Processing Principals and Details

There are two problems in the manufacture of PS removal of the heat of polymeriza tion (ca 700 kj /kg (300 Btu/lb)) of styrene polymerized and the simultaneous handling of a partially converted polymer symp with a viscosity of ca 10 mPa(=cP). The latter problem strongly aggravates the former. A wide variety of solutions to these problems have been reported for the four mechanisms described earlier, ie, free radical, anionic, cationic, and Ziegler, several processes can be used. Table 6 summarizes the processes which have been used to implement each mechanism for Hquid-phase systems. Free-radical polymerization of styrenic systems, primarily in solution, is of principal commercial interest. Details of suspension processes, which are declining in importance, are available (208,209), as are descriptions of emulsion processes (210) and summaries of the historical development of styrene polymerization processes (208,211,212). 

The safe design and operation of chemical processing equipment requires detailed attention to the hazards inherent in certain chemicals and processes. Chemical plant hazards can occur from many sources. Principal hazards arise from ... 

Apply Abstraction and Re-refine to Each Development Layer. Do this for the business model, the system context model, and the abstract and detailed layers of design, as listed in Section 13.5, Main Process Patterns. Each of the three principal layers can be approached differently. 

The markets for PVC are manifold and are summarized in Table III along with information on the fabrication techniques used and the reasons why PVC was chosen for the indicated use (other than cost). In 1981, the U.S. consumption of PVC resins amounted to 2,551,000 metric tons or approximately 5.62 billion lb. Over one-half of this amount was made up of extruded products of which pipe and conduit are the major category. A summary of the principal processing methods and 1981 consumption is shown in Table XII and is further detailed in Table III. 

Thoriuin recovery processes. Because of the many elements in the solution, their chemical similarity, and the presence of phosphoric acid, separation of thorium from this acid solution has proved to be difficult. Wylie [WS] has reviewed the numerous separatirm processes that have been developed. Figure 6.5 shows the principal steps in seven of these processes and gives references for more details. Processes 4 and 6 appear to be the most economic when thorium, rare earths, and uranium all are to be recovered. Process 4, involving separation of thorium and rare earths from phosphate and uranium by precipitation with oxalic acid, is described next. Process 6, involving separation by solvent extraction with organic amines, is described in Sec. 8.6. 

Processing is the final step that converts the compounded material into a useful plastic product. Basically, the compounded resin needs to be melted into a liquid and heated to a temperature that allows easy handling of the fluidized plastic or the melt. This melt is fed into molds or dies to force the material into required shapes and quickly cooled to obtain the product. Usually, some minor finishing is needed before the product is made available to the consumer. The different processes used and the equipment employed are determined by the type of product being manufactured. A detailed discussion of the various processing techniques available for common thermoplastics is beyond the scope of this discussion. However, the basic principals involved in common processing methods associated with high-volume products will be discussed briefly below. 

The principal advantages of this type of cyclic system with transient operating techniques are apparent in bioprocesses whose maximum productivity is in a transient region. The products of secondary metabolism (Pirt, 1974) are a typical example of this group of processes. Another group consists of processes whose optimal operation requires an optimal substrate concentration— biomass production with bakers yeast, for example (Aiba et al., 1976)—or where the process is subject to substrate inhibition. An important area of application for this is in biological waste water purification. These periodic modes of operation generally show increased productivity. More systematic and detailed study is needed in this area. 

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