(77e) A Z Step Cascade Procedure for Extraction of Styrene from a Mixture of Styrene and Ethylbenzene Using Diethylene Glycol as Solvent

Rather than the raffinate as feed to the subsequent stages, the extract is used as feed to the subsequent stage inorder to produce a product high in content of the extract. The stair-case combined graph procedure yields steps of Z for a multi-stage cross-current operation. This is different from the vertical rise steps in the design of the binary distillation column using the McCable Thiele method with constant overflow and underflow. For example, a solution containing 50% ethylbenzene (A) and 50% styrene (C) need be separated at 25 0C at a rate of 1000 kg/h. The extract product composition at the end of the final stage is 92% styrene. Diethylene glycol is the solvent. It is added in a cross current fashion. The slope of ?R/E at each stage was maintained a constant and equal to 1. The equilibrium data in solute free coordinates between the raffinate and extract phases are given in Figure 1.0. Rather than the composited extract the extract is removed at each stage and fed into the next stage. 10 ideal stages are required to achieve 92% styrene concentration in the final extract phase. Inorder to make a product rich in the solute the extract from each stage is given as a feed into the next stage. Operating lines at each stage with a sloop of -1 are constructed starting with the feed composition of 0.5 at Y = X line. The extract from stage 1 is used as feed of stage 2 and so on and so forth. 10 ideal stages are required to achieve the target styrene composition. The composited raffinate composition can be calculated from the graph in Bancroft coordinates.