Separation of particulates and reaction

Step 4 Define the System Boundaries. This depends on the nature of the unit process and individual unit operations. For example, some processes involve only mass flowthrough. An example is filtration. This unit operation involves only the physical separation of materials (e.g., particulates from air). Hence, we view the filtration equipment as a simple box on the process flow sheet, with one flow input (contaminated air) and two flow outputs (clean air and captured dust). This is an example of a system where no chemical reaction is involved. In contrast, if a chemical reaction is involved, then we must take into consideration the kinetics of the reaction, the stoichiometry of the reaction, and the by-products produced. An example is the combustion of coal in a boiler. On a process flow sheet, coal, water, and energy are the inputs to the box (the furnace), and the outputs are steam, ash, NOj, SOj, and CO2. 

Ion exchange (IX) is a very useful technique for the concentration, the purification and the separation of chemically similar metallic elements present in an aqueous solution. In its most popular form of application, the metal-bearing aqueous solution is passed through a bed of solid organic resin in a particulate form wherein the sorption of the metal ions on the resin takes place by ion-exchange reactions. The pregnant resin is washed free of the entrapped feed solution and then brought into contact with an eluant of suitable composition and volume so that the resin releases the metal ions back to the eluant. The ratio of the volume of the feed and that of the eluant determines the extent of concentration that can be achieved. Purification and separation are achievable if the resin is selective or specific with respect to the metal ions of interest in comparison to impurity ions. 

The first case covers for example flue-gas treatment, which requires the filtration of fly-ash and the reduction of NOx, or gasification processes, where particulates and high-boiling tars have to be removed. An example of the second case is that of combustion processes, where incomplete combustion leads to the emission of carbonaceous particulates. The most relevant topic in this category is the reduction of diesel particulate emissions ( diesel soot ) by catalytic filtration. A more exotic example is the reaction cyclone for the thermal conversion of biomass, which also combines chemical reactions and separation in one apparatus, though its separation mechanism is not filtration. 

MSC Air-Pollution-Control Systems MSCs generate flue gas that contains particulates, acid gases and trace amounts of organic and volatile metals. Particulates have traditionally been removed Dy use of cyclone separators and electrostatic precipitators. Acid gases require neutralization and removal from the gas stream. This can be accomplished by adding solutions or chemicals to the gas stream and removing the products of the chemical reaction when these materials are mixed together. Two major types of APCs are employed ... 

In this Chapter we briefly consider the production and prompt isolation of the nuclear reaction products. The thermalization of recoils and the synthesis of compounds are discussed in more detail, as is the transportation of thermalized recoils by aerosol particulates to remote equipment for chemical experiments. The separations on chromatographic principles are discussed in Chapter 4. Some basic information about detection and measurement was given in Chapter 1 when describing concrete experiments. 

Teichner and his group have used a direct method to detach the donee from the donor.They devised an apparatus in which the donor, in a bucket, is first immersed in a bed of particulate donee (to give good contact) and then drawn up by a windlass out of the bed, into a separate, isolatable reaction chamber. Thus the donor and donee can be given various treatments in a lower... 

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