FR2467619A1 - PROCESS FOR THE PREPARATION OF HYDROPHILIZED SURFACE LINING FOR INTERPHASE MASS AND / OR HEAT EXCHANGE PLANTS - Google Patents

Abstract

at. Process for the manufacture of hydrophilized surface linings, intended for installations for interphase exchange of masses and / or heat, by the action of gaseous sulfur dioxide b. Characterized in that the polypropylene packing disposed in a container is contacted with a gas containing 0.5 to 10% by volume, especially 1.5 to 5% by volume, sulfur trioxide gas, and less than 5% by volume of free oxygen, at a packing temperature of 10 to 50 degrees C, the gas temperature being at most 10 degrees C or at most 35 degrees C lower than the temperature of the packing, and that after interruption of the contact between the gas containing sulfur trioxide and the packing, the latter is brought into contact with a gaseous or liquid medium, containing a substance reactive with respect to sulfur trioxide. vs. Packings applicable in particular to contact separation columns

Description

The invention relates to a method for manufacturing packings.

  hydrophilized on the surface, intended for installations for interphase exchange of masses and / or heat, by the action of gaseous sulfuric anhydride, such as for example fillers wettable by water for

absorption or extraction columns, cooling towers

  such facilities.

The Czech document nO 169 o54 describes packings for installations of mass exchangers or

  heat, made up of thermoplastic materials with

  essentially hydrophobic, such as polyethylene, poly-

  propylene, polyvinyl chloride, etc., the surface of which is coated with a coherent thin layer of another water-wettable polymer. In the case of linings of this type, their surface is better exploited, because, on the one hand, a larger surface area than in the case of traditional hydrophobic plastic lining, is covered with a flowing film, in phase aqueous liquid0

  On the other hand, the hydrodynamic behavior

of the flowing film, thus becomes more favorable

  corn. It follows that, compared to a lining of identical shape but made of hydrophobic plastic, the active interphase surface in which the exchange of mass and / or heat takes place, is incidentally doubled, or in others terms - that the height of the installation in question can be reduced by about half,

at equal capacity.

Plastic linings with a hydrophilic surface layer are produced by subjecting the surface of the hydrophobic lining to an appropriate chemical reaction - for example sulfonation or oxidation. The reaction and the conditions under which it takes place must be selected so that a coherent and resistant layer of a hydrophilic-water-wettable but insoluble polymer is formed on the surface of the lining. Since most hydrophilization reactions - when a certain degree of conversion is involved lead to water-soluble products, and that between hydrophobic layers not

  when wet, tangential tension is created, causing the

the hydrophilic layer, the reaction ratios are

considerably limited.

2.-

  The hydrophilization reaction is generally

Rally to be completed by a simultaneous crosslinking of the hydrophilic layer, and the diffusion of the reagent in the hydrophobic polymer is to be conducted in such a way that a wettability gradient is obtained between the two layers and that the tangential tension is reduced to the separation surface. Another factor limiting the choice of an appropriate reaction is the price of the filling, taking into account the cost of

hydrophilization treatment.

The plastic materials most often used for this application are polyolefins, in particular polyethylene, and preferably because of its specific weight, its thermomechanical properties and its low cost price - isotactic polypropylene. Its disadvantage is that it has a highly crystalline character, so that the low molecular weight reagents can only diffuse inside slowly, while the hydrophilization reaction proceeds with a speed

  considerable. It therefore occurs, in various reactions

  tions - such as surface oxidation with chromic acid - a corrosion action, which has the effect

  to decompose and mop the immediate hydrophilic thin layer

  after its constitution, which constantly exposes the hydrophobic surface. Consequently, the processes recommended for polyethylene cannot be used for polypropylene,

  for example liquid phase oxidation. As a practical means-

  As practicable, cold sulfonation has been used up to now with oleum; which is not accompanied, in particular

oxidation, only to a small extent.

  Sulfonation with liquid oleum, however, has various drawbacks, which consist in particular in that the surface of the sulfonated lining is easily wetted by the oleum, and consequently it contains a relatively high amount. Working with large quantities of oleum and removing residues adhering to the filling is inconvenient, and requires severe measures of

safety and hygiene.

Obviously because of the grip

  considerable amounts of liquid reagent it is generally-

  It is more advantageous to carry out the reaction in the gas phase.

3. -

  One difficulty, however, is that, in the case of poly-

propylene, because of the constitution of the lining, it is not possible to implement a process used for polypropylene sheets - such as for example the oxidation initiated by Corona discharge. With such methods, the degree of hydrophilization of the lining is not satisfactory, since these specific methods have only been developed for

  allow to make prints on the materials of

  ballage. In this case, the requirements concerning hydrophilicity

are incomparably lower.

Sulfonation with anhydride

  sulfuric gas has so far posed significant problems

  maple trees. With high concentrations of sulfur anhydride

  that bubbles and islets are formed on the surfaces to

high degree of reaction, as a result of which the hydrophilic layer

  edged flakes after wetting. By diluting sulfuric anhydride with air, there is an induced oxidation with oxygen, which leads to the formation of dark tarry products, soluble in water and in particular in alkali solutions. The main difficulty is that the reaction has a self-accelerating character, in particular when it is accompanied by oxidation - and a high activation energy. The combination of these effects results in the reaction taking place for a period of time without any modification of the hydrophilicity of the surface (called the induction phase), after which it takes place with

high speed and degree of conversion.

A reaction having such a course is very difficult to control, since there appear to be significant differences in reaction degree between the surface zones which first come into contact with the gaseous reagent, the latter acting longer and at a higher concentration. , and areas where the reagent does not arrive until a little later, and at slightly lower concentrations. This is due, on the one hand, to the actual reaction, on the other hand, to the sorption of sulfuric anhydride in the layer subjected to the

reaction, and on its surface.

In the case of habitual implementation

  reaction time - for example when sulfuric anhydride vapor is supplied to a reactor containing a polypropylene packing, or to a column - the result is very unfavorable, because on the one hand, near the gas inlet , the surface of the lining is already "burnt", that is to say that it is sulfonated, over an excessive thickness and with a too high degree of conversion, on the other hand it is oxidized, then

that at the outlet of the gas, the surface of the lining remains practical-

hydrophobic. If the reaction time is chosen, for a temperature and a concentration of sulfuric anhydride

  data, so that the conversion in the main area

  blade - that is to say at the center of the reactor - is sufficient and optimal, then, at the gas inlet, the part of the lining reacting a little longer and at slightly higher sulfuric anhydride concentrations, transforms with a too high degree of conversion, while the lining located near the gas outlet, which comes into contact with the reagent a little later and at slightly lower concentrations, is until then in the period so-called induction and therefore obviously remains practically hydrophobic. A situation of this type is illustrated in the attached diagram, where curve a represents the reaction near the arrival of the gas, curve b, at the center of the charge, and curve c, near the outlet of the gas. The ordinates ta, tb, tc represent the corresponding reaction times and the

abscissa alpha a, alpha b, alpha c, degrees of conversion.

  From the scheme, it is clear that even small, apparently unimportant differences between the periods of contact between the packing and the reagent can result in serious differences in the degree of conversion obtained. These differences become all the greater as the

gas is hotter or contains oxygen in a con-

centering such that exothermic induced oxidation takes place

in high proportion, so that in addition, in the center of the garnis

wise there is a temperature gradient. These negative effects

can also be combined.

The result is very noticeable, so that the packing - although the total contact period does not exceed a few tens of seconds or a few minutes, and the gas speed has a value such that the difference between the moments when the contact is not more than a few

seconds - appears after the reaction as burnt to the flame.

  The filling located near the gas inlet, as well as its outer edge, its edges and its protruding parts are "burnt", and dark, while the concave surface portions diverted from the gas stream and distant from the inlet of gases, remain practically unchanged. It follows that such a reaction, although advantageous, is practically not usable if it is applied according to the traditional technique, by subjecting the filling to be treated, to a gas containing anhydride

sulfuric.

  The object of the invention is to eliminate the drawbacks mentioned above, of the prior art, and to propose an improved process for obtaining hydrophilized packing on the surface, for mass and / or heat exchange devices at Itinterphase, per anhydride action

sulfuric gas.

To this end, the invention relates to a process characterized in that the polypropylene lining

  placed in a container is brought into contact with a gas

holding from 0.5 to 10% c by volume, in particular from 1.5 to 5% by volume, of gaseous sulfur dioxide, and less than 5% by volume of free oxygen, at a packing temperature of 10 to 500 C, the temperature of the gas being at most 100 C or at most 350 C lower than the temperature of the packing, and after the contact between the gas containing sulfuric anhydride and the packing is interrupted, the latter is brought into contact with a gaseous or liquid medium containing a substance

  reactive towards sulfuric anhydride.

  According to another characteristic of the invention, as reactive substance vis-à-vis sulfuric anhydride, at least one substance belonging to the group consisting of water, ammonia, alkali carbonates or bicarbonates is used, and alkali or alkaline earth metal hydroxides. During the reaction the position of the individual packing elements is profoundly changed during the reaction, both in relation to the container and in their reciprocal position. It is also possible to set

  carries out the reaction in a rotating container.

  According to the last characteristic of the invention, as a gas containing sulfuric anhydride, a contact gas for the production of sulfuric acid is used.

preferably a gas having passed through at least one absorber.

  The action of the invention eliminates the influences mentioned during the study of the process. According to the method of the invention, a convergence is obtained of the reaction times of the individual packing elements, and for their surface parts, a good profile, so that the fluctuations in duration and concentration in the different

parts of the surface subjected to the reaction, become neglected

geables, taking into account the practical requirements concerning homo-

generosity of hydrophilization.

  This can be done in practice in several ways: the linings can be either agitated or kept in suspension in the reaction gas, that is to say that the reaction can be carried out in a rotary container around '' a horizontal or olique axis, the inner wall of the

container can be lined with protrusions or ribs favori-

health agitation. This latter embodiment was found to be

more practicable, and more appropriate from a technical point of view

  logical, insofar as it can be implemented in conventional devices, requiring only a slight adaptation, such as rotary dryers, mixers, granulators and others, and the intensity of the stirring process does not depend , in this case, neither the speed of the gas stream, nor the

  shape or size of the packing elements.

It is advantageous to continuously carry out the process according to the invention and this above all because the

  product is more homogeneous and the reaction volume is constant

  filled with the reaction gas. In this way, corrosion caused by sulfuric acid formed as a result of the reaction between sulfuric anhydride and moisture can be avoided.

  air, so the reactor should not be mandatory -

  made up of a precious metal alloy.

  The linings continuously advanced by the rotary reactor along an oblique axis, roll on its wall in a helical path and present to the gas stream all the parts of their surfaces, one after the other. The gas can be introduced here into the container in any way, according to the principle of parallel current or countercurrent, or through a perforated central tube; the latter 7.- must be arranged in such a way that the concentration of

sulfuric anhydride is identical in each zone of the reactor.

  In a device of this type, the reaction can also be carried out discontinuously, for example when a gas with a relatively low sulfuric anhydride content is available,

and requiring a longer reaction period.

  It is advantageous that the gas containing sulfuric anhydride is colder on entering the reactor than the lining to be treated, since the linings reacting to higher concentrations of sulfuric anhydride and for longer periods can react at lower temperatures. Thus the curves a, b, c extend partially in a straight line (see diagram), which positively influences the homogeneity of the product. The optimal temperature difference depends on the other parameters, but must not exceed 350 C, it will most often be 100 C. To dilute sulfuric anhydride, or a gas containing this in predominant concentration, one can use a gas any inert, with a low content of free oxygen, for example nitrogen, carbon dioxide, or cooled, filtered or purified combustion gases, having a

low oxygen content.

  After the reaction, sulfuric anhydride remains absorbed by the surface layer, so that, even after direct contact between the lining and the

gas reagent has ceased, the reaction can continue spontaneously

  nement. If the packing is now subjected to dry air, where the sulfuric anhydride is liquefied, not quite like the humidity of the air, the undesirable induced oxidation and the

  dark coloring of the resulting product may occur.

An essential process to stop

the sulfonation reaction therefore consists, in accordance with the information

  vention, in that after the cessation of contact between the garnis-

  sage and the gas containing sulfuric anhydride, the packing is subjected to the action of a gaseous or fluid medium, which contains

  a required amount of substance capable of reacting with the anhy-

  sulfuric dride, forming non-detrimental compounds for

the intended application. An environment of this type can be

  killed by moist air, water, water vapor, liquid or gaseous or suitably diluted ammonia, aqueous solutions 8.-

  of alkaline reacting substances like carbonates or bicar-.

  alkali metal bonates, alkali metal hydroxides

or alkaline earth, and others.

  Aqueous solutions of alkalis are not recommended here, as they are capable of transforming the sulfone, sulfate and carbonyl groups in the thin surface layer into an innate, neutralized form, which is therefore no longer hydrophilic. In addition, dark-colored products are soluble in alkali solutions, so that the packings lose their possible dark color, and even the slight local differences in color disappear. This is not really detrimental to the function of the filling, but it is considered in general, from a commercial point of view,

as questionable for quality.

  1_, The advantage of neutralizing the adherent sulfuric anhydride with gaseous ammonia, results above all in a technological simplification of the whole process, since it becomes unnecessary to dry the lining, and the reaction can be interrupted either, by continuous process, in separate sections after the actual reactor, or, in a batch process, directly in a cycle (reaction, rinsing with dry inert gas, neutralization with ammonia, rinsing with air). Although the lining has, on the surface, a small amount of. ammonium sulfate, this is not an obstacle in most applications. If necessary,

however, ammonium sulfate can be removed by washing.

  Among the gaseous reagents suitable for

This application, the contact gas available in the manufacturing

  tion of sulfuric acid is practically the most suitable, the least expensive and the most accessible. It is available in large quantities, and its composition, as its properties, can be selected according to the place of racking in manufacturing. The gas withdrawn after the first or the second absorber is preferably used. By composition, the gas from the first absorber corresponds to equilibrium with the oleum, and it is already colder than before its penetration into the first absorber. Before its introduction into the reactor containing the lining, the gas is preferably cooled to a temperature lower than that of the lining. However, it is also possible to use

absorption contact gas. These, although they do not contain-

2 4 6 7 6 19

  9.- do not have much sulfuric anhydride, but are colder,

  so that with the disadvantage of a reaction time pro-

longer, you can get a higher homogeneity of the product.

  In addition, terminal gases represent waste and are therefore available free of charge. It is therefore advantageous to implement the hydrophilization process according to the invention directly in the contact sulfuric acid manufacturing plant, where the leon can also have ammonia

intended for the manufacture of fertilizers.

The invention will be better understood using

following examples.

EXAMPLE 1 -

A rotating cylindrical glass vase, with a slope of 450 on the vertical, is filled with linings of

cylindrical polypropylene shape (Raschig rings).

A hot gas at C is introduced into the vase, containing 4% by volume of sulfuric anhydride and 96% by volume of nitrogen. The gas was prepared by bubbling dry nitrogen through loleum. After 5 minutes, the vase is rinsed with pure nitrogen, without interrupting its rotation, then the

charge is poured into a 55% aqueous solution of bicarbo-

  sodium nate, After washing with water, the rings are dried at 6oo C.

  They are practically colorless, whole-

wettable with water and suitable solutions, which can flow out in the form of a thin film. Compared to identical linings, but not hydrophilized, the effective interface surface is more than doubled, so that the height of the cooling or absorption towers considered can be reduced by half, keeping the same capacity, ie at otherwise, with the same dimensions, increase the capacity

more than double.

EXAMPLE 2 -

  This example is used to illustrate a negative result, when the previously mentioned reports of the

  reaction could not be respected.

  Polypropylene saddle-shaped filling bodies are hydrophilized at 230 ° C., in a cylindrical, static glass vase, with a contact gas containing 8% by volume of sulfuric anhydride, 7.5% / 0 by volume of oxygen 10.- (02), 1% by volume of sulfur dioxide and 83.5% by volume of nitrogen (N2); the gas is cooled to 40 C in the space of 5 minutes. After rinsing with dried air and washing with water, the filling near the gas inlet has a dark color, and the hydrophilic upper layer tends to flake. Near the gas outlet, the filling is not,

  in places, not completely hydrophilized.

EXAMPLE 3 -

  A cylindrical reactor, rotating around a horizontal axis, made of stainless steel, is filled at 25 ° C. with filling bodies in the form of saddles. A gas containing 7% by volume of sulfuric anhydride, 2.2% by volume of oxygen (02) and 90.8% by volume of nitrogen (N2) is introduced into the reactor at 25 C. The reaction lasts 40 minutes, with 40 revolutions per minute. After displacement of the gas by dry nitrogen, the reactor is filled with a mixture of 9 parts by volume of dry nitrogen and 1 part by volume of ammonia. After washing with water, the filling stools are hydrophilic and have the same properties and the same effects as filling according to

Example 1.

EXAMPLE 4 -

Pall polypropylene rings are subjected, in a rotary concrete mixer, at 30 rpm and 30 C, to a final gas stream containing about 1% sulfuric anhydride and about the same amount of oxygen, and cooled to 22 C, for 20 minutes. The concrete mixer is fitted with leak-proof gas inlet and outlet. It is then rinsed with dry nitrogen, then with nitrogen containing 10% by volume of ammonia and finally with air. The rings are

  become hydrophilic, as in Example 1.

EXAMPLE 5 -

Raschig rings of isotactic polypropylene (15 mm in diameter and height) are hydrophilized, without stirring, in a column at 20 C, with a gas at the same temperature, containing 0.5% by volume of sulfuric anhydride and 99 , 5% / by volume of nitrogen, in 70 minutes. The column is then rinsed with a mixture of 9 parts of nitrogen and 1 part of ammonia,

then with air. The surface of the linings becomes more uniform

formally hydrophilic, than with the process described in Example 2.

11._

Claims (3)

1.- Process for the manufacture of garnishes   wise hydrophilized on the surface, intended for installations for inter-phase exchange of masses and / or heat, by the action of gaseous sulfuric anhydride, characterized in that the polypropylene lining placed in a container is placed in contact with a gas containing from 0.5 to 10% by volume, in particular-- 1.5 to 5% by volume, gaseous sulfur dioxide, and less than 5% by volume of free oxygen, at a packing temperature of 10 to 500 ° C., the temperature of the gas being at most   100 C higher or at most 350 C lower than the temperature ture of the lining, and that after interruption of the contact between the gas containing sulfuric anhydride and the lining, the latter is brought into contact with a gaseous or liquid medium, containing a substance reactive with respect to the anhydride sulfuric. 2, - Method according to claim 1, characterized in that as reactive substance vis-à-vis   sulfuric anhydride, at least one apparent substance is used belonging to the group consisting of water, ammonia, alkali carbonates or bicarbonates, and alkali metal hydroxides or alkaline earth.   3.- Method according to claims 1 and 2,   characterized in that the position of the individual packing elements is profoundly changed during the reaction, also that relative to the container, that their reciprocal position that, 4.- Method according to any one of   Claims 1 to 3, characterized in that the reaction takes place kills in a container that can be rotated.   - 5.- Method according to any one of   claims 1 to 4, characterized in that as containing gas   sulfuric anhydride, a contact gas for the production of sulfuric acid is used, preferably a gas having passed by at least one absorber.