| Polytetrahydrofuran is a type of high-performance, high-polymer material. This material is mainly used to produce spandex, a new type of synthetic fiber that is widely applied to fields such as textile, chemical fiber, military, petrochemical, daily chemical, construction, medical, aeronautics and astronautics, and automobile manufacturing. In addition, this material also exhibits considerable potential in non-fiber sectors. At present, polytetrahydrofuran is mainly produced through two methods, namely, furfural and petroleum-based methods. Most overseas polytetrahydrofuran producers adopt the petroleum-based method. However, petroleum resources are limited. Unlike petroleum, furfural is made from straws, corn cobs, bagasse, and agricultural wastes, which have abundant resources. Inevitably, the decrease in petroleum resources and rise in price will promote the development of the furfural method for the production of polytetrahydrofuran. However, wastewater treatment remains a critical bottleneck for the method to develop. To date, only an American company, namely, Quaker Oats, has adopted the furfural method for the production of polytetrahydrofuran, and its yields account for about 8% of the total world output. The company is also reported to adopt the burning method for wastewater treatment. However, this method requires the consumption of a considerable amount of energy and chemical agents, and temperature is difficult to control. As a result, secondary pollution may occur in the case of incomplete combustion. In China, the first furfural-based polytetrahydrofuran production facility with a yearly output of 20.000 tons has been built by Petro China’s Qian’guo Petroleum Petrochemical Branch. During the trial production stage, the actual amount of wastewater exceeds the design value, and the available heating value of the wastewater is low. Phosphorus generated during production can be recovered, so the burning method is not appropriate for this project. Accordingly, wastewater originating from production is temporarily stored in a newly constructed sewage tank. If the wastewater treatment issue cannot be resolved, then the production facility cannot be put into normal production, indicating a substantial economic loss for the enterprise. For this reason, this study aimed to investigate the technologies of phosphorus recovery from wastewater, as well as wastewater treatment. In addition, this study also analyzed the engineering design for the treatment of factory wastewater and domestic wastewater by considering wastewater originating from polytetrahydrofuran production in Petro China’s Qian’guo Petrochemical Branch as the object of study.Organic solvent-induced crystallization is an easy, efficient, and energy-saving method to recover phosphorus from wastewater generated during the production of polytetrahydrofuran through the furfural method. In this paper, methyl alcohol-induced crystallization and ethyl alcohol-induced crystallization methods were used to recover phosphorus from polytetrahydrofuran production wastewater. The ratio of organic solvent dosage to wastewater was 3:2 when the p H value of the original polytetrahydrofuran production wastewater was 6.7. Wastewater was stirred at 100 r/min for 10 s, and the reaction duration was set to 2 h. The study results indicated that 88% of phosphorus was recovered when methyl alcohol was used as crystallizing agent, whereas 93% was recovered when ethyl alcohol was adopted. Ethyl alcohol is regarded as the optimal crystallizing agent when the crystallizing effect and properties of both agents are considered. When ethyl alcohol was adopted and the ratio between ethyl alcohol dosage and wastewater was 1:1 at a p H of polytetrahydrofuran production wastewater of 9, the recovery percentage of phosphorus could reach up to 99% after the wastewater was stirred at 100 r/min for 10 s and the reaction duration was set to 5 min. Through electron microscope analysis, most crystals were found to be rod-like. Based on the energy spectrum, the crystals were determined to mainly contain elements, such as O, Na, and P. Results of XRD and TGA showed that the crystalline substance contained Na2HPO4·2H2O. Recovery of phosphorus in the form of disodium hydrogen phosphate is a novel recycling approach. The results of ion chromatography analysis showed that impurities, such as K+, Ca2+, F–, Cl–, and SO42–, were also present in crystals, as well as Na+ and HPO42–. The charge balance method and analytic process failed to detect the existence of phosphate oligomer anions. An ethanol recovery experiment was conducted over the supernatant liquid after crystallization was completed, and the recovery cycle of ethyl alcohol was determined to be 2.For the first time in this study, iron–carbon micro-electrolysis technology was used for the treatment of wastewater from the furfural method-based production of polytetrahydrofuran. The following conclusions were drawn from this study. Through an orthogonal experiment with four factors and three levels, we found that the iron/carbon ratio was the major factor that affected the removal rate of chemical oxygen demand(COD) from wastewater, followed by the iron/water ratio, reaction duration, and p H. The optimal operating parameters were as follows: iron/carbon ratio=1:1; iron/water ratio=1:7; reaction duration=90min; and p H=3. The reaction process during the iron–carbon micro-electrolysis technology-based treatment of wastewater roughly followed the rules of second-order reaction kinetics. The use of the second-order attenuation equation model,(1)aybx=+, could reflect the reaction kinetics of COD under micro-electrolysis technology. Origin Pro software was used to conduct second-order attenuation equation fitting, and the equation was determined to be 6607.941 0.30 tC t=+, with a correlation coefficient of R2=0.98064. An experiment was conducted by adding a free-radical scavenger, and the comparative results of the effects of polytetrahydrofuran production wastewater treatment showed that the free-radical ·H played an important role in COD removal.For the first time in this study, the UV–Fenton method was used for the treatment of wastewater from the furfural method-based production of polytetrahydrofuran. The orthogonal experiment demonstrated that p H was the major reaction parameter that affected treatment results, followed by the quantity of Fe SO4·7H2O, temperature, reaction duration, and H2O2:Fe SO4·7H2O. Through a single-factor experiment, the optimal operating parameters for the treatment of polytetrahydrofuran production wastewater through the UV–Fenton method were as follows: p H=1.5; Fe SO4·7H2O dosage=1.315 mg; temperature=30°C; reaction duration=40 min; and H2O2:Fe SO4·7H2O =5:1. Regarding the function of the UV–Fenton reagent in degrading polytetrahydrofuran production wastewater via oxidation reaction, a kinetic model was established. The reaction kinetic equation could be expressed as 1.02321 1.3607 1.0256 V =0.0007586 ′P ′F ′E, and the reaction order of the UV–Fenton reaction for degrading polytetrahydrofuran production wastewater was 3.40951. The results of gas chromatography showed that furfural in the water could be removed the fastest, followed by furan and tetrahydrofuran. An investigation of their mechanism confirmed the aforementioned conclusion, that is, the aldehyde group of furfural was at α, so carbon–oxygen bonds near the aldehyde group may break apart easily. Moreover, furan oxidation occurred at carbon–oxygen single bonds, whose activity was weaker than that of furfural α. Finally, the reactivity of tetrahydrofuran was the weakest among the three compounds, and the reaction initially took place at carbon–oxygen bonds and generated butanedial through oxidative cleavage.Crystallization-, oxidation-, and biological method-based treatment processes have been proposed to address polytetrahydrofuran production wastewater based on the summary of experimental results and survey results obtained from other practical wastewater treatment projects. A study has been conducted on process design, and the costs of different technologies have been compared. Study results showed that the operating cost will be 70% lower than that of the burning method if 10 tons of polytetrahydrofuran production wastewater are treated daily. |
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