JP6979656B2 - Methane fermentation method, methane fermentation system, waste recycling method and waste recycling system - Google Patents

Description

The present invention relates to a methane fermentation method, and in particular, a by-product containing glycerin (also referred to as “waste glycerin” in the present specification) obtained in the process of producing biodiesel fuel, a soap factory, an oil / fat factory, and a cosmetics factory. Efficient biogas containing methane from glycerin-containing waste produced as a by-product in processing processes using fats and oils as raw materials in pharmaceutical factories, and fatty acid glycerin ester-containing waste such as waste cooking oil and high acid value oil. It relates to a well-produced methane fermentation method. The present invention also relates to a methane fermentation system capable of realizing the above-mentioned methane fermentation method, a waste recycling method and a recycling system containing at least one of glycerin and a fatty acid glycerin ester.

In recent years, from the viewpoint of preventing global warming, the development of fuels that can replace conventional fossil fuels by reducing the generation of carbon dioxide and leading to the recycling of resources has been promoted. Biodiesel fuels made from such materials are attracting attention. As a method for synthesizing biodiesel fuel, a method of synthesizing fats and oils such as animal and plant oils and waste cooking oils and monohydric alcohols by transesterification reaction using an alkaline substance as a catalyst is the mainstream (for example, non-patented). Document 1). In this synthetic reaction, a by-product containing glycerin (waste glycerin) is also produced.

Examples of methods for industrially producing free fatty acids from fats and oils include high-temperature and high-pressure decomposition methods and enzymatic decomposition methods, all of which hydrolyze fats and oils derived from animals and plants to release fatty acids. .. Such hydrolysis also produces glycerin-containing by-products.

Waste containing glycerin contains a large amount of impurities such as catalysts and unreacted fats and oils. Therefore, although glycerin itself has a use as a raw material for pharmaceuticals and cosmetics, the above-mentioned glycerin-containing waste must be purified at a great cost in order to be used as a raw material for pharmaceuticals and cosmetics. , Was not practical. Therefore, glycerin-containing waste is often disposed of as industrial waste.

On the other hand, when fats and oils such as edible oil deteriorate, hydrolysis occurs, carbon chains are broken and further oxidation occurs, so that the oil has a high acid value (high acid value oil). Further, in the deoxidizing step in the refining of vegetable oils and fats, oil slag is separated from the oils and fats (crude oil). These high acid oils and slags are wastes containing fatty acid glycerin esters.

Under such circumstances, various attempts have been made to effectively utilize glycerin-containing waste such as waste glycerin from the viewpoint of reducing the environmental load. For example, when methane fermentation is performed using food waste, livestock manure, sludge, etc. as the main raw material, a method of using glycerin-containing waste as an auxiliary raw material for the purpose of promoting fermentation has been proposed (Patent Documents 1 to 5). .. Further, a method of utilizing glycerin-containing waste for the purpose of solubilizing the solid raw material when methane fermentation is performed using a raw material containing solid organic waste and oil-containing waste has also been proposed (Patent Document 6). ). Further, when methane fermentation is carried out using waste glycerin as a main raw material, a method of adding sugar to the raw material in order to promote methane fermentation has also been proposed (Patent Document 7).

Japanese Unexamined Patent Publication No. 2007-098239 Japanese Patent No. 5036938 Japanese Unexamined Patent Publication No. 2010-193767 Japanese Unexamined Patent Publication No. 2006-348191 Japanese Unexamined Patent Publication No. 2012-39912 Japanese Unexamined Patent Publication No. 2005-279411 Japanese Unexamined Patent Publication No. 2012-039975

Journal of Japanese Society of Marine Engineering, 2012, Vol. 47, No. 1, pp. 45-50

However, in the methods disclosed in Patent Documents 2 to 6, the glycerin-containing waste is merely used as an auxiliary raw material, and is still insufficient from the viewpoint of effective utilization of the glycerin-containing waste. Further, also in the method disclosed in Patent Document 7, the glycerin-containing waste is only used for solubilizing the raw material. On the other hand, in the method disclosed in Patent Document 8, sugar must be added to waste glycerin in order to promote methane fermentation, which is not yet sufficient from the viewpoint of production cost and practical use.

The present invention has been made in view of the above problems, and is a methane fermentation method for efficiently producing biogas containing methane from a raw material containing waste containing glycerin and waste containing fatty acid glycerin ester. The purpose is to provide.

As a result of diligent research to solve the above problems, the present inventor adjusts the raw material containing at least one of glycerin and fatty acid glycerin ester to an appropriate pH and separates and removes oil from the raw material in this separation / removal step. We have found that if methane fermentation is carried out using the obtained glycerin-containing liquid, biogas containing methane can be efficiently produced, and the present invention has been completed.
Specifically, the present invention is as follows.

[1] A methane fermentation method for producing biogas containing methane from a raw material containing at least one of glycerin and a fatty acid glycerin ester.
The first separation step of mixing the raw material and the inorganic acid to separate the first oil component and the first glycerin-containing liquid,
A neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance, and
A second separation step of separating the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A fermentation step in which methane fermentation is performed using the second glycerin-containing liquid, and
A methane fermentation method characterized by comprising.
[2] After the second separation step, alcohol is removed from the second glycerin-containing liquid, and the methane fermentation is performed using the second glycerin-containing liquid from which the alcohol has been separated and removed [1]. ] The methane fermentation method described in.
[3] The methane fermentation method according to [1] or [2], wherein in the first separation step, the pH of the mixed solution of the raw material and the inorganic acid is 3 or less.
[4] The methane according to any one of [1] to [3], which comprises neutralizing the first glycerin-containing liquid so that the pH becomes 4 to 8 in the neutralization step. Fermentation method.
[5] Any of [1] to [4], wherein in the methane fermentation step, an auxiliary raw material containing nitrogen and / or phosphorus is charged into the methane fermentation tank in addition to the second glycerin-containing liquid. The methane fermentation method according to item 1.
[6] The auxiliary raw material is one or more selected from the group consisting of food waste, livestock manure, phosphoric acid, phosphate, ammonia, and ammonium salt [5]. The described methane fermentation method.
[7] The auxiliary raw material is added so that the total nitrogen (TN) concentration of the digested sludge in the methane fermentation tank is 100 to 10,000 mg / L [5] or [6]. ] The methane fermentation method described in.
[8] It is characterized in that the input amount of the second glycerin-containing liquid is adjusted so that the CODcr load in the methane fermentation tank is 2 to 20 kg / m ^{3 · day [1] to [7].} The methane fermentation method according to any one of the above.
[9] It is characterized in that the supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than the methane fermentation of the second glycerin-containing liquid [1] to [ 8] The methane fermentation method according to any one of the items.
[10] A method other than the alkali catalyst method, at least selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. It comprises an esterification step to produce a fatty acid alkyl ester by one method.
The esterification step is characterized in that the first oil separated in the first separation step and / or the second oil separated in the second separation step is used as a raw material [1]. The methane fermentation method according to any one of [9].
[11] The methane fermentation method according to [10], which comprises a power generation step of generating electricity using at least a part of the fatty acid alkyl ester obtained in the esterification step.
[12] The supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than methane fermentation of the second glycerin-containing liquid, and the demand for the fatty acid alkyl ester is met. The methane fermentation method according to [11], wherein the supply amount of the fatty acid alkyl ester to the power generation step is adjusted accordingly.
[13] A methane fermentation system for producing biogas containing methane from a raw material containing at least one of glycerin and a fatty acid glycerin ester.
A first separation device that mixes the raw material and an inorganic acid to separate the first oil and the first glycerin-containing liquid.
A neutralizing device that neutralizes the first glycerin-containing liquid with an alkaline substance,
A second separation device that separates the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A methane fermentation apparatus that performs methane fermentation using the second glycerin-containing liquid, and
A methane fermentation system characterized by being equipped with.
[14] A glycerin storage tank for storing the second glycerin-containing liquid is provided after the second separation device.
The glycerin storage tank includes a detector for detecting the amount of the stored second glycerin-containing liquid.
The methane fermentation system according to [13], wherein the second glycerin-containing liquid is supplied to the methane fermentation apparatus when the amount of the second glycerin-containing liquid becomes a predetermined amount or more.
[15] A method other than the alkali catalyst method, which is selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. Esterification equipment for producing fatty acid alkyl esters by one method
The first oil separated in the first separation step and / or the second oil separated in the second separation step is supplied to the esterification apparatus as a raw material [13]. ] Or [14]. The methane fermentation system.
[16] A fatty acid alkyl ester storage tank for storing the fatty acid alkyl ester is provided after the esterification device.
A power generation device that generates electricity using the fatty acid alkyl ester is provided after the fatty acid alkyl ester storage tank.
The fatty acid alkyl ester storage tank comprises a detector that detects the amount of the stored fatty acid alkyl ester.
The methane fermentation system according to [15], wherein the fatty acid alkyl ester is supplied to the power generation device when the amount of the fatty acid alkyl ester exceeds a predetermined amount.
[17] A method for reusing waste containing at least one of glycerin and a fatty acid glycerin ester.
The first separation step of mixing the waste and the inorganic acid to separate the first oil and the first glycerin-containing liquid,
A neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance, and
A second separation step of separating the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A fermentation step in which methane fermentation is performed using the second glycerin-containing liquid, and
A waste recycling method characterized by providing.
[18] The second glycerin-containing liquid is characterized in that the supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than methane fermentation [17]. How to reuse waste.
[19] At least a method other than the alkali catalyst method, which is selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. It comprises an esterification step to produce a fatty acid alkyl ester by one method.
The esterification step is characterized in that the first oil separated in the first separation step and / or the second oil separated in the second separation step is used as a raw material [17]. Alternatively, the waste recycling method according to [18].
[20] The present invention comprises a power generation step of generating electricity using at least a part of the fatty acid alkyl ester obtained in the esterification step.
The supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than methane fermentation of the second glycerin-containing liquid, and the supply amount of the second glycerin-containing liquid is adjusted according to the demand for the fatty acid alkyl ester. The waste recycling method according to [19], wherein the supply amount of the fatty acid alkyl ester to the power generation process is adjusted.
[21] A system for reusing waste containing at least one of glycerin and a fatty acid glycerin ester.
A first separation device that mixes the waste with an inorganic acid and separates the first oil and the first glycerin-containing liquid.
A neutralizing device that neutralizes the first glycerin-containing liquid with an alkaline substance,
A second separation device that separates the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A methane fermentation apparatus that performs methane fermentation using the second glycerin-containing liquid, and
A waste recycling system characterized by being equipped with.
[22] A glycerin storage tank for storing the second glycerin-containing liquid is provided after the second separation device.
The glycerin storage tank includes a detector for detecting the amount of the stored second glycerin-containing liquid.
The waste reuse according to [21], wherein the second glycerin-containing liquid is supplied to the methane fermentation apparatus when the amount of the second glycerin-containing liquid becomes a predetermined amount or more. system.
[23] At least a method other than the alkali catalyst method, which is selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. Esterification equipment for producing fatty acid alkyl esters by one method
The first oil separated in the first separation step and / or the second oil separated in the second separation step is supplied to the esterification apparatus as a raw material [21]. ] Or the waste recycling system according to [22].
[24] A fatty acid alkyl ester storage tank for storing the fatty acid alkyl ester is provided after the esterification device.
A power generation device that generates electricity using the fatty acid alkyl ester is provided after the fatty acid alkyl ester storage tank.
The fatty acid alkyl ester storage tank comprises a detector that detects the amount of the stored fatty acid alkyl ester.
The waste recycling system according to [23], wherein the fatty acid alkyl ester is supplied to the power generation device when the amount of the fatty acid alkyl ester exceeds a predetermined amount.

According to the present invention, biogas containing methane can be efficiently produced from glycerin-containing waste and fatty acid glycerin ester-containing waste. In addition, the recovery rate of methane from glycerin-containing waste is dramatically increased as compared with the conventional method.

It is a figure which shows the flow of the methane fermentation method which concerns on one Embodiment of this invention. It is a figure which shows the flow of the esterification step (second esterification step) provided with the preferable embodiment of this invention. It is a figure explaining the methane fermentation system (waste reuse system) which concerns on one Embodiment of this invention. It is a schematic diagram which shows the experimental apparatus used in an Example. It is a graph which shows the gas generation amount in an Example.

Hereinafter, embodiments of the present invention will be described.
[Methane fermentation method]
The methane fermentation method according to the embodiment of the present invention is a method for producing a biogas containing methane from a raw material containing at least one of glycerin and a fatty acid glycerin ester, in which the raw material and an inorganic acid are mixed. From the first separation step of separating the first oil and the first glycerin-containing liquid; the neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance; from the neutralized glycerin-containing liquid. It comprises a second separation step of separating the second oil component and the precipitated inorganic salt to obtain a second glycerin-containing liquid; and a fermentation step of performing methane fermentation using the second glycerin-containing liquid.

FIG. 1 is a diagram showing a flow in a particularly suitable embodiment of the methane fermentation method according to the present embodiment. In FIG. 1, a first separation step of mixing an inorganic acid with a raw material containing glycerin-containing waste or fatty acid glycerin ester-containing waste to separate and remove a first oil component, followed by a first glycerin-containing liquid. The neutralization step, the second separation step of separating and removing the second oil and the inorganic salt from the neutralized glycerin-containing liquid, and the subsequent alcohol removing step of separating and removing the alcohol from the second glycerin-containing liquid are performed. It is illustrated. Further, a step of performing methane fermentation using the second glycerin-containing liquid obtained through these steps is illustrated. The alcohol removing step is an optional step, and the second glycerin-containing liquid may be supplied to the methane fermentation step without going through the alcohol removing step.

(1) Raw Material The raw material used in the present embodiment is not particularly limited as long as it contains at least one of glycerin and fatty acid glycerin ester.
Examples of the raw material containing glycerin include waste containing glycerin. Further, since the raw material containing the fatty acid glycerin ester produces glycerin by an acid-catalyzed transesterification reaction or the like in the first separation step described later, these can also be suitably used.
Hereinafter, the glycerin-containing waste and the fatty acid glycerin ester-containing waste will be described in some detail.

(1-1) Glycerin-containing waste The glycerin-containing waste used in this embodiment includes waste glycerin produced as a by-product in the biodiesel fuel production process, glycerin waste liquid produced as a by-product in the free fatty acid production process, and sweetness. Water, washing waste water of fatty acid alkyl ester, etc. can be used.

Here, the glycerin waste liquid produced as a by-product in the process of producing a free fatty acid is a waste produced as a by-product when hydrolyzing fats and oils of animals and plants to produce a free fatty acid. Examples of the method for producing free fatty acid by hydrolysis include a high-temperature high-pressure decomposition method and an enzymatic decomposition method. The glycerin waste liquid produced as a by-product in such a production process includes unreacted fats and oils, partially hydrolyzed fats and oils, and the like, in addition to glycerin.
In addition, sweet water is a by-product in the case of saponifying (alkaline hydrolysis) fats and oils to produce fatty acid salts (for example, in the manufacturing process of soap), and contains glycerin, water, alkali and the like.
Washing wastewater of fatty acid alkyl ester is wastewater generated when a reactant is washed in the process of manufacturing fatty acid alkyl ester such as biodiesel fuel, and is produced as a by-product in the production reaction of fatty acid alkyl ester in addition to water. It contains glycerin, and further contains unreacted free fatty acids and salts thereof, monohydric alcohols and the like.

Next, the waste glycerin produced as a by-product in the manufacturing process of biodiesel fuel will be described in a little more detail.
The fatty acid alkyl ester used as a biodiesel fuel can be obtained by adding a monohydric alcohol such as methanol and an alkaline catalyst such as potassium hydroxide to a raw material fat such as vegetable oil and performing a transesterification reaction.

Raw oils and fats for biodiesel fuel include vegetable oils such as rapeseed oil, palm oil, olive oil, sunflower oil, soybean oil, rice oil and cannabis oil; animal fats such as fish oil, pork fat and cow pig; waste cooking oil such as tempura oil; Can be used.
As the monohydric alcohol, methanol, ethanol, 1-propanol, ethylhexanol and the like can be used, and methanol and ethanol are preferable, and methanol is particularly preferable.
Potassium hydroxide, sodium hydroxide, calcium oxide and the like can be used as the alkaline catalyst, but potassium hydroxide is preferable from the viewpoint of precipitation property and ease of reuse of the salt separated and recovered in the present embodiment. ..

In the transesterification reaction, the fatty acid glycerin ester contained in the raw material fat and oil reacts with the monohydric alcohol to produce the fatty acid alkyl ester and glycerin. The obtained reaction solution is separated into a fatty acid alkyl ester phase and a waste glycerin phase, and in the production of biodiesel fuel, the obtained fatty acid alkyl ester phase is recovered and washed to obtain a biodiesel fuel. do.

On the other hand, the waste glycerin phase contains unreacted monohydric alcohol (especially methanol), unreacted fats and oils, fatty acids and salts thereof, alkaline catalysts, and impurities derived from raw material fats and oils, in addition to containing glycerin in a high concentration. included. The waste glycerin may be liquid waste glycerin or solid waste glycerin, but liquid waste glycerin is preferable from the viewpoint of workability, handling and the like.
The content of glycerin, monohydric alcohol, fat and oil, fatty acid and its salt in waste glycerin is not particularly limited, but usually, glycerin is 25% by mass or more and 65% by mass or less, and monohydric alcohol is 2% by mass with respect to the whole waste glycerin. % Or more and 20% by mass or less, and the total amount of fats and oils, fatty acids and salts thereof is often 30% by mass or more and 50% by mass or less.

Since the waste glycerin contains a large amount of an alkaline catalyst, the pH is often 9 or more, and in the present embodiment, it may be 9 to 13.
In the first separation step, the water content in the waste glycerin shall be 5% by mass or less from the viewpoint of facilitating the acid-catalyzed esterification reaction by the unreacted fats and oils and the monohydric alcohol contained in the waste glycerin. Is preferable, and it is particularly preferable that the content is 3% by mass or less. The water content of the waste glycerin can be appropriately adjusted by heating, depressurizing, using a desiccant or the like, permeating the purified glycerin, and the like.

Here, glycerin can be used as a raw material for pharmaceuticals and cosmetics, but in order to use glycerin contained in waste glycerin for such purposes, it is necessary to purify it with high purity, which requires a great deal of cost and energy. Therefore, waste glycerin has a considerably low utility value as glycerin, and has been difficult to process in the past.
However, according to the present embodiment, waste glycerin can be used as a main raw material for methane fermentation, and the environmental load can be reduced from the viewpoint of effectively utilizing waste glycerin, which is an industrial waste.

In the present embodiment, from the viewpoint of ease of use in the first separation step described later, among the glycerin-containing wastes described above, waste glycerin produced as a by-product in the manufacturing process of biodiesel fuel and free fatty acids It is preferable to use at least one kind of glycerin waste liquid produced as a by-product in the production process of the above, and it is particularly preferable to use waste glycerin produced as a by-product in the production process of biodiesel fuel.

(1-2) Fatty acid glycerin ester-containing waste In this embodiment, fatty acid glycerin ester-containing waste can also be used as a raw material. In the present embodiment, since the first separation step, the neutralization step and the second separation step using an inorganic acid are carried out, a raw material containing a fatty acid glycerin ester is used, and an acid catalyst ester in the first separation step is used. The yield of glycerin can also be increased by the chemical reaction.
Wastes containing fatty acid glycerin esters include, for example, waste cooking oil, foods containing expired oils and fats (temple oil, mayonnaise, dressings, butter, cream, cheese, etc.), animal and vegetable oils, and high acid value oils (glistrap oil, sewage). Oils, ground groove oils, waste liquid-treated recycled oils, etc.) containing fatty acid glycerin esters as main components; compositions containing fatty acid salts such as oil slags and soaps as main components; and the like can be mentioned.
In addition, in this specification, "the main component" means the component having the highest content in the composition (however, when the most abundant component is water, the component having the second highest content). This means that the content is preferably 40% by mass or more, more preferably 50% by mass or more.

Here, the high acid value oil refers to an oil or fat having an acid value of 10 mgKOH / g or more, and contains free fatty acid and the like in addition to the fatty acid glycerin ester which is the main component of the oil and fat. The acid value may be 20 mgKOH / g or more, and further may be 50 mgKOH / g or more. The upper limit of the acid value is usually 200 mgKOH / g or less.
The oil slag is a by-product separated from the oil (crude oil) in the deoxidizing step in the refining of vegetable oil, and contains fatty acid salts, fatty acid glycerin esters, alkalis, water and the like.

(1-3) Auxiliary raw materials In the present embodiment, as auxiliary raw materials, food waste, livestock manure, sludge, domestic wastewater (sewage / sewage), industrial wastewater, deodorized wastewater, and other chemical substances containing phosphorus and nitrogen, such as , Phosphate, phosphate, ammonia, ammonium salt, specifically, ammonium phosphate, ammonium chloride, ammonium sulfate, phosphoric acid, potassium phosphate, magnesium phosphate and the like can be added. The auxiliary raw material is used in the methane fermentation step described later, and when the second glycerin-containing liquid obtained by performing the neutralization step and the separation step of the waste glycerin or the like as the main raw material is put into the methane fermentation tank. Put it in the fermenter according to.

(2) First Separation Step In the first separation step, a raw material containing at least one of glycerin and a fatty acid glycerin ester is mixed with an inorganic acid, and the first oil component and the first glycerin-containing liquid are phased with each other. This is the process of separation.
The oil content separated in this step includes fatty acid glycerin ester and free fatty acid in addition to fatty acid alkyl ester.

When a raw material containing glycerin is used, particularly when waste glycerin is used, in this step, the salt of the fatty acid contained in the waste glycerin or the like is converted into a free fatty acid by an inorganic acid. Further, the fatty acid and its salt use an inorganic acid as an acid catalyst and produce a fatty acid alkyl ester by an esterification reaction with an unreacted monohydric alcohol contained in waste glycerin.

When a fatty acid glycerin ester-containing waste is used as a raw material, a fatty acid alkyl ester and glycerin are produced by a transesterification reaction with a monohydric alcohol. The monohydric alcohol in this case can be added separately, and for example, the monohydric alcohol recovered in the alcohol separation step described later can be used. Further, by treating the waste glycerin at the same time as the fatty acid glycerin ester-containing waste, the unreacted monohydric alcohol contained in the waste glycerin may be utilized.
When the first separation step is performed in the presence of a monohydric alcohol, this step can also be referred to as an acid-catalyzed esterification step. In comparison with the second esterification reaction described later, the first separation step may be referred to as "first esterification step".

Even when the monohydric alcohol is not contained, the fatty acid glycerin ester produces free fatty acid and glycerin in the presence of an acid in the first separation step. When the raw material contains a fatty acid salt, the fatty acid salt is converted into a free fatty acid by the acid, and it becomes easy to separate from glycerin.
Therefore, even when the raw material does not contain monohydric alcohol, the present embodiment can be suitably applied.

In this embodiment, since the first separation step is performed in the presence of an inorganic acid, various raw materials can be processed at the same time. In addition, by performing the first separation step, wastes containing glycerin and fatty acid glycerin esters such as waste glycerin, waste cooking oil, and high acid value oil can be effectively utilized, which can contribute to reduction of environmental load. can.
Among them, high acid value oil has a high acid value of 10 mgKOH / g or more, so that it is difficult to use it as a raw material for the transesterification reaction using the alkali catalyst described above. However, in the first separation step, which can be called an acid-catalyzed esterification reaction, high acid value oil can also be suitably used as a raw material.

When waste glycerin or fatty acid glycerin ester-containing waste is used as a raw material, the fatty acid alkyl ester and free fatty acid produced in the first separation step move to the oil phase consisting of the first oil, so that the first glycerin It can be separated from the contained liquid. When the oil phase is recovered, the obtained first oil (fatty acid alkyl ester, free fatty acid, etc.) is subjected to a further esterification reaction (esterification step described later), and finally biodiesel fuel, etc. Can be used as a raw material for.
On the other hand, the first glycerin-containing liquid is acidified by the addition of an inorganic acid. In addition, the first glycerin-containing liquid may contain an inorganic salt produced from an inorganic acid and an alkali contained in the glycerin-containing waste. A part of the inorganic salt may be precipitated, that is, the first glycerin-containing liquid may contain an acidic glycerin phase and the precipitated inorganic salt.

The raw material that can be used in the first separation step preferably has a water content of 10% by mass or less, and preferably 5% by mass or less. By using a raw material having a low water content (for example, waste glycerin having a low water content), it becomes easy to reduce the water content of the reaction solution described later. The water content of the raw material can be appropriately adjusted by heating, reducing the pressure, using a desiccant or the like, or permeating the purified glycerin.

Examples of the inorganic acid used in the first separation step include concentrated sulfuric acid, phosphoric acid, concentrated nitric acid, hydrogen chloride and the like, but concentrated sulfuric acid and phosphoric acid having a low water content are preferable, and concentrated sulfuric acid is particularly preferable.

In the first separation step, the pH of the mixed solution (reaction solution) of the raw material and the inorganic acid is preferably 3 or less, and particularly preferably 1 or less. The pH of the reaction solution can be adjusted by the amount of the above-mentioned inorganic acid added.
The water content of the reaction solution is preferably 10% by mass or less, and particularly preferably 0.5% by mass or less. The water content of the reaction solution can be appropriately adjusted by adjusting the water content and the input amount of each raw material, using a desiccant in the reaction solution, and the like.
By setting the pH and water content of the reaction solution within the above ranges, the efficiency of the acid-catalyzed esterification reaction can be enhanced, and the first oil component and the first glycerin-containing solution (containing an acidic glycerin phase and an inorganic salt) can be contained. ) And can be well separated.

The temperature of the reaction solution in the first separation step can be 30 to 64 ° C, and further can be 50 to 60 ° C. The reaction time can be 0.5 to 12 hours, more can be 4 to 12 hours. During this period, it is preferable to stir the reaction solution.
After the above reaction (or stirring) is completed, the mixture is allowed to stand for 0.2 to 12 hours to contain the first oil containing fatty acid alkyl ester, unreacted fat and oil, and the first containing an acidic glycerin phase and an inorganic salt. Separates from the glycerin-containing liquid. The first oil can be used to produce a fatty acid alkyl ester by subjecting it to a further acid-catalyzed esterification reaction. On the other hand, the first glycerin-containing liquid is subjected to the subsequent neutralization step.

(3) Neutralization Step The neutralization step is a step of neutralizing the first glycerin-containing liquid obtained in the first separation step with an alkaline substance.
As such an alkaline substance, hydroxides such as potassium hydroxide and sodium hydroxide can be used.

Further, as the alkaline substance, a substance containing glycerin can be used. Examples of such glycerin-containing alkaline substances include the above-mentioned waste glycerin and other by-products of the alkali-catalyzed transesterification reaction of fats and oils. Since these can not only neutralize acidic glycerin but also increase the yield of glycerin, the use of glycerin-containing alkaline substances is preferable from this viewpoint as well. The glycerin-containing alkaline substance may contain a fatty acid salt or a fatty acid glycerin ester.
The glycerin-containing alkaline substance preferably has a glycerin content of 25% by mass or more, and particularly preferably 50% by mass or more. The upper limit is not particularly limited, but may be, for example, 99% by mass or less, and may be 90% by mass or less.
The pH of the glycerin-containing alkaline substance is preferably 9 or more, and particularly preferably 9 to 13.

Further, as the alkaline substance, a composition containing a fatty acid salt as a main component may be used. Examples of alkaline substances containing fatty acid salts as main components include oil slags and alkaline soaps.

In the above neutralization step, the pH of the glycerin-containing liquid is 4.0 to 8.0, further 4.5 to 7.0, and particularly 5.0 to 6.5. It is preferable to neutralize to. By neutralizing the glycerin-containing liquid so that the pH is within such a range, the oil component can be easily separated and the inorganic salt can be easily precipitated in the subsequent second separation step. The pH of the glycerin-containing liquid can be appropriately adjusted by controlling the amount of the alkaline substance added.

In the neutralization step, it is preferable to add the alkaline substance while stirring the acidic glycerin-containing liquid so that the liquid property shifts from acidic to near neutral. As described above, a substance containing a fatty acid salt may be used as the alkaline substance used for neutralization, but the fatty acid salt is converted into a free fatty acid by the acid by the above addition order. The free fatty acid shifts from the glycerin-containing liquid to the phase-separated oil phase, and even if the pH of the glycerin-containing liquid becomes high, it becomes difficult to redissolve in the glycerin-containing liquid. This makes separation in the subsequent second separation step even easier. The fatty acid salt is contained not only in the above-mentioned substance containing a fatty acid salt as a main component, but also in a by-product of an alkali-catalyzed transesterification reaction of fats and oils and alkali hydrolysis.

The alkaline substance neutralizes the first glycerin-containing liquid obtained in the first separation step. The neutralized glycerin-containing liquid is subjected to the subsequent second separation step.

(4) Second Separation Step In the second separation step, the second oil and the precipitated inorganic salt are separated from the neutralized glycerin-containing liquid obtained in the neutralization step, and the second glycerin is contained. This is the process of obtaining a liquid.

Here, the second oil to be separated includes fats and oils and fatty acids that were not separated even in the first separation step and remained in the first glycerin-containing liquid, as well as fats and oils derived from alkaline substances added in the neutralization step. And free fatty acids are included.

The inorganic salt separated in the second separation step is a salt of an inorganic acid (concentrated sulfuric acid, etc.) added in the first separation step and an alkali (potassium, sodium, etc.), preferably potassium sulfate. Is. The alkali is contained in a raw material (waste glycerin or the like) added to the first separation step or an alkaline substance added in the neutralization step, and an inorganic salt is contained in the first separation step or neutralization step. It is precipitating.

On the other hand, the glycerin-containing liquid contains, in addition to glycerin, monohydric alcohol derived from waste glycerin, water and the like. Since oil and inorganic salts have low solubility in such a glycerin-containing liquid, they are separated from the glycerin-containing liquid.

In this second separation step, after the neutralized raw material is allowed to stand for about 3 to 12 hours, the upper liquid (oil) and the lower liquid (glycerin-containing liquid) are separately recovered, and the glycerin-containing liquid to be the lower liquid is collected. Although it can be obtained, it is preferable to increase the separation rate by centrifugation or the like. In such a centrifuge, a three-phase separation type centrifuge capable of separating an upper liquid (that is, an oil content), a lower liquid (that is, a glycerin-containing liquid) and a solid substance (that is, an inorganic salt) can be preferably used. .. When a large amount of inorganic salt is deposited, a certain amount of inorganic salt is separated in advance by a centrifuge capable of solid-liquid separation such as a decanter type, and then the liquid phase portion is further separated by a three-phase separation type centrifuge. It is preferable to separate by.

The second oil component obtained in the second separation step is, for example, combined with the first oil component separated in the first separation step and subjected to a further acid-catalyzed esterification reaction (esterification step described later). It can be used to produce fatty acid alkyl esters. Specifically, the second oil component obtained in the second separation step can be used as a raw material for producing fatty acid methyl ester (FAME) as a biodiesel fuel. That is, methanol and a catalyst are added to this oil to cause a methyl esterification reaction.
Further, the inorganic salt can be used as a raw material for an inorganic fertilizer or the like through, for example, a washing step or the like.
On the other hand, the second glycerin-containing liquid obtained as described above can be used as it is as a carbon source for methane fermentation in the methane fermentation step described later, but when removing the monohydric alcohol derived from the raw material or the like. May be further subjected to an alcohol removing step.
Further, by subjecting it to the alcohol removal step, it may be preferable from the viewpoint of improving the efficiency of methane fermentation, from the viewpoint of workability, and from the viewpoint of avoiding the need to treat it as a dangerous substance. On the other hand, from the viewpoint of reducing the operating cost required for alcohol removal, or when the presence of the monohydric alcohol does not matter in the second glycerin-containing liquid (for example, the raw material does not contain the monohydric alcohol and contains the second glycerin). If the liquid does not contain monohydric alcohol, etc.), the second glycerin-containing liquid may be supplied to the methane fermentation step as it is without being subjected to the alcohol removal step.

(5) Alcohol removal step The alcohol removing step is a step of removing monovalent alcohol (methanol, etc.) from the second glycerin-containing liquid obtained in the second separation step, and is an optional step to be carried out as necessary. Is.
The second glycerin-containing liquid may contain a monohydric alcohol derived from waste glycerin and remaining in the first separation step (acid-catalyzed esterification reaction). The monohydric alcohol can be used for methane fermentation even if it remains, but the efficiency of methane fermentation can be improved by removing it.

In the step of separating / removing the monohydric alcohol, a vacuum distillation method, a gas-liquid contact method, a membrane separation method and the like can be adopted.
The vacuum distillation method is a method in which a glycerin-containing liquid is heated (for example, about 60 ° C.) to evaporate a monohydric alcohol such as methanol, and then the pressure is reduced to separate the monohydric alcohol or the like. The separated monohydric alcohol or the like can be cooled and recovered.
The gas-liquid contact method is a method in which a glycerin-containing liquid is brought into contact with the gas phase as fine droplets, and a monohydric alcohol having a low boiling point is transferred to the gas phase for separation. Can be adopted for.
The membrane separation method is a method using a membrane that preferentially permeates a monohydric alcohol.
Incidentally, the monohydric alcohol such as methanol recovered by distilling the second glycerin-containing liquid can be positively used for the production of biodiesel fuel.

The second glycerin-containing liquid may further contain water. Such water does not interfere with the effect as a carbon source in methane fermentation and may remain in purified glycerin, but in, for example, in a vacuum distillation method or a gas-liquid contact method, the water moves to the gas phase together with the monohydric alcohol. Therefore, it is possible to remove water.
Further, before or after the alcohol separation step of separating the monohydric alcohol, further purification treatment may be performed using an ion exchange method, activated clay, diatomaceous earth, carbon, zeolite or the like.

The monohydric alcohol separated in this step can be purified as it is or, if necessary, by redistillation or the like, and can be reused as a raw material for an alkali-catalyzed transesterification reaction or an acid-catalyzed esterification reaction. Further, it may be used as a cleaning liquid or the like for the inorganic salt or the like separated in the second separation step.

The glycerin obtained by the above method has a high purity, and for example, the purity of glycerin can be 85% by mass or more, 90% by mass or more, 97% by mass or more, and further 99% by mass or more. In the above method, by going through the above-mentioned first separation step, neutralization step and second separation step, although waste glycerin or the like is a raw material, and although it is a relatively simple method, the above method is used. Purified glycerin with high purity as in the numerical range can be obtained.

The second glycerin-containing liquid obtained by the above method is subjected to the methane fermentation step described later, and is also used as a release agent for asphalt-containing compositions and cement-containing compositions; as an organic carbon source in biological nitrification and denitrification treatment. Denitrifying agents used; can be used in a variety of applications such as industrial raw materials (eg, raw materials for fatty acid glycerin esters). Further, by further subjecting it to a process such as distillation, it can be applied to applications requiring higher purity (for example, cosmetics, foods and drinks, pharmaceuticals, etc.).

(6) Methane fermentation step The methane fermentation step can be carried out according to a conventional method except that methane fermentation is carried out using the second glycerin-containing liquid obtained through the above-mentioned steps.
More specifically, the above-mentioned second glycerin-containing liquid is put into the methane fermenter, and at this time, it is preferable to add the above-mentioned auxiliary raw material.

The methane fermentation tank is a closed reaction tank, and the inside is filled with methane bacteria, which are anaerobic microorganisms, and is maintained under anaerobic conditions. Further, in the methane fermentation tank, a stirrer is installed so that methane bacteria are uniformly dispersed and act in a mixture of sludge, main raw material, auxiliary raw material, and other organic substances / essential elements that promote methane fermentation. In the methane fermentation tank, the above-mentioned mixture is decomposed by anaerobic microorganisms, and methane gas and digestive juice are produced as the methane fermentation progresses. Specifically, in the methane fermentation tank, biogas mainly composed of methane gas produced by methane fermentation stays in the uppermost cavity of the fermenter, and digestive juice is stored in the lower part.
In the present embodiment, either medium-temperature fermentation performed while keeping the inside of the fermenter at around 37 ° C. or high-temperature fermentation performed while keeping the temperature around 55 ° C. may be used, and methane fermentation is performed while stirring the contents in an anaerobic atmosphere. It is preferable to carry out.

The second glycerin-containing liquid used in the present embodiment preferably has an n-hexane extractant (n-Hex) of 10,000 mg / kg or less, more preferably 5,000 mg / kg or less. It is particularly preferably 2,000 mg / kg or less. Here, the n-hexane extract substance is a general term for non-volatile substances extracted by n-hexane, which is an organic solvent, and is used as an index showing the amount of "oil, etc." in water. The second glycerin-containing liquid used in the present embodiment has a small value of n-Hex because oil is removed from the glycerin-containing waste. By using the second glycerin-containing liquid from which the oil component has been removed, the efficiency of methane fermentation (particularly the methane production rate) can be improved.

In the present embodiment, it is preferable to appropriately adjust the input amount of the second glycerin-containing liquid so that the CODcr load in the methane fermentation tank in the methane fermentation step is within the range of 2 to 20 kg / m ^{3 · day.} .. More preferably, the CODcr load in the methane fermenter is 5 to 10 kg / m ³ · day. If the CODcr load is applied too much, it becomes difficult for methane fermentation to proceed rapidly. By adjusting the inside of the fermenter to the range of the CODcr load as described above, it becomes easy to maintain the rate of methane fermentation.

The addition of auxiliary materials is for the purpose of supplementing nutrients (nitrogen, phosphorus, and other essential elements) necessary for the activity of methane bacteria. The amount of the auxiliary raw material added is preferably adjusted so that the total nitrogen (TN) concentration of the digested sludge in the methane fermenter is 100 to 10,000 mg / liter. More preferably, it is added so that the TN concentration is 500 to 5,000 mg / liter. When the input amount of the auxiliary raw material is adjusted so as to have such a concentration, methane fermentation proceeds favorably and the amount of methane produced increases.

The methane gas produced in the methane fermenter is appropriately recovered and used as a fuel for power generation, etc., and after purification, it is used for various purposes as high-purity methane gas.

(7) Esterification Step In the first and second separation steps described above, the first and second oil components are recovered from the separated oil phases, respectively. It is conceivable that these are circulated and supplied as raw materials in the production of fatty acid alkyl esters by the alkaline catalyst method, but since the purity is not necessarily high, if they are used as raw materials as they are, the fatty acid alkyl esters can be efficiently produced. It can be difficult to do. Further, the first and / or the second oil contains oils and fats having a high acid value such as free fatty acids, and in particular, the first oil can be said to be an esterification reaction using an acid catalyst. Since it was separated in one separation step (first esterification step), it has an acidic oil content. Therefore, it becomes more difficult to use the first and second oils as they are as a raw material for producing a fatty acid alkyl ester using an alkali catalyst.

However, if it is a method other than the alkaline catalyst method, it is possible to produce a fatty acid alkyl ester even with a fat or oil having a high acid value. Therefore, in the present embodiment, it is preferable to include an esterification step of producing a fatty acid alkyl ester by a method other than the alkaline catalyst method.
In comparison with the above-mentioned first separation step (first esterification step), this step may be referred to as "second esterification step".

In the second esterification step, it is preferable to use the first oil separated in the first separation step and / or the second oil separated in the second separation step as a raw material.
As the other raw material, the same raw material (high acid value oil or the like) as in the above acid reaction step (first esterification step) can be used.

By using these as raw materials, it becomes possible to more efficiently recycle industrial waste in the above-mentioned methane fermentation method. Any method other than the alkaline catalyst method can be preferably used even with these raw materials.

Further, in the second esterification step, it is preferable to use the monohydric alcohol separated in the alcohol separation step as a raw material. This makes it possible to recycle industrial waste more efficiently in the above-mentioned methane fermentation method.

The method that can be adopted in the second esterification step is a method other than the alkali catalyst method, and more specifically, an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, and the like. Subcritical methods and solid catalyst methods are exemplified. With these methods, transesterification reaction can be carried out with a monohydric alcohol such as methanol, even if it is a waste cooking oil or fat or oil having a high acid value, or even a fat or oil containing unreacted free fatty acid. ..

In the second esterification step, glycerin is by-produced together with the oil containing the fatty acid alkyl ester. The oil content obtained in the second esterification step and the glycerin-containing liquid can be phase-separated by standing, centrifuging or the like. The separated oil can be used as a biodiesel fuel by recovering the fatty acid alkyl ester. On the other hand, the by-produced glycerin can be supplied to the neutralization step together with the first glycerin-containing liquid obtained in the first separation step (first esterification step), for example. With this configuration, the glycerin produced as a by-product in the second esterification step can be made into a part of the second glycerin-containing liquid through the neutralization step, the second separation step, and the like. It can be recycled more efficiently.

Among the methods other than the alkaline catalyst method described above, it is particularly preferable to adopt the acid catalyst method as the second esterification step.
As shown in FIG. 2, when the acid catalyst method is adopted as the second esterification step, the first oil component and / or the second oil component is used as a raw material. As other raw materials, monovalent alcohol recovered in the alcohol removing step can be used, and further, the same raw materials (high acid value oil, etc.) as in the first separation step (first esterification step) can be used. May be used.
The reaction solution obtained in the second esterification step is separated into an oil component containing a fatty acid alkyl ester and a glycerin-containing solution containing by-produced glycerin, an acid catalyst and a salt thereof. Both the obtained oil and the glycerin-containing liquid are acidic, and the acidic glycerin-containing liquid can be supplied to the neutralization step or the like.

On the other hand, it is preferable to neutralize or dehydrate the oil containing the fatty acid alkyl ester. Here, as a method of neutralization / dehydration, a method using waste glycerin produced as a by-product in the manufacturing process of biodiesel fuel is preferably exemplified. Specifically, waste glycerin produced as a by-product in the manufacturing process of biodiesel fuel is dealcoholicized and stored in a tank or the like, and neutralizing oil is added from the lower part of the tank to bring it into contact with waste glycerin. .. As a result, the acidic oil is neutralized by the alkali of the waste glycerin, and the water and the monohydric alcohol contained in the oil are absorbed by the waste glycerin solution. Then, the oil content charged from the lower part overflows from the upper part due to the difference in specific gravity, so that it can be easily recovered. By such a method, neutralization, dehydration and dealcoholization can be performed at the same time, and high-quality oil can be easily obtained. The waste glycerin liquid that has absorbed water and the monohydric alcohol can be supplied to the above-mentioned neutralization step, and can be made into a part of the second glycerin-containing liquid through the second separation step and the like.

In the second esterification step, as a method other than the acid catalyst method, a biocatalyst method, a supercritical method, and a subcritical method can be preferably exemplified.
The biocatalyst method is a method for promoting a transesterification reaction by using a lipase or a phospholipase having a catalytic activity for a transesterification reaction. The biocatalyst method has a characteristic that the reaction conditions are mild, but the transesterification reaction can be promoted even for fats and oils having a high acid value, and there are few by-products.
In the supercritical method and subcritical method, the phase state of a substance is changed from two phases of gas and liquid to two phases of liquid and liquid, and further, by adjusting the temperature and pressure to change the raw material to the supercritical state or the subcritical state. This is a method of promoting hydrolysis by lowering the reaction system to one phase and changing the reaction system, which originally required the use of a catalyst, to a non-catalytic system.

By performing such a second esterification step, it becomes possible to recycle industrial waste more efficiently. The obtained fatty acid alkyl ester can be shipped as biodiesel fuel, bioheavy oil, etc., and energy can be recovered by subjecting it to power generation or the like. That is, it may further include a power generation step of generating electricity using the fatty acid alkyl ester obtained in the second esterification step.

(8) Modification Example The method according to the present invention is not limited to the above embodiment, and can be variously modified at the implementation stage without departing from the gist thereof.
For example, the methane fermentation method can be "a method of reusing waste containing at least one of glycerin and fatty acid glycerin ester".

Further, as described above, the second glycerin-containing liquid obtained in the second separation step or the glycerin-containing liquid obtained by separating and removing alcohol in the alcohol removing step can be applied to various uses as purified glycerin.
Therefore, in the present invention, the obtained second glycerin-containing liquid (purified glycerin) may be used for applications other than methane fermentation, and the balance may be subjected to the above-mentioned methane fermentation step.
That is, the obtained second glycerin-containing liquid (purified glycerin) is provided with the above-mentioned first separation step, neutralization step and second separation step (including, if necessary, the alcohol removal step). ) Is used for applications other than methane fermentation, and the remainder of the second glycerin-containing liquid is subjected to the above-mentioned methane fermentation step, which is one of the modifications of the present invention.
When a part of the purified glycerin is used for a purpose other than methane fermentation, the method of this embodiment can be "a method of purifying glycerin from a raw material containing at least one of glycerin and a fatty acid glycerin ester".

Applications other than methane fermentation include, for example, stripping agents for asphalt-containing compositions and cement-containing compositions; denitrifying agents used as organic carbon sources in biological nitrification and denitrification treatments; industrial raw materials (eg, fatty acid glycerin esters). Raw material); Applications that require high purity of glycerin (for example, cosmetics, foods and drinks, pharmaceuticals, etc.) and the like can be mentioned.
In this modification, the amount of the second glycerin-containing liquid to be subjected to methane fermentation may be adjusted according to the demand for applications other than methane fermentation.

Further, as described above, in the above-mentioned method, glycerin-containing waste and fatty acid glycerin ester-containing waste can be used as raw materials, and a second glycerin-containing liquid (purified glycerin) and an oil component (first and) can be used. / Or a second oil) can be obtained. The second glycerin-containing liquid can be used for applications other than methane fermentation, while the oil content can be subjected to the above-mentioned second esterification step to produce a fatty acid alkyl ester.
Here, the glycerin-containing waste and the fatty acid glycerin ester-containing waste, which are raw materials, have various origins, compositions, and the like, and the content ratios of glycerin and fatty acid glycerin ester differ greatly depending on the raw materials. Therefore, the ratio of the ratio of the glycerin-containing liquid separated by the above method to the oil content (first and / or second oil content) also differs depending on the raw material, and the obtained second glycerin-containing liquid is also obtained. The ratio of (purified glycerin) to the fatty acid alkyl ester also varies depending on the raw material. In this case, it may be difficult to adjust the production amount according to the demand for refined glycerin (uses other than methane fermentation) and the demand for fatty acid alkyl esters (biodiesel fuel, etc.).

On the other hand, the supply amount of the second glycerin-containing liquid to the methane fermentation process is adjusted according to the demand for applications other than methane fermentation, and the fatty acid alkyl ester power generation process is adjusted to meet the demand for the fatty acid alkyl ester. Supply amount can be adjusted.
That is, it is provided with the above-mentioned first separation step, neutralization step, second separation step and methane fermentation step, and further provided with the above-mentioned second esterification step and power generation step, and is obtained in the second separation step. The supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than methane fermentation of the second glycerin-containing liquid, and the fatty acid alkyl obtained in the second esterification step is adjusted. The aspect of adjusting the supply amount of the fatty acid alkyl ester to the power generation process according to the demand for the ester is one of the modifications of the present invention.
The demand for the second glycerin-containing liquid for purposes other than methane fermentation can be rephrased as the shipment amount of the second glycerin-containing liquid that is not supplied to the methane fermentation step. Further, the demand for the fatty acid alkyl ester can be rephrased as the shipment amount of the fatty acid alkyl ester that is not supplied to the power generation process.

With this configuration, even if the content ratio of glycerin or fatty acid glycerin ester fluctuates greatly depending on the raw material, it is possible to flexibly respond to the demand for purified glycerin or fatty acid alkyl ester. Therefore, the method of this embodiment is particularly suitable as a method for reusing waste containing at least one of glycerin and fatty acid glycerin ester.

[Methane fermentation system]
A methane fermentation system according to an embodiment of the present invention, which can realize the methane fermentation method according to the above-described embodiment, will be described.
Similar to the above-mentioned methane fermentation method, the methane fermentation system described below can be a system for reusing waste containing at least one of glycerin and fatty acid glycerin ester.

As shown in FIG. 3, the methane fermentation system (waste recycling system) 100 includes a first separation device 101, a neutralization device 102, a second separation device 103, and a methane fermentation device 104. It is configured.
The methane fermentation system 100 exemplified in FIG. 3 further includes storage tanks 105 and 107 for storing glycerin-containing liquids, an alcohol removing device 106, a second esterification device 111, and a storage tank 112 for storing fatty acid alkyl esters. And are illustrated to include a power generator 113.

A composition containing glycerin or fatty acid glycerin ester as a raw material (showing glycerin-containing waste and fatty acid glycerin ester-containing waste in FIG. 3) is charged into the first separation device 101 together with an inorganic acid, and the acid is charged. A catalytic transesterification reaction or the like is carried out. After a certain period of time, the reaction solution is phase-separated into an acidic glycerin phase (first glycerin-containing solution) and an oil phase (first oil component).
The first glycerin-containing liquid contains glycerin, an inorganic salt, a monohydric alcohol and the like, and the first glycerin-containing liquid is supplied to the neutralizing device 102, and an alkaline substance is added to neutralize the first glycerin-containing liquid.

The neutralized glycerin-containing liquid obtained by neutralizing with the neutralizing device 102 is supplied to the second separation device 103 and separated into a second glycerin-containing liquid, an oil component (second oil component), and an inorganic salt. Will be done. As the second separation device 103, a three-phase separation type centrifuge or the like can be preferably used, and a centrifuge or the like capable of solid-liquid separation such as a decanter type may be provided in front of the three-phase separation type centrifuge or the like.
The inorganic salt separated from the second separation device 103 can be used as fertilizer or the like.

The second glycerin-containing liquid separated by the second separation device 103 is supplied to the methane fermentation device 104. A storage tank 105 for storing the second glycerin-containing liquid may be provided between the second separation device 103 and the methane fermentation device 104.

If the monohydric alcohol remains in the second glycerin-containing liquid separated by the second separation device 103, it may be separated and removed by the alcohol removing device 106. The second glycerin-containing liquid from which the alcohol has been removed is stored in the glycerin storage tank 107 and can be used for applications other than methane fermentation. Further, the separated and removed monohydric alcohol may be configured to be supplied to the second esterification apparatus 111 described later.
When the presence of the monohydric alcohol does not matter in the second glycerin-containing liquid (for example, when the raw material does not contain the monohydric alcohol and the second glycerin-containing liquid does not contain the monohydric alcohol). , As shown by the one-point chain line in FIG. 3, the second glycerin-containing liquid may be configured to bypass the alcohol removing device 106 and be supplied to the storage tank 107.

By the way, as described above, the content ratio of glycerin and fatty acid glycerin ester in the raw material varies greatly depending on the raw material. When the production amount of the second glycerin-containing liquid is larger than the demand for the second glycerin-containing liquid for applications other than methane fermentation (the shipment amount of the second glycerin-containing liquid not supplied to the methane fermentation apparatus 104), the second glycerin-containing liquid is produced. The amount of storage of the second glycerin-containing liquid increases.
Therefore, in a preferred embodiment, the glycerin storage tank 107 includes a level meter L1 for detecting the level of the second glycerin-containing liquid. Then, when the level meter L1 detects that the level of the second glycerin-containing liquid is equal to or higher than the predetermined value, the methane fermentation system 100 opens the valve V1 and uses the second glycerin-containing liquid in the methane fermentation apparatus 104. Can be configured to supply to.
With this configuration, even if the content ratio of glycerin or fatty acid glycerin ester fluctuates greatly depending on the raw material, it is possible to flexibly respond to the demand for purified glycerin.
In this case, the glycerin storage tank 107 may be provided with a detector capable of detecting the amount of the second glycerin-containing liquid, and for example, a weighing scale may be used instead of the level meter.

Although it is shown in FIG. 3 that the second glycerin-containing liquid separated by the second separating device 103 is separately supplied to the methane fermentation device 104 and the alcohol removing device 106. The embodiments are not limited to this. For example, from the viewpoint of improving the efficiency of methane fermentation, the glycerin-containing liquid from which the alcohol has been removed by the alcohol removing device 106 may be supplied to the methane fermentation device 104.
In such a configuration, when the glycerin storage tank 107 further includes a level meter L1, a valve V1 is provided in a path for supplying a second glycerin-containing liquid from the alcohol removing device 106 (or the glycerin storage tank 107) to the methane fermentation device 104. The valve V1 can be opened and closed according to the level of the glycerin-containing liquid detected by the level meter L1.

Further, the alcohol removing device 106 has an arbitrary configuration and can be omitted in this system. In such a case, the storage tank 105 can also be omitted. In such a configuration, when the glycerin storage tank 107 further includes a level meter L1, a valve V1 is provided in the path for supplying the second glycerin-containing liquid from the glycerin storage tank 107 to the methane fermentation apparatus 104, and the valve V1 is detected by the level meter L1. The valve V1 may be opened and closed according to the level of the second glycerin-containing liquid.

In a preferred embodiment of the present embodiment, the methane fermentation system 100 further comprises a second esterification device 111. The second esterification apparatus 111 is composed of an esterification reaction tank for producing a fatty acid alkyl ester by a method other than the alkaline catalyst method. The second esterification device 111 contains the oil component (first oil component) separated by the first separation device 101 and / or the oil component (second oil component) separated by the second separation device 103. Be supplied. Further, the monohydric alcohol separated / removed by the alcohol removing device 106 may be supplied.

In the second esterification apparatus 111, a method other than the alkali catalyst method, more specifically, an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method or a solid is used. The catalytic method is carried out. An esterification reaction (including a transesterification reaction) is carried out by any of these methods to separate the oil containing the fatty acid alkyl ester from the glycerin-containing liquid. The by-produced glycerin-containing liquid can be, for example, supplied to the above-mentioned neutralization device 102, neutralized and separated, and recycled as a raw material for methane fermentation and the like.
When the esterification reaction is carried out by the acid catalyst method in the second esterification apparatus 111, the oil component containing the fatty acid alkyl ester is acidic. Such acidic oil may be neutralized, dehydrated, and dealcoholicized at the same time by injecting the acidic oil component from the lower part of a tank or the like (not shown) storing waste glycerin and overflowing it to the upper part of the glycerin phase.
The fatty acid alkyl ester thus obtained is stored in the fatty acid alkyl ester storage tank 112.

In a more preferred embodiment, the methane fermentation system 100 according to the present embodiment may include a power generation device 113 that generates power using a fatty acid alkyl ester after the storage tank 112. By providing the power generation device 113, not only the fatty acid alkyl ester can be shipped as a biodiesel fuel or the like, but also energy can be recovered from the fatty acid alkyl ester in the methane fermentation system 100.

Further, as described above, the content ratio of glycerin and fatty acid glycerin ester in the raw material varies greatly depending on the raw material. When the production amount of the fatty acid alkyl ester is larger than the demand for the fatty acid alkyl ester (the shipment amount of the fatty acid alkyl ester not supplied to the power generation 113), the storage amount of the fatty acid alkyl ester is large.
Therefore, in a preferred embodiment, the fatty acid alkyl ester storage tank 112 includes a level meter L2 for detecting the level of the fatty acid alkyl ester. Then, when it is detected by the level meter L2 that the level of the fatty acid alkyl ester exceeds a predetermined value, the methane fermentation system 100 opens the valve V2 and is configured to supply the fatty acid alkyl ester to the power generation device 113. be able to.
With this configuration, even if the content ratio of glycerin or fatty acid glycerin ester fluctuates greatly depending on the raw material, it is possible to flexibly respond to the demand for the fatty acid alkyl ester.

The embodiments described above are described for facilitating the understanding of the present invention, and are not described for limiting the present invention. Therefore, each element disclosed in the above embodiment is intended to include all design changes and equivalents belonging to the technical scope of the present invention.

Hereinafter, the present invention will be described in more detail by showing examples and the like, but the present invention is not limited to the following examples and the like.

(Preparation of waste glycerin)
Biodiesel fuel was produced by transesterifying waste cooking oil and methanol by an alkaline catalyst method using potassium hydroxide as a catalyst. The by-product containing glycerin produced at this time was recovered as waste glycerin.

20 g of zeolite was added to this waste glycerin per 1 kg of waste glycerin to remove water. The zeolite-added waste glycerin was passed through a 250 mesh filter to remove zeolite and solid impurities.
The composition and physical properties of the waste glycerin as a raw material thus obtained (hereinafter referred to as “raw material waste glycerin”) are as shown in Table 1.

(First separation step)
500 kg of raw material waste glycerin and 300 kg of high acid value oil (150 mgKOH / g) were put into a reaction tank having a capacity of 1,000 L (liter) having a heating / cooling function, and heated to 55 ° C. with stirring (120 rpm). In this state, 32 L of concentrated sulfuric acid was added into the reaction vessel over 15 minutes. When adding concentrated sulfuric acid, care was taken not to exceed the temperature of the mixture in the reaction vessel at 65 ° C. The pH of the reaction solution after the total amount of concentrated sulfuric acid was added was 1. After the addition of concentrated sulfuric acid was completed, stirring was continued for 240 minutes. After that, it is allowed to stand for 10 hours to separate it into an oil phase (first oil content) and an acidic glycerin phase (first glycerin-containing liquid), and the first glycerin-containing liquid (including the acidic glycerin phase and precipitated potassium sulfate). Was recovered. By repeating the above operation, 5,000 kg of the first glycerin-containing liquid was obtained.

(Neutralization process)
A reaction tank having a capacity of 15,000 L was charged with 5,000 kg of the first glycerin-containing liquid and 5,000 kg of waste glycerin with stirring. The pH was 7.1. After that, stirring was continued for 4 hours, and then the mixture was allowed to stand for 24 hours.

(Second separation step)
The neutralized glycerin was treated with a decanter type centrifuge (product name: Z18H-V, manufactured by Tanabe Wiltec) at 5,500 rpm for 180 minutes, and the precipitated potassium sulfate was separated and recovered. The liquid phase was further treated with a three-phase separator (manufactured by Alfa Laval) at 8,000 rpm for 180 minutes, and the second oil, the second glycerin-containing liquid, and potassium sulfate were separated and recovered. The second glycerin-containing liquid obtained in this step was used as sample 1.

(Alcohol removal process)
The second glycerin-containing liquid obtained in the second separation step was distilled in a batch system at a distillation temperature of 110 ° C. for 10 minutes using a vacuum distillation apparatus, and methanol and water were separated and removed. The obtained second glycerin-containing liquid (glycerin-containing liquid after removal of methanol and water) was used as sample 2.
For the purpose of comparison, the first obtained raw material waste glycerin was used as sample 3.

For each of Samples 1 to 3, pH, BOD, TOC, CODcr, TN, n-Hex, T-P, total chlorine, glycerin concentration, methanol concentration, and specific gravity were measured. The results are shown in Table 2.
Here, each item described below was measured according to JIS K0102. BOD (Biochemical Oxygen Demand) is the amount of organic matter in water expressed by the amount of oxygen required by microorganisms for its oxidative decomposition. TOC (total organic carbon) is an index expressing the total amount of organic matter in water as "the amount of carbon contained in the organic matter". The COD (Chemical Oxygen Demand) is an index that expresses the amount of organic matter in water as "the amount of oxygen consumed when decomposed by an oxidant", depending on the type of oxidant used and the reaction conditions. There are multiple types. In the present embodiment, "COD _Cr " using potassium dichromate as an oxidizing agent can be preferably used as a COD index. _{This is because "COD Mn} ", which uses potassium permanganate as an oxidizing agent, has a low capture rate with respect to the actual amount of organic matter. Further, TN (total nitrogen) indicates the total amount of nitrogen compounds contained in water. Next, n-Hex (n-hexane extractant) was measured by the extraction / gravimetric method in Appendix Table 4 of Notification No. 64 of the Ministry of the Environment in 1974. n-Hex is a general term for non-volatile substances extracted by n-hexane, which is an organic solvent, and is used as an index showing the amount of "oil, etc." in water. Here, the oil content and the like include animal and vegetable fats and oils, fatty acids, fatty acid esters, fatty acid derivatives such as phospholipids, waxes, greases, petroleum-based hydrocarbons and the like. Further, T-P (total phosphorus) is the total amount of phosphorus compounds contained in water. Total chlorine is the total amount of chlorine and chloride contained in water as measured by combustion ion chromatography.
The methanol concentration was measured by a gas chromatograph method, and the glycerin concentration was measured by a liquid chromatograph method.

As can be seen from Table 2, there are not so large differences in the values of BOD, TOC, and CODcr between Samples 1 and 2 (Examples in the present invention) and Sample 3 used for comparison, and a remarkable tendency is particularly remarkable. can not see. However, in n-Hex used as an index of the oil content present in water, sample 1 (a sample in which alcohol was not removed after the separation step) and sample 2 (a sample in which alcohol was removed after the separation step) were used. There is a big difference in the value from the sample 3 (waste glycerin) used for comparison. That is, it can be seen that according to the method of the present invention, the oil content in the glycerin-containing waste can be separated and removed with extremely high efficiency.

Next, each of the samples 1 to 3 was subjected to a methane fermentation experiment as shown below using the methane fermentation apparatus shown in FIG. 4, and the amount of biogas generated in each sample was measured. The test was terminated when 15 days had passed from the start of the test (start of methane fermentation).

The methane fermentation apparatus used in the examples will be described with reference to FIG. The methane fermentation apparatus 1 has a fermentation tank 2, a stirrer 4, a heating apparatus 6, a thermometer 8, a raw material input port 10, a drain 12, and a gas outlet 14. The fermenter 2 is a closed cylindrical tank having a capacity of 20 L and made of SUS. A gas tube 16 is attached to the gas outlet 14 of the fermenter 2, and the gas tube 16 is connected to a flow meter 18 (volumetric flow meter). The flow meter 18 has a built-in data logging device, which can monitor and record the amount of gas generated continuously for 24 hours. Further, an aluminum gas pack 22 for collecting the generated gas is connected to the flow meter 18 via another gas tube 20.

First, 3.5 L of sludge acclimated with food residue containing nitrogen and phosphorus was put into the fermenter 2 as seed sludge. Next, each of the samples 1 to 3 was put into the 50-gram fermenter 2 while heating the inside of the fermenter to 37 ° C. The atmosphere in the fermenter 2 was purged with nitrogen, the stirrer 4 was constantly operated while keeping the temperature in the tank at 37 ° C. ± 0.5 ° C., and the inside of the fermenter 2 was continuously stirred. The amount of gas generated was measured using the flow meter 18, and the entire amount of gas was collected by the gas pack 22 connected to the flow meter. Here, the amount of gas generated was continuously recorded by a data logger attached to the flow meter 18.

FIG. 5 shows the change over time in the amount of gas generated for each of the samples 1 to 3 when they were used. As can be seen from FIG. 5, in the method according to the present invention (when samples 1 and 2 are used), the biogas production rate is higher than that when waste glycerin is used (when sample 3 is used). It can be seen that the speed is much faster and the amount of biogas produced is also higher.
Here, the carbon source that can be a raw material for biogas has the same level of biogas production rate in samples 1 and 2 regardless of whether BOD, TOC, or CODcr is used as an index. It is considered that the efficiency of methane fermentation was dramatically improved by removing the oil from the glycerin-containing waste because the speed was increased and the amount produced was also increased.

According to the present invention, biogas containing methane can be efficiently produced by methane fermentation using waste glycerin or the like, which is an industrial waste, as a raw material. Glycerin-containing waste such as waste glycerin, which was conventionally considered to have low utility value, can be actively utilized, and there are some that have great industrial utility value. For example, the biogas produced by the method according to the present invention can be sent to a desulfurization step, and the obtained gas can be supplied to a gas engine to generate electricity. It is also possible to remove carbon dioxide contained in the separation membrane or the like and supply it as a household gas.
Further, the oil content obtained in the separation step in the middle of the methane fermentation method according to the present invention can be used as a raw material for producing biodiesel fuel. Furthermore, the glycerin-containing liquid obtained as an intermediate product in the method of the present invention can be appropriately diluted and used as a water treatment denitrifying agent and an asphalt adhesion inhibitor.
As described above, according to the present invention, glycerin-containing waste such as waste glycerin, which has been treated as waste, can be used in various uses and fields, and is stable by securing many destinations. Recycling flow becomes possible. As a result, the industrial utility value is great.

Claims (25)

A methane fermentation method for producing biogas containing methane from a raw material containing a fatty acid glycerin ester.
The first separation step of reacting the raw material with an inorganic acid in the presence of a monohydric alcohol to separate the first oil and the first glycerin-containing liquid.
A neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance, and
A second separation step of separating the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A fermentation step in which methane fermentation is performed using the second glycerin-containing liquid, and
Equipped with
The reaction in the first separation step is a methane fermentation method, wherein the pH of the reaction solution is 3 or less. At least one method other than the alkali catalyst method, which is selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. With an esterification step to produce a fatty acid alkyl ester
In the esterification step, claim 1, which comprises using the second oil separated by the first oil and / or the second separation step are separated by the first separation step as a raw material The methane fermentation method described in. The methane fermentation method according to claim 2, further comprising a power generation step of generating electricity using at least a part of the fatty acid alkyl ester obtained in the esterification step. The supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than methane fermentation of the second glycerin-containing liquid, and the supply amount of the second glycerin-containing liquid is adjusted according to the demand for the fatty acid alkyl ester. The methane fermentation method according to claim 3, wherein the supply amount of the fatty acid alkyl ester to the power generation step is adjusted. The methane fermentation method according to any one of claims 1 to 4, wherein the raw material containing the fatty acid glycerin ester contains waste glycerin produced as a by-product in the process of producing a biodiesel fuel. Claims 1 to 5 are characterized in that alcohol is removed from the second glycerin-containing liquid after the second separation step, and the methane fermentation is performed using the second glycerin-containing liquid from which the alcohol has been separated and removed. The methane fermentation method according to any one of the above. The methane fermentation method according to any one of claims 1 to 6, wherein in the neutralization step, the first glycerin-containing liquid is neutralized so as to have a pH of 4 to 8. The invention according to any one of claims 1 to 7, wherein in the methane fermentation step, an auxiliary raw material containing nitrogen and / or phosphorus is charged into the methane fermentation tank in addition to the second glycerin-containing liquid. Methane fermentation method. The methane according to claim 8, wherein the auxiliary raw material is one or more selected from the group consisting of food waste, livestock manure, phosphoric acid, phosphate, ammonia, and ammonium salt. Fermentation method. The methane according to claim 8 or 9, wherein the auxiliary raw material is added so that the total nitrogen (TN) concentration of the digested sludge in the methane fermentation tank is 100 to 10,000 mg / L. Fermentation method. One of claims 1 to 10, wherein the input amount of the second glycerin-containing liquid is adjusted so that the CODcr load in the methane fermentation tank is 2 to 20 kg / m ^{3 · day.} The methane fermentation method described in. One of claims 1 to 11, wherein the supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for uses other than the methane fermentation of the second glycerin-containing liquid. The methane fermentation method according to item 1. A methane fermentation system that produces biogas containing methane from raw materials containing fatty acid glycerin esters.
A first separation device that separates the first oil and the first glycerin-containing liquid by reacting the raw material with an inorganic acid in the presence of a monohydric alcohol.
A neutralizing device that neutralizes the first glycerin-containing liquid with an alkaline substance,
A second separation device that separates the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A methane fermentation apparatus that performs methane fermentation using the second glycerin-containing liquid, and
Equipped with
The reaction in the first separation device is a methane fermentation system characterized in that the pH of the reaction solution is 3 or less. At least one method other than the alkali catalyst method, which is selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. Esterification equipment for producing fatty acid alkyl esters.
Claims second oil separated by the first oil and / or the second separation step are separated by the first separation step, characterized in that it is supplied to the esterification device as a raw material 13. The methane fermentation system according to 13. A fatty acid alkyl ester storage tank for storing the fatty acid alkyl ester is provided after the esterification device.
A power generation device that generates electricity using the fatty acid alkyl ester is provided after the fatty acid alkyl ester storage tank.
The fatty acid alkyl ester storage tank comprises a detector that detects the amount of the stored fatty acid alkyl ester.
The methane fermentation system according to claim 14, wherein the fatty acid alkyl ester is supplied to the power generation device when the amount of the fatty acid alkyl ester exceeds a predetermined amount. A glycerin storage tank for storing the second glycerin-containing liquid is provided after the second separation device.
The glycerin storage tank includes a detector for detecting the amount of the stored second glycerin-containing liquid.
One of claims 13 to 15, wherein the second glycerin-containing liquid is supplied to the methane fermentation apparatus when the amount of the second glycerin-containing liquid becomes a predetermined amount or more. The methane fermentation system described in. A method of reusing waste containing fatty acid glycerin esters.
The first separation step of reacting the waste with the inorganic acid in the presence of a monohydric alcohol to separate the first oil and the first glycerin-containing liquid.
A neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance, and
A second separation step of separating the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A fermentation step in which methane fermentation is performed using the second glycerin-containing liquid, and
Equipped with
The reaction in the first separation step is a waste recycling method, wherein the pH of the reaction solution is 3 or less. At least one method other than the alkali catalyst method, which is selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. With an esterification step to produce a fatty acid alkyl ester
17. In the esterification step, which comprises using the second oil separated by the first oil and / or the second separation step are separated by the first separation step as a raw material Waste reuse method described in. A power generation step of generating electricity using at least a part of the fatty acid alkyl ester obtained in the esterification step is provided.
The supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than methane fermentation of the second glycerin-containing liquid, and the fatty acid alkyl ester is used according to the demand. The waste recycling method according to claim 18, wherein the supply amount of the fatty acid alkyl ester to the power generation process is adjusted. Any of claims 17 to 19, wherein the supply amount of the second glycerin-containing liquid to the methane fermentation step is adjusted according to the demand for applications other than methane fermentation of the second glycerin-containing liquid. The waste reuse method described in paragraph 1. A system for reusing waste containing fatty acid glycerin esters.
A first separation device that reacts the waste with an inorganic acid in the presence of a monohydric alcohol to separate the first oil and the first glycerin-containing liquid.
A neutralizing device that neutralizes the first glycerin-containing liquid with an alkaline substance,
A second separation device that separates the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
A methane fermentation apparatus that performs methane fermentation using the second glycerin-containing liquid, and
Equipped with
The reaction in the first separation device is a waste recycling system characterized in that the pH of the reaction solution is 3 or less. At least one method other than the alkali catalyst method, which is selected from the group consisting of an acid catalyst method, an acid alkali catalyst method, a biocatalyst method, an ion exchange resin method, a supercritical method, a subcritical method and a solid catalyst method. Esterification equipment for producing fatty acid alkyl esters.
Claims second oil separated by the first oil and / or the second separation step are separated by the first separation step, characterized in that it is supplied to the esterification device as a raw material 21. The waste recycling system. A fatty acid alkyl ester storage tank for storing the fatty acid alkyl ester is provided after the esterification device.
A power generation device that generates electricity using the fatty acid alkyl ester is provided after the fatty acid alkyl ester storage tank.
The fatty acid alkyl ester storage tank comprises a detector that detects the amount of the stored fatty acid alkyl ester.
The waste recycling system according to claim 22, wherein the fatty acid alkyl ester is supplied to the power generation device when the amount of the fatty acid alkyl ester exceeds a predetermined amount. A glycerin storage tank for storing the second glycerin-containing liquid is provided after the second separation device.
The glycerin storage tank includes a detector for detecting the amount of the stored second glycerin-containing liquid.
One of claims 21 to 23, wherein the second glycerin-containing liquid is supplied to the methane fermentation apparatus when the amount of the second glycerin-containing liquid becomes a predetermined amount or more. Waste recycling system described in. A method for producing a carbon source for methane fermentation from a raw material containing a fatty acid glycerin ester.
The first separation step of reacting the raw material with an inorganic acid in the presence of a monohydric alcohol to separate the first oil and the first glycerin-containing liquid.
A neutralization step of neutralizing the first glycerin-containing liquid with an alkaline substance, and
A second separation step of separating the second oil and the precipitated inorganic salt from the neutralized first glycerin-containing liquid to obtain a second glycerin-containing liquid.
Equipped with
In the reaction in the first separation step, the pH of the reaction solution is 3 or less, and the reaction solution has a pH of 3 or less.
The second glycerin-containing liquid is used as a carbon source for the methane fermentation.
A method for producing a carbon source for methane fermentation, which is characterized by the above.

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