Processing steps, typical

The conventional production consisted of many process steps, typical for a fine chemical process. These process steps are given in Figure 6. The selectivity of the enzyme is rather high. The downstream processing is rather laborious,... 

Once the plastic packaging is collected, it must be processed into an appropriate form for an end-use application. While the details of the processing can vary considerably with the feedstock and the application, the major process steps typically include size reduction, cleaning and sorting, often followed by extrusion and pelletizing. Baling, which is usually done to increase the bulk density of the material if it must be transported, can also be considered a processing activity. 

FIGURE 24,6 The signal processing steps typically performed to obtain a high resolution EGG are shown in panels A to D. See text for a fall description. 

Figure 7.1. Processing steps typically required to convert filjers into end-use textile products.

Process step Typical microbial species and by-products... 

Regardless of the choice of method, excited-state modeling usually requires a multistep process. The typical sequence of steps is ... 

Steam-Reforming Natural Gas. Natural gas is the single most common raw material for the manufacture of ammonia. A typical flow sheet for a high capacity single-train ammonia plant is iadicated ia Figure 12. The important process steps are feedstock purification, primary and secondary reforming, shift conversion, carbon dioxide removal, synthesis gas purification, ammonia synthesis, and recovery. 

The tert-huty hydroperoxide is then mixed with a catalyst solution to react with propylene. Some TBHP decomposes to TBA during this process step. The catalyst is typically an organometaHic that is soluble in the reaction mixture. The metal can be tungsten, vanadium, or molybdenum. Molybdenum complexes with naphthenates or carboxylates provide the best combination of selectivity and reactivity. Catalyst concentrations of 200—500 ppm in a solution of 55% TBHP and 45% TBA are typically used when water content is less than 0.5 wt %. The homogeneous metal catalyst must be removed from solution for disposal or recycle (137,157). Although heterogeneous catalysts can be employed, elution of some of the metal, particularly molybdenum, from the support surface occurs (158). References 159 and 160 discuss possible mechanisms for the catalytic epoxidation of olefins by hydroperoxides. 

RO is also used to produce ultrapure water for many laboratory uses (90) as weU as in the medical and pharmaceutical industries (91). As for the electronics industry, purity is achieved using a combination of processes. A typical hybrid process for the production of ultrapure water is shown in Figure 11. The order in which the various steps take place may vary from case to case. 

Of these, the most commonly used for air pollution control are the fixed-bed and canister units. Fixed beds are also used in solvent-recovery applications. Major process steps include adsorption, regeneration, and further treatment of the desorbed organic compounds. Typically, further treatment includes condensation and separation. 

Another approach is to use an easily oxidized substance such as acetaldehyde or methylethyl ketone, which, under the reaction conditions, forms a hydroperoxide. These will accelerate the oxidation of the second methyl group. The DMT process encompasses four major processing steps oxidation, esterification, distillation, and crystallization. Figure 10-16 shows a typical p-xylene oxidation process to produce terephthalic acid or dimethyl terephthalate. The main use of TPA and DMT is to produce polyesters for synthetic fiber and film. 

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