GB2142837A - Agents for defoaming and deaerating aqueous systems - Google Patents

Abstract

Dispersions containing a C14-C26 alcohol, an emulsifier, and a fatty acid ester of a polyhydric alcohol having at least 4 hydroxyl groups, the number of carbon atoms in the fatty acid being 14 or higher, show a marked synergistic action in defoaming and deaerating aqueous systems. Partial stearic acid esters of pentaerythritol, dipentaerythritol, or ditrimethylol propane are preferred fatty acid esters. The weight ratio of the alcohol to the ester is preferably 3.5:1 to 4.5:1. The dispersions have a wide field of use and are suitable e.g. for deaerating and defoaming aqueous systems in the paints, pulp, paper, foods and drilling industries, as well as for deaerating and defoaming transport water in the processing of sugar beet and potatoes, or waste water and sewage.

Description

SPECIFICATION Agents for defoaming and deaerating aqueous systems and their use The present invention relates to agents for defoaming and deaerating aqueous systems based on aqueous dispersions, which contain conventional defoaming and deaerating alcohols and conventional emulsifiers.

In industrial processes performed in aqueous media, the latter frequently have high air contents and/or form disturbing foams, which impair the performance of the process and the quality of the products obtained. Thus, a number of methods and agents for deaerating and defoaming aqueous systems have already been proposed. The literature, and particularly the patent literature, dealing with this subject is very comprehensive. The summary description given in German patent 2,157,033 may be cited as an example.

German patent 2,1 57,033 proposes aqueous emulsions (or more correctly dispersions) for defoaming aqueous systems containing conventional defoaming Ct2 to C22-alkanols and/or Ct2 to C224atty acid esters of dihydric or trihydric alcohols, as well as up to 50%, based on the weight of the non-aqueous components, of paraffin oils and/or C,2 to C22fatty acids as foam removers, as well as known additives of surfactants of an anionic, cationic or nonionic type as emulsifiers.According to the teaching of this patent specification, these known emulsions are relatively universally usable, provided that the average particle size of the emulsified, water-insoluble substances is 4 to 9ym. The deaerating and defoaming agents according to German patent 2,1 57,033 are widely used in practice, but have proved to be ineffective in drilling muds.

Besides the defoaming compounds referred to in German patent 2,157,033, pentaerythritol fatty acid esters, and particularly pentaerythritol monostearate, are known as defoaming compounds (see e.g. Austrian patent 330,728 and US patent 2,715,613). In addition, example 2 of Austrian patent 330,728 describes a defoaming agent dispersion which, in a non-aqueous medium, contains 820 parts by weight of a long chain alcohol, namely isotridecyl alcohol, as well as further conventional constituents, and 70 parts by weight of pentaerythritol monostearate. However, this combination of pentaerythritol monostearate and isotridecyl alcohol in the form of a non-aqueous dispersion has an inferior defoaming action to a corresponding combination of oxystearyl monobehenate and isotridecyl alcohol.Moreover, the isotridecyl alcohol according to Austrian patent 330,728 mainly acts as a dispersion medium and can also be replaced by mineral oils. Repetition of Example 2G of this Austrian patent has shown that it gives results far inferior to those obtained with the present invention.

Although the defoaming systems according to German patent 2,1 57,033 offer very satisfactory results, there is still a considerable need for improved products and particularly those which can be more universally used both for defoaming and deaerating purposes.

This invention provides agents for defoaming and deaerating aqueous systems, which are more effective than those hitherto known, i.e. which have a better deaerating and defoaming action over a wide pH-range, or which can be used in smaller quantities, so that the probability of undesired effects on the quality of the end product is still further reduced. The new agents for defoaming and deaerating aqueous systems are more universally usable and are, e.g. suitable for drilling muds.

The present invention provides an agent for defoaming and deaerating aqueous systems in the form of a dispersion comprising a C14 to C26-alcohol, an emulsifier, and a fatty acid ester of a polyhydric alcohol having at least 4 hydroxyl groups, the number of carbon atoms in the fatty acid being 14 or more. It has surprisingly been found that in these agents there is a marked synergistic action by the fatty alcohol and the fatty acid ester, when the agents are used for defoaming and deaerating aqueous systems. The defoaming and deaerating action of these mixtures is not only much better than that of the individual components, but is also better than that of the best commercially available agents. A particular advantage of the agents of the invention is that they can be used in small quantities and provide an excellent deaerating and defoaming action over a wide pH-range.In addition, the tests performed have shown that the agents of the invention have a wide field of use and are, e.g. suitable for deaerating and defoaming aqueous systems in the paint,pulp, paper, food and drilling industries, as well as for deaerating and defoaming transport water in the processing of sugar beet and potatoes, and in waste water or sewage. Special examples for the use of the agents of the invention are inter alia in fibrous suspensions such as paper pulps, clay dispersions, aqueous paint systems, drilling muds, waste water, sewage and the aforementioned transport water for sugar beet and potato processing.

The agents of the invention may be prepared by melting together the C,4 to C26- alcohols and the fatty acid esters of the polyhydric alcohols in water at temperatures above their melting points and generally at approximately 75QC. Alternatively, the alcohols and esters can be melted together in a preliminary stage and then introduced into hot water. After adding emulsifiers, the mixture is then homogenized by per se known equipment and cooled to ambient temperature, with thorough mixing (homogenization). After hom ogenization, additional emulsifiers may be added to improve, if desired, the rheological properties of the agents. Thickening agents may also be used for the same purpose, added either before or after homogenization.

Suitable emulsifiers are known to the expert, and are preferably anionic and non ionic emulsifiers, such as ethoxylated nonyl phenol, alkane sulfonates, alkyl aryl sulphonic acid salts and the like. As thickening agents a variety of different product types may be used. These thickening agents are well known to the expert and include for example polyacrylates, alginates, bentonite, carboxy methyl cellulose and guar gum.

The mean arithmetic particle size of the dispersed, water-insoluble substances, which may be determined according to the Coulter Counter method (cf Special Technical Publication No. 234 of the American Society for Testing Materials, "Electronic Size Analysis of Subsieve Particles by Flowing Through a Small Liquid Resistor", by Robert H. Berg, 1958, pp. 1-5), is advantageously in the range of 1 to 6 um and particularly approximately 2 to 3,us.

In order that the synergistic action of the mixture of the fatty alcohols and the fatty acid esters is as marked as possible, the correct weight ratio between the components of the mixture should be maintained. The optimum weight ratio of the components of the mixture depends on the fatty alcohols and esters used, but it can generally be stated that a weight ratio of fatty alcohols to fatty acid esters of polyhydric alcohols of 2:1 to 10:1 and preferably 3.5:1 to 4.5:1 is preferred. The solids content of the dispersions of the invention is usually 10 to 40% by weight. The lower limit is mainly fixed by purely economic consideration, whilst solids contents above 40% by weight make it more difficult to handle the dispersions. Preference is given to solids contents of 20 to 30% by weight.

The quantity of the agents of the invention necessary for good deaerating and defoaming is obviously dependent on the aqueous system to be deaerated and defoamed and can correspondingly range within wide limits.

Thus, in deaerating and defoaming paper making fibre suspensions, very good results are obtained with only a few ppm of the new agents of the invention, whereas, e.g., when deaerating and defoaming drilling muds, higher concentrations are generally required.

The optimum concentration of the new agent in eacn case can easily be determined by a hew tests. In general, the quantities known for agents of tne prior art, and frequently even smaller quantities, can be used.

The Ct4 to C26-alcohois used in the invention are conventional constituents of defoaming and deaerating agents and are commercially available. The esters which are also present in the agents of the invention are esterification products of fatty acids with 14 or more carbon atoms and polyhydric alcohols, containing at least 4 hydroxyl groups.

However, preference is given to esters of C16 to C,s-fatty acids. In practice technical grade fatty acids (C14 to C,8) can be used wherein e.g. the content of C14 is less than about 2(, mol%, the C,8 content is from 40 to 60 mol% and the balance is 018. In particular, pentaerythritol, dipentaerythritol and ditrimethylol propane have proved suitable as polyhydric alcohols containing at least 4 hydroxyl groups. Dipentaerythritol and ditrimethylol propane are dimers of pentaerythritol and trimethylol propane, in which the monomers are linked via an ether bond. Thus, dipentaerythritol has 6 hydroxyl groups, whilst ditrimethylol propane has 4 hydroxyl groups.On the basis of the tests performed, partial esters of the aforementioned fatty acids and alcohols have proved to be particularly suitable. Thus, it has been found that a partial pentaerythritol stearic acid ester, which largely consists of pentaerythritol distearate, gives better results than pentaerythritol monostearate or pentaerythritol tetrastearate. The partial esters are in practice never unitary compounds, because, as a result of the chemical equilibrium, products esterified to a varying degree always appear side by side, i.e. the aforementioned pentaerythritol distearate contains some pentaerythritol monostearate and pentaerythritol tristearate as well as probably small amounts of pentaerythritol itself and pentaerythritol tetrastearate. Thus, in the present invention, the term "partial ester" refers to the main component of the ester mixture due to the chemical equilibrium.Such partial esters are commercially available.

Although this is not generally necessary, the agents of the invention can obviously also contain further constituents acting in a defoaming and deaerating manner. Such additional constituents, such as e.g. mineral oil, are well known to the expert, and further details are unnecessary (see, e.g. the aforementioned prior art). When using such additional defoaming and deaerating constituents, it is necessary to ensure that the effectiveness of the synergistic mixture of the invention is not impaired or significantly reduced. Thus, such known constituents are generally only used in minor amounts.

The following Examples are given for illustrative purposes only. In all cases, unless otherwise noted, parts and percentages are by weight.

Example 1 19 parts by weight of C18 to C26-alcohols are melted with 5 parts by weight of the aforementioned partial pentaerythritol stearate, whose essential component is pentaerythritol distearate, in 75 parts by weight of water at 75 > C. After adding 0.5 parts by weight of ethoxylated nonyl phenol and 0.5 parts by weight of alkane sulphonates as emulsifiers, the mixture is homogenized and then cooled to 25 C, with further thorough mixing.

Comparison Example 1 24 parts by weight of C,8 to C26-alcohols are melted in 75 parts by weight of water at 75 C, followed by the addition of the same emulsifiers as in Example 1. The subsequent homogenization and cooling take place as in Example 1.

Comparison Example 2 24 parts by weight of the pentaerythritol stearate as used in Example 1 are melted in 75 parts by weight of water at 75 C, followed by the addition of the same emulsifiers as in Example 1. The subsequent homogenization and cooling also take place as in Example 1.

Comparison Example 3 19 parts by weight of C,8 to C26-alcohols and 5 parts of weight of ethylene glycol distearate are melted together in 75 parts by weight of water at 75 C. After adding 0.5 parts by weight of ethoxylated nonyl phenol and 0.5 parts by weight of sodium alkyl aryl sulphonate as emulsifiers, the mixture is homogenized and then cooled to 25 C, with thorough mixing.

Comparison Example 4 19 parts by weight of C,6 to C22-alcohols and 5 parts of ethylene glycol distearate are melted together in 75 parts by weight of water at 75 C, followed by the addition of the same emulsifiers as in comparison Example 3.

The subsequent homogenization and cooling take place as in Example 1 or comparison Example 3.

Comparison Example 5 19 parts by weight of C,6 to C22-alcohols and 5 parts by weight of tallow are melted together in 75 parts by weight of water at 75 C, followed by the addition of the same emulsifiers as in comparison Example 3. The homogenization and cooling of the mixture take place as in Example 1 or comparison Example 3.

Example 2 19 parts by weight of C,8 to C26-alcohols and 5 parts by weight of the pentaerythritol stearate used in Example 1 are melted together in 75 parts by weight of water at 75 C, followed by the addition of the same emulsifiers as in comparison Example 3. Homogenization and cooling of the mixture take place in the manner described in Example 1 or comparison Example 3.

Example 3 19 parts by weight of C,6 to C22-alcohols and 5 parts by weight of the pentaerythritol stearate used in Example 1 are melted in 75 parts by weight of water at 75 C, followed by the addition of the same emulsifiers as in comparison Example 3. Homogenization and cooling of the mixture take place as in Example 1 or comparison Example 3.

The average arithmetic particle size of the dispersions prepared according to Examples 1 to 3 and comparison Examples 1 to 5 is determined by the Coulter counter method using a computer and is 2.2 jim in all the emulsions.

Example 4 In order to investigate the effectiveness of the dispersions prepared according to Examples 1 to 3 and comparison Examples 1 to 5, a test furnish was prepared from 0.5 parts by weight of bleached sulphate pulp, 0.02 parts by weight of lignosulphonate, 0.004 parts by weight of rosin acids (sizing agents) and 99.47 parts by weight of tap water. In a few cases, the sulphate pulp is replaced by newspaper waste and cellulose.

The air content of the thus-prepared test furnish is measured by means of a special Plexiglass (RTM) foam box, equipped with a return line, a circulating pump and a sampling and measuring device. In each test, 10 litres of the composition are used and are circulated by the circulating pump. Reference is made to Norsk Skogindustri, Vol. 21, No. 12, pp.

503-506, 1967 in connection with the sampling and measuring device and the air content determination carried out with it. When using this device, it is possible to directly read off the air content as a percentage from the calibrated unit of measurement. The tests are performed in such a way that the foam box is filled with the furnish, the pump is put into operation and after a certain time, the deaerating and defoaming agent is added. The tests are normally performed at a pH-value of 7 and a temperature of 35 C. The air content is then determined as a function of the time.

The results are obtained and graphically represented, by plotting the air content against time.

The dispersions according to Example 1 and comparison Examples 1 and 2 are investigated in the aforementioned manner. The quantity of active substance used (based on the solids content) is in each case 16 ppm, the temperature is 35 C and the pH-value 7.0. The test results given in graph form in Fig. 1 show the considerable synergistic action of the mixture of C6 to C26-alcohols and pentaerythritol stearates compared with the individual components.

The dispersions of Example 2 and comparison Examples 3 to 5 are investigated in the same way, i.e. the concentration is in each case 16 ppm, the temperature 35 C and the pH-value 7.0. The results given in Fig. 2 clearly show the superiority of the inventive mixture of fatty alcohol and pentaerythritol stearate.

In addition, three commercial products are investigated in the same way and compared with the dispersion according to Example 2.

The commercial products are based on (a) Cg to C,O-alcohols (solution and not dispersion), (b) a mixture of fatty alcohols and paraffin wax (dispersion, particle size approx. 1 calm) and (c) fatty alcohols (dispersion, particle size approx. 2 to 3 yam). With regard to commercial products (b) and (c), it is pointed out that the composition given is based on empirical investigations which are subject to uncertainty. As is clear from the results given in Fig. 3, the dispersions according to Example 2 are far superior to the commercial products.

Example 5 Using the dispersion according to Example 3, the influence of the pH-value is investigated using the process described in Example 4. Tests are performed at pH-values of 4,5, 7 and 10. For comparison purposes, the corresponding tests are carried out with a commercial aqueous dispersion (probably a dispersion of a mixture of fatty alcohol and glycerol monostearate, particle size approx. 2 to 3 #m), which is one of the best commercially available deaerating agents. In each case, 0.6 g of both products are used for each measurement. The test results given in graph form in Fig. 4 show the excellent deaerating action of the dispersion according to the invention in the investigated pH-range, compared with the commercially available product.

Example 6 The following procedure has been adopted for investigating the suitability of the agents of the invention for drilling muds. A mud is prepared from 8 parts by weight of bentonite, 3 parts by weight of sea salt, 1.5 parts by weight of lignosulphonate and 87.5 parts by weight of tap water, whose pH-value is adjusted to 9.5. The resulting mud is mixed for 15 minutes at high speed using a domestic mixer, after which the mud is transferred into a measuring cylinder. The air content as ml of air/100ml of mud is calculated after a given time from the difference of the density determined before and after mixing.

Whereas, without addition, the air content is 37.9 ml/ 100 ml of mud, after adding 0.5% of the dispersion according to Example 3, an air content of 19.1 my/100 is measured. The commercial product used in Example 5 is ineffective.

Comparative Example The composition of Example 2b of Austrian patent 330728 was prepared as specified.

Commercial materials were used, except that the reaction product of isotridecylalcohol + 2 moles ethyleneoxide + 4 moles propyleneox ide was prepared by a standard method. The formulated product was tested using the process described in Example 4. The test result, given in graphical form in Fig. 5, shows the inferior deaerating effect of this product com pared with the agent of the present invention.

Claims (13)

1. An agent for defoaming and deaerating aqueous systems in the form of a dispersion comprising a C14 to C26-alcohol, an emulsifier, and a fatty acid ester of a polyhydric alcohol having at least 4 hydroxyl groups, the number of carbon atoms in the fatty acid being 14 or more.

2. An agent according to claim 1, in which the fatty acid ester is an ester of pentaerythritol, dipentaerythritol or ditrimethylol propane.

3. An agent according to claim 1 or 2, in which the fatty acid ester is a partial fatty acid ester.

4. An agent according to any one of claims 1 to 3 in which the number of carbon atoms in the fatty acid of the fatty acid ester is 16 to 18.

5. An agent according to claim 4, in which the fatty acid of the fatty acid ester is stearic acid.

6. An agent according to any one of claims 1 to 5, in which the weight ratio of alcohol to ester is 2:1 to 10:1.

7. An agent according to claim 6 in which the said ratio is 3.5:1 to 4.5:1.

8. An agent according to any one of claims 1 to 7, in which the mean particle size of the dispersed, water-insoluble substances is 1 to 6 yam.

9. An agent according to claim 8 in which the said mean particle size is 2 to 3 ym.

10. An agent according to claim 1 substantially as, described in any one of the foregoing Examples 1 to 6.

11. Method of defoaming and deaerating an aqueous system which comprises adding thereto an agent as claimed in any one of claims 1 to 10.

12. Method according to claim 11, in which the said aqueous system is a system used in the paint, pulp, paper, food or drilling industry, in the processing of sugar beet or potatoes, or waste water or sewage.

13. Method according to claim 11 substantially as hereinbefore described.