Method for removing organic acid

Abstract

To provide a method for removing organic acid, capable of efficiently removing organic acid without reducing sugar in organic acid containing sugar solution.SOLUTION: A method for removing organic acid comprises removing organic acid from an organic acid containing sugar solution. Oxides of four group elements or lanthanoids having an ion radius of less than 1 angstrom are applied as an adsorbent for adsorbing the organic acid.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] This specification discloses a method for removing organic acids.

Background Art

[0002] Conventionally, a method has been proposed in which a cellulosic biomass raw material is treated with sulfuric acid at a concentration of 70% by mass (acid hydrolysis) to produce a solubilized treatment liquid, and one side of an ion exchange membrane is brought into contact with the treatment liquid while the other side is brought into contact with water (recovered water) to recover sulfuric acid in the treatment liquid (see, for example, Patent Document 1).

[0003] In addition, a method has been proposed in which the acid resistance of yeast is improved by genetic recombination, enabling efficient ethanol fermentation even in the presence of fermentation inhibitors (acetic acid, formic acid) in saccharified biomass (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the method described in Patent Document 1 that uses an ion exchange membrane for recovering the acid contained in the solubilized treatment liquid, the sulfuric acid removal rate is about 86.0% with respect to 70% sulfuric acid, and the sulfuric acid removal rate is not sufficient. By increasing the flow rate of the recovered water, it is possible to increase the sulfuric acid removal rate, but since the sugar throughput also increases, it is difficult to ensure a high sugar recovery rate. Further, in the method described in Patent Document 2, a decrease in the ethanol fermentation rate is observed when 30 mM of formic acid is contained, and there are cases where it cannot sufficiently cope with a high formic acid concentration.

[0006] The organic acid removal method of the present disclosure mainly aims to provide an organic acid removal method capable of selectively removing organic acids in a sugar solution containing organic acids.

Means for Solving the Problems

[0007] The organic acid removal method of the present disclosure has adopted the following means to achieve the above main object.

[0008] The organic acid removal method of the present disclosure is an organic acid removal method for removing organic acids from a sugar solution containing organic acids, wherein an oxide of a Group 4 element or a lanthanoid having an ionic radius of less than 1 angstrom is applied to the sugar solution containing organic acids as an adsorbent for adsorbing the organic acids. This is the gist.

[0009] As a result of intensive research, the inventors of the present application have found that when an oxide of a Group 4 element or a lanthanoid having an ionic radius of less than 1 angstrom is used as an adsorbent, the sugar concentration in the sugar solution containing organic acids does not decrease so much, and the organic acids are quickly adsorbed by the adsorbent and removed from the solution. When an oxide of a Group 4 element or a lanthanoid having an ionic radius of 1 angstrom or more is used as an adsorbent, although the organic acids are removed, the sugar concentration in the sugar solution decreases. It is considered that the reason for the decrease in the sugar concentration in the latter case is that in elements with a large ionic radius, the basicity of the oxide becomes strong, causing side reactions such as decomposing sugar. Therefore, by applying an oxide of a Group 4 element or a lanthanoid having an ionic radius of less than 1 angstrom to the sugar solution containing organic acids as an adsorbent, the organic acids can be selectively removed from the sugar solution containing organic acids.

Brief Description of the Drawings

[0010]

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Embodiments for Carrying Out the Invention

[0011] Next, embodiments for carrying out the present disclosure will be described. FIG. 1 is a process diagram showing an example of the process of a method for producing bioethanol including an organic acid removal method as an embodiment of the present disclosure. In the method for producing bioethanol according to the embodiment, cellulose (general formula (C6H 10 O5)n: n = several hundreds to several thousands) - containing cellulosic biomass (for example, rice straw, wood, used clothes, household leftovers, etc.) is extracted as a solubilized product by physicochemical treatment (mechanochemical) (solubilization step), and an aqueous solution of the extracted solubilized product is hydrolyzed to glucose (molecular formula C6H 10It is saccharified up to O6) (saccharification step), fermented (fermentation step), and distilled and purified (distillation and purification step) to obtain bioethanol. In this embodiment, in the solubilization step, for example, biomass is roughly pulverized and pulverized while heating (heat pulverization) to extract cellulose as a soluble substance such as oligosaccharide. Heat pulverization is performed, for example, using a heat pulverizer such as a planetary ball mill at a temperature of 120 °C or higher. In the saccharification step, as a catalyst for hydrolyzing the aqueous solution of the soluble substance, for example, solid catalysts such as activated carbon, MnO2, ZrO2, and enzymes are used.

[0012] The organic acid removal step of this embodiment is executed after the saccharification step and before the fermentation step. The saccharified liquid contains organic acids such as formic acid generated in the solubilization step and the saccharification step, and since the organic acids inhibit the fermentation in the subsequent fermentation step, it is necessary to remove them. As shown in FIG. 2, in the organic acid removal step, the saccharified liquid is introduced into a tank filled with an adsorbent, and the organic acids contained in the saccharified liquid are adsorbed onto the adsorbent by the batch method or the flow method. In this embodiment, the organic acid removal step is performed using one of the two tanks. When the adsorbent in one tank reaches the saturation state, it is exchanged with the other tank, and the organic acid removal step is performed using the other tank while regenerating the adsorbent in one tank with sulfuric acid or hydrochloric acid. By repeating this, it becomes possible to seamlessly execute the organic acid removal step without requiring a waiting time due to the regeneration of the adsorbent.

[0013] As the adsorbent, oxides of group 4 elements or lanthanoids with an ionic radius of less than 1 angstrom, more preferably less than 0.9 angstrom, are used. As shown in FIG. 2, among the group 4 elements, Ti (titanium), Zr (zirconium), and Hf (hafnium), which have a valence of +3 and a coordination number of 6 when they become ions, all have an ionic radius of less than 0.9 angstrom, and their oxides can be suitably used as the adsorbent. Suitable group 4 element oxides as the adsorbent include TiO2, ZrO2, HfO2, etc.

[0014] Also, as shown in Fig. 3, among the lanthanoids, Pr (praseodymium), Nd (neodymium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium), which have a valence of +3 and a coordination number of 6 when they become ions, all have an ionic radius of less than 1.0 angstroms, and their oxides can be suitably used as adsorbents. In particular, the oxides of Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium), which have an ionic radius of less than 0.9 angstroms, can be more suitably used. Furthermore, Ce (cerium) and Pr (praseodymium), which have a valence of +4 and a coordination number of 6 when they become ions, both have an ionic radius of less than 0.9 angstroms, and their oxides can be more suitably used as adsorbents. Particularly suitable lanthanoid oxides as adsorbents are CeO2, Er2O3, Tm2O3, Yb2O3, Lu2O3, Pr6O 10 or Pr6O 11 and the like. On the other hand, La and Ce, which have a valence of +3 and a coordination number of 6 when they become ions among the lanthanoids, have an ionic radius exceeding 1.0 angstroms, and their oxides are excluded from suitable adsorbents.

[0015] An experiment was conducted in which a saccharified solution containing glucose, xylose, and formic acid was prepared, an adsorbent was added thereto, and after a certain period of time, the remaining amount (adsorption amount) of formic acid contained in the saccharified solution was measured. The experiment was carried out for each of a plurality of different adsorbents. The saccharified solution used was a 5.00 mL aqueous solution containing 300 mM (5.4 wt%), 200 mM (3.0 wt%), and 91 mM (0.42 wt%) of glucose, xylose, and formic acid, respectively. As the adsorbents, 0.500 g and 0.200 g of ZrO2, 0.500 g of CeO2, 0.500 g of hydrotalcite, and 0.500 g of La2O3 were used.

[0016] Figure 5 is an explanatory diagram as experimental results showing the remaining amounts of glucose, xylose, and formic acid contained in the saccharified solution when ZrO2 is used as the adsorbent. When 0.500 g of ZrO2 is used as the adsorbent, as shown in the figure, it was confirmed that the formic acid contained in the saccharified solution rapidly (after several minutes) decreased to 8%. On the other hand, the glucose and xylose contained in the saccharified solution hardly decreased. Also, ZrO2 did not dissolve in the saccharified solution. Therefore, it can be seen that by using ZrO2 as the adsorbent, the formic acid contained in the saccharified solution can be selectively removed in a short time.

[0017] Figure 6 is an explanatory diagram as experimental results showing the remaining amounts of glucose, xylose, and formic acid contained in the saccharified solution when CeO2 is used as the adsorbent. When 0.500 g of CeO2 is used as the adsorbent, as shown in the figure, it was confirmed that the formic acid contained in the saccharified solution, although the amount of decrease was less than that of ZrO2, rapidly (after several minutes) decreased to 38%. On the other hand, the glucose and xylose contained in the saccharified solution hardly decreased. Also, CeO2 did not dissolve in the saccharified solution. Therefore, it can be seen that by using CeO2 as the adsorbent, the formic acid contained in the saccharified solution can be selectively removed in a short time.

[0018] Figure 7 is an explanatory diagram as experimental results showing the remaining amounts of glucose, xylose, and formic acid contained in the saccharified solution when a small amount of ZrO2 is used as the adsorbent. When 0.200 g of ZrO2 is used as the adsorbent, as shown in the figure, the formic acid contained in the saccharified solution immediately (in about 30 seconds) decreased, but after decreasing to 48%, the adsorption amount became saturated and hardly decreased any further. Therefore, from the experimental results of Figure 5 and Figure 7, it can be seen that by appropriately adjusting (increasing) the amount of ZrO2 as the adsorbent according to the input amount of the saccharified solution and the formic acid concentration in the saccharified solution, the formic acid contained in the saccharified solution can be selectively removed in a short time. Also, it is considered that even when CeO2 is used as the adsorbent as described above, if the amount of CeO2 is increased, the remaining amount of formic acid in the saccharified solution can be further decreased.

[0019] Figure 8 is an explanatory diagram as experimental results showing changes in the remaining amounts of glucose, xylose, and formic acid contained in the saccharified solution when hydrotalcite is used as the adsorbent. Note that the hydrotalcite used was obtained by calcination at 500°C. When 0.500 g of hydrotalcite was used, as shown in the figure, although the remaining amount of formic acid decreased, the rate of decrease was slower compared to the case where ZrO2 or CeO2 was used as the adsorbent, and it took 60 minutes to decrease to 17%. Also, when hydrotalcite was used as the adsorbent, it was confirmed that the remaining amounts of glucose and xylose also decreased. Furthermore, it was confirmed that hydrotalcite dissolved in the saccharified solution. Therefore, it can be seen that hydrotalcite not only requires a long time for the removal of formic acid (organic acid removal step), but also decreases the sugar concentration in the saccharified solution.

[0020] Figure 9 is an explanatory diagram as experimental results showing the remaining amounts of glucose, xylose, and formic acid contained in the saccharified solution when La2O3 is used as the adsorbent. In the experiment of Figure 9, a 5.00 mL aqueous solution containing 300 mM (5.4 wt%), 200 mM (3.0 wt%), and 200 mM (0.92 wt%) of glucose, xylose, and formic acid respectively was used for the saccharified solution. When 0.500 g of La2O3 was used as the adsorbent, as shown in the figure, although the formic acid contained in the saccharified solution decreased to 28% after 30 minutes, a decrease in glucose and xylose was also observed. Also, it was confirmed that La2O3 dissolved in the saccharified solution. Therefore, it can be seen that although the formic acid contained in the saccharified solution can be removed by using La2O3 as the adsorbent, the sugar concentration in the saccharified solution decreases. This is considered to be because among group 4 elements or lanthanoids, in La and trivalent Ce with a low valence when becoming ions and a large ionic radius (1.0 angstrom or more), the effect of the positive charge weakens, resulting in an increase in the basicity of the oxide and causing side reactions such as decomposition of sugar.

[0021] From the above experimental results, it can be seen that by using oxides (such as ZrO2 and CeO2) of Group 4 elements or lanthanoids with an ionic radius of less than 1 angstrom, particularly Group 4 elements or lanthanoids with an ionic radius of less than 0.9 angstrom, as adsorbents, formic acid (organic acid) contained in the saccharified solution can be selectively removed in a short time. Therefore, by performing a fermentation process after the organic acid removal step, bioethanol can be efficiently produced.

[0022] As described above, the embodiments for carrying out the present disclosure have been explained. However, the present disclosure is not limited to such embodiments, and it goes without saying that it can be implemented in various forms without departing from the gist of the present disclosure.

[0023] For example, in the above-described embodiment, the organic acid removal step was carried out after the saccharification step and before the fermentation step. However, as shown in the process diagram of FIG. 10, it may also be carried out after the solubilization step and before the saccharification step.

[0024] Also, in the above-described embodiment, the organic acid removal step was applied to a process in which cellulosic biomass was extracted as a solubilized product by physicochemical treatment, and the aqueous solution of the extracted solubilized product was hydrolyzed (saccharified) using a catalyst such as activated carbon. However, it is not limited thereto, and the organic acid removal step may be applied to any method of producing a saccharified solution as long as it removes the organic acid contained in the saccharified solution, such as hydrolysis (acid hydrolysis) using dilute sulfuric acid or concentrated sulfuric acid.

Industrial Applicability

[0025] The present disclosure can be used in the manufacturing industry of bioethanol and the like.

Claims

1. An organic acid removal method for removing an organic acid from an organic acid-containing sugar solution, wherein, as an adsorbent for adsorbing the organic acid, an oxide of a Group 4 element or a lanthanoid having an ionic radius of less than 1 angstrom is applied to the organic acid-containing sugar solution, Organic acid removal method.

2. The organic acid removal method according to Claim 1, wherein, as the adsorbent, an oxide of a Group 4 element or a lanthanoid having an ionic radius of less than 0.9 angstrom is applied to the organic acid-containing sugar solution, Organic acid removal method.

3. The organic acid removal method according to Claim 2, wherein the oxide of the Group 4 element or the lanthanoid is ZrO 2 or CeO 2 and is, Organic acid removal method.

4. The organic acid removal method according to any one of Claims 1 to 3, wherein the adsorbent is applied to the organic acid-containing sugar solution generated during or after the step of producing a saccharified solution from biomass to remove the organic acid from the organic acid-containing sugar solution, Organic acid removal method.

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