硫碘循環(huán)制氫中電化學(xué)Bunsen反應(yīng)特性研究
發(fā)布時間：2018-09-12 12:50
【摘要】：作為清潔、高效、安全和可持續(xù)的替代能源,氫能日漸受到人類青睞,未來有望建立集成制氫、儲氫、輸運(yùn)及轉(zhuǎn)化利用等多環(huán)節(jié)的氫能系統(tǒng),實現(xiàn)全球化石能源經(jīng)濟(jì)向氫能經(jīng)濟(jì)的轉(zhuǎn)型。氫氣制備是構(gòu)建氫能系統(tǒng)的首要工作,而利用資源豐富且無污染的水制取氫氣是公認(rèn)的最佳選擇。其中,熱化學(xué)循環(huán)水分解制氫方法由于具備諸多優(yōu)點(diǎn)而受到重視,尤其是硫碘循環(huán)被認(rèn)為是最有前景的方法之一。熱化學(xué)硫碘循環(huán)水分解制氫中第一步Bunsen反應(yīng)(SO2+12+2H2O→ H2SO4+2HI)的實現(xiàn)方法及進(jìn)行程度等影響后續(xù)HI和H2SO4分解反應(yīng),制約著整個硫碘循環(huán)系統(tǒng)。傳統(tǒng)Bunsen反應(yīng)延續(xù)的是美國GA公司提出的在過量碘和水的條件下進(jìn)行反應(yīng),生成HI和H2SO4自發(fā)分層。為了減少甚至避免過量碘和水的加入,電化學(xué)Bunsen反應(yīng)方法應(yīng)運(yùn)而生,有望實現(xiàn)硫碘循環(huán)系統(tǒng)的簡化。鑒于實際硫碘循環(huán)系統(tǒng)中有HI返回Bunsen反應(yīng),針對初始HI存在下的四元多相Bunsen反應(yīng)動力學(xué)和熱力學(xué)平衡進(jìn)行研究。提高初始HI濃度或者溫度加快了反應(yīng)動力學(xué)速率,液。液分層提前出現(xiàn),且縮短了達(dá)到熱力學(xué)平衡的時間。但HI量過高不利于兩相分離,故HI/H2O摩爾比須控制在0～1/18的合理范圍內(nèi)。提高初始HI量增加了H2SO4相雜質(zhì),但提高溫度改善了液-液相平衡分離特性。加入初始HI使HIx相中HI濃度達(dá)到了超恒沸,有利于減少后續(xù)HI濃縮步驟,實現(xiàn)硫碘循環(huán)系統(tǒng)的優(yōu)化。提高初始HI量或溫度造成SO2平衡轉(zhuǎn)化率略有降低。綜合考慮,較高溫度345～358K、HI/H2O摩爾比0～1/36是比較理想的工況范圍。圍繞電化學(xué)Bunsen反應(yīng)開展了基礎(chǔ)實驗研究,探討了兩極酸溶液濃縮和電池電壓的變化規(guī)律。隨著電解進(jìn)行,陽極H2SO4和陰極HI的濃度均呈上升趨勢,陰極12濃度降低,而電壓整體呈現(xiàn)上升趨勢。提高電流密度增加了單位時間內(nèi)得失電子數(shù),生成H2SO4和HI量增加且電壓增大,但電壓超過3V會造成陽極側(cè)石墨電極的腐蝕。提高溫度加快了電極反應(yīng)速率。增加12/HI摩爾比既可降低過電勢也可增大溶液歐姆電阻。大部分工況條件下電流效率大于90%,甚至接近100%,表明了該電池能量轉(zhuǎn)化性能較好。增加電流密度增大了能耗,而提高溫度或H28O4濃度則相反；改變HI濃度或12/HI摩爾比時,則出現(xiàn)峰值能耗。以代表性的Nafion 117和115膜為研究對象,探討了質(zhì)子交換膜在電池中的特性。膜的質(zhì)子傳遞數(shù)t+基本上大于0.9,甚至接近1,除了在高溫下,Nafion 115膜的質(zhì)子傳遞能力顯著下降；水的滲透系數(shù)β依據(jù)工況條件變化不一。膜的傳輸特性與酸濃縮效果密切相關(guān),高t+和低β值易獲得高濃度HI；相反,可生成高濃度H2SO4。分析膜兩側(cè)交叉污染時,發(fā)現(xiàn)陽極HI比陰極H2S04的濃度高2-10倍。提高電流密度、溫度或初始I-/HI摩爾比,HI和1-12S04的摩爾通量均增加。提高H2SO4濃度促進(jìn)H2S04傳遞而抑制HI滲透,提高HI濃度時情況相反。膜的微觀表征表明電化學(xué)反應(yīng)后的膜出現(xiàn)褶皺且有固體顆粒沉積,造成了BET表面積增大和平均孔徑減小。經(jīng)活化后,膜的性能得到恢復(fù),有利于延長其壽命。對電化學(xué)Bunsen反應(yīng)的平衡電勢進(jìn)行了實驗和理論研究,首先基于電化學(xué)原理推導(dǎo)出平衡電勢的理論模型,其次通過實驗探討了各參數(shù)對平衡電勢的影響。提高S02或12濃度會降低平衡電勢,而提高H2SO4或HI濃度則相反；溫度升高,平衡電勢會降低。通過對實驗數(shù)據(jù)擬合分析驗證了該模型的準(zhǔn)確性,并確定了代表電解質(zhì)非理想特性和膜內(nèi)濃度分布的參數(shù)M和Z均與溶液濃度無關(guān),Z基本不隨溫度變化,但M與溫度存在指數(shù)關(guān)系,溫度越高,M值越低。最后,提出了平衡電勢經(jīng)驗公式,可以很好地重現(xiàn)實驗數(shù)據(jù),實現(xiàn)了電池平衡電勢的預(yù)測。基于電化學(xué)工作站原理研究了電化學(xué)Bunsen反應(yīng)的電極反應(yīng)機(jī)理及動力學(xué)特性,利用循環(huán)伏安法測量兩極反應(yīng),判斷出陽極SO2氧化和陰極12還原均不可逆：依據(jù)峰值電流定性分析了擴(kuò)散傳質(zhì)速率。測量兩極反應(yīng)的電化學(xué)阻抗譜,并對Nyquist圖作等效電路擬合。陰極反應(yīng)等效電路為一個溶液歐姆電阻串聯(lián)著一對并聯(lián)的電荷傳遞電阻和常相位角元件；陽極反應(yīng)等效電路由電荷傳遞電阻和常相位角元件并聯(lián)組成。計算并評估了交換電流密度(j0)和標(biāo)準(zhǔn)反應(yīng)速率常數(shù)(k0)兩個重要動力學(xué)參數(shù),當(dāng)陰極HI濃度為8mol/kgH2o、I2/HI摩爾比為0.5,陽極H2SO4濃度為13mol/kgH2O時可以獲得較高的電極反應(yīng)動力學(xué)速率。對基于電化學(xué)Bunsen反應(yīng)的硫碘循環(huán)系統(tǒng)進(jìn)行了流程設(shè)計和模擬,計算了產(chǎn)氫量為1mol/s時的系統(tǒng)質(zhì)量平衡和能量平衡�？紤]內(nèi)部換熱、廢熱回收發(fā)電,計算出系統(tǒng)熱效率達(dá)48.98%。相比于使用傳統(tǒng)Bunsen反應(yīng)的硫碘循環(huán)系統(tǒng),使用電化學(xué)Bunsen反應(yīng)的硫碘循環(huán)系統(tǒng)極大地簡化了流程,降低了能耗,從而提高了熱效率。通過改進(jìn)優(yōu)化,未來有望進(jìn)一步提高系統(tǒng)熱效率及經(jīng)濟(jì)性。
[Abstract]:As a clean, efficient, safe and sustainable alternative energy source, hydrogen energy is becoming more and more popular. It is expected to build an integrated hydrogen production, hydrogen storage, transportation and conversion system in the future, and realize the transition from global fossil energy economy to hydrogen economy. Hydrogen production from non-polluted water is recognized as the best choice. Thermochemical cycling water decomposition is one of the most promising methods because of its many advantages, especially the sulfur-iodine cycle. The traditional Bunsen reaction continues the spontaneous stratification of HI and H2SO4 by the reaction of excessive iodine and water proposed by GA Company in the United States. In order to reduce or even avoid the addition of excess iodine and water, the electrochemical Bunsen reaction method is applied. In view of the fact that HI returns to Bunsen reaction in the actual sulfur-iodine cycle system, the kinetics and thermodynamic equilibrium of the quaternary-multiphase Bunsen reaction in the presence of initial HI are studied. However, the high HI content is not conducive to the separation of the two phases, so the HI/H2O molar ratio should be controlled within a reasonable range of 0-1/18. Increasing the initial HI content increases the impurities of H2SO4 phase, but improves the liquid-liquid equilibrium separation characteristics by increasing the temperature. Adding the initial HI makes the HI concentration in the HIx phase reach super-boiling, which is conducive to reducing the subsequent HI concentration. Increasing the initial HI or temperature results in a slight decrease in the equilibrium conversion of SO2. Considering the high temperature of 345-358K, the HI/H2O molar ratio of 0-1/36 is an ideal operating range. The basic experimental study was carried out around the electrochemical Bunsen reaction, and the concentration of bipolar acid solution and the voltage of the battery were discussed. With the electrolysis proceeding, the concentration of H2SO4 on the anode and HI on the cathode increased, the concentration of 12 on the cathode decreased, while the voltage on the cathode increased as a whole. Increasing the 12/HI molar ratio can reduce the overpotential and increase the ohmic resistance of the solution. The current efficiency is more than 90% or even close to 100% under most operating conditions, indicating that the energy conversion performance of the battery is good. Increasing the current density increases the energy consumption, while changing the HI concentration or the high temperature or H28O4 concentration is opposite. The characteristics of proton exchange membranes in batteries were studied. The proton transfer number T + of the membranes was more than 0.9 or even close to 1. Except at high temperature, the proton transfer capacity of Nafion 115 membrane decreased significantly; the water permeability coefficient beta depended on the operating conditions. The transport characteristics of the membrane are closely related to the concentration of acid. On the contrary, high concentration of H2SO4 can be obtained easily with high T + and low beta values. When analyzing the cross contamination on both sides of the membrane, it is found that the concentration of anodic HI is 2-10 times higher than that of cathode H2S04. Increasing the concentration of H2SO4 promotes the transmission of H2S04 and inhibits the infiltration of HI, whereas increasing the concentration of HI is contrary. The microscopic characterization of the membrane shows that the membrane after electrochemical reaction has folds and solid particles deposition, resulting in the increase of BET surface area and the decrease of average pore size. The equilibrium potential of en reaction was studied experimentally and theoretically. Firstly, the theoretical model of equilibrium potential was deduced based on electrochemical principle. Secondly, the effect of various parameters on equilibrium potential was discussed experimentally. The accuracy of the model is verified by fitting and analyzing the experimental data. The parameters M and Z, which represent the non-ideal characteristics of electrolyte and the concentration distribution in the membrane, are independent of the solution concentration. Z does not change with the temperature. However, there is an exponential relationship between M and temperature. The higher the temperature, the lower the M value. Based on the principle of electrochemical workstation, the electrode reaction mechanism and kinetic characteristics of electrochemical Bunsen reaction were studied. The cyclic voltammetry was used to measure the bipolar reaction and the irreversibility of anodic SO2 oxidation and cathode 12 reduction was judged. The cathode reaction equivalent circuit consists of a solution ohmic resistance in series with a pair of parallel charge transfer resistors and constant phase angle elements; the anode reaction equivalent circuit consists of a charge transfer resistor and a constant phase angle element in parallel. Exchange current density (j0) and standard reaction rate constant (k0) are two important kinetic parameters. When the cathode HI concentration is 8mol/kg H2o, the I2/HI molar ratio is 0.5, and the anode H2SO4 concentration is 13mol/kg H2O, a higher electrode reaction kinetic rate can be obtained. The mass balance and energy balance of the system with hydrogen yield of 1 mol/s are calculated. Considering internal heat transfer and waste heat recovery, the thermal efficiency of the system is calculated to be 48.98%. Compared with the traditional Bunsen reaction sulfur-iodine cycle system, the electrochemical Bunsen reaction sulfur-iodine cycle system greatly simplifies the process, reduces the energy consumption and thus improves the energy consumption. By improving and optimizing, it is expected to further improve the thermal efficiency and economy of the system.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TQ116.2
本文編號：2239054
[Abstract]:As a clean, efficient, safe and sustainable alternative energy source, hydrogen energy is becoming more and more popular. It is expected to build an integrated hydrogen production, hydrogen storage, transportation and conversion system in the future, and realize the transition from global fossil energy economy to hydrogen economy. Hydrogen production from non-polluted water is recognized as the best choice. Thermochemical cycling water decomposition is one of the most promising methods because of its many advantages, especially the sulfur-iodine cycle. The traditional Bunsen reaction continues the spontaneous stratification of HI and H2SO4 by the reaction of excessive iodine and water proposed by GA Company in the United States. In order to reduce or even avoid the addition of excess iodine and water, the electrochemical Bunsen reaction method is applied. In view of the fact that HI returns to Bunsen reaction in the actual sulfur-iodine cycle system, the kinetics and thermodynamic equilibrium of the quaternary-multiphase Bunsen reaction in the presence of initial HI are studied. However, the high HI content is not conducive to the separation of the two phases, so the HI/H2O molar ratio should be controlled within a reasonable range of 0-1/18. Increasing the initial HI content increases the impurities of H2SO4 phase, but improves the liquid-liquid equilibrium separation characteristics by increasing the temperature. Adding the initial HI makes the HI concentration in the HIx phase reach super-boiling, which is conducive to reducing the subsequent HI concentration. Increasing the initial HI or temperature results in a slight decrease in the equilibrium conversion of SO2. Considering the high temperature of 345-358K, the HI/H2O molar ratio of 0-1/36 is an ideal operating range. The basic experimental study was carried out around the electrochemical Bunsen reaction, and the concentration of bipolar acid solution and the voltage of the battery were discussed. With the electrolysis proceeding, the concentration of H2SO4 on the anode and HI on the cathode increased, the concentration of 12 on the cathode decreased, while the voltage on the cathode increased as a whole. Increasing the 12/HI molar ratio can reduce the overpotential and increase the ohmic resistance of the solution. The current efficiency is more than 90% or even close to 100% under most operating conditions, indicating that the energy conversion performance of the battery is good. Increasing the current density increases the energy consumption, while changing the HI concentration or the high temperature or H28O4 concentration is opposite. The characteristics of proton exchange membranes in batteries were studied. The proton transfer number T + of the membranes was more than 0.9 or even close to 1. Except at high temperature, the proton transfer capacity of Nafion 115 membrane decreased significantly; the water permeability coefficient beta depended on the operating conditions. The transport characteristics of the membrane are closely related to the concentration of acid. On the contrary, high concentration of H2SO4 can be obtained easily with high T + and low beta values. When analyzing the cross contamination on both sides of the membrane, it is found that the concentration of anodic HI is 2-10 times higher than that of cathode H2S04. Increasing the concentration of H2SO4 promotes the transmission of H2S04 and inhibits the infiltration of HI, whereas increasing the concentration of HI is contrary. The microscopic characterization of the membrane shows that the membrane after electrochemical reaction has folds and solid particles deposition, resulting in the increase of BET surface area and the decrease of average pore size. The equilibrium potential of en reaction was studied experimentally and theoretically. Firstly, the theoretical model of equilibrium potential was deduced based on electrochemical principle. Secondly, the effect of various parameters on equilibrium potential was discussed experimentally. The accuracy of the model is verified by fitting and analyzing the experimental data. The parameters M and Z, which represent the non-ideal characteristics of electrolyte and the concentration distribution in the membrane, are independent of the solution concentration. Z does not change with the temperature. However, there is an exponential relationship between M and temperature. The higher the temperature, the lower the M value. Based on the principle of electrochemical workstation, the electrode reaction mechanism and kinetic characteristics of electrochemical Bunsen reaction were studied. The cyclic voltammetry was used to measure the bipolar reaction and the irreversibility of anodic SO2 oxidation and cathode 12 reduction was judged. The cathode reaction equivalent circuit consists of a solution ohmic resistance in series with a pair of parallel charge transfer resistors and constant phase angle elements; the anode reaction equivalent circuit consists of a charge transfer resistor and a constant phase angle element in parallel. Exchange current density (j0) and standard reaction rate constant (k0) are two important kinetic parameters. When the cathode HI concentration is 8mol/kg H2o, the I2/HI molar ratio is 0.5, and the anode H2SO4 concentration is 13mol/kg H2O, a higher electrode reaction kinetic rate can be obtained. The mass balance and energy balance of the system with hydrogen yield of 1 mol/s are calculated. Considering internal heat transfer and waste heat recovery, the thermal efficiency of the system is calculated to be 48.98%. Compared with the traditional Bunsen reaction sulfur-iodine cycle system, the electrochemical Bunsen reaction sulfur-iodine cycle system greatly simplifies the process, reduces the energy consumption and thus improves the energy consumption. By improving and optimizing, it is expected to further improve the thermal efficiency and economy of the system.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TQ116.2
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