Reaction Kinetics of the Formation of Poly(oxymethylene) Dimethyl Ethers from Formaldehyde and Methanol in Aqueous Solutions

Poly­(oxymethylene) dimethyl ethers (OME) are attractive oxygenated fuel additives and physical solvents for the absorption of carbon dioxide. This works studies the synthesis of OME from formaldehyde and methanol in aqueous solutions. The reaction kinetics of OME formation is studied experimentally in a stirred batch reactor on a laboratory scale using the heterogeneous catalyst Amberlyst 46. The influences of the ratio of formaldehyde to methanol, the amount of water, and the temperature (303.15–363.15 K) are investigated. A model of the reaction kinetics is developed that differentiates two competing reaction mechanisms. The model explicitly accounts for the intermediates poly­(oxymethylene) hemiformals and poly­(oxymethylene) glycols

Method for Estimating Activity Coefficients of Target Components in Poorly Specified Mixtures

Mixtures that contain a known target component but are otherwise poorly specified are important in many fields. Previously, the activity of the target component, which is needed, e.g., to design separation processes, could not be predicted in such mixtures. A method was developed to solve this problem. It combines a thermodynamic group contribution method for the activity coefficient with NMR spectroscopy, which is used for estimating the nature and amount of the different chemical groups in the mixture. The knowledge of the component speciation of the mixture is not required. Test cases that are inspired by bioprocess engineering applications show that the new method gives surprisingly good results

Chemical Equilibrium and Reaction Kinetics of the Heterogeneously Catalyzed Formation of Poly(oxymethylene) Dimethyl Ethers from Methylal and Trioxane

Poly­(oxymethylene) dimethyl ethers (OMEs) are attractive components for tailoring diesel fuels. They belong to the group of oxygenates that reduce soot formation in the combustion when added to diesel fuels and can be produced on a large scale based on gas-to-liquid technology. This work deals with a particularly favorable route for their large scale production in which they are formed from methylal and trioxane. Reaction kinetics and chemical equilibrium of the OME formation via this route were studied in a batch reactor using the ion-exchange resin Amberlyst 46 as heterogeneous catalyst at temperatures between 323 and 363 K and for a wide range of feed compositions. An adsorption-based kinetic model is presented that represents both reaction kinetics and equilibrium well

Simultaneous determination of thermal conductivity and shear viscosity using two-gradient non-equilibrium molecular dynamics simulations

<p>A method for the simultaneous determination of the thermal conductivity <i>λ</i> and the shear viscosity <i>η</i> of fluids by non-equilibrium molecular dynamics simulations is presented and tested using the Lennard-Jones truncated and shifted fluid as example. The fluid is studied under the simultaneous influence of a temperature gradient and a velocity gradient and the resulting heat flux and momentum flux are measured to determine <i>λ</i> and <i>η</i>. The influence of the magnitude of and on <i>λ</i> and <i>η</i> is investigated. The cross-effects are negligible, even for large gradients. The same holds for the influence of on <i>λ</i>. However, there is a significant influence of on <i>η</i>, i.e. shear-thinning. The two-gradient method is applied in different ways: for small temperature-averaged values of <i>λ</i> and <i>η</i> are obtained. As has no significant influence on the results, simulations with large are evaluated using the local-equilibrium assumption, such that values are obtained at different temperatures in a single simulation. In addition to the results for <i>λ</i> and <i>η</i>, also results for the self-diffusion coefficient <i>D</i> are determined from evaluating the mean squared displacement. The new two-gradient method is robust, efficient and yields accurate results.</p

Molecular Dynamics and Experimental Study of Conformation Change of Poly(<i>N</i>-isopropylacrylamide) Hydrogels in Mixtures of Water and Methanol

The conformation transition of poly­(<i>N</i>-isopropylacrylamide) hydrogel as a function of the methanol mole fraction in water/methanol mixtures is studied both experimentally and by atomistic molecular dynamics simulation with explicit solvents. The composition range in which the conformation transition of the hydrogel occurs is determined experimentally at 268.15, 298.15, and 313.15 K. In these experiments, cononsolvency, i.e., collapse at intermediate methanol concentrations while the hydrogel is swollen in both pure solvents, is observed at 268.15 and 298.15 K. The composition range in which cononsolvency is present does not significantly depend on the amount of cross-linker. The conformation transition of the hydrogel is caused by the conformation transition of the polymer chains of its backbone. Therefore, conformation changes of single backbone polymer chains are studied by massively parallel molecular dynamics simulations. The hydrogel backbone polymer is described with the force field OPLS-AA, water with the SPC/E model, and methanol with the model of the GROMOS-96 force field. During simulation, the mean radius of gyration of the polymer chains is monitored. The conformation of the polymer chains is studied at 268, 298, and 330 K as a function of the methanol mole fraction. Cononsolvency is observed at 268 and 298 K, which is in agreement with the present experiments. The structure of the solvent around the hydrogel backbone polymer is analyzed using H-bond statistics and visualization. It is found that cononsolvency is caused by the fact that the methanol molecules strongly attach to the hydrogel’s backbone polymer, mainly with their hydroxyl group. This leads to the effect that the hydrophobic methyl groups of methanol are oriented toward the bulk solvent. The hydrogel+solvent shell hence appears hydrophobic and collapses in water-rich solvents. As more methanol is present in the solvent, the effect disappears again

Conceptual Design of a Novel Process for the Production of Poly(oxymethylene) Dimethyl Ethers from Formaldehyde and Methanol

Poly­(oxymethylene) dimethyl ethers (OME) are environmentally benign alternative fuels. This work presents the conceptual design of a novel OME process which employs aqueous solutions of formaldehyde and methanol as feedstock. In this process, OME of the desired chain lengths <i>n</i> = 3–5 and water are separated from the reactive mixture (formaldehyde + water + methanol + methylal + OME). Thermodynamic limits are identified by studying distillation boundaries and chemical equilibria. By that it is shown that OME of chain lengths <i>n</i> = 3–5 can be separated from the reactor outlet by distillation. The separation of water is carried out using either an adsorption or a membrane process. Adsorption isotherms of water on Zeolite 3A are determined experimentally. The OME process is simulated and optimized using a reduced process model accounting for the mass balances and the thermodynamic limits. Favorable operating points of the process are identified using multi-objective optimization

Notion of Public Administration in European Law

У статті розглядається поняття публічної адміністрації у європейському прав

Molecular Dynamics and Experimental Study of Conformation Change of Poly(<i>N</i>-isopropylacrylamide) Hydrogels in Mixtures of Water and Methanol

The conformation transition of poly­(<i>N</i>-isopropylacrylamide) hydrogel as a function of the methanol mole fraction in water/methanol mixtures is studied both experimentally and by atomistic molecular dynamics simulation with explicit solvents. The composition range in which the conformation transition of the hydrogel occurs is determined experimentally at 268.15, 298.15, and 313.15 K. In these experiments, cononsolvency, i.e., collapse at intermediate methanol concentrations while the hydrogel is swollen in both pure solvents, is observed at 268.15 and 298.15 K. The composition range in which cononsolvency is present does not significantly depend on the amount of cross-linker. The conformation transition of the hydrogel is caused by the conformation transition of the polymer chains of its backbone. Therefore, conformation changes of single backbone polymer chains are studied by massively parallel molecular dynamics simulations. The hydrogel backbone polymer is described with the force field OPLS-AA, water with the SPC/E model, and methanol with the model of the GROMOS-96 force field. During simulation, the mean radius of gyration of the polymer chains is monitored. The conformation of the polymer chains is studied at 268, 298, and 330 K as a function of the methanol mole fraction. Cononsolvency is observed at 268 and 298 K, which is in agreement with the present experiments. The structure of the solvent around the hydrogel backbone polymer is analyzed using H-bond statistics and visualization. It is found that cononsolvency is caused by the fact that the methanol molecules strongly attach to the hydrogel’s backbone polymer, mainly with their hydroxyl group. This leads to the effect that the hydrophobic methyl groups of methanol are oriented toward the bulk solvent. The hydrogel+solvent shell hence appears hydrophobic and collapses in water-rich solvents. As more methanol is present in the solvent, the effect disappears again

Diffusion Coefficients in Mixtures of Poly(oxymethylene) Dimethyl Ethers with Alkanes

Poly(oxymethylene) dimethyl ethers (OME, CH3O(CH2O)nCH3) are new synthetic fuels that can be produced from renewable resources. An interesting application of OME fuels is the use of them in mixtures with hydrogenated vegetable oils (HVO), which mainly consist of alkanes. Data on diffusion coefficients of OME containing mixtures are lacking in the literature but are needed for modeling OME production processes and OME combustion. Therefore, in the present work, self-diffusion coefficients of binary mixtures of OME and alkanes were measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR). OME with chain lengths n = 1...4 were studied; the alkanes were n-dodecane (C12) and n-hexadecane (C16). The measurements in the binary mixtures were carried out at high dilution of the diffusing components and extrapolated to obtain the self-diffusion coefficients at infinite dilution that are identical with the mutual diffusion coefficient. For completeness, the self-diffusion coefficients of the pure components were also measured. The experiments were carried out at temperatures between 298.15 and 353.15 K at ambient pressure. The experimental data for the diffusion coefficients at infinite dilution were compared with the results from established prediction methods (SEGWE and Wilke and Chang), revealing considerable discrepancies. Furthermore, entropy scaling (ES) was applied here for the first time for modeling diffusion coefficients at infinite dilution. By coupling the results from entropy scaling with the Vignes equation, mutual diffusion coefficients in mixtures of OME and alkanes can now be predicted as a function of temperature, pressure, and composition for a wide range of conditions

Chemical Equilibrium of the Synthesis of Poly(oxymethylene) Dimethyl Ethers from Formaldehyde and Methanol in Aqueous Solutions

Poly­(oxymethylene) dimethyl ethers (OME) reduce soot formation during the combustion process when added to diesel fuels. OME are a gas-to-liquid option as they can be produced via methanol from natural gas or renewable feedstocks. This work deals with the synthesis of OME from the educts formaldehyde and methanol in aqueous solutions. The studied mixtures are complex reacting systems in which, poly­(oxymethylene) glycols and poly­(oxymethylene) hemiformals), in addition to OME are present. The chemical equilibrium of OME formation is studied in a stirred batch reactor in which the educts’ overall ratio of formaldehyde to methanol, the amount of water, and the temperature (333.15 and 378.15 K) varies. A mole fraction-based and an activity-based model of the chemical equilibrium of the OME formation are developed, which explicitly account for the formation of poly­(oxymethylene) glycols and poly­(oxymethylene) hemiformals. Information on the latter reactions from the literature are confirmed by NMR experiments in the present work