Page 67 - Materials Chemistry, Second Edition

LIFE CYCLE INVENTORY MODELING IN PRACTICE 49

Methanol recycle
w
Natural g Methanol DMT Melt phase and
production manufacture manufacture solid state PET h
polymerization
from DMT
TPA
Acetic acid
manufacture manufacture
Natural gas (1) Melt phase and
PTA solid state PET h
manufacture t polymerization
Carbon from PTA
monoxide
manufacture
Ethylene I Ethylene |
Crude oil Ethylen« oxide I H glycol 1
production manufacture I manufacture I manufacture I
ture

Distillation/
desalting
Hydrotreating
Paraxylene
Mixed H
xylenes extraction
Figure 3.3 Cradle-to-resin production of virgin PET.

Before making the decision to exclude a life cycle stage, the implications must
be carefully considered, as illustrated in the following example.
A company wishes to conduct an LCA to compare a new flexible composite
packaging option with a current rigid mono-material package. Both packages
hold the same quantity of product. The flexible packaging option is lighter in
weight than the current package, but the current package is recyclable and
the new composite package is not. Based on these differences in the packages,
the decision is made to include the following life cycle stages in the analy-
sis: raw material extraction through container manufacturing, and end-of-life
management.
This choice of boundaries excludes several potentially significant differences
from the analysis. First, it is likely that the rigid container will have higher
burdens for empty container transport to the filler. The flexible package can
be shipped flat, so that shipping is much more efficient compared to the rigid
packages, which occupy a large amount of space per empty container. Second,
even though the containers hold the same volume of product, there was no
consideration of potential differences in the filling operation for the two types
of containers. A third overlooked area was transport of the packages after fill-
ing. Although the rigid containers are heavier than the flexible packages, the
flexible packages may require more secondary packaging to stabilize and pro-
tect the filled packages during shipment. For example, the rigid containers
might be packed in corrugated trays, while the flexible package might require
the extra support and protection of a fully enclosed box, adding secondary
packaging material and weight.
Systems providing functional equivalence may have very different life cycle
operations. An example is single-use and reusable container systems.