Diatomaceous filter aids

Xmax) 850 (287nm) in hexane, X ax 275, 287 and 297nm nm. Purified by chromatography on columns of magnesium oxide-Supercel (a diatomaceous filter aid) or alumina [Rabourn et al. Arch Biochem Biophys 48 267 1954]. Stored as a solution in pet ether under nitrogen at -20°. 

Citranaxanthin [3604-90-8] M 456.7, m 155-156°, A(Xmax) 410 (349nm), 275 (466nm) in hexane. Purified by chromatography on a column of 1 1 magnesium oxide and HyfloSupercel (diatomaceous filter aid). Crystd from pet ether. Stored in the dark, under inert atmosphere, at 0°. 

Ethyl (6-Methoxy-l,2-naphthoquinonyl-6) Cyanoacetate. The above naphthoquinone (21.7 g) is added to a solution of 500 cc of ethanol and 14 cc of ethyl cyanoacetate, followed by the addition of 32 cc triethylamine. A deep purple color will develop and the mixture should be swirled for 4 min to dissolve the quinone completely. A solution of 75.9 g of potassium ferricyanide in 320 cc of water is then added to the solution, causing a thick dark complex to form and separate. Redissolve by adding a soluhon of 24 g of sodium carbonate in 1,600 cc of water. Swirl or stir and filter through diatomaceous filter aid. Acidify the filtrate with 100 cc of 6 M sulfuric acid to precipitate 34.8 g of red-orange powder, which is oven dried at 70°. Reciystallize from ethyl acetate to get 19.3 g, mp 157-158.5°. The remaining filtrate is evaporated to a small bulk and reciystallization from ethyl acetate gives an additional 2.8 g of product. 

Methoxy-4-Cyanomethyl-l,2-Naphthoquinone. 10 g of the above acetate in 50 cc of alcohol is treated with 50 cc of 10% NaOH and 50 cc of water. Swirl or stir the solution for 25 minute to see the color change from purple to deep red. Filter with diatomaceous filter aid and acidify with 6 N hydrochloric acid. A resulting red-brown solid is collected and air dried to give 7.2 g of product. 

Celite No. 535, a diatomaceous filter aid, is a product of the Johns-Manville Co., New York, N. Y., and is often used for this purpose. 

Purify it by chromatography on a coluttm of 1 1 MgO and HyfloSupercel (diatomaceous filter aid). Crystallise it from petroleum ether. Store it in the dark under N2 or argon at 0". 

Materials suitable as filter aids include diatomaceous earth, expanded perilitic rock, asbestos, ceUulose, nonactivated carbon, ashes, ground chalk, or mixtures of those materials. The amount of body feed is subject to optimisa tion, and the criterion for the optimisa tion depends on the purpose of the filtration. Maximum yield of filtrate per unit mass of filter aid is probably most common but longest cycle, fastest flow, or maximum utilisation of cake space are other criteria that requite a different rate of body feed addition. The tests to be carried out for such optimisation normally use laboratory or pilot-scale filters, and must include variation of the filtration parameters such as pressure or cake thickness in the optimisation. 

In diatomaceous-earth filtration, the powdered filter aid is built upon a relatively loose septum to screen out suspended soHds. The filter becomes clogged, and pressure losses become excessive backwashing is then necessary. The smallest removable particle is 0.5—1 p.m (see Diatomite). 

Batch-stirred vessels are most often used in treating material with powdered activated carbon (72). The type of carbon, contact time, and amount of carbon vary with the desired degree of purification. The efficiency of activated carbon may be improved by applying continuous, countercurrent carbon—Hquid flow with multiple stages (Fig. 3). Carbon is separated from the Hquid at each stage by settling or filtration. Filter aids such as diatomaceous earth are sometimes used to improve filtration. 

Filter aids should have low bulk density to minimize settling and aid good distribution on a filter-medium surface that may not be horizontal. They should also be porous and capable of forming a porous cake to minimize flow resistance, and they must be chemically inert to the filtrate. These characteristics are all found in the two most popular commercial filter aids diatomaceous silica (also called diatomite, or diatomaceous earth), which is an almost pure silica prepared from deposits of diatom skeletons and expanded perhte, particles of puffed lava that are principally aluminum alkali siheate. Cellulosic fibers (ground wood pulp) are sometimes used when siliceous materials cannot be used but are much more compressible. The use of other less effective aids (e.g., carbon and gypsum) may be justified in special cases. Sometimes a combination or carbon and diatomaceous silica permits adsorption in addition to filter-aid performance. Various other materials, such as salt, fine sand, starch, and precipitated calcium carbonate, are employed in specific industries where they represent either waste material or inexpensive alternatives to conventional filter aids. 

Diatomaceous Silica Filter aids of diatomaceous silica have a dry bulk density of 128 to 320 kg/m (8 to 20 Ib/fU), contain paiiicies mostly smaller than 50 [Lm, and produce a cake with porosity in the range of 0.9 (volume of voids/total filter-cake volume). The high porosity (compared with a porosity of 0.38 for randomly packed uniform spheres and 0.2 to 0.3 for a typical filter cake) is indicative of its filter-aid ability Different methods of processing the crude diatomite result in a series of filter aids having a wide range of permeability. 

Graded Adsorbents and Solvents. Materials used in columns for adsorption chromatography are grouped in Table 12 in an approximate order of effectiveness. Other adsorbents sometimes used include barium carbonate, calcium sulfate, calcium phosphate, charcoal (usually mixed with Kieselguhr or other form of diatomaceous earth, for example, the filter aid Celite) and cellulose. The alumina can be prepared in several grades of activity (see below). 

Caution The catalyst is ojten pyrophoric and should be kept moistened with alcohol. Celite is a diatomaceous earth filter aid. 

Filter aids as well as flocculants are employed to improve the filtration characteristics of hard-to-filter suspensions. A filter aid is a finely divided solid material, consisting of hard, strong particles that are, en masse, incompressible. The most common filter aids are applied as an admix to the suspension. These include diatomaceous earth, expanded perlite, Solkafloc, fly ash, or carbon. Filter aids build up a porous, permeable, and rigid lattice structure that retains solid particles and allows the liquid to pass through. These materials are applied in small quantities in clarification or in cases where compressible solids have the potential to foul the filter medium. 

Diatomaceous earths may resemble the forms of the charcoals. The earths are primarily filter aids, precoats or adsorbents, the hmction of the filter medium being secondary. Fuller s earth and clays are used for decoloring applications diatomaceous earths are used for clarification. The adsorbtivity of diatomaceous earth works in the same fashion as activated carbon, but isotherms (affinity) for many chemical species like the hydrocarbons is weaker. For this reason, activated charcoal or carbon is much preferred in wastewater treatment applications expecially when taste and odor issues are priorities. 

Another method, which is even more successful in preventing binding of the septum, is the use of a precoat.53 Before filtration is begun a coating of 2-6 in (5-15 cm) of diatomaceous earth or perlite filter aid is deposited on the surface of the septum. During filtration operations the scraper is set so that it slowly removes the precoat and, of course, with it the materials that would have plugged the filter. Since the precoat causes a considerable pressure drop, the rate of filtration is slowed down. Flow rates may vary from 2 to 50 gal/hr/ft2 (0.025-0.60 m/hr). The precoat material costs around 3 or 40/lb and is used at the rate of 10- 15 lb/1,000 gal of feed (1,200 to 1,800 kg/m3). 

In case 4, the increasing pressure compresses the cake to such as extent that it actually squeezes off the flow so that as the pressure increases the flow rate decreases. This situation can be compensated for by adding a filter aid to the slurry. This is a rigid dispersed solid that forms an incompressible cake (diatomaceous earth, sand, etc.). This provides rigidity to the cake and enhances its permeability, thus increasing the filter capacity (it may seem like a paradox that adding more solids to the slurry feed actually increases the filter performance, but it works ). 

Gas chromatography (GC) employs a gaseous mobile phase, known as the carrier gas. In gas-liquid chromatography (GLC) the stationary phase is a liquid held on the surface and in the pores of a nominally inert solid support. By far the most commonly used support is diatomaceous silica, in the form of pink crushed firebrick, white diatomite filter aids or proprietary variants. Typical surface areas of 0.5-4 m2/g give an equivalent film thickness of 0.05-1 pm for normal liquid/support loadings of 5-50 per cent by mass. 

The problem received concentrated attention. One method (87) introduced used naphtha as a diluent, with an inert material, such as diatomaceous earth, to build up the wax crystal structure artificially, so that relatively good filtration rates were obtained and a wash could be applied to the wax cake on the filter to displace the retained oil.. This method was identified as the Weir process or filter-aid dewaxing process and was placed in commercial operation about 1928 (30). It was the first commercial process capable of successfully dewaxing the intermediate distillates, as well as paraffin distillates of lowest viscosity and residual stocks of highest viscosity. 

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