WO1997021782A1

WO1997021782A1 - Non-toxic thermal oils

Info

Publication number: WO1997021782A1
Application number: PCT/EP1996/005338
Authority: WO
Inventors: Arno Behr; Wolfgang Ritter; Johannes Lintorf; Hans-Peter Handwerk
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1995-12-11
Filing date: 1996-12-02
Publication date: 1997-06-19
Also published as: DE19546117A1

Abstract

The invention relates to non-toxic thermal oils and their use. The base oils used for producing the thermal oils in question are at least single-branched esterification products of long-chain carboxylic acids containing at least 16 carbon atoms with long-chain alcohols containing at least 16 carbon atoms, if necessary mixed with other additives.

Description

"Non-toxic heat transfer oils

Field of the Invention

The invention relates to non-toxic heat transfer oils, which are preferably produced on the basis of renewable raw materials. The oils according to the invention are, in particular, esters of long-chain, branched fatty acids with preferably long-chain, branched fatty alcohols. The products have a wide range of applications and are still easy to pump even at low temperatures.

State of the art

While the temperature range for heat transfer covered by water and gases theoretically also includes high-temperature applications, neither of the two media can be used for many industrial applications. The use of water or steam depends on the one hand due to the high vapor pressure of this heat exchanger -?

at higher temperatures, an increased technical effort, on the other hand, the corrosiveness of the overheated water requires complex water treatment systems and strict control of the pipe systems for early detection of leaks.

The use of gases for heat transfer is limited to a few areas of application due to their poor thermal conductivity (especially at low pressures).

Special organic liquids, mostly formulated as oils, therefore meet the needs of industrial users in a relatively small but particularly important temperature range between 150 and 400 ° C. The advantage of such organic heat exchangers is the good heat transfer characteristic and the generally low vapor pressure of such organic liquids.

While water vapor is a commonly used alternative to such oils in the temperature range between 200 and 250 ° C, the range above 250 ° C is almost exclusively covered by organic liquids. These can be used particularly advantageously where, for example, products reactive with water are processed, where it is not possible to work at high pressures or where precise temperature control must be ensured.

So far, two different types of heat transfer oils have mainly been used: mineral oils and synthetic liquids. While the mineral oils are by-products of the cracking process in crude oil processing, the synthetic oils can be adapted much better to the particular circumstances of the intended use. In the temperature range between 250 and 300 ° C, the mineral oil-based products and the synthetic products still compete with each other, but the ratio shifts with increasing temperature in favor of the synthetic heat transfer oils. This is a consequence of the requirements placed on such an oil. The highest possible operating temperature should be opposed to satisfactory low-temperature behavior, which mainly concerns the mobility, and thus the pumpability, of the heat transfer oil. In particular when operating a system for heat transfer in cold climates, a correspondingly low viscosity must be guaranteed.

Another important aspect is the environmental compatibility, and thus the toxicity of the heat exchanger, especially with regard to use in those industrial areas in which the toxicity of the operating materials used plays a major role. The industrial applications of organic liquids for heat transfer are so diverse that a detailed list has to be omitted here, but relevant industries are, for example, the chemical industry, the textile industry, the food industry, the plastics and rubber industry and the pharmaceutical industry.

The synthetic products used in addition to the mineral oils can mainly be divided into three classes:

- synthetic aromatic oils,

- high-boiling, polymeric silicone compounds

- and polyethylene glycols.

While the mineral oil products show somewhat unsatisfactory high temperature behavior, the synthetic aromatic oils offer the desired physical properties in the temperature range up to 370 ° C. This class of substances includes, in particular, the sterically hindered alkylated and halogenated di- and triaryls, the use of which is increasingly being avoided due to the considerable toxicity and the unfavorable bioaccumulation behavior. In particular, the polychlorinated biphenyls on the one hand show the tendency to form highly toxic dibenzodioxins and furans at elevated temperatures, and on the other hand this class of substances has become almost ubiquitous and has a mutagenic potential. Such heat transfer oils pose a considerable risk, in particular in areas of application which are physiologically relevant to humans and animals, such as, for example, in the food or pharmaceutical industries. Although the high-molecular polysiloxanes have good properties in terms of their high-temperature behavior and toxicity, due to their high price they are only an economical alternative to the previously known mineral oil-based heat transfer oils in only a few exceptional cases in the range up to 350 ° C.

Polyethylene glycols show satisfactory high-temperature behavior in some cases. The disadvantage of this class of substances is hygroscopy, which, if improperly operated or stored, causes a strong water absorption, causing the oil to lose its high-temperature properties. This must be remedied by operation and storage in the absence of air, for example under inert gas, which can lead to considerable operating costs.

There was therefore a need for non-toxic heat transfer oils whose profile of properties allows economical substitution of the previously preferred aromatic oils in almost all areas of application.

Surprisingly, it has now been found that heat transfer oils based on at least mono-branched esters of long-chain carboxylic acids with long-chain alcohols at low vapor pressure permit surprisingly high long-term use temperatures without significant coking or other decomposition taking place.

Description of the invention

The invention accordingly relates to the use of the at least single-branched esterification products of long-chain carboxylic acids with at least 16 carbon atoms with long-chain alcohols with at least 16 carbon atoms, optionally in admixture with other additives, as base oils in heat transfer oils. In the following, the main composition of the heat transfer oils will be explained. However, it goes without saying for the person skilled in the art that the description of the composition and the chemical structure of the heat transfer oils likewise reproduces the description of the use of such heat transfer oils as media for transferring thermal energy between two substrates of different temperatures. In the following, reference should therefore be made to the use of the compositions described as heat transfer oils in detail, but it is hereby part of every description of the ingredients of the disclosed compositions.

The main component of the heat transfer oils according to the invention are base oils, which are contained in the heat transfer oils in a proportion of at least 60% by weight. However, the base oils are usually used in a proportion of at least 70% by weight, preferably at least 80% by weight and particularly preferably at least 90% by weight. In a particularly advantageous embodiment of the invention, the proportion of the base oil should not fall below 95% by weight.

The at least mono-branched esterification products of long-chain carboxylic acids with long-chain alcohols are suitable as the base oil. In the context of the invention, at least one branch is understood to mean those esters which have at least one tertiary or quaternary carbon atom at least either in the alkyl radicals of the long-chain carboxylic acids or in the alkyl radicals of the long-chain alcohols. Carboxylic esters which have more than one branch or two, three or more branches are also suitable for use in the context of the invention. It does not matter whether these branches occur alone in the alkyl radical of the long-chain carboxylic acid, in the alkyl radical of the long-chain alcohol or in both of the alkyl radicals mentioned. In the case of an odd number of branches, such as three or five, it is irrelevant to the technical feasibility of the invention which of the alkyl radicals carries the majority of the branches. In exceptional cases, however, it can happen that for certain applications in which, for example, a particularly low viscosity or a particularly high hydrolysis stability arrives, the targeted arrangement of a Melir number of branches on one of the two alkyl radicals is required. Such special embodiments are also included in the scope of the present invention. It is equally irrelevant to the feasibility of the invention whether a certain number of branches, which are greater than one, are produced on one of the two alkyl radicals by tertiary or quaternary carbon atoms. For example, two branches on an alkyl radical can be produced on a single or on two different carbon atoms, which leads to the formation of a quaternary carbon atom in the first case and two tertiary carbon atoms in the second case. Both embodiments are in accordance with the invention. In special cases, the branches of the alkyl radicals can be arranged in such a way that cyclic products, that is to say products which have one or more ring-shaped closed carbon skeletons, are formed in the alkyl radical concerned. Examples of such ester components are the preferably saturated derivatives of dimer fatty acids and dimer alcohols.

Dimer alcohols are understood by those skilled in the art to mean those products which result from the reduction of the carboxyl groups of dimer fatty acid or, if appropriate, of the ester groups of dimer fatty acid esters.

The use of esters which have at least one branch both in the alkyl radical of the long-chain carboxylic acid and in the alkyl radical of the long-chain alcohol can be regarded as advantageous in the sense of the invention.

For the purposes of the invention, long-chain carboxylic acids and alcohols are generally understood to mean those carboxylic acids and alcohols which have a carbon number of at least 16. However, it is preferred if the number of carbon atoms is at least 18 and in particular at least 20. Particularly good results are achieved when using components which have at least 36 carbon atoms. Just as the two alkyl chains of the components constituting the esters can have a different number of branches, the number of carbon atoms can also be different. For example, esters of acids with 36 carbon atoms, such as the Dimer fatty acid, and alcohols with 20 carbon atoms, such as the C ₂₀ Guerbet alcohols. usable in the sense of the invention.

Branched, long-chain fatty acids which can be used for the purposes of the invention are described, for example, in EP-Bl-511 981, EP-Bl-511 982 and EP-Bl-511 986, the products of which are hereby expressly the subject of the present application . Mainly, these are adducts of ethylene with fatty acids with 18 to 22 carbon atoms or fatty acid esters of the fatty acids mentioned, the olefinic double bonds of which are hydrogenated after their preparation. The basis for the production of these initially unsaturated adducts are generally unsaturated fatty acids with 18 to 22 carbon atoms and more than one olefinic double bond such as linoleic acid, isomerized linoleic acid with conjugated double bonds (so-called C18: 2 conjuene fatty acid), linolenic acid, arachidonic acid, docosadienic acid, Docosahexenoic acid and eicosapentaenoic acid, which can be obtained in the form of their technical mixtures with other fatty acids from renewable natural resources such as sunflower oil, tall oil or fish oil. These polyunsaturated fatty acids are, as is customary in fat chemistry, generally not used in pure form but in the form of their technical mixtures for the preparation of the adducts. The subsequent hydrogenation leads to the fatty acids or fatty acid esters preferred in the sense of the invention. As a rule, the hydrogenation should proceed largely completely in order to obtain the lowest possible residual proportion of unsaturated esterification products in the heat transfer oil. However, iodine numbers of 180 or less can be sufficient here. However, iodine numbers below 120 are advantageous. However, for particularly powerful heat transfer oils, such as are included in the invention, the iodine numbers should be even lower. Values of less than 80, in particular less than 50 and preferably less than 20 increase the stability of the heat transfer oils in long-term use. For particularly high performance requirements, the heat transfer oils should have an iodine number of less than 10.

Another group of branched, long-chain carboxylic acids are the fatty acids which are preferred in the layered silicate-catalyzed reaction of unsaturated fatty acids with olefins alpha-olefins such as pent-1-ene, hex-1-ene, cyclohexene, hept-1-ene, oct-l-ene, cyclooctene, non-l-ene, dec-l-ene, undec-1-ene , Dodec-1-ene, cyclodecene, tetradec-1-ene, hexadec-1-ene, octadec-1-ene and their double bond and branched framework isomers. Subsequent to the reaction, the remaining double bonds can be hydrogenated. This process is described, for example, in US Pat. No. 5,364,949 and leads to products which can be used in the sense of the invention.

Another group of substances which can be used in the context of the invention are the oligomerization products of unsaturated fatty acids known as dimer and trimer fatty acid. The group of substances described here can be used in the form of its olefinic, but also in the form of the partially or fully hydrogenated species for the subsequent esterification.

The oligomerization of unsaturated fatty acids is a well-known electrocyclic reaction, which is reviewed in articles such as Λ. Behr in Fat Sei. Techno !. 22, 340 (1991), G. Spiteller in Fat Sei. Technol. 94, 41 (1992) or P. Daute et al. in Fat Sei.

Technol. 95, 91 (1993). In oligomerization, an average of two to three fatty acids come together and form dimers or trimers, which predominantly have cycloaliphatic structures. In addition to the fraction of the dimers and trimers, a so-called monomer fraction is obtained in which there are unreacted starting materials and branched monomers which have arisen in the course of the reaction by isomerization. In addition, there is of course also a fraction of higher oligomers, but this is generally not of major importance. The oligomerization can be carried out thermally or in the presence of noble metal catalysts. The reaction is preferably carried out in the presence of clays such as montmorillonite. The regulation of the content of dimers and trimers and the extent of the monomer fraction can be controlled by the reaction conditions. Technical mixtures can finally also be purified by distillation.

As already mentioned, technical unsaturated fatty acids with 12 to 22 and preferably 16 to 18 carbon atoms are suitable as starting materials for the oligomerization. Typical examples are palmoleic acid, oleic acid, elaidic acid, petroselinyl acid, Linoleic acid. Linolenic acid, conjuene fatty acid, elaeostearic acid, ricinoleic acid, gadoleic acid. Erucic acid and its technical mixtures with saturated fatty acids. Typical examples of suitable technical mixtures are uncured split fatty acids of natural triglycerides with iodine numbers in the range from 40 to 140, such as palm fatty acid, tallow fatty acid, rapeseed oil fatty acid, sunflower fatty acid and the like. Split fatty acids with a high oleic acid content are preferred.

In addition to the fatty acids, their esters, preferably methyl esters, can also be oligomerized, preferably dimerized and / or trimerized. This can be followed by the transesterification with long-chain, optionally branched alcohols to give the corresponding esters, which are used as base oil in heat transfer oils after the partial or, preferably, complete hydrogenation of the olefinic double bonds.

Suitable alcohol components for use in the esterification reaction are all alcohols which have at least 16 carbon atoms. Alcohols which have only one, two or three OH functionalities are used to a particular extent. If the functionality of one of the two esterification components, acids and alcohols, is two or more, then the second component should either be monofunctional or be used in large excess, since otherwise there is a risk of crosslinking reactions, especially in the presence of trifunctional compounds.

According to the invention, preference is given to using esterification products whose alcohol component comprises long-chain alcohols having at least 18, particularly preferably at least 20, carbon atoms. Long-chain oils are particularly suitable for use as base oils in particularly temperature-stable heat transfer oils. branched alcohols with at least 36 carbon atoms are suitable. As a rule, the number of carbon atoms should not exceed 72 and preferably 56.

Typical examples are cetyl alcohol, palmoleyl alcohol, stearyl alcohol, oleyl alcohol, elaidyl alcohol, petroselinyl alcohol, linolyl alcohol, linolenyl alcohol. Elaeostearyl alcohol, Arachyl alcohol, gadoleyl alcohol, behenyl alcohol, erucyl alcohol and brassidyl alcohol and their technical mixtures, which are obtained, for example, in the high-pressure hydrogenation of technical methyl esters based on fats and oils or aldehydes from Roelen's oxosynthesis and as a monomer fraction in the dimerization and trimerization of unsaturated fatty alcohols. Alcohols which have one or more olefinic double bonds are partially or completely hydrogenated on the olefinic double bond after or preferably before the esterification with the corresponding carboxylic acids.

However, those alcohols which have at least one branch in their alkyl chain, such as isostearic acid, are particularly preferred. Such alcohols can be prepared, inter alia, by reducing the hydrogenation of the olefin adducts already described with unsaturated fatty acids. For this purpose, the esters are generally used, preferably the methyl ester. Another group of alcohols that have branching in the alkyl chain are the so-called Guerbet alcohols.

By condensing primary alcohols at 250 to 300 ° C in the presence of alkaline catalysts and traces of metal ions branched, saturated, monofunctional alcohols can be produced in 2-position to the hydroxyl group. In terms of their physical properties, Guerbet alcohols behave similarly to unsaturated fatty alcohols, but show a significantly higher oxidation stability.

In particular, Guerbet alcohols with at least 16 carbon atoms, such as those from the Guerbetization of the so-called palm kernel as C ₁₆ . ₂₀ - Guerbet alcohols are produced. The use of C ₃₆ Guerbet alcohols, as can be seen from the examples, leads to particularly good results with regard to the high temperature stability of the heat transfer oils.

The esterification of the acids described with the alcohols described can be carried out according to all known esterification variants. The esterification is usually carried out on the methyl esters of the carboxylic acids with the elimination of methanol. However, the use of the unesterified acids is also possible. Advantageously Accelerating the reaction rate known esterification catalysts such as sulfuric acid, trifluoromethanesulfonic acid, toluenesulfonic acid or transition metal alkoxylates such as titanium tetraalkoxylate added. If the unesterified acid is used as the acid component for the esterification, it may be advantageous to carry out the esterification reaction using a water tractor, such as toluene. The end product can usually be largely freed from volatile impurities by applying a vacuum and heating, while solid or low-volatile impurities can be removed by separation operations known to those skilled in the art, such as filtration or, if the purity demands are particularly high, by chromatography.

It is of technical importance for the invention that the catalysts used are at least largely removed from the end product, since the contaminated ester has only a reduced stability compared to the purified product. For complete purification, the end product can optionally be subjected to distillation under vacuum conditions, but chromatographic purification of the product is also possible, in which case the polar impurities can be separated from the product ester or the product ester mixture. Which of the procedures is preferred must be decided in individual cases depending on the desired degree of purity of the product. In principle, however, all operations for cleaning and working up esters and / or ester mixtures as are known to the person skilled in the art are suitable for ensuring the desired degree of purity.

In many cases it is advantageous to use esters which have as little residual free carboxylic acid groups as possible, since this can greatly reduce the corrosion effect of the heat transfer oils. The acid number can be reduced in the usual way, for example by liquid or solid phase neutralization with alkali and / or alkaline earth metal hydroxides, carbonates, oxides, alkoxides or the like. A reduction in the acid number naturally also occurs in all the other cleaning operations mentioned, in particular in the chromatography. A special feature of the heat transfer oils claimed here is that they are movable and pumpable at 5 ° C, in particular at -10 ° C.

The physiological compatibility of the heat transfer oils according to the invention permits use in industrial areas in which contamination of the product with toxic substances, such as, for example, conventional heat transfer oils based on alkylated or halogenated aromatics, must be avoided at all costs. The food industry and the pharmaceutical industry, in particular, are to be mentioned here, the products of which the consumer observes with a high level of sensitivity with regard to toxic ingredients. The use of the heat transfer oils according to the invention in pharmacy and / or in food technology creates additional safety and thus additional consumer benefits in these application areas.

In addition to the base oils described so far, the heat transfer oils according to the invention may also contain other additives which serve, for example, to protect against corrosion, to stabilize against hydrolysis or to dry. Antioxidants or rheological additives can also advantageously change the properties of the heat transfer oils. The additives can be used in the heat transfer oils in proportions of up to 40% by weight, but usually only amounts of, for example, 30 or 20% by weight are used. Certain additives, such as corrosion protection or antioxidants, are usually used in even smaller quantities. Here, proportions of 10 or 5% by weight of the heat transfer oil may be sufficient; if necessary, even these amounts can be reduced to 2 or 1% by weight.

A surprising advantage of the heat transfer oils according to the invention is their ease of handling at low temperatures. The oils according to the invention can generally still be pumped at a temperature of -10 ° C. In particular, the heat transfer oils according to the invention have a viscosity of less than 5000 (mPas), preferably less than, at 25 ° C. 2000 (mPas) and particularly preferably less than 1000 (mPas) on (Brookfield. 10 U / min. Spindles 3 and 4).

Another object of the invention is therefore a method for transferring heat between any two substrates by means of heat transfer oils, with the proviso that there is a different temperature between the substrates and neither of the two substrates is soluble in the heat transfer oils, characterized in that at least as heat transfer oils mono-branched esterification products of long-chain carboxylic acids with at least 16 carbon atoms with long-chain alcohols with at least 16 carbon atoms, optionally in a mixture with other additives.

The following examples serve to describe the invention in more detail, but are not intended to limit it to what is shown by way of example.

Examples T a b e l l e 1

Thermal data of heat transfer oils

Examples 1 to 4 represent comparative examples with different raw materials not based on esters.

The limit temperature determined by thermogravimetric analysis (TGA) provides information about the temperature at which the TGA curve of the substance examined showed a deviation of 1% from the initial value at a heating rate of 20K / min.

The abbreviation DSC stands for Differential Scanning Calorimetry.

Ser. Product-Product Sdp. [° C] Limit Temp. [° C] No. Name Composition according to DSC according to TGA

1 diglycerol diglycerin sample 373 220

2 polyglycerin polyglycerin 381 240

3 Eumulgin 535 C16 / 18 fatty alcohol 391 210 + 6 ethylene oxide

4 Hostarex Tri-n-octyl / 382 200

A327 n-decylamine (Hoechst)

BeHa-5474-14 ester from dimer fatty acid 403 340 and C20-Guerbet alcohol

BeHa-5474-16 ester from trimer fatty acid 394 340 and C20-Guerbet alcohol

BeHa-5474-20 ester of silica and 417 210

C20 Guerbet alcohol

BeHa-5474-22 ester from isopalmitic acid 395 240 and C20-Guerbet alcohol BeHa-5474-28 esters of silica and 428 210 C36-Guerbet alcohol

BeHa-5474-30 ester from trimer fatty acid 421 330 and C36-Guerbet alcohol

BeHa-5474-38 ester of dimer fatty acid 416 330 and C36-Guerbet alcohol

BeHa-5474-42 ester from isopalmitic acid> 360 260 and C36-Guerbet alcohol

Claims

claims

1. Use of at least single-branched esterification products of long-chain carboxylic acids with at least 16 carbon atoms with long-chain alcohols with at least 16 carbon atoms, optionally in admixture with other additives, as base oils in heat transfer oils.

2. Use according to claim 1, characterized in that such at least mono-branched esterification products are used which, as long-chain carboxylic acids, contain those with at least 18 and preferably with at least 20 carbon atoms.

3. Use according to one of claims 1 or 2, characterized in that such at least mono-branched esterification products are used which as long-chain alcohols contain those having at least 18 and preferably at least 20 carbon atoms.

4. Use according to one of claims 1 to 3, characterized in that such at least mono-branched esterification products are used in which both the long-chain carboxylic acid and the long-chain alcohol are branched.

5. Use according to one of claims 1 to 4, characterized in that such at least mono-branched esterification products are used which are still pumpable at -5 ° C.

6. Use according to one of claims 1 to 5, characterized in that the heat transfer oils contain the base oil in a proportion of at least 60 wt .-%, preferably 70 wt .-%.

7. Use according to one of claims 1 to 6, characterized in that antioxidants, anticorrosive agents, hydrolysis stabilizers and / or rheological additives are used as further additives.

8. Use according to one of claims 1 to 7, characterized in that the heat transfer oils are used in pharmacy or in food technology.

9. Method of transferring heat between any two substrates using heat transfer oils. with the proviso that there is a different temperature between the substrates and neither of the two substrates is soluble in the heat transfer oils, characterized in that as heat transfer oils at least single-branched esterification products of long-chain carboxylic acids with at least 16 C atoms with long-chain alcohols with at least 16 C atoms , may be used in admixture with other additives.