Experimental study and mathematical modeling of the alcoholic fermentation process considering thermal effects

Abstract

The world's population has practically doubled in the last fifty years, increasing energy consumption due to the development of new technologies and industrial processes, which are based on an energy matrix derived from fossil fuels. Among biofuels, ethanol produced from sugarcane is widely used as a fuel and, additionally, it is also used as a blend in gasoline in its anhydrous form. The fermentation of cane sugar by Saccharomyces cerevisiae is one of the most used for the production of ethanol, however, the fermentation process with these microorganisms requires knowledge of the kinetic characteristics of cell growth and ethanol production for efficient and effective operation in the industry. Many studies have modelled the process of alcoholic fermentation performed by this microorganism. However, the literature lacks a validated model under broad process conditions that systematically include the thermal effects and energy balance involved in this process, as well as special attention to the Brazilian production process and its peculiar characteristics. Thus, the present work, part of a thematic project of FAPESP (Process 2015/50684-9 "Sustainable gas pathways for Brazil: from microcosm to macrocosm"), proposes the experimental study and mathematical modelling of the fermentation process under comprehensive and systematic conditions, including thermal effects and energy balances.The model will be based on macroscopic mass balances for each of the components, the apparent kinetics of the transformations present in the process and the energy balanceThe parameters of the kinetic model will be collected in the laboratory in isothermal batch operations. The selected strains of the microorganisms will be PE-2 (reference strain used in the Brazilian industry) and CEN.PK112 (diploid strain from the haploid strain CEN.PK113-7D, considered as a laboratory reference for studies of quantitative microbial physiology), proposing the verification and the comparison of the kinetic and operational characteristics obtained in each of them. The culture medium used will also simulate the Brazilian industry, for that, the work proposes initially the adequacy of semi-synthetic media, reported by Lino et al. (2018), to a completely defined medium that reproduces the conditions found in molasses. Different concentrations of sugars and cells, as well as the temperature, will have their influence in the evaluated process, aiming to verify its influence in the kinetic models.The work also proposes, in an unprecedented way, the experimental determination and evaluation of the reaction heat for ethanol production and cell growth in different stages of metabolism (respiratory, respiratory-fermentative and fermentative). For this purpose, reactors will be used to control the process and determine the thermal loads involved in these reactions.