In the U.S., a topic for Hollywood ("Promised Land", German Release Date: June 13, 2013), in Germany, in all the papers from the feuilleton to science part: the social debate on fracking - the method to gain shale gas - gets rolling. (Shale gas is natural gas, present in mudstones and also called "unconventional" natural gas.) "Cheap shale gas makes chemistry from fossil fuels more competitive ... and will give the bio-based products a hard time!" This you might think at first glance. But this is a simple view. With the help of plastics it can be shown how complex the connection is between shale gas extraction and bio-based products:
Shale gas ethylene instead of bioethanol as raw material for PVC & PE?
In the United States a shale gas boom became recently apparent. This affects not only the products directly depending from methane as the main constituent of shale gas (such as hydrogen and methanol), but is for all energy-intensive processes of high importance. The shale gas also contains the associated gases ethane (up to 11 percent) and propane (up to 3 percent) as a source of short-chain olefins. The large number of crackers in the United States that operate on natural gas will produce with the cheap shale gas particularly ethylene cheaper. The situation for the derivatives of polyethylene (PE), polyvinyl chloride (PVC), etc. is herewith clear: the future outlook for bioethanol as a source of these plastics is likely to worsen dramatically. The harbingers are recognizable: Dow Chemical and Solvay have already postponed projects for PE and PVC-based bioethanol production in Brazil, or set them "on hold".
Polypropylene (PP) - Cheaper by fracking?
Many C3-based chemicals depend on propene, for example plastic polypropylene (= Polypropene) that is obtained by the polymerization of propylene. The price development of propene, however, cannot be clearly predicted as the European naphtha crackers have a higher propene output, in turn, the propane content in the shale gas is not high. In addition, however, there are alternative ways of producing propene from ethylene or methanol, whose price will again decrease due to the shale gas.
Glycerol and lactic acid as biogenic basis for attractive chemical building blocks
The basis of renewable raw materials, however comes up with the intermediates glycerol and lactic acid, which can be processed via several synthetic pathways to various (bio)plastics.
Glycerin can be processed, inter alia to epichlorohydrin which is used for example for the production of car tires. This synthesis is now already industrially established by Solvay. Moreover, by the processing of glycerol to acrylic acid can be produced superabsorbent (among others used in diapers) and a variety of other plastics. However, the available quantities of glycerol must be kept in mind: estimated 2 to 3 million tons of glycerine as a coproduct of biodiesel production worldwide face now approximately 4.5 million tons of acrylic acid production. The regional distribution is very unequal.
For the path of lactic acid from glucose, this limitation is eliminated. In principle, the lactic acid could be chemically converted to acrylic acid, while the lactic acid production today is already established for the large scale production of the polymer polylactic acid (PLA) in a large scale (greater than 100,000 metric tons). However, it will be difficult for this bioplastic to compete with cheaper polyethylene with similar property profile in the packaging sector.
For C4 (butene, butadiene, butane, succinic acid) and C5-blocks (isoprene, levulinic acid) this discussion does not arise, natural gas crackers provide no C4 and C5 products as opposed to naphtha crackers. A shift to shale gas at the expense of naphtha crackers would even strengthen the need for a bio-based access.
What about aromatic compounds?
Benzene (adipic acid, and thus for nylon) and xylene (for polyethylene terephthalate, phthalic acid, and thus - PET) are currently sufficiently produced on the basis of oil. Cheaper methanol by fracking could possibly make the production of aromatics through the MtA (methanol-to-aromatics) process economically.
So why should aromatics be produced on a biogenic basis (C5 and C6 sugars) with at least actually relatively complex procedures? Will consumers pay higher prices for "green PET", when PET anyway seems pretty sustainable due to its excellent recyclability? Coca-Cola seems to see it that way as it has initiated appropriate developments in early 2009 (www.plantbottle.info).
Outlook - or where politics comes into play?
With all the economic considerations, however, we must not forget the following: the arguments in favor of the cheap shale gas from ethylene and its derivatives are of limited suitability, if policy decisions, strategically motivated by agriculture and supply, support the production of bioethanol.
That is, if bioethanol is due to subsidies still available cheaply and in large quantities, the situation presented above could change in favor of bio-based products. Despite the shale gas boom, currently particularly obvious in the United States, there is no real independence from foreign resources. But it is precisely the argument of independence that has strongly influenced the promotion of bioethanol.
It will be interesting to see what political discussions will follow.