On-demand production

AH these processes faced competition from the on-demand production of isobutene through a combined process of isomerization of n-butane to isobutane... 

A second field of application may be in the on-site and on-demand production [3,8,25]. A number of chemicals, especially those which are explosive or toxic, can not be efficiently produced at present on a medium or small scale, although large-scale processes exist. A parallelization of several microreactor units could synthesize flexible amounts of chemicals and may even allow a transport of the reaction units if desired. 

In our current work, we are aiming to develop parallel systems of this nature for a variety of applications where on-demand production of high-quality nanoparticles is required. 

However, design constraints may limit our ability to exercise this strategy concerning fresh reactant makeup, An upstream process may establish the reactant feed flow sent to the plant. A downstream process may require on-demand production, which fixes the product flowrate from the plant. In these cases, the development of the control strategy becomes more complex because we must somehow adjust the setpoint of the dominant variable on the basis of the production rate that has been specified externally. We must balance production rate with what has been specified externally. This cannot be done in an open-loop sense, Feedback of information about actual internal plant conditions is required to determine the accumulation or depletion of the reactant components. This concept was nicely illustrated by the control strategy in Fig. 2.16, In that scheme we fixed externally the flow of fresh reactant A feed. Also, we used reactor residence time (via the effluent flowrate)... 

Suppose our plantwide control system requires on-demand products. As discussed in Chap. 3, the fourth step in the plant wide control design procedure is to establish where production rate is set. If the flowrate of one of the product streams leaving the column is fixed by a downstream unit or customer, the column control structure must be set up in an appropriate way. 

Step 4. Because of the objective to achieve on-demand production rate, the product stream leaving the stripper base is flow-controlled via the bottoms control valve. This is a good example of how a degree of freedom must be used to satisfy a design or business constraint. 

A plantwide control design procedure was used to develop a simple but effective regulatory control system for the Eastman process with an on-demand product control objective. With this strategy, control of production rate is essentially instantaneous. Drastic upsets and disturbances are handled by simple proportional-only overrides. 

Figure 1.8 Microfabricated silicon packed-bed reactor for phosgene on-demand production, (a) Top-view of reactor partially loaded with 60-mm activated carbon particles - the reactor channel is 20 mm long, and the image is spliced to fit the 20 mm reaction channel by omitting the long channel midsection ...

However, phosgene is clearly highly toxic (threshold limit value-TLV of 0.1 ppm), but acrolein, for example, has the same TLV and is produced in quantities of several millions worldwide. Acrolein is also produced at barbecue parties by roasting foods, without provoking health alarms. Clearly, a low TLV implies the adoption of special safety procedures and limited storage. On-demand production and other safety procedures, such as those discussed above, are the solution to minimizing the risk to a sustainable level. 

An example for the safe production of toxic materials in a microsystem was given by Ajmera et al. [40]. A micropacked-bed reactor made from silicon was used for phosgene synthesis to demonstrate the reactor s potential for safe on-site and on-demand production of a hazardous compound. 

R. C. Richter, D. Link, and H. M. Kingston, On-Demand Production of High-Purity Acids in the Analytical Laboratory, Spectroscopy, 15(1) (2000) 38. Describes preparation using a commercial sub-boiling system. 

Figure 20.13 Control structure for on-demand product flow.

On-demand production of risk-heavy compounds (to minimize... 

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