Overview of spray drying applications in the dye industry

Dyestuffs and pigments belong to the same category of fine chemicals. In recent years, with the changes in the international pattern of dyestuffs production, China has become the world's largest dyestuffs producer, and has risen to the top of the list of dyestuffs production as far as output is concerned. In the process of dyestuff production, spray drying is most widely used, and several forms of spray drying are applied in dyestuff factories.



Dyestuffs are heat-sensitive materials, and many dyestuffs are susceptible to particle agglomeration and deterioration when dried with other drying equipment such as box drying, drum drying, and rake drying due to the long residence time of the material in the high temperature zone. The method of spray drying gives full play to the advantages of instantaneous drying and plays an important role in improving the quality of dyestuffs. However, dyestuffs are characterised by a large number of varieties, each of which has different characteristics reflected in the drying, and the heat-resistant temperature of dyestuffs is not high, generally ranging from 120 to 250°C (hot air inlet). In addition, the heat source requirements are high, and the hot air used is clean air after heat exchange (except natural gas which can be directly heated). As far as the heat-resistant temperature is concerned, there is the following law: water-soluble dyestuffs are higher than non-water-soluble dyestuffs, dark dyestuffs are higher than light dyestuffs, and the heat-resistant temperature is correspondingly higher when more additives are added. In addition, the drying of dyestuffs is also related to the strength of the dyestuffs before drying, the composition of the processing formula, the particle size and so on. For spray drying technology, the design and operation in combination with specific dyestuffs is also a complex element.



At present, the main varieties that can be dried by spray drying method are disperse dyes, reducing dyes, reactive dyes, individual varieties of acid dyes, direct dyes, food dyes, basic dyes, fluorescent whiteners, auxiliaries and intermediates, organic pigments, and inorganic pigments. Due to the different requirements of the products, the selection of the dryer is also different, therefore, there should be a clearer understanding of the performance of several dryers in the drying of dyestuffs.