Synthesis, And Design Of Chemical Process

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Introduction Appendix B.3 of the textbook Analysis, Synthesis, and Design of Chemical Process 4th Edition summarizes a styrene synthesis process from an equilibrium, de-hydrogenation of ethylbenzene. The equilibrium leaves various amounts of impurities as well as unspent ethylbenzene which is removed by a two stage separation process. The process can be improved upon and optimized for higher product throughput and lower operational and maintenance costs. The separation system was modeled on Aspen Plus V8.6 and a cost analysis performed on CapCost 2012. Methodology Figure 1 shows the Aspen model generated for only the separation process of appendix B.3. after the reaction step. A 99.9% by mole stream of styrene is desired for profit from the separation scheme. The first step in optimization is determining the order of separations from the reactor. All the possible chemicals present in the exiting stream are ethylbenzene, styrene, benzene, ethylene, toluene, methane, hydrogen, and water. Water is introduced as superheated steam to elevate reaction temperature and is an inert, driving the equilibrium reaction to the right, favoring styrene. Hydrogen will remain a gas at 65oC and 80 kPa (Reactor exiting stream temperature and pressure after series exchangers) while all other components will be majority in the liquid-liquid phase. A simple liquid gas separator can be used to remove all of the hydrogen with little residual impurity vapors. For ease, a flash tank with no sudden
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