Modelling Sorption Thermodynamics and Mass Transport of n-Hexane in a Propylene-Ethylene Elastomer

Optimization of post polymerization processes of polyolefin elastomers (POE) involving solvents is of considerable industrial interest. To this aim, experimental determination and theoretical interpretation of the thermodynamics and mass transport properties of POE-solvent mixtures is relevant. Sorption behavior of n-hexane vapor in a commercial propylene-ethylene elastomer (V8880 VistamaxxTM from ExxonMobil, Machelen, Belgium) is addressed here, determining experimentally the sorption isotherms at temperatures ranging from 115 to 140 °C and pressure values of n-hexane vapor up to 1 atm. Sorption isotherms have been interpreted using a Non Random Lattice Fluid (NRLF) Equation of State model retrieving, from data fitting, the value of the binary interaction parameter for the n-hexane/V8880 system. Both the cases of temperature-independent and of temperature-dependent binary interaction parameter have been considered. Sorption kinetics was also investigated at different pressures and has been interpreted using a Fick’s model determining values of the mutual diffusivity as a function of temperature and of n-hexane/V8880 mixture composition. From these values, n-hexane intra-diffusion coefficient has been calculated interpreting its dependence on mixture concentration and temperature by a semi-empiric model based on free volume arguments.

Drop Size Dependence of the Apparent Surface Tension of Aqueous Solutions in Hexane Vapor as Studied by Drop Profile Analysis Tensiometry

Surface tension experiments were performed using the drop profile analysis tensiometry method. The hexane was injected into the measuring cell at certain times before the formation of the solution drop. The influence of the capillary diameter and solution drop size on the measured apparent dynamic surface tension was studied. The amount of hexane transferred from the vapor phase to the drop was estimated. For large pure water drops, it was shown that the ageing of the drop in the hexane vapor during a long time resulted in the formation of a liquid hexane phase covering the drop, but the volume of this phase did not exceed 0.5 mm3. On the contrary, for surfactant solution drops the volume of the hexane phase covering the drop was essentially larger. Experiments with solution drops were performed to measure the surface tension within a wide range of surfactant concentration. It was found that the dependencies of dynamic surface tension on the C13DMPO and C14EO8 solutions concentration exhibit maxima at concentrations of about 1–2 μmol/L for C14EO8 and 2–5 μmol/L for C13DMPO at ageing times of 100 to 1000 s; these maxima were shown to exist also at equilibrium. This phenomenon is presumably ascribed to the competitive character of simultaneous adsorption of hexane and surfactant.

Interfacial Properties of Tridecyl Dimethyl Phosphine Oxide Adsorbed at the Surface of a Solution Drop in Hexane Saturated Air

The surface tension of C13DMPO aqueous solution drops in hexane vapor is studied using the drop profile method. The hexane was injected into the measuring cell at three different conditions: before the formation of the solution drop, at a certain moment during the adsorption process, and after reaching the equilibrium of surfactant adsorption. The surface tension values for all experiments at the same concentration and different injection situations ultimately coincide with each other after attaining the final equilibration stage. The equilibrium surface tension isotherms of C13DMPO solutions, and the adsorption of both components—surfactant and hexane—were calculated. It was shown that the presence of surfactant leads to an increased hexane adsorption.

Preparation of a Composite Material AC/Cu-BTC with Improved Water Stability and n-Hexane Vapor Adsorption

The Cu-BTC, a widely studied metal-organic framework (MOF), has been applied in various fields such as gas adsorption, separation, storage, and catalysis. However, the Cu-BTC collapses due to the replacement of the organic linker by water molecules under humid conditions, which limits its practical application in industries. In consideration of the undesirable water effect on the framework stability of Cu-BTC, a stable activated carbon (AC) was incorporated into it by the in situ method to yield a composite material AC/Cu-BTC with high water stability. XRD and SEM patterns proved that the AC7%/Cu-BTC successfully retains its crystal structure after being exposed to water molecules. The adsorption amount of n-hexane vapor of the AC7%/Cu-BTC after water vapor adsorption-thermal desorption is 307% of that of the Cu-BTC. The addition of the AC changes the adsorption active sites and reduces the strong affinity of the Cu-BTC to water molecules, resulting in the AC7%/Cu-BTC having a much lower adsorption rate for water vapor than the Cu-BTC. Therefore, the AC7%/Cu-BTC can be protected from a large amount of water molecules and avoid structural collapse caused by the disconnection between the copper center and the organic linker. The composite displays a potential value for stable applications of MOF-based materials under ambient conditions.

Adsorption performance of hydrophobically modified silica gel for the vapors of n-hexane and water

An ordinary silica gel (SG-1) was chosen as the raw material and hydrophobically modified with trimethylchlorosilane under different microwave exposure. The orthogonal experiment was designed to screen the optimized modification method. The hydrophobic properties modified silica gel (SG-2) was analyzed by comparing the difference changes of surface chemistries. Then, the adsorption capacities of SG-1 and SG-2 to the n-hexane vapor and water vapor, respectively, were investigated and compared with the capacities of activated carbon and SG-3 (hydrophobically modified using the same composite modifier without microwave exposure). Meanwhile, there cyclable adsorptions of SG-2 to the two vapors were conducted while the desorptions of vacuum and heat was observed. The results showed that the effect of hydrophobic modification to SG-1 under microwave exposure was obvious and SG-2 also had a very good effect of adsorption for the n-hexane vapor. The modified silica gel shows great potential and effect for the recovery of volatile organic compounds with high content of water.