Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION ;
Field of the Invention
This invention relates to the production of 2-ethyl
hexanol by the condensation of n-butyraldehyde in the presence
of an alkali metal hydroxide and the conversion of the resul-
tant 2-ethyl hexenal to 2-ethyl hexanol by hydrogenation. -~
More particularly, this invention relates to a continuous
process for the preparation of 2-ethyl hexanol by such a `
route wherein steps are taken to minimize the deterioration of
hydrogenation catalysts used in the hydrogenation zone wherein
the 2-ethyl hexenal is hydrogenated to 2-ethyl hexanol.
This invention is particularly directed to a continuous process
for preparing 2-ethyl hexanol wherein a portion of a residual
organic fraction having a major amount of higher condensation
products is recycled to the condensation zone whereby addition-
al 2-ethyl hexenal is realized with concomitant reduction in
the amount of higher condensation product deposited upon the
hydrogenation catalyst in the hydrogenation zone.
N-butyraldehyde has been known to be a starting
material for the production of 2-ethyl hexanol and has been
used on a commercial scale. The aldehyde is converted into
butyraldole by the action of an alkali metal hydroxide. The
2-ethyl hexenal is formed by cleavage of water from this
butyraldol and the 2-ethyl hexenal is subsequently hydrogenated
to form 2-ethyl hexanol.
In one process which has been carried out on a
commercial scale, n-butyraldehyde is introduced into an aqueous
sodium hydroxide solution which is recycled from a separation
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l ~ zo to a condensntion zone. The qu~ntity of the recycled
caustic solution is dependent upon its concentration and is
3 usually 3 to 30 times the amount of n-butyraldehyde charged.
4 Caustic solution which is consumed during the course of the
re~ction i8 replenished by the addition of fresh caustic
6 solution. The aldehyde is condensed in the condensation zone
7 at temperatures of 80 to 140C employing pressures on the
order of 1 to 7 kgs./cm2 gauge. The condensation takes place
over a period of time between 5 and 60 seconds.
After water i8 separated from the condensation
11 product the resultant raw 2-ethyl hexenal undergoes a treatment
12 or the removal of the alkali metal salts therefrom. The
13 alkali metal ~alts are removed by treatlng the raw 2-ethyl
14 hexènal fraction with water. Thereafter purified 2-hexQnal
is charged into a hydrogenation zone containlng hydrogen and
- 16 a hydrogenation catalyst. Invariably, the 2-ethyl hexenal
17 which is charged into the hydrogenation zone i8 accompanied
18 by minor a unts of higher boiling products, i.e., higher
19 condensation products which have resulted from the condensation
of more than 2 moles of n-butyraldehyde. The subsequent
f 21 hydrogenation of the unsaturated aldehyde to form 2-ethyl
; 22 hexanol is carried out in the gaseous phase. For this purpose
23 the raw product is heated in an evaporator to temperatures
24 wh~ch are sufficiently high that the 2-ethyl hexenal can be
carried into the hydrogenation reactor by me~ns of recycled
26 hydrogen. However, invariably ~here is present the higher
;; condensation products (higher boiling products) and alkali
28 metal salts which have become entrained in the overhead
0 57 3 1 3
1 ~ pro uct from the evaporator. m ese materials are carried into ¦ ~
2 ¦ the hydrogenation reactor along with the 2-ethyl hexenal -
3 ¦ material. They have been found to have a marked deteriorating
4 1 effect on the hydrogenation catalyst and the hydrogenation
5 ¦ reactor.
6 ¦ It has therefore become desirable to minimize the
7 ¦ deleterious effect which has been visited upon the hydrogenatio
8 ¦ catalyst. More especially it has become desirable to provide
9 a means for minimizing the activity deterioration of the
lO ¦ hydrogenation catalyst so that it deteriorates to as low an
11 ¦ extent as possible. To minimize this activity decrease it
12 has been proposed to withdraw a fraction containing the higher
13 ¦ condensation products including the alkali metals contained
14 ¦ therein from the sump of the evaporator which i8 arranged
15 ¦ upstream of the hydrogenation reactor. However, to recover
16 ¦ the 2-ethyl hexenal contained in the effluent from the 8ump
17 ¦ it has been necessary to distill the latter in a separate
18 ¦ operation with the addition, if necessary or desired, of alkali
19 ¦ metal hydroxide. The distillate comprising a ~econd 2-ethyl
20 ¦ hexenal fraction has then been sub~ected to hydrogenation.
21 ¦ It will be realized that this additional distillation step is
22 ¦ commercially expensive owing in particular to the fact that
23 ¦ it is necessary to carry the same out in a stainless steel
24 column due to the corrosiveness of the material charged. In
25 ¦ addition it represente losses of valuable product which effect
26 ¦ the overall economy of the process and raise the cost of the
27 ¦ production of the 2-ethyl hexenal.
28 It has therefore become desirable to provide an
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alternate and less expensive means for minimizing the activity
decrease of the hydrogenation catalyst. More particularly,
it has become desirable to provide a process which will provide
additional quantities of 2-ethyl hexenal while simultaneously
preserving the life of the hydrogenation catalyst. Still
more especially it has become desirable to provide a process
, which will minimize the amount of higher condensation products
realized and maximize the amount of 2-ethyl hexenal produced
. from the condensation process.
SUMMARY OF THE INVENTION
In accordance with the present invention it has
been found that the hydrogenation catalyst life can be preserved
and that more 2-ethyl hexenal can be produced at a given cost
; than heretofore provided. The present process is an improvement
in a continuous process for preparing 2-ethyl hexanol wherein:
s A) One mole of n-butyraldehyde is condensed with
another mole of n-butyraldehyde in a condensation zone in the
presence of an alkali metal hydroxide whereby there is formed
2-ethyl hexenal and higher condensation products;
B~ The resultant product is contacted with water to
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separate alkali metal salts therefrom and an organic phase
comprising 2-ethyl hexenal and higher condensation products
is separated therefrom and unused alkali metal hydroxide is
recycled to the condensation zone;
- C) The organic phase is separated in a separation
; zone into a 2-ethyl hexenal rich fraction and a residual
fraction having from 30 to 60 % by weight of higher condensation
product;
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l D) The 2-ethyl hexenal rich fraction i8 introduced
2 into a hydrogenation zone containing hydrogen and a hydrogen-
3 ation catalyst, the improvement residing in recycling to the
4 condensation zone at least a portion of the residual fraction.
In accordance with the invention it has been dis-
6 covered that if a portion of the res~dual fraction conta~ning
the ma~or amount of higher condensation product ~s recycled
8 to the condensation zone that the same will break up into
molecules of lower lecular weight which will be converted
into 2-ethyl hexenal. Moreover, the amount of higher con-
11 densation product passing through the streams downstream of
12 the condensation product will be reduced so that the amount
13 of higher condensation product deposited on the hydrogenation
14 catalyst will be minimized. It has been found by the technique
of the present invention that significantly greater quantities
16 of 2-ethyl hexenal can be realized while minimizing the
17 teleterious effects these higher condensation products have on
18 thehydrogenation catalyst.
19 The continuous process of the present invention is
conducted by sub~ecting the n-butyraldehyde to the aldol
21 condensation at a temperature of 80 to 140C in the presence
22 of an alkali metal hydroxide as described above. The product
23 is sub~ected to the action of water to separate alkal~ metal
24 salts therefrom and an organic phase i8 obtaLned. This organic
phase com~ri~es the 2-ethyl hexenal together with the higher
26 condensation products. By the term "higher condensation
27 products" there i8 meant those products obtained by the con-
28 densation of m~re than 2 moles of n-butyraldehyde. The~e
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higher condensation products have a higher molecular weight
and, accordingly, have higher boiling points. It is these
products that deleteriously effect the activity of the hydro-
genation catalyst.
The organic phase also contains minor quantities
of unreacted n-butyraldehyde, some entrained water and minor
quantities of alkali metal. According to the invention this
organic phase is subjected to a separation technique designed
to separate a phase rich in 2-ethyl hexenal which, in turn,
is fed to the hydrogenation zone. The separation technique
will also provide a residual phase having a major amount of
higher condensation products. By the term "major amount"
there is meant an amount of higher condensation product of
between about 30 and 60 % by weight. It is this residual
fraction which is recycled to the condensation zone in
accordance with the improvement of the invention. G~nerally,
; speaking, the separation can take place by a distillative-
type technique such as through the use of an evaporator.
B~ using an evaporator a stream rich in 2-ethyl hexenal can
; 20 be obtained which, in turn, can be used as feed to the hydro-
genation zone. Generally speaking, the overhead from the
evaporator has between about 96 and 97 % by weight 2-ethyl
hexenal. Additionally, the residual product generally con-
tains between 40 and 70 % 2-ethyl hexenal (in addition, of
course, to the higher condensation products).
In accordance with the improvement of the inven-
tion this residual fraction - about 4 to 8 % by weight of 2-
ethyl-hexenal fed to the separation zone - is recycled from the
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separation zone e.g. evaporator sump, to the condensation
zone. The residue to be returned to this aldol condensation
step desirably contains between 40 and 70 % by weight 2-
ethyl hexenal which, of course, is in addition to the highercondensation constituents and alkali metal salts.
Surprisingly, it has been found that the higher
condensation materials in this residual fraction are largely
split in the aldolization step with the formation of 2-ethyl
hexenal thus reducing to about one-third the amount which
would be produced if the same were not recycled. Thereby,
only minor amounts of higher boiling materials become en-
trained into the feed to the hydrogenation zone. Conse-
quently, about one-third or less higher condensation pro-
ducts can become deposited on the catalyst. This signi-
ficantly decreases the deterioration of the catalyst and
considerably improves its life.
The recycling technique of the present inven-
tion has the further advantage that the yield of 2-ethyl
hexenal in the aldolization step is improved due to reduced
formation of higher condensation products. The yield of 2-
ethyl hexenal is increased additionally owing to the fact
that it is no longer required to distill the sump residue in
a separate operational step to obtain the additional 2-ethyl
~ e~c~
hexenal fraction for-~eet to the hydrogenation zone.
It must further be considered in this connection
that the distillation step of the heretofore practice on the
sump product was an expensive step owing to the fact that the
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distillation column had to be made of stainless steel to
2 co~bat the corrosiveness of the ms~erial so charged.
3 Finally, it is no longer necessary wi~h the improvemel It
4 of the present invention to take special measures for the com-
plete elimination of alkali metal salts from the raw aldoliza-
6 tion product. It has been found, surprisingly, that a s~mple
7 scrubbing technique as by contactin~ the aldolization product
8 with water is sufficient. The resultant organic phase con-
9 taining the decreased higher condensation product content is
compatible with the hydrogenation cataly~t even at the same
11 levels of alkali metal salts.
12 In order to more fully illustrate the nature of the
13 in~ention and the manner of practicing the same the following
14 two examples are presented:
16 Example 1 (presented for purposes of comparison).
17 In the example set forth below there is illustrated
18 the known technique for the production of 2-ethyl hexenal
19 from n-butyraldehyde. In this technique no recycle of evapor-
ator sump product to the aldolization step was performed.
21 In a continuously operated aldolization unit there
22 was introduced 5.0 metric tons per hour of n-butyraldehyde and
23 75 liters per hour of a 207o aqueous sodium hydroxide solution.
24 There was also introduced a 3Z by weight aqueous sodium
hydroxide aqueous recycle solution. Within a short period of
26 time, 98a8% of the n-butyraldehyde were con~erted at 120 to
27 130C, After the reaction liquor was separated the raw 2-
28 ethyl hexenal was treated with water to remove sodium salts
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1 ¦ adhering thereto and the water was separated. The organic
2 ¦ phase comprising the raw 2-ethyl hexenal was introduced into
3 ¦ an evaporator of a gaseous phase hydrogenation unit positioned
¦ do~mstream of the aldolization unit. The charge to the
5 ¦ evaporation unit had the following composition:
6 ¦ 95.5% by weight 2-ethyl hexenal
7 ¦ 1.3X by weight n-butyraldehyde
8 ~ 1.8Z by weight higher boiling products (largely
9 I higher condensation products)
10 ¦ 1.4X by weight water
11 ¦ The sump of the evaporator was maintained at a
12 ¦ temperature of 165C. Overhead there was withdrawn a product
13 ¦ stream. 96~070 by weight of the raw 2-ethyl hexenal charget
14 ~ was withdrawn from the overhead line of the evaporator by
15 ¦ means of recycled hydrogen and the ~ame was introduced into
16 ~ the hydrogenation reactor. The overhead product from the
17 ¦ evaporator had the following composition:
18 ¦ 1.3Z by weight n-butyraldehyde
19 1 96~970 by weight 2-ethyl hexenal
20 ¦ 0.4X by weight higher boiling product
21 ¦ 1.4% by weight water
22 ¦ The higher boiling products which were withdrawn
I from the sump had the following composition:
24 ¦ 65.0% by weight 2-e~hyl hexenal
25 ¦ 35.07. by weight higher boiling products
26 ¦ 25 mg. Na/liter
27 ¦ After processing of the evaporator bottoms by dis-
28 ¦ tillation, hydrogenation of the total raw 2-ethyl hexenal and
1057313
~, distillation of the raw 2-ethyl hexanol only 2.5 kgs. of
100 kgs. n-butyraldehyde were reacted to form higher boiling
products.
Example 2
In this example there is shown the results of a pro-
cess similar to that of Example 1 except wherein a portion of
the evaporator sump product was recycled to the aldolization
, step.
The aldolization was carried out in the manner des-
cribed in Example 1. However, additionally, the higher
boiling residue from the evaporator in an amount of about 5 %
by weight based on the raw 2-ethyl hexenal charged to the
gaseous phase hydrogenation was added to the caustic solution
which was recycled to the aldolization step.
The conversion of n-butyraldehyde was 98.8 %.
After the raw 2-ethyl hexenal had been separated from the reac-
tion liquor and, by treatment with water and separation of
water, largely freed from the sodium salts adhering thereto, it
was charged to the gaseous phase hydrogenation.
At a bottom (sump) temperature of 165C, 95.5 % by
weight of the raw 2-ethyl hexenal charged to the evaporator
was withdrawn from the top of the evaporator and fed in the
gaseous phase to the hydrogenation unit containing the hydro-
genation catalyst. The composition of the raw 2-ethyl hexenal
composition charged to the eYapOrator was as follows:
. 94.4 % by weight 2-ethyl hexenal
1.2 % by weight n-butyraldehyde
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1 3.1% by weight higher boiling products
2 1.3Z by weight water
3 1.2 mg./l. of sodium
4 The composition of the overhead product from the
evalporator that was charged to the hydrogenation zone was
6 as follows
7 1.3Z by weight butanal
8 96~77o by weight 2-ethyl hexenal
9 0.6X by weight higher boiling products
1.4~ by weight water
11 0~1 mg./l of sodium
12 From the sum~ of the evaporator there was withdrawn
13 4.5% by weight, ba~ed on the amount of raw product charged,
14 o~ a mixture composed of:
4770 by weight 2-ethyl hexenal
16 53% by weight higher boiling products
17 21 mg. of Na per liter
18 The same was recycled into the aldolization unit.
19 After hydrogenation to fonm raw 2-ethyl hexanol
followed by distillation of the alcohol, only 1.1 kgs. out of
21 100 kgs~ n-butyraldehyde had been converted into higher
22 boiling products whereby the yield of 2-ethyl hexanol was
23 increased by 1.4 kgs. as compared to the yield obtained by
24 Example 1 supra.
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27
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