Case study of comprehensive treatment for high-concentration thujic acid wastewater
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Abstract: A waste liquid resource recovery and comprehensive treatment plant with a processing capacity of 67 m3/d was constructed to treat high-concentration 2-amino-naphthalene sulfonic acid waste liquid using the N235-kerosene-H2SO4-NaOH chemical extraction-reextraction system and chemical oxidation methods. The test results show that after extraction, the CODCr in the waste liquid decreased from 15,000 mg/L to 20,000 mg/L to 721 mg/L to 1,503 mg/L. The main components of the recovered concentrate are tarsic acid and hydroxytarsic acid, which can be directly reused in the production process, increasing the product recovery rate by about 10% and yielding significant environmental and economic benefits. Keywords: Dye intermediates; Tobias acid wastewater; Extraction; Process designPractice for High-Level Tobias Acid Wastewater Treatment by Li Zhonghe et al.
Abstract: A comprehensive treatment plant with a capacity of 67 cubic meters per day has been developed to handle highly concentrated Tobias acid (2-amino-naphthalene sulfonic acid) wastewater. This plant utilizes a chemical extraction–stripping system involving N235, kerosene, H2SO4, and NaOH, along with a chemical oxidation process. Operational results show that the CODCr level of the wastewater can be reduced from 15,000–20,000 mg/L to 721–1,503 mg/L through the extraction process. The main compounds present in the treated wastewater are Tobias acid and 2-hydroxynaphthalene sulfonic acid; these can be sent back to the appropriate units in the production process to recover useful substances. This method achieves a conversion rate of 10%. Thus, this treatment system offers significant economic and environmental advantages.
This project focuses on treating wastewater generated from Tobias acid, a typical naphthene-based dye intermediate. It employs a chemical extraction–back-extraction system using N235, kerosene, H2SO4, and NaOH, along with a chemical oxidation method using Fenton’s reagent, to carry out comprehensive resource recovery. The plant was completed and successfully put into operation in September 1995. Over the past two years, the operational results have basically met the design requirements, achieving good outcomes. ?This project was awarded the title of “Outstanding Model Project of the Eighth Five-Year Plan” by the **Environmental Protection Administration. 1 Project Overview 1.1 Company Overview The manufacturing enterprise is a state-owned chemical plant in Shandong Province. The thioic acid production system is a new project at this plant, with a designed production capacity of 2,000 tons per year; the current production volume is 1,000 tons per year. Approximately 10 m3 of acid-containing waste mother liquor is generated for each ton of product produced. The wastewater resourceization-comprehensive treatment system is a project that follows the \"three simultaneities\" principle; it was built in the same year as the production facilities, successfully commissioned, and has been operating normally to this day. 1.2 Design Parameters and Design Standards 1.2.1 Design Parameters Design capacity: 67 m3/d ； Wastewater quality: CODCr = 15,000 mg/L to 20,000 mg/L; pH = 0.5 to 1.0 ； Extraction ratio O/A: 1∶3～1∶4 ； Reaction time: 10min ； Two-phase separation time: 30min ； Reaction temperature: >18℃ ； Anti-extraction ratio to O/A: 3∶1～4∶1 ； Anti-extraction reaction time: 10 min ； Two-phase separation time: 40min ； Reaction temperature: >20℃ ； Dosage of chemical oxidation treatment agents: Fe2+ 100 mg/L, H2O2 (25%): 4 g/L ； Reaction time: 4h ； Lime neutralization: pH = 7–8 ； Settling time: 2h. 1.2.2 Treatment Standards Extraction efficiency (based on CODCr) > 90% ； Extract the concentrate: the concentration ratio is 8–10 times, with a CODCr concentration of >100 g/L to 150 g/L (1 kg of CODCr is equivalent to 0.6 kg of tarsic acid) ； Emission requirements: CODCr < 200 mg/L, pH = 6–9. 2 Process Flow and Main Process Equipment 2.1 Process Flow This project is divided into two stages: the resource recovery stage and the chemical oxidation treatment stage of the raffinate. 2.1.1 Extraction-Back extraction process flow The extraction-back extraction process flow for resource recovery is shown in Figure 1. This process features the following characteristics: http://gw.wanfangdata.com.cn/periodical/periodical.articles/jsps/jsps99/jsps9912/image12/t3001.gif Figure 1 Process flow in the recycling section (1) The entire system operates in a continuous manner, with automation playing a key role during operation. (2) Extraction is carried out via two-stage continuous counter-current operation, while back-extraction is one-stage, resulting in an integrated unit. (3) Easy to operate and occupies a small area. 2.1.2 Chemical oxidation process for the raffinate The process flow is shown in Figure 2. A separation and recovery device for entrained extractant in the raffinate was considered in the design. http://gw.wanfangdata.com.cn/periodical/periodical.articles/jsps/jsps99/jsps9912/image12/t3101.gif Figure 2 Process flow of chemical oxidation of the raffinate 2.2 Main process equipment 2.2.1 Continuous extraction-re_extraction integrated reactor The extraction-re_extraction tank is designed as an integrated reactor, with the extraction tank operating in a continuous counter-current two-phase mode. The effective volume of the mixing reaction chamber is 0.62 m3, while the effective volume of the two-phase separation chamber is 1.865 m3. The stirrer uses a four-blade straight paddle with a diameter of 270 mm, a blade height of 68 mm, and a rotation speed of 180 r/min to 200 r/min. The counter-extraction tank is of single stage; the effective volume of the mixing reaction chamber is 0.27 m3, while the effective volume of the two-phase separation chamber is 0.81 m3. The stirrer uses a four-blade straight paddle, with a blade diameter of 220 mm and a blade height of 55 mm, operating at a speed of 200 r/min to 220 r/min. Three sets of stirring devices are driven by 3 sets of variable-speed motors. 2.2.2 Waste liquid storage and regulation equipment: Two sets of waste liquid storage and regulation tanks, each with a capacity of 10 m3, were created by modifying existing equipment; these tanks are equipped with 2 transfer pumps to deliver the liquid to the higher-level tanks. 2.2.3 High-level tank feeding equipment Includes waste liquid high-level tanks, extractant high-level tanks, and anti-extractant high-level tanks; their effective volumes are 2.6 m3, 0.8 m3, and 0.28 m3 respectively. All of them are equipped with automatic level controllers to control the start and stop of the feeding pumps. 2.2.4 Chemical oxidation treatment system for raffinate Includes an oil separator, an oxidation reaction tank, and a neutralization and precipitation tank. The oil separator has dimensions of length × width × height = 2m × 4m × 1.5m. There is 1 underground oxidation tank with a residence time of 9 hours; its planar dimensions are 1.6m × 3.4m, and the effective water depth is 1.6m. Polyvinyl chloride baffle plates are installed in it. There are 2 neutralization and precipitation tanks, each 2m wide and 6m long. 3 Production and Operation Status The resource chemical processing unit of the Tussah acid wastewater comprehensive treatment system at this plant began trial operation in September 1995, and soon entered normal operation, with its treatment capacity meeting the design requirements. 3.1 Operating Process Conditions The pH of the extractant solution is controlled between 0.7 and 1.3 by adding acid or base; the extraction ratio (O/A) is 1:3 to 1:4, the extraction reaction time is 10 minutes, and the reaction temperature is room temperature. The counter-extraction process conditions are: extractant concentration of 20%–24%, counter-extraction ratio (O/A) of 4:1–3:1, reaction time of 10 min, and reaction temperature of 20°C–45°C. In winter, when preparing the anti-extraction agent, it is necessary to heat the water with low-pressure steam before preparation. 3.2 Operation Status The extraction-re_extraction process is a linked system, and its startup and operation present certain difficulties, especially in maintaining the stability of the interface between the two phases. There could be two reasons: first, the sump is 0.5 m lower than the designed level, resulting in unstable head pressure ； Secondly, the ABS globe valves required for regulating flow were not purchased; ball valves were actually installed, which makes it very difficult to regulate the flow. 3.3 Treatment Effect CODCr levels of the inlet and outlet water were monitored after treatment, and the treatment effects for each batch of water samples are shown in Table 1. Table 1 Performance Results: Sample Number, Raw Water CODCr/mg/L, Treated Water CODCr/mg/L, Treatment Efficiency/%
1#: 14,500 / 1,370 – 91.4%
2#: 16,100 / 1,430 – 91.4%
3#: 14,760 / 721 – 95.1%
4#: 16,510 / 843 – 94.95%
5#: 16,100 / 2,039 – 92.56%
6#: 14,600 / 1,503 – 92.57%
7#: 16,900 / 1,420 – 91.6%
As can be seen from Table 1, the CODCr level in the tarsic acid waste liquid produced by this plant ranges from 14,500 mg/L to 16,900 mg/L, while the CODCr level in the raffinate is only between 721 mg/L and 1,503 mg/L. The treatment efficiency lies between 91% and 95.1%, meeting the design requirements. 4 Discussion of Issues 4.1 Acid Extraction All Tulsic acid production lines in China use the 2-naphthol method, and hydrochloric acid and sulfuric acid can be employed in the final acid extraction stage. The wastewater used in the experimental studies was provided by another thioic acid plant; it is the filtrate obtained after acidification with sulfuric acid, and chemical oxidation of this effluent can reduce its CODCr level to below 200 mg/L. The plant uses hydrochloric acid for acid extraction, which results in a reduced extraction efficiency; the raffinate cannot be effectively kept below 1,000 mg/L. Most seriously, Cl- has a negative impact on the subsequent catalytic oxidation process, making it difficult to reduce CODCr to below 200 mg/L. To this end, in-depth research is being conducted on wastewater after hydrochloric acid acidification one year after the plant’s operation. 4.2 Possibility of using extraction methods to treat wastewater containing high concentrations of dyes or dye intermediates The use of an N235-kerosene-H2SO4-NaOH extraction-reextraction system to treat wastewater containing dye intermediates is a result of experiments conducted during the \"Eighth Five-Year Plan\" period. This project represents the first practical application of this technology, and the actual production results were close to those obtained in experiments, proving that it is feasible to use this technology for treating dye wastewater containing sulfonic acid groups. The recovered concentrate is directly reused in the production process, increasing the product recovery rate by about 10%. 4.3 Potential for widespread application The anion-associated chemical extraction system exhibits broad-spectrum extraction and separation capabilities for the intermediates present in wastewater containing high-concentration naphthyl sulfonic acid dye intermediates, with extraction rates as high as 90%–95%. The recovered materials can be reused in production processes to manufacture products; therefore, it can be applied to the treatment of wastewater containing dye intermediates such as similar J-acid, H-acid, resorcinol red acid, and DSD acid.