The electrolysis of sodium chloride produces chlorine.
It also necessarily produces caustic soda. One ton of chlorine, 1.13 tons of soda. The ratio is not a choice. It belongs to the conservation of matter. The chlorine industry is structurally a soda industry. The inverse also holds.
When PVC demand increases, soda production increases with it, even if soda asked for nothing. When soda demand recedes, chlorine plants encounter the limit of the compound they cannot stop producing. The market for one product governs the availability of the other according to a proportion fixed by chemistry.
The by-product is not secondary. It is only less desired at the moment it appears.
Coal coking gives another form to this constraint. Metallurgical coke was sought after. Coal tar remained. This thick, lateral, cumbersome matter opened an entire chemistry: synthetic dyes, aromatic intermediates, then certain sections of therapeutic chemistry and explosives. A decisive part of the German chemical industry was built on what the process left behind.
The residue was not awaiting a destiny. It was awaiting a market.
The boundary between product and waste is not chemical. The same molecule can cross several statuses without changing structure. When a use appears, waste becomes resource. When use disappears, resource becomes burden again. Matter does not follow these categories. It suffers them.
The process engineer therefore does not design a reaction for a single product. He designs an output balance. Target product, co-product, by-product, impurity, purge, effluent, heat, gas, solid, sludge. Each fraction will have to circulate, be sold, burned, neutralized, stored, retreated, or declared.
What comes out decides as much as what was sought.
The future waste, its quantity, its toxicity, its treatment cost, its absence of outlet, enters the process before the first reaction. The market can designate a main product. Chemistry never delivers this solitude. It delivers the whole.
Doctrine
Industry never produces a single object. It produces a balance.
The product is the fraction of the balance that a market accepts to name. Waste is the fraction that remains without a regime of use. Chemistry does not make this distinction. It imposes the proportions. The market assigns the statuses.
Open vector
Refining does not obey the same strict stoichiometric coupling. It nonetheless gives a more flexible version of the same problem. Crude does not enter a refinery to become a single fuel. It becomes a set of cuts, gases, naphthas, distillates, residues, that secondary units can displace without abolishing.
The energy transition modifies demand for certain fractions faster than it modifies the whole of industrial outputs. When a main product recedes, its material neighbors do not disappear in the same proportion.
What becomes of a production system when the market withdraws its name from the fraction that organized all the rest?
