A novel hybrid organosolv: steam explosion method for the efficient fractionation and pretreatment of birch biomass
© The Author(s) 2018
Received: 30 March 2018
Accepted: 1 June 2018
Published: 8 June 2018
The main role of pretreatment is to reduce the natural biomass recalcitrance and thus enhance saccharification yield. A further prerequisite for efficient utilization of all biomass components is their efficient fractionation into well-defined process streams. Currently available pretreatment methods only partially fulfill these criteria. Steam explosion, for example, excels as a pretreatment method but has limited potential for fractionation, whereas organosolv is excellent for delignification but offers poor biomass deconstruction.
In this article, a hybrid method combining the cooking and fractionation of conventional organosolv pretreatment with the implementation of an explosive discharge of the cooking mixture at the end of pretreatment was developed. The effects of various pretreatment parameters (ethanol content, duration, and addition of sulfuric acid) were evaluated. Pretreatment of birch at 200 °C with 60% v/v ethanol and 1% w/wbiomass H2SO4 was proven to be the most efficient pretreatment condition yielding pretreated solids with 77.9% w/w cellulose, 8.9% w/w hemicellulose, and 7.0 w/w lignin content. Under these conditions, high delignification of 86.2% was demonstrated. The recovered lignin was of high purity, with cellulose and hemicellulose contents not exceeding 0.31 and 3.25% w/w, respectively, and ash to be < 0.17% w/w in all cases, making it suitable for various applications. The pretreated solids presented high saccharification yields, reaching 68% at low enzyme load (6 FPU/g) and complete saccharification at high enzyme load (22.5 FPU/g). Finally, simultaneous saccharification and fermentation (SSF) at 20% w/w solids yielded an ethanol titer of 80 g/L after 192 h, corresponding to 90% of the theoretical maximum.
The novel hybrid method developed in this study allowed for the efficient fractionation of birch biomass and production of pretreated solids with high cellulose and low lignin contents. Moreover, the explosive discharge at the end of pretreatment had a positive effect on enzymatic saccharification, resulting in high hydrolyzability of the pretreated solids and elevated ethanol titers in the following high-gravity SSF. To the best of our knowledge, the ethanol concentration obtained with this method is the highest so far for birch biomass.
Valorization of lignocellulosic biomass from forestry, agricultural, or other industrial side streams for the production of energy, chemicals, and materials, has been the subject of intensive research over the past decades . This interest is based on the fact that lignocellulose is an abundant, renewable, and sustainable resource that can be used as raw material in environmentally friendly and economically beneficial processes. The technologies available for the utilization of lignocellulose are dictated by its chemical composition and structure. With a composition of as high as 70% sugars in the form of cellulose and hemicellulose polymers [2, 3], lignocellulose represents the feedstock of a glucocentric biorefinery process, which was focused initially on production of bioethanol via fermentation of the glucose fraction. The natural recalcitrance of lignocellulose to enzymatic degradation has led to the development of pretreatment strategies that disrupt its complex structure allowing an increased saccharification yield . A number of acidic, aqueous-based pretreatment methods, such as steam explosion , dilute acid , and hydrothermal  have been evaluated toward this direction. The primary goal of these methods is to remove the hemicellulosic barrier around cellulose, while also partly disrupting the lignocellulosic structure, in order to reduce biomass resistance to enzymatic saccharification. Steam explosion causes a dramatic disruption of biomass structure with immediate reduction of particle size and defibration of the substrate . These physical effects, combined with the removal of hemicellulose, lead to enhanced enzymatic saccharification of even the toughest substrates such as softwood-derived biomass . Consequently, steam explosion has been considered for many years as a state-of-the-art pretreatment method in bioethanol production. However, such glucocentric strategy has been marred by a combination of high process costs—particularly regarding the production of cellulolytic enzymes —and relatively small profit margins afforded by bioethanol . To improve profitability, the hemicellulosic sugar fraction has been used as a feedstock for cofermentation with cellulose, and hence to increase the overall ethanol yield . At the same time, lignin—the third polymeric component of lignocellulosic biomass—has been utilized as a low-cost fuel for generating heat or electricity and thus bringing down the overall cost of the process . A more resource-efficient approach would be to utilize the entire biomass in a biorefinery concept, where the different process streams can be directed toward a wide range of products . In this view, all lignocellulose components are potential sources of value-added products.
Implementation of biorefinery concepts depends greatly on the efficiency of the fractionation technologies used to separate cellulose, hemicelluloses, and lignin, and how well-defined the resulting streams are . This has led to a shift regarding the role of lignin. In typical second-generation bioethanol production processes, lignin has been collected as a low-value byproduct and used for cogeneration of heat or electricity. However, when targeting added values from all biomass components, production of a high-purity lignin stream becomes a new necessity; especially since the phenolic components of lignin have been identified as a platform for the production of a variety of chemicals and polymers . A comprehensive strategy for isolating lignin in the first step of the pretreatment/fractionation process is paramount to achieve a high-purity lignin-stream . The requirement for ‘lignin-first’ removal is enhanced by the fact that lignin negatively affects the enzymatic saccharification of cellulose. This negative influence is the result of irreversible adsorption of cellulolytic enzymes onto lignin, and causes physical blockage of the enzymes on cellulose chains, as well as the inhibition of cellulolytic enzymes by soluble lignin-derived molecules . Therefore, lignin removal during the first process step does not only provide a cleaner lignin stream, but can also improve the economics of traditional fermentation-based bioethanol processes as lignin can be used in high-value-added applications . Organosolv pretreatment/fractionation represents one of the most promising biomass delignification and fractionation methods within the biofuels and biorefinery context [19, 20]. In the organosolv pretreatment/fractionation, biomass is heated up to a temperature range of 100–250 °C in an aqueous-organic solvent solution  for a specified duration resulting in three fractions: a solid dry lignin, an aqueous hemicellulose fraction, and a cellulose-rich solid fraction . Low molecular weight aliphatic alcohols, such as ethanol, are frequently used as the organic solvent as they are easy to be recovered by distillation at the end of the organosolv and re-used in subsequent treatments [18, 23]. Implementation of such pretreatment/fractionation technologies is expected to facilitate the coexistence of traditional fermentation-based technologies with novel processes for the utilization of hemicellulose and lignin in broader biorefinery concepts, thus allowing for a multitude of products and higher profit margins . It was previously shown that organosolv treatment and steam explosion pretreatment could be combined in a sequential way for the pretreatment of wheat straw  and fescue ; however, this significantly increases the process complexity (e.g., multiple stages of heating/cooling cycles and increased total process time).
The main aim of the current study was to develop a novel pretreatment method allowing for efficient fractionation of lignocellulosic biomass into cellulose, hemicellulose, and lignin streams. At the same time, the improved pretreatment method should be able to allow for high enzymatic saccharification yields of the cellulose stream for use in biochemical conversion processes. To attain this goal, we combined the fractionation efficiency of conventional organosolv processes with the benefit of physical biomass size reduction achieved during steam explosion into a single stage process. The suggested process was performed in a horizontal design steam explosion reactor, modified to also operate as an organosolv cooking vessel, as shown previously . The novel method was carried out with an explosive discharge of the reactor’s content after conventional ethanol organosolv cooking. Process parameters such as time, ethanol content, and the addition of acid catalyst were studied for the effective pretreatment and fractionation of a representative hardwood biomass (birch). The effect of the explosion step on enzymatic saccharification of cellulose was also investigated. Finally, the ability of the proposed method to produce a cellulose-rich solid fraction that could effectively be saccharified and used during a biochemical conversion method was tested during high-gravity ethanol fermentation.
Results and discussion
Evaluation of fractionation efficiency of the hybrid method
Effect on biomass solubilization and composition of the pretreated solids
Composition of pretreated solids at different pretreatment conditions
Biomass solubilization (% of initial biomass)
Cellulose (% w/w)
Hemicellulose (% w/w)
Lignin (% w/w)
15 min—60% v/v ethanol
A reduction of ethanol content from 70 to 50% v/v during constant treatment led to an increase in biomass solubilization from 41.5 to 48–49% (calculated as the dry-mass fraction recovered as pretreated solids). This increase could be explained by the increased chemical hydrolysis of carbohydrates, and possible cleavage of α- and β-ether bonds of lignin , caused by the higher water content and its increased chemical activity in the pretreatment liquor. Reduced ethanol content in the pretreatment liquor also had a positive effect on cellulose level, which increased from 61.7% at 70% v/v ethanol to 65.9% at 50% ethanol and was accompanied by a reduction in hemicellulose content from 21.9 to 15.1%. Cellulose solubilization during pretreatment was not affected by the varying ethanol concentration employed (Table 1) and cellulose was completely recovered in the pretreated solid. Hemicellulose solubilization increased from 59 to 66 and 75% as ethanol decreased from 70 to 60 and 50%, respectively (Table 1). The latter had also a positive impact on delignification (Table 1). A similar trend had been observed during organosolv treatment of wheat straw, where delignification decreased from 38.8 to 20.8% when ethanol content increased from 50 to 80% w/w . Increased delignification with decreasing ethanol content is a consequence of the higher chemical activity of water, resulting in the cleavage of ether linkages and concomitant lignin fragmentation [27, 29].
An ethanol content of 60% v/v was used to evaluate the effect of cooking time. Increasing cooking time from 15 to 30 min had a positive impact on biomass solubilization, whereas a further increase to 60 min had a negative effect (Table 1). Moreover, increasing the treatment time from 15–30 to 60 min led to a drop in cellulose content in the pretreated solids from 66–67 to 61% w/w, respectively (Table 1), even though no cellulose solubilization was observed during the pretreatment. Prolonged pretreatment time (60 min) resulted in a higher lignin content and a decreased delignification of the materials, possibly due to the formation of pseudo-lignin [30, 31], as well as lower hemicellulose content in the solid fraction and increased hemicellulose solubilization. Formation of insoluble lignin-like compounds or pseudo-lignin (mainly from the hemicellulose decomposition) is well documented in the literature, and these compounds are normally measured as lignin content, thus increasing the determined lignin content in the pretreated solids [32–34]. The decrease in solubilization under harsher pretreatment conditions could also be attributed to the formation of the pseudo-lignin.
Using the 15-min treatment as a reasonable compromise between time and efficiency, addition of an acidic catalyst (sulfuric acid) on pretreatment efficiency was examined. Addition of the catalyst at 0.2% w/w of biomass had almost no impact on the overall biomass solubilization, whereas a 1% w/w catalyst concentration increased biomass solubilization to 63%, mainly due to extensive cleavage of carbohydrates and aryl-ether bonds of lignin [35, 36]. Addition of 1% w/w acid catalyst resulted in very high cellulose content (78%) and increased solubilization of hemicellulose (Table 1), with part of the cellulose being solubilized due to the acid. In contrast, addition of 0.2% acid catalyst did not improve hemicellulose solubilization compared to pretreatment without catalyst. The same trend was observed for delignification: at the lower concentration the catalyst had only a minor positive impact, whereas at the higher concentration delignification increased from 77 to 86% (Table 1). The extended solubilization of hemicellulose and lignin is a result of the severe conditions during the pretreatment caused by the higher acid concentration.
In general, the novel pretreatment system resulted in pretreated solids with high cellulose content. Hemicellulose was resilient to all pretreatment conditions and its content in the pretreated solids was relatively high (Table 1). Indeed, with the exception of the high-concentration acid catalyst pretreatment (where 89.5% of the initial hemicellulose solubilized), the percentage of hemicellulose solubilization was between 54.5 and 74.8% of the initial hemicellulose fraction (Table 1). The main advantage of the proposed pretreatment method when using birch biomass was its effective lignin removal. Specifically, lignin content of the pretreated solids was below 9% in most cases, and dropped to 7% when 1% acid was used. Such highly efficient delignification, combined with elevated cellulose content in some pretreated solids, is very promising not only as a biomass fractionation method, but also for effective and low-cost enzymatic hydrolysis of pretreated solids . In addition, high cellulose content is necessary to achieve high ethanol titers in bioethanol production.
Sugar composition in the liquid fraction
Apart from hemicellulosic sugars in the liquor, treatment conditions affected also the ratio between monomeric and oligomeric sugars. In general, sugars found in monomeric form were lower compared to oligomers; only when 0.2% sulfuric acid was used as a catalyst were monomeric sugars approximately nine times more abundant than oligomers. Ethanol content had a minor impact on the ratio between monomeric and oligomeric sugars: it increased initially when ethanol rose from 50 to 60%, but decreased thereafter, probably due to the lower water content and therefore lower generation of hydronium ions that can selectively depolymerize hemicellulose . A short treatment time of 15 min yielded only oligomeric hemicellulosic sugars, whereas a 30-min treatment increased the amount of monomeric sugars in the liquor. Notably, the ratio between monomeric and oligomeric sugars declined when treatment time was prolonged to 60 min, probably due to extended decomposition of hemicellulosic sugars as sugars of hemicellulosic origin (especially xylose) are generally sensitive to thermal degradation under harsher pretreatment conditions . Finally, the addition of acidic catalyst initially increased the ratio of monomeric sugars due to the more acidic conditions created that promoted the depolymerization of oligomeric sugars, whereas, at the highest concentration of 1% w/w, the amount of monomeric sugars was considerably reduced. Recovery of the hemicellulosic sugars in the liquid fraction after the organosolv pretreatment has been found to be significantly dependent on the concentration of the acid catalyst employed as increasing the acid catalyst decreased the recovery .
Evaluation of saccharification efficiency of pretreated solids
Apart from achieving good fractionation yields, one important aspect of establishing a pretreatment process is to produce pretreated solids that present high saccharification yields. High glucose concentration is very important for the subsequent bioconversion processes, such as ethanol fermentation, as it can result in high product titers. Therefore, the first step to assess the potential of the pretreated solids prior to bioconversion is to assess their saccharification yields. For this reason, we performed enzymatic saccharification trials at low solids content aiming to select the materials with high saccharification yields and subsequently evaluate them as raw materials for ethanol production.
Assessing the role of explosive discharge
What differentiates the proposed hybrid solvent organosolv-steam explosion pretreatment approach from more conventional organosolv methods is the combination of solvent cooking with the explosive discharge at the end of pretreatment. This step was applied in an effort to combine the fractionation efficiency of organosolv-type treatments with the positive effect of explosion on enzymatic saccharification, as observed in conventional steam explosion . To evaluate the effect of explosion on enzymatic saccharification of the solids, experiments without explosive discharge were performed (the chosen conditions were 60% v/v ethanol for 15 min without addition of acidic catalyst). The reason to perform the evaluation of the explosive discharge without the use of the acid catalyst was to study the effect of the explosion ‘independently’ without the additive effect of the acid catalyst. Moreover, steam pretreatment experiments with and without explosion (see “Methods” section) were also performed to compare the proposed hybrid process in terms of pretreatment efficiency with a state-of-the-art pretreatment method.
Effect of explosive discharge on the composition of pretreated solids
Cellulose (% w/w)
Hemicellulose (% w/w)
Lignin (% w/w)
Organosolv (200 °C—60% v/v ethanol—15 min)
Steam explosion (200 °C—5 min—0.14% w/w H2SO4)
Ethanol fermentation with pretreated solids
Ethanol production reported in the literature for high-gravity fermentation of various wood lignocellulosic raw materials
30 FPU/g glucan
S. cerevisiae from Angel Yeast Co. Ltd
Eastern red cedar
46 FPU/g glucan
Hybrid organosolv—steam explosion
Efficient and complete utilization of forest biomass for the production of portfolio of products including renewable fuels such as ethanol, requires the development of a novel biorefinery concept capable of utilizing each biomass component. To achieve this, new fractionation technologies need to be developed. In the present study, we propose a novel hybrid pretreatment/fractionation method that combines the fractionation efficiency of traditional organosolv processes with the explosive discharge at the end of pretreatment. Optimization of pretreatment parameters resulted in 86% delignification and pretreated solids with high cellulose (78%) and low lignin (7%) content. The pretreated solids allowed for high saccharification yields, of up to 68% with low enzyme load and full hydrolysis when enzyme load increased. Finally, use of the pretreated solids as raw material for high-gravity fermentation resulted in an ethanol titer of 80 g/L.
In the present work, wood chips from silver birch (Betula pendula L.) originating from mills in Northern Sweden were used. Bark-free chips were air-dried and milled in a Retsch SM 300 knife mill (Retsch GmbH, Haan, Germany) through a 1-mm screen and used for the pretreatment experiments. The composition of untreated birch (expressed in dry basis) was 34.7% w/w cellulose, 31.2% w/w hemicellulose, and 18.7% w/w lignin. The moisture of the chips used during the experiments was 6.0% w/w.
Control experiments were performed in the same reactor to determine the effect of solvent pretreatment and of explosive decompression of the pretreatment slurry. These included steam explosion pretreatment, steam non-explosion pretreatment, and organosolv non-explosion pretreatment. Specifically, organosolv non-explosion experiments were performed in the same way as hybrid organosolv-steam explosion with one difference: at the end of the pretreatment time, the discharge valve was not opened. Instead, the valve to the blowout tank was opened, allowing removal of the liquor into the blowout tank and a gradual reduction of pressure; thus avoiding the explosion of the biomass that remained inside the reactor. After removal of the liquid through the valve, the reactor lid was opened, and the pretreated biomass was manually collected from the reactor. The organosolv non-explosion pretreatment was performed at the optimal conditions obtained in the current work, without the addition of the acidic catalyst to better study the effect of the explosion step. Steam explosion experiments (200 °C for 5 min with 0.14% w/w H2SO4) were performed as previously described . Steam non-explosion experiments were performed by the removal of pretreatment liquid into the blowout tank via the respective valve and the manual collection of biomass from the reactor (as previously described for the organosolv non-explosion pretreatment).
After the organosolv-steam explosion experiment, the pretreatment slurry was vacuum-filtered to separate the solids from the liquor. Ethanol was removed from the liquor in a rotary evaporator to reduce lignin solubility. Lignin was finally isolated by centrifugation (14,000 rpm, 29,416×g, at 4 °C for 15 min), air-dried, and analyzed for its purity (composition in carbohydrates and ash—see “Chemical analysis” section). The clear liquor obtained after centrifugation and containing solubilized sugars was collected for sugars determination. Pretreated biomass solids were washed with ethanol to remove surface-bound lignin, air-dried, and stored until further use.
In the steam pretreatment experiments, lignin was not isolated, but the liquid and solid fractions were separated by vacuum filtration, and the solids were washed with deionized water until a neutral pH of the filtrate was achieved.
Analysis of the chemical compositions of untreated and pretreated solid biomass was performed as described elsewhere . Carbohydrates were determined by HPLC analysis employing an Aminex HPX-87P column (BioRad, Hercules, CA, USA), with a column temperature of 85 °C, H2O as mobile phase at a flow of 0.6 mL/min, and an RI (refractive index) detector. Acetyl groups were determined by measuring acetic acid with an Aminex HPX-87H column (BioRad, Hercules, CA, USA), 5 mM H2SO4 as mobile phase at a flow of 0.6 mL/min, and 65 °C. To determine inorganic ash, samples were ashed at 550 °C for 3 h to remove any organic content and the ash was determined gravimetrically. To determine carbohydrate and ash contents in recovered lignin, samples underwent the same procedure as pretreated solid biomass. The same HPLC method as above was used to calculate sugar monomers in pretreatment liquid. To determine sugar oligomers, concentrated sulfuric acid was added to liquid samples to a final concentration of 4%, samples were hydrolyzed at 121 °C for 1 h, and then neutralized, filtrated, and analyzed as described above. Ethanol produced during fermentation was analyzed on an Aminex HPX-87H column using the conditions described before. Biomass moisture content was analyzed with a Sartorius MA 30 (Sartorius AG, Goettingen, Germany) moisture analyzer.
Samples were prepared by mounting them on conducting carbon tapes. They were imaged with a scanning electron microscope (JEOL 7800-F Prime) in low vacuum (100 Pa) and high vacuum (10−4 Pa or lower), with an acceleration voltage of 3.0 kV. To image the samples in high vacuum, and therefore increase image resolution, a thin coating with palladium was performed. A layer of a few nanometers increased the conductivity sufficiently to image in high vacuum. Images in low vacuum and high vacuum were compared to ensure that the coating did not affect sample morphology.
Enzymatic hydrolysis trials
Ethanol fermentation trial at low solid concentration
For SSF (simultaneous saccharification and fermentation) at low gravity, samples pretreated with (60% ethanol, 1% H2SO4, 15 min) and without acid catalyst (60% ethanol, 60 min) were used. As the saccharification yield among non-acid-treated samples was the highest for a 60-min treatment, we used this condition rather than the 15-min one. Biomass was prehydrolyzed for 8 h with 6% w/w solids and then diluted to 5% w/w with the addition of Saccharomyces cerevisiae Ethanol Red® and nutrients (1 g/L yeast extract, 0.5 g/L (NH4)2HPO4, and 0.025 g/L MgSO4.7H2O) for a pitching load of 20 mg dry cell matter/g solids. Samples were taken every 24 h over 5 days for ethanol measurement. They were centrifuged, the supernatant was filtered through a 0.2-µm nylon filter, and analyzed by HPLC as described before. Fermentations were performed in duplicates.
High-gravity ethanol fermentation
During high-gravity fermentation, birch pretreated for 15 min with 60% ethanol (v/v) and 1% H2SO4 (w/w) was used. Saccharification took place in a gravimetric saccharification chamber as described previously [47, 48]. Pretreated birch biomass was saccharified at a dry material content of 20% w/w in citrate buffer (50 mM) with 18.5 FPU of Cellic® CTec2 per gram of solids. Saccharification took place at 50 °C for 8 h, after which the slurry was collected and used for SSF. The slurry was supplemented with nutrients to achieve a final concentration of 1 g/L yeast extract, 0.5 g/L (NH4)2HPO4, and 0.025 g/L MgSO4·7H2O from a concentrated stock solution so that the volume change after addition was < 2% (v/v). The SSF experiment was initiated by addition of S. cerevisiae Ethanol Red® suspension (from an overnight YPD culture grown in 250 mL flasks at 35 °C and 180 rpm) amounting to an initial cell concentration of 1 g/L dry cell matter. Samples were taken regularly throughout the cultivations, which were performed in duplicates at 35 °C and 120 rpm. Samples were diluted five times based on mass, filtered through a 0.2-µm nylon filter, and analyzed by HPLC as described in the chemical analysis section.
LM: participated in the experimental design and data analysis, performed the pretreatments, participated in the analysis of the recovered fraction and in high-gravity fermentation, and drafted the manuscript. CN: participated in experimental design and data analysis and drafted the manuscript. VR: performed enzymatic hydrolysis of pretreated samples and SSF at low- and high-gravity, and wrote parts of the manuscript. OY: performed the pretreatments and analyzed the recovered fractions. GP: performed SEM analysis. EO: analyzed SEM pictures. UR: conceived the study and participated in experimental design and data analysis. LO: conceived the study and participated in experimental design and data analysis. PC: conceived the study and participated in experimental design and data analysis. All authors read and approved the final manuscript.
The authors would like to thank Sveaskog, Sweden, for providing the birch chips; Novozymes A/S, Denmark, for providing the Cellic® CTec2 enzyme solution; and Lesaffre Advanced Fermentations, France, for providing the Ethanol Red® that were used during this work.
The authors declare that they have no competing interests.
Availability of data and materials
The materials produced during the current study are available from the corresponding author on reasonable request.
Consent for publication
Ethics approval and consent to participate
This work was funded by Swedish Energy Agency as part of the SolveFuels project (funded by Swedish Energy Agency). Leonidas Matsakas, Ulrika Rova, and Paul Christakopoulos thank Bio4Energy, a strategic research environment appointed by the Swedish government, and Kempe Foundations, for supporting this work. Vijayendran Raghavendran and Lisbeth Olsson thank Chalmers Area of Advance Energy for financial support via the strategic research environment funding.
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
- Menon V, Rao M. Trends in bioconversion of lignocellulose: biofuels, platform chemicals and biorefinery concept. Prog Energy Combust Sci. 2012;38:522–50.View ArticleGoogle Scholar
- Zhao X, Zhang L, Liu D. Biomass recalcitrance. Part I: the chemical compositions and physical structures affecting the enzymatic hydrolysis of lignocellulose. Biofuels Bioprod Biorefin. 2012;6:465–82.View ArticleGoogle Scholar
- Haghighi Mood S, Hossein Golfeshan A, Tabatabaei M, Salehi Jouzani G, Najafi GH, Gholami M, et al. Lignocellulosic biomass to bioethanol, a comprehensive review with a focus on pretreatment. Renew Sustain Energy Rev. 2013;27:77–93.View ArticleGoogle Scholar
- Kumar P, Barrett DM, Delwiche MJ, Stroeve P. Methods for pretreatment of lignocellulosic biomass for efficient hydrolysis and biofuel production. Ind Eng Chem Res. 2009;48:3713–29.View ArticleGoogle Scholar
- Eklund R, Galbe M, Zacchi G. The influence of SO2 and H2SO4 impregnation of willow prior to steam pretreatment. Bioresour Technol. 1995;52:225–9.View ArticleGoogle Scholar
- Torget RW, Kim JS, Lee YY. Fundamental aspects of dilute acid hydrolysis/fractionation kinetics of hardwood carbohydrates. 1. Cellulose hydrolysis. Ind Eng Chem Res. 2000;39:2817–25.View ArticleGoogle Scholar
- Nitsos CK, Matis KA, Triantafyllidis KS. Optimization of hydrothermal pretreatment of lignocellulosic biomass in the bioethanol production process. Chemsuschem. 2013;6:110–22.View ArticleGoogle Scholar
- Pielhop T, Larrazábal GO, Studer MH, Brethauer S, Seidel C-M, Rudolf von Rohr P. Lignin repolymerisation in spruce autohydrolysis pretreatment increases cellulase deactivation. Green Chem. 2015;17:3521–32.View ArticleGoogle Scholar
- Monavari S, Bennato A, Galbe M, Zacchi G. Improved one-step steam pretreatment of SO2-impregnated softwood with time-dependent temperature profile for ethanol production. Biotechnol Prog. 2010;26:1054–60.Google Scholar
- Tu M, Chandra RP, Saddler JN. Evaluating the distribution of cellulases and the recycling of free cellulases during the hydrolysis of lignocellulosic substrates. Biotechnol Prog. 2007;23:398–406.View ArticleGoogle Scholar
- Bozell JJ. An evolution from pretreatment to fractionation will enable successful development of the integrated biorefinery. BioResources. 2010;5:1326–7.Google Scholar
- Öhgren K, Bengtsson O, Gorwa-Grauslund MF, Galbe M, Hahn-Hägerdal B, Zacchi G. Simultaneous saccharification and co-fermentation of glucose and xylose in steam-pretreated corn stover at high fiber content with Saccharomyces cerevisiae TMB3400. J Biotechnol. 2006;126:488–98.View ArticleGoogle Scholar
- Eriksson G, Kjellström B, Lundqvist B, Paulrud S. Combustion of wood hydrolysis residue in a 150 kW powder burner. Fuel. 2004;83:1635–41.View ArticleGoogle Scholar
- Cherubini F. The biorefinery concept: using biomass instead of oil for producing energy and chemicals. Energy Convers Manag. 2010;51:1412–21.View ArticleGoogle Scholar
- Isikgor FH, Becer CR. Lignocellulosic biomass: a sustainable platform for the production of bio-based chemicals and polymers. Polym Chem. 2015;6:4497–559.View ArticleGoogle Scholar
- Ragauskas AJ, Beckham GT, Biddy MJ, Chandra R, Chen F, Davis MF, et al. Lignin valorization: improving lignin processing in the biorefinery. Science. 2014;344:1246843.View ArticleGoogle Scholar
- Saini JK, Patel AK, Adsul M, Singhania RR. Cellulase adsorption on lignin: a roadblock for economic hydrolysis of biomass. Renew Energy. 2016;98:29–42.View ArticleGoogle Scholar
- Nitsos C, Rova U, Christakopoulos P. Organosolv fractionation of softwood biomass for biofuel and biorefinery applications. Energies. 2018;11:50.View ArticleGoogle Scholar
- Nitsos C, Stoklosa R, Karnaouri A, Vörös D, Lange H, Hodge D, et al. Isolation and characterization of organosolv and alkaline lignins from hardwood and softwood biomass. ACS Sustain Chem Eng. 2016;4:5181–93.View ArticleGoogle Scholar
- Park N, Kim HY, Koo BW, Yeo H, Choi IG. Organosolv pretreatment with various catalysts for enhancing enzymatic hydrolysis of pitch pine (Pinus rigida). Bioresour Technol. 2010;101:7046–53.View ArticleGoogle Scholar
- Matsakas L, Nitsos C, Vörös D, Rova U, Christakopoulos P. High-titer methane from organosolv-pretreated spruce and birch. Energies. 2017;10:263.View ArticleGoogle Scholar
- Duff SJB, Murray WD. Bioconversion of forest products industry waste cellulosics to fuel ethanol: a review. Bioresour Technol. 1996;55:1–33.View ArticleGoogle Scholar
- Zhao X, Cheng K, Liu D. Organosolv pretreatment of lignocellulosic biomass for enzymatic hydrolysis. Appl Microbiol Biotechnol. 2009;82:815–27.View ArticleGoogle Scholar
- Hongzhang C, Liying L. Unpolluted fractionation of wheat straw by steam explosion and ethanol extraction. Bioresour Technol. 2007;98:666–76.View ArticleGoogle Scholar
- Maniet G, Schmetz Q, Jacquet N, Temmerman M, Gofflot S, Richel A. Effect of steam explosion treatment on chemical composition and characteristic of organosolv fescue lignin. Ind Crops Prod. 2017;99:79–85.View ArticleGoogle Scholar
- Nitsos C, Matsakas L, Triantafyllidis K, Rova U, Christakopoulos P. Investigation of different pretreatment methods of Mediterranean-type ecosystem agricultural residues: characterisation of pretreatment products, high-solids enzymatic hydrolysis and bioethanol production. Biofuels. 2017. https://doi.org/10.1080/17597269.2017.1378988.Google Scholar
- Pan X, Gilkes N, Kadla J, Pye K, Saka S, Gregg D, et al. Bioconversion of hybrid poplar to ethanol and co-products using an organosolv fractionation process: optimization of process yields. Biotechnol Bioeng. 2006;94:851–61.View ArticleGoogle Scholar
- Huijgen WJJ, Telysheva G, Arshanitsa A, Gosselink RJA, de Wild PJ. Characteristics of wheat straw lignins from ethanol-based organosolv treatment. Ind Crops Prod. 2014;59:85–95.View ArticleGoogle Scholar
- Zhang Z, Harrison MD, Rackemann DW, Doherty WOS, O’Hara IM. Organosolv pretreatment of plant biomass for enhanced enzymatic saccharification. Green Chem. 2016;18:360–81.View ArticleGoogle Scholar
- Ma X, Yang X, Zheng X, Chen L, Huang L, Cao S, et al. Toward a further understanding of hydrothermally pretreated holocellulose and isolated pseudo lignin. Cellulose. 2015;22:1687–96.View ArticleGoogle Scholar
- Bensah EC, Mensah M. Chemical pretreatment methods for the production of cellulosic ethanol: technologies and innovations. Int J Chem Eng. 2013;2013:1–21.View ArticleGoogle Scholar
- Sun SL, Sun SN, Wen JL, Zhang XM, Peng F, Sun RC. Assessment of integrated process based on hydrothermal and alkaline treatments for enzymatic saccharification of sweet sorghum stems. Bioresour Technol. 2015;175:473–9.View ArticleGoogle Scholar
- Kumar R, Hu F, Sannigrahi P, Jung S, Ragauskas AJ, Wyman CE. Carbohydrate derived-pseudo-lignin can retard cellulose biological conversion. Biotechnol Bioeng. 2013;110:737–53.View ArticleGoogle Scholar
- Verdía P, Brandt A, Hallett JP, Ray MJ, Welton T. Fractionation of lignocellulosic biomass with the ionic liquid 1-butylimidazolium hydrogen sulfate. Green Chem. 2014;16:1617.View ArticleGoogle Scholar
- Sturgeon MR, Kim S, Lawrence K, Paton RS, Chmely SC, Nimlos M, et al. A mechanistic investigation of acid-catalyzed cleavage of aryl-ether linkages: implications for lignin depolymerization in acidic environments. ACS Sustain Chem Eng. 2014;2:472–85.View ArticleGoogle Scholar
- Kobayashi T, Kohn B, Holmes L, Faulkner R, Davis M, MacIel GE. Molecular-level consequences of biomass pretreatment by dilute sulfuric acid at various temperatures. Energy Fuels. 2011;25:1790–7.View ArticleGoogle Scholar
- Sannigrahi P, Ragauskas AJ, Miller SJ. Lignin structural modifications resulting from ethanol organosolv treatment of loblolly pine. Energy Fuels. 2010;24:683–9.View ArticleGoogle Scholar
- Huijgen WJJ, Reith JH, Den Uil H. Pretreatment and fractionation of wheat straw by an acetone-based organosolv process. Ind Eng Chem Res. 2010;49:10132–40.View ArticleGoogle Scholar
- Ruiz HA, Vicente AA, Teixeira JA. Kinetic modeling of enzymatic saccharification using wheat straw pretreated under autohydrolysis and organosolv process. Ind Crops Prod. 2012;36:100–7.View ArticleGoogle Scholar
- Ximenes E, Kim Y, Ladisch MR. Biological conversation of plants to fuels and chemicals and the effects of inhibitors. In: Wyman CE, editor. Aqueous pretreatment of plant biomass for biological and chemical conversion to fuels and chemicals. Chichester: Wiley; 2013. p. 39–60.View ArticleGoogle Scholar
- Pan X, Xie D, Yu RW, Lam D, Saddler JN. Pretreatment of Lodgepole pine killed by mountain pine beetle using the ethanol organosolv process: fractionation and process optimization. Ind Eng Chem Res. 2007;46:2609–17.View ArticleGoogle Scholar
- Pereira Ramos L. The chemistry involved in the steam treatment of lignocellulosic materials. Quim Nova. 2003;26:863–71.View ArticleGoogle Scholar
- Seidel C-M, Pielhop T, Studer MH, Rudolf Von Rohr P. The influence of the explosive decompression in steam-explosion pretreatment on the enzymatic digestibility of different biomasses. Faraday Discuss. 2017;202:269–80.View ArticleGoogle Scholar
- Pielhop T, Amgarten J, von Rohr PR, Studer MH. Steam explosion pretreatment of softwood: the effect of the explosive decompression on enzymatic digestibility. Biotechnol Biofuels. 2016;9:152.View ArticleGoogle Scholar
- Zacchi G, Axelsson A. Economic evaluation of preconcentration in production of ethanol from dilute sugar solutions. Biotechnol Bioeng. 1989;34:223–33.View ArticleGoogle Scholar
- Koppram R, Tomás-Pejó E, Xiros C, Olsson L. Lignocellulosic ethanol production at high-gravity: challenges and perspectives. Trends Biotechnol. 2014;32:46–53.View ArticleGoogle Scholar
- Matsakas L, Christakopoulos P. Fermentation of liquefacted hydrothermally pretreated sweet sorghum bagasse to ethanol at high-solids content. Bioresour Technol. 2013;127:202–8.View ArticleGoogle Scholar
- Matsakas L, Kekos D, Loizidou M, Christakopoulos P. Utilization of household food waste for the production of ethanol at high dry material content. Biotechnol Biofuels. 2014;7:4.View ArticleGoogle Scholar
- Katsimpouras C, Zacharopoulou M, Matsakas L, Rova U, Christakopoulos P, Topakas E. Sequential high gravity ethanol fermentation and anaerobic digestion of steam explosion and organosolv pretreated corn stover. Bioresour Technol. 2017;244:1129–36.View ArticleGoogle Scholar
- Wang R, Koppram R, Olsson L, Franzén CJ. Kinetic modeling of multi-feed simultaneous saccharification and co-fermentation of pretreated birch to ethanol. Bioresour Technol. 2014;172:303–11.View ArticleGoogle Scholar
- Koppram R, Olsson L. Combined substrate, enzyme and yeast feed in simultaneous saccharification and fermentation allow bioethanol production from pretreated spruce biomass at high solids loadings. Biotechnol Biofuels. 2014;7:54.View ArticleGoogle Scholar
- Yáñez-S M, Rojas J, Castro J, Ragauskas A, Baeza J, Freer J. Fuel ethanol production from Eucalyptus globulus wood by autocatalized organosolv pretreatment ethanol-water and SSF. J Chem Technol Biotechnol. 2013;88:39–48.View ArticleGoogle Scholar
- Bertilsson M, Olofsson K, Lidén G. Prefermentation improves xylose utilization in simultaneous saccharification and co-fermentation of pretreated spruce. Biotechnol Biofuels. 2009;2:8.View ArticleGoogle Scholar
- Frankó B, Galbe M, Wallberg O. Influence of bark on fuel ethanol production from steam-pretreated spruce. Biotechnol Biofuels. 2015;8:15.View ArticleGoogle Scholar
- Dong C, Wang Y, Zhang H, Leu SY. Feasibility of high-concentration cellulosic bioethanol production from undetoxified whole Monterey pine slurry. Bioresour Technol. 2018;250:102–9.View ArticleGoogle Scholar
- Katsimpouras C, Kalogiannis KG, Kalogianni A, Lappas AA, Topakas E. Production of high concentrated cellulosic ethanol by acetone/water oxidized pretreated beech wood. Biotechnol Biofuels. 2017;10:54.View ArticleGoogle Scholar
- Ramachandriya KD, Wilkins M, Atiyeh HK, Dunford NT, Hiziroglu S. Effect of high dry solids loading on enzymatic hydrolysis of acid bisulfite pretreated Eastern redcedar. Bioresour Technol. 2013;147:168–76.View ArticleGoogle Scholar
- Sluiter A, Hames B, Ruiz R, Scarlata C, Sluiter J, Templeton D, et al. NREL/TP-510-42618 analytical procedure—determination of structural carbohydrates and lignin in biomass. Lab Anal Proced. 2012;1617:17.Google Scholar
- Koppram R, Mapelli V, Albers E, Olsson L. The presence of pretreated lignocellulosic solids from birch during saccharomyces cerevisiae fermentations leads to increased tolerance to inhibitors—a proteomic study of the effects. PLoS ONE. 2016;11:e0148635.View ArticleGoogle Scholar