GB2194752A

GB2194752A - Method for producing anion exchange fibres

Info

Publication number: GB2194752A
Application number: GB08621384A
Authority: GB
Inventors: Mikhail Petrovich Zverev; Armady Naumovich Barash; Tatyana Fedorovna Kostina; Monstantin Konstantinovich; Nadezhda Fedorvna Kalyanova
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-09-04
Filing date: 1986-09-04
Publication date: 1988-03-16
Anticipated expiration: 2006-09-04
Also published as: DE3630192A1; GB8621384D0; FR2603501B1; FR2603501A1; GB2194752B

Abstract

The method for producing polyacrylonitrile based anion exchange fibres comprises the forming of fibres, treating them either with an aqueous solution of hydrazine hydrate then an aqueous solution of sodium hydrate until 5-20% of nitrile groups are hydrolyzed into carboxyl groups, or treating the fibres with an aqueous solution of hydroxyalamine until 3-10% of nitrile groups are transformed into hydroxamic groups. The fibres containing 3-20 mass % carboxyl or hydroxyamic groups are subjected to the effect of aminating agents, then washed and dried.

Description

SPECIFICATION Method for producing anion exchange fibres The present invention relates to polymer industry, more particularly to polymer fibres and still more particularly to a method for producing anion exchange fibres.

The present invention will prove useful in the fabrication of bonded materials used in the capacity of filters in industrial plants for purification of water or air from toxic agents, mostly acidic gaseous substances such as H2S, NO2, HCI, HCN, CH3COOH.

The present invention consists in that in a method for producing anion exchange fibres based on polyacrylonitrile comprising forming of the fibres, their treatment with an aminating agent followed by washing and drying, in which, according to the invention, after forming the fibres and before treating them with the aminating agent, they are treated with an aqueous solution of hydrazine hydrate then with an aqueous solution of sodium hydrate to the degree when 5-20% of nitrile groups are hydrolized into carboxyl groups or said fibres are treated with an aqueous solution of hydroxylamine unitl 3-10% of nitrile groups are transformed into hydroxamic groups.

It is expedient, according to the present invention, that the fibres be treated with an aminating agent at 80-95"C, using an aqueous solution of hydrazine hydrate for the aminating agent, said solution having been used in the herein-proposed process at the stage of introducing carboxyl groups into the fibres, or an aqueous solution of alkyleneamine. It is expedient that the function of alkyleneamine be performed by ethylenediamine, tr[ethylenetet- ramine, or polyethylenepolyamine.

Further objects and advantages of the present invention will become apparent from the following detailed description of the method for producing anion exchange fibres based on polyacrylonitrile and of its embodiments.

The fibres based on polyacrylonitrile or copolymers of acrylonitrile are produced by a conventional method, by forming them from polymer of copolymer solutions into a spinning bath, stretching, washing, drying, goffering and cutting.

It is known that ion exchange properties are imparted to the polyacrylonitrile fibres by treating them with an aminating agent for aminating the nitrile groups of acrylonitrile. The authors of the herein-proposed invention have discovered that, in order to achieve high degrees of transformation of nitrile groups during amination it is expedient to carry out treatment with an aminating agent of the fibres containing 80-97 mass % of acrylonitrile and 20-3 mass % of carboxyl or hydroxamic groups.

Introduction of carboxyl or hydroxamic groups into the polymer chain of polyacrylonitrile fibre increases the reaction capacity of nitrile groups during amination thus ensuring the production of anion exchange fibre possessing a sufficiently high exchange capacity and chemical stability to the effect of reclaiming agents while retaining high physical and mechanical properties characteristic of polyacrylonitrile.

The carboxyl groups are introduced into polyacrylonitrile fibres by treating them successively first with an aqueous solution of hydrazinehydrate then with a solution of sodium hydrate to a point when 5-2056 of nitrile groups are hydrolized into carboxyl groups.

The treatment with an aqueous solution of hydrazonehydrate ensures chemical stability of the fibre during alkaline hydrolysis due the formation of chemical crosslinks. The treatment is accomplished with 15-30% aqueous solutions of hydrazine hydrate at 90-95"C in the course of 2-3 h. An increase in the concentration of hydrazine hydrate te or in the duration of treatment impairs the physical and mechanical properties of the fibre. The alkaline hydrolysis of the fibres treated with hydrazine hydrate is accomplished by treating them with aqueous solutions of alkaiies at 70-80"C in the course of 10-30 min, the concentration of alkali being 2.0-2.5 mass 9ó. Under these process conditions the degree of hydrolysis of nitrile groups of fibres ranges from 5 to 20%.

Higher degrees of transformation of nitrile groups (over 20to) during alkaline hydrolysis are impracticable since they impair the physical and mechanical properties of the fibre and reduce the relative quantity of the reactive nitrile groups that are capable of entering the reactions of amination. Smaller degrees of transformation (under 5%) of nitrile groups in alkaline hydrolysis fail to ensure the required degree of transformation of nitrile groups at the subsequent amination stage.

We suggest that the hydroxamic groups be introduced into the polymer chain by treating the polyacrylonitrile fibres with aqueous solutions of hydroxylamine to a point when 3-10% of nitrile groups are transformed into hydroxamic groups. The treatment is performed by solutions of hydroxylamine, concentration 10-15 g/l, at 90"C during 30-60 min.

The above-specified conditions of treatment of polyacrylonitrile fibre with hydroxylamine provide for the required 3-10% degree of transformation of nitrile groups. A reduction of the transformation degree of nitrile groups at the hydroxylation stage (under 3%) slows down the reaction rate of the subsequentami- nation of the fibre and decreases the reached value of exchange capacity. An increase to the transformation degree of nitrile groups over 10% during hydroxylatin improves the amphoteric properties of the fibre and reduces the relative quantity of reactive nitrile groups in the fibre during subsequent amination.

Amination of the fibres containing 80-97 mass % acrylonitrile and 5-20 mass % carboxyl groups or 3-10 mass % hydroxamic groups is carried out by treating them with aqueous solutions of hydrazine hydrate or alkyleneamines at 80-950C. The use of hydrazine hydrate is expedient when it is used at the stage preceding the alkaline hydrolysis of polyacrylonitrile fibres. The parameters of the process of treating the fibres with hydrazine hydrate (reaction time 20-120 min, concentration of hydrazine hydrate 1530%, temperature 80-95"C) are selected on the basis of the values of fibre exchange capacity sought for. The milder parameters of the process improve the physical and mechanical properties of the fibre and cut down the expenditure of aminating agents.Proceeding from these considerations, we have selected the lower limit of said amination parameters; however, lower concentrations of hydrazine hydrate or a lower temperature extend the duration of the process considerably and fail to produce the required values of exchange capacity. Concentration of the aminating agent in the aqueous solution depends upon its chemical nature.If ethyleneamine is used, satisfactory exchange capacities are obtained at its concentration of 2-5 mass % while in case of ethylenediamine, triethylenetetramine or polyethyelenepolyamine a high exchange capacity of the fibre will be attained by increasing the concentration of amine in the aqueous solution to 80% in which case a good practice for improving the physical and mechanical properties of the fibres will be to reduce the temperature to 70"C and the duration of the process, to 30 main.

After the amination stage the fibres are washed with water to neutral reaction and dried in air at 70-90"C.

The exchange capacity of produced anion exchange fibres with relation to the acid ions, reaches 5.2 mg-equiv/g for 0.1 N HCI and they retain the high physical and mechanical properties which stay unchanged after repeated use in the processes of ion exchange.

Example 1 Polyacrylonitrile fibre is produced by forming from 15% solutions of copolymer of acrylonitrile (94 mass %), methylacrylate (4 mass %) and itaconic acid (2 mass %) in dimethylformamide.

The function of precipitant is fulfilled by a 55% aqueous solution of dimethylformamide.

Then the fibre is stretched three times in length in a plasticizing bath containing 10 mass % dimethylformamide and 90 mass water at 80"C then 2.5 times in length in steam, washed in water at 50"C, dried, goffered and cut. The obtained fibre is treated with a 30-fold amount of a 20% aqueous solution of hydrazinehydrate at 90"C in the course of 2 h then with a 30-fold amount of 2.5 aqueous solution of NaOH in the course of 30 min at 700C. As a result, 20% of nitrile groups of the fibre is hydrolyzed into carboxyl groups which corresponds to an exchange capacity of 1.6 mg-equiv/g. Then the fibre is again treated with a 30-fold amount of a 20% solution of hydrazinehydrate at 95"C in the course of 90 min.The exchange capacity of the fibre with respect to anion exchange groups is 4.5 mg-equiv/g, strength of the fibre, 15.8 cN/tex, elongation, 22.8%.

Example 2 Polyacrylonitrile fibre is produced and treated with an aqueous solution of hydrazine hydrate as in Example 1. Then the fibre is treated with a 30-fold amount of 2.5% aqueous solution of NaOH within 20 min at 70"C.

The degree of hydrolysis of the obtained fibre is 5% which corresponds to an exchange capacity of 0.4 mg-equiv/g with respect to carboxyl groups. The exchange capacity with respect to amino groups is absent. Then the fibre is treated with a 30% aqueous solution of hydrazine hydrate at 80"C in the course of 60 min. The exchange capacity of the fibre of the main groups is 2.8 mg equiv/g.

Example 3 Polyacrylonitrile fibre based on copolymer of acrylonitrile (95 mass %) with methacrylic acid (5 mass %) is obtained as described in Example 1 then treated with a 20% aqueous solution of hydrazine hydrate within 10 min at 85"C. The obtained fibre is treated with a 2.0% aqueous solution of NaOH at 70"C in the course of 20 min. The degree of hydrolysis of nitrile groups is 10% which corresponds to an exchange capacity of 0.8 mgequiv/g with respect to carboxyl groups. Then the fibre is treated with a 5% aqueous solution of hydrazine hydrate within 30 min at 90"C. The exchange capacity of the fibre with respect to the main groups is 2.6 mg-equiv/g, strength 21.5 cN/tex, elongation, 10%.

Example 4 Polyacrylonitrile fibre is derived as described in Example 1, then treated with an aqueous solution of hydroxylamine at a concentration of 10 g/l, temperature 90"C, within 30 min.

The degree of transformation of nitrile groups into hydroxamic groups is 3% corresponding to the exchange capacity of 0.3 mg-equiv/g for the above-mentioned groups. Then the fibre is treated with a 2% aqueous solution of ethylenediamine at 95"C within 1.5 h. The exchange capacity of amino groups is 2.8 mgequiv/g, strength of fibre, 15 cN/tex, elongation, 21%.

Example 5 Polyacrylonitrile fibre is derived similarly to Example 1 and treated with an aqueous solution containing 20 g/l hydroxylamine under the conditions similar to those specified in Example 4. The degree of transformation of nitrile groups into hydroxamic ones is 10 which corresponds to the exchange capacity of hydroxamic groups of 0.95 mg-equiv/g.

Then the fibre is treated with a 80% aqueous solution of triethylenetetramine at 800 in the course of 2 h. The exchange capacity of the anion exchange groups in the fibre is 5.2 mgequiv/g, strength 9.5 cN/tex, elongation 30%.

Example 6 Polyacrylonitrile fibre is derived similarly to Example 1 and treated with an aqueous solution of hydroxylamine, concentration 15 g/l, at 85"C during 60 min. The degree of transformation of nitrile groups into hydroxamic ones is 6% which corresponds to the exchange capacity of oxime groups of 0.6 mg-equiv/g.

Then the fibre is treated with a 60% aqueous solution of polyethyleneamine at 90"C within 1 h. The exchange capacity of anion exchange groups in the fibre is 2.6 mg-equiv/g, strength, 15 cN/tex, elongation, 20%.

Owing to the present invention the exchange capacity of derived anion exchange fibres with relation to acid ions runs to 5.2 mg-equiv/g for 0.1 N HCI with high physical and mechanical properties of said fibres which stay unchanged after repeated utilization of said fibres in the ion exchange processes.

Claims

1. A method for producing anion exchange fibres based on polyacrylonitrile comprising the forming of fibres; their treatment with an aqueous solution of hydrazine hydrate then with an aqueous solution of sodium hydrate until 5-20% of nitrile groups are hydrolyzed into carboxyl groups, or treatment of the fibres with an aqueous solution of hydroxylamine until 3-10% of nitrile groups are transformed into hydroxamic groups; exposure to the effect of aminating agent on the fibres containing 3-20% carboxyl groups or hydroxamic groups; washing and drying of the derived anion exchange fibres.

2. The method for producing anion exchange fibres as claimed in Claim 1, wherein the polyacrylonitrile fibres are treated with an aminating agent at a temperature of 80-95"C, the function of the aminating agent being fulfilled by an aqueous solution of hydrazine hydrate or alkyleneamine.

3. A method for producing anion exchange fibres as claimed in Claim 2, wherein the function of alkyleneamine is fulfilled by ethylenediamine, triethylenetetramine, polyethylenepolyamine.

4. A method for producing anion exchange fibres according to any one of the preceding claims, essentially as disclosed in the description and examples of realization.