紫外光液相光化学法分解硫化氢制氢

采用波长为253.7 nm的紫外光为光源,以Na2S溶液为反应液,进行了紫外光液相光化学法分解硫化氢(H2S)制氢反应。考察了S的存在形式、Na2S溶液的浓度、Na2SO3溶液浓度及H2S通入流量对制氢的影响。研究结果表明,溶液中S以HS-的形式存在有利于紫外光的分解;加入Na2SO3可以提高体系的产氢量;在体系中通入H2S可以使产氢速率保持稳定。     

光催化法对分解硫化氢制氢的影响

文中采用波长为253.7 nm的紫外光为光源,以Na2S/Na2SO3混合水溶液作为反应介质,采用不同种的光催化剂进行紫外光液相分解硫化氢(H2S)制氢反应。考察了不同种紫外响应的光催化剂对产氢的影响、TiO2-P25光催化剂、TiO2-P25光催化剂加入量、焙烧温度对ZnO光催化剂活性对产氢的影响。研究结果表明,加入光催化剂有助于反应的进行,使反应的产氢量有所提高,不同的光催化剂对分解硫化氢制氢的影响不同;TiO2-P25光催化剂其分解Na2S溶液与紫外光子激发HS-有协同作用;250 mL 0.1 mol/L Na2S水溶液中最佳催化剂用量为0.05 g;不同焙烧温度下制得的ZnO光催化剂对反应体系的产氢速率影响较大,随着焙烧温度的提高,反应的产氢速率也相应提高。     

混合菌种利用淀粉在光照及黑暗条件下的产氢

进行了混合菌种利用淀粉进行光反应和暗反应的产氢对比试验.结果发现光合反应的产氢率以及产氢速率均高于暗反应,但产氢时间滞后于暗反应.对反应的菌液进行了DNA提取、纯化以及PCR扩增,通过对DGGE图谱分析,发现光反应和暗反应的样品条带在数量和亮度上都存在一定差异,暗反应条件下产氢的优势菌群要略多于光合反应的菌群.随着淀粉浓度的增加,光合反应和暗反应的产氢总量均增大,但产氢率降低,其中光合反应的降低尤为明显,从2g/L淀粉浓度时的9.8mmol H2/g淀粉降低到40g/L淀粉浓度时的3.3mmol H2/g淀粉,产氢率降低了66%,而暗反应产氢率降低了43%.光合反应的尾液中,丁酸含量最高,而暗反应的尾液中,乙酸含量最高.     

玉米秸秆酶解与厌氧发酵产氢实验研究

以粒度小于0.088 mm秸秆粉的酶解液为底物与热预处理活性污泥(其中TS%为6.77%,VS%为47.90%,COD为36.665 g/L)进行厌氧发酵产氢实验,以累积产氢量和产氢速率为考察指标,研究不同热预处理(100℃水浴)时间、初始p H值、酶解液浓度、发酵温度对厌氧发酵产氢的影响,并利用修正的Gompertz方程对产氢过程进行回归分析,优化出最佳玉米秸秆酶解液厌氧发酵产氢的工艺参数。结果表明:活性污泥利用玉米秸秆酶解液进行厌氧发酵产氢时,当活性污泥热预处理时间为15 min、初始p H值为5.0、玉米秸秆粉酶解液浓度为22.34 mg/m L、发酵温度为40℃时,产氢效果最佳,此时最大累积产氢量达到653.98 m L,最大产氢速率为15.89 m L/h。     

CaO对松木锯末水蒸气气化过程的影响

采用CaO在生物质气化过程中通过吸收CO2促进产氢的方法,对生物质松木锯末进行水蒸气气化实验研究。分析了CaO、水蒸气、温度和停留时间对产气组分的影响。实验结果表明:添加CaO能显著提高产氢量。当Ca/B0.5时,产氢量随着Ca/B的增加而显著增加,当Ca/B0.5后,产氢量略微下降。添加CaO后促进了水煤气反应的进行。当温度高于800℃时,添加CaO后,生物质气化挥发分释放阶段与半焦气化阶段出现了重叠,半焦气化反应提前发生。随着温度和停留时间的延长,H2浓度逐渐升高,且在较长时间内维持在较高的浓度。     

松木屑水蒸气催化气化制氢及其大物料量气化动力学研究

利用松木屑在自制固定床气化系统上进行水蒸气催化气化实验研究.考察反应温度、水蒸气/生物质比(S/B)以及催化剂加入量对气体成分、产氢率和潜在产氢率的影响.结果表明:反应温度为850℃、S/B为3.27、催化剂量,木屑进料量比为2%时合成气品质较优,氢气浓度可达40.13%,产气率为0.718m3·kg-1.该文也进行大物料量松木屑催化气化等温热重实验研究,加入催化剂使木屑气化反应活化能降低,加快了反应进程.     

焦炉荒煤气重整提质制氢的热力学分析

为了验证吸附强化焦炉荒煤气重整制氢工艺的可行性,并为相关的实验研究提供理论依据,文章采用HSC Chemistry软件对焦炉荒煤气全组分蒸汽重整反应进行热力学分析,研究反应温度、反应压力、S/C,CaO/C对H_2产率、浓度等的影响。研究结果表明:焦炉荒煤气蒸汽重整反应能够有效地脱除焦油组分,随着S/C的增大,H_2产率会得到明显提升,且最佳H2产率所对应的反应温度会随之降低,当S/C为5∶1,反应温度为700℃时,H_2产率为1.62 mol/mol,但H_2浓度仅为75%左右;CO_2吸附剂的加入会强化蒸汽重整反应,H_2产率、浓度均会显著提升,最佳重整反应区的反应温度会随之降低,当反应温度为500~600℃,S/C为5∶1,CaO/C为3∶1时,H2产率、浓度能够分别达到1.83 mol/mol,98%以上。     

暗间歇时长对光合生物制氢的影响

通过改变暗间歇时长,考察HAU-M1光合产氢细菌的生长及pH值和底物浓度的变化情况,研究暗间歇时长与光合细菌产氢量及其工艺参数之间的相关关系。实验结果表明:暗间歇时长为0(持续光照)、6、12、18h时,累计产氢量分别为351、380、275和181mL;反应器内的光合细菌浓度最大值分别为0.547、0.632、0.665和0.449g/L;反应残液的p H值分别为5.58、5.17、4.98和4.71。表明适宜的暗间歇时长可促进光合生物制氢反应过程中光合细菌的生长,同时有利于光合生物产氢过程的进行,可为光合生物制氢工艺技术的进一步优化和产业化发展提供科学参考。     

发酵条件对发酵产氢细菌B49产氢的影响

采用间歇发酵实验，研究了葡萄糖浓度、接种量、温度、氮源、不同有机底物对发酵产氢产酸细菌新菌种IM9(AF481148 in EMBL)生物产氢的影响。结果表明，接种量影响IM9的产氢；IM9生长和产氢适宜温度均为35℃；IM9不能利用无机氮源，而有机氮是IM9生长、产氢的适宜氮源；葡萄糖是IM9发酵产氢的最适宜底物，当浓度为10g／L时，IM9的葡萄糖利用率为100％，氢气得率为1．69molH2／mol glucose；此外，IM9可利用小麦、大豆、玉米、土豆及糖蜜废水和啤酒废水产氢，其中利用糖蜜废水、啤酒废水产氢分别为137．9ml H2／g COD和49．9ml H2／g COD。     

填料塔中碳酸丙烯酯脱除沼气中的CO_2

以木薯渣发酵产生的沼气为原料气,采用10 m3/d脱碳工艺试验装置,以碳酸丙烯酯为吸收剂脱除沼气中的CO2,分别考察了吸收气液比、吸收压力、吸收温度、空气气提气液比、原料沼气中硫化氢浓度对脱碳效果的影响。试验结果表明,吸收气液比为55、吸收压力为800 kPa、吸收温度15℃、空气气提气液比为10时,净化气中CO2浓度为(6.44±0.34)%,CO2脱除率为(92.48±0.39)%。原料沼气中H2S浓度对碳酸丙烯酯的脱碳效果影响显著,当H2S浓度增加到0.4%时,与以脱硫后沼气为原料气时的脱碳情况相比,净化气中CO2浓度增加了1.66%。     

Solution combustion synthesis of CoSx,MoSx, CoSx-MoSx and their catalytic activity in H2 production from H2S decomposition

Production of hydrogen from H₂S is desirable and can meet partly the ever-increasing demand on cheaper and greener hydrogen as a cleaner energy resource since it makes better use of H₂S than the various Claus processes. Medium temperature effective catalysts for H₂S decomposition would help developing a sulfur looping process to overcome the thermodynamic limitation for H₂S decomposition. However, developing such medium temperature catalyst for direct H₂S decomposition is still a great challenge. This work adapts solution combustion synthesis (SCS) method to synthesize oxide and sulfide of molybdenum and cobalt with fine crystalline and their activities in H₂S decomposition were investigated. The in-situ sulfurization with thiourea in SCS process leads to higher surface area and higher activity of the resultant catalysts. The presence of CoS_x enchances the activity of MoS_x in H₂S decomposition. The H₂S decomposition activity of the CoS_x-MoS_x composite is higher than that of each single component one. The H₂S decomposition kinetics analysis shows that an activation energy of 43.3 kJ/mol was achieved on 20%CoS_x-MoS_x which is much lower than that reported in literatures.     

Hydrogen production from biogas reforming and the effect of H2S on CH4 conversion

Biogas produced during anaerobic decomposition of plant and animal wastes consists of high concentrations of methane (CH₄), carbon dioxide (CO₂) and traces of hydrogen sulfide (H₂S). The primary focus of this research was on investigating the effect of a major impurity (i.e., H₂S) on a commercial methane reforming catalyst during hydrogen production. The effect of temperature on CH₄ and CO₂ conversions was studied at three temperatures (650, 750 and 850 °C) during catalytic biogas reforming. The experimental CH₄ and CO₂ conversions thus obtained were found to follow a trend similar to the simulated conversions predicted using ASPEN plus. The gas compositions at thermodynamic equilibrium were estimated as a function of temperature to understand the intermediate reactions taking place during biogas dry reforming. The exit gas concentrations as a function of temperature during catalytic reforming also followed a trend similar to that predicted by the model. Finally, catalytic reforming experiments were carried out using three different H₂S concentrations (0.5, 1.0 and 1.5 mol%). The study found that even with the introduction of small amount of H₂S (0.5 mol%), the CH₄ and CO₂ conversions dropped to about 20% each as compared to 65% and 85%, respectively in the absence of H₂S.     

Influence on hydrogen production of the minor components of natural gas during its decomposition using carbonaceous catalysts

In this work, the catalytic decomposition of the minor hydrocarbons present in natural gas, such as ethane and propane, over a commercial carbon black (BP2000) is studied. The influence of the reaction temperature on the product gas distribution was investigated. Increasing reaction temperatures were found to increase both hydrocarbon conversion and hydrogen selectivity. Carbon produced by ethane and propane was predominantly deposited as long filaments formed by spherical aggregates with diameters on the order of nanometres. Furthermore, the influence of ethane and propane on methane decomposition over BP2000 was also investigated, showing enrichment in hydrogen concentration with the addition of small amounts of these hydrocarbons in the feed. Additionally, the positive catalytic effect of H₂S on methane decomposition over BP2000 is addressed.     

Hydrogen production by H2S decomposition over ceria supported transition metal (Co,Ni, Fe and Cu) catalysts

Hydrogen sulphide (H₂S) is one of the most poisonous and corrosive chemical substances existing in several natural and industrial gas streams, further considered as a valuable H₂ source. Hence, H₂S decomposition to H₂ is of paramount importance toward a sustainable energy future. In the present work, the catalytic decomposition of H₂S is explored in the temperature range of 550–850 °C and at atmospheric pressure, employing a series of ceria-based transition metal composites (i.e., Co, Ni, Fe, and Cu) as catalysts. Various characterization methods, involving BET, XRD, SEM, XPS and elemental analysis, were employed to reveal possible relationships between the obtained catalytic performance and catalysts physicochemical characteristics. The best activity and stability behaviour was exhibited by the 20 wt.% Co/CeO₂ catalyst, achieving H₂S conversions close to thermodynamic equilibrium. The superiority of Co/CeO₂ catalyst is mainly attributed to its in situ reduction and sulfation, toward the formation of highly active and stable phases (Co_1-xS_y and Ce₁₀S₁₄O_y) for H₂S decomposition.     

Combining electrochemical hydrogen separation and temperature vacuum swing adsorption for the separation of N2, H2 and CO2

In biohydrogen processes, H₂ is often present in gas mixtures with CO₂ and N₂. Therefore, we present a separation process that combines electrochemical hydrogen separation (ECHS) and amine-based temperature vacuum swing adsorption (TVSA). Such a separation process does not require the compression of the bulk feed. For the ECHS, a trade-off between cell potential, i.e. power consumption, and stack size, i.e. investment costs, existed. The optimal cell voltage laid in the range of 0.1–0.2 V resulting in costs of 0.37 €/kg_H2. Equivalently, the energy consumption and throughput for the TVSA must be balanced. The optimal desorption pressure and temperature of 0.025 bar and 100 °C resulted in costs of 2.30 €/kg_H2. Thus, the total costs for the separation process were 2.67 €/kg_H2, which are in the range of the separation costs of a binary H₂/CO₂ mixture with a similar H₂ feed fraction.     

Hydrogen production via decomposition of hydrogen sulfide by synergy of non-thermal plasma and semiconductor catalysis

Direct H₂S decomposition induced by plasma with an aid of alumina-supported metal sulfide semiconductors (ZnS/Al₂O₃ and CdS/Al₂O₃) for the production of hydrogen was investigated in a dielectric barrier discharge (DBD) reactor. Effects of specific input energy (SIE), feed flow rate, metal sulfide loading, and added hydrogen on the performance of H₂S decomposition were studied. With the aids of ZnS/Al₂O₃ and CdS/Al₂O₃, full conversion was obtained at reasonably low energy costs. The 100-h test runs indicated that both ZnS/Al₂O₃ and CdS/Al₂O₃ were stable in the course of H₂S decomposition. A supported metal sulfide solid solution (Zn_0.4Cd_0.6S/Al₂O₃) exhibited higher performance than ZnS/Al₂O₃ and CdS/Al₂O₃, achieving full conversion at a reduced energy cost. The mechanism of the plasma-induced H₂S decomposition with an aid of a semiconductor catalyst was tentatively proposed.     

Hydrogen and syngas production through dynamic chemical looping reforming-decomposition of methane

This work introduces CeZr_0.5GdO₄ spinel particles as novel oxygen carriers for use in the reforming and decomposition of methane into H₂ and CO via the chemical looping technique. These particles were prepared by a modified sol-gel combustion method to increase their reactivity by increasing the surface area and consequently more accessibility of the gas feed to the solid phase. The performance of the synthesized materials was dynamically evaluated in terms of activity and stability at different operating temperatures (800–900 °C). The air used in the oxidation step eliminates almost all of the deposited solid carbon and converts it to CO, while providing the oxygen consumed in the reduction step. Oxygen carrier particles showed a conversion of more than 90% in all cycles after about 30 min of reduction operations. By the optimal operating path proposed in this research, more than 90% of the reactor exhaust gas is allocated to the production of H₂ and CO with almost complete elimination of CO₂ and H₂O in a shorter period of time. This will also reduce the time required for coke gasification and lattice oxygen replenishment of the spinel. Finally, the CeZr_0.5GdO₄ proved to be a successful oxygen carrier for the continuous production of hydrogen and carbon monoxide with almost no remarkable reduction in activity during successive redox cycles.     

H2 production from methane decomposition by fullerene at low temperature

Carbon materials have previously been reported to work as catalysts for hydrogen (H₂) production from hydrocarbons. Mechanisms of the catalytic behavior of graphite and carbon black (CB) have often been discussed in literature. Graphite and CB is constructed from mainly 6-membered rings with sp² bonds. To understand the catalytic behavior of carbon materials for H₂ production by methane (CH₄) decomposition, the catalytic behavior of fullerenes with 6-membered rings and also those comprising 5- and 7-membered rings with sp² bonds and their associated mechanisms should be investigated. In this study, the fullerene catalyst activity has been investigated using gas chromatography and the electronic states and nanoscale structures have been analyzed.H₂ production started at 400 °C and the H₂ production rate gradually increased with time, and the activation energy of the fullerene for H₂ production by CH₄ decomposition was found to be 166 kJ/mol. Moreover, in situ heating X-ray photon spectroscopy (XPS) measurements showed that the π-π1 transition signal becomes stronger with increasing temperature above the threshold of 300 °C. The transition of the π electrons to π1 orbitals upon heating is expected to decompose CH₄ absorbed on fullerene. Moreover, transmission electron microscopy (TEM) analysis revealed that the generated carbon atoms from the CH₄ decomposition were deposited onto the surfaces of the fullerenes, forming amorphous and layered concentric sphere carbon. Amorphous carbon is reported to not work as a catalyst for CH₄ decomposition at around 400 °C. From XPS analysis and TEM observations of these two structures, it is anticipated that the ring structures without 6-membered rings in carbon materials with sp² bonding contribute to this catalytic behavior for CH₄ decomposition at a low temperature of 400 °C.