Diffusion of organic penetrants through low density polyethylene (LDPE) films: Effect of size and shape of the penetrant molecules

The diffusion coefficient at zero penetrant concentration D₀ of dichloromethane, chloroform, carbon tetrachloride, cyclohexane, benzene, o-xylene, m-xylene, and p-xylene, and n-hexane in LDPE were measured at 25°C, using the desorption method. The D₀ values obtained in this way are correlated with the size, shape, and chemical nature of the penetrant molecules. The temperature dependence of the diffusion coefficients of toluene and n-hexane in LDPE are also reported in the limited temperature range of 25–45°C. It indicates that, in spite of a size larger than that of toluene, n-hexane has a lower activation energy of diffusion.     

Supported reagents—preparation analysis and applications. J. H. Clark,A. P. Kybett and D. J. Macquarrie. VCH,Weinheim, New York,Basle, Cambridge, 1992. pp. xi+152, price £40.50, DM108.00. ISBN 3-527-28043-X/1-56081-010-6

It is shown quantitatively that the formation of holes through the skin of membranes, prepared by the quick immersion in water of polyetherimides in solution in N-methylpyrrolidone, is governed by the solvent mobility. The surface pattern observed by videomicroscopy exhibits a characteristic distance between neighbouring holes (?5 μm) which is a linear function of D^?1_s; D_s is the solvent diffusion coefficient in the polymeric solution, measured using a pulsedfield gradient NMR technique. The dependence of this distance on the solvent concentration in water is also characterized.     

Application of taylor dispersion technique to measure mutual diffusion coefficient in hexane + bitumen system

A novel approach with fewer technical and analytic limitations in liquid solvent‐bitumen diffusion studies is used in this article. The Taylor dispersion technique was selected for its convenient short run time experiments and reliable data analysis to find mutual diffusion coefficients in a hexane + bitumen mixture. For the first time, the infinite‐dilution molecular diffusion coefficients of bitumen in hexane were measured in both the presence and relative absence of asphaltene particles in the solution at atmospheric pressure and temperatures of 303.15, 310.15, and 317.15 K. The polydisperse nature of bitumen was clearly revealed. Results were compared with common predictive tools. Also, the asphaltene surface charge in the hexane precipitating solvent was demonstrated. Through concentration dependency investigations at atmospheric pressure and 303.15 K, it was determined that the mutual diffusion coefficients monotonically decrease as the viscosity of mixture increases within the studied 0–34% volumetric concentration of bitumen. The Taylor dispersion technique shows great potential for diffusion studies of liquid solvent‐bitumen systems. © 2014 American Institute of Chemical Engineers AIChE J, 60: 2670–2682, 2014     

Solvent screening for non‐aqueous extraction of Alberta oil sands

Non‐aqueous extraction of bitumen from oil sands has the potential to reduce fresh water demand of the extraction process and eliminate tailings ponds. In this study, different light hydrocarbon solvents, including aromatics, cycloalkanes, biologically derived solvents and mixtures of solvents were compared for extraction of bitumen from Alberta oil sands at room temperature and ambient pressure. The solvents are compared based on bitumen recovery, the amount of residual solvent in the extracted oil sands tailings and the content of fine solids in the extracted bitumen. The extraction experiments were carried out in a multistage process with agitation in rotary mixers and vibration sieving. The oil sands tailings were dried under ambient conditions, and their residual solvent contents were measured by a purge and trap system followed by gas chromatography. The elemental compositions of the extraction tailings were measured to calculate bitumen recovery. Supernatants from the extraction tests were centrifuged to separate and measure the contents of fine solid particles. Except for limonene and isoprene, the tested solvents showed good bitumen recoveries of around 95%. The solvent drying rates and residual solvent contents in the extracted oil sands tailings correlated to solvent vapour pressure. The contents of fine solids in the extracted bitumen (supernatant) were below 2.9% for all solvents except n‐heptane‐rich ones. Based on these findings, cyclohexane is the best candidate solvent for bitumen extraction, with 94.4% bitumen recovery, 5 mg of residual solvent per kilogram of extraction tailings and 1.4 wt% fine solids in the recovered bitumen. © 2012 Canadian Society for Chemical Engineering     

The effect of styrene grafting on the diffusion and solubility of organic liquids in polyethylene

The effect of grafting styrene onto low-density polyethylene on the diffusion and solubility of benzene and n-hexane in the graft copolymer has been investigated. The diffusion coefficient at zero concentration D_{c = 0} for both benzene and n-hexane decreased with the amount of styrene grafting in the polyethylene–styrene graft copolymer membrane. The free volume parameters of the polyethylene–styrene graft copolymer were calculated using benzene and n-hexane as the diffusing species. Results show that there is a large decrease in free volume as grafting proceeds and the effect is more pronounced at low levels of grafting. Solubility was found to be a function of the per cent grafting, there being a 50%–90% increase in benzene solubility in a 26% graft compared to polyethylene. The increase in solubility for n-hexane was considerably lower. The effect of crystallinity on the free volume parameters has also been calculated.     

Solubility and diffusion behavior of compressed CO2 in polyurethane oligomer

In CO₂-assisted polyurethane (PU) foaming, the solubility and diffusion coefficient of CO₂ is vitally important to the cell nucleation and growth. This work is aimed at the effect of molecular weights (M _n) and crosslinking densities (V _e) on the solubility and diffusion coefficient of CO₂ in PU oligomers. A series of PU oligomers with different M _n and V _e were synthesized. The solubility and diffusivity of CO₂ in PU oligomers were measured experimentally in the temperature from 80 to 140 °C and with pressures up to 15 MPa. It was shown that the solubility and diffusion coefficients of CO₂ was decreased 20.5 and 21.0%, respectively, with the M _n increasing from 5864 to 153,754 g mol⁻¹ at 80 °C, 15 MPa. The solubility and the diffusion coefficient also decreased 11.1 and 38.0% as the V _e was increased from 64 to 1493 mol m⁻³. Furthermore, the diffusion mechanism of CO₂ in PU oligomers was explored via molecular dynamics simulations. The results indicated that the calculated diffusivity of CO₂ showed the same changing trend as the experimental values, and the smaller M _n or crosslinking degree contributed to an increase in fractional free volume and stronger polymer–CO₂ interactions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47100.     

Diffusion of semi‐flexible polyelectrolyte through nanochannels

The diffusion of sodium polystyrene sulfonate through polycarbonate nanochanels was studied in salt‐free dilute aqueous solution. A stronger molecular weight dependence of diffusion was observed compared to free diffusion in dilute solution. Scaling exponentials relating polymer size to diffusivity were between Flory's theory (D_eff ∝ N^?0.6) and Rouse's model (D_eff ∝ N^?1), revealing a crossover regime from 3‐D diffusion to 1‐D diffusion. Diffusion was less hindered for the polyelectrolyte (D_eff/D₀), than for a rigid sphere, when the polymer/channel size ratio exceeded 0.2. This is attributed to elongated chains with reduced frictional hindrance. Simulation of the confined diffusion based on an elongated cigar model gave D ∝ N^?1 ${R_{\rm t}^{2/3}}$ while the experimental results agree with D ∝ N^?0.94${R_{\rm t}^{ 2/3}}$ . For charged polyelectrolytes, the transition to 1‐D diffusion therefore begins before the polymer radius of gyration exceeds the channel size contrary to model assumptions. We attribute this to the charged nature of the polyelectrolytes causing extended chain conformations. © 2009 American Institute of Chemical Engineers AIChE J, 2010     

Solvent engineering applied to lipase-catalyzed glycerolysis of triolein

Solvent engineering was applied to lipase-catalyzed glycerolysis of triolein for the selective synthesis of monoolein and diolein. The effect of different binary mixtures of n-hexane and 2-methyl-2-butanol (2M2B) on the selective production of mono- or diacylglyceride was established. Conditions for high selectivity toward monoolein synthesis were enhanced from 10.6 mol% in pure n-hexane to 64 mol% in 2M2B. On the contrary, the highest production of diolein, corresponding to 62 mol%, was achieved in n-hexane. Concerning triolein conversion, the best results were obtained in 100% 2M2B, with a conversion of 75%. The effect of the n-hexane/2M2B ratio on diolein regioisomer production during triolein glycerolysis was also evaluated. Two different profiles of diolein regioisomers were observed as a function of solvent composition: Although the production of the 1,2-diolein isomer was favored as the proportion of 2M2B in n-hexane was increased, the 1,3-isomer was preferentially synthesized in reactions where n-hexane was the predominant solvent. When 100% n-hexane was used as a solvent, 1,3-diolein comprised 72 mol% of the total diolein population (58 mM). On the contrary, when the reaction was carried out in 100% 2M2B, the total concentration of diolein was lower (21 mM) but the 1,2-diolein regioisomer was preferentially formed (89%). These results were explained as a consequence of the different extents of hydrolysis-synthesis reactions involved in the glycerolysis process, which are strongly dependent on solvent mixtures and water concentration. Finally, some advantages of the use of binary mixtures of solvents compared with other strategies applied to glycerolysis reactions are discussed.     

Carrier Facilitated Transport of Europium(III) Across Supported Liquid Membranes Containing N,N,N′,N′-tetra-2-ethylhexyl-3-oxapentane-diamide (T2EHDGA) as the Extractant

Studies on the solvent extraction and pertraction behavior of europium(III) was carried out from acidic feed solutions using N,N,N′,N′-tetra-2-ethylhexyl-3-oxapentane-diamide (T2EHDGA) in n-dodecane as the solvent. The nature of the extracted species from the solvent extraction studies conformed to Eu(NO₃)₃ · 3T2EHDGA which is in variance with the analogous Eu(III) – TODGA (linear homolog of T2EHDGA) extraction system. The transport behavior of Eu(III) was investigated from a feed containing 3.0 M HNO₃ into a receiver phase containing 0.01 M HNO₃ across a PTFE flat sheet supported liquid membrane (SLM) containing 0.2 M T2EHDGA in n-dodecane as the carrier solvent and 30% iso-decanol as the phase modifier. Effects of feed acidity, carrier extractant concentration, membrane pore size, and Eu concentration in the feed on the transport rates of Eu(III) were also investigated. Membrane diffusion coefficient (D _o) for the pertracted species was calculated using the Wilke-Chang equation as 4.25 × 10^?6 cm² · s^?1. The influence of Eu concentration on the flux was also investigated. The role of temperature on the transport rates was investigated and the thermodynamic parameters were calculated.     

Actual Concentration Profiles in Membrane Permeation

Abstract

The concentration profiles and the concentration dependent diffusion coefficient, at steady-state liquid permeation, were investigated in plastic films by directly measuring the concentration profile. A stacked film packet was developed which permitted peeling of film sections and measuring incremental concentration of permeate. The membrane-permeate systems studied were: nylon 6-water, nylon 6-dioxane, cellulose acetate-water, and polyethylene-dioxane. Membrane thickness was varied from 2 to 53 mil and temperature from 35 to 75°C. Also, poylethylene-benzene and polyethylene–n.-hexane systems were studied at 17 mil and 35°C only.

The analysis of the experimental data showed that the exponential model, D = _{0 ^{e α C}} , represented the directly measured concentration profiles to a satisfactory degree. The use of this exponential model leads to a linear variation of the diffusion coefficient with distance within the membrane, but nonlinear as a function of concentration.     

Comparison of dissolution and mutual diffusion coefficients during dissolution of poly(methyl methacrylate) films

Steady state fluorescence measurements have been used for studying the dissolution of polymer films. These films are formed by free radical polymerization of methyl methacrylate (MMA) in which pyrene ( P_y ) was introduced as a fluorescence probe. Dissolution of poly(methyl methacrylate) (PMMA) films in chloroform–heptane mixtures were monitored in real-time by the P_y fluorescence intensity change. Dissolution coefficients D_d of P_y molecules were measured during dissolution of PMMA films, and found to be about 10⁻⁶ cm² s⁻¹. After dissolution, fluorescence quenching measurements were performed and the Stern–Volmer equation was employed to measure the mutual diffusion coefficients of heptane (D_h) and P_y (D_Py) molecules; these were found to be about 10⁻⁵ cm² s⁻¹. © 1999 Society of Chemical Industry     

Sorption and diffusion of n-alkanes into bromobutyl rubber membranes

Sorption and diffusion of n-alkanes into bromobutyl rubber membranes were investigated in the temperature interval 25–60°C by a sorption gravimetric method. The Fickian diffusion equation was used to calculate the diffusion coefficients, which were dependent on the size of the alkanes, their interactions with the chain segments of the polymer and temperature. The diffusion coefficients varied from 0.34×10^?7 cm²/s (n-hexadecane) to 9.94×10^?7 cm²/s (n-hexane). The activation energy for diffusion varied from 14kJ/mol (n-hexane) heptane to 2.0kJ/mol for n-hexadecane. The sorption/swelling results are discussed in terms of first and second order kinetic equations. The molar mass between chain-entanglement-crosslinks was estimated from swelling data. The experimental and calculated results showed a systematic dependence on the increasing size of the alkanes. None of the solvents showed any degradative effects on the polymer.     

On the correlation between the viscosity of partially hydrolyzed polyacrylamide solution and the diffusion coefficient in the semidilute concentration regime

The solution viscosity of neutral polyacrylamide (PAM), the partially hydrolyzed polyacrylamide (70% HPAM), and polyacrylic acid (PAA) were measured concurrently with the apparent diffusion coefficient in the dilute and semidilute concentration regimes. We identified the scaling relation η − η_s = A/D in the semidilute regime, where η is the solution viscosity, η_s is the solvent viscosity, D is the coefficient of the slow diffusion mode obtained from dynamic light scattering, and A is a prefactor found to have a unique value of ∼1.0 × 10⁻⁸ cP cm²/s. The scaling relation as well as the prefactor are independent of the the ionic strength, the solvent quality, the molecular weight, the charge density, the polyelectrolyte, and salt concentrations. For the neutral PAM, the product [η – η_s]D is proportional to the polyelectrolyte concentration C_p, consistent with Rouse theory and previous experimental findings.     

Cottonseed extraction with mixtures of acetone and hexane

Cottonseed flakes were extracted with mixtures of n-hexane and acetone, with the concentration of acetone varying between 10 and 75%. Adding small amounts of acetone (≤25%) to n-hexane significantly increased the extraction of free and total gossypol from cottonseed flakes. Sensory testing detected no difference in the odor of cottonseed meals produced either by extraction with 100% n-hexane or by extraction with a 10∶90 (vol/vol) mixture of acetone/hexane. More than 80% of the free gossypol was removed by the 10∶90 mixture of acetone/hexane, whereas pure n-hexane extracted about 47% of the free gossypol from cottonseed flakes. A solvent mixture containing 25% acetone removed nearly 90% of the free gossypol that was removable by extraction with pure acetone; the residual meal had only a minimal increase in odor. In contrast, cottonseed meals produced by extraction with pure acetone had a much higher odor intensity. The composition of the cottonseed crude oil was insignificantly affected by the acetone concentration of the extraction solvent. The results indicate that mixtures of acetone and n-hexane can be used as extraction solvents to produce cottonseed crude oil without the concomitant development of odorous meals.     

The influence of mineral variability of Callovo-Oxfordian clay rocks on radionuclide transfer properties

The upper part of the Callovo-Oxfordian clay-rich rock formation (C2c unit) (Meuse/Haute-Marne, France) displays large variations in mineralogical composition of quartz, carbonate and clay minerals. This study deals with the effects of this composition variability on the diffusion-dominated transport properties of HTO (tritiated water)³, ³⁶Cl⁻ and ¹³⁷Cs⁺ for these rocks. Effective diffusion coefficients D_e and accessible porosities ε were determined using the through-diffusion method for a set of C2c unit samples characterized by a contrasted mineralogy especially in terms of clay mineral content (4–29%).The relative variations of the effective diffusion coefficients measured for HTO, ³⁶Cl⁻ and ¹³⁷Cs⁺ remain limited within a range of a factor 5 down to a clay mineral content of ~ 10%. In the range of clay mineral content higher than 15%, the effective diffusion coefficient tends to increase for ¹³⁷Cs⁺ and decreases for ³⁶Cl⁻ whereas D_e(HTO) stays relatively stable. Anion exclusion and surface enhanced diffusion for caesium were quantified and can explain this behaviour. Below 10% of clay minerals, these effective coefficients and the accessible porosities decreased drastically. For 4% of clay minerals, D_e were equal to 1.3 · 10^− 12 m² s^− 1 for HTO, 3.5 · 10^− 13 m² s^− 1 for ³⁶Cl⁻ and 7 · 10^− 12 m² s^− 1 for ¹³⁷Cs⁺. One of the main findings is that the anion exclusion and the enhanced diffusion for caesium still occur for the samples characterized by the lowest clay mineral contents. Finally, the set of diffusion data has been analysed against the well-known Archie's relation linking the accessible porosity to the effective diffusion coefficient.     

Stress dependence of water diffusion in epoxy resin

The effect of stress on the diffusion of water in glassy polymers is analytically treated. Utilizing the free volume concept the effect of stress on the free volume fraction is established and in turn is related to the diffusion coefficient yielding the following formula: D_σ = D_oe^{(6 to 10)σ/G} where D_σ and D_o are the diffusion coefficients in the presence and absence of stress respectively, G is the shear modulus, and σ is the stress. Experiments are described which demonstrate that in a bent epoxy bar, more water is picked up at the tension side than at the compression side. Theory and experiment are discussed and compared.     

Membrane transport of organics. II. Permeation of some carboxylic acids through strongly basic polymer membrane

The permeability characteristics of the strongly basic polymer membrane Neosepta® AFN‐7, (Tokuyama Soda) have been studied for acetic, propionic, lactic, tartaric, oxalic, and citric acid. The results were interpreted by using the model of transport in reactive membranes. The specific constants, that is, the maximum flux J_max, the reactivity constant K, and the permeability coefficient (P), were calculated using the experimental quasi‐stationary fluxes and the equation derived as a sum of reaction–diffusion (Michaelis–Menten‐type), and the solution–diffusion transport equation. The constants K and J_max were found to range from 0.1 to 5 dm³ mol⁻¹ and from 0.4 × 10⁻⁷ to 2.5 × 10⁻⁷ mol cm⁻² s⁻¹ depending, on the acid properties. The values of K and J_max were correlated with the dissociation constants K_dis.acid, and the diffusion coefficients D_aq.acid in aqueous media, respectively. It was found that the reaction–diffusion flux is predominating for all acids, except for the lactic one, when the feed concentration is lower than 0.5 mol dm⁻³. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2179–2190, 1999     

Free volume model and diffusion of organic solvents in natural rubber

The concentration dependence of the diffusion coefficients and the equilibrium isotherms of benzene, o-xylene, ethylbenzene, and chloroform in natural rubber membranes at 303 K were experimentally determined. The data were used to critically test the predictive capability of the Vrentas–Duda free volume model. It was found that although the model works well for some polymer–solvent systems such as toluene-polystyrene, the use of some of the parameters from pure component properties yields unacceptably low diffusion rates for the rubber–solvent systems studied. The parameters D_o1 and ξ obtained from experimental zero-concentration diffusivity data, and parameter V?₁^* calculated from the solvent molecular geometries are needed to achieve good predictions. The diffusion coefficients described by the revised model can be used to predict quite well the breakthrough times of the rubber–solvent systems that were also experimentally measured by a permeation method. © 1995 John Wiley & Sons, Inc.     

Determination of binary diffusion coefficients in supercritical chlorotrifluoromethane and sulphurhexafluoride with supercritical fluid chromatography (SFC)

Binary diffusion coefficients D₁₂ have been determined in supercritical chlorotrifluoromethane and in liquid as well as supercritical sulphurhexafluoride with supercritical fluid chromatography (SFC) using the peak broadening method. D₁₂ values of benzene, methylbenzene, 1,4-dimethylbenzene, 1,3,5-trimethylbenzene, 1,3-dibromobenzene, 2-propanone and tetrachloromethane are reported at temperatures and pressures from 283 to 338 K and 3 to 15 MPa respectively; this corresponds to densities from 400 to 1000 kg m⁻³ for CClF₃ and 300 to 1400 kg m⁻³ for SF₆. The binary diffusion coefficients D₁₂ are of the order of 10⁻⁸ m² s⁻¹. At constant temperature they exhibit a considerable dependence on density whereas the influence of temperature at constant density is relatively small.     

Flow injection analysis estimation of diffusion coefficients of pauci- and polydisperse polymers such as polystyrene sulfonates

Flow injection analysis, often used for determination of diffusion coefficients of nonpolymeric substances, has now been applied to the characterization of pauci- and polydisperse polymers in solution. A relative method was found useful for obtaining moderate quality evaluations of diffusion coefficients and related parameters of polymers. The width at half-height W_1/2 of the trace peak is found to be proportional to the number average molecular weight M?_n of pauci- and polydisperse polymers, allowing estimation of M?_r and diffusion coefficients. For sodium polystyrene sulfonates at substantially infinite dilution in 1.0 g L^?1 Na₂SO₄, a linear relation has been observed between the logarithms of the molecular weight M?_n and the mean diffusion coefficient D in the M?_n range of 1000–90,000 g mol^?1 or the D range of 30 × 10^?7 to 2 × 10^?7 cm² s^?1.