Shear enhanced microfiltration and rejection of crude oil drops through a slotted pore membrane including migration velocities

Shear enhanced microfiltration of crude oil/water emulsion is investigated and the effect of an applied shear rate on the rejection of droplets by the membrane is reported. Applying vibration provides shear rate at the membrane surface leading to shear-induced migration and an inertial lift of drops/particles. Both phenomena tend to move the droplets away from the membrane surface. The shear-induced migration and inertial lift increase with increasing of the shear rate. A mathematical model is presented to account for the presence of both phenomena. The developed model is used for theoretical prediction of 100% cut-off of crude oil droplets by the membrane with, and with-out, vibration applied. A satisfactory agreement of the model predictions with experimental data shows that the model can be successfully used for a theoretical prediction of 100% cut-off of droplets by slotted pore membranes. Rejection of droplets increased with applying shear rate: at 8000 s-1 shear rate and 200 l m-2 hr-1 flux rate 3 to 4 μm radius droplets were almost completely rejected reducing 400 ppm of crude in the feed to 7 ppm in the permeate

Stability and deformation of oil droplets during microfiltration on a slotted pore membrane

The effect of interfacial tension between two fluids, on the passage and rejection of oil droplets through slotted pore membranes is reported. A mathematical model was developed in order to predict conditions for 100% cut-off of oil droplets through the membrane as a function of permeate flux rate. Good agreement of theoretical predictions with experimental data shows that the model can be applied to the filtration of deformable droplets through slotted pore membranes. At high interfacial tension (40 mN/m) with lower flux (200 l m−2 hr−1)droplets of crude oil (27 API) were 100% rejected at droplet diameter 4.3 μm using a 4 μm slotted pore membrane. At lower interfacial tension (5 mN/m), with the same flux rate, 100% rejection occurred at 10 μm droplet diameter using the same membrane. It was also found that the droplet rejection efficiency below the 100% cut-off was roughly linear with drop size, down to zero rejection at zero drop diameter. Hence, the model, coupled with this approximate correlation, can be used to predict dispersed oil drop concentration from a known feed drop size distribution

Prediction of size distribution of crude oil drops in the permeate using a slotted pore membrane

Permeate size distribution of various crude oil drops with, and without, oscillating the membrane has been predicted using the 'Linear Fit' approach. Drops pass through the membrane due to drag force created by the flow of fluid around the drops. Static force is the force responsible for the rejection of drops through the membrane and is directly proportional to the interfacial tension between dispersed and continuous phases. Without applied shear, 100% cut-off of drops though the membrane is assumed when the drag force and the static force balances each other. With the applied shear, 100% cut-off of drops through the membrane is when drops moves away from the membrane surface due to migration velocities and do not pass the membrane into the permeate. Extrapolating 100% cut-off to the origin of the rejection graphs gives a straight line that is referred as 'Linear Fit' and can be used for predicting rejection below 100% cut-off. Linear fit can be used for predicting drop rejection below 100% cut-off. The portion of oil that would not be rejected by the membrane and would pass through the membrane into the permeate can be calculated using this approach. For a given size of drops in a feed suspension, permeate size distribution can be predicted by multiplying the fraction of oil passing through the membrane and the feed size distribution data. Overall concentration of oil in the permeate can be calculated by knowing size distribution of drops in the permeate, and that provides an idea whether the concentration of oil in the permeate is below the standard set by international regulatory authorities

Hysteresis of the Contact Angle of a Meniscus Inside a Capillary with Smooth, Homogeneous Solid Walls

This paper was accepted for publication in the journal Langmuir: the ACS journal of surfaces and colloids and the definitive published version is available at http://dx.doi.org/10.1021/acs.langmuir.6b00721.A theory of contact angle hysteresis of a meniscus inside thin capillaries with smooth, homogeneous solid walls is developed in terms of surface forces (disjoining/ conjoining pressure isotherm) using a quasi-equilibrium approach. The disjoining /conjoining pressure isotherm includes electrostatic, intermolecular, and structural components. The values of the static receding θr, advancing θa , and equilibrium θe contact angles in thin capillaries were calculated on the basis of the shape of the disjoining/conjoining pressure isotherm. It was shown that both advancing and receding contact angles depend on the capillary radius. The suggested mechanism of the contact angle hysteresis has a direct experimental confirmation: the process of receding is accompanied by the formation of thick β-films on the capillary walls. The effect of the transition from partial to complete wetting in thin capillaries is predicted and analyzed. This effect takes place in very thin capillaries, when the receding contact angle decreases to zero

Influence of the molecular architecture on the secondary relaxations of Poly(styrene-co-methylmethacrylate) copolymers

The processes of adsorption of grafted copolymers onto negatively charged surfaces were studied using a dissipative quartz crystal microbalance (D-QCM) and ellipsometry. The control parameters in the study of the adsorption are the existence or absence on the molecular architecture of grafted polyethyleneglycol (PEG) chains with different lengths and the chemical nature of the main chain, poly(allylamine) (PAH) or poly(L-lysine) (PLL). It was found out that the adsorption kinetics of the polymers showed a complex behavior. The total adsorbed amount depends on the architecture of the polymer chains (length of the PEG chains), on the polymer concentration and on the chemical nature of the main chain. The comparison of the thicknesses of the adsorbed layers obtained from D-QCM and from ellipsometry allowed calculation of the water content of the layers that is intimately related to the grafting length. The analysis of D-QCM results also provides information about the shear modulus of the layers, whose values have been found to be typical of a rubber-like polymer system. It is shown that the adsorption of polymers with a charged backbone is not driven exclusively by the electrostatic interactions, but the entropic contributions as a result of the trapping of water in the layer structure are of fundamental importance

Evaporation of pinned sessile microdroplets of water on a highly heat-conductive substrate: Computer simulations

The aim of the current numerical study is to investigate the influence of individual effects (kinetic effects, latent heat of vaporization, Marangoni convection, Stefan flow, droplet's surface curvature) on the rate of evaporation of a water droplet placed on a highly heat conductive substrate for different sizes of the droplet (down to submicron sizes). We performed simulations for one particular set of parameters: the ambient relative air humidity is set to 70%, the ambient temperature is 20 ∘C, the contact angle is 90∘, and the substrate material is copper. The Suggested model combines both diffusive and kinetic models of evaporation. The obtained results allow estimation of the characteristic droplet sizes where each of the mentioned above phenomena becomes important or can be neglected

Sessile Droplets on Deformable Substrates

Wetting of deformable substrates has gained significant interest over the past decade due to a multiplicity of industrial and biological applications. Technological advances in the area of interfacial science have given rise to the ability to capture interfacial behavior between a liquid droplet and an elastic substrate. Researchers have developed several theories to explain the interaction between the two phases and describe the process of wetting of deformable/soft substrates. A summary of the most recent advances on static wetting of deformable substrates is given in this review. It is demonstrated that action of surface forces (disjoining/conjoining pressure) near the apparent three-phase contact line should be considered. Any consideration of equilibrium droplets on deformable (as well as on non-deformable) substrates should be based on consideration of the excess free energy of the system. The equilibrium shapes of both droplet and deformable substrate should correspond to the minimum of the excess free energy of the system. It has never been considered in the literature that the obtained equilibrium profiles must satisfy sufficient Jacobi’s condition. If Jacobi’s condition is not satisfied, it is impossible to claim that the obtained solution really corresponds to equilibrium. In recently published studies, equilibrium of droplets on deformable substrates: (1) provided a solution that corresponds to the minimum of the excess free energy; and (2) the obtained solution satisfies the Jacobi’s condition. Based on consideration of disjoining/conjoining pressure acting in the vicinity of the apparent three-phase contact line, the hysteresis of contact angle of sessile droplets on deformable substrates is considered. It is shown that both advancing and receding contact angles decrease as the elasticity of the substrate is increased and the effect of disjoining/conjoining pressure is discussed. Fluid inside the droplet partially wets the deformable substrate. It is shown that just these forces coupled with the surface elasticity determine the deformation of the deformable substrates

Filtration of suspensions using slit pore membranes

This paper is in closed access.A slit pore membrane is used for a membrane filtration of silica suspensions of two concentrations: a relatively low volume fraction when supposedly only pore blocking mechanism is responsible for a membrane flux decline and a relatively high volume fraction when cake layer formation is supposed to dominate. A theory is developed for both cases. It is shown that the membrane filtration proceeds in two different regimes depending on the applied pressure difference and the theory is developed for both cases. It is shown that the theory predictions are in a reasonable agreement with our experimental data