Title of Invention

DEHYDRATION OF WATER CONTAINING SOURCE OF FORMALDEHYDE, AND A METHOD FOR PRODUCING AN ETHYLENICALLY UNSATURATED

CARBOXYLIC ESTER

Technical Field

[0001]

The present invention relates to a method for dehydration of water containing source of formaldehyde, and a method for producing (meth)acrylic acid alkyl ester. Background Art

[0002]

Recently, a method for producing (meth)acrylic acid alkyl ester by reacting a carboxylic acid ester with formaldehyde in the presence of a catalyst (vapor-phase condensation reaction) has been developed. For example, when methyl propionate is used as carboxylic acid ester, methyl methacrylate is obtained as shown in the following formula (I).

[0003]

Formaldehyde is used in the form of formalin in many cases. Formalin is an aqueous solution containing formaldehyde, and generally contains methanol as a stabilizer. Therefore, when formalin is used as a raw material of (meth)acrylic acid alkyl ester, water is introduced into the reaction system. When water is present in the reaction system, inhibition of the reaction progression and deterioration of the catalyst are more likely to occur.

A further reaction with an acetal is shown in the following formula (II).

A theoretical example of formula (II) with a dimethoxymethane is shown in the following formula (III).

The use of dimethoxymethane thus theoretically provides an anhydrous system which avoids the difficulty of subsequent water separation and/or subsequent product hydrolysis. In addition, the use of dimethoxymethane avoids the use of free formaldehyde but nevertheless acts in a general sense as a source of formaldehyde. The absence of water and free formaldehyde could greatly simplify the separation of methyl methacrylate from the product stream.

However, in practice, formula (III) is problematic because methanol dehydrates to dimethyl ether and water. In addition, dimethoxymethane decomposes under catalytic conditions to dimethylether and formaldehyde. Any water formed in these reactions can hydrolyse the ester feedstock or product to its corresponding acid which may be undesirable.

In addition, the presence of water in the reaction mixture increases catalyst decay so that the presence of water may be undesirable even in the production of ethylenically unsaturated carboxylic acids.

[0004]

Therefore, when (meth)acrylic acid alkyl ester is produced, there is a demand to reduce the amount of water which is introduced to the reaction system, and, for example a method of dehydration by distillation of an aqueous solution of formaldehyde has been proposed (see PTL 1).

Citation List

Patent Literature

[0005]

[PTL 1] JP-A-2006-265123

Summary of Invention

Technical Problem

[0006]

However, the method disclosed in PTL 1 had an insufficient dehydration performance.

[0007]

The present invention is made from the viewpoint of these problems, and it provides a method for dehydration of a water containing source of formaldehyde having an excellent dehydration performance, and a method for producing (meth)acrylic acid alkyl ester using a dehydrated source of formaldehyde obtained by dehydration of the water containing source of formaldehyde.

Solution to Problem

[0008]

According to a first aspect of the present invention, there is provided a method for dehydration of a water containing source of formaldehyde comprising the step of contacting the source of formaldehyde with a zeolite membrane in a manner effective to separate at least part of the water from the source of formaldehyde.

Preferably, the water is separated from the said water containing source of formaldehyde by zeolite membrane pervaporation or zeolite membrane vapor permeation,and more preferably, the water is separated by vapor permeation.

Typically, in the process of the invention, the water enriched fluid is the permeate and the dehydrated source of formaldehyde is the retentate. However, it is possible for the dehydrated source of formaldehyde to be the permeate and the water enriched fluid to be the retentate.

According to a further aspect of the present invention there is provided a method for producing an ethylenically unsaturated carboxylic ester, preferably, an α, β ethylenically unsaturated carboxylic ester by contacting a source of formaldehyde with a carboxylic acid ester in the presence of a catalyst, wherein a dehydrated source of formaldehyde obtained by the method for dehydration of the water containing source of formaldehyde according to the first aspect of the invention, is used as the source of formaldehyde for the said method.

A particular preferred feature of the aspects of the present invention is that the water containing source of formaldehyde contains a separation enhancer having a relative (static) permittivity of between 2.5 and 20, more preferably between 3 and 15, and most preferably between 4 and 10 at 20°C and atmospheric pressure.

It has been found that the separation enhancer carboxylic acid ester is particularly effective. The carboxylic acid ester is preferably methyl propionate, methyl acrylate or methyl ethanoate, more preferably, the carboxylic acid ester is methyl propionate or methyl ethanoate, and most preferably, the carboxylic acid ester is methyl propionate. A preferred feature of the second aspect of the present invention is that a water containing source of the separation enhancer is combined with the water containing source of formaldehyde to produce a combined source and wherein the combined source is dehydrated in accordance with the first aspect of the invention to provide the said dehydrated source of formaldehyde which contains a separation enhancer.

In preferred embodiments, the water containing source of formaldehyde and, optionally, the water containing source of the separation enhancer contains methanol.

Typically, the ethylenically unsaturated ester is selected from the list consisting of methyl methacrylate and methyl acrylate.

The zeolite membrane is preferably a Linde Type-A zeolite membrane, more preferably, a Linde type-4A zeolite membrane.

The concentration of water in the water containing source of formaldehyde is preferably 0.5% by mass or more.

[0009]

[1] A method for dehydrating a water containing source of formaldehyde comprising: contacting the source of formaldehyde with a zeolite membrane in a manner effective to separate at least part of the water from the source of formaldehyde.

[2] The method for dehydrating a water containing source of formaldehyde according to [1], wherein the manner is selected from the group consisting of zeolite membrane pervaporation or zeolite membrane vapor permeation.

[3] The method for dehydrating a water containing source of formaldehyde according to [2], wherein water is separated from the water containing source of formaldehyde by zeolite membrane vapor permeation.

[4] The method for dehydrating a water containing source of formaldehyde according to any one of [1] to [3], wherein the separated water is a permeate and, a dehydrated source of formaldehyde is a retentate.

[5] The method for dehydrating a water containing source of formaldehyde according to any one of [1] to [4], wherein the water containing source of formaldehyde comprises a separation enhancer having a relative (static) permittivity of between 2.5 and 20.

[6] The method for dehydrating the water containing source of formaldehyde according to any one of [1] to [5], wherein the water containing source of formaldehyde contains carboxylic acid ester.

[7] The method for dehydrating the water containing source of formaldehyde according to any one of [6], wherein the carboxylic acid ester is either methyl propionate or methyl ethanoate.

[8] The method for dehydrating the water containing source of formaldehyde according to [7], wherein the carboxylic acid ester is methyl propionate.

[9] The method for dehydrating the water containing source of formaldehyde according to any one of [1] to [8], wherein the zeolite membrane is a Linde Type-A zeolite membrane.

[10] The method for dehydrating the water containing source of formaldehyde according to [9], wherein the zeolite membrane is a Linde Type-4A zeolite membrane.

[11] The method for dehydrating the water containing source of formaldehyde according to any one of [1] to [10], wherein the concentration of water in the water containing source of formaldehyde is at least 0.5% by mass based on 100% by mass of the water containing source of formaldehyde.

[12] The method for dehydrating the water containing source of formaldehyde according to any one of [1] to [11], wherein the water containing source of formaldehyde further contains methanol.

[13] A method for producing an ethylenically unsaturated carboxylic ester, preferably, an α, β ethylenically unsaturated carboxylic ester, comprising: contacting a source of formaldehyde with a carboxylic acid ester in the presence of a catalyst, wherein the source of formaldehyde is obtained by the method for dehydrating the water containing source of formaldehyde according to any one of [1] to [12] to produce a dehydrated source of formaldehyde.

[14] The method for producing an ethylenically unsaturated carboxylic ester according to [13], wherein the dehydrated source of formaldehyde further comprises carboxylic acid ester.

[15] The method for producing an ethylenically unsaturated carboxylic acid ester according to [13] or [14] comprising: combining a water containing source of the separation enhancer with the water containing source of formaldehyde to produce a combined source, and dehydrating the combined source in accordance with the method for dehydrating the water containing source of formaldehyde according to any one of [1] to [12] to provide the dehydrated source of formaldehyde which contains the separation enhancer.

[16] The method for producing an ethylenically unsaturated carboxylic acid ester according to any one of [13] to [15], wherein the water containing source of formaldehyde and, optionally, the water containing source of the separation enhancer further contains methanol.

[17] The method for producing an ethylenically unsaturated carboxylic acid ester according to any one of [13] to [16], wherein the ethylenically unsaturated acid ester is selected from the group consisting of methyl methacrylate and methyl acrylate. Advantageous Effects of Invention

[0010]

The present invention can provide a method for dehydration of the water containing source of formaldehyde having an excellent dehydration performance and a method for producing (meth)acrylic acid alkyl ester by using a dehydrated source of formaldehyde obtained by such dehydration.

Brief Description of Drawings

[0011]

FIG 1 is a schematic configuration view showing one example of a separation device where water is separated from the water containing source of formaldehyde.

Description of Embodiments

[0012]

The present invention will be described in detail below.

A method for dehydration of the water containing source of formaldehyde (hereinafter, simply referred to as "dehydration method") of the present invention separates water from water containing source of formaldehyde by using a zeolite membrane.

In the invention, a water containing source of formaldehyde is defined as a solution containing formaldehyde, water and an organic solvent other than

formaldehyde. An example of a dehydrated source of formaldehyde is a solution where at least some water has been separated from the water contining source of formaldehyde. Generally herein, a "dehydrated source of formaldehyde" refers to a water containing source of formaldehyde that has had at least some water removed by the method of the present invention.

[0013]

The water containing source of formaldehyde contains formaldehyde and water. Since formaldehyde is easily polymerized, the water containing source of formaldehyde preferably contains an organic solvent other than formaldehyde, for preventing polymerization of formaldehyde in the water containing source of

formaldehyde. The organic solvent other than formaldehyde is not specifically limited, and various organic solvents can be used. Typically, however, by "organic solvents" mentioned herein is not meant the separation enhancer described below. A preferred organic solvent is methanol.

The water containing source of formaldehyde is available in the form of formalin. Commercially available formalin contains methanol as a stabilizer.

[0014]

The content of formaldehyde is not specifically limited, but is preferably 5 to 50% by mass with respect to 100% by mass of water containing source of formaldehyde. When commercially available formalin is used as the water containing source of formaldehyde, the content of formaldehyde is generally 37% by mass or more. When the content of formaldehyde is low, for instance, below 5%, and the formaldehyde is used as a raw material in the reaction of producing (meth)acrylic acid alkyl ester, a sufficient yield is not obtained. When the content of formaldehyde is high, for instance, above 50%, a polymerization reaction of formaldehyde may occur and stability tends to deteriorate.

On the other hand, the content of organic solvent other than formaldehyde is preferably 5 to 90% by mass of 100% by mass of water containing source of

formaldehyde. When the content of the organic solvent other than formaldehyde is lower than 5% by mass, the formaldehyde may not be sufficiently stable. When the content of the organic solvent other than formaldehyde is higher than 90% by mass, the concentration of the raw material for producing (meth)acrylic acid alkyl ester is lowered, and thus a sufficient yield tends not to be obtained.

[0015]

In the present invention, when water is separated from water containing source of formaldehyde using a zeolite membrane, separation enhancer is preferably added to the water containing source of formaldehyde. Thereby, the dehydration performance is increased. The separation enhancer may be in solution with an organic solvent such as methanol. In addition, the separation enhancer may be in solution with water. Preferably, the separation enhancer is in solution with water and methanol.

Accordingly, the separation enhancer may be added as a water containing, and optionally, methanol containing, source of separation enhancer. Accordingly, the combined water containing source of formaldehyde and separation enhancer may contain methanol as well as water.

The content of separation enhancer is preferably 10% by mass or more, more preferably 20% by mass or more, with respect to 100% by mass of water containing source of formaldehyde. When the amount of separation enhancer is lower than 10% by mass, it is hard to obtain a sufficient dehydration performance. The upper limit of the amount of separation enhancer added is not specifically limited, but is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0016]

The preferred separation enhancers are preferably medium polarity solvents. Suitable separation enhancers may be selected from trifluoromethane, m-difluorobenzene, fluorobenzene, trifluoromethylbenzene, o-fluorotoluene, m-fluorotoluene, p-fluorotoluene, l,3-bis(trifluoromethyl)benzene; methyl formate, ethyl formate, methyl acetate, methyl acrylate, propyl formate, ethyl acetate, methyl propanoate, ethyl acrylate, methyl trans-2-butenoate ,methyl methacrylate, dimethyl malonate, butyl formate, isobutyl formate, propyl acetate, ethyl propanoate, methyl butanoate, ethyl 2-butenoate ethyl methacrylate, diethyl oxalate, dimethyl succinate, ethylene glycol diacetate, pentyl formate, isopentyl formate, butyl acetate, tert-butyl acetate, propyl propanoate, ethyl butanoate, methyl pentanoate, ethylene glycol monoethyl ether acetate, cyclohexyl formate, butyl acrylate, diethyl malonate, dimethyl glutarate, l,2,3,-propanetriol-l,3-diacetate, pentyl acetate, butyl propanoate, propyl butanoate, ethyl pentanoate, ethyl 3-methylbutanoate, methyl hexanoate, benzyl formate, phenyl acetate, methyl benzoate, methyl salicylate, diethyl maleate, diethyl fumarate, methyl cyclohexanecarboxylate, cyclohexyl acetate, diisopropyl oxalate, diethyl succinate, dimethyl adipate, hexyl acetate, pentyl propanoate, isopentyl propanoate, butyl butanoate, propyl pentanoate, ethyl hexanoate, methyl heptanoate, ethyl benzoate, methyl 4-methylbenzoate, benzyl acetate, phenyl propanoate, ethyl salicylate, methyl

2-methoxybenzoate, triacetin, cyclohexyl propanoate, ethyl cyclohexanecarboxylate, diethyl glutarate, heptyl acetate, pentyl butanoate, methyl octanoate, methyl

2-(acetyloxy)benzoate, dimethyl phthalate, 2-phenylethyl acetate, benzyl propanoate, phenyl propanoate, propyl benzoate, ethyl phenylacetate, cyclohexyl butanoate, diethyl adipate, octyl acetate, 2-methylheptyl acetate, pentyl pentanoate, ethyl trans-cinnamate, benzyl butanoate, phenyl pentanoate, butyl benzoate, pentyl hexanoate, propyl cinnamate , diethyl phthalate, pentyl benzoate, pentyl salicylate, 1-bornyl acetate, dibutyl tartrate, phenyl salicylate, hexyl benzoate, diethyl nonanedioate, benzyl benzoate, benzyl salicylate, pentyl cinnamate, diisobutyl adipate, diethyl sebacate, phenyl

2-(acetyloxy)benzoate , tributyrin, dibutyl phthalate, 2-naphthyl salicylate, dipentyl phthalate, dicyclohexyl adipate, dibutyl sebacate, dihexyl phthalate, 1,2,3-propanetriyl hexanoate, butyl oleate, dioctyl phthalate, dioctyl sebacate; 2-methyl-2-butanol, 2,2-dimethyl-l-propanol, 1-methylcyclopentanol, 3-hexanol, 3-methyl-3-pentanol,

2- ethyl-l-butanol, o-cresol ,cyclohexanemethanol, 2-methylcyclohexanol, 2-heptanol,

3- heptanol, 4-heptanol, 3-methyl-2-hexanol, 2,2-dimethyl-l-pentanol, 2,3-xylenol, 2,4-xylenol, 2,5-xylenol, 2,6-xylenol, 3,4-xyleno, 3,5-xylenol, 1-phenylethanol,

2- octanol, 3-octanol, 4-octanol, 2-methyl-l-heptanol, 4-methyl-l-hepanol,

5 -methyl- 1-heptanol, 3-methyl-2-heptanol, 5-methyl-2-heptanol, 6-methyl-2-heptanol,

3- methyl-4-heptanol, 2-ethyl-l-hexano, 2,2-dimethyl-l-hexano, 2,2-dimethyl-l-hexanol, alpha-ethylbenzenemethanol, alpha, alpha-dimethylbenzenemethanol,

l-phenyl-2-propanol, 1-nonanol, 2-nonanol, 3-nonano, 1-naphthol, 2-naphthol, l-phenyl-2-methyl-2-propanol, thymol, 1-decanol, 2-decanol, 3-decanol,

2,2-dimethyl-l-octanol, 1-undecanol, 1-dodecanol, 1-tridecano, 1-tetradecanol;

dimethyl ether, ethoxyacetylene, tetrahydrofuran, diethyl ether, ethylene glycol dimethyl ether, tetrahydropyran, 2-methyltetrahydrofuran, phenoxyacetylene, butoxyacetylene, diethylene glycol dimethyl ether, anisole, triethoxymethane, ethyl phenyl ether,

1,2-dimethoxybenzene, 1,3-dimethoxybenzene, 1 ,4-dimethoxybenzene, triethylene glycol dimethyl ether, eucalyptol, tetraethylene glycol dimethyl ether,

1-methoxynaphthalene; 1,4-cyclohexanedione, 2-octanone, 2-nonanone, di-tert-butyl ketone, 2,6-dimethyl-4-heptanone, 2-decanone, 2-undecanone, 7-tridecanone,

9-heptadecanone, 10-nonadecanone; pentanal, 2,2-dimethylpropanal and 1-heptanal.

In addition, the separation enhancer extends to mixtures of two or more of the above solvents or mixtures of one or more of the above solvents with one or more other solvents which mixtures in either case have relative static permittivity falling within the range 2.5 to 20 at 20°C. The separation enhancer is preferably a carboxylic acid ester represented by the following formula (IV).

In formula (IV), R ¹ is a hydrogen atom or an organic group, and the organic group is preferably an organic group having 1 to 4 carbon atoms. The organic group is a group essentially having a carbon atom, and for example includes an alkyl group, or an alkoxy group.

R ² is an alkyl group, and the alkyl group is preferably an alkyl group having 1 to 4 carbon atoms.

[0017]

Specific examples of the carboxylic acid ester include methyl propionate, methyl methacrylate, ethyl propionate, methyl acetate, or ethyl acetate. Of these, when methyl propionate is used as a separation enhancer, a permeation flux tends to be increased. In addition, methyl propionate can be used as a raw material of a reaction which produces methyl methacrylate by reaction of formaldehyde and methyl propionate, and therefore methyl propionate is particularly preferable in the present invention.

[0018]

The water containing source of formaldehyde is subjected to dehydration using a zeolite membrane.

The zeolite membrane is a membrane having excellent separation, heat resistance, and chemical resistance properties.

Examples of the zeolite membrane include a Linde Type-A (LTA) zeolite membrane, a T-type (ERI-OFF) zeolite membrane, a X-type (FAU) zeolite membrane, a Y-type (FAU) zeolite membrane, a mordenite (MOR) membrane, a ZSM-5 (MFI) zeolite membrane, a BEA zeolite membrane, and a silicalite membrane. The structures of these zeolites are described in "The Atlas of Zeolite Framework Types", 6 ^th revised edition , by Ch Baerlocher, L B McCusker and D H Olsen, Elsevier, ISBN

978-0-444-53064-6. Of these, a Linde Type-A zeolite membrane, a T-type zeolite membrane, a X-type zeolite membrane and a Y-type zeolite membrane are preferable. From the viewpoint that water can be selectively separated from the water containing source of formaldehyde, a Linde Type-A zeolite membrane having high Al content is preferable.

In addition, the present invention provides advantageously high flux rates. Generally, as a zeolite type, the higher the Al content, the more the affinity to water is increased, and the more the dehydration performance tends to be improved.

[0019]

When Linde Type-A zeolite membrane is used as zeolite membrane, from the viewpoint of water resistance thereof, a concentration of water in water containing source of formaldehyde is preferably 15% by mass or less, more preferably 10% by mass or less. When a concentration of water in water containing source of

formaldehyde is more than 15% by mass, deterioration of separation performance may occur due to the elution of the Linde Type-A zeolite membrane. However, if the concentration of water in the water containing source of formaldehyde is reduced, the permeation flux tends to be reduced. Therefore, the concentration of water in the water containing source of formaldehyde is preferably 0.5% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more based on 100% by mass of the water containing source of formaldehyde.

The amount of zeolite is sufficient to dehydrate the water containing source of formaldehyde by preferably at least 10%, more preferably at least 20%, and most preferably at least 30%. Typically, more than 50% of the total water present is separated from the water containing source of formaldehyde.

Generally, the higher the Si/Al molar ratio in a zeolite composition, the more the water separation performance tends to decrease. In comparison with Linde Type-A zeolite (Si/Al « 1.0), T-type zeolite (Si/Al = 3.6) and a mordenite (Si/Al = 5.1) have a lower water separation performance. The Si:Al molar ratio ranges for the Linde Type-A Zeolite membrane are preferably between 1:1 and 1.5:1, more preferably between 1 : 1 and 1.2:1, and most preferably between 1 : 1 and 1.1:1.

[0020]

The Linde Type-A zeolite membrane can be formed by precipitating Linde Type-A zeolite crystals on the surface of a porous support.

Examples of the porous support include ceramics such as dumina, silica, zirconia, silicon nitride, and silicon carbide, metals such as aluminum and stainless steel, and polymers such as polyethylene, polypropylene, and polytetrafluoroethylene. From the viewpoint of the separation performance of the membrane, inorganic compounds such as ceramics or metals are preferable. The shape of the porous support is not specifically limited, but a tube shape is preferable.

A method where a Linde Type-A zeolite crystal is precipitated on the surface of a porous support includes a method in which a Linde Type-A zeolite seed crystal is applied on the surface of the support, followed by precipitation by a synthesis method such as a hydrothermal synthesis method or a vapor phase method, in the presence of a silica raw material (for example, sodium silicate, silica gel, silica sol, silica powder, or the like) or an alumina raw material (for example, sodium aluminate, aluminum hydroxide, or the like). The Linde Type-A zeolite can be in the form of its sodium salt in which form it is usually synthesized or can be ion exchanged with solutions of metal ions, for examples, chloride or nitrate salts, particularly potassium or calcium ions or mixtures of these with sodium ions. Preferably part of the sodium ions are ion exchanged with calcium ions to produce the structure known as Linde Type-5A zeolite. Most preferably the Linde Type-A zeolite is in the 100% sodium form known as Linde Type-4A zeolite.

X-type and Y-type zeolites are preferably in their sodium forms or acid forms. A commercially available product can be used as the Linde Type-A zeolite membrane.

[0021]

As mentioned above, a method of separating water from a water containing source of formaldehyde using a zeolite membrane includes pervaporation, or vapor permeation. From the viewpoint that the size of the device can be reduced, pervaporation is preferable, whereas from the viewpoint that consumption of heat energy can be lowered without being associated with phase transition, vapor permeation is preferable.

As described above, in dehydration by a zeolite membrane, a separation factor and a permeation flux tend to be increased in accordance with increase of a

concentration of water in the water containing source of formaldehyde. Generally, a permeation flux tends to be increased in accordance with the rising of temperature of the water containing source.

In the present invention, the temperature of the water containing source of formaldehyde during separation is preferably 0 to 200°C, more preferably, 30 to 180°C, and most preferably 50 to 150°C.

[0022]

One example of pervaporation will be specifically described using FIG. 1. FIG 1 shows a separator 10 for separating water from the water containing source of formaldehyde using a zeolite membrane by pervaporation. The separator 10 of the example includes a vessel 11 storing an water containing source of formaldehyde, a zeolite membrane 12 provided in the vessel 11, and a thermometer 13, a thermostatic bath 14 for maintaining the constant temperature of the water containing source of formaldehyde in the vessel 11, a vacuum pump 15 for reducing pressure inside the decompression line 16 and the zeolite membrane 12, a decompression line 16 connecting the zeolite membrane 12 to vacuum pump 15, a first collection device 17 and a second collection device 18 provided in the decompression line 16 and a vacuum gauge 19.

[0023]

In the zeolite membrane 12, one end is sealed and the other end is connected to the decompression line 16 through a plug 12a such as a stainless steel tube.

Examples of the thermometer 13 include a thermocouple, or the like.

A first collection device 17 and second collection device 18 collect components (permeation solution) separated from the water containing source of formaldehyde. These devices include Dewar flasks 17a and 18a, which store a refrigerant for cooling components which permeate a zeolite membrane 12 in a vapor state and pass through the first and the second collection devices 17 and 18, and trapping tubes 17b and 18b for trapping the component (permeation solution) in a cooled liquid state or solid state. Examples of the refrigerant include liquid nitrogen.

[0024]

Specific examples of the pervaporation using a separator 10 shown in FIG. 1 will be described. A case using the Linde Type-A zeolite membranes as a zeolite membrane 12 is described below. First, the water containing source of formaldehyde is stored in a vessel 11. The temperature of the water containing source of formaldehyde in the vessel 11 is maintained by thermostatic bath 14 so as to be constant. The temperature of the water containing source of formaldehyde is preferably 50 to 150°C. In the specific examples below it is 60°C.

[0025]

Separately, liquid nitrogen is stored in Dewer flasks 17a and 18a.

Then, a vacuum pump 15 operates to reduce the pressure of an inner portion of a decompression line 16 and the zeolite membrane 12. Then, water in the water containing source of formaldehyde permeates the zeolite membrane 12 in the form of vapor. The water vapor permeating the zeolite membrane 12 is cooled by liquid nitrogen filled in the Dewar flask 17a in a first collection device 17 and collected by a trap tube 17b.

The second collection device 18 need not be provided. However, when the second collection device 18 is provided, in a case where water vapor is not collected by the first collection device 17, the water vapor passing therethrough can be collected by the second collection device 18, and thus infiltration of water into the vacuum pump 15 can be suppressed.

[0026]

In order to realize efficient membrane separation, it is necessary to provide a concentration difference in the water at the supply side and at the permeation side in respect to the zeolite membrane. As a specific device for providing a concentration difference, one providing a pressure difference which is as large as possible between the permeation and supply sides, or one flowing gas other than water so as not to retain water on the permeation side, can be exemplified. For providing as large a pressure difference as possible, the supply side may be pressurized, or the permeation side may be depressurized. In consideration of ease and permeability, the pressure of the supply side is preferably 50 to 800 kPa, the pressure of the permeation side is preferably 15.0 kPa or lower, the pressure of the supply side is more preferably atmospheric pressure to 500 kPa, and the pressure of the permeation side is more preferably 5.0 kPa or lower.

As the gas other than water so as not to retain water in the permeation side, in consideration of inertness not reacting with water and ease of availability, nitrogen or argon is preferable.

[0027]

According to the aforementioned method, water can be separated from the water containing source of formaldehyde. The separated water is collected in a trapping tube 17b of the first collection device 17. On the other hand, the dehydrated source of formaldehyde is stored in a vessel 11.

[0028]

The aforementioned method permeates water into a zeolite membrane 12, and separates the water from the water containing source of formaldehyde, however, the present invention is not limited thereto. For example, when kinds of the zeolite membrane 12 are changed, components other than water can be made to permeate the zeolite membrane 12 and separate from the water containing source of formaldehyde. In this case, the dehydrated source of formaldehyde is collected in the trapping tube 17b of the first collection device 17 as the permeation solution and water may be retained as the retentate.

The term "a source of formaldehyde" is that free formaldehyde may either form in situ from the source under reaction conditions or that the source may act as the equivalent of free formaldehyde under reaction conditions, for example it may form the same reactive intermediate as formaldehyde so that the equivalent reaction takes place.

A suitable source of formaldehyde may be a compound of formula (V).

wherein R ⁵ and R ⁶ are preferably independently selected from Ci - C ₁₂ hydrocarbons or H, X is O, n is an integer from 1 to 100, and m is 1.

R ⁵ and R ⁶ are independently selected from Q - C ₁₂ alkyl, alkenyl or aryl as defined herein, or H, more preferably Ci - Cio alkyl, or H, most preferably Ci - C ₆ alkyl or H, and especially methyl or H. n is an integer preferably from 1 to 10, more preferably 1 to 5, and especially 1 to 3.

However, other sources of formaldehyde may be used including trioxane or trioxane containing sources.

Therefore, a suitable source of formaldehyde includes any equilibrium composition which may provide a source of formaldehyde. Examples of such include but are not restricted to dimethoxymethane, trioxane, polyoxymethylenes

R ¹ -0-(CH ₂ -0)i-R ² wherein R ¹ and/or R ² are alkyl groups or hydrogen, i = 1 to 100, paraformaldehyde, formalin (formaldehyde, methanol, water) and other equilibrium compositions such as a mixture of formaldehyde, methanol and methyl propionate.

Typically, the polyoxymethylenes are higher formals or hemiformals of formaldehyde and methanol CH ₃ -0-(CH ₂ -0)i-CH ₃ ("formal-i") or CH ₃ -0-(CH ₂ -0)i-H ("hemiformal-i"), wherein i =1 to 100, preferably i =1 to 5,and especially i =1 to 3, or other polyoxymethylenes with at least one non methyl terminal group. Therefore, the source of formaldehyde may also be a polyoxymethylene of formula R -O- (CH2-0-)i R ³² , where R ³¹ and R ³² may be the same or different groups and at least one is selected from a Ci - C o alkyl group, for instance R ³¹ = isobutyl and R ³² = methyl.

Preferably, the term formalin is a mixture of formaldehyde: methanol: water in the ratio 25 to 65%: 0.01 to 25%: 25 to 70% by weight. More preferably, the term formalin is a mixture of formaldehyde: methanol: water in the ratio 30 to 60%: 0.03 to 20%: 35 to 60% by weight. Most preferably, the term formalin is a mixture of formaldehyde: methanol: water in the ratio 35 to 55%: 0.05 to 18%: 42 to 53% by weight.

Preferably, the mixture comprising formaldehyde, methanol and methyl propionate contains less than 50% water by weight. More preferably, the mixture comprising formaldehyde, methanol and methyl propionate contains less than 1% water by weight. Most preferably, the mixture comprising formaldehyde, methanol and methyl propionate contains 0.1 to 0.5% water by weight.

Typically, the water containing source of formaldehyde is a formaldehyde solution comprising formaldehyde, water and, optionally, methanol. It should be appreciated that the source of formaldehyde may not contain water, for instance where it is in the form of trioxane, but water may be added by mixing this stream with a second water containing source of formaldehyde and/or with a water containing source of the separation enhancer, such as wet methyl propionate.

[0029]

The dehydrated source of formaldehyde obtained by the process of the present invention, either as permeate or as retentate from which water has been removed as permeate, may be advantageously used as a raw material for producing (meth)acrylic acid alkyl ester.

A method of producing (meth)acrylic acid alkyl ester will be described below as an example.

(Meth)acrylic acid alkyl ester may be obtained by reacting carboxylic acid ester and formaldehyde in the presence of a catalyst in a vapor-phase condensation reaction. Therefore, it is possible to use a dehydrated source of formaldehyde obtained by the present invention as raw material for the reaction. Since water is sufficiently removed from the dehydrated source of formaldehyde, the undesirable introduction of water into the reaction system can be reduced. Therefore, suppression of the progression of the reaction and deterioration of the catalyst does not easily occur.

[0030]

Examples of the catalyst for this vapor-phase condensation reaction include base catalysts, specifically a catalyst where alkali metals such as potassium, rubidium, and cesium are supported on carriers such as silica, alumina, zirconia, and titania.

[0031]

A suitable molar ratio of carboxylic acid ester to formaldehyde in the vapor-phase condensation reaction is 1:1 to 20:1.

The reaction temperature of the vapor-phase condensation reaction is preferably 250 to 400°C and the reaction pressure is preferably

[0032]

Advantageously, when the dehydrated source of formaldehyde contains formaldehyde and carboxylic acid ester, and when the molar ratio in the dehydrated source of formaldehyde is within the aforementioned ratio for the vapor-phase condensation reaction, lower or no carboxylic acid ester raw material need be added during the reaction. When the ratio of carboxylic acid ester in the dehydrated solution is too low or absent, carboxylic acid ester is added separately to the dehydrated solution to achieve the necessary level and the solution is subjected to the vapor-phase condensation reaction.

[0033]

As the carboxylic acid ester added to the dehydrated source of formaldehyde, the carboxylic acid ester mentioned in the dehydration method of water containing source of formaldehyde can be exemplified. The carboxylic acid ester added to the dehydrated source of formaldehyde is preferably the same as the carboxylic acid ester added to the water containing source in the dehydration of the water containing source of formaldehyde.

[0034]

As the carboxylic acid ester added to the dehydrated source of formaldehyde, a commercially available product or a synthetic compound may be used.

The synthesis method of carboxylic acid ester is not specifically limited, but a synthesis method will be described by an example of methyl propionate.

Ethylene and methanol are reacted with carbon monoxide in the presence of a catalyst to obtain methyl propionate (liquid-phase homogeneous reaction).

[0035]

Examples of the catalysts include a precious metal complex catalyst, specifically a complex catalyst or the like coordinating phosphine or the like to precious metal.

A molar ratio of ethylene and methanol to carbon monoxide in the liquid-phase homogeneous reaction is preferably as follows:

ethylene : methanol : carbon monoxide = 1:0.1 to 100:0.1 to 10.

A reaction temperature of liquid-phase homogeneous reaction is preferably 10 to 150°C.

[0036] A vapor-phase condensation reaction produces water in addition to

(meth)acrylic acid alkyl ester which is objective substance by reacting carboxylic acid ester and formaldehyde. The (meth)acrylic acid alkyl ester is hydrolyzed by water. Therefore, vapor-phase condensation reaction is preferably performed in the presence of alcohol for suppressing hydrolysis of (meth)acrylic acid alkyl ester.

[0037]

When as the carboxylic acid ester, methyl propionate produced by the aforementioned liquid-phase homogeneous reaction is added to the dehydrated source of formaldehyde and subjected to vapor-phase condensation reaction, methanol is used in excess, in comparison with ethylene, and therefore the resultant methyl propionate contains unreacted methanol. Since the vapor-phase condensation reaction is preferably performed in the presence of alcohol, the unreacted methanol need not be separated from methyl propionate, and may be provided in the vapor-phase

condensation reaction in addition to methyl propionate.

The dehydrated source of formaldehyde obtained by dehydrating methanol and the water containing source of formaldehyde contains methanol.

Therefore, when the methanol-containing dehydrated solution is used or methyl propionate produced by a liquid-phase homogeneous reaction is added to the dehydrated solution, the vapor-phase condensation reaction can be performed in the presence of alcohol without separate addition of alcohol in a reaction system.

[0038]

The reaction product obtained by vapor-phase condensation reaction contains water in addition to (meth)acrylic acid alkyl ester which is the desired product. In vapor-phase condensation reaction, carboxylic acid ester is used in large excess in comparison with formaldehyde, and therefore the reaction product contains unreacted carboxylic acid ester. Moreover, when vapor-phase condensation reaction is performed in the presence of alcohol, the reaction product contains alcohol.

Therefore, (meth)acrylic acid alkyl ester should be separated from the reaction product.

[0039]

A method for separating (meth)acrylic acid alkyl ester from the reaction product is not specifically limited, and for example the (meth)acrylic acid alkyl ester may be separated by distilling the reaction product.

[0040]

On the other hand, the residue after separating (meth)acrylic acid alkyl ester from the reaction product contains unreacted carboxylic acid ester and water.

Therefore, when carboxylic acid ester and water are separated from the residue, carboxylic acid ester is recovered and recycled as a reactant in the production of (meth)acrylic acid alkyl ester.

[0041]

The residue of the reaction product above can be used as carboxylic acid ester added to water containing source of formaldehyde in the aforementioned dehydration method of the present invention. Accordingly, dehydration of water containing source of formaldehyde and separation of water from unreacted carboxylic acid ester can be performed at the same time.

[0042]

The dehydrated source of formaldehyde produced when the residue of reaction product is added to the water containing source of formaldehyde and dehydrated, contains unreacted carboxylic acid ester in addition to formaldehyde.

Therefore, when the dehydrated source of formaldehyde is used as raw material of (meth)acrylic acid alkyl ester, unreacted carboxylic acid ester is reused.

The residue of reaction product is added to the water containing source of formaldehyde and dehydrated and the resultant solution containing dehydrated formaldehyde is used as a raw material of (meth)acrylic acid alkyl ester. Thereby, the dehydration method of the present invention can be incorporated into a portion of a method for producing (meth)acrylic acid alkyl ester, whereby production costs can be reduced.

[0043]

As described above, according to the dehydration method of the present invention, water can be highly efficiently separated from the water containing source of formaldehyde. In particular, when a separation enhancer is added and dehydrated, the dehydration performance is excellent. In this case, if the permeate is enriched in water then the retentate is enriched, with respect to the separation enhancer and water containing source of formaldehyde, in formaldehyde and separation enhancer or if the retentate is enriched in water then the permeate is enriched in formaldehyde and separation enhancer. It is preferred that the permeate is enriched in water.

The dehydrated source of formaldehyde obtained by the dehydration method of the present invention is preferable as a raw material of (meth)acrylic acid alkyl ester. In particular, it is preferable when methyl methacrylate is produced from methyl propionate. Further, when the dehydrated source of formaldehyde is used as a raw material, the introduction of water into the reaction system can be reduced, and therefore, progress of reaction is not easily suppressed and the catalyst is not easily deteriorated.

[Examples]

[0044] Hereinafter, specific description will be given in regard to the present invention by giving examples. However, the invention is not limited to these.

[Preparative Example 1]

The Linde Type-4A zeolite membranes were prepared generally in accordance with the examples of EP 1930067. Specifically, seed crystals to assist uniform membrane formation were formed on the support. Linde Type-4A zeolite fine particles (seed crystals, particle size: 100 nm) were placed in water and stirred to yield a suspension with a concentration of 0.5% by weight.

The sealed body was used for this example. Specifically, a tubular porous body made of a-alumina and having opening sections at both ends was prepared. The porous body had a mean pore size of 1.3 μπι, an outer diameter of 12 mm, an inner diameter of 9 mm and a length of 10 cm. A sealing member was tightly fitted in one opening section of the porous body, and a sealing member penetrated by an open air conduit was tightly fitted in the other opening section.

The sealed body was immersed in the aforementioned suspension. The entire porous body was immersed in the suspension, and the tip of the open air conduit was not immersed in the suspension. The sealed body was immersed in the suspension for 3 minutes. The sealed body was then drawn out at a rate of about 0.2 cm/s. The porous body obtained by removing the sealing members and from the sealed body was dried for 2 hours in a thermostatic bath at 25 °C, and then dried for 16 hours in a thermostatic bath at 70°C to produce a seed crystal-attached porous body.

Sodium silicate, aluminum hydroxide and distilled water were mixed to yield a reaction solution. 1 part by mole of alumina (AI2O3), 2 parts by mole of silicon dioxide (Si0 ₂ ) and 2 parts by mole of sodium oxide (Na ₂ 0) were added to 150 parts by mole of water to yield a reaction solution. The seed crystal-attached porous body was immersed in the reaction solution and held at 80°C for 3 hours to form a zeolite membrane on the surface of the seed crystal-attached porous body.

The obtained zeolite membrane was then cleaned with a brush. Further, it was immersed for 16 hours in warm water at 40°C. A Linde Type-4A zeolite membrane was thus obtained.

[Preparative Example 2]

The T-type zeolite membranes were prepared generally in accordance with the examples of US6387269.

Amorphous silica is introduced with stirring into an aqueous solution comprising sodium aluminate, sodium hydroxide and potassium hydroxide and allowed to age for 48 hours. The composition of the solution corresponds to the following molar ratios: SiO ₂ /Al ₂ O ₃ = 112, OH-/SiO ₂ = 0.77, Na+/(Na+ + K+) = 0.77, and

H ₂ O/(Na+ + K+) = 20.75.

Then a porous tubular support whose surface is provided with seed crystals of the T-type zeolite is immersed in the above reaction mixture. The support consisted of "Mullite", had a length of 10 cm, an external diameter of 1.2 cm, a thickness of 1.5 mm, a pore diameter of 1.3 μπι and a porosity of 40%. The average size of seed crystals is 100 μπι. The quantity of seed crystals on the porous support is 30 mg/cm ² . The hydrothermal synthesis is carried out for 24 hours at 100°C, followed by rinsing for 12 hours and drying at 70°C.

[0045]

[Example 1]

Formaldehyde (HCHO), water (H ₂ O), methanol (MeOH), and methyl propionate (MeP) were mixed so that the mass ratio (HCHO : H ₂ O : MeOH : MeP) was 10 : 9 : 11 : 70, to prepare a sample (feed solution). Water was separated from the feed solution in accordance with the following methods by using a separator 10 shown in Fig. 1.

[0046]

A Linde Type-4A zeolite membrane (manufactured in a manner of preparative example 1 above, effective membrane area : 2.64x10 ^-3 m ² ) as the zeolite membrane 12, and the thermocouples as a thermometer 13 were provided in the vessel 11. One end of the zeolite membrane 12 was sealed, and the other end was connected with the decompression line 16 through the plug 12a made of stainless-steel, then, the zeolite membrane 12 and the vacuum pump 15 were connected by the decompression line 16. Moreover, the first collection device 17, the second collection device 18, and the vacuum gauge 19 were provided at the middle of the decompression line 16.

500ml of previously prepared feed solution was stored in the vessel 11. Then, the temperature of the feed solution in the vessel 11 was controlled at the thermostatic bath 14 so that the temperature was 60°C.

The liquid nitrogen was stored in the Dewar flasks 17a and 18a respectively.

Then, the vacuum pump 15 was operated for 30 minutes, and pressure inside the decompression line 16 and the zeolite membrane 12 was reduced so that pressure on the permeation side became 3.OkPa or less. Vapor that permeated the zeolite

membrane 12 was cooled in the first collection device 17 with the liquid nitrogen with which Dewar flask 17a was filled, and the permeation liquid was collected in a trap tube 17b.

[0047]

The separation performance of the zeolite membrane was evaluated to obtain the permeation flux, the concentrations of water in the collected permeate and the separation factor in accordance with the following methods. The results are shown in Table 1.

(1) Permeation flux

The mass of the permeate that was collected in the trap tube 17b after separation was measured, and the permeation flux was calculated from the following expression (I). In the expression (I), "w" is weight of permeate [kg], "A" is the effective membrane area of the zeolite membrane [m ], and "t" is the permeation time [h]. This permeation flux is an index that shows the weight of permeate per unit area of the membrane, and per unit time.

[0048]

(2) Concentration of water in permeate

The concentration of water in the permeate was obtained by using a gas-chromatograph (detector: TCD (Thermal Conductivity Detector), separation column : porapakQ) at the column temperature of 170°C.

[0049]

(3) Separation factor

In the same manner as in the concentration of water in permeate (2), the concentration of water in the feed solution was obtained and the separation factor was calculated from the following expression (II). In the expression (II), "X" is concentration of water in the feed solution [% by mass], and "Y" is concentration of water in the permeate [% by mass].

[0050]

[Example 2]

Water was separated again by using the zeolite membrane used in example 1 from the feed solution in the same manner as in example 1. Then, the separation performance in the repetitive use of the zeolite membrane was evaluated. The results are shown in Table 1.

[0051]

[Example 3]

Water was separated from the feed solution in the same manner as in example 1, except using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MeP) became 10 : 9 : 41 : 40. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0052]

[Example 4]

Water was separated from the feed solution in the same manner as in example 1, except using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MeP) became 10 : 9 : 61 : 20. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0053]

[Example 5]

Water was separated from the feed solution in the same manner as in example 1, except using a T-type zeolite membrane (manufactured in a manner of preparative example 2, effective membrane area: 2.64 X 10 ^" m ) as the zeolite membrane, and using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MeP) became 10 : 9 : 41 : 40. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1. [0054]

[Example 6]

Water was separated from the feed solution in the same manner as in example 1, except methyl acetate (MeAc) instead of the MeP, and using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MeAc) became 10 : 9 : 41 : 40. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0055]

[Example 7]

Water was separated from the feed solution in the same manner as in example 1, except using methyl methacrylate (MMA) instead of the MeP, and using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MMA) became 10 : 9 : 41 : 40. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0056]

[Example 8]

Water was separated from the feed solution in the same manner as in example 1, except using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MeP) became 11 : 0.6 : 12 : 76.4. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0057]

[Example 9]

Water was separated from the feed solution in the same manner as in example 1, except using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MeP) became 11 : 3 : 12 : 74. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0058]

[Example 10]

Water was separated from the feed solution in the same manner as in example 1, except using an aqueous solution (feed solution) prepared so that the mass ratio in the aqueous solution (HCHO : H ₂ 0 : MeOH : MeP) became 10 : 6 : 11 : 73. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0059]

[Example 11]

Water was separated from the feed solution in the same manner as in example 1, except the temperature of the feed solution was adjusted to 50°C. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0060]

[Example 12]

Water was separated from the feed solution in the same manner as in example 1 , except the temperature of the feed solution was adjusted to 40°C. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0061]

[Example 13]

Water was separated from the feed solution in the same manner as in example 1, except using an aqueous solution (feed solution) prepared by mixing HCHO, H ₂ 0 and MeOH so that the mass ratio (HCHO : H ₂ 0 : MeOH) became 10 : 9 : 81. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0062]

[Example 14]

Water was separated from the feed solution in the same manner as in example 1, except using an aqueous solution (feed solution) prepared by mixing HCHO, H ₂ 0, MeOH and MeP so that the mass ratio (HCHO : H ₂ 0 : MeOH : MeP) became 6 : 9 : 15 : 70. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0063]

[Example 15]

Water was separated from the feed solution in the same manner as in example 14, except using an aqueous solution (feed solution) prepared by mixing HCHO, ¾0 , MeOH and 1-pentanol so that the mass ratio (HCHO : H ₂ 0 : MeOH : 1-Pentanol) became 6 : 9 : 15 : 70. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0064]

[Example 16]

Water was separated from the feed solution in the same manner as in example 14, except using an aqueous solution (feed solution) prepared by mixing HCHO, H ₂ 0 , MeOH and 1,4-butanediol so that the mass ratio (HCHO : H ₂ 0 : MeOH :

1,4-Butanediol) became 6 : 9 : 15 : 70. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1. [0065]

[Example 17]

Water was separated from the feed solution in the same manner as in example 14, except using an aqueous solution (feed solution) prepared by mixing HCHO, ¾0 , MeOH and glycerol (1,2,3-trihydroxypropane) so that the mass ratio (HCHO : ¾0 : MeOH : Glycerol) became 6 : 9 : 15 : 7Q. Then, the separation performance of the zeolite membrane was evaluated. The results are shown in Table 1.

[0066]

[Table 1]

[0067]

As is apparent from Table 1, in examples 1 to 13, water was able to be separated from the feed solution (an aqueous solution of formaldehyde) efficiently, and the dehydration performance was excellent. Particularly, the values for the permeation flux and the separation factor in the examples 1 to 4, 6, 7, 11, 12, 14 and 15 in which dehydration was performed using the Linde Type-4A zeolite membrane with containing the separation enhancer in the aqueous solution, were higher and the separation performance (dehydration performance) was improved compared to the example 13 in which dehydration was performed using the Linde Type-4A zeolite membrane without containing the separation enhancer in the aqueous solution.

Moreover, it is confirmed from the results of examples 1 and 2 that the separation performance is maintained excellently even though the zeolite membrane is used again.

Therefore, it is especially preferable to apply the present invention to the process for the production of (meth)acrylic acid alkyl ester comprising reacting carboxylic acid ester with formaldehyde in the presence of a catalyst, wherein a dehydrated source of formaldehyde is used as a raw material for the above reaction.

Industrial availability

[0068]

The present invention can provide a method for dehydration of the water containing source of formaldehyde having an excellent dehydration performance and a method for producing (meth)acrylic acid alkyl ester by using a dehydrated source of formaldehyde obtained by such dehydration.

Reference signs list

[0069]

10: separator

11 : vessel

12: zeolite membrane

12a: plug

13: thermometer 14: thermostatic bath 15: vacuum pump

16: decompression line 17: first collection device 18: second collection device 17a, 18a: Dewar flask 17b, 18b: trap tube

19: vacuum gauge