An article in the May 2024 edition of the journal Chemical Engineering Progress reminded me of the famous question, ‘How many angels can dance on the head of a pin?’ (It is unlikely that medieval theologians actually did debate this topic. But the question has become a metaphor for arguing about issues of no practical value while society is faced with urgent and immediate problems that need to resolved in the here and now.)
The title was Mapping the Path to a Net-Zero Chemical Industry. The article is difficult to follow, but apparently the authors have developed a ‘general modeling framework to facilitate transitions to net-zero ‘cradle-to-cradle’ emissions through optimal combinations of technologies, supply chains and innovations’. The authors use the recycling of grocery bags to illustrate the development of such a model.
The authors appear to have lost sight of the second law of thermodynamics which tells us that any time we use energy we increase the entropy of overall system. It is not possible to recycle grocery bags without some low-entropy energy being dissipated ― every time we recycle one of those bags.
The Carnot Cycle expresses the same concept. Sadi Carnot (1796-1832), a junior officer in the post-Napoleonic French army, developed the following basic thermodynamic equation,
Ƞ = 1 – (TC / TH)
where Ƞ is efficiency, and TC and TH are the temperatures of the source and of the heat sink respectively.
This equation shows that even the most efficient systems use only 45% of the energy supplied to them to create useful work. The remainder is emitted as high entropy exhaust (including the CO2 we dump into the atmosphere).
Recycling is helpful at reducing the pace at which the climate changes. But that’s all. If we want to effectively address climate change we need to stop using grocery bags altogether.
