Miguel Mattea

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.

Modeling and simulation of an oilseed meal desolventizing process

Abstract Most oilseed crushing industries use solvent extraction with commercial hexane to produce crude oils. Desolventization with steam in a desolventizer-toaster (DT) is used to remove the residual solvent from oilseed meals. In this study, a mathematical model is developed to simulate the desolventizing process and analyze the influence of operating variables in continuous equipment. Mass transfer phenomena are outlined to take into account different retention and transport mechanisms. Solvent diffusion through pores from the solid to the vapor phase is analyzed and the contribution of axial dispersion along the bed is evaluated. The final equations describing solvent flow in meal particles and through the desolventizer are solved by numerical techniques. The influence of processing variables such as desolventizing temperature and residence time as well as the effect of some process parameters, like particle size, oil content and void fraction in the bed, on the meal residual solvent is simulated by the model.

A computer-aided model to simulate membrane fouling processes

A computer model based on a 2-D Voronoi tessellation is proposed to represent the porous structure of an asymmetric inorganic membrane and to simulate the fouling process that takes place during filtration of particle suspensions. Voronoi tessellation has proved to be an effective tool in modeling this kind of porous media. It consists of dividing the space into irregular convex polygonal entities (polygons in 2-D). The tessellation structure can be changed by imposing different constraints on the pattern of convex polygons that form it, allowing to represent very close the cross section of an inorganic membrane. Several ways to transform a tessellation in a model of porous media have been implemented. In this study, edges between polygons are considered to be pore segments making a whole pore space embedded into a solid structure. The geometry of each pore segment is completely specified by three parameters: pore body diameter, pore throat diameter and pore length. The first one is computed so that the pore volume fraction matches the porosity of the clean membrane. Pore throat diameter is randomly assigned to each pore segment from a previously specified pore size distribution. Basic fluid dynamics is used to evaluate the fluid flow along a pore segment in terms of its geometry and the pressure difference at its ends. These local flows are used to determine total fluid flow through the membrane and its effective permeability. The filtration process of a suspension of solid particles with a given size distribution is simulated. Particles larger than pore bodies located on the active surface cannot move into the tessellation (membrane) but they can produce a surface layer leading to cake formation. Otherwise, particles small enough penetrate the tessellation (membrane) blocking an interior pore segment (the fluid flow through that segment ceases) or reducing its size. In both cases, a reduction in the total flow because of interior fouling is produced. Data are presented for membrane permeability and flow reduction at different degrees of fouling. The effect of pore size distribution as related to particle size on the prevalent type of fouling is considered.