Method for degreasing metal parts and use of a solvent stabilizer in a distillation process in a degreasing process for metal parts

Abstract

A process for degreasing metal parts with a solvent, wherein: during degreasing the solvent becomes contaminated with cleaned residues, the contaminated solvent is fed to a distillation process in which the solvent boiling at a lower temperature is separated from the purified residues and recycled, characterized in that To avoid acid formation, a solvent stabilizer is added to the solvent during the distillation process, which consists exclusively of the following components: overbased calcium sulfonate with a total base number greater than 300, alkylphenol as antioxidant and high-boiling mineral oil distillate as base oil, whereby the proportion of overbased calcium sulfonate corresponds to the sum of the two proportions of alkylphenol and high-boiling mineral oil distillate.

Description

[0001] The invention relates to a method for degreasing metal parts, wherein a low-boiling solvent is used for degreasing metal parts, and to the use of a solvent stabilizer in a distillation process in a degreasing process for metal parts.

[0002] When degreasing metal parts with modified alcohols, acidification can occur due to the decomposition of the solvent used. This can lead to corrosion damage in the system and damage to the parts being degreased. However, by adding stabilizers to the solvent, acid formation can be reduced or the acid that has formed can be bound.

[0003] As examples of prior art, reference is made to the publications DE 698 14 162 T2 and EP 1 907 505 B1, which describe a composition of an amine and a hydrocarbon as a stabilizer. According to DE 698 14 162 T2, the stabilizer composition is used only for halogenated hydrocarbons such as perchloroethylene as solvents.

[0004] Furthermore, it is known from the document EP 92 304 138 A or DE 692 16 291 T2 that overbased calcium sulfonate is added to a lubricating oil in order to neutralize oil decomposition products that arise, for example, during the operation of internal combustion engines.

[0005] Further prior art is referred to the documents DE 10 2014 203 599 A1 and US 2002 / 0 160 924 A1.

[0006] It is therefore an object of the invention to provide an improved method for degreasing metal parts and the corresponding use of a solvent stabilizer in a distillation process in a degreasing process.

[0007] This problem is solved by the features of the independent patent claims. Advantageous developments of the invention are the subject of subordinate claims.

[0008] The inventor has recognized that the addition of a stabilizer or a stabilizer composition to a solvent for degreasing metal parts reduces or prevents acidification due to decomposition of the solvent used or the introduction of acid from outside. If a modified alcohol is used as the solvent, a salt of a sulfonic acid (sulfonate) is particularly suitable as a stabilizer, especially overbased calcium sulfonate. Other substances such as an antioxidant as an oxygen scavenger and a base oil to improve handling are also added to the stabilizer.

[0009] Metal degreasing systems are closed systems that comprise a cleaning chamber, a varying number of solvent tanks, and a distillation unit. Contaminated parts are cleaned in the cleaning chamber using a solvent, preferably a modified alcohol.

[0010] The contaminated solvent, enriched with the detached residues from the cleaned and degreased components, then flows back into the solvent tanks. These tanks continuously feed the distillation unit integrated into the degreasing system with the contaminated solvent. During the distillation process, the solvent, which boils earlier or at a lower temperature, is separated from the previously cleaned residues. During this distillation process, acidification can occur due to self-decomposition of the solvent. For example, the use of modified alcohol as a solvent can produce low-boiling components, especially acids. This acidification can, in turn, lead to corrosion damage in the cleaning system and surface corrosion on the cleaned parts.

[0011] To counteract acid formation in the distillation apparatus, the stabilizer according to the invention is added to the distillation process. The stabilizer binds the resulting acids in the distillation sump and remains there. The stabilizer thus remains in the distillation apparatus throughout the entire solvent purification and treatment process.

[0012] The distillate, i.e., the distilled and purified solvent, is then returned to the solvent tanks via a water separator. The distillation sump is emptied and disposed of at regular intervals. The thus used stabilizer is discharged along with the purified component residues.

[0013] Using a quick test procedure for solvent testing, the user can determine the quality, i.e. the acid content, of the solvent used directly on the system.

[0014] Knowing the determined acidity of the solvent, i.e. the proportion of free acids in the solvent, and the system volume of the degreasing system, the required addition amount of the stabilizer according to the invention can be determined by means of stoichiometric calculation in order to neutralize the acid content.

[0015] Accordingly, the inventor proposes a solvent stabilizer for degreasing metal parts, comprising at least: a.) overbased calcium sulfonate with a total base number greater than 300, b.) an alkylphenol as an antioxidant and c.) a high-boiling mineral oil distillate as base oil, whereby the proportion of overbased calcium sulfonate corresponds to the sum of the two proportions of alkylphenol and mineral oil distillate.

[0016] According to the invention, overbased calcium sulfonate with a total base number greater than 300 (TBN>300), preferably equal to 400 (TBN=400), is used. The use of sodium or barium sulfonate is possible in principle, but is not within the scope of the invention.

[0017] According to the invention, the solvent stabilizer comprises an antioxidant as a further substance. Antioxidants act as oxygen scavengers and thus advantageously prevent oxidation and self-decomposition of the solvent. Advantageously, an alkylphenol is used as the antioxidant, for example, an o- and / or p-alkylphenol containing several straight-chain or branched alkyl chains.

[0018] A non-inventive embodiment of a solvent stabilizer or stabilizer composition comprising overbased calcium sulfonate and alkylphenol can be used in any mixing ratio. A mixing ratio in which the proportion of overbased calcium sulfonate is 99.8% and the proportion of alkylphenol is 0.2% has proven particularly favorable.

[0019] According to the invention, the solvent stabilizer comprises a base oil as a carrier component. The addition of this substance advantageously improves the handling of the stabilizer composition, i.e., the stabilizer composition is further liquefied. Accordingly, it is easier to first introduce the stabilizer composition into the degreasing system and then remove it from the distillation unit.

[0020] According to the invention, a high-boiling mineral oil distillate is used as an additional substance, for example aliphatic and cycloaliphatic hydrocarbon mixtures.

[0021] The stabilizer composition according to the invention with overbased calcium sulfonate, alkylphenol, and mineral oil distillate has a mixing ratio in which the proportion of overbased calcium sulfonate corresponds to the sum of the two proportions of alkylphenol and mineral oil distillate. An advantageous embodiment provides for the proportion of alkylphenol to be the smallest. A mixing ratio in which the proportion of overbased calcium sulfonate is 50%, the proportion of alkylphenol is 0.2%, and the proportion of mineral oil distillate is 49.8% has proven particularly favorable. Other mixing ratios are possible in principle, but are not within the scope of the invention.

[0022] In particular, the invention relates to the use of a solvent stabilizer in a distillation process in a degreasing process for metal parts, wherein a solvent is used for degreasing metal parts, and: - during degreasing the solvent is contaminated with cleaned residues, - the contaminated solvent is fed into a distillation process in which the solvent boiling at a lower temperature is separated from the purified residues and recycled, - a solvent stabilizer is added during the distillation process, which: - overbased calcium sulfonate with a total base number greater than 300, - Alkylphenol as antioxidant and - high-boiling mineral oil distillate as base oil, wherein the proportion of overbased calcium sulfonate corresponds to the sum of the two proportions of alkylphenol and high-boiling mineral oil distillate.

[0023] A favorable variant provides that the solvent stabilizer binds the acids formed in a distillation sump of the distillation process and remains there until the distillation sump is emptied and disposed of.

[0024] Another advantageous variant is to use a total base number of 400 for the overbased calcium sulfonate.

[0025] It is also advantageous that the proportion of alkylphenol is the smallest.

[0026] It is particularly advantageous to use a solvent stabilizer in which the proportion of overbased calcium sulfonate is 50%, of alkylphenol 0.2% and of mineral oil distillate 49.8%.

[0027] The following tables show the effectiveness of overbased calcium sulfonate in reducing the acidity of modified alcohol.

[0028] In the test series shown in Table 1, a real sample was taken from a metal degreasing plant in which modified alcohol was used as the solvent. 100 mL of the solvent, with an acidity of 559 ppm, were mixed with varying volumes of pure overbased calcium sulfonate, and the solvent was then distilled off. The acidity indicated is the acidity measured in the distillate.

[0029] The measured acidity values ​​according to Table 1 clearly demonstrate the correlation between the amount of calcium sulfonate added and the reduction in acidity in the modified alcohol. The more calcium sulfonate added, the more the acidity decreased. Calcium sulfonate is particularly effective at a concentration of at least 1.2% per 100 mL of solvent. Table 1: Amount of overbased calcium sulfonate [mL] Distillate quantity [L] Acidity [ppm] 0,5 93 182 0,7 88 109 1, 2 92 49 2, 0 91 41

[0030] In the test series shown in Table 2, acetic acid was added to modified alcohol. 100 mL of the modified alcohol with an acidity of 577 ppm was mixed with varying volumes of a stabilizer composition consisting of 49.8% base oil, 0.2% antioxidant, and 50.0% calcium sulfonate, and the solvent was then distilled off. The acidity stated is the acidity measured in the distillate.

[0031] These measured acidity values ​​according to Table 2 also clearly demonstrate the correlation between the amount of stabilizer added and the reduction in acidity in the solvent. The more stabilizer added, the more the acidity decreased. The stabilizer's effect is particularly effective at a concentration of at least 2.0% per 100 mL of solvent. Table 2: Amount of stabilizer [mL] Distillate quantity [L] Acidity [ppm] 0,1 94 571 0,2 95 515 0,3 96 484 0,4 96 445 0,5 96 405 0,6 95 378 0,8 96 326 1,0 96 266 1,5 95 157 2,0 97 66 3,0 97 27 4,0 96 9 5,0 97 8

[0032] In a further embodiment, the mixture comprises two solvents (blend). Preferably, the first solvent is a modified alcohol and the second solvent is a hydrocarbon composition.

[0033] The invention also relates to a method for degreasing metal parts with a solvent, wherein: - during degreasing the solvent is contaminated with cleaned residues, - the contaminated solvent is fed into a distillation process in which the solvent boiling at a lower temperature is separated from the purified residues and recycled, characterized in that To avoid acid formation, a solvent stabilizer is added to the solvent in the distillation process, which comprises: - overbased calcium sulfonate with a total base number greater than 300, - Alkylphenol as antioxidant and - high-boiling mineral oil distillate as base oil, whereby the proportion of overbased calcium sulfonate corresponds to the sum of the two proportions of alkylphenol and high-boiling mineral oil distillate.

[0034] It is particularly advantageous if, in the process, the solvent stabilizer binds the acids formed in a distillation sump of the distillation process and remains there until the distillation sump is emptied and disposed of.

[0035] Furthermore, a method for checking the acid content in a solvent is proposed, in which the following parameters are advantageously determined in the solvent: - Measuring the proportion of free acids in the acidic range, - Determination of alkalinity in the alkaline range, and - Test the solvent for chlorides.

[0036] A method for determining the amount of a stabilizer composition required to neutralize acid in a solvent is also proposed. Knowing the acidity of the solvent, i.e., the proportion of free acids in the solvent, and the volume of the degreasing system, the required addition amount of the stabilizer composition according to the invention can be determined by means of stoichiometric calculation to neutralize the acid content in the solvent.

[0037] The stabilizer according to the invention acts as a sump stabilizer, slowing acid formation in the degreasing system and reducing acids already formed. Acidification due to self-decomposition of the solvent used or due to external acid input can be reduced, thereby significantly increasing the service life of the modified alcohols. The stabilizer according to the invention thus prevents corrosion damage in the system and surface corrosion on the degreased parts. Damage to the system can be prevented, thus increasing process reliability.

[0038] In summary, the following advantages arise from using the stabilizer composition according to the invention: - Reduction of acidity, - Avoiding acidification of the solvent, - Reduction of the self-decomposition of the solvent, - Increase in solvent life, - Increased process reliability, - Prevention of corrosion damage, surface corrosion and damage to the system, - cost savings, and - Resource efficiency through longer solvent usage time.

Claims

[1] A process for degreasing metal parts with a solvent, wherein: during degreasing the solvent becomes contaminated with cleaned residues, the contaminated solvent is fed into a distillation process in which the solvent boiling at a lower temperature is separated from the purified residues and recycled, characterized by , that To avoid acid formation, a solvent stabilizer is added to the solvent during the distillation process, which consists exclusively of the following components: overbased calcium sulfonate with a total base number greater than 300, alkylphenol as antioxidant and high-boiling mineral oil distillate as base oil, whereby the proportion of overbased calcium sulfonate corresponds to the sum of the two proportions of alkylphenol and high-boiling mineral oil distillate. [2] Method according to the preceding claim 1, characterized by that the solvent stabilizer binds the acids formed in a distillation sump of the distillation process and remains there until the distillation sump is emptied and disposed of. [3] Method according to one of the preceding claims 1 to 2, characterized by that a total base number of 400 is used for the overbased calcium sulfonate. [4] Method according to one of the preceding claims 1 to 3, characterized by that the proportion of alkylphenol is the smallest. [5] Method according to one of the preceding claims 1 to 4, characterized by that a solvent stabilizer is used in which the proportion of overbased calcium sulfonate is 50%, of alkylphenol 0.2% and of mineral oil distillate 49.8%. [6] Use of a solvent stabilizer in a distillation process in a degreasing process of metal parts, wherein a solvent is used to degrease metal parts, and: during degreasing the solvent becomes contaminated with cleaned residues, the contaminated solvent is fed into a distillation process in which the solvent boiling at a lower temperature is separated from the purified residues and recycled, a solvent stabilizer is added during the distillation process, which consists exclusively of the following components: overbased calcium sulfonate with a total base number greater than 300, alkylphenol as antioxidant and high-boiling mineral oil distillate as base oil, where the proportion of overbased calcium sulfonate corresponds to the sum of the two proportions of alkylphenol and high-boiling mineral oil distillate. [7] Use according to the preceding claim 6, characterized by that the solvent stabilizer binds the acids formed in a distillation sump of the distillation process and remains there until the distillation sump is emptied and disposed of. [8] Use according to one of the preceding claims 6 to 7, characterized by that a total base number of 400 is used for the overbased calcium sulfonate. [9] Use according to one of the preceding claims 6 to 8, characterized by that the proportion of alkylphenol is the smallest. [10] Use according to one of the preceding claims 6 to 9, characterized bythat a solvent stabilizer is used in which the proportion of overbased calcium sulfonate is 50%, of alkylphenol 0.2% and of mineral oil distillate 49.8%.