JP2006193497A - Method for producing fatty acid alkyl ester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a fatty acid alkyl ester in high efficiency and purity even from a stock oil containing free fatty acids. <P>SOLUTION: The method for the production of a fatty acid alkyl ester comprises a step to form a reaction product by the esterification reaction of a stock oil containing free fatty acids with an alcohol, and a step to purify the reaction product. The purification step comprises the contact of the reaction product with a basic adsorbent to remove unreacted free fatty acids from the reaction product. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to acidic fats and oils such as free fatty acids separated in the deoxidation step of vegetable oils and animal fats and oils, waste fatty acids of the fats and oils or free fatty acids separated from yellow grease, etc. The present invention relates to a method for producing a fatty acid alkyl ester using oil and fat contained therein as a raw material oil.

  In recent years, biodiesel fuel has attracted attention. Biodiesel fuel is generally obtained by subjecting vegetable oil to chemical conversion called methyl esterification to produce diesel engine fuel. Biodiesel fuel is an oxygen-containing fuel that contains oxygen in its chemical structure, and since it contains almost no sulfur, it emits less harmful exhaust gases such as black smoke. In addition, because it is derived from plants, carbon dioxide emissions are set to zero in accordance with the provisions set forth in the Kyoto Protocol. For this reason, biodiesel fuel has been attracting attention as a light oil alternative fuel with a low environmental impact, and standards and legal systems have already been established in Europe and the United States, and over 2.5 million tons are produced and used annually from soybeans and rapeseed oil.

  On the other hand, in Japan, about 5000 tons / year of biodiesel fuel is produced from waste cooking oil and used in some local governments. In Japan, standards are not yet established, but in recent years, bioethanol and biodiesel fuels will be standardized.

  It has long been known that fatty acid alkyl esters can be obtained by transesterification of monoglycerides, diglycerides, and triglycerides, which are the main components of fats and oils, with alkyl alcohols (for example, JP-A-2002-167356 (Patent Documents). 1), JP 2002-294277 A (Patent Document 2), JP 2000-44984 A (Patent Document 3)). It is also known that a fatty acid alkyl ester can be obtained by an esterification reaction between a free fatty acid and an alkyl alcohol (for example, “Organic Chemistry Handbook”, Gihodo Publishing, 1988, p1407 to p1409 (Non-patent Document 1)).

In addition, various technologies (supercritical methods) for producing biodiesel fuel oils from fats and oils under supercritical alcohol conditions have been studied so far (for example, JP 2002-241786 A (Patent Document 4), 2001-302588 (Patent Document 5), JP-A 2000-109883 (Patent Document 6), etc.).
JP 2002-167356 A JP 2002-294277 A JP 2000-049484 A Japanese Patent Laid-Open No. 2002-241786 JP 2001-302584 A JP 2000-109883 A "Organic Chemistry Handbook", Gihodo Publishing, 1988, p1407-p1409

  However, if free fatty acids are present in the feedstock, unreacted free fatty acids are likely to be present after the esterification reaction, and the quality of the diesel fuel is poor. Vegetable oils are easy to produce free fatty acids essentially or in the manufacturing process, yellow greases are easily hydrolyzed in the recovery system, and waste edible oils that have deteriorated contain a lot of free fatty acids. From the circumstances, it was not necessarily suitable as a raw material oil for the production of fatty acid alkyl esters.

  The conventional method for producing a fatty acid ester is a study on transesterification, and there is a description that the reaction is not inhibited even if free fatty acid is contained in a part of the raw material oil, or that the alkyl esterification proceeds similarly. . However, since free fatty acids and alkyl esters have similar boiling points, separation by distillation is extremely difficult. Even when the free fatty acid was esterified under these conditions, the conversion rate was 98% at the maximum. According to the standard of biodiesel fuel in Europe, the amount of free fatty acids is 0.3% or less, and even using conventional methods, unreacted free fatty acids cannot be removed by purification only by distillation. Alkyl esters that meet the standards cannot be produced.

  In addition, as a method for removing unreacted free fatty acids, there is a washing method with a weak alkaline aqueous solution, but this eliminates the superiority of the supercritical method with no catalyst and low environmental load.

  By the way, since the esterification reaction is an equilibrium reaction, one of the raw materials, alkyl alcohol, is used in excess or the water generated as a side reaction product is removed to shift the equilibrium to the production system to increase the yield. ing. In order to further increase the reaction rate, a catalyst is generally used.

  However, in reactions using supercritical alcohols or subcritical alcohols, it is extremely difficult to release only water out of the system regardless of the presence or absence of a catalyst. Especially, alcohols with lower boiling points than water such as methanol, ethanol, and propanol Then, after azeotropy, a dehydrating agent or the like must be used. Therefore, in the conventional method, in principle, water dehydrated during alkyl esterification remains in the system, and further, under supercritical conditions such as methanol and ethanol, the ionic product of water increases to about 100 times the room temperature. Therefore, the hydrolysis reaction, which is a reverse reaction, is likely to proceed.

  In addition, the reaction using a fixed bed catalyst has been attempted together with these alone, but the reaction conversion rate is low at present.

  The present invention has been made paying attention to the above-mentioned circumstances, and its object is to provide a method capable of producing a fatty acid alkyl ester efficiently and with high purity even in a feedstock containing free fatty acids. It is what.

  The present invention is a method for producing a fatty acid alkyl ester comprising a step of obtaining a reaction product by an esterification reaction between a raw oil containing a free fatty acid and an alcohol, and a step of purifying the reaction product, The said refinement | purification process provides the manufacturing method of the fatty-acid alkylester characterized by making the said reaction product contact a basic adsorbent, and removing an unreacted free fatty acid from the said reaction product.

  In the method for producing a fatty acid alkyl ester according to the present invention, unreacted free fatty acids that have been difficult to separate can be easily removed. Therefore, the feed oil is a free fatty acid or a feed oil containing free fatty acids in the feed oil. However, the fatty acid alkyl ester can be produced efficiently and with high purity.

  Preferred embodiments of the present invention are as follows. The amount of the basic adsorbent used is preferably 1 to 5% by weight based on the amount of the reaction product. The basic adsorbent is preferably basic alumina. Furthermore, it is preferable that the process of obtaining a reaction product by the esterification reaction of the raw material oil containing the free fatty acid and the alcohol and the process of purifying the reaction product are performed continuously.

  According to the method for producing a fatty acid alkyl ester according to the present invention, vegetable oils that are prone to generate free fatty acids essentially or in the production process, yellow greases that are easily hydrolyzed on the recovery system, and waste edible oils that have deteriorated. Even when oils that have been difficult to use are used as raw materials, fatty acid alkyl esters that are highly efficient and conform to biodiesel fuel standards can be produced.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. The conceptual diagram of the manufacturing system used for the manufacturing method of the fatty-acid alkylester which concerns on FIG. 1 at this embodiment is shown. As shown in FIG. 1, the production system used in the method for producing a fatty acid alkyl ester according to the present invention includes a pretreatment unit 1, a reaction unit 2, an alcohol removal unit 3, a glycerin removal unit 4, and a first purification treatment unit 5. The second purification processing unit 6 is configured.

  In the pretreatment unit 1, the raw material oil is filtered, superheated, centrifuged, and dehydrated and deodorized. For example, in addition to oil content of 80% and free fatty acid content of 10%, solid impurities in raw material oil containing 1% solid content, 7% moisture content, 2% impurity content such as odorous substances are filtered through a filter, and then statically kept for 4 hours or more Then, supersaturated water and other high specific gravity impurities are removed from the drain.

  Raw material oils can be broadly classified into vegetable oils and animal oils, but vegetable oils and fats include rapeseed oil, soybean oil, palm oil, palm kernel oil, sunflower oil, rice oil, sesame oil, and corn oil. Coconut oil, safflower oil, safflower oil, peanut oil, cottonseed oil, linseed oil, mustard oil and the like, and animal fats and oils include beef tallow, pork tallow, whale oil, fish oil and the like. The pretreatment as described above is not necessarily essential, but when a fatty acid containing impurities is used as the raw material oil, the above treatment is preferably performed.

  This raw material oil is heated to about 90 to 100 ° C. with a heat exchanger or the like, and further subjected to specific gravity separation with a centrifuge. By this treatment, for example, the amount of solid impurities in the raw material oil is 0.02% or less, and the water content is also 0.5% or less.

  Furthermore, this raw material oil is introduced into a vacuum dehydration tower. In the introduction, the raw material oil is preferably introduced by a method that increases the gas-liquid interface, such as a mist or spiral. Further dehydration and deodorization are performed while the raw material oil passes through the vacuum dehydration tower. That is, water and odorous substances in the raw material oil heated to about 100 ° C. under a reduced pressure of less than 100 mmHg are rapidly vaporized and released out of the system. For example, dehydration and deodorization are performed so that the water content in the raw material oil is 0.05% or less and the odorous substance content is 0.01% or less. In addition, the treated raw material oil is heated to the subsequent reaction temperature by the heat exchanger.

  In addition, when using the raw material oil which does not contain a solid impurity, a water | moisture content, or an odor substance, the process in the pre-processing part 1 can be abbreviate | omitted.

  In the reaction unit 2, an esterification reaction is performed. The esterification reaction may be an esterification reaction with a subcritical or supercritical alcohol or a catalytic reaction using a fixed catalyst. Here, “subcritical” means a state in which the reactant alcohol is above the boiling point and below the critical point (in the case of methanol, 64 to 239 ° C.) and has a vapor pressure of 1 atm or higher. The term “alcohol” as a reactant means a state in which the alcohol is above the critical pressure and above the critical temperature. For example, in the case of a supercritical reaction without using a catalyst, the alcohol to be reacted is heated and pressurized in advance at a temperature of 240 ° C. to 300 ° C. and a pressure of 4 MPa to 40 MPa. Then, the temperature of the raw material oil that has been subjected to the treatment as described above is increased to a temperature of 240 ° C. to 300 ° C. and a pressure of 8 MPa to 40 MPa. Thereafter, the esterification reaction can be carried out by mixing the alcohol and the raw material oil in a flow-type reaction tube and allowing the reaction tube to flow under the same conditions over a predetermined reaction time. During the esterification reaction, the alcohol is in a supercritical state.

  In the case of using a fixed catalyst, for example, a mixed solution of methanol and fat (methanol: fat / oil = 13: 100 (weight ratio)) is 12 ml / hr in a reaction tube equipped with an iron oxide fixed catalyst carrying potassium. The esterification can be performed by passing the oil under conditions of 60 ° C. and normal pressure.

  As the alcohol used for the esterification reaction, it is preferable to use a lower alkyl alcohol having about 1 to 5 carbon atoms such as methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol and the like.

  In the alcohol removing unit 3, excess alcohol is removed from the reaction product after completion of the esterification reaction. In the subcritical reaction and supercritical reaction described above, the reaction temperature is equal to or higher than the boiling point of the alcohol at normal pressure. Therefore, sufficient alcohol can be removed simply by returning to normal pressure while passing through a heat exchanger or the like. When a solid catalyst is used, alcohol can be removed by distillation under reduced pressure.

  In the glycerin removing unit 4, glycerin as a by-product is separated from the reaction product. Separation of glycerin can be performed with a centrifuge or the like. In addition, when raw material oil is 100% free fatty acid, since glycerol does not byproduce, this process is unnecessary.

  In the 1st refinement | purification process part 5, the refinement | purification of the reaction product which removed glycerol by the glycerol removal part 4 is performed. Since about 2% of unreacted free fatty acid remains in the reaction product, the free fatty acid is adsorbed and removed from the reaction product by bringing the reaction product into contact with a basic adsorbent. For example, free fatty acids can be efficiently adsorbed and removed by filling a column with a basic adsorbent and passing the reaction product through the column.

  The amount of the basic adsorbent used is not particularly limited as long as free fatty acid can be removed from the reaction product, but about 2% of unreacted free fatty acid remains in the reaction product. If the amount of basic adsorbent used is a standard (100% by weight), it may be about 0.5 to 5% by weight, more preferably about 1 to 2% by weight. .

  Specific examples of the basic adsorbent include basic alumina, alkali-treated activated carbon, basic silica gel and the like, and basic alumina is particularly preferable from the viewpoint of adsorption efficiency.

  In the 2nd refinement | purification process part 6, further refinement | purification can be suitably performed according to the state of the reaction product processed by the 1st refinement | purification process part. For example, an activated clay column treatment for removing pigments, a centrifugal separation treatment for removing solids, glycerin, and the like, or a vacuum distillation treatment for removing traces of alcohol, moisture, and the like can be performed.

  In addition, by using a continuous reaction tube in the supercritical reaction or subcritical reaction in the reaction unit 2 and using a centrifuge in the glycerin removal unit 4, esterification of the raw material oil containing the free fatty acid and the alcohol is performed. The step of obtaining a reaction product by the reaction and the step of purifying the reaction product can be performed continuously.

  The fatty acid alkyl ester thus obtained has a high purity and can meet the standard as a diesel fuel oil, and therefore can be used as a fuel for diesel vehicles and other diesel engines.

  As raw material oil, palmitic acid (C16-0) marketed as a reagent was used, and methanol was used as an alcohol for esterification. And it mixed in the ratio of methanol: fatty acid = 20 mol: 1 mol, and esterification reaction was performed with the reaction tube of diameter 10mm and length 100mm, and the reaction product was obtained. A pressure / flow rate control valve was provided at the outlet of the reaction tube to adjust the pressure, flow rate and reaction time. The reaction conditions were a reaction temperature of 290 ° C., a reaction pressure of 20 Mpa, and a time of 15 min.

  Subsequently, excess methanol was distilled off from the reaction product by returning from the pressurized state to the normal pressure state. Thereafter, as a first purification treatment step, the reaction product from which methanol was distilled off was passed through a basic alumina column to adsorb unreacted palmitic acid (free fatty acid) to the basic alumina. The amount of basic alumina used was 1% by weight with respect to the amount of reaction product to be treated.

  Subsequently, as a 2nd refinement | purification process process, the desired fatty-acid alkylester was obtained by performing an activated clay column process, a centrifugation process, and a pressure reduction process, respectively.

  Except having used stearic acid (C18-0) as raw material oil, the same process as Example 1 was performed and the desired fatty-acid alkylester was obtained.

  Except having used oleic acid (C18-1) as raw material oil, the process similar to Example 1 was performed and the desired fatty-acid alkylester was obtained.

  Except having used linoleic acid (C18-2) as raw material oil, the process similar to Example 1 was performed and the desired fatty-acid alkylester was obtained.

  Fatty acid (by-product fatty acid 90% (palmitic acid 45%, stearic acid 5%, oleic acid 40%, linoleic acid 10%), water content 5% as a by-product generated during the refinement of palm oil Other impurities amount 5%, iodine value 50) were used. This raw material oil was poured into the raw material oil storage tank in the pretreatment section 1 through a filter of mesh 120, and then allowed to stand for 4 hours.

  After removing the drain, the supernatant was heated to 95 ° C. by a heat exchanger, and this was passed through a centrifuge (centrifugal force 1000 G, flow rate 15 liters per minute).

  The raw material oil after passing through the centrifuge was put into a vacuum dehydration tower. The processing conditions of the vacuum dehydration tower were an absolute pressure of 80 mmHg and a residence time of 15 minutes. This raw material oil was heated to 270 ° C. by a heat exchanger and used for the esterification reaction. The esterification reaction was carried out under the same conditions as shown in Example 1.

  After the esterification reaction, the excess methanol in the reaction product was distilled off by returning from the pressurized state to the normal pressure state, and then glycerin in the reaction product was removed by centrifugation.

  Thereafter, in the same manner as in Example 1, unreacted free fatty acids were removed in the first purification treatment step, and other impurities were removed in the second purification treatment step, thereby obtaining a desired fatty acid alkyl ester.

[Comparative Example 1]
Fatty acid alkyl ester was obtained in the same manner as in Example 1. However, the basic alumina column treatment in the first purification treatment step was omitted.

[Comparative Example 2]
Fatty acid alkyl ester was obtained in the same manner as in Example 2. However, the basic alumina column treatment in the first purification treatment step was omitted.

[Comparative Example 3]
A fatty acid alkyl ester was obtained in the same manner as in Example 3. However, the basic alumina column treatment in the first purification treatment step was omitted.

[Comparative Example 4]
Fatty acid alkyl ester was obtained in the same manner as in Example 4. However, the basic alumina column treatment in the first purification treatment step was omitted.

[Comparative Example 5]
Fatty acid alkyl ester was obtained in the same manner as in Example 5. However, the basic alumina column treatment in the first purification treatment step was omitted.

[Test Example] Measurement of Yield, Purity and Acid Value The yield, purity and acid value were measured using the fatty acid alkyl esters obtained in Examples 1 to 5 and Comparative Examples 1 to 5 described above as samples.

  In addition, the yield was shown by the ratio (%) of the weight of the sample with respect to the weight of raw material oil. The purity was measured by gas chromatography. The acid value was expressed in mg of potassium hydroxide required to neutralize a 1 g sample.

  Since the fatty acid alkyl ester according to the present invention satisfies the standard as a diesel fuel oil, it has industrial applicability as a fuel for diesel vehicles and other diesel engines.

It is a conceptual diagram of the manufacturing system used for the manufacturing method of the fatty-acid alkylester which concerns on this embodiment.

Explanation of symbols

1: Pretreatment unit, 2: Reaction unit, 3: Alcohol removal unit, 4: Glycerin removal unit, 5: First purification processing unit, 6: Second purification processing unit

Claims (6)

A method for producing a fatty acid alkyl ester comprising: a step of obtaining a reaction product by an esterification reaction between a raw oil containing free fatty acids and an alcohol; and a step of purifying the reaction product,
The said refinement | purification process makes the said reaction product contact a basic adsorption agent, and removes the unreacted free fatty acid from the said reaction product, The manufacturing method of the fatty-acid alkylester characterized by the above-mentioned.   The method for producing a fatty acid alkyl ester according to claim 1, wherein the amount of the basic adsorbent used is 1 to 5% by weight based on the amount of the reaction product.   The method for producing a fatty acid alkyl ester according to claim 1 or 2, wherein the basic adsorbent is basic alumina.   The process of obtaining a reaction product by esterification reaction of the raw material oil containing the said free fatty acid and alcohol, and the process of refine | purifying the said reaction product are performed continuously. The manufacturing method of fatty acid alkylester.   The fuel containing the fatty-acid alkylester manufactured by the manufacturing method of any one of Claims 1-4. The fuel for diesel engines containing the fatty-acid alkylester manufactured by the manufacturing method of any one of Claims 1-4.

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