Solid/liquid separation experiments

Table 7.3 Residual moisture content as provided by different techniques of solid-liquid separation (experiences from potash manufacture) [12].

The performance of solid-liquid separation equipment is difficult to predict by the engineer without some specific experience in this area. Unfortunately, it must be again recommended that the... 

The first step is solvolysis and, as proposed by YU, we used phenol or phenol based solvents to perform the dissolution of wood, which should be complete, in order to avoid a difficult solid-liquid separation. So we carried out a lot of experiments in order to find the optimal conditions, i.e., a quantity of phenolic solvent as small as possible, low temperature and low pressure. Analysis of material balances of different runs shows that it is necessary to keep the weight solvent/wood above 4. To complete the dissolution of wood, the minimum amounts of water and phenol in the solvent mixture are respectively 20 wt % and 25 wt % (Figures l.a and l.b). In this case, the liquid phase is completed... 

Precipitation technology is not yet very advanced, and many industrial companies experience problems with small crystals that cannot be separated easily. Furthermore, for some purposes, it is necessary to produce very small crystals (e.g., pigments, paper-coating materials, and paper fillers) and, therefore, solid-liquid separation becomes inevitably difficult. In the paper industry, submicron-sized paper-coating agents may be produced in a process in connection to the paper mill so that the suspension is transported as slurry and no filtration is required. If the filtration of small crystals is needed, the problem is the need to be handled by filtration specialists. 

Expert systems in solid-liquid separation have now gone out of fashion somewhat and the pre-selection of equipment now tends to be built into much larger design software. In any case, computerized advice, although helpful to complete beginners as a first approach, is no substitute for experience and in-depth knowledge of the subject. 

Another problem related to solid-liquid separations occurs if the solubility of sorting material is exceeded in the bulk solution or at the sorbent siuface. It is crucial in experiments whenever solubilities may be exceeded. For full control of the system, it is necessary to use acidified metal ion solutions and to avoid a rapid increase of the pH values (by a highly concentrated base solution). Otherwise, the solution phase may be at least partially oversaturated or polynuclear compounds may form. If solubilities are exceeded, the solute is precipitated and might be (completely, partially, or not at all) found in the supernatant phase depending on the conditions chosen for the separation step (i.e., filter width, centrifugation speed). Distinction between adsorption and (surface) precipitation is usually not possible based on macroscopic data alone, so that the interpretation of the macroscopic data is difficult. 

Note that filter aid selection must be based on planned laboratory tests. Guidelines for selection may only be applied in the broadest sense, since there is almost an infinite number of combinations of filter media, filter aids, and suspensions that will produce varying degrees of separation. The hydrodynamics of any filtration process are highly complex filtration is essentially a multiphase system in which interaction takes place between solids from the suspension, filter aid, and filter medium, and a liquid phase. Experiments are mandatory in most operations not only in proper filter aid selection but in defining the method of application. Some general guidelines can be applied to such studies the filter aid must have the minimum hydraulic resistance and provide the desired rate of separation an insufficient amount of filter aid leads to a reduction in filtrate quality — excess amounts result in losses is filtration rate and it is necessary to account for the method of application and characteristics of filter aids. 

The vegetable soup preparation is a solid-liquid extraction. So is coffee making. You extract some component(s) of a solid directly into the solvent. You might do a solid-liquid extraction in lab as a separate experiment liquid - liquid extractions are routine. They are so common that if you are told to do an extraction or a washing, it is assumed, you will use two liquids—two INSOLUBLE liquids—and a separatory funnel. The separatory funnel, called a sep funnel by those in the know, is a special funnel that you can separate liquids in. You might look at the section on separatory funnels (later in this chapter) right now, then come back later. 

Thermal uniformity in the cold zone was found to be from 0.01 to 0.02 °C, and that in the hot zone was found to be better than + 0.5 °C vertically and + 0.1 °C horizontally. Thermal gradients near the solid-liquid interface were achieved in excess of 30 °C cm " in the crystal region and up to 20 °C cm" in the melt. The growth of crystals was performed in a sealed transparent silica ampoule, which has two rooms for As source and GaAs polycrystalline, respectively, separated by a quartz diffusion barrier. For details of the growth process the reader is referred to Ref. 43. In this experiment the As source temperature T. was systematically reduced by 2 °C at 3 h intervals from 620 °C to 614 °C. 

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