Recovery Of 5-sulfoisophthalic-like Acids From Third-monomer Production Wastewater By Solvent Extraction

As a new type of anionic surfactant,trimer(dimethyl isophthalate-5-sulfonate,SIPM)plays an important role in terylene(PET)dyeing and modification.However,a large quantity of wastewater containing sodium sulfate and high concentration of 5-Sulfoisophthalic-like acids such as 5-Sulfoisophthalic acid monosodium salt(5-SSIPA),dimethyl isophthalate-5-sulfonate(SIPM),and monomethyl ester-5-sulfonate(SSPM)is produced during the SIPM production.It would cause huge waste of resource and serious environmental pollution if it is discharged directly to water environment without proper treatment.In this paper,a neutralization mother liquor produced during the SIPM production from a company in Shandong Province was chosen as the research object and the complexation extraction method was applied to recover the 5-Sulfoisophthalic-like acids and sodium sulfate.In order to better investigate the effectiveness of the extraction,100.0 g·L-1 5-SSIPA solution was utilized as the simulated wastewater.The composition of the extractant was determined as follows:triisooctylamine as the complexing agent,xylene and n-decanol as the diluent.The work was carried out by researching the reaction process of the extraction and the optimum extraction parameter was obtained firstly,and then the complex extraction of neutralizing mother liquor was carried out.For the solution of 5-SSIPA,the optimal extraction parameters were determined to be as the followed:initial pH 0.4,V(xylene):V(n-decanol)2.5:1,the oil to water ratio(O/W)0.8:1,and extraction temperature 25℃,where the removal of COD was 98.7%and the extraction ratio of 5-SSIPA was 99.1%.When the organic phase was back-extracted with 3%NaOH solution,70%of 5-SSIPA can be recovered and the purity of the recovered sample is 99.16%.The extraction ratio of the extractant for 5-SSIPA was still above 90%after being subjected to 6 cycles of extraction and back extraction.The extraction mechanism of 5-SSIPA simulated wastewater was studied by high-performance liquid chromatography and infrared spectroscopy,and it was found that there were both ion exchange and ion association reaction for 5-SSIPA complex extraction.The parameter model of cross-flow extraction was established by response surface optimization method.After analysis of variance and response surface analysis,the order of extraction conditions on COD removal was analyzed to be as:the volume ratio of xylene and n-decanol(V(xylene)/V(n-decanol))>the initial solution pH>the oil-water ratio.For the neutralization mother liquor,after a series of extraction conditions optimizing experiments,the optimal extraction process parameters were determined to be:initial pH 0.4,oil-water ratio 1:1,V(Triisooctylamine):V(xylene):V(n-decanol)3:5:2.After primary extraction,the extraction ratio of 5-SSIPA,SIPM,SSPM was 98.0%,90%,and 82.9%,respectively,where the removal of COD was 57%.After adding 3%NaOH solution for back extraction,the back extraction ratio of isophthalic acid-5-sulfonic acid was 63.7%.After the extraction,COD of the neutralized mother liquor raffinate was about 1.5×105 mg·L-1.COD decreased to 32011 mg·L-1 with fractionation,where the sulfate content was 104.94 g·L-1.When 100 g·L-1(0.42 mol·L-1)sodium persulfate was added to the raffinate,where the strong oxidant sulfate radical(·SO4-)was generated by thermal activation to oxidize the organic matter in the raffinate.As a result,the sodium sulfate can be recycled after evaporation to dryness,and the theoretical mass of sodium sulfate recovered in 100 mL of raffinate is 27.4 1g.