US3567574A

US3567574A - Composition and method for reducing foaming and soda losses in the recovery of fibrous particles from aqueous media

Info

Publication number: US3567574A
Application number: US656260A
Authority: US
Inventors: Leo D Braitberg; Donald C Roylance
Original assignee: US MOVIDYN CORP
Current assignee: UNITED STATES MOVIDYN CORP; US MOVIDYN CORP
Priority date: 1967-07-26
Filing date: 1967-07-26
Publication date: 1971-03-02
Anticipated expiration: 1988-03-02

Abstract

COMPOSITIONS AND METHODS FOR IMPROVING RECOVERY OF FIBROUS PARTICLES FROM AQUEOUS MEDIA ARE PROVIDED WHICH EMPLOY BOTH A PRIMARY HYDROPHOBIC MATERIAL, SUCH AS SILICON-COATED SILICA, AND AN ADDITIONAL HYDROPHOBIC MATERIAL, SUCH AS DIMETHYLIDIOCTADECYL AMMONIUM BENTONITE, DISPERSED IN A LOW POLARITY OIL FOR WHICH THE ADDITIONAL HYDROPHOBIC MATERIAL IS NOT A GELLANT. EVEN WITH SOLIDS CONTENTS UP TO 35% BY WEIGHT, THE COMPOSITIONS ARE PUMPABLE LIQUIDS.

D R A W I N G

Description

March 2 1971 COMPOSITION AND L. D. BRAITBERG Filed July 26, 1967 ADDITIUE common 2 v Q P 159.5. CHEMICAL RECOVERY I A 5 4 i lLF G N 5 I E C- .3 Il I 32 E I 1 G7 I a I //I g [I a I600 I700 I800 I900 2000 VISCOSITY I/V Cf'NT/PO/ 3,567,514 METHOD FOR REDUCING FOAMING AND SODA LOSSES IN THE RECOVERY OF FIBROUS PARTICLES FROM AQUEOUS MEDIA I WASH W474?! I TO SCREEN INVENTORS ATTORNEYS United States Patent 3,567,574 COMPOSITION AND METHOD FOR REDUCING FOAMING AND SODA LOSSES IN THE RE- COVERY OF FIBROUS PARTICLES FROM AQUEOUS MEDIA Leo D. Braitberg, Park Forest, Ill., and Donald C. Roylance, Potomac, Md., assignors to United States Movidyn Corporation, Chicago, Ill.

Filed July 26, 1967, Ser. No. 656,260 Int. Cl. D21c 3/28 US. Cl. 162-70 17 Claims ABSTRACT OF THE DISCLOSURE Compositions and methods for improving recovery of fibrous particles from aqueous media are provided which employ both a primary hydrophobic material, such as silicone-coated silica, and an additional hydrophobic material, such as dimethyldioctadecyl ammonium bentonite, dispersed in a low polarity oil for which the additional hydrophobic material is not a gellant. Even with solids contents up to 35% by Weight, the compositions are pumpable liquids.

This invention relates to additives for improving the recovery of suspended fibrous solids from aqueous media, to methods for producing such additives, and to improved methods employing such additives for accomplishing such recovery. The invention is particularly useful in connection with alkaline pulping processes, especially in the recovery of the pulp from the brown stock; in paper mill operations; in the hypochlorite bleaching of pulp; in the neutral sulfite semichemical pulping process; and in similar processes involving fibrous solids and aqueous suspension media.

In the production of pulp for paper and the like, cellulose fibers are freed from the natural binding materials found in wood by a cooking operation which yields an aqueous suspension of the pulp, commonly referred to as brown stock. Since the fibers have a great affinity for aqueous liquids, a significant amount of undesirable material remains on and in the fibers after the fibers have been recovered from the liquid, and it is therefore necessary to wash the fibers with an aqueous wash liquid to remove the undesirable material. The washing operation can be carried out in apparatus of various kinds, it being common practice to employ a rotary vacuum washer which includes a rotary cylindrical vacuum filter partially immersed in the liquid and operated to carry a filter cake of the pulp fibers, in the nature of a mat, upwardly out of the liquid and through a wash spray, the washed fibers then being discharged into a repulper and, typically, delivered to another such washing apparatus for further treatment.

Though such washing operations have long been employed, the industry still encounters severe problems, particularly in achieving an effective separation of the pulp fibers from the liquid in a manner such that the washing action is efficient and the apparatus can be operated at high feed rates. Such difficulties stem from the strong tendency of the aqueous liquids of the brown stock to foam, with the foam occurring both as surface foam which builds up on the surface of the liquid in the washer and as internal foam, appearing as microbubbles contained within the body of aqueous liquid. One particularly severe difiiculty caused by the foam, and particularly by internal foam, is a marked tendency for the liquid not to drain and flow freely through the washing apparatus. Other difiiculties arise because of the formation of deposits on the surfaces of the fibers, which deposits decrease the eifectiveness of the washing operation. Additionally, the kraft (or alkaline) or sulfate pulping process suffers from undue losses of soda in the mother liquid which is carried out with the fibers and also because of ionic attachment of the soda to the fibers.

Prior-art workers have found that foams, including both surface foams and internal foams, can be combatted by use of additive compositions, commonly called defoamers, comprising hydrophobic silica (e.g., silica the particles of which have been coated and reacted with a silicone oil) dispersed in a water-insoluble organic liquid. Such compositions are disclosed, for example, in US. Pats. 3,076,768, issued Feb. 5, 1963, to Francis J. Boylan, and 3,207,698, issued Sept. 21, 1965, to Raymond Liebling et al. Though defoamers of this general type have achieved marked success and are in wide commercial use, there has been a continuing need for more effective compositions capable of abating internal foam and of generally increasing the efliciency of the washing operation. Difficulties have also been encountered because the hydrophobic silica tends to settle during storage of the defoamer, so that the composition must be agitated to redisperse the silica before use.

Similar problems are encountered in other processes involving fibrous solids suspended in an aqueous medium. Thus, for example, in the usual paper mill, employing a suction box to establish the paper web on a Fourdrinier wire or the like, foams are frequently encountered which tends to cause bubbles and resulting discontinuities in the paper web.

It is accordingly an object of the invention to provide a composition effective to abate foams in aqueous liquid systems so that, for example, the liquids can be passed more quickly through processing equipment such as the brown stock washers and the like.

Another object is to provide such a composition which is particularly effective as a drain-aid additive for brown stock systems, paper mill White Water systems, and other aqueous systems containing suspended fibers or other solids from which the liquid must be separated.

A further object is to provide additive compositions of the type described which are in the form of pumpable dispersions stable against settling of the particles during prolonged storage.

Yet another object is to provide an improved method for the recovery of pulp from brown stock in alkaline pulping systems.

A still further object is to reduce significantly the soda losses presently encountered in alkaline pulping processes employing sodium sulfate.

Another object is to provide an improved method for manufacturing additive compositions of the type described.

Broadly considered, the additive compositions of the invention employ both a primary hydrophobic ingredient and at least one additional hydrophobic ingredient dispersed in a low polarity water insoluble oil. The primary hydrophobic ingredient is a finely particulate solid material, e.g., silica, having a coating of silicone reacted therewith. The additional hydrophobic ingredient is a reaction product of a solid finely particulate anionic material, e.g., bentonite, with an organic ammonium salt containing 10-22 carbon atoms, such reaction product being hydrophobic but essentially a nongellant for the low polarity oil. The composition can include a minor proportion of finely divided silica or equivalent anionic material which is free of silicone.

In method, embodiments of the invention, the additive composition is dispersed in the aqueous liquid involved, such as brown stock when the invention is employed to improve the alkaline pulping process, under such circumstances of agitation and flow that the additional hydrophobic material becomes attached to the fibrous particles to increase the rate and extent of contact between the fibrous particles and the aqueous medium.

The primary hydrophobic constituent of the composition can comprise any solid particulate material which is capable of reacting with a silicone oil to provide a physically stable, chemically bonded silicon film or coating and which is available in an effective average particle size range of 005-50 microns, advantageously 0.1-2.0 microns, the primary requirements being that the particles be of the stated size and capable of reacting with the silicone to provide the desired hydrophobic surface. By effective average particle size, we mean to include as unagglomerated individual but also that of the aggregates of ultimate particles. The solid particulate material can be silica, synthetic aluminum silicate, talc, diatomaceous earth, sodium silicate, or calcium carbonate, for example. It is particularly advantageous to employ silica prepared by reacting an aqueous solution of sodium silicate at pH 8-10 with a dilute inorganic acid so as to precipitate the silica. The particulate material can be rendered hydrophobic by spraying a polysiloxane oil onto the solid particles and then heating the coated particles at temperatures on the order of 150-300 C. for from 1 hour to hours. Though the broad class of polysiloxane oils are useful, it is particularly advantageous to employ a dimethyl polysiloxane oil having a viscosity range of 20-1000 centistokes at C. As an alternative procedure, the particles can be rendered hydrophobic by treatment with an organosilicon halide in vapor form in conventional fashion.

Oils useful in accordance with the invention are the water insoluble oils, usually paraflinic or naphthenic, which are of low polarity, have a viscosity in the range of 50-200 S.U.S. at 100 F., and have a boiling point of at least 300 F. Particularly advantageous are the oils which are predominantly of aliphatic hydrocarbons and have a dielectric constant not exceeding 2.3 at 20 C., a viscosity in the range of 70-150 S.U.S. at 100 F., and a boiling point of at least 345 F.

As the additional hydrophobic material, we can employ any hydrophobic product obtained by reacting a finely particulate solid anionic material with at least one organic ammonium salt containing 10-22 carbon atoms, so long as the hydrophobic reaction product is not a gellant for the low polarity oil. Base-exchange materials, including the base-exchange clays, and particularly the bentonites, are especially useful as the anionic solid material. Also useful are natural and synthetic zeolites, glauconite, and the cationic ion-exchange resins. In all cases, the solid anionic material employed should have an effective average particle size (using that term as hereinbefore described) of not more than 5.0 microns. We have found dimethyldioctadecyl ammonium bentonite, available commercially under the trademark Bentone 34 from National Lead Company, 111 Broadway, New York, N.Y., to be particularly advantageous. Such hydrophobic materials can be prepared in the manners described in U.S. Pat. 2,966,506, issued Dec. 27, 1960, to John W. Jordan. Though the particular hydrophobic materials referred to have long been employed as gelling agents for organic materials of moderate polarity, such as vegetable oils, turpentine, and kerosene, they are essentially nongellants for the low polarity oils hereinbefore described. Thus, for example, when dimethyldioctadecyl ammonium bentonite is dispersed in a mineral oil of the type described, the bentonite remains completely unaffected and will settle out completely, even though the dispersion is subjected to five passes through a homogenizer. Yet, when both the dimethyldioctadecyl ammonium bentonite and the hydrophobic silica are dispersed in the mineral oil, and the dispersion suitably homogenized, the composition is adequately stable and can be stored for periods of several months without undue settling of the par- Z terial, such as dimethyldioctadecyl ammonium bentothe 'size not only of such ultimat'e pa'rticles'asare present nite, combining to provide a total solide content which,

correspondingly, is 35-51% by weight of the total composition, so long as the final composition does not have a viscosity substantially higher than 3000 centipoises. Compositions containing relatively high proportions of hydrophobic silica plus smaller proportions of dimethyldioctadecyl ammonium bentonite and still having a viscosity not exceeding 3000 centipoises can be prepared with relative ease. Thus, satisfactory compositions in which the hydrophobic silica constitutes 2.5-20% by weight of the total composition and the dimethyldioctadecyl ammonium bentonite constitutes 01-10% of the total composition weight can be made with the hydrophobic silicas now commonly employed, and with the initial viscosity of the dispersion at fairly high levels, e.g., 1200- 1650 centipoises. By initial viscosity, we mean the viscosity of the composition at a time when it has first been mixed and subjected to only a smaller homogenizing action, such as one pass through a homogenizer, so that, though extensive homogenization has not occurred, the particles will no longer settle out immediately on standing. However, to prepare compositions of proper viscosity with the primary and additional hydrophobic materials totalling more than 20% of the composition weight, and particularly with the additional hydrophobic material then amounting to 10-32.5% of the composition Weight, requires that there be substantially no uncoated silica present and that the initial viscosity of the dispersion not exceed 1200 centipoises. By substantially no uncoated silica, we mean that the amount of uncoated silica present is equal to 0-0.5 of the weight of hydrophobic silica employed. In such cases, the relatively higher solids contents, up to 35% of the composition weight, and the relatively higher weight of the additional hydrophobic material, such as dimethyldioctadecyl ammonium bentonite, can be employed without driving the final viscosity of the composition significantly above 3000 centipoises. Excellent results have been obtained in pulp and paper mill applications with compositions wherein the additional hydrophobic material, e.g., dimethyldioctadecyl ammonium bentonite, is employed in an amount which is small as compared to the amount of primary hydrophobic material employed. In other cases, it is advantageous to increase the proportion of the additional hydrophobic material and the amount of this constituent can exceed that of the primary hydrophobic material, so long as at least 2.5% by weight of the latter is used.

The compositions can be prepared by initially dispersing the hydrophobic material in the oil, homogenizing the dispersion, then introducing the additional hydrophobic material or materials, and mixing or again homogenizing. Alternatively, the hydrophobic silica and the additional hydrophobic material can both be dispersed in the oil, and this initial dispersion then suitably homogenized.

In certain embodiments of the invention, the presence of a relatively small proportion of finely particulate solid anionic material, such as silica, which is free of the silicone coating which characterizes the primary hydrophobic ingredient, results in a unique chemical interaction, apparently involving a transfer of a portion of the amine content of the additional hydrophobic material.

When dimethyldioctadecyl ammonium bentonite alone is dispersed in a low polarity oil of the type described, 110 significant increase in viscosity is observed, even after extensive homogenization involving a large amount of Work under conditions of high shear. However, if hydrophobic silica is dispersed in the low polarity oil to provide a composition containing 20% by weight hydrophobic silica, an amount of uncoated silica equal to 0.1- of the weight of the hydrophobic silica is added and dispersed, and an amount of the additional hydrophobic material, such as dimethyldioctadecyl ammonium bentonite, equal to 0.1l0.0% of the total composition weight, is also added and the composition then homogenized under conditions of high shear, so that good intermolecular contact is achieved between the uncoated silica and the additional hydrophobic ingredient, a significant increase in viscosity occurs, indicating occurrence of a chemical change which is probably a shift of a part of the amine radical content of the additional hydrophobic ingredient to the uncoated silica. If the proportion of uncoated silica, for example, employed does not exceed 15% of the weight of the main hydrophobic ingredient, the viscosity of the final composition remains sufficiently low for the composition to be pumpable.

The following examples are illustrative of compositions in accordance with the invention, and their preparations.

EXAMPLE 1 Hydrophobic silica is prepared by coating 15.25% by weight dimethyl polysiloxane oil of a viscosity of 50 centistokes onto 84.75% by weight precipitated silica (QUSO G30, made and sold by Philadelphia Quartz Company, Philadelphia, Pa. having an ultimate particle size of 0.012 micron, and effective average particle size of 1.7 microns, and a pH of 8.2, and then heating the mixture at approximately 200 C. for 5 hours.

The hydrophobic silica so obtained is dispersed in a solvent processed, dewaxed, paraffinic mineral oil having a viscosity of 105.5 SUS at 100 F., a specific gravity of 0.865 at 60 F, a dielectric constant of 2.2 at C., a flash point of 400 F., and a pour point of 5 F., to provide a composition consisting of 89.5% by weight oil and 10.5% by weight of the hydrophobic silica. The dispersion is homogenized in a sonic homogenizer, employing four passes through the homogenizer at an inlet temperature of 135 F., and a pressure of approximately 350500 lbs. per sq. in.

Dimethyldioctadecyl ammonium bentonite (Bentone 34, made and sold by National Lead Company, New York, NY.) is then added to the homogenized dispersion in an amount equal to 0.25% of the total composition weight. The composition is mixed for 1.5 hrs. in a tank with good agitation and then subjected to four passes through the sonic homogenizer, commencing with an inlet temperature of 90 F. for the first pass, the temperature increasing with each pass, due to the physical work in the homogenizer, until a temperature on the order of 105 F. is reached on the fourth pass. The temperature in the mixing tank, prior to homogenizing, can be 80150 E, higher temperatures reducing the required number of passes through the homogenizer. The dispersion is homogenized until no significant increase in viscosity results from successive passes. The final viscosity obtained is 6001800 centipoises, determined with an LVT Brookfield viscometer using a No. 2 spindle at 12 rpm, at C.

The finished composition is a pumpable liquid which is stable in the sense that undue settling of the hydrophobic silica does not occur during storage on the order of several months. Being surfactant free, the composition does not spread on water, but can be dispersed effectively as hereinafter described.

EXAMPLE 2 The procedure of Example 1 is repeated, save that the dimethyldioctadecyl ammonium bentonite is added to the homogenized dispersion in an amount equal to 2.5% by weight of the total composition. The final composition is closely similar in all respects to that of Example 1.

EXAMPLE 3 A dispersion of hydrophobic silica in oil was prepared as in Example 1, and the dimethyldioctadecyl ammonium bentonite was added in an amount such that the composition contained by Weight of the silica-oil dispersion and 5% by weight of the dimethyldioctadecyl ammonium bentonite. The composition was subjected to five passes in a conventional hand-operated homogenizer, the initial temperature being approximately 25 C. and the initial viscosity being 1570 centipoises, determined as in Example 1. The final viscosity was 1980 centipoises, determined in the same fashion. The final composition was similar to that obtained in Example 1, save for the higher viscosity.

EXAMPLE 4 The procedure of Example 3 was followed, save that the dimethyldioctadecyl ammonium bentonite amounted to 10% of the weight of the final composition. The initial viscosity was 1510 centipoises, and the viscosity after the last pass through the hand homogenizer was 2120 centipoises, viscosities again being determined as in Example 1.

EXAMPLE 5 A dispersion of hydrophobic silica in parafiinic mineral oil was prepared as described in Example 1. To four separate samples of this dispersion, amounts of the same precipitated silica employed in Example 1, but without the silicone coating, were added to provide uncoated silica contents of 2.5%, 5.0%, 10%, and 15%, respectively, based on the weight of silicone-coated silica present. Dimethyldioctadecyl ammonium bentonite was then added to each sample in an amount equal to 0.25% of the total sample Weight. The samples were then homogenized by subjecting them to 5 passes through a conventional hand-operated homogenizer. The final product in each case was similar to that obtained in Example 1, save that the viscosity increased with the increasing proportion of uncoated silica.

When the usually employed silicone-coated silica materials are employed, containing an amount of uncoated silica substantially in excess of 0.5% of the weight of the silicone-coated silica, compositions of relatively high solids content, and a relatively high proportion of dimethyldioctadecyl ammonium bentonite, can be adequately homogenized, yet have sufficiently low end viscosities to be easily pumpable, as will be apparent from the graph in FIG. 1 of the accompanying drawings. In FIG. 1, each curve shows the increase in viscosity of the composition, as homogenization proceeds, for a different composition pre pared as in Example 3, curve A being for a control composition consisting of the hydrophobic silica and oil without the dimethyldioctadecyl ammonium bentonite, and curves B-G being for like compositions containing 0.25%, 0.5%, 1.0%, 2.0%, 5.0% and 10.0%, respectively, of the dimethyldioctadecyl ammonium bentonite. Curves B-E are all closely similar, with only curves F and G showing relatively wide increases in viscosity, the viscosity for even curve G still being completely acceptable at the end of the fifth pass through the hand homogenizer.

The relatively lower viscosities indicated by curves BE,

for compositions containing dimethyldioctadecyl ammonium bentonite in the range of 0.25-2.0% by weight, make these compositions particularly advantageous since they are more easily pumped and droplets of the composition break up more readily in contact with aqueous media at moderate shear.

In employing the additive compositions in accordance with the invention to improve the recovery of suspended fibrous particles from aqueous media, it is necessary to disperse the additive composition in the aqueous media in an amount equal to 1.5-50 parts per million, based on weight of the material being treated, and in such fashion that the suspended particles and the additive composition are both uniformly distributed in the aqueous medium well prior to recovery of the particles. Particularly advantageous results are obtained when the additive composition is employed in an amount equal to 4-10 parts per million, based on the material being treated.

Since the additive compositions contain no surfactant or spreading agent, particular attention must be given to accomplishing thorough and uniform dispersion of the composition in the aqueous liquid. It is particularly advantageous to employ an atomizing device as the means by which the additive composition is introduced. Thus, for example, the composition can be added by means of a conventional air operated aspirating atomizer, such devices being effective to break the composition up into discrete droplets of very small size, with the droplets being projected into the air above the body of aqueous liquid and falling into the liquid in such fashion as to be readily and thoroughly dispersed. In brown stock washing systems employing repulpers, it is advantageous to supply the additive composition to the first repulper in the system, relying on the operation of the repulper to disperse the composition. Where the brown stock washing system employs a series of rotary vacuum washers to which aqueous liquid is supplied in part as a spray or shower and the liquid is recycled in countercurrent relation to the brown stock flow, the additive composition can be introduced in the spray or shower of the first washer or, advantageously, of a washer subsequent to the first washer in the series. When the aqueous medium involved has a high native content of soaps of dispersing materials, it is frequently practical to supply the additive composition directly to the surface of the liquid without relying on mechanical dispersing operations such as atomization or vigorous spraying.

When the invention is employed to combat the adverse effects of foams in a paper mill, the additive composition is usually best added at the fan pump, though addition at the machine chest, the head box, or the wire pit is also effective. The additive composition is employed in an amount equal to 0.25-5 lbs. per ton of dry paper product.

FIG. 2 illustrates a three-stage brown stock washing system forming part of a conventional alkaline pulping plant and employing identical conventional rotary vacuum washers 1, 2 and 3. Pulp stock from the blow tank (not shown) is supplied continuously to the vat of washer 1, strong liquor from that washer, having been delivered to tank 4, being metered continuously into the stock via conduit 5. Fibers in the liquid in the vat of washer I collect in the form of a mat on the cylindrical wire filter drum 6 of washer 1, the mat of fibers being carried continuously beneath the spray discharged from spray device 7. Aqueous liquor from within drum 6 is delivered to tank 4 via conduit 8. The mat of fibers on drum 6 is removed by a doctor roller 9 and delivered to the repulper 10, as indicated by line 11. The repulped material is flowed to the vat of Washer 2, via conduit 12. In washer 2, the fibers are collected as a mat on filter drum 13, the mat being carried beneath the spray discharged by spray device 14, the fibers ultimately being removed by doctor roller 15 and delivered to the second repulper 16. Aqueous liquor from within drum 13 is delivered via conduit 17 to weak liquor storage tank 18. Liquor is pumped from tank 18 via conduit 19 for supply to the spray device 7 of washer 1 and for delivery, via conduit 20, to repulper 10.

The repulped material from the second repulper 16 is delivered to the vat of washer 3. In washer 3, the fibers collect as a mat on filter drum 21, and rotation of the drum carries the mat under spray device 22 and to doctor roller 23, the latter removing the collected fibers for delivery to the screen room. Spray device 22 is supplied with fresh Water via conduit 24. Aqueous liquor from within drum 21 is delivered to storage tank 25, via conduit 26, and is pumped from that tank to spray device 14, via conduit 27, and to the second repulper 16, via conduit 28.

The additive composition of the invention can be introduced into the system of FIG. 2 in various Ways. In many applications, the additive composition is advantageously metered into the first repulper 10, as indicated by line 29, the action of the repulper serving to accomplish initial distribution of the additive composition through the aqueous liquid so that a major portion of the task of dispersing the composition has already been accomplished by the time the feed enters the vat of washer 2. In such cases, a large proportion of the additive composition finds its way to washer 1 via conduit 17, tank 18, and recycle conduit 19. In other cases, the additive composition can be metered into the spray device 14 as indicated by line 30, so as to be initially distributed in the liquid by action of the spray device. When this is done, a significant portion of the additive composition passes through filter drum 13 and thence via conduit 17 to tank 18 so as to be recycled to the first washer.

Systems of the type illustrated in FIG. 2 frequently present severe foaming problems at the surface of the liquid in the vat of the first Washer, and in such cases, it is advantageous to have the composition present and thoroughly dispersed in the liquid at the first washer. To accomplish this, the additive composition can be delivered directly to the vat of washer 1, as indicated by line 31, FIG. 2, and atomized above the surface of the liquid by means of an air operated aspirating atomizer 32, as seen in FIG. 3. Here, the atomizer discharges the additive composition toward the surface of the brown stock liquid, the discharge being in the form of extremely fine droplets so that dispersion of the additive composition occurs readily in the aqueous liquid of the brown stock even when there is only moderate agitation. The atomizer 32 can be of any suitable conventional construction, embodying a feed duct 33 terminating within a hollow body 34 which defines a duct or ducts for conducting air around and past the tip of the feed duct at highvelocity so that the air and additive liquid are discharged through a downwardly directed aperture 35. Advantageously, a plurality of the atomizers 32 are employed, spaced apart horizontally, so that the atomized additive composition is distributed substantially uniformly over the entire surface 36 of the brown stock flowing into the washer vat. Alternatively, the additive composition can be added via the spray 7 for the first washer.

It will be understood that the system shown in FIG. 2 is illustrative and that, for example, a series of more than three of the rotary vacuum washers can be employed.

Employed in the manner described, the additive compositions of the invention function both as defoamers and as improvers for the overall washing operation, so that a more effective and economical recovery of the fibers is achieved. Though the precise reason or reasons for the improved effectiveness of the compositions is not fully understood, it appears that success of the compositions stems from the dual ability of the dimethyldioctadecyl ammonium bentonite to (1) act at the interfaces of the microbubbles of internal foam to introduce a strain effective to cause the bubbles to rupture, with the ruptured microbubbles combining into bubbles too large to exist as internal foam, and (2) adhering to the surfaces of the fibers, act to increase the rate of penetration of the aqueous liquid into the fibers so as to combat the formation of barrier films on the fibers and assure not only that the fibers will be better washed but also that less of the aqueous liquid will be carried out of the system with the recovered fibers. In general, use of the additive compositions in the manner described achieves higher stock feed rates, lower liquid levels in the various vessels, a marked reduction in problems normally arising from foam, and a distinctly lower soda loss when the invention is applied to alkaline pulping systems.

When the invention is practiced in connection with paper mills subject to foam difiEiculties, a marked decrease in rejected paper is achieved, the paper product being more uniform overall and having a more uniform thickness.

The following examples illustrate method embodiments of the invention.

EXAMPLE 6 Working in a commercial alkaline pulp mill to improve the brown stock washing operation, comparative runs were made with the additive composition of Example 1, on the one hand, and with a control composition prepared in accordance with Example 1 but omitting the dimethyldioctadecyl ammonium bentonite. In both runs, the brown stock feed rate was initially 1500 gal. per min., with 750 gal. per min. of fresh wash water. The additive composition Was metered into the first repulper at a rate of 50 cc. per min. in both runs.

Distinctly less foam was encountered during the run employing the additive composition of Example 1, vat levels throughout the system being distinctly lower than for the control run. Thus, for example, the level in the vat of the third washer was 3.1 ft. during the control run and only 2.2 ft. during the run with the additive composition of Example 1. While the 1500 gal. per min. stock feed rate was the best which could be achieved during the control run, the stock feed rate was increased to 1900 gal. per min. for the run with the dimethyldioctadecyl ammonium bentonite-containing composition. Surface foam was particularly troublesome at the second washer in the control run, the foam amounting to 3-6". This foam disappeared entirely when the composition in accordance with Example 1 was employed.

EXAMPLE 7 Again working in a full scale commercial alkaline pulp mill to improve the brown stock washing operation, the additive composition of Example 1 was compared with a commercially available defoamer composition containing an oil and hydrophobic silica, with primary emphasis in the comparison being placed on soda loss. In this case, the commercially available defoamer was the product marketed by Drew Chemical Corporation, New York, N.Y., under the designation 913BL. In the run employing the commercially available defoamer, the defoamer was sup plied to the system at a rate maintained in the range of 125-170 cc. per min. and the soda loss was 20-30 lbs. per ton of pulp processed. When the composition of Ex ample l was employed at the same feed rate, the soda loss fell to -25 lbs. per ton.

EXAMPLE 8 In a full scale commercial alkaline pulp mill, the com position of Example 1 was compared with a defoamer composition marketed by Hercules, Inc., Wilmington, Del., identified as Hercules 1052, and comprising an oil, hydrophobic silica and a surfactant. In both runs, the system was monitored for foaming difficulties, and the soda loss was determined conventionally by measuring the electrical conductivity of a 100 g. washed pulp sample in 750 ml. of hot distilled Water. The Hercules defoamer was metered into the second washer at the rate of 75 cc. per min. For all stock feed rates, it was found that the composition of Example 1 accomplished the same defoaming action when metered into the second washer at a rate less than that for the Hercules defoamer. The conductivity value for pulp samples from the run with the Hercules defoamer was 1800 mohs. With the additive composition according to Example 1, metered into the washer at a rate of 60 cc. per minute, conductivity values of test samples of the Washed pulp were in the range of 1200-1400 mohs., indicating a markedly smaller carryover of soda with the pulp fibers.

EXAMPLE 9 Tests were carried out in a full scale commercial alkaline pulp mill to compare the effectiveness of the compo sitions of Examples 1-3. The pulp mill involved had a designed maximum capacity of 300 tons of pulp per day. The tests were conducted in sequence, under essentially identical conditions, with a brown stock feed rate of 1400 gal. per min., providing a yield of 500 tons of pulp per day. The additive compositions were introduced to the first repulper, each at the rate of 65 cc. per min., and the runs were monitored by observing the vat level at the second washer, a level of 3.5 ft. having been stated as satisfactory for the high pulp production rate involved. For the run with the composition of Example 1, containing 0.25% by weight of the additional hydrophobic ingredient, the vat level was observed to be in the range of 3.0-3.4 ft. With the composition of Example 2, wherein the additional hydrophobic ingredient amounted to 2.5% by weight, the observed vat level was 2.8-3.2 ft. In the final run, with the composition of Example 3 containing 5% by weight of the additional hydrophobic ingredient, the vat level was observed to be in the range of 3.0-3.3 ft.

EXAMPLE 10 The additive composition of Example 1 was used very effectively to combat foam on a Fourdrinier paper machine producing unbleached kraft paper. Prior to use of the additive composition, the foam caused overflow at the wire pit and other places, and a nonuniform sheet was produced as a result of dispersed air in the furnish. The addition of the composition of Example 1 at the rate of 0.5 lb. per ton of dry paper markedly reduced the foam in the wire pit and improved the uniformity of the sheet as to its dimensional and strength characteristics.

The following example illustrates the manner in which additive compositions according to the invention can be prepared for applications requiring an especially high solids content.

EXAMPLE 11 Fifteen parts by weight of a silicone-coated silica, prepared generally as in Example 1 but with more rigorous coating and more extended heating so as to contain less than 0.5% by weight uncoated silica, and 15 parts by weight of dimethyldioctadecyl ammonium bentonite are mixed with 70 parts by weight of the mineral oil described in Example 1. The resulting composition is subjected to one pass through a hand homogenizer. The initial dispersion so obtained exhibits no significant immediate settling of particles on standing, and has a viscosity of 1100- 1170 centipoises, determined with an LVT Brookfield viscometer in the manner described in Example 1. The composition is subjected to 4 additional passes through the hand homogenizer. The end product is a relatively thick pumpable liquid, tending to be thixotropic, having a viscosity of 2930-2950 centipoises, determined with an LVT Brookfield viscometer as described in Example 1.

We claim:

1. An additive composition, effective as a defoamer and as an aid in the recovery of particles from an aque ous medium, comprising:

a low polarity water insoluble oil having a viscosity of 50-200 S.U.S. at F. and a boiling point of at least 300 F.;

a primary hydrophobic constituent; and

an additional hydrophobic constituent,

said primary and additional hydrophobic constituents being uniformly dispersed in said oil;

said primary hydrophobic constituent being a finely particulate solid material having a silicone coating reacted therewith and an elfective particle size of 0.05-5 microns;

said additional hydrophobic constituent being a reaction product of a finely particulate solid anionic baseexchange clay and at least one organic ammonium salt containing at least 10 carbon atoms,

said additional hydrophobic constituent being essentially a non-gellant for said oil;

said oil constituting 6594.9% by weight of the total composition, said primary hydrophobic constituent and said additional hydrophobic constituent being present in amounts totalling 51-35% of the total weight of the composition, with the amounts of said hydrophobic constituents being not less than 2.5% and 0.1%, respectively, based on the total composition weight;

the composition being in the form of a homogeneous,

stable, pumpable liquid.

2. A composition according to claim 1, wherein:

said additional hydrophobic constituent is dimethyldioctadecyl ammonium bentonite.

""3; A composition according to claim 2, wherein:

said oil predominantly comprises aliphatic hydrocarbons and has a dielectric constant not exceeding 2.3 at 20 C., a viscosity of 70-150 S.U.S. at 100 F., and a boiling point of at least 345 F.

4. A composition according to claim 1, wherein:

the solid material of said primary hydrophobic constituent is silica and said primary hydrophobic constituent has an etlective average particle size of 0.1-2.0 microns; and

the solid anionic material of said additional hydrophobic material has an effective average particle size not exceeding 5 microns.

5. A composition according to claim 1, wherein:

said additional hydrophobic material is dimethyldioctadecyl ammonium bentonite and is present in an amount smaller than the amount of said primary hydrophobic material.

6. A composition according to claim 1, wherein:

said primary hydrophobic material is silicone-coated silica containing substantially no uncoated silica;

the weights of said primary and additional hydrophobic materials total at least of the weight of the composition; and

the composition has a viscosity not exceeding 3000 centipoises as determined with an LVT Brookfield viscometer at C. using a No. 2 spindle at 12 r.p.m.

7. The method of producing a composition which is etfective as a defoamer and as an aid in the recovery of particles from an aqueous medium, comprising:

dispersing a primary hydrophobic constituent and at least one additional hydrophobic constituent in a low polarity water insoluble oil having a vicosity of 2000 S.U.S. at 100 F. and a boiling point of at least 300 F.,

said primary hydrophobic constituent being a finely particulate solid material having a silicone coating reacted therewith and an effective particle size of 0.05-5 microns, said additional hydrophobic constituent being a reaction product of a finely particulate solid anionic base-exchange clay and at least one organic ammonium salt containing at least 10 carbon atoms, said reaction product having an etfective average particle size not exceeding 5 microns and being a nongellant for said oil; said oil also containing an amount of an uncoated finely particulate solid anionic material having an effective average particle size of 0.05-5 microns; and homogenizing the resulting composition under conditions of high shear to bring said uncoated finely particulate material into good intermolecular contact with said additional hydrophobic material; said oil constituting 70-94.9% by weight of the total composition, the amount of said primary hydrophobic constituent being about 520% of the weight of the total composition, the amount of said uncoated particulate material being equal to 01-15% of the weight of said primary hydrophobic material, and the amount of said additional hydrophobic constituent Cir 12 being about 01-10% by weight of the total composition; the homogenized composition being a stable, pumpable liquid having a viscosity not exceeding 2500 centipoises as determined with an LVT Brookfield viscometer using a No. 2 spindle at 12 r.p.m. at 25 C. 8. A method according to claim 7, wherein: said uncoated particulate material is silica; and said additional hydrophobic material is dimethyldioctadecyl ammonium bentonite. 9. A method for improving the separation of fibrous particles from an aqueous liquid medium comprising:

uniformly dispersing in the aqueous medium an additive composition comprising a primary hydrophobic constituent and at least one additional hydrophobic constituent both dispersed in a low polarity water insoluble oil,

said primary hydrophobic constituent being a finely particulate solid material having a coating of silicone reacted therewith and an effective particle size of 0.05-5 microns, said additional hydrophobic constituent being a reaction product of a finely particulate solid anionic base-exchange clay and at least one organic ammonium salt containing at least 10 carbon atoms, said reaction product being highly hydrophobic but essentially a nongellant for said oil, said oil constituting 6594.9% by weight of the total additive composition, said primary hydrophobic constituent and said additional hydrophobic material being present in amounts totalling 5.135% of the total weight of the additive composition with the amounts of said hydrophobic constituents being not less than 2.5 and 0.1% respectively, based on the total weight of the additive composition, said additive composition being incorporated in the aqueous medium at the rate of 15-50 parts per million based on the total weight of the aqueous medium and its solids content, agitating the aqueous medium to assure intimate contact between said additional hydrophobic constituent and the fibrous particles, and separating the fibrous particles from the aqueous medium.

10. A method according to claim 9, wherein: the solid material of said primary hydrophobic constituent is silica and said constituent has an effective average particle size of 0.1-2.0 microns; said additional hydrophobic constituent is dimethyldioctadecyl ammonium bentonite; and said oil predominantly comprises aliphatic hydrocarbons and has a dielectric constant not exceeding 2.3 at

20 C. p 11. In the recovery of pulp from brown stock by passing the brown stock through a series of washers each including a vacuum filter arranged to separate the pulp fibers from the brown stock in the form of a mat and to pass the mat of fibers through a spray of aqueous wash liquid, the recovered and washed fibers from one washer being repulped in a repulper and delivered to the next successive washer, and liquid from the downstream washers in the series being recycled to at least the wash liquid sprays of washers earlier in the series, the improvement comprising:

incorporating in the brown stock a composition comprising:

a low polarity water insoluble oil having a viscosity of 50-200 S.U.S. at F., and a boiling point of at least 300 F., a primary hydrophobic constituent consisting of a finely particulate solid material having a coating 13v of silicone reacted therewith and an effective particle size of 005- microns, an additional hydrophobic constituent obtained by reaction of a finely particulate solid anionic base-exchange clay with at least one organic ammonium salt containing at least carbon atoms, said additional hydrophobic constituent being a nongellant for said oil, said oil constituting 6594.9% by weight of the total composition, said primary hydrophobic constituent and said additional hydrophobic constituent being present in amounts totalling 5.1- 35% of the total weight of said composition with the amounts of said primary hydrophobic constituent and said additional hydrophobic constituent being not less than 2.5% and 0.1% respectively, based on the total composition weight, said primary hydrophobic constituent and said additional hydrophobic constituent being uniformly dispersed in said oil and said composition having a viscosity not exceeding 2500 centipoises as determined at 25 C. by an LVT Brookfield viscometer using a No. 2 spindle at 12 r.p.m., said composition being employed in an amount equal to 1.5-50 parts per million, based on the weight of the brown stock, said composition at least minimizing internal and external foam in the liquid in the washers of the series, and said additional hydrophobic constituent being retained on the surfaces of the recovered fibers and being effective to increase the rate at which the wash liquid can penetrate the fibers. 12. A method according to claim 11, wherein: said primary hydrophobic constituent is hydrophobic silica having an effective average particle size of 0.12.0 microns;

said additional hydrophobic constituent is dimethyldioctadecyl ammonium bentonite; and

said oil predominantly comprises aliphatic hydrocarbons and has a dielectric constant not exceeding 2.3 at 20 C.

5 13. A method according to claim 12, wherein:

the amount of said dimethyldioctadecyl ammonium bentonite is equal to 0.l73% of the total weight of said composition.

10 14. A method according to claim 13, wherein:

said composition is incorporated in the brown stock in an amount equal to 415 parts per million, on a weight basis.

15. A method according to claim 11, wherein:

15 said composition is introduced into one of the washers by atomizing the composition above the surface of the liquid in the washer.

16. A method according to claim 11, wherein: said composition is introduced into the repulper which delivers to the second washer in the series.

17. A method according to claim 11, wherein: said composition is introduced with the wash liquid supplied to a washer other than the first washer in the series.

References Cited UNITED STATES PATENTS 2,702,793 2/1955 Smith 25232l 3,207,698 8/1965 Liebung 23182 3,408,306 10/1968 Boylan 252-321 3,445,385 5/ 1969 Vartanian 252-28 S. LEON BASHORE, Primary Examiner R. H. ANDERSON, Assistant Examiner 35 US. Cl. X.R.