Formaldehyde → Naphthalene

Examples of a method of production of naphthalenesulfonic acid-formaldehyde condensate include condensation of naphthalenesulfonic acid with formaldehyde. The resultant condensate may be neutralized. Water-insoluble bi-products generated by neutralization may be removed. A specific process of the method is as follows. To produce naphthalenesulfonic acid, 1 mol of naphthalene is reacted with 1.2 to 1.4 mol of sulfuric acid for 2 to 5 hours at 150 to 165° C. to give a sulfonated product. To 1 mol of the sulfonated product is added formalin in an amount equivalent to 0.95 to 0.99 mol of formaldehyde dropwise for 3 to 6 hours at 85 to 95° C., and then condensated at 95 to 105° C. A neutralizing step may be then performed by adding water and a neutralizing agent to the condensate and reacting at 80 to 95° C. The neutralizing agent is preferably added in 1.0 to 1.1 times the molar amount to each of naphthalenesulfonic acid and unreacted sulfuric acid. Water insoluble matters generated by neutralization may be removed, preferably by filtration. Through these steps, an aqueous solution of water-soluble salt of naphthalenesulfonic acid-formaldehyde condensate is obtained. The aqueous solution can be used as the component (B) as is or by being added with other ingredients appropriately. A content of solid in the aqueous solution as the component (B) is, which may be varied according to applications, preferably 0.3 to 50% by weight, more preferably 5 to 45% by weight, and even more preferably 30 to 45% by weight, from the viewpoints of properties for dispersing a hydraulic powder and ease of handling depending on an adequate viscosity of the aqueous solution. The aqueous solution may further be dried and powderized to give a powder of water-soluble salt of naphthalenesulfonic acid-formaldehyde condensate according to need. The powder may be used as the powdery component (B). Drying and powderizing can be carried out by spray-drying, drum drying, freeze drying, or the like.