DE1494755B - Process for the regeneration of concentrated aqueous zinc chloride solutions - Google Patents

Description

The invention relates to a process for the regeneration of a concentrated aqueous Solution of zinc chloride and optionally other inorganic salts, which by use for the polymerization of acrylonitrile impurities in the form of non-volatile organic compounds contains and thereby adversely affects polymerization when it is used again, the Saline solution is subjected to an oxidizing treatment.

Concentrated aqueous solutions which contain zinc chloride as the main component are used as solvents used for homogeneous solution polymerization or copolymerization of acrylonitrile. When such a salt solution is used repeatedly for this purpose, exercise the active organic compounds, which have accumulated therein exert undesirable influences on the polymerization reaction. In the production of acrylic fibers, acrylic acid esters, such as acrylic acid methyl ester, Ethyl acrylate and the like, methacrylic acid esters such as methyl methacrylate or vinyl acetate and the like as Monomers used, which are to be polymerized in addition to acrylonitrile, and also Vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, vinylbenzenesulfonic acid or their sodium salts can be used to improve dyeability. Some of them which have a high boiling point have or are not volatile, should be partially in the solution after the end of the polymerization lag behind. Therefore, when using the dope directly and continuously from the monomer the concentrated aqueous solution of zinc chloride is prepared as a solvent, then Inevitably, the non-volatile monomers or lower polymerization products collect, which are formed at the end of the reaction in this solution. In the production of blunt fibers Titanium oxide or the like is also added. The surface-active agent, which higher quality Aliphatic acids or the like. Contains, often used for the dispersion of titanium oxide, such surfactant should remain in the solution. The organic impurities are in the in the following description also referred to as active organic compounds.

The spinning solution produced by solution polymerization, which contains these active organic compounds contains, is pressed in a known manner through spinnerets into the coagulation belt, which contains a dilute aqueous solution of one or more inorganic salts, the fibers being formed and most of the active organic compounds due to their low molecular weight is transferred into the coagulation bath.

The coagulation bath, which is a comparatively dilute saline solution, becomes by evaporation concentrated and again as a solvent to prepare a spinning solution with polyacrylonitrile or Copolymers used, however, exercise the active organic compounds contained in the solution undesirable influences, since they are radicals or polymer radicals originating from the polymerization initiator consume the polymer solution, which extremely lowers the yield of undesired polymer discolored, the fiber that can be obtained from it becomes brittle and the production of a white fiber is hindered will. - So far there has been no satisfactory method of removing and inactivating the organic impurities in the concentrated salt solution, which are mainly zinc chloride contains, proposed. Even if a strong oxidizing agent is used, the desired Not having an effect.

For cleaning a concentrated zinc chloride solution from impurities in the form of inorganic see Metal salts is already a process known, whereby the solution with a water-soluble Persulfate is treated (U.S. Patent 2,746,840). The solution to be cleaned has not yet been made for the Polymerization of acrylonitrile used and consequently does not contain any impurities in the form of active organic compounds. Purification by application of hydrogen peroxide resulted not to the desired success because of possible side reactions.

It is well known that hydrogen peroxide is readily decomposable to under alkaline conditions To give off oxygen; however, the oxidizing power in the acidic state is rather poor. The pH of the concentrated aqueous solution of zinc chloride is very low. This value is roughly the same, for example Zero in a 60% solution, and it's about 1 in a 50% solution. Even when tried would raise the pH of the solution, increasing the pH above 3 is very difficult, and zinc hydroxide can precipitate, which has undesirable effects on the polymerization exercises and results in difficulties in storage and transportation of the solution. Consequently was the use of hydrogen peroxide to remove and inactivate the active organic Compounds in a concentrated zinc chloride solution previously considered practically impossible.

The object of the invention is to provide a method for effective removal and inactivation of organic impurities to create.

The invention consists in that the salt solution is oxidized in the presence of 0.1 to 1.0 percent by weight of basic compounds at a temperature of 90 to 100 ^° C. with 0.3 to 1.0 percent by weight of hydrogen peroxide and then filtered. The invention is based on the finding that hydrogen peroxide can be used effectively in the presence of basic compounds in order to remove and inactivate the active organic compounds in the concentrated zinc chloride solution. If the basic compounds are added in an amount by weight of at least 0.1% and preferably in an amount by weight of 0.4 to 1.0%, hydrogen peroxide is activated to remove the organic compounds despite the low pH of the saline solution, for example close to 2 lies, effective to remove and inactivate. The fact that hydrogen peroxide in particular is so effective in removing and inactivating organic impurities must be regarded as surprising because this was not to be expected due to the known, less good success in removing and inactivating inorganic metal salt impurities.

The basic compounds used are preferably one or more of the following compounds: Zinc oxide, ammonium hydroxide, ammonium carbonate, sodium hydroxide, sodium carbonate, calcium oxide, Calcium hydroxide, magnesium oxide, magnesium hy-

droxid. Zinc oxide is primarily preferable because it, like the solution salt, is a zinc compound is. However, a mixture of two or more of the aforementioned basic compounds can also be used as an additive use. Preferably, one or more of these basic compounds will be used accordingly the composition of the solution salts in the solution to be treated is selected. Self when 1.0% by weight or more of the basic compounds is added, the detergency can hardly be improved. In some cases, the Excess of basic compound cannot be dissolved. The excess is not only worthless, it is It can also have difficulties in storing or transporting the solution and it can also be an obstacle be in the process of polymerization.

The determination or setting of the concentration of the basic compound is made in accordance carried out with JIS-K 1428 and JIS-K8111, using a solution of about 10 g of pure zinc chloride is taken in about 10 ml of water and several drops of the indicator a methyl orange solution (0.1%) can be added to the resulting solution. By titrating IN hydrochloric acid the basic compound concentration can be determined from the color change according to the following equation calculate the indicator:

C =

0.041 ■ D

100,

Basic compound 0.2 0.4 0.6 0.8 (Weight percent) ... Zinc chloride (Weight percent) 1 7 -> ι ^ 3 ~> 4 54 1 2 1 4 1 6 1 8 58 0.8 1.3 1.5 U 60

preferably as a solvent for the preparation of the spinning solution of acrylonitrile homopolymers or copolymers used.

To the effect of the method according to the invention.

for removing and inactivating the organic impurities, the following Table 2 shows the test results, wherein the concentrated aqueous zinc chloride solution was used as a solvent for the polymerization of the monomer of acrylonitrile in an amount of at least 85 percent by weight. This solution was purified by treating the salt solution already used as a solvent for the polymerization, which was removed from the coagulation bath after the spinning process, evaporated and treated with zinc oxide in such a way that the concentration of the basic compounds contained in this solution was 0.6 Percent by weight had, whereupon the treatment with hydrogen peroxide was carried out at a temperature of 95 ⁰ C for 60 minutes. The viscosity is given by the time in seconds during which a steel ball 0.315 cm in diameter at a temperature of 45 ° C. penetrates the polymeric solution to a depth of 20 cm.

The condition that the light wavelength serves as the basis for the specified values of transparency 420 ma and the test piece is 20 mm thick.

Table 2

where C is the basic compound concentration in percent by weight, S is the material to be tested in grams and D is the IN hydrochloric acid used in milliliters.

It is absolutely necessary to keep the concentration of the basic compounds from 0.4 to 1.0 percent by weight adhere to in order to remove and inactivate the active organic compounds, since on the other hand, the polymerization is hindered. If this condition is not met, the desired Failure to achieve the purpose satisfactorily. The presence of the basic compounds leaves hydrogen peroxide become active even in the acidic state of the aqueous zinc chloride solution. The change the pH of the aqueous zinc chloride solution to which zinc oxide has been added is shown in the following Table 1 indicated:

50 Table 1

A preferred embodiment of the invention consists in that one from the coagulation bath saline solution extracted from acrylonitrile polymer fibers is used, which is produced by evaporation of water and other lubricious ingredients to a predetermined one Salt concentration has been brought. After the reunification, this salt solution is

H ₂ O ₂
(Weight
percent) Polymeri
station yield
(Polymeri
sation time
5 hours) transparency
(%)
(420 m _: x
Thickness 20 mm) viscosity
(Sec.) 0 89.5 53 85 0.1 90.7 55 98 0.2 92.5 58 113 0.3 94.3 62 133 0.4 94.6 65 130 0.5 94.5 66 131 0.6 94.5 65 132

From these results it can be seen that the treatment with hydrogen peroxide contributes very much to increasing the polymerization yield and to preventing the discoloration of the spinning solution. Hydrogen peroxide is preferably used with more than 0.1 percent by weight as a pure component with respect to the solution to be treated and with 0.3 to 1.0 percent by weight if the active organic compounds are present in larger amounts. The reaction is effectively carried out at a temperature of at least 90 ⁰ C and preferably at a temperature ° between 95 and 100 C.

On the other hand, by changing the basic compound content in the reaction, if the Oxidation treatment with hydrogen peroxide is carried out, which are summarized in Table 3 Results obtained, the acid content in percent by weight of free hydrochloric acid and the basic compound content in percent by weight of the basic compound is indicated in the concentrated aqueous zinc chloride solution. Treatment was when in use of hydrogen peroxide in an amount of 0.4 percent by weight as a pure component at a speed

temperature of 97 ° C for 30 minutes with stirring accomplished. Column 1 in Table 3 shows the results obtained when checking a concentrated aqueous zinc chloride solution were achieved, which not by the method according to the invention was treated.

Table 3

Acidity (percent by weight) ....

Basic compound

Br value

Absorption index of the treated
Solution (wavelength 265 m)
(Thickness 10 mm)

Carbon component in the
Solution (weight percent)

Polymerization yield (%)

2 3 test 4th No. 5 6th 7 ' 1 0.2 0.3 - - - - - - 0.1 0.2 0.4 0.6 - 6.75 6.38 2.63 0.80 0.32 0.28 7.58 0.93 0.80 0.68 0.60 0.59 0.50 10.7 0.043 0.037 0.030 0.025 0.022 0.018 0.044 83.2 89.3 93.6 94.0 94.9 94.8 70.3

0.015
95.0

From the above results it can be seen that the treatment with hydrogen peroxide does so is more effective if the content of basic compounds is greater than 0.1 percent by weight. The solution is filtered immediately after the treatment.

The problem on which the invention is based can therefore by and large be regarded as being solved will. However, if not consumed hydrogen peroxide and insufficiently treated active organic compounds remain, the solution is subjected to a reduction to this To completely remove and inactivate the rest, so that the polymerization is not hindered. When Many substances can be used as reducing agents, of which zinc powder is particularly effective has proven. The zinc treatment is done by adding 0.1 to 0.3 percent by weight of zinc powder Solution is carried out under the same circumstances as for the hydrogen peroxide treatment. To the To carry out cleaning even more effectively, active charcoal can be used in an amount of 0.1 to 0.2 percent by weight be added to the solution after the zinc treatment has been completed, the Reaction conditions are the same as in the hydrogen peroxide treatment.

The polymerization or copolymerization of acrylonitrile in the concentrated aqueous solution an inorganic salt or inorganic salts which are purified by the process according to the invention can be carried out according to any method known per se. Especially However, it can be advantageous if an organic compound such as for example α, α'-azobis-iso-butylnitrile and the like, or the oxidizing compounds such as hydrogen peroxide, ammonium persulfate, potassium persulfate and Sodium persulfate or redox catalysts which contain the aforementioned oxidizing agent, and a reducing agent such as sodium metbisulfite or potassium metbisulfite is used.

If the solution treated by the process according to the invention is used as a solvent, the polymerization yield can reach a satisfactory level after a lapse of time are increased, so that it is shown that the process according to the invention is also extremely economically advantageous is because the solution salt, such as zinc chloride,

is hardly lost.

It should also be pointed out that the method according to the invention also metal ions, such as iron-containing ions, from the concentrated aqueous solution of inorganic salts as well as the

can remove active organic compounds. The process of the present invention is described below explained in detail using an implementation example.

35

example

The monomeric solution of 89.0 parts by weight of acrylonitrile, 9.5 parts by weight of methyl acrylate and 1.5 parts by weight of sodium allyl sulfonate in 1000 parts by weight of concentrated aqueous solution of inorganic

Nischer salts according to column A in Table 4 was stirred thoroughly and using hydrogen peroxide polymerized as a polymerization initiator. The resulting dope was through Spinnerets spun in a coagulation bath, wel-

Ches contained 15 percent by weight of the same salts as the spinning solution. The inorganic salts in the Spinning solutions were gradually added to the coagulation bath along with the untreated monomers and water-soluble organic contaminants

compounds which were formed at the end of the polymerization reaction, transferred. The concentration of the inorganic salts in the coagulation bath was approximately 18 percent by weight at the end. Under reduced pressure, water and the

untreated volatile monomers removed from the solution, so that the concentration of inorganic Salts therein was 58 percent by weight. The concentrated aqueous solution treated in this way, which is referred to as Solution 1 has been identified as

Solvent used for polymerization. 500 parts by weight of Solution 1 became 44.5 parts by weight Acrylonitrile, 4.75 parts by weight methyl acrylic and 0.75 parts by weight sodium acrylic sulfonate added. The resulting solution were

after vigorous stirring was added 0.064 parts by weight of hydrogen peroxide as a polymerization initiator and 6 hours allowed to stand in the reaction vessel which maintained at a temperature of 45 ⁰ C

would. The polymerization yield, the transparency and the viscosity of the polymeric solution obtained are shown in column B of the table, which was determined in the same manner as in Table 2. As can be seen from the results, it is impossible to carry out the spinning operation cleanly and smoothly and to achieve an excellent fiber in complete clarity and manner.

On the other hand, 1000 parts by weight of the solution 1 became the compounds shown in column C of the table added. The resulting solution was heated and treated so that its content of basic compounds could be brought to the values given in column D. Then the solution was made by adding hydrogen peroxide under the conditions given in column E. treated, stirred and filtered off after the reaction was complete, so that the organic impurities removed and inactive

fourth in order to no longer be able to adversely affect the polymerization. In some cases a post-treatment with zinc powder and active charcoal was carried out, as in columns F and G is indicated. The concentrated aqueous solution of the inorganic salts, which after the Method according to the invention was treated, and is referred to as solution 2, was clear and transparent and had hardly any organic impurities. The results are given in column H, which represents the Effects in the removal and inactivation of the organic contaminants according to the invention indicates. The polymerization results using Solution 2 as a solvent in the same manner as in solution 1 are given in column I, which proves that the saline solution, which after the Process according to the invention was regenerated readily as a solvent for the polymerization suitable.

• Table 4

Salts of the solvent
Zinc chloride

(Weight percent)

Sodium chloride

(Weight percent)

Ammonium chloride

(Weight percent)

Pure water

(Weight percent)

Polymerization with
untreated solvent polymerization yield (%) ..

Transparency of the polymer solution (%)

Viscosity of the polymer solution (sec.)

Added basic
links
zinc oxide

(Parts by weight)

Ammonium hydroxide

(Parts by weight)

Ammonium carbonate

(Parts by weight)

Sodium hydroxide

(Parts by weight)

Sodium carbonate

(Parts by weight)

Content of basic compounds (percent by weight)

Added hydrogen peroxide (percent by weight) Treatment ^{temperature (0} C) .. Treatment time (min.) ...

Added zinc powder

(Weight percent)

Treatment ^{temperature (0} C) .. Treatment time (min.)

0 0 0 0

0.70

0.3 95 30

0.2 100 30 0
0
0
0
0

4th
42

90.7

89

7th
0
0
0
0

0.61

0.5
95
30th

0 0 0 7 0 0 0 9 0 0 0 0 0 0 0 0.62 0.59 0.3
100
30th • 0.3
95
30th 0.2
100
30th 0

0
0

109 508/352

To continue

Active charcoal

(Weight percent)

Treatment temperature (° C) .. Treatment time (min.)

Treated solution

Br value

Transparency (%)

Carbon content

(Weight percent)

Absorption index

Polymerization with treated solution
Polymerization yield (%) ..

Transparency (%)

Viscosity (%)

0 0 0 0 '0 0.1 - - - - - 100 0 0 - - - 30th 0.32 0.33 7.58 0.31 0.33 0.27 98 99 87 99 99 98 0.018 0.018 0.031 0.018 0.015 0.019 0.50 0.50 1.03 0.48 0.51 0.38 94.6 94.7 87.3 94.8 94.7 95.0 68 70 43 66 68 67 130 131 100 131 133 129

(Continuation)'

87.2
42
100

A. 8th 54 0 0 0 8th 0 0 50 0 0 0 0 4th 0 0 0 0 7th 0 4th 0 0 0 0 0 0 0 0 0 0 9 4th 0 0 0 0 42 7th 0 0 0 0 0 42 7th 0 0 B. 0 87.6 0 11th 0 0 0 0 88.4 0 11th 0 0.68 57 0.54 0.63 0 0.71 0.60 0.59 53 0.54 0.63 0 0.3 83 0.5 0.3 0 0.3 0.5 0.5 87 0.5 0.6 0 C. 100 95 97 - 100 100 97 100 95 - 30th 30th 30th - 30th 30th 30th 30th 30th - 0 0.2 0 0 0 0.2 0 0.2 0 0 - 100 - - - 100 - 100 - - - 30th - - - 30th - 30th - - D. 0 0 0.1 0 0 0.2 0 0 0.1 0 E. - - 100 - - 100 - - 100 - - - 30th ■ - - 30th - - 30th - 0.29 0.33 0.31 7.29 0.29 0.30 0.31 0.29 0.27 7.64 F. 99 97 99 88 98 97 99 99 98 86 0.016 0.017 0.015 0.033 0.015 0.014 0.016 0.017 0.016 0.031 0.34 0.37 0.40 1.26 0.39 0.42 0.47 0.32 0.39 1.10 G. 95.0 94.8 .94.7 86.0 94.7 94.3 94.6 95.0 95.8 87.3 65 65 68 42 68 66 69 67 64 44 132 133 137 99 132 134 135 130 129 102 H. I.

Claims (4)

Patent claims: 1. Process for the regeneration of a concentrated aqueous solution of zinc chloride and optionally other inorganic salts which can be used for the polymerization of acrylonitrile contains impurities in the form of non-volatile organic compounds and therefore a Polymerization adversely affected, the salt solution being subjected to an oxidizing treatment is, characterized in that the salt solution in the presence of 0.1 to 1.0 percent by weight of basic compounds at a temperature of 90 to 100 ° C with 0.3 to 1.0 weight percent hydrogen peroxide is oxidized and then filtered. 2. The method according to claim 1, characterized in that one or as the basic compounds several of the following compounds are used: zinc oxide, ammonium hydroxide, ammonium carbonate, Sodium hydroxide, sodium carbonate nat, calcium oxide, calcium hydroxide, magnesium oxide, magnesium hydroxide. 3. The method according to claim 1 or 2, characterized in that one from the coagulation bath saline solution removed from acrylonitrile polymer fibers is used, which by evaporation of water and other volatile components to a given salt concentration has been brought. 4. Use of the salt solution obtained according to claim 3 as a solvent for the preparation of the Spinning solution of acrylonitrile homopolymers or copolymers.