2 replies to this topic

[Yajnavalkya]

Messers

 

I am to work on a separation process for extracting MEG, DEG and TEG from spent / crude glycols after removing the water present. The column can be a batch / continuous one as of now, because

 

I understand from a preliminary literature survey that this operation is carried out usually in differenct ways:

 

(a) 5-6 columns each separating MEG / DEG / TEG / PEG etc.

 

(b ) 2 batch columns, operating under vacuum, water being separated in the first and MEG, DEG and TEG removed as top cuts in successive operations in the second column.

 

I have started simulating this system in Chemcad based on an assumed feed composition.

 

However, I feel I need to further read up on the process and understand how to optimally carry out this design  for this system. Can someone please direct to some literature / journals / publications dealing with similar process so that I can decide if the column will be a batch / continuous / tray / packed etc.

 

Thanks

[ankur2061]

What is the source of your spent glycol?

 

A major continuous source of spent glycol is the production of Polyethelene Terephthalate (PET) from monoethylene glycol and terephthalic acid . Spent glycol from this process has mostly water, monoethylene glycol, acetaldehyde, 2-methyl-1,3-Dioxalane and other volatile organic . Small quantities of Diethylene Glycol (DEG) is also found. TEG is only found in traces. The recovery of MEG form spent glycol generated in PET plants is a semi-continuous process where large quantities of spent glycol stored are processed in a 2-stage continuous distillation process. The first column removes the water and other volatile organic compounds. the bottom product of the first column which is mostly a mixture of MEG/DEG/TEG is fed to the second column. The top product from the second column is relatively pure MEG and the bottom product is a mixture of DEG/TEG/PEG and other heavier compounds. Generally, DEG/TEG/heavier residues are not recovered in a PET plant and disposed off suitably. The MEG recovered from the recovery plant is not of the same grade as virgin MEG and hence blended with virgin MEG to get acceptable quality of MEG for the PET process.

 

RIL, Hazira has a spent glycol recovery plant of the type described above and I was involved in the pre-commissioning activities related to this plant in 1997. If I recall correctly, the 2 columns were trayed columns with conventional bubble cap trays. Since I haven't kept track, I am not aware of the current status of the plant and any changes or modifications to it.

 

Regards,

Ankur.

[Yajnavalkya]

Ankur Sir

 

Source of the spent glycol is unclear as of now. Client is essentially a trader, who is setting up a storage terminal along with a process block for BTX, O-M-P Xylene, GLycol separations. It is most likely that spent glycol will be sourced from PET plants and other sources in Iran. The following composiotion if available:

 

 

Source Specifications : Crude Glycol Parameter Lower Limit Higher Limit Density 1.18 1.20 Color DARK BROWN IBP in deg cel 190 220 FBP in deg cel 260 300 GLYCOL Contens in Wt%     MEG 20 50 DEG 10 70 TEG 7 70 Heavier Glycols 0 1 Water Content in wt% 10 50 Salt Content in wt% 5 20

 

I have read up in some patents that the operating pressure and temperature for the columns are 605 mmHg and 165 °C at bottom and 60 °C at the bottom. However, I am unable to finalize the scheme and parameters.

 

Can please refer me to some literature so that I can further read up the on same.