Filtration adjuvants

Methyl ethyl (7-methoxy-10-methyl-3-phenthiazinyl)malonate (62.2 grams) followed by methyl iodide (45.7 grams) is added to a solution of sodium (4.45 grams) in anhydrous ethanol (500 cc). The reaction mixture is heated under reflux for 1 hour at 45°C, then for 6 hours at 55°C, and finally concentrated to dryness under reduced pressure (20 mm Hg). The residue is taken up in methylene chloride (300 cc) and water (250 cc), filtered in the presence of a filtration adjuvant, washed with methylene chloride (150 cc) and water (150 cc), and decanted. The aqueous solution is extracted once again with methylene chloride (100 cc), and the combined organic solutions washed with water (100 cc), aqueous 0.1 N sodium hyposulfite solution (200 cc) and finally with water (200 cc). After drying over anhydrous sodium sulfate and evaporation to dryness under reduced pressure (20 mm Hg), there is obtained an oil (64.8 grams) which is dissolved in methylene chloride (100 cc) and... 

Diatomaceous earth has been used as a filtration adjuvant since the late 19th century, due to the extreme porosity of the powder obtained by processing the rock. The filter layer represents 80% of the total mass, with a surface of 20-25 m /g. These characteristics are highly favorable for filtration. Around 1920, a new treatment process was developed for making high-permeability diatomaceous earths. 

Fig. 11.8. Diagram of the circuits in a diatomaceous earth filter with continuous accretion 1, inlet of wine to be clarified 2, main feed pump 3, inspection glass for wine to be clarified 4, filtration vat with horizontal filter units 5, filter cake removal 6, external residnal filtration nnit 7, inspection glass for clarified wine 8, clarified wine outlet 9, tank containing the filtration adjnvant in snspension 10, filtration adjuvant metering pnmp...

Table 11.4. Filtration adjuvants in a filter press (Paetzold, 1993)...

A rotary filter (Figure 11.10) consists of a cylindrical drum covered with a perforated sieve which supports a filter cloth. The drum rotates around its horizontal axis at adjustable speed, in a tank equipped with an agitating device to homogenize the liquid and keep the filtration adjuvant in suspension during preparation of the filter layer. Diatomaceous earth may be used, but perlite also gives good results at lower cost. A vacuum, created inside the drum by a vacuum pump, draws tlie liquid in. A layer of filtration adjuvant is deposited on the drum during each... 

Microbial contamination is prevented by sulfur dioxide and certain other processes or adjuvants (Volume 1, Chapters 8 and 9), as well as sterilizing and low microbe filtration (Section 11.3.4). Germs may also be destroyed by heating (Section... 

Perlite makes it possible to run longer filtration cycles as it is much more porous than diatomaceous earth and its low density (20-30% lower) reduces the weight of adjuvant required. However, perlite has a lower adsorbent capacity and is most efficient in a fine precoat. 

A two-layer precoat must be prepared on the filter rack prior to starting filtration. The second layer activates the filtration cycle. The first, mechanical, layer is made using a coarse adjuvant (permeability above 1 Darcy), with the possible addition of 10% of a cellulose-based product. The quantities... 

It is recommended that both precoats should be prepared with water or filtered wine. Filtration of the wine may start as soon as the filter precoat has been prepared. The outer surface of the filter layer is constantly renewed by continuous accretion, generally with the same adjuvant or mixture of adjuvants. This prevents rapid clogging of the precoat and increases the length of the filtration cycle. 

The wine to be clarified requires no particular preparation prior to processing in the filter press. An adjuvant (Table 11.4) is added and the mixture is fed into the filter. The impurities, mixed with the adjuvant, are directly retained by the cloth. This is a self-regulating filtration system, as the impurities retained by the cloth act as a filter layer. The filtrate is drained off through internal collectors. Extremely turbid liquids are clarified reasonably well, but it is not possible to achieve very low turbidity. Table 11.4 gives an indication of flow rates observed. In order to filter 240 hi in 8 hours, with a flow rate of 1 hFh/m, a 30 m filter is required, or approximately 45 (80 cm x 80 cm) trays. 

Formulation as Sprays. Virus formulations have usually been for application as sprays using conventional application equipment. Most viruses tested by researchers in field trials have been aqueous suspensions of filtrates or precipitates from macerated virus-killed cadavers. These are stable for long periods under refrigeration or when frozen and usually are easily tank-mixed with water and other adjuvants (12, 13). Performance of these simple formulations in field trials usually is equal or superior to more elaborate formulations. They are seldom practical for commercialization, however. Commercial formulations are concentrated precipitates because stable and concentrated product is needed for storage and shipping. 

Wedlock, D.N. Keen, D.L. McCarthy, A.R. Andersen, P. Buddie, B.M. (2002). Effect of different adjuvants on the immune responses of Mycobacterium tuberculosis culture filtrate proteins, Vet Immunol Immunopathol, 86, 79-88. 

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