强化电容去离子脱盐的实验与机理研究

发布时间：2018-06-27 14:20

本文选题：电容去离子 + 脱盐　；参考：《东北大学》2015年博士论文

【摘要】：电容去离子(Capacitive deionization, CDI)脱盐是一种新兴的、环境友好型水处理技术。与蒸馏、反渗透等传统脱盐技术相比,CDI是在电场力的作用下,直接将水中离子吸附分离出来,而不是把水从原水中分离出来,无需高温、高压,因而具有低能耗、低污染、低成本等技术优势,越来越受到国内外学者的关注。针对目前CDI技术脱盐效率不高、提升CDI脱盐性能的机理尚不完善等不足,首先构建了流通式电吸附除盐实验装置,并利用该装置进行了传统CDI脱盐性能、工艺条件的优化等实验研究。在此基础上,进行了传统CDI脱盐技术的强化与改进,以及提升CDI脱盐效率与降低能耗的实验研究与机理分析。研究结果对完善CDI脱盐技术体系,提高CDI脱盐效率及CDI大规模开发利用有所裨益。主要研究内容与结果如下：将活性炭粉末、粘结剂PVDF和导电剂石墨粉的组分按85：10：5的质量配比,在石墨板(集流板)上涂覆制备CDI用活性炭涂层电极。经BET和DFT材料比表面积与孔径分布测试后,测试结果表明电极涂层材料活性炭的比表面积为1770m2/g,中孔分布约占总孔径分布的35%；对所制备电极的SEM图像与EDX分析表明,粘结剂PVDF与活性炭粉末完整地粘结在集流板上,电极性能稳定。通过Box-Behnken实验设计,分别以电吸附量和能耗为评价指标,根据响应面(RSM)理论构建了二次响应面优化模型；方差分析表明模型显著性、准确度和可信度均较高；根据RSM法优化结果,选择电源工作电压1.57 V、溶液初始浓度1000 mg/L、溶液流速25 mL/min、极板间距2 mm,在此条件下可获得最大的电吸附量为10.53 mg/g,而选择电源工作电压1.38 V、初始浓度900 mg/L、溶液流速40 mL/min、极板间距2mm可获得吸附去除单位质量NaCl最小的电能消耗9.81kWh/kg,两者均与模型预测值(10.60 mg/g和9.13 kWh/kg)相吻合,表明基于RSM的CDI工艺优化是可行且有效的。综合考虑脱盐效果与电能消耗,采用工作电压1.3-1.6 V、原水初始浓度800-1000 mg/L、溶液流速25-40 mL/min、极板间距2mm的运行参数,CDI脱盐过程是最经济高效的。以KOH为活化剂,在850℃活化温度、1h活化时间的活化条件下,二次活化改性电极涂层材料活性炭,使涂层材料的比表面积从1770 m2/g增至1902 m2/g,改善了孔径分布(中孔比例由35%提升到41%),以此涂层材料制备的电极活性更高,比电容量由73.62 F/g增至97.71 F/g,电极的电吸附量为12.73 mg/g,较改性前提高了20.9%。通过在CDI模块内加入阴阳离子交换膜,采用MCDI强化脱盐,活性炭电极的电吸附量与脱盐率分别为13.78 mg/g与41.34%,较传统CDI的电吸附量与脱盐率提高了30.8%,且离子交换膜的引入并未改变其吸附机制与吸附方式。在改性电极涂层材料基础上,通过在CDI装置中加入离子交换膜组成MCDI,进一步强化CDI脱盐,电吸附量与脱盐率分别为14.75 mg/g和44.26%,较传统CDI的电吸附量和脱盐率提高了40%,并且在相同工艺条件下,吸附去除单位质量NaCl的能耗由CDI的12.24 kWh/kg降至11.01 kWh/kg,下降了10%。根据电极电压与电源电压、极板间距、溶液浓度及电流密度等因素的关系,推导了计算CDI电极电压的公式；由该计算式所揭示的电源电压、极板间距及电流密度等之间的规律可知：当含盐废水初始浓度较高时,为了既保证脱盐效果又节省能耗,可适当选择较低电源工作电压或采用较大的极板间距；而处理低浓度含盐废水时,则需在保证不发生电极反应的前提下,尽可能增大电源电压并缩短极板间距。通过CDI用活性炭电极的Nyquist阻抗图谱分析了CDI系统的阻抗与近似等效电路,证实了由于浓差极化作用产生的极化电阻的存在,实际CDI研究中可通过增大溶液流速、增强电极表面活性、增大电极有效面积、缩小电极板间距等,减弱浓差极化效应,减小极化电阻,提升脱盐效果并降低吸附去除单位质量盐离子的能耗。另外,电极的CV曲线测试分析表明,离子的吸附去除是由于电场静电力作用,而非发生了电化学氧化还原反应。利用准一级和准二级吸附动力学模型以及Langmuir和Freundlich吸附等温方程,探讨了CDI脱盐的吸附机制。结果表明：NaCl在活性炭涂层电极上的电吸附符合准一级动力学模型与Langmuir吸附等温模型,属于单分子层吸附,且以物理吸附为主；工作电压和溶液初始浓度的升高会加快离子迁移速率,提升脱盐效率,使吸附平衡时电极的电吸附容量增大。综上,通过CDI工艺运行参数的合理调控优化、电极材料的改性、MCDI强化脱盐可以有效提升脱盐效率并降低能耗；关于强化CDI脱盐的机理分析,对CDI技术的进一步开发利用有所裨益。
[Abstract]:Capacitive deionization (CDI) desalination is a new and environmentally friendly water treatment technology. Compared with the traditional desalting technology such as distillation and reverse osmosis, CDI is directly separated from the water ion under the action of the electric field force, instead of separating water from the original water without high temperature and high pressure, thus having low energy. The technical advantages of consumption, low pollution, low cost and so on are getting more and more attention at home and abroad. In view of the lack of high desalination efficiency of CDI technology and the imperfect mechanism of improving the desalination performance of CDI, a circulation type electric adsorption desalting experiment device is first constructed, and the traditional desalting performance of CDI and the optimization of process conditions are carried out with this device. On this basis, the strengthening and improvement of traditional CDI desalting technology, as well as the experimental research and Mechanism Analysis on improving the desalting efficiency and reducing energy consumption of CDI are carried out. The results are beneficial to improving the CDI desalting technology system, improving the efficiency of CDI desalting and the large-scale development and utilization of CDI. The carbon powder, the binder PVDF and the composition of the conductive graphite powder were prepared on the graphite plate (the collector plate) by the mass ratio of 85:10:5. After testing the specific surface area and pore size distribution of the BET and DFT materials, the test results showed that the specific surface area of the activated carbon of the electrode coating material was 1770m2/g, and the distribution of the mesopore was about the total. The pore size distribution is 35%. The SEM image and EDX analysis of the prepared electrodes show that the binder PVDF and the activated carbon powder are fully bonded on the collector plate and the electrode performance is stable. Through the Box-Behnken experimental design, the electro adsorption quantity and energy consumption are evaluated respectively, and the response surface (RSM) theory is constructed for the two response surface optimization model. The analysis shows that the model is significant, accurate and reliable. According to the RSM method, the power supply voltage is 1.57 V, the initial concentration of the solution is 1000 mg/L, the solution velocity is 25 mL/min and the plate spacing is 2 mm. Under this condition, the maximum electric adsorption capacity is 10.53 mg/g, and the power supply voltage is 1.38 V, and the initial concentration is 900 mg/L, The solution flow rate of 40 mL/min and the plate spacing 2mm can obtain the minimum energy consumption 9.81kWh/kg for the adsorption removal unit mass NaCl, both of which are in agreement with the model prediction value (10.60 mg/g and 9.13 kWh/kg). It shows that the optimization of CDI process based on RSM is feasible and effective. The operation voltage 1.3-1.6 V, raw water is used to consider the desalting effect and the electrical energy consumption. The initial concentration of 800-1000 mg/L, the flow velocity of 25-40 mL/min, the operating parameters of the plate spacing 2mm, the CDI desalination process is the most economical and efficient. With KOH as activator, at the activation temperature of 850 C and the activation time of 1H activation, the activated carbon of the modified electrode coating material is activated to increase the specific surface area of the coating material from 1770 m2/g to 1902 m2/g. The pore size distribution (the ratio of the mesopore from 35% to 41%) was improved, and the electrode activity was higher, the specific capacitance increased from 73.62 F/g to 97.71 F/g, and the electroadsorption capacity of the electrode was 12.73 mg/g. The 20.9%. was enhanced by adding the Yin and Yang exchange membrane in the CDI module and using MCDI to enhance the desalination and the electric absorption of the activated carbon electrode. The rate of desorption and desalination is 13.78 mg/g and 41.34% respectively. The adsorption capacity and desalination rate of the traditional CDI are increased by 30.8%, and the introduction of the ion exchange membrane does not change its adsorption mechanism and adsorption mode. On the basis of the modified electrode coating material, the ion exchange membrane is added to the CDI device to make up the MCDI, further strengthening the desalination of CDI and the electrical adsorption capacity. The rate of desalination and desalination are 14.75 mg/g and 44.26% respectively. The electric adsorption and desalting rate of the traditional CDI is increased by 40%. Under the same process conditions, the energy consumption of the adsorbed unit mass NaCl is reduced from 12.24 kWh/kg to 11.01 kWh/kg, and the 10%. is reduced by the 10%. electrode voltage and the power supply voltage, the plate spacing, the solution concentration and current density. The formula for calculating the voltage of CDI electrode is derived. The rule of power supply voltage, plate spacing and current density revealed by this formula shows that when the initial concentration of salt water is high, in order to ensure the effect of desalting and save energy, the lower power supply voltage or the larger plate spacing can be selected properly. When the low concentration of salt water is treated, the voltage of the power supply and the distance of the plate are shortened as much as possible without the electrode reaction. The impedance and the approximate equivalent circuit of the CDI system are analyzed by the Nyquist impedance Atlas of the activated carbon electrode by CDI. The existence of the polarization resistance caused by the concentration polarization polarization is confirmed. In the study of CDI, it is possible to increase the surface activity of the solution, increase the surface activity of the electrode, increase the effective area of the electrode, reduce the spacing of the electrode plate and so on, weaken the concentration polarization effect, reduce the polarization resistance, improve the effect of desalting and reduce the energy consumption of removing unit mass salt ions by adsorption. In addition, the CV curve test and analysis of the electrode show that the removal of ions is removed. The electrochemical oxidation reduction reaction was not occurred due to the electrostatic force of the electric field. The adsorption mechanism of CDI desalination was discussed by using the quasi first and quasi two stage adsorption kinetic models and the adsorption isotherm equation of Langmuir and Freundlich. The results showed that the electroadsorption of NaCl on the activated carbon coated electrode accorded with the quasi first order kinetic model and Langmuir The adsorption isotherm model belongs to the single molecular layer adsorption and mainly by physical adsorption. The increase of the working voltage and the initial concentration of the solution will accelerate the ion migration rate, improve the desalination efficiency and increase the electric adsorption capacity of the electrode when the adsorption equilibrium is balanced. In a sum, the optimization of the operation parameters of the CDI process, the modification of the electrode materials, and the strengthening of the MCDI Desalination can effectively improve desalination efficiency and reduce energy consumption. The mechanism analysis of strengthening CDI desalination is beneficial to further development and utilization of CDI technology.
【学位授予单位】：东北大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：P747

【相似文献】