STRUCTURAL CHARACTERIZATION OF BIOMASS PYROLYSIS TARS OILS FROM EUCALYPTUS WOOD WASTE - EFFECT OF H-2 PRESSURE AND SAMPLE CONFIGURATION/

Changes in yields and structural characteristics of tars/oils produced in the first stage of a two-stage fixed-bed ('hot-rod') reactor were determined as a function of sample configuration and pressure. The wor k included a critical evaluation of analytical methods for monitoring structural changes in biomass-derived liquids. Total volatile and tar/ oil yields decreased and significant structural changes were observed with increasing sample bed height and pressure, leading to 'lighter' t ars/oils. Products were observed to become more aromatic and less oxyg enated. Less intense degradation reactions were observed under hydroge n than under helium. 1-Methyl-2-pyrrolidinone (NMP) was used as eluent in size-exclusion chromatography; solubility limitations were found w ith tetrahydrofuran as eluent. Good agreement was obtained between str uctural changes inferred from size-exclusion chromatography and u.v. f luorescence and u.v. absorption spectroscopies. The characterization o f liquid products by H-1 n.m.r. was found to be less informative than expected, due to the multiplicity of structural assignments in relativ ely narrow bands. The work suggests that mild hydropyrolysis in Peeper beds may be considered as a process step more likely to produce light er, less oxygenated and more stable tars/oils than liquids produced at atmospheric pressure. However, the reforming process achieved by extr aparticle reactions and by the effect of pressure gave rise to signifi cant loss of liquid product. (C) 1997 Elsevier Science Ltd.