IE51266B1 - Preparation of titanyl ammonium disulphate,and use thereof for tanning leather - Google Patents

Description

The present invention is concerned with a method of preparing titanyl ammonium disulphate, for use as a tanning agent in leather tanning.

In leather manufacture, in addition to 5 vegetable tanning agents, various mineral tanning agents are widely employed, such as chromium, zirconium and aluminium compounds. It is also known that titanium compounds, such as titanium salts, for example sulphates, e.g. titanyl sulphate, chlorides, oxalates, gluconates, tartrates and lactates, have tanning properties.

German Patent 517,446 describes a method for the preparation of titanyl sulphate, which comprises dissolving the titanium-containing starting material in sulphuric acid, and recovering titanyl sulphate by neutralization of the solution with lime, filtering-off precipitated calcium sulphate and evaporation of the filtrate .

However, this known method is complicated; also it is difficult to obtain the product in a form suitable for use as a tanning agent and the tanning agent thus obtained does not have good tanning properti es.

U.S. Patent 393θ951 describes the use of titanyl ammonium disulphate for tanning delimed and pickled and (optionally) chromed hides but the quality 512 6 6 of the resulting leather is not entirely satisfactory. USSR Inventor's Certificate 668878, 1979 describes a method of preparing titanyl ammonium sulphate, which comprises mixing an oxidizing agent with a titanium-ferriferous solution in aqueous sulphuric acid, adding ammonium sulphate and aqueous sulphuric acid so at to precipitate titanyl ammonium sulphate monohydrate (() ) g'HgO) which is then stabilized by washing with an aqueous solution of ammonium sulphate. However, the tanning agent produced by this method contains an undesirable quantity of impurities.

We have now developed an improved method of preparing titanyl ammonium sulphate, for us· as a tanning agent for leather, which is as mentioned above with reference to USSR Inventor's Certificate 6C8878, with the improvement that the oxidizing agent used is a peroxy-titanium complex, used in the form of a solution in aqueous sulphuric acid containing 0.01 to 2 grammes per litre of the complex, calculated as titanium dioxide, in excess of the stoichiometric amount necessary to oxidize ferrous iron in the starting solution to ferric iron.

The use of the peroxy-titanium complex solution enables a mild oxidation and thus makes it possible to avoid over-oxidation of the titanium ferriferous solution and under-oxidation of the ferrous iron therein.

Therefore, the peroxy-titanium complex solution ensures efficient oxidation of iron under mild conditions, thus improving the quality of the resulting tanning agent, substantially all ferrous iron present in the solution being converted to ferric iron.

If the peroxy-titanium complex is used in an excess amount greater than 2 grammes per litre (that is the method is not according to the invention), a lower yield of titanium is obtained in the final product, 1266 whereas if the excess amount is less than 0.01 grammes per litre (again the method being not according to the invention) this is technically inexpedient.

The titanium-ferriferous solution in sulphuric acid, used as a starting material in the method of the invention, is obtained by treating a titanium-ferriferous concentrate with sulphuric acid. The conditions of treatment, such as temperature, duration and acid concentration, depend on the composition of the concentrate employed. The cake resulting from the treatment is generally leached with water using return liquors. Titanium passes into the sulphuric acid solution while being freed of insoluble impurities remaining in the residue. The precipitate is filtered-off, and washed with water which is then used for leaching as the return liquor.

The solution of peroxy-titanium complex in aqueous sulphuric acid may be obtained by oxidation of a portion of the solution obtained after leaching of the cake. Oxidation may be effected by means of any known oxidizing agents such as ozone, hydrogen peroxide or ammonium persulphate, or by way of electrolysis. The sulphate solution of the peroxytitanium complex is added in an excess of 0.01 to 2 g/1 based on TiOg relative to the stoichiometric amount necessary to convert ferrous iron to ferric iron.

The use of the solution of peroxy-titanium complex improves labour conditions, since this product is neither harmful nor toxic.

After introduction of the peroxy-titanium complex into the titanium-ferriferous starting material solution, ammonium sulphate and sulphuric acid are added, generally to a total content of free ammonium sulphate and sulphuric acid of from 450 to 600 g/1, and from this solution a double sulphate, titanyl ammonium disulphate monohydrate (NH^)2 Ti0‘(NH^igiSO^ig'H^O), is precipitated. The precipitation duration under discontinuous process conditions generally ranges from 5 to 20 hours, the temperature being generally from 12 to 30°C. At a temperature above 30°C a double anhydrous sulphate of titanyl and ammonium can precipitate which is unsuitable for use as a tanning agent.

In the method according to the present invention, the amount of titanyl ammonium disulphate precipitated is preferably from 75 to 85% hy weight based on titanium dioxide, whereafter the precipitated salt is separated and washed, the resulting filtrate and washing waters being combined and treated with ammonium sulphate to ensure after-deposition of the salt which is then separated and recycled into the titanium-ferriferous starting material solution. This method of precipitation helps to additionally purify the salt.

In this preferred embodiment of preparation of the titanyl ammonium disulphate, the titanium-ferriferous solution preferably contains more than 15 g/1 of FeO, and the total content of free ammonium sulphate and sulphuric acid is preferably from 300 to 400 g/1. In this embodiment, the precipitate is generally separated and washed with a solution containing 350-450 ¢/1 of ammonium sulphate, the contaminating iron content in the precipitate being generally from 0.03 to 0.05%. The resulting filtrate and washing waters are combined and treated, for after-precipitation of the salt, with ammonium sulphate generally to a total content of anmionium sulphate and sulphuric acid of from 450 to 600 g/1. The salt is separated and recycled to the titanium-ferriferous starting material solution, since the content of iron therein ia 2-3%· The degree of precipitation of titanium in this embodiment is generally 13-22% of the starting content thereof. The yield of the titanium salt in the case of utilization of a recycled product after three turnovers is generally 1266 95-98%.

The residual content of titanium in the solution after precipitation of tho salt is generally from 3 to 10 g/1 of TiO^, the degree of recovery of titanium from the starting material being from 55 to 90% depending on the concentrate employed.

The precipitated titanyl ammonium disulphate is generally filtered and washed with a solution containing 300 to 450 g/1 of sulphuric aci<- and 180-300 g/1 of (NH^J^SO^ taken in an amount of from 0.4 to 0.7 a? per ton of the precipitate. The filtered and washed precipitate may then be treated with a solution containing ammonium sulphate in an amount of from 300 to 400 g/1 at a rate of consumption of from 0.4 +0 0.7 nr per ton of the salt for stabilization of the monohydrate form of the titanyl ammonium disulphate, which is a white powder. Under microscope it has the form of isotropic crystals-tetrahedrons. The composition thereof is as fellows, in percent by weight: TiO^ - 19-21; SO^ - 44-48; (NH^)gO - 15—17; Ρβ,,Ο^ not more than 0.05; insoluble residue - not more than 0.3; the balance being moisture .

An advantage of the method according to the present invention is that the resulting tanning agent has a minimal iron content (0.05% of FegO^ a*1*below) and contains little other impurities. The method according to the present invention enables the use of a sulphuric acid titanium-ferriferous solution with a higher content of iron therein, namely above 10 g/1 of FeO, while obtaining a high-quality tanning agent. These advantages make this method commercially more promising as compared to the prior art methods, while the use of titanyl ammonium disulphate produced according to the present invention as a tanning agent improves the quality of the tanned leather.

Accordingly the present invention also comprises a process for tanning delimed hide which comprises treating the hide with a tanning promoter selected from a sodium salt of diaulphodinaphthylmethane, phthalic anhydride, aluminium alum, a mixture of aluminium alum with Urotropin, ammonium titanylsulphate and phenol oligomers dispersed in lignosulphonic acids, followed by tanning the hide with titanyl ammonium disulphate prepared according to the invention. These promoters make it possible to accelerate the tanning process and improve bonding between the tanning agent and collagen. This results in an increased content of the tanning agent in the leather thus improving the leather quality: the bulk yield and the wear-resistance are increased, and the water-absorption is reduced.

The sodium salt of disulphodinaphthylnethane ia preferably used in an amount of from 1.5 to 2.5% based on the weight of the hide; the preferred amounts of the other tanning promoters mentioned above are as follows (on the same basis): phthalic anhydride - 1.2 to 2.2%, aluminium alum - 1.0 to 5.0%, the mixture of aluminium alum with urotropin - 1.8 to 5·θ% (the mixture preferably containing 0.5 to 3-4 parts by weight of aluminium alum per part by weight of urotropin), ammoniuatitanylsulphate - from 5 to 15%, and a phenol oligomer dispersed in lignosulphonic acid - from 2.5 to 5.0%.

When using a phenol oligomer dispersed in lignosulphonic acid, the hide is preferably preliminarily chromed (before treatment with the tanning promoter).

The use of the tanning promoters mentioned above in the process according to the present invention accelerates the tanning process, increases the welding temperature of semi-finished products, thus resulting in a better quality leather; for example, the dry wear266 resistance of leather which has been tanned according to the invention may be 10-2095 higher than leather according to the prior art.

The titanyl ammonium disulphate which has been prepared according to the present invention can also be used for tanning delimed hides; delimed and pickled hides or delimed, pickled and chromed hides in the presence of an agent selected from lactic acid, aluminium alum and condensation products of synthetic fatty acids with triethanolamine. These latter agents are generally added to the tanning bath in an amount of from 0.5 to 2.5% by weight of the hide. The use of these agents makes it possible to increase the bulk yield of leather and lower the water-absorption thereof.

The resulting tanned hide is preferably treated with chloroprene rubber latex in an amount of from 1.0 to 6.0% based on dry solids (by weight of the hide) to improve the wear-resistance of the final leather.

The use of titanyl ammonium disulphate according to the present invention makes it possible to produce light elastic leather with improved wearresistance, water-absorption and hydrothermal stability.

The tanning process is preferably as follows: hides produced from cattle raw materials (butts, offals) are charged into a rotary drun, charged with water at 23 to 26°C in a water-to-hide ratio of 1.2 and a tanning promoter (as mentioned above) added thereto.

The tanning agent is then added, preferably in an amount of from 4 to 6% by weight of hides as calculated for TiOg, together with ammonium sulphate in an amount of from 4 to 6% by weight of the hides.

The actual amount of the tanning agent and ammonium sulphate depends on the density and thickness of the hides.

Tanning generally takes place with drum rotation for 18-20 hours; the resulting semi-finished leather is preferably neutralized with sodium sulphite and urotropin, (for example, in an amount of 3.5% hy weight of the hides).

The neutralization is generally terminated when the pH of the semi-finished leather is from 4.0 to 4.5 Then the semi-finished product may be rinsed and after-tanned with synthetic tanning agents in an amount of from 15 to 17% of tannins by weight of the hides. The retanning may be advantageously effected at a water-to-hide ratio of 7.2 to 1.4, a temperature of 38 to 43°C for 2 to 3 days.

The thus-prepared semi-finished product may be rinsed, wrung out, dip-filled and greased. In dipfilling use may be mad’ of magnesium sulphate in an amount of from 5 to 10% and treacle in an amount of from 5 to 10%. Greasing is effected using solid synthetic greasing agents. Further finishing operations may be carried out in a conventional manner.

Vhen using delimed, pickled and chromed hides the pickling process may be performed by means of sulphuric acid in th*» presence of sodium chloride or ammonium sulphate. In this ease, the rate of consumption of the acid is generally 0.9-1.0% by weight of the hides, that of sodium chloride and ammonium sulphate is generally 8-7% by weight of the hides; the water-to-hides ratio is generally 0.8 to 1.0, the temperature is generally from 18 to 20°C, and the pH of the semi-finished product by the end of pickling is generally 3.8-4.5 (outer layer) and 5*06.0 (inner layer).

The chrome-treatment is generally effected by means of a chrome extract in a waste pickling bath, the rate of consumption of the chrome tanning agent being 0.4-0.5% by weight of the hides. Then tanning is effected using a fresh bath in the presence of phenol oligomers dispersed in lignosulphonic acids taken in an amount of from 2.5 to 5.0% by weight of the hides. Further opera5 tions are performed as described hereinabove.

Lactic acid, aluminium alum and the product of condensation of synthetic fatty acids with triethanolamine may be used in the tanning according to the invention of delimed hides, or delimed and pickled hide, or delimed, pickled and chromed hides. These complex-forming agents improve the quality of the leather, in particular increase the wear-resistance of leather and reduce the waterabsorption thereof. After tanning in this way, the semifinished leather product is preferably treated in a drum with poly-chloroprene latex taken in an amount of from to 6% by weight of the hides as calculated for dry solids In order that the invention may be more fully understood, the following Examples are given by way of illustration only.

Example 1 To 1000 litres of a titanium-ferriferous solution in sulphuric acid (having the composition, g/1: Ti02 - 100, HjSOjj - 300, FeO - 15, and obtained from leaching of cake) was added a sulphuric acid solution containing 100 g/1 of a peroxy-titanium complex based on Ti02 in an amount to provide a final content of the complex in the titanium ferriferous solution in sulphuric acid of 0.01 g/1 based on Ti02· Ammonium sulphate and sulphuric acid were then added to the solution to a total content of free sulphuric acid and free ammonium sulphate of 500 g/1. A double sulphate of titanyl and ammonium in the monohydrate form ()2TiO(SO^)2*H20 was precipitated from the solutions, the degree of precipitation of the salt being 97% as calculated for Ti02· 51866 The precipitate was filtered, washed with 0.3 m of a solution containing 300 g/1 of HjSOjj and 200 g/1 of Thereafter the precipitate was treated with 0.25 m^ of a solution containing ammonium sulphate in an amount of 400 g/1. The yield of the final product was 480 kg, containing, in percent by weight: Ti02 - 20; SOg 46; )20 - 16; Fe20g 0»θ^5; insoluble residue 0.25; the balance being moisture.

Example 2 To 1000 litres of titanium-ferriferous solution in sulphuric acid (having the following composition, g/1: Ti02 - 120, HjSOjj - 400, FeO - 20) was added a sulphuric acid solution containing 100 g/1 of peroxy-titanium complex based on titanium dioxide in an amount to provide a final content of the complex in the titanium ferriferous solution in sulphuric acid of 2 g/1 based on Ti02- Ammonium sulphate was then added in an amount of 80% relative to titanium dioxide, the total content of free ammonium sulphate and free sulphuric acid then being 400 g/1. The precipitated salt was separated and washed with 0.5 mJ of a solution containing 400 g/1 of ammonium sulphate.

The resulting salt was obtained in a yield of 480 kg, containing, in percent by weight: Ti02 - 20; SOg - 47; - 17; PegOg - 0.04; insoluble residue - 0.3, the balance being moisture.

The filtrate obtained after separation of the salt and washings were combined (the volume obtained was 1,170 litres) and ammonium sulphate was added to produce a total content of free ammonium sulphate and sulphuric acid of 600 g/1. A precipitate was produced, the amount of titanium precipitated being 15% of that initially present. The precipitate was separated by filtration, to give 100 kg of the 1266 final salt which contains, in percent by weight: TiO2 - 18, Γ®2°3 “ ^·5· The thus-produced salt was recycled to the starting titanium-ferriferous sulphate solution. The yield of titanium salt in the case of utilization oi the return product after three turnovers was 97%· Example 3 Cattlehides (butts, offals and the like) were charged into a rotary drum, water was added thereto at a temperature ox' 23-26°C in a liquid-to-hides ratio of 1.2 and then the sodium salt of disulphodinapthylmethane was introduced in an amount of 2% based on the weight of the hides.

The hides were treated with this solution in the rotary drum for 1.5 hours, whereafter titanyl ammonium disulphate was added in the amount of 6% by weight of the hides as calculated for TiOg and ammonium sulphate in the amount of 6% by weight of the hides. All these components were introduced in the dry state.

The hides were tanned during the drum rotation for 20 hours, and the thus-produced semi-finished leather was neutralized with sodium sulphite and urotropin, each introduced in the amount of 3*5% by weight of the hides. The neutralization was stopped when the semi-finished product pH was 4-5· Then the semi-finished product was washed with water and retanned with synthetic tanning agents in an amount of 17% of tanning by weight of the hides.

As the synthetic tanning agents use is made of such agents which are resistant to acidic media and tc ammonium sulphate.

The retanning was effected at a water-to-hides ratio of 1.4, and a temperature of 4o°C for two days.

The initial pH of the solution was not less than 4 and, to minimize foaming upon retanning, a dressing paste or sulphonated blubber was introduced in the amount of 0.8% along with the tanning agent.

Then the semi-finished product waa washed, wrung out, dip-filled and greased. The following compounds are used for dip-filling: magnesium sulphate or ammonium sulphate in the amount of 5%. treacle in the amount of 8%. Stuffing is effected using solid synthetic greasing agents. Further finishing operations were carried out in a conventional manner. The thusproduced leather had the following characteristics: bulk yield 102%, dry abrasion-resistance 200 r.p.m., water-absorption for two hours 45%.

Example 4 Preliminary dslimed hides were charged into a drum, and water was added at 26°C in a water-to-hides ratio of 1.2 and phthalic anhydride is added thereto in the amount of 2.0% by weight of the hidee. Further treatment of the hides waa effected under the conditions described in Example 3· The resulting leather characteristics were similar to those obtained in Example 3· Example 5 Treatment of hides waa effected following the procedure described in Example 3, except that prior to tanning the hides were treated with aluminium alum in the amount of 3% by weight of the hides. The final leather characteristics were similar to those obtained in Example 3· Example 6 Tanning of delimed hides was effected under the conditions described in Example 3« Prior to tanning the hides were treated with a mixture of 2.5 parts by weight of aluminium alum and 1 part by weight of urotropin in the amount of 3-5% by weight of the hides.

The final leather characteristics were similar to those obtained in Example 3* 'Example 7 Tanning of delimed hides was effected as in Example 3· Prior to tanning the hides were treated with ammonium titanyl sulphate in the amount of 3% by weight of the hides. The final leather characteristics were similar to those obtained in Example 3· Example 8 Pre-chromed hides were treated, prior to tanning, with phenol oligomers dispersed in lignosulpho:iic acids in the amount of 3·5% by weight of the hides. The leather semi-finished product was subsequently treated under the conditions described in Example 3· The final leather had characteristics similar to those obtained in Example 3* Example 9 Delimed cattle hides were charged into a drum, and water was added at 26°C in a water-to-hides ratio of 1.2. Titanyl ammonium disulphate was added in an amount of 6% by weight of the hides as calculated for TiOg along with ammonium sulphate in the amount of 6% by weight of the hides. At the same time, lactic acid was added to the tanning bath in the amount of 0.8% by weight of the hides.

The hides were tanned in this solution for 22 hours, the resulting semi-finished leather product being neutralized wi th sodium sulphite and urotropin, each in the amount of 3.5% by weight of the hides. The neutralized was stopped when the semi-finished product pH was 4.5: the leather semi-finished product was then washed with water and retanned with synthetic tanning agents. Further treatment of the leather semi-finished product was effected as described in Example 3. The use of lactic acid in the tanning process improved the final leather quality. The bulk yield was 105%, the dry wear-resistance was 210 r.p.m. and the water-absorption for 2 hours was 4J%.

Example 10 Tanning of delimed hides was effected as described in Example $, except that after neutralization of the semi-finished leather, it was treated for one hour with polychloroprene latex in the amount of 3% by weight of the hides, calculated for dry solids This treatment substantially enhanced thi wear-resistance of the final leather - the wear-resistance was increased to 250 r.p.m.

Example 11 Delimed and pickled hides were treated following the procedure described in Example 9 with the introduction of aluminium alum in the amount of 2% by weight of the hides. The final leather characteristics were similar to those obtained in Example 9.

Example 12 Delimed and pickled hides were treated as described in Example 9 with the introduction of aluminium alum in the amount of 2% by weight of the hides during tanning. After neutralization, the semi-finished leather product was treated with polychloroprene latex in the amount of 2% by weight of the hides, calculated for dry solids. The final leather characteristics were similar to those obtained in Example 10.

Example 13 Delimed, pickled and chromed hides were treated following the procedure described in Example-9 with the introduction of a condensation product of synthetic fatty acids with triethanolamine in the amount of 1.0% by weight of the hides during tanning. The final leather characteristics were similar to those obtained in Example 9 hereinbefore.

Example 14 Delimed, pickled and chromed hides were treated as in Example 9 with the introduction, during tanning, of a product of condensation of synthetic fatty acids with triethanolamine in the amount of 1%. After neutralization of the semi-finished leather product it was treated with polychloroprene latex in the amount of 2% by weight of the hides, calculated for dry solids.

The final leather characteristics were similar to those obtained in Example 10.

The leather produced with the use of titanyl ammonium disulphate as tanning agent according to Example; 3 to 14 had the following properties: tensile strength elongation wear-resistance (abrasionresistance) , dry wet water-absorption for 2 hours hydrothermal stability Furthermore, the tanned leather had increased water-resistance, sweat-fastness, mould-resistance, and could be stored for a long time without losing its quality. 26-31 MPa; 13-14%; 180-250 r.p.m. 5.8-9.0 hr/mm; 42-45% 90-100%.

Claims (10)

1. 51866 CLAIMS:

1. A method of preparing titanyl ammonium disulphate, which comprises mixing a solution containing titanium and ferrous iron in aqueous sulphuric acid, with a solution of a peroxy-titanium complex in aqueous sulphuric acid, the amount of the complex being 0.01 to 2 grammes, calculated as titanium dioxide, per litre in excess of the stoichiometric amount necessary to convert said ferrous iron to ferric iron, adding ammonium sulphate and aqueous sulphuric acid to the mixture so as to precipitate titanyl ammonium disulphate monohydrate, and washing the precipitate with aqueous ammonium sulphate solution.

2. A method according to claim 1, in which 75 to 85% by weight of the titanyl ammonium disulphate is first precipitated, separated and washed, and the resulting filtrate end washing waters are combined and treated with ammonium sulphate so as to precipitate further titanyl ammonium disulphate, which is recycled to the said aolution containing titanium and ferrous iron in aqueous sulphuric acid.

3. A method according to claim 1, substantially as herein described in Example 1 or in Example 2.

4. A process of tanning delimed hide, which comprises treating the hide with a tanning promoter selected from a sodium salt of disulphodinaphthylmethane, phthalic anhydride, aluminium alum, aluminium alum mixed with urotropin, ammonium titanyl sulphate and phenolic «ligomera dispersed in lignosulphonic acids, followed by tanning the hide with titanyl ammonium disulphate prepared according to any of claims 1 to 3* 51366

5. A process according to claim 4, wherein the tanning-promoter is a sodium salt of disulphodinaphthylmethane, in an amount of from 1.5 to 2.5%, based on the weight of the hide. 56. A process according to claim 4, wherein the tanning promoter is phthalic anhydride, in an amount of from 1.2 to 2.2%, based on the weight of the hide.

6. 7. A process according to claim 4, wherein the tanning promoter is aluminium alum, in an amount of IQ fron 1 to 3%, based on the weight of the hide.

7. 8. A process according to claim 4, wherein the tanning promoter is a mixture of 0.5 to 3.4 parts by weight aluminium alum and one part by weight urotropin, in an amount of from 1.8 to 5% based on the weight of 15 the hide.

8. 9. A process according to claim 4, wherein the tanning promoter is ammonium titanylsulphate, in an amount of from 5 to 15%, based on the weight of the hide. 20 10. A process according to claim 4, wherein the tanning promoter is a phenol oligomer dispersed in lignosulphonic acids, in an amount of 2.5 to 5.0%, based on the weight of the hide. 11. A process according to claim 10, wherein 25 prior to the treatment with the tanning promoter, the hide is preliminarily chromed. 12. A process of tanning delimed hide, delimed and pickled hide, or delimed, pickled and chromed hide, using as the tanning agent titanyl' ammonium disulphate prepared according to any of claims 1 to 3, tanning being carried out in the presence of a complex-forming agent selected from lactic acid, aluminium alum and 5 condensation products of synthetic fatty acids with triethanolamine, said complex-forming agents being used in an amount of from 0.5 to 2.0% by weight of the hide. 13. A process according to claim 12, wherein the

9. 10 tanned hide is treated with chloroprene rubber latex in an amount of from 1 to 6% by weight of the hide (dry solids basis).

10. 14. A process of tanning hide, substantially as herein described in any of Examples 3 to 14.