep eutectic solvents (DES), as these have shown promising results in the processing of lignocellulosic biomass. Herein, we have focused on the development of a FTIR method to infer about the compounds solubility owing to its simplicity, fast determination and low cost. Lignin monomeric compounds (benzene, 1,3-dimethoxybenzene, phenol and syringol) were studied in presence of [ChCl]:Urea and [ChCl]:Glycerol at different concentrations (20, 50, 100, 200 and 300 g.L−1) and at two temperatures (25 and 40 °C). Results showed that syringol displays a high solubility in both DES: 700 ± 20 g.L−1 in [ChCl]:U and 810 ± 20 g.L−1 in [ChCl]:G at 25 °C, respectively. Besides, effective solubility was observed for phenol in [ChCl]:U (930 ± 20 g.L−1) at 40 °C, whereas in [ChCl]:G, solubility was higher at 25 °C. In contrast, lignin showed very poor solubility in [ChCl]:U and was insoluble in [ChCl]:G, at 40 °C.

Potency of Deep Euteutic Solvent as an Alternative Solvent on Pretreatment Process of Lignocellulosic Biomass: Review

During the last decade Deep Euteutic Solvent (DES) is an alternative solvent and has proven to be effective in removing lignin and hemicellulose bonds, as well as reducing the crystallinity of cellulose in the pretreatment process of lignocellulosic biomass delignification. Until now, it has been reported that DES is a solvent that is widely used in various studies. DES is a solvent consisting of two or three ionic compositions which can be associated through hydrogen bonds, to form a euteutic mixture with a melting point lower than each individual component. In literature and research, these solvents are often referred to as environmentally friendly solvents. It is known that DES has physicochemical properties similar with ionic liquids but is more environmentally friendly and cheaper. Over the years, a number of studies have reported that the pre-treatment of lignocellulosic biomass delignification is carried out chemically and physically, such as the use of dilute acids, alkalis, and steam explosions. It was reported that this method is a process that uses a lot of energy, because it requires high temperature and pressure to remove lignin. However, the proposed method is currently based on the use of DES solvents which require less energy from chemical and physical processes. DES dissolves lignin and increases the availability of cellulose at low temperatures and pressures during the pre-treatment process. In this review it aims to explain the recent progress made regarding the contribution of DES and its potential on lignocellulosic biomass pre-treatment process. It also discussed the advantages of DES solvents that are environmentally friendly, cheap, non-toxic and low energy use.

Light-driven transformation of biomass into chemicals using photocatalysts – Vistas and challenges

Lignocellulosic biomass has become an important sustainable resource for fuels, chemicals and energy. It is an attractive source for alternative fuels and green chemicals because it is non-edible and widely available in the planet in huge volumes. The use of biomass as starting material to produce fuels and chemicals leads to closed carbon cycle and promotes circular economy. Although there are many thermo-chemical methods such as pyrolysis, liquefaction and gasification close at hand for processing lignocellulosic biomass and transforming the derived compounds into valuable chemicals and fuels, the photocatalytic method is more advantageous as it utilizes light and ambient conditions for reforming the said compounds. Appraisal of recent literature indicates a variety of photocatalytic systems involving different catalysts, reactors and conditions studied for this purpose. This article reviews the recent developments on the photocatalytic oxidation of biomass and its derivatives into value-added chemicals. The nature of the biomass and derived molecules, nature of the photocatalysts, efficiency of the photocatalysts in terms of conversion and selectivity, influence of reaction conditions and light sources, effect of additives and mechanistic pathways are discussed. Importance has been given also to discuss the complementary technologies that could be coupled with photocatalysis for better conversion of biomass and biomass-derived molecules to value-added chemicals. A summary of these aspects, conclusions and future prospects are given in the end.

Effects of formaldehyde on fermentable sugars production in the low-cost pretreatment of corn stalk based on ionic liquids

Low cost processing of lignocellulosic biomass is of great importance for sustainable chemistry and engineering. Herein, a low cost system composed of 1-butyl-3-methylimidazolium chloride ([C 4 C 1 im]Cl), HCl and formaldehyde (FA) was developed for the pretreatment of corn stalk at 80 °C. The efficiency of this technology was compared with that in dioxane system or without FA addition. Due to FA stabilization, the extent of acid-hydrolysis of carbohydrate fraction can be significantly decreased while 70% above of lignin was removed with the pretreatment of [C 4 C 1 im]Cl/HCl/FA system at 80 °C for 2 h. A maximum reducing sugar yield of 93.7% and glucose concentration of 7.0 mg⋅ml −1 were subsequently obtained from enzymatic hydrolysis of the slurry. There were great differences in compositions of small molecule degraded products obtained with FA addition or not. The present [C 4 C 1 im]Cl based system exhibits great potential of substituting volatile organic solvents ( i . e . dioxane) in developing low cost lignocellulosic biomass pretreatment at low temperature. Also, this work would gain insight into understanding on the roles of stabilization methods on the economic improvement of IL based biomass processing.

Insights into reductive depolymerization of Kraft lignin to produce aromatics in the presence of Pt/HZSM-23 catalyst

Lignin is one of the primary residues obtained after the processing of lignocellulosic biomass. However, most residual lignin is burnt directly to get rid of it, albeit one of the few biorenewable waste resources that can yield aromatics. Therefore, the present study investigates reductive depolymerization of Kraft lignin into aromatics in the presence of Pt/HZSM-23 catalyst. In this regard, the lignin conversion experiments were performed under mild reaction conditions at a temperature range of 100 °C to 200 °C for 1 h to 12 h in a high-pressure batch reactor. Besides, a comparative study was done on the effect of the supply of external hydrogen and in-situ hydrogenation. Eventually, 87.3% lignin conversion was measured yielding 65.1% bio-oil, primarily aromatics at optimized experimental conditions. It was observed that the mesopores in the Pt/HZSM-23 catalyst facilitate the transfer of larger molecules derived from the Kraft lignin, thus causing an overall improvement in the catalytic activity. A mechanistic study based on experimental conditions and products detected using GC-MS revealed that the in-situ hydrogen transfer route is more favorable for lignin depolymerization than externally supplied hydrogen.

Ionic liquids as potential pretreatment agent for bioconversion of biomass to biofuels.

Ionic liquids (ILs) have been greatly exploited as a good solvent and/or reagent with various applications because of their green properties and also their physiochemical and biological properties. One of the applications is pretreatment of biomass such as lignocellulosic biomass precedent to enzymatic hydrolysis for bioenergy production and other biomaterial production. Generally, the method collected of an IL pretreatment or recovery forwarded by hydrolysis of lignocellulosic biomass. Another approach came in vision in which simultaneously pretreatment process and saccharification of lignocellulosic biomass were used. However, the employment of ILs during this integrated process, within which enzymatic hydrolysis is finished within the presence of IL applied for biomass pretreatment, will simply inactivate the enzymes. Cellulases emerged as one of the important enzymes which are used to catalyze the polysaccharide from biomass and showed a higher level of stability in various ILs. Also, numerous approaches were created together with the synthesis of enzyme-compatible ILs, screening ILs-tolerant enzymes, and media engineering to boost cellulases performance. This review highlights the advancement and use of IL for the pretreatment or hydrolysis of lignocellulosic biomass. The structure of ILs and cellulase stabilization approaches are also discussed. From this review, this tends to powerfully believe that IL-compatible cellulase systems would eliminate the requirement to recover the regenerated biomass and cause simple, saccharification of cellulosic materials, which might be helpful in developing integrated bioprocesses.

Ideal Feedstock and Fermentation Process Improvements for the Production of Lignocellulolytic Enzymes

The usage of lignocellulosic biomass in energy production for biofuels and other value-added products can extensively decrease the carbon footprint of current and future energy sectors. However, the infrastructure in the processing of lignocellulosic biomass is not well-established as compared to the fossil fuel industry. One of the bottlenecks is the production of the lignocellulolytic enzymes. These enzymes are produced by different fungal and bacterial species for degradation of the lignocellulosic biomass into its reactive fibers, which can then be converted to biofuel. The selection of an ideal feedstock for the lignocellulolytic enzyme production is one of the most studied aspects of lignocellulolytic enzyme production. Similarly, the fermentation enhancement strategies for different fermentation variables and modes are also the focuses of researchers. The implementation of fermentation enhancement strategies such as optimization of culture parameters (pH, temperature, agitation, incubation time, etc.) and the media nutrient amendment can increase the lignocellulolytic enzyme production significantly. Therefore, this review paper summarized these strategies and feedstock characteristics required for hydrolytic enzyme production with a special focus on the characteristics of an ideal feedstock to be utilized for the production of such enzymes on industrial scales.

Lignocellulosic Biomass for the Synthesis of Nanocellulose and Its Eco-Friendly Advanced Applications.

Nanocellulose is a unique and natural compound extracted from native cellulose using different extraction techniques. Nanocellulose is currently attracting attention due to its excellent properties such as special surface chemistry, exceptional physical and chemical strength, and rich hydroxyl groups for modification. In addition, its significant biological properties, like biodegradability, biocompatibility, and non-toxicity, accompanied by being environmentally friendly, are added advantages. The current review is focused on the lignocellulosic biomass processing methods for nanocellulose production and their usage for eco-friendly and environmental sustainability. We have also described insights into different techniques by which cellulosic materials can be changed into cellulose nanofibers (CNFs) and cellulose nanocrystals (CNCs). Lastly, we further discussed how nano-cellulosic materials are being used in a variety of industries such as the food sector, biomedical hygiene products, health care, water purification, and sensors. In the review, the unique uses of nanocelluloses in the production of nanocomposite materials, like flexible supercapacitor and polymer matrix, toward minimizing the utilization of global fossil energy and environmental pollution are envisaged. Finally, the significant application of nanomaterials in the areas of packaging industries, health and hygienic sector, cosmetics, and other important sectors are discussed. In the aspect of techno-economically feasibility, nano-cellulose-based materials may prove to be outstanding, environment friendly, and mitigate effluent load.

Dissolution reaction kinetics and mass transfer during aqueous choline chloride pre-treatment of oak wood

Lignocellulosic biomass processing employing ionic liquids is of recent research interest for the biorefinery industry. The data on biomass dissolution kinetics in ionic liquids is important for designing scale-up pre-treatment reactor design. In this study, the reaction mechanism and kinetics of oak wood dissolution in aqueous choline chloride was investigated. In an extended effort, a correlation of dimensionless numbers was developed for the estimation the mass transfer coefficient. The analyses suggested that oak wood dissolution in choline chloride occurred in two stages. The diffusion of ionic liquid through the product layer was the dominating rate-controlling step in the first stage of dissolution followed by the surface chemical reaction in the second stage. The diffusivity of choline chloride into the oak wood matrix was ranging between 2.96E−14 and 2.84E−13 m2/s. The activation energy of the diffusion controlled stage and surface chemical reaction controlled stage was approximately 24.2 and 40.3 kJ mol−1, respectively. The proposed mathematical correlation for mass transfer coefficient fitted well with the experimental mass transfer coefficient values.

Water retention value predicts biomass recalcitrance for pretreated biomass: biomass water interactions vary based on pretreatment chemistry and reflect composition

Processing of lignocellulosic biomass is complex due to the heterogeneity of the substrate, but also due to lengthy unit operations, which complicates process control including for enzymatic saccharification. Methods for predicting enzymatic saccharification yield based on the properties of the pretreated biomass would be advantageous to process optimization and control. Biomass-water interaction measurements provide a method for quickly predicting biomass recalcitrance. Correlating water retention value (WRV) and enzymatic saccharification yield (ESY) on pretreated biomass has shown promise, especially when assessing only single biomass types pretreated with one specific chemistry. However, with comparisons between different types of biomasses, predictive powers have been low. We investigate the effect of pretreatment chemistry on the predictive power of WRV, when keeping the biomass static. Wheat straw was pretreated with dilute acid, hydrothermal, or alkaline chemistries at five different temperatures. Furthermore, low field nuclear magnetic resonance was used to measure water constraint in the pretreated materials, to better understand how biomass-water interactions change with pretreatment severity and chemistry. We show that the correlation of WRV and ESY is highly pretreatment dependent, while WRV strongly predicts ESY within each pretreatment chemistry. While ESY and WRV correlated under all chemistries, the direction of the correlations were divergent, suggesting a more complex interplay between recalcitrance and biomass-water interactions. Using T2 relaxation profiles, reductions in hemicellulose composition was related to the decrease in size of the most constrained water population present in the pretreated biomasses for all chemistries, suggesting a new identification of this population of constrained water.

Biomass Pretreatment with the Szego Mill™ for Bioethanol and Biogas Production

Results from an investigation of the mechanical size reduction with the Szego Mill™ as a pretreatment method for lignocellulosic biomass are presented. Pretreatment is a highly expensive and energy-consuming step in lignocellulosic biomass processing. Therefore, it is vital to study and optimize different pretreatment methods to find a most efficient production process. The biomass was milled with the Szego Mill™ using three different approaches: dry milling, wet milling and for the first time nitrogen assisted wet milling was tested. Bioethanol and biogas production were studied, but also fibre analysis and SEM (scanning electron microscope) analysis were carried out to characterize the effect of different milling approaches. In addition, two different process flows were used to evaluate the efficiency of downstream processing steps. The results show that pretreatment of barely straw with the Szego Mill™ enabled obtaining glucose concentrations of up to 7 g L−1 in the hydrolysis mixture, which yields at hydrolysis efficiency of 18%. The final ethanol concentrations from 3.4 to 6.7 g L−1 were obtained. The lowest glucose and ethanol concentrations were measured when the biomass was dry milled, the highest when nitrogen assisted wet milling was used. Milling also resulted in an 6–11% of increase in methane production rate during anaerobic digestion of straw.