Soda Ash & Caustic Soda

Two chemicals sit on this sheet because industry treats them as substitutes at the margin, but they are made in completely different ways and behave completely differently. Soda ash is sodium carbonate. Caustic soda is sodium hydroxide. Both are alkalis, both start from salt, and in some applications a buyer can switch between them on relative price. That is where the similarity ends.

Soda ash comes by two routes that are now in open competition. The Solvay process, invented by Ernest Solvay in the 1860s and still roughly 70 percent of world capacity, reacts salt brine with limestone and ammonia. The alternative is simply to mine it: natural trona ore, concentrated in Wyoming's Green River Basin and in Turkey, is processed into soda ash directly. World production runs on the order of 76 million tonnes, with the United States around 12 million tonnes of that. The competition between the two routes is being reshaped by carbon policy: trona-based production emits roughly 40 percent less CO2 per tonne than Solvay, and the EU carbon border adjustment mechanism widens that cost gap by tens of dollars a tonne, which is quietly pushing the retirement of legacy synthetic capacity in Europe and pulling volume toward Wyoming and Turkey.

Where soda ash goes is mostly one place: glass. Container glass, flat glass for buildings and cars, and increasingly solar panel glass, which links this sheet to the polysilicon and solar story elsewhere in the book. After glass come detergents, chemicals, and one modern use worth flagging: soda ash is a reagent in converting lithium brines and concentrates into lithium carbonate, so battery growth pulls on it too. Asia is roughly 46 percent of world consumption, driven by Chinese glass.

Caustic soda is the different animal, and the reason is the chlor-alkali reaction described in the story above. Because it arrives as a joint product with chlorine in a fixed ratio, its price is only loosely connected to its own demand. When chlorine derivatives, principally PVC, are booming, operators run hard, caustic floods out as a co-product, and the caustic price falls. When PVC is weak, caustic tightens. Anyone modelling caustic has to model PVC first, which is an unusual and counter-intuitive dependency, and it is the cleanest example of forced co-production in this book alongside the sulphur sheet.

Caustic's own demand list runs through several other markets covered here. It is the reagent in the Bayer process that digests bauxite into alumina, so aluminium production is a large caustic buyer. It is used in pulp and paper processing, in soaps and detergents, in water treatment, in textiles, and across chemical manufacturing. A caustic price move therefore lands on aluminium refiners and paper mills who had no view whatever on the chlorine market that caused it.

On trading, the two diverge again. Soda ash has a real futures contract: the Zhengzhou Commodity Exchange listed it in December 2019, and it has become an actively traded Chinese contract, with options added later, giving the alkali complex a screen price it never previously had. Caustic soda has no futures market anywhere and is sold on contract and assessment, quoted dry basis or as a solution, with freight and concentration mattering a great deal. So one half of this sheet is exchange-traded in China and the other half is a bilateral market priced off a co-product it cannot control.