JP2008024841A - Method for producing biodiesel fuel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a high purity biodiesel fuel even without washing with water as a post-treatment. <P>SOLUTION: This method for producing the biodiesel fuel comprises (i) a pre-treating process of mixing waste glycerol produced as a byproduct in producing the biodiesel fuel by reacting waste edible oil with a linear lower alcohol in the presence of an alkali catalyst, with waste edible oil used as a raw material and then removing a glycerol phase, and (ii) an ester interchange reaction process of performing the ester interchange reaction by adding the alkali catalyst and linear lower alcohol to the waste edible oil and separating the glycerol produced as the byproduct. In the above method, the method for performing the (ii) ester interchange reaction by 2-stage reactions is provided. In the above process, the process of obtaining the biodiesel fuel is also provided by mixing glycerol with crude biodiesel fuel obtained by separating the glycerol phase in the (ii) ester interchange reaction and then separating the glycerol phase. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing biodiesel fuel.

  Biodiesel fuel is a fuel obtained by using a vegetable oil and a linear lower alcohol such as methanol as a raw material and reacting with an appropriate catalyst, and has attracted worldwide attention as an alternative fuel for light oil. In Japan, many efforts have been made using waste cooking oil as a raw material. Although it can be manufactured relatively easily, if the raw materials and manufacturing method are inappropriate, the vehicle used may be damaged.

  Since the waste cooking oil contains a large amount of fatty acid and moisture, when the reaction is carried out, potassium hydroxide or the like, which is an alkali catalyst, reacts with the fatty acid to reduce the amount of the catalyst, thereby reducing the reaction rate and increasing the amount of unreacted components. Moreover, when there is much water | moisture content in raw waste cooking oil, soap is produced | generated from the fats and oils which are raw materials, and the produced | generated biodiesel fuel with an alkali catalyst, resulting in the fall of a yield.

  In general, an excess amount of a catalyst that neutralizes fatty acids contained in waste cooking oil is added to cause the reaction. However, by increasing the amount of the alkali catalyst, the generation of soap as a side reaction also proceeds. Therefore, this method is not an effective method because it requires washing with water as a post-treatment, the cost for waste water treatment is high, and a large amount of energy is required for waste water treatment (for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-182518

  An object of the present invention is to provide a method capable of producing a high-purity biodiesel fuel without washing with water as a post-treatment.

The gist of the present invention is as follows.
(1) The following steps:
(I) The waste glycerin produced as a by-product when producing biodiesel fuel by reacting the waste edible oil with a linear lower alcohol in the presence of an alkali catalyst and the waste edible oil used as a raw material are mixed, And (ii) a method for producing biodiesel fuel, comprising a transesterification step in which an alkali catalyst and a linear lower alcohol are added to waste cooking oil, a transesterification reaction is performed, and a by-produced glycerin phase is separated.
(2) The method according to (1) above, wherein the linear lower alcohol is methanol or ethanol.
(3) The method according to (1) or (2) above, wherein the waste glycerin used for the pretreatment contains an alkali catalyst.
(4) The method according to any one of (1) to (3), wherein the transesterification step of (ii) is performed in a two-stage reaction.
(5) The method according to any one of (1) to (4), wherein the glycerin phase separated in the transesterification step of (ii) is used as waste glycerin of the pretreatment step of (i).
(6) The crude biodiesel fuel obtained by separating the glycerin phase in the transesterification step of (ii) and glycerin are mixed, and then the glycerin phase is separated to obtain biodiesel fuel (1) to (1) to The method according to any one of (5).
(7) A method for purifying biodiesel fuel comprising mixing crude biodiesel fuel and glycerin and then separating the glycerin phase to obtain biodiesel fuel.

  According to the present invention, high-purity biodiesel fuel can be produced without washing with water as a post-treatment.

  The waste cooking oil used as a raw material in the biodiesel fuel production method of the present invention is not particularly limited as long as it can be a raw material for biodiesel fuel. For example, rapeseed oil, sunflower oil, soybean oil, palm oil, salad oil, olive oil The thing containing the waste cooking oil of vegetable oils and fats, such as, is mentioned.

  The acid value of the waste cooking oil before pretreatment is usually 5 or less, preferably 3 or less, and the water content is usually 0.5% by weight or less, preferably 0.2% by weight or less. Here, the acid value means the number of mg of potassium hydroxide necessary to neutralize free fatty acids contained in 1 g of fats and oils, and this value is not constant depending on the fats and oils, but its purity and storage state This is one of the important characteristic values for determining the quality of fats and oils.

  Waste glycerin (by-product glycerin) is an unnecessary substance by-produced when producing biodiesel fuel, and is usually only discarded. However, since it contains alkali components such as potassium hydroxide used as a catalyst, it can react with fatty acids in waste cooking oil and be removed by mixing and stirring with waste cooking oil. is there. In addition, since waste glycerin also contains surplus methanol that was not used in the reaction, biodiesel fuel generation reaction proceeds in the pretreatment, which may contribute to an increase in yield. Furthermore, since glycerin also melt | dissolves water, it turned out that the quantity of the water | moisture content contained in waste cooking oil can also be reduced by pre-processing by waste glycerin. Thus, by reducing the amount of fatty acid and moisture, it becomes easy to reduce the amount of unreacted components when producing biodiesel fuel from waste cooking oil. That is, the yield can be maintained while reducing the amount of catalyst and linear lower alcohol such as methanol. In addition, since this pretreatment agent is a substance that is inevitably generated by reaction, it does not cost.

  The concentration of alkali metals (potassium, sodium, etc.) in the waste glycerin used for the pretreatment is usually 2 to 10% by weight, preferably 4 to 8% by weight, and the water content is usually 5% by weight or less, preferably 2% by weight or less.

  The usage-amount of the waste glycerin used for a pre-processing is 5-20 weight part normally with respect to 100 weight part of waste edible oil used as a raw material, Preferably it is 10-15 weight part. The treatment temperature in the pretreatment is usually 30 to 65 ° C., preferably 35 to 55 ° C., and the mixing and stirring time is usually 5 minutes to 1 hour, preferably 10 minutes to 30 minutes.

  After mixing and stirring the waste cooking oil and waste glycerin, the phase of glycerin is changed by standing (the standing time is usually 30 minutes to 8 hours, preferably 1 hour to 6 hours) or by centrifugation (usually 20 minutes or less). Below, the edible oil phase separates up. From there, the upper phase of the edible oil is taken out by separation utilizing the difference in specific gravity and subjected to a transesterification reaction. By the pretreatment, the acid value and water content of the waste cooking oil are reduced. When an alkali metal hydroxide such as purified glycerin or potassium hydroxide is added to waste glycerin, the effect is further improved.

  The alkali catalyst used in the transesterification step of (ii) is not particularly limited as long as it can be used for the production of biodiesel fuel. For example, alkali metal hydroxides such as potassium hydroxide and sodium hydroxide are used. Is mentioned. The linear lower alcohol is not particularly limited as long as it can be used for the production of biodiesel fuel, and examples thereof include methanol and ethanol.

  The reaction temperature is usually 30 to 65 ° C., preferably 35 to 55 ° C., and the reaction time is usually 20 to 90 minutes, preferably 30 to 60 minutes.

  Currently, large plants such as those possessed by the city of Kyoto are manufactured with the goal of meeting the standards equivalent to European standards by analyzing the composition of the fuel produced. On the other hand, in Japan, local governments, waste disposal contractors, transporters, etc. purchase small plants to produce biodiesel fuel. Even in such a small-scale plant, it is necessary to devise a production method to produce a high-quality fuel.

  There is a demand for a method capable of producing biodiesel fuel (hereinafter, sometimes referred to as “BDF”) having a quality equivalent to that of a European or other quality standard even when a small-scale apparatus is used. The main components of BDF are alkyl esters such as fatty acid methyl esters (ME), and so long as they are produced from waste oils, mainly vegetable oils and fats, it is considered that the standards can be satisfied with appropriate reaction processes and purification systems. It is done. However, in a small-scale device, the balance between cost and quality becomes a problem.

  The main impurities are triglyceride (TG), which is the main component of the vegetable oil that is the raw material, diglyceride (DG) and monoglyceride (MG), which are the intermediate products, fatty acids, moisture, and BDF that are abundant in the waste oil. One raw material component during production, methanol as a by-product, glycerin as a by-product, potassium hydroxide used as a catalyst, and potassium salt (soap) of a fatty acid produced therefrom can be considered.

  In order to remove these components from the product BDF, there are a substance that can be reduced in concentration in the reaction process and a substance that should be removed in the separation process, which is a subsequent step. Therefore, it is preferable to employ a method corresponding to each.

  From the above, it is preferable to employ a reaction process using waste cooking oil as a raw material so that the impurities are not contained in the crude BDF. For that purpose, it is only necessary to obtain nearly 100% ME in the reaction path shown in FIG. Since this reaction is a sequential reaction, it can be considered to take a long reaction time so that diglyceride and monoglyceride as intermediate products do not remain. However, since the produced lower alkyl ester (for example, methyl ester) reacts with the catalyst to become a potassium salt of fatty acid (soap), it is not preferable to lengthen the reaction time.

  According to European standards, the concentrations of TG, DG and MG must be 0.2% or less, 0.2% or less and 0.8% or less, respectively, and the total glycerin is 0.25% or less. Yes. On the other hand, in the US standard (ASTMD 6751), individual concentrations are not shown, and the total glycerol is 0.24% or less.

  In order to reduce the total concentration of TG, DG and MG to 1.2% or less, the reaction is usually performed by adding an excess of lower alcohol such as methanol, which is one of the reaction raw materials, and excess lower alcohol which has not reacted. Is separated by distillation or the like after completion of the reaction.

However, this method requires an operation such as distillation, which requires heating costs.
Therefore, with the goal of reducing the total concentration of TG, DG, and MG to 1.2% or less, the reaction is performed in two stages, while reducing the amount of lower alcohol used as one of the reaction raw materials, The reaction operation to reduce the unreacted content was examined.

  In this method, when the batch reaction is performed in two stages, the unreacted content can be suppressed to a standard value or less. For example, the amount of lower alcohol is about 1/2 of the normal amount, and the amount of excess lower alcohol is 1/3 or less of the normal amount. Thus, an extra process for separating the lower alcohol becomes unnecessary. In this method, as described above, the effect is further enhanced by using the pre-treated waste cooking oil as a raw material.

  The amount of lower alcohol used in the second-stage reaction is usually 120 to 160 g, preferably 130 to 150 g in the first-stage reaction, and usually 15 to 15 in the second-stage reaction in the case of methanol per 1 kg of waste cooking oil used as a raw material. In the case of ethanol, it is usually 180 to 220 g, preferably 190 to 210 g, and in the second stage reaction, usually 25 to 65 g, preferably 35 to 55 g. .

  The reaction temperature in the first stage reaction is usually 30 to 65 ° C., preferably 35 to 55 ° C., the reaction time is usually 20 to 90 minutes, preferably 30 to 60 minutes, and the reaction in the second stage reaction. The temperature is usually 30 to 65 ° C., preferably 35 to 55 ° C., and the reaction time is usually 20 to 90 minutes, preferably 30 to 60 minutes.

  The glycerin phase by-produced by the transesterification reaction is separated, for example, by the difference in specific gravity, and is used as waste glycerin in the pretreatment step as it is without purification, if necessary. It can be used in the treatment (purification step).

  In addition, in the second stage reaction, excess lower alcohol, catalyst and soap can be dissolved in the glycerin phase by adding glycerin used in the post-treatment described later at the end of the reaction, and separation after the reaction can be performed. Can be easily.

  The present invention further provides a method for purifying biodiesel fuel, which comprises mixing crude biodiesel fuel and glycerin and then separating the glycerin phase to obtain biodiesel fuel.

  In this refining method, the target crude biodiesel fuel is not limited to those produced from waste cooking oil, and crude biodiesel fuel produced from new oil is also targeted.

  This purification method is more effective when combined with the method for producing biodiesel fuel by the two-stage reaction.

  The purpose of this purification method is to reduce alkali metals, moisture, and lower alcohol contained in biodiesel fuel produced by the reaction.

  According to the biodiesel fuel specifications, the impurities to be removed are potassium, moisture, methanol and glycerin. Of these, potassium is a substance that is difficult to separate. If potassium remains in the biodiesel fuel as soap, it may be deposited in the storage tank or deposited in the tank after being supplied to the vehicle. Therefore, the concentration in the biodiesel fuel must be lowered as much as possible. In the EU standard, it is 5 ppm.

  Generally, the potassium component is removed by washing the biodiesel fuel with 10 to 20% water. However, since the wastewater after washing cannot be discharged into the environment as it is, a water treatment facility is required, This will increase the production cost of diesel fuel. Further, since water is dissolved in biodiesel fuel by water treatment, a process for removing water is also required, and extra energy is required for heating.

  Therefore, in the purification method of the present invention, glycerin is used as a post-treatment agent. Since this is a substance that is also produced in the reaction, the glycerin used in this treatment can be mixed with the glycerin produced in the reaction and used as a pretreatment agent. In addition, since glycerin is also effective in removing moisture and lower alcohol, the load can be reduced in operations of dehydration and delowering alcohol performed after this treatment.

  As the glycerin used here, it is preferable to use purified glycerin such as commercially available glycerin, but it can be reused as long as it is used about once in the post-treatment, and it is also produced as a by-product by the transesterification. The obtained glycerin can be purified by distillation or the like. The usage-amount of glycerol is 3-20 weight part normally with respect to 100 weight part of crude biodiesel fuel, Preferably it is 5-10 weight part.

  The processing temperature in this post-processing is 30-65 degreeC normally, Preferably it is 35-55 degreeC, and mixing stirring time is 10 minutes-1 hour normally, Preferably it is 20 minutes-30 minutes.

  Crude biodiesel fuel and glycerin are mixed and stirred and allowed to stand (the standing time is usually 30 minutes to 8 hours, preferably 1 hour to 6 hours) or centrifuged (usually 20 minutes or less) to obtain a glycerin phase. Below, the biodiesel fuel phase separates above. A purified biodiesel fuel can be obtained by taking out the biodiesel fuel phase therefrom.

  The refined biodiesel fuel obtained as described above is subjected to heat treatment according to a known method as necessary to remove methanol and moisture.

  FIG. 2 shows a biodiesel fuel production process that combines the pretreatment, the biodiesel fuel production method by the two-stage reaction, and the post-treatment.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further more concretely, the scope of the present invention is not limited to these Examples. In the following, the acid value, water content, methanol concentration, and potassium concentration were measured as follows.
Measurement of acid value: The oil value to be measured was put into a mixed solution having a volume ratio of methanol and diethyl ether of 1: 2, and titration was performed with a 0.1N aqueous potassium hydroxide solution using phenolphthalein as an indicator to determine the acid value.

Measurement of water content in oil phase: Water content was measured using a Karl Fischer moisture meter (Kyoto Electronics Co., Ltd., MKA-610-ST). The measurement principle is volumetric titration.
Measurement of methanol concentration: Analysis of methanol in the oil phase was performed by high performance liquid chromatography (HPLC). A GPC column (Shim-pack, GPC-801, Shimadzu Corporation) was used as the column, tetrahydrofuran was used as the solvent, and a differential refractometer was used as the detector.
Method for measuring potassium concentration: Flame atomic absorption photometer (AAnalyst 2000, Perkin Elmer Japan Co., Ltd.) was used. The oil to be measured was dissolved in methanol and used as a sample solution. A calibration curve was prepared using a standard solution with a known concentration, and the potassium concentration was determined from the measurement results.

(Example 1)
Waste cooking oil (mixed oil; acid value: 5.3, water content 0.09 wt%) (hereinafter referred to as “Sample A”) and waste cooking oil (mixed oil; acid value: 6.0, water content 0.19 wt. %) (Hereinafter referred to as “Sample B”), waste glycerin (potassium concentration: 6.1) produced as a by-product in the production of biodiesel fuel by transesterification of waste cooking oil (using methanol and potassium hydroxide) %, Water content 1.2% by weight) and mixed and stirred, and then allowed to stand.

  The amount of waste glycerin used was the amount generated by a single reaction. The waste glycerin produced by the previous production was stored and used for the next reaction. By mixing and stirring the waste cooking oil and waste glycerin and allowing to stand, the glycerin phase was separated and the edible oil phase was separated upward. From there, the upper phase of the edible oil was taken out, and the acid value (fatty acid amount) and water content before and after the treatment were measured. The resulting edible oil will be subjected to the next reaction process. The result of the preprocessing is shown in FIG. In both samples, the acid value decreased by about 1 and the water content decreased to about 0.05% by weight, indicating the effect of pretreatment.

(Example 2)
In order to remove fatty acids contained in raw oil, mainly waste cooking oil or vegetable oil, glycerin discharged in the biodiesel fuel production process (using methanol and potassium hydroxide) Processed. Dissolved glycerin (potassium concentration: 6.1%, water content 0.8% by weight) 50g was mixed with waste cooking oil (mixed oil; acid value: 3.5, water content 0.08% by weight) 300g. The mixture was stirred in a container at 40 ° C. for 10 minutes. Next, after leaving still for 1 hour, the lower phase glycerin phase was removed. The upper oil phase was used as a raw material for the reaction. The acid value, which is an index representing the fatty acid content, was 3.5 before the pretreatment and decreased to 2.0 after the pretreatment.

  A solution obtained by dissolving 4 g of potassium hydroxide in 47 g of methanol was mixed with 300 g of waste cooking oil, followed by stirring and mixing at 55 ° C. for 1 hour. Then, after stirring was stopped and heating was stopped for 8 hours, the components contained in the upper phase separated into two phases were analyzed. However, when the waste edible oil was used as a raw material, the unreacted content was 2.5%.

(Example 3)
In order to increase the yield of methyl ester, the reaction is carried out in a large excess of methanol, which is one of the raw materials, in many literatures and actual processes. Excess methanol is usually separated and recovered by a method such as flash distillation and reused. In this example, in a small-scale apparatus, in order to make it possible to avoid such a recovery portion, a condition was sought that would reduce the amount of excess methanol added as much as necessary.

  The experimental apparatus is shown in FIG. 300 g of waste cooking oil was put into a separable flask, and 3.6 g of potassium hydroxide dissolved in 42 g of methanol was mixed as the first stage reaction, and the reaction was carried out at 37 ° C. with stirring and mixing for 1 hour. After completion of the reaction, the mixture was allowed to stand for 1 hour, and then the upper methyl ester phase was separated with a separatory funnel and placed in a separable flask again. In the second stage reaction, 0.8 g of potassium hydroxide dissolved in 9.3 g of methanol was mixed, and the reaction was performed at 37 ° C. with stirring and mixing for 1 hour. Then, after leaving still for 8 hours, the upper phase was taken out as biodiesel fuel. The components contained in the product were analyzed by high performance liquid chromatography (HPLC). The column used was Shim-pack GPC-801 (Shimadzu Corporation).

  Table 1 shows the conditions for keeping the unreacted oil content below the standard value. As general conditions, numerical values of literature (Fujii et al., 7th Environmental Engineering Symposium '97 Proceedings, PP.175-178 (1997)) were also added to this table. Since methanol consumed in the reaction is 110 to 120 g per kg of waste cooking oil, about 180 g of unreacted methanol exceeding the consumption amount appears in a general method, but under this condition, it can be suppressed to about 50 g. Even in this condition, 220 g of methanol was required when pretreatment with waste glycerin was not performed.

Example 4
In order to remove alkali soap and methanol from biodiesel fuel produced using waste cooking oil as a raw material, post-treatment was performed using glycerin. 15 g of glycerin was mixed with 300 g of biodiesel fuel produced using a potassium hydroxide catalyst in the same manner as in Example 2, and the mixture was stirred in a container at 40 ° C. for 30 minutes. Next, after leaving still for 1 hour, the lower phase glycerin phase was removed. The potassium concentration in the biodiesel fuel before the treatment was 374 ppm, but it decreased to 28 ppm after the treatment. In addition, the methanol concentration decreased from 3.3% to 1.4%. The same treatment was performed once more on the biodiesel fuel after the treatment. At this time, the potassium concentration was 3 ppm, and the methanol concentration was reduced to 0.5%.

(Example 5)
In order to remove alkali soap and methanol from biodiesel fuel produced using waste cooking oil as a raw material, post-treatment was performed using glycerin. Into a container, 15 g of glycerin separated from the lower phase used in the second treatment of Example 4 was mixed with 300 g of biodiesel fuel produced using a potassium hydroxide catalyst in the same manner as in Example 2. At 40 ° C. for 30 minutes. Next, after leaving still for 1 hour, the lower phase glycerin phase was removed. To 300 g of the upper phase biodiesel fuel, 15 g of glycerin was mixed and stirred in a container at 40 ° C. for 30 minutes. Next, after leaving still for 1 hour, the lower phase glycerin phase was removed. This glycerin can be used for the first washing in the subsequent post-treatment. The potassium concentration in the biodiesel fuel before the treatment was 380 ppm, but it decreased to 26 ppm after the treatment. In addition, the methanol concentration decreased from 3.7% to 1.1%.

It is a figure which shows a fatty-acid methyl ester production | generation reaction pathway. It is a figure which shows the biodiesel fuel manufacturing process which combined the manufacturing method and post-processing of the biodiesel fuel by pre-processing and a two-stage reaction. It is a figure which shows the result of pre-processing. It is a figure which shows the experimental apparatus in a flask scale.

Claims (7)

The following steps:
(I) The waste glycerin produced as a by-product when producing biodiesel fuel by reacting the waste edible oil with a linear lower alcohol in the presence of an alkali catalyst and the waste edible oil used as a raw material are mixed, And (ii) a method for producing biodiesel fuel, comprising a transesterification step in which an alkali catalyst and a linear lower alcohol are added to waste cooking oil, a transesterification reaction is performed, and a by-produced glycerin phase is separated.   The process according to claim 1, wherein the linear lower alcohol is methanol or ethanol.   The method according to claim 1 or 2, wherein the waste glycerin used for the pretreatment contains an alkali catalyst.   The method according to any one of claims 1 to 3, wherein the transesterification step (ii) is performed in a two-stage reaction.   The method according to any one of claims 1 to 4, wherein the glycerin phase separated in the transesterification step (ii) is used as waste glycerin in the pretreatment step (i).   The crude biodiesel fuel obtained by separating the glycerin phase in the transesterification step of (ii) and glycerin are mixed, and then the glycerin phase is separated to obtain a biodiesel fuel. 2. The method according to item 1.   A method for purifying biodiesel fuel, comprising mixing a crude biodiesel fuel and glycerin and then separating the glycerin phase to obtain biodiesel fuel.

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