Direct catalytic conversion of agro-forestry biomass wastes into ethylene glycol over CNT supported Ru and W catalysts

Abstract

This work focuses on the one-pot catalytic conversion of forestry, agricultural and urban waste lignocellulosic materials into ethylene glycol (EG), by an environmentally friendly process that uses only water as solvent, avoiding the use of acids (and the problems associated with their use). Ru and W catalysts supported on commercial and oxidized carbon nanotubes were coupled in the catalytic transformation of the different wastes and the effects of ball-milling and the presence of lignin on the activity were investigated. The properties of the different materials were characterized by several techniques, such as XRD, TG, SEM, EDS, FTIR, determination of contact angles and elemental analysis. Holocelluloses were obtained by removal of lignin from the various wastes and were intensively characterized. Both characterizations and catalytic tests of the different materials were performed before and after pre-treatment (ball-milling and/or lignin removal) to study the properties of biomass and disclose the critical factors for directly converting biomass to EG. The woody biomass (pine, oak, eucalyptus, platanus and australia) as well as pine cones and corncob were the materials that allowed producing a higher amount of EG (over 23 %). Among them, the highest EG yield of 32.4 % was attained after 5 h from the conversion of australia holocellulose. However, since the lignin removal process is not green, the conversion of the original biomass wastes was also evaluated without any pre-treatment besides ball-milling. As expected, due to their higher amount of holocellulose, the woody biomass allowed to obtain higher yields of EG, similar to those obtained from the conversion of cellulosic materials (cotton wool and tissue paper). As result, the maximum yield of EG obtained from forestry residues was increased to 40.7 % in the case of eucalyptus wood. In addition to the woody wastes, if the cellulosic materials are also considered, this maximum EG yield can be still slightly increased to 41.5 %. These results are two of the highest ever reached from the direct conversion of biomass wastes using a green process. Moreover, the catalytic mixture proved to be reusable for at least four successive runs without significant yield loss. As far as we are concerned, there is no report about the direct conversion of raw biomass wastes (or their extracted holocelluloses) into glycols using carbon supported Ru and W catalysts in just water using an environmentally friendly process.