Issue 06/2018

From Science & Research
To obtain land use data from production capacities in this
bottom-up approach (see Table 1), it needs producer-specific
production capacities of a type of bioplastics to be multiplied by
the output data of the corresponding process routes. If producerspecific
feedstock was known, it was taken into consideration.
In other cases, where these data were missing, only the most
common used crop per material was taken into consideration (e.g.
corn starch for PLA).
For the basic assumptions referring to PLA, previous estimates
of IfBB resulted in a need of 0.37 hectares land for feedstock
cultivation per tonne of material. This is a corn-based, PLAspecific
global average land use factor, for which the following
calculation impact factors (CIF) are assumed.
One obvious impact factor on land use of bioplastics might be
the production capacity itself. According to own research, total
annual installed capacity for PLA worldwide in 2017 was roughly
240,000 tonnes, which gives 88,300 hectares according to the
basic assumptions. However, is relying on the installed capacity
correct? Very few industrial plants run at full degree of capacity
continuously, so an optimistic sensitivity would be 85 % degree of
capacity.
Another impact factor is the region specific yield of a feedstock
in different countries. While for the basic estimation for PLA made
out of corn, a global average yield of 6.5 tonnes of corn per hectare
over the past decade (weighted by production amount) (FAO 2018),
corn being grown in the United States in the same period would
yield in 9.5 tonnes per hectare and the same acreage in China
delivered 40 % less of corn (5.5 t / ha). This is even more important,
as corn from USA makes up to 37 % of world’s corn production,
but China, with its significantly lower yield per hectare still ranks at
an important one fifth (20 %) of global corn production. Therefore it
has a decreasing effect on the global average corn yield (6.5 t / ha).
Further impacts derive from natural harvesting fluctuation.
Using single year data leads to tremendous deviation in calculating
PLA land use. Comparing available corn yields between 2002
and 2013 for e.g. corn in the USA shows, that there is a deviation
between minimum and maximum of 3.2 tonnes per hectare
(Average yield: 9.1 t / ha). By using either minimum or maximum
yield data of a given period for calculation will result in this case in
a fluctuation of land use of +43 % or -30 %.
But even when looking at a global average yield for corn, the
choice of a certain decade leads to different results. Using a global
average yield over a mid-term period (10 years) helps to minimize
natural harvesting fluctuation while at the same time provides
data, which are not influenced by single local yield deviations.
When comparing two different time periods (2002 – 2011 and 2003
– 2014), the worldwide general increase in harvesting yields of
corn raised by 2.5 %. For other (food) crops relevant in bioplastics
production, the increase is at the same level or even higher, e.g.
sugar beet (+ 5.9 %), sugar cane (+ 1.9 %) and castor oil (+ 17.1 %).
Advances in crop growing techniques and better feedstock yields
result in a lower land use, which decreases to the same extent
for each bioplastic material. Even without changes in bioplastics
technology (1st, 2nd, 3rd generation), future land use per tonne of
bioplastic material will de facto decrease.
Additional impact factors could arise from the source of
feedstock (e.g. PLA made from sugar cane versus corn starch)
and allocation assumptions. Allocation is in detail also a very
complex topic and would go beyond the scope of this comparison
as there are different factors itself, which can be used. In general,
this would be mass-balanced, energy-balanced or economicbalanced
allocation. In this case, if using residues is being taken
into account, the bioplastic material will only be burdened with
parts of the full impact of its land use. To make a proposal, the
results will cover 30 % use of residues.
Stepping back from the different impact factors and having a
look at the resulting effects on land use of PLA Figure 3 shows
the impact for the recent global capacity of about 240,000 tonnes
for PLA.
If all raw material was from one country (USA), depending on
different yields per year, this amount of PLA land use ranges from
nearly 80,000 up to almost 115,000 hectares. And even using a
global average yield can still cause slight variations, depending
on which time horizon is assumed (± 2,600 hectares). Last
comparison in Figure 3 shows the influence of locally produced
feedstock as displayed here for Chinese and US-American corn,
resulting in a difference of nearly 43,000 hectares.
Figure 4 compares further impact factors concerning a
more realistic degree of plant capacity being used or an overall
Yield [ t PLA/ha]
6
4
2
0
Figure 3 Figure 4
2.7
Land use for PLA derived from corn
Comparing effects of different feedstock impact factors
240,000 t PLA (2017)
2.1
3.0
114,500 ha
88,300 ha 80,000 ha
Base calculation Local harvest
fluctuation (USA)
2.7 2.8
88,300 ha
Time horizon
Global average
2.3
3.9
104,300 ha
USA vs. China
Global / regional
higher is better
85,700 ha 61,500 ha
Base
Low
High
Yield [ t PLA/ha]
8
6
4
2
0
Land use for PLA derived from corn
Comparing effects of various impact factors
2.7 2.7
Base calculation Prod. capacity
85 %
240,000 t PLA (2017)
88,300 ha 75,000 ha 61,500 ha 38,100 ha
3.9
Allocation
overall 30 %
6.3
Source of
feedstock
higher is better
Base
Variations
bioplastics MAGAZINE [06/18] Vol. 13 43