The oxidative destruction of lignin in the ozonation of wood

The oxidative destruction of lignin in the ozonation of aspen wood was studied. The kinetic curves of ozone consumption for samples with different contents of water were obtained. The consumption of ozone increased as the content of water grew. The second derivatives of the UV absorption spectra of lignin were obtained to show that the principal direction of lignin transformations under the action of ozone was the destruction of its aromatic constituents with the formation of carboxyl- and carbonyl-containing compounds. Measurements of the UV diffuse reflectance and EPR spectra of wood showed that the ozonation of wood caused the destruction of lignin quinoid structures. Part of lignin remained unchanged under the action of ozone. A key role in the destruction of wood lignin was played by ozone dissolved in water. Varying the content of water in wood samples allows various lignin transformation products to be obtained through ozonation.     

Effect of ozonation on the reactivity of lignocellulose substrates in enzymatic hydrolyses to sugars

The efficiency of pre-treatment of aspen wood with ozone for subsequent enzymatic hydrolysis into sugars is determined by the amount of absorbed ozone. The ozone absorption rate depended on the water content in the sample being ozonized and was maximum at a relative humidity of wood of ～40%. As a result of ozone pre-treatment, the initial rate of the enzymatic hydrolysis of wood under the action of a cellulase complex increased eightfold, and the maximum yield of sugars increased tenfold depending on the ozone dose. The ozonation at ozone doses of more than 3 mol/PPU (phenylpropane structural unit of lignin) led to a decrease in the yield of sugars because of the oxidative destruction of cellulose and hemicellulose. The alkaline ozonation in 2 and 12% NaOH was inefficient because of the accompanying oxidation of carbohydrates and considerably decreased the yield of sugars.     

Ozonation of deciduous wood in the presence of hydrogen peroxide

The kinetic curves of the dependence of ozone specific absorption (Q _{r, sp} ) upon aspen wood ozonation in the presence and absence of hydrogen peroxide are obtained. It is established that the rate of ozone and Q _{r, sp} absorption increase in the O₃/H₂O₂ system. It is demonstrated by ESR, IR, and UV spectroscopy of diffuse reflection that wood ozonation in the O₃/H₂O₂ system results in the destruction of lignin aromatic and quinoid structures. The ozonation process in the presence of H₂O₂ is accompanied by destruction of the carbohydrate component of the lignocarbohydrate complex. We conclude that O₃/H₂O₂ can be used in the deep delignification of wood. It is shown that the presence of hydrogen peroxide upon ozonation increases the efficiency of the process, allowing its duration and total ozone consumption to be reduced.     

Structural changes in wood during ozonation

It is found that ozone treatment of aspen wood leads to changes in its structural characteristics, i.e., its specific surface area and the crystallinity index of cellulose. Using optical microscopy, it is shown that ozonation is accompanied by a decrease in the average size and visible surface of wood particles. The values for the specific area of the outer surface of samples are calculated. The specific surface area available to the enzyme molecules is determined from data on the adsorption of inert protein hemoglobin on wood. It is shown that this value is an order of magnitude higher than that of the outer surface and increases considerably for an ozonized sample. Based on the results from X-ray analysis, it is established that the structure of cellulose is disordered during ozone delignification, as is indicated by a reduction in the crystallinity index and crystallite sizes.     

Improvement of the wetting and absorption properties of lignocellulosic fibers by means of gas phase ozonation

Gas phase ozonation was done on sheets made from chemical thermomechanical pulp in order to improve the wetting properties of the lignocellulosic fibers. The degree of modification was varied by letting the reaction continue for different lengths of time, ranging from 1 to 60 min. Changes in the chemistry of the fibers after ozone exposure were investigated using Fourier transform infrared (FT-IR) spectroscopy and electron spectroscopy for chemical analysis (ESCA). The evolution of a carbonyl signal and the decrease of aromatic absorption over time was observed with FT-IR spectroscopy. The carbonyl peak grew in intensity as the reaction continued throughout the whole range of treatment times. The ESCA showed that carbonyl and carboxyl functionalities were introduced after 10 min of ozone exposure and that the intensity of the peak from the aliphatic and aromatic carbons decreased. However, an ozone treatment longer than 15 min did not affect the chemical surface composition, as analyzed by ESCA. The single-fiber contact angle with water, measured using a Cahn balance, decreased with extended ozonation. Measuring the time required for the sheet to absorb a water droplet with a high speed camera showed that even a very short ozone exposure (1 min) dramatically affected the absorption behavior. The rate of absorption dramatically increased after as little as 1 min of ozone exposure. This improvement in absorption rate was most likely due to the formation of low molecular weight degradation products, acting as wetting agents, created during the ozonation.     

Degradation of lignin by ozone. III. The fate of the carbohydrate matrix during the degradation of spruce protolignin by ozone

Solvent-extracted spruce wood meal was ozonized in 45% aqueous acetic acid at room temperature. The ozone-treated wood meal was then extracted with dilute alkali at 65°C for 1 h. Lignin, α-cellulose, and hemicellulose content and the viscosities of the pulped wood-meal samples were measured as a function of the time of ozonization. Results indicate that although the attack on the wood components by ozone is not selective in this medium cellulose and hemicelluloses are degraded slowly compared with lignin. Lignin degraded approximately four times faster than the carbohydrates. At the fiber liberation point the pulp retained 78% of the original hemicelluloses and about 90% of the α-cellulose compared with 25% of the lignin. The pulp samples obtained during ozonization of the wood meal showed a slow decrease in the average degree of polymerization (DP); the limit reached near 350 was attributed to the inaccessibility of the ordered regions in native cellulose to ozone.     

Delignification of deciduous wood under the action of hydrogen peroxide and ozone

Kinetic curves of the dependence of ozone specific absorption (Q _{r, sp} ) upon the ozonation of aspen wood pretreated with solutions of hydrogen peroxide of various concentrations (from 5 × 10^?4 to 2 × 10^?1 mol/L) are obtained. The water content in the samples being 56 ± 3%. The initial rate of ozone absorption and total ozone consumption (Q _inlet) are determined. Wood samples are investigated by IR and UV diffuse reflection spectroscopy. Based on the kinetics and spectral data, it is concluded that pretreating wood with a H₂O₂ solution allows the degree of delignification (DD) to be increased at a constant Q _inlet value. The DD is maximal at $ C_{H_2 O_2 } = 5 \times 10^{ - 3} $ mol/L and is 88% in contrast to a sample ozonated without H₂O₂ (DD = 85%). The role of pretreatment with hydrogen peroxide and the subsequent action of the O₃/H₂O₂ system in the process of delignification of wood is analyzed.     

SnO2的制备及催化臭氧氧化活性

采用沉淀法制备了SnO2催化剂,以SnO2催化臭氧氧化降解糖蜜酒精废水脱色为探针反应,对催化剂的活性进行了评价.采用X射线衍射、红外光谱及热分析(TG-DSC)等技术对催化剂进行表征,研究了沉淀剂及焙烧温度等制备参数对SnO2催化臭氧氧化活性的影响.结果表明,SnO2催化剂对臭氧氧化降解糖蜜酒精废水脱色具有较高的催化活性,反应60 min后,糖蜜酒精废水的脱色率从单独臭氧氧化的43.04%提高到60.24%.沉淀剂对SnO2催化剂的活性影响很大,其中以氨水为沉淀剂制备的SnO2催化剂去羟基化反应程度高,所制得的催化剂活性最大.催化剂适宜的焙烧温度为723 K.SnO2吸附吡啶的红外光谱表明,催化剂表面存在L酸中心.臭氧在SnO2表面吸附的红外光谱表明,通过臭氧的末端氧原子与表面羟基及L酸中心成键,生成的活性氧可氧化降解糖蜜酒精废水.     

Ozone pretreatment and fermentative hydrolysis of wheat straw

Principles of the ozone pretreatment of wheat straw for subsequent fermentation into sugars are investigated. The optimum moisture contents of straw in the ozonation process are obtained from data on the kinetics of ozone absorbed by samples with different contents of water. The dependence of the yield of reducing sugars in the fermentative reaction on the quantity of absorbed ozone is established. The maximum conversion of polysaccharides is obtained at ozone doses of around 3 mmol/g of biomass, and it exceeds the value for nonozonated samples by an order of magnitude. The yield of sugar falls upon increasing the dose of ozone. The process of removing lignin from the cell walls of straw during ozonation is visualized by means of scanning electron microscopy.     

Atmospheric Pressure Plasma Pretreatment of Sugarcane Bagasse: the Influence of Biomass Particle Size in the Ozonation Process

Atmospheric pressure O₂ plasma was used to produce ozone in order to treat sugarcane bagasse as a function of particle sizes. The fixed bagasse moisture content was 50 %. The delignification efficiency had small improvement due to ozonation process as a function of particle size, varying from 75 up to 80 %. Few amounts of hemicellulose were removed, but the ozonation has not been affected significantly with particle size variance as well (from 30 up to 35 %). The cellulose presented some losses below 1.0 mm size (8–15 %) which was an unexpected result. The conversion of cellulose content into free sugar has shown a significant increase as the particle size has diminished as well. The best condition of the bagasse particle size was for 0.08 mm. For this case, a great quantity of cellulose (78.8 %) was converted into glucose. Optical absorption spectroscopy was applied to determine ozone concentrations in real time where the samples with typical bagasse particle sizes equal or below to 0.5 mm had shown a better absorption of ozone in comparison with greater particle size samples.     

Atmospheric Pressure Plasma Pretreatment of Sugarcane Bagasse: The Influence of Moisture in the Ozonation Process

Sugarcane bagasse samples were pretreated with ozone via atmospheric O₂ pressure plasma. A delignification efficiency of approximately 80 % was observed within 6 h of treatment. Some hemicelluloses were removed, and the cellulose was not affected by ozonolysis. The quantity of moisture in the bagasse had a large influence on delignification and saccharification after ozonation pretreatment of the bagasse, where 50 % moisture content was found to be best for delignification (65 % of the cellulose was converted into glucose). Optical absorption spectroscopy was applied to determine ozone concentrations in real time. The ozone consumption as a function of the delignification process revealed two main reaction phases, as the ozone molecules cleave the strong carbon–carbon bonds of aromatic rings more slowly than the weak carbon–carbon bonds of aliphatic chains.     

The mechanism and pathway of the ozonation of 4-chlorophenol in aqueous solution

Chlorophenols (CPs) have been widely used in dif- ferent formulations as preservatives, herbicides, insec- ticides, bactericides and solvents. Parts of chlorophe- nols were released to the natural environment during the usage. As a result, many water sources were con- taminated with CPs[1,2]. Furthermore, they also can be formed during the disinfection of phenol containing water by chlorination. Several CPs are recognized as the priority pollutants by the United States EPA (En- vironmenta…     

Removal of selected chlorinated micropollutants by ozonation

Feasibility of ozone oxidation for the elimination of selected dissolved organic micropollutants from water and wastewaters was studied. Five organochlorine pesticides, i.e. hexachlorobutadiene, pentachlorobenzene, hexachlorobenzene, lindane, and heptachlor, were used as organic contaminants of model water. The first four of them are classified as priority hazardous substances. The oxidation treatment process was performed in a jet loop reactor. Ozone was prepared from pure oxygen. Quantification of the organochlorine pesticides in water was achieved by the gas chromatographic method after liquid-liquid extraction. Significant contribution of stripping to the removal of the investigated compounds during the ozonation treatment was also proven by the results. Effective ozonation time with regard to treatment efficiencies was 30 min, which corresponds to the ozone input of 317 mg per liter of active volume of the ozonation reactor. Single power law kinetic models were used to describe experimental data and kinetic parameters were estimated. The best fit of the experimental degradation data of all studied pollutants was obtained by the second order kinetic model. It can be concluded, based on the results obtained, that the applied ozonation process is a promising procedure for the removal of the investigated pesticides from aquatic environment.     

Aggregation stability of gold citrate hydrosol: Effect of ozone

Optical spectroscopy, dynamic light scattering, electrophoresis, and transmission electron microscopy are used to study the action of ozone on the stability of a gold hydrosol produced by the citrate method. It is shown that gold nanoparticles are not oxidized, even upon long-term ozonation. At short times of ozonation, changes that occur in the state of the sol are reversible. Nevertheless, even at this stage, organic ligands, which stabilize the hydrosol, are oxidized, while adsorbed ozone molecules can play the role of a stabilizer. At long ozonation times, when the oxidation of organic substances present in the system is actually completed, the colloidal solution loses its aggregation stability.     

Kinetics and products of ozonation of C.I. Reactive Red 195 in a semi-batch reactor

Textile wastewater shows great threats to the environment if not well pretreated before discharge. A promising technique, ozonation, was applied to remove the color in dye solutions containing C.I. Reactive Red 195 (RR195) in a semi-batch reactor. The decolorization of RR195 by the ozone process followed pseudo-first-order kinetics. Several factors which influenced the efficiency of decolorization were studied and the reaction rate constant (k) obtained with different operational parameters was compared. Our results showed that RR195 was more easily degraded in acidic than in alkaline conditions. The dyeing auxiliaries (sodium carbonate and sodium chloride) that acted as radical scavengers could enhance the decolorization process, and the ozonation time for total color removal lengthened if the initial dye concentration was higher. The analysis of the ozonation products was performed by liquid chromatography-tandem mass spectrometer and a possible degradation pathway was predicted according to the ozonation products and structure of RR195. Our results indicated that ozonation was effective in the color removal of dyes, but further treatment might be necessary since the ozonation products are high toxic.     

Characterization of atenolol transformation products in ozonation by using rapid resolution high-performance liquid chromatography/quadrupole-time-of-flight mass spectrometry

This experiment investigated the transformation pathway of atenolol, a widely used β-blocker, in the ozonation process through the identification of generated intermediate compounds. In order to characterize the contribution of ozone and hydroxyl radical (•OH) in the transformation of atenolol, ozonation were performed at pH 2, 7 and 9. 15 major transformation products have been identified based on the chromatographic behavior of these compounds and the information obtained from accurate mass MS and MS/MS spectra. By comparing to the elution pattern of the identified transformation products and its fragmentation pattern in the MS/MS spectrum, a variety of isomers of the transformation products were characterized.Identified transformation products of atenolol are including its mono-, di and tri-hydroxylated derivatives as well as the aliphatic and aromatic ring breakdown products. Transformation of atenolol in the ozonation involved hydroxylation reaction, aromatic ring opening reaction, oxidation and cleavage of 2-hydroxy-3-(isopropylamino)propoxy group of atenolol. In ozonation, aromatic ring of atenolol was transformed through the reaction with both ozone and •OH whereas the aliphatic chain of atenolol was degraded mainly through the reaction with •OH. The results also indicated that both •OH and ozone involved in the aromatic ring opening reaction.     

Ozone-based electrochemical advanced oxidation processes

Novel processes have recently been developed that provide for the enhancement of ozonation through combination with electrochemical treatments. These are processes that can be included among those defined as advanced oxidation processes as they proceed via electrogeneration of highly oxidizing radical species.These processes are generally carried out by sparging ozone in both divided and undivided electrochemical cells in order to promote its decomposition through different mechanisms, depending on the electrode materials adopted, and in some cases still debated.This mini review presents the most recent advances in the field of electrochemically assisted ozonation.In particular, the first section is focused on the process known as electroperoxone (EP) where the ozone decomposition is enhanced by the adoption of carbon-based cathodes, due to the electrogeneration of hydrogen peroxide, while the second section is focused on the process that implies ozonation in a cell adopting metal-based cathodes.     

Degradation of 4-Chlorophenol by High-Voltage Pulse Corona Discharges Combined with Ozone

Degradation of aqueous 250 mg/L 4-chlorophenol (4-CP) by high-voltage pulse corona discharges combined with ozone was investigated to gain insight into factors affecting enhancement of the combined system. High-voltage pulse corona discharges, ozonation, and a combination of the two were used to facilitate the degradation of aqueous 4-CP. Experimental results indicate that the treatment of 4-CP using a combination of high-voltage pulse corona discharges and ozonation within 30 min resulted in the almost degradation (96%) and a 51% reduction of the chemical oxygen demand (COD). This apparent synergistic effect may be attributed to the enhancement of ozone decomposition. The degradation of aqueous 4-CP by high-voltage pulse corona discharges combined with ozone was found to be affected by ozone concentration, substrate concentration, and interelectrode separations. The increase of ozone concentration leads to an increase of 4-CP conversion and COD removal. The conversion of 4-CP decreased with increase in 4-CP concentration and interelectrode separations.     

铜和铝离子/UV催化臭氧降解偶氮二异丁腈废水研究

利用多相催化臭氧(O3)工艺处理偶氮二异丁腈(AIBN)废水,探讨不同催化O3体系(Cu2+、Al3+、Cu2++Al3+/UV催化O3)对AIBN废水中氰类污染物的降解特性,并对不同催化O3体系的动力学特性进行研究。结果表明,金属离子对催化O3工艺的处理效率具有明显影响,不同催化O3工艺对CN-去除作用都呈现起始去除速率较高而后减弱的特点,其中Cu2+和Al3+共同催化O3工艺的整体去除率较高,优于单独Cu2+和Al3+的催化性能。这可能是由于p H变化、金属离子与CN-配合作用、金属离子和O3作用的综合影响结果。动力学研究结果表明,不同催化O3体系降解AIBN废水中的CN-污染物的氧化反应符合准一级动力学反应,表观反应速率常数k在0.0245~0.00301 min-1之间。     

SnO2的表面酸性及其催化臭氧氧化活性的研究

以SnO2催化臭氧化降解高浓度糖蜜酒精废水为探针反应,研究SnO2催化臭氧氧化降解糖蜜酒精废水的活性,并采用吸附吡啶的红外光谱研究SnO2及金属氧化物改性的SnO2催化剂表面的酸性.催化剂吸附吡啶的红外光谱表明:吡啶分子在SnO2表面吸附时,形成六元环振动峰1 449 cm-1,说明SnO2表面存在Lewis酸中心.掺入第二组分对SnO2进行酸性调变后,酸类型和酸中心发生了变化.CuO-SnO2催化剂表面仅存在L酸,NiO-SnO2,Fe2O3-SnO2及CoO-SnO2等的表面不仅存在L酸,还存在不同强度的B酸,且Fe2O3-SnO2与CoO-SnO2存在与SnO2不同的第二类L酸.水的存在使得NiO-SnO2,Fe2O3-SnO2及CoO-SnO2催化剂表面的L酸减弱,B酸强度增强;而CuO-SnO2表面出现了弱的B酸.将催化剂的酸类型与催化臭氧氧化活性进行关联,发现B酸的存在是造成催化剂活性降低的一个原因.