US 12,076,670 B2
Method for operating a distillation column
Klaus Mertens, Moers (DE); and Sabine Pegel, Düsseldorf (DE)
Assigned to Covestro Deutschland AG, Leverkusen (DE); and Covestro Intellectual Property GmbH & Co. KG, Leverkusen (DE)
Appl. No. 17/781,413
Filed by Covestro Deutschland AG, Leverkusen (DE); and Covestro Intellectual Property GmbH & Co. KG, Leverkusen (DE)
PCT Filed Dec. 9, 2020, PCT No. PCT/EP2020/085198
§ 371(c)(1), (2) Date Jun. 1, 2022,
PCT Pub. No. WO2021/116146, PCT Pub. Date Jun. 17, 2021.
Claims priority of application No. 19215603 (EP), filed on Dec. 12, 2019; and application No. 20210976 (EP), filed on Dec. 1, 2020.
Prior Publication US 2023/0008804 A1, Jan. 12, 2023
Int. Cl. B01D 3/42 (2006.01); C07C 201/16 (2006.01)
CPC B01D 3/425 (2013.01) [C07C 201/16 (2013.01)] 5 Claims
OG exemplary drawing
 
1. A method of continuously operating a distillation column set up for separation of a substance mixture S consisting essentially of a substance A and a substance B which is higher-boiling than substance A, wherein the distillation column comprises:
(I) a column body in a vertical arrangement, the column body comprising a stripping section and a rectifying section arranged above the stripping section;
(II) a column bottom arranged beneath the stripping section for accommodating a liquid bottom product B1 at a bottom temperature T(B1) up to a bottoms level H(B1);
(III) a column top arranged above the rectifying section for accommodating an evaporated top product A1;
(IV) a feeding point for the substance mixture S, the feeding point being configured to feed the substance mixture S to the distillation column with a flow rate m(S);
(V) a circulation evaporator configured to heat the column bottom by indirect heating of a first portion B11 of the liquid bottom product B1, wherein the circulation evaporator is supplied with a heat carrier medium W with a mass flow rate m(W) and the circulation evaporator has a heat carrier medium valve for adjustment of the mass flow rate m(W);
(VI) a withdrawal unit configured to remove a second portion B12 of the liquid bottom product B1 with a mass flow rate m(B12), where the withdrawal unit has a bottoms withdrawal valve configured to adjust the mass flow rate m(B12);
(VII) a top condenser configured to condense the evaporated top product A1 to obtain a liquefied stream A2;
(VIII) a recycling and withdrawal unit configured to return a first portion of the liquefied stream A2 to the distillation column with a mass flow rate m(A21) and for removing a second portion of the liquefied stream A2 from the distillation column with a mass flow rate m(A22), where the recycling and withdrawal unit comprises a reflux valve configured to establish a reflux ratio r=m(A21)/m(A22); and
(IX) a closed-loop control unit comprising a reflux controller, a bottoms level controller, a stripping section temperature controller, a bottom temperature limiting controller and a mass flow controller for the heat carrier medium W;
wherein the method comprises:
(i) defining, for the reflux ratio r, a target value rTARGET within a range from r1 to r2, wherein the reflux controller uses rTARGET and the value for the mass flow rate m(S), taking account of the value of r1 for r, to calculate the setting of the reflux valve;
(ii) defining, for the bottoms level H(B1), a target value H(B1)TARGET within the range from H(B1)1 to H(B1)2, wherein the bottoms level controller uses H(B1)TARGET, the bottoms level at a given time, H(B1)CURR, and the mass flow rate m(S) to calculate the setting of the bottoms withdrawal valve;
(iii) defining, for a stripping section temperature T(AT), a target value T(AT)TARGET within the range from T(AT)1 to T(AT)2, wherein the stripping section temperature controller uses T(AT)TARGET, the stripping section temperature at a given time, T(AT)CURR, and the mass flow rate m(S) to calculate the setting of the heat carrier medium valve and transmits the setting of the heat carrier medium valve thus calculated thereto by means of the mass flow controller;
(iv) defining, for the bottom temperature T(B1), a target value T(B1)TARGET within the range from T(B1)1 to T(B1)2, wherein the bottom temperature limiting controller is set up such that when the temperature goes below the temperature T(B1)1:
(1) the setting of the heat carrier medium valve according to (iii) is disabled;
(2) the setting of the heat carrier medium valve is altered such that the mass flow rate m(W) is increased; and
(3) the setting of the heat carrier medium valve according to (iii) is re-enabled as soon as the bottom temperature T(B1) is again within the range from T(B1)1 to T(B1)2.