Fractionation of Wheat Bran for Utilisation in Biorefinery
Abstract: Wheat bran is a by-product from the production of wheat flour. Nowadays wheat bran is mostly used as feed for animals, in the food and baking industry or it is simply burned in open air. However, wheat bran could be used in biorefineries for production of value-added products such as bioplastics, biofuels and chemicals as a substitute for fossil feedstocks as petroleum. Since wheat bran is an agricultural by-product it will not compete for field area with other crops. Furthermore, using biomass for the production of energy will not result in an increase of greenhouse gases since the carbon dioxide released in the production of fuels is re-used by the new crops in their photosynthesis. The composition of wheat bran can vary but it consists among other things of starch, protein, lipids, cellulose, hemicellulose and lignin. To enable valorization of wheat bran it needs to be separated into its different components. The components can then be used for different purposes. Starch and cellulose can for example be used in the production of biodegradable packaging materials or for bioethanol production. The aim of this thesis is to develop and compare different methods for extraction and separation of starch, protein, lipid and lignin with the goal that the different components end up in separate fractions with low amounts of impurities. From this thesis work it can be concluded that starch, lipids, protein and lignin can be extracted from wheat bran. During this thesis, starch was extracted through leaching with warm water during different incubation times. The longer incubation time used, the more starch could be extracted. Different solvents, ethanol and hexane, were used in Soxhlet extraction of lipids. It was discovered that starch might be co-extracted with the lipids when using ethanol. This made hexane more suitable to use. Protein was extracted with NaOH and de-ionized water during a three step procedure, where most of the protein was extracted during the first step. Overall this method resulted in a 95 % protein yield. A reduced factorial design with different combinations of temperature, residence time, alkali concentration and solids loading was used for lignin extraction with microwave treatment. It was possible to extract lignin with this microwave treatment; however, there were major difficulties with the separation of the lignin from the rest of the slurry. Several separation techniques were tested to solve this issue. It was discovered that samples treated at 170 °C gave the highest yields. These samples were also the easiest to filter. Sugar analysis on the filtrate showed a very low presence of soluble sugars, which indicates a good separation between lignin and cellulose plus hemicellulose.
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