JP2007153943A - Process for producing ester by transesterification - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an ester usable for diesel fuel by carrying out a transesterification reaction in a process in which catalyst separation is easy and in a high yield.
An ester production method comprises contacting a raw material ester and an alcohol in two stages with a solid catalyst containing 70 to 95% by mass of amorphous zirconium oxide and 5 to 30% by mass of titanium oxide, and The transesterification reaction is performed by extracting glycerin between the first stage and the second stage.
[Selection figure] None

Description

  The present invention relates to a method for producing esters such as fatty acid esters from a raw material ester of fats and oils by a transesterification reaction.

The transesterification reaction is used, for example, to produce a fatty acid ester using an oil or fat that is an ester of a fatty acid and glycerin as a raw material. As such a transesterification catalyst, an alkali catalyst such as caustic soda, a zinc catalyst, and an enzyme such as lipase are used. Patent Documents 1 and 2 disclose a method for producing a diesel fuel by subjecting waste edible oil and methanol to a transesterification reaction in the presence of caustic soda. Moreover, in patent document 3, when manufacturing fatty-acid ester from fats and oils and alcohol, making it react on the conditions by which fats and oils and / or alcohol will be in a supercritical state, without adding a catalyst is proposed.
Patent Document 4 discloses a two-stage reaction using an alkali metal as a catalyst. In this case, a water-absorbing resin is used in order to remove the water that has washed the alkali metal.
JP-A-9-235573 JP-A-7-197047 JP 2000-143586 A Japanese Patent Publication No. WO2003-070859

Although the homogeneous reaction using mainly an alkali metal as a catalyst proceeds at a high yield, it requires a process for separating the reaction product and the catalyst, and it is a complicated process such as an alkali washing step. In addition to this, spills of alkali metals into products and saponification of free fatty acids were also problems. On the other hand, in a transesterification reaction using a heterogeneous catalyst, a high product yield could not be obtained.
Under such circumstances, an object of the present invention is to provide a method for producing an ester, which can easily separate a catalyst from a transesterification product and has a high product yield.

As a result of diligent research to solve the above problems, the inventors of the present invention have a simple catalyst separation process and a high product yield by using an appropriate solid catalyst and setting an appropriate reaction system. An ester production method was found. That is, the method for producing an ester according to the present invention comprises a solid catalyst containing 70 to 95% by mass of amorphous zirconium oxide and 5 to 30% by mass of titanium oxide. In the method for producing an ester by a transesterification reaction brought into contact with glycerin, glycerin is extracted between the first stage and the second stage.
That is, the present invention
[1] In a method for producing an ester by transesterification by bringing a raw material ester and an alcohol into contact with a solid catalyst containing 70 to 95% by mass of amorphous zirconium oxide and 5 to 30% by mass of titanium oxide. ,
As a first step reaction, a raw material ester that is oil and fat and a reaction liquid consisting of alcohol are introduced into a reaction apparatus, and the reaction is performed by bringing the raw material ester into contact with the catalyst in a liquid phase state and alcohol in a gas phase state,
Separate glycerin from the reaction solution obtained by the first stage reaction,
Then, as a second reaction, the reaction liquid composed of unreacted raw material ester and alcohol in the reaction liquid after separation of glycerin is introduced into the reaction apparatus, the raw material ester is in the liquid phase state, and the alcohol is in the gas phase state. A method for producing an ester by transesterification, wherein the reaction is carried out by contacting with the catalyst,
[2] The ratio of the alcohol to the raw material ester in the reaction solution composed of the raw material ester and the alcohol is 5 to 15 mol / mol in the first-stage reaction liquid, and 2 to 12 mol / mol in the second-stage reaction liquid. The method for producing an ester according to [1], characterized in that:
[3] The method for producing an ester according to [1] or [2], wherein the alcohol is methanol or ethanol,
[4] The method for producing an ester according to any one of [1] to [3], wherein the reaction temperature of the first-stage and second-stage reactions is 200 to 300 ° C.
[5] The ester reaction according to any one of [1] to [3], wherein the first stage reaction temperature is 230 to 270 ° C., and the second stage reaction temperature is 210 to 250 ° C. Production method,
[6] The method for producing an ester according to any one of [1] to [5], wherein the reaction pressure is 0.5 to 3.0 MPa.
[7] The method for producing an ester according to any one of [1] to [6], wherein a catalyst having a central pore diameter D50 of the catalyst of 2 to 100 nm is used.
[8] The reaction is performed using a catalyst with a yield of 90% or more in the second-stage reaction when the glycerin removal rate after completion of the first stage is 50%. [1] To the method for producing an ester according to any one of to [7].

In the present invention, by performing a transesterification reaction in two stages using a solid catalyst containing titanium oxide and zirconium oxide, a catalyst separation process is unnecessary and the transesterification reaction can be performed in a high yield. The manufacturing method of ester which can be provided can be provided.

[Raw material ester]
The raw material fat used in the present invention may be a glyceride of a saturated or unsaturated aliphatic carboxylic acid (the carboxylic acid has about 8 to 24 carbon atoms). Specifically, triglycerides called oils and fats are preferably used. Such fats and oils include vegetable oils such as soybean oil, palm oil, olive oil, peanut oil, coconut oil, sesame oil, palm oil, castor oil, beef fat, pork fat, horse fat, whale oil, sardine oil, mackerel Animal fats and oils such as oil are listed. Moreover, these mixtures and used waste oil can also be used. In the raw material ester, 0.1 to 30% by mass, particularly 1 to 20% by mass of a free fatty acid may be contained.

〔alcohol〕
As the alcohol used in the present invention, for example, alcohol having 1 to 3 carbon atoms such as methanol, ethanol and propanol can be used, and methanol is particularly preferable.

〔catalyst〕
The catalyst used in the present invention contains amorphous zirconium oxide as a main component and contains 70 to 95% by mass of amorphous zirconium oxide. Here, the zirconium oxide includes the case of a hydrated oxide form. In addition, it can be confirmed by X-ray diffraction (XRD) that the zirconium oxide is amorphous because there is substantially no diffraction peak. Specifically, when the intensity of the diffraction peak is below the detection limit, or when the diffraction intensity by the crystalline zirconium oxide is 100, when only the peak of intensity 2 or less is detected, the zirconium oxide is “ It can be considered to be “amorphous”. When the zirconium oxide content is less than 70% by mass or exceeds 95% by mass, the catalytic activity is lowered.

  The catalyst used in the present invention contains 5 to 30% by mass of titanium oxide. Since the transesterification reaction is usually performed at a high temperature of 100 ° C. to 300 ° C., it is necessary to prevent the amorphous zirconium oxide having high catalytic activity from crystallizing. In the catalyst of the present invention, it is considered that titanium oxide suppresses crystal growth of zirconium oxide. For this reason, when the content of titanium oxide is less than 5% by mass, crystal growth of zirconium oxide is promoted, and the catalytic activity is lowered. On the other hand, if the titanium oxide exceeds 30% by mass, the catalytic activity is lowered because many surfaces of the zirconium oxide are covered with the titanium oxide. Here, the crystallization temperature of the zirconium oxide can be set to 450 ° C. or higher, particularly 500 ° C. or higher by including titanium oxide. The crystallization temperature of zirconium oxide is usually 900 ° C. or lower. The crystallization temperature can be measured as a peak temperature of an exothermic peak that appears in a state in which no mass change occurs in a thermobalance-differential heat (TG-DTA) analysis when heated from room temperature.

  The catalyst containing 70 to 95% by mass of amorphous zirconium oxide and 5 to 30% by mass of titanium oxide used in the present invention is generally available as a composite oxide powder. For example, the first rare element It can be obtained from Chemical Industry Co., Ltd.

The average particle diameter of the catalyst particles used in the present invention is preferably ^{2 to} 200 μm, particularly 4 to 60 μm, and the specific surface area is preferably 100 to 400 m ² / g, particularly 150 to 400 m ² / g, more preferably 200 to 400 m. ² / g. The central pore diameter D50 of the catalyst particles is preferably 2 to 100 nm, more preferably 2 to 15 nm, and still more preferably 5 to 10 nm. If it is less than 2 nm, the diffusion of the raw materials and products in the pores of the catalyst particles is hindered, which is not preferable. If the thickness exceeds 100 nm, the specific surface area decreases, which is not preferable. Further, the total pore volume of the catalyst particles is preferably 0.3 cc / g or more, and in particular, the volume of the pores having a pore diameter of 2 to 15 nm is preferably 0.1 cc / g or more. The specific surface area and the central pore diameter can be measured by the BET method and the BJH method by the nitrogen adsorption / desorption method, respectively. In forming the catalyst, alumina having crystallinity such as γ-alumina may be used as a binder.

式中、R1、R2、R3は炭化水素基を示す。この反応を二段で行う。一段目の反応温度は、原料エステルが液相状態にあり、アルコールが気相状態となる温度であり、具体的には１００℃以上、好ましくは２００〜３００℃であり、より好ましくは２３０〜２７０℃である。また、反応圧力は、０．５〜３ＭＰａが好ましく、さらに好ましくは０．８〜２ＭＰａである。流通式反応においては、ＷＨＳＶ（重量空間速度）０．５〜３／時程度で生成物を十分に得ることができる。さらに、原料油脂に対するアルコールの比率を５〜１５ｍｏｌ／ｍｏｌとなるように、アルコールを導入することが好ましい。
ここで、アルコール比率が５ｍｏｌ／ｍｏｌより少ない場合には、原料転化率、エステル収率が低下する。また、１５ｍｏｌ／ｍｏｌより多い場合には、余剰アルコールにエステルが多く溶け込むため分離効率が悪くなるうえ、リアクターの規模が大きくなるのでリアクターに供給する熱量も多くなり好ましくない。 [Transesterification]
An example of the transesterification reaction of triglyceride used in the production method of the present invention is shown below.

In the formula, R1, R2, and R3 each represent a hydrocarbon group. This reaction is carried out in two stages. The reaction temperature in the first stage is a temperature at which the raw material ester is in a liquid phase and the alcohol is in a gas phase, specifically 100 ° C. or higher, preferably 200 to 300 ° C., more preferably 230 to 270. ° C. The reaction pressure is preferably 0.5 to 3 MPa, more preferably 0.8 to 2 MPa. In the flow reaction, the product can be sufficiently obtained at a WHSV (weight space velocity) of about 0.5 to 3 / hour. Furthermore, it is preferable to introduce the alcohol so that the ratio of the alcohol to the raw material fat becomes 5 to 15 mol / mol.
Here, when the alcohol ratio is less than 5 mol / mol, the raw material conversion rate and the ester yield are lowered. On the other hand, when the amount is higher than 15 mol / mol, a large amount of ester dissolves in the surplus alcohol, resulting in poor separation efficiency and an increase in the scale of the reactor, which increases the amount of heat supplied to the reactor, which is not preferable.

  After completion of the first stage reaction, glycerin produced from the reaction solution is removed. As for the glycerin removal step, for example, stationary separation, centrifugation, precision distillation separation, water washing, washing with warm water, etc. are used, but the third component, specifically alcohols represented by methyl alcohol and ethyl alcohol, etc. In addition, the addition of ethers typified by diethyl ether enables more efficient separation. Finally, it is preferable to remove 50% or more of glycerin contained in the reaction liquid after completion of the first stage. When the glycerin removal rate is less than 50%, the progress of the reaction is inhibited by the equilibrium, which is not preferable.

The reaction temperature in the second stage is a temperature at which the raw material ester is in a liquid phase and the alcohol is in a gas phase, specifically 100 ° C. or higher, preferably 200 to 300 ° C., more preferably 210 to 200 ° C. 250 ° C. The reaction pressure is preferably 0.5 to 3 MPa, more preferably 0.8 to 2 MPa. A product can be sufficiently obtained at a WHSV (weight space velocity) of about 0.5 to 3 / hour. The alcohol is preferably introduced so that the ratio of the alcohol to the unreacted raw material ester in the reaction solution coming out from the first-stage outlet under the above conditions is 2 to 12 mol / mol.
Here, when the alcohol ratio is less than 2 mol / mol, the raw material conversion rate and the ester yield are lowered. On the other hand, when the amount is higher than 12 mol / mol, a large amount of ester is dissolved in the surplus alcohol, resulting in poor separation efficiency and an increase in the scale of the reactor, which increases the amount of heat supplied to the reactor.
Moreover, when the reaction temperature of the 1st stage and the 2nd stage is less than 200 degreeC, since sufficient conversion rate and a yield cannot be obtained, it is unpreferable. When it exceeds 300 ° C., the product ester undergoes isomerization and low temperature fluidity is deteriorated, which is not preferable. Further, when the reaction pressure is less than 0.5 MPa, a sufficient conversion rate and yield cannot be obtained, which is not preferable. If it exceeds 3 MPa, the apparatus becomes large, which is not preferable.

  In addition, the reaction is carried out using a catalyst that gives a yield of 90% or more in the second stage reaction when the removal rate of glycerin after completion of the first stage is 50%. More preferably, a catalyst having a second stage yield of 95% or more, a catalyst having a second stage yield of 98% or more, particularly a catalyst having a second stage yield of 99% or more is used. It is desirable.

The ester produced by this reaction is preferably obtained in a liquid phase because of its ease of separation from the catalyst. As the reaction format, a batch system, a fluid system, or the like can be used. The catalyst of the present invention is preferably used as a fixed bed, whereby it is separated and recovered without being contained in the product.
Examples Hereinafter, the ester production method of the present invention will be described in detail with reference to Examples.

Examples 1-3
As the catalyst, a composite oxide composed of zirconium oxide (ZrO ₂ ) -titanium oxide (TiO ₂ ) manufactured by Daiichi Rare Elementalization Co., Ltd. was used. Table 1 shows the composition, average particle diameter, specific surface area, and median pore diameter of this composite oxide. It was confirmed by X-ray diffraction that the zirconium oxide was amorphous. The presence or absence of an X-ray diffraction peak is detected by RAD-1C (CuKα, tube voltage 30 KV, tube current 20 mA) manufactured by Rigaku Denshi, with a scan speed of 4 ° / min, a scan width of 0.02 °, and a diffraction peak exceeding the detection limit. Decided by whether or not it was done. When there was no peak exceeding the detection limit, or when the peak intensity of the crystalline zirconium oxide was 100, and there was only a peak of 2 or less, there was no peak. The crystallization temperature was raised from room temperature to 1500 ° C. with a heating rate of 20 ° C./min under air flow using a thermobalance-differential thermal analyzer (TG-DTA) manufactured by Mac Science (TG-DTA2000S). Measured.

  As a first-stage reaction, 3 g of the catalyst was packed in a fixed bed flow reactor having a vertical length of 50 cm and an inner diameter of 1 cm. Trioleic acid glyceride (manufactured by Tokyo Chemical Industry Co., Ltd.) as a raw material ester and methanol as an alcohol were introduced into this reactor from the upper end at raw material supply rates of 2.25 g / hour and 0.75 g / hour, respectively. The WHSV at this time was 0.75 / hour, and the methanol / oil ratio was 9.2 mol / mol. The reaction temperature was 250 ° C. and the reaction pressure was 1.0 MPa. The product oil was collected at a reaction time of 24 hours.

In order to remove glycerin from the liquid taken out from the lower end (outlet) of the first-stage reactor, distilled water and methanol were added and stirred. The product oil, methanol, and water were in a weight ratio of 1: 1: 1.5. After allowing to stand for a while, the upper oil layer was taken out and treated at 3500 to 4000 rpm for 10 to 15 minutes with a centrifuge to take out only the oil layer. Furthermore, it was dried at 70 ° C. for 3 hours using an evaporator.
As a result of this operation, it was confirmed by gel permeation chromatography that glycerin produced as a by-product in the first reaction was removed to 1% by mass or less of the by-product amount.

  In the second stage reaction, 2 g of the catalyst was packed in a fixed bed flow reactor having a vertical length of 50 cm and an inner diameter of 1 cm. The oil after removal of the glycerin as a raw material and methanol as an alcohol were introduced into this reactor from the upper end at a raw material supply rate of 1.3 g / hour and 0.35 g / hour, respectively. The WHSV at this time was 0.65 / hour, and methanol was introduced in an amount corresponding to the unreacted component in the first stage. The reaction temperature was 210-250 ° C., and the reaction pressure was 1.0 MPa. The product oil was collected at a reaction time of 24 hours.

  Monooleic acid glyceride, dioleic acid glyceride, trioleic acid glyceride and methyl oleate in the liquid taken out from the lower end (exit) of the first and second stage reactors were subjected to gel permeation chromatography (GPC). The product oil collected at a reaction time of 24 hours was measured. Here, it was assumed that the four compounds were made of trioleic glyceride, and the conversion was calculated from the remaining amount of trioleic glyceride, and the yield was calculated from the amount of methyl oleate produced. The conversion rate of the first transesterification reaction was 92%, and the yield was 84%. As shown in Table 2, the conversion rate and yield of the second stage were 99% and 96 to 98%, respectively. From the above, it can be seen that the fatty acid ester can be produced with a very high yield.

Examples 4-6
As a model raw material when glycerin removal is incomplete and glycerin remains, 50% of the theoretical amount of glycerin obtained from the first-stage ester yield in the oil from which glycerin has been removed as in Examples 1-3. A glycerin corresponding to the amount of glycerol was added and used as a raw material for the second-stage reaction. A transesterification reaction was carried out under the same conditions as in Examples 1 to 3 except that the raw material for the second stage was changed. As shown in Table 3, the conversion rate and yield of the second stage were 99% and the yield was 95 to 99%, respectively. It can be seen that the fatty acid ester can be produced with a very high product yield even if the transesterification reaction in the second stage is not in a state where glycerin is completely removed.

Comparative Example As a comparative example, Table 1 shows the result of only one stage without performing the two-stage process. Using a reactor filled with an equivalent amount of catalyst as in Examples, trioleic acid glyceride and methanol were introduced from the upper end at a raw material supply rate of 2.25 g / hour and 0.75 / hour, respectively. At this time, the WHSV was 0.75 / hour, and the methanol / oil ratio was 9.2 mol / mol. The reaction temperature was 250 ° C. and the reaction pressure was 1.0 MPa. When the reaction is carried out without removing glycerin, the conversion rate and yield reach saturation at a certain level due to reaction equilibrium inhibition, and it is difficult to obtain a high conversion rate and yield.

  According to the ester production method by transesterification using the zirconium oxide-titanium oxide catalyst of the present invention, an ester can be produced in a high yield. Therefore, the present invention is suitable for the production of diesel fuel using waste oil or the like, and contributes to the protection of the global environment by reducing CO2 emissions.

Claims (8)

In a method for producing an ester by transesterification by bringing a raw material ester and an alcohol into contact with a solid catalyst containing 70 to 95% by mass of amorphous zirconium oxide and 5 to 30% by mass of titanium oxide,
As a first step reaction, a raw material ester that is oil and fat and a reaction liquid consisting of alcohol are introduced into a reaction apparatus, and the reaction is performed by bringing the raw material ester into contact with the catalyst in a liquid phase state and alcohol in a gas phase state,
Separate glycerin from the reaction solution obtained by the first stage reaction,
Then, as a second reaction, the reaction liquid composed of unreacted raw material ester and alcohol in the reaction liquid after separation of glycerin is introduced into the reaction apparatus, the raw material ester is in the liquid phase state, and the alcohol is in the gas phase state. A method for producing an ester by transesterification, wherein the reaction is carried out by contacting with the catalyst. The ratio of the alcohol to the raw material ester in the reaction liquid composed of the raw material ester and the alcohol is 5 to 15 mol / mol in the first-stage reaction liquid and 2 to 12 mol / mol in the second-stage reaction liquid. The method for producing an ester according to claim 1. The method for producing an ester according to claim 1 or 2, wherein the alcohol is methanol or ethanol. The method for producing an ester according to any one of claims 1 to 3, wherein the reaction temperature of the first stage reaction and the second stage reaction is 200 to 300 ° C. The method for producing an ester according to any one of claims 1 to 3, wherein the first stage reaction temperature is 230 to 270 ° C, and the second stage reaction temperature is 210 to 250 ° C. The method for producing an ester according to any one of claims 1 to 5, wherein the reaction pressure is 0.5 to 3.0 MPa. The method for producing an ester according to any one of claims 1 to 6, wherein the catalyst has a central pore diameter D50 of 2 to 100 nm. The reaction is carried out using a catalyst with a yield of 90% or more in the second stage reaction when the removal rate of glycerin after completion of the first stage is 50%. 8. The method for producing an ester according to any one of 7 above.