Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Reexamination Certificate
2001-01-09
2003-04-22
Hruskoci, Peter A. (Department: 1724)
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
C205S755000, C205S756000, C210S721000, C210S737000, C210S748080, C210S757000, C210S758000, C210S759000, C210S761000, C210S762000, C422S184100, C422S186000, C588S253000, C588S253000, C588S253000, C588S253000, C588S253000, C588S253000
Reexamination Certificate
active
06551517
ABSTRACT:
DESCRIPTION
The present invention concerns a process for converting chemical structures, that is to say a process for conducting chemical reactions in a fluid under pressure and at temperature, in particular in a supercritical fluid, and a device for its implementation.
More precisely, the invention relates to a process for converting chemical structures, that is to say a process for conducting chemical reactions in a fluid under pressure and at temperature, in particular in a supercritical fluid, containing a solvent and at least on electrolyte such as a salt, in which reactive species are generated in situ by electrolysis.
The invention finds applications in widely varying fields. It may be applied, for example, to the modification of molecular structures, especially in molecular engineering or in pharmacology. It may also be applied to the degradation of industrial waste, for example the degradation of de-inking sludge or of metallic hydroxide sludge and to the treatment of all kinds of waste, aqueous waste in particular containing organic and mineral compounds for example, more particularly aqueous waste containing halogen compounds.
The invention may also be applied to the destruction of explosives or hazardous products, such as for example pesticides (polychlorobiphenyls). A further area of use is the recycling of natural substances such as for example liquid manure, vineyard waste and waste from milk treatment.
The processes used to conduct chemical reactions, in particular in a fluid medium under pressure and at temperature, especially a supercritical fluid, are generally conducted in equipment called reactors.
Among these reactors, the so-called tubular reactor, that is to say which is generally in cylindrical in shape whose length is distinctly greater than its diameter, is the easiest reactor to use, the most flexible and the least costly.
However, the use of these reactors is limited by problems related to salt deposits leading to blockage of the reactor and corrosion.
Tubular reactors have been the subject of numerous patents, among which mention may be made of the patents by N. L. DICKINSON: U.S. Pat. No. 4,380,960, by J. F. WELCH and J. D. SLEGWARTH: U.S. Pat. No. 4,861,497, by L.LI and E. F. GLOYNA. PCT/US 92 06459, or further by M.MODELL: U.S. Pat. No. 5,252,224.
All these patents aim at remedying the disadvantages of the tubular reactors mentioned above, however the solutions put forward based on the use of resistant materials that are difficult to apply at acceptable cost, the neutralisation of acids, or fluid speeds inside the tubular reactor greater than the critical speed of salt sedimentation, only bring an imperfect solution to the defects of tubular reactors.
The same applies to “porous wall” tubular reactors which are the subject of patents U.S. Pat. No. 5,387,398, U.S. Pat. No. 5,571,424 and EP-A-0 708 058, or mobile surface tubular reactors which are the subject of patent U.S. Pat. No. 5,543,057 TO which the salts adhere which are, moreover, of increased complexity both in respect of their manufacture and their operation.
Other reactors are so-called “reservoir reactors”, that is to say reactors which generally have a low Length/Diameter ratio (L/D), in the region of 3 for example or less.
This type of reactor appears to be better suited than the tubular reactor to face the problems of salt precipitation and corrosion.
One reservoir reactor of the type operating in the supercritical domain is described in patent U.S. Pat. No. 4,822,497.
This reactor is formed of two zones: the upper part of the reactor being placed under supercritical conditions for water, namely at a temperature greater than 374° C., and the lower part of the reactor being placed under subcritical conditions, namely a temperature of less than 374° C.
Supply is fed via the top of the reactor in the supercritical zone, the site of the oxidation reaction. The salts, whose solubility varies between 1 ppb and. 100 ppm above 450° C. precipitate and fall together with the other solid particles down towards the lower part of the reactor.
This lower part, maintained under subcritical conditions, either through the injection of a cold liquid, or by a heat exchanger, makes it possible to resolubilize part of the mineral salts and to evacuate the brine that is formed. As for the fluid to be treated, this falls into the subcritical zone then moves up towards the outlet (supercritical zone) protected by a filter.
Two other patents also put forward improvements to this type of reactor: patent U.S. Pat. No. 5,100,560 describes the installation of a scraper inside the cylindrical chamber used to detach the salts which deposit on the inner wall of the reservoir reactor, and patent WO-92/21621 uses a curtain of water under subcritical conditions on the inner wall of the reactor in order to protect the latter against salt deposits and corrosion.
Reservoir reactors have the advantage of confining the solid/liquid reaction and separation within one same reactor: but they have the disadvantage in particular of requiring considerable volumes in order to obtain relatively long stay times so that the reactions can be completed, which has repercussions on the overall cost of the process.
Moreover, here again, these reservoir reactors only bring an imperfect solution to the problems of salt deposits and corrosion and it is necessary in particular to have recourse, for the manufacture of the reactor, to materials able to withstand such conditions, or to lining the reactor with the same resistant, costly materials such as titanium.
Moreover, the two types of reactors described above, whether tubular reactors or reservoir reactors, comprise means for adding the various reagents needed for the reaction which are often complex, voluminous and costly and in addition do not bring homogenous distribution of these reagents inside the reactor and therefore no optimal control over the reactions. This is the case in particular for reactors in which oxidation of substances is conducted in an aqueous medium, and in which the air required for the reaction is collected then compressed and finally injected into the medium. The compression of air makes a major contribution to the high cost of the process, and molecular oxygen is distinctly less active than oxygen in atomic form.
It is in order to eliminate said means for adding the reagents that reactors have been developed in which the essential reactive species are generated in situ by electrochemical means in a subcritical or supercritical aqueous medium.
Therefore, document U.S. Pat. No. 4,581,105 relates to an electrochemical cell containing an aqueous electrolyte under supercritical conditions. The electrolyte solution contains at least one species, so-called “electroactive species” which, when a current is applied to the electrodes, reacts to give “electrochemical products” soluble in the supercritical fluid, and to minimize the quantities of energy consumed by promoting mass transfers of the reagents and products to and from the electrodes.
In the anode and cathode compartments, which are generally separated by a separator element, oxygen and hydrogen may be generated, for example in water.
Document EP-A-0 535 3 20 concerns a process for oxidizing organic and inorganic substances of aqueous waste. In this process, the substances to be treated are firstly stored and optionally mixed in a reservoir, and are then directed by means of a high pressure pump into an electrolysis zone situated immediately before or in the reaction zone itself.
According to the figure illustrating this patent, the electrolysis zone is located at the inlet to the reactor.
Before entering the electrolysis zone, the substances to be treated are brought to a temperature close to the critical temperature of water, namely 374° C. In the electrolysis zone, the generated oxygen initiates the oxidation reactions. Owing to the exothermal nature of these reactions, the reaction mixture heats up to a temperature possibly reaching 650° C. This temperature is maintained, in the reaction zone, until occurren
Aymonier Cyril
Berdeu Bernard
Cansell François
Sentagnes Dominique
Hruskoci Peter A.
L'Electrolyse
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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