Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-09-26
2003-06-17
Barts, Samuel (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S872000
Reexamination Certificate
active
06580008
ABSTRACT:
The present invention relates to a process for producing an alkylene glycol by reacting an alkylene oxide with water in the presence of a catalytic composition.
BACKGROUND OF THE INVENTION
Alkylene glycols, in particular monoalkylene glycols, are of established commercial interest. For example, monoalkylene glycols are being used in anti-freeze compositions, as solvents and as base materials in the production of polyalkylene terephtalates e.g. for fibres and bottles.
The production of alkylene glycols by liquid phase hydrolysis of alkylene oxide is known. The hydrolysis is performed without a catalyst by adding a large excess of water, e.g. 20 to 25 moles of water per mole of alkylene oxide, or it is performed with a smaller excess of water in a catalytic system. The reaction is considered to be a nucleophilic substitution reaction, whereby opening of the alkylene oxide ring occurs, water acting as the nucleophile. Because the primarily formed monoalkylene glycol may also act as a nucleophile, as a rule a mixture of monoalkylene glycol, dialkylene glycol and higher alkylene glycols is formed. In order to increase the selectivity to monoalkylene glycol, it is necessary to suppress the secondary reaction between the primary product and the alkylene oxide, which competes with the hydrolysis of the alkylene oxide.
One effective means for suppressing the secondary reaction is to increase the relative amount of water present in the reaction mixture. Although this measure improves the selectivity towards the production of the monoalkylene glycol, it creates a problem in that large amounts of water have to be removed for recovering the product.
Considerable efforts have been made to find an alternative for increasing the reaction selectivity without having to use a large excess of water. Usually these efforts have focused on the selection of more active hydrolysis catalysts and various catalysts have been disclosed.
Both acid and alkaline hydrolysis catalysts have been investigated, whereby it would appear that the use of acid catalysts enhances the reaction rate without significantly affecting the selectivity, whereas by using alkaline catalysts generally lower selectivities with respect to the monoalkylene glycol are obtained.
Certain anions, e.g. bicarbonate (hydrogen carbonate), bisulphite (hydrogen sulphite), formate and molybdate, are known to exhibit good catalytic activity in terms of alkylene oxide conversion and selectivity towards monoalkylene glycol. However when the salts of these anions are used as the catalyst in a homogeneous system, work-up of the reaction product by distillation will pose a problem because the salts are poorly soluble in the glycol and tend to make it semi-solid.
High conversions, good selectivity and a low water/alkylene oxide ratio can be obtained with the process, disclosed in EP-A 0 156 449 and EP-A 0 160 330 (both of Union Carbide). According to these documents the hydrolysis of alkylene oxides is carried out in the presence of a selectivity-enhancing metalate anion-containing material, preferably a solid having electropositive complexing sites having affinity for the metalate anions. The said solid is preferably an anion exchange resin, in particular a styrene-divinyl benzene copolymer. The electropositive complexing sites are in particular quaternary ammonium, protonated tertiary amine or quaternary phosphonium. The metalate anions are specified as molybdate, tungstate, metavanadate, hydrogen pyrovanadate and pyrovanadate anions. A complication of this process is that the alkylene glycol-containing product stream also comprises a substantial amount of metalate anions, displaced from the electropositive complexing sites of the solid metalate anion containing material. In order to reduce the amount of metalate anions in the alkylene glycol product stream, this stream is contacted with a solid having electropositive complexing sites associated with anions which are replaceable by the said metalate anions.
In U.S. Pat. No. 5,064,804 and in EP-A 0 529 726 (both of Union Carbide) there are disclosed solid catalysts comprising a metalate complexed with a hydrotalcite-type clay. In both specifications it is mentioned that the subject process can be carried out either as a batch or a continuous process with recycle of unconsumed reactants if required. Recycle of reactor output is not mentioned.
In RU-C 2 002 726 (Shvets et al.) there is disclosed a process for the production of alkylene glycols by catalytic hydration of alkylene oxides, whereby alkylene glycol is added to the starting mixture. No recycle of reactor output is mentioned.
In WO 95/20559 (Shell) there is disclosed a process for the preparation of alkylene glycols wherein an alkylene oxide is reacted with water in the presence of a catalyst composition comprising a solid material having one or more electropositive sites, in particular a strongly basic anion exchange resin of the quaternary ammonium type, which electropositive sites are coordinated with one or more anions other than metalate or halogen anions, e.g. bicarbonate, bisulphite and carboxylate—with the proviso that when the solid material is an anionic exchange resin of the quaternary ammonium type and the anion is bicarbonate the process is performed in the substantial absence of carbon dioxide.
A drawback shared by the conventional anionic exchange resins is their limited tolerance to heat and their susceptibility to swelling.
For example, in WO 99/31033 (Dow) it is described how processes comprising anion exchange resins, e.g. as described in WO 95/20559, suffer from undesirable swelling, particularly at temperatures greater than 95° C. This document further describes a method of minimising such swelling comprising adding to the reaction mixture a combination of additives comprising carbon dioxide and a base in an amount sufficient to maintain a pH between 5.0 and 9.0.
Further, WO 99/31034 (Dow) proposes a method of minimising the swelling of an anion exchange resin by using an adiabatic reactor. In one embodiment two or more adiabatic reactors are operated in series, each reactor containing a separate batch of catalyst.
Catalyst swelling is problematic as it can result in flow of reactants through the reactor being slowed or blocked. Therefore, it would be advantageous if there was a means by which swelling of a catalyst based on an anion exchange resin employed in the conversion of alkylene oxides to alkylene glycols could be minimised and/or the life-time of that catalyst prolonged.
SUMMARY OF THE INVENTION
The present invention provides a process for the production of an alkylene glycol comprising:
a) introducing a feed mixture comprising an alkylene oxide and water to at least one inlet of a reactor containing a fixed bed of a solid catalyst based on an anion exchange resin, and
b) removing a reactor output mixture comprising an alkylene glycol and unreacted feed mixture from at least one outlet of the reactor,
c) recycling at least a part of the reactor output mixture to at least one inlet of the same reactor.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that by recycling reactor output from a reactor containing a catalyst based on an anion exchange resin back through the same reactor, swelling of the catalyst may be reduced.
In the present invention, a part of the reactor output is recycled to at least one inlet of the same reactor. The part of the reactor output to be recycled may be conveniently separated from the part not to be recycled after the reactor output has left the reactor; or alternatively the part of the reactor output to be recycled may be conveniently removed from the reactor via a different outlet of the reactor than that from which the part of the reactor output not to be recycled is removed.
Accordingly, in one preferred embodiment of the present invention, an outlet of the reactor for the part of the reactor output mixture which is to be recycled is positioned upstream of an outlet of the reactor for the part of the reactor output mixture which is not to be recycled.
In a further prefe
Derks Willem
Godfried Andre Van Kruchten Eugene Marie
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