Development of an extractive fermentation process for ethanol production by gas stripping

Author(s)

Gustavo Henrique Santos Florês Ponce

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Engenharia Química
• Defense date: 2015-11-19

Examining board members

Maria Regina Wolf Maciel; Viktor Oswaldo Cárdenas Concha; Mylene Cristina Alves Ferreira Rezende; Jonas Nolasco Junior; Júlio Pereira Maia

• Advisor: Maria Regina Wolf Maciel

Abstract

After stagnation and loss of government incentives of the 70s, the ethanol production in Brazil resumed its growth after the introduction of flex-fuel cars in 2003. Brazil is now the world's second largest producer of ethanol by fermentation, second only by the US. A more flexible process is obtained when the sugar and ethanol are produced jointly. Thus, sugarcane molasses, a byproduct from sugar manufacturing, can be used for production of ethanol. Coupling the fermentor to a method for continuous inhibitor removal, such as the gas stripping technique, it is possible to enhance the use of the molasses so that higher substrate concentrations in the feed are allowable, without reaching the threshold of toxicity of ethanol in the medium. Thus the use of a less diluted sugarcane must can reduce the separation costs (distillation, centrifugation) and project, generating a smaller amount of residue (vinasse) against the amount of ethanol produced. Therefore, the objective of this study was to develop experiments of an extractive fermentation in laboratory scale, which consisted basically of a fermentor (in which gases would be injected to promote ethanol stripping) and a condenser, for recovery of the stripped ethanol. The steps of this work consisted of the computer simulation of the process (using, therefore, commercial software), which was helpful in finding compatible ranges for the use of variables and mounting the prototype in bench scale. Fermentation experiments in batch mode, with the coupling condenser, used Saccharomyces cerevisiae and molasses as substrate. The analytical monitoring was done through total reducing sugars, ethanol, glycerol and dry weight determinations. The results show the effectiveness of the technique since it was possible to keep the ethanol concentration in the broth below the threshold of toxicity (concentrations below 60 g/L) with almost total consumption of the sugars, even for the highest concentrations (300 g/L). The condensate, in turn, was free of other organic compounds, apart from ethanol, where concentrations predominantly between 200-250 g/L were obtained. Compared with conventional batch fermentation, the technique showed improvements in productivity (2.39 to 3.58 g/L.h an increment of 43 %) presented larger substrate consumption as well (5.8 to 7.87 g/L.h an increment of 42 %) in a shorter fermentation time. Higher sugar concentrations and lower gas flow rates become the process more attractive, since in these conditions, less water is added to the fermentation, and more concentrated condensate in ethanol is reached (selectivity ranging from 5.19 to 11.34) (AU)

• FAPESP's process: 12/17706-0 - Development of a extractive fermentation process of ethanol production by gas stripping.
• Grantee: Gustavo Henrique Santos Flores Ponce
• Support Opportunities: Scholarships in Brazil - Doctorate