Hardly any contemporary-trained chemist or physicist can say they do not recognise this picture, a selection of people at the then-frontier of their own fields, and whose legacy we largely uphold as the backbone of the modern physical sciences.
If you are keen on history, you might even remember that the occasions they gathered were called the Solvey Conferences, an initiative first started by Belgian industrialist Ernest Solvay (1838 – 1922).
Who was he? How did he get his riches?
A. Piccard, E. Henriot, P. Ehrenfest, E. Herzen, Th. de Donder, E. Schrödinger, J. E. Verschaffelt, W. Pauli, W. Heisenberg, R. H. Fowler, L. Brillouin;
P. Debye, M. Knudsen, W.L. Bragg, H. A. Kramers, P. A. M. Dirac, A. H. Compton, L. de Broglie, M. Born, N. Bohr;
I. Langmuir, M. Planck, M. Curie, H.A . Lorentz, A. Einstein, P. Langevin, Ch.-E. Guye, C. T. R. Wilson, O. W. Richardson
Soda ASH
Soda ash or washing soda (Na2CO3·10H2O, sodium carbonate in its various hydrate forms) is a crucial industrial ingredient. I would even argue that the invention of large-scale soda production was one of the most significant testaments of, and a strong incentive for, human technological growth.
In English, the element Na is even named after soda (instead of a much more natural and abundant form, sea salt, NaCl, though you might argue that chlorine won’t be happy with that arrangement).
We take one of the uses of soda ash to illustrate its importance, via a chain of reasoning that might resemble a slippery slope to some — bear with me. Imagine if (the Western[1]) history unfolded without soda: were there no reliable supply of soda ash, it would be difficult to manufacture cheap glass; a population without access to glass might not get to play with lenses or beakers, and a science faculty without those might have a hard time stumbling across modern astronomy, physics, biology, or chemistry, which all still run on glass to a large extent.
Across the Eurasian Continent, the first reliable way to get soda ash was … ash. Sodium and potassium carbonate are still readily obtainable from burnt plant residues. For the longest time, Na2CO3 was merely regarded as a food additive that takes care of various food acids, such as those generated by yeast during fermentation, and I’d imagine countless children calling it bitter salt, in honour of its bubbly after-taste — don’t ask me how I found out. (baking soda is bad enough; this is worse. Do not attempt.)
Burning dry grass is slow, unreliable and prone to contamination, but for thousands of years, it sufficed for generations who simply wanted their food to taste better. Additional supply sometimes were also provided by Trona ores, a naturally occurring mixture of sodium carbonate and sodium bicarbonate).
However, this wasn’t good enough for the Industrial Age. As humanity began to run on steam and factories, the first strain on the soda supply was soon evident: food production had increased so much, naturally obtained soda couldn’t cover this demand alone. This, in addition to new needs brought about by glass manufacturing, paper making, and fabric weaving, called for artificial ways of soda production.
Scheele method, One of the The First
Contemporary to the Boulton and Watt steam engine (1776), a significant first attempt at industrial soda production was made by the Swedish Carl Wilhelm Scheele (1773),
2NaCl + 2PbO + H2O = 2NaOH + 2PbOCl·PbCl
2NaOH + CO2 = Na2CO3 + H2O
The pathways and reagents from this age all looked quite different from what you might recall from high school chemistry textbooks. But keep in mind that both NaOH and ammonia were still difficult things to manufacture at the time. The person who would go on and first identify sodium in 1807, Humphry Davy, incidentally also the person “whose biggest discovery was Michael Faraday”, was not born until 1778.
Though humanity didn’t know what sodium was during this age, all mainstream methods all agreed to start with common salt, NaCl. This may be attributed to the analytical work done by the famed Antoine Lavoisier (1743 – 1794), who established that salt and soda share some common ingredients.
LeBlanc Method, A Personal Tragedy
In the late 1700s, the French lost their supply of natural soda ash due to warfare with the British, prompting the French government to encourage research of better industrial production routines. Previously a surgeon working for the Duc d’Orléans, Nicolas Leblanc (1742 – 1806) managed to successfully improve the previous methods in 1789.
His first step is the now logical-sounding reaction between common salt and sulphuric acid[2].
2NaCl + H2SO4 = Na2SO4 + 2HCl
This was already known by Scheele et al., but the second step is creative. He would reduce the sodium sulphate with coal in the presence of limestone,
Na2SO4 + 2C = Na2S + 2CO2
Na2S + CaCO3 = Na2CO3 + CaS
Since neither coal, calcium sulphide, or calcium carbonate is water soluble, the product can simply be obtained by washing the resulting black ash with water.
LeBlanc was not rewarded, however. The year he made his discovery, Louis XVI was executed, and two years later his patron. His own soda production plant was also seized, leading to him committing suicide out of poverty and sickness in 1806.
The LeBlanc method was an ingenious twist on early methods, leading to easy separation of the final product. However, it still relied on heating a solid mixture, which is less effective than reactions in a solution, and it is extremely wasteful when considering the by-products. Tonnes of sulfuric acid and limestone would be converted into a messy black ash with dubious value for repurposing.
Still, progress was being made; the stage was largely set. It’d soon be Solvay’s time.
Ammonia Enters
Back in as early as 1811, the following routine was established in a lab setting, mixing air, ammonia, and salt to get baking soda first.
NaCl + NH3 + CO2 + H2O = NaHCO3 + NH4Cl
2NaHCO3 = Na2CO3 + H2O + CO2
The only by-product, ammonium chloride, would be packaged and sold as fertiliser.
With ammonia getting cheaper and cheaper thanks to the coal industry, the above pathway gradually became more and more feasible to implement in a factory setting. However, many industrialists who tried to see through these reactions saw their businesses fail: though the reactions looked reasonable on paper, simply pumping ammonia into brine (NaCl solution) is a really wasteful way to start the reaction as ammonia readily escapes (ever try to smell it?), let alone the irreversible loss of ammonia into solid waste. The limited supply of ammonia became the bottleneck of the scalability of production of this age.
Solvay’s father owned a salt factory, and his uncle operated a coal plant. He arguably got his chemistry enlightenment working in the coal plant. In the late 1850s, almost playfully, he pumped coal plant waste gas (full of carbon dioxide and ammonia) into saturated brine and obtained white solids.
If you recall from above, he got sodium bicarbonate, though Solvay himself was oblivious, having skipped his literature review. Not having realised he is embarking on a path proven to be treacherous, Solvay soon was faced with the same problems that defeated people before him. However, undeterred, he proceeded to invent the world-renowned Solvay tower plant, inside which ammoniated brine flows from top to bottom, while carbon dioxide flows the other way. Further, he developed a simple way to reclaim the ammonia from waste,
Ca(OH)2 + 2NH4Cl = CaCl2 + 2H2O + 2NH3 (recycle)
How to get the calcium hydroxide, you ask? Heating limestone…
CaCO3 = CaO + CO2
Solvay started implementing his design in 1863 and reached consistent capacity in 1865. His factory remained in operation till 1993. Comically, he himself remarked, had he learned about the earlier attempts to do the same which all failed, he might not have tried this method either.
The ability to reuse ammonia, as well as the dramatic reduction of solid-state waste as compared to the LeBlanc method, benefited large-scale and continual production. Solvay’s method led to a dramatic reduction in soda price, and his successful business was the foundation of the science activities in his later life.
The Solvay process was superseded by Hou’s Process, invented by Chinese chemical engineer, Hou Debang (1890 – 1974) in 1933. This new procedure conducts the production of ammonia and soda in sync and achieves the recycling of ammonia by clever controls of the waste brine solution’s temperature.
Notes
[1]
China never went around and invent glass for daily uses. I think the ceramics were just too good.
[2]
Industrial production of sulphuric acid was developed quite early, via the contact process, for example.