The Research Of Oxidative Condensation And Clean Technology Of 4-nitrotoluene-2-sulfonic Acid

It is the key step in the production process of 4,4'-diaminostilbene-2,2'-disulfonic acid (DSD) that 4-Nitrotoluene-2-sulfonic acid (NTS) oxidize to form 4,4'-dinitrostilbene-2,2'-disulfonic acid(DNS).But this reaction have many side reactions and much wastwater and occur phenomenon of red material easily,also its yield is very low.So the traditional batch process cann't adapt to the new situations.So this topic make a study on its influencing factors,synthetic technology,catalyst, reactor type,and so on.The study on oxidative condensation of NTS was carried out under the same pilot equipment. Through tracking the reaction process by HPLC,tried to find the influence law of different process conditions.It was found that the reaction included two steps,the influence of the NTS concentration and the alkali concentration to reaction was more notable when NTS oxidized to form 4,4'-dinitrobibenzyl-2,2'-disulfonic acid(DND).However, the influence of temperature was more notable when DND oxidized to form DNS.The main by-product 4-nitrobenza ldehyde-2-sulfonic acid (NBS) and 4-nitro-2-sulfobenzoic acid (NSB) could not only be generated by the deep oxidation of the DNS's bond-breaking as well as direct oxidation of NTS.At the condition of higher temperature and higher NTS concentration, DND and NTS quickly aggregated, which increased the viscosity of the material,reduced the effect of mass transfer and gas dispersion. So the air was uneven in the system and the oxidation was inadequate in the local area,which easily induced the phenomenon of red material.At the same time,The reaction system after red material became more viscous and aggravated the phenomenon of red material and accelerates over-oxidation of the DNS's the bond-breaking more seriously and increases more NSB.When the process conditions tha influence the oxidative condensation reaction of NTS, it was carried out to synthesize DNS in the continuous stirred tank reactor (CSTR) linked by four stirred tank.The stepped control technology was applied to control the reaction process.It showed that the conversion of NTS in stages could be completed well by reasonably control of feed concentration,reaction temperature and alkali concentration. The feed concentration has great influence on the oxidative condensation reaction of NTS.The higher feed concentration was easy to aggravate the generation of by-product NBS and NSB from the direct oxidation of NTS. The optimum feed concentration was 20%, at which the oxidation effect was optimal and compared with traditional batch process,the volume of wastewater and the consumption of liquid caustic respectively decreased by 38.3%,48.25%, the equipment capacity increased by 38.3% and the production process was more stable.The Semi-continuous oxidative process of NTS,which was linked by two and one stirred tank was designed on the basis of CSTR linked by four stirred tank.The total by-product in one tank that increased as the feed concentration increased was much more than two tanks and the amount of DNS in one tank was influenced by feed concentration slightly.But the amount of DNS in two tanks,firstly decreased,then increased,finally decreased again as the increase of feed concentration, the maximum which was at the feed concentration of 20%.And the least by-product in two tanks was at the feed concentration of 19%,the amount of by-product increased when the feed concentration was higher than 20%,so by comprehensive consideration of production cost,the fedd concentration of 20% was optimal.The reactor linked by two tanks was better than one tank.Before diluted alkali concentration,the reaction rate of NTS and the formation rate of DNS was the fastest at Fe2+ catalyst and the most slowly at Cu2+, the formation rate of DND was fastest at Mn2+ catalyst. After diluted alkali concentration, the formation rate of DNS was the fastest at Mn2+ catalyst and the most slowly at Ni2+. The formation rate and total amount of by-products were the biggest at Cu2+ catalyst and the least at Mn2+.As the increase of atomic number that is the electron number of p track. and total amount of by-products was gradually increase.The composite catalyst didn't improve the reaction effect of NTS.According to the gas-liquid two-phase simulation of air-loop reactor (ALR),flat bottom reactor's gas distribution was better than the elliptic bottom reactor's.