Page 360 - Pressure Swing Adsorption

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336 PRESSURE SWING ADSORPTION APPENDIX C 337

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C.2.20 Sircar and Co-Workers
Several patents were awarded to Sircar and his colleagues m the span of
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1977-1988 that applied to hydrogen purificat10n, 60 air separatmn, ·ZJ air
ourifi.Cation, 61 solittmg reformer off-gas to get hydrogen and carbon dioxide,
/2 and recovering hydrogen and methane from hydrodesulfunzat1on oiant ef-
fluent.62·63 The key unifying feature of these patents was: two or more sets of
parallel beds were connected sequentially, and the sets usually contarned
different adsorbents in order to 1soiatc different component~ of the feed
mixture. They were also orchestrated to ensure that each product was
obtamed With as little power mput as practical, and that each byproduct was
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fully exploited before 1t was released.

C.2.21 Jones, Keller, and Wells
The patent by Jones, Keller, and Wells, which issued m I 980,"' pushed the
limits of fast cycling close to the limits allowed by fluid mechanics and valve
~ w:6 dynamics (see Figure C.5). That IS, 1t employed feed step times of about 0.5
to 2.0 s, and eXhaust times of 0.5 to 20 s. It also systematically eXDlored the
relations between bed length, particle size, feed pressure, and adsorbent type
on product ounty and recovery. It covered several applications, including air
~,R~~Oz
separation, splitting nitrogen and ethylene, and splitting hydrogen from
3 4 methane, carbon monoxide, and carbon dioxide.
Figure C.4 Flowshcct of the kincl!cs-bascd PSA apparatus suggested by Juntgcn
et al. m 1979, which appeared in U.S. Patent No. 4,264,339 in 1981. This earnoment
was designed for splittrng nitrogen from air, usmg a carbon molecular sieve.·
20) cf'
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notice the mmor differences between this process and the one suggested by V /4
Perley.

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C.2.19 Collins
One of the less conventional patent applications was filed by Collins m 1975
for PSA oxygen separation from air. The patent, awarded m 1977 34 sheds
light on the deviations from isothermal behavior of relatively large diameter ~
beds of zeolite (e.g., 30 cm diameter or larger). It shows that exoected
recoveries often exceed those achieved m such large columns due to de- /6
pressed temperatures within the bed. Accordingly, it shows actual tempera- Figure C.5 Flowsheet of the rapid PSA process suggested by Jones et al. m 1979,
ture Profiles along the bed axis durmg the PSA cycle. The Primary contribu- which appeared in U.S. Patent No. 4,264,339 m 1981. This eautpment was designed
tion was a means for suppressing the temperature deviations by inserting for splitting oxygen from a1r, usmg a zeolite molecular sieve. ft employed smaller
particles and exploited pressure waves that propagate along the axis by coupling flow-
aluminum oiates or rods m the bed to conduct heat axially, thus reducing or
and pressure shifts in a synchronous way. Tuo relatively pure products are produced,
elimmatmg temperature gradients.
and the adsorbent oroduct1v1ty is high.