Page 28 - Pressure Swing Adsorption

3
2 PRESSURE SWING ADSORPTION INTRODUCTION
ferred ootion smce a modesl change or temperature o:~duces, m gen~ral, a
q
relatively large change m the gas-solid adsorption equll1hnum constafH.
. ----;;j:l PSA processes are no more complex than most of the more c?nvcnuo~al
___ To_ds
•
\>.'{), T Swing seoaratton processes, bu1 they are d~ffcrent in o~~ essential t~a.1.ure:/~1:
nroccss operates under trnns1cnt cond1t1ons, wher~as most r,roccsscs s~c 1 ·
la] "'' ' ~
qde _ (,f;~~t,.,--' Ides ~bsorotio~. cxtractJOn, and distillation opcrntc under stcadv-stutc cond1t1on,.
' .
p
120
TOTAL PATENTS 696 /\
110 -{1975-1990) 49 9Q~ \I
JAPAN
1 100 us 277~0 !
ADSORPTION DESORPTION <f) u K 8 2.,.,o / --ALL
f-
, 0. f-
DES0A8AfE !Extract) z 90 GERMANY, B J•r ~ (21 rUNTRIES)
w
A<P ~~ 80
I\ I
,,-
lb] w i= 70 I i \ I
9 z 60
\
a c::( so I ,_f t-JAPJ:'N
--' (/l
a: o. 40 I I \ I
OJ:
,:t: 30 ) I /°'-J--U,S.A.
RAFFINATE PURE 8 (•Pl PURGE.P (inr.>~tl "-,:
0 20 __ / 1 ~u,K. i
Fii.?tirc LI The Cl)nccpt of a PSA process. (:i) Change 1n cqui/ihnum loading with / 6
0 P ..---;-GERMANY
prl:~surc. (h) ldc,dizcd sketch i-howmg nHwernc11t of the adsorbed phase conccnlration z 10 ,.-J ,,. -_1/
profile for the more strongly atisorbcd socc1cs in a sunok two-bed PSA process. 0 ,~ ,ro•',,/
1975 1980 1985 1990 1995
YEAR-
(a)
agent (although a low-pressure ourge stco 1s commonly mciuded in the cycle).
The orocess operates under approx1mateiy isothermal condit10ns so that the ?O TOT AL PUBLICATIONS: 424 (1975· 1990)
useful capacity 1s the difference m loading between two oomts, corresponding u.s.: 31.8%
60 - JAPAN: 22.4%
to the Feed and regeneration pressures, on the same isotherm [Figure 1. l(a)l. (/l GERMANY: 13.2%
z
Figure J .l(b) shows schematically the movement of the concentration profiles 0.,: 50 -LANGUAGE:
;::u, ENGLISH: 59.0%
during the high-pressure feed and low-pressure regeneration steps, The feed JAPANESE: 17 .7%
" 0 Cl 40 GERMAN: 9.9%
Q.
step 1s normally termmated before the more strongly adsorbed component ::;a: CHINESE: 3.5%
lllO
breaks through the bed, while the regeneration step 1s generally terminated ::, ,: 30 ~ POLISl-1: 2.8%
Q. >-
before the bect is fully desorbed. At cyclic steady state the profile therefore u_ w
oscillates about a mean 00s1tion in the bed. 0 ~ 20
a: :,:
A major advantage of PSA, relative to other types of adsorotton process UJ f-
~ §: 10
such as thermal swrng, 1s that the pressure can he changed much more ::,
rapidly than the temperature, thus making 1t possible to operate a PSA z
orocess on a much faster cycle, thereby increasing the throughout per u111t of
adsorbent bed volume. The major limitation 1s that PSA processes are
restricted to components that are not too strongly adsorbed. If the oreferen- Figure 1.2 The growth of PSA tcchnolog~ from I 975 to _I 99(: ;s ~ o;.n -~v l~:
iially adsorbed species is too strongly adsorbed, an uneconom1cally high 1
vacuum is requrred to effect ctesorotion during the regeneratmn step. Thus, numbers of patents and (b) numbers of publicattons. (Courtesy o r. · irca •
for very strongiy adsorbed comoonenl'.s thermal swing 1s generally the ore- Products and Chemicals, Inc.)