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Title:
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KBBPPS - Overview of current relevant sampling and biogenic carbon standards on global level
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Author(s):
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Published by:
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Publication date:
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ECN
Environment & Energy Engineering
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18-6-2013
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ECN report number:
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Document type:
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ECN-E--13-035
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ECN publication
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Number of pages:
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Full text:
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66
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Abstract:
In this report all relevant standards on a global level are reviewed with respect to the biogenic carbon content determination. In general it is an overview of all standards that can be used when determining the biogenic carbon content and will give directions when no relevant standards are available.
This review is focussed in all standards concerning the sampling, pre-treatment and C14 determination of all product types, which includes solids, liquids, gasses and mixtures of these. Due to the fact that all three steps in the process of biogenic carbon determination are equally important, all the three steps are covered in separate chapters.
Sampling with respect to biogenic carbon determination
The main purpose of sample preparation is that a sample is reduced to one or more test portions that are in general smaller than the original sample. The main principle for sample reduction is that the composition of the sample as taken on site shall not be changed during each stage of the sample preparation. Each sub sample shall be representative of the original sample. To reach this goal every particle in the sample before sample division shall have an equal probability of being included in the sub-sample following sample division.
Both ISO 13833 and ASTM D7459 give some sampling guides and cover determination of the ratio biomass (biogenic) and fossil-derived carbon dioxide using radiocarbon sampling and analysis.
Solid materials in most cases introduce no practical difficulties in obtaining a representative sample. However, practical difficulties can occur when sampling materials containing volatile components. When sampling, all liquids should be either single phase or relatively homogeneous. The homogeneity in many cases can be achieved by stirring or centrifuging of a sample. Another approach is to separate the clear liquid and the sediment by centrifuging and then to examine them separately. In case of viscous liquids or materials with volatile components the transfer problems exaggerate weighing problems. Effort should be made to obtain the sample weight in the combustion tube, rather than transferring a previously weighed sample to the oxidation tube.
Generally, independently of solid, liquid or gaseous state of a material or product to sample, attention should be paid to representativeness of a sample, its required minimal size, its homogeneity and pretreatment procedure.
Pre-treatment with respect to biogenic carbon determination
Generally, to make all carbon free, material needs to be completely combusted, irrespectively of solid, liquid, or gaseous state of material. After combustion procedure, all available carbon is gathered as CO2 in some absorber: the CO2 present in a representative stack gas sample is absorbed in an alkaline medium or transferred to a gas bag or lecture bottle. After sampling, the collected CO2 is prepared for 14C analysis.
Sampling of CO2 in stack gas is in principle not different from sampling of other acid gaseous substances. As CO2 is present in relatively high concentrations compared to other acidic gaseous substances, the capacity of the absorption media requires careful consideration and excess of alkaline media shall be used to ensure complete absorption during the sampling period.
In this report a list of the Standards that can be used for sample preparation procedures for different samples depending of their state is presented. Due to the large amount of different pre-treatments, care should be taken with regard to the procedure.
For solid sample preparation procedures especially the complete combustion of the material, so that all (also non-organic carbon) is transformed to CO2 is essential.
For liquid sample preparation procedures especially the presence of volatile liquid components is cause for concern.
For gaseous sample preparation procedures care should be taken by the combustion of some gasses, due to the large amount of energy produced. Also care should be taken by combusting mixtures to be sure that a good homogeneous sample is combusted.
Irrespectively of solid, liquid, or gaseous state of materials or products, the American ASTM D6866 standard can be applied if there is no other standardized pretreatment procedure for a specific material or product.
C14 determination with respect to biogenic carbon determination
Generally, there are three methods known for the determination of the bio-based content of materials or products:
a) selective dissolution method (SDM)
b) manual sorting method (MS).
c) biogenic carbon (14C) determination method.
Within the 14C determination method, three techniques are distinguished:
1) AMS - accelerator mass spectrometry
2) LSC - liquid scintillation counting
3) BI - beta-ionization technique
These three techniques are considered to be equivalent. Each of these techniques requires different amount of the CO2: for AMS measurements the minimum amount of CO2 is 4 ml, for BI measurements 2 – 10 liter CO2 is required, and for LSC measurements the required amount of CO2 depends on the way the sample is prepared for measurement, but at least a few gram will be required.
While the selective dissolution and the manual sorting methods allow us only the distinguishing between organic and inorganic content of materials or products, the 14C method and the techniques involved distinguish the 14C and the 12C isotopes and thus allow us the biogenic content determination.
To summarize, the 14C isotope method is applied in a variety of samples to determine the ratio of biogenic and fossil carbon. Biogenic and fossil carbon can be distinguished based on the measured amount of the 14C isotope in the sample.
Complete combustion is carried out in a way to comply with the requirements of the subsequent measurement of the 14C content and shall provide the quantitative recovery of all carbon present in the sample as CO2 in order to yield valid results. The calculation of the bio-based carbon content includes the following steps:
- determination of the total carbon content of the sample expressed as a percentage of the total mass or the determination of the total organic carbon content of the sample expressed as a percentage of the total mass;
- calculation of the bio-based carbon content by mass using the 14C content value, determined by calculation from one of the test methods mentioned in ASTM D6866.
- calculation of the bio-based carbon content as a fraction of the total carbon content or as a fraction of the total organic carbon content.
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