Gas Removal Research Articles

Déjà vu all over again: Greenhouse gas (GHG) removals and legal liability

Déjà vu all over again: Greenhouse gas (GHG) removals and legal liability

Review of Plasma Technologies for Contribution of Environmental Purification

Since the beginning of the 20th century, plasma technology has been used in a variety of fields. In the 1980s, R&D related to arc plasma welding and waste disposal, as well as etching, painting, and gas removal equipment that used plasma technology in the processes associated with semiconductor manufacturing. In the 1990s, research on removing air pollutants using atmospheric pressure plasma technology became active. In the 2000s, research on the application of thermal/non-thermal plasma technology to air pollution, waste and water treatment became active. Electrostatic precipitators (ESP) can remove a wide variety of particles such as soot from thermal power plants, coal, and oil mist, resin powder, glass powder, dust, and iron powder generated from incinerators, boilers, and various manufacturing plants. Waste treatment aims to reduce the volume of garbage, recycle incinerated materials, and utilize waste heat from incineration, and plasma technology is used in each process. Various techniques have been used for making purified water. Water quality requirements vary according to the objective. Plasma technology uses an electrical field to encourage seed germination and growth. Due to the spread of such applied technology, plasma technology has attracted attention again in recent years.

Data-driven Models for Advanced Control of Acid Gas Treatment in Waste-to-energy Plants

This paper presents a study of identification and validation of data-driven models for the description of the acid gas treatment process, a key step of flue gas cleaning in waste-to-energy plants. The acid gas removal line of an Italian plant, based on the injection of hydrated lime, Ca(OH)2, for the abatement of hydrogen chloride, HCl, is investigated. The final goal is to minimize the feed rate of reactant needed to achieve the required HCl removal performance, also reducing as a consequence the production of solid process residues. Process data are collected during dedicated plant tests carried out by imposing Generalized Binary Noise (GBN) sequences to the flow rate of Ca(OH)2. Various input-output and state-space models are identified with success, and related model orders are optimized. The models are then validated on different datasets of routine plant operation. The proposed modeling approach appears reliable and promising for control purposes, once implemented into advanced model-based control structures.

ОЦЕНКА ЗАПАСОВ ОРГАНИЧЕСКОГО УГЛЕРОДА В ПОЧВЕННОМ ПОКРОВЕ ОСТРОВНЫХ ЭКОСИСТЕМ КУЙБЫШЕВСКОГО ВОДОХРАНИЛИЩА

Assessment of organic carbon stocks in soils and other components of ecosystems are becoming increasingly important as a necessary reference point for a reliable determination of the amount of greenhouse gas removals at country scale. The gradual tightening of carbon balance requirements dictates the urgency of the problem under consideration. The aim of the work was to assess the stocks of organic carbon in the soils of the islands of the Kazan region of the variable backwater of the Kuibyshev reservoir in the 0–20 cm layer, and also to determine which type of soils makes the greatest contribution to the sequestration of carbon. The reserves of organic carbon in the soils of the islands of the Kuibyshev water reservoir were determined in the area from the Zelenodolsk – Nizhnie Vyazovye bridge (55°49’27.1 «N; 48°31’05.6″E) to the islands in front of the Teteyevo village (55°24’11.8 «N; 49°07’59.6» E). Surveys of the islands’ soil cover and selection of the soil samples were carried out in 2018-2019. The calculation of the organic carbon content was carried out for the 0–20 cm layer. The calculations took into account the total carbon content in the organogenic, organic-mineral and mineral horizons. It was found that the highest carbon content in the upper soil layer was observed in the profile of marsh-podzolic soils – 51.7 t / ha. The lowest organic carbon content was noted in sod-alluvial soils (12.0 t / ha) and artificial sandy deposits (3.8 t / ha). Carbon stocks in soil profiles and proportion of carbon in organogenic horizons increased with increasing of hydromorphic properties in the following row: 1) sod-podzolic soil < marsh-podzolic soil; 2) light gray forest soil < gray forest gley soil; 3) sod-alluvial soil < alluvial meadow-marsh soil < marsh-alluvial soil. The total reserves of organic carbon in the islands’ soils were calculated taking into account the areas occupied by individual soil contours. The total stock of organic carbon in the 0–20 cm layer of the studied area of the water reservoir was 49,190.9 tons. About 83 % of the total stock of organic carbon stored in the form of humus of accumulative mineral horizons and only 17 % in the organogenic and organic-mineral horizons. It was shown that alluvial meadow-marsh (23,125.9 t) and sod-podzolic soils (8,957.5 t), occupying the largest areas on the territory of the islands, make the largest contribution to the organic carbon reserves. An interesting point is that on the islands of floodplain origin, a greater contribution to the total humus reserves was made by soils with pronounced hydromorphic properties – alluvial meadow-marsh soils and alluvial meadow soils. On the islands of terrace origin, the bulk of carbon was concentrated in automorphic soils. A possible reason is the features of the islands’ relief of different origins. Reasonable data on the rate of organic carbon accumulation were obtained only for alluvial marsh soils, the organogenic horizon of which was formed after the creation of the reservoir – 390 kg / ha annually. Flooded soils are the most promising reservoirs for organic carbon deposition from greenhouse gases. Thanks to the research carried out using accurate GPS referencing of soil profiles, the islands’ soils are becoming a very valuable object for monitoring the rate of organic carbon accumulation, the volume of absorption of greenhouse gases and the increase in total organic carbon stocks.

Difference in VMAT dose distribution for prostate cancer with/without rectal gas removal and/or adaptive replanning.

We investigated differences in the volumetric-modulated arc therapy (VMAT) dose distribution in prostate cancer patients treated by rectal gas removal and/or adaptive replanning. Cone-beam computed tomography (CBCT) scans were performed daily for 22 treatments in eight prostate cancer patients with excessive rectal gas, and the CBCT images were analyzed. Rectal gas removal was performed, and irradiation was delivered after prostate matching. We compared dose-volume histograms for the daily CBCT images before and after rectal gas removal. Plan A was the original plan on CBCT images before rectal gas removal. Plan B was a single reoptimized plan on CBCT images before rectal gas removal. Plan C was the original plan on CBCT images after rectal gas removal. Plan D was a single reoptimized plan on CBCT images after rectal gas removal. D95 of the planning target volume (PTV) minus the rectum of Plan C (94.7% ± 6.6%) was significantly higher than that of Plan A (88.5% ± 10.4%). All dosimetric parameters of Plan C were improved by rectal gas removal compared with Plan A, regardless of the initial rectal gas volume. Dosimetric parameters of PTV minus the rectum of Plan B were significantly improved compared with Plan C. Additionally, the V78 of the rectal wall of Plan B (0.2% ± 0.5%) was significantly improved compared with Plan C (3.9% ± 6.3%, p = 0.003). The dosimetric parameters of Plan D were not significantly different from Plan B. The dose distribution of prostate VMAT was improved by rectal gas removal and/or adaptive replanning. An adaptive replanning on daily CBCT images might be a better method than rectal gas removal for prostate cancer patients with excessive rectal gas.

Prediction of vapour-liquid equilibrium ratios for the CH<SUB align="right">4-CO<SUB align="right">2-H<SUB align="right">2S systems using artificial neural networks

Acid gas removal is an important part of natural gas processing which is designed based on the type and concentration of impurities and the final specifications for the outlet gas. The typical process for removing acid gas involves their absorption from natural gas into a regenerative solvent. The efficiency of this process is affected by the mass transfer process between gas and liquid phases; so, it is necessary to study the phase equilibrium encountered in acid gas mixtures at different pressures and temperatures. In this work, an artificial neural network (ANN) has been developed to predict the vapour-liquid equilibrium ratio (KLV) for the CH4-CO2-H2S binary and ternary systems. Results show that a neural-network-based method provides an accurate estimation (93-98%) of KLV while considering all affecting parameters, compared to limited reported correlations. This work can be considered as an introduction to using ANNs for predicting the physical properties of mixtures. [Received: March 7, 2020; Accepted: March 10, 2021]

Performance Analysis of the Acid Gas Removal from Syngas Based on Self-Heat Recuperation Technology

Performance Analysis of the Acid Gas Removal from Syngas Based on Self-Heat Recuperation Technology

Performance Evaluation of Pressurized Anaerobic Digestion (PDA) of Raw Compost Leachate

Anaerobic digestion (AD) represents an advantageous solution for the treatment and valorization of organic waste and wastewater. To be suitable for energy purposes, biogas generated in AD must be subjected to proper upgrading treatments aimed at the removal of carbon dioxide and other undesirable gases. Pressurized anaerobic digestion (PDA) has gained increasing interest in recent years, as it allows the generation of a high-quality biogas with a low CO2 content. However, high pressures can cause some negative impacts on the AD process, which could be accentuated by feedstock characteristics. Until now, few studies have focused on the application of PAD to the treatment of real waste. The present work investigated, for the first time, the performance of the pressurized anaerobic digestion of raw compost leachate. The study was conducted in a lab-scale pressurized CSTR reactor, working in semi-continuous mode. Operating pressures from the atmospheric value to 4 bar were tested at organic loading rate (OLR) values of 20 and 30 kgCOD/m3d. In response to the rise in operating pressure, for both OLR values tested, a decrease of CO2 content in biogas was observed, whereas the CH4 fraction increased to values around 75% at 4 bar. Despite this positive effect, the pressure growth caused a decline in COD removal from 88 to 62% in tests with OLR = 20 kgCOD/m3d. At OLR = 30 kgCOD/m3d, an overload condition was observed, which induced abatements of about 56%, regardless of the applied pressure. With both OLR values, biogas productions and specific methane yields decreased largely when the pressure was brought from atmospheric value to just 1 bar. The values went from 0.33 to 0.27 LCH4/gCODremoved at 20 kgCOD/m3d, and from 0.27 to 0.18 LCH4/gCODremoved at 30 kgCOD/m3d. Therefore, as the pressure increased, although there was an enhanced biogas quality, the overall amount of methane was lowered. The pressured conditions did not cause substantial modification in the characteristics of digestates.

Modeling of H2S solubility in ionic liquids using deep learning: A chemical structure-based approach

Hydrogen sulfide (H2S) is a toxic, flammable, corrosive, and acidic gas that can have harmful impacts on the environment. Ionic liquids (ILs) are relatively new solutions that have desirable characteristics such as high thermal and electrochemical stabilities, negligible vapor pressure, non-combustibility, and high solubility, allowing them to be an appropriate choice of liquid solvents in gas removal processes. In this study, deep learning (DL) approaches were utilized to predict the H2S solubility in ionic liquids (ILs). The proposed models include convolutional neural network (CNN), recurrent neural networks (RNNs), deep belief networks (DBN), and deep neural network initialization with decision trees (DJINN). To this end, a large databank in a broad range of pressure and temperature encompassing 1516 data points of H2S solubility in 37 various ILs was used for developing models. In these models, the chemical structure of ILs, temperature, and pressure were considered as the model’s inputs, while H2S solubility was the model’s output. The results reveal that the CNN model provides more accurate, rapid, flexible, and inexpensive estimations for H2S solubility in ILs with an average absolute percent relative error (AAPRE) of 2.92% and a determination coefficient (R2) of 0.99. The results were then compared to those of previously proposed techniques in the literature. According to the results of the sensitivity analysis, it was found that pressure and OH (as substructure) impose the highest positive and the highest negative impacts on the solubility of H2S in ILs, respectively. Also, based on sensitivity analysis, temperature has a reverse effect on the solubility of H2S and with increasing temperature, the H2S solubility decreases. The Taylor diagram illustrated that the CNN approach is very efficient, accurate, and realistic for predicting the solubility of H2S in diverse ILs based on the chemical structure, pressure, and temperature. Finally, trend analysis revealed that the trends of CNN predictions are in great agreement with the measured data of H2S solubility in ILs as a function of pressure. The findings of this work may be used not only to overcome the difficulties of calculating H2S solubility in ILs, but also to develop novel and accurate forecasting algorithms for a large dataset that cover a broad range of temperatures and pressures.

Taking deliberative research online: Lessons from four case studies

Researchers using deliberative techniques tend to favour in-person processes. However, the COVID-19 pandemic has added urgency to the question of whether meaningful deliberative research is possible in an online setting. This paper considers the reasons for taking deliberation online, including bringing people together more easily; convening international events; and reducing the environmental impact of research. It reports on four case studies: a set of stakeholder workshops considering greenhouse gas removal technologies, convened online in 2019, and online research workshops investigating local climate strategies; as well as two in-person processes which moved online due to COVID-19: Climate Assembly UK, a Citizens’ Assembly on climate change, and the Lancaster Citizens’ Jury on Climate Change. It sets out learnings from these processes, concluding that deliberation online is substantively different from in-person meetings, but can meet the requirements of deliberative research, and can be a rewarding and useful process for participants and researchers alike.

Hydrodynamics of an Airlift Column for Aeration in Molten Sulfur

The airlift column is a promising technology for the removal of volatile gas from high-viscosity molten sulfur. However, a detailed analysis is lacking on the hydrodynamic properties inside the column, due to the difficulty in flow behavior detection in the opaque molten sulfur. In this work, we adopted the computational fluid dynamics simulation to understand the hydrodynamic behaviors in an airlift column for molten sulfur aeration. In addition, we analyzed the impacts of the superficial gas velocity (UGr) and column height on the hydrodynamic characteristics, such as gas holdup, average bubble diameter, and liquid circulation velocity (ULr) in the column. The simulation shows that at a constant column height of 15 m, an increase on gas holdup can be obtained with the increase of the superficial gas velocity, while the bubble diameter remains almost constant. Once the superficial gas velocity exceeded 0.333 m/s, the liquid circulation velocity increased slowly. With a variation on the column height from 5 to 25 m, a negligible change on gas holdup, but an obvious increase on liquid circulation velocity and bubble diameter is observed at the given superficial gas velocity of 0.0389 m/s. Furthermore, the simulation shows a similar trend, but with considerably more detailed information, on the relationship between the gas holdup and liquid circulation velocity when compared to the predictions from the Chisti correlation (1988) and an optimized correlation proposed in this work.

Оцінка летучих викидів у газовій галузі України з врахуванням Уточнень 2019 р. до керівних принципів МГЕЗК 2006 р. з національних інвентаризацій парникових газів

The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 to assess the risks and possible consequences of anthropogenic climate change. The IPCC includes a task force on national inventories, which develops methodological documents for national greenhouse gas inventories. The report 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories was adopted and accepted during the 49th Session of the IPCC in May 2019. The development of 2019 Refinement is related to the improvement of existing and the emergence of new technologies in the world economy, which has led to the need to update emission parameters and take into account new sources of greenhouse gas emissions and removals. The purpose of the article is to study and apply changes in the methods of estimating fugitive emissions in Ukraine’s gas industry, taking into account 2019 Refinement to the 2006 IPCC Guidelines for national greenhouse gas inventories. The article examines the state of greenhouse gas emissions in the gas industry in 2019 according to the Ukraine’s Greenhouse Gas Inventory Report data. The formation methane and carbon dioxide fugitive emissions in the last National Inventory Report according to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories is analyzed. The changes in the methods for national inventories in the energy sector 2019 Refinement are compared to the 2006 IPCC Guidelines. The estimation methane and carbon dioxide fugitive emissions in Ukraine’s gas industry in 2019 according to 2019 Refinement is made (taking into account the new emission factors and a new subcategory of abandoned wells). The article provides a comparative analysis the results with fugitive emissions in the gas industry in 2019 according to data of National Inventory Report. A study of the results shows that the use of 2019 Refinement for future greenhouse gas inventories will reduce methane and carbon dioxide emissions. Keywords: gas industry, greenhouse gas emissions, methane, carbon dioxide, inventory

Techno-economic Analysis of Direct Air Carbon Capture with CO2 Utilisation

Carbon capture technologies are crucial for mitigating climate change and play an important role in the net zero roadmap. Recently the greenhouse gas removal (GGR) technology has come under scrutiny as a negative emission solution which will remove CO2 from the atmosphere, either capturing it directly from the air or indirectly via biomass. This study proposed and designed a novel direct air carbon capture process integrated with a solid oxide electrolysis unit for the chemical utilisation of the captured CO2. A detailed techno-economic analysis is performed to determine if the addition of CO2 utilisation is able to offset the high cost of carbon capture. An initial net present value (NPV) and levelised cost of -$4.6B and $382 tCO2−1 were calculated, indicating the unfavourable techo-economics. However, a scenario analysis suggested that in the near future (i.e., in 4-5 years) the NPV could be positive and the levelised cost could be neutral with the advances of technology maturity and the net zero economy. A carbon emissions assessment calculated that during plant operation over 24.2B kg of carbon dioxide would be removed, and hence the real term carbon removal would be approximately 97% of the theoretical maximum.

Attractions of delay: Using deliberative engagement to investigate the political and strategic impacts of greenhouse gas removal technologies

Concerns have been raised that a focus on greenhouse gas removals (GGR) in climate models, scientific literature and other media might deter measures to mitigate climate change through reduction of emissions at source – the phenomenon of ‘mitigation deterrence’. Given the urgent need for climate action, any delay in emissions reduction would be worrying. We convened nine deliberative workshops to expose stakeholders to futures scenarios involving mitigation deterrence. The workshops examined ways in which deterrence might arise, and how it could be minimized. The deliberation exposed social and cultural interactions that might otherwise remain hidden. The paper describes narratives and ideas discussed in the workshops regarding political and economic mechanisms through which mitigation deterrence might occur, the plausibility of such pathways, and measures recommended to reduce the risk of such occurrence. Mitigation deterrence is interpreted as an important example of the ‘attraction of delay’ in a setting in which there are many incentives for procrastination. While our stakeholders accepted the historic persistence of delay in mitigation, some struggled to accept that similar processes, involving GGRs, may be happening now. The paper therefore also reviews the claims made by participants about mitigation deterrence, identifying discursive strategies that advocates of carbon removal might deploy to deflect concerns about mitigation deterrence. We conclude that the problem of mitigation deterrence is significant, needs to be recognized in climate policy, and its mechanisms better understood. Based on stakeholder proposals we suggest ways of governing GGR which would maximize both GGR and carbon reduction through other means.

L-Galaxies 2020: the formation and chemical evolution of stellar haloes in Milky Way analogues and galaxy clusters

ABSTRACT We present an analysis of the formation and chemical evolution of stellar haloes around (a) Milky Way analogue (MWA) galaxies and (b) galaxy clusters in the L-Galaxies 2020 semi-analytic model of galaxy evolution. Observed stellar halo properties are better reproduced when assuming a gradual stripping model for the removal of cold gas and stars from satellites, compared to an instantaneous stripping model. The slope of the stellar mass–metallicity relation for MWA stellar haloes is in good agreement with that observed in the local Universe . This extends the good agreement between L-Galaxies 2020 and metallicity observations from the gas and stars inside galaxies to those outside. Halo stars contribute on average only ∼0.1 per cent of the total circumgalactic medium enrichment by z = 0 in MWAs, ejecting predominantly carbon produced by asymptotic giant branch stars. Around a quarter of MWAs have a single ‘significant progenitor’ with a mean mass of ∼$2.3\times {}10^{9}\, \rm {M}_{\odot }$, similar to that measured for Gaia Enceladus. For galaxy clusters, L-Galaxies 2020 shows good correspondence with observations of stellar halo mass fractions, but slightly overpredicts stellar masses. Assuming a Navarro–Frenk–White profile for the stellar halo mass distribution provides the best agreement. On average, the intracluster stellar component is responsible for 5.4 per cent of the total intracluster medium iron enrichment, exceeding the contribution from the brightest cluster galaxy by z = 0. We find that considering gradual stripping of satellites and realistic radial profiles is crucial for accurately modelling stellar halo formation on all scales in semi-analytic models.

WALLABY pilot survey: H i gas disc truncation and star formation of galaxies falling into the Hydra I cluster

ABSTRACT We present results from our analysis of the Hydra I cluster observed in neutral atomic hydrogen (H i) as part of the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY). These WALLABY observations cover a 60-square-degree field of view with uniform sensitivity and a spatial resolution of 30 arcsec. We use these wide-field observations to investigate the effect of galaxy environment on H i gas removal and star formation quenching by comparing the properties of cluster, infall, and field galaxies extending up to ∼5R200 from the cluster centre. We find a sharp decrease in the H i-detected fraction of infalling galaxies at a projected distance of ∼1.5R200 from the cluster centre from $\sim 85{{\ \rm per\ cent}}$ to $\sim 35{{\ \rm per\ cent}}$. We see evidence for the environment removing gas from the outskirts of H i-detected cluster and infall galaxies through the decrease in the H i to r-band optical disc diameter ratio. These galaxies lie on the star-forming main sequence, indicating that gas removal is not yet affecting the inner star-forming discs and is limited to the galaxy outskirts. Although we do not detect galaxies undergoing galaxy-wide quenching, we do observe a reduction in recent star formation in the outer disc of cluster galaxies, which is likely due to the smaller gas reservoirs present beyond the optical radius in these galaxies. Stacking of H i non-detections with H i masses below $M_{\rm {HI}}\lesssim 10^{8.4}\, \rm {M}_{\odot }$ will be required to probe the H i of galaxies undergoing quenching at distances ≳60 Mpc with WALLABY.

Study of dynamics and mechanism of HCl, SO2, or NO removal by MnO2/Mg–Al layered double hydroxide

The gas exhaust generated by waste incinerators contains toxic acid gases such as HCl, SO2, and NOx, which require appropriate treatment following their release. Although several methods exist for this purpose, they have various drawbacks. Thus, toward the search for a new removal method, the ability of Mg–Al layered double hydroxide (Mg–Al LDH) to eliminate HCl, SO2, and NO gases from simulated exhaust gas was examined. In addition, the impact of the amount of LDH employed was investigated in terms of the toxic gas removal efficiencies and process temperature. Furthermore, the mechanism of removing HCl, SO2, and NO by MnO2/Mg–Al LDH was considered. More specifically, HCl removal proceeded mainly by the reaction of HCl with the CO32− and OH− species present between the Mg-Al LDH layers, while that of SO2 took place through the adsorption of SO2 onto the LDH and MnO2 surfaces. Moreover, NO was removed through the oxidation of NO to NO2 by MnO2, followed by the reaction of NO2 with the CO32− and OH− species present between the Mg–Al LDH layers. These results are expected to help pave the way for the use of Mg–Al LDH to remove toxic acid gases from the gas exhausts of waste incinerators, thereby addressing the various issues related to the use of current technologies.

Decarbonization of the Economy – the General Trend of Development of Russia and Its Regions in the 21st Century

Today the issue of Russia’s low-carbon development and the necessity in cutting down Greenhouse emissions, first of all, carbon dioxide (СO2) is very acute. Over the recent years a lot of documents and regulatory legal acts have appeared in Russia, one way or another related to the decarbonization of the economy, including “National Climate Change Adaptation Plan”, the Decree of the President of the Russian Federation “On Reducing Greenhouse Gas Emissions”, “Strategy for the Long-Term Development of Russia with Low Greenhouse Gas Emissions up to 2050”, draft Federal Law “On State Regulation of Greenhouse Gas Emissions and Removals”, “The Plan for the Development of Hydrogen Energy in Russia up to 2050”. Russia needs a network of carbon landfills, its own non-discriminatory system for measuring the balance of greenhouse gases, this is the most important factor of national security today. In the near future, the system of calculations will be worked out on the territory of seven regions: the Chechen Republic, the Krasnodar Krai, Kaliningrad, Sakhalin, Sverdlovsk, Novosibirsk and Tyumen Regions. Since 2020, a pilot project of a carbon landfill has been implemented in Kaluga Region, on lands located within the borders of the Ugra National Park. To finance these projects, it is necessary to attract funds from national projects, first of all, the NP “Clean Air”. Carbon farms are a complex of technologies that enable the absorption of greenhouse gases, and so far for Russia it is mainly forest rather than agricultural technologies. There are about 11 million square kilometers of forests in Russia, and this is a unique reservoir for absorbing CO2, so the 21st century is the century of Russia, which has every chance to become the most important player in the sequestration industry. It is fundamentally important for Russia to become a world leader and gain a high rate of carbon farms development throughout the country. However, there is an acute shortage of qualified personnel for this type of activity in the country, so one of the strategic tasks for Russian universities today is to train specialists for the new sequestration industry in the conditions of a new and inevitable reality – total decarbonization of the economy.

Sustainability criteria as a game changer in the search for hybrid solvents for CO2 and H2S removal

• Robust multi-criteria screening for CO 2 and H 2 S absorption in water-free solvents. • Polar soft-SAFT validated for a wide range of solvent properties and conditions. • Water-free solvents have a competitive technical edge over aqueous solvents. • Sustainability metrics of water-free solvents calls for greener options. • Holistic solvent evaluation is essential for proper selection. The appearance of hybrid solvents in recent years introduced a potential replacement for aqueous amines for acid gas removal in order to mainly overcome the high energy of regeneration. Yet, the assessment of solvent potentiality remains haphazard with limited information and assessment criteria. In this contribution, we develop and apply a multi-criteria assessment approach built on the use of a molecular-based equation of state, namely, polar soft-SAFT, in combination with sustainability indicators to examine the performance of hybrid solvents for acid gas removal (CO 2 and H 2 S). The first stage of the approach relies on the robust development of the thermodynamic model with available experimental data. Subsequently, with assured fidelity, the model is used in a fully predictive manner to obtain relevant assessment criteria for technical performance evaluation. This is inclusive of standard key performance indicators such as cyclic capacity and energy of regeneration, along with key solvent properties at conditions representative of acid gas removal processes. Additionally, we examine the environmental, health and safety impact of the investigated solvents as a sustainability criteria to select them. This framework has been applied for the first time to six solvents for acid gas removal, including the benchmark solvents aqueous monoethanolamine (MEA) and aqueous diethanolamine (DEA), along with hybrid solvents formulated from chemical solvents such as MEA, or DEA, with physical co-solvents including N-methyl-2-pyrrolidone (NMP), or sulfolane (SFL). The results of the multi-criteria assessment demonstrate that among the six solvents investigated in this work, the overall best performer remains to be the benchmark aqueous MEA. Results also indicate the potentiality of MEA + NMP hybrid solvent in terms of an acceptable compromise between reduced absorption capability and reduced energy of regeneration, compared to aqueous MEA; however, the hybrid solvents fail when applying the sustainability metrics. This work clearly indicates that potential solvents for acid gas removal should be examined following a holistic approach, inclusive of their technical performance and environmental footprint.

H2S–CO2 gas separation with ionic liquids on low ratio of H2S/CO2

Acid gas removal, especially H2S and CO2, is an essential process in natural gas processing. In this research, 1-butyl-3-methylimidazolium bromide [bmim][Br] ionic liquid was analyzed as a hydrophobic solvent with has high selectivity to H2S as an environmentally friendly solvent to absorb acid gas from natural gas with low H2S/CO2 concentration in ambient temperature and pressure. The absorption performance of pure [bmim][Br] ionic liquid was compared with various amine solutions, such as monoethanolamine (MEA), triethanolamine (TEA), and methyldiethanolamine (MDEA), as well as the mixture of [bmim][Br]-MDEA with various concentration. As a result, pure [bmim][Br] ionic liquid had high selectivity to H2S compared with conventional amine solutions. In addition, the mixture of [bmim][Br]-MDEA with the mass ratio of 1:3 provided the highest H2S/CO2 selectivity of 6.2 in certain absorption conditions due to free tertiary amine attached in the cations of ionic liquids that can attract more H2S to its functional site.