METHOD OF REGENERATING HETEROPOLYACID

CATALYST USED IN THE DIRECT PROCESS OF PREPARING

DICHLOROPROPANOL BY REACTING GLYCEROL AND

CHLORINATING AGENT, METHOD OF PREPARING DICHLOROPROPANOL COMPRISING THE METHOD OF REGENERATING HETEROPOLYACID CATALYST AND

METHOD OF PREPARING EPICHLOROHYDRIN COMPRISING THE METHOD OF PREPARING DICHLOROPROPANOL

Technical Field

[1] An embodiment of the present invention relates to a method of regenerating a het- eropolyacid catalyst used in the direct process of preparing dichloropropanol by reacting glycerol with a chlorinating agent , a method of preparing dichloropropanol including the method of regenerating the heteropolyacid catalyst, and a method of preparing epichlorohydrin including the method of preparing dichloropropanol, and more particularly, to a method of regenerating a heteropolyacid catalyst including a simple evaporation stage and a calcination stage, and selectively including a recrystal- lization stage. Background Art

[2] Recently, bio-diesels have been competitively developed and produced worldwide, and also domestically manufactured and brought to markets as an additive to petro- diesel.

[3] During the production of bio-diesel, a large amount of glycerol, corresponding to about 10% of the amount of the produced bio-diesel, is generated as a by-product. However, supply of glycerol is greater than demand therefor and oversupply of glycerol decreases its value. Thus, it is economically advantageous to convert glycerol into dichloropropanol which is a higher-value added product compared to glycerol.

[4] Meanwhile, dichloropropanol is a raw material used to produce epichlorohydrin which is applied to a variety of fields as a raw material for epoxy resins, synthesized glycerin, ion exchange resins, flame retardants, solvents, medicines, dyes, and the like. Most of the dichloropropanol which is currently supplied to markets is manufactured from propylene. More particularly, a method of preparing dichloropropanol includes a two-stage process of preparing allyl chloride through chlorination reaction of propylene at a high temperature and preparing dichloropropanol by reacting the allyl chloride with hydrochloric acid using an excess amount of industrial water (US Patent Nos. 4,479,020, 6,051,742, and 6,333,420). However, the method of preparing dichloropropanol using propylene has problems in terms of instability of propylene supply and demand caused by increased price of propylene, generation of a large amount of waste water and other waste, excessive initial investment costs due to the two-stage manufacturing process and difficulty of modifying the process.

[5] Accordingly, a single-stage process of directly preparing dichloropropanol by reacting glycerol with hydrochloric acid is more economical. The single-stage process using glycerol is advantageous in that costs of raw materials can be reduced by using inexpensive glycerol as a reactant, the amount of waster water and other waste can be dramatically reduced since industrial water is not required for the process, thereby being environmentally friendly and initial investment costs related to the process and environment can be reduced. In addition, the method of preparing dichloropropanol from glycerol using a single-stage process is environmentally friendly since dichloropropanol is directly prepared from glycerol which is a by-product generated in the preparation of bio-diesels, which is different from the conventional method of preparing dichloropropanol through the two-stage manufacturing process.

[6] In addition, manufacturing costs for dichloropropanol and energy consumption can be reduced by using glycerol, which is inexpensive and a by-product generated in the preparation of bio-diesel, instead of propylene as a reactant and by developing an efficient catalyst by which a single-stage process is used instead of using a two-stage manufacturing process of preparing dichloropropanol. Thus, when an excellent catalyst process by which dichloropropanol can be directly prepared using glycerol is developed, technological competitiveness in the preparation of dichloropropanol can be gained with regard to environmental, economical, and investment cost factors.

[7] Dow Chemical Company, U.S.A. and Solvay, S.A., Germany are major companies currently manufacturing epichlorohydrin from glycerol. These companies manufacture dichloropropanol from glycerol by using a continuous process using a carboxylic acid- based homogeneous catalyst and hydrogen chloride gas as a chlorinating agent (International Publication Nos. WO2006/020234, WO2005/054167 and WO2005/021476).

[8] In addition, Chinese Patent Publication No. CN 10100775 IA discloses a method of preparing dichloropropanol in which consumption of hydrogen chloride gas is decreased by performing a first reaction in a plug flow reactor using a nitrile-based catalyst and continuously removing water from a second reaction performed using a bubble cap tray.

[9] In addition, a method of preparing dichloropropanol by diluting glycerol in a solvent and passing the diluted glycerol and hydrogen chloride gas through a packed bed packed with glass beads without using a catalyst is reported by Isu Chemical Company, Korea (Korean Patent Publication No. 2008-0038284).

[10] However, apart from the above publications, inventions related to a method of directly preparing dichloropropanol from glycerol have not been disclosed. Disclosure of Invention Technical Problem

[11] The present invention provides a method of regenerating a heteropolyacid catalyst used in the direct process of preparing dichloropropanol by reacting glycerol with a chlorinating agent, the method including a simple evaporation stage and a calcination stage, and selectively including a recrystallization stage.

[12] The present invention also provides a method of directly preparing dichloropropanol, the method including the method of regenerating a heteropolyacid catalyst, wherein the regenerated heteropolyacid catalyst is re-used.

[13] The present invention also provides a method of preparing epichlorohydrin, the method including the method of preparing dichloropropanol. Technical Solution

[14] According to an aspect of the present invention, there is provided a method of regenerating a heteropolyacid catalyst used in the direct process of preparing dichloropropanol by reacting glycerol with a chlorinating agent, the method including:

[15] separating a solid heteropolyacid catalyst from a reaction mixture by simply evaporating components having a boiling point lower than that of the heteropolyacid catalyst in a simple evaporation stage; and

[16] calcining the separated solid heteropolyacid catalyst in a calcination stage.

[17] The method may further include recrystallizing the calcined heteropolyacid catalyst in a recrystallization stage.

[18] The recrystallization stage may include: preparing a catalyst solution by dissolving the calcined heteropolyacid catalyst in water; removing impurities from the catalyst solution by filtering the catalyst solution; and heating the filtered catalyst solution to a temperature in the range of about 50 to about 100 ⁰ C for about 1 to about 20 hours.

[19] The method of claim 3 may further include drying the recrystallized heteropolyacid catalyst at a temperature in the range of about 50 to about 100 ⁰ C for about 1 to about 48 hours (drying stage) after the recrystallization.

[20] The simple evaporation stage may include heating the reaction mixture to a temperature in the range of about 100 to about 400 ⁰ C for about 10 minutes to about 5 hours.

[21] The calcination stage may further include heating the separated solid heteropolyacid catalyst in the presence of oxygen to a temperature in the range of about 200 to about 400 ⁰ C for about 1 to about 40 hours.

[22] The heteropolyacid catalyst may include a Keggin-type heteropolyacid catalyst in which the ratio of the number of central atoms to the number of coordinated atoms is 1:12.

[23] The Keggin-type heteropolyacid catalyst may include 12-tungstophosphoric acid (H ₃

PW ₁₂ O ₄₀ ).

[24] According to another aspect of the present invention, there is provided a method of directly preparing dichloropropanol by reacting glycerol with a chlorinating agent, constituting a chlorination reaction, using a heteropolyacid catalyst, the method including the method of regenerating a heteropolyacid catalyst, wherein the regenerated heteropolyacid catalyst is re-used.

[25] The chlorinating agent may include hydrogen chloride gas or hydrochloric acid.

[26] The chlorination reaction may be performed at a temperature in the range of about 50 to about 300 ⁰ C at a pressure in the range of about 0.1 to about 30 bar for about 10 minutes to about 50 hours.

[27] The chlorination reaction may be performed in at least one reactor selected from a group consisting of a batch reactor, a semi-batch reactor, a constant stirred tank reactor (CSTR), and a plug flow reactor.

[28] According to another aspect of the present invention, there is provided a method of preparing epichlorohydrin (ECH) after directly preparing dichloropropanol by reacting glycerol with a chlorinating agent using a heteropolyacid catalyst, the method including the method of preparing dichloropropanol. Description of Drawings

[29] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

[30] FIG. 1 is a graph illustrating infrared (IR) analysis results of regenerated heteropolyacid catalysts according to embodiments of the present invention and a pure heteropolyacid catalyst. Mode for Invention

[31] Hereinafter, a method of regenerating a heteropolyacid catalyst according to an embodiment of the present invention will be described.

[32] A method of regenerating a heteropolyacid catalyst used in the direct process of preparing dichloropropanol by reacting glycerol with a chlorinating agent according to an embodiment of the present invention includes a simple evaporation stage and a calcination stage. [33] The simple evaporation stage is a stage by which a solid heteropolyacid catalyst is separated from a reaction mixture including reactants, products, heteropolyacid catalyst and/or water by simply evaporating components having a boiling point lower than that of the heteropolyacid catalyst from the reaction mixture. The calcination stage is a stage by which impurities contained in the separated solid heteropolyacid catalyst are removed by being burned.

[34] The simple evaporation stage may include heating the reaction mixture to a temperature in the range of about 100 to about 400 ⁰ C for about 10 minutes to about 5 hours. If the simple evaporation stage is performed at a temperature higher than 100 ⁰ C or for longer than 10 minutes, the reaction mixture except for the heteropolyacid catalyst is smoothly evaporated. On the other hand, if the simple evaporation stage is performed at a temperature lower than 400 ⁰ C or for shorter than 5 hours, pyrolysis of the heteropolyacid catalyst may be inhibited, thereby preventing the chemical structure of the heteropolyacid catalyst from being broken.

[35] The calcination stage may include heating the separated solid heteropolyacid catalyst in the presence of oxygen to a temperature in the range of about 200 to about 400 ⁰ C for about 1 to about 40 hours. If the calcination stage is performed at a temperature higher than 200 ⁰ C or for longer than 1 hour, contact time with oxygen is long enough, and thus impurities such as carbon attached to the heteropolyacid catalyst are sufficiently burned. On the other hand, if the calcination stage is performed at a temperature lower than 400 ⁰ C or for shorter than 40 hours, pyrolysis of the heteropolyacid catalyst may be inhibited, thereby preventing the chemical structure of the heteropolyacid catalyst from being broken.

[36] For example, the calcination stage may be performed under an air atmosphere. Impurities (reactants and/or products) are attached to the solid heteropolyacid catalyst obtained through the simple evaporation stage, and most of the impurities are burned and removed during the calcination stage.

[37] The method of regenerating a heteropolyacid catalyst according to the present embodiment may further include recrystallizing the calcined heteropolyacid catalyst (recrystallization stage). As a result of the recrystallization stage, impurities remaining in the heteropolyacid catalyst are further removed, and the amount of water of crystallization contained in the heteropolyacid catalyst is controlled. Accordingly, the crystal structure of the heteropolyacid catalyst is changed.

[38] The recrystallization stage may include: preparing a catalyst solution by dissolving the calcined heteropolyacid catalyst in water; removing impurities from the catalyst solution by filtering the catalyst solution using filter paper; and heating the filtered catalyst solution to a temperature in the range of about 50 to about 100 ⁰ C for about 1 to about 20 hours. If the recrystallization stage is performed at a temperature higher than 50 ⁰ C or for longer than 1 hour, water constituting water of crystallization is easily evaporated during the recrystallization of the heteropolyacid catalyst so that the amount of the water of crystallization is not changed, thereby preventing the chemical structure of the heteropolyacid catalyst from being changed. On the other hand, if the recrystallization stage is performed at a temperature lower than 100 ⁰ C or for shorter than 20 hours, all water constituting water of crystallization, may not be evaporated during the recrystallization of the heteropolyacid catalyst, thereby preventing the heteropolyacid catalyst from being burned.

[39] The method of regenerating a heteropolyacid catalyst according to the present embodiment may further include drying the recrystallized heteropolyacid catalyst at a temperature in the range of about 50 to about 100 ⁰ C for about 1 to about 48 hours (drying stage) after the recrystallization stage. The drying is performed in order to remove water still remaining in the recrystallized heteropolyacid catalyst. If the drying is performed at a temperature higher than 50 ⁰ C or for longer than 1 hour, the remained water other than water constituting water of crystallization is sufficiently removed. On the other hand, if the drying is performed at a temperature lower than 100 ⁰ C or for shorter than 48 hours, energy and time consumed during the drying stage may be reduced.

[40] The heteropolyacid catalyst may include a Keggin-type heteropolyacid catalyst in which the ratio of the number of central atoms to the number of coordinated atoms is 1:12. For example, the Keggin-type heteropolyacid catalyst may include 12-tungstophosphoric acid (H ₃ PWi ₂ O ₄₀ ).

[41] The present invention also provides a method of directly preparing dichloropropanol by reacting glycerol with a chlorinating agent using a heteropolyacid catalyst. The method of directly preparing dichloropropanol includes the method of regenerating a heteropolyacid catalyst according to the embodiment described above, and re-using the regenerated heteropolyacid catalyst.

[42] The chlorinating agent used in the chlorination reaction may include hydrogen chloride gas or hydrochloric acid.

[43] The chlorination reaction may be performed at a temperature in the range of about 50 to about 300 ⁰ C, for example, about 100 to about 200 ⁰ C. If the chlorination reaction is performed at a temperature higher than 50 ⁰ C, the reaction rate may be sufficiently high. On the other hand, if the chlorination reaction is performed at a temperature lower than 300 ⁰ C, energy loss may be minimized.

[44] In addition, generally, the chlorination reaction may be performed at a pressure in the range of about 0.1 to about 30 bar, for example, about 1 to about 15 bar. Even though higher activity may be observed at a higher reaction pressure, when the pressure is higher than a predetermined level (30 bar), the reaction activity is not increased any longer. The reaction pressure is regulated by the pressure of the chlorinating agent. The reaction may be performed for about 10 minutes to about 50 hours, and preferably for about 1 to about 20 hours. If the reaction is performed for longer than 10 minutes, the glycerol-conversion rate is high. On the other hand, if the reaction is performed for longer than 50 hours, the reaction is nearly terminated, and thus the conversion rate or selectivity is not increased any longer.

[45] Here, the 'dichloropropanol' indicates a mixture of isomers including l,3-dichloropropane-2-ol and l,2-dichloropropane-3-ol. In the method of preparing dichloropropanol, l,3-dichloropropane-2-ol, which is a suitable reactant for the preparation of epichlorohydrin, is mainly produced.

[46] The chlorination reaction may be performed in at least one reactor selected from a group consisting of a batch reactor, a semi-batch reactor, a constant stirred tank reactor (CSTR), and a plug flow reactor. The reactor may be formed of a material which has resistance to a chlorinating agent or may include interior structures coated with such material. The material having resistance to the chlorinating agent may be Hastelloy C, Teflon, or the like.

[47] In addition, the heteropolyacid catalyst is regenerated after the chlorination reaction and re-used. That is, the regenerated heteropolyacid catalyst according to the present invention may be added to the reactor and re-used. Since the heteropolyacid catalyst and the reaction mixture except for the heteropolyacid catalyst do not form an azeotrope after the reaction, the heteropolyacid catalyst may be regenerated and reused. As in the case of using a conventional carboxylic acid-based catalyst, if a reaction mixture except for the catalyst and the catalyst form an azeotrope, equilibrium is established between liquid and gas phases. Thus, the catalyst may not be simply separated from the reaction mixture since the ratio of components between the liquid and gas phases is constantly maintained and the boiling point of each component is not changed.

[48] The addition of the catalyst may be performed in a continuous or discontinuous way in the reactor.

[49] In the direct preparation of dichloropropanol from glycerol using the heteropolyacid catalyst, the glycerol-conversion rate, the selectivity for dichloropropanol, and the yield of dichloropropanol are respectively calculated using Equations 1 to 3 below.

[50] Equation 1

[51] Glycerol-conversion rate (%) = (the number of moles of reacted glycerol/the number of moles of supplied glycerol)xl00

[52] Equation 2

[53] Selectivity for dichloropropanol (%) = (the number of moles of produced dichloro- propanol/the number of moles of reacted glycerol)xl00 [54] The selectivity for dichloropropanol is calculated based on the mixture of isomers of l,3-dichloropropane-2-ol and l,2-dichloropropane-3-ol. [55] Equation 3

[56] Yield of dichloropropanol (%) = (the number of moles produced dichloropropanol/ the number of moles of supplied glycerol) x 100 [57] Meanwhile, the present invention also provides a method of preparing epichlorohydrin including the method of preparing the dichloropropanol. In particular, a method of preparing epichlorohydrin from glycerol using a heteropolyacid catalyst is shown in Reaction Scheme 1 below. [58] Reaction Scheme 1

[59]

OH OH Cl

^N ^Q ilor inat ing agent JL JL

G ^O l ^H yce ^O ro ^H l £xs ^lyac 1 ^ld ,3-dichlo &ropro ipane-2 ⁺ -ol 1,2 £-dich &loropropane-3-ol

NaOH

Epiehlorohydrin

[60] Hereinafter, the present invention will be described in greater detail with reference to the following examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[61] Examples

[62] Experimental Example 1 (Comparative Example 1-1): Method of regenerating het- eropolvacid catalyst including simple evaporation

[63] Dichloropropanol was directly prepared from glycerol and hydrogen chloride gas using a heteropolyacid catalyst. The reaction was performed in a liquid phase in a 200 ml batch reactor from which water was completely removed. The interior structures of the batch reactor were formed of Hastelloy C and Teflon which has resistance to a chlorinating agent. First, 100 g of glycerol and 3 g of 12-tungstophosphoric acid, as a pure Keggin-type heteropolyacid catalyst were added to the batch reactor. The term 'pure catalyst' used herein indicates 'unused catalyst with high purity'. Then, the reaction temperature was fixed at 13O ⁰ C, and the reaction was performed by continuously supplying 99.7 wt% of hydrogen chloride gas, as a chlorinating agent, at a constant pressure of 3 bar to the batch reactor for 3 hours while stirring at 900 rpm to directly prepare dichloropropanol. [64] After the reaction was terminated, the heteropolyacid catalyst was collected by heating the batch reactor at 300 ⁰ C for 2 hours so that components having a boiling point lower than that of the heteropolyacid catalyst were removed. As a result, a solid 12-tungstophosphoric acid catalyst was obtained.

[65] Example 1-1: Method of regenerating heteropolvacid catalyst including simple evaporation and calcination

[66] The 12-tungstophosphoric acid catalyst regenerated according to Experimental

Example 1 was added to an electric furnace and calcined at 35O ⁰ C for 20 hours under an air atmosphere to regenerate the 12-tungstophosphoric acid catalyst.

[67] Example 1-2: Method of regenerating heteropolvacid catalyst including simple evaporation, calcination, recrystallization. and drying

[68] The 12-tungstophosphoric acid regenerated according to Example 1-1 was dissolved in water to prepare a catalyst solution. The catalyst solution was filtered using filter paper to remove impurities. Then, the catalyst of the catalyst solution was recrys- tallized by heating the catalyst solution at 8O ⁰ C for 5 hours. And then the catalyst solution was dried in a drying device at 8O ⁰ C for 24 hours.

[69] Dichloropropanol was prepared from glycerol using a pure 12-tungstophosphoric acid catalyst, and the 12-tungstophosphoric acid catalysts regenerated according to Experimental Example 1, Example 1-1, and Example 1-2, respectively. Then, glycerol- conversion rates, selectivities for dichloropropanol, and yields of dichloropropanol were calculated by analyzing the reaction mixtures after the reactions were terminated.

[70] Experimental Example 2-1 (Comparative Example 2-1): Direct preparation of dichloropropanol from glycerol using pure Keggin-tvpe heteropolvacid catalyst. 12-tungstophosphoric acid (H^PW _12- O _* n)

[71] Dichloropropanol was directly prepared by reacting glycerol with hydrogen chloride gas in the same manner as in Experimental Example 1, except that a catalyst was not used, or 12-tungstophosphoric acid (H ₃ PWi ₂ O ₄₀ ) was used as a pure Keggin-type heteropolyacid catalyst by the amounts described in Table 1 below . After each of the reactions was terminated, the reactor was cooled to room temperature. Then, the reaction mixtures were analyzed using gas chromatography. In addition, glycerol- conversion rates, selectivities for dichloropropanol, and yields of dichloropropanol were calculated using Equations 1 to 3, and the results are shown in Table 1 below. 'MCPD' and 'DCP' of Table 1 respectively indicate monochloropropandiol and dichloropropanol. Products of the reaction mainly include monochloropropandiol and dichloropropanol. The products may further include a small amount (less than 3 wt%) of by-products such as epichlorohydrin and trichloropropane (TCP).

[72] Table 1

[73] Table 1

[74] Referring to Table 1, the yield of dichloropropanol increases as the amount of the 12-tungstophosphoric acid catalyst increases. Thus, dichloropropanol may be more efficiently prepared when a large amount of the catalyst is used.

[75] Experimental Example 2-2 (Comparative Example 2-2): Direct preparation of dichloropropanol from glycerol using 12-tungstophosphoric acid (HJW i ₁ Om) re- generated according to Experimental Example 1 (simple evaporation)

[76] 3 g of the 12-tungstophosphoric acid catalyst used in Experimental Example 2-1 was regenerated using the simple evaporation stage according to Experimental Example 1, and dichloropropanol was prepared in the same manner as in Experimental Example 2-1 using the regenerated 12-tungstophosphoric acid catalyst. Then, this process of regenerating the 12-tungstophosphoric acid catalyst used in the preparation of dichloropropanol and preparing dichloropropanol using the regenerated the 12-tungstophosphoric acid catalyst was repeated (the 12-tungstophosphoric acid catalyst was regenerated three times and dichloropropanol was prepared three times using the each regenerated 12-tungstophosphoric acid catalyst). After each of the reactions was terminated, the reaction mixtures were analyzed in the same manner as in Experimental Example 2-1. Glycerol-conversion rates, selectivities for dichloropropanol, and yields of dichloropropanol were calculated, and the results are shown in Table 2 below. The result of the analysis using 3 g of the catalyst which is shown in Table 1 is also shown in Table 2.

[77] Table 2 [78] Table 2

[79] [80] Referring to Table 2, the yield of dichloropropanol decreases as the number of times the catalyst is regenerated increases when dichloropropanol is directly prepared using the 12-tungstophosphoric acid catalyst regenerated using the simple evaporation process according to Experimental Example 1.

[81] Example 2-1: Direct preparation of dichloropropanol from glycerol using 12-tungstophosphoric acid (H^PW _12- O _* n) catalyst regenerated according to Example 1-1

[82] A process of regenerating a 12-tungstophosphoric acid catalyst and preparing dichloropropanol was repeated in the same manner as in Experimental Example 2-2, except that 3 g of the 12-tungstophosphoric acid catalyst like the catalyst used in Experimental Example 2-1 was regenerated according to Example 1-1 and used to prepare dichloropropanol. After each of the reactions was terminated, the reaction mixture was analyzed in the same manner as in Experimental Example 2-1. Glycerol- conversion rates, selectivity for dichloropropanol, and yields of dichloropropanol were calculated, and the results are shown in Table 3 below. The result of the analysis using 3 g of the catalyst which is shown in Table 1 is also shown in Table 3.

[83] Table 3 [84] Table 3

[85] Referring to Table 3, the yield of dichloropropanol is not much changed even if the number of times the catalyst is regenerated increases when dichloropropanol is directly prepared using the 12-tungstophosphoric acid catalyst regenerated according to Example 1-1.

[86] Example 2-2: Direct preparation of dichloropropanol from glycerol using 12-tungstophosphoric acid (IHkPW r _2- O Δ _Q ) catalyst regenerated according to Example hi

[87] A process of regenerating a 12-tungstophosphoric acid catalyst and preparing dichloropropanol was repeated in the same manner as in Experimental Example 2-2, except that 3 g of the 12-tungstophosphoric acid catalyst like the catalyst used in Experimental Example 2-1 was regenerated according to Example 1-2 and used to prepare dichloropropanol. After each of the reactions was terminated, the reaction mixture was analyzed in the same manner as in Experimental Example 2-1. Glycerol- conversion rates, selectivity for dichloropropanol, and yields of dichloropropanol were calculated, and the results are shown in Table 4 below. The result of the analysis using 3 g of the catalyst which is shown in Table 1 is also shown in Table 4.

[88] Table 4 [89] Table 4

[90] Referring to Table 4, the yield of dichloropropanol is not much changed even if the number of times the catalyst is regenerated increases when dichloropropanol is directly prepared using the 12-tungstophosphoric acid catalyst regenerated according to Example 1-2. Furthermore, there is no big difference between the yield of dichloropropanol using the 12-tungstophosphoric acid catalyst regenerated according to Example 1-2 and the yield of dichloropropanol using the pure 12-tungstophosphoric acid catalyst (the yield of DCP in case of using the pure 12-tungstophosphoric acid catalyst: 81.0%, and the yield of DCP in case of using the 12-tungstophosphoric acid catalyst regenerated three times: 79.0%).

[91] Evaluation Examples [92] Evaluation Example 1: IR analysis results of pure 12-tungstophosphoric acid (TLPW I ₂ O AH ) catalyst: and 12-tungstophosphoric acid catalyst regenerated according to Ex- perimental Example 1 (simple evaporation). Example 1-1. and Example 1-2

[93] IR analysis results of a pure 12-tungstophosphoric acid (H ₃ PWi ₂ O ₄₀ ) catalyst, and 12-tungstophosphoric acid catalysts regenerated according to Experimental Example 1 (simple evaporation), Example 1-1, and Example 1-2 are shown in FIG. 1.

[94] Referring to FIG. 1, the 12-tungstophosphoric acid catalyst regenerated according to Experimental Example 1 (Comparative Example 1-1, simple evaporation) does not exhibit IR peaks indicating intrinsic properties of the pure 12-tungstophosphoric acid catalyst. However, the 12-tungstophosphoric acid catalysts regenerated according to Example 1-1 (simple evaporation+calcination) and Example 1-2 (simple evaporation+calcination+recrystallization+drying) exhibit IR peaks indicating intrinsic properties of the pure 12-tungstophosphoric acid catalyst.

[95] Evaluation Example 2: CHNS analysis results of 12-tungstophosphoric acid catalysts regenerated according to Experimental Example 1 (simple evaporation). Example 1-1. and Example 1-2

[96] CHNS analysis results of a pure 12-tungstophosphoric acid (H ₃ PWi ₂ O ₄₀ ) catalyst, and 12-tungstophosphoric acid catalysts regenerated according to Experimental Example 1 (simple evaporation), Example 1-1 (simple evaporation+calcination), and Example 1-2 (simple evaporation+calcination+recrystallization+drying) are shown in Table 5.

[97] Table 5 [98] Table 5

[99] Referring to Table 5, the 12-tungstophosphoric acid catalyst regenerated according to Experimental Example 1 (simple evaporation) has a larger amount of carbon than the 12-tungstophosphoric acid catalysts regenerated according to Example 1-1 and Example 1-2. Thus, it can be seen that carbon deposits are not completely evaporated during the evaporation but remain on the surface of the 12-tungstophosphoric acid catalyst regenerated by the simple evaporation of Experimental Example 1. However, in the 12-tungstophosphoric acid catalysts regenerated according to Example 1-1 and Example 1-2, a large amount of carbon attached to the 12-tungstophosphoric acid catalysts is removed during the calcination stage under an air atmosphere, and thus only a small amount of carbon remains.

[100] While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.