ABSTRACT
We have developed a ternary equation of state (EOS) model for the N(2)O/CO(2)/1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF(4)]) system in order to understand separation of these gases using room-temperature ionic liquids (RTILs). The present model is based on a generic RK (Redlich-Kwong) EOS, with empirical interaction parameters for each binary system. The interaction parameters have been determined using our measured VLE (vapor-liquid equilibrium) data for N(2)O/[bmim][BF(4)] and CO(2)/[bmim][BF(4)] and literature data for N(2)O/CO(2). The binary EOS models for the N(2)O/[bmim][BF(4)] and CO(2)/[bmim][BF(4)] systems correctly predicted the liquid-liquid phase separation found in VLLE experiments. The validity of the ternary EOS model has been checked by conducting VLE experiments for the N(2)O/CO(2)/[bmim][BF(4)] system over a range in temperature from 296 to 315 K. With this EOS model, solubility (VLE) behavior has been calculated for various (T, P, and feed compositions) conditions. For both large and small N(2)O/CO(2) feed ratios, the N(2)O/CO(2) gas selectivity [α(N(2)O/CO(2)) = (y(N(2)O)/x(N(2)O))/(y(CO(2))/x(CO(2)))] is α = 1.4-1.5, compared with (α = 0.96-0.98) in the absence of ionic liquid. While the concentration of the ionic liquid does not affect the selectivity, the addition of an ionic liquid provides the only practical means of separating CO(2) and N(2)O.
ABSTRACT
The current understanding of how receptors diffuse and cluster in the plasma membrane is limited. Data from single-particle tracking and laser tweezer experiments have suggested that membrane molecule diffusion is affected by the presence of barriers dividing the membrane into corrals. Here, we have developed a stochastic spatial model to simulate the effect of corrals on the diffusion of molecules in the plasma membrane. The results of this simulation confirm that a fence barrier (the ratio of the transition probability for diffusion across a boundary to that within a corral) on the order of 10(3)-10(4) recreates the experimentally measured difference in diffusivity between artificial and natural plasma membranes. An expression for the macroscopic diffusivity of receptors on corralled membranes is derived to analyze the effects of the corral parameters on diffusion rate. We also examine whether the lattice model is an appropriate description of the plasma membrane and look at three different sets of boundary conditions that describe diffusion over the barriers and whether diffusion events on the plasma membrane may occur with a physically relevant length scale. Finally, we show that to observe anomalous (two-timescale) diffusion, one needs high temporal (microsecond) resolution along with sufficiently long (more than milliseconds) trajectories.
