The production of so-called advanced bioethanol offers several advantages compared to traditional bioethanol production processes in terms of sustainability criteria. This includes, for instance, the ...use of nonfood crops or residual biomass as raw material and a higher potential for reducing greenhouse gas emissions. The present review focuses on the recent progress related to the production of advanced bioethanol, (i) highlighting current results from using novel biomass sources such as the organic fraction of municipal solid waste and certain industrial residues (e.g., residues from the paper, food, and beverage industries); (ii) describing new developments in pretreatment technologies for the fractionation and conversion of lignocellulosic biomass, such as the bioextrusion process or the use of novel ionic liquids; (iii) listing the use of new enzyme catalysts and microbial strains during saccharification and fermentation processes. Furthermore, the most promising biorefinery approaches that will contribute to the cost-competitiveness of advanced bioethanol production processes are also discussed, focusing on innovative technologies and applications that can contribute to achieve a more sustainable and effective utilization of all biomass fractions. Special attention is given to integrated strategies such as lignocellulose-based biorefineries for the simultaneous production of bioethanol and other high added value bioproducts.
Eucalyptus biomass was studied as a feedstock for sugars release using an alkaline extrusion plus a neutralization-based pretreatment. This approach would be a first step in a bioconversion process ...aimed at obtaining fuel bioethanol from eucalyptus biomass. The best operation conditions of extrusion (screw speed, temperature, liquid to solid ratio and NaOH amount) that lead to an effective destructuration of lignocellulose and enhanced sugar release were investigated. Two process configurations, with and without filtration inside the extruder, were tested. In the case without filtration, washed and not washed extrudates were compared. It was demonstrated that filtration step was convenient to remove inorganic salts resulting from neutralization and to promote the mechanical effect of extrusion, but limitations in the machine used in the work prevented testing of temperatures above 100 °C using this configuration. In the no filtration strategy, a temperature of 150 °C allowed attaining the highest glucan and xylan conversion rates by enzymatic hydrolysis of extruded biomass, almost 40% and 75%, respectively, of the maximum yield that could be attained if all carbohydrates contained in raw eucalyptus were converted to sugars. Some of the mechanisms and individual effects underlying alkaline extrusion of eucalyptus were figured out in this work, providing guidelines for a successful pretreatment design that needs to be further studied.
This work addresses for the first time the study of olive stone (OS) biomass pretreatment by reactive extrusion technology using NaOH as the chemical agent. It is considered as a first step in the ...biological conversion process of the carbohydrates contained in the material into bio-based products. OS is a sub-product of the olive oil extraction process that could be used in a context of a multi-feedstock and multi-product biorefinery encompassing all residues generated around the olive oil production sector. OS biomass is pretreated in a twin-screw extruder at varying temperatures—100, 125 and 150 °C and NaOH/biomass ratios of 5% and 15% (dry weight basis), in order to estimate the effectiveness of the process to favour the release of sugars by enzymatic hydrolysis. The results show that alkaline extrusion is effective in increasing the sugar release from OS biomass compared to the raw material, being necessary to apply conditions of 15% NaOH/biomass ratio and 125 °C to attain the best carbohydrate conversion rates of 55.5% for cellulose and 57.7% for xylan in relation to the maximum theoretical achievable. Under these optimal conditions, 31.57 g of total sugars are obtained from 100 g of raw OS.
Olive trees constitute one of the largest agroindustries in the Mediterranean area, and their cultivation generates a diverse pool of biomass by-products such as olive tree pruning (OTP), olive ...leaves (OL), olive stone (OS), and extracted olive pomace (EOP). These lignocellulosic materials have varying compositions and potential utilization strategies within a biorefinery context. The aim of this work was to carry out an integral analysis of the aqueous extractives fraction of these biomasses. Several analytical methods were applied in order to fully characterize this fraction to varying extents: a mass closure of >80% was reached for EOP, >76% for OTP, >65% for OS, and >52% for OL. Among the compounds detected, xylooligosaccharides, mannitol, 3,4-dihydroxyphenylglycol, and hydroxytyrosol were noted as potential enhancers of the valorization of said by-products. The extraction of these compounds is expected to be more favorable for OTP, OL, and EOP, given their high extractives content, and is compatible with other utilization strategies such as the bioconversion of the lignocellulosic fraction into biofuels and bioproducts.
(TEMPO)-mediated oxidation (TMO) is a widely recognized pretreatment for producing highly fibrillated cellulose nanofibrils (CNFs) because of its efficiency and selectivity. However, the challenges ...of scaling up this process is limiting its implementation. This study explores enhancing the production of oxidized pulps (OPs) by performing the TMO reaction within a pilot-plant twin-screw extruder (TSE). This approach aims to oxidize large volumes of cellulose at high concentrations while simultaneously applying a soft mechanical fibrillation, making the upscaling process more sustainable and feasible. OPs and CNFs were characterized and compared to those obtained from the traditional TMO pretreatment in a stirred reactor as well as those pretreated by mechanical TSE. Results demonstrate that TMO within the TSE is more efficient and increase the yield fibrillation using 0.8, 0.08 and 2 mmol/g pulp of NaBr, TEMPO and NaClO, respectively. Multiple TSE steps decrease polymerization degree, enhance the process yield, and reduce the number of large fibers. Gradual addition of oxidants in multiple TSE steps prevents harsh reaction conditions and avoids yellowing of the final products.
Display omitted
Pretreatment of lignocellulosic biomass is an essential step to obtain sugars from such biomasses, aimed at breaking the recalcitrant structure of lignocellulose and facilitate the access of ...enzymatic hydrolytic agents to carbohydrates. Among the variety of pretreatment technologies that have been investigated in the past years, extrusion is a promising thermo-mechanical pretreatment. It is a continuous process, highly versatile, having good mixing and heat transfer capabilities and being able to operate at high solids loadings. However, its energetic and economic feasibility needs still to be evaluated before it can be an actual alternative to conventional biomass pretreatments.
With the aim to provide a further insight into extrusion pretreatment, this work reviews its fundamentals and the influence of the most relevant operation variables (screw profile and speed, residence time, temperature, liquid to solid ratio and downstream operations) on extrusion performance, analyzed according to the existing bibliography. To complete this overview, the effects of extrusion on lignocellulosic biomass structure, composition and enzymatic digestibility are studied, with a focus on the performance of catalyzed extrusion.
•Extrusion is effective in pretreating lignocellulosic biomass, mostly herbaceous type.•Various process configurations with catalysts and/or other pretreatments are feasible.•Key extrusion operation variables (temperature, screw profile, etc.) are discussed.•Main effects on biomass structure, composition and enzymatic hydrolysis are described.
Greenhouse cultivation and harvesting generate considerable amounts of organic waste, including vegetal waste from plants and discarded products. This study evaluated the residues derived from tomato ...cultivation practices in Almería (Spain) as sugar-rich raw materials for biorefineries. First, lignocellulose-based residues were subjected to an alkali-catalyzed extrusion process in a twin-screw extruder (100 °C and 6-12% (
) NaOH) to assess maximum sugar recovery during the subsequent enzymatic hydrolysis step. A high saccharification yield was reached when using an alkali concentration of 12% (
/
), releasing up to 81% of the initial glucan. Second, the discarded tomato residue was crushed and centrifuged to collect both the juice and the pulp fractions. The juice contained 39.4 g of sugars per 100 g of dry culled tomato, while the pulp yielded an extra 9.1 g of sugars per 100 g of dry culled tomato after an enzymatic hydrolysis process. The results presented herein show the potential of using horticulture waste as an attractive sugar source for biorefineries, including lignocellulose-based residues when effective fractionation processes, such as reactive extrusion technology, are available.
Combined soda and enzyme-catalyzed extrusion pretreatment (bioextrusion) of barley straw was evaluated for bioethanol production. The effect of the enzyme dose on the bioextrudate was for the first ...time analyzed. The enzyme load (5–10 FPU/g DM) had a significant impact on the solubilization of sugars during bioextrusion and also affected the saccharification yield at long incubation times. The solids concentration (17–25% w/w) in the extended incubation of bioextrudates was also studied and its effect on the carbohydrate conversion and sugar release was evaluated. An enzyme dose of 10 FPU/g dry matter and a solids content of 20% (w/w) were selected as the best conditions to submit the bioextrudate to a liquefaction plus simultaneous saccharification and co-fermentation (LSSCF) process using a modified S. cerevisiae strain. At the end of the process, an ethanol concentration close to 38 g/l was obtained, corresponding to a production of 15.8 g ethanol/100 g raw barley straw.
•Combined alkali- and enzyme-extrusion is a suitable pretreatment for barley straw.•The effect of enzyme dose and solids content in sugar release was studied.•Fermentation was carried out with a co-fermenting S. cerevisiae strain.•High glucan and xylan conversions of 75% and 61% respectively were obtained.•Ethanol production reaches 15.8 g per 100 g of raw barley straw.
Display omitted
•Food and lignocellulose residues are sustainable feedstocks for use in biorefineries.•Physical pretreatments can provide key advantages in comparison to other methods.•Advances in ...milling, extrusion, ultrasonication and microwave pretreatment are given.•Further research is needed to make feasible the scaling up of these technologies.
The complete deployment of a bio-based economy is essential to meet the United Nations' Sustainable Development Goals from the 2030 Agenda. In this context, food waste and lignocellulosic residues are considered low-cost feedstocks for obtaining industrially attractive products through biological processes. The effective conversion of these raw materials is, however, still challenging, since they are recalcitrant to bioprocessing and must be first treated to alter their physicochemical properties and ease the accessibility to their structural components. Among the full pallet of pretreatments, physical methods are recognised to have a high potential to transform food waste and lignocellulosic residues. This review provides a critical discussion about the recent advances on milling, extrusion, ultrasound, and microwave pretreatments. Their mechanisms and modes of application are analysed and the main drawbacks and limitations for their use at an industrial scale are discussed.
One characteristic necessary to make ethanol production from biomass economically feasible is to optimize enzymatic dosage, since enzymes production is expensive. This work investigated the efficacy ...of different enzymes dosages and solid loadings on wheat straw enzymatic hydrolysis, aimed at obtaining process conditions that lead to good sugars yields from pretreated material. Alkaline extrusion was employed as pretreatment at 70 °C and 10% NaOH solution (w/v). Enzymatic hydrolysis was performed at 5, 10, 15 and 20% solids loading (w/v). Enzyme doses ranged from 6.92 to 20 FPU/g of glucan. Cellulase was also supplemented with xylanase at various proportions. Alkaline extrusion provided a substrate easier to hydrolyze than untreated material. Even the assay with the lowest enzyme dosage (6.92 FPU) achieved a good carbohydrate hydrolysis yield in relation to the theoretical; the glucose yield was 73.8% and xylose yield was 82.8%. A medium containing 100 g/L of fermentable sugar was obtained at 20% solids loading (w/v) and 20 FPU/g of glucan. The supplementation of cellulase with xylanase at U to FPU activity ratio of 3.11:1 improved the glucose yield about 21% over the assay with no xylanase.
•Alkaline-extrusion is an effective method to alter lignocellulose in wheat straw.•Alkaline-extrusion enhances enzymatic digestibility of extruded material.•Cellulase supplementation with xylanase improves glucose release.•Good hydrolysis yield is reached at reasonable enzyme load and high solid content.
PDF
