A fractionation apparatus, comprising: a dividing wall column having a dividing wall forming a feed side and a product side , the dividing wall column having a separator positioned above the dividing wall of the dividing wall column , an aqueous reflux outlet above the dividing wall and an organic reflux outlet above the dividing wall , the feed side having a feed inlet below a top of the dividing wall and above the bottom of the dividing wall , a feed side reflux inlet below a top of the dividing wall and above the feed inlet in fluid communication with the organic reflux outlet, and the product side having a product outlet below a top of the dividing wall and above the bottom of the dividing wall , and a product side reflux inlet below the top of the dividing wall and above the product outlet in fluid communication with the aqueous reflux outlet and the organic reflux outlet; wherein the apparatus further comprises: a ratio controller , an associated flow rate controller (50; 56), and a control valve controlling reflux flow in communication with the organic reflux outlet of the separator to maintain a desired flow rate to the product side and the feed side of the dividing wall column ; and a ratio controller , an associated flow rate controller (39; 46), and a control valve controlling reflux flow in communication with the aqueous reflux outlet of the separator to maintain a desired flow rate to the feed side and the product side of the dividing wall column . a dividing wall column having a dividing wall forming a feed side and a product side , the dividing wall column having a separator positioned above the dividing wall of the dividing wall column , an aqueous reflux outlet above the dividing wall and an organic reflux outlet above the dividing wall , the feed side having a feed inlet below a top of the dividing wall and above the bottom of the dividing wall , a feed side reflux inlet below a top of the dividing wall and above the feed inlet in fluid communication with the organic reflux outlet, and the product side having a product outlet below a top of the dividing wall and above the bottom of the dividing wall , and a product side reflux inlet below the top of the dividing wall and above the product outlet in fluid communication with the aqueous reflux outlet and the organic reflux outlet; wherein the apparatus further comprises: a ratio controller , an associated flow rate controller (50; 56), and a control valve controlling reflux flow in communication with the organic reflux outlet of the separator to maintain a desired flow rate to the product side and the feed side of the dividing wall column ; and a ratio controller , an associated flow rate controller (39; 46), and a control valve controlling reflux flow in communication with the aqueous reflux outlet of the separator to maintain a desired flow rate to the feed side and the product side of the dividing wall column . a ratio controller , an associated flow rate controller (50; 56), and a control valve controlling reflux flow in communication with the organic reflux outlet of the separator to maintain a desired flow rate to the product side and the feed side of the dividing wall column ; and a ratio controller , an associated flow rate controller (39; 46), and a control valve controlling reflux flow in communication with the aqueous reflux outlet of the separator to maintain a desired flow rate to the feed side and the product side of the dividing wall column . <EOS>