JP2007022988A - Method for producing alkyl ester of fatty acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a practical method for producing an alkyl ester of a fatty acid which can be carried out with the use of an inexpensive solid catalyst at an inexpensive operating cost as well. <P>SOLUTION: The method for producing an alkyl ester of a fatty acid by transesterification of oils and fats with an alcohol in the presence of calcium oxide comprises a pretreatment step of adjusting the water content in the oils and fats to ≤0.03 wt.% and the amount of free fatty acids to ≤0.05 wt.% before performing the transesterification and performing the transesterification of the oils and fats treated in the pretreatment step with an alcohol in a fixed catalyst bed reactor filled with calcium oxide. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a fatty acid alkyl ester. More specifically, a method for producing a fatty acid alkyl ester by a transesterification reaction with an alcohol using a fat or oil derived from a plant or the like, or a waste edible oil discarded from a restaurant, a food factory, a general household, or the like using the same. About.

  Fatty acid alkyl esters are important as a raw material for oil and fat products, for example, various surfactants, in the oil and fat chemical industry. Therefore, the manufacturing process is one of the most important processes as upstream processes in the oil and fat chemical industry.

  Among fatty acid alkyl esters, fatty acid alkyl esters obtained from lower alcohols as raw materials can be used as biomass-derived diesel fuel, and are thus attracting attention as new energy alternatives to petroleum.

  Cooking oil (waste cooking oil) that is used and disposed of in restaurants, food factories, general households, etc. is treated with a coagulant and buried in the soil, or discarded as household waste and incinerated. Although it is generally treated by a method, in recent years, with the increase in the philosophy of purification of the global environment, the movement of effective reuse of these waste cooking oils has been activated. As one of them, it has been a long time since attempts to produce fatty acid methyl esters by transesterification with methanol to produce oils suitable for diesel fuels have started.

  In other words, fatty acid methyl esters obtained from vegetable oils used as edible oils are similar to diesel oil in physical properties such as viscosity and specific gravity, and flammability, and can be used as biodiesel fuels that can be used without engine modification. Although it has been pointed out for a long time, it has recently been highlighted as a biofuel that can be recycled and is widely used especially in the United States and Europe.

  In the process of transesterification of fats and oils (triglycerides) and alcohol, which is currently in practical use in the oil and fat chemical industry and biodiesel fuel production, alcohol-soluble alkali catalysts such as sodium hydroxide and potassium hydroxide are used. ing. The fatty acid alkyl ester obtained contains a small amount of these alkali catalysts, but the alkali catalyst must be removed in consideration of the use as a fuel. Therefore, a method of generating wastewater such as water washing is adopted, but this wastewater treatment is costly. In addition, the alkali catalyst is also contained in the by-product glycerin layer obtained by separating the layers after the reaction, but glycerin itself has added value as a chemical product, and is intended to be purified and used for chemical products. It has been refined in view of its cost of purification.

  Therefore, the use of a solid catalyst that hardly elutes in the reaction solution has been proposed. Since the transesterification reaction is known to proceed even with an acid catalyst, various inorganic and organic solid acid catalysts have been proposed. However, its activity is much smaller than that of an alkali catalyst, and when an acid catalyst is used, the cost of the reaction is only equal to or higher than that of the case of employing ester water washing and glycerin purification. It hasn't arrived.

On the other hand, the use of an alkali solid catalyst having high activity has also been proposed (see Patent Documents 1 and 2). Patent Documents 1 and 2 disclose alcohol-insoluble, alkaline earth metal-containing hydroxides, oxides, and composite oxides, for example, alkaline earth metal compounds such as calcium oxide, calcium hydroxide, and calcium titanate. Has been.
JP 2001-271090 A JP 2002-294277 A

  However, in the method of Patent Document 1, since the reaction is carried out under a high reaction temperature of 90 to 240 ° C., a pressurizing condition is required when using a lower alcohol having a low boiling point such as methanol or ethanol. Therefore, since the reaction container which can be used is also limited, it is not economical. Moreover, since the perovskite type complex oxide used in the method of Patent Document 2 is obtained through a complicated process that is costly, development of a method capable of producing a fatty acid alkyl ester more economically is desired.

  In view of the prior art, an object of the present invention is to provide a practical method for producing a fatty acid alkyl ester that can be carried out using an inexpensive solid catalyst and at low operating costs.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have adjusted the amount of water and free fatty acid contained in fats and oils used as raw materials, and by using a fixed catalyst layer reactor, it is inexpensive. It has been found that fatty acid alkyl esters can be obtained with sufficient reaction efficiency efficiently and at a temperature below the boiling point of the lower alcohol using calcium oxide as a solid catalyst.

  The present invention is a method for producing a fatty acid alkyl ester by performing a transesterification reaction between fat and alcohol in the presence of calcium oxide, and before performing the transesterification reaction, the water content in the fat and oil is 0.03% by weight or less. , Having a pretreatment step of adjusting the amount of free fatty acid to 0.05% by weight or less, and performing a transesterification reaction between the fat and alcohol treated in the pretreatment step in a fixed catalyst layer reactor filled with calcium oxide. The present invention relates to a method for producing a fatty acid alkyl ester.

  According to the present invention, a fatty acid alkyl ester can be produced economically by using an inexpensive solid catalyst and at low operating costs.

  The fatty acid ester of the present invention is obtained by a transesterification reaction between fats and alcohols.

  The fatty acid alkyl ester obtained by the present invention is preferably in a liquid state for use as a diesel fuel. From this point of view, the fat used as a raw material in the present invention preferably contains a triglyceride having a saturated or unsaturated aliphatic alkyl group having 10 to 18 carbon atoms, more preferably 12 to 18 carbon atoms. . Preferred examples of the fats and oils in the present invention include one or a mixture of two or more selected from the group consisting of vegetable oils such as rapeseed oil, sesame oil, soybean oil, corn oil, palm oil, and papaya seed oil. But papaya seed oil is more preferred. Papaya seed oil contains ingredients that are toxic to animals and humans and cannot be used as edible oil (JOUNAL OF FOOD SCIENCE, Vol. 43 (1978), P225, Food Chemistry, 22 (1986) ), P259). Therefore, it can be rationally used by using it as a raw material for fatty acid alkyl esters suitably used for diesel fuel and the like.

  In addition, animal oil such as beef tallow is extremely important as a fuel raw material, and therefore animal oil-derived triglycerides may be appropriately contained as desired.

  The fats and oils used in the present invention are not limited to unused ones and may be waste edible oils, and waste edible oils are preferred from the viewpoints of economic and social demands. The waste edible oil in the present invention refers to edible oil that is used and discarded in restaurants, food factories, general households, and the like.

  Examples of the alcohol used in the present invention include 1 selected from the group consisting of alkyl alcohols having 1 to 4 carbon atoms such as methyl alcohol (methanol), ethyl alcohol (ethanol), propyl alcohol (propanol), and butyl alcohol (butanol). A seed | species or 2 or more types of mixtures is mentioned. The purity of the alcohol is not particularly limited, but a lower water content is preferable. Further, among the alkyl alcohols having 1 to 4 carbon atoms, methyl alcohol and ethyl alcohol are preferable, and methyl alcohol is more preferable in consideration of use of a fatty acid alkyl ester as a diesel fuel oil.

  In the present invention, it is preferable to use an alcohol in which an alkali metal hydroxide is dissolved. By using alcohol in which an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide is dissolved, free fatty acid reacts with the hydroxide in advance, so that it can be oxidized without affecting calcium oxide. The catalyst life of calcium can be further extended. Moreover, since the reaction rate is accelerated by the catalytic action of the hydroxide, the required amount of the calcium oxide catalyst can be reduced. However, in this case, soap produced by free fatty acid and hydroxide is mixed with glycerin produced as a by-product, and it is necessary to remove it. Therefore, both economic efficiency and technical simplicity are required in the entire process. In consideration of the above, it is preferable to select the amount of the hydroxide used.

  The amount of the alkali metal hydroxide dissolved in the alcohol is preferably 0.01 to 0.3 parts by weight with respect to 100 parts by weight of the fats and oils.

  In the present invention, the transesterification reaction between fat and alcohol is performed in the presence of calcium oxide. Calcium oxide is insoluble in fats and oils and is the most economically advantageous catalyst as a basic solid catalyst, but its reaction activity is very small compared to soluble catalysts such as sodium hydroxide and potassium hydroxide. . Therefore, in order to obtain practically sufficient activity, it is necessary to increase the reaction temperature or the catalyst concentration.

  However, as in the method of Patent Document 1, the reaction under high temperature conditions is not only energetically disadvantageous, but, for example, in order to produce fatty acid methyl ester which is the most common fuel, methanol as alcohol When using, higher pressure conditions are required. Accordingly, usable reactors are limited to pressure-resistant devices and the like, and in any case, it is not economical.

  On the other hand, as a method for increasing the catalyst concentration, a method using a fixed catalyst layer reactor capable of increasing the catalyst concentration as much as possible is known to those skilled in the art. It is usual to estimate and suggest the possibility of using a bed reactor. However, when calcium oxide is used, the catalytic activity is remarkably lowered, and it is extremely difficult to apply a flow system using a fixed catalyst bed reactor. For example, in Patent Document 1, it is said that the reaction mode may be performed by a batch method or a distribution method, but in Patent Document 1, an example specifically shows that It is only a batch method, that is, a batch method performed in a stirring tank using a powder catalyst.

  However, in the present invention, the transesterification reaction is carried out in a fixed catalyst layer reactor filled with calcium oxide by performing a pretreatment step for adjusting the water content and the free fatty acid content in the fat and oil before performing the transesterification reaction. Even if it goes, a fatty-acid alkylester can be manufactured efficiently. By performing the pretreatment step, the decomposition of calcium oxide into calcium hydroxide fine particles due to moisture in the raw material is suppressed, and not only the consumption of calcium oxide is reduced, but also the soap produced from calcium oxide and free fatty acids It is presumed that the decrease in the catalytic activity of calcium oxide due to is suppressed.

  From the above viewpoint, in the pretreatment step, the water content in the fat is adjusted to 0.03% by weight or less, preferably 0.01% by weight or less, and the free fatty acid content is adjusted to 0.05% by weight or less, preferably 0.02% by weight or less.

  Vegetable oils such as palm oil, which are considered to be optimal as raw materials for diesel fuel, usually contain about 0.2% by weight of water and about 2.5 to 3% by weight of free fatty acids. In addition, waste cooking oil is deteriorated and usually contains about 0.2% by weight of water and about 0.5-2% by weight of free fatty acids. Therefore, in the present invention, these oils and fats must be subjected to a pretreatment step, and the water content and free fatty acid content must be adjusted within a predetermined range.

  The method for adjusting the amount of water and free fatty acids in fats and oils is not particularly limited. For example, by adding alkaline water and removing the aqueous layer containing the generated soap, the pressure is reduced under a temperature condition of about 200 ° C. A method of removing free fatty acid by blowing steam under (2 to 5 mmHg) and further removing moisture by reducing pressure to reduce the amount of water and the amount of free fatty acid can be mentioned. Since carbon dioxide and the like are removed by such a method, the production of calcium carbonate can also be suppressed.

  As another method for reducing the amount of free fatty acids, there is a method in which free fatty acids in fats and oils are esterified under conditions of a large excess of alcohol under a solid acid catalyst. Water needs to be removed. When an alcohol having a boiling point lower than that of water is used, it is not easy to remove only water, and a complicated process such as dehydration by a molecular sieving method may be required.

  The fixed catalyst layer reactor used in the present invention is not particularly limited as long as it has a form in which the catalyst particles are packed in a state where the catalyst particles do not move from the reactor to the outside and from the outside to the reactor. The transesterification reaction may be either a batch type or a continuous type. However, in the present invention in which the consumption of calcium oxide is reduced, inexpensive calcium oxide is continuously supplied while being replenished in a practically reasonable cycle. A transesterification reaction can be performed.

  From the viewpoint of preventing accumulation of insoluble matter in the reactor, calcium oxide has an purity of preferably 90% or more, more preferably 95% or more, compared to calcium oxide supported on the carrier of insoluble matter. Calcium is preferable, and from the same viewpoint, granular calcium oxide having a size of about 1 to 5 mm is preferable.

  The amount of oil and alcohol supplied to the fixed catalyst layer reactor is preferably adjusted so that the liquid space velocity based on oil and fat is 0.1 to 10 / hr in the continuous type from the economical viewpoint, and the reaction is performed around the storage tank. In the case of a batch system in which a reactor is installed and the reaction liquid is circulated, it is preferable to adjust the liquid space velocity based on fats and oils to be 10 to 20 / hr from the viewpoint of increasing the contact efficiency between the reaction liquid and the catalyst. As for the usage-amount of alcohol, 15-35 weight part is preferable with respect to 100 weight part of fats and oils. Here, the liquid space velocity based on fat / oil is defined by a value obtained by dividing the volume of fat / oil to be supplied per unit time (supply volume velocity) by the volume of the reactor (catalyst layer volume). : Volume / hr) / (catalyst layer volume) = 1 / hr.

  The reaction temperature is preferably near the boiling point (approximately ± 2 ° C.) or lower than the boiling point of the alcohol to be used from the viewpoint of performing the reaction simply under normal pressure. In the method of the present invention, since the reaction can be carried out efficiently even at a temperature of 55 to 90 ° C., even in the case of producing a fatty acid methyl ester using methanol having a low boiling point, The transesterification reaction can proceed without increasing the pressure.

  By a transesterification reaction between fat and alcohol, a mixture composed mainly of the desired fatty acid alkyl ester and glycerin as a by-product is obtained.For example, after completion of the reaction, by leaving the reaction mixture or using a centrifuge, The fatty acid alkyl ester can be easily separated by phase-separating the reaction mixture using the specific gravity difference.

  Since the fatty acid alkyl ester obtained by the present invention has reduced mixing of alkali components, the fatty acid alkyl ester can be used as an alternative to light oil such as diesel fuel by purification such as washing with a small amount of water. In addition, glycerin produced as a by-product contains calcium hydroxide. This calcium hydroxide becomes a calcium sulfate precipitate when neutralized with sulfuric acid, and can be easily removed from glycerin. Therefore, glycerin produced as a by-product can be reused by a simple operation.

Example 1
Standard waste cooking oil collected from ordinary households and restaurants was prepared. The waste edible oil had a water content of 0.2% by weight and a free fatty acid content of 0.6% by weight.

[Pretreatment process]
Free fatty acids were removed by blowing 2 parts by weight of steam into 100 parts by weight of waste edible oil under the conditions of 200 ° C. and 2 to 5 mmHg. After stopping the steam supply, dehydration was performed under the same conditions. The obtained edible oil had a water content of 0.01% by weight and a free fatty acid content of 0.02% by weight.

[Transesterification]
The pretreated waste edible oil and methanol were supplied to each of the fixed catalyst bed reactors filled with the catalyst under the following reaction conditions, and transesterification was performed.
[Reaction conditions]
Reactor: total volume 70ml, catalyst bed volume 50ml
Catalyst: Calcium oxide provided by Yabashi Kogyo Co., Ltd. (purity 95%)
Select and collect 1mm square granules with amorphous particles, and fill 46g into the reactor. Reaction temperature: Controlled to 60 ° C with heat exchanger Waste cooking oil supply: 45g / hr (Liquid space velocity based on fat and oil 1 / hr)
Methanol supply amount: 9g / hr

  The reaction continued for 24 hours, and the product liquid was sampled every 5 hours from the start of the supply of waste edible oil and methanol. The sample was allowed to stand and separated, and the content of fatty acid alkyl ester contained in the upper layer was measured by gas chromatography after removing the topping of methanol from the sample. The lower glycerin layer was heated 24 hours later, and methanol topping was removed to determine its weight. In addition, after methanol topping, since the ester and oil which were melt | dissolved in glycerol with methanol isolate | separate, this is removed. The obtained glycerin layer was neutralized with sulfuric acid, and the calcium hydroxide content was estimated from the weight of the precipitate (calcium sulfate). In addition, for calcium oxide filled as a catalyst, after the reaction is completed, washed with hexane and dried, the reduction amount and the reduction rate (reduction amount / 46 × 100) with respect to the calcium oxide amount (46 g) charged in the reactor Calculated. The results are shown in Table 1.

Comparative Example 1
Fatty acid alkyl esters were produced in the same manner as in the Examples except that the waste edible oil was subjected to a transesterification reaction without being pretreated. Table 1 shows the analysis results of the samples.

  From the above results, it can be seen that in Example 1, the rate of decrease in calcium oxide is small and within a range that can be periodically replenished economically, and therefore it is possible to continuously produce fatty acid alkyl esters. On the other hand, in Comparative Example 1, the reduction rate of calcium oxide is large and the reaction rate is also reduced.

  The fatty acid alkyl ester obtained by the present invention can be suitably used as a diesel fuel that is attracting attention as a new energy substitute for petroleum.

Claims (4)

  A method for producing a fatty acid alkyl ester by performing a transesterification reaction between fat and alcohol in the presence of calcium oxide, and before performing the transesterification reaction, the water content in the fat and oil is 0.03% by weight or less, and the free fatty acid content. Of the fatty acid alkyl ester, having a pretreatment step of adjusting the content of the oil and fat to 0.05% by weight or less, and performing a transesterification reaction between the fat and alcohol treated in the pretreatment step in a fixed catalyst layer reactor filled with calcium oxide. Production method.   The production method according to claim 1, wherein the fat and oil to be used in the pretreatment step is waste edible oil or papaya seed oil.   The production method according to claim 1 or 2, wherein an alcohol in which an alkali metal hydroxide is dissolved is subjected to a transesterification reaction.   The production according to any one of claims 1 to 3, wherein the fat and alcohol are continuously supplied to the fixed catalyst layer reactor so that the liquid space velocity based on the fat and oil becomes 0.1 to 10 / hr to perform the transesterification reaction. Method.