Compositions: coating or plastic – Coating or plastic compositions – Alkali metal silicate containing
Reexamination Certificate
2000-03-31
2002-04-23
Marcheschi, Michael (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Alkali metal silicate containing
C106S624000, C106S406000, C106S407000, C106S482000, C106S492000, C423S335000, C423S338000, C428S403000, C502S405000, C502S407000
Reexamination Certificate
active
06375735
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to precipitated silicas and silica gels, wherein each silica type has adhered or deposited activated carbon produced from a caustic biomass ash solution.
BACKGROUND OF THE INVENTION
Commercially available precipitated silicas are produced through an acidulation process utilizing a caustic silicate solution, such as sodium silicate solution, with a mineral acid, such as sulfuric acid. Commercially available caustic silicate solutions are conventionally made by fusing high purity soda ash and silica sand in furnaces at temperatures of 1300° to 1500° C. and higher to produce a solid glass. The silicate solution is made by dissolving the glass with steam and hot water. This is the foundation of all commercial processes for making sodium or other soluble silicate solutions today. Both processes are very energy intensive, thus very expensive, and the silicates generally contain metal contaminants found in the earth in amounts from about 500 to 10,000 ppm. Processes for producing precipitated silicas are described in detail in U.S. Pat. Nos. 2,657,149; 2,940,830; 4,157,920; 4,495,167; and 4,681,750, the entire disclosures of which are incorporated herein by reference, including the processes for producing precipitated silicas and the properties of the product. In general, acid and silicate solutions are added to a reactor and by manipulation of the process conditions, the chemical and structural properties can be controlled. After completion of the precipitation reaction, the solid precipitate is filtered, washed to remove soluble byproducts, dried and milled to the desired size.
Silica gels, another form of amorphous silica with slightly different properties, are produced in a similar manner as previously described, however, in lower pH solutions. The process for commercially produced silica gels, entails treating a solution of soluble metal silicate, usually sodium silicate, with a strong mineral acid such as sulfuric or hydrochloric acid. Since the gel phase does not settle out, silica gel is customarily described as a non-precipitated, homogenous mixture of colloidal amorphous silica particles. The end product is then washed to remove soluble salts, dried, and reduced to a suitable particle size range. There are generally two types of silica gels, namely, hydrogels and aerogels. Hydrogels are prepared as previously described and aerogels are usually prepared from unrefined hydrogels by displacing the water with an alcohol, which is recovered during the drying process. Silica gel, a glassy material, has immense internal pore area, giving it the capacity to absorb large quantities of moisture as well as other substances.
Precipitated silicas with added carbon adhered or deposited on them are utilized for various rubber applications, which require high strength and abrasion resistance, such as tires and industrial products. The current methodology for using combinations of silica and carbon as reinforcing agents in rubber entails blending the solid components into the rubber composition, which usually requires the addition of dispersants and coupling agents to achieve a homogenous mixture. In practice, the carbon is normally selected from carbon blacks that are commercially available and conventionally used in tires, treads, hoses, etc. Examples include carbon blacks with ASTM designated N-numbers, which are well known to those skilled in the rubber compounding art. These carbon blacks are produced commercially by subjecting heavy residual oil feedstock to extremely high temperatures in a carefully controlled combustion process. This production process is very energy and labor intense, which results in high manufacturing costs.
In practice, the commonly used siliceous compounds (silicas) employed in rubber compounding applications are typically precipitated silicas, such as those obtained by the acidification of soluble silicates, i.e., sodium silicate. The preferred silicas include those marketed by AKZO, PPG, DuPont, Rhone-Poulenc, Huber and Degussa. Also, coupling agents capable of reacting with both the silica surface and the rubber elastomer are utilized to cause the particulate precipitated silica to have a reinforcing effect on the rubber.
As mentioned previously, precipitated silicas and silica gels are utilized as reinforcing fillers in many applications, particularly, in the rubber industry. For various rubber applications, which require high strength and abrasion resistance, such as tires and industrial products, a combination of silica and amorphous carbonaceous components are utilized. Carbon black and silica with or without a coupling agent are commonly used as reinforcing fillers for various rubber products, including the treads, undertreads, and sidetreads of tires; industrial hoses, conveyor belts, rolls; rubber shock absorbers; and the like. The use of silica and carbon as reinforcing fillers for elastomers, including sulfur curable rubber, is well known to those skilled in such art.
U.S. Pat. No. 5,610,216 discloses a rubber composition with the combination of silica and carbon black utilized as reinforcing filler, with a ratio of silica to carbon black in the range of 3/1 (75% silica and 25% carbon) to about 30/1 (96.77% silica and 3.23% carbon). The rubber composition comprises about 25 to about 100 parts of reinforcing filler composed of silica and carbon black per 100 parts by weight of rubber (phr).
As previously mentioned, carbon black is produced commercially by subjecting heavy residual oil feedstock to extremely high temperatures in a carefully controlled combustion process. By adjusting conditions in the combustion process, dozens of commercial grades with varying structure and particle size, are produced. Carbon black structural properties such as, surface area and pore volume, are evaluated and measured using methods similar to those utilized for precipitated silicas and silica gels. The principle measurement of a carbon black's structure, i.e., the degree of interlinkage between particles, is usually determined by the DBP (dibutyl phthalate) oil absorption in accordance with ASTM D2414, with values in milliliters absorbed per 100 grams of carbon (ml/100 g). The measurement of surface area is customarily performed by a BET (Brunauer, Emmett, Teller) nitrogen adsorption test method, ASTM D3037 or ASTM D4820 with values in square meters per gram of carbon (m
2
/g). Some manufacturers use ASTM D3765, CTAB (cetyltrimethylammonium bromide) adsorption for surface area, which results in values in m
2
/g identical to the BET values, in most cases. Also, some manufacturers utilize ASTM D1510, Standard Test Method for Carbon Black-Iodine Adsorption Number, as a measurement of surface area. For example, a higher Iodine Number, expressed in mg/g, is indicative of smaller particle size and higher surface area, which typically indicates a better reinforcing carbon black for rubber elastomers.
Iodine Numbers and DBP Numbers together with ASTM designated N- numbers for carbon blacks, may be found in
The Vanderbilt Rubber Handbook,
13th Edition (1990). The DBP number is indicative of structure with a higher number indicating a higher structure and usually larger aggregate size. The BET nitrogen adsorption number is indicative of surface area with a higher number indicating a higher surface area and, usually, a smaller particle size.
U.S. Pat. Nos. 5,168,106; 5,679,728; and 5,798,405 disclose carbon blacks suitable for the aforementioned uses, with structure properties as follows: DBP (dibutylphthalate) Adsorption Numbers ranging from 80 to 135 ml/100 g, BET Nitrogen Adsorption Numbers ranging from 20 to 300 mg/g, and Iodine Numbers ranging from 25 to 300 mg/g.
U.S. Pat. No. 5,807,494 discloses a silica gel composition with a carbonaceous component attached to a gel component. The carbonaceous component may be selected from the group consisting of: carbon blacks, carbon fibers, activated carbons and graphite carbons. If necessary, the carbonaceous component may be modified so that it will attach to the gel com
Kubiak Kenneth F.
Smith Jeffrey B.
Stephens Douglas K.
Wellen Clyde W.
Agritec, Inc.
Marcheschi Michael
Weiler James F.
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