Preparation,Characteration And Flocculation Effect Of Poly(N-vinylformamide-acrylonitrile) Amidine

In this study, aqueous solution copolymerization reaction and supercritical CO2 (SCCO2) precipitation polymerization reaction were used to prepare intermediate. Then, the intermediate was hydrolyzed and amidinized to form cationic poly (N-vinylformamide-acrylonitrile) amidine (PVAA, hereinafter referred to as polyamidine) with five-membered ringlike structural unit. The influence factors of two-step synthesis process and the optimum synthesis conditions were investigated. FT-IR, NMR and other various methods were employed to characterize the prepared polyamidine. On this basis, the sludge dewatering by using polyamidine as flocculant, deoiling efficiency were studied and the flocculating mechanism was discussed. In addition, the polyamidine was used as coagulant aids with iron salt coagulant for reactive blue (K-GL) simulated water treatment. The enhancing effects of polyamidine on flocculating performance were researched. The mechanisms of coagulation were also investigated through zeta potential and floc properties. Moreover, the prepared polyamidine was refined by using SCCO2 as purification carrier. And the effect of purification was also studied. The mean research contents and conclusions were summarized as follows:1. Aqueous solution copolymerization and SCCO2 precipitation polymerization method were used to synthesize polyamidine. In aqueous solution copolymerization method, two kinds of initiators-redox system initiators and azobisisoheptonitrile (AIVN) were used. The influence factors of copolymerized reaction, hydrolyzed and amidinzed reaction were investigated, and the optimum synthesis conditions were found out. The experimental results showed that the major factors of impacting productivity and viscosity were reaction temperature, monomer ratio, monomer concentrations, initiator dosage and reaction time. Both of the two approaches could obtain higher productivity under optimum condition. The productivity of aqueous solution copolymerization method by using organic initiator and SCCO2 precipitation polymerization method could achieve more than 90%. The viscosity of aqueous solution copolymerization method by using redox system initiator was minimal (74.3 mL/g). While, the viscosity of SCCO2 precipitation polymerization method was maximal (93.4 mL/g). The reaction time of aqueous solution copolymerization method was more than 2 h. While, the reaction time of SCCO2 precipitation polymerization method only needed 1 h or better. What is clear from the above data is that SCCO2 precipitation polymerization method had a better advantage on reaction time and viscosity because of the superhigh mass transfer rate under super-critical state. The influence factors of productivity and cationic charge density under hydrolyzed and amidinzed reaction mainly included amidinzed temperature, dosage of hydrochloric acid and reaction time. The amidinzed temperature of 98℃, time of 5 h and 7.4 mL of hydrochloric acid were employed for optimizing the hydrolyzed and amidinzed reaction conditions of polyamidine. The productivity was 79.4% and electric density was 5.66 mmol/L under the optimum condition.2. The study on structure of the prepared copolymer showed that the average composition of two monomers was 1:1, when nNVF:nAN was 1:1. The probability of radial arrangement of these two monomers was almost 64%. The copolymerization between N-vinylformamide and acrylonitrile, and the five-membered ringlike structural unit were demonstrated by a series of characterization, such as:FT-IR, UV, XPS and NMR. DSC-TG characterizations showed that the prepared polyamidine had higher purity and good stability. The GPC results showed that the polyamidine was possessed of high molecular weight and narrow distribution.3. The sludge dewatering experiments have been carried out and the results showed that the SVI of sludge was 86% without polyamidine. While the polyamidine was 40 mg/L, the sludge sedimentation rate was maximal and the SVI reached to 45%. The sludge sedimentation rate of polyamidine had better effects than the cationic polyacrylamide (CPAM). And the turbidity measurement showed that the removal rate of turbidity could reach to 82% when the polyamidine was 50 mg/L.4. The polyamidine was used as coagulant aids with FeCl3 coagulant for oily wastewater treatment. The best oil removal rate could be achieved to over 99%. Polyamidine and FeCl3 played an equally important role in the oil removal process. FeCl3 gave full play to charge neutralization, while polyamidine mainly exerted effects of charge neutralization, adsorption bridging action and furl mechanism. When the FeCl3 was 166 mg/L and polyamidine was 5.5 mg/L, oil removal rate could reach maximum-99.9%. The adsorption bridging and furl action could be effectively deployed when polyamidine with annular structure was unfolded state in solution. The positive charge of polyamidine caused charge neutralization. The cyclic structure and carbon chain play a role of hydrophobic interaction to squeeze water. All of the characteristics let the polyamidine have good flocculation and dewatering properties.5. The color removal efficiency could be significantly improved by introducing polyamidine with FeCl3 and polymerization ferric chloride (PFC) coagulants to the decontamination process of reactive blue simulated dye wastewater. The optimum dosage of FeCl3-PVAA was 55 mg/L+1 mg/L, the optimum pH was 6, the color removal rate would reach to 99%. On the other hand, the optimum dosage of PFC-PVAA was 40 mg/L+3 mg/L. High color removal rate could be reached within the range of pH 6-9, and the best color removal rate was 96%. The addition of polyamidine could enhance the recovery ability of floc after breakage. With the breaking force increased, flocs of FeCl3-PVAA and PFC-PVAA would become fragile to break and have strong regenerative potency. The FeCl3-PVAA showed stronger anti-shear ability than PFC-PVAA. Under the studying condition, FeCl3-PVAA had a higher removal rate and a wider applicable scope of pH for reactive blue treatment. The results showed FeCl3-PVAA had better practical applications.6. The SCCO2 was employed to purify the prepared polyamidine. Response surface equation was used to investigate the influence of temperature, pressure, flow rate and time to purifying effect. The purification conditions were optimized, the prepared polyamidine was characterized, and the dewatering performance of both before and after purification was also compared. By comparison viscosity and electric density before and after purification the polyamidine, the results indicated that supercritical fluid refine could remove residual monomer, initiator, and small molecules effectively. The largest mass removal ratio was 10%, and the viscosity and electric density were increased. The experiments showed that the temperature and time affected purifying effect most, pressure did less, and the flow rate did the least. The optimum processing conditions were:temperature at 49.64℃, pressure at 19.77 MPa, flow rate at 30.55 L/h time at 4.69 h. The viscosity was 590.08 mPa-s, and electric density was 5.06 mmol/g in this conditions. The FT-IR showed the residual monomers (acrylonitrile and NVF) were removed effectively. It indicated the obvious effects of supercritical fluid purification. Moreover, the processed polyamidine was used tocarry out the sludge dewatering test. The moisture content of filter cake was decreased by up to 8.9%. The results showed that the treatment effect was obvious.