Chemistry of inorganic compounds – Miscellaneous process
Reexamination Certificate
2000-01-06
2001-04-03
Jones, Deborah (Department: 1775)
Chemistry of inorganic compounds
Miscellaneous process
C095S090000, C428S408000, C428S402000, C428S312200
Reexamination Certificate
active
06210652
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active composite having a laminate structure, consisting of a compressed support in the form of sheets and of an agent that is active with respect to a gas, the active agent being dispersed between the sheets in the form of granules.
The present invention also relates to a method of implementing gas-solid or gas-liquid physico-chemical processes using an active composite of this type as a reaction medium.
2. Description of Related Art
In certain fields such as, for example, that of chemical heat pumps based on the endothermicity or exothermicity of the reaction between a solid and a gas, or of the adsorption of a gas on a solid, a mixture of a divided material, such as expanded graphite, and of a solid reactant, for example a salt, or an adsorbent, such as a zeolite, is used. The mixture of expanded graphite and this solid, the site of a chemical reaction or of a physical adsorption, has many advantages during a chemical reaction or a physical adsorption between the solid and a gas. Expanded graphite, being in the form of sheets or of laminate particles, has a very large specific surface area and allows diffusion of the gas even in a confined medium.
The substantial improvement in the reversible solid-gas reaction kinetics which is observed, as resulting from the mixture of the active solid and natural graphite expanded by thermal means, in given mass proportions, and compacted in a fixed volume, results from an excellent permeability of the fixed bed prepared in this way to the reactive gas and from a thermal conductivity accompanied by a good coefficient of heat exchange with the walls. Conventionally, the preparation of such a reactant leads to an essentially homogeneous anisotropic bed whose anisotropic conductivity has values ranging from 0.5 to 2 Wm
−1
K
−1
depending on the conditions of preparation (proportion and compacting) and whose coefficient of exchange with the walls lies between 50 and 150 Wm
−1
K
−1
.
Despite these advantages, the use of such mixtures in the granular state has drawbacks because of the difficulty involved in obtaining genuinely homogeneous mixtures, because of the difficulty involved in handling them and because of the large volume they occupy. In addition, the reactant, which is often hygroscopic, tends to absorb moisture if the mixing operation is a long one; a subsequent dehydration step is lengthy, and indeed expensive, and may affect the quality of the end-product, even after dehydration.
Document WO91/15292 describes an active composite in the form of a block, which comprises recompressed expanded graphite, which is subsequently impregnated with an active agent, for example a salt. This type of active composite has major advantages compared with the powder mixtures containing expanded graphite which are described above, but it may nevertheless be difficult to produce since, when the block is impregnated with a liquid, it may take a long time to dry out the block.
The methods of manufacturing expanded graphite are well known, in particular from U.S. Pat. No. 3,404,061. These methods, called graphite exfoliation methods, include a step in which a graphitic complex is rapidly expanded by heating, producing a powder of vermicular expanded graphite.
Document FR-A-2,732,242 describes an active composite formed by a series of compressed-graphite sheets superposed on top of one another, an active agent being dispersed within the sheets. Typically, during the manufacture of this type of composite, the sheets are immersed in a solution of the active agent, then dried afterwards.
Document FR-A-2,715,081 discloses a reactant, for thermochemical systems, in the form of granules. Each granule comprises a support formed by recompressed expanded natural graphite which is impregnated with an active agent. The impregnation with the active agent takes place by immersing the granules in a solution of the agent, then by drying them afterwards.
Since the method of manufacturing the two previous types of reactant includes an impregnation step followed by a drying step, it may prove to be long and expensive.
SUMMARY OF THE INVENTION
The subject of the present invention is therefore an active composite which has a laminate structure which offers excellent permeability to a gas flow and has good thermal conductivity properties, but is still easy to produce.
To do this, the invention provides an active composite consisting of a compressed support and of at least one agent that is active with respect to a gas, the compressed support, comprising recompressed expanded graphite having a relative density of between 0.02 and 1.5, being formed by a series of sheets superposed on top of one another, characterized in that the active agent is dispersed between the sheets in the form of granules.
According to a preferred embodiment, the active composite having a laminate structure comprises from 5 to 95% by weight of recompressed expanded graphite and from 95 to 5% by weight of active agent.
The invention also provides a method of implementing solid-gas or solid-liquid physico-chemical processes, this method being characterized in that it uses as reaction medium an active composite consisting of a compressed support and of an agent that is active with respect to a gas, the compressed support comprising recompressed expanded graphite having a relative density of between 0.02 and 1.5, being formed by a series of sheets superposed on top of one another, the active agent being dispersed between the sheets in the form of granules.
An active composite of this type is intended to be used for carrying out either a reaction of the solid-gas type, or an adsorption between a gas and a solid, or a reaction catalysed by a solid between a gas and a liquid, or the condensation/evaporation of a gas, or finally a solid-catalysed gas transformation reaction. Thus, the present invention provides a method of carrying out either reactions of the gas-solid type, or gas-solid absorption reactions, or finally catalytic transformation reactions of a gas using as reaction medium a block of active composite according to the invention.
The active composite according to the invention must have a very high anisotropy in terms of heat transfer, which will result from the ordered compression of the highly thermally conductive graphite sheets, while still maintaining a high porosity allowing good diffusion of the gas to each active site, the active sites being located substantially uniformly within the composite.
The active composite according to the invention, the relative density of the graphite in which is between 0.02 and 1.5, has a high thermal conductivity anisotropy, that is to say that the thermal conductivity C
1
along a first direction D
1
in the active composite is markedly greater than that obtained along another direction D
2
in the composite, perpendicular to the first. The active composite according to the invention has an anisotropy coefficient, which is the ratio C
1
/C
2
, of between 2 and 200 and preferably between 10 and 100, wherein C
1
is the thermal conductivity along a first direction D
1
and C
2
is the thermal conductivity on another direction D
2
.
Moreover, the active composite according to the invention must have a high porosity allowing the gases to reach the active sites.
According to one aspect of the invention, the active composite comprises a stack of similar sheets, combined in pairs so that in each pair the two faces provided with granules are in contact with each other. Thus, a passage is created between two sheets of a pair which makes the granules readily accessible to a gas.
According to alternative forms of the invention, in order further to increase the accessibility of the active sites to the liquids and gases:
at least one layer of highly porous material is placed between two adjacent layers of active agent;
and/or passing through the compressed support are diffusion holes, of various cross-sections, which cross the plane of the sheets;
and/or pas
Bou Pierre
Guilleminot Jean Jacques
Pons Michel
Blank Rome Comisky & McCauley
Centre National de la Recherche Scientifique
Jones Deborah
Savage Jason
LandOfFree
Active composite having a laminate structure comprising an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Active composite having a laminate structure comprising an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Active composite having a laminate structure comprising an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2472568