2nd Generation Ethanol Production Research Articles

Extended fed-batch fermentation of a C5/C6 optimised yeast strain on wheat straw hydrolysate using an online refractive index sensor to measure the relative fermentation rate

In the production of 2nd generation ethanol, using Saccharomyces cerevisiae, the highest productivity obtained using C5/C6 fermenting yeast is in the co-fermentation phase, in which xylose and glucose are fermented simultaneously. Extending this phase in a fed-batch process increases the yield, rate and additionally reduces needed yeast amount for pitching. Extending this phase, as long as possible, would further enhance yield and economy of the process. To realise the concept a fermentation monitoring technique was developed and applied. Based on online measured refractive index an optimal residual sugar concentration could be maintained in the primary fermentor during the feed phase, requiring little knowledge of the nature of the substrate. The system was able to run stably for at least five fermentor volumes giving an ethanol yield >90% throughout the run. This was achieved with addition of only urea to the wheat straw hydrolysate and with an initial yeast pitch of 0.2 g/L total of finished broth. It has the potential to improve the fermentation technology used in fuel ethanol plants, which could help to meet the growing demand for more sustainable fuels.

Rendimento de hidrólise e produção de etanol lignocelulósico a partir de biomassa de capim elefante

Due to search for alternative biomasses, that are easy to access, low cost and high in cellulose concentration, for the production of 2nd generation ethanol - or lignocellulosic - this study was carried out with Pennisetum purpureum, known as elephant grass. The study was conducted to determine the chemical composition of elephant grass forage to evaluate its use in the production of lignocellulosic ethanol. The elephant grass stems were reaped in the experimental area of Feira Agrotecnologica de Palmas (AGROTINS) on august 2015. The results have shown that the elephant grass presented approximately 60% cellulose, demonstrating the potential use of this biomass to obtain reducing sugars. The biomass underwent chemical pretreatment before the enzymatic hydrolysis step using commercial cellulase enzyme Cellic CTEC2. After hydrolysis, gave a 54% yield of reducing sugars, which has shown a yield of 53,9% in the hydrolysis. In addition, the yield for ethanol production was 87,8%. Due to this, it is possible to assure that the elephant grass biomass has a great potential as cellulose source, therefore it can be used as an alternative that is cheap and huge in availability to the production of lignocellulosic ethanol.

Perspectives on the production of polyhydroxyalkanoates in biorefineries associated with the production of sugar and ethanol

Polyhydroxyalkanoates (PHA) are biodegradable and biocompatible bacterial thermoplastic polymers that can be obtained from renewable resources. The high impact of the carbon source in the final cost of this polymer has been one of the major limiting factors for PHA production and agricultural residues, mainly lignocellulosic materials, have gained attention to overcome this problem. In Brazil, production of 2nd generation ethanol from the glucose fraction, derived from sugarcane bagasse hydrolysate has been studied. The huge amounts of remaining xylose will create an opportunity for the development of other bioprocesses, generating new products to be introduced into a biorefinery model. Although PHA production from sucrose integrated to a 1G ethanol and sugar mill has been proposed in the past, the integration of the process of 2G ethanol in the context of a biorefinery will provide enormous amounts of xylose, which could be applied to produce PHA, establishing a second-generation of PHA production process. Those aspects and perspectives are presented in this article.

Assessment of sugarcane trash for agronomic and energy purposes in Brazil

Due to new possibilities for using sugarcane (Saccharum spp.) trash for electricity generation, and the production of 2nd generation ethanol and others chemicals, the interest for its recovery has increased. However, the question of how much trash can be removed from sugarcane field still needs to be clarified. This study evaluated the amount of dry matter, nutrients content, structural compounds and efficiency of the enzymatic hydrolysis of the hydrothermal pretreated materials for tops and dry leaves in samples from sugarcane varieties. Tops and dry leaves present differences in nutrients content and moisture. Therefore, the amount of trash to be collected should not be simply based on percentages, but also should take into account the different fractions of the crop residues. For instance, around 80 % of N, P and K were derived from tops. Therein, the environmental indicators of the entire chain of sugarcane could be benefited because more nutrients would be recycled and less mineral fertilizers might be used for sugarcane production if tops are left on the field. Further, the tops have seven times more moisture than dry leaves and higher amounts of extractives (organic compounds of low molecular weight). Moreover, as the result of yield obtained in the pretreatment steps for dry leaves were superior to the tops and the glucose yields obtained in the enzymatic hydrolysis step were similar, it can be predicted that for second generation ethanol production, it is more viable to recover parts of the dry leaves fraction, leaving the tops on the field.