• TO EPICHLOROHYDRIN-BASED QUATERNARY SYSTEM

."
•
Application of Residue Curve Mapping
TO EPICHLOROHYDRIN-BASED
QUATERNARY SYSTEM
S
eparationof azeotropic mixtures is
a topic of great practical and
,'..
industrial interest. Oxygenated
v--t organic compounds like alcohols, ketones,
",.... .::}thers and organic
acids, unlike
··::jydrocarbon/petroleum
fractions make
thedistillative separation complex d~e to
the non-ideal behaviour, particularly
formation of azeotropes. Knowledge of
topological structures of VLEdiagrams is
crucial for process design and analysis of
distillation systems. It is now common
,....
knowlt'dJ;" Ihill ilZt'olrupie mixtures
exhibit distillation
boundaries
and
existence
of
multiple
azeotropes
indicate
r
: existence of multiple distillation regions.
An often-quoted example of this is the
, binary azeotrope-of ethanol-water and
i the techniques developed to obtain
! absolute alcohol from rectified spirit.
! These distillation boundaries limit the
~ reachable
product
purity
or its
/> composition by any simple or sequential
" operation of distillation
columns.
" "\ddition of an extractive agent or an
i entrainer to the azeotropic mixtures
i enables one to cross the distillation
boundaries. Application of pressure or
vacuum is also an acceptable alternative.
'
Residue curves and distillation lines are
/, described in literature with reference to
: ternary or quaternary mixturest':", An
analysis of ternary mixture, ideal or nonideal, azeotropic or non-azeotropic is
! ideally based on the residue curve maps
• (RCMs) and distillation region diagrams
(DRDs).They provide a crucial insight into
various aspects of distillative separation
in the form of practical and graphical
, visualization. They provide the designer
with a visualization of the physical and
,....
thermodynamic limits of the system
! making
it easier .Ior the designer to
I
r:
rationalize synthesis of distillation
I systems. Applications and utility of ReM
r
I have been recorded in the recent edition
i
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Heterogeneous distillution involving cpichlorohydrin. water and
methanol is quite sensitive to process conditions and compositions.
The residue curve mapping approach not only helps in delineating
the appropriate ternary and quaternary compositions but also
selects feasible terminal compositions and assign tasks/do column
St.'(llIl'ncing. thereby. meeting the sepuration ohjl'Clives.ln a novel
catalytic process for epichlorohydrin (ECH), a highly non-ideal.
four-component mixture consisting of allyl chloride, methanol,
epichlorohydrln and water is encountered. The system consists
three hina.)· clzl'ulmpt'S. two of them hdug hl'll'rugl'IIl'OtlS.
Distillation-based separation scheme and flow sheet development of
this liquid mixture is reported using the residue curve mapping
(ReM) technique, which helps in identifyinj; feasible solution" and
- -theRb~,-cil"(:wnvcllting-han:icrsand-unstablc-process
conditions.
The ReM analysis is reported based on experimentally determined
residue curves for the ternary system ECH-water-methanol
and
LLE data of the system. For the first time, applicability of ReM to
systems other than esters and ethers and to an industrially
important system is reported.
Mrudula M Joshi. Kavita SKulkam~ J 0 Bapat A RJoshi. RVNaik
or
.
.
Sr.
No.
System
BP'C
.
Azeotropic Data
BpoC Composition
(mole %)
Upper Layer Lower Layer
(wt%)
(wt%)
99.92
0.08
at 200C
0.36
99.64
at 200c
1
Allyl Chloride
Water
44.9
100:0
43.2
2
Allyl Chloride
Methanol
EpichIorohydrin
Water
44.9
64.1
116
100
39.0
74.30
-
-
88.5
74
26
6.6
93.4
at 200C
98.1
1.9
at 20°C
3
91.3
8.7
I·
Table 1: Reported binary azeotropes of the syste,"" •."I.
of Perry's
Handbook!",
Several
engineering software tools have been
developed by Aspen, Hypro and other
developers around RCMs and DRDs as
process design tools.
Strategies and policies of carrying out .
separation of non-ideal, multi-component
mixtures, circumventing the distillation
boundaries have been the central themes
of a large! number of publicationsl6-'O),
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CIIemicalbgiaeering Wodd+FEBRUARY 2005+49
Uquid .
;Temperatttre 'C
1~';.:;-~'
,?~At~
3
4
540·
6
7
. ,8;.;
9
10
.11
,<;- :12
13
14
15
.,' -.:+:
.',~'~'..
(ll·
2.52.
'.' vapor aJmpo.ltlOh
. :.~
.. (2) ..
.'
.: 17.4 . '.' 27,1;
.. 70.1·~:·:;.;~..;: .~~9.
"<'::
"
.,46.S:};'-;·
·~i3.71·;·.
'65.79
6.9~
.0.85:': ..:.. '.68.42;':':
3.23
58.85
2.18
58.84
91.98
0.85
68.9
6.3
51.2
15.8
90.55
0.82
60.0
9.5'
9.51
24.25
Table3: Experimental data of VLE for temary systl!m:Allyi'Chloride
'r
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The ALC-wakr-methanol system has
two distillation regions; Region I, marked
b-e-f is very small compared to Region II,
enclosed by e-a-c-f. Region J contains ALC
vertex as.a-s~ablc-node, azeotropic point
'e' as an unstable node and the heteroazeotropic point 'f as a saddle point. In
Region II, there is a large portion of the
homogeneous liquid mixture, where the
residue curves originating from point 'e'
distinctly move closer to methanol apex,
1', and turn back to 'c', Finally these
residue curves terminate at the water
apex, which has the highest boiling point
and hence called as a stable node. This
indicates that at total reflux or high reflux,
it is possible to obtain either 'e' as distillate
(direct split) or 'c' as bottoms (indirect
split), Due to the self-entraining property
of methanol, we intend to get neither 'e'
~--~~~2~5~~O~'5~0~~O~'7~5~~1~
Water
(b)
101
,.,::~~,<:"
~ol~~.;.X~~,
~ '.~1.26:~
,"f'! :<;90.95":':<' ·j:l.36
44
39.5
38.5
11.5
61.5
64.5
38
38
41
38
41
60.5
'. Liquld ~mposltion
. :"mole %::
/JG<(2) .
: 287'.. .' ;'49.19
88.871
·286
38.79:"
!,;.!J14:!~r
89.95 ';'."~ :/1-ili
. 75.76""
". 4..96':
91.38 ..; ~+·~i.43:,
27'i'i:.
50.0
10.29.
20.89
9J3;··
19;89
90.38
0.73
88.32'
3.32
96.21
1.57
88.14
2.Sj·.
91.25
0.08
22.59
11.21
.. ' ..(1),
•
-f .•••••
(1) -Water (2)-Methanol (3~
nor 'c' as products, We intend to collect a
mixture of methanol-water with boiling
point below 410Cand collect ECH-watermethanol, free (rom ALC, as heavies; this
can ha ve a mild heterogeneity, The nature
of the binodal curve and orientation of
the tie lines are favorable to do so,
F.ell-water-methanol
system also
exhibits two distillation regions; one
bound by 'a-dog' and another, 'a-c-g', The
distillation
boundary
is not firmly
delineated by VLE/ RCM
data, It is
influenced
by the reflux and other
operating
parameters,
For both the
regions, apex of methanol is an unstable
node and a hetero-azeotrope of ECHwater, 'g', is a saddle point. ECH is a stable
node in Region I and water is a stable node
in Region II. The residue curve and
distillation lines generated experimentally
l'OO<=__ ~
o
0-25
ALe
,--__ -,-__ -::>O
O'!SO 0,75
1-0
,
Water
(0)
,
\.
\
.
••·-~-·0ietfII_/eft~
·--..w...
.,.•...--.. ....
_·_-
••••••••
ew •••
c ••••.••
.~
•••
"' ••• 0.4 ••••• ALe
I.'
•••••••• "'Alc!"w..., Ct.
Figure 4: ReM for ternary mixture ALe-water-
MeOH.
clearly indicate existence of the separatrix
and the distinct tendency of the residue
curves to diverge towards the respective
stable nodes, Methanol, which i~ a
solvent, works as an 'anti' entrainer in this
case; as one proceeds towards the nodal
points of the residue curve, the stripping
section exhibits liquid phase immiscibility.
The phase split is quite' pronounced and
not amenable to side stream tapping.
Rationale of Design in Multicomponent Systems
Residue curves are nicknamed as
McCabe-Thiele diagrams of ternary and
azeotropic systems. The theory and
applications of residue curves are nicely
explained by Doherty and Maloner'J.
Triangular diagrams used for presenting
residue curves of ternary mixtures are also
suited to express material balance lines.
The relative stream quantities are found
by the well-known 'lever arm' rule. All
classes of material balance lines, namely,
stream mixing, stream splitting and phase
splitting can be represented along with
the RCMs. This is explained in several texts
and articles listed earlier'< •..4 and 161. Some
of the quotable facts are:
1. Liquid trajectories of a plate column
lie on the same residue curve.
2, For satisfying mass and component
balance, the stream split in a distillation
column should be collinear with feed
composition point and
R
F·
.B'·
D,
0.2, HL-l
i~
D
TIbIt 5: iIasi, com'ponentbalance ~Option 'A'.
'.-::.
The topology I RCM of ALC-watermethanol system indicate two note-.
worthy features, which influence feasible
terminal conditions of Column, C-l.
1) It is easy to get ALC-methanol mixture
as distillate from the four-component
mixture; the distillate can be of various
compositions ranging from the binary
azeotrope to methanol-rich mixture,
We choose to operate the column-with- tray composition, represented by an
RCM, close to the binary mixture
compositions.
This will ensure
distillate free from water or ECH. We
do not wish to reach the azeotropic
composition of ALC-methanol
in
the distillate.
.
2) When we try to make the reboiler
liquid of column C-l free from
methanol and 'A~C, we go through
liquid compositions on plates, which
experience severe phase split due to
ECH-water
immiscibility.
It is
impractical to try and persist with two
liquid phases because the two ends of
the line, on the ternary diagram, fall
--into1wo-dlfterent distillation regions,
generating
distinctly
different
distillation
lines. This makes the
column unstable. Logic suggests that
we should not make the heavies of
the column, C-1 depleted of methanol;
instead, we allow right 'amount of
methanol to be present in the ternary
mixture, which can make it marginally
heterogeneous.
This situation is
beneficial to process design because
the phase split is riot severe and
pressure or ?P across .the column, in
this eventuality, are in control. The
reboiler liquid is passed on to a
decanter and separated into two liquid
phases.
The
light
liquid
is
predominantly
an aqueous layer,
while the heavy liquid is an organic
one. Under certain selected operating
conditions, the two layers belong to
two different distillation regions.
The heavy organic layer is fed to one
column, C-2 and the aqueous· layer, to
another column, C-3. Both the streams are
fed to the top tray, making t!.e columns
operate as strippers. This arrangement
recognizes the fact that the-two ends of a
tie line, representing the liquid in the
decanter,
belong to two different
distillation regions and the respective
RCMs move in different dlrections.
Fortunately in this system, the distillates
•...
e-,
..,
.
,
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!
!
:
II
,
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.7 -;
;1;
i-.iT
---- -----_._-----
'tn_~'~~~~1::':>·.:::.::...:~_'_---
__
·'v.:
-""""""-"r-
-~~"-':"'_~C'"-'":'-''';'''
f.
._---_.-----------,----.s
(biEr''''
ALe
V
(f)
(e),Cf)
!IO'lC.
w.,.,
\(c)
FIg&n 11: Distillation boundaries & column mass balance for column,
..•..
'AI
.~ ,.--1
-
handbook of Chemical Engineers, 7th
Ed.McGraw-HilI pubL,1996.
6. Sticklmair J., Fair J.R. and Bravo J.L.
CEP,1989,55,63.
71 Urdanetra
R.Y.,
Bausa
J.,
Bruggemann S. and Marquardt W. I
& B C Res. 2002,41, 3849.
8. Pham H.N. and Doherty M.L. Chem.
Bng.Sc., 1990,45, 1845.
9. KnightJ.R. and Doherty M.L. I & EC
Res 1989, 28, 564.
10. Manan Z.A. and Rene B-A., I &EC Res,
2001,40, 5795.
11. Westerberg A.W. and Wahnschaff
C.M. 'Advances
in Chemical
V
·C·;' .,:;......
(9)!IO'lI.
1\(c)
W;;~
••.
(9) 8,n." Gte.trope<_"hon
tt"'Oty Ul,ulroptc Compol.l'lotIl
c-1:0ptI0n 'B'.
••,';.
Figure 12: Distillation boundaries & column massbalance for columns,
C·2 and c-3: Option 'B'.
Engineering, Academic Press PubL
1996, Volume 23, p.99.
12. Ryan P.J. and Doherty M.F. AIChE J.
1989,35, 1592.
13. Vaidya
P.S.
and
Naik
R.V.
J.Chem.Eng.Data, 2003,48, 1015.
14. Joshi Mrudula M. Thesis submitted in
partial fulfillment of M.E. Degree,
BVDU, Pune, 2004.
15. Kulkarni Kavita S. Thesis submitted
in partial fulfillment of M.E. Degree,
Shivaji University, Kolhapur, 2004.
16. Fien Gart-Jan A.F. and LiuY.A., I &
EC Res ;I.994,33, 2505.
17. WahnschafftO.M., Koehler J.W., Blass
F. and Westerberg A.W., 1& BC Res
1992,31,2345.
18. Jurgen Gmehling, jochen Menke,
Jotg, Krafczyk
and Kaifischer,
•.Azeotropic data", VCH publication,
Part I, 134, (1970).
19. Jurgen Gmehling, Jochen Menke,
Iorg, Krafczyk and Kaifischer,
"Azeotropic data", VCH publication,
Part II,
169,
(1970).
•
.
.
.
·
·_·
·H·_.
· •.
MrARJoshi and Mr RVlaik ani associated with a & PO
Division. National ChemicallaboralDfy. Puna. MrJ DBapat
Ms MnnWa MJoshi & Ms IMa SKulbmi ani associated with
the CoIege of Ef9neeIirg. BharaIi'lldyapeeth. Pune.
- - -.- ...---~--_ .. -- - -
.....
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and the project will be included in Foster
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Foster ,Wm.-cler will be responsible for
detaile~ ~ngineering, equipment and
Ir
I
"....
r
rr:
r-
II
.i
.
material supply, and construction, up to
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