NO301080B1 - Process for the cleaning of industrial lubricants - Google Patents

Abstract

Use of polymeric two-phase systems for removing microbial contaminants from industrial lubricating agents, a method of purifying microbial contaminated lubricating agents by mixing the lubricating agent with a polymeric two-phase system, allowing the mixture to separate so as to form a top-phase containing the lubricating agent and a bottom-phase containing at least part of the microbial contaminants, and separating at least a major part of the microbially enriched bottom-phase from the top-phase, a plant for microbial purification of lubricating agents comprising a mixing tank (4) having means (7, 8) for feeding microbially contaminated lubricating agent (S) to the mixing tank, means (13) for feeding a polymeric two-phase system to the mixing tank, a stirrer (5) in the mixing tank, means (9, 10) for feeding the mixture to a separation device (6) for separating the mixture into a top-phase (T) containing lubricating agents, and a bottom-phase (B) containing microbial contaminants, and means (18) for recovering the top-phase of the two-phase system, and a lubricating agent concentrate, in which at least part of the lubricating agent at the same timeforms part of the top-phase component of the polymeric two-phase system.

Description

The present invention relates to the technical area of industrial lubricants and/or coolants, especially those for metalworking. More specifically, the invention relates to the purification of such agents, hereinafter referred to as "lubricants", with the intention of microbial contamination using polymeric two-phase systems, where the invention consists of a method for separating microbial contamination from contaminated lubricants.

Background for the invention

A common type of industrial lubricants are cutting oils and cutting fluids that are usually used in the workshop industry in connection with milling, turning, drilling, grinding and similar metalworking. Their main function is to increase the life of the tools by acting as a cooling and lubricating agent between the tools and the work materials. Cutting oils, and also lubricants in general, are made up of so-called base oils. These can be mineral oil-based, synthetic or semi-synthetic. By cutting fluids/lubricating fluids is meant water emulsions of cutting oils or lubricating oils.

A rapid microbial growth of bacteria, but also fungi, often limits the cutting fluid's useful life to a few months. Even after such a short period of use, the bacterial concentration may have increased from zero to in the order of 10<8> cells/ml. The growth of microorganisms not only leads to the deterioration of the cutting fluid's properties, it also leads to the development of an unpleasant smell. When grinding and turning, for example, airborne bacteria can also be spread in aerosol form and thereby create a further work environment problem.

Cutting fluids contain many components, ranging from bactericidal preparations to anti-foaming and corrosion-inhibiting agents. Many of these components, together with a micro-flora of bacteria and fungi, are considered to be able to cause discomfort, above all in the form of eczema and skin irritation, in industrial workers (Wahlberg, J.E. 1976, Skin effects of oil, Essos symposium 1976 ).

As there are currently no practical/economically applicable methods for cleaning the cutting fluid during operation, the usual measure against microbial contamination is to throw away the entire contaminated cutting fluid and replace it with fresh cutting fluid. This not only entails large disposal costs and costs for fresh cutting fluid, but also large additional costs due to the interruption of operation that is necessary to empty and clean the tanks and the distribution system for the cutting fluid as well as refilling new cutting fluid in the system.

Microbial growth in cutting fluids is such a big problem in today's workshop industry and there is a great need to extend the life of the cutting fluids. As an example, it can be mentioned that in 1977 in Sweden alone, approx. 1,000 tonnes of cutting fluids, of which 2,000 tonnes are emulsion concentrate (LO's report on cutting oils). The acquisition and disposal costs were then calculated to be in the region of 140-200 million Swedish kroner. To this must be added the much higher costs for downtime in connection with changing the cutting fluid.

Similar problems with microbial contamination occur during the use and disposal of other types of lubricating oils, e.g. various hydraulic oils, waste oils, etc.

Derwent abstract no. 76-65593x/35, JP 51079959 describes a means for treating contaminated waste water, including waste cutting oil, by adsorbing the contaminants. The adsorbent consists of very small complex substances consisting of inorganic particles and an organic polymer. The inorganic particles can be made up of activated carbon or

certain metal hydroxides.

Aqueous polymeric two-phase systems in themselves have been known for a long time and they have come to be used laboratory-wise in analysis and separation methods in biochemistry and microbiology for e.g. to separate macromolecules, cell particles and whole cells (for example Albertsson P.Å. 1960, Partition of Cell particles and Macromolecules, 2nd edition. Almquist & Wiksell, Uppsala; Blomquist G. and Strom G. 1984, Fordelning av mogelsampsconidia i polymera tvåfas-system, Arbete och Halsa no. 31, Strom G. 1986, Qualitative and quantitative analysis of microorganisms particularly fungal spores - methodological developments, academic thesis, Umeå University). However, polymeric two-phase systems have few purely technical applications.

Polymeric two-phase systems mainly consist of two water solutions of polymers with different molecular weights. When the two polymer solutions are mixed with each other in certain proportions, two immiscible water phases are formed. The top phase mainly contains the low molecular polymer, while the bottom phase mainly contains the high molecular polymer. The water content in the system is high, usually between 80-98% depending on the choice of phase polymers. In an alternative type of polymeric two-phase system, the same results can in principle be achieved by replacing the high molecular weight polymer with a suitable water-soluble salt, such as phosphate buffer.

In polymeric two-phase systems, particles or cells are mainly distributed between the top phase, the interphase (the interface between the phases) and the bottom phase, while soluble macromolecules are distributed between the top and bottom phases.

In order to simplify the presentation, we will subsequently use the expression "top phase component", respectively "bottom phase component", to denote the component or components of the polymeric two-phase system which, after mixing and separation of the system, are mainly found in the top phase and the bottom phase respectively.

Purpose of the invention

The purpose of the method according to the present invention is to reduce or eliminate the above-mentioned problems and disadvantages of the known systems for the use, handling and disposal of industrial lubricants, especially cutting fluids within the workshop industry.

A particular purpose of the method according to the invention is to provide lubricant/cutting fluid systems which have a considerably longer useful life than current systems.

Another special purpose of the method according to the invention is to provide a cleaning method which makes it possible to clean lubricating fluids microbially during operation and thereby considerably reduce the time for interruption of operation due to fluid replacement.

A further purpose of the method according to the invention is to provide cleaning procedures and devices for lubricating fluids that meet strict requirements for occupational hygiene and the working environment.

Another purpose of the method according to the invention is to provide a lubricant which can simultaneously function as top phase polymer in a polymeric two-phase system to separate microbial contaminants from the lubricant.

These and other purposes and advantages of the method according to the present invention will be explained in more detail below.

Summary of the invention

The characteristics that are particularly characteristic of the invention are stated in the characteristics of claim 1 and otherwise in the attached patent claims. Various features of the invention are specified in the subclaims. The subclaims indicate preferred embodiments of the invention.

In summary, it can be said that the invention in its various aspects is based on the basic idea of utilizing polymeric two-phase systems for the separation of microbial contaminants from contaminated lubricants. In the method according to the invention, the polymeric two-phase system is designed so that, after mixing with a lubricant and phase separation, a top phase containing lubricant and a bottom phase containing at least part of the microbial contaminants are formed, so that at least a major part of the microbial contaminants can be carried away with the bottom phase, which phase is easily separated from the top phase.

(For simplicity, the interphase of the bottom phase is included in the description.)

A feature of the invention is a method for cleaning microbially contaminated lubricants, characterized by the steps of mixing the lubricant with a polymeric two-phase system, allowing the mixture to separate so that a top phase containing the lubricating liquid and a bottom phase containing at least part of the the microbial contaminants, and separate at least a major part of the microbially enriched bottom phase from the top phase.

To carry out the method according to the invention, a plant for microbial cleaning of lubricating fluids can be used. This facility is characterized in that it includes a mixing tank equipped with devices for supplying microbially contaminated lubricating fluid to the mixing tank, devices for supplying at least one component of a polymeric two-phase system to the mixing tank, at least one agitator in the mixing tank, devices for feeding the mixture to a separation device arranged to separate the mixture into a top phase containing lubricant and a bottom phase containing microbial contaminants, as well as devices for feeding back the top phase of the two-phase system.

Brief description of the drawings

In the attached drawings show

fig. 1 a schematic representation of a plant for carrying out the method according to the invention for cleaning industrial cutting fluids, where the dashed lines illustrate alternative embodiments, and

fig. 2 is an overview diagram of the results of comparison tests with regard to the effect of the cutting fluids on the tool life in spiral drilling.

Description of preferred embodiments

The accompanying drawing schematically shows a cleaning system that illustrates how the principles of cutting fluid cleaning according to the invention can be carried out. The plant includes a tank 1 for cutting fluid S which contains the top phase component. The cutting fluid S is continuously circulated between the tank 1 and processing stations (not shown) via the tank's inlet pipelines 2 and outlet pipelines 3. To transport cutting fluid to and from the processing stations, suitable distribution pipelines, pumps etc. are used. This is conventional technique and will therefore not be described in more detail in this connection.

In the embodiment shown, the plant comprises a mixing tank 4 with an agitator 5 placed therein and a separator 6. A pipeline 7 equipped with a shut-off valve 8 connects the cutting fluid tank S with the mixing tank 4. The latter can also be connected to the separator 6 via a line 9 with a shut-off valve 10. Furthermore, shown a storage tank 11 for fresh or recovered bottom phase component and a collection tank 12 for used bottom phase. The storage tank 11 is connected to the mixing tank 4 via a pipeline 13, and a pipeline 14 connects the collection tank 12 to the bottom part of the separator 6. Fresh bottom phase component can be taken into the storage tank 11 from a warehouse (not shown) via a pipeline 15 provided with a valve. A connecting pipeline 16 makes it possible, if desired, to reuse the bottom phase from the tank 12 via a (dotted line) pipeline 16, which can be equipped with a suitable coarse filter 17. A return pipeline 18 reintroduces cleaned cutting fluid to the tank 1.

The described plant can, by the method according to the invention, i.a. is used in the following way to clean microbially contaminated cutting oil that circulates through tank 1. It should be noted here that the cleaning is carried out without having to interrupt the supply of cutting fluid to the application stations, i.e. that the cutting fluid circulation through pipelines 2 and 3 can proceed continuously as usual.

Contaminated cutting fluid S is taken into the mixing tank 4 by opening the valve 8 in the pipeline 7. Fresh or recirculated bottom phase is taken into the mixing tank 4 via pipeline 13. The supply valves are closed and the top and bottom phase components are mixed with the contaminated cutting fluid. After complete mixing, the valve 10 is opened and the mixture is transferred to the separator 6, where it is separated into a top phase T and a bottom phase B. In this way, a larger or smaller part of the microbial contamination passes from the top phase T to the bottom phase B, while the cutting fluid remains in the top phase T.

When the separation is ready, the purified top phase is fed back into the cutting oil tank 1 via pipeline 18. The bottom phase B with its newly absorbed microbial contaminants is taken out through the bottom pipeline 14. Depending on which bottom phase component is used, the bottom phase B can either be discarded via a drain 19 or fed back into the tank 11, advantageous after coarse filtration and/or other purification in the generally designated device 17. Discarding is best suited when the bottom phase component consists of cheap material, while reuse is preferable when it contains expensive material, such as fractionated dextran.

If the bottom phase component contains inorganic salts, such as phosphates and/or sulphates, the reintroduced top phase will also contain a smaller amount of corresponding salt. Such salts can have an adverse effect on the properties of the cutting fluid, and in this case it is advantageous to desalt the top phase before it is reintroduced into the tank 1. To achieve this, the plant shown in the drawing has been provided with a desalination device 20 which can be built on and known desalination principles.

Preferred top phase components are relatively low molecular weight, hydrophilic polymers, especially those that are not solid at room temperature. However, higher molecular hydrophilic polymers, which are solid at room temperature, can also be used within the scope of the invention. In the latter case, it is preferred to also add an organic solvent, in which the polymer is soluble. With the addition of solvent, it can be achieved that the lubricating fluid does not leave any solid residue upon evaporation, which could have a detrimental effect on the usability of the lubricating fluid by leaving a hard crust on the processing machines.

In a preferred embodiment, the top phase component of the two-phase system comprises at least one polyalkylene glycol, especially a polyethylene glycol, with a molecular weight of 200-20,000, especially 400-10,000, preferably approx. 600-4000.

According to another preferred embodiment, other hydrophilic polymers which are liquid at room temperature and/or the application temperature and which are in themselves usable in synthetic cutting oils as the only cutting oil component or together with other cutting oil components in whole or semi-synthetic cutting oils. Polyoxyalkylene polyalcohol ethers, such as polyoxyalkylene glycol ethers, linear polymers of ethylene and/or propylene oxide are some examples of preferred polymers which can simultaneously function as lubricating fluid and top phase component. Such lubricating fluids can for example contain at least 2% by weight, especially at least 4, often at least 6% by weight of the polymer, especially at least 7% by weight. For the top phase polymers, it generally applies that their concentration in the lubricating fluid is lower the higher the molecular weight.

In the embodiment where the bottom phase component also contains a polymer, this preferably has a higher average molecular weight than the top phase polymer. The bottom phase polymer preferably has an average molecular weight of at least 40,000, and it is preferably cross-linked. Examples of suitable bottom phase polymers include polysaccharides in raw or refined form, especially cross-linked polysaccharides, especially cross-linked dextran, starch, cellulose, polyglycose or cross-linked mono-, di- or oligosaccharides. Polyvinyl alcohols with different average molecular weights can be mentioned as examples of other types of suitable bottom phase polymers. Pplyvinyl alcohols can be recovered from the bottom phase by, for example, precipitation.

The bottom phase component can advantageously also contain a small amount of a suitable agent which distributes in the bottom phase and promotes the transition of the microbial contaminants from the top phase to the bottom phase. Such agents preferably exhibit positive electrical charges that attract the negative charges on the bacteria's cell surfaces. The system is thereby advantageously kept at a pH of from neutral to slightly basic so that the charges on the bacteria's cell surfaces are exposed. Examples of such charge-exposing agents include hydrophilic polymers containing positively charged groups, such as DEAE groups. Such positively charged agents can be included in very low concentrations (in the range 10"<2>% - 10"<3>%) and still produce a powerful effect.

In the embodiment where the bottom phase component contains inorganic salts instead of a high molecular bottom phase polymer, these salts can for example be made up of ordinary buffer salts, such as alkali metal phosphates and sulphates and mixtures thereof. The amount of such salts can vary within relatively wide limits and depends, among other things, of which particular salts and which particular top phase polymer is used. As an example, it can be mentioned that when using a two-phase system including phosphate buffer in combination with low molecular weight polyethylene glycol, good results are achieved with approx. 10-2 0% of each component.

The used lubricating fluids preferably contain 1-16% by weight of lubricating oil, especially 2-10% by weight of lubricating oil, at least 2% by weight of top phase component, especially at least 4% by weight of top phase component, and in the case of a top phase component containing a low molecular weight polymer which is not solid at room temperature, preferably at least 8% by weight top phase component, the remainder being essentially water. The upper limit for the amount of top phase component is not particularly critical and it is therefore chosen primarily with regard to what is practical/economical.

The method according to the invention, which uses polymeric two-phase systems to separate microbial contaminants from contaminated lubricating fluids, can also be advantageously used to separate the water phase with a view to analyzing microbial microbial contaminants. Such an analysis, which is preferably carried out mainly quantitatively or semi-quantitatively, provides a very quick and reliable basis for assessing the quality of the lubricating fluid and guidance on what measures may need to be initiated, for example the addition of biocides, changing the lubricating fluid etc. Today these analyzes are carried out by growing suitable nutrient substrates which are usually shaped like sticks which are dipped into the lubricating liquid. Cultivation takes several days and the margins of error are large, which is a major disadvantage as the growth of contaminated biomass (this includes both bacteria and fungi) can happen very quickly, especially when the contaminants approach critical concentrations. There is thus a great need for an analysis method that provides reliable analysis results within a few hours. Analysis using polymeric two-phase systems provides reliable answers within minutes. It is also desirable to be able to distinguish between live biomass and dead biomass during the analysis, as the latter normally does not significantly deteriorate the quality of the lubricating fluid. This is also made possible by the method according to the invention using markers which are split into detectable molecules, especially fluorescent molecules, of living biomass.

The analysis can be carried out on the separated bottom phase of cutting oils resulting from the cleaning method according to the invention, but it is preferred to take a special sample for the analysis. As bottom phase, it is preferred to use salts of the above type instead of high molecular weight polymers. Although it is possible to carry out the separation in a single step, it is preferred to use separation in two (possibly more) steps.

Some preferred special embodiments of the method according to the invention are to be described in the following section of the description, which also explains the results of comparison tests carried out.

As previously mentioned, the starting point for using the two-phase technique for continuous cleaning of lubricating fluids is that by adding cutting oils/emulsion concentrate to a two-phase system, a top phase with the character of a lubricating fluid/polymer phase is well separated from a bottom phase with collected microbial pollutants. As an example of factors that can influence the distribution of a microbial particle between the top, inter- and bottom phase, the choice of polymer-charged/uncharged polymers - the polymer concentration, choice of pH and ionic strength can be mentioned.

An important prerequisite for successfully using polymeric two-phase systems as a continuous cleaning technique for lubricating fluids is that the properties of the lubricating fluid are not adversely affected by the polymer addition in terms of lubricating and cooling properties, corrosion, stickiness, etc. That the polymer additives used in the method according to

.the invention does not have any adverse effects on the effectiveness of the lubricating fluid, rather in certain cases, on the contrary, it provides additional advantages, as can be seen from the below described

attempt. In these experiments, cutting fluids were tested with regard to physical and chemical properties against a reference fluid in the form of the same cutting fluid without polymer addition. Experiments carried out with some different bottom-phase polymers are also described, as well as separation experiments on cutting fluids containing bacterial cells and spores from moulds.

Sample of cutting fluid with and without polmer addition

(top phase polymer)

All experiments were carried out at the Institute for Workshop Technical Research in Gothenburg.

In the experiment, a mixture of 6 kg of Polyethylene glycol 600 (Kebo lab AB, Solna) suspended in 4 kg of water was added to a mixture of 28 liters of water plus 2 liters of emulsion concentrate (mineral oil-based, fine emulsion) - liquid 2. As a reference sample, a mixture of 2 liters of emulsion concentrate and 28 liters of water - liquid 1.

The following properties of the two cutting fluids were studied:

<*> Impact on tool life when spiral drilling

* Crevice corrosion

* Impact on copper and aluminium

* Excretion of play oil

<*> Foam formation

<*> Sedimentation

<*> Residue after water evaporation, holding strength The machining test was carried out with machining data applicable in the production of heat-hardening steel (SS 2541-03) and with a stable machine tool.

Machining test - spiral drilling

Equipment

Processing data

Pretreatment of equipment

The workpieces are taken out of a "charge" and rolled one after the other, after which they are cut to size 200 x 30 x 3 75 mm (approx. 400 holes/plate) and face milled. The tools are standardized with narrow geometric tolerances and hardness variations.

Execution

The workpieces (2 pcs.) are clamped in the machine, and their work program is designed so that the processing is distributed on both plates for each tool. This is to avoid local unevenness in the material. The cutting speed is varied for different drills so that a connection is achieved between cutting speed and wear time (vT curve).

Degradation of the tool manifests itself in the form of vibrations and changed chip formation (the tip melts). This happens within a few seconds.

Other tests were carried out according to the test program in IVF report 87-03-18, a supplement to revision of IVF result no. 71607.

Results

When evaluating these cutting fluid samples, the scale 0, 1 and 2 was applied. Grade 1 is generally acceptable for tool products and 2 indicates increased effect in the respective sample.

Note: For both samples, the same Cu content amount of 51.4 mg/l was measured with an atomic absorption spectrophotometer after a copper tin had been in the liquids for two weeks.

Note: Liquid 1 has a cloudy boundary zone, coarse emulsion, while the boundary zone for liquid 2 is clear.

The test could not be carried out, as liquid 2 could not be evaporated in a drying cabinet at 40°C. A surface layer prevents evaporation of water.

The test results show that the addition of a top phase polymer according to the invention to a mineral oil-based fine emulsion results in a number of positive effects with regard to the properties of the cutting fluid. Cutting machining tests, which are an indirect measure of the fluid's cooling and lubricating properties, showed reduced tool wear when using polymer-containing cutting fluid. At a cutting speed of, for example, 22 m/min, a service life expressed in the number of holes/drills recorded was approx. 28 for the normal cutting fluid and 130 for the corresponding polymeric cutting fluid mixture (see vT curve in Fig. 2).

An important feature when it comes to the lifetime of a cutting fluid is the ability to efficiently separate contaminated play oils that originate from, among other things, hydraulic systems. Comparison experiments with and without polymer mixing showed a lower tendency for play oil to emulsify into the cutting fluid according to the invention, which means that play oil can be more easily removed from the system.

Minimal attacks on the metals copper and aluminum were noted for the two cutting fluid types, and leaching of Cu ions from copper tin was identical (51.4 mg/l).

When it comes to corrosion, the cutting fluid according to the invention had a clear anti-corrosive effect on cast iron, while the reference fluid had an unacceptable effect from a workshop product point of view. On steel, both products showed an increased effect.

Often used as corrosion inhibitors in cutting fluid

amine derivatives. However, these amines often create work environment problems. Carbon/nitrogen compounds of the amine type can also be easily used as a substrate by microorganisms and thereby have a beneficial effect on microbial growth. The clear corrosion-inhibiting effect of mixing in the top phase polymer according to the invention can make it possible for amino compounds to be completely excluded from these products.

The foaming tendency and breakdown of foam in cutting fluid products is an important characteristic for the workshop industry. The results of comparison between cutting fluid with and without stoning of top phase polymer according to the invention showed no significant difference in foaming tendency.

Adding polymer to a cutting fluid results in some increase in viscosity. The results of this increase in viscosity were also shown in sedimentation tests carried out with a fine particulate powder consisting of reduced iron. With cutting fluid without polymer addition, it was found that 30% of the added amount of iron powder had not sedimented after 30 seconds. The corresponding value for cutting fluid according to the invention was 50%.

Furthermore, it can be mentioned that inorganic particles, in the polymeric two-phase system, do not distribute in the top phase, i.e. the cutting fluid phase. The result is that inorganic particles in the system will also be removed in each case of separation together with microorganisms in the bottom phase.

Hard crystalline evaporation residues from a cutting fluid can have a negative effect on moving machine parts and precision tools. The evaporation experiments with the mineral oil-based fine emulsion with added polymer resulted in the product not being able to evaporate, probably because a formed surface layer prevented water evaporation. Other evaporation experiments with both mineral oil-based and semi-synthetic emulsion concentrates containing added polymer according to the invention and water showed that no hard crystalline evaporation residue was formed. In the case of the mineral oil-based concentrate, two phases were obtained, one consisting of concentrate and a second of the added top phase polymer.

The fact that polyethylene glycol after evaporation does not form a homogeneous liquid with mineral oil-based concentrates is not of significant importance.

Separation test

In all separation experiments, the following two types of emulsion concentrate were used; semi-synthetic fine emulsion (5-Star-40, Cincinatti, Millacron) and mineral oil-based coarse emulsion (Multan 94-2, Henkel Kemi).

Each emulsion was tested as follows:

1. 0.6 grams of polyethylene glycol 6 00 was mixed with 1.2 g of emulsion concentrate and 3.2 g of water with suspended bacterial cells (approx. 2 x 10<8> bacterial cells/ml), alternatively fungal spores (approx. 5 x 10<7 > spores/ml) . 2. 0.8 grams of polyethylene glycol 600 was mixed with 0.2 g of emulsion concentrate and 3.0 g of water according to the above. 3. 0.5 grams of polyethylene glycol 600 and 0.1 g of polyethylene glycol 800 0 (Carbowax 6000, Union Carbide, New York, USA) were mixed with 3.2 g of water according to the above.

During the separation, a polymer mixture consisting of diethylaminoethyldextran (DEAE-dextran) and the polymers listed below was added to each of the systems: a) Dextran 500 (molecular weight 500,000, Pharmacia fine chemicals, Uppsala)

b) Dextran (batch 30-0472-00)

c) Dextane (fraction I)

d) soluble potato starch (Kebo lab AB, Solna)

The final concentration in the system was for DEAE-dextran

0.001% and for the other polymers 1% by weight.

After mixing and phase separation, 1 ml of the top phase was removed (emulsion + polyethylene glycol phase) which was then diluted in steps of 10<1> and after each dilution step was inoculated onto growth substrates for fungi and bacteria.

Cultivation media and cultivation conditions

Quantification of the number of fungal elements was carried out by dipping on a substrate composed of 2 wt% malt extract (Oxoid, L 39), 1.5% Agar (Oxoid, L 28) and 30 mg/l streptomycin sulphate (Sigma Chemical Co. ). Incubation was carried out at room temperature (22°C) over 4 days, after which the number of colony-forming units could be determined.

The concentration of bacteria was determined by cultivation on a substrate composed of 2.4% by weight Tryptone Glucose Extract Agar (CM 127, Oxoid), 0.2% Casein Hydrolysate (Acid) (L 41, Oxoid) and 50 mg/l Actidione ( Sigma). After six days' incubation at room temperature, the number of colony-forming units was determined.

The results of the separation experiments that were carried out with different dextran fractions, alternatively soluble starch, as bottom phase polymer and with the top phase composition described above, are presented in Tables 1 and 2.

TABLE 1

Separation of bacterial cells of Bacillus subtilis using different bottom phase polymers. The amount of bacterial cells before separation was 1.6 x 10<8>/ml in systems 1 and 3 and 1.5 x 10<8> in system 2. The final concentration of the bottom phase polymers was 1%. A semi-synthetic fine emulsion (5-Star-40) was used as emulsion concentrate.

In one case, a semi-synthetic fine emulsion was used together with the top phase polymers (table 1) and in the other case a mineralogy-based coarse emulsion (table 2). Along with the bottom phase polymers, diethylaminoethyldextran (DEAE-dextran) was also added to a final concentration of 0.001%.

The separation of a known quantity of bacterial cells from the top basins containing semi-synthetic fine emulsion proved to be very good (87-95%), and very independent of the choice of bottom phase polymer (table 1). The effect was enhanced by the presence of the positively substituted diethylaminoethyl dextran which distributes in the bottom phase of the system. At the high pH values that prevail in the system, negative charges on the bacteria's cell surface will be exposed, whereby the cells are attracted towards the positively charged bottom phase (cutting fluids usually have a pH of 7-9).

Corresponding separations of fungal spores from a mineral oil-based coarse emulsion are set out in table 2. As was the case with bacterial cells, a very high degree of separation (96-98%) was also achieved here, enhanced by the presence of DEAE-dextran and the high pH value in the system .

TABLE 2

Separation of mold spores of Penicillium brevicompactum using different bottom phase polymers. The amount of fungal spores before separation was 4 x 10<7>/ml (systems 1 and 3) and 3.8 x 10<7> in system 2. The final concentration of the bottom phase polymers was 1%. A mineral oil-based coarse emulsion (Multan 94-2) was used as emulsion concentrate.

In summary, it appears from the experiments carried out that top-phase polymers used in the method according to the invention can with excellent results be included in cutting fluids and at the same time function as top phase in a two-phase system for microbial cleaning of the cutting fluid.

As far as dextran is concerned, a number of fractions, from finely fractionated dextran 500 (molecular weight 500,000) to more unfractionated (and thus cheaper) raw dextran, have been tested and found to be very useful. When using high molecular weight dextran, it has been found to be particularly advantageous with a top phase concentration of approx. 19% by weight polyethylene glycol 600, alternatively approx. 12.5% polyethylene glycol 600 + 2.5% polyethylene glycol 8000. In the latter case, it is advantageous to use a semi-synthetic cutting fluid concentrate.

The amount of dextran when purifying these systems can be around 1%, which results in a bottom phase volume of approx. 3-5% of the total system.

As mentioned earlier, dextran can be replaced as bottom phase polymer by other high molecular weight polymers, e.g. soluble starch, glycogen and synthetic polyglucose.

In tests carried out with soluble starch, polyethylene glycol 600 (16% solution) was mixed with soluble starch to a final concentration of 1%. As in the case of dextran, a small bottom phase volume was obtained in relation to the total system. However, unlike dextran, soluble starch gives a more gel-like bottom phase.

High molecular weight polyethylene glycols (mw>1000) which at room temperature occur in crystalline form, are not soluble in only mineral oil-based concentrates, but to a high extent in synthetic emulsion concentrates. Evaporation tests performed with a mixture of 2.5% by weight polyethylene glycol 8000 (Carbovax 6000), 5% by weight semi-synthetic emulsion concentrate (fine emulsion) and 12.5% by weight polyethylene glycol 600 did not result in any crystalline residue.

As mentioned above, the bottom phase polymer can consist of unfractionated, or essentially unfractionated, crude extract. Such raw dextran preferably has a molecular weight of 5-40 million and is preferably used in admixture with a small amount of positively charged polymer, such as DEAE-dextran. Rådextran is today the preferred material for the bottom phase polymer as it is both cheap and effective. It is particularly preferred to use raw dextran which is substituted with a small amount of positively charged groups, such as DEAE groups, whereby one does not need to add any separately charged polymer when there is a need for such. Crude fractions of other polysaccharides can also be used in a similar way. The amount of polymer can be as low as approx. 0.01%.

In particular, it has been shown that the combination of this type of bottom phase polymer (raw extract, etc.) with the above-mentioned "dual functions" top phase polymer (itself functions both as top phase polymer and cutting oil) gives both excellent separation results and excellent cutting fluid properties, which is illustrated by the following experiments.

Top phase polymer as fully synthetic cutting fluid

A fully synthetic cutting fluid was prepared by mixing the following components in water to the indicated concentrations.

Emkarox VG 68 0W 6%

(a polyoxyalkylene glycol ether from ICI)

Synperonic T/701 (a defoamer from ICI) 0.1% Phosphate buffer to pH approx. 7 Water q.s.

The usability of the cutting fluid obtained was tested by processing tests and thereby classified as category 2, which means first-class cutting fluid.

The applicability of the cutting fluid as a top phase system for cleaning according to the invention was tested in the following way. The cutting fluid according to the above was provided with bacterial cells and fungal spores (in a similar way as described above) to simulate a microbially contaminated cutting fluid. Raw dextran was used as bottom phase polymer (molecular weight 5-40 million, final concentration 0.1%) with the addition of DEAE-dextran (final concentration 0.01%). The top and bottom phases were mixed and then separated, whereby 97-99% of the bacteria and approx. 99% of the fungus passed into the bottom phase and was excreted.

Microbial analysis of contaminated cutting fluid

A currently preferred embodiment of the analysis method for quantifying the microbial contamination of cutting fluids will now be described in the form of an illustrative example. The analysis result can example-.

vis is used to assess the quality of a used cutting fluid.

A given quantity of a polymeric two-phase system used in the method according to the invention is filled into a sample bottle provided with a closable, preferably "pipette-shaped" stopper. A bottle that holds approx. 50 ml can, for example, be filled with 20 ml of the system in advance, closed and delivered to the user. When sampling, an equal amount (20 ml) of the cutting fluid sample is "pipetted" into the bottle, which is then shaken so that the phases are mixed and allowed to separate with the opening facing down. The bottle can advantageously be pressed together and preferably with visible volume graduations. The separation is usually very good already after 10-20 seconds, but it is advantageous to allow it to proceed for a few minutes. Already during this period, one can get a good idea of the degree of microbial contamination of the cutting fluid by turbidimetric reading of the bottom phase (which mainly consists of salt solution, e.g. phosphate buffer, pH approx. 6.8) and comparison with a known in and of itself manner produced standard curve for corresponding systems. However, it is preferable to carry out a further separation step, in which the bottom phase enriched in biomass from the first step (e.g. 10 ml bottom phase) is mixed with a suitable polymer for a second phase system (e.g. 4 g polypropylene glycol with a molecular weight of about 425). As the bottom phase from the first separation in the preferred embodiment (separation in an upside-down bottle) is found closest to the bottle's preferably "pipette-shaped" opening, transfer and dosing to the second system can be done very easily. This second separation can also be carried out in a pre-prepared bottle designed analogously to the first bottle. The second bottle is shaken well so that the phases are well mixed, allowed to stand until the phases are separated (usually the same separation times as in the first separation are preferable) and a given amount of bottom phase enriched in biomass is taken out for turbidimetric analysis and comparison with a standard curve ( which term also includes a predetermined connection or other relationship for quantifying the measured value). Before reading, the sample can possibly be diluted with e.g. particle-free water (in the particular example given, e.g. 2 ml of sample plus 2 ml of particle-free water). If desired, the amount of living biomass can be determined in the manner indicated above, for example using fluorescein diacetate (FDA) as a marker.

High concentration of diluted polymer solutions

The separation method according to the invention can also be advantageously used to make used cutting fluids or other lubricating fluids, e.g. waste oil, depositable. Currently, it is a very expensive process to get rid of, for example, fully and semi-synthetic cutting fluids, as diluted polymer mixtures are often difficult to concentrate (and the polymer cannot be deposited in any way). The disposal costs can often be as large as the purchase costs. With the method according to the invention, this problem can easily be solved by concentrating the polymer strongly, for example in the following way.

A used cutting fluid containing approx. 7% by weight Emkarox (see above) as top phase polymer is mixed with approx. 60% phosphate buffer (bottom phase) to a final concentration of 25%, these are mixed and allowed to separate (from a few minutes to an hour), whereby a highly concentrated and easily separable polymer top phase is formed (e.g. approx. 35-50% , total volume approx. 5% of the cutting fluid volume) which can be destroyed, while the water phase can usually be deposited immediately.

Claims (8)

1. Process for separating microbial contaminants from contaminated lubricants, characterized by the steps of mixing the lubricant with a polymeric two-phase system, allowing the mixture to separate to form a top phase containing the lubricant and a bottom phase containing at least part of the microbial contaminants, and separating at least a major portion of the microbially enriched bottom phase from the top phase. 2. Method according to claim 1, characterized in that the lubricants are cutting fluids. 3. Method according to any one of claims 1 to 2, characterized in that at least part of the lubricant is also included as part of the top phase component of the polymeric two-phase system. 4. Method according to any of the preceding claims, characterized in that a relatively low molecular weight hydrophilic polymer which is not solid at room temperature, a hydrophilic polymer which is solid at room temperature, together with a preferably organic solvent for the polymer, a polyoxyalkylene glycol ether or a preferably linear polymer of ethylene and/or propylene oxide. 5. Method according to claim 1, characterized in that a polymer with an average molecular weight of at least 40,000 is used as bottom phase and which is preferably a polysaccharide, a polyvinyl alcohol, cross-linked mono-, di- or oligosaccharide such as dextran, starch, cellulose and polyglucose. 6. Method according to claim 5, characterized in that a cross-linked polysaccharide is used. 7. Method according to claim 6, characterized in that a bottom phase polymer is used which is a mixture of polyvinyl alcohols with different molecular weights. 8. Method according to any of the preceding claims, characterized in that a bottom phase component is used which further comprises a charge exposing agent that carries a positive electric charge to attract negative charges on the cell surface of the microbial contaminants, where said charge exposing agent is a hydrophilic polymer which contain positively charged groups.