(193f) Acid Functionalized Nanoparticles for Hydrolysis of Lignocellulosic Feedstocks

One potential source of renewable energy for a sustainable economy is cellulosic ethanol. Cellulosic ethanol has advantages over other ethanol sources such as corn ethanol, in that cellulose is overly abundant and the production of cellulosic ethanol does not require specific crops or influence global food prices. Currently, the limiting factor for the utilization of cellulosic ethanol is the high cost of converting the cellulose into glucose.

The current methods for converting cellulose to glucose involve the use of either enzymes or acids. Enzymes are relatively expensive and cannot be reused. Acids are cheaper, but necessitate costly separations before reuse or require neutralization before disposal. They also have the additional unwanted effect of degrading some of the glucose produced into waste by-products. For cellulosic ethanol to become economically competitive with fossil fuels, the cost of converting cellulose to glucose must be lowered. An ideal catalyst would provide fast conversion of cellulose to glucose, minimal degradation of glucose into waste products, and energy efficient, inexpensive recycling and re-use capabilities.

Nanosized particles with superparamagnetic cores and acidic functional ligands possess the desired catalyst traits. Unlike enzymes, the acidic ligands are stable, and are not poisoned quickly through oxidation. Because the acidic ligands are attached firmly to the particle cores, it is possible to remove the acid catalyst from the aqueous solution simply by removing the particles. Superparamagnetic nanoparticle cores have diameters that are smaller than the magnetic domains of the material, allowing them to be pulled from solution by the presence of a moderate external magnetic field, and return to a non-magnetic state when the external magnetic field is removed.

Preliminary work has been conducted on the ability of some acid functionalized magnetic nanoparticles to catalyze cellulose hydrolysis. Citric Acid functionalized magnetite particles were created according to a procedure outlined by Prasad et. al (2004). Cobalt spinel ferrite (CoFe2O4) particles functionalized coated with a layer of silica were functionalized with sulfonic and perfluoroalkylsulfonic acid according to a procedure outlined in the literature (Phan and Hones 2006; Gill et. al. 2007; Rondinone 1999). The silica coated cobalt spinel ferrite particles were characterized by TEM and FTIR, confirming the monodisperse size of the particles and the attachment of the acid functional groups. The citric acid functionalized magnetite nanoparticles were analyzed by FTIR, and their spectra compared well with published spectra.

Hydrothermolysis of cellulose at 80°C in the presence of the functionalized nanoparticles was seen to be more effective than hydrothermolysis alone, as revealed by analysis of the sugars released into the liquid fraction. Although the nanoparticles did not convert the cellulose directly to glucose, the increased fraction of water soluble sugars indicates that the particles did catalyze the hydrolysis to some degree. Particles functionalized with perfluorosulfonic acid slightly outperformed the citric acid and perfluoroalkylsulfonic acid functionalized particles. The PFS-MNPs' increased capability to break glucosidic bonds was attributed to the higher amount of hydronium ions in solution and the correspondingly lower pH.