Earth boring – well treating – and oil field chemistry – Earth boring – Contains inorganic component other than water or clay
Reexamination Certificate
1999-10-27
2002-04-16
Tucker, Philip (Department: 1712)
Earth boring, well treating, and oil field chemistry
Earth boring
Contains inorganic component other than water or clay
C507S141000, C507S145000, C106S626000, C106S600000, C106S636000, C162S124000, C427S207100, C428S449000
Reexamination Certificate
active
06372694
ABSTRACT:
The present invention relates to suspensions, having a high storage stability, comprising an aqueous silicate solution and filler material.
Such a suspension is for instance disclosed in U.S. Pat. No. 4,361,659. Said suspension comprises crystalline calcium carbonate and quartz powder as fillers. To obtain a reasonable stability, an alkali resistant organic polymer is included in the suspension.
Organic chemicals are frequently not desirable in environmentally/health sensitive applications. Safety can be a serious issue when applied in the proximity of higher temperature equipment, e.g. when dried at higher temperatures. Furthermore, suspensions stabilized with organic stabilizers are also very sensitive to small variations in composition. For instance they may turn into gels during storage in case of slight overdosing of the stabilizing agent. Further suspensions stabilized with organic compounds are often not stable any more when only slightly diluted or at a different ionic strength of the aqueous phase.
In U.S. Pat. No. 4,403,059, a composition is described based upon an aqueous solution of alkali metal silicate with a content from 10 to 40% by weight of a powdered inorganic filler, having a good storage stability by using at least one zinc soap of a fatty acid, having from 12 to 22 carbon atoms as a stabilizer. With the composition according to this US-patent specification it is difficult to define the specific amount of organic stabilizer needed for optimum control of the stability, without excessively increasing the viscosity.
Furthermore the use of stabilizers containing zinc soap and polymers limits the possible application areas of such a suspension as a result of environmental and safety requirements.
Suspensions may also be stabilized with inorganic stabilizers as inorganic clays, with particles of around 0.1 micrometer in diameter, which clays are also used as thickeners, having swelling properties. Further these stabilizers may interfere with other components used in the specific composition.
Suspensions stabilized with inorganic stabilizers have generally high viscosities, due to the thickening properties of the stabilizer, which limits the applicability as well as the level of solids, that can be added.
In this respect reference is made to GB-A-2 058 818, in which an aqueous spray coating adhesive composition is disclosed comprising (i) a solution of an alkali metal silicate (ii) 1 to 10% by weight of finely divided inorganic powder containing, mineralogically, more than 15% kaolinite and (iii) finely divided silica. The silica is preferably included in the form of silicic acid. In this patent application, the kaolinite clay is used as filler/stabilizer. The total amount of fine filler material is limited to a maximum of 10% by weight.
At present it is not known how to manufacture aqueous silicate suspensions including relatively high amounts of fine filler materials, yet maintaining a sufficient storage stability in the absence of a stabilizer.
The present invention now provides a suspension having high storage stability, comprising an aqueous silicate solution and a filler material, wherein the silicate solution has a silicate content of at least 20% by weight, the filler material has an average particle size of 0.8-15 &mgr;m and a specific weight of below 2.75 kg/l, the filler being chosen from the group consisting of a) zeolites, b) fine particulate or fibrous amorphous inorganic material being relatively inert in an alkaline aqueous solution, comprising amorphous alkali metal alumino silicate c) fine particulate of graphite or carbon black, or d) mixtures thereof, said suspension having a high storage stability in the absence of a stabilizer. It is deemed surprising that the suspensions according to the invention have excellent storage stability in the absence of a stabilizer. Usually no settling of the fine filler material will take place within five days in a liquid column with a height of 24 cm. Preferably the specific weight of the filler material is below 2,5 kg/l.
It is noted that with the suspension according to the invention the use of stabilizers is by no means excluded, as it may sometimes for specific applications be advantageous to add a stabilizer e.g. to improve the stability of the suspension even further.
In the prior art aqueous silicate solutions are used for many applications where filling or binding properties are required. For instance leaking sewer pipes can be repaired in the ground by pumping a concentrated aqueous silicate solution into the leaking sewer system. Said silicate solution leaks out of this system filling up the space in the ground around the leaking locations. After some time the silicate in the sewer system is replaced by a hardener which also leaks into the leaking locations and the surrounding ground neutralizing the silicate and thus sealing the leaks. The silicate and the hardener thus fill up the space between the ground particles around the leaks.
Usually hardeners in the form of relatively expensive esters of organic acids are used, which hydrolyse and thereby release an acid which is needed for neutralization of the silicate.
It is of environmental and economic importance to minimize the amount of ester (and consequently of the silicate, needing neutralization) required.
The presence of the filler material in the suspension according to the invention has the advantage that for instance in the application of sewer system repair, this filler material may partially fill up the spaces between the ground particles, which reduces the amount of silicate needed and consequently also reduces the amount of ester needed. Moreover some of the pores in the ground will be blocked by the filler which reduces the penetration of silicate and ester into the ground, thus further reducing the amount of silicate and ester required. Also the solids content of the suspension is increased, thereby further increasing the density and the strength of the material filling up the pores in the ground and consequently further reducing the permeability of the layer around the leaking locations of the sewer system.
Usually in silicate liquors which are used for sewage system repair the SiO
2
content is limited to maximum about 33% by weight, which of course limits the amount of silica in silicagel (Dry Solids content), which can be formed by addition of the hardener. This limited solids content has a major influence on the physical and mechanical properties of the gel which can be obtained, limiting the density, strength and also limiting the attainable minimum for the permeability of the bound material, like sand, ground or soil. Also the hydrolysis of the ester into the acid can be relatively slow and uncontrolled.
As filler in the suspension according to the present invention advantageous zeolites are used. Zeolites are crystalline aluminosilicates.
Most zeolites are well known relatively inert environmentally harmless substances. Examples of zeolites, that are available or can be produced in fine particulate form are zeolites 4A, zeolite P, zeolite X and zeolite Y. Zeolite P is preferred, because of its layered structure, being non abrasive and relatively soft, also implicating less wear in machinery.
A suspension according to the present invention comprising synthetically produced zeolite P can be made, having the additional advantage of not containing carcinogenic crystalline silica (quartz, cristobalite) as can be the case when inorganic mineral fillers are applied. These crystalline silicas are declared to be carcinogenic, and it is to be expected, that the use thereof will be prohibited or restricted globally.
It is preferred to use zeolite P, prepared according to the method described in EP-B-0 384 070, having a silicon to aluminium ratio of not higher than 1,33, and a calcium binding capacity as defined in EP-B-0 384 070 of at least 150 mg CaO per g anhydrous aluminosilicate.
The filler material may advantageously comprise a fine particulate or fibrous amorphous inorganic material, being relatively inert in an alkaline aqueous so
Howarth Ian Maurice
Osinga Theo Jan
Crosfield Ltd.
Pillsbury & Winthrop LLP
Tucker Philip
LandOfFree
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