Hemicellulose biorefineries: a review on biomass pretreatments

Biomass pretreatment (BP) plays a crucial role in a lignocellulose feedstock-based biorefinery (LCFBR) for processing of three major output streams (cellulose, hemicelluloses and lignin) into chemicals and biofuels. BP includes processing of lignocellulosic material (LCM) under aqueous, dilute acid or alkaline media to obtain a cellulosic fraction, which is then fermented to produce bioethanol. Hemicellulose is usually treated as a secondary stream due to lack of efficient fermentation of hemicellulosic sugars to ethanol. This review provides BPs assuming that hemicellulose stream should be integrated in LCFBR as a primary fraction for converting into value-added compounds other than bioethanol. Different LCM treatments are analyzed foreseeing bio-based products possible to obtain from hemicellulose path

An overview of lignin pathways of valorization: from isolation to refining and conversion into value‑added products

ABSTRACT: The increasing demand for greener and sustainable alternatives to fossil-derived fuels, chemicals, and materials has attracted huge attention to lignin, the largest renewable source of aromatic building blocks on earth. This natural polymer accounts for 15 to 40% of all lignocellulosic biomass. As such, in the pulp and paper industries, for example, huge amounts of lignin are produced worldwide. However, most applications for these lignins are of low value, such as their burning for energy. Furthermore, with the introduction of second-generation ethanol biorefineries, the overall lignin production increased. To attain a circular bio-based economy, all side-streams of lignocellulosic biomass and, particularly, lignin should be valorized to as high of a value as possible. Lignin's rich structure has allowed achieving various high-value products over the years, not only in the production of biofuels but also regarding chemicals and materials. The present paper addresses a broad vision of the several stages of lignin valorization, from the isolation of lignin through pre-treatments of lignocellulosic biomass and the current industrial lignin production to fractionation methodologies that provide homogeneous lignins more adequate for valorization and the conversion of lignin into value-added products via chemical and biological routes.info:eu-repo/semantics/publishedVersio

Hydrothermal processing of corn residues:process optimisation and products characterisation

Hydrothermal processing was used as pre-treatment method for the selective solubilisation of hemicellulose from corn residues (leaves and stalks). The raw material was treated at a liquidto- solid ratio of 10 g/g, under non-isothermal conditions (150-240ºC) and the effect of treatment on the composition of both liquid and solid phases was evaluated. The yields of solid residue and soluble products, e.g., oligosaccharides, monosaccharides, acetic acid and degradation compounds, such as furfural, hydroxymethylfurfural are presented and interpreted using the severity factor (log R0). The operational conditions leading to the maximum recovery of XOS (53% of initial (arabino)xylan) and for highest glucan content of the solid residue (64%) were established for log R0 of 3.75 and 4.21, respectively. Under the severest condition 95% of xylan was selectively solubilised and 90% of initial glucan was recovered on the solid residue, making it very attractive for further processing in a biorefinery framework

Green Fractionation Approaches for the Integrated Upgrade of Corn Cobs

ABSTRACT: Corn cob is an abundant agricultural residue worldwide, with high potential and interesting composition, and its valorization still needs to be studied. Selectively fractionating its structural components (hemicellulose, cellulose, and lignin), value-added products can be produced, eliminating waste. In this work, integrated fractionation approaches were developed and evaluated. First, an organosolv process was optimized (ethanol:water, 50:50, w/w). Then, as a comparative method, alkaline delignification (using NaOH, 1-2%) was also studied. The organosolv process allowed a significant delignification of the material (79% delignification yield) and, at the same time, a liquid phase containing a relevant concentration (14.6 g/L) of xylooligosaccharides (XOS). The resulting solid fraction, rich in cellulose, showed an enzymatic digestibility of 90%. The alkaline process increased the delignification yield to 94%, producing a solid fraction with a cellulose enzymatic digestibility of 83%. The two later techniques were also used in a combined strategy of hydrothermal processing (autohydrolysis) followed by delignification. The first allowed the selective hydrolysis of hemicellulose to produce XOS-rich hydrolysates (26.8 g/L, 67.3 g/100 g initial xylan). The further delignification processes, alkaline or organosolv, led to global delignification yields of 76% and 93%, respectively. The solid residue, enriched in glucan (above 75% for both combined processes), also presented high enzymatic saccharification yields, 89% and 90%, respectively. The fractionation strategies proposed, and the results obtained are very promising, enabling the integrated upgrading of this material into a biorefinery framework.info:eu-repo/semantics/publishedVersio

Simplex optimization and mathematical modeling of wheat straw dilute acid hydrolysisand

Wheat straw is an interesting biorefinery raw material, due to its abundance, chemical composition, and cost. Among the different pretreatments suitable for its processing, dilute acid hydrolysis still presents some benefits due to its simplicity. Nevertheless, it requires a careful optimization to avoid excessive by-products formation and catalyst spending. An attractive and simple optimization approach is the Sequential Simplex Method, an iterative procedure that enables to rapidly screen a large area ofoperational conditions and effectively encircle the optimal. In this work, dilute acid hydrolysis of wheat straw was optimized to selectively hydrolyze the hemicellulose fraction and obtain a pentose-rich fermentable hydrolyzate. The influence oftime (up to 180 min), and sulfuric acid concentration (up to 4%, w/w) were studied. The hydrolyzates obtained in the optimized conditions mainly contain free sugars (total content higher than 46 giL). The main potential microbial inhibitors found were acetic acid, furfural, and HMF, in concentrations lower than 4.8,1.7 and 0.3 giL, respectively. Empirical models describing the influence ofthe studied variables on sugars and by-products formation were validated for the entire domain. Sulfuric acid concentration was found to be the most influential variable, although both variables are statistically significant for xylose recovery. Interaction effects play a significant (negative) role. Data was also modeled based on the combined severity parameter (CS) and the results of these two approaches are compared and discussed. These hydrolyzates were easily utilized by Debaryomyces hansenii, a natural pentose assimilating yeast

Utilizarea ligninei pentru îndepărtarea particulelor de microplastic din apă

ABSTRACT: The focus of the research was to evaluate the use of lignin from different sources as an agent for the removal of diverse types of microplastics when present in wastewater. Organosolv lignin was obtained from three different sources (Miscanthus sp., pine bark and solid anaerobic digestates from Organic Fraction of Municipal Solid Wastes) by an ethanol-based organosolv treatment carried out in a pressurized stirred-tank reactor. The lignins obtained were evaluated as an adsorbent for diverse types of microplastics: High-density polyethylene (HDPE), Polystyrene (PS), Expanded Polystyrene (EPS), and Polypropylene (PP). All lignins used had the capacity to capture plastic particles from all plastic types, but a differential absorbance potential was found both for plastic types and lignin samples. EPS was the least adsorb type for all lignin sources, with the remaining plastics presenting equivalent results. Pine bark lignin was the best adsorbent among the tested feedstocks, always presenting the best performance for all plastic types. The direct utilization of organosolv hydrolysates, avoiding lignin recovery presented a similar behaviour. These results open the possibility to develop new natural, plant-based, adsorbents for microplastic removal from contaminated wastewater.REZUMAT: Scopul cercetării a fost evaluarea utilizării ligninei din diferite surse ca agent pentru îndepărtarea diferitelor tipuri de microplastic atunci când sunt prezente în apele uzate. Lignina a fost obținută prin metoda organosolv din trei surse diferite (Miscanthus sp., scoarță de pin și digestat anaerob solid din fracțiunea organică a deșeurilor solide municipale) printr-un tratament pe bază de etanol, realizat într-un reactor sub presiune cu agitare. Lignina obținută a fost evaluată ca adsorbant pentru diverse tipuri de microplastic: polietilenă de înaltă densitate (HDPE), polistiren (PS), polistiren expandat (EPS) și polipropilenă (PP). Toate tipurile de lignină au avut capacitatea de a capta particule de plastic din toate tipurile de plastic, dar a fost observant un potențial de absorbție diferențiat atât pentru tipurile de plastic, cât și pentru mostrele de lignină. EPS a fost tipul cel mai puțin captat pentru toate sursele de lignină, materialele plastice rămase prezentând rezultate echivalente. Lignina din scoarța de pin a fost cel mai bun adsorbant dintre materiile prime testate, prezentând cea mai bună performanță pentru toate tipurile de plastic. Utilizarea directă a hidrolizatelor de organosolv, evitând recuperarea ligninei a prezentat un comportament similar. Aceste rezultate deschid posibilitatea de a dezvolta noi absorbanți naturali, pe bază de plante, pentru îndepărtarea microplasticului din apele uzate contaminate.info:eu-repo/semantics/publishedVersio

Prebiotic xylo-oligosaccharides as high-value co-products on an integrated biorefinery approach from lignocellulosic feedstock

The present work proposes the production of prebiotic xylo-oligosaccharides (XOS) as high-value co-products of the Lignocellulose Feedstock Biorefinery concept, foreseeing potential applications on food, feed and nutraceutical industries. Autohydrolysis was used to selectively solubilise the hemicellulosic fraction of several xylan-rich, widely available, agricultural, agro-industrial and forestry by-products: corn cobs, brewery’s spent grain and Eucalyptus wood chips. The soluble hemicellulose-rich and the solid cellulose- and lignin-rich fractions were separated, and the crude XOS-rich hydrolysates were further purified by gel filtration chromatography. Selected fractions of purified XOS within the desired ranges of polymerization degree were characterised and their prebiotic potential was investigated in in vitro fermentations by bifidobacteria, lactobacilli and intestinal inocula. Parameters such as bacterial growth and XOS consumption were evaluated and compared with commercially available xylo-oligosaccharides. The differences observed were considered of relevance for the formulation of symbiotic preparations and the future design of targeted, tailor-made prebiotic xylo-oligosaccharides

The pros and cons of the dedicated upgrade of the hemicellulosic sugar stream in a biorefinery framework

The challenge of the future integrated biorefineries is the full economically utilization of all biomass components with the simultaneously production of fuels and chemicals, preferably of added-value. This can only be achieved by the selective fractionation of the lignocellulosic biomass into its polymeric components, thus increasing their individual upgradeability to enhance the process economics. To reach this goal, the fractionation methods used are of crucial importance. Yet, many of the most widely accepted biochemical biorefineries potential lay-outs, are mainly concerned with cellulose hydrolysis and fermentation and the hemicellulosic fractions are, at best, clamped with cellulose, averting its differential upgrade. Therefore, a change in perspective by which the fractionation processes, as well as the overall biorefinery lay-out, are thought and evaluated is needed. The objective of this work is to review, compare and discuss the main advantages and bottlenecks of the currently available biomass pre-treatment technologies, particularly those leading to the selective fractionation of hemicelluloses. The advantages and disadvantages of the methods will be analysed foreseeing the added-value products possible to obtain from the hemicellulose path, and the most relevant factors which influence both product yield and consistency. Actually, the chemical composition and structural diversity of hemicelluloses constitutes an opportunity for the production of many chemicals, which has not yet been fully exploited. The integration of potential added-value products, e.g. oligosaccharides, polyols, and enzymes in a biorefinery framework will also be presented and discussed based on data for the upgrade of agro-food industrial residues and by-products. Examples will compare the use of mild processes for the selective recovery of hemicelluloses such autohydrolysis and dilute acid hydrolysis of brewery's spent grain, wheat straw, and eucalypt wood and the biotechnological processing of the hydrolysates. It is foreseen that hemicellulose-derived chemicals will become an ever more relevant category of products, as they hold a promise of economic benefit for the biorefineries

Effective fractionation of microalgae biomass as an initial step for its utilization as a bioenergy feedstock

Scenedesmus obliquus, a biotechnologically relevant microalgae, was grown in 70 L vertical photobioreactors using non-supplemented secondary brewery wastewater as a culture medium. Upon collection, by mechanical means, the cells were subjected to hydrothermal (autohydrolysis) and dilute acid hydrolysis (0.5 % sulfuric acid) pre-treatments carried out using pressure micro-reactors under isothermal conditions up to 300 min. Both processes enabled a high recovery of soluble sugars (~50 %) that were, in a great majority, present in the added-value oligomeric form (92 % and 90.5 % for autohydrolysis and dilute acid hydrolysis, respectively). Protein solubilization also presented relevant yields (35 % removal), with dilute acid hydrolysis allowing both higher oligosaccharides and protein productivities at a milder temperature. As compared to the current whole microalgae biomass-based upgrade strategies, the use of these mild processes is extremely promising, as they will enable the future co-production of added-value oligosaccharides, and protein, which can be relevant co-products of a biofuels-based biorefineryinfo:eu-repo/semantics/publishedVersio

Development of an innovative macroalgae biorefinery: Oligosaccharides as pivotal compounds

ABSTRACT: Macroalgae have significant advantages over land-living biomass resources and are promising pivotal feedstocks for the onset of the blue bioeconomy. Among these, Ulva lactuca has demonstrated a high potential due to its wide distribution and high productivity. In this work, a detailed chemical characterization of U. lactuca enabled the identification of polysaccharides as the main macromolecular component of the organic fraction. They present a high diversity of sugar constituents and hence can be a relevant source of added-value oligosaccharides for the food/feed industries. Four processes, with increasing operational temperatures, were compared for the selective production of oligosaccharides: Conventional Soxhlet Extraction, Accelerated Solvent Extraction, Hydrothermal treatment (HT) and Dilute Acid Hydrolysis (DAH). All processes presented high oligosaccharide/monosaccharide ratios, with HT and DAH exhibiting the highest oligosaccharides yields (10.6 and 16.6 g/100 g initial biomass, respectively). These oligosaccharides were obtained under milder, more economic conditions than the reported for lignocellulosic (land) plants and can represent an important added-value income of the algae biorefineries and thus contribute to their economic sustainability.info:eu-repo/semantics/publishedVersio