EP0592277A1 - Foam process for making paper or non-woven - Google Patents

Abstract

According to the invention the surface-active agent employed, forming the foam, is a composition including from 40 to 100 % by weight of an alpha -olefinsulphonate containing 16 carbon atoms and from 0 to 60 % by weight of one or more alpha -olefinsulphonates containing at least 10 carbon atoms. The invention finds application especially in the papermaking industry.

Description

The invention generally relates to a process for manufacturing paper or nonwoven in a foam medium.

The invention finds application in the paper industry and more particularly in the manufacture of household and sanitary papers.

A process for manufacturing paper in a foam medium is described in European patent application No. 0,481,746 in the name of James River Corporation of Virginia.

This process consists in preparing a fiber-based manufacturing composition in the form of a foaming fiber dispersion by mixing a suspension of fibers in water with a foaming liquid comprising a surfactant, forming a fibrous sheet on a paper machine, recovering foaming liquid, recycle part of the foaming liquid recovered for the preparation of the manufacturing composition and treat another part of the foaming liquid recovered by separating the surfactant from the liquid.

More specifically, this patent application relates to a process for recovering the surfactant from the foaming liquid which has been recovered during the formation of the fibrous web, by decanting the foaming liquid, thus forming a liquid depleted in surfactant which almost no longer comprises bubbles and a foam enriched in surfactant, and by separating this foam enriched in surfactant from the liquid depleted in surfactant.

A wide range of surfactants can be used: nonionic, anionic and cationic surfactants suitable for the formation of a fibrous web and certain amphoteric surfactants.

A method using such surfactants requires heavy and costly foaming liquid treatment facilities in order to recover the surfactant, on the one hand, to reject water essentially free of surfactant satisfying the regulations relating to environmental protection and, on the other hand, to reuse the surfactant in the process.

By using α-olefin sulfonates as surfactant in the process for making paper in the foam medium described above, it can be seen that α-olefin sulfonates have a different behavior depending on the length of their carbon chain.

It has therefore been discovered that the C₁₆ α-olefin sulfonate (AOS - C16) exhibits surprising and very advantageous characteristics. This component concentrates much more easily in the foam than a conventionally used surfactant, and there is a much faster separation of the foaming liquid into a liquid depleted in surfactant and in a foam enriched in surfactant. -active.

The object of the invention is to facilitate the separation of the surfactant from the foaming liquid in the processes for the production of paper or nonwoven in a foam medium, known hitherto, while reducing the size of the installations. foaming liquid treatment and recovery of the surfactant.

The present invention relates to a process for manufacturing a sheet of paper or nonwoven in a foam medium, characterized in that the surfactant used, forming the foam, is a composition comprising from 40 to 100% by weight of an α-olefin sulfonate having 16 carbon atoms and from 0 to 60% by weight of one or more other α-olefin sulfonates having at least 10 carbon atoms.

According to an advantageous characteristic of the invention, the abovementioned composition comprises between approximately 40 and approximately 99% by weight of α-olefin sulfonate having 16 carbon atoms and between approximately 1 and approximately 60% by weight of α-olefin- sulfonate having 14 carbon atoms.

According to yet another characteristic of the invention, the gas content of the foaming liquid prepared from the above-mentioned surfactant varies in the range of about 55 to 75% by volume.

The term "foam-based" process here means a process for the manufacture of paper or nonwoven by the wet method where the water is replaced by an aqueous solution comprising a surfactant. forming a foam.

Other characteristics and advantages of the invention will appear on detailed reading of the invention which follows, with reference to the appended drawing in which:
- The single figure schematically represents a device for implementing the method according to the invention according to one embodiment, using Figure 1 simplified from European patent application No. 0.481.746.

The anionic surfactant used in the invention is provided either in the pure form of α-olefin sulfonate having 16 carbon atoms, or in the form of a mixture comprising an α-olefin sulfonate having 16 carbon atoms and one or more other α-olefin sulfonates having at least 10 carbon atoms in a proportion of 40 to 99% and 1 to 60% by weight respectively.

The various α-olefin sulfonates (AOS) that can be used are available commercially alone or as a mixture, for example from WITCO, Houston, Texas, United States and WITCO, Elbeuf, France.

The AOS - C16, an essential component according to the invention, is marketed by WITCO under the name WITCONATE AOS-16.

This component is a sodium salt and has the formula:

C₁₆ H₃₂ O₃ S.Na.

It is in the form of a light yellow liquid with a density of 1.01.

Furthermore, this C16 component does not present any risk of toxicity in effluents, at concentrations of 3 to 5 ppm, and satisfies the required biodegradability conditions.

In addition, the surfactant residual in the paper obtained according to the process according to the invention does not cause irritation of the skin for users. It has been determined that for OSA - C16 contents at most equal to 1700 mg / kg of paper, the product obtained by the process is not irritating to the skin.

The technical and economic advantages that this surfactant provides, will emerge more clearly from the description of the process using it, with reference to the figure.

This embodiment of the invention is not limiting and any other implementation of a process for manufacturing paper in a foam medium, may be envisaged.

In the process illustrated here, the paper machine 10 corresponds to a machine of the "crescent former" type described in US Pat. No. 3,326,745. The wet part forming the sheet comprises a felt 11 permeable to liquid and a fabric 12, of the type used in the manufacture of nonwoven. The fabric 12 is supported by rollers 18 and 19 which are positioned with the head roller 15 so as to converge the fabric 12 on the felt 11 at the level of the head roller at a precise angle relative to the felt 11. The felt 11 and the fabric 12 move in the same direction, at the same speed and in the direction of rotation of the head roller 15.

In this machine, the fabric 12 and the felt 11 converge on the upper surface of the head roller 15 to form a spacer or lip inside which a jet of foaming fiber dispersion from the head box 20 is projected. A multijet (two or three way) system can also be provided for the production of a laminated product.

The fabric 12 is stretched so as to pass over the felt 11 on the surface of the head roller 15, the dispersion of foaming fibers is pressed between the fabric 12 and the felt 11 forcing the liquid to pass through the fabric 12 in the Bacholle 22 where the foaming liquid is recovered. The sheet formed in the process is transported by the felt 11 to a suction press 16 where it is transferred to the cylinder 26 of a drying cylinder.

The tablecloth forming the paper is dried, then creped by the knife 27.

The paper is collected on the receiving cylinder roller 28. Part of the surfactant used to prepare the foaming liquid remains in the manufactured paper.

The foaming liquid, an aqueous solution comprising the surfactant, is prepared and stored in the silo 30. To initiate the formation of the foam, the silo 30 is supplied with water via line 31. The concentration of surfactant in the foaming liquid at the headbox is preferably in the range of about 100 to about 350 parts per million by weight.

A gas content, here in air of around 55 to 75% by volume for the foam formed from the composition of the surfactant comprising AOS - C16, is provided for the entire process. and in particular at the level of the headbox.

The paper pulp from tank 36 is fed through line 33 with the foaming liquid in the headbox 20 by means of a positive displacement pump 32.

The formation of the foam takes place at the time of the projection of the manufacturing composition coming from the headbox at the level of the lip, by the fabric 12 and the felt 11 on the upper surface of the head roller 15.

The pressure of the fabric 12 on the felt 11 and the force of the sprayed liquid cause the foaming liquid to flow through the fabric 12 in the Bacholle 22.

The forces produced by the approximation of the fabric 12 on the felt 11, the linear speed and the force of the jet on the fabric 12 produce compression and shear forces on the liquid, sufficient to cause the transport of air in the canvas and its interstices thus generating the foam containing 55 to 75% by volume of air.

The foaming liquid recovered in the Bacholle 22 is reintroduced via line 28 into the silo 30 containing the foaming liquid. And the excess foaming liquid recovered in the Bacholle 22 is brought into a liquid separation unit 45 via the line 42. The decantation carried out in the separation unit 45 leads to the recovery of a foam phase enriched in agent surfactant which is separated and recovered by line 47, from the foaming liquid introduced into the liquid separation unit 45. A liquid phase depleted in surfactant is then separated from the foam phase enriched in surfactant active and is recovered by line 56.

• un isomère d'α-oléfine-sulfonate en C₁₄ (Fraction C₁₄) ;
• un mélange isomère d'α-oléfine-sulfonate en C₁₄ et C₁₆ (Fraction C₁₄-C₁₆)
• un isomère d'α-oléfine-sulfonate en C₁₆ (Fraction C₁₆).

By using in the process as surfactant a mixture of C₁₆ α-olefin sulfonate and C₁₄ α-olefin sulfonate (Process mixture), it has been possible to determine recovery rates and enrichment factors for different components of the surfactant, at the liquid separation unit 45. To do this, we analyzed the foams and liquids containing the surfactant, by ion chromatography, a technique allowing quantitative separation several fractions including:

• a C₁₄ α-olefin sulfonate isomer (C₁₄ fraction);
• an isomeric mixture of α-olefin-sulfonate in C₁₄ and C₁₆ (Fraction C₁₄-C₁₆)
• a C₁₆ α-olefin sulfonate isomer (C₁₆ fraction).

The analyzes were performed using a DIONEX 4500 device with pre-column and 10 µ MPIC column.

Detection is carried out by conductivity after chemical removal of the eluent via a semi-permeable membrane. The acetonitrile is used as the concentration gradient. And as eluent, an ammonium hydroxide solution is preferably used.

Q2 :

quantité d'agent tensio-actif récupéré en kg/h

Q1 :

quantité d'agent tensio-actif entrant en kg/h

The recovery rate of the surfactant in the foam is defined by the formula: $$\text{Recovery rate = 100 x}\frac{\text{Q2}}{\text{Q1}}$$

Q2:

amount of surfactant recovered in kg / h

Q1:

quantity of surfactant entering in kg / h

C2 :

concentration d'agent tensio-actif récupéré en ppm

C1 :

concentration d'agent tensio-actif entrant en ppm

The surfactant enrichment factor at the foam phase is defined by the ratio: $$\text{Enrichment factor =}\frac{\text{C2}}{\text{C1}}$$

C2:

concentration of surfactant recovered in ppm

C1:

surfactant concentration entering ppm

The results are given in Table I below. TABLE I Surfactant Recovery rate% Enrichment factor Process mixing 30.6 9.2 Fraction C₁₄ 11.2 3.6 Fraction C₁₄-C₁₆ 30.4 11.3 Fraction C₁₆ 50.1 20.3

It is found that the recovery rates and enrichment factor are much higher for the C₁₆ isomer than for the C₁₄ isomer. It can therefore be thought that by using a composition rich in the C₁₆ isomer as surfactant, the size of the separation unit 45 can be reduced.

At the outlet of the separation unit 45, the foam phase enriched in AOS - C16, broken in the unit 48 is then recycled in the silo 30 for the preparation of the manufacturing composition.

The liquid phase depleted in surface-active agent at the outlet of the liquid separation unit 45 is brought via line 56 to a unit for recovering the surface-active agent.

Foaming liquid is also recovered during the draining which takes place during the manufacture of the fibrous web, at the suction press 16 or else the suction box 84, by means of a collector 82. This foaming liquid is then supplied to the surfactant recovery unit 55 by means of the line 86 which joins the line 56 for supplying foaming liquid already depleted in surfactant, coming from the liquid separation unit 45.

The unit 55 comprises specific means 60 for introducing gas or air in order to generate foam from the foaming liquid introduced into this separation unit 55.

These means or aerators 60 are of the type described in European patent application No. 0,481,746 in the name of James River Corporation of Virginia.

The foam formed is recovered by line 64 and is broken in unit 65, then the surfactant is recycled into the silo 30 by line 51.

The resulting liquid, even more depleted of surfactant, is recovered in line 68 and can be treated again by another recovery unit 69 for surfactant, connected in series with the first unit.

Two to five recovery units can thus be connected in series.

Analyzes were carried out on an industrial installation comprising five recovery units: A, B, C, D and E in series, using the same surfactant and the same method of analysis as the study carried out on the liquid separation unit 45 and described above.

The results are reported in Table II below. The recovery rate (I) in the first column relating to the recovery rate is given for a single unit A, B, C, D or E.

And the recovery rate (II) in the second column relating to the recovery rate, corresponds to the rate of the cumulative units. In other words, for example for unit C, the recovery rate (II) corresponds to the rate calculated for all units A, B and C. TABLE II Recovery unit Surfactant Recovery rate I Recovery rate II Enrichment factor AT Mixing Process 25.2 5.5 Fraction C₁₄ 12.6 2.7 Fraction C₁₄-C₁₆ 28.0 3.3 Fraction C₁₆ 41.3 5.1 B Mixing Process 26.3 44.9 14.4 Fraction C₁₄ 16.4 26.9 9.1 Fraction C₁₄-C₁₆ 29.6 49.3 16.7 Fraction C₁₆ 36.5 62.7 15.0 VS Mixing Process 24.4 58.3 24.8 Fraction C₁₄ 23.9 44.3 24.1 Fraction C₁₄-C₁₆ 37.3 68.3 20.3 Fraction C₁₆ 19.9 70.2 16.0 D Mixing Process 28.3 69.3 50.1 Fraction C₁₄ 29.4 60.7 74.1 Fraction C₁₄-C₁₆ 42.7 81.8 40.7 Fraction C₁₆ 28.0 78.5 24.8 E Mixing Process 26.7 77.5 39.0 Fraction C₁₄ 32.0 73.3 70.8 Fraction C₁₄-C₁₆ 51.2 91.1 47.5 Fraction C₁₆ 37.5 86.6 32.4

It can be seen that the recovery rates and the enrichment factors are higher for the fraction C₁₆ and the fraction C₁₄-C₁₆, especially for the first two recovery units.

We can also observe that the recovery rate of the fraction C₁₄ becomes greater from unit C and then increases more and more to unit E. Indeed, the fraction C₁₆ has been largely already recovered in the first two units.

It can also be noted that there is a recovery rate (II) of the fraction C₁₆ of about 70% at the outlet of unit C, (70.2%) while a recovery rate (II) of the fraction C₁₄, which is substantially identical, is found only at the exit from unit E (73.3%).

Comparative recovery tests were carried out on a pilot corresponding to the recovery units, using on the one hand as a surfactant a mixture of C₁₄ α-olefin sulfonate and C₁₆ α-olefin sulfonate, and on the other hand, a pure C₁₆ α-olefin sulfonate.

Under identical operating conditions, the concentration of surfactant in the liquid at the outlet of the recovery units is less than 3 ppm for the two surfactants, and the surfactant, α-olefin- C₁₆ sulfonate, recovered in the foam is 2.5 times more concentrated than the surfactant in the form of a mixture.

In addition, the amount of C₁₆ α-olefin sulfonate recovered is greater than 65% at the maximum possible on this unit using the surfactant in the form of a mixture.

Consequently, it is possible to modify the operating conditions of all the recovery units by using Cα α-olefin sulfonate as surfactant, for example by limiting the number of recovery units.

Space is thus gained in industrial installations by the elimination of recovery units for the surfactant, which gives a non-negligible advantage in the manufacture of paper in a foam medium.

The water recovered at the outlet of the recovery units has a very low concentration of AOS - C16, at most equal to around 3 ppm and can then be rejected or reused, no longer having a foaming character.

The use of AOS - C16 therefore clearly facilitates the treatment of the foaming liquid for the recovery and recycling of the surfactant.

The method according to the invention was tested on a pilot apparatus at high speed.

The machine has a "crescent former" configuration. The speed of the drying cylinder is 609.6 m / min. And the paper obtained has a grammage of approximately 30 g / m².

Pure OSA - C16 was used as the surfactant. Two types of sheets were produced. A first type of laminated sheet of heavy grammage comprises external and internal layers of different fibrous composition. A second type of lighter weight laminated sheet has a similar structure.

No operational problem relating to the use of the AOS - C16, on the pilot aircraft, was encountered.

The air content in the headbox is approximately 62% by volume throughout the test.

OSA concentrations were noted.

In the headbox, the concentration of AOS - C16 is 210 ppm for an air content of 62% by volume.

In the foaming liquid supply line, from the liquid separation unit, the concentration of AOS - C16 is 151 ppm - At the outlet of this unit, the concentration of AOS - C16 of the liquid depleted in surfactant is 88 ppm while that of the foam enriched with surfactant is 990 ppm. The AOS - C16 concentration of the liquid supplied to the surfactant recovery unit is 29 ppm and finally, the AOS - C16 concentration at the outlet of this last unit is 3.4 ppm.

A difference can be observed between the AOS - C16 concentration of the headbox and the AOS - C16 concentration of the foaming liquid at the inlet of the liquid separation unit. This difference, combined with the relatively low air content of the recycled surfactant, indicates that the foams formed from OSA - C16 decant more easily and are more easily broken than foams formed from conventional surfactants.

It can also be noted that the concentration of AOS - C16 in the foam enriched with surfactant at the outlet of the liquid separation unit is very high.

The present invention is not limited to the embodiments described above and includes all the technical equivalents within the reach of those skilled in the art.

Claims (3)

1) Process for manufacturing a sheet of paper or non-woven fabric in a foam medium, characterized in that the surfactant used, forming the foam, is a composition comprising from 40 to 100% by weight of an α-olefin sulfonate having 16 carbon atoms and from 0 to 60% by weight of one or more other α-olefin sulfonates having at least 10 carbon atoms. 2) Method according to claim 1, characterized in that the above composition comprises between about 40 and about 99% by weight of α-olefin sulfonate having 16 carbon atoms and between about 1 and about 60% by weight of α -olefin-sulfonate having 14 carbon atoms. 3) Method according to one of the preceding claims, characterized in that the gas content of the foaming liquid prepared from the above-mentioned surfactant varies in a range of about 55 to 75% by volume.

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