Valoración de la fracción hemicelulósica y obtención de furfural a partir de Eucalyptus globulus y paja de trigo

Abstract

The aim of this study was to optimize the production of furfural by some hydrolysis processes (isothermal and non isothermalauthodydrolysis, acid hydrolysis with dilute acid and cold alkaline extraction) of Eucalyptus globulus wood and wheat straw, using factorial experimental design and multiple regression models to maximize furfural yields. Non isothermal autohydrolysis processes for furfural production from Eucalyptus globulus and wheat straw In the first part, samples of Wheat Straw and Eucalyptus globulus were subjected to non-isothermal autohydrolysis, defined by: temperature: 180-240ºC In that form, 4.25 g/100 g raw material (26% of the initial xylan in wheat straw) could be found at 220ºC, and an increase temperature (240ºC) yielded 4.54 g/100 g raw material, 28% of the initial xylan. In Eucalyptus globulus the increase in the hydrolysis temperature (240ºC) yielded liquor with higher contents of furfural (4.45 g/100 g raw material, 25% of the initial xylan) and acetic acid (4.49 g/100 g raw material) and smaller contents of arabinose and xylan. Isothermal autohydrolysis processes for furfural production from Eucalyptus globulus and wheat straw For isothermal autohydrolysis processes, samples of Eucalyptus globulus where subjected to temperature ranges between 220 and 250 ºC and isothermal residence times between 0 and 60 min. The effect of the R0 factor on the sugar yield and composition of both liquid and solid phases obtained after treatments has been studied. A central composite experimental design, in conjunction with the neural fuzzy model, was used to the furfural content maximization under isothermal autohydrolysis. Under optimum experimental conditions, the yield of furfural (4.4 g/100 g dry raw material) could be obtained at 60 min and 220 ºC. For wheat straw, samples of raw material were subjected to isothermal autohydrolysis at same conditions of temperature and residence time that Eucalyptus globulus wood.. In that form, in wheat straw, the increase in the hydrolysis temperature yielded liquor with higher contents of furfural and low xylan contents. Acid hydrolysis processes for furfural production from Eucalyptus globulus and wheat straw To optimize the production of furfural by hydrolysis with dilute acid of Eucalyptus globulus wood, two stages of hydrolysis were used. The optimization process was carried out using a factorial experimental design and multiple regression models to maximize furfural yieldsThe operational ranges are especially suitable for the extraction of xylose, which was virtually quantitative at 170 ºC and virtually independent of the operation time. This is quite important if one considers the low acid concentration used. Conversions to furfural were quite substantial (greater than 10 g/L). Hemicelluloses in the raw material were extracted by 32–57.7% and xylan by 40.5–84%. The highest conversions to furfural were obtained by using a medium operation time (15 min) and low temperature (170 ºC) and pH=2. The review of bibliographic information on the extraction of hemicelluloses from wheat straw seemed to indicate that it might be of a suitable material. In fact, the rates of extraction of hemicelluloses have been acceptable, but the transformation to furfural has been very little effective in the range of operational conditions tested. Cold alkaline extraction processes for furfural production from Eucalyptus globulus and wheat straw In this section, a method for the selective extraction of hemicellulose from wheat straw involving cold alkaline extraction and subsequent separation by precipitation with ethanol is proposed. These hemicelluloses, selectively obtained could be used for their conversion to furfural. The hemicellulose yield was optimized by using a 2n factor design to examine the influence of temperatures from 20 to 40 °C, operation times from 30 to 60 min and alkali concentrations from 80 to 120 g/L. The optimum conditions for cold alkaline extraction of hemicellulose from wheat straw were thus found to be a temperature of 40 °C, an operation time of 90 min and an alkali concentration of 100 g/L. However, in the study of the results obtained from the cold alkaline extraction of hemicelluloses of Eucalyptus globulus wood to low temperature are low concentrations of glucose, xylose, and arabinose in retrieved liquor. The general conclusion is that the wood of Eucalyptus globulus is much more refractory to this extraction process than other materials in the range of variation of the operational conditions tested.