Batch filtration

The choice of filtration (batch, continuous vacuum, cross flow, etc.)... 

Batch filtration. Batch filtration involves the separation of suspended solids from a slurry of associated liquid. The required product could be either the solid particles or the liquid filtrate. In batch filtration, the filter medium presents an initial resistance to the fluid flow that will change as particles are deposited. The driving forces used in batch filtration are2 ... 

Figure 2. Pressure filtration batch concentration system.

However, it can be assumed for most electrochemical applications of ionic liquids, especially for electroplating, that suitable regeneration procedures can be found. This is first, because transfer of several regeneration options that have been established for aqueous solutions should be possible, allowing regeneration and reuse of ionic liquid based electrolytes. Secondly, for purification of fiesh ionic liquids on the laboratory scale a number of methods, such as distillation, recrystallization, extraction, membrane filtration, batch adsorption and semi-continuous adsorption in a chromatography column, have already been tested. The recovery of ionic liquids from rinse or washing water, e.g. by nanofiltration, can also be an important issue. 

This study focuses firstly on the transfer of regeneration principles as they have been developed in the field of water-based electroplating and of purification options for ionic liquids as they are experienced in other fields of ionic liquid application. A number of purification procedures for fresh ionic liquids have already been tested on the laboratory scale with respect to their finishing in downstream processing. These include distillation, recrystallization, extraction, membrane filtration, batch adsorption and semi-continuous chromatography. But little is known yet about efficiency on the technical scale. Another important aspect discussed is the recovery of ionic liquids from rinse or washing water. 

In batch SPPS (solid-phase peptide synthesis), the resin is contained in a vessel, usually equipped for bottom filtration. After a washing solvent or a reagent is added, the resin is mixed and the solvent or reagent is removed by filtration. Batch synthesizers use a variety of methods to mix the resin the wrist-action shaker, vortex mixing, nitrogen bubbling, or overhead stirring. 

Figure 2. Tetrahymena concentration by tangential flow filtration. Batch size 100 1. Area 15 ft (1.39 m ). Circulation rate 6.0 1/min. Pin/ out 8/6. Final volume 4.5 1. Concentration factor 22. Flux 0.79 l/m min. Recovery initial...

Filtration Batch Microfiltration, ultrafiltration, reverse osmosis, diaflllration, dead end filtration, Nutsche filtration, plate and frame filtration, baghouse filtration, electrostatic precipitation... 

Until recently purification had been carried out by classical low-performance techniques such as gel filtration, batch adsorption chromatography, and others (Burgus et ai, 1970), which lacked the necessary... 

Cells in suspension CSTR and mechanical stirring with turbines mounted on a stirring shaft CSTR and mechanical stirring as above but equipped with a cell recycling system, typically filtration Batch, fed-batch, continuous Perfusion... 

The trend in the use of deep bed filters in water treatment is to eliminate conventional flocculators and sedimentation tanks, and to employ the filter as a flocculation reactor for direct filtration of low turbidity waters. The constraints of batch operation can be removed by using one of the available continuous filters which provide continuous backwashing of a portion of the medium. Such systems include moving bed filters, radial flow filters, or traveling backwash filters. Further development of continuous deep bed filters is likely. Besides clarification of Hquids, which is the most frequent use, deep bed filters can also be used to concentrate soflds into a much smaller volume of backwash, or even to wash the soflds by using a different Hquid for the backwash. Deep bed filtration has a much more limited use in the chemical industry than cake filtration (see Water, Industrial water treatment Water, Municipal WATERTREATiffiNT Water Water, pollution and Water, reuse). 

Optimization of Cycle Times. In batch filters, one of the important decisions is how much time is allocated to the different operations such as filtration, displacement dewatering, cake washing, and cake discharge, which may involve opening of the pressure vessel. Ah. of this has to happen within a cycle time /. which itself is not fixed, though some of the times involved may be defined, such as the cake discharge time. 

Vacuum filters are available in a variety of types, and are usually classified as either batch operated or continuous. An important distinguishing feature is the position of the filtration area with respect to gravity, ie, horizontal or non-horizontal filtering surface. 

In general, pan filters are selected for freely filtering soHds and thick filter cakes. Cake washing can be introduced easily. Most appHcations are in the mining and metallurgical industries for small-scale batch filtration. 

Continuous Compression Filters. The variable chamber principle appHed to batch filtration, as described before, can also be used continuously in belt presses and screw presses. 

Reaction times can be as short as 10 minutes in a continuous flow reactor (1). In a typical batch cycle, the slurry is heated to the reaction temperature and held for up to 24 hours, although hold times can be less than an hour for many processes. After reaction is complete, the material is cooled, either by batch cooling or by pumping the product slurry through a double-pipe heat exchanger. Once the temperature is reduced below approximately 100°C, the slurry can be released through a pressure letdown system to ambient pressure. The product is then recovered by filtration (qv). A series of wash steps may be required to remove any salts that are formed as by-products. The clean filter cake is then dried in a tray or tunnel dryer or reslurried with water and spray dried. 

Filtration. In many mineral processing operations, filtration follows thickening and it is used primarily to produce a soHd product that is very low in moisture. Filtration equipment can be either continuous or batch type and either constant pressure (vacuum) or constant rate. In the constant pressure type, filtration rate decreases gradually as the cake builds up, whereas in the constant rate type the pressure is increased gradually to maintain a certain filtration rate as the cake resistance builds. The size of the device is specified by the required filter surface area. 

The older methods have been replaced by methods which require less, if any, excess sulfuric acid. For example, sulfonation of naphthalene can be carried out in tetrachloroethane solution with the stoichiometric amount of sulfur trioxide at no greater than 30°C, followed by separation of the precipitated l-naphthalenesulfonic acid the filtrate can be reused as the solvent for the next batch (14). The purification of 1-naphthalenesulfonic acid by extraction or washing the cake with 2,6-dimethyl-4-heptanone (diisobutyl ketone) or a C-1—4 alcohol has been described (15,16). The selective insoluble salt formation of 1-naphthalenesulfonic acid in the sulfonation mixture with 2,3-dimethyl aniline has been patented (17). 

Manufacture. Aqueous sodium hydroxide, sodium bicarbonate, sodium carbonate, or sodium sulfite solution are treated with sulfur dioxide to produce sodium metabisulfite solution. In one operation, the mother Hquor from the previous batch is reinforced with additional sodium carbonate, which need not be totally in solution, and then is treated with sulfur dioxide (341,342). In some plants, the reaction is conducted in a series of two or more stainless steel vessels or columns in which the sulfur dioxide is passed countercurrent to the alkaH. The solution is cooled and the sodium metabisulfite is removed by centrifuging or filtration. Rapid drying, eg, in a stream-heated shelf dryer or a flash dryer, avoids excessive decomposition or oxidation to which moist sodium metabisulfite is susceptible. 

Both batch and continuous processes employ excess sulfur and operate at 85—110°C. Trace amounts of polysulftdes produce a yellow color which iadicates that all the ammonium sulfite has been consumed. Ammonium bisulfite is added to convert the last polysulfide to thiosulfate and the excess ammonia to ammonium sulfite. Concentrations of at least 70% (NH 2S2 3 obtained without evaporation. Excess sulfur is removed by filtration and color is improved with activated carbon treatment or sodium siUcate (66). Upon cooling the aqueous concentrated solution, ammonium thiosulfate crystallines. 

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