Production of second generation ethanol by Schefferspmyces stipitis from pentoses by vacuum extractive process

Author(s)

Daniele Farias

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia de Alimentos
• Defense date: 2014-07-11

Examining board members

Francisco Maugeri Filho; Eloizio Julio Ribeiro; Fátima Aparecida de Almeida Costa; Marcio Antonio Mazutti; Rosana Goldbeck

• Advisor: Francisco Maugeri Filho; Daniel Ibraim Pires Atala

Abstract

The biotechnological production of second generation ethanol (2G) through the cultivation of Scheffesomyces stipitis on pentoses obtained from hemicellulose hydrolyzates of agro-industrial wastes is of great economic interest. This is because, this process can add value to these wastes, replace fossil fuels, and promote a complete recovery of materials. Adding to this, the use of fermentation media with high concentration of substrate is of great interest to industry because it reduces significantly the volume of reactors and vinasse. Large amounts of ethanol in the culture medium consume less energy in the extraction process. However, this high concentration of ethanol inhibits the process, so its remotion during fermentation is advisable. The use of extraction techniques improves the performance of the process. The use of flash evaporator allows the use of high concentrations sugars, which results in increased production of ethanol, reducing the cost of distillation. Facing this, the objective of this study is to develop an alternative technology to bridge the currently existing bottlenecks in the production of 2G ethanol from pentoses through a fermentatiton process with cell retention, coupled to a vaccum evaporator type flash. With the proposed prototype, ethanol production from xyloses was studied in a process utilizing high cell concentration of S. stipitis. The reason for the use of this technology is due to the low tolerance of this strain to ethanol as well as the low productivity. Initial studies were conducted in order to investigate the inhibitory effects of ethanol and substrate concentrations in the kinetic behavior of the strain S. stipitis. To promote this, experiments were performed in batch and continuous mode, with substrate concentration ranging from 7.5 to 145 g.L-1. The results showed a strong inhibitory effect promoted on the specific growth rate, substrate consumption and ethanol production when high initial substrate concentrations were administered, leading to high concentrations of ethanol. Based on these experimental data, a mixed mathematical model that combines models of Andrews and Levenspiel to describe the inhibitory effect prmoted by substrate and ethanol concentrations, respectively, has been proposed. The kinetic model was able to satisfactorily describe the kinetic profile of the experimental data. However, mathematical modeling of kinetic parameters is a difficult task and it consumes a considerable period of time. A parametric sensitivity analysis was performed with the aid of a Plackett-Burman design using the Statistic software. The kinetic parameters were varied and the effect of this variation was evaluated in the cell, substrate and ethanol concentration profiles. The most relevant model parameters were ?max, Pmax, Yx, n and Yp/x, which were chosen to be re-estimated whenever there are changes in the operation conditions. In order to enhance the 2G ethanol production by strain S. stipitis, experiments were performed in fed-batch mode. This strategy was used to avoid the catabolic repression of this strain as well as to ensure optimal substrate feeding to the reactor. The operate of the system whit this strategy resulted in high concentrations of ethanol with high yields and productivities. The maximum ethanol concentration achivied was 46 g.L-1 obtained for xylose concentration in the feed medium of 200 g.L-1. The yield and productivity were 1.1 and 2.3 times higher than when operated in the batch mode. Finally, experiments were conducted to test the effectiveness of the technology developed in order to evaluate the efficiency of `extractive retentostato vacuum¿. The toxic effect caused by high ethanol concentrations was minimized by intermittent extraction in the flash tank operated on vacuum. This strategy allowed maintaining a low concentration of ethanol in the fermentation medium (~25 ¿ 35 g.L-1) and an alcohol concentration in the condenser at 40°GL. The maximum ethanol productivity obtained was 1 g.L 1.h-1, obtained with 100 g.L-1 of xylose in the feed medium, and this value was 4.35 times higher compared with experiments performed in bacth mode. The technology proposed here may contribute to enhance future research in 2G ethanol production through the development of processes for low cost industrial scale (AU)

• FAPESP's process: 10/01606-1 - Production of second generation ethanol from pentoses by Pichia stipitis using extractive fermentation process vacuum
• Grantee: Daniele Farias
• Support Opportunities: Scholarships in Brazil - Doctorate