Plastics - Environmental aspects

*********************************************************************

The main problem is, that parts of the plastics production can be counted as crude oil use, partly they are not. And there are also important differences between different types of plastics.

The parts which are oil related are the amount of directly oil related raw materials, and the energy use directly involved in distilling the fractions of crude oil or used for cracking of these fractions into plastics raw materials, like ethylene and propylene. In most (but not all!) cases this energy is based on crude oil wastes.

Also for the manufacturing of petrol, the energy used to distill crude oil and for reformers/crackers to make high grade petrol is mainly based on crude oil/cracking wastes, and should be added to the total crude oil consumption of petrol.

The same applies for electricity used inside the refineries and - if integrated - the heat/electricity use of polymerisation units for the plastics involved.

The parts which are not directly oil related are parts of the raw materials: chlorine from salt for PVC and oxygen from air for PET and PC. Other energy related sources CAN be oil products, but also electricity, natural gas and (brown)coal for heating and gas-, (brown)coal-, nuclear-, solar-, hydro- or windenergy for electricity generation. That makes a lot of difference.

We have tried to give an impression of the minimum and maximum directly oil related energy use for different plastics. "Oil" being the used oil derivatives as raw materials and the minimal direct oil related energy use to derive these raw materials.


              energy use in MJ/kg

        material      Total   "oil"  "others"
        PVC             53      24      29
        PE              70      55      15
        PP              73      58      15
        PS              80      55      25
        PET             84      31      53
        PC             107      36      71
Source for total energy use: Environmentaly friendly packaging in the future, 1991, Stichting Milieudefensie (Environmental Defense Group) of The Netherlands.

Source of "oil"/"others" partition: own interpretation, based on oil related material content and direct oil related energy use.

These figures inlude the average energy efficiency of mixed electricity generation in Europe (ca. 40%). If more low-efficiency electricity is used (e.g. nuclear - 31%), the "others" figures will be higher, if high-efficiency electricity is used (e.g. cogeneration - appr. 90%, hydropower - 87%), they will be lower.

With a 90% efficiency at the source and 8% energy use, 1 l of petrol (0.76 kg) needs appr. 0.9 kg of crude oil, with 1 kg crude oil counted for 44 MJ/kg. This gives a plastics to petrol ratio in kg/l:


        material        min     max
        
	PVC             0.75    1.65
	PE              0.57    0.72
	PP              0.54    0.68
	PS              0.50    0.72
	PET             0.47    1.28
	PC              0.37    1.10
Minimum is when all "others" are counted as oil based. Maximum when all "others" are not oil based.

PVC and PC in reality will be more to the maximum side, because of relatively high electricity consumption, mainly not produced from oil, and low oil base as feedstock. For PE, PP and PS the balance is more toward the minimum, because they are more oil dependent. PET is somewhere in between. But this depends very strongly on the (inter) national or local and sometimes on site electricity production.

In the literature, the amount of "crude oil" used to make PE varies between 1.55 and 1.95 kg/kg. That is comparable with the preceding estimates.

We have no energy figures for other plastics, but if known and if the balance of oil/non-oil components is known, the ratio can be calculated in the same way.

Some remarks to end:

Plastics manufacturing in the world counts for appr. 4% of crude oil use. If crude oil was only used to make plastics, it would be an abundant material. At the end of their usefull life, plastics can be burned and can give a part of the energy back, mainly depending on their carbon content.


	Glossary:
	
	PVC:    Polyvinylchloride
	PE:     Polyethylene
	PP:     Polypropylene
	PS:     Polystyrene
	PET:    Polyethyleneterephtalate
	PC:     Polycarbonate
Ferdinand Engelbeen Chairman Chlorophiles

Ferdinand.Engelbeen@ping.be http://www.ping.be/~ping5859/

BACK TO *********************************************************************