Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
1999-07-29
2001-10-23
Hendrickson, Stuart L. (Department: 1754)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C423S448000, C423S460000
Reexamination Certificate
active
06306264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing an expanded graphite by using SO
3
gas produced from fuming sulfuric acid or anhydrous sulfuric acid.
2. Description of the Prior Art
Graphites are made of carbon atoms like coke and diamond, and the hexagonal structure of graphite forms a layer structure to give a specific lamellar crystal structure. When graphite is oxidized by using an appropriate oxidant, chemical ions such as SO
3
2−
and NO
3
− are introduced between the laminated layers to produce an interlayer compound. When thus obtained graphite is heated, the chemical ions in the interlayer compound become gases and the interlayer compound expands several hundred times to several thousand times of its original size due to the pressure of the generated gases. The c-axis of thus expanded graphite is from 20 to 250 times of c-axis of the common graphite.
Conventionally, expanded graphites are manufactured by oxidizing natural and/or pyrolyzed graphite with a mixture of sulfuric acid and oxidant, such as a mixture of sulfuric acid and nitric acid, sulfuric acid and potassium permanganate, sulfuric acid and hydrogenperoxide, or sulfuric acid and perchloric acid. The oxidized graphite is then washed with water and dried. The dried product is rapidly heated so that thus obtained graphite compound can expand to obtain the resulting expanded graphite.
The above-described conventional method will be described as follows. Japanese Patent Laid-Open No. sho 59-35078 discloses a method for producing an expanded graphite form. The expanded graphite is manufactured by impregnating the graphite with an acid mixture of 50% sulfuric acid and 60% perchloric acid in a ratio of 100:5 by weight and then heating the graphite at 1000° C.
Japanese Patent Laid-Open No. sho 61-72609 discloses a method for producing an expanded graphite by using sodium and tetrahydrofurane. The obtained expanded graphites are commonly used for a material for gasket, a composite material of cement and mortar, an expanded graphite sheet and the like. Additionally, expanded graphites obtained by using acid mixtures containing sulfuric acid as an oxidant and as a main intercalating agent have more specific use as a material for an expanded graphite sheet, an oil adsorbent and an inorganic fiber composite material as disclosed by U.S. Pat. No. 5,149,518. Alternatively, U.S. Pat. No. 5,503,717 discloses a method of producing an expanded graphite by electrochemically immersing ZnCl
2
between the graphite layers in an aqueous solution and then heating thus obtained product.
However, in the above described conventional methods, graphite particles should be impregnated with a large amount of concentrated acid mixture (about 1.5 times of the amount of graphite particles) for a prolonged period of time. Consequently, the consuming amount of the acid mixture is very large while generating a large amount of waste acid. Moreover, since the waste acid contains various compounds of acids and oxidants, the treatment of the waste acid become a complicated task.
Due to these problems, the commercialization of these methods for producing the expanded graphite is difficult to implement. In addition, SO
3
gas and SO
2
gas generated during the producing process of the expanded graphite are environmentally hazardous agents. Further, sulfur remained within the expanded graphite cause corrosion of metals when the expanded graphite is applied to the packing, the gasket sheet and the like. Although these problems are not a factor for an expanded graphite manufactured by utilizing alkaline metal and hydrofuran and the electrochemical method utilizing ZnCl
2
, the use of alkaline metal is expensive and a current having a current density of from 2000 to 5000 A/m
2
should be applied, hence increasing the energy consuming cost and so the manufacturing cost.
SUMMARY OF THE INVENTION
Accordingly, it is an object in the present invention to provide a novel method for producing an expanded graphite for a material for an oil adsorbent, a packing sheet and a volatile organic compound(VOCs) adsorbent, in which the expansion of granular graphite particles, using a single oxidant such as fuming sulfuric acid or anhydrous sulfuric acid, is implemented by contacting the graphite particles with SO
3
gas generated from fuming sulfuric acid or anhydrous sulfuric acid, and as a result, the amount of the consuming acid and hazardous waste acids along with manufacturing costs can be minimized and reduced by continuously recycling the sulfuric acid, while reducing remaining sulfur in the expanded graphite.
Another object of the present invention is to provide an oil adsorbent having an excellent adsorption property by utilizing the expanded graphite of the present invention.
To accomplish the above object, there is provided in the present invention a method for producing an expanded graphite comprising the steps of producing SO
3
-graphite interlayer compound by contacting graphite particles with SO
3
gas generated from fuming sulfuric acid or anhydrous sulfuric acid, separating excessive amount of condensed SO
3
from the SO
3
-graphite interlayer compound, and expanding the SO
3
-graphite interlayer compound by applying energy thereto.
The other object of the present invention can be accomplished by an oil adsorbent comprising an expanded graphite manufactured by a method comprising the steps of producing SO
3
-graphite interlayer compound by contacting graphite particles with SO
3
gas generated from fuming sulfuric acid or anhydrous sulfuric acid, separating excessive amount of condensed SO
3
from the SO
3
-graphite interlayer compound, and expanding the SO
3
-graphite interlayer compound by applying energy thereto.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in more detail below.
In the present invention, the graphite is expanded by forming a SO
3
-graphite interlayer compound through introducing SO
3
between graphite layers by contacting the granular graphite particles with SO
3
gas generated from fuming sulfuric acid or anhydrous sulfuric acid and then applying energy to the SO
3
-graphite interlayer compound by heat or exposing the resulting interlayer compound to microwave.
The fuming sulfuric acid or anhydrous sulfuric acid is used to oxidize the SO
3
the graphite in the present invention. After removing SO
3
remaining on the surface of the surface of the oxidized graphite particles, energy is applied to expand the resulting graphite. The amount of the waste acid can be minimized by absorbing SO
3
gas generated during the expansion process into the sulfuric acid and reusing thus obtained acid.
Further, since the waste acid generated in the present invention has a single chemical component, detoxification of the waste acid can be simply carried out by neutralization, and the product of the neutralization, that is, mirabilite(Na
2
SO
4
) is reusable. Hence, the method of the present invention is more economical and environmentally friendly than the conventional methods.
The amount of the oxidant having the single chemical component such as the fuming sulfuric acid or the anhydrous sulfuric acid according to the present invention can be reduced to {fraction (1/10)}-{fraction (1/100)} compared to the amount of the oxidant used in the conventional methods. In addition, the oxidant according to the present invention can be continuously reused and the amount of the generated waste acid can be largely reduced. Thus, the present invention can resolve the difficult problem of treating the waste acid, which is prevalent in the conventional methods.
In the present invention, a reactor having the fuming sulfuric acid or anhydrous sulfuric acid is stood at room temperature or is heated to generate SO
3
gas. The preferred mixing ratio of the amount of the fuming sulfuric acid or anhydrous sulfuric acid to the amount of the graphite is 100:20-300 by weight. More preferably, the mixing ratio is 100:100-200 by weight.
The SO
3
-graphite interlayer comp
Choi Sang Won
Kim Seung Won
Kwon Oh Yun
Kwon Young Bae
Fish & Richardson P.C.
Hendrickson Stuart L.
Korea Institute of Machinery and Materials
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