8 replies to this topic

[vikash_488]

Hi,

 

I have the feed containing about Methanol(96%), Ethanol (3%), Acetone(0.1%), Water (0.9%); all the compositions are in weight %.

The water can be maintained from 0.1% to 5% if it affects the product purity. The product purity required is about (Top): 99.95%, Ethanol: 50 ppm, Acetone :30 ppm, water: 0.1% and (Bottom), maximum possible weight% of ethanol. This is unconventional to those process in which Ethanol is the desired product; For us, MeOH is the desired product.

 

1st Question: would this be possible in single column with high no. of trays (40-60 trays)?

 

2nd Question: What would be most economical way to achieve such a product purity.

 

I am using ChemCAD for this simulation but not getting the purity of this level, The top for me is 99.85% MeOH, 500 ppm EtOH, 300ppm Acetone, Water: 0.1%. I am using UNIFAC/LATE in almost atmospheric condition. Will this be a good choice? I have many other unit operations which UNIFAC is suited to. I have almost the similar result with NRTL as well.

 

Please suggest me the ways.

 

Thanks. 

 

[Bobby Strain]

If you want higher purity you must use more reflux with a fixed number of trays.

 

Bobby

[Tolinorton]

vikash_488,

 

 

Use SCDS module and Wilson as Global K-value Model

[panoskagiou]

Do you have azeotropes?

[vikash_488]

Tolinorton:

 

Actually I am using SCDS only with UNIFAC, Wilson was not giving expected results.

[vikash_488]

panoskagiou:

 

Not between Methanol and ethanol, but of course for ethanol-water.  That's why I am keeping 0.1% water in the feed to improvise the separation. 

[vikash_488]

I am already using high reflux ratio of about 8 with 30 ideal trays. Do you think I should go beyond this? I have already very high steam and cooling water consumption.

[Bobby Strain]

Use more trays.

 

Bobby

[panoskagiou]

I would like to ask you why you dont use design specs or a sensitivity analysis to see  what number of stages or reflux ratio you need?