NO773072L - PROCEDURE FOR NEUTRALIZATION OF SULPHONATED, NORMALLY SOLID POLYMERS - Google Patents

Description

The invention relates to the neutralization of sulfonated, normally solid polymers with a gaseous neutralizing agent, e.g. e.g. ammonia...

It is known that exposure to gaseous ammonia or immersion in aqueous ammonia will neutralize a sulfo-

nerted or chlorosulfonated surface of resin material and that

water or steam can be used after gaseous ammonia treatment for washing water-soluble sulfur-containing compounds from plastic objects. Reference is made to US patent no. 3,625,751. This patent also teaches that a mixture of water vapor and gaseous ammonia can be used for neutralizing sulfonated polymers.

The previously known treatments of sulfonated surfaces of resin polymers to neutralize the acid groups are slow or require additional processing which creates a bottleneck in the production of these articles. Spraying or rinsing these surfaces with a liquid neutralizing agent necessitates the addition of a drying step to the production pro-

f

the session. Treating the surface with gaseous ammonia involves a relatively long exposure period to complete the neutralization, even if an atmosphere of pure ammonia is used. The use of one atmosphere |of. pure ammonia is an inadequate and wasteful application of the 4 reagent.

The present invention provides a method for neutralizing sulfonated, normally solid, polymers with a gaseous mixture of an inert gas and ammonia or an organic amine in the presence of a hydroxyl compound, and the method is characterized in that essentially complete neutralization is accelerated by the sulfonated polymer is brought into contact with an inert gas containing a vaporous hydroxyl compound, without making the sulfonated polymer visibly moist. The amount of vaporous hydroxyl compound used is preferably . sufficient to accelerate the rate of neutralization by at least 25% relative to the rate of neutralization obtained by the prior art method of vapor phase reneutralization in the absence of the hydroxyl compound, but does not visibly wet the sulfonated polymer. The sulfonated polymer can be brought into contact with the vaporous hydroxyl compound either before or simultaneously with the essentially complete neutralization.

Surprisingly, the embodiment of the present invention greatly accelerates the speed, e.g. as much as from 100 to 400% of the normal rate in the absence of hydroxyl compound at which the gaseous neutralizing agent neutralizes the sulfonated polymer. The sulfonated polymer is unexpectedly neutralized much more easily by the method according to the invention to a degree that is sufficient to eliminate hygroscopic properties. In contrast, the previously known surface neutralization method with a dry gaseous neutralizing agent neutralizes the sulfonic acid groups to an extent insufficient to eliminate the hygroscopic nature of the surface of the sulfonated polymer.

The method according to the invention is useful for the production of sulphonated polymers which can be used as containers for hydrocarbon or other organic materials which penetrate untreated non-aromatic polymers. The method is also useful in the production of sulphonated polymers which are to be spray-coated electrostatically.

A particularly preferred embodiment of the invention where great applicability is achieved is when producing a sulfonated polymer enclosure part for storing a hydrocarbon liquid, e.g. petrol, kerosene, diesel oil and other similar fuels. In such an embodiment, the enclosure part is preferably in the form of a molded container, e.g. a gas tank, a

oil drum or an oil barrel..

The polymers to which the invention is applicable can be classified as sulfonable, normally solid polymers. A sulfonable polymer must have a majority of exchangeable hydrogen atoms bonded to carbon atoms near the surface. The following groups or classes exemplify such sulfonable polymers:

a. aromatic polymers, e.g. polystyrene, polyvinyltoluene, polyphenylene, and poly(p-xylene); b. polyolefins, e.g. polyethylene, polypropylene, polyisobutylene, polybutene-1 and polymethylpentenes; c. polyacrylic acid esters, e.g. polymethyl acrylate and polyethyl methacrylate; d. polyvinyl esters, e.g. polyvinyl acetate and polyvinyl butyrate;

e. polyvinylidene halides, e.g. polyvinylidene chloride and polyvinylidene fluoride;

f. halogenated polyolefins, e.g. chlorinated polyethylene and chlorinated polypropylene;

g. polyvinyl halides, fceks. polyvinyl fluoride and polyvinyl chloride;

h. Polycarbonates, e.g. poly(bisphenol-A) carbonate;

and

i. polyesters, e.g. polyethylene terephthalate.

Mixtures of the above-mentioned polymers and copolymers of the related monomers are also included within the scope of the invention. The sulfonated polymers which are preferred for use in connection with the method according to the invention,

are the poly-monoolefins, e.g. H. D. and L.D. the polyethylenes, polypropylene, ethylene/propylene copolymers, ethylene/butene-1 copolymers and mixtures thereof.

Central to this invention is the unexpected discovery that the presence of a gaseous hydroxyl compound, e.g. water vapor or a gaseous organic hydroxyl compound, e.g. methanol, ethanol or ethylene glycol, accelerates the rate at which a gaseous neutralizing agent., e.g. ammonia or a gaseous organic amine, e.g. methylamine, will effect essentially complete neutralization of a sulphonated surface of a normally solid polymer. Substantially complete neutralization has been accomplished when a strip of litmus paper moistened with distilled water and brought into contact with the sulfonated surface indicates a pH value of at least 5, preferably a pH value in the range of 5-7 and more preferably 5.3-7.

It is preferred that the hydroxyl compound or the neutralizing agent used in accordance with the invention is of low molecular weight, due to the generally higher vapor pressures that low molecular weight compounds have. Accordingly, such a low molecular weight organic hydroxyl compound is one that achieves the concentration in moles of hydroxyl compound per liters of gas necessary to accelerate neutralization at operating conditions suitable for carrying out the invention. Examples of preferred compounds are methanol, ethanol and ethylene glycol. A low molecular weight neutralizing agent is an organic amine which achieves the concentration in moles of organic amine per liters of gas required to neutralize the sulfonated polymer in a short period of time in accordance with

see with the invention. Examples of preferred compounds include methylamine, dimethylamine and ethylamine. It is preferable that the required concentrations are achieved with organic amines and hydroxyl compounds in the vapor phase, but a suspension of fine droplets of the compound in an inert gas can also be used if the droplets are small enough that the sulphonated polymer is not visibly wetted during contact.

The invention is most preferably carried out using water vapor and gaseous ammonia, as these reagents neutralize the surface faster and more completely in accordance with the invention and because these reagents are inherently more economical to use than organic hydroxyl compounds or gaseous organic amine neutralizing agents . For. for the sake of brevity and because the teaching of the method according to the invention does not depend on the reagents used, the invention shall be described by

using the preferred reagents, steam and ammonia.

The method by which the polymers are sulfonated is not critical. The preferred method for sulfonating the polymer is to immerse them at room temperature in a tank containing a dry, inert gas with approx. 0.1-25% by volume of sulfur trioxide (SO^) mixed in over a period of time varying from 0.1-20 minutes. Examples of the inert gases to be used in this method are nitrogen, carbon dioxide, sulfur dioxide and air.

It is desirable to exclude water vapor from the above gases by means of a conventional drying tube since SO2 in the presence of water in liquid or vapor form is converted into droplets of sulfuric acid of varying concentration and the sulfonation of the polymer is either inhibited or prevented.

The sulfonation of a polymer gives water-soluble sulfur-containing compounds as well as the sulfonic acid groups that are bound to the polymer. For purposes where the presence of these water-soluble compounds does not affect the suitability of the sulfonated polymer for its intended purpose, these compounds, although not removed by subsequent gaseous neutralization, need not be washed away from the surface. An example of such an application is a fuel tank in which the solubility of these compounds in petrol makes it unnecessary for them to be washed away from the polymer. If no rinsing is necessary, the drying step normally required if an aqueous neutralization solution is used can be eliminated by carrying out the neutralization method according to the invention. Even if the sulfonated polymer is to be used for a purpose which makes it desirable that these soluble compounds are washed away from the surface, the use of the neutralization method according to the invention may be preferable to the use of an aqueous solution for neutralization due to the fact that easy to recycle unused ammonia and because it is easy to neutralize bulky objects of unusual configuration.

The acceleration of the rate of neutralization for sulfonated polymers observed in accordance with the invention is not dependent on the degree of sulfonation. For example, any concentration in the range of sulfonate group concentrations that are typically used to improve barrier properties for sulfonable polymer, i.e. from 0.015 to 50 mg of sulfur trioxide equivalents per cm 2 , is advantageously neutralized when carrying out the invention. The saving in time that comes with this invention may be less where the degree of sulfonation is less than indicated above, but a certain advantage persists even at very low degrees of sulfonation, e.g. at as little as 0.001 mg of sulfur trioxide equivalent per cm 2.

Although the concentration of water vapor in inert gas may exceed the saturation point for the inert gas in accordance with the method according to the invention, it is generally less desirable to exceed the saturation point as condensation often occurs under such conditions. Excess condensation is undesirable because it necessitates a drying step which could otherwise be eliminated in many cases. What is more important is that if the sulfonated polymer is not neutralized immediately or simultaneously with exposure to water vapor, sulfuric acid is formed by the reaction between water and the water-soluble sulfur-containing compounds deposited on the polymer surface during sulfonation. The acid can damage the polymer and other adjacent surfaces and hinder the effective and rapid neutralization of the sulphonated surfaces which are isolated from contact with neutralizing gas by acid condensation. It is therefore preferable that the concentration of water vapor in the inert gas used in carrying out the invention does not exceed the saturation point of the inert gas which is in contact with the sulphonated polymer.

If the atmosphere of air containing water vapour, but not ammonia, to which the sulphonated polymer is exposed, has a pressure of 1 atmosphere at 21°C, it is preferred when carrying out the invention that the gas mixture has a relative humidity in the range 20-100%, more preferably 50-100%, more preferably 85-100%. The preferred ranges for relative humidities at a pressure of 1 atmosphere at 21°C correspond to a preferred concentration in moles of water vapor per liter gas mixture of from 0.005 to 0.024, with 0.012-0.024 being more preferred and 0.020-0.024 being most preferred.

The lower limits for the aforementioned preferred, more preferred and most preferred concentrations of water vapor are applicable in carrying out the invention, regardless of whether the neutralization follows the exposure to the moist atmosphere or takes place simultaneously with and independently of the temperature and pressure, when only the conditions are suitable for carrying out the invention. The upper limit of the above preferred range of concentrations is controlled by the saturation point of the humidified atmosphere at the temperature, pressure and composition of the atmosphere used in the execution of the invention. If the neutralization is to occur

simultaneously with the exposure to water vapor, the gas mixture will also contain ammonia, and the above preferred concentrations are applicable to the mixture of gases including ammonia.

Neutralization of the sulphonated polymer with ammonia by the method practiced in connection with the invention can follow exposure to water vapour, can occur simultaneously with exposure to water vapor or can occur within both of these time frames as when ammonia is used to flush water vapor from contact with the surface and is used for neutralization of the surface. If the neutralization method involves bringing the sulfonated polymer simultaneously into contact with water vapor and ammonia, the molar ratio of ammonia to water vapor concentration, NH^tH^O, is

an important parameter .when performing the fastest and most effective neutralization. The most preferred area of such conditions'

is 1:1 to 3:1. But self. at higher, less preferred conditions

(the upper limit is 10:1) will an inert atmosphere that is saturated

with water vapor accelerate the neutralization remarkably. The lower limit of preferred conditions that give an unexpected acceleration of the rate of neutralization with a water-saturated inert atmosphere is usually a ratio NH3:H20 of approx. 4:5. The limits set by the preferred range of water concentrations and the preferred ratios of the concentrations of ammonia to water vapor during simultaneous exposure determine that the ammonia should constitute roughly 1-20% by volume of the preferred high-trailing atmosphere when simultaneous contact between the sulfonated polymer and ammonia and water vapor is carried out in carrying out the invention.

The ratio between the concentration of ammonia and water vapor is not particularly critical when the sulfonated polymer is first exposed to an inert gas containing water vapor followed by exposure to an inert gas containing ammonia. In the successive exposure of the sulfonated polymer to water vapor and ammonia atmosphere at 1 atmosphere pressure at 21°C, the neutralizing atmosphere may preferably contain 5-100 volume% ammonia, more preferably 50-100 volume% ammonia and most preferably 85-100 volume % ammonia. Mixtures of 16-25% by volume ammonia in air are potentially explosive, and it is therefore desirable to avoid such mixtures when carrying out the invention. The above preferred ranges for percent ammonia by volume in the neutralizing atmosphere, compared to the water vapor content of a saturated atmosphere at the same temperature and pressure, determine preferred mole ratios of ammonia to water vapor from 1.9:1 to 38.5:1, more preferred molar ratio from 19.2:1 to 38.5:1, most preferred molar ratio from 32.7:1 to 38.5:1. The preferred concentration range for ammonia for neutralization of a sulfonated polymer immediately after exposure to a humidified atmosphere by the method according to the invention, calculated from the above-mentioned volume percentages of ammonia at a pressure of 1 atmosphere at 21°C, is from 0.002 to 0.04 , more preferably 0.034-0.04, moles of ammonia per liter of the inert gas/ammonia mixture. The lower limits of the above preferred ranges of concentrations of ammonia are applicable when the humidified atmosphere precedes the neutralized atmosphere for carrying out the invention at all temperatures and pressures suitable for carrying out the invention. The upper limit of the preferred and most preferred range a,v concentrations of ammonia is controlled by the concentration of an atmosphere of pure ammonia gas at the operating temperature used.

The methods by which the sulphonated polymer can be brought into successive or simultaneous contact with water vapor and ammonia in accordance with the invention will generally be obvious to the person skilled in the field and are not part of this invention. The sulfonated polymer may be transported through the treating atmosphere(s). The sulfonated polymer can be placed in a vessel, and the atmosphere surrounding the sulfonated polymer is then displaced or modified to the neutralizing atmosphere according to the invention. Alternatively, a stream of inert gas containing suitable amounts of the reagents can be directed is carried over the surface of the sulfonated polymers for a sufficient period of time to provide practically complete neutralization

in the case of a sulphonated surface on the inner side of a normally solid polymer enclosure part, the complete enclosure itself can be used as a neutralization chamber. It is preferred that, regardless of which method is used, intimate contact between the sulfonated polymers and the water and ammonia vapors over the duration of the exposure is ensured.

The mixtures of. gases used in the above-mentioned methods can be easily produced by methods that are known in the field. An atmosphere saturated with water vapor can be produced by bubbling the inert gas through water. The preferred concentration ratio between ammonia and water vapor can be established by bubbling

of the inert gas through an aqueous solution containing a suitable concentration of ammonia. The concentrations of ammonia and

water vapor can be reduced by mixing the inert gas that has previously been bubbled through the aqueous solution with dry inert gas. There are other methods for controlling the concentrations of ammonia and water vapor, e.g. use of flow meters or laminar flow valves for regulating the injection of these gases into a stream of inert gas with a known flow rate. The implementation of this invention is not limited to any specific techniques used for the production of mixtures of ammonia and/or water vapor in inert gases with a concentration that is suitable for neutralizing sulphonated polymers by the method according to the invention.

The temperature is not critical when performing the above

mentioned methods of neutralization, but it is advantageous

to carry out the methods in the temperature range from 4 to 93°C, preferably 21-82°C. If the temperature is in the lower part of the above-mentioned range, the vapor pressure or the partial vapor pressure of the water vapor is too low to induce the most effective neutralization of the sulfonated surface. If the temperature of the atmosphere saturated with water vapor exceeds the temperature of the sulfonated polymer, condensation often occurs. Steam or heated steam can be used when carrying out the method according to the invention, but is not preferred because safety measures must be taken, e.g. heating the polymer before neutralization, to prevent condensation of the steam or the heated water vapor on the sulfonated surface.

The pressure at which the surface is neutralized by the above-mentioned methods is not critical either. Although for reasons of convenience it is preferable to carry out the treatment at atmospheric pressure, the neutralization methods can advantageously be carried out at pressures in the range of 0.1-5 atmospheres. However, excessive pressure can lead to unwanted condensation of water vapor. Very low pressure can result in concentrations of ammonia that are too low for the most effective neutralization. . When the neutralization progresses simultaneously with exposure to the water vapor, i.e. when ammonia and water vapor are present in the same atmosphere, the duration of contact between the sulfonated polymer and the above-mentioned atmosphere is preferably controlled by the time required for substantially complete neutralization of the sulfonated polymer. If the exposure takes place simultaneously, the time required for neutralization will for a given molar ratio of ammonia to water vapor concentrations, generally decrease as the concentration of ammonia is increased. Under preferred conditions, the typical time required for relatively complete neutralization of a sulfonated polymer upon simultaneous exposure to ammonia and water vapor is 20-30 seconds.

If water vapor contact precedes exposure to ammonia, the duration of contact between the sulfonated polymer and the atmosphere containing the water vapor is the contact period necessary to accelerate neutralization. Although the duration of contact with water vapor can advantageously be as little as 5 seconds, exposure from 20 to 90 seconds is preferred. A period of time from the initiation of contact with water vapor to the initiation of neutralization which is longer than ea. 180 seconds, may result in deterioration of the surface due to the formation of sulfuric acid by the reaction between water and the water-soluble sulfur-containing material on the surface of the sulfonated polymer. The time required for relatively complete neutralization of the sulfonated polymer after contact with an atmosphere saturated with water vapor for the preferred period of time can be as short as 20 seconds if the neutralization atmosphere is pure, anhydrous ammonia.

The following examples are given for illustration, but not for limitation of the invention.

Example 1

A series of HD polyethylene bottles of 497.6 gram capacity are connected in turn to an apparatus which allows the bottles to be flushed with any of the following vapor phase mixtures: sulfur trioxide in nitrogen, nitrogen bubbled through an aqueous solution of ammonia, nitrogen bubbled through distilled water, anhydrous ammonia, or anhydrous nitrogen. Each of the bottles is sulphonated by flushing them through for 3 minutes with the sulfur trioxide and nitrogen mixture that appears in a 65-70% oleum bubbler. The sulfonation is followed by a 1-minute purge with dry nitrogen. The bottles were neutralized using one of three methods.

Method 1 involves neutralizing the bottles with mixtures of anhydrous ammonia and nitrogen of varying concentrations. Method 1 corresponds to previously known methods.

In method 2, the bottle is flushed with dry nitrogen that has been bubbled through aqueous ammonia solutions with a number of different concentrations. The purge gas is assumed to be a saturated vapor, and the volume % for each component is calculated on this basis.

In method 3, the bottle is first flushed for varying periods of time with nitrogen which is saturated with water vapour, and is followed by a flush with anhydrous ammonia. A ratio between ammonia and water vapor concentrations is calculated even if the reagents do not simultaneously come into contact with the sulphonated polymer.

A piece of litmus paper moistened with distilled water can be used to determine when the surface has been well neutralized.

All the above operations are carried out at 22°C and 1 atmosphere. The neutralization times required by the above-mentioned neutralization methods are given in Table I below.

It appears from the data presented, in table i,

that exposure of the sulphonated polymer to water vapor and ammonia simultaneously or successively as in methods 2 and 3, respectively, results in a large acceleration of the neutralization in relation to the state-of-the-art treatment of the surface with gaseous ammonia as shown in method 1. In particular, neutralization using method 2 is not only faster, but more efficient with regard to the utilization of ammonia than the method according to the state of the art. Neutralization using method 3 is much faster than neutralization without pre-treatment of the surface with steam in all reported tests with the exception of sample No. A^.

The 5-second pre-treatment of the surface with water vapor in sample No. A was insufficient at the test pressure, temperature

and concentration of water vapor in the pretreatment atmosphere to produce acceleration of the neutralization.

Example 2

A range of 45.4 L capacity HDPE containers, suitable for use as automotive petrol tanks, are sulphonated to the same extent to provide a barrier for the storage of hydrocarbon liquids, e.g. gasoline. A stream of dry air containing 30% anhydrous ammonia, by volume, and flowing at a rate of 9.6 standard cubic feet per minute is used for neutralizing some of the sulphonated HDPE tanks in accordance with the method according to the state of the art. Addition of atomized water at a rate of 1/60 gallon per my. is made into the above gas flow. The moistened stream is also used for neutralizing some of the sulphonated tanks. Provision is made to allow some of the larger water droplets to condense out of the gas stream before the wetted stream is directed into the sulfonated tank.

After continuous treatment for a period of 90 seconds, tanks flushed with a stream of anhydrous ammonia and

■air,■ high surface acidity, a pH value of 2. The moistened gas stream achieves essentially complete neutralization of the sulfonated polymer, a surface pH value of 6.5-7.0, in a period of 25-30 seconds.

Claims (9)

1. Process for neutralizing sulfonated, normally solid polymers with a gaseous mixture of an inert gas and ammonia or an organic amine in the presence of a hydroxyl compound, characterized in that substantially complete neutralization is accelerated by bringing the sulfonated polymer into contact with an inert gas containing a vaporous :hydroxyl compound, without making the sulphonated polymer visibly moist. 2. Method as stated in claim 1, characterized in that the sulfonated polymer is brought into contact with water vapor or an organic hydroxyl compound with a low molecular weight, and that the concentration of the hydroxyl compound in the inert gas is at least 0.005 mol of the hydroxyl compound per liters of the gas mixture. 3. Method as stated in claim 2, characterized in that both the neutralizing agent and the hydroxyl compound are present in the inert gas that comes into contact with the sulfonated polymer and that the ratio between the concentrations of the neutralizing agent and the hydroxyl compound is in the range from 4: 5 to 10 :1. 4. Method as stated in claim 2, characterized in that the concentration of the neutralizing agent in the inert gas is from 0.002 mol.per liters to 100% of the neutralizing gas, by volume, and in that exposure to the neutralizing agent follows exposure to the hydroxyl compound. ,5. Method as stated in any one of claims 1 to 4, characterized in that the ratio between the molar concentrations of ammonia and water vapor is in the range 1:1 to 3:1. 6. Method as stated in any one of claims 1 to 5, characterized in that the exposure to the neutralizing atmosphere is carried out for at least 20 seconds at a temperature in the range from 4' to 93°c, at a pressure in the range from 0.1 to 5 atmospheres, and that the polymer is sulphonated to a concentration of 0.001 to 50 milligrams of sulfur trioxide equivalents per square centimeter. 7. Method as stated in claim 6, characterized in that the exposure to water vapor is carried out for at least 15 seconds and neutralization with ammonia for at least 10 seconds at a temperature in the range 21 to 82°C. 8. Method as set forth in any one of claims 1 to 7, characterized in that the sulfonated polymer is a polyolefin, a mixture of olefin polymers, or copolymers of different olefins. 9. Process for accelerating the neutralization of sulfonated polymers, essentially as described here.