超临界甲烷在活性炭上的吸附平衡分析

为分析由吸附平衡时的热力参数确定吸附量、吸附模型和等量吸附热精度的影响因素,选择在温度268.15~338.15 K和压力0~13.5 MPa测试的甲烷在Ajax活性炭上的吸附平衡数据,通过引入甲烷分子可进入活性炭吸附空间内的容积和可以不考虑甲烷在孔内吸附的临界孔宽的概念,依据甲烷在吸附平衡前后的总量守恒,确定甲烷在吸附池内的总量、绝对吸附量和过剩吸附量三者之间的关系式。结果表明,在引入吸附质分子可进入吸附空间内的容积和临界孔宽后,经由活性炭的孔径分布(PSD),可以准确计算甲烷在活性炭上的过剩吸附量;应用实验数据非线性回归Toth方程参数后,可由Gibbs关于吸附的定义确定甲烷在活性炭上的绝对吸附量。比较结果时发现,由于未考虑本体相中甲烷分子对吸附甲烷分子的影响,采用过剩吸附量的等量吸附线标绘确定的等量吸附热数值偏高,工程应用时应由绝对吸附量来确定等量吸附热。     

超临界甲烷在活性炭与典型金属有机框架材料上的吸附平衡

针对吸附天然气（ANG）应用的吸附剂研发,试制了SAC-02活性炭、HKUST-1和MIL-101(Cr),通过微观形貌观察、氮气物理吸附和293.15–313.15 K、0–4 MPa条件下甲烷吸附等温线测定,采用Toth、D-A和Ono-Kondo等方程对实验数据进行关联预测比较,由等量吸附热和吸附相密度分析这些吸附剂样品对甲烷的吸附性能。结果表明,在测试范围内,Toth方程预测的吸附平衡数据精度最高,可用于ANG系统的吸附平衡分析;甲烷在MIL-101(Cr)上的平均等量吸附热最大,吸附相密度比液态甲烷的密度小但随压力的增高而增大,比活性炭和HKUST-1更适合于甲烷吸附。     

甲烷在MIL-101上的吸附平衡分析及充放气特性

为研制吸附储存天然气(ANG)用的金属有机框架物(MOFs),选择MIL-101(Cr)试样进行甲烷的吸附平衡与充放气实验。试样由溶剂热法合成,经测试77.15 K氮吸附数据作表征结构后,在温度293-313 K、压力0-100 k Pa和0-7 MPa条件下测试甲烷吸附平衡数据,运用亨利定律标绘和Toth方程确定甲烷在试样上的极限吸附热和绝对吸附量,比较了ClausiusClapeyron(C-C)方程和Toth势函数计算的等量吸附热。最后,在工程应用对应的流率10-30 L/min,对装填940 g试样、容积为3.2 L的适型储罐吸附床进行甲烷充放气实验。结果表明,甲烷在试样上的平均极限吸附热为23.89 k J/mol,测试范围内Toth方程预测的平均相对误差为1.06%,由C-C方程和Toth势函数确定的平均等量吸附热分别为15.51和13.56 k J/mol;在有效充放气时间内,储罐在10和30 L/min流率时的总充/放气量分别为347 L/338 L和341 L/318 L,放气率为98.3%和94.1%。工程应用应选用C-C方程确定的等量吸附热,并采取慢充/放以增大充/放气量和提高吸附床脱气率。     

甲烷在石墨化热解碳黑和活性炭上的吸附

为研究影响碳基吸附剂吸附超临界温度气体的主要因素,选择石墨化热解碳黑BP280和Ajax活性炭,分析超临界温度高压甲烷在其上的吸附平衡。应用容积法,在压力0~20.5 MPa、温度253 K~313 K测定甲烷的吸附平衡数据,并由等量吸附线标绘和亨利定律常数确定等量吸附热。引入通用吸附等温方程,再由方程的Langmuir标绘确定最大吸附容量,进而通过方程的线性化计算吸附平衡态中甲烷分子的作用能。结果表明,甲烷在两种吸附剂上的最大吸附容量均随温度而变化,并都小于液态甲烷的密度;甲烷在碳黑和活性炭上的等量吸附热分别为11.9 kJ/mol~12.5 kJ/mol和17.5 kJ/mol~22.5 kJ/mol,体现了两种吸附剂不同的表面能量分布;甲烷分子间作用能随吸附量的变化特点反映了超临界温度甲烷以类似于压缩气体状态聚集的特点和吸附剂结构上的差异。碳基吸附剂的比表面积和微孔容积是影响其储存甲烷容量的重要因素。     

甲烷在层状石墨烯和活性炭上的吸附平衡

以吸附式天然气（ANG）吸附剂的工程应用为目的,以0-10 MPa、283.15-303.15 K甲烷在层状石墨烯（GS（3D）,比表面积2062 m²/g）和活性炭SAC-01（比表面积1507 m²/g）上的吸附平衡数据作分析。首先,在77.15 K下由氮气吸附表征样品的孔径大小及分布（PSD）和比表面积。其次,选择极低压力下的吸附平衡数据标定亨利定律常数,确定甲烷在两吸附剂上的极限吸附热,并由维里方程和10-4-3势能函数计算甲烷与两吸附剂壁面之间的相互作用势。最后,依据测试的甲烷在吸附剂上的高压吸附平衡数据,比较了Langmuir系列方程的关联数据后的拟合精度,并由绝对吸附量计算了甲烷的等量吸附热。结果表明,甲烷在GS（3D）和活性炭SAC-01上的平均极限吸附热为23.07、20.67 kJ/mol;283.15 K下甲烷分子与GS（3D）和活性炭SAC-01之间的交互作用势ε_sf/k为67.19、64.23 K,与洛伦混合法则的计算值64.60 K相近;Toth方程关联甲烷在活性炭SAC-01和GS（3D）上吸附平衡数据的拟合累计相对误差为0.25%和2.29%;甲烷在活性炭SAC-01和GS（3D）上的等量吸附热平均值为16.8和18.3 kJ/mol。相对于活性炭SAC-01,比表面积和微孔容积均较高的GS（3D）对甲烷的吸附更具有优势。     

吸附等温方程参数估算方法的分析

采用定容容量法,在温度6~60℃、平衡压力达106Pa的条件下,测得N2和O2在5A分子筛上系统的吸附相平衡数据。通过Langmuir和Toth等温方程关联这些相平衡数据,结果表明:线性化拟合的方法不可靠,其中用1/q~1/P形式线性化Langmuir方程,会得到误差很大的结果;用非线性法在各温度下单独拟合的等温方程和实验结果吻合很好,但是参数不符合其物理意义,进一步处理则误差较大。应当用非线性最小二乘法将所有温度下的相平衡数据一起拟合吸附等温方程。Langmuir和Toth方程都能用于描述体系的平衡吸附量随温度和压力的变化关系,而Toth方程的误差更小。     

Gibbs系综Monte Carlo模拟甲烷的吸附平衡

在263、298和313 K下,对甲烷在1.91 nm的活性炭孔中的吸附平衡进行了Gibbs系综Monte Carlo(GEMC)模拟的研究.改进了GEMC方法,使之可用于模拟指定压力下的吸附平衡.通过改进的GEMC模拟,得到了在1.91 nm的活性炭中甲烷在263、298和313 K时的吸附等温线;发现263 K时的超额吸附量要大于298 K、313 K时的超额吸附量; 且不同温度下的超额吸附等温线均存在一最大超额吸附.263 K时,超额吸附量在5.0 MPa时出现最大值;而298 K、313 K时超额吸附量则在7.0 MPa时出现最大值.此工作为不同温度下天然气吸附存贮过程的开发及设计提供了依据.     

超临界条件下甲烷在纳米活性炭表面的吸附机理

在273-373 K、0-10 MPa范围内测量了甲烷在纳米活性炭表面的吸附等温线和等量吸附热. 结果发现, 在实验涉及的温度范围内, 吸附平衡特性在低压下能够很好地遵循Dubinin-Astakhov (DA)微孔填充模型, 但是当压力超过特定范围时, 吸附等温线及等量吸附热测量数据都与DA模型计算结果发生了偏离, 吸附行为更接近单层定位吸附.文中参照Cerofolini对亚单层吸附提出的Freundlich-Dubinin-Radushkevich (FDR)混合模型, 对纳米活性炭在较高压力条件下的吸附使用通用Freundlich (GF)模型进行了修正, 从而提出了一种分段模型GFDA. 根据GFDA模型对甲烷在广泛的压力范围内在纳米活性炭表面的吸附机理进行了完整的解释, 并对纳米活性炭表面的能量非均匀性进行了分析.     

应用超临界温度氢吸附数据表征活性炭结构

为准确研究氢在活性炭上的吸附平衡,本文对比分析了由氮和氢在活性炭上吸附数据确定的活性炭的孔径分布(PSD)。首先,应用容积法,在0～12.5MPa压力范围、3个温度(113.15K、193.15K、273.15K)下测定氢在K05活性炭上的吸附平衡数据,并由引入系统内氢的质量衡算确定吸附池内氢的总量。其次,以77K氮吸附数据确定的PSD为初值、以吸附池内氢的总量为基准,通过优化非局域密度泛函理论(NDFT)计算值确定活性炭的PSD,进而比较表征介质、温度及平衡压力对PSD的影响。研究表明,应用氢吸附数据表征孔宽小于0.8nm的超细微孔的微分容积较大;平衡压力较高时,由不同温度氢吸附数据确定的超细微孔的PSD相近;孔宽大于1.2nm时,不同温度氢吸附数据确定的PSD间有明显偏差。须应用超临界温度高压氢或氢在亚临界温度区域的吸附数据,同时结合77K氮吸附等温线来表征吸附剂在超细微孔和微孔范围的PSD。     

沥青基球形活性炭对葡萄糖分子的吸附行为研究

考察了沥青基球形活性炭(PSAC)对葡萄糖分子的吸附行为,以探讨其治疗糖尿病的可能性.在不同吸附时间、不同活性炭用量及不同浓度等条件下,测定沥青基球形活性炭对葡萄糖分子的吸附量,根据Langmuir和Freundlich等温线方程对吸附等温线数据进行拟合,检验实验数据与方程的吻合度,确定方程参数.同时,研究了葡萄糖和α-淀粉酶在沥青基球形活性炭上的竞争吸附行为.结果表明,所选用沥青基球形活性炭对葡萄糖分子的吸附在5h内达到吸附平衡;葡萄糖的初始浓度为3g/时,平衡吸附量为71mg/g;平衡吸附量受葡萄糖分子空间构象的影响,且随葡萄糖浓度的升高而增加,吸附等温线数据与Langmuir方程吻合,说明该吸附为单分子层吸附.在葡萄糖分子和α-淀粉酶的共存环境下,沥青基球形活性炭对葡萄糖有较好的吸附选择性.     

Adsorption isotherms of CO2, CO,N2, CH4, Ar and H2 on activated carbon and zeolite LiX up to 1.0 MPa

The adsorption isotherms of CO₂, CO, N₂, CH₄, Ar, and H₂ on activated carbon and zeolite LiX were measured using a volumetric method. Equilibrium experiments were conducted at 293, 308, and 323 K and pressures up to 1.0 MPa. The adsorption isotherm and heat of adsorption were analyzed for two pressure regions of experimental data: pressures up to 0.1 MPa and up to 1.0 MPa. Each experimental isotherm was correlated by the Langmuir, Sips, Toth and temperature dependent Sips isotherm models, and the deviation of each model was evaluated. The Sips and Toth models showed smaller deviation from the experimental data of adsorbents than the Langmuir model. Isosteric heats of adsorption were calculated by the temperature dependent Sips model and are presented along with surface loading. From deviation analysis, it is recommended that the isotherm in the proper pressure range be used to appropriately design adsorptive processes.     

Adsorption equilibrium of binary methane/ethane mixtures in BPL activated carbon: isotherms and calorimetric heats of adsorption

The adsorption of pure methane and ethane in BPL activated carbon has been measured at temperatures between 264 and 373 K and at pressures up to 3.3 MPa with a bench-scale high-pressure open-flow apparatus. The same apparatus was used to measure the adsorption of binary methane/ethane mixtures in BPL at 301.4 K and at pressures up to 2.6 MPa. Thermodynamic consistency tests demonstrate that the data are thermodynamically consistent. In contrast to two sets of data previously published, we found that the adsorption of binary methane/ethane in BPL behaves ideally (in the sense of obeying ideal adsorbed solution theory, IAST) throughout the pressure and gas-phase composition range studied. A Tian-Calvet type microcalorimeter was used to measure low-pressure isotherms, the isosteric heats of adsorption of pure methane and ethane in BPL activated carbon, and the individual heats of adsorption in binary mixtures, at 297 K and at pressures up to 100 kPa. The mixture heats of adsorption were consistent with IAST.     

Multicomponent adsorption on activated carbons under supercritical conditions

Adsorption of binary mixtures onto activated carbon Norit R1 for the system nitrogen-methane-carbon dioxide was investigated over the pressure range up to 15 MPa. A new model is proposed to describe the experimental data. It is based on the assumption that an activated carbon can be characterized by the distribution function of elements of adsorption volume (EAV) over the solid-fluid potential. This function may be evaluated from pure component isotherms using the equality of the chemical potentials in the adsorbed phase and in the bulk phase for each EAV. In the case of mixture adsorption a simple combining rule is proposed, which allows determining the adsorbed phase density and its composition in the EAV at given pressure and compositions of the bulk phase. The adsorbed concentration of each adsorbate is the integral of its density over the set of EAV. The comparison with experimental data on binary mixtures has shown that the approach works reasonably well. In the case of high-pressure binary mixture adsorption, when only total amount adsorbed was measured, the proposed model allows reliably determining partial amounts of the adsorbed components.     

A fully consistent experimental and molecular simulation study of methane adsorption on activated carbon

The adsorption of pure methane in activated carbon Ecosorb was studied by combining grand canonical ensemble Monte Carlo molecular simulations and an experimental approach based on a gravimetric device. Experimental and calculated adsorption isotherms of methane were determined in supercritical conditions at 303.15 and 353.15 K and pressures up to 10 MPa. The comparison between both experimental and estimated data proves the consistency of the methodology used in this work, starting from the characterization of the porous media in terms of pore size distribution, the determination of the experimental adsorption isotherms, and the final estimation of computational results through estimated isotherms determination. Moreover, additional differential enthalpy of adsorption calculations were compared with experimental values obtained by means of a manometric/calorimetric technique. The good agreement shows the strength and the originality of this paper by combining experimental and computational homemade results allowing a complete characterization of the activated carbon substrate and its methane storage capacity.     

Adsorption of Pentafluorophenol onto Powdered,Granular, and Cloth Activated Carbons

In the present study, the adsorption of pentafluorophenol from aqueous solution onto granular activated carbon, powdered activated carbon, and activated carbon cloth has been investigated from the equilibrium and kinetic points of view. To the best of our knowledge, the removal of pentafluorophenol from aqueous solution onto activated carbon have not been reported in the literature. The experimental equilibrium data, suitably fitted by the Toth, Langmuir-Freundlich, and Redlich-Peterson isotherms, have shown that the cloth and powdered carbons exhibit the highest adsorption capacity. For all the investigated samples, the experimental kinetic data have been satisfactorily interpreted by a pseudo-second-order model. From the fitting results it has been observed that the highest rate constant and initial rate of adsorption is shown by powdered activated carbon.     

Theory of volume filling of micropores applied to the description of methane adsorption on the microporous carbon adsorbent AUK

Methane adsorption on the microporous carbon adsorbent AUK was calculated on the basis of Dubinin’s theory of volume filling of micropores in the temperature range 177.7—393 K and at pressures from 1 Pa to 6 MPa. The calculated isotherms of absolute adsorption were compared with the isotherms of methane obtained experimentally. Good agreement between the calculated and experimentally measured amounts adsorbed is observed in the area of applicability of the theory at micropore ranging in coverage θ from 0.25 to 0.95. The adsorption isosters were calculated for the same pressure and temperature ranges. The adsorption isosters satisfactorily represent the temperature dependence of the amount of methane adsorbed obtained experimentally. The calculations gave for the thermal coefficient of limiting adsorption a value of 6h_calc = 1.64• 10^-3 K^-1., which exceeds the experimental value by ∼15%.