Dimethylacetamide (DMAC) RECOVERY PLANT

DMAC RECOVERY PLANT
• Foreword
DMAC (dimethylacetamide) is a solvent mixable with water that in many application can substitute DMF (dimethylformamide).
Hereunder are some technological information about the DMAC recovery Plant based on a distillation process, to recover the DMAC from H2O-DMAC solution coming from coagulation bath of PU synthetic leather manufacturing Plant, acrylic fibre production Plant, polyurethane elastic yarn, etc.
The DMAC recovery Plant is normally including the following unit:
• distillation unit;
• squeezing column unit;
• DMA (dimethylamine) stripping unit.
For plants having a capacity over 2.500 kg/h a multiple effect distillation unit has been studied, in order to reduce the energy costs, with the recovery of the heat from one effect to the other one. Recent thermal compression system has been developed.
MFC has already designed and operated a four effects plant: the first effect operates at the atmospheric pressure, the other three under vacuum up to a capacity of 50,000 kg/h at 25% of DMF.
For plants having a capacity lower than 2000 kg/h, a batch distillation unit can be designed.
• Process description
- Distillation unit
The DMF-H2O solution is fed from the intermediate storage tank to the evaporator of the distillation Column to feed the Column with a vapour-phase mixture.
Water vapours coming from the top of the distillation column are condensed and collected in a holding tank: part of the water is used for reflux and the excess is sent to the DMA (Dimethylamine) stripping unit to reuse all the water into the vapour washing unit and into the production lines.
A side stream on the column is provided to purify DMAC vapour removing DMA and Acetic Acid.
It is needed to purge the evaporator and the reboilers periodically to remove polymers, heavy products and acetic acid: the purge stream is collected into a squeezing column in order to improve the recovery yield of the DMAC
DMA Stripping unit
The waters coming from the top of the distillation unit, contain small quantities of DMA (dimethylamine) which is a product of DMAC hydrolysis. Before to recycle such waters it is necessary to remove the DMA in a proper stripping unit. The waters with a content less than 20 ppm of DMA exit the bottom of this column and can be completely reused in the process; DMA can be removed as a concentrated stream from the top and can be burned.
Squeezing Column unit
The purge streams from the distillation unit are re-evaporated again in order to have a further separation of the DMAC from acetic acid and low polymers.
A special design of such unit can increase the overall recovery yield up to 99,5% in relation to the purity of the DMF-H2O initial feed.
Low polymer together with formic acid can be discharged as concentrated liquid mud.
• Advantage of the MFC Progetti technology
Due to the large experience in the design of such plants, the MFC Progetti technology can achieve very high purity (99,99%) of the recovered DMAC, together with low energy costs and high recovery yield.
Particular attention has been also dedicated to safety and ecological matters and in material selection doe to the corrosion problem connected with the presence of acetic acid.