Due to the environmental concerns associated with the use of fossil fuels, the member states of the European Union (EU) like other countries in the world are in the process of developing the use of alternative sources of energy including biomass, wave, and nuclear energies (Rajasekhar
Among the sources of renewable energy, biomass used for biofuel production is obtained from forestry, microbial and agricultural systems (Kim
Liquid form of fuel (known as bio-oil) produced from biomass has several environmental advantages. Bio-oil is considered CO2 neutral and can produce the credits of CO2 without emitting sulphur oxides (SOX) (Fan
The use of biomass to produce biofuels including bio-oils that provide renewable and clean energy is one of the initiatives of the United Nations (UN) implemented for sustainable development goals (SDG) (Arun
To investigate the environmental changes that may be caused by the use of fuels in the member states of the EU, the isotope methods are being developed in several laboratories to determine the biocomponent contents in liquid fuels (Oinonen
Because of old age, fossil fuels no longer contain the measurable 14C whereas the contemporary biosphere contains a lot of this radioisotope. As a result, the Member States of the EU are encouraged to produce energy from renewable resources such as biomass, and tax measures are applied to ensure that biofuel prices are comparable to those of fossil fuels (Dijs
AMS is an ultrasensitive technique to analyse the cosmogenic isotope including 14C, 26Al, 10Be and 36Cl (Tuniz
This study aimed to determine the 14C content in bio-oils by means of a compact modern AMS system known as the Mini Carbon Dating System (MICADAS) in the Gliwice Radiocarbon and Mass Spectrometry Laboratory. The measurement results for the tested biofuels and the biomass used as the reference material were compared. Furthermore, this work will contribute to the accreditation of the tested method in the Gliwice Radiocarbon and Mass Spectrometry Laboratory.
In the present study, four samples were used: three samples of bio-oils from the catalytic process of biomass depolymerisation, and the biomass (pistachio shells) used for their production. The samples were provided by a manufacturer, and according to the information from the Safety Data Sheet the bio-oils are mixtures with the main constituent by weight of 30–90% of distillate-petroleum and hydrotreated heavy paraffinic oil. The other substances are 1H-Pyrrole (<10%) and 4-(2-Methoxyethyl)phenol (<10%), phenol (<8%), diisooctyl phthalate (<7%) and water (<5%).
The 14C measurement by AMS requires graphite targets (Wacker
Radiocarbon measurement process by AMS technique in the Gliwice Radiocarbon and Mass Spectrometry Laboratory. AMS, accelerator mass spectrometry.
The produced CO2 from the combusted samples was graphitized by its reaction with hydrogen (H2) using iron powder as a catalyst. The obtained graphite targets consisting of 1 mg carbon and 5 mg iron were pressed using a pneumatic sample press (PSP) and measured by MICADAS accelerator to get radiocarbon content in the tested bio-oil fuels. Oxalic Acid II standard was used for normalisation, and the 14C-free petroleum prepared in the same way was used as a blank reference. The correction for isotope fractionation is based on simultaneous analysis of 13C and 12C in the AMS spectrometer. The standard uncertainty of the MICADAS is 0.3% for Oxalic Acid II.
Radiocarbon measurement results of all bio-oils and the reference material were reported in percent modern carbon (pMC) which is a percentage of 14C isotope concentration in the so-called modern biosphere. In addition, the calculations of biocarbon content were performed according to the EN 16640:2017 (E) using the following equation for biogenic carbon content relative to the reference value (
The biogenic carbon content in% by mass (
The content of carbon in percentage (% C) by mass was the foremost parameter of concern in this study. According to the results reported in
Reproducibility test for radiocarbon measurements in bio-oil fuels.
Bio-oil-1 | GdA-6968.1.5 | Experiment-1 | 27.72 ± 0.59 | 28.14 ± 0.36 | χ2 = 1.21 |
GdA-6968.1.3 | Experiment-2 | 28.31 ± 0.18 | Significant | ||
GdA-6968.1.4 | Experiment-3 | 28.40 ± 0.19 | |||
GdA-6968.1.2 | Experiment-4 | 29.46 ± 0.56* | |||
Bio-oil-2 | GdA-6969.1.1 | Experiment-1 | 74.71 ± 0.32 | 74.95 ± 0.22 | χ2 = 1.08 |
GdA-6969.1.2 | Experiment-2 | 74.95 ± 0.32 | Significant | ||
GdA-6969.1.3 | Experiment-3 | 75.18 ± 0.32 | |||
GdA-6969.1.5 | Experiment-4 | 76.07 ± 0.32* | |||
GdA-6969.1.4 | Experiment-5 | 73.29 ± 0.32* | |||
Bio-oil-3 | GdA-6970.1.1 | Experiment-1 | 113.00 ± 0.28 | 112.92 ± 0.07 | χ2 = 0.15 |
GdA-6970.1.2 | Experiment-2 | 112.85 ± 0.28 | Significant | ||
GdA-6970.1.5 | Experiment-3 | 112.91 ± 0.28 | |||
GdA-6970.1.3 | Experiment-4 | 110.85 ± 0.40* | |||
GdA-6970.1.4 | Experiment-5 | 110.11 ± 0.41* | |||
Pistachio shell (reference material) | GdA-6971.1.1 | Experiment-1 | 102.58 ± 0.29 | 102.61 ± 0.21 | χ2 = 0.41 |
GdA-6971.1.2 | Experiment-2 | 102.82 ± 0.29 | Significant | ||
GdA-6971.1.3 | Experiment-3 | 102.61 ± 0.29 |
Shows inhomogeneous sub-samples.
Results presented as pMC, and the uncertainties are calculated from AMS measurements.
AMS, accelerator mass spectrometry; CV, critical value; pMC, percent modern carbon.
As can be seen in
However, the main objective of this study was not only in getting the radiocarbon values, but in testing the reproducibility of the sample preparation procedure in the Gliwice radiocarbon laboratory.
Graphical presentation of reproducibility test for radiocarbon measurement in bio-oils by AMS; 2-sigma error bars are invisible at this scale. AMS, accelerator mass spectrometry.
The biogenic carbon content values were determined based on 14C concentration. The results in
Calculated radiocarbon, carbon and biocarbon contents in bio-oil samples.
Bio-oil-1 | GdA-6968 | 79.7 ± 1.7 | 28.14 ± 0.36 | 27.43 ± 0.42 | 21.87 ± 1.76 |
Bio-oil-2 | GdA-6969 | 68.7 ± 2.1 | 74.95 ± 0.22 | 73.04 ± 0.30 | 50.16 ± 2.09 |
Bio-oil-3 | GdA-6970 | 47.0 ± 1.1 | 112.92 ± 0.07 | 110.04 ± 0.22 | 51.73 ± 1.10 |
Reference material | GdA-6971 | 48.82 ± 0.25 | 102.61 ± 0.21 | 100.00 ± 0.29 | 48.82 ± 0.39 |
pMC, percent modern carbon.
Surprisingly, the results showed a higher 14C value of bio-oil-3 (111.94 ± 0.31 pMC) compared to biomass used as reference material (102.61 ± 0.21 pMC). The calculated biogenic carbon content relative to the reference value was also higher for bio-oil-3 (110.04 ± 0.22) compared to the reference sample (100.00 ± 0.29). Additionally, as shown in
Calibration of F14C results for bio-oil sample-3
This phenomenon indicated that only two samples including bio-oil-1 and bio-oil-2 were produced by mixing distillate with the investigated pistachio shell while bio-oil-3 was produced from another unknown biomass whose details were not provided by the sample provider. This conclusion was confirmed by the company that provided the samples, but further information was confidential.
Each aliquot of the original bio-oil sample should always be representative for getting accurate and reproducible results, but in reality, it needs to be tested by running multiple measurements. The findings of the study showed reliable results for the reproducibility test of homogenous bio-oil samples, which proved the precision of the AMS technique by MICADAS for 14C measurement in the Gliwice Radiocarbon and Mass Spectrometry Laboratory. The results for radiocarbon content showed that the submitted reference material (Pistachio) was not used to produce the bio-oil-3. Furthermore, the biogenic carbon content was determined based on 14C content because only carbon was taken into consideration, and no other biogenic elements, such as oxygen and hydrogen, were not considered. Moreover, due to the high increase in demand for biofuels for energy production in this rapidly developing world, many systematic studies on biofuels need to be done to deduce the consequences of biocomponents in different areas such as greenhouse gas emissions, toxicology, and life cycle. Eventually, in the future, additional tests will be conducted using different samples to confirm the precision of the AMS technique in the Gliwice Radiocarbon Laboratory.