U.S. patent application number 11/631630 was filed with the patent office on 2007-10-11 for separation of propylene oxide from a mixture comprising propylene oxide and methanol.
This patent application is currently assigned to BASF AKTIENGESELLSCHAFT. Invention is credited to Hans-Georg Goebbel, Renate Patrascu, Henning Schultz, Peter Schultz, Malte Schulz, Meinolf Weidenbach.
Application Number | 20070238888 11/631630 |
Document ID | / |
Family ID | 35311496 |
Filed Date | 2007-10-11 |
United States Patent
Application |
20070238888 |
Kind Code |
A1 |
Goebbel; Hans-Georg ; et
al. |
October 11, 2007 |
Separation of Propylene Oxide from a Mixture Comprising Propylene
Oxide and Methanol
Abstract
A method of separating propylene oxide from a mixture (M)
comprising 5 to 50 percent by weight propylene oxide and 50 to 85
percent by weight methanol, said method comprising (i) introducing
said mixture (M) into an extractive distillation column; (ii)
additionally introducing a polar solvent into said extractive
distillation column; (iii) distilling propylene oxide overhead from
said extractive distillation column at a bottoms temperature of
from 40 to 70.degree. C. and at a pressure of from 300 to 750
mbar.
Inventors: |
Goebbel; 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
2030 Dow Center
Ludwigshafen
MI
67056
THE DOW CHEMICAL COMPANY
Midland
48674
|
Family ID: |
35311496 |
Appl. No.: |
11/631630 |
Filed: |
July 6, 2005 |
PCT Filed: |
July 6, 2005 |
PCT NO: |
PCT/EP05/07300 |
371 Date: |
January 5, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10884968 |
Jul 7, 2004 |
|
|
|
11631630 |
Jan 5, 2007 |
|
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|
Current U.S.
Class: |
549/541 |
Current CPC
Class: |
C07D 301/32
20130101 |
Class at
Publication: |
549/541 |
International
Class: |
C07D 301/32 20060101
C07D301/32 |
Claims
1. A method of separating propylene oxide from a mixture (M)
comprising 5 to 50 percent by weight propylene oxide and 50 to 85
percent by weight methanol, said method comprising (i) introducing
said mixture (M) into an extractive distillation column; (ii)
additionally introducing a polar solvent into said extractive
distillation column; (iii) distilling propylene oxide overhead from
said extractive distillation column at a bottoms temperature of
from 40 to 70.degree. C. and at a pressure of from 300 to 750
mbar.
2. The method as claimed in claim 1, said mixture (M) comprising 5
to 15 percent by weight propylene oxide and additionally comprising
10 to 25 percent by weight water.
3. The method as claimed in claim 1, wherein the polar solvent is
introduced in an amount of 2 percent by weight of the mixture (M)
or less.
4. The method as claimed in claim 1, wherein said extractive
distillation column has up to 80 theoretical plates.
5. The method as claimed in claim 1, wherein water is used as polar
solvent.
6. The method as claimed in claim 5, wherein the water is
introduced as vapor at a pressure of not more than 2 bar.
7. The method as claimed in claim 1, wherein the distillate
obtained overhead from (iii) is partially refluxed into said
extractive distillation column and wherein the ratio of reflux to
distillate is smaller than or equal to 4.
8. The method as claimed in claim 1, wherein the top stream
distilled overhead comprises 100 ppm methanol or less.
9. The method as claimed in claim 1, wherein the bottoms stream
withdrawn from said extractive distillation column has a propylene
oxide content of 100 ppm or less.
10. The method as claimed in claim 1, wherein the mixture (M) is
formed by reacting propene with hydrogen peroxide in methanol as
solvent and in the presence of a titanium zeolite fixed-bed
catalyst.
11. A method of separating propylene oxide from a mixture (M)
comprising 5 to 15 percent by weight propylene oxide, 50 to 85
percent by weight of methanol, and 10 to 25 percent by weight
water, said method comprising (i) introducing said mixture (M) into
an extractive distillation column having up to 80 theoretical
plates; (ii) additionally introducing water into said extractive
distillation column in an amount of 2 percent by weight of the
mixture (M) or less; (iii) distilling propylene oxide overhead from
said extractive distillation column at a bottoms temperature of
from 40 to 70.degree. C. and at a pressure of from 300 to 750 mbar,
wherein the distillate obtained overhead from (iii) is partially
refluxed into said extractive distillation column and wherein the
ratio of reflux to distillate is smaller than or equal to 4,
wherein the top stream distilled overhead comprises 100 ppm
methanol or less, and wherein the bottoms stream withdrawn from
said extractive distillation column has a propylene oxide content
of 100 ppm or less.
12. The method as claimed in claim 11, wherein the mixture (M) is
formed by reacting propene with hydrogen peroxide in methanol as
solvent and in the presence of a titanium zeolite fixed-bed
catalyst.
13. The method as claimed in claim 11, wherein the water is
introduced as vapor at a pressure of not more than 2 bar.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of separating
propylene oxide from a mixture (M) comprising from 5 to 50 percent
by weight propylene oxide and from 50 to 85 percent by weight
methanol. This method comprises [0002] (i) introducing said mixture
(M) into an extractive distillation column; [0003] (ii)
additionally introducing a polar solvent into said extractive
distillation column; and [0004] (iii) distilling propylene oxide
overhead from said extractive distillation column at a bottoms
temperature of from 40 to 70.degree. C. and at a pressure of from
300 to 750 mbar.
[0005] According to a preferred embodiment of the present
invention, the mixture (M) is formed by a reaction of propene with
hydrogen peroxide in methanol as solvent and in the presence of a
titanium zeolite fixed-bed catalyst. Therefore, the present
invention also provides a method of preparing propylene oxide,
wherein said reaction comprises reacting propene with hydrogen
peroxide in methanol as solvent and in the presence of a titanium
zeolite fixed-bed catalyst. This epoxidation reaction results,
either directly or after at least one work-up step, in a mixture
(M) which comprises from 5 to 50 percent by weight propylene oxide
and from 50 to 85 percent by weight methanol, and the method of the
present invention further comprises [0006] (i) introducing said
mixture (M) into an extractive distillation column; [0007] (ii)
additionally introducing a polar solvent into said extractive
distillation column; and [0008] (iii) distilling propylene oxide
overhead from said extractive distillation column at a bottoms
temperature of from 40 to 70.degree. C. and at a pressure of from
300 to 750 mbar.
BACKGROUND OF THE INVENTION
[0009] At atmospheric pressure or superatmospheric pressures,
essentially in the range from 1 to 5 bar, propylene oxide and
methanol can be separated by distillation only when a distillation
column having a very large number of theoretical plates is used and
a very high reflux ratio is set at the same time, owing to the
entraining azeotrope.
[0010] These mixtures comprising propylene oxide and methanol
result, e.g., from epoxidation processes where propene is reacted
with a hydroperoxide such as hydrogen peroxide in the presence of
methanol as solvent.
[0011] U.S. Pat. No. 5,849,938 discloses a process where propene is
separated from methanol in a crude olefin epoxidation product by
means of an extractive distillation wherein a relatively heavy
polar solvent having hydroxy groups such as water or propylene
glycol is used as the extracting solvent, propylene glycol being
particularly preferred. According to this document of the prior
art, the distillation column used ordinarily has from 20 to 60
theoretical plates, and the reflux/distillate ratio is generally in
the range of from 5 to 15. According to the examples, a typical
ratio is 9. Typical bottoms temperatures are in the range of from
90 to 120.degree. C., the pressure under which distillation is
carried out being from 0.55 to 3.44 bar. According to the example,
a preferred bottom pressure of the distillation column is 2.76 bar
and therefore well above standard pressure. As typical propylene
oxide fractions, fractions are obtained comprising 300 or 1,500 ppm
of methanol. The bottoms fractions obtained according to the
examples comprise up to 6,300 ppm of propylene oxide.
[0012] U.S. Pat. No. 6,500,311 B1 discloses a process wherein a
separation of methanol and propylene oxide takes place. As
extracting solvent, a non-polar solvent, namely a C7-C9 hydrocarbon
such as n-octane is used.
[0013] It is an object of the present invention to provide a method
of separating propylene oxide from methanol which, compared to the
processes described in the prior art, has an improved energy
balance and, additionally, leads to top streams and bottoms streams
having a lesser degree of impurity with regard to methanol and
propylene oxide, respectively.
[0014] It is a further object of the present invention to provide a
method of separating propylene oxide from methanol in which a cheap
extracting solvent is employed which simultaneously allows for
milder distillation conditions than those described in the prior
art.
[0015] It is still another object of the present invention to
provide a method of producing propylene oxide in the course of
which propylene oxide is separated from methanol wherein this
separation has the above-mentioned advantages thus rendering the
method for producing propylene oxide energetically and also with
respect to the purity of the distillation fractions advantageous
over the prior art.
SUMMARY OF THE INVENTION
[0016] The present invention relates to a method of separating
propylene oxide from a mixture (M) comprising 5 to 50 percent by
weight propylene oxide and 50 to 85 percent by weight methanol,
said method comprising [0017] (i) introducing said mixture (M) into
an extractive distillation column; [0018] (ii) additionally
introducing a polar solvent into said extractive distillation
column; [0019] (iii) distilling propylene oxide overhead from said
extractive distillation column at a bottoms temperature of from 40
to 70.degree. C. and at a pressure of from 300 to 750 mbar.
[0020] The present invention relates to a method of separating
propylene oxide from a mixture (M) comprising 5 to 15 percent by
weight propylene oxide, 50 to 85 percent by weight methanol, and 10
to 25 percent by weight water, said method comprising [0021] (i)
introducing said mixture (M) into an extractive distillation
column; [0022] (ii) additionally introducing water into said
extractive distillation column in an amount of 2 percent by weight
of the mixture (M) or less; [0023] (iii) distilling propylene oxide
overhead from said extractive distillation column at a bottoms
temperature of from 40 to 70.degree. C. and at a pressure of from
300 to 750 mbar.
[0024] The present invention relates to a method of separating
propylene oxide from a mixture (M) comprising 5 to 15 percent by
weight propylene oxide, 50 to 85 percent by weight methanol, and 10
to 25 percent by weight water, said method comprising [0025] (i)
introducing said mixture (M) into an extractive distillation
column; [0026] (ii) additionally introducing water into said
extractive distillation; [0027] (iii) distilling propylene oxide
overhead from said extractive distillation column at a bottoms
temperature of from 40 to 70.degree. C. and at a pressure of from
300 to 750 mbar; wherein the distillate is partially refluxed into
said extractive distillation column and wherein the mass ratio of
reflux to distillate is smaller than or equal to 4.
[0028] The present invention relates to a method of separating
propylene oxide from a mixture (M) comprising 5 to 15 percent by
weight propylene oxide, 50 to 85 percent by weight methanol, and 10
to 25 percent by weight water, said method comprising [0029] (i)
introducing said mixture (M) into an extractive distillation
column; [0030] (ii) additionally introducing water into said
extractive distillation; [0031] (iii) distilling propylene oxide
overhead from said extractive distillation column at a bottoms
temperature of from 40 to 70.degree. C. and at a pressure of from
300 to 750 mbar; [0032] (iv) withdrawing a bottoms stream from said
extractive distillation column, said bottoms stream comprising 100
ppm propylene oxide or less, and withdrawing a top stream from said
extractive distillation column, said top stream comprising 100 ppm
methanol or less.
[0033] The present invention relates to a method of separating
propylene oxide from a mixture (M) comprising 5 to 15 percent by
weight propylene oxide, 50 to 85 percent by weight methanol, and 10
to 25 percent by weight water, said method comprising [0034] (i)
introducing said mixture (M) into an extractive distillation
column; [0035] (ii) additionally introducing water as vapor at a
pressure of not more than 2 bar into said extractive distillation
column; [0036] (iii) distilling propylene oxide overhead from said
extractive distillation column at a bottoms temperature of from 40
to 70.degree. C. and a pressure of from 300 to 750 mbar.
[0037] The present invention relates to a method of separating
propylene oxide from a mixture (M) comprising 5 to 15 percent by
weight propylene oxide, 50 to 85 percent by weight methanol, and 10
to 25 percent by weight water, said method comprising [0038] (i)
introducing said mixture (M) into an extractive distillation
column; [0039] (ii) additionally introducing water into said
extractive distillation column in an amount of 2 percent by weight
of the mixture (M) or less; [0040] (iii) distilling propylene oxide
overhead from said extractive distillation column at a bottoms
temperature of from 40 to 70.degree. C. and a pressure of from 300
to 500 mbar; [0041] (iv) withdrawing a bottoms stream from said
extractive distillation column, said bottoms stream comprising 100
ppm propylene oxide or less, and withdrawing a top stream from said
extractive distillation column, said top stream comprising 10 ppm
methanol or less.
[0042] The present invention relates to a method of preparing
propylene oxide, said reaction comprising reacting propene with a
hydroperoxide in methanol as solvent, said reaction resulting in a
mixture (M) comprising 5 to 15 percent by weight propylene oxide,
50 to 85 percent by weight methanol, and 10 to 25 percent by weight
water, or resulting in a mixture being worked up to give said
mixture (M), said method further comprising [0043] (i) introducing
said mixture (M) into an extractive distillation column; [0044]
(ii) additionally introducing water as vapor at a pressure of not
more than 2 bar into said extractive distillation column in an
amount of 0.45 to 1 percent by weight of the mixture (M); [0045]
(iii) distilling propylene oxide overhead from said extractive
distillation column as top stream at a pressure of from 450 to 500
mbar and a bottoms temperature of from 50 to 60.degree. C.; [0046]
(iv) withdrawing a bottoms stream from said extractive distillation
column, said bottoms stream comprising 100 ppm propylene oxide or
less, and withdrawing a top stream from said extractive
distillation column, said top stream comprising 50 ppm methanol or
less.
BRIEF DESCRIPTION OF THE DRAWINGS
[0047] The accompanying
[0048] FIG. 1 provides a diagram showing a preferred embodiment of
the present invention,
[0049] FIG. 2 provides a diagram showing a process of the prior
art,
[0050] FIG. 3 provides a diagram showing another process of the
prior art.
DETAILED DESCRIPTION OF THE INVENTION
[0051] According to the present invention, propylene oxide is
separated from a mixture (M) which comprises 5 to 50 percent by
weight propylene oxide and 50 to 85 percent by weight methanol. In
a preferred embodiment of the present invention, the mixture (M)
comprises from 5 to 15 percent by weight, preferably from 6 to 12
percent by weight and particularly preferably from 8 to 10.5
percent by weight of propylene oxide, and from 55 to 85 percent by
weight, preferably from 60 to 80 percent by weight and particularly
preferably from 65 to 75 percent by weight, of methanol.
[0052] With regard to the method of the present invention, mixture
(M) may comprise one or more additional compounds. As to these
compounds, no specific restrictions exist on the condition that
propylene oxide can be distilled overhead from the extractive
distillation column so as to separate propylene oxide from the
methanol comprised in (M).
[0053] According to a preferred embodiment, the mixture (M)
additionally comprises water, more preferably water in an amount of
up to 25, more preferably from 1 to 25, more preferably from 2 to
25, more preferably from 3 to 25 percent by weight, more preferably
from 4 to 25, more preferably from 5 to 25, more preferably from 6
to 25, more preferably from 7 to 25, more preferably from 8 to 25,
more preferably from 9 to 25 and still more preferaby from 10 to 25
percent by weight of water, based on the total weight of mixture
(M). Therefore, the mixture (M) for example may comprise from 10 to
25 or from 10 to 20 or from 10 to 15 or from 15 to 25 or from 15 to
20 or from 20 to 25 percent by weight water, based on the total
weight of mixture (M).
[0054] According to a preferred embodiment where (M) comprises from
10 to 25 percent by weight of water, (M) preferably comprises from
5 to 45, more preferably from 5 to 40, more preferably from 5 to
35, more preferably from 5 to 30, more preferably from 5 to 25,
more preferably from 5 to 20 and still more preferably from 5 to 15
percent by weight of propylene oxide, based on the total weight of
mixture (M).
[0055] Therefore, the present invention also provides a method as
described above wherein the mixture (M) comprises form 50 to 85
percent by weight methanol, from 5 to 15 percent by weight
propylene oxide, and from 10 to 25 percent by weight water, based
on the total weight of the mixture (M).
[0056] In addition to methanol and propylene oxide and, preferably,
water, the mixture (M) may comprise at least one further
compound.
[0057] According to a preferred embodiment of the present
invention, the mixture (M) directly or indirectly results from a
process where propylene oxide is prepared by reacting propene with
a hydroperoxide in the presence of methanol as solvent. Therefore,
the mixture (M) may additionally comprise unreacted propene and/or
unreacted hydroperoxide and/or at least one by-product of said
epoxidation reaction such as propylene glycol and/or
acetaldehyde.
[0058] The reaction mixture obtained from said epoxidation reaction
may be directly introduced in (i) as mixture (M) if the content of
(M) regarding methanol, propylene oxide and preferably water is
within above-mentioned ranges.
[0059] According to an especially preferred embodiment of the
present invention, the reaction mixture obtained from said
epoxidation reaction is worked up prior to the introduction in (i)
of the inventive method. Working up the reaction mixture obtained
from said epoxidation reaction may be carried out in each
conceivable way on the condition that a mixture (M) is obtained
which may be introduced in (i). Said work up may comprises the
separation and/or the addition of at least one compound from and/or
to the mixture obtained from the epoxidation reaction. Preferably,
at least one compound is separated from the mixture obtained from
the epoxidation reaction.
[0060] According to an even more preferred embodiment of the
present invention, at least one compound is separated from the
mixture obtained during work up from the epoxidation reaction, said
at least one compound having a lower boiling point than propylene
oxide, methanol and preferably water.
[0061] Depending on the reaction conditions applied and the
reactants used for the epoxidation reaction, these low boilers may
be, for example, unreacted propene and/or propane the latter being
introduced, for example, in the epoxidation reaction in case, e.g.,
chemical grade propene is used as reactant having a volume ratio of
propene:propane of from about 99.5:0.5 to 94:6.
[0062] According to a still further preferred embodiment of the
present invention, unreacted propene is separated from the reaction
mixture obtained from the epoxidation reaction in at least one
distillation column, and the high boiling fraction whose respective
content regarding methanol, proylene oxide and water are within the
above-mentioned ranges is introduced as (M) in (i) of the method of
the present invention.
[0063] Therefore, the present invention also provides a method of
preparing propylene oxide, said reaction comprising reacting
propene with a hydroperoxide in methanol as solvent, said reaction
resulting in a mixture (M) comprising 5 to 15 percent by weight
propylene oxide, 50 to 85 percent by weight methanol, and 10 to 25
percent by weight water, or preferably resulting in a mixture
comprising propylene oxide, methanol, water, unreacted propene and
optionally propane, said mixture being worked up to give said
mixture (M) comprising 5 to 15 percent by weight propylene oxide,
50 to 85 percent by weight methanol, and 10 to 25 percent by weight
water, and said mixture being further subjected to at least steps
(i) to (iii) as described hereinabove and hereinunder. According to
this embodiment of the present invention, working up preferably
comprises separating propene and, if present, preferably also
propane and/or acetaldehyde, by distillation so as to give a
mixture (M), preferably comprising not more than 500 ppm,
preferably not more than 400 ppm and especially preferably not more
than 350 ppm of propene and comprising not more than 50 ppm,
preferably not more than 25 ppm and especially preferably not more
than 10 ppm of propane, and preferably not more than 200 ppm, more
preferably not more than 150 ppm and especially preferably not more
than 100 ppm of acetaldehyde. Accordingly, a mixture (M) is
obtained comprising especially preferably not more than 350 ppm of
propene and not more than 10 ppm of propane and not more than 100
ppm of acetaldehyde. According to a still further preferred
embodiment of the present invention, the mixture (M) introduced in
(i) comprises not more than 1 percent by weight, more preferably
not more than 0.75 percent by weight and especially preferably not
more than 0.65 percent by weight of high boiling compounds such as
methoxypropanols and/or hydroperoxide.
[0064] In the context of the present invention, the term
"hydroperoxide" refers to a compound of the formula ROOH. Details
regarding the preparation of hydroperoxides and regarding
hydroperoxides which can be used, inter alia, in the method of the
present invention may be found in DE-A-198 35 907 the respective
content of which is incorporated in the context of the present
invention by reference. Examples of hydroperoxides which can be
used for the purposes of the present invention are, inter alia,
tert-butyl hydroperoxide, ethylbenzene hydroperoxide, tert-amyl
hydroperoxide, cumene hydroperoxide, cyclohexyl hydroperoxide,
methylcyclohexyl hydroperoxide, tetrahydronaphthalene
hydroperoxide, isobutylbenzene hydroperoxide, ethylnaphthalene
hydroperoxide, peracids such as peracetic acid and hydrogen
peroxide. Mixtures of two or more hydroperoxides can also be used
according to the present invention. Preference is given to using
hydrogen peroxide as hydroperoxide in the method of the present
invention, and further preference is given to using an aqueous
hydrogen peroxide solution. Most preferably, the aqueous hydrogen
peroxide solution comprises hydrogen peroxide in a concentration in
the range of from 1 to 90, more preferably of from 10 to 70 and
especially preferably of from 30 to 50 wt.-%, based on the total
weight of the solution. It is also possible to use a mixture of two
or more different hydroperoxides.
[0065] The epoxidation reaction the mixture (M) directly or
indirectly is obtained from may be carried out in the presence of
each suitable catalyst or a suitable combination of two or more
catalysts. Particularly preferred, a zeolite containing titanium is
employed, wherein zeolites known to the person skilled in the art
as "titanium silicalites" (TS) are particularly preferred. Such
zeolites containing titanium, in particular those having a
crystalline structure of the MFI-type as well as ways for producing
them are described, for example, in WO 98/55228, EP-A-0 311 983, or
EP-A-0 405 978. The respective content of these documents is hereby
incorporated by reference. In addition to Si and Ti, said zeolite
materials may contain additional elements, such as aluminum,
zirconium, tin, iron, cobalt, nickel, gallium, boron, or small
amounts of fluorine. It is possible that the titanium of the
zeolite is partly or completely replaced by vanadium, zirconium, or
niobium, or any mixture of two or more of these components.
Zeolites containing titanium and having a MFI-structure are known
to yield a characteristic pattern in X-ray diffraction.
Furthermore, these materials display a vibration band in the
infrared (IR) at approximately 960 cm.sup.-1. Therefore, it is
possible to distinguish the zeolites containing titanium from
crystalline or amorphous TiO.sub.2-phases or from alkaline metal
titanates. In a further preferred embodiment, the at least one
zeolite catalyst comprises at least one of the elements titanium,
germanium, tellurium, vanadium, chromium, niobium, zirconium.
Particularly preferred are zeolite catalysts having a pentasil
zeolite structure, in particular the structural types that can be,
via X-ray diffraction, assigned to the structure types of ABW-,
ACO-, AEI-, AEL-, AEN-, AET-, AFG-, AFI-, AFN-, AFO-, AFR-, AFS-,
AFT-, AFX-, AFY-, AHT-, ANA-, APC-, APD-, AST-, ATN-, ATO-, ATS-,
ATT-, ATV-, AWO-, AWW-, BEA-, BIK-, BOG-, BPH-, BRE-, CAN-, CAS-,
CFI-, CGF-, CGS-, CHA-, CHI-, CLO-, CON-, CZP-, DAC-, DDR-, DFO-,
DFT-, DOH-, DON-, EAB-, EDI-, EMT-, EPI-, ERI-, ESV-, EUO-, FAU-,
FER-, GIS-, GME-, GOO-, HEU-, IFR-, ISV-, ITE-, JBW-, KFI-, LAU-,
LEV-, LIO-, LOS-, LOV-, LTA-, LTL-, LTN-, MAZ-, MEI-, MEL-, MEP-,
MER-, MFI-, MFS-, MON-, MOR-, MSO-, MTF-, MTN-, MTT-, MTW-, MWW-,
NAT-, NES-, NON-, OFF-, OSI-, PAR-, PAU-, PHI-, RHO-, RON-, RSN-,
RTE-, RTH-, RUT-, SAO-, SAT-, SBE-, SBS-, SBT-, SFF-, SGT-, SOD-,
STF-, STI-, STT-, TER-, THO-, TON-, TSC-, VET-, VFI-, VNI-, VSV-,
WIE-, WEN-, YUG-, ZON, as well as mixed structures of at least two
or more of the aforementioned structures. Furthermore, it is
conceivable to use zeolite catalysts containing titanium with the
structure of ITQ-4, ITQ-9, SSZ-24, TTM-1, UTD-1, CIT-1 or CIT-5.
Furthermore zeolites containing titanium are such of the structure
types ZSM-48 or ZSM-1 2. Zeolites containing titanium of the
structure MFI, MEL or MFI/MEL mixed structures, as well as MWW, BEA
or mixed structures thereof are preferred in the context of the
present invention. In the context of the present invention, zeolite
catalysts containing titanium that are referred to, in general, as
"TS-1", "TS-2" or "TS-3", as well as zeolites containing titanium
displaying a structure that is isomorphous to zeolite beta are
further preferred.
[0066] Although it is possible to carry out the reaction using a
suspension catalyst, particular preference is given to a
heterogeneous catalyst and still more preferably a fixed-bed
catalyst. Therefore, according to this preferred embodiment of the
present invention, it is not necessary to separate the catalyst
from the reaction mixture obtained from the epoxidation
reaction.
[0067] Therefore, the present invention also provides a method of
separating propylene oxide from a mixture (M) comprising propylene
oxide, methanol and preferably water, as described above, wherein
the mixture (M) is directly or indirectly, after at least one work
up step, obtained from an epoxidation process wherein propene is
reacted with a hydroperoxide, preferably hydrogen peroxide, in the
presence of methanol as solvent and in the presence of a fixed-bed
catalyst, preferably a fixed-bed zeolite catalyst, more preferably
a fixed-bed titanium zeolite catalyst, still more preferably a
fixed-bed TS-1 type titanium silicalite catalyst, and wherein said
catalyst does not have to be separated from the reaction mixture
resulting from the epoxidation process.
[0068] Accordingly, the present invention also provides a method of
preparing propylene oxide, said reaction comprising reacting
propene with a hydroperoxide, preferably hydrogen peroxide, in
methanol as solvent, said reaction resulting in a mixture (M)
comprising 5 to 15 percent by weight propylene oxide, 50 to 85
percent by weight methanol, and 10 to 25 percent by weight water,
or preferably resulting in a mixture comprising propylene oxide,
methanol, water, unreacted propene and optionally propane, said
mixture being worked up to give said mixture (M) comprising 5 to 15
percent by weight propylene oxide, 50 to 85 percent by weight
methanol, and 10 to 25 percent by weight water, and said mixture
being further subjected to at least steps (i) to (iii) as described
hereinabove and hereinunder, wherein the epoxidation is carried out
in the presence of a fixed-bed catalyst, preferably a fixed-bed
zeolite catalyst, more preferably a fixed-bed titanium zeolite
catalyst, still more preferably a fixed-bed TS-1 type titanium
silicalite catalyst, and wherein said catalyst does not have to be
separated from the reaction mixture resulting from the epoxidation
process.
[0069] In (i) of the present invention, any suitable extractive
distillation column may be used. Preferably, the column has up to
80 theoretical plates such as from 10 to 80 or from 20 to 80 or
from 30 to 80 or from 40 to 80 of from 50 to 80 or from 60 to 80 or
preferably from more than 60 to 80 such as from 61 to 80 or from 65
to 80 or from 70 to 80 or from 75 to 80. Preferably, the column has
more than 60 theoretical plates such as from 61 to 65 theoretical
plates. Two or more columns may be used according to the present
invention wherein two or more columns may be connected in series
and/or two or more columns may be arranged in parallel. Preferably,
one column is used.
[0070] According to (ii) of the present invention, at least one
polar solvent is added. As to the chemical nature of the at least
one polar solvent, no specific limitations exist on the condition
that extractive distillation is possible under the conditions of
(iii). Accordingly, no hydrocarbons, especially no C7-C9
hydrocarbons such as n-octane are used as extracting solvents,
neither alone nor in combination with a polar solvent such as
water.
[0071] Preferred polar solvents are water, alcohols having one or
more hydroxy groups such as one, two, three or more hydroxy groups,
preferably monools and diols, or ethers, preferably ether compounds
having at least one hydroxy groups, preferably one hydroxy group
such as 1-methoxy-2-propanol and/or 2-methoxy-1-propanol.
Especially preferred is water wherein, for example, demineralized
water, potable water, suitable industrial water, suitable waste
water, especially suitably treated waste water, suitable process
water or a mixture of two or more thereof can be used. The water
introduced in the process of the present invention should be
essentially free of organic material, especially essentially free
of methanol. According to one embodiment of the present invention,
the water introduced in (ii) is a process water from a suitable
process such as a process carried out in the epoxidation plant in
which the method of the present invention is conducted. According
to one aspect of the present invention, the process water is taken
from a process in the epoxidation plant where methanol as solvent
of the epoxidation reaction and water are separated from each other
as it is the case in step (v) described hereinunder. Preferably,
the water is taken from the bottom of at least one distillation
column in which methanol as solvent of the epoxidation reaction and
water are separated. More preferably, the water resulting from said
separation process, optionally after one or more additional
purification steps, is introduced in (ii), and the methanol
resulting from said separation process, optionally after one or
more additional purification steps, is recirculated as solvent into
the epoxidation reaction. Thus, the present invention also relates
to a method as described above wherein an integrated process is
implemented by working up a mixture comprising methanol and water
by separating methanol and water from each other, and by
recirculating the separated water, optionally after one or more
additional purification steps, preferably without any additional
purification steps, into (ii), and optionally recirculating the
separated methanol, optionally after one or more additional
purification steps, as solvent into the epoxidation reaction from
which the mixture (M) introduced in (i) results.
[0072] Therefore, the present invention also provides a method of
separating propylene oxide from a mixture (M) as described above
wherein water is introduced as polar solvent into said extractive
distillation column in (ii).
[0073]
[0074] According to an even more preferred embodiment, no other
solvent except water is introduced as polar solvent in (ii).
According to another preferred embodiment, no propylene glycol is
used as polar solvent.
[0075] The preferred embodiment according to which water and no
propylene glycol is used as polar solvent, shows, among others, the
advantages that water is cheaply available compared to propylene
glycol and can be discarded without having disadvantageous
ecological impacts. Therefore, in case propylene glycol is used as
polar solvent, working up and recirculating the propylene glycol is
necessary in order to render the process ecologically and
economically efficient. However, working up necessarily includes at
least one additional process step which is superfluous in case
water is used as polar solvent.
[0076] According to a preferred embodiment of the present
invention, the at least one polar solvent is introduced in the
extractive distillation column about 15 theoretical plates, more
preferably about 10 theoretical plates below the upper end of the
extractive distillation column.
[0077] The at least one solvent, preferably water, may be
introduced in the column as liquid or as vapor or as liquid as well
as as vapor. If two or more solvents are used, at least one solvent
may be introduced as liquid and at least one other solvent may be
introduced as vapor.
[0078] According to a preferred embodiment, water is used as polar
solvent and introduced in the extractive distillation column as
liquid and/or as vapor, more preferably as vapor. Still more
preferably, the vapor introduced in (ii) has a pressure of not more
than 2 bar, more preferably of not more than 1 bar, more preferably
not more than 900 mbar and especially preferably not more than 800
bar.
[0079] As far as the amount of polar solvent introduced in the
extractive distillation column according to (ii) is concerned, no
specific limitations exist. Preferably, polar solvent, in
particular water, is introduced in an amount of not more than 2
percent by weight, based on the weight of the mixture (M). More
preferably, the polar solvent is introduced in an amount of not
more than 1.8, more preferably not more than 1.6, more preferably
not more than 1.4, more preferably not more than 1.2 and still more
preferably not more than 1 percent by weight, based on the weight
of the mixture (M). Further preferred are amounts of polar solvent
of at least 0.2, more preferably at least 0.25, more preferably at
least 0.3 and still more preferably at least 0.4 percent by weight,
based on the weight of the mixture (M). Therefore, preferred ranges
are, for example, from 0.2 to 2, more preferably from 0.3 to 1.6,
more preferably from 0.4 to 1.2, and still more preferably from
0.45 to 1 percent by weight, based on the weight of the mixture
(M).
[0080] Therefore, the present invention also provides a method of
separating propylene oxide from a mixture (M), as described above,
wherein in (ii), at least one polar solvent, in particular water,
preferably as vapor at a pressure of preferably not more than 2
bar, is introduced in an amount of from 0.45 to 1 percent by
weight, based on the weight of the mixture (M).
[0081] Preferred mass ratios of propylene oxide comprised in (M):
extracting solvent added in (ii) are from 0.6:1 to 70:1, more
preferably from 1:1 to 20:1 and especially preferably from 3:1 to
8:1 such as, for example, from 4:1 to 7:1 or from 5:1 to 7:1 or
from 6:1 to 7:1.
[0082] Distillation in (iii) is carried out at a bottoms
temperature of from 40 to 70.degree. C. at a pressure in the range
of from 300 to 750 mbar. Other preferred ranges of the pressure at
which distillation is carried out are from 300 to 700, more
preferably from 300 to 650, more preferably from 300 to 600, more
preferably from 300 to 550 and still more preferably from 300 to
500 mbar, or from 350 to 750, more preferably from 400 to 750, more
preferably from 450 to 750, more preferably from 450 to 700, more
preferably from 450 to 650, more preferably from 450 to 600, more
preferably from 450 to 550 and especially preferably from 450 to
500 mbar.
[0083] Therefore, the present invention also provides a method of
separating propylene oxide from a mixture (M) as described above,
wherein in (iii), distillation is carried out at a pressure of from
300 to 500 mbar, in particular from 450 to 500 mbar.
[0084] The term "pressure at which the distillation is carried out"
as used in the context of the present invention relates to the
pressure at the top of the column in which the distillation is
carried out.
[0085] Especially preferred bottoms temperatures of the extractive
distillation are for example from 40 to 70.degree. C. or from 40 to
65.degree. C. or from 40 to 60.degree. C. or from 45 to 70.degree.
C. or from 45 to 65.degree. C. or from 45 to 60.degree. C. or from
50 to 70.degree. C. or from 50 to 65.degree. C. or from 50 to
60.degree. C.
[0086] Especially preferred combinations of pressure ranges and
bottoms temperature ranges are for example from 300 to 750 mbar and
from 40 to 70.degree. C. or from 300 to 500 mbar and from 40 to
60.degree. C. or from 450 to 500 mbar and from 50 to 60.degree.
C.
[0087] Therefore, the present invention also provides a method of
separating propylene oxide from a mixture (M) as described above,
wherein in (iii), distillation is carried out at a pressure of from
300 to 500 mbar and at a temperature of from 40 to 60.degree. C.,
more preferably at a pressure of from 450 to 500 mbar and at a
temperature of from 50 to 60.degree. C.
[0088] Therefore, the present invention provides a method of
separating propylene oxide from a mixture (M) by extractive
distillation, preferably using water as extracting solvent in an
amount of not more than 2 percent by weight based on the weight of
(M), wherein the extractive distillation is carried out at low
pressures of 750 mbar and below, preferably from 300 to 750 mbar,
more preferably from 300 to 500 mbar and especially preferably from
450 to 500 mbar, and simultaneously at low temperatures of
70.degree. C. and below, preferably from 40 to 70.degree. C., more
preferably from 40 to 60.degree. C. and still more preferably from
50 to 60.degree. C. such as at about 51, 52, 53, 54, 55, 56, 57, 58
or 59.degree. C.
[0089] As extractive distillation column, it is essentially
possible to use any column. Particular preference is given to a
distillation column configured as a packed column, more preferably
a packed column containing ordered packing. Such a packed column
has a high separation efficiency per meter of packing and displays
only a very small pressure drop. While the ordered packing
mentioned can essentially be of any type, preference is given to
packing which has a specific surface area in the range from 100 to
750 m.sup.2/m.sup.3. It is possible to use sheet metal packing, for
example from Montz (type B1 100 to B1 500) or from Sulzer ChemTech
(Mellapak 125 to Mellapak 750), or mesh packing from Montz (type A3
500 to A3 750) or from Sulzer ChemTech (type BX or CY). The unit
m.sup.2/m.sup.3 refers to the geometric surface area of the
material forming the packing per cubic meter of packing.
[0090] According to the present invention, the propylen oxide
fraction separated from methanol and water is preferably distilled
overhead.
[0091] The propylene oxide fraction distilled overhead in (iii)
preferably comprises at least 99.0, more preferably at least 99.5,
more preferably at least 99.6, and still more preferably at least
99.7 percent by weight propylene oxide, based on the total weight
of the propylene oxide fraction.
[0092] The propylene oxide fraction distilled overhead in (iii)
preferably comprises not more than 500 ppm, more preferably not
more than 200 ppm, more preferably not more than 100 ppm, more
preferably not more than 50 ppm, more preferably not more than 20
ppm and still more preferably not more than 10 ppm of methanol,
based on the total weight of the propylene oxide fraction.
[0093] The propylene oxide fraction distilled overhead in (iii)
preferably comprises not more than 200 ppm, more preferably not
more than 100 ppm, more preferably not more than 50 ppm, more
preferably not more than 25 ppm, and still more preferably not more
than 20 ppm of water, based on the total weight of the propylene
oxide fraction.
[0094] The propylene oxide fraction distilled overhead in (iii)
preferably comprises not more than 0.5, more preferably not more
than 0.3, and still more preferably not more than 0.25 percent by
weight of propene and propane, based on the total weight of the
propylene oxide fraction.
[0095] At the extractive distillation conditions according to the
present invention, the high boiler fraction at the bottom of the
column comprises, in addition to water and methanol, not more than
100 ppm, preferably not more than 75 and especially preferably not
more than 50 ppm of propylene oxide, based on the weight of the
high boiler fraction.
[0096] At the extractive distillation conditions according to the
present invention where no propylene glycol but preferably water is
used as extracting polar solvent in (ii), the high boiler fraction
comprises, in addition to water and methanol, not more than 1,
preferably not more than 0.5 and especially preferably not more
than 0.2 percent by weight of propylene glycol, based on the weight
of the high boiler fraction.
[0097] According to an especially preferred embodiment of the
present invention, the propylene oxide fraction distilled overhead
in (iii) is partially refluxed into the extractive distillation
column. According to an even more preferred embodiment, the mass
ratio of reflux:distillate is smaller than 5, more preferably
smaller than or equal to 4.5 and especially preferably smaller than
or equal to 4 such as about 3.5 or about 3.6 or about 3.7 or about
3.8 or about 3.9 or 4.
[0098] Therefore, the present invention also provides a method of
separating propylene oxide from a mixture (M) as described above,
wherein the distillate obtained overhead from (iii) is partially
refluxed into said extractive distillation column and wherein the
ratio of reflux to distillate is smaller than or equal to 4.
[0099] Thus, the extractive distillation process of the present
invention combines the advantages of low distillation pressures,
low distillation temperatures and, simultaneously, a low
reflux:distillate ratio.
[0100] The propylene oxide fraction distilled overhead may be used
as such or subjected to at least one further work up step in case
the content of this fraction with regard to compounds such as
propene, propane, and/or acetaldehyde is too high for the purpose
the propylene oxide is meant for. Such a work up may comprise, for
example, a fractional distillation where low boilers are withdrawn
overhead and a purified propylene oxide fraction is withdrawn as
bottoms stream or as side stream. Subsequently, if necessary, this
bottoms stream may be subjected to at least one additional
purification process.
[0101] The bottoms stream withdrawn from the extractive
distillation column in (iii) may be used as such or after at least
one work up step in at least one other process or may be
recirculated in the method of the present invention. According to a
preferred embodiment of the present invention, the bottoms stream
is worked up in one, two or more steps to give a mixture comprising
at least 97 percent by weight of methanol, not more than 2 percent
by weight of water, and not more than 50 ppm of acetaldehyde, based
on the total weight of said mixture, and the methanol thus purified
is recirculated in the method of the present invention, preferably
as solvent for the epoxidation reaction the mixture (M) results
from.
[0102] Depending on the polar solvent used in (ii) as extracting
solvent, this solvent may be suitably separated from the bottoms
stream and recirculated in the method of the present invention,
preferably as polar solvent in (ii). A further advantage of the
preferred method of the present invention according to which water
is used as polar solvent, working up the bottoms stream obtained in
(iii) so as to obtain the purified polar solvent to be recirculated
in (ii) is not necessary since water is cheaply available, contrary
to, e.g., propylene glycol described in U.S. Pat. No. 5,849,938 as
preferred extracting solvent.
[0103] Accordingly, the present invention provides a method of
preparing propylene oxide, said reaction comprising reacting
propene with a hydroperoxide, preferably hydrogen peroxide, in
methanol as solvent and preferably in the presence of a fixed-bed
titanium silicalite catalyst, said reaction resulting in a mixture
comprising propylene oxide, methanol, water, unreacted propene and
optionally propane, said mixture being worked up to essentially
completely remove unreacted propene, to give a mixture (M)
comprising 15 percent by weight propylene oxide, 50 to 85 percent
by weight methanol, and 10 to 25 percent by weight water, said
method further comprising [0104] (i) introducing said mixture (M)
into an extractive distillation column; [0105] (ii) additionally
introducing a polar solvent, preferably water, more preferably
water as vapor, wherein the vapor is introduced at a pressure of
not more than 2 bar, preferably not more than 1 bar, more
preferably not more than 900 mbar and especially preferably not
more than 800 mbar, into said extractive distillation column in an
amount of not more than 2, preferably from 0.45 to 1 percent by
weight of the mixture (M); [0106] (iii) distilling propylene oxide
overhead from said extractive distillation as top stream at a
pressure of from 300 to 750, more preferably from 300 to 500,
especially preferably from 450 to 500 mbar and a bottoms
temperature of from 40 to 70.degree. C., preferably from 40 to
60.degree. C. and especially preferably from 50 to 60.degree. C.;
[0107] (iv) withdrawing a bottoms stream from said extractive
distillation column, said bottoms stream comprising 100 ppm
propylene oxide or less, preferably 75 ppm propylene oxide or less,
especially preferably 50 ppm propylene oxide or less, based on the
total weight of the bottoms stream, and withdrawing a top stream
from said distillation column, said top stream comprising 500 ppm
methanol or less, preferably 200 ppm methanol or less, more
preferably 100 ppm methanol or less, more preferably 50 ppm
methanol or less, more preferably 20 ppm methanol or less and
especially preferably 10 ppm methanol or less, based on the total
weight of the top stream, and [0108] (v) optionally at least
partially recirculating the methanol comprised in the bottoms
stream of (iv) as solvent into the reaction where the propene is
reacted with the hydroperoxide.
[0109] The following examples and figures are used to illustrate
the present invention and are not meant to be limiting.
DETAILED DESCRIPTION OF THE FIGURES
[0110] FIG. 1 shows a preferred embodiment according to the
invention. A mixture (M) and an extracting solvent (1) are
introduced into an extractive distillation column (K200) (steps (i)
and (ii)). Propylene oxide is distilled overhead from (K200) as top
stream (step (iii)). A heat exchanger (W230) is used to condense
the top stream of the extractive distillation column (K200). As
cooling agent (3) used in the heat exchanger (W230), chilled water
and cooling water, respectively, is employed. To heat the reboiler
of the column (K200), a heat exchanger (W200) is employed, and low
pressure steam (2) is used as heating source. Heat exchanger (W220)
is used to preheat mixture (M) before it is introduced into the
column (K200).
[0111] FIG. 2 shows an embodiment where no polar solvent is used
for the distillation. A mixture (M) is introduced into a
distillation column (K100). Propylene oxide is distilled overhead
from (K100) as top stream which is compressed in an electric
compressor (C100), and the compressed vapor stream is condensed in
a heat exchanger (W100) where at least part of the heat of
condensation is transferred to a reboiler employed in the
extractive distillation column (K100). The heat exchanger (W110) as
shown in FIG. 2 is only used for starting the distillation process,
i.e., during a continuous distillation process this heat exchanger
(W110) is not used. The cooled and condensed stream leaving the
heat exchanger (W100) is then divided, and a part of the stream is
passed to a first heat exchanger (W130). The cooled stream leaving
heat exchanger (W130) is then passed to a second heat exchanger
(W140) where the stream is cooled further and ultimately
recirculated as reflux on the top of the column (K100). If
necessary and/or desired, part of the energy stored in the bottom
stream of the distillation column may be used in a further heat
exchanger (W120) where the mixture (M) is heated or preheated
before it is introduced into column (K100).
[0112] FIG. 3 shows another embodiment where no polar solvent is
used for the distillation. In contrast to the process depicted in
FIG. 2, the process according to FIG. 3 encompasses a further heat
exchanger (W101). Depending on the amount of energy which shall be
withdrawn from the compressed vapor stream and be transferred to a
reboiler employed in the distillation column (K100), it might be
necessary to divide the compressed vapor stream, and pass one part
of the stream to heat exchanger (W100) and one part to heat
exchanger (W101).
EXAMPLES
[0113] A stream, the outlet of an epoxidation unit from which
nearly all light boiling components were separated off, is
subjected to different PO/MeOH separation units (examples 1 to 3).
In all examples, this stream has the composition according to table
1: TABLE-US-00001 TABLE 1 composition of stream stream mass %
propylene 0.013423 formaldehyde 0.011839 acetaldehyde 0.026834
propylene oxide 9.446765 methanol 71.97108 water 17.54493 glycol
ethers 0.43074 propylene glycol 0.051477 others (heavy boilers) up
to 100
Example 1
Extractive Distillation in vacuo with Water
[0114] The process of example 1 is carried out in a unit of
appartuses as shown in FIG. 1. In FIG. 1, a heat exchanger (W230)
is shown in which the top stream of an extractive distillation
column (K200) is cooled using chilled water and cooling water,
respectively. To heat the reboiler of the column, a heat exchanger
(W200) is employed, and low pressure steam (2) is used as heating
source. Heat exchanger (W220) is used to preheat mixture (M), i.e.
the feed according to table 1, before it is introduced into the
column (K200).
[0115] The above described stream (table 1) is fed to an extractive
distillation tower (K200) containing 80 theoretical stages. Low
pressure steam (2) is used to heat the reboiler of the column via
heat exchanger (W200). The condenser (W230) is operated with
chilled water (3), which is prepared in a chilled water unit (not
shown in FIG. 1). The column (K200) is operated in vacuo at 500
mbar, and water is used as extracting solvent (1). The feeding
point are as follows: feed stream of the column is fed on stage 45
from the top of the column, water as extracting agent is fed on
stage 12 from the top of the column, at a flow rate of 5.2% with
respect to the propylene oxide contained in the feed stream.
Purified propylene oxide is taken at the top of the tower. The
tower is operated at a mass reflux ratio (reflux:distillate) of
3.9. The top propylene oxide stream contains, beside the light
boilers, 10 ppm of MeOH and 55 ppm of water. The bottom stream
contains 50 ppm of propylene oxide, MeOH, water and all other heavy
boilers.
Example 2
Extractive Distillation with (a) Water and (b) Propylene Glycol at
2 Bar
(Comparative Examples)
[0116] The processes of example 2 are carried out in a unit of
appartuses as shown in FIG. 1. In FIG. 1, a heat exchanger (W230)
is shown in which the top stream of an extractive distillation
column (K200) is cooled using chilled water and cooling water,
respectively. To heat the reboiler of the column, a heat exchanger
(W200) is employed, and low pressure steam (2) is used as heating
source. Heat exchanger (W220) is used to pre-heat mixture (M), i.e.
the feed according to table 1, before it is introduced into the
column (K200). [0117] (a) The above described stream (table 1) is
fed to an extractive distillation tower (K200) containing 80
theoretical stages. The column (K200) is operated at a pressure of
2 bar. Water is used as extracting solvent (1). Low pressure steam
is used as an external heating source to heat the reboiler of the
column. The condenser (W230) is operated with cooling tower water.
The reboiler duty is 31.5 MW, the condenser duty 30.2 MW. The
feeding points are as follows: the feed stream of the column is fed
on stage 50 from the top of the column, water as extracting agent
is fed on stage 12 from the top of the column, at a flow rate of
10.4% with respect to the propylene oxide contained in the feed
stream. The tower is operated at a mass reflux ratio
(reflux:distillate) of 6.1. Purified propylene oxide is taken at
the top of the tower. The top propylene oxide stream contains,
beside the light boilers, 10 ppm of MeOH and 1,500 ppm of water.
The bottom stream contains 50 ppm of propylene oxide, MeOH, water
and all other heavy boilers. [0118] b) The above described stream
(table 1) is fed to an extractive distillation tower (K200)
containing 80 theoretical stages. The column (K200) is operated at
a pressure 2 bar. Propylene glycol is used as extracting solvent
(1). Low pressure steam is used as an external heating source to
heat the reboiler of the column. The condenser (W230) is operated
with cooling tower water. The reboiler duty is 36.5 MW, the
condenser duty 34.5 MW. The feedings point are as follows: the feed
stream of the column is fed on stage 60 from the top of the column,
propylene glycol as extracting solvent is fed on stage 2 from the
top of the column, at a flow rate of 30% with respect to the
propylene oxide contained in the feed stream. The tower is operated
at a mass reflux ration (reflux:distillate) of 7.3. Purified
propylene oxide is taken at the top of the tower. The top propylene
oxide stream contains, beside the light boilers, 10 ppm of MeOH.
The bottom stream contains 50 ppm of propylene oxide, MeOH, water,
the added propylene glycol and all other heavy boilers.
Example 3
Fractional Distillation Without Polar Solvent Including Compressing
Top Stream of Distillation Column
(Comparative Example)
[0119] The process of example 3 is carried out in a unit of
appartuses as shown in FIG. 3.
[0120] The above described stream (table 1) is fed to a
distillation tower (K100) containing 80 theoretical stages,
equipped with a compressor (C100) to compress the top vapour outlet
stream of the top of column. This stream is used as a heating
source for the reboiler of the distillation column. The column is
operated in vacuo at 500 mbar. No extracting solvent is used. The
feeding point of the feed stream is on stage 68 from the top of the
column. Purified propylene oxide is taken at the top of the tower.
The tower is operated at a mass reflux ratio (reflux:distillate) of
9.4. The reboiler duty is 49.5 MW. The top propylene oxide stream
contains beside the lights 10 ppm of MeOH. The bottom stream
contains 50 ppm of propylene oxide, MeOH, water and al the other
heavies.
[0121] The following table 2 gives an overview of the described
examples: TABLE-US-00002 TABLE 2 overview of the described
examples. example 1 2a 2b 3 extracting solvent water water prop. --
glycol top pressure [bar] 0.5 2 2 0.5 top temperature [.degree. C.]
16.1 54.8 54.8 16.1 compression of top no no no yes vapor stream
theoretical stages 80 80 80 80 feeding point (from 45 50 62 68 top)
feeding point extract- 12 12 2 -- ing solvent (from top) mass ratio
extr. 5.2 10.4 30 -- solvent/propylene oxide [%] mass reflux ratio
3.9 6.1 7.3 9.4 bottom temperature 55.9 89.5 91.5 55.8 of
(K100/200) [.degree. C.] propylene oxide 50 50 50 50 traces in
bottom stream [ppm] MeOH traces in distil- 10 10 10 10 late stream
[ppm] reboiler duty [MW] of 22 31.5 36.5 49.5 (K100) or (K200)
electr. condenser -- -- -- 14.5 energy consumption [MW] (C100)
condenser capacity -- 30.2 34.5 -- cooling tower water [MW] (W230)
condenser capacity 21.1 -- -- -- chilled water [MW] (W230) cooling
tower water -- -- -- 6.0 [MW] (W130) chilled water [MW] -- -- --
3.6 (W140) heating source re- low low low compr. boiler (K100/200)
pressure pressure pressure top steam steam steam stream vapor
* * * * *