TECHNICAL FIELD OF THE INVENTION

The present invention relates to an oil purification filter and to an oil purification system comprising such an oil purification filter and to a method for producing an oil purification filter.

BACKGROUND

Purification of contaminated oil, such as for example industrial oil, lubrication oil, hydraulic oil or processing oil is important for the possibility to reuse the oils and therefore an important factor for the environmental future and the limited nature resources of oils. Filtering of oil through different types of filters is often used for purification of contaminated oil. However, the efficiency in these filtering techniques is not always enough. Furthermore, there may be a risk that also valuable components such as additives are removed by the filtering.

There is a need to improve the possibility to reuse oils.

SUMMARY

It is an object of the present invention to provide an improved oil purification filter.

A further object of the invention is to provide an improved oil purification system which can be used for cleaning oil used in a technical equipment, such as for example gear boxes and hydraulic systems.

This is achieved by an oil purification filter, by an oil purification system and by a method for producing an oil purification filter according to the independent claims.

According to one aspect of the invention an oil purification filter is provided comprising a filter body which is, at least in a first part of a volume of the filter body, impregnated with a separation aid, which separation aid composition is substantially insoluble in a contaminated oil to be purified by said oil purification filter because of its polar properties and which separation aid will by chemical interactions adsorb/absorb contaminating solids or dissolved impurities in the oil to be purified.

According to another aspect of the invention a method for producing an oil purification filter comprising a filter body, wherein said method comprises the steps of: providing a filter material; impregnating at least a part of said filter material with a separation aid, which separation aid composition is substantially insoluble in a contaminated oil to be purified by said oil purification filter because of its polar properties and which separation aid will by chemical interactions adsorb/absorb contaminating solids or dissolved impurities in the oil to be purified; producing a filter body of said filter material.

According to another aspect of the invention an oil purification filter is provided comprising a filter body which is, at least in a first part of a volume of the filter body, impregnated with a separation aid, which separation aid composition is substantially insoluble in a contaminated oil to be purified by said oil purification filter because of its polar properties and which separation aid will by chemical interactions adsorb/absorb contaminating solids or dissolved impurities in the oil to be purified, wherein said oil purification filter is produced by said method.

According to another aspect of the invention an oil purification system comprising an oil purification filter as defined above is provided, wherein said oil purification system is configured for being connected to a technical equipment which is using oil such that the oil is circulated through the oil purification filter for purification of the oil.

Hereby a very effective oil purification filter is achieved. Even very small contamination particles, as small as micro and nano particles, are caught in the filter thanks to the separation aid which is impregnated in at least a part of the filter volume. The separation aid is designed to, by chemical interactions adsorb/absorb contaminating solids. The actual filter pore dimensions can in this filter be provided large enough for allowing certain additives to pass. Hereby additives which are valuable to keep in the oil can be kept in the oil during filtration, i.e. will not be caught in the filter. This is a great advantage compared to other types of fine filters where also valuable additives may be filtered out from the oil. In some embodiments of the invention said oil purification filter is configured for cleaning a contaminated oil comprising at least one specific additive and wherein said separation aid is designed to be passive onto, i.e. not attracting, said at least one specific additive in the contaminated oil to be purified. Hereby valuable additives can be kept in the oil, i.e. will not be caught in the oil purification filter during purification of the oil.

In some embodiments of the invention the filter body comprises a network of cellulose fibers and wherein the separation aid is bonded to the cellulose fibers in at least the first part of a volume of the filter body. Separation aid can be effectively bonded to a network of cellulose fibers whereby an effective impregnation is achieved.

In some embodiments of the invention a total volume of the filter body comprises at least a first part and a second part of the volume of the filter body wherein the first part is provided between an inlet of the filter and the second part and the second part is provided between an outlet of the filter and the first part and wherein only the first part of the volume is impregnated with the separation aid. Hereby a risk that separation aid would come loose and pass through the filter together with the oil can be minimized.

In some embodiments of the invention the filter body comprises a number of layers of sheets of filter material which are provided onto each other as a stack of separate sheets and/or as a cylinder with one or more sheets wound in layers around an inner cylinder, wherein said layers of sheet of filter material comprise a network of cellulose fibers and at least some of the sheets of filter material or at least one of the sheets or at least a part of at least one sheet, further comprise separation aid which is bonded to the cellulose fibers. The interfaces between individual sheets may aid in retaining the separation aid within individual sheets and therefore minimize a risk that separation aid would come loose and pass the filter together with the oil.

In some embodiments of the invention said oil purification filter is designed as a filter insert for use in a filter housing for purification of an oil. Hereby the filter insert can easily be changed if needed.

In some embodiments of the method of the invention the step of providing a filter material comprises providing a cellulose fiber filter material.

In some embodiments of the invention the step of impregnating comprises applying the separation aid to a network of the cellulose fibers when a dryness of the cellulose fiber network is a suitable dryness for effective up-take of the separation aid onto and into the cellulose fibers due to their swollen state in water, wherein said suitable dryness is within 20- 60% dry mass of cellulose fiber to total mass of the cellulose fiber network. Hereby the separation aid will be bonded stronger to the cellulose fibres. The binding can be both hydrogen bonds and an effect of separation aid being caught within the cellulose fibres when they are drying and are collapsing after having had a wet swollen state.

In some embodiments of the invention the step of producing a filter body of said filter material comprises providing layers of sheets of filter material onto each other by stacking separate sheets onto each other and/or by winding one or more sheets in layers around an inner cylinder, where at least one of said sheets or at least a part of one sheet is impregnated with the separation aid.

In some embodiments of the invention the step of impregnating at least a part of said filter material is performed at least partly during the step of producing a filter body, wherein the step of producing a filter body comprises the steps of: forming sheets of the filter material, wherein the filter material is a cellulose fiber filter material; impregnating at least one of said sheets with separation aid; and stacking said sheets onto each other and/or winding said sheets around an inner cylinder for forming the filter body, wherein said step of forming sheets comprises suspending the cellulose fiber filter material in water into a cellulose fiber suspension comprising cellulose fibers in a singularized, swollen state, and de-watering the cellulose fiber suspension, using gravity or gravity and vacuum, and possibly, but not necessarily, pressing the de watered cellulose fiber suspension, wherein said de-watering and possibly pressing is performed to a degree such that the sheet has a suitable dryness for effective up-take of the separation aid onto and into the cellulose fibers due to their swollen state in water, wherein the suitable dryness is 20-60 % dry mass of cellulose fiber to total mass of the cellulose fiber network, wherein the step of impregnating is performed to at least one of said sheets when the suitable dryness of the sheets is achieved. In some embodiments of the invention the step of impregnating comprises soaking at least a part of the filter material in the separation aid or in a solution of separation aid and water and/or spraying at least a part of the filter material with a separation aid or with a solution of separation aid and water and/or flowing the separation aid mixed with an oil over at least a part of the filter material.

In some embodiments of the invention the method further comprises the step of drying the impregnated filter material to 90-100% dry mass of cellulose fiber to total mass of the cellulose fiber network after the step of impregnating.

In some embodiments of the invention the step of impregnating comprises impregnating only a first part of the filter material and wherein the step of producing a filter body comprises combining a first part with filter material which is impregnated with separation aid and at least a second part with filter material which is not impregnated with separation aid, wherein the first part is provided between an inlet of the filter and the second part and the second part is provided between an outlet of the filter and the first part.

In some embodiments of the oil purification system according to the invention the oil purification system comprises a filter housing in which said oil purification filter is removably provided with an inlet of the filter connected to an inlet of the filter housing and an outlet of the filter connected to an outlet of the filter housing, said oil purification system further comprising an inlet fluid connection connected to the inlet of the filter housing, an outlet fluid connection connected to the outlet of the filter housing such that a fluid can be transferred into the inlet of the filter housing via the inlet fluid connection, through the filter housing and through the oil purification filter and further out from the filter housing through the outlet of the filter housing and further through the outlet fluid connection.

In some embodiments of the invention the oil purification system further comprises at least one oil condition monitoring sensor for measuring a value indicative of a condition of an oil being purified in said oil purification system. Hereby values from the sensor can indicate if the oil purification filter needs to be changed. BRIEF DESCRIPTION OF THE DRAWINGS

Figures la- lb show schematically two different general principles of an oil purification filter according to the invention.

Figures lc-lg show schematically five different, more specific examples, of oil purification filters according to the invention.

Figure 2 shows schematically an industrial oil purification system according to one embodiment of the invention which is connected to a technical equipment using oil.

Figure 3 is a flow chart showing method steps of a method according to one embodiment of the invention.

Figure 4 is a flow chart of one embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Figures la and lb show schematically two different general principles of an oil purification filter 1; E in accordance with some embodiments of the invention. In Figures lc and Id the basic principle is the same as shown in Figure la and in Figures le and If the basic principle is the same as shown in Figure lb. In Figure lg a filter 1” is illustrated comprising a mix of the two basic principles as shown in Figures la and lb. The oil purification filter can be configured for cleaning contaminated oil, such as for example industrial oil, lubrication oil, hydraulic oil or processing oil for example used in gear boxes, hydraulic systems, automotive equipment and construction equipment.

The filter 1; G; 1” comprises a filter body 3; 3’; 3” which is, at least in a first part 5a; 5a’ of a volume of the filter body 3; 3’; 3”, impregnated with a separation aid. In both embodiments shown in Figures la and lb there is a first part 5a, 5a’ of the filter body 3, 3’ which comprises separation aid which has been provided to the filter such that the separation aid is bonded to the filter, here also called impregnated with separation aid. A second part 5b; 5b’ of the filter body 3; 3’ comprises in these embodiments no separation aid, i.e. is not impregnated with separation aid. However, the impregnation with separation aid can also be provided to the whole filter body volume in another embodiment of the invention. By only impregnating a first part 5a; 5a’ of the filter body volume 3; 3’ the risk that separation aid will come loose and pass the filter together with the filtered oil can be minimized, which may be advantageous. The relation between the volumes of the first and second parts 5a; 5a’, 5b; 5b’ can be varied. In some embodiments of the invention the volume of the second part 5b; 5b’ is larger than the volume of the first part 5a, 5a’. This is however not necessary. The first part 5a; 5a’ can be provided between an inlet 7a of the filter 1; ; 1” and the second part 5b; 5b’ and the second part 5b; 5b’ can be provided between an outlet 7b of the filter 1; ; 1” and the first part 5a; 5a’ and in some embodiments only the first part 5a; 5a’ or only the second part 5b; 5b’ of the volume is impregnated with the separation aid. The filter body 3; 3’; 3” can comprise more than two parts. The part which is referred to as the first part 5a; 5a’ need not be provided closest to the inlet 7a of the filter 1; ; 1” in all embodiments but one or more other parts of the filter body can be provided between the first part 5a; 5a’ and the inlet 7a in some embodiments. Similarly, the part referred to as the second part 5b; 5b’ need not to be provided closest to the outlet 7b of the filter 1; ; 1” in all embodiments but one or more other parts of the filter body volume may be provided between the second part 5b; 5b’ and the outlet 7b. The first and second parts 5a, 5b; 5a’, 5b’ may also shift places such that the first part 5a, 5a’ is provided closer to the outlet 7b of the filter than the second part 5b; 5b’ is and the filter body 3; 3’; 3” can also in some embodiments comprise only one part. There may be different parts of the filter body 3; 3’; 3’ comprising different properties, such as impregnated with separation aid or not, impregnated to different degrees with separation aid, different porosity and/or density of the filter, different material of the filter etc. The different parts can in some embodiments of the invention diffuse into each other, i.e. there may not be a distinct border between the different parts of the filter. This may for example be the case in the examples where the filter 1; ; 1” is impregnated with separation aid after a filter body 3; 3’; 3” has been produced as is described in relation to Figure 4.

The separation aid composition is substantially insoluble in a contaminated oil to be purified by said oil purification filter because of its polar properties and the separation aid will by chemical interactions adsorb/absorb contaminating solids or dissolved impurities in the oil to be purified.

A separation aid which is used in this invention has in some embodiments a density being different from that of the oil to be purified. The separation aid attracts impurities in the oil when oil and separation aid come in contact. The use of a separation aid, also called a chemical booster or separation booster, for capturing impurities in contaminated oil has been described before, see for example WO 2018/199839. Here a liquid separation booster/aid is added to the oil and mixed therewith and impurities in the oil will be captured by the separation aid and will accumulate in a phase which can be separated, for example a bottom phase.

The separation aid will by chemical interactions adsorb/absorb contaminating solids, or dissolved impurities in the contaminated target oil. The separation aid can be liquid at the temperature at which the step of impregnation is carried out. The separation aid composition should be substantially insoluble in the contaminated target oil, forming a two-phase liquid mixture if mixed with the contaminated oil. The liquid separation aid can also have a density different from that of the contaminated oil to be purified.

The separation aid is not soluble in the contaminated target oil because of its polar properties and will through chemical interactions (hydrophilic, hydrophobic, and/or charge interactions) adsorb/absorb unwanted solid or dissolved impurities in the contaminated target oil.

The liquid separation aid/booster for use in the invention can generally be made up based on the following components: a) a polar polymer; b) a hydrotrope/solubilizer; and, c) a co- tenside.

Suitable separation aids with the properties described above, that can be used in the inventive process, may e.g. constitute a composition comprising a mixture of polar polymers such as polyethylene glycols, polypropylene glycols or similar polyalkylene glycols, organic surface active components with nonionic, anionic, cationic and amphoteric properties with the ability to enhance the solubility of solid or dissolved impurities in to the separation aid.

One example of a separation aid which can be used in this invention comprise: a) at least one polar polymer not soluble in oil and with a higher density than the oil, such as polyethylene glycol with an average molecular weight of 190-210 g/mole, e.g. Carbowax PEG 200 (Dow Chemical Company); b) at least one surface active hydrotrope/solubilizer, such as anionic sulfonic acids, phosphate ester-based substances or non-ionic surfactants from the poly glycoside family, such as Simulsol SL 4, Simulsol SL 7 G and Simulsol AS 48 (Seppic, Air Liquide group); c) at least one amphoteric Co-surfactant, such as an propionate type e.g. Ampholak YJH-40 (Akzo Nobel) which is a sodium caprylimino dipropionate. The separation aid may further have a sufficiently big difference in polarity compared to a polarity of at least one specific additive in the contaminated oil to be purified such that the at least one specific additive is not soluble in the separation aid.

In some embodiments of the invention said oil purification filter 1; ; 1” is configured for cleaning a contaminated oil comprising at least one specific additive and wherein said separation aid is designed to be passive onto, i.e. not attracting, said at least one specific additive in the contaminated oil to be purified. Hereby, at least this specific additive can travel through the filter 1; G; 1” together with the clean oil. The sizes of the filter pores are in some embodiments of the invention dimensioned such that valuable additives can pass the filter. The use of the separation aid for impregnating at least a first part of the filter will assure that other contaminations will be caught in the filter even if the sizes of the filter pores are somewhat bigger. However, the separation aid will not attract this specific additive and will hereby let it pass through the filter. Hereby valuable additives can be kept in the filtered oil while small contamination particles still can be filtered out from the oil. Of course, said separation aid can be designed to be passive onto more than one specific additive. Furthermore, an oil to be used in a technical equipment and which should be filtered in the filter 1; G; 1” according to the invention, can be designed to comprise suitable additives which are designed or chosen in relation to the features of the separation aid provided to the filter 1; G; 1”.

The filter body 3; 3’; 3” can be a depth filter and may comprise cellulose fibers. In some embodiments of the invention a network of cellulose fibers is provided in the filter body 3; 3’; 3”. The separation aid can be bonded to the cellulose fibers in at least the first part 5a; 5a’ or at least the second part 5b; 5b’ of a volume of the filter body 3; 3’; 3”. The impregnation of separation aid to the filter material can be done in different ways. A method for producing a filter according to the invention is described in further detail below in relation to Figure 3. However, a part of the filter material can be soaked into the separation aid (possibly into a solution of separation aid and water), or be sprayed with separation aid (possibly separation aid and water) or the separation aid mixed with oil can be flowed over the filter material for providing the impregnation. In order to achieve a stronger bond between the cellulose fibers and the separation aid the cellulose fibers can be wetted before or during impregnation. Optionally a bonding agent could also be added for providing an even stronger and possibly tailor-made bond between the cellulose fibers and the separation aid. In one embodiment the separation aid is applied to the filter material during a sheet forming process where a cellulose fiber suspension is processed into sheets. By applying the separation aid during this process, i.e. during a stage in the process where the cellulose fibers are still wet and before a final filter product is achieved the bond between the separation aid and the cellulose fibers will be stronger. Wet cellulose fibers are swollen and separation aid can be caught within the fibers when the cellulose fibers are dried and their swollen state collapses. The separation aid may also be bonded to the cellulose fibers by hydrogen bonds. Hereby, in some embodiments of the invention said bonding between the separation aid and the cellulose fibers has been provided by applying the separation aid to the cellulose fibers during a process for forming the cellulose fibers to a filter body at a stage in the process where a dryness is 20-60 % dry mass of cellulose fiber to total mass of the cellulose fiber network.

In some embodiments of the invention the filter body 3; 3’; 3” comprises a number of layers of sheets 9; 9’ of filter material which are provided onto each other as a stack of separate sheets 9, as shown in Figure la, and/or as a cylinder with one or more sheets 9’ wound in layers around an inner cylinder 11, as shown in Figure lb. Each of said layers of sheets 9; 9’ of filter material comprise a network of cellulose fibers and at least some of the sheets 9; 9’ or at least one sheet or at least a part of a sheet of filter material further comprise separation aid which is bonded to the cellulose fibers. The interfaces between individual sheets 9; 9’ will aid in retaining the separation aid within individual sheets 9; 9’.

The filter body can for example comprise a cellulose fiber material having a density without bonded separation aid within the interval of 100-600 kg cellulose/m ³ . With separation aid bonded to 50% in this filter material the density of the filter body would be within the interval of 150-900 kg/m ³ . If instead talking about basis weight of a suitable cellulose filter it can for example be within the interval of 50-1500 kg cellulose/m ² for filter material without bonded separation aid and with 50% bonded separation aid this would be within the interval of 75- 2250 kg/m ² .

Figures la and lb show two different general principles of a filter 1; G; 1” according to the invention, while Figures lc-lg show more specific examples of filters according to the invention. In Figures lc and Id the basic principle is the same as shown in Figure la and therefore their reference numbers correspond to the reference numbers of Figure la and in Figures le and If the basic principle is the same as shown in Figure lb and therefore their reference numbers correspond to the reference numbers of Figure lb. In Figure lg a filter 1” is illustrated comprising a mix of the two basic principles as shown in Figures la and lb. Figures la-lg are now described in order in more detail.

Figure la shows a filter 1 comprising a filter body 3 comprising two parts, called a first part 5a and a second part 5b. Only one part can also be provided according to the invention and more than two parts can be provided. The parts can also diffuse into each other. However, in some embodiments of the invention only one of the parts, possibly the first part 5a or the second part 5b, is impregnated with separation aid as described above. The impregnation can be provided during production of the filter as described in relation to Figure 3 or after the production of the filter as described in relation to Figure 4. The filter body 3 may comprise a network of cellulose fibers, whereby the separation aid is bonded to the cellulose fibers in at least a first part 5a or a second part 5b of the filter body 3. The filter 1 comprises an inlet 7a and an outlet 7b whereby the filter body 3 is provided between the inlet 7a and the outlet 7b whereby a fluid to be filtered in the filter 1 is received via the inlet 7a into the filter body 3 and is transferred out from the filter 1 via the filter outlet 7b. In this example the filter body 3 may comprise a number of stacked layers of sheets 9 of filter material. At least some of the sheets or at least one sheet may be impregnated with separation aid as described above and will be further described below. If the filter body 3 comprises stacked layers of sheets 9 the fluid to be filtered is transferred across the sheets 9 when the fluid enters via the inlet 7a and exits through outlet 7b. However, according to the invention filtering along sheets 9 of filter material is also possible. This is schematically illustrated in Figure la by the inlet 77a and outlet 77b and will be further described below in relation to Figures If and lg. However, in this case there will be no difference between the first part 5a and the second part 5b.

Figure lb shows a filter G comprising a filter body 3’ in the form of a cylinder comprising two parts, called a first part 5a’ and a second part 5b’. The filter G comprises an inlet 7a and an outlet 7b whereby the filter body 3’ is provided between the inlet 7a and the outlet 7b whereby a fluid to be filtered in the filter G is received via the inlet 7a into the filter body 3’ and is transferred out from the filter G via the filter outlet 7b. As can be seen in Figure lb the inlet 7a and the outlet 7b can change places and hereby also the first part 5a’ and the second part 5b’ can change places. I.e. fluid to be filtered can either be received through a mantel surface of the cylindrical filter body 3’ and transferred out from a center of the filter body 3’ (most likely) or fluid to be filtered can be received into the center of the cylindrical filter body 3’ and transferred out via a mantel surface. Both alternatives are schematically illustrated in Figure lb. Two parts 5a’, 5b’ are shown in Figure lb but only one part can also be provided according to the invention and more than two parts can be provided. The parts can also diffuse into each other. However, in some embodiments of the invention only one of the parts, possibly the first part 5a’ or the second part 5b’, is impregnated with separation aid as described above. The impregnation can be provided during production of the filter as described in relation to Figure 3 or after the production of the filter as described in relation to Figure 4. The filter body 3’ may comprise a network of cellulose fibers, whereby the separation aid is bonded to the cellulose fibers in at least a first part 5a’ or a second part 5b’ of the filter body 3’. In this example the filter body 3 may comprise a number of wound layers of sheets 9’ of filter material. At least some of the sheets or at least one sheet or at least a part of at least one sheet may be impregnated with separation aid as described above and will be further described below. If the filter body 3’ comprises wound layers of sheets 9’ the fluid to be filtered is transferred across the sheets 9’ when the fluid enters via the inlet 7a and exits through outlet 7b. However, according to the invention filtering along sheets 9’ of filter material is also possible. This is schematically illustrated in Figure lb by the inlet 77a and outlet 77b and will be further described below in relation to Figures If and lg.

The two basic principles as shown in Figures la and lb can be combined and embodied in different ways as will be exemplified in examples as shown in Figures lc-lg.

In Figure le a filter 1 comprises a filter body 3 comprising a number of stacked layers of sheets 9. The sheets 9 are in this embodiment circular and the filter body 3 will form a cylindrical shape. The filter 1 comprises an inlet 7a and an outlet 7b whereby the filter body 3 is provided between the inlet and the outlet 7a, 7b. The filter body 3 comprises a first part 5a which is impregnated with separation aid and a second part 5b which is not impregnated with separation aid. The filtering is provided across the sheets 9.

Figure Id is almost the same filter 1 as shown in Figure lc but only to illustrate that there may be more than two parts and that different parts of the filter body 3 may have different properties. In the example of Figure Id a first part 5a is provided which is impregnated with separation aid and a second part 5b is provided which is not impregnated. However, two additional parts are also provided: one part 5c which in this example is not impregnated with separation aid and is provided between the inlet 7a and the first part 5a and one part 5d which is impregnated to another degree (i.e. comprises a larger or smaller proportion of separation aid) than the first part 5a and which is provided in between the first part 5a and the second part 5b. Other properties of the different parts 5a, 5b, 5c, 5d can also be varied, such as porosity of the filter, density of the filter, degree of impregnation and filter material. The number and order of different parts 5a, 5b, 5c, 5d in the filter body 3 can hereby be varied.

Figure le shows a filter G comprising a filter body 3’ comprising one or more sheets 9’ wound in layers around an inner cylinder 11 according to the basic principle as shown in Figure lb. In this example an inlet 7a of the filter is provided via a mantel surface of the cylindrical filter body 3’ and an outlet 7b is provided in a center of the filter body 3’. The filter body 3’ comprises a first part 5a which is impregnated with separation aid and a second part 5b which is not impregnated. More parts can be provided as described above and said parts can comprise different properties, such as different porosity, different density, different filtering material and different degree of impregnation of separation aid.

All the examples discussed so far has been describing a filtration across sheets 9, 9’ of filter material. However, according to the invention filtration along sheets 9, 9’ of filter material may also be provided. Above in relation to Figures la and lb this is schematically illustrated by inlet and outlet 77a, 77b. Examples where filtration along filter sheets 9, 9’ is shown in Figures If and lg.

Figure If shows a filter G comprising a filter body 3’ comprising one or more sheets 9’ wound in layers around an inner cylinder 11 according to the basic principle as shown in Figure lb. In this example an inlet 77a is provided at a first end 90a of the cylindrical filter body 3’ such that fluid will flowing along the sheets 9’ and an outlet 77b is provided at a second end 90b of the cylindrical filter body 3’. A first part 5a’ of the filter body 3’ is impregnated with a separation aid. This can either be done during production of the filter material by only impregnating a part of the sheets 9’ to be wound or instead after production of the filter body 3’ according to the flow chart of Figure 4. Another alternative would be to produce two filter bodies 3’ with wound sheets of filter material whereby one of them is impregnated with separation aid and the other is not and then combine the two filter bodies 3’. There may be a decreased risk for clogging and stop in the filter when the filtering is provided along layers of filter material instead of across the layers. This may be advantageous. Pores of the filter may have less risk to be clogged by components in the fluid to be filtered.

Figure lg shows a filter 1” where filtering along sheets 9 and filtering across sheets 9’ have been combined in the same filter 1”. The filter 1” comprises a filter body 3” comprising a first part 5a which is impregnated with separation aid and which is provided as sheets 9 of filter material which are stacked onto each other. The filter 1” comprises an inlet 77a which will provide the fluid to be filtered into the filter body 3” such that the fluid will flow along the filter sheets 9. The filter sheets 9 have in this embodiment an annular form and they are enclosing an inner part of the filter body 3” which is a second part 5b’ which is in the form of one or more sheets 9’ which are wound around an inner cylinder 11. Hereby the fluid being filtered will enter the second part 5b’ via a mantel surface of the second part 5b’ and the fluid will flow across the sheets 9’ of the second part 5b’ whereafter it will exit the filter 1” via an outlet 7b in the center. The second part 5b’ is in this example not impregnated with separation aid. There may of course be more combinations of parts which are impregnated or not and which are filtering along sheets of filter material or across sheets of filter material and filter material having different properties may be combined in any way.

The oil purification filter 1; ; 1” according to the invention can be designed as a filter insert for use in a filter housing 21 for purification of an oil. Figure 2 shows schematically an industrial oil purification system 31 according to one embodiment of the invention which is connected to a technical equipment 33 using oil.

The oil purification system 31 according to the invention comprises an oil purification filter 1; ; 1” according to the invention as described above. Said oil purification system 31 is configured for being connected to a technical equipment 33 which is using oil such that the oil can be circulated through the oil purification filter 1; ; 1” for purification of the oil. Hereby oil used in the technical equipment 33 can be continuously cleaned in the oil purification system 31. A technical equipment 33 which is using oil can for example be an industrial equipment, an automotive equipment, a construction equipment or metalworking machines using industrial oil, hydraulic oil and/or lubrication oil, such as for example gear boxes, hydraulic systems etc.

The oil purification system 31 can comprise a filter housing 21 in which said oil purification filter 1; 1 can be removably provided with an inlet 7a of the filter 1; G; 1” connected to an inlet 23 a of the filter housing 21 and an outlet 7b of the filter 1; G; 1” connected to an outlet 23b of the filter housing 21. Said oil purification system 31 can further comprise an inlet fluid connection 33a connected to the inlet 23a of the filter housing 21, an outlet fluid connection 33b connected to the outlet 23b of the filter housing 21 and a pump 35 (a pump may be omitted if a pump in the connected technical equipment can be used) connected to at least one of the inlet and outlet fluid connections 23 a, 23b such that a fluid can be transferred into the inlet 23 a of the filter housing 21 via the inlet fluid connection 33 a, through the filter housing 21 and through the oil purification filter 1; ; 1” and further out from filter housing 21 through the outlet 23b of the filter housing 21 and further through the outlet fluid connection 33b. Hereby oil used in the technical equipment 33 can be continuously transferred through the oil purification system 31 according to the invention and be cleaned in the impregnated oil purification filter according to the invention.

In some embodiment of the invention the oil purification system 31 further comprises at least one oil condition monitoring sensor 37 for measuring a value indicative of a condition of an oil being purified in said oil purification system 31. Due to the pressure drop over the oil purification filter 1 such a sensor is suitably positioned at a distance from the filter housing 21, i.e. not at a distance where it is affected by the pressure drop. Output from this oil condition monitoring sensor 37 can be used as input for a decision of changing the oil purification filter 1; G; 1” in the filter housing 21 to a new one.

Figure 3 is a flow chart showing method steps of a method for producing an oil purification filter 1; G; 1” comprising a filter body 3; 3’; 3” according to one embodiment of the invention. The steps of the method are described below with reference to Figure 3.

SI : Providing a filter material. In some embodiments of the invention the filter material is a cellulose fiber filter material.

S2: Impregnating at least a part of said filter material with a separation aid, which separation aid composition is substantially insoluble in a contaminated oil to be purified by said oil purification filter because of its polar properties and which separation aid will by chemical interactions adsorb/absorb contaminating solids or dissolved impurities in the oil to be purified. In some embodiments of the invention the step of impregnating, S2, comprises applying the separation aid to a network of the cellulose fibers when a dryness of the cellulose fiber network is a suitable dryness for effective up-take of the separation aid onto and into the cellulose fibers due to their swollen state in water, wherein said suitable dryness is within 20- 60% dry mass of cellulose fiber to total mass of the cellulose fiber network.

S3: Producing a filter body 3; 3’; 3” of said filter material. In some embodiments of the invention the step of producing, S3, a filter body 3; 3’; 3” of said filter material comprises providing layers of sheets 9; 9’ of filter material onto each other by stacking separate sheets 9 onto each other and/or by winding one or more sheets 9’ in layers around an inner cylinder 11, where at least one of said sheets or at least a part of at least one sheet is impregnated with the separation aid. Stacking and winding can also be combined in the same filter as shown in Figure lg. The interfaces between individual sheets aid in retaining the separation aid within individual sheets.

In some embodiments, as shown in the flow chart of Figure 4, the steps of impregnating, S2, and producing a filter body, S3, can change places. Hereby a filter body can be produced before at least a part of it is impregnated. This impregnation can be provided by for example injecting separation aid by a syringe or a pipette or the like to chosen parts of the filter body.

In some embodiments of the invention the step of impregnating at least a part of said filter material, S2, is performed at least partly during the step of producing, S3, a filter body 3; 3’; 3”, wherein the step of producing, S3, a filter body comprises the steps of:

S3a: Forming sheets of the filter material, wherein the filter material is a cellulose fiber filter material. Wherein said step of forming sheets, S3a, comprises suspending, S3aa, the cellulose fiber filter material in water into a cellulose fiber suspension comprising cellulose fibers in a singularized, swollen state, and de-watering, S3ab, the cellulose fiber suspension over for example a wire mesh, using gravity or gravity and vacuum, and possibly, but not necessarily, pressing, S3ab, the de-watered cellulose fiber suspension, wherein said de-watering and possibly pressing, S3ab, is performed to a degree such that the sheet has a suitable dryness for effective up-take of the separation aid onto and into the cellulose fibers due to their swollen state in water, wherein the suitable dryness is 20-60 % dry mass of cellulose fiber to total mass of the cellulose fiber network.

S3b: Impregnating at least one of or at least a part of one of said sheets with separation aid. Wherein the step of impregnating, S3b, is performed to at least one of or at least a part of one of said sheets when the suitable dryness of the sheets is achieved.

S3c: Stacking said sheets onto each other and/or winding said sheets around an inner cylinder 11 for forming the filter body 3, 3 ’ ; 3 ” .

The step of impregnating, S2, S3b, may comprise soaking at least a part of the filter material in the separation aid (or into a solution of separation aid and water) and/or spraying at least a part of the filter material with a separation aid (or separation aid and water) and/or flowing the separation aid mixed with an oil over at least a part of the filter material. After the step of impregnation the method may comprise a further step of drying the impregnated filter material to 90-100% dry mass of cellulose fiber to total mass of the cellulose fiber network after the step of impregnating,. The drying can be performed at normal room temperature or at an elevated temperature, for example within the range of 80-120 degrees Celsius.

The step of impregnating, S2; S3b may comprise impregnating only a first part 5a of the filter material and the step of producing, S3, a filter body may comprise combining a first part 5a of filter material which is impregnated with separation aid and a second part 5b of filter material which is not impregnated with separation aid, wherein the first part 5a is provided between an inlet 7a of the filter 1; G; l”and the second part 5b and the second part 5b is provided between an outlet 7b of the filter 1; G; 1” and the first part 5a.

An oil purification filter 1; G; 1” which is produced by a method as described above is also provided according to the invention.