JPS6249095B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for making surfaces hydrophilic by the action of gaseous sulfur trioxide, such as packings for equipment such as absorption and extraction columns, cooling towers, etc., which can be wetted with water. The invention relates to packings for interfacial materials and/or heat exchange devices.

Chieko Inventor Certificate No. 169054, polyethylene,
Packings for mass and heat exchange devices consisting of a substantially hydrophobic thermoplastic material, such as polypropylene, polyvinyl chloride, etc., coated on the surface with a thin layer of another polymeric material that swells with water. Disclosed. Such a filling surface is, on the one hand, covered with a flowing aqueous film over a larger area of the filling surface than in the case of conventional fillings made of hydrophobic thermoplastic materials, and on the other hand, it The improved hydrodynamic conditions for film flow make it more usable. And the end result is that compared to a geometrically identical packing of hydrophobic thermoplastic material, there are almost twice as many active interfaces at which mass and/or heat exchange takes place, or in other words Then, each exchange device is reduced in size by half while effectively maintaining the same power output.

Thermoplastic fillings with a hydrophilic surface layer are preferably prepared by subjecting the surface of the filling of hydrophobic thermoplastic material to a suitable chemical reaction, such as sulfation or oxidation. Then,
It has been adjusted. The type and conditions of the reaction are selected such that a continuous, resistant coating of hydrophilic, water-swellable but insoluble polymer is formed. Most hydrophilic reactions produce water-soluble products when a certain conversion is exceeded, and between an unswollen hydrophobic layer and a swollen hydrophilic layer. It is clear that suitable reaction conditions are quite limited, since tangential tensions occur, leading to the hydrophilic layer peeling off. In principle, such hydrophilicizing reactions should be carried out while simultaneously crosslinking the hydrophobic layer and promoting the diffusion of the reagent into the hydrophobic layer, creating a swelling force gradient between the two layers. and reduce the tangential tension at the interface. Another limitation in choosing a suitable reaction comes from the demands placed on the price of the filler in terms of the manufacturing costs that must be spent on the hydrophilic treatment.

The thermoplastic materials most often used for this purpose are based on polyolefins, especially polyethylene and isotactic polypropylene. Isotactic polypropylene is a particularly preferred material because of its specific gravity and suitable thermoplasticity, and is also relatively inexpensive. However, it has the disadvantage of being quite crystalline, and the diffusion of low molecular weight reagents into it is too slow, while the hydrophilization reaction proceeds at a relatively fast rate. Therefore, in various reactions such as surface oxidation with chromic acid, the surface undergoes an etching action, and the thin hydrophilic layer on the surface is immediately decomposed and washed away after being formed. It keeps peeling off. For this reason, certain technically suitable methods available for polyethylene, such as oxidation in the liquid phase, cannot be applied to polypropylene. The only viable method consists of a cold sulfation reaction with oleum, with only a small amount of oxidation.

However, in the case of sulfation reactions with liquid oleum, the disadvantages of the sulfated surface, which absorbs oleum well and retains much of it even after the reaction has finished, must be overcome. Must be. The handling of large quantities of oleum and the disposal of its residues attached to the fillings are
There are problems with both safety and hygiene.

It is clear that it is generally advantageous to carry out the reaction in the gaseous phase, since a considerable amount of liquid reagent is deposited on the packing. However, the shape of the filling precludes the use of methods using polypropylene foil, such as oxidation initiated by corona discharge. Apart from that, such hydrophilization methods are insufficient in the case of fillers, since the degree of hydrophilicity that can be printed on wrapping paper is clearly incomparably small.

So far, sulfation with gaseous sulfur trioxide has been accompanied by great difficulties. Relatively high concentrations of sulfur trioxide lead to the formation of blisters or islands in areas of high reaction progress, eventually causing the hydrophilic layer to slough off after swelling. During dilution of sulfur trioxide with air, oxygen-induced oxidation takes place, resulting in a dark-colored tar-like product, which is soluble in water and especially alkaline solutions. The main difficulty is that especially when oxidation is not involved and there is an activation energy,
Based on the property that the reaction is automatically accelerated. These effects combine to allow the reaction to occur for some time without any change in the nature of the hydrophilic surface - the induction phase - and then the reaction is considerably accelerated to a high conversion. It is almost impossible to control the reaction when it proceeds in this manner. This is because the area that first comes into contact with the gaseous reagent and is acted upon by the reagent for a somewhat longer period of time and at a higher concentration, and the area that is exposed to the reagent somewhat later and at a lower concentration, has a substantial This is because differences in the progress of the reaction occur; on the one hand, this is due to the reaction itself and, on the other hand, due to the absorption of sulfur trioxide in the reacted layer and its surface.

In a typical reaction mode, for example when introducing sulfur trioxide vapor into a column or reactor containing a polypropylene packing, the packing surface is immediately "burned" at the inlet of each unit.
i.e. the reaction is too deeply sulfated and the reaction proceeds with oxidation to a high conversion - but on the other hand, at the gas outlet the surface of the polypropylene packing remains practically hydrophobic, so that the result is practically negative. It is something. By varying the temperature and sulfur trioxide concentration,
If the reaction time is adjusted in such a way that a sufficient and optimal amount of conversion takes place in the main or middle part of the reactor, the parts of the packing that are exposed to the reagents at the inlet for a relatively long time and in a relatively high concentration are already exposed to undesired conditions. At the same time that the reaction is proceeding to a substantially high conversion, the part of the charge which comes into contact with the sulfur trioxide at the outlet a little later and at a much lower concentration is still in the induction phase and remains unreacted. Hydrophobic in nature. This situation is illustrated in the accompanying drawing, where the curve
a is at the gas inlet, curve b is at the center of the filling,
Curve c corresponds to the reaction at the gas outlet; ordinate t
_a , t _b , t _c are the respective reaction times, and the abscissa α
_a , α _b and α _c indicate the respective conversion rates.
As can be seen, even negligible and seemingly insignificant differences in the contact time between the charge and the reagents result in significant differences in the conversions obtained. Such differences may be even more pronounced if the gas is warmer than the packing, or if it contains oxygen at a concentration that results in an induced oxidation that is so substantially exothermic as to create a temperature gradient within the group of packings. growing. These negative outcomes can also be compounded. This result is so striking that even when the total contact time is forced to tens of seconds or even minutes, and at travel velocities such that the difference in contact onset is at most a few seconds, the gas Even if the filling progresses, the filling will appear as if it has been burned. Most of the filling near the gas inlet,
The protruding portions and outer edges of the individual packings are ``burned'' and darkened, while the portions hidden by the gas flow or far from the inlet remain essentially unreacted. From the foregoing, it is clear that such a reaction, which exposes the packing to a stream of sulfur trioxide-containing gas, although advantageous in principle, is impractical when carried out in the manner described. Dew.

Eliminating the above-mentioned deficiencies in the prior art and providing an improved method for producing packings for interfacial mass and/or heat exchange units whose surfaces have been made hydrophilic by the action of gaseous sulfur trioxide. It is an object of the present invention to provide.

According to the invention, said method comprises a polypropylene filling in a container containing from 0.5 to 10 volume percent, preferably from 1.5 to 5 volume percent sulfur trioxide and less than 5 volume percent free oxygen. contact with a gaseous medium at a filling temperature of 10 to 50°C, the temperature of the gas being at most 10°C higher or at most 35°C lower than the temperature of the filling; and sulfur trioxide, thereby bringing the charge into contact with a gaseous or liquid medium containing substances that tend to react with sulfur trioxide.

According to another aspect of the invention, the substance which tends to react with sulfur trioxide is at least one selected from the group consisting of water, ammonia, alkali or carbonic acid, and alkali or alkaline earth metal hydroxide. Use seed substances. During the reaction, the position of the individual fillings may be changed strongly, both with respect to the container and between each other.
It is also possible to carry out the reaction in a rotating vessel.

Another minor embodiment of the invention uses as the sulfur trioxide-containing medium the contact gas present in sulfuric acid production, preferably the gas that has passed through at least one absorber.

An advantage of the invention is that it eliminates the undesirable effects identified during the study of the method. According to the invention, the reaction times in the individual packings as well as in the area of their surface are averaged and
Variations in time and concentration in the parts undergoing the reaction can be made negligible from the point of view of practical requirements for uniformity of the hydrophilic treatment. In practice, this effect can be achieved in a variety of ways; the charge can be vibrated or kept suspended in the air by a reactive gas, or it can be rotated about a horizontal or oblique axis. The reaction can also be carried out in a container provided with known protrusions or blades on the inside of the container to promote stirring. The last-mentioned embodiment is the most practicable and technically most suitable, since it can be carried out with equipment that does not substantially change the conventional rotary drying, mixer, crusher, etc.; , the intensity of agitation is independent of either the velocity of the moving gas or the shape or dimensions of the packing.

Furthermore, it is preferred to carry out the method of the invention in a continuous process. This is because, in particular, the product becomes more homogeneous and the reaction space is continuously filled with reaction gas. Such treatment prevents corrosion caused by sulfuric acid, which is produced by the reaction of sulfur trioxide with moisture, and
The reactor need not be of expensive, corrosion-resistant metal; it may be, for example, iron. The packing, which passes continuously through the oblique rotary reactor, rolls in a spiral over the walls of the reactor, with every part of its surface being continuously exposed to the gas flow. The sulfur trioxide-containing gas may be passed in any manner, ie, in parallel or countercurrent flow, or through a central tube with holes so that the sulfur trioxide concentration is similar everywhere in the reactor. In such devices, it is also possible to carry out the reaction discontinuously, for example if only gases with a relatively low sulfur trioxide content are available, which requires long reaction times to be applied. It is.

It is preferred that the sulfur trioxide-containing gas at the entrance to the reaction space is cooler than the charge to be treated, since the parts that react with high sulfur trioxide concentrations and long times react at low temperatures. In this way, the curves a , b ,
c (see drawings) and has an effect on the uniformity of the product. This optimal temperature difference depends on other factors, but should not exceed 35°C;
The most common value is 10°C.

Any gas having an excessive sulfur trioxide concentration or an inert gas such as nitrogen, carbon dioxide, or flue gas with a low oxygen content purified by cooling, filtration, etc., to dilute the sulfur trioxide. It is also possible to use

After the reaction, the surface layer contains absorbed sulfur trioxide, so that the reaction proceeds even though the packing is no longer in direct contact with the gaseous reagent. Here, exposure of the fill to dry air where the oxygen is not readily disposed of by the moisture of the air results in undesirable induced oxidation and consequent darkening of the product. This is an essential step of the invention, after the charge has been removed from exposure to the sulfur trioxide-containing gas. This is why it includes a step of interrupting the sulfation, which is carried out by bringing the medium into contact with the charge to form a compound that does not impair its original purpose. Such media can be, for example, humid air, water, water vapor,
Can be liquid or gaseous ammonia (in appropriate dilution), aqueous solutions of alkaliferaus substances such as alkali metal carbonates or bicarbonates, alkali and alkaline earth metal hydroxides, etc. .

Alkaline aqueous solutions are preferred for our purposes because they can convert the sulfonic, sulfate, and carboxyl groups of the surface layer to a neutral and, as a result, more hydrophilic ionized state. Apart from this, the dark colored oxidation products are soluble in alkaline solutions and the filling does not lose its dark color;
and at the same time some small local color irregularities also disappear; although the latter are functionally harmless, they are, in principle, something to complain about from a commercial point of view.

Neutralizing the deposited sulfur trioxide is the most advantageous of the above and simplifies the overall process. This is because the packing does not need to be dried and can be carried out continuously in a separate location downstream of the reactor or by the following steps: reaction, cleaning with inert gas, neutralization with ammonia, air. This is because the reaction can be immediately and discontinuously interrupted in the reactor by cleaning with:. Although it is true that the packing surface contains small amounts of solid ammonium sulfate in this case, it is not harmful in most applications. If necessary, the ammonium sulfate can be washed at any time.

The most practically suitable, most available and least expensive reagent for this purpose is the contact gas present in the production of sulfuric acid. These gases are available in large quantities, and their composition and properties can be selected depending on the extraction. first or second
Most preferred is gas withdrawn from an absorber. This corresponds to a composition that is in equilibrium with the oleum and is already cooler than before entering the first absorber. Before being introduced into the reactor containing the polypropylene packing, the gas must be cooled, preferably below the temperature of the packing. However, it is also possible to use the final gas of the absorption step, which contains a small amount of sulfur trioxide but has already been cooled and which compromises the long reaction times and the high yield of products to be achieved. make possible various aspects. Apart from this, the final gas is waste and does not cost money. It is therefore advantageous to carry out the hydrophilization treatment according to the invention directly in the sulfuric acid production plant, so that ammonia for fertilizer production is also available.

The following examples are provided to illustrate the invention, but are not intended to limit the scope of the claims.

Example 1 A rotatable cylindrical glass container with an inclination of 45° to the vertical axis was filled with a cylindrical packing made of polypropylene - a Raschchiling - at a temperature of 25°C. A gaseous medium at 20°C containing 4 volume percent sulfur trioxide and 96 volume percent nitrogen, prepared by bubbling oleum with dry nitrogen, was fed to the vessel. After 5 minutes, the vessel was purged with pure nitrogen with constant rotation, and a 5 percent aqueous solution of sodium bicarbonate was poured into the charge. The Laschichiring was washed once with water and then dried at 60°C. It has been found that the Lasschchillings are substantially colorless and completely wetted by water and aqueous solutions, allowing them to run off in a thin film. Compared to an otherwise identical packing without hydrophilic treatment, there are more than twice as many active interfaces, allowing the height of the absorption or cooling tower to be reduced by more than half or to its original dimensions, respectively. It has been confirmed that the output can be increased by more than double.

Example 2 This example shows negative results when the reaction conditions described above are not maintained.

A saddle-shaped polypropylene filling was heated at 23° C. in a fixed cylindrical glass container with 8% by volume sulfur trioxide, 7.5% by volume oxygen (O ₂ ), 1% by volume sulfur dioxide and 83.5% by volume. of nitrogen (N ₂ ) and cooled to 40° C. for 5 minutes.
Treated to make it hydrophilic. After cleaning with dry air and washing with water, the packing had a dark tint at the gas inlet and the thin hydrophilic layer on its surface tended to peel off. On the other hand, the filling material near the gas outlet was locally partially rendered hydrophilic.

Example 3 A stainless steel cylindrical reactor rotatable about a horizontal axis was packed with a saddle-shaped packing at 25°C. Then, 7% by volume of sulfur trioxide was added to the reactor;
It was filled with a gaseous medium (25° C.) containing 2.2% by volume of oxygen (O ₂ ) and 90.8% by volume of nitrogen (N ₂ ). The reaction lasted for 10 minutes at 40 rpm. After replacing the reactor gas with dry nitrogen, the reactor was filled with a mixture of 9 parts by volume of dry nitrogen and 1 part by volume of ammonia. The polypropylene packing washed with water was hydrophilic at the surface and exhibited properties similar to those of Example 1.

EXAMPLE 4 A polypropylene Pallring is prepared in a concrete mixer rotating at 30 rpm using the final gas remaining from the production of sulfuric acid, which contains about 1 percent sulfur trioxide and about the same amount of oxygen. and exposed to a stream of gas cooled to 22°C for 20 minutes at 30°C. The mixer has gas-tight inlets and outlets for the gaseous medium. The mixer was first cleaned with dry nitrogen, then with dry air containing 10% by volume ammonia, and finally with air. The Pall ring was seen to have a hydrophilic surface similar to that described in Example 1.

Example 5 An isotactic polypropylene Raschitz ring (diameter and height, 15 mm) was heated in a column at 20°C with a gas containing 0.5% by volume of sulfur trioxide and 99.5% by volume of nitrogen. The mixture was made hydrophilic for 70 minutes without stirring. The column was then cleaned with a mixture of 9 parts by volume of nitrogen and 1 part by volume of ammonia and finally with air. This charge was more uniformly hydrophilic than that treated according to Example 2.

[Brief explanation of the drawing]

The conversion rate is expressed as a function of the reaction time depending on the parts a to c of the charge.

Claims (1)

[Scope of Claims] 1. A method for producing an interfacial material and/or a packing for a heat exchange device whose surface is made hydrophilic by the action of gaseous sulfur trioxide, the method comprising:
A gaseous medium containing from 0.5 to 10 volume percent sulfur trioxide and less than 5 volume percent free oxygen is placed in a polypropylene filling in the container.
At a charge temperature of 10-50°C, the temperature of the gas is at most 10°C higher or 35°C lower than the charge temperature; contact between the charge and the sulfur trioxide-containing gas is interrupted. and contacting said filling with a gaseous or liquid medium containing a substance that has a tendency to react with sulfur trioxide;
A method consisting of 2. Claim 1, wherein said gaseous medium contains 1.5 to 5 volume percent sulfur trioxide.
The method described in section. 3. Using at least one substance selected from the group consisting of water, ammonia, alkali carbonates or carbonic acids, and hydroxides of alkali or alkaline earth metals as said substance that tends to react with sulfur trioxide; A method according to claim 1 or 2. 4. A method according to any one of claims 1 to 3, wherein during the reaction the position of the individual charges changes both with respect to the container and with respect to each other. 5. A method according to any of claims 1 to 4, wherein the reaction is carried out in a rotating vessel. 6. The method according to claim 1, wherein the gaseous medium containing sulfur trioxide is a contact gas present in the production of sulfuric acid. 7. Process according to claim 6, characterized in that the gaseous medium containing sulfur trioxide is a contact gas which has passed through at least one absorber in the production of sulfuric acid.