Synthesis of cellulose-based flocculants and performance tests

Dissertação de Mestrado em Engenharia Química apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.One of the objectives of this work was to synthesize water soluble cellulose-based flocculants using extracted cellulose from Eucalyptus Kraft bleached pulp. Both cationic and anionic flocculants have been synthesized based on information from the in literature. To increase cellulose reactivity, it was applied cellulose alkalization with NaOH aqueous solution and oxidation by sodium periodate. The cationization of cellulose was performed by using CHPTAC (3-chloor-2-hydroxypropyl trimethylammonium chloride) as reagent. The anionization was performed by using sodium metabisulfite as reagent. Some reaction variables have been changed in order to synthesize flocculants with different characteristics. Once the water soluble flocculants were obtained, they have been characterized according to several techniques in order to determine the effective cellulose modification and other characteristic of the flocculants synthesized. To detect the modification spectroscopy techniques such as FTIR and 1H NMR were used. To characterize the flocculants techniques like like DLS (Dynamic Light Scattering), SLS (Static Light Scattering) and ELS (Electrophoretic Light Scattering) were used, to determine, respectively, the average hydrodynamic diameter of the coils, the molecular weight and the zeta potential. Moreover, from the elemental analysis measurements the degree of substitution (DS) was calculate. The characterization has shown a certain variability of the flocculants obtained in terms of charge and DS as a confirmation that their characteristic can be modulated by tuning the reaction variables. The industrial application of the obtained cellulose-based flocculants was verified in wastewater treatment, in particular in the color removal from model effluents. The dyes selected for the performance test are among the ones frequently industrially used: Crystal Violet (liquid), Malachite Green (liquid) and Duasyn Direct Red 8 BLP (liquid) and Flora red 4bs, Orange 2, Acid Black 2, Basic Green 1 and Brilliant Yellow in the solid state. The performance has been evaluated calculating the percentage of color removed as a function of time, based on the decrease of absorbance of the supernatant water. The results show that both for CC (cationized cellulose) and ADAC (anionic dialdehyde cellulose) color removal percentages over 90% can be obtained for most dyes. Thus, these natural based polyelectrolytes can constitute good alternatives to the use of synthetic non- biodegradable flocculants in the treatment of very common and industrially frequent colored effluents