Separation of oil drops from produced water using a slotted pore membrane

Microfiltration is one of the most important processes in membrane sciences that can be used for separating drops/particles above 1 µm. Depth microfiltration membranes retain drops/particles inside the surface of the membrane, the process is expensive and membranes quickly become fouled. On the other hand, surface microfiltration membranes stop drops/particles on the surface of the membrane and the process is less fouling. Higher permeate flux and lower trans-membrane pressure is obtained with a shear enhanced microfiltration technique. Production of specific size of drops and stability of the drops are very important in testing the microfiltration of crude oil drops/water emulsions. Oil drops from 1-15 µm were produced with a food blender, operated at its highest speed for the duration of 12 mins. In addition, vegetable oil drops were stabilised with 1% polyvinyl alcohol (PVA), Tween 20 and gum Arabic, stability was assessed on the basis of consistency in the size distribution and number of drops in each sample analysed at 30 mins interval. A slotted pore Nickel membrane with the slot width and slot length of 4 and 400 µm respectively has been used in the filtration experiments. The slot width to the slot length ratio (aspect ratio) of the used membrane is 100. Vibrating the membrane at various frequencies created shear rates of different intensities on the surface of the membrane. Membrane with a tubular configuration is preferred over the flat sheet because it is easy to control in-case of membrane oscillations both at lab and industrial scale. Besides this, a tubular membrane configuration provides a smaller footprint as compared to the flat sheet. The influence of applied shear rate on slots/pore blocking has been studied. Applying shear rate to the membrane reduced the blocking of the slots of the membrane; and reduction of slots blocking is a function of the applied shear rate. At higher shear rate, lower blocking of the slots of the membrane was verified by obtaining lower trans-membrane pressure for constant rate filtration. The experiments are in reasonable agreement with the theoretical blocking model. Divergence of the experimental data from the theory may be due to involvement of deforming drops in the process. During microfiltration of oil drops, the drops deform when passing through the slots or pores of the membrane. Different surfactants provided different interfacial tensions between the oil and water interface. The influence of interfacial tension on deformation of drops through the slots was studied. The higher the interfacial tension then the lower would be the deformation of drops through the slots. A mathematical model was developed based on static and drag forces acting on the drops while passing the membrane. The model predicts 100% cut-off of drops through the membrane. Satisfactory agreement of the model with the experiments shows that the concept of static and drag force can be successfully applied to the filtration of deformable drops through the slotted pore membranes. Due to the applied shear rate, inertial lift migration velocities of the drops away from the surface of the membrane were created. Inertial lift velocities are linear functions of the applied shear rate. A mathematical model was modified based on inertial lift migration velocities. The critical radius of the drops is the one above which drops cannot pass through the surface of the membrane into the permeate due to the applied shear rate and back transport. The model is used as a starting point and is an acceptable agreement with the experiment. The model can be used to predict the 100% cut-off value for oil drops filtration and a linear fit between this value and the origin on a graph of grade (or rejection) efficiency and drop size to slot width ratio was used to predict the total concentration of dispersed oil left after filtration. Hence, it is shown how it is possible to predict oil discharge concentrations when using slotted filters

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

Passage and deformation of oil drops through non-converging and converging micro-sized slotted pore membranes

The model presented in the paper is the continuation of the previous work where a mathematical model was developed for the passage and deformation of micro-sized oil drops through a 4 μm converging slotted pore membrane. In the previous work, it was assumed that drops deform from a spherical shape to a prolate spheroid when pass through a converging slot. In the present study, it has been assumed that drops deform into an oblate spheroid while passing through a non-converging slot and a mathematical model is developed for the deformation of drops through non-converging slots. After extending the idea of static and drag forces, it is readily seen that the magnitude of static force (Fcx) for the non-converging slotted pore membrane is higher than the static force for the converging slotted pore membranes. This is because of drops deform suddenly in the non-converging slots, while, in case of converging slots, the drops deform gradually. Micro-sized oil drops of two systems with different interfacial tensions (4 and 9 mN/m) have been used in the study and it is observed that a higher interfacial tension leads to a higher rejection rate for both converging and non-converging slotted pore membranes at various in-pore filtration velocities

Microfiltration of deforming oil droplets on a slotted pore membrane and sustainable flux rates

Oil droplets from an emulsion were filtered using a slotted pore membrane with a 4 m slot width and 400 m slot length. Droplets up to 15 m in diameter were filtered at various flux rates (200–1200 l m−2 h−1) using oscillatory membrane microfiltration. Surface shear rates at the membrane of various intensities (0, 1200, 3200 and 8100 s−1) were applied and the effect on permeate flux rate and trans-membrane pressure were investigated. Near constant filtration flux was obtained for all the tests. Without shear the trans-membrane pressure increased quickly, but at the highest shear rate (8100 s−1) nearly constant trans-membrane pressure and flux rate were observed and may be described as sustainable, or weak form of critical flux. A filtration membrane blocking model was used to investigate the filtration and identify when sustainable, or critical, flux was achieved

The number of iterations and time (in seconds) for distinct blurs and gamma noise levels showed in [38] using M1-model for ADM scheme and the number of ADMM iterations and time (in seconds) for different blurs and gamma noise levels reported using our model-M4.

<p>The number of iterations and time (in seconds) for distinct blurs and gamma noise levels showed in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0161787#pone.0161787.ref038" target="_blank">38</a>] using M1-model for ADM scheme and the number of ADMM iterations and time (in seconds) for different blurs and gamma noise levels reported using our model-M4.</p

Restoration models (M2 and M4) evaluated using PSNR, number of iterations and time.

<p>Recall that the PSNR, number of iterations and time of M2-model are reported in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0161787#pone.0161787.ref001" target="_blank">1</a>].</p

Performance of M4-model on Rice image.

<p>(a) original image; (b) blur image with (fspecial(‘motion’,7)); (c) gamma noise variance is 0.03; (d) the given image degraded by the Gamma noise (Gn) with variance 0.03 and motion blur; (e) the output image by M4-model.</p

Performance of M4-model on Cameraman image.

<p>(a),(f),(k) original image; (b),(g),(l) blur image with (fspecial(‘motion’,5,30)), (fspecial(‘gaussian’,[7,7],2)), (psfMoffat(‘motion’,[7,7],1,5)); (c),(h),(m) degraded image with L = 10; (d),(i),(n) the clean image contaminated by motion blur, gaussian blur, Moffat and the Gamma noise with (L = 10); (e),(j),(o) the restored result by the M4-model.</p

Performance of M4-model on Parrot image.

<p>(a) original image; (b) blur image with (fspecial(‘motion’,5,30)); (c) corrupted image with L = 10; (d) the original image contaminated by multiplicative noise with L = 10 and motion blur; (e) the recovered image by M4-model.</p