Process operations mixing

The process operated by ACl is outlined in Figure 7. Bales of cotton linter are opened, cooked in dilute caustic soda, and bleached with sodium hypochlorite. The resulting highly purified ceUulose is mixed with pre-precipitated basic copper sulfate in the dissolver, and 24—28% ammonium hydroxide cooled to below 20°C is added. The mixture is agitated until dissolution is complete. If necessary, air is introduced to aUow oxidative depolymerization and hence a lowering of the dope viscosity. 

Lost work, EW, is the irreversible loss in exergy that occurs because a process operates with driving forces or mixes material at different temperatures or compositions. 

Mixed liberated particles can be separated from each other by flotation if there are sufficient differences in their wettability. The flotation process operates by preparing a water suspension of a mixture of relatively fine-sized particles (smaller than 150 micrometers) and by contacting the suspension with a swarm of air bubbles of air in a suitably designed process vessel. Particles that are readily wetted by water (hydrcmhiric) tend to remain in suspension, and those particles not wetted by water (hydrophobic) tend to be attached to air bubbles, levitate (float) to the top of the process vessel, and collect in a froth layer. Thus, differences in the surface chemical properties of the solids are the basis for separation by flotation. 

In batch operations, mixing takes place until a desired composition or concentration of chemical products or solids/crystals is achieved. For continuous operation, the feed, intermediate, and exit streams will not necessarily be of the same composition, but the objective is for the end/exit stream to be of constant composition as a result of the blending, mixing, chemical reaction, solids suspension, gas dispension, or other operations of the process. Perfect mixing is rarely totally achieved, but represents the instantaneous conversion of the feed to the final bulk and exit composition (see Figure 5-26). 

This is another common processing operation, usually for chemical reactions and neutralizations or other mass transfer functions. Pilot plant or research data are.needed to accomplish a proper design or scale-up. Therefore, generalizations can only assist in alerting the designer as to what type of mixing system to expect. 

As a rule, sulfonation takes place continually in a cascade or a falling film reactor (Table 14) at about 50-70°C. The S03 is steadily diluted to a concentration of 5-10 vol % with air or an inert gas. The LAB conversion reaches a value between 92% and 98% [156,157]. Mixing of the already formed alkyl-benzenes with fresh S03 leads to undesired highly sulfonated byproducts. In order to prevent these side reactions, all processes operate concurrently. 

Undesired premature vulcanisation of a rubber compound during the processing operations of mixing, extruding or calendering. See Heat History. 

For simulating computationally the spatial and temporal evolution of both physical and chemical processes in mixing devices operated in a turbulent singlephase mode, two essentially different approaches are available the Lagrangian approach and the Eulerian technique. These will be explained briefly. 

HF A predecessor of the DHD petroleum reforming process, operated in Germany in 1939. The catalyst was a mixed Mo03/Zn0/Al203 system. 

Possible causes of uncontrolled reactions associated with heat-generating mixing or physical processing operations include abnormal events such as the following ... 

The process operates in the liquid phase by dissolving the ethylene in an inert solvent such as cyclohexane or isopentane. The metallocene catalyst is also injected to the mix. The solvent has several important functions. It keeps in solution the alpha olefins produced as well as the ethylene and catalyst. It also enhances the catalyst activity and selectivity. 

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