Well adapted use of Biofuels

Energy

The industrialised world finds itself caught in a pincer movement. On the one side, it feels the effects of the price rises caused by a combination of dwindling resources and international politics. On the other side, there is growing evidence that we are heading for imminent disaster (with potential tipping points of the order of a mere decade or two away) with our output of greenhouse gases, notably carbon dioxide, into the atmosphere (released from carbon sources that the planet had removed from the carbon cycle many millions of years ago).

The ultimate solution to both of these problems would be to give up our dependence on oil. Nuclear fission offers many advantages, but has its own political and resource problems, as well as waste-disposal and decommissioning problems. Nuclear fusion promises to be much better, but is proving to be a difficult technology to get running. Many people believe that we should to turn to renewable energy sources such as solar power, but it is unclear how to provide this on a sufficient scale that does not pollute the countryside with eyesores.

Given that giving up our dependence on oil, or renouncing our need to consume so much energy in the first place, is unlikely to happen quickly, and given that plants are the most efficient collectors of solar power known to us, one option would appear to be to use plants to collect solar energy and to convert it to a form that can be released in our machines.

Initially, in the short term, it is convenient to choose crops that allow us to continue to use our current machines (such as diesel and gasoline engines) and to adapt gradually, in a carbon-neutral way, to a reduced dependence on mineral oils. It need not be all sectors of fuel consummation that need to adapt immediately: the initial steps need only target those uses for which biofuel is best suited, and most likely to make an impact.

Most obviously, fruits and seeds are the places where plants stock up energy for use by the next generation; but roots, stalks, leaves, and wood (biomass) are significant, too, (places where plants stock up energy for use by themselves through the winter, or for building-on in the future). It turns out, though, that for temperate climate regions, none of this would be enough to satisfy even the present aims to grow between 5% and 10% of our fuel needs, and for equatorial climates, it takes land away from food production or natural forest (NS, 23-Sep-2006, p36).

Already, three generations of biofuel production have been identified. Better than using crops and land that might otherwise be used for food (first generation biofuel), with its multiple serious down-sides (NS, 27-Jul-2019, p23), and better even than using agricultural waste (second generation, with the biofuel produced from biomass), algae can be grown on sewerage (third generation). Even better still, algae can be fed on CO₂-rich flue gases (NS, 07-Oct-2006, p28), thereby promising to take the waste products from the greatest consumer of fossil fuel (the electricity generation industry) to supply biofuel for the second largest (transport). Moreover, the cooling water from the electricity generators can be used to warm the tubes of algae (NS, 16-Aug-2008, p34). Better, yet, the tubes of algae do not require intense sunlight, but can be housed under cover, with the sunlight diffused across them from collectors of a tenth of their surface area, thereby reducing land usage for the project by an order of magnitude. A significantly large amount of energy is used for pumping the fluids at a sufficiently high rate of circulation (NS, 24-Jul-2010, p22) but the ability to use a cheap source of concentrated nutrients, via the establishment of a double household sewerage system (NS, 23-Dec-2006, p45) would appear to compensate for this (NS, 30-Jan-2010, p6).

Carboxylic Acid: R-CH₂-COOH

adding Na gives

R-CH₂-COO-Na

adding NaOH gives

Alkane: R-CH₃ (C removed)

adding halogen gives

Alkyl halide: R-CH₂-halogen

adding metallic Na gives

Alkane: R-CH₂-CH₂-R (C doubled)

...

Carboxylic Acid: R-CH₂-COOH

adding moist AgO₂ gives

R-CH₂-COO⁼ Ag⁺

adding Br₂ (60-90%) gives

Alkyl bromide: R-CH₂-Br (C removed)

adding KCN with [alcohol] gives

Alkyl cyanide: R-CH₂-CN (C added)

...

Ketone: R-C-O-CH₃

adding H₂ over [Ni] gives

Alcohol: R-CH₂-CH₂-OH

adding Carboxylic Acid: R-CH₂-COOH over [H₂SO₄] gives

Ester: R-CH₂-CO-O-CH₂-CH₂-R

Alkene: R-CH=CH₂

adding H₂O over [H₂PO₃] gives

Alcohol: R-CH₂-CH₂-OH

adding H⁺₂ Cr₂O₇⁼ gives

Aldehyde: R-CH₂-CHO

adding H⁺₂ Cr₂O₇⁼ gives

Carboxylic Acid (fatty acid): R-CH₂-COOH

adding SOCl₂ or PCl₅ (60%+) gives

Acyl chloride: R-CH₂-COCl

adding NH₄OH (cold, conc=50%+) gives

Amide: R-CH₂-CONH₂

adding P₂O₅ gives

Alkyl nitrile: R-CH₂-CN

adding H₂ over [Ni, 50%+] gives

Amine: R-CH₂-CH₂-NH₂

adding NaNO₂ + HCl gives

Alcohol: R-CH₂-CH₂-OH

Thermodynamics

The cortex of a plant is like the barrier between two chambers in an experiment on the second law of thermodynamics. On one side of the barrier consists of a volume of concentrated monosaccharide ring molecules (such as glucose and fructose) and their polymers (the disaccharides, such as cellobiose, maltose and sucrose; and the polysaccharides, such as cellulose, glycogen and starch). On the other side of the barrier is a volume of O₂ gas at 21% concentration, with pools of H₂O and relqtively small concentrations (0.04%) of CO₂. This highly ordered, low-entropy state is achieved by harnessing solar energy to take molecules of H₂O and CO₂ from one side of the barrier, and to assemble them as more structured saccharide molecules on the other side.

According to the second law of thermodynamics, a machine could then be connected between the two sides of the barrier, and made to do work. In just such a way, animal cells digest plant cells, and man-made machines burn fossil and bio fuels.

Saccharides, along with their related ketones and aldehydes, already represent the first by-product of partial oxidation from the alkanes. Oxidising further, by fermentation, these produce alcohols. Oxidising still further, these produce carboxylic acids (notably vinegar). Performing an acid-alkali reaction with other alcohols, these produce esters. Ultimately, the final oxidation returns us to the original raw materials: H₂O and CO₂.

Chemical processing

The two main classes of biofuel presently considered are bioethanol, as a gasoline replacement, and biodiesel. Bioethanol is presently obtained from sugars and starches in crops such as sugar cane or cereals; biodiesel is presently obtained from oils in crops such as soybean, palm or rapeseed, or from animal fat. There is also promise of being able to produce alkanes from sugars using bacteria that have been modified with genes from cyanobacteria (NS, 07-Aug-2010, p20).

The biofuel can be blended with conventional fuel, starting with low proportions (such as E10, which is 10% bioethanol to 90% conventional gasoline; and B10, which is 10% biodiesel to 90% conventional diesel), gradually building to higher proportions (such as E85 or B85, containing 85% biofuel) as the years pass, and as our machinery is adapted.

Once the crop has been harvested, and the problem has been handed over to the chemical engineers, the first process might be the extraction of sugars, or other silage juices, and oils. Any remaining biomass consists largely of starch, lignin and cellulose. Lignocellulosic processing uses enzymes to hydrolyse these to sugars (NS, 21-Jun-2008, p30), or Ammonia Fibre-Expansion can be used to split the fibres mechanically (NS, 29-May-2010, p22). The sugars are then fermented (though, an alternative process using acetogenic bacteria has been proposed, to reduce the proportion of carbon that is lost to the biofuel production via the giving off of carbon dioxide). The fermentation process, though, offers the possibility of producing high protein yeast as a sellable by-product to improve the economics of the overall process (NS, 29-May-2010, p22).

Converting vegetable oils to biodiesel requires a catalyst. Most of these involve sulphuric acid, which is expensive, or ones that are derived from petrochemicals (thereby eroding a major aim of biofuels).

In any case, the energy needs of the processing plant should be supplied from biofuel sources (ideally from waste products of the process itself).

Monosaccharides (24 possible)

Aldose

Galactose: {-O-C(OH)H-C(OH)H-CH(OH)-CH(OH)-CH}-C(OH)H₂
Mannose: {-O-C(OH)H-CH(OH)-CH(OH)-C(OH)H-CH}-C(OH)H₂
Glucose (grape sugar): {-O-C(OH)H-C(OH)H-CH(OH)-C(OH)OH-CH}-C(OH)H₂

Ketose

Fructose (fruit sugar): {-O-C(CH₂OH)H-CH(OH)-C(OH)H-C(OH)(CH₂OH)}

Disaccharides

Lactose (milk sugar): Galactose + Glucose - H₂O
Cellobiose (from cellulose): Glucose + Glucose - H₂O
Maltose (from starch): Glucose + Glucose - H₂O
Sucrose (cane sugar): Glucose + Fructose - H₂O

Polysaccharides

Cellulose; Starch; Glycogen

Alkyne (acetylenes): R-C=CH

adding H₂ over [Ni] gives

Alkene (olefines): R-CH=CH₂

adding H₂ over [Pt, or Ni] with heat and pressure gives

Alkane (paraffins): R-CH₂-CH₃

...

Alkene: R-CH=CH₂

adding O₂ with [Ag] gives

Epioxide: {-O-CH₂-CH}-R

adding H₂O gives

Alcoh-diol: R-C(OH)H-C(OH)H₂

...

There have been many attempts to supplement the periodic table with further information (NS, 02-Mar-2019, p36; NS, 12-Jul-2014, p38: NS, 12-Feb-1994, p36) mainly concentrating more on the properties of the molecules and bonding. One particular type of radical is classified as 'cluster superatoms' (NS, 16-Apr-2005, p30). One interest is in annotating the periodic table with information about rare earths, and other element ores, and their availability or recycling (NS, 14-Feb-2015, p35). There is always the interest in adding new superheavy elements to replace their temporary, place-marker naming using the 'nudtqphsoe' (0123456789) alphabet, and the search for an island of stability (NS, 26-Jul-2008, p32). It is pointed out that, like pre-Copernican astronomy, the familiar periodic table is very NTP-centric, and that most material in the universe, or even on the planet, is not at STP (NS, 12-Sep-2015, p28). All of this leads on to work on studying forbidden chemistry (NS, 21-Jan-2012, p30).

Some terminology

With many thanks to colleagues on Quora for helping to fill in some of this information.