Solid/liquid separation membrane filters

The solid-liquid separation of shinies containing particles below 10 pm is difficult by conventional filtration techniques. A conventional approach would be to use a slurry thickener in which the formation of a filter cake is restricted and the product is discharged continuously as concentrated slurry. Such filters use filter cloths as the filtration medium and are limited to concentrating particles above 5 xm in size. Dead end membrane microfiltration, in which the particle-containing fluid is pumped directly through a polymeric membrane, is used for the industrial clarification and sterilisation of liquids. Such process allows the removal of particles down to 0.1 xm or less, but is only suitable for feeds containing very low concentrations of particles as otherwise the membrane becomes too rapidly clogged.2,4,8... 

MF may be used to remove these heavy metals provided pretreatment chemicals are added to precipitate the metals to particles of filterable size. The chemical pretreatment step is crucial since it will affect the performance of the membrane and the resultant sludge volume as well as the contaminant removal efficiency. Reduction/oxidation, absorption/oxidation, and/or catalytic reactions are utilized along with pH adjustment to provide the optimum precipitation. Although conventional methods of waste water treatment may use a similar pretreatment chemistry, the final solid/liquid separation by gravity settling is usually not as effective as membrane filtration. 

Hollow-fibre membrane modules are similar to the capillary type described above, but with fibres of outside diameters ranging from 80 to 500 pm. It is usual to pack a hollow-fibre module with many hundreds or thousands of these fibres, thus membrane area per unit volume is extremely hi. It should be apparent that filtration using hollow-fibre modules is only realistic with process fluids prefiltered to prevent fibre blockage fins limits the technology and it is applied mainly in UF. Also used in uhrafiltration is a spiral-wound membrane module which is often compared to a Swiss roD. The membrane and a spacer are wound round a former, with an appropriate permeate spacer flow is introduced and removed from the ends. This module design is not appropriate for solid-liquid separation, even when filtering colloids, because of the possibility of flow channel blockage and so it will not be discussed any finther. 

Process Description Gas-separation membranes separate gases from other gases. Some gas filters, which remove liquids or solids from gases, are microfiltration membranes. Gas membranes generally work because individual gases differ in their solubility and diffusivity through nonporous polymers. A few membranes operate by sieving, Knudsen flow, or chemical complexation. 

I tp 7. Stirred-flow reactor method experimental setup. Background solution and solute are pumped from (he reservoir through thc stirred reactor containing the solid phase and are. (tlkcied us aliquots by (he fraction collector. Separation of solid and liquid phases is accom-plished by a membrane filter al the oiillel end of the stirred reactor. 

Dry Fractionation—is the simplest fractionation technique because no additives or posttreatment of the end product is involved. Fractionation is basically a two-stage process. First the oil is crystallized by cooling the oil in a controlled manner to the required temperature in a crystallizer. The oil is then filtered to separate the liquid from the solid fraction by means of a vacuum filter or membrane filter press. Recent developments of new and more efficient crystallizers and reliable high-pressure membrane filters moved dry fractionation from a third choice to a good alternative for solvent fractionation in many cases. 

Membrane filtration is a mechanical filtration technique, which uses an absolute barrier to the passage of particulate material as any technology currently available in water treatment. The term membrane covers a wide range of processes, including those used for gas/gas, gas/liquid, liquid/liquid, gas/solid, and liquid/solid separations. Membrane production is a large-scale operation. There are two basic types of filters depth filters and membrane filters. 

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