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I've been looking at ways to re-concentrate a formic acid-water binary mixture with the VLE diagram below.

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Am I correct in saying that to concentrate a solution of say , 40% formic acid by weight I could (excluding all recycle streams for simplicity) implement a distillation column at 1 bar to produce a distillate at the azeotrope (78%) and then pass this distillate into a second column operating at 0.1 bar to distill further to 95%?

Aditionally, would operating the 1bar column for a distillate of say only 70% (past the 0.1 bar azeotrope) then performing the remaining concentration in the low pressure column result in any significant energy savings due to less steam required at the lower pressure?

Lastly, if I was to START with a solution of 85% formic acid, already beyond both azeotropes, I could just perform simple distillation in a single column at either pressure point to obtain the 95% product?

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OP Quote:

Am I correct in saying that to concentrate a solution of say , 40% formic acid by weight I could (excluding all recycle streams for simplicity) implement a distillation column at 1 bar to produce a distillate at the azeotrope (78%) and then pass this distillate into a second column operating at 0.1 bar to distill further to 95%?

Answer: Yes

OP Quote:

Additionally, would operating the 1bar column for a distillate of say only 70% (past the 0.1 bar azeotrope) then performing the remaining concentration in the low pressure column result in any significant energy savings due to less steam required at the lower pressure?

Answer: Significant is relative. But if the feed solution for the 1 bar column is 70 wt% as compared to 40 wt% in the first paragraph, you will save energy in operating at the 70 wt% specification because you will have less stages to get to the azeotrope and likely less vapor to generate to meet formic acid production rate targets. The lower pressure column will work and use the same amount of energy whether the feed to the first column is 40 wt% or 70 wt% because the second column always has azeotrope condition feed.

OP Quote:

Lastly, if I was to START with a solution of 85% formic acid, already beyond both azeotropes, I could just perform simple distillation in a single column at either pressure point to obtain the 95% product?

Answer: Yes

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