GB2346569A - Method for the production of fibrous catalysts - Google Patents

Abstract

There is disclosed a method for the production of a fibrous catalyst comprising the steps of:<BR> ```providing a fabric comprising PAN threads;<BR> ```treating the fabric with an alkaline solution of a hydrazine salt, a hydroxylamine salt, and sodium nitrite;<BR> ```and treating the fabric with a solution containing at least one transition metal salt.

Description

Method for the production of fibrous catalysts The invention refers to methods for the production of fibrous catalysts. Fibrous catalysts thus produced can be used in the chemical, petroleum chemical and light industries, in particular, for treatment of textile effuents, for example, waste water and waste gas purification from sulphides, organic admixtures, dyes and phenols.

Homogeneous catalysts for the realisation of these processes are well known, and typically utilise various transition metal compounds having variable valency. Such catalysts have the disadvantage that toxic compounds are introduced into the waste water, sometimes in large amounts; in this case their removal is a very expensive process.

Heterogeneous catalysts do not suffer from this disadvantage ; however, reaction rates during heterogeneous catalysis are limited by high intradiffusional resistances and it is difficult to regulate them. This problem can be solved by the use of fibrous catalysts, having developed surfaces; this characteristic simplifies the access of the reactant substances to the active catalyst centres and reduces intradiffusional resistances greatly.

The fibres exhibit high strength. They are susceptible to treatments by various traditional methods into various woven and nonwoven forms suitable for the installation into various types of devices, and have low hydraulic resistance during the operation.

A known production method for bulky fibrous textile catalysts comprises a two stage treatment of a knitted fabric consisting of an inert filament and complex polyacrilonitrile (PAN) threads: 1) by treatment with a hot alkaline solution of hydrazine hydrochloride; 2) by treatment with an aqueous transition metal salt solution As a result of the alkaline-hydrazine treatment the modification of polyacriloni trile fibres included into the fabric is accomplished at the first stage. It gives them ion-exchange and complexing properties. A representative method comprises immersion of the fabric into an aqueous solution containing 100-140 g/l of hydrazine hydrochloride and 100-140 g/l of sodium hydroxide, solution temperature 95-99 C. Exposure period of the fibre in the solution is 30-90 minutes. Moreover, some of the nitrile groups in polyacrylonitrile reacts with the hydrazine with the subsequent stitching of polymer chains; the other nitrile groups are hydrolysed up to produce carboxyl groups, and an amino-carboxyl ion-exchanger is thus formed. At the second stage the fabric is immersed into the aqueous transition metal salt solution.

Ni2+, Cu2+, Mn2+, Co2+, Cor", Fe compounds are used as salts. The ion-exchange material absorbs the characteristic ion having variable valency and catalytic properties are thus obtained. Such materials have been used for sulphide oxidation in waste water.

The main disadvantages associated with catalysts produced by this method are: short life service, narrow application range and insufficiently high catalytic activity.

These disadvantages are connected with the low fixing strength of the transition metal on the fibre. Fast metal erosion (washing out) from the catalyst and the catalytic property loss happens in the presence of substances forming strong bonds with metal ions having the variable valency or substances capable to displace these ions in the fibrous ion-exchanger (for instance, Na+, K+, Ca+2 and, especially, H+) in the solution where the catalytic reaction takes place. The requirement for the absence of such substances in the catalytic reaction medium leads to the significant reduction in the application area of such catalysts. This disadvantage is connected with the method of imparting ion-exchange properties to polyacrylonitrile fibres.

It is known to produce fibrous sorbents, but not catalysts, in processes which can be illustrated by the equations: --COO... Me"+... NH2--+ H±-COOH + NH2--+ Men+, --COO-... Me'+... NH2--+ Na+ > --COONa + NH2--+ Met+, -COO... Met+... NH2--+ RH--COOH + NH2--+ Men+... R, where -COO-, NH2---are sorption groups of the aminocarboxyl ion-exchanger, Men+ is a transition metal, and RH-is the substance forming strong bonds with the transition metal.

The fibrous sorbents operate in the sorption-desorption from the fibre-it is very important for them.

All these processes will result in rapid catalyst damage. On the contrary, for use as a catalyst, maximal difficulty in the desorption is necessary after the sorption stage. Another disadvantage connected with insufficient strength of the metal fixing is an insufficiently high catalysis rate.

The transition metal complexes with ligand polymer groups are the catalytically active centres; furthermore, the metal role consists in electron transportation from the reducing agent to the oxidising agent. Therefore, the more stable the electron donating properties of the ligands, the stronger the metal complexes with polymer ligands. At the same time, the electron potential on the metal is greater. The electron potential increase on the metal results in the growth of its capability to interchange electrons and, consequently, in the intensification of its catalytic activity. However, such dependence is not always observed in practise-in each case the catalytic activity rise depending on the growth of the metal bond with the fibre is not predictable.

It is known in the prior art to utilise a hot hydrazine hydroxylamine sodium treatment for PAN fibre modification to impart anion exchange and complex forming properties. Treatment of the PAN material"Bulana AG"is also known.

The modification conditions are as ~ Concentrations, g/1 NH20H * HCl 42 N2H4* 10 Temperature, C 90 Treatment period, 1 solution mass/charged PAN fibre mass 50 ratio (bath ratio), kg solution per kg fibre pH of modifying solution 6.3-6.5 This material was also designed as an ion-exchanger. Unlike the claimed invention the modification conditions were selected to make the hydrolysis of the forming amidoxime groups maximally difficult. Also, the sorption of transition metal ions is characterised on this material by its reversibility and, as a result, the fixing strength of the metal on material is not high and, consequently, the application of such materials a catalyst is characterised by the same disadvantages as aformentioned.

The present invention enable the production of fibrous catalysts having improved service life, increased activity and a wider range of possible application areas.

According to the invention there is provided a method for the production of fibrous catalyst comprising the steps of : providing a fabric comprising PAN threads; treating the fabric with an alkaline solution of a hydrazine salt, a hydroxylamine salt, and sodium nitrite; and treating the fabric with a solution containing at least one transition metal salt.

The application of such additional reagents as hydroxylamine hydrochloride and sodium nitrite, and the change of treatment conditions results in a significant change in the catalytic properties of the material. The hydroxylamine addition to the nitrile groups of polyacrylonitrile leads to the amidoxime group formation, and under the treatment conditions the amidoxime groups are hydrolysed forming products having the complex structure: carboxyl, hydroxylamine acid groups, glutarimine and other cycles. This fact results in a strong increase of the metal fixing strength on the fibre. Furthermore, in general, examples where the metal fixing strength was significant were not always characterised by the catalytic activity which was higher than in the prior art. It was defined experimentally that when the-metal fixing strength on the fibre is satisfactory, the maximal catalytic activity can be obtained by means of the combination of all significant characteristics in the invention, that is to obtain such a hydrolysis product ratio in the amidoxime groups on the fibre when the irreversible transition metal sorption on the fibre and, consequently, high linkage strength between the metal and the fibre. Long service life is connected with it, as is high catalytic activity. This opens the way to a wide range of application areas. The sodium nitrite is thought to improve the"fixing"of the metal ions, although its precise role is not yet fully understood. However, it is found out experimentally that when the nitrite content is reduced in the solution, the metal fixing strength on the fibre is less significant and, consequently, results in a decrease in catalyst service life decrease. (see examples N 7-9 below).

The alkaline solution may be at a pH in the range 8 to 12, preferably in the range 9 to 11.

The alkaline solution may be at a temperature of greater than 80 C, preferably in the range 95 to 180 C, most preferably in the range 100 to 105 C.

The concentration of the hydrazine salt may be less than 30 g/1, and preferably may be in the range 5 to 9 girl.

The concentration of the hydroxylamine salt may be less than 42 g/1, and preferably may be in the range 7 to 14 g/l.

The concentration of sodium nitrite may be in the range 10 to 20 g/l.

The fabric may be treated with an additional alkaline solution after the treatment with the alkaline solution of the hydrazine salt, hydroxylamine salt and sodium nitirite, and before the treatment with the solution containing a transition metal salt. The additional alkaline solution may be a NaOH solution, preferably with a NaOH concentration in the range 50 to 100 g/1.

The additional alkaline solution may be at a temperature of greater than 80 C, preferably in the range 95 to 180 C, most preferably in the range 100 to 105 C.

The transition metal salt or salts may comprise at least one nickel, copper, manganese, cobalt, chromium or iron salt.

In a non-limiting example of the method, hydroxylamine hydrochloride, sodium carbonate, and sodium nitrite are added to a hot alkaline hydrazine hydrochloride solution at the treatment stage of the knitted, fabric comprising of an inert support (such as polypropylene filaments) and complex PAN threads. The concentrations of hydrazine hydrochloride and hydroxylamine hydrochloride are 5 to 9 g/l and 7 to 4 g/1, respectively.

Sufficient sodium carbonate is added to completely neutralise the solution (other alkaline additives, such as sodium hydrozide, might be used for this purpose). Sodium hydroxide is added up to pH 9 to 11. The sodium nitrite concentration is 10 to 20 g/l. The sodium nitrite is added after the alkali, at a solution temperature of 10 to 105 C, for a treatment period of 1.6 to 2 hours. Additional treatment of the fabric is carried out with an aqueous solution having a sodium hydroxide concentration of 50 to 100 g/l at a temperature of 10 to 105 C for 0.5 to 15 minutes. Subsequent treatment with an aqueous solution containing a salt of a variable valency transition metal is performed for 24 to 36 hours.

Further example of methods according to the invention will be described below.

The catalyst preparation process includes the following.

At the first treatment stage the textile fabric is knitted, for instance, according to the method"polufang", using conventional equipment.

The fabric contains inert strong warp, for example formed from polypropylene PP filaments (Technical conditions: 6-06-537-87) and a PAN complex thread (for example according to Standard: 6-06-2-80). In non-limiting examples, the ratio between filament mass in the support and PAN complex thread mass was 66.9%, linear density of PAN threads 32/3 tex, loop surface modules 3.19, total linear density of warp and weft threads 184 tex.

The textile fabric is immersed into an autoclave containing the aqueous solution preheated up to 101-105 C and having concentrations of hydrazine hydrochloride 59 g/l, of hydroxylamine hydrochloride 7-14 g/l and Na2CO3 in the amount required for the complete neutralisation of introduced hydrazine and hydroxylamine salts in accordance with the reactions: N2H4 * 2 HCl + Na2C03 = > N2H4 + 2 NaCl + H20 + CO2 ; NH2OH * HCI + Na2C03 = > 2 NH2OH + 2 NaCI + H20 + CO2 ; Note that M (Na2CO3) = (2 * M (N2 * 2 Cl)/104. 97 + M (NH OH * Cl)/69. 49) * (105.99/2), where M (...) are charged reagent masses, gel, 104.97,69.49,105.99 are the molecular masses of hydrazine hydrochloride, hydroxylamine hydrochloride and sodium carbonate, respectively. Moreover, NaOH in the amount required to achieve pH 9-11, sodium nitrite in a concentration 10-20 g/l are also added to the solution. Furthermore, the sodium nitrite should be added after the alkali to avoid reactions between it and hydrazine or hydroxylamine which are possible in the acid medium. The ratio of the solution mass to the PAN fibre mass is preferably within 40-50 kg/kg. The fabric is kept at the given temperature during 1.6-2 hours, then it is taken out and washed with the water free of salt. Then at the second stage the fabric is treated in the autoclave with the hot NaOH solution having the concentration 50-100 g/l and at temperature 101-105 C for 0.515 min with subsequent washing with desalted water. The ratio of the solution mass to the PAN fibre mass ratio is preferably within the limits 40-50 kg/kg. At the third stage the fabric is immersed in aqueous transition metal salt solution, for instance, having a metal ion concentration of 1-5 %. The fabric is kept there during 24-36 hours; after desalted water washing and drying in drying chambers and on rollers at temperature not higher than 120 C the catalyst is ready to use. Experiments were performed on the catalyst under the following conditions: reactor diameter D = 0.01 m, height H=0. 18 m, air supply volumetric rate Q=2 1/min, masses of the catalytically active fibre m = 2.8 g. are calculated from the formula taken from reference works, the reactor cross section S = 3.1416 * D2/4 = 3.1416* 0.01* 0. 1* 0.01/4 = 7.854*10-5 m2, reactor volume V = S * H = 7. 854 * 10-5 * 0.18 = 1.414 * 10-5 m 3 given air flow rate W = Q * (10- ? 60)/S = 2 * (10 3/60)/ (7.854 * 10-5) = 0.424 mlsec, The ratio of the catalytically active fibre mass to the reactor volume M (modules) = (m * 10-3)/V-2. 8 * 10'/ (1. 414 * 1 fez = 198.1 kg/h.

Since the heterogeneous cataytic process takes place on the catalyst fibre surface the process rate is proportional to the catalyst amount (to the modules).

Generally speaking, high module values indicate insufficient specific catalysis rate (the catalysis process rate related to the fibre mass unit), hereinafter called the catalysis process rate. The same can be said about the given air flow rate, high values of which are required for attaching a conversion degree approaching 100 %. These high values indicate insufficiently high characteristics of the catalysis process rate and vice versa. So hereinafter the modules and the given air flow rate values required for attaining a conversion degree approaching 100 per cent within a certain period of time are used as standards of catalysis process rates. As a test for controlling the metal fixing strength on the fibre (and, consequently, the service life duration) the following characteristics were selected. They are: Catalyst sample treatment with then acid test solution having a standard buffer composition: 0.04 M H3PO4, 0.04 M CH3COOH 0.04 M HBO2 * H20, X NaOH, where X is the variable NaOH content required for regulating pH = 2, for determining of the metal fixing strength on the catalyst in the hydrogen ion presence on the salt background; and treatment with 0.1 M test solution of ethylenediaminetetraacetic acid (EDTA) dinatrium salt for determining the metal fixing strength on the catalyst in the presence of the strongest complexing agent-EDTA; the test solution mass and the catalyst mass ratio was equal to 90-100 g/g, the test solution treatment period was 160-170 hours. The percentage value of the metal removal from the catalyst during the corresponding treatment served as the criterion of the metal fixing strength on the catalyst.

Example le The fabric was knitted, for example, by means of the"polufang"method using standard equipment. It contained the strong inert weft produced, for example, from PP filaments (Technical conditions: 6-06-537-86) and a PAN complex thread (for example, according to Standard: 6-06-2-80), the ratio between filament support mass and PAN complex thread mass-66.9%, the linear density of PAN threads-32.3 tex, the loop surface modules-3.10, the total linear density of weft and warp threads-184 tex. At the first treatment stage the fabric was immersed into the autoclave containing a preheated aqueous solution (up to 103 C) including concentrations of 5 g/1 hydrazine hydrochloride, 10 g/1 hydroxylamine hydrochloride and Na2C03in the amount: (2 * 5/104.97 + 10/69.49) * (105.99/2) = 14.7 g/1. And likewise the NaOH amount required for pH 9-1 1 was introduced into the solution, the pH value being controlled by means of a pH-meter having a glass electrode, and sodium nitrite was added in the amount of 15 g/l.

Furthermore, sodium nitrite was added after alkali to avoid reactions between it and hydrazine or hydroxylamine in the acid medium. The solution mass and PAN thread mass ratio was equal, for instance, to 50 kg/kg. The fabric was maintained at the given temperature during 1.8 hours, then it was taken out and washed with desalted water. At the second stage the fabric was treated in the autoclave with the hot aqueous NaOH solution having concentration of 70 g/l and temperature 103 C during 7 min with subsequent desalted water washing, the ratio of the solution mass to the PAN thread mass was also equal to 50 kg/kg. At the last stage the fabric was immersed into the aqueous NiSO4 solution having a metal ion concentration of 5% and it was kept there during 30 hours. The catalyst was ready to use after washing with the desalted water and drying in the drying chambers at a temperature not higher than 105 C. The nickel content on the catalyst was 0.81 mmol/g. The metal removal degree in the acid buffer solution was 30 % and in the EDTA solution 9. 3 %.

Aminocarboxyl ion-exchanging fibres were obtained under the PAN complex thread treatment with the hot alkali-hydrazine solution. Since in the prototype case these fibres were used during such treatments, the metal removal degree out of the prototype would be 100 % as the metal fixing strength on the aminocarboxyl ion exchangers is not high as it was described above. This points to a higher metal fixing strength on the fibre and, consequently, to the longer service life in comparison with the prior art. The oxidation process of model solution of sodium sulphide having the ion sulphide concentration 2000 mg/1 with atmospheric oxygen, temperature of the reaction medium 20 C was selected as the oxidation process. The oxidation takes place according to the reaction: 2 S2-+ 2 2 + H2O = > S2032-+ 2 OH-. During 75 minutes of the oxidation the purification rate from sulphides came up to 99.1 % at the ratio of the catalyst mass to the solution volume 15.2 kg/m3. This is less by a factor of 198.1/15.2 = 13.0 than in the prior art, and the air flow rate through the reactor of 0.24 m/sec, i. e., less by a factor of 0.424/0.24 = 1.77 than in the prior art-this points to in increased reaction rate increase in comparison with the prior art (see table 2). Examples 1-3 illustrate the influence of the hydrazine hydrochloride concentration on the technical result in the sulphide oxidation with atmospheric oxygen. It is connected with the reaction rate fall to the level lower than in the prior art. The rise of the hydrazine salt content higher than 9 gA does not appear to lead further growth in the catalytic reaction rate.

Examples 4-6 illustrate the influence of the hydroxylamine hydrochloride concentration on sulphide oxidation with atmospheric oxygen. Examples 7-9 show the influence of the sodium nitrite content on sulphide oxidation with atmospheric oxygen.

The increase of the sodium nitrite content higher than 20 g/l does not appear to lead to further growth of the metal fixing strength on the fibre and, consequently, to the service life rise, but it results in a decrease in catalytic activity to a level that is lower than in obtained with prior art methods.

Examples 10-12 illustrate the pH solution influence on the sulphide oxidation with atmospheric oxygen. Use of a pH lower than 9 or higher than 11 gives a reduction of the metal fixing strength on the fibre and, consequently, 9 to 11 is the preferred-but non-limiting-pH range.

At the first stage examples 13-15 illustrate the temperature influence on sulphide oxidation with atmospheric oxygen. Temperatures lower than 101 C appear to cause the catalytic activity to decrease. Temperatures higher than 105 C result a decrease of the metal fixing strength on the catalyst. Consequently, 101 to 105 C is a preferred temperature range, although the invention is not limited in the respect, it being conceviable that the use of different temperatures in combination with different reaction conditions might provide advantageous results.

At the first stage examples 16-18 show the time treatment influence on sulphide oxidation with atmospheric oxygen.

At the second stage examples 19-21 demonstrate the alkali concentration influence on sulphide oxidation with atmospheric oxygen.

At the second stage examples 22-24 illustrate the temperature treatment influence on sulphide oxidation with atmospheric oxygen.

At the second stage examples 25-27 show the time treatment influence on sulphide oxidation with atmospheric oxygen.

Example 31 shows the application possibility of the cobalt-containing catalyst for the waste water purification from sulphides.

Example 32 illustrates the possibility of waste water purification from mercaptans using a bulky fibrous catalyst. The mercaptide solution having 300 mg/1 by mercaptan sulphur was selected as a model. Reaction solution temperature was 20 C, oxidation time was 20 min; furthermore, the purification degree from mercaptan was 99.9 %. The oxidation was carried out with atmospheric oxygen according to the reaction: CH3S-+ 3/2 Q = > C1 ; S (?-. It is not possible to use catalysts prepared by prior art methods for this purpose due to the insufficiently high metal fixing strength on the catalyst, as mercaptans form stronger complexes with transition metals in comparison with aminocar boxyl groups on the fibre. This would lead, in prior art catalsts, to metal precipitation from catalyst fibres in the mercaptan presence and to the catalytic activity loss as described above.

Example 33 demonstrates the catalytic decomposition of acid blue dye in a model waste water solution under the action of hydrogen peroxide. The model solution was represented by the universal buffer having the following composition; 0.04 M H3PO4, 0.04 M CH3COOH, 0.04 M HBQ * U O, X NaOH, where X is the variable NaOH content required for pH = 4, for maintaining the salt background and the acid medium, and containing additionally 20 mgll of the dye, the oxidant concentration H202 was equal to 50 mg/l, and the reaction solution temperature was 20 C. After 15 min of the decomposition the dye decolorization degree was 73.1 %. It is not possible to use catalysts prepared by prior art methods for this as in acid medium and in the presence of the salt background the transition metal will be displaced from the fibre aminocarboxyl groups, being substituted by hydrogen ions. In this instance the transition metal goes into solution, leading to consequent loss of catalytic activity.

Example 34 demonstrates the catalytic decomposition of acid blue dye in a model waste water solution under the action of hydrogen peroxide with Fe3+ catalyst. The fibre was prepared in a similar manner to example 1, except at the last stage the fabric was immersed into aqueous FeC 13 solution instead of the nickel solution. The model solution was represented by addition of X NaOH, where X is the variable NaOH content required for pH = 4 and containing additionally 10 mg/1 of the dye, the oxidant concentration H202 was equal to 50 mg/l, and the reaction solution temperature was 20 C. After 15 min. of the decomposition the degree of dye decolorisation was 100%.

Example 35 demonstrates the catalytic decomposition of acid blue 45 dye in a model waste water solution under the action of hydrogen peroxide using Fe3+/Mn2+ catalyst. The catalyst was prepared in a similar manner to example 34, but using equimolar amounts of FeCl3 and MnSp solutions. After 10 minutes of the decomposition the degree of dye decolorisation was 100%.

Although the foregoing relates to treatment of PAN fabrics with transition metal salts, it is possible that other metal salts, such as salts of calcium and magnesium, might be used instead.

Table 1 Technical parameters of the catalyst production Technical parameters Treatment stages

1 Stage 2 Stage 3 Stage Example Con Conc Conc Temper Time, Conc, NaOH, Temperanire Time min Metal Content of c. NH2O NaNO2, ature, h. g/l C the catalyst N2 H@ g/l C monol/g H4 HNI, g/l Cl, 1 5 10 15 10 103 1.8 70 103 7 Ni2+ 30 0.81 2 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1.03 3 9 10 15 10 103 1. 8 70 103 7 Ni2+ 30 1.04 4 7 7 15 10 103 1.8 70 103 7 Ni2+ 30 1.11 5 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1.03 6 7 14 15 10 103 1.8 70 103 7 Ni2+ 30 1.03 7 7 10 10 10 103 1.8 70 103 7 Ni2+ 30 0. 96 8 7 10 15 10 103 1.8 70 103 7 Nif 30 1.03 9 7 10 20 10 103 1. 8 70 103 7 Ni2+ 30 1.23

10 7 10 15 9 103 1.8 70 103 7 Ni2+ 30 0. 85 11 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 12 7 10 15 11 103 1.8 70 103 7 Ni2+ 30 1.28 13 7 10 15 10 101 1.8 70 103 7 Ni2+ 30 0.98 14 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 15 7 10 15 10 105 1.8 70 103 7 Ni2+ 30 1. 06 16 7 10 15 10 103 1. 6 70 103 7 Ni2+ 30 0 74 17 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 18 7 10 15 10 103 1.2 70 103 7 Ni2+ 30 1. 04 1971015101031. 8501037Ni300. 81 20 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 21 7 10 15 10 103 1.8 100 103 7 Ni2+ 30 1. 06 22 7 10 15 10 103 1.8 70 101 7 Ni2+ 30 0. 94 23 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 24 7 10 15 10 103 1.8 70 105 7 Ni2+ 30 1.12 2571015101031. 8701030. 5NP"300. 78 26 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 27 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1.03 28 7 10 15 10 103 1.8 70 103 7 Ni2+ 24 0. 75 29 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 30 7 10 15 10 103 1.8 70 103 7 Ni2+ 36 1. 04 31 7 10 15 10 103 1.8 70 103 7 Co2+ 30 1. 15 32 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 03 33 7 10 15 10 103 1.8 70 103 7 Ni2+ 30 1. 15 34 30 42 15 9.5 101 1.5 50 101 5 Fe3+ 30 0. 76 35 30 42 15 9.5 101 1.5 50 1201 5 Fe3+ 30 0. 55 Mn2+ 30 0. 50 Table 2 Dependence of metal fixing strength and catalytic activity on the catalyst production parameters given in table 1.

Example Metal Metal Catalytic Catalyst Linear Time of Initial Conversion removal removeal process mass/rate of oxidation Concentration degree, % degree after degree after solution air, min mg/l acid buffer EDTA volume m. sec solution solution ratio treatment, % treatment, % (moulus) kgtnL 1 30 9.3 S2--oxidation 15.2 0.24 48 2000 99.1 2 30 9. 3 S2--oxidation 11. 5 0. 15 48 2000 99.0 3 30 9.3 S2--oxidation 11.5 0.15 48 2000 98.8 4 45 17. 5 S'--oxidation 20. 1 0. 35 48 2000 98.2 5 30 9. 3 S2--oxidation 11. 5 0. 15 48 2000 99.0 6 23 7. 4 S2--oxidation 59. 2 0. 388 2000 99.2 7 41 15. 1 S'--oxidation 22. 0 0. 20 48 2000 98.5 8 30 9. 3 S2--oxidation 11. 5 0. 15 48 2000 99.0 9 25 8.5 S2--oxidation 10.1 0.10 48 2000 99.3 10 35 10. 8 S2--oxidation 16. 2 0. 19 48 2000 99.4 11 30 9. 3 S2--oxidation 11. 5 0. 15 48 2000 99.0 12 39 17.2 S2--oxidation 16.7 0.21 48 2000 99.8 13 29 9.0 S2--oxidation 17.2 0.20 48 2000 98.9 14 30 9.3 S2--oxidation 11.5 0.15 48 2000 99. 0 15 35 7. 4 S--oxidation 13. 8 0. 17 48 2000 99.3 16 31 10. 5 S2--oxidation 23. 1 0. 16 48 2000 99.4 17 30 9. 3 S2--oxidation 11. 5 0. 15 48 2000 99.0 18 21 5.3 S2--oxidation 39.4 0.22 48 2000 98.2 19 25 8.8 S2--oxidation 16.9 0.19 48 2000 98.3 20 30 9. 3 S2--oxidation 11. 5 0. 15 48 2000 99. 0 21 40 29. 3 S2~-oxidation 14. 5 0. 16 48 2000 99. 7

22 21 16.2 S'--oxidation 21. 1 0.18 48 2000 99.1 23 30 9. S'--oxidation 11. 5 0. 15 48 2000 98.2 24 35 12.5 S2~-oxidation 10. 1 0.12 48 2000 98.5 25 38 14.6 S'--oxidation 9.3 0.09 48 2000 99.0 26 30 9.3 S2--oxidation 11. 5 0.15 48 2000 99.3 27 22 7.2 S2--oxidation 17. 1 0.24 48 2000 98.7 28 22 6. S2--oxidation 16.2 0.18 48 2000 99.0 29 30 9. S2--oxidation 11. 5 0.15 48 2000 99.1 30 30 9.3 S2--oxidation 11. 5 0.15 48 2000 98.2 31 30 9.3 S--oxidation 11. 5 0.15 48 2000 99. 9 32 30 9.3 CH3SH-9. 2 0.08 20 300 73.1 Oxidation 33 22 7. 2 decompositi 5.3---15 20 on of dye 34 30 9. 3 decompositi 5.3 15 10 100 on of dye 35 30 9. 3 decompositi 5. 3 10 10 100 on of dye

Claims (10)

1. CLAIMS 1. A method for the production of a fibrous catalyst comprising the steps of : providing a fabric comprising PAN threads; treating the fabric with an alkaline solution of a hydrazine salt, a hydroxylamine salt, and sodium nitrite; and treating the fabric with a solution containing at least one transition metal salt.
2. 2. A method according to claim 1 in which the alkaline solution is at a pH in the range 8 to 12, preferably in the range 9 to 11.
3. 3. A method according to claim 1 or claim 2 in which the alkaline solution is at a temperature of greater than 80 C, preferably in the range of 95 to 180 C, most preferably in the range of 100 to 105 C.
4. 4. A method according to any previous claims in which the concentration of the hydrazine salt is less than 30g/l, and preferably is in the range 5 to 9 g/1.
5. 5. A method according to any previous claims in which the concentration of the hydroxylamine salt is less than 42g/l, and preferably is in the range 7 to 14 g/1.
6. 6. A method according to any previous claims in which the concentration of sodium nitrite is in the range 10 to 20 g/l.
7. 7. A method according to any previous claims in which the fabric is treated with an additional alkaline solution after than treatment with the alkaline solution of the hydrazine salt, hydroxylamine salt and sodium nitrite, and before the treatment with the solution containing a transition metal salt.
8. 8. A method according to claim 7 in which the additional alkaline solution is a NaOH solution, preferably with a NaOH concentration in the range 50 to 100 g/l.
9. 9. A method according to claim 7 or 8 in which the additional alkaline solution is at a temperature of greater than 80 C, preferably in the range 95 to 180 C, most preferably in the range 100 to 105 C.
10. 10. A method according to any previous claims in which the transition metal salt or salts comprise at least one nickel, copper, manganese, cobalt, chromium or iron salt.