EP0112744B1 - Process for the accelerated neutralisation of cellulosic textile materials, and apparatus therefor - Google Patents

Abstract

There is effected an accelerated direct neutralization in-situ of the substrates which are impregnated with alkaline hydroxide which is free or fixed on the cellulose, by contact with a neutralizing fluid containing carbon dioxide in a gaseous, aqueous or combined phase, this fluid being introduced in accordance with requirements related to the quantity of alkali to be neutralized. The process may be used in the textile industry in continuous and discontinuous treatments and is adaptable to all types of textile machines employing an aqueous method.

Description

The present invention relates to an accelerated neutralization process for cellulosic textile substrates and to processing apparatuses.

The textile industry and more particularly that of the development of particular qualities of cotton in yarn, woven, knitted, pure or in mixture uses techniques known as mercerization or caustification. These operations are carried out by bringing the cellulosic material into contact with an aqueous solution of caustic soda.

German patent 120,344 describes a mercerization method during which a treatment with carbon dioxide takes place in order to eliminate the shrinking effect of the sodium hydroxide solution. The material having acquired the particular qualities sought, leaves the mercerizing or causticizing machine, impregnated with sodium hydroxide solution. Pressing roller pressing makes it possible to limit the amount of soda lye entrained. Rinses are then carried out to remove the residual alkali. However, cellulose has a great chemical affinity for soda, and the divided nature of the fibers is favorable for liquid retention by capillarity. It is therefore necessary to multiply the rinses with large volumes of water and to intercalate rinses with acidulated water intended to remove the caustic soda and to break the chemical bond soda-cellulose, called alkali-cellulose, C ₁₂ H ₂₀ 0 ₁₀ .2NaOH.

One of the conventional, discontinuous processes for removing alkali consists in practicing a succession of rinses requiring the use of repetitive loads of cold, hot, acidulated water on the same machine, for a given load of textile.

Another usual, continuous process consists in using a series of rinsing machines, in series, which can be tanks on casters; the textile scrolling continuously.

• 1ère opération, rinçage avec 1000 litres d'eau froide, durée 15 minutes;
• 2ème opération, rinçage avec 1000 litres d'eau à 60° C, durée 15 minutes ou plus
• 3ème opération, rinçage avec 1000 litres d'eau froide chargée de quelques kg d'acide acétique, durée 15 minutes;
• 4ème opération, rinçage avec 1000 litres d'eau froide, durée 15 minutes;
• 5ème opération identique à la précédente.

By way of example, a cotton jersey leaving a causticizing machine and rid of as much excess soda lye as possible by pressing between two pressure rollers requires, according to the known technique for 100 kg of dry matter, impregnated with a substantially equal weight of causticizing soda lye, at approximately 25% of NaOH caustic soda, the following series of rinses, batchwise and in the same machine:

• 1st operation, rinsing with 1000 liters of cold water, duration 15 minutes;
• 2nd operation, rinsing with 1000 liters of water at 60 ° C, duration 15 minutes or more
• 3rd operation, rinsing with 1000 liters of cold water charged with a few kg of acetic acid, duration 15 minutes;
• 4th operation, rinsing with 1000 liters of cold water, duration 15 minutes;
• 5th operation identical to the previous one.

The total duration of the operations, including the idle times, is around two hours, or more if the hot rinse water is not preheated. The continuous variant uses the same baths, in a succession of machines or enclosures.

The abundance of cold, hot or acidulated water volumes is essential to avoid any trace of residual alkali, detrimental to the quality and which can even disturb other subsequent operations, dyeing for example.

The drawbacks of the technique thus described are clearly apparent and industry practice confirms them. The discontinuous technique is costly in water, in labor for handling, by the controls and the downtime of the machine; and the continuous technique is expensive in terms of water, machine investment and floor space.

In addition, there is always a risk of alkali retention. It is therefore necessary to carry out pH checks to ensure that it is not necessary to carry out an additional rinsing operation.

Another drawback common to both methods relates to the environment. Indeed, the rinsing of 100 kg of textile according to the example above, produces 5000 liters of water polluted by about 25 kg of pure caustic soda, very incompletely neutralized by the intermediate charge of acidulated water. Indeed, for example, 3 kg of acetic acid would neutralize only 2 kg of caustic soda, and there would still be 23 kg or 92 /% in the free state. It is therefore imperative, in order to comply with the standards for discharging waste water, to provide a purification station capable of neutralizing this alkalinity, which corresponds to additional technical and economic constraints for the textile company.

Work has been undertaken to develop a process making it possible to completely eliminate the risks of residual alkalinity in textile fibers, while producing an effluent whose pH corresponds to a total absence of caustic soda. In addition, we sought to avoid large water consumption and pollution, while saving energy and reducing treatment times.

According to the proposed process, direct accelerated in-situ neutralization of cellulosic textile substrates impregnated with free or fixed alkali hydroxide on the cellulose by contact with carbon dioxide, without prior rinsing. The neutralizing medium is at a temperature between 70 and 90 ° C.

Carbon dioxide vis-à-vis alkaline cellulosic textile substrates behaves like an active gas reacting on the one hand on caustic soda NaOH, and on the other hand on the chemical bond known as alkali-cellulose. The direct reaction of carbon dioxide with free caustic soda and alkali-cellulose has the advantageous consequence of immediate in-situ neutralization, with formation in both cases of sodium hydrogen carbonate, known as sodium bicarbonate, practically neutral and harmless to the environment.

The hygroscopicity of caustic soda, its property of giving viscous solutions and its great chemical affinity for cellulose were responsible for the significant difficulties in its elimination. Since the hydrogen carbonate is a mineral salt with different physical and chemical properties, it can be eliminated much more easily. As a result, the alkalinity of impregnation of the textile is instantly transformed into sodium hydrogen carbonate which is eliminated by a brief rinsing with water and the rinsing operations in multiple baths are eliminated.

Another advantage of the present invention lies in the fact that the sodium bicarbonate, neutral salt does not disturb a possible subsequent operation of treatment of the caustified or mercerized textile, for example, bleaching or dyeing. Consequently, it is not always essential to rinse the neutralized textile load abundantly before said operation, which represents a saving of time and a saving of water.

The effluents leaving neutralization and its possible rinses are, by definition neutral or at a pH close to 8, at most 8.3, a value compatible with the standards for discharging waste water. Thus, they can be rejected directly, without further processing. In addition, an accidental discharge of water loaded with sodium hydroxide, which can therefore be at a pH of 10 to 14, well above the discharge tolerances, is not possible, which has a predominantly favorable impact on the risks. accidental pollution.

The reactions of alkali cellulose and caustic soda with carbonic acid H ₂ CO ₃ are practically instantaneous. The neutralization time therefore only depends on the temperature, the speed of injection of carbon dioxide into the neutralization enclosure and of course, the capacity of the neutralization machine, to ensure rapid contact between the reagent and the products to be neutralized.

The contact between the substrate impregnated with free alkali hydroxide or fixed on cellulose and the neutralizing fluid containing carbon dioxide can be carried out in the gas phase, in the aqueous phase or in the combined gas and aqueous phases, the order of the phases being dependent of the type of continuous or discontinuous process. The neutralizing fluid is introduced as a function of demand in relation to the quantity of alkali to be neutralized.

Carbon dioxide can be brought into contact with the cellulose substrate, impregnated with alkali hydroxide, in the gaseous state, which corresponds to the creation of a neutralizing atmosphere.

It is also possible, and even advantageous, to carry out direct neutralization of the free or fixed alkali hydroxide on the cellulose, by spraying spray onto the cellulosic textile substrate of an aqueous solution saturated with carbon dioxide or a solution aqueous charged with carbonic acid, H ₂ COg. The carbon dioxide can be sprayed simultaneously with steam.

The spraying projection onto the alkaline cellulosic substrate of a solution of carbonic acid that is supersaturated with carbon dioxide gas, therefore a gas-water-carbonic acid emulsion corresponds to an advantageous possibility of implementing the method of the invention.

The water of said solutions can be brought to a temperature of 30 to 90 ° C, preferably 70 to 80 ° C, which significantly improves the kinetics of the reaction, compared to the use of cold water. The technique of spraying an emulsion has the advantage of allowing the textile spun, therefore crushed by the pressure rollers of the mercerizing or causticizing machine, to regain volume by swelling under the action of the water emulsion - C0 ₂ - C0 ₃ H ₂ from where supply to the heart, neutralizing solution and activation of the process.

All the treatments creating a neutralizing gas atmosphere can be considered as treatments in the gas phase.

The process of accelerated neutralization of cellulosic textile substrates with carbon dioxide is applicable in the treatment of textiles by the aqueous route in the continuous and discontinuous processes, in contact apparatus.

In a continuous process, whether one has to treat a tablecloth, a knitted fabric or a thread, it is considered that the textile leaves the caustification or the mercerization by passing through a system intended to express the maximum of caustic liquor; and it is the cotton impregnated with residues of sodium liquor as well as the alkali-cellulose formed which should be neutralized.

The in-situ neutralization technique consists of spraying on the textile material in constant movement, a gaseous stream of carbon dioxide or an aqueous emulsion water-C0 ₂ -C0 ₃ H ₂ as previously described, with distribution at one or more points depending on the width of the textile sheet. The gas or emulsion supply pressure is adjusted so that the neutralizing jet passes through the material and already performs a pre-neutralization to the core.

Neutralization being implemented in a closed enclosure, it remains permanently filled with carbon dioxide, which makes it possible to obtain contact with the textile material, conducive to possible additional neutralization with carbon dioxide gas.

The consumption of carbon dioxide by the alkali permeating the fibers can imply a depression inside the treatment enclosure, also a regulation of the gas pressure ensures the supply of carbon dioxide gas, with a view to neutralization complementary.

The regulation is independent of the textile impregnation rate and the alkali concentration, it only reacts to the demand for neutralizing gas, itself dependent on the presence of caustic soda and alkali-cellulose in the material. treatment.

This regulation mode gives great safety in use and allows a saving of reagent because, in case of stopping the introduction of alkaline textile or in case of passage of a non-alkaline product, the injection of fluid neutralizer will be automatically stopped as soon as the set pressure is reached.

The very short contact time between the textile material and the neutralizing reagent, of the order of 15 to 20 seconds, is compatible with the running speeds of the material.

It has been found advantageous to follow the previous neutralization phase, called the gaseous phase, with an aqueous phase. The treatment in aqueous phase is carried out by impregnating the textile with water saturated with carbon dioxide. This impregnation with water containing carbonic acid H ₂ CO ₃ makes it possible to remove, if necessary, the last traces of the alkalinity of the textile while ensuring pre-rinsing.

The combination of a neutralizing treatment with carbon dioxide in the gas phase, with a treatment in the aqueous phase represents a technically very advantageous mode of implementation.

During the treatment in aqueous phase, the introduction of carbon dioxide into the water is controlled and adjusted so as to introduce carbon dioxide as soon as the pH of the aqueous impregnation solution returns to alkaline values. This introduction is supplemented by a supply of fresh water and a purge, the flow rates of which are calculated so as to avoid the accumulation of sodium hydrogen carbonate. In the case of using the injection of a water emulsion - C0 ₂ - C0 ₃ H ₂ , the supply of fresh water is ensured by this injection, and it is therefore not necessary to renew the water of the base serving as a pre-rinse. Excess neutral water is removed continuously in a conventional manner.

A final rinse in water is carried out for the textile, considered as finished material. This rinsing can be brief if the textile undergoes a complementary bleaching or dyeing treatment because it is only impregnated with sodium hydrogen carbonate.

All effluents leaving the continuous treatment are neutral or at maximum at pH 8.3, compatible with the standards for discharging industrial effluents.

The characteristics of direct and accelerated neutralization are applicable in batch processes, and usable in contact apparatus.

The neutralization treatment is carried out by charge; the general principles of processing being identical to those set out for the continuous system. As before, a so-called gas phase neutralization treatment is carried out with the creation of an atmosphere of carbon dioxide. Then, this first treatment is completed by neutralization in the aqueous phase by impregnation in a saturated aqueous solution of carbon dioxide, or an emulsion ea _U -C0 ₂ -CO ₃ H ₂ .

The treatment is preferably carried out in an enclosure filled with a carbon dioxide anhydride, preferably provided with a tank bottom containing dissolved carbon dioxide in which the textile is bubbled. The textile strip, the ends of which are connected to form a loop, circulates in the enclosure for neutralization, then rinsing.

The devices making it possible to implement the accelerated neutralization process for cellulosic substrates can be of a conventional type, to which are added a gas pressure detector, connected to a gas pressure regulator, in the sealed treatment enclosure in relation to a neutralizing fluid flow meter from a storage facility and means for distributing and injecting the neutralizing fluid.

However, it has been found advantageous to produce certain devices more specifically adapted to the process.

In the context of a batch neutralization device, the point of injection of the neutralizing fluid is located at the bottom of the treatment enclosure and the point of insertion of the detector in the upper half of said enclosure.

In Figure 1 of the accompanying drawing, is shown by way of example, a discontinuous textile machine.

This equipment of the discontinuous dyeing machine type consists of a sealed sealed enclosure (1) provided with a turnstile (2), with a door or with an airlock system (3) for the introduction and removal of the textile.

This dyeing machine is equipped with a device specific to neutralization with carbon dioxide which comprises a gas pressure regulator (4) which controls the arrival of the neutralizing fluid, the detector member of the regulator (5) regulates a pressure gas in the enclosure (1) by controlling the distribution of carbon dioxide from a storage (6), via the flow meter (7) and the distribution piping (8) and the point of injection (9) at the bottom of the treatment enclosure. The gas distribution via (7) and (4) is provided with a bypass (10) by which the air is purged, if necessary, while saturating the base of the vessel (11) by water, introduced by the valve (12), (used for filling or rinsing). The valve (1), calibrated a few millibars above the calibration of the pressure regulator (4) allows the product to be evacuated from the purge and serves as an anti-pressure safety device. The turnstile (2) is then started and circulates the sheet of fabric (14) both in the upper part of the enclosure (1) filled with carbon dioxide and in the foot the tank (11) water saturated with carbon dioxide.

The reaction for neutralizing sodium hydroxide in sodium hydrogen carbonate is instantaneous and its duration depends only on the capacity for introduction of carbon dioxide controlled by the pressure regulator (4); the consumption of carbon dioxide depends only on the alkaline demand provided by the fabric.

The indication of end of reaction is obtained by observation of the flow meter (7) which indicates the stopping of the circulation of carbon dioxide in the distribution circuit (8). The water at the bottom of the tank, loaded with sodium bicarbonate, can be removed without further treatment by commissioning the purge valve (15).

Application example

Through the door or through an airlock system, a load of cotton fabric is introduced, leaving a causticizing machine, impregnated with causticizing liquor, the content of which, corresponding to caustic soda and alkali-cellulose, cumulative amount is 25 kg, expressed as NaOH. The enclosure is optionally purged of its air while saturating the base with water, the valve being tared once and for all a few millibars above the setting of the gaseous pressure regulator of the enclosure. The turnstile is started up so as to circulate the sheet of fabric both in the enclosure filled with C0 ₂ gas and in the bottom of the tank saturated with C0 ₂ . The indication of end of reaction being given by the stopping of the passage of the gas flow visualized by the flow meter, a new water charge of 1,000 liters is optionally introduced for rinsing the 100 kg of neutralized tissue.

The bottom of the tank is heated to 70-80 ° C, for 10 minutes in the particular case of this example. The time required for neutralization and rinsing is maximum 20 minutes.

A consumption of C0 ₂ of 29 kg is observed, ie a utilization yield of 95%. The additional 5% of C0 ₂ corresponds to the inevitable losses due to leaks in the system.

Figure 2 of the accompanying drawing shows by way of example a continuous textile machine which includes the neutralization and rinsing installations.

This apparatus for vertical unwinding of textile consists of a sealed sealed enclosure comprising a vertical section in which the neutralizing treatment of the textile material in the gas phase is carried out, extended by a curved section in which the treatment in the aqueous phase is carried out , supplemented by the rinsing section proper and the vertical section for raising the treated fabric.

The operation of this assembly is as follows, taking the example of a sheet fabric leaving a causticizing machine, after expressing the excess sodium liquor by pressure rollers.

The upper part of the first vertical section (1) is provided with sealing means (2) such as flexible lips, the material to be treated (3) is introduced into the enclosure by a system of distributing rollers (13), the rotation speed adjusts the speed of the fabric. This first part of this vertical section (1) of the downward unwinding of the cellulosic substrate is provided with at least one series of means (14) for projecting the neutralizing fluid, arranged perpendicularly to the direction of unwinding of the textile and to the two faces thereof. ci, upstream or downstream of the distributor rollers (13). These spraying means (14) are of a conventional type, constituted for example by a series of nozzles or perforated tubes, placed opposite each side of the textile and staggered with respect to each other, so as to project an emulsion of carbon dioxide and water on the tissue with sufficient upstream pressure for the jets to pass through the tissue, without adversely affecting their effect, and allowing neutralization at the core. The pressure of the neutralizing fluid is adjusted according to the thickness of the fabric.

FIG. III shows a representation of a ramp (14) of perforated tubes arranged on either side of the fabric, supplied with emulsion by a conventional mixer-emulsifier system (23) to which the C0 ₂ pipe (15) and the hot water pipe (16) (representation by a ramp). In the particular case the temperature of around 70 ° C for the water is favorable.

After neutralization treatment by spraying-spraying at the nozzles (14), the fabric sheet approaches the middle and lower part (17) of the first vertical section, the atmosphere of which is formed by the projected excess carbon dioxide. The length of this second section is determined so as to obtain a contact time of 15 to 30 seconds. Additional neutralization can be ensured if necessary, by introduction of gaseous carbon dioxide in (15) pilot by a regulator of the type described (4) with another detector (5).

The section of the enclosure (1) is delimited, at its upper part by the entry or sealing airlock (2) and at its lower part by the water level (11), the latter being contained in the curved part (12) of the installation, water level known as the base of the tank.

The flow of C0 ₂ is automatically regulated using a pressure regulator (4) identical to that described in figure (1), the detector (5) of which is placed in the vertical part charged with gas, for example at the level indicated on Figure II.

An overpressure of a few millibars is permanently ensured by this regulation which controls the entry of C0 ₂ by the emulsion injection system C0 ₂ -ea _U -CO ₃ H ₂ . The demand for C0 ₂ is regulated by consumption due to the alkalinity of the textile. Any excess of C0 ₂ results in non-absorption by the textile and is found unused in the enclosure (1), causing an overpressure immediately detected by the regulation; it reacts by stopping the injection. The consumption of carbon dioxide is thus automatically adjusted according to the demand for the textile.

The pressure sensing member (5) controls the distribution of carbon dioxide via the flow meter (7) and the distribution pipes (10) and (8), the latter ending in (10), from the storage of C0 ₂ (6).

Neutralization safety, the optional use of which depends on the degree of alkalinity of the fabric, is ensured by an additional injection of carbon dioxide in (9) inside the curved lower section (12) of the treatment, in the base (11). This additional injection of carbon dioxide is controlled by a standard pH regulation of the base (11); this probe (18) being placed for example at the point indicated in FIG. II. This so-called security system can absorb an exceptional point of alkalinity.

The fabric after neutralization treatment leaves the curved section (12) by an optional airlock (19), having the function of additional safety, although the carbon dioxide by the rollers (20), is drawn towards the rinsing section (21) then guided by the rollers (22), the rotational speed of which, coupled with that of the rollers (20) and (13), controls the movement of the fabric.

The liquid levels are adjusted by conventional devices such as overflows (not shown), and the water flow rates are adjusted according to the criteria for elimination of the hydrogen carbonate, to avoid its accumulation.

All the effluents leaving the installation are at a pH of 8 to 8.3. The results and performances are identical to those obtained in discontinuous treatment.

In addition, a system of safety valve (24) and bypass (25) of the pressure regulator, identical to that of FIG. 1, is arranged on the treatment enclosure to allow it to be purged of air.

Claims (9)

1. Process for neutralization of cellulosic substrates impregnated with alkali hydroxide free or fixed to the cellulose, characterized in that a direct and accelerated neutralization of the said impregnated substrates in situ is realized without preceeding washes by contact with a neutralizing fluid containing carbon dioxide in gaseous, aqueous or combined phase, the neutralizing medium being at a temperature between 70 and 90°C and the regulation of the pressure during the treatment controlling the introduced quantity of the neutralizing fluid in function of the demand bound to the quantity of alkali to be neutralized.

2. Process for neutralization of cellulosic substrates impregnated with alkali hydroxide according to claim 1, characterized in that the direct neutralization in gaseous phase is carried out by spraying on the cellulosic substrate either in aqueous solution saturated with carbon dioxide or in aqueous solution loaded with carbon dioxide or an aqueous solution of carbonic acid saturated with carbon dioxide, the temperature of the water of the said solutions being preferably between 70 and 80°C.

3. Process for neutralization of cellulosic substrates impreganted with alkali hydroxide according to claim 1, characterized in that the neutralization is carried out by impregnation of the cellulosic substrate within an aqueous liquid containing the carbon dioxide dissolved, the content of which is controlled by a regulation of the pH which responds to the alkalinity by allowing injection of carbon dioxide.

4. Process for discontinuous neutralization of cellulosic substrates according to claim 1, characterized in that the cellulosic substrate runs off in an atmosphere of carbon dioxide and then is impregnated in the vat sump consisting of an aqueous liquid containing the dissolved carbon dioxide.

5. Process for continuous neutralization of cellulosic substrates impregnated with alkali hydrogide according to claim 1, characterized in that the oellulosic substrate is subjected to a treatment in gaseous phase with constant running off by spraying carbon dioxide according to claim 2, followed by a possible supplementing neutralization by gaseous carbon dioxide and then by a possible treatment in gaseous phase.

6. Apparatus for carrying out the accelerated process of neutralization of cellulosic substrates according to claim 1, characterized in that it comprises a pressure detector (5) connected with a gas pressure regulator (4) within the treatment zone (1) in relation with a throughput meter (7) for the neutralizing fluidcoming from a storage (6) and additionally means of districution (8) amid injection (9) of neutralizing fluid.

7. Apparatus for discontinuous neutralization according to claim 6, characterized in that the point of injection (9) of neutralizing fluid is situated at the bottom of the treatment zone (1) and the point of insertion of the detector (4) is the upper half of the said zone (1).

8. Apparatus for continuous neutralization according to claim 6, characterized by a tight zone comprising a vertical section (1) in which the neutralizing treatment in gaseous phase is effected, prolonged by a curved section (12) in which the treatment in aqueous phase is carried out, completed by the rinsing section (21) and the vertical section of descending of the treated substrate (26), and further in that the zone comprises at its upper extremity tightening means (2) and in the upper part of the section of the descending run of the substrate at least one series of means for spraying (14) the neutralizing fluid disposed perpendicularly relating to the running direction of the substrate and displaced against each other, that upstreamwardly or downstreamwardly from the distributor rolls (13) in the middle part of the section of the descending run of the substrate a pressure detector (5) connected with a gas pressure regulator (4) feeding the spraying means is proided, and the curved section is provided with a pH probe (18) and means for injection of carbondioxide (9) connected with a storage (6).

9. Apparatus for continuous neutralization according to claim 8, characterized in that the lower part of the vertical section of the descending run of the substrate is provided with a pressure detector (5) connected with a pressure regulator (4).

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