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The core objective of this work was to take advantage of the unexploited wheat straw biomass, currently considered as a broadly available waste stream from the Greek agricultural sector, towards the integrated valorization of sugar streams for the microbial production of polyunsaturated omega-3 fatty acids (PUFAs). The OxiOrganosolv pretreatment process was applied using acetone and ethanol as organic solvents without any additional catalyst. The results proved that both celluloserich solid pulp and hemicellulosic oligosaccharides-rich aqueous liquid fraction after pretreatment can be efficiently hydrolyzed enzymatically, thus resulting in high yields of fermentable monosaccharides. The latter were supplied as carbon sources to the heterotrophic microalga Crypthecodinium cohnii for the production of PUFAs, more specifically docosahexaenoic acid (DHA). The solid fractions consisted mainly of hexose sugars and led to higher DHA productivity than their pentose-rich liquid counterparts, which can be attributed to the different carbon source and C/N ratio in the two streams. The best performance was obtained with the solid pulp pretreated with ethanol at 160 °C for 120 min and an O2 pressure of 16 bar. The total fatty acids content reached 70.3 wt% of dried cell biomass, of which 32.2% was DHA. The total DHA produced was 7.1 mg per g of untreated wheat straw biomass. [ABSTRACT FROM AUTHOR]

Lactic acid is one of the most important high added value chemicals with various applications in diverse fields, e.g. food industry, pharmaceuticals, and plastics. Recently, it has been gaining even more attention as the starting material for the synthesis of bio-based chemicals such as acrylic acid, 2,3-pentanedione and acetaldehyde. The current industrial process for lactic acid synthesis is based on enzymatic fermentation of carbohydrates (e.g. glucose and sucrose), which is a sensitive process in terms of feed quality/purity, requires strict control of the reaction conditions and produces a considerable amount of waste. Therefore, increasing research effort is being placed on the development of alternative green and sustainable chemocatalytic processes. Lactic acid can be synthesized from glucose via a retro-aldol reaction pathway, which is favored under basic conditions, or via catalysts with pronounced Lewis acidity. On the other hand, glucose is produced from cellulose hydrolysis, which requires Brønsted acidity. In view of developing a one-pot chemocatalytic process for the synthesis of lactic acid from cellulose, the present work investigates the effect of oxides (SiO2, SiO2-Al2O3, Nb2O5, Nb2O5-SiO2, Nb2O5-Al2O3), heteropolyacids (HPAs) (TSA, PTA) and supported HPAs on the oxides as bifunctional catalysts with varying ratios of Lewis to Brønsted acid sites on cellulose conversion into lactic acid. According to the experimental results, the type of acidity played a key role in the reaction pathway and consequently in the product distribution. Among the supported catalysts tested, TSA/SiO2-Al2O3 with the highest Lewis to Brønsted acidity ratio led to the highest lactic acid selectivity (38.4%) and yield (23.5%), at 61.2% cellulose conversion. For this catalyst the effect of reaction conditions, catalyst concentration, cellulose crystallinity and the presence of other biomass components (hemicellulose and lignin) was further evaluated. The stability and reuse of TSA/SiO2-Al2O3 were confirmed for at least 3 reaction cycles, whereas the reaction pathway of cellulose conversion was confirmed and validated via a power law kinetic modeling scheme. [ABSTRACT FROM AUTHOR]

Biomass fractionation, as an alternative to biomass pretreatment, has gained increasing research attention over the past few years as it provides separate streams of cellulose, hemicellulose, and lignin. These streams can be used separately and can provide a solution for improving the economics of emerging biorefinery technologies. The sugar streams are commonly used in microbial conversions, whereas during recent years lignin has been recognized as a valuable compound as it is the only renewable and abundant source of aromatic chemicals. Successfully converting lignin into valuable chemicals and products is key in achieving both environmental and economic sustainability of future biorefineries. In this work, lignin retrieved from beechwood sawdust delignification pretreatment via an organosolv process was depolymerized with thermal and catalytic pyrolysis. ZSM-5 commercial catalyst was used in situ to upgrade the lignin bio-oil vapors. Lignins retrieved from different modes of organosolv pretreatment were tested in order to evaluate the effect that upstream pretreatment has on the lignin fraction. Both thermal and catalytic pyrolysis yielded oils rich in phenols and aromatic hydrocarbons. Use of ZSM-5 catalyst assisted in overall deoxygenation of the bio-oils and enhanced aromatic hydrocarbons production. The oxygen content of the bio-oils was reduced at the expense of their yield. Organosolv lignins were successfully depolymerized towards phenols and aromatic hydrocarbons via thermal and catalytic pyrolysis. Hence, lignin pyrolysis can be an effective manner for lignin upgrading towards high added value products. [ABSTRACT FROM AUTHOR]

In the present work, a novel OxiOrganosolv pretreatment was developed for the fractionation of beechwood. Τhe process employs a mixture of water and common organic solvents, polyoxometalate complexes (POMs) as homogeneous catalysts and O 2 that acts as an oxidative agent enabling their regeneration. Due to their strong oxidizing ability and redox reversibility, POMs can achieve efficient biomass fractionation by catalyzing simultaneously hemicellulose hydrolysis and oxidation of lignin ether bonds that leads to its depolymerization, dissolution in the organic solvent and removal from the cellulose-rich pulp. According to the results, both commercially available phosphomolybdic acid (HPMo) and also the in-house produced Fe- and Cu- exchanged salts successfully promoted delignification and hemicellulose removal compared to the OxiOrganosolv pretreatment in the absence of catalyst. Most importantly, catalytic lignin depolymerization was achieved without the use of mineral acids that are typically used in a traditional organosolv. Evaluation of the enzymatic digestibility of the pulps revealed HPMo as the most favorable catalyst for increased saccharification yields and production of sugar-rich hydrolysates that were further used as carbon sources for fermentation and production of ω -3 polyunsaturated fatty acids (ω -3 PUFAs) from the heterotrophic microalgae Crypthecodinium cohnii. Hydrolysates produced from HPMo and Fe-PMo-assisted OxiOrganosolv pretreatment supported cell growth and led to high accumulation of ω -3 PUFAs, while severe inhibition was observed with the hydrolysates from Cu-PMo pretreated biomass. This study demonstrates the possibility of using POMs as catalysts for efficient biomass delignification with the aim to obtain sugar-rich streams that can be utilized for the production of nutraceuticals. • A novel OxiOrganosolv process with POMs as homogeneous catalysts was developed. • POMs led to efficient delignification and hemicellulose removal from beechwood. • HPMo was the best catalyst to increase cellulose digestibility and glucose yields. • HPMo and Fe-PMo hydrolysates promoted ω3 accumulation in microalgae C. cohnii. • The presence of Cu in Cu-PMo hydrolysates significantly hindered microbial growth. [ABSTRACT FROM AUTHOR]

Thermal and catalytic pyrolysis are efficient processes for the transformation of biomass to bio-oil, a liquid energy carrier and a general source of chemicals. The elucidation of the bio-oil's composition is essential for a rational design of both its production and utilization process. However, the complex composition of bio-oils hinders their complete qualitative and quantitative analysis, and conventional chromatographic techniques lack the necessary separation power. Two-dimensional gas chromatography with time-of-flight mass spectrometry (GC × GC–ToFMS) is considered a suitable technique for bio-oil analysis due to its increased separation and resolution capacity. This work presents the tentative qualitative and quantitative analysis of bio-oils resulting from the thermal and catalytic pyrolysis of standard xylan, cellulose, lignin and their mixture by GC × GC–ToFMS. Emphasis is placed on the development of the quantitative method using phenol-d 6 as internal standard. During the method development, a standard solution of 39 compounds was used for the determination of the respective Relative Response Factors (RRF) employing statistical methods, ANOVA and WLSLR, for verification of the data. The developed method was applied to the above mentioned bio-oils and their detailed analysis is presented. The different compounds produced and their diverse concentration allows for an elucidation of the pyrolysis mechanism and highlight the effect of the catalyst. [ABSTRACT FROM AUTHOR]

Highlights: [•] Pyrolysis of biomass component mixtures in both TGA and pyrolysis reactor setups. [•] Comparison between experimental and calculated product yields and composition. [•] Heat transfer lag was evident during the pyrolysis of biomass component mixtures. [•] Elucidation of thermal and catalytic reaction pathways of each biomass component. [ABSTRACT FROM AUTHOR]

• OxiOrganosolv – an acid free agnostic organosolv pretreatment was developed. • Up to 97% of lignin was removed both from hardwood and softwood in a single stage. • 100% cellulose recovery and high hemicellulose recovery in oligo- and mono-sugars. • Close to zero sugar degradation products, pulps enzymatic conversion was 80%. • High added value lignin oxidation products vanillin, syringaldehyde were produced. The valorization of lignocellulosic biomass towards the production of value-added products requires an efficient pretreatment/fractionation step. In this work we present a novel, acid-free, mildly oxidative organosolv delignification process -OxiOrganosolv- which employs oxygen gas to depolymerize and remove lignin. The results demonstrate that the OxiOrganosolv process achieved lignin removal as high as 97% in a single stage, with a variety of solvents; it was also efficient in delignifying both beechwood (hardwood) and pine (softwood), a task in which organosolv pretreatments have failed in the past. Minimal amounts of sugar degradation products were detected, while cellulose recovery was ~100% in the solid pulp. Enzymatic hydrolysis of pulps showed >80 wt% cellulose conversion to glucose. Overall, the OxiOrganosolv pretreatment has significant advantages, including high delignification efficiency of hardwood and softwood biomass, absence of acid homogeneous catalysis and all corresponding challenges involved, and close to zero losses of sugars to degradation products. [ABSTRACT FROM AUTHOR]