KR100942893B1 - Method for producing a catalyst with high methacrylic acid selectivity - Google Patents

Abstract

The present invention relates to a method for preparing a catalyst having high methacrylic acid selectivity and a method for producing methacrylic acid using the catalyst, and more particularly, to methacrylic acid from methacrolein using a kegin type catalyst. The method for producing an acid is characterized by including a step of pretreatment of a kegin type catalyst with methacrylic acid as a target product. According to the method for producing methacrylic acid according to the present invention, it is possible to obtain an effect of changing the structure of the catalyst by simply pretreating the final product in the pretreatment step of the catalyst to increase the selectivity of the final product.

Methacrylic acid, methacrolein, selectivity, keggin type catalyst, heteropolyacid-based catalyst, polyoxometalate

Description

Method for producing a catalyst having high methacrylic acid selectivity {CATALYST PREPARATION METHOD FOR METHACRYLIC ACID PRODUCTION WITH HIGH SELECTIVITY}

1 is a schematic view of an experimental apparatus according to the present invention.

2 is a graph showing the conversion rate and selectivity to methacrylic acid according to the inflow rate of methacrolein.

3A to 3C are graphs of pulses of reactants and products when using catalysts (solid line-dashed) pretreated with methacrylic acid and catalysts (dotted line) not pretreated (dashed line).

4 is an FTIR of a Cs ₂ H ₂ PMo ₁₁ VO ₄₀ sample.

5 is an XRD pattern of Cs ₂ H ₂ PMo ₁₁ VO ₄₀ sample.

6 is a graph showing changes in lattice parameters of Cs ₂ H ₂ PMo ₁₁ VO ₄₀ salt.

The present invention relates to a process for preparing a catalyst for producing methacrylic acid (MAA) with high selectivity and to a process for producing methacrylic acid using the catalyst, in particular using a keggin type heteropolyacid (HPA) catalyst It relates to a method of preparing an acid.

As one of the methods for producing methacrylic acid, it is a well known method to vapor-phase catalytic oxidize methacrolein using a heteropolyacid-based catalyst.

U.S. Patent 4,558,028 (registered Dec. 10, 1985) discloses Mo _a P _b A _c B _d C _e D _f O _x (where Mo is molybdenum, P is phosphorus, A is As, Sb, Ge , At least one element selected from the group consisting of Bi, Zr and Se, B is at least one element selected from the group consisting of Cu, Fe, Cr, Ni, Mn, Co, Sn, Ag, Zn and Rh, and C Is at least one element selected from the group consisting of V, W and Nb, D is at least one element selected from the group consisting of alkali metals, alkaline earth metals and thallium, O is oxygen, a is 12, b Is 0.5-4, c is 0-5, d is 0-3, e is 0-4, f is 0.01-4, and x is a value considering the oxidation state of each element). A method is disclosed.

The catalyst having the composition as described above is subjected to a process of forming into a predetermined shape after drying and then calcined again to become a final catalyst. Through the molding process, a pellet having a diameter of about 5 mm and a length of about 5 mm is generally formed, and the decomposable ammonium or nitrate form is decomposed during the firing process to finally form a catalyst having a desired structure and composition. At this time, the firing temperature is 300 to 500 ° C and is carried out in an oxygen atmosphere or a nitrogen atmosphere.

U.S. Patent No. 4,621,155 (registered Nov. 4, 1986) includes preparing a catalyst by adding pyridine, piperidine, or piperazine, an N-containing material, to prepare a heteropolyacid catalyst. It is claimed to increase the moldability, physical strength and reproducibility of catalyst production.

The method of preparing the catalyst depends on the precursor of the metal component, but metal nitrate (NO ₃ ⁻ ) is generally used.

The bar disclosed in Example 1 of US Pat. No. 6,333,293B1 (registered Dec. 25, 2001) is as follows. Ammonium paramolybdate and ammonium paravanadate are dissolved in heated water and stirred. The catalyst is prepared by heating and drying a solution made by injecting an appropriate amount of 85% phosphoric acid and injecting cesium nitrate and copper nitrate.

U.S. Patent No. 6,458,740B2 (registered Oct. 1, 2002) contains ammonium paramolybdate and ammonium metavanadate in pyridine and 85% phosphoric acid, which is then added thereto. Disclosed is a method of coprecipitation by adding nitrate, cesium nitrate and copper nitrate, followed by heat drying. In addition, the patent claims that the activity and selectivity of the catalyst are affected by the ratio of NH ₄ / Mo ₁₂ and NH ₄ / NO ₃ included in the precursor.

Despite the known techniques with respect to such various catalysts, the activity of the existing heteropolyacid catalysts is still low, and thus, an improvement in the conversion rate of methacrolein and the selectivity of methacrylic acid is required.

An object of this invention is to provide the manufacturing method of methacrylic acid with high selectivity.

In view of the problems described above, while continuously studying the method for producing methacrylic acid, the inventors of the present invention pretreated the catalyst in the reactor with the product in the process of producing methacrolein with methacrylic acid, It was found that the structure changes, and the present invention was completed by focusing on the fact that the selectivity of methacrylic acid can be increased by using the same.

The present invention is a method for producing methacrylic acid from methacrolein using a keggin type catalyst, methacrylic acid characterized in that it comprises the step of pretreating the keggin type catalyst with methacrylic acid as a target product It provides a method for producing.

Hereinafter, the present invention will be described in more detail.

It is very common to use heteropolyacids as catalysts in the synthesis of methacrylic acid from methacrolein.

In particular, the acid cesium salt of _{1 -} banado- _{11 -} molybdo phosphoric acid Cs _x H _{4 - x} PVMo ₁₁ O ₄₀ Silver is well known as a catalyst with excellent efficacy in oxidizing methacrolein to methacrylic acid. A number of patents and research papers show this point in the polyoxometalate (POM) group (see N. Mizuno, M. Misono, Chemical Reviews (Washington, DC) 98 (1998) 199.). One well-known feature of polyoxometalates (POMs) is that the change to active catalyst is very slow. A study of the catalyst, spectrum and phase of these polyoxometallates revealed that the slow transition from the POMs to the mixture of the respective oxides changed the actual active state to a metastable phase. It became. The most potent candidate as an active site is the lacunary Keggin unit, which is a secondary structure of HPA as a product in which VOx and MOx units are removed from the Keggin unit. Thus, one of the efficient ways to reduce the equilibrium time is to simply synthesize a catalyst based on heteropolyacids at pH 4 to derive the Lakunary keggin structure.

According to Marosi et al., The equilibrium of Cs ₁ H ₃ PMo ₁₁ VO ₄₀ during methacrolein oxidation causes line broadening of the X-ray diffraction (XRD). This is due to methacrolein and Cs ₁ H ₃ PMo ₁₁ VO ₄₀ This is because the catalyst disintegrates crystallites as a result of the interaction. However, the prolonged contact time of the mixture of methacrolein and oxygen causes not only the interaction between methacrolein and the catalyst but also the interaction between the catalyst and the product (methacrylic acid). This fact suggests that the study of equilibrium suggests that the interaction between the product, methacrylic acid, and the catalyst should not be overlooked.

Accordingly, the present inventors have found that the selectivity of methacrylic acid can be increased by pretreatment of methacrylic acid with a catalyst by studying the equilibrium process of methacrylic acid, thereby completing the present invention.

The following describes a series of effects that occur by pretreating the Cs ₂ H ₂ PVMo ₁₁ O ₄₀ catalyst with methacrylic acid.

First, the following experiment was conducted to explain the principle of the present invention. The following examples are not intended to limit the invention, it is apparent that the invention is capable of various modifications in the same principles and scope as the following examples.

EXAMPLE

Nippon Inorganic Color and Chemical Co. H ₄ PVMo ₁₁ O ₄₀ (1-vanado-11-molybdophosphoric acid) was extracted with diethyl ether and recrystallized with water for further purification. The phase composition of the obtained crystals was checked by XRD.

Purified H ₄ PVMo ₁₁ O ₄₀ was vigorously mixed with cesium carbonate solution and then dried at 120 ° C. overnight to prepare Cs ₂ H ₂ PMo ₁₁ VO ₄₀ salt. The salt was pretreated by soaking in liquid methacrylic acid (MAA, 300 μl of methacrylic acid per 1 g of salt) for about 1 hour.

X-ray diffraction patterns were obtained using Cu Kα radiation (λ = 1.5418 kHz) with a D4 Endeavor diffractometer (Brucker) at room temperature. Phase analysis was performed using EVA program. TOPAS2 software was used to evaluate the grid parameters.

The catalyst test was carried out at 300 ° C. with a continuous flow stainless tubular reactor (9.5 mm i.d., 28 cm long). 0.5 g catalyst (0.25-0.5 mm fraction) was diluted with SiC granules (0.25-0.5 mm fraction) to a total volume of 2 ml and placed between glass wool plugs. The injection gas consisted of 3.6% methacrolein, 10% oxygen, 10% water vapor and helium in balance. Methacrolein and water, together with helium used as the carrier gas, are delivered through a saturated-condensation system operated at constant pressure and temperature (FIG. 1). Prior to the catalytic test, the MAA-treated samples were flowed with 10% oxygen, 10% water vapor and helium in balance, identified by GC for a time sufficient to remove traces of MAA from effluent, typically 30-40 minutes) It pretreated at the catalyst reaction temperature (280-300 degreeC). Total product, Supelco 15ft filled with carboxen 1000. x 1/8 in. Columns and on-line GC using an Alltech AT-1000 (30m × 0.53m × 1.2μm i.d.) capillary column and on-line quadrupole MS units (GeneSys ESS2846) equipped with capillary inlets were analyzed. All lines were heated to 200 ° C. to prevent condensation.

Work on the present invention was initiated by problems encountered during the catalyst performance evaluation process. In evaluating catalyst performance, an initial 20 hour time of stream (TOS) treatment was performed under constant reaction injection flow rate to ensure that the catalyst reached equilibrium. After equilibration, the contact time gradually increased or decreased by varying the flow rate every two hours. This procedure exhibited a strong “biography” effect of the reaction injection flow rate used during the initial 20 h of equilibrium of the catalyst. At low flow rates (67 ml / min,-▲-) and high flow rates (173 ml / min,-■-), a graph measuring the relationship between the conversion and selectivity of methacrolein to methacrylic acid 2 is shown. It is clear that catalysts that have reached equilibrium at low flow rates, ie catalysts with longer contact times, show higher selectivity of methacrylic acid. Since the partial pressure of methacrolein at the feed port is kept constant, the longer the contact time, the higher the concentration of methacrylic acid (MAA). Thus, the catalytic activity effect shown in FIG. 2 is assumed to be related to the difference in MAA concentration produced in the reaction.

Thereafter, experiments were carried out using catalysts pretreated with methacrylic acid as in Examples and catalysts not pretreated with methacrylic acid for comparison. This experiment is to determine the effect caused by pretreatment of the catalyst with pure MAA.

Significant differences were seen in the experiments between the MAA-pretreated catalyst and the unpretreated catalyst. A certain amount of methacrolein (MACR) was injected into the flow of the reaction injection consisting of oxygen, water vapor and helium as balance. The results are shown in Figures 3A-3C. 3a shows methacrolein and oxygen, FIG. 3b shows methacrylic acid and methacrolein, and FIG. 3c shows measurement results of water, methacrylic acid, methacrolein and oxygen.

For the MAA-pretreated catalyst (solid line-dotted line in FIG. 3A), the amplitude of the O 2 pulses was higher than that of the non-MAA-pretreated catalyst (dashed line in FIG. 3A) and the amplitude of the MACR pulse was lower. Thus, the MACR conversion rate is higher. Figure 3b also shows that the amplitude of the product MAA is higher even for the MAA-pretreated catalyst. Yields of other products such as water, acetic acid and carbon dioxide were also higher. Only acrolein, as shown in FIG. 3B, was exceptional, in which case MAA-pretreatment appears to reduce certain sub-products.

More detailed results are shown in Figure 3c. Is shown in. The solid line (----) represents the sample without MAA pretreatment, and the dotted line (---) represents the sample pretreated with MAA. For MAA and water, there is evidence of significant tailing. This result means a better interaction between these molecules and the catalyst caused by the penetration of MAA and water into the bulk. Cesium salts of Keggin type heteropolyacids are known to have a significant amount of water in the secondary structure, and some small organic polar molecules can be stabilized in the lattice of heteropolyacids. However, no data has yet been reported on the structural aspects of the interaction of MAA with Cs _x H _{4 - x} PVMo ₁₁ O ₄₀ . Therefore, we performed preliminary XRD studies on the interaction of mesacrylic acid and methacrolein with Cs ₂ H ₂ PVMo ₁₁ O ₄₀ at ambient conditions. The change of the lattice parameter with time is shown in FIG. Simply impregnation of the catalytic solid salt with methacrylic acid significantly increases the lattice parameters over time. On the other hand, there was no expansion of the crystal lattice when impregnation with methacrolein. It can be seen that methacrylic acid can be stabilized in the lattice of Cs ₂ H ₂ PVMo ₁₁ O ₄₀ , but not methacrolein. A common feature of impregnation with methacrolein and methacrylic acid is that the lattice contracts in both cases initially. This contraction can be explained by the rapid removal of water molecules from the secondary structure of the cesium salt. In the case of methacrylic acid, a gradual increase in lattice parameters is achieved by slowly infiltrating methacrylic acid into the lattice over two hours with initial lattice shrinkage. If MAA penetrates into the lattice of POM, it may be unreasonable to make the existing claim that catalytic oxidation of MACR by POMs is a pure surface type reaction. Although the interaction of the MACR with the cesium salt of heteropolyacid is a surface type reaction, the product of the reaction can be stabilized in bulk and change the nature of the catalyst. This makes it difficult to define this reaction as a pure surface type.

크리스탈 시메트리를 변화시키지 않는다(도 5). 도 5는 Cs₂H₂PMo₁₁VO₄₀ 샘플의 XRD 패턴을 나타낸다. a는 120℃ 에서 공기건조한 샘플, b 는 72시간동안 액상 MAA로 전처리 하고 공기 흐름으로 300℃ 에서 하소한 샘플, c는 액상 MAA 로 20 시간 동안 전처리한 샘플을 각각 나타낸다. 세 경우 모두 피크가 나타나는 위치가 동일하다. 그럼에도 불구 하고 c 의 경우에, q=26.2°에서의 피크 넓이는 상당히 변화하였고, 몇 피크의 강도는 감소하였다(도 5c). 이것은, 촉매의 조직 변화를 나타내는 것이다. Pretreatment with MAA under ambient conditions (or the same pretreatment combined with a subsequent calcination at 100 or 300 ° C.)

It does not change the crystal geometry (FIG. 5). 5 shows an XRD pattern of Cs ₂ H ₂ PMo ₁₁ VO ₄₀ samples. a represents an air-dried sample at 120 ° C., b is a sample pretreated with liquid MAA for 72 hours, calcined at 300 ° C. with air flow, and c is a sample pretreated for 20 hours with liquid MAA. In all three cases, the position at which the peak appears is the same. Nevertheless, in the case of c, the peak area at q = 26.2 ° changed significantly, and the intensity of several peaks decreased (FIG. 5C). This represents a change in the structure of the catalyst.

의 시메트리를 나타내는 XRD 패턴의 형태가 때때로 관찰되었다. 이러한 시메트리는 예를들면, H_{3 -2x}[VO]_xPMo₁₂O₄₀ 에 전형적이며, MAA 전처리가 2차 구조에 바나딜 이온의 제거를 유도할 수 있다는 것을 제안한다. 불행하게도,

패턴의 형태는 상이한 Cs₂H₂PVMo₁₁O₄₀ 샘플의 MAA 전처리시 XRD 패턴 상으로는 반복재현성이 좋지 않았다. 그러나, MAA 처리로 케긴 이온으로부터 바나딜 종을 제거하는 것은 IR 스펙트로스코피를 사용하여 확인할 수 있었다. 도 6은, 액상 메타크릴산(○) 과 액상 메타크롤레인(●)을 주입(impregnation)시킨 후 Cs₂H₂PMo₁₁VO₄₀ 염의 격자 파라미터의 변화를 나타낸 그래프이다. Also in MAA Cs ₂ H ₂ PVMo ₁₁ O ₄₀ After impregnation the MAA

The shape of the XRD pattern, which represents the geometry of, was sometimes observed. This geometry is typical for example H _{3 -2x} [VO] _x PMo ₁₂ O ₄₀ , suggesting that MAA pretreatment can lead to the removal of vanadyl ions in the secondary structure. Unfortunately,

The pattern shape was not good repeatability on the XRD pattern during MAA pretreatment of different Cs ₂ H ₂ PVMo ₁₁ O ₄₀ samples. However, the removal of vanadil species from Keggin ions by MAA treatment could be confirmed using IR spectroscopy. 6 is a graph showing changes in lattice parameters of Cs ₂ H ₂ PMo ₁₁ VO ₄₀ salt after impregnation of liquid methacrylic acid (○) and liquid methacrolein (●).

FTIR of MAA-pretreated Cs ₂ H ₂ PVMo ₁₁ O ₄₀ (left of FIG. 4) shows that the keggin structure is well maintained. Nevertheless, as the pretreatment temperature increases, PO _a The disappearance of the shoulder in the oscillating (1060 cm ⁻¹ ) (FIG. 4 right) band is quite apparent. According to a number of papers, the substitution of molybdenum with vanadium in a nearly spherical Keggin unit twists the central tetrahedron (tetrahedron) around phosphorus to cause splitting of a single PO band. Thus, the gradual 1060 cm ^- removal of the shoulder in the ^first, can be shown that the vanadium is moved from kegin unit in the secondary structure. It is very important to know that the migration of VO _x species occurs at a moderate temperature (at ca 100 ° C.) when invading MAA. As a result, it can be seen that MAA will induce the formation of lacunary structures at lower temperatures than those used for catalytic reactions.

Pretreatment of polyoxo metalate (POM) with methacrylic acid (MAA) affects both structural and catalytic effects. Structural effects are supported by (i) expansion of the POM lattice by stabilization of the carboxylic acid in the bulk and (ii) removal of the oxovanadium species from the keggin unit at low temperatures.

The nature of catalytic activation by the reaction product is currently unclear. Desorption of MAA occurs fairly slowly, even at catalyst temperatures. This is supported by the tailing of the MAA peaks. This means that the interaction between the MAA and the POM is strong. However, MAA, Cs _x H _{3 -x + y} PV _y Mo _{12 - y} O ₄₀ Since the oxidation rate of methacrolein in the phase is independent of the partial pressure of methacrylic acid, it cannot bind directly to the active site of the catalyst. Thus, if the MAA binds to a specific site, this site will be different from the active site where the reaction occurs. However, if MAA binding changes the catalytic activity, the MAA binding site will have to be adjacent to the active site.

If this binding is not specific, ie there are no specific MAA-binding sites on the bulk or on the catalyst surface, there will be enough space for the MAA molecules to stabilize within the secondary structure of the POM host. Centi. Et al. In this book, we can consider this situation as the term "living active surface". According to the idea of a "living active surface", the bound MAA molecules can exist as coadsorbates or simply as dissolved species in the lattice of the POM. These nonspecifically bound “spectator” molecules can be significantly altered by changing the catalytic properties of the POM, such as the geometric site of the active site, the POM-MACR interaction, oxygen transport, and the like. Currently it is not possible to identify the nature of the MAA binding to the POM.

POM catalysts are very non-selective at the beginning of the reaction. Thereafter, the gradual accumulation of MAA over the reaction time converts the catalyst to an optional one. The selectivity of the POM catalyst thus depends on the MAA concentration in the catalyst.

Research into reaction mechanisms describing the binding nature of MAA with POM catalysts, the effect of MAA pretreatment on the steady-state performance, and the observed effects are ongoing.

In conclusion, the present invention found that the general view regarding the formation of i) non-specific metastable phases due to hydrolysis-reduction and ii) lacunary Keggin units as potent active sites is not complete. The interaction between POM and MAA is very important. MAA, on the one hand, promotes the formation of a lacunary structure for interaction with POM, and on the other hand, binding of POM and MAA converts the catalyst into a selective state.

From this fact, the mechanism for producing methacrylic acid from methacrolein using a heteropolyacid catalyst is not a pure surface reaction as previously known, but a reaction involving a structural change of the catalyst, and using this principle, It has been found that when methacrylic acid is prepared using a catalyst pretreated with methacrylic acid, the selectivity of the product can be significantly increased.

The same principle can be applied not only to methacrylic acid but also to the preparation of carboxylic acid including the same, and in this case, similar results are expected.

Similar results are expected in the case of using other heteropolyacid catalysts having a kegin structure as well as an acidic cesium salt of phosphoric acid as well as the kegin type vanadium molybdenum used in the present invention, and thus may be widely applied. .

It will be apparent to those skilled in the art that various embodiments of the present invention described above are merely illustrative of the present invention and that various changes and modifications can be made within the scope and spirit of the present invention, and such modifications and modifications belong to the appended claims. It is also natural.

As described above, according to the present invention, in the method for producing methacrylic acid from methacrolein using a kegin-type heteropolyacid catalyst, the activity of the catalyst is simply obtained by simply pretreating the catalyst with methacrylic acid as a product. It has been found that there is an excellent effect in improving the selectivity of methacrylic acid by improving. When used in similar types of products and catalysts, various applications will be possible.

Claims (11)

Pretreatment by immersing the kegin type catalyst with carboxylic acid; And preparing a carboxylic acid from aldehyde using a pretreated catalyst. The method of claim 1, The kegin-type catalyst is a production method, characterized in that the kegin-type heteropoly acid salt. 3. The method of claim 2, Wherein said heteropolyacid is an acidic cesium salt of 1-vanado-11-molybdo phosphoric acid. The method of claim 3, The cesium salt is represented by the following Formula 1 [Formula 1] Cs _x H _{4 - x} PVMo ₁₁ O ₄₀ Where x is a natural number less than 4 The manufacturing method characterized by the above-mentioned. The method of claim 1, The aldehyde is a production method, characterized in that the acrylate compound. The method of claim 5, The acrylate compound is a manufacturing method characterized in that the methacrolein. In the process for preparing a keggin type heteropolyacid catalyst used to prepare carboxylic acid from aldehyde by vapor phase catalytic oxidation, Independent of the vapor phase catalytic oxidation, stabilizing the carboxylic acid in the lattice of the catalyst by immersing the kegin type heteropolyacid catalyst in the carboxylic acid which is the product of the vapor phase catalytic oxidation. Method for preparing a catalyst. The method of claim 7, wherein The heteropolyacid catalyst is represented by the following Formula 1 [Formula 1] Cs _x H _{4 - x} PVMo ₁₁ O ₄₀ Where x is a natural number less than 4 Method of producing a kegin type heteropolyacid catalyst, characterized in that represented by. The method of claim 7, wherein The aldehyde is a method for producing a kegin type heteropolyacid catalyst, characterized in that the acrylate compound. The method of claim 9, The acrylate-based compound is a method for producing a kegin type heteropolyacid catalyst, characterized in that the methacrolein. The method of claim 7, wherein The immersion time is a method for producing a kegin type heteropolyacid catalyst, characterized in that more than 1 hour.

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