Note: Descriptions are shown in the official language in which they were submitted.
'1 Zoo
PROCESS FOR WORKING UP AQUEOUS Salutations
OF SODIUM METHALLYL SULFONATE
I Background of the Invention
¦ This invention relates to a process fox working up
5 aqueous solutions of sodium methallyl sulf~nate,espe
Shelley as obtained in the industrial manufacture of
sodium methallyl sulfonate (MA) by reaction of methallyl
chloride IMAC) with aqueous Nazi solution.
In this process version, described, for example, in
10 US. Patent 4,171,324, aqueous solutions are produced
which contain sodium methallyl sulfonate and sodium
chloride in almost equimolar amounts, for example about
25% MA and about 10% Nikko, by weight.
Various processes are known for working up these
15 solutions and separating the MA from the Nail; these
involve either extraction methods, e.g. according to
US. Patent 2/601,256, or methods using fractional cry-
stylization, e.g. according to US. Patent 3,829,472,
or a combination of these unit operations, for example
20 according to British Patent 1,244,074.
- These processes have in common that the Miscount-
in solutions to be worked up are concentrated by
- evaporation at least in a partial step, under reduced
pressures as well as under normal or excess pressures.
25 The MA contained in the solutions to be evaporated
is thermally sensitive and depending on the evaporation
temperature and residence time, secondary reactions
occur in some cases with the formation of undesirable
33~7
by-products.
The thermal sensitivity of MA it less of a problem
in the extraction processes because the necessary
evapoxatlon to dryness takes place preferably under
5 a vacuum, i.e. at low temperatures. Yet, the extraction
methods have not gained industrial significance since
they require the use of large amounts of externally
supplied solvents and/or extract ants and involve solvent
recovery, solvent losses, additional apparatus and
10 high energy requirements.
In contrast thereto, fractional crystallization as
described, for example, in US. Patent 3,8~9,472, has
become popular industrially despite the problems also-
elated with the MA thermal sensitivity because the sepal
15 ration of MA from Nail requires no additional auxiliary materials and is simpler to handle with respect logon-
dueling the process
In this method, evaporation is effected preferably
under normal pressure under boiling temperatures ox
20 about 100-110 C up to a weight ratio of the salts to
the remaining water of 1.3:1 to 1.5:1 in the solution,
wherein initially only the largest part of the Nail is
crystallized, without concomitant precipitation of MAST
This is due to the fact that volubility of Nail in a
25 solution with equimolar amounts of MA and Nail lies
below 12~ and is only slightly dependent on the tempera-
lure, whereas the volubility of MA in such solutions
greatly increases with rising temperatures and at 110 C,
is approximately around 50%. Shortly before MA begins
30 to precipitate, the evaporation is interrupted; the
precipitated Nail is separated in the hot state, and
the resultant hot filtrate is subjected, after adding
0.1 - I by weight of water, to crystallization by
cooling, thus crystallizing only MA without concomitant
35 precipitation of the still dissolved Nail. In this
1%2~3~7
crystallization the higher the final temperature during
evaporation, and the lower the final temperature after
cooling, the more the MA precipitates. Therefore, it
is desirable to conduct the evaporation preferably at
the boiling temperature under normal pressure. The thus-
crystallized MA is separated in a suitable separator,
such awl e.g. a filter centrifuge or a suction filter,
as a moist crystallized product from the mother liquor
In this way, a relatively NaCl~depleted crystallized MA
product is obtained which can be freed still further
from Nail by an additional water washing step.
This process operates especially economically if
all resultant mother liquors and wash waters are
recycled into the evaporation stage since then, at least
theoretically, the entire MA can be isolated as a cry-
stylized product. By means of this recirculation
method, part of the MA is exposed to constantly repeated
thermal stress. Consequently, undesired by-products be-
come enriched in the mother liquor, contaminating the
crystallized MA product.
As is known, the normal procedure for avoiding imp
purities in crystallized products caused by mother
liquors that contain by-products comprises washing of the
crystallized product with part of the wash waters or
Of the mother liquors being purged, i.e. not recycled
but rather discarded. In this way, while losing part
of the intended product, in this case MAST it is possible
to maintain the content of by-products in the to be no-
cycled and recirculated mother liquors at a low,
acceptable level.
The extent of the losses of intended product in-
valved in the purging of mother liquor is a function
of the reaction rate for the formation of by-products
during evaporation and processing of the reaction Swahili
lion, the higher the ratio the higher the losses.
I
Summary of the Invention
In view of the preceding discussion, an object of the present
invention is to obtain US in as pure a form as possible from sneakily-
containing aqueous solutions, by a process involving evaporation of the
solutions while minimizing the formation of undesired by-products.
Surprisingly, it has now been found that the formation of
by-products due to thermal stress during the evaporation of aqueous
solutions containing sodium methallyl sulfonate and sodium chloride can be
considerably reduced by maintaining the pi value of the solution and/or
the thus-evolving suspension, during evaporation, within a range of 7.5 -
10.5, preferably 8.5 - 9.5.
Thus the present invention provides a process for isolating
sodium methallyl sulfonate from an aqueous solution containing sodium methallyl
sulfonate and sodium chloride, which process comprises:
evaporating the aqueous solution to just below the volubility
limit of sodium methallyl sulfonate while maintaining the pi value at
7.5 - 10.5 and the temperature at 75 - 110C. thereby crystallizing sodium
chloride;
separating from the hot solution only sodium chloride in
crystallized form;
cooling the resultant hot solution from which the sodium chloride
has been separated to effect crystallization of only sodium methallyl
sulfonate;
and separating the crystallized sodium methallyl sulfonate from
the resultant mother liquor.
Preferably the mother liquor separated from the crystalline sodium
_
I
methallyl sulfonate is recycled into the evaporating step.
Accordingly, this invention is especially useful for working up
an aqueous solution containing an approximately equimolar amount of sodium
methallyl sulfonate and NaClJ particularly a solution containing about
25% of MA and 10% of Nail weight basis) and obtained by the reaction of
methallyl chloride with an aqueous Nazi solution.
Evaporation takes place within a temperature range of 75 - Luke,
preferably 85 - 95C, preferably under reduced pressure, i.e. less than
atmospheric pressure.
Since MA and Nail which are both salts of strong acids and
strong bases, exhibit a neutral reaction in an aqueous solution and a pi
of about 7 is measured at room temperature which is even lower at higher
temperatures), it could not be expected that it is more advantageous to
adjust such MAS/NaCl-containing solutions to be weakly alkaline, and to
evaporate in an alkaline medium in a specific pi range. Heretofore pi was not
even considered a variable to have any effect during the working up process.
When evaporating at a pi value below 7, it has been surprisingly
discovered that the formation of by-products tends to increase; it is assumed
that divers and/or oligomers of US are formed. This assumption is supported
by NOR analyses of MAS-containing solutions which have been heated (i.e.
subjected to thermal stress) in a neutral to weakly acidic medium. In the
evaluation of such NOR spectra, it has been unexpectedly found that the tendency
toward formation of divers, when increasing the pi value by one omit, under
otherwise identical conditions, is reduced by a factor of about 2.5. It was
therefore apparently logical that the evaporation of MAS-containing solutions
should be effected at the highest possible pi value in order to further
decrease the formation of divers.
~Z;~9~3~7
It has furthermore been discovered, however, that the extent that the
pi value can be increased is limited by the fact that, with an increasing pi
value, the formation of another undesired by-product is observed. It is probable
that this by-product, based on NOR analyses, is isocrotyl sulfonate (ITS) which
begins to form from MA at pi values above about 9.5 by double-bond isomerization.
Moreover by raising the pi value by one unit, the velocity of (ITS) formation
(rate of reaction) increases by a factor of about 10, under otherwise
identical conditions.
Consequently, to keep the assumed dimerization as well as isomerizat-
ion of MA at a low level, a pi range of 7.5 - 10.5, preferably 8.5 - 9.5, is
thus to be set and maintained during evaporation. It has been found surprisingly
that the thus-set pi value of MAS-containing solutions generally does not remain
constant during the evaporation step but rather drops asymptotically by 1 to 1.5
pit units. The origin of this drop in pi is Imknown, because no hydroxyl ions
are consumed in the dimerization or the isomerization. Therefore it is
usually necessary for maintaining the pi value within the desired range, to add
a small amount of an alkaline solution, e.g. an Noah solution, during the
entire evaporation period.
It has furthermore been found that the range of the pi value is
preferably maintained within a narrow range at a higher evaporation temperature.
In other words, the pi range to be maintained is especially narrow at a high
evaporation temperature where the velocity of the by-product formation is also
high. For example, a pi of 9.0 - 0.5 should, if at all possible, be maintained
during evaporation under normal pressure and at an evaporation temperature of
about 100C.to about 110C, whereas, for example, the maintenance of a pi of
9.0 - 1.0 is sufficient for evaporation under reduced pressure at an
evaporation temperature of 85 - 100C. With an evaporation temperature of
3~7
75 - 85C, it is enough to maintain a pi value of about 9.0 - 1.5. If the
aforementioned pi ranges are broadened, increased amounts of by-products are
formed; however, this may in some cases be tolerable if the evaporation
periods are brief.
In view of the fact that, at a low evaporation temperature, less
stringent pi adjustment and control are required since the rate of by-product
formation is low, it is advantageous to conduct at least a portion of the
evaporation under reduced pressure at temperatures of up to 100C. As the
reduced pressure, i.e. less than atmospheric, it is preferred to employ 250 to
750, particularly 350 to 750 mar.
Conversely, since the volubility of US drops with
- pa -
~Z~3~
reduced temperature, the evaporation temperature
cannot be lowered arbitrarily; otherwise, correspondingly
less MA is crystallized during the crystallization
by cooling after evaporation, and therefore a greater
5 amount of MA must be recirculated with the mother
liquors. Thus, an evaporation temperature of 75-110 C,
preferably about 85-95 C, is set, and the solutions
are evaporated to a preferred weight ratio of the
dissolved salts to the remaining water in the solution
10 of 0.8:1 to 1.5:1, preferably Lyle to 1,2~1.
Subsequently, the thus-crystallized Nail is separated
in the hot state, preferably at the evaporation tempera-
lure, and the resultant filtrate is cooled preferably
to temperatures of 10-30 C, especially 15-25 C until
the MA crystallizes. After separation of the MAST
the mother liquor is recycled to the evaporation
step.
In general, the largest portion of the mother
liquor is recycled into the subsequent evaporation
process. A small portion, for example 2-20~ of the
mother liquor, is optionally purged to prevent a
buildup of by-products in the system. The particular
quantity purged is dependent on the content of dumpier
and isomer in the mother liquor.
A preferred embodiment of the invention involves
evaporation in two or more pressure stages, wherein,
first, while maintaining the pi range of this invention,
the primary quantity, Abbott% to 38%, preferably 25 %
to 35 %, of water is vaporized under reduced pressure,
preferably 250-750 mar, at temperatures of 75-100 C,
preferably 85-95 C, to such an extent that there
it just barely no precipitation of MA as yet, besides
the crystallizing Nail. This is generally achieved,
depending on the evaporation temperature, at a weight
ratio of the dissolved salts to the remaining water
of I - 1.3. Thereafter, under an elevated pressure,
preferably under normal pressure, in a temperature
range from 100 to 110 C, the residual amount of
water, likewise while maintaining the pi range of
this invention, is vaporized down to the desired
final concentration, but at most to such an extent
that the volubility limit of MA it not exceeded.
This is generally the case with a weight ratio of
the dissolved salts to the remaining water of 1.3
to 1.5. There is of course a temperature difference
between the two stages as well as a pressure differ-
once, the temperature difference being generally
about 10 to 35, preferably 15 to 25 C.
This embodiment of the process has the advantage
that the primary evaporation can be conducted at
a lower temperature within the pi range of this
invention without appreciable formation of by-products,
and only the residual evaporation is conducted at
an elevated temperature, likewise within the pi range
Of this invention. In this way the formation of
by-products even at higher temperatures is kept at
a minimum, on the one hand, and the solution can
be concentrated to the maximum on account of the
higher volubility of MA at elevated temperatures
25 on toe other hand. Thus, the formation of by-products
is minimized and simultaneously the amount of crystal-
lived WAS product obtained during the subsequent
cooling crystallization is at a maximum. Furthermore,
a very pure sodium methallyl sulfonate is produced
(above 99.8% strength).
Without further elaboration, it is believed that
one skilled in the art can, using the preceding de-
ascription, utilize the present invention to its fullest
extent The following preferred specific embodiments
are, therefore, to be construed as merely illustrative,
2939L7
and not limitative of the remainder of the disclosure
in any way whatsoever. In the following examples,
all temperatures are set worth uncorrected in degrees
Celsius; unless otherwise indicated, all parts and
percentages are by weight.
` 10
~293~
Example 1
An agitated container with heating jacket in the
lower third of the container and a recirculating pump, having
a rapacity of 3 my, is charged with 2,500 kg of a solution
with 27.4% MA and 10.4% Nail, heated to 90 C under normal
pressure, and adjusted to pi 9 at this temperature by adding
sodium hydroxide solution. Thereafter the pressure is lowered
to about 500 mar so that the solution begins to boil. At
this temperature, thy solution is evaporated while maintain-
in the pi value range of 8.5 - 9.5 by further addition ox
small amounts of sodium hydroxide solution. The amounts
of water removed are controlled by measuring. After evapora-
lion of about 440 kg of water, Nail begins to crystallize.
Evaporation of the thus--Eormed suspension is continued at
90 C in a pi range of 8.5 - 9.5 until about 820 kg of water
has been evaporated. The thus-evaporated water corresponds
to a quantitative proportion of about 33% of the original
amount of solution. At this point, evaporation is ton-
minuted at 90 C to avoid concomitant precipitation of MAST
In the normal easer the crystallized Nail can, at this point,
be suctioned off in the hot state at at least 90 C, and the
filtrate can be cooled from 90 C to about 20 C to bring
the MA to crystallization. In this procedure, about 420 kg
of MA is crystallized.
In the preferred embodiment
however, the pressure is raised to normal pressure and, at
a boiling point of about 110 Or another 120 kg of water is
~L2293~7
evaporated, corresponding to a total quantity of water of
about 38% of the original amount of solution. In this step,
about 160 kg of Nail is crystallized without accompanying
precipitation of MAST The thus-crystallized Nail is suctioned
off under boiling heat; the filtrate is transferred into a
cxystallizerr and the crystallized Nail product is washed
most extensively free of MA with water. The wash waters
are recycled into the subsequent evaporation process The
filtrate conducted into the crystallizer is subjected to
cooling crystallization down to about 20 C. During this
process, about 460 kg of MA is crystallized whereas Nail no-
mains dissolved with the residual MAST The filtrate is no-
circulated for the largest part into the subsequent evapora-
lion process. A smaller portion is transferred out in order
to avoid enrichment of by-products in the recirculated
mother liquors. The partial amount to be transferred out is
dependent on the content of divers and isomers, respectively,
in the recirculated mother liquor. Under the parameters
chosen in this example removal of about I of the mother
liquor is adequate in continuous operation, corresponding
to a MA loss of about 2% of the total quantity. Accordingly,
under the conditions of this invention, about 98~ of the MA
can be isolated in pure form in continuous operation.
The crystallized MA product is filtered in the
cold state by means of a filter centrifuge and washed most
extensively -fret of Nail with cold water Also these
wash waters are recycled into the subsequent evaporation
process. An MA of 99% purity is obtained.
12 ~L2~47
Example 2
Respectively 2,500 kg of a solution with 25.8% MA
and loo 1% Nail is charged into an agitated container having
a capacity of 3 my with jacket heating in the lower third of
the container and a recirculating pump; under normal pros-
sure/ the solution is heated to the temperatures indicated
in Table 1 (75 90, and 105 C), and the pi values are
set as indicated in Table 1 ~8~0; 9.0; 10.0; and 10.5) by
adding sodium hydroxide solution. At this point in time,
the pressure is in each case reduced to such an extent that
the solutions boil at the respective temperatures and can be
concentrated by evaporation
During evaporation, the indicated pi values are
maintainer by further addition of smell amounts of sodium
hydroxide solution, to be extensively constant (+ 0.5).
Evaporation is continued until the volubility limit of
methallyl sulfonate or the indicated temperatures has
been reached. Evaporation is terminated and the thus-
crystallized Nail is separated in the hot state at the
evaporation temperature. The filtrate is cooled to 20 C
to crystallize the MAST and the thus-recystallized MA is
separated. The resultant mother liquor is recycled into the
evaporation process; optionally, small amounts are trays-
furred out during this step (see Table 1). The crystallized
MA product is washed with cold water in such a way that
it has a residual chloride content of less than 0.1%. The
wash water is recycled into the evaporation stage.
13 7
After recycling for five times samples are taken
from the solution before separation o* Nail, and analysis
for by-products is performed by NOR. In this process, the
NOR signal at 1.3 Pam is associated with the dimerized
product, the NOR signal at 6.1 Pam with the isocrotyl
sulfonate, and the NOR signal at 1.9 Pam with MAST The
chemical shifts relate to an internal standard. Evaluation
is performed in relative area units extensively corresponding
to the actual molar concentrations of by-products r based
on MAST
The yields of MA during continuous operation white
transferring out the indicated quantities of mother liquor
obtained at varying evaporation temperatures and pi values t
per puzzler indicated in Table 1.
14
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. 15 ~2~3~'7
Comparative Example A
It was found when conducting a test with the same
charge as in Example 1, but evaporating from the beginning
under normal pressure in a temperature range from 100 to
110 C all with the pi value of the solution being in the
normal range from about 5 to 7, that in continuous operation
about 25% of the mother liquors must be transferred out
upon evaporation of the solution and/or the resultant suspend
soon to about the same final condition as in Example 1. This
corresponds r in continuous operation to a loss of MA of
about 10% of the originally present total amount; consequently,
in this case merely 90% of MA can be isolated in the pure
form
16 ~2~3~7
The preceding examples can be repeated with similar
success by substituting the generically or specifically
described reactants and/or operating conditions of
this invention for those used in the preceding examples.
From the foregoing description, one skilled in the
art can easily ascertain the essential characteristics
of this invention, and without departing from the spirit
and scope thereof, can make various changes and modify-
rations of the invention to adapt it to various usages
and conditions.
