CHARACTERIZATION OF LIQUID FRACTION OF STEAM ASSISTED PYROLYSIS PRODUCTS OF ARUNDO DONAX AND HEMICELLULOSE, CELLULOSE AND LIGNIN MIXTURES

Slow steam pyrolysis of Arundo donax is proposed as possible process for the recovery of a solid material suitable to be used as biochar. In view of the evaluation of the feasibility of such a process, products yields, char properties and energetic content of gaseous and liquid products (bio-oils), needed to assist energetically the process, are relevant data to be evaluated in dependence on process operating conditions and biomass characteristics. Biomass main components (hemicellulose, cellulose and lignin) contribute to a different extent to the determination of products yield and characteristics both for their own intrinsic chemical nature and for the onset of possible interactions due to their simultaneous presence in a real biomass. Moreover, it is known that inorganic elements present in the biomass can affect pyrolysis mechanisms and consequently products yields and characteristics. The investigation of combustion behavior of bio-oils cannot disregard the analysis of their chemical composition responsible of their peculiar chemical and physical properties: chemical instability, high density, viscosity and surface tension, low pH and calorific value, a wide evaporation range represent critical aspects for their utilization in the traditional combustion systems. Definitely, chemical characterization of pyrolysis derived bio-oils is fundamental to investigate their reactivity in view of the exploitation of their energetic content. In the present aper the influence of inorganic species and of possible interactions between biomass main components on liquid derived from pyrolysis of Arundo donax has been studied. To this aim steam assisted pyrolysis ests have been carried out on a mixture of hemicellulose, cellulose and lignin resembling the composition of Arundo donax canes in a proper experimental apparatus up to 973 K, at pressure P=5×105 Pa and heating rate HR=5 K/min. Liquid composition has been compared to the data computed from the superposition of the results obtained for the single components and to the behavior of untreated and emineralized sample of Arundo donax canes processed in the same experimental apparatus at the same operating conditions. Given the high chemical complexity typical of these liquids, an overall haracterization has required the application of different experimental approaches and analytical techniques leading to the tailoring of specific analytical procedures to face the high dilution of pyrolysis liquid in process water.