Biomass: miracle cure for the climate? - The life of ideas
COP26 is being held this week in Glasgow, and decisions should be taken there to try to limit greenhouse gas emissions and their impact on the climate. It will therefore discuss alternatives to fossil resources and the trapping of atmospheric CO2. On these two issues, we often hear about biomass and the benefits that technological building blocks using plants, or more generally materials of natural origin, could have. There is, however, a preliminary problem which is that of availability: despite their immense efficiency, the biological processes involved in plant growth are thermodynamically restricted. In many areas, such as natural fibers for textiles, the physical production limit has even been reached for decades. There remains the trapping of CO2, which can be either technological (capture and sequestration) or ecological (reforestation). Currently and probably for the next few decades, the only effective trapping remains that carried out by plants during their growth. Nor do the most virtuous capture and sequestration technological scenarios make it possible to significantly offset greenhouse gas emissions due to the overexploitation of fossil resources, and cannot compete with plants in terms of combined scale, universality, environmental harmlessness and even performance. In a broader framework including massive reforestation in addition to storage in consumer goods, the reduction in atmospheric CO2 would only offset two or three decades of emissions in the long term. Consequently, only a renunciation of the combustion of fossil reserves will make it possible to curb CO2 emissions. The solution to the CO2 problem cannot therefore be based solely on biomass. It will necessarily be much more complex, global but also difficult to accept and implement. Nor will it necessarily be technological.
Biomass: a thermodynamic singularity
We must first understand what biomass is. In the world of thermodynamics, there is a very general notion called entropy. Entropy is often associated with a level of order or disorder. In an energy context, it is associated with the amount of energy that can be drawn from any source, this source being able for example to be light radiation such as solar radiation, or matter such as a liter of gasoline or a kilogram of sugar, in a given context of use. The use of an energy source is always, it is the second law of thermodynamics, linked to an increase in the entropy of the system. Thus, easily usable energy will be associated with low entropy, and vice versa. Take the example of light radiation: solar radiation is a low entropy energy, because it contains a whole spectrum of wavelengths, including UV radiation which is very energetic – and very easily usable. For example, plants use this radiation for photosynthesis, and certain molecular compounds use it to initiate chemical reactions, such as photo-polymerization reactions, for example. On the other hand, the radiative radiation of a hot body is made up of infrared radiation, which is a low quality radiative energy because it is less easily usable: for example the radiation from a wall which would have been exposed to the sun all a day. The entropy of a liter of gasoline is very low and this is associated with its very high energy density during combustion, a density from which we all benefit. Conversely, the combustion emissions of this same liter of gasoline will have a high entropy. Take the case of the CO2 emitted: the molecules of this gas will be dispersed in the atmosphere where the residual concentration is very low (around 410 ppm today, which is already half the pre-industrial rate). Outside, CO2 itself has an energy potential, and it could be reused, but its strong diffusion in the atmosphere makes the exercise complicated. We therefore measure what a passage from low to high entropy means: a conversion of energy into less usable forms.
We can also consider that the planet earth is a battery, or rather several batteries put in parallel: it is mainly a chemical battery that is biomass, another chemical battery that are fossil resources, and a last physical battery that are the radioactive ores that can be used in the nuclear industry. Each of these batteries has low entropy, or high energy potential, gained over time scales of millions, or even billions, of years. Yet the rapid depletion of these three sub-batteries by human use shows that the planet's battery is draining at an alarming rate. This rate is particularly threatening with regard to biomass since at the current rate, according to a study published in the journal PNAS, only a thousand years of " potential " remain to feed the population. world and much less in the absence of rapid change in habits (we lose the equivalent of 200 years of potential every 10 years) (Schramski, Gattie and Brown, 2015). To say that the planet is rapidly discharging is to say that the energy necessary for life is rapidly diminishing. This also means that the products of transformation of this energy have a higher entropy, and that they are therefore less easily usable than they were in their initial form. But by the way, how did this battery get charged, since the planet was originally only an accretion of mineral elements, and sterile ?
The answer is wonderfully simple when it comes to biomass and fossil resources: plants. Indeed, plants have the characteristic of being based on an extremely complex, efficient, and of course renewable machinery: photosynthesis. Photosynthesis achieves this magical operation of combining low-entropy radiative energy, solar radiation, and high-entropy chemical energy, atmospheric CO2, into plants including leaves, stems, fibers, wood, roots, bark, fruit or flowers. These organs are all made up of so-called “ condensed organic matter, i.e. solid or liquid. However, this plant matter has a low entropy, while it comes largely from atmospheric CO2. It is therefore in this way that the recharging of the planetary battery takes place, whether in the form of ecosystems renewing and enriching themselves, or on geological time scales, in the form of sedimented organic matter and stored in the ground in the form of gas, coal or crude oil. This entropy reduction paradox, apparently against the second law of thermodynamics, has fascinated physicists for decades. Ernest Schrödinger, famous for his work on quantum mechanics, himself described plants as being capable of bringing order to their environment, a quality intuitively associated with a reversal of the arrow of time, time which would then pass to the past (Schrodinger, 1951).
Plants are in fact relatively autonomous on the trophic level, since their metabolism requires only solar energy, and a few simple elements (carbon dioxide, water, phosphorus, nitrogen, etc.) to live (this statement deserves to be discussed). be nuanced, but it will suffice for this discussion). Plants are therefore called photoautotrophs. In addition, plants form a “ basic trophic level on which rest higher trophic levels whose metabolisms need more elaborate organic molecules (sugars, oils, acids amino acids, etc.) to function. This is the case for humans, regardless of their diet. Plants represent 82.5% of the total biomass, followed by bacteria (12.8%), fungi (2.2%), archaea (1.3%), protists (0.7%), animals (0.4%) and viruses ( 0.1%) (Bar-On, Phillips and Milo, 2018). Among plants, only a very small fraction of around 0.2% is found in marine environments in the form of algae. Forests cover 31% of the earth's surface and represent between 60 and 75% of so-called biogenic carbon, i.e. carbon present in organisms and not in mineral form, in soils for example (Roux et al. , 2020).
Many perspectives of use
Materials derived from biomass (sometimes called biobased) have many uses, and have done so since time immemorial: in food, in construction (wood, insulation materials), cabinetmaking (furniture, oils , dyes, lacquers), agriculture (fertilizers, mulch, tools), in textiles (natural fibers such as cotton, wool and silk, viscose), in medicine or pharmacopoeia (compresses, anointings, suture materials, etc. .), in stationery, packaging, the rubber industry (rubber sap), in plumbing (fiber seals) or even in electricity (electrical insulating paper). Video recordings were supported by nitrocellulose films until the 1950s, before being replaced by cellulose acetate films until the 1980s. Nitrocellulose and cellulose acetates are derived from plant matter. Nitrocellulose was also used as an explosive powder. Today, it is still found in nail polishes or in cellulosic lacquers used in violin making.
Other materials derived from biomass are the subject of more recent developments. It must be emphasized that many advances have been made in recent decades in research laboratories. These advances concern both the understanding of molecules of plant or animal origin, their association within living organisms, but also their uses for technical purposes. A huge field of research is for example that of nanocelluloses, which are nanometric fragments of cellulose. These nanomaterials retain the chemistry and biodegradability of the original material, but they can be functionalized in many ways and can help in the manufacture of advanced materials, such as supercapacitors, batteries or flexible displays.
These natural materials are therefore not only at the heart of our food, but also at the heart of our intellectual, technological and scientific developments. They are already ubiquitous. Yet they aren't nearly as available as you might think.
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— Shilpa P ❤️ 🧠 Fri May 21 14:35:22 +0000 2010