Diffusion Coefficients Of Alcohols Research Articles

Diffusion in Binary Aqueous Solutions of Alcohols by Molecular Simulation

Based on the molecular dynamics method, the calculations for diffusion coefficients were carried out in binary aqueous solutions of three alcohols: ethanol, isopropanol, and tert-butanol. The intermolecular potential TIP4P/2005 was used for water; and five force fields were analyzed for the alcohols. The force fields providing the best accuracy of calculation were identified based on a comparison of the calculated self-diffusion coefficients of pure alcohols with the experimental data for internal (Einstein) diffusion coefficients of alcohols in solutions. The temperature and concentration dependences of the interdiffusion coefficients were determined using Darken’s Equation. Transport (Fickian) diffusion coefficients were calculated using a thermodynamic factor determined by the non-random two-liquid (NRTL) and Willson models. It was demonstrated that for adequate reproduction of the experimental data when calculating the transport diffusion coefficients, the thermodynamic factor has to be 0.64. Simple approximations were obtained, providing satisfactory accuracy in calculating the concentration and temperature dependences of the transport diffusion coefficients in the studied mixtures.

Modelling of evaporative losses in n-alcohol/diesel fuel blends

Alcohol/diesel fuel blends allow reducing the formation of soot in diesel engines. However, its use in a large scale framework still faces the challenge of high evaporative losses under storage conditions which is hindered by the high volatility of the alcohols. Since the design of the most adequate fuelling system for each blend requires detailed knowledge about the evaporation losses from the liquid phase, in this work a method for calculating the evaporation of pure n-alcohols (from C1 to C5 carbon atoms) and blends of these alcohols with ultra-low sulphur diesel (ULSD) was proposed. Alcohols vapour pressure was determined with the Antoine equation, while the diffusion coefficient of alcohols in air was calculated as a function of carbon number and temperature. The coefficients of activity were obtained by the combination of continuous thermodynamic (gamma distribution function) and a modified UNIFAC-Dortmund-Continuous method. The evaporation losses model is based on Fick’s law and exhibited good agreement with experimental data for all alcohols and blends at 20% content of all alcohols and at 20–60% contents of n-butanol with diesel fuel. The evaporation was found to decrease approximately with an inversely proportional rate with respect to the increase in the carbon chain length of the alcohol. The paradox of faster evaporative losses from blends with lower alcohol content is explained.

Fabrication of nanochannels on polystyrene surface.

Solvent-induced nanocrack formation on polystyrene surface is investigated experimentally. Solubility parameter and diffusion coefficient of alcohols are employed to elucidate the swelling and cracking processes as well as the crack size. Experimental results show that the crack size increases with the heating temperature, heating time, and the concentration and volume of the alcohols. A guideline on fabricating single smaller nanocracks on polymers by solvent-induced method is provided. Nanocracks of approximately 64 nm in width and 17.4 nm in depth were created and replicated onto PDMS (polydimethylsiloxane) slabs to form nanochannels.

Selective Sorption and Desorption of Organic Solvent for δ-Syndiotactic Polystyrene

The desorption and sorption kinetics of organic solvents in the cavity of δ- and empty δ-forms of syndiotactic polystyrene (sPS) were investigated as a function of molar volume and shape of the solvent molecules. The desorption process was performed for films cast from chloroform, benzene, chlorobenzene, toluene, and p-xylene in supercritical CO2 at 40 °C and 10 MPa. The nanoporous structure of δ-sPS after extraction of solvent molecules was dependent on the solvent used. Large size solvent molecules were slowly excluded from δ-sPS. The relation between the cavity volume of δ-sPS and the dimensions of the solvent molecule suggests that desorption is slow for solvent molecules that are tightly packed in the cavities. The sorption kinetics of alcohols was investigated as a function of chain length using the nanoporous structure of empty δ-sPS. When empty δ-sPS was soaked in a linear alcohols with carbon numbers from 1 to 10, the alcohols with carbon number less than 6 could be incorporated in the cavity of empty δ-sPS. The diffusion coefficient of alcohols into the cavity was estimated using the Fickian equation. The diffusion became slower for longer chain length alcohols. In order to compare the sorption of different molecular shaped alcohols, structural isomers of 4 and 5 carbon number alcohols were investigated. These isomers were classified into two categories; alcohols with hydroxyl side groups and those with methyl side groups. Alcohols with hydroxyl side groups could be incorporated into empty δ-sPS; however, the methyl side group prevented the insertion of alcohol molecules into the cavity of empty δ-sPS.

Diffusion of Volatile Organic Chemicals in Porous Media. 1. Alcohol/Natural Zeolite Systems

The aim of the present paper was to measure the diffusion coefficients, mode of transport, and activation energies of some alcohols into the porous structure of a Turkish natural zeolite. Diffusion coefficients, modes of transport, and activation energies of methanol, ethanol, n-propanol, 2-propanol, and n-butanol into the porous structure of the Turkish Manisa Gordes natural zeolite were measured at 24-28 C. The diffusion coefficients of alcohols were calculated from the slope of graphs of Mt/M versus t1/2. As the molecular weight of the alcohols increased, diffusion coefficients decreased, the activation energy for diffusion increased, and the time necessary to reach equilibrium was increased. The diffusion constants increased linearly with an increase in the temperature. The diffusion of alcohols in the zeolite obeyed the anomalous transport mechanism. Diffusion rate constants remained unchanged as the temperature was increased. With increasing molecular weight of the volatile alcohols, the activation energies also increased. The calculated activation energies of diffusion were 18.3, 46.4, 79.7, 57.3, and 90.1 kJ/mol for methanol, ethanol, n-propanol, i-propanol, and n-butanol, respectively.

Sorption, diffusion and vapor permeation of various penetrants through dense poly(dimethylsiloxane) membranes: a transport analysis

A detailed analysis of the transport of chloroform, isomeric butanols, methanol and water vapors at 40°C through dense silicone rubber membranes has been undertaken by the vapor permeation technique. The variation of fluxes versus upstream activity, coupled to sorption isotherms of the investigated compounds in silicone rubber at 40°C (determined by the swelling technique), offer the possibility to determine the sorption and diffusion steps in the overall permeant flux. It is shown that the chloroform isotherm follows the Flory-Huggins theory, while alcohols require a more sophisticated approach (Koningsveld and Kleinjtens type) in order to fit the isotherms. The water sorption isotherm shows a typical sigmoid shape which could not be fitted correctly by classical sorption equations. The diffusion coefficient of chloroform in PDMS appears to be almost unaffected by solvent concentration in the membrane, similarly to the results obtained with other good solvents in PDMS. Diffusion coefficients of alcohols and water show, however, a common tendency to decrease with their local concentration. An interpretation of the sorption isotherms based on the cluster integral of Zimm and Lundberg suggests some clustering behavior, which seems consistent with the diffusion coefficient variation. The clustering tendency of the solvent molecules in the PDMS matrix was related to their proton donating power, which follows the sequence: water > methanol > 1-butanol > 2-butanol > 2-methyl-2-propanol > chloroform.

The use of Fourier transform infrared (FT-IR) spectroscopy to determine the diffusion coefficients of alcohols in polydimethylsiloxane.

A variable long path gas cell was used to measure the sorption of organic vapors by a polymer slab. Unfilled polydimethylsiloxane (PDMS) slabs were cast and used to study the sorption of a series of aliphatic alcohols. The PDMS slab was suspended in the gas cell and exposed to low relative pressures of an alcohol vapor. The sorption rate of the alcohol vapor by the PDMS slab was obtained by measuring the decrease in the amount of free diffusant in the gas cell. The diffusion coefficients of the alcohols in the PDMS slab were then calculated from the curves of amount of diffusant sorbed versus time. The results show that the values of the diffusion coefficients at nearly infinite dilution, D0, for methanol, ethanol, 1-propanol, and 1-butanol are 1.01 x 10(-5), 0.61 x 10(-5), 0.54 x 10(-5), and 0.33 x 10(-5) cm2/sec, respectively. The isotherms for the sorption of the alcohols by the PDMS slab were also constructed from the data.