Concentration filter aids

In the precoat mode, filter aids allow filtration of very fine or compressible soHds from suspensions of 5% or lower soHds concentration on a rotary dmm precoat filter. This modification of the rotary dmm vacuum filter uses an advancing knife continuously to skim off the separated soHds and the... 

In the precoat and body feed mode, filter aids allow appHcation of surface filtration to clarification of Hquids, ie, filtration of very dilute suspensions of less than 0.1% by volume, such as those normally treated by deep bed filters or centrifugal clarifiers. Filter aids are used in this mode with pressure filters. A precoat is first formed by passing a suspension of the filter aid through the filter. This is followed by filtration of the feed Hquid, which may have the filter aid mixed with it as body feed in order to improve the permeabiUty of the resulting cake. The proportion of the filter aid to be added as body feed is of the same order as the amount of contaminant soHds in the feed Hquid this limits the appHcation of such systems to low concentrations. Recovery and regeneration of filter aids from the cakes normally is not practiced except in a few very large installations where it might become economical. 

Continuous Cake Filters Continuous cake filters are apphcable when cake formation is fairly rapid, as in situations in which slurry flow is greater than about 5 L/min (1 to 2 gal/min), shiny concentration is greater than 1 percent, and particles are greater than 0.5 [Lm in diameter. Liquid viscosity below 0.1 Pa s (100 cP) is usually required for maintaining rapid liquid flow through the cake. Some designs of continuous filters can compromise some of these guidelines by sacrificial use of filter aid when the cake is not the desired product. 

To 40 g. of dry chitin in a 500-ml. beaker is added 200 ml. of concentrated hydrochloric acid (c.p., sp. gr. 1.18), and the mixture is heated on a boiling water bath for 2.5 hours with continuous mechanical agitation. At the end of this time solution is complete, and 200 ml. of water and 4 g. of Norite are added. The beaker is transferred to a hot plate, and the solution is maintained at a temperature of about 60° and is stirred continuously during the process of decolorization. After an hour the solution is filtered through a layer of a filter aid such as Filter-Cel. The filtrate is usually a pale straw color however, if an excessive color persists, the decolorization may be repeated until the solution becomes almost colorless. The filtrate is concentrated under diminished pressure at 50° until the volume of the solution is 10-15 ml. The white crystals of glucosamine hydrochloride are... 

The ability of an admix to be retained on the filter medium depends on both the suspension s concentration and the filtration rate during this initial precoat stage. The same relationships for porosity and the specific resistance of the cake as functions of suspension concentration and filtration rate apply equally to filter aid applications. 

Once the precoating stage is completed the process slurry is pumped into the filter, the forming cake is retained on the plates and the filtrate flows to further processing. When the solids are fine and slow to filter a body-aid is added to the feed slurry in order to enhance cake permeability. However, it should be kept in mind that the addition of body-aid increases the solids concentration in the feed so it occupies additional volume between the plates and increases the amount of cake for disposal. Likewise, for all those applications when the cake is the product, precoat and filter-aid may not be used since they mix and discharge together with the cake. 

A mixture of iron, ferric chloride and water is added to the toluene solution. The mixture is heated to reflux and concentrated hydrochloric acid is added dropwise at a rate calculated to keep the mixture refluxing vigorously. After the hydrochloric acid Is all added, the refluxing is continued by the application of heat for several hours. A siliceous filter aid is then added to the cooled reaction mixture and the material is removed by filtration. The filter cake is washed four times, each time with 90 ml of benzene. The organic layer is then separated from the filtrate. The water layer is acidified to a pH of 2 and extracted three times with 90 ml portions of benzene. 

A suspension of the oxime 27 (475 g, 1.70 mol) arid 5% Ru/ C ( 9g) in fvleOH (8 L) was warmed to 50 C and stirred in a closed, evacuated autoclave. Hydrogen was admitted and the pressure inside the autoclave was maintained at 40 psi while the temperature was increased to 68-74 C. The mixture was stirred for 19-24h, cooled and filtered through Filter Aid and the solid was washed with MeOH (2x4 L). The combined filtrate and washings were concentrated to 4 L under reduced pressure, MeCN (4 L) was added and the mixture was again concentrated to 4L and the cycle was repeated twice more. The MeCN solution was cooled to 10 C and benzenesulfonic acid (260 g, 1.64 mol) in MeCN (1.6L) was added, whereupon the benzenesulfonate of the amine 28 separated yield 579 g (80%). The free amine had mp 110-112 C. 

A fermentation broth containing Streptomyces kanamyceticus cells is filtered by a vacuum rotary filter. The feed rate is 120kg h1 each kilogram of broth contains 60g of cells. To improve filtration, filter aids are added at a rate of 10kg-h. The concentration of kanamycin in the broth is 0.05%. The filtrate is collected at a rate of 112 kg h. The concentration of kanamycin in the filtrate is 0.045%. The filter cake contains cells, and filter aid is continuously removed from the filter cloth. 

A mixture of 132.5 g. (1.05 moles) of sodium sulfite, 99.5 g. (0.5 mole) of bis-4-chlorobutyl ether (Note 1), and 450 ml. of water is placed in a creased 1-1. three-necked flask fitted with an efficient sealed stirrer and a reflux condenser. The third neck of the flask is closed with a stopper, and the mixture is heated and stirred vigorously under reflux until the ether has dissolved (Note 2). At the end of this time, heating is discontinued, and 60 ml. of concentrated c.p. hydrochloric acid is cautiously added to the solution. The mixture is then boiled with stirring until sulfur dioxide is no longer evolved. Solid barium chloride dihydrate (or a 10% aqueous solution of this salt) is added to the hot solution (Note 3) until all sulfate has been precipitated then the barium sulfate is removed by suction filtration through a layer of filter aid. 

The apparatus is dismantled, and the reaction mixture is filtered quickly by suction through a 1.5-cm. layer of filter aid on an 11-cm. Buchner funnel placed on a 2-1. filter flask. The filter cake is pressed down well and washed with three 50-ml. portions of methylene chloride. The filtrate is immediately protected from moisture by calcium chloride tubes, and the solvent is removed by distillation from a 2-1. flask. After the solution has been concentrated to about 225 ml., the hot liquid is poured into a suitable container (Note 6), and the remaining solvent is removed under reduced pressure (Note 7). The yield is 192-199 g. (81-84%) of a white, crystalline solid which melts at 155-156°. 

A 2-L filter flask is equipped with an 11-cm Buchner funnel with filter paper. The funnel is charged with Celiteto a depth of 1 cm (Note 10) and 50.0 g of Florisilis spread evenly on top of the Celite. The above mixture is filtered through this pad of filter aid (Note 11). The filter cake is rinsed with ethyl acetate, 2 x 100 mL. The resulting pale yellow filtrate is concentrated under reduced pressure to yield 47.3 g (96.2%) of pale yellow crystals (Note 12). 

The mixture is shaken vigorously, and the lower layer is separated and stored in ice. The aqueous layer is extracted with two 50-ml. portions of dichloromethane. The organic extracts are combined and shaken with 100 ml. of ice-cold, concentrated aqueous ammonia (35% w/w), and this mixture is filtered through a filter-aid cake and separated (Note 12). The extraction and filtration are repeated with fresh ammonia solution using the same filter (Note 13). The filter is washed with 50 ml. of dichloromethane, and the organic layer is separated and dried over anhydrous magnesium sulfate. The dried solution is filtered, the filter is washed with 50 ml. of dichloromethane, and the solvent is removed on a rotary evaporator at 30°. The flask containing, the residual oil after removal of the dichloromethane is cooled to 0° before exposure to air (Note 14). 

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. 

The naphtha is recovered from the dewaxed oil solution in conventional distillation equipment. The wax cake containing the filter aid is discharged from the dewaxing filter into a heated vessel, where the wax is taken into solution and the inert filter aid settles to the bottom in the form of a concentrated slurry. The aid separated from the wax solution is slurried with kerosene and this slurry is filtered on a continuous filter at a temperature sufficiently high to flash off water adsorbed on the aid. The dried and recovered aid on the filter is subjected to a chilled naphtha wash to displace the kerosene and cool the aid, which is then recycled to the chilled oil-naphtha mixture. Recovery of the aid in this manner permits its re-use indefinitely. 

That depends on what you are analyzing. Interfering compounds need to be removed as much as possible proteins precipitated, lipids extracted, cells and particulates filtered or removed. Some samples need to be concentrated to aid in detecting trace amounts in dilute samples. Check the literature for your particular compound, use traditional procedures for compound purifications, and look into the possibility of using SPE columns for pre-column purification and concentration (see Chapter 12). 

---