JPH062699B2 - Formaldehyde production method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a method for producing formaldehyde. Specifically, in the case of producing formaldehyde by dehydrogenating methanol in the substantial absence of oxygen, a specific zinc oxide-
The present invention relates to a method for producing formaldehyde, which is characterized by using a silica-based catalyst.

<Prior art and problems to be solved by the invention> Formaldehyde is a resin raw material such as polyacetal resin, urea resin, and phenol formaldehyde resin, or
It is used as a raw material for various industrial chemicals such as pentaerythritol and hexamethylenetetramine, and is an important basic raw material in the chemical industry.

As a formaldehyde industrial production method, a method of catalytically oxidizing and dehydrogenating methanol with a silver catalyst under air circulation, or a catalytic oxidation method using a mixed catalyst of iron oxide and molybdenum oxide in place of the silver catalyst is well known. In addition to formaldehyde, a large amount of water is by-produced by this method, and formaldehyde is usually absorbed in water.
It is also well known that it is recovered as an aqueous solution having a concentration of 0 to 50%.

However, these methods have drawbacks in that they require complicated and expensive equipment and a large amount of energy for prevention of catalyst deactivation, removal of by-products, and the like. There is a problem in that a large amount of water needs to be removed from the raw materials in the field where the demand for water is remarkably increased, particularly in the field of resins such as polyacetal resin, which consumes a large amount of energy. .

In order to solve the problems of the catalytic oxidative dehydration method and the catalytic oxidation method, various methods are proposed for the so-called catalytic dehydrogenation method, in which formalin is produced by dehydrogenating methanol in the substantial absence of oxygen. Has been done.

For example, as a catalyst, a method using a catalyst composed of copper, silver and silicon (Japanese Patent Publication No. 41-11858), a method using molten zinc, gallium, indium, aluminum or the like (Japanese Patent Publication No. 47-19251) 48-
97808), and a method using a catalyst composed of copper, zinc and sulfur or selenium (JP-A-51-1407,
Nos. 51-76209 and 52-215) have been proposed, but none of them simultaneously satisfy the basic performance of the catalyst such as the yield of formaldehyde, the selectivity and the life of the catalyst.

The present inventors have made various studies to solve the above problems of the catalytic dehydrogenation method of methanol, and have already used a metal oxide obtained by calcining a specific zinc salt and / or indium salt as a catalyst, zinc. Has proposed a method using a catalyst in which the above oxide and / or the oxide of indium are supported on silica (JP-A-60-4147 and 60).
-6629 publication).

The inventors of the present invention have conducted extensive studies in order to find a further excellent method for producing formaldehyde, and if a zinc oxide-silica-based catalyst obtained in a specific formulation is used, a higher yield and a long period of time are obtained. The inventors have found that formaldehyde can be produced stably, and have completed the present invention.

<Means for Solving Problems> That is, according to the present invention, a solution containing a precursor of zinc oxide and an organosilicon as a catalyst for dehydrogenating methanol to produce formaldehyde in the substantial absence of oxygen. Zinc oxide obtained by adding urea to the above to form a precipitate, and then subjecting the precipitate to a calcination treatment
The present invention provides an industrially excellent method for producing formaldehyde, which is characterized by using a silica-based catalyst.

The present invention uses the zinc oxide-silica catalyst obtained by the specific formulation as described above, but the zinc content is usually 5 to 75 wt%, preferably 20 to 60%. Silicon has an atomic ratio to zinc of usually 1/10 to 10/1.

Examples of zinc oxide precursors used in preparing such a catalyst include various salts of zinc, such as nitrates, sulfates, organic carboxylates, carbonates, hydroxides, and ammonium oxyacid salts. Of these, nitrates and organic carboxylates are preferable.

Further, as the organosilicon compound, the following general formula (I) (In the formula, each of A, B, C and D represents oxygen or a simple bond, and at least one is oxygen. R ₁ , R ₂ ,
R ₃ and R ₄ are each hydrogen, an alkyl group, an alkenyl group,
It represents an alkynyl group, an aryl group, an aralkyl group, or an organic carbonyl group, and is not all hydrogen at the same time. ) And organopolysiloxanes in which these are condensed to form a siloxane bond (-Si-O-Si).

Examples of R ₁ , R ₂ , R ₃ and R ₄ include hydrogen, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, sec-butyl, pentyl, cyclopentyl, hexyl and cyclohexyl. Alkyl groups such as vinyl, propenyl, allyl, isopropenyl, cyclohexenyl, etc., alkynyl groups such as ethynyl, 2-propynyl, aryl groups such as phenyl, tolyl, xylyl, aralkyl groups such as benzyl, formyl, acetyl. , An organic carbonyl group such as propionyl, and the like.

More specific organic compounds include tetramethoxysilane, methoxytrimethylsilane, dimethoxydimethylsilane, methyltrimethoxysilane, methoxydimethylvinylsilane, acetoxytrimethylsilane, ethoxytrimethylsilane, diethoxymethylsilane, ethyltrimethoxysilane, and 2-propynyl. , Diacetoxydimethylsilane, trimethylpropoxysilane, triethylsilanol, diethoxydimethylsilane, triethoxysilane, methyltriethoxysilane, triacetoxyvinylsilane, diethoxydimethylsilane, triethoxysilane, methyltriethoxysilane, triacetoxyvinylsilane, diacetoxysilane Acetoxyvinylsilane, diethoxydiethylsilane, dimethyldipropoxysilane, ethyltriethoxysilane, TE La silane, phenyl trimethoxy silane, allyl triethoxy silane, etc., and which like condensate of it can be exemplified.

The catalyst used in the present invention is obtained by calcining a precipitate produced by adding urea to a solution containing the above-mentioned zinc oxide precursor and an organosilicon compound. Urea used, for example, one commercially available as an industrial chemical, can be sufficiently used.

The amount of urea used is usually 1 to 20 per 1 mol of zinc used.
It is preferably 2 to 10 mol.

Here, a catalyst using an alkali such as sodium hydroxide, potassium hydroxide, sodium carbonate, sodium hydrogencarbonate, or ammonia, which is usually used as a metal ion precipitating agent instead of urea, has remarkably poor activity and extremely low aldehyde yield. In contrast to this, the catalyst using urea as a precipitant has a very high activity, and retains a high activity for a long period of time as compared with known catalysts.

Although the action of such urea has not been completely clarified, when urea is used, the BET surface area is extremely high, so that reactions such as formation of zinc hydroxide and hydrolysis of organosilicon proceed simultaneously. It is presumed that it plays a role in producing a precipitate having a uniform composition.

As a specific method for preparing the catalyst, for example, the precursor of zinc oxide and organosilicon are dissolved in an organic solvent such as alcohol or water or a mixture of both, and urea is dissolved therein.

A precipitate is then formed by heating at 60-150 ° C for 2-100 hours.

The desired catalyst can be obtained by subjecting such a precipitate to washing with water, drying, and then calcination.

Here, the firing treatment is usually performed in air or nitrogen stream at 40
It is carried out at a temperature of 0 to 1000 ° C, preferably 500 to 900 ° C.

Thus, the catalyst used in the present invention can be obtained, but dehydrogenation of methanol is usually carried out by a gas phase flow system, and methanol is supplied to the catalyst layer as a gas.

The catalyst layer temperature is usually 450 to 650 ° C., 500 to 6
00 ° C is preferred. The reaction pressure is not particularly limited, but is usually atmospheric pressure to 10 kg / cm ² .

Here, methanol may be supplied after being diluted with an inert gas such as nitrogen or methane and / or hydrogen. Although the amount of methanol supplied depends on the size and shape of the reactor, it is usually 0.1 to 10 kg / hr per 1 kg of the catalyst. If it is less than 0.1 kg / hr, it is inferior in practical use. It shows a downward trend.

The reaction gas discharged from the reactor is cooled and formaldehyde is recovered by an ordinary chemical industrial method, for example, a heat exchange type condensation tower, an absorption tower and the like.

Here, the amount of water contained in the reaction gas is 0.02 mol or less per 1 mol of formaldehyde, which is extremely small, which is advantageous for obtaining high-purity formaldehyde containing no water. For example, when a higher alcohol such as polyethylene glycol, diethylene glycol or cyclohexanol is used as the absorbent, it is recovered as a higher alcohol hemiformal solution, and high-purity formaldehyde can be easily obtained by heating and decomposing it.

<Effects of the Invention> Formaldehyde is thus produced. According to the present invention, the conversion of methanol is extremely high and formaldehyde can be obtained in a high yield, and further, the deposition of carbonaceous matter on the catalyst and the blocking of the catalyst. Etc. are hardly observed, the catalyst exhibits high activity for a long time, and formaldehyde is obtained in a high yield for a long time.

Further, according to the present invention, since the formaldehyde obtained has a very small water content, water can be easily removed,
It is also advantageous as a raw material in the field where moisture is absent. Further, since hydrogen produced as a by-product can be obtained in a high yield, off-gas can be effectively used as a heat source or a chemical raw material.

Since the method of the present invention has such various advantages, a method for producing a corresponding aldehyde or ketone by dehydrogenation of alcohols other than methanol, for example, by dehydrogenating ethanol, butanol, isopropanol, cyclohexanol and the like. Can also be applied to.

<Examples> Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto.

(1) Preparation of Catalyst <Catalyst A> zinc nitrate _{Zn (NO 3) 2 · 6H} 2 O 23.93g ethanol 100g
, And a solution of 16.66 g of triethoxysilane dissolved in 100 g of ethanol was added and stirred for 30 minutes at room temperature, and then a solution of 28.8 g of urea dissolved in 84.6 g of distilled water was added and stirred for 30 minutes at room temperature. .

Next, the liquid temperature was raised to 80 ° C. with stirring, and the mixture was heated and stirred at the same temperature for 9 hours to obtain a white slurry liquid. Over white solids,
After washing with water, it was dried at 150 ° C. for 12 hours, and then calcined in an electric furnace at 350 ° C. for 2 hours and further at 600 ° C. for 5 hours to obtain a catalyst A.

The obtained catalyst has a Zn content of 36.2 wt% and a Si content of 25.5 w.
The surface area measured by the BET method was 29.65 m ² / g.

<Catalyst B> In the preparation of Catalyst A, 28 wt% was used instead of the urea aqueous solution.
Ammonia water (58.8 g) was used, and this was stirred at room temperature for 30
It was prepared in the same manner as in the case of catalyst A except that the solution was added dropwise over a period of minutes.

The obtained catalyst B has a Zn content of 34.6 wt% and a Si content of 24.5 w.
t%, and the surface area by the BET method was 6.6 m ² / g.

<Catalyst C> zinc nitrate _{Zn (NO 3) 2 · 6H} 2 and O 53.4 g was dissolved in ethanol 39.5g, which ethanol 39.5g triethoxysilane 3
After adding a solution of 7.2 g and stirring at room temperature for 30 minutes, a solution of 61.5 g of urea and 150 g of distilled water was added and stirred at room temperature for 30 minutes.

Next, the liquid temperature was raised to 80 ° C. with stirring, and the mixture was heated and stirred at the same temperature for about 6 hours to obtain a white slurry liquid.

The white solid was washed with water and washed with water, dried at 150 ° C. for 12 hours, then calcined in an electric furnace at 350 ° C. for 2 hours and further at 600 ° C. for 1 hour to obtain a catalyst C.

The obtained catalyst has a Zn content of 44.6 wt% and a Si content of 19.5 wt.
%, And the surface area according to the BET method was 225 m ² / g.

<Catalyst D> Catalyst C was prepared in the same manner as catalyst C except that 26.7 g of zinc nitrate, 39.5 g of methanol as a solvent thereof, 30.7 g of urea and 170 g of distilled water as a solvent thereof were used.

The obtained catalyst D had a Zn content of 31.3 wt% and a Si content of 27.7 w.
The surface area measured by the BET method was 371 m ² / g.

<Catalyst E> zinc nitrate Zn a _{(NO 3) 2 · 6H 2} O 18.27g was dissolved in distilled water 200 ml, which was added silica gel (Nissan Chemical trade name Snowtex -N, SiO ₂ content 20 wt%) and 25g . Next, after thoroughly stirring this slurry mixture on a hot water bath at 80 ° C. for 1 hour, it was dried under reduced pressure by a rotary evaporator,
The obtained solid matter was calcined in air at 350 ° C. for 2 hours and at 600 ° C. for 5 hours to obtain a catalyst E.

The obtained catalyst has a Zn content of 40.2 wt% and a Si content of 23.4 wt.
%, And the surface area according to the BET method was 78 m ² / g.

<Catalyst F> In the preparation of the catalyst E, 14.6 g of zinc nitrate was used, and instead of the silica sol, 20 g of silica that had been dried at 300 ° C. for 5 hours was used in advance, and the catalyst F was obtained in the same manner as the catalyst E to obtain a medium F. .

The obtained catalyst has a Zn content of 12.9 wt% and a Si content of 38.0 wt%.
%, And the surface area measured by the BET method was 75 m ² / g.

The properties of the silica used are as follows.

Bulk specific gravity about 0.50 Chemical composition Porosity about 60% SiO ₂ 93 to 95% BET surface area 110 m ² / g Al ₂ O ₃ about 0.5% Fe ₂ O ₃ 0.5% IgLoss 4 to 6% or more Preparation of catalysts A to F However, the prepared catalyst was molded into a particle size of 24-48 mesh and then stored in a desiccator.

The specific surface area was measured using a monosorb (manufactured by Cantachrome) after dehydration treatment at 200 ° C. for 30 minutes in a nitrogen stream.

(2) Catalytic reaction test 1.0 g of the catalyst is filled in a quartz tube reactor having an inner diameter of 10 m / m. Then, a mixed gas of methanol and nitrogen (CH ₃ OH / N ₂ = 1) which was vaporized and mixed at 150 ° C. in advance in this reactor.
850 mmol / h or a mixed gas of methanol and hydrogen (CH ₃ OH / N ₂ = 18/82 molar ratio).
The mixture was circulated under conditions of r and atmospheric pressure to carry out the dehydrogenation reaction of methanol at a reaction temperature of 550 ° C.

The outlet gas of the reactor is introduced as it is into a thermoelectric conductivity type gas chromatograph using an APS-201 20% FlusinT (manufactured by Gascro Industrial Co., Ltd.) column 3 m and a molecular sieve 13X column 2 m by a heat-insulated gas sampler to generate a reaction. Formaldehyde [HCHO],
Analysis and quantification of methyl formate, dimethyl ether [DME], hydrogen [H ₂ ], carbon monoxide [CO], methane [CH ₄ ] and unreacted methanol [outlet CH ₃ OH], and nitrogen were performed.

The reaction results are shown in Table-1 and are the values after the reaction was continued for 20 hours and 50 hours after reaching the set temperature.
Gas chromatographic analysis produced almost no methyl formate.

In addition, [HCHO], [CO], [CH ₄ ] and [DME] are the production rates (mmol / hr) of each component, and [CH ₃ OH] is the unreacted methanol (mmol / hr) at the outlet of the reaction tube. Indicates.

Claims (1)

[Claims] 1. When producing formaldehyde by dehydrogenating methanol in the substantial absence of oxygen, urea is added to a solution containing a precursor of zinc oxide and organosilicon as a catalyst to form a precipitate. A method for producing formaldehyde, characterized by using a zinc oxide-silica catalyst obtained by subsequently subjecting the precipitate to a calcination treatment.