Development of advanced fermentation technology for the production of n-butanol, isopropanol and ethanol from sugar cane bagasse

Abstract

The economical viability of the biobutanol production process by ABE (acetone-butanol-ethanol) fermentation using Clostridium strains faces challenges such as high product inhibition, low yields and productivity, and high substrate costs. However, if the production of n-butanol reaches the scale of billions liters in response to the demand of the automotive fuels market, it is certain that there will be an over-supply of acetone. Due to this market risk, an interesting alternative is the production of n-butanol via IBE (isopropanol-butanol-ethanol) fermentation. This mixture can be used directly as biofuel or as additive in gasoline because it does not contain acetone, which is corrosive to the engines. In addition, an energetic gain is expected because of the need for separation of the IBE blend. However, the technical limitations in the fermentation stage persist. The proposal of this project is the development of a fermenter that integrates, in the same vessel, the in-situ recovery of the products through the use of vacuum, and the immobilization of cells. The main goal of the in-situ recovery is the energetic gains by eliminating or drastically reducing IBE toxicity to cells; cellular immobilization aims to increase productivity and to use of more compact fermenters. The immobilizing agent for the cells will be organically constituted from the sugarcane bagasse itself, which will be kept submerged in the fermentation broth by packaging in a cage-like polymeric structure which, together with the rising motion of the bubbles generated during vacuum evaporation, will assist in the creation of an internal circulation of liquid, similar to an air-lift system. The 3D printing technique will be used for the manufacture of polymer structures with different geometries. In this way, the final product of this project is an advanced fermentation system that combines in a single vessel the advantages of the internal circulation of an air-lift type reactor, the immobilization of cells in fixed beds, and the in-situ recovery of products.