Distillation: apparatus – Apparatus – Systems
Reexamination Certificate
1999-07-20
2001-12-04
Manoharan, Virginia (Department: 1764)
Distillation: apparatus
Apparatus
Systems
C202S181000, C203S001000, C203S002000, C203S003000, C203SDIG001, C210S201000, C210S096200, C210S198200, C210S294000, C210S266000
Reexamination Certificate
active
06325898
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a device intended for continuous regulation of the composition of a binary mixture of components, and to a constituent separation system including this regulating device.
The regulating device according to the invention finds many applications. It can be used individually for homogeneity control of liquid mixtures, or it can be combined notably:
with separation systems referred to as simulated moving bed systems,
with separation systems referred to as “batch” systems of preparative HPLC type for example,
with distillation columns for on-line analysis of the composition of the distillate or of the boiler and to optimize control of batch binary distillation processes,
with separation systems comprising one or more nanofiltration membranes.
BACKGROUND OF THE INVENTION
There are many well-known continuous separation processes in industry using selective adsorption of at least one component among several in a mixture of fluids, notably chromatography processes referred to as simulated countercurrent processes using the property of porous solids, in the presence of liquid, gaseous or supercritical mixtures, to retain more or less significantly the various constituents of the mixture.
Separation or fractionation processes based on chromatography are most often implemented in a system comprising a series of columns or fractions of columns interconnected in series and forming a loop. A porous solid of determined grain size constitutes the stationary phase. The mixture F to be separated is fed into the loop, then displaced by means of a carrier fluid, eluent E, and the various constituents flow out successively according to whether they are retained more or less significantly by the stationary phase. Injection points for the mixture F to be separated and the solvent or eluent E, and fluid extraction points, for extract EX and raffinate RA, delimiting different zones, are distributed along this loop. The number of zones can vary but the separation systems most often comprise four main zones.
In simulated moving bed separation processes, the solid phase is placed in a certain number n of fixed beds (generally 4≦n≦24) arranged in series and it is the concentration profile that is displaced at a substantially uniform speed around a closed loop by successive shift of the injection and extraction points by means of a rotary valve or more simply of a series of suitably controlled on-off valves. This circular shifting, at each period T, of the various liquid inflows-outflows in a given direction allows to simulate displacement of the solid adsorbent in the other direction. The main liquid inflows are the flow of feed F and the flow of eluent S. According to the configuration selected, according to whether a recycling pump is used or not in the cycle, the outflows of extract EX or of raffinate RA can be controlled by the pressure at the inlet of the recycling pump or by means of flowmeters.
Simulated moving bed chromatography processes are for example described in patents EP-0,415,822; 0,568,407; FR-2,699,917; 2,704,158, and in patent applications FR-97/05,485 or 97/07,756.
In industrial chromatography processes, one of the main parameters allowing selective adsorption of the species to be separated and/or their solubility in the eluent is the polarity of the eluent. Most often, the eluent allowing optimum productivity of the process is a binary mixture of two solvents of different polarities.
For good stability of the working point of the loop, it is important that the fluid mixture (eluent) used as a carrier fluid for the constituents of the feed in the separation loop has a well-defined composition, where the proportion of each solvent remains really constant. Now, the eluent is generally recycled by evaporation and/or distillation at the outlet of the separation system. The solvents forming the eluent often have different volatilities. In the case of non-ideal mixtures in the presence of an azeotrope, the composition of the eluent may also be different from that of the azeotrope. The composition of the mixture recycled after use is consequently modified. It is therefore necessary to restore the set composition and to be able to perform continuous measurement of its variations.
SUMMARY OF THE INVENTION
The separation system according to the invention comprises a separation unit (simulated moving beds, distillation column, etc) and a device for supplying the separation unit with a mixture of liquids consisting of at least two components of different polarities.
The system is characterized in that the supply device comprises a storage tank receiving a mixture coming from the separation system, at least one auxiliary vessel containing one of the components of the mixture. and means for controlling transfer of this component from the auxiliary vessel to the storage tank, these means comprising at least a capacitive sonde totally immersed in the fluid mixture, a sonde for measuring the temperature of the mixture, a sonde for measuring the mixture level in the storage tank, and a regulating unit connected to the various sondes and suited to determine the volume of at least one of the components to be transferred to the storage tank, in order to restore a set composition for the mixture.
Immersed capacitive sondes suited to generate a current depending on the instantaneous composition of the mixture of components and on the temperature are preferably used, and the regulating unit is suited to determine the volume of at least one of the components of the mixture according to the instantaneous composition of the mixture, the set composition, the volume of the mixture in the tank and the composition of at least one makeup component.
The system preferably comprises stirring means in the storage tank and means associated therewith in order to maintain the temperature of the mixture substantially constant.
According to an embodiment, the system comprises a capacitive reference sonde immersed in a liquid mixture of known composition (obtained for example by mixing the same components) and maintained at a constant temperature, and the regulating unit is suited to regulate the composition of the mixture in the storage tank by reference to the intensity of the current delivered by said reference sonde.
It is notably possible to use immersed capacitive sondes comprising an elongate central electrode surrounded by an earth electrode that can be tubular and preferably open-worked in order to allow better circulation of the mixture through the inter-electrode space, and a generator producing a current proportional to the variations of the inter-electrode capacity.
The separation unit comprises, for example, a loop for separating the constituents of a feed, that is connected to the supply device and comprises means for injecting the feed into the separation loop and means for separating from the liquid mixture the constituents extracted from the feed.
According to an embodiment, the system comprises auxiliary feed preparation vessels and circuits for connecting the outlet of the tank to the auxiliary vessels on demand.
The separation unit can comprise, according to circumstances, a simulated moving bed unit or a distillation column or one or more chromatographic columns for supercritical chromatography for example, or one or more nanofiltration membranes.
According to an embodiment, the separation unit comprises for example falling-film evaporation means and a condenser connected to the storage tank.
REFERENCES:
patent: 3998704 (1976-12-01), Follain et al.
patent: 4877522 (1989-10-01), Toei et al.
patent: 5464504 (1995-11-01), Beauford
patent: 5522660 (1996-06-01), O'Dougherty
patent: 754491 (1997-01-01), None
Blehaut Jean
Nicoud Roger-Marc
Antonelli Terry Stout & Kraus LLP
Institut Francais du Pe'trole
Manoharan Virginia
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