Non-linear modeling of kinetic and equilibrium data for the adsorption of hexavalent chromium by carbon nanomaterials:Dimension and functionalization

The adsorption capacities for the removal of hexavalent chromium from aqueous solutions by six carbon nanomaterials have been evaluated. Single-walled and multi-walled carbon nanotubes as received and after oxidation treatment, graphene oxide and reduced graphene oxide are the materials with different dimension and functionalization compared in this research. Carbon nanotubes have been modified using hydrogen peroxide as oxidizing agent under microwave radiation. The oxidation treatment on carbon nanotubes has a positive effect increasing the adsorbent–adsorbate interaction. Rate-controlling mechanisms and equilibrium data are analyzed using non-linear models. Non-linear method is proposed as the most suitable method for determining the kinetic and equilibrium parameters. The values of adsorption energy(E) obtained from the Dubinin–Radushkevich isotherm,have been found around 0.371 and 0.870 k J·mol~(-1), indicating physical adsorption. Therefore, the pseudo-second order model represents better the kinetic experimental data. The results show that the Langmuir isotherm provides a slightly better fit to the experimental data compared with the Freundlich isotherm, indicating homogeneous distribution of active sites on carbon nanomaterials and monolayer adsorption. The separation factors RLare found in the range of 0–1, suggesting that the adsorption process is suitable for all adsorbents. The mechanisms for hexavalent chromium removal have been proposed as electrostatic interactions and hydrogen bonding.     

天然气分散制氢的技术经济分析(英文)

It is well established that hydrogen has the potential to make a significant contribution to the world energy production.In U.S.,majority of hydrogen production plants implement steam methane reforming(SMR) for centralized hydrogen production.However,there is a wide lack of agreement on the nascent stage of using hydrogen as fuel in vehicles industry because of the difficulty in delivery and storage.By performing technological and economic analysis,this work aims to establish the most feasible hydrogen production pathway for automotives in near future.From the evaluation,processes such as thermal cracking of ammonia and centralized hydrogen production followed by bulk delivery are eliminated while on-site steam reforming of methanol and natural gas are the most technologically feasible options.These two processes are further evaluated by comprehensive economic analysis.The results showed that the steam reforming(SR) of natural gas has a shorter payback time and a higher return on investment(ROI) and internal rate of return(IRR).Sensitivity analysis has also been constructed to evaluate the impact of variables like NG feedstock price,capital of investment and operating capacity factor on the overall production cost of hydrogen.Based on this study,natural gas is prompted to be the most economically and technologically available raw material for short-term hydrogen production before the transition to renewable energy source such as solar energy,biomass and wind power.     

炼油厂氢气网络建模与多目标优化(英文)

The demand of hydrogen in oil refinery is increasing as market forces and environmental legislation, so hydrogen network management is becoming increasingly important in refineries. Most studies focused on single-objective optimization problem for the hydrogen network, but few account for the multi-objective optimization problem. This paper presents a novel approach for modeling and multi-objective optimization for hydrogen network in refineries. An improved multi-objective optimization model is proposed based on the concept of superstructure. The optimization includes minimization of operating cost and minimization of investment cost of equipment. The proposed methodology for the multi-objective optimization of hydrogen network takes into account flow rate constraints, pressure constraints, purity constraints, impurity constraints, payback period, etc. The method considers all the feasible connections and subjects this to mixed-integer nonlinear programming (MINLP). A deterministic optimization method is applied to solve this multi-objective optimization problem. Finally, a real case study is intro-duced to illustrate the applicability of the approach.     

不同处理方式对竹节状碳纳米管吸氢量的影响

Bamboo-like carbon nanotubes were prepared by decomposing C_2H_2 on ferric catalyst. Acid immersion, ball milling and KOH etching were performed before hydrogen adsorption measurement. TEM, HREM, SEM and IR analyses were used to characterize the microstructure. The maximum hydrogen adsorption capacity of the raw sample reached 1.53% (mass) at 300 K under 7 MPa. The unusual structure of carbon nanotubes plays a dominant role for hydrogen adsorption. But some treatments will destroy the structure and decrease hydrogen uptake capacity.     

用于PEMFC的丙烷自热重整制氢操作条件优化研究

Autothermal reforming （ATR） is one of the leading methods for hydrogen production from hydrocarbons. Liquefied petroleum gas, with propane as the main component, is a promising fuel for on-board hydrogen producing systems in fuel cell vehicles and for domestic fuel cell power generation devices. In this article, propane ATR process is studied and operation conditions are optimized with PRO/Ⅱ from SIMSCI for proton exchange membrane fuel cell application. In the ATR system including water gas shift and preferential oxidation, heat in the hot streams and cold streams is controlled to be in balance. Different operation conditions are studied and drawn in contour plots. The region for ATR reforming with the highest efficiency can thus be identified. One operation point was chosen with the following process parameters： feed temperature for the ATR reactor is 425℃, steam to carbon ratio S/C is 2.08, air stoichiometry is 0.256. Thermal efficiency for the integrated system is calculated to be as high as 84.0 % with 38.27 % H2 and 3.2μl·L^-1 CO in the product gas.     

Pd-SiO2复合膜的氢气选择渗透特性

Palladium membranes were prepared on an a-alumina support by metal-organic compound chemical vapor deposition (MOCVD) method from palladium(Ⅲ) acetate precursor. Permeation properties of hydrogen and helium gas were studied as a function of the number of times of deposition of palladium on the peeling off phenomenon of palladium, which is common in electroless plated membrane, was observed. Silica was introduced into the pores to prevent the palladium grain from peeling off. The palladium-silica conjugated membrane does not show the peeling off phenomenon and can withstand the high temperature up to 800℃ which is the upper limit of our apparatus.The separation factor for hydrogen gas over carbon dioxide gas was improved with the increase of number of times of silica coating by sacrificing the H2 permeation and finally increased to four times. The improvement on the separation of hydrogen gas over carbon dioxide for pulladium-silica conjugated membrane was evaluated and a model of permeation pattern (palladium and silica) was proposed. This model suggests that the separation factor for hydrogen over carbon dioxide could be improved by introducing silica layer because the silica layer fills the pores and reduces the gas permeation without sacrificing the hydrogen permeation through the palladium region. These results indicate that the introduction of silica into the palladium grain is a promising means to improve the hydrogen separation performance of palladium based composite membranes.     

INTERNAL PRESSURE AND SOLUBILITY PARAMETER FOR LIQUIDS

Based on a modified van der Waals model, in which the excluded volume is expressed as a linear function of density, the internal pressure and the physical contribution of two - dimensional solubility parameter suggested by Bagley et al. can be expressed as functions of density and a size dependent parameter A. A group contribution method for estimating parameter A and then the solubility parameter has been developed. Average relative deviation of the predicted solubility parameters in comparison will the experimental values for more than sixty liquids including non- polar and polar species as well as those with strong hydrogen bonding is 0.8%. Further correlation with topological indices of molecules makes this method applicable to various isomers of saturated alkanes. Average relative deviation of prediction for 34 saturated alkanes is only 0.6%.     

具有多个不同质量资源网络的设计与目标值确定

This paper presents a new design procedure for the networks with multiple resources, such as hydrogen and water, of different qualities. The minimum consumption targets of the resources and pinch-causing sources can be identified as well during design. The objective of this work is to reduce the consumption of the resources with higher quality due to their higher cost. A few examples are investigated to show the proposed method. For a net-work of single resource with single contaminant, there is often only one pinch point for the resource. On the other hand, for a network of multiple resources with single contaminant, there might be a few different pinch points. Each resource might have its own pinch point, if its amount is sufficient. The contaminant concentration of the pinch-causing source for a resource with lower concentration will be below that of the higher-concentration resource(s).     

NUCLEAR HYDROGEN DEVERLOPMENT AND DEMONSTRATION PROGRAM IN KOREA

The Korea Atomic Energy Research Institute (KAERI) launched a nuclear hydrogen program to develop and demonstrate a hydrogen mass production system by 2019. The key feature of the system is to produce the hydrogen from water using nuclear power. No fossil fuel (energy) will be used and no greenhouse gas will be emitted. The high temperature gas-cooled reactor (HTGR), which has high safety characteristics with competitive economy, is being developed to provide a high temperature heat (about 1000℃) required to produce hydrogen from water. A decision will be made on the reactor specifications after the pre-conceptual design works. Both thermo-chemical process and high temperature electrolysis are to he used for the production of hydrogen from water using nuclear heat. The production of hydrogen from water by nuclear power is one of the most viable options for the mass production of the hydrogen using non-fossil fuels. In 2020s, the nuclear based hydrogen is planned to provide about 20% of total energy consumed in the transportation of Korea. The nuclear hydrogen is expected to make a considerable contribution to the national energy security of Korea.     

The cooperation effect of Ni and Pt in the hydrogenation of acetic acid

The catalytic hydrogenation of carboxylic acid to alcohols is one of the important strategies for the conversion of biomass.Herein,a series of Ni-doped PtSn catalysts were prepared,characterized and studied in the hydrogenation of acetic acid.The Ni dopant has a strong interaction with Pt,which promotes the hydrogen adsorption,providing an activated hydrogen-rich environment for the hydrogenation.Meanwhile,the presence of Ni also improves the Pt dispersion,giving more accessible active sites for hydrogen activation.The cooperation of Pt and Ni significantly promotes the catalytic activity of the hydrogenation of acetic acid to ethanol.As a result,the catalyst with 0.1%Ni exhibits the best reaction activity,and its space time yield is twice as that of the PtSn/SiO2 catalyst.It provides a meaningful instruction on the catalyst design for the carboxylic acid hydrogenation.     

Structural properties of water around uncharged and charged carbon nanotubes

Studying the structural properties of water molecules around the carbon nanotubes is very important in a wide variety of carbon nanotubes applications. We studied the number of hydrogen bonds, oxygen and hydrogen density distributions, and water orientation around carbon nanotubes. The water density distribution for all carbon nanotubes was observed to have the same feature. In water-carbon nanotubes interface, a high-density region of water molecules exists around carbon nanotubes. The results reveal that the water orientation around carbon nanotubes is roughly dependent on carbon nanotubes surface charge. The water molecules in close distances to carbon nanotubes were found to make an HOH plane nearly perpendicular to the water-carbon nanotubes interface for carbon nanotubes with negative surface charge. For uncharged carbon nanotubes and carbon nanotubes with positive surface charge, the HOH plane was in tangential orientation with water-carbon nanotubes interface. There was also a significant reduction in hydrogen bond of water region around carbon nanotubes as compared with hydrogen bond in bulk water. This reduction was very obvious for carbon nanotubes with positive surface charge. In addition, the calculation of dynamic properties of water molecules in water-CNT interface revealed that there is a direct relation between the number of Hbonds and selfdiffusion coefficient of water molecules.     

Hetero-atoms as activation centers for hydrogen absorption in carbon nanotubes

Carbon materials should have specific centers for hydrogen adsorption/absorption. The role of heteroatom substitution in carbon nanotubes as an activator has been identified by Density Functional Theory. The effect of various hetero-atoms like nitrogen, phosphorus, sulphur and boron for hydrogen activation and their geometrical positions has been recognized as the one of the possible reasons for easy hydrogenation. Experimentally, nitrogen and boron containing carbon nanotubes have been synthesized by using template method. The hydrogen absorption capacity of these materials has been evaluated. It is shown that, there is a need to stabilize nitrogen in the carbon nanotube framework for reproducible hydrogen uptake. In the case of boron containing carbon nanotubes, two different chemical environment of boron facilitates hydrogen interaction. They exhibit a maximum of 2 wt.% of hydrogen storage capacity at 80 bar and 300 K. This configuration has a bearing in hydrogen sorption characteristics.     

过渡金属修饰的碳纳米管降低烟气中氢氰酸

分别制备了高产率的修饰铁、钴、镍的碳纳米管,将铁、钴、镍修饰的碳纳米管添加到卷烟嘴棒中可提高烟气中有害成分氢氰酸的吸附效果。实验结果表明：添加了修饰铁、钻、镍的碳纳米管的卷烟嘴棒,可明显选择性降低烟气中有害成分氢氰酸的含量,其中铁修饰碳纳米管降低氢氰酸和焦油的效果最好,随着铁修饰碳纳米管的添加量增加,烟气中氢氰酸和焦油的量减少,烟气中氢氰酸的含量减少16．8％-32％,焦油的含量降低9．8％～26％。     

新型贮氢材料的研究进展

氢能作为资源丰富、绿色环保的清洁能源而被广泛研究,氢的贮存和运输是氢能应用的关键。金属络合氢化物、碳纳米管、沸石具有较高的贮氢容量,成为贮氢材料研究的热点。综述了金属络合氢化物、碳纳米管、沸石等新型贮氢材料的研究进展,讨论了各种贮氢材料的特点与性能,对其实用性和应用前景进行了分析。     

碳纳米管储氢性能的研究进展

介绍了单壁碳纳米管和多壁碳纳米管对氢气的吸附实验和模拟计算研究进展;综述了该领域的最新研究成果;讨论了碳纳米管储氢性能的可行性和应用前景。     

Why boron nitride nanotubes are preferable to carbon nanotubes for hydrogen storage?: An ab initio theoretical study

Using ab initio calculations we investigated the hydrogen storage in single-walled boron nitride nanotubes. We present the nature of hydrogen interaction in selected sites of a (5,5) and (9,9) BN nanotube. Our results show that BN nanotubes are preferable to carbon nanotubes for hydrogen storage applications due to their heteropolar binding nature of their atoms. In addition, by increasing the nanotube's diameter – decreasing its curvature, more efficient binding energies of hydrogen can be achieved.     

GCMC simulation of hydrogen physisorption on carbon nanotubes and nanotube arrays

Properties of hydrogen physisorption in single-walled carbon nanotubes (SWCNTs), multi-walled carbon nanotubes (MWCNTs) and SWCNT arrays are investigated in detail by grand canonical Monte Carlo simulation. The optimization of hydrogen storage capacity at 298 K and 10 MPa as a function of SWCNT diameter, MWCNT inter-tube spacing, and SWCNT array configuration is discussed.     

铌酸钾纳米管的制备及其光催化还原水制氢研究

以铌酸钾颗粒为前驱体,经酸化和剥落处理,在简单、温和的条件下制得铌酸钾纳米管。透射电镜结果表明,产物具有管状形貌,且管形完整、管径分布窄、长径比大。研究了铌酸钾纳米管在紫外光照射下的光催化还原水制氢性能,铌酸钾纳米管的活性明显高于铌酸钾颗粒,负载Pt的铌酸钾纳米管的制氢活性明显提高,在pH=3的10%(体积分数)甲醇水溶液中负载1.5%铂的铌酸钾纳米管的产氢活性(18.8 mmol/g.h)最高,是铌酸钾纳米管负载前(0.385 mmol/(g.h))的48.8倍。     

镍纳米管的制备及电化学储氢性能

本文以多孔氧化铝(AAO)为模板,采用电化学沉积法制备了镍纳米管,通过透射电镜(TEM),能谱仪(EDX),选区电子衍射图(SAED)对镍纳米管的形貌、微观结构及组成进行了表征。并将所制备的镍纳米管制成微电极,用循环伏安法测试了其电化学储氢性能。结果表明,所制备的镍纳米管管径约20nm,管长可达微米级,且相比于镍粉,镍纳米管的电化学储氢性能更好。     

Intrinsic linear scaling of hydrogen storage capacity of carbon nanotubes with the specific surface area

The linear scaling of the gravimetric hydrogen storage capacity of single- and multi-walled carbon nanotubes (SWNTs and MWNTs) with the specific surface area is investigated at ambient temperature (298 K) and technically relevant pressures (0.9–1.6 MPa). All samples are found to adsorb hydrogen reversibly and their adsorption exhibits type-II BET isotherms according to the IUPAC classification. While there is strong sample-dependency on their pressure–composition isotherms, all of them follow the Henry's Law in the pressure range under consideration. A comparison of the observed slope of specific surface area versus gravimetric storage capacity with that of a theoretically predicted one using a hypothetical condensation model and that of chemically modified carbon nanotubes revealed that the hydrogen storage capacity depends on the accessibility of internal surfaces of nanostructured carbon. The linear scaling of hydrogen storage capacity with the respective specific surface area suggests that the hydrogen adsorption in carbon nanotubes depends on the specific surface area and is irrespective of the type of the nanotubes that is used.