Study On The Synthesis Of N,N-dimethylacetamide Via Reaction-separation Coupling Technology

N,N-dimethyl acetamide(DMAC)is an aprotic organic solvent with high boiling pointand strong polarity,having the ability to dissolve,good stability,low volatility,hard tobe hydrolyzed,hard to change and low corrosion.It can be widely used in the fields of petroleum processing and industrial organic synthesis.At present,the demand of DMAC consumption from the domestic acrylic fiber industry and spandexindustry accounts for the most part.And with the development of the chemical industry,DMAC will maintain a broader prospect for development and application.At the atmosphere pressure,acetic acid and DMAC can form azeotrope(84.9%wt%DMAC),which can’t be separated by conventional distillation.So the subsequent processing is very complex for coping with the azeotrope in the process of traditional acetic acid method.In this paper,semi-continuous catalytic reactive distilation method to synthesize DMAC at the atmosphere pressure with acetic acid and dimethylamine was first discussed.Single factor experiments were conducted to analyze the influence of four factors on the reaction and the factors are the concentration of catalyst,reflux ratio,n(dimethylamine)/n(acetic acid),and reaction temperature.Then experiments were designed based on response surface methodology design for analyzing the function ralations between the factors and the yiled of DMAC.The optimum conditions were determined to be the concentration of catalyst 3%(weight percentage),reflux ratio 2.8,reaction temperature 172℃,n(dimethylamine)/ n(acetic acid)1.4 and under this condition the yield of DMAC can be researched about 93.3%.On the basis of semi-continuous catalytic reactive distilation method,using a new continuous catalytic reactive distilation method to synthesize DMAC at the atmosphere pressure.The process consists of three reactive zone and a distillation column.The dimethylamine flows into the system from the third reactive zone while acetic acid enters from the upper part of the reactive distilation column.As the result of gas-liquid countercurrent contact reaction,the water of reaction was removed in the top of column and the raw product of DMAC was obtained in the third reactive zone.Process optimization experiments of DMAC in a catalytic distillation column were carried out using single factor experiments and response surface methodology.The optimum conditions were determined to be the suitable feeding position for acetic acid is100 mm from the top of the tower,the feeding rate of acetic acid 7(m L/min),catalyst 3%(weight percentage),reflux ratio 2.5 and n(dimethylamine)/ n(acetic acid)1.6.The result shows that the qualitity of DMAC reached 99.5% in the third reactive zone,which no longer need to be neutralized,filtered and distilled.The high-purity DMAC product can be obtained directly by the conventional distillation,meeting the requirements of each application area.