Simulated Landfill Gas Research Articles

Catalytic activity of Cu/H-ZSM-5 zeolite for the removal of oxygen in the landfill gas

The upgrading of landfill gas (LFG) to bio-methane is a feasible scheme to make full use of its energy and solve the environmental pollution problems caused by its emissions. In the process of LFG upgrading, deoxygen is an essential procedure. In order to develop highly efficient and low-cost catalysts for LFG deoxygen, a series of Cu/H-ZSM-5 zeolites with the content of copper (Cu) in the range of 0.95 wt%-10.48 wt% were prepared by incipient wetness impregnation method, and used in the removal of oxygen in simulated LFG. The results of deoxygen experiments showed that the Cu/H-ZSM-5 zeolite had an excellent catalytic activity comparable to noble-metal based catalysts. The light-off temperature of Cu(3.63)/H-ZSM-5 was as low as 321 °C under the experimental conditions with a gas hourly space velocity (GHSV) of feed gas (55 vol% methane, 1 vol% oxygen and 44 vol% carbon dioxide) at 68,790 h−1. According to the characterization results of the catalysts, it was supposed that the excellent catalytic deoxygen performance of the Cu/H-ZSM-5 zeolite might be mainly due to that it contains a variety of highly dispersed active Cu species, which could significantly reduce the activation energy barrier of methane. This work provides new insights into the development of low-cost high-performance LFG deoxygen catalysts in practical LFG upgrading engineering applications.

Coking of Pt/γ-Al2O3 catalyst in landfill gas deoxygen and its effects on catalytic performance

Catalytic oxidation of CH4 has been proved to be an attractive option for landfill gas (LFG) upgrading. However, coking of catalysts in catalytic LFG deoxygen has been clearly observed in industrial applications. In this regard, it is necessary to investigate whether coke deposition originates from CH4 or volatile organic compounds present in LFG, and the influence of coke deposition on catalytic performance. Herein, we evaluate the LFG deoxygen on Pt/γ-Al2O3 catalyst in simulated LFG (CH4, CO2, O2, N2) and its co-feed with representative volatile organic compounds, ethylbenzene, toluene, benzene and cyclohexane. The results show that the coking of the catalyst is originated from volatile organic compounds rather than CH4. The Pt/γ-Al2O3 catalyst does not deactivate during LFG deoxygen process, even significant amount of coke deposited, up to 18.15% (mass). Characterization analyses reveal that although coke deposition overall covers the catalyst surface, resulting in mesopores blockage and a reduced number of accessible Pt sites, however, the coke formed, H-rich carbonaceous components, behaves as counterpart for O2 elimination. Besides, the coke deposited is mainly filamentous. Thus, coke formation has little negative effect on the overall catalytic performance of Pt/γ-Al2O3 catalyst ultimately. The results obtained in this work are helpful for the rational design of robust Pt based catalysts for LFG deoxygen without undue attention to their coking properties, and also favor the innovation of more attractive purification scheme configurations.

Catalytic Activity of Cu/H-Zsm-5 Zeolite for the Removal of Oxygen in the Simulated Landfill Gas

Catalytic Activity of Cu/H-Zsm-5 Zeolite for the Removal of Oxygen in the Simulated Landfill Gas

Scale-up of immobilized amine sorbent pellets for landfill gas upgrading, using benchtop and pilot equipment

Upgrading CO2/CH4 enriched biogas effluents, especially from landfills, is a viable route towards simultaneously generating renewable methane for energy production and purified carbon dioxide for industries like oil and gas, whose main use is enhanced oil recovery. Pelletized basic immobilized amine sorbents (BIAS) previously utilized for post-combustion CO2 capture are prime candidates for CO2 removal from landfill gas (inherent CH4 enrichment) because of the pellets' high CO2 selectivity and tunability for optimized performance at different temperatures and gas compositions. This work examines the process parameters and material properties that are key in the production scale-up of our previously developed polychloroprene latex-polyethylenimine (PEI, MW = 25,000) binder/silica-fly ash pellet supports. Thicker pastes with aqueous binder solution/powder ratios between 2.9/1 and 3.24/1 exhibited average storage moduli of G' ≥ 9.5 × 106 ± 1.2 × 105 Pa and were easily prepared then transformed into separable cylindrical ropes via a lab-scale mixer-extruder machine. The dried supports displayed good crush strength and a > 98% efficient amine impregnation. Pellets containing 32 wt% PEI800/N-N-diglycidyl-4-glycidyloxyaniline crosslinker (1/0.13 wt. ratio) showed a high 1.95 mmol CO2/g capture from simulated landfill gas (60% CO2/39% CH4/1% O2) at 75 °C that dropped <30% after 24 h at 105 °C under the same gas environment. Scalability of the material was demonstrated by producing a 3.3 kg batch of pellet supports with pilot-scale mixer and extruder equipment. Similar strength and CO2 capture performance for the PEI-functionalized commercial pellets as those for the lab-scale pellets strongly indicate the viability of these materials for pilot-scale landfill gas CO2 capture/upgrading.

Field Testing of a UV Photodecomposition Reactor for Siloxane Removal from Landfill Gas

We present in this paper the results of the field testing at a California Landfill of a UV photodecomposition reactor (PhoR) used for the removal of siloxane impurities from landfill gas (LFG). Prior to its field testing, the PhoR technology was tested in the laboratory with simulated LFG and was shown to be capable of completely removing the trace siloxane compounds and to convert them into silica particulates. The key objective of the field test was to validate the ability of the PhoR system to treat real LFG in a practical setting. The field-scale PhoR again proved quite efficient in attaining complete siloxane removal at different concentrations in the real landfill environment. These promising findings have led us to propose a scaled-up, commercial size PhoR system, competitive to conventional adsorption systems that can be practically applied in existing landfill plants to obtain 99+% siloxanes removal rates without associated secondary emissions.

Effect of siloxane on performance of the Pt-doped γ-Al2O3 catalyst for landfill gas deoxygen

Catalytic oxidation of methane using platinum (Pt) or platinum-rhodium (Pt-Rh) doped γ-Al2O3 has been proved to be a reliable deoxygen method for landfill gas (LFG) upgrading. As siloxanes are ubiquitous in LFG, their effect on the performance of the deoxygen catalyst is an extremely important element for the design of LFG upgrading procedures. To investigate the effect of siloxanes on the deoxygen catalyst reactivity, two experiments for the simulated LFG deoxygen were designed and carried out using Pt/γ-Al2O3 as the catalyst, and octamethylcyclotetrasiloxane (D4) as the siloxane representative. The fresh and used catalysts were characterized by means of various techniques. Results of the deoxygen experiments demonstrated that the presence of siloxanes in LFG would cause deactivation of the deoxygen catalyst. For the catalyst prepared in this study, at reaction temperature of 350 °C, deoxygen conversion of the catalyst decreased to 16.6% after 7 h of running under the condition of the experiment in this study, and the light-off temperature of this used catalyst increased to 415 °C. The results of X-ray photoelectron spectroscopy (XPS) characterization indicated that compared with Pt of higher chemical states, elementary Pt presented higher catalytic deoxygen reactivity. Through various characterization techniques, the deactivation of the catalyst could be explained as that D4 was oxidized by the small amount of oxygen in the simulated LFG and converted to amorphous silicon dioxide (SiO2), which blocked the contact between the active sites of the catalyst and the gas molecules, and resulted in the catalyst failure.

Effect of basic oxygen furnace slag particle size on sequestration of carbon dioxide from landfill gas.

The mineral carbon sequestration capacity of basic oxygen furnace (BOF) slag offers great potential to absorb carbon dioxide (CO2) from landfill emissions. The BOF slag is highly alkaline and rich in calcium (Ca) containing minerals that can react with the CO2 to form stable carbonates. This property of BOF slag makes it appealing for use in CO2 sequestration from landfill gas. In a previous study, CO2 and CH4 removal from the landfill gas was investigated by performing batch and column experiments with BOF slag under different moisture and synthetic landfill gas exposure conditions. The study showed two stage CO2 removal mechanism: (1) initial rapid CO2 removal, which was attributed to the carbonation of free lime (CaO) and portlandite [(Ca(OH)2)], and (2) long-term relatively slower CO2 removal, which was attributed to be the gradual leaching of Ca2+ from minerals (calcium-silicates) present in the BOF slag. Realising that the particle size could be an important factor affecting total CO2 sequestration capacity, this study investigates the effect of gradation on the CO2 sequestration capacity of the BOF slag under simulated landfill gas conditions. Batch and column experiments were performed with BOF slag using three gradations: (1) coarse (D50 = 3.05 mm), (2) original (D50 = 0.47 mm), and (3) fine (D50 = 0.094 mm). The respective CO2 sequestration potentials attained were 255 mg g-1, 155 mg g-1, and 66 mg g-1. The highest CO2 sequestration capacity of fine BOF slag was attributed to the availability of calcium containing minerals on the slag particle surface owing to the highest surface area and shortest leaching path for the Ca2+ from the inner core of the slag particles.

Effect of basic oxygen furnace slag type on carbon dioxide sequestration from landfill gas emissions

This study investigates the carbon dioxide (CO2) sequestration potential of three different basic oxygen furnace (BOF) slags (IHE-3/15, IHE-9/17, and Riverdale) subjected to simulated landfill gas (LFG) conditions (50% CH4 and 50% CO2 v/v) in a series of batch and column experiments. Batch experiments were performed at different moisture contents (0%, 10%, 15% and 20% moisture by weight) and temperatures (7 °C, 23 °C and 54 °C) to examine the effect of moisture and temperature on the CO2 sequestration potential of the BOF slags. The column experiments were conducted under continuous humid gas flow conditions. The results from the batch experiments show that the CO2 sequestration was significantly higher in a moist state (10%, 15%, 20% moisture (w/w)) versus the dry state (0% moisture). The optimum moisture content (w/w) for CO2 sequestration was different for each BOF slag; IHE-3/15 (10%), IHE-9/17 (20%) and Riverdale (20%). The variation in ambient temperature did not show any significant effect on the CO2 sequestration capacity of the BOF slags. The CO2 sequestration capacity of IHE-3/15, IHE-9/17 and Riverdale BOF slags determined by long-term batch experiments were 105 mg/g, 80 mg/g and 67 mg/g, respectively. The IHE-3/15 slag demonstrated the highest carbonation potential and was attributed to its finer particle size and higher free lime, portlandite and larnite content. The IHE-9/17 and Riverdale slags showed significantly lower CO2 sequestration capacity in comparison to the IHE-3/15 slag. The amount of free lime, portlandite and larnite, which are considered to be the most reactive minerals during carbonation, was nearly 1.3 times less than that of the IHE-3/15 slag in the IHE-9/17 and Riverdale slags. Also, the Riverdale slag showed relatively lower CO2 sequestration in column experiment in comparison to the batch experiments, perhaps due to a high in-situ density which limited CO2 diffusion and hence the CO2 uptake. Overall, this study provides a means to analyze the suitability of the use of BOF slags in landfill covers for mitigating fugitive CO2 emissions from landfills.

Synthesis of Highly Porous Coordination Polymers with Open Metal Sites for Enhanced Gas Uptake and Separation.

Metal-containing amorphous microporous polymers are an emerging class of functional porous materials in which the surface properties and functions of polymers are dictated by the nature of the metal ions incorporated into the framework. In an effort to introduce coordinatively unsaturated metal sites into the porous polymers, we demonstrate herein an aqueous-phase synthesis of porous coordination polymers (PCPs) incorporating bis(o-diiminobenzosemiquinonato)-Cu(II) or -Ni(II) bridges by simply reacting hexaminotriptycene with CuSO4·5H2O [Cu(II)-PCP] or NiCl2·6H2O [Ni(II)-PCP] in H2O. The resulting polymers showed surface areas of up to 489 m2 g-1 along with a narrow pore size distribution. The presence of open metal sites significantly improved the gas affinity of these frameworks, leading to an exceptional isosteric heat of adsorption of 10.3 kJ·mol-1 for H2 at zero coverage. The high affinities of Cu(II)- and Ni(II)-PCPs toward CO2 prompted us to investigate the removal of CO2 from natural and landfill gas conditions. We found that the higher affinity of Cu(II)-PCP compared to that of Ni(II)-PCP not only allowed for the tuning of the affinity of CO2 molecules toward the sorbent, but also led to an exceptional CO2/CH4 selectivity of 35.1 for landfill gas and 20.7 for natural gas at 298 K. These high selectivities were further verified by breakthrough measurements under the simulated natural and landfill gas conditions, in which both Cu(II)- and Ni(II)-PCPs showed complete removal of CO2. These results clearly demonstrate the promising attributes of metal-containing porous polymers for gas storage and separation applications.

Direct Utilization of Elemental Sulfur in the Synthesis of Microporous Polymers for Natural Gas Sweetening

Summary Elemental sulfur, which is produced by a process called hydrodesulfurization mainly as a byproduct of the purification of natural gas, is one of the most abundant elements in the world. Herein, we describe solvent- and catalyst-free synthesis of ultramicroporous benzothiazole polymers (BTAPs) in the presence of elemental sulfur in quantitative yields. BTAPs were found to be highly porous and showed exceptional physiochemical stability. Moreover, in situ chemical impregnation of sulfur within the micropores increased CO 2 affinity of the sorbent while limiting diffusion of CH 4 . As low-cost, scalable solid sorbents, BTAPs showed promising CO 2 separation ability and high regenerability under vacuum swing adsorption for the simulated flue gas, natural gas, and landfill gas conditions. The fact that elemental sulfur can be directly utilized in the synthesis of BTAPs means that it can be recycled back to the natural gas sweetening process for efficient CO 2 /CH 4 separation, thus offering a high-value, scalable, large-scale application for elemental sulfur.

Hydrate-based Capture CO2 and Purification CH4 from Simulated Landfill Gas with Synergic Additives Based on Gas Solvent

Treatment and subsequent use of Landfill gas (LFG) are garnering huge interest for both energy recovery and mitigation of environmental impact. This work presents the thermodynamic, kinetic and separation efficiency studies of purifying simulated LFG (45.0 mol% CO2/CH4 binary mixture) based on hydrate crystallization approach. Particularly, creative synergic additives (comprise traditional hydrate promoter (tetra-n-butyl ammonium bromide, TBAB and tetrahydrofuran, THF) and gas solvent (dimethyl sulfoxide, DMSO)) were proposed to enhance the separation process. The hydrate crystallization process was conducted at a certain driving pressure with proportional integral derivative (PID) isochoric controller. The residual gas phase and the decomposition gas phase of the hydrate slurry were sampled and analyzed. Based on the above experimental data, the gas storage capacity, unit system gas consumed rate, gas selectivity and separation efficiency were calculated to evaluate the separation process. For the synergic additives with the fixed concentrations studied in this work, it was found that, the synergic additives (TBAB-DMSO) could not only remarkably reduce the equilibrium LFG hydrate formation pressure, but also accelerate the formation rate and improve the gas storage capacity of LFG through promote the solubility of CO2 and further enhance the selectivity of CO2 in the hydrate process. It will be of practical interest in relation to the development of hydrate-based gas separation and of potential importance for the industry application of gas hydrate.

Phase equilibrium conditions for simulated landfill gas hydrate formation in aqueous solutions of tetrabutylammonium nitrate

Hydrate phase equilibrium conditions for the simulated landfill gas (LFG) of methane and carbon dioxide (50mol% methane, 50mol% carbon dioxide) were investigated with the pressure range of (1.90 to 13.83)MPa and temperature range of (280.0 to 288.3)K at (0.050, 0.170, 0.340, and 0.394) mass fraction (w) of tetrabutylammonium nitrate (TBANO3). The phase boundary between liquid–vapor–hydrate (L–V–H) phases and liquid–vapor (L–V) phases was determined by employing an isochoric pressure-search method. The phase equilibrium data measured showed that TBANO3 appeared a remarkable promotion effect at wTBANO3=0.394, corresponding to TBANO3·26H2O, but inhibition effect at wTBANO3=(0.050, or 0.170) on the semiclathrate hydrate formation. In addition, the application of TBANO3 at 0.340 mass fraction, corresponding to TBANO3·32H2O, displayed promotion effect at lower pressures (below 6.38MPa) and inhibition effect at higher pressures (above 6.38MPa).

Adsorption characteristics of activated carbon for siloxanes

The adsorption capacity of several kinds of activated carbons (ACs) for octamethylcyclotetrasiloxane (D4) in simulated landfill gas (LFG) was investigated and the main textural characteristics for AC adsorptive removal of siloxanes were studied. It was found that most of the ACs employed in this work showed good D4 adsorption capacity, and the D4 adsorption capacities of them ranged from 21.94mg/g to 224.63mg/g. Positive correlation was observed between D4 adsorption capacity and the BET surface area and the micropore volume of these ACs. Through analyzing nitrogen adsorption isotherms of these ACs, a conclusion was made that the super micropores and small mespores (pores of diameter∼1.7–3.0nm) in the ACs are the most favorable pores for siloxane adsorption.

Thermodynamic Equilibrium Conditions for Simulated Landfill Gas Hydrate Formation in Aqueous Solutions of Additives

This work presents the thermodynamic study of separating CH4 and CO2 from the simulated landfill gas (LFG) [CO2 (0.45) + CH4 (0.55)] based on hydrate crystallization in the presence of tetra-n-butyl ammonium bromide (TBAB), tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), and their mixtures. The mole fractions of TBAB, THF, and DMSO aqueous solutions were fixed at 0.0234, 0.0556, and 0.0165, respectively. The equilibrium hydrate formation conditions were measured by T-cycle method in the temperature range of (274.15 to 294.95) K and the pressure ranges up to 6.72 MPa. The gas phase in the crystallizer at the equilibrium points was also sampled and analyzed. For the additives with the fixed concentrations studied in this work, it was found that both TBAB and THF can remarkably reduce the equilibrium hydrate formation pressure of LFG mixture gas, but the effect of THF is better than that of TBAB in the high temperature region, while DMSO have no obvious pressure drop effect on the equilibrium hydrate formation conditions but can promote the solubility of CO2 in the solution. However, the mixture additives of TBAB + DMSO and THF + DMSO can not only remarkably promote the solubility of CO2 but also remarkably reduce the equilibrium hydrate formation pressure of CO2 + CH4 + H2O hydrate. Moreover, the pressure drop effect of THF + DMSO is better than that of TBAB + DMSO on the CO2 + CH4 + H2O equilibrium hydrate formation in the high temperature region.

Effect of biocover equipped with a novel passive air diffusion system on microbial methane oxidation and community of methanotrophs

A novel biocover with passive air diffusion system (PADS) was designed in this study. Its effect on landfill gas components in the macrocosms of simulated biocover systems was also investigated. The results show that O2 concentration increased in the whole profile of the macrocosms equipped with PADS. When simulated landfill gas (SLFG) flow rate was no more than 40 mL min−1, the methane oxidation rate was 100%. The highest CH4 oxidation capacity reached to 31.34 mol m−3 day−1. Molecular microbiology analysis of the soil samples taken from the above macrocosm showed that the growth of type I methanotrophs was enhanced, attributable to enhanced air diffusion and distribution, whereas the microbial diversity and population density of type II methanotrophs were not so affected, as evidenced by the absence of any difference between the biocover equipped with PADS and that of the control. According to a phylogenic analysis, Methylobacter, Methylosarcina for type I, and Methylocystis, Methylosinus for type II, were the most prevalent species in the macrocosm with PADS. Implications Semiaerobic landfill technology was reported to be an effective in situ CH4 emission reduction method. A semiaerobic status is achieved through a continuous supply of fresh air sucked passively through the open end of a leachate collection pipe, with a temperature gradient created by organic matter degradation. In this research, a novel passive air diffusion system (PADS) was designed, and O2 concentration increased in the whole profile of the microcosms equipped with PADS. The constant supply of fresh air reduced CH4 production and enhanced biodegradation. Through molecular microbiology analysis, it was found that growth of methanotrophs was enhanced, and species of prevalent methanotrophs were found. Supplemental Materials Supplemental materials are available for this article. Go to the publisher's online edition of the Journal of the Air & Waste Management Association for a list of abbreviations and PCR protocol.

Can a breathing biocover system enhance methane emission reduction from landfill?

Based on the aerothermodynamic principles, a kind of breathing biocover system was designed to enhance O 2 supply efficiency and methane (CH 4) oxidation capacity. The research showed that O 2 concentration (v/v) considerably increased throughout whole profiles of the microcosm (1 m) equipped with passive air venting system (MPAVS). When the simulated landfill gas SLFG flow was 771 g m −3 d −1 and 1028 g m −3 d −1, the O 2 concentration in MPAVS increased gradually and tended to be stable at the atmospheric level after 10 days. The CH 4 oxidation rate was 100% when the SLFG flow rate was no more than 1285 g m −3 d −1, which also was confirmed by the mass balance calculations. The breathing biocover system with in situ self-oxygen supply can address the problem of O 2 insufficient in conventional landfill covers and/or biocovers. The proposed system presents high potential for improving CH 4 emission reduction in landfills.

Performance of an Internal Combustion Engine Operating on Landfill Gas and the Effect of Syngas Addition

The performance of a four-stroke Honda GC160E spark ignition (SI) internal combustion (IC) engine operating on landfill gas (LFG) was investigated, as well as the impact of H2 and CO (syngas) addition on emissions and engine efficiency. Tests were performed for engine loads from 0.2 to 0.8 kW over a range of CO2 to CH4 ratios (0−0.50). In addition, variation across both the syngas content (up to 15%) and the ratio of H2 to CO in the syngas (H2/CO = 0.5, 1, and 2) were tested. Catalytic testing provided reactor data on the amount of syngas and H2/CO ratios that can be obtained by autothermally reforming LFG. The emissions obtained from the test engine fueled with the simulated LFG were found to be comparable to emissions from commercial LFG to energy (LFGTE) systems currently deployed. Syngas addition was found to not only significantly reduce CO, unburned hydrocarbon (UHC), and NOx emissions but also improve brake efficiency of the engine. CO emissions were reduced from 802 to 214 ppm for a 5% syngas addi...

Extension of the lean limit through hydrogen enrichment of a LFG-fueled spark-ignition engine and emissions reduction

In this experimental investigation the affect of hydrogen addition to a landfill gas-fueled naturally-aspirated spark-ignition engine was explored. Hydrogen concentrations of 0%, 30%, 40%, and 50% by volume were added to simulated landfill gas (60% CH 4 and 40% CO 2). Efficiency, coefficient of variance of indicated mean effective pressure, and CO emissions were measured from near stoichiometric mixtures up to the lean operating limit. Engine-out NOx emissions were compared to predicted future best available control technology targets for NOx emissions in landfill gas-to-energy projects. From this study, it was determined that with 40% hydrogen by volume untreated exhaust NOx emissions can meet the 0.22 g/kWh NOx target while retaining 95% of baseline power and low CO emissions.

Incorporating in-cylinder pressure data to predict NO x emissions from spark-ignition engines fueled with landfill gas/hydrogen mixtures

A 0.745 L 2-cylinder spark-ignition engine was operated with compressed natural gas and with simulated landfill gas (60% CH 4 and 40% CO 2 by volume) containing hydrogen concentrations of 0, 30%, 40%, and 50% (by volume of the CH 4 in the fuel) at constant rpm. This empirical data was compared with predictions from three existing semi-empirical engine models, using a first-law-based finite heat release model to correlate measured in-cylinder pressure data and burn rate for each fuel mixture. Of the three models only a two zone model incorporating thermal and prompt NO x came within 25% of predicting the measured NO x emissions.

Thermodynamics on Landfill Gas Reforming

AbstractLandfill gas is a type of methane‐rich biogas which supplies renewable resources for clean fuels production. In this paper, the characteristics and optimum conditions of simulated landfill gas and biogas reforming reactions for H2 production are investigated. The temperature, varied from 373.15 K to 1273.15 K, and pressure, varied from 1.013 bar to 40.013 bar, applied for the reforming system are evaluated. In addition, the effect of steam concentration, traces of hydrocarbons, and the ratio of C/H/O are analyzed using thermodynamic theories. Both the calculation and analyzed results demonstrate that the reforming system is primarily comprised of endothermic reactions. It favors lower pressure and higher temperature. Traces of hydrocarbons would result in a slight increase to CO for this system. A high ratio of CO2 would result in more production of CO in the reforming process. Preliminary experiments on fuel cells indicate this gas‐reforming simulation is an elementary theory for fuel supply.