JP5587425B2 - Purification method of glycerin - Google Patents

Description

  The present invention relates to a method for purifying glycerin waste produced as a by-product in a production process of biodiesel fuel, and more particularly, to a starting material in a process for synthesizing acrolein, which is a raw material of 1,3-propanediol, by supercritical water treatment. The present invention relates to a method for purifying certain glycerin.

  Since 1,3-propanediol is a raw material for high-quality polyester fibers such as polytrimethylene terephthalate, demand has increased in recent years. One method for synthesizing 1,3-propanediol is the acrolein hydration / hydrogenation method shown in (Non-patent Document 1). This method is produced by subjecting acrolein obtained by air oxidation of propylene as a petroleum raw material in the presence of a catalyst to a hydration / hydrogenation reaction, and is established as an industrial production method. However, due to the recent rise in crude oil prices, development of a synthesis method from bio raw materials is desired.

  The present inventors are researching and developing a process for synthesizing acrolein, which is a precursor of 1,3-propanediol, from glycerin waste by-produced in the production process of biodiesel fuel.

  Biodiesel fuel is generally produced by an alkali catalyst method as described in (Patent Document 1). This method is a method for producing biodiesel fuel by transesterifying triglycerides such as rapeseed oil in the presence of an alkali catalyst such as potassium methoxide. In this reaction, one molecule of glycerin is generated from one molecule of triglyceride. Since this glycerin contains an alkali catalyst, there is no inexpensive method for recycling, and most factories currently incinerate by paying treatment costs.

  On the other hand, a method for synthesizing acrolein from glycerin using supercritical water is described in (Non-Patent Document 2). In this method, an aqueous solution of glycerin, which is a bio raw material, and high-temperature supercritical water are mixed at 35 MPa, and the temperature is instantaneously increased to 400 ° C. to synthesize acrolein. It is characterized by functioning as a catalyst for accelerating the dehydration reaction of glycerin. However, when the glycerin waste generated in the production process of biodiesel fuel is directly treated with supercritical water, there is a possibility that the piping may be clogged. This is because the alkali catalyst contained in the glycerin waste precipitates in supercritical water having a low dielectric constant. Therefore, it is necessary to remove the alkali metal from glycerin by-produced in the production process of biodiesel fuel.

  A method for purifying glycerin using ion exchange is described in (Patent Document 2). This method is a method of purifying glycerin by passing glycerin waste containing impurities such as organic fatty acid and alkali generated in the production process of biodiesel fuel through an ion exchange resin and removing the impurities. This glycerin waste contains about 4% by weight of alkali metal in terms of ions and 10% by weight or more of organic fatty acid. For this reason, when glycerin waste is processed without pretreatment, the time until the ion exchange resin breaks through is shortened, the regeneration frequency is increased, and the purification cost is increased.

  On the other hand, the purification method of glycerin using distillation is described in FIG. 1 of (Patent Document 3). This method is a purification method of glycerin generated when transesterifying methanol into fats and oils in the presence of an alkali catalyst. It is characterized in that hydrochloric acid is added to a glycerin solution containing an alkali to precipitate an alkali metal chloride, and then the chloride is roughly separated by filtration and then purified by distillation. However, since purification by distillation is performed, a lot of energy is required for reheating the raw material, leading to an increase in the purification cost of glycerin.

Kentaro Shima, Manufacture of 1,3-PDO, PTT Applications and economics, CM Planet Division, August 2000 Masaru Watanabe et..al., Acrolein synthesis from glycerol in hot-compressed water., Bioresource Technology 98, 1285-1290 (2007)

JP-A-7-197047 JP 58-144333 A JP-A-6-184024

  An object of the present invention is to produce a biodiesel fuel in order to prevent pipe clogging in a pipe for supercritical water reaction when acrolein is synthesized by allowing supercritical water and an acid to act on glycerin. Is to provide an inexpensive method for removing impurities from waste glycerin.

  The present inventor has found that the above-mentioned problems can be solved by adding alkaline earth metal sulfate after neutralizing glycerin waste containing alkali metal with sulfuric acid and completed the present invention. That is, the gist of the present invention is as follows.

(1) A step of removing alcohol and moisture by heating glycerin containing alkali metal, alcohol, organic fatty acid and moisture under reduced pressure; a step of neutralizing by adding sulfuric acid to glycerin from which alcohol and moisture have been removed; Centrifugating the neutralized glycerin, separating and removing alkali metal sulfate and organic fatty acid, adding alkaline earth metal sulfate to glycerin recovered by centrifugation, and mixing, Centrifuging the glycerin mixed with the alkaline earth metal sulfate and mixing to separate and remove the alkali metal sulfate and the alkaline earth metal salt of the organic fatty acid.
(2) A method for purifying glycerin, wherein the glycerin obtained by the purification method according to (1) above is further passed through a cation exchange resin to separate and remove the alkali metal.
(3) A method for purifying glycerin, wherein the glycerin obtained by the purification method according to (2) above is further passed through an anion exchange resin to separate and remove impurities.
(4) The method for purifying glycerin according to any one of (1) to (3) above, wherein the alkaline earth metal sulfate is magnesium sulfate.

  According to the present invention, since alcohol and water are removed from glycerin and then neutralized with sulfuric acid, the separation / removal performance of the alkali metal catalyst can be improved. This is because alkali metal sulfate is formed by neutralizing alkali metal with sulfuric acid, but alkali metal sulfate has high solubility in alcohol and water, whereas solubility in glycerin is low. . Since the removal performance of the alkali metal catalyst is improved, the running cost can be reduced.

  In addition, since glycerin is neutralized with sulfuric acid, corrosion of the supercritical water pipe can be reduced. In the reaction of synthesizing acrolein from glycerin using supercritical water, sulfuric acid is used as a catalyst. For this reason, by neutralizing glycerin with the same sulfuric acid as the catalyst, the anions present in the supercritical water can be made into only sulfate ions, so that corrosion of the piping material can be reduced.

  Moreover, since centrifugation is performed after adding an alkaline earth metal to the crude glycerin, the alkali metal concentration in the purified glycerin can be reduced. Since alkaline earth metal ions have a smaller ionic radius and a larger charge than alkali metal ions, alkaline earth metals have a strong tendency to take anions from alkali metal salts. For this reason, an alkaline earth metal salt of an organic fatty acid and an alkali metal sulfate are formed by reacting an alkali metal salt of an organic fatty acid and an alkaline earth metal sulfate contained in the crude glycerin. In general, the alkaline earth metal salts and alkali metal sulfates of higher fatty acids formed are precipitated because of their low solubility in glycerin. Therefore, since the alkali metal concentration in the crude glycerin can be reduced, blockage in the supercritical water pipe can be prevented. Moreover, since the alkali metal concentration in glycerin can be reduced with an inexpensive alkaline earth metal sulfate, the purification cost can be reduced.

  Furthermore, after neutralization with sulfuric acid and desalination treatment with alkaline earth metal sulfate, glycerin is purified by ion exchange, so the amount of ions adsorbed on the ion exchange resin can be reduced, and ion exchange Resin regeneration frequency and purification costs can be reduced. In addition, alkali metal salts and alkaline earth metal salts of lower fatty acids such as formic acid, acetic acid, and propionic acid have solubility in glycerin, so that the above-described neutralization with sulfuric acid and addition by addition of alkaline earth metal salts are effective. It cannot be separated from glycerin by salt treatment. Since the lower fatty acid salt that could not be separated and removed can be reliably removed with an ion exchange resin, clogging in the supercritical water pipe can be prevented, and the stability of the plant operation can be improved and the operation cost can be reduced. .

It is a figure which shows a biodiesel manufacturing process. It is a figure which shows the refinement | purification process of a glycerol waste. It is a figure which shows the supercritical water reaction process which manufactures acrolein from refinement | purification glycerol. It is a figure which shows the refinement | purification process of a glycerol waste. It is a flowchart which shows the synthetic | combination process of the biodiesel fuel with the byproduct of glycerol waste. It is a flowchart which shows the refinement | purification process of a glycerol waste. It is a graph which shows the neutralization titration curve of a glycerol waste. It is a graph which shows the correlation with the addition amount of magnesium sulfate, and various components.

  Hereinafter, referring to the drawings, a process in which glycerin waste is by-produced when producing biodiesel fuel from fats and oils, a process for refining by-produced glycerin waste, and supercritical water from purified glycerin are used. A process until synthesis of acrolein, which is a precursor of 1,3-PDO, will be described.

  FIG. 1 shows a process in which by-product glycerin is involved in a biodiesel fuel production process. First, fats and oils are fed from the fat and oil header 110 to the fat and oil tank 111 and stored. The fats and oils described here are oily plants such as rapeseed, soybean, and jatropha, or animal fats and oils, discarded cooking oils, and the like, but are not limited thereto. After the oil and fat is fed to the fat and oil filter 113 by the oil and fat pump 112 to remove the solid content, the oil and fat receiving tank 114 is dehydrated by vacuum heating, and the fat and oil pump 115 is sent to the transesterification tank 121.

  Meanwhile, methanol is sent from the methanol header 100 to the methanol tank 101 and stored. Here, ethanol may be used as an alternative to methanol. This methanol is sent to the potassium methoxide production tank 104 by the methanol pump 102. Next, potassium hydroxide is supplied to the potassium methoxide production tank 104 using the potassium hydroxide feeder 103. Instead of potassium hydroxide, sodium hydroxide may be supplied.

Methanol and potassium hydroxide are mixed at room temperature in the potassium methoxide production tank 104 to form methanol containing potassium methoxide. The amount of potassium hydroxide or sodium hydroxide added per 1 m ^{3 of} methanol is preferably about 37.3 kg and 26.6 kg, respectively. Methanol containing potassium methoxide is sent to the transesterification tank 121 by the potassium methoxide pump 105.

In the transesterification tank 121, methanol containing fats and oils and potassium methoxide is stirred at about 50 ° C. for about 3 hours. Thereby, transesterification shown in Chemical Formula (1) proceeds, and glycerin is produced as a by-product with the production of biodiesel fuel. Since the reaction of the chemical formula (1) is an equilibrium reaction, the transesterification reaction is generally performed by adding methanol containing potassium methoxide in two portions. In the first time, 0.1 m ^{3 of} methanol containing potassium methoxide is added to 1 m ^{3 of} fat and oil. After reacting at about 50 ° C. for 3 hours, the mixture is allowed to stand for 30 minutes, and a biodiesel fuel layer and a glycerin waste layer are separated into two layers in the upper layer portion and the lower layer portion, respectively. Only the lower glycerin waste is fed to the subsequent glycerin purification step. The boundary between glycerin waste and biodiesel fuel is detected by a conductivity meter 122 at the bottom of the tank. That is, the biodiesel fuel layer has low conductivity, but the glycerin waste layer contains water and alkali metal ions, and thus exhibits high conductivity. For this reason, the electrical conductivity of the liquid discharged from the tank is measured, and the place where the electrical conductivity is lowered is detected as the boundary position between the glycerin waste and the biodiesel fuel.

  After the glycerin waste layer is discharged from the transesterification tank 121 and the equilibrium reaction of the chemical formula (1) moves to the right side, a second transesterification reaction is performed. To the remaining biodiesel fuel layer, methanol containing potassium methoxide, which is half of the first addition amount, is added and stirred at 50 ° C. for 1 hour to perform a transesterification reaction. Thereafter, the reaction solution is allowed to stand for 30 minutes, and again separated into two layers, a biodiesel fuel and a glycerin waste layer. After the separation, only the lower glycerin waste layer is fed to the glycerin purification step 127. The biodiesel fuel remaining in the transesterification tank 121 is sent and stored in the BDF tank 124 before purification. Thereafter, refined biodiesel fuel is obtained through neutralization, washing, and dehydration treatment, but description regarding details of the biodiesel fuel purification process is omitted.

In the above description of the production process of biodiesel fuel, an example in which potassium hydroxide is used as a catalyst has been described. However, biodiesel fuel can also be produced using sodium hydroxide instead of potassium hydroxide. However, it is more desirable to use potassium hydroxide for the following three reasons. The first reason is that glycerin waste containing sodium is solid at room temperature, and therefore, when liquid is sent by a pump, it is necessary to heat and liquefy it at 60 ° C. or higher. The second reason is that when potassium hydroxide is used, the amount of alkali remaining in the biodiesel fuel is less than that of sodium hydroxide, and the water used for washing and desalting treatment in the biodiesel fuel purification process. This is because the amount of can be reduced. The third reason is that the potassium compound has lower solubility in glycerin than the sodium compound. Therefore, it is because the desalination process of glycerol becomes easier when potassium hydroxide is used. Tables 1 and 2 show the solubility of potassium salt and sodium salt in glycerin.

  Next, a process for purifying glycerin waste will be described with reference to FIG. The glycerin waste is stored in the waste glycerin tank 201 and then sent to the neutralization tank 206 by the waste glycerin pump 202. The amount of glycerin waste sent is measured by a waste glycerin integrated flow meter 209. Further, the pH of glycerin is measured in a neutralization tank. The state of glycerin waste is liquid at room temperature when potassium methoxide is used as a production catalyst for biodiesel fuel, but is solid at room temperature when sodium methoxide is used. Therefore, when sodium methoxide is used, the waste glycerin tank 201 and the neutralization tank 206 need to be kept warm to 60 ° C. or higher and stirred.

Concentrated sulfuric acid for neutralizing glycerin containing potassium is sent from the sulfuric acid tank 204 to the neutralization tank 206 using the sulfuric acid pump 205. When the hydrogen ion concentration calculated by the pH meter 207 of the waste glycerin tank is [H ⁺ ] (mol / L), and the amount of glycerin waste liquid measured by the glycerin waste integrated flow meter is V (L). The amount of sulfuric acid fed is preferably about [H ⁺ ] × V / 2 (mol). Further, during the neutralization operation, the jacket of the neutralization tank 206 is set to 80 ° C. while stirring, and the tank is evacuated to evaporate water and methanol. By performing evacuation during the neutralization operation, the heat of neutralization can be used for heating the reaction solution, so that the purification cost can be reduced. The pH of glycerol is adjusted from 6 to 8 by the neutralization step.

  As described above, since alcohol and water are removed from glycerin and then neutralized with sulfuric acid, the separation / removal performance of the alkali metal catalyst can be improved. This is because the alkali metal sulfate is formed by neutralizing the alkali metal with sulfuric acid, but the alkali metal sulfate has high solubility in alcohol and water, whereas it has low solubility in glycerin. Yes (see Tables 1 and 2 above). Since the removal performance of the alkali metal catalyst is improved, the purification cost can be reduced.

  In the reaction of synthesizing acrolein from glycerin using supercritical water, sulfuric acid is used as a catalyst. For this reason, by neutralizing glycerin with the same sulfuric acid as the catalyst, the anions present in the supercritical water can be made into only sulfate ions, so that corrosion of the piping material can be reduced.

  The neutralized glycerin waste is sent to the continuous centrifuge 211 by the neutralization liquid pump 208. In the continuous centrifuge 211, glycerin waste is fed into a rotating conical cylinder and separated from the outer layer into potassium sulfate, crude glycerin, and organic fatty acid. Potassium sulfate is scraped off by a screw rotating at a different rotational speed from that of the conical cylinder and discharged out of the apparatus. On the other hand, crude glycerin and organic fatty acid are respectively discharged from two outlets having different distances from the rotation axis. Potassium sulfate is discharged into the potassium sulfate pit 212 and then washed with acetone to be used as a raw material for potassium fertilizer and alum. On the other hand, after the organic fatty acid is discharged to the organic fatty acid tank 213, it is sent to the organic fatty acid treatment step 215 and converted into biodiesel fuel by transesterification. The crude glycerin is added to the liquid feed flow rate by the crude glycerin flow meter 224 and fed to the magnesium sulfate mixing tank 221. In addition, although embodiment using a continuous centrifuge is described in FIG. 2, it isolate | separates into three layers of potassium sulfate, crude glycerol, and an organic fatty acid from a lower layer by leaving still in the neutralization tank 206 for 3 hours. You may do it. Alternatively, the neutralized glycerin waste may be filtered with a filter. In this case, it is desirable that the filter has a pore diameter of 1 μm or less.

  Crude glycerin from which potassium sulfate and organic fatty acids have been easily removed is fed to a magnesium sulfate mixing tank 221. In the tank, magnesium sulfate is added by a magnesium sulfate screw feeder 222 and mixed at 90 ° C. for 3 hours. The amount of magnesium sulfate added is preferably about the same weight as the organic fatty acid content by sampling crude glycerin and measuring the organic fatty acid content. When the amount of organic fatty acid cannot be measured, it is desirable to add about 1% by weight based on the weight of crude glycerin. By mixing magnesium sulfate and crude glycerin, the organic fatty acid potassium salt in the crude glycerin is converted into a magnesium salt of an organic fatty acid having low solubility in glycerin, so that the organic fatty acid magnesium is precipitated from glycerin. By removing the organic fatty acid potassium, which has been a cause of increasing the solubility of the potassium component, the solubility of the potassium is lowered and the potassium sulfate is further separated and removed.

  Since the centrifugal separation is performed after the alkaline earth metal is added to the crude glycerin, the alkali metal concentration in the purified glycerin can be reduced. Since alkaline earth metal ions have a smaller ionic radius and a larger charge than alkali metal ions, alkaline earth metals have a strong tendency to take anions from alkali metal salts. For this reason, an alkaline earth metal salt of an organic fatty acid and an alkali metal sulfate are formed by reacting an alkali metal salt of an organic fatty acid and an alkaline earth metal sulfate contained in the crude glycerin. In general, the alkaline earth metal salts and alkali metal sulfates of higher fatty acids formed are precipitated because of their low solubility in glycerin. Therefore, the alkali metal concentration in the crude glycerin can be reduced. Thereby, blockage in the supercritical water pipe can be prevented, and the alkali metal concentration in glycerin can be reduced by an inexpensive alkaline earth metal sulfate, so that the purification cost can be reduced.

  Crude glycerin mixed with magnesium sulfate is fed to a continuous centrifuge 231 by a mixed liquid feed pump 223 and separated into potassium sulfate, simple purified glycerin, and organic fatty acid. The structure of the continuous centrifuge 231 is the same as that of the continuous centrifuge 211 described above. Potassium sulfate is discharged into the potassium sulfate pit 212, and the organic fatty acid is stored in the organic fatty acid tank 213, and then sent to the organic fatty acid treatment step 215, where it is transesterified in the presence of sulfuric acid and methanol to produce biodiesel fuel. Converted. In addition, although embodiment using a continuous centrifuge is described in FIG. 2, three layers of potassium sulfate, simple refinement | purification glycerin, and an organic fatty acid are formed from a lower layer by leaving still in the magnesium sulfate mixing tank 221 for 3 hours. May be separated. Alternatively, crude glycerin added with magnesium sulfate may be filtered with a filter. In this case, it is desirable that the filter has a pore diameter of 1 μm or less.

  The glycerin simply purified by the continuous centrifuge 231 is stored in the purified glycerin tank 233 and then sent to the cation exchange tower 241. Is separated and removed. After the neutralization with sulfuric acid and the desalination treatment with alkaline earth metal sulfate, the ion exchange of purified glycerin is performed, so the amount of ions adsorbed on the ion exchange resin can be reduced, and the ion exchange Resin regeneration frequency and purification costs can be reduced. In addition, alkali metal salts and alkaline earth metal salts of lower fatty acids such as formic acid, acetic acid and propionic acid have solubility in glycerin. It cannot be separated from glycerin by salt treatment. Since the lower fatty acid salt that could not be separated and removed can be reliably removed with an ion exchange resin, clogging in the supercritical water pipe can be prevented, and the stability of the plant operation can be improved and the operation cost can be reduced. .

  The ion-exchanged glycerin is stored in the cation exchange glycerin tank 243 and then sent to the supercritical water reaction step 270.

  Next, a process of synthesizing acrolein from purified glycerin by supercritical water treatment will be described with reference to FIG. First, purified glycerin, concentrated sulfuric acid, and water are fed from the respective headers (purified glycerin header 320, sulfuric acid header 321 and water header 322) to the raw material tank 323, and adjusted to a predetermined concentration by stirring and mixing. . This raw material is fed at 35 MPa by a raw material high-pressure pump 325 and heated to 250 ° C. by a raw material preheater 326. Further, the ultrapure water stored in the water tank 311 is fed at 35 MPa by the supercritical water high-pressure pump 312 and heated to 500 ° C. by the supercritical water preheater 313. Both are mixed at the junction 327, instantaneously brought to 400 ° C. and 35 MPa, and the reaction is started. Under supercritical water reaction conditions at 400 ° C. and 35 MPa, the concentrations of potassium sulfate and sodium sulfate that do not cause clogging of the pipes are 0.04 wt% and 0.06 wt%, respectively. There is a need.

The concentration of glycerin immediately after mixing the raw material and supercritical water is preferably 15% by weight or more and 30% by weight or less. This is because the initial concentration of glycerin in the reaction solution is 15% by weight or more, thereby reducing the cost of heating and pressurizing supercritical water and making it cost competitive for the process of synthesizing acrolein from petroleum raw materials. This is to have it. On the other hand, when the initial concentration of glycerin in the reaction solution is 30% by weight or more, as shown in chemical formula (2), the side reaction in which formaldehyde and acetaldehyde are generated becomes dominant, and the reaction yield decreases. The production cost of acrolein may be high. In general, when the glycerin concentration is low and the number of coordination water around the glycerin is sufficient, the hydrogen ion activity is high, so that protons are added to the secondary hydroxyl group of glycerin, resulting in two-stage dehydration. This is because the acrolein synthesis reaction proceeds by the reaction, but if the glycerin concentration is high and the number of coordination water contributing to the reaction decreases, the dehydration reaction proceeds at the terminal hydroxyl group and the main reaction becomes less dominant.

Moreover, the reaction yield can be improved to 70% or more by prescribing the proton concentration in the reaction solution to be within the range of the formula (a). Here, [H ⁺ ] is the proton concentration (mM) in the reaction solution due to the addition of sulfuric acid, and [G] is the glycerin concentration (wt%).

  Improving the reaction yield leads to a reduction in the amount of by-products generated, and is therefore extremely effective in preventing piping blockage and equipment wear.

The reaction yield can be improved by setting the reaction time t to be within the range represented by the formula (b) using the glycerin concentration [G] (% by weight) in the reaction solution.

  In order to improve the mixing property of supercritical water and raw material, a plurality of mixers using a swirl flow described in JP 2010-46634 A are installed in parallel at the junction 327 of supercritical water and raw material. By mixing, the yield can be improved.

  Next, after the optimal reaction time has elapsed, in order to stop the reaction, the cooling water is sent from the cooling water tank 341 in FIG. 3 to the junction 343 of the reaction liquid and the cooling water using the cooling water high-pressure pump 342. The reaction is stopped by direct mixing of cooling water. In order to stop the reaction, it is necessary to lower the reaction solution to 300 ° C. or lower, preferably 250 ° C. Note that the optimal reaction time for this reaction is on the order of seconds, and the internal diameter of the reaction pipe is as thick as about 10 cm in the actual machine. Controllability is improved. For this reason, it is extremely effective in reducing the amount of by-products generated.

  Since impurities are removed from glycerin containing potassium by neutralization with sulfuric acid and mixing with magnesium sulfate, pipe corrosion in the supercritical water reaction process can be prevented. In this reaction, sulfuric acid is used as a catalyst in the reaction of synthesizing acrolein from glycerin using supercritical water. Therefore, by neutralizing glycerin with the same sulfuric acid as the catalyst, the anions present in the supercritical water can be made into only sulfate ions, so that corrosion of the piping material can be reduced.

  The reaction liquid that has stopped the reaction is separated from tar and carbon particles by the subsequent filters 351a and 351b, and only the carbon particles are captured by the filter, and the tar passes through while maintaining high viscosity. Prevents blockage of pipes due to aggregation. Here, in order to prevent clogging of the filter due to tar, the reaction liquid temperature after mixing with cooling water needs to be 100 ° C. or higher, preferably 250 ° C. The method of removing impurities by cooling the reaction solution after cooling is extremely effective in reducing the corrosion rate of the filter. Since the pore diameter of the carbon particles generated by the reaction is distributed in the range of 40 μm to 2 mm, the separation and removal performance of the carbon particles can be improved by setting the filter pore diameter to 40 μm or less.

  In addition, the carbon particle cake discharging operation by backwashing can be alternately performed by preparing two or more carbon particle separation / removal filters. This eliminates the need to stop the entire plant, improving continuous operability, reducing heat loss associated with plant startup, and reducing operating costs.

  The reaction liquid from which the carbon particles have been removed is cooled to 80 ° C. by the second cooler 361, then the pressure is reduced to atmospheric pressure by the orifice 362 and the pressure control valve 363, and the liquid is sent to the subsequent acrolein distillation apparatus. Here, the reason for cooling the reaction liquid to 80 ° C. is to prevent volume expansion of water when the pressure is released to atmospheric pressure, and to ensure process stability and safety.

  Next, the third cooler 364 cools to 50 ° C., which is lower than the boiling point of acrolein. Thereby, the heating efficiency of a distillation process can be improved and an operating cost can be reduced. In addition, although pressure adjustment is performed only by the pressure control valve 363, there is no problem, but it is desirable to use the orifice 362 together for the purpose of reducing the load on the valve body.

  FIG. 4 shows another embodiment of the glycerin purification step of the present invention, in which a process for removing anionic impurities contained in glycerin is added after the glycerin purification process shown in FIG. 2 is performed. Specifically, glycerin that has passed through the cation exchange column 241 is sent to the anion exchange column 251 to remove a small amount of anion impurities. The ion exchanged glycerin is stored in the anion exchange glycerin tank 253 and then sent to the supercritical water reaction step 270. The step of passing through the cation exchange resin and the step of passing through the anion exchange resin may be performed in the reverse order depending on the case.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, the scope of the present invention is not limited to this.
Example 1
1. Production of waste glycerin By-product experiment of glycerin waste from waste oil was conducted. FIG. 5 shows a flow chart of a glycerin by-product experiment accompanying the synthesis of biodiesel fuel. First, 1000 mL of waste cooking oil generated from a school lunch center was vacuum heated and dehydrated at 300 torr and 80 ° C. for 1 hour. Further, 5.6 g of potassium hydroxide was stirred in 150 mL of methanol at room temperature to prepare methanol containing potassium methoxide. 100 mL of methanol containing potassium methoxide was added to waste cooking oil dehydrated by heating under vacuum, and the mixture was stirred at 50 ° C. for 3 hours to perform the first transesterification. Thereafter, the reaction solution was allowed to stand for 30 minutes, and the lower glycerin waste was discharged. To the remaining waste edible oil, 50 mL of methanol containing the remaining potassium methoxide was added, and the mixture was stirred at 50 ° C. for 1 hour to perform the second-stage transesterification reaction. Then, it left still for 30 minutes and discharged | emitted the glycerin waste of the lower part. Table 3 shows the results of component analysis of the glycerin waste collected in two steps. Gas chromatography was used to measure the concentration of organic matter. The potassium and magnesium concentrations were quantified by ion chromatography, and the water concentration was measured by the Karl Fischer method. Potassium is contained in the glycerin waste in an amount of 9.37% by weight in terms of the chemical form of potassium sulfate. When preparing a reaction liquid with a glycerin concentration of 30% by weight from this glycerin waste, it is necessary to add 127 g of glycerin to 100 g of water, so the potassium sulfate concentration in the reaction liquid is 5.24% by weight. Since this concentration exceeds the allowable concentration of potassium sulfate of 0.06% by weight, pipe clogging may occur.

2. Purification of waste glycerin Purification experiment of glycerin waste was conducted. FIG. 6 shows a flow of the purification experiment of glycerin waste. Since waste glycerin contains a solid content, first, solid content such as tempura residue was removed with a sieve having a wire diameter of 71 μm and an opening of 106 μm. Next, a predetermined amount of concentrated sulfuric acid shown in Table 4 was added to 50 g of this waste glycerin and stirred for 10 minutes while measuring the pH. This was heated to 80 ° C. for 1 hour at 300 torr to remove methanol and moisture. Note that concentrated sulfuric acid was used instead of dilute sulfuric acid for neutralization in order to prevent excess water from being mixed. FIG. 7 shows a titration curve when waste glycerin is neutralized with concentrated sulfuric acid. When the neutralized glycerin waste was allowed to stand for 30 minutes, separation was observed in three layers of potassium sulfate, crude glycerin, and organic fatty acid from the lower layer. This was transferred to a centrifuge tube and centrifuged at 3000 rpm for 10 minutes to remove the upper higher fatty acid and the lower layer potassium sulfate, and the intermediate layer of crude glycerin was collected. The component analysis results of this crude glycerin are shown in Table 5. When attention is focused on potassium ions in the crude glycerin, the potassium ion concentration is the lowest in Case B where the pH is neutral. However, when a reaction liquid having a glycerin concentration of 30% by weight is prepared from this crude glycerin, the potassium sulfate concentration in the reaction liquid is 0.23% by weight, which exceeds the allowable potassium sulfate concentration of 0.06% by weight. There is a possibility of clogging in the water reaction process.

In cases E and F where the pH is near 0, the concentration of glycerin is the highest, but it is necessary to remove sulfuric acid later. Therefore, the subsequent desalting treatment was performed only on the crude glycerin in Case B.

Subsequently, a predetermined amount of magnesium sulfate shown in Table 6 was added to this crude glycerin and stirred at 90 ° C. for 3 hours. The crude glycerin was centrifuged at 3000 rpm for 10 minutes to separate and remove the magnesium salt of the upper organic fatty acid and the lower layer potassium sulfate, and the purified glycerin of the intermediate layer was collected. The results of component analysis of purified glycerin are shown in Table 7 and FIG. By adding 5 mg or more of magnesium sulfate to 1 g of crude glycerin, the concentration of organic fatty acid and the concentration of potassium sulfate were reduced. When purified glycerin in Case d, which has the lowest potassium ion concentration, is used, the potassium sulfate concentration in the reaction solution with a glycerin concentration of 30% by weight is 0.03% by weight, and the possibility of avoiding clogging in the supercritical water reaction pipe may be avoided. There is.

  Next, 10% by weight of water was added to the purified glycerin and uniformly mixed, and the glycerin was desalted with a cation exchange resin. Diaion PK216 (trade name) manufactured by Mitsubishi Chemical was used as the cation exchange resin. Since this cation exchange resin has a sodium functional group, ion exchange was performed after passing hydrochloric acid to convert the functional group to a hydrogen type.

  Finally, the cation-exchanged glycerin was passed through an anion exchange resin to separate and remove lower organic fatty acids. Diaion PA316 (trade name) manufactured by Mitsubishi Chemical was used as the anion exchange resin.

Table 8 shows the component analysis results of purified glycerin subjected to cation exchange and anion exchange. In purified glycerin after cation exchange, potassium sulfate and magnesium sulfate remaining in the purified glycerin before ion exchange are removed, and in glycerin after anion exchange, it is removed by adding magnesium sulfate. The lower fatty acids that could not be removed were removed.

3. Supercritical reaction experiment Next, using the supercritical water reaction experimental apparatus shown in FIG. 3, glycerin waste, crude glycerin, purified glycerin, purified glycerin subjected to cation exchange, and cation exchange and anion exchange were performed. A supercritical water reaction experiment using purified glycerin was conducted. As a result, in the glycerin waste and the crude glycerin having a high potassium sulfate concentration, pipe clogging occurred in the supercritical water reaction pipe. On the other hand, with purified glycerin from which impurities were removed by adding magnesium sulfate, pressure fluctuations were observed in the supercritical water reaction piping due to the precipitation of magnesium sulfate, but there was no blockage of the piping and acrolein with a reaction yield exceeding 70%. Was able to be synthesized. The glycerin sample subjected to ion exchange had no pressure fluctuation and an acrolein reaction yield of 70% or more was obtained.

  The method for purifying glycerin of the present invention can remove impurities such as alkali metals from glycerin waste without using means such as distillation and ion exchange, which have high operating costs. For this reason, when synthesizing acrolein by allowing supercritical water and acid to act on glycerin, it is possible to prevent clogging of the pipe that occurs in the supercritical water reaction pipe, and the industrial utility value is high.

  All publications, patents and patent applications cited herein are incorporated herein by reference in their entirety.

DESCRIPTION OF SYMBOLS 100 Methanol header 101 Methanol tank 102 Methanol pump 103 Potassium hydroxide feeder 104 Potassium methoxide production tank 105 Potassium methoxide pump 110 Oil and fat header 111 Oil and fat tank 112 Oil and fat pump 113 Oil and fat filter 114 Oil and fat receiving tank 115 Oil and fat pump 121 Transesterification tank 122 Conductivity Rate meter 123 Liquid feed pump 124 BDF tank 125 before purification BDF pump 126 before purification BDF purification process 127 Glycerine purification process 200 Waste glycerin header 201 Waste glycerin tank 202 Waste glycerin pump 203 Sulfuric acid header 204 Sulfuric acid tank 205 Sulfuric acid pump 206 Neutralization tank 207 pH meter 208 Neutralizing liquid pump 209 Waste glycerin integrated flow meter 210 Concentrated sulfuric acid integrated flow meter 211 Continuous centrifugation Release machine 212 Potassium sulfate pit 213 Organic fatty acid tank 214 Organic fatty acid feed pump 215 Organic fatty acid treatment step 216 Crude glycerin pump 221 Magnesium sulfate mixing tank 222 Magnesium sulfate screw feeder 223 Mixed liquid feed pump 224 Crude glycerin flow meter 231 Continuous centrifugal separation Machine 232 Purified glycerin pump 233 Purified glycerin tank 234 Purified glycerin pump 235 Water header 241 Cation exchange tower 242 Cation exchange glycerin pump 243 Cation exchange glycerin tank 244 Cation exchange glycerin pump 251 Anion exchange tower 252 Anion exchange glycerin pump 253 Anion exchange glycerin tank 254 Anion exchange glycerin pump 270 Supercritical water reaction process 310 Water header 311 Water Tank 312 Supercritical water high pressure pump 313 Supercritical water preheater 320 Purified glycerin header 321 Sulfuric acid header 322 Water header 323 Raw material tank 324 pH meter 325 Raw material high pressure pump 326 Raw material preheater 327 Junction point 331 Reaction tube heater 340 Cooling water header 341 Cooling Water tank 342 Cooling water high pressure pump 343 Junction points 350a, 350b Backwash fluid headers 351a, 351b Filters 352a, 352b Filter backwash fluid inlet valve 353a, 353b Filter reaction fluid inlet valve 354a, 354b Filter reaction fluid outlet valve 355a 355b Filter drain valve 356a, 356b Drain 361 Cooler 362 Orifice 363 Pressure control valve 364 Cooler 365 Reaction liquid outlet

Claims (4)

  A process of removing alcohol and moisture by heating glycerin containing alkali metal, alcohol, organic fatty acid and moisture under reduced pressure, a step of neutralizing by adding sulfuric acid to glycerin from which alcohol and moisture have been removed, and neutralized Centrifuging the glycerol, separating and removing the alkali metal sulfate and organic fatty acid, adding the alkaline earth metal sulfate to the glycerin recovered by centrifugation and mixing, and alkaline earth Centrifuging the glycerol mixed with the addition of the metal sulfate to separate and remove the alkali metal sulfate and the alkaline earth metal salt of the organic fatty acid.   A method for purifying glycerin, wherein the glycerin obtained by the purification method according to claim 1 is further passed through a cation exchange resin to separate and remove alkali metals.   A method for purifying glycerin, wherein the glycerin obtained by the purification method according to claim 2 is further passed through an anion exchange resin to separate and remove impurities.   The method for purifying glycerin according to any one of claims 1 to 3, wherein the alkaline earth metal sulfate is magnesium sulfate.

Images