Reactor design, distillate processing

Figure 7-4. The Scientific Design Co. process for producing ethylene glycols from ethylene oxide (1) feed tank, (2) reactor, (3,4,5) multiple stage evaporators, 4 operates at lower pressure than 3, while 5 operates under vacuum, evaporated water is recycled to feed tank, (6) light ends stripper, (7,8) vacuum distillation columns.

The transfer hydrogenation methods described above are sufficient to carry out laboratory-scale studies, but it is unlikely that a direct scale-up of these processes would result in identical yields and selectivities. This is because the reaction mixtures are biphasic liquid, gas. The gas which is distilled off is acetone from the IPA system, and carbon dioxide from the TEAF system. The rate of gas disengagement is related to the superficial surface area. As the process is scaled-up, or the height of the liquid increases, the ratio of surface area to volume decreases. In order to improve de-gassing, parameters such as stirring rates, reactor design and temperature are important, and these will be discussed along with other factors found important in process scale-up. 

By comparison, the catalyzed transesterification reaction between ethylene carbonate and methanol (Equation 7.3) offers an alternative for greening DMC production. In this Asahi Kasei process [27], the preferred catalyst is based on an anion-exchange resin operating under catalytic distillation conditions between 333-353 K. This reactor design shifts the thermodynamic equilibrium towards complete conversion of ethylene carbonate, such that both the yield and selectivity for DMC and monoethylene glycol are 99.5%. The process is capable of supplying monoethylene glycol to the market, and DMC for captive use to produce DPC. 

MRH process a hydrocracking process to upgrade heavy feedstocks containing large amounts of metals and asphaltene, such as vacuum residua and bitumen, and to produce mainly middle distillates using a reactor designed to maintain a mixed three-phase slurry of feedstock, fine powder catalyst and hydrogen, and to promote effective contact. 

Today, there is an increasing interest in the theoretical study and the practical application of integrated reactive separation processes such as reactive distillation columns [1-3] or membrane-assisted reactors [37]. However, to date there is no general method available for designing such processes. For practical applications, it is important to be able to evaluate quickly whether a certain reactive separation process is a suitable candidate to reach certain targets. Therefore, feasibility analysis tools being based on minimal thermodynamic and kinetic information of the considered system are valuable. 

Since the reactor feed may contain inert species (e.g., nitrogen and solvents) and since there may be unconverted feed and by-products in the reactor effluent, a number of unit operations (distillation, filtration, etc.) may be required to produce the desired product(s). In practice, the flow of mass and energy through the process is captured by a process flow sheet. The flow sheet may require recycle (of unconverted feed, solvents, etc.) and purging that may affect reaction chemistry. Reactor design and operation influence the process and vice versa. 

The section titled Production Systems concentrates more on in-process environmental protection (e.g. improved reactor design, the use of dry-running vacuum pumps, and optimising distillation arrangements to improve energy efficiency). 

Naturally, the type of controller plays an important role. In this chapter we limit the analysis to classical PID controllers. These form over 90% of the control loops in industry. As mentioned, from a plantwide control viewpoint multi-SISO controllers are the most adapted. Naturally, we do not exclude more sophisticated MIMO control systems, as DMC or Model Based Control systems, but these are typically applied to stand-alone complex units, as FCC reactors, complex distillation units in refining, etc. Hence, the controllability analysis presented here aims more to get a conceptual insight in the dynamics of a process related to its design than to offer a high-performance control solution. 

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