Catalyst for producing unsaturated carboxylic acids and their derivatives

Abstract

The present invention provides a catalyst for producing unsaturated carboxylic acids and their derivatives, which can produce unsaturated carboxylic acids and their derivatives in high yield over a long period of time during the dehydration reaction of hydroxycarboxylic acids or their derivatives.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0118052, filed September 19, 2022, and Korean Patent Application No. 10-2023-0117559, filed September 5, 2023, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a catalyst for producing unsaturated carboxylic acids and derivatives thereof. [Background technology]

[0003] Acrylic acid is generally synthesized through a two-step oxidation reaction of propylene, a petroleum-derived raw material. However, due to the rapid rise in crude oil prices and concerns about future depletion, research is being conducted to obtain unsaturated carboxylic acids such as acrylic acid from biomass raw materials.

[0004] Lactic acid can be mass-produced from starch through fermentation, and acrylic acid can be produced by the dehydration of lactic acid. Metal phosphate, metal sulfate, or zeolite catalysts are mainly used for the dehydration of lactic acid. Of these, metal phosphate has been the subject of much research, but the yield of acrylic acid is low.

[0005] Specifically, International Publication WO2011 / 052178 describes a method for producing hydroxyapatite (Ca 10 (PO4)6(OH)2) and Sr 10 A synthesis method has been proposed in which unsaturated carboxylic acids and their derivatives are synthesized by dehydration of hydroxycarboxylic acids and their derivatives using (PO4)6(OH)2 as a catalyst. However, when acrylic acid is synthesized from lactic acid using hydroxyapatite, the yield of acrylic acid is about 50-70%. 10In the case of (PO4)6(OH)2, the yield of acrylic acid is even lower, at around 30%.

[0006] This has created a demand for the development of a production method and catalyst that can synthesize unsaturated carboxylic acids such as acrylic acid and their esters in high yield. Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide a catalyst that can produce unsaturated carboxylic acids and derivatives thereof in high yield over a long period of time when producing unsaturated carboxylic acids and derivatives thereof by dehydration of hydroxycarboxylic acids or derivatives thereof, and a method for producing carboxylic acids and derivatives thereof using the same. [Means for solving the problem]

[0008] According to the present invention, there is provided a catalyst for producing an unsaturated carboxylic acid or a derivative thereof, which comprises two or more types of hydroxyapatite having different alkali metal contents in the crystal, and in which phosphorus (P), calcium (Ca), and alkali metal (M) present on the catalyst surface satisfy the following conditions (i) and (ii): (i) The molar ratio of calcium to phosphorus (Ca / P molar ratio) is 1.0 or more and 1.2 or less. (ii) The total molar ratio of calcium and alkali metal (M) to phosphorus ((Ca+M) / P molar ratio) is 1.2 or more and 1.6 or less.

[0009] Furthermore, the present invention provides a method for producing a catalyst for producing an unsaturated carboxylic acid or a derivative thereof, comprising the steps of adding an alkali metal source material to a mixture containing hydroxyapatite and pyrophosphate, and then reacting the mixture at a temperature of 130°C to 250°C and a pressure of 3 atm to 40 atm, wherein the hydroxyapatite, pyrophosphate, and alkali metal source materials are added in amounts such that the phosphorus (P), calcium (Ca), and alkali metal (M) present on the surface of the final catalyst satisfy the conditions (i) and (ii).

[0010] Furthermore, according to the present invention, there is provided a method for producing an unsaturated carboxylic acid or a derivative thereof, which comprises a step of dehydrating a hydroxycarboxylic acid or a derivative thereof in the presence of the catalyst for producing an unsaturated carboxylic acid or a derivative thereof. [Effects of the Invention]

[0011] By using the catalyst of the present invention, unsaturated carboxylic acids and their derivatives can be produced in high yield over a long period of time when dehydrating hydroxycarboxylic acids or their derivatives. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a graph showing the results of X-ray diffraction (XRD) analysis of a mixture of hydroxyapatite (HAP) and calcium pyrophosphate (CaPP) (A) used in the preparation of a catalyst according to Preparation Example 1, and the resulting catalyst (B). [Figure 2] 1 is a graph showing the results of XRD analysis of the catalyst produced in Comparative Production Example 1. [Figure 3A] 1 is a transmission electron microscope (TEM) photograph of an analysis position point 1 in a catalyst produced in Production Example 1. [Figure 3B] FIG. 10 shows the results of elemental analysis by energy dispersive spectroscopy (EDS) at the same position. [Figure 4A] 1 is a TEM observation photograph taken at analysis position point 2 in the catalyst produced in Production Example 1. [Figure 4B] FIG. 10 is a diagram showing the results of elemental analysis by EDS at the position. [Figure 5] FIG. 1 is a diagram showing the results of XPS elemental analysis as a function of etching time during elemental analysis of the catalyst surface of Comparative Preparation Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0013] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the invention. The singular expressions include the plural expressions unless the context clearly indicates otherwise. It should be understood that the terms "comprise," "comprise," or "have" used in this specification are intended to specify the presence of embodied features, steps, components, or combinations thereof, and do not preclude the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0014] Although the invention can be embodied in various forms and with various modifications, specific embodiments are exemplified and described in detail below, but it should be understood that this is not intended to limit the invention to the particular disclosed embodiments, and that the invention includes all modifications, equivalents, and alternatives falling within the spirit and technical scope of the invention.

[0015] The catalyst for producing unsaturated carboxylic acids and derivatives thereof according to the present invention and the method for producing unsaturated carboxylic acids and derivatives thereof using the catalyst will be described below.

[0016] In the present invention, when preparing a catalyst for producing unsaturated carboxylic acids and their derivatives, hydroxyapatite and pyrophosphate are mixed together, and an alkali metal salt is added in an optimum content range and reacted under high temperature and pressure conditions. The catalyst thus prepared contains two or more hydroxyapatite compounds with different alkali metal contents in the hydroxyapatite crystals, and the content ratio of phosphorus (P), calcium (Ca) and alkali metal (M) on the catalyst surface is controlled within an optimum range. This confirmed that unsaturated carboxylic acids and their derivatives can be produced with high conversion and high yield during the dehydration reaction of hydroxycarboxylic acids or their derivatives, and the invention was completed based on this confirmation.

[0017] Specifically, the catalyst for producing an unsaturated carboxylic acid or a derivative thereof according to the present invention contains two or more types of hydroxyapatites having different alkali metal contents in the crystal, and phosphorus (P), calcium (Ca), and alkali metal (M) present on the catalyst surface satisfy the following conditions: (i) Molar ratio of calcium to phosphorus (Ca / P): 1.0 or more and 1.2 or less (ii) The total molar ratio of calcium and alkali metal (M) to phosphorus ((Ca+M) / P molar ratio): 1.2 or more and 1.6 or less.

[0018] In the hydroxyapatite compound used as a catalyst for the production of unsaturated carboxylic acids or their derivatives, the content of alkali metal in the compound affects the selectivity during the production of unsaturated carboxylic acids and their derivatives. Specifically, if the content of alkali metal in the catalyst, especially on the catalyst surface, is low, the selectivity decreases, but if the content of alkali metal is high, the selectivity is maintained.

[0019] In addition, the molar ratio of calcium to phosphorus (Ca / P) on the catalyst surface affects the yield of unsaturated carboxylic acids and their derivatives, i.e., the conversion rate of acrylic acid. If the Ca / P molar ratio is too high or too low, the yield decreases.

[0020] Furthermore, in the production of unsaturated carboxylic acids or their derivatives, the selectivity and the conversion rate show a trade-off relationship, so it is difficult to improve the selectivity and the conversion rate simultaneously.

[0021] On the other hand, hydroxyapatite has difficulty incorporation of high amounts of alkali metal due to its crystalline structure, but pyrophosphate allows relatively high amounts of alkali metal to be incorporated into its crystalline structure compared to hydroxyapatite.Furthermore, when pyrophosphate is reacted at high temperature and pressure in the presence of hydroxyapatite, it is converted to hydroxyapatite using hydroxyapatite as a seed.

[0022] Therefore, in the present invention, when preparing a catalyst for producing an unsaturated carboxylic acid or its derivatives, hydroxyapatite and pyrophosphate are mixed and an alkali metal salt is added in an optimal content range and reacted under high temperature and pressure conditions to introduce the alkali metal into the hydroxyapatite and pyrophosphate, respectively, and simultaneously convert the pyrophosphate with a high alkali metal content into hydroxyapatite. As a result, the catalyst produced contains hydroxyapatite derived from the raw material hydroxyapatite and having a relatively low alkali metal content, and hydroxyapatite derived from the pyrophosphate and having a relatively high alkali metal content.

[0023] In addition, hydroxyapatite with a high content of alkali metals derived from pyrophosphates can increase the content of alkali metals on the catalyst surface, which in turn can further improve the selectivity and conversion rate in the production of unsaturated carboxylic acids and their derivatives by controlling the mixing ratio of Ca and P.

[0024] Specifically, in the catalyst according to the present invention, the molar ratio of calcium to phosphorus (P) (Ca / P molar ratio) on the catalyst surface is 1.0 or more and 1.2 or less, more specifically, it may be 1.0 or more, or 1.05 or more, or 1.1 or more, and 1.2 or less, or less than 1.2, or 1.15 or less.

[0025] The total molar ratio of calcium and alkali metal to phosphorus on the catalyst surface ((Ca+M) / P molar ratio) is 1.2 or more and 1.6 or less. More specifically, it may be 1.2 or more, 1.3 or more, or 1.5 or more, and 1.6 or less, or less than 1.6, or 1.55 or less.

[0026] Furthermore, the catalyst has a high alkali metal content present on the catalyst surface of 4% by weight or more and 8% by weight or less, based on the total weight of the elements present on the catalyst surface, more specifically, 4% by weight or more, or 5% by weight or more, or 6% by weight or more, or 6.5% by weight or more, and 8% by weight or less, or 7.5% by weight or less, or 7% by weight or less.

[0027] Meanwhile, in the present invention, the element contents (atomic %, at %) of elements such as phosphorus, calcium, and alkali metals on the catalyst surface based on atomic weight can be measured by XPS analysis. Specific measurement and calculation methods will be described in detail in the following experimental examples.

[0028] The molar ratio of calcium to phosphorus on the catalyst surface can be calculated from the ratio of the Ca element content (Ca at%) / P element content (P at%) calculated by the XPS analysis of the calcium (Ca), phosphorus (P), and alkali metal (M) element contents (at%). The total molar ratio of calcium and alkali metal to phosphorus can be calculated from the ratio of (Ca at%) + M at%) / (P at%).

[0029] The content (by weight %, wt%) of the alkali metal present on the catalyst surface can be calculated from the calculated element content (at%).

[0030] For example, the element content (atomic %) of each element based on atomic weight can be converted to the element content (wt %) based on weight using the following Equation 1, and then the relative content (wt %) of alkali metals present on the catalyst surface can be calculated from the converted element content (wt %) of each element based on weight using the following Equation 2.

[0031] [Formula 1] Element content by weight (wt%) = [(element content by atomic weight of the element × atomic weight of the element) / Σ (element content of each element measured on the catalyst surface × atomic weight of each measured component)] × 100

[0032] As an example, the Ca element content (at%) can be converted to the weight-based element content (wt%) using the formula: [(Ca at% × Ca atomic weight) / Σ(at% of each measured component × atomic weight of each measured component)] × 100.

[0033] [Formula 2] Alkali metal content (wt%) = [weight-based content (wt%) of alkali metals present on the catalyst surface converted from their elemental content / Σ (weight-based content (wt%) of each element present on the catalyst surface converted from its elemental content)] × 100

[0034] The catalyst surface is the XPS depth in XPS analysis, and the catalyst surface in the present invention refers to a region corresponding to a depth of 10 nm from the interface where the catalyst comes into contact with the atmosphere toward the center of the catalyst. Since the XPS depth varies depending on the measurement conditions and the material, the XPS analysis conditions may be appropriately changed so that the catalyst surface region can be analyzed, or XPS analysis may be performed while scraping the catalyst surface from the interface where the catalyst comes into contact with the atmosphere toward the center of the catalyst to a depth of 10 nm.

[0035] In addition to controlling the content ratio of phosphorus, calcium, and alkali metal on the catalyst surface as described above, the catalyst of the present invention can further control the contents of these elements within the catalyst, thereby further improving the selectivity and conversion rate during the production of unsaturated carboxylic acids or derivatives thereof.

[0036] Specifically, the alkali metal content in the catalyst may be 2 wt% or more and 5 wt% or less, based on the total weight of the catalyst, and more specifically, may be 2 wt% or more, or 2.5 wt% or more, or 2.6 wt% or more, or 3 wt% or more, or 3.2 wt% or more, based on the total weight of the catalyst, and 5 wt% or less, or 4.5 wt% or less, or 4 wt% or less, or 3.7 wt% or less.

[0037] The molar ratio of calcium to phosphorus (Ca / P molar ratio) in the catalyst may be 1.3 or more and 1.5 or less, more specifically, 1.3 or more, or 1.35 or more, or 1.4 or more, and 1.5 or less, or 1.45 or less.

[0038] The total molar ratio of calcium and alkali metal (M) to phosphorus in the catalyst (the molar ratio of (Ca+M) / P) may be 1.2 or more and 2 or less. More specifically, it may be 1.2 or more, or 1.35 or more, or 1.5 or more, or 1.65 or more, and 2 or less, or 1.9 or less, or 1.8 or less, or 1.75 or less, or 1.7 or less.

[0039] Meanwhile, in the present invention, the contents of elements such as phosphorus, calcium, and alkali metals in the catalyst (weight % (wt%) based on the total weight of the catalyst) can be calculated by inductively coupled plasma spectrometry (ICP), more specifically, inductively coupled plasma optical emission spectrometry (ICP-OES). Specific measurement and calculation methods will be described in detail in the following experimental examples.

[0040] The molar ratio of calcium to phosphorus (Ca / P molar ratio) and the total molar ratio of calcium and alkali metals to phosphorus ((Ca+M) / P molar ratio) in the catalyst can be calculated from the calcium (Ca) content (wt%), phosphorus (P) content (wt%), and alkali metal (M) content (wt%) contained in the catalyst based on the total weight of the catalyst calculated by the ICP analysis.

[0041] Furthermore, as described above, the catalyst according to the present invention comprises two or more types of hydroxyapatites having different alkali metal contents in the crystals. Specifically, the catalyst comprises a first hydroxyapatite having an alkali metal content in the crystals of 0.8 wt% or less, or 0 to 0.8 wt%, or more than 0 wt% and 0.8 wt% or less, and a second hydroxyapatite having an alkali metal content in the crystals of 3 to 5 wt%.

[0042] Meanwhile, in the present invention, the alkali metal may be sodium, potassium, etc., and among these, sodium may be used in consideration of the superior improving effect.

[0043] As described above, the catalyst according to the present invention can simultaneously achieve high selectivity and high conversion rate in the production of unsaturated carboxylic acid or its derivatives by controlling the content ratio of phosphorus, calcium, and alkali metal within an optimal range on the catalyst surface and over the entire surface.

[0044] The catalyst can be prepared by a method including the steps of adding an alkali metal source material to a mixture containing hydroxyapatite (HAP) and pyrophosphate, and then reacting the mixture at a temperature of 130°C to 250°C and a pressure of 3 atm to 40 atm. The hydroxyapatite, pyrophosphate, and alkali metal source materials are added in amounts such that the phosphorus (P), calcium (Ca), and alkali metal (M) present on the surface of the final catalyst satisfy the above conditions (i) and (ii).

[0045] Unlike conventional hydroxyapatite catalysts, which are prepared using either HAP or CaPP alone, the present invention uses a mixture of HAP and pyrophosphate to produce a catalyst with different alkali metal contents in the crystalline structure, specifically, HAP with little alkali metal substitution and HAP with a high alkali metal content. The inclusion of HAP with such varying alkali metal contents is advantageous in terms of selectivity and conversion rate when preparing unsaturated carboxylic acids or their derivatives.

[0046] As evidenced by the following experimental examples, when a catalyst was produced using only HAP by treating it with an alkali metal salt under high-temperature and high-pressure conditions, the alkali metal was hardly substituted into the HAP crystal structure, or was substituted at a low content. Furthermore, when only CaPP was used, conversion to HAP was either almost nonexistent or was converted at a low conversion rate. This is because HAP acts as a seed during the conversion of CaPP to HAP, facilitating the phase transition of CaPP.

[0047] Meanwhile, in the method for producing a catalyst according to the present invention, the pyrophosphate specifically includes calcium pyrophosphate (Ca2P2O7CaPP), Ca2P2O7·2H2O, CaNa2P2O7, CaHPO4, CaHPO4·2H2O, Ca(H2PO4)2, Ca(H2PO4)·2H2O, Na6(PO4)2, Na 10 (P3O 10 )2, Ca3(PO4), Ca8(HPO4)2(PO4)4·5H2O, Ca8H2(PO4)6·3H2O, Ca3H2(PO4)6·5H2O, Ca9(PO4)6, K6(PO4)2, or K 10 (P3O 10 ) 2, and the like, and one or a mixture of two or more of these can be used.

[0048] The pyrophosphate is converted to hydroxyapatite in the presence of hydroxyapatite during high-temperature, high-pressure reaction. In the absence of hydroxyapatite, conversion to hydroxyapatite is difficult, and a larger amount of alkali metal salt and a longer reaction time are required to convert pyrophosphate to hydroxyapatite.

[0049] The hydroxyapatite (Ca5(PO4)3(OH) or Ca 10 The mixing ratio of (PO4)6(OH)2 (HAP) and pyrophosphate can be appropriately determined taking into consideration the contents of Ca, P, and alkali metals in the final catalyst. For example, hydroxyapatite and pyrophosphate can be used in a molar ratio of 1:9 to 9:1.

[0050] The alkali metal source may be an alkali metal-containing hydroxide, bicarbonate, or carbonate, more specifically NaOH, KOH, NaHCO3, Na2CO3, KCO3, etc., and any one or a mixture of two or more of these may be used.

[0051] The alkali metal raw material is added in an amount that satisfies the alkali metal content on the surface of the final catalyst, specifically, the total molar ratio of calcium and alkali metal to phosphorus ((Ca+M) / P molar ratio) of 1.2 to 1.6. For example, the alkali metal raw material is added in an amount of 0.1 to 5 mol per 1 mol of Ca.

[0052] Meanwhile, after the alkali metal raw material is added, the reaction is carried out at a temperature of 130° C. or more and 250° C. or less and a pressure of 3 atm or more and 40 atm or less.

[0053] More specifically, the reaction is carried out at a temperature of 130° C. or higher, or 150° C. or higher and 250° C. or lower, or 200° C. or lower, and at a pressure of 3 atm or higher, or 5 atm or higher and 40 atm or lower, or 20 atm or lower, or 10 atm or lower. When the reaction is carried out under these temperature and pressure conditions, the occurrence of side reactions and overreactions can be suppressed, and the catalyst can be produced in a high yield.

[0054] A high-temperature, high-pressure reactor may also be used for the reaction under the high-temperature, high-pressure conditions.

[0055] As a result of the reaction, the catalyst precipitates and is obtained by filtration and washing.

[0056] The catalyst produced by the above production method contains two or more hydroxyapatite compounds with different alkali metal contents in the hydroxyapatite crystals, and the molar ratio of calcium and alkali metal to phosphorus (P) in the catalyst is controlled within an optimal range, so that unsaturated carboxylic acids and their derivatives can be produced in high yield over a long period of time during the dehydration reaction of hydroxycarboxylic acids or their derivatives.

[0057] Thus, the present invention provides a method for producing unsaturated carboxylic acids and derivatives thereof using the catalyst.

[0058] Specifically, the production method includes a step of dehydrating a hydroxycarboxylic acid or a derivative thereof in the presence of the catalyst for producing the unsaturated carboxylic acid or a derivative thereof.

[0059] Specific examples of hydroxycarboxylic acids that can be used as raw materials in the method for producing unsaturated carboxylic acids and derivatives thereof according to the present invention include lactic acid, citric acid, 3-hydroxypropionic acid, 3-hydroxy-2-methylpropionic acid, 3-hydroxybutanoic acid, 3-hydroxy-2-methylbutanoic acid, and 2,3-dimethyl-3-hydroxybutanoic acid, and derivatives such as salts, esters, or dimers thereof can also be used.

[0060] The hydroxycarboxylic acid or its derivative may be used in the form of an aqueous solution dissolved in water, or in the form of a solution dissolved in a mixed solvent prepared by mixing water with a hydrophilic organic solvent such as an alcohol or an ether.

[0061] In this case, the concentration of the hydroxycarboxylic acid or its derivative is not particularly limited, but may be 20% by weight or more and 60% by weight or less in consideration of efficiency.

[0062] More specifically, in the production method, the hydroxycarboxylic acid may be lactic acid, and the unsaturated carboxylic acid may be acrylic acid.

[0063] The amount of catalyst used in the dehydration reaction can be appropriately selected in consideration of the types of reactants, reaction time, etc. For example, the hydroxycarboxylic acid or its derivative can be added in an amount of 0.05 g to 3 g per hour per 1 g of catalyst, more specifically, in an amount of 0.1 g to 1 g per hour, or 0.5 g per hour.

[0064] The dehydration reaction can be carried out by a continuous reaction using a fixed-bed reactor or a batch reaction. More specifically, the dehydration reaction can be carried out by a continuous reaction in which the catalyst is packed in a fixed-bed reactor and reactants are continuously supplied to the reactor to react, thereby continuously producing a product.

[0065] In the continuous reaction using the fixed-bed reactor, an inert gas such as nitrogen, argon, or helium can be used as a carrier gas. The amount of carrier gas introduced is not particularly limited and can be appropriately determined depending on reaction conditions such as the amount of reactants introduced. For example, the carrier gas is introduced at a rate of 5 mL / min or more and 500 mL / min or less per gram of catalyst.

[0066] The dehydration reaction is carried out at a temperature of 300° C. or higher and 500° C. or lower. More specifically, the dehydration reaction is carried out at a temperature of 300° C. or higher, or 350° C. or higher, or 360° C. or higher, and 500° C. or lower, or 450° C. or lower, or 370° C. or lower.

[0067] Furthermore, the dehydration reaction is carried out at a pressure of 0.5 bar or more and 5 bar or less, more specifically, 0.5 bar or more, or 0.8 bar or more, and 5 bar or less, or 2 bar or less, and even more specifically, under atmospheric pressure (1±0.2 bar).

[0068] The reactant, hydroxycarboxylic acid or its derivative, was -1 Over 3 hours -1 It is injected at a Weight Hour Space Velocity (WHSV) of 0.05h -1 or more, or 0.1h -1 or more, or 0.3h -1 More than 3 hours -1 Less than or equal to 1 hour -1 or less, or 0.8h -1 It will be deployed at the following WHSV speeds:

[0069] The reaction temperature is above 500°C, the reaction pressure is below 0.5 bar, or the reactant supply rate WHSV is less than 0.1 h -1 If the reaction temperature is less than 300°C, the reaction pressure is more than 5 bar, or the reactant feed rate WHSV is less than 1 h, the catalytic activity may increase excessively, which may cause hydrogenolysis side reactions, resulting in a decrease in selectivity. -1 If it is exceeded, the conversion rate will decrease and other reaction conditions will have to be increased severely, which may result in a shortened catalyst life and increased costs in the product separation and recovery stage.

[0070] In such a dehydration reaction, at least a portion of the hydroxycarboxylic acid or its derivative is converted into an unsaturated carboxylic acid or its derivative.

[0071] In the method for producing an unsaturated carboxylic acid or a derivative thereof according to the present invention, the conversion rate of the unsaturated carboxylic acid is improved by using the above-mentioned catalyst, and the unsaturated carboxylic acid and its derivative can be produced in high yield.

[0072] Preferred examples are presented below to aid in understanding the present invention, but the following examples are merely for illustrative purposes and are not intended to limit the scope of the present invention.

[0073] (Production Example 1) 35 g of HAP and 65 g of CaPP were mixed and placed in a high-temperature, high-pressure reactor, after which 500 ml of 1 M NaOH solution was added and the reaction was carried out at 150°C and 5 atm for 4 hours. The resulting white precipitate was filtered and washed to obtain a catalyst (yield: 90%).

[0074] (Production Example 2) 30 g of HAP and 70 g of CaPP were mixed and placed in a high-temperature, high-pressure reactor, after which 500 ml of 1 M NaOH solution was added and the reaction was carried out at 150°C and 5 atm for 4 hours. The resulting white precipitate was filtered and washed to obtain a catalyst (yield: 90%).

[0075] (Production Example 3) 50 g of HAP and 50 g of CaPP were mixed and placed in a high-temperature, high-pressure reactor, after which 500 ml of 1 M NaOH solution was added and the reaction was carried out at 150°C and 5 atm for 4 hours. The resulting white precipitate was filtered and washed to obtain a catalyst (yield: 90%).

[0076] (Comparative Manufacturing Example 1) A catalyst was prepared in the same manner as in Example 1, except that only HAP was used without adding CaPP.

[0077] (Comparative Manufacturing Example 2) A catalyst was prepared in the same manner as in Example 1, except that only CaPP was used without adding HAP.

[0078] (Comparative Manufacturing Example 3) Without the addition of CaPP, calcium-deficient hydroxyapatite (HAP, CDHAP) was prepared. 10-x (PO4) 6-x (HPO4) x (OH) 2-x After placing only (x=1) (Ca / P molar ratio=1.5) in a high-temperature, high-pressure reactor, 500 ml of 1 M NaOH solution was added and the reaction was carried out at 150°C and 5 atm for 4 hours. The resulting white precipitate was filtered and washed to obtain the catalyst (yield: 95%).

[0079] Example 1 The catalyst prepared in Preparation Example 1 was packed in a fixed-bed reactor, and a 30 wt % aqueous solution of lactic acid was added at a reaction temperature of 360°C and atmospheric pressure (1±0.2 bar) for WHSV 0.32 h. -1 The dehydration reaction was carried out by supplying the

[0080] The initial 4 hours of the reaction were used as a reaction stabilization time, during which the reactants were received and removed, and the liquid product obtained after 2 to 4 hours was collected as a liquid sample using a 4°C cooled collector.

[0081] Example 2 The catalyst prepared in Preparation Example 1 was packed in a fixed-bed reactor, and a 40 wt % aqueous solution of lactic acid was added at a reaction temperature of 370°C under atmospheric pressure for WHSV 0.43 h. -1 The procedure was the same as in Example 1, except that the dehydration reaction was carried out by supplying the water at 1000 kJ / min.

[0082] Example 3 The catalyst prepared in Preparation Example 2 was packed in a fixed-bed reactor, and a 30 wt % aqueous solution of lactic acid was added at a reaction temperature of 360°C under atmospheric pressure for WHSV 0.32 h. -1 The procedure was the same as in Example 1, except that the dehydration reaction was carried out by supplying the water at 1000 kJ / min.

[0083] Example 4 The catalyst prepared in Preparation Example 2 was packed in a fixed-bed reactor, and a 60 wt % aqueous solution of lactic acid was added at a reaction temperature of 380°C and atmospheric pressure for WHSV 0.68 h.-1 It was carried out in the same manner as in Example 1 except that a dehydration reaction was carried out by supplying it at

[0084] (Example 5) The catalyst produced in Production Example 3 was filled in a fixed-bed reactor, and a 30 wt% aqueous solution of lactic acid was supplied at WHSV 0.32 h -1 It was carried out in the same manner as in Example 1 except that a dehydration reaction was carried out by supplying it at

[0085] (Comparative Examples 1 to 3) It was carried out in the same manner as in Example 1 except that the catalysts produced in Comparative Production Examples 1 to 3 were used respectively.

[0086] (Experimental Example 1) The mixture of HAP and CaPP used in the production of the catalyst according to Production Example 1 and the resulting produced catalyst were subjected to phase analysis using XRD, and the results are shown in FIG. 1. [[ID=2))

[0087] <XRD analysis conditions> Equipment used: XRD-D8_Advance (Powder XRD) Sample powder was placed in the recessed groove in a general powder holder (Holder), and the surface was made uniform using a slide glass, and the height was made the same as the periphery of the holder (Holder). 1 st Using Slit 2 mm, the region from 2θ (theta) 10° to 60° was measured at 3 sec / step every 0.017°.

[0088] (A) in FIG. 1 is the analysis result for the mixture of hydroxyapatite (HAP) and calcium pyrophosphate (CaPP) used in the production of the catalyst according to Production Example 1, and (B) is the analysis result for the produced catalyst.

[0089] Also, XRD analysis was carried out on the catalyst produced in Comparative Production Example 1 in the same manner as above, and the results are shown in FIG. 2.

[0090] From the experimental results shown in Figures 1 and 2, it was confirmed that the catalyst of Production Example 1 was composed of hydroxyapatite compounds with different Na contents, whereas the catalyst of Comparative Production Example 1 was composed of a single HAP phase with a high Na content.

[0091] (Experimental Example 2) Two analysis points (Point 1 and Point 2) were arbitrarily set for the catalyst prepared in Preparation Example 1, and spot energy dispersive spectroscopy (EDS) analysis was performed for each point using a transmission electron microscope (TEM) under the following conditions. The results are shown in Figures 3A to 4B below.

[0092] <Analysis conditions> Experimental equipment: Titan G2 80-200 Field Emission Transmission Electron Microscope FE-TEM(Field Emission Transmission Electron Microscopy) STEM-HAADF (Scanning transmission electron microscopy-High angle annular dark field imaging) STEM-EDS(Energy dispersive X-ray spectroscopy)Spectrum Experimental conditions: Accelerating voltage 200 kV

[0093] Fig. 3A is a TEM photograph taken at analysis position Point 1 in the catalyst produced in Production Example 1, Fig. 3B is a diagram showing the results of elemental analysis by EDS analysis at that position, Fig. 4A is a TEM photograph taken at analysis position Point 2 in the catalyst produced in Production Example 1, and Fig. 4B is a diagram showing the results of elemental analysis by EDS at that position.

[0094] From the above analysis results, it was confirmed that the catalyst produced according to the present invention contains at least two types of hydroxyapatite compounds having different alkali metal contents in the hydroxyapatite crystals.

[0095] (Experimental Example 3) 1) Elemental analysis of the catalyst surface XPS analysis was performed on the surfaces of the catalysts produced in the above Production Examples and Comparative Production Examples under the following conditions, and the results are shown in Table 1 below.

[0096] <XPS analysis method> Using a photoelectron spectrometer (X-ray Photoelectron Spectroscopy, model name: Nexsa, manufacturer: Thermo Fisher Scientific Inc.) equipped with an Ar ion etching device, the content of elements on the catalyst surface was analyzed and calculated as a relative content ratio (atomic percent: atom% (at%)). At this time, the catalyst surface means a region corresponding to a depth of 10 nm from the interface where the catalyst contacts the atmosphere to the inner center of the catalyst. Accordingly, during XPS surface analysis, the catalyst surface was etched by 1 to 3 nm per second using an etching method with Ar ions, specifically, the Ar ion etching device provided in the photoelectron spectrometer, and the elemental distribution was analyzed by XPS while etching.

[0097] Also, during XPS analysis, monochromatic Al Kα (1486.6 eV) was used as the X-ray source, and the Shirley Peak background, ALTHERMO1 Sensitivity factor, and TPP-2M Energy compensation factor were applied. Also, the content (atomic percent, based on the total atomic weight of the elements present in the catalyst surface, at%) of the elements present on the catalyst surface was calculated using the Avantage software, respectively.

[0098] The elements present on the catalyst surface are Ca, P, Na, C, and O. Among these, the calculation results for Ca, P, and Na are shown in Table 1 below.

[0099] Furthermore, the content of Na present in the catalyst surface (weight % (wt%) based on the total weight of the elements present in the catalyst surface) was calculated from the calculated element content (at%).

[0100] [Table 1]

[0101] In Comparative Production Example 1, which was produced using only HAP without adding CaPP, the Na content on the catalyst surface was 0.8 at%, while in Comparative Production Example 2, which was produced using only CaPP without adding HAP, the Na content on the catalyst surface was 5 at%, indicating that the two catalysts differed in the Na content contained in the hydroxyapatite. These results show that in the catalysts of Production Examples 1 and 2, which used a mixture of HAP and CaPP, both a hydroxyapatite compound derived from HAP and having a low Na content of 0.8 at% and a hydroxyapatite compound derived from CaPP and having a high Na content were formed.

[0102] In addition, the results of XPS elemental analysis of the catalyst surface of Comparative Preparation Example 2 as a function of etching time, that is, depth from the catalyst surface, are shown in FIG.

[0103] As shown in Figure 5, when the catalyst surface was scraped and analyzed, the Na concentration was high on the catalyst surface side and decreased toward the interior of the catalyst.

[0104] The reason why the Na concentration on the catalyst surface is higher than that inside is thought to be because the Na content on the surface of CaPP, which is the hydrothermal reaction precursor, is high, which affects the high Na content during the phase transition to the catalyst.

[0105] 2) Elemental analysis of catalysts In addition, the catalysts produced in the above Production Examples and Comparative Production Examples were subjected to ICP analysis under the following conditions, and the content of each element present in the catalyst (based on the total weight of the catalyst, wt%) from the results is shown in Table 2 below.

[0106] Furthermore, the molar ratios of Ca / P and Ca+Na / P present in the catalyst were calculated from the Ca, P, and Na contents (total weight basis of the elements present in the catalyst surface, wt%) in the catalyst, respectively, and are shown in Table 2 below.

[0107] <ICP analysis conditions> Equipment used: ICP-OES (Perkin Elmer, OPTIMA 7300DV) After accurately measuring the weight of the sample (0.01 g), it was dissolved using an acid. If the sample dissolved cleanly, ultrapure water was added and Sr was added as an internal standard substance. The final volume was made constant, and the final concentration and measurement mode were adjusted considering the sensitivity and concentration of the elements, and ICP-OES analysis was performed.

[0108]

Table 2

[0109] (Experimental Example 4) The reaction products obtained in the above Examples and Comparative Examples were quantitatively analyzed using high performance liquid chromatography (HPLC), and using the analysis results, the conversion rate (%), acrylic acid selectivity (C%), and acetaldehyde selectivity (C%) of the hydroxycarboxylic acid or its derivative were calculated according to the following Mathematical Formulas 3 to 5, respectively. At this time, the hydroxycarboxylic acid or its derivative in the Examples and Comparative Examples was lactic acid, and the experimental results are shown in Table 3 below.

[0110] <HPLC analysis conditions> The reaction products obtained in the above Examples and Comparative Examples were diluted 15-fold using distilled water and then quantitatively analyzed using HPLC (Agilent 1260 Infinity II).

[0111] -Eluent: 0.005 mol H2SO4(aq) -Eluent flow rate: 0.4 mL / min -Column: Aminex HPX-87H -Column temperature: 10℃ -Detector: UV210~300nm -Analysis time: 70 minutes -Analysis pressure: up to 70 bar

[0112] [Formula 3] Conversion rate of hydroxycarboxylic acid or its derivative (%) = 100 × (AB) / A In the above formula 3, A is the number of moles of the hydroxycarboxylic acid or its derivative before the reaction, B is the number of moles of the hydroxycarboxylic acid or its derivative after the reaction.

[0113] [Formula 4] Acrylic acid selectivity (C%) = 100 × (E / D) × C A In the above formula 4, D is the number of moles of the reacted hydroxycarboxylic acid or its derivative, and corresponds to the value of (the number of moles of the hydroxycarboxylic acid or its derivative before the reaction - the number of moles of the hydroxycarboxylic acid or its derivative after the reaction), E is the number of moles of acrylic acid produced, C A is the carbon selectivity for acrylic acid and is 1.

[0114] [Formula 5] Acetaldehyde selectivity (C%) = 100 × (F / D) × C AD In the above formula 5, D is the number of moles of the reacted hydroxycarboxylic acid or its derivative, and corresponds to the value of (the number of moles of the hydroxycarboxylic acid or its derivative before the reaction - the number of moles of the hydroxycarboxylic acid or its derivative after the reaction), F is the number of moles of acetaldehyde produced C AD is the carbon selectivity for acetaldehyde, which is 2 / 3 (≒0.667).

[0115] [Table 3]

[0116] As a result of the experiment, Examples 1 to 5 using the catalysts of Production Examples 1 to 3 showed a high conversion rate of 95% or more, a high acrylic acid selectivity of 61% or more, and a low acetaldehyde selectivity of 15% or less.

Claims

1. It contains two or more types of hydroxyapatite with different alkali metal content in the crystal, The phosphorus, calcium, and alkali metals present on the catalyst surface satisfy the following conditions (i) and (ii): A catalyst for the production of unsaturated carboxylic acids or their derivatives. (i) The molar ratio of calcium to phosphorus is 1.0 or greater and 1.2 or less. (ii) The total molar ratio of calcium and alkali metals to phosphorus is 1.2 or greater and 1.6 or less.

2. The alkali metal content present on the catalyst surface is 4% by weight or more and 8% by weight or less, based on the total weight of elements present on the catalyst surface. A catalyst for producing an unsaturated carboxylic acid or a derivative thereof, as described in claim 1.

3. The catalyst surface is a region corresponding to a depth of 10 nm from the interface where the catalyst contacts the atmosphere toward the center of the catalyst. A catalyst for producing an unsaturated carboxylic acid or a derivative thereof, as described in claim 1.

4. The alkali metal content in the catalyst is 2% by weight or more and 5% by weight or less based on the total weight of the catalyst. A catalyst for producing an unsaturated carboxylic acid or a derivative thereof, as described in claim 1.

5. The alkali metal is sodium or potassium. A catalyst for producing an unsaturated carboxylic acid or a derivative thereof, as described in claim 1.

6. The process includes adding alkali metal raw materials to a mixture containing hydroxyapatite and pyrophosphate, and then reacting it at a temperature of 130°C or higher and 250°C or lower, and at a pressure of 0.3 MPa (3 atm) or higher and 4.1 MPa (40 atm) or lower. The hydroxyapatite, pyrophosphate, and alkali metal raw materials are added in amounts such that the phosphorus, calcium, and alkali metals present on the final catalyst surface satisfy the following conditions (i) and (ii). A method for producing a catalyst for producing an unsaturated carboxylic acid or its derivative, according to any one of claims 1 to 5. (i) The molar ratio of calcium to phosphorus is 1.0 or greater and 1.2 or less. (ii) The total molar ratio of calcium and alkali metal (M) to phosphorus is 1.2 or greater and 1.6 or less.

7. The pyrophosphate is Ca 2 P 2 O 7 、Ca 2 P 2 O 7 ・2H 2 O、CaNa 2 P 2 O 7 、CaHPO 4 、CaHPO 4 ・2H 2 O、Ca(H 2 PO 4 ) 2 、Ca(H 2 PO 4 )・2H 2 O、Na 6 (PO 4 ) 2 、Na 10 (P 3 O 10 ) 2 、Ca 3 (PO 4 )、Ca 8 (HPO 4 ) 2 (PO 4 ) 4 ・5H 2 O、Ca 8 H 2 (PO 4 ) 6 ・3H 2 O、Ca 3 H 2 (PO 4 ) 6 ・5H 2 O、Ca 9 (PO 4 ) 6 、K 6 (PO 4 ) 2 、or K 10 (P 3 O 10 ) 2 is, A method for producing a catalyst for producing an unsaturated carboxylic acid or its derivative, as described in claim 6.

8. The alkali metal raw material includes alkali metal-containing hydroxides, bicarbonates, or carbonates. A method for producing a catalyst for producing an unsaturated carboxylic acid or its derivative, as described in claim 6.

9. The step includes dehydrating a hydroxycarboxylic acid or its derivative in the presence of a catalyst for producing an unsaturated carboxylic acid or its derivative according to any one of claims 1 to 5. A method for producing unsaturated carboxylic acids or their derivatives.

10. The hydroxycarboxylic acid is lactic acid, The aforementioned unsaturated carboxylic acid is acrylic acid. A method for producing an unsaturated carboxylic acid or a derivative thereof according to claim 9.

11. The dehydration reaction is carried out as a continuous reaction using a fixed-bed reactor. A method for producing an unsaturated carboxylic acid or a derivative thereof according to claim 9.

12. The dehydration reaction is carried out at a temperature of 300°C or higher and 500°C or lower, and a pressure of 0.05 MPa (0.5 bar) or higher and 0.5 MPa (5 bar) or lower, using a weight-time-space velocity (WHSV) of 0.05 h. -1 The above and 3 hours -1 The following will be performed by introducing the following: A method for producing an unsaturated carboxylic acid or a derivative thereof according to claim 9.

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