Two-Step Fermentation Process for Lignocellulosic Ethanol Production
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Solution Overview
Problem
The fermentation of lignocellulosic feedstock hydrolyzates to produce ethanol is hindered by low sugar concentrations, presence of inhibitory compounds, and biological contaminants, leading to high costs and inefficiencies in yeast propagation and fermentation processes.
Innovation Solution
A two-step process involving a first conversion step with aerobic conditions to propagate yeast and a second conversion step under anaerobic conditions, where genetically modified yeast converts water-soluble glucose and xylose into yeast biomass and ethanol, without the need for sterilization or additional nutrients, using a lignocellulosic feedstock hydrolyzate slurry as the primary carbon source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sterilization is practiced to prevent biological contaminants, then reliability is improved, but loss of substance increases due to sugar consumption by contaminants
Solution Approach 1:
Yeast is propagated in advance in a first conversion step to generate a sufficient yeast population before the main fermentation step. This preliminary yeast production ensures that when fermentation begins, there are enough yeast cells to quickly consume sugars and outcompete any biological contaminants, eliminating the need for sterilization while preventing sugar loss to contaminants.
2Productivity
If yeast propagation is conducted in aerobic conditions, then productivity is improved, but use of energy increases due to high air flow and agitation requirements
Solution Approach 1:
The process dynamically transitions between aerobic and anaerobic conditions. The first conversion step uses aerobic conditions to maximize yeast propagation rate. After sufficient yeast is produced, the system switches to anaerobic conditions for the second conversion step to produce ethanol while minimizing energy consumption, as anaerobic fermentation requires no air injection or high-intensity agitation.
3Manufacturing precision
If separate propagation and fermentation steps are used, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The patent combines propagation and fermentation into a single integrated two-step conversion process using the same bioreactor system. The first conversion step performs yeast propagation under aerobic conditions, and the second conversion step performs ethanol fermentation under anaerobic conditions. This merging eliminates the need for separate propagation and fermentation equipment, reducing device complexity while maintaining product specificity through controlled environmental transitions.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process effectively reduces yeast production costs, minimizes the use of expensive carbon sources, and allows for fermentation in the presence of biological contaminants without sterilization, achieving high ethanol yields with a low power consumption.
Implementation Method 1
a yeast capable of converting glucose and xylose to a propagated yeast and a fermentation product
Implementation Method 2
air at a flow rate which is in a range selected from the group consisting of from 0.1 vvh to 10 vvh
Data Source
AI summary
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.