Process for the manufacture of concentrated solutions

Details Process for the manufacture of concentrated solutions Process for the manufacture of concentrated solutions

2000-10-05

2004-08-24

Manoharan, Virginia (Department: 1764)

Distillation: processes, separatory

Distilling to separate or remove only water

C159S049000, C203S072000, C203S073000, C423S584000

Reexamination Certificate

active

06780288

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a process for the manufacture of concentrated solutions in safe and economical conditions, using an apparatus which is easy to dismantle and to transport. The invention also relates to the use of the process of the present invention to produce concentrated hydrogen peroxide solutions, and to these concentrated hydrogen peroxide solutions.
BACKGROUND OF THE INVENTION
It is known that some c solutions, like concentrated hydrogen peroxide solutions, can be made to explosively decompose. Known processes for the manufacture of such concentrated solutions mostly start from diluted solutions and use evaporation and/or distillation techniques. Since the energy required for the detonation decreases when temperature and/or concentration increases, the probability of an explosive decomposition increases with increasing temperature and/or concentration, and is therefore critical during concentration processes. Furthermore, the magnitude of such potential explosions depends on the build-up of concentrated solution, which are therefore critical in the apparatus used in concentration processes.
The final concentration obtainable by such processes is usually limited not only because of the already mentioned safety hazards but also because of the thermodynamic limit of some processes, the pressure and temperature conditions being dependent on the design of the equipment and more particularly, on the design of the distillation column.
Moreover, the costs in investment and/or energy consumption of such known processes are high.
And finally, the known installations used therefor are often operating under vacuum. Consequently, their assembling and tightness is critical and may constitute a problem if the apparatus is intended to be dismantled and/or transported. In the case of concentrated hydrogen peroxide solutions for instance, it is very convenient to have the concentration apparatus near the site where it is used, in order to avoid the danger of transporting the concentrated solution.
Some of the known processes solve one or more of the above mentioned problems, but none of them solves them all.
GB 668874 relates to a process for the manufacture of high concentrated hydrogen peroxide solutions by distillation of diluted solutions, where the high boiling fraction resulting from the distillation is vaporized in two superposed pans. The drawback of this process is that it operates with at least two horizontal layers of liquid. The pressure drop induced by these layers increases the boiling temperature of the liquid, thereby increasing the probability of explosive decomposition. In addition, these horizontal liquid layers result in liquid build-ups in the area where the concentration of the solution is the highest. Another drawback of the process according to GB 668874 is the high heat consumption of the vaporizer.
EP 835680 relates to a distillation column consisting of at least one packed section and an evaporator on a same vertical axis, and which comprises at least two evaporators and/or two condensers. This kind of apparatus, using either two evaporators and/or two condensers, is complicated and expensive. Besides, it doesn't provide means for avoiding the accumulation of concentrated solution. Therefore, it is preferably applied to produce solutions limited to a concentration of 70%. Moreover, it is very difficult to dismantle and/or transport.
SUMMARY OF THE INVENTION
The present invention is aimed at overcoming the disadvantages of the known processes by providing a process for the manufacture of a concentrated solution in safe and economical conditions, using an apparatus being easy to dismantle and transport near to the place where the concentrated solution is used.
To this end, the invention relates to a process for the manufacture of a concentrated solution from a dilute solution, in which the distillation and the evaporation are carried out in a distillation column and in an evaporator which constitute two distinct pieces of equipment which are easy to dismantle and to transport.
The fact that the pieces of equipment are distinct means that they both include a bottom and a top through which fluids can flow, and that they are able to function separately.
The main advantage of using two distinct pieces of equipment for the distillation column and the evaporator is that the complete apparatus is easier to dismantle and to transport than when one single column is used. The use of two distinct pieces of equipment surprisingly didn't lead to problems arising from the accumulation of liquids which were expected to arise in the connecting pieces, especially if they contain reduced area portions.
In a preferred embodiment of the present invention, the connection between the distillation column and the evaporator is made through a distributor which has a cross-sectional area at is narrowest point which is smaller than the cross-sectional area of the distillation column.
The cross-sectional area of the distillation column is calculated as being the average cross-sectional area of the horizontal sections in the effective packed section of the column, excluding the above mentioned bottom and top.
The distributor according to the invention may be any known kind of liquid distributor which enables the formation of a thin film of liquid along the walls of the falling film evaporator, provided that is has the geometric requirement stated above. Good results have been obtained with a distributor having a bigger cross-sectional area at one end and a smaller cross-sectional at the other end. In that case, the biggest cross-sectional area is connected to the distillation column, while the smallest one is connected to the falling film evaporator.
Preferably, the distillation column and the evaporator are assembled in a way that allows the liquid to flow from the distillation column to the evaporator through the distributor under the action of gravity only.
More preferably, the distillation column is assembled on top of the evaporator, the axes of both pieces of equipment being aligned.
The process according to the invention preferably uses a feeding device at one or more points along the distillation column. This feeding device is for instance located in the upper ⅔ of the column.
The distillation column may be filled with an appropriate number of fractionating devices or packings. These devices may be chosen from the various fractionating devices which are known per se in the technology of distillation columns, such as, for example, perforated trays, valve trays, bubble cap trays and various packings such as, for example, Raschig rings, Pall rings and woven mats. Structured packing such as, for example, structured packing-SULZER® BX type, is preferred.
Vertical surfaces are preferred inside the distillation column, in order to limit liquid build-up. The bottom of the column is preferably also designed to avoid any liquid buildup.
In another advantageous embodiment of the present invention, the evaporator is a falling film evaporator. The falling film evaporator according to this embodiment is generally a long tube vertical evaporator in which the concentrated solution leaving the bottom of the distillation column is fed continuously to the top of the tube(s) and flows down the walls as a film. The number and the dimension of the tubes are such that the hold-up of hydrogen peroxide in the evaporator is minimized.
Preferably, the process according to the invention uses a heating device for the falling film evaporator, in which hot water is circulating.
The process according to the invention may also use a cooler and a distributor for connecting the falling film evaporator to the cooler. The cooler is preferably a falling film cooler. It can be cooled by any medium commonly used for heat transfer. Preferably, the cooling medium is water and/or ethylene glycol.
The materials of construction of all parts of this apparatus must be fully compatible with the solutions for as far as corrosion and stability of the product are concerned. Aluminium,

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