Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-12-19
2004-04-20
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S529000
Reexamination Certificate
active
06723861
ABSTRACT:
The present invention relates to a process for manufacturing oxirane by reaction between an olefin and a peroxide compound in the presence of a catalyst and a solvent. In particular, the invention relates to the manufacture of propylene oxide (or epichlorohydrin) by epoxidation of propylene (or allyl chloride) using hydrogen peroxide in the presence of a catalyst containing TS-1.
It is known practice to manufacture propylene oxide by reaction between propylene and a peroxide compound in the presence of TS-1. For example, in U.S. Pat. No. 5,849,937, such a process is performed in several reactors arranged in series.
The Applicant has found that this process has the drawback of resulting in the formation of by-products, for example when an aqueous hydrogen peroxide solution is used as peroxide compound and methanol is used as solvent in this known process. Specifically, when propylene oxide is manufactured under these conditions, by-products are formed by reaction between the propylene oxide and water or methanol, and in particular propylene glycol and methoxypropanols of formulae CH
3
—CHOH—CH
2
—OCH
3
and CH
3
—CH(OCH
3
)—CH
2
OH. When epichlorohydrin is manufactured, by-products are formed by reaction between the epichlorohydrin and water or methanol, and in particular 1-chloropropanediol and chloromethoxypropanols of formulae ClCH
2
—CHOH—CH
2
—OCH
3
and Cl—CH
2
—CH(OCH
3
)—CH
2
OH. The formation of by-products reduces the selectivity of the process and consequently its yield.
The present invention is directed towards overcoming this drawback by providing a novel process of high selectivity, while at the same time maintaining high activity (or a high reaction rate).
To this end, the invention relates to a process for manufacturing oxirane by reacting an olefin with a peroxide compound in the presence of a catalyst and a solvent in at least two reactors arranged in series, each of which contains a portion of the catalyst, according to which a first portion of the olefin, the solvent and the peroxide compound are introduced into a first reactor, an epoxidation of the first portion of the olefin is carried out therein in order to form a first portion of the oxirane, a medium comprising the first portion of oxirane formed, the solvent, the unconverted olefin and, where appropriate, the unconsumed peroxide compound is removed from this reactor and introduced into a distillation column, the majority of the oxirane formed and of the unconverted olefin is collected at the top of the column, the medium depleted in oxirane and containing, where appropriate, the unconsumed peroxide compound is collected at the bottom of the column, the medium depleted in oxirane and another portion of the olefin and optionally another portion of the peroxide compound are introduced into a subsequent reactor, an epoxidation of the other portion of the olefin is carried out therein in order to form another portion of the oxirane, and the other portion of the oxirane thus formed is collected.
One of the essential characteristics of the present invention lies in the intermediate distillation carried out between the two epoxidation reactions. Specifically, this makes it possible to minimize the formation of by-products.
The distillation serves to remove the oxirane as quickly as possible as it is formed in the reaction medium in order to prevent it from being in contact with the other constituents of the reaction medium and to prevent by-products from being thus formed. This separation is carried out in a distillation column which is separate and distinct from the epoxidation reactor. Since the catalyst does not leave the epoxidation reactor, the distillation is thus carried out in the absence of the epoxidation catalyst in order to prevent contact between the oxirane formed and the epoxidation catalyst, since the latter promotes the formation of by-products.
The distillation makes it possible to separate the majority of the oxirane formed from the epoxidation reaction medium. This majority is generally greater than or equal to 80% of the amount of oxirane formed in the first reactor. It is usually greater than or equal to 90%. Usually, it is less than or equal to 99%. In particular, it is less than or equal to 95%.
The conditions under which the distillation is carried out depends on the nature of the oxirane (and in particular its boiling point), its concentration in the medium introduced into the distillation column, the nature of the other constituents of the medium (the unconverted olefin and the solvent), their boiling point and the desired distillation yield.
The distillation is generally carried out at a temperature of greater than or equal to 10° C., preferably greater than or equal to 35° C., values of greater than or equal to 45° C. being recommended. The temperature is usually less than or equal to 125° C., most commonly less than or equal to 100° C., values of less than or equal to 90° C. being preferred.
The distillation is commonly carried out at a pressure of greater than or equal to 0.1 bar, preferably greater than or equal to 0.5 bar, values of greater than or equal to 1 bar being the most common. The pressure is generally less than or equal to 10 bar, in particular less than or equal to 5 bar, values of less than or equal to 2 bar being most particularly recommended. In the present description, any reference to the distillation pressure corresponds to the absolute pressure measured at the top of the distillation column.
The distillation column which may be used in the process according to the invention is known per se. It is possible to use, for example, a column with conventional plates or a column with plates of “dual-flow” type or alternatively a column with loose or structured packing.
The number of theoretical plates in the distillation column is generally greater than or equal to 20 and more especially greater than or equal to 30. A number of less than or equal to 80 gives good results. A number of less than or equal to 60 is recommended.
The degree of molar reflux (which corresponds to the molar flow rate of liquid sent to the top of the column relative to the entire distillate—vapour plus liquid—taken from the top of the column) in the distillation column is usually greater than or equal to 0.5 and preferably greater than or equal to 0.8. This degree is commonly less than or equal to 5 and usually less than or equal to 2.5.
In the process according to the invention, a plant comprising at least two epoxidation reactors arranged in series and connected together is used. Each reactor is fed with olefin. The peroxide compound and the solvent are introduced into the first reactor. Fresh peroxide compound may also be introduced into one or more subsequent reactors. Each reactor contains a portion of the catalyst which does not leave this reactor. When the catalyst is present in the form of a fixed bed, it is generally not necessary to take precautions to keep the catalyst in the reactor. Alternatively, the catalyst may be present in the form of particles, at least some of which are in a form fluidized by a liquid stream or by mechanical stirring or by a gas. When a liquid stream is used, it is recommended to include a fall-out zone above the fluid bed in order to stop the catalyst particles which are in motion and/or to include a filter at the reactor outlet.
Needless to say, the plant may comprise more than two reactors connected in series. In this case, the first reactor of the series is fed with olefin, the peroxide compound, the solvent (and optionally a fraction of the medium obtained at the bottom of the distillation column corresponding to this reactor) and each subsequent reactor is fed with the olefin, the remainder of the medium obtained from the preceding reactor of the series and optionally fresh peroxide compound. Preferably, 3 reactors in series are used.
In the process according to the invention, reactors of identical size are preferably used. This makes it possible to interchange the function of the reactors when the deactivated catalyst in one reactor is replaced wit
Solvay ( Societe Anonyme)
Trinh Ba K.
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