Methods for recycling used oil

Abstract

To efficiently reduce metal content, inorganic impurity, and water content in a waste oil in a simple method to obtain a high quality regenerated heavy oil having a characteristic equal to or more than a JIS type 1 regenerated heavy oil.SOLUTION: There is provided a method for regenerating waste oil, comprising: a first step for adding and mixing an unsaturated aqueous solution of ammonium sulfate compound and acids to the waste oil; and a second step for separating and recovering oil content from the obtained mixture. There is also provided a method for regenerating treated aqueous solution that enables repeated use of a used regenerated treated aqueous solution in a simple method, particularly only by adding acids as much as a consumed amount.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for recycling waste oil, and more specifically, to a method for recycling waste oil that can remove or reduce metals, moisture, and the like from waste oil to produce high-quality recycled fuel oil with low ash and moisture content. [Background technology]

[0002] In recent years, from the perspective of effective resource utilization and environmental conservation, proper waste disposal and promotion of recycling have been given great attention as urgent social issues, and in response to these issues, the establishment of legislation such as the Waste Disposal Law and Recycling Law is underway. In the industrial sector, the development of recycling technology is underway to reduce waste emissions and to recycle and effectively use waste. For used lubricating oil, the development of technology to produce high-quality recycled fuel oil is also desired from the above-mentioned perspective. For example, the amount of used engine oil and industrial lubricating oil generated annually is 800,000 KL, of which 670,000 KL is recovered to save for recycling and in-house fuel consumption, and about 70% of that, or 470,000 KL, is used as recycled heavy oil. However, since this recycled heavy oil is produced by simple refining such as heating, static separation, or centrifugation, it is of poor quality, with a high metal content and corresponding ash content, as well as a high water content, and its uses are limited.

[0003] Currently, most recycled heavy oil contains a lot of ash, and when used in boilers, a lot of ash adheres to the smoke tubes, reducing thermal efficiency. As a result, the main uses for recycled oil are in aluminum melting furnaces, lime kilns, cement kilns, etc., which use direct heat, and it is no exaggeration to say that it is simply incinerated waste oil.

[0004] The composition of used lubricating oils to be recycled is approximately 70% engine oil and approximately 30% industrial lubricating oil. Metallic detergent dispersants, zinc dialkyldithiophosphates, and organic molybdenum compounds are added to normal engine oils to maintain engine cleanliness and anti-wear performance over a long period of time, and these additives contain Ca, Zn, Mo, P, etc. For this reason, fuel oils recycled from waste oils containing a large amount of used engine oils cannot be used in small once-through boilers or internal combustion engines because they contain a large amount of metal (ash) content.

[0005] If it were possible to remove the ash from used lubricating oil, that is, if it were possible to remove the metal and water content in a simple and inexpensive way, the range of uses would be greatly expanded. For example, the oil could be used in agricultural vinyl greenhouse heaters and small once-through boilers for seafood processing. Even if crude oil prices remain high due to soaring crude oil prices, it could provide an inexpensive alternative fuel to heavy oil A, thereby contributing to supporting primary industries whose business is suffering.

[0006] Methods for separating and removing major metals such as Ca, Zn, and Mo, i.e., ash and moisture, from used lubricating oil include a method using concentrated sulfuric acid (Non-Patent Document 1), a method using acetic acid or phosphoric acid (Non-Patent Document 2), a distillation separation method (Patent Document 1), and a separation method using a membrane (Non-Patent Document 3). However, all of these methods have problems such as the difficulty of treating the waste generated, the low metal removal rate, and the high cost.

[0007] Other methods proposed include washing waste oil with an aqueous solution of sodium silicate, followed by secondary washing with an aqueous solution of mineral acid, organic acid or aldehyde (Patent Document 2), and treating the oil with an aqueous solution of urea, saturated ammonium sulfate, or an aqueous solution of ammonium nitrate and a chelating agent (e.g., EDTA: sodium ethylenediaminetetraacetate) to produce recycled oil (Patent Document 3). However, the former method has problems such as emulsification of the treatment liquid and the inclusion of silicon from the treatment agent in the treated oil, while the latter method requires expensive treatment agents. However, there are problems such as the need for a large amount of treatment liquid, which increases the cost of treatment, and the weak ability to remove the main target metals such as Zn and Mo, which means that the ash content of the produced recycled heavy oil is limited to 0.3 mass%. For this reason, a process of adding aliphatic carboxylic acids, sulfuric acid, etc. to remove metals such as Zn and Mo, and a water washing process to remove acids remaining in the recycled oil have been proposed. However, in the third process, in which the treatment liquid is treated with an aqueous solution of aliphatic carboxylic acids, aldehydes, sulfuric acid, etc. to reduce the ash content, although Zn can be reduced, the yield of recycled heavy oil decreases due to emulsification of the treatment liquid. Furthermore, in order to return the acidity of the obtained recycled heavy oil (reaction test; JIS K 2252) to neutral, the water washing process in the fourth process must be performed at least twice, which is a factor that significantly increases the cost of producing recycled oil.

[0008] In addition, as a problem in the manufacturing process, ammonium nitrate is a strong oxidizing agent that may explode due to impact, friction, heat, or the mixing of reducing materials, and it is a dangerous material that requires careful handling, as it is known to be prone to spontaneous combustion when mixed with flammable substances such as mineral oil, and it reacts violently with organophosphorus compounds in waste oil. On the other hand, saturated ammonium sulfate liquid precipitates due to temperature changes, which can cause problems such as blockages in pipes used to transport the regenerated liquid.

[0009] Even in the recycled oil produced through the above-mentioned processing steps, the ash content does not fall below 0.2% by mass, and it does not meet the JIS standard for heavy oil (class 1) of 0.05% by mass or less ash content and 0.3% by volume or less moisture content.

[0010] In a method of treating waste oil with an aqueous aluminum sulfate solution (Patent Document 4), recycled heavy oil is obtained with a moisture content of 0.3 volume % or less and an ash content of about 0.15 mass %. However, a further processing step is required to remove the remaining 200 to 400 ppm of Al, and measures against corrosion of the manufacturing equipment caused by the aluminum sulfate regeneration treatment agent are also required, which increase the cost of producing recycled oil. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 4355363 [Patent Document 2] JP 2003-176492 A [Patent Document 3] JP 2006-249419 A [Patent Document 4] JP 2016-53125 A [Non-patent literature]

[0012] [Non-Patent Document 1] Recycling Possibilities and Potential Uses of Used Oils [Non-Patent Document 2] Recycling of Waste Engine Oils Using a New Washing Agent [Non-Patent Document 3] Yoshiie, Ueki et al.: Transactions of the Japan Society of Mechanical Engineers (Series B), No. 78, Vol. 789, (2012-5), p. 1048 Summary of the Invention [Problem to be solved by the invention]

[0013] The present invention provides a method for regenerating waste oil, which uses a regenerating treatment agent that is inexpensive and easily available, and which can easily and efficiently reduce and remove impurities such as metals (ash) and moisture in the waste oil at low cost to the low level required by the JIS standard for heavy oil (class 1). Another object of the present invention is to provide a method for regenerating a used regenerated aqueous solution, which can be used repeatedly by simply and at low cost after the used regenerated aqueous solution has been used in the above-mentioned regeneration method. A further object of the present invention is to provide a method for producing reclaimed oil by utilizing the above-mentioned regeneration treatment method or the method for regenerating a regenerated aqueous solution. [Means for solving the problem]

[0014] As a result of intensive research into the above-mentioned problems, the present inventors have found that the metal content, inorganic impurities, and further moisture in waste oil can be efficiently reduced by treating the waste oil with an unsaturated aqueous solution of an ammonium sulfate compound and an acid, and have thus completed the present invention. Further, the present inventors have found a method for easily regenerating and reusing the aqueous reprocessing solution used after treating waste oil with the aqueous reprocessing solution, thereby completing the present invention. Furthermore, the present inventors have found that the method of the present invention makes it possible to obtain high-quality recycled heavy oil having properties equal to or better than those of JIS Class 1 recycled heavy oil, and have thus completed the present invention.

[0015] (1) The present invention provides a method for regenerating waste oil, comprising a first step of adding an unsaturated aqueous solution of an ammonium sulfate compound and an acid to the waste oil and mixing them, and a second step of separating and recovering the oil from the resulting mixture. The ammonium sulfate compound is preferably ammonium sulfate ((NH4)2SO4) and / or ammonium sulfate hydrate represented by (NH4)2SO4·nH2O (n is 1 to 10). The acids are preferably selected from organic acids and / or inorganic acids. The unsaturated aqueous solution of the ammonium sulfate compound preferably has an unsaturated dissolved concentration of 5.0% by mass or more calculated as anhydrous ammonium sulfate. It is preferable to add 0.005 to 1.0 times the mass of the ammonium sulfate compound in terms of anhydride relative to the waste oil. The amount of the acid added is preferably 0.005 to 0.5 times the mass of ammonium sulfate in terms of anhydride of the ammonium sulfate. The method for separating and recovering the oil from the mixture in the second step is preferably a static separation method and / or a centrifugation method. The waste oil is preferably used lubricating oil mainly composed of used engine oil and / or used industrial lubricating oil, or recycled heavy oil or bio-recycled heavy oil produced using these as raw materials.

[0016] (2) The present invention provides a method for regenerating a used regenerated aqueous solution, which comprises purifying the used regenerated aqueous solution used in the above-mentioned waste oil regeneration treatment method, quantitatively analyzing the contents of ammonium sulfate and acids in the aqueous solution, and adding ammonium sulfate and acids in an amount equivalent to the consumption calculated from the values ​​obtained, to the purified aqueous solution. (3) The present invention provides a method for regenerating a used regenerated aqueous solution, which comprises purifying the used regenerated aqueous solution used in the above-mentioned waste oil regeneration treatment method, and then adding a certain amount of ammonium sulfate and acids in the amounts consumed to the purified aqueous solution. It is preferred to add only the amount of acids that will be consumed. (4) The present invention provides a method for regenerating waste oil, which utilizes the above-mentioned method for regenerating used regenerated aqueous solution and carries out the regeneration treatment of waste oil at least five times. (5) The present invention provides a method for producing regenerated oil from waste oil by utilizing the waste oil regeneration method (1), the method for regenerating a used regenerated aqueous solution (2) to (3), or the waste oil regeneration method (4). Effect of the Invention

[0017] According to the method of the present invention, impurities such as metals (ash) and water in waste oil can be efficiently removed very simply and inexpensively by using an unsaturated aqueous solution of an ammonium sulfate compound and an acid (or its aqueous solution) (hereinafter sometimes referred to as a regeneration treatment agent or a regeneration treatment agent aqueous solution) in the waste oil. In particular, according to the method of the present invention, high-quality regenerated heavy oil having properties equal to or better than JIS Class 1 regenerated heavy oil can be obtained from used lubricating oil, especially used lubricating oil containing a large amount of engine oil. In addition, the regenerating agent used in the method of the present invention is inexpensive and easily available. The processing process is simple, and waste oil can be recycled at low cost. Furthermore, by adjusting the concentration of the regenerating agent in the used regenerated aqueous solution after the regeneration process based on the amount consumed in the regeneration process, the regeneration performance of the aqueous solution can be easily restored to the state before use, so that the used regenerated aqueous solution can be repeatedly used. In particular, in the present invention, the used regenerated aqueous solution can be repeatedly used by adjusting the concentration of only the acids. [Brief description of the drawings]

[0018] [Figure 1] 1 is an example of a flow sheet of the waste oil regeneration method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention will be described in detail below. The method for regenerating waste oil of the present invention includes a first step of adding a regeneration agent containing an unsaturated aqueous solution of an ammonium sulfate compound and an acid to the waste oil and mixing them, and a second step of separating and recovering the oil from the resulting mixture.

[0020] The waste oil to be regenerated in the present invention is not particularly limited, but includes not only used lubricating oils containing a large amount of impurities such as water and ash of metals, but also regenerated heavy oils (e.g., regenerated heavy oils represented by JIS K2170) and bio-regenerated heavy oils (e.g., bio-regenerated heavy oils represented by JIS K2171) produced using such used lubricating oils as raw materials. Examples of used lubricating oils include used engine oils containing a relatively large amount of ash such as metals, hydraulic oils other than chlorine-based cutting oils, used industrial lubricating oils such as rolling oils, etc.

[0021] Examples of the ammonium sulfate compound used in the regeneration treatment of the present invention include ammonium sulfate anhydride ((NH4)2SO4) and ammonium sulfate hydrate represented by (NH4)2SO4·nH2O (n is 1 to 10). The hydration number n is not particularly limited, but is usually 1 to 10. From the viewpoint of availability and economy, n is preferably 2 to 5, more preferably 1 to 2. The ammonium sulfate compound may be either ammonium sulfate anhydride or ammonium sulfate hydrate used alone, or a mixture thereof. The hydrate may be a mixture of hydrates with different hydration numbers.

[0022] The purity of the ammonium sulfate compound is preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and particularly preferably 95% or more, in terms of ammonium sulfate concentration. If the purity of the ammonium sulfate compound is less than 70%, there is a high possibility that metals such as sodium and potassium and sulfate ions contained as impurities will remain in the treated oil, albeit in very small amounts.

[0023] The amount of ammonium sulfate compound added to the waste oil is not particularly limited, but the lower limit is preferably 0.01 times by mass or more, more preferably 0.05 times by mass or more, and even more preferably 0.10 times by mass or more, based on the anhydrous ammonium sulfate, relative to the waste oil. On the other hand, the upper limit is preferably 1.0 times by mass or less, more preferably 0.5 times by mass or less, and particularly preferably 0.3 times by mass or less. Even when ammonium sulfate hydrate is used, the amount is based on ammonium sulfate excluding the hydrated portion.

[0024] The concentration of the ammonium sulfate compound as an unsaturated aqueous solution is usually 3% by mass or more, preferably 5% by mass or more, more preferably 10% by mass or more, and particularly preferably 15% by mass or more, based on anhydrous ammonium sulfate. If the concentration of the unsaturated aqueous solution is less than 3% by mass, the ammonium sulfate compound is too diluted, the ash reduction reaction is slowed down, and the amount of ammonium sulfate compound required to achieve a predetermined ash reduction reaction is not sufficient. On the other hand, the upper limit is not particularly limited as long as it is within the unsaturated concentration range of −5° C. to 100° C., and is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less, from the viewpoints of workability and economy in addition to the effect of reducing the ash content.

[0025] The ratio of the unsaturated aqueous solution of the ammonium sulfate compound to be added to the waste oil varies depending on the concentration of the aqueous solution of the ammonium sulfate compound, but when used within the above range of aqueous solution concentration of the ammonium sulfate compound, the unsaturated aqueous solution is usually preferably 0.05 volume times or more, more preferably 0.1 volume times or more, and even more preferably 0.15 volume times or more, relative to the waste oil. On the other hand, it is preferably 5 volume times or less, more preferably 2 volume times or less, and even more preferably 1 volume times or less. The amount of the aqueous solution of the regeneration treatment agent to be added to the waste oil may be added in excess so that metal components and the like contained in the waste oil can be sufficiently captured, and even if it is added in excess, it does not cause any particular problem because it is recovered and reused after treatment as described below.

[0026] The acids used in the regeneration treatment of the present invention are not particularly limited, but are water-soluble and insoluble in mineral oil. In the present invention, the acids are preferably organic acids and / or inorganic acids. Examples of organic acids include formic acid and acetic acid. Acetic acid is particularly preferred. Examples of inorganic acids include sulfuric acid, hydrochloric acid, and phosphoric acid. Sulfuric acid is particularly preferred. It is desirable that the acids have a high purity and a small amount of impurities. For example, the concentrations of formic acid, acetic acid, sulfuric acid, and phosphoric acid are preferably 80% by mass or more, more preferably 90% by mass or more. Furthermore, the concentration of hydrochloric acid is preferably 30% by mass or more, more preferably 35% by mass or more.

[0027] The method of adding acids in the regeneration treatment of waste oil is not particularly limited. A predetermined amount of acids may be dissolved in an unsaturated aqueous solution of an ammonium sulfate compound and added as a mixture, or an unsaturated aqueous solution of an ammonium sulfate compound may be added to the waste oil first, and then the acids may be added as a single substance or as an aqueous solution of a predetermined concentration. It is preferable to add the acids as an aqueous solution of a predetermined concentration. In addition, the timing of adding the acids is not particularly limited, but it is preferable to add them almost simultaneously with the unsaturated aqueous solution of an ammonium sulfate compound or immediately after adding the unsaturated aqueous solution of an ammonium sulfate compound. The amount of the acid used in the regeneration treatment varies depending on the regeneration treatment conditions, but in any case, the amount is preferably 0.005 to 0.5 times by mass, more preferably 0.005 to 0.1 times by mass, even more preferably 0.01 to 0.07 times by mass, and particularly preferably 0.015 to 0.04 times by mass, relative to the amount of ammonium sulfate used (in anhydride equivalent).

[0028] The first step in the present invention is a step of adding an aqueous solution of an ammonium sulfate compound to an acid to waste oil, or adding an aqueous solution of an ammonium sulfate compound and an aqueous solution of an acid to waste oil almost simultaneously or separately, and mixing them. The mixing is preferably carried out under stirring, so that the regeneration treatment agent comes into contact with the metal components in the waste oil, and a reaction proceeds to produce a solid matter. The temperature during mixing and stirring is usually 5 to 95°C, preferably 20 to 80°C, and more preferably 30 to 70°C. The reaction time varies depending on the stirring method and temperature, but is usually 0.1 seconds to 24 hours, preferably 0.5 seconds to 10 hours, and more preferably 1 second to 5 hours. The stirring conditions are preferably 20 to 3,000 rpm, more preferably 50 to 1,000 rpm, using a commonly used stirrer. Mixing and stirring can also be performed using a line mixer. In this case, a circulation tank is installed and the same effect as stirring can be obtained by passing the mixture through the line mixer many times.

[0029] The second step in the present invention is a step of separating and recovering oil from the mixture in which the regeneration treatment agent and waste oil are brought into contact with each other in the first step and the reaction proceeds. The oil from which the water has been removed is separated and recovered. The method for separating and recovering the oil from the mixture may be a static separation method, a centrifugal separation method or a combination of both methods. The static separation method is a method in which the mixture is allowed to stand and separated into solids (sludge of metals, etc.), oil, and water (water contained in the added treatment agent and water removed from the waste oil) based on differences in density. The static separation time is usually preferably 0.5 hours or more, more preferably 5 hours or more, even more preferably 10 hours or more, and most preferably 24 hours. On the other hand, there is no particular upper limit, but it is usually 3 days (72 hours) or less. The temperature at which the mixture is left to stand is not particularly limited, but is usually 5 to 95°C, preferably 30 to 80°C, and more preferably 50 to 80°C. To further increase the efficiency of separation, it is preferable to perform separation using a centrifuge. It is desirable that the centrifuge used is capable of separating solids (solids), liquids (oil), and liquids (moisture), and is capable of automatically discharging sludge (solids). There are no particular limitations on the centrifugation conditions, but the temperature of the regenerated liquid during centrifugation is usually 20 to 90°C, preferably 30 to 80°C, and more preferably 50 to 80°C.

[0030] The waste oil regeneration method of the present invention can remove water and metals (ash) from the waste oil. Waste oil and commercially available regenerated heavy oil contain 1 to 5% water by volume. This water can be reduced by 40 to 60% by regeneration treatment using an unsaturated aqueous solution of an ammonium sulfate compound. Furthermore, by adding an acid (e.g., acetic acid, sulfuric acid, etc. are preferred), the water content in the regenerated oil measured by a distillation method can be reduced to 0.2% by volume or less, preferably 0.1% by volume or less, and more preferably 0.05% by volume or less. In particular, in the case of regenerated heavy oil, an emulsification phenomenon frequently occurs during regeneration treatment, which not only reduces the yield of regenerated heavy oil but also inhibits the reduction of water. However, by adding an acid, the separation of the oil layer and the water layer can be improved and the formation of emulsions can be significantly suppressed. As a result, the yield of the regenerated heavy oil obtained is improved and the water content can be reduced to 0.05% by volume or less.

[0031] Waste oil contains metal components such as Ca, Zn, Mo, Si, and Fe, which become ash. The only metal component that can be removed by recycling waste oil using an unsaturated aqueous solution of ammonium sulfate compound is mainly Ca, and the Ca removal rate is up to about 70%. On the other hand, there is almost no effect in removing metal components such as Zn, Mo, and Fe. For this reason, when recycling waste oil, which is mainly made up of normal engine oil, using only ammonium sulfate compound, the ash reduction rate is limited to about 40%.

[0032] According to the method of the present invention, by adding an unsaturated aqueous solution of an ammonium sulfate compound and an acid and treating the waste oil, it is possible to remove almost 100% of the Ca and Zn among the metal components such as Ca, Zn, Mo, Si, and Fe contained in the waste oil, and it is also possible to remove about 60% of the metal components such as Mo and Si. The metal content in the recycled oil measured by inductively coupled plasma emission spectrometry (ICP) is reduced to 100 mass ppm or less, preferably 50 mass ppm or less, and more preferably 10 mass ppm or less, for Ca and Zn, which are particularly abundant in waste oil. The reduction rate of these metals is 70 to 99%, which is a very high efficiency. The reduction rate of Mo, which is contained in the waste oil at 100 to 150 mass ppm, is 40 to 60%, and 40 to 60 mass ppm remains in the recycled heavy oil, but the contribution rate to the ash content is a maximum of 0.01 mass% or less. The ash content in the recycled oil (ash content as defined by JIS K2272) is 0.7% by mass or less, preferably 0.3% by mass or less, more preferably 0.1% by mass or less, and particularly preferably 0.05% by mass or less. By making it 0.05% by mass or less, recycled heavy oil equivalent to Class 1 (so-called heavy oil A) of the JIS standard for heavy oil can be obtained.

[0033] The used regenerated aqueous solution separated in the second step is filtered to remove solid matter, purified, and the concentration of the used regenerating agent in the aqueous solution is adjusted, so that the used regenerated aqueous solution can be reused. The concentration of the treatment agent can be adjusted by quantitative analysis or by adding a predetermined amount of acids without quantitative analysis, thereby making up for the amount of treatment agent consumed in the regeneration process. This concentration adjustment also makes it possible to regenerate the treatment agent into one having the same performance as the original treatment agent. Reusing such used regenerated treatment agents is preferable from the viewpoints of cost reduction and reduction of waste materials, and also contributes to the object of the present invention to provide an inexpensive treatment method.

[0034] The method for regenerating used aqueous treatment solution of the present invention will now be described in further detail. The method for purifying the used regenerated aqueous solution is not particularly limited, but is usually carried out by a filtration method using a filter such as a filter cloth, filter paper, or wire mesh. In addition, the concentration adjustment of ammonium sulfate and acids in the used regeneration treatment aqueous solution is generally performed based on the results of quantitative analysis, such as the formaldehyde method (JIS K8872) and alkali neutralization titration, and can be performed using these methods. In addition, the concentration adjustment of ammonium sulfate and acids can be performed based on the consumption of ammonium sulfate and acids per amount of waste oil treated. By using this consumption, the quantitative analysis work that has been used in the past can be omitted. Specifically, when ordinary waste oil (for example, waste oil cited as an example of waste oil to which the regeneration method of the present invention can be applied) is regenerated with an unsaturated aqueous solution of ammonium sulfate and acids, the amount of ammonium sulfate compound consumed in this regeneration treatment was found to be 2 to 3 g per 1 kg of ordinary treated waste oil from the experimental results of the inventor's study. This amount is an extremely small amount of ammonium sulfate compound consumed in one regeneration treatment of waste oil. Therefore, the concentration of ammonium sulfate may be adjusted using the consumption amount obtained based on the experimental results, but in the present invention, the aqueous solution of ammonium sulfate compound to be reused can be repeatedly used for regeneration treatment at least five times at the initial concentration of the aqueous solution of aluminum sulfate compound without adjusting the concentration.

[0035] On the other hand, the acids are almost entirely consumed in one waste oil treatment. For this reason, the amount of acid newly added when reusing the used regenerated aqueous solution may be the amount of acid added initially, and the acid concentration of the used regenerated aqueous solution can be returned to the initial concentration, thereby ensuring the regeneration performance of the aqueous solution. In this case, the amount of acid to be added can be determined by quantifying the amount of acid in the used aqueous regenerating agent solution, but as a simple method, the amount of addition can be determined by measuring the pH. That is, this is a method in which a predetermined amount of acid is added to the used aqueous regenerated aqueous solution to return the pH to the initial level. In this method, the pH (20 to 30°C) of the aqueous regenerated aqueous solution is preferably within the range shown below. In addition, the concentration of the acid amount is preferably adjusted by measuring the pH during each regenerating treatment that is performed repeatedly. In the following example, sulfuric acid is used as the acid, but it is preferable that other acids are in the same range. (1) Ammonium sulfate aqueous solution (20-30% aqueous solution): pH 5.5-6 (2)(1) + sulfuric acid (add 3% to (1)): pH 2.5 to 3 (3) (2) Used processing solution (used processing solution after one-time processing of waste oil): pH 5-6 (4)(3) + sulfuric acid (added at 3% to ammonium sulfate compound): pH 2.5-3

[0036] In the waste oil regeneration treatment method of the present invention, the waste oil to be treated is not limited, and can be applied to, for example, used lubricating oil containing a large amount of impurities such as water and ash such as metal components, and regenerated heavy oil or bio-regenerated heavy oil produced from such used lubricating oil as a raw material. In particular, it is suitable for waste oil such as used engine oil containing a relatively large amount of ash components such as metal components, or used industrial lubricating oil such as hydraulic oil other than chlorine-based cutting oil and rolling oil. In addition, the method of the present invention is also effective for waste oil such as recovered oil from gas stations (S / S) and automobile repair shops, used and flushing oil from various manufacturing plants, and lubricating oil that is out of specification due to long-term inventory, etc. EXAMPLES

[0037] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. It is not something that can be done.

[0038] The properties of the sample oils (waste oils) used in the Examples and Comparative Examples are shown in Table 1, and the elemental analysis results are shown in Table 2. Quantitative elemental analysis was performed according to ICP emission spectrometry (JPI-5S-38-92: solvent dilution method) on the waste oil after centrifugation (2,000 rpm x 20 min, 980 G). The sample oils (waste oils) were waste diesel engine oil (DEO) and waste gasoline engine oil (GEO) collected from a gas station in Toyohashi City, Aichi Prefecture. Recycled heavy oil (RCO) was obtained from a recycled heavy oil manufacturing company in Hokkaido that regenerated a mixture of used engine oil and industrial lubricating oil. The main reasons for conducting experiments on the above three types of waste oil are as follows: Calcium, the main metal component of ash contained in waste oil, comes from calcium-based metal detergent-dispersants added to engine oil. These additives are broadly classified into sulfonate, phenate, and salicylate types, and different types are used depending on the type of oil. Therefore, experiments were conducted with three types of oil to prove that the method of the present invention is effective even when different types of calcium-based detergent-dispersants are contained.

[0039] [Table 1]

[0040] [Table 2]

[0041] The compounds used in the examples and comparative examples are as follows. Purified water: Purified water produced using a pure water production device manufactured by Shimadzu Corporation Ammonium sulfate (hereinafter sometimes simply referred to as "ammonium sulfate"): Yoneyama Chemical Industry Co., Ltd. First-class (purity: min. 99%) Ammonium nitrate: Wako Pure Chemical Industries, Ltd. special grade (purity: min. 99%) Disodium Ethylenediaminetetraacetate (EDTA): Dojindo Research Institute Co., Ltd. (purity: min.99%) Concentrated sulfuric acid: Yoneyama Chemical Industry Co., Ltd. Special grade (purity: min. 98%) Acetic acid: Wako Pure Chemical Industries, Ltd. special grade (purity: min. 99.7%)

[0042] The above compounds were dissolved or diluted with the above purified water to prepare aqueous solutions having the following concentrations: Ammonium sulfate aqueous solution: 40, 30, 20 and 15% by weight Ammonium nitrate aqueous solution: 0.16% by mass (0.02M) EDTA aqueous solution: 0.37% by mass (0.01M) Sulfuric acid aqueous solution: 10% by mass Acetic acid aqueous solution: 10% by mass

[0043] The experiment was carried out in the following procedure. (i) The sample oil and ammonium sulfate (or other treatment agent) or its aqueous solution were placed in a hard beaker (diameter 70 mm, height 100 mm) and placed in a thermostatic bath (circular hole) at a specified temperature. (a) 80 g of sample oil (waste oil) and an aqueous solution of ammonium sulfate corresponding to the "specified waste oil / aqueous solution of ammonium sulfate" (mass ratio). Unless otherwise specified, the mass ratio was waste oil / aqueous solution of ammonium sulfate = 10 / 5. (b) When an aqueous sulfuric acid solution is added, a predetermined amount of sulfuric acid is added based on the amount of the aqueous ammonium sulfate solution (converted into anhydrous form), for example, 2% by mass. (ii) The above mixtures were added to a reaction vessel at almost the same time, and the mixture was stirred at 400 rpm for 1 hour using a three-blade stirrer (L15 mm x 3). The temperatures were as follows: (a) When the treatment agent is ammonium nitrate or ammonium nitrate-EDTA, room temperature (15-18°C) (b) Otherwise, 60°C. The conditions were different only in the cases of ammonium nitrate and ammonium nitrate·EDTA because they were in accordance with JP 2006-249419 A. (iii) After stirring and reaction, the oil, solids and water (treatment solution) were separated using a centrifuge. The sample liquid was heated to 50°C and placed in a centrifuge (Kokusan H-2000A), after which the temperature was left unchanged (room temperature), and the centrifugation was carried out at 2,000 rpm for 30 minutes at 900 G. The rotor temperature was kept at 25°C during the centrifugation procedure. (iv) The properties of the separated oil (treated oil or reclaimed oil) obtained were evaluated by the following methods. Quantitative analysis of elements: Quantitative analysis of elements (ICP method) Moisture: Distillation method according to JIS K2275 Sulfated ash: Sulfated ash measurement method according to JIS K2272 (ash was determined as sulfated ash, which has higher measurement accuracy) Reaction: Reaction test according to (JIS K2252) Method for evaluating the appearance of emulsion layer Measured by leaving the treatment liquid at room temperature for 1 hour Emulsified layer (mm) % of treated liquid layer thickness (standard condition: 51 mm (oil layer 30 mm + treated water layer 21 mm)) No: 0~less than 2; Yes A: 2~less than 20; Yes B: 20~less than 50

[0044] Example 1 and Comparative Example 1 In the experiment, various regeneration treatment agents shown in Tables 4 and 5 were used to regenerate waste oil according to the experimental procedure described above. The experimental results are summarized in Tables 4 and 5. For reference, the solubility of ammonium sulfate in water is shown in Table 3.

[0045] [Table 3]

[0046] [Table 4]

[0047] [Table 5]

[0048] The results of Example 1 and Comparative Example 1 shown in Tables 4 and 5 reveal the following. (1) Sulfated ash content The reclaimed oil (Example) obtained by the method of the present invention showed an excellent ash reduction rate of 90% or more for sulfated ash. In addition, the reduction rate of calcium, which is the main constituent element of sulfated ash, was also 95% or more, and zinc, which has a high contribution rate to sulfated ash, was also reduced by 95% or more, and it was found that the method of the present invention can achieve an excellent ash reduction rate that could not be achieved by existing treatment methods. In addition, it was found that the method of the present invention exhibits an excellent ash reduction effect in all types of waste oil, DEO, GEO, and RCO, and there is no significant difference due to the difference in oil type.

[0049] In contrast, the sulfated ash content of the reclaimed oils in the comparative examples was at a high level (0.14 to 1.42% by mass) compared to the reclaimed oils obtained by the method of the present invention, and it was found that the performance was inferior. In particular, in the treatment of Comparative Example 1-03 (ammonium sulfate alone: ​​fine powder), the sulfated ash content was (1.42% by mass), and the reduction rate was 30% or less. In addition, as seen in the examples of Comparative Example 1-01 (ammonium nitrate aqueous solution) and Comparative Example 1-02 (aqueous solution of ammonium nitrate and EDTA in combination / Patent Document 3: based on the conditions described in JP 2006-249419 A), even when waste DEO oil was treated using these treatment agents, the quality of the reclaimed oil obtained was low. The sulfated ash content was relatively high at 0.72% by mass and 0.61% by mass, respectively. Furthermore, in Comparative Example 1-06 (sulfuric acid aqueous solution) and Comparative Example 1-07 (treated oil treated with ammonium sulfate aqueous solution and then washed with sulfuric acid aqueous solution), the sulfated ash content of the reclaimed oil from the waste oil GEO was relatively high, similar to the above. Even in the treatment of Comparative Example 1-04 (ammonium sulfate saturated water), the sulfated ash content was 0.43 mass%, and a sufficient reduction effect was not observed. For this reason, in the method described in JP 2006-249419 A, after the treated oil is separated and recovered, it is washed with an acid, for example, an aqueous sulfuric acid solution, and then a fourth and fifth treatment steps are added to remove the sulfuric acid from the reclaimed heavy oil by a water washing treatment.

[0050] (2) Moisture and reactivity tests The recycled oil of the present invention has a moisture content reduced to 0.05 to 0.1% by volume compared to the waste oil shown in Table 1 (DEO: 3.50% by volume; GEO: 2.70% by volume; and RCO: 5.40% by volume). This shows that the moisture content in recycled oil can be reduced to a level that is acceptable for use as normal fuel. In addition, the moisture content of the reclaimed oils obtained by the processing method of the present invention (Examples 1-02 (DEO), 1-05 (GEO) and 1-07 (RCO)) was measured by the Karl Fischer method, which is a trace moisture measurement method, and it was confirmed that all of them were in the range of 300 to 350 ppm by mass. Furthermore, all of the reclaimed oil obtained was neutral, did not require a separate water washing step to remove acidic components, and was confirmed to be suitable for use as fuel oil.

[0051] The moisture content of the reclaimed oil in the comparative examples was 0.45 to 2.40% by volume, which was a high level regardless of which reclaiming agent was used to treat the waste oil. In particular, in the case of waste oil DEO, the reclaimed oil in Comparative Example 1-03 had a moisture content of 2.40% by volume, and the reduction rate was 30% or less. In the case of waste oil RCO, the reclaimed oil in Comparative Examples 1-08 (saturated water of ammonium sulfate) and 1-09 (treated oil treated with an aqueous ammonium sulfate solution and then washed with an aqueous sulfuric acid solution) also had moisture contents of 1.20% by volume and 1.40% by volume, respectively, both of which were high. Recycled oil that is acidic is not preferable as fuel oil, and examples that showed such a property were Comparative Examples 1-05 to 1-07 and 1-09. In particular, in Comparative Example 1-05, the reaction test of the treated oil treated with ammonium sulfate saturated water is originally considered to be neutral, but the subsequent treatment with a sulfuric acid aqueous solution to reduce the ash content (sulfate ash content) of the treated oil caused emulsification, and it was found that the rate at which the recycled heavy oil became acidic was also reduced. In addition, in Comparative Example 1-06, the acidity of the obtained reclaimed oil is due to the remaining sulfuric acid, and generally, in the method of removing ash by sulfuric acid treatment, washing with water, finishing with white clay, etc. are performed after the sulfuric acid treatment (for example, Recycling Possibilities and Potential Uses of Used Oils). As described above, the method of reclaiming used oil by sulfuric acid treatment not only does not sufficiently improve the properties of the obtained reclaimed oil, but also involves complicated processes such as neutralization, washing with water, and white clay treatment for removing the remaining sulfuric acid. For this reason, the sulfuric acid treatment has problems such as the need to separately treat the waste sulfuric acid, sulfuric acid sludge, and waste white clay.

[0052] (3) Appearance of emulsion layer Generally, in experiments in which engine oil and other waste oils were treated with various aqueous solutions to reduce ash content, the emulsifying properties (water solubility) of engine oils and other oils caused severe emulsification and the formation of emulsions. This resulted in a decrease in the oil recovery rate (regeneration rate) due to separation of the emulsions, and furthermore, the need to remove moisture from the recovered oil made the waste oil regeneration process more complicated and less easy to work with. However, in the regeneration process using the method of the present invention, no emulsification phenomenon (formation of an emulsified layer) was observed during the stirring and reaction treatment of the waste oil in any of the examples.

[0053] In the regeneration treatment of the comparative examples, the emulsion layer was thinned in all examples except for Comparative Examples 1-03 and 1-04. The occurrence of emulsification was observed. In particular, in the cases of Comparative Example 1-02 (EDTA added) and 1-06 (sulfuric acid aqueous solution), emulsification occurred severely. In the case of Comparative Example 1-02, the treated water clearly separated by static separation was less than 50% of the treated water used in the experiment. This shows that when attempting to reduce the ash (sulfuric acid ash) and water content of used oil (waste oil) such as engine oil using aqueous solutions of various compounds as treating agents, there is a high possibility that severe emulsification will occur due to the emulsifying properties (water solubilization) of engine oil, etc., and it is very difficult to find conditions under which emulsification will not occur. For this reason, in this type of case, a demulsifier that is both effective and has a wide range of application has not yet been found. In addition, in the case of Comparative Example 1-06, it was found that application to waste oil, especially waste oil mainly composed of used engine oil, is not a preferable method from the viewpoint of the tendency of the treating liquid to emulsify. It was also found that Reference Examples 1-01 to 1-03 (in which an aqueous ammonium sulfate solution was used alone) had relatively high sulfated ash and moisture contents, and did not have sufficient performance as the desired reclaimed oil.

[0054] Regarding the saturated aqueous ammonium sulfate solution used as a waste oil treatment agent in Comparative Examples 1-04, 1-05, 1-08 and 1-09 In order to stably obtain a saturated aqueous solution of ammonium sulfate in response to temperature changes, it is necessary to always have an excess of solid ammonium sulfate in the saturated aqueous solution of ammonium sulfate, that is, to keep the aqueous solution in a so-called supersaturated state. Furthermore, dissolved ammonium sulfate precipitates due to a decrease in temperature, and so on, so that an excess of ammonium sulfate always exists as an insoluble component in the saturated aqueous solution of ammonium sulfate used as an ash-reducing treatment agent. This not only makes the regeneration treatment work of waste oil complicated and difficult, but also complicates the regeneration process for repeatedly using the saturated aqueous solution of ammonium sulfate, reduces the regeneration efficiency of the used treatment liquid, and increases the cost of regeneration treatment of waste oil. The effects of compounds produced in the regeneration treatment aqueous solution when the regeneration treatment is performed with a saturated aqueous ammonium sulfate solution will be specifically described below. In the treatment of waste oil with a saturated aqueous solution of ammonium sulfate, the aqueous solution contains mainly calcium sulfates and a small amount of zinc sulfates as compounds insoluble in mineral oil produced by the reaction of ammonium sulfate with oil-soluble Ca and Zn components. The solubility of zinc sulfate in water is high, for example, 61.3 g / 100 ml water at 30°C, while the solubility of calcium sulfate is very low, for example, the solubility of the dihydrate, which is a common form in aqueous solutions, in water is 0.26 g / 100 ml water at 30°C. The solubility of ammonium sulfate in water is 78.1 g / 100 ml water at 30°C and 87.4 g / 100 ml water at 60°C. This means that when the oil is separated and recovered from the regeneration treatment liquid by centrifugation or static separation, zinc sulfate is highly soluble in water and therefore almost completely dissolves in the treatment water and does not get mixed in with the oil. In addition, calcium sulfate is separated almost 100% as a deposit (solid matter) because it has low solubility in water and high density, and neither compound is mixed with the recovered oil. However, ammonium sulfate in a supersaturated state exists as a solid matter in the treatment aqueous solution, and is separated together with calcium sulfate in the oil separation process. Furthermore, when the temperature of the treatment aqueous solution is reduced to 30°C, for example, from an ammonium sulfate saturated aqueous solution in which the treatment temperature is 60°C, more than 10% by mass of the dissolved ammonium sulfate precipitates, and as mentioned above, it is removed as a solid matter together with insoluble substances such as calcium sulfate, resulting in a loss of a large amount of ammonium sulfate. For this reason, in order to prevent the precipitation loss of ammonium sulfate, it is necessary to raise the temperature of the centrifugation or static separation treatment in the regenerated oil recovery process to the treatment temperature or higher. Furthermore, in order to smoothly transport the treatment aqueous solution in the treatment process, sufficient measures such as heating equipment are required to prevent the clogging of piping and filters by precipitated ammonium sulfate. Thus, in the regeneration treatment of waste oil using a saturated aqueous solution of ammonium sulfate, there are many difficult problems to be solved for practical use, such as the complexity of not only the regeneration treatment process but also the regeneration process for repeated use of the treated aqueous solution, which becomes a factor of increased costs.

[0055] Example 2 During regeneration treatment, the mixing ratio of the regeneration treatment solution to the waste oil depends on the properties of the regenerated oil obtained. The following experiment was conducted to investigate the effect of Experimental conditions A regeneration treatment aqueous solution was prepared by using 3% by mass of sulfuric acid relative to an aqueous ammonium sulfate solution (concentration: 20 or 30% by mass) (calculated as anhydrous). The waste oil was regenerated in the same manner as in Example 1, except that the mixing ratio (volume ratio) of the above-mentioned aqueous treatment solution to 100 g of waste oil was 10 / 1 to 10 / 5. The results are shown in Table 6.

[0056] [Table 6]

[0057] From the results shown in Table 6, it was found that the regeneration treatment agent used in the method of the present invention can exhibit excellent low-ash and water reduction effects even when the mixing ratio of the regeneration treatment aqueous solution to the waste oil (GEO and DEO) was changed to 10 / 1 to 10 / 5 (volume ratio). The obtained regenerated oil had a sulfated ash content of 0.02 mass% or less, a water content of 0.05 mass%, and was neutral in the reaction test, confirming that it was a good quality regenerated oil. In addition, regarding the emulsified layer, it was confirmed that the oil-water layer was clearly separated when the mixed treatment aqueous solution with the waste oil was left to stand at room temperature in the treatment process, and no emulsified layer was formed.

[0058] Example 3 If the aqueous solution used in the regeneration treatment method of the present invention could be reused, the treatment cost could be significantly reduced. In the experiments related to the metal and moisture reduction treatment that led to the present invention, it was found that the average consumption of ammonium sulfate and acids (particularly sulfuric acid) relative to waste oil was 0.2 mass% for the former and 0.3 mass% for the latter. In addition, the average amount of zinc sulfate generated during the regeneration process is about 0.15% by mass per used waste oil, and it easily dissolves in the treatment solution. It was also found that if the zinc sulfate content of the treatment solution exceeds 6% by mass, the effect of reducing metals is slightly reduced. Based on these new findings, experiments were carried out under the following conditions and procedures to demonstrate that the regeneration method of the present invention can be easily and excellently applied to repeated use.

[0059] Experimental conditions Regeneration treatment aqueous solution: Ammonium sulfate aqueous solution concentration 30 mass% / sulfuric acid added 1.2 mass% to ammonium sulfate Waste oil (GEO) / regeneration treatment solution (mass ratio): 10 / 4 (12% ammonium sulfate and 0.26% sulfuric acid relative to the waste oil) The amount of ammonium sulfate consumed in the repeatedly used aqueous solution of treated oil is a maximum of about 1.2 g per 1 kg of treated waste oil, usually as low as 0.3 to 0.5 g, and even when used five times, the amount consumed is about 3 g. Therefore, no adjustment of the concentration of the aqueous solution of treated oil by adding additional ammonium sulfate was performed during repeated use. On the other hand, since almost all of the sulfuric acid is consumed in the regeneration process, The other experimental conditions were the same as those in Example 1.

[0060] Experimental procedure First, the treated liquid after regeneration treatment was separated into an oil layer, an aqueous solution layer, and a solid layer using a centrifuge (Kokusan Co., Ltd. H-215: 2,000 rpm x 20 min. 970 G). The oil layer was used for property analysis as it was, and the aqueous solution layer was filtered with filter paper (Toyo Roshi Kaisha, Ltd. 5B) to remove insoluble foreign matter, after which the pH was measured and the solution was used for reuse. The experiment was carried out multiple times under the same conditions, and the recovered treated aqueous solutions were collected and used as reused treated aqueous solutions for subsequent repeated experiments. The treatment performance evaluation (use life evaluation) of the reused treated aqueous solution was carried out according to the following experimental procedure. The results are shown in Tables 7 and 8. Experimental procedure: New liquid (3-01) ⇒ regeneration treatment ⇒ recovery of the treated aqueous solution, purification, addition of sulfuric acid ⇒ 3-02 treated aqueous solution ⇒ regeneration treatment ⇒ recovery of the treated aqueous solution, purification, addition of sulfuric acid ⇒ 3-03 treated aqueous solution ⇒ regeneration treatment ⇒ recovery of the treated aqueous solution, purification, addition of sulfuric acid ⇒ 3-04 treated aqueous solution ⇒ regeneration treatment ⇒ recovery of the treated aqueous solution, purification, addition of sulfuric acid ⇒ and the same process is continued.

[0061] [Table 7]

[0062] [Table 8]

[0063] As is clear from the results shown in Tables 7 and 8, the used regenerated aqueous solution (Example 3- The reclaimed oil (recovered oil) treated with the new oil of Example 3-01 had a sulfated ash content of 0.02 mass% and a moisture content of 0.05 volume% except for Example 3-03, and the reaction had excellent neutral properties, similar to the reclaimed oil treated with new oil of Example 3-01. In addition, in the reclaiming treatments performed in Examples 3-01 to 3-06, no emulsification occurred in any of them, and it was confirmed that the oil layer and the treated aqueous solution layer were clearly separated by leaving the treatment liquid to stand.

[0064] The pH of the treated aqueous solution before and after the regeneration treatment in Examples 3-01 to 3-06 was in the range of 2.6 to 2.7 before the treatment and 5.5 to 6.0 after the treatment, and no significant difference was observed between the pH of the new solution and the used treated aqueous solution. This indicates that the added sulfuric acid was almost entirely consumed in the regeneration treatment. In addition, the ammonium sulfate concentration of the used regenerated aqueous solution was consumed by 0.2 mass% per treatment, but the properties of the regenerated oil obtained using the regenerated aqueous solution after five treatments were equivalent to those of the regenerated oil obtained by the new solution treatment. From this, it was found that even the used treated aqueous solution that had been repeatedly used five times (i.e., even if the aqueous solution had a concentration of ammonium sulfate reduced by about 1 mass%) did not affect the ash and moisture reduction performance.

[0065] Reference Examples 3-01 and 3-02 show the effect of zinc sulfate on the treatment performance of the treatment aqueous solution. Zinc sulfate is a compound derived from oil-soluble zinc compounds contained in raw oils such as waste oil, and becomes zinc sulfate, which is insoluble in mineral oil and soluble in water, during treatment and migrates to the treatment aqueous solution. For this reason, zinc sulfate is the main compound that is thought to contaminate the treatment aqueous solution and affect the ash and moisture reduction performance of the treatment aqueous solution. The oil-soluble zinc compounds contained in waste oil are up to about 1000 mass ppm as zinc (Zn). From this value, the amount of zinc sulfate generated under these experimental conditions is 0.25 g per treatment, and the concentration of zinc sulfate in the treatment aqueous solution is about 0.6 mass %. That is, in Reference Example 3-01, the example in which 3 mass % zinc sulfate was added to the new solution corresponds to 5 treatments. Similarly, Reference Example 3-02 (6 mass % zinc sulfate added) corresponds to 10 treatments. As is clear from the results of the Reference Example, the effect of zinc sulfate on the performance of the used regenerated aqueous solution is not significant when the zinc sulfate content is 3% by mass, which corresponds to 5 treatments, and is only slightly reduced when the zinc sulfate content is 6% by mass, which corresponds to 10 treatments. Therefore, it is clear that the performance of the aqueous solution obtained by reusing the used regenerated aqueous solution of the present invention is not affected by zinc sulfate, at least when the regeneration treatment is carried out 5 times.

[0066] In the above Example 3, the amount of ammonium sulfate consumed in the regeneration process was not newly added to the used aqueous solution. This is because the amount of ammonium sulfate consumed in the repeated regeneration process is small. This, and also from the results of Example 3, makes it clear that in the regeneration process method according to the present invention, when the used aqueous solution is repeatedly used, the aqueous solution can be reused (at least five times) by simply adding an acid to adjust the concentration. In the following experiment, the above was confirmed by quantifying the amount of ammonium sulfate in the treated aqueous solution used in Example 3 in Tables 7 and 8. The amount of ammonium sulfate was determined by the Kjeldahl method (Handbook of Analytical Chemistry (1981, Maruzen), edited by the Japan Society for Analytical Chemistry). The results are shown in Table 9.

[0067] [Table 9]

[0068] As is clear from the results in Table 9, the amount of ammonium sulfate consumed in the regeneration process is very small. In the above analysis, ammonium sulfate is calculated from the amount of nitrogen, so about 0.3 mass% of the ammonium sulfate added is consumed in one regeneration process. This consumption amount corresponds to 0.3 to 0.4 g per 1 kg of waste oil to be treated.

[0069] In the regeneration process of the present invention, the oil-soluble Ca components contained in the waste oil react with ammonium sulfate to become calcium sulfate, which is precipitated and separated from the oil-water layer. That is, by the regeneration process, 95% or more of the Ca content in the waste oil becomes sulfate. In other words, the Ca (molar concentration) in the waste oil is almost equal to the ammonium sulfate (molar concentration) consumed. That is, the consumption of ammonium sulfate can be estimated from the Ca content in the waste oil without quantifying ammonium sulfate. This estimated value can then be used to adjust the concentration of ammonium sulfate in the used treated aqueous solution. Table 10 shows the results of calculating the amount of ammonium sulfate consumed by reacting with the oil-soluble Ca components in the waste oil from the Ca content.

[0070] [Table 10]

[0071] As is clear from the results in Table 10, even in DEO, which has a very high Ca content, the amount of ammonium sulfate consumed is only about 1%, and in RCO, which has a low Ca content of 860 mass ppm, it is 0.2%. In addition, the ammonium sulfate consumption of GEO, 0.52 mass%, is almost consistent with the ammonium sulfate consumption of 0.4 mass% calculated from the ammonium sulfate quantitative analysis results shown in 4-02 (Waste Oil GEO) in Table 9. For example, the concentration of ammonium sulfate in the used treated aqueous solution can be adjusted by adding and dissolving 0.5 to 1.0 g of ammonium sulfate per 1 kg of treated waste oil per regeneration treatment, assuming that the waste oil has an average Ca content (about 2000 mass ppm), and this can reduce the labor required for concentration adjustment work such as ammonium sulfate quantitative analysis. This method, combined with the quantitative analysis method, is a powerful method for adjusting the ammonium sulfate concentration. It is particularly effective when the regenerated aqueous solution, which is considered to require adjustment of the ammonium sulfate concentration in the used treated aqueous solution, is used five or more times. [Industrial Applicability]

[0072] The method of the present invention can remove sulfated ash and water with extremely high efficiency, and therefore can obtain high-quality regenerated oil with good properties. The regenerating treatment agent used in the present invention is also very inexpensive and easy to obtain. Furthermore, the used aqueous treatment solution can be reused at least five times. The concentration of the aqueous treatment solution during repeated use can be adjusted using only acids to obtain an aqueous treatment solution with the desired performance. The treatment steps in the method of the present invention are also simple, and the production costs can be significantly reduced. Furthermore, the method of the present invention has few waste problems and is therefore extremely useful industrially. In particular, the provision of the technology for obtaining recycled fuel oil according to the present invention can contribute to the effective utilization of resources and the proper disposal of waste from the viewpoint of environmental conservation, which are major social issues. Furthermore, it is also effective as a pretreatment technology for producing recycled lubricating oil, which is a more advanced form of recycling than recycled fuel oil.

Claims

1. A method for regenerating waste oil, comprising: a first step of adding an unsaturated aqueous solution of an ammonium sulfate compound and acids to waste oil and mixing them; and a second step of separating and recovering oil from the resulting mixture, in which the acids are added in an amount of 0.012 to 0.04 times the mass of ammonium sulfate, calculated as an anhydrous form of the ammonium sulfate.

2. The ammonium sulfate compound is ammonium sulfate ((NH ４ ) ２ SO ４ ) and / or (NH ４ ) ２ SO ４ ・nH ２ 2. The method for regenerating waste oil according to claim 1, wherein the ammonium sulfate is ammonium sulfate hydrate represented by the formula: O (n is 1 to 10).

3. 3. The method for regenerating waste oil according to claim 1 or 2, wherein the acids are selected from organic acids and / or inorganic acids.

4. The method for regenerating waste oil according to any one of claims 1 to 3, wherein the unsaturated aqueous solution of the ammonium sulfate compound has an unsaturated soluble concentration of 5.0 mass% or more in terms of anhydrous ammonium sulfate.

5. The method for regenerating waste oil according to any one of claims 1 to 4, wherein the ammonium sulfate compound is added in an amount of 0.005 to 1.0 times the mass of the waste oil in terms of anhydrous ammonium sulfate.

6. A method for regenerating waste oil described in any one of claims 1 to 5, wherein the oil separated and recovered in the second step is neutral in a reaction test conforming to JIS K2252.

7. The method for recycling waste oil according to any one of claims 1 to 6, wherein the method for separating and recovering the oil from the mixture in the second step is a static separation method and / or a centrifugation method.

8. The waste oil regeneration method according to any one of claims 1 to 7, wherein the waste oil is a used lubricating oil mainly composed of used engine oil and / or used industrial lubricating oil, or a regenerated heavy oil or bio-regenerated heavy oil produced using them as raw materials.

9. A method for regenerating a used regenerated aqueous solution, comprising purifying a used regenerated aqueous solution used in the method for regenerating waste oil according to any one of claims 1 to 8, quantitatively analyzing the contents of ammonium sulfate and acids in the aqueous solution, and adding ammonium sulfate and acids in an amount equivalent to a consumption amount calculated from the values ​​to the purified aqueous solution.

10. A method for regenerating a used regenerated aqueous solution, comprising purifying the used regenerated aqueous solution used in the method for regenerating waste oil according to any one of claims 1 to 8, and then adding a certain amount of ammonium sulfate and acids in the amount of consumption to the purified aqueous solution.

11. 11. The method for regenerating a used regenerated aqueous solution according to claim 10, wherein only the amount of acids consumed is added.

12. A method for regenerating waste oil, comprising carrying out the regeneration treatment of waste oil at least five times using the method for regenerating a used regenerated aqueous solution according to claim 11.

13. A method for producing regenerated oil from waste oil by using the method for regenerating waste oil according to any one of claims 1 to 8, the method for regenerating a used regenerated aqueous solution according to any one of claims 9 to 11, or the method for regenerating waste oil according to claim 12.

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