Note: Descriptions are shown in the official language in which they were submitted.
38
~ his invention reLates to conjugating unconjugated unsaturation of
Eatty ackls ancl in pa-rticular to a continuous flow process for accomplishing
such conjugation with control of the cls/trans to trans/trans ratio of the
conjugated fatty acid product.
Several prior proposals produce conjugated fatty aci~s in the presence
of alkali bases. Yor example, it has been proposed (United States Patent
2~350J583) to conjugate unsaturated highe:r Eatty acids by heating a reaction
mixture of an aqueous solution of alkali soaps of the fatty acids containing
an excess of alkali in water for several hours at elevated temperature and
under autogenic pressure for producing such conjugated fatty acids. Similar
conjugation processes operate under substantially anhydrous conditions (for
example, United States Patents 2,389,260 and 2,2~3,230). Another prior proposal
utilizes an ether of a polyhydric alcohol which contains a f-ree hydroxyl group
as a solvent to dissolve the fatty acid soaps in order to cause the conjugation
to occur (United States Patent 2,343,6~
The present invention provides a continuous flow process for con-
jugating unconjugated unsaturation of fatty acids wherein the cis/trans to
trans/trans ratio of the conjugated fatty acid product is monitored during
the reaction and such ratio of the crude product is controlled therebyn The
present flow process also is extremely efficient and rapid.
The present invention is a flow process for conjugatlng unconjugated
unsaturation of fatty acids, typically linoleic and linolenic acid, in feed-
stock containing same and controlling the cis/trans to trans/trans ratio of
the resulting conjugat0d fatty acid product in the presence of requisite
aqueous alkali metal hydroxide for providing a minor proportion of free alkali
in the resulting reaction mixture and the dissolution of the resulting alkali
metal soap in the aqueous phase of said reaction mixture. Such flow process
comprises continuously charging said feedstock, said alkali metal hydroxide,
3~
and wlter into a flow rcaction zone maintaincd under at least autogenous
pressure and thereln llca-ting the resultlng reaction mixture to a temperature
of about 200 to 370C. From the flow reaction zone, a crude product stream
is continuously wlthdrawn when the unconjugatecl fatty acid value therein has
been reduced essentially to 0 and a cis/trans to trans/trans fatty acid ratio
of the crude product stream ls between abo1lt 50:1 and about 0.1-1. The
withdrawn crude fatty acid stream then is ~acidulated to spring a crude
conjugated fatty acid product, which product is recovered. The crude fatty
acid product then is refined.
Preferably, the residance time of the reaction mixture in the
reaction zone is trom about 1 to about 40 minutes.
Although any unconjugated polyunsaturat0d fatty acid can be
conjugated according to the present process, the unconjugated unsaturated
fatty acids of the most practical interest are linoleic acid and linolenic
acid as these acids can be found in significant amounts in natural glyceride
oils and especially in vegetable oils. Conjugated unsaturated fatty acids
find utility in the manufacture of alkyd paints, lacquers, varnishes, drying
oils and waxes, and the like, because of their superior drying properties
and good performance which they contribute to such paints.
Vegetable oil reining operations provide a good source of supply
of linoleic and linolenic acids useful as feedstock for the present process.
~or convenience herein, linoleic acid will be used to refer to those
unconjugated unsaturated fatty acids useful in the present process as linoleic
acid is perhaps the most plentiful fatty acid available for use in this process.
Linoleic acid can appear in various forms in the feedstock for the present
process. The linoleic acid can be a part of a mixture of free fatty acids
wherein various saturated or mono-unsaturated fatty acids make up th0 remainder
of such free fatty acid mixture. Other useful feedstocks containing linoleic
-2-
acicl include partial and full fatty acicl glycerides, fatty acid esters such
as alkyl estcrs, ~tty acid salts (SOflpS) and mixtures thereof. One con-
venient feedstock source for the present :invention is known as "acid oil"
which is that product obtained from the acidulation of crude soapstock with
mineral acid and generally contalns free Eatty acids, various glycerides, and
a variety of minor lmpurities. While the present process performs efficiently
on feedstock contalning but a few percent linoleic acid, efficiency and
economy are best served with feedstocks containing appreciable content Oe
linoleic acid, for example~ from about 30% to about 80% linoleic acid.
Representative oils containing appreciable unconjugatecl Eatty acids for the
present process include, Eor example, the oils: corn, cottonseed, peanut,
safflower, sunflower, soybean, linseed, dehydrated castor, rapeseed, and
some marine (fish) oils.
The alkaline agent preferably is a water soluble alkali metal base
such as an alkali metal hydroxide (or oxide) for efficiency and economy,
though other water soluble alkali metal bases can find use in the present
process. Sufficient alkali metal hydroxide, sodium hydroxide for economy,
is used to completely (stoichiometrically)saponiEy the fatty acid content
of the feedstock (the neutralization point being at a pH of about 11.7) and
preferably somewhat in excess of this amount so that a minor amount of free
alkali is present in the aqueous reaction mixture. Typically about 1% to 20%
stoichiometric excess alkali provides a good working range Eor the present
process, though lower excess alkali quantities are preferred for minimizing
costs.
The present process is practiced by continuously charging the
linoleic acid-containing feedstock and aqueous alkali metal hydroxid0 into a
flow reaction zone maintained under at least autogenous pressure. Alter-
natively, the feedstock~ base, and water can be charged separately to the
. ~3-
138
reaction zone or a preformc(l aqueous soap of the eatty acids can be charged
into the zone. Typ;cally, sufficient water Ls admitted to the flow reaction
zone to d;ssolve tlle alkali metal soaps which are formed thereln. Generally,
from about 40% to a~out 85% water by weight of the reaction mixture in the
flow reaction zone is used in the present process. The flow reaction zone
contents, held under at least autogenic pressure, are heated to a temperature
of about 200 to 370C., advantageously about 220 to 330C. with temperatures
of about 250 to about 300C. being prefeYred. Of course, the reaction
temperature should not exceed the critical temperature of water (374C~.
Use of greater than autogenic pressure can be used for minimizing flashing
or vaporization of water in the flow reaction zone. The flow reaction zone
conveniently can be a simple tubular flow-reactor provided with an inlet for
feed, an outlet for product removal, and means to monitor the composition
of the products from such flow reactor, Reaction times for the present
conjugation process are quite small and generally range from about 1 to about
40 minutes, depending upon a variety of factors such as concentration of
linoleic acid in the feedstock, desired composition of the crude product
stream being made, reaction temperature, and free alkali concentration.
The contents of the flow reaction zone are periodically monitored
to determine the value of unconjugated linoleic acid in the reaction zone.
Also, the cis/trans to trans/trans fatty acid ratio of the crude product
stream is monitored. l~hen the unconjugated linoleic acid value of the
contents of the zone has been determined;to be prac~ically 0 and the cis/trans
to trans/trans fatty acid ratio is between about 50:1 and about ~1 1J the
crude fatty product stream is continuously withdrawn from the zone. Gas
phase chromotography is a simple and convenient monitoring means to determine
the extent of conjugation of linoleic acid in the zone and the desired
cis/trans to trans/trans fatty acid ratio, though other techniques, such as
; -4-
17~
infr~recl spcc~roscopy an~ the like, can be employed. It shoul(l be noted that
about 3%-4~ artifacts may register as uncorlJugate(l linoleic acid 'oy gas phase
chromatography when such linoleic acid has disappeared; thus, the conjugation
is deemed to be virtually complete when the unconjugated linoleic acid value
has been reduced to "practically ~ero'~. Conjungation of at least about 95%
of the unconjugated linoleic acid fed to the process usually is acheived in
the present process. The cls/trans to trans/trans fatty acid ratio o~ the
conjugated linoleic acid determines the reactivity of such conjugated l:inoleic
acid. A desirable cis/trans to trans/trans fatty acid ratio of the conjugated
linoleic acid is about 2.5:1.
The withdrawn crude product stream then is acidulatedJ pre~erably
with mineral acidJ to spring the crude fatty acid product therefrom. The
acidulated crude product stream then forms a lower aqueous layer and an upper
fatty acid oil layer containing the crude fatty acid product. The upper
fatty acid oil layer is separated conventionally by decantating, centrifuging
or the like. The separated crude fatty acid product then is refined to provide
a purified conjugated fatty acid product. Conventional refinin~ techniques
include dehydrating the crude fatty acid product at about 80 to 100C. Imder
vacuum, followed by stripping operationsJ such as vacuum distillation
techniques or the like, to provide a conjugated linoleic acid stream.
The following examples show in detail how the present invention can
be practiced but should not be construed as limitingO In this specification
all temperatures are in degrees Centigrade, all percentages are weight
percentages, and all units are in the metric system, unless otherwise expressly
indicated.
EXAMPLE
4,631 parts by weight of a mixture of soybean and cottonseed fatty
acids containing 61% linoleic acid was added to 27,306 parts by weight of
~L~l17~3~
wa-ter ancl sufficient 50~ n(llleous sodium h~droxide at about 80C. to form a
fat-ty acid soap mixture having 1 pH of 12.5. '~he aqueous soap mixture was
continuously charged into a tubwlar Elow reactor, held at a pressure of 2,300
psig, at a flow rate of about 0,25 liters/sec.(4 gallons/minute). The
temperature of the reaction ~one was 252C. and the residence time of the soap
in the reactor was about 25 minutes.
The conjugated soap was acidulated with sulfuric acid to spring
the conjugated fatty acid product whlch then was dehydrated and distilled.
Gas phase chromatography of the product fatty acids indicated about 59%
conjugated linoleic acid having a cis/trans ratio of about 6:1. These
results show the exceptional speed of reaction and efficiency of conjugation
~about 97%) obtained in the present process.
EXAMPLE 2
The procedure of Example 1 was repeated except that the reaction
temperature was adjusted to 271C. The distilled fatty acid product was
found to contain about 58% conjugated linoleic acid having a cis/trans to
trans/trans rat~o of about 3:1.
-- 6
