JP5780513B2 - Method for synthesizing lactate ester - Google Patents

Description

  The present invention relates to a method for synthesizing a lactic acid ester using glycerin as a raw material.

  In recent years, diesel fuel (biodiesel fuel: BDF) using vegetable oil as a raw material has been actively produced. In this method, a fatty acid ester is taken out of fats and oils by transesterifying fats and alcohols, which are triester bodies of glycerin, and used as diesel fuel. However, according to this technique, the fatty acid ester extracted from fats and oils can be effectively used as a biodiesel fuel, but glycerin is produced as a by-product in the production at a weight of about 10% of the raw material. Since glycerin as a by-product is mixed with a catalyst, unconverted fatty acid, and the like, a method for effectively utilizing this has not been found. Most of the fuel is incinerated as fuel or discarded as it is.

  As the production of biodiesel fuel increases, the amount of by-produced glycerin also increases. Glycerin is a constituent of fats and oils such as vegetable oils and animal fats, and is abundant in nature. It is separated and produced from various fats and oils in the food and oil industries and is available in large quantities at a low price. be able to. Therefore, not only glycerin as a by-product but also effective utilization of glycerin, which is a material available at low cost, is required.

  Conventionally, the following methods have been proposed as methods for utilizing glycerin. As a method for producing biodiesel fuel using acid fats and deteriorated fats and the like as raw materials, there is a method (Patent Document 1) in which by-produced glycerin and glycerin derivatives are neutralized with an acid and further purified by distillation, specific gravity separation operation or the like. Proposed.

  Hydrolysis of glycerin produced as a by-product in the production of biodiesel fuel by transesterification from fats and oils in the presence of an alkali catalyst, or glycerin chemically synthesized from vegetable oils and animal fats, under alkaline conditions. Thus, a method for producing lactic acid (Patent Document 2, Non-Patent Document 1) has been proposed.

  Furthermore, glycerin produced as a by-product when producing biodiesel fuel from animal and vegetable oils and fats using an alkali catalyst is made acidic using acid, then supercritical water is allowed to act on the glycerin to produce acrolein. A method (Patent Document 3) has also been studied.

  However, the method for purifying glycerin of Patent Document 1 has a problem that it is expensive to purify and is not suitable for commercial use because the purity of glycerin obtained cannot always be increased. In the alkaline hydrothermal methods of Patent Document 2 and Non-Patent Document 1, an excessive amount of alkali is required, which causes problems such as corrosion of the reaction apparatus and waste liquid treatment. Furthermore, the method of Patent Document 3 is a reaction in which raw material glycerin is acidic and supercritical water is used as a medium, and there are problems such as corrosion of the reaction apparatus and waste liquid treatment.

On the other hand, lactic acid is used as a raw material monomer for polylactic acid, which is a carbon-neutral biodegradable plastic material. Since polylactic acid is a biodegradable plastic material, it is one of the solutions to the problem of waste disposal, and since it is biologically derived, it has been attracting attention for its effects such as saving petroleum resources and reducing CO ₂ generation. The amount used is also increasing, and demand is expected to increase in the future. Here, even in the form of lactic acid ester instead of lactic acid as a raw material monomer for polylactic acid, lactic acid ester can be easily converted into lactic acid by hydrolysis reaction. This is significant because it is equivalent to the production of lactic acid.

  For this reason, glycerin produced as a by-product in the production of biodiesel fuel, lactic acid ester, which is a raw material monomer of polylactic acid, from glycerin separated and produced from various types of fats and oils is a problem in corrosion of reactors and waste liquid treatment If it can be produced simply and easily, it is useful as an effective utilization measure of by-product glycerin in evaluating the production process of biodiesel fuel, and establishment of production technology is desired.

JP-A-2005-350631 International Publication No. 2007/001043 Pamphlet JP 2011-12007 A

Kishida, H., Chemical Engineering Papers, Vol.32, No.6, pp.535-541 (2006)

  The present invention has been made in view of the above circumstances, including glycerin produced as a by-product in the production of biodiesel fuel, and using glycerin separated and generated from various fats and oils, and is inexpensive and industrial. It is an object of the present invention to provide a method for easily producing a lactic acid ester, which is expected to be in demand, without causing problems of reactor corrosion and waste liquid treatment.

  As a result of intensive studies to solve the above problems, the inventors of the present invention decided to use a solid base catalyst without using a conventionally used alkali or acid, and further, the viscosity of glycerin was high, and the catalyst surface It has been found that the lowering of the reactivity due to the low material diffusion coefficient can be mitigated by using alcohol in a high-temperature and high-pressure state as a reaction medium to solve the above-mentioned problems.

  The inventors have invented a method for synthesizing a lactic acid ester from glycerin in one step by using the action of a solid base catalyst by using an alcohol in a high temperature and high pressure state as a reaction medium.

That is, the present invention
[1] A method of synthesizing a lactic acid ester using glycerol in the presence of a solid base catalyst and an alcohol in a high temperature and high pressure state as a reaction medium.
[2] The method according to [1] above, wherein the glycerin is glycerin by-produced in the production of biodiesel fuel.
[3] The method according to claim 1 or 2, wherein the solid base catalyst contains one or more selected from the group consisting of magnesium oxide, calcium oxide, calcium hydroxide, strontium oxide and barium oxide.
[4] The method according to any one of [1] to [3], wherein the alcohol is any one of methanol, ethanol, and isopropanol.
[5] The method according to any one of [1] to [4], wherein the high-temperature and high-pressure state is a supercritical state or a subcritical state.

  According to the present invention, by-products in the production of biodiesel fuel, and glycerin discarded from the food industry, oil industry, etc. as raw materials, lactate can be produced by a green process without using alkali or acid. it can. In addition, by using alcohol in a high temperature and high pressure state, corrosion of the reaction apparatus can be prevented and an inexpensive reaction apparatus can be obtained, and by using a solid base catalyst, post-treatment of products and catalysts can be easily performed. it can. As the reaction, the time required for the conversion reaction from glycerin to lactic acid ester is short, and there are very few reaction by-products. Since lactic acid ester as a product can be easily produced by hydrolysis reaction, it can be used as a useful raw material for polylactic acid, and can also be used as a solvent and industrial raw material.

2 is a gas chromatogram showing the product of Example 1 with a reaction time of 60 minutes. It is a mass spectrum which methyl lactate which is a product in reaction time of Example 1, and a standard substance show.

  The glycerin used as a raw material in the present invention may be any origin and produced by a method. Among these, it is preferable to use as a starting material those produced from glycerin, vegetable oils, animal fats and the like by-produced during the production of biodiesel fuel. In particular, from the viewpoint of effective utilization of by-products, it is more preferable to use a glycerin-containing waste liquid generated during the production of biodiesel fuel as a raw material.

  The solid base catalyst used in the present invention is a solid that exhibits surface basicity among metal oxides, metal salts, supported bases, composite oxides, zeolites, and the like. For example, magnesium oxide, calcium oxide, strontium oxide, barium oxide, lanthanum oxide, cerium oxide, calcium hydroxide, strontium hydroxide, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate, barium carbonate, potassium bicarbonate, silicon oxide Examples include magnesium oxide composite oxide, silicon oxide-calcium oxide composite oxide, silicon oxide-strontium oxide composite oxide, Na ion-exchanged X-type zeolite, and K ion-exchanged Y-type zeolite.

  Among these, a catalyst containing at least one selected from the group consisting of magnesium oxide, calcium oxide, calcium hydroxide, strontium oxide and barium oxide is preferable. Among these, it is more preferable to use an alkaline earth metal oxide. Further, layered double hydroxide (hydrotalcite), zeolite (KY), or a commonly used carrier may be supported with calcium oxide, magnesium oxide, or the like. As the carrier, any inorganic porous carrier that is neutral or basic can be used. Examples thereof include alumina and diatomaceous earth.

Hydrotalcite is a typical example of the layered double hydroxide. The general formula of hydrotalcites is represented by [M ^{2 +} _1−X M ³⁺ _X (OH) ₂ ] [A ⁿ⁻ _{X / n} · mH ₂ O].
(However, M ²⁺ is a divalent metal ion, M ³⁺ is a trivalent metal ion, and A ⁿ⁻ _{X / n} is an interlayer anion.)
A hydrotalcite compound is a layered clay mineral and has a positive charge as a whole, but has a characteristic that anions are adsorbed between layers and on the surface, and OH ⁻ and CO ₃ ^{2− on the} surface function as a base.

  The solid base catalyst can be produced by a conventionally known synthesis method. For example, sol-gel method, coprecipitation method, impregnation method, urea method and the like are exemplified. The amount of the solid base catalyst used is preferably 0.001 to 1 part by weight, more preferably 0.1 to 1 part by weight with respect to 1 part by weight of glycerin.

  In the present invention, since a solid base catalyst is used, post-treatment for separating the catalyst from the reaction system is easy. That is, since it is a solid catalyst, it can be easily recovered by filtration and can be reused with little decrease in catalyst activity. This solid base catalyst is a safe, inexpensive and highly selective catalyst system that does not use harmful metals.

  The alcohol in a high temperature and high pressure state in the present invention means that the alcohol is in a supercritical state or a subcritical state. That is, the alcohol in the supercritical state refers to a state where the temperature in the reaction system is higher than the critical temperature (Tc) and the pressure is higher than the critical pressure (Pc), and the subcritical state is near the critical point. In this state, the temperature and pressure are lower than the critical point, and the property conforms to the critical state. Specifically, the subcritical alcohol is a temperature within the reaction system that is equal to or higher than the boiling point of the alcohol and approximately 150 ° C. or higher, and the pressure is equal to or higher than the vapor pressure of the alcohol at the reaction temperature, and approximately 2.0 MPa. This refers to the above state.

  In the present invention, the alcohol in the high temperature and high pressure state, that is, the alcohol in the supercritical state or subcritical state, is adjusted to an appropriate range at least at a temperature of 150 to 600 ° C. and a pressure of 2.0 to 200 MPa. That's fine. The temperature is preferably 200 to 400 ° C. and the pressure is 10 to 20 MPa.

  The alcohol used as the reaction medium in the present invention is not particularly limited as long as it is a monohydric alcohol. For example, methanol, ethanol, n-propyl alcohol, isopropanol, n-butanol, isobutanol, t-butanol and the like can be mentioned. Of these, methanol, ethanol, isopropanol, and isobutanol are preferable, and methanol, ethanol, and isopropanol are more preferable. Table 1 shows the critical temperature (Tc) and critical pressure (Pc) of these alcohols.

  In the present invention, by using alcohol in a high-temperature and high-pressure state as a reaction medium, the reaction can be performed without a decrease in reactivity even when the viscosity of the raw material glycerin is high and the material diffusion coefficient on the catalyst surface is small. In addition, alcohols as a reaction medium have low corrosive properties, and by using a solid base catalyst, the reaction can proceed without using alkalis and acids that are conventionally required when using high-temperature and high-pressure water as a reaction medium. be able to. Thereby, it is not necessary to use a material having high corrosion resistance as a material for a reactor as a reaction apparatus and peripheral equipment, and it can be made inexpensive.

  The reaction mechanism for forming a lactic acid ester from glycerin in the present invention is a dehydrogenation reaction of glycerin using alcohol as a reaction medium under a high temperature and high pressure condition and an esterification reaction between the produced lactic acid and an alcohol. For example, when methanol is used as a reaction medium, the following reaction occurs in one stage.

  As the reaction apparatus in the present invention, a batch reaction apparatus or a continuous reaction apparatus can be used. In the continuous type, for example, a fixed bed flow type reaction apparatus, a fluidized bed type reaction apparatus or the like can be used.

  In the present invention, the lactic acid ester of the reaction product can be easily separated using a separation technique that has conventionally existed as separation and purification from the production system. For example, it can be separated using a distillation method. The separated and recovered lactic acid ester can be easily converted to lactic acid by a hydrolysis reaction, and alcohol can also be recovered at the same time. The recovered alcohol can be used repeatedly as a reaction medium.

  The alkyl lactic acid ester produced in the present invention can be converted to lactic acid by a hydrolysis reaction and is useful not only as a raw material monomer for polylactic acid but also as it is as a high-boiling solvent, a cleaning agent, and a synthetic raw material.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

<Reaction procedure>
The batch-type reaction tube used for the experiment is made of SUS316, the internal volume is 10 cm ³ , and the maximum use conditions are a temperature of 537 ° C. and a pressure of 35 MPa. The reaction tube is charged with about 0.1 to 3 g of glycerin and about 1 to 6 g of alcohol at a weight ratio of about 1:30, and 0.10 g of catalyst is charged and sealed, and then charged into a molten metal bath set at a predetermined temperature. The reaction was started. The temperature was set to 250 to 400 ° C., the pressure was set to 4 to 30 MPa, and the reaction time was set to 0.5 to 24 hours (including a heating time of about 1 minute). After a predetermined time, the reaction tube was pulled up from the metal molten salt bath and quenched in a cold water bath to stop the reaction. Thereafter, 1,4-dioxane was added as an internal standard substance to the recovered liquid, and the product was subjected to qualitative and quantitative analysis by the following analysis means.

<Analytical means (GC / MS)>
Qualitative and quantitative analysis of the product was performed with a gas chromatograph / mass spectrometer GC / MS (GCMS-QP2010) and a gas chromatograph / hydrogen flame ionization detector GC / FID (GC-2010) manufactured by Shimadzu Corporation. The column is DB-5 manufactured by Shimadzu GL Corporation, the injection volume is 1.0 μL, the vaporization chamber temperature is set to 250 ° C., the column oven temperature is set to 40 ° C., the column temperature is held at 40 ° C. for 5 minutes, and 10 The temperature was raised to 150 ° C. at a rate of ° C./min, held for 5 min and analyzed. After confirming that the retention time of the peak considered to be the target product matches that of the standard substance, the peak part is analyzed by mass spectrum, and the molecular weight of the main part and the pattern of decomposition products are those of the standard substance. Qualitative analysis was performed by agreeing with. For the quantitative analysis, an internal standard method using 1,4-dioxane as an internal standard substance was used.

[Example 1]
In a reaction tube, 0.12 g of glycerin and 3.57 g of methanol as a solvent, CaO / Al ₂ O ₃ (loading rate of 80 wt%, aluminum triisoproxide (manufactured by Wako Pure Chemical Industries) and calcium nitrate (Wako Pure Chemical Industries, Ltd.) as catalysts. The pH of the reaction tube was adjusted with nitric acid (manufactured by Wako Pure Chemical Industries, Ltd., prepared by a sol-gel method), and 0.10 g was charged. After the air in the reaction tube was replaced with nitrogen gas, the reaction tube was sealed. The reaction conditions were a reaction temperature of 300 ° C., a reaction pressure of 20 MPa, and a reaction time of 30 minutes to 150 minutes. Table 2 shows the reaction time and the yield at that time. The results of chromatogram and mass spectrum obtained by qualitative analysis and quantitative analysis of the reaction product are shown in FIGS. FIG. 1 is a GC chromatogram of the product data with a reaction time of 60 minutes, and the horizontal axis represents the retention time. FIG. 2 is a mass spectrum of a product sample (upper part) and a pure substance lactic acid methyl ester (lower part) as a standard substance, and the horizontal axis indicates the molecular weight. From the above results, it was confirmed that methyl lactate was formed.

The yield is calculated according to the following formula.
Lactic acid ester yield (mol%)
= Amount of reaction product (mol) / Amount of charged glycerin (mol) × 100

As an internal standard method, 1,4-dioxane is added to a standard sample as an internal standard substance, and the area ratio between the internal standard substance and the standard sample (peak area of the standard sample / peak area of the internal standard substance) and the concentration ratio (standard sample) (Concentration / internal standard concentration) as a calibration curve. The calibration curve was a straight line passing through the origin, and a relative molar sensitivity of 0.2857 was obtained from the slope. At the end of each experiment, precisely weighed 1,4-dioxane was added to the product, and the amount of methyl lactate produced from the peak area ratio and relative molar sensitivity of the internal standard substance and methyl lactate in the chromatogram obtained by gas chromatography. Asked.

[Example 2]
In Example 1, the catalyst was changed to CaO / Al ₂ O ₃ and MgO / Al ₂ O ₃ (loading rate 80 wt%, aluminum triisoproxide (Wako Pure Chemical Industries) and magnesium nitrate (Wako Pure Chemical Industries) Using nitric acid (manufactured by Wako Pure Chemical Industries, Ltd., adjusting the pH and preparing by a sol-gel method), the reaction conditions were 20 to 100 minutes. The other conditions were the same as in Example 1. Table 3 shows the reaction time and the yield at that time.

[Example 3]
In Example 1, MgO (Catalyst Society Reference Catalyst, JRC-MGO-500A) was used instead of CaO / Al ₂ O ₃ as the catalyst, and the reaction conditions were 30 minutes to 90 minutes. The other conditions were the same as in Example 1. Table 4 shows the reaction time and the yield at that time.

[Example 4]
In Example 1, the catalyst was changed to CaO / Al ₂ O ₃ and MgO (manufactured by Wako Pure Chemical Industries) was used, and the reaction conditions were 30 minutes to 90 minutes. The other conditions were the same as in Example 1. Table 5 shows the reaction time and the yield at that time.

[Example 5]
In Example 1, the catalyst was changed to CaO / Al ₂ O ₃ and MgO (manufactured by Wako Pure Chemical Industries) was used. The reaction conditions were a reaction temperature of 270 ° C. and a reaction time of 60 minutes to 90 minutes. The other conditions were the same as in Example 1. Table 6 shows the reaction time and the yield at that time.

[Example 6]
In Example 1, the catalyst was changed to CaO / Al ₂ O ₃ and CaO (manufactured by Wako Pure Chemical Industries, Ltd.) was used, and the reaction conditions were 60 to 180 minutes. The other conditions were the same as in Example 1. Table 7 shows the reaction time and the yield at that time.

[Example 7]
In Example 1, the catalyst was changed to CaO / Al ₂ O ₃ and BaO / Al ₂ O ₃ (loading rate 80 wt%, aluminum triisoproxide (manufactured by Wako Pure Chemical Industries) and barium nitrate (manufactured by Wako Pure Chemical Industries)) Using nitric acid (manufactured by Wako Pure Chemical Industries, Ltd., adjusting the pH and preparing by a sol-gel method), the reaction conditions were 30 to 90 minutes. The other conditions were the same as in Example 1. Table 8 shows the reaction time and the yield at that time.

[Example 8]
In a reaction tube, 0.12 g of glycerin and 3.57 g of methanol as a solvent, hydrotalcite (magnesium nitrate (manufactured by Wako Pure Chemical Industries)) and aluminum nitrate (manufactured by Wako Pure Chemical Industries, Ltd.) in a molar ratio of 3: 1 as a catalyst Filled with 0.10 g of sodium hydroxide (manufactured by Wako Pure Chemical Industries, Ltd.) and sodium carbonate (manufactured by Wako Pure Chemical Industries, Ltd.) 0.10 g, and the air in the reaction tube was replaced with nitrogen gas, The reaction tube was sealed. The reaction conditions were a reaction temperature of 300 ° C. and a reaction time of 90 minutes. The yield at that time was 1.5 mol%.

[Example 9]
In Example 8, it carried out on the same conditions as Example 8 except having changed the reaction solvent into methanol and using ethanol. In this reaction, ethyl lactate was obtained in a yield of 2.37 mol%.

[Example 10]
In Example 8, it carried out on the same conditions as Example 8 except having changed the reaction solvent into methanol and using isopropanol. In this reaction, isopropyl lactate was obtained in a yield of 2.35 mol%.

[Comparative Example 1]
A reaction tube was filled with 0.12 g of glycerin, 3.57 g of ultrapure water as a solvent, 0.10 g of MgO (catalyst society reference catalyst, JRC-MGO-500A) as a catalyst, and the air in the reaction tube was filled with nitrogen gas. After replacement, the reaction tube was sealed. The reaction conditions were a reaction temperature of 300 ° C., a reaction pressure of 8.59 MPa, and a reaction time of 90 minutes. In this reaction, formation of lactic acid and its derivatives could not be confirmed.

  According to Examples 1 to 8, lactate esters could be synthesized using various solid base catalysts. It can be seen that the yield increases as the reaction time elapses. According to Examples 9 and 10, lactate ester could be synthesized using ethanol and isopropanol as reaction solvents. However, as shown in Comparative Example 1, the production of lactic acid and its derivatives could not be confirmed using supercritical water.

  Using by-products in the production of biodiesel fuel and glycerin discarded from the food industry, oil industry, etc. as raw materials, using high temperature and high pressure alcohol in the presence of a solid base catalyst that is a lactic acid ester as a green process It can be produced without using an alkali or an acid. The product lactic acid ester is chemically stable and can be easily converted into lactic acid by hydrolysis, and can also be used as various raw materials such as high-boiling solvents and detergents.

Claims (5)

A method of synthesizing a lactic acid ester using glycerin in the presence of a solid base catalyst as a reaction medium with alcohol at a high temperature and high pressure at a temperature of 150 to 600 ° C. and a pressure of 2.0 to 200 MPa .   The method according to claim 1, wherein the glycerin is glycerin by-produced during production of biodiesel fuel.   The method according to claim 1 or 2, wherein the solid base catalyst contains one or more selected from the group consisting of magnesium oxide, calcium oxide, calcium hydroxide, strontium oxide, and barium oxide.   The method according to claim 1, wherein the alcohol is any one of methanol, ethanol, and isopropanol.   The method according to claim 1, wherein the high temperature and high pressure state is a supercritical state or a subcritical state.