Study On The Continuous Synthetic Process Of Azo Pigments

Azo pigments are indispensable products in people’s lives.Nowadays,the production method of azo pigments in China is mainly batch process,which has a large potential for development in terms of product quality stability and environmental protection.The continuous process can not only solve these problems,but also reduce energy consumption and improve production efficiency.This paper set up a continuous reaction device,and studied the continuous control mechanism of Pigment Yellow 12,optimized its process,and studied the continuous synthesis process of Pigment Red 146.Firstly,3,3’-dichlorobenzidine(DCB)diazonium salt aqueous solution was synthesized from slightly soluble 3,3’-dichlorobenzidine hydrochloride by continuous-flow method via a collision mixer.A yield of 98.3% was achieved under the optimized reaction conditions of mass concentration of DCB 70g/L,feed temperature 20℃,flow rate 1.1m/s,n(HCl)∶n(DCB)=4.Compared with a batch process,the continuous-flow process requires less hydrochloric acid,improves reaction efficiency,and can carry out at room temperature(20℃),which significantly reduces energy consumption.Before the continuous azo-coupling reaction,the preparation process of the coupling agent slurry was explored,and the following better conditions were obtained:acetic acid dropping time was 20 min,acid precipitation stirring time was 20 min,acid precipitation temperature was 5℃,and stirring time was 2h.Then,the PY12 with a yield of 98.5%,a similar chroma,a 12% increase in coloring strength,a high transparency,and a high reflectance was synthesized under the optional azo-coupling conditions of the initial p H of coupling component 11.2,sodium acetate 30 g,reaction temperature 15℃,feed flow 40L/h,heating temperature85℃.Finally,the important red azo pigment PR146 was synthesized continuously with a yield of 98.1% under the conditions of n(HCl):n(red base KD)=3,feed temperature of the diazotization 20℃,flow rate of the diazotization 1.1m/s,the p H of the coupling outlet product solution 5.0,and coupling reaction temperature 15℃,coupling flow rate 0.88 m/s and heating temperature 85℃.