Recycled vegetable oil and uses thereof

Abstract

The present invention relates to a recycled vegetable oil and to a process for obtaining it by the treatment of a waste cooking oil with a mixture of magnesium silicate and an alkali and subsequent treatment with a zeolite. The invention also relates to the use of the recycled oil as lubricant or as cooling liquid. The invention also relates to a lubricant composition comprising the recycled oil ant to its use for lubrication of mechanical devices, for example, bicycle, electric bicycle or motorbike chains, or for the lubrication of other transmission chains, chainsaws or garden cutters.

Description

TECHNICAL FIELD

[0001] The present invention relates to waste recycling, more particularly, to a process for the purification of used frying oils and to the use of the obtained purified oils, in particular, as biolubricants or as cooling liquids.BACKGROUND ART

[0002] The term "waste cooking oils" (WCOs), also known as "used cooking oils" (UCOs) refers to the oily waste material discarded after the repetitive use of vegetable oils for cooking or frying, both at commercial and home settings.

[0003] Waste cooking oils, previously considered as a by-product of food production, are now considered an important raw material for several industries.

[0004] The most common uses of WCOs are direct burning or the synthesis of biofuels. Furthermore, due to the similar properties of WCOs and the original vegetable oils, their possible use to replace vegetable oils in the production of various oleochemicals has been explored, thus providing WCO as a cheap feedstock for preparing, for example, animal feed, green solvents, fermentative products, grease or biolubricants, among other (Foo W.H. et al., Recent advances in the conversion of waste cooking oil into value-added products: A review, Fuel, 2022, 324(Part A), 124539).

[0005] A well-established use of recycled WCOs is the preparation of biolubricants, where WCO is considered a promising alternative to the use of fresh vegetable oils, for example, as disclosed in Joshi et al., Waste cooking oil as promising source for bio lubricants - A review, J. Indian Chem. Soc., 2023, 1000820; or in Li et al., Bio-lubricants derived from waste cooking oil with improved oxidation stability and low-temperature properties, J. Oleo Sci., 2015, 64(4), 367-374, among others.

[0006] However, the use of WCOs as lubricants involves some challenges, as their chemical composition, though similar to their parent fresh oils, differs from them due to the presence of decomposition and leaching products originated by thermal oxidative and hydrolytic reactions occurred during the frying process. Their composition varies depending on the number of frying cycles, frying time, temperature, and the specific vegetable oil. WCOs mainly consist of a mixture of triglycerides with free fatty acids (FFA), di- and mono-glycerides, heterocycles, Maillard reaction products, and metal traces, spices, and other organic molecules originated from pads and food leaching (Mannu et al., Available technologies and materials for waste cooking oil recycling, Processes 2020, 8, 366).

[0007] Therefore, the WCOs need to be subjected to treatment to make them suitable to be used as biolubricants. Most of the disclosures available so far are mainly based on the chemical modification of the WCOs, for example, using esterification, transesterification, epoxidation, or estolide formation reactions, as disclosed in Joshi et al., op.cit.

[0008] Another strategy to improve the performance of WCOs as biolubricants is the use of molecular distillation, as disclosed in Fernandez-Silva et al., Potential valorization of waste cooking oils into sustainable bio-lubricants, Ind. Crops Prod., 2022, 185, 115109.

[0009] The international patent application WO-A-01 / 66679 discloses a process for recycling WCOs comprising the combination of two steps, the first one involving different combinations basic processes such as filtration, centrifugation and adsorption, and the second one involving a chemical transformation of the product obtained in the first step, using transesterification reactions and immobilized enzymes as catalysts. The use of the recycled oil in lubrication compositions is not disclosed.

[0010] The international patent application WO-A-96 / 39044 discloses a process for the treatment of cooking oil or fat, with the purpose of extending the usable life of the oil or fat for cooking, said process involving contacting the cooking oil or fat wit magnesium silicate and at least one alkali material.

[0011] The international patent application WO-A-2014 / 098957 discloses a method for purifying an unrefined edible oil or fat comprising contacting it with an adsorbent material comprising magnesium silicate, preferably in combination with one organic acid, such as citric acid or malic acid. The use of the purified oil for lubrication is not disclosed.

[0012] Therefore, there remains the need to provide improved, economical and simple processes for treating used oils, to make them optimal to be used as biolubricants and, potentially, also for other applications.SUMMARY OF THE INVENTION

[0013] The object of the present invention is a process for treating a waste cooking oil (WCO).

[0014] Another aspect of the invention is the purified WCO obtainable with such process.

[0015] Another aspect of the invention is the use of such purified WCO as biolubricant.

[0016] Another aspect of the invention is the use of such purified WCO as cooling liquid.

[0017] Another aspect of the invention is a biolubricant composition comprising said purified WCO.

[0018] Another aspect of the invention is a cooling liquid composition comprising said purified WCO.DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 shows a picture of the bicycle prototype used in the lubrication performance tests performed in Examples 5.1 to 5.4. Figure 2 is a graphical representation of the results of the comparative test of Example 5.2, where lubricant C3 (according to the invention) was compared to commercial products A to F, with regards to their influence on bicycle speed during a 24h period. The y-axis represents the speed (Km / h) and the x-axis represents the time (h). Figure 3 is a graphical representation of the results of the comparative test of Example 5.3, where lubricant C3 (according to the invention) was compared to commercial products A to F, with regards to their durability, as assessed by measuring the noise of the rotating chain along time. The y-axis represents the the noise (in dB) and the x-axis represents the time (h). DETAILED DESCRIPTION OF THE INVENTION

[0020] The object of the present invention is a process for purifying a waste cooking oil comprising the following two consecutive steps: i) treating the waste cooking oil with a mixture of magnesium silicate and an alkali; and ii) treating the product obtained after step i) with a zeolite.

[0021] The authors of the present invention have developed a particular process for the treatment of waste cooking oils, based on double treatment, first with a mixture of magnesium silicate and an alkali and then with a zeolite, which, surprisingly, is outstandingly effective for purifying the used oil and provides a purified oil with optimal properties to be used as biolubricant and cooling liquid.

[0022] Along the present description, as well as in the claims, singular expressions, generally preceded by the articles "a", "an" or "the", are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0023] The terms "about" or "approximately" referred to amounts, as used herein, are meant to include the exact amount and also a certain deviation around the stated amount, namely of ±5%.

[0024] Unless stated otherwise, the percentages are meant to be by weight (wt% or % w / w).

[0025] The numerical ranges disclosed herein, generally expressed as "from ... to ..." or as "between ... and ...", are meant to include any number falling within the ranges and also the lower and upper limits.Waste cooking oil

[0026] The term "waste cooking oil", generally abbreviated as WCO, is a well-recognized term to designate a vegetable oil material, which has been discarded after the continued use for deep frying, when it is replaced with fresh one. It is a common waste material generated from food industries, restaurants, fast-food establishments and homes.

[0027] The main components of waste cooking oils (WCOs) are triglycerides, as well as diglycerides, monoglycerides and free fatty acids, derived from hydrolysis reactions taking place during frying process.

[0028] They also generally contain volatile compounds (volatile fraction), which are responsible from the intense smell typical of WCOs, and which are typically decomposition compounds originated from the oxidation of triglycerides and from the Maillard process, for example.

[0029] The composition of WCOs is necessarily not uniform, as it depends on the composition of the vegetable oil or oils from which is derived, the number of frying cycles employed, and the specific use made with it.

[0030] WCOs are available from accredited recycling points, where they are collected.

[0031] Regarding the fatty acid composition, the WCO according to the present invention is generally mainly made up of mixtures of olive oil and sunflower oil, in variable proportions. The oil mixture can also contain other vegetable oils, such as rapeseed oil, soybean oil or high oleic sunflower oil, for example.

[0032] Accordingly, the fatty acid composition of the WCO typically used as starting material of the process according to the present invention may be defined as follows: oleic acid (C18:1): from 14% to 83%; linoleic acid (C18:2): from 3% to 74%; palmitic acid (C16:0): from 5% to 20%; and stearic acid (C18:0): from 0.5% to 7%.

[0033] As the skilled in the art can readily understand, depending on the relative proportion of olive oil or sunflower oil in the mixture, the fatty acid composition varies. Thus, when olive oil is the majority component, the content of oleic acid is higher, in accordance with the oleic acid content of olive oil (generally comprised between 55% and 83%), while when sunflower oil is the majority component, the content of linoleic acid is higher, in accordance with the linoleic acid content of sunflower oil (generally comprised between 48% and 74%).

[0034] It is understood that the WCO also contains minor amounts of other fatty acids.

[0035] It is also understood that the fatty acid composition of the WCO, as above defined, means the total fatty acid content, which is mainly in the form of triglycerides, but also occasionally in the form of di- or monoglycerides, or as free fatty acid.

[0036] The iodine index or iodine value is a measure the degree of unsaturation of the fatty acid components of an oil, and is expressed as the mass of iodine in grams that is consumed by 100 grams of the oil. The WCO starting material, according to the present invention has a iodine index value typically ranging from about 75 to about 145, which varies depending on the composition of the vegetable oil mixture, being typically closer to the lower endpoint when olive oil is the major component of the mixture, and closer to the upper endpoint when sunflower oil is the major component, in agreement with the iodine index of olive oil and sunflower oil, which are of about 75-95 and about 110-145, respectively.

[0037] The WCO starting material generally has an acidity index ranging from about 1.5 to about 6. The acidity index of an oil, as is well-known for the expert in the field, is a measure of the content of free fatty acids in said oil, and it is expressed as mg of potassium hydroxide (KOH) required to neutralize the free fatty acids in 1 g of oil.First step: treatment with a mixture of magnesium silicate and an alkali

[0038] The first step of the process according to the present invention comprises treating the WCO with a mixture of magnesium silicate and an alkali.

[0039] The term magnesium silicate, as used herein, means any type of magnesium silicate, either naturally occurring magnesium silicate or synthetic magnesium silicate.

[0040] Naturally occurring magnesium silicate includes, for example, talc or sepiolite, and is generally crystalline.

[0041] Synthetic magnesium silicate is typically prepared by precipitation reaction of a water-soluble silicate, mainly sodium silicate, and a water-soluble magnesium salt such as magnesium chloride, magnesium nitrate or magnesium sulfate. Synthetic magnesium silicate is generally amorphous.

[0042] In an embodiment of the invention, magnesium silicate is synthetic.

[0043] Synthetic magnesium silicate is available as a white powder, having an average particle size typically ranging from about 20 µm to about 200 µm, and / or a surface area generally ranging from about 50 m 2< / g to about 700 m 2< / g and / or a bulk density generally ranging from about 0.25 g / ml to about 0.60 g / ml. Therefore, different types or grades of synthetic magnesium silicate are available, having characteristics within the above defined ranges, and all of them are suitable to be used in the process according to the present invention.

[0044] Synthetic magnesium silicate is commercially available from several suppliers, for example under the trademarks Florisil ®< . Magnesia 430 ®< or Magnesol ®< .

[0045] The alkali used in the first step is preferably selected from calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, and mixtures thereof.

[0046] In an embodiment of the invention, the alkali is calcium hydroxide.

[0047] The weight ratio magnesium silicate:alkali is generally comprised between 20:1 and 1:1, preferably comprised between 15:1 and 4:1, more preferably comprised between 10:1 and 8:1, and more preferably is about 9:1.

[0048] The treatment according to step 1 is typically performed in a suitable vessel provided with stirring and heating means, where the WCO, the magnesium silicate and the alkali are added. The mixture is stirred for a period of time generally ranging from about 15 to 180 minutes, for example.

[0049] The amount of the mixture magnesium silicate-alkali used in this step generally ranges from about 5 g to about 100 g, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of the mixture per litre of WCO.

[0050] The treatment is typically performed under stirring, and preferably at a temperature comprised between 30 °C and 60 °C, more preferably comprised between 35 °C and 55 °C, and still more preferably at a temperature of about 50 °C.

[0051] In an embodiment, before the treatment with the mixture of magnesium silicate and alkali, the WCO is first subjected to centrifugation, to remove possible solid particles suspended therein.

[0052] This centrifugation is typically carried out at speed comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm. The centrifugation may be carried out, for example, at a temperature comprised between 20 °C and 25 °C, and for a time period which can range, for example, from about 15 minutes to about 1h, while these conditions are not critical and may otherwise be adjusted.

[0053] Once the treatment according to step i) is finished, the treated oil is separated from the adsorbent mixture using any conventional method, for example, by decantation or centrifugation.

[0054] The obtained oil is then subjected of the second step of the process.Second step: treatment with zeolite

[0055] The oil recovered after the first step, is subjected to a treatment with a zeolite.

[0056] Zeolites are a well-known group of substances, which are crystalline microporous hydrated aluminosilicates of alkali and alkaline earth metals. Primarily, zeolites are built from [SiO 4 ] 4-< and [AlO 4 ] 5-< tetrahedral which are infinitely extended in a three dimensional network that is linked together by a shared oxygen atom (see, for example, Payra et al., Zeolites: A primer, in: Handbook of Zeolite Science and Technology, Auerbach SM, Carrado KA and Dutta PK editors, Marcel Dekker, 2003, Chapter 1 or Mgbemere et al., Zeolite Synthesis, Characterization and Application Areas: A Review, Int. Res. J. Environ. Sci., 2017, 6(10): 1-15).

[0057] There are different types zeolites, either natural or synthetic, and they can be identified, for example, by their Silicon-Aluminium (Si / AI) mole ratio, with the lowest value being 1 for zeolite type A. Examples of zeolite include, but are not limited to, zeolite naturally occurring minerals such as analcite, chabazite, clinoptilotine, erionite, heulandite, mordenite, natrolite, stilbite, or thomsonite, among other, or synthetic zeolites, such as zeolites type A, X, Y, L, F or W, ZSM-5, MCM-22, among many other, and that are well-known for the skilled in the art.

[0058] They are all suitable to be used in the process according to the present invention and are widely commercially available.

[0059] In an embodiment, the zeolite is a naturally occurring zeolite.

[0060] In another embodiment, the zeolite is a synthetic zeolite A. In a particular embodiment, the zeolite is zeolite A.

[0061] In a more particular embodiment, zeolite is zeolite 4A, which is the sodium form of zeolite A. The chemical formula of zeolite 4A can be represented as Na 12 (AlO 2 ) 12 (SiO 2 ) 12 ·27 H 2 O.

[0062] The zeolite treatment, according to step ii) is typically performed in a suitable vessel provided with stirring means, where the oil obtained in the previous step and the zeolite are mixed. The mixture is typically vigorously stirred, and then allowed to stand, preferably under stirring, for a certain period of time, which is not critical, and preferably is of at least 12h, preferably at least 24h. The mixture may be allowed to stand for a longer period of time, such as one week, or more.

[0063] The treatment with zeolite is generally performed at room temperature, i.e., from about 20 °C to about 25 °C.

[0064] The amount of zeolite used in this step generally ranges from about 5 g to about 100 g of zeolite per litre of oil, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of zeolite per litre of oil.

[0065] After the treatment according to step ii), the oil is separated from the zeolites by conventional process, preferably by centrifugation.

[0066] The centrifugation can be performed at a speed typically comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm.

[0067] The centrifugation may be carried out, for example, at a temperature comprised between 20 °C and 25 °C, and for a time period which can range, for example, from about 15 minutes to about 1 hour, while these conditions are not critical and may otherwise be adjusted.Purified oil obtained with the process according to the invention

[0068] Another aspect of the invention is the purified oil obtainable according to the process of the present invention. The terms "purified oil" or "recycled oil" are used herein interchangeably and both designate the oil obtainable with the purification process according to the invention.

[0069] As discussed in Example 2, the purified waste cooking oil according to the present invention has optimal properties to be used, for example, as a lubricant.

[0070] In particular, it is noted that the acidity index is outstandingly reduced, from 3.1 mg KOH / g of oil to 0.27 mg KOH / g of oil. The high acidity index in WCOs is mainly due to the presence of free fatty acids, which appear as a consequence of the hydrolysis of the triglycerides during the frying process. Said high concentration of fatty acids is an obstacle for the use of unpurified WCO as lubricants, in particular, for the lubrication of metallic pieces, because the high acid content may increase the risk of corrosion.

[0071] The purified oil according to the present invention has, therefore, lower acidity index than the original WCO, and is typically comprised between 0.1 and 1, preferably comprised between 0.1 and 0.5, expressed as mg of KOH per g of oil.

[0072] On the other hand, it was also found that the anti-wear performance of the purified oil is optimal for its use as lubricant, with values in the Brugger test which are similar to rapeseed, soya or castor oils.

[0073] Additionally, the treated oil has reduced volatiles compared to the original WCO and has therefore also optimal smell properties, which make it particularly suitable for consumer applications.

[0074] Another aspect of the invention is the use of said purified oil as lubricant. It is suitable for any lubricating use, for example, for industrial lubrication, including food production machinery or agricultural machinery, for lubrication of gardening equipment, including chainsaws and cutters, or for the lubrication of bicycle chains, among many other lubricating uses.

[0075] In an embodiment, the use is for the lubrication of bicycle chains.

[0076] Furthermore, the purified oil obtained according to the present invention can also be used for the preparation of coolant liquids, in particular, coolant liquids for batteries.

[0077] Another aspect of the invention is, therefore, the use of said purified oil for the preparation of a coolant liquid. One particular use is for cooling of batteries.Lubricant composition

[0078] Another aspect of the present invention is a lubricant composition comprising the purified oil obtained according to the process of the present invention.

[0079] The lubricant according to the present invention is a "biolubricant" (or bio-based lubricant), as it is derived from biodegradable and renewable resources, as are vegetable oils. Furthermore, it has the advantage of being mainly based on a recycled waste vegetable oil.

[0080] The lubricant composition according to the present invention comprises at least 50% by weight of the purified oil, preferably from 50% to 95%, more preferably from 60% to 85%, and still more preferably comprises from 65% to 75% by weight of the purified oil.

[0081] Generally, the lubricant composition according to the present invention additionally comprises another oil, typically, a vegetable oil, mixed with the purified oil. Said vegetable oil is, for example, castor oil, soybean oil, sunflower oil, or rapeseed oil, among others, or mixtures thereof. Said vegetable oils may be available in different grades, namely, with some variations in their fatty acid content, depending on the different sources, and all of them are included within the scope of the invention.

[0082] Preferably, the additional vegetable oil is selected from soybean oil and castor oil, and more preferably is castor oil.

[0083] The mixture of the purified oil and the additional vegetable oil constitutes the base oil of the lubricant composition.

[0084] In an embodiment, the lubricant composition comprises: between 85 wt% and 99.05 wt% of a base oil; and between 0.5 wt% and 15 wt% of an additive. wherein the base oil is a mixture of the purified oil and a vegetable oil, as hereinabove described.

[0085] In a particular embodiment, the lubricant composition consists of the above defined ingredients.

[0086] The weight ratio purified WCO:vegetable oil in the base oil generally ranges from about 50:50 to about 90:10, preferably from about 60:40 to about 80:20, and more preferably from about 65:35 to about 80:20.

[0087] In another embodiment, the lubricant composition is made up of said base oil, without additional components.

[0088] Preferably, the lubricant composition of the invention also contains from about 0.5 to about 15 wt% of one or more additives, more preferably from about 1 wt% to about 12 wt%, still more preferably from about 2 wt% to about 10 wt%, and still more preferably from about 4 wt% to about 6 wt%, relative to the total weight of the lubricant composition.

[0089] The additive may be selected from an antioxidant, a corrosion inhibitor, an anti-wear additive, a viscosity improver, a pour point depressant and mixtures thereof, and preferably is selected from an antioxidant, a corrosion inhibitor, an anti-wear agent, and mixtures thereof.

[0090] The additives used in the composition according to the present invention are environmentally acceptable, typically, either they natural substances or they are substances complying with EU Ecolabel criteria, namely, within the limits stated in the LUSC-List (Lubricant Substance Classification List).

[0091] The purpose of antioxidant additives is to delay or prevent the oxidation process by protecting the lubricant from oxidative degradation. Suitable antioxidant additives may be of natural origin, such as tocopherols, esters of gallic acid, citric acid, citric acid derivatives, L-ascorbic acid or ascorbyl palmitate, among others. Antioxidants may be also synthetic, for example, bis(disubstituted dithiocarbamates), particularly methylene bis(dialkyldithiocarbamates); dithiocarbamate esters; sterically hindered phenols, such as butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, or thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], among many others; or aromatic amines, in particular, dialkylated diphenylamines such as butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, or dioctyldiphenylamine, among others, or alkylated phenyl alpha naphthylamines. Any one of them, among others, may be suitable for being added to the lubricant composition according to the present invention.

[0092] In an embodiment of the invention, the antioxidant is selected from the group consisting of butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol; 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, dioctyldiphenylamine and mixtures thereof.

[0093] When there is an antioxidant additive it is generally in an amount comprised between about 0.05 wt% and about 5 wt%, preferably comprised between about 0.1 wt% and about 2 wt%, more preferably comprised between about 0.2 wt% and about 1 wt%, and more preferably comprised between about 0.3 wt% and about 0.8 wt%, relative to the total weight of the lubricant composition.

[0094] The purpose of anti-wear additives is to protect materials against wear. There are also many substances disclosed in the art which can be used as anti-wear additives (for example, as disclosed in L.O. Farng, Ashless Anti-wear and Extreme-Pressure Additives, in: Lubricant Additives. Chemistry and Applications, Second Edition, op. cit., Chapter 8, 213-249). Some typical anti-wear additives are, for example, triesters of phosphoric acid or thiophosphoric acid, which may be alkyl esters, aryl esters, or mixed alkyl aryl esters, for example, tricresyl phosphates or trixylenyl phosphates or triphenyl phosphorothionate (TPPT); amine salts of phosphoric acid esters; dithiophosphates; dithiocarbamates, such as methylene bis(dialkyldithiocarbamates); or sulfur additives such as sulfurized olefins, sulfurized esters and sulfurized oils; among others. Some natural substances can also be used as anti-wear additives, for example, polyphenols such as curcumin, xanthophylls, such as astaxanthin, lutein or zeaxanthin, or cashew nut shell liquid (CNSL), among others. Any one of them may be used in the compositions according to the present invention.

[0095] Some preferred anti-wear additives are methylene bis(dialkyldithiocarbamates) and sulfurized fatty acid esters. One particularly preferred anti-wear additive is, for example, methylene bis-dibutyldithiocarbamate.

[0096] When there is an anti-wear additive in the formulation, it is generally in an amount comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.5 wt% and about 6 wt%, and more preferably between about 1 wt% and 5 wt%, relative to the total weight of the lubricant composition.

[0097] The purpose of corrosion inhibitors is to avoid rust in the metallic components in contact with the lubricant composition. There are many substances disclosed in the art which can be used as corrosion inhibitors (see for example Z. Tang, A review of corrosion inhibitors for rust preventive fluids, Curr. Opin. Solid State Mater. Sci., 2019, 23, 100759 or in the book chapter M.T. Costello, Corrosion Inhibitors and Rust Preventives, in: Lubricant Additives. Chemistry and Applications, Second Edition, L.R. Rudnick Ed., CRC Press, 2009, Chapter 17, 421-444). Some suitable corrosion inhibitors are, for example, dicarboxylates, in particular, succinic acid derivatives; alkyl amines; amino acids; sulfonic acid esters; derivatives of some nitrogen containing heterocycles, for example, imidazoline, thiazole, thiadiazole or benzothiazole, such as dimercaptothiadiazoles or mercaptobenzothiazole derivatives; among many others. Also many natural substances can be used as corrosion inhibitors, for example, curcumin, linseed oil, limonene or rosemary oil, for example, among many others.

[0098] A preferred corrosion inhibitors is, for example, a sulfonic acid ester.

[0099] When there is a corrosion inhibitor in the formulation, it is generally in an amount comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.2 wt% and about 6 wt%, and more preferably comprised between about 0.5 wt% and about 2 wt%, relative to the total weight of the lubricant composition. The most suitable concentration, however, varies depending on the specific substance used, and will be easily adjusted by the skilled in the art.

[0100] Other possible additives of the lubricant composition are viscosity improvers and pour point depressants.

[0101] Viscosity improvers are typically thickeners, used to adjust the viscosity of the composition. Typical viscosity improvers are, for example, esters of polymethacrylic acid with hydrocarbon side chains of different lengths. Pour point depressants are polymeric molecules that can be added to improve the flow properties of the biolubricant. Examples of pour point depressants are acrylates, alkylated styrenes, alpha olefins, ethylene / vinyl acetates, methacrylates, styrene / maleic anhydrides, and vinyl acetate / fumarates (see, for example, B.G. Kinker, Polymethacrylate viscosity modifiers and pour point depressants, in: Lubricant Additives. Chemistry and Applications, Second Edition, op. cit., Chapter 11, 315-337).

[0102] The base oil according to the present invention, i.e., consisting of a mixture of the purified WCO and a vegetable oil, has suitable properties, in particular, optimal viscosity and pour point so, in general, viscosity improvers or pour point depressants are not necessary.

[0103] In an embodiment, the additive is selected from an antioxidant, a corrosion inhibitor, an anti-wear additive and mixtures thereof.

[0104] In a particular embodiment, the lubricant composition composition consists of: between 92 wt% and 96 wt% of a base oil consisting of a mixture of the purified oil of the invention and castor oil, wherein the weight ratio purified oil:castor oil is comprised between 65:35 and 80:20; and between 4 wt% and 8 wt% of an additive consisting of: ∘ between 0.25 wt% and 1.5 wt% of an antioxidant; ∘ between 0.5 wt% and 2 wt% of a corrosion inhibitor; and ∘ between 3 wt% and 6 wt% of an anti-wear agent.

[0105] In the above composition, it is understood that the sum of the percentages of antioxidant, corrosion inhibitor and anti-wear agent is in the range 4-8 wt%.

[0106] In the practice, some additives may advantageously perform more than one function. As used herein, the terms anti-wear additive, antioxidant, corrosion inhibitor, viscosity improver or pour point depressant are meant to include also those substances having additional functions.

[0107] For example, some additives simultaneously perform an antioxidant and anti-wear function (anti-wear / antioxidant additive).

[0108] The lubricant composition can be prepared according to conventional mixing processes, typically, by first mixing the two components of the base oil, i.e., the purified oil and the vegetable oil, to obtain a homogeneous mixture, and then adding the additives under stirring. Other mixing order of the components is also suitable.Use of the lubricant composition

[0109] Another aspect of the invention is the use of the lubricant composition of the invention for the lubrication of mechanical devices.

[0110] As shown in Example 2, the purified oil according to the present invention has optimal anti-wear and anti-corrosive efficacy, which make it suitable for lubrication.

[0111] The biolubricant composition of the present invention, containing said purified oil, can be used for any lubricating application, either for industrial machinery or for any other purpose. For example, for industrial lubrication, including food production machinery or agricultural machinery, for lubrication of gardening equipment, including chainsaws and cutters, or for the lubrication of bicycle or motorbike chains, among many other lubricating uses.

[0112] One particular application is for the lubrication of chains, particularly, bicycle or motorbike chains. As shown in the tests performed in Example 5, the lubricant composition of the present invention shows excellent performance in several tests particularly intended to assess its suitability for this use.

[0113] For example, the anti-wear effect was assessed in a test performed with bike chains in use, and the lubricant composition according to the invention showed the best results, compared to several commercial lubricants.

[0114] The effect of the lubricant on the bicycle speed was also assessed and the lubricant of the invention was found either similar or superior to the commercial lubricants used as comparators.

[0115] The durability of the effect of the lubricant, when applied to bicycle chains, was also assessed by measuring the increase in the noise of the rotating chain as an indicator of lubricant loss of efficacy. Again, the the lubricant according to the invention was either similar or superior to the comparators.

[0116] Another aspect assessed in Example 5 is dirt repelling efficiency. This effect is important for lubricants used in outdoor applications, such biking, which involve contact with the environment, to avoid getting contaminated with dust or other particles present in the environment.

[0117] Lubricant splatter was also assessed, as a measure of losses of the product, ending up in the environment. The composition according to the invention showed moderate spatter, similar to other commercial lubricants.

[0118] Finally, the effect of the temperature on lubrication performance was also assessed, and the composition according to the invention showed only very small changes in its anti-wear performance with the temperature.

[0119] Therefore, the properties found for the biolubricant composition of the present invention make it particularly suitable, for chain lubrication, either in bicycles or in any other transmission chain in a variety of machines.

[0120] A particular aspect of the invention is the use of the lubricant composition of the invention for the lubrication of bicycle chains. It includes typically mechanical bicycles and electric bicycles (e-bikes), and also motorcycles (or motorbikes).

[0121] Another aspect of the invention is the use of the lubricant composition of the invention for the lubrication of transmission chains in industrial machinery of any kind.

[0122] Furthermore, the lubricant composition is environmentally friendly as it is composed of substantially biodegradable components, which are nontoxic to the environment, and mainly based on renewable sources. It makes also the composition of the invention particularly suited for the lubrication of bicycle or motorbike chains, as part of lubricant may be released to the environment during its use.

[0123] The present invention may be defined by the following embodiments: 1.- Process for purifying a waste cooking oil comprising the following two consecutive steps: i) treatment of the waste cooking oil with a mixture of magnesium silicate and an alkali; and ii) treatment of the product obtained after step i) with a zeolite. 2.- Process according to embodiment 1, wherein the waste cooking oil has the following fatty acid composition: oleic acid (C18:1): from 14% to 83%; linoleic acid (C18:2): from 3% to 74%; palmitic acid (C16:0): from 5% to 20%; and stearic acid (C18:0): from 0.5% to 7%. 3.- Process according to embodiments 1 or 2, wherein the waste cooking oil has iodine index value comprised between 75 and 145. 4.- Process according to any one of embodiments 1 to 3, wherein the waste cooking oil has an acidity index comprised between 1.5 and 6. 5.- Process according to any one of embodiments 1 to 4, wherein the magnesium silicate is selected from a naturally occurring magnesium silicate and a synthetic magnesium silicate. 6.- Process according to embodiment 5, wherein magnesium silicate is synthetic magnesium silicate. 7.- Process according to embodiment 6, wherein magnesium silicate has average particle size ranging from about 20 µm to about 200 µm. 8.- Process according to embodiments 6 or 7, wherein magnesium silicate has surface area ranging from about 50 m 2< / g to about 700 m 2< / g. 9.- Process according to any one of embodiments 6 to 8, wherein magnesium silicate has bulk density ranging from about 0.25 g / ml to about 0.60 g / ml. 10.- Process according to any one of embodiments 1 to 9, wherein the alkali in step i) is selected from calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, and mixtures thereof. 11.- Process according to embodiment 10, wherein the alkali is calcium hydroxide. 12.- Process according to any one of embodiments 1 to 11, wherein the weight ratio magnesium silicate:alkali is comprised between 20:1 and 1:1, preferably comprised between 15:1 and 4:1, more preferably comprised between 10:1 and 8:1, and more preferably is about 9:1. 13.- Process according to any one of embodiments 1 to 12, wherein the amount of the mixture magnesium silicate-alkali used in step i) ranges from about 5 g to about 100 g, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of the mixture per litre of waste cooking oil. 14.- Process according to anyone of embodiments 1 to 13, wherein the waste cooking oil is centrifugated before step i). 15.- Process according to embodiment 14, wherein the centrifugation is carried out at speed comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm. 16.- Process according to any one of embodiments 1 to 15, wherein in step ii) the zeolite is either a naturally occurring zeolite or a synthetic zeolite. 17.- Process according to embodiment 16, wherein the zeolite is zeolite A, preferably is zeolite 4A. 18.- Process according to any one of embodiments 1 to 17, wherein the amount of zeolite used in step ii) ranges from about 5 g to about 100 g, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of zeolite per litre of oil. 19.- Process according to any one of embodiments 1 to 18, wherein the purified oil obtained after step ii) is centrifuged. 20.- Process according to embodiment 19, wherein the centrifugation is carried out at speed comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm. 21.- Purified oil obtainable with the process according to any one of embodiments 1 to 20. 22.- Purified oil according to embodiment 21, wherein it has an acidity index comprised between 0.1 and 1, preferably comprised between 0.1 and 0.5. 23.- Use of the purified oil according to embodiments 21 or 22 as lubricant. 24.- Use of the purified oil according to embodiments 21 or 22 as cooling liquid, preferably as cooling liquid for batteries. 25.- Cooling liquid comprising the purified oil according to embodiments 21 or 22. 26.- Cooling liquid according to embodiment 25, wherein the cooling liquid is for cooling batteries. 27.- Lubricant composition comprising the purified oil according to embodiments 21 or 22. 28.- The lubricant composition according to embodiment 27, wherein the lubricant composition comprises: between 85 wt% and 99.05 wt% of a base oil consisting of a mixture of the purified oil of embodiments 21 or 22 and a vegetable oil; and between 0.5 wt% and 15 wt% of an additive. 29.- Lubricant composition according to embodiment 27, wherein the lubricant composition consists of: between 85 wt% and 99.05 wt% of a base oil consisting of a mixture of the purified oil of embodiments 21 or 22 and a vegetable oil; and between 0.5 wt% and 15 wt% of an additive. 30.- Lubricant composition according to embodiments 28 or 29, wherein the vegetable oil in the base oil is selected from the group consisting of castor oil, soybean oil, sunflower oil, rapeseed oil, and mixtures thereof. 31.- Lubricant composition according to embodiment 30, wherein the vegetable oil is castor oil. 32.- Lubricant composition according to any one of embodiments 28 to 31, wherein the weight ratio purified oil:vegetable oil in the base oil ranges from about 50:50 to about 90:10, preferably from about 60:40 to about 80:20, and more preferably from about 65:35 to about 80:20. 33.- Lubricant composition according to any one of embodiments 28 to 32, wherein the composition comprises or consists of: between 90 wt% and 98 wt%, and preferably between 92 wt% and 96 wt% of the base oil; and between 2 wt% and 10 wt%, and preferably between 4 wt% and 6 wt% of the additive. 34.- Lubricant composition according to any one of embodiments 28 to 33, wherein the additive is selected from the group consisting of an antioxidant, an anti-wear agent, a corrosion inhibitor and mixtures thereof. 35.- The lubricant composition according to embodiment 34, wherein the additive comprises an antioxidant, which is preferably selected from a tocopherol, an ester of gallic acid, citric acid or citric acid derivatives, L-ascorbic acid, ascorbyl palmitate, a methylene bis(dialkyldithiocarbamate), a dithiocarbamate ester, butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, dioctyldiphenylamine, and mixtures thereof. 36.- The lubricant composition according to embodiment 35, wherein the antioxidant is selected from the group consisting of butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol; 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, dioctyldiphenylamine and mixtures thereof. 37.- The lubricant composition according to embodiments 35 or 36, wherein the amount of antioxidant is comprised between about 0.05 wt% and about 5 wt%, preferably comprised between about 0.1 wt% and about 2 wt%, more preferably comprised between about 0.2 wt% and about 1 wt%, and more preferably comprised between about 0.3 wt% and about 0.8 wt%, relative to the total weight of the lubricant composition. 38.- The lubricant composition according to any one of embodiments 34 to 37, wherein the additive comprises an anti-wear agent, which is preferably selected from a triester of phosphoric acid or of thiophosphoric acid, such as a tricresyl phosphate, a trixylenyl phosphate, or a triphenyl phosphorothionate (TPPT); an amine salt of phosphoric acid esters; a dithiophosphate; a dithiocarbamate, such as a methylene bis(dialkyldithiocarbamate); a sulfur additive such as a sulfurized olefin, a sulfurized ester or a sulfurized oil; a polyphenol such as curcumin; a xanthophyll, such as astaxanthin, lutein or zeaxanthin; cashew nut shell liquid (CNSL), and mixtures thereof. 39.- The lubricant composition according to embodiment 38, wherein the anti-wear agent is selected from a methylene bis(dialkyldithiocarbamate) and a sulfurized fatty acid ester, preferably is a methylene bis(dialkyldithiocarbamate), and more preferably is methylene bis-dibutyldithiocarbamate. 40.- The lubricant composition according to embodiments 38 or 39, wherein the amount of anti-wear agent is comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.5 wt% and about 6 wt%, and more preferably between about 1 wt% and 5 wt%, relative to the total weight of the lubricant composition 41.- The lubricant composition according to any one of embodiments 34 to 40, wherein the composition comprises a corrosion inhibitor, which is preferably selected from a succinic acid derivative; an alkyl amine; an amino acid; a sulfonic acid ester; a derivative a nitrogen containing heterocycle, such as a dimercaptothiadiazole or mercaptobenzothiazole derivative; curcumin; linseed oil; limonene and rosemary oil. 42.- The lubricant composition according to embodiment 41, wherein the corrosion inhibitor is a sulfonic acid ester. 43.- The lubricant composition according to embodiments 41 or 42, wherein the amount of corrosion inhibitor is comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.2 wt% and about 6 wt%, and more preferably comprised between about 0.5 wt% and about 2 wt%, relative to the total weight of the lubricant composition. 44.- Lubricant composition according to any one of embodiments 27 to 43, wherein the lubricant composition consists of: between 92 wt% and 96 wt% of a base oil consisting of a mixture of the purified oil of embodiments 21 or 22 and castor oil, wherein the weight ratio purified oil:castor oil is comprised between 65:35 and 80:20; and between 4 wt% and 8 wt% of an additive consisting of: ∘ between 0.25 wt% and 1.5 wt% of an antioxidant; ∘ between 0.5 wt% and 2 wt% of a corrosion inhibitor; and ∘ between 3 wt% and 6 wt% of an anti-wear agent. 45.- Use of the lubricant composition according to any one of embodiments 27 to 44 for the lubrication of mechanical devices. 46.- Use according to embodiment 45, for the lubrication of bicycle chains, electric bicycle chains or motorbike chains. 45.- Use according to embodiment 45, for the lubrication of transmission chains in industrial machinery. 47.- Use according to embodiment 45, for the lubrication of chainsaws or garden cutters. Examples Example 1.- Purification of a waste cooking oil

[0124] A waste cooking oil was obtained from an authorized recycling company (Ecovirea, Spain).

[0125] The sample was analysed to determine the fatty acid content. The results are shown in Table 1 below. TABLE 1Fatty acidPercentageOleic acid (C18:1)76.71%Linoleic acid (C18:2)12.25%Palmitic acid (C16:0)5.01%Stearic acid (C18:0)3.50%Behenic acid (C22:0)0.94%Lignoceric acid (C24:0)0.35%Other1.24%

[0126] The acidity index of this oil was 2.9 (expressed as mg of KOH required to neutralize the acidic constituents in 1 g of oil) and the iodine index was 83.5 (expressed as g iodine per 100 g of oil).

[0127] A sample of this WCO was centrifuged at 5100 r.p.m. at 20 °C, during 20 minutes. The centrifuged oil was separated from the precipitated solids by decantation. The amount of solids removed amounted to 2.3% by weight relative to the weight of initial untreated WCO.

[0128] After centrifugation, the acidity index of the oil was 3.1.

[0129] 1 litre of the centrifuged oil was then treated with 20 g a mixture of magnesium silicate (Florisil ®< ) and calcium hydroxide in a weight ratio magnesium silicate to calcium hydroxide of 9:1. The treatment was performed under stirring, at a temperature of 50 °C, for 1.5h. After the treatment, the oil was separated from the solid mixture by decantation.

[0130] To 1 litre of the oil obtained after the above treatment, 20 g of zeolite (Zeolite ZC2 (98% of zeolite 4A), IQE Group, Spain) were added and the mixture was vigorously stirred and then left to stand for 24h.

[0131] After that, the mixture was centrifuged at 5100 r.p.m. at 20 °C, during 20 minutes and the oil was separated by decantation.

[0132] The obtained product was a clear, yellowish oil.Example 2.- Properties of the purified oil

[0133] Some characteristics of the purified oil obtained in Example 1 were analysed.Stability

[0134] A stability study was carried out for a week at different temperatures (5°C, room temperature and 40°C). The purified oil of Example 1 remained clear in all tested conditions, without any turbidity or precipitation detected.Acidity

[0135] The acidity index of the treated oil was 0.27, therefore showing a substantial reduction compared value before the treatment (3.1).Volatiles

[0136] Headspace gas chromatography with flame ionization detection (HS-GC-FID) was used to assess the effect of treatment on the volatile compounds generated by the oil, which have an effect on the smell of the product.

[0137] The oil was introduced into a chromatography vial and a syringe sample was taken from the gas phase, to analyse the volatile compounds emitted by the oil.

[0138] The analytical conditions were as follows: Headspace conditions Vial temperature60 °CSample loop70 °CTransfer line80 °CVial heating time20 minGC-FID conditions ColumnDB-WAX UI: high-polarity polyethylene glycol column (30m x 0.250mm x 0.25 µm)Constant flow1 ml / minTemperature program50°C (hold 3 min) to 200 °C at 12°C / min (hold 4 min)Injector temperature250°CDetector temperature250°CSplit modesplitlessCarrier gasHelium

[0139] The samples were prepared by weighing 2 grams of oil (in triplicate) into 20 mL vials. The vials were closed and inserted into the headspace module. A blank sample, i.e., an empty vial, was also analysed to confirm that the peaks found corresponded to substances released from the oil. The samples tested were the original WCO (A) and the purified WCO (B), as described in Example 1. The volatiles reduction was calculated as the difference between the sum of peak areas (volatiles) in sample WCO (B) compared to WCO (A). 45.4% reduction of volatiles was found.Smell sensory analysis

[0140] On the other hand, a sensory analysis with a panel of 5 volunteers was performed, in order to assess the perception of the smell generated by the purified oil.

[0141] For performing this analysis, samples in 5 mL vials were provided to the volunteers, with an opening of 4 mm diameter.

[0142] The results are summarized in the Table 2, where the values shown are the average for all the volunteers: TABLE 2Smell characteristics Results Intensity (1 to 10)4.4Synthetic - natural (-1 to 1)0.2Acceptability (-5 to 5)-0.6Suitability for use (-5 to 5)1.4 Anti-wear performance

[0143] The anti-wear performance of the obtained oil was measured, in order to assess its suitability for use as biolubricant.

[0144] A Brugger test machine was used, which is a standardized method (DIN 51347 parts 1 and 2) based on the friction conditions in the contact zone between a friction ring and a test cylinder. All tests were conducted with a rotating 25 mm ring and a fixed test cylinder of 18 mm x 18 mm. The tested lubricant was applied on the surface of the fixed test cylinder, which was then pressed against the ring by applying a normal force of 400 N and the ring was allowed to rotate during 30 seconds. After that, the elliptical wear scar produced on the roller's surface was measured. The two diameters (a and b) of the ellipse were used to calculate the Brugger value (N / mm 2< ) through the formula: Brugger value N mm 2 = 4 × 400 a × b × π

[0145] For each test, approximately 5 mL of the oil sample were placed on the surface of the fixed test cylinder. For each sample, the procedure was repeated five times and the mean value was calculated. The higher the Brugger value the better anti-wear capacity.

[0146] The samples tested were the purified WCO oil obtained in Example 1, according to the present invention. Some vegetable oils were also tested, for comparative purposes. The results are shown in Table 3. TABLE 3Sample Brugger value (N / mm 2< ) Example 135.79Soya oil37.27Rapeseed oil36.64Sunflower oil29.12Castor oil44.10 Anti-corrosive properties

[0147] In order to assess anti-corrosive properties on steel of the purified oil, a test based on ASTM D665 was performed.

[0148] The procedure comprised the following steps: 1. A mixture was prepared with 25 mL of the tested oil and 5 mL of tap water. 2. The mixture was mechanically stirred at 1200 rpm and heated to 60 °C. 3. A steel plate was cleaned with hexane to eliminate any particle on the surface. 4. Half of the steel panel was submerged into the above mixture, maintaining the temperature and stirring conditions. 5. After 30 minutes the steel panel was extracted from the mixture and was inserted into a jar with a solution of 2g of NaCl in 100 mL of tap water, and the jar was closed to air. 6. After 24h, the panel was removed from the jar and was placed inside the oven at 80 °C for drying. 7. After 1h of drying, the appearance of corrosion in the panel, namely, in the lower half part of it, was visually evaluated.

[0149] The purified WCO obtained in Example 1 was subjected to this test. The results were satisfactory, and no rust was observed on the steel plate.Example 3.- Lubricant compositions

[0150] Two lubricant compositions (C1 and C2) were prepared by mixing 70 wt% of the purified oil of Example 1 with 30 wt% of either castor oil or soya oil.

[0151] The anti-wear and anti-corrosive properties of these oil mixtures were assessed, using analogous tests as described in Example 2.

[0152] The results are shown in Table 4: TABLE 4Sample Example 1 (wt%) Castor oil (wt%) Soya oil (wt%) Anti-wear (N / mm 2< ) Corrosion C17030--40.56ModerateC270--3034.99No corrosion Example 4.- Lubricant compositions

[0153] A lubricant composition according to the invention (composition C3) was prepared with the ingredients listed in the following table: TABLE 5Ingredients Function Amount (wt%) Purified WCO (Example 1)Base oil70.07Castor oilBase oil24.50Additin ®< RC6430Anti-wear additive4.00Additin ®< RC4810Corrosion inhibitor0.93Irganox ®< 67Antioxidant0.25Irganox ®< 135Antioxidant0.25

[0154] Additin ®< RC6430 is a commercial anti-wear additive, consisting of methylene bis-dibutyldithiocarbamate.

[0155] Additin ®< RC4810 is a commercial corrosion inhibitor additive, which is a sulfonic acid ester.

[0156] Irganox ®< 67 is a commercial antioxidant, consisting of bis(nonylphenyl)amine.

[0157] Irganox ®< 135 is a commercial antioxidant, consisting of consisting of octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0158] The two base oil components were first mixed and the additives were next added and thoroughly mixed. The formulation was a brownish, clear oil.

[0159] The lubricant composition was subjected to stability assays, using samples of 100 mL into closed clear glass bottles, and allowing to stay for 4 weeks at the following temperatures: 5 °C, room temperature and 37 °C.

[0160] The composition was found to be stable during the 4-week period of the assay, at all the assayed temperatures. The formulation remained clear, without any turbidity or precipitate.

[0161] The anti-wear performance of this composition was 76.23 N / mm 2< , according to the Brugger test, using analogous conditions as described in Example 2.

[0162] Furthermore, the anti-corrosive efficiency was optimal, and no significant rust was detected, following analogous method as described in Example 2.Example 5.- Comparative lubricant efficiency of the lubricant composition

[0163] The effectiveness of the lubricant composition of Example 4 (composition C3) for bicycle chain lubrication was compared to 6 commercial lubricant compositions (A to F), according to different tests, as described below.

[0164] The tests on bicycle chain wear, bicycle speed, durability and lubricant splatter (sections 5.1 to 5.4) were performed using a bicycle prototype.

[0165] Said bicycle prototype was designed to simulate the behaviour of the lubricant in a realistic environment. The prototype consisted of two gears connected by a bicycle chain and a motor to move one of the gears (Figure 1).

[0166] The prototype was provided with the following sensors: infrared sensor for recording the temperature on the chain surface, sound sensor for recording the noise emitted by the chain, and speed sensor for recording speed and number of rotations of the chain.

[0167] For each lubricant analysed using this prototype, a new chain (NX Eagle Chain, model CN-EAGL-NX-A1, principally made of low-carbon steel) was fitted to the prototype and a controlled amount of lubricant (0.2- 0.4 mL) was applied to each spur in the chain. The motor was set to a constant power output of 0.18kW throughout the 24 hours of continuous running.5. 1. Bicycle chain wear

[0168] To assess the bicycle chain wear after continued use, the distance between the chain links in the bicycle prototype was measured with a caliper. The following table shows the results of the test, after 24 hours of use, wherein the chain wear is calculated as the difference between the initial and final distance between the chain links. TABLE 6Lubricant tested Chain wear after 24h of use (mm) Composition C3 (Example 4)0.12Comparative A0.16Comparative B0.15Comparative C0.13Comparative D0.14Comparative E0.14Comparative F0.13

[0169] It was found that the lubricant composition according to the invention showed best anti-wear results.5.2. Effect on bicycle speed

[0170] The effect of the different lubricants on the bicycle speed along a period of 24h was assessed using the bicycle prototype. The results of the test are shown in Figure 2. The y-axis represents the speed (Km / h) and the x-axis represents the time (h).

[0171] It can be observed that the behaviour of the lubricant of the invention (C3) was similar to the comparatives C, D, E and F, while commercial products A and B showed worse performance.5.3. Durability of the lubricant

[0172] The durability of the lubricant was assessed using a sensorial test, consisting in measuring the noise of the rotating chain along time, based on the fact that when a lubricant loses efficiency, the noise of the chain increases. A noise sensor was used. The results are shown in Figure 3, where y-axis shows the noise recorded in decibels (dB) and the x-axis shows the time, in hours.

[0173] It was found that the lubricant composition according to the invention showed similar behaviour in this test as comparators B, D and E, and better results than comparators A, C and F.5.4. Lubricant splatter

[0174] This test consisted in the visual characterization of splatter (excess lubricant) due to unadhered lubricant, which would end up in the environment. A sheet of white paper was placed next to the chain, and the splatters after 5 minutes, 15 minutes and 5 hours were observed. For each test, a punctuation from 1 to 5 was given, where 5 means the best results (virtually no splashes) and 1 means worse results (more splashes).

[0175] The results are summarized in Table 7. TABLE 7Lubricant tested Spatter (1 to 5) Composition C3 (Example 4)3Comparative A2Comparative B5Comparative C2Comparative D4Comparative E3Comparative F1

[0176] It can be observed that, in terms of slatter, the lubricant composition according to the invention had satisfactory behaviour, similar the commercial formulas. In particular, it showed the behaviour as comparative E, better than comparatives A, C and F, and more splatter than comparatives B and D.5.5. Dirt repelling

[0177] A dirt repelling test was performed, to assess the performance of the lubricant for dirt repelling during use under adverse weather conditions, of rain and mud.

[0178] For this test, a standardized sand mixture was prepared (mixture of sand plant fertilizer & coarse aggregate, with a weight relation 1:10), and the mixture was filtered through a stainless-steel sieve of 0.5 mm mesh.

[0179] Steel panels (90 x 50 x 1 mm) were used. The panels were cleaned with hexane before the test, and each panel was weighed before lubricant application. In each panel a specific area was delimited by drawing two parallel lines, and 4 to 6 drops of each tested lubricant was applied using a pipette and spread in order to cover all the surface marked in the panel. The excess of lubricant was drained with paper by capillarity. After lubricant application, the panels were again weighed. Then sand was then applied using a spray gun controlling the pressure at, 2, 2.5 and 3 atm. for 3 seconds each application, 3 times for each pressure. After sand application, the panels were again weighed.

[0180] In this way, the weights of (1) the initial panel, (2) the panel plus lubricant, and (3) the panel plus lubricant plus adhered dirt were recorded. The difference between (3) and (2) allowed to measure the dirt adhered. The difference between (2) and (1) allowed to measure the amount of lubricant, to check that comparative amounts were used.

[0181] Each test, for each lubricant, was performed in duplicate, and the average value was calculated.

[0182] The results are shown below in Table 8 TABLE 8Lubricant tested Amount of lubricant (g) Amount of adhered dirt (g) Composition C3 (Example 4)0.0850.025Comparative A0.0650.035Comparative B0.090.015Comparative C0.070.01Comparative D0.090.025Comparative E0.0650.01Comparative F0.070.03

[0183] It can be observed that the dirt repellency of the lubricant composition according to the invention is satisfactory, similar the commercial formulas. In particular, it showed the same dirt repellency value as comparative D, better than comparatives A and F, and slightly worse than comparatives B, C and E.5.5. Change in anti-wear performance with the temperature.

[0184] The anti-wear performance of composition C3, according to the Brugger test, was 76.23 N / mm 2< , as disclosed in Example 4 above. The Brugger test was repeated but by first cooling the composition to 0 °C. There was only a 4% reduction in the anti-wear performance of the composition (to 72.9 N / mm 2< ).

[0185] The same assay was performed with the comparative commercial composition C. In this case, the anti-wear performance at room temperature was 57.67 N / mm 2< , while this value significantly decreased at 0 °C, namely, to 50.12 N / mm 2< (13% reduction).

Examples

example 1

- Purification of a waste cooking oil

[0124]A waste cooking oil was obtained from an authorized recycling company (Ecovirea, Spain).

[0125]The sample was analysed to determine the fatty acid content. The results are shown in Table 1 below.

TABLE 1

Fatty acidPercentage

Oleic acid (C18:1)76.71%

Linoleic acid (C18:2)12.25%

Palmitic acid (C16:0)5.01%

Stearic acid (C18:0)3.50%

Behenic acid (C22:0)0.94%

Lignoceric acid (C24:0)0.35%

Other1.24%

[0126]The acidity index of this oil was 2.9 (expressed as mg of KOH required to neutralize the acidic constituents in 1 g of oil) and the iodine index was 83.5 (expressed as g iodine per 100 g of oil).

[0127]A sample of this WCO was centrifuged at 5100 r.p.m. at 20 °C, during 20 minutes. The centrifuged oil was separated from the precipitated solids by decantation. The amount of solids removed amounted to 2.3% by weight relative to the weight of initial untreated WCO.

[0128]After centrifugation, the acidity index of the oil was 3.1.

[0129]1 litre of th...

example 2

- Properties of the purified oil

[0133]Some characteristics of the purified oil obtained in Example 1 were analysed.

Stability

[0134]A stability study was carried out for a week at different temperatures (5°C, room temperature and 40°C). The purified oil of Example 1 remained clear in all tested conditions, without any turbidity or precipitation detected.

Acidity

[0135]The acidity index of the treated oil was 0.27, therefore showing a substantial reduction compared value before the treatment (3.1).

Volatiles

[0136]Headspace gas chromatography with flame ionization detection (HS-GC-FID) was used to assess the effect of treatment on the volatile compounds generated by the oil, which have an effect on the smell of the product.

[0137]The oil was introduced into a chromatography vial and a syringe sample was taken from the gas phase, to analyse the volatile compounds emitted by the oil.

[0138]The analytical conditions were as follows:

Headspace conditions

Vial temperature60 °C

Sample loop70 °C

Tran...

example 135.79

Example 135.79

Soya oil37.27

Rapeseed oil36.64

Sunflower oil29.12

Castor oil44.10

Anti-corrosive properties

[0147]In order to assess anti-corrosive properties on steel of the purified oil, a test based on ASTM D665 was performed.

[0148]The procedure comprised the following steps:

1. A mixture was prepared with 25 mL of the tested oil and 5 mL of tap water. 2. The mixture was mechanically stirred at 1200 rpm and heated to 60 °C. 3. A steel plate was cleaned with hexane to eliminate any particle on the surface. 4. Half of the steel panel was submerged into the above mixture, maintaining the temperature and stirring conditions. 5. After 30 minutes the steel panel was extracted from the mixture and was inserted into a jar with a solution of 2g of NaCl in 100 mL of tap water, and the jar was closed to air. 6. After 24h, the panel was removed from the jar and was placed inside the oven at 80 °C for drying. 7. After 1h of drying, the appearance of corrosion in the panel, namely, in the...

TECHNICAL FIELD

[0001] The present invention relates to waste recycling, more particularly, to a process for the purification of used frying oils and to the use of the obtained purified oils, in particular, as biolubricants or as cooling liquids.BACKGROUND ART

[0002] The term "waste cooking oils" (WCOs), also known as "used cooking oils" (UCOs) refers to the oily waste material discarded after the repetitive use of vegetable oils for cooking or frying, both at commercial and home settings.

[0003] Waste cooking oils, previously considered as a by-product of food production, are now considered an important raw material for several industries.

[0004] The most common uses of WCOs are direct burning or the synthesis of biofuels. Furthermore, due to the similar properties of WCOs and the original vegetable oils, their possible use to replace vegetable oils in the production of various oleochemicals has been explored, thus providing WCO as a cheap feedstock for preparing, for example, animal feed, green solvents, fermentative products, grease or biolubricants, among other (Foo W.H. et al., Recent advances in the conversion of waste cooking oil into value-added products: A review, Fuel, 2022, 324(Part A), 124539).

[0005] A well-established use of recycled WCOs is the preparation of biolubricants, where WCO is considered a promising alternative to the use of fresh vegetable oils, for example, as disclosed in Joshi et al., Waste cooking oil as promising source for bio lubricants - A review, J. Indian Chem. Soc., 2023, 1000820; or in Li et al., Bio-lubricants derived from waste cooking oil with improved oxidation stability and low-temperature properties, J. Oleo Sci., 2015, 64(4), 367-374, among others.

[0006] However, the use of WCOs as lubricants involves some challenges, as their chemical composition, though similar to their parent fresh oils, differs from them due to the presence of decomposition and leaching products originated by thermal oxidative and hydrolytic reactions occurred during the frying process. Their composition varies depending on the number of frying cycles, frying time, temperature, and the specific vegetable oil. WCOs mainly consist of a mixture of triglycerides with free fatty acids (FFA), di- and mono-glycerides, heterocycles, Maillard reaction products, and metal traces, spices, and other organic molecules originated from pads and food leaching (Mannu et al., Available technologies and materials for waste cooking oil recycling, Processes 2020, 8, 366).

[0007] Therefore, the WCOs need to be subjected to treatment to make them suitable to be used as biolubricants. Most of the disclosures available so far are mainly based on the chemical modification of the WCOs, for example, using esterification, transesterification, epoxidation, or estolide formation reactions, as disclosed in Joshi et al., op.cit.

[0008] Another strategy to improve the performance of WCOs as biolubricants is the use of molecular distillation, as disclosed in Fernandez-Silva et al., Potential valorization of waste cooking oils into sustainable bio-lubricants, Ind. Crops Prod., 2022, 185, 115109.

[0009] The international patent application WO-A-01 / 66679 discloses a process for recycling WCOs comprising the combination of two steps, the first one involving different combinations basic processes such as filtration, centrifugation and adsorption, and the second one involving a chemical transformation of the product obtained in the first step, using transesterification reactions and immobilized enzymes as catalysts. The use of the recycled oil in lubrication compositions is not disclosed.

[0010] The international patent application WO-A-96 / 39044 discloses a process for the treatment of cooking oil or fat, with the purpose of extending the usable life of the oil or fat for cooking, said process involving contacting the cooking oil or fat wit magnesium silicate and at least one alkali material.

[0011] The international patent application WO-A-2014 / 098957 discloses a method for purifying an unrefined edible oil or fat comprising contacting it with an adsorbent material comprising magnesium silicate, preferably in combination with one organic acid, such as citric acid or malic acid. The use of the purified oil for lubrication is not disclosed.

[0012] Therefore, there remains the need to provide improved, economical and simple processes for treating used oils, to make them optimal to be used as biolubricants and, potentially, also for other applications.SUMMARY OF THE INVENTION

[0013] The object of the present invention is a process for treating a waste cooking oil (WCO).

[0014] Another aspect of the invention is the purified WCO obtainable with such process.

[0015] Another aspect of the invention is the use of such purified WCO as biolubricant.

[0016] Another aspect of the invention is the use of such purified WCO as cooling liquid.

[0017] Another aspect of the invention is a biolubricant composition comprising said purified WCO.

[0018] Another aspect of the invention is a cooling liquid composition comprising said purified WCO.DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 shows a picture of the bicycle prototype used in the lubrication performance tests performed in Examples 5.1 to 5.4. Figure 2 is a graphical representation of the results of the comparative test of Example 5.2, where lubricant C3 (according to the invention) was compared to commercial products A to F, with regards to their influence on bicycle speed during a 24h period. The y-axis represents the speed (Km / h) and the x-axis represents the time (h). Figure 3 is a graphical representation of the results of the comparative test of Example 5.3, where lubricant C3 (according to the invention) was compared to commercial products A to F, with regards to their durability, as assessed by measuring the noise of the rotating chain along time. The y-axis represents the the noise (in dB) and the x-axis represents the time (h). DETAILED DESCRIPTION OF THE INVENTION

[0020] The object of the present invention is a process for purifying a waste cooking oil comprising the following two consecutive steps: i) treating the waste cooking oil with a mixture of magnesium silicate and an alkali; and ii) treating the product obtained after step i) with a zeolite.

[0021] The authors of the present invention have developed a particular process for the treatment of waste cooking oils, based on double treatment, first with a mixture of magnesium silicate and an alkali and then with a zeolite, which, surprisingly, is outstandingly effective for purifying the used oil and provides a purified oil with optimal properties to be used as biolubricant and cooling liquid.

[0022] Along the present description, as well as in the claims, singular expressions, generally preceded by the articles "a", "an" or "the", are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0023] The terms "about" or "approximately" referred to amounts, as used herein, are meant to include the exact amount and also a certain deviation around the stated amount, namely of ±5%.

[0024] Unless stated otherwise, the percentages are meant to be by weight (wt% or % w / w).

[0025] The numerical ranges disclosed herein, generally expressed as "from ... to ..." or as "between ... and ...", are meant to include any number falling within the ranges and also the lower and upper limits.Waste cooking oil

[0026] The term "waste cooking oil", generally abbreviated as WCO, is a well-recognized term to designate a vegetable oil material, which has been discarded after the continued use for deep frying, when it is replaced with fresh one. It is a common waste material generated from food industries, restaurants, fast-food establishments and homes.

[0027] The main components of waste cooking oils (WCOs) are triglycerides, as well as diglycerides, monoglycerides and free fatty acids, derived from hydrolysis reactions taking place during frying process.

[0028] They also generally contain volatile compounds (volatile fraction), which are responsible from the intense smell typical of WCOs, and which are typically decomposition compounds originated from the oxidation of triglycerides and from the Maillard process, for example.

[0029] The composition of WCOs is necessarily not uniform, as it depends on the composition of the vegetable oil or oils from which is derived, the number of frying cycles employed, and the specific use made with it.

[0030] WCOs are available from accredited recycling points, where they are collected.

[0031] Regarding the fatty acid composition, the WCO according to the present invention is generally mainly made up of mixtures of olive oil and sunflower oil, in variable proportions. The oil mixture can also contain other vegetable oils, such as rapeseed oil, soybean oil or high oleic sunflower oil, for example.

[0032] Accordingly, the fatty acid composition of the WCO typically used as starting material of the process according to the present invention may be defined as follows: oleic acid (C18:1): from 14% to 83%; linoleic acid (C18:2): from 3% to 74%; palmitic acid (C16:0): from 5% to 20%; and stearic acid (C18:0): from 0.5% to 7%.

[0033] As the skilled in the art can readily understand, depending on the relative proportion of olive oil or sunflower oil in the mixture, the fatty acid composition varies. Thus, when olive oil is the majority component, the content of oleic acid is higher, in accordance with the oleic acid content of olive oil (generally comprised between 55% and 83%), while when sunflower oil is the majority component, the content of linoleic acid is higher, in accordance with the linoleic acid content of sunflower oil (generally comprised between 48% and 74%).

[0034] It is understood that the WCO also contains minor amounts of other fatty acids.

[0035] It is also understood that the fatty acid composition of the WCO, as above defined, means the total fatty acid content, which is mainly in the form of triglycerides, but also occasionally in the form of di- or monoglycerides, or as free fatty acid.

[0036] The iodine index or iodine value is a measure the degree of unsaturation of the fatty acid components of an oil, and is expressed as the mass of iodine in grams that is consumed by 100 grams of the oil. The WCO starting material, according to the present invention has a iodine index value typically ranging from about 75 to about 145, which varies depending on the composition of the vegetable oil mixture, being typically closer to the lower endpoint when olive oil is the major component of the mixture, and closer to the upper endpoint when sunflower oil is the major component, in agreement with the iodine index of olive oil and sunflower oil, which are of about 75-95 and about 110-145, respectively.

[0037] The WCO starting material generally has an acidity index ranging from about 1.5 to about 6. The acidity index of an oil, as is well-known for the expert in the field, is a measure of the content of free fatty acids in said oil, and it is expressed as mg of potassium hydroxide (KOH) required to neutralize the free fatty acids in 1 g of oil.First step: treatment with a mixture of magnesium silicate and an alkali

[0038] The first step of the process according to the present invention comprises treating the WCO with a mixture of magnesium silicate and an alkali.

[0039] The term magnesium silicate, as used herein, means any type of magnesium silicate, either naturally occurring magnesium silicate or synthetic magnesium silicate.

[0040] Naturally occurring magnesium silicate includes, for example, talc or sepiolite, and is generally crystalline.

[0041] Synthetic magnesium silicate is typically prepared by precipitation reaction of a water-soluble silicate, mainly sodium silicate, and a water-soluble magnesium salt such as magnesium chloride, magnesium nitrate or magnesium sulfate. Synthetic magnesium silicate is generally amorphous.

[0042] In an embodiment of the invention, magnesium silicate is synthetic.

[0043] Synthetic magnesium silicate is available as a white powder, having an average particle size typically ranging from about 20 µm to about 200 µm, and / or a surface area generally ranging from about 50 m 2< / g to about 700 m 2< / g and / or a bulk density generally ranging from about 0.25 g / ml to about 0.60 g / ml. Therefore, different types or grades of synthetic magnesium silicate are available, having characteristics within the above defined ranges, and all of them are suitable to be used in the process according to the present invention.

[0044] Synthetic magnesium silicate is commercially available from several suppliers, for example under the trademarks Florisil ®< . Magnesia 430 ®< or Magnesol ®< .

[0045] The alkali used in the first step is preferably selected from calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, and mixtures thereof.

[0046] In an embodiment of the invention, the alkali is calcium hydroxide.

[0047] The weight ratio magnesium silicate:alkali is generally comprised between 20:1 and 1:1, preferably comprised between 15:1 and 4:1, more preferably comprised between 10:1 and 8:1, and more preferably is about 9:1.

[0048] The treatment according to step 1 is typically performed in a suitable vessel provided with stirring and heating means, where the WCO, the magnesium silicate and the alkali are added. The mixture is stirred for a period of time generally ranging from about 15 to 180 minutes, for example.

[0049] The amount of the mixture magnesium silicate-alkali used in this step generally ranges from about 5 g to about 100 g, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of the mixture per litre of WCO.

[0050] The treatment is typically performed under stirring, and preferably at a temperature comprised between 30 °C and 60 °C, more preferably comprised between 35 °C and 55 °C, and still more preferably at a temperature of about 50 °C.

[0051] In an embodiment, before the treatment with the mixture of magnesium silicate and alkali, the WCO is first subjected to centrifugation, to remove possible solid particles suspended therein.

[0052] This centrifugation is typically carried out at speed comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm. The centrifugation may be carried out, for example, at a temperature comprised between 20 °C and 25 °C, and for a time period which can range, for example, from about 15 minutes to about 1h, while these conditions are not critical and may otherwise be adjusted.

[0053] Once the treatment according to step i) is finished, the treated oil is separated from the adsorbent mixture using any conventional method, for example, by decantation or centrifugation.

[0054] The obtained oil is then subjected of the second step of the process.Second step: treatment with zeolite

[0055] The oil recovered after the first step, is subjected to a treatment with a zeolite.

[0056] Zeolites are a well-known group of substances, which are crystalline microporous hydrated aluminosilicates of alkali and alkaline earth metals. Primarily, zeolites are built from [SiO 4 ] 4-< and [AlO 4 ] 5-< tetrahedral which are infinitely extended in a three dimensional network that is linked together by a shared oxygen atom (see, for example, Payra et al., Zeolites: A primer, in: Handbook of Zeolite Science and Technology, Auerbach SM, Carrado KA and Dutta PK editors, Marcel Dekker, 2003, Chapter 1 or Mgbemere et al., Zeolite Synthesis, Characterization and Application Areas: A Review, Int. Res. J. Environ. Sci., 2017, 6(10): 1-15).

[0057] There are different types zeolites, either natural or synthetic, and they can be identified, for example, by their Silicon-Aluminium (Si / AI) mole ratio, with the lowest value being 1 for zeolite type A. Examples of zeolite include, but are not limited to, zeolite naturally occurring minerals such as analcite, chabazite, clinoptilotine, erionite, heulandite, mordenite, natrolite, stilbite, or thomsonite, among other, or synthetic zeolites, such as zeolites type A, X, Y, L, F or W, ZSM-5, MCM-22, among many other, and that are well-known for the skilled in the art.

[0058] They are all suitable to be used in the process according to the present invention and are widely commercially available.

[0059] In an embodiment, the zeolite is a naturally occurring zeolite.

[0060] In another embodiment, the zeolite is a synthetic zeolite A. In a particular embodiment, the zeolite is zeolite A.

[0061] In a more particular embodiment, zeolite is zeolite 4A, which is the sodium form of zeolite A. The chemical formula of zeolite 4A can be represented as Na 12 (AlO 2 ) 12 (SiO 2 ) 12 ·27 H 2 O.

[0062] The zeolite treatment, according to step ii) is typically performed in a suitable vessel provided with stirring means, where the oil obtained in the previous step and the zeolite are mixed. The mixture is typically vigorously stirred, and then allowed to stand, preferably under stirring, for a certain period of time, which is not critical, and preferably is of at least 12h, preferably at least 24h. The mixture may be allowed to stand for a longer period of time, such as one week, or more.

[0063] The treatment with zeolite is generally performed at room temperature, i.e., from about 20 °C to about 25 °C.

[0064] The amount of zeolite used in this step generally ranges from about 5 g to about 100 g of zeolite per litre of oil, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of zeolite per litre of oil.

[0065] After the treatment according to step ii), the oil is separated from the zeolites by conventional process, preferably by centrifugation.

[0066] The centrifugation can be performed at a speed typically comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm.

[0067] The centrifugation may be carried out, for example, at a temperature comprised between 20 °C and 25 °C, and for a time period which can range, for example, from about 15 minutes to about 1 hour, while these conditions are not critical and may otherwise be adjusted.Purified oil obtained with the process according to the invention

[0068] Another aspect of the invention is the purified oil obtainable according to the process of the present invention. The terms "purified oil" or "recycled oil" are used herein interchangeably and both designate the oil obtainable with the purification process according to the invention.

[0069] As discussed in Example 2, the purified waste cooking oil according to the present invention has optimal properties to be used, for example, as a lubricant.

[0070] In particular, it is noted that the acidity index is outstandingly reduced, from 3.1 mg KOH / g of oil to 0.27 mg KOH / g of oil. The high acidity index in WCOs is mainly due to the presence of free fatty acids, which appear as a consequence of the hydrolysis of the triglycerides during the frying process. Said high concentration of fatty acids is an obstacle for the use of unpurified WCO as lubricants, in particular, for the lubrication of metallic pieces, because the high acid content may increase the risk of corrosion.

[0071] The purified oil according to the present invention has, therefore, lower acidity index than the original WCO, and is typically comprised between 0.1 and 1, preferably comprised between 0.1 and 0.5, expressed as mg of KOH per g of oil.

[0072] On the other hand, it was also found that the anti-wear performance of the purified oil is optimal for its use as lubricant, with values in the Brugger test which are similar to rapeseed, soya or castor oils.

[0073] Additionally, the treated oil has reduced volatiles compared to the original WCO and has therefore also optimal smell properties, which make it particularly suitable for consumer applications.

[0074] Another aspect of the invention is the use of said purified oil as lubricant. It is suitable for any lubricating use, for example, for industrial lubrication, including food production machinery or agricultural machinery, for lubrication of gardening equipment, including chainsaws and cutters, or for the lubrication of bicycle chains, among many other lubricating uses.

[0075] In an embodiment, the use is for the lubrication of bicycle chains.

[0076] Furthermore, the purified oil obtained according to the present invention can also be used for the preparation of coolant liquids, in particular, coolant liquids for batteries.

[0077] Another aspect of the invention is, therefore, the use of said purified oil for the preparation of a coolant liquid. One particular use is for cooling of batteries.Lubricant composition

[0078] Another aspect of the present invention is a lubricant composition comprising the purified oil obtained according to the process of the present invention.

[0079] The lubricant according to the present invention is a "biolubricant" (or bio-based lubricant), as it is derived from biodegradable and renewable resources, as are vegetable oils. Furthermore, it has the advantage of being mainly based on a recycled waste vegetable oil.

[0080] The lubricant composition according to the present invention comprises at least 50% by weight of the purified oil, preferably from 50% to 95%, more preferably from 60% to 85%, and still more preferably comprises from 65% to 75% by weight of the purified oil.

[0081] Generally, the lubricant composition according to the present invention additionally comprises another oil, typically, a vegetable oil, mixed with the purified oil. Said vegetable oil is, for example, castor oil, soybean oil, sunflower oil, or rapeseed oil, among others, or mixtures thereof. Said vegetable oils may be available in different grades, namely, with some variations in their fatty acid content, depending on the different sources, and all of them are included within the scope of the invention.

[0082] Preferably, the additional vegetable oil is selected from soybean oil and castor oil, and more preferably is castor oil.

[0083] The mixture of the purified oil and the additional vegetable oil constitutes the base oil of the lubricant composition.

[0084] In an embodiment, the lubricant composition comprises: between 85 wt% and 99.05 wt% of a base oil; and between 0.5 wt% and 15 wt% of an additive. wherein the base oil is a mixture of the purified oil and a vegetable oil, as hereinabove described.

[0085] In a particular embodiment, the lubricant composition consists of the above defined ingredients.

[0086] The weight ratio purified WCO:vegetable oil in the base oil generally ranges from about 50:50 to about 90:10, preferably from about 60:40 to about 80:20, and more preferably from about 65:35 to about 80:20.

[0087] In another embodiment, the lubricant composition is made up of said base oil, without additional components.

[0088] Preferably, the lubricant composition of the invention also contains from about 0.5 to about 15 wt% of one or more additives, more preferably from about 1 wt% to about 12 wt%, still more preferably from about 2 wt% to about 10 wt%, and still more preferably from about 4 wt% to about 6 wt%, relative to the total weight of the lubricant composition.

[0089] The additive may be selected from an antioxidant, a corrosion inhibitor, an anti-wear additive, a viscosity improver, a pour point depressant and mixtures thereof, and preferably is selected from an antioxidant, a corrosion inhibitor, an anti-wear agent, and mixtures thereof.

[0090] The additives used in the composition according to the present invention are environmentally acceptable, typically, either they natural substances or they are substances complying with EU Ecolabel criteria, namely, within the limits stated in the LUSC-List (Lubricant Substance Classification List).

[0091] The purpose of antioxidant additives is to delay or prevent the oxidation process by protecting the lubricant from oxidative degradation. Suitable antioxidant additives may be of natural origin, such as tocopherols, esters of gallic acid, citric acid, citric acid derivatives, L-ascorbic acid or ascorbyl palmitate, among others. Antioxidants may be also synthetic, for example, bis(disubstituted dithiocarbamates), particularly methylene bis(dialkyldithiocarbamates); dithiocarbamate esters; sterically hindered phenols, such as butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, or thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], among many others; or aromatic amines, in particular, dialkylated diphenylamines such as butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, or dioctyldiphenylamine, among others, or alkylated phenyl alpha naphthylamines. Any one of them, among others, may be suitable for being added to the lubricant composition according to the present invention.

[0092] In an embodiment of the invention, the antioxidant is selected from the group consisting of butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol; 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, dioctyldiphenylamine and mixtures thereof.

[0093] When there is an antioxidant additive it is generally in an amount comprised between about 0.05 wt% and about 5 wt%, preferably comprised between about 0.1 wt% and about 2 wt%, more preferably comprised between about 0.2 wt% and about 1 wt%, and more preferably comprised between about 0.3 wt% and about 0.8 wt%, relative to the total weight of the lubricant composition.

[0094] The purpose of anti-wear additives is to protect materials against wear. There are also many substances disclosed in the art which can be used as anti-wear additives (for example, as disclosed in L.O. Farng, Ashless Anti-wear and Extreme-Pressure Additives, in: Lubricant Additives. Chemistry and Applications, Second Edition, op. cit., Chapter 8, 213-249). Some typical anti-wear additives are, for example, triesters of phosphoric acid or thiophosphoric acid, which may be alkyl esters, aryl esters, or mixed alkyl aryl esters, for example, tricresyl phosphates or trixylenyl phosphates or triphenyl phosphorothionate (TPPT); amine salts of phosphoric acid esters; dithiophosphates; dithiocarbamates, such as methylene bis(dialkyldithiocarbamates); or sulfur additives such as sulfurized olefins, sulfurized esters and sulfurized oils; among others. Some natural substances can also be used as anti-wear additives, for example, polyphenols such as curcumin, xanthophylls, such as astaxanthin, lutein or zeaxanthin, or cashew nut shell liquid (CNSL), among others. Any one of them may be used in the compositions according to the present invention.

[0095] Some preferred anti-wear additives are methylene bis(dialkyldithiocarbamates) and sulfurized fatty acid esters. One particularly preferred anti-wear additive is, for example, methylene bis-dibutyldithiocarbamate.

[0096] When there is an anti-wear additive in the formulation, it is generally in an amount comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.5 wt% and about 6 wt%, and more preferably between about 1 wt% and 5 wt%, relative to the total weight of the lubricant composition.

[0097] The purpose of corrosion inhibitors is to avoid rust in the metallic components in contact with the lubricant composition. There are many substances disclosed in the art which can be used as corrosion inhibitors (see for example Z. Tang, A review of corrosion inhibitors for rust preventive fluids, Curr. Opin. Solid State Mater. Sci., 2019, 23, 100759 or in the book chapter M.T. Costello, Corrosion Inhibitors and Rust Preventives, in: Lubricant Additives. Chemistry and Applications, Second Edition, L.R. Rudnick Ed., CRC Press, 2009, Chapter 17, 421-444). Some suitable corrosion inhibitors are, for example, dicarboxylates, in particular, succinic acid derivatives; alkyl amines; amino acids; sulfonic acid esters; derivatives of some nitrogen containing heterocycles, for example, imidazoline, thiazole, thiadiazole or benzothiazole, such as dimercaptothiadiazoles or mercaptobenzothiazole derivatives; among many others. Also many natural substances can be used as corrosion inhibitors, for example, curcumin, linseed oil, limonene or rosemary oil, for example, among many others.

[0098] A preferred corrosion inhibitors is, for example, a sulfonic acid ester.

[0099] When there is a corrosion inhibitor in the formulation, it is generally in an amount comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.2 wt% and about 6 wt%, and more preferably comprised between about 0.5 wt% and about 2 wt%, relative to the total weight of the lubricant composition. The most suitable concentration, however, varies depending on the specific substance used, and will be easily adjusted by the skilled in the art.

[0100] Other possible additives of the lubricant composition are viscosity improvers and pour point depressants.

[0101] Viscosity improvers are typically thickeners, used to adjust the viscosity of the composition. Typical viscosity improvers are, for example, esters of polymethacrylic acid with hydrocarbon side chains of different lengths. Pour point depressants are polymeric molecules that can be added to improve the flow properties of the biolubricant. Examples of pour point depressants are acrylates, alkylated styrenes, alpha olefins, ethylene / vinyl acetates, methacrylates, styrene / maleic anhydrides, and vinyl acetate / fumarates (see, for example, B.G. Kinker, Polymethacrylate viscosity modifiers and pour point depressants, in: Lubricant Additives. Chemistry and Applications, Second Edition, op. cit., Chapter 11, 315-337).

[0102] The base oil according to the present invention, i.e., consisting of a mixture of the purified WCO and a vegetable oil, has suitable properties, in particular, optimal viscosity and pour point so, in general, viscosity improvers or pour point depressants are not necessary.

[0103] In an embodiment, the additive is selected from an antioxidant, a corrosion inhibitor, an anti-wear additive and mixtures thereof.

[0104] In a particular embodiment, the lubricant composition composition consists of: between 92 wt% and 96 wt% of a base oil consisting of a mixture of the purified oil of the invention and castor oil, wherein the weight ratio purified oil:castor oil is comprised between 65:35 and 80:20; and between 4 wt% and 8 wt% of an additive consisting of: ∘ between 0.25 wt% and 1.5 wt% of an antioxidant; ∘ between 0.5 wt% and 2 wt% of a corrosion inhibitor; and ∘ between 3 wt% and 6 wt% of an anti-wear agent.

[0105] In the above composition, it is understood that the sum of the percentages of antioxidant, corrosion inhibitor and anti-wear agent is in the range 4-8 wt%.

[0106] In the practice, some additives may advantageously perform more than one function. As used herein, the terms anti-wear additive, antioxidant, corrosion inhibitor, viscosity improver or pour point depressant are meant to include also those substances having additional functions.

[0107] For example, some additives simultaneously perform an antioxidant and anti-wear function (anti-wear / antioxidant additive).

[0108] The lubricant composition can be prepared according to conventional mixing processes, typically, by first mixing the two components of the base oil, i.e., the purified oil and the vegetable oil, to obtain a homogeneous mixture, and then adding the additives under stirring. Other mixing order of the components is also suitable.Use of the lubricant composition

[0109] Another aspect of the invention is the use of the lubricant composition of the invention for the lubrication of mechanical devices.

[0110] As shown in Example 2, the purified oil according to the present invention has optimal anti-wear and anti-corrosive efficacy, which make it suitable for lubrication.

[0111] The biolubricant composition of the present invention, containing said purified oil, can be used for any lubricating application, either for industrial machinery or for any other purpose. For example, for industrial lubrication, including food production machinery or agricultural machinery, for lubrication of gardening equipment, including chainsaws and cutters, or for the lubrication of bicycle or motorbike chains, among many other lubricating uses.

[0112] One particular application is for the lubrication of chains, particularly, bicycle or motorbike chains. As shown in the tests performed in Example 5, the lubricant composition of the present invention shows excellent performance in several tests particularly intended to assess its suitability for this use.

[0113] For example, the anti-wear effect was assessed in a test performed with bike chains in use, and the lubricant composition according to the invention showed the best results, compared to several commercial lubricants.

[0114] The effect of the lubricant on the bicycle speed was also assessed and the lubricant of the invention was found either similar or superior to the commercial lubricants used as comparators.

[0115] The durability of the effect of the lubricant, when applied to bicycle chains, was also assessed by measuring the increase in the noise of the rotating chain as an indicator of lubricant loss of efficacy. Again, the the lubricant according to the invention was either similar or superior to the comparators.

[0116] Another aspect assessed in Example 5 is dirt repelling efficiency. This effect is important for lubricants used in outdoor applications, such biking, which involve contact with the environment, to avoid getting contaminated with dust or other particles present in the environment.

[0117] Lubricant splatter was also assessed, as a measure of losses of the product, ending up in the environment. The composition according to the invention showed moderate spatter, similar to other commercial lubricants.

[0118] Finally, the effect of the temperature on lubrication performance was also assessed, and the composition according to the invention showed only very small changes in its anti-wear performance with the temperature.

[0119] Therefore, the properties found for the biolubricant composition of the present invention make it particularly suitable, for chain lubrication, either in bicycles or in any other transmission chain in a variety of machines.

[0120] A particular aspect of the invention is the use of the lubricant composition of the invention for the lubrication of bicycle chains. It includes typically mechanical bicycles and electric bicycles (e-bikes), and also motorcycles (or motorbikes).

[0121] Another aspect of the invention is the use of the lubricant composition of the invention for the lubrication of transmission chains in industrial machinery of any kind.

[0122] Furthermore, the lubricant composition is environmentally friendly as it is composed of substantially biodegradable components, which are nontoxic to the environment, and mainly based on renewable sources. It makes also the composition of the invention particularly suited for the lubrication of bicycle or motorbike chains, as part of lubricant may be released to the environment during its use.

[0123] The present invention may be defined by the following embodiments: 1.- Process for purifying a waste cooking oil comprising the following two consecutive steps: i) treatment of the waste cooking oil with a mixture of magnesium silicate and an alkali; and ii) treatment of the product obtained after step i) with a zeolite. 2.- Process according to embodiment 1, wherein the waste cooking oil has the following fatty acid composition: oleic acid (C18:1): from 14% to 83%; linoleic acid (C18:2): from 3% to 74%; palmitic acid (C16:0): from 5% to 20%; and stearic acid (C18:0): from 0.5% to 7%. 3.- Process according to embodiments 1 or 2, wherein the waste cooking oil has iodine index value comprised between 75 and 145. 4.- Process according to any one of embodiments 1 to 3, wherein the waste cooking oil has an acidity index comprised between 1.5 and 6. 5.- Process according to any one of embodiments 1 to 4, wherein the magnesium silicate is selected from a naturally occurring magnesium silicate and a synthetic magnesium silicate. 6.- Process according to embodiment 5, wherein magnesium silicate is synthetic magnesium silicate. 7.- Process according to embodiment 6, wherein magnesium silicate has average particle size ranging from about 20 µm to about 200 µm. 8.- Process according to embodiments 6 or 7, wherein magnesium silicate has surface area ranging from about 50 m 2< / g to about 700 m 2< / g. 9.- Process according to any one of embodiments 6 to 8, wherein magnesium silicate has bulk density ranging from about 0.25 g / ml to about 0.60 g / ml. 10.- Process according to any one of embodiments 1 to 9, wherein the alkali in step i) is selected from calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, and mixtures thereof. 11.- Process according to embodiment 10, wherein the alkali is calcium hydroxide. 12.- Process according to any one of embodiments 1 to 11, wherein the weight ratio magnesium silicate:alkali is comprised between 20:1 and 1:1, preferably comprised between 15:1 and 4:1, more preferably comprised between 10:1 and 8:1, and more preferably is about 9:1. 13.- Process according to any one of embodiments 1 to 12, wherein the amount of the mixture magnesium silicate-alkali used in step i) ranges from about 5 g to about 100 g, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of the mixture per litre of waste cooking oil. 14.- Process according to anyone of embodiments 1 to 13, wherein the waste cooking oil is centrifugated before step i). 15.- Process according to embodiment 14, wherein the centrifugation is carried out at speed comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm. 16.- Process according to any one of embodiments 1 to 15, wherein in step ii) the zeolite is either a naturally occurring zeolite or a synthetic zeolite. 17.- Process according to embodiment 16, wherein the zeolite is zeolite A, preferably is zeolite 4A. 18.- Process according to any one of embodiments 1 to 17, wherein the amount of zeolite used in step ii) ranges from about 5 g to about 100 g, preferably from about 10 g to about 50 g, and more preferably from about 15 g to about 25 g of zeolite per litre of oil. 19.- Process according to any one of embodiments 1 to 18, wherein the purified oil obtained after step ii) is centrifuged. 20.- Process according to embodiment 19, wherein the centrifugation is carried out at speed comprised between 1000 rpm and 10000 rpm, preferably comprised between 2000 rpm and 9000 rpm, more preferably comprised between 3000 rpm and 8000 rpm, still more preferably comprised 4000 rpm and 70000 rpm, and still more preferably comprised between 5000 rpm and 6000 rpm. 21.- Purified oil obtainable with the process according to any one of embodiments 1 to 20. 22.- Purified oil according to embodiment 21, wherein it has an acidity index comprised between 0.1 and 1, preferably comprised between 0.1 and 0.5. 23.- Use of the purified oil according to embodiments 21 or 22 as lubricant. 24.- Use of the purified oil according to embodiments 21 or 22 as cooling liquid, preferably as cooling liquid for batteries. 25.- Cooling liquid comprising the purified oil according to embodiments 21 or 22. 26.- Cooling liquid according to embodiment 25, wherein the cooling liquid is for cooling batteries. 27.- Lubricant composition comprising the purified oil according to embodiments 21 or 22. 28.- The lubricant composition according to embodiment 27, wherein the lubricant composition comprises: between 85 wt% and 99.05 wt% of a base oil consisting of a mixture of the purified oil of embodiments 21 or 22 and a vegetable oil; and between 0.5 wt% and 15 wt% of an additive. 29.- Lubricant composition according to embodiment 27, wherein the lubricant composition consists of: between 85 wt% and 99.05 wt% of a base oil consisting of a mixture of the purified oil of embodiments 21 or 22 and a vegetable oil; and between 0.5 wt% and 15 wt% of an additive. 30.- Lubricant composition according to embodiments 28 or 29, wherein the vegetable oil in the base oil is selected from the group consisting of castor oil, soybean oil, sunflower oil, rapeseed oil, and mixtures thereof. 31.- Lubricant composition according to embodiment 30, wherein the vegetable oil is castor oil. 32.- Lubricant composition according to any one of embodiments 28 to 31, wherein the weight ratio purified oil:vegetable oil in the base oil ranges from about 50:50 to about 90:10, preferably from about 60:40 to about 80:20, and more preferably from about 65:35 to about 80:20. 33.- Lubricant composition according to any one of embodiments 28 to 32, wherein the composition comprises or consists of: between 90 wt% and 98 wt%, and preferably between 92 wt% and 96 wt% of the base oil; and between 2 wt% and 10 wt%, and preferably between 4 wt% and 6 wt% of the additive. 34.- Lubricant composition according to any one of embodiments 28 to 33, wherein the additive is selected from the group consisting of an antioxidant, an anti-wear agent, a corrosion inhibitor and mixtures thereof. 35.- The lubricant composition according to embodiment 34, wherein the additive comprises an antioxidant, which is preferably selected from a tocopherol, an ester of gallic acid, citric acid or citric acid derivatives, L-ascorbic acid, ascorbyl palmitate, a methylene bis(dialkyldithiocarbamate), a dithiocarbamate ester, butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol, 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, dioctyldiphenylamine, and mixtures thereof. 36.- The lubricant composition according to embodiment 35, wherein the antioxidant is selected from the group consisting of butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol; 2,6-di-tert-butyl-p-cresol, 6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol, mono-tert-butylhydroquinone, 4,4'-methylenebis(2,6-di-tert-butylphenol), octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, thiodiethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], butyl-octyl-diphenylamine, dibutyldiphenylamine, bis(nonylphenyl)amine, dioctyldiphenylamine and mixtures thereof. 37.- The lubricant composition according to embodiments 35 or 36, wherein the amount of antioxidant is comprised between about 0.05 wt% and about 5 wt%, preferably comprised between about 0.1 wt% and about 2 wt%, more preferably comprised between about 0.2 wt% and about 1 wt%, and more preferably comprised between about 0.3 wt% and about 0.8 wt%, relative to the total weight of the lubricant composition. 38.- The lubricant composition according to any one of embodiments 34 to 37, wherein the additive comprises an anti-wear agent, which is preferably selected from a triester of phosphoric acid or of thiophosphoric acid, such as a tricresyl phosphate, a trixylenyl phosphate, or a triphenyl phosphorothionate (TPPT); an amine salt of phosphoric acid esters; a dithiophosphate; a dithiocarbamate, such as a methylene bis(dialkyldithiocarbamate); a sulfur additive such as a sulfurized olefin, a sulfurized ester or a sulfurized oil; a polyphenol such as curcumin; a xanthophyll, such as astaxanthin, lutein or zeaxanthin; cashew nut shell liquid (CNSL), and mixtures thereof. 39.- The lubricant composition according to embodiment 38, wherein the anti-wear agent is selected from a methylene bis(dialkyldithiocarbamate) and a sulfurized fatty acid ester, preferably is a methylene bis(dialkyldithiocarbamate), and more preferably is methylene bis-dibutyldithiocarbamate. 40.- The lubricant composition according to embodiments 38 or 39, wherein the amount of anti-wear agent is comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.5 wt% and about 6 wt%, and more preferably between about 1 wt% and 5 wt%, relative to the total weight of the lubricant composition 41.- The lubricant composition according to any one of embodiments 34 to 40, wherein the composition comprises a corrosion inhibitor, which is preferably selected from a succinic acid derivative; an alkyl amine; an amino acid; a sulfonic acid ester; a derivative a nitrogen containing heterocycle, such as a dimercaptothiadiazole or mercaptobenzothiazole derivative; curcumin; linseed oil; limonene and rosemary oil. 42.- The lubricant composition according to embodiment 41, wherein the corrosion inhibitor is a sulfonic acid ester. 43.- The lubricant composition according to embodiments 41 or 42, wherein the amount of corrosion inhibitor is comprised between about 0.1 wt% and about 8 wt%, preferably comprised between about 0.2 wt% and about 6 wt%, and more preferably comprised between about 0.5 wt% and about 2 wt%, relative to the total weight of the lubricant composition. 44.- Lubricant composition according to any one of embodiments 27 to 43, wherein the lubricant composition consists of: between 92 wt% and 96 wt% of a base oil consisting of a mixture of the purified oil of embodiments 21 or 22 and castor oil, wherein the weight ratio purified oil:castor oil is comprised between 65:35 and 80:20; and between 4 wt% and 8 wt% of an additive consisting of: ∘ between 0.25 wt% and 1.5 wt% of an antioxidant; ∘ between 0.5 wt% and 2 wt% of a corrosion inhibitor; and ∘ between 3 wt% and 6 wt% of an anti-wear agent. 45.- Use of the lubricant composition according to any one of embodiments 27 to 44 for the lubrication of mechanical devices. 46.- Use according to embodiment 45, for the lubrication of bicycle chains, electric bicycle chains or motorbike chains. 45.- Use according to embodiment 45, for the lubrication of transmission chains in industrial machinery. 47.- Use according to embodiment 45, for the lubrication of chainsaws or garden cutters. Examples Example 1.- Purification of a waste cooking oil

[0124] A waste cooking oil was obtained from an authorized recycling company (Ecovirea, Spain).

[0125] The sample was analysed to determine the fatty acid content. The results are shown in Table 1 below. TABLE 1Fatty acidPercentageOleic acid (C18:1)76.71%Linoleic acid (C18:2)12.25%Palmitic acid (C16:0)5.01%Stearic acid (C18:0)3.50%Behenic acid (C22:0)0.94%Lignoceric acid (C24:0)0.35%Other1.24%

[0126] The acidity index of this oil was 2.9 (expressed as mg of KOH required to neutralize the acidic constituents in 1 g of oil) and the iodine index was 83.5 (expressed as g iodine per 100 g of oil).

[0127] A sample of this WCO was centrifuged at 5100 r.p.m. at 20 °C, during 20 minutes. The centrifuged oil was separated from the precipitated solids by decantation. The amount of solids removed amounted to 2.3% by weight relative to the weight of initial untreated WCO.

[0128] After centrifugation, the acidity index of the oil was 3.1.

[0129] 1 litre of the centrifuged oil was then treated with 20 g a mixture of magnesium silicate (Florisil ®< ) and calcium hydroxide in a weight ratio magnesium silicate to calcium hydroxide of 9:1. The treatment was performed under stirring, at a temperature of 50 °C, for 1.5h. After the treatment, the oil was separated from the solid mixture by decantation.

[0130] To 1 litre of the oil obtained after the above treatment, 20 g of zeolite (Zeolite ZC2 (98% of zeolite 4A), IQE Group, Spain) were added and the mixture was vigorously stirred and then left to stand for 24h.

[0131] After that, the mixture was centrifuged at 5100 r.p.m. at 20 °C, during 20 minutes and the oil was separated by decantation.

[0132] The obtained product was a clear, yellowish oil.Example 2.- Properties of the purified oil

[0133] Some characteristics of the purified oil obtained in Example 1 were analysed.Stability

[0134] A stability study was carried out for a week at different temperatures (5°C, room temperature and 40°C). The purified oil of Example 1 remained clear in all tested conditions, without any turbidity or precipitation detected.Acidity

[0135] The acidity index of the treated oil was 0.27, therefore showing a substantial reduction compared value before the treatment (3.1).Volatiles

[0136] Headspace gas chromatography with flame ionization detection (HS-GC-FID) was used to assess the effect of treatment on the volatile compounds generated by the oil, which have an effect on the smell of the product.

[0137] The oil was introduced into a chromatography vial and a syringe sample was taken from the gas phase, to analyse the volatile compounds emitted by the oil.

[0138] The analytical conditions were as follows: Headspace conditions Vial temperature60 °CSample loop70 °CTransfer line80 °CVial heating time20 minGC-FID conditions ColumnDB-WAX UI: high-polarity polyethylene glycol column (30m x 0.250mm x 0.25 µm)Constant flow1 ml / minTemperature program50°C (hold 3 min) to 200 °C at 12°C / min (hold 4 min)Injector temperature250°CDetector temperature250°CSplit modesplitlessCarrier gasHelium

[0139] The samples were prepared by weighing 2 grams of oil (in triplicate) into 20 mL vials. The vials were closed and inserted into the headspace module. A blank sample, i.e., an empty vial, was also analysed to confirm that the peaks found corresponded to substances released from the oil. The samples tested were the original WCO (A) and the purified WCO (B), as described in Example 1. The volatiles reduction was calculated as the difference between the sum of peak areas (volatiles) in sample WCO (B) compared to WCO (A). 45.4% reduction of volatiles was found.Smell sensory analysis

[0140] On the other hand, a sensory analysis with a panel of 5 volunteers was performed, in order to assess the perception of the smell generated by the purified oil.

[0141] For performing this analysis, samples in 5 mL vials were provided to the volunteers, with an opening of 4 mm diameter.

[0142] The results are summarized in the Table 2, where the values shown are the average for all the volunteers: TABLE 2Smell characteristics Results Intensity (1 to 10)4.4Synthetic - natural (-1 to 1)0.2Acceptability (-5 to 5)-0.6Suitability for use (-5 to 5)1.4 Anti-wear performance

[0143] The anti-wear performance of the obtained oil was measured, in order to assess its suitability for use as biolubricant.

[0144] A Brugger test machine was used, which is a standardized method (DIN 51347 parts 1 and 2) based on the friction conditions in the contact zone between a friction ring and a test cylinder. All tests were conducted with a rotating 25 mm ring and a fixed test cylinder of 18 mm x 18 mm. The tested lubricant was applied on the surface of the fixed test cylinder, which was then pressed against the ring by applying a normal force of 400 N and the ring was allowed to rotate during 30 seconds. After that, the elliptical wear scar produced on the roller's surface was measured. The two diameters (a and b) of the ellipse were used to calculate the Brugger value (N / mm 2< ) through the formula: Brugger value N mm 2 = 4 × 400 a × b × π

[0145] For each test, approximately 5 mL of the oil sample were placed on the surface of the fixed test cylinder. For each sample, the procedure was repeated five times and the mean value was calculated. The higher the Brugger value the better anti-wear capacity.

[0146] The samples tested were the purified WCO oil obtained in Example 1, according to the present invention. Some vegetable oils were also tested, for comparative purposes. The results are shown in Table 3. TABLE 3Sample Brugger value (N / mm 2< ) Example 135.79Soya oil37.27Rapeseed oil36.64Sunflower oil29.12Castor oil44.10 Anti-corrosive properties

[0147] In order to assess anti-corrosive properties on steel of the purified oil, a test based on ASTM D665 was performed.

[0148] The procedure comprised the following steps: 1. A mixture was prepared with 25 mL of the tested oil and 5 mL of tap water. 2. The mixture was mechanically stirred at 1200 rpm and heated to 60 °C. 3. A steel plate was cleaned with hexane to eliminate any particle on the surface. 4. Half of the steel panel was submerged into the above mixture, maintaining the temperature and stirring conditions. 5. After 30 minutes the steel panel was extracted from the mixture and was inserted into a jar with a solution of 2g of NaCl in 100 mL of tap water, and the jar was closed to air. 6. After 24h, the panel was removed from the jar and was placed inside the oven at 80 °C for drying. 7. After 1h of drying, the appearance of corrosion in the panel, namely, in the lower half part of it, was visually evaluated.

[0149] The purified WCO obtained in Example 1 was subjected to this test. The results were satisfactory, and no rust was observed on the steel plate.Example 3.- Lubricant compositions

[0150] Two lubricant compositions (C1 and C2) were prepared by mixing 70 wt% of the purified oil of Example 1 with 30 wt% of either castor oil or soya oil.

[0151] The anti-wear and anti-corrosive properties of these oil mixtures were assessed, using analogous tests as described in Example 2.

[0152] The results are shown in Table 4: TABLE 4Sample Example 1 (wt%) Castor oil (wt%) Soya oil (wt%) Anti-wear (N / mm 2< ) Corrosion C17030--40.56ModerateC270--3034.99No corrosion Example 4.- Lubricant compositions

[0153] A lubricant composition according to the invention (composition C3) was prepared with the ingredients listed in the following table: TABLE 5Ingredients Function Amount (wt%) Purified WCO (Example 1)Base oil70.07Castor oilBase oil24.50Additin ®< RC6430Anti-wear additive4.00Additin ®< RC4810Corrosion inhibitor0.93Irganox ®< 67Antioxidant0.25Irganox ®< 135Antioxidant0.25

[0154] Additin ®< RC6430 is a commercial anti-wear additive, consisting of methylene bis-dibutyldithiocarbamate.

[0155] Additin ®< RC4810 is a commercial corrosion inhibitor additive, which is a sulfonic acid ester.

[0156] Irganox ®< 67 is a commercial antioxidant, consisting of bis(nonylphenyl)amine.

[0157] Irganox ®< 135 is a commercial antioxidant, consisting of consisting of octyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

[0158] The two base oil components were first mixed and the additives were next added and thoroughly mixed. The formulation was a brownish, clear oil.

[0159] The lubricant composition was subjected to stability assays, using samples of 100 mL into closed clear glass bottles, and allowing to stay for 4 weeks at the following temperatures: 5 °C, room temperature and 37 °C.

[0160] The composition was found to be stable during the 4-week period of the assay, at all the assayed temperatures. The formulation remained clear, without any turbidity or precipitate.

[0161] The anti-wear performance of this composition was 76.23 N / mm 2< , according to the Brugger test, using analogous conditions as described in Example 2.

[0162] Furthermore, the anti-corrosive efficiency was optimal, and no significant rust was detected, following analogous method as described in Example 2.Example 5.- Comparative lubricant efficiency of the lubricant composition

[0163] The effectiveness of the lubricant composition of Example 4 (composition C3) for bicycle chain lubrication was compared to 6 commercial lubricant compositions (A to F), according to different tests, as described below.

[0164] The tests on bicycle chain wear, bicycle speed, durability and lubricant splatter (sections 5.1 to 5.4) were performed using a bicycle prototype.

[0165] Said bicycle prototype was designed to simulate the behaviour of the lubricant in a realistic environment. The prototype consisted of two gears connected by a bicycle chain and a motor to move one of the gears (Figure 1).

[0166] The prototype was provided with the following sensors: infrared sensor for recording the temperature on the chain surface, sound sensor for recording the noise emitted by the chain, and speed sensor for recording speed and number of rotations of the chain.

[0167] For each lubricant analysed using this prototype, a new chain (NX Eagle Chain, model CN-EAGL-NX-A1, principally made of low-carbon steel) was fitted to the prototype and a controlled amount of lubricant (0.2- 0.4 mL) was applied to each spur in the chain. The motor was set to a constant power output of 0.18kW throughout the 24 hours of continuous running.5. 1. Bicycle chain wear

[0168] To assess the bicycle chain wear after continued use, the distance between the chain links in the bicycle prototype was measured with a caliper. The following table shows the results of the test, after 24 hours of use, wherein the chain wear is calculated as the difference between the initial and final distance between the chain links. TABLE 6Lubricant tested Chain wear after 24h of use (mm) Composition C3 (Example 4)0.12Comparative A0.16Comparative B0.15Comparative C0.13Comparative D0.14Comparative E0.14Comparative F0.13

[0169] It was found that the lubricant composition according to the invention showed best anti-wear results.5.2. Effect on bicycle speed

[0170] The effect of the different lubricants on the bicycle speed along a period of 24h was assessed using the bicycle prototype. The results of the test are shown in Figure 2. The y-axis represents the speed (Km / h) and the x-axis represents the time (h).

[0171] It can be observed that the behaviour of the lubricant of the invention (C3) was similar to the comparatives C, D, E and F, while commercial products A and B showed worse performance.5.3. Durability of the lubricant

[0172] The durability of the lubricant was assessed using a sensorial test, consisting in measuring the noise of the rotating chain along time, based on the fact that when a lubricant loses efficiency, the noise of the chain increases. A noise sensor was used. The results are shown in Figure 3, where y-axis shows the noise recorded in decibels (dB) and the x-axis shows the time, in hours.

[0173] It was found that the lubricant composition according to the invention showed similar behaviour in this test as comparators B, D and E, and better results than comparators A, C and F.5.4. Lubricant splatter

[0174] This test consisted in the visual characterization of splatter (excess lubricant) due to unadhered lubricant, which would end up in the environment. A sheet of white paper was placed next to the chain, and the splatters after 5 minutes, 15 minutes and 5 hours were observed. For each test, a punctuation from 1 to 5 was given, where 5 means the best results (virtually no splashes) and 1 means worse results (more splashes).

[0175] The results are summarized in Table 7. TABLE 7Lubricant tested Spatter (1 to 5) Composition C3 (Example 4)3Comparative A2Comparative B5Comparative C2Comparative D4Comparative E3Comparative F1

[0176] It can be observed that, in terms of slatter, the lubricant composition according to the invention had satisfactory behaviour, similar the commercial formulas. In particular, it showed the behaviour as comparative E, better than comparatives A, C and F, and more splatter than comparatives B and D.5.5. Dirt repelling

[0177] A dirt repelling test was performed, to assess the performance of the lubricant for dirt repelling during use under adverse weather conditions, of rain and mud.

[0178] For this test, a standardized sand mixture was prepared (mixture of sand plant fertilizer & coarse aggregate, with a weight relation 1:10), and the mixture was filtered through a stainless-steel sieve of 0.5 mm mesh.

[0179] Steel panels (90 x 50 x 1 mm) were used. The panels were cleaned with hexane before the test, and each panel was weighed before lubricant application. In each panel a specific area was delimited by drawing two parallel lines, and 4 to 6 drops of each tested lubricant was applied using a pipette and spread in order to cover all the surface marked in the panel. The excess of lubricant was drained with paper by capillarity. After lubricant application, the panels were again weighed. Then sand was then applied using a spray gun controlling the pressure at, 2, 2.5 and 3 atm. for 3 seconds each application, 3 times for each pressure. After sand application, the panels were again weighed.

[0180] In this way, the weights of (1) the initial panel, (2) the panel plus lubricant, and (3) the panel plus lubricant plus adhered dirt were recorded. The difference between (3) and (2) allowed to measure the dirt adhered. The difference between (2) and (1) allowed to measure the amount of lubricant, to check that comparative amounts were used.

[0181] Each test, for each lubricant, was performed in duplicate, and the average value was calculated.

[0182] The results are shown below in Table 8 TABLE 8Lubricant tested Amount of lubricant (g) Amount of adhered dirt (g) Composition C3 (Example 4)0.0850.025Comparative A0.0650.035Comparative B0.090.015Comparative C0.070.01Comparative D0.090.025Comparative E0.0650.01Comparative F0.070.03

[0183] It can be observed that the dirt repellency of the lubricant composition according to the invention is satisfactory, similar the commercial formulas. In particular, it showed the same dirt repellency value as comparative D, better than comparatives A and F, and slightly worse than comparatives B, C and E.5.5. Change in anti-wear performance with the temperature.

[0184] The anti-wear performance of composition C3, according to the Brugger test, was 76.23 N / mm 2< , as disclosed in Example 4 above. The Brugger test was repeated but by first cooling the composition to 0 °C. There was only a 4% reduction in the anti-wear performance of the composition (to 72.9 N / mm 2< ).

[0185] The same assay was performed with the comparative commercial composition C. In this case, the anti-wear performance at room temperature was 57.67 N / mm 2< , while this value significantly decreased at 0 °C, namely, to 50.12 N / mm 2< (13% reduction).

Examples

example 1

- Purification of a waste cooking oil

[0124]A waste cooking oil was obtained from an authorized recycling company (Ecovirea, Spain).

[0125]The sample was analysed to determine the fatty acid content. The results are shown in Table 1 below.

TABLE 1

Fatty acidPercentage

Oleic acid (C18:1)76.71%

Linoleic acid (C18:2)12.25%

Palmitic acid (C16:0)5.01%

Stearic acid (C18:0)3.50%

Behenic acid (C22:0)0.94%

Lignoceric acid (C24:0)0.35%

Other1.24%

[0126]The acidity index of this oil was 2.9 (expressed as mg of KOH required to neutralize the acidic constituents in 1 g of oil) and the iodine index was 83.5 (expressed as g iodine per 100 g of oil).

[0127]A sample of this WCO was centrifuged at 5100 r.p.m. at 20 °C, during 20 minutes. The centrifuged oil was separated from the precipitated solids by decantation. The amount of solids removed amounted to 2.3% by weight relative to the weight of initial untreated WCO.

[0128]After centrifugation, the acidity index of the oil was 3.1.

[0129]1 litre of th...

example 2

- Properties of the purified oil

[0133]Some characteristics of the purified oil obtained in Example 1 were analysed.

Stability

[0134]A stability study was carried out for a week at different temperatures (5°C, room temperature and 40°C). The purified oil of Example 1 remained clear in all tested conditions, without any turbidity or precipitation detected.

Acidity

[0135]The acidity index of the treated oil was 0.27, therefore showing a substantial reduction compared value before the treatment (3.1).

Volatiles

[0136]Headspace gas chromatography with flame ionization detection (HS-GC-FID) was used to assess the effect of treatment on the volatile compounds generated by the oil, which have an effect on the smell of the product.

[0137]The oil was introduced into a chromatography vial and a syringe sample was taken from the gas phase, to analyse the volatile compounds emitted by the oil.

[0138]The analytical conditions were as follows:

Headspace conditions

Vial temperature60 °C

Sample loop70 °C

Tran...

example 135.79

Example 135.79

Soya oil37.27

Rapeseed oil36.64

Sunflower oil29.12

Castor oil44.10

Anti-corrosive properties

[0147]In order to assess anti-corrosive properties on steel of the purified oil, a test based on ASTM D665 was performed.

[0148]The procedure comprised the following steps:

1. A mixture was prepared with 25 mL of the tested oil and 5 mL of tap water. 2. The mixture was mechanically stirred at 1200 rpm and heated to 60 °C. 3. A steel plate was cleaned with hexane to eliminate any particle on the surface. 4. Half of the steel panel was submerged into the above mixture, maintaining the temperature and stirring conditions. 5. After 30 minutes the steel panel was extracted from the mixture and was inserted into a jar with a solution of 2g of NaCl in 100 mL of tap water, and the jar was closed to air. 6. After 24h, the panel was removed from the jar and was placed inside the oven at 80 °C for drying. 7. After 1h of drying, the appearance of corrosion in the panel, namely, in the...

Claims

1. Process for purifying a waste cooking oil comprising the following two consecutive steps: i) treatment of the waste cooking oil with a mixture of magnesium silicate and an alkali; and ii) treatment of the product obtained after step i) with a zeolite.

2. Process according to claim 1, wherein the waste cooking oil has the following fatty acid composition: - oleic acid (C18:1): from 14% to 83%; - linoleic acid (C18:2): from 3% to 74%; - palmitic acid (C16:0): from 5% to 20%; and - stearic acid (C18:0): from 0.5% to 7%.

3. Process according to claims 1 or 2, wherein the waste cooking oil has iodine index value comprised between 75 and 145.

4. Process according to any one of claims 1 to 3, wherein the waste cooking oil has an acidity index comprised between 1.5 and 6.

5. Process according to any one of claims 1 to 4, wherein the alkali in step i) is selected from calcium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, sodium hydrogencarbonate, potassium hydrogencarbonate, and mixtures thereof, and preferably is calcium hydroxide.

6. Process according to anyone of claims 1 to 5, wherein the waste cooking oil is centrifugated before step i).

7. Process according to any one of claims 1 to 6, wherein in step ii) the zeolite is either a naturally occurring zeolite or a synthetic zeolite, preferably is a synthetic zeolite, more preferably the zeolite is zeolite A, and more preferably is zeolite 4A.

8. Purified oil obtainable with the process according to any one of claims 1 to 79. Use of the purified oil according to claim 8 as lubricant or cooling liquid.

10. Lubricant composition comprising the purified oil according to claim 8.

11. The lubricant composition according to claim 10, wherein the lubricant composition comprises or consists of: - between 85 wt% and 99.05 wt% of a base oil consisting of a mixture of the purified oil of claim 8 and a vegetable oil; and - between 0.5 wt% and 15 wt% of an additive.

12. Lubricant composition according claims 10 or 11, wherein the lubricant composition consists of: - between 92 wt% and 96 wt% of a base oil consisting of a mixture of the purified oil of claim 8 and castor oil, wherein the weight ratio purified oil:castor oil is comprised between 65:35 and 80:20; and - between 4 wt% and 8 wt% of an additive consisting of: ∘ between 0.25 wt% and 1.5 wt% of an antioxidant; ∘ between 0.5 wt% and 2 wt% of a corrosion inhibitor; and ∘ between 3 wt% and 6 wt% of an anti-wear agent.

13. Use of the lubricant composition according to any one of claims 10 to 12 for the lubrication of mechanical devices.

14. Use according to claim 13, for the lubrication of bicycle chains, electric bicycle chains or motorbike chains.

15. Use according to claim 13, for the lubrication of transmission chains in industrial machinery or for the lubrication of chainsaws or for the lubrication of garden cutters.

Images