Biogas Purification Research Articles

Towards net-zero: CO2 capture and biogas purification through electric potential swing desorption to achieve SDGs 7 and 13

Currently, the potential of biomethane derived from biogas is substantial, positioning it to fulfill a considerable share of the United Kingdom’s total energy needs. The primary challenge associated with raw biogas lies in purifying it to produce biomethane, a process that necessitates the removal of carbon dioxide and hydrogen sulfide. Among the various methods, adsorption of activated carbon (AC) stands out as a particularly effective and cost-efficient approach for converting biogas into biomethane, provided that the regeneration of AC proves economically viable. In this research, a segment of activated carbon was utilized to assess the adsorption properties when exposed to a gas mixture of CO2, H2S, and N2 within a regenerative activated carbon setup. This investigation encompassed the analysis of adsorption and desorption behaviors, process capacities, and the impact of regeneration. To enhance the adsorption of CO2, electro-conductive polymers (ECPs) were incorporated into the AC samples, leading to an extension in breakthrough time. Subsequent to adsorption, the electric potential swing desorption (EPSD) was employed for in situ regeneration of activated carbon samples, involving potentials of up to 30 V. The findings exhibited that the newly introduced EPSD technique considerably diminished desorption durations for both H2S and CO2. Moreover, it successfully rejuvenated the accessible adsorption sites, resulting in reduced desorption times compared to the initial breakthrough time during adsorption. Consequently, the EPSD system proves to be a promising candidate for in situ regeneration of activated carbon to eliminate CO2 and H2S from biogas. Notably, this approach offers inherent advantages over conventional methods including thermal swing adsorption (TSA) and pressure swing adsorption (PSA) in terms of regeneration. The demonstrated method underscores the potential for more efficient and economically viable cycles of adsorption and desorption, thereby enhancing the overall biogas-to-biomethane conversion process to achieve SDGs 7 and 13 for clean and green energy applications.

Innovative design and operational strategies to improve CO2 mass transfer during photosynthetic biogas upgrading

Several innovative strategies of design and operation, such as biogas recirculation, centrate pH manipulation and liquid nanoparticle addition, were tested to assess their potential to improve CO2 mass transfer during photosynthetic purification of biogas in a microalgae-bacteria pond connected to a biogas scrubbing column. Biogas recirculation in the column was not effective since the biogas and cultivation broth had reached chemical equilibrium under the operational conditions and configuration without biogas recirculation. Feeding the centrate at pH 10 (with and without ammonium desorption) directly to the absorption column substantially improved CO2 removal efficiency (from 58 to 91 %) achieving a biomethane complying with European standards. The supplementation of liquid nanoparticles considerably increased biomass concentration in the pond (from 1.2 to 3.5 g/L), revealing an enhanced photosynthetic activity. However, this promising approach requires additional research to elucidate the best conditions to boost CO2 absorption and guarantee a biomethane fulfilling most international standards.

Hierarchical nanocomposites derived from UiO-66 framework and zeolite for enhanced CO2 adsorption

In this study, a new nanocomposite composed of zeolite Y incorporated into the UiO-66 framework has been synthesized by solvothermal growth of UiO-66 on the support of zeolite Y, and investigated for CO2 adsorption and separation of CO2/CH4 gas mixtures. The aim of this work was to increase the CO2 uptake and the selectivity of the base framework, as well as to increase its thermal stability. Various weight ratios of UiO-66/zeolite Y were prepared to achieve the optimal composition subject to the highest adsorption capacity. The formation of UiO-66/zeolite Y nanocomposites was verified with different characterization methods. It was observed that UiO-66/zeolite Y with a weight ratio of 90:10 has the same morphology as pristine UiO-66 but with superior porosity. Compared to base UiO-66, its surface area and micropore volume increased by about 80 % and 50 %, respectively. Moreover, the results indicate a substantial improvement of 50 % in the CO2 adsorption capacity of nanocomposite (14.6 mmol/g, 298 K, 30 bar) compared to pristine UiO-66. To our knowledge, the newly synthesized nanocomposites exhibited the record-highest CO2 adsorption capacity among the reported UiO-66 composites. The predicted CO2/CH4 adsorption selectivity of the nanocomposite based on IAST is also higher than that of the pristine MOF. Finally, the cyclic adsorption/desorption test revealed more than 95 % desorption efficiency after ten cycles. Due to the high capacity, selectivity, and reversibility of CO2 adsorption on the UiO-66/zeolite Y, and also the high thermal stability of the nanocomposite, it is suggested as an excellent potential adsorbent for the practical application of biogas and natural gas purification. Furthermore, this contribution also presents an insight into the role of zeolite Y in the nanocomposite framework which could comprehend pore size distribution control by varying its amount.

Corn ethanol production with thin stillage anaerobic digestion for bioenergy recovery: A technical and economic evaluation

The generation of bioenergy from thin stillage in a corn ethanol mill provides a new perspective for the use of by-products in a circular economy concept. Alternative technological routes for the corn ethanol by-products energy and nutrients recovery must be investigated to assess present and future decision-making toward economic and environmental indicators. The theoretical biogas production from an up-flow anaerobic sludge blanket (UASB) reactor in a corn-ethanol mill and the potential thermal and electrical power generation along with the avoided greenhouse gas (GHG) emissions were estimated for a large-scale industrial facility. This work aimed to assess the anaerobic digestion (AD) contribution to techno-economic indicators of a corn ethanol mill in three scenarios: 1) Standard corn-to-ethanol mill; 2) AD-CHP - thin stillage AD to produce biogas and its burning in a combined heat and power (CHP) system; 3) AD-BU - biogas purification to obtain and commercialize biomethane. The existent Brazilian market and fuels and biofuel policies place the system without AD in a slightly better position when analyzing financial indicators related to investment return. In contrast, the global energy and mass balances considering thin stillage AD showed that in the AD-CHP scenario, processing 1 ton of thin stillage would produce 10.37 m³ of biogas, which could generate 119.9 MJ of heat and 24.7 kWh of electricity in a CHP system, favoring a greener energy scenario. The energy recovered from biogas returns to the industry, supplying 7.15% of the heat required for steam production and 52.74% of the electricity requirement for industrial processing. As a renewable energy source, biogas would replace fossil sources for energy generation avoiding GHG emissions. Extrapolating the results of the present work to the Brazilian national scale, the biogas yield from the corn-to-ethanol industry would be 179.68 million m³ , the thermal energy generation from biogas could mitigate 125,574.42 ton CO2eq, and the electricity replacement could mitigate 58,193.02 ton CO2eq. Besides the mentioned energy generation and environmental benefits, the financial indicators for the examined scenarios showed that the Brazilian market and public policies related to biogas/biomethane are constraints to overcoming to larger adoption of AD by the corn-to-ethanol industry.

Biogas Purification by Adsorption Method Using Activated Carbon and Zeolite Adsorbents

<p><strong>Abstract.</strong> Biogas is an alternative energy that is formed from the fermentation of organic matter in gaseous form. Biogas consists of several gas mixtures with the main components methane (CH4) and carbon dioxide (CO2) with a small amount of steam. Biogas is an alternative technology that produces environmentally friendly, cheap and renewable fuel because it comes from biomass, organic liquid waste, food scraps, organic waste, leaves and animal manure resulting from the fermentation process. This study aims to purify biogas by adsorption method using activated carbon and zeolite adsorbents to obtain optimal methane gas by varying the biogas flow rate and the amount of adsorbent composition. Variation in the ratio of the amount of adsorbent (activated carbon: zeolite) is 0%:100%, 30%:70%, 50%:50%, 70%:30%, 100%:0% and the flow rate variation used is 0.2 liter/minute, 0.4 liter/minute, and 0.6 liter/minute. From the purification results, an analysis of the gas content contained in the biogas was carried out using a gas analyzer. The results showed that the best flow rate was the smallest flow rate, which was 0.2 liter/minute, and the best variation in the amount of adsorbent was 0%:100% adsorbent (activated carbon: zeolite) with 81.40% methane content.</p><p align="left"><strong>Keywords:</strong></p><p align="left">Biogas, Activated Carbon, Zeolie, Adsorption, Purification,</p>

Adsorption of Carbon Dioxide and Methane on Cobalt Gallate-Based Metal-Organic Framework (Co-Gallate): Equilibrium Isotherm, Thermodynamic and Kinetic Studies

Biogas is mainly consisted of methane and carbon dioxide in the presence of other contaminants. The biogas purification by adsorption using metal-organic frameworks is getting attention due to the low-cost operation and high-efficiency process. Co-gallate was predicted to give a promising performance in CO2 and CH4 adsorption. However, the behaviours of CO2 and CH4 adsorption on Co-gallate are not well-explained. Therefore, this work is to synthesize Co-gallate and its performance was discussed in terms of adsorbed amount of CO2 and CH4. The experimental CO2 and CH4 pure adsorption isotherms were then fitted with equilibrium isotherm and kinetic models to describe the adsorption behaviours. Co-gallate offered a greater CO2 adsorption capacity than CH4 due to a stronger adsorbent-adsorbate interaction. The experimental pure adsorption isotherms were best fitted with Toth model compared to Langmuir, Freundlich and Sips models according to the values. Toth model described the CO2 adsorption was multilayer and heterogeneous. Thermodynamic property suggested the CO2 and CH4 adsorption were classified as exothermic process and physisorption. For kinetic models, pseudo-first order model brought the highest goodness-of-fit in terms of rate of adsorption compared to pseudo-second order and Elovich models. Pseudo-first order model reflects the adsorption rate is proportional to the number of vacant sites. It confirmed CO2 adsorption was more favourable than CH4, at lower temperature condition. In this work, the equilibrium isotherm and kinetic models were employed to select the best-fitted model in explaining the adsorption behaviours. Therefore, these behaviours of CO2 and CH4 adsorption on Co-gallate are useful in designing the future practical operation of CO2/CH4 gas adsorption.

Optimization of Biogas Purification Employing High-Pressure Water Scrubbing

Purification of biogas is the pre-requisite of the commercial application of anaerobic digestion in the renewable energy sector. In this study, Aspen Plus V11.1 was used to determine the optimum process conditions for biogas purification using high-pressure water scrubbing. The non-random two-liquid model (NRTL) coupled with Henry' s law was used as the fluid package in this study. According to henry' s law solubility of CO2 is higher than CH4 and thus water was used as an adsorbent. The ideal parameter values for the scrubber were as follows: water pressure: 8 atm, biogas temperature: 37°C or 55°C, scrubber stages: 15, water to biogas mass flowrate ratio: 50. The composition of the biogas i. e., CH4 and CO2 mole fractions can vary in a wide range without effecting the efficiency of the process.

Energy Utilization of Sewage Sludge Using High-Solids Anaerobic Digestion and Biogas Purification

Energy Utilization of Sewage Sludge Using High-Solids Anaerobic Digestion and Biogas Purification

Preparation And Characterization of MCM-41 Membrane for Biogas Purification

Preparation And Characterization of MCM-41 Membrane for Biogas Purification

Optimization of hydrogen sulfide adsorption performance by tar based porous carbon prepared by template method

This study provides a method of preparation of tar based porous carbon (TPC) for H2S adsorption by high-temperature carbonization with tar as precursor and zinc chloride (ZnCl2) as template. Response surface methodology (RSM) was used to systematically investigate the effects of carbonization temperature, mass percentage of template and carbonization time on the cumulative adsorption (CAC) of H2S. The adsorption kinetics and isotherms, thermodynamics, and TPC’s properties were explored to obtain its adsorption mechanism on H2S. The results demonstrate that TPC was a microporous material with a rich surface functional group structure. The specific surface area and pore volume of the optimal sample (TPC-750-66-90) could reach 890.08 m2/g and 0.440 cm3/g, respectively, accompanied by a CAC of 34.01 mg/g. FTIR and XPS analysis results indicate that there were abundant oxygen- and nitrogen-containing groups on the surface of TPC, which helped to promote the chemisorption on H2S. The adsorption kinetics and isotherms fitting and thermodynamic calculation of H2S adsorption demonstrate that both physisorption and chemisorption played important roles, and the adsorption was a spontaneous, exothermic, random, and monolayer process. According to the regeneration tests, TPC could maintain at least 70% of its initial capacity after three rounds of regeneration. All the above results demonstrated that porous carbon preparation through high-temperature carbonization is a promising method for tar utilization, and the prepared porous carbon as adsorbent for gas pollutants like H2S has wide application potential in areas including kitchen trash, sewage treatment facilities, and biogas purification.

CO2 and H2S Absorption in Tofu Liquid Waste Biogas using Packed Bed Scrubber with Variation of MEA Concentration and Flow Rate

Biogas technology has become an alternative fuel that is often used in Indonesia. One of the raw materials for biogas that has the potential and is easy to obtain is waste from the tofu industry. Liquid waste still contains a lot of organic elements. The organic materials contained in the exhaust of the tofu industry are generally very high. The gases commonly found in tofu waste are nitrogen gas (N2), oxygen (O2), hydrogen sulfide (H2S), ammonia (NH3), carbon dioxide (CO2) and methane (CH4). These gases come from the decomposition of organic materials contained in wastewater. So that biogas produced from tofu liquid waste still contains CO2 and H2S gases which are quite high. Therefore, in this study the process of purification or refining of biogas products will be carried out using the absorption method through an absorber column using monoethanolamine (MEA) solution as a chemical absorbent through a 8 mm packed bed scrubber. The results showed that the best biogas flow rate in the purification process which produced the highest CH4 concentration of 95.12% was 40% MEA concentration and 0.8 L/min flow rate. The effect of MEA concentration on biogas purification causes the concentration of CO2 and H2S in the purified biogas to decrease as the MEA concentration increases. The best combination of 0.8 L/min biogas flow rate and 10 mm packing area reduces CO2 and H2S concentrations to 1.88% and 0 ppm.

Understanding the influences of different associated gas impurities and the kinetic modelling of biogas hydrate formation at the molecular scale

The biological degradation of organic waste generates biogas that mostly comprises a mixture of CH4 and CO2. The separation of CO2 and other gas impurities from CH4 using a hydrate-based technique has recently gained interest as an option. The captured CO2 and impurities can then be sequestered in natural gas hydrate (NGH) geological sites leading to an exchange of the in situ CH4 hydrate over to CO2-dominated hydrate and a simultaneous CH4 release from these huge natural sources of energy in permafrost sediments. Consequently, the effects of associated gas impurities such as SO2, H2S, N2, and H2 on either hydrate-based biogas purification or residual sequestration in NGH deposits need to be well-understood. In this work, the influence of different biogas compositions on the process of clathrate hydrate formation using molecular dynamics (MD) simulations was investigated. Additionally, a kinetic model for predicting the progress of biogas crystal growth based on the formation of the number of hydrogen bonds as well as total energy is proposed. The results elucidate that the concentration of dissolved gas in liquid water at the solid-solution interface is one of the key controllers of the growth rate but it has less impact on the filling percentage of formed both types the clathrate hydrate cages. The presence of H2S and SO2 molecules was found to slightly increase the formation of biogas hydrate. On the other hand, N2, and H2 molecules reduce the rate of biogas hydrate generation.

Model development for biogas generation, purification and hydrogen production via steam methane reforming

Biogas, a renewable energy source produced by the anaerobic digestion of organic matter, can reduce greenhouse gas emissions. The purification and hydrogen conversion of biogas enhance its versatility as an energy carrier and reduce dependency on fossil fuels. This sustainable process fosters a cleaner future. In this study, simulation models were used to optimize the process conditions and assess the technical feasibility of the biogas-to-hydrogen production. In addition to the anaerobic digestion process, simulation models were also developed for biogas purification via water scrubbing and hydrogen production via steam methane reforming (SMR) using Aspen Plus simulation software. Simulation results demonstrated that the maximum methane yield of 520 mL/gVS was achieved at an organic loading rate of 20 g/L, while the minimum yield of 230 mL/gVS was observed below 10 g/L. Optimal anaerobic digestion temperature for maximum gas yield (548 mL/gVS) was found to be 30 °C, with a decrease in biogas production above 40 °C. In the water scrubbing model, maximum CO2 absorption occurred at 15 bar pressure, whereas reducing the pressure to 5 bar significantly lowered the absorption rate. The SMR model yielded the highest hydrogen production rate of 10.15 kg/h using purified methane (99%) as feed, but the methane content was affected by the biogas composition.

Solar-assisted approach for the synthesis of nanoadsorbents for biogas desulfurization using wastes

Minimizing food wastes and finding a second life use for industrial residuals have become some of the top priorities of modern society. This work considers the use of spent eggs and mussels shells, as well as marble dust, as raw sources to develop nanoparticles involving renewable resources in both their preparation and adoption in technological applications. Specifically, Ca/Mg-based nanoparticles were obtained by evaporating such wastes in a physical vapor deposition system using concentrated solar beam and explored as high capacity H2S adsorbents for the purification of biogas. The evaluation of their uptake performance in a fixed-bed configuration indicates that the formation of a thick layer of Ca(OH)2 on very small nanoparticles (<70 nm) inhibits H2S uptake, whereas the presence of Mg phases (dolomite) favors its potentiation. Importantly, the co-evaporation of iron provides an extra amplification of the absorption capacity due to the synergy of the Ca/Mg neutralizing character and the affinity of Fe for sulfur. In the best case, the nanoparticles obtained from mussels and 10 %wt. Fe reached an uptake capacity of 0.92 mg/g. This high yield is attributed to the formation of oxides, such as Ca2Fe2O5, that allow a sulfide to sulfate oxidation-adsorption mechanism.

Robust and Transparent Polyamide 1012 Membranes for Biogas Purification Controlled by the Degree of Hydrogen Bonding Order

Robust and Transparent Polyamide 1012 Membranes for Biogas Purification Controlled by the Degree of Hydrogen Bonding Order

ANALYSIS AND EVALUATION OF THE BIOGAS PURIFICATION TECHNOLOGIES FROM H2S

H2S concentrations in biogas are limited by environmental regulations. Because these gases are toxic to human health, cause corrosion, and damage the combined heat and power (CHP) engines and other metallic parts after burning. Hence, the following requirements must be met by a biogas purification method: 1 – high H2S removal efficiency (RE), 2 – stability over a long period of time, 3 – low cost, 4 – minimal biogas dilution, and 5 – straightforward structure. There are various physical, chemical, and biological technologies, which can be undertaken to meet earlier mentioned criteria and efficiently remove H2S from biogas. In this study, electrochemical oxidation, adsorption by zeolite, pressure swing adsorption, adsorption on activated carbon, adsorption on metal oxides, adsorption on nano-particles, metal sulfide precipitation, water scrubbing, membrane separation, organic solvents (amine), microaeration, and purification by sulfur-oxidizing bacteria (anoxic, aerobic, anaerobic), will be introduced, while their pros and cons are compared and discussed in detail.

Pathways for the thermally optimal design and practice of anaerobic digestion in large-scale biogas plants: Heat transfer modeling and energy analysis

A flexible and configuration-dependent heat model framework is developed, validated, and used to perform in-depth energy analyses and to identify the optimal design and operating conditions in wet anaerobic digesters in stirred reactors with multi-membrane gasholders in modern biogas plants. This framework enables a detailed geometrical representation of the gasholder and digester at different scales, such that different gasholder designs from single- to multi-membrane systems with varying configurations can be studied and compared to increase thermal efficiency. The model operates in the dynamic regime and includes longwave infrared surface-to-surface heat exchanges. This includes the impact of dynamic environmental conditions (e.g., ambient air temperature, wind, rain, and solar radiation) on the thermal behavior of the unit. Throughout the parametric analyses, the influences of key operating and design parameters, as well as synergistic features such as the feasibility and efficiency of various waste heat recovery strategies, are investigated on the basis of the thermal performance of the digester. The analysis shows that, based on a 3,000-m3 double-membrane biogas plant with a raw biogas self-consumption of 7.4%, thermal autarky can be achieved using (i) a three-membrane gasholder (−2.1%), (ii) outgoing digestate heat recovery (−3.7%), and (iii) recovery of heat from biogas purification (−1.6%).

Simultaneous removal of sulfide and bicarbonate from synthetic wastewater using an algae-assisted microbial fuel cell

ABSTRACT The anaerobic digestion (AD) process is one of the most practiced technologies for the remediation of organic waste and maximization of energy recovery in terms of biogas or biomethane. The presence of other gaseous components in biogas, e.g. CO2 and H2S, often makes its direct application in engines and electricity production unsuitable. This work aimed to develop and utilize an algae-assisted microbial fuel cell (AMFC) for the purification of biogas by removing both CO2 and H2S and simultaneous bioelectricity generation. In addition to biogas clean-up, elemental sulfur recovery and CO2 utilization for algae cultivation add value to the proposed AMFC process. Experiments were performed with both sulfide and bicarbonate in their dissolved form, in the respective anodic and cathodic chambers of the AMFC. The sulfide concentration was varied from 100 to 800 mg/l and the AMFC exhibited a sulfide removal efficiency exceeding 97% at all concentrations tested. The process efficiency dropped, however, at sulfide concentrations above 300 mg/l in terms of both sulfide removal and power output. The AMFC performed best at 400 mg/l sulfide by exhibiting a power density of 24.99 mW/m3 and sulfide removal efficiency of 98.87%. The system exhibited columbic efficiency (CE %) in the range of 7.85–80%. The total alkalinity representing CO2, carbonate and bicarbonate levels in the algae-based system was reduced by 49.54%. The electrical energy recovered from the AMFC was 0.1 kWh/m3 and the total energy recovery, which is the sum of the electrical and algal lipid energy, amounted to 7.25 kWh/m3.

Unveiling the potential of composite water-swollen spiral wound membrane for design of low-cost raw biogas purification

The present study aims to verify a novel purification method for raw biogas using water-swollen composite membranes. In two module configurations, we generated water-swollen polymer gel layers on thin-film composite membranes to separate methane from other biogas species. The primary driving force of the biogas separation is the solubility differences between major biogas species. The carbon dioxide solubility, many times higher than methane, effectively rejected methane from the water-swollen membranes and resulted in the retentate concentration of 97 vol% methane for raw biogas and 98 vol% for synthetic gas. Two membrane modules connected in parallel increased the methane recovery ratio up to 58 %. At a pressure of 3 bar the water-swollen membrane proved efficient in desulfurizing feed biogas producing an outlet stream containing a low concentration of H2S of an order of 10 ppmv.

Design studies of a pure hydrogen production plant from biogas

The present paper focus in design studies of a process for pure hydrogen production at decentralized scale. 9000 Nm3/h biogas are proposed as feedstock to the process. The plant includes a biogas-to-biomethane purification unit, a convective reformer equipped with bayonet-type tubes, a Pd-based membrane reactor profiting simultaneous hydrogen extraction and extra hydrogen production via water-gas shift, a combustion chamber and auxiliary units. Three optimization scenarios were considered where the hydrogen production is maximized and reformer and membrane reactors areas are minimized using different weights. All designs are fully thermally integrated aiming self-sustainability in terms of energy. To these ends, the retentate of the membrane reactor and the permeate of the biogas purification unit are both used as fuel to the combustion chamber. Results show the feasibility of operation with an overall thermal efficiency for the process of ca. 77.0–77.5% (based on LHV), comparable with values reported for processes of similar scale.