WO2008075901A1

WO2008075901A1 - Method for preparing catalyst for partial oxidation of methylbenzenes

Info

Publication number: WO2008075901A1
Application number: PCT/KR2007/006663
Authority: WO
Inventors: Dong Il Lee; Won Ho Lee; In Kyu Park; Jong Hyun Chae; Hyun Kyung Yoon; Ji Hyang Son; Won Jae Lee
Original assignee: Lg Chem, Ltd.
Priority date: 2006-12-21
Filing date: 2007-12-20
Publication date: 2008-06-26
Also published as: KR20080058099A; KR100983024B1

Abstract

The present invention relates to a novel method for preparing a catalyst for partial oxidation of methylbenzenes, in which the method comprising (a) preparing tungsten oxide by sol-gel process; (b) preparing tungsten oxide slurry by wet milling; (c) supporting the slurry obtained from the step (b) on inorganic carrier; (d) drying the catalyst obtained from the step (c); and (e) calcining the dried catalyst obtained from the step (d), wherein, tungstic acid is treated with hydrogen peroxide in the step (a). The catalyst according to the method of the present invention has the advantage of lowering the reaction temperature on the basis of equivalent yield due to high conversion rate of methylbenzens as compared with the catalyst according to the conventional impregnation or heating evaporation.

Description

METHOD FOR PREPARING CATALYST FOR PARTIAL OXIDATION OF METHYLBENZENES

Technical Field

[1] The present invention relates to a method for preparing a catalyst for partial oxidation of methylbenzenes. More specifically, the present invention relates to the novel method for preparing the catalyst which is suitable for gas phase oxidizing the methyl- benzenes with molecular oxygen to produce the corresponding aromatic aldehydes with high selectivity.

[2]

Background Art

[3] Aromatic aldehydes have wide ranged usage since they have aldehyde groups having high a reactivity. Especially, terephthalaldehyde having two aldehyde groups at para position has been brought to attention as law materials for medicinal products, agro- chemicals, pigments, liquid crystal polymers, or plastic having heat resistance.

[4] The conventional methods for preparation of terephthalaldehyde known to the art are hydrolysis method of intermediate prepared by chlorination of p-xylene, and hydro- genation method of dimethyl terephthalate. However, these conventional methods are not suitable for economical mass production since the processes are complicated and should be carried out under high pressure and environment-unfriendly conditions.

[5] In order to solve these problems, there has been continuous study for mass production of terephthalaldehyde by gas phase oxidizing p-xylene with molecular oxygen.

[6] For examples, Japanese Patent Publication No. 47-002086 discloses a complex oxide catalyst having the W and Mo ratio range of from 1:1 to 20: 1 , and Japanese Patent Publication No. 48-0097830 discloses a catalyst comprising V and Rb or Cs.

[7] US Patent Publication No. 3,845,137 discloses a catalyst consisting of two components of W and Mo and one or more components selected from the group consisting of Ca, Ba, Ti, Zr, Hf, Tl, Nb, Zn and Sn. Also, US Patent Publication No. 4,017,547 discloses a catalyst consisting of Mo oxide, W oxide or silicotungstic acid and Bi oxide. However, the industrial practical use of the above catalysts has been limited since the catalysts have low selectivity and yield of the objected terephthalaldehyde.

[8] Also, US Patent Publication No. 5,324,702 discloses a catalyst comprising a first component which is a compound of an element selected from the group consisting of Fe, Zn, Zr, Nb, In, Sn, Sb, Ce and Bi, and a second component which is a compound of an element selected from the group consisting of V, Mo and W, which the first and the second components are distributed on a deboronized borosilicate crystal molecular sieve by chemical vapor deposition (CVD). The above catalyst shows relatively higher conversion rate of p-xylene and yield of terephthalaldehyde than the conventional catalysts. However, the catalyst is limited to increase the selectivity due to the various by-products, and so there is difficulty to separate and purify terephthalaldehyde.

[9] Also, US Patent Publication No. 6,458,737 discloses a catalyst comprising a major component of W and one or more components selected from the group consisting of Sb, Fe, Co, Ni, Mn, Re, Cr, V, Nb, Ti, Zr, Zn, Cd, Y, La, Ce, B, Al, Tl, Sn, Mg, Ca, Sr, Ba, Li, Na, K, Rb and Cs. The catalyst can provide such high yield of terephthalaldehyde as having industrial availability. However, the catalyst also has limitation of separation and purification since the selectivity of terephthalaldehyde is not high for high conversion rate of p-xylene. Also, the catalyst has problems in heat stability and life since it comprises Sb component which is sublimated to loss at high temperature.

[10] Therefore, the conventional catalysts have low yield of the objected terephthalaldehyde, or low selectivity even though they have high yield, and so the separation and the purification are difficult. Also, it is difficult to prepare the catalysts having homogeneous composition and performance since they use a complex oxide having multi-component. Further, the industrial practical use of the catalyst is limited due to the short life caused by comprising some components having low heat stability.

[11] On the other hand, Korean Patent Application No. 10-2004-0089376 filed by the present inventor disclosed a single component catalyst comprising tungsten oxide and fire-resistant inorganic carrier as an optional component. The catalyst has advantage in that it is easier to prepare homogenous catalyst and has higher selectivity and yield of terephthalaldehyde than complex oxide having multi-component. However, the catalysts having higher conversion rate and selectivity are still needed.

[12]

Disclosure of Invention Technical Problem

[13] Considering the above problems, the object of the present invention is to provide a method for preparing a catalyst for partial oxidation of methylbenzenes which can lower the reaction temperature based on equivalent yield in the process for preparing corresponding aromatic aldehydes from methylbenzenes.

[14]

Technical Solution

[15] To accomplish the above object, the present invention provides a novel method for preparing a catalyst of the formula (1), [16] WOx...(l)

[17] for partial oxidation of methylbenzenes.

[18] Specifically, the method comprises the steps of:

[19] (a) preparing tungsten oxide by sol-gel process;

[20] (b) preparing tungsten oxide slurry by wet milling;

[21] (c) supporting the slurry obtained from the step (b) on inorganic carrier;

[22] (d) drying the catalyst obtained from the step (c); and

[23] (e) calcining the dried catalyst obtained from the step (d),

[24] wherein tungstic acid is treated with hydrogen peroxide in the step (a).

[25] The term "methylbenzene" used herein means any compound having one or a plurality of methyl groups directly joined to the benzene ring, and may includes methylbenzenes containing 8 to 10 carbon atoms, such as p-xylene, o-xylene, m- xylene, psudocumene, mesitylene, and durene, but are not limited thereto.

[26] The use of catalyst for partial oxidation according to the present invention is to prepare corresponding aromatic aldehydes by gas-phase oxidation of the said methyl- benzenes with the molecular oxygen. For example, the method for preparing aromatic aldehydes may comprise preparing terephthalaldehyde and p-tolualdehyde from p- xylene; phthalaldehyde and o-tolualdehyde from o-xylene; isophthalaldehyde and m- tolualdehyde from m- xylene; 2-methylterephthalaldehyde, 2,4-dimethylbenzaldehyde, 2,5-dimethylbenzaldehyde, and 3,4-dimethylbenzaldehyde from pseudocumene; 3,5-dimethylbenzaldehyde, 5-methylisophthalaldehyde and 1,3,5-triformylbenzene from mesitylene; and 2,5-dimethylterephthalaldehyde, 4,5-dimethylphthalaldehyde, 2,4,5-trimethylbenzaldehyde, 2,4,5-triformyltoluene and 1,2,4,5-tetraformylbenzene from durene; but is not limited thereto.

[27] Particularly, the catalyst for partial oxidation of methylbenzenes prepared by the present invention is suitable for preparing terephthalaldehyde from p-xylene.

[28]

Advantageous Effects

[29] The catalyst prepared by the present method can reduce the reaction temperature on the basis of equivalent yield in the preparation of corresponding aromatic aldehydes from methylbenzenes since the catalyst has high conversion rate caused by increasing the surface areas, as compared to the catalyst according to the conventional impregnation or heating evaporation.

[30]

Brief Description of the Drawings

[31] A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, wherein:

[32] FIG. 1 is a graphical illustration showing effect of reaction temperature on p-xylene conversion rate of the partial oxidation catalysts for methylbenzenes of Example 1 and Comparative example 1 of the present invention.

[33] FIG. 2 is a graphical illustration showing effect of reaction temperature on selectivity of TPAL of the partial oxidation catalysts for methylbenzenes of Example 1 and Comparative example 1 of the present invention.

[34] FIG. 3 is a graphical illustration showing effect of reaction temperature on yield of

TPAL of the partial oxidation catalysts for methylbenzenes of Example 1 and Comparative example 1 of the present invention.

[35]

Best Mode for Carrying Out the Invention

[36] Below, the present invention will be described more specifically.

[37] The present invention provides a novel method for preparing a catalyst of the formula (1),

[38] W0x...(l)

[39] wherein, W represents tungsten atom, O represents oxygen atom and x represents a value determined by oxidative state of W, preferably the value from 2 to 3,

[40] for partial oxidation of methylbenzenes.

[41] Specifically, the method comprises the steps of:

[42] (a) preparing tungsten oxide by sol-gel process;

[43] (b) preparing tungsten oxide slurry by wet milling;

[44] (c) supporting the slurry obtained from the step (b) on inorganic carrier;

[45] (d) drying the catalyst obtained from the step (c); and

[46] (e) calcining the dried catalyst obtained from the step (d),

[47] wherein tungstic acid is treated with hydrogen peroxide in the step (a).

[48] Hereinafter, each step of the present invention will be described more specifically.

[49] The step (a) of the present invention relates to prepare tungsten oxide by sol-gel process, characterized in which tungstic acid is treated with hydrogen peroxide.

[50] The step (a) comprises preferably the steps of,

[51] (i) treating tungstic acid with hydrogen peroxide;

[52] (ii) preparing sol by dispersing the output obtained from the step (i) into a dispersion medium; and

[53] (iii) gelating the sol obtained from the step (ii).

[54] The step (i) relates to treat tungstic acid with hydrogen peroxide. More specifically, the step (i) relates to dissolve tungstic acid in hydrogen peroxide by stirring over 1 day, and if necessary, resolving unreacted hydrogen peroxide in the solution with platinum net.

[55] The preferable amount of tungstic acid treated with hydrogen peroxide is 5~ 15 weight % of said solution. Considering treatment efficiency, the more preferable amount of tungstic acid is 8~12 weight %. When the amount of tungstic acid is too small, the efficiency is reduced. And, when the amount of tungstic acid is too large, it is unfavorable since the succeeding steps take a long time.

[56] Also, there is no specific limitation in resolving unreacted hydrogen peroxide in the solution with platinum net, and the resolving procedure may be continued until gas bubbles formed by resolution of hydrogen peroxide are not observed.

[57] The step (ii) relates to prepare sol by dispersing the output obtained from the step (i) into the dispersion medium. More specifically, the step (ii) relates to disperse the output obtained from the step (i) into the dispersion medium, if necessary, a surfactant can be further added.

[58] The dispersion medium is not particularly limited, but water, alcohol and mixtures thereof may be used. It is preferable to use the mixtures of water and alcohol (for example, methanol, ethanol or isopropanol, and the like). It is more preferable to use the mixture of water and methanol having weight ratio of 1 : 1. An preferable amount of the dispersion medium is 10~30 times to the weight of tungstic acid. When the amount is less than 10 times, dispersion effect may be decreased, and when the amount is more than 30 times, gelating process may be delayed.

[59] Also, the surfactant is not particularly limited, but the surfactant of block copolymer series, more preferably F127 or P123 composed of EO-PO-EO form may be used. If the surfactant is used, it must be stirred over 1 hour to dissolve the surfactant sufficiently.

[60] The step (iii) relates to gelate the sol obtained from the step (ii). There is no specific limitation in the step (iii) except for temperature, but it is preferable to use water bath to keep temperature. The temperature is preferably less than 4O⁰C, more preferably 35-4O⁰C. When the temperature is less than 35⁰C, gelating time may be lengthened. When the temperature is more than 4O⁰C, gelation is exceeded to disintegrate the structure.

[61] The resulting gel may be dried and calcined to prepare tungsten oxide. There is no specific limitation in drying and calcining the gel, and general drying and calcining methods being described in the below may be used.

[62]

[63] The step (b) of the present invention relates to prepare tungsten oxide slurry by mixing a tungsten oxide and a dispersant, and wet-milling the mixture by using a milling apparatus.

[64] Alcohol may be used as the dispersant for tungsten oxide. As for alcohol, methanol, ethanol or iso-propanol may be used. Considering malfeasance of the process, it is preferable to use ethanol.

[65] There is no specific limitation in the amount of dispersant to tungsten oxide, but 2 to

3 times to the weight of tungsten oxide is generally preferred since the preparation time during the supporting step may be increased when the amount is large, and it is difficult to input it into a pore of carrier when the amount is small.

[66] The apparatuses for wet-milling the mixture of tungsten oxide and alcohol are not particularly limited. Any conventional milling apparatus can be used. When a ball mill apparatus for pulverizing is used, the pulverizing and mixing effects can be increased, and the milling effect can be increased by adjusting the size of ball.

[67] In the wet-milling, milling time is preferably more than 2 hours due to decrease efficiently a particle size of tungsten oxide, more preferably, 2 to 5 hours considering work efficiency.

[68]

[69] The step (c) of the present invention relates to support the tungsten oxide slurry obtained from the step (b) on fire-resistant inorganic carrier. Among the above fire- resistant inorganic carrier, it is preferable to use -alumina, silica, titania, zirconia or silicon carbide. The shape of the fire-resistant inorganic carrier is not particularly limited, and spheres, pellets, rings, or a honeycomb, and the like, can be selectively used.

[70] The method for supporting the tungsten oxide slurry on inorganic carrier is not particularly limited, but it is preferable to use impregnation method due to increase an amount of supported material and the homogeneity of catalyst as compared with coating method.

[71] Also, the step (c) is preferable to be carried out under reduced pressure or vacuum condition since the reduced pressure or vacuum of the container having carrier enables the active ingredient to be supported up to the inner surface of the catalyst.

[72]

[73] The steps (d) and (e) of the present invention relates to dry and calcine the prepared catalyst.

[74] The method or atmosphere for drying and calcining is not particularly limited. The unlimited examples of the method may include vacuum dry, refrigeration dry, spray dry, microwave dry, rotary evaporation, or air dry, and the like. The operations can be carried out in any of an air, an oxygen-rich or oxygen-lean atmosphere, a reducing atmosphere, an inert gas atmosphere or vacuum.

[75] The temperature condition of the above steps (d) and (e) is also not particularly limited, but preferable dry temperature is 80 ~ 200⁰C, and calcinations temperature is 300 ~ 700⁰C. When the dry temperature is less than 8O⁰C, dry efficiency may be decreased, when the temperature is more than 200⁰C, performance of catalyst may be decreased. When the calcinations temperature is less than 300⁰C, it is difficulty to remove the reaction impurities, when the temperature is more than 700⁰C, the morphology of the catalyst may be deformed. Also, time condition of the above steps (d) and (e) is not particularly limited, but each step (d) and (e) is preferred to be carried out during sufficient time more than 2 hours.

[76] Those skilled in the art will appreciate that the concepts and specific embodiments disclosed in the foregoing description may be readily utilized as a basis for modifying or designing other embodiments for carrying out the same purposes of the present invention. Those skilled in the art will also appreciate that such equivalent embodiments do not depart from the spirit and scope of the invention as set forth in the appended claims.

[77]

[78] Hereinafter, the present invention will be more specifically illustrated by the following examples. However, the following examples should not be construed as limiting the scope of the present invention in any way.

[79] The conversion rate, selectivity and one-pass yield of the reaction, taking byproducts into account, are defined as follows.

[80] Conversion rate (mole %) = (the number of moles of the reacted starting compound/ the number of moles of the fed starting compound) 100

[81] Selectivity (mole %) = (the number of moles of each product compound/the number of moles of the reacted starting compound) = (the number of carbon atoms of each product compound/the number of carbon atoms of the fed starting compound) xlOO

[82] One-pass yield (mole %) = (the number of moles of each product compound/the number of moles of the fed starting compound) = (the number of carbon atoms of each product compound/the number of carbon atoms of the fed starting compound) xlOO

[83]

Mode for the Invention

[84] Example 1

[85] 30% aqueous solution of hydrogen peroxide of 180g was added to tungsten oxide of

2Og to be total 20Og. The solution was dissolved with stirring for 1 day and insoluble components were filtered by filter paper. Platinum net was put in the filtered solution to resolve non-reactive hydrogen peroxide, and then it was allowed to sit until gas bubbles forming from resolution of hydrogen peroxide were not produced. The reaction was performed with cooling the container in ice-bath to remove heat produced from resolution of hydrogen peroxide. When gas bubbles were not formed any more, the mixture solution of water and methanol (weight ratio of water :methanol=l : 1) of 40Og was added thereto. And, F 127 block polymer of 8g was added thereto, and stirred vigorously for 1 hour. The well mixed solution was allowed to sit in water bath at 4O⁰C, and thus gelated. The completely gelated sample was dried and calcined to prepare sol-gel tungsten oxide.

[86] The above sol-gel tungsten oxide of 1Og was poured into 125mL-PP bottle, and ethanol of 30g as a dispersant was added thereto and mixed. Zirconia ball was added into the mixture, and wet-milling was carried out for 3 hours by using oscillator milling apparatus.

[87] The above slurry was poured into a container including a-alumina carrier, SA5205

30g (Norton Co., 5mm of sphere), which was preheated to 12O⁰C, and was heated under stirring in water bath to carry out evaporation. The resultant was dried at 12O⁰C for 18 hours and was calcined under air atmosphere at 65O⁰C for 2 hours to obtain the final catalyst. The weigh percent of the WOx component was 14.8% of the total weight of the catalyst, and thus the final catalyst has the composition of 14.8 wt% WOx/ SA5205.

[88] The above catalyst (1.5g) was poured into a conventional continuous reactor, and the reaction was carried out under the following conditions:

[89] Reaction pressure: normal pressure

[90] The composition ratio of gas reactant (volume ratio):

[91] p-xylene/oxygen/nitrogen=0.25/6.25/93.5 (oxygen/p-xylene=25)

[92] Feeding rate of gas reactant: lOOmL/min

[93] Reaction temperature: 520, 550 and 58O⁰C

[94]

[95] Comparative Example 1

[96] An aqueous solution of ammonium metatungstate (2mmol/g) as tungsten raw material was prepared. The aqueous solution was heated under stirring in water bath to carry out evaporation. Thus, the resultant was dried at 12O⁰C for 18 hours, followed by calcinating at 65O⁰C under air atmosphere for 2 hours to obtain tungsten oxide. The catalyst was prepared by the same manner as Example 1 except for using tungsten oxide prepared from the above, thus the catalyst having the composition of 18.1 wt% of WOx/SA5205 was obtained.

[97] The reaction was carried out in the same manner as Example 1 using the catalyst of

1.5g obtained from the above. The reaction results are shown in Table 1 and Drawings 1 to 3.

[98]

[99] Table 1 [Table 1] [Table ]

[100] TPAL: terephthalaldehyde, PTAL: p-tolualdehyde [101] As shown in the above Table 1 and Drawings 1 to 3, the catalyst according to Example 1 of the present invention shows superior conversion rate of p-xylene in the whole range to the catalyst prepared by conventional wet-milling of Comparative Example 1 (see fig. 1). Also, Example 1 shows superior selectivity of TPAL at low temperature to Comparative Example 1 (see fig. 2). Also, as shown in Fig. 3, the catalyst of Comparative Example 1 shows maximum yield at the temperature of 58O⁰C. However, the catalyst of Example 1 shows superior maximum yield to the catalyst of Comparative Example 1 at temperature of 55O⁰C. Therefore, it is confirmed that the catalyst according to the method of the present invention can lower the reaction temperature to obtain an equivalent level of TPAL yield due to the increase of the conversion rate as compared to the catalyst according to the conventional method.

[102]

Industrial Applicability

[103] The catalyst according to the method of the present invention can lower the reaction temperature on the basis of equivalent yield in the preparation of corresponding aromatic aldehydes from methylbenzenes since the catalyst has high conversion rate caused by increasing the surface areas, as compared to the catalyst according to the conventional impregnation or heating evaporation.

Claims

[1] A method for preparing a catalyst of the formula (1), for partial oxidation of methylbenzenes , W0x...(l) wherein, W represents tungsten atom, O represents oxygen atom and x represents a value determined by oxidative state of W, comprisesing the steps of:

(a) preparing tungsten oxide by sol-gel process;

(b) preparing tungsten oxide slurry by wet milling;

(c) supporting the slurry obtained from the step (b) on inorganic carrier;

(d) drying the catalyst obtained from the step (c); and

(e) calcining the dried catalyst obtained from the step (d), wherein tungstic acid is treated with hydrogen peroxide in the step (a).

[2] The method according to claim 1, wherein the step (a) comprises the steps of:

(i) treating tungstic acid with hydrogen peroxide;

(ii) preparing sol by dispersing the output obtained from the step (i) into a dispersion medium; and

(iii) gelating the sol obtained from the step (ii).

[3] The method according to claim 2, wherein the step (i) comprises the steps of: preparing an aqueous solution by dissolving tungstic acid in hydrogen peroxide; and resolving unreacted hydrogen peroxide in the solution with platinum net.

[4] The method according to claim 3, wherein an amount of the tungstic acid is 5~15 weight % of the solution.

[5] The method according to claim 2, wherein the dispersion medium in the step (ii) is any one selected from the group consisting of water, alcohol and mixtures thereof.

[6] The method according to claim 5, wherein the dispersion medium is a mixture of water and methanol.

[7] The method according to claim 5, wherein an amount of the dispersion medium is 10~30 times to the weight of tungstic acid.

[8] The method according to claim 2, wherein the sol in the step (ii) further comprises a surfactant.

[9] The method according to claim 8, wherein the surfactant is a block copolymer including ethylene oxide unit and propylene oxide unit.

[10] The method according to claim 2, wherein the step (iii) is carried out at a temperature of less than 4O⁰C.

[11] The method according to claim 1, wherein the step (b) is carried out by mixing tungsten oxide and alcohol as a dispersant and wet-milling the mixture by using a milling apparatus.

[12] The method according to claim 11, wherein the milling apparatus is a ball mill apparatus.

[13] The method according to claim 11, wherein the dispersant is one or more selected from the group consisting of methanol, ethanol and iso-propanol.

[14] The method according to claim 1, wherein the step (c) is carried out at a temperature of 80~200°C.

[15] The method according to claim 1, wherein the step (d) is carried out at a temperature of 300~700°C.