Page 270 - Pressure Swing Adsorption

I

246 PRESSURE SWING ADSORPTION PSA PROCESSES 247
(CO- • N , 0 ) diffuse mto the adsorbent much faster than methane. which 1s
2 2 2
therefore produced as the raflinate product. A high recovery (over 90%) IS
reported, with the product contammg 87-89% methane with the balance .. .. <i:
a:
CO + N • a: UJ CL
"'
2
2
w
a:
a: 0
a,
w u a: w 0 a, w, 0
w
J ~ Q. U> w w, CL. ' UJ
;l
z
w
w
CL a,
6.8 Hydrocarbon Separations E w <( w 0 0: u. .,,, a, u.
.. l 11/~
,.,
<l--2 .. ._ l
The separation of linear from branched and cyclic hydrocarbons using 5A a: ..
a:
a:
zeolite as the adsorbent is one of the earliest examples of a moiecular sieve .. Q. UJ
UJ
separation process. In the low-molecu1ar-we1ght range (up to C 10 ) a pressure w u a: w .......£... ,___«:_
a:
w
swing version of the "Isos1v" process is commonly used. The system, which 1s '-- ~ Q. "' 0 w "'"' 0 w w a,
z
w
o. I
o. I
w
J
w
.,,,
w 0 0: u. e a, u. a,
m essence a standard pressure /vacuum swing system, 1s shown schematically w <( ~ ~
o. I
m Figure 6.19. High-purity linear paraffins are produced as the desorbate a, w <( ~.,,(/' ..
o. I
a,
ctunng the evacuation step, while durmg the adsorotion steo a raffinate .. a:
a:
a: Q.
stream deoieted of normals 1s produced. The operating temperature and Q. w w
w a: 0
oressures depend on the molecular weight range, but for the C feedstock, u a: w 0 w a: 0 w w"'
6
w
U>
Q.
350° C with a pressure swmg from 20 to 0.2 atm 1s typical. 27 A somewhat ;l w z u. J e ~ w D.: l w '\'
w
.. a,
u.
w
0
0:
similar process has been developed by B.P. 32 "' <( .,,, w <
o. I
.,
a, .s-,, .. .. 1
Q. ..
a: a:
6.9 Process for Simultaneous Production of H and CO from a: w w
2 2 Q. a: 0
w
Reformer Off-Gas a: "' 0 a: u w., 0
.,
Q. Ul "' '-- UJ"' .. ! w
J
o. l
w z "' w e ~ a, w
0 0: u. w < "' .,,, u.
The crude hydrogen stream 'from a steam reformer contains significant o. I UJ <(
,rnantities of carbon dioxide, which, by appropriate design of the seoarallon a, <l--2 .. .. '
a,
.. ..
a:
a:
a: w
Q. UJ
CRUDE H, w u a: .........e.... ~
a:
a,
0
FEED "' 0 "' ~ Q. ~ 'f w ....
Ul
UJ i
;l
UJ
z
J
. COMP 0: "' w e w "' ~
u.
0
u.
..,,,
w <( ~
o. I w<
a, .. J, <l--2 ..
=..--·· .,__Ptl'\!O"'QUCT CO,
..
t
a: " !l:
Q.
w
w
w a: 0
..
p 0 w a: 0 a: w 0 w., w ..
w J '---- Ul w
w
w e ll w z u. .. ' .. ~
u. w 0 0: a,
w <( ..,,,
.. J, w <(
<l--2 .. o. I
a,
N N
<( a,
S038V S038 B
/a)
Figqr~ 6.20 (a) Simplified process flow sheet. (b) flow schedule for the Gernini-9
prcfcess for simultaneous production of H 2 and CO 2 from reformer gases. (From
Sircar 17 and Kumar et al., 34 with pern11ss10n.)