Page 117 - Materials Chemistry, Second Edition

3.3 Allocation 101

5[¤kg ]
−1
Weighting factor B = 300[kg]× = 0.097
15500[¤]
With this allocation thus approximately 90% instead of 70% (= unweighted
mass-proportional allocation) is allocated to the product system A and only
approximately 10% instead of 30% to product system B. The choice of allocation
method thus changes the result of the LCA.
Problems with price-proportional allocations are often considerable with
market-dependent price fluctuations. In order to adjust these, average values
for longer periods (e.g. 10 a) or, more simply, for the reference year or reference
period of the LCA (defined in Goal and Scope) should be formed. Furthermore,
the geographical basis has to be defined (World market? European Union?
OECD? On the basis of which currency?) This allocation is complicated
by the fact that many prices are based on secret arrangements. Despite
these difficulties the price-weighted allocation per mass represents the only
universally applicable ‘subjective rule’. It is, even though not scientifically
verifiable, by no means arbitrary, because economic activities are usually
accomplished in view of the most valuable product (extreme case: see diamond
example) and not in order to produce by-products or waste. In modern economy
the latter is avoided as far as possible, or again included into production by
recycling.
7. Further proposals for allocation:
As further reference units for allocation, molecular mass and calorific value
have been suggested. Both units are not universally applicable. They are,
however, occasionally used for special applications. The calorific (heating)
value is applied for an allocation of refinery products but because of very
comparable calorific values of the co-products this leads to similar results as
with an allocation per mass. The mol mass as basis for allocations is not
suited for chemically badly defined mixtures. It was, for example, used in
ecoprofiles of Plastics Europe (APME studies) for an allocation of chlorine
alkali electrolysis 90) (see above allocation per mass). For a comparison of
approximately 15 (!) further possibilities of allocations for the same process
(some probably humorously meant) see Boustead (1994b).
Considering the fact that allocations cannot be conducted with total objec-
tivity, in ISO 14044 a transparent reasoning is required for a deviation from
scientific methods; this always results in an avoidance of allocations. In case
of using subjective allocation methods, the conduct and discussion of at least
one sensitivity analysis in the interpretation phase is mandatory (see Chapter
5). This is to evaluate the impact of the choice of the allocation method on the
final result.

3.3.2.4 Further Approaches to the Allocation of Co-products
The above discussion shows a historically grown argumentation line which has pre-
dominantly developed from common practice in assessment and by International

90) Boustead, 1994b.