Method for removing mineral oil from grease and grease obtained

Abstract

The present invention belongs to the technical field of oil refining, and specifically relates to a method for removing mineral oil from oil and fat, and the resulting oil and fat. The method comprises the following steps: introducing steam into the oil and fat under vacuum conditions for treatment; wherein the total amount of steam introduced is 15% to 95% of the mass of the oil and fat. The method for removing mineral oil from oil and fat provided by the present invention is particularly advantageous for removing mineral oil from polyunsaturated fatty acid oils and fats. It can effectively and simply remove mineral oil from oil and fat without changing the existing oil and fat production process steps, and obtain oil and fat with a mineral oil content of less than 5 ppm.

Description

Technical Field

[0001] The invention belongs to the technical field of oil refining, and particularly relates to a method for removing mineral oil from oil and fat and the obtained oil and fat. Background Art

[0002] Mineral oil, a complex hydrocarbon, primarily consists of two main groups: straight-chain and branched alkanes, alkyl-substituted cycloalkanes (MOSHs), and alkyl-substituted aromatic hydrocarbons (MOAHs). It also contains very small amounts of non-alkyl-substituted polycyclic aromatic hydrocarbons, as well as sulfur- and nitrogen-containing compounds. MOSH, which is ingested through the diet, accumulates most in the human body. Low- to medium-viscosity MOSHs can accumulate in animals and cause microgranulomas in organs such as the liver, spleen, and lymph nodes. MOSH has low to moderate toxicity. Long-term consumption of MOSH-contaminated food can cause significant harm to human health. For example, long-term consumption of large amounts of mineral oil-contaminated food can cause vomiting, diarrhea, and coma. More seriously, ingesting industrial mineral oil can cause acute and chronic poisoning, damaging cells throughout the body and potentially the nervous system. It can also damage the respiratory system, reducing the number of red blood cells and leading to respiratory failure.

[0003] Infant formula companies pay special attention to the mineral oil content in related foods and have relatively strict requirements. However, the mineral oil problem is difficult to avoid during the processing and production of food raw materials. For example, if the raw materials and solvents used in processing are contaminated with mineral oil, they will migrate into the food after a series of production processes; leakage of heat transfer oil (liquid paraffin) from equipment in the oil refining process; environmental migration during the storage process and lubricant migration of plastic packaging materials, etc., will all cause mineral oil risks in food raw materials and end foods.

[0004] The methods for removing mineral oil from grease or lipid products in the prior art mainly include:

[0005] CN107903236A discloses a method for removing mineral oil from natural vitamin E, which uses a chromatography column to remove mineral oil from vitamin E by utilizing the polarity difference between mineral oil and natural vitamin E.

[0006] CN111269209A discloses a method for removing mineral oil from vitamin E by using multi-stage adsorption.

[0007] CN113337338A discloses a method for reducing mineral oil in edible vegetable oil, wherein the vegetable oil containing excessive mineral oil is subjected to molecular distillation and emulsification and stratification treatment in sequence, and then the oil phase and the emulsified phase are treated with a high-voltage pulse electric field to obtain edible vegetable oil with reduced mineral oil.

[0008] WO2022177839A1 discloses a method for reducing the content of MOSH and / or MOAH in lauric oil, comprising the following steps: a) decomposing the lauric oil into a fatty acid fraction and a hydrous glycerol fraction, b) purifying the fatty acid fraction from step a) into fully distilled lauric fatty acids, and c) esterifying the fully distilled lauric fatty acids from step b) with glycerol to obtain lauric oil with reduced MOSH and / or MOAH.

[0009] It can be seen from the above patents that the currently commonly used methods for removing mineral oil all require adding additional steps to the traditional oil production process, and the chromatographic adsorption method also involves the use of a large amount of organic solvents. The fractionation, emulsification, separation and reconversion method has complicated steps and is quite different from the oil production process. There is no method for removing mineral oil that can fully match the existing oil production process. Summary of the Invention

[0010] In view of the shortcomings of the existing technology, a method for removing mineral oil from grease and the resulting grease are provided, which can effectively remove the mineral oil in the grease simply and quickly without changing the original grease production process steps.

[0011] To achieve the above object, the present invention adopts the following technical solutions:

[0012] A method for removing mineral oil from grease, comprising the following steps:

[0013] Under vacuum conditions, steam is introduced into the grease for treatment;

[0014] The total amount of steam introduced is 15% to 95% of the mass of the oil.

[0015] Taking microbial oils as an example, mineral oil contamination may be introduced in various stages of oil production, such as fermentation of raw materials, extraction, transportation, etc. Mineral oil contamination is difficult to avoid. The present invention has found through various attempts that vacuum steam distillation of oils at a specific distillation temperature and steam supply amount can reduce the mineral oil content, especially having a significant effect on reducing mineral oil in polyunsaturated fatty acid oils.

[0016] The mineral oil includes mineral oil saturated hydrocarbons (MOSH) and polyolefin oil saturated hydrocarbons (POSH).

[0017] The oils and fats described in the present invention may be unrefined oils and fats or oils and fats that have undergone one or more refining steps. As the oils and fats that have undergone one or more refining steps, oils and fats that have undergone any known refining operation (for example, an operation involving one or more, or any one or all of a degumming step, a deacidification step, a decolorization step, a dewaxing step, and a deodorization step) may be used.

[0018] Since absolute vacuum conditions do not exist, the vacuum conditions described in this invention refer to a gas state below one atmosphere. In some conventional operations in this field, vacuum conditions are usually reflected by the vacuum degree on a negative pressure gauge, for example, the pressure can be selected to be -0.06MPa. Further, -0.1MPa can be selected. Other vacuum conditions can be reflected directly by pressure, such as 300Pa, 350Pa, or 500Pa, whichever is sufficient to smoothly extract the steam that has come into contact with grease from the equipment.

[0019] The present invention has found that the total amount of steam introduced cannot be less than 15%, otherwise the removal effect of mineral oil will be significantly reduced. At the same time, the steam amount should not exceed 95%, otherwise the energy consumption will be too high, and the amount of natural antioxidants removed from the oil will increase, reducing the oxidative stability of the oil and easily causing oil splashing and loss.

[0020] Preferably, in the step of introducing steam into the oil, the total amount of steam introduced is 35 to 95% of the mass of the oil.

[0021] Preferably, in the above-mentioned method for removing mineral oil from oil, the step of introducing steam into the oil is carried out at a temperature of 160°C to 220°C. If the temperature is too low, the mineral oil removal effect is poor; if the temperature is too high, energy consumption increases and some oil may be hydrolyzed, producing undesirable substances such as thermal polymers and trans fatty acids. Furthermore, at high temperatures, polyunsaturated fatty acids in oils and fats will produce secondary products such as aldehydes, ketones, and quinones. These secondary products easily complex with the oil and fat, making them difficult to remove, resulting in a higher Anisidine Value (AnV) in the oil and fat.

[0022] Preferably, in the above-mentioned method for removing mineral oil from grease, the step of introducing steam into the grease lasts for 60 to 210 minutes. The steam may be introduced intermittently or continuously, with the steam introduction rate determined by the designed steam volume and distillation time. The present invention has found that the distillation time is preferably controlled within the range of 60 to 210 minutes. Too short a distillation time results in poor mineral oil removal, while too long a distillation time results in prolonged heating of the grease, affecting its quality.

[0023] The above method can have a good effect on the removal of mineral oil, which can make the mineral oil content lower than 5ppm, and has a significant effect on reducing the mineral oil content of C10-C25, making its content lower than 1ppm.

[0024] In a more preferred embodiment, the process of introducing steam into the grease is a staged process:

[0025] Adjust the temperature to 210-220°C (excluding the endpoint value of 210°C), the amount of steam introduced is 20-35% of the mass of the oil, and the time of steam introduction is 15-30 minutes;

[0026] Adjust the temperature to 190-210°C (excluding the endpoint value of 190°C), the amount of steam introduced is 15-35% of the mass of the oil, and the steaming time is 15-60 minutes;

[0027] The temperature is adjusted to 160-190°C, the amount of steam introduced is 10-30% of the mass of the oil, and the time of steam introduction is 30-120 minutes.

[0028] It is more appropriate to operate in a segmented order from high temperature to low temperature.

[0029] The above-mentioned segmented steam introduction method is effective in removing long-chain (C25-50) mineral oils, while also effectively retaining long-chain polyunsaturated fatty acids and active lipid accompaniments such as carotenoids in the oil. Typically, when processing polyunsaturated fatty acid oils, relatively low temperatures are selected to avoid the effects of prolonged high temperatures on fatty acids or other active substances. However, the present invention achieves a more thorough removal of mineral oil through a specific segmented aeration process, without affecting the retention of nutrients and avoiding the formation of secondary products.

[0030] As one of the beneficial effects of the present method, the step of introducing steam into the oil in the aforementioned method for removing mineral oil from fats and oils is effective for deodorizing the oil and oil, and can replace or be integrated with the deodorization step in conventional oil and oil refining operations. Furthermore, since most oil and oil production processes include a steam deodorization step to remove small odorous molecules, compared to other mineral oil removal methods that add additional steps, the present method does not result in a loss in oil and oil yield, and the modification cost is low.

[0031] While existing oil deodorization processes also employ steam, they primarily remove odorous substances, free fatty acids, and a small amount of residual solvent from oils and fats. Crude oils containing polyunsaturated fatty acids, in particular, contain a high concentration of specific odor molecules, all of which can be effectively removed during the deodorization process. Current improvements to deodorization processes primarily focus on lowering the deodorization temperature to preserve more fat-soluble nutrients and shortening the deodorization time to prevent an increase in free fatty acid content. However, there is no public evidence that improvements to the deodorization process can remove mineral oil contamination from oils and fats.

[0032] Preferably, the oil is an oil that has undergone one or more refining steps of a degumming step, a deacidification step, a decolorization step, a dewaxing step, and a deodorization step.

[0033] Preferably, the oil is a polyunsaturated fatty acid oil, wherein the unsaturated fatty acid content with a carbon chain length of more than 20 carbon atoms and a double bond number of more than 4 accounts for more than 40% by weight of the total fatty acids;

[0034] Polyunsaturated fatty acid oils are mainly derived from microbial fermentation extraction, extraction from marine animals, and some from some special genetically modified plants. The biggest difference between them and conventional vegetable oils and animal oils is that they are saturated with long-chain polyunsaturated fatty acids. Long-chain polyunsaturated fatty acids are more sensitive to the environment during extraction and refining. It is even more necessary to simplify the process flow and minimize the time the oil is exposed to high temperature without affecting the purpose of the invention. The method described in the present invention has obvious advantages in removing mineral oil from polyunsaturated fatty acid oils.

[0035] The present invention also provides application of the above method in removing mineral oil from grease.

[0036] The present invention also provides a grease obtained by the above method of removing mineral oil from grease;

[0037] The mineral oil content in the grease is less than 5 ppm, more preferably, the mineral oil content is less than 3 ppm.

[0038] Preferably, the oil has an acid value of ≤1.0 mgKOH / g, an anisidine value of ≤5, and a trans fatty acid content of ≤1.0 w%.

[0039] The present invention also provides a polyunsaturated fatty acid oil, wherein the acid value of the polyunsaturated fatty acid oil is ≤1.0 mgKOH / g, the anisidine value is ≤5, and the trans fatty acid content is ≤1.0 w%; the mineral oil content in the polyunsaturated fatty acid oil is less than 5 ppm, and more preferably, the mineral oil content is less than 3 ppm.

[0040] Preferably, the polyunsaturated fatty acid oil contains unsaturated fatty acids with a carbon chain length of at least 20 carbon atoms and at least four double bonds, accounting for at least 40% by weight of the total fatty acids. More preferably, the polyunsaturated fatty acid oil is derived from a microorganism. Common oil-producing microorganisms in the field include Mortierella alpina, yeast, Schizochytrium, Microchrysogenum, Dunaliella salina, or Dinoflagellate. Microbial-derived polyunsaturated fatty acid oils contain a high content of polyunsaturated fatty acids, especially those containing a high proportion of triglyceride-type long-chain unsaturated fatty acids with at least four double bonds. This can lead to increased variability and risks during the refining process, such as increased free fatty acids and the risk of elevated peroxide values ​​due to prolonged high temperatures. The method of the present invention can avoid or eliminate these risks during the refining process and achieve the technical effect of reducing mineral oil. It is particularly suitable for removing mineral oil from microbial-derived polyunsaturated fatty acid oils.

[0041] Those skilled in the art will appreciate that if the mineral oil content in the oil is already close to a relatively low level, reducing it to a lower level will be more challenging. The advantage of the present invention lies in the fact that the method of the present invention overcomes this technical difficulty and can effectively reduce the mineral oil content of the feedstock even if the initial mineral oil content is relatively low.

[0042] The beneficial effects of the present invention are at least:

[0043] According to the present invention, a method for removing mineral oil from oils and fats can be provided, which is particularly effective for removing mineral oil from polyunsaturated fatty acid oils and fats of microbial origin. It can effectively remove mineral oil from oils and fats in a simple and quick manner without changing the original oil production process steps, and obtain oils and fats with a mineral oil content of less than 5 ppm, and further obtain oils and fats with a mineral oil content of less than 3 ppm. DETAILED DESCRIPTION

[0044] The present invention will be further described below with reference to the examples, but the present invention is not limited to the following examples.

[0045] Where specific techniques or conditions are not specified in the examples, the procedures were carried out in accordance with those described in the literature in the field or in the product specifications. Reagents or instruments used, where the manufacturer is not specified, are all conventional products available through reputable distributors. The oils and fats used in the following examples and comparative examples were all extracted from microorganisms and obtained through conventional hydration, alkali refining, decolorization, and desolventization processes. The oil obtained from Mortierella alpina has an arachidonic acid content of 45.5% and is referred to as AA oil. The oil obtained from Schizochytrium sp. has a DHA content of 56.0% and is referred to as DHA oil.

[0046] The detection method of mineral oil in the following examples and comparative examples: EN 16995-2017; the main detection instrument: liquid chromatography-gas chromatography.

[0047] Example 1

[0048] Example 1 provides a method for removing mineral oil from AA grease:

[0049] Under vacuum conditions, steam is continuously introduced into the AA grease according to the designed steam volume for treatment;

[0050] Grease temperature: 185°C, pressure: 350Pa, treatment time: 90min, steam volume: 94.5% (relative to AA grease mass).

[0051] Example 2

[0052] Example 2 provides a method for removing mineral oil from AA grease:

[0053] Under vacuum conditions, steam is continuously introduced into the AA grease according to the designed steam volume for treatment;

[0054] Grease temperature: 185°C, pressure: 350Pa, treatment time: 90min, steam volume: 15% (relative to AA grease mass).

[0055] Example 3

[0056] Example 3 provides a method for removing mineral oil from AA grease:

[0057] Under vacuum conditions, steam is continuously introduced into the AA grease according to the designed steam volume for treatment. The process of introducing steam is as follows:

[0058] (1) The temperature was controlled at 215°C, the pressure was 350 Pa, the treatment time was 20 min, and the steam volume was 25% (relative to the mass of AA oil);

[0059] (2) Adjust the temperature to 200°C, the pressure to 350 Pa, the treatment time to 30 min, and the steam volume to 20%;

[0060] (3) Adjust the temperature to 185°C, the pressure to 350 Pa, the processing time to 40 min, and the steam volume to 15%.

[0061] Comparative Example 1

[0062] Comparative Example 1: Conventional deodorization process conditions were used to treat AA grease:

[0063] Under vacuum conditions, steam is continuously introduced into the AA grease according to the designed steam volume for treatment;

[0064] Grease temperature: 185°C, pressure: 350Pa, treatment time: 90min, steam volume: 8% (relative to AA grease mass).

[0065] Content test

[0066] 1. The oils obtained in Examples 1-3 and Comparative Example 1 had an acid value / (mgKOH / g) ≤ 1.0; anisidine value ≤ 5.0; and trans fatty acid / (w / %) ≤ 1.0. The difference in AA retention rate after treatment was less than 1%, indicating no significant difference.

[0067] 2. The oils and fats after distillation treatment in Examples 1-3 and Comparative Example 1 were subjected to mineral oil testing. The results are shown in Table 1 below.

[0068] Table 1

[0069]

[0070] Note: MOSH / POSH represents the total content of mineral oil saturated hydrocarbons (MOSH) and polyolefin oil saturated hydrocarbons (POSH); the mineral oil content in different carbon atom number ranges is calculated segmentally and will not be counted repeatedly; MOAH was not detected in AA oils and fats, so it is not listed in Table 1.

[0071] Comparative Example 2

[0072] In this comparative example, based on Example 1, the oil treatment temperature was increased to 260° C., the pressure was 350 Pa, the treatment time was 90 min, the steam volume was 10% (relative to the mass of AA oil), the removal ratio of C10-C50MOSH was 23.2%, and the anisidine value was as high as 48.

[0073] Example 4

[0074] Example 4 provides a method for removing mineral oil from DHA grease:

[0075] Under vacuum conditions, steam is continuously introduced into the DHA oil according to the designed steam volume for treatment;

[0076] The oil temperature is 200°C, the pressure is 400 Pa, the processing time is 120 min, and the steam volume is 80.2% (relative to the mass of DHA oil).

[0077] Example 5

[0078] Example 5 provides a method for removing mineral oil from DHA grease:

[0079] Under vacuum conditions, steam is continuously introduced into the DHA oil according to the designed steam volume for treatment;

[0080] The oil temperature is 200°C, the pressure is 400 Pa, the processing time is 120 min, and the steam volume is 35% (relative to the mass of DHA oil).

[0081] Example 6

[0082] Example 6 provides a method for removing mineral oil from DHA grease:

[0083] Under vacuum conditions, steam is continuously introduced into the DHA oil according to the designed steam volume for treatment, wherein the process of introducing steam is as follows:

[0084] (1) The temperature was controlled at 212°C, the pressure was 400 Pa, the treatment time was 15 min, and the steam volume was 30% (relative to the mass of DHA oil);

[0085] (2) Adjust the temperature to 195°C, the pressure to 400 Pa, the treatment time to 20 min, and the steam volume to 20%;

[0086] (3) Adjust the temperature to 175°C, the pressure to 400 Pa, the processing time to 55 min, and the steam volume to 20%.

[0087] Comparative Example 3

[0088] Comparative Example 3: Conventional deodorization process conditions were used to treat DHA oil:

[0089] Under vacuum conditions, steam is continuously introduced into the DHA oil according to the designed steam volume for treatment;

[0090] The oil temperature is 200°C, the pressure is 400Pa, the processing time is 120min, and the steam volume is 6% (relative to the mass of DHA oil).

[0091] Content test

[0092] 1. The oils obtained in Examples 4-6 and Comparative Example 3 had an acid value / (mgKOH / g) ≤ 1.0; anisidine value ≤ 5.0; and trans fatty acid / (w / %) ≤ 1.0. The difference in DHA retention rate after treatment was less than 1%, indicating no significant difference.

[0093] 2. The oils and fats after distillation treatment in Examples 4-6 and Comparative Example 3 were subjected to mineral oil testing. The results are shown in Table 2 below.

[0094] Table 2

[0095]

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for removing mineral oil from grease, characterized in that: The following steps are involved: Under vacuum conditions, steam is introduced into the grease; The process of introducing steam into the grease is a staged process: Adjust the temperature to 210-220°C, introduce steam in an amount of 20-35% of the mass of the oil, and introduce steam for 15-30 minutes; Adjust the temperature to 190-210°C, introduce steam in an amount of 15-35% of the mass of the oil, and introduce steam for 15-60 minutes; The temperature is adjusted to 160-190°C, the amount of steam introduced is 10-30% of the mass of the oil, and the time of steaming is 30-120 minutes.

2. The method for removing mineral oil from grease according to claim 1, characterized in that: The time for the step of introducing steam into the oil is 60 minutes to 210 minutes.

3. The method for removing mineral oil from grease according to claim 1, characterized in that: The step of introducing steam into the oil is effective for deodorizing the oil; and / or, The oil is subjected to one or more refining steps of degumming, deacidification, decolorization, dewaxing and deodorization.

4. The method for removing mineral oil from grease according to claim 1, characterized in that: The oil is a polyunsaturated fatty acid oil, wherein the unsaturated fatty acid content with a carbon chain length of more than 20 carbon atoms and a double bond number of more than 4 accounts for more than 40% by weight of the total fatty acids.

5. A fat obtained by the method according to any one of claims 1 to 4; The content of mineral oil in the grease is less than 5 ppm.

6. The grease according to claim 5, characterized in that The acid value of the oil is ≤1.0 mgKOH / g, the anisidine value is ≤5, and the trans fatty acid content is ≤1.0 w%.

7. A polyunsaturated fatty acid oil obtained by the method according to claim 4, characterized in that: The acid value of the polyunsaturated fatty acid oil is ≤1.0 mgKOH / g, the anisidine value is ≤5, and the trans fatty acid content is ≤1.0 w%; the mineral oil content in the polyunsaturated fatty acid oil is lower than 5 ppm.

8. The polyunsaturated fatty acid oil according to claim 7, characterized in that The content of unsaturated fatty acids with a carbon chain length of more than 20 carbon atoms and a double bond number of more than 4 in the polyunsaturated fatty acid oil accounts for more than 40% by weight of the total fatty acids.

9. The polyunsaturated fatty acid according to claim 8, characterized in that The source of the polyunsaturated fatty acid oil is microorganism.

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