Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2002-06-26
2003-04-01
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
active
06541648
ABSTRACT:
The present invention relates to an integrated process for the preparation in continuous of epoxides by the direct oxidation of an olefin with hydrogen peroxide.
More specifically, the present invention relates to an integrated process for the preparation in continuous of propylene oxide consisting in the production of an alcoholic or hydro-alcoholic solution of hydrogen peroxide by the reaction between hydrogen and oxygen in the presence of a bimetallic catalyst based on palladium or platinum as active components, feeding said solution to an epoxidation process of propylene in the presence of an epoxidation catalyst, and feeding the recycled alcoholic solvent leaving the epoxidation plant, suitably pretreated, to the hydrogen peroxide production plant.
Epoxides, or olefin oxides, are intermediates which can be used for the preparation of a wide variety of compounds. For example, epoxides can be used for the production of glycols, condensation polymers such as polyesters or for the preparation of intermediates used in the synthesis of polyurethane foams, elastomers, seals and similar products.
Current technologies adopted on an industrial scale for the production of propylene oxide (PO) are based on processes via chlorohydrin and processes via indirect oxidation with hydroperoxides as oxygen source.
In particular, the commercialized chlorohydrin process involves the synthesis of propylene chlorohydrin (PCH) and subsequent dehydrohalogenation of PCH to propylene oxide (PO).
This process however has the following disadvantages:
the production of high quantities of aqueous effluents (40-60 kg/kg of PO) containing sodium or calcium chlorides;
the coproduction of chlorinated organic products which, depending on their end-use, must undergo suitable treatment.
Processes via oxidation preferably use ter butyl hydroperoxide and ethylbenzene hydroperoxide as hydroperoxides.
These processes cause the formation of a higher quantity of co-products of commercial interest with respect to PO.
For example, the process via ter butyl hydroperoxide co-produces 2.5-3.5 Kg of ter butyl alcohol per Kg of PO, whereas that via ethylbenzene hydroperoxide co-produces 2.2-2.5 Kg of styrene per Kg of PO.
The presence of these co-products can be of little advantage if the request for PO and the respective coproducts is not suitably balanced. For example, when the demand for styrene or MTBE, obtained from ter butyl alcohol, is high, the economics of this process are competitive with those of the process via chlorohydrin, otherwise these processes are not economic.
Other synthetic techniques for the indirect oxidation of propylene involve the use of hydrogen peroxide and essentially consist in:
1) synthesis of hydrogen peroxide; and
2) its use in the epoxidation process of propylene to propylene oxide.
Aqueous solutions of H
2
O
2
are typically obtained industrially by means of a complex two-step process. In this process a solution of anthraquinone, such as butylanthraquinone or ethylanthraquinone, in an organic medium immiscible with water, is first hydrogenated and then oxidized with air to produce H
2
O
2
which is subsequently extracted in aqueous phase. This process is onerous due to the high costs deriving from the investment necessary for setting up the complex production unit, the necessity of separating and disposing of the by-products generated during the oxidation phase, and purifying and reintegrating the anthraquinone solution before its re-use.
A second method for the production of hydrogen peroxide comprises the use of secondary alcohols such as isopropanol and methylbenzylalcohol (U.S. Pat. No. 2,871,102, EP-378,388) or high-boiling secondary alcohols such as diaryl methanol (U.S. Pat. No. 4,303,632) with oxygen.
These known processes, however, substantially suffer from disadvantages deriving from the necessity of operating at high reaction temperatures (generally ranging from 100 to 180° C.), the partial oxidation of the ketone which is formed as main co-product, the necessity of using a hydrogen peroxide stabilizer (orthophosphoric acid or sodium pyrophosphate).
Furthermore, these processes are complicated by the necessity of separating and recovering the ketone and by-products from the reaction mixture before using the hydrogen peroxide solution in a subsequent epoxidation process.
Another method for the production of hydrogen peroxide, which seems attractive from a technical and economic point of view, is based on the direct synthesis of hydrogen peroxide from H
2
and O
2
.
These processes generally use a catalytic system consisting of a noble metal, particularly metals of the platinum group or their mixtures, in the form of salts or as supported metals, by reacting the two gases in a solvent consisting of an aqueous medium or an aqueous-organic medium.
The industrial embodiment of these processes however has proved to be difficult for the following reasons:
A) the use of mixtures of H
2
and O
2
in concentrations falling within the explosivity range, as the mixture becomes explosive when the concentration of H
2
exceeds a value which, in relation to the pressure and concentration of O
2
, varies from 4.5 to 6% by volume;
B) even when operating outside the explosivity range of H
2
-O
2
mixtures, the use of high concentrations of O
2
is risky to handle and has a limited compatibility with the presence of flammable organic solvent mediums;
C) the use in the reaction medium of high concentrations of promoters, for example acid promoters, halogenated products and/or other additives, makes the catalytic system or H
2
O
2
solution unstable. This makes it necessary to add stabilizers, with onerous purification operations of the H
2
O
2
solution before its use;
D) low productivity and selectivity of the reaction and the production of H
2
O
2
solutions which are too dilute for economic industrial exploitation;
E) poor stability of the catalytic system under the reaction conditions.
Patent application EP-812836, for example, describes a process for the preparation of propylene oxide which consists in reacting hydrogen and oxygen in the presence of a catalytic system based on supported palladium, in a hydro-alcoholic medium and using the hydro-alcoholic mixture of hydrogen peroxide thus obtained in the epoxidation process.
The illustrative examples of this document describe the production of hydro-alcoholic solutions containing H
2
O
2
in concentrations ranging from 0.15 to 0.39% by weight.
Using these solutions in the subsequent epoxidation reaction, after 1 hour, hydrogen peroxide conversions equal to 99% and 65% respectively, are obtained, with a selectivity to propylene oxide ranging from 70% to 95%, i.e. with a maximum yield to PO of 70%.
This process does not seem to be of industrial interest for the following reasons:
A) The use, in the reaction medium for the production of hydrogen peroxide, of high concentrations of promoters, for example acid promoters, halogenated products and/or other additives, makes it necessary to add considerable quantities of neutralizers before its use in the subsequent epoxidation process;
B) Overall low process concentration, productivity and selectivity. This requires the use of high reaction volumes in both steps of the integrated process;
C) Production of a high stream of waste products to be disposed of in the epoxidation process;
D) The use of diluted hydro-alcoholic solutions of hydrogen peroxide implies the production of a stream of alcoholic distillate whose entity makes the process rather uneconomic.
The Applicant has now found that by using a well defined group of metallic catalysts and operating conditions in the initial reaction between hydrogen and oxygen, and by suitably treating the recycled alcoholic solvent leaving the epoxidation plant before being fed to the hydrogen peroxide production plant, an overall high process efficiency is obtained in terms of productivity and selectivity.
In particular, on operating according to the process of the present invention, the following advantages are obtained:
reduction in waste products in the ep
D'Aloisio Rino
De Alberti Giordano
Forlin Anna
Paparatto Giuseppe
Tegon Paolo
Polimeri Europa S.r.l.
Trinh Ba K.
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