Über die Produkte der Reaktion von Methylbromid und Ethylbromid mit Kaliumhydroxid in wäßrig–methanolischen Lösungen und den Verlauf dieser SN2-Reaktion

Concerning the Products of the Reaction of Methyl Bromide and Ethyl Bromide with Potassium Hydroxide in Aqueous Methanolic Solutions and the Progress of this S_N2-Reaction Investigations of the reaction of methyl bromide and ethyl bromide with potassium hydroxide in methanolic and aqueous methanolic solutions show that the main products of these reactions are dimethyl ether and ethylmethyl ether. The reaction rates measured in methanolic or aqueous methanolic solutions are the same whether potassium hydroxide or potassium methoxide are used. These results are caused by an equilibrium between hydroxide and methoxide ions with which we could establish the equilibrium constant near 0.6. This means that a solution of sodium hydroxide c = 0.1 moll⁻¹ in methanol contains roughly 99.8% of methoxide ions. The reaction rates in methanolic as well as in aqueous methanolic solutions are strict second order. The reaction rate measured at several temperatures permitted the calculation of E_A^≠, ΔH^≠, ΔS^≠ and ΔG^≠. Furthermore the kinetic investigations show that the nucleophilicity of methoxide ions is lower compared to hydroxide ions. The calculation of the Swain–Scott-parameter n results in a nucleophilicity scale in order to methoxide, hydroxide, ethoxide ions. The kinetic investigations of the reaction of ethyl bromide with methoxide and hydroxide ions in methanolic solutions demonstrate that at high temperatures the rate constant of methoxide ions is higher than that of hydroxide ions. The opposite case can be observed at lower temperatures. At the temperature of 20 °C the rate constants of both reactions are equal. This is to do with the isokinetic effect which one is rarely able to observe at room temperatures.     

Kinetics of hydroxymethyl phenols formation by in‐line FTIR spectroscopy

The kinetics of phenol–formaldehyde prepolymers catalyzed by sodium hydroxide at various temperatures was studied. Several reactions were conducted with different phenol to formaldehyde as well as phenol to sodium hydroxide molar ratios. The React‐IR system was used to monitor the reaction as well as to determine residual free phenol and formaldehyde. The changes in the concentrations of phenol and formaldehyde with the reaction time were determined. The value of the concentration of the hydroxide ion, [OH^?], was obtained by measuring the pH value of reaction mixture. The concentration of the hydroxide ion, [OH^?], expressed as a function of reaction time, was fitted by the six‐order polynomial to the experimental data. On the basis of the proposed reaction scheme the kinetic model was developed. The kinetic parameters were obtained by adjusting the experimental evolution of phenol and formaldehyde during the synthesis. Using this method the changes in the concentrations of five species of hydroxymethyl phenols with the reaction time was also been calculated. The activation energy and preexponential factor have been calculated for individual reactions. The accuracy of the kinetic model was confirmed by comparing experimental concentration profiles of formaldehyde and phenol with the calculated ones for different molar ratios. The experimental tendencies are in agreement with the results of the model. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Separation of phenol and formaldehyde from industrial wastes. Modelling of the phenol extraction equilibrium

BACKGROUND: The manufacture of phenolic resins causes the generation of hazardous wastes composed of high concentrations of phenol and formaldehyde together with low molecular weight polymers in lower concentrations. The separation of phenol, mainly from synthetic aqueous solutions, has been successfully achieved by means of solvent extraction, 8 - 17 but few references tackle the treatment of industrial wastes because of their complex behaviour. This work aims at the experimental and theoretical analysis of the recovery of phenol from industrial aqueous wastes using CYANEX 923 as organic extractant. RESULTS: Aqueous condensates containing phenol in the concentration range 40–280 g L^?1, and formaldehyde in the range 30–110 g L^?1, were contacted with CYANEX 923 to analyse the influence of feed pH and of concentration of the selective extractant on the extraction equilibrium. Concerning the pH of the feed phase, it was observed that for values higher than 8.0 a decrease in the distribution ratio of phenol between the organic and the aqueous phases took place. Additionally, caustic conditions promoted formaldehyde degradation reactions in the feed phase. Phenol recovery from the loaded organic extractant was obtained by stripping with NaOH solutions. Best results were obtained working with a CYANEX 923 concentration 0.6 mol L^?1. CONCLUSION: Analysis of the experimental data established the optimum conditions of the selective extraction of phenol from industrial condensates. A mathematical model based on the extraction reaction of 2 moles of phenol per mole of Cyanex 923 described successfully the experimental results. The equilibrium parameter was estimated from the fitting of experimental data to the mathematical model obtaining a value of K = 750.9 (mol L^?1)^?2. Copyright © 2010 Society of Chemical Industry     

An experimental/computational study of steric hindrance effects on CO2 absorption in (non)aqueous amine solutions

The reaction kinetics and molecular mechanisms of CO₂ absorption using nonaqueous and aqueous monoethanolamine (MEA)/methyldiethanolamine (MDEA)/2-amino-2-methy-1-propanol (AMP) solutions were analyzed by the stopped-flow technique and ab initio molecular dynamics (AIMD) simulations. Pseudo first-order rate constants (k₀) of reactions between CO₂ and amines were measured. A kinetic model was proposed to correlate the k₀ to the amine concentration, and was proved to perform well for predicting the relationship between k₀ and the amine concentration. The experimental results showed that AMP/MDEA only took part in the deprotonation of MEA-zwitterion in nonaqueous MEA + AMP/MEA + MDEA solutions. In aqueous solutions, AMP can also react with CO₂ through base-catalyzed hydration mechanism beside the zwitterion mechanism. Molecular mechanisms of CO₂ absorption were also explored by AIMD simulations coupled with metadynamics sampling. The predicted free-energy barriers of key elementary reactions verified the kinetic model and demonstrated the different molecular mechanisms for the reaction between CO₂ and AMP.     

甲醛+1,3,5-三聚甲醛+硫酸+水体系汽液相平衡实验和理论研究

工业上利用甲醛水溶液在硫酸催化下的反应精馏工艺生产1,3,5-三聚甲醛,因此,1,3,5-三聚甲醛生产工艺的优化和新型催化剂的开发受到了广泛关注。这需建立反应体系的汽-液相平衡模型,研究1,3,5-三聚甲醛合成过程中催化剂可能发挥的多重作用。为此,测定了(甲醛+1,3,5-三聚甲醛+硫酸+水)体系的汽-液相平衡数据,采用扩展型UNIFAC模型对汽-液相平衡数据进行了关联,确定了模型参数,并对该体系进行了系统的计算,揭示了硫酸催化剂在该反应精馏工艺中的三重作用。上述成果对优化1,3,5-三聚甲醛生产工艺和开发1,3,5-三聚甲醛新型催化剂具有重要意义。     

甲缩醛催化精馏过程宏观动力学研究

以强酸型阳离子交换树脂为催化剂,甲醇、稀甲醛为原料在间歇反应釜中合成甲缩醛(二甲氧基甲烷)。实验中,各组分的测定采用校正面积归一化法与亚硫酸钠分析法相结合的方式。通过实验,考察了催化剂用量与不同温度对甲醛反应速率的影响,测定了反应平衡常数。文章采用拟均相模型对实验数据进行拟合,考察了313,318,323,328 K 4个温度下的正逆反应速率。实验结果表明:催化剂A的最佳用量为总溶液质量分数的3%;采用拟均相模型对实验线性拟合,线性关系显著,验证了假设的反应机理,并回归得到了在313—328 K下的指前因子k0、活化能Ea及宏观动力学方程,反应表现级数为二级。通过对实验与计算值的比较验证,此宏观动力学方程合理,可用于模拟计算。     

Long chain phenols—part 30: A rate study of the mannich reaction of phenols (with particular reference to 3-pentadecylphenol)

The rate of the Mannich reaction between 3-pentadecylphenol, di-n-propylamine and 40% aqueous formaldehyde in aqueous ethanol under basic conditions has been studied by an HPLC analytical technique following preliminary experiments with dimethylamine, diethylamine and morpholine. The effect of excess amine and excess formaldehyde, different temperatures and the influence of pH were investigated. Kinetic expressions involving the concentrations of the phenol, amine and formaldehyde have been obtained on the assumption of the participation of either (a) the aminal (methylene-bis-amine) or (b) the aminol (methylolamine) for five cases covering the various molar proportions of reactant used experimentally. Initially, to test the equations for reactions effected at constant water concentration, theoretical values of t (time) were obtained as the initial concentration (a) of the phenol was varied by increments by a/20 using trial values for the composite rate constant. In this manner the best visual fit between the experimental points and the theoretical curves was obtained. The rate constant corresponding to such a curve was subsequently refined using a least squares procedure to yield the value which minimised the sum of the residuals between the experimental and theoretical values. In all cases the sum of the residuals was smaller when the kinetic expression derived assuming participation of the aminal was employed. The latter assumption also led to a smaller dispersion in the values obtained for the composite reaction constant from the different experiments.     

Kinetics of the absorption of carbon dioxide into mixed aqueous solutions of 2-amino-2-methyl-l-propanol and piperazine

The reaction kinetics of the absorption of CO₂ into aqueous solutions of piperazine (PZ) and into mixed aqueous solutions of 2-amino-2-methyl-l-propanol (AMP) and PZ were investigated by wetted wall column at 30-40 °C. The physical properties such as density, viscosity, solubility, and diffusivity of the aqueous alkanolamine solutions were also measured. The N₂O analogy was applied to estimate the solubilities and diffusivities of CO₂ in aqueous amine systems. Based on the pseudo-first-order for the CO₂ absorption, the overall pseudo first-order reaction rate constants were determined from the kinetic measurements. For CO₂ absorption into aqueous PZ solutions, the obtained second-order reaction rate constants for the reaction of CO₂ with PZ are in a good agreement with the results of Bishnoi and Rochelle (Chem. Eng. Sci. 55 (2000) 5531). For CO₂ absorption into mixed aqueous solutions of AMP and PZ, it was found that the addition of small amounts of PZ to aqueous AMP solutions has significant effect on the enhancement of the CO₂ absorption rate. For the CO₂ absorption reaction rate model, a hybrid reaction rate model, a second-order reaction for the reaction of CO₂ with PZ and a zwitterion mechanism for the reaction of CO₂ with AMP was used to model the kinetic data. The overall absolute percentage deviation for the calculation of the apparent rate constant k_app is 7.7% for the kinetics data measured. The model is satisfactory to represent the CO₂ absorption into mixed aqueous solutions of AMP and PZ.     

Extractive reactions with cationic exchange resins as catalysts (acetalization of aldehydes with alcohols)

The acid catalysed acetalization of aldehydes such as formaldehyde, acetaldehyde, glyoxal and glyoxylic acid, with alcohols are reversible reactions. In order to enhance the conversion of aldehydes, extractive reactions were carried out with the alcohols (e.g. 2-ethyl hexanol and n-butanol) having very low to low solubility in water. In such cases alcohols, in addition to being reactants act as extractive solvents for the acetals formed in the reaction. An experimental investigation was carried out using cation-exchange resins (Indion-130, Amberlist-15 and Amberlite IR-120) as catalysts and significant conversion levels were realised for the reactions of formaldehyde and acetaldehyde; results were not encouraging for the extractive reactions of glyoxal and glyoxylic acid. The effect of different parameters, such as catalyst loading, temperature, mole ratio and aqueous phase concentration of aldehyde on the rate of reaction was studied.     

Polymerization of melamine and formaldehyde in homogeneous continuous-flow stirred-tank reactors using functional group approach: Part A: Conversion of functional groups

A comprehensive kinetic model using the functional group approach has been proposed for the polymerization of melamine and formaldehyde. The kinetic model is consistent with the basic chemistry of polymerization and involves five rate constants which have been estimated using the experimental data of Tomita. Homogeneous continuous-flow stirred-tank reactors (HCSTRs) have been modelled and the mole balance relations for various functional groups have been written. The performance of HCSTRs is governed by algebraic equations and, for any specified residence time, is found by the method of successive substitution using the Brown's algorithm. The computations show that as long as free formaldehyde is present, the reaction mass would consist predominantly of substituted melamine molecules. However, after formaldehyde is completely reacted, larger oligomers are formed in larger concentrations. On comparison of results with batch reactors, it is found that for the same reaction time HCSTRs yield polymer with higher branching.     

Kinetics of carbon dioxide absorption and desorption in aqueous alkanolamine solutions using a novel hemispherical contactor—II: Experimental results and parameter estimation

In Part 1 of this paper, detailed design of the hemispherical apparatus and a rigorous mathematical model applied to CO₂ absorption and desorption in and from aqueous alkanolamine solutions was presented with some preliminary results. This part of the paper provides detailed results on CO₂-amine kinetics under absorption and desorption conditions and present new estimates of the kinetic parameter for aqueous solutions of monoethanolamine (MEA), diethanolamine (DEA), methyl-diethanolamine (MDEA) and 2-amino-2-methyl-1-propanol (AMP). The absorption experiments were conducted at near atmospheric pressure with pure humidified CO₂ at 293-323 K using initially unloaded solutions. The desorption experiments were performed at 333-383 K for CO₂ loadings between 0.02 to 0.7 mol of CO₂ per mole of amine using humidified nitrogen gas as a stripping medium at total system pressure ranging from 110 to 205 kPa.The new rigorous mathematical model discussed in Part 1 was used in conjunction with a non-linear regression technique to estimate the kinetic parameters. In all cases, the new model predicts the experimental results well. Also, the new results clearly demonstrate that the theory of absorption with reversible chemical reaction could be used to predict desorption rates. The zwitterion mechanism adequately describes the reactions between CO₂ and carbamate forming amines such as MEA, DEA and AMP. The reactions between CO₂ and aqueous MDEA solutions are best described by a base-catalyzed hydration reaction mechanism. The kinetic data obtained show that desorption experiments could be used to determine both forward and backward rate constants accurately. The absorption experiments, on the other hand, could only be used to determine forward rate constants. It was found that at all operating conditions used in this study, the kinetic parameters for MEA, DEA and AMP obtained using absorption data could not be extrapolated to predict desorption rates. However, for MDEA, these data could be used successfully to obtain reasonably good predictions of desorption rates.     

Resorcinol formaldehyde xerogels modified with mercapto functional groups as mercury adsorbent

Resorcinol formaldehyde xerogels are modified by mercaptopropyl‐trimethoxysilane during the sol–gel process used to produce the xerogel. The chemical modification is confirmed by Fourier‐transform infrared spectroscopy. The xerogel is then used to adsorb mercury ions from aqueous solutions. The effects of the molar ratios of the precursors as well as the catalyst and the modifier are studied on the textural properties of the xerogel and the adsorption efficiency. It is shown that the chemical modification of the resorcinol formaldehyde xerogels creates the chemical sites on the structure of the xerogel to adsorb more mercury ions and increase the adsorption efficiency. At the same time, chemical modification decreases the xerogel surface area which results in a reduction of the mercury adsorption. Therefore, there exists an optimum value for the chemical modification of the xerogel to achieve the highest adsorption efficiency. Adsorption kinetics as well as equilibrium isotherm of xerogels were examined using pseudo‐first‐ and second‐order kinetic equations, and Freundlich and Langmuir isotherm models. The adsorption kinetics was found to follow the pseudo‐second‐order kinetic equations. The experimental data was also fitted into the Longmuir model more precisely comparing the Freundlich model. Finally, a series of mercury adsorption–desorption tests proved that the optimized mercapto‐modified resorcinol formaldehyde xerogel was an efficient reusable adsorbent for mercury ions. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42543.     

Kinetics of formaldehyde oxidation on a vanadia-titania catalyst

The heterogeneous catalytic oxidation of formaldehyde in the gas phase may be considered as an alternative to the multistep liquid-phase synthesis of formic acid. Monolayer vanadia-titania catalysts are active and selective in the oxidation of formaldehyde to formic acid. Detailed investigation of kinetics of formaldehyde oxidation over a monolayer vanadia-titania catalyst was carried out. It was established that byproduct form via a consecutive-parallel reaction network. CO₂ results from formaldehyde oxidation via parallel pathway and from formic acid overoxidation via consecutive pathway; CO forms from formic acid via consecutive pathway. It was shown that oxygen and water accelerate formic acid formation and that water retards CO formation. Based on experimental data, a kinetic model of formaldehyde oxidation was developed. The kinetic model was used in the mathematical simulation of the formaldehyde oxidation process and in the determination of dynamic and design parameters of the reactor. Formic acid production by the gasphase oxidation of formaldehyde is unique and does not have any analogue. As opposed to conventional technologies, it is energy-saving, environmentally friendly, and technologically simple. An enlarged-scale pilot plant using this technology is under construction.     

羟基新戊醛合成工艺及其动力学

羟基新戊醛是合成多种精细化学品的重要中间体。以叔胺溶液为催化剂,利用正交实验法优化了甲醛异丁醛缩合制备羟基新戊醛的工艺条件,并考察了缩合反应动力学。由正交实验结果得到最佳反应条件为:催化剂的用量为3%质量分数,反应温度75℃,甲醛与异丁醛的物质的量之比为1.1:1,反应压力0.3 MPa,反应时间80 min,在此条件下产物收率可达98.33%。动力学的研究结果表明:缩合主副反应的表观活化能分别为40.801 k J/mol和64.088 k J/mol;主反应对异丁醛、甲醛反应级数分别为1和1.2,副反应对羟基新戊醛的反应级数为2。通过残差分析和统计检验,表明动力学模型是适定的。     

Pyrolysis of 1,3-butanediol as a model reaction for wood liquefaction in supercritical water

1, 3-Butanediol was pyrolyzed at 425°C in a batch reactor as a model system for liquefaction of lignocellulosic materials such as wood. The observed gas and liquid products were consistent with fragmentation, dehydration, and condensation/polymerization reaction pathways. Reaction in supercritical water altered the selectivity of the reactions to give mainly propene and formaldehyde. Dehydration and the formation of two-carbon products were suppressed by water. The conversion of 1, 3-butanediol in dilute aqueous solutions increased three to four fold when the reaction density was increased by 33%. Trace oxygen was an important inhibitor, particularly in the dilute solution, but had only a minor effect on the reaction selectivity.     

KINETICS AND MECHANISM OF THE INTERFACIAL MASS TRANSFER OF Zn2+, Co2+, Ni2+ IN THE SYSTEM: BIS(2-ETHYLHEXYL)PHOSPHORIC ACID,n-DODECANE - KNO3, WATER

ABSTRACT

The mass transfer rate of Zn(II), Co(II) and Ni(II) between aqueous nitrate solutions and n-dodecane solutions of the organic soluble ligand HDEHP has been investigated using a forced convection, constant interfacial area stirred cell. The distribution ratios necessary to evaluate the kinetic experiments have been determined and the equilibrium constants which describe the heterogeneous complex formation reaction between Zn²⁺, Co²⁺, Ni²⁺ and HDEHP have been evaluated. The results have been interpreted according to two limiting models: 1) the mass transfer rate is controlled by slow reversible interfacial reactions, 2) the mass transfer is controlled by interfacial film diffusion. Both models are adequate to Interpret the experimental data. The conclusion Is reached that, if interfacial chemical reactions are rate controlling, rate constants of interfacial complex formation reactions independent of the nature of the cation are obtained. This result supports a reaction mechanism which is rate controlled by the microscopic diffusion of the cation through a viscous and structured layer of interfacial water adjacent to the liquid interface     

Irreversible Bildung von Nebenprodukten bei der Synthese von Poly(oxymethylen)dimethylethern

Poly(oxymethylene) dimethyl ethers gain increasing interest as potential diesel fuels due to their excellent combustion properties. In their synthesis from methanol and formaldehyde side products play an important role in the design and feasibility of the process. This work presents experimental data for the formation of the side products trioxane, methyl formate and formic acid under different reaction conditions. Furthermore, a kinetic model from the literature is extended by the observed side reactions.     

Kinetic analysis utilizing a recirculating flow reactor system

A system which recirculates reactants from a stirred vessel through a remote reactor is described. Highly reproducible kinetic measurements are achieved for liquid phase reactions in general and those requiring isolation in particular. Typical reactions which require isolation involve high pressure, intense radiation, explosive mixtures, etc. The conversion history within the vessel is related to reaction rate through a mathematical model which facilitates interpretation of kinetic data. The stirred vessel is modeled as a perfectly uniform reservoir coupled to the arbitrary reaction element by two transfer lines modeled as time delays. The analysis includes the effects of a parabolic velocity profile attendant to the use of low circulation rates or high viscosities. Analytical solutions are obtained for limiting cases and the model system simulated on an analog computer. The results are compared to experimental data on a radiation induced vinyl polymerization     

Kinetic studies of cobalt ion removal from aqueous solutions using fly ash-based geopolymer and zeolite NaX as sorbents

This study explored the cobalt ions removal efficiency from aqueous solutions by the sorption process on geopolymer and zeolite NaX. The influence of concentration and temperature on the sorption process was examined. FTIR and SEM analyses were conducted to elucidate the structure of sorbents. An additional goal was to test the experimental kinetic data using several kinetic models. A kinetic study has shown that the best ?t is achieved when the Blanchard model was applied, suggesting that the sorption of cobalt ions on geopolymer and zeolite NaX is a second-order reaction.