Environmental Engineering Reference
In-Depth Information
Such approaches provide a means of verifying the origin of a product, though
this is relatively costly and time consuming. This approach is adopted in many
standards, including
ASTM D6866 Standard Test Methods for Determining the
Biobased Content of Solid, Liquid and Gaseous Samples Using Radiocarbon
Analysis
, used to determine and independently audit the biobased content of listed
products in the US BioPreferred Programme. This approach is also adopted in
assessing the biobased content of polymers (CEN/TS 16137).
While this approach may enable quantification of bio- and fossil-derived
ethanol produced from mixed fossil and biomass feedstock streams for example,
this approach is not universal in its applicability (even within the energy sector).
In Europe for example, the use of carbon ratio isotope analysis has been advocated
for measuring the carbon isotope ratio in CO
2
emissions from power plant stacks
fuelled by mixed waste. These would then be used to reward the energy generation
deemed to be derived from biomass combustion on a similar proportionate basis.
However, biomass materials tend to be partially oxygenated compared to fossil
feedstocks such as polymers. Most biomass-derived feedstocks therefore tend to
have lower calorific values and contribute less to power generation for the same
level of carbon throughput. Such approaches therefore have to be supported by
additional analyses.
In addition, changes in product formulation may have no (or in contrast, a very
significant) impact on the biobased content of a material (assessed on a biogenic
carbon basis) as an example from Beta Analytics [8] demonstrates:
A hypothetical fibreboard composite containing 30% silica with 70% cellulose will
have a bio-based content of 100%. If the formula is modified to contain 20% silica
and 80% cellulose, the fibreboard will still be 100% bio-based. All the carbon in the
fibreboard is still coming from the cellulose.
If the silica is replaced with graphite fibres derived from petrochemicals (100%
fossil carbon), the bio-based content will decrease significantly. The cellulose
(which itself is only 44% carbon) now represents a significantly smaller proportion
of the total carbon in the fibreboard. The same composite, now made with 70%
cellulose and 30% carbon fibres will only be 51% bio-based.
8.6.1.2
Mass Calculations
Reporting on biobased content by weight percentage follows directly from the
'recipe' the producer uses. For example, a copolyester blend of 30% cellulose by
weight and 70% fossil-based copolyester by weight would be classed as having
30% biobased content. The carbon isotope approach would show a much lower
biobased value in this instance, as a much higher proportion of the cellulose
element comprises oxygen.
Given the difference in outputs, some companies use both methods [9]. For
example, for its biobased Sorona product description, DuPont quotes both the
biobased carbon content (28%) and the renewable content by weight (37%).
