ASPEN simulation of parameter problems for pressure-swapped distillation of acetonitrile-water
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ASPEN was used to simulate pressure-swapped distillation of acetonitrile-water, with a ratio of 0.6 for acetonitrile and 0.4 for water. In one example, the D/F value for the vacuum distillation column was set to 0.9; the simulation converged easily, but the diameter of the distillation column turned out to be too large. Later, different D/F values were tried; some led to convergence while others did not. How is the value of this D/F determined? Because different D/F values correspond to different circulation rates, the diameter of the distillation column varies significantly. Additionally, when calculated separately, it converges; however, including sensitivity analysis leads to errors in the obtained values ； Or the values in the sensitivity analysis converge, but when they are directly entered into the input for recalculation, convergence is no longer achieved. What’s going on? Additionally, a side-stream extraction was simulated; the purity of the heavy components at the bottom of the tower met the requirements, but actual re-vaporization was needed. I would like to use side-stream extraction from the bottom of the tower as a substitute for re-vaporizing the product from that area. A distributor is placed beneath the packing at the very bottom of the tower, and liquid-phase side-stream extraction is carried out through this distributor. Are the components obtained through this side-stream extraction identical to those at the bottom of the tower?
Pressure swing distillation of acetonitrile-water – learn about it!
It’s sufficient for the distillate at the top of the tower to have a composition close to the azeotropic one; there’s no need to define D/F
In ASPEN’s settings, there is no parameter for the composition at the top of the tower; only parameters such as the flow rate at the top of the tower, the flow rate at the bottom of the tower, D/F, and B/F are available. So how can we achieve a top-of-tower product composition that is close to the azeotropic composition?
Pressure swing distillation of acetonitrile-water – learn about it!
It is sufficient to directly define the reflux ratio and the top draw ratio (or top draw amount); these ratios can be optimized by defining design variables. The purity of the acetonitrile side-stream extract may not meet the requirements.