Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Reexamination Certificate
2000-10-30
2001-07-24
Trinh, Ba K. (Department: 1625)
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
C549S229000
Reexamination Certificate
active
06265592
ABSTRACT:
The present invention relates to an improved process for continuous production of l,3-dioxolan-2-ones such as ethylene carbonate or propylene carbonate from the corresponding oxiranes and carbon dioxide in the liquid phase in the presence of a catalyst.
In Ind. Eng. Chem. 50 (1958), 767-770, there is described a process for producing ethylene carbonate by reacting ethylene oxide with carbon dioxide in a tubular reactor whose top end is fed with ethylene oxide and catalyst solution at 155° C. and whose bottom end (at 195° C.) is fed with the carbon dioxide and discharges the ethylene carbonate produced. An after-reaction is carried out in a downstream, separate tank. The pressure in the reactor is 1500 psig (103 bar). It can be operated continuously. The carbon dioxide is offered in excess. Given the temperature gradient of 40° C. in the reactor, backmixing conditions are not present. A conversion of just below 99% is reached in the after-reactor, but a number of by-products are formed; the ethylene carbonate yield is thus about 93%.
It is an object of the present invention to provide an improved process which provides a particularly high conversion of the oxirane, in particular an oxirane conversion of not less than 99.9%, coupled with high selectivity and high space-time yield. Also, the product shall be so pure that by-products appear only in the ppm range. The desired high conversion is achieved in particular when a two-part reactor with countercurrent operation between oxirane and carbon dioxide is used for the purposes of the present invention.
We have found that this object is achieved by a process for continuous production of 1,3-dioxolan-2-ones of the general formula I
where R
1
is hydrogen or an organic radical having up to 40 carbon atoms and R
2
and R
3
are each hydrogen or C
1
-C
4
-alkyl, in which case R
2
and R
3
may also combine to form a five- or six-membered ring,
by reaction of an oxirane of the general formula II
with carbon dioxide in the liquid phase in the presence of a catalyst, which comprises conducting the reaction in a two-part reactor in whose first part the reaction is taken with backmixing to a conversion of not less than 80%, especially not less than 90%, of the oxirane II and in whose second part the reaction is completed under nonbackmixing conditions, and passing the carbon dioxide in countercurrent to the oxirane II in the entire reactor.
Both parts of the reactor may each consist of a single stage or of a plurality of consecutive or parallel stages. The entire reactor may be constructed from one or more pieces of apparatus. Advantageously, the fresh oxirane II and the fresh catalyst are fed into the first part of the reactor and the fresh carbon dioxide is fed into the second part of the reactor.
It is important for the success of the process to ensure adequate backmixing within the first part of the reactor. The specific design of the first part of the reactor promotes backmixing or makes it possible in the first place, for example through the choice of a loop reactor. Furthermore, it is also possible and advantageous to use external backmixing systems, for example by pumping a portion of the product stream which leaves the first or second part of the reactor back into the first part.
The reaction in the first part of the reactor is advantageously carried out isothermally by removing the heat of reaction. Since the conversion of the oxiranes II to the 1,3-dioxolan-2-ones I is usually highly exothermic, effective heat removal is needed. In general, the heat of reaction is removed by an internal or external heat exchanger having a volume flow rate of from 30 to 500 times the throughput through the reactor. In general, the temperature fluctuations in the first part of the reactor do not exceed ±50° C., especially ±3° C.
The pressure under which the reactor is operated is normally within the range from 2 to 50 bar, especially within the range from 5 to 40 bar, in particular within the range from 10 to 30 bar, in both parts of the reactor. These relatively low pressures mean that the process of the invention is usually uncomplicated in terms of equipment requirements.
A further significant factor for the process of the invention to be economically successful is the maintenance of a certain temperature range within both parts of the reactor. The temperature should not exceed 150° C. in any part of the reactor. Preferred temperature ranges extend from 70 to 150° C., especially from 90 to 145° C., in particular from 100 to 140° C. The second part of the reactor may have a temperature which is up to 40° C., especially up to 25° C., in particular up to 10° C., above the temperature in the first part of the reactor.
A high conversion of not less than 80%, preferably not less than 90%, especially not less than 95%, in particular not less than 98%, in the first part of the reactor and the good backmixing in this part of the reactor generally ensure that oxirane concentrations do not exceed 20% by weight, preferably 10% by weight, especially 5% by weight, in particular 2% by weight, anywhere in the reactor. This not only has safety relevance (ethylene oxide!) but also has a significant bearing on the selectivity. It was found that an elevated oxirane concentration leads to increased by-product formation.
The first part of the reactor is preferably isothermal owing to a high adiabatic temperature increase. The heat of reaction can be removed by an internal or external heat exchanger, depending on the design of the reactor. The good backmixing in the reactor prevents the appearance of undesirable temperature spikes. Also, to support the reaction, it is advantageous for the gaseous carbon dioxide, which the invention has passing countercurrent to the oxirane II, to be finely dispersed in every part of the reactor in order that high mass transfer areas may be obtained. Normally, the carbon dioxide is present in a saturated state in the liquid phase. This ensures that sufficient carbon dioxide is available in the entire reactor. According to the present invention, a particularly advantageous way of carrying out the countercurrent procedure is for unconverted oxirane to be stripped from the second reactor part into the first part in which the main conversion takes place. This technique reduces the oxirane exit concentration in the alkylene carbonate produced and consequently promotes high conversion.
The reactor is generally built with the first, backmixed part as the upper part. The mixing in this part of the reactor is preferably obtained with a jet of liquid. To augment the mixing and gas absorption, the reactor may be fitted with internals, for example with a draft tube or a momentum transfer tube. The dispersing of the gas phase in this part of the reactor can take place via the jet of liquid or a finely divided supply of gas at the bottom. The catalyst and the fresh oxirane can be introduced at any desired point of this part of the reactor. Preference is given to introducing the oxirane in the jet of liquid, so that it comes to be present in the liquid in a state of uniform disbursement.
The catalyst passes with the liquid effluent from the first step into the second part of the reactor. The liquid effluent can leave the first part at any desired point, but preferably at the bottom. Inerts (noble gases, nitrogen) and unconverted carbon dioxide can be removed from the reaction mixture at the top of the reactor. A bleed stream of the off-gas can be returned to the second part of the reactor together with the fresh gas.
The second part of the reactor can be embodied as a multistage countercurrent gas and liquid contacting apparatus (operated with cooling or adiabatically). Preference is given to its embodiment as a bubble column battery, but other designs are also possible, for example a stirred tank battery. Division of this part of the reactor into a plurality of stages can be provided by internal fitments such as foraminous sheets, bubble cap trays or specific mixing elements or by using a plurality of pieces of apparatus. The
Benfer Regina
Bieg Walter
Birnbach Stefan
Dockner Toni
Mohr Jurgen
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Trinh Ba K.
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