(707f) Continuous-Flow Synthesis of the Azo Pigment Yellow 14 Using a Three-Stream Feeding Micromixer

Organic coloured pigment is one of the most important chemical fines. The demand for organic coloured pigments continuous to grow with the growing use in the field of colour printing、cosmetics、coatings、plastics and so on. Among the organic coloured pigments, the most well-known class is the azo pigment. One example is azo pigment yellow 14, which is a typical bisazo pigment. The yellow pigment is usually the last component of the printing process^[1] and therefore, they often need to have some special properties, such as a high transparency、a high strength of colour and a high tinctorial power^[1]. The colour properties of azo pigments are connected with the particle size and the particle size distribution. They are affected by the production process ^[1].

In industry, the azo pigments are often synthesized by batch process using stirred tanks with volumes varied from 20 m ³ to 80 m ^3[1]. However, batch processes are possible to lead to a relatively board size and a low conversion of the coupling component, which seriously affects the quality of the azo pigments. For the synthesis process of azo pigment yellow 14, it includes double diazotization and double coupling reaction, which need an accurate regulation of the pH during reaction process. Therefore, a better mixing effect and a more precise adjustment of synthesis process are needed. In last 20 years, the microreactor technology has been widely used in both industry and academia^[2]. Compared with traditional batch vessels, the microreactor technology has many advantages, such as better mass and thermal transfer, more accurate control parameters^[3].

The first successful synthesis of azo pigments in microfluidic devices was reported by Wille et al.^[4] The azo pigments showed improvements in color properties compared with batch processes. Then, the synthesis of Pigment Yellow 12 in a micromixer apparatus was developed by Pennemann et al.^[1] Using a Micromixer-based process, they improved the properties of the azo pigment yellow 12. However, the azo pigments synthesized above were not sensitive to the changing of the pH during reaction process compared with the azo pigments yellow 14.

In this work, a three-stream feeding process for the synthesis of azo pigment was considered to control the pH of the coupling reaction process accurately. The acetic acid/sodium acetate buffer solution was pumped into the micromixer as a separate stream which was different from the two-stream feeding process and batch process. The pH of the reaction process was not necessary to be monitored at any time if the pH of the buffer solution was controlled. Furthermore, a three inlets microreactor for easy scale-up study was designed to carry out the coupling reaction. Then, the effects of pH of the buffer solution、reactants flow rates and reaction temperature on the purity and the particle size distribution of the azo pigments were discussed. Finally, the hue and transparency of the products compared with pigments standard (commercial products, SHENYANG RESEARCH INSTITUTE OF CHEMICAL INOUSTRY) were also studied. The results show that under optimal conditions, a higher purity (94.54%) of the pigment can be obtained using three-stream feeding process than that using two-stream feeding process (83.34%) and a monomodal particle distribution can be obtained compared the batch process getting a bimodal distribution. According to the coordinates of CIELab colour space (L*, a*, b*) evaluated for azo pigments, it illustrated that the red hue and the blue hue of the azo pigment products were larger compared with pigment yellow 14 standard. The lightness L* of the pigments synthesized by three-stream feeding process was larger than that by two-stream feeding process. The transparency was increased by 98% compared to a commercially available yellow 14. Overall, the micromixer-based three-stream feeding process led to a significant improvement of the azo pigment yellow 14 process, which had a good industrial application value.

References:

[1]Pennemann, S. Forster, Kinkel, Improvement of Dye Properties of theAzo Pigment Yellow 12 Using a Micromixer-Based Process. Org. Process Res. Dev. 9 (2005) 188-192.

[2]J.S. Zhang, K. Wang, Y. C. Lu, G. S. Luo, Characterization and modeling of micromixing performance in micropore dispersion reactors. Chem. Eng. Prog. 49 (2010) 740-747.

[3]Z. Q. Yu, X. Ye, Q. L. Xu, X. X. Xie, H. Dong, W. Su, A fully continuous-flow process for the synthesis of p-Cresol:Impurity Analysis and process optimization. Org. Process Res. Dev. 21(2017) 1644-1652.

[4]C. Wille, V.Autze, H. Kim, U. Nickel, S. Oberbeck, T. Schwalbe, L. Unverdorben, In Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6, March 11-14,2002, New Orleans, LA, U.S.A.; pp 7-17.