Patent ID: 11155838

Abstract:
It is disclosed a process to produce a fermentation product from a ligno-cellulosic feedstock hydrolyzate slurry which comprises water, water soluble glucose and xylose and water insoluble pretreated ligno-cellulosic feedstock. The process comprises at least two conversion step. A first conversion medium comprising a first portion of the ligno-cellulosic feedstock hydrolyzate slurry and a yeast capable to ferment glucose and xylose is first created, then the yeast is allowed to convert at least 50% of the glucose and less than 20% of the xylose of the first conversion medium to a first propagated yeast and a first portion of the fermentation product in a first conversion step having a first sugar-to-cells conversion ratio in a range of from 5% to 25%. A second conversion medium comprising at least a portion of the first propagated yeast and a second portion of the ligno-cellulosic feedstock hydrolyzate slurry is then created, then the yeast is allowed to convert at least a portion of the water soluble glucose and xylose in the second conversion medium to at least a second propagated yeast and a second portion of the fermentation product in a second conversion step having a second sugar-to-cells conversion ratio which is less than the first sugar-to-cells conversion ratio. Preferably, the first conversion step comprises at least a first phase which is an aerobic phase and a second phase which is an anaerobic phase.