JP4963011B2 - Method for producing fatty acid lower alkyl ester - Google Patents

Description

  The present invention relates to a method for producing a fatty acid lower alkyl ester.

  Examples of the method for producing a fatty acid lower alkyl ester include a method of transesterifying an oil (fatty acid triglyceride) and a lower alcohol (particularly methanol) in the presence of an alkaline catalyst.

  In fatty acid lower alkyl esters obtained by transesterification of fatty acid triglyceride and lower alcohol in the presence of an alkali catalyst, in addition to water-soluble impurities such as glycerin, free alkali and soap, intermediate monoglyceride, diglyceride and Reactive triglycerides are included. Water-soluble impurities can be removed by washing the fatty acid lower alkyl ester with water. However, since unreacted glycerides are oil-soluble, it is necessary to devise their separation.

As a method for separating unreacted glycerides, for example, a method of concentrating and removing to a distillation residue by distillation is known (Patent Document 1). As a method for reducing unreacted glyceride, Patent Document 2 discloses that after the transesterification step, a phase containing glycerin as a main component is separated, an alkali catalyst is added to the ester phase containing monoglyceride, and methanol is added under reduced pressure. A method is disclosed in which monoglyceride is converted to triglyceride by carrying out the reaction while distilling, and an ester having a low monoglyceride content is obtained by distillation.
U.S. Pat. No. 2,383,580 Japanese Patent Laid-Open No. 3-200743

  In the distillation method described in Patent Document 1, triglyceride, fatty acid diglyceride and the like can be removed to the residue because the boiling point of fatty acid lower alkyl ester is significantly different from that of monoglyceride, but monoglyceride has a boiling point similar to that of fatty acid lower alkyl ester. Therefore, some of them are mixed into the fraction and cannot be completely removed.

  In addition, in the reaction using the alkali catalyst described in Patent Document 2, a step such as filtration after washing the catalyst and by-product soap with water or adsorbent is required before the distillation step. The yield of the ester is reduced. Further, the conversion rate from monoglyceride to triglyceride is insufficient, and monoglyceride still remains in the ester phase after distillation.

  Therefore, the subject of this invention is providing the manufacturing method of the fatty-acid lower alkyl ester which can obtain a highly purified fatty-acid lower alkyl ester in a high yield.

The present invention provides a method for producing a fatty acid lower alkyl ester comprising the following steps (I), (II), (III) and (IV).
Step (I): Triglyceride and lower alcohol having 1 to 4 carbon atoms are transesterified using a solid catalyst to produce a fatty acid lower alkyl ester-containing mixture Step (II): The mixture obtained in Step (I) Separating into an ester phase rich in fatty acid lower alkyl ester and containing monoglyceride, diglyceride and triglyceride, and a glycerin-rich glycerin phase Step (III): Using the solid phase of the ester phase separated in Step (II) Step (IV) of converting monoglyceride contained into diglyceride or triglyceride by transesterification: Step of obtaining fatty acid lower alkyl ester by distillation from ester mixture obtained in step (III) Low from fatty acid lower alkyl ester containing mixture before (II) A step (hereinafter referred to as step (V)) distillation using an alcohol, to provide a method for producing the fatty acid lower alkyl esters.

  According to the present invention, a high-purity fatty acid lower alkyl ester with few impurities can be produced in a high yield.

[Raw material triglyceride and lower alcohol]
Examples of the raw material triglyceride used in the present invention include natural vegetable oils and animal fats. Examples of vegetable oils include palm oil, palm kernel oil, palm oil, soybean oil, rapeseed oil, olive oil, and sesame oil. Examples of animal oils include fish oil, beef fat, pork fat, and whale oil.

  Examples of the lower alcohol used in the present invention include alcohols having 1 to 4 carbon atoms such as methanol, ethanol, propanol, butanol and the like. In particular, methanol is preferable because of its easy recovery.

[Solid catalyst]
In the present invention, the solid catalyst used in the steps (I) and (III) is preferably a free fatty acid contained in the raw oil and fat and a solid acid catalyst that does not dissolve in water. In the steps (I) and (III), The same catalyst or different catalysts may be used. Use of an insoluble catalyst eliminates the need for a step of mixing the catalyst or by-product soap with water or an adsorbent before the step (IV) and filtering, thereby improving the yield of fatty acid lower alkyl ester. be able to. In addition, conventionally used homogeneous catalysts form fatty acid salts, which have surface activity, thus inhibiting phase separation in the separation step and reducing separation efficiency. In the present invention, by using a solid catalyst, the phase separation efficiency can be increased, and the yield of the fatty acid lower alkyl ester can be improved.

  Examples of such solid catalysts include single or mixed metal oxides, metal phosphates, metal sulfates, immobilized acids supported or immobilized on supports, natural minerals and layered compounds, solid heteropolyacids, super strong acids , Synthetic zeolite, ion exchange resin and the like.

  Examples of the single or composite metal oxide include calcium carbonate, barium titanate, calcium titanate, hydrous zirconium oxide, niobic acid, silica alumina, silica titania, silica zirconia, and titania zirconia.

  Examples of the metal phosphate include aluminum phosphate and iron phosphate. Examples of the metal sulfate include aluminum sulfate. Examples of the immobilized acid supported or immobilized on the carrier include sulfate ion-supported zirconia and sulfuric acid. Examples thereof include ion-supported titania and antimony pentafluoride-supported silica alumina.

Examples of natural minerals and layered compounds include acid clay, kaolin, montmorillonite, etc., and solid heteropolyacids include M _x H _(3-x) PMo ₁₂ O ₄₀ (M is H, Cs, NH ₄ , K, etc.) And x represents a number of 1 to 3). Examples of the super strong acid include a fluorinated sulfone resin (for example, Nafion manufactured by DuPont). Examples of the synthetic zeolite include ZCP-50 manufactured by Catalyst Kasei Kogyo Co., Ltd. Examples of the ion exchange resin include cation exchange resins such as high porous cation resin RCP-160H manufactured by Mitsubishi Chemical Corporation.

Among these, a solid acid catalyst that does not dissolve in the free fatty acid contained in the raw material fat is preferable. Examples of such a solid acid catalyst include niobic acid, silica alumina, silica titania, silica zirconia, titania zirconia, aluminum phosphate, iron phosphate, aluminum sulfate, sulfate ion supported zirconia, sulfate ion supported titania, and antimony pentafluoride. Examples include supported silica alumina, acid clay, kaolin, montmorillonite, M _x H _(3-x) PMo ₁₂ O ₄₀ (M and x have the above meanings), fluorosulfone resin, synthetic zeolite, and cation exchange resin.

  Furthermore, the esterification reaction activity is high, the ether compound by dehydration reaction of two molecules of lower alcohol or glycerin, and the production amount of olefin by the intramolecular dehydration reaction of one molecule of lower alcohol or glycerin is small, metal phosphate is more preferable.

[Step (I)]
Step (I) is a step of transesterifying triglyceride and a lower alcohol having 1 to 4 carbon atoms using a solid catalyst to produce a fatty acid lower alkyl ester-containing mixture.

  The molar ratio of lower alcohol to triglyceride is preferably 1.5 to 50 times the stoichiometrically required amount, preferably 1.5 to 30 times, more preferably 1.5 to 20 times. good. If it is 1.5 times or more, the reaction rate is high, and if it is 50 times or less, the amount of alcohol recovered is small, which is economical.

  The reaction temperature is appropriately selected depending on the activity and selectivity of the catalyst, but is usually 50 to 260 ° C, preferably 130 to 260 ° C, and more preferably 150 to 200 ° C. By reacting at a higher temperature, the activity of the catalyst is increased, which is efficient. On the other hand, from the viewpoint of suppressing by-products and decomposition products, 260 ° C. or lower is preferable, and 200 ° C. or lower is more preferable. The reaction pressure may be any of normal pressure, reduced pressure, and increased pressure.

  The reaction mode of step (I) may be either a batch type or a continuous type, and may be either a tank type reactor having a stirrer or a fixed bed reactor filled with a catalyst, but does not require catalyst separation. A bed reactor is preferred.

  When the reaction is carried out in a tank reactor, the catalyst amount is usually 0.01 to 10% by weight based on the raw material triglyceride. The liquid space velocity (LHSV) based on triglyceride when the reaction is continuously performed in a fixed bed reactor is appropriately determined depending on the catalyst activity and the desired conversion rate, but is usually 0.01 to 5.0 / h. It is economically preferable to carry out at 0.1 to 3.0 / h.

  As a reaction method of the step (I), a liquid (in which alcohol is brought into contact with liquid in a three-phase reaction comprising gas (alcohol) -liquid (triglyceride) -solid (catalyst) by gasifying an alcohol such as methanol ( Alcohol) -liquid (triglyceride) -solid (catalyst) reaction method may be used. The reaction solution may be contacted by either a gas-liquid co-current method or a gas-liquid countercurrent method in a gas-liquid-solid reaction. In the liquid-liquid-solid reaction, the mixed solution of both is flowed upward or downward and brought into contact.

[Step (II)]
Step (II) is a step of separating the fatty acid lower alkyl ester-containing mixture obtained in Step (I) into a fatty acid lower alkyl ester-rich ester phase containing monoglyceride, diglyceride and triglyceride, and a glycerin-rich glycerin phase. It is.

  Although there is no restriction | limiting in particular in the separation method, As the 1st aspect of process (II), the method of isolate | separating and removing the glycerol phase which generate | occur | produced with progress of reaction is mentioned.

  As a 2nd aspect of process (II), water or warm water can be added to the fatty-acid lower alkyl ester containing mixture obtained by process (I), and the phase containing glycerol can also be isolate | separated. By adding water or warm water, the glycerin and lower alcohol concentrations in the ester phase can be effectively reduced.

The separation temperature in step (II) is usually preferably 30 to 100 ° C, more preferably 40 to 70 ° C. Above 30 ° C., the separation rate is high and there is no fear that unreacted glyceride will precipitate. Further, at 100 ° C. or lower, the amount of glycerol dissolved in the ester phase is small, and the yield of the lower alkyl ester in the next step (III) does not decrease.
There are no particular limitations on the method of phase separation, but stationary separation and centrifugation are preferred.

  Furthermore, the monoglyceride content in the ester may be reduced by repeating the steps (I) and (II) using the ester phase obtained in the step (II) as a raw material. By reducing the monoglyceride content in the ester phase subjected to step (III), it is possible to suppress a decrease in the yield of the lower alkyl ester in step (III), which is preferable.

[Step (III)]
Step (III) is a step of converting the monoglyceride contained therein to diglyceride or triglyceride by transesterifying the ester phase obtained in step (II) using a solid catalyst. Therefore, it is preferable to carry out under the condition where the lower alcohol is reduced.

  The reaction temperature in step (III) is preferably 130 to 260 ° C, more preferably 150 to 200 ° C. Above 130 ° C, the activity of the catalyst is high, and below 260 ° C, there are few by-products and decomposition products. The reaction pressure may be any of normal pressure, reduced pressure, and increased pressure, but preferably normal pressure and reduced pressure at which the produced lower alcohol can be efficiently discharged out of the system.

  The reaction mode of step (III) may be either a batch type or a continuous type, and either a tank type reactor having a stirrer or a fixed bed reactor filled with a catalyst may be used, but a fixed bed that does not require catalyst separation. A reactor is preferred. The ester-based liquid space velocity (LHSV) when continuously carried out in a fixed bed reactor is usually 0.01 to 10.0 / h, preferably 0.1 to 5.0 / h. Is good.

  As a reaction method of the step (III), a liquid that does not use an inert gas even in a three-phase reaction consisting of gas (nitrogen) -liquid (ester) -solid (catalyst) using an inert gas such as nitrogen. An (ester) -solid (catalyst) reaction method may be used. The reaction solution may be contacted by either a gas-liquid co-current method or a gas-liquid countercurrent method in a gas-liquid-solid reaction. In the liquid-solid reaction, the reaction solution is caused to contact by flowing upward or downward.

  Further, the step (III) can be divided into multiple stages, and the lower alcohol can be removed out of the system. In this case, conversion from monoglyceride to diglyceride or triglyceride is promoted, which is efficient. Specifically, a method of reducing the pressure in the system and a method of circulating an inert gas as a purge gas in the system are exemplified.

  Since the reaction product is a reaction with a solid catalyst, it contains almost no soap or catalyst components, and is used as it is in the next step (IV) without performing post-treatment steps such as washing with water and treatment with an adsorbent. be able to.

[Step (IV)]
Step (IV) is a step of obtaining a fatty acid lower alkyl ester by distillation from the ester mixture obtained in step (III).

  In the present invention, by performing the step (III), the monoglyceride content is reduced and the soap component and the catalyst component are not included, so that the separation efficiency in the step (IV) is improved. Thus, separation is performed until the distillation residue is less than 10% by weight, preferably less than 8% by weight, and more preferably less than 6% by weight, to obtain a fatty acid lower alkyl ester.

  Distillation is generally carried out under reduced pressure. The pressure is preferably 0.01 to 10 kPa. If it is 0.01 kPa or more, the burden on the equipment is small, and if it is 10 kPa or less, the temperature of the distillation bottom does not become too high, and decomposition of the fatty acid lower alkyl ester can be suppressed.

  The distillation column used in the distillation process is a column packed with a regular packed plate of metal plate or wire mesh for contact with gas and liquid, or an irregular packing such as Raschig ring or pole ring, or perforated plate tray, foam Either a rectifying column provided with a shelf such as a bell-type tray or a flash column not provided with a gas-liquid contact portion in the column may be used. The distillation operation of the present invention can be carried out continuously, batchwise, or semi-batch.

  The distillation residue is mainly composed of diglyceride and triglyceride, and does not contain soap or catalyst components. Therefore, it can be recovered in step (I) without any treatment or purification.

[Step (V)]
In the present invention, the fatty acid lower alkyl ester-containing mixture obtained in the step (I) may be separated as it is by the step (II), but before the step (II), It is preferable to perform the step of separating the alcohol, that is, the step (V), and after removing the remaining lower alcohol, the separation is performed according to the step (II).

  Specific examples of the separation in the step (V) include a distillation separation method and a stripping separation method using an inert gas flow. Although there is no restriction | limiting in particular in the conditions of the distillation separation method, The conditions of 1-101 kPa and 30-150 degreeC can be used suitably. In the stripping separation method, the conditions are not particularly limited. For example, the lower alcohol can be removed from the system by flowing an inert gas under conditions of 30 to 150 ° C. Nitrogen and hydrogen are exemplified as the inert gas.

  By removing the lower alcohol and then performing the separation in step (II), the amount of glycerin dissolved in the ester phase is reduced. In the next step (III), the lower alkyl ester is esterified with a lower alkyl ester and glycerin. It is possible to suppress a decrease in yield. Further, since the lower alcohol is present in the step (III), monoglyceride can be efficiently reduced from the viewpoint of thermodynamic equilibrium.

  “%” In the examples is “% by weight” unless otherwise specified.

Example 1
Step (I-1): Purified coconut oil was supplied from the top of the tower to a reaction tower filled with 1000 ml of extruded aluminum phosphate at a feed rate of 400 ml / h and methanol at 235 ml / h, and a pressure of 3.0 MPa. The reaction was performed at 170 ° C.

  Step (V-1): The reaction solution obtained in Step (I-1) was heated to 100 ° C. under a reduced pressure of 13 kPa to remove methanol.

  Step (II-1): The reaction liquid from which methanol was removed in Step (V-1) was allowed to stand at 50 ° C. for 1 hour to separate an ester phase and a phase mainly composed of glycerin.

  Step (I-2): The ester phase obtained in Step (II-1) is fed to the reaction tower from the top of the tower at a feed rate of 800 ml / h and methanol at 470 ml / h, and 170 MPa at a pressure of 3.0 MPa. The reaction was performed at 0 ° C.

  Step (V-2): The reaction solution obtained in Step (I-2) was heated to 100 ° C. under a reduced pressure of 13 kPa to remove methanol.

  Step (II-2): The reaction liquid from which methanol was removed in Step (V-2) was allowed to stand at 50 ° C. for 1 hour to separate an ester phase and a phase mainly composed of glycerin. The methyl ester content in this ester phase (crude ester) was 96.6%, and the monoglyceride content was 1.06%.

  Step (III): 500 ml / h of the crude ester obtained in the above step (II-2) was supplied from the top of the column under normal pressure to a reaction column filled with 250 ml of extruded aluminum phosphate and reacted at 170 ° C. Went. At this time, methanol was not supplied. The monoglyceride content in the obtained reaction liquid was 0.17%.

  Step (IV): 232.9 g of the reaction solution obtained in Step (III) was heated to 240 ° C. under a reduced pressure of 0.7 kPa and subjected to simple distillation to obtain 219 fatty acid methyl esters having a monoglyceride content of 0.06%. .8 g was obtained.

Comparative Example 1
Step (III ′): To 407.2 g of the crude ester having a monoglyceride content of 1.06% obtained in Step (II-2) of Example 1, 2.0 g of a 30% sodium methoxide-methanol solution was added and 13 kPa. For 3 hours at 80 ° C. under reduced pressure. This mixture was washed with hot water at 50 ° C. and allowed to stand for 1 hour, and then the lower water-soap emulsion phase was separated to obtain 398.4 g of an ester phase. Next, 1% of activated clay (Galleon Earth V2 manufactured by Mizusawa Chemical Co., Ltd.) was added to the ester phase, and the mixture was stirred for 5 minutes at room temperature and then filtered. After filtration, 388.2 g of ester having a monoglyceride content of 0.41% was obtained.
Step (IV): 229.5 g of the ester obtained in Step (III ′) was heated to 240 ° C. under a reduced pressure of 0.7 kPa and distilled to give 217. Fatty acid methyl ester having a monoglyceride content of 0.24%. 7 g was obtained.

Comparative Example 2
Step (IV): 231.4 g of the crude ester having a monoglyceride content of 1.06% obtained in Step (II-2) of Example 1 was heated to 240 ° C. under a reduced pressure of 0.7 kPa and distilled. 222.0 g of a fatty acid methyl ester having a monoglyceride content of 0.54% was obtained.

  The results obtained in Example 1 and Comparative Examples 1 and 2 are summarized in Table 1.

Claims (2)

A method for producing a fatty acid lower alkyl ester comprising the following steps (I), (II), (III) and (IV) :
The manufacturing method of a fatty-acid lower alkyl ester which has the process of distilling and separating a lower alcohol from a fatty-acid lower alkyl ester containing mixture before process (II) .
Step (I): A step of transesterifying triglyceride and a lower alcohol having 1 to 4 carbon atoms using a solid acid catalyst to produce a fatty acid lower alkyl ester-containing mixture Step (II): obtained in Step (I) the mixture rich in fatty acid lower alkyl esters, monoglyceride, an ester phase containing diglyceride and triglyceride, step separating the glycerine phase rich in glycerol (III): the separated ester phase in step (II), a solid acid Step of converting monoglyceride contained into diglyceride or triglyceride by transesterification using a catalyst Step (IV): Step of obtaining fatty acid lower alkyl ester by distillation from ester mixture obtained in step (III) Performing step (III) is within the temperature range of 130-260 ° C., the production method of fatty acid lower alkyl ester of claim 1, wherein.