Continuous ethanol production using yeast immobilized on sugar-cane stalks

Abstract

-Sugar-cane stalks, 2.0 cm long, were used as a support for yeast immobilization envisaging ethanol production. The assays were conducted in 38.5 L fermenters containing a bed of stalks with 50% porosity. The operational stability of the immobilized yeast, the efficiency and stability of the process, as well as the best dilution rate were evaluated. Molasses from demerara sugar production was used in the medium formulation. It was diluted to obtain 111.75 1.51 g/L without any further treatment. Sulfuric acid was used to adjust the pH value to around 4.2. Every two days Kamoran HJ (10 ppm) or with a mixture containing penicillin (10 ppm) and tetracycline (10 ppm), was added to the medium. Ethanol yield and efficiency were 29.64 g/L.h and 86.40%, respectively, and the total reducing sugars (TRS) conversion was 74.61% at a dilution rate of 0.83 h -1 . The yeast-stalk system was shown to be stable for over a 60 day period at extremely variable dilution rates ranging from 0.05 h -1 to 3.00 h -1 . The concentration of immobilized cell reached around 10 9 cells/gram of dry sugar-cane stalk when the fermenter was operating at the highest dilution rate (3.00 h -1 ).

Diluted Acid Pretreatment of Pinus Radiata for Bioethanol Production Using Immobilized Saccharomyces Cerevisiae Ir2-9 in a Simultaneous Saccharification and Fermentation Process

“…Among their disadvantages are the high cost of microbial recycling and installation, high contamination risks and susceptibility of the microorganism to environmental variations. 5 The use synthetic or natural polymers to immobilize yeasts, as calcium alginate, carrageenin-oligochitosan, chitosan-carboxymethylcellulose, agarose, polyamide, among others, allows to protect the cells from inhibitors maintaining a high concentration of cells in the capsules, improving the thermal stability, maintaining a long time of operational stability of the encapsulated yeast and obtaining higher ethanol yields than in fermentations with the free yeast cells. 6,7 Saccharomyces cerevisiae is the yeast frequently used in the alcohol industry (wine, spirits and fuels) to ferment sugars from different kind of raw material such as grapes and other fruits, cereals, sugarcane, and lignocellulosic materials.…”

Kinetic Modeling of 1‐G Ethanol Fermentations

“…Bioethanol can be produced from batch, fed-batch, and continuous processes, as well as in some cases using flocculating yeasts [1][2][3][4][5][6].…”

“…The hydrolysis of sucrose promoted by the invertase present in the yeast is not the limiting step of ethanol production in industrial processes. The stoichiometry of ethanol-formation reaction from glucose is given by the classical Gay-Lussac equation: C 6 H 12 O 6 !2CH 3 CH 2 OH + 2CO 2 According to Doran [8], both Saccharomyces cerevisiae yeast and Zymomonas mobilis bacteria produce ethanol from glucose under anaerobic conditions without external electron acceptors. The biomass yield from glucose is 0.11 g/g for yeast and 0.05 g/g for Z. mobilis.…”

Microencapsulation of Baker’s Yeast in Gellan Gum Beads Used in Repeated Cycles of Glucose Fermentation

“…Nevertheless, recent studies [2][3][4] have pointed out the interest of attaching yeast to polymeric matrices. The following practical advantages of using immobilized yeast cells are important for industrial scale-up: (a) increasing productivity of the fermenter which will permit the use of important flow rates in a continuous operating mode, avoiding the yeast cells destruction and obtaining of high yields in the fermentation processes [5][6][7]; (b) improving the process control, which is done by the continuous operation, product separation, and removal of the metabolic inhibitors, as well as by the improving product recovery (continuous extraction); (c) permitting recycling of the biological catalyst; 2 International Journal of Polymer Science (d) maintaining the biocatalyst in a stable and active state (the extension of the stationary phase); (e) protecting sensitive cells against destruction (e.g., shear forces); and (f) reducing the risk of microbial contamination.…”