Deterioration of Nafion 115 membrane in direct methanol fuel cells

A membrane electrode assembly (MEA) based on a Nafion 115 membrane shows a 29% loss in power density after continuous testing in a single direct methanol fuel cell for 1000 h at 50 °C. One of the main reasons for this behaviour is a deterioration of the membrane, namely, its ion-exchange capacity is reduced by 17%. The thermal decomposition behaviour of an untested and degraded membrane is studied by evolved gas analysis-mass spectrometry, pyrolysis-gas chromatography-mass spectrometry, thermo-gravimetric analysis, differential scanning calorimetry, and in situ FTIR reflectance absorption spectra. The results reveal a decrease in thermal stability of the degraded membrane. The Nafion 115 membrane is suggested to lose ion-exchange capacity after the sulfonic acid group is transformed to a thermally less-stable group, such as the persulfonic acid -SO₂OOH group during MEA operation. The structural changes may prevent the formation of ionic clusters.     

聚三氟氯乙烯纯氧环境热解气体产物分析

使用针筒采样法采集聚三氟氯乙烯纯氧环境等温(400℃/450℃)热解气体产物,通过气相色谱-质谱联用技术和真空紫外光电离质谱技术,定性分析热解气体产物组成成分,为评估氧气系统在设计和使用过程中的安全性提供参考．结果表明：聚三氟氯乙烯纯氧热解气体产物中共检出13种气体成分,其中氟氯烷类4种,单烯类5种,小分子类4种．分析认为氟氯烷类和单烯类气体产物的生成是由于聚三氟氯乙烯在热解过程中发生碳链、碳氯键及碳氟键的无规则断裂和重新结合,而小分子类气体产物的生成是由于聚三氟氯乙烯在热解过程中发生氧化生成中间体(COF₂、COFCl),中间体进一步分解产生CO、CO₂、Cl₂和F₂.     

CuO对木粉/PVC复合材料热解和燃烧过程中烟释放行为的影响

采用热重分析法、锥形量热仪测试及Py-GC-MS联机方式研究了CuO对木粉/PVC复合材料(WF-PVC)热解和燃烧过程烟释放行为的影响.实验结果表明,WF-PVC热解过程具有PVC热解的特性;与WF-PVC相比,用CuO处理WF-PVC能明显提高第1阶段质量损失,降低第2阶段的质量损失,提高成炭量;WF-PVC燃烧过程中烟释放速率和总烟量低于PVC,用CuO处理WF-PVC总烟量降低更显著;Py-GC-MS分析结果表明,与PVC相比,WF-PVC以及用CuO处理的WF-PVC,燃烧气相组分中芳香族化合物含量分别降低52.29%和49.34%;加入CuO,抑制了气相组分中多环化合物的生成.     

Combustion chemistry and flame structure of furan group biofuels using molecular-beam mass spectrometry and gas chromatography – Part II: 2-Methylfuran

This is Part II of a series of three papers which jointly address the combustion chemistry of furan and its alkylated derivatives 2-methylfuran (MF) and 2,5-dimethylfuran (DMF) under premixed low-pressure flame conditions. Some of them are considered to be promising biofuels. With furan as a common basis studied in Part I of this series, the present paper addresses two laminar premixed low-pressure (20 and 40 mbar) flat argon-diluted (50%) flames of MF which were studied with electron–ionization molecular-beam mass spectrometry (EI-MBMS) and gas chromatography (GC) for equivalence ratios ? = 1.0 and 1.7, identical conditions to those for the previously reported furan flames. Mole fractions of reactants, products as well as stable and reactive intermediates were measured as a function of the distance above the burner. Kinetic modeling was performed using a comprehensive reaction mechanism for all three fuels given in Part I and described in the three parts of this series. A comparison of the experimental results and the simulation shows reasonable agreement, as also seen for the furan flames in Part I before. This set of experiments is thus considered to be a valuable additional basis for the validation of the model. The main reaction pathways of MF consumption have been derived from reaction flow analyses, and differences to furan combustion chemistry under the same conditions are discussed.     

A high pressure ignition delay time study of 2-methylfuran and tetrahydrofuran in shock tubes

Ignition delay time studies for tetrahydrofuran (THF) and 2-methylfuran (2MF) as well as optical investigations of combustion for 2MF have been carried out using two shock tubes. The experiments with undiluted THF/air mixtures were performed at 20 and 40 bar in a high pressure shock tube (HPST) at an equivalence ratio of Ф = 1 covering an overall temperature range of 780–1100 K and 691–1006 K, respectively. Undiluted 2MF/air mixtures (Ф = 1) were also investigated in the HPST at 40 bar in the temperature range of 820–1215 K. The experimental data of 2MF obtained at 40 bar were supported with kinetic simulations of existing models from literature. Additionally, sensitivity analyses of 2MF at several temperatures were performed for finding out the most sensitive reactions. Schlieren imaging was employed in a rectangular shock tube (RST) utilizing a high speed video camera through which the ignition process was captured for a stoichiometric 2MF/O₂/Ar mixture at pressures of about 10 bar and in the temperature range of 871–1098 K.     

Geochemical correlation of Asmari/Jahrum reservoir of Nargesi oilfield with seeps nearby

In case of maintaining the reservoir pressure by gas injection, connection between the reservoir and oil seeps around the oilfield should be investigated. Existence of probable conduits from reservoir to surface would cause problems such as environmental issues and capital losses. Comprehensive geochemical analyses were performed on Nargesi oilfield and nearby seep samples in order to investigate their geochemical correlation. Biomarker and diamondoid distributions as well as stable carbon isotope analysis on selected samples were determined by GC-MS and Finnigan Delta Plus mass spectrometer, respectively. Two active petroleum systems were identified in the region. A Jurassic petroleum system charged Nargesi oilfield, whereas the seeps appear to be charged by an older petroleum system. Higher maturity of seep samples identified by methylnaphthalenes, trisnorhopanes, and triaromatic steroid ratios implied that the second petroleum system should be older than Jurassic. Biomarker ratios confirmed that Marl-Carbonate source rocks deposited under anoxic to dysoxic conditions in open marine environment were the main oil-generating facies for the oilfield. Diamondoid indexes further support the concept developed by biomarker data and reveal that the seeps should be probably charged by shaly source rock. The negative correlation implies that gas injection would be effective.     

Estimating kinetic parameters in TGA using B-spline smoothing and the Friedman method

The pyrolysis of biomass occurs via several parallel/serial decomposition reactions. The kinetic parameters, namely the activation energy (E) and the pre-exponential factor (k_o), do not remain constant during the pyrolysis process. A modified empirical method is introduced for calculating the activation energy (E) and the pre-exponential factor (k₀) based on the Friedman analysis [Friedman HL. Kinetics of thermal degradation of char-forming plastics from thermogravimetry – application to a phenolic plastic. J Polym Sci C 1963;6: 183–95]. The kinetic parameters are expressed as a function of the conversion (x) during the biomass pyrolysis process. The reactions are assumed to be of first order. At least three data sets obtained at different dynamic heating rates are required. From the Friedman analysis, the conversion (x) related functions E = E(x) and k_o = k_o(x) can be obtained by a B-spline regression method. The pyrolysis can hence be described as: x/t=k(1−x)=k_o(x)·exp(−E(x)/RT)(1−x).In this paper, the adapted method is applied to pyrolysis of cellulose and two biomass fuels (meat & bone meal, chicken litter). Experiments were carried out at 2, 10 and 50 K min⁻¹ by thermogravimetric analysis. A good fit of the calculated conversion with experimental data was found.     

Analysis of sugars by liquid chromatography-mass spectrometry in Jerusalem artichoke tubers for bioethanol production optimization

Sustainability of biofuels is increasingly taken into account; therefore, sustainable production technologies are needed. There has been a long history of converting Jerusalem artichoke into ethanol. Jerusalem artichoke (Helianthus tuberosus L.) is a low-requirement crop, it has a high carbohydrates yield and, nowadays, it does not interfere with food chain. It is, then, a promising energy crop for sustainable bioethanol production. However, the main storage carbohydrate of Jerusalem artichoke, inulin, can not be directly fermented by classic fermentation yeasts, so, either a hydrolysis followed by fermentation with classical yeast or the use of yeasts with inulinase activity are required to obtain bioethanol. Therefore, it is needed to know not only total sugar content, but also their composition, for the bioethanol production optimization from Jerusalem artichoke tubers. Several methods have been used in literature for carbohydrates analysis present in Jerusalem artichoke tubers. However, for further development of carbohydrate analysis, faster and more reliable identification and peak confirmation, mass spectrometry (MS) detection is required. In this paper, liquid chromatography with electrospray ionization mass spectrometry (LC-ESI-MS) was used as an alternative technique to analyse sugars content and composition in tubers from Jerusalem artichoke. Two simple, rapid, sensitive and specific LC-ESI-MS methods were developed under the positive ionization mode. Glucose, fructose, sucrose, kestose and inulin were determined. Furthermore, inulin profile can be characterized. Analytical reversed phase LC columns were used using only water as eluent. These methods can be useful to optimize the whole bioethanol production chain from Jerusalem artichoke.     

大体积程序升温汽化进样技术用于柴油机多环芳香烃的检测

为了降低气相色谱-质谱联用法(GC-MS)中多环芳香烃(PAHs)的检测限,使GC-MS技术能够更准确地检测柴油机燃烧生成的痕量PAHs,选择了程序升温汽化(PTV)进样与GC-MS技术联用(PTV-GC-MS),并对PTV进样参数进行了优化.结果表明,进样初始温度为40,℃、出口时刻为0.55,min及出口流量为10,mL/min时,与分流/不分流进样相比,PTV进样对16种PAHs检测限降低,相对标准偏差(RSD)在1.12%～6.07%,完全满足柴油机燃烧过程痕量PAHs的检测要求.     

Thermogravimetric analysis as a new method to determine the lignocellulosic composition of biomass

Biomass energy uses organic matter such as wood or plants - lignocellulosic biomass - for creating heat, generating electricity and producing green oil for cars. Modern biomass energy recycles organic leftovers from forestry and agriculture, like corn stovers, rice husks, wood waste and pressed sugar cane, or uses special, fast-growing “energy crops” like willow and switchgrass, as fuel. Biomass is composed of three major components: cellulose, hemicelluloses, and lignin. Their differences in chemical structures lead to different chemical reactivities, making the relative composition in cellulose, hemicelluloses and lignin in the biomass a crucial factor for process design. In this paper thermogravimetric analysis is investigated as a new method to obtain lignin, hemicellulose and ??-cellulose contents in biomass. It is shown that this alternative method lead to comparable results than common methods used for the determination of the ??-cellulose content, with an enhancement of the accuracy in the determination of the hemicellulose content. Unfortunately, this method cannot be adopted for the determination of the lignin amount.     

太阳电池用CuInSe_2薄膜的电化学可控沉积

采用恒电位电沉积法制备了CuInSe_2薄膜材料,通过循环伏安分析探讨了Cu~(2+)、In~(3+)和H_2SeO_3单独沉积和共沉积的电化学行为,并研究了沉积电位对薄膜化学计量组成、形貌和物相组成的影响规律。研究表明:柠檬酸根离子对Cu~(2+)和H_2SeO_3具有络合作用,而对In~(3+)的络合不明显。共沉积时,Cu最先还原,然后诱导Se的沉积,两者反应形成的铜硒化合物Cu_xSe又诱导In的欠电位沉积,并与之反应生成CuInSe_2。在阴极电位为-0.58～-0.90Vvs.SCE时出现了不随电位变化的极限还原电流,在该电位范围内进行电沉积获得了化学计量组成稳定可控且相对致密平整的CuInSe_2薄膜。     

燃烧条件下硫铁矿(FeS2)颗粒的分解特性

采用美国Ｍｉｃｒｏｍｅｒｉｔｉｃｓ公司的ＡＳＡＰ２０００型比表面孔容测定仪,用等温吸附法,对硫铁矿（ＦｅＳ２）在反应前及一维沉降管炉不同炉温条件下的孔径、比表面积和孔容积等参数的变化特性及硫的释出现律进行了测定,得到了对ＦｅＳ２及其反应产物形态的一定认识,研究表明,ＦｅＳ２颗粒的分解、氧化是由外表面向中心进行的,并可能出现氧化和分解同时进行的过程。     

Two dimensional Cu based nanocomposite materials for direct urea fuel cell

In this work, Cu₂O nanoparticles were successfully prepared onto the surface of two-dimensional graphitic carbon nitride (g-C₃N₄) by using a simple solution chemistry approach. An environment-friendly reducing agent, glucose, was used for the synthesis of Cu₂O NPs onto the surface of g-C₃N₄ without using any surfactant or additives. The surface composition, crystalline structure, morphology, as well as other properties have been investigated using XPS, XRD, SEM, FTIR, FESEM, EDS, etc. The electrochemical measurements of the prepared materials demonstrated that Cu₂O exhibited a weak oxidation activity towards urea, while g-C₃N₄ has no activity towards urea oxidation. The Cu₂O supported on the surface of g-C₃N₄ (Cu₂O-g-C₃N₄) demonstrated a significant activity towards urea oxidation that reached two times that of the unsupported one. The significant increase in the performance was related to the synergetic effect between the Cu₂O and g-C₃N₄ support. The prepared composite materials demonstrated high stability towards urea oxidation as confirmed from the stable current discharge for around 3 h without any noticeable degradation performance.     

GK1F和GK2B型机车柴油机窜气故障的分析与处理

对莱芜钢铁集团有限公司GK1F和GK2B型机车柴油机窜气故障进行了调查统计,分析了GK1F和GK2B型机车柴油机窜气故障产生的原因,提出了有效的故障判断方法和控制措施。     

Thermal pretreatment of wood (Lauan) block by torrefaction and its influence on the properties of the biomass

The purpose of this study is to investigate the torrefaction behavior of woody biomass (Lauan) blocks and its influence on the properties of the wood. Three different torrefaction temperatures of 220, 250 and 280 °C, corresponding to light, mild and severe torrefactions, and four torrefaction times of 0.5, 1, 1.5 and 2 h were considered. After analyzing the torrefied woods, it was found that the torrefaction temperature of 280 °C was able to increase the calorific value of the wood up to 40%. However, over 50% of weight was lost from the wood. The grindability of the torrefied wood could be improved in a significant way if the torrefaction temperature was as high as 250 °C and the torrefaction time longer than 1 h. Therefore, the torrefaction temperature of 250 °C along with the torrefaction time longer than 1 h was the recommended operation to intensify the heating value and grindability as well as to avoid too much mass loss of the wood. This study also suggested that over 50% of the reacted wood was converted into condensed liquid. The main components in the liquid were monoaromatics; little amount of heterocyclic hydrocarbons were also obtained from the torrefactions, especially at the torrefaction temperature of 280 °C.     

An interval type-2 fuzzy logic controller for TCSC to improve the damping of power system oscillations

In this paper an interval type-2 fuzzy logic controller (IT2FLC) was proposed for thyristor controlled series capacitor (TCSC) to improve power system damping. For controller design, memberships of system variables were represented using interval type-2 fuzzy sets. The three-dimensional membership function of type-2 fuzzy sets provided additional degree of freedom that made it possible to directly model and handle uncertainties. Simulations conducted on a single machine infinite bus (SMIB) power system showed that the proposed controller was more effective than particle swarm optimization (PSO) tuned and type-1 fuzzy logic (T1FL) based damping controllers. Robust performance of the proposed controller was also validated at different operating conditions, various disturbances and parameter variation of the transmission line parameters.