Isolation and purification of concentrated and non-concentrated hemicellulose alkaline extracts

•Xylans are extracted from bleached pulp, with NaOH, to give an alkaline extract.•Isolation of xylans from alkaline extract is made by precipitation with HNO3.•Precipitates are washed either with methanol or water for purification.•High purity xylans (by FTIR) are obtained for acid precipitation and...

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Bibliographic Details
Published in:Separation and purification technology 2017-02, Vol.173, p.233-239
Main Authors: Silva, Felipe F., Alves, Ana Maria Brites, de Lurdes Serrano, Maria, de Sousa, António P. Mendes
Format: Article
Language:English
Subjects:
Consumption
Eucalyptus globulus
Extraction
Hemicellulose
Methyl alcohol
Nitric acid
Precipitates
Precipitation
Purification
Reduction
Ultrafiltration
Xylans
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Summary:•Xylans are extracted from bleached pulp, with NaOH, to give an alkaline extract.•Isolation of xylans from alkaline extract is made by precipitation with HNO3.•Precipitates are washed either with methanol or water for purification.•High purity xylans (by FTIR) are obtained for acid precipitation and water washing.•The isolated xylans had molecular weights between 24,100 and 31,000Da. The xylan rich filtrate obtained from alkaline extraction of bleached pulp was isolated by precipitation followed by washing and drying of the precipitate. This isolation/purification process was applied to a filtrate as is (non-concentrated) and to a filtrate previously concentrated by ultrafiltration (UF). The advantages achieved by implementing the UF concentration process are significant when compared with results obtained with the non-concentrated filtrate. The membrane used in the concentration step, UFX5pHt, (MWCO 5kDa), has an average flux of 30L/h/m2 for previously optimized conditions of cross flow velocity (1ms−1) and operating pressure (6bar). Xylans were isolated from the concentrated filtrate using two different methods: neutralization/precipitation with HNO3 (7.5N), and precipitation with methanol (20, 30, and 50wt/wt%). For the concentrated filtrate a reduction of up to 61% in the consumption of nitric acid for the precipitation was achieved. On the other hand, products of lower purity were obtained with methanol as precipitating agent. The molecular weights of the obtained xylans were determined by SEC leading to values between 24,100 and 31,000Da.
ISSN:1383-5866
1873-3794
DOI:10.1016/j.seppur.2016.09.033