Sohd separations

Suspend 0 25 g. of 2 4-dinitrophenylhydrazine in 5 ml. of methanol and add 0-4 0-5 ml. of concentrated sulphuric acid cautiously. FUter the warm solution and add a solution of 0 1-0-2 g. of the carbonyl compound in a small volume of methanol or of ether. If no sohd separate within 10 minutes, dUute the solution carefuUy with 2N sulphuric acid. CoUect the solid by suction filtration and wash it with a little methanol. RecrystaUise the derivative from alcohol, dUute alcohol, alcohol with ethyl acetate or chloroform or acetone, acetic acid, dioxan, nitromethane, nitrobenzene or xylene. 

The following is an alternative method of purifying the crude aspirin. Dissolve the solid in about 30 ml. of hot alcohol and pour the solution into about 75 ml. of warm water if a sohd separates at this point, warm the mixture until solution is complete and then allow the clear solution to cool slowly. Beautiful needle-like crystals will separate. The yield is 13 g. The air-dried crude product may also be recrystallised from benzene or from ether - light petroleum (b.p. 40-60°). 

Refining Processes. AH the reduction processes yield an impure metal containing some of the minor elements present in the concentrate, eg, cadmium in 2inc, or some elements introduced during the smelting process, eg, carbon in pig iron. These impurities must be removed from the cmde metal in order to meet specifications for use. Refining operations may be classified according to the kind of phases involved in the process, ie, separation of a vapor from a Hquid or soHd, separation of a soHd from a Hquid, or transfer between two Hquid phases. In addition, they may be characterized by whether or not they involve oxidation—reduction reactions. 

P perApplications. In beater additions, the latex is mixed with the beaten paper pulp either by addition at the beater or to the stock chest at the wet end of the paper machine. In either case, the pH of the pulp is reduced to 4.0—4.5, usually by the addition of a solution of alum to the pulp—latex mixture which has been thoroughly agitated. The latex, which for this appHcation must be based on an anionic emulsifier, coagulates as the pH drops. The latex soHds separate ia intimate associatioa with the pulp fibers. The pulp is thea screeaed and the paper web formed ia the coaveatioaal way. A latex for this purpose must possess the proper balance between mechanical and chemical stabiHty. 

In sohd—sohd separation, the soHds are separated iato fractions according to size, density, shape, or other particle property (see Size reduction). Sedimentation is also used for size separation, ie, classification of soHds (see Separation, size separation). One of the simplest ways to remove the coarse or dense soHds from a feed suspension is by sedimentation. Successive decantation ia a batch system produces closely controUed size fractions of the product. Generally, however, particle classification by sedimentation does not give sharp separation (see Size MEASUREMENT OF PARTICLES). 

After precipitation is complete, the slurry is pumped to vacuum dmm filters where a nearly complete Hquid-soHds separation is accompHshed. The hquid is dilute sodium sulfide solution, which is concentrated by evaporation to a flaked 60 wt % sodium sulfide product. The filter cake is a 60 wt % strontium carbonate soHd which is fed to a carbonate dryer. After drying, the strontium carbonate product is cooled, ground, and screened for packaging. 

If the product in no way adheres to the dryer parts and simple cyclone collectors are sufficient for gas-sohds separation, batch operation of a spray dryer may be considered. Otherwise, the time and costs for cleaning the large equipment parts make them rarely economical for other than continuous processing of a single material. 

Practical separation techniques for hquid particles in gases are discussed. Since gas-borne particulates include both hquid and sohd particles, many devices used for dry-dust collection (discussed in Sec. 17 under Gas-Sohds Separation ) can be adapted to liquid-particle separation. Also, the basic subject of particle mechanics is covered in Sec. 6. Separation of liquid particulates is frequently desirable in chemical processes such as in countercurrent-stage contacting because hquid entrainment with the gas partially reduces true countercurrency. Separation before entering another process step may be needed to prevent corrosion, to prevent yield loss, or to prevent equipment damage or malfunc tion. Separation before the atmospheric release of gases may be necessaiy to prevent environmental problems and for regula-toiy compliance. 

Dust Separation It is usuaUy necessaiy to recover the solids carried by the gas leaving the disengaging space or freeboard of the fluidized becl GeneraUy, cyclones are used to remove the major portion of these sohds (see Gas-Sohds Separation ). However, in a few cases, usuaUy on small-scale units, filters are employed without the use of cyclones to reduce the loading of solids in the gas. For high-temperature usage, either porous ceramic or sintered metal has been employed. Multiple units must be provided so that one unit can be blown back with clean gas while one or more are filtering. 

As cyclones are less effec tive as the particle size decreases, secondary collection units are frequently required, i.e., filters, elec trostatic precipitators, and scrubbers. When dry collec tiou is not required, ehmiuatlou of cyclones is possible if allowance is made for heavy solids loads in the scrubber (see Gas-Sohds Separations see also Sec. 14). 

Each is discussed in Sec. 17 of this handbook under Gas-Sohds Separations. The effectiveness of conventional air-poUution-control equipment for particulate removal is compared in Fig. 25-23. These fractional efficiency cui ves indicate that the equipment is least efficient in removing particulates in the 0.1- to 1.0- Im range. For wet... 

Strongly acidify the residual sodium bicarbonate solution to Congo red with dilute sulphuric acid. If a sohd acid forms, filter. Extract the filtrate or the acidified solution with two 20 ml. portions of ether keep the aqueous solution (A). Distil off the ether, and add the residual acid (if a sohd) to the sohd separated by filtration. Identify the acid. 

Many larger installations also feature a batch still. Material to be separated may be high in sohds content, or it might contain tars or resins that would plug or foul a continuous unit. Use of a batch unit can keep sohds separated and permit convenient removal at the termination of the process. 

An example of a solid-liquid phase separation - often referred to as a mechanical separation - is filtration. Filters are also used in gas-sohd separation. Filtration may be used to recover liquid or sohd or both. Also, it can be used in waste-treatment processes. Walas [6] describes many solid-hquid separators, but we will only consider the rotary-drum filter. Reliable sizing of rotary-drum filters requires bench and pilot-scale testing with the slurry. Nevertheless, a model of the filtering process will show some of the physical factors that influence filtration and will give a preliminary estimate of the filter size in those cases where data are available. 

Whatever the mechanism and the method of operation, it is clear that the leaching process will be favored by increased surface per unit volume of solids to be leached and by decreased radial distances that must be traversed within the sohds, both of which are favored by decreased particle size. Fine solids, on the other hand, cause slow percolation rate, difficult sohds separation, and possible poor quahty of solid product. The basis for an optimum particle size is established by these characteristics. 

Temperature Most industrial wastes tend to be on the warm side. For the most part, temperature is not a critical issue below 37°C if wastewaters are to receive biological treatment. It is possible to operate thermophihc biological wastewater-treatment systems up to 65°C with acchmated microbes. Low-temperature operations in northern chmates can result in very low winter temperatures and slow reaction rates for both biological treatment systems and chemical treatment systems. Increased viscosity of wastewaters at low temperatures makes sohd separation more difficult. Efforts are generally made to keep operating temperatures between 10 and 30°C if possible. 

L.A.S. determination was carried out on the filtered water as well as on the suspended sohds separated by filtration. Extraction and concentration of L.A.S. have been done using a reverse phase resin (C-18). The... 

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