Methods for producing a bioproduct selected from acetone, isopropanol and a combination thereof with a microorganism in a fermentor are disclosed. The methods include separating cells of the microorganism from a fermentation broth to form separated cells and recycling at least a fraction of the separated cells to the fermentor to achieve one or more of the following: (1) cell concentration in said fermentor greater than 2 g/L; mass yield on a first feedstock greater than 32%; productivity greater than 0.12 g/L/h; and bioproduct titer greater than 10 g/L.