Editorial Article
Four Tonnes of Chlorine Per Tonne of Phosphorus
Phosphorus trichloride is 22.55 per cent phosphorus by mass. The other 77.45 per cent is chlorine. Move one tonne of the element as PCl3 and you move 4.44 tonnes of molecule, of which 3.44 tonnes is chlorine — a chlor-alkali consignment wearing a phosphorus label.
Nothing else in this chain has that ratio. Sodium tripolyphosphate carries 25.3 per cent phosphorus and glyphosate 18.3, but each of those is assembled from an acid that was already made near a mine. PCl3 is the one molecule in the segment built from two commodities that come from different industries: yellow phosphorus out of a submerged-arc furnace, chlorine out of an electrolytic cell. Its geography is the intersection of two maps, and its cost is a chlor-alkali cost with a phosphate cost added on top.
The ratio, and where it lands
| PCl3 by mass (g/mol) | Value | Share |
|---|---|---|
| Phosphorus (30.97) | 30.97 | 22.55% |
| Chlorine (35.45 × 3) | 106.36 | 77.45% |
| Molecule | 137.33 | 100% |
| Tonnes of PCl3 per tonne of P | 4.44 | |
| Tonnes of chlorine per tonne of P | 3.44 | |
Carry that through the herbicide chain and it stops being an abstraction. A tonne of glyphosate is 18.32 per cent phosphorus, so it needs 0.81 tonnes of PCl3-equivalent to deliver its phosphorus — which is 0.63 tonnes of chlorine for every tonne of finished herbicide. The chlorine does not disappear; it leaves as hydrogen chloride from the esterification and has to be sold, scrubbed or neutralised.
Three and a half per cent, and most of it is the chlorine
PCl3 at RMB 5,773 a tonne against a cost base that leaves RMB 201 of gross spread: 3.5 per cent. It is the thinnest margin of any product in this segment — a sixth of the 21.78 per cent earned by sodium tripolyphosphate, a fifteenth of the 52 per cent earned by a one-step neutralisation in the phosphite market.
The chlorine does not arrive as a cost. It arrives partly as a payment: the hydrogen chloride the reaction throws off is credited at RMB 138.6 a tonne of product, which is 69 per cent of the entire spread. Take that credit away and the molecule is not made at a profit at any of the volumes this market runs. The phosphorus alone exceeds 100 per cent of the theoretical cash cost; the by-product hydrochloride is what turns a loss into a 3.5 per cent business.
A price set by caustic, not by rock
Because three-quarters of the mass is chlorine, the cost of a tonne of PCl3 responds to the chlor-alkali cycle — alumina, pulp and paper, water treatment, PVC — none of which has any relationship to phosphate. In a year when caustic is long, the chloride gets cheaper for reasons a phosphorus producer cannot influence. In a year when caustic is tight, the same producer’s raw material doubles while the acid market is flat.
That is why the product is usually made inside someone else’s fence. A 3.5 per cent merchant spread is smaller than the working-capital swing on either input; the integrated producer captures the same margin without having to finance the inventory between them.
Parity, which is what a courier charges
PCl3 sells its phosphorus at 1.05 times the price of the element. It is the only product in the chain priced at parity: the acid sits at 0.88, feed phosphate at 0.70, the salt at 1.32, the herbicide at 5.58. Parity is what a courier charges — the chloride does not add value to the phosphorus, it converts it into a form the next reaction can actually use. A five per cent fee for the conversion, of which the by-product chloride pays most.
Which is also why the value in this market is not at the phosphorus end. USD 961.2m in 2025, reaching USD 1,585.0m by 2033 in the parent report, is a market for a courier — and couriers are paid by the parcel, not by the distance.
What to watch
The PCl3 price is a poor signal on its own, because a 10 per cent move in yellow phosphorus is worth roughly 2.7 times the entire spread — the arithmetic behind the first article in this pair. The cleaner signal is the relationship between the chloride’s parity and the chloride’s spread: when the index holds near 1.05 while the spread compresses, the phosphorus half is doing the work and the chlorine credit has weakened. When the spread widens and the index falls, the chlor-alkali cycle has loosened and the market is passing it through.