Nelio A. Ochoa

Fouling behaviour of polyethersulfone UF membranes made with different PVP

Abstract Several polyethersulfone (PES) ultrafiltration membranes have been made with small quantities of polyvinyl-pyrrolidone (PVP) of different molecular weights to increase the permeability without a significant reduction in selectivity. The corresponding fouling mechanism and subsequent structural modifications have been analyzed when in contact with bovine serum albumin (BSA) and dl -histidine (DLH). It has been shown that according to the relative sizes of solute and pores of the membranes: BSA fouls the three membranes externally whereas DLH fouls them internally. Moreover, BSA fouls the non-PVP membranes faster than DLH fouls them slower, according to the action of hydrophobic and electrostatic forces acting at the working pH (4.9). The changes in structure, remaining after water rinsing, is quite similar for the three membranes and both the solutes, as obtained by a r etention test of adequate polyethylene glycols (PEGs).

Pore size distributions based on AFM imaging and retention of multidisperse polymer solutes: Characterisation of polyethersulfone UF membranes with dopes containing different PVP

Abstract Several polyethersulfone ultrafiltration membranes have been made with small quantities of polyvinyl-pyrrolidone of different molecular weights. Our aim was to increase the permeability without significant changes in selectivity. Different approaches to get effective pore size distributions have been compared between them and with the topographic results obtained from atomic force microscopy (AFM) image analysis. In particular, the use of cumulative retention coefficients have proved to be preferable to adequately obtain effective pore size distributions based on retention of multidisperse solutions. Within this frame, it has been proved that small PVP content of the studied membranes leads to different increasing permeabilities with very similar selectivities.

Ultrafiltration of vegetable oils: Degumming by polymeric membranes

Abstract In this work, four different membranes synthesized in our laboratories have been tested for their permeation flux, phospholipid retention and stability in hexane during membrane degumming of crude soybean oil. Membranes were made of three different polymeric materials, i.e. Polyvinylidenfluoride (PVDF), Polyethersulfone (PES) and Polysulfone (PSf), and prepared by the phase inversion process. Raw membranes were characterized by the molecular weight cut-off (MWCO) and the water permeability, L h,w . Ultrafiltration (UF) of an oil–hexane miscella was performed in a stirred dead-end UF cell, pressurized with N 2 . All membranes were soaked in solvent of decreasing polarities to minimize the action of solvent on pore size. Each membrane was tested with pure solvent first and the membrane permeability to pure hexane, L h,h , was determined. The degumming experiments were carried out with a 25% crude soybean oil–hexane mixture right after the pure solvent test. The ratio ( L h,h / L h,w ) is used to indicate the degree of change in membrane structure due to the organic solvent. Results show that PVDF is more stable with hexane than PES and PSf. In addition to membrane material, pore size influences membrane stability also. Small pore sizes give more stable membranes. During degumming, a sharp decrease in the permeate flux with time occurs at the beginning of the permeation process. This behaviour is explained in terms of concentration polarization effects and internal fouling. PES and PSF membranes have a larger initial decrease than PVDF ones.

Effect of coating procedure on composite gas separation membrane performance

Abstract The influence of different coating procedures on the transport and separation properties of composite gas separation membranes was studied. The composite membrane (CM) comprises a coating material (silicone rubber) in occluding contact with an asymmetric polysulfone flat membrane (AM). Permeabilities, ideal separation factors and structure of the CM were found to depend strongly on the evaporation time, volume and concentration of the coating solutions. Gas permeation experiments (H2, N2, CO2, CH4) indicated that gas permeabilities decreased rapidly with an increasing amount of coating. A maximum in the H2/N2, H2/CH4 ideal separation factor was reached as the amount of coating was increased. Scanning electron microscopy (SEM) studies revealed the presence of a dense isotropic layer of coating material above an anisotropic layer comprised of a mixture of polysulfone nodules and silicone material. The results showed that the CM prepared with a concentration of 6% silicone solution and contact time of 1 min has the best gas separation performance.

PVDF/PMMA membranes for lemon juice clarification: fouling analysis

Microfiltration/ultrafiltration membranes with different degrees of hydrophilicity and structural characteristics from poly(vinylidene fluoride) (PVDF), polymethylmetacrylate (PMMA), and polyvinylpirrolidone (PVP) in dimethylformamide (DMF) solvent were prepared to be used in the lemon juice clarification. The effect of transmembrane pressure (Δp= 0.4‐1 bar) and tangential feed velocity (v = 0.2‐1 m/s) on permeate flux and juice quality at T= 20˚C was examined. The membrane containing 15% of PVDF, 5% PMMA, and 5% PVP (mean pore radii rpm= 0.25 μm and porosity e= 0.25) achieved the best performance at Δp= 1 bar and v= 1 m/s, with a final permeate flux at quasi-steady state of 32.5 (L/hm 2 ). The clarified lemon juice presented physical, chemical, and nutritional characteristics comparable to the fresh lemon juice, and 100% of total solid rejection. Membrane fouling was evaluated by applying different fouling models. Results indicated that a good fitting correlation between the experimental data and both complete blocking and cake models was achieved.