Pilot plant, necessity

The maintenance of analytical instmmentation requkes trained personnel and is a time-consuming task (39,40). An additional problem is the necessity of frequentiy checking the caUbration of the analysis instmmentation and recahbrating if requked. Stand-alone data gathering instmmentation, once common in pilot plants, has been vktuaHy replaced in all but the simplest pilot plants by a data gathering computer, usually used for process control as well. 

There are several factors that may be invoked to explain the discrepancy between predicted and measured results, but the discrepancy highlights the necessity for good pilot plant scale data to properly design these types of reactors. Obviously, the reaction does not involve simple first-order kinetics or equimolal counterdiffusion. The fact that the catalyst activity varies significantly with time on-stream and some carbon deposition is observed indicates that perhaps the coke residues within the catalyst may have effects like those to be discussed in Section 12.3.3. Consult the original article for further discussion of the nonisothermal catalyst pellet problem. 

Another concern relates to the necessity to obtain Federal or state pollution control permits for pilot plants. This requirement is further delaying the commercialization process as well as raising costs which are often charged to R D budgets. 

Pilot plant processes and manufacturing activities include formulation and process development studies, clinical supply manufacture, and technology evaluation, scale-up, and transfer. Packaging for stability and clinical studies may also occur in the pilot plant, but these activities are often performed in separate, well-defined facilities. It is beyond the scope of this article to discuss all of these areas in detail. Since pilot plant construction is often driven by the strategic necessities defined earlier, only these areas are addressed. 

At the conditions reported in this paper where the total pressure is closer to 1000 psig and the feed gas to the FDP reactor is an approximately equimolar mixture of hydrogen and methane, the total carbon conversions are closer to the fraction of carbon that instantaneously reacts and kinetic interpretation is even more difficult. Therefore the kinetic analysis is not yet complete. However for the purposes of FDP reactor simulation, a mathematical model was used that assumed all the carbon reacts at a rate dictated by Equation 1 rather than assuming a portion of this carbon reacts instantaneously. This assumption is felt to be conservative because it does not allow for the fraction of carbon that may react at a considerably faster rate than the final amount of carbon conversion which was used to evaluate the rate constant k. The temperature dependency of k used for our initial reactor simulation studies (11) has been reported (I). While the more detailed kinetic analysis may result in a modified rate equation, the results of our simulation study (11) indicate that radiant heat transfer plays a dominant role in small FDP reactors such as the one used in this study. Because the effect of radiant heat transfer from the reactor walls diminishes as the diameter of the reactor increases, temperature profiles in commercial reactors will be considerably different from those existing in our present 3-inch id FDP reactor this indicates the necessity of using larger diameter pilot plants to obtain reliable scaleup data. 

All of the reaction steps take place at moderate temperatures and pressures, the highest pressure being in the hydrogenation step, which is typically operated at 35 bar. The overall selectivity for the conversion of CO is greater than 90%, and the NO efficiency to methyl nitrite is almost 100%. This process was developed to pilot plant scale in the early 1980s and probably still represents the best option in terms of an indirect synthesis gas based route to ethylene glycol. Economic penalties are of course three stage operation and the necessity to separate synthesis gas into its pure components. 

Since the first production of low density polyethylene in a continuous pilot plant in 1937, there has been an extraordinary divergence of manufacturing processes. Despite the diversity of plants in use, they all share certain characteristics. Figure 2 outlines the key components eommon to high pressure polymerization facilities. This process scheme and all subsequent ones are, of necessity, greatly simplified. A full description of the many teehnical difficulties that must be overcome in producing polyethylene is beyond the scope of this work. 

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