Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
2000-12-19
2003-06-10
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C423S44500R, C423S447600, C423S447800, C423S447900, C502S430000
Reexamination Certificate
active
06576212
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a process of producing a carbonized material from biomass.
One known method of producing activated carbon includes carbonizing a wood material, such as wood chips or sawdust, at a temperature of at least 250° C. The carbonized product is then activated with a gas such as steam.
During the heating step, the carbonization starts at surfaces and gradually proceeds towards the inside. Thus, the known method has a problem that tar produced by pyrolysis is apt to deposit within pores of the carbonized product. In particular, when the raw material is large sized wood chips, the tar deposition becomes significant and, additionally, the carbonization requires a long time in order to carbonize the central region thereof.
JP-B-H06-72003 discloses a method of simultaneously producing anhydo-saccharides and a carbonized product from a cellulose material by microwave heating. The specific surface area of the carbonized product obtained with the method is 600-660 m
2
/g at a center region thereof, about 250 m
2
/g at an intermediate region and as small as 6-10 m
2
/g at a surface region.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a process of producing a carbonized material having a large specific surface area with high efficiency from biomass.
In accordance with the present invention there is provided a process of producing a medium grade carbonized material from a biomass having an inner region and an outer region contiguous to the inner region, comprising the steps of:
(a) treating the biomass with a microwave for a period of time sufficient to carbonize the inner region but insufficient to carbonize the outer region, thereby obtaining a partly carbonized product;
(b) contacting the partly carbonized product with an oxidizing gas for a period of time sufficient to carbonize the outer region, thereby obtaining a completely carbonized product; and
(c) cooling the completely carbonized product in a non-oxidizing atmosphere.
By subjecting the cooled product obtained in step (c) to a gas activation treatment, a high grade carbonized material may be obtained.
The present invention has the following effects:
(1) A large sized carbonized material may be obtained by using a large sized biomass in the carbonized material producing step. Thus, unlike the conventional method which should handle fine char, the working environment is greatly improved.
(2) A great cost down can be achieved, because costs for crushing raw material wood into saw dust or chips are no longer necessary. Since a carbonized material in the form of a large block is brittle, it is very easy to pulverize the material. Therefore, it is not necessary to use an expensive high-strength pulverizing machine. A raw material having any size and any shape may be used.
(3) It is possible to easily prepare coarse carbonized material having different sizes by sieving coarsely pulverized carbonized material of any size. Thus, a briquetting step is no longer needed and, hence, reduction of activity due to the use of a binder for briquetting is not caused. If finely divided material is desired, it is easy to obtain such a material by simply pulverizing a coarse material.
(4) The use of the coarsely pulverized carbonized material is effective for reducing pressure loss in a packed bed and preventing scattering of particles in a packed tower.
(5) A high grade carbonized material can be produced within a short time without a briquetting step or a step of using a binder.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments of the invention to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
A biomass is used as a raw material for carbonization in the present invention. As the biomass, any plant material may be used as long as it can be carbonized by heating, such as a material containing cellulose, hemicellulose and lignin as major components. Examples of biomass include wood materials, plant cellulose materials, corn cores, shells of fruits (e.g. shells of coconut, walnut and ivory nut), seeds of fruit (e.g. seed of peach), husks (husks of chestnut, buckwheat and rice), bagasse, cotton, cotton fibers, paper and pulp. The wood materials include large sized materials, such as raw wood, wood blocks and timber, small sized wood materials, such as saw dust and wood chip, and molded bodies of the small sized wood materials. The size of the biomass raw material is not specifically limited and ranges from small particles to large sized materials. The volume of one piece of the biomass raw material is at least 0.05 cm
3
, preferably at least 70 cm
3
. The upper limit of the volume is not specifically limited but is generally about 50,000 cm
3
.
In the present invention, the use of large sized wood materials is preferred. Such materials include raw wood, wood blocks, timber and molded bodies of small wood materials such as saw dust and wood chips. The wood blocks include blocks obtained by removing bark from raw wood, blocks obtained by cutting raw wood, and blocks obtained by press molding pulp fibers and drying the molding. The sectional area of an end of wood block is 1.5-2000 cm
2
, preferably 80-800 cm
2
, whole the length thereof is 1-700 cm, preferably 2-40 cm. The timber may be large chips obtained by cutting wood or chips obtained by cutting wood into a determined size. The wood materials may have a major axis having a length of 1-200 cm, preferably 10-40 cm and may have any shape, such as preferably, columns, spheres and rectangular parallelepiped.
In the process for producing carbonized materials according to the present invention, the above-mentioned biomass raw material is subjected to a microwave heating treatment in an irradiation chamber. The microwave having a frequency of 1000-6000 MHz may be used. From the standpoint of the Wireless Telegraphy Act, penetration depth and heating speed, the use of a microwave having a frequency of 2450 MHz will be advantageous. When microwave irradiation is applied to the material, the irradiation chamber may be maintained in an inert gas atmosphere, a low oxygen concentration atmosphere. The chamber may be kept under a flow of a non-oxidizing gas such as nitrogen, carbon dioxide or steam. By this, the carbonization of the raw material may be performed with ease without danger. When the microwave irradiation chamber is maintained under a reduced pressure and in a low oxygen concentration atmosphere, it is easy to withdraw thermally decomposed gases generated from the raw material. It is also possible to prevent tar deposition on the carbonized product.
The carbonization of the biomass material by microwave irradiation rapidly proceeds from inside thereof. The microwave treatment time of course varies with an output power and load of the microwave. In the case of a columnar wood material having a diameter of 6 cm and a water content of 10%, the irradiation time is generally 4-15 minutes with an output power of 0.5-3 kW. In the case of a columnar wood material having a diameter of 30 cm, the treatment time is generally 30-120 minutes. A columnar material having a diameter of 30 cm generally requires 30-100 minutes treatment time with 3 kW output power.
In the carbonization of the biomass by microwave irradiation, the microwave irradiation is stopped before it has been completely carbonized. The carbonization of the material with the microwave irradiation proceeds from inside thereof so that the inside region is carbonized with good efficiency. However, the surface region is not easily carbonized. A long microwave irradiation time is required in order to completely carbonize the material up to the surface region. This causes high costs for electric power. Thus, in the present invention, the microwave irradiation is stopped when the inside region has been carbonized but the outside and surface region remains uncarbonized (partly carbonized state).
The fact that the inside region has been carbonized may be con
Ishizaki Kozo
Kaga Harumi
Miura Masakatsu
Bos Steven
Kuhar Anthony
Lorusso, Loud & Kelly
Secretary of Agency of Industrial Science and Technology
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