Conventional and non-conventional distillation schemes for the separation of ternary mixture are investigated and optimized based on shortcut calculations, pinch analysis and rigorous simulation in order to achieve the highest saving values in energy and total annual cost (TAC) as the optimization objective function. The optimum direct or indirect conventional sequence is selected as the base case for comparison. The investigated non-conventional heat-integrated distillation schemes are: direct sequence with forward heat integration (DQF), direct sequence with backward heat integration (DQB), indirect sequence with forward heat integration (IQF), indirect sequence with backward heat integration (IQB), sloppy sequence with prefractionator (SP), sloppy sequence with forward heat integration (SQF), sloppy sequence with backward heat integration (SQB) and sloppy sequence with double heat integration (SQD).

The studied chemical system is benzene–toluene–m-xylene known as BTX with 99.9 mol % product purity, the optimization parameters are feed compositions: (45/10/45), (33.3/33.3/33.3), and (10/80/10). The state of feed condition is considered as one of the optimization variables by investigating different feed states; feed at 20 °C temperature, liquid at bubble point and vapor at dew point.

The results from shortcut and pinch analysis are found to be very close to rigorous simulation results regarding number of stages, reflux ratios and utilizing trim reboiler or trim condenser in studied distillation schemes. Applying shortcut and pinch analysis results as initial input parameters for rigorous simulation prove to be efficient in order to reach the global optimum solutions faster. The utilization of shortcut and pinch analysis results as preliminary screening tool for different distillation scheme alternatives especially in case of complex distillation configurations could be very attractive. Rigorous optimization results indicate that savings in energy and total annual cost of the configurations are affected by the states of the feed conditions and feed compositions.