The Davy NMP flowsheet separately generates two compounds, gamma-butyrolactone (GBL) and monomethylamine (MMA), before reacting them together to form NMP.
The process feedstock for producing GBL is molten maleic anhydride (MAH), obtainable by the oxidation of butane or benzene.
The amination process, which yields the MMA reactant, requires liquid methanol and liquid ammonia, which mix with a composite stream of recycled methanol, ammonia and methylamines from downstream distillation.
Molten maleic anhydride reacts with methanol vapour in the Davy esterification reaction column to produce liquid-phase dimethyl maleate (DMM):
Vapour-phase hydrogenolysis follows to produce gamma-butyrolactone (GBL):
Some GBL also hydrolises to butanediol (BDO), which subsequently dehydrates to tetrahydrofuran (THF). Distillation separates these compounds to yield high-grade liquid GBL.
The amination feed stream, comprising methanol, ammonia and methylamines, 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 MMA, dimethylamine (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 MMA stream which proceeds to NMP conversion, and water-free DMA and TMA streams that recycle back to amination.
Residual methanol is extracted from the water and also recycles to the amination stage.
Stoichiometric quantities of GBL and MMA proceed to the specialised NMP synthesis reactor, in which they undergo non-catalysed liquid-phase reaction.
The reaction takes place in two stages. First, the GBL and MMA combine to form a long-chain amide by cleavage of the GBL ring and attachment of the MMA. The resulting intermediate is 4-hydroxy-n-methylbutylamide (HMB):
In the second stage, cylisation restores the cyclic molecular structure as the HMB molecule dehydrates to form NMP:
Distillation separates organic heavies, MMA and reaction water to yield solvent-quality NMP, which is sent to storage.
The reaction heavies and MMA are recycled back to synthesis.
+Process option: anhydrous or aqueous feed
The Davy NMP process can utilise either anhydrous or aqueous MMA feestock.