HU188117B - Process for chrome tanning leathers particularly oxhide - Google Patents

Abstract

According to the invention, the soaked, limed, calcined, pickled and 0.2-1.4% masking acid, preferably formic acid, naphthalene sulphonic acid in the presence of the pellet used in the used pellet, preferably 0.5-2% aldehyde-based fixing pre-tanning agent, preferably glutaraldehyde, is used. Formaldehyde is poured and after the process is completed, the juice is removed after 2-3 hours. Chromium digestion is carried out in a reversing barrel or other rotary equipment with a tanning spoon of 1-1.8% dry chromium oxide without juice, and after rotation for 3-4 hours, 0.1-0.5% magnesium oxide is added to the rotary system in spray form. it spins 2-3 hours without skin juice. After tanning, the skins are rested for at least 10 hours.

Description

It is known that the concentration of the leather industry on large-scale plants and the increase in the amount of chemicals that are not completely absorbed by the skin, as well as the toxic nature of some of their components, pose serious environmental problems.

The issue of sulfides and chromium ions, which are toxic substances, is particularly acute.

As is known, the most widely used chromium plating method in the leather industry is the so-called one-bath tanning process, in which Cr'-sulphate and Cr ₂ (SO ₄ ) ₃ complexes are replaced. The chromium compounds used for this purpose contain up to a minimum amount of Cr ^vl ions.

The VI-valent chromium salts not only dangers ¹⁵ dangerous because they damage the biological wastewater treatment bacterial flora by highly toxic properties, but also because - unlike Cr ⁿⁱ A lot - difficult or costly way may be brought out liquid phases, it sa leather industrial effluents are in dissolved form.

The Cr'-salt content of the tannery wastewater is found in the precipitate at pH 8 of the combined sewage in the form of chromium oxide. Therefore, one of the main problems is caused by the chromium hydroxide in the sewage sludge, which can only be eliminated by depositing, which practically does not allow the use of sewage sludge for artificial manure, and even makes the sewage sludge hazardous, also requiring certain requirements for disposal.

As environmental problems worsen, the price of chromium salt worldwide has increased significantly recently, with _{3g in} the market.

These phenomena warrant worldwide research to reduce chromium salts in waste water from the leather industry. The following ways to reduce the amount of chromium salt entering the wastewater include:

(a) Recycling (recycling) of used chrome tanning fleets

The principle of recycling used chromium is not new. It was already in the II. It was used before World War I - not for environmental reasons, but for chromium- ^for reasons of economy and quality. This method presents a relatively simple but costly complication in collecting the chromium-containing waste liquors produced at various sites. Australian researchers Davis and Seroggie have published mainly on this topic (eg ⁵⁰ ISLTC 60,106,1976).

The practical implementation was reported by JM Constantin and GB Stockman (Das Leder. 1980,31,4.52) on the basis of the experience of a US leather factory employing 4,000 pieces of cowhide daily. ⁵⁵

b) Regeneration of used chromium juice

The method of precipitating and dissolving used chromium juice with alkali is also not new, but has been forgotten in many places and the equipment needed has been damaged. Here the problem is the same as in the previous case ⁶⁰ : collecting the resulting juice.

c) Increasing chromium binding, chromium-saving tanning

The disadvantages of the methods referred to in points (a) and (b) have been addressed by the development and application of ⁶⁵ different tanning methods that save chromium or increase chromium binding.

It is known from chromium tanning chemistry that the diffusion rate of the chromium salt is increased by the concentration of the tannic juice and by increasing the temperature. Using this principle, the so-called short-fleet or incorrect nomenclature 'dry tanning' methods were developed, whereby 30 to 40 wt.% Of the fleets were replaced with skins and the fleet was diluted to 80 to 100 wt.%. Dr. Géza Tóth et al., During the exchange of 7 mm thick hair with Cr ₂ O ₃ equivalent to 2.7 wt% Cr ₂ O ₃ for 4 hours, showed the following exchange and chromium distribution values:

Concentration of tannins

Cr ₂ Oj g / 1

Fleet Ratio Weight%

Middle layer transitions

The distribution of chromium oxide content in the skin cross-section as a percentage of the average Cr ₂ Oj content is cattle.

middle, layers of meat.

90 30 complete 108 89 108 60 45 thin stripe in the middle fish- - - 40 70 approx. 20% gene weak _H2 72 133 20 140 approx. 30% gene weakness - - 10 300 approx. 60% gene weakness - -

Referring to Gustavson's work (Leather and Shoe Technology 1971, 4, 101), the aforementioned authors explain the fact that as the concentration increases, the amount and ratio of non-ionic tannins, i.e. of lower affinity, in chromium sulphate solutions increases. This is supported by the following data:

Cr ₂ O ₃ content in solution g / l non-ionic /the cationic % /She anions <> / / 0 250 46 40 14 25 9 91 - 5 2 98 -

The rapid permeation of concentrated chromium exchange fluids through the skin and one of the reasons for the associated uniform chromium distribution is due to the charge conditions of the tanning agent.

In addition to the use of tanning fleets, the following factors, which are consistent with the basic physico-chemical knowledge of chromium tanning, also increase the uptake of chromium, ie reduce the amount of chromium entering the wastewater:

- raising the pH of the tanning solution

188 117

- low chromium oxide addition

- extension of tanning time *

These "classic" factors are almost as old as chrome tanning.

Extending the tanning time generally did not fit into the natural working pattern.

Raising the pH of the tanning agent, so-called damping in a relatively low fleet and high barrel loading, is often not feasible in practice. Already in the late fifties, it was shown that chromium salt powder formulations and so-called sulfate masking help in this field (H. Spahrkás and H. Schmid: Das Leder 1959, 10,145). Unlike the old practice, this method does not contain bulk tanning solutions aged for several days, but powdered chromium preparations cast into the tanning fleet

I made the tanning.

'' The said authors have shown that the turbidity and precipitation of a freshly prepared solution of powdered basic chromium sulphate occurs after the addition of substantially more soda solution than the old chromium sulphate solutions.

A further result of classical chromium utilization enhancements was the discovery and application of so-called self-sealing chromium preparations (M. Spahrkás and H. Schmid, Das Leder 1966,17,249).

According to the literature, when using self-sealing chromium preparations, it is possible to obtain 20% less chromium added to the conventional tanned leathers containing the same amount of chromium oxide.

Such "self-sealing" chromium products are not manufactured in Hungary. Their method of production, their composition is a secret of production. A classic such preparation is e.g. Baychrom A from Bayer.

According to Bayer studies, the percentage of skin shrinkage (%) during the cooking test that depends on tanning temperature, tanning time and fleet length is as follows (powdered tanning, 2.4% Cr ₂ O ₃ addition):

Fleet overweight: 60% 100% 140%

Temperature: 25 'C after 4.5 hours a 40'C 25 'C 40'C 25 'C 40'C shrinkage: 20% After 7.0 hours a 15% 20% 10% 20% 20% shrinkage: 10% overnight the zhu- 0 15% 0 20% 0 rumble: 0% 0 0 0 5% 0

In the course of chromium trapping based on the aforementioned chromium-saving principles, the chromium balance was examined in a model experiment by K. Backer, H. Heinze, W. Luck and H. Spahrkás (Das Leder 1977, 28.57).

In their thinking, they kept in mind the fact that the non-bound chromium salt is present in the same concentration as the chromium used, not only in the juice used, but also in the wet chrome-tanned skin.

Assuming that

- after chrome tanning, the weight of the skin is 90% of the lean weight

- chromium exchange leather moisture or chromium content 657 ,,

- Ά part of the non-bound chromium content of chromium-tanned leather binds during trimming and ¼ part is discharged after pressing and washing

- the sulfur oxide content of the juice used is 7 g / l

- the amount of tanning flot 80%, based on the amount of chromium oxide discharged per 100 kg of flour.

a) in the brine used (80 x 7) = 560 g Cr, O,

b) in wet skin (0.9 x 65 x 7 x 0.75) = 300 µl Cr ₂ O ₃ total: 860 g Cr ₂ O ₃

This means that even when using the most efficient and state-of-the-art methods developed in the early 1970s, the amount of chromium oxide added is approx. Part of Vs goes to unused waste (sewage sludge). This 860 kg / 100kg of Cr ₂ O ₃ 50 1 / kg of hides and skins in the effluent pool will result in approx. Corresponds to 172 mg / l Cr ₂ O ₃ and 118 mg / l Cr respectively.

Since, according to literature, new ways have to be found in the case of precipitation based chromium regeneration using 250-50 mg Cr / l and using the recirculation method 50-60 mg Cr / l in combined sewage with 501 / kg of hides.

Literature describes the relatively high loss of chromium in regeneration and re-circulation at the expense of the amount of chromium that is spilled and removed by leaching. The research thus focused on the amount of chromium that remains in the skin after tanning and is removed before washing to remove acidity.

According to the literature, two tanning methods and families of products have been developed as a result of the research.

Bayer and BASF have experimented with a similar method: a stable complexation of a chromium composition.

The relevant statement by Bayer states:

In 1974, a new process was developed which, while almost completely pulling out the tanning fleet, produced impeccable quality leather. The process requires a special grade chromium formulation, Baychrom 9000, which is a self-sealing chromium formulation containing dibasic carboxylic acid as a complexing agent (Das Leder 1977, 28.57 and 1980, 31, 142).

The BASF process also uses complexing dicarboxylic acid, but it is added separately to the pickle or in the salt form to the chromium tannic acid.

Henkel dampens the chrome tanning fleet with alkali aluminum silicates (Das Leder, 1979, 22, 23).

Both methods have been reported to contain less than 1 g / l of Cr ₂ O ₃ in the tannins used.

For this reason, approx. With 30% less chromium oxide you can get the right quality skin.

However, none of these procedures was able to become established in the Hungarian leather industry

188 117 price of products or quality reasons. The procedures suggested by classical methods (eg fleet shortening) have resulted in lower surface yields.

The essence of the present invention, in contrast to the methods known so far, is that 0.2-1.4% of masking acid (naphthalenesulfonic acid, formic acid, etc.) and 0. 5-2% of fiber anchoring precursor (e.g. glutaraldehyde, formaldehyde, etc.) is added, and the dowel is lowered and the chromium tanning and damping are carried out in bulk using dry chromium salt or powdered MgO in a rotary, reversible barrel or other apparatus. The dry chromium salt gradually dissolves in the moisture on the surface of the pickled skin as it rotates, and after two to three hours of rotation, the resulting high concentration, high diffusion chromium salt penetrates the entire cross-section of the skin. The damping is performed on dry MgO based on the gradual dissolution principle, taking care to distribute the material evenly throughout the equipment. After complete tanning, the skin is rested for at least ten hours.

The chromium tanning is carried out with _{1 to} 1.8% by weight of Cr ₂ O ₃ -chrome-tanning salt without juice, which is significantly less than what is commonly used in the prior art. · The low chromium consumption is due to virtually waste chromium in dry tanning and dehydration. no or hardly any.

One embodiment of chromium tanning is to add 0.4-0.5% by weight of a 0% basic chromium salt of Cr ₂ O ₃ to the pretreated skin, followed by 0.6-0.3% by weight after 1-1.5 hours of rotation. A dry chromium tanning salt of 33% basic Cr ₂ O _{3 was} added, and the juice was spun for an additional 2-3 hours, and then proceeded as described.

A second embodiment of chromium tanning is the addition of 1-1.8% by weight of dry chromium tanning salt having a basicity of 25-33% Cr ₂ O ₃ to the pre-treated skin, and the process is continued for 3 to 4 hours without juice.

A third embodiment of chromium tanning is by adding to the pre-treated skin 1 to 1.8% by weight of a Cr ₂ O ₃ anti-caking chromium tanning agent and proceeding as described.

The amount of MgO added (0.1-0.5% by weight) to dampen it depends on the type of tanning. The invention will now be described in more detail with reference to specific embodiments. The percentages given are in percent by weight of the hair.

Example 1

Soaking, liming, splitting, descaling, pickling is done in the traditional way.

Peeling rotates 5% of 80% water

8% common salt + 10% water

0.6% formic acid rotates 5 'with 0.4% sulfuric acid

+ him 10% water 0.4% sulfuric acid Rotates 2 ^h + him 0.4% naphthalene sul- l ^h -t rotates acid • + him 1% glutaraldehyde. juice released Rotates 2 ^h Chrome tanning without water 3% chromium alum l ^h -t rotates 0.8% for Cr ₂ O ₃ Rotates 3-4 ^h

a suitable 33% basic powdered chromium tanning agent

0.5% MgO equation is rotated for 3 ^h

Relaxation The skins are undisturbed for 10 ^hours less than the rest

The use of the process according to the invention has the following advantages:

(a) It is significant from an environmental point of view that Cr is only present in traces in the sewage and sludge.

b) 30-60% reduction in the use of chromium salt (import savings).

Example 2

After marinating, the pretreated as described in the previous example is treated as follows:

pickling 80% water 8% common salt 5 minutes + to it 10% water 0.6% formic acid 0.4% sulfuric acid 5 minutes + to it 10% water 0.4% sulfuric acid 1.5% powdered acid also Rotates for 3 hours + to it 2% formaldehyde Rotates for 2 hours

juice down.

The skins are mechanically dehydrated or subjected to other conventional mechanical operations.

Chrome tanning (without water)

Dehydrated skins are replaced with reduced chromium of 150-200 g / l Cr ₂ O _{3 in} standard tanning equipment:

0.5% Cr ₂ O ₃ , ca. 40% reduced juice rotates for 30 minutes at + 0.8% Cr ₂ O ₃ , approx. 40% basic reduced juice rotates for 2 hours

Cooking trial.

If the cooking test is unsatisfactory, continue

0.2% reduced chromium equivalent to Cr ₂ O ₃ and dissolved therein

0.2% MgO rotates for 1 hour

After the cooking test, the skins are rested either by loosening or, without resting, the normal production is continued.

Claims (3)

Patent claims 1. Procedure for tanning leather in a reversible barrel or other rotating device, 188 117 after liming, descaling and pickling in known manner, characterized in that in the presence of 0.2-1.4, of a masking acid, preferably formic acid, naphthalene sulfonic acid, to the used pellet, 0.5-2% aldehyde-based surface fixative The pre-tanning agent, preferably glutaraldehyde, formaldehyde, is poured, rotated for 2 to 3 hours, the juice is removed, and the skin is treated with 1 to 1.8% Cr ₂ O ₃ chromium tanning salt, rotated for 2 to 4 hours, then Dilute with -0.5% MgO for 2 to 3 hours and then allow the skin to rest. (Priority: December 29, 1981) 2. The method of claim 1, wherein the post-tanning damping is performed with dry MgO by spraying the powder material into a chromium-skinned machine or kink. while rotating. Apply it gradually to the skin in 5 increments of 3-4 minutes. (Priority: December 29, 1981) The process according to claim 1, characterized in that it is applied in powder form from chromium tanning. (Priority: December 29, 1981) 10 4. Ace l. A process according to claim 1 wherein: ve chromium tanning salt is used in the form of reduced chromium at a concentration of 150-200 g / l Cr, O., after mechanical dehydration of the skin. (Priority: March 19, 1984)