Dimethylacetamide is known as DMAC with a chemical formula CH3CON(CH3)2. Its boiling point is about 166oC. It has the capability to undergo hydrolysis, saponification and alcoholysis reactions and can be stored in mild steel containers. Acetic acid and dimethylamine are reacted in continuous stirred tank reactor for dimethylacetamide production in small scale and for large scale industrial processing a plug flow reactor is used.
Reaction takes place at liquid state in a CSTR/ PFR :
- CH3COOH + (CH3)2NH → CH3CON(CH3)2 + H2O
Process flow diagram of Dimethylacetamide production:
Process description of Dimethylacetamide production:
Acetic acid and dimethylamine are pumped by a centrifugal pump to the heat exchanger eventually developing the pressure up to 6.5MPa. By using steam the temperature of the reactants are raised to around 325oC. The heated stream is feed to PFR to provide enough contact time and complete the reaction. A flash separator separates dimethylamine from the reactor effluent stream. Based on unreacted acetic acid, caustic soda is added to the solution in a CSTR. NaOH reacts with acetic acid forming sodium acetate, which forms a precipitate. Filters like filter press for batch process or centrifugal separator for continuous process remove the so formed solid phase. The azeotropic solution is fed to a distillation column to separate water. The bottom stream of distillation column is passed to purifier to separate the traces of acetic acid in DMAC. Recovered acetic acid and dimethylamine is recycled to feed stream of reactor.
Bottleneck in Dimethylacetamide production:
The drawback in this process was the azeotrope formation. DMAC and unreacted acetic acid form an azeotrope having the boiling point of 170oC. At 6.2MPa and 320oC with excess dimethylamine we can prevent formation of azeotrope for some extent. Based on the conversion of acetic acid the quantity of azeotrope formation can be controlled. The synthesis process needs to be developed to improve the yield of DMAC from 45% to 90%. The process designing for this process is still insufficient, leading to the scope for new methods and reactor designs.