Research On Strengthening Hydrothermal Recycling Technology Of Phenolic Waste Liquid

The phenolic waste liquid mainly comes from the chemical production and the distillation of phenolic wastewater,the main component of which is phenol.The production of phenolic waste liquid is not very large,which belongs to hazardous waste because of its high concentration,strong toxicity and difficult treatment.At present,incineration and extraction are the most commonly used methods for the treatment of phenolic waste liquid,but the cost is high and it is easy to produce secondary pollution,and a new process needs to be developed.Hydrothermal carbonization（HTC）has simple operation and mild reaction conditions.A large number of studies have shown that the process can carbonize many biomass materials and prepare carbon materials or carbon composites with different morphologies by controlling the technological conditions,so as to realize the recycling of waste biomass.In recent years,the HTC process has been gradually applied to chemical waste liquid and organic solid waste treatment to realize the recycling of waste.However,the treatment of phenolic waste liquid with this process was not reported.In this study,simulated waste liquid was used as the research object and its preparation concentration refers to the actual waste liquid concentration of a chemical plant in Zhejiang Province.The phenol concentration is 50 g/L.HTC process is proposed to be used for harmless and resource-based treatment.The main contents of the study include the following three parts:（1）Study on HTC of waste liquid and its strengthening condition.The results show that the phenol waste liquid is difficult to carbonize under the temperature range of180-220℃and reaction time of 4-8 h.Under the optimum conditions,the removal rate of chemical oxygen demand（COD）is 17.5%and the removal rate of phenol is 15.4%.Using sulfuric acid（98%）as catalyst,the mixture ratio of phenol waste liquid and sulfuric acid（98%）volume is in the range of 1:1 to 1:4,in the temperature range of 180-220℃,and the reaction time is 4-8 h,phenol waste liquid is also difficult to carbonize.When the volume ratio is 1:2 and above,the residue of phenol cannot be detected,but the removal effect of COD is not ideal.In the carbonization experiment using H₂O₂ as additive,the mixture ratio of waste liquid and H₂O₂ was in the range of 2:0.3 to 2:1,phenol waste liquid was carbonized at 180°C for 4 h.The removal rate of COD can be further improved by increasing the dosage of H₂O₂,but no carbonation occurs.When the volume ratio was2:0.9,the highest yield of hydrochar was 37.0%,the removal rate of COD was 77.0%,and no phenol residue was detected.（2）Diatomite and Fe₂O₃ modified diatomite with strong catalytic activity were used as solid media to strengthen the hydrothermal carbonation of phenol waste liquid.The results showed that the waste liquid and diatomite or Fe₂O₃ modified diatomite could not be successfully carbonized at 180-220℃for 4 h under different dosage,and the highest removal rate of COD was 18.3%and 19.9%,respectively.In the presence of diatomite and Fe₂O₃ modified diatomite,adding appropriate amount of H₂O₂ can promote the carbonization of waste liquid,and the degree of carbonization is higher than the reaction only adding H₂O₂.The highest yield of hydrothermal carbon is 38.5%and 63.5%,and the removal rate of COD is 83.1%and 79.0%,respectively.The solid-phase interface can promote the oxidation of phenol waste liquid by H₂O₂,which leads to the carbonization of waste liquid.（3）Nonylphenol ethoxylate（NP-10）was used to strengthen the HTC of phenol waste liquid.The results showed that adding NP-10 is greatly beneficial to the carbonization of phenol wastewater,and a small dosage of NP-10 can trigger the successful carbonization of phenol wastewater.The optimum htc condition,2 ml phenol waste liquid,4 ml sulfuric acid（98%）and 0.075 ml NP-10 at 180°C for 4 h,was obtained by changing the reaction conditions and optimizing the process parameters.The hydrochar obtained under this condition has abundant surface functional groups with a specific surface area of 14.05 m²/g and showed great methylene blue（MB）adsorption capacities,the maximum adsorption capacity was 698 mg/g,which was higher than that of commercial activated carbon（363 mg/g）.The COD of washing water is 499.408 mg/L,and the secondary pollution is not serious.Thus,the hydrochar could be a promising adsorbent for wastewater treatment.