Note: Descriptions are shown in the official language in which they were submitted.
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Purification of propylene oxide
The present invention is concerned with a process for purifying propylene
oxide.
Such processes have been widely described.
. US 3578568 discloses a method of separating water, methanol, acetone, and
acetaldehyde from propylene oxide by extractive distillation using ethylene
glycol,
propylene glycol, ethylene glycol monomethylether or diethylene glycol
monomethylether
as the extractive solvent. US 4692535 discloses a process for purifying
propylene oxide
by contacting the propylene oxide (PO) with an activated carbon or attapulgite
adsorbent.
The amount of poly (propylene oxide) is reduced. In comparative tests it is
indicated that
distilled propylene oxide containing poly (propylene oxide} leads to foam
collaps and that
distilled propylene oxide which has been heated to 82°C in a carbon
steel container for 2
and 7 days also leads to foam collapse; the specification neither discloses
how these
propylene oxides were distilled nor that distilled propylene oxide could be
used; it actually
discloses that the way to prevent foam collaps is to use propylene oxide which
has been
treated with the aforementioned adsorbent.
US 3580819 discloses a process for recovering propylene oxide from a crude
propylene
oxide comprising propylene, water and higher boiling oxygen-containing
impurities by
subjecting it to a two-stage distillation process followed by contacting with
a liquid
aqueous selective solvent for propylene oxide (PO) and distilling PO from the
solvent.
The starting material has a PO content of 8.1 % w only. FR 1469339 and US
3398062
discloses the purification of crude propylene oxide comprising propylene
chloride, water,
dissolved gas, acetaldehyde and propionaldehyde by distillation and leading
the top
stream through a separator. The starting material contains a relatively low
amount of
propylene oxide (88%) and the distillation is conducted at relatively extreme
conditions
using steam. GB 1040783 discloses a process for making poiyethers wherein the
PO is
introduced trough a reflux column into a reaction vessel. Most of the PO in
the reaction
vessel evaporates and is returned to the refiux column where it is condensed
and the
liquid mixture at the bottom of the refiux column is fed back into the
reaction vessel.
Apart from removal of inert gas no purification of PO takes place. US 5160587
and US
5133839 are other examples of disclosures of extractive distillation of PO. In
516058? a
comparative distillation without extractive distillation solvent is shown; the
distillation
column has a rather high number of plates and the amount of impurities in the
PO which -
is used as starting material is still rather high. Despite the sophisticated
purification
SUBSTITUTE SHEET {RULE 26~
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improvement. It was found that over time the quality of the propylene oxide
deteriorates
which is reflected in the quality of the polyether polyols prepared thereof
and in the quality
of polyurethanes made of such polyols. It seems that storage or transport of
the PO at
ambient temperature could have a negative effect; such storage or transport
preferably
should take place at a temperature as low as possible but above the melting
point of PO.
Further it seems that storage or transport of the PO while in contact with
mild steel or
carbon steel could have a negative effect especially when such steel has been
allowed to
be in contact with air, moisture, water or oxygen; such storage or transport
preferably
should take place while the PO is in conctact with stainless steel or steel
coated with an
~p inert layer. Since variable ways of storage and transport are being used by
PO
producers, users are faced with commercial grades of PO of variable quality,
such quality
ultimately effecting the quality of products made thereof. To date it is not
fully
understood which change in the propylene oxide causes the deterioration of the
polyol
and polyurethane quality. In view of the above, there is a need for a PO
having a good
~ 5 and consistent quality for use in making materials, in particular
polyether polyols and
there is a need for a simple process to achieve this.
Surprisingly it was found that, despite the fact that the cause is not fully
known, the
quality of polyols and polyurethanes could be greatly improved if the
propylene oxide is
subjected to a simple distillation shortly before it is consumed to make the
polyols.
20 Further it was surprisingly found that the quality of PO, which already has
a high degree
of purity, can be improved by a simple distillation process.
Therefore the invention is concerned with a process for purifying propylene
oxide by
distillation characterized in that the distillation is conducted shortly
before the propylene
oxide will be used and with the use of PO which PO has been subjected to
distillation
25 shortly before its use and to a process for preparing a material from PO
wherein the PO
has been subjected to distillation shortly before its use. Further the
invention is
concerned with a process for purifying PO by distillation wherein the PO
starting material
preferably has less than 0.2% by weight, more preferably less than 0.1 %
weight and .
most preferably less than 0.05% by weight of impurities and wherein 1-10
actual trays are
30 used.
The distillation preferably is carried out less than 1 week before the PO is
used, more
preferably less than 4 days before it is used and most preferably less than 2
days before
i
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it is used. The PO may be used immediately after the distillation.
The PO used for the distillation may be any PO containing low amounts of
impurities, in
particular any commercially available PO may be used. Preferably the PO
comprises
less than 0.2% by weight, more preferably less than 0.1 % weight and most
preferably
less than 0.05% by weight of impurities.
The distillation may be conducted by simply evaporating the PO and collecting
the
evaporated PO and preferably is conducted in a conventional distillation
column supplied
with a heater at the bottom or mounted with a heating jacket and coil and a
condenser at
or near the top of the column together with a vent for releasing inert gas
which is supplied
~0 together with the PO. In order to avoid entrainment of droplets in the
vapour stream the
column may contain 1-10 actual trays and preferably 2-8 actual trays. The PO
is
supplied from a main storage tank for PO under an inert gas blanket at the
bottom of the
distillation column, heated and allowed to condens in the condensor. From the
condensor it is stored as a liquid in an intermediate storage tank until the
purified PO is
used for making a material or it is fed directly into the process using it.
The inert gas
preferably is N2. The distillation process may be conducted at atmospheric
pressure or
slightly increased pressure (1-3 bar abs) and at 35-60°C or at a
pressure of 0.99 to 0.5
bar abs and ambient temperature ( a heater is not needed then). The first
alternative is
preferred. The distillation process may be conducted batchwise, semi-
continuously and,
preferably, continuously. No chemicals other than the inert gas are added to
the PO.
The devices used for the storage and distillation are preferably designed in
such a way
that all contact of PO with metal surfaces are with stainless steel surfaces.
The
condensor may be supplied with water at ambient temperature as the means to
cool.
Preferably, no additional purification of the PO takes place between the
distillation
according to the present invention and the use of the thus purified PO.
At the bottom of the distillation column impurities will accumulate. This
bottom fraction
may be removed continuously or discontinuously. The bottom fraction may be
incinerated, purified separately, fed back to the main storage tank or used
for applications
wherein the presence of such impurities have no or less effect, like for the
making of
9lYcols and glycol ethers and for making polyols used for making rigid
polyurethane
foams.
The purified PO may be used for any application for PO known, especially for
the
preparation of polymers and more in particular for polyether polyols,
especially those
having an equivalent weight of 500 or more, preferably of 1000 or more and
containing at
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least 10% by weight, preferably at least 25% by weight and most preferably at
least 50%
by weight of oxypropylene units.
Such polyether potyols are known in the art as well as the processes to make
them. The
PO is fed as a liquid from the intermediate storage tank or the condensor of
the
distillation column to the reactor to make the polyether polyols. They may be
homopolymers of PO and copolymers of PO with other alkylene oxides, like
ethylene
oxide and butylene oxides. The copolymers may be block copolymers, random
copolymers or combinations thereof. The present invention is also concerned
with such
materials, especially such polyether polyols made from PO purified according
to the
~ 0 present invention.
Such polyether polyols may be used in the preparation of poiyurethanes, in
particular
polyurethane foams, especially flexible foams and elastomers. The present
invention is
further related to such polyurethanes.
The present invention is illustrated by the following examples.
Example 1
a) Commercial propylene oxide which was transported via a carbon steel
pipeline
of about 300 meters and which had an amount of impurities of less than 0.2% by
weight
was used. Half the amount of this PO was distilled at 50°C and
atmospheric pressure,
condensed and collected (using NZ as inert gas and a reactor with 1 actual
tray mounted
with a jacket and coil, a condenser near the top and venting means at the
top).
b) The undistilled PO was added to an equal amount of polyol (Arcol 1374, a
polyol
widely used for preparing flexible polyurethane foams, sold by Arco). Next the
PO was
removed from the polyol by vacuum distillation until less than 50 parts per
million (ppm) of
PO is left in the polyol.
c) Step b) was repeated with fresh Arco1 1374 and PO distilled in step a),
which
was used within 1 day after distillation.
Flexible foams where made in identical ways using Arcol 1374 treated with
undistilled PO
_(code TAU) and Arcol 1374 treated with distilled PO (code TAD}.
110 parts by weight of the following polyol composition was reacted with 75
parts by
weight of Suprasec 2420, which is an MDI-based polyisocyanate prepolymer
obtainable
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from Imperial Chemical Industries PLC (Suprasec is a trademark of ICl). Step 1
b), 1 c)
and the flexible foam preparation were conducted within 3 days after
distillation of the PO
in step a).
Polyol composition (in parts by weight)
TAU 90 -
TAD 90
Daltocel F 417 " 10 10
water 3.8 3.8
diethanolamine 0.1 0.1
diethyltoluene diamine 0.6 0.6
DabcoT"" 88020, catalyst 2' 0.3 0.3
Dabco 8154, catalyst z' 0.4 0.4
NiaxT"" A1, catalyst 2' 0.1 0.1
TegostabT"" 84113, surfactant 2' 0.5 0.5
5'' polyol from ICI, Daltocel is a trademark of ICI
2' commercially available
The ingredients were poured, mixed and allowed to react in an open container.
The
height/weight ratio (H/V1~ of the foams was determined.
The results are as follows
H/V11 Structure
TAU 147 very coarse cell
structure
TAD 182 nice cell structure
1 p Examale 2
Propylene oxide which was shipped in a stainless steel cylinder and which had
a level of
impurities of less than 0.2% by weight was used.
PO was charged to a 12 liter stainless steel reactor, which was 3 times
flushed with N2 to
remove all air. The distillation outlet of the reactor was opened (the reactor
did not
15 contain a fractionation column; hence the number of actual trays was one)
and the PO
was heated from ambient temperature to 40-45°C and kept at that
temperature for 5
hours (the reactor was mounted with a heating jacket with a coil; water was
used as the
heating fluid in the coil). A small nitrogen bleed was applied at the end of
the distillation.
The PO was collected at the bottom of the condensor in a glass flask. The
amount of
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distilled PO collected was about 14.9 kg (the distillation was conducted in 2
batches).
Examples 1 b and 1 c were repeated using undistilled PO from the above
cylinder and
distilled PO made as described above and which had been stored for 2 days in
said glass
flasks. Flexible foams were made as described in example 1. The H/W ratio for
TAD
was 18% higher than the ratio for TAU.
Example 3
In this example undistilled and distilled PO (after 2 days storage in the
glass flask) from
example 2 was used.
In a standard way a glycerol initiated polyoxypropylene polyol having an OH
value of 352
1p mg KOH/g was propoxylated and ethoxylated to give a polyol with an OH value
of 28 mg
KOH/g and with 15.4% by weight oxyethylene groups (all tipped).
The propoxylation of part of the polyol with OH value of 352 mg KOH/g was
conducted
with undistilled PO while the propoxylation of the other part was conducted
with distilled
PO.
From the polyols so obtained foams were made as in example 1.
The flexible polyurethane foam wherein undistilled PO was used had a coarse
cell
structure, a recession of 11.4% and a HIV11 ratio of 176 while the foam
wherein distilled
PO was used had a nice, fine cell structure, a H/V1I ratio of 188 and a
recession of 7%.
(all measurements conducted 24 hours after the foam was made).
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