EP0235832A1 - Process and installation for degreasing raw hides, and raw hides degreased by this process - Google Patents

Abstract

1. Process of degreasing moist raw skins received from a rendering establishment, consisting in placing the raw skins in their initial moist state within a liquid bath based on trichloro-1,1,2 trifluoro-1,2,2 ethane, during a period necessary for separation of the interstitial fats and residual superficial fats.

Description

The invention relates to an improved process and installation for degreasing raw hides rendered, having a moisture content which is generally of the order of 60%; it applies to raw hides coming directly from rendering or raw hides having undergone certain preliminary treatments, such as fleshing, pickling, stripping. It extends to the degreased raw skins obtained, skins of sheep, cattle, pigs, mestizos, goats ...

At the degreasing stage, the raw skins coming from rendering are very wet, especially if they have undergone preliminary treatments, in particular fleshing. They contain interstitial fats, sometimes in very large quantities linked to the origin of the skins, and residual surface fats, in smaller quantities if the skins have undergone prior fleshing. Interstitial fats are made up of reserve fats between cells and cell-building fats. It is essential in the skin treatment industries to extract these fats to allow correct implementation of subsequent treatments (tanning, dyeing) and obtaining good quality leathers.

For fat specialists, this type of degreasing poses difficult technical problems due to the presence of the above-mentioned interstitial fats and the humidity of the skin which forms a barrier vis-à-vis the usual organic degreasers. Various known degreasing treatment of fats specialists are listed in a general development presented in the following publication: "THE JOHNSON, LUSAS EW, Journal of the American Oil Chemist Sty; vol 60 ^no 2, 1983, pp 229- 242. "

To solve the particular problem of extracting interstitial fats from wet raw skins, one of the methods referred to in this publication is currently being used, which has been modified and perfected to meet the specific requirements of this application, namely the treatment process with a liquid hydrocarbon bath. This method was chosen because it operates cold, because the raw hides do not withstand bath temperatures above 35 ° C, which eliminates a large number of processes which take place hot. However, the hydrocarbon process had to be modified and perfected, since a treatment with hydrocarbon alone does not provide the desired degreasing effect: it has proved necessary to carry out the treatment by means of a mixture of hydrocarbon and surfactant. At the level of the skin, an emulsion phenomenon then occurs which allows the hydrocarbon to penetrate inside the latter despite the presence of water, to access the interstitial fats in order to dissolve them. At the end of a subsequent rinsing, the greases are thus eliminated for the most part and a satisfactory degreasing is obtained in this respect.

However, this method has several drawbacks. First, the hydrocarbon / surfactant emulsion, in which the fats are dissolved, is difficult to recover and leads to pollution whose destruction is expensive. The rejection of this emulsion containing fats is all the more penalizing as the skin professionals then need fats to carry out, at the level of tanning and dyeing, a nourishment of the skins by artificial regreasing: they are thus, paradoxically, led to reject grease, and forced to buy it later. In addition, these food fats must be compatible with the skins concerned, whereas the rejected fats were since they were derived from them.

In addition, approximately 50% of the hydrocarbon used remains in the skin, which is troublesome for two reasons: this retention leads to a significant consumption of hydrocarbon, however it confers on the skin a hydrophobic character which is not not favorable to the subsequent treatments which it must undergo (in particular the attachment of the dyes). In addition, the skin carries, after degreasing, traces of surfactants which accentuate the aforementioned defect.

Thus, the degreasing of raw skins coming from rendering, that is to say the elimination of superficial fats but also of interstitial fats of skins in a very humid state, is currently poorly resolved, and the prior art shows that we do not know how to operate such a treatment in the absence of additives such as surfactants which have the above-mentioned defects. These difficulties are illustrated in numerous documents which show that there is a real prejudice towards the degreasing of wet bodies:
- Technicuir, February 1975 - Degreasing in taverns (G. GAVEND et al.),
- Technicuir, February 1974 - Prevention and treatment of pollution in taverns (Mme FOLACHIER et al.),
- Journal of Americal Oil Chemistry, 1978 - Solvent Extraction of Soybeans (W. BECKER),
- Journal of American Oil Chemistry, 1983 - Mass Balance of Hexane Losses in an Extraction Plant. (JAH DAHLEN et al.).

The present invention proposes to provide a new deep degreasing process for wet raw skins coming from rendering.

An object of the invention is to provide a degreasing process which lends itself to extremely easy recovery of fats without being polluted by other products.

Another objective is to avoid charging the skin with an organic solvent or a surfactant so as not to modify its characteristics.

Another objective is to reduce the cost of the treatment, on the one hand, thanks to a complete recovery of the basic products, on the other hand, thanks to a valorization of the fats allowing either to resell them, or to use them then for the skin nourishment, if any, after appropriate treatment.

The method according to the invention for separating wet raw skins from rendering, interstitial fats and residual surface fats consists in putting said raw skins in their wet state in the presence of a liquid bath based on fluorocarbon compound (s), in particular trichloro-1,1,2 trifluoro-1,2 , 2 ethane or monofluorotrichloromethane, for a time necessary for the separation of said greases, generally between 15 minutes and 2 hours. This treatment is carried out cold in a temperature range which can range from 10 ° C. to 30 ° C. It is possible to choose liquid compounds in this temperature range and to use pure baths of these compounds; in this case, if monofluorotrichloromethane is used, the temperature will be limited to 23 ° C, the boiling point of this body.

It has been unexpectedly found that the fluorocarbon compounds perform a completely satisfactory deep degreasing of wet skins rendered with no additives, comparable in terms of degreasing efficiency to the current process at hydrocarbon / surfactant.

The skins obtained can be very easily rid of all of the fluorocarbon compound simply by isolating them from the liquid phase and by heating them in air at a temperature of 35 ° C to 55 ° C. This heating can be obtained by circulation hot air. It should be noted that, in a draft, the skins can withstand the temperatures mentioned above without any damage.

The fluorocarbon compounds are thus entirely removed due to their volatile nature and can be entirely recovered by simple condensation of the vapors. In addition, any residual traces are naturally removed very quickly during subsequent handling or mixing of the skins.

This degreasing effect of wet raw skins by the fluorocarbon compounds which makes it possible to separate both the superficial fats and the interstitial fats from it is quite surprising because it implies, first of all, that the compounds penetrate cold inside the skin despite the presence of water to access the interstitial fats, and then that they dissolve in locate these fats to extract them. The first step, which takes place in the presence of water, is very unexpected for those skilled in the art, in the absence of any surfactant and any additive.

It should be noted that certain fluorocarbon compounds are also known to have fat-solubilizing properties. For example, 1,1,2-trifluoro-1,2,2 ethane has already been used for degreasing dry clothes or furs tanned (Japanese patent ^No. 77.64401), or to extract laboratory oils homogenates soybeans, or to degrease components in the electronics industries.

However, in these applications, the eliminated fats are superficial fats, directly accessible. In addition, their dissolution is always done dry and most often using another means (heating, activation with ultrasound ...). In the case of degreasing tanned furs, they have been subjected to extensive drying beforehand, so that their moisture content is negligible.

Thus, the conditions for implementing these techniques (absence of water) and their performance (only surface degreasing) allow us to understand that specialists have never imagined using them for the thorough degreasing of wet raw skins coming from rendering which necessarily takes place under radically different conditions and which requires performance of another order.

Furthermore, it has been observed that the time necessary to obtain satisfactory degreasing was between 15 minutes and 2 hours; this time much less than that required in the hydrocarbon / surfactant process is an additional advantage of the process of the invention.

The fats and the fluorocarbon compound can be easily separated and recovered, by subjecting the bath resulting from the degreasing treatment to a distillation of the compound. The fluorocarbon compound can thus be recycled, while the recovered fats are clean and usable in many industrial sectors: cosmetology, soap, detergent ... Of course, some of these fats can be used on site to then nourish the skins after tanning, after having undergone if necessary an appropriate treatment.

The invention extends to an installation allowing the degreasing of the skins by implementing the method defined above. This installation is of the type comprising a rotating barrel provided with a door for introducing the skins and means for emptying the bath. According to the invention, it is characterized in that said barrel is associated with a closed loop comprising air heating means, circulation means and a steam condenser.

The invention also extends to degreased raw skins of quality corresponding to that obtained by implementing the above method. These skins are characterized in that they are free from traces of hydrophobic bodies or foreign surfactants.

They lend themselves optimally to subsequent tanning and dyeing treatments. It has been found by comparative tests that obtaining a given shade leads to the consumption of lower amounts of dyes in the case of skins covered by the invention than in the case of skins degreased with hydrocarbons / surfactants . The saving in dyeing appears to be around 15%.

The description which follows with reference to the single figure of the appended drawing presents, by way of nonlimiting example, an embodiment of a degreasing installation in accordance with the invention.

This installation comprises a rotating barrel 1 intended to receive a liquid bath of one or more fluorocarbon compounds. This barrel is provided on either side with two hollow shafts 2 and 3 placed in fixed bearings 4 and 5.

On one side, the barrel is externally provided with a toothed crown 6 engaged with a gear system associated with an electric motor 7.

The barrel has a door 8 for introducing the skins and means for draining the bath, constituted in the example by a drain hole on which a stop valve 9 is mounted.

Traditionally, this barrel is internally provided with pegs 10 driving the skins in rotation and ensuring their mixing in the bath.

The barrel 1 is associated with a closed loop which enters it by one of the hollow shafts 2 by means of a rotary joint 11, and which exits therefrom by the other hollow shaft 3 by means of a another rotating joint 12. This loop comprises a gas / liquid separation enclosure 13, making it possible to send the liquid to a conduit 14 provided with a valve, and the vapors to a conduit 15 also provided with a valve.

The conduit 15 is equipped with a condenser 16 associated with a separator 17. This separator makes it possible to separate any traces of water present in the fluorocarbon compound.

At the outlet of the condenser 16 is arranged an air circulator 18 and an air heater 19.

Thus, after each degreasing and emptying phase of the bath, the circulator 18 and the heater 19 make it possible, by opening a valve 20, to circulate air at a temperature between 35 ° C and 55 ° C in order to clear the skins of the residual fluorocarbon compound and recovering this compound in the condenser 16.

The barrel 1 preferably comprises on the side of the shaft 3 a double wall 21, partially formed by a grid in order to allow possible recovery of the bath by the hollow shaft, without being hindered by the skins.

In practice, the volume of liquid fluorocarbon compound placed in the barrel will be between 0.25 and 4 liters per kilogram of skin.

The examples which follow illustrate the degreasing of lamb skins carried out in accordance with the process of the invention.

Examples 1 to 5 were implemented on a pilot installation having a barrel of capacity of the order of 0.55 m³ into which 2 dozen were introduced. skins. Example 6 was implemented on an industrial-size installation having a barrel with a capacity of the order of 5 m³ into which 10 dozen skins were introduced.

EXAMPLE 1 Degreasing phase

We use lamb skins from New Zealand which are picked, skinned and drained. These skins (approximately 20 kg) have an average fat content of approximately 20% fat relative to the weight of dry leather, in the fatty areas of the skin (collar, abutment, etc.). These fats are essentially made up of interstitial fats. These skins are wet, their water content is around 60%.

These skins are introduced into the barrel. A bath of trichloro-1,1,2 trifluoro-1,2,2 ethane (7.5 1 per dozen skins, or 0.75 1 per kg of skin) is then introduced into the barrel. The barrel is rotated for 1 hour at room temperature (20 ° C). The residual bath is recovered.

Part of the solvent remains absorbed by the skins.
Recovery of 1,12,2 trichloro 1,2,2 trifluoroethane
About 1.5 liters of solvent remains absorbed per dozen of skin.

A circulation of hot air (50-55 ° C) for half an hour makes it possible to evaporate the solvent remaining on the skins; the latter is recovered after condensation. During this operation, the barrel continues to rotate. It takes about 175 joules to recover one gram of solvent. It takes about 5 times more energy to heat the skins and take into account the various heat losses.

The operation makes it possible on the one hand to rid the skins of all traces of solvent and on the other hand to recover almost all of the 1,12,2-trichloro-1,2,2-trihane ethane and to recycle it.
Separation of 1,12,2-trichloro-1,2,2-trifluoroethane and fats.

The vapor pressure of fats is very low, on the other hand 1,1,2 trichloro-1,2,2 trihane is a compound with high vapor pressure and low latent heat of vaporization (147 kJ / kg). Distillation is therefore a separation process which is both inexpensive in energy and efficient, which makes it possible to collect 1,1,2-trichloro-1,2,2-trifluoroethane and pure fat. The traces of solvent remaining in the fats can be easily removed by entrainment under a stream of air or nitrogen.

The amount of fat recovered is 600 g (i.e. 30 g / kg of skin).

Analyzes

Skin samples were taken before and after degreasing. The humidity percentage has been determined. The fat content of these skins was determined by quantitative analysis, which made it possible to calculate the degreasing efficiency. The quantitative analysis includes grinding the sample, extracting the fat with a chloroform-methanol mixture, and weighing the fat after evaporation of the solvents. The efficiency is 82%.

The chromatographic analysis of the extracted organic phase did not reveal traces of the 1,1,2-trichloro-1,2,2-trifluoroethane compound nor of course of hydrocarbons or surfactant.

The fatty acid composition of the fats extracted was determined qualitatively and quantitatively by gas chromatography. It includes for the main constituents: oleic acid, palmitic acid and stearic acid.

The acidity of these fats (free fatty acids) is 5.6% in oleic acid.

The quantity of fat extracted is comparable and even slightly higher than that obtained by the hydrocarbon-surfactant method.

The composition and the content of free fatty acids are comparable to those obtained after a degreasing of hydrocarbon-surfactant.

Furthermore, the quality of the finished product is satisfactory.

It should be noted that the extracted fats are pure and usable, subject to any suitable transformations (deacidification ...) for the subsequent stages of leather nourishment.

In addition, by comparative tests with skins degreased in a conventional manner with a hydrocarbon / surfactant, it was observed during dyeing that skins degreased according to the above conditions made it possible to save approximately 20% of dyeing. to get a given shade.

EXAMPLE 2

Degreasing and recovery phase of 1,12,2 trichloro-1,2,2 ethane

The experimental procedure is identical to that followed in Example 1, but the quantity of 1,1,2-trichloro-1,2,2-trifluoroethane is lower: 2.5 1 per dozen skins (i.e. 0.25 1 / kg of skin), the barrel rotation time is 15 minutes.

The efficiency is 76% and the quality of the finished product is satisfactory.

EXAMPLE 3

The experimental procedure is identical to that followed in Example 1, but the quantity of 1,1,2-trichloro-1,2,2-trifluoroethane is 10 1 per dozen of skin (i.e. 0.91 1 / kg of skin). In this example, the skins (22 kg) have a higher fat content, about 30% relative to the weight of dry leather, in the oily areas of the skin. Their water content is around 60%. The barrel rotation time is 2 hours.

The efficiency is 77% and the quality of the finished product is satisfactory.

The amount of fat recovered is 980 g (i.e. 45 g / kg of skin).

EXAMPLE 4

The experimental procedure is identical to that followed in Example 1, but the amount of 1,1,2-trichloro-1,2,2-trifluoroethane is 20 liters per dozen of skin (i.e. 2 1 / kg of skin) . The barrel rotation time is 30 minutes.

The efficiency is 78% and the quality of the finished product is satisfactory.

EXAMPLE 5

The experimental procedure is identical to that followed in Example 4 with regard to the degreasing and recovery phase of the 1,1,2,2-trifluoro-1,2,2 ethane trichloro absorbed on the skins, but a bath is used. which comes from a previous implementation: in this example, the bath is composed of the residual bath and 1,1,2-trichloro-1,2,2-trihane-ethane, recovered after a test carried out according to example 4.

The efficiency is 76% and the quality of the finished product is satisfactory.

Direct recycling can be done multiple times.

EXAMPLE 6

The experimental procedure is identical to that followed in Example 1, but the quantity of skin is greater: 10 dozen, or approximately 100 kg. The efficiency is 79%.

EXAMPLE 7

The experimental procedure is identical to that followed in Example 3, but we use lamb skins called "country". The skins (25 kg) have a fat content of around 25% in fatty areas. Their texture is different from that of New Zealand lambskins.

The efficiency is 75% and the quality of the finished product is satisfactory.

Claims (13)

1 / - Process for degreasing wet raw skins from rendering, consisting in putting said raw skins in their initial wet state, in the presence of a liquid bath based on fluorocarbon compound (s) for a necessary period to the separation of interstitial fats and residual surface fats. 2 / - Process for degreasing raw skins according to claim 1, wherein the treatment bath is at a temperature between 10 ° C and 35 ° C. 3 / - Process for degreasing raw skins according to one of claims 1 or 2, in which a fluorocarbon compound is chosen which is liquid at the treatment temperature and a pure bath of said compound is used. 4 / - Process for degreasing raw skins according to one of claims 1, 2 or 3, in which a bath of 1,1,2-trichloro-1,2,2-trifluoroethane is used. 5 / - Process for degreasing raw skins according to one of claims 1, 2 or 3, in which a monofluorotrichloromethane bath is used at a temperature below 23 ° C. 6 / - Method for degreasing raw skins according to one of claims 4 or 5, characterized in that the skins are placed in the presence of the bath for a period of between 15 minutes and 2 hours. 7 / - Process for degreasing raw skins according to one of claims 1, 2, 3, 4, 5 or 6, characterized in that, after treatment with the fluorocarbon bath, the skins are isolated from the liquid phase and subjecting said liquid phase to a separation treatment to recover, on the one hand, the fats and, on the other hand, the fluorocarbon compound, in particular by distillation of said compound. 8 / - Process for degreasing raw skins according to one of claims 1, 2, 3, 4, 5, 6 or 7, characterized in that, after treatment with the fluorocarbon bath, the skins are isolated from the liquid phase, the skins are heated in air to a temperature between 35 ° C and 55 ° C and the vapors are recovered by condensation. 9 / - Degreasing process for raw hides according to claim 8, characterized in that the heating of the skins is carried out by a circulation of hot air in a closed circuit. 10 / - Degreasing method according to one of the preceding claims, in which the raw skins and the bath are placed in a rotating barrel, providing a bath volume of between 0.25 and 4 liters per kilogram of skins. 11 / - Installation for degreasing skins according to one of the preceding claims, comprising a rotating barrel (1) provided with a door for introducing the skins (2) and means for draining the bath (9), characterized in that said barrel is associated with a closed loop comprising air heating means (19), circulation means (18) and a steam condenser (16). 12 / - Installation according to claim 11, wherein the rotating barrel (1) is provided with two opposite hollow shafts (2, 3), characterized in that the closed loop enters the barrel by one of the hollow shafts (2 ) by means of a rotary joint (11) and out of it by the other hollow shaft (3) by means of another rotary joint (12), the heating means (19), setting means circulating (18) and condenser (16) being located outside of said barrel. 13 / - Raw degreased skin of quality corresponding to that obtained by implementing the method according to one of claims 1 to 10, characterized in that it is free of traces of hydrophobic bodies or foreign surfactants.

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