U.S. patent application number 11/036051 was filed with the patent office on 2006-07-20 for process for the epoxidation of an olefin with improved energy balance.
This patent application is currently assigned to BASF Aktiengesellschaft. Invention is credited to Hans-Georg Gobbel, Renate Patrascu, Henning Schultz, Peter Schultz, Malte Schulz, Meinolf Weidenbach.
Application Number | 20060161010 11/036051 |
Document ID | / |
Family ID | 36216999 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060161010 |
Kind Code |
A1 |
Gobbel; Hans-Georg ; et
al. |
July 20, 2006 |
Process for the epoxidation of an olefin with improved energy
balance
Abstract
The invention relates to a process for the epoxidation of an
olefin comprising (a) reacting the olefin with hydrogen peroxide in
the presence of methanol as solvent in at least two reaction stages
to obtain a mixture (M-a) comprising olefin oxide, unreacted
olefin, methanol and water, wherein between at least two reaction
stages, olefin oxide is separated by distillation; (b) separating
unreacted olefin from the mixture (M-a) by distillation to obtain a
mixture (M-bi) comprising at least 80 wt.-% of olefin and a mixture
(M-bii) comprising methanol, water and at least 7 wt.-% of olefin
oxide; (c) separating olefin oxide from the mixture (M-bii) in at
least one distillation stage to obtain a mixture (M-ci) comprising
at least 99 wt.-% of oletin oxide and a mixture (M-cii) comprising
water and at least 55 wt.-% of methanol; (d) separating methanol
from the mixture (M-cii) in at least one distillation stage to
obtain a mixture (M-di) comprising at least 85 wt.-% of methanol
and up to 10 wt.-% of water, and a mixture (M-dii) comprising at
least 90 wt.-% of water; wherein a vapor top stream (Td) obtained
from at least one distillation column used in (d), said vapor top
stream (Td) comprising at least 85 wt.-% methanol, is used to
operate at least partially at least one vaporizer used in at least
one distillation column used in at least one of stages (a), (b) and
(c).
Inventors: |
Gobbel; Hans-Georg;
(Kallstadt, DE) ; Schultz; Henning; (Mannheim,
DE) ; Schultz; Peter; (Bad Durkheim, DE) ;
Patrascu; Renate; (Stade, DE) ; Schulz; Malte;
(Hollern-Tw., DE) ; Weidenbach; Meinolf;
(Drochtersen, DE) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
BASF Aktiengesellschaft
Ludwigshafen
MI
The Dow Chemical Company
Midland
|
Family ID: |
36216999 |
Appl. No.: |
11/036051 |
Filed: |
January 18, 2005 |
Current U.S.
Class: |
549/531 |
Current CPC
Class: |
C07D 301/12 20130101;
Y02P 20/582 20151101 |
Class at
Publication: |
549/531 |
International
Class: |
C07D 301/12 20060101
C07D301/12 |
Claims
1. A process for the epoxidation of an olefin comprising (a)
reacting the olefin with hydrogen peroxide in the presence of
methanol as solvent in at least two reaction stages to obtain a
mixture (M-a) comprising olefin oxide, unreacted olefin, methanol
and water, wherein between at least two reaction stages, olefin
oxide is separated by distillation: (b) separating unreacted olefin
from the mixture (M-a) by distillation to obtain a mixture (M-bi)
comprising at least 80 wt.-% of olefin and a mixture (M-bii)
comprising methanol, water and at least 7 wt.-% of olefin oxide;
(c) separating olefin oxide from the mixture (M-bii) in at least
one distillation stage to obtain a mixture (M-ci) comprising at
least 99 wt.-% of olefin oxide and a mixture (M-cii) comprising
water and at least 55 wt.-% of methanol; (d) separating methanol
from the mixture (M-cii) in at least one distillation stage to
obtain a mixture (M-di) comprising at least 85 wt.-% of methanol
and up to 10 wt.-% of water, and a mixture (M-dii) comprising at
least 90 wt.-% of water; wherein a vapor top stream (Td) obtained
from at least one distillation column used in (d), said vapor top
stream (Td) comprising at least 85 wt.-% methanol, is used to
operate at least partially at least one vaporizer used in at least
one distillation column used in at least one of stages (a), (b) and
(c).
2. The process as claimed in claim 1, wherein from 5 to 60 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(a), from 1 to 20 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), and from 1 to 50 wt.-% of (Td)
are used to operate at least partially a vaporizer used in (c).
3. The process as claimed in claim 1, wherein the olefin is propene
and the olefin oxide is propylene oxide.
4. The process as claimed in claim 3, wherein in (a), the mixture
(M-a) additionally comprises propane, wherein in (b), unreacted
propene is separated from the mixture (M-a) by distillation to
obtain the mixture (M-bi) comprising the unreacted propene and
propane, said process additionally comprising (x) separating the
propene from the mixture (M-bi) by distillation to obtain a mixture
(M-x) comprising at least 90 wt.-% of propene, and wherein the
vapor top stream (Td) is used to operate at least partially at
least one vaporizer used in at least one distillation column used
in at least one of stages (a), (b), (c) and (x).
5. The process as claimed in claim 4, wherein from 5 to 60 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(a), from 1 to 20 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 1 to 50 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (c), and
from 1 to 20 wt.-% of (Td) are used to operate at least partially a
vaporizer used in (x).
6. The process as claimed in claim 3, wherein in (c), the mixture
(M-cii) additionally comprises at least one compound having a
boiling temperature lower than methanol and lower than water at a
given pressure, said process comprising (y) separating the at least
one compound having a boiling point lower than methanol and lower
than water from the mixture (M-cii) by distillation to obtain a
mixture (M-y) comprising from 40 to 80 wt.-% of methanol and from
10 to 55 wt.-% of water; (d) separating methanol from the mixture
(M-y) in at least one distillation stage to obtain a mixture (M-di)
comprising at least 85 wt.-% of methanol and up to 10 wt.-% of
water, and a mixture (M-dii) comprising at least 90 wt.-% of water,
and wherein the vapor top stream (Td) is used to operate at least
partially at least one vaporizer used in at least one distillation
column used in at least one of stages (a), (b), (c) and (y).
7. The process as claimed in claim 6, wherein from 5 to 60 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(a), from 1 to 20 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 1 to 50 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (c), and
from 5 to 60 wt.-% of (Td) are used to operate at least partially a
vaporizer used in (y).
8. The process as claimed in claim 3, wherein in (c), the mixture
(M-cii) additionally comprises at least one compound having a
boiling temperature lower than methanol and lower than water at a
given pressure, said process comprising (d) separating methanol
from the mixture (M-cii) in at least one distillation stage to
obtain a mixture (M-di) comprising at least 85 wt.-% of methanol,
up to 10 wt.-% of water and the at least one compound having a
boiling temperature lower than methanol and lower than water, and a
mixture (M-dii) comprising at least 90 wt.-% of water, (z)
separating the compound having a boiling point lower than methanol
and lower than water from the mixture (M-di) by distillation to
obtain a mixture (M-z) comprising from 85 to 99.5 wt.-% of methanol
and from 0.5 to 10 wt.-% of water; and wherein the vapor top stream
(Td) is used to operate at least partially at least one vaporizer
used in at least one distillation column used in at least one of
steps (a), (b), (c) and (z).
9. The process as claimed in claim 8 wherein from 5 to 60 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(a), from 1 to 20 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 1 to 50 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (c), and
from 5 to 60 wt.-% of (Td) are used to operate at least partially a
vaporizer used in (z).
10. The process as claimed in claim 1, wherein in (c), the olefin
oxide is separated in two distillation columns, and wherein from 0
to 20 wt.-% of (Td) is used to at least partially operate a
vaporizer of the first distillation column from which a mixture
comprising at least 98 wt.-% of olefin oxide is obtained, said
mixture being introduced into the second distillation column, and
from 1 to 30 wt.-%. of (Td) are used to at least partially operate
a vaporizer of the second distillation column from which an olefin
oxide stream comprising at least 99.8 wt.-% olefin oxide is
obtained.
11. The process as claimed in claim 1, additionally comprising (e)
evaporating the mixture (M-dii).
12. The process as claimed in claim 11, wherein from 5 to 60 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(a), from 1 to 20 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 1 to 50 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (c), and
from 1 to 50 wt.-% of (Td) are used to operate at least partially a
vaporizer used in (e).
13. The process as claimed in claim 1, wherein from 1 to 50 wt.-%
of (Td) are used to at least partially operate at least one control
heat exchanger used in the process.
14. The process as claimed in claim 1, wherein the feed of at least
one distillation column used in stages (a), (b), (c), and (d) is
heated with the bottom stream of this distillation column.
15. The process as claimed in claim 1, wherein the top stream
obtained from at least one distillation column used in stages (a),
(b), and (c) is condensed in two stages, wherein in the first
stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
16. The process as claimed in claim 15, wherein in (c), the olefin
oxide is separated in two distillation columns, and wherein from 0
to 20 wt.-% of (Td) are used to at least partially operate a
vaporizer of the first distillation column from which a mixture
comprising at least 98 wt.-% of olefin oxide is obtained, said
mixture being introduced into the second distillation column, and
from 1 to 30 wt.-% of (Td) are used to at least partially operate a
vaporizer of the second distillation column from which an olefin
oxide stream comprising at least 99.8 wt.-% olefin oxide is
obtained, said olefin oxide stream comprising at least 99.8 wt.-%
olefin oxide being condensed in two stages, wherein in the first
stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
17. The process as claimed in claim 1, wherein in (d), methanol is
separated from the mixture (M-cii) in a two pressure distillation
process, where in a first distillation column, distillation is
carried out at a top pressure which is different from the top
pressure of a second distillation column and wherein the condenser
used to condense the top stream of the first or second distillation
column is used simultaneously as the vaporizer of the second or
first distillation column.
18. The process as claimed in claim 17, wherein the top pressure of
the first distillation column is from 2 to 8 bar and the top
pressure of the second distillation column is from 8 to 15 bar.
19. The process as claimed in claim 1, wherein in (d), (i) the
mixture (M-cii) is introduced into a first distillation column (K1)
from which the vapor top stream (Td) is obtained, the distillation
in (K1) being carried out at a top pressure of from 2.5 to 6 bar;
and (ii) the bottoms stream obtained from (K1) is introduced into a
second distillation column (K2), the distillation in (K2) being
carried out at a top pressure of from 9 to 13 bar, wherein prior to
introducing into (K2), the bottoms stream obtained from (K1) is
heated to a temperature from 110 to 180.degree. C. with the bottoms
stream obtained from (K2), and wherein the condenser used to
condense the top stream obtained from (K2) is simultaneously used
as vaporizer of (K1).
20. The process as claimed in claim 19, wherein (K2) is a dividing
wall column.
21. The process as claimed in claim 1, wherein the olefin separated
in (c) is reintroduced into (a).
22. The process as claimed in claim 1, wherein the methanol
separated in (d) is reintroduced into (a).
23. A process for the epoxidation of propene, comprising (a)
reacting the propene with hydrogen peroxide in the presence of
methanol as solvent in at least two reaction stages to obtain a
mixture (M-a) comprising propylene oxide, unreacted propene,
propane, methanol and water, wherein between at least two reaction
stages, propylene oxide is separated by distillation; (b)
separating unreacted propene from the mixture (M-a) by distillation
to obtain a mixture (M-bi) comprising propane and at least 80 wt.-%
of propene, and a mixture (M-bii) comprising methanol, water and at
least 7 wt.-% of propylene oxide; (x) separating propene from the
mixture (M-bi) by distillation to obtain a mixture (M-x) comprising
at least 95 wt.-% of propene, and re-introducing (M-x) into (a);
(c) separating the propylene oxide from the mixture (M-bii) in at
least one distillation stage to obtain a mixture (M-ci) comprising
at least 99 wt.-% of propylene oxide and a mixture (M-cii)
comprising water, at least one compound having a boiling
temperature lower than methanol and lower than water at a given
pressure, and at least 60 wt.-% of methanol; (y) separating the at
least one compound having a boiling point lower than methanol and
lower than water from the mixture (M-cii) by distillation to obtain
a mixture (M-y) comprising from 40 to 80 wt.-% of methanol and from
10 to 55 wt.-% of water; (d) separating methanol from the mixture
(M-y) in at least one distillation stage to obtain a mixture (M-di)
comprising at least 85 wt.-% of methanol and up to 10 wt.-% of
water, and a mixture (M-dii) comprising at least 90 wt.-% of water,
and re-introducing (M-di) into (a); (e) evaporating the mixture
(M-dii), wherein a vapor top stream (Td) obtained from at least one
distillation column used in (d), said vapor top stream (Td)
comprising at least 85 wt.-% methanol, and wherein from 15 to 50
wt.-% of (Td) are used to operate at least partially a vaporizer
used in (a), from 2 to 15 wt.-% of (Td) are used to operate at
least partially a vaporizer used in (b), from 1 to 10 wt.-% of (Td)
are used to operate at least partially a vaporizer used in (x),
from 1 to 40 wt.-% of (Td) are used to operate at least partially a
vaporizer used in (c), from 15 to 50 wt.-% of (Td) are used to
operate at least partially a vaporizer used in (y), and from 10 to
40 wt.-% of (Td) are used to operate at least partially a vaporizer
used in (e).
24. The process as claimed in claim 23, wherein in (c), the
propylene oxide is separated in two distillation columns, and
wherein from 0 to 20 wt.-% of (Tf) is used to at least partially
operate a vaporizer of the first distillation column from which a
mixture comprising at least 98 wt.-% of propylene oxide is
obtained, said mixture being introduced into the second
distillation column, and from 1 to 30 wt.-% of (Tf) are used to at
least partially operate a vaporizer of the second distillation
column from which an propylene oxide stream comprising at least
99.8 wt.-% propylene oxide is obtained.
25. The process as claimed in claim 23, additionally comprising at
least one further integration method selected from the group
consisting of (I) using 1 to 40 wt.-% of (Td) to at least partially
operate at least one control heat exchanger used in the process;
(II) heating the feed of at least one distillation column used in
stages (a), (b), (x), (c), (y), (d) and (e) with the bottom stream
of this distillation column; and (III) condensing the top stream
obtained from at least one distillation column used in stages (a),
(b), (x), (c), (y), and (e) in two stages, wherein in the first
stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
26. The process as claimed in claim 23, wherein in (d), (i) the
mixture (M-y) is introduced into a first distillation column (K1)
from which the vapor top stream (Td) is obtained, the distillation
in (K1) being carried out at a top pressure of from 2.5 to 6 bar;
and (ii) the bottoms stream obtained from (K1) is introduced into a
second distillation column (K2), the distillation in (K2) being
carried out at a top pressure of from 9 to 13 bar, wherein prior to
introducing into (K2), then bottoms stream obtained from (K1) is
heated to a temperature from 120 to 180.degree. C. with the bottoms
stream obtained from (K2), and wherein the condenser used to
condense the top stream obtained from (K2) is simultaneously used
as vaporizer of (K1).
27. The process as claimed in claim 26, wherein (K2) is a dividing
wall column.
28. A process for the epoxidation of propene, comprising (a)
reacting the propene with hydrogen peroxide in the presence of
methanol as solvent in at least two reaction stages to obtain a
mixture (M-a) comprising propylene oxide, unreacted propene,
propane, methanol and water, wherein between at least two reaction
stages, propylene oxide is separated by distillation in a divided
wall column, wherein separated methanol is recycled into (a); (b)
separating unreacted propene from the mixture (M-a) by distillation
to obtain a mixture (M-bi) comprising propane and at least 80 wt.-%
of propene, and a mixture (M-bii) comprising methanol, water and at
least 7 wt.-% of propylene oxide; (x) separating propene from the
mixture (M-bi) by distillation to obtain a mixture (M-x) comprising
at least 95 wt.-% of propene, and re-introducing (M-x) into (a);
(c) separating the propylene oxide from the mixture (M-bii) in two
distillation columns, wherein from the first distillation column, a
first mixture comprising at least 99 wt.-% of propylene oxide and a
mixture (M-cii) comprising water, at least one compound having a
boiling temperature lower than methanol and lower than water at a
given pressure, and at least 60 wt.-% of methanol, are obtained,
said first mixture being introduced into the second distillation
column from which a mixture (M-ci) comprising at least 99.8 wt.-%
propylene oxide is obtained; (y) separating the at least one
compound having a boiling point lower than methanol and lower than
water from the mixture (M-cii) by distillation to obtain a mixture
(M-y) comprising from 40 to 80 wt.-% of methanol and from 10 to 65
wt.-% of water; (d) separating methanol from the mixture (M-y)
wherein (i) the mixture (M-y) is introduced into a first
distillation column (K1) from which the vapor top stream (Td) is
obtained, the distillation in (K1) being carried out at a top
pressure of from 2.5 to 6 bar; and (ii) the bottoms stream obtained
from (K1) is introduced into a second distillation column (K2), the
distillation in (K2) being carried out at a top pressure of from 9
to 13 bar, (K2) being a dividing wall column, and wherein, prior to
introducing into (K2), the bottoms stream obtained from (K1) is
heated to a temperature from 130 to 175.degree. C. with the bottoms
stream obtained from (K2), and wherein the condenser used to
condense the top stream obtained from (K2) is simultaneously used
as vaporizer of (K1), and wherein (Td) and the top stream obtained
from (K2) are reintroduced into (a); (e) evaporating the mixture
(M-dii), wherein a vapor top stream (Td) obtained from at least one
distillation column used in (d), said vapor top stream (Td)
comprising at least 85 wt.-% methanol, is used to operate at least
partially at least one vaporizer used in at least one-distillation
column used in at least one of stages (a), (b), (c), (e), (x) and
(y).
29. The process as claimed in claim 28, wherein from 15 to 50 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(a), from 2 to 15 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 2 to 10 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (x), from 0
to 156 wt.-% of (Td) are used to operate at least partially a
vaporizer used in the first distillation column in (c), from 1 to
25 wt.-% of (Td) are used to operate at least partially a vaporizer
used in the second distillation column in (c), from 15 to 50 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(y), and from 10 to 40 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (e).
30. The process as claimed in claim 29, additionally comprising at
least one further integration method selected from the group
consisting of (I) using 1 to 40 wt.-% of (Td) to at least partially
operate at least one control heat exchanger used in the process;
(II) heating the feed of at least one distillation column used in
stages (a), (b), (x), (c), (y), (d) and (e) with the bottom stream
of this distillation column; and (III) condensing the top stream
obtained from at least one distillation column used in stages (a),
(b), (x), (c), (y), and (e) in two stages, wherein in the first
stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
31. A process for the epoxidation of propene, comprising (a)
reacting the propene with hydrogen peroxide in the presence of
methanol as solvent in at least two reaction stages to obtain a
mixture (M-a) comprising propylene oxide, unreacted propene,
propane, methanol and water, wherein between at least two reaction
stages, propylene oxide is separated by distillation; (b)
separating unreacted propene from the mixture (M-a) by distillation
to obtain a mixture (M-bi) comprising propane and at least 80 wt.-%
of propene, and a mixture (M-bii) comprising methanol, water and at
least 7 wt.-% of propylene oxide; (x) separating propene from the
mixture (M-bi) by distillation to obtain a mixture (M-x) comprising
at least 95 wt.-% of propene, and re-introducing (M-x) into (a);
(c) separating the propylene oxide from the mixture (M-bii) in two
distillation columns, wherein from the first distillation column, a
first mixture comprising at least 99 wt.-% of propylene oxide and a
mixture (M-cii) comprising water, at least one compound having a
boiling temperature lower than methanol and lower than water at a
given pressure and at least 60 wt.-% of methanol, are obtained,
said first mixture being introduced into the second distillation
column from which a mixture (M-ci) comprising at least 99.8 wt.-%
propylene oxide is obtained; (y) separating the at least one
compound having a boiling point lower than methanol and lower than
water from the mixture (M-cii) by distillation to obtain a mixture
(M-y) comprising from 40 to 80 wt.-% of methanol and from 10 to 55
wt.-% of water; (d) separating methanol from the mixture (M-y)
wherein (i) the mixture (M-y) is introduced into a first
distillation column (K1) from which the vapor top stream (Td) is
obtained, the distillation in (K1) being carried out at a top
pressure of from 2.5 to 6 bar; and (ii) the bottoms stream obtained
from (K1) is introduced into a second distillation column (K2), the
distillation in (K2) being carried out at a top pressure of from 9
to 13 bar, (K2) being a dividing wall column, and wherein, prior to
introducing into (K2), the bottoms stream obtained from (K1) is
heated to a temperature from 140 to 170.degree. C. with the bottoms
stream obtained from (K2), and wherein the condenser used to
condense the top stream obtained from (K2) is simultaneously used
as vaporizer of (K1), and wherein (Td) and the top stream obtained
from (K2) are reintroduced into (a); (e) evaporating the mixture
(M-dii), wherein a vapor top stream (Td) obtained from at least one
distillation column used in (d), said vapor top stream (Td)
comprising at least 85 wt.-% methanol, wherein from 20 to 40 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(a), from 3 to 10 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 3 to 10 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (x), from 0
to 10 wt.-% of (Td) are used to operate at least partially a
vaporizer used in the first distillation column in (c), from 2 to
20 wt.-% of (Td) are used to operate at least partially a vaporizer
used in the second distillation column in (c), from 20 to 40 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(y), from 15 to 35 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (e), and from 3 to 30 wt.-% of (Td)
are used to at least partially operate at least one control heat
exchanger used in the process, said process further comprising at
least one further integration method selected from the group
consisting of (II) heating the feed of the distillation column used
in stage (a) with the bottoms stream of this column and the feed of
at least one distillation column used in stage (d) with the bottoms
stream of this column; (III) condensing the top stream obtained
from at least one distillation column used in stages (a), (b), (x),
(c), (y), and (e) in two stages, wherein in the first stage, the
condenser is cooled with water having an inlet temperature of from
15 to 40.degree. C. and in the second stage, the condenser is
cooled with water having an inlet temperature of from 5 to
20.degree. C., wherein the inlet temperature of the water used in
the second stage is lower than the inlet temperature of the water
used in the first stage.
Description
BACKGROUND OF THE INVENTION
[0001] Among publications on the subject of the preparation of
propylene oxide, there are only a few which are concerned with
energy integration aspects.
[0002] EP 1 293 505 A1 describes a process for the epoxidation of
olefins wherein a product stream from the epoxidation reaction
which contains olefin, olefin oxide, water-miscible organic
solvent, hydrogen peroxide and water, is separated into an overhead
product containing olefin, olefin oxide and organic solvent, and
into a bottom product containing organic solvent, hydrogen peroxide
and water, whereby 20 to 60% of the total amount of organic solvent
is removed with the overhead product, and wherein a pre-evaporator
with less than 10 theoretical separation stages is used, the
separation being carried out at a pressure of 1.5 to less than 3
bar. As the only vague hint to an energy integration aspect, it is
stated that there is a possibility to use an integrated heat
management in order to improve energy efficiency. In this context,
it is disclosed that said pre-evaporator and an optionally present
stripper can be heated with the condensation heat of vapors
resulting from subsequent distillation stages. In case methanol is
used as solvent, a methanol head product having a higher
temperature than the bottom temperature of said pre-evaporator and
said stripper can be used the heat the pre-evaporator and the
stripper. Thus, EP 1 293 505 A1 restricts the heat management to a
very specific process in which a pre-evaporator and a stripper are
used as apparatuses in an epoxidation process.
[0003] WO 02114298 A1 describes a continuous process for the
preparation of an olefinic oxide by direct oxidation of an olefin
with hydrogen peroxide. Among other stages, this process comprises
feeding a reaction product comprising unreacted hydrogen peroxide,
epoxidation reaction by-products, water and reaction solvent into a
decomposition zone to decompose hydrogen peroxide. For this
purpose, an aqueous basic solution is additionally fed into the
decomposition zone. According to a preferred embodiment, a
suspension catalyst is used as epoxidation catalyst, In the context
of WO 02/14298 A1, it is disclosed that the condensation heat
recovered at the top of a specific distillation zone is used to
serve at least some of the boiling needs of the process, Into this
distillation zone, two streams are fed, one of which is a liquid
phase comprising reaction by-products, water and solvent, the other
being obtained from a condensation zone and comprising solvent. As
to the stages of the overall process and to any specifics about the
amounts the condensation heat is used, WO 02/14298 A1 is
silent.
[0004] U.S. Pat. No. 6,756,503 B2 relates to a process for
producing propylene oxide which comprises reacting propene with
hydrogen peroxide in the presence of methanol thus obtaining a
mixture comprising propylene oxide, methanol, water and unreacted
hydrogen peroxide, separating therefrom a mixture comprising
methanol, water and hydrogen peroxide, and separating therefrom
water thus obtaining a mixture comprising methanol and methyl
formate. It is disclosed that, in case heat recovery is to be
realized, two or more distillation columns are preferred. As to any
specifics about heat recovery, this document is silent.
[0005] WO 2004/074268 A1 discloses a process for the production of
an organic compound having at least one C--C double bond with
hydrogen peroxide in the presence of at least one catalytically
active substance and methanol wherein water is separated from a
product stream comprising methanol and water and a resulting
product stream comprising methanol and at least 3 wt.-% of water is
recycled into process. It is disclosed that a top stream from a
distillation column can be used to directly heat up an evaporator
in the epoxidation process or in a different process. In the
context of WO 2004/074268 A1, it is described that two distillation
columns can be used to separate water from above-mentioned mixture
wherein the top fractions of both columns are combined to give a
product stream having a water content of at least 3 wt.-%. As to
any specifics about the stage or the stages said evaporator is used
for, this document is silent.
[0006] US 2003/146080 A1 describes a process for the production of
propylene oxide in the presence of methanol in which propylene
oxide is separated from a mixture comprising propylene oxide and
methanol, and in which the resulting mixture is worked up wherein
methanol is separated from a mixture comprising methanol and methyl
formate. It is disclosed that from a mixture comprising methanol
and water, water can be separated wherein two distillation columns
can be used. It is explicitly described that other process streams
can be heated up with the condensation heat obtained at the top of
these columns by cooling the condenser of at least one of said
columns with water and using the hot water or the steam resulting
from cooling.
[0007] WO 2004/009572 A1 describes a process for the continuous
distillation of a solvent used for the synthesis of an oxirane in
which a mixture comprising solvent and resulting from synthesis and
subsequent work up is separated in a dividing wall column, wherein
the solvent is taken as medium boiling fraction from the side of
the dividing wall column. The dividing wall column can be
configured as thermally coupled columns which are spatially
separated from each other.
[0008] WO 2004/009566 A1 discloses a process for the continuously
operated distillation of methanol which is used as solvent in a
process for producing propylene oxide. It is disclosed that a
solvent mixture is separated in a dividing wall column so that a
top fraction comprising methanol, a fraction taken from the side
comprising methoxy propanols as an azetrope with water, and a
bottoms fraction comprising water and propylene glycol are
obtained. The methanol obtained as top fraction can be condensed
and recycled into the epoxidation process.
[0009] Accordingly, the prior art describes either a mere concept
concerning the possibility of heat integration or relates to very
specific embodiments of epoxidation processes in which not more
than one or two stages of the overall process are involved in the
heat integration aspect.
[0010] Therefore, it is an object of the present invention to
provide a highly integrated process for the production of an olefin
oxide in which at least three process stages of the overall process
are involved with regard to minimization of energy consumption.
[0011] It is a further object of the present invention to provide a
highly integrated process for the production of an olefin oxide in
which the top vapor stream obtained from the separation of methanol
from a product stream of the epoxidation process is used to operate
evaporators used in at least three process stages of the overall
epoxidation process.
[0012] It is another object of the present invention to provide a
highly integrated process for the production of propylene oxide in
which the top vapor stream obtained from the separation of methanol
from a product stream of the propene epoxidation process is used to
operate evaporators used in at least three process stages of the
overall epoxidation process.
[0013] It is still another object of the present invention to
provide a highly integrated process for the production of an olefin
oxide, preferably propylene oxide, in which not only the top vapor
stream obtained from the separation of methanol from a product
stream of the propene epoxidation process is used to operate
evaporators used in at least three process stages of the overall
epoxidation process, but in which at least one suitable additional
method is employed rendering the process economically and
ecologically still more positive concerning the overall energy
balance.
[0014] It is yet another object of the present invention to provide
a highly integrated process for the production of an olefin oxide,
preferably propylene oxide, in which above-mentioned advantages are
further combined with an optimized, preferably energetically
optimized methanol separation.
SUMMARY OF THE INVENTION
[0015] Therefore, the present invention provides a process for the
epoxidation of an olefin comprising [0016] (a) reacting the olefin
with hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mixture (M-a) comprising
olefin oxide, unreacted olefin, methanol and water, wherein between
at least two reaction stages, olefin oxide is separated by
distillation; [0017] (b) separating unreacted olefin from the
mixture (M-a) by distillation to obtain a mixture (M-bi) comprising
at least 80 wt.-% of olefin and a mixture (M-bii) comprising
methanol, water and at least 7 wt.-% of olefin oxide; [0018] (c)
separating olefin oxide from the mixture (M-bii) in at least one
distillation stage to obtain a mixture (M-ci) comprising at least
99 wt.-% of olefin oxide and a mixture (M-cii) comprising water and
at least 55 wt.-% of methanol: [0019] (d) separating methanol from
the mixture (M-cii) in at least one distillation stage to obtain a
mixture (M-di) comprising at least 85 wt.-% of methanol and up to
10 wt.-% of water, and a mixture (M-dii) comprising at least 90
wt.-% of water; [0020] wherein a vapor top stream (Td) obtained
from at least one distillation column used in (d), said vapor top
stream (Td) comprising at least 85 wt.-% methanol, is used to
operate at least partially at least one vaporizer used in at least
one distillation column used in at least one of stages (a), (b) and
(c).
[0021] The present invention also provides a process for the
epoxidation of propane comprising [0022] (a) reacting propene with
hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mixture (M-a) comprising
propylene oxide, unreacted propene, methanol and water, wherein
between at least two reaction stages, propylene oxide is separated
by distillation; [0023] (b) separating unreacted propane from the
mixture (M-a) by distillation to obtain a mixture (M-bi) comprising
at least 80 wt.-% of propene and a mixture (M-bii) comprising
methanol, water and at least 7 wt.-% of propylene oxide; [0024] (c)
separating propylene oxide from the mixture (M-bii) in at least one
distillation stage to obtain a mixture (M-ci) comprising at least
99 wt.-% of propylene oxide and a mixture (M-cii) comprising water
and at least 55 wt.-% of methanol; [0025] (d) separating methanol
from the mixture (M-cii) in at least one distillation stage to
obtain a mixture (M-di) comprising at least 85 wt.-% of methanol
and up to 10 wt.-% of water, and a mixture (M-dii) comprising at
least 90 wt.-% of water; [0026] wherein a vapor top stream (Td)
obtained from at least one distillation column used in (d), said
vapor top stream (Td) comprising at least 85 wt.-% methanol, is
used to operate at least partially at least one vaporizer used in
at least one distillation column used in at least one of stages
(a), (b) and (c).
[0027] The present invention also relates to a process for the
epoxidation of propene, comprising [0028] (a) reacting the propene
with hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mixture (M-a) comprising
propylene oxide, unreacted propene, propane, methanol and water,
wherein between at least two reaction stages, propylene oxide is
separated by distillation; [0029] (b) separating unreacted propene
from the mixture (M-a) by distillation to obtain a mixture (M-bi)
comprising propane and at least 80 wt.-% of propene, and a mixture
(M-bii) comprising methanol, water and at least 7 wt.-% of
propylene oxide; (x) separating propene from the mixture (M-bi) by
distillation to obtain a mixture (M-x) comprising at least 95 wt.-%
of propene, and re-introducing (M-x) into (a); [0030] (c)
separating the propylene oxide from the mixture (M-bii) in at least
one distillation stage to obtain a mixture (M-ci) comprising at
least 99 wt.-% of propylene oxide and a mixture (M-cii) comprising
water, at least one compound having a boiling temperature lower
than methanol and lower than water at a given pressure, and at
least 60 wt.-% of methanol; [0031] (y) separating the at least one
compound having a boiling point lower than methanol and lower than
water from the mixture (M-cii) by distillation to obtain a mixture
(M-y) comprising from 40 to 80 wt.-% of methanol and from 10 to 55
wt.-% of water; [0032] (d) separating methanol from the mixture
(M-y) in at least one distillation stage to obtain a mixture (M-di)
comprising at least 85 wt.-% of methanol and up to 10 wt.-% of
water, and a mixture (M-dii) comprising at least 90 wt.-% of water,
and re-introducing (M-di) into (a); [0033] (e) evaporating the
mixture (M-dii), [0034] wherein a vapor top stream (Td) obtained
from at least one distillation column used in (d), said vapor top
stream (Td) comprising at least 85 wt.-% methanol, and wherein from
15 to 50 wt.-% of (Td) are used to operate at least partially a
vaporizer used in (a), from 2 to 15 wt.-% of (Td) are used to
operate at least partially a vaporizer used in (b), from 1 to 10
wt.-% of (Td) are used to operate at least partially a vaporizer
used in (x), from 1 to 40 wt.-% of (Td) are used to operate at
least partially a vaporizer used in (c), from 15 to 50 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(y), and from 10 to 40 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (e).
[0035] The present invention also relates to a process for the
epoxidation of propene, comprising [0036] (a) reacting the propene
with hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mixture (M-a) comprising
propylene oxide, unreacted propene, propane, methanol and water,
wherein between at least two reaction stages, propylene oxide is
separated by distillation in a divided wall column, wherein
separated methanol is recycled into (a); [0037] (b) separating
unreacted propene from the mixture (M-a) by distillation to obtain
a mixture (M-bi) comprising propane and at least 80 wt.-% of
propene, and a mixture (M-bii) comprising methanol, water and at
least 7 wt.-% of propylene oxide; [0038] (x) separating propene
from the mixture (M-bi) by distillation to obtain a mixture (M-x)
comprising at least 95 wt.-% of propene, and re-introducing (M-x)
into (a); [0039] (c) separating the propylene oxide from the
mixture (M-bii) in two distillation columns, wherein from the first
distillation column, a first mixture comprising at least 99 wt.-%
of propylene oxide and a mixture (M-cii) comprising water, at least
one compound having a boiling temperature lower than methanol and
lower than water at a given pressure, and at least 60 wt.-% of
methanol, are obtained, said first mixture being introduced into
the second distillation column from which a mixture (M-ci)
comprising at least 99.8 wt.-% propylene oxide is obtained; [0040]
(y) separating the at least one compound having a boiling point
lower than methanol and lower than water from the mixture (M-cii)
by distillation to obtain a mixture (M-y) comprising from 40 to 80
wt.-% of methanol and from 10 to 55 wt.-% of water; [0041] (d)
separating methanol from the mixture (M-y) wherein [0042] (i) the
mixture (M-y) is introduced into a first distillation column (K1)
from which the vapor top stream (Td) is obtained, the distillation
in (K1) being carried out at a top pressure of from 2.5 to 6 bar;
and [0043] (ii) the bottoms stream obtained from (K1) is introduced
into a second distillation column (K2), the distillation in (K2)
being carried out at a top pressure of from 9 to 13 bar, (K2) being
a dividing wall column, [0044] and wherein, prior to introducing
into (K2), the bottoms stream obtained from (K1) is heated to a
temperature from 130 to 175.degree. C. with the bottoms stream
obtained from (K2), and wherein the condenser used to condense the
top stream obtained from (K2) is simultaneously used as vaporizer
of (K1), and wherein (Td) and the top stream obtained from (K2) are
re-introduced into (a); [0045] (e) evaporating the mixture (M-dii),
[0046] wherein a vapor top stream (Td) obtained from at least one
distillation column used in (d), said vapor top stream (Td)
comprising at least 85 wt.-% methanol, is used to operate at least
partially at least one vaporizer used in at least one distillation
column used in at least one of stages (a), (b), (c), (e), (x) and
(y).
[0047] The present invention also relates to a process for the
epoxidation of propane, comprising [0048] (a) reacting the propene
with hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mixture (M-a) comprising
propylene oxide, unreacted propane, propane, methanol and water,
wherein between at least two reaction stages, propylene oxide is
separated by distillation; [0049] (b) separating unreacted propene
from the mixture (M-a) by distillation to obtain a mixture (M-bi)
comprising propane and at least 80 wt.-% of propene, and a mixture
(M-bii) comprising methanol, water and at least 7 wt.-% of
propylene oxide; [0050] (x) separating propene from the mixture
(M-bi) by distillation to obtain a mixture (M-x) comprising at
least 95 wt.-% of propene, and re-introducing (M-x) into (a);
[0051] (c) separating the propylene oxide from the mixture (M-bii)
in two distillation columns, wherein from the first distillation
column, a first mixture comprising at least 99 wt.-% of propylene
oxide and a mixture (M-cii) comprising water, at least one compound
having a boiling temperature lower than methanol and lower than
water at a given pressure and at least 60 wt.-% of methanol, are
obtained, said first mixture being introduced into the second
distillation column from which a mixture (M-ci) comprising at least
99.8 wt.-% propylene oxide is obtained; [0052] (y) separating the
at least one compound having a boiling point lower than methanol
and lower than water from the mixture (M-cii) by distillation to
obtain a mixture (M-y) comprising from 40 to 80 wt.-% of methanol
and from 10 to 55 wt.-% of water: [0053] (d) separating methanol
from the mixture (M-y) wherein [0054] (i) the mixture (M-y) is
introduced into a first distillation column (K1) from which the
vapor top stream (Td) is obtained, the distillation in (K1) being
carried out at a top pressure of from 2.5 to 6 bar; and [0055] (ii)
the bottoms stream obtained from (K1) is introduced into a second
distillation column (K2), the distillation in (K2) being carried
out at a top pressure of from 9 to 13 bar, (K2) being a dividing
wall column, [0056] and wherein, prior to introducing into (K2),
the bottoms stream obtained from (K1) is heated to a temperature
from 140 to 170.degree. C. with the bottoms stream obtained from
(K(2), and wherein the condenser used to condense the top stream
obtained from (K2) is simultaneously used as vaporizer of (K1), and
wherein (Td) and the top stream obtained from (K2) are
re-introduced into (a); [0057] (e) evaporating the mixture (M-dii),
[0058] wherein a vapor top stream (Td) obtained from at least one
distillation column used in (d), said vapor top stream (Td)
comprising at least 85 wt.-% methanol, wherein from 20 to 40 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(a), from 3 to 10 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 3 to 10 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (x), from 0
to 10 wt.-% of (Td) are used to operate at least partially a
vaporizer used in the first distillation column in (c), from 2 to
20 wt.-% of (Td) are used to operate at least partially a vaporizer
used in the second distillation column in (c), from 20 to 40 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(y), from 15 to 35 wt.-% of (Cd) are used to operate at least
partially a vaporizer used in (e), and from 3 to 30 wt.-% of (Td)
are used to at least partially operate at least one control heat
exchanger used in the process, said process further comprising at
least one further integration method selected from the group
consisting of [0059] (II) heating the feed of the distillation
column used in stage (a) with the bottoms stream of this column and
the feed of at least one distillation column used in stage (d) with
the bottoms stream of this column; [0060] (III) condensing the top
stream obtained from at least one distillation column used in
stages (a), (b), (x), (c), (y), and (e) in two stages, wherein in
the first stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
DETAILED DESCRIPTION OF THE INVENTION
[0061] According to the present invention, the process for the
epoxidation of an olefin comprises [0062] (a) reacting the olefin
with hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mixture (M-a) comprising
olefin oxide, unreacted olefin, methanol and water, wherein between
at least two reaction stages, olefin oxide is separated by
distillation; [0063] (b) separating unreacted olefin from the
mixture (M-a) by distillation to obtain a mixture (M-bi) comprising
at least 80 wt.-% of olefin and a mixture (M-bii) comprising
methanol, water and at least 7 wt.-% of olefin oxide; [0064] (c)
separating olefin oxide from the mixture (M-bii) in at least one
distillation stage to obtain a mixture (M-ci) comprising at least
99 wt.-% of olefin oxide and a mixture (M-cii) comprising water and
at least 55 wt.-% of methanol; [0065] (d) separating methanol from
the mixture (M-cii) in at least one distillation stage to obtain a
mixture (M-di) comprising at least 85 wt.-% of methanol and up to
10 wt.-% of water, and a mixture (M-dii) comprising at least 90
wt.-% of water; [0066] wherein a vapor top stream (Td) obtained
from at least one distillation column used in (d), said vapor top
stream (Td) comprising at least 85 wt.-% methanol, is used to
operate at least partially at least one vaporizer used in at least
one distillation column used in at least one of stages (a), (b) and
(c). Stage (a)
[0067] As to the olefin used according to stage (a), there are no
specific restrictions. For example, ethene, propylene, 1-butene,
2-butene, isobutene, butadiene, pentenes, piperylene, hexenes,
hexadienes, heptenes, octenes, diisobutene, trimethylpentene,
nonenes, dodecene, tridecene, tetradecene to eicosene, tripropene
and tetrapropene, polybutadienes, polyisobutenes, isoprene,
terpenes, geraniol, linalool, linalyl acetate,
methylenecyclopropane, cyclopentene, cyclohexene, norbornene,
cycloheptene, vinylcyclohexane, vinyloxirane, vinylcyclohexene,
styrene, cyclooctene, cyclooctadiene, vinylnorbornene, indene,
tetrahydroindene, methylstyrene, dicyclopentadiene, divinylbenzene,
cyclododecene, cyclododecatriene, stilbene, diphenylbutadiene,
vitamin A, betacarotene, vinylidene fluoride, allyl halides, crotyl
chloride, methallyl chloride, dichlorobutene, allyl alcohol,
methallyl alcohol, butenols, butenediols, cyclopentenediols,
pentenols, octadienols, tridecenols, unsaturated steroids,
ethoxyethene, isoeugenol, anethole, unsaturated carboxylic acids
such as acrylic acid, methacrylic acid, crotonic acid, maleic acid,
vinylacetic acid, unsaturated fatty acids such as oleic acid,
linoleic acid, palmitic acid, naturally occurring fats and oils can
be reacted with hydrogen peroxide.
[0068] Preference is given to using alkenes containing from 2 to 8
carbon atoms. Particular preference is given to reacting ethene,
propene and butene. Very particular preference is given to reacting
propylene.
[0069] Therefore, the present invention relates to a process as
described above wherein the olefin employed in stage (a) is propene
and the respective olefin oxide is propylene oxide.
[0070] According to stage (a) of the process, an olefin is reacted
with hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mature (M-a) which comprises
olefin oxide, unreacted olefin, methanol and water. Between at
least two of these reaction stages, olefin oxide is separated by
distillation. Therefore, the inventive process comprises at least
the following sequence of stages (i) to (iii): [0071] (i) reaction
of the olefin, preferably propene, with hydrogen peroxide to give a
mixture comprising olefin oxide, preferably propylene oxide, and
unreacted olefin, [0072] (ii) separation of the unreacted olefin
from the mixture resulting from stage (i), [0073] (iii) reaction of
the olefin which has been separated off in stage (ii) with hydrogen
peroxide.
[0074] Therefore, stage (a) can comprise, in addition to stages (i)
and (iii), at least one further reaction stage and, in addition to
stage (ii), at least one further separation stage. According to a
preferred embodiment, the process stage (a) consists of these three
stages.
[0075] As to stages (i) and (iii), there are no specific
restrictions as to how the reaction is carried out.
[0076] Accordingly, it is possible to carry out one of the
reactions stages in batch mode or in semi-continuous mode or in
continuous mode and independently thereof, the other reaction stage
in batch mode or in semi-continuous mode or in continuous mode.
According to an even more preferred embodiment, both reaction
stages (i) and (iii) are carried out in continuous mode.
[0077] The epoxidation reaction in stages (i) and (iii) is
preferably carried out in the presence of at least one zeolite
catalyst. Zeolites are, as is known, crystalline aluminosilicates
having ordered channel and cage structures and containing
micropores which are preferably smaller than about 0.9 nm. The
network of such zeolites is made up of SiO.sub.4 and AlO.sub.4
tetrahedra which are joined via shared oxygen bridges. An overview
of the known structures may be found, for example, in W. M. Meier,
D. H. Olson and Ch. Baer-Iocher, "Atlas of Zeolite Structure
Types", Elsevier, 5th edition, Amsterdam 2001.
[0078] Zeolites in which no aluminum is present and in which part
of the Si(IV) in the silicate lattice is replaced by titanium as
Ti(IV) are also known. These titanium zeolites, in particular those
having a crystal structure of the MFI type, and possible ways of
preparing them are described, for example, in EP 0 311 983 A2 or EP
0 405 978 A1. Apart from silicon and titanium, such materials can
further comprise additional elements such as aluminum, zirconium,
tin, iron, cobalt, nickel, gallium, germanium, boron or small
amounts of fluorine. In the zeolite catalysts which have preferably
been regenerated by the process of the invention, part or all of
the titanium of the zeolite can have been replaced by vanadium,
zirconium, chromium or niobium or a mixture of two or more thereof.
The molar ratio of titanium and/or vanadium, zirconium, chromium or
niobium to the sum of silicon and titanium and/or vanadium and/or
zirconium and/or chromium and/or niobium is generally in the range
from 0.01:1 to 0.1:1.
[0079] Titanium zeolites, in particular those having a crystal
structure of the MFI type, and possible ways of preparing them are
described, for example, in WO 98/55228, EP 0 311 983 A2, EP 0 405
978 A1, EP 0 200 260 A2.
[0080] It is known that titanium zeolites having the MFI structure
can be identified via a particular X-ray diffraction pattern and
also via a lattice vibration band in the infrared (IR) region at
about 980 cm.sup.-1 and thus differ from alkali metal titanates or
crystalline and amorphous TiO.sub.2 phases.
[0081] Specific mention may be made of titanium-, germanium-,
tellurium-, vanadium-, chromium-, niobium-, zirconium-containing
zeolites having a pentasil zeolite structure, in particular the
types which can be assigned X-ray-crystallographically to the
structures ABW, ACO, AEI, AEL, AEN, AET, AFG, AFI, AFN, AFO, AFR,
AFS, AFT, AFX, AFY, AHT, ANA, APC, APD, AST, ASV, ATN, ATO, ATS,
ATT, ATV, AWO, AWW, BCT, BEA, BEC, BIK, BOG, BPH, BRE, CAN, CAS,
CDO, CFI, CGF, CGS, CHA, CHI, CLO, CON, CZP, DAC, DDR, DFO, DFT,
DOH, DON, EAB, EDI, EMT, EPI, ERI, ESV, ETR, EUO, FAU, FER, FRA,
GIS, GIU, GME, GON, GOO, HEU, IFR, ISV, ITE, ITH, ITW, IWR, IWW,
JBW, KFI, LAU, LEV, LIO, LOS, LOV, LTA, LTL, LTN, MAR, MAZ, MEI,
MEL, MEP, MER, MMFI, MFS, MON, MOR, MSO, MTF, MTN, MTT, MTW, MWW,
NAB, NAT, NEES, NON, NPO, OBW, OFF, OSI, OSO, PAR, PAU, PHI, PON,
RHO, RON, RRO, RSN, RTE, RTH, RUT, RWR, RWY, SAO, SAS, SAT, SAV,
SBE, SBS, SBT, SFE, SFF, SFG, SFH, SFN SFO, SGT, SOD, SSY, STF,
STI, SNT, TER, THO, TON, TSC, UEI, UFI, UOZ, USI, UTL, VET, VFI,
VNI, VSV, WEI, WEN, YUG and ZON, and also mixed structures of two
or more of the abovementioned structures. Furthermore,
titanium-containing zeolites having the ITM-4, SSZ-24, TTM-1,
UTD-1, CIT-1 or CIT-5 structure are also conceivable for use in the
process of the invention. Further titanium-containing zeolites
which may be mentioned are those having the ZSM-48 or ZSM-12
structure.
[0082] For the purposes of the present invention, preference is
given to using Ti zeolites having an MFI structure, an MEL
structure, an MFI/MEL mixed structure or an MWW structure. Further
preference is given specifically to the Ti-containing zeolite
catalysts which are generally referred to as "TS-1", "TS-2",
"TS-3", and also Ti zeolites having a framework structure
isomorphous with beta-zeolite. Very particular preference is given
to using zeolite catalysts of the TS-1 structure and the Ti-MWW
structure.
[0083] The catalysts, especially preferably the titanium zeolite
catalysts and still more preferably the catalysts having TS1 or MWW
structure, can be employed as powder, as granules, as microspheres,
as shaped bodies having, for example, the shape of pellets,
cylinders, wheels, stars, spheres and so forth, or as extrudates
such as extrudates having, for example, a length of from 1 to 10,
more preferably of from 1 to 7 and still more preferably of from 1
to 5 mm, and a diameter of from 0.1 to 5, more preferably of from
0.2 to 4 and especially preferably of from 0.5 to 2 mm. In order to
increase the bulk density of the extrudates, it is preferred to cut
the extrudates with a stream essentially consisting of an inert
gas.
[0084] For each of these forming methods, it is possible to use at
least one additional binder and/or at least one pasting agent
and/or at least one pore forming agent. Prior to using the catalyst
in the epoxidation reaction of the present invention, it is
possible to suitably pretreat the catalyst. In case the catalyst is
used as supported catalyst, a carrier can be preferably used which
are inert, i.e. which do not react with hydrogen peroxide, olefin,
and olefin oxide.
[0085] Most preferably, a Ti-TS1 or Ti-MWW catalyst is employed
which is produced by first forming microspheres, for example
microspheres formed according to EP 0 200 260 A2, and then forming
said microspheres to obtain shaped bodies, preferably extrudates as
described above.
[0086] Therefore, the reactions in stages (i) and (iii) are
preferably carried out in suspension or fixed-bed mode, most
preferably in fixed-bed mode.
[0087] In the inventive process, it is possible to use the same or
different types of reactors in stages (i) and (iii). Thus, it is
possible to carry out one of the reactions stages in an isothermal
or adiabatic reactor and the other reaction stage, independently
thereof, in an isothermal or adiabatic reactor. The term "reactor"
as used in this respect comprises a single reactor, a cascade of at
least two serially connected reactors, at least two reactors which
are operated in parallel, or a multitude of reactors wherein at
least two reactors are serially coupled and wherein at least two
reactors are operated in parallel. According to a preferred
embodiment, stage (I) of the present invention is carried out in at
least two reactors which are operated in parallel, and stage (iii)
of the present invention is carried out in a single reactor.
[0088] Each of the reactors described above, especially the
reactors according to the preferred embodiment, can be operated in
downflow or in upflow operation mode.
[0089] In case the reactors are operated in downflow mode, it is
preferred to use fixed-bed reactors which are preferably tubular,
multi-tubular or multi-plate reactors, most preferably equipped
with at least one cooling jacket. In this case, the epoxidation
reaction is carried out at a temperature of from 30 to 80.degree.
C., and the temperature profile in the reactors is maintained at a
level so that the temperature of the cooling medium in the cooling
jackets is at least 40.degree. C. and the maximum temperature in
the catalyst bed is 60.degree. C. In case of downflow operation of
the reactors, it is possible to chose the reaction conditions such
as temperature, pressure, feed rate and relative amounts of
starting materials such that the reaction is carried out in a
single phase, more preferably in a single liquid phase, or in a
multiphase system comprising, for example, 2 pr 3 phases. As to the
downflow operation mode, it is especially preferred to conduct the
epoxidation reaction in a multiphase reaction mixture comprising a
liquid aqueous hydrogen peroxide rich phase containing methanol and
a liquid organic olefin rich phase, preferably a propene rich
phase.
[0090] In case the reactors are operated in upflow mode, it is
preferred to use fixed-bed reactors. It is still further preferred
to use at least two fixed-bed reactors in stage (i) and at least
one reactor in stage (iii). According to a still further
embodiment, the at least two reactors used in stage (i) are
serially connected or operated in parallel, more preferably
operated in parallel. Generally, it is necessary to equip at least
one of the reactors used in stage (I) and/or (iii) with a cooling
means such as a cooling jacket. Especially preferably, at least two
reactors are employed in stage (i) which are connected in parallel
and can be operated alternately. In case the reactors are operated
in upflow mode, the two or more reactors connected in parallel in
stage (i) are particularly preferably tube reactors, multi-tube
reactors or multi-plate reactors, more preferably multi-tube
reactors and especially preferably shell-and-tube reactors
comprising a multitude of tubes such as from 1 to 20 000,
preferably from 10 to 10 000, more preferably from 100 to 8000,
more preferably from 1000 to 7000 and particularly preferably from
3000 to 6000, tubes. To regenerate the catalyst used for the
epoxidation reaction, it is possible for at least one of the
reactors connected in parallel to be taken out of operation for the
respective reaction stage and the catalyst present in this reactor
to be regenerated, with at least one reactor always being available
for reaction of the starting material or starting materials in
every stage during the course of the continuous process.
[0091] As cooling medium used for cooling the reaction media in
above-mentioned reactors equipped with cooling jackets, there are
no specific restrictions. Especially preferred are oils, alcohols,
liquid salts or water, such as river water, brackish water and/or
sea water, which can in each case, for example, preferably be taken
from a river and/or lake and/or sea close to the chemical plant in
which the reactor of the invention and the process of the invention
are used and, after any necessary suitable removal of suspended
material by filtration and/or sedimentation, be used directly
without further treatment for cooling the reactors. Secondary
cooling water which is preferably conveyed around a closed circuit
is particularly useful for cooling purposes. This secondary cooling
water is generally essentially deionized or demineralised water to
which at least one antifouling agent has preferably been added.
More preferably, this secondary cooling water circulates between
the reactor of the invention and, for example, a cooling tower.
Preference is likewise given to the secondary cooling water being,
for example, countercooled in at least one countercurrent heat
exchanger by, for example, river water, brackish water and/or sea
water.
[0092] In stage (iii), particular preference is given to using a
shaft reactor, more preferably a continuously operated shaft
reactor and particularly preferably a continuously operated,
adiabatic shaft reactor.
[0093] Therefore, the present invention also relates to a process
as described above wherein in stage (i), at least two
shell-and-tube reactors each having of from 1 to 20,000 internal
tubes and being continuously operated in upflow mode, said reactors
being operated in parallel, are employed, and wherein in stage
(iii), an adiabatic shaft reactor being being continuously operated
in upflow mode, is employed. Still more preferably, the reaction in
at least one of these reactors, more preferably in the at least two
reactors of stage (i) and still more preferably in all reactors
used in states (I) and (iii) is conducted such that in the
respective reactor, a single liquid phase is present. Even more
preferably, in each of the reactors used in stages (i) and (iii),
the catalyst used for the epoxidation reaction is employed as
fixed-bed reactor wherein the catalyst is a titanium zeolite
catalyst, more preferably a Ti-TS1 or Ti-MWW catalyst and even more
preferably a Ti-TS1 catalyst.
[0094] The hydrogen peroxide is used in the process according to
the invention in the form of an aqueous solution with a hydrogen
peroxide content of generally of from 1 to 90 wt.-%, preferably of
from 10 to 70 wt.-%., more preferably from 10 to 60 wt.-%. A
solution having of from 20 to less than 50 wt.-% of hydrogen
peroxide is particularly preferred.
[0095] According to another embodiment of the present invention, a
crude aqueous hydrogen peroxide solution can be employed. As crude
aqueous hydrogen peroxide solution, a solution can be used which is
obtained by extraction of a mixture with essentially pure water
wherein the mixture results from a process known as anthrachinone
process (see, e.g., Ullmann's Encycolpedia of Industrial Chemistry,
5th edition, volume 3 (1989) pages 447-457). In this process, the
hydrogen peroxide formed is generally separated by extraction from
the working solution. This extraction can be performed with
essentially pure water, and the crude aqueous hydrogen peroxide is
obtained. According to one embodiment of the present invention,
this crude solution can be employed without further purification.
The production of such a crude solution is described, for example,
in European patent application EP 1 122 249 A1. As to the term
"essentially pure water", reference is made to paragraph 10, page 3
of EP 1 122 249 A1 which is incorporated by reference.
[0096] To prepare the hydrogen peroxide which is preferably used,
it is possible to employ, for example, the anthraquinone process by
means of which virtually the entire world production of hydrogen
peroxide is produced. An overview of the anthraquinone process is
given in "Ullmann's Encyclopedia of Industrial Chemistry", 5th
edition, volume 13, pages 447 to 456.
[0097] It is likewise conceivable to obtain hydrogen peroxide by
converting sulfuric acid into peroxodisulfuric acid by anodic
oxidation with simultaneous evolution of hydrogen at the cathode.
Hydrolysis of the peroxodisulfuric acid then leads via
peroxomonosulfuric acid to hydrogen peroxide and sulfuric acid
which is thus obtained back.
[0098] Of course, the preparation of hydrogen peroxide from the
elements is also possible.
[0099] Before hydrogen peroxide is used in the process of the
invention, it is possible to free, for example, a commercially
available hydrogen peroxide solution of undesirable ions.
Conceivable methods are, inter alia, those described, for example,
in U.S. Pat. No. 5,932,187, DE 42 22 109 A1 or U.S. Pat. No.
5,397,475. It is likewise possible to remove at least one salt
present in the hydrogen peroxide solution from the hydrogen
peroxide solution by means of ion exchange in an apparatus which
contains at least one nonacidic ion exchanger bed having a flow
cross-sectional area F and a height H which are such that the
height H of the ion exchanger bed is less than or equal to
2.5F.sup.1/2, in particular less than or equal to 1.5F.sup.1/2. For
the purposes of the present invention, it is in principle possible
to use all nonacidic ion exchanger beds comprising cation
exchangers and/or anion exchangers. It is also possible for cation
and anion exchangers to be used as mixed beds within one ion
exchanger bed. In a preferred embodiment of the present invention,
only one type of nonacidic ion exchangers is used. Further
preference is given to the use of basic ion exchange, particularly
preferably that of a basic anion exchanger and more particularly
preferably that of a weakly basic anion exchanger.
[0100] The reaction in the reactors according to stage (i) is
preferably carried out at reaction conditions such that the
hydrogen peroxide conversion is at least 80%, more preferably at
least 85% and still more preferably at least 90%. The pressure in
the reactors is generally in the range of from 10 to 30 bar, more
preferably from 15 to 25 bar. The temperature of the cooling water
is in the range of preferably from 20 to 70.degree. C., more
preferably from 25 to 65.degree. C. and particularly preferably
from 30 to 60.degree. C.
[0101] According to the preferred embodiment of the invention
according to which the reactor or the reactors in stage (i) are
fixed-bed reactors, the product mixture obtained therefrom
essentially consists of olefin oxide, preferably propylene oxide,
unreacted olefin, preferably propene, methanol, water, and hydrogen
peroxide.
[0102] According to a preferred embodiment, the product mixture
obtained from stage (i) has a methanol content in the range of from
55 to 75 wt.-%, especially preferably of from 60 to 70 wt.-%, based
on the total weight of the product mixture, a water content in the
range of from 5 to 25 wt.-%, especially preferably of from 10 to 20
wt.-%, based on the total weight of the product mixture, an olefin
oxide content in the range of from 5 to 20 wt.-%, especially
preferably of from 8 to 15 wt.-%, based on the total weight of the
product mixture, and an olefin content in the range of from 1 to 10
wt.-%, especially preferably of from 1 to 5 wt.-%, based on the
total weight of the product mixture.
[0103] The temperature of the product mixture obtained from stage
(i) is preferably in the range of from 40 to 60.degree. C., more
preferably of from 45 to 55.degree. C. Prior to being fed to the
distillation column of (ii), the product mixture is preferably
heated up in at least one heat exchanger to a temperature in the
range of from 50 to 80.degree. C., more preferably of from 60 to
70.degree. C.
[0104] According to an object of the present invention, heating up
the product stream obtained from stage (i) is carried out using, at
least partially, the bottoms stream of the distillation column of
stage (ii). Thus, heat integration of the overall epoxidation
process is still further improved. According to a preferred
embodiment, of from 50 to 100%, more preferably of from 80 to 100%
and especially preferably of from 90 to 100% of the bottoms stream
obtained from the distillation column used in (ii) are used for
heating up the product stream obtained from (i) from a temperature
in the range of from 45 to 55.degree. C. to a temperature in the
range of from 65 to 70.degree. C.
[0105] According to stage (ii), unreacted olefin is separated from
the mixture resulting from stage (i). This separation is carried
out by distillation using at least one distillation column. The
reaction mixture obtained from the at least one reactor, preferably
from the at least two reactors used in stage (i), comprising
unreacted olefin, olefin oxide, methanol, water and unreacted
hydrogen peroxide, is introduced in the distillation column. The
distillation column is preferably operated at a top pressure of
from 1 to 10 bar, more preferably of from 1 to 5 bar, more
preferably of from 1 to 3 bar and still more preferably of from 1
to 2 bar such as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or
2 bar. According to an especially preferred embodiment, the
distillation column has from 5 to 60, preferably from 10 to 50 and
especially preferably from 15 to 40 theoretical stages.
[0106] According to a still further preferred embodiment, the
reaction mixture obtained from (i) is fed to the distillation
column of (ii) from 2 to 30 theoretical stages below the top,
preferably from 10 to 20 theoretical stages below the top of the
column.
[0107] At the top of the distillation column of (ii), a stream
essentially consisting of olefin oxide, preferably propylene oxide,
methanol and unreacted olefin, preferably propene, is obtained. At
the top of the column, a mixture is obtained having a water content
of not more than 0.5 wt.-%, preferably of not more than 0.4 wt.-%
and still more preferably of not more than 0.3 wt.-%, and having a
hydrogen peroxide content of not more than 100 ppm, preferably of
not more than 20 ppm and still more preferably of not more than 10
ppm, in each case based on the total weight of the mixture obtained
at the top of the column.
[0108] At the bottom of the distillation column, a stream
essentially consisting of methanol, water and unreacted hydrogen
peroxide is obtained. At the bottom of the column, a mixture is
obtained having an olefin, preferably a propene content of not more
than 50 ppm, preferably of not more than 10 ppm and still more
preferably of not more than 5 ppm, and having a olefin oxide,
preferably a propylene oxide content of not more than 50 ppm,
preferably of not more than 20 ppm and still more preferably of not
more than 10 ppm, in each case based on the total weight of the
mixture obtained at the bottom of the column.
[0109] Therefore, depending on the respective point of view,
distillative separation according to stage (ii) can be described as
separation of unreacted olefin or, alternatively, as separation of
olefin oxide.
[0110] The evaporator of the distillation column used in stage (ii)
is at least partially operated using at least partially the top
stream (Td). Preferably, from 5 to 60%, more preferably from 15 to
50 and especially preferably from 20 to 40% of (Td) are used to
operate the evaporator of the distillation column of stage
(ii).
[0111] According to a still further preferred embodiment, the
distillation column used in (ii) is configured as dividing wall
column having at least one side-offtake, preferably one
side-offtake, Preferably, the dividing wall column preferably has
from 20 to 60, more preferably from 30 to 50 theoretical
stages.
[0112] The upper combined region of the inflow and offtake part of
the dividing wall column preferably has from 5 to 50%, more
preferably from 15 to 30%, of the total number of theoretical
stages in the column, the enrichment section of the inflow part
preferably has from 5 to 50%, more preferably from 15 to 30%, the
stripping section of the inflow part preferably has from 15 to 70%,
more preferably from 20 to 60%, the stripping section of the
offtake part preferably has from 5 to 50%, more preferably from 15
to 30%, the enrichment section of the offtake part preferably has
from 15 to 70%, more preferably from 20 to 60%, and the lower
combined region of the inflow and offtake part of the column
preferably has from 5 to 50%, more preferably from 15 to 30%, in
each case of the total number of theoretical stages in the
column.
[0113] It is likewise advantageous for the inlet via which the
product mixture obtained from (i) is fed into the column and the
side ofltake via which the a part of the methanol, preferably of
from 0 to 50%, more preferably of from 1 to 40%, still more
preferably of from 5 to 30% and especially preferably of from 10 to
25% of the methanol, is taken off as intermediate boiler and, still
more preferably, directly fed back to stage (i), to be arranged at
different heights in the column relative to the position of the
theoretical stages. The inlet is preferably located at a position
which is from 1 to 25, more preferably from 5 to 15 theoretical
stages above or below the side offtake.
[0114] The dividing wall column used in the process of the present
invention is preferably configured either as a packed column
containing random packing or ordered packing or as a tray column.
For example, it is possible to use sheet metal or mesh packing
having a specific surface area of from 100 to 1000 m.sup.2/m.sup.3,
preferably from about 250 to 750 m.sup.2/m.sup.3, as ordered
packing. Such packing provides a high separation efficiency
combined with a low pressure drop per theoretical stage.
[0115] In the abovementioned configuration of the column, the
region of the column divided by the dividing wall, which consists
of the enrichment section of the inflow part, the stripping section
of the offtake part, the stripping section of the inflow part and
the enrichment section of the offtake part, or parts thereof is/are
provided with ordered packing or random packing. The dividing wall
can be thermally insulated in these regions.
[0116] The differential pressure over the dividing wall column can
be utilized as regulating parameter for the heating power. The
distillation is advantageously carried out at a pressure at the top
of from 1 to 10 bar, preferably from 1 to 5 bar, more preferably
from 1 to 3 bar and still more preferably of from 1 to 2 bar such
as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 or 2 bar.
[0117] Accordingly, the heating power of the vaporizer at the
bottom of the column is selected so as to maintain this pressure
range. Consequently, the amount of (Td) used for operating the
vaporizer, being preferably from 5 to 60%, more preferably from 15
to 50 and especially preferably from 20 to 40% of the total amount
of (Td), can be adapted to comply with the differential pressure to
be obtained.
[0118] The distillation is then preferably carried out in a
temperature range from 65 to 100.degree. C., more preferably from
70 to 85.degree. C. The distillation temperature is measured at the
bottom of the tower.
[0119] In case such a divided wall column is used, at the top of
the distillation column of (ii), a stream essentially consisting of
olefin oxide, preferably propylene oxide, methanol and unreacted
olefin, preferably propene, is obtained. At the top of the column,
a mixture is obtained having a water content of not more than 500
ppm, preferably of not more than 400 ppm, and still more preferably
of not more than 300 ppm, and having a hydrogen peroxide content of
not more than 50 ppm, preferably of not more than 20 ppm and still
more preferably of not more than 10 ppm, in each case based on the
total weight of the mixture obtained at the top of the column.
Furthermore, the top stream obtained has an olefin, preferably a
propene content of from 15 to 35 wt.-%, preferably of from 20 to 30
wt.-% and still more preferably of from 20 to 25 wt.-%, an olefin
oxide, preferably a propylene oxide content of from 50 to 80 wt.-%,
preferably of from 55 to 75 wt.-% and especially preferably of from
60 to 70 wt.-%, and a methanol content of from 5 to 20 wt.-%, more
preferably of from 7.5 to 17.5 wt.-% and especially preferably of
from 10 to 15 wt.-%, in each case based on the total weight of the
top stream.
[0120] At the side-offtake of the distillation column, a stream
essentially consisting of methanol and water is obtained. At the
side-offake of the column, a mixture is obtained having a methanol
content of at least 95 wt.-%, preferably at least 96 wt.-% and
still more preferably at least 97 wt.-%, and having a water content
of not more than 5 wt.-%, preferably of not more than 3.5 wt.-% and
still more preferably of not more than 2 wt.-%, in each case based
on the total weight of the mixture obtained at the side-offtake of
the column.
[0121] At the bottom of the distillation column, a stream
essentially consisting of methanol, water and unreacted hydrogen
peroxide is obtained. At the bottom of the column, a mixture is
obtained having an olefin, preferably a propene content of not more
than 50 ppm, preferably of not more than 10 ppm and still more
preferably of not more than 5 ppm, and having a olefin oxide,
preferably a propylene oxide content of not more than 50 ppm,
preferably of not more than 20 ppm and still more preferably of not
more than 10 ppm, in each case based on the total weight of the
mixture obtained at the bottom of the column.
[0122] At least part of the stream taken from the side of the
dividing wall column can be recycled as solvent into stage (i) of
the inventive process. Preferably, at least 90%, more preferably at
least 95% of the stream taken from the side-offtake are recycled
into stage (i).
[0123] The bottoms stream taken from the of the distillation
column, preferably the dividing wall distillation column,
essentially consisting of methanol, water and unreacted hydrogen
peroxide, is then fed to the reactor of stage (iii). Preferably,
the bottoms stream is cooled prior to being introduced into the
reactor via, for example, one-stage cooling or two-stage cooling,
more preferably to a temperature of from 20 to 40.degree. C., still
more preferably to a temperature of from 30 to 40.degree. C. Still
more preferably, fresh olefin, preferably propene, is additionally
added directly in to the reactor of stage (iii) or added to the
bottoms stream obtained from (ii) prior to introducing same into
the reactor of stage (iii). Alternatively or additionally, fresh
hydrogen peroxide can be added.
[0124] The selectivity of this reaction in stage (iii) in respect
of hydrogen peroxide is preferably in the range from 64 to 99%,
more preferably in the range from 72 to 90% and particularly
preferably in the range from 75 to 87%.
[0125] The selectivity of the overall process with stages (i) to
(iii) in respect of hydrogen peroxide is preferably in the range
from 78 to 99%, more preferably in the range from 88 to 97% and
particularly preferably in the range from 90 to 96%.
[0126] The total hydrogen peroxide conversion is preferably at
least 99.5%, more preferably at least 99.6%, more preferably at
least 99.7% and particularly preferably at least 99.8%.
[0127] The reaction mixture obtained from stage (iii) preferably
has a methanol content of from 50 to 90 wt.-%, more preferably of
from 60 to 85 wt.-% and especially preferably of from 70 to 80
wt.-%, based on the total weight of the reaction mixture. The water
content is preferably in the range of from 5 to 45 wt.-%, more
preferably of from 10 to 35 wt.-% and especially preferably of from
15 to 25 wt.-%, based on the total weight of the reaction mixture.
The olef in oxide, preferably the propylene oxide content,
preferably in the range of from 1 to 5 wt.-%, more preferably of
from 1 to 4 wt.-% and especially preferably of from 1 to 3 wt.-%,
based on the total weight of the reaction mbiture. The olefin,
preferably the propene content is preferably in the range of from 0
to 5 wt.-%, more preferably of from 0 to 3 wt.-% and especially
preferably of from 0 to 1 wt.-%, based on the total weight of the
reaction mixture.
[0128] The product mixture taken from the reactor of stage (iii)
can be fed as mixture (M-a) into stage (b) of the inventive
process. Additionally, the stream taken from the top of the
distillation column of stage (ii) ca be combined with the product
mixture taken from the reactor of stage (iii) to give mixture (M-a)
which is then fed into stage (b) of the inventive process.
Alternatively, it is possible to separately feed the product
mixture taken from the reactor of stage (iii) and the top stream of
the distillation column of stage (ii) into stage (b), the latter
embodiment wherein both streams are regarded as constituting
mixture (M-a) being preferred.
Stage (b)
[0129] According to stage (b), unreacted olefin is separated from
the mixture (M-a) by distillation to obtain a mixture (M-bi)
comprising at least 80 wt.-% of olefin and a mixture (M-bii)
comprising methanol, water and at least 7 wt.-% of olefin
oxide.
[0130] Separation according to stage (b) is preferably carried out
in at least one distillation column, more preferably in one
distillation column. Preferably, this column has of from 5 to 40,
more preferably of from 10 to 35 and especially preferably of from
15 to 30 theoretical stages.
[0131] The distillation column is preferably operated at a top
pressure of from 1 to 5 bar, more preferably of from 1 to 4 bar,
more preferably of from 1 to 3 bar and still more preferably of
from 1 to 2 bar such as 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8,
1.9 or 2 bar.
[0132] According to a still further preferred embodiment, a mixture
(M-bi) is obtained at the top of the distillation column comprising
at least 85 wt.-% of olefin, still more preferably of from 85 to 90
wt.-% of olefin, preferably of propene.
[0133] In the context of the present invention, it is possible to
introduce propene as chemical grade propene in which propane is
present in a volume ratio of propylene to propane of from about
97:3 to about 95:5. In case chemical grade propene is used, the
mixture (M-bi) can additionally comprise up to 15 wt.-%, preferably
of from 5 to 10 wt.-% of propane, based on the total weight of
mixture (M-bi).
[0134] Preferably, the mixture (M-bii) obtained as bottoms stream
comprises of from 55 to 80 wt.-%, more preferably from 60 to 75
wt.-% and especially preferably from 65 to 70 wt.-%, of methanol,
of from 13 to 25 wt.-%, more preferably from 15 to 20 wt.-% of
water, and at least 7 wt.-%, more preferably at least 8 wt.-%, more
preferably at least 9 wt.-% and especially preferably at least 10
wt.-%, for example from 10 to 15 wt.-% such as about 10, about 11,
about 12, about 13, about 14 or about 15 wt.-% of olefin oxide,
preferably propylene oxide.
[0135] The evaporator of the distillation column used in stage (b)
of the inventive process is at least partially operated with at
least a part of (Td). More preferably, 1 to 20 wt.-% of (Td), more
preferably from 2 to 15 wt.-% of (Td) and especially preferably
from 3 to 10 wt.-% of CTd) are used to operate the evaporator used
in stage (b).
[0136] If necessary, at least one feed stream fed into stage (b)
can be heated with the bottoms stream obtained from the column used
in stage (b).
Stage (c)
[0137] According to stage (c), mixture (M-bii) obtained from stage
(b) as bottoms stream is subjected to a further distillative
separation process in which a mixture (M-ci) comprising at least 99
wt.-% of olefin oxide and a mixture (M-ci) comprising water and at
least 55 wt.-% of methanol are obtained.
[0138] Separation according to stage (c) is preferably carried out
in at least one distillation column, more preferably in one
distillation column. Preferably, this column has of from 30 to 110,
more preferably of from 40 to 100 and especially preferably of from
50 to 90 theoretical stages.
[0139] The distillation column is preferably operated at a top
pressure of from 1 bar or less. Especially preferably, the
distillation column is operated as a vacuum column at a top
pressure of less than 1 bar, more preferably at not more than 0.9
bar, more preferably at not more than 0.8 bar, more preferably at
not more than 0.7 bar, and still more preferably at not more than
0.6 bar. Preferred ranges of the top pressure are, for example,
from 0.3 to 0.9 bar, more preferably from 0.4 bar to 0.8 bar.
Preferred top pressures are, for example, about 0.4 bar or about
0.5 bar or about 0.6 bar or about 0.7 bar or about 0.8 bar.
[0140] According to a preferred embodiment of the inventive
process, the mixture (M-ci) obtained as top stream comprises at
least 99.1 wt.-%, more preferably at least 99.2 wt.-%, more
preferably at least 99.3 wt.-%, more preferably at least 99.4
wt.-%, and still more preferably at least 99.5 wt.-% of olefin
oxide, preferably propylene oxide. Preferred contents of (M-ci)
with respect to olefin oxide are, for example, in the range of from
99.1 to 99.9 m more preferably from 99.2 to 99.9, more preferably
from 99.3 to 99.9, more preferably from 99.4 to 99.9 and still more
preferably from 99.5 to 99.9 wt.-%, based on the total weight of
mixture (M-ci).
[0141] According to a preferred embodiment of the inventive
process, the mixture (M-cii) obtained as bottoms stream comprises
of from 55 to 85 wt.-%, more preferably from 66 to 80 wt.-% and
especially preferably from 75 to 80 wt.-% of methanol, and of from
15 to 45 wt.-%, more preferably from 20 to 35 wt.-% and especially
preferably of from 20 to 25 wt.-% of water, wherein the content of
mixture (M-cii) regarding methanol as well as water is higher than
the respective content of mixture (M-bii).
[0142] The evaporator of the distillation column used in stage (c)
of the inventive process is at least partially operated with at
least a part of (Td). More preferably, 1 to 50 wt.-% of (Td), more
preferably from 1 to 40 wt.-% of (Td) and especially preferably
from 2 to 30 wt.-% of (Td) are used to operate the evaporator used
in stage (c).
[0143] In order to further improve the energy balance of the
overall process, the present invention also provides an additional
possibility of heat integration. According to this possibility, the
top stream obtained from the distillation column of stage (c)
having a pressure in the above-mentioned ranges, especially
preferably in the range of from 0.4 to 0.8 bar, and temperature in
the range of from 10 to 40.degree. C., preferably from 10 to
30.degree. C. and especially preferably from 10 to 20.degree. C.,
is compressed to obtain a stream having a preferred pressure in the
range of from 1 to 10 bar, more preferably from 1 to 5 bar and
especially preferably from 2 to 5 bar and a temperature of up to
100.degree. C., more preferably in the range of from 80 to
100.degree. C. The compressed stream obtained is then at least
partially used to partially operate the evaporator of the
distillation column used in stage (c). Preferably, from 50 to 100%
of the top stream, still more preferably from 80 to 95% of the top
stream are used to partially operate the evaporator of the
distillation column used in stage (c).
[0144] According to a further embodiment of the present invention,
preferably from 1 to 50 wt.-%, of (ed), more preferably from 1 to
40 wt.-% of (Td) and especially preferably from 2 to 30 wt.-% of
(Td) are specifically used to start the operation of the evaporator
of the distillation column of stage (c), and preferably from 50 to
100% of the top stream, still more preferably from 80 to 95% of the
top stream are used to completely operate the evaporator of the
distillation column used in stage (c) once the distillation column
fully operates. Therefore, (Td) is partially used to start the
operation of the evaporator, and the compressed top stream obtained
from stage (c) takes over operation of the evaporator,
[0145] Thus, in addition to a part of (Td), the top stream obtained
from the distillation column of stage (c) is used to operate this
distillation column.
[0146] According to a further embodiment of the present invention,
separation of olefin oxide, preferably propylene oxide, in stage
(c) is performed in at least two, more preferably in two
distillation columns.
[0147] Therefore, the present invention also relates to a process
as described above, wherein in (c), the olefin oxide is separated
in two distillation columns, and wherein from 0 to 20 wt.-% of (Td)
are used to at least partially operate a vaporizer of the first
distillation column from which a mixture comprising at least 98
wt.-% of olefin oxide is obtained, said mixture being introduced
into the second distillation column, and from 1 to 30 wt,-%, of
(Td) are used to at least partially operate a vaporizer of the
second distillation column from which an olefin oxide stream
comprising at least 99.8 wt.-% olefin oxide is obtained.
[0148] Still more preferably, the olefin oxide stream obtained from
the second distillation column comprises at least 99.9 wt.-% of
olefin oxide, still more preferably at least 99.99 wt.-% of olefin
oxide.
[0149] Preferably, the first column has of from 30 to 110, more
preferably of from 40 to 100 and especially preferably of from 50
to 90 theoretical stages.
[0150] The first column is preferably operated at a top pressure of
from 1 bar or less. Especially preferably, the distillation column
is operated as a vacuum column at a top pressure of less than 1
bar, more preferably at not more than 0.9 bar, more preferably at
not more than 0.8 bar, more preferably at not more than 0.7 bar,
and still more preferably at not more than 0.6 bar. Preferred
ranges of the top pressure are, for example, from 0.3 to 0.9 bar,
more preferably from 0.4 bar to 0.8 bar. Preferred top pressures
are, for example, about 0.4 bar or about 0.5 bar or about 0.6 bar
or about 0.7 bar or about 0.8 bar.
[0151] Preferably, the second column has of from 25 to 60, more
preferably of from 30 to 55 and especially preferably of from 35 to
50 theoretical stages.
[0152] The second column is preferably operated at a top pressure
of from 1 bar to 7 bar, more preferably from 2 to 6 bar and
especially preferably from 3 to 5 bar.
[0153] The mixture obtained from the top of the first column which
is fed as feed stream to the second column can further contain
certain by-products resulting from one or more stages of the
overall epoxidation process, having boiling points lower than the
olefin, oxide, preferably the propylene oxide. Examples for such
by-products are aldehydes such as, for example, acetaldehyde and/or
formaldehyde. These by-products can be contained in the top stream
of the first column in an amount of up to 0.3 wt.-%, preferably up
to 0.20 wt.-% and especially preferably up to 0.15 wt.-%, based on
the total weight of (M-cii) and referring to the sum of the
respective weights of these low-boiling compounds.
[0154] It was surprisingly found that choosing a distillation top
pressure of this range allows for obtaining a ultrahigh degree of
purity of the olefin oxide, preferably propylene oxide, with regard
to the low boiling compounds, and simultaneously using at least
partially, further preferred exclusively (Td) to operate the
vaporizer of the second distillation column of stage (c).
[0155] In case two distillation columns are used in stage (c), from
0 to 20 wt.-% of (Td) are used to operate the vaporizer of the
first column and from 1 to 30 wt.-% of (Td) are used to operate the
vaporizer of the second column. More preferably, from 0 to 15 wt.-%
of (Td) are used to operate the vaporizer of the first column and
from 1 to 25 wt.-% of (Td) are used to operate the vaporizer of the
second column. Especially preferably, from 0 to 10 wt.-% of (Td)
are used to operate the vaporizer of the first column and from 2 to
20 wt.-% of (Td) are used to operate the vaporizer of the second
column.
[0156] If necessary, at least one feed stream fed into at least one
distillation column used in stage (c) can be heated with the
bottoms stream obtained from this column.
Stage (d)
[0157] According to stage (d), mixture (M-cii) obtained from stage
(c) as bottoms stream is subjected to a further distillative
separation process in which a mixture (M-di) comprising at least 85
wt.-% of methanol and up to 10 wt.-% of water, and a mixture
(M-dii) comprising at least 90 wt.-% of water are obtained.
[0158] Distillation in stage (d) can be performed in one, two,
three or more distillation columns.
[0159] According to one aspect of the present invention,
distillation in stage (d) is carried out in one distillation
column. Preferably, this distillation column has of from 10 to 100,
more preferably of from 20 to 90 and especially preferably of from
30 to 70 theoretical stages.
[0160] The distillation column is operated at a pressure preferably
of from 1 to 12 bar, more preferably of from 2 to 11 bar and
especially preferably of from 3 to 10 bar.
[0161] The mixture (M-di) obtained from the top of the column
comprises at least 85 wt.-% of methanol and up to 10 wt.-% of
water, more preferably at least 90 wt.-% of methanol and up to 10
wt.-% of water, more preferably at least 95 wt.-% of methanol and
up to 5 wt.-% of water, more preferably at least 98 wt.-% of
methanol and up to 4 wt.-% of water and especially preferably at
least 97 wt.-% of methanol and up to 3 wt.-% of water.
[0162] The reflux ratio of this column is preferably in the range
of 1 to 10, more preferably in the range of 2 to 8.
[0163] According to a preferred embodiment of the present
invention, distillation in stage (d) is performed in a two-pressure
distillation process, where in a first distillation column (K1),
distillation is carried out at a top pressure which is different
from the top pressure of a second distillation column (K2).
[0164] According to a still further preferred embodiment of the
present invention, the columns (K1) and (K2) are thermally coupled.
According to one embodiment, the condenser used to condense the top
stream of the first or second distillation column is used
simultaneously as the vaporizer of the second or first distillation
column. Preferably, the condenser used to condense the top stream
obtained from the second distillation column is used simultaneously
as the vaporizer of the first distillation column. According to
another embodiment, the bottoms stream obtained from column (K1)
which is fed as input stream into column (K2) is heated, prior to
being introduced into (K2), with the bottoms stream obtained from
column (K2). According to a preferred embodiment, these thermal
coupling possibilities are combined.
[0165] Therefore, the present invention also relates to a process
as described above, wherein in stage (d), a two-pressure
distillation is performed and the condenser used to condense the
top stream obtained from the second distillation column (K2) is
used simultaneously as the vaporizer of the first distillation
column (K1) and wherein the bottoms stream obtained from column
(K1) which is fed as input stream into column (K2) is heated, prior
to being introduced into (K2), with the bottoms stream obtained
from column (K2).
[0166] The term "first column (K1)" as used in the context of the
present invention relates to the column into which the mixture
(M-cii) is fed. The term "second column (K2)" as used in the
context of the present invention relates to the column into which
the bottoms stream obtained from (K1) is fed.
[0167] The distillation in the first column (K1) is preferably
carried out at a top pressure in the range of from 2 to 8 bar, more
preferably of from 2 to 6 bar and especially preferably in the
range of from 2.5 to 6 bar. The distillation in the second column
(K2) is preferably carded out at a top pressure in the range from 8
to 15 bar, more preferably of from 8.5 to 14 bar, and especially
preferably in the range from 9 to 13 bar.
[0168] Therefore, the present invention also relates to a process
as described above, wherein the top pressure of the first
distillation column is from 2 to 8 bar and the top pressure of the
second distillation column is from 8 to 14 bar.
[0169] Therefore, the present invention also relates to a process
as described above, wherein in (d), [0170] (i) the mixture (M-cii)
is introduced into a first distillation column (K1) from which the
vapor top stream (Td) is obtained, the distillation in (K1) being
carried out at a top pressure of from 2.5 to 6 bar; and [0171] (ii)
the bottoms stream obtained from (K1) is introduced into a second
distillation column (K2), the distillation in (K2) being carried
out at a top pressure of from 9 to 13 bar, [0172] wherein prior to
introducing into (K2), the bottoms stream obtained from (K1) is
heated to a temperature from 100 to 180.degree. C. with the bottoms
stream obtained from (K2), and wherein the condenser used to
condense the top stream obtained from (K2) is simultaneously used
as vaporizer of (K1).
[0173] Preferably, the bottoms stream obtained from (K1) is heated
to a temperature from 110 to 180.degree. C., more preferably from
120 to 180.degree. C., more preferably from 130 to 175.degree. C.
and still more preferably from 140 to 170.degree. C.
[0174] The reflux ratio of column (K2) is preferably in the range
of from 1 to 5, more preferably of from 2 to 4. The reflux ratio is
defined as the mass flow of the top stream obtained from column
(K2) divided by the mass flow of the fraction of this stream fed
back to the top of (K2).
[0175] Distillation column (K1) has preferably of from 5 to 30,
more preferably from 7 to 25 and especially preferably of from 10
to 20 theoretical stages.
[0176] Distillation column (K2) has preferably of from 5 to 60,
more preferably from 10 to 55 and especially preferably of from 15
to 50 theoretical stages.
[0177] According to a still further preferred embodiment, the
distillation column (K2) is configured as dividing wall column
having at least one side-offtake, preferably one side-offtake.
Preferably, the dividing wall column preferably has from 10 to 60,
more preferably from 15 to 50 theoretical stages.
[0178] The upper combined region of the inflow and offtake part of
the dividing wall column preferably has from 10 to 70%, more
preferably from 15 to 55%, the enrichment section of the inflow
part preferably has from 5 to 50%, more preferably from 15 to 30%,
the stripping section of the inflow part preferably has from 5 to
50%, more preferably from 15 to 30%, the stripping section of the
oftake part preferably has from 5 to 50%, more preferably from 15
to 30%, the enrichment section of the offtake part preferably has
from 5 to 50%, more preferably from 15 to 30%, and the lower
combined region of the inflow and offlake part of the column
preferably has from 5 to 50%, more preferably from 15 to 30%, in
each case of the total number of theoretical stages in the
column.
[0179] The dividing wall column (K2) used in the process of the
present invention is preferably configured either as a packed
column containing random packing or ordered packing or as a tray
column. For example, it is possible to use sheet metal or mesh
packing having a specific surface area of from 100 to 1000
m.sup.2/m.sup.3, preferably from about 250 to 750 m.sup.2/m.sup.3,
as ordered packing. Such packing provides a high separation
efficiency combined with a low pressure drop per theoretical
stage.
[0180] In the abovementioned configuration of the column, the
region of the column divided by the dividing wall, which consists
of the enrichment section of the inflow part, the stripping section
of the offtake part, the stripping section of the inflow part and
the enrichment section of the offtake part, or parts thereof is/are
provided with ordered packing or random packing. The dividing wall
can be thermally insulated in these regions.
[0181] Compared to a conventional distillation column, the dividing
wall column used in stage (d) has the advantage that certain
by-products resulting from one or more stages of the overall
epoxidation process can be easily separated from methanol. Since
mixture (M-di) is most preferably fed back as solvent into stage
(a), it was found that using dividing wall columns prevents these
by-products from exceeding undesirable concentrations in the
methanol loop. Examples for such by-products are compounds such as
glycol ethers.
[0182] Therefore, the present invention is characterized in that it
encompasses, in specific reaction stages, i.e. stages (a) and (d),
two dividing wall columns, thus rendering the overall epoxidation
process still more effective.
[0183] Therefore, the present invention also relates to a process
as described above wherein column (K2) is a dividing wall
column.
[0184] In case stage (d) is performed as two-pressure distillation
using a conventional distillation column (K1) and a dividing wall
column (K2), the top stream (Td) obtained from the top of column
(K1) comprises at least 85 wt.-% of methanol and up to 10 wt.-% of
water, more preferably at least 90 wt.-% of methanol and up to 10
wt.-% of water, more preferably at least 95 wt.-% of methanol and
up to 5 wt.-% of water, more preferably at least 96 wt.-% of
methanol and up to 4 wt.-% of water and especially preferably at
least 97 wt.-% of methanol and up to 3 wt.-% of water. According to
particularly preferred embodiment, the top stream (Td) comprises
less than 3 wt.-% of water such as, for example, from 1 to 2 wt.-%
of water.
[0185] The temperature of (Td) is preferably in the range of from
90 to 130.degree. C., more preferably of from 95 to 120.degree. C.
and especially preferably of from 100 to 110.degree. C.
[0186] The bottoms stream obtained from (K1) has a preferred
temperature of from 100 to 140.degree. C., more preferably in then
range of from 110 to 130.degree. C. According to the
above-described preferred embodiment, this bottoms stream is fed in
to (K2) and, prior to feeding, heated with the bottoms stream of
(K2) to a temperature of from 110 to 180.degree. C., more
preferably from 120 to 180.degree. C., more preferably from 130 to
175.degree. C. and still more preferably from 140 to 170.degree.
C.
[0187] The bottoms stream obtained from (K1) has a preferred
methanol content of from 40 to 70 wt.-% and a preferred water
content of from 30 to 60 wt.-%.
[0188] The top stream (M-di) obtained from column (K2) comprises at
least 85 wt.-% of methanol and up to 10 wt.-% of water, more
preferably at least 90 wt.-% of methanol and up to 10 wt.-% of
water, more preferably at least 95 wt.-% of methanol and up to 5
wt.-% of water, more preferably at least 96 wt.-% of methanol and
up to 4 wt.-% of water and especially preferably at least 97 wt.-%
of methanol and up to 3 wt.-% of water. According to particularly
preferred embodiment, the top stream obtained from column (K2)
comprises less than 3 wt.-% of water such as, for example, from 1
to 2 wt.-% of water.
[0189] The mixture (M-dii) obtained from the bottom of column (K2)
comprises at least 90 wt.-% of water, more preferably at least 95
wt.-% of water and especially preferably at least 97 wt.-% of
water. Preferably (M-dii) is essentially free of methanol, i.e. it
has a methanol content of less than 5 ppm, more preferably of less
than 1 ppm. Additionally to water, (M-dii) can comprise certain
by-products resulting from one or more stages of the overall
epoxidation process. Examples for such by-products are glycol
compounds such as propylene glycols. These by-products can be
contained in (M-dii) in an amount of up to 4 wt.-%, preferably up
to 3 wt.-%.
[0190] According to the process of the present invention, it is
possible that the mixture (M-cii) introduced into stage (d)
comprises by-produces produced in at least one stage of the overall
epoxidation process such as glycol ethers like methoxypropanols. As
to these mixtures, it was surprisingly found that above-described
two-pressure distillation, additionally comprising a dividing-wall
column, allows, on the one hand, for producing (Td) used as main
source of heat integration of the overall process, and
simultaneously, on the other hand, for simultaneously separating
these by-products from the methanol stream (Td) which is fed back
as solvent into stage (a) and obtaining a mixture (M-dii) as
described above having a very low content regarding these
by-products of not more than 4 wt.-%, preferably not more than 3
wt.-%.
[0191] A mixture (M-diii) taken from the sideofftake of the
dividing-wall column (K2) comprises at least 10 wt.-% of glycol
ethers, more preferably at least 15 wt.-% of glycol ethers and
especially preferably at least 20 wt.-% of glycol ethers. Still
more preferably, (M-diii) has a methanol content of not more than 5
wt.-%, more preferably less than 2 wt.-%, more preferably not more
than 2 wt.-% and especially preferably less than 2 wt.-%.
[0192] If the separation process according of stage (d) is
performed using a two-pressure distillation using a conventional
distillation column (K1) together with a dividing wall column (K2),
wherein the bottoms stream obtained from (K1) is heated with the
bottoms stream obtained from (K2), and wherein the condenser used
to condense the top stream obtained from (K2) is simultaneously
used as vaporizer of (K1), the energy balance of stage (d) can be
significantly improved. Based on a one-pressure distillation using
at least one conventional distillation column as standard of
comparison, an energy saving of from 40 to 70%, preferably from 50
to 60% is possible, provided that mixtures (M-di) and (M-dii)
having essentially the same composition are obtained in the
one-pressure or the two-pressure processes. Thus, the two-pressure
distillation process further improves heat integration of the
overall epoxidation process.
[0193] According to a preferred embodiment of the present
invention, heat integration of the process is still further
improved by heating the fed stream fed into at least one
distillation column of stage (d) with the bottoms stream of this
column. More preferably, the feed stream fed into the second
column, preferably the dividing wall column, is heated with bottoms
stream obtained from this column. Still more preferably, the
temperature of the feed stream fed into the dividing wall column is
heated from a temperature of from 100 to 140.degree. C., more
preferably from 110 to 130.degree. C. to a temperature of from 140
to 180.degree. C., more preferably from 150 to 170.degree. C.
Stage (x)
[0194] According to a preferred embodiment wherein [0195] (a)
propene is reacted with hydrogen peroxide in the presence of
methanol as solvent in at least two reaction stages to obtain a
mixture (M-a) comprising propylene oxide, unreacted propene,
propane, methanol and water, wherein between at least two reaction
stages, propylene oxide is separated by distillation; [0196] (b)
unreacted propene is separated from the mixture (M-a) by
distillation to obtain a mixture (M-bi) comprising propane and at
least 80 wt.-% of propene, and a mixture (M-bii) comprising
methanol, water and at least 7 wt.-% of propylene oxide the process
of the present invention additionally comprises a further stage (x)
of separating propene from mixture (M-bi).
[0197] Optionally, prior to separation of propene from (M-bi),
(M-bi) can be subjected to at least one further separation process
where by-products resulting from the epoxidation reaction can be
removed from the mixture, and/or be subjected to at least one
cooling stage.
[0198] The mixture (M-bi) fed to the distillation process of stage
(x) has a propene content of at least 85 wt.-%, still more
preferably of from 85 to 90.
[0199] Separation according to stage (x) is preferably carried out
in at least one distillation column, more preferably in one
distillation column. Preferably, this column has of from 80 to 160,
more preferably of from 90 to 140 and especially preferably of from
100 to 140 theoretical stages.
[0200] The distillation column is preferably operated at a top
pressure of from 1 to 50 bar, more preferably of from 10 to 40 bar,
more preferably of from 20 to 30 bar.
[0201] According to a still further preferred embodiment, a mixture
(M-x) is obtained comprising at least 85 wt.-% of olefin, still
more preferably of from 85 to 90 wt.-% of olefin, preferably of
propene.
[0202] More preferably, the mixture (M-x) comprises from 92 to 99
wt.-%, more preferably from 94 to 99 wt.-%, and especially
preferably from 96 to 99 wt.-% of propene. Depending on the exact
distillation conditions, (M-x) can be obtained at the top of the
column or as a side stream of the distillation column. The propane
content of (M-x) is preferably less than 5 wt.-%, more preferably
less than 4 wt.-% and especially lees than 3 wt.-%, based on the
total weight of mixture (M-x).
[0203] Therefore, the present invention also relates to a process
as described above, wherein in (a), the mixture (M-a) additionally
comprises propane, wherein in (b), unreacted propene is separated
from the mixture (M-a) by distillation to obtain the mixture (M-bi)
comprising the unreacted propene and propane, said process
additionally comprising [0204] (x) separating the propene from the
mixture (M-bi) by distillation to obtain a mixture (M-x) comprising
at least 90 wt.-% of propene, [0205] and wherein the vapor top
stream (Td) is used to operate at least partially at least one
vaporizer used in at least one distillation column used in at least
one of stages (a), (b), (c) and (x).
[0206] Preferably, from 1 to 20 wt.-%, more preferably from 2 to 15
wt.-% and especially preferably from 3 to 10 wt.-% of (Td) are used
to operate the vaporizer of the distillation column used in stage
(x).
[0207] Therefore, the present invention also relates to a process
as described above wherein from 5 to 60 wt.-% of (Td) are used to
operate at least partially a vaporizer used in (a), from 1 to 20
wt.-% of (Td) are used to operate at least partially a vaporizer
used in (b), from 1 to 50 wt.-% of (Td) are used to operate at
least partially a vaporizer used in (c), and from 1 to 20 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(x).
[0208] Optionally, it is possible that the vaporizer of the
distillation column of stage (x) is additionally operated by low
pressure steam having, for example, a pressure of about 1.5 bar, or
hot water.
[0209] According to a further preferred embodiment, mixture (M-x)
is recycled and fed back as starting material stream into stage
(a), either into at least one of the reactors used in stage (i) of
stage (a) or into at least one of the reactors used in stage (iii)
of stage (a) or into at least one of the reactors used in stage (i)
and at least one of the reactors used in stage (iii) of stage
(a).
[0210] Thus, stage (x) of the present invention not only provides
an improvement regarding heat integration of the overall process
but also an ideal possibility of recovering propene in a degree of
purity so as to recycle propene as starting material for the
epoxidation reaction. Hence, stage (x) provides an improvement of
energy balance and simultaneously of material balance of the
overall process.
[0211] If necessary, at least one feed stream fed into at least one
distillation column used in stage (x) can be heated with the
bottoms stream obtained from this column.
Stage (v)
[0212] According to the present invention, a mixture (M-cii) is
obtained from stage (c) comprising of from 55 to 85 wt.-%, more
preferably from 65 to 80 wt.-% and especially preferably from 75 to
80 wt.-% of methanol, and of from 15 to 45 wt.-%, more preferably
from 20 to 35 wt.-% and especially preferably of from 20 to 25
wt.-% of water.
[0213] Mixture (M-cii) can further contain certain by-products
resulting from one or more. stages of the overall epoxidation
process, having boiling points lower than water and lower than
methanol. Examples for such by-products are aldehydes such as, for
example, acetaldehyde and/or propionaldehyde, or other compounds
such as dioxolanes. These by-products can be contained in (M-cii)
in an amount of up to 0.3 wt.-%, preferably up to 0.15 wt.-% and
especially preferably up to 0.12 wt.-%, based on the total weight
of (M-cii) and referring to the sum of the respective weights of
these low-boiling compounds.
[0214] Therefore, the present invention also relates to a process
wherein prior to stage (d), at least one of these low boiling
compounds is separated from mixture (M-cii) to give a mixture (M-y)
which is then fed to stage (d).
[0215] In stage (y), at least one, preferably one distillation
column is used. Preferably, this column has of from 2 to 40, more
preferably of from 5 to 30 and especially preferably of from 10 to
25 theoretical stages.
[0216] The distillation column is preferably operated at a top
pressure of from 1 to 2 bar, more preferably of from 1 to 1.5 bar,
more preferably of from 1 to 1.2 bar. It was surprisingly found
that choosing a distillation top pressure of this range allows for
obtaining a high degree of purity of the bottoms stream with regard
to the low boiling compounds, and simultaneously using at least
partially (Td) to operate the vaporizer of the distillation column
of stage (y).
[0217] Therefore, the present invention also relates to a process
as described above, wherein in (c), the mixture (M-cii)
additionally comprises at least one compound having a boiling
temperature lower than methanol and lower than water at a given
pressure, said process comprising [0218] (y) separating the at
least one compound having a boiling point lower than methanol and
lower than water from the mixture (M-cii) by distillation to obtain
a mixture (M-y) comprising from 40 to 80 wt.-% of methanol and from
10 to 55 wt.-% of water; [0219] (d) separating methanol from the
mixture (M-y) in at least one distillation stage to obtain a
mixture (M-di) comprising at least 85 wt.-% of methanol and up to
10 wt.-% of water, and a mixture (M-dii) comprising at least 90
wt.-% of water, [0220] and wherein the vapor top stream (Td) is
used to operate at least partially at least one vaporizer used in
at least one distillation column used in at least one of stages
(a), (b), (c) and (y).
[0221] Accordingly, the present invention also provides a process
as described above, wherein from 5 to 60 wt.-% of (Td) are used to
operate at least partially a vaporizer used in (a), from 1 to 20
wt.-% of (Td) are used to operate at least partially a vaporizer
used in (b), from 1 to 60 wt.-% of (Td) are used to operate at
least partially a vaporizer used in (c), and from 5 to 60 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(y).
[0222] More preferably, from 15 to 50 wt.-%, still more preferably
from 20 to 40 wt.-% of (Td) are used to operate at least partially
a vaporizer used in (y). Especially preferably, only (Td) is used
to operate the vaporizer used in (y).
[0223] According to a still further preferred embodiment, a mixture
(M-y) is obtained as bottoms stream comprising less than 0.06
wt.-%, more preferably less than 0.05 wt.-% and especially
preferably less than 0.04 wt.-% of the low-boiling compounds, based
on the total weight of (M-cii) and referring to the sum of the
respective weights of these low-boiling compounds.
[0224] Thus, using only (Td) to operate the distillation column, it
is possible to decrease the amount of low-boiling compounds for at
least 50%, preferably more than 50%. Using no additional external
energy source, the inventive process therefore allows for
preventing these low-boiling compounds from exceeding undesirable
concentrations in the methanol loop.
[0225] If necessary, at least one feed stream fed into at least one
distillation column used in stage (y) can be heated with the
bottoms stream obtained from this column.
[0226] In the context of the present invention, it was additionally
found that the top stream obtained from the distillation column of
stage (y) can be advantageously employed for operating at least one
of the distillation columns in the overall epoxidation process.
Most preferably, the top stream obtained from the distillation
column of stage (y) is employed for operating at least one
distillation column used in stage (c).
[0227] Therefore, the present invention also relates to a process
according to the invention, wherein preferably from 1 to 80 wt.-%,
more preferably from 10 to 60 wt.-% and still more preferably from
15 to 40 wt.-% of the top stream obtained from the distillation
column of stage (y) are used to operate the vaporizer of the at
least one distillation column of stage (c).
Stage (z)
[0228] According to another embodiment of the present invention,
the by-products mentioned above which result from one or more
stages of the overall epoxidation process and which have boiling
points lower than water and lower than methanol, for example
aldehydes such as, for example, acetaldehyde and/or
propionaldehyde, or other compound such as dioxolanes, which
by-products can be contained in (M-cii) in an amount of up to 0.3
wt.-%, preferably up to 0.15 wt.-% and especially preferably up to
0.12 wt.-%, based on the total weight of (M-cii) and referring to
the sum of the respective weights of these low-boiling compounds,
can be separated in a stage (z) which is performed after stage
(d).
[0229] Therefore, the present invention also relates to a process
according to one of above-mentioned embodiments, wherein in (c),
the mixture (M-cii) additionally comprises at least one compound
having a boiling temperature lower than methanol and lower than
water at a given pressure, said process comprising [0230] (d)
separating methanol from the mixture (M-cii) in at least one
distillation stage to obtain a mixture (M-di) comprising at least
85 wt.-% of methanol, up to 10 wt.-% of water and the at least one
compound having a boiling temperature lower than methanol and lower
than water, and a mixture (M-dii) comprising at least 90 wt.-% of
water, [0231] (z) separating the compound having a boiling point
lower than methanol and lower than water from the mixture (M-di) by
distillation to obtain a mixture (M-z) comprising from 85 to 99.6
wt.-% of methanol and from 0.5 to 10 wt.-% of water; [0232] and
wherein the vapor top stream (Td) is used to operate at least
partially at least one vaporizer used in at least one distillation
column used in at least one of steps (a), (b), (c) and (z).
[0233] As to stage (d), reference is made to the paragraph above
describing stage (d) and its preferred embodiments. Hence, stage
(d) is preferably carried out using two, three or more columns,
more preferably tow columns, still more preferably one conventional
column (K1) and one dividing-wall column (K2), and especially
preferably as two-pressure distillation using one conventional
column (K1) and one dividing-wall column (K2), as described
hereinabove.
[0234] Thus, especially if stage (d) is performed as two-pressure
distillation using a conventional distillation column (K1) and a
dividing wall column (K2), and wherein methanol is separated from
the mixture (M-cii) to obtain a mixture (M-di) comprising at least
85 wt.-% of methanol, up to 10 wt.-% of water and the at least one
compound having a boiling temperature lower than methanol and lower
than water, and a mixture (M-dii) comprising at least 90 wt.-% of
water, the top stream (Td) is obtained from (K1), and the mixture
(M-di) is obtained as top stream from (K2), the mixture (M-dii) is
obtained as bottoms stream from (K2) and the mixture (M-diii) is
obtained from the side-offtake from (K2). The top stream (Td) is
used as described above, and the condensate of (Td) resulting, for
example, from at least one of the vaporizers as described
hereinabove and hereinunder, said condensate containing the at
least one compound having a boiling temperature lower than methanol
and lower than water, is fed into stage (z) to obtain a mixture
(M-z) as bottoms stream comprising from 85 to 99.5 wt.-% of
methanol and from 0.5 to 10 wt.-% of water.
[0235] The mixture (M-dii) obtained from the bottom of column (K2)
comprises at least 90 wt.-% of water, more preferably at least 95
wt.-% of water and especially preferably at least 97 wt.-% of
water. Preferably (M-dii) is essentially free of methanol, i.e. it
has a methanol content of less than 5 ppm, more preferably of less
than 1 ppm. Additionally to water, (M-dii) can comprise certain
by-products resulting from one or more stages of the overall
epoxidation process. Examples for such by-products are glycol
compounds such as propylene glycols. These by-products can be
contained in (M-dii) in an amount of up to 4 wt.-%, preferably up
to 3 wt.-%.
[0236] A mixture (M-diii) taken from the side-offtake of the
dividing-wall column (K2) comprises at least 10 wt.-% of glycol
ethers, more preferably at least 15 wt.-% of glycol ethers and
especially preferably at least 20 wt.-% of glycol ethers. Still
more preferably, (M-diii) has a methanol content of not more than 5
wt.-%, more preferably less than 2 wt.-%, more preferably not more
than 2 wt.-% and especially preferably less than 2 wt.-%.
[0237] According to a still further preferred embodiment, mixture
(M-di) obtained as top stream from (K2) is additionally fed into
stage (z).
[0238] According to a further embodiment, a part of mixture (M-di)
obtained as top stream from (K2) is fed as reflux to the top of
column (K1).
[0239] According to a further embodiment, a part of the condensate
of (Td) is fed as reflux to the top of column (K1).
[0240] According to a further embodiment, a part of mixture (M-di)
obtained as top stream from (K2) and a part of the condensate of
(Td) are fed as reflux to the top of column (K1).
[0241] Stage is preferably carried out using one distillation
column having, for example, from 2 to 40, preferably from 5 to 30
and especially preferably from 10 to 25 theoretical stages.
Distillation is carried out at a preferred pressure of from 1 to 2
bar, more preferably from 1 to 1.5 bar and especially from 1 to 1.2
bar. It was surprisingly found that choosing a distillation top
pressure of this range allows for obtaining a high degree of purity
of the bottoms stream with regard to the low boiling compounds, and
simultaneously using at least partially (Td) to operate the
vaporizer of the distillation column of: stage (z).
[0242] Accordingly, the present invention also provides a process
as described above, i wherein from 5 to 60 wt.-% of (Td) are used
to operate at least partially a vaporizer, used in (a), from 1 to
20 wt.-% of (Td) are used to operate at least partially a vaporizer
used in (b), from 1 to 50 wt.-% of (Td) are used to operate at
least partially a vaporizer used in (c), and from 5 to 60 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(z).
[0243] More preferably, from 15 to 50 wt.-%, still more preferably
from 20 to 40 wt.-% of (Td) are used to operate at least partially
a vaporizer used in (z). Especially preferably, only (Td) is used
to operate the vaporizer used in (z).
[0244] According to a still further preferred embodiment, a mixture
(M-z) is obtained as bottoms stream comprising less than 0.06
wt.-%, more preferably less than 0.05 wt.-% and especially
preferably less than 0.04 wt.-% of the low-boiling compounds, based
on the total weight of (M-cii) and referring to the sum of the
respective weights of these low-boiling compounds. Further, (M-z)
comprises at least 85 wt.-% of methanol and up to 10 wt.-% of
water, more preferably at least 90 wt.-% of methanol and up to 10
wt.-% of water, more preferably at least 95 wt.-% of methanol and
up to 5 wt.-% of water, more preferably at least 96 wt.-% of
methanol and up to 4 wt.-% of water and especially preferably at
least 97 wt.-% of methanol and up to 3 wt.-% of water. According to
particularly preferred embodiment, (M-z) comprises less than 3
wt.-% of water such as, for example, from 1 to 2 wt.-% of
water.
[0245] Mixture (M-z) is most preferably fed back as solvent into
stage (a).
[0246] Thus, using only (Td) to operate the distillation column of
stage (z), it is possible to decrease the amount of low-boiling
compounds for at least 50%, preferably more than 50%. Using no
additional external energy source, the inventive process therefore
allows for preventing these low-boiling compounds from exceeding
undesirable concentrations in the methanol loop.
[0247] If necessary, at least one feed stream fed into at least one
distillation column used in stage (z) can be heated with the
bottoms stream obtained from this column.
[0248] The present invention also comprises an embodiment according
to which a stage (y) is performed prior to stage (d) and
simultaneously a stage (z) is performed after stage (d).
Stage (e)
[0249] According to stage (d), a mixture (M-dii) is obtained
preferably comprising at least 90 wt.-% of water, more preferably
at least 95 wt.-% of water and especially preferably at least 97
wt.-% of water Preferably (M-dii) is essentially free of methanol,
i.e. it has methanol content of less than 5 ppm, more preferably of
less than 1 ppm. Additionally to water, (M-dii) can comprise
certain by-products resulting from one or more stages of the
overall epoxidation process. Examples for such by-products are
glycol compounds such as propylene glycols. These by-products can
be contained in (M-dii) in an amount of up to 4 wt.-%, preferably
up to 3 wt.-%.
[0250] In order to separate at least one of these glycols from
mixture (M-dii), it was surprisingly found that a vaporization
process is suitable for this purpose. In this context, it was found
that vaporization can be performed using at least partially the
methanol steam, i.e. top the stream (Td).
[0251] Therefore, the present invention also relates to a process
as described above, additionally comprising [0252] (e) evaporating
the mixture (M-dii).
[0253] Therefore, the present invention also relates to a process
additionally comprising a stage (e), wherein from 5 to 60 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(a), from 1 to 20 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 1 to 50 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (c), and
from 1 to 50 wt.-% of (1d) are used to operate at least partially a
vaporizer used in (e).
[0254] Still more preferably, 10 to 40 wt.-%, especially preferably
from 15 to 35 wt.-% of (Td) are used to operate at least one
vaporizer used in stage (e).
[0255] Thus, yet another instrument is provided to still further
improve the energy balance of the overall epoxidation process and
simultaneously to recover a product of value, i.e. propylene glycol
which can be separated having a degree of purity of preferably at
least 80 wt.-% and a water content of preferably not more than 5
wt.-%, more preferably not more than 4 wt.-% and still more
preferably not more than 3 wt.-%.
[0256] If necessary, a feed stream fed into a distillation column
used in stage (e) can be heated with the bottoms stream obtained
from this column.
[0257] According to a still further preferred embodiment of the
present invention, the overall epoxidation process also
encompasses, in addition to the heat exchangers used to at least
partially transfer the heat contained in (Td) to the evaporators
used in the distillation columns described above, at least one
additional heat exchanger which serves as a control heat exchanger
for the overall process.
[0258] Due to the number and various possibilities of improving the
energy balance of the overall epoxidation process by using the
methanol vapor (Td) as heat source for operating respective
vaporizers in distillation columns, it was found that this at least
one additional heat exchanger serves as an ideal instrument to
remove part of (Td) if, at a given point in time, more (Td) is
produced in stage (d) than the needs of the overall process
requires. In this case, surplus (Td) is fed into the at least one
control heat exchanger from which a methanol stream can be obtained
which is recycled into stage (a) as solvent.
[0259] Therefore, the present invention also provides a process as
described above, additionally comprising at least one control heat
exchanger.
[0260] According to a preferred embodiment, from 1 to 50 wt.-% of
(Td), more. preferably from 2 to 40 wt.-% of (Cd) and especially
preferably from 3 to 30 wt.-% of (Td) are used to at least
partially as feed stream of at least one control heat exchanger and
therefore to operate said at least one control heat exchanger used
in the process.
[0261] According to a preferred embodiment of the present
invention, the methanol vapor (Td) used to operate the vaporizers
of the distillation columns, as described above, is subsequently
re-used, optionally after collecting and/or storing, as solvent in
stage (a) of the process. Alternatively or additionally, it can be
used in at least one further process. Most preferably, it is
recycled into the inventive epoxidation process thus improving the
energy balance of the overall process and simultaneously the
material balance of the overall balance.
[0262] According to yet another embodiment of the present
invention, the inventive process comprises still another control
heat exchanger which can act as counterpart of above-described
control heat exchanger (fly wheel exchanger). This additional heat
exchanger can serve as a source of methanol steam in case at a
given point in time, there is not enough (Td) produced in stage (d)
to meet the needs of the overall process. In this case, fresh
methanol and/or methanol condensate obtained from (Td) after having
served as heat source in the process, optionally collected and
stored, can be fed to this additional control heat exchanger where
methanol steam is produced. As heat source of this additional
control heat exchanger, each suitable stream can be used. Most
preferred is water steam.
[0263] Therefore, the present invention also relates to an
epoxidation process comprising two heat exchangers acting as
counterparts for meeting the needs of the epoxidation process
regarding methanol steam as heat source for operating the
distillation columns as described above.
[0264] Thus, by providing two counterpart control heat exchangers,
the present invention provides a flexible instrument to meet, at
any given point in time, the actual needs of the process regarding
methanol steam as heat source.
[0265] As already described above, the present invention also
provides a process wherein the feed of at least one distillation
column used in stages (a), (b), (c), and (d), optionally also at
least one of stages (x), (y) and (e), is heated with the bottom
stream of this distillation column. Most preferably, at least one
distillation column used in stages (a) and (d) is heated with the
bottom stream of this distillation column.
[0266] In addition to the heat integration improvements described
above, i.e. the inventive process encompassing an effective use of
the methanol steam (Td), optionally together with an effective use
of certain bottoms stream for heating feed streams, it was found
that the overall process can be further improved by specific
condensation stages wherein top streams obtained from specific
columns are condensed in more than one stages, most preferably in
two stages.
[0267] Therefore, the present invention also provides a process
according to any one of above-mentioned embodiments, wherein the
top stream obtained from at least one distillation column used in
stages (a), (b), and (c), optionally additionally in at least one
of stages (x), y) and (e), is condensed in two stages, wherein in
the first stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
[0268] Most preferably, this two-stage condensation is applied to
the top streams obtained from the columns used in stages (b) and
(c).
[0269] Therefore, the present invention also provides a process
according to any one of above-mentioned embodiments, wherein in
(c), the olefin oxide is separated in two distillation columns, and
wherein from 0 to 20 wt.-% of (Td) is used to at least partially
operate a vaporizer of the first distillation column from which a
mixture comprising at least 98 wt.-% of olefin oxide is obtained,
said mixture being introduced into the second distillation column,
and from 1 to 30 wt.-% of (Td) are used to at least partially
operate a vaporizer of the second distillation column from which an
olefin oxide stream comprising at least 99.8 wt.-% olefin oxide is
obtained, said olefin oxide stream comprising at least 99.8 wt.-%
olefin oxide being condensed in two stages, wherein in the first
stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
[0270] According to an especially preferred embodiment, the present
invention provides a process for the epoxidation of propene,
comprising [0271] (a) reacting the propene with hydrogen peroxide
in the presence of methanol as solvent in at least two reaction
stages to obtain a mixture (M-a) comprising propylene oxide,
unreacted propene, propane, methanol and water, wherein between at
least two reaction stages, propylene oxide is separated by
distillation; [0272] (b) separating unreacted propene from the
mixture (M-a) by distillation to obtain a mixture (M-bi) comprising
propane and at least 80 wt.-% of propene, and a mixture (M-bii)
comprising methanol, water and at least 7 wt.-% of propylene oxide;
[0273] (x) separating propene from the mixture (M-bi) by
distillation to obtain a mixture (M-x) comprising at least 95 wt.-%
of propene, and reintroducing (M-x) into (a); [0274] (c) separating
the propylene oxide from the mixture (M-bii) in at least one
distillation stage to obtain a mixture (M-ci) comprising at least
99 wt.-% of propylene oxide and a mixture (M-cii) comprising water,
at least one compound having a boiling temperature lower than
methanol and lower than water at a given pressure, and at least 60
wt.-% of methanol; [0275] (y) separating the at least one compound
having a boiling point lower than methanol and lower than water
from the mixture (M-cii) by distillation to obtain a mixture (M-y)
comprising from 40 to 80 wt.-% of methanol and from 10 to 55 wt.-%
of water; [0276] (d) separating methanol from the mixture (M-y) in
at least one distillation stage to obtain a mixture (M-di)
comprising at least 85 wt.-% of methanol and up to 10 wt.-% of
water, and a mixture (M-dii) comprising at least 90 wt.-% of water,
and re-introducing (M-di) into (a); [0277] (e) evaporating the
mixture (M-dii), [0278] wherein a vapor top stream (Td) obtained
from at least one distillation column used in (d), said vapor top
stream (Td) comprising at least 85 wt.-% methanol, and wherein from
15 to 50 wt.-% of (Td) are used to operate at least partially a
vaporizer used in (a), from 2 to 15 wt.-% of (Td) are used to
operate at least partially a vaporizer used in (b), from 1 to 10
wt.-% of (Td) are used to operate at least partially a vaporizer
used in (x), from 2 to 40 wt.-% of (Td) are used to operate at
least partially a vaporizer used in (c), from 15 to 50 wt.-% of
(Td) are used to operate at least partially a vaporizer used in
(y), and from 10 to 40 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (e).
[0279] As to this embodiment, it is still further preferred that in
(c), the propylene oxide is separated in two distillation columns,
and wherein from 0 to 20 wt.-% of (Td) is used to at least
partially operate a vaporizer of the first distillation column from
which a mixture comprising at least 98 wt.-% of propylene oxide is
obtained, said mixture being introduced into the second
distillation column, and from 1 to 30 wt.-% of (Td) are used to at
least partially operate a vaporizer of the second distillation
column from which an propylene oxide stream comprising at least
99.8 wt.-% propylene oxide is obtained.
[0280] Additionally or alternatively to the separation in two
distillation columns, this embodiment comprises at least one
further integration method selected from the group consisting of
[0281] (I) using 1 to 40 wt.-% of (Td) to at least partially
operate at least one control heat exchanger used in the process;
[0282] (II) heating the feed of at least one distillation column
used in stages (a), (b), (x), (c), (y), (d) and (e) with the bottom
stream of this distillation column; and [0283] (III) condensing the
top stream obtained from at least one distillation column used in
stages (a), (b), (x), (c), (y), and (e) in two stages, wherein in
the first stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
[0284] Additionally or alternatively to the separation in two
distillation columns and at least one of the methods (I) to (III),
this embodiment comprises a preferred embodiment of stage (d),
according to which [0285] (i) the mixture (M-y) is introduced into
a first distillation column (K1) from which the vapor top stream
(Td) is obtained, the distillation in (K1) being carried out at a
top pressure of from 2.5 to 6 bar; and [0286] (ii) the bottoms
stream obtained from (K1) is introduced into a second distillation
column (K2), most preferably a dividing wall column (K2), the
distillation In (K2) being carried out at a top pressure of from 9
to 13 bar, [0287] wherein prior to introducing into (K2), then
bottoms stream obtained from (K1) is heated to a temperature from
120 to 180.degree. C. with the bottoms stream obtained from (K2),
and wherein the condenser used to condense the top stream obtained
from (K2) is simultaneously used as vaporizer of (K1).
[0288] According to a still further preferred embodiment, the
present invention provides a process for the epoxidation of
propene, comprising [0289] (a) reacting the propene with hydrogen
peroxide in the presence of methanol as solvent in at least two
reaction stages to obtain a mixture (M-a) comprising propylene
oxide, unreacted propene, propane, methanol and water, wherein
between at least two reaction stages, propylene oxide is separated
by distillation in a divided wall column, wherein separated
methanol is recycled into (a): (b) separating unreacted propene
from the mixture (M-a) by distillation to obtain a mixture (M-bi)
comprising propane and at least 80 wt.-% of propene, and a mixture
(M-bii) comprising methanol, water and at least 7 wt.-% of
propylene oxide; [0290] (x) separating propene from the mixture
(M-bi) by distillation to obtain a mixture (M-x) comprising at
least 95 wt.-% of propene, and re-introducing (M-x) into (a);
[0291] (c) separating the propylene oxide from the mixture (M-bii)
in two distillation columns, wherein from the first distillation
column, a first mixture comprising at least 99 wt.-% of propylene
oxide and a mixture (M-cii) comprising water, at least one compound
having a boiling temperature lower than methanol and lower than
water at a given pressure, and at least 60 wt.-% of methanol, are
obtained, said first mixture being introduced into the second
distillation column from which a mixture (M-ci) comprising at least
99.8 wt.-% propylene oxide is obtained; [0292] (y) separating the
at least one compound having a boiling point lower than methanol
and lower than water from the mixture (M-cii) by distillation to
obtain a mixture (M-y) comprising from 40 to 80 wt.-% of methanol
and from 10 to 55 wt.-% of water; [0293] (d) separating methanol
from the mixture (M-y) wherein [0294] (i) the mixture (M-y) is
introduced into a first distillation column (K1) from which the
vapor top stream (Td) is obtained, the distillation in (K1) being
carried out at a top pressure of from 2.5 to 6 bar; and [0295] (ii)
the bottoms stream obtained from (K1) is introduced into a second
distillation column (K2), the distillation in (K2) being carried
out at a top pressure of from 9 to 13 bar, (K2) being a dividing
wall column, [0296] and wherein, prior to introducing into (K2),
the bottoms stream obtained from (K1) is heated to a temperature
from 130 to 175.degree. C. with the bottoms stream obtained from
(K2), and wherein the condenser used to condense the top stream
obtained from (K2) is simultaneously used as vaporizer of (K1), and
wherein (Td) and the top stream obtained from (K2) are
re-introduced into (a); [0297] (e) evaporating the mixture (M-dii),
[0298] wherein a vapor top stream (Td) obtained from at least one
distillation column used in (d), said vapor top stream (Td)
comprising at least 85 wt.-% methanol, is used to operate at least
partially at least one vaporizer used in at least one distillation
column used in at least one of stages (a), (b), (c), (e), (x) and
(y).
[0299] As to this embodiment, it is still further preferred that
from 15 to 50 wt.-% of (Td) are used to operate at least partially
a vaporizer used in (a), from 2 to 15 wt.-% of (Td) are used to
operate at least partially a vaporizer used in (b), from 2 to 15
wt.-% of (Td) are used to operate at least partially a vaporizer
used in (x), from 0 to 15 wt.-% of (Td) are used to operate at
least partially a vaporizer used in the first distillation column
in (c), from 2 to 25 wt.-% of (Td) are used to operate at least
partially a vaporizer used in the second distillation column in
(c), from 15 to 50 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (y), and from 2 to 20 wt.-% of (Td)
are used to operate at least partially a vaporizer used in (e).
[0300] Additionally or alternatively, this embodiment comprises at
least one further integration method selected from the group
consisting of [0301] (I) using 1 to 50 wt.-% of (Td), more
preferably 2 to 40 wt.-% of (Td) and still more preferably from 3
to 30 wt.-% of (Td) to at least partially operate at least one
control heat exchanger used in the process; [0302] (II) heating the
feed of at least one distillation column used in stages (a), (b),
(x), (c), (y), (d) and (e), preferably in stages (a) and/or (d),
with the bottom stream of this distillation column; and [0303]
(III) condensing the top stream obtained from at least one
distillation column used in stages (a), (b), (x), (c), (y), and
(e), more preferably in stages (b) and/or (c), in two stages,
wherein in the first stage, the condenser is cooled with water
having an inlet temperature of from 15 to 40.degree. C. and in the
second stage, the condenser is cooled with water having an inlet
temperature of from 5 to 20.degree. C., wherein the inlet
temperature of the water used in the second stage is lower than the
inlet temperature of the water used in the first stage.
[0304] According to a still further preferred embodiment, the
present invention provides a highly integrated process for the
epoxidation of propene, comprising. [0305] (a) reacting the propene
with hydrogen peroxide in the presence of methanol as solvent in at
least two reaction stages to obtain a mixture (M-a) comprising
propylene oxide, unreacted propene, propane, methanol and water,
wherein between at least two reaction stages, propylene oxide is
separated by distillation: [0306] (b) separating unreacted propene
from the mixture (M-a) by distillation to obtain a mixture (M-bi)
comprising propane and at least 80 wt.-% of propene, and a mixture
(M-bii) comprising methanol, water and at least 7 wt.-% of
propylene oxide; [0307] (x) separating propane from the mixture
(M-bi) by distillation to obtain a mixture (M-x) comprising at
least 95 wt.-% of propene, and re-introducing (M-x) into (a);
[0308] (c) separating the propylene oxide from the mixture (M-bii)
in two distillation columns, wherein from the first distillation
column, a first mixture comprising at least 99 wt.-% of propylene
oxide and a mixture (M-cii) comprising water, at least one compound
having a boiling temperature lower than methanol and lower than
water at a given pressure and at least 60 wt.-% of methanol, are
obtained, said first mixture being introduced into the second
distillation column from which a mixture (M-ci) comprising at least
99.8 wt.-% propylene oxide is obtained; [0309] (y) separating the
at least one compound having a boiling point lower than methanol
and lower than water from the mixture (M-cii) by distillation to
obtain a mixture (M-y) comprising from 40 to 80 wt.-% of methanol
and from 10 to 55 wt.-% of water; [0310] (d) separating methanol
from the mixture (M-y) wherein [0311] (i) the mixture (M-y) is
introduced into a first distillation column (K1) from which the
vapor top stream (Td) is obtained, the distillation in (K1) being
carried out at a top pressure of from 2.5 to 6 bar; and [0312] (ii)
the bottoms stream obtained from (K1) is introduced into a second
distillation column (K2), the distillation in (K2) being carried
out at a top pressure of from 9 to 13 bar, (K2) being a dividing
wall column, [0313] and wherein, prior to introducing into (K2),
the bottoms stream obtained from (K1) is heated to a temperature
from 140 to 170.degree. C. with the bottoms stream obtained from
(K2), and wherein the condenser used to condense the top stream
obtained from (K2) is simultaneously used as vaporizer of (K1), and
wherein (Td) and the top stream obtained from (K2) are
re-introduced into (a); [0314] (e) evaporating the mixture (M-dii),
[0315] wherein a vapor top stream (Td) obtained from at least one
distillation column used in (Td), said vapor top stream (Td)
comprising at least 85 wt.-% methanol, wherein from 20 to 40 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
(a), from 3 to 10 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (b), from 3 to 10 wt.-% of (Td) are
used to operate at least partially a vaporizer used in (x), from 0
to 10 wt.-% of (Td) are used to operate at least partially a
vaporizer used in the first distillation column in (c), from 2 to
20 wt.-% of (Td) are used to operate at least partially a vaporizer
used in the second distillation column in (c), from 20 to 40 wt.-%
of (Td) are used to operate at least partially a vaporizer used in
i), from 15 to 35 wt.-% of (Td) are used to operate at least
partially a vaporizer used in (e), and from 3 to 30 wt.-% of (Td)
are used to at least partially operate at least one control heat
exchanger used in the process, said process further comprising at
least one further integration method selected from the group
consisting of [0316] (II) heating the feed of the distillation
column used in stage (a) with the bottoms stream of this column and
the feed of at least one distillation column used in stage (d) with
the bottoms stream of this column; [0317] (III) condensing the top
stream obtained from at least one distillation column used in
stages (a), (b), (x), (c), (y), and (e) in two stages, wherein in
the first stage, the condenser is cooled with water having an inlet
temperature of from 15 to 40.degree. C. and in the second stage,
the condenser is cooled with water having an inlet temperature of
from 5 to 20.degree. C., wherein the inlet temperature of the water
used in the second stage is lower than the inlet temperature of the
water used in the first stage.
EXAMPLES
Example 1
Heat-Integrated Process According to the Invention, Comprising
Stages (a), (b), (c), and (d)
[0318] Propylene (chemical grade) is converted to propylene oxide
with crude hydrogen peroxide having a concentration of 40 wt.-% in
the presence of methanol as solvent and TS-1 catalyst in two
reaction stages (i) and (iii), wherein between the two reaction
stages, propylene oxide is separated in a stage (ii) by
distillation.
[0319] Reaction in stage (i) is performed at 20 bar, in stage (iii)
at 10 bar. H.sub.2O.sub.2 conversion in stage (i) is 91%. The
distillation is running at a top pressure of 1.2 bar. From the
divided wall column in stage (ii) (40 theoretical stages, dividing
wall from stage 8 to 32), a stream containing surplus propylene and
propylene oxide is separated by distillation over the top. The side
stream with a concentration of 98 wt.-% methanol and 2 wt.-%
H.sub.2O is directly recycled to reaction stage (i) in an amount of
13.5% of the MeOH solvent stream applied in the process. The bottom
stream containing methanol, water, unreacted hydrogen peroxide and
epoxidation byproducts, e.g. glycolethers, is sent together with
fresh propylene to reaction stages (iii) to convert H.sub.2O.sub.2
to 99.9%. The stream (M-a) is a mixture of the distillation top
stream and the outlet stream of stage (iii) and comprises olefin
oxide, unreacted olefin, methanol and water. (M-a) is sent to stage
(b).
[0320] The unreacted olefin from the mixture (M-a) is separated by
distillation (b) in a distillation column with 14 theoretical
stages at a pressure of 1.1 bar to obtain a mixture (M-bi) at the
top of the column comprising 89 wt.-% olefin, 5.6 wt.-% of propane,
4 wt.-% methanol and 1.4 wt.-% oxygen and to obtain further a
mixture (M-bii) comprising methanol, water and 11.1 wt.-% of olefin
oxide.
[0321] Subsequently, the crude olefin oxide is separated from the
mixture (M-bii) in a distillation stage (c) at 0.5 bar in a
distillation tower having 80 theoretical stages to obtain a top
mixture (M-ci) comprising 99.8 wt.-% of olefin oxide, 0.04 wt.-% of
propylene, 0.04 wt.-% of acetaldehyde, 0.01 wt.-% of methanol, 0.01
wt.-% of methanol and a mixture (M-cii) comprising 76.2 wt.-% of
methanol, 22.7 wt.-% water; the rest being heavy boiling byproducts
of the epoxidation. The pure olefin oxide (>99.9 wt.-% propylene
oxide) is separated from the mixture (M-ci) by distillation at a
pressure of 4 bar in a distillation tower having 45 theoretical
stages as a side stream product from theoretical stage 5.
[0322] The solvent methanol is separated from the mixture (M-cii)
in two thermally coupled distillation columns in a stage (d).
(M-cii) is introduced into a first distillation column (13
theoretical stages) from which the vapor top stream (Td) is
obtained, the distillation being carried out at a top pressure of
3.9 bar. The bottoms stream obtained is introduced into a second
distillation column, a divided wall column (40 theoretical stages,
dividing wall from stage 6 to stage 30), the distillation being
carried out at a top pressure of 10.8 bar. Two thermally coupled
distillation towers are realized such that the condenser used to
condense the top stream obtained of the second tower is
simultaneously used as vaporizer for the first column. The mixture
(M-di) (liquid top product of the second column) comprises 98 wt.-%
of methanol and 2 wt.-% of water, the mixture (M-dii) (bottom
product of the second column) comprises 97.5 wt.-% of water, 2
wt.-% propylene glycol, 0.05 wt.-% monoglycol ethers, 0.45 wt.-%
higher glycol ethers, and the mixture (M-diii) (side stream product
of the second column) comprises 22 wt.-% glycol ethers and 88 wt.-%
water, The second methanolvwater separation column is operated with
16 bar steam (water steam) from the grid.
[0323] The top vapor stream (Td), obtained from the first
distillation column used in (d) having a pressure of 3.9 bar and a
temperature of 104.degree. C., and comprsing 98 wt.-% of methanol
and 2 wt.-% of water, is used to operate the vaporizers (reboilers)
used in the distillation column used as mentioned in the separation
stages (a), (b) and (c).
[0324] The following heat duties, calculated per metric ton/h
recycled methanol as solvent, are needed to operate the
above-described process:
[0325] A heat duty of 428 KW/(t.sub.MeOH/h) is necessary. Stage
(ii) consumes 37% (a heat duty of 158 KW/(t.sub.MeOH/h)), stage (b)
consumes 5% (a heat duty of 21 KW/(t.sub.MeOH/h)), stage (c)
consumes 12% (a heat duty of 50 KW/(t.sub.MeOH/h)) of the
MeOH-vapour top stream (Td), obtained from the first distillation
column used in (d) having a pressure of 3.9 bar and a temperature
of 104.degree. C.
Example 2
Process According to the Prior Art, Comprising Stages (a), (b),
(c), and (d) Without Heat Integration (Comparative Example)
[0326] Propylene (chemical grade) is converted to propylene oxide
with crude hydrogen peroxide having a concentration of 40 wt.-% in
the presence of methanol as solvent and TS-1 catalyst in two
reaction stages (i) and (iii), wherein between the two reaction
stages propylene oxide is separated in a stage (ii) by
distillation.
[0327] Reaction in stage (i) is performed at 20 bar, in stage (iii)
at 10 bar. H.sub.2O.sub.2 conversion in stage (i) is 91%. The
distillation is running at top pressure of 1.2 bar. From the
divided wall column in stage (ii) (40 theoretical stages, dividing
wall from stage 8 to 32), a stream containing surplus propylene and
propylene oxide is separated by distillation over the top. The side
stream with a concentration of 98 wt.-% methanol and 2 wt.-%
H.sub.2O is directly recycled to reaction stage (i) in an amount of
13.5% of the MeOH solvent stream applied in the process. The bottom
stream containing methanol, water, unreacted hydrogen peroxide and
epoxidation byproducts, e.g. glycolethers, is sent together with
fresh propylene to reaction stages (iii) to convert H.sub.2O.sub.2
to 99.9%. Stream (M-a) is a mixture of the distillation top stream
and the outlet stream of stage (iii) and comprises olefin oxide,
unreacted olefin, methanol and water. (M-a) is sent to stage
(b).
[0328] The unreacted olefin is separated from the mixture (M-a) by
distillation (b) in a distillation column with 14 theoretical
stages at a pressure of 1.1 bar to obtain a mixture (M-bi) at the
top of the column comprising 89 wt.-% of olefin, 5.6 wt.-% of
propane, 4 wt.-% methanol and 1.4 wt.-% of oxygen, and a mixture
(M-bii) comprising methanol, water and 11.1 wt.-% of olefin
oxide.
[0329] Subsequently, the crude olefin oxide is separated from the
mixture (M-bii) in a distillation stage (c) at 0.5 bar in a
distillation tower having 80 theoretical stages to obtain a top
mixture (M-ci) comprising 99.8 wt.-% of olefin oxide 0.04 wt.-% of
propylene, 0.04 wt.-% of acetaldehyde, 0.01 wt.-% of methanol, 0.01
wt.-% of methanol and a mixture (M-cii) comprising 76.2 wt.-% of
methanol, 22.7 wt.-% water; the rest being heavy boiling byproducts
of the epoxidation. The pure olefin oxide (>99.9 wt.-% propylene
oxide) is separated from the mixture (M-ai) by distillation at a
pressure of 4 bar in a distillation tower having 45 theoretical
stages as a side stream product from theoretical stage 5.
[0330] The solvent methanol is separated from the mixture (M-cii)
in a stage (d) in two thermally coupled distillation columns.
(M-cii) is introduced into a first distillation column (13
theoretical stages) from which the vapor top stream (Td) is
obtained, the distillation being carded out at a top pressure of
3.9 bar. The bottoms stream obtained is introduced into a second
distillation column, a divided wall column (40 theoretical stages,
dividing wall from stage 6 to stage 30), the distillation being
carried out at a top pressure of 10.8 bar. Two thermally coupled
distillation towers as realized such that the condenser used to
condense the top stream obtained of the second tower is
simultaneously used as vaporizer for the first column. The mixture
(M-di) (liquid top product of the second column) comprises 98 wt.-%
of methanol and 2 wt.-% of water, the mixture (M-dii) (bottom
product of the second column) comprises 97.5 wt.-% of water, 2
wt.-% propylene glycol, 0.05 wt.-% monoglycol ethers, 0.45 wt.-%
higher glycol ethers, and the mixture (M-diii) (side stream product
of the second column) comprises 22 wt.-% glycol ethers, and 88
wt.-% water. The second methanoliwater separation column is
operated with 16 bar steam (water steam) from the grid.
[0331] In contrast to example 1, water steam from grid is used to
operate vaporizers (reboilers) used in distillation column as
mentioned in the separation stages (a), (b) and (c).
[0332] The following heat duties, calculated per metric ton/h
recycled methanol as solvent, are needed to operate the
above-described process:
[0333] A heat duty of 676 KW/(t.sub.MeOH/h) is necessary. Stage (a)
consumes additionally a heat duty of 158 KW/(t.sub.MeOH/h), stage
(b) additionally a heat duty of 21 KW/(t.sub.MeOH/h), stage (c)
additionally a heat duty of 50 KW/(t.sub.MeOH/h) of steam from the
grid. Altogether, a heat duty of 904 KW/(t.sub.MeOH/h) is consumed.
Compared to the heat consumption in example 1, the heat consumption
is increased by 111%. This example clearly shows the benefit of the
inventive heat integrated process.
Example 3
Heat-Integrated Process According to the Invention, Comprising
Stages (a), (b), (c), (d), (x), and (y)
[0334] Propylene (chemical grade) is converted with crude hydrogen
peroxide having a concentration of 40 wt.-% in the presence of
methanol as solvent and TS-1 catalyst to propylene oxide in two
reaction stages (i) and (iii), wherein between the two reaction
stages propylene oxide is separated in a stage (ii) by
distillation.
[0335] Reaction in stage (I) is performed at 20 bar, in stage (iii)
at 10 bar. H.sub.2O.sub.2 conversion in stage (i) is 91%. The
distillation is running at a top pressure of 1.2 bar. From the
divided wall column in stage (ii) (40 theoretical stages, dividing
wall from stage 8 to 32), a stream containing surplus propylene and
propylene oxide is separated by distillation over the top. The side
stream with a concentration of 98 wt.-% methanol and 2 wt.-%
H.sub.2O is directly recycled to reaction stages (I) in an amount
of 13.5% of the MeOH solvent stream applied in the process. The
bottom stream containing methanol, water, unreacted hydrogen
peroxide and epoxidation byproducts, e.g. glycolethers, is sent
together with fresh propylene to reaction stages (iii) to convert
H.sub.2O.sub.2 to 99.9%. Stream (M-a) is a mixture of the
distillation top stream and the outlet stream of stage (iii) and
comprises olefin oxide, unreacted olefin, methanol and water. (M-a)
is sent to stage (b).
[0336] The unreacted olefin from the mixture (M-a) is separated by
distillation (b) in a distillation column with 14 theoretical
stages at a pressure of 1.1 bar to obtain a mixture (M-bi) at the
top of the column comprising 89 wt.-% of olefin, 5.6 wt.-% of
propane, 4 wt.-% methanol and 1.4 wt.-% of oxygen, and a mixture
(M-bii) comprising methanol, water and 11.1 wt.-% of olefin oxide.
After separation of oxygen by adsorption from stream (M-bi),
propylene is separated from the resulting mixture in a stage (x) by
distillation in a distillation tower with 130 theoretical stages
operated at a pressure of 24.5 bar to obtain a mixture (M-x)
comprising 96 wt.-% of propylene and 4 wt.-% propane. (M-x) is
re-introduced into stage (a). A mixture of 88 wt.-% propane, 5
wt.-% propylene and 7 wt.-% MeOH is obtained at the bottom of the
tower.
[0337] Subsequently, the crude olefin oxide is separated from the
mixture (M-bii) in a distillation stage (c) at 0.5 bar in a
distillation tower having 80 theoretical stages to obtain a top
mixture (M-ci) comprising 99.8 wt.-% of olefin oxide, 0.04 wt.-% of
propylene, 0.04 wt.-% of acetaldehyde, 0.01 wt.-% of methanol, 0.01
wt.-% of methanol and a mixture (M-cii) comprising 76.2 wt.-% of
methanol, 22.7 wt.-% water; the rest being heavy boiling byproducts
of the epoxidation. The pure olefin oxide (>99.9 wt.-% propylene
oxide) is separated from the mixture (M-ci) by distillation at a
pressure of 4 bar in a distillation tower having 45 theoretical
stages as a side stream product from theoretical stage 5.
[0338] Low boiling compounds having a boiling point lower than
methanol and lower than water are separated in a stage (y) from the
mixture (M-cii) over the top of a distillation tower having 15
theoretical stages by distillation at a pressure of 1 bar to obtain
a top stream mixture comprising 20 wt.-% lower boiling components
such as acetaldehyde and propionaldehyde and 7 wt.-% water. The
rest is MeOH. A bottoms stream (M-y) is obtained.
[0339] The solvent methanol is separated from the bottoms stream
mixture (M-y) in two thermally coupled distillation columns. (M-y)
is introduced into a first distillation column (13 theoretical
stages) from which the vapor top stream (Td) is obtained, the
distillation being carried out at a top pressure of 3.9 bar. The
bottoms stream obtained is introduced into a second distillation
column, a divided wall column (40 theoretical stages, dividing wall
from stage 6 to stage 30), the distillation being carried out at a
top pressure of 10.8 bar. Two thermally coupled distillation towers
are realized such that the condenser used to condense the top
stream obtained from the second tower is simultaneously used as
vaporizer for the first column. The mixture (M-di) (liquid top
product of the second column) comprises 98 wt.-% of methanol and 2
wt.-% of water, the mixture (M-dii) (bottom product of the second
column) comprises 97.5 wt.-% of water, 2 wt.-% propylene glycol,
0.05 wt.-% monoglycol ethers, 0.45 wt.-% higher glycol ethers, and
the mixture (M-diii) (side stream product of the second column)
comprises 22 wt.-% glycol ethers and 88 wt.-% water. The second
methanovwater separation column is operated with 16 bar steam
(water steam) from the grid.
[0340] The MeOH-vapour top stream (Td), obtained from the first
distillation column used in (d) having a pressure of 3.9 bar and a
temperature of 104.degree. C., and comprising 98 wt-% methanol and
2 wt-% H.sub.2O, is used to operate vaporizers (reboilers) used in
distillation column used as mentioned in the separation stages (a),
(b), (x), (c), and (y).
[0341] The following heat duties, calculated per metric ton/h
recycled methanol as solvent, are needed to operate the
above-described process:
[0342] A heat duty of 428 KW/(t.sub.MeOH/h) is necessary Stage (a)
consumes 37% (a heat duty of 158 KW/(t.sub.MeOH/h)), stage (b)
consumes 5% (a heat duty of 21 KW/(t.sub.MeOHh)), stage (x)
consumes 6% (a heat duty of 25 KW/(t.sub.MeOH/h)), stage (c)
consumes 12% (a heat duty of 50 KW/(t.sub.MeOH/h)) and stage (y)
consumes 33% (a heat duty of 140 KW/(t.sub.MeOH/h)) of the
MeOH-vapour top stream (Td), obtained from the first distillation
column used in (d) having a pressure of 3.9 bar and a temperature
of 104.degree. C.
Example 4
Process According to the Prior Art, Comprising Stages (a), (b),
(c), (d), (x), and (y) Without Heat Integration (Comparative
Example)
[0343] Propylene (chemical grade) is converted with crude hydrogen
peroxide having a concentration of 40 wt.-% in the presence of
methanol as solvent and TS-1 catalyst to propylene oxide in two
reaction stages (i) and (iii), wherein between the two reaction
stages propylene oxide is separated in a stage (ii) by
distillation.
[0344] Reaction in stage (i) is performed at 20 bar, in stage (iii)
at 10 bar. H.sub.2O.sub.2 conversion in stage (i) is 91%. The
distillation is running at a top pressure of 12 bar. From the
divided wall column in stage (ii) (40 theoretical stages, dividing
wall from stage 8 to 32), a stream containing surplus propylene and
propylene oxide is separated by distillation over the top. The side
stream with a concentration of 98 wt.-% methanol and 2 wt.-%
H.sub.2O is directly recycled to reaction stages (i) in an amount
of 13.5% of the MeOH solvent stream applied in the process. The
bottom stream containing methanol, water, unreacted hydrogen
peroxide and epoxidation byproducts, e.g. glycolethers, is sent
together with fresh propylene to reaction stages (iii) to convert
H.sub.2O.sub.2 to 99.9%. Stream (M-a) is a mixture of the
distillation top stream and the outlet stream of stage (iii) and
comprises olefin oxide, unreacted olefin, methanol and water. (M-a)
is sent to stage (b).
[0345] The unreacted olefin from the mixture (M-a) is separated by
distillation (b) in a distillation column with 14 theoretical
stages at a pressure of 1.1 bar to obtain a mixture (M-bi) at the
top of the column comprising 89 wt.-% of olefin, 5.6 wt.-% of
propane, 4 wt.-% methanol and 1.4 wt.-% of oxygen, and a mixture
(M-bii) comprising methanol, water and 11.1 wt.-% of olefin oxide.
After separation of oxygen by adsorption from stream (M-bi),
propylene is separated from the resulting mixture in a stage (x) by
distillation in a distillation tower with 130 theoretical stages
operated at a pressure of 24.6 bar to obtain a mixture (M-x)
comprising 96 wt.-% of propylene and 4 wt.-% propane. (M-x) is
re-introduced into stage (a). A mixture of 88 wt.-% propane, 5
wt.-% propylene and 7 wt.-% MeOH is obtained at the bottom of the
tower.
[0346] Subsequently, the crude olefin oxide is separated from the
mixture (M-bii) in a distillation stage (c) at 0.5 bar in a
distillation tower having 80 theoretical stages to obtain a top
mixture (M-ci) comprising 99.8 wt.-% of olefin oxide, 0.04 wt.-% of
propylene, 0.04 wt.-% of acetaldehyde, 0.01 wt.-% of methanol, 0.01
wt.-% of methanol and a mixture (M-cii) comprising 76.2 wt.-% of
methanol, 22.7 wt.-% water; the rest being heavy boiling byproducts
of the epoxidation. The pure olefin oxide (>99.9 wt.-% propylene
oxide) is separated from the mixture (M-ci) by distillation at a
pressure of 4 bar in a distillation tower having 45 theoretical
stages as a side stream product from theoretical stage 5.
[0347] Low boiling compounds having a boiling point lower than
methanol and lower than water are separated in a stage (y) from the
mixture (M-cii) over the top of a distillation tower having 15
theoretical stages by distillation at a pressure of 1 bar to obtain
a top stream mixture comprising 20 wt.-% lower boiling components
such as acetaldehyde and propionaldehyde and 7 wt.-% water. The
rest is MeOH. A bottoms stream (M-y) is obtained.
[0348] The solvent methanol is separated from the bottoms stream
mixture (M-y) in two thermally coupled distillation columns. (M-y)
is introduced into a first distillation column (13 theoretical
stages) from which the vapor top stream (Td) is obtained, the
distillation being carried out at a top pressure of 3.9 bar. The
bottoms stream obtained is introduced into a second distillation
column, a divided wall column (40 theoretical stages, dividing wall
from stage 6 to stage 30), the distillation being carried out at a
top pressure of 10.8 bar. Two thermally coupled distillation towers
are realized such that the condenser used to condense the top
stream obtained from the second tower is simultaneously used as
vaporizer for the first column. The mixture (M-di) (liquid top
product of the second column) comprises 98 wt.-% of methanol and 2
wt.-% of water, the mixture (M-dii) (bottom product of the second
column) comprises 97.5 wt.-% of water, 2 wt.-% propylene glycol,
0.05 wt.-% monoglycol ethers, 0.45 wt.-% higher glycol ethers, and
the mixture (M-diii) (side stream product of the second column)
comprises 22 wt.-% glycol ethers and 88 wt.-% water. The second
methanovwater separation column is operated with 16 bar steam
(water steam) from the grid.
[0349] In contrast to example 3, water steam from grid is used to
operate vaporizers (reboilers) used in distillation column as
mentioned in the separation stages (a), (x) (b), (c) and (y).
[0350] The following heat duties, calculated per metric ton/h
recycled methanol as solvent, are needed to operate the
above-described process:
[0351] A heat duty of 676 KW/(t.sub.MeOH/h) is necessary in stage
(d). Stage (a) consumes additionally 37% (a heat duty of 158
KW/(t.sub.MeOH/h)), stage (b) additionally 5% (a heat duty of 21
KW/(t.sub.MeOH/h)), stage (x) additionally 6% (a heat duty of 25
KW/(t.sub.MeOH/h)), stage (c) consumes 12% (a heat duty of 50
KW/(t.sub.MeOH/h)) and stage (y) additionally 33% (a heat duty of
140 KW/(t.sub.MeOH/h)) ) of steam from the grid. Altogether a heat
duty of 1068 KW/(t.sub.MeOH/h) is consumed.
[0352] Compared to the heat consumption in example 1 the heat
consumption is increased by 150%. This example clearly shows the
benefit of the inventive heat integrated process.
Example 5
Heat-Integrated Process According to the Invention, Comprising
Stages (a), (b), (c), (d), (x), (y), and Further Heat Integration
Methods According to the Invention
[0353] Propylene (chemical grade) is converted with crude hydrogen
peroxide having a concentration of 40 wt.-% in the presence of
methanol as solvent and TS-1 catalyst to propylene oxide in two
reaction stages (i) and (iii), wherein between the two reaction
stages propylene oxide is separated in a stage (ii) by
distillation.
[0354] Reaction in stage (i) is performed at 20 bar, in stage (iii)
at 10 bar. H.sub.2O.sub.2 conversion in stage (i) is 91%. The
distillation is running at a top pressure of 1.2 bar. From the
divided wall column in stage (ii) (40 theoretical stages, dividing
wall from stage 8 to 32), a stream containing surplus propylene and
propylene oxide is separated by distillation over the top. The side
stream with a concentration of 98 wt.-% methanol and 2 wt.-%
H.sub.2O is directly recycled to reaction stages (i) in an amount
of 13.5% of the MeOH solvent stream applied in the process. The
bottom stream containing methanol, water, unreacted hydrogen
peroxide and epoxidation byproducts, e.g. glycolethers, having a
temperature of 79.degree. C., is additionally used to heat up the
feed mixture to the divided wall distillation tower in a counter
current exchanger, before it is sent together with fresh propylene
to reaction stages (iii) to convert H.sub.2O.sub.2 to 99.9%. Stream
(M-a) is a mixture of the distillation top stream and the outlet
stream of stage (iii) and comprises olefin oxide, unreacted olefin,
methanol and water. (M-a) is sent to stage (b).
[0355] The unreacted olefin from the mixture (M-a) is separated by
distillation (b) in a distillation column with 14 theoretical
stages at a pressure of 1.1 bar to obtain a mixture (M-bi) at the
top of the column comprising 89 wt.-% of olefin, 5.6 wt.-% of
propane, 4 wt.-% methanol and 1.4 wt.-% of oxygen, and a mixture
(M-bii) comprising methanol, water and 11.1 wt.-% of olefin oxide.
After separation of oxygen by adsorption from stream (M-bi),
propylene is separated from the resulting mixture in a stage (x) by
distillation in a distillation tower with 130 theoretical stages
operated at a pressure of 24.5 bar to obtain a mixture (M-x)
comprising 96 wt.-% of propylene and 4 wt.-% propane. (M-x) is
re-introduced into stage (a). A mixture of 88 wt.-% propane, 5
wt.-% propylene and 7 wt.-% MeOH is obtained at the bottom of the
tower.
[0356] Subsequently, the crude olefin oxide is separated from the
mixture (M-bii) in a distillation stage (c) at 0.5 bar in a
distillation tower having 80 theoretical stages to obtain a top
mixture (M-ci) comprising 99.8 wt.-% of olefin oxide, 0.04 wt.-% of
propylene, 0.04 wt.-% of acetaldehyde, 0.01 wt.-% of methanol, 0.01
wt.-% of methanol and a mixture (M-cii) comprising 76.2 wt.-% of
methanol, 22.7 wt.-% water; the rest being heavy boiling byproducts
of the epoxidation. The pure olefin oxide (>99.9 wt.-% propylene
oxide) is separated from the mixture (M-ci) by distillation at a
pressure of 4 bar in a distillation tower having 45 theoretical
stages as a side stream product from theoretical stage 5.
[0357] Low boiling compounds having a boiling point lower than
methanol and lower than water are separated in a stage (y) from the
mixture (M-cii) over the top of a distillation tower having 15
theoretical stages by distillation at a pressure of 1 bar to obtain
a top stream mixture comprising 20 wt.-% lower boiling components
such as acetaldehyde and propionaldehyde and 7 wt.-% water. The
rest is MeOH. A bottoms stream (M-y) is obtained.
[0358] The solvent methanol is separated from the bottoms stream
mixture (M-y) in two thermally coupled distillation columns. (M-y)
is introduced into a first distillation column (13 theoretical
stages) from which the vapor top stream (Td) is obtained, the
distillation being carried out at a top pressure of 3.9 bar. The
bottoms stream obtained is introduced into a second distillation
column, a divided wall column (40 theoretical stages, dividing wall
from stage 6 to stage 30), the distillation being carried out at a
top pressure of 10.8 bar. Additionally the feed mixture to the
divided wall distillation tower is heated up in a counter current
exchanger with the bottom stream of this tower. Two thermally
coupled distillation towers are realized such that the condenser
used to condense the top stream obtained from the second tower is
simultaneously used as vaporizer for the first column. The mixture
(M-di) (liquid top product of the second column) comprises 98 wt.-%
of methanol and 2 wt.-% of water, the mixture (M-dii) (bottom
product of the second column) comprises 97.5 wt.-% of water, 2
wt.-% propylene glycol, 0.05 wt.-% monoglycol ethers, 0.45 wt.-%
higher glycol ethers, and the mixture (M-diii) (side stream product
of the second column) comprises 22 wt.-% glycol ethers and 88 wt.-%
water. The second methanovwater separation column is operated with
16 bar steam (water steam) from the grid.
[0359] The MeOH-vapour top stream (Td), obtained from the first
distillation column used in (d) having a pressure of 3.9 bar and a
temperature of 104.degree. C., and comprising 98 wt-% methanol and
2 wt.-% H2O is used to operate vaporizers (reboilers) used in
distillation column used as mentioned in the separation stages (a),
(b), (x), (c), and (y).
[0360] The following heat duties, calculated per metric ton/h
recycled methanol as solvent, are needed to operate the
above-described process;
[0361] A heat duty of 383 KW/(t.sub.MeOH/h) is necessary. Stage (a)
consumes 35% (a heat duty of 135 KW/(t.sub.MeOH/h)), stage (b)
consumes 6% (a heat duty of 21 KW/(t.sub.MeOH/h)), stage (x)
consumes 6% (a heat duty of 25 KW/(t.sub.MeOH/h)), stage (c)
consumes 13% (a heat duty of 50 KW/(t.sub.MeOH/h)) and stage (y)
consumes 36% (a heat duty of 140 KW/(t.sub.MeOH/h)) of the
MeOH-vapour top stream (Td), obtained from the first distillation
column used in (d) having a pressure of 3.9 bar and a temperature
of 104.degree. C.
[0362] Compared to the heat consumption in example 3 the heat
consumption is additionally decreased by 9%. This example clearly
shows the benefit of the further extended heat integrated process
compared to the processes without heat integration.
* * * * *