Investigation of lignin deposition on cellulose during hydrothermal pretreatment, its effect on cellulose hydrolysis, and underlying mechanisms.

In dilute acid pretreatment of lignocellulosic biomass, lignin has been shown to form droplets that deposit on the cellulose surface and retard enzymatic digestion of cellulose (Donohoe et al., 2008; Selig et al., 2007). However, studies of this nature are limited for hydrothermal pretreatment, with the result that the corresponding mechanisms that inhibit cellulosic enzymes are not well understood. In this study, scanning electron microscope (SEM) and wet chemical analysis of solids formed by hydrothermal pretreatment of a mixture of Avicel cellulose and poplar wood showed that lignin droplets from poplar wood relocated onto the Avicel surface. In addition, nuclear magnetic resonance (NMR) showed higher S/G ratios in deposited lignin than the initial lignin in poplar wood. Furthermore, the lignin droplets deposited on Avicel significantly impeded cellulose hydrolysis. A series of tests confirmed that blockage of the cellulose surface by lignin droplets was the main cause of cellulase inhibition. The results give new insights into the fate of lignin in hydrothermal pretreatment and its effects on enzymatic hydrolysis.

Pulsed corona discharge oxidation of aqueous lignin: decomposition and aldehydes formation.

Lignin is the mass waste product of pulp and paper industry mostly incinerated for energy recovery. Lignin is, however, a substantial source of raw material for derivatives currently produced in costly wet oxidation processes. The pulsed corona discharge (PCD) for the first time was applied to lignin oxidation aiming a cost-effective environmentally friendly lignin removal and transformation to aldehydes. The experimental research into treatment of coniferous kraft lignin aqueous solutions was undertaken to establish the dependence of lignin oxidation and aldehyde formation on the discharge parameters, initial concentration of lignin and gas phase composition. The rate and the energy efficiency of lignin oxidation increased with increasing oxygen concentration reaching up to 82 g kW-1 h-1 in 89% vol. oxygen. Oxidation energy efficiency in PCD treatment exceeds the one for conventional ozonation by the factor of two under the experimental conditions. Oxidation at low oxygen concentrations showed a tendency of the increasing aldehydes and glyoxylic acid formation yield.

Fluorescence lifetime imaging of lignin autofluorescence in normal and compression wood.

Wood cell walls fluoresce as a result of UV and visible light excitation due to the presence of lignin. Fluorescence spectroscopy has revealed characteristic spectral differences in various wood types, notably normal and compression wood. In order to extend this method of characterising cell walls we examined the fluorescence lifetime of wood cell walls using TCSPC (Time-Correlated Single Photon Counting) as a method of potentially detecting differences in lignin composition and measuring the molecular environment within cell walls. The fluorescence decay curves of both normal and compression wood from pine contain three exponential decay components with a mean lifetime of τm = 473 ps in normal wood and 418 ps in compression wood. Lifetimes are spatially resolved to different cell wall layers or cell types where individual lifetimes are shown to have a log-normal distribution. The differences in fluorescence lifetime observed in pine compression wood compared to normal wood, are associated with known differences in cell wall composition such as increased p-hydroxyphenyl content in lignin as well as novel deposition of ß(1,4)-Galactan. Our results indicate increased deposition of lignin fluorophores with shorter lifetimes in the outer secondary wall of compression wood. We have demonstrated the usefulness of fluorescence lifetime imaging for characterising wood cell walls, offering some advantages over conventional fluorescence imaging/spectroscopy. For example, we have measured significant changes in fluorescence lifetime resulting from changes to lignin composition as a result of compression wood formation that complement similar changes in fluorescence intensity.

[Study on chemical compositions and crystallinity changes of bamboo treated with gamma rays].

The structures and qualities of main chemical compositions in cell wall of bamboo treated with gamma rays were tested by nuclear magnetic resonance spectrometer (NMR) and X-ray Diffraction (XRD). The result indicated that the bamboo crystallinity increased at the beginning of irradiation process, while the crystallinity reduced when the irradiation dose was raised to about 100 kGy. During the whole irradiation process, hemicellulose degraded, and with the irradiation doses increased the non-phenolic lignin changed to the phenolic.

Colloidal Lignin Particles and Epoxies for Bio-Based, Durable, and Multiresistant Nanostructured Coatings.

There is a need for safe and sustainable alternatives in the coating industry. Bio-based coatings are interesting in this perspective. Although various oils and waxes have been used as traditional wood coatings, they often lack sufficient durability. Lignin is an abundant natural polyphenol that can be used to cure epoxies, but its poor water solubility has impeded the use of unmodified lignin in coatings in the past. To address this issue, water-dispersible colloidal lignin particles (CLPs) and an epoxy compound, glycerol diglycidyl ether (GDE), were used to prepare multiprotective bio-based surface coatings. With the GDE/CLP ratios of 0.65 and 0.52 g/g, the cured CLP-GDE films became highly resistant to abrasion and heat. When applied as a coating on wooden substrates, the particulate morphology enabled effective protection against water, stains, and sunlight with very thin layers (less than half the weight of commercial coatings) while retaining the wood's breathability excellently. Optimal hydrophobicity was reached with a coat weight of 6.9 g(CLP)/m2, resulting in water contact angle values of up to 120°. Due to their spherical shape and chemical structure, the CLPs acted as both a hardener and a particulate component in the coating, which removed the need for an underlying binding polymer matrix. Light interferometry measurements showed that while commercial polymeric film-forming coatings smoothened the substrate noticeably, the particulate morphology retained the substrate's roughness in lightweight coatings, allowing for a high water contact angle. This work presents new strategies for lignin applications in durable particulate coatings and their advantages compared to both currently used synthetic and bio-based coatings.

Strong biodegradable cellulose materials with improved crystallinity via hydrogen bonding tailoring strategy for UV blocking and antioxidant activity.

It has been a huge challenge to obtain simultaneously excellent mechanical strength and desirable multifunctionality from the cellulose nanocrystals (CNC) based food packing materials. In this work, we demonstrated a hydrogen bonding tailoring strategy that can produce CNC/lignin films with UV blocking and antioxidant activity, while bypassing the loss of mechanical strength. Using a hyperbranched polyester, lignin was first functionalized to increase the amount of hydroxyl groups, thereby increasing the intermolecular interactions. By assembling the polyester modified lignin (H-lignin) into CNC matrix, the hydrogen bonding crosslinks between the H-lignin and CNC chains were successfully promoted, resulting in the CNC composites with the significantly improved mechanical strength, UV blocking and antioxidant activity. The phenolic structure and the hydrogen donation of H-lignin also endowed the resulting CNC composites with excellent UV blocking and antioxidant activity. The experimental results indicated that the H-lignin could bring about 34% and 63% increase in tensile strength and Young's modulus, respectively, higher than the reported ones. The CNC-based composites showed better thermal stability and improved crystallinity property. The H-lignin provides a new insight into the multifunctional exploration of CNC-based composite. This work opens a new avenue for the next generation's biodegradable food packing materials from cellulose-sourced composites.

Studies on TiO(2)/ZnO photocatalysed degradation of lignin.

The photocatalytic degradation of lignin obtained from wheat straw kraft digestion has been investigated by using TiO(2) and ZnO semiconductors. ZnO has been found to be a better photocatalyst than TiO(2). The different variables studied, include catalyst dose, solution pH, oxidant concentration and initial concentration of the substrate. The degradation of lignin was favorable at pH 11. Optimum values of catalyst dose and oxidant concentration were found to be 1g/l and 12.2 x 10(-6) M, respectively. The degradation of the organic compound was also evaluated as COD removal and increase in the COD removal was observed with increase in degradation rate. An attempt has also been made to explore the applicability of ZnO in immobilized mode for the degradation of lignin under solar light for industrial scale application. Further the comparative evaluation of ZnO in slurry/immobilized mode has been carried out.

Photodegradation of acidolysis lignin from BCMP.

A mild acidic dioxane extraction method was employed to isolate lignin from hardwood bleached chemimechanical pulp (BCMP). The isolated lignin was then purified and undergone elemental analysis. To study the photodegradation behavior, the lignin samples were impregnated onto the Whatman filter papers and irradiated with UV light for various periods. The photolyzed lignin was then recovered and analyzed by (1)H-NMR spectroscopy. Phenylpropane-based formula (C(9)) of CMP pulp lignin and the photolyzed samples were then established with elemental analysis and (1)H-NMR spectroscopy data. The results indicated that the benzaldehyde and benzoic acid type compounds were the main photodegradation products of BCMP lignin. The lignin photodegradation probably involved the degradation of phenylcoumaran units. Irradiation also increased the phenolic hydroxyl group content and decreased that of methoxyl groups, due to demethoxylation. The degrees of aromatic ring condensation were increased upon continuing the irradiation time, which imples the formation of condensed structures in photolyzed lignin.

Decolourization and removal of some organic compounds from olive mill wastewater by advanced oxidation processes and lime treatment.

BACKGROUND: Olive mill wastewater (OMW) generated by the olive oil extracting industry is a major pollutant, because of its high organic load and phytotoxic and antibacterial phenolic compounds which resist biological degradation. Mediterranean countries are mostly affected by this serious environmental problem since they are responsible for 95% of the worldwide olive-oil production. There are many methods used for OMW treatment, such as adsorption, electro coagulation, electro-oxidation, biological degradation, advanced oxidation processes (AOPs), chemical coagulation, flocculation, filtration, lagoons of evaporation and burning systems, etc. Currently, there is no such economical and easy solution. The aim of this study was to evaluate the feasibility of decolourization and removal of phenol, lignin, TOC and TIC in OMW by UV/H2O2 (AOPs). The operating parameters, such as hydrogen peroxide dosage, times, pH, effect of UV and natural sunlight were determined to find the suitable operating conditions for the best removal. Moreover, there is no study reported in the literature related to the use of METHODS: OMW was obtained from an olive-oil producing plant (Mugla area of Turkey) which uses a modern production process. No chemical additives are used during olive oil production. This study was realised by using two different UV sources, while taking the time and energy consumption into consideration. These two sources were mercury lamps and natural sunlight. Before starting AOPs experiments, one litre of OMW was treated by adding lime until a pH of 7.00. Then, 100 ml was taken from each sample, and 1 to 10 ml of a 30% H2O2 (Riedel-deHaen) solution was added. These solutions in closed vessels were laid in the natural sunlight for a week and their compositions and colour changes were analysed daily by UV-Vis spectrophotometer. At the end of the one-week period, they were treated with lime. In this study, the effect of changes in the initial pH, times and H2O2 concentrations on removal was investigated. At the end of all experiments, changes in colour, phenol, lignin, TOC and TIC concentrations were analysed according to standard methods. RESULTS AND DISCUSSION: In the samples exposed to natural sunlight and having an H2/OMW ratio of 3 ml/100 ml, a significant colour removal was achieved approximately 90% of the time at the end of 7 days. When the same samples were treated with lime (pH: up to 7), 99% efficiency was achieved. When phenol and lignin removals were examined in the same concentration, phenol and lignin removal were found 99.5%, 35%, respectively. However, for maximum lignin removal, more use of H2O2 (10 ml H2O2/100 ml OMW) was found to be necessary. Under these conditions, it was found that lignin can be removed by 70%, but to 90% with lime, at the end of a seven-day period. Rate constants obtained in the experiments performed with direct UV were found to be much higher than those of the samples exposed to natural sunlight (k(a)lignin=0.3883>> k(b)lignin=0.0078; k(a)phenol=0.5187>> k(b)phenol = 0.0146). Moreover, it should be remembered in this process that energy consumption may induce extra financial burden for organisations. CONCLUSIONS: It was found, in general, that colour, lignin, total organic carbon and phenol were removed more efficiently from OMW by using H2O2 UV and lime OMW. Moreover, in the study, lime was found to contribute, both initially and after radical reactions, to the efficiency to a great extent. RECOMMENDATIONS AND PERSPECTIVES: Another result obtained from the study is that pre-purification carried out with hydrogen peroxide and lime may constitute an important step for further purification processes such as adsorption, membrane processes, etc.

Irradiation pretreatment facilitates the achievement of high total sugars concentration from lignocellulose biomass.

This study evaluated the two hydrolysis strategies, involving one thermal and one dilute acid/enzymatic hydrolysis, to produce high xylose and glucose concentrations from lignocellulose assisted with irradiation pretreatment. Prior to hydrolysis, lignocellulose was pretreated by γ-irradiation at 800KGy. The merits of irradiation pretreatment on lignocellulose were contributed to size-reduced particle distributions and low shear rate of material, which allowed high biomass loadings up to 30-40%(w/v, equals to 23-29wt.%) for the consequent hydrolysis process. Results showed that hemicellulose fraction could achieve ∼84g/L of total sugars containing ∼55g/L xylose and ∼21g/L glucose through this two steps hydrolysis. Cellulose fraction would release ∼251g/L of total sugars consisting of ∼235g/L glucose and ∼16g/L xylose in the ultimate enzymatic hydrolysate. To the best of our knowledge, it was the first report of achieving 235g/L glucose in cellulose enzymatic hydrolysate derived from lignocellulose.

Microwave irradiation--A green and efficient way to pretreat biomass.

As a non-traditional heating way, microwave irradiation (MWI) has long been used for lignocellulose pretreatment with the advent of commercial microwave oven since the 1970s. MWI pretreatment using MWI as heating source is similar to other pretreatment methods. Although MWI pretreatment solves some problems caused by other pretreatment methods, such as low heating rate and thermal efficiency, uneven heating, it brings some new challenges such as reaction vessel selection and pretreatment process design. Over 30 years of development, researchers have achieved good pretreatment performance with MWI which has been applied gradually from laboratory scale to pilot-scale. It should be noted that MWI pretreatment is facing some problems: high cost of pretreatment, short of large-scale equipment, the non-thermal effects in pretreatment is still controversial. If MWI pretreatment reaction mechanism could be further clarified and large-scale industrialized reactor be designed, MWI pretreatment might be widely used in biorefinery.

Depolymerization of lignin by microwave-assisted methylation of benzylic alcohols.

A new two-step lignin depolymerization strategy was developed, in which the benzylic alcohols in lignin was methylated under microwave irradiation, followed by a hydrogenolysis for the cleavage of ßO4 bond with Pd/C as the catalyst. The results showed that an efficient and selective catalytic methylation of benzylic alcohols was achieved with various lignin model compounds, and the acidic environment promoted the methylation of benzylic alcohol. Methylation of benzylic alcohol increased the ßO4 bond cleavage rate by 55.9%, and improved products selectivity. Preliminary study of lignin depolymerization illustrated that methylation pretreatment of benzylic alcohols facilitated lignin depolymerization to produce aromatic monomers and reduced the oxygen content of aromatic monomers.

A Comparative study of microwave-induced pyrolysis of lignocellulosic and algal biomass.

Microwave (MW) pyrolysis of algal and lignocellulosic biomass samples were studied using a modified domestic oven. The pyrolysis temperature was recorded continuously by inserting a thermocouple into the samples. Temperatures as high as 1170 and 1015°C were achieved for peanut shell and Chlorella vulgaris. The activation energy for MW pyrolysis was calculated by Coats-Redfern method and the values were 221.96 and 214.27kJ/mol for peanut shell and C. vulgaris, respectively. Bio-oil yields reached to 27.7wt.% and 11.0wt.% during pyrolysis of C. vulgaris and peanut shell, respectively. The bio-oil samples from pyrolysis were analyzed by a gas chromatography-mass spectrometry (GC-MS). Bio-oil from lignocellulosic biomass pyrolysis contained more phenolic compounds while that from microalgae pyrolysis contained more nitrogen-containing species. Fourier transform infrared spectroscopy (FTIR) analysis results showed that concentration of OH, CH, CO, OCH3, and CO functional groups in char samples decreased significantly after pyrolysis.

Photocatalytic degradation of lignin on synthesized Ag-AgCl/ZnO nanorods under solar light and preliminary trials for methane fermentation.

New photocatalysts, Ag-AgCl/ZnO nanorods, were successfully synthesized in this study by using microwave assisted chemical precipitation and deposition-precipitation-photoreduction methods. The optimal preparation condition was determined as pH 9 in distilled water and 40min for UV light photoreduction of Ag (i.e. Ag40-AgCl/ZnO) by degradation of methyl orange. This work investigated the feasibility of using Ag40-AgCl/ZnO to degrade lignin under natural solar light and then subsequent methane production with influencing factors like solution pH, dosage of catalyst and initial lignin concentration being considered. OH radicals were found to play the most important role in the photocatalytic process, and the new prepared catalyst possessed stable photocatalytic activity after 7 cycles' utilization. During the subsequent biogasification, the degraded lignin obtained from 120min photocatalysis yielded 184ml methane and 325ml biogas for per gram of removed total organic carbon, increased by 10.9% and 23.1%, respectively compared to the control.

Topographical characterization and surface force spectroscopy of the photochemical lignin model compound.

By combining the results from atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM), herein we investigate properties of photochemical lignin model compounds. We provide evidence that photochemical lignin forms random, probably non-functional structures. The topography of such structures is explored using ESEM. Non-functionality of such structures is proved by AFM and atomic force spectroscopy experiments wherein the photochemical lignin functionalized tip is approached to the substrate covered with photochemical lignin. There was no evidence of existence of any kind of host-guest interaction during the approach/retraction experiments. These results provide evidence for our previously stated hypothesis that photochemical lignin polymerization may be one of the degrading effects of UV radiation to the plant cell.

Photo- and radiation chemical induced degradation of lignin model compounds.

The basic mechanistic aspects of the photo- and radiation chemistry of lignin model compounds (LMCs) are discussed with respect to important processes related to lignin degradation. Several reactions occur after direct irradiation, photosensitized or radiation chemically induced oxidation of LMCs. Direct irradiation studies on LMCs have provided supportive evidence for the involvement of hydrogen abstraction reactions from phenols, beta-cleavage of substituted alpha-aryloxyacetophenones and cleavage of ketyl radicals (formed by photoreduction of aromatic ketones or hydrogen abstraction from arylglycerol beta-aryl ethers) in the photoyellowing of lignin rich pulps. Photosensitized and radiation chemically induced generation of reactive oxygen species and their reaction with LMCs are reviewed. The side-chain reactivity of LMC radical cations, generated by radiation chemical means, is also discussed in relation with the enzymatic degradation of lignin.

Yellowing and IR-changes of spruce wood as result of UV-irradiation.

The yellowing and IR-changes of spruce wood as a result of UV-irradiation were studied using two different types of xenon lamps (lambda>300 nm; I(o)=50 mW cm(-2) and lambda>280 nm; I(o)=17.5 mW cm(-2)). Changes in the IR spectra as well as the yellowing of the irradiated wood surfaces show the influence of UV light on the wood modules. The UV-irradiation (72 h; lambda>300 nm; I(o)=50 mW cm(-2)) decreased the lignin content on the surface by up to 20% of the original values. The colour difference of yellowing (deltaE) exhibited a systematic trend to higher values with increasing irradiation time. Our results show that the photoyellowing (UV-Vis detection) correlates very well with lignin degradation (IR detection). This result is in agreement with the quinone formation as the chromophoric reaction product of lignin decay. The degradation, yellowing, and oxidation kinetics differed only little using different light sources. The absorbed light intensity, which depends on wavelength, the intensity distribution of the light source and the absorption spectrum of lignin, influenced the degradation rate. Under the current experimental conditions, the absorption spectrum of lignin was the most important factor. Therefore, irradiation with lambda>280 nm is useful for rapidly monitoring the UV-degradation of wood

Degradation of calcium lignosulfonate using gamma-ray irradiation.

Gamma-ray irradiation was proven to be a promising means for the removal of calcium lignosulfonate (CaLS). At a dose rate of 55Gy min(-1), over 90% of CaLS was mineralized to CO(2), H(2)O and sulfates within 3-d irradiation. The degradation of CaLS with the initial CaLS concentrations ranging from 40 to 200mg l(-1) followed zero-order kinetics at the dose rates of 16-150Gy min(-1). The zero-order degradation rate constant was functionally related with irradiation dose rate. Experiments performed with or without addition of radical scavengers demonstrated that the role of *OH was predominant in CaLS degradation and the reductive species made minor contributions to CaLS degradation. Addition of appropriate amounts of H(2)O(2) significantly enhanced the mineralization of CaLS, e.g., addition of 10mM H(2)O(2) at a dose rate of 55Gy min(-1) elevated the mineralization rate constant by five times. The addition of Fenton's reagent to irradiated CaLS solutions facilitated the degradation of CaLS, but no obviously synergistic effect was observed.

Remediation of phenol, lignin and paper effluents by advanced oxidative processes.

The tremendous environmental impact of pulping and bleaching effluents and the relatively low efficiency of the current biological remediation processes represent one of the most important problems of the paper industry. In this work the efficiency of heterogeneous and homogeneous advanced oxidative processes was evaluated toward the degradation of model substrates (phenol and lignin) and the remediation of paper effluents. Best results were found by application of the UV-H2O2 system, with almost total discoloration of both pulping and bleaching effluents and typical COD removal higher than 60%, at reaction times of 120 min. In view of the reported results, and mainly on account of the simplicity of the UV-H2O2 system, shows good potential for the advanced process to remediation of recalcitrant effluents like those studied in this present work.

Effect of essential inorganic metals on primary thermal degradation of lignocellulosic biomass.

This study employed thermogravimetric analysis (TGA) and analytical Py-GC/MS in order to examine the catalytic effect of main inorganic metals (K, Mg and Ca) on the thermal degradation and the formation of pyrolytic products in lignocellulosic biomass. In addition, potential mechanisms of the primary pyrolysis in presence of the inorganic metals were derived. TG analysis showed that when potassium content increased in the biomass, char formation increased from 10.5 wt.% to 19.6 wt.% at 550 °C, and temperatures at which the maximum degradation rate was achieved shifted from 367 °C to 333 °C. With increasing magnesium content, the maximum degradation rate increased from 1.21 wt.%/°C to 1.43 wt.%/°C. Analytical Py-GC/MS revealed that potassium had a distinguished catalytic effect promoting the formation of low molecular weight compounds and suppressing the formation of levoglucosan. An increase in the yield of C6 and C2C6 lignin derivatives with increasing potassium content was also observed.