Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
2003-02-21
2003-12-16
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C423S335000, C423S339000
Reexamination Certificate
active
06663963
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to novel silica products and, more particularly, to hybrid precipitated/gel amorphous silica products and similar materials having very high liquid absorption and very high liquid carrying capacities, as well as methods of producing such materials.
2. Description of the Related Art
From a general standpoint, commercially available synthetic silicas can be broadly divided into two basic categories of manufacture, as described in “Cosmetic Properties and Structure of Fine-Particle Synthetic Precipitated Silicas”, J. Soc. Cosmet. Chem., 29, 497-521, (August 1978). These categories are those provided from a liquid phase and those from a vapor phase process.
Vapor process silicas, called fumed or pyrogenic silicas, are prepared by hydrolysis of silicon tetrachloride vapor with an oxygen-hydrogen gas at high temperatures to produce silica and gaseous hydrogen chloride by-product. Pyrogenic silicas have high external surface areas and differ from other silicas (e.g., gels, precipitated silicas, and so forth) prepared by the liquid phase process in terms of morphology and other physical parameters.
Liquid phase silicas include amorphous precipitated silicas, silica gels and colloidal silicas produced by acidulating an alkali metal silicate with a mineral or organic acid such as sulfuric acid. In recent years, and to further expand the utility of precipitated silicas, such as for liquid carrier applications, among other things, prior art workers have pursued new techniques for producing precipitated amorphous silicas tailored to have desired properties.
Silica carriers for oils and other liquids are used to deliver precise dosages of absorbed liquid for inclusion in materials such as livestock feed, rubber and plastics. Silica carriers provide a predictable dosage of liquid under conditions where viscosity variations in an uncarried liquid would render dosage control extremely difficult. Further, the particulate 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 carrying capacities, and good flow properties for the combined liquid solid mixture.
A problem associated with conventional silicas having high carrying capacities of various liquids is the friable nature of the silicas, which causes them to break down during manufacturing and customer processing, which results in significant loss of carrying capacity. Therefore, the provision of an efficient method for producing a high structure precipitated/gel silica or hybrid (geltate) carrier for liquid that measurably boosts the liquid (e.g., oil) carrying capacity without sacrificing structural robustness or otherwise undermining the structural strength or integrity of the silica product, would represent a significant improvement over known production methods.
SUMMARY OF THE INVENTION
The present invention relates to a new group of hybrid amorphous silicas that are robust, very high structure materials endowed with a very high liquid carrying capacity and reduced friability. For purposes herein, the terminology “hybrid amorphous silicas” means amorphous silicas having characteristics of both precipitated silicas and silica gels, and this hybrid silica material is also referred to as a “geltate.”
These and other advantages are achieved by the provision in the present invention of a hybrid silica or gel-like precipitated amorphous silica product having a percent carrying capacity DBP value equal or greater than 76.0 and a linseed oil absorption value exceeding 250 cc/100 g. According to one embodiment, the inventive silica product of this invention has a % carrying capacity DBP value in the range of 76.0 to 85.0, a linseed oil absorption of about 250 to about 425 cc/100 g, a BET in the range of about 300 to about 675 m
2
/g, a CTAB specific surface area ranging from about 200 to about 475 m
2
/g, and a total pore volume (Hg) greater than about 4.5 cc/g.
The present invention also provides methods for producing such a very high liquid carrying capacity hybrid silica in which the silica product is produced by acidulation of an alkali metal silicate under unique reaction protocols.
In one general mode of making the inventive hybrid silica, the method includes the steps, in this sequence, of:
providing an aqueous reaction medium heated to a temperature of from about 30° C. to about 57° C.;
adding simultaneously an acid and alkali metal silicate to the heated aqueous reaction medium at respective rates that maintain the pH of the reaction medium at between 5.0 to 7.0 to form a slurry;
raising the temperature of the reaction medium to about 65° C. to about 95° C.; and
separating and recovering precipitated amorphous silica product from the slurry.
Experimental data, such as reported herein, demonstrates the unexpected importance of conducting the step of raising the temperature of the reaction medium to about 65° C. to about 95° C. after performing the prior low temperature/low pH acidulation reaction step involving the co-addition of acid and alkali metal silicate. The filtration characteristics are also enhanced by this protocol including the step of ramping up the temperature of the reaction medium after the initial acidulation reaction step and before conducting further processing.
In one further embodiment of the invention, the inventive method includes the steps, in this sequence, of:
(a) providing an aqueous reaction medium heated to a temperature of from about 30° to about 57° C.;
(b) adding simultaneously an acid and alkali metal silicate to the heated aqueous reaction medium at respective rates that maintain the pH of the reaction medium at between 5.0 to 7.0 to form a slurry;
(c) discontinuing the acid addition while continuing addition of the alkali metal silicate until the pH of the reaction medium becomes 5.5 to 9.5;
(d) raising the temperature of the reaction medium to about 65° C. to about 95° C.;
(e) optionally adding acid to adjust the pH of the slurry to about 5.0 to about 6.5; and
(f) separating and recovering precipitated amorphous silica product from the slurry.
Additional experimental studies, reported herein, have shown that even further enhancements in the liquid carrying capacity properties of the very high structure silica product of this invention are achievable by additionally including the above-identified process step (c) in the inventive process scheme. Step (c) forms part of an “aging” procedure where alkali metal silicate alone is added for a time period immediately following the initial acidulation reaction performed in step (b) involving the co-addition of the acid and alkali metal silicate, but before the subsequent heating of the aged reaction medium to about 65° C. to about 95° C. in step (d) to complete the aging procedure.
The hybrid amorphous silica of this invention has numerous and diverse utilities. The inventive silica is implementable as carrier silica, anti-caking silica and free flow silica, among other things. The inventive silica also can be used advantageously as an additive in paper, thixotropes, rubber, paint and coatings.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention provides a new group of hybrid amorphous silicas in the form of a precipitate/gel amorphous materials, which are produced as very high structure materials with enhanced microporosity to provide excellent absorptive power yet without rendering the silica products fragile and friable.
The precipitated amorphous silicas of the present invention are characterized by a % carrying capacity DBP value that is at least 76.0 or greater in value, while maintaining a robust particulate morphology and favorable performance attributes such as a linseed oil absorption exceeding about 250 cc/100 g. The % carrying capacity DBP value range imparted to the silica product of
Fultz William C.
Preston Barry W.
Hoch Raymond
J. M. Huber Corporation
Le H. Thi
Nieves Carlos
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