Gas-phase dehydration reaction process

Details Gas-phase dehydration reaction process Gas-phase dehydration reaction process

2001-01-26

2002-12-03

Kumar, Shailendra (Department: 1609)

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

C548S560000, C548S579000, C585S654000, C585S661000

Reexamination Certificate

active

06489515

ABSTRACT:

TECHNICAL FIELD TO WHICH THE INVENTION BELONGS
This invention relates to a gas-phase dehydration reaction process of a hydroxyl group-containing compound. More detailedly, the invention relates to an improvement in a gas-phase dehydration reaction process of a hydroxyl group-containing compound using a solid oxide catalyst containing an alkali metal element.
PRIOR ART
Known as examples of a process of carrying out gas-phase dehydration reaction of a hydroxyl group-containing compound using a solid oxide catalyst containing an alkali metal element are a process of preparing a cyclic amine by gas-phase intermolecular dehydration of an alkanolamine (Japanese Laid-open Patent Publication No. 126556/88, etc.), a process of preparing an unsaturated ether by gas-phase intermolecular dehydration of a glycol ether (Japanese Laid-open Patent Publication No. 143497/96, etc.), a process of preparing an N-alkenylcarboxylic acid amide by gas-phase intermolecular dehydration of a tertiary N-(2-hydroxyalkyl)carboxylic acid amide (Japanese Laid-open Patent Publication No. 141402/96, etc.), a process of preparing an alkylene sulfide by gas-phase intermolecular dehydration of a mercaptoalkanol (Japanese Laid-open Patent Publication No. 202027/93, etc.), a process of preparing a tertiary amine compound by gas-phase intermolecular dehydration of a secondary amine compound and an alcohol (Japanese Laid-open Patent Publication No. 241220/97, etc.), a process of preparing an alkyl ether of a phenol by gas-phase intermolecular dehydration of the phenol and an alcohol (Japanese Laid-open Patent Publication No. 235248/97, etc.).
Hydroxy group-containing compounds as raw materials of the gas-phase dehydration reaction, particularly alkanolamines, glycol ethers and hydroxyethyl compounds such as N-(2-hydroxyalkyl)carboxylic acid amides have a hydroxyl group and an amino group or an amido group or an ether group in the molecule and thermally unstable, and when they contact with an acidic substance at high temperature, decomposition reaction takes place to form acetaldehyde, ethanol and high boiling products. Further, unsaturated ethers, N-alkenylcarboxylic acid amides and cyclic amines as the objective products have a high reactivity and are liable to cause polymerization, formation of high boiling substances, etc. Such reaction would lead not only to a decrease in the reaction yield but also to an increase in the costs for the recovery and purification of the raw materials and the products.
Therefore, in order to put the gas-phase dehydration reaction into an industrial practice, it is important to heat the raw material gas vaporized in the vaporator up to a predetermined temperature without deteriorating it inside the heater (gas preheater) and/or at the inlet side of the catalyst layer in the reactor, and immediately feed it into the catalyst layer, and immediately cool the reaction gas which came out of the catalyst layer.
When the gas-phase dehydration reaction is carried out using a fixed bed reactor, the catalyst needs to be supported by some supporting material for fixing the position of the catalyst. In this occasion, it is important to prevent deterioration of the raw materials and the products on the catalyst supporting material.
However, the above-mentioned official bulletins only describe catalysts capable of converting the raw materials into the objective products selectively at a high space time yield, and they do not describe a process of preheating the raw material gas, a process of cooling the reaction gas and a process of supporting the catalyst at all.
On the other hand, Japanese Patent Publication No. 40792/72 discloses a reaction process comprising gas-phase intermolecular dehydration of N-(2-hydroxyethyl)-2-pyrrolidone to prepare N-vinyl-2-pyrrolidone. This prior art publication discloses loading Raschig rings (outside diameter 5 mm, length 5 mm, porcelain) as an evaporation preheating band of the raw material into the upper part of a vertical stainless steel reaction tube, loading an oxide of zirconium or thorium as a catalyst into a reaction band of the lower part thereof and carrying out gas-phase dehydration reaction. However, it does not disclose decomposition of the raw material at the evaporation preheating band and the composition of the porcelain Raschig ring. Further, Raschig rings for general purposes have problems, for example, that since they have an outside diameter of as large as 4 mm or more and a void ratio of as large as 0.6 to 0.9, they are liable to cause thermal denaturation of the raw material and cannot be used as a supporting material of catalysts having a small particle size.
PROBLEMS TO BE SOLVED BY THE INVENTION
The object of the invention lies in providing, in a gas-phase dehydration reaction process of a hydroxyl group-containing compound using a solid oxide catalyst containing an alkali metal element, the improvement which makes it possible to inhibit decomposition of the raw materials and the objective products thereby to carry out the gas-phase dehydration reaction efficiently.
MEANS FOR SOLVING THE PROBLEMS
The present inventors have intensively studied in order to provide a gas-phase dehydration reaction process capable of solving the above problems, and as a result, they have found that the stability of the raw materials used in the reaction is strikingly influenced not only by the catalyst itself, but by the composition of a loading material for preheating of the raw material gas as well as the composition of a supporting material for fixation of the position of the catalyst.
Thus, the invention provides, a process of gas-phase dehydration reaction comprising contacting a raw material gas with a solid oxide catalyst containing an alkali metal element, wherein a sintered oxide comprising an alkali metal element and silica and/or alumina is used as a loading material for preheating of the raw material gas and/or as a supporting material for fixation of the position of the catalyst.
The invention is particularly useful when the solid oxide catalyst is a solid oxide containing an alkali metal element and silicon.
In the invention, the sintered oxide is preferably a sintered oxide obtained by adding a compound containing an alkali metal element to a sintered oxide comprising an alkali metal element and silica and/or alumina, followed by calcining the mixture.
The invention is useful when the raw material of the gas-phase dehydration reaction is a hydroxyethyl compound represented by the following general formula (I)
Z
1
—CH(R
1
)—CH(R
2
)—OH  (I)
[wherein Z
1
is an amino group, a monoalkylamino group having 1 to 6 carbon atoms, a mercapto group, an alkoxy group having 1 to 10 carbon atoms, an alkylcarboxylic acid amido group wherein the alkylcarboxylic acid moiety has 1 to 6 carbon atoms and the group binding to the N atom of the amido moiety is a hydrogen atom or a methyl group, or a cyclic carboxylic acid amido group including an alkylene group having 3 to 5 carbon atoms and R
1
and R
2
are each, independently, a hydrogen atom, a methyl group or an ethyl group].
Further, the invention is particularly useful when the gas-phase dehydration reaction is a reaction comprising gas-phase inter-molecular dehydration of a hydroxyethyl compound represented by the following general formula (II)
Z
2
—CH
2
—CH
2
—OH  (II)
[wherein Z
2
is an alkoxy group having 1 to 10 carbon atoms, an alkylcarboxylic acid amido group wherein the alkylcarboxylic acid moiety has 1 to 6 carbon atoms and the group binding to the N atom of the amido moiety is a hydrogen atom or a methyl group, or a cyclic carboxylic acid amido group including an alkylene group having 3 to 5 carbon atoms]
to convert it to a vinyl compound represented by the following general formula (III)
Z
2
—CH═CH
2
  (III)
[wherein Z
2
is as defined in the formula (II)].
Further, the invention is particularly useful when the gas-phase dehydration reaction is a reaction comprising gas-phase inter-molecular dehydration of a hydroxyethyl compound

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