US 11,702,381 B1
Method for operating a rectification column
Bernd Pennemann, Bergisch Gladbach (DE); Shuang Liang, Houston, TX (US); Zhangyong Ming, Shanghai (CN); and Juergen Bausa, Kürten (DE)
Assigned to Covestro Deutschland AG, Leverkusen (DE); and Covestro LLC, Pittsburgh, PA (US)
Filed by Covestro Deutschland AG, Leverkusen (DE); and Covestro LLC, Pittsburgh, PA (US)
Filed on Feb. 23, 2022, as Appl. No. 17/678,360.
Int. Cl. B01D 3/42 (2006.01); C07C 209/86 (2006.01); B01D 3/32 (2006.01)
CPC C07C 209/86 (2013.01) [B01D 3/322 (2013.01); B01D 3/4205 (2013.01); B01D 3/4211 (2013.01)] 15 Claims
OG exemplary drawing
 
1. A method for operating a rectification column (1000) for separating a mixture (S) containing a component A and a component B having a boiling point higher than that of the component A at an operating pressure of the rectification column (1000) below ambient pressure,
wherein a sum of mass fractions of the components A and B in the mixture (S) is, based on a total mass of the mixture (S), 95.0% to 100%, and wherein a first product stream (P1) comprising the component A and a second product stream (P2) comprising the component B are obtained from the mixture (S);
wherein the rectification column (1000) comprises:
(I) a vertical column body (100) comprising a stripping section (110) with separating internals and a rectifying section (120) arranged over top of the stripping section (110) and having separating internals;
(II) a column bottom (130) arranged below the stripping section (110) to accommodate a liquid bottom fraction (B1), wherein a first temperature measuring device (TM1) for measuring a first reference temperature (T1) is arranged in the stripping section (110) or in the column bottom (130);
(III) a column top (140) arranged above the rectifying section to accommodate a gaseous overhead fraction (A1);
(IV) a feeding point (150) for the mixture (S) arranged between the stripping section (110) and the rectifying section (120), wherein the mixture (S) is fed into the rectification column (1000) at a mass flow ms;
(V) an evaporator (200) for heating the column bottom (130);
(VI) a bottom outlet unit or side outlet unit (220) for discharging the second product stream (P2) at a mass flow mP2;
(VII) a condenser (300) arranged within or outside the rectification column (1000) for partially condensing the gaseous overhead fraction (A1) to give a liquid overhead fraction (A2) and a fraction composed of uncondensed constituents (A3);
(VIII) a top outlet unit or side outlet unit (310) for taking off the first product stream (P1) as a first part of a distillate fraction (A4) at a mass flow mP1, wherein a second part of the distillate fraction (A4) is conveyed as reflux (A42) at a mass flow mA42 in such a way that the reflux (A42) travels through at least part of the rectifying section (120) so that a reflux ratio r=mA42/mP1 is established;
(IX) a second temperature measuring device (TM2) for measuring a second reference temperature (T2), wherein the second temperature measuring device is arranged in the rectifying section (120) or in the column top (140); and
(XI) a third temperature measuring device (TM3) for measuring a control temperature (TC), wherein the third temperature measuring device (TM3) is arranged in the column body (100) between the first temperature measuring device (TM1) and the second temperature measuring device (TM2);
wherein the method comprises operating the rectification column (1000) at a pressure below ambient pressure and controlling a mass fraction of the component B in the first product stream (P1) to a value within a first target range from 0.1% to 5.0%, based on a total mass of the first product stream (P1), and a mass fraction of the component A in the second product stream (P2) to a value within a second target range from 0.1% to 5.0%, based on a total mass of the second product stream (P2), wherein the controlling is carried out as a function of the control temperature (TC) for which a setpoint TCsetpoint is calculated according to an equation
TCsetpoint=T2+F·(T1−T2),
where F is a factor in the range from 0.1 to 0.9;
wherein the first reference temperature (T1), the second reference temperature (T2) and the control temperature (TC) are measured continuously or at intervals and when there is a deviation of a measured control temperature (TC) from the set point TCsetpoint the control temperature (TC) is adjusted to the setpoint TCsetpoint by adjusting one or more of the following actuating variables:
(i) the heating of the column bottom (130) by the evaporator (200), (ii) the mass flow mA42 of the reflux (A42) fed back into the rectification column, (iii) the mass flow mP2 of the second product stream (P2) and (iv) the mass flow mP1 of the first product stream (P1).