Impurities In Biogas Research Articles

Impact of the biogas impurities on the quality of the precipitated calcium carbonate in the regenaration stage of a chemical absorption biogas upgrading unit

Combining Carbon Capture and Storage (CCS) with producing competitive secondary raw materials is key to decarbonizing industry and reducing resource extraction. Biogas upgrading to biomethane stand out as an alternative, but a significant gap remains in integrating this process within a circular economy framework. This issue has been recently addressed by a process that integrates biogas upgrading via caustic absorption with the production of Precipitated Calcium Carbonate (PCC) and the recovery of sodium hydroxide from waste brine solution using membrane technologies. The profitability of this approach depends on the quality of the PCC, a critical factor that this work addresses. By characterizing PCC is determined whether trace compounds in biogas contaminate the PCC and potentially affect its commercial value. It also examines the CO2 absorption process and analyzes the aqueous samples from the filtration phase of the PCC slurry. Results confirm the high purity of PCC obtained from biogas treatment using Raman spectroscopy, X-Ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). The analyses show that the PCC is pure calcium carbonate, mainly in the stable calcite form, with a typical tetrahedral morphology and no detectable impurities. Characterization of aqueous solutions revealed organic trace compounds from biogas, with TOC concentrations of 9.7 (± 6.4) and 16.0 (± 8) mg C/l. Silicon measurements showed similar concentrations in the absorbent solution and filtrated PCC slurry. Additionally, ammonia escapes as gas, and hydrogen sulfide in the biogas likely contributed to sulfate salt formation. Analysis of the CO₂ absorption shows a first-order reaction with OH-, where the amount of CO₂ absorbed (46.3–50.0 g) closely matches the theoretical value of 48 g. The study reveals that most of the biogas impurities dissolve into the aqueous solution, being crucial for future studies and downstream membrane treatments, and the PCC is unaffected by these impurities with a purity suitable for commercial applications.

Comparison of optical feedback cavity enhanced absorption spectroscopy and gas chromatography for the measurement of the main components and impurities in biogas, landfill gas, biomethane and carbon dioxide streams

In this study, we evaluated the performances of a custom-built optical feedback cavity enhanced absorption spectroscopy (OFCEAS) instrument for the determination of the composition of energy gases, focusing on methane and carbon dioxide as main components, and carbon monoxide as impurities, in comparison with the well-established, validated, and traceable gas chromatographic method. A total of 115 real sample gases collected in biogas plants or landfills were analyzed using with both techniques over a period of 12 months. The comparison of the techniques showed that the virtual model which allows the measurement, needs to be optimized using real samples of varied compositions. The OFCEAS measurement technique was found to be capable of measuring both the main components and a trace component in different matrices; to within a 2% measurement uncertainty (higher than the gas chromatograph/thermal conductivity detector (GC/TCD) method). The OFCEAS method exhibits a very fast response, does not require daily calibration, and can be implemented online. The agreements between the OFCEAS technique and the GC/TCD method show that the drift of the OFCEAS instruments remains acceptable in the long term as long as no change is made to the virtual model. Matrix effects were observed, and those need to be taken into consideration when analyzing different types of samples.

A Mini Review on Risk and Potential of Biogas Fed Solid Oxide Fuel Cell

Solid oxide fuel cell (SOFC) can reduce the carbon footprint due to their flexibility of fuel usage by using hydrogen and light hydrocarbon as fuel to convert the chemical to electrical energy. This has made the SOFC an interesting device for renewable applications. SOFC which is able to convert the biogas produces from the water treatment plant directly to electrical energy is a reliable renewable energy application. The performance of SOFC itself can be greatly influenced by the characteristics of the biogas. This is caused by the impurities of the biogas that would degrade the internal reforming aspect of SOFC. Mainly on the anode side degradation due to the formation of carbon, sulfur poisoning, and mechanical instability. The commonly found biogas impurities from the wastewater treatment plant are Siloxanes. The compound is coming from sewage sludge digestion which is the common compound in household cleaning products and cosmetics. The presence of Siloxanes in internal reforming SOFC would lead to the formation of SiO2 which degrade the anode layer and consequently reduces the power generation of SOFC. Hydrogen sulfide and ammonia were also present in the biogas fed from the wastewater treatment plant. These contaminations also showed degradation in the SOFC of the anode. Thus, this work will discuss the contamination compound and its effect on SOFC.

Deep eutectic solvents and conventional solvents as VOC absorbents for biogas upgrading: A comparative study

We are currently witnessing an increase in biogas production in the context of fossil fuel decline and the future circular economy. However, raw biogas contains undesirable compounds such as hydrogen sulfide, volatile organic compounds (VOCs) and carbon dioxide that should be removed to upgrade biogas to biomethane. Absorption is an effective method to capture undesirable compounds from biogas. In this work, we evaluated and compared the efficiency of hydrophobic deep eutectic solvents (DESs) based on fatty acids and conventional absorbents for the absorption of three major VOCs found as impurities in biogas (toluene, limonene and octamethylcyclotetrasiloxane). The vapor–liquid partition coefficient (K) of the VOCs in the studied solvents were determined using static headspace-gas chromatography. The effect of temperature and water content was assessed. Results show a decrease of K value in all solvents compared to water, hydrophobic DESs being the most effective solvents with an up to 20000-fold lower K value in the case of limonene. Interestingly, lowering temperature allows the conventional solvents to reach absorption efficiency close to DESs. Negative values of ΔG (from −6.95 to −22.89 kJ⋅mol−1) were obtained showing that all VOCs are favorably solubilized in absorbents. Obtained negative ΔH values (from −34.86 to −51.17 kJ⋅mol−1) indicate that the dissolution of VOCs is an exothermic process. For all studied absorbent the |ΔH| of VOC absorption is always higher than |TΔS|, showing an enthalpically driven process. The obtained results indicate that efficient VOC absorption can be achieved by the proposed hydrophobic DESs and conventional solvent also providing easy recycling, and recovering process.

Biogas Impurities: Environmental and Health Implications, Removal Technologies and Future Perspectives – A Review

Biogas Impurities: Environmental and Health Implications, Removal Technologies and Future Perspectives – A Review

Metal-organic frameworks as adsorbents for impurities of biogas

Biogas is an alternative energy source that has been promoted to reduce the environmental impact of fossil fuels. Because biogas contains impurities such as CO2, H2S, volatile organic compounds, water vapor, and ammonia, the calorific value of the biogas is reduced, and direct use causes corrosion/abrasion of the combustion equipment. This review focused on the recent generation materials known as metal–organic frameworks (MOFs) used as adsorbents for biogas impurities. In general, MOFs showed high adsorption capacity for individual compounds and good selectivity in impurities mixtures. An extensive exploration of MOF was also found for CO2 capture but to a lesser extent for other biogas impurities.

Direct Methanation of Biogas—Technical Challenges and Recent Progress

The direct methanation of biogas using hydrogen from electrolysis is a promising pathway for seasonal storage of renewables in the natural gas network. It offers particular advantages over the methanation of carbon dioxide separated from biogas, as it eliminates a costly and unnecessary carbon dioxide separation step. The key implementation challenges facing direct methanation of biogas are reviewed here: 1) treatment of biogas impurities; 2) competing reactor concepts for methanation; and 3) competing process concepts for final upgrading. For each of these three aspects, the state of the art is reviewed, focusing especially on results which have been validated at a high Technology Readiness Level (TRL) at recent long-duration demonstrations. The different technology solutions have advantages and disadvantages which may fit best to different technical and economic boundary conditions, which are discussed. As a final outlook, TRL 8 demo plants will be necessary to show the full potential of these systems, and to obtain consistent operation data to allow a cost comparison.

Long-term operation of a solid oxide fuel cell with MoNi–CeO2 as anode directly fed by biogas containing simultaneously sulphur and siloxane

This work analyses the long-term behaviour of MoNi–CeO2 (MoNi–Ce) anode in a direct internal reforming solid oxide fuel cell (DIR-SOFC) fed by biogas containing simultaneously sulphur and siloxanes. Both impurities are common in biogas and it is considered that they damage SOFC performance. An electrolyte supported cell with MoNi–Ce was operated under load demand (140 mA cm−2) at 750 °C in clean biogas for 116 h, followed by biogas with 10 ppm(v) H2S and 0.5 ppm(v) D4 siloxane (octamethylcyclotetrasiloxane) for 1737 h, and finally, clean biogas again for 96 h. Cell performance was periodically evaluated using electrochemical methods. Post-test analyses were conducted by SEM-EDS and XPS. The results show a stable cell performance in clean biogas, while the presence of both impurities in biogas initially led to a drop in performance, but without significant degradation after testing. A partial recovery in performance is observed after stopping both impurities in biogas. Silicon and small traces of carbon and sulphur were detected on the anode surface. It is demonstrated that MoNi–Ce exhibits high tolerance to the co-presence of H2S and D4 in biogas and good resistance to carbon deposition.

Mineral Deposit Formation in Gas Engines During Combustion of Biogas from Landfills and Municipal WWTP

Abstract The biogas produced in municipal wastewater-treatment plants (WWTP) should be cleaned before it can be used as a fuel in internal combustion engines. Efficient running of such engines is possible only subject to using high quality biogas and lubricating oil. Otherwise, biogas impurities in course of complex chemical reactions may form deposits on various engine parts as well as seriously contaminate the lubricating oil. In this paper, mineral deposits containing high concentration of bismuth, silicon, sulphur, calcium and zinc are studied. Silicon deposits demonstrating strong friction properties are formed during combustion of volatile silica compounds. As these deposits build up, abrasion problems, ignition failure and even engine failure result. The bismuth containing deposits comes from bearings degradation, zinc and calcium were derived from the additives present in commercially available lubricating oil, while lead, aluminium, copper, nickel, iron and chromium were introduced by engine wear phenomena. The highest bismuth content was located at the engine cylinder heads and the lowest at the exhaust elements, whereas highest calcium content was registered on the pistons. Silicon containing deposits are highest in the exhaust and lowest at the engine head. Zinc deposits are highest at the piston.

Cryptogamic Packed Biofilter as Potential Adsorbent for CO2, NH3, and H2S Impurities from Biogas

The presence of elevated concentrations of carbon dioxide, hydrogen sulfide, ammonia, and trace impurities in biogas affect its caloric value as well as causes corrosion and is extremely toxic. There are various methods in existence for removal of these impurities, but most are chemically based and expensive and are limited in use. In our work, cryptogams (moss) integrated with soil and biochar packed in a filter have been employed for simultaneous removal of CO2, H2S, and NH3, from biogas. Different soil types rich in metallic oxides at different masses of 100 g, 150 g, and 200 g with a fixed mass of moss and biochar were tested in an on-site experiment to determine the removal efficiency (RE) and sorption capacity (SC). The adsorption dynamics of the filters were investigated at two flow rates, 80 ml/min and 100 ml/min, by determining removal efficiency. For the contribution of each substrate, sorption capacity and breakthrough time were determined by considering 5 g of each substrate that made up the filter. The soils with a high content of extractable cations showed excellent adsorption capacity for H2S by about 20 g S/100 g, which was higher than other adsorbents tested. It was found that integrated biofilter made up of bed arrangement of the soil, biochar, and moss plant improved the quality of biogas with SC of 11 g S and RE of 93% for H2S, 72% for NH3, and 68% for CO2.

Carbon molecular sieve production from defatted spent coffee ground using ZnCl2 and benzene for gas purification

The aim of the current study is to manufacture molecular sieve from the defatted spent coffee ground. The defatted spent coffee ground for the specified particle size (100 μm) was chemically activated with different agents (ZnCl2, H3PO4, KOH) and then carbonized at different temperatures (400–900 °C). A thorough characterization of the produced activated carbon was performed and activated carbons with the highest BET surface area were subsequently used to produce carbon molecular sieve. The surface modification was performed with benzene vapor at different temperatures (600–900 °C) and different combustion times (30–90 min.). In addition to the BET analysis, SEM, TGA and FT-IR analysis were also undertaken. The results obtained through characterizations showed that the pore diameters of carbon molecular sieve produced from defatted spent coffee ground varied from 2 to 4 Å. To conclude, the results suggest that the fabricated carbon molecular sieve can be used for the removal of impurities such as CH4, CO2, NOx and other impurities in natural and biogas considering the porosity of the sieves.

Biogas purification through membrane bioreactors: Experimental study on siloxane separation and biodegradation

Sewage biogas valorization to different energy applications is hampered by the presence of volatile methyl siloxanes. Despite the high operating costs, adsorption onto activated carbon is the most implemented technology for siloxane removal from biogas. In order to purify biogas sustainably, the current work explores the diffusion of siloxanes (octamethylcyclotetrasiloxane and decamethylcyclopentasiloxane) together with other biogas impurities (limonene, toluene and hexane) through polydimethylsiloxane membranes. Abiotic tests revealed transport efficiencies above 75% towards a clean air stream for most compounds, although the transport of the most hydrophobic pollutants was challenged when water was circulated through the shell side of the membrane. Moreover, the performance of a hollow-fiber membrane bioreactor, inoculated with anerobic active sludge, was evaluated towards biogas purification in anoxic conditions. Toluene and limonene were successfully degraded, hexane’s removal efficiency was positively correlated with the residence time, and siloxanes removal was achieved up to 21%. CO2 was detected in the outlet gas as the mineralization product as well as some byproducts from the degradation of limonene and siloxanes. The presence of 1% of O2 in the gas, as a strategy to substitute NO3−, efficiently supported high removal for volatile organic compounds and moderate for siloxanes, which would ultimately reduce the operating costs of the technology.

Simultaneous removal of hydrogen sulfide and ammonia using a combined system with absorption and electrochemical oxidation

Hydrogen sulfide (H2S) and ammonia (NH3), common impurities in biogas, need to be removed before utilizing it. In this study, a combined system, which consisted of an absorption column and an electrochemical oxidation reactor, was tested to simultaneously remove these impurities. The effects of the current density and the chemical loading rate on the system performance were investigated. Firstly, the mass transfer coefficients for the absorption column were determined at various gas flow rates. More mass of NH3 was transferred, compared with that of H2S, because of its higher solubility. In the electro-oxidation reactor, reactive chlorine species (RCSs) were generated and oxidized both H2S and NH3; however, NH3 started to degrade only after H2S was completely eliminated. At a current density of 400 A/m2, the current efficiencies of H2S and NH3 were 23.1% and 5.9%, respectively. In the combined system, the removal efficiency of H2S was closely related to the mass ratio of the H2S transferred and the RCSs generated. The removal efficiency of H2S was greater than 99% when the ratio was less than 1. The mass transfer potential and the oxidation kinetics should be balanced to improve the system performance for the simultaneous removal of H2S and NH3.

Determining modified reaction parameters for the real-time measurement of BTEX in biogas and nitrogen using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS)

The increasing demand for high-quality biogas and the reduction of reliance on natural gas have driven the need for a well-defined framework to ensure conformity and quality of biogas by the introduction of traceable reference materials and methods across the community. Furthermore, there is a great need to quantify critical trace impurities in biogas. Here, we perform real-time measurements on reference gas standards containing trace hydrocarbons in biogas that are traceable to the international system of units using Selected Ion Flow Tube Mass Spectrometry (SIFT-MS). There are limited data on reaction rate constants in biogas matrices for SIFT-MS, and here we use the traceable gas standards to determine and compare the reaction rate constants of trace hydrocarbons in biogas and nitrogen. Here, we modify SIFT-MS constants for biogas avoiding the current 30 % bias and prevent the overestimation in the concentration of hydrocarbon amount fractions.

Recent advances in technologies for the removal of volatile methylsiloxanes: A case in biogas purification process

Volatile methylsiloxanes (VMS) exist as trace impurities in biogas and hamper the effective utilization of biogas. Various technologies, including adsorption, absorption, membrane separation and biological degradation, are used for the removal of VMS in biogas purification process. This work aims to summarize the recent advances of these technologies. Their advantages/disadvantages and factors that affect the removal efficiency of VMS are analyzed and discussed. Particular attention is paid to adsorption for its highest purification efficiency among the current VMS control technologies. Decrease of the adsorbed capacity under high humidity atmosphere and incomplete desorption are unavoidable conundrums at the present stage. The origination and influenced pathways of these issues are elaborated. Finally, research directions of these technologies for a further development are suggested to fulfill a high VMS removal efficiency and deep understanding of mechanisms.

The experimental study of biogas production when digesting chicken manure with a biochar additive

AbstractThe research aims to evaluate the output of biogas and the concentration of CH4 and gaseous impurities such as CO2 and H2S in the process of digesting chicken manure without additives (experiment A) and with 10% of biochar additive (by mass of the dry load) (experiment B) under anaerobic and mesophilic conditions. It has been found that the average output of biogas from a particular amount of chicken manure (experiments A and B) obtained in the 45‐day experimental research is similar in both cases and reaches 12.88 l d–1 and 12.36 l d–1, respectively. However, the biochar additive increases CH4 concentration in biogas and reduces the concentration of gaseous impurities (CO2 and H2S) in biogas. The maximum concentration of CH4 in biogas obtained from a load of manure with biochar additive is higher than that in biogas obtained by using a load without a biochar additive, and reaches 72.0% and 68.5%, respectively. The average CO2 concentration, reaching 33.09% and 47.5%, respectively, in biogas obtained from the load with 10% of biochar additive is lower than that in biogas obtained from the manure load without an additive. The average concentration of H2S in the biogas obtained in experiment B is lower than that in experiment A and reaches 95.9 mg m–3 and 195.5 mg m–3, respectively. The biochar additive adsorbs gaseous impurities (CO2 and H2S) from biogas without adsorbing CH4. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.

Plasma activation on natural mordenite-clinoptilolite zeolite for water vapor adsorption enhancement

Water vapor is one of the crucial impurities in biogas which have to be removed for optimal performance. Utilization of natural zeolites as water vapor adsorbents is one of the proposed solutions. However, the small specific surface area of natural zeolite needs to be improved to increase the material adsorption capacity, one of the methods being physicochemical treatment. The consequences of the increased specific surface area by physicochemical treatment are the Si/Al ratio and hydrophobicity enhancement which counterbalance the benefits of the increased specific surface area. In this work, plasma activation treatment was applied successfully to increase the water adsorption capacity of natural zeolites after dealumination. The transformations of the chemical and physical properties of the material after plasma treatment are discussed. Our results point that the certain intrinsic properties on the zeolites in terms of Si/Al ratio and specific surface area are prerequisite to benefit from plasma activation. This work offers a new perspective on improving porous silica-based materials water adsorption characteristics which could lead to improved adsorbents in the future.

Competitive siloxane adsorption in multicomponent gas streams for biogas upgrading

Biogas, produced in anaerobic digesters, is used as a renewable fuel after undergoing several upgrading processes. Adsorption onto activated carbon is the most widely used technology to remove harmful volatile compounds, such as siloxanes. However, the competition for the adsorptive sites with other biogas impurities reduces the performance of the adsorbents increasing the operative costs.This work studies the competitive adsorption of volatile organic compounds and siloxanes into activated carbons of different sources and activation processes. Ten selected materials were exhaustively characterized in terms of textural and chemical properties. Dynamic competitive adsorption tests displayed different equilibrium uptakes for each target compound depending on the properties of each carbon type. Chemically activated carbons demonstrated a higher adsorption capacity and higher selectivity for bulky siloxanes, being the most suitable adsorbents for biogas upgrading. The performance of the adsorbents was also investigated in the presence of moisture, which enable siloxane hydrolysis reactions in the carbon surface, leading to the formation of α-ω-silanediols, especially on phosphoric acid-activated carbons.The technical implications of this work are discussed in terms of biogas volume treated per volume of adsorbent at the first siloxane breakthrough. Phosphoric acid activated carbons are capable of treating higher number of bed volumes, reducing the costs associated to the adsorbent replacement.

PEMURNIAN BIOGAS DENGAN SISTEM BERLAPIS MENGGUNAKANN Fe2O3, ZEOLIT SINTETIK DAN ZEOLIT ALAM

Abstract: Biogas purification process aims to reduce biogas impurities such as carbon dioxide (CO2) and hydrogen sulfide (H2S) to obtain higher methane (CH4) concentration. Adsorption is one method for purifying biogas using solids. The research used 3 adsorbent materials such as natural zeolite mordenite, synthetic zeolite 3A and Fe2O3. To maximize the performance of natural zeolite as adsorbent, it is necessary to activate with NaOH solution which NaOH concentration used is 0%, 5%, and 15% NaOH and then they were activated by physical activation under heating treatment at 250oC for 4 hours. The best biogas purification result with natural zeolite activation mode was obtained at activation of 5% NaOH and followed by 15% and 0% NaOH. This is because activation using NaOH with 1-2N concentration (molarity) led to a macro pore size of the zeolite, more uniform, and the pores on the micro pore can be cleaned. After obtaining the best quality of natural zeolite, a study on the adsorbent ratio of adsorbent tubes obtained from the best results in Fe2O3, synthetic zeolite and natural zeolite (1: 1: 2) was observed because the ability of natural zeolite adsorption is better than of synthetic zeolite and Fe2O3. Therefore, the more natural zeolite in the adsorbent tube the better the refining result.

Performance analysis of a pressure swing adsorption unit in removing biogas impurities using zeolite 13X

This study aims to assess the performance of a Pressure Swing Adsorption (PSA) unit in removing the carbon dioxide from biogas by evaluating the breakthrough and adsorption capacity of the adsorption process as well as determining the effects of cyclic regeneration of the adsorbent. The PSA system developed and composed only a main vessel made up of 316 stainless steel components. It was then operated up to 10 bars pressure at ambient temperatures and gas flows at a rate from 0 to 15 L min-1. Use of physical adsorbent (zeolite 13X) will consume the gaseous impurities such as CO2. Product gas was collected into 1 L Tedlar bags and analyzed using SRI gas chromatograph with TCD and HID detector to validate the CO2 and CH4 composition. The results of the pressure swing adsorption (PSA) experiments showed an average increase of 160% in the net heating value over that of a certified gas standard. The amount of methane was also significantly higher although the amount of the other gasses (i.e. nitrogen) remained comparatively the same. The number of other gases was significantly lower and leaving no traces of carbon dioxide was observed in the PSA system product gas indicating that carbon dioxide had been completely adsorbed by the system. This study greatly helps to reduce CO2 emitted to the atmosphere from the anaerobic co-digestion of biogas to produce high energy content bio-methane fuel.