JPH0314532A - Production of formaldehyde - Google Patents

Abstract

PURPOSE:To produce the subject compound which is important as a key feedstock in chemical industry, through stabilized operations in high yield by using a specific catalyst obtained by ion-exchange method in the catalytic dehydrogenation of methanol in the absence of oxygen. CONSTITUTION:A zinc oxide/zeolite catalyst, which is prepared by the ion- exchange method, is used to effect catalytic dehydrogenation of methanol in the absence of oxygen whereby the subject compound is produced. In the reaction, the catalyst temperature is usually 450 to 650 deg.C, preferably 500 to 600 deg.C. The methanol feed rate is suitably 0.1 to 10.0g/h per gram of the catalyst. Further, the methanol is preferably diluted with an inert gas such as nitrogen, methane and/or hydrogen. The catalyst is prepared by dipping zeolite in aqueous zinc salt and the zinc ion is adsorbed to the zeolite by the ion-exchange method and firing the zeolite so that zinc oxide is formed on the zeolite.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for producing formaldehyde by catalytic dehydrogenation of methanol. More specifically, it relates to a method for producing formaldehyde in good yield using a zeolite catalyst. (Prior art) Formaldehyde is an important basic raw material in the chemical industry, and is used as a raw material for resins such as polyacetic resin, urea resin, and phenol resin, and as a raw material for chemicals such as pentaerythritol and hexamethylenetetramine. The industrial method for producing formaldehyde is to catalytically oxidize and dehydrogenate methanol in the presence of oxygen, specifically in air, using a silver catalyst or a mixed catalyst of iron oxide and molybdenum oxide as shown in the following formula. It is. CH. OH+ 1/20■→HCHO+H. 0 In this method, water is produced as a by-product as is clear from the reaction formula, and the formaldehyde produced is usually absorbed and collected in water, so the product is an aqueous solution with a formaldehyde concentration of 30 to 1%. ．． This method requires complicated and expensive equipment, large amounts of steam, power, etc. to prevent catalyst deactivation and remove byproducts, and furthermore, because the obtained product is an aqueous solution, transportation costs are high. It has disadvantages such as being bulky. In particular, polyacecool resin, whose demand has been increasing in recent years, has problems such as the need for a high degree of dehydration as it strongly dislikes the presence of water during resin production, which consumes a large amount of energy. Ta. As a production method that can solve the problems of such oxidative dehydrogenation methods, a simple dehydrogenation method in which formaldehyde is produced by catalytic dehydrogenation of methanol in the absence of oxygen as shown in the following formula is also known. Various proposals regarding this method have been made so far. CH. ○H-HCH○+H. For example, a method using a catalyst consisting of copper, silver, and silicon (U.S. Pat. No. 2,939,883), a method using a catalyst with metallic zinc adhered to the surface of metallic copper (Japanese Patent Publication No. 41
-11853), a method using molten zinc, gallium, indium, aluminum, etc. as a catalyst (Japanese Patent Publication No. 47-19251 and JP-A-48-97808), copper, zinc, and sulfur or selenium. A method using a catalyst (JP-A-51-1407, JP-A-51-1407)
No. 76209, Publication No. 52-215), etc. However, none of these methods simultaneously satisfied the basic performance of the catalyst, such as formaldehyde yield, selectivity, and catalyst life. Furthermore, methods developed in recent years, specifically methods using copper-substituted mica as a catalyst (Japanese Unexamined Patent Application Publication No. 59-48429), and methods using specific zinc salts and/or indium salts as catalysts, A method using metal oxides supported on silica (Japanese Patent Application Laid-Open No. 60-4147
No. 60-6629), a method using zinc-substituted composite mica as a catalyst (Japanese Patent Application Laid-open No. 61130252),
Even the method using a catalyst consisting of copper, phosphorus, and silica gel (Japanese Patent Application Laid-open No. 148443/1983) is still insufficient in simultaneously satisfying the above-mentioned basic performance of the catalyst. Among these methods, the method using zinc oxide as a catalyst is considered to be a promising method because of its high formaldehyde yield and selectivity. Regarding zinc oxide catalysts, a method using a zinc-silicon composite oxide obtained by mixing an aqueous solution of an inorganic silicate compound with an aqueous solution of a zinc compound and burning a precipitate (Japanese Unexamined Patent Application Publication No. 1983-1999) 79851), or a method using a catalyst consisting of zinc oxide, silver oxide and silica (Japanese Patent Application Laid-open No. 89411/1983) has also been proposed. These methods can maintain the activity of the catalyst for a relatively long time, but the former method does not operate stably, and the latter method uses silver, which increases the catalyst cost. (Problems to be Solved by the Invention) As mentioned above, the simple dehydrogenation method in which formaldehyde is produced by catalytic dehydrogenation of methanol in the absence of oxygen has the advantage that it is possible to reduce the water content of formaldehyde products. Zinc oxide is promising as a catalyst for this method because it increases the yield and selectivity of formaldehyde, but the following problems still remain.

■When zinc oxide is supported on silica or made into a zinc-silicon composite oxide, the zinc oxide is easily reduced to metallic zinc by hydrogen and carbon monoxide produced as by-products in the dehydrogenation reaction.
Since the dehydrogenation reaction temperature is higher than the melting point of metallic zinc, the reduced metallic zinc evaporates, resulting in a short catalyst life and difficulty in reusing the catalyst.

■Pipe clogging occurs due to adhesion of evaporated metallic zinc, making stable operations impossible.

■Catalysts containing silver or indium oxides have high activity, but are expensive.

An object of the present invention is to provide an improved method for producing formaldehyde that can stably produce formaldehyde in high yield over a long period of time, as well as a method for producing and regenerating a catalyst used in this method. (Means for Solving the Problems) As a result of intensive studies to achieve the above object using an inexpensive catalyst, the present inventors found that a zinc oxide/zeolite catalyst prepared using an ion exchange method was found. They found it useful and perfected the invention. The gist of the present invention is a method for producing formaldehyde by catalytic dehydrogenation of methanol in the absence of oxygen, which comprises using a zinc oxide/zeolite catalyst obtained by an ion exchange method. It is. Furthermore, the zinc oxide/zeolite catalyst used in the method of the present invention is produced by adsorbing zinc ions onto zeolite using an aqueous solution of a zinc compound, followed by calcination, and after use, it is produced by calcination in an oxygen-containing atmosphere. It can be played and used repeatedly. (Function) In the method of the present invention, a zinc oxide/zeolite catalyst prepared using an ion exchange method is used as a methanol dehydrogenation catalyst. The alkali metal or alkaline earth metal cations contained in zeolites are easily exchanged with other cations in aqueous solutions. Taking advantage of this property, zeolite catalysts in which a certain amount of catalyst is supported on zeolite are used in various reactions, but the reason why such zinc oxide/zeolite catalysts are particularly effective for simple dehydrogenation of methanol is this. It was not known until then. The zeolite used as a catalyst carrier in the present invention is not particularly limited, and may be either a zeolite such as a molecular sieve or a natural zeolite. The shape of the zeolite is also not particularly limited, but a pellet-shaped molecular sieve is preferable, and among these, a pellet-shaped molecular sieve is preferable. Molecki error sieve 13X is particularly excellent. Powdered zeolite is not preferred because it tends to clog the reactor when used as a catalyst, making it difficult to operate the process stably.
The catalyst used in the present invention can be produced by the method described below using zeolite and a suitable water-soluble zinc source as raw materials and using ion exchange treatment. As the zinc source, any water-soluble zinc salt such as nitrate, sulfate, organic carboxylate, etc. can be used, but nitrate is particularly preferred. Compared to other salts, nitrates are easier to remove anions from after ion exchange, so there is no contamination due to residual anions, and they are superior in terms of catalytic activity. In the ion exchange method, zeolite is immersed in an aqueous solution of zinc salt, such as zinc nitrate, and ion exchange with zinc ions is performed. For ion exchange, remove the exchange solution by decanting every hour.
It is preferable to perform this by repeating the operation of removing the replacement solution and adding a new replacement solution. This operation continues until a predetermined amount of zinc ions are adsorbed onto the zeolite by ion exchange.
For example, it can be repeated 10 times or more.

Although the concentration of the zinc salt in the aqueous solution is not particularly limited, IN
Concentrations above are preferred. After completing the ion exchange, the obtained zeolite that has adsorbed zinc ions is washed with water, filtered, dried, and then calcined in the air to produce zinc oxide on the zeolite, which produces the zinc oxide/zeolite catalyst used in the present invention. is obtained. The burning temperature at this time is preferably 300°C or higher, particularly 500 to 700°C. The content of zinc oxide in this catalyst is not particularly limited, but from the viewpoint of catalytic activity and reaction stability, 5% zinc oxide per 100g of catalyst.
~30g is preferable. The zinc oxide/zeolite catalyst obtained as described above has a high methanol reaction rate;
Formaldehyde can be obtained in extremely high yield and with high selectivity. Furthermore, this catalyst has an excellent catalyst life and is very advantageous in that it does not cause any scattering of metal zinc caused by the reduction action of the produced gas, which tends to occur with conventional zinc-based catalysts. This is thought to be a comprehensive result of various factors, such as the extremely strong binding force of zinc oxide to zeolite because it was prepared by ion exchange, and the structure of the zeolite's pores that prevent it from scattering. According to the method of the present invention, methanol is catalytically dehydrated in the gas phase using the above catalyst. The temperature of the catalyst layer during the reaction is usually 450 to 650°C, preferably 500 to 600°C. If the temperature is lower than 450°C, the reaction rate of methanol will decrease, and if it is higher than 650°C, a decomposition reaction of formaldehyde will occur. The reaction pressure is not particularly limited, but the reaction is usually carried out at normal pressure. The amount of methanol supplied into the reactor depends on the size and shape of the reactor, but is preferably 0.1 to 10.0 g/h per 1 g of catalyst, 0.1 k
If it is less than 10.0 kg/h, it is difficult to put it into practical use.
If the value exceeds 1, the reaction rate of methanol decreases. Methanol can be mixed with inert gases such as nitrogen, methane, carbon dioxide and/or
Alternatively, it is preferable to dilute it with hydrogen or the like and supply it. These inert gases and hydrogen have the effect of preventing the formaldehyde produced in the dehydrogenation reaction from decomposing into hydrogen and carbon monoxide. The reaction products are formaldehyde, unreacted methanol,
a gaseous mixture containing by-products and diluting gas;
By cooling this or absorbing it in a suitable aqueous solvent, an organic solvent solution of formaldehyde containing almost no water can be recovered. The zinc oxide/zeolite catalyst used in the method of the invention is
Even after long-term use reduces activity, it can be regenerated and used repeatedly by activating it using a simple method. This makes it possible to reduce the catalyst consumption rate and at the same time to stably produce formaldehyde for a long period of time. The present inventors investigated the cause of the decrease in catalyst activity due to the method of the present invention and found that the decrease in activity due to the method of the present invention is mainly caused by carbon deposited in the catalyst layer. Therefore, in order to burn off this carbon, we regenerated the spent catalyst by burning it in an oxygen-containing atmosphere, and it was found that the catalyst activity was restored and the regenerated catalyst could be reused for the reaction. At this time, zinc oxide is also produced by oxidizing the metal zinc contained in the spent catalyst, which contributes to improving the activity of the catalyst. As a burning method for regeneration, it is preferable to place a catalyst for regeneration in an electric furnace or the like and burn carbon deposited on the surface of the catalyst at 300 to 600°C.

Alternatively, it is also possible to burn carbon, etc. by heating the reactor while directly blowing air into the reactor once the activity of the catalyst has decreased. The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these. Actual Jlj Difference L (Catalyst Preparation) Add 3 times the volume of IN zinc nitrate (Zn(NOs)!' 6 to 20 g of commercially available molecular sieve 13X powder.
}1zo) Ion exchange with zinc ions was performed by adding an aqueous solution and immersing it at a liquid temperature of 80°C. Remove the zinc nitrate aqueous solution by decantation approximately every hour.
Added new replacement fluid. This operation was repeated 10 times, and finally, after washing with water, the zeolite was filtered to recover the zeolite that had adsorbed zinc ions through ion exchange. Heat this to 110°C
A zinc oxide/zeolite catalyst was prepared by drying at 650°C for 3 hours and then calcining at 650°C for 3 hours. The zinc oxide content of this catalyst was approximately 15.1 g per 100 g of catalyst.

(Reaction) 1 g of the above catalyst was packed into a flow-through quartz reaction tube with an inner diameter of 15 mm. After raising the temperature inside the reaction tube to 550°C, methanol was added at 4 g/h and nitrogen was added at 500 cc/win under normal pressure conditions.
The dehydrogenation reaction of methanol was carried out by introducing the methanol at a flow rate of . The outlet gas of the reactor was separated into a gaseous product and a liquid product using n-butanol as an absorbent in an absorption tube maintained at -80°C. Gaseous products were analyzed using a thermal conductivity type gas chromatograph using a 2 m column packed with molecular sieve 13X, and hydrogen, nitrogen, and carbon monoxide IC0
1. Analyzed for methane [CHsl.

The liquid product is APS-201 20% Flusin↑
Formaldehyde [HCHO], methyl formate, dimethyl ether, methanol [CH30 old, and water] were analyzed using a thermal conductivity gas chromatograph using a 4 m column packed with . As a result, methyl formate and dimethyl ether were hardly viable. The reaction performance was evaluated by calculating the methanol conversion rate, formaldehyde yield, and formaldehyde selectivity using the following formulas. In the following formula, each quantity indicates the molar amount. [ICHO] + [(:O] + [CH
4] + [Outlet CH20H] [HCHO] + [CO
I + [CH4] + [Exit CIIIOII+[}
ICIIO+ + [GO] + [CI+4] Real Ju
l Using Molecular Sheep 4A as a carrier, Example 1
A zinc oxide/zeolite catalyst (zinc oxide-containing II 7.6 g/100 g) was prepared in the same manner as in Example 1, and a methanol dehydrogenation reaction was carried out in the same manner as in Example 1. Tip Twisting 1 Using Molecule Sieve 5A as a carrier, Example 1
A methanol dehydrogenation reaction was carried out in the same manner as in Example 1 using a zinc oxide/zeolite catalyst (zinc oxide content T, Tg/100g) using the same method as in Example 1. A zinc oxide/zeolite catalyst (zinc oxide content: 8.5 g/100 g) was prepared in the same manner as in Example 1 using NaY-type zeolite as a soil carrier, and was used in the same manner as in Example 1. A dehydrogenation reaction of methanol was carried out. Example 1 Using molecular sieve 3^ as a carrier
A zinc oxide/zeolite catalyst (zinc oxide content: 124.3 g/100 g) was prepared in the same manner as in Example 1, and a methanol dehydrogenation reaction was carried out in the same manner as in Example 1. Zinc oxide/zeolite catalyst (zinc oxide content: 15.1
g/100g) was prepared, and using this, methanol dehydrogenation reaction was performed in the same manner as in Example 1. Zinc oxide/zeolite catalyst (zinc oxide content 7.6 g/
100g) was prepared, and using this, methanol dehydrogenation reaction was performed in the same manner as in Example 1. Zinc oxide/zeolite catalyst (zinc oxide content 7.7g/
100g) was prepared, and using this, methanol dehydrogenation reaction was carried out in the same manner as in Example 1. A zinc oxide/zeolite catalyst (zinc oxide containing ffi8.
5g/100g) was prepared, and using this, methanol dehydrogenation reaction was performed in the same manner as in Example 1. A zinc oxide/zeolite catalyst (containing 124.3 g of zinc oxide) was prepared in the same manner as in Example 5 except that the burning temperature was 600°C.
/100g) was prepared, and using this, methanol dehydrogenation reaction was performed in the same manner as in Example 1.

2. Zinc oxide/zeolite catalyst (zinc oxide content 15.5 g/100
g) was prepared and used to carry out the dehydrogenation reaction of methanol in the same manner as in the example. Back twisting U Zinc oxide/zeolite catalyst (zinc oxide content 10.3 g/I
QOg) was prepared, and using this, methanol dehydrogenation reaction was carried out in the same manner as in Example 1. Disaster Gai U Zinc oxide/zeolite catalyst (zinc oxide content: 15.
1g/100g) was prepared, and using this, methanol dehydrogenation reaction was performed in the same manner as in Example 1. Ura-kan Group■ A zinc oxide/zeolite catalyst (zinc oxide-containing itl4.
6g/100g) was prepared, and using this, methanol dehydrogenation reaction was performed in the same manner as in Example 1. Kono Kei U raw L 10% by weight to 20g of commercially available silica gel (average particle size 0.5+s+m) heat-treated in air at 800°C for 6 hours
A zinc oxide/silica gel catalyst was prepared by adding 20 g of an aqueous zinc nitrate solution, allowing it to stand for a while, filtering to remove the liquid, and calcining at 350°C for 2 hours and 600°C for 5 hours. Using this catalyst, methanol dehydrogenation reaction was carried out in the same manner as in Example 1. Comparison group 1 20g of silica gel heat-treated in the same manner as Comparative Example 1 was added with IO
20 g of a wt % zinc nitrate aqueous solution was added and allowed to stand for a while. Next, a solution of 44 g of sodium carbonate dissolved in 35.8 g of pure water was added to the above mixture with stirring to precipitate basic zinc carbonate on the silica. A basic zinc carbonate/silica catalyst was prepared by thoroughly washing the solid with water, filtering and drying at 110"C for 3 hours. Using this catalyst, methanol dehydrogenation reaction was carried out in the same manner as in Example 1. Five grams of silica gel, which had been heat-treated in the same manner as in Comparative Example 1, and 5 grams of commercially available zinc oxide powder (average particle size 0.5+lIl) were physically mixed and oxidized by baking at 300°C in air for 3 hours. A zinc/silica catalyst was prepared. Using this catalyst, a methanol dehydrogenation reaction was carried out in the same manner as in Example 1. 5 g of Hokukan Teido Molekier Sieve 5^ and 5 g of zinc oxide as in Comparative Example 3 Physically mix and heat at 350℃ in air.
by annealing at 600"C for 5 hours.
A zinc oxide/zeolite catalyst that does not rely on ion exchange was prepared. Using this catalyst, methanol dehydrogenation reaction was carried out in the same manner as in Example 1. The results of the above examples and comparative examples are summarized in Table 1. In the example, no significant decrease in activity was observed even after 400 hours compared to the steady activity after the reaction was continued for 15 to 20 hours after reaching the set temperature. In addition, the scattering of metallic zinc is 400%
It was hardly recognized even after hours. In the comparative example, the CI308 conversion rate and HCI{O yield decreased significantly after a short reaction time of 2 to 6 hours, compared to the initial activity immediately after the set temperature was reached. In addition, scattering of metallic zinc was also observed. The used catalyst after passing through the oil for 400 hours in Example 1 was taken out of the reactor and burned in an electric furnace set at 550"C in an atmospheric atmosphere for 3 hours to remove carbon etc. deposited on the catalyst. The regenerated material was then filled into the reaction tube again, and an experiment was conducted in the same manner as in Example 1.The results are shown in Table 2.
From the table, it can be seen that results equivalent to those obtained with the new catalyst can be obtained, confirming that the method of the present invention can maintain sufficient activity even when using a regenerated catalyst. (Margins below) (Continued on next page) (Continued in Table 1) (Effects of the invention) According to the method of the present invention, by using a zinc oxide/zeolite catalyst prepared by an ion exchange method, the conversion rate of methanol is is very high, and formaldehyde can be obtained in high yield. In addition, the scattering of metallic zinc due to catalyst reduction, which was likely to occur with conventional zinc-based catalysts, is suppressed in the present invention, and formaldehyde can be obtained in high yield over a long period of time, and piping is not clogged. Stable operation becomes possible.

Furthermore, the zinc oxide/zeolite catalyst used in the present invention has an economical advantage because it can be regenerated and used even after long-term use.

Claims (3)

[Claims] (1) A method for producing formaldehyde by catalytically dehydrogenating methanol in the absence of oxygen, the method comprising using a zinc oxide/zeolite catalyst obtained by an ion exchange method. (2) Formaldehyde by dehydrogenation of methanol, which consists of soaking zeolite in an aqueous solution of zinc salts to adsorb zinc ions onto the zeolite through ion exchange, and then calcining the zeolite to form zinc oxide on the zeolite. A method for producing a zinc oxide/zeolite catalyst for the production of. (3) A method for regenerating a zinc oxide/zeolite catalyst for the production of formaldehyde by dehydrogenating methanol, which comprises regenerating a used zinc oxide/zeolite catalyst produced by an ion exchange method by calcination in an oxygen-containing atmosphere. .