Compositions – Co – s – negative element – or acid – bindant containing – Alkali-metal or alkali-metal compound containing
Reexamination Certificate
1998-09-10
2001-09-18
Warden, Jill (Department: 1743)
Compositions
Co, s, negative element, or acid, bindant containing
Alkali-metal or alkali-metal compound containing
C252S193000, C510S509000, C423S244080
Reexamination Certificate
active
06290872
ABSTRACT:
The subject-matter of the present invention is a novel composition comprising at least sodium bicarbonate, its process of preparation and its uses, in particular in the treatment of flue gases, in the field of detergency and in animal food.
The treatment of flue gases comprising all kinds of pollutants, for example inorganic acids, such as acids of formula HX, in which X represents a halogen, or compounds of the SO
x
or NO
x
type, organic derivatives, such as dioxins or furans, for example, and metals regarded as toxic, is exhibiting a particular rapid expansion due to the increasing pressure of environmental regulations exerted on companies emitting such waste gases.
Mention may be made, among processes which generate such gases, of, inter alia, incinerators of domestic waste, incinerators of hospital waste and of special industrial waste, thermal power stations or furnaces of glass manufacturing type but also some production processes in the chemical industry.
Conventional plants for the treatment of gases employ so-called dry route or semi-wet route treatments. In the first case, the agent for neutralizing the flue gases is introduced in the form of a solid and, in the second case, the said agent is employed in the form of an aqueous suspension or solution, the amount of water of which is calculated so that the product resulting from the treatment is a solid, as in the first case.
One of the oldest processes of dry type uses lime as reactant, which requires a high stoichiometric ratio because of the low reactivity of lime.
These processes, in addition, exhibit the disadvantage of creating solid waste which is very difficult to recover in value and which has to be disposed of on a special landfill site, due to the presence of metals regarded as toxic. The amounts of solids in this case are relatively high and result in high additional costs for the process.
A more advantageous process consists in using sodium bicarbonate. The use of this neutralizing agent makes it possible to have a solid waste which can itself be readily recycled. Furthermore, the molar amount of sodium bicarbonate, with respect to the compounds to be neutralized present in the gases to be treated, is much lower than in the case of lime.
This latter type of process constitutes a technological advance in this field. However, it remains important to reduce the costs of such treatments and be able to use a readily available product with a sufficient sodium bicarbonate content and which is free from troublesome impurities.
The subject-matter of the present invention is a novel composition, comprising at least sodium bicarbonate, intended for the treatment of flue gases resulting from incineration of domestic waste, of hospital waste or of special industrial waste, or of flue gases resulting from thermal power stations or from glass manufacturing furnaces, but also for the field of detergency and for animal food.
It also relates to a simple process for producing the said composition.
Thus, a first subject-matter of the invention is a novel composition comprising at least sodium bicarbonate.
The second subject-matter of the invention is composed of the preparation of a composition comprising at least sodium bicarbonate, characterized in that a heat treatment of an ammoniacal bicarbonate is carried out at a temperature of between 20 and 150° C.
A preferred alternative form of the invention consists in carrying out the heat treatment under a controlled atmosphere which can comprise water and/or carbon dioxide.
Furthermore, a third subject-matter of the present invention relates to the treatment of flue gases comprising mainly acids of the HX type, with X representing a halogen, or mainly compounds of the SO
x
type, these compounds being alone or as a mixture, and metals regarded as toxic, in which treatment the bicarbonate resulting from the process according to the invention is used as reactant.
However, other characteristics and advantages of the present invention will become more clearly apparent on reading the description and examples which will follow.
Before describing the process according to the invention in more detail, it should be made clear that the heat-treated ammoniacal bicarbonate is the intermediate product obtained by employing the process for the preparation of sodium carbonate by the ammonia soda technique, also known under the name of “Solvay process”.
More specifically, the name ammoniacal bicarbonate is given, for the purposes of the present invention, to the product obtained after dissolution of gaseous ammonia in an aqueous sodium chloride solution, so as to produce an ammoniacal brine. The latter is subsequently treated with a gas containing carbon dioxide in order to give ammoniacal bicarbonate crystals.
Ammoniacal bicarbonate in fact denotes a composition comprising mainly sodium bicarbonate, sodium carbonate and, to a lesser extent, ammonia in the form of ammonium salts, such as bicarbonate, carbonate and/or carbamate, and water.
By way of indication, this composition comprises: 70 to 90% by weight of sodium bicarbonate (NaHCO
3
), 2 to 20% by weight of sodium carbonate (Na
2
CO
3
), 0.2 to 1.0% by weight of ammonia, expressed in the form of the ammonium ion, 0.3 to 2.0% by weight of ammonium carbamate (NH
4
O
2
CNH
2
) and 5 to 20% by weight of water.
In contrast to what was expected, the treatment of ammoniacal bicarbonate within the specified temperature range, more particularly at high temperature, and under a controlled atmosphere with respect to water and/or carbon dioxide, makes it possible to dry and to decompose selectively the ammonium salts present, such as bicarbonate, carbonate and/or carbamate, to ammonia and carbon dioxide, without substantial decomposition of the sodium bicarbonate present in the mixture to sodium carbonate.
This is because it should not be forgotten that the final stage in the Solvay process consists in calcining the ammoniacal bicarbonate at a temperature of the order of 200° C. in order to give sodium carbonate. Consequently, it was not obvious that a heat treatment at temperatures which can be as high as 120° C.-130° C. would have allowed such a result to be achieved.
As was indicated previously, the heat treatment according to the invention is carried out at a temperature of between 20 and 150° C., preferably under a controlled atmosphere which can comprise water and/or carbon dioxide.
According to a preferred embodiment of the invention, the heat treatment can take place at a temperature of between 20 and 130° C.
More particularly, the heat treatment is carried out in the presence of an atmosphere with a water vapour content of between 0 and 10 molar %.
As regards the carbon dioxide, the heat treatment is carried out in the presence of an atmosphere with a carbon dioxide content of between 0 and 100 molar %.
Furthermore, the heat treatment according to the invention is carried out under an atmosphere which can comprise air or any other inert gas, such as rare gases or nitrogen. The content of this type of gas, if it is used, provides the complement in order to reach the desired total pressure.
According to a preferred embodiment of the invention, the heat treatment is carried out in the presence of water vapour and of carbon dioxide.
It is has been found that the temperature for treatment of ammoniacal bicarbonate could be adjusted according to the amount of water vapour present and the amount of carbon dioxide present.
Thus, in the case where the atmosphere is a nitrogen/oxygen or air mixture, the temperature range for the heat treatment will preferably be below 80° C.
Furthermore, if the treatment is carried out under an atmosphere comprising a mixture of carbon dioxide and water vapour, and optionally air or an inert gas, it is then possible to envisage carrying out the latter at a temperature close to 120° C.-130° C., although lower temperatures remain possible.
For the preceding, the temperature values are expressed at atmospheric pressure. A person skilled in the art is capable of adjusting the temperature values according to the pressur
Fourcot Fabrice
Pouxviel Jean-Claude
Zing Christophe
Burns Doane Swecker & Mathis L.L.P.
Cross LaToya
Novacarb
Warden Jill
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