US3839226A

US3839226A - Highly absorbent, low bulk density alkali metal sodium silicates

Info

Publication number: US3839226A
Application number: US00355500A
Authority: US
Inventors: P Yates
Original assignee: EI Du Pont de Nemours and Co
Current assignee: DU PONT AND POWER SILICATES Inc A CORP OF; NEW SOUTH WALES Ltd
Priority date: 1973-04-30
Filing date: 1973-04-30
Publication date: 1974-10-01
Anticipated expiration: 1991-10-01
Also published as: CA1023918A

Abstract

High surface area, low bulk density, highly absorbent powders of amorphous, hydrous, water soluble alkali metal silicate particles of very small size having a unique microfibrous structure and an unusually high degree of internal porosity are provided by a process in which a concentrated solution of alkali metal silicate in water is contacted with a water miscible lower molecular weight alcohol at a weight ratio of alcohol to aqueous silicate solution of at least 1:1 with vigorous agitation. The precipitated silicate is separated from the supernatant, washed and dried.

Description

United States Patent [1 1 Yates [451 Oct. 1, 1974 HIGHLY ABSORBENT, LOW BULK DENSITY ALKALI METAL SODIUM SILICATES [75] Inventor: Paul C. Yates, Talleyville, Del.

[73] Assignee: E. I. du Pont de Nemours and Company, Wilmington, Del.

22 Filed: Apr. 30, 1973 21 Appl.No.:355,500

3,201,196 8/1965 Gier 423/332 X 3,418,357 12/1968 Bjornson et al..... 260/4653 3,494,876 2/1970 Bjornson et al 252/454 3,755,183 8/1973 Fahn et al 252/454 X Primary Examiner-Daniel E. Wyman Assistant ExaminerPaul F. Shaver 5 7] ABSTRACT High surface area, low bulk density, highly absorbent powders of amorphous, hydrous, water soluble alkali metal silicate particles of very small size having a unique microfibrous structure and an unusually high degree of internal porosity are provided by a process in which a concentrated solution of alkali metal silicate in water is contacted with a water miscible lower molecular weight alcohol at a weight ratio of alcohol to aqueous silicate solution of at least 1:1 with vigorous agitation. The precipitated silicate is separated from the supernatant, washed and dried.

12 Claims, No Drawings HIGHLY ABSORBENT, LOW BULK DENSITY ALKALI METAL SODIUM SILICATES BACKGROUND OF THE INVENTION As people concentrate into highly industrialized, heavily populated regions, serious problems of water and air pollution have arisen. A contributing factor to such pollution has been the buildup of phosphate nutrients in rivers and lakes, leading to an excessive growth of algae. The dying and decaying algae have depleted the oxygen content of the rivers and lead to fish-kills and a general inability of the rivers to sustain sufficient aquatic life to purify themselves. As aconsequence, a number of states, cities, and counties have passed legislation limiting or banning the use of phosphates in household detergents. This, in turn, has created problems in properly formulating detergent compositions to replace the established, efficient phosphate formulations in which phosphate builders act as chelating agents for water hardening minerals, provide the necessary alkalinity, help deflocculate and suspend both organic and inorganic dirt particles and increase the salt concentration of solutions, thus lowering the critical micelle concentration of the soaps and detergents.

In addition to these functions, the phosphate builders served as solid bulking agents which allowed the absorption of minor amounts of liquid components such as nonionic detergents into the formulation without causing caking or poor flow properties.

To compensate for the loss of chelating action by the phosphates, many formulators have increased the content of nonionic surfactants. Water-soluble sodium silicate powders have also been added to perform some of the dirt-suspending and deflocculating functions of the phosphates and provide the necessary alkalinity for a satisfactory cleaning operation. Enhanced cleaning has also been sought by increasing the concentration of ionic detergents such as sodium salts of linear alkyl-aryl sulfonates.

Problems have been encountered in using these modified formulations because of the increase in the low melting, relatively soft sodium alkyl-aryl sulfonates and the substantial increase in the amount of liquid nonionic materials. This has led to soft, sticky powders which do not flow well and which cake badly in the boxon storage.

It is also undesirable to introduce large amounts of liquid nonionic detergents into a spray drying tower in the conventional manufacturing process for preparing complex detergent formulations since these liquids are entrained in the escaping steam from the spray drying operation and cause serious air pollution.

It is therefore imperative that a highly absorbent material be provided which is suitable in both an ecologigents. Drum-dried silicate solutions and ground anhydrous silicate powders are similarly unsuitable as highly absorbent carriers.

SUMMARY OF THE INVENTION It has now been found that high surface area, low

bulk density, highly absorbent powders of amorphous,

, pernatant, washed and dried. In a preferred embodical sense and in a commercial sense, the latter being as a constituent of detergent formulations which can serve as a carrier to absorb large amounts of nonionic detergents. Water-soluble silicate powders and silicate solutions used heretofore do not have satisfactory characteristics to fulfill this function. For example, spraydried hydrous sodium silicate powdershave negligible absorption and absorb only l0 percent of their own weight of organic liquids such as nonionic detergents. Further, aqueous silicate solutions introduced into the spray-drying operation do not dry in a form which would allow them to efficiently absorb nonionic determent, ammonia is incorporated into the alcoholaqueous silicate mixture in any quantity up to a maximum of about 30 percent by weight based on the weight of the alcohol.

In one modification of the invention, the particles of silicate thus prepared are contacted with an aqueous solution of hydrogen peroxide at a temperature of between 0 and 35C., the hydrogen peroxide is allowed to diffuse or migrate into the internal structure of the silicate during a diffusion time of from about 5 to about minutes and the silicate is then heated to about 60C. to decompose the peroxide. This treatment expands the pores in the silicate structure while aggregating and cohering it. The silicates of this invention are compounded of Sl0 and any suitable alkali metal oxide including, for example, sodium oxide, potassium oxide, lithium oxide and the like at a mo] ratio of SiO to alkali metal oxide of 2.0 to 4.0, preferably 2 to 3 and sodium silicates are preferred.

DETAILED DESCRIPTION OF THE INVENTION The Product Stereoscan electron micrographs show that the products of the alcohol precipitation have a unique microfibrous structure which enables the structure to have a high degree of porosity with pores which are large enough to permit rapid absorption and yet not so large that they fail to retain the absorbed materials as a result of capillary attraction. In the peroxide modification of the invention, the microfibers are connected tangentially and the extension of the microfibers in space is preserved and even increased to yield a stable structure which is attrition resistant. Bycontrast to other products which do not possess this unique microfibrous structure but rather consist of clusters of spheroidal particles, the products of this invention possess a much greater extension in space and cohesion due to the tangential connection of the fibers. As a. result, the products of this invention are sufficiently strong to be attrition resistant, particularly compared to the aggregates of spheroidal particles which, because the areas of contact. are less substantial, are more fragile and, hence, not greatly attrition resistant,

The products of this invention are high surface area, low bulk density powders of amorphous, hydrous, water soluble alkali metal silicates which are highly absorbent. The absorptive structure of the products of this invention can be characterized by the application of three different techniques: tamped bulk density, oil

3 absorption and mercury penetration using the mercury porosimeter.

Three different techniques must be used since each technique has certain limitations if used alone. For example, measurements of the bulk density determine both the spacewithin particles, which is useful for absorptive purposes, the space between particles, which is of little value for absorptive purposes and the closed porosity, which is of no value. The oil absorption index as determined by ASTM designation D-28l-31 is not completely definitive since it measures the amount of oil required to turn the powder into a gummy mixture. This exceeds the absorptive capacity which is desirable in terms of the contemplated end uses. Mercury porosimeter measurements give information not only about the porosity, but the pore size distribution of the products of the invention. Accordingly, these last two tests are more useful in a relative sense than as absolute determining measurements.

The desired range of bulk densities for the products of the invention should be between 0.1 g./cc. to 0.5 g./cc. with the range between 0.2 g./cc. and 0.3 g./cc. being preferred. Above about 0.5 g./cc. there is simply not enough porosity, even if it were all available (that is, none of the pores were closed) to exhibit the high absorption desirable. Below 0.1 g./cc. the handling characteristics of the products become quite difficult since such light materials are difficult to mix satisfactorily with other components having higher densities. Within the preferred range of 0.2 to 0.3 g./cc., an excellent balance is achieved between good handling characteristics and satisfactory mixing with other constituents of detergent compositions without segregation due to density differences on one hand and a high absorbency on the other.

The preferred range determined by the ASTM oil absorption test is from 1 gram to 6 grams of linseed oil per gram ofalkali metal silicate. Below one gram per gram, the oil absorption is so low that the product simply does not have sufficient internal porosity to be useful for the major purposes of this invention. It is difficult to achieve oil absorption values in excess of 6 grams of linseed oil per gram of silicate without going to bulk densities which are too low to be employed satisfactorily.

With respect to mercury porosimeter measurements, it is desirable that at least 1 cc. of mercury be absorbed per gram of alkali metal silicate at applied pressures of 2,000 psi, which correspond to pores of approximately 1 micron in diameter. Phrased another way, it is important that the porosity of the products of this invention comprise relatively large pores. In the mercury porosimeter technique, mercury is forced under pressure into the pores and the size of the pores is determined by the amount of pressure which must be exerted to fill a given number of ccs of pore volume. As stated previously, relatively large pores are desirable, because they can quickly absorb the nonionic surfactants. The upper limit onmercury porosimeter measurements is approximately 5 cc. of mercury per gram of alkali metal silicate.

The alkali metal silicates of this invention have a high degree of absorbency for nonionic surfactants and absorb from at least 50 percent by weight of their own weight of nonionic detergent or any other liquid of comparable density with a preferred range of from about 80 percent to 100 percent. The degree of absor-' and titrating with a mineral acid to determine the dis-' bency may be measured by adding nonionic surfactant slowly to a weighed amount of the silicate in a glass container, stirring after each addition. The percentage of the nonionic surfactant that can be added before the glass becomes wet with surfactant is the percent absorption. Other indications of the limit of absorption are that the powder cakes and aggregates at about this samepoint.

The products of this invention are also characterized by an unusual degree of internal porosity, with the pores being of large enough pore diameter to permit rapid absorption, and yet not so large that they fail to retain materials as a result of capillary attraction. This is achieved by controlled aggregation of very small alkali metal silicate particles into open porous aggregates. Spray-dried silicate materials and ground silicate materials of the'prior art seldom attain particle sizes smaller than 15 to 20 microns (or through 325 mesh). If one attempts to build highly absorbent open networks of such large particles, the number of contact points between the silica particles is small, and the area of contact is small, with the resulting problem that the structure is quite weak. Thus, mechanical attrition attendant upon processes for loading the nonionic absorbent into the porous alkali metal silicate structure can lead to a breakdown of the structure, a loss of porosity, and a resultant deterioration in the utility of the product. For this reason, it is much better to build a porous structure of much finer particles.

A convenient measure of particle size combined with surface roughness is the specific nitrogen surface area of the products expressed in square meters per gram. The products of this invention are characterized by a nitrogen surface area greater than 2 mf /g. Surface areas can range as high as 7 m. /g., depending on the degree of agitation and drying conditions employed in the processes of the invention.

A further important property of the products of this invention is the rate of solution in water which is related to particle size, water content, and the SiO to al-.

kali metal oxide weight ratio of the product. In general, the rate of solution increases as the particle size diminishes, the water contentincreases and the ratio of SiO. to alkali metal oxide lowers. Since one of the uses of the products of this invention is in detergent applications, it is important that they have very high rates of solution. Stated in absolute terms, at least percent of the particles totally dissolve in cc. of water in 5 minutes at 25C. The rate of solution can be determined by dissolving a one-gram sample in 100 ml. of water, filtering after a specified time (e.g., 5 minutes) solved alkalinity.-A similar degree of solution will occur in less than 30 seconds at a temperature of 60C., or normal hot water washing temperatures. Since the hydrated amorphous silicates of this invention are infinitely miscible with water, they have no definite solubility limit sinceat no time does a separation into two phases occur. Consequently, no residual undissolved residue remains behind when the silicates of this invention are added to water.

The water content of the products of the invention is another critical variable which must be maintained within closely regulated limits. As the water content of silicate solutions gets higher, the products become softer and exhibit viscous flow to a degree which completely precludes the possiblity of isolating and maintaining the type of open, porous structure which is necessary for many uses. Therefore, it is vital that the water content of the silicate does not exceed 25 percent by weight of the silicate. Since, as previously noted, the solubility must also be maintained at very high values, it is also undesirable to allow the water content to approach too low a value or a slow rate of solution will result. Therefore, it is necessary to have at least percent and preferably 14 percent by weight of water based on the weight of the silicate in products of the invention. The most preferred range is from 14 percent to 18 percent by weight of water.

The silicate products of this invention have an active oxygen content of no more than 1.33 percent by weight. In other words, any active oxygen present would remain essentially as an impurity because hydrogen peroxide is one of the starting materials used in the practice of the invention. The negligible active oxygen content is important since appreciable amounts of active oxygen may adversely effect the chemical properties and reactivities of the compositions in which the silicates are used. Even in those end uses in which active oxygen releasing agents are used such as in laundry and dishwashing detergents, cleansers and the like, the addition of further quantities of active oxygen is often deleterious. For example, indiscriminate addition of active oxygen containing compounds to detergents can result in destruction of or damage to fabric, optical brighteners, fabric dyes, perfumes, disinfectants and other readily oxidizable organic ingredients in the detergent compositions. Use of active oxygen containing compounds in dishwashing detergents containing citrate or nitrilotriacetate sequestering agents will result in an oxidative attack of the peroxide on the organic moieties. No such results arise when the products of this invention are used since they either contain no active oxygen or else only harmless residual amounts as an impurity.

It is also necessary that the SiO to alkali metal oxide ratio in the silicate is maintained within certain limits, generally from about 2 to approximately 4. More alkaline compositions having silica to alkali metal oxide ratios below two are difficult to precipitate from solution in the process'of this invention while higher ratio materials, such as those having a ratio greater than 4 are too limited in terms of solubility.

The products of this invention are amorphous alkali metal silicate materials. The art is familiar with lower ratio crystalline water-soluble sodium silicates such as sodium metasilicates, sodium orthosilicates, and sodium sesquisilicates. These very low ratio (alkaline) silicates are rapidly water-soluble, but their high alkalinity makes them unsuitable for many uses, including uses in general purpose detergents. Silicates having weight ratios of SiO to alkali metal oxide within the range of the preferred products of this case, that is from a weight ratio of 2 to l to 4 to 1, cannot be crystallized and exist, so far as is known, only as amorphous materials. The amorphous nature can be determined by examination with X-rays. When so examined, the products of the invention show only broad diffuse rings characteristic of amorphous materials.

The compositions of this invention represent a significant advance in the art, especially since, in termsof physical structure and chemical composition, they are particularly suited to act as highly efficient carriers of nonionic detergents. They thus answer heretofore unfulfilled needs of the art and facilitate the preparation of satisfactory no-phosphate and low phosphate detergent formulations.

The Process In the process of this invention, a concentrated aqueous solution of a silicate having an SiO to alkali metal oxide ratio of from about 2 to about 4 is contacted with at least once its weight of a water miscible lower molecular weight alcohol, preferably having one to three carbon atoms such as, for example, methanol, ethanol, normal propyl alcohol, isopropyl alcohol and the like. Alcohols having chain lengths greater than 3 are not completely miscible with water in most instances and are substantially more costly; they are therefore not preferred.

Broadly, the aqueous silicate solution contains from 10 percent by weight to 60 percent by weight of the silicate. Concentrations lower than 10 percentby weight introduce so much water'that excessive quantities of the dehydrating and precipitating alcohols of the invention must be used to extract sufficient water from the products, and so these are not preferred. Concentrations higher than 60 percent by weight are extremely difficult to handle, since their viscosity is very high. The viscosity varies with the ratio and temperature as well as concentration and must be less than 200 cps and preferably less than (cps in order to be easily pumped, mixed, and otherwise processed. The most preferred concentrations are between about 20 percent silicate and 50 percent silicate. Within this range the silicate solutions are fluid enough to be easily pumped, mixed, and otherwise processed, but the water content introduced with them does not require the use of an inordinately high concentration'of the alcohol precipitating and dehydrating reagents of the invention. I

While the low molecular weight alcohols of the invention can be employed as the sole precipitating and dehydrating agentsin the processes of'the invention, the solubility of silicates in such alcohols, particularly methanol and ethanol, is appreciable, and this sometimes decreases the yield of the desired products.'This is particularly true when quantities of alcohol near the lower 1 to 1 weight ratio are employed and when more dilute silicate solutions are used such as'the lower limit of 10 percent silicate, for example. The solubility of silicates in mixtures of ammonia with the lower chain alcohols of the invention is substantially lower than their.

solubility in an equivalent quantity of alcohol containing no ammonia. For this reason, quantities of ammonia ranging up to 30 percent by weight based on the In recovering and reusing the solvents of the invention by distillation, the ammonia will flash off first and can be reabsorbed in recycled alcohol. The methanol or other alcohol can be separated by conventional distillation procedures and used as an absorbentfor the ammonia. This reconstituted mixture of methanol and ammonia can then be employed to wash the precipitated silicate product prior to its use as a precipitant for the next batch of aqueous silicate solution.

It is advantageous to employ a weight ratio of the alcohol phase to aqueous silicate higher than the lower limit of one to one and generally ratios as high as 6 parts by weight of the alcohol phase to l part by weight of the silicate solution can be used. Since the alcohol generally acts to abstract water from the alkali metal silicate, larger quantities of alcohol serve no particularly useful function and add to the expense of recovery of the alcohol phase in the cyclical process of the invention. Quantities of alcohol lower than the desired 1 to 1 ratio do not abstract sufficient water from the solidified alkali metal silicate particles, and lead to a sticky, gummy precipitate which quickly cements itself back together into large, nonporous particles.

Vigorous agitation while mixing the silicate solution with the alcohol or alcohol-ammonia mixture is important to the achievement of the products of the invention. Relatively mild mixing or simply dropping the silicate solution into quiescent alcohol. results in large particles and particles which have too high a water content. The silicate solution must be broken up into extremely fine particles 7 which will have high surface areas so that the rate of extraction of water can be virtually instantaneous, thus rendering the particles unlikely to recombine and lose the open structure and fine particle size achieved by this process. Generally, a degree of agitation equivalent to or in excess of 5,000 sec. of circumferential shear and preferably in excess of 10,000 sec. of circumferential shear should be employed. For all practical purposes, there is no upper limit except that the shear rate should not be sufficiently high to cause'excessive cavitation and heating of the mixing solution.

For this reason, it is convenient to introduce the silicate solution to the alcohol as a stream delivered by a device such as a mechanically driven pump and to mix it under extremely high shear conditions with the alcohol in the mixing zone. Jet mixers, turbine mixers, homogenizers, colloid mills and high speed spinning disc mixers are suitable types of equipment which can deliver the very high shear characteristics required for this stage of the operation.

Normally, the silicate is mixed with the alcohol at room temperature. The temperature is not critical, however, and any temperatures within the range of C. to the boiling point of the mixture can be employed. Even higher temperatures may be used if adequate pressure is applied to avoid boiling the mixture. Generally speaking, temperatures as high as 200C. can be employed.

The products of the invention precipitate virtually simultaneously with the mixing operation and are recovered in any convenient manner such as, for example, by filtration or centrifugation. Some care must be exercised at this point not to subject the products to excessively high forces such as very high speed centrifugation since this has a tendency to reagglomerate the particles to an undesirable degree.

A substantial quantity of the entrained alcoholwater precipitating mixture remains entrained in the particles after centrifugation or filtration or the completion of any other method used to recover the particles. Therefore, the particles are washed with'fresh water-miscible lower molecular weight alcohol which may be thesame or different from the alcohol used as the precipitant to lower the water content of the interstitial liquid to a low value. If this is not done, the lower boiling alcohol and ammonia are eliminated first upon subsequent drying. The water in the interstitial liquid then recombines with the silicate to yield an undesirably high water content which in turn causes collapse of the open structure, particle growth and the sintering together of the products of the invention.

After they are washed, the products of the invention must be dried at temperatures sufficiently low to preclude the alkali metal silicate hydrated products from becoming plastic, agglomerating and flowing together. Drying temperatures can range broadly from about room temperature to approximately C. Higher temperature drying is not advisable except perhaps for very short periods of time, because of the risk of agglomeration and collapse of the structure. The preferred drying temperatures are between 25C. and 60C. Drying can be carried out either with a heated inert gas or under vacuum.

The gas should be inert to adverse chemical reactions with the alcohol, ammonia, and the silicates of the invention. For example, an excessive concentration of oxygen would create a fire and explosion hazard with the alcohol components of the process and is not desirable. However, as long as the alcohol vapor-gas mixture is not hazardous, air can be employed as a suitable inert gas. Nitrogen is, of course, suitable, as are gases such as hydrogen, helium, neon, argon and the like and mixtures thereof. In general, any gas which does not react with the alcohol, ammonia and/or alkali metal silicate components of the invention is satisfactory."Clearly, in the case of air thenature of the gas, the temperatures and relative proportions of alcohol vapor and air which are used are determinatives since mixtures which are within the explosive range should be avoided.

Acidic gases should not be major components of the drying atmospheres since they have a tendency to gel the sodium silicate particle surfaces by neutralization reactions. This includes carbon dioxide in appreciable amounts, although the quantities present in ambient air are not deleterious.

At this stage, the dried product of the process of the invention is a very fine powder having the characteristics described in the preceding section. As a preferred product of the invention, such powdered product may be employed for any application in which a powdered form of alkali metal silicate is desired.

For many applications, however, a granulated form of alkali metal silicate similar in particle size and bulk density to detergent particles normally sold in commerce is a more preferred form. However, because of their sensitivity to heat and the tendency of the particle structure to agglomerate, the alkali metal silicate particles thus produced cannot be subjected to the granulating techniques heretofore employed in agglomerating alkali metal silicate materials, particularly sodium silicates.

However, it has been found that these products can be treated with hydrogen peroxide to granulate them into a structure of suitable particle size while still retaining and even enhancing their high absorptivity. In this second phase of the process of this invention, a solution of hydrogen peroxide is sprayed onto a' tumbling mass of the dried particles of the first phase of the process of the invention at a temperature of 0C. to 35C. After a suitable period of tumbling, from 5 minutes to 60 minutes, during which the hydrogen peroxide miperoxide decomposes, thus maintaining and even expanding the pores in the structure, while the structure becomes aggregated at that temperature.

In prior art techniques of accomplishing aggregation of silicate powders, the temperatures used are too high for the products of this invention to maintain their open pore structure since temperatures substantially greater than 60C. lead to plastic flow, sintering, loss of surface area, loss of porosity and the closing of pores. By means of the liberated hydrogen peroxide and the maintenance of temperature at the desired levels below 60C. but above 35C., the structure of the particles of this invention is maintained in an open absorptive form.

In this second step of the process of the invention the tulantities of hydrogen peroxidebased on the weight of the alkali metal silicate product of the first step of the sensitivity of alkali metal silicates to sintering which causes a loss of surface area. While l percent perox ide can be used and is very effective in this application, the hazards associated with handling and using such concentrated peroxide solutions make this less than a preferred concentration. The preferred concentrations of from 30 to 70 percent hydrogen peroxide are safe, effective and easy to handle.

The hydrogen peroxide may be added, applied, sprayed onto or in any other manner introduced to the alkali metal silicate free flowing powder or granules. Preferably, the hydrogen peroxide is sprayed at a temperature of from 0C. to 35C. onto a moving bed of alkali metal silicate granules using any standard device for spraying a liquid onto a solid. In one particularly efficientoperation, the alkali metal silicate is placed ihside a rotating drum mixer having the shape of an elongated cylinder, the interior walls of which are scraped by a rotating screw which simultaneously mixes the contents and moves them slowly along the length of the cylinder. The hydrogen peroxide solution may be sprayed onto the silicate granules by jets located at the entrance or near the entrance of the cylinder. The particles thus contacted are then conveyed through the cylinder which may have a residence time of from minutes to several hours. While diffusion times in this or any other embodiment of as long as an hour or even longer can be employed, an hour is generally more than adequate for penetration into the center of particles in the general size range of from to 125 microns (the usual range for spraydried or mechanically-ground hydrated alkali metal silicates). Accordingly, longer diffusion times accomplish little. The cylinder preferably contains a heating zone to control the temperature within the range of 0C. to 35C. during the diffusion time in which the hydrogen peroxide diffuses into the inner hydrated alkali metal silicate structure. if desired, the granules may be subjected to a current of dry air or inert gas may be blown over the tumbling powderin the mixer. Because the vapor pressure of water is substan- 10 tially higher than that of hydrogen peroxide, the water will be removed continuously while the hydrogen peroxide migrates into the alkali metal silicate particles which are thus maintained in a relatively dry'state. If desired, the granules may then be recycled through the mixer and recontacted with hydrogen peroxide solution until the desired amount of peroxide has been applied.

After the desired oxygen content has been introduced into the structure and the diffusion time is over, the temperature is raised preferably rapidly to about 60C. to decompose the peroxide and sinter the, microfibers at their points of contact.

The decomposition of hydrogen peroxide is a complex process, being influenced by temperature, pH, and impurity content, as well as heat transfer in those instances where the decomposition rate is appreciable. For this reason, the temperature ranges given can be taken only as general guides. At temperatures below 30C.,decomposition rates of peroxide are quite slow, amounting to less than a few percent per hour. This is true even in relatively unfavorable pH regions. In the temperature range from Cpto C., the rate in'- creases substantially, and can become quite rapid at about 45C., particularly when the pH of the solutions is high as occurs, for example, when a silicate having a ratio of 2 to 3.0 is used. 1

Above 45C. the rate of decomposition of peroxide becomes increasingly-rapid, and at 60C. it is extremely rapid, resulting in a total decomposition within a matter of a relatively few minutes.

Diffusion rates are also a function of temperature as well as of water content and ratio. The temperature coefficient for diffusion does not appear to be nearly as high as that governing the peroxide decomposition reaction. Thus, it is possible, in certa'in'limited temperature ranges, to achieve simultaneously substantial diffusion of peroxide into the structure and decomposition of the peroxide as it enters the more basic hydrated silicate phase. Thus, at temperatures in the rangeof from 40 to C., diffusion and decomposition both pro ceed at an observably fast rate. 1

Because the silicate particles-are somewhat plastic,

the more rapidly the temperature is raised, the more efficient will be the process of the invention. Preferably, the temperature is increasedat a rate of from 1C. to 10C. per minute, most preferably, 2 to 7C. per

vminute. The temperature is held at no higher than C. until the destruction of the peroxide is substantially complete. It is important that the hydrogen peroxide be completely destroyed since, if organic materials are absorbed into the structure, any remaining hydrogen peroxide could create an extremely hazardous condition via oxidation of the absorbed organic material.

' ionic detergent into their structure thereby allowing the dium silicate powder or granules with the nonionic liquid under conditions of mild agitation, such as tumbling in a cone-blender or drum blending by spraying the nonionic liquid onto the powder or granules to achieve a uniform distribution of the liquid to be absorbed while agitating the powder particles. The products of the invention canbe loaded until a limit approaching roughly 40 to 80 percent of the'oil absorption index is achieved, preferably approximately 40 to 60 percent. The product at this .time has essentially all of its internal pores filled but still remains a freeflowing' powder which does not agglomerate upon storage and which mixes easily with other powder'constituents of detergents. The products of this invention are particularly advantageous over other hydrous silicates, such as spraydried silicates, since they absorb water and carbon dioxide from the atmosphere at a very slow rate. This result arises because most of the particle surface is protected by the absorbed pools of nonionic detergentthrough -which carbon dioxide and water. vapor must migrate in order to adversely react with the surface of the silicate. I

The invention is further illustrated but is not intended to be limited thefollowing examples in which all parts, percentages and ratios are by weight'unless otherwise specified.

EXAMPLE I Fourteen hundredfifty grams of a 37 percent solids aqueous solution of sodium silicate having a ratio of 2.4 parts of SiO per part of Na Ower e delivered by means ofa pump through a /s inch orifice .into a rapidly stirred mixingzone in a beaker containing 4,000 g. of methanol to which 400 g. of anhydrous ammonia had previously been added. The orifice of the pump was located approximately three-fourths inch below the head of a highspeedmixing device called a homomixer which consists of a slotted circularwheeLfapproximately 42 inch in diameter, turning inside a slotted housing at 7.200rpm The silicate was pumped into the violently I 12 of to 33C.) as the nonionic surface active agent beforea thin film of the surfactant ordetergent was apparent on the glassware in which the mixing operation was carried out. Even after having absorbed this quantity of nonionicdetergent, the product remained freeflowing and nonaggregated. V

The rate of solution of this powderin water was extremely fast even at room temperature, and its rate of solution was approximately three times as rapid as a spray-dried sodium silicate :of comparable silicate to sodium oxide weight ratio and degree of hydration.

One. gram of the product was essentially 100 percent dissolved in the 100 cc. of water in less than 2 minutes at room temperature.

Stereoscan electron micrographs showed the product to consist of interlocking fibers or filamentous ribbons to form a very looseropen structure. The fibers or ribbons were approximately .1 micron in average diameter. They were several times as long as they were thick.

One hundred grams of this material was placed in a 2 liter stainless steel beaker which had baffles welded at a 90 angle to its side. This reactor was turned at approximately 15 revolutions per minute while inclined at an angle of 30? from a horizontal position. The, baffles coupled with jthis rate of rotation caused a smooth cascading motion of the powder. Thirty grams of a 35 percenthydrogen peroxide solution ,were sprayed onto the cascading silicate at room temperature over a period of approximately 5 minutes. Thereactor was then heated with infrared lamps to 60C.. In this stage of the process,

" the peroxide wasdecomposed and the product agglomerated from an'extremely fine powder into granules of approximately 35 mesh particle size, I v

The bulk density of this materialwas determined and found to be substantially identical with that of the start- I ing powder, namely 0.26 g./ cc. l'tsn'itro'gen surface area stirred vortex over 'a' p'eriod of'approx'imately one hour.

The resulting finely divided precipitate of hydrated sodium silicate was iilteredand washed four times with 1000 g. portions of methanol. The process was repeated to prepare a double quantity. The product was then dried overnight at Cl'in a vacuum oven. The water content was found to be 17.85 percent. This finely divided amorphous silicate powder had a nitrogen surface area of 4.67 m /g.. and a bulk density of 0.25 g.'/cc. v a

Measurements of the pore volume and pore diameter by means ofa mercury porosimeter showed pores ranging in size from about 90 microns tov about 0.8. micron with a fairly uniform distribution of the porosity within these limits. The total porosity was 2.44 cc. of mercury per gram of sodium silicate hydrated powder.

was also determined and this was found to be 4.87 m /g. or almost identical to that of the starting powder. Determination of the porosity and pore diameter distribution by mercury porosimetry again showed relatively little change, with a total porosity of 2.20 cc./g.'in a general particle size rangeof from about'80 microns to 0.8 micron. It was 'noted th'at a larger fraction of the pores was in the greater than 10 micronsize' range than with the methanol precipitated powder.

The absorptivity of nonionic surfactant Neodol Ethoxylate 25-l2 was measured as described above and was found to haveincreased to l0] percent by weight based on the weight of the sodium silicate hydrated powder granules.

- locking network as before the peroxide treatment but with a much larger number of these units cemented together wtih one another. Accordingly, the resulting This product absorbed 79 percent of its own weight I of Neodol Ethoxylate 25-12 (a Shell Chemical Com-' pany linear alcohol ethoxylate comprising a mixture of alcohols having-l2-15 carbon atoms condensed with twelve mols of ethylene oxide to anaverage molecular weight of 745, a density of 1.003 and a melting point.

granules were substantially more'rigid and less likely to be damaged by attrition than the granules originally obtained via methanol precipitation.

l Example 2 A 2.44 ratio aqueous solution of sodium silicate was stainlesssteel tubing having 21 Va inch diameter orifice directly underneath the vortex of a high speed mixing device which rotated at about 7,200 rpm, as described in Example 1. Seventeen hundred fifty grams of the silicate solution were pumped into 4,000 grams of a percent ammonia, 90 percent methanol anhydrous mixture containing a total of 4,000 grams of methanol. The light and fluffy powder which precipitated is filtered and washed with excess methanol. It was then dried in a vacuum oven at 80C. for 16 hours.

The resulting amorphous product contained 15.13 percent water. The rate of solution of this powder in water was extremely fast even at room temperature and essentially 100 percent of one gram dissolved in 100 cc. of water in less than two minutes at room temperature. Stereoscan electron micrographs showed that the product consists of interlocking fibers or filamentous ribbons of about 1 micron average diameter with lengths several times the thickness.

The product was found to absorb 52 percent of its own weight of the nonionic surface active agent described in Example 1 before a thin film of oil appeared on the walls of the beaker in which the mixing operation was being performed. The nitrogen surface area of this material was found to be 4.59 m /g. The ASTM oil absorption was 1.28 cc. per gram of sodium silicate hydrated powder indicating a high degree of porosity. Fifty grams of this material were placed in a 2 liter stainless steel beaker equipped with internal baffles and sprayed with grams of a 35 percent aqueous hydrogen peroxide solution while the reactor was inclined at an angle of to the horizontal and rotating at a speed of 15 rpm to impart a smooth cascading motion to the powder. After allowing about 5 minutes for absorption of the hydrogen peroxide solution, the temperature was raised to 60C. and the powder was allowed to continue to tumble for another 8 to 10 minutes. This was removed and the bulk density determined to be 0.26 g./cc., which is virtually unchanged from the 0.26 g./cc. value found on the methanol precipitated powder.

The nitrogen surface area of this material was 4.52 m'-/g., which is again essentially unchanged from the surface area of the starting methanol precipitated powder. However, the absorbency of the nonionic detergent or surfactant described in Example 1 had increased from 50 percent to 93 percent by weight based on the weight of the silicate. The ASTM oil absorption index had also increased to 1.90 g./g. of sodium silicate hydrated powder indicating an increase in porosity. The fine, dusty powder was agglomerated into granules having an average particle size of approximately mesh.

EXAMPLE 3 Eight pounds of ammonia were dissolved in 80 lb. of methanol in a gal tank provided with a 3,450 rpm double cone agitator. Forty pounds ofa 37 percent 2.4 ratio sodium silicate aqueous solution were introduced into the methanol/ammonia mixture through a 1/16 v inch nozzle directed at the head of the agitator'and lo- 14 uum tray dryer at 50C. The dried amorphous product had 22.1 wt. percent water, a bulk density of 0.26 g./cc. and a surface area of 3-4 m /g. The powder absorbed without caking an amount of the nonionic detergent described in Example 1 equivalent to 65 percent of its weight.

The rate of solution of this powder in water was extremely fast, even at room temperature and essentially 100 percent dissolved in less than 2 minutes at room temperature. Stereoscan electron micrographs showed that the product consists of interlocking fibers or filamentous ribbons of about l micron average diameter with lengths several times the diameter. The ASTM oil absorption was 1.70 g./g. of sodium silicate powder indicating a high degree of porosity.

In a subsequent processing step, 10 lbs. of this powder were sprayed with 3 lbs. of. a 30 percent aqueous hydrogen peroxide solution in a rotating open drum .and heated to 60C. for about 15 minutes. The end product contained 18.4 wt. percent water and had a bulk density of 0.24 g./cc., a surface area of 3.3 m /g, and an ability to absorb the nonionic detergent described in Example 1 in amounts equivalent to percent of its weight.

EXAMPLE 4 Four thousand grams of methanol were placed in a tank provided with a homomixer having a maximum velocity of 8000 rpm. Two thousand grams of a 37 percent 2.4 ratio sodium silicate aqueous solution were pumped into the methanol through a 1/16 inch nozzle at the rate of l gal/hr. The nozzle was directed vertically upward so that the silicate solution was fed into the mixing zone of the agitator running at the maximum speed of 8000 rpm. The precipitate formed was intermittently filtered and the filtrate was returned to the mixing vessel. The filter cake was dried overnight in a vacuum oven at 50C.

The dried powder had a water content of 22.3 percent, a specific surface area of 3.6 m' /g. as determined by nitrogen adsorption and absorbed 85 percent of its own weight of the nonionic detergent described in Example 1 before visible film of non-absorbed detergent appeared on the glass walls of the beaker in which the absorption experiment was performed, The amorphous product had a bulk density of 0.38 g./cc. and an ASTM oil absorption of 1.63 g./g. of sodium silicate powder indicating a high degree of porosity. The rate of solution of this powder in water was extremely high, even at room temperature, and one gram dissolved percent in 100 cc. H O in less than two minutes at room temperature. Stereoscan electron micrographs showedthat the product consists of interlocking fibers or filamentous ribbons of about 1 micron average diameter with lengths several times the diameter.

EXAMPLES 5 THROUGH 10 alcohol is ammonia free in all cases. After being washed, each sample was dried for 3 hours at 60C. in an air circulating oven.

The' rate of solution of the resulting powders in water was extremely fast, even at room temperature, and essentially 100 percent of a one gram sample dissolved in 100 cc. of water in less than 2 minutes at room temperature. Stereoscan electron micrographs showed that the product consists of interlocking fibers or filamentous ribbons of about 1 micron average diameter with lengths several times greater than the diameter. The weight of the amorphous product, the percent water content, the yield of silicate solids calculated from these, the tamped bulk density, the oil absorption as an indication of porosity, the nitrogen surface area, and the percent of their own weight of the nonionic detergent described in Example 1 which could be absorbed to the point of depositing a thin film of detergent on the walls of the glass beaker in which the absorption experiment was carried out, are tabulated in Table I].

TABLE 1 the invention by those skilled in the art without departing from the spirit and scope of the invention except as set forth in the claims.

What is claimed is:

1. Microfibrous amorphous, water soluble alkali metal silicates having an SiO- to alkali metal oxide density of between about 0.1 g./cc. and 0.5 g./cc. and

a water content of 10 to 18 percent by weight of the silicate.

3. The alkali metal silicates of claim 1 having a rate of solution of at least 90 percent.

Weight Proper Concentration of tion of Solvent Sodium Silicate ASTM Oil Solvent SiO INa O to Silicate Solids in Sili- Absorption in Example System Ratio Solution cate Solution g./g. of Silicate 5 Methanol- 2.00 4/1 45% 1.20

6 Ethanol 3.25 4/1 30% 1.43

7 Isopropanol 3.75 6/1 15% 1.54

8 n-Propanol 2.40 6/1 20% 1.30

9 Methanol- 3.25 1/1 30% 1.18

30% NH l Methanol 2.40 4/1 37% 1.28

TABLE I1 Specific Sur- 71 Nonionic Product H O Yield as of Sodium Tamped Bulk Denface Area Detergent Example weight Content Silicate Solids sity, gram/cc. in mlg. Absorbed The percent active oxygen for the products of each of Examples ll0 was determined by the following procedure:

About 0.3 to 0.5 gram of silicate was weighed accurately and transferred in a 400 ml. beaker. After all of the solid dissolves, l to 2 ml. of 2 percent ammonium molybdate solution are added. Immediately thereafter ml. of K1 solution are added and stirring is continued for two minutes before the liberated iodine is titrated against .1 normal thiosulfate using 5 to 10 ml. of 1 percent starch solution as the indicator. The end point is a color change from blue to colorless. Percent active oxygen=ml. of .IN sodium thiosulfate X 0.08 divided by the weight of the sample in grams. In every case, the active oxygen content was below detectable limits.

It is to be understood that any of the components and conditions mentioned as suitable herein can be substituted for its counterpart in the foregoing examples and that although the invention has been described in considerable detail in the foregoing, such detail is solely for the purpose of illustration. Variations can bemade in 4. The alkali metal silicates of claim 1 having a bulk density of from 0.2 g./cc. to 0.3 g./cc.

5. The alkali metal silicates of claim 1 having an oil absorption of from 1 to 6 grams of linseed oil per gram of silicate.

6. The alkali metal silicates of claim 1 wherein the alkali metal is sodium. 1

7. A process for preparing the alkali metal silicates of claim 1 which comprises contacting a concentrated solution of the alkali metal silicate in water with a watermiscible lower molecular weight alcohol at a weight ratio of alcohol to aqueous silicate solution of at least 1:1 at a degree of agitation of at least 5,000 sec. of circumferential shear to precipitate the silicate.

8. The process of claim 7 wherein the silicate has an SiO to alkali metal oxide ratio of from about 2 to about 4 and is contacted while in an aqueous solution having a viscosity less than 200 cps. at a concentration of from about 10 percent to about 60 percent with from 1 to 6 parts by weight of an alcohol having from one to three carbon atoms per part by weight of the silicate solution at a degree of agitation of at least 5,000 sec. of circumferential shear to precipitate the silicate which is separated from the alcohol-water solution, washed with a lower molecular weight water-miscible alcohol and dried.

9. The process of claim 8 wherein the shear is at least 10,000 sec. of circumferential shear.

10. The process of claim 8 wherein up to about 30 percent by weight of ammonia based on the weight of the alcohol is incorporated in the alcohol.

11. The process of claim 8 wherein the precipitated silicate is separated from the alcohol water solution, washed with a lower molecular weight water-miscible alcohol, dried, contacted with an aqueous solution of hydrogen peroxide which diffuses into the sodium silicate structure and heated to destroy substantially all of the hydrogen peroxide.

12. The process of claim 11 wherein the silicate is contacted at a temperature of from 0C. to 35C. with from 2 to 100 percent by weight of hydrogen peroxide in an aqueous solution at a concentration of from 2.0 to 100 percent by weight and the hydrogen peroxide is allowed to diffuse into the sodium silicate structure for from about 5 minutes to about 1 hour at a temperature of from 20 to 35C. after which the sodium silicate is rapidly heated to a temperature of from about 40 to C. to destroy the hydrogen peroxide.

Claims

1. MICROFIBROUS AMORPHOUS, WATER SOLUBLE ALKALI METAL SILICATES HAVING AN SIO2 TO ALKALI METAL OXIDE MOLAR RATIO OF 2 TO 4, A SPECIFIC NITROGEN SURFACE AREA OF BETWEEN 2 TO 7 M2/G., AN INTERNAL POROSITY MEASURED BY MERCURY POROSIMETRY OF FROM 1 TO 5 CC. OF MERCURY PER GRAM OF SILICATE AT A PRESSURE OF 2,000 PSI, AN ABSORBENCY FOR NONIONIC SURFACTANTS OF AT LEAST 50 PERCENT BY WEIGHT, A MAXIMUM WATER CONTENT OF 25 PERCENT BY WEIGHT AND A MAXIMUM ACTIVE OXYGEN CONTENT OF 1.33 PERCENT BY WEIGHT.

2. The alkali metal silicates of claim 1 having a bulk density of between about 0.1 g./cc. and 0.5 g./cc. and a water content of 10 to 18 percent by weight of the silicate.

4. The alkali metal silicates of claim 1 having a bulk density of from 0.2 g./cc. to 0.3 g./cc.

6. The alkali metal silicates of claim 1 wherein the alkali metal is sodium.

7. A process for preparing the alkali metal silicates of claim 1 which comprises contacting a concentrated solution of the alkali metal silicate in water with a water-miscible lower molecular weight alcohol at a weight ratio of alcohol to aqueous silicate solution of at least 1:1 at a degree of agitation of at least 5, 000 sec. 1 of circumferential shear to precipitate the silicate.

8. The process of claim 7 wherein the silicate has an SiO2 to alkali metal oxide ratio of from about 2 to about 4 and is contacted while in an aqueous solution having a viscosity less than 200 cps. at a concentration of from about 10 percent to about 60 percent with from 1 to 6 parts by weight of an alcohol having from one to three carbon atoms per part by weight of the silicate solution at a degree of agitation of at least 5,000 sec. 1 of circumferential shear to precipitate the silicate which is separated from the alcohol-water solution, washed with a lower molecular weight water-miscible alcohol and dried.

9. The process of claim 8 wherein the shear is at least 10,000 sec. 1 of circumferential shear.

12. The process of claim 11 wherein the silicate is contacted at a temperature of from 0*C. to 35*C. with from 2 to 100 percent by weight of hydrogen peroxide in an aqueous solution at a concentration of from 2.0 to 100 percent by weight and the hydrogen peroxide is allowed to diffuse into the sodium silicate structure for from about 5 minutes to about 1 hour at a temperature of from 20* to 35*C. after which the sodium silicate is rapidly heated to a temperature of from about 40* to 60*C. to destroy the hydrogen peroxide.