Method for controlling the process of separating mixtures containing several substances

A method for process control of distillation columns having a lower column section (9) and an upper column section (10) with control of the liquid phase concentration to separate a plurality of components A, B wherein

• a) the concentration of at least one of the components A, B is measured online at a point (29) between the uppermost tenth and the lowermost tenth of the length of the overall column (9, 10), by an analytical instrument (3),
• b) the concentration measured in a) of at least one of the components A or B is taken and used by an online process model in a computer unit (6) of a process control system (28), and the process model, within a time interval determined by the process control system (28) in accordance with the control technique, calculates a liquid phase concentration XALP using the concentration measured in a) and further parameters measured directly in the column (9, 10) selected from the group consisting of temperature, pressure and mass flows of feed (15), reflux (22), heating medium feed, and vapor feed (18);
• the temperature at the top of the column and the temperature at the feed location (27) of column (10),
• c) the liquid phase concentration XALP calculated using the process model is used for control, by treating the liquid phase concentration XALP calculated by the model for control purposes as the actual value of the liquid phase concentration control parameter,
• d) the number of theoretical plates of structured packings or random packings and/or the degree of tray efficacy, are adapted over predetermined time intervals, to the prevailing column conditions, including, but not limited to, the degree of fouling, on the basis of analyses of the end product and introduction of the analytical data into the process model.