Filter aids composition

Filter aids should have a narrow fractional composition. Fine particles increase the hydraulic resistance of the filter aid, whereas coarse particles exhibit poor separation. Desired particle-size distributions are normally prepared by air classification, in which the finer size fractions are removed. 

Filter aids are widely used in die fermentation industry to improve the efficiency of filtration. It is a pre-coated filter medium to prevent blockage or blinding of the filter by solids, which would otherwise wedge diemselves into the pores of the cloth. Filter aid can be added to the fermentation broth to increase the porosity of the cake as it formed. This is only recommended when fermentation product is extracellular. Filter aid adds to the cost of filtration. The minimum quantity needed to achieve the desired result must be established experimentally. Fermentation broths can be pretreated to improve filtration characteristics. Heating to denature proteins enhances the filterability of mycelial broths such as in penicillin production. Alternatively, electrolytes may be added to promote coagulation of colloids into larger, denser particles, which are easier to filter. The filtration process is affected by the viscosity and composition of the broth, and the cell cake.5... 

In surface filtration the solids retained are those that do not pass through the smallest cross-section of the capillary flow channels of the filtering layer. Many particles are trapped by adsorption in the labyrinthine three-dimensional sieve of the filter aid. This means that substances can be retained that are smaller than the mesh size of the filter aid. In depth filtration, on the other hand, the solids are trapped in the interior of the layer this is due to the mechanical retention capacity (inertia and size of the particles, sedimentation, diffusion) and to the composition of the juice. 

The composition of the first treatment can be checked by filtering a sample in the laboratory and then adding a small amount of dilute ferric chloride or aluminum sulfate to the filtrate. Any precipitate indicates that the reaction has not been taken to completion (11-13). The contents of the first treatment tank are then filtered, typically in an open plate and frame filter. The filter cake is discharged periodically for disposal. Filter aid can be added, if required. 

Any substances that can enhance the filtration efficiency are termed a filter aid. Diatomaceous earth is the most common filter aid for the precoat filtration system. An efficient, economical filter aid must (a) have rigid, intricately shaped, porous, individual particles (b) form a highly permeable, stable, incompressible filter cake (c) remove even the finest solids at high rates of flow and (d) he as chemically inert and essentially insoluble in the Uquid being filtered. Commercial diatomaceous earth, such as Celite diatomite, meets these requirements due to the wide variety of intricately shaped particles and inert composition that makes it practically insoluble in all hut a few liquids. 

The use of asbestos has been greatly diminished because of its identification with health hazards. There have been proposed replacement materials such as the Zeta Plus filter media from the AMF Cuno Division, consisting of a composite of cellulose and inorganic filter aids that have a positive charge and provide an electrokinetic attraction to hold colloids (usually negatively charged). These media therefore provide both mechanical straining and electrokinetic adsorption. 

The precoat and the body feed can be the same material, or two different filter aids can be used. In the process industries in general, diatomaceous earth is the most widely used filter aid. Purified diatomaceous earth is hydrated silica in amorphous form. Its source is the fossilized external skeletons of microscopic organisms. Artificial perlite, which also is primarily silica, is a frequently used alternative. Table 7.14 shows typical chemical compositions of these materials. 

Brine polishing filters (Section T.5.4.2) usually employ solid filter aids, which become part of the disposal problem. Their most obvious effect is to add to the volume of solids requiring disposal. Since most filter aids are cellulosic or siliceous, again the toxic hazard is quite low. The operator handling these wastes, however, should be familiar with their detailed analyses, because trace contaminants (e.g., metals in the filter aids) may need special attention. The filtered solids are of approximately the same composition as the clarifier sludges discussed in Section 16.5.1.3. 

The catalytic activity of metal oxide composites depends both on the acidity and basicity of the surface that can be characterized by the level of ammonia sorption and The catalyst should adsorb 100-200 pmol/g NH3 and its pAT, should be in the range 15-17.5 [31]. Catalysts having low basicity and acidity of the snrface have too low activities, but a lot of undesired by-products (dioxane and PEGs) are formed when their acidities are too high. The activity of Al-Mg composite oxide catalyst increases with an increase in the calcination temperature and reaches a maximum of approximately 700°C [22]. Further increase in the calcination temperature results in reduced activities, attributed to the sintering of the catalyst surface. The catalyst activity increases with inaeasing aluminum content, but less narrow distributed products are formed. Filtration of the catalyst is not always possible. Therefore, addition of water (180 g of water/1063 g of oxyethylation product) and the use of activated clay or diatomaceous earth as a filter aid are proposed [33]. 

Some special requirements of continuous systems are (1) Metering the feed. A continuous system must be fed at a precise, uniform rate. (See Sec. 21.) (2) Dust collection. This is a necessary part of most diy-processing systems. Filters are available that can effectively remove dust down to 10 mg/m or less, and operate automatically. (Dust collection is covered in Sec. 17.) (3) Ondine analysis. For more precise operation, on-line analysis of product particle size and composition may be desirable. (4) Computer control. SiiTuilation can aid in optimizing system design and computer control. 

In the development of Gai and Boyes (87,88,90), the ECELL, atomic-resolution (HRTEM), STEM, hot stage and PEELS/Gatan imaging filter (GIF) functionalities were combined in a single instalment. The combination is required to aid simultaneous dynamic structure and composition of the reactor contents. 

Mobile phase compositions for this experiment are polar methanol-water mixtures in the ratios 90/10, 80/20, and 70/30 by volume. The stationary phase is C18. Prepare 200 mL of each mobile phase and then filter and degas each through 0.45-/./m filters with the aid of a vacuum (instructor will demonstrate). Slowly pour each (so as to avoid reaeration by splashing) into individual mobile phase reservoirs that are labeled appropriately. 

WA water quality labs by atomic absorption and autoanalyzer techniques. Charge balance calculations Indicated that all dissolved species of significance were analyzed. Comparison of filtered and unflltered aliquots suggested that un-lonlzed species were not present In appreciable quantities. Sampling and analysis uncertainties were determined by the operation of two co-located samplers for 16 weeks. The calcium and sulfate data were corrected for the Influence of sea salt to aid In the separation of the factors. This correction was calculated from bulk sea water composition and the chloride concentration In rainwater (11). Non seasalt sulfate and calcium are termed "excess" and flagged by a ... 

FIGURE lO.S. Ibe left figure shows the schematic illustration of laser-induced fluorescence microscopy under the toud internal reflection for the detection of single Dil molecules at the dodecane- ater interface. Abbreviations ND, ND filter A72, A72 plate M, mirror L, lens C, microcell containing dodecane and aqueous phases O, objective (60 x ) F, bandpath filter P, pinhole AID, avalanche photodiode detector. The right portion of the figure shows the composition of the microcell. 

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