WO1998035751A1

WO1998035751A1 - Method of making a silica carrier for liquid and product

Info

Publication number: WO1998035751A1
Application number: PCT/US1998/002636
Authority: WO
Inventors: Albert G. Landers; Alvin E. Steelman; Robert C. Fitton; Gregory B. Parks; Michel J. Martin
Original assignee: J.M. Huber Corp.
Priority date: 1997-02-14
Filing date: 1998-02-13
Publication date: 1998-08-20

Abstract

A method of producing a silica carrier for liquid, comprising the steps involving compressing dried silica into lumps which are about 20-100 % denser than the dried silica; breaking up said lumps into smaller particles wherein at least some of the smaller particles are fines having a particle size of less than about 100 mesh; isolating the fines from said smaller particles; mixing the fines with additional dried silica to form a feedstock mixture; compressing the feedstock mixture into feedstock lumps which are about 20-100 % denser than said feedstock mixture; breaking up the feedstock lumps into particles of various sizes, the particles comprising coarse, moderate and fine particle size fractions; and isolating said moderate particle size fraction as said silica carrier for liquid.

Description

METHOD OF MAKING A SILICA CARRIER FOR LIQUID AND PRODUCT

BACKGROUND OF THE INVENTION

Field of the invention The invention relates to a method of making silica carrier for liquid and a silica carrier product. More particularly, the invention relates to a method of making a silica carrier suitable for carrying oils such as vitamin E. and processing oils such as linseed oil and the like, wherein the method results in a high-density, low-friability product which also possesses surprisingly high flow and high oil carrying capacities.

Description of the Related Art

Silica carriers for oils and other liquids are commonly used to deliver precise dosages of absorbed liquid for inclusion in materials such as livestock feed, rubber and plastics, for example. Silica carriers provide a predictable dosage of liquid under conditions where viscosity variations in an unearned liquid would render dosage control extremely difficult. Further, the paniculate form of the silica carrier facilitates transport and storage of the carried liquid.

Ideally, carrier silicas for liquids would possess a combination of desirable characteristics which facilitate handling, loading (liquid onto the carrier) and mixing, including high bulk density, low friability, high oil absorption and good flow properties. High bulk density in a silica carrier increases the efficiency of liquid loading processes by maximizing carrier throughput. High bulk density also decreases packaging costs associated with the carrier, and can inhibit segregation of the carried liquid and other materials of similar density with which it is mixed. Low friability reduces the dust generation which occurs during handling of the silica, thereby improving work conditions. High oil absorption generally correlates to liquid carrying capacity and reduces the amount of silica required to carry a given volume of liquid. However, excessively high oil absorption/carrying capacity is often accompanied by greater friability /excessive dust in the silica carrier before liquid loading and. when loaded with liquid, the flow of said silica can be severely and unacceptably restricted. Good flow properties are very important to silica carriers because they facilitate transport, dispersability and handling in automated feed systems. Conventional silica carriers are dried feedstock silica panicles that can be spray dried, nozzle dried or rotary tumbled dried. The nature of the feedstock and the drying process both are known to significantly affect the density and liquid carrying capacity. Products can also be made by compressing dried feedstock into lumps. The nature of the feedstock and the magnitude of the compressive force exerted on the feedstock during processing both are known to significantly affect the density and liquid carrying capacity of the silica. Thus, these process parameters, especially compressive force, must be carefully controlled to produce an end product suitable as a liquid carrier. If too much force is applied to a given silica feedstock, the capacity of the carrier will be insufficient; if too little force is applied, the carrier will lack sufficient density and will be friable.

Further, prior art methods have not completely solved the problem of particle size fractions outside of the desired silica carrier end product ranges (created when the lumps are broken up). While some conventional methods try to minimize waste by attempting to further break down the coarse particles into particles of acceptable carrier size, the fine particle fraction has conventionally been considered a by-product of the carrier manufacturing process which must be removed.

Accordingly, providing an efficient, low-waste/low-cost method for producing a silica carrier for liquid which is less compressive-force sensitive would represent a significant improvement over known production methods. Likewise, producing a silica having a combination of high bulk density, low friability, good flow properties and high carrying capacity (but not excessively high wherein flow and friability are unacceptable), i.e. properties optimized specifically for carrying liquid, has proven to be a surprisingly frustrating endeavor for those in the art. OBJECT OF THE INVENTION

It is object of the invention to provide an efficient method of producing a silica having the improved combination of properties as carrier for liquids. Other objects will become apparent from the following description of the invention. SUMMARY OF THE INVENTION

The invention is a method of producing a silica for use as a carrier for liquid. The method involves the compression of dried silica base stock to form compacted bodies (also referred to as lumps) which are about 20-100% denser than the base stock. The compacted bodies are broken up to produce particles of varying size, including a fraction of compressed fines having a particle size of less than about 100 mesh, and preferably less than about 80 mesh. The fines are isolated, then mixed with additional dried silica base stock to form a feedstock mixture. This feedstock mixture is compressed into lumps, broken up into smaller particles of varying sizes, then separated to isolate a silica end product from a coarse particle fraction and a fraction of compressed fines. Preferably, the feedstock mixture is deaerated prior to compression. Moreover, the coarse particle fraction is preferably broken up and recycled to the separation step, while the compressed fine fractions isolated from the silica carrier end product are preferably recycled for mixing with dried silica base stock.

The method of the invention is preferably performed as a balanced recycling system wherein dried silica base stock is fed to a compressor at a substantially constant rate to form compressed bodies, the compressed bodies are broken up into smaller particles including a fraction of once-compressed fines, and the once-compressed fines are isolated and recycled into the base stock feed. This process is repeated until fines are generated at a substantially constant rate. When the production of fines reaches this equilibrium, a silica carrier end product and coarse particle fraction are recovered from the broken-up lumps, while the fines generated from the broken-up lumps continue to be recycled to the base stock feed. Preferably, the coarse panicle fraction is broken up and recycled to the screening step.

The invention is also directed to a silica for carrying liquid comprising a sphericity of no greater than about 0.655. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic depiction of an apparatus which may be employed in the method of the invention.

Fig. 2 is a scanning electron micrograph of a prior an silica carrier.

Fig. 3 is a scanning electron micrograph of a silica carrier in accordance with the present invention.

Fig. 4 is a graph of the relationship between recycle rate during production and bulk density of a silica end product in accordance with a statistical model.

Fig. 5 is a graph of the relationship between recycle rate during production and linseed oil carrying capacity of a silica end product in accordance with a statistical model.

Fig. 6 is a graph of the relationship between recycle rate during production and flow time of a silica end product in accordance with a statistical model. DETAILED DESCRIPTION OF THE INVENTION

We have discovered a silica carrier production method by which bulk density, liquid carrying capacity and flow properties of a silica carrier end product can further be controlled other than by carefully selecting a silica base stock (starting material) and/or by carefully controlling the compressive force applied to the silica base stock. More specifically, we have discovered a method of producing a silica liquid carrier which involves a combining dried silica base stock with compressed silica fines produced from the breaking up of compressed silica bodies to produce a unique feedstock silica. Surprisingly, important physical and performance properties of the silica carrier end product can be controlled by adjusting the dried silica base stock/compressed fines mixture, independent of the physical properties of the dried silica base stock and of the compressive force applied to the silica feed. The invention can also be performed as a balanced production system wherein compressed fines (from the breaking up of compressed silica bodies) are recycled to a feed stream of dried silica base stock until the rate of fines production becomes substantially constant, whereby the production system is balanced and can be run continuously with great efficiency.

The method of the invention involves compressing a dried silica base stock into compressed bodies (also refened to herein as "lumps") which are about 20-100% denser than the base stock. The base stock silica is an amorphous silica which is not particularly limited, and can be selected on the basis of facilitating control of the end product characteristics. Compression of the dried silica base stock can be performed in accordance with conventional silica processing methods, including compression via tandem rolls. The compressive forces applied to the silica can vary depending on the properties of the base stock. but enough force should be applied to produce a lump which will substantially maintain its physical integrity after the compressive forces are removed.

The lumps are then broken into smaller particles, and the fraction of smallest particles (referred to herein as compressed fines or fines) is isolated. Conventional means for breaking up the lumps may be used, with an attrition mill or a flake breaker being preferable. The fines are less than about 100 mesh, and preferably less than about 80 mesh in size. The fines may be isolated by screening, with the use of a 20 mesh top screen (to remove the coarse fraction) and an 80 mesh bottom (to isolate the fine fraction) screen being preferable. Coarser particle fractions which are removed may be milled and recycled or used for other purposes.

The isolated fines are mixed with dried silica base stock to form a feedstock mixture. The feedstock mixture preferably comprises about 20-50 wt% compressed fines and about 50-80 wt% dried base stock silica. The feedstock mixture has a higher density than the dried silica base stock alone because of the presence of the fines, which have already been compressed. To further increase density, a deaeration may be performed on the feedstock mixture. The feedstock mixture is subsequently compressed into lumps. As in the compression of the dried silica base stock, the compression of the feedstock mixture can be performed using conventional mechanisms, with tandem roll compressors being preferable. The compressive pressures used will depend on the nature of the feedstock mixture and the characteristics desired in the silica carrier end product.

The compressed lumps of the feedstock mixture are then broken up into smaller particles of varying sizes. Means for breaking up the compressed lumps can be chosen from conventional silica processing techniques, though the use of either an attrition mill or flake breaker is preferable. Particles within the appropriate size range are isolated as the silica carrier end product, preferably by screening, and more preferably by using a 20 mesh top screen and an 80 mesh bottom screen. Particle fractions coarser than the silica carrier end product are preferably recycled to the mechanism used to break up the lumps of compressed feedstock mixture, while the fines are preferably recycled for mixing with dried silica base stock to form additional feedstock mixture.

The method of the invention is preferably performed as a balanced recycling system wherein dried silica base stock is fed to a compressor at a substantially constant rate to form lumps, the lumps then being broken up into smaller particles including a fraction of once compressed fines, and the once-compressed fines then being isolated and recycled into the substantially constant base stock feed. This process is repeated continuously until fines are generated at a substantially constant rate. When the production of fines reaches this equilibrium, a silica carrier end product and coarse particle fraction are each isolated from the broken up lumps, while the fines generated from the lumps continue to be recycled to the base stock feed. Preferably, the coarse particle fraction is broken up and recycled to the screening step.

While the mechanism has not yet been ascertained, it is thought that the denser feedstock created by mixing the compressed fines with dried silica particles results in a unique compacted body which, when granulated, forms the novel silica carrier of the invention having an unexpectedly good flow properties. particularly in light of its relatively low sphericity.

An apparatus with which the invention may be practiced is depicted in Fig. 1. Referring to Fig. 1, dried silica base stock is fed into a feed bin 10 through feed line 1. and is then fed from feed bin 10 to tandem roll compactor

11. The dried silica base stock is compressed by compactor 11 into lumps approximately 20-100% denser than the feed silica. The lumps are then fed to flake breaker 12 where they are broken into smaller particles which includes a compressed fines fraction. The smaller particles emerging from flake breaker 12 are fed to screener 13 via transfer screw 3 and bucket elevator 4, and the screener isolates the compressed fine fraction which preferably has a particle size range of less than about 100 mesh, and preferably less than about 80 mesh. The isolated fines are fed into feed bin 10 via feed line 5, where it is mixed with dried base stock silica from feed line 1 to form a feedstock mixture preferably comprising about 20-50 wt% compressed fines and about 50-80 wt% dried silica. Much as described above, the feedstock mixture is fed through tandem roll compactor 11 to form lumps, and the lumps are run through flake breaker 12 to form smaller particles which include a fraction of particles within the desired end product particle size range, a coarse fraction and a fraction of fines. The smaller particles are fed to screener 13 where the silica carrier end product is isolated and fed to product drum 7 through feed line 6. The coarse particle fraction is isolated at screener 13 and fed to granulator 14 through feed line 8, where it is broken up and recycled to the screener via bucket elevator 4. The fraction of fines recovered from screener 13 are recycled to feed bin 10 for mixing with dried base stock silica as described above. Thus, the processing apparatus of Fig. 1 can be utilized in a balanced recycling system in accordance with the invention, thereby minimizing by-product loss and maximizing the efficiency of the process.

Fig. 2 is a scanning electron micrograph (SEM) of a prior art silica carrier (Zeosil 175, manufactured by Rhone-Poulenc Chemie). As can be readily seen in the SEM. the carrier is substantially spherical. Fig. 3 is a scanning electron micrograph of a silica earner in accordance with the invention. The SEM shows the rough, substantially non-spherical shape of the carrier. EXAMPLE 1 The invention will now be described through specific examples.

While some of the examples are illustrative of preferred embodiments of the invention, they are not intended to limit the scope of the invention defined in the appended claims.

Utilizing an apparatus as depicted in Fig. 1 , a method in accordance with the invention was utilized to produce silica carriers in accordance with the invention. Several trials were run using one of three commercially-available dried silica base stock materials: Zeosyl® 1 10SD (manufactured by J.M. Huber Corporation); Hubersil® 1714 (manufactured by J.M. Huber Corporation); and Sipemat 22S (manufactured by DeGussa AG). The system feed hopper was loaded with one of the dried silica feedstocks (the system feed hopper is not depicted in Fig 1, but it is the source of the dried silica base stock in the example and would be attached to the distal end of feed line 1). In the case of 22S, feed hopper vacuum deaeration was used to improve feed density. The compaction/milling process was set up using a Schugi mill as the flake breaker with no retaining screen. A 20 mesh top screen and 80 mesh bottom screen were installed in the screener. An RD8 mill was used as the granulator. and was operated at 3000 rpm and with a 5/32" screen to mill the coarse screen oversize. The silica carrier end product was collected from between the 20 and 80 mesh screens in the screener. The system was started up and run according to the experimental design conditions compiled in Table 1. Each dried base stock silica was fed to the system from the system feed hopper at various rates. In addition, three fines recycle rates were used, ranging from no recycling of fines (represented as 0 in the recycle column of Table 1), a "normal" fines recycle rate as determined by the balanced system (represented as 1 in the recycle column of Table 1) and a fines recycle rate approximately double the balanced system rate (represented as 2 in the recycle column of Table 1 , recycle from prior runs were added to achieve this high recycle rate). A third process parameter, compactor roll pressure, was also varied over the series of runs as indicated in Table 1.

The process system was allowed to run for at least five minutes to balance (i.e., equilibrate to a substantially constant fines production rate), and silica earner product samples were collected at 6 and 8 minutes for evaluation. Each of these samples was evaluated for average particle size (APS), angle of repose, loose bulk density, vitamin E carrying capacity, linseed oil carrying capacity, and flow time. These characteristics were evaluated as follows: Average Particle Size CAPS')

Average particle size was determined using Microtrac II (Model 7998) Particle Size Analyzer. Angle of Repose

Angle of Repose is determined in the following manner: Attach a stainless steel funnel with an 8 mm aperture to a mechanical vibrator and elevate the assembly so that the funnel orifice is three inches above the center of the 3x2" plastic cylinder, which has a diameter of 2" and therefore, a radius of 1 ". Seal the funnel orifice with a small piece of tape. Place a 25 g sample in the funnel and remove the tape. Start the vibrator. Measure the height on the cylinder of the cone, when all of the sample has been discharged. If no distinguished cone has formed, a larger sample should be used. Calculate angle of repose as follows:

Angle of Repose = Arctangent (inverse tangent) (height, in) Vitamin E and Linseed Oil Carrying Capacity

This procedure uses a Spex Mill (Spex Industries, Inc., #8000

Mixer/Mill) which imparts a wrist action non-shear motion to the materials being tested. Suitable test jars have a 125 mi capacity and may be purchased from VWR Scientific (#IR 120-0125). The test is conducted by simply weighing carrier into the test jar, adding the test liquid, and shaking in the Spex Mill. Carrier weights are measured to O.Olg accuracy and vary with the carrier being tested. The test jar should be about half full and typical weights are from 5 to 10 grams. Addition of the liquid to the powder is facilitated by making a small hole in the powder. pouring the liquid into it, and covering it with dry powder from the sides. This prevents liquid from sticking to the sides of the jar and the lid while shaking. An equal weight of liquid and carrier are added to the jar and the sample is shaken on the Spex Mill for 30 seconds. This represents 50% carrying capacity as a starting point. If a noticeable amount of liquid adheres to the sides of the jar, it should be scraped off with a spatula prior to adding additional liquid. The sample is observed to confirm that all of the liquid has in fact been taken into the carrier. More liquid is then added to the same jar and the mixture shaken for an additional 30 seconds. This procedure is repeated until one observes a condition where a mixture of dry powder and wet lumps or granules has resulted. Small increments of liquid are added at this point (about 0.3 to 0.5 grams).' The mixture will gradually change from powder and lumps to a condition where all of the powder has disappeared. This represents the end point and has the appearance of "play dough". The end point is a condition where the carrier has been completely saturated and the resulting product becomes sticky to the touch. At a capacity of 1% less than the end point, the mixture exists as a true powder and will flow while avoiding caking problems encountered with over saturation.

% Carry Capacity = liquid wt. added / (powder wt. + liquid wt.) X 100

Loose Bulk Density

Loose Bulk Density is measured by pouring 100 g sample into a 250 ml graduated cylinder and is expressed as g/cc. Funnel Flow Time Flow by definition is a measure of the time required for a specific weight of material to pass from a container of specified geometry through an aperture of specified dimensions. The primary resistance to flow is due to the present of frictional and cohesive forces. Frictional forces are related to the size and shape of the product. Attach a metal funnel with a 5 mm aperture to a laboratory ring stand. Lay a carpenter's level across the top of the funnel and adjust it to a level position. Place a piece of scotch tape over the aperture of the funnel. Add 50 g of sample to the funnel. Simultaneously remove the tape and start the stopwatch. Stop the watch when the last portion of the material leaves the funnel. This is recorded as the funnel flow time. Tests should be performed in duplicate until the standard deviation is ± 1 second for flow time. The data obtained from the standard linear least squares statistical models were prepared from the raw data of Table 1 for the relationship of each of the process variables (base stock, fines recycle rate, roll pressure and dried silica base stock feed rate) to the end product silica carrier characteristics of bulk density, linseed oil carrying capacity and flow time. The results can be summarized as follows :

(1) Roll pressure, basestock. and recycle fines rate each had a statistically significant effect on bulk density, linseed oil carrying capacity, and flow time; base stock feed rate did not. (2) Similar product density ranges were generated for each basestock. (3) Roll pressure and recycle fines rate can be controlled to target a particular density regardless of feed stock used. Figs. 4-6 are graphical depiction's of the statistical modeling described above for the relationships between fines recycle rate and product bulk density, linseed oil carrying capacity and flow time when 110SD was used as the dried silica base stock. The R-square values for each relationship are 0.95, 0.87 and 0.92, respectively, thereby confirming the statistical significance of the linear relationships depicted in Figs 4-6. Virtually identical results were found for analyses performed for 1714 and 22 S.

Example 1 and Figs. 4-6 confirm our discovery that feed recycle rate is a significant process parameter to control the important carrier properties of bulk density, linseed oil carrying capacity and flow time of a product silica. IABLLI

Tol — Marling Kecycle Rot — Wed Hale Loose Hulk Ueπ i arrying l arrying I apacily Mow t hrough. ΛI'S Angle ol

Number Basesloc amount Pressure Kl'M g cc Capacity % Linseed Oil Smm funnel (set) Mi i ns Kcposc k V. Vitamin f 56% Oil

19 Hubersil 1 2000 45 0 3504 54 28 55 21 64 1 400 54 5 1714

20 Ilubcibil 1 1000 55 0 2833 59 81 56 31 84 3 180 33 6 1714

21 ilubeisil 2 2000 50 0 3389 55 25 55 67 65 5 102 ' 56 2 1714

22 Hubersil 1 1500 40 0 3166 57 49 56 10 69 9 104 55 5 1714

23 Hubersil 1 2000 50 0 3475 57 1 54 47 61 5 198 54 1 1714

24 Hubersil 1 2000 45 0 3466 58 01 53 98 64 9 197 51 4 1714

25 1 1500 10 0 3102 59 51 56 27 69 9 402 55 7 1714

26 Hubersil 1 1500 40 0 3156 56 70 56 31 70 4 198 55 8 1714

27 Hubersil 1 2000 30 0 3373 56 09 5641 64 6 401 57 1 1714

28 Hubersil 1 1000 50 0 2845 59 46 59 70 85 8 181 40 2 1714

29 Ilubeisil 0 1000 50 0 2826 60 51 59 99 88 2 186 17 1 1714

30 1 lubeisil 1 1000 30 0 2799 62 00 59 93 79 7 412 15 9 1714

31 Ilubeisil 2 1000 50 0 2770 59 28 59 76 86 4 179 12 1 1714

32 Ilubeisil 0 1000 50 0 2771 59 69 60 75 81 2 181 12 8 1714

33 Ilubeisil 1 1000 50 0 2824 59 57 59 89 81 8 182 40 7 1714

14 Ilubeisil 0 2000 50 0 1125 57 07 5 1 80 67 1 186 5 / 6 1714

15 0 2000 50 0 3332 55 89 55 84 65 9 199 60 8 1714

16 llllt- ISll 2 1000 50 0 2796 59 70 59 75 82 6 186 11 2

1714

37 llulieisil 1 1000 10 0 2850 59 46 59 46 77 6 670 41 8 1714

— Ra — Marling Kecycle Roll Fee Ra.^™ Loose Hulk υen I arrying i arrying apacity Mow I nrough — SPS — Angle ol

Number Basesloc amount Pressure RP g/cc Capacity % Linseed Oil Smm funnel (se ) Microns tteμose k DSI % Vitamin E 56% Oil

38 Sipemat 0 1000 50 0 2695 59 31 58 20 91 8 171 40 b

22S

39 Siμcma! 0 1000 50 0 2677 58 12 58 71 1 0 172 31 1

22S

40 Sipemat 2 2000 50 0 3513 51 29 51 40 61 0 180 1 50 1

22S

41 Sipemal 1 2000 50 0 3312 55 46 51 66 65 5 171 55 2

22S

42 1 1000 50 0 2775 59 05 57 10 98 7 166 41 1

22S

41 2 2000 50 0 1418 55 5 1 51 91 61 180 57 7

22S

44 2 1000 50 0 2844 58 68 57 14 78 7 165 ■10 5

22S

45 Sipemal 2 1000 50 0 2726 57 95 57 92 87 4 188 12 1

22S

46 Sipemal 1 2000 50 0 3311 54 50 51 98 66 1 191 5 1 5

22S

47 Sipemat 0 2000 50 0 3014 56 28 54 76 71 1 167 51 2

22S

48 Sipemat 1 1000 . 50 0 2808 57 96 57 50 84 2 170 42 9

22S

49 Sipemat 0 2000 50 0 3039 57 03 54 25 71 0 184 55 0

22S

EXAMPLE 2

Products in accordance with the invention were prepared in accordance with the method described in Example 1 , after which sphericity and flow time evaluations were taken and compared with comically available silica carriers. The results are summarized in Table 2.

TABLE 2

Particle sphericity or roundness is determined using Global Lab Image Software by Data Translations. The silica sample is dusted onto double-sided sticky carbon tape, which was previously affixed to a microscope slide. The black carbon tape provides a good contrast to the white particles. The slide is viewed under a microscope to select several representative particle fields. The total number of fields is chosen to give between 150 and 350 analyzed particles. Global Lab

Image software draws lines around the perimeter of each particle in the field and determines each particle's perimeter and area. The sphericity vaiues for all individual particles are averaged to give a total average sphericity. The closer the sphericity value is to one (1). the more round is a particle.

Sphericity = 411 x Area perimeter Surprisingly, Table 2 reveals that the Examples of the Invention have very low flow times (i.e. they flow well) even though they are much less spherical than the prior art silica. This runs counter to conventional thinking that high sphericity is required for good flow properties.

While the invention has been described with reference to specific preferred embodiments, it is understood that various changes, substitutions, modifications and omissions may be effected without departing from the spirit and scope of the invention defined in the appended claims.

Claims

What is claimed is:

1. A method of producing a silica carrier for liquid, comprising the steps of: ^" A. compressing dried silica into lumps which are about 20- 100% denser than said dried silica; B. breaking up said lumps into smaller particles wherein at least some of said smaller particles are fines having a particle size of less than about 100 mesh;

C. isolating said fines from said smaller panicles;

D. mixing said fines with additional dried silica to form a feedstock mixture;

E. compressing said feedstock mixture into feedstock lumps which are about 20-100% denser than said feedstock mixture;

F. breaking up said feedstock lumps into particles of various sizes, said particles comprising coarse, moderate and fine particle size fractions; and G. isolating said moderate particle size fraction as said silica carrier for liquid.

2. The method according to claim 1 , wherein said fines have a particle size of less than about 80 mesh.

3. The method according to claim 1 wherein said mixing is performed such that said feedstock mixture comprises about 20-50% fines and about 50-80% additional dried silica.

4. The method according to claim 1 , wherein at least one of said dried silica, said additional dried silica, and said feedstock mixture is subject to deaeration.

5. The method according to claim 1 , wherein said moderate particle size fraction is isolated by screening and is between about 20 mesh and about 80 mesh.

6. The method according to claim 1, wherein said fine particle size fraction is isolated by screening and is smaller than about 80 mesh.

7. The method according to claim 1 , wherein said coarse particle size fraction is isolated by screening and is larger than about 20 mesh. 8. The method according to claim 1 , wherein said fine particle size fraction is isolated and recycled to said mixing step.

9. The method according to claim 1, wherein said coarse particle size fraction is isolated, broken into particles of lesser size, and recycled to said isolating said moderate particle size fraction step.

10. The method according to claim 8, wherein said coarse particle size fraction is isolated, broken into particles of lesser size, and recycled to said isolating said moderate particle size fraction step.

11. The method according to claim 8. wherein said additional dried silica is fed at a substantially constant rate during said mixing step, and said recycling of said fine particle size fraction occurs at a substantially constant rate. 12. The method according to claim 10, wherein said additional dried silica is fed at a substantially constant rate during said mixing step, and said recycling of said fine particle size fraction occurs at a substantially constant rate.

13. A silica carrier for liquid, produced by a process comprising the steps of: compressing dried silica into lumps which are about 20-100% denser than said dried silica;

A. breaking up said lumps into smaller particles wherein at least some of said smaller particles are fines having a particle size of less than about 100 mesh;

B. isolating said fines from said smaller particles; mixing said fines with additional dried silica to form a feedstock mixture;

C. compressing said feedstock mixture into feedstock lumps which are about 20-100% denser than said feedstock mixture;

D. breaking up said feedstock lumps into particles of various sizes, said particles comprising coarse, moderate and fine particle size fractions; and E. isolating said moderate particle size fraction as said silica carrier for liquid.

14. The silica carrier for liquid according to claim 13, further comprising a sphericity of no greater than 0.655.

15. The silica carrier for liquid according to claim 13, wherein said fines have a particle size of less than about 80 mesh. AMENDED CLAIMS

[received by the International Bureau on 22 July 1998 (22.07.98) ; original claims 1 -2 , 13 and 15 amended ; original claim 3 cancel led ; remaining claims unchanged (3 pages ) ] 1. A method of producing a silica carrier for liquid, comprising the steps of:

A. compressing dried silica into lumps which are about 20- 100% denser than said dried silica; B. breaking up said lumps into smaller particles wherein at least some of said smaller particles are fines having a particle size of less than about 80 mesh;

C. isolating said fines from said smaller particles;

D. mixing said fines with additional dried silica to form a feedstock mixture comprising about 20-50 wt% fines and about 50-80 wt% additional dried silica;

2. The method according to claim 1 , wherein said fines have a particle sⁱze of less than about 100 mesh.

3. Cancelled.

4. The method according to claim 1 , wherein at least one of said dried silica, saⁱd additional dried silica, and said feedstock mixture is subject to deaeration.

5. The method according to claim 1 , wherein said moderate particle size fractⁱon is isolated by screening and is between about 20 mesh and about 80 mesh.

6. The method according to claim 1 , wherein said fine particle size fraction is isolated by screening and is smaller than about 80 mesh.

7. The method according to claim 1 , wherein said coarse particle size fraction is isolated by screening and is larger than about 20 mesh.

8. The method according to claim 1, wherein said fine particle size fraction is isolated and recycled to said mixing step.

9. The method according to claim 1 , wherein said coarse particle size fraction is isolated, broken into particles of lesser size, and recycled to said isolating said moderate particle size fraction step.

11. The method according to claim 8, wherein said additional dried silica is fed at a substantially constant rate during said mixing step, and said recycling of said fine particle size fraction occurs at a substantially constant rate.

12. The method according to claim 10, wherein said additional dried silica is fed at a substantially constant rate during said mixing step, and said recycling of said fine particle size fraction occurs at a substantially constant rate.

13. A silica carrier for liquid, produced by a process comprising the steps of: compressing dried silica into lumps which are about 20-100%) denser than said dried silica;

A. breaking up said lumps into smaller particles wherein at least some of said smaller particles are fines having a particle size of less than about 80 mesh; B. isolating said fines from said smaller particles; mixing said fines with additional dried silica to form a feedstock mixture comprising about 20-50 wt% fines and 50-8 wt% additional dried silica;

C. compressing said feedstock mixture into feedstock lumps which are about 20-100%) denser than said feedstock mixture; D. breaking up said feedstock lumps into particles of various sizes, said particles comprising coarse, moderate and fine particle size fractions; and

E. isolating said moderate particle size fraction as said silica carrier for liquid.

15. The silica carrier for liquid according to claim 13, wherein said fines have a particle size of less than about 100 mesh.