Wet Oxidation Pretreatment Research Articles

Influence of substrate particle size and wet oxidation on physical surface structures and enzymatic hydrolysis of wheat straw

In the worldwide quest for producing biofuels from lignocellulosic biomass, the importance of the substrate pretreatment is becoming increasingly apparent. This work examined the effects of reducing the substrate particle sizes of wheat straw by grinding prior to wet oxidation and enzymatic hydrolysis. The yields of glucose and xylose were assessed after treatments with a benchmark cellulase system consisting of Celluclast 1.5 L (Trichoderma reesei) and Novozym 188 beta-glucosidase (Aspergillus niger). Both wet oxidized and not wet oxidized wheat straw particles gave increased glucose release with reduced particle size. After wet oxidation, the glucose release from the smallest particles (53-149 mum) reached 90% of the theoretical maximum after 24 h of enzyme treatment. The corresponding glucose release from the wet oxidized reference samples (2-4 cm) was approximately 65% of the theoretical maximum. The xylose release only increased (by up to 39%) with particle size decrease for the straw particles that had not been wet oxidized. Wet oxidation pretreatment increased the enzymatic xylose release by 5.4 times and the glucose release by 1.8 times across all particle sizes. Comparison of scanning electron microscopy images of the straw particles revealed edged, nonspherical, porous particles with variable surface structures as a result of the grinding. Wet oxidation pretreatment tore up the surface structures of the particles to retain vascular bundles of xylem and phloem. The enzymatic hydrolysis left behind a significant amount of solid, apparently porous structures within all particles size groups of both the not wet oxidized and wet oxidized particles.

Wet oxidation pretreatment, enzymatic hydrolysis and simultaneous saccharification and fermentation of clover–ryegrass mixtures

The potential of clover ( Trifolium repens) and ryegrass ( Lolium perenne) mixtures as raw materials for ethanol production was investigated. Wet oxidation, at 175, 185 or 195 °C during 10 min at two different oxygen pressures and with either addition or no addition of sodium carbonate, was evaluated as pretreatment method for clover–ryegrass mixtures. The enzymatic hydrolysis of cellulose was significantly improved after pretreatment. The highest conversion efficiency, 93.6%, was achieved for the sample pretreated at 195 °C, 10 min, 1.2 MPa and no addition of Na 2CO 3. For that sample, the overall glucose yield after pretreatment and hydrolysis was 75.5%. No inhibition of cellulose enzymatic conversion by the filtrates was observed. The simultaneous saccharification and fermentation of the pretreated material yielded cellulose conversions of 87.5 and 86.6%, respectively, with Saccharomyces cerevisiae and the filamentous fungus Mucor indicus, and revealed that no addition of nutrients is needed for the fermentation of clover–ryegrass hydrolysates.

Study of the phenolic compounds formed during pretreatment of sugarcane bagasse by wet oxidation and steam explosion

Abstract The formation of phenolic compounds during pretreatment of sugarcane bagasse was investigated. Bagasse was pretreated by wet oxidation (WO) at 195°C during 15 min under either alkaline or acidic conditions and by steam explosion (STEX) at 205°C during 10 min. The total content of phenolic compounds in the prehydrolysates was determined spectrophotometrically. Under acidic and alkaline WO conditions, 3.8% (w/w) and 3% phenols were found, respectively. STEX gave rise to 1.9% phenols. Individual phenols were identified by GC-MS. Phenylpropanoid derivatives, such as p-coumaric and ferulic acids, accounted for more than 50% of the phenols identified in STEX prehydrolysates. In WO prehydrolysates, on the other hand, phenols lacking the propanoid side chain were predominant. Of the latter, p-hydroxybenzaldehyde was the most abundant phenol, with concentrations of 0.27% (acidic conditions) and 0.15% (alkaline conditions). As expected, high concentrations of oxidised compounds were generally observed in WO prehydrolysates, such as carboxylic acids, aldehydes and ketones. This is a true reflection of the oxidative conditions during WO pretreatment.

Wet oxidation pretreatment of lignocellulosic residues of sugarcane, rice, cassava and peanuts for ethanol production

AbstractWet oxidation (WO) pretreatment of sugarcane bagasse, rice hulls, cassava stalks and peanut shells was investigated. WO was performed at 195 °C for 10 min, with 2 g kg−1 of Na2CO3 and under either 3 or 12 bar of oxygen. Oxygen pressure and the type of raw material used had a major effect on the fractionation of the materials, formation of sugars and by‐products, and cellulose enzymatic convertibility. Cellulose content in the solid fraction increased after pretreatment of all materials, except rice hulls. The greatest increase, from 361 g kg−1 to almost 600 g kg−1, occurred for bagasse. The solubilisation of individual components was different for each material. Bagasse xylan was solubilised to a large extent, and 45.2% of it was recovered as xylose and xylo‐oligosaccharides in the liquid fraction. In the prehydrolysates of rice hulls around 40% of the original glucan was recovered as gluco‐oligosaccharides, due to hydrolysis of starch contained in grain remains. The formation of by‐products was modest for all the materials, but increased with increasing oxygen pressure. The highest yield of acetic acid (34–36 g kg−1 of raw material) and furfural (0.7–1.8 g kg−1) occurred for bagasse. The pretreatment enhanced the enzymatic convertibility of cellulose giving the best result (670.2 g kg−1) for bagasse pretreated at the highest oxygen pressure. However, for the other materials the pretreatment conditions were not effective in achieving cellulose conversions above 450 g kg−1. Some enzymatic conversion of xylan was observed. Copyright © 2007 Society of Chemical Industry

Wet oxidation as a pretreatment method for enhancing the enzymatic convertibility of sugarcane bagasse

The effect of six different conditions of wet oxidation (WO) pretreatment on fractionation and enzymatic convertibility of sugarcane bagasse was investigated. WO resulted in an increase of cellulose content of bagasse as a result of the solubilisation of hemicelluloses and lignin. The highest cellulose content, nearly 70%, was obtained in the pretreatment at 195 °C, 15 min and alkaline pH. Pretreatments at 195 °C and 15 min solubilised 93–94% of hemicelluloses and 40–50% of lignin, while pretreatment at 185 °C, 5 min and alkaline pH solubilised only 30% of hemicelluloses and 20% of lignin. The highest sugar yield in the liquid fraction, 16.1 g/100 g, was obtained at 185 °C, 5 min and acidic pH. The highest formation of carboxylic acids, phenols and furaldehydes occurred at 195 °C, 15 min and acidic pH. Alkaline pH reduced the formation of furaldehydes, which was irrelevant for most WO conditions. All pretreatment conditions improved the enzymatic convertibility of cellulose. The highest convertibility, 74.9% was achieved in the hydrolysis of the material obtained by pretreatment at 195 °C, 15 min and alkaline pH. Some xylan convertibility was also observed.

Wet oxidation pretreatment for the increase in anaerobic biodegradability of newspaper waste

Wet oxidation was investigated for its process performance on methane fermentation of newspaper waste. The mechanisms of solubilization of newspaper waste were investigated using the following criteria: destruction of total COD (TCOD), production of soluble COD (SCOD), production of volatile fatty acids, production of soluble carbohydrates, production of soluble lignin derivatives (SLD), production of furan (F) and destruction of lignin and cellulose. Wet oxidation was carried out at 170, 190, and 210 °C, with a retention time of 1 h. The highest removal efficiencies of TCOD and cellulose were achieved at 210 °C, approximately 40% and 69% were destroyed, respectively. On the other hand, highest lignin removal efficiency was achieved at 190 °C in which approximately 65% was removed. Batch methane fermentation tests were performed in 2–l glass bottles filled with the wet oxidized newspaper samples. Methane fermentation of newspaper pretreated at 190 °C gave the highest CH 4 conversion efficiency (59% of the initial TCOD was recovered as CH 4 gas). Anaerobic cellulose removals varied from 74% to 88%.

Wet oxidation: a pre-treatment procedure for sludge

Wet oxidation process is specially effective for wastes with a high organic matter which can not be removed by conventional treatment methods. The digested and raw activated sludges of PAKMAYA yeast factory are treated by wet oxidation process. The liquid-phase organic matter concentration [as total organic carbon (TOC)] was increased by 16.5% in 10 min during the wet oxidation in the presence of Cu as catalyst and H 2O 2. Lenghtening the period of the wet oxidation, the TOC-concentration was increased by 66% in 120 min. The biodegradability of the sludge after wet oxidation process was also examined. A very little development in the biodegradability was observed, when wet oxidation was applied as pre-treatment to the digested sludge (5% decrease as TOC, in the presence of Cu catalyst and H 2O 2). However, in the case of digestion of the raw sludge after the application of wet oxidation, the biodegradability increased significantly (approximately 75%, as TOC). Moreover, wet oxidation improved the ability of settling of sludge solids, as well as enhancing the treatment efficiency. Finally, the volume of settled solids was decreased by 80% in the presence of Cu and H 2O 2. NH 3 +–N, NO 2 −–N and NO 3 −–N concentrations in the supernatant decreased with the wet oxidation. pH value of the sludge increased from 6.6 to 7.8–8.0. Since stable sludge was taken from the digester where the nitrification process was progressing, a decrease in the nitrite concentration, with an increase in nitrate was observed in the digestion continuing after the wet oxidation pre-treatment. However, in the raw activated sludge, there was a nitrite formation only in the non-pretreated sludge.

Characterization of degradation products from alkaline wet oxidation of wheat straw

Alkaline wet oxidation pre-treatment (water, sodium carbonate, oxygen, high temperature and pressure) of wheat straw was performed as a 2 4−1 fractional factorial design with the process parameters: temperature, reaction time, sodium carbonate and oxygen. Alkaline wet oxidation was an efficient pre-treatment of wheat straw that resulted in solid fractions with high cellulose recovery (96%) and high enzymatic convertibility to glucose (67%). Carbonate and temperature were the most important factors for fractionation of wheat straw by wet oxidation. Optimal conditions were 10 min at 195 °C with addition of 12 bar oxygen and 6.5 g l −1 Na 2 CO 3 . At these conditions the hemicellulose fraction from 100 g straw consisted of soluble hemicellulose (16 g), low molecular weight carboxylic acids (11 g), monomeric phenols (0.48 g) and 2-furoic acid (0.01 g). Formic acid and acetic acid constituted the majority of degradation products (8.5 g). The main phenol monomers were 4-hydroxybenzaldehyde, vanillin, syringaldehyde, acetosyringone (4-hydroxy-3,5-dimethoxy-acetophenone), vanillic acid and syringic acid, occurring in 0.04–0.12 g per 100 g straw concentrations. High lignin removal from the solid fraction (62%) did not provide a corresponding increase in the phenol monomer content but was correlated to high carboxylic acid concentrations. The degradation products in the hemicellulose fractions co-varied with the pre-treatment conditions in the principal component analysis according to their chemical structure, e.g. diacids (oxalic and succinic acids), furan aldehydes, phenol aldehydes, phenol ketones and phenol acids. Aromatic aldehyde formation was correlated to severe conditions with high temperatures and low pH. Apart from CO 2 and water, carboxylic acids were the main degradation products from hemicellulose and lignin.

Early Human Occupation at Devil's Lair, Southwestern Australia 50,000 Years Ago

New dating confirms that people occupied the Australian continent before the earliest time inferred from conventional radiocarbon analysis. Many of the new ages were obtained by accelerator mass spectrometry 14C dating after an acid–base–acid pretreatment with bulk combustion (ABA-BC) or after a newly developed acid–base–wet oxidation pretreatment with stepped combustion (ABOX-SC). The samples (charcoal) came from the earliest occupation levels of the Devil's Lair site in southwestern Western Australia. Initial occupation of this site was previously dated 35,000 14C yr B.P. Whereas the ABA-BC ages are indistinguishable from background beyond 42,000 14C yr B.P., the ABOX-SC ages are in stratigraphic order to ∼55,000 14C yr B.P. The ABOX-SC chronology suggests that people were in the area by 48,000 cal yr B.P. Optically stimulated luminescence (OSL), electron spin resonance (ESR) ages, U-series dating of flowstones, and 14C dating of emu eggshell carbonate are in agreement with the ABOX-SC 14C chronology. These results, based on four independent techniques, reinforce arguments for early colonization of the Australian continent.

Radiocarbon Dating of “Old” Charcoal Using a Wet Oxidation, Stepped-Combustion Procedure

We present results that validate a new wet oxidation, stepped-combustion procedure for dating “old” charcoal samples. An acid–base–wet oxidation (ABOX) pretreatment procedure has been developed that is used in place of the conventional acid-base-acid (ABA) pretreatment. Combustions and graphitizations are performed in a vacuum line that is insulated from the atmosphere by a second backing vacuum to eliminate the risk of atmospheric leakage into the line at any stage of the procedure. Combustions are performed at 3 temperatures (330 °, 630 ° and 850 °) with a graphite target produced from the CO2 evolved during each combustion step. In this way, the removal of any contamination can be monitored, and a high degree of confidence can be placed on the final age. The pretreatment, combustion, graphitization, and measurement blank for the procedure, based on the analysis of a “radiocarbon-dead” graphite, is 0.5 ± 0.5 μg C (1σ, n=14), equivalent to 0.04 ± 0.02 pMC or an “age” of approximately 60 ka for a 1 mg graphite target. Analyses of a “radiocarbon-dead” natural charcoal after ABOX pretreatment and stepped combustion suggest that the total blank (including contamination not removed by pretreatment) may be higher than for graphite, ranging up to 0.10 ± 0.02 pMC. Additional experiments confirm good agreement with accepted values for the international low-14C “New Kauri” standard (0.16–0.25 pMC). They also confirm excellent reproducibility, with 3 separate dates on different aliquots of a charcoal sample from Ngarrabullgan Cave (Queensland, Australia) ranging from 35.2 to 35.5 ka 14C BP. It is also demonstrated that the ABOX pretreatment, in conjunction with the new vacuum line described here, is able to remove contamination not removed by the conventional ABA pretreatment, suggesting that the technique can be used to produce reliable 14C dates on charcoal up to at least 50 ka.

Optimization of wet oxidation pretreatment of wheat straw

The wet oxidation process (water, oxygen and elevated temperature) was investigated under alkaline conditions for fractionation of hemicellulose, cellulose, and lignin from wheat straw. At higher temperature and longer reaction time, a purified cellulose fraction (69% w/w) was produced with high enzymatic convertibility to glucose (66% w/w). At 185°C, nearly three times more hemicellulose was solubilized than at 150°C. Optimum conditions for hemicellulose solubilization and cellulose convertibility were for 60 g l −1 straw: 185°C, 6.5 g l −1 Na 2CO 3, and 12 bar O 2 with a 15-min reaction time. Under these conditions, 55% of the lignin and 80% of the hemicellulose were solubilized, while 95% of the cellulose remained in the solid fraction. At 185°C, the reaction kinetics was of pseudo first-order. The rate constant for hemicellulose solubilization was higher than that for lignin, whereas the rate for cellulose was very low. The cellulose recovery (95–100%) was significantly higher than that for hemicellulose (60%). At temperatures above 185°C, recoveries decreased due to increased degradation. Only half of the COD-content could be accounted for by saccharides and carboxylic acids; hence, a significant proportion of reaction products remained unidentified.