Environmentally friendly chrome-tanning method

Abstract

A method for tanning a hide wherein said method comprises treating a tannable hide with a tanning composition comprising from 25 to 75% by weight (wt. %) of at least one chromium(III) salt; from 5 to 70% by weight (wt. %) of at least one zeolite having the general formula (1): Mx/n [(AlO.sub.2)x(SiO.sub.2)y] wH.sub.2O, wherein M is an alkali metal cation, a bivalent cation, a trivalent cation or a mixture thereof, n is the valence of the cation, w is the number of water molecules per unit cell, y is a number from 0.8 to 50 and the ratio y to x is ranging from 0.7 to 100, treated with at least one acid selected from the group consisting of a monocarboxylic acid and a polycarboxyic acid; and from 1 to 70 wt. % of at least one aluminium(III) salt; wherein all wt. % are relative to the total weight of the composition (T).

Claims

1. A method for tanning a hide, wherein said method comprises treating a tannable hide (H.sub.t) with a tanning composition (T) comprising: from 40 to 65% by weight (wt. %) of chromium(III) sulfate, from 7 to 50% by weight (wt. %) of at least one treated zeolite (Z) prepared by treating at least one zeolite (Z) having the general formula (1): M.sub.x/n [(AIO.sub.2).sub.x(SiO.sub.2).sub.y] wH.sub.2O, wherein M is an alkali metal cation, a bivalent cation, a trivalent cation or a mixture thereof, n is the valence of the cation, w is the number of water molecules per unit cell, y is a number from 0.8 to 50 and the ratio y to x is ranging from 0.7 to 100 with at least one acid (C), from 7 to 50 wt. % of aluminum(III) sulphate at least one aluminum(III) salt, and wherein all wt. % are relative to the total weight of the composition (T), thereby obtaining a tanned hide and a waste solution; where in waste solution comprises a residual chromium content of less than 150 mq/l of chromium oxide wherein the at least one acid (C) is formic acid.

2. The method according to claim 1, wherein the zeolite (Z) is of the general formula (1): M.sub.x/n[(AIO.sub.2).sub.x(SiO.sub.2).sub.y] wH.sub.2O, , wherein M is an alkali metal cation, w is a number from 1 to 10, y is a number from 0.8 to 15 and the ratio y to x is ranging from 0.7 to 6.

3. The method according to claim 1, wherein the ratio of formic acid to the zeolite (Z) is from 5 to 50% by weight.

4. The method according to claim 1, wherein the weight ratio of the aluminum(III) sulphate to the treated zeolite (Z) is greater than 0.5.

5. The method according to claim 1, wherein the composition (T) further comprises from 0.1 to 20% by weight of other ingredients selected from complexation agents and bases.

6. The method according to claim 1, wherein said method comprises the steps of: Step 1. subjecting a hide (H) to a beam house treatment, thereby obtaining a tannable hide (H.sub.t), and Step 2. treating the tannable hide (H.sub.t), as formed in Step 1., with the composition (T), thereby obtaining a tanned hide and a waste solution.

7. The method according to claim 1, wherein the weight percent of the composition (T), relative to the tannable hide Ht mass to which it is added, is from 4 wt. % to 14 wt. %.

8. The method according to claim 6, wherein the weight percent of the composition (T), relative to the tannable hide Ht mass to which it is added, is from 4 wt. % to 14 wt. %.

9. The method according to claim 1, wherein the concentration of the acid (C) is 84% by weight or more.

Description

EXAMPLES

(1) The invention will be now described in more details with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

(2) General Procedure for Tanning a Hide

(3) The hides were subjected to a beamhouse process; presoaking, soaking, liming/dehairing, fleshing/splitting, deliming, bating, pickling according to known practice in the art in a beamhouse process for leather based on a tanning process with chromium (III) sulfate. The presoaking, soaking, liming and dehairing formulations were performed relative to the raw salted weight of the hides. The deliming, bating, pickling formulations were based on the weight of the splitted hides in limed stage. At the end of the bearnhouse processes, pickled hides were obtained in a in 50% aqueous solution, relative to the limed weight of the hides. Said 50% aqueous solution is also containing 0.6% formic acid 85%, relative to the limed weight, 0.9% sulfuric acid 96%, relative to the limed weight and 7% salt, relative to the limed weight. The pH obtained was between 2.8 and 3.2.

(4) For each of the examples, as detailed below, a composition (T), as detailed below, was added to said pickled hides.

Comparative Example 1

(5) The comparative composition had following components:

(6) 93.3 wt. % of chromium(III) sulphate (Cr.sub.2(SO.sub.4).sub.3 26/33 obtained from Lanxess, thus chromium(III) sulphate having 33% basicity and 26% chromium oxide

(7) 6.7 wt. % of magnesium oxide

(8) A total of 7.5% by weight of the comparative composition, relative to the limed hide mass was introduced in the tanning vessel containing 21.4 kg of the limed hide in 50% aqueous solution, relative to the limed hide. The starting pH was 2.90.

(9) The following dosing scheme was applied:

(10) step (a): 7.0% by weight of Cr.sub.2(SO.sub.4).sub.3 26/33, relative to the hide (Ht) mass, was first added, running (i.e mixing) time was 180 minutes, pH after treatment was 2.97 no step (b) step (c): 0.5% by weight of magnesium oxide, relative to the hide (Ht) mass, was then added, running time was 12 hours, pH after treatment was 3.98.
The chromium content of the waste solution obtained by Atomic Absorption Spectrometric Methods (AAS) according to a standard method UNE-EN 1233 was 3955 mg/l.
The chromium exhaustion was 74.20%.
The shrinkage temperature is 95° C.

Example 2

(11) The composition (T) had following components:

(12) a 53.3 wt. % of Cr.sub.2(SO.sub.4).sub.3 26/33 obtained from Lanxess 17.5 wt. % of formic acid treated zeolite A4 (zeolite A4 87% by weight treated with 13% by weight of formic acid (purity 99%, from Kemira Poland) 20.9 wt. % of aluminium(III) sulphate 14*H.sub.2O (from Lanxess) 1.6 wt. % of citric acid, anhydrous (from Brenntag) 6.7% of magnesium oxide
A total of 7.5% by weight of the composition (T), relative to the limed hide mass was introduced in the tanning vessel containing 13.8 kg of the limed hide in 50% aqueous solution, relative to the limed hide having. The starting pH was 2.90. The following dosing scheme was applied: a step (a): 4.0% by weight of Cr.sub.2(SO.sub.4).sub.3 26/33, relative to the limed hide mass, was first added, running (i.e mixing) time was 180 minutes, pH after treatment was 3.0 step (b): 1.3 wt. % of formic acid treated zeolite A4, 1.6 wt. % of aluminium(III) sulphate 14*H.sub.2O and 0.1 wt. % of citric acid, anhydrous, were added together, running time was 180 minutes, pH after treatment was 3.0 step (c): 0.5% by weight of magnesium oxide, relative to the limed hide mass, was then added, running time was 12 hours, pH after treatment was 4.90.
The chromium content of the waste solution obtained by Atomic Absorption Spectrometric Methods (AAS) according to a standard method UNE-EN 1233 was 45 mg/l.
Based on this chromium content of 45 mg/l, the average chromium content present in the accumulated waste waters over the whole process including soaking, liming, deliming, pickling and tanning is 0.8 mg/l. Thus, below the maximum allowed value of 1.5 mg/l according to the Chinese legislation as of Jul. 1, 2014.
The shrinkage temperature is 105° C.

Comparative Example 3

(13) The comparative composition of Example 3 had following components: 54.8 wt. % of Cr.sub.2(SO.sub.4).sub.3 26/33 obtained from Lanxess 40.4 wt. % of formic acid treated zeolite A4 (zeolite A4 87% by weight treated with 13% by weight of formic acid (purity 99%, from Kemira Poland) 0.7 wt. % of citric acid, anhydrous (from Brenntag) 4.1% of magnesium oxide
A total of 7.3% by weight of the comparative composition of Example 3, relative to the limed hide mass was introduced in the tanning vessel containing 11.85 kg of the limed hide in 50% aqueous solution, relative to the limed hide. The starting pH was 2.80.
The following dosing scheme was applied: step (a): 4.0% by weight of Cr.sub.2(SO.sub.4).sub.3 26/33, relative to the hide (Ht) mass, was first added, running (i.e mixing) time was 180 minutes, pH after treatment was 2.40 step (b): 1.15 wt. % of formic acid treated zeolite A4 and 0.05 wt. % of citric acid, anhydrous, were added together, running time was 180 minutes, pH after treatment was 3.39 step (c): 1.8 wt. % of formic acid treated zeolite A4, was added, running time was overnight, pH after treatment was 3.70 step (c): 0.3% by weight of magnesium oxide, relative to the limed hide mass, was then added, running time was 2 hours, pH after treatment was 4.50.
The chromium content of the waste solution obtained by Atomic Absorption Spectrom was 178.1 mg/l.
The chromium exhaustion was 97.84%.
The shrinkage temperature is 108° C.
All 3 tanned hides of comparative examples 1, 3 and example 2 were further processed according to known practice in the art.
In particular, the 3 tanned hides of comparative examples 1, 3 and example 2 were sammed and shaved according to the state of the art, to a thickness of 1.0 mm.
For the wet-end process, said sammed and shaved hides were retanned using a state-of-the-art formulation for e.g. automotive seats leather or leather for sofas. The wet end formulation was based on: 5% Tara 3% Phenolic retaning 3% Polymeric retanning 4% Lecithine 6% Fat Liquor based on sulphite ester
Drying was performed by vacuum drying (2 minutes, 45° C.), followed by hanging drying overnight and milling for 8 hours.
The organoleptic evaluation was performed on all three finished tanned leathers of comparative examples 1, 3 and example 2.
Dyeing was very good in the finished tanned leather of example 2 (color was even).
Based on the organoleptic evaluation, the finished tanned leather of example 2 was considered to be the best leather, as summarized below: grain tightness was better in the finished tanned leathers of example 2 and comparative example 3, compared to the finished tanned leather of comparative example 1 softness was slightly better in the finished tanned leather of comparative example 1 compared to the finished tanned leather of example 2, and much better in the finished tanned leather of example 2 compared to the finished tanned leather of comparative example 3 fullness was better in the finished tanned leathers of example 2 and comparative example 3, compared to the finished tanned leather of comparative example 1 filling of difficult parts such as bellies was better in the finished tanned leathers of example 2 and comparative example 3, compared to the finished tanned leather of comparative example 1.
In conclusion, the combination of all relevant parameters for the touch and feel of the leather show an optimum in the finished tanned leather of example 2.
Tear strength for all three finished tanned leathers of comparative examples 1, 3 and example 2 was not superior, just in the “approved” level, the tensile strength was very good in all of them.