AGENT FOR REDUCING ACID VALUE OF USED COOKING OIL AND METHOD FOR REGENERATING USED COOKING OIL USING SAME

Abstract

An agent for reduction of the acid value of used cooking oil that exerts the effects required for a regeneration agent for used cooking oil, and a regeneration treatment method for used cooking oil using it are provided. The agent is an agent for reduction of the acid value of used cooking oil containing a hydrotalcite-related compound as an effective component, wherein the agent has a decoloration capacity that reduces the acid value by 70% or more. The agent also has a deacidification capacity that reduces yellowness due to deterioration by 15%. The hydrotalcite-related compound is a hydrotalcite-related compound calcined at 150 to 400 C. The hydrotalcite-related compound is a hydrotalcite-related compound granulated to have an average particle size of 50 to 200 m.

Claims

1-12. (canceled)

13. An agent for reduction of the acid value of used cooking oil, the agent comprising a hydrotalcite-related compound as an effective component, wherein the agent has a deacidification capacity that reduces the acid value by 70% or more, and has a decoloration capacity that reduces yellowness due to deterioration by 15%, characterized in that the hydrotalcite-related compound is a silica-supported MgAl-based hydrotalcite-based compound in which silica is supported in the interlayer or on the surface of a MgAl-based hydrotalcite-based compound; the molar ratio (MgO/Al.sub.2O.sub.3) is 4 to 8; in X-ray diffraction, the peak for the (003) face of the silica-supported hydrotalcite-based compound is shifted toward the low-angle side relative to the peak for the (003) face of the MgAl-based hydrotalcite-based compound; the specific surface area according to the BET method is 150 m.sup.2/g or more; the total specific surface area according to the t-plot method is 200 m.sup.2/g or more; the pore specific surface area according to the t-plot method is 140 m.sup.2/g or more; and the pore specific surface area according to the t-plot method accounts for 70% or more of the total specific surface area.

14. The agent for reduction of the acid value of used cooking oil according to claim 13, wherein the silica-supported hydrotalcite-based compound has a specific surface area of 200 m.sup.2/g or more according to the BET method, a total specific surface area of 250 m.sup.2/g or more according to the t-plot method, and a pore specific surface area of 180 m.sup.2/g or more according to the t-plot method, wherein the pore specific surface area according to the t-plot method accounts for 70% or more of the total specific surface area.

15. The agent for reduction of the acid value of used cooking oil according to claim 14, wherein the silica-supported hydrotalcite-based compound has a specific surface area of 250 m.sup.2/g or more according to the BET method, a total specific surface area of 300 m.sup.2/g or more according to the t-plot method, and a pore specific surface area of 220 m.sup.2/g or more according to the t-plot method, wherein the pore specific surface area according to the t-plot method accounts for 70% or more of the total specific surface area.

16. The agent for reduction of the acid value of used cooking oil according to claim 13, wherein the silica-supported MgAl-based hydrotalcite-based compound is represented by the following Formula (2):
Mg.sub.1-xAl.sub.x(OH).sub.2(A.sub.1.sup.n).sub.a(A.sub.2.sup.m).sub.b.yH.sub.2O(2)
[Mg.sub.1-xAl.sub.x(OH).sub.2].sup.x+[(A.sub.1.sup.n).sub.a(A.sub.2.sup.m).sub.b.yH.sub.2O] (wherein in the formula, A.sub.1.sup.n represents an n-valent silicate anion, wherein the n-valent silicate anion is an anion selected from the group consisting of SiO.sub.3.sup.2, HSiO.sub.3.sup., Si.sub.2O.sub.5.sup.2, and HSi.sub.2O.sub.5.sup.; A.sub.2.sup.m represents an anion selected from the group consisting of CO.sub.3.sup.2, SO.sub.4.sup.2, NO.sub.3.sup., Cl.sup., and OH.sup.; x and y satisfy the inequality 0.18x0.44 and the inequality 0y<2; and a and b satisfy the inequality 0.28na+mb0.4).

17. The agent for reduction of the acid value of used cooking oil according to claim 14, wherein the silica-supported MgAl-based hydrotalcite-based compound is represented by the following Formula (2):
Mg.sub.1-xAl.sub.x(OH).sub.2(A.sub.1.sup.n).sub.a(A.sub.2.sup.m).sub.b.yH.sub.2O(2)
[Mg.sub.1-xAl.sub.x(OH).sub.2].sup.x+[(A.sub.1.sup.n).sub.a(A.sub.2.sup.m).sub.b.yH.sub.2O] (wherein in the formula, A.sub.1.sup.n represents an n-valent silicate anion, wherein the n-valent silicate anion is an anion selected from the group consisting of SiO.sub.3.sup.2, HSiO.sub.3.sup., Si.sub.2O.sub.5.sup.2, and HSi.sub.2O.sub.5.sup.; A.sub.2.sup.m represents an anion selected from the group consisting of CO.sub.3.sup.2, SO.sub.4.sup.2, NO.sub.3.sup., Cl.sup., and OH.sup.; x and y satisfy the inequality 0.18x0.44 and the inequality 0y<2; and a and b satisfy the inequality 0.28na+mb0.4).

18. The agent for reduction of the acid value of used cooking oil according to claim 13, wherein the hydrotalcite-related compound is a hydrotalcite-related compound calcined at 150 to 400 C.

19. The agent for reduction of the acid value of used cooking oil according to claim 13, wherein the hydrotalcite-related compound is a hydrotalcite-related compound granulated to have an average particle size of 50 to 200 m.

20. The agent for reduction of the acid value of used cooking oil according to claim 13, wherein the used cooking oil is used cooking oil heated to a temperature of 200 C. or less.

21. A regeneration treatment method for used cooking oil, characterized in that the agent for reduction of the acid value of used cooking oil according to claim 13 is brought into contact with used cooking oil heated to a temperature of 200 C. or less.

22. A regeneration treatment method for used cooking oil, characterized in that the agent for reduction of the acid value of used cooking oil according to claim 14 is brought into contact with used cooking oil heated to a temperature of 200 C. or less.

Description

DESCRIPTION OF EMBODIMENTS

Hydrotalcite-Related Compound

[0039] The hydrotalcite-related compound of the invention is a MgAl-based hydrotalcite-based compound and/or a silica-supported MgAl-based hydrotalcite-based compound.

[0040] The MgAl-based hydrotalcite is represented by the following Formula (1).

Mg.sub.1-xAl.sub.x(OH).sub.2(A.sup.n).sub.x/n.yH.sub.2O(1)

[Mg.sub.1-xAl.sub.x(OH).sub.2].sup.x+[(A.sup.n).sub.x/n.yH.sub.2O]

In the formula, A.sup.n represents an anion selected from the group consisting of CO.sub.3.sup.2, SO.sub.4.sup.2, NO.sub.3.sup., Cl.sup., and OH.sup.; n represents 1 or 2; and x and y satisfy the inequality 0.18x0.44 and the inequality 0m<1.

[0041] The silica-supported MgAl-based hydrotalcite-based compound is represented by the following Formula (2).

Mg.sub.1-xAl.sub.x(OH).sub.2(A.sub.1.sup.n).sub.a(A.sub.2.sup.m).sub.b.yH.sub.2O(2)

[Mg.sub.1-xAl.sub.x(OH).sub.2].sup.x+[(A.sub.1.sup.n).sub.a(A.sub.2.sup.m).sub.b.yH.sub.2O]

In the formula, A.sub.1.sup.n represents an n-valent silicate anion, wherein the n-valent silicate anion is an anion selected from the group consisting of SiO.sub.3.sup.2, HSiO.sub.3.sup., Si.sub.2O.sub.5.sup.2, and HSi.sub.2O.sub.5.sup.. A.sub.2.sup.m represents an anion selected from the group consisting of CO.sub.3.sup.2, SO.sub.4.sup.2, NO.sub.3.sup., Cl.sup., and OH.sup..

[0042] x and y satisfy the inequality 0.18x0.44 and the inequality 0y<2.

[0043] a and b satisfy the inequality 0.28na+mb0.4.

[0044] The method for synthesizing the MgAl-based hydrotalcite-based compound represented by Formula (1) is basically the same method as the method for synthesizing a known hydrotalcite particle (for example, PTL 7).

[0045] More specifically, the compound can be obtained by reaction of a magnesium compound, an aluminum compound, and, when necessary, an alkali metal hydroxide and an anion. Examples of the magnesium compound include magnesium chloride, magnesium sulfate, magnesium nitrate, magnesium acetate, magnesium hydroxide, magnesium oxide, and magnesium carbonate. Examples of the aluminum compound include aluminum chloride, aluminum sulfate, aluminum nitrate, sodium aluminate, and aluminum hydroxide. Examples of the alkali metal hydroxide include sodium hydroxide, potassium hydroxide, and lithium hydroxide. Examples of the anion include sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, ammonium carbonate, sodium sulfate, potassium sulfate, ammonium sulfate, sodium nitrate, potassium nitrate, ammonium nitrate, sodium chloride, potassium chloride, ammonium chloride, sulfuric acid, nitric acid, and hydrochloric acid.

[0046] The agent for reduction of the acid value of used cooking oil has a specific surface area of 60 m.sup.2/g or more, preferably 100 m.sup.2/g or more, more preferably 200 m.sup.2/g or more according to the BET method, and a pore volume of 0.5 cm.sup.3/g or more, preferably 0.7 cm.sup.3/g or more, more preferably 0.8 cm.sup.3/g or more. As the specific surface area increases, contact with free fatty acid in the cooking oil increases, leading to production of a higher deacidification effect. As the pore volume increases, the amount of adsorption of free fatty acid in the cooking oil increases, leading to production of a higher deacidification effect.

[0047] The MgAl-based hydrotalcite-based compound as a precursor of the silica-supported hydrotalcite-based compound represented by Formula (2) is a MgAl-based hydrotalcite-based compound represented by Formula (1), and the method for synthesizing it is not limited. The method is basically the same as the method for synthesizing a known hydrotalcite particle (for example, PTL 7). For example, the compound can be obtained by mixing the magnesium chloride and the aluminum sulfate together at a ratio at which the ratio between magnesium atoms and aluminum atoms (Mg/Al) becomes 1.5 to 5, and then the sodium hydroxide and the sodium carbonate are further added thereto, followed by allowing the reaction to proceed at 0 to 40 C., preferably 5 to 35 C.

[0048] The reaction pH is 8 to 12, preferably 8 to 10. In cases where the reaction pH is 8 or less, the production rate of the MgAl-based hydrotalcite-based compound decreases, while in cases where the reaction pH is 12 or more, the MgAl-based hydrotalcite-based compound particles easily aggregate, leading to a smaller specific surface area of the particles, and poorer deacidification effect and decoloration effect.

[0049] Examples of the silica to be supported in the interlayer or on the surface of the MgAl-based hydrotalcite-based compound include water-soluble silicate compounds. Examples of the water-soluble silicate compounds include sodium silicate, sodium metasilicate, and sodium orthosilicate, which are commonly called water glass and represented by the general formula Na.sub.2O.nSiO.sub.2 (n=2 to 4), and alkali salts of silicic acid such as potassium silicate. No. 3 water glass is especially preferred.

[0050] The method for supporting silica in the interlayer or on the surface of the MgAl-based hydrotalcite-based compound is not limited. It may be obtained by adding the water-soluble silicate compound to a suspension of a MgAl-based hydrotalcite-based compound, and wet-mixing the resulting mixture at 30 to 100 C., preferably 40 to 95 C. for 1 to 8 hours, preferably 2 to 6 hours.

[0051] The amount of the silica to be supported in the interlayer or on the surface of the MgAl-based hydrotalcite-based compound is 0.8 to 2.2 equivalents, preferably 1.0 to 1.8 equivalents with respect to the MgAl-based hydrotalcite-based compound. In cases where the amount of silica is 0.8 or less, the supported amount is insufficient, leading to a small specific surface area, which results in a poor decoloration effect. In cases where the amount of silica is 2.2 or more, the excess silica that cannot be supported partially aggregate, leading to a small specific surface area, which results in a poor decoloration effect.

[0052] Since, in X-ray diffraction, the peak for the (003) face of a silica-supported hydrotalcite-based compound is shifted toward the low-angle side relative to the peak for the (003) face of a MgAl-based hydrotalcite-based compound, it can be seen that silicate ions are intercalated in the interlayer of the MgAl-based hydrotalcite-based compound.

[0053] The agent for reduction of the acid value of used cooking oil has a specific surface area of 150 m.sup.2/g or more, preferably 200 m.sup.2/g or more, more preferably 250 m.sup.2/g or more according to the BET method, a total specific surface area of 200 m.sup.2/g or more, preferably 250 m.sup.2/g or more, more preferably 300 m.sup.2/g or more according to the t-plot method, and a pore specific surface area of 140 m.sup.2/g or more, preferably 180 m.sup.2/g or more, more preferably 200 m.sup.2/g or more according to the t-plot method. As these specific surface areas increase, contact with free fatty acid in the cooking oil increases, leading to production of a higher deacidification effect. Similarly, as the specific surface areas increase, contact with colored substances in the used cooking oil increases, leading to production of a higher decoloration effect.

[0054] The t-plot method is a known technique, and described in, for example, NPL 1 in detail. In the t-plot method, a reference isotherm prepared by plotting the thickness of the adsorbed layer (t) against the relative pressure (P/P0) is used to convert the abscissa of an adsorption isotherm (t) to the thickness of the adsorbed layer (t). The plot obtained by plotting the adsorbed amount (V) against the thickness of the adsorbed layer (t) is called t-plot. In a t-plot, in cases where an upward shift relative to an approximate straight line passing through the origin occurs as t increases, the sample has mesopores. The total specific surface area (a1) is calculated from an approximate curve passing through the origin, and the external specific surface area (a1) is calculated from a second approximate curve. The value obtained by subtracting the external specific surface area (a2) from the total specific surface area (a1) is the pore specific surface area (a3).

[0055] In the agent for reduction of the acid value of used cooking oil, the pore specific surface area (a3) according to the t-plot method is preferably 70% or more with respect to the total specific surface area (a1). In cases where the pore specific surface area (a3) is less than 70%, infiltration of cooking oil into the cooking oil regeneration agent is insufficient, and simultaneous exertion of the deacidification effect and the decoloration effect is impossible.

[0056] The agent for reduction of the acid value of used cooking oil of the invention can be calcined at 150 to 400 C. By the calcination, the particle surface of the MgAl-based hydrotalcite-based compound is activated, and this allows production of a higher deacidification effect. The calcination may be carried out either in the atmosphere or under vacuum.

[0057] The agent for reduction of the acid value of used cooking oil of the invention may be subjected to granulation after the regeneration treatment in order to enable easy separation from the regenerated oil. The granulation method is not limited, and a method known as a wet granulation method may be used. Specific examples of the method include spray drying, fluidized bed granulation, tumbling granulation, mixing granulation, and extrusion granulation.

Regeneration Treatment Method for Cooking Oil

[0058] Similarly to known deacidifying agents and decoloring agents, the agent for reduction of the acid value of used cooking oil of the invention can be used for treatment of cooking oil by bringing the agent into contact with used cooking oil at 200 C. or less. The amount of the cooking oil regeneration agent of the invention used is 0.05 to 20 parts by weight, preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of cooking oil.

[0059] In the regeneration treatment method of the invention, the agent for reduction of the acid value of used cooking oil of the invention may be used in combination with a decoloring agent. By the combined use of a decoloring agent, an excellent deacidification effect and decoloration effect can be exerted at the same time. The decoloring agent may be a known decoloring agent or a commercially available product. For example, at least one of silicon oxide, acid clay, activated clay, activated carbon, and the like may be used.

[0060] Examples of the method of the contacting include, but are not limited to, the following methods.

[0061] After directly adding the agent for reduction of the acid value of used cooking oil of the invention to used cooking oil, and stirring the resulting mixture, the agent for reduction of the acid value of used cooking oil is separated from regenerated oil by filtration.

[0062] After directly adding the agent for reduction of the acid value of used cooking oil of the invention to used cooking oil, and stirring the resulting mixture, the agent for reduction of the acid value of used cooking oil is separated from regenerated oil by sedimentation.

[0063] After directly adding the agent for reduction of the acid value of used cooking oil of the invention to used cooking oil, and stirring the resulting mixture, the agent for reduction of the acid value of used cooking oil is separated from regenerated oil by centrifugation.

[0064] The agent for reduction of the acid value of used cooking oil of the invention is filled into a filter paper bag or a filter cloth bag, and the bag is then fed into used cooking oil, followed by removing the bag after a certain period of time.

[0065] A filter in which the agent for reduction of the acid value of used cooking oil of the invention is laid between filter papers or filter cloths is prepared, and used cooking oil is passed through the filter.

[0066] The cooking oil to which the agent for reduction of the acid value of used cooking oil of the invention can be applied is not limited, and examples of such cooking oil include soy oil, olive oil, rapeseed oil, sesame oil, sunflower oil, corn oil, peanut oil, rice oil, and linseed oil.

[0067] For regeneration treatment of cooking oil, calcium oxide, calcium hydroxide, calcium silicate, magnesium oxide, magnesium hydroxide, or magnesium silicate is used as a deacidifying agent. However, the reaction of the deacidifying agent with free fatty acid in the cooking oil is reaction of an acid with a solid base, that is, a neutralization reaction. In contrast, in cases where hydrotalcite is used as an agent for reduction of the acid value (=deacidifying agent), effective adsorption removal of free fatty acid is possible by using the high acidic-substance adsorption capacity of the hydrotalcite.

[0068] Free fatty acid in cooking oil reacts with an alkali metal to become a metal soap. Thus, the degree of elution of an alkali metal into cooking oil is preferably as low as possible. Since the degree of elution of magnesium ions of MgAl-based hydrotalcite into cooking oil is lower than the degree of elution of magnesium ions of magnesium hydroxide or magnesium oxide into cooking oil, production of a metal soap in cooking oil can be suppressed.

[0069] The content of the invention is described below in more detail by way of Examples and Comparative Examples. However, the invention is not limited to these Examples.

EXAMPLES

[0070] 1. In the Examples and the Comparative Examples, agents for reduction of the acid value of used cooking oil of the invention, and other deacidifying agents and decoloring agents, were analyzed by the following methods.

[0071] (1) Molar ratio (MgO/Al.sub.2O.sub.3): X-ray fluorescence analyzer RIX2000, manufactured by Rigaku Corporation

[0072] (2) BET specific surface area, pore volume: high-precision specific surface area/pore distribution measuring apparatus BELSORP-max, manufactured by MicrotracBEL Corp.

[0073] (3) X-ray structure analysis: all-in-one X-ray diffractometer EMPYREAN, manufactured by PANalytical

[0074] 2. In the deacidification tests in Examples and Comparative Examples, the acid value was evaluated by the following method, and the amount of eluted magnesium ions was measured by the following method.

[0075] (1) Acid value: Evaluation is carried out using a test strip for thermal degradation of frying oils, manufactured by ADVANTEC, or according to JISK0070-1992. More specifically, regenerated oil is dissolved in diethyl ether/ethanol mixture (1:1), and phenolphthalein is added thereto as an indicator, followed by performing titration with a potassium hydroxide ethanol solution to determine the acid value.

[0076] (2) Amount of eluted magnesium ions: ICP emission spectrophotometer SPS3500DD, manufactured by Hitachi High-Tech Science Corporation

[0077] (3) Yellowness: Colorimetric color difference meter ZE-2000, manufactured by Nippon Denshoku Industries Co., Ltd.

[0078] 3. The agents for reduction of the acid value of used cooking oil and the cooking oil regeneration agents used in Examples and Comparative Examples, and the measurement results are shown in Tables 1 and 2.

Example 1

[0079] As an agent for reduction of the acid value of used cooking oil, a MgAl-based hydrotalcite-based compound KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd., was used for cooking oil regeneration.

[0080] The molar ratio (MgO/Al.sub.2O.sub.3) was 5.94; the BET specific surface area was 101.6 m.sup.2/g; and the pore volume was 0.779 cm.sup.3/g.

[0081] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 2.5), the agent for reduction of the acid value of used cooking oil was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 0 to 0.5. The filtered regenerated oil was carbonized, and the resulting residue was dissolved in dilute hydrochloric acid, followed by quantification of magnesium ions eluted into the oil, by ICP. As a result, the amount was found to be 23.4 ppm.

[0082] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the agent for reduction of the acid value of used cooking oil was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 0.5 to 1.0.

Example 2

[0083] As an agent for reduction of the acid value of used cooking oil, a MgAl-based hydrotalcite-based compound KYOWAAD 1000, manufactured by Kyowa Chemical Industry Co., Ltd., was used for cooking oil regeneration.

[0084] The molar ratio (MgO/Al.sub.2O.sub.3) was 4.6; the BET specific surface area was 111.8 m.sup.2/g; and the pore volume was 0.876 cm.sup.3/g.

[0085] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 2.5), the agent for reduction of the acid value of used cooking oil was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 0 to 0.5.

[0086] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the agent for reduction of the acid value of used cooking oil was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 0.5 to 1.0.

Example 3

[0087] As an agent for reduction of the acid value of used cooking oil, a MgAl-based hydrotalcite-based compound KYOWAAD 300SN, manufactured by Kyowa Chemical Industry Co., Ltd., was used for cooking oil regeneration.

[0088] The molar ratio (MgO/Al.sub.2O.sub.3) was 2.58; the BET specific surface area was 240.7 m.sup.2/g; and the pore volume was 0.882 cm.sup.3/g.

[0089] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 2.5), the agent for reduction of the acid value of used cooking oil was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 0.5.

[0090] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the agent for reduction of the acid value of used cooking oil was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 1.0.

Comparative Example 1

[0091] As a cooking oil regeneration agent, magnesium hydroxide KISUMA F, manufactured by Kyowa Chemical Industry Co., Ltd., was used.

[0092] The BET specific surface area was 53.9 m.sup.2/g, and the pore volume was 0.363 cm.sup.3/g.

[0093] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 2.5), the cooking oil regeneration agent was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 1.0. The filtered regenerated oil was carbonized, and the resulting residue was dissolved in dilute hydrochloric acid, followed by quantification of magnesium ions eluted into the oil, by ICP. As a result, the amount was found to be 55.2 ppm.

[0094] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the cooking oil regeneration agent was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 2.0.

Comparative Example 2

[0095] As a cooking oil regeneration agent, magnesium silicate KYOWAAD 600S, manufactured by Kyowa Chemical Industry Co., Ltd., was used.

[0096] The BET specific surface area was 154.8 m.sup.2/g, and the pore volume was 0.252 cm.sup.3/g.

[0097] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 2.5), the cooking oil regeneration agent was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 2.0.

[0098] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the cooking oil regeneration agent was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 3.0.

Comparative Example 3

[0099] As a cooking oil regeneration agent, aluminum hydroxide KYOWAAD 200S, manufactured by Kyowa Chemical Industry Co., Ltd., was used.

[0100] The BET specific surface area was 143.2 m.sup.2/g, and the pore volume was 0.492 cm.sup.3/g.

[0101] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 2.5), the cooking oil regeneration agent was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 0.5.

[0102] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the cooking oil regeneration agent was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 2.5.

Example 4

[0103] As an agent for reduction of the acid value of used cooking oil, a MgAl-based hydrotalcite-based compound KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd., was used for cooking oil regeneration.

[0104] The molar ratio (MgO/Al.sub.2O.sub.3) was 5.94; the BET specific surface area was 101.6 m.sup.2/g; and the pore volume was 0.779 cm.sup.3/g.

[0105] Deacidification Test) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the agent for reduction of the acid value of used cooking oil was added at 2.5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 1.0.

Example 5

[0106] As an agent for reduction of the acid value of used cooking oil, a MgAl-based hydrotalcite-based compound KYOWAAD 1000, manufactured by Kyowa Chemical Industry Co., Ltd., was used for cooking oil regeneration.

[0107] The molar ratio (MgO/Al.sub.2O.sub.3) was 4.6; the BET specific surface area was 111.8 m.sup.2/g; and the pore volume was 0.876 cm.sup.3/g.

[0108] Deacidification Test) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the agent for reduction of the acid value of used cooking oil was added at 2.5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 0.5 to 1.0.

Comparative Example 4

[0109] As a cooking oil regeneration agent, magnesium hydroxide KISUMA F, manufactured by Kyowa Chemical Industry Co., Ltd., was used.

[0110] The BET specific surface area was 53.9 m.sup.2/g, and the pore volume was 0.363 cm.sup.3/g.

[0111] Deacidification Test) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the cooking oil regeneration agent was added at 2.5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 3.5.

Comparative Example 5

[0112] As a cooking oil regeneration agent, magnesium silicate KYOWAAD 600S, manufactured by Kyowa Chemical Industry Co., Ltd., was used.

[0113] The BET specific surface area was 154.8 m.sup.2/g, and the pore volume was 0.252 cm.sup.3/g.

[0114] Deacidification Test) To rapeseed cooking oil heated to 120 C. (evaluated acid value: 4.0), the cooking oil regeneration agent was added at 2.5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. According to evaluation of the color of the test strip for thermal degradation of frying oils AV-CHECK, the acid value of the filtered regenerated oil was found to be 4.0.

Example 6

[0115] As an agent for reduction of the acid value of used cooking oil, a MgAl-based hydrotalcite-based compound KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd., was used for cooking oil regeneration.

[0116] The molar ratio (MgO/Al.sub.2O.sub.3) was 5.94; the BET specific surface area was 93.7 m.sup.2/g; the pore volume was 0.779 cm.sup.3/g; the total specific surface area according to the t-plot method was 78.5 m.sup.2/g; the pore specific surface area according to the t-plot method was 38 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 48%.

[0117] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), a hydrotalcite KYOWAAD 500SH (BET specific surface area, 93.7 m.sup.2/g; total specific surface area according to the t-plot method, 78.5 m.sup.2/g; pore specific surface area according to the t-plot method, 38 m.sup.2/g; pore specific surface area/total specific surface area according to the t-plot method, 48%), manufactured by Kyowa Chemical Industry Co., Ltd., was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.228.

[0118] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (acid value: 3.049), the KYOWAAD 500SH was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 0.822.

[0119] Decoloration Test 1) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the KYOWAAD 500SH was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 106.05.

[0120] Decoloration Test 2) To used rapeseed cooking oil heated to 120 C. (yellowness: 120.61), the KYOWAAD 500SH was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 107.31.

Comparative Example 6

[0121] As cooking oil regeneration agents, a MgAl-based hydrotalcite-based compound KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd., and a silica MIZUKASIL, manufactured by Mizusawa Industrial Chemicals, Ltd., were used.

[0122] Deacidification Test) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the MgAl-based hydrotalcite-based compound KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd., and the silica MIZUKASIL, manufactured by Mizusawa Industrial Chemicals, Ltd., were added at 3.5 wt % and 1.5 wt %, respectively, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.36.

[0123] Decoloration Test) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the KYOWAAD 500SH and the MIZUKASIL were added at 3.5 wt % and 1.5 wt %, respectively, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 70.51.

Example 7

[0124] Production Method) An aqueous magnesium chloride solution and an aqueous aluminum sulfate solution are mixed together to prepare a mixture in which the molar ratio (MgO/Al.sub.2O.sub.3) is 4, to provide Solution A. An aqueous sodium hydroxide solution and an aqueous sodium carbonate solution are mixed together to provide Solution B. By pouring Solution A and Solution B at the same time at 30 C. with stirring, coprecipitation was allowed to proceed. The reaction pH in this process was 8.5. The obtained coprecipitate was dehydrated and washed with water to obtain a MgAl-based hydrotalcite-based compound.

[0125] To a suspension of the MgAl-based hydrotalcite-based compound, 1.0 equivalent of No. 3 water glass was added, and the resulting mixture was stirred under heat at 45 C. for 2 hours, to obtain a silica-supported hydrotalcite-based compound.

[0126] The obtained silica-supported hydrotalcite-based compound is referred to as an agent for reduction of the acid value of used cooking oil (a). In the agent for reduction of the acid value of used cooking oil (a), the specific surface area according to the BET method was 260.9 m.sup.2/g; the total specific surface area according to the t-plot method was 296.4 m.sup.2/g; the pore specific surface area according to the t-plot method was 195.22 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 72%. In X-ray diffraction, the peak for the (003) face was 2=10.7.

[0127] Deacidification Test) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the agent for reduction of the acid value of used cooking oil (a) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 0.9.

[0128] Decoloration Test) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the agent for reduction of the acid value of used cooking oil (a) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 82.

Example 8

[0129] Production Method) An aqueous magnesium chloride solution and an aqueous aluminum sulfate solution are mixed together to prepare a mixture in which the molar ratio (MgO/Al.sub.2O.sub.3) is 4, to provide Solution A. An aqueous sodium hydroxide solution and an aqueous sodium carbonate solution are mixed together to provide Solution B. By pouring Solution A and Solution B at the same time at 30 C. with stirring, coprecipitation was allowed to proceed. The reaction pH in this process was 8.5. The obtained coprecipitate was dehydrated and washed with water to obtain a MgAl-based hydrotalcite-based compound.

[0130] To a suspension of the MgAl-based hydrotalcite-based compound, 2.0 equivalents of No. 3 water glass was added, and the resulting mixture was stirred under heat at 45 C. for 2 hours, to obtain a silica-supported hydrotalcite-based compound.

[0131] The obtained silica-supported hydrotalcite-based compound is referred to as an agent for reduction of the acid value of used cooking oil (b). In the agent for reduction of the acid value of used cooking oil (b), the specific surface area according to the BET method was 193 m.sup.2/g; the total specific surface area according to the t-plot method was 223.6 m.sup.2/g; the pore specific surface area according to the t-plot method was 160.2 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 72%.

[0132] Deacidification Test) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the agent for reduction of the acid value of used cooking oil (b) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.1.

[0133] Decoloration Test) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the agent for reduction of the acid value of used cooking oil (b) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 79.

Example 9

[0134] Production Method) An aqueous magnesium chloride solution and an aqueous aluminum sulfate solution are mixed together to prepare a mixture in which the molar ratio (MgO/Al.sub.2O.sub.3) is 6, to provide Solution A. An aqueous sodium hydroxide solution and an aqueous sodium carbonate solution are mixed together to provide Solution B. By pouring Solution A and Solution B at the same time at 30 C. with stirring, coprecipitation was allowed to proceed. The reaction pH in this process was 8.83. The obtained coprecipitate was dehydrated and washed with water to obtain a MgAl-based hydrotalcite-based compound.

[0135] To a suspension of the MgAl-based hydrotalcite-based compound, 1.2 equivalents of No. 3 water glass was added, and the resulting mixture was stirred under heat at 45 C. for 2 hours, to obtain a silica-supported hydrotalcite-based compound.

[0136] The obtained silica-supported hydrotalcite-based compound is referred to as an agent for reduction of the acid value of used cooking oil (c). In the agent for reduction of the acid value of used cooking oil (c), the specific surface area according to the BET method was 235.3 m.sup.2/g; the total specific surface area according to the t-plot method was 297 m.sup.2/g; the pore specific surface area according to the t-plot method was 217.2 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 73%.

[0137] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the agent for reduction of the acid value of used cooking oil (c) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 0.837.

[0138] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (acid value: 3.049), the agent for reduction of the acid value of used cooking oil (c) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 0.67.

[0139] Decoloration Test 1) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the agent for reduction of the acid value of used cooking oil (c) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 83.94.

[0140] Decoloration Test 2) To used rapeseed cooking oil heated to 120 C. (yellowness: 120.61), the agent for reduction of the acid value of used cooking oil (c) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 86.19.

Example 10

[0141] Production Method) An aqueous magnesium chloride solution and an aqueous aluminum sulfate solution are mixed together to prepare a mixture in which the molar ratio (MgO/Al.sub.2O.sub.3) is 6, to provide Solution A. An aqueous sodium hydroxide solution and an aqueous sodium carbonate solution are mixed together to provide Solution B. By pouring Solution A and Solution B at the same time at 30 C. with stirring, coprecipitation was allowed to proceed. The reaction pH in this process was 8.83. The obtained coprecipitate was dehydrated and washed with water to obtain a MgAl-based hydrotalcite-based compound.

[0142] To a suspension of the MgAl-based hydrotalcite-based compound, 1.2 equivalents of No. 3 water glass was added, and the resulting mixture was stirred under heat at 90 C. for 2 hours, to obtain a silica-supported hydrotalcite-based compound.

[0143] The obtained silica-supported hydrotalcite-based compound is referred to as an agent for reduction of the acid value of used cooking oil (d). In the agent for reduction of the acid value of used cooking oil (d), the specific surface area according to the BET method was 241.9 m.sup.2/g; the total specific surface area according to the t-plot method was 300.7 m.sup.2/g; the pore specific surface area according to the t-plot method was 223.8 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 74%.

[0144] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the agent for reduction of the acid value of used cooking oil (d) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.248.

[0145] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (acid value: 3.049), the agent for reduction of the acid value of used cooking oil (d) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 0.854.

[0146] Decoloration Test 1) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the agent for reduction of the acid value of used cooking oil (d) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 82.21.

[0147] Decoloration Test 2) To used rapeseed cooking oil heated to 120 C. (yellowness: 120.61), the agent for reduction of the acid value of used cooking oil (d) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 81.89.

Example 11

[0148] Production Method) An aqueous magnesium chloride solution and an aqueous aluminum sulfate solution are mixed together to prepare a mixture in which the molar ratio (MgO/Al.sub.2O.sub.3) is 8, to provide Solution A. An aqueous sodium hydroxide solution and an aqueous sodium carbonate solution are mixed together to provide Solution B. By pouring Solution A and Solution B at the same time at 30 C. with stirring, coprecipitation was allowed to proceed. The reaction pH in this process was 9.03. The obtained coprecipitate was dehydrated and washed with water to obtain a MgAl-based hydrotalcite-based compound.

[0149] To a suspension of the MgAl-based hydrotalcite-based compound, 1.2 equivalents of No. 3 water glass was added, and the resulting mixture was stirred under heat at 45 C. for 2 hours, to obtain a silica-supported hydrotalcite-based compound.

[0150] The obtained silica-supported hydrotalcite-based compound is referred to as an agent for reduction of the acid value of used cooking oil (e). In the agent for reduction of the acid value of used cooking oil (e), the specific surface area according to the BET method was 204.7 m.sup.2/g; the total specific surface area according to the t-plot method was 252.7 m.sup.2/g; the pore specific surface area according to the t-plot method was 180.7 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 72%.

[0151] Deacidification Test) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the agent for reduction of the acid value of used cooking oil (e) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 0.859.

[0152] Decoloration Test) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the agent for reduction of the acid value of used cooking oil (e) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 81.65.

Example 12

[0153] Production Method) An aqueous magnesium chloride solution and an aqueous aluminum sulfate solution are mixed together to prepare a mixture in which the molar ratio (MgO/Al.sub.2O.sub.3) is 8, to provide Solution A. An aqueous sodium hydroxide solution and an aqueous sodium carbonate solution are mixed together to provide Solution B. By pouring Solution A and Solution B at the same time at 30 C. with stirring, coprecipitation was allowed to proceed. The reaction pH in this process was 9.03. The obtained coprecipitate was dehydrated and washed with water to obtain a MgAl-based hydrotalcite-based compound.

[0154] To a suspension of the MgAl-based hydrotalcite-based compound, 1.2 equivalents of No. 3 water glass was added, and the resulting mixture was stirred under heat at 90 C. for 2 hours, to obtain a silica-supported hydrotalcite-based compound.

[0155] The obtained silica-supported hydrotalcite-based compound is referred to as an agent for reduction of the acid value of used cooking oil (f). In the agent for reduction of the acid value of used cooking oil (f), the specific surface area according to the BET method was 220.3 m.sup.2/g; the total specific surface area according to the t-plot method was 277.1 m.sup.2/g; the pore specific surface area according to the t-plot method was 203.4 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 73%.

[0156] Deacidification Test) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the agent for reduction of the acid value of used cooking oil (f) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.175.

[0157] Decoloration Test) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the agent for reduction of the acid value of used cooking oil (f) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 76.62.

Comparative Example 7

[0158] Production Method) To 300 parts by weight of ion-exchanged water, 70 parts by weight of a MgAl-based hydrotalcite-based compound KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd., and 30 parts by weight of a silica MIZUKASIL, manufactured by Mizusawa Industrial Chemicals, Ltd., were added, and the resulting mixture was stirred under heat at 90 C. for 30 minutes, followed by filtration and drying. The obtained wet mixture of the hydrotalcite and the silica is referred to as a cooking oil regeneration agent (g). In the cooking oil regeneration agent (g), the specific surface area according to the BET method was 161.9 m.sup.2/g; the total specific surface area according to the t-plot method was 195.1 m.sup.2/g; the pore specific surface area according to the t-plot method was 113.7 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 58%. X-ray diffraction showed a peak similar to that of the hydrotalcite KYOWAAD 500SH, wherein 2=11.2.

[0159] Deacidification Test 1) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the cooking oil regeneration agent (g) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.423.

[0160] Deacidification Test 2) To rapeseed cooking oil heated to 120 C. (acid value: 3.049), the cooking oil regeneration agent (g) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.12.

[0161] Decoloration Test 1) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the cooking oil regeneration agent (g) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 79.66.

[0162] Decoloration Test 2) To used rapeseed cooking oil heated to 120 C. (yellowness: 120.61), the cooking oil regeneration agent (g) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 86.92.

Comparative Example 8

[0163] Production Method) In 300 parts by weight of ion-exchanged water, 70 parts by weight of a hydrotalcite-based compound KYOWAAD 500SH, manufactured by Kyowa Chemical Industry Co., Ltd., was suspended, and an equivalent of No. 3 water glass was added thereto, followed by stirring the resulting mixture under heat at 90 C. for 30 minutes. Thereafter, filtration was carried out under reduced pressure, and then the mixture was dried. The obtained wet mixture of the hydrotalcite and the No. 3 water glass is referred to as a cooking oil regeneration agent (h). In the cooking oil regeneration agent (h), the specific surface area according to the BET method was 145.7 m.sup.2/g; the total specific surface area according to the t-plot method was 187.1 m.sup.2/g; the pore specific surface area according to the t-plot method was 98.5 m.sup.2/g; and the pore specific surface area/the total specific surface area according to the t-plot method was 53%. X-ray diffraction showed a peak similar to that of the hydrotalcite KYOWAAD 500SH.

[0164] Deacidification Test) To rapeseed cooking oil heated to 120 C. (acid value: 4.164), the cooking oil regeneration agent (h) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The acid value of the filtered regenerated oil was measured. As a result, the acid value was found to be 1.86.

[0165] Decoloration Test) To used rapeseed cooking oil heated to 120 C. (yellowness: 99.34), the cooking oil regeneration agent (h) was added at 5 wt %, and the resulting mixture was stirred under heat for 30 minutes, followed by leaving the mixture to stand at room temperature for 10 minutes and then performing filtration. The yellowness of the filtered regenerated oil was measured. As a result, the yellowness was found to be 96.27.

TABLE-US-00001 TABLE 1 Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 1 Example 2 Example 3 KYOWAAD 500SH wt % 5 KYOWAAD 1000 wt % 5 KYOWAAD 300SN wt % 5 KISUMA F wt % 5 KYOWAAD 600S wt % 5 KYOWAAD 200S wt % 5 BET specific surface area m.sup.2/g 97.0 111.8 240.7 53.9 154.8 143.2 Pore volume cm.sup.3/g 0.778 0.876 0.882 0.363 0.252 0.492 Deacidification test (acid 0 to 0.5 0 to 0.5 0.5 1.0 2.0 0.5 value before treatment: 2.5) Deacidification test (acid 0.5 to 1.0 0.5 to 1.0 1.0 2.0 3.0 2.5 value before treatment: 4.0) Comparative Comparative Example 4 Example 5 Example 4 Example 5 KYOWAAD 500SH wt % 2.5 KYOWAAD 1000 wt % 2.5 KYOWAAD 300SN wt % KISUMA F wt % 2.5 KYOWAAD 600S wt % 2.5 KYOWAAD 200S wt % BET specific surface area m.sup.2/g 97.0 111.8 53.9 154.8 Pore volume cm.sup.3/g 0.778 0.876 0.363 0.252 Deacidification test (acid value before treatment: 2.5) Deacidification test (acid 1.0 0.5 to 1.0 3.5 4 value before treatment: 4.0)

TABLE-US-00002 TABLE 2 Comparative Example 6 Example 6 Example 7 Example 8 Example 9 Example 10 KYOWAAD 500SH wt % 5 3.5 Agent for reduction of acid value (a) wt % 5 Agent for reduction of acid value (b) wt % 5 Agent for reduction of acid value (c) wt % 5 Agent for reduction of acid value (d) wt % 5 Agent for reduction of acid value (e) wt % Agent for reduction of acid value (f) wt % Cooking oil regeneration agent (g) wt % Cooking oil regeneration agent (h) wt % MIZUKASIL wt % 1.5 BET method Specific surface area m.sup.2/g 93.7 260.9 193.0 235.3 241.9 t-Plot method Total specific surface area m.sup.2/g 78.5 296.4 223.6 297 300.7 Pore specific surface area m.sup.2/g 38 195.2 160.2 217.2 223.8 Pore specific surface area/total % 48 72 72 73 74 specific surface area Deacidification test (acid value 1.228 1.36 0.9 1.1 0.837 1.248 before treatment: 4.164) Deacidification test (acid value 0.822 0.67 0.854 before treatment: 3.049) Decoloration Test (yellowness 106.05 70.51 82 79 83.94 82.21 before treatment: 99.34) Decoloration Test (yellowness 107.31 86.19 81.89 before treatment: 120.61) Comparative Comparative Example 11 Example 12 Example 8 Example 9 KYOWAAD 500SH wt % 2.5 Agent for reduction of acid value (a) wt % Agent for reduction of acid value (b) wt % Agent for reduction of acid value (c) wt % Agent for reduction of acid value (d) wt % Agent for reduction of acid value (e) wt % 5 Agent for reduction of acid value (f) wt % 5 Cooking oil regeneration agent (g) wt % 5 Cooking oil regeneration agent (h) wt % 5 MIZUKASIL wt % BET method Specific surface area m.sup.2/g 204.7 220.3 161.9 145.7 t-Plot method Total specific surface area m.sup.2/g 252.7 277. 195.9 187.1 Pore specific surface area m.sup.2/g 180.7 203.4 113.7 98.5 Pore specific surface area/total % 72 73 58 53 specific surface area Deacidification test (acid value 0.859 1.175 1.423 1.504 before treatment: 4.164) Deacidification test (acid value 1.12 before treatment: 3.049) Decoloration Test (yellowness 81.65 76.62 79.66 96.01 before treatment: 99.34) Decoloration Test (yellowness 86.92 before treatment: 120.61)

INDUSTRIAL APPLICABILITY

[0166] As described above, the cooking oil regeneration agent of the invention has an excellent deacidification effect, or has both an excellent deacidification effect and an excellent decoloration effect. Therefore, a cooking oil subjected to regeneration treatment using the agent has a sufficiently satisfactory taste, color, and flavor, and allows cooking of fried foods with sufficiently satisfactory qualities. Thus, the agent can extend the life of cooking oil, and can significantly reduce the amount of waste oil not only when it is used at home, but also when it is used in a store or a factory where a large amount of cooking oil is used. Therefore, the agent can contribute to reduction of the cost of fried foods and reduction of a cause of environmental pollution.