Title of Invention	"A PROCESS FOR THE PREPARATION OF SPHERICAL PELLETS OF SILICA"
Abstract	A process for the preparation of spherical pellets of silica which comprises mixing a slurry of precipitated silica, in presence of a binder in a ratio of 0.1-0.3% wt/wt, along with dry powder of precipitated silica in a mixer pelletizer and drying the spherical pellets at a temperature in the range of 100-150°C for a period of 1 to 4 hours to obtain spherical pellets of silica.

Full Text

This invention relates to a process for the preparation of spherical pellets of silica. This invention particularly relates to a method of preparing spherical pellets of silica, for using advantageously in different industrial processes relating to reinforcement of rubber and plastics, thickening and thixotropy of coating and paints, painting inks and cosmetics, free running and flowing of sticky solids and liquid substances, carrier for pesticides and insecticides. The process of the present invention more particularly relates to a method of preparing spherical pellets of light and fine particles of silica into spherical balls using plain water or inorganic binder like bentonite clay or organic binder like starch solution. Precipitated silica is a versatile inorganic material, the demand of which is increasing day by day. Precipitated silica being very fine, light and bulky material creates problem during transportation and use. Dusting of the fine silica particles during handling also causes serious health hazards. Moreover, due to its fineness, the material is not much free flowing and is inconvenient for easy dispensing. In view of above, pelletization of such fines into spherical balls for their use is very much advantageous. The factors for such advantages are - (a) densification for convenience in transport and storage, (b) prevention of material loss, (c) prevention of dusting, (d) production of free flow solids, (e) convenience in dispensing and (f) prevention of caking. Several pelletizing processes have been developed for agglomerating fines like iron ores, alumina, zeolite, f umed s i1ica etc. S. N. Dutta et. al. in Indian patent No. 119163 (1968), have described the preparation of iron ore pellets using cement as binder for making burden material for blast furnace. D. K. Dutta et. al. in Indian Patent No. 171191 (1993), have made an improvement upon this process where lesser amount of binder has been used. M. A. Goksel, (Fundamentals of cold bond agglomeration process, Proceedings 2nd International Symposium on Agglomeration, Atlanta, 1977, p-877) also described a process of cold bonded pe11etization of iron ore fines using cementitious binders. Al1 the above processes involve utilization of dense and coarse particles of iron ore fines as wel1 as cementitious binder for pelletizing in a disc / drum pelletizer. Pe11etization of very fine and light particles like precipitated silica is not possible by such pelletizer and method. Moreover, cementitious binder can not be used for pelletizing the precipitated silica because of the end use of such pellets in industries like rubber, paint etc. R. Waterman and F. F. Apian (Pe11etization of natural sedimentary zeolite fines, Proceedings 4th International Symposium on Agglomeration, Toronto, Canada, publisher L. G. Kuhn, 1985, p-357) described pe11etization of natural sedimentary zeolite fines using a number of clay and non-clay binders by a drum or disc pelletizer for using as cation exchanger. R. P. Usman and D. V. S. Murthy (Studies in pe11etization of phsphogypsum, Proceedings 4th International Symposium on Agglomeration, Toronto, Canada, publisher L. G. Kuhn, 1985, p-367) have described a process of pe11etization of phosphogypsum powder by a rotary drum pelletizer for using in cement industry. The above processes involve binders like clay, cement etc., denser & coarser particles of zeolite, phosphogypsum and a disc / drum pelletizer. Such method of pe11etization can not be used for very fine and light particles of precipitated silica. A few pe11etization processes of fumed silica (obtained as by product from silicon and ferrosilicon industries) are also known CV. P. Mehrotra, Palletizing fumed silica to facilitate handling and transport, Pat. No. DE 3525247 (1986); E. Sakai and Y. Shibayama, Silica pellets with low bulk volume and excellent dispersibi1ity, Pat. No. JP 62,202,848 (1987); M. Nakamura, Pe11etization of silica , Pat. No. JP 01,45,711 (1989) and H. F. W. Taylor, Cement chemistry, Academic Press, 1990, p-305)]. In all these processes of pel 1etization of fumed silica, binders were not used. The process of emulsion peI 1etization was followed by Nakamura. The pellets of fumed silica prepared by the above methods are in general used in cementing technology. Since the pellets of fumed silica do not contain any suitable binder, during transportation through long distance and rough terrain, considerable amount of fines may generate. However, pelletization of very light and fine particles like precipitated silica having very low bulk density and very high surface area (compared to fumed silica) into spherical balls is not hitherto known. On the other hand, subically shaped bodies are available commercially. But such angular bodies are less free flowing during its use and more friable compared to spherical pellets and therefore, less advantageous in handling and use. The main object of the present invention is to provide a method for preparing spherical pellets having suitable size, adequate mechanical strength, abrasion resistance and other desired properties from a slurry or dry powder of precipitated fine silica for using in different industries like rubber, plastics, paints. Accordingly, the present invention provides a process for the preparation of spherical pellets of silica which comprises mixing a slurry of precipitated silica, in presence of a binder in a ratio of 0.1-0.3% wt/wt, along with dry powder of precipitated silica in a mixer pelletizer and drying the spherical pellets at a temperature in the range of 100-150°C for a period of 1 to 5 hours to obtain spherical pellets of silica. In some cases only water has been used as binder for making the green pellets. Since, cementitious binder cannot be used in making pellets of precipitated silica considering their end use, other types of binders have been used in the present invention. The binder used may be water soluble organic polymer like starch or inorganic binder like bentonite clay. The binder content in the pel lets is in the range of 0. 1 to 0. 5 % (wt./wt.). The green pellets are prepared by using a slurry of precipitated silica and water and a dry powder of precipitated silica. 55 - 75 % of the slurry and 25 - 45 % of dry powder are usrad to prepare the pellets. Solid content in the slurry is in the range of 1O - 3O %. The surface area of the dry silica powder may be in the range of about 170 sq. m / g (as determined by nitrogen adsorption method). The pellets so obtained are dried in an air oven at a temperature in the range of 1OO - 15O degree Celsius for a period in the range of 1 - 5 hours. In an embodiment of the present invention, dry powder of the precipitated silica is pelletized using a spray of starch solution (5 % solid content) as binder in a mixer pelletizer and finally drying the green pellets in an air oven at the temperature 1OO - 150 degree Celsius for a period of 1 - 5 hours. In an another embodiment of the present invention, dry powder of the precipitated silica is pelletized using a spray of water only as binder in a mixer pelletizer and finally drying the green pellets in an air oven at the temperature 100 - 150 degree Celsius for a period of 1 - 5 hours. In an another embodiment of the present invention, dry powder of the precipitated silica is mixed evenly with dry bentonite clay powder as binder and then pelletized using a spray of water in a mixer pelletizer and finally drying the green pellets in an air oven at the temperature 100 - 150 degree Celsius for a period of 1 - 5 hours. The process of the present invention is illustrated with the following examples which should not be construed to limit the scope of the invention. The chemical composition and analyses of ingredients are presented in Table - 1. The Table 1. Analyses of ingredients. (Table Removed) ppt. - precipitated physico-chemical characteristics of the precipitated silica used in this invention meet the specifications of various industries like rubber and plastics, coating and paints, painting ink and cosmetics, pesticides and insecticides etc. where the prepared pellets find their end use. Other types of silica powder like fumed silica can not be used in this invention because of its low surface area and other characteristics which do not meet the specifications of the above mentioned industries. Example 1 750 ml slurry of precipitated silica (20 % solid content. Table 1) was poured into a rotating mixer pelletizer (dia - 12 inch, rpm - 32, collar height - 6 inch, impeller rpm - 5O to 6OOO) and the impel Ier was rotated at a speed of about 150 rpm. About 2 0 g of dry precipitated silica (Table 1) was added continu us 1y to dry up the slurry to a stage where water of the lurry acts as binder and sufficient pellets of desired ize (1-4 mm dia) were produced. During this period the rpm of impeller was increased to about 1000. The pel lets so formed were col lected into another simple disc pelletizer (dia - 12 inch, rpm - 36, collar height - 6 inch) where the pellets were made spherical by spraying water (about 170 ml) and sprinkling dry powder (about 100 g). The pellets so obtained were dried at 12O + 5 deg.C for a period of 2 and 5 hours in an air oven. Examplt 2 150 g of the dry precipitated silica powder (Table 1) was poured into the rotating mixer pelletizer. The impeller of the pelletizer was rotated at 100 rpm. About 400 ml of water (acting as binder for green pel lets) was sprayed over the powder during which the impeller rpm was gradually enhanced to 500. Seed pellets of desired size (1-3 mm dia) were formed. The pellets were then taken into another simple rotating disc pelletizer, where water (15 ml) was sprayed over the seed pel lets and dry powder (9O g) was added in order to obtain spherical pellets. The pellets so obtained was then dried at 12O +5 deg.C for a period of 2 and 5 hours. Example 3 750 ml slurry of precipitated silica (20 % solid content, Table 1) was mixed with 3O ml of organic binder (starch solution of 5 % solid content, Table 1) and the whole mass was poured into a rotating mixer pelletizer. About 250 g of dry precipitated silica (Table 1) was then added to it slowly in 5 minutes. The initial rpm of the impeller was gradually increased from 10O to 150O in order to make desired sized pellets (1-4 mm dia). The rotation of the drum was continued for about 1O minutes during which the rpm of the impeller was fixed at about 15O. The pellets so obtained were then taken into another disc pelletizer and rotated for about 15 minutes during which 24O ml of starch solution ( O.OO23 X) and dry powder about 150 g was added slowly for obtaining desired shape of the pel lets. The pel lets were then dried at 120 +5 deg.C for a period of 2 and 5 hours. Exanplt 4 150 g of the dry precipitated silica powder (Table 1) was thoroughly mixed with 0.45 g of inorganic binder (bentonite clay, Table 1) and was poured into the rotating mixer pelletizer. The impeller of the pelletizer was rotating at 100 rpm during which water (400 ml) was sprayed over the powder and the impeller rpm was gradually enhanced to 5OO. Seed pellets of desired size (1-3 mm dia) were formed. The pellets were then taken into another simple rotating disc pelletizer, where water (15 ml) was sprayed over the seed pellets and dry powder (90 g) was added in order to obtain spherical pel lets. The pel lets so obtained was then dried at 120 + 5 deg. C for a period of 5 hours. Friability and crushing strength of the dried pellets were determined and are presented in Table 2. The pellets obtained from Example 1 showed higher strength and less friability for higher size pellets (Table 2, si. no. 1 & 2) and similar results were also found for pellets obtained from Example 2 (Table 2, si. no. 3 & 4). Pellets obtained from Example 3 where starch binder was used (Table 2, si. no. 5 -8) showed higher strength and lower value of friability than those prepared without starch binder (Examples 1 & 2). Pellets prepared using bentonite binder (Example 4, Table 2, si. no. 9) showed lowest value of friability. Table 2 Crushing strength and friability of precipitmted silioa pollet. (Table Removed) 1 - with respect to dried pellet; *2 drying temperature 120 +5 deg.C; *3 - friability test was carried out with the help of Friability Test Apparatus, make : Indian Equipment Corporation, Bombay; *4 - average value; *5 - Starch binder; *6 - Bentonite binder The advantages of the invention are (a) free flowing behaviour of the spherical pellets (b) adequate mechanical strength and abrasion resistance for transportation and handling of the pellets prepared using binders and (c) reduced volume of the materials. We claim : 1. A process for the preparation of spherical pellets of silica which comprises mixing a slurry of precipitated silica, in presence of a binder in a ratio of 0.1-0.3% wt/wt, along with dry powder of precipitated silica in a mixer pelletizer and drying the spherical pellets at a temperature in the range of 100-150°C for a period of 1 to 4 hours to obtain spherical pellets of silica. 2. A process as claimed in claim 1 wherein the binders used are water soluble organic polymer (starch) and inorganic material (bentonite clay). 3. A process for the preparation of spherical pellets of silica substantially as herein described with reference to the examples.

Documents:

1267-del-1994-abstract.pdf

1267-del-1994-claims.pdf

1267-del-1994-correspondence-others.pdf

1267-del-1994-correspondence-po.pdf

1267-del-1994-description (complete).pdf

1267-del-1994-form-1.pdf

1267-del-1994-form-2.pdf

1267-del-1994-form-4.pdf

1267-del-1994-form-5.pdf

1267-del-1994-form-6.pdf

1267-del-1994-form-9.pdf