The Davy DMF process comprises two main steps: vapour-phase methylamines production to yield the key reactant dimethylamine (DMA); then a homogeneously catalysed reaction of liquid DMA and CO gas to produce DMF.
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 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), DMA and trimethylamine (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 DMA stream which proceeds to DMF conversion, and water-free MMA and TMA steams that recycle back to amination.
Residual methanol is extracted from the water and also recycles to the amination stage.
Liquid DMA enters the reactor, which also contains catalyst. Carbon monoxide gas enters the vessel via jet nozzles, which creates the necessary turbulence for good reactant contact.
The overall exothermic reaction proceeds in two stages, the first being a slow reaction that forms the intermediate compound methylformate:
A fast reaction then yields DMF:
The reactor product, a hot liquid, proceeds to the DMF vaporiser, which flashes DMF, unreacted DMA and methanol vapour from the catalyst solution.
Subsequent distillation and stripping steps then separate pure DMF liquid, with DMA and methanol recycling to the DMF reactor.