Process for the preparation of ethylene glycol
The invention relates to a process for the preparation of ethylene glycol from ethylene, which comprises contacting the carbon dioxide stream resulting from hydrolysing ethylene carbonate, or the condensate stream resulting from condensing said carbon dioxide stream, or the waste water stream resulting from removing water from the ethylene glycol stream, such stream comprising water, 2-chloroethanol and ethylene glycol and additionally comprising 2-iodoethanol or 2-bromoethanol, with an alkali metal containing basic compound to form a mixture comprising water, 2-chloroethanol and ethylene glycol and additionally comprising alkali metal iodide or alkali metal bromide which mixture is dehydrated.
1. A process for the preparation of ethylene glycol from ethylene involves:
i) converting ethylene in the presence of oxygen, an epoxidation catalyst and a chloride moderator to ethylene oxide in an ethylene oxide reactor;
ii) absorbing the ethylene oxide in an aqueous absorbent and then stripping said absorbent to provide an aqueous ethylene oxide stream;
iii) converting the aqueous ethylene oxide stream in the presence of a catalyst and carbon dioxide in a carboxylation reactor to an ethylene carbonate stream;
iv) converting the ethylene carbonate stream in the presence of a catalyst in a hydrolysis reactor to an ethylene glycol stream and a carbon dioxide stream;
v) removing water from the ethylene glycol stream in a dehydration column to form a dehydrated ethylene glycol stream and a waste water stream;
vi) purifying the dehydrated ethylene glycol stream in a glycol distillation column to form a purified ethylene glycol product stream and a catalyst recycle stream;
wherein in step iii) and/or step iv) the catalyst is an iodide catalyst or a bromide catalyst;
the carbon dioxide stream resulting from step iv) comprises carbon dioxide, water, 2-chloroethanol and ethylene glycol and additionally comprises 2-iodoethanol or 2-bromoethanol and is condensed in a condenser to form a recycle carbon dioxide stream and a condensate stream; and
the carbon dioxide stream resulting from step iv), or the condensate stream, or the waste water stream resulting from step v) is contacted with an alkali metal containing basic compound to convert 2-iodoethanol or 2-bromoethanol into alkali metal iodide or alkali metal bromide and the resulting mixture comprising water, 2-chloroethanol and ethylene glycol and additionally comprising alkali metal iodide or alkali metal bromide is dehydrated.
2. The process according to claim 1 , wherein the temperature during contacting the carbon dioxide stream resulting from step iv), or the condensate stream, or the waste water stream resulting from step v) with the alkali metal containing basic compound is of from 20 to 200 ° C.
3. The process according to claim 1 wherein the time period of contacting the carbon dioxide stream resulting from step iv), or the condensate stream, or the waste water stream resulting from step v) with the alkali metal containing basic compound is of from 0.1 second to 5 hours.
4. The process according to claim 1 , wherein the carbon dioxide stream resulting from step iv) is contacted in the condenser with an alkali metal containing basic compound, and the condensate stream comprising water, 2-chloroethanol and ethylene glycol and additionally comprising alkali metal iodide or alkali metal bromide is dehydrated.
5. The process according to claim 4 , wherein the condensate stream is dehydrated in step v) and is fed to the dehydration column at a position which is above the position at which the ethylene glycol stream is fed.
6. The process according to claim 1 , wherein the ethylene glycol stream comprises an alkali metal containing basic compound, and the condensate stream comprises water, 2-chloroethanol and ethylene glycol and additionally comprises 2-iodoethanol or 2-bromoethanol and is contacted with the ethylene glycol stream, and the resulting ethylene glycol stream comprising water, 2-chloroethanol and ethylene glycol and additionally comprising alkali metal iodide or alkali metal bromide is fed to and dehydrated in step v).
7. The process according to claim 1 , wherein the condensate stream comprises water, 2-chloroethanol and ethylene glycol and additionally comprises 2-iodoethanol or 2-bromoethanol and is contacted with an alkali metal containing basic compound, and the resulting condensate stream comprising water, 2-chloroethanol and ethylene glycol and additionally comprising alkali metal iodide or alkali metal bromide is dehydrated.
8. The process according to claim 7 , wherein the resulting condensate stream is dehydrated in step v) and is fed to the dehydration column at a position which is above the position at which the ethylene glycol stream is fed.