Adsorption - Principles of Chemical Separations with Environmental Applications - page 192

Table 7.4 Waste reduction through process improvements using zeolites [9].
Reproduced with permission of the American Institute of Chemical Engineers.
Copyright c

1999, AIChE. All rights reserved.

Application Zeolites used Advantages

Production of
alpha-terpinyl alkyl
ethers

Beta Excellent yields in continuous reactor

Eliminates use of HCl, H 2 SO 4 , AlCl 3 ,
toluene, sulfonic acid, boron trifluoride
etherate, and acidic cation resins as
catalysts

Cumene synthesis Dealuminated

mordenite; MCM-22;
beta; Y; omega

Lower impurities
Transalkylation function
Lower benzene-to-propylene ratio
allows higher capacity, great unit
efficiency
High selectivity
Regenerable, non-hazardous,
non-corrosive

Direct oxidation of
benzene to phenol

ZSM-5 Eliminates cumene as an intermediate

Enables possible use of N 2 O as oxidant

Caprolactam (via
oxidation)

Titanium-framework-
substituted ZSM-5
(TS-1)

Dramatic reduction in number of
processing steps and waste streams
Possible further reduction by using
another zeolite in the last step of the
process

Gasoline from
methanol

ZSM-5 Produces methanol from coal, natural

gas, or biomass and then converts it into
liquid fuel
Conservation of crude oil, elimination
of many waste streams

The regenerability of an adsorbent determines the fraction of capacity, or working ca-
pacity, that is recovered for future use. In most cases, a constant decrease in working
capacity occurs after the first cycle and is maintained for up to approximately 50-
100 cycles. Eventually, however, slow aging or gradual poisoning causes the working
capacity to be reduced to the point that the adsorbent needs to be replaced.
For liquid feeds, the situation is changing. Historically, sorbents would be used for only
one cycle and then discarded. The costs of this disposal are rising very rapidly and can usu-
ally only be justified for the processing of small fluid volumes. For regeneration, as much
liquid as possible is drained from the sorbent initially. If the sorbate is volatile, the sorbent
bed can be heated for the desorption step and the sorbate recovered by condensation. A
sweep gas can be used to assist in the removal. Another possibility is to pass a second
fluid through the bed that has a high partition coefficient for the sorbate. This approach