DE4018562A1 - USE OF ESTER AROMATIC CARBONIC ACIDS AS LUBRICANTS FOR REFRIGERANT COMPRESSORS - Google Patents

Abstract

According to the invention, esters of aromatic carboxylic acids and monohydric alcohols are used as lubricants for refrigerant compressors which are operated with chlorine-free, partially fluorinated hydrocarbons as refrigerant.

Description

The invention relates to the use of aromatic esters shear carboxylic acids as a lubricant for refrigerant denser, with chlorine-free, partially fluorinated coal water be operated as refrigerants.

For refrigeration in industrial, commercial as well in the private sector, refrigerants are used on a large scale compressor used. These devices work with mechanical compressors that compress the refrigerant, in the condenser by cooling with air, water or a liquefy other medium and in the evaporator under heat Evaporate the recording from the medium to be cooled. As a calf ammonia for large plants and Chlorofluorocarbons such as dichlorodifluoromethane, Chlorotrifluoromethane for large systems, commercial refrigeration systems gene and used for household appliances.

One uses for the lubrication of refrigerant compressors highly refined, white oil-like, generally naphthenic basic mineral oils. As fully synthetic oils for refrigerants Telcompressors get alkyl aromatics and also poly alpha-olefins for use.

The task of the lubricating oils is the moving compressors parts to lubricate the heat from the hot compressor part len and the compression chamber as well as the valves to seal. These tasks also determine the properties which the lubricating oils must meet. You must ther mixing loads and also with the tempe evaporator temperature remain fluid. Moreover, is to take into account that the lubricating oils from the compressor  in the refrigerant circuit and not completely removed by downstream oil separators can be removed. You must therefore use the refrigerant miscible in wide temperature and concentration ranges be so that the return of lubricating oil that in the Refrigerant circuit has entered the compressor safely is provided.

Chlorofluorocarbons have been around for some time Suspected to damage the ozone layer in the earth's atmosphere. Therefore, efforts are being made to use them in such cases limit in which they can not be exchanged. For the rest, you try to work through it, however to replace harmless substances. In the field of cold in future refrigerants will be chlorine-free fluorinated hydrocarbons such as 1,1,1,2-tetrafluoroethane, 1,1,1,2,3,3,3-heptafluoropropane, pentafluoroethane, 1,1,1,3,3,3-hexafluoropropane and trifluoromethane are used will. These substances are characterized by high thermal Stability and corresponding thermodynamic properties in the temperature ranges when operating cold medium compressors occur.

The disadvantage, however, is that these chlorine-free, aliphati fluorocarbons can only be mixed very slightly speed with the lubricants used previously for calves have systems. In wide concentration ranges the two classes of substances form a two-phase mixture the result that the return of the from the compressor discharged lubricant, especially at deep evaporation temperature is significantly hindered. The well-known Lubricants are therefore used in systems with chlorine-free cold medium substitutes are generally no longer usable.  

Attempts have been made to overcome these difficulties by using Reverse lubricants based on polyalkylene glycols hen. Most types of polyalkylene glycol are between -40 and + 50 ° C with the chlorine-free refrigerants mentioned constantly miscible. Only at temperatures above about 50 ° C there are gaps in the mixture, which lead to higher temperatures expand to a large concentration range.

Nevertheless, it can be expected that polyalkylene glycols only be limits can be used as a lubricant because they are highly hygroscopic. Your drying on a rest humidity of <100 ppm requires a lot of effort. That Furthermore, care must be taken to ensure that there is no air at all wear that avoided re-absorption of moisture becomes. You can therefore only in hermetically sealed, small refrigeration systems, e.g. B. household refrigerators, use be det. In large refrigeration systems where maintenance with occasional interventions in the refrigerant Circulation is required over time significant moisture absorption. The on the polyalkylene glycol bound moisture can be also with the help of filter dryers. There are therefore problems with metallic materials in the system the consequence. In addition, the thermal stability of the Polyalkylene glycols do not meet all requirements. Already above half around 180 ° C, such a temperature can be extreme Operating conditions occur in the compressor pressure valve they start to decompose.

The task was therefore lubricants for refrigerants to provide compressors that are free of the described Defects of known lubricants are always there can be used if chlorine-free, partially fluorinated Find hydrocarbons as refrigerants.  

The invention thus consists in the use of aro matic carboxylic acids and monohydric alcohols provided esters as lubricants for refrigerant compression ter with chlorine-free, partially fluorinated hydrocarbon substances are operated as refrigerants.

Carboxylic acid esters, which are different from aromatic carboxylic acids and derived monohydric alcohols are widely used used as a plasticizer for polyvinyl chloride. The required for this application from the carboxylic acid esters However, property picture differs fundamentally from the characteristics that lubricants for compression refrigeration must have machines. It was therefore not predictable that a compound class that is mainly based on the Field of plastics has proven itself, even in a completely other areas of technology can be used successfully can.

The esters used according to the invention are derived from aro Matic mono-, di- and polycarboxylic acids. examples for such acids are benzoic acid, phthalic acid, isophthalic acid re, terephthalic acid, trimellitic acid, pyromellitic acid, Trimesic acid.

These carboxylic acids or their anhydrides are reversed sets with straight-chained or branched, primary one term alcohols, including those with 2 to 20 carbon atoms are preferred. Have proven to be particularly suitable branched chain, primary alcohols with at least 4 carbons atoms of matter proven. Examples of such alcohols are n- Butanol, isobutanol, n-pentanol, 2-methylbutanol, 3-methyl butanol, 2-ethylbutanol, 2-methylpentanol, n-hexanol, Heptanol (in the form of the isomer mixture), octanol (in the form of the isomer mixture), 2-ethylhexanol, n-octanol, i- Nonanol, i-decanol, i-tridecanol, i-hexadecanol and i- Octadecanol.  

The alcohols mentioned are obtained predominantly from olefins by oxosynthesis and subsequent hydrogenation of the entstan which aldehydes or by aldol condensation. For the oxo All olefins are suitable for synthesis. It usually leads to a mixture of isomeric alcohols. To make the It is not necessary for esters to separate these mixtures.

Suitable esters for use as lubricants are e.g. B. di-2-ethylhexyl phthalate, di-isononyl phthalate and di isodecyl phthalate, di-n-butyl phthalate, di-2-ethylhexyl terephthalate, di-isodecyl terephthalate. Special meaning have the esters of phthalic acid, e.g. B. Di-2-ethylhexyl phtha lat, di-isononyl phthalate, di-isodecyl phthalate.

The esters are known from the aforementioned Acids and alcohols in the presence of acidic catalysts produced. Mineral acids are suitable as catalysts such as sulfuric acid, phosphoric acid, and their acid salts, also trialkyl or triaryl phosphates and p-toluenesulfone acid. To achieve the most complete implementation possible len, it is recommended that one of the reactants in the over apply shot and / or the water of reaction by distillation, optionally with the addition of an azeotrope such as Separate benzene or toluene. Special arrangements for Achieving a high level of color stability, as used in ver use of the esters as plasticizers are unnecessary when used as a lubricant.

The lubricants used according to the invention have good ones Miscibility with the chlorine used as refrigerants free, partially fluorinated hydrocarbons -40 ° C, so in the temperature ranges that in compresses refrigeration systems can occur. Your viscosity is at 40 ° C between about 10 and 150 cSt and thus corresponds  the requirements for the lubricant for the area of application. You point in addition to the exclusion of atmospheric oxygen and Moisture, that is, under conditions in a cold middle circuit must be fulfilled, excellent ther mix up stability. The esters are not hygroscopic. They can therefore be dried without much effort. Residual moisture, according to the German standard DIN 51 503 35 ppm must not be exceeded without further ado to reach.

The esters used as lubricants can be in pure Form, as a mixture of isomeric compounds and as a mixture of two or more esters of different chemical Composition can be used.

Claims (5)

1. Use of aromatic carboxylic acids and a esters of high quality alcohols as lubricants for refrigerant compressors with chlorine-free, partially fluo hydrocarbons as refrigerants the. 2. Use of esters according to claim 1, characterized records that the esters of monocarboxylic acids, esp special benzoic acid. 3. Use of esters according to claim 1, characterized records that the esters of aromatic dicarboxylic acid ren, in particular phthalic acid, isophthalic acid or Allow terephthalic acid to be drained off. 4. Use of esters according to claim 1, characterized characterizes that the esters of aromatic carboxylic acids, derive in particular trimellitic acid and pyromellitic acid to let. 5. Use of esters according to one of claims 1 to 4, characterized in that the esters of straight ketti gen or branched, primary monohydric alcohols with 4 up to 20 carbon atoms.