BPL Carbon Research Articles

Single-Component Adsorption Equilibria of CO2, CH4, Water, and Acetone on Tapered Porous Carbon Molecular Sieves.

Engineered carbon molecular sieves (CMSs) with tapered pores, high surface area, and high total pore volume were investigated for their CO2, CH4, water, and acetone adsorption properties at 288.15, 298.15, 308.15 K, and pressures of <1 bar. The results were compared with BPL carbon. The samples exhibited higher adsorption capacity for CO2 compared to BPL carbon, with Carboxen 1005 being the highest due to the presence of ultramicropores (pores smaller than 0.8 nm). Similar observations were made for CH4 except at 288.15 K. Although the CMSs exhibited higher hydrophobicity than BPL carbon, the latter had the highest acetone uptake for all investigated temperatures due to its higher oxygen content, which facilitates stronger interactions with polar VOC molecules. Heats of adsorption were calculated using the Clausius-Clapeyron equation after fitting the isotherms with the dual-site Langmuir-Freundlich model, and results largely corroborated the order of adsorption capacities of CO2, CH4, and water on the carbon materials.

Electrothermal regeneration of BPL activated carbon: possibilities for improvement of process efficiency

In this study, possibilities of increasing the efficiency of electrothermal regeneration of the granular BPL carbon were evaluated. The adsorbent was used to purification of propan-2-ol (IPA)-laden air streams with specified concentrations ranging from 2 to 11 g/m3. The experiments were carried out in the fixed beds containing either a single layer of BPL 4 × 6 carbon or a double layer of BPL 4 × 6 and BPL 6 × 16 carbons (volume ratio 9:1). The adsorbent bed was placed between two pyramid-shaped electrodes and was regenerated using direct resistance heating method. The regeneration measurements were carried out in the following parameter range: voltage 14–19 V, temperature set point 403 K, and nitrogen flow rate 0.06 m3/h. Electrical resistance of the double-layer bed was lower than the single layer due to the larger contact area between the fine BPL carbon particles and the upper electrode. This caused an increase in desorption degree by ca. 4% and a decrease in total energy consumption by 10%. The use of thermal insulation of the double-layer bed resulted in increasing the process energy efficiency. The regeneration was more energy efficient with a higher initial IPA content in the regenerated bed.

Effect of adsorbent heterogeneity on performance of a PSA process for bulk gas separation: a parametric simulation

The effect of adsorbent heterogeneity on the performance of an adiabatic pressure swing adsorption (PSA) process for separation of bulk C2H4 from an inert gas (helium) using the BPL carbon as the adsorbent was numerically estimated employing a detailed mathematical model for the process. The heterogeneous Toth model was used to describe the equilibrium adsorption isotherms for C2H4 and a linear driving force model was used to describe the adsorbate mass transfer rate in the simulation. The variations in the isosteric heat of adsorption of C2H4 with adsorbate loading was included in the simulation. The study indicates that adsorbent heterogeneity negatively affects the key process performance variables by increasing the bed size factor and reducing the helium recovery. Actual performance data for a PSA process using a bench or pilot scale unit is required to reliably estimate the complexity introduced by adsorbent heterogeneity.

Dimethyl Methylphosphonate Adsorption Capacities and Desorption Energies on Ordered Mesoporous Carbons.

In this study, we determine effective adsorption capacities and desorption energies for DMMP with highly ordered mesoporous carbons (OMCs), 1D cylindrical FDU-15, 3D hexagonal CMK-3, 3D bicontinuous CMK-8, and as a reference, microporous BPL carbon. After exposure to DMMP vapor at room temperature for approximately 70 and 800 h, the adsorption capacity of DMMP for each OMC was generally proportional to the total surface area and pore volume, respectively. Desorption energies of DMMP were determined using a model-free isoconversional method applied to thermogravimetric analysis (TGA) data. Our experiments determined that DMMP saturated carbon will desorb any weakly bound DMMP from pores >2.4 nm at room temperature, and no DMMP will adsorb into pores smaller than 0.5 nm. The calculated desorption energies for high surface coverages, 25% DMMP desorbed from pores ≤2.4 nm, are 68-74 kJ mol-1, which is similar to the DMMP heat of vaporization (52 kJ mol-1). At lower surface coverages, 80% DMMP desorbed, the DMMP desorption energies from the OMCs are 95-103 kJ mol-1. This is overall 20-30 kJ mol-1 higher in comparison to that of BPL carbon, due to the pore size and diffusion through different porous networks.

Structural, Magnetic, and Gas Adsorption Study of a Two-Dimensional Tetrazole-Pyrimidine Based Metal−Organic Framework

A new two-dimensional (2D) metal−organic framework, Cu-TP-1, has been synthesized under solvothermal conditions (DMF) from the transition metal cation Cu(II) and 2-tetrazole pyrimidine (C5H5N6, H-TP). The structure has been determined by single crystal X-ray crystallography which shows a (6,3) honeycomb 2D net with perpendicular one-dimensional channels. Permanent porosity of Cu-TP-1 has been determined by the nitrogen adsorption isotherm. Cu-TP-1 show interesting H2 and CO2 uptake. CO2 uptake of Cu-TP-1 (at 298 K, 1 atm pressure) is seen to be comparable to the recently reported ZIF-95 which outperforms ZIF-100 and BPL carbon. The magnetic properties show an antiferromagnetically coupled Cu···Cu interaction down to 8 K with a Weiss temperature around 108 K.

Metal-organic frameworks with high capacity and selectivity for harmful gases

Benchmarks have been established for the performance of six metal-organic frameworks (MOFs) and isoreticular MOFs (IRMOFs, which have the same underlying topology as MOF-5), MOF-5, IRMOF-3, MOF-74, MOF-177, MOF-199, and IRMOF-62, as selective adsorbents for eight harmful gases: sulfur dioxide, ammonia, chlorine, tetrahydrothiophene, benzene, dichloromethane, ethylene oxide, and carbon monoxide. Kinetic breakthrough measurements are used to determine the calculated dynamic adsorption capacity of each "benchmark" MOF for each gas. The capacity of each MOF is compared to that of a sample of Calgon BPL activated carbon. We find that pore functionality plays a dominant role in determining the dynamic adsorption performance of MOFs. MOFs featuring reactive functionality outperform BPL carbon in all but one case and exhibit high dynamic adsorption capacities up to 35% by weight.

A new low temperature approach to developing mesoporosity in metal-doped carbons for adsorption and catalysis

Key factors in achieving effective adsorption are the size of the pores relative to those of the adsorbate molecules and often the presence of small metal particles which can confer catalytic activity. While microporous carbons are excellent adsorbents for small molecules they are not as effective for larger species. A new low temperature approach to activation using an oxygen gas pulsing technique to achieve a carbon with controllable meso/micropore structure is described which also minimises metal sintering. The porosity of the samples was analysed by nitrogen adsorption at 77 K. Microporous metal-doped ASC carbon showed significant increases in the level of mesoporosity, its mesopore volume increasing from 0.06 to 0.24 cm3 g−1. However, undoped BPL carbon treated under the same conditions remained unchanged. The catalytic effect of the metals in the ASC carbon is thought to account for the observed mesopore development. At the temperatures used, a continuous oxidative activation yielded no pore widening in either carbon, suggesting that the gas pulsing method is far more effective in increasing mesopore sizes.

Kinetic Restriction of Simple Gases in Porous Carbons: Transition-State Theory Study

The separation of simple gases such as N2, Ar, CO2, and CH4 is an industrially important problem, particularly for the mitigation of greenhouse emissions. Furthermore, these gases are widely accepted as standard probing gases for the characterization of the microstructure of porous solids. However, a consistent set of microstructural parameters of a microporous solid determined from the use of adsorption measurements of these different gases is not always achieved because of differences in their pore accessibility. This is a long-standing and poorly understood problem. Here, we present the calculated results of the crossing time of N2, Ar, CO2, and CH4 between two neighboring cages through a constricted window in a realistic structural model of saccharose char, generated from hybrid reverse Monte Carlo (HRMC) simulation (Nguyen, T. X.; Bhatia, S. K.; Jain, S. K.; Gubbins, K. E. Mol. Simul. 2006, 32, 567-577) using transition state theory (TST), as described in our recent work (Nguyen, T. X.; Bhatia, S. K. J. Phys. Chem. 2007, 111, 2212-2222). The striking feature in these results is that whereas very fast diffusion of carbon dioxide within the temperature range of 273-343 K, with crossing time on the molecular dynamics scale (10-4-10-6 s), leads to instantaneous equilibrium and no hysteresis on the experimental time scale, slower diffusion of Ar and N2 at the low temperature of analysis indicates an accessibility problem. These results rationalize the experimental results of hysteresis for N2 at 77 K and Ar at 87 K but not for CO2 at 273 K in Takeda 3 A carbon molecular sieves. Furthermore, it is shown that CH4 diffusion through narrow pore mouths can be hindered even at ambient temperature. Finally, we show that the use of pore size and wall thickness distributions extracted from the adsorption of Ar at 87 K using the finite wall thickness (FWT) model (Nguyen, T. X.; Bhatia, S. K. Langmuir 2004, 20, 3532-3535 and Nguyen, T. X.; Bhatia, S. K. J. Phys. Chem. B 2004, 108, 14032-14042) provides the correct prediction of experimental CO2 adsorption in BPL and PCB carbons whereas that from N2 at 77 K gives a significant underprediction for both CO2 and CH4 in the BPL carbon. These trends are in excellent agreement with those predicted using the calculated crossing times.

Interactions of Ammonia with the Surface of Microporous Carbon Impregnated with Transition Metal Chlorides

The BPL carbon samples impregnated with chlorides of copper, nickel, and zinc were used as ammonia adsorbents in dynamic conditions with various amounts of water present in the systems. The initial and exhausted samples were characterized using adsorption of nitrogen, XRF, XRD, FTIR, SEM, and thermal analysis. The results indicate that metal chlorides are active centers for ammonia adsorption via formation of complexes. Water enhances the amount of ammonia adsorbed, promoting its dissolving into the film of water adsorbed in micropores and formation of NH4+ ions. Even though the pore system of activated carbon provides spaces for dispersion of metals, it still contributes significantly to the amount of ammonia adsorbed (about 80%) via dispersive forces. The most efficient adsorbent for ammonia removal is the carbon impregnated with copper. In this material the efficiency is governed by the amount of copper introduced to the carbon and its dispersion on the surface.

Prediction of the Adsorption Capacity for Volatile Organic Compounds onto Activated Carbons by the Dubinin–Radushkevich–Langmuir Model

Prediction of the adsorption capacity for volatile organic compounds (VOCs) onto activated carbons is elucidated in this study. The Dubinin–Radushkevich (D–R) equation was first used to predict the adsorption capacity of nine aromatic and chlorinated VOCs onto two different activated carbons. The two key parameters of the D–R equation were estimated simply from the properties of the VOCs using quantitative structure-activity relationship and from the pore size distribution of the adsorbent. The approach based on the D–R equation predicted well the adsorption capacity at high relative pressures. However, at the relative pressures lower than ~1.5 × 10-3, the D–R approach may significantly overestimate adsorption capacity. To extrapolate the approach to lower relative pressures, the integration of the D–R equation and the Langmuir isotherm, called the D–R–L model, was proposed to predict adsorption capacity over a wide range of relative pressures of VOCs. In this model, the Langmuir isotherm parameters were extracted from the predicted D–R isotherm at high relative pressures. Therefore, no experimental effort was needed to obtain the parameters of the D–R–L model. The model successfully predicted the adsorption capacity of aromatic and chlorinated hydrocarbons tested onto BPL and Sorbonorit B carbons over relative pressures ranging from 7.4 × 10-5 to 0.03, suggesting that the model is applicable at the low relative pressures of VOCs often observed in many environmental systems. In addition, the molecular size of organic compounds may be an important factor affecting the adsorption capacity of activated carbons. For BPL carbon, an ultramicroporous adsorbent, the limiting pore volume W o of the D–R equation decreased when the kinetic diameter of the adsorbate was larger than 6 Å. However, for Sorbonorit B carbon, no reduction of W o was found, suggesting that the W o may be related to the pore size distribution of the adsorbents, as well as to their molecular size. This size exclusion effect may play an important role in predicting the adsorption capacity of VOCs onto micro-porous adsorbents in the D–R–L model and in the corresponding D–R equation.

Degradation of Adsorbed Sarin on Activated Carbons: A 31P‐MAS‐NMR Study

AbstractThe fate of the OP nerve agent isopropyl methylphosphonofluoridate (sarin) on granular activated and metal‐impregnated activated carbons that are used in gas‐mask filters was investigated by means of 31P magic‐angle‐spinning (MAS) NMR spectroscopy. The results show that most of the adsorbed sarin on extensively dried carbons decomposes with a half‐life of 5–12 days. A MAS‐NMR signal of the degradation product isopropyl methylphosphonic acid (IMPA) appears in the spectra of sarin on non‐impregnated carbons. The IMPA signal is not visible in the spectra from metal‐impregnated carbons, probably due to strong binding of the acid molecule to paramagnetic Cr3+ and Cu2+ ions. Exposure of BPL and ASC carbons to air of 53% relative humidity shortens the degradation time by approximately an order of magnitude. Wetting shortens the half‐life of sarin on BPL carbon to approximately 2 hours.

Natural gas storage cycles: Influence of nonisothermal effects and heavy alkanes

A mathematical model is developed for examining the influence of nonisothermal effects and accumulation of heavy alkanes on natural gas storage cycles. The model is solved for the charge and discharge steps of the cycle. This is the first study to solve the natural gas storage problem for a nonisothermal charge of natural gas containing impurities. We examine both adiabatic and isothermal operation of natural gas and pure methane storage cycles on BPL carbon and an activated carbon prepared from coconut shells. Our simulations show for both carbons that the adiabatic gas storage cycles operate under subcooled conditions with respect to the feed temperature due to long discharge times and the desorption heat. It is also shown that degradation of gas storage performance due to impurities depends more on selectivity of the material for heavy alkanes than on adsorption capacities.

Monte Carlo Simulation Study of Water Adsorption in Activated Carbon

We present a Monte Carlo simulation study of adsorption and desorption for two molecular models of water in activated carbon, focusing on the temperature range for which the system exhibits hysteresis. The activated carbon is modeled using an adaptation of the platelet model developed by Segarra and Glandt (Chem. Eng. Sci. 1994, 49 (17), 2953−2965). The active sites in the carbon are modeled by placing interaction sites at the periphery of the platelets. To model water we have used two model potentials: the simple point charge (SPC) model and adaptation of the primitive model of water developed by Kolafa and Nezbeda (Mol. Phys. 1987, 61 (1), 161−175). We find that both models considered yield quite good qualitative agreement with the experimental data for water in BPL carbon obtained by Levan and co-workers (Ind. Eng. Chem. Res. 1992, 31 (4), 1122−1130). In particular both the shape of the hysteresis loops and their temperature dependence are correctly described by the simulation results. The sensitivity...

Adsorbed-Phase Heat Capacities: Thermodynamically Consistent Values Determined from Temperature-Dependent Equilibrium Models

In this paper, adsorbed-phase heat capacities are determined from thermodynamic relations (Ind. Eng. Chem. Res. 2003, 42, 6938−6948; J. Phys. Chem. 1999, 103, 2467−2479) applied to temperature-dependent adsorption equilibrium models and are shown to vary widely depending on the equation used. Two common gas adsorption models, the Langmuir and Dubinin−Astakov (D−A) equations, are used to determine thermodynamically consistent heat capacities. The common temperature-dependent Langmuir equation results in an adsorbed-phase heat capacity that is equal to the gas-phase heat capacity, while the original kinetic theory derivation of Langmuir (J. Am. Chem. Soc. 1918, 40, 1361−1403) gives a value less than the gas-phase value by a constant amount. The D−A equation as modified by Ye et al. (Carbon 2003, 41, 681−686) leads to an adsorbed-phase heat capacity that is equal to the liquid-phase heat capacity. We also determine adsorbed-phase heat capacities from the standard Dubinin−Radushkevich equation in which the adsorbed-phase molar volume is set equal to that of liquid at the adsorption temperature. This analysis shows that, for n-hexane on BPL carbon, the isosteric heat and adsorbed-phase heat capacity behave unrealistically at high loadings; the heat capacity can become negative with increasing temperature, indicating a deficiency in this adsorption equilibrium model.

Predicting adsorption of water/organic mixtures using molecular simulation

AbstractThe use of Monte Carlo simulation to predict the adsorption of mixtures of polar and nonpolar species on activated carbon was investigated using water and ethane on BPL carbon as a prototype system. The structure of the adsorbent was modeled by an array of slit‐shaped pores, characterized by a pore‐size distribution. The chemical heterogeneity of the carbon was taken into account by including oxygen‐containing sites on the surface of the pores. The pore‐size distribution was obtained from pure‐ethane adsorption on the same carbon sample, while the concentration and distribution of surface sites were determined by analyzing pure‐water adsorption. Model predictions agree well with experimental multicomponent data.

Prediction of adsorption equilibrium using a modified D–R equation: pure organic compounds on BPL carbon

A method for predicting adsorption equilibrium using a modified Dubinin–Radushkevich (D–R) equation is presented in this paper. We focus on adsorption of pure organic compounds on BPL-activated carbon. We introduce a new variable k v, a volume adjusting coefficient, and simply use V b, the constant molar volume of the adsorbate at its normal boiling temperature, instead of V m, the temperature-dependent molar volume of the adsorbate at the adsorption temperature. The model parameters in the modified D–R equation for an adsorbate are predicted from V b. Overall, the modified D–R equation gives more accurate results than the traditional one.

Adsorption and enthalpy of phenol on BPL carbon

The displacement process of adsorption of phenol from aqueous solution on carbons with various surface properties has been studied using a flow calorimeter. The carbon surface was oxidised, chlorinated and treated with ethylene. The enthalpy of exchange of water with phenol was measured along with the quantitative uptake of phenol on a column of carbon from a flowing solution. It was determined that the uptake of phenol was primarily a pore filling phenomenon and surface alterations must be severe to have a significant influence on the enthalpy.

Evaluation of Two Sulfur Impregnation Methods on Activated Carbon and Bentonite for the Production of Elemental Mercury Sorbents

ABSTRACT Adsorption of vapor-phase elemental mercury by virgin and modified bentonite and activated carbon was evaluated at 140°C, empty-bed contact time in a fixed-bed adsorber of 0.011 s, and influent mercury concentration of 55 μg/m3. Acid-treated bentonite had somewhat higher capacity than the virgin bentonite due to higher surface area and perhaps some active surface sites created by acid treatment. Sulfur impregnation through hydrogen sulfide oxidation enhanced mercury removal efficiency over the nonimpregnated bentonite. However, mercury removal efficiency was promoted to a limited extent, due to predominance of nonreactive sulfur allotropes and significant reduction in surface area. Sulfur impregnation of bituminous coal-based carbon (BPL) was performed using thermal deposition of elemental sulfur (BPLS) at high temperature (600°C) or hydrogen sulfide oxidation (BPLHS) at low temperature (150°C). Both BPLS and BPLHS performed significantly better than virgin BPL carbon. Although sulfur content of ...

Vapor-phase elemental mercury adsorption by activated carbon impregnated with chloride and chelating agents

The dynamic adsorption capacity for vapor-phase elemental mercury (Hg 0) of commercially available granular activated carbon (BPL) impregnated with copper chloride (BPL-C), β-aminoanthraquinone (BPL-A), 2-(aminomethyl)pyridine (BPL-P), and 2-aminoethanethiol (BPL-T) was studied in an attempt to produce economical and effective sorbents for the control of elemental mercury emissions from combustion processes. The dynamic adsorption capacity of BPL-C was found to increase as empty bed contact time (EBCT) and chloride content increased and to decrease with an increase in operating temperature when dry nitrogen was used as a carrier gas. BPL carbon impregnated with 5 wt.% chloride exhibited a higher dynamic adsorption capacity than sulfur impregnated carbon tested previously. However, the observation of oxidized forms of mercury in the effluent from a fixed-bed adsorber under all experimental conditions used in this study indicates that the bond between adsorbed mercury and BPL-C is unstable or that the BPL-C itself lacks the thermal stability required for full-scale applications. BPL-A and BPL-T exhibited high dynamic adsorption capacities at 25°C but had much lower dynamic adsorption capacities at 140°C, while BPL-P showed very poor performance at both temperatures. Due to the high production costs, these chelating agent-impregnated carbons would likely be considerably less cost-effective for the full-scale removal of mercury from combustion flue gases than the chloride- or sulfur-impregnated carbons. Impregnation with thiol was the only promising approach that could provide effective mercury sorbents at room temperature.

Chlorine and oxygen on the carbon surface

A series of carbons have been prepared with slight variations in oxygen content by treating BPL carbon with hydrogen at a number of temperatures and by ageing samples in a humid environment. These carbons were subsequently chlorinated at 180°C and washed to remove physisorbed chlorine. For the original oxidised series the primary water adsorption sites were observed to decrease with decreasing oxygen content determined from temperature-programmed desorption. The immersional enthalpy in water increased with increasing oxygen concentration on the surface of the carbon as did the number of hydrophilic surface sites measured by preferentially adsorbing 1-butanol from heptane. The relationships established for the oxidised carbons did not fit the chlorinated series with preliminary indications that the interaction of water with the oxygen functional groups is reduced from about 17 kJ mol −1 atomic oxygen on the surface to 5 kJ mol −1 by the influence of neighbouring chlorine atoms. Chlorination of the surface also appears to alter the measurement of hydrophilic oxygen sites and the interaction of water with the porous carbon structure.