高比表面积活性炭吸附存储天然气性能研究

天然气中少量乙烷和丙烷的存在会直接影响活性炭对天然气的吸附存储容量。为此,体积法测定了高比表面积活性炭对甲烷、乙烷和丙烷的吸附等温线,吸附温度分别为283,293,303和313K;采用Langmuir-Freundlich(LF)方程拟合吸附等温线,得到各气体的方程参数,进而采用LRC关联式预测多组分吸附平衡数据,并计算活性炭对模拟天然气的存储能力。结果表明:活性炭对3种气体的吸附等温线都属于I型等温线,采用L-F方程可以很好地描述各气体的吸附等温线;高比表面积活性炭对模拟天然气的存储量随吸附温度的升高而显著降低,在吸附存储压力为3.5 MPa,吸附温度从283 K上升到313 K,相应的存储量(体积比)由139降低为103;与纯甲烷的吸附存储相比,模拟天然气的吸附储量(体积比)提高约20。     

金属有机骨架材料Cu-BTC的成型及储甲烷性能研究

为探索Cu-BTC材料在天然气吸附存储中的应用,采用滚动成型法对Cu-BTC粉末进行成型,考察了成型前后样品的晶体结构、孔结构和甲烷吸附量,并与活性炭小球进行对比。结果表明,虽然成型后Cu-BTC小球损失了部分比表面积、孔容和23%的甲烷吸附量,但比表面积和总孔容仍高达1 259 m2/g和0. 56 cm~3/g。在298 K、3. 5 MPa下,Cu-BTC小球的甲烷质量吸附量为161 cm~3/g,高于活性炭小球的114 cm~3/g,体积吸附量为110 cm~3/cm~3,可交付使用的甲烷量为145 cm~3/g。     

炭化对活性炭孔结构及甲烷吸附性能的影响

在惰性气氛下对以石油焦为原料 ,以 KOH为活化剂制得的超级活性炭进行了二次炭化处理 ,并考察了处理前后超级活性炭的孔结构变化及不同压力下该活性炭对甲烷的吸附行为 .结果发现 :活性炭经 1 2 0 0℃下二次炭化处理后其 BET比表面积及孔容有所下降 ,孔径分布变窄 ;其对甲烷的质量吸附量下降 ,对甲烷的体积吸附量在较低压力下 ( <3MPa)稍有增加 ,而在较高压力下 ( >3MPa)时明显减少     

甲烷在成型前后活性炭上吸附的初步试验

通过对比试验,分析成型对活性炭储存甲烷特性的影响。首先,应用丙烯酸甲酯乳胶黏合剂对活性炭SAC-02成型,在温度区间268.15～338.15 K、压力范围0～15 MPa测试甲烷的吸附等温线;通过确定吸附量和等量吸附热,比较甲烷在成型前后活性炭上的吸附平衡。其次,测试储罐吸附床中心在室温、4个压力（6.5 MPa、5.5 MPa、4.5 MPa和3.5 MPa）下快速充放气过程的温度变化,分析成型对吸附过程热效应的影响。结果表明,成型活性炭的密度增大、比表面积减小、单位质量吸附剂上的甲烷吸附量减小;甲烷在成型前后活性炭上的等量吸附热均处于13～20.5kJ·mol^-1;成型活性炭吸附床中心温度在充放气过程中的变化幅度和变化速率均增大。比较试验结果时发现,选用黏合剂成型须综合考虑其对吸附床热导率、传质阻力及吸附剂微观结构的影响。     

甲烷、乙烷、丙烷和丁烷在中孔活性炭上的吸附平衡

以活性炭AC1为吸附剂,在体积法实验装置上分别测定了其对甲烷、乙烷、丙烷和丁烷4种气体的吸附等温线,吸附温度分别为283、293、303和313 K。利用77 K吸附氮气数据表征AC1,得到其比表面积为956 m²·g^-1,孔体积为1.36 mL·g^-1,孔径分布在1~5 nm,中孔的比例达到了61%。AC1对4种气体的吸附等温线均为I型等温线,分别采用Langmuir方程和Langmuir-Freundlich方程(简称L-F方程)对吸附平衡数据进行拟合,结果表明,L-F方程具有更好的拟合效果,为后序的多组分吸附平衡研究提供了基础数据。AC1对乙烷/丙烷的吸附平衡选择性系数在1.7~2.5,吸附选择性随吸附压力的增大而减小,吸附温度对吸附选择性无明显影响。     

氢在YK-1活性炭上的吸附平衡

运用容积法在温度区间113—293 K、压力范围0—12.5 MPa测定氢在椰壳活性炭YK-1上的吸附等温线,由等量吸附线标绘和低覆盖率区域等温线的亨利定律标绘确定等量吸附热和极限吸附热,引入格子理论Ono-Kondo方程对吸附等温线进行模型分析。结果表明,氢在YK-1活性炭上等量吸附热随吸附量的变化平缓,等量吸附热的平均值和极限值分别为4.64 kJ/mol和5.37 kJ/mol;基于Ono-Kondo模型的方程能较好地预测吸附等温线,氢在吸附空间的最大吸附容量随温度变化,其值比液氢在相同吸附空间的吸附容量小。须改善材料结构和降低储存系统温度才能提高活性炭的储氢性能。     

活性炭去除氦气中CH4和N2杂质的性能研究

旨在有效去除氦气中存在的甲烷和氮气杂质组分,通过对活性炭77 K下N2吸附脱附等温线测试,比较不同活性炭的结构性能,选择性能较优的活性炭AC-1吸附材料,测试了吸附剂在不同温度下对甲烷和氮气的吸附性能.采用氢氧化钠溶液对活性炭AC-1进行了表面改性,研究了改性活性炭对甲烷和氮气的吸附性能.结果表明:不同温度时活性炭AC-1的吸附量有明显的差异;活性炭AC-1经改性后,其比表面积和孔容均有所增大,孔径分布得到优化,对甲烷与氮气的吸附量明显提高.     

甲烷在石墨烯和活性炭上的吸附

以研制新型吸附式天然气(ANG)吸附剂为目的,比较了甲烷在石墨烯和活性炭上的吸附平衡。首先,在温度区间273~293 K、压力范围0~8 MPa,测试甲烷在比表面积分别为300和2074 m²·g^-1石墨烯和活性炭上的吸附平衡数据。其次,应用格子理论导出的通用吸附等温方程,通过吸附平衡态能量分析及10-4-3相互作用势函数求解,确定甲烷分子在石墨烯平面和活性炭上的最大面密度、受到的壁面吸附作用势及其在吸附层内的作用能。结果表明,在相同温度下,吸附甲烷分子在石墨烯上吸附层内的相互作用能较其在活性炭上的大,甲烷分子在石墨烯平面上的集聚更为密集。提高石墨烯的比表面积将有效提高甲烷在其上的吸附容量。     

吸附法脱除天然气中少量丙烷和丁烷的研究

天然气中的少量丙烷和丁烷对活性炭的吸附存储能力有很大的影响,而且被其污染的活性炭常温下难以再生,因而有必要将其脱除后再充入吸附储罐。通过实验比较了几种活性炭和硅胶吸附剂脱除少量丙烷和丁烷时的处理能力及其再生性能。结果表明,活性炭具有较大的处理能力,但常温下不易再生;硅胶的处理能力不及活性炭,但常温下易于再生;微孔硅胶的综合性能好于中孔硅胶和大孔硅胶,并且较高的操作压力有利于提高其处理能力。     

文摘

20 0 2 0 0 1不加粘结剂制备活性炭球及其甲烷吸附性 [刊 ,日 ]/ＫａｚｕｈｉｒｏＫａｎａｚａｗａ ,等 / /ＴＡＮＳＯ ,2 0 0 1,196:2～ 8用纤维素微晶不加粘结剂制备活性炭球。通过加压法将纤维素微晶进行热处理后 ,活性炭球形成圆柱型。活性炭球的体积密度随压缩原材料压力的增大而增大 ,而总孔容则减小。在相同烧结条件下 ,这种活性炭球的体积密度是活性炭粉的 3 .5倍。在 0 .86ＭＰａ、3 0℃的条件下 ,甲烷的吸附量为 82ｍｇ/ ｇ。其对甲烷气贮存的总效率是 :1ｃｍ3的活性炭球能吸附 2 80ｃｍ3的甲烷气体 ,比在 13 .0ＭＰａ下压缩的甲…     

Computer Simulation Studies of the Storage of Methane in Microporous Carbons

Abstract

Simulated isotherm and energies of adsorption are reported for methane in a number of model porous solids at 300 K. The solids are made up of graphite basal planes arranged to make either parallel-walled slit pores or pores of triangular cross section. The limiting low coverage behavior was characterized by direct calculations of Henry's law constants and average gas–solid energies for the pore systems considered. The isotherms were evaluated for pressures ranging up to 50 atm by utilizing the Widom particle insertion algorithm. The simulations and calculations were carried out for a range of pore sizes and, in the case of the triangular cross-section, for a range of apex angles in the isosceles triangles considered. Methane storage capacities of model solids were evaluated for values of the porosity based on two different choices of pore wall thickness. Although it is shown that adsorption is not limited to monolayer formation under these conditions, capacities obtained are not sufficiently large to meet or exceed the commonly stated requirements for use in automotive fuel storage.     

巨正则系综蒙特卡罗法研究活性炭吸附

近年来,巨正则系综蒙特卡罗计算机模拟在研究炭素材料,特别是活性炭的吸附特性以及炭材料的结构表征和新材料设计方面得到应用。对巨正则系综蒙特卡罗法,目前在活性炭吸附特征研究中所普遍采用的活性炭微孔模型和分子与原子之间相互作用的模型进行较为详细的介绍。同时还给出了作者有关活性炭吸附氮和甲烷的基本特性的研究结果。     

ADSORPTION OF POLAR AND NONPOLAR FLUIDS IN FINITE-LENGTH CARBON SLIT PORE: A MONTE CARLO SIMULATION STUDY

A grand canonical Monte Carlo simulation (GCMC) method is used to study adsorption in a carbon slit pore of finite length. Methane is used as a model for the nonpolar molecule, while the polar molecule is modeled as water. The behavior of a nonpolar molecule in the finite-length pore is investigated and compared with that obtained for a commonly used infinite slit pore. The adsorption of methane in the finite pore is significantly different from that in the infinite pore, both the capacity and the hysteresis loop. In addition to nonpolar molecules, the adsorption of water in finite pores has also been studied. The adsorption of water on activated carbon is very complex, and it strongly depends on the concentration as well as the position of the functional groups in the pore. For both cases of nonpolar and polar fluids, effects of pore size on the behavior of adsorption isotherms are also investigated.     

Increased H2 gravimetric storage capacity in truncated carbon slit pores modeled by Grand Canonical Monte Carlo

Hydrogen adsorption in slit shaped pores built up from truncated graphene fragments has been simulated using Grand Canonical Monte Carlo technique and the influence of pore wall edges on hydrogen storage by physisorption has been analyzed. We show that due to the additional gas adsorption at the pore edges the adsorbed gravimetric amount significantly increases (by a factor of two) with respect to models of pores with infinite graphene walls. The contribution of the edges’ adsorption to the total hydrogen uptake is independent of the pore wall shape but it depends on its surface. We also show that the maximum of the excess adsorption shifts towards higher pressures when the edge contribution increases. This information can be used to characterize experimentally structures of porous adsorbents and complement pore size distribution analysis usually performed with gases others than hydrogen. We suggest that porous carbons built from polycyclic hydrocarbons can achieve storage performances required for practical applications.     

Experimental measurements and computer simulation of methane adsorption on activated carbon fibers

Three activated carbon fibers (ACFs) with different BET specific surface areas (SSAs) were prepared. Experimental characterization and methane adsorption on the ACFs were measured by the intelligent gravimetric analyzer (IGA-003, Hiden) at 258 and 298 K. Correlations proposed between the methane adsorption capacity and SSA indicate that the SSA plays an important role on storage amount at a given temperature. A detailed experimental investigation was focused on the sample ACF3 of the highest SSF of 1511 m²/g at five temperatures, from 258 to 298 K. The temperature dependence for methane adsorption amount on ACF3 at 1.8 MPa is proposed. It shows that temperature is vital to methane storage capacity for ACF3, and adsorption storage at the temperatures below 280 K is recommended for favorite uptakes. To model ACF3, the pores are described as slit-shaped with a pore size distribution that was determined by molecular simulation and the statistics integral equation. Predictions of methane adsorption, carried out at 258 and 298 K and high pressures by molecular simulation, indicate that our sample ACF3 can reach the uptake of 14.99 wt% at 4.0 MPa and 298 K, which is comparable with the best result in the literature.     

Computer Simulations of Adsorption Characteristics of Carbon Dioxide in Slit Graphite Pores

An extensive grand canonical Monte Carlo simulation has been performed to study the adsorption behavior and the orientational structure of CO₂ confined in slit graphite pores, with a wide pore width range of 0.61 to 3.04 nm and pressures up to 3.41 MPa. The simulation results show that the minimum pore width for the adsorption of CO₂ is 0.57 nm, the maximum adsorption occurs at pore width H = 2.43 nm and pressure P = 2.56—3.41 MPa, and capillary condensation takes place only for H>2 nm. It is also found that the wall‐perpendicular orientation becomes preferential with the increase of pressure.     

分子模拟二氧化碳在狭缝炭微孔中的吸附

Both the grand canonical Monte Carlo and molecular dynamics simulation methods are used to investigate the adsorption and diffusion of carbon dioxide confined in a 1.86 nm slit carbon pore at 4 temperatures from subcritical (120 K) to supercritical (313 K) conditions. Layering transition, capillary condensation and adsorption hysteresis are found at 120 K. The microstructure of carbon dioxide fluid in the slit carbon pore is analyzed. The diffusion coefficients of carbon dioxide parallel to the slit wall are significantly larger than those normal to the slit wall.     

Adsorption of methane on corn cobs based activated carbon

Activated carbon was prepared with corn cobs and potassium hydroxide under optimized variables. Due to their botanical origin, corn cobs can be an excellent starting material to produce nanoporous carbon for natural gas storage. Samples with different BET surface areas were chosen to perform methane adsorption experiments. Methane adsorptions on corn cob based activated carbon were studied at four different pressures (500, 1000, 1500 and 2000 psi) and two different temperatures (298 K and 323 K) in a volumetric adsorption apparatus. The volume based methane adsorption results specified an ‘increase in the methane adsorption capacities of activated carbon with increasing surface area and showed that adsorption capacity of methane depends on pressure and temperature. The highest methane storage capacity was found to be 160 (v/v) at 298 K and 1500 psi. The applications include use in the transportation of natural gas, natural gas based vehicles, and adsorption of gas from landfills.     

An improved theoretical procedure for the pore-size analysis of activated carbon by gas adsorption

Amorphous carbon materials play a vital role in adsorbed natural gas (ANG) storage.One of the key issues in themore prevalent use of ANG is the limited adsorption capacity,which is primarily determined by the porosity and surface characteristics of porous materials.To identify suitable adsorbents,we need a reliable computational tool for pore characterization and,subsequently,quantitative prediction of the adsorption behavior.Within the framework of adsorption integral equation (AIE),the pore-size distribution (PSD) is sensitive to the adopted theoretical models and numerical algorithms through isotherm fitting.In recent years,the classical density functional theory (DFT) has emerged as a common choice to describe adsorption isotherms for AIE kernel construction.However,rarely considered is the accuracy of the mean-field approximation (MFA) commonly used in commercial software.In this work,we calibrate four versions of DFT methods with grand canonical Monte Carlo (GCMC) molecular simulation for the adsorption of CH4 and CO2 gas in slit pores at 298 K with the pore width varying from 0.65 to 5.00 nm and pressure from 0.2 to 2.0 MPa.It is found that a weighted-density approximation proposed by Yu (WDA-Yu) is more accurate than MFA and other non-local DFT methods.In combination with the trapezoid discretization of AIE,the WDA-Yu method provides a faithful representation of experimental data,with the accuracy and stability improved by 90.0％ and 91.2％,respectively,in comparison with the corresponding results from MFA for fitting CO2 isotherms.In particular,those distributions in the feature pore width range (FPWR)are proved more representative for the pore-size analysis.The new theoretical procedure for pore characterization has also been tested with the methane adsorption capacity in seven activated carbon samples.