Feed Separation System

Production of polypropylene from a feed of propylene and propane. Propane, which is not involved in the propylene polymerization reaction, is removed from the propylae by distillation. 

Production of acetaldehyde by the dehydrogenation of ethanol using a chromium-copper catalyst. If the feed is a dilute solution of ethanol in water, distillation is used to concentrate the ethanol to the near-azeotrope composition (89.4 mol% ethanol at 1 atm) before it enters the reactor. 

Production of formaldehyde by air-oxidation of methanol using a silver catalyst. The entering air is scrubbed with aqueous sodium hydroxide to remove any SO2 and COj which are catalyst poisons. 

Production of vinyl chloride by the gas-phase reaction of HCl and acetylene with a mercuric chloride catalyst. Small amounts of water are removed from both feed gases by adsorption to prevent corrosion of the reactor vessel and acetaldehyde formation. 

Production of phosgene by the gas-phase reaction of CO and chlorine using an activated carbon catalyst. Both feed gases are treated to remove oxygen, which poisons the catalyst sulfur compounds, which form sulfur chlorides hydrogen, which reacts with Iwth chlorine and phosgene to form HCl and water and hydrocarbons, which also form HQ. 

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As shown in Figure 7.1, the combined feed to a reactor section may consist of one or more feed streams and one or more recycle streams when conversion of reactants is incomplete. When a feed separation system is needed and more than one feed enters the process, it is usually preferable to provide separate separation operations for the individual feed streams Ik-fore mixing them with each other and with any recycle streams. Some industrial examples of chemical processes that require a feed separation system are ... 

Economy of time and resources dictate using the smallest sized faciHty possible to assure that projected larger scale performance is within tolerable levels of risk and uncertainty. Minimum sizes of such laboratory and pilot units often are set by operabiHty factors not directly involving internal reactor features. These include feed and product transfer line diameters, inventory control in feed and product separation systems, and preheat and temperature maintenance requirements. Most of these extraneous factors favor large units. Large industrial plants can be operated with high service factors for years, whereas it is not unusual for pilot units to operate at sustained conditions for only days or even hours. 

The factors which may make CCD a preferred choice over other separation systems include the following rapidly settling solids, assisted by flocculation relatively high ratio of solids concentration between underflow and feed moderately high wash ratios allowable (2 to 4 times the volume of hquor in the thickened underflows) large quantity of sohds to be processed and the presence of fine-size sohds that are difficult to concentrate by other means. A technical feasibihty and economic study is desirable in order to make the optimum choice. 

Considering that the separation system is fully characterized, i.e., adsorbent and mobile phases, column dimensions, SMB configuration and feed concentration, the optimization of the TMB operating conditions consists in setting the liquid flow rates in each section and also the solid flow rate. The resulting optimization problem with five variables will be certainly tedious and difficult to implement. Fortunately, the... 

In general, all electrostatic separator systems contain at least four components (i) a chargingdischarging mechanism (ii) an external electric field (iii) a nonelectrical particle trajectory device and (iv) feed and product collection systems. Depending primarily on the charging mechanism involved, the electrostatic separator systems are classified into three categories (i) free fall separators (ii) high tension separators and (iii) conduction separators. 

The subgroups were determined based on a hierarchical decomposition strategy for a FCCU (Ramesh et al, 1992). The FCCU was decomposed into four separate units feed.system, catalyst.system, reactor/regenera-tor.system, and separation.system as shown in Fig. 32. Each of these units was further divided into more detailed functional, structural, or behavioral... 

However, this so far assumes that the feed to the column is fixed. Even if the overall feed to the separation system is fixed, the feed to each column can be changed by changing the amount of entrainer recycled. Such a trade-off has already been seen in Figure 12.21. As the amount of entrainer recycled is increased, this helps the azeotropic separation. This allows the reflux ratio to be decreased. However, as the entrainer recycle increases, it creates an excessive load on the overall system. The amount of entrainer recycled is therefore an important degree of freedom to be optimized. 

A method to reduce degradation/deactivation of a phosphite modified rhodium hydroformylation catalyst in the separation system involves feeding a diene such as butadiene to the vaporizer to convert the phosphite-modified rhodium catalyst to a more stable form. [34] In the reactor, the diene is hydrogenated and catalyst activity is restored. 

Membrane gas-separation systems have found their first applications in the recovery of organics from process vents and effluent air [5]. More than a hundred systems have been installed in the past few years. The technique itself therefore has a solid commercial background. Membranes are assembled typically in spiral-wound modules, as shown in Fig. 7.3. Sheets of membrane interlayered with spacers are wound around a perforated central pipe. The gas mixture to be processed is fed into the annulus between the module housing and the pipe, which becomes a collector for the permeate. The spacers serve to create channels for the gas flow. The membranes separate the feed side from the permeate side. 

We need to complicate these definitions further by noting that the above definitions are the per pass yield of a reactor. If unreacted A can be recovered and recycled back into the feed, then the overall yield of the reactor plus the separation system becomes the single-pass selectivity of the reactor because no unreacted A leaves the reactor system. 

In addition to recycling reactants back into the reactor, there are several other tricks to keep reactants in the reactor and thus attain higher conversions and yields. Aunong these are formation of vapor-phase products from liquid or solid feeds and the use of membranes that pass products but retain reactants. We will discuss the integration of reactor-separation systems in Chapter 12. 

Therefore, complex processes are frequently simplified to assume (1) a single reaction in which the major reactant is converted into the major product or for a more accurate estimate (2) simple series or parallel processes in which there is a major desired and a single major undesired product. The fust approximation sets the approximate size of the reactor, while the second begins to examine different reactor types, operating conditions, feed composition, conversion, separation systems required, etc. 

It is important to highlight the interactions taking place among the three aforementioned subsystems which are also indicated in Figure 7.2. The feed streams can be directly fed to the reactor system, or they can be directed to the separation system first for feed purification and subsequently directed to the separation system where valuable components are recovered and are directed back to the reactor system via the recycle system. Note that if several reactors are employed in the reactor system (e.g., reactors 1 and 2) then alternatives of reactor 1-separator- recycle-reactor 2-separator-recycle may take place in addition to the other alternatives of reactor system-separation system-recycle system. 

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