AU2024298670A1 - Method for producing biofuel and method for improving methyl esterification efficiency of tamanu oil - Google Patents

Abstract

The present invention provides a method for producing a biofuel, the method including: (a) a tamanu oil purification step which comprises a deoxidization step for deoxidizing a crude oil of a tamanu oil, wherein the absorbance of the refined tamanu oil at the wavelength of 330 nm is 0.08 or less; and (b) a methyl esterification step in which methanol is added to the refined tamanu oil so as to produce a fatty acid methyl ester (FAME) by a transesterification reaction. The present invention also provides a method for improving the methyl esterification efficiency of a tamanu oil.

Description

DESCRIPTION

Title of Invention: Title of Invention:

METHOD FOR PRODUCING BIOFUEL AND METHOD FOR IMPROVING ESTERIFICATION METHYLESTERIFICATION METHYL EFFICIENCY OF OF EFFICIENCY TAMANU TAMANU OIL OIL

Technical Field Technical Field

[0001] The present invention relates to a method for producing a biofuel and a method for improving methyl esterification efficiency of tamanu oil.

Background Art

[0002] The world has faced energy crisis in recent years due to the exhaustion of fossil resources and aggravated environmental problems. Under these circumstances, biofuels whose raw materials originate from sustainable biomass resources have received attention as a means of diversifying energy sources and carbon reducing and are under active research and development toward full-scale spread. Non-edible oil resources grow in many regions worldwide and, particularly, even in barren areas unsuitable for the cultivation of food crops. Use of the non- edible oil resources for biofuel production reduces use of food crops and leads to decrease in competition with food markets. Tamanu is widely cultivated in tropical and semitropical zones worldwide and is abundantly available. Tamanu oil, which is obtained from the seeds of tamanu, is used as a traditional drug or a cosmetic component and is also known to have a high calorific value and a large oil yield. Patent Literature 1 describes a method for producing biodiesel using tamanu oil as a raw material. The literature states that tamanu oil is pretreated with toluene and then methyl-esterified.

Citation List Citation List

Patent Literature

[0003] Patent Literature 1: Australian Patent Application Publication No. 2011200655

Summary of Invention Technical Problem

[0004] It is desired to provide a method for efficiently producing a biofuel using a non- edible oil resource while reducing an environmental burden.

Solution to Problem

[0005] The present invention encompasses the following aspects and embodiments.

[1] A method for producing a biofuel, the method comprising: (a) a tamanu oil purification step comprising a deacidification step in which crude tamanu oil is deacidified, wherein absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less, and (b)a methyl esterification step in which methanol is added to the purified tamanu oil, and fatty acid methyl ester (FAME) is produced through transesterification reaction.

[2] The method for producing a biofuel according to [1], wherein the deacidification step comprises deacidification treatment by an alkaline deacidification method using an alkaline aqueous solution, and an addition ratio of an alkaline substance based on a neutralization equivalent of an acidic substance contained in the crude tamanu oil is 0.6 or more and 1.2 or less.

[3] The method for producing a biofuel according to [1] or [2], wherein in the methyl esterification step, the fatty acid methyl ester is produced through the transesterification reaction in the presence of an alkali metal catalyst.

[4] The method for producing a biofuel according to any one of [1] to [3], wherein a content of pyranocoumarins in the tamanu oil purified in the purification step is 18% by mass or less based on the mass of the purified tamanu oil.

[5] The method for producing a biofuel according to any one of [1] to [4], wherein the biofuel is a biodiesel fuel. the biofuel is a biodiesel fuel.

[6] The method for producing a biofuel according to [5], wherein a content of the

fatty acid methyl ester in the biodiesel fuel is 96.5% by mass or more.

[7] A method for improving methyl esterification efficiency of tamanu oil, the method comprising: (a) a tamanu oil purification step comprising a deacidification step in which crude

tamanu oil is deacidified, wherein absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less, and (b) a methyl esterification step in which methanol is added to the purified tamanu oil, and fatty acid methyl ester (FAME) is produced through transesterification reaction.

[8] The method for improving methyl esterification efficiency of tamanu oil according to [7], wherein the deacidification step comprises deacidification treatment by an alkaline deacidification method using an alkaline aqueous solution, and an addition ratio of an alkaline substance based on a neutralization equivalent of an acidic substance contained in the crude tamanu oil is 0.6 or more and 1.2 or less.

[9] The method for improving methyl esterification efficiency of tamanu oil according to [7] or [8], wherein in the methyl esterification step, the fatty acid methyl ester is produced through the transesterification reaction in the presence of an alkali metal catalyst.

[10] The method for improving methyl esterification efficiency of tamanu oil according to any one of [7] to [9], wherein a content of pyranocoumarins in the tamanu

oil purified in the purification step is 18% by mass or less based on the mass of the purified tamanu oil.

Advantageous Effects of Invention

[0006] The present invention can efficiently produce a biofuel from crude tamanu oil while reducing an environmental burden. The present invention can provide a sustainable biofuel without competing with food markets because a non-edible oil resource is used.

Brief Description of Drawing

[0007]

[Figure 1] Figure 1 is a graph showing a calibration curve for use in the quantitative analysis of pyranocoumarins in tamanu oil obtained in Examples.

Description of Embodiments

[0008] Hereinafter, the present invention will be specifically described.

[0009] The present inventors have attempted to remove impurities and the like contained in crude tamanu oil by subjecting the crude tamanu oil to purification treatment that is used for edible oil resources and has a smaller environmental burden than that of conventional techniques. While conducting various studies, the present inventors completed the present invention by finding that deacidification treatment can effectively remove components inhibiting the methyl esterification reaction of tamanu oil, which are contained in crude tamanu oil, and allows subsequent methyl esterification reaction to progress efficiently. Specifically, the method for producing a biofuel according to the present invention comprises (a) a tamanu oil purification step comprising a deacidification step in which crude tamanu oil is deacidified, wherein absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less, and

(b) a methyl esterification step in which methanol is added to the purified tamanu oil, and fatty acid methyl ester (FAME) is produced through transesterification reaction.

[0010] The tamanu oil used as a raw material oil for a biofuel in the present invention is a non-edible oil derived from a tamanu seed. Tamanu (scientific name: Calophyllum inophyllum L.), a tall evergreen tree of the family Callophyllaceae, is widely cultivated in tropical and semitropical zones with tropical coastal regions from the Indian Ocean through the Pacific (Madagascar to India and Marquesas Islands of Polynesia), Commonwealth of the Northern Mariana Islands, Okinawa Islands, and the like as its places of origin. The yield of tamanu fruits is on the order of 20 to 100 kg per tree a year, and its seeds contain 50 to 70% by mass of oil. In the case of mature trees, 1 to 10 kg of oil is reportedly extractable per tree a year (see BFPRO (Business of Forest Products) "Tamanu Oil (tamanu seed oil) https://jifpro.or.jp/bfpro/product/1334/).

[0011] The crude tamanu oil used in the present invention is not limited, and a pressed oil obtained by pressing tamanu seeds may be used, or an extracted oil obtained by extracting tamanu seeds may be used. Alternatively, a mixture of the pressed oil and the extracted oil may be used as the crude oil. The pressing method is not limited and can be performed using, for example, an expeller press made of a casing formed in a cylindrical shape and a screw rotatably disposed in the inside thereof. The extraction method is not limited and can be performed, for example, by compressing or pressing tamanu seeds, bringing a solvent into contact with the resulting residues, and distilling off the solvent from a solution obtained by extraction thereof to obtain oil matter. thereof to obtain oil matter.

[0012] Hereinafter, each step will be described.

[0013] (a) Purification step

The purification step is the step of removing impurities and the like contained in crude tamanu oil. The purification step of the present invention includes at least a deacidification step in which crude tamanu oil is deacidified. Phospholipids, free fatty acids, and trace metals, etc. contained in the crude tamanu oil can be removed by performing the deacidification step. Also, components inhibiting methyl esterification reaction, contained in the crude tamanu oil can be effectively removed by performing the deacidification step. When the absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less, components inhibiting methyl esterification reaction can be sufficiently removed. The purification step may consist of the deacidification step alone. The deacidification step alone can sufficiently purify the crude tamanu oil and however, may be combined with other purification steps without inhibiting the object of the present invention.

[0014] [Deacidification step] The deacidification step is not limited and is preferably deacidification treatment by an alkaline deacidification method using an alkaline aqueous solution. The deacidification step can be performed, for example, by treating the crude oil with an aqueous solution of an alkaline substance dissolved in water. Examples of the alkaline substance can include sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, and sodium bicarbonate. Among them, sodium hydroxide and potassium hydroxide are preferred. Only one of these alkaline substances may be used, or two or more thereof may be combined. The amount of the alkaline substance added, as an addition ratio of the alkaline substance to the neutralization equivalent of an acidic substance contained in the crude tamanu oil, is preferably 0.6 or more and 1.2 or less, more preferably 0.6 or more and 1.1 or less, further preferably 0.6 or more and 1.0 or less. If the addition ratio of the alkaline substance is too low, impurities may be insufficiently removed. If the amount is more than 1.2, a yield may be deteriorated due to saponification reaction. The water for use in the alkaline aqueous solution is not limited and is preferably purified water.

[0015] In one embodiment, the deacidification step can be performed by stirring a mixed liquid containing the crude tamanu oil and the alkaline aqueous solution, followed by the separation and removal of an aqueous layer. The deacidification step may be performed in a batch manner or a continuous manner. The stirring method can be appropriately selected depending on a reaction treatment system or the type of a reactor, etc., and a known stirring method can be applied thereto. The stirring is preferably performed under warming and is performed at, for example, 60°C or higher and 100°C or lower, preferably 70°C or higher and 90°C or lower. The stirring time can fall within a range in which impurities contained in the crude tamanu oil can be sufficiently removed. Those skilled in the art can appropriately select the stirring time depending on a reaction treatment system or the type of a reactor, etc. For example, for the deacidification step in a batch manner, the stirring time can be appropriately selected with approximately 30 minutes to 60 minutes as a guide. After stirring, an aqueous layer is separated and removed by centrifugation or the like, if necessary. Water is added, if necessary, to an oil layer, which is then

washed with water by stirring and the aqueous layer is subsequently removed. The washing with water is preferably performed under warming and is preferably performed, for example, by warming the oil layer to 70°C or higher and 110°C or

lower, preferably 80°C or higher and 100°C or lower, followed by the addition of water. The washing with water may be repeated a plurality of times, if necessary. The oil layer is then dried under reduced pressure, if necessary, to remove moisture, for example.

[0016] In the deacidification step, an aqueous solution of an acid selected from an organic acid and an inorganic acid such as oxalic acid, citric acid, and phosphoric acid may be added to the crude oil and stirred, if necessary, for pretreatment. Gum substances contained in the crude oil can thereby be removed together in the deacidification step. The aqueous solution of the acid does not have to be removed, and the alkaline aqueous solution can be added directly thereto to perform deacidification treatment. The amount of the acid added, as addition ratio of the acid to phosphorus matter (phospholipids) contained in the crude tamanu oil, is, for example, preferably 1.0 or more and 2.0 or less, more preferably 1.0 or more and 1.7 or less, further preferably 1.0 or more and 1.5 or less. If the amount is less than 1.0, phosphorus matter may be insufficiently removed. If the amount is more than 2.0, a purification burden may be increased due to an increased amount of the alkali added required for neuralization. Alternatively, the amount of the acid added is preferably 0.03 to 0.15% by mass, more preferably 0.03 to 0.12% by mass, further preferably 0.03 to 0.10% by mass, based on the mass of the crude tamanu oil. If the amount is less than 0.03% by mass, phosphorus matter may be insufficiently removed. If the amount is more than 0.15% by mass, a purification burden may be increased due to an increased amount of the alkali added required for neuralization. The water for use in the aqueous solution of the acid is not limited and is preferably purified water.

[0017] Free fatty acids contained in the crude oil are converted to soap through the alkaline aqueous solution. The soap can be removed to remove the free fatty acids from the crude oil. The deacidification step can also remove phospholipids and trace metals, etc. and can further effectively remove components inhibiting methyl esterification reaction, contained in the crude tamanu oil. Also, in the case of performing subsequent hydrogenation reaction, its efficiency may be enhanced.

[0018] The purification step of the present invention may combine the deacidification step, if necessary, with other purification steps. Specifically, the purification step may include one or more steps selected from the group consisting of other purification treatment steps used for edible oil resources, for example, a degumming step, a bleaching step, and a deodorization step.

[0019] [Bleaching step] The bleaching step is the step of removing dyes contained in the crude oil. The bleaching step is not limited and can be performed, for example, by adsorbing the dyes onto activated earth, active carbon, silica (silicon dioxide), or the like. The activated earth or the like with the dyes attached thereto is removed by, for example, filtration under reduced pressure.

[0020] [Degumming step] The degumming step is the step of hydrating and removing gum substances composed mainly of phospholipids, contained in the crude oil. The degumming step is not limited and can be performed, for example, by adding steam or water to the crude oil, stirring the mixture, and removing an aqueous layer. The degumming step may be performed by the addition of a degumming agent. For example, a degumming agent composed of an aqueous solution of an organic acid such as oxalic acid, citric acid, or phosphoric acid can be used.

[0021] [Deodorization step] The deodorization step is the step of removing odorous components contained in the crude oil. The deodorization step is not limited and can be performed by, for example, steam distillation under reduced pressure.

[0022] The degumming step, the bleaching step, and the deodorization step can be steps generally used in an edible oil resource purification step. In the case of performing the degumming step, the bleaching step, and the deodorization step in addition to the deacidification step, the degumming step, the deacidification step, the bleaching step, and the deodorization step are preferably performed in this order, as in the edible oil resource purification step. In this case, any of the degumming step, the bleaching step, and the deodorization step may be omitted, and the degumming step is preferably omitted.

[0023] The acid value of the purified tamanu oil in the purification step is, for example, 40 or less, preferably 20 or less, more preferably 15 or less, further preferably 10 or less. less.

[0024] The crude tamanu oil contains various impurities such as phenols, flavonoids, and pyranocoumarins. Among them, pyranocoumarins are likely to inhibit methyl esterification reaction and subsequent hydrogenation reaction, and these pyranocoumarins are preferably removed as much as possible in the purification step. In this context, the "pyranocoumarins" refer to a compound group including inocalophyllin A, inocalophyllin B, inophyllum C, inophyllum E, inophyllum P, inophyllum D, calophyllolide, calanolide GUT70, calanolide A, calanolide B, epicalanolide C, 12-oxocalanolide A, calanolide D, (-)-tamanolide D, (-)-tamanolide P, and tamanolide. In the present invention, pyranocoumarins in the tamanu oil purified in the purification step are preferably 18% by mass or less, more preferably 16% by mass or less, further preferably 10% by mass or less, even preferably less than 9% by mass, still further preferably 8% by mass or less, particularly preferably 7 by mass or less, especially preferably 6% by mass or less, based on the mass of the purified tamanu oil. The lower limit value is not particularly limited, and pyranocoumarins may partially remain and may be, for example, 0.1% by mass or more. The content of pyranocoumarins in the purified tamanu oil can be measured by a method described in Examples.

[0025] As described above, in the present invention, the purification step includes at least the deacidification step as purification treatment thereof, whereby impurities can be removed, and the subsequent methyl esterification step can progress efficiently.

[0026] In the present invention, the amount of the alkaline substance added or the addition ratio of the alkaline substance is set to a proper range in the deacidification step, whereby the purification step can be performed such that the absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less. When the absorbance at a wavelength of 330 nm of the tamanu oil thus purified is 0.08 or less, next methyl esterification reaction progresses efficiently. The absorbance at a wavelength of 330 nm of the tamanu oil thus purified is preferably 0.075 or less, more preferably 0.070 or less, further preferably 0.065 or less. The absorbance at a wavelength of 330 nm falls within the range described above, whereby methyl esterification efficiency can be improved in the methyl esterification step.

[0027] (b) Methyl esterification step The methyl esterification step is the step of adding methanol to the tamanu oil purified in the purification step and producing fatty acid methyl ester (FAME) through transesterification reaction (methanolysis). The transesterification reaction of an oil with an alcohol is known reaction. In the present invention, a generally known

methodcan method be used. canbe used.

[0028] In the present invention, the methyl esterification step is preferably performed in the presence of a basic catalyst. An alkali metal catalyst, an alkaline earth metal catalyst, or an ion exchange resin such as an aminic base, for example, can be used as the basic catalyst. Among them, an alkali metal catalyst is preferred because of its high catalytic activity. Examples of the alkali metal catalyst include: alkali metal hydroxides such as

sodium hydroxide, potassium hydroxide, and lithium hydroxide; alkali metal carbonates such as sodium carbonate and potassium carbonate; alkali metal

11 bicarbonates; alkali metals; and alkali metal oxides. One of these catalysts may be used singly, or two or more thereof may be used in combination. Among them, sodium hydroxide or potassium hydroxide is preferred, and potassium hydroxide is particularly preferred. The amount of the basic catalyst used is preferably 0.5% by mass or more and 3.0% by mass or less, more preferably 1.0% by mass or more and 2.5% by mass or less, further preferably 1.0% by mass or more and 2.0% by mass or less, based on the mass of the substrate.

[0029] In one embodiment of the present invention, an acid catalyst may be used with the basic catalyst. Methanol and the acid catalyst are added to the purified tamanu oil and reacted so that a proton coordinates to a carbonyl group of the tamanu oil and can increase the electrophilicity of the carbonyl group. The transesterification reaction can be efficiently performed by the subsequent addition and reaction of methanol and the basic catalyst. The acid catalyst can be selected from, for example, inorganic acids such as sulfuric acid and phosphoric acid; inorganic oxides such as tin oxide and zinc oxide; alcoholates such as tetraproxy titanium; and cation exchange resins. The amount of the acid catalyst used is preferably 0.05% by mass or more and 3.0% by mass or less, more preferably 0.1% by mass or more and 2.0% by mass or less, further preferably 0.1% by mass or more and 1.5% by mass or less, based on the mass of the substrate.

[0030] The methyl esterification step is preferably performed in the presence of a solvent. The solvent that can be used may be methanol alone or may be a mixed solvent of methanol and a different solvent. For example, use of not only methanol but a cosolvent tetrahydrofuran as the solvent may be able to uniformly dissolve the substrate purified tamanu oil in the reaction system and be able to further enhance reactivity.

[0031] The methyl esterification step may be performed in a batch manner or a continuous manner. The stirring method can be appropriately selected depending on a reaction treatment system or the type of a reactor, etc., and a known stirring method can be applied thereto. The stirring is preferably performed under warming and is performed at, for example, 25°C or higher and 80°C or lower, preferably 30°C or higher and 70°C or lower, more preferably 40°C or higher and 65°C or lower. The stirring may be performed under increased pressure. Those skilled in the art may select a preferred temperature and pressure depending on a desirable reaction time or the like. The stirring time can fall within a range in which transesterification reaction progresses sufficiently. Those skilled in the art can appropriately select the stirring time depending on a reaction treatment system or the type of a reactor, etc. For example, for the methyl esterification step in a batch manner, the stirring time can be appropriately selected with approximately 30 minutes to 60 minutes as a guide.

[0032] The methyl esterification step is generally performed in a batch manner using a stirring vessel. Alternatively, continuous reaction may be performed in a circulation scheme such as a fixed-bed scheme in which the purified tamanu oil and methanol are circulated through concurrent flow or parallel flow in a catalytic bed, or a fluidized-bed scheme in which a solid catalyst is fluidized, because transesterification reaction performed in the presence of a basic catalyst progresses relatively easily. After the completion of reaction, unreacted methanol is separated by distillation under reduced pressure or the like from the reaction liquid discharged from a reactor, and a by-product glycerin, water, and catalyst residues phase-separating from fatty acid methyl ester (FAME) are separated using, for example, decantation, centrifugation, or a solvent to obtain the fatty acid methyl ester.

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Water may be added, if necessary, to an oil layer, which is then washed with water by stirring. The washing with water is preferably performed under warming and is preferably performed, for example, by warming the oil layer to 40°C or higher and 90°C or lower, preferably 50°C or higher and 70°C or lower, followed by the addition of water. The washing with water may be repeated a plurality of times, if necessary. Moisture can then be removed by, for example, drying under reduced pressure, if necessary, to obtain fatty acid methyl ester (FAME).

[0033] The obtained fatty acid methyl ester (FAME) can be used directly as a biodiesel fuel. If necessary, the fatty acid methyl ester may be hydrogenated, for example, to produce a biofuel such as a hydrotreated vegetable oil (HVO) or a sustainable aviation fuel (SAF).

[0034] (c) Hydrogenation step In the hydrogenation step, hydrogen is preferably added, for hydrogenation, in an amount that saturates unsaturated matter in the methyl ester.

[0035] The hydrogenation step is preferably performed in the presence of a catalyst.

[0036] The catalyst preferably contains one or more metals selected from groups 7 to 10 of the periodic table and more preferably contains one or two or more metals selected from the group consisting of iridium, palladium, platinum, rhenium, rhodium, ruthenium, and nickel. The metal may be supported on a catalyst support. The amount of the metal supported is preferably 1% by mass or more and 20% by mass or less, more preferably 2% by mass or more and 10% by mass or less, further preferably 3% by mass or more and 5% by mass or less, based on the mass of the catalyst support.

[0037] The catalyst support is not particularly limited as long as the catalyst support is a solid inert substance capable of supporting the catalyst metal. Examples thereof include metal oxides (e.g., silica, alumina, zeolite, and titania) and active carbon. The catalyst support can be used in a form such as a powder, granules, or pellets.

[0038] The catalyst can be prepared by an impregnation method. For example, a solution of a metal chloride in hydrochloric acid is added in advance to the catalyst support so as to attain a predetermined amount of the catalyst support. After stirring, the resultant is dried at approximately 60°C or higher and 80°C or lower for approximately 1 to 3 hours and further dried at approximately 90°C or higher and 110°C or lower for approximately 5 to 24 hours, and the dried product can be calcined at approximately 400°C or higher and 600°C or lower for approximately 3 hours to 4 hours to prepare the catalyst. The metal chloride is not limited as long as the metal is contained. Examples

thereof include ruthenium chloride (RuC13.3H2O), rhodium chloride (RhCl3.3H2O), palladium chloride (PdC12), hexachloroiridic acid (H2IrC16), and chloroplatinic acid (H2PtC16).

[0039] The amount of the catalyst (including the metal and the catalyst support) used is preferably 3% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 30% by mass or less, further preferably 15% by mass or more and 20% by mass or less, based on the mass of a substrate.

[0040] The catalyst may optionally contain one or more promoters. The promoter more preferably contains one or more metals selected from groups 6 to 10 of the periodic table. The promoter can be provided in a salt or acid form as, for example, an oxyanion of perrhenic acid, molybdic acid, or tungstic acid. The promoter may be supported on a catalyst support or may be further supported on a support on which the catalyst metal is supported. The amount of the metal is preferably 0.25 or more and 10 or less, more preferably 0.5 or more and 6 or less, further preferably 1 or more and 4 or less, in terms of a molar ratio to the catalyst metal. metal.

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The promoter can be supported on the catalyst support by an impregnation method, as in the catalyst metal. For example, an aqueous solution of the promoter is added in advance to the catalyst support so as to attain a predetermined amount of the promoter supported. After stirring, the resultant is dried at approximately 60°C or higher and 80°C or lower for approximately 1 to 3 hours and. further dried at approximately 90°C or higher and 110°C or lower for approximately 5 to 24 hours, and the dried product can be calcined at approximately 400°C or higher and 600°C or lower for approximately 3 hours to 4 hours to prepare the promoter. In the case of further supporting the promoter on a support on which the catalyst metal is supported, the support on which the catalyst metal is supported is dried, and an aqueous solution of the promoter is then added to the support before calcination so as to attain a predetermined amount of the promoter supported. After stirring, the resultant is dried at approximately 60°C or higher and 80°C or lower for approximately 1 to 3 hours and further dried at approximately 90°C or higher and 110°C or lower for approximately 5 to 24 hours, and the dried product can be calcined at approximately 400°C or higher and 600°C or lower for approximately 3 hours to 4 hours to prepare the promoter.

[0041] The description above illustrates one example, and those skilled in the art can appropriately select the types and combination of the catalyst, the promoter, and the catalyst support, their amounts of use, preparation methods, and the like in order to optimize hydrogenation reaction.

[0042] The hydrogenation step can be performed in the presence or absence of a solvent. In the case of using a solvent, an arbitrary solvent commonly used in hydrogenation reaction can be used. Examples thereof include: Cs to C12 hydrocarbon solvents, for example, hexane, cyclohexane, and dodecane; C4 to C8 ethers, for example, tetrahydrofuran and methyl t-butyl ether; C4 to CIO esters, for example, ethyl acetate; chlorinated CI to C2 hydrocarbons, for example, dichloromethane; C2 to C6 primary or secondary alcohols, for example, isopropanol and ethanol; other polar solvents, for example, dimethylformamide, acetonitrile, dimethyl sulfoxide, and acetone; and mixtures thereof. Those skilled in the art can select a proper solvent in order to optimize hydrogenation reaction in each case, depending on the type of the catalyst, etc.

[0043] In the hydrogenation step of the present invention, the hydrogenation treatment is preferably carried out at an I-I2 pressure of 0.1 MPa to 30 MPa or, if necessary, at a higher pressure and more preferably carried out at 0.5 MPa to 3 MPa, further preferably 0.5 MPa to 2.5 MPa, particularly preferably 1 MPa to 2.5 MPa. Those skilled in the art are also capable of adjusting the pressure depending on an added catalyst or depending on the dilution of a substrate in a solvent.

[0044] The temperature at which the hydrogenation treatment is carried out is

preferably 50°C to 300°C, more preferably 100°C to 200°C, further preferably 150°C to 200°C. Those skilled in the art can also select a preferred temperature depending on a desirable reaction time or the like.

[0045] The hydrogenation step is preferably carried out in an atmosphere consisting of hydrogen gas alone and may be carried out in a mixed gas containing an inert gas such as nitrogen or argon without influencing hydrogenation reaction.

[0046] The reaction vessel is preferably a fixed-bed system. The reaction is

preferably performed through continuous reaction. The reaction is preferably performed with stirring. The stirring method can be appropriately selected depending on a purpose, and a known stirring method can be applied thereto.

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[0047] After the completion of hydrogenation reaction, the reaction liquid is collected with a solvent. Examples of the solvent that can. be used can include the same solvents as those used in the hydrogenation step.

[0048] The obtained linear hydrocarbon can be used as a biofuel such as a hydrotreated vegetable oil (HVO) or a sustainable aviation fuel (SAF). This linear hydrocarbon is inferior in low-temperature flowability, though having a high cetane number. Therefore, the linear hydrocarbon, when used as a sustainable aviation fuel (SAF), is treated through isomerization/hydrocracking so as to satisfy specifications as SAF.

[0049] (d) Isomerization/hydrocraeking step The isomerization/hydrocracking step is the step of isomerizing or hydrocracking the hydrocarbon obtained in the hydrogenation step. In this step, the linear hydrocarbon obtained in the hydrogenation step is converted to a desired hydrocarbon, i.e., isoparaffins containing one or more methyl groups in a molecule or paraffins having a smaller number of carbon atoms, by isomerization and hydrocracking so as to satisfy a high flash point and favorable flow characteristics in cold.

[0050] The isomerization and the hydrocracking are well known techniques, and those skilled in the art can appropriately select a catalyst and reaction conditions so as to satisfy the specifications of various fuels. In this step, the respective reactions of isomerization and hydrocracking may be simultaneously performed or continuously performed.

[0051] The isomerization can convert the linear hydrocarbon to isoparaffins and thereby decrease a freezing point. The isomerization can be performed in the presence of an acidic catalyst. A binary functional catalyst having a metal site for hydrogenation/dehydrogenation and an acid site for skeletal isomerization mediated by a carbocation is preferably used as the isomerization catalyst. Examples thereof include Pt/SAPO-11/Al2O3, Pt/ZSM-22/Al2O3, Pt/ZSM-23/Al2O3, and Pt/SAPO- 11/SiO2.

[0052] Typically, the linear hydrocarbon is dehydrogenated on the metal site of the catalyst and reacted on the acid site so that an alkyl carbocation is formed to produce a protonated olefin. The alkyl carbocation is transferred to monobranched, dibranched, and tribranched alkyl carbocations on the acid site. The branched alkyl carbocations are deprotonated and hydrogenated to produce corresponding paraffins.

[0053] The hydrocracking is an exothermic reaction and produces liquid or gas paraffins having a smaller number of carbon atoms. Since the reaction is relatively slow, hydrocracking is mostly performed in a final section of a reactor. The

hydrocracking mainly involves the degradation and saturation of paraffins. Excessive degradation is not preferred because lower paraffins (CI to C4) and naphtha (C5 to Cs) are produced.

[0054] After the isomerization/hydrocracking step, a fractional distillation step is performed in which the mixture is separated into paraffinic kerosene (C9 to C16), paraffinic diesel (C16 to C18), naphtha, and light gas. Paraffins having a large number of carbon atoms (e.g., C7 to C16) are then distilled and can be used as SAF.

[0055] According to the present invention, crude tamanu oil is deacidified, whereby components inhibiting the methyl esterification reaction of tamanu oil, contained in the crude tamanu oil can be effectively removed. Specifically, in one aspect, the present invention also encompasses a method for improving methyl esterification efficiency in methyl esterification treatment of tamanu oil, the method comprising a deacidification step in which crude tamanu oil is deacidified. The method preferably comprises

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(a) a tamanu oil purification step comprising a deacidification step in which crude tamanu oil is deacidified, wherein absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less, and (b) a methyl esterification reaction in which methanol is added to the purified tamanu oil, and fatty acid methyl ester (FAME) is produced through transesterification reaction. The deacidification step in which crude tamanu oil is deacidified and the steps (a) and (b) are as already mentioned, so that the description is omitted here.

Examples

[0056] Next, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited by these Examples by any means.

[0057] [Purification step] Pressed tamanu oil (mixture with acid values (AV) of around 20 to 30: AV = 21.9 mg/g) from Miyako Island, Okinawa prefecture, Japan was used as a raw material and subjected to any of the following purification steps.

[0058] <Deacidification step> 250 g of the pressed tamanu oil was placed in a 500 ml beaker and warmed to 80°C. Then, an aqueous solution containing 75% by mass of phosphoric acid was added at 0.06% by mass based on the mass of the pressed tamanu oil and stirred for 10 minutes. Then, an aqueous solution containing 16% by mass of sodium hydroxide or an aqueous solution containing 16% by mass of potassium hydroxide was added thereto at an alkali addition ratio of 0.4 to 1.2 and stirred at 80°C for 20 minutes using a stirring blade, the mixture was centrifuged at 3,000 rpm for 3 minutes to remove an aqueous layer.

The oil layer thus centrifuged was warmed to 90°C. Then, 10% by mass of distilled water was added thereto, and the oil layer was washed with water for 10 minutes and also centrifuged at 3,000 rpm for 3 minutes to remove an aqueous layer. Washing with water was performed again under the same conditions as above, and the obtained oil layer was dried under reduced pressure at 20 hPa at 60°C for 30 minutes to obtain a deacidified oil. The alkali addition ratio described above refers to the addition ratio of the The alkali addition ratio described above refers to the addition ratio of the

alkaline substance with respect to the neutralization equivalent of an acidic substance contained in the oil subjected to the deacidification step (i.e., the pressed tamanu oil). The addition ratio of the alkaline substance based on the neutralization equivalent of an acidic substance contained in the oil is, for example, "1.2", which means an amount (molar quantity) corresponding to 1.2 times the amount of the alkaline substance required for the neutralization of the acidic substance contained in the oil.

[0059] <Degumming step> 250 g of the pressed tamanu oil was placed in a 500 ml beaker and warmed to 80°C. Then, an aqueous solution containing 75% by mass of phosphoric acid was added at 0.06% by mass based on the pressed tamanu oil and stirred for 10 minutes. Then, 3% by mass of distilled water was added to the pressed tamanu oil, stirred at a stirring rate of 300 rpm for 20 minutes using a stirring blade, and then centrifuged at 3,000 rpm for 3 minutes. The obtained upper layer was used as a degummed oil.

[0060] <Bleaching step> 340 g of the pressed tamanu oil was placed in a 1000 ml Erlenmeyer flask and

warmed to 80°C. Then, 2% by mass of silica gel ("Sorbsil R92" manufactured by PQ Corporation) was added to the pressed tamanu oil. Then, the mixture was stirred at 300 rpm at 10 hPa for 30 minutes using a stirring blade, left standing, and filtered through a filter paper for qualitative analysis

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(No. 2 Filter Paper manufactured by Advantec Toyo Kaisha Ltd.) to obtain a bleached oil.

[0061] [Methyl esterification step (alkali method)] A 200 to 300 ml Erlenmeyer flask was charged with a raw material and warmed to 60°C. Then, methanol and potassium hydroxide were added at 18% by mass and 1.5% by mass, respectively, to the raw material, and the mixture was stirred for 30 minutes. Then, the reaction liquid was transferred to a 500 ml separating funnel and left standing at ordinary temperature for 40 minutes for separation, and a lower layer was removed. A 300 ml Erlenmeyer flask was charged with an upper layer and warmed to 60°C. Then, 20% by mass of distilled water was added to the raw material, and the mixture was washed with water by stirring for 20 minutes. The reaction liquid thus washed with water was transferred to a 500 ml separating funnel and left standing at ordinary temperature for 40 minutes for separation, and a lower layer was removed. Again, a 300 ml Erlenmeyer flask was charged with an upper layer. After washing with water and lower layer separation and removal under the same conditions as above, the obtained upper layer liquid was dried under reduced pressure at 60°C and 20 hPa for 30 minutes to obtain a biodiesel fuel. Special grades of methanol and potassium hydroxide were used.

[0062] [Methyl esterification step (acid-alkali method)] A 300 ml Erlenmeyer flask was charged with a raw material and warmed to 60°C. Then, methanol and concentrated sulfuric acid were added at 3.6% by mass and 0.4% by mass, respectively, to the raw material, and the mixture was stirred for 60 minutes.

Then, methanol and potassium hydroxide were added at 16% by mass and 3%

by mass, respectively, to the reaction liquid, and the mixture was stirred at 60°C for 30 minutes. Then, the reaction liquid was transferred to a 500 ml separating funnel and left standing at ordinary temperature for 40 minutes for separation, and a lower layer was removed. A 300 ml Erlenmeyer flask was charged with an upper layer and warmed to 60°C. Then, 20% by mass of distilled water was added to the raw material, and the mixture was washed with water by stirring for 20 minutes. The reaction liquid thus washed with water was transferred to a 500 ml separating funnel and left standing at ordinary temperature for 40 minutes for separation, and a lower layer was removed. Again, a 300 ml Erlenmeyer flask was charged with an upper Iayer. After washing with water and lower layer separation and removal under the same conditions

as above, the obtained upper layer liquid was dried under reduced pressure at 105°C and atmospheric pressure for 60 minutes to obtain a biodiesel fuel. Special grades of methanol, concentrated sulfuric acid, and potassium hydroxide were used.

[0063] <Yield quantity and yield of biodiesel fuel> A yield quantity (g), a biodiesel reaction yield (% by mass), and a biodiesel yield (% by mass) were determined for the biodiesel fuel obtained in the methyl esterification step. The biodiesel reaction yield (% by mass) and the biodiesel yield (% by mass) were calculated according to the following expressions. Biodiesel reaction yield (% by mass) = Biodiesel yield quantity (g) / Amount

of the raw material added (g) x 100 yield (% Biodiesel yield Biodiesel by mass) (% by mass)==Purification yield (% Purification yield bymass) (% by x Biodiesel mass)Biodiesel reaction yield (% by mass) / 100

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[0064] <Quantitative analysis of FAME> The content of FAME was measured by gas chromatography with reference to 2.4.2.3-2013 of Standard Methods for the Analysis of Fats, Oils and Related Materials. Approximately 30 mg of the biodiesel fuel obtained by preparation was precisely weighed, supplemented with 1 ml of a solution of methyl heptadecanoate in hexane as a standard substance, and used as an analysis sample. The FAME content (% by mass) was calculated according to the following expression. FAME content (% by mass) = (Each peak area x Amount of the standard substance added/ Peak area of the standard substance/ Amount of the sample collected) x 100

[0065] <Quantitative analysis of pyranocoumarins> The content of pyranocoumarins was measured as to unpurified crude tamanu oil (AV26 and AV80) and the tamanu oil obtained after the purification step (hereinafter, referred to as the tamanu oil) by the following procedures. (1) Preparation of calibration curve Coumarin (undiluted solution, 118 µg/ml, molecular weight, 146.14) was serially diluted into specific concentrations with hexane, and a wavelength at 330 nm was measured with a spectrophotometer. The analysis conditions were as shown below. - Equipment: Spectrophotometer UV2600-i (Shimadzu Corp.) - Analysis: Analysis data system "LabSolutions UV-vis" (Shimadzu Corp.) - Wavelength: 330 tam The results are shown in Table 1. A calibration curve was prepared on the basis of the results of Table 1. As shown in Figure 1, a calibration curve having very high linearity was able to be prepared.

[0066] [Table 1]

Table 11 Table Concentration Absorbance Absorbance (pg/ml) 1 39.33 39.33 0.687 2 2 19.67 19.67 0.348 0.348 3 9.83 0.175 4 4.92 0.089 5 2.46 0.045 6 6 0 0 0

[0067] (2) Measurement of 330 nm light-absorbing substance (inocalophyllins) in tamanu oil 2 mg of the purified tamanu oil was weighed into a 15 ml Falcon tube, and 10 ml of hexane was added thereto using Vollpipette. A given amount of this solution was weighed into a PMMA (polymethyl methacrylate) disposable cuvette, and absorbance at a wavelength of 330 nm was measured. A concentration was calculated as a coumarin equivalent. On the

assumption that absorption coefficients were equivalent, mg/g corresponding to pyranocoumarins was calculated using the average molecular weight 548.22 of inocalophyllins A and B, and % by mass was measured.

[0068] Table 2 shows the relationship between the type of the tamanu oil purification step and the yield and yield quantity of the biodiesel fuel. As shown in Table 2, the yield quantity, reaction yield, and the yield of the biodiesel fuel were improved by performing the deacidification treatment in the purification step.

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[0069] [Table 2] Table 2. Results of evaluating blodlesel yield Puriflcatl Amount of Biodiesel Alkali Blodlesel Blodiesel Biodiesel AV AV on yield Methylesterif raw raw Blodiesel yield Purification step addition addition yield reaction yield (mg/g) (% by ication step material material (% by mass) ratio ratio quantity (g) (% by mass) mass) added (q) Comparative Alkali Alkall -- 21.9 21.9 0 0 - - 40.38 40.38 Not Not obtained obtained - - Example 1 method Comparative Acid-alkali -- 21.9 21.9 0 0 -- 228.6 228.6 128.25 128.25 56.1 56.1 56.1 56.1 Example 2 method Comparative Acid-alkali Degumming 21.2 0 0 94.1 205.67 205.67 147.34 147.34 71.6 71.6 67.4 67.4 Example 3 method method Comparative Acid-alkali Bleaching 21.5 0 0 94.2 231.28 231.28 146.22 146.22 63.2 63.2 59.6 59.6 Example 4 method method Deacidification Alkali Example 1 0.17 1.2 1.2 80.2 181.2 181.2 170.68 170.68 94.2 94.2 75.5 75.5 (NaOH) method Deacidiflcation Deacidification Alkali Example 2 0.20 1.2 1.2 79.8 79.8 176.53 176.53 165.79 165.79 93.9 93.9 74.9 74.9 (KOH) method

[0070] Next, Table 3 shows the relationship between the deacidification conditions and the quality of the biodiesel fuel. The quality of fatty acid methyl ester (FAME) was evaluated with reference to JIS K2390, and 96.5% or more was regarded as being satisfactory while other values were regarded as being not satisfactory.

[0071] [Table 3] Table 3. Deacidification conditions and quality of biodiesel fuel Purificati Pyranocou Alkali Biodiesel on yield AV Absorbance/ marins Methylesterif Modlesel yield FAME Quality Purification step addition reaction yield (% by (mg/g) mg (330nm) (% by Ication step quantity (g) (wt%) evaluation ratio (% by mass) mass) mass) Comparative Alkali Not -- 0 0 -- 35.1 0.106 22.4 68.0 68.0 -- 63.4 Example 5 method satisfactory

Comparative Deaddification Alkali Not 0.4 80.1 18.6 0.090 19.2 75.2 60.2 94.7 Example 6 (Na0H) method satisfactory Deaddification Deacidification Alkali Alkali Example 3 0.6 0.6 78.2 9.8 0.066 14 82.7 64.7 64.7 97.7 97.7 Satisfactory (NaOH) method Example Example 4 4 DeacidincatIon 0.8 74.4 3.82 0.028 5.8 Alkali 89.2 0.8 74.4 3.82 0.028 5.8 89.2 66.4 66.4 96.8 96.8 Satisfactory (NaOH) method Deacidification Alkali Example 5 1.0 73.5 0.69 0.023 4.8 92.8 68.2 97.1 Satisfactory (NaOH) method

[0072] As shown in Table 3, the absorbance at a wavelength of 330 nm of the purified tamanu oil became 0.08 or less by performing the deacidification step in the purification step. Thus, components inhibiting methyl esterification reaction, such as pyranocoumarins, contained in the crude tamanu oil were able to be effectively removed.

[0073] The deacidification step performed in the purification step allowed the methyl esterification step to progress efficiently. The yields of the biodiesel fuel and the fatty acid methyl ester (FAME) were further improved by appropriately setting the alkali addition ratio. Thus, fatty acid methyl ester (FAME) having favorable quality was obtained. It is considered that the deacidification step is performed in the purification step, whereby the components inhibiting methyl esterification reaction, contained in the crude tamanu oil were able to be effectively removed so that the subsequent methyl esterification step progressed efficiently.

[0074] As described above, according to the method of the present invention, a purification step for use in an edible oil resource is used, whereby a biofuel can be efficiently produced while an environmental burden is reduced, using a non-edible oil resource. resource.

Claims (10)

1. [Claim 1] A method for producing a biofuel, the method comprising: (a) a tamanu oil purification step comprising a deacidification step in which crude tamanu oil is deacidified, wherein absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less, and (b) a methyl esterification step in which methanol is added to the purified tamanu oil, and fatty acid methyl ester (FAME) is produced through transesterification reaction.
2. [Claim 2] The method for producing a biofuel according to claim 1, wherein the deacidification step comprises deacidification treatment by an alkaline deacidification method using an alkaline aqueous solution, and an addition ratio of an alkaline substance based on a neutralization equivalent of an acidic substance contained in the crude tamanu oil is 0.6 or more and 1.2 or less. crude tamanu oil is 0.6 or more and 1.2 or less.
3. [Claim 3] The method for producing a biofuel according to claim 1, wherein in the methyl esterification step, the fatty acid methyl ester is produced through the transesterification reaction in the presence of an alkali metal catalyst.
4. [Claim 4] The method for producing a biofuel according to claim 1, wherein a content of pyranocoumarins in the tamanu oil purified in the purification step is 18% by mass or less based on the mass of the purified tamanu oil.
5. [Claim 5] The method for producing a biofuel according to claim 1, wherein the biofuel

   is a biodiesel fuel.
6. [Claim 6]

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   The method for producing a biofuel according to claim 5, wherein a content of the fatty acid methyl ester in the biodiesel fuel is 96.5% by mass or more.
7. [Claim 7] A method for improving methyl esterification efficiency of tamanu oil, the method comprising: (a) a tamanu oil purification step comprising a deacidification step in which crude tamanu oil is deacidified, wherein absorbance at a wavelength of 330 nm of the purified tamanu oil is 0.08 or less, and (b) a methyl esterification step in which methanol is added to the purified tamanu oil, and fatty acid methyl ester (FAME) is produced through transesterification reaction.
8. [Claim 8] The method for improving methyl esterification efficiency of tamanu oil according to claim 7, wherein the deacidification step comprises deacidification treatment by an alkaline deacidification method using an alkaline aqueous solution, and an addition ratio of an alkaline substance based on a neutralization equivalent of an acidic substance contained in the crude tamanu oil is 0.6 or more and 1.2 or less.
9. [Claim 9] The method for improving methyl esterification efficiency of tamanu oil according to claim 7, wherein in the methyl esterification step, the fatty acid methyl ester is produced through the transesterification reaction in the presence of an alkali metal catalyst.
10. [Claim 10] The method for improving methyl esterification efficiency of tamanu oil according to claim 7, wherein a content of pyranocoumarins in the tamanu oil purified in the purification step is 18% by mass or less based on the mass of the purified tamanu oil.

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    0.8 0.8 y = 0.0174x + 0.0024

    0.7 R² = 1 = 1 0.7 R~ ...."*. Absorbance

    Absorbance

    0.6 0.6 .•••• 0.5 0.5 .•••• .** • 0.4 0.4 .•••• AY' 0.3 0.3 ...** ../ 0.2 0.2 ..... 11 ••• 0.1 0.1 Ay' ig 0 0 tli 0 0 10 10 20 20 30 30 40 40 50 50

    Concentration (µg/ml)

    Fig. 1

    1/1 1/1