The Davy choline chloride process comprises two main steps: vapour-phase methylamines production which yields the key substrate trimethylamine (TMA); then a two-stage reaction system for the liquid-phase conversion of TMA to ChCl.
The process feedstocks are liquid methanol and liquid ammonia, which mix with a composite stream of methanol, ammonia and methylamines recycled from downstream distillation.
The ChCl reaction system employs aqueous hydrochloric acid (HCl) and pure ethylene oxide (EO) feeds.
The feed stream passes through several heat exchangers, first vaporising and then superheating before entering the methylamines converter.
Here, the vapours pass over catalyst, facilitating an exothermic reaction between the methanol and ammonia to produce monomethylamine (MMA), dimethylamine (DMA) and TMA:
Additional disproportionation and transmethylation reactions create amines from other amines.
The hot vapour product stream exiting the converter contains the three methylamine products, reaction water and unreacted ammonia and methanol.
The individual quantities of each amine produced are determined by the converter’s feed composition. This in turn is a function of the amounts of each reactant and methylamine product recycled from distillation to join the fresh methanol and ammonia feed.
After passing through a heat recovery system and then a condenser, the process stream, now a liquid, progresses to the distillation stage.
The distillation system, comprising a number of columns in series, purifies and separates the crude methylamine products firstly by separating unreacted ammonia and recycling it to the amination stage.
Subsequent distillation then produces a pure anhydrous TMA stream which proceeds to ChCl conversion, and a water-free MMA/DMA mixture that recycles back to amination.
Residual methanol is extracted from the water and also recycles to the amination stage.
The ChCl reaction system consists of a single continuous reaction stream proceeding through two reactors in series, both of which operate under mild conditions.
In the first reaction stage, aqueous HCl and anhydrous liquid TMA react exothermically to yield the intermediate trimethylamine hydrochloride (TMA-HCl):
Proceeding to the second reactor, the TMA-HCl solution mixes with pure liquid ethylene oxide, resulting in another exothermic reaction to this time produce the final ChCl product:
Excess TMA, water and trace organics are flashed from the crude product, and subsequent heating concentrates the solution by evaporation. The recovered TMA recycles to the ChCl synthesis stage.
In storage, chemical dosing controls the final product pH and prevents oxidation and discolouring.