Adsorption Of Phenylhydrazine Compounds On Hypercrosslinked Polymeric Adsorbents And Its Application In Wastewater Treatment

Phenylhydrazine compounds are important intermediates for synthesis of fine chemicals. In their production processes, enormous amount of high-strength organic wastewaters with poor biodegradability is generated. Therefore, how to effectively treat the highly concentrated organic industrial wastewaters has been a critical issue and has thus become a great challenge for environmental engineers, even though a variety of chemical wastewater treatment technologies have been developed before. In recent years, there has been much progress in development of the technologies for treating high-strength organic industrial wastewaters with resin adsorption in China. Especially synthesis and use of novel adsorbents have eventually become an active research goal in the area of environmental protection. Accordingly the present work aims at study of the adsorption properties of four phenylhydrazine derivatives toward hypercrosslinked polymeric adsorbents from aqueous solutions as well as treatment and resource reuse of the industrial wastewaters from phenylhydrazine production. Two novel hypercrosslinked polymeric adsorbents NG-99 and NG-100, which were developed by Jiangsu N & G Environmental Technology Co. Ltd., were chosen for adsorption of phenylhydrazine(PH), 1-methyl-1-phenylhydrazine(1-MPH), 1-acetyl-2-phenylhydrazine(1-APH), and p-methyl-1-phenylhydrazine(p-MPH) so as to observe their thermodynamic and kinetic properties in the specific adsorption system. Based on the study of adsorption behaviors of phenylhydrazine on the adsorbents, NG-99 was eventually appraised for treating wastewaters containing phenylhydrazine from industry. Finally a wastewater treatment and resource reuse process with resin adsorption technology for the waste stream containing phenylhydrazine sulfate was successfully developed and put into practice. The main works and conclusions of the present study are as follows: The adsorption properties of the homemade amine modified hypercrosslinked adsorptive resin NG-99 and carbonyl modified resin NG-100 for PH, 1-MPH, 1-APH, and p-MPH are better than that of macroporous adsorbent Amberlite XAD-4 made in USA. The thermodynamic study showed that Langmuir and Freundlich isotherms were found to fit well the adsorption data of the four phenylhydrazine compounds onto the three adsorbents, in which the relevant parameter R is >0.98 in all cases and the exponent factor n>1 in Freundlich isotherm equations, the adsorption is thus favourable. In the same equilibrium concentration, the adsorption capacity(Qe) of the four phenylhydrazine compounds onto NG-99 and NG-100 is higher than that of Amberlite XAD-4 by 20~70%, in which the highest Qe for NG-100 resin, the second for NG-99, and the lowest for XAD-4. The order of adsorptive capability of each adsorbent is: p-MPH>1-MPH >PH>1-APH. In addition, the thermodynamic study demonstrated that lower temperature is favourable to adsorption, indicating a predominant physisorption process herein. It was found that the microporous structure and partial polarity of the hypercrosslinked network of NG-99 and NG-100 are advantageous for adsorption of phenylhydrazine compounds, which become the primary reasons for the high adsorption capacity of NG-99 and NG-100 compared to Amberlite XAD-4. On the other hand, the Qe discrepancy of the same adsorbent for different adsorbates is mainly attributed to different hydrophobicity and molecular structure of the compound. As for aromatic compounds, the adsorbates with electron-supplying groups, such as p-MPH in the present study, tend to enhance the π-πinteraction between the adsorbent and themselves, while those with electron-withdrawing groups, such as 1-APH, have adverse effect on the π-πinteraction. All these factors would result in different adsorption capacities of a resin for different solutes. The values of enthalpy change ?H for adsorption of the four phenylhydrazine compounds onto the three adsorbents are all negative, in which the magnitude of maximum absolute value is less than 42 kJ/mol, suggesting a spontaneous adsorption process. The absolute value of adsorption free energy changes ?G for adsorption of PH derivatives on NG-99 and NG-100 are higher compared to that on Amberlite XAD-4. This suggests NG-99 and NG-100 have good affinity toward phenylhydrazine compounds. The fact that the absolute value of adsorption free energy change ?G decreases with increasing temperature indicates that high temperature is not favourable to adsorption, which is in agreement with the exothermic characteristic of physical adsorption. Kinetic study showed that adsorption of PH on NG-99 and NG-100 resins fitted well to homogeneous particle diffusion model(HPDM), and thus it can be described by a first-order irreversible adsorption rate equation. The rate constants of adsorption equations of PH on NG-99 and NG-100 at 283 K are 1.8×10-3 min-1 and 2.2×10-3 min-1 respectively. At initial concentration of 1,000 mg/L, on the other hand, the studydemonstrated that NG-99 and NG-100 adsorbents possess a quick adsorption property toward PH, and they thus have good potential for treating the wastewater containing phenylhydrazine compounds with high removal efficiency. With addition of 1~2‰(W/V) sulphite as antioxidant agent into the influent, the oxidization of aromatic amines such as phenylhydrazine in the solution can be effectively inhibited, which is an economical and reliable technique for developing wastewater treatment process of similar waste streams. On the other hand, the contamination and cumulation of the amine oxides inside the resin particles has been successfully eliminated by a two-step desorption process with dilute acid and ammonia solutions, respectively. The invention of this technology is significant theoretically as well as practically for treatment and resource reuse of the wastewaters containing similar aromatic compounds. In the present work, practice of the two-step regeneration process resulted in both high desorption efficiency of phenylhydrazine and complete removal of the amine oxides from the resin network, thus the total adsorption capacity of the adsorbent was recovered. In addition, desorption with 5% dilute acid and 5% ammonia solutions also led to easy recovery of the amine product with high purity. With study of wastewater treatment by resin adsorption, it is believed that the two hypercrosslinked adsorptive resins NG-99 and NG-100 all exhibited better adsorption property compared to Amberlite XAD-4, especially NG-99 resin with partial amino groups in its structure is favourable to adsorption of PH. However the carbonyl groups in the structure of NG-100 resin tend to facilitate the oxidization process of aromatic amines, and are not favourable to regeneration of the adsorbent. It is concluded that the process for treating the wastewater containing phenylhydrazine sulfate with two resin columns in series is stable and reliable. Its optimum operation conditions are as follows: CODCr of raw wastewater is 19,400 mg/L, CODCr of influent 20,000~24,000 mg/L, pH 6.5~7.0, adsorption temperature 20~30oC(ambient temperature), batch volume treated is 12 BV, combination of regenerant is 1.5BV5%HCl+1BV4%HCl+1BVH2O+1BV5%NH4OH+1BVH2O, desorption temperature 50~60 oC, desorption flow rate 1~1.5 BV/h, CODCr of effluent 1,500~2,000 mg/L, CODCr removal efficiency 89~93%, CODCr desorption rate 97~99%, performance adsorption capacity of resin 241.0 gCODCr/L. In addition, the by-product phenylhydrazine hydrochloride can be finally recovered by acidification and refrigeration of the high concentrated desorption liquor as well as filtration.The scale-up test for treating the wastewater containing phenylhydrazine sulfate further demonstrated that both adsorption and desorption in the process are stable with NG-99 resin as adsorbent, and satisfactory result was obtained even with higher CODCr of the raw wastewater by 40%. As a result, the CODCr of the effluent was 1,500~2,500 mg/L, and CODCr removal efficiency of 93% was also achieved. Finally, 6.28 kg phenylhydrazine hydrochloride with purity of 93~94% was recovered from per cubic meter wastewater, and the structure of the recovered by-product was found to be consistent with that of the standard compound by IR and 1HNMR analysis. As for treatment of the wastewater containing PH sulfate by NG-99 resin adsorption technology, the operation cost for 1 m3 wastewater is about 50 RMB; the value of the recovered material from 1 m3 wastewater is 94 RMB; and the profit for treating 1 m3 wastewater is thus estimated to be 44 RMB. The pilot engineering operation of the treatment and resource reuse process for PH sulfate wastewater with resin adsorption showed that design of the facilities in the project is reasonable, and the technology herein is reliable. Based on the practical appraisal, the wastewater treatment and resource reuse project in Zhejiang Xinnong Chemical Industry Co. Ltd. is expected to have better environmental and economic benefits. And it is believed that the resin adsorption technology of the present study for treating the wastewater containing PH sulfate has paved a new way for treatment and resource reuse of the organic wastewaters containing aromatic amines as well.