Kinetics of peracetic acid decomposition: Part I: Spontaneous decomposition at typical pulp bleaching conditions

Peracetic acid may become one of alternative non-chlorine bleaching chemicals in the production of fully bleached chemical pulps. In this paper, the stability of peracetic acid was studied in an aqueous solution under conditions most likely encountered in the industrial processes. It was found that three potential reactions, namely i) the spontaneous decomposition, ii) the hydrolysis and iii) the transition metal catalyzed decomposition, are responsible for the consumption of peracetic acid. Furthermore, the kinetics of the spontaneous decomposition was developed. It was found that the reaction follows a second-order kinetics with the maximum rate at pH 8.2, which is the pK_a of peracetic acid. Finally, the developed kinetic equation can describe very well the experimental results obtained in this study as well as the earlier data from Koubek (1964).     

高浓度过氧乙酸的实验室制备方法

提出了一种实验室条件下简便、安全制备高浓度过氧乙酸的方法.先把低质量分数的双氧水浓缩到78％左右.然后比较了用乙酸和乙酸酐分别与过氧化氢反应制备所得的过氧乙酸的质量分数.采用乙酸酐(97％)/过氧化氢反应,当过氧化氢质量分数为78.5％时,在40℃下反应4h,室温放置2h,制得过氧乙酸质量分数为48.2％.     

烷基多苷的过氧乙酸漂色及组合漂色工艺研究

对烷基多苷(APG)的过氧乙酸(CH3COOOH)漂色工艺进行了优化,优化条件是:烷基多苷(APG)水溶液的浓度为50%,CH3COOOH用量为5%,漂色时间90 m in,漂色温度80℃,初始pH 12~12.5。在此条件下漂色,可使APG水溶液的消光系数由6~7降至0.4左右;采用质量分数分别为3%的H2O2与CH3COOOH组合漂色,可使漂色效果进一步提高;对H2O2与CH3COOOH漂色前后的APG样品进行了红外光谱对比分析。     

Effect of several factors on peracetic acid pretreatment of sugarcane bagasse for enzymatic hydrolysis

BACKGROUND: Lignocellulose should undergo pretreatment to enhance its enzymatic digestibility before being saccharified. Peracetic acid (PAA) is a strong oxidant that can remove lignin under mild conditions. The sulfuric acid in the PAA solution also can cause degradation of hemicelluloses. The objective of the present work is to investigate the effect of several factors on peracetic acid pretreatment of sugarcane bagasse. RESULTS: It was found that PAA charge, liquid/solid (l/s) ratio, temperature, time, interactions between PAA charge and l/s ratio, temperature and time, all had a very significant effect on the enzymatic conversion ratio of cellulose. The relative optimum condition was obtained as follows: PAA charge 50%, l/s ratio 6:1, temperature 80 °C and time 2 h. More than 80% of the cellulose in bagasse treated under the above conditions was converted to glucose by cellulase of 20 FPU g^?1 cellulose. Compared with H₂SO₄ and NaOH pretreatments under the same mild conditions, PAA pretreatment was the most effective for enhancement of enzymatic digestibility. CONCLUSION: PAA pretreatment could greatly enhance the enzymatic digestibility of sugarcane bagasse by removing hemicelluloses and lignin, but removal of lignin was more helpful. This study can serve as a step to further optimization of PAA pretreatment and understanding the mechanism of enhancement of enzymatic digestibility. Copyright © 2007 Society of Chemical Industry     

Kinetics of glucose decomposition in formic acid

Cellulose is abundantly available in the form of forestry and agricultural lignocellulosic residues. These residues offer the most potential source for the production of cellulosic glucose, which is a prerequisite for the sustainable production of glucose-based fuels and chemicals. Acid catalysis is one path to lignocellulosic glucose and further to its dehydration end products. Furthermore, many studied lignocellulose pretreatment methods for enzymatic hydrolysis are carried out in acidic conditions, in which the unwanted release of hemicellulose-based glucose and its further reactions to harmful end products are possible. Thus, in order to maximize glucose production from non-food cellulosic raw materials, data on the kinetics of cellulose decomposition and formation rates of end products are required. Glucose decomposition is a complex reaction system that has often been modelled with empirical, simplified models. In this study, a kinetic model was developed for glucose decomposition in formic acid solution. The experimentation was carried out in batch reactors at 180-220 °C in 5-20% (w/w) formic acid. The model developed relies on a mechanistic step through an unknown substance and gives excellent correspondence to the experimental data despite the pseudo-elementary nature of the model structure.     

椰壳酸水解制备木糖的反应动力学

本文研究了椰壳经酸水解制备木糖的反应温度、反应时间和酸浓度对水解液中木糖浓度的影响,探讨了椰壳酸水解反应的机理,建立了木聚糖降解与木糖分解的均相不可逆连串水解反应动力学模型,求出了反应活化能Ea,木糖生成与分解反应速率常数k_1、k₂,建立了k₁ 与酸浓度C和反应温度T的关系式,分析了提高k₁与k₁/k₂比值的酸水解条件,其规律可供实现工业化生产借鉴。     

醋酸水解玉米芯中木聚糖的动力学

利用醋酸作为催化剂水解玉米芯中半纤维素来制备还原糖,测定了温度在160-200℃、固液质量比为1∶15、搅拌速度为500 r/min下,不同水解时间水解液中还原糖的收率以及副产物糠醛的收率.利用半纤维素高温液态水的Garrote模型拟合还原糖生成过程.实验表明,该模型能够较好地描述还原糖生成过程以及副产物糠醛的产生过程...     

氯乙酸碱性水解法合成羟基乙酸单体的研究

以氯乙酸和氢氧化钠为主要原料,碘化钠为催化剂碱性水解法合成羟基乙酸,并采用单因素法对影响因素进行了研究,得到最优化条件:反应温度90℃,反应时间8 h,催化剂NaI用量为氯乙酸质量的0.8%。羟基乙酸的产率可达到73.1%。     

金属离子影响过氧乙酸分解速度的探讨及对策

本文考察了部分金属离子对过氧乙酸分解速度的影响.结果发现一些金属离子(Cr3 、AL3 、Ni2 、Co2 )引起过氧乙酸快速分解,一些金属离子(Hg2 、Cu26、Zn2 、Pb26、Ag )引起过氧乙酸缓慢分解,还有一些金属离子(Mg2 、K )对过氧乙酸起稳定作用.本文探讨了金属离子对过氧乙酸分解的机理.有针对性地选择一些配位剂(8-羟基喹啉、邻二氮菲、酒石酸盐、草酸钠)作为过氧乙酸稳定剂,这些配位剂与金属离子形成稳定的配合物,从而把金属离子有效地隐蔽起来,增加过氧乙酸的稳定性.     

生物质稀酸水解动力学及其反应器的研究进展

木质纤维素类生物质经过稀酸水解可制取可发酵性糖,进而形成糖平台,生产纤维素乙醇等能源和化工产品。不同类型和结构的反应器中,原料的水解行为不同,被水解的效果也就不同。本文从稀酸水解反应器和反应动力学两方面入手,综述了近年提出的木质纤维素类生物质稀酸催化动力学模型和反应器。通过比较不同反应器的水解效果,推测出多步处理、逆流过程、动态反应是木质纤维素类生物质稀酸高效水解反应的发展趋势。     

一元稳定性过氧乙酸溶液主要性能的分析测试研究

以过氧化氢与乙酸为原料,合成了稳定型过氧乙酸溶液,研究了合成的过氧乙酸溶液的稳定性、金属腐蚀性及微生物杀灭效果。结果显示,合成的过氧乙酸溶液在室温留样360 d后,产品浓度下降率为8.71%。以质量浓度为1 500 mg/L过氧乙酸溶液浸泡金属72 h,对碳钢、不锈钢基本无腐蚀,对铝片轻度腐蚀,对铜片中度腐蚀。质量浓度为200 mg/L过氧乙酸对大肠杆菌、金黄色葡萄球菌、铜绿假单胞菌、粪链球菌、产气荚膜梭菌作用1 min,杀灭对数值>5;质量浓度为1 000 mg/L过氧乙酸对枯草杆菌黑色变种芽孢作用3 min,杀灭对数值>5;过氧乙酸质量浓度为400 mg/L对白色念珠菌作用5 min,杀灭对数值>5;质量浓度为2 000 mg/L过氧乙酸对黑曲霉作用5 min,杀灭对数值>5。     

Preparation of Peracetic Acid from Acetic Acid and Hydrogen Peroxide: Experimentation and Modeling

Based on the kinetic equations and equilibrium constants, some mathematic models were developed for calculating peracetic acid (PAA) concentration, equilibrium conversion rate of hydrogen peroxide, etc. The effects of several parameters on PAA synthesis were investigated by experimentation and modeling. The equilibrium constants determined from the forward and reverse rate constants at 293, 303, 313 and 323 K were 2.91, 2.81, 2.72 and 2.63, respectively. The models could predict the values of equilibrium concentration of PAA with average relative deviation of less than 10%. Both of the experimental and model-calculated results demonstrated that temperature and catalyst loading were the most important factors affecting the rate of PAA synthesis, but high temperature led to the decrease of equilibrium concentration of PAA. According to the model, the reaction could achieve equilibrium within 24 h when operated at 303 K with 1%~1.5%(w) sulfuric acid as catalyst. Additionally, when using anhydrous acetic acid and 30% hydrogen peroxide to prepare PAA, the volumetric ratio of the two solutions should be in the range of 1.2~1.5 in order to obtain the highest equilibrium concentration of PAA. This study can serve as a step towards the further optimization of PAA synthesis and some other related investigations.     

过氧乙酸的合成及工业应用研究进展

介绍了过氧乙酸合成工艺及在环境、能源、聚合物/树脂和仿生化学领域的最新应用研究进展。分析了合成工艺的缺陷并提出了工艺改进的建议。指出过氧乙酸的重要作用除了其广谱杀菌能力外,更体现在合成化学与工业领域的各类特殊氧化反应中。建议加强过氧乙酸合成工艺尤其是乙醛液相一步氧化工艺的开发和工业领域的应用研究,以促进相关工业的发展。     

pH值对双氧水绝热分解特性的影响

为了考察pH值对双氧水热危害的影响,利用VSP2绝热量热仪对pH值分别为1.8,4,5,6,7及8的质量分数为27.5%的双氧水进行了绝热条件下测试,得到了不同pH值双氧水的绝热分解特征,求得了双氧水的分解动力学,并计算得到双氧水在起始温度为30℃时绝热条件下到达最大反应速率所需时间。结果表明:当双氧水pH值增加时,起始放热温度降低,到达最大反应速率所需时间缩短,热失控危险性明显增加,双氧水在工业条件下存储时,当pH值增加至6时就有一定危险性,当pH值增加至7以上时热失控几乎不可避免。     

Kinetics of the heterogeneous catalytic decomposition of methane

Experiments have clearly demonstrated that dissociation of CH₄ on (supported) metal catalyst (e.g. Pt, Ru, Rh, Ir, Pd) occurs to give hydrogen, a small amount of ethane and surface carbonaceous species. For this catalytic decomposition of methane and its conversion into higher hydrocarbons (especially to ethane and surface carbon) model has been developed to investigate the kinetics. Rate constants of the elementary steps have been estimated. The problem with experimental data (especially for the surface species CH_m-s) is also treated for the sake of future improvement in the kinetics studies. A comparison with catalytic hydrogenolysis of ethane kinetics is also outlined.     

Kinetics and mechanism of homogeneous catalytic hydroxylation of maleic acid by hydrogen peroxide: III. Kinetics of the hydrolysis of cis‐epoxysuccinic acid

The objective of this work was to study the hydrolysis kinetics and also the character of the involvement of the epoxidation catalyst (Na₂WO₄ – sodium tungstate) on the hydrolysis of cis‐epoxysuccinic acid (the initial product in the hydroxylation reaction of maleic acid by hydrogen peroxide). The results obtained at 65 °C clearly revealed that the hydrolysis reaction exhibits a considerably low rate in the absence of a catalyst whilst the rate is significantly enhanced by the introduction of catalytic quantities of Na₂WO₄. The phenomenon of end‐product inhibition was observed in this study and the results obtained permitted the development of a kinetic model consistent with experimental observations. Analysis of the kinetic model shows that the reaction is first order with respect to the concentrations of the catalyst and the epoxide. However, tartaric acid has a strong inhibitive influence on the overall reaction rate. © 1999 Society of Chemical Industry     

Investigation on Purification of Saturated LiNO3 Solution Using Titanium Phosphate Ion Exchanger: Kinetics Study

Lithium compounds are of high interest to many industries. The presence of undesirable impurities in Li precursors leads to uncontrolled change in the functional properties of final compounds. Therefore, the development of reliable methods for lithium salt purification is considered a key factor for their application in various industries. This work focuses on the application of a titanium phosphate ion exchanger (Li-TiOP) toward Cu²⁺, Co²⁺, Mn²⁺, Ni²⁺, and Cr³⁺ ions in the purification of a saturated LiNO₃ solution. The sorption kinetics of the selected ions, considering external and internal mass transfer, as well as chemical interaction, were deeply studied. The kinetic study showed that the values of intraparticle diffusion rate and effective diffusion coefficients for the studied ions decreased in the following order: Cr(III) ˃ Cu(II) Mn(II) ˃ Co(II) ˃ Ni(II). For all the selected ions, chemical interaction was described with a pseudo-second-order reaction model. The sorption kinetics were controlled by the size of the solvated metal ion, its effective charge, the electronic structure of the adsorbed ion, and the interaction with the functional groups of the sorbent. Due to fast kinetics, the high degree of removal of trace quantities of the impurities this material gives it consideration as a promising sorbent for the deep purification of lithium salts.     

水相中甲酸自催化制备过氧甲酸的反应动力学(英文)

Performic acid (PFA) is an oxidant used in chemical processing, synthesis and bleaching. The macro kinetic models of synthesis, hydrolysis and decomposition of PFA were investigated via formic acid-autocatalyzed reaction. It was found that the intrinsic activation energies of PFA synthesis and hydrolysis were 75.2 kJ·mol-1 and 40.4 kJ·mol-1 respectively. The observed activation energy of PFA decomposition was 95.4 kJ·mol-1. The experi-mental results indicated that the decomposition of PFA was liable to occur even at the ambient temperature. Both the spontaneous decomposition and the radical-introduced decomposition contributed to the decomposition of PFA.     

Kinetic study of cellulose hydrolysis with tungsten-based acid catalysts

Tungsten plays an important role in transforming cellulose to C2 C3 polyols. In previous reports, the research focus was mainly on the C C cleavage reactions of cellulose catalyzed by various tungsten-containing catalysts, but less on its catalytic role in cellulose hydrolysis although it is usually considered as the rate-determining step in cellulose conversion. In this article, the method of determining kinetics parameters for hydrolyzing cellulose into glucose was developed. The effects of reaction temperature, different tungsten-based acid catalysts, and H⁺ concentration on reaction rate of hydrolyzing cellulose into glucose were quantitatively addressed. The relevant reaction rate equations with using H₃O₄₀PW₁₂, H₄O₄₀SiW₁₂, and H₂WO₄ as tungsten acid catalysts were obtained in developed batch continuous stirred tank reactors and validated by experimental data. The simulating analysis indicates that the reaction mechanism of cellulose hydrolysis can change with the temperature. H₃O₄₀PW₁₂ is the best candidate catalyst for obtaining the maximum glucose concentration.