Note: Descriptions are shown in the official language in which they were submitted.
-"~ 1085089
The present invention relates to a ~rocess for
producing strongly acidic cation-exchange fiber and, more
particularly, to a process for producing strongly acidic cation-
exchange fiber of the sulfonated type based on fibrous polyethylene.
It has been known that the sulfonic acid group may
be introduced into polyethylene by treating the polyethylene
with chlorosulfonic acid or fuming sulfuric acid in the liquid
phase, or by first introducing the sulfonyl chloride qroup into
polyethylene by allowing polyethylene to react with sulfur -
dioxide and chlorine under exposure to ultraviolet rays and
thereafter hydrolyzing the sulfonyl chloride group with an
alkali. However, the former process has disadvantages in that
since the reaction is carried out by immersing the fibrous-
material in a liquid sulfonating agent, the removal of excess
sulfonating agent from the fibrous material is very difficult,
giving rise to a large amount of waste liquor which is difficult
to be treated and causes an increase in the material cost for
sulfonation. The aforesaid latter process requires more
complicated equipment and operations and still involves similar
disadvantages to those mentioned above, because the hydrolysis
is conducted in the liquid phase.
According to the present invention there is provided
a process for introducing the sulfonic acid group into fibrous
polyethylene, which process comprises a process for producing
strongly acidic cation-exchange fibre, which comprises trèating
fibrous polyethylene at 10 to 90C with a gas comprising 10
to 80% by volume of gaseous sulfur trioxide and 90 to 20% by
volume of an inert gas.
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1085089
According to the present invention, since the reagent
used in the reaction is a gas, the amount of the unreacted
reagent adsorbed by the fiber is very small and may be easily
removed, thus contributing to the economy of material cost.
Being sulfonated in ~he form of fiber, the sulfonated
product of fibrous polyethylene obtained according to this
invention can be imparted with a high cation-exchange ability
in the portion near the fiber surface. Such an ion-exchanger
having the ion-exchange portion near the fiber surface has a
remarkable feature of rapid diffusion and exchange of the ion,
quite different from conventional ion-exchangers of the styrene-
divinylbenzene type and other crosslinked types which utilizes
micropores as the site of ion-exchange. The present fibrous
ion-exchanger is expected to be industrially useful and may find
uses in a variety of fields such as, for example, biochemical
field, treatment of industrial waste water, treatment of
radioactive substances, and purification of contaminated air.
Although both of the high-density and low-density
polyethylene can be used in the present process, the high-density
type is preferable, because it is more easily made into fiber.
The fibrous polyethylene to be used is produced by any of the
known methods such as melt spinning, flush spinning, cutting
and splitting of stretched tape into fibrous form, and
1085089
1 polymerization under shearing stress to form fibrous
polymer.
As for the type of polyethylene fiber, although
melt-spun continuous filament may of course be used,
it is most preferred, for the purpose of introducing
a great number of sulfonic acid groups in the surface
layer, to use fibrous product obtained by the so-called
flush spinning which is carried out in such a way that,
as disclosed in Japanese Patent Application Laid-Open
~os. 83,529/75 and 17,330/76, a polyethylene solution
is ejected under an applied pressure through a nozzle.
The flush-spun fibrous product is of low manufacturing
cost and has a very large specific surface owing to
its three-dimensional net-work structure composed
of very fine fibrils, 1 - 5~ in diameter. The flush-
spun product is advantageous as a base material, because
it can be used either as spun, that is, in the form
of cord or net, or after having been subjected to
beating and made into pulp.
The present process is characterized by
introducing the sulfonic acid group into polyethylene
in a heterogeneous reaction system so as to keep the
fiber form unchanged. This sulfonation process is
applicable not only to raw fibers but also to textile
products such as, for example, woven fabrics, ropes,and nonwoven fabrics. The sulfonation proceeds by
simply exposing fibrous polyethylene to an atmosphere
containing sulf`ur trioxide.
A number of procedures for sulfonating fibrous
polyethylene with gaseous sulfur trioxide are conceivable.
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10~5089
1 For instance, sulfonated fibrous polyethylene is
actually obtained by passing an inert gas stream
containing sulfur trioxide through a bed of fibrous
polyethylene packed in a column (column method), or by
introducing the above-noted gas mixture into a reactor
in which fibrous polyethylene is kept stirred by means
of a stirring device, or by introducing gaseous sulfur
trioxide into an evacuated reactor containing fibrous
polyethylene (reduced pressure method).
Further, it was found that one of the most
preferable modes of uniformly sulfonating a large lot
of fibrous polyethylene is to treat the material in
- a rotating reactor (rotation method). This method
has proved industrially advantageous, because it
enabled a large amount of fibrous material to be easily
kept stirred, uniformly treated, and little affected in
uniformity of reaction by the flow rate of the gaseous
mixture. This method is particularly useful for
sulfonating polyethylene in the form of staple fiber
or pulp.
The rotation method is illustrated below in
detail.
The reactor may be of any shape such as, for
example, spherical, cylindrical, prismatic, or V-shape.
It can be provided with baffles on the interior wall.
Fibrous polyethylene is sulfonated, for example, in
such a reactor rotating about a horizontal axis. A
stream of gas containing sulfur trioxide enters the
reactor through an inlet on one side and leaves through
an outlet on the opposite side after passing through
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1085089
1 the fibrous polyethylene being agitated. The adequate
quantity of a charge of fibrous polyethylene varies
depending on the shape, length, and bulk density of
the fiber. It is desirable to charge the material so
that it may be agitated by the rotation of the reactor.
The adequate amount is easily determined in each case
by trial. The rate of revolution of the reactor may
also be easily determined.
If a large quantity of fibrous polyethylene
is sulfonated in a stationary column, the reactant gas
containing sulfur trioxide must be passed through at
a high speed in order to ensure uniform sulfonation.
Such an operational mode encounters with difficulties
of locally excessive sulfonation which results in a
decrease in mechanical strengths of the fiber and an
injurious effect on the form OI fiber, leading in
some cases to a sulfonated product contaminated with
significant amounts of powdered material.
If a large quantity of fibrous polyethylene
is tried to be sulfonated in a stationary reactor
provided with a stirrer to ensure uniform contact
of the gas with polyethylene, satisfactory agitation
is not realizable owing to entanglement of the fibrous
material or its twining around the stirrer.
~he invention is further illustrated below
in detail.
The concentration of sulfur trioxide used in
this invention may be any of those at which sulfonation
is able to proceed, but is preferably in the range
from about 10 to about 80~o by volume in order to render
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1085089
1 the reaction to proceed effectively. At a concentration
above 80%, uniform progress of the reaction is difficult,
while at a concentration below 10~ the reaction is
undesirably retarded. The inert gas for use in diluting
sulfur trioxide may be air, nitrogen, helium, neon,
argon, or other gases having no adverse effect on
sulfonation. Of these, nitrogen and air are particularly
preferred also for economical reasons. The inert gas
should be dried before use, otherwise the mist of
sulfuric acid formed by the reaction of sulfur trioxide ~,~
with the moisture contained in the gas will cause
agglomeration of the fibrous material, thus interfering
with uniform progress of the reaction. Further, the
fibrous polyethylene, before treating with the gaseous
sulfur trioxide, should be also dried.
The reaction temperature is in the range from
the temperature at which sulfonation may proceed to
the melting point of polyethylene, preferably from
10 to 90C, depending on the way of carrying out the
reaction.
The rate of introducing sulfur trioxide
depends to a great extent on the concentration. In
the rotation method and the column method, sulfur
trioxide is introduced at a rate (per hour per g of
polyethylene) of 0.001 to 10 g, preferably 0.01 to
1.0 g for the sake of easy control of the reaction.
In the present process, the degree of sulfo-
nation may be controlled by regulating the concentration
of sulfur trioxide, reaction temperature, rate of flow
of sulfur trioxide, total amount of sulfur trioxide
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1085089
1 fed, or reaction period. The degree of sulfonation
may be estimated from determination of the sulfur
content by elementary analysis or of the ion-exchange
capacity. A suitable sulfonation degree for the cation-
exchange fiber is 0.1 to 30, preferably 2 to 20% by weight
in terms of sulfur content, or 0.01 to 10 meq/g in
terms of ion-exchange capacity. If the sulfur content
exceeds 30~ by weight, the fiber becomes undesirably
deteriorated in mechanical strengths or undergoes a
change in the fiber form, whereas if the sulfur content
is below 0.1%, the sulfonated fiber shows only a slight
ion-exchange capacity.
According to this invention, it is possible
to select polyethylene of any fiber length and to
obtain sulfonated polyethylene of corresponding length,
long or short as required.
The fibrous ion-exchanger obtained according
to the present invention is convenient in handling and
may be utilized in the form of flock, string or cord,
mat, felt, woven fabric, etc. The fibrous sulfonated
polyethylene beaten to pulp-like short fiber form may
be utilized in the form of sheet made by conventional
paper~making techniques. The present fibrous ion-
exchanger can be reinforced or held together by use -
of other materials. For instance, continuous filaments
of sulfonated polgethylene are cut to suitable length
and bound together into a bundle to be used as an ion-
exchange cartridge; cut fibers in flock orm can be
loaded in a cylinder to be used as cartridge.
The cation-exchange fiber obtained by the
1085089
1 present process is used similarly to conventional
cation-exchangers.
Since, in the present ion-exchanger, active
sites are distributed in the surface layer rather than
in micropores, diffusion and exchange of the ion are
both rapid and regeneration as well as recovery of
exchanged ion are both easy. These features may be
utilized to the best advantage. Further, when subjected
to repeated cycles of ion-exchange and regeneration,
10 the present ion-exchanger hardly suffers from deteriora- ~;
tion due to alternate swelling and contraction and to
the impact exerted by osmotic pressure, in contrast to
conventional ion-exchangers which utilize micropores
as the site of ion-exchange. Consequently, the present
ion-exchanger has an outstanding advantage of withstandlng
long service at a high concentration of electrolytes
without undergoing deterioration.
The cation-exchange fiber obtained according
to this invention may be successfully used in desalting
and softening of utility water, separation and recovery
of metal ions, and in various other fields, by taking
advantage of the above-mentioned characteristic features.
The invention is illustrated below in detail
with reference to Examples. ~; -
Example 1
Fibrous polyethylene with three-dimensional
net-work structure obtained by flush spinning from
high-density polyethylene (Sumikathene ~ard ~ of
Sumitomo Chemical Co.; melt index, 6.2) was cut and
1085089
:
l beaten into pulp form. In a 50-liter rotary tank, was
charged l kg of the resulting pulp-like high-density
polyethylene. ~ stream of gaseous sulfur trioxide
diluted with nitrogen to about 50~0 by volume was
introduced at a rate of l liter per minute into the
tank while having been rotated. In about lO hours,
l kg of sulfur trioxide was introduced. Thereafter,
the unreacted sulfur trioxide remained in the reaction
system was purged by use of nitrogen. The sulfonated
polyethylene pulp was discharged from the tank into
30 liters of water, collected by filtration, and washed
with water. The first washing showed an acid concentration
of about 0.1 N and was easily treated.
For comparison, the same high-density polyethylene
pulp as used above was immersed in chlorosulfonic acid
and allowed to react at 60C for 3 hours. The sulfonated
polyethylene was collected by filtration and poured into
ice water. The quantity of chlorosulfonic acid adhered
to the sulfonated polyethylene after customary filtration
was nearly the same as that of polyethylene. The washing
showed an acid concentration of as high as about 3 N,
rendering the treatment of waste liquor very difficult.
The loss in acid was large enough to make the process
uneconomical.
The sulfonated polyethylene pulp showed an
ion-exchange capacity of 1.5 meq/g.
Fxample 2
In a glass column, 50 mm in diameter, was
filled 50 g of the same high-density polyethylene in
~0850~39
1 pulp form as used in Example 1. A nitrogen stream
containing about 25~ of sulfur trioxide was passed at
a rate of 5 liters/minute through the polyethylene bed
at room temperature. After about 8 hours, nitrogen
was passed through the column to expel the unreacted
sulfur trioxide. The sulfonated polyethylene, which
had been turned black, was poured into 1 liter of water.
The washing showed an acid concentration of 0.08 N.
The sulfonated polyethylene pulp, after having been
washed and dried, showed an ion-exchange capacity of
1.0 meq/g.
Example 3
~ive grams of the same fibrous polyethylene
as used in Example 1 were wound around a glass frame
and placed in a reactor. After evacuation of the
reactor, gaseous sulfur trioxide was introduced. The
glass frame was rotated to ensure uniform progress of
the reaction. As the sulfur trioxide concentration
in the reactor decreased, the gas phase in the reactor
was removed by means of an exhauster and fresh sulfur
trioxide was introduced.
When whole polyethylene had turned black, the
feed of sulfur trioxide was interrupted and the residual
gas was removed by applying vacuum. The sulfonated
polyethylene was immersed in 200 ml of water which
thereafter showed an acid concentration of 0.04 N.
The sulfonated polyethylene was thoroughly washed
with water and dried to obtain 7.5 g of black fibrous
material having an ion-exchange capacity of 1.2 meq/g.
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1085089
1 Example 4
In a 2-liter g]ass vessel, was charged 50 g
of the same high-density polysthylene in pulp form as
used in Example 1. Gaseous sulfur trioxide diluted
with about 40~0 by volume of nitroger. was introduced at
a rate of 500 ml/minute into the glass vessel while
being rotated at 40 - 50 rpm. After about 2 hours the
residual sulfur trioxide in the vessel was expelled
by introducing nitrogen. The sulfonated polyethylene
pulp was poured into 1 liter of water, filtered, and
washed thoroughly with water. ~he first washing showed
an acid concentration of about 0.1 ~. ~he resulting
sulfonated polyethylene in pulp form had an ion-exchange
capacity of 2.4 maq/g.
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