Abstract
A three-step process consisting of biomass hydrolysis, fermentation and in-situ gas stripping by a vacuum assisted recovery system, was optimized to increase the ethanol production from sugar beet pulp. The process combines the advantages of stripping and vacuum separation and enhances the fermentation productivity through in-situ ethanol removal. Using the design of experiment and response surface methodology, the effect of major factors in the process, such as pressure, recycling ratio and solids concentration, was tested to efficiently remove ethanol after the combined hydrolysis and fermentation step. Statistical analysis indicates that a decreased pressure rate and an increased liquid phase recycling ratio enhance the productivity and the yield of the strip-vacuum fermentation process. The results also highlight further possibilities of this process to improve integrated bioethanol production processes. According to the statistical analysis, ethanol production is strongly influenced by recycling ratio and vacuum ratio. Mathematical models that were established for description of investigated processes can be used for the optimization of the ethanol production.
Highlights
Conventional ethanol fermentation is a typically product inhibiting process leading to low productivity and yield
The response surface methodology (RSM) was applied to the output data to evaluate the impact of process variables on the efficiency of the in-situ gas stripping vacuum assisted system for ethanol removal
The process was conducted as a three-step process including the (i) enzyme hydrolysis as the initial step; (ii) yeast fermentation and ethanol production as the second step and (iii) in-situ gas stripping, vacuum distillation and ethanol removal as the third step
Summary
Conventional ethanol fermentation is a typically product inhibiting process leading to low productivity and yield. This problem can be alleviated by continuous removal of ethanol from the fermentation broth. Several processes based on continuous ethanol removal during fermentation have been developed, which include: vacuum fermentation [1], flash fermentation [2], stripping fermentation [3], extraction fermentation [4] and membrane separation [5,6]. Flash fermentation and stripping fermentation processes are straightforward, suitable for implementation in industrial applications and have little influence on the culture medium. Their overall low separation efficiency and compressor restrictions limit the efficiency of these processes.
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