(56k) Development of Cellulosic Aerogel for Oil Spill Treatment

Wang, Z., Imperial College London
Cellulose is the most abundant organic polymer on earth and is used to manufacture an aerogel for butanol separation from water. It is a polysaccharide consisting of D-glucose and is inherently renewable due to its origin; green plant and bacteria cell walls. Cellulose can be accessed in its pure form from seed hairs of cotton, or in its native composite material with lignin and hemicellulose.
Cellulose aerogels have received academic attention for use as an effective sorbent. Cellulose aerogels have been successfully used for the absorption of oil and dyes which can be owed to its high porosity and very low density.
Cellulose is inherently highly crystalline, and many inter- and intra- molecular hydrogen bonds are present which makes cellulose insoluble in water and most organic solvents.
The synthesis of a hydrogel is initiated when cellulose is dissolved and many solvents have been investigated such as N-methylmorphine-N-oxide (NMMO), lithium chloride/N,N-dimethylacetamide (LiCl/DMAC), NH3/NH4SCN, and NaOH/PEG. NaOH/urea was chosen due to its success as a solvent for cellulose as well as its availability and environmental-friendliness compared to the alternatives. Hydrochloric acid is used for the regeneration of cellulose. The gelation step involves the use of an anti-solvent to extract solidified castings from the previous step and initiate cellulose aggregation. Many different antisolvents can be used and are investigated, namely, acetone, methanol, ethanol, propanol, and sulfuric acid.
The hydrogel can be converted to an aerogel through various techniques with the most common being supercritical CO2 exposure. Freeze drying has also been investigated with successful formation of a cellulose aerogel through lyophilization. Lyophilization is achieved as the vacuum creates an atmosphere that favours sublimation where ice crystals change directly from solid to vapour without passing through a liquid phase. Cellulose is inherently hydrophilic due to the presence of hydroxyl (OH) groups so must be treated to achieve the necessary level of hydrophobicity to be used as an effective sorbent for butanol in water.