Valorisation of waste fractions from autohydrolysis of selected lignocellulosic materials

Non‐isothermal processing of lignocellulosic materials in aqueous media (autohydrolysis reaction) under mild conditions leads to solutions containing valuable chemicals (oligosaccharides, sugars and acetic acid) and other, undesired, compounds (belonging to the extractive and acid‐soluble lignin fractions) which have to be removed in further purification treatments. Liquors obtained by non‐isothermal autohydrolysis of Eucalyptus globulus wood and corncobs under a variety of operational conditions were extracted with ethyl acetate in order to remove non‐saccharide components, and the suitability of the fraction dissolved in the organic phase was assayed for possible utilisation as an antioxidant. The yield and antioxidant activity of ethyl acetate extracts (measured by the α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) radical scavenging capacity) showed a strong dependence on the autohydrolysis conditions. The antioxidant activity of extracts obtained under selected operational conditions compared well with synthetic antioxidants. © 2003 Society of Chemical Industry     

Experimental evaluation of alkaline treatment as a method for enhancing the enzymatic digestibility of autohydrolysed Acacia dealbata

BACKGROUND: Acacia dealbata wood samples were subjected to hydrothermal processing in aqueous media, yielding a liquid phase (containing xylooligosaccharides) and a solid phase, enriched in cellulose, which was treated with alkaline solutions to obtain solids with improved susceptibility towards enzymatic hydrolysis. The effects of the most influential variables involved in the alkaline processing (sodium hydroxide concentration, temperature and reaction time) on solid yield, solid composition and kinetic parameters involved in the modelling of the enzymatic hydrolysis were assessed using the response surface methodology (RSM). RESULTS: Analysis of the RSM equations allowed selection of operational conditions (temperature = 130 °C, sodium hydroxide concentration = 4.5%, time of alkaline processing = 3 h), leading to selective removal of non‐cellulosic components and to a solid substrate highly susceptible to enzymatic hydrolysis. Operating at an enzyme loading of 20 FPU (filter paper units) g^?1 autohydrolysed, extracted solids (denoted AES) with a liquor to solid ratio of 30 g liquor g^?1 AES, solutions containing 29.7 g glucose L^?1 (corresponding to a yield of 47.3 g glucose per 100 g solids from autohydrolysis) were obtained after 48 h. CONCLUSION: Samples of Acacia dealbata wood were processed by autohydrolysis, sodium hydroxide treatment and enzymatic hydrolysis, yielding xylooligomers and processed solids highly susceptible to the enzymatic hydrolysis. Copyright © 2009 Society of Chemical Industry     

Fractionation of lignocellulosics. Solubilization of corn stalk hemicelluloses by autohydrolysis in aqueous medium

This paper discusses the variation profiles of the three main polymeric families (hemicelluloses, cellulose and lignin) of milled corn stalk (Zea maÿs) after aqueous thermomechanochemical treatment. The experimental system used combine explosion and shear effects facilitating the solubilization of hemicelluloses in the aqueous medium.

Two starting materials (ethanol–benzene extracted and ethanol–benzene and water extracted) was used. Hemicelluloses are totally solubilized at 220°C (10 min) although there is a loss of lignin (up to a third); cellulose is practically unaffected.

A kinetic analysis for the solubilization step was done for calculating the frequency factor and the activation energy for the main treatment using the analytical characterization data from the obtained solid residues.     

Valorization of residual woody biomass (Olea europaea trimmings) based on aqueous fractionation

BACKGROUND: Olive tree trimmings, a widely available agricultural residue lacking added value applications, were subjected to treatments with hot, compressed water under a variety of operational conditions. As a result of treatments, hemicelluloses were solubilized, and the treated solids were enriched in cellulose and lignin. Spent solids from autohydrolysis were assayed as substrates for enzymatic hydrolysis and for bioethanol production by simultaneous saccharification and fermentation. RESULTS: Liquors from the aqueous fractionation stage resulted in the formation of soluble hemicellulose‐derived saccharides (mainly of oligomeric nature) at yields up to 26.2 g per 100 g oven‐dry raw material. Enzymatic hydrolysis of spent solids from the aqueous fractionation step led to solutions containing up to 58.8 g glucose L^?1 (corresponding to cellulose to glucose conversions up to 83.2%). Simultaneous saccharification and fermentation assays using spent solids as substrates enabled the production of media containing up to 38.2 g ethanol L^?1, corresponding to 72% of the stoichiometric amount. CONCLUSION: Aqueous (or hydrothermal) processing is a technology enabling the recovery of hemicelluloses (as soluble saccharides) and the production of spent solids with high susceptibility to enzymatic hydrolysis (suitable for bioethanol production by simultaneous saccharification and fermentation). Copyright © 2011 Society of Chemical Industry     

Fermentation of enzymatic hydrolysates from olive stones by Pachysolen tannophilus

BACKGROUND: Olive stones were pretreated with liquid hot water (LHW or autohydrolysis) at maximum temperatures between 175 and 225 °C (severity factors, logR₀, between 2.73 and 4.39) to be subjected (both liquid and solid components) afterwards to enzymatic hydrolysis with cellulases from Trichoderma viride. Ethanol fermentation of hydrolysates was performed with the non‐traditional yeast Pachysolen tannophilus ATCC 32691. RESULTS: After the enzymatic step, yields of hemicellulose solubilization reached 100%, while the cellulose was only partially hydrolysed (23%, logR₀ = 4.39). The maximum yields in total reducing sugars and acetic acid, at the upper end of the severity range, was close to 0.25 and 0.04 g g^?1 dry stone, respectively. During the fermentation stage, the increase in R₀ reduced the maximum specific growth rate, biomass productivity, and overall biomass yield. The overall yields of ethanol and xylitol ranged, respectively, from 0.18 to 0.25 g g^?1 and from 0.01 to 0.13 g g^?1. CONCLUSIONS: The results demonstrate the possibility of producing ethanol from olive stones, making use of the cellulose and hemicellulose fraction of the waste. It was confirmed that the overall yield in xylitol strongly depended on severity factor, while the overall yield in ethanol remained practically constant for all the pretreatment conditions tested. Copyright © 2008 Society of Chemical Industry     

热水预水解过程杨木及水解液中组分的变化

探究了热水预水解对杨木组分、微观结构的影响及预水解液中降解产物含量变化的规律。结果表明,在保温时间60 min、保温温度155~175℃以及在保温时间0~120 min、保温温度170℃的条件下,随保温温度的升高或时间的延长,杨木热水预水解后的得率、聚戊糖和Klason木素的相对含量整体减少,纤维素的相对含量和结晶度有所增加;杨木热水预水解后的纤维形貌发生变化,出现不规则碎片和孔洞;预水解液中的酸溶木素含量增加,甲酸、乙酸、糠醛和5-羟甲基糠醛的浓度增加,糖含量随保温温度的升高不断增加,但随保温时间的延长呈先增加后减少的趋势。     

Beyond Yield Optimization: The Impact of Organosolv Process Parameters on Lignin Structure

When optimizing the process parameters of the acidic ethanolic organosolv process, the aim is usually to maximize the delignification and/or lignin purity. However, process parameters such as temperature, time, ethanol and catalyst concentration, respectively, can also be used to vary the structural properties of the obtained organosolv lignin, including the molecular weight and the ratio of aliphatic versus phenolic hydroxyl groups, among others. This review particularly focuses on these influencing factors and establishes a trend analysis between the variation of the process parameters and the effect on lignin structure. Especially when larger data sets are available, as for process temperature and time, correlations between the distribution of depolymerization and condensation reactions are found, which allow direct conclusions on the proportion of lignin's structural features, independent of the diversity of the biomass used. The newfound insights gained from this review can be used to tailor organosolv lignins isolated for a specific application.     

Two-Step Autohydrolysis Pretreatment: Towards High Selective Full Fractionation of Wheat Straw

Pretreatment is necessary to increase the enzymatic digestibility of lignocellulosic biomass. Here, degradation reactions of solubilized pentoses to furfural and others are undesired regarding the reduced product yield and increasing downstream processing efforts. In this work, the use of the unit operation configuration was successfully shown to reduce degradation reactions. In the used two-step autohydrolysis pretreatment, the reaction is stopped before degradation takes place. The pentoses are removed by water leaching to make them unavailable for degradation in a second autohydrolysis treatment. The overall sugars yield is increased, and the furfural formation is decreasing while maintaining the high lignin purity using the two-step autohydrolysis pretreatment.     

Hydrothermal processing of rice husks: effects of severity on product distribution

BACKGROUND: Treatment in aqueous media (hydrothermal or autohydrolysis reactions) is an environmentally friendly technology for fractionating lignocellulosic materials. Rice husks were subjected to hydrothermal processing under a variety of operational conditions to cause the selective breakdown of xylan chains, in order to assess the effects of reaction severity on the distribution of reaction products. RESULTS: The effects of severity (measured by the severity factor, R₀) on the concentrations of the major autohydrolysis products (monosaccharides, xylo‐ and glucooligosaccharides, xylooligosaccharide substituents, acetic acid, acid‐soluble lignin and elemental nitrogen) were assessed. The interrelationship between the severity of treatment and molecular weight distribution was established by high‐performance size‐exclusion chromatography. Selected samples were subjected to refining treatments as ethyl acetate extraction and ion exchange for refining purposes, and the concentrates were assayed by high‐performance anion‐exchange chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. CONCLUSIONS The protein equivalent of the products present in liquors accounted for 43 to 51% of the protein present in the raw rice husks. The concentrations of glucose (derived from starchy material) and arabinose (split from the xylan backbone) were fairly constant with severity. Even in treatments at low severity, high molecular weight compounds derived from xylan accounted for a limited part of the stoichiometric amount. Operating under harsh conditions, about 50% of the total xylan‐derived compounds corresponded to fractions with a degree of polymerization (DP) < 9. After refining, saccharides accounted for more than 90% of the non‐volatile components of the sample. The refined products showed a series of xylose oligomers up to about DP 13, and a series of acetylated xylose oligomers up to about DP 15. Copyright © 2008 Society of Chemical Industry     

Manufacture of fibrous reinforcements for biodegradable biocomposites from Citysus scoparius

BACKGROUND: Cytisus scoparius samples were processed with hot, compressed water (autohydrolysis treatments) to obtain both fiber‐containing solids (suitable as reinforcements for composites) and a liquid phase containing sugar oligomers derived from hemicelluloses. The solid phase from autohydrolysis, mainly made up of cellulose and lignin, was employed for manufacturing polylactic acid (PLA)‐based biodegradable composites. The mechanical properties, water uptake and thermal properties of composites were assessed. RESULTS: The hydrolysis of the major hemicellulose polysaccharide components of Cytisus scoparius was interpreted using kinetic models based on sequential pseudo‐homogeneous first‐order, irreversible reactions. Operating under non‐isothermal conditions, the autohydrolysis experiment carried out at up to 215 °C led to the maximum concentration of sugar oligomers (accounting for about 71% of the initial xylan). These compounds can be employed for a variety of purposes, including applications as prebiotics. Composites containing autohydrolyzed fibers presented both improved impact strength and reduced water absorption ability. CONCLUSIONS: Autohydrolysis of Cytisus scoparius led to a liquid phase containing xylooligosacharides with commercial value, and to a solid phase suitable as a reinforcement for PLA‐based composites with reduced water retention ability. Copyright © 2010 Society of Chemical Industry