Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
2000-07-31
2002-07-09
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
Reexamination Certificate
active
06417414
ABSTRACT:
This application is a 371 of PCT/EP98/07444 filed Nov. 19, 1998.
DESCRIPTION
“Oxychlorination” is understood as meaning the reaction of an alkene—in this case ethene—with hydrogen chloride and oxygen or an oxygen-containing gas, such as air, the formation of a saturated chlorinated alkane—in this case 1,2-dichloroethane, referred to below as “EDC”. The reaction takes place according to the equation
C
2
H
4
+2HCl+½O
2
<=>Cl—CH
2
—CH
2
—Cl+H
2
O.
The byproduct of the reaction, water, can thus form corrosive hydrochloric acid with the unconverted starting material hydrogen chloride, so that correspondingly resistant—and hence expensive—materials must be used for the apparatuses.
In an embodiment of this process which is frequently carried out on an industrial scale, a fluidized bed serves as the catalyst, the catalyst essentially comprising copper chloride on an alumina carrier.
In the usual industrial processes, the fluidized catalyst is deposited in the upper part of the oxychlorination reactor by a plurality of cyclones connected in series and thus retained for the most part in the reactor. However, a small proportion passes over with the exit gas of the reaction and thus enters the EDC working-up, where it has to be separated off.
DE-A-41 32 030 discloses a process for removing abraded catalyst material which is obtained in the reaction zone in the preparation of EDC by the oxychlorination process and is removed from the reaction zone with the crude EDC gas stream, wherein the abraded catalyst material removed is separated from the crude EDC gas stream in a purification zone operated under dry conditions. In preferred embodiments of this process, the abraded catalyst material is separated off on a dust separator or in an electric filter as a purification zone, the dust separator is equipped with bag filters which are cleaned with compressed circulating gas, the abraded catalyst material deposited in the purification zone is freed from adsorbed reaction products in a downstream desorption zone, the desorption zone is operated at a temperature from 50 to 350° C., in particular from 150 to 180° C., by gassing or at reduced pressure, air, nitrogen or circulating gas is used for the gassing, and the abraded catalyst material is treated for from 0.5 to 5 hours, preferably from 1 to 2 hours, at an elevated temperature in the desorption zone. This process avoids the formation of a wastewater contaminated with heavy metal and inorganic sludge during the removal of water formed and of the washwater used in the working-up. However, the fine catalyst fraction separated off must be discarded and disposed of properly.
DE-A-195 46 068 relates to a process for reducing the catalyst consumption and contaminated catalyst wastes in the preparation of EDC by the oxychlorination process over a copper-containing fluidized-bed catalyst in a reaction zone, in which the abraded catalyst material is separated off from the crude EDC gas stream in a separation zone operated under dry conditions, wherein the abraded catalyst material is classified and specific particle fractions are recycled to the reaction zone. In preferred embodiments of this process, the abraded catalyst material is classified into a coarse fraction and a fine fraction, the coarse fraction corresponds to a particle size >5 &mgr;m and the fine fraction to a particle size <5 &mgr;m, the coarse fraction is recycled to the reaction zone, the fine fraction is aftertreated thermally at from 300 to 800° C., preferably from 600 to 800° C., the aftertreated exit gases are passed into an incineration furnace, the incineration furnace has a temperature above 900° C., preferably more than 1000° C., copper and/or aluminum are recovered from the fine fraction, the fine fraction is disposed of in a landfill in a controlled manner, and the dioxins and/or furans are removed from the abraded catalyst material. This process thus overcomes the disadvantages of the process according to DE-A-41 32 030, but at the cost of considerable cost of apparatuses and work for operating and maintaining them.
Common to both known processes is the fact that the separation of the discharged fine catalyst fractions is carried out in a zone separated from the reactor.
It has now been found that the discharge of the catalyst from the reactor itself can be avoided if the catalyst is virtually completely retained in the upper part of the reactor by means of superfine filtration.
The invention therefore relates to a process for the preparation of EDC by oxychlorination, ethene reacting with hydrogen chloride and oxygen or an oxygen-containing gas over a fluidized bed comprising a copper-containing catalyst, and the reaction gas emerging from the reactor being freed from catalyst in the reactor by a superfine filtration and said catalyst thus being retained in the reactor.
“Superfine filtration” is understood as meaning a process which retains the fine fraction of the oxychlorination catalyst. While the cyclones customary to date allowed a fine fraction below about 10 &mgr;m to enter the product stream, according to the invention, particles below about 1 &mgr;m are retained, i.e. virtually the entire catalyst.
Surprisingly, it was furthermore found that, according to the invention, the separation of a coarse catalyst fraction by means of the cyclones can be dispensed with. Thus, the coarse fraction and fine fraction of the catalyst are retained in one step by the superfine filtration. This has a number of advantages.
By dispensing with the cyclones, not only are the cost of apparatuses and the inconvenient maintenance of these poorly accessible components avoided but it is also possible significantly to reduce the installed height of the reactors. This makes the reactor considerably cheaper and of course also reduces the space required in the plant and hence the construction cost.
In comparison, the apparatuses—known per se—required for the superfine filtration can be easily installed in readily accessible form in the upper part of the reactor, for example in each case in separate connections which permit easy maintenance or rapid replacement of the filter apparatus with only short downtimes. Furthermore, such a design permits individual apparatuses to be put out of operation during ongoing operation.
For example, filter candle apparatuses made of material suitable for the EDC preparation are suitable, for example metals, alloys, glass or ceramic, preferably with filter candles of porous, sufficiently corrosion-resistant metal, such as sintered metal powders or woven wire fabrics or nonwoven wire fabrics of stainless steel or highly corrosion-resistant alloys, as commercially available under the names ®INCONEL (trademark of Inco Ltd.; nickel-chromium alloy), ®MONEL (trademark of Inco Ltd.; nickel-copper alloy), ®HASTELLOY (nickel alloy), and of porous ceramic material.
Furthermore, fabric filters of sufficiently heat-resistant, in particular fluorinated plastics, such as polytetrafluoroethylene, for example bag filters, can be used.
All superfine filters which retain particles of about 1 &mgr;m or above, i.e. preferably allow through only particles below about 0.8 &mgr;m, in particular below about 0.5 &mgr;m or even below 0.2 &mgr;m, are suitable.
The separation of the catalyst filter cake built up on filter materials is effected—as usual—advantageously by passing through gas countercurrently, preferably reaction gases (starting materials),. inert gases or circulated gas (recycled gas), for example in pulses, preferably at regular time intervals, or as soon as a predetermined thickness of the filter cake has built up and/or a corresponding pressure drop has occurred.
It is very surprising that, with this simple arrangement of the superfine filter in the reactor itself, discharge of the catalyst can be reliably avoided and hence the effort required to date involving the recovery and working up, which was always associated with losses, can be dispensed with. In addition, the abrasion caused by the catalyst, in the plant part up to disch
Ertl Horst
Kammerhofer Peter
Mielke Ingolf
Schwarzmaier Peter
Frommer & Lawrence & Haug LLP
Santucci Ronald R.
Siegel Alan
Vinnolit Monomer GmbH & Co. KG
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