Process for purifying allyl alcohol

A process for purifying allyl alcohol, comprising adding at least one member selected from the group consisting of dipotassium hydrogenphosphate, potassium phosphate, potassium pyrophosphate, potassium tripolyphosphate and potassium carbonate to an aqueous solution of allyl alcohol to separate the solution into an aqueous phase and an organic phase, removing the aqueous phase, and optionally subjecting the organic phase to distillation to obtain allyl alcohol having a high purity.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for purifying allyl alcohol. 
More particularly, the present invention relates to a process for 
obtaining allyl alcohol having a high purity by efficiently removing water 
from an aqueous solution of allyl alcohol. 
2. Description of the Related Art 
Allyl alcohol is an industrially valuable substance used for the synthesis 
of various chemicals such as glycerol and diallyl phthalate and as an 
intermediate for the synthesis of synthetic resins. 
As the process for preparing allyl alcohol, there is known a process in 
which, as indicated by the following reaction formulae (1) and (2), allyl 
chloride is formed by high-temperature chlorination of propylene and allyl 
chloride is subjected to alkali hydrolysis: 
EQU CH.sub.2 .dbd.CHCH.sub.3 +Cl.sub.2 .fwdarw.CH.sub.2 .dbd.CHCH.sub.2 
Cl.sub.2 +HCl (1) 
EQU CH.sub.2 .dbd.CHCH.sub.2 Cl+NaOH.fwdarw.CH.sub.2 .dbd.CHCH.sub.2 OH+NaCl 
(2) 
This process is defective in that expensive chlorine should be used in a 
large amount and since hydrogen chloride gas is handled, corrosion of 
apparatus is serious. 
Another process is known in which allyl alcohol is prepared by 
isomerization of propylene oxide using lithium phosphate as a catalyst: 
##STR1## 
This process is also defective in that the starting material is expensive. 
Recently, there has been proposed a process in which propylene is used as 
the starting material and allyl alcohol is prepared without handling 
chlorine or hydrogen chloride. According to this process, as indicated by 
the following formulae (3) and (4), propylene is reacted in the presence 
of acetic acid with oxygen or an oxygen-containing gas by using a catalyst 
comprising an alkaliacetate and palladium, optionally together with a 
copper compound, supported on a carrier, in the gas phase, at 100.degree. 
to 300.degree. C. and 0 to 30 atmospheres (gauge pressure), to obtain 
allyl acetate, formed allyl acetate is collected by cooling, an aqueous 
solution of acetic acid is added to collected allyl acetate to form a 
homogeneous solution, the homogeneous solution is passed through a tubular 
reaction vessel filled with a strong-acid cation-exchange resin and heated 
by a heating medium, and the reaction liquid is subjected to distillation 
to obtain allyl alcohol [see, Japanese Unexamined Patent Publication 
(Kokai) No. 60-32747 and Japanese Unexamined Patent Publication (Kokai) 
No. 60-258171]: 
EQU CH.sub.2 .dbd.CH--CH.sub.3 +AcOH+1/2O.sub.2 .fwdarw.CH.sub.2 
.dbd.CH-CH--CH.sub.2 OAc+H.sub.2 O (4) 
EQU CH.sub.2 .dbd.CH--CH.sub.2 OAc+H.sub.2 O.fwdarw.CH.sub.2 .dbd.CH--CH.sub.2 
OH+AcOH (5) 
According to this preparation process, allyl alcohol is obtained in the 
form of an aqueous solution. However, since allyl alcohol (having a 
boiling point of 96.degree. to 97.degree. C.) forms an azeotropic mixture 
(having a boiling point of 87.5.degree. C.) with water, water cannot be 
removed only by distillation. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a purification process 
in which allyl alcohol having a high purity is obtained by removing water 
from allyl alcohol prepared in the form of an aqueous solution. 
Thus, in order to attain the above-mentioned object, the present invention 
provides a process for purifying allyl alcohol, which comprises adding at 
least one potassium salt selected from the group consisting of dipotassium 
hydrogenphosphate, potassium phosphate, potassium pyrophosphate, potassium 
tripolyphosphate and potassium carbonate to an aqueous solution of allyl 
alcohol to separate the solution into an aqueous phase and an organic 
phase, removing the aqueous phase, and subjecting the organic phase to 
distillation to obtain allyl alcohol having a high purity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As means for removing water from an aqueous solution of allyl alcohol, 
there may be considered a process in which, as practised for ethanol or 
isopropanol, a large amount of a third component such as benzene is added 
as an entrainer and separation is effected by distillation. However, in 
case of allyl alcohol, this process is not practical because the water 
content in the azeotropic mixture is high and a great quantity of energy 
is necessary for the separation. 
It has hitherto been known that when a salt is added to a homogeneous 
mixture of an organic substance and water, the mixture is separated into 
two phases, and this phenomenon is often utilized for the 
liquid-separating operation. We made research with a view to obtaining 
allyl alcohol having a high purity by efficiently removing water from an 
aqueous solution of allyl alcohol having a composition close to the 
azeotropic composition by utilizing this phenomenon. 
When a salt customarily used, such as sodium chloride (NaCl), is added in a 
saturation amount to an aqueous solution of allyl alcohol, the water 
content is merely reduced to about 20% from the initial level of about 
30%, and it is confirmed that the process is industrially insufficient. It 
have been found that dipotassium hydrogenephosphate (K.sub.2 HPO.sub.4), 
potassium phosphate (K.sub.3 PO.sub.4), potassium pyrophosphate (K.sub.4 
P.sub.2 O.sub.7), potassium tripolyphosphate (K.sub.5 P.sub.3 O.sub.10) 
and potassium carbonate (K.sub.2 CO.sub.3) are very effective for 
attaining the above-mentioned object. We have now completed the present 
invention based on this finding. 
According to the purification process of the present invention, dipotassium 
hydrogenphospate, potassium phosphate, potassium pyrophosphate, potassium 
tripolyphosphate and/or potassium carbonate (these salts may be anhydrous 
salts or may contain water of crystallization) is added in the form of a 
solid or a concentrated aqueous solution to an aqueous solution of allyl 
alcohol, and the mixture is stirred to dissolve the added salt and the 
solution is allowed to stand still to separate it into an organic phase 
and an aqueous phase. 
As the amount added of the salt is larger, the water content is 
proportionally reduced in the separated organic phase (allyl alcohol 
phase) and better results are obtained. However, if the salt is added in 
an amount exceeding the saturation amount, troubles are caused by 
precipitation of the salt, and the process becomes disadvantageous from 
the industrial viewpoint. 
Water solubilities of dipotassium hydrogenphosphate, potassium phosphate, 
potassium pyrophosphate, and potassium carbonate are as shown in Table 1 
given below [Handbook of Chemistry, 3rd edition, Basic Volume II, page 170 
(compiled by the Japanese Chemical Association)]. Potassium 
tripolyphosphate has a water solubility of about 67% at 20.degree. C. 
[Ullmanns Encyklopadie der Technichen Chimie, Volume 18, page 332]. It is 
necessary that care should be taken so that the salt concentration does 
not exceed the saturation concentration at the operation temperature. 
TABLE I 
__________________________________________________________________________ 
Water Solubilities (% by weight) 
Temperature 
(.degree.C.) 
K.sub.2 HPO.sub.4.xH.sub.2 O* 
K.sub.2 CO.sub.3 .3/2H.sub.2 O 
K.sub.3 PO.sub.4.nH.sub.2 O* 
K.sub.4 P.sub.2 O.sub.7.7/2H.sub.2 
__________________________________________________________________________ 
O 
25 62.0 52.85 51.42 -- 
30 63.2 53.2 53.08 66.7 
40 66.6 53.9 62.73 -- 
50 71.9 54.8 63.6-63.8 
67.33 
60 72.2 55.9 64.08 -- 
70 -- -- -- 68.81 
80 72.2 58.3 -- -- 
__________________________________________________________________________ 
Note 
When the temperature is 25 to 40.degree. C., x is 3 and n is 7, and when 
the temperature is 50.degree. C. or higher, x is 0 and n is 3. 
When a mixture of dipotassium phosphate and a cheaper salt (such as sodium 
carbonate) is used, a high effect can be attained by using a small amount 
of dipotassium phosphate. 
According to the purification process of the present invention, the water 
content can be reduced to 5 to 10% in an aqueous solution of allyl alcohol 
having a composition (water content of about 30%) close to the azeotropic 
composition, and if the remaining organic phase is subjected to 
distillation, allyl alcohol having a high purity can be obtained as the 
main distillate. By ordinary distillation, allyl alcohol having a purity 
of 98 to 99% or more can be easily obtained. Furthermore, the azeotropic 
mixture obtained as the initial distillate can be utilized as the starting 
material of the purification process again. Furthermore, if water is 
evaporated from the aqueous phase, the salt can be recovered in the form 
of a concentrated solution or a solid, and this salt can be recycled and 
used again. 
A flow chart of an example of an industrial process utilizing the 
purification process of the present invention is shown in the FIGURE. 
In this example, the starting aqueous solution 1 of allyl alcohol (allyl 
alcohol/water ratio=about 70/30) and at least one of the above-mentioned 
salts 2 are sufficiently stirred in a mixing tank B to dissolve the salt, 
and the solution is allowed to stand still in a phase separator C to 
separate the solution into an aqueous phase 4 and an organic phase 5. In a 
distillation column D, the azeotropic mixture is removed from the organic 
phase (allyl alcohol phase) 5 and the azeotroic mixture is returned to the 
mixing tank B. The water-free bottom residue is subjected to distillation 
in a distillation column E. Allyl alcohol 8 containing a small amount of 
the salt is returned to the phase separator through a line 3. The majority 
of water is evaporated from the aqueous phase containing a large amount of 
the salt in a water evaporator A and the residue is recycled to the mixing 
tank. 
In the process for purifying allyl alcohol according to the present 
invention, the water content is reduced to 5 to 10% in the allyl alcohol 
phase obtained by the phase separation. Accordingly, the quantity of steam 
necessary for the subsequent distillation refining is much smaller than in 
the conventional distillation process. 
The salt used for the phase separation has not a corrosive action as 
possessed by a chloride or the like. Accordingly, an apparatus composed of 
a cheap material can be used. 
The purification process of the present invention will now be described 
with reference to the following examples and comparative examples. 
Incidentally, all of "%" in the following description are by weight. 
EXAMPLE 1 
To 300 ml of a solution comprising 30.8% of water and 69.2% of allyl 
alcohol was added 160 g of dipotassium hydrogenphosphate (anhydride), and 
the mixture was shaken at 40.degree. C. for 10 minutes and was then 
allowed to stand still, whereby the liquid was separated into two phases. 
The volume ratio of the organic phase to the aqueous phase was about 1.8. 
The upper organic phase was composed mainly of allyl alcohol, and from the 
results of the analysis by the Karl Fischer's method, it was found that 
the water content was reduced to 5.0%. From the results of the analysis by 
the neutralization titration, it was found that dipotassium phosphate was 
contained only in an amount of 0.01%. 
The lower aqueous phase consisted of a concentrated aqueous solution of the 
salt, and from the results of the analysis by the gas chromatography, it 
was found that the allyl alcohol content was as low as 0.013%. 
EXAMPLE 2 
The treatment was carried out in the same manner as described in Example 1 
except that the amount added of dipotassium hydrogenphosphate was changed 
to 80 g and the operation was carried out at room temperature. It was 
found that the water content in the upper phase was reduced to 9.7% and 
the salt content was as low as 0.02%. Furthermore, the allyl alcohol 
content in the lower phase was only 0.02% 
EXAMPLE 3 
To 300 ml of a solution comprising 70.1% of allyl alcohol and 29.9% of 
water was added 90 g of potassium carbonate (anhydride), and the mixture 
was shaken at room temperature for 10 minutes. A part of the salt was left 
undissolved, but when the mixture was allowed to stand still, the liquid 
phase was separated into two phases. 
When the allyl alcohol phase was analyzed, it was found that the water 
content was reduced to 5.4% and the salt content was 2.6%. In the aqueous 
phase, the allyl alcohol content was as low as 0.13%. 
EXAMPLE 4 
To 300 ml of a solution comprising 71.5% of allyl alcohol and 28.5% of 
water was added 300 ml of a saturated aqueous solution of dipotassium 
hydrogenphosphate, and the mixture was stirred and allowed to stand still, 
whereby the mixture was separated into two phases. It was found that the 
water content in the allyl alcohol phase was reduced to 9.8%. Water in the 
aqueous phase was evaporated and the aqueous phase was concentrated almost 
to the saturation concentration. This operation was repeated 10 times. In 
each case, the water content in the allyl alcohol phase was 9.7 to 9.8%, 
and the obtained results had a good reproducibility. 
When the obtained allyl alcohol phase was subjected to distillation in an 
Oldershaw column type distillation apparatus, a mixture comprising 72% of 
allyl alcohol and 28% of water and having a composition close to the 
azeotropic composition was obtained from the column head, while allyl 
alcohol substantially free of water, having a water content of 0.2%, was 
obtained from the column bottom. 
EXAMPLE 5 
The procedures of Example 1 were repeated in the same manner except that 
the amount used of dipotassium hydrogenphosphate was changed to 80 g and 
sodium carbonate was further added in a saturation amount. It was found 
that the water content in the allyl alcohol phase was reduced to 6.0% and 
the salt content was lower than 0.1%. In the lower phase (aqueous phase), 
the allyl alcohol content was low as 0.01%. 
COMATIVE EXAMPLE 1 
The procedures of Example 3 were repeated in the same manner except that 
sodium chloride was used in an amount much larger than the saturation 
amount instead of potassium carbonate. The water content in the allyl 
alcohol phase was 20%. 
COMATIVE EXAMPLE 2 
The procedures of Comparative Example 1 were repeated in the same manner 
except that disodium hydrogenphosphate was used instead of sodium 
chloride. The liquid was not separated into two phases. 
COMATIVE EXAMPLE 3 
The procedures of Comparative Example 1 were repeated in the same manner 
except that sodium dihydrogenphosphate was used instead of sodium 
chloride. In the allyl alcohol phase, the water content was 19.8% and the 
salt content was 0.4%. In the aqueous phase, the allyl alcohol content was 
0.9%. 
COMATIVE EXAMPLE 4 
The procedures of Comparative Example 1 were repeated in the same manner 
except that sodium carbonate was used instead of sodium chloride. The 
volume of the aqueous phase was about 1/2 of the volume of the aqueous 
phase in Comparative Example 1, and separation of water from allyl alcohol 
was insufficient. 
EXAMPLE 6 
To 500 ml of a solution (A) comprising 30% of water and 70% of allyl 
alcohol was added a solution (B) of 320 g of potassium phosphate in 180 g 
of water, and the mixture was vigorously agitated and was then allowed to 
stand still, whereby the liquid was separated into two phases. The upper 
phase was composed mainly of allyl alcohol, and it was found that the 
water content 11.5% and the potassium phosphate content was 0.87%. 
The lower phase consisted mainly of a concentrated aqueous solution of 
potassium phosphate, and it was found that the allyl alcohol content was 
0.72%. 
When the upper allyl alcohol phase was subjected to distillation in an 
Oldershaw column type distillation apparatus, a mixture comprising 74% of 
allyl alcohol and 26% of water having a composition close to the 
azeotropic composition was obtained from the column head, while allyl 
alcohol substantially free of water, having a water content of 0.15%, was 
obtained from the column bottom. The liquid obtained from the column 
bottom was colored yellow. When the yellow liquid was subjected to 
distillation until 95% of the liquid was distilled off, the distillate was 
pure allyl alcohol and the colored material and potassium phosphate were 
retained at the bottom of the distillation still. 
EXAMPLE 7 
50 ml of a solution comprising 66.2% of allyl alcohol and 33.8% of water 
was introduced into a separatory funnel, potassium phosphate was added in 
portions while shaking the mixture until potassium phosphate no more 
dissolved therein. The mixture was then allowed to stand still, whereby 
the liquid was separated into two phases. The upper phase was composed 
mainly of allyl alcohol and the water content was reduced to 4.8%. 
EXAMPLE 8 
The treatment was carried out in the same manner as described in Example 7 
except that potassium pyrophosphate was used instead of potassium 
phosphate. It was found that the water content in the upper phase was 
reduced to 6.7% 
EXAMPLES 9 THROUGH 11 
The treatment was carried out in the same manner as described in Example 6 
except that 60% aqueous solution of potassium pyrophosphate was used as 
the solution (B) and the added amount thereof was changed to 250 g, 500 g 
or 1,000 g. The results were as shown in Table 2. 
TABLE 2 
______________________________________ 
Amount of potassium Residue of 
pyrophosphate Water content 
upper phase 
Example 
solution in upper phase 
distillation* 
No. (g) (%) (%) 
______________________________________ 
9 250 19.8 0.11 
10 500 14.0 0.070 
11 1,000 11.9 0.058 
______________________________________ 
Note 
The residue was composed mainly of potassium pyrophosphate. 
EXAMPLE 12 
The procedures of Example 7 were repeated in the same manner except that 
potassium tripolyphosphate was used instead of potassium phosphate. The 
water content in the upper phase was 6.5%. 
COMATIVE EXAMPLE 5 
The procedures of Comparative Example 1 were repeated in the same manner 
except that sodium phosphate was used instead of sodium chloride. The 
liquid was not separated into two phases.