Reaction zone, isotherms

Apparatus. The experiments were conducted in a high-pressure microreactor capable of operating up to 3000 psig. The reactor, enclosed by a three-zone heater, had an isothermal reaction zone holding up to 10... 

Mehta (34) has carried out a reactor network optimization study to find improved designs for the production of acrylonitrile in a collaboration between UMIST and one of its industrial partners. Most industrial installations employ fluidized-bed reactors (BP/Sohio process) with a well-mixed reaction zone. Previous process improvements have mainly resulted from better catalysts, which have produced an increase in yield from 58% to around 80%. The reaction model employed in the optimization study is taken from Ref. 81 and considers seven reactions and eight components. Air, pure oxygen, and propylene are available as raw material streams. The optimization study assumes negligible pressure drop along the reaction sections, isothermal and isobaric operation, and negligible mass gas-solid transfer effects. 

Figure S. Isotherms of moving reaction zones calculated with nonuniform flow.

A three-zone furnace (top to bottom are 31, 6", and 3", respectively) was used to maintain isothermal conditions along the reaction zone. Pressure was controlled by a back pressure regulator on the exit stream. A post reactor dropout trap was installed to condense the steam and hydrocarbon condensates. Downstream dry product flow rates were measured by a wet test meter. 

Operating temperatures are also critical. The listed reactions are endothermic. The best yields occur along isothermal reaction zones, but are difficult to achieve. Instead, the reaction beds are separated into a number of adiabatic zones operating at 500-1000°F with heaters between stages to supply the necessary energy to promote reaction of heat and hold the overall train near or at a constant... 

First Cycle Poisoning Dynamics. Upon attaining an isothermal temperature profile for an impurity free feed, the next phase of the experiment was begun. Thiophene was introduced into the benzene feed as the feed impurity. The thiophene also caused another problem which manifested itself as a migrating temperature depression, a result of the active zone moving towards the end of the reactor. This movement of the reaction zone decreased the heat generation at the upper section of the reactor and therefore a temperature depression resulted. A comparsion between the simulated activity profile and the temperature migration in Fig.4 illustrates the above phenomena. 

Description The CD column (1) combines reaction and fractionation in a single-unit operation. Alkylation takes place isothermally and at low temprature. CD also promotes the continuous removal of reaction products from reaction zones. These factors limit byproduct impurities and enhance product purity and yield. Low operating temperatures and pressures also decrease capital investment, improve operational safety and minimize fugitive emissions. 

Tsotsis et al. [1992] considered a case where two reaction zones exist in a porous membrane reactor one inside the membrane matrix and the other in the tubular region which is packed with catalyst particles. They presented a packed-bed catalytic membrane tubular reactor model under isothermal and co-current flow conditions. Thus, Equations (10-37), (10-6) and (10-45) ail reduce to the condition... 

Fig. 5. 17. Self-healing in the slow reaction zone above the second limit in the H2 -I- O2 system (a) large vessel, equimolar mixture (b) small vessel equimolar mixture (c) small vessel stoichiometric mixture. The numbers indicate the maximum instantaneous temperature excess observed at a given p-T location and the isotherms connect points at which the same AT is observed. (Reprinted with permission from reference [24], Royal Society...

This chapter discusses propagation of polymerization waves. In a polymerization wave, a spatially localized reaction zone, in which the polymerization reactions occur, propagates into initial reactants (the monomer) leaving the reaction product (the polymer) in its wake. Two types of polymerization waves, thermal and isothermal, have been observed experimentally, and the mechanism of wave propagation for each is markedly different. Thermal polymeriza-... 

---