Organic compounds -- part of the class 532-570 series – Organic compounds – Halogen containing
Reexamination Certificate
1999-07-29
2001-02-20
Siegel, Alan (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Halogen containing
C570S224000, C570S244000, C570S245000
Reexamination Certificate
active
06191329
ABSTRACT:
FIELD OF THE INVENTION
The invention is generally directed to saving energy, particularly during oxychlorination processes.
BACKGROUND OF THE INVENTION
It is known that the reaction mixture at the outlet of an oxychlorination reactor mainly comprises the EDC (1,2-dichloroethane), water gas and recycling gas (carbon dioxide, nitrogen, argon) and has a temperature of 220° C. at a pressure of approx. 4.2 bar. Because friction occurs in the catalyst, the stream leaving the reactor is passed through a micron filter to catch the dust discharged by the catalyst and/or through a cyclone and is then fed into the quenching column. The column is used for washing the hydrogen chloride out of the reactor discharge stream and for neutralizing it and for promoting the alkaline decomposition of chlorinated by-products, such as chloral.
Sensible heat is withdrawn from the reaction mixture in the quenching column. The temperature at the head of the column is 102′ C. The reaction products., water and EDC, are condensed in the raw EDC condenser downstream of the column before being individually separated and removed from the recycling gas in an EDC settling vessel. The water obtained and the caustic soda (which serves to neutralize and decompose by-products) are fed back to the quenching column as reflux at a temperature of approx. 400C. A part-stream, approximately equal in volume to that of the reaction water, is drawn off at the bottom of the quenching column and fed to a waste water treatment stage.
A sufficient quantity of liquid must be constantly supplied to the quenching column to ensure that it functions correctly. The column discharge can be split into two constituents: one being the reaction water which enters the column with the reactor discharge stream prior to being condensed in the raw-EDC condenser; the other being the water from the column, which is evaporated using some of the sensible heat from the reactor discharge stream before being condensed in the raw-EDC condenser.
This last constituent is thus in constant circulation as a result of the continuous evaporation and subsequent condensation processes- most of the sensible heat at the reactor outlet is dissipated by cooling water.
SUMMARY OF THE INVENTION
The invention is applied at this stage. Its aim is to recover as much heat as possible to enable as much sensible heat from the oxychlorination reactor as possible to be used for other purposes. A process of the type described above meets this requirement by cooling the gas mixture leaving the oxychlorination reactor before it enters the quenching column. The heat produced is then used to preheat the ethylene recycled gas feed stream.
The invention permits the creation of quench reflux and the cooling of the reactor discharge stream to be carried out separately. Consequently, most of the sensible heat at the outlet of the oxychlorination reactor can be used for other purposes, One other particular advantage of the invention is that the condensation system at the quenching column head can be designed for lower throughputs which ultimately results in reduction in costs.
To enable the heat potential from the gas mixture leaving the oxychlorination reactor to be fully utilized, one embodiment of the invention provides for the gas mixture to be cooled to a temperature just above its dew point, the latter being influenced by the reaction water content.
This ensures that most of the reaction water formed in the oxychlorination reactor is fed into the quenching column as steam and can then be drawn off at the head of the quenching column in the form of steam together with the EDC. It is then condensed and separated in the settling vessel so that it can be used as the aqueous quench reflux required. If this were not the case and the dew point were not reached, some of the reaction water would trickle directly into the bottom of the quenching column in liquid form. This would then lead to increased caustic soda consumption to maintain the required pH level in the bottom of the quenching column.
If the gas mixture can be cooled using a single-pass heat exchanger with co-current flow, the outlet temperature of the gas mixture should be brought so close to the dew point that a temperature difference of only 5K remains. Practical experience has shown this to be the acceptable limit value for ensuring a stable process operation.
The present invention is certainly not limited for use exclusively with outlet temperatures above the dew point. For example, an alteration to the reaction flow in the oxychlorination reactor can lead to reduced caustic soda requirements, which could in turn cause a part-stream of the reaction water, which has liquefied due to the dew point not being reached, to trickle directly into the quenching water vessel.
Further embodiments of the process according to the invention can be seen in the dependent claims.
REFERENCES:
patent: 3987119 (1976-10-01), Kurtz et al.
patent: 4042639 (1977-08-01), Gorden et al.
Krupp Uhde GmbH
Rosenman & Colin LLP
Siegel Alan
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