Dimethylformamide (DMF) RECOVERY PLANT

1) FOREWORD

The DMF (Dimethylformamide) distillation unit can be designed for a capacity from 2.000 kg/h of water solution to 15.000 kg/h or more, according to our standard design.
The DMF concentration in water can vary from 20% up to 30%, but it is even possible to take into consideration different concentrations (i.e. 10% ÷ 50%).
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.

2) PROCESS DESCRIPTION

The process application can be offered in the following fields:
- DMF recovery from polyurethane synthetic leather manufacturing plants;
- DMF recovery from PU elastic filament production plants;
- DMF recovery from acrylic fibre production plants;
- DMF recovery from pharmaceutical plants.
- DMF recovery from food production plants.
Similar process can be also used for DMAC (dimethylacetamide) recovery plants.
The typical recovery plant includes the following units:

Vapours washing unit
The vapours leaving the production lines and containing 2 ÷ 10 gr/Nm3 of DMF are conveyed to a blower having the necessary head for winning the pressure drop of the blow-down column.
The vapours entering into the bottom of the blow-down column are first washed with a DMF water solution at 10 ÷ 20 % DMF concentration, which is cooled by recirculation in a heat exchanger. The vapours then goes to a special section for the final washing, the water needed to keep at constant value the DMF concentration is fed at the top of the column.
The exhaust vents coming out the column are dispersed into the atmosphere with a very low DMF content (expected value normally less than 20 mg/Nm3).
A level indicator controller of the column bottom controls the discharge of the recovered DMF water solution.
Under the local authorities request it is possible to achieve also effluent value less than 2 mg/Nm3.

Distillation unit
The DMF-H2O solution, coming out the above unit and the production lines, 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 DMF vapour removing DMA and HCOOH (Formic Acid).
It is needed to purge the evaporator and the reboilers periodically to remove polymers, heavy products and formic acid: the purge stream is collected into a squeezing column in order to improve the recovery yield of the DMF.

DMA Stripping unit
The waters coming from the top of the distillation unit, contain small quantities of DMA (dimethylamine) which is a product of DMF 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 DMF from formic 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.

3) DMF PURITY

The purity of DMF obtained with the distillation process, whereas a sidestream column is provided, is the following:
- H2O lower than 100 ppm
- HCOOH lower than 30 ppm
- DMA lower than 20 ppm

4) UTILITIES CONSUMPTION

Considering 25% DMF solution, the utility consumptions are the following:

Single effect Double effect Triple effect
Capacity [kg/h] 2.500 5.000 7.500
Heat requirement [kcal/h] 2.500.000 2.650.000 2.850.000
Cooling water [m3/h] 300 300 300
Electrical power [kW]
negligible negligible negligible

5) 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 DMF, together with low energy costs and high recovery yield.
Particular attention has been also dedicated to safety and ecological matters

6) APPLICATION AND RELATED TECHNOLOGIES

Besides the technology for recovery and purification of DMF directly from M.F.C. Progetti or through related company is available the complete technology for:
- Synthetic leather production plant
- Acrilyc fibre production plant
- PU elastomeric yarn production plant
- Food industry and electronic industry
- Yarn and Pharmaceutical