HU214199B - Process for making skin from animal hides - Google Patents

Abstract

(57) EXTRACT The skin of the process of the present invention is first produced by pretreatment of animal skins with lime and, in the case of sodium chloride, by treatment with sodium sulfide, which is deactivated in a container filled with aqueous treatment liquids at the addition of carbon dioxide to the treatment fluid. The essence of the invention is that the water treatment fluid vapor retardant anti-oxidant material is added. Preferably, an oxidation agent is used as an oxidation agent, which is fed in the aqueous treatment fluid. ŕ

Description

(57) EXTRAS

The process of the present invention first provides a skin precursor of animal skins by treatment with lime milk and optionally with sodium sulfide, which is descaled in a container filled with aqueous treatment liquid by addition of carbon dioxide to the treatment liquid.

It is an object of the invention to add an oxidizing agent to the aqueous treatment fluid. Preferably, the oxidizing agent is an oxygen-containing gas which is dissolved in the aqueous treatment fluid.

Description: 4 pages (including 1 page illustration)

HU 214 199 B

HU 214 199 Β

The present invention relates to a method of making leather from animal skins by first treating the animal skins by treatment with lime milk and optionally sodium sulfide, which is dehydrated in a container filled with aqueous treatment liquid by addition of carbon dioxide to the treatment liquid.

In the case of leather made from animal skins, the animal skin is first subjected to tanning with lime milk and sodium sulfide. The leather product thus obtained is then subjected to a second processing step where it is treated with an organic acid or ammonium sulfate to dissolve the calcium hydroxide embedded in the collagen backbone. This process is called descaling.

However, this descaling agent causes a significant load on the wastewater. Therefore, carbon dioxide has recently been used as a descaling agent. However, carbon dioxide formed from carbon dioxide dissolves the embedded calcium hydroxide, which essentially causes the water to harden. However, this CO? It was used in Gerb drums. In this closed treatment unit, carbon dioxide could be introduced without the release of intense odor sulfur compounds. Such a process is described in WO-A1-88 / 10,317.

However, in open treatment facilities, such CO ₂ emissions are reduced. methods, so far, could not be applied for the following reasons.

If the carbon dioxide used to decalcify the skin product is dissolved in the treatment fluid in the container, the pH will drop below seven. At such low pH values, even sulfur compounds in the protein skeleton produce mercaptans and hydrogen sulfide. Both compounds are volatile, toxic, aggressive and have an unpleasant odor. If open controls were used, these environmentally harmful compounds would be released into the atmosphere. Therefore, the CO ₂ method has so far only been used in closed treatment plants.

It is an object of the present invention to modify the process mentioned in the introduction so that toxic compounds are not produced during the descaling of skin products.

The invention is based on the discovery that this object can be solved by the addition of an oxidizing agent to the aqueous treatment fluid.

By adding carbon dioxide and an oxidizing agent, two problems were solved simultaneously.

On the one hand, carbon dioxide from carbon dioxide dissolves calcium hydroxide embedded in the collagen backbone of the skin so that it is decalcified without harmful chemicals. On the other hand, the oxidizing agent introduced into the aqueous treatment fluid oxidizes the compounds formed by the shift in pH, hydrogen sulfide and mercaptans, and the thioester to thiosulphates, sulphites, sulphonates and sulphates.

Preferably, the oxidizing agent is an oxygen-containing gas which is dissolved in the aqueous treatment fluid.

In practice, the treatment liquid is preferably drained from the tank and fed to a reactor in which the oxygen-containing gas is dissolved in the treatment liquid together with the carbon dioxide. Finally, the treatment fluid is drained from the reactor and returned to the tank.

In order to easily dissolve the oxygen-containing gas and carbon dioxide in the treatment fluid, the reactor is preferably operated at a pressure above atmospheric.

In view of the fact that the process according to the invention no longer produces substances harmful to the environment, the skin products can be descaled in a container open to the atmosphere. Such open mixers are significantly cheaper to produce, which can result in significant investment savings.

The process of the invention is applicable to both descaling of cowhide and to descaling of fat-rich pigskin. Given that only starch constituents (HCO3-10nok) are discharged into the process, expensive wastewater treatment plants that are designed to eliminate nitrogen can be dispensed with.

The invention will now be described in detail with reference to an exemplary embodiment.

The figure is a schematic drawing of an apparatus for carrying out the process of the invention.

The figure shows a descaling container 1 open to the atmosphere in which the skin product and the aqueous treatment liquid are disposed. In order to mix the skin product and the treatment fluid, the descaling container 1 is designed to rotate about its longitudinal axis. The descaling vessel 1 is inclined with its longitudinal axis relative to the vertical and lies on rollers. The decalcification tank 1 is rotated by an axially arranged propeller 4 on the bottom of the tank and not shown. Such a control device is commonly referred to as a Gerb mixer.

The treatment fluid is discharged from the descaling tank 1 via a suction line 3. The suction line 3 passes through the through opening of the holder 4. A drain grate 8 is arranged in the lower region of the container to hold the leather products in the descaling container.

The suctioned treatment fluid is fed to reactor 6 via 2 pumps. Pure oxygen is supplied to the reactor tube 6 through an oxygen inlet 11 from an oxygen tank such as a liquid oxygen tank. Through a second inlet 14, carbon dioxide is introduced. The carbon dioxide is kept in a liquid reservoir 10 and fed into the inlet 14 via a meter and regulator 9.

In 6 reactors designed as a column reactor, carbon dioxide and technically pure oxygen are dissolved in the treatment liquid at an excess pressure of 1.3 bar. In order to achieve the required pressure in the reactor, a pressure regulating shut-off valve 7 is integrated in the reactor line 6.

The treatment fluid treated in the reactor 6 is finally returned via line 15 to the decalcification tank 1. There, carbon dioxide from carbon dioxide dissolved in the treatment liquid dissolves calcium hydroxide embedded in the skin's collagen backbone. With this decalcification, the pH drops below seven with the formation of hydrogen sulfide, mercaptans and thioester. These compounds are converted into thiosulphates by oxygen dissolved in the treatment fluid,

EN 214 199 Β oxidised to sulphites, sulphonates and sulphates. Overall, no toxic product is produced during the decalcification process.

The apparatus used for the process according to the invention thus has a descaling tank 1, a pump 2, a holder 4 with a suction line 3, a pH meter 5 and a reactor 6. It is further provided with a pressure regulating shut-off valve 7 mounted in the treatment fluid return line 15. The descaling vessel 1 is provided with a drain grate 8, while the apparatus further comprises a CO ₂ measuring and regulating panel 9, a CO ₂ supply unit 10, and a conduit 11 for introducing oxygen. In addition, 12 numbers indicate the oxygen supply. The unit also includes 14 CO ₂ injection lines.

The following example relates to the descaling of leather products made of pigskin. The parameters of the process of the present invention are illustrated in connection with a conventional process using ammonium sulfate as a descaling agent.

Useful volume of the decalcification tank: V = 10 m ³ .

Tank rotation speed: approx. 30 rpm.

Treatment time: approx. 3 hours.

Descaling Consumption:

(a) 5% ammonium sulphate per tonne;

(b) 1.3% of carbon dioxide per tonne of the invention.

Skin weight applied per serving approx. 61st

The weight of the skin is 25% dry and 75% water.

Specifications of pump for rotating operating fluid: V = 20 m ³ / h, H = 63 m lift height, P _max = 8 kW. The temperature of the treatment liquid is 32-35 ° C.

The process:

(a) At the present state of the art, 61 skins + 300 kg ammonium sulfate are intensively mixed. Thereafter, the treatment fluid will be pumped out.

b) In the present invention, 6 t of skin is mixed with 5 m ^{3 of} water and optionally with a surfactant. The resulting treatment liquid is pumped through a pressure reactor over a 3 hour run with 80 kg of carbon dioxide and 1.6 kg of oxygen.

The pressure reactor:

The CO _{2 requirement is} 1.3% per tonne of skin, equivalent to 13 kg of skin precursor per tonne, ie 80 kg per serving.

Descaling time: 3 hours.

The amount of circulating treatment fluid is 10 m ³ / h. Reactor operating pressure: 2.3 bar (abs.).

Amount of CO ₂ added:

for one hour 20 m ³ / h = 37 kg of carbon dioxide / hour for thirty minutes 15 m ³ / h = 27.7 kg of carbon dioxide / hour for ninety minutes 10 m ³ / h = 18.5 kg of carbon dioxide / hour total : 83.2 kg of carbon dioxide.

PATENT CLAIMS

Claims (6)

CLAIMS 1. A method of producing leather from animal skins, comprising first treating the animal skins by treatment with lime milk and optionally sodium sulfide, which is descaled in a container filled with aqueous treatment fluid by adding carbon dioxide to the treatment fluid, characterized in that the aqueous treatment fluid is added. 2. The process of claim 1 wherein the oxidizing agent is an oxygen-containing gas dissolved in an aqueous treatment fluid. The process according to claim 2, wherein the treatment liquid is introduced from the vessel into a reactor in which the oxygen-containing gas together with carbon dioxide is dissolved in the treatment liquid and finally the treatment liquid is recycled back to the vessel. Process according to claim 2 or 3, characterized in that the oxygen-containing gas is technically pure oxygen. Process according to claim 3 or 4, characterized in that the oxygen-containing gas and carbon dioxide are dissolved in the reactor at a pressure above atmospheric pressure. 6. A process according to any one of claims 1 to 3, wherein the skin precursor is descaled in a container open to the atmosphere.