The performance of the VPSA cycles can be evaluated according to product
purity, product recovery, and adsorbent productivity which are defined as follows
[112]:
Heavy Compound Purity %
ð Þ ¼
R t blowdown
0
C heavy u 0
z¼0
dt þ
R t purge
0
C heavy u 0
z¼0
dt
P n
i¼1
R t blowdown
0
C i u 0
z¼0
dt þ
R t purge
0
C i u 0
z¼0
dt
 100
ð34Þ
Light Compound Purity %
ð Þ ¼
R t ads
0 C light u 0
z¼L
dt þ
R t CocD
0
C light u 0
z¼L
dt þ
R t rinse
0
C light u 0
z¼L
dt
P n
i¼1
R t ads
0 C i u 0
z¼L
dt
 100
ð35Þ
Heavy Compound Recovery %
ð Þ ¼
R t blowdown
0
C heavy u 0
z¼0
dt þ
R t purge
0
C heavy u 0
z¼0
dt À
R t rinse
0
C heavy u 0
z¼0
dt
R t ads
0 C heavy u 0
z¼0
dt
 100
ð36Þ
Light Compound Recovery %
ð Þ ¼
R t ads
0 C light u 0
z¼L
dt þ
R t CocD
0
C light u 0
z¼L
dt þ
R t rinse
0
C light u 0
z¼L
dt
R t ads
0 C light u 0
z¼0
dt
þ
þ
À
R t purge
0
C light u 0
z¼L
dt À
R t press
0
C light u 0
z¼L
dt
R t ads
0 C light u 0
z¼0
dt
 100
ð37Þ
Heavy Compound Productivity mol=kg adsorbent =h
ð
Þ ¼
R t blowdown
0
C heavy u 0
z¼0
dt þ
R t purge
0
C heavy u 0
z¼0
dt À
R t rinse
0
C heavy u 0
z¼0
dt
m adsorbent  t cycle
ð38Þ
Light Compound Productivity mol=kg adsorbent =h
ð
Þ ¼
R t ads
0 C light u 0
z¼L
dt þ
R t CocD
0
C light u 0
z¼L
dt þ
R t rinse
0
C light u 0
z¼L
dt
m adsorbent  t cycle
þ
þ
À
R t purge
0
C light u 0
z¼L
dt À
R t press
0
C light u 0
z¼L
dt
m adsorbent  t cycle
ð39Þ
The best VPSA cycle suggested by Narin et al. to obtain polymer-grade propylene from 0.28/0.72 propane/propylene mixture is illustrated in Fig. 8.
The cycle was designed to start with pressurization of the bed with a pure propane
stream countercurrently at a pressure above the atmospheric (P H ) that, in this case,
was 150 kPa. In the adsorption step, performed at 150 kPa (P H ), a stream rich in
propane was obtained, while the mixture containing 0.28/0.72 propane/propylene
174
V. F. D. Martins et al.