Recycing And Purifing Terephthalic Acid From Wastewater Of Alkali Deweighting Finishing Of Polyester

Polyester pongee fabrics have good wearing characteristics, and therefore there is agrowing need for them. A part of polyester fiber is used for alkali deweighting finishing toproduce the polyester pongee fabics. However a considerable amount of high waste water isproduced during the finishing. The waste water concludes organic pollutant of highconsertration, which is difficult to be degraded. Therefore the alkali deweighting process hasbrougt serious environmental pollution. Although there were so much literature on recovery ofterephthalic acid (TPA) from the waste water of polyester alkali deweighting, most of thereported treatment processes are unsatisfied and cannot adapt industrial production. Therecovered TPA also has poor properties, such as low purity and recycling efficiency. Therealso is a lack of systematic research. For the purpose of effectve recovery of TPA from thewaste water of polyester alkali deweighting finishing, we investigated the effect ofultrafiltration, dissolving-crystallization and adductive crystallization method on the TPArecovery, results obtained are as follows.1) Firstly, the process of ultrafiltration-flocculation-acidification is applied to recoverthe TPA from the wastewater. The functional groups in the product are identified by infraredspectrum (IR), the surface morphology of the product is observed by scanning electronmicroscope (SEM), and the purity and acid value of the product are determined by UVspectrophotometer and acid value titration, respectively. The reasonable treatment process isas follows: pH of the acidification and the flocculation is2.6and7.0, respectively; usage ofcoagulation is0.8g/L. The purity of recycled TPA is close to that of the standard TPA reagent(purity≥99%). The acid value reaches96.29%of that of the standard TPA reagent.Recycling rate is89.03%. The research is technically feasible. However, the efficiency is low,and the diameter of the recovery TPA is small and uneven.2) Secondly, the dissolving-crystallization method is introduced to seperate the TPAfrom the waster residue, using N, N-dimethylformamide (DMF) as solvent, distilled water asprecipitating agent and activated carbon as discoloriser. The functional groups in the productare identified by IR, the surface morphology of the product is observed by SEM, and thepurity and acid value of the product are determined by UV spectrophotometer and acid valuetitration, respectively. The rational mass ratios of the waste residue to DMF and the activatedcarbon to the waste residue are1:12and0.6:1, respectively. The purity of recycled TPA isclose to that of the standard TPA reagent (purity≥99%). The acid value reaches96.43%ofthat of the standard TPA reagent. Recycling rate is86.54%. The TPA in alkali peelingwastewater can be recycled effectively by using DMF solvent. The efficiency of the process ishigher; however the diameter of the recovery TPA is smaller than that obtained by theultrafiltration process.3) Finally adductive crystallization method is applied to separatation of the TPA fromthe wastewater residue, using the N, N-dimethylformamide (DMF) as solvent to dissolve theTPA. Then the solution is distilled to remove the DMF and obtain adductive crystallizationproducts of TPA and DMF, which is formed in the process of cooling the distilled solution. TPA is obtained through drying the adductive crystallization product to separate the TPA andthe DMF. The product are characterized by IR, SEM, TG, acid value and UVspectrophotometer, respectively. When the distillation temperature is164℃and the dryingtemperature is105℃, the purity of recycled TPA is close to that of the standard TPA reagent,and the acid value reaches96.8%of the standard TPA reagent. The drying temperature haseffect on the recycled TPA. The diameter of the recovery TPA is bigger than above twomethods, and the result of the process is well.In this paper we conducted a systematic study on the recovery of the TPA from thepolyester alkali deweighting finishing wastewater and obtained good results. With theincreasingly value on the clean production and resource sustainable development, theobtained results will provide a technological supports for the reutilization of the alkalideweighting finishing wastewater, and are of theoretical interest and also of relevance toapplications.