Study of the production of hydrogen bubbles at low current densities for electroflotation processes

BACKGROUND: Flotation processes are widely used in waste‐water treatment and it is quite important to have a tool to determine and optimize the size distribution of the bubbles produced. In this work, the electrochemical production of bubbles to enhance the performance of electrocoagulation processes by flotation is studied. To do this, a current density range characteristic of electrocoagulation processes is used to produce microbubbles (<5 mA cm^?2), instead of the higher values used in other studies to characterize electroflotation in non‐combined processes. RESULTS: Current density and pH were found to influence the process significantly. In the range used, higher current densities allow a larger number of small size bubbles to be obtained, appropriate for use in electroflotation processes. However, at the boundaries of the range, the size of the bubbles was increased advising against use. Neutral pH values also favour the formation of small bubbles, and the presence of possible competing reactions have to be considered because they diminish the gas flow and affect the number of bubbles and their size. The roughness of the surface of the electrode material also has an important influence. CONCLUSIONS: The image acquisition and analysis system developed allows measurement of the size distribution of hydrogen bubbles in the range of current densities studied. Current density and pH seem to be the main parameters affecting the mean diameter of bubbles and the amount of gas produced, and the electrode material may also influence hydrogen production significantly. Copyright © 2010 Society of Chemical Industry     

乙炔与氯化氢在低温下混合的安全性研究

乙炔与氯化氢混合气体中含有由游离氯与乙炔反应生成的氯乙炔和二氯乙炔组分时,存在着易燃、易爆的安全隐患,这两种组分的产生原因主要是混合温度高。笔者提出了将乙炔和氯化氯气体先分别在-14℃下进行除水后再混合的预防措施,可使气体混合工段生产的安全性在原来的基础上提高70%。     

燃料电池氢源技术--中低温乙醇水蒸气重整制氢研究

采用浸渍-热分解法制备了一种纳米Ni/Y2O3催化剂,并应用X射线衍射、BET比表面测试分析手段对该催化剂的结构性能进行了表征,采用固定床反应器对催化剂的催化性能进行测试。结果表明:该催化剂对乙醇的水蒸气重整反应表现出较高的活性和稳定性,可作为燃料电池氢源技术中乙醇重整器的候选催化剂。     

基于金属氢化物固态氢源的氢燃料电池动力系统特性的研究

以基于金属氢化物的固态储氢技术,与质子交换膜燃料电池(PEMFC)耦合,搭建了基于金属氢化物固态氢源的氢燃料电池动力系统试验台,测试了吸氢压力、放氢温度、氢流量等关键操作参数对氢燃料电池动力系统性能的影响。结果表明,当吸氢压力大于等于0.60 MPa时,固态储氢反应器放氢流量稳定的时间最长可达4500 s以上。当放氢温度大于60℃时,储氢反应器能完全释放氢气,且放氢时间基本相同。放氢流量越小,氢燃料电池动力系统稳定工作的时间越长。     

Desulfurization of digester gas: prediction of activated carbon bed performance at low concentrations of hydrogen sulfide

Three chemically modified/impregnated activated carbons (supplied by manufactures) were used for adsorption–catalytic removal of hydrogen sulfide from digester gas. The performance of samples was studied in dynamic conditions at 1000, 2000 and 5000 ppm of H₂S in digester gas. The results showed differences in the H₂S removal capacities related to the type of carbon and conditions of the experiment. A decrease in H₂S concentration resulted in an increase in a breakthrough capacity, which is linked to slow kinetics of oxidation process. No significant changes were observed when the oxygen content increased from 1 to 2% and the temperature from 38 to 60 °C. On the surface of carbons studied hydrogen sulfide was oxidized predominantly to sulfur, which was deposited in micropores, either on the walls or at the pore entrances. The capacities at low concentrations, 50 and 100 ppm, of H₂S were determined using an approach based on known theoretical solution of a dynamic model where the parameters of the model were determined from the experimental data at a high concentration of an adsorbate.     

电沉积Ni-P-ZrO2复合电极析氢电催化性能的研究

用电沉积方法制备了镍－磷－二氧化锆复合电极。通过阴极极化曲线,交流阻抗等电化学技术研究其析氢催化性能,并用扫描电镜观察电极的表面形貌。实验结果表明,在80℃,25％氢氧化钠碱性溶液中镍－磷－二氧化锆的表观交换电流密度及表面粗糙度皆大于镍,镍－磷电极,而反应电阻较小。说明镍－磷中引入二氧化锆所形成的复合镀层具有较高的析氢催化活性和良好的电化学稳定性。     

脉冲和直流电沉积Ni-P合金电极析氢电催化性能的研究

在由250 g/L NiSO4·6H2O、45 g/L NiCl2·6H2O、36 g/LH3BO3、20 g/L NaH2PO2·H2O和0.05～0.10 g/L十二烷基硫酸钠组成的镀液(pH 4.0～5.5)中,分别用脉冲和直流电沉积法在镍片上获得了Ni-P合金镀层,并进行了对比研究,SEM测试结果表明,脉冲电沉积方法获得的Ni-P合金镀层表面更加细致,电化学测试结果表明,脉冲电沉积镀层的交换电流密度较大,具有良好的析氢电催化活性,优良的电化学稳定性和良好的结合力及耐蚀性.     

电沉积制备镍-铁-钨合金析氢电极的工艺研究

以紫铜片为基体电沉积制备了Ni–Fe–W合金电极。研究了镀液中不同组分的浓度和工艺条件对Ni–Fe–W合金析氢性能的影响,得到最佳镀液配方和工艺条件为:NiSO4·6H2O80g/L,FeSO4·7H2O20g/L,Na2WO4·2H2O0.020mol/L,Na3C6H5O7·2H2O 0.5 mol/L,H3BO3 0.65 mol/L,Na2SO4 0.1 mol/L,十二烷基硫酸钠0.1 g/L,pH 5~6,温度30°C,电流密度4 A/dm2,磁力搅拌800 r/min,时间30 min。在该条件下所得Ni–Fe–W合金电极表面Ni、Fe和W的原子分数为63.79%、34.35%和1.86%,具有较大的比表面积,在30%KOH溶液中的析氢催化活性较好。     

膨润土负载钌催化剂制备及其催化氨硼烷水解产氢研究

采用浸渍-化学还原法制备了钌/膨润土（Ru/Ben）催化剂,考察了钌含量、还原剂硼氢化钠用量、还原温度以及反应条件等对Ru/Ben催化氨硼烷（NH₃BH₃）水解产氢的影响。结果表明,在钌负载量为0.3%（质量分数）、钌与还原剂硼氢化钠物质的量比为1∶2.5、还原温度为303 K条件下,制备的Ru/Ben中Ru微晶尺寸为3.8 nm,Ru/Ben催化NH₃BH₃水解产氢的转化频率（TOF）为145 mol/（mol·min）;搅拌转速为450 r/min时,外扩散限制消除,产氢速率最大;产氢速率与Ru/Ben浓度成正比,催化剂界面反应是氨硼烷水解产氢反应的控速步骤,Ru/Ben催化NH₃BH₃水解产氢反应对催化剂浓度的反应级数为0.7;反应温度越高,氨硼烷向催化剂表面的传质速率越高、产物氢气及副产物偏硼酸钠从催化剂表面越易脱附,产氢速率越大。动力学计算表明,Ru/Ben催化NH₃BH₃水解产氢反应的产氢速率与氨硼烷浓度无关,活化能为15 kJ/mol。     

双脉冲电沉积制备Ni-聚苯胺复合电极及其析氢性能的研究

采用控制双脉冲电位沉积技术制备N i-聚苯胺复合电极。扫描电镜下观察电极表面呈菜花状结构,比表面积约为普通镀N i电极的4~50倍。N i-PAN复合电极的X射线衍射谱图中分别出现了N i和PAN的特征峰。通过测试复合电极在模拟氯碱工业电解液中的阴极极化曲线,研究了N i-PAN电极的析氢性能,结果显示当电流密度为0.10 A/cm2时,析氢过电位较镀N i电极降低约350 mV。复合电极性能稳定,可作为氯碱工业用活性阴极,能显著降低能耗。     

Oxidation of low concentrations of hydrogen sulphide: Process optimization and kinetic studies

Low concentrations (e.g. < 3) of H₂ S in natural gas can be selectively oxidized over an “granular Hydrodarco” activated carbon catalyst to elemental sulphur, water and a small fraction of by-product sulphur dioxide, SO₂. To optimize the H₂ S catalytic oxidation process, the process was conducted in the temperature range 125—200 °C, at pressures 230—3200 kPa, with the O/H₂ S ratio being varied from 1.05 to 1.20 and using different types of sour and acid gases as feed. The optimum temperature was determined to be approximately 175 °C for high H₂ S conversion and low SO₂ production with an O/H₂ S ratio 1.05 times the stoichiometric ratio. The life of the activated carbon catalyst has been extended by removing heavy hydrocarbons from the feed gas. The process has been performed at elevated pressures to increase H₂ S conversion, to maintain it for a longer period and to minimize SO₂ production. The process is not impeded by water vapour up to 10 mol% in the feed gas containing low concentrations of CO₂ (< 1.0). A decrease in H₂ S conversion and an increase in SO₂ production were obtained with an increase in water vapour in the feed gas containing a high percentage of CO₂. The process works well with “sour natural gas” containing approximately 1% H₂ S and with “acid gas” containing both H₂ S and CO₂. It gives somewhat higher H₂ S conversion and low SO₂ production with feed gas containing low concentrations of CO₂. A kinetics study to determine the rate-controlling step for the H₂ S catalytic oxidation reaction over “granular Hydrodarco” activated carbon has been conducted. It was concluded that either adsorption of O₂ or H₂ S from the bulk phase onto the catalyst surface is the rate-controlling step of the H₂ S catalytic oxidation reaction.     

磷酸氢铁铵的低热固相合成及其对乙酸丁酯的催化作用

以硫酸亚铁和磷酸二氢铵为原料,以聚乙二醇-400(PEG-400)为表面活性剂,经低热固相反应合成得到磷酸氢铁铵,经XRD分析表征证实了产物的分子式为(NH4)Fe(HPO4)2.用磷酸氢铁铵为催化剂进行了乙酸丁酯的合成试验.试验中应用了均匀设计试验法及数据挖掘技术,在数据挖掘成果的指导下进行了试验,考察了催化剂用量、醇酸物质的量比、反应时间及催化剂重复使用次数等因素对收率的影响,获得了催化反应的最佳工艺条件.催化试验结果表明,磷酸氢铁铵具有良好的催化活性,在最优工艺条件下,酯转化率可达到96.4%.研究结果表明,低热固相法合成磷酸氢铁铵不仅合成工艺简单、可行,而且合成的磷酸氢铁铵作为乙酸丁酯的催化剂时具有良好的催化活性,故其具有良好的工业应用潜质.     

Electrochemical sensors for detection of hydrogen in air: model of the non-Nernstian potentiometric response of platinum gas diffusion electrodes

The potentiometric response of three different platinum gas diffusion electrodes deposited on H₃PO₄ doped polybenzimidazole (PBI) was investigated under humidified atmospheres that contained H₂ or mixtures of H₂ and O₂. Continuum modelling was used to analyse the response. It is shown that the non-Nernstian response under H₂H₂ON₂ mixtures can be explained by a difference of water activity on both sides of the membrane. Under H₂O₂N₂ mixtures, the oxygen mass transport parameters have a strong effect on the electrode sensitivity.     

全pH范围下MoS2/Ni3S2/NF的高效电催化析氢行为

在全pH（0~14）范围下设计开发低廉、高活性的析氢电催化剂对新能源开发和利用具有重要实际意义。通过简单的溶剂热法在镍网（NF）上原位构筑了纳米线结构MoS2/Ni3S2/NF电催化剂，该催化剂在全PH范围下表现出优异的析氢（HER）活性。电化学测试结果表明，使用41 mg四硫代钼酸铵制得的MoS2/Ni3S2/NF-41电极,在电流密度10 mA/cm2时，其在碱性（1 moL/L KOH，pH=14）、中性（0.5 moL/L PBS，pH=7）和酸性（0.5 moL/L H2SO4，pH=0）介质中HER过电位分别为87、113和195 mV，并相应表现出较低的Tafel斜率。另外，SEM、TEM、EDX、XPS等表征手段表明该催化剂具有良好的结构稳定性。本研究为过渡金属硫化物在全pH环境下高效析氢提供了新途径。     

From soil to lab: Utilization of clays as catalyst supports in hydrogen generation from sodium borohydride fuel

The stabilized aqueous solution of sodium borohydride NaBH₄ is a promising hydrogen fuel but the stored hydrogen has to be released with the help of a catalyst through hydrolysis. In the present study, we developed Co- and clay-based supported catalysts. Three raw clays were taken from soil in Lebanon. Once purified and annealed, they were used as supports. Two of them, mainly composed of kaolinite and illite respectively, showed to be promising owing to their attractive specific surface areas (58.0 and 67.1 m² g⁻¹) as well as the high reactivity of the corresponding 15 wt.% Co catalysts (i.e. NaBH₄ conversions of 100% and hydrogen generation rates up to ∼31 L(H₂) min⁻¹ g⁻¹(Co)). A kinetic study was also carried out. The main results are reported and discussed herein.     

Study of the oxygen reduction reaction (ORR) at Pt interfaced with phosphoric acid doped polybenzimidazole at elevated temperature and low relative humidity

The oxygen reduction reaction on platinum interfaced with phosphoric acid doped PBI at elevated temperature and low relative humidities has been investigated by using a micro band electrode technique. Both the kinetic and the mass transport parameters in the Pt/PBI-H₃PO₄ system are comparable to those of the Pt/H₃PO₄ system under similar conditions. The study suggests that it is the amorphous H₃PO₄ phase that functions as the electrolyte. The oxygen reduction reaction is first order with respect to both proton concentration and oxygen saturation concentration in the electrolyte, which indicates that the proton transfer is the rate-determining step in oxygen reduction. The H₃PO₄ doping level and the water content of the electrolyte affect the ORR exchange current density, oxygen diffusion, and the oxygen solubility in PBI-H₃PO₄ membranes. The dissolved O₂ molecules permeate mainly through the amorphous H₃PO₄. However, the oxygen solubility in PBI-H₃PO₄ is higher than its solubility in H₃PO₄, which is explained by the presence of the crystalline PBI region formed during electrolyte preparation.     

Reduction of metal ions in dilute solutions using a GBC-reactor Part II: Theoretical model for the hydrogen oxidation in a gas diffusion electrode at relatively low current densities

The GBC-reactor is based on the combination of a gas diffusion anode and a porous cathode. A theoretical model for gas diffusion electrode, valid at relatively low current densities, is derived. This is based on the pseudohomogeneous film model including an approximation of the Volmer–Tafel mechanism for the hydrogen oxidation kinetics. Results show a severe mass transfer limitation of the hydrogen oxidation reaction inside the active layer of the gas diffusion electrode, even at low current densities. Empirical formulae are given to estimate whether leakage of dissolved hydrogen gas into the bulk electrolyte occurs at specific process conditions. A simplified version of the model, the reactive plane approximation, is presented.     

AuPd bimetal immobilized on amine-functionalized SBA-15 for hydrogen generation from formic acid: The effect of the ratio of toluene to DMF

The volume ratio of toluene to N,N-dimethylformamide (DMF) was adjusted during the amine functionalization of SBA-15 to change the amine content of SBA-15. XPS, FTIR, and TGA analyses indicated that under the experimental synthetic conditions the number of amine groups varies with the ratio of toluene/DMF, and the highest content of amine could be obtained with a volume ratio of toluene/DMF = 3:2. The hydrogen production experiment of formic acid decomposition showed that the hydrogen production efficiency over the Au-Pd-SBA-15-NH₂ catalysts increased with the increase in the surface amine content of the Au-Pd-SBA-15-NH₂. The optimal Au-Pd-SBA-15-NH₂-TD (toluene/DMF = 3:2) catalyst proved to have the smallest Au-Pd bimetal nanoparticle size and exhibited a turnover frequency (TOF) = 631 hours⁻¹ and an activation energy (Ea) = 20.8 kJ · mol⁻¹ at 25°C. The catalytic performance of hydrogen generation from the formic acid was improved due to the synergistic effect between the amine-functionalized SBA-15 and the Au-Pd bimetal (metal-support interactions).     

废轮胎热解炭低温催化焦油重整制备富氢气体的研究

以全钢型废旧轮胎为原料,通过热解、活化、浸渍、焙烧的流程制备了三种热解炭催化剂,分别为轮胎热解炭（Raw char）、轮胎热解活性炭（AC）和负载Zn的活性炭（Zn/AC）。采用N₂吸/脱附、SEM、EDS、XRD等表征方法对催化剂进行了一系列表征和分析,发现CO₂/H₂O活化可显著提高催化剂BET比表面积,最高可达380 m²·g^-1,有效改善催化剂表面结构性质,同时浸渍法使催化剂表面负载大量ZnO活性位。对三种催化剂在纤维素热解焦油重整制氢过程中的催化性能进行了研究,发现Raw char（600℃）具有最佳催化效果,相较于空白组（500℃）,热解气中H₂体积分数提高了12.4%,达到19.3%,其次为Zn/AC（500℃）组的17.8%,实现了低温下催化纤维素焦油热解制得高产率H₂。