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ThermalNet, WP 2A: Characterisation and Analysis.

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Table 1. Analytical methods for wood-based pyrolysis liquids

Analysis Method Comment
Water, wt % ASTM E 203 1
Homogeneity 7-day standing test 2
Solids, wt % MeOH-DCM-insolubles 3
Si, wt % XRF, ICP 4
Flash point, C ASTM D 93 5
Stability test 80 C, 24 hours 6
Viscosity (20 and 40 C), cSt ASTM D 445 7
Viscosity, mPas Rotational viscometry 7
Density (15 C), kg/dm3 ASTM D 4052 8
HHV, MJ/kg DIN 51900 9
LHV, MJ/kg HHV [J/g] - 218.13 x H% [wt %]. 9
Particle size distribution Microscopy and particle counter 10
Ash, wt % EN 7 11
CHN, wt % ASTM D 5291 12
Sulfur and chlorine, wt % Capillary electrophoresis 13
Metals, wt % AAS, ICP 14
Pour point, C ASTM D 97 15
pH pH meter 16
  1. Karl-Fischer titration. 50 ml solvent for two determinations. Sample size about 0.25 g (water content >20 wt %). Stabilization time 30 s. Sample solvent chloroform:methanol (1:3), K reagents (Composite 5K and Working Medium K) in case of a fading titration end-point. Titration reagent e.g. 2-methoxyethanol. The system is calibrated with pure water (25 µm distilled water), water standards (e.g. 5mg water/ml MERCK 1.09259 250), and using the water addition method [5]. Accuracy of the titre is re-checked on daily basis. Titration is done in triplicates.
  2. In the method [6] a homogenous sample is let to stand for a week in room temperature and the water content from different depths are determined by Karl Fischer titration. Criterias for poor-quality liquid product are: water content above 30 wt % and/or duplicates differ more than 1 wt %.
  3. Solids content of pyrolysis liquids is recommended to be measured as insoluble material in MeOH (methanol)-DCM (dichloromethane)-solution (1:1). In the method the sample size (1, 5, 10 g) is determined in order to obtain 10 - 20 mg of dry solid residue. A representative sample of pyrolysis liquid is dissolved in excess (10 folds) of solvent. The solution is filtered through a 1 µm pore size filter (i.e. Schleicher & Schüll, GF50, ? 47 mm, glass fibre papers) using e.g. Millipore or multi-place filtration system,. The solids content is calculated based on the original pyrolysis liquid sample. Maximum 10 wt % difference between duplicates can be accepted. Ethanol can also be used for white wood liquids if similar solid content is obtained. This solvent does not dissolve properly all extractives in bark-containing liquids.
  4. Si and metals can be analysed from ash either by XRF (X-Ray Fluorescence spectrometry) or by ICP (Inductively Coupled Plasma Emission spectrometry).
  5. Elimination of air bubbles before sampling. The flash point cannot be measured for pyrolysis liquids at 70–100°C, where the evaporation of water suppresses the ignition [5, 6].
  6. The use of accelerated ageing test (24 h @80°C, viscosity @40°C) is recommended as a rapid test for measuring the stability [14]. In the method pyrolysis liquid is mixed properly and let to stand, until the air bubbles are removed. 90 ml of the sample is poured in 100 ml tight glass bottles (or 45 ml in 50 ml bottles). The bottles are firmly closed and pre-weighed before placing to 80 °C in a heating oven. The bottles are re-tightened a few times during the heating-up period. After 24 hours the closed sample bottles are cooled under tempered water, weighed, and analyses are performed. The samples are mixed and measured for viscosity and water. The viscosity of the liquid at 40 °C is measured as kinematic viscosity by the standard method ASTM D 445. The water content is analysed by Karl Fischer titration according to ASTM E 203. For obtaining representative results the test should each time be carried out exactly by the same way.
  7. Cannon-Fenske viscometer tubes at room temperature and for non-transparent liquids, Ubbelohde tubes may be used for transparent liquids. No prefiltration of the sample. Elimination of air bubbles before sampling. Equilibration time 15 minutes. Dynamic viscosity by rotating viscotesters can also be used for measuring the viscosity of pyrolysis liquid, eventhough it is not as accurate as kinematic viscosity. The evaporation of the sample can cause too high viscosity values, especially above 60°C, and hence a cover should be used on the sample cup.
  8. Careful mixing of foam-prone forestry residue liquids in order to avoid air bubbles. The method covers the materials which can be handled as liquids between 15 oC and 35 oC. Vapor pressure of the samples should be lower than 80 kPa and viscosity below 15 000 mm2/s.
  9. Use of a fine cotton thread for ignition. The heat content of the thread is subtracted from the result. No subtraction of free water has to be done [5] because the water in the pyrolysis liquid cannot be removed by centrifugation as for heavy petroleum fuel oils.
  10. Light microscopy with photoanalysis program (Leica Qwin).
  11. Controlled evaporation of water to avoid foaming.
  12. Because of the small sample size, the reproducibility of the elemental analysis is dependent on the homogeneity of pyrolysis liquids. At least triplicates are recommended, if the sample is inhomogeneous. As large a sample size as possible.
  13. Sample pretreatment by combustion according to ASTM D 4208.
  14. Wet combustion as a pretreatment method. In samples with a large amount of silicates, Si can precipitate as SiO2 during the sample pretreatment. For accurate determination of Si, the sample should be ashed by dry combustion and a fusion cake prepared from the ash.
  15. No preheating of the sample.
  16. The fouling of electrodes causes error to the result. Hence pH is recommended to be used mainly for determination of pH level [14].Cleaning and calibration of the pH meter after each measurement.
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