Gas Sweetening Research Articles

Design of blend-amine solid adsorbents for CO2 capture: Enhances adsorption- equilibrium cycle strategies and mechanism

Blend amine-functionalized absorbents show great potential in the field of amine scrubbing for CO2, as they harness the absorption benefits of various monomer amines in combination. However, there is a lack of research on the application of the emerging concept of blend amines to solid amine adsorbents. Building upon this foundation, this study firstly incorporated Aminoethylethanolamine (AEEA) into Polyethyleneimine (PEI) of varying molecular weights to create a range of new binary solid amine adsorbents. The research then compared the adsorption performance differences between these binary adsorbents and pure PEI adsorbents. The enhanced dispersion of PEI by AEEA results in an increase in the effective active sites available. The amine efficiency and CO2 adsorption capacity of the AEEA-PEI blend amine system were maximally increased by 92.0% and 84.6%, respectively, compared to the pure PEI system. Furthermore, through DFT calculations, it is clear that the presence of AEEA lowers the overall activation energy of the reaction due to its superior proton acceptance compared to PEI. However, the AEEA-PEI system exhibits weak cycling stability attributed to the limited regeneration capacity of AEEA. Fortunately, this issue can be successfully addressed by introducing a strong base, N,N,N',N'',N''-pentamethyl diethylenetriamine (PMDETA). The CO2 adsorption cycling stability for AEEA-PEI-PMDETA system maximally improved by up to 17.1% compared to the AEEA-PEI system. The mechanism behind the effectively suppression of cycling losses by PMDETA was further elucidated through DFT calculations. Consequently, the novel ternary amine solid adsorbent introduced in this study, aimed at enhancing the CO2 adsorption performance of monomer amine solid adsorbents, offers a fresh strategy for fundamental theoretical investigations into CO2 adsorption.

A thermodynamic approach to energy requirements for CO2 capture and a comparison between the minimum energy for liquid and solid sorbent processes

There has been an increased interest in the use of solid sorbents for CO2 capture from flue gases to reduce emissions from fossil energy. This work uses a simple Carnot engine-like model to compare the energy requirements for a CO2 capture process using a solid adsorbent in a circulating fluidized bed with its minimal thermodynamic needs and with the performance of a conventional liquid solvent process. The energy requirements for CO2 capture using thermal swing separation sorption are dominated by the standard Gibbs free energy of separation from the sorbent (Δg0,sep), the sensible heat needed to reach the desorption temperature, and loading optimization to avoid thermodynamic pinching effects. The Δg0,sep is an invariant of the system, so only its value at reference conditions is required and it is independent of the desorption temperature or the heat of evaporation of a liquid solvent. A baseline is established using the Δg0,sep as well as the equivalent work for a well-established amine process. In all cases the energy requirements are found to be well above the minimum thermodynamic values and those of conventional liquid absorption. Higher-capacity solid sorbents and challenging improvements on heat recovery will be needed to close the gap.

Proposing novel predictive group and atomic contribution models for hydrogen sulfide absorption by Deep Eutectic Solvents

Hydrogen sulfide (H2S) is one of the most dangerous impurities of natural gas which cause human and environmental issues. Thus, the main process of gas sweetening plants is H2S removal from natural gas. Amine solutions are the commonly used solvents for gas-sweetening processes in petroleum industries. However, amin solutions are not safe and cause many environmental issues especially in the post-process treatment of used amine. Thus, the issue of proposing green sustainable solvents for gas sweetening is vital for petroleum industries. Deep Eutectic Solvents (DESs) are the most recently introduced green solvents which have shown good capability for H2S absorption. Thus, DESs are one of the most possible candidates for green solvents to replace amine solutions. Experimental studies to choose suitable solvents is a tough challenge because working with H2S is very dangerous and requires expensive facilities. Therefore, an accurate and global thermodynamic model is necessary to predict the solubilities of H2S in DESs without the requirement of experimental data. This study for the first time in open literature, proposes two accurate and global thermodynamic models of group contribution (GC) and atomic contribution (AC) for predicting the H2S solubilities in various nature DESs. The largest and most updated data bank for H2S solubility in DESs was developed from open literature, including 415 solubility data of 37 different nature DESs. The proposed GC and AC models were developed according to the gathered data bank and their results were analyzed by statistical parameters. Both GC and AC models show normal behavior and promising results concerning experimental data by the calculated AARD% of 9.64, and 12.86, respectively.

Techno-economic assessment of bio-hythane upgrading processes based on ionic liquids

Hythane, the blending of hydrogen (H2) and methane (CH4), is attracting attention as it could accelerate the H2 economy. H2 and CH4 can be extracted from organic material by fermentation and anaerobic digestion, respectively, but this alternative bio-hythane also contains carbon dioxide (CO2) that must be removed. This work addresses the use of Aprotic N‑Heterocyclic Anion-based ionic liquids (AHA-ILs) for bio-hythane upgrading. Three AHA-ILs ([P2228][2-CNPyr], [P2228][3-IPyra], and [P2228][4-BrIm]) were evaluated at process scale by conducting rate-based COSMO-based/Aspen Plus simulations of the upgrading processes. A wide range of operating conditions were screened by modifying key process variables such as the absorption pressure and the desorption temperature, and the bio-hythane composition. Energy and AHA-IL consumptions were analyzed together with variable operating cost (VOC). Energy demand and VOC were used to identify the Pareto optimal for each case study using a Python code. In addition, a detailed economic study was performed for the best three systems. The proposed processes are very versatile and are capable of handling bio-hythane of different compositions, being 10 %mol H2, 60 %mol CH4, and 30 %mol CO2 the most suitable for better process performance. For this case, the energy demand is about 0.51–0.56 kWh/Nm3 and VOC is about 1 cent. $/Nm3. The AHA-IL [P2228][3-IPyra] exhibited the best results for both variables. The energy requirement is in line with the minimum energy required for amine scrubbing technology, while VOC can be reduced by up to 17–48 % compared with electricity-intensive water scrubbing, pressure swing adsorption or membranes. Although higher investment is necessary, the assessed bio-hythane upgrading processes have the potential to operate around 0.1 $/Nm3, with VOC contributing about 8 % to the total cost.

Streamlining the Synthesis of Pyridones through Oxidative Amination of Cyclopentenones

AbstractHerein we report the development of an oxidative amination process for the streamlined synthesis of pyridones from cyclopentenones. Cyclopentenone building blocks can undergo in situ silyl enol ether formation, followed by the introduction of a nitrogen atom into the carbon skeleton with successive aromatisation to yield pyridones. The reaction sequence is operationally simple, rapid, and carried out in one pot. The reaction proceeds under mild conditions, exhibits broad functional group tolerance, complete regioselectivity, and is well scalable. The developed method provides facile access to the synthesis of 15N‐labelled targets, industrially relevant pyridone products and their derivatives in a fast and efficient way.

An Engineered Imine Reductase for Highly Diastereo- and Enantioselective Synthesis of β-Branched Amines with Contiguous Stereocenters.

β-Branched chiral amines with contiguous stereocenters are valuable building blocks for preparing various biologically active molecules. However, their asymmetric synthesis remains challenging. Herein, we report a highly diastereo- and enantioselective biocatalytic approach for preparing a broad range of β-branched chiral amines starting from their corresponding racemic ketones. This involves a dynamic kinetic resolution-asymmetric reductive amination process catalyzed using only an imine reductase. Four rounds of protein engineering endowed wild-type PocIRED with higher reactivity, better stereoselectivity, and a broader substrate scope. Using the engineered enzyme, various chiral amine products were synthesized with up to >99.9% ee, >99:1 dr, and >99% conversion. The practicability of the developed biocatalytic method was confirmed by producing a key intermediate of tofacitinib in 74% yield, >99.9% ee, and 98:2 dr at a challenging substrate loading of 110 g L-1. Our study provides a highly capable imine reductase and a protocol for developing an efficient biocatalytic dynamic kinetic resolution-asymmetric reductive amination reaction system.

Onboard carbon capture and storage (OCCS) for fossil fuel-based shipping: A sustainability assessment

Limiting the carbon intensity of maritime transport is crucial to meet 2050 net-zero targets. Onboard carbon capture and storage (OCCS) offers a practical short-term solution for reducing shipping-related CO2 emissions until cleaner technologies are ready for large-scale adoption. This study introduces an innovative multi-objective approach to integrate sustainability into the conceptual design and decision-making phases of OCCS. A systematic technology screening identified possible OCCS solutions, which were then assessed for onboard feasibility. Specific indicators were defined to evaluate OCCS performance based on technological, economic, environmental, and social criteria, and aggregated sustainability perspectives. Using a fossil fuel-powered cruise ship as a case study, results were benchmarked against zero-carbon alternatives. Among the alternatives considered, chemical absorption by amine scrubbing (AS) and advanced cryogenic carbon capture (A3C) appeared as the only feasible solutions considering onboard energy requirements. The emerging cryogenic A3C concept resulted in being outperformed by benchmark AS, primarily due to an environmental impact 1.5 times higher. All alternative technologies, whether OCCS- or cleaner fuel-based, were found to be more sustainable than the baseline fossil fuel-based engine, lowering the environmental impact by at least 61%. Hydrogen as a marine fuel leads to the most promising scenario for future cleaner shipping operations, reducing the sustainability footprint by up to 76%. The robustness of the proposed method was confirmed by a probabilistic Monte Carlo sensitivity analysis. Overall, the results obtained can guide toward more informed solutions and policies promoting the sustainability of ship propulsion systems.

Direct amination of toluene with hydroxylamine to produce toluidine over vanadium catalysts

In this study, metallic vanadium was used as catalysts for direct amination of toluene with hydroxylamine to produce toluidine under mild conditions. High toluene conversion and toluidine selectivity were obtained, corresponding to 87.62% and 96.45% respectively. Additionally, thermodynamic and kinetic calculations were carried out. It was concluded that the reaction was dominated by kinetics, with the distribution of three products being para > ortho > meta. The computational and experimental results indicated that the amination process involves an amino radical mechanism.

Engineered loose nanofiltration membrane for efficient dye/salt separation by starting from poly(ether sulfone) powder modification

Loose nanofiltration (LNF) is increasingly considered as the powerful technique for dye desalination due to its clear advantages at energy efficiency, selectivity and low pollution. But the membrane materials for loose nanofiltration process still suffer from the low permeance, unsatisfactory selectivity, membrane fouling and high cost. Herein, we propose a new three-step route to fabricate efficient poly(ether sulfone) (PES) LNF membrane, which starts from PES powder modification via mutual radiation-induced grafting polymerization and ensues immersion precipitation phase inversion and amination processes. The obtained PES-based LNF membrane possessed a thinner skin layer and an unusual irregular vesicular pore structure in sublayer instead of the finger-like macrovoids of conventional PES membrane. Thus, it achieved larger filtration permeance (35.5 L m–2 h−1 bar−1), high dye rejection (93.7 % to Congo Red) but low salt rejection (2.9 % to NaCl) during the filtration process of Congo red-containing saline water. It also showed excellent separation stability at high operation pressure and tolerance to acidic, alkaline and chlorine-oxidative conditions. Therefore, such a three-step strategy could endow the PES membrane with both loose and thinner skin layer in a reliable and scalable way, enlightening the development of high-performance LNF membrane for wastewater treatment and resource recovery.

Synthesis of Polybenzoxazine as an environmentally friendly adhesive material from cardanol and post-consumer PET source

In this study, a thermosetting benzoxazine was successfully prepared from environmentally friendly sources to be used as an adhesive. The phenolic component used for the synthesis of the benzoxazine monomer is cardanol derived from the cashew nutshell, while the amine fractions are terephthalamide, which is a product of the amination process of used polyethylene terephthalate plastic bottles (PET). The structure of the benzoxazine monomer was determined by FT-IR and 1H-NMR spectroscopy. The thermal and curing behavior of the materials was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). A lap-shear adhesion testing (ASTM D1002-10) was performed to measure the bond strength of the material to the CT3 steel surface. The adhesive properties with a shear strength of 7.29 MPa are excellent compared to other commercial adhesives. This result indicates the great potential of this benzoxazine for adhesive applications in practice.

Hollow Fiber Contactors with Improved Hydrophobicity for Acid Gas Removal: Progress and Recent Advances

The gas–liquid membrane contactor technology, which integrates the absorption process with membranes, is a developing membrane technology that is especially pertinent to acid gas absorption. When it comes to removing acid gases from natural gas or after combustion, membrane technology has demonstrated potential as a substitute for conventional absorption columns. The membrane contactor offers exceptional operating flexibility and a high mass transfer area. In addition to summarizing the key elements of membrane materials, absorbents, and membrane contactor design, this paper presents the working principle and wetting mechanism of hollow membrane contactors and focuses the most recent advancements in membrane contactor research in gas separation from gas mixtures. The state-of-the-art overview of highly hydrophobic microporous membranes is presented after a discussion of the main challenges to the preparation of superhydrophobic membranes.

Book Review Carbon Membrane Technology Fundamentals and Applications

Carbon membrane has shown great advantages with high separation performance, especially under high temperature and pressure condition with its strong mechanical and chemical stabilities, as well as well-defined pores structures [1]. An overview of the fundamental aspect and industrial application of carbon membrane is thus important to demonstrate the potential development of the membrane. This recent published book summarized both aspects in two parts. For the first part, the formation, state-of-art of the performance, characterization and transport mechanism of carbon membranes were discussed. For the second part, the application of carbon membrane in biogas upgrading, natural gas sweetening, hydrogen purification, micro-, ultra- or nanofiltration and other applications were reported. Subsequently, future perspectives of the carbon membrane were also analysed. In short, the book offers a thorough discussion on the fundamentals and applications of carbon membrane towards a sustainable development, which is a valuable resource for both academic and industrial researchers.

Enhancing the amination activity of meso-diaminopimelate dehydrogenase from Symbiobacterium thermophilum by modifying the crucial residue His154 for deamination

During the deamination and amination processes of meso-diaminopimelate dehydrogenase (meso-DAPDH) from Symbiobacterium thermophilum (StDAPDH), residue R71 was observed to display distinct functions. H154 has been proposed as a basic residue that facilitates water molecules to attack the D-chiral carbon of meso-DAP during deamination. Inspired by the phenomenon of R71, the effects of H154 during deamination and amination were investigated in this study with the goal of enhancing the amination activities of StDAPDH. Single site saturation mutagenesis indicated that almost all of the H154 mutants completely lost their deamination activity towards meso-DAP. However, some H154 variants showed enhanced kcat/Km values towards pyruvic acid and other bulky 2-keto acids, such as 2-oxovaleric acid, 4-methyl-2-oxopentanoic acid, 2-ketobutyric acid, and 3-methyl-2-oxobutanoic acid. When combined with the previously reported W121L/H227I mutant, triple mutants with significantly improved kcat/Km values (2.4-, 2.5-, 2.5-, and 4.0-fold) towards these 2-keto acids were obtained. Despite previous attempts, mutations at the H154 site did not yield the desired results. Moreover, this study not only recognizes the distinctive impact of H154 on both the deamination and amination reactions, but also provides guidance for further high-throughput screening in protein engineering and understanding the catalytic mechanism of StDAPDH.

Rational design of melamine-crosslinked poly(ethylene glycol) membranes for sour gas purification

Natural gas accounts for about a quarter of the world's energy consumption; however, most of the current natural gas reservoirs are sour. Sour natural gas containing significant amounts of hydrogen sulfide (H2S) along with carbon dioxide (CO2) must be purified to meet the strict requirements for transportation and storage in the industry. Sour natural gas purification involves two steps: acid gas removal (AGR) and acid gas enrichment (AGE), which currently use highly energy-intensive technologies. Membrane separation represents the most attractive technology to lower the operating cost and carbon footprint of these large processes. Guided by density functional theory (DFT) calculations, we rationally designed a crosslinked poly(ethylene glycol) (PEG) membrane for AGR and AGE applications. Specifically, PEG-bisazide monomers were crosslinked with a novel trialkyne-functionalized H2S-philic melamine via azide-alkyne cycloaddition click chemistry. The developed membranes were characterized and tested for (H2S + CO2)/CH4 and H2S/CO2 separations under realistic industrial conditions, targeting the AGR and AGE applications, respectively. These novel membranes achieved high H2S permeability while maintaining attractive H2S/CO2 selectivity.

Simulation of Gas Sweetening Process using Extended NRTL and Stages Efficiency as Modeling Approach

Gas sweetening is a process to remove CO2 and H2S from natural gas. The current established technology is by using Amine contactor where the solvent used is in form of Amine solution. To simulate the effect of different solvent, electrolyte-NRTL is used to model the equilibrium, and mass transfer-kinetic is used to model the rate-based processes. This modeling approach is rather complex and available only in commercial and proprietary process simulation software. Therefore we propose an alternative modeling approach where we use extended NRTL and stage efficiency to model the acid gas absorption processes. We find that this approach is quite good to describe CO2 absorption, yet unsuccessful to calculate the H2S absorption. Inadequate vapor liquid equilibrium parameter regression for H2S, specifically at low partial pressure might cause the problem. However the stage efficiency approach shows good result where it is comparable to rate-based model and corresponds to current understanding of physico-chemical phenomenon of acid gas absorption.

Inter-crosslinked spirocyclic mixed matrix membranes exhibiting enhanced gas permeability, selectivity, and plasticization resistance

Poor interfacial compatibility is the most common issue inhibiting performance enhancement in mixed matrix membranes (MMM) for gas and liquid separations. To address this issue, we fabricated highly selective and permeable inter-crosslinked mixed matrix membranes (IcMMMs) based on carboxylic-acid functionalized polymer of intrinsic microporosity-1 (CPIM) containing up to 30 wt % triptycene-isatin polymer porous network (PPN) particles. Polymer-filler inter-crosslinking is accomplished via thermal decarboxylation at 200 °C, which is the lowest temperature this reaction has been found to occur in the literature. This low temperature circumvents potential issues with degradation of porous supports or gutter layer materials, and thus enables these materials to be integrated into traditional membrane processes. The resulting IcMMMs exhibit gel fractions above 90 %. Beyond IcMMMs, membranes based on neat CPIM, thermally crosslinked CPIM, as well as non-crosslinked CPIM-PPN mixed matrix membranes were fabricated to elucidate the individual and synergistic effects of filler inclusion and thermal treatment. In addition to showing upper bound permeability-selectivity performance, IcMMMs also exhibit an almost unprecedented stability against plasticization upon extended exposure to CO2 up to 50 atm or above. This study shows that crosslinking across the polymer-filler interface is the key feature to achieve simultaneous enhancement in permeability, selectivity, and stability. To elucidate the molecular mechanism of these enhancements in the IcMMMs with respect to the baseline materials, permeability was broken into its sorption and diffusion contributions and an energetic analysis of sorption was performed. The low cost of PPNs coupled with the mild crosslinking temperature make this approach highly scalable, resulting in materials exhibiting high rigidity and structural stability with the potential to excel in aggressive separations, such as organic solvent separations or high-CO2 content, high-pressure natural gas sweetening.

A Comprehensive Review on Biomethane Production from Biogas Separation and its Techno-Economic Assessments.

Biogas offers significant benefits as a renewable energy source, contributing to decarbonization, waste management, and economic development. This comprehensive review examines the historical, technological, economic, and global aspects of biomethane production, focusing on the key players such as China, the European Union, and North America, and associated opportunities and challenges as well as future prospects from an Australia perspective. The review begins with an introduction to biogas, detailing its composition, feedstock sources, historical development, and anaerobic digestion (AD) process. Subsequently, it delves into major biomethane production technologies, including physicochemical absorption, high-pressure water scrubbing (HPWS), amine scrubbing (AS), pressure swing adsorption (PSA), membrane permeation/separation (MP), and other technologies including organic solvent scrubbing and cryogenic separation. The study also discusses general guidelines of techno-economic assessments (TEAs) regarding biomethane production, outlining the methodologies, inventory analysis, environmental life cycle assessment (LCA), and estimated production costs. Challenges and opportunities of biogas utilization in Australia are explored, highlighting and referencing global projections, polarization in production approaches, circularity in waste management, and specific considerations for Australia. The review concludes discussing future perspectives for biomethane, emphasizing the importance of technological advancements, policy support, and investment in realizing its full potential for sustainable energy and waste management solutions.

Liquid carry-over control using three-phase horizontal smart separators in Khor Mor gas-condensate processing plant

Liquid carry-over phenomenon, where liquid droplets escape with gas, is a prevalent operational challenge in gas–liquid separators. Liquid carry-over leads to foaming issue and performance reduction within separator downstream absorption processes. In order to ascertain whether liquid carry-over is inducing foaming within the gas sweetening process’s absorption tower at Iraq’s Khor Mor gas-condensate processing plant, this study initiated an evaluation of the liquid droplet size distribution in the gas product and gas/liquid separation efficiency of upstream Alpha, Bravo #1, Bravo #2, and Charlee separators that feed into the aforementioned tower by using the Horizontal Vessel and ProSeparator correlations in Aspen HYSYS v.11 software. The study revealed that Alpha and Bravo #2 experienced liquid carry-over issues. In response to these challenges, an innovative smart separator design, referred to as an adjustable separator, was proposed, employing the Arnold-Stewart semi-empirical procedure. This design allows for easy adjustment to accommodate changes in feed composition and operational conditions, mitigating the liquid carry-over problem. The smart design demonstrated a significant increase in gas/liquid separation efficiency for Alpha separator, improving by 31.11% under current conditions and 77.65% under future conditions. Similarly, under both current and future conditions, the smart design of Bravo #2 separator yielded an enhancement of 21.31% and 28.23%, respectively. These results suggest that the smart design can be considered an optimal solution for controlling liquid carry-over. This innovation not only maintains high gas/liquid separation efficiency but also prevents foaming, offering a robust solution for ensuring sustained operational performance and productivity in gas–liquid separation processes.

Synthesis and Characterization of Biochars and Activated Carbons Derived from Various Biomasses

Reducing CO2 emissions is urgently needed to slow down the impacts of climate change. CO2 capture using an amine solution has been developed and implemented at pilot and commercial scales. However, amine scrubbing, in particular, produces a lot of degraded solvents as waste and is energy intensive. Solid sorbents have been used to overcome these drawbacks. In this work, waste biomass-derived carbon materials were developed and characterized. Advanced thermal chemical processes, i.e., hydrothermal and pyrolysis processes, were applied to produce materials from agrifood waste, such as soybean and okara. It was found that functional groups (-C=O and -OH) appeared in the synthesized materials, implying the generation of surface oxygenated groups. Preliminary results showed that synthesized activated carbons were obtained with good yields and relatively high surface areas, which may be applied as CO2 adsorption materials to solve CO2 emission problems.

Streamlining the Synthesis of Pyridones through Oxidative Amination of Cyclopentenones.

Herein we report the development of an oxidative amination process for the streamlined synthesis of pyridones from cyclopentenones. Cyclopentenone building blocks can undergo in situ silyl enol ether formation, followed by the introduction of a nitrogen atom into the carbon skeleton with successive aromatisation to yield pyridones. The reaction sequence is operationally simple, rapid, and carried out in one pot. The reaction proceeds under mild conditions, exhibits broad functional group tolerance, complete regioselectivity, and is well scalable. The developed method provides facile access to the synthesis of 15N-labelled targets, industrially relevant pyridone products and their derivatives in a fast and efficient way.