Adsorptive reactor

Fedorov, A. G., Viskanta, R., Heat and mass transfer dynamics in the micro-channel adsorption reactor. Microscale Therm. Eng. 3 (1999) 111-139. 

Another special application of adsorption in space is presented by Grover et al. (1998). The University of Washington has designed an in situ resource utilization system to provide water to the life-support system in the laboratory module of the NASA Mars Reference Mission, a piloted mission to Mars. In this system, the Water Vapor Adsorption Reactor (WAVAR) extracts water vapor from the Martian atmosphere by adsorption in a bed of type 3A zeolite molecular1 sieve. Using ambient winds and fan power to move atmosphere, the WAVAR adsorbs the water vapor until the zeolite 3A bed is nearly saturated, and then heats the bed within a sealed chamber by microwave radiation to drive off water for collection. Tire water vapor flows to a condenser where it freezes and is later liquefied for use in tire life-support system. 

Diethylacetal from ethanol and 92 Fixed-bed adsorptive reactor... 

Steam methane reforming 93 Pressure-swing adsorptive reactor (PSAR)... 

The benefits obtained by integrating adsorption into regenerative heat exchange demonstrate the synergies available between these two related processes. Similar advantages accrue when heat regeneration is incorporated into adsorptive reactors, in which concentration profiles are manipulated to improve reactor performance through selective ad- and desorption of components in the reaction medium. 

Yongsunthon I, Alpay E. Design of periodic adsorptive reactors for the optimal integration of reaction, separation and heat exchange. Chem. Eng. Sci 1999 54 2647-2657. 

Fig. 7.1. Principle of an adsorptive reactor for enhancing conversion of an equilibrium-limited reaction.

Adsorptive reactors discontinuous operation adsorption rapid Jj capacity vs. selectivity t thermal regeneration... 

Closer inspection reveals that this somewhat superficial and largely self-evident evaluation is by no means exhaustive, and concrete experimental studies on adsorptive reactors expose both additional pitfalls and benefits that are often specific for a particular reaction system and decisive for the success or otherwise of adsorptive reactor concepts. Before illustrating this point with the help of four examples with which the author is personally acquainted - the Claus reaction, the direct hydrogen cyanide synthesis from ammonia and carbon monoxide and, to a lesser extent, the water-gas shift reaction and the Deacon process - it is worthwhile briefly reviewing other reaction systems for which the potential of adsorptive reactors has been examined (Tab. 7.2). 

Table 7.2. Reaction systems studied for adsorptive reactors. The adsorbed species is underlined in the reaction equations. 

The study of adsorptive reactors for the Claus process represents a departure from most previous studies in that the equilibrium position is already well on the product side, with a conversion of 93 % being achievable for isothermal operation of gas with 10 mol% H2S without additional measures [30]. The need to attain conversions in excess of 99.5 % to ensure that the residual sulfur emissions meet environmental specifications [31] nevertheless makes the reaction system an interesting candidate for adsorptive equilibrium displacement. 

The second reaction used to illustrate various features of adsorptive reactors is the direct synthesis of hydrogen cyanide from ammonia and carbon monoxide ... 

The use of an adsorptive reactor operation with reactant enrichment, in which adsorption is used to maintain a high level of excess steam within the catalytic reaction zone, has attracted comparatively little attention. 

Fig. 7.7. Flowsheet for the production of hydrogen from methane for ammonia synthesis and fuel cell applications indicating the potential for rationalization using an adsorptive reactor.

The inherent ability of selective catalytic reduction (SCR) catalysts for stack gas denitrification to store ammonia adsorptively can be exploited with appropriate control algorithms to damp out the influence of fluctuations in the amount of gas and level of nitrogen oxides being treated. Moreover, it also forms the basis of the adsorptive reactor concept for the total denitrification of flue gases without ammonia... 

A variety of fixed- and fluidized-bed reactors configurations can be used as adsorptive reactors (Fig. 7.12). 

Fig. 7.12. Adsorptive reactor designs, a) Fixed-beds b) moving beds and c) fluidized beds.

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