Areas of Work
Biogenic Carbon

For the purposes of energy production, materials, which consist exclusively of organic matter (high heating value), are combusted in heating and power plants and in energy-intensive industries. On the one hand, these materials are products from renewable resources like paper, board, or wood (biomass), on the other hand they consist of combustible synthetics, which are primarily attained by polymerization, e.g. polyethylene or poly-propylene and long-chained hydrocarbons.

In general, both sorts of combustible materials are used in the heating and power plants. Hence, these materials are a mixture of bio-mass and synthetics. To classify the used combustible material it is important to determine the respective mass fractions of both of the material groups.

The determination of the ¹⁴C content in the carbon of the combustion material is a sophisticated method for the determination of the renewable fraction (radiocarbon dating).

The characteristic ¹⁴C content of the carbon in both categories allows the direct determination of the fraction of biomass in a mixed sample, considering the mean carbon content of both, biomass and synthetics

In addition, the determination of the isotope ratio ¹³C/¹²C (= δ¹³C value) of the combustion material allows the verification if the carbon is exclusively of organic origin or if there is an admixture of inorganic carbon (carbonate).

The atmosphere contains the β-radiating carbon isotope ¹⁴C in traces in the carbon dioxide (CO₂). In the course of geological development, an equilibrium concentration of ¹⁴CO₂ was established in the atmosphere. The equilibrium concentration currently corresponds to 13.56 ¹⁴C decays per gram carbon per minute. This activity concentration is defined as 100 % modern carbon (also 100 pmc, percent modern carbon, or in Germany shortly: 100 % - modern). Due to a half time of 5760 years of the radioactive carbon isotope ¹⁴C, it can be used for age determination of historic and prehistoric organisms and substances (radiocarbon dating).

Biological, i.e. plant material is composed by means of photosynthesis from the carbon dioxide in the atmosphere. The ¹⁴C content of the materials of plantal origin corresponds therefore exactly with the atmospheric carbon dioxide, i.e. 100 % - modern. Even if paper, which was produced from the wood of a 50 years old tree, is part of the mixture of fuels, it is analytically not distinguishable from other plantal materials of the past few years due to the high half-life of ¹⁴C. Taking into account the measurement accuracy of the method, the obtained results would be 100 % - modern in both cases.

The carbon of today's synthetic plastics origins practically exclusively from fossil carbon sources (oil). This material has such a high age that it doesn’t contain any ¹⁴C. The ¹⁴C content in synthetic plastics therefore corresponds to 0 %-modern.

Between these two extreme values (biomass: 100 %-modern, fossil sources: 0 % - modern) there is not known any other ¹⁴C content, or rather it is not conceivable for fuels. Therefore it is possible to determine the biomass percentage of a fuel mixture by an appropriate mixture calculation. This calculation bases on the assumption that the mean carbon content in biomass is 44 % and 85 % in synthetics.

The crushed sample material is dried and burned entirely in a combustion apparatus (bomb calorimeter). By this process, carbon dioxide (CO₂) is generated, whose carbon is completely derived from the fuel material. The CO₂  is separated from the combustion gas in several purification steps.

A portion of the carbon dioxide is used for the determination of the δ¹³C value. However, most of it gets dissolved in an absorber liquid and prepared as a measurement sample (cocktail) after the addition of a scintillation solution.
By applying Liquid Scintillation Counting (LSC) to the measurement cocktail, the proportion of ¹⁴C content of the analyzed sample is determined. Taking the mean carbon content in biomass and synthetics into consideration, the proportion of biomass in a mixed sample then can be identified.

A power plant operator is offered a delivery of a combustion material which consists of biomass and synthetics. The supplier specifies a particular composition of the combustion material.

This composition has to be verified as on the one hand, the composition of the combustion material determines the quality and thus also the price. On the other hand, electricity which is produced from biomass is rewarded with a significantly higher rate according to EEG (§ 8 EEG). Thus, it is of a considerable interest for the power plant operator to ascertain the actual composition of the offered combustion material in two respects.

The evaluation must be done quickly and reliably.

This can be determined by means of the isotopic signature of carbon (¹⁴C) in the combustion material appropriately.

Radiocarbon dating can also be applied in order to determine the percentage of renewable resources in so-called bioplastics (plastic bottles, plastic bags etc.), as they have recently been advertised by e.g. mineral water producers and discount stores.

Bioplastics are made using new technologies e.g. from molasses, which is a byproduct from sugar fabrication. These packaging synthetics have the same characteristics as conventional crude oil based synthetics, however, they are produced either partly or even 100 % of renewable resources and are easier to recycle.
This percentage of renewable resources can be examined and quantified by means of ¹⁴C determination.

Also the proportion of bioethanol in fuels can be examined by radiocarbon dating.

In Germany, the requirements and test procedures for ethanol fuel are standardized in DIN 51625.

Independently of its production method pure ethanol has consistent properties. There is no chemical difference between fossil ethanol and ethanol from a biological raw material. Physically, however, bioethanol has a considerably higher quantity of the radioactive carbon isotope ¹⁴C.