This paper reports the physico-chemical characteristics of the products derived from the thermolysis (thermolytic distillation) of waste silver fir (Abies alba Mill.) wood at different temperatures (400℃- 600℃) in a pilot scale plant. Depending on the thermolysis temperature, the procedure yielded 45 - 53 wt% pyroligneous acid with a high water content (80 - 86 wt%) and pH ≈ 3.6. The process also produced a carbonaceous solid or biochar (23 - 26 wt%), its properties strongly dependent on the thermolysis temperature. Gases (20 - 31 wt%) were also produced; these were transformed into electrical energy via a gas turbine. The pyroligneous acid was centrifuged to isolate a subfraction composed mostly of phenols (phenol, mequinol and furfural) with a total C content of 68 - 74 wt%. The remainder was subjected to fractionated distillation at laboratory scale, and the distillate subjected to liquid-liquid extraction using diethyl ether in two stages to obtain a bio-oil composed mainly of acetic acid (≈47%), aldehydes, ketones and alcohols (≈31%), phe- nols (≈18%) and aliphatic alcohols. The characteristics of the bio-oil depended on the thermolysis temperature.
Lignocellulose biomass is the only renewable source of fixed carbon that can be converted into liquid, solid and gaseous fuels with no contribution to net CO2 emissions. The pyrolysis of biomass is a promising method of producing solid (charcoal), liquid (tar and other organic compounds) and gaseous products [1-3] that could provide alternative sources of fuel and chemicals [
The silver fir wood used in the present work came from the clearing of forests in the Catalan Pyrenees in Spain’s northeast. All wood was reduced to a size of 250 × 100 × 50 mm before thermolysis. Proximate and ultimate analysis of this waste wood (WW) was performed using a LECO TGA 701 analyser and a LECO CHNS 923 analyser respectively. Its higher heating value (HHV) was estimated using an IKAWEEME C4000 automatic bomb calorimeter. The lignin content was determined using the Tappi method T22 [
aWeight percentage (in terms of dry mass); bBy difference.
aWeight percentage (in terms of dry mass).
The non-condensed gases were filtered and the gas led to a TOTEM (Total Energy Module) turbine (3) for the production of electricity. Batches of WW were heated for 4 h (treatment capacity 18 kg×h−1) at 400˚C, 500˚C and 600˚C. After completing the thermolytic process, the reactors were cooled for 4 h, opened, and the biochar removed by aspiration. The composition and yield (by weight) of the PA and biochar fractions were then determined; the difference between the weight of the initial WW sample and the combined weights of the PA and biochar is equal to the weight of the gas produced. The PA (2) was then centrifuged, producing a heavier tar fraction (4) and a lighter fraction (5). The latter fraction was separated into its components in a Vitreux fractionated distillation column. The residue left over (7) was added to the tar fraction obtained by centrifugation (4) to produce a combined fraction (8). The distillate from the fractionated distillation process (6) was extracted with diethyl ether (proportion 1:3 by volume) in two stages to obtain an aqueous (9) and an organic fraction (10). The organic fraction was evaporated in a rotary evaporator at 42˚C to recover the ether and obtain a final bio-oil (11).
The proximate and ultimate compositions of the PAs, bio-chars and bio-oils produced at each thermolysis temperature were determined using an automated LECO CHNS 923 analyser. Their HHV was determined using an IKAWEEME C4000 automatic bomb calorimeter. The water content of these products was determined by KarlFischer titration using Hydranal Composite 5K [Fluka] and employing a Karl-Fischer MKS-520 Moisture Titrator apparatus. The total acid number (TAN) was determined in a KEM Mod. AT-500N automated potentiometric titrator with two electrodes (glass and reference). The titration agent was a standard solution of KOH (F = 1). The bio-oils were also analysed by gas chromatography/mass spectroscopy (GC/MS) using a SHIMADZU GCMS-QP2010-Plus apparatus equipped with a 10 m × 0.1 mm × 0.1 µm TRB-5MS TEKNOKROMA capillary column (95% dimethyl-5% diphenyl polysiloxane). Samples of the gases produced at each thermolysis temperature were collected from the uncondensed gas exit tube after having passed through water, activated carbon and lead carbonate solution filters; all samples were captured in TEDLAR® bags. The samples were then analysed by gas chromatography using a HEWLETT-PACKARD 5890 gas chromatograph equipped with a Porapak N and Molecular Sieve multicolumn system, a thermal conductivity detector (TCD) and a flame ionisation detector (FID). The porous characteristics of the chars were determined using a Beckman Coulter SA1100 automatic adsorption analyser. Their surface areas were determined using the BET equation in the p/p0 range 0.015 - 0.15 (r2 > 0.9999).
The TAN for this light fraction remained practically constant at around 13 g/l. The pH also remained constant at approximately 3.6. Fractionated distillation of the light fraction and subsequent extraction showed water soluble compounds to be the major component (9). The tar (8) and bio-oil (11) yields fell with increasing thermolysis temperature.
The yield of biochar decreased with increasing thermolysis temperature, due either to the greater primary decomposition of the biomass at higher temperature, or secondary decomposition of the char residue. Such secondary decomposition at higher temperatures may also
have given rise to some non-condensable gaseous products that contributed to an increasing gas yield with the thermolysis temperature.
a consequence of a reduction in H2 and CH4. However, the electrical energy production (Θ) via the gas turbine increased with temperature (range 434 - 562 kWh×t−1), a consequence of the relatively greater CO volume. The mean yield of the turbine was 70%.
aWeight percentage (in terms of dry mass); bBy difference.
88.9%. This corresponds to a very high C content (92%).
The biochars had essentially a macroporous structure (
The bio-oil was composed mostly of carboxylic acids (acetic acid ≈ 40% [in terms of the area of the gas chromatography peak], propanoic acid ≈ 4%, and butanoic acid ≈ 2%) derived from plus aldehydes and ketones (furfural, 2-propanone 1-hydroxy and 2-cyclopenta-1-one) derived from the breakage of the cellulose bonds. Phenols (phenol,2-methoxy phenol and 1,2 2-methoxy-5- methylphenol) produced by the depolymerisation of lignin and alcohols (mequinol and glycerine) were present in smaller proportions. The quantity of aldehydes and ketones fell with increasing thermolysis temperature (39% at 400˚C compared to 30% at 600˚C). The content in carboxylic acids and phenols did not vary significantly, remaining at around 44% and 17% respectively. The alco
VT: Total pore volume estimated at P/P0 = 0.95 (cm3/g); V micro: Micropore volume (cm3/g); Vmeso: Mesopore volume (cm3/g); L0: Average width of the micropores (nm); Smicro: Micropore surface area (m2/g); Sext: External surface area (m2/g); SBET: BET surface area determined by N2 adsorption at 77 K (m2/g).
aWeight percentage (in terms of dry mass); bBy difference.
hol content rose slightly with temperature from 1% at 400˚C to 4% at 600˚C. The bio-oils obtained at the different temperatures had pH and density values, O and H contents and HHVs similar to those of other pyrolytic bio-oils, though their C content was slightly lower [
This work focuses on the valorisation of waste silver fir wood via a simple thermolysis process. Its success lies mainly in the large amount of energy recovered from the gases generated. The biochars produced show great aptitude for CO2 capture, and could be used as activated compounds in animal feed for the removal of toxins from the intestinal tract. However, unlike that seen with other pyrolytic techniques, the present procedure produces large quantities of pyroligneous acids, the transformation of which into bio-oils is poor in terms of yield. Nonetheless, the properties of the bio-oils thus obtained are similar to those obtained by other pyrolytic techniques.
Dr. O. Rodríguez is the recipient of contract JAEDoc_ 09-00121 (CSIC), co-funded under the FSE 2007-2013 Multiregional Adaptability and Employment Operational Programme. The experimental work undertaken was performed with the financial support of ENRECO 2000 Ltd.