Abstract
In order to exploit a fast-growing Paulownia hardwood as an energy crop, a xylose-enriched hydrolysate was obtained in this work to increase the ethanol concentration using the hemicellulosic fraction, besides the already widely studied cellulosic fraction. For that, Paulownia elongata x fortunei was submitted to autohydrolysis treatment (210 °C or S0 of 4.08) for the xylan solubilization, mainly as xylooligosaccharides. Afterwards, sequential stages of acid hydrolysis, concentration, and detoxification were evaluated to obtain fermentable sugars. Thus, detoxified and non-detoxified hydrolysates (diluted or not) were fermented for ethanol production using a natural xylose-consuming yeast, Scheffersomyces stipitis CECT 1922, and an industrial Saccharomyces cerevisiae MEC1133 strain, metabolic engineered strain with the xylose reductase/xylitol dehydrogenase pathway. Results from fermentation assays showed that the engineered S. cerevisiae strain produced up to 14.2 g/L of ethanol (corresponding to 0.33 g/g of ethanol yield) using the non-detoxified hydrolysate. Nevertheless, the yeast S. stipitis reached similar values of ethanol, but only in the detoxified hydrolysate. Hence, the fermentation data prove the suitability and robustness of the engineered strain to ferment non-detoxified liquor, and the appropriateness of detoxification of liquor for the use of less robust yeast. In addition, the success of hemicellulose-to-ethanol production obtained in this work shows the Paulownia biomass as a suitable renewable source for ethanol production following a suitable fractionation process within a biorefinery approach.
Highlights
The depletion of fossil resources and the increase of environmental concerns related to the CO2 emissions are promoting the production of biofuels from lignocellulosic materials
This study aims to evaluate, for the first time, the acid hydrolysis and fermentation of hemicellulose from Paulownia wood to obtain ethanol
Paulownia wood was subjected to autohydrolysis treatment under non-isothermal regime at a severity of 4.08
Summary
The depletion of fossil resources and the increase of environmental concerns related to the CO2 emissions are promoting the production of biofuels from lignocellulosic materials. The processing of this biomass to obtain biofuels, as ethanol, requires costly steps of operation. In this sense, fermentation of all sugars (including xylose from hemicellulosic fraction) would improve the economics of the process by 25% [1,2,3]. Suzuki 2010), is one of the most studied, being able to reach high ethanol yields [11]. Albeit, this yeast is highly sensitive to inhibitors, which can hugely impede its growth, and ethanol production feasibility [12]
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