JP4543177B2 - Method for producing fatty acid alkyl ester - Google Patents

Description

  The present invention relates to a method for producing a fatty acid alkyl ester (also referred to as “fatty acid ester”). More specifically, the present invention relates to a method for producing a fatty acid alkyl ester used as a biodiesel fuel.

  Biodiesel fuel generally abbreviated as “BDF” is a transesterification of vegetable oil, animal oil or fatty acid triglyceride (also referred to as “fatty acid glyceride”), which is the main component of these waste oils (for example, waste cooking oil). Or it is the fuel which consists of fatty acid ester obtained by the method of esterifying the fatty acid obtained by hydrolysis with alcohol. This fuel can be used for vehicles having diesel engines, ships, agricultural and industrial machinery, generators, and the like.

  Compared to light oil, this biodiesel fuel has less sulfur oxides that cause graphite and acid rain in its exhaust gas, and generates less suspended particulate matter (PM). Since it is a fuel derived from biomass resources, it has already been used as an alternative to fossil fuels because it has the advantage of not disrupting the global carbon balance. In addition, several methods for industrially producing fatty acid esters from fats and oils have been developed, and this method can be roughly divided into an alkali catalyst method, an acid catalyst method, and a lipase enzyme method.

  The alkali catalyst method is a method for obtaining a target fatty acid methyl ester by adding a methanol and a basic catalyst to an oil and fat and conducting a transesterification reaction. This method allows the reaction to proceed under relatively mild temperature and pressure conditions, but requires a step of removing the alkali catalyst in the purification step. In addition, the free fatty acid in the raw oil and fat reacts with the alkali catalyst to produce alkali soap, and the water in the raw oil and fat reduces the catalytic function, resulting in a decrease in ester yield. Yes.

  The acid catalyst method does not generate alkali soap like the alkali catalyst method, but, like the alkali catalyst method, the catalytic function is lowered by the moisture in the raw oil and fat, and the reaction rate is also slow. Therefore, it is difficult to make an industrial process.

  The lipase enzyme method is a method of converting raw oils and fats to biodiesel fuel by the catalytic action of the lipase enzyme, and there is an advantage that neutralization of the product is unnecessary and it is not affected by free fatty acids in the raw material. However, control of the amount of methanol added is essential, and there are problems such as slow reaction rate and high cost.

  For these production methods, the present inventor has proposed a technique for producing a fatty acid ester under non-catalytic conditions. For example, in Patent Document 1, a fatty acid ester composition is produced without a catalyst by performing a transesterification reaction and an esterification reaction using raw material fats and oils in a supercritical or subcritical alcohol at a high temperature and high pressure as a solvent. The technology to do is proposed. In this technology, there is a reverse reaction in which the fatty acid alkyl ester and glycerin react to return to the fatty acid monoglyceride. Therefore, it is necessary to use a large excess of alcohol to tilt the reaction in the direction of fatty acid alkyl ester formation, Pressure conditions were severe and there was room for improvement.

  The inventor of the present application has proposed an improved technique of Patent Document 1 in Patent Document 2 and Non-Patent Document 1. More specifically, hydrolysis is performed by coexisting raw material fats and oils containing fatty acid triglycerides and water to obtain fatty acids and glycerin from the fatty acid triglycerides, and alcohol is added to the product of the first step, and a predetermined temperature is obtained. A second process (that is, an esterification process) for converting a fatty acid in the product into a fatty acid alkyl ester under pressure conditions (hereinafter referred to as “non-catalytic / two-stage process”). is suggesting.

  In this non-catalytic two-step method, after the first step, glycerin is separated and removed to effectively prevent the reverse reaction in the second step, and water in the fatty acid obtained from the first step is removed. Since the esterification reaction in the second step can proceed more preferentially, the fatty acid alkyl ester can be produced efficiently. This method is particularly useful as an industrial process for producing fatty acid alkyl esters using raw oils and fats such as waste oil containing water and free fatty acids.

In addition, Patent Document 3 discloses a technique for producing a fuel comprising a triglyceride such as triacetin (glycerin triacetate) obtained by subjecting a triglyceride and a carboxylic acid ester to an ester exchange reaction and a carboxylic acid ester. ing. That is, a technique for producing a fatty acid alkyl ester that does not use alcohol as a solvent is disclosed.
JP 2000-204392 A. PCT International Publication WO 03/106604. JP 2004-149742 A. Journal of the Japan Institute of Energy, Vol. 84, 413-419 (2005).

  As described above, conventional techniques related to a method for producing a fatty acid alkyl ester useful for BDF are generally based on esterification reaction or transesterification reaction using alcohol as a solvent. In the alcohol solvent system, for example, by making alcohol a supercritical condition, the esterification reaction can proceed even for free fatty acids in the raw oil and fat, but it takes time to convert fatty acid triglycerides to glycerol. I have a problem. In addition, the technique disclosed in Patent Document 3 that does not use an alcohol solvent is useful when the main component of the raw material fat is a fatty acid triglyceride, but the main component of the raw material fat is a free fatty acid (for example, Dark oil) is difficult to handle.

  In the future, when the production technology for fatty acid alkyl esters is put to practical use, it will be possible to handle a wide variety of raw oils and fats, simplify the reaction process, relax reaction conditions (eg, temperature and pressure), improve reaction efficiency, Avoiding the use of a catalyst, suppressing or preventing the generation of byproducts (for example, water, glycerin, etc.) unsuitable for fuel, and, consequently, improving the quality of the final fuel composition are important technical issues in the future.

  Therefore, the present invention aims to solve the above technical problem and to produce a fatty acid alkyl ester that is more suitable for industrial production. More specifically, the present invention is a reaction system that does not use an alcohol solvent as a solvent, has high reaction efficiency, and a wide range. The main object is to provide a novel method for producing a fatty acid alkyl ester that can be applied to various raw oils and fats.

  The inventor of the present application has greatly changed the idea from the method using an alcohol solvent, which has been the mainstream in the production technology of fatty acid alkyl esters, and has conducted earnest research on more advantageous production methods assuming industrial production of fatty acid alkyl esters. went. As a result, the fatty acid or fatty acid glyceride is reacted with a carboxylic acid ester or carboxylic acid under supercritical or subcritical conditions, and the esterification reaction or transesterification reaction is advanced, so that the target fatty acid alkyl ester is efficiently produced. I found out that I could get well.

  Therefore, the present invention provides a method for producing a fatty acid alkyl ester by first proceeding an esterification reaction between a fatty acid and a carboxylic acid ester under supercritical or subcritical conditions of the carboxylic acid ester.

  As the fatty acid in this production method, free fatty acids present in the raw oil and fat can be used effectively. Moreover, the fatty acid obtained through a predetermined process from raw material fats and oils can also be utilized as the said fatty acid in this manufacturing method. Both the fatty acid and the free fatty acid can be used.

  The above-mentioned predetermined step for obtaining a fatty acid from the components in the raw oil and fat is not particularly limited, but for example, the fatty acid glyceride and the carboxylic acid in the raw oil and fat are supercritical or subcritical of the carboxylic acid. A step of obtaining a fatty acid by transesterification under the above conditions can be employed. Or the process of obtaining a fatty acid by hydrolyzing the fatty acid triglyceride in the said raw material fats and oils on supercritical or subcritical conditions is employable.

  In addition to the fatty acid alkyl ester obtained by advancing the esterification reaction between the fatty acid and the carboxylic acid ester, the fatty acid alkyl ester that is the target product of the production method according to the present invention is from other reaction routes. The resulting fatty acid alkyl ester may be included. If an example is given, the fatty-acid alkylester obtained by the transesterification between the fatty-acid glyceride and carboxylic acid ester in the said raw material fats and oils may be contained.

  In this manufacturing method, it is good to compatibilize a fatty acid phase and a carboxylic acid ester phase by adding a third component to the esterification reaction system. This compatibilization further promotes the transesterification reaction between the fatty acid and the carboxylic acid ester, and therefore can be effectively used in industrial production.

  Also, the fatty acid glyceride phase and the carboxylic acid phase, or the fatty acid glyceride phase and the carboxylic acid ester phase may be compatibilized by adding a third component to the transesterification reaction system. This compatibilization promotes the transesterification reaction, and is effective in industrial production.

  The carboxylic acid ester that can be used in the esterification reaction or transesterification reaction in the present production method is not particularly limited, but formic acid esters such as methyl formate can also be used.

  In the present invention, “oil / fat” includes at least one of fatty acid glycerides (including fatty acid triglycerides, fatty acid diglycerides, and fatty acid monoglycerides) and fatty acids. “Fatty acid alkyl ester” means (1) a free fatty acid originally contained in the raw oil and fat, (2) a fatty acid produced by a reaction of components in the raw oil and fat, and (3) contained in the raw oil and fat. Means fatty acid ester obtained through esterification reaction or transesterification reaction.

  According to the present invention, a fatty acid alkyl ester can be efficiently produced without adding a catalyst from the outside to the reaction system. Further, in the method of producing a fatty acid alkyl ester by proceeding an esterification reaction between a fatty acid and a carboxylic acid ester under supercritical or subcritical conditions of the carboxylic acid ester, alcohol is not used as a solvent. For example, unlike the conventional method of producing a fatty acid alkyl ester by esterifying a fatty acid and an alcohol, generation of water unsuitable as a composition in fuel does not occur in the reaction system.

  In the reaction system according to the production method of the present invention, a carboxylic acid ester or a carboxylic acid is present until the final stage of the reaction. Since this carboxylic acid ester or carboxylic acid exhibits an acid catalyst function, the reaction efficiency is high. As a result, a high-quality fatty acid alkyl ester can be produced.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments for carrying out the invention will be described with reference to the accompanying drawings. Each embodiment shown in the accompanying drawings shows a typical embodiment of the manufacturing method according to the present invention, and the scope of the present invention is not interpreted narrowly.

  First, FIG. 1 is a conceptual diagram of a basic production process (X process) of a fatty acid alkyl ester according to the present invention, and FIG. 2 is a diagram for explaining in more detail an esterification reaction related to the basic production process (X process).

Here, R ¹ and R ³ shown in FIG. 2 mean hydrocarbon groups, and these R ¹ and R ³ may be different types of hydrocarbon groups, or all or one of R ¹ and R ³ . Two may be the same kind of hydrocarbon groups. Further, R ¹ and R ³ are not limited to a narrow number of carbon atoms, and may have a carbon-carbon unsaturated bond. In some cases, other functional groups such as an alkoxy group are bonded. (Hereinafter, the same applies to other steps). In addition, R ² related to the carboxylic acid ester is hydrogen or a hydrocarbon group. When R ² is hydrogen, R ² COOR ^{3 in} FIG. 2 means a formic acid alkyl ester, while R ² is a hydrocarbon group. In some cases, the number of carbon atoms is not narrowly limited, and there may be a carbon-carbon unsaturated bond in R ² , and in some cases, other functional groups such as alkoxy groups may be bonded. Good (hereinafter, the same applies to other processes).

  The “esterification reaction” relating to the step X shown in FIGS. 1 and 2 preferably proceeds by treating the raw oil and fat with the carboxylic acid ester as the temperature and pressure under supercritical or subcritical conditions. Can do.

  The “supercritical state” of the carboxylic acid ester as the solvent means a state in which the temperature in the reaction system is higher than the critical temperature (Tc) of the carboxylic acid ester and the pressure is higher than the critical pressure (Pc) of the carboxylic acid ester. . Further, the “subcritical state” means that the temperature in the reaction system is not less than the boiling point of the carboxylic acid ester and is generally not less than 100 to 150 ° C., and the pressure is not less than the vapor pressure of the carboxylic acid ester at the reaction temperature, and The state of about 0.5-2 MPa or more is said.

  Examples of the carboxylic acid ester include methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, Ethyl butyrate, propyl butyrate, butyl butyrate and the like can be used. In addition, the critical temperature (Tc) and critical pressure (Pc) of main carboxylic acid esters are summarized in the following “Table 1”.

  The fatty acid that is the target of this esterification reaction is either a free fatty acid contained in the raw material fat or oil from the beginning, or a fatty acid obtained through a predetermined step from a component (eg, fatty acid glyceride) contained in the raw material fat or oil. Either or both can be used. In the production method according to the present invention, the esterification reaction step shown in FIGS. 1 and 2 is positioned as an essential basic step.

  In the present invention, it is desirable to make the fatty acid phase and the carboxylic acid ester phase compatibilized by adding a third component to the esterification reaction system. This is because the compatibilization can promote the esterification reaction. As the third component, a component that contributes to compatibilization of the fatty acid phase and the carboxylic acid ester phase can be widely used. For example, alkanes such as pentane and hexane and petroleum ether can be used.

  Next, FIG. 3 is a figure which shows the example of another reaction path | route which can be utilized in the manufacturing method which concerns on this invention. FIG. 4 is a diagram showing a reaction example of the step A (transesterification step) which is the first step of this reaction path.

  First, the purpose of the step A (transesterification step) shown in FIG. 3 and FIG. 4 is from the fatty acid glyceride (in FIG. 3, fatty acid triglyceride is exemplified) to the X step (esterification reaction, The fatty acids that can be used in FIG. 1 and FIG. 2 are obtained.

That is, in the production method according to the present invention, when the step A which is a transesterification step is adopted, the fatty acid is obtained from the fatty acid (R ¹ COOH) and acetin (acetin, which is exemplified by triacetin in FIG. 4) obtained by the reaction. 1 and FIG. 2, the fatty acid is then esterified under supercritical or subcritical conditions with a carboxylic acid ester to obtain the desired fatty acid alkyl ester (FIG. 3). reference).

Here, in the reaction example of Step A shown in FIG. 4, a so-called transesterification reaction is performed between the fatty acid triglyceride and the carboxylic acid under supercritical or subcritical conditions of the carboxylic acid, and acetin and the fatty acid (R ¹ The process of obtaining (COOH) is shown. In addition to fatty acid triglyceride, fatty acid glyceride includes fatty acid diglyceride and fatty acid monoglyceride, and acetin includes diacetin and monoacetin in addition to triacetin.

  The “supercritical state” of the carboxylic acid as the solvent means a state in which the temperature in the reaction system is higher than the critical temperature (Tc) of the carboxylic acid and the pressure is higher than the critical pressure (Pc) of the carboxylic acid. The “subcritical state” of carboxylic acid means that the temperature in the reaction system is not lower than the boiling point of carboxylic acid and is generally not lower than 200 ° C., and the pressure is not lower than the vapor pressure of carboxylic acid at the reaction temperature, and is approximately The state of 2-3 MPa or more is said. However, since unsaturated fatty acids are thermally decomposed particularly under temperature conditions exceeding 350 ° C., conditions of 350 ° C. or less, more preferably 300 ° C. or less are desired. The critical temperatures (Tc) and critical pressures (Pc) of main carboxylic acids are summarized in the following “Table 2”.

  From the above, in the present invention, a two-stage supercritical process of biodiesel fuel based on the A process (transesterification reaction) and the X process (esterification reaction) can be proposed. For example, the fatty acid glyceride contained in the raw oil and fat is fractionated together with the fatty acid obtained by transesterification with the supercritical or subcritical carboxylic acid, together with the fatty acid originally coexisting in the raw oil and fat. A production method can be proposed in which an ester is used to esterify the fatty acid under supercritical or subcritical conditions of the carboxylic acid ester to obtain a fatty acid alkyl ester (biodiesel fuel).

  In such a production method, the fatty acid glyceride phase and the carboxylic acid phase may be compatibilized by adding a third component to the transesterification reaction system (step A). This is because by performing the compatibilization, the transesterification reaction can be promoted, and as a result, the reaction treatment conditions, for example, the treatment temperature can be reduced. As the third component that can be used for this compatibilization, components that contribute to compatibilization of the fatty acid glyceride phase and the carboxylic acid phase are widely targeted. For example, alkanes such as pentane and hexane and petroleum ether can be used.

  Next, FIG. 5 is a figure which shows the example of the other reaction path | route which can be utilized in the manufacturing method which concerns on this invention. FIG. 6 is a diagram illustrating a reaction example of a process B (hydrolysis process) which is a first stage process of the reaction path.

  The purpose of the step B (hydrolysis step) shown in FIG. 5 is to esterify the fatty acid glyceride (in FIG. 6, fatty acid triglyceride is exemplified in FIG. 6) contained in the raw oil and fat as in the above step A. The fatty acids that can be used in

That is, when the B process which is a hydrolysis process is adopted as the initial stage process, only the fatty acid is separated and recovered from the fatty acid (R ¹ COOH) and glycerin obtained by the B process, and then this fatty acid is recovered as X in FIGS. It is possible to propose a reaction route that shifts to a process and esterifies with a carboxylic acid ester under supercritical or subcritical conditions to obtain the desired fatty acid alkyl ester (see FIG. 5).

  After the hydrolysis process, which is the initial stage process, glycerin produced from the raw oil and fat can be easily separated from the fatty acid because it dissolves in water (described later). For this reason, since it becomes possible to suppress the reverse reaction with the fatty acid ester produced | generated by the esterification reaction which is the next process step, highly purified fatty-acid alkylester is obtained.

  Here, in the reaction example of the B process shown in FIG. 6, the fatty acid glyceride contained in the raw oil and fat is hydrolyzed to obtain a fatty acid and glycerin, for example, a temperature of 150 to 300 ° C., particularly 250 ° C. to It is carried out under subcritical water conditions of 300 ° C. and a pressure of 5 to 25 MPa, particularly 7 to 20 MPa, and 15 to 60 minutes, particularly preferably 20 to 40 minutes. There is an advantage that almost no unreacted fatty acid triglyceride remains in the product obtained from the step B.

  In FIG. 6, fatty acid triglyceride is shown as a representative example. However, it is not intended to be limited to this, and fatty acid diglyceride and fatty acid monoglyceride that can be contained in the raw oil and fat are also subjected to a fatty acid reaction by hydrolysis reaction as in FIG. 6. Can be obtained.

  The “pressurized hot water” in the reaction formula shown in FIG. 6 means the subcritical water, but it is not limited to the subcritical water. Supercritical water or subcritical water at low temperature / low pressure is used. Widely encompass.

  When the reaction solution containing the product obtained from the step B which is the hydrolysis step is allowed to stand, phase separation into an oil phase and an aqueous phase occurs (phase separation step). The oil phase separated by this step contains fatty acids and one aqueous phase contains glycerin, a by-product. By separating and recovering this oil phase, it is possible to recover the fatty acid used in the subsequent step X (see FIGS. 1 and 2), which is the esterification step. These fatty acids contain free fatty acids originally contained in fatty acids and raw oils and fats produced by hydrolysis (see FIG. 6).

  If water remains in the oil phase obtained by such a phase separation process, a part of the fatty acid ester undergoes hydrolysis and returns to the fatty acid in the subsequent process X, so as much water as possible is removed from the oil phase. It is preferable to do. In consideration of the energy efficiency of the entire manufacturing process, it is not preferable to cool the product after the hydrolysis step (step B) to room temperature.

  Therefore, in the present invention, the phase separation step is devised so as to be performed near the hydrolysis temperature (for example, 250 to 300 ° C.). This eliminates the need to cool the product and provides the advantage that the energy for heating again for the esterification reaction (see FIGS. 1 and 2) is then unnecessary.

  From the above, in the present invention, fatty acid glycerides contained in raw fats and oils containing fatty acids are hydrolyzed with supercritical or subcritical water (pressurized hot water), and the resulting fatty acids originally coexisted in the fats and oils. It is possible to propose a method for producing a biodiesel fuel which is fractionated together with the fatty acid, and esterified with a carboxylic acid ester under supercritical or subcritical conditions to obtain a fatty acid alkyl ester.

Next, FIG. 7 attached shows an example of a two-step reaction path when methyl formate (HCOOCH ₃ ), which is a carboxylic acid ester, is used as a solvent in the X step (esterification step). In this reaction route, formic acid (HCOOH) is generated in the reaction system by the esterification reaction in the X step, and thus the effect of the acid catalyst of the formic acid can be expected.

  Next, FIG. 8 is a diagram showing a reaction example of a transesterification step (step C) that can be used to increase the yield of fatty acid alkyl ester in the production method according to the present invention.

  The transesterification reaction related to Step C shown in FIG. 8 utilizes fatty acid glycerides present in the reaction system related to the production method of the present invention, and for example, between the fatty acid glycerides and the carboxylic acid ester, This is a reaction for obtaining a fatty acid alkyl ester by proceeding a transesterification reaction under supercritical or subcritical conditions of the carboxylic acid ester. This C process is a reaction process contributing to the improvement of the yield of the fatty acid alkyl ester.

  As shown in the above-mentioned “Table 1”, the transesterification reaction is carried out using alkyl formate critical temperature (Tc): 214 to 285 ° C., critical pressure (Pc): 3.5 to 6.0, acetic acid. Since the critical temperature (Tc) of alkyl is 234 to 306 ° C. and the critical pressure (Pc) is 3.3 to 4.7 MPa, the supercriticality of the carboxylic acid ester is taken into consideration that decomposition of the components occurs at 300 ° C. or higher. The subcritical conditions of 200 ° C. to 300 ° C. and 2.0 MPa to 15 MPa are preferable.

  In the present invention, the fatty acid glyceride phase and the carboxylic acid ester phase may be compatibilized by adding a third component to the transesterification reaction system illustrated in FIG. This is because by performing the compatibilization, the transesterification reaction can be promoted, and as a result, the reaction treatment conditions, for example, the treatment temperature can be reduced.

  As the third component that can be used for this compatibilization, components that contribute to the compatibilization of the fatty acid glyceride phase and the carboxylic acid ester phase are widely targeted. For example, alkanes such as pentane and hexane and petroleum ether can be used.

  FIG. 9 is a diagram summarizing the concept of the reaction route from the C step (transesterification step) represented by the reaction example shown in FIG. 8 to the X step (esterification step) described above.

  First, the fatty acid and acetin (for example, triacetin) obtained through the step A shown in FIG. 4, that is, the transesterification step between the fatty acid glyceride and the carboxylic acid are separated. And the isolate | separated fatty acid is introduce | transduced into X process (esterification process), and fatty-acid alkylester is obtained (refer FIG. 8).

  On the other hand, the separated acetin can be used as BDF as it is (see Patent Document 3), but this acetin (for example, triacetin) is used in the C step (transesterification step) as in the reaction route shown in FIG. ). In this C process, transesterification (refer FIG. 8) between acetin (namely, fatty acid glyceride) and carboxylic acid ester is advanced, and fatty-acid alkylester is obtained.

  Therefore, in the reaction route shown in FIG. 9, in addition to the fatty acid alkyl ester obtained through the X step (esterification step) between the fatty acid and the carboxylic acid ester, between the fatty acid glyceride and the carboxylic acid. The fatty acid alkyl ester can be obtained through the C process (transesterification process) between the fatty acid glyceride (acetin) and the carboxylic acid ester produced from the A process (transesterification process). That is, in this reaction route, the yield of fatty acid alkyl ester from the reaction system can be improved.

  In the reaction system according to the production method of the present invention described above, a carboxylic acid ester or a carboxylic acid is present until the final stage of the reaction. Since this carboxylic acid ester or carboxylic acid effectively exhibits an acid catalyst function, the reaction efficiency is good, and as a result, a high-quality fatty acid alkyl ester can be produced.

<Verification of esterification reaction (process X) using carboxylic acid ester>

First, methyl formate (HCOOCH ₃ ) was used as a carboxylic acid ester. Whether or not the esterification reaction proceeds was examined by treating oleic acid with this methyl formate as a supercritical condition.

  experimental method. Oleic acid (manufactured by Nacalai) and methyl formate (manufactured by Aldrich, 99%) were sealed in a batch-type reaction tube having an internal volume of 5 mL at a molar ratio of 1: 2, 1: 7, 1:15, and 3 ° C. at 350 ° C. Treated for ~ 9 minutes. The solvent was distilled off from the reaction product after the treatment with an evaporator and analyzed by gel permeation chromatography (GPC). In addition, oleic acid and methyl oleate were also analyzed by GPC. The GPC environment at the time of analysis is as shown in “Table 3” below.

  FIG. 10 shows the GPC chromatogram after treatment at each molar ratio, which is the result of this verification experiment. Further, the yield of methyl oleate determined from these peak areas is shown in “Table 4” below, and the graph thereof is shown in FIG. Note that the peak seen in the vicinity of the retention time of 13 minutes in FIG. 10 is considered to be an impurity contained in the original sample.

  Consideration. It was found that the amount of oleic acid decreased and the amount of methyl oleate obtained increased as the molar fraction of methyl formate increased and the treatment time increased. However, the difference in yield between the treatment for 6 minutes and the treatment for 9 minutes is very small for any molar ratio of the solution, and it is considered that the reaction is considerably completed after the treatment for 6 minutes. From this, it was clarified that the esterification reaction proceeds when the fatty acid is treated using methyl formate, which is a carboxylic acid ester, as a solvent.

<Verification of transesterification reaction of raw oil and fat using supercritical carboxylic acid (step A)>

In this verification experiment, acetic acid (CH ₃ COOH) was used as the carboxylic acid. The rapeseed oil and oleic acid were treated using this acetic acid as a supercritical condition, and it was verified whether or not the transesterification reaction related to the above step A proceeded.

  experimental method. A batch type reaction tube having an internal volume of 5 mL was filled with 1.4 mL of rapeseed oil and 3.6 mL of acetic acid (molar ratio 1:42) and treated at 270 ° C. for 9 minutes. Next, the distilled water was added to the liquid after the treatment, and the mixture was stirred and centrifuged, and then the aqueous layer was removed. After repeating this operation once more, unnecessary substances were distilled off by an evaporator and analyzed by high performance liquid chromatography (HPLC). The same operation was performed for 2.2 mL of oleic acid and 2.8 mL of acetic acid (molar ratio 1: 7). The environment at the time of analysis by HPLC is as shown in Table 5 below.

  Attached FIG. 12 shows an HPLC chromatogram. As shown in FIG. 12, in the treatment of rapeseed oil, in addition to the diglyceride that is a reaction intermediate, a peak that is considered to be a fatty acid was observed. This is considered that the transesterification reaction (an example of A process) shown by FIG. 13 advanced between the fatty acid triglyceride and acetic acid contained in rapeseed oil. On the other hand, in the oleic acid treatment system, there was not much change from the untreated one, and it is considered that the reaction hardly occurred.

<Verification of compatibilization in reaction system>

  In Example 3, the compatibilization in the reaction system of the production method according to the present invention was verified. The mixed system shown in the following "Table 6" was created under normal temperature and normal pressure conditions, and the dissolved state was observed. Furthermore, each mixed system was cooled overnight in a refrigerator (5 ° C.), and changes in the dissolved state were observed. The experimental results relating to Example 3 are shown in FIGS.

(1) About methyl formate + rapeseed oil (1: 1).
Although it was almost dissolved at room temperature, it was observed that a small amount of white precipitate remained on the bottom (see FIG. 14). When this was cooled overnight in a refrigerator (5 ° C.), it was divided into a golden upper layer and a colorless and transparent lower layer. The height ratio of both layers was approximately 4: 1 (see FIG. 15).

(2) About methyl formate + rapeseed oil + pentane (1: 1: 0.1).
It dissolved almost completely at room temperature (see FIG. 16). When this was cooled overnight in a refrigerator (5 ° C.), it was divided into a light golden upper layer and a colorless and transparent lower layer. The ratio of the heights of both layers was approximately 8: 1 (see FIG. 17).

(3) About methyl formate + rapeseed oil + hexane (1: 1: 0.1).
It was almost completely dissolved at room temperature (see FIG. 18). When this was cooled overnight in a refrigerator (5 ° C.), it was divided into a light golden upper layer and a colorless and transparent lower layer. The ratio of the heights of both layers was approximately 8: 1 (see FIG. 19).

(4) About methyl formate + rapeseed oil + petroleum ether (1: 1: 0.1).
Dissolved almost completely at room temperature (see FIG. 20). When this was cooled overnight in a refrigerator (5 ° C.), it was divided into a light golden upper layer and a colorless and transparent lower layer. The height ratio of both layers was approximately 8: 1 (see FIG. 21). The results of the above (1) to (4) are summarized in the following “Table 7”.

  As can be seen from this result, the mixed system of methyl formate and oil (rapeseed oil) has a two-phase precipitate. On the other hand, the systems to which the third component is added are all in one phase, and a good transesterification reaction can be expected even under supercritical conditions or subcritical conditions. For this reason, relaxation of reaction conditions can be achieved. For example, it can be sufficiently expected that the reaction temperature is lowered from 350 ° C. to 300 ° C. or less.

  INDUSTRIAL APPLICABILITY The present invention can be used as a technique for efficiently producing a high-quality fatty acid alkyl ester that can be suitably used as a biodiesel fuel without using a catalyst.

It is a conceptual diagram of the basic manufacturing process (X process) of the fatty-acid alkylester which concerns on this invention. It is a figure explaining the esterification reaction concerning the basic manufacturing process in more detail. It is a figure which shows the example of the reaction path | route which can be utilized in the manufacturing method which concerns on this invention. It is a figure which shows the reaction example of A process (transesterification process) which is an example of the first step of the reaction path. It is a figure which shows the example of the other reaction path | route which can be utilized in the manufacturing method which concerns on this invention. It is a figure which shows the reaction example of B process (hydrolysis process) which is the first step of the same reaction path | route. X Step methyl formate is a carboxylic acid ester in (esterification step) (HCOOCH ₃₎ is a diagram showing an example of a two-step reaction pathway in the case of using as the solvent. In the manufacturing method which concerns on this invention, it is a figure which shows the reaction example of the transesterification process (C process) which can be utilized in order to raise the yield of a fatty-acid alkylester. It is the figure which put together the concept of the reaction pathway from C process (transesterification process) to X process (esterification process). 2 is a GPC chromatogram after treatment at each molar ratio as a result of a verification experiment according to Example 1. FIG. It is a graph of the yield of methyl oleate calculated | required from the peak area of GPC chromatogram (FIG. 10). 3 is an HPLC chromatogram that is a result of a verification experiment according to Example 2. FIG. It is a figure which shows an example of transesterification (A process) between the fatty acid triglyceride contained in rapeseed oil, and acetic acid. 10 is a drawing-substituting photograph showing an observation result at normal temperature of the mixed system classification (1) in the verification experiment according to Example 3. FIG. It is a drawing substitute photograph which shows the observation result after overnight cooling of the mixed system division (1). 10 is a drawing-substituting photograph showing an observation result at normal temperature of the mixed system classification (2) in the verification experiment according to Example 3. FIG. It is a drawing substitute photograph which shows the observation result after overnight cooling of the mixed system division (2). 10 is a drawing-substituting photograph showing an observation result at normal temperature of the mixed system classification (3) in the verification experiment according to Example 3. FIG. It is a drawing substitute photograph which shows the observation result after overnight cooling of the mixed system division (3). 10 is a drawing-substituting photograph showing an observation result at normal temperature of the mixed system classification (4) in the verification experiment according to Example 3. FIG. It is a drawing substitute photograph which shows the observation result after overnight cooling of the same mixed system division (4).

Explanation of symbols

X process (fatty acid and carboxylic acid ester) esterification process A process (fatty acid glyceride and carboxylic acid) transesterification process (first stage process)
Process B (fatty acid glyceride) hydrolysis process (first stage process)
C process (transesterification process of fatty acid glyceride and carboxylic acid ester)

Claims (11)

  A method for producing a fatty acid alkyl ester by allowing an esterification reaction to proceed between a fatty acid and a carboxylic acid ester under supercritical or subcritical conditions of the carboxylic acid ester.   The manufacturing method according to claim 1, wherein the fatty acid is a free fatty acid present in the raw material fat. The fatty acid method according to claim 1 or 2, characterized in that the fatty acids obtained through predetermined steps from the raw material oils and fats.   The predetermined step is a step of obtaining a fatty acid by performing a transesterification reaction between the fatty acid glyceride and the carboxylic acid in the raw material fat under supercritical or subcritical conditions of the carboxylic acid. The manufacturing method of Claim 3.   4. The method according to claim 3, wherein the predetermined step is a step of obtaining a fatty acid by hydrolyzing a fatty acid glyceride in the raw material fat under supercritical or subcritical conditions. The fatty acid alkyl ester includes a fatty acid alkyl ester obtained by a transesterification reaction between a fatty acid glyceride and a carboxylic acid ester in the raw material fat and oil, according to any one of claims 1 to 5. The manufacturing method as described. The method according to any one of claims 1 to 6 , wherein the fatty acid phase and the carboxylic acid ester phase are compatibilized by adding a third component to the esterification reaction system.   The method according to claim 4, wherein the fatty acid glyceride phase and the carboxylic acid phase are compatibilized by adding a third component to the transesterification reaction system.   The method according to claim 6, wherein the fatty acid glyceride phase and the carboxylic acid ester phase are compatibilized by adding a third component to the transesterification reaction system. The carboxylic acid ester, A process according to any one of claims 1 9, characterized in that the formic acid ester. The manufacturing method according to claim 10 , wherein the formic acid ester is methyl formate.