Study On Sulfonation Process In The Production Of 4, 4'-diaminostilbene-2, 2'-disulfonic Acid And The Treatment Of The Waste Sulfuric Acid

The sulfonation of pNT is a key procedure to manufacture DSD acid, which is an important intermediate for the synthesis of fluorescent whitening agents. The commercial method sulfonating of pNT is the process of sulfonation with 20% sulfuric acid fuming for its simple operation and steady quality and yield of the product. However, this conventional process is associated with various problems, e.g., low yield and lots of waste sulfuric acid with high COD and color.In the present work, laboratory scale experiments of pNT sulfonation were performed. The mechanism and advantages of the 20% sulfuric acid fuming method and the SO3/solvent method were referred as the≥50% (in concentration) sulfuric acid fuming being the sulfonate agent and the mother liquor being the solvent which was separated from the NTS crystal. The experimental results demonstrated the effects of temperature, time, quality of raw material and mother liquor on the conversion of pNT and the yield of NTS as well. Accordingly, the process was improved gradually by selecting proper conditions for providing the fundamental data to support the scale-uping.The macroporous adsorption resin is a new kind of synthetic sorbents with a variety of advantages and simple equipments and low costs. The H1020 macroporous adsorption resin was selected to treat the waste sulfuric acid. The COD removal ratio was 66.8% at static conditions.and 92% at the best dynamic conditions proposed. The resin could be easily regenerated by dilute NaOH solution. The collected NaOH solution was applied in the oxidation process as a part of raw material which could lead no influence on the quality and yield of product. When the treated sulfuric acid was applied as a substitute to 98% sulfuric acid in the reduction of DSD acid, there was no significant difference between two products in quality and yield.The system of NTS adsorbed onto H1020 resin was conducted at static conditions. The results indicated that Freundlich model could reflect the process accurately and the Gibbs free energy, enthalpy and entropy obtained confirmed it was an exothermic process. A pseudo-second order adsorption kinetics equation was developed for the process, and relevant parameters were calculated. Furthermore, results showed that the process was controlled by the film diffusion.