## 1 Introduction
GC/MS and FTIR analyses of bio-oil produced from empty palm fruit bunches showed that it contained esters, nonane, acids and phenols [13]. The oil phase from the co-pyrolysis of different refuse-derived fuel (RDF) samples in a rotary kiln reactor at 500 \({}^{\circ}\)C consisted of n-aliphatic, branched aliphatic compounds and primary alcohols [21]. Very few investigations have analyzed the physicochemical features of bio- oils from forest waste. In one study, the physical properties of bio- oils produced from pitch pine and Japanese cedar using fast pyrolysis at 500 \({}^{\circ}\)C, including pH, water content and viscosity, as well as elemental analysis and calorific value, were found to be similar regardless of feedstock. These bio- oils were acidic (pH = 2.4-2.5), had water contents of 20-24%, and their heating value was determined to be 18-19 MJ/kg [17]. In another study, a fast pyrolysis bio-oil, produced at 450 \({}^{\circ}\)C from softwood sawmill residues in a pilot-scale auger reactor, was distilled in an advanced distillation curve apparatus at atmospheric pressure and at a vacuum of 5 kPa, and a thermodynamic model was used to predict its bulk physicochemical properties. The density of oil was 1.2 g/mL, the water content was 23.7%, the solid content was 3.75%, the kinematic viscosity at 40 \({}^{\circ}\)C was 18.1 cSt and the gross heat of combustion was 18.2 MJ/kg [22]. Some studies have examined the catalytic pyrolysis of forest residues using CaO, MgO, alkali carbonates, zeolites, bauxite ores and marble dust to improve the quality of the bio-oil in terms of oxygen content [23; 24]. With regard to the gases evolved during the pyrolysis of sawdust and various agricultural residues, including rice husk, date seeds, banana peel and coffee residues [8; 25; 26; 27; 28; 29], GC, TG/MS or TG/FTIR analysis techniques were employed, mainly for qualitative measurements and to identify the evolution pathway/mechanism. Analyses of gaseous components from forest residues are rare. The effect of alkali and alkaline metals on gas formation behavior during the pyrolysis of pinewood was examined. It was observed that alkali metals enhanced gas yield at low temperatures, while they reduced it at high temperatures [30]. Forest and organic waste materials are generated in vast quantities around the world. The availability of energy from forest waste could range from 10 to 16 EJ/y globally, while that from municipal solid waste (MSW) could vary from 1 to 3 EJ/y, depending on the composition, consumption pattern and economic development. In Greece, about 1.7 Mt of forest waste and 3.5 Mt of MSW are produced annually [31]. Woody residues from forests, with very low ash content and high calorific value, could be very useful for the production of biofuels [32]. MSW, on the other hand, with its diverse composition and problematic elements in the ash produced, creates technical and environmental barriers [33; 34], and requires a detailed study of its properties and uses in order to accelerate its promotion in the energy sector. As discussed above, there is limited research on the physical and chemical properties of all solid, liquid and gaseous pyrolysis products as a function of temperature, particularly in reference to forest residues and MSW, and there is lack of information on the pyrolysis products of RDF from municipal solid waste fractions. Accordingly, the present work aimed to quantitatively characterize the products generated from fixed bed pyrolysis of selected forest waste and RDF, to determine their energy potential and to predict the slagging/fouling propensities of the ash they produce, in order to evaluate their suitability as energy sources. Various techniques, such as elemental analysis, bomb calorimetry, X-ray fluorescence spectrometry, Couette viscometry and TG-MS (thermogravimetric-mass spectrometry), were employed for the quantitative measurements.