Fig. 4 shows an analogous behaviour, for a column operating
at 14.2 MPa with isothermal section at 60 ◦C. However, in this
case a larger temperature variation at the top stage is needed in
order to vary the operating conditions of the column. Comparing
Figs. 3 and 4, it can be observed that to increase the recovery from
approximately 70% to 95%, a temperature variation at the top
stage of about 3–4 ◦C is needed, if the isothermal section operates
at 42 ◦C, whereas a variation in the range (12–20) ◦C is needed if
the isothermal section operates at 60 ◦C. In particular, operating
the column at T = 60 ◦C leads to top stage temperatures quite
high (approaching 100 ◦C) at high S/F, which have probably to be
regarded as an upper limit, considering the thermolabile nature of FOEE. Consistently with the change in the composition profile in
the column, the optimal feed location in Figs. 3 and 4 was found to
shift downwards, as T1 increases.