Recovery of Na2SO4 from remediation of wastewater and reuse for preparation of sodium 4-nitrotoluene-2-sulfonate (NTSNa)

Electro‐generation of NaOH–H2SO4 and simultaneous degradation of Acid orange 7 fromNa2SO4‐containing wastewater by Ti/IrO2 electrodes

“…7 suggests the establishment of equilibrium between the AO7 monomers and its aggregates. In other words, the hyperchromicity before 90 min in the cathode compartment partly contributes to the shift of the aggregates → monomers with the decrease of sulfate in the electro-migration process, as shown in reaction (8). According to general electrochemical theory, decolorization after 90 min in the cathode compartment is mainly through two pathways.…”

“…For example, the wastewater (black liquor) from kraft pulping plants contains a lot of aliphatic carboxylic acids in addition to high Na 2 SO 4 . The wastewater from the production of 4,4 N‐diaminostilbene‐2,2 N‐disulfonic acid, an important compound intermediate of many direct dyes, contains about 0.15 mol L −1 Na 2 SO 4 and many organic pollutants (COD: about 20 000–30 000 mg L −1 ), such as 4‐nitrotoluene‐2‐sulphonic acid, 4,4 N‐dinitrostilbene 2,2 N‐disulfonic acid, azo‐compounds, phenols and nitro compounds . More extensively, the productions of many organic chemicals involve in sulphonating of organic compounds with H 2 SO 4 followed by neutralization with NaOH,leading to Na 2 SO 4 wastewater with organics and product residuals.…”

“…7 The wastewater from the production of 4,4 N-diaminostilbene-2,2 N-disulfonic acid, an important compound intermediate of many direct dyes, contains about 0.15 mol L −1 Na 2 SO 4 and many organic pollutants (COD: about 20 000-30 000 mg L −1 ), such as 4-nitrotoluene-2-sulphonic acid, 4,4 N-dinitrostilbene 2,2 N-disulfonic acid, azo-compounds, phenols and nitro compounds. 8 More extensively, the productions of many organic chemicals involve in sulphonating of organic compounds with H 2 SO 4 followed by neutralization with NaOH,leading to Na 2 SO 4 wastewater with organics and product residuals. As a result, in terms of practical use, there is a strong demand for investigation of electrochemically splitting Na 2 SO 4 into H 2 SO 4 and NaOH from wastewaters containing both Na 2 SO 4 and organic pollutants.…”

A novel method for the recovery of 4,4′-dinitrostilbene-2,2′disulfonic acid from the wastewater obtained from 4,4′-diaminostilbene-2,2′-disulfonic acid production

“…The preparation of DSD includes three steps [6] namely, sulfonation of p-nitrotoluene (PNT) to p-nitrotoluene-o-sulfonic acid (PNTSA) [7,8], oxidation of PNTSA to 4,4 0 -dinitrostilbene-2,2'disulfonic acid (DNS) [9], and reduction of DNS to DSD with iron powder [10]. 4-amino-4 0 -nitrostilbene -2,2 0 -disulfonic acid (ANSD) is another intermediate that can be further reduced to DSD, and is thus usually regarded as a minor byproduct of DSD.…”

Coupling of anodic oxidation and adsorption by granular activated carbon for chemical oxygen demand removal from 4,4′-diaminostilbene-2,2′-disulfonic acid wastewater

“…Consequently, DSD acid manufacturing wastewater is characterized by high value of chemical oxygen demand (COD, about 10-30gL') and abundant salinity (Na2SO4, about 20-45gL"'), which causes difficulty in treating by conventional biological processes (Zhu et al 2001). So far, many methods have been developed for treatment of the wastewater such as ionexchange (Chai et al 2005), extraction , and multiple-evaporation (Li et al 2006). However, the transfer of these technologies is limited due to their high cost as well as difficulty in control, reliability and efficiency.…”