Sorbent Regeneration Research Articles

Solid acid catalysts for low-temperature regeneration of non-aqueous sorbents: An innovative technique for energy-efficient CO2 capture processes

Chemical absorption of CO2 from flue gases by using aqueous amine sorbents is regarded as the most mature and effective technology for reducing CO2 emissions, but the high energy cost of sorbent regeneration has so far greatly limited its industrial application. One of the best strategies developed by researchers in recent years to reduce energy requirements is to improve CO2 desorption kinetics by adding catalysts during sorbent regeneration. Moreover, non-aqueous sorbents have recently been gaining increasing attention as alternatives to conventional aqueous amines as they have the potential to lower the energy demand for sorbent regeneration. In this paper, we propose an innovative technique that combines and further develops these two emerging technologies, non-aqueous absorbent and catalyst-assisted regeneration, to enable less energy-intensive CO2 capture processes. In particular, in this screening study, we evaluate the regeneration behaviour of a CO2-saturated solution of 2-(2-aminoethoxy)ethanol (DGA) in diethylene glycol monomethyl ether (DEGMME) when heated to 85 °C in the absence and presence of different types of solid acid catalysts. In order to assess the potential benefits of this innovative technique over conventional systems, the results obtained were compared with the desorption performance of an aqueous solution of DGA under the same operating conditions and with the same catalysts, which highlighted the possibility of obtaining rapid desorption at relatively low temperatures when conducted with suitable acid catalysts using amines in organic diluents.

Photochemically‐Driven CO2 Release Using a Metastable‐State Photoacid for Energy Efficient Direct Air Capture

AbstractOne of the grand challenges underlying current direct air capture (DAC) technologies relates to the intensive energy cost for sorbent regeneration and CO2 release, making the massive scale (GtCO2/year) deployment required to have a positive impact on climate change economically unfeasible. This challenge underscores the critical need to develop new DAC processes with substantially reduced regeneration energies. Here, we report a photochemically‐driven approach for CO2 release by exploiting the unique properties of an indazole metastable‐state photoacid (mPAH). Our measurements on simulated and amino acid‐based DAC systems revealed the potential of mPAH to be used for CO2 release cycles by regulating pH changes and associated isomers driven by light. Upon irradiating with moderate intensity light, a ≈55 % and ≈68 % to ≈78 % conversion of total inorganic carbon to CO2 was found for the simulated and amino acid‐based DAC systems, respectively. Our results confirm the feasibility of on‐demand CO2 release under ambient conditions using light instead of heat, thereby providing an energy efficient pathway for the regeneration of DAC sorbents.

Photochemically-Driven CO2 Release Using a Metastable-State Photoacid for Energy Efficient Direct Air Capture.

One of the grand challenges underlying current direct air capture (DAC) technologies relates to the intensive energy cost for sorbent regeneration and CO2 release, making the massive scale (GtCO2/year) deployment required to have a positive impact on climate change economically unfeasible. This challenge underscores the critical need to develop new DAC processes with substantially reduced regeneration energies. Here, we report a photochemically-driven approach for CO2 release by exploiting the unique properties of an indazole metastable-state photoacid (mPAH). Our measurements on simulated and amino acid-based DAC systems revealed the potential of mPAH to be used for CO2 release cycles by regulating pH changes and associated isomers driven by light. Upon irradiating with moderate intensity light, a ~55% and ~68% to ~78% conversion of total inorganic carbon to CO2 was found for the simulated and amino acid-based DAC systems, respectively. Our results confirm the feasibility of on-demand CO2 release under ambient conditions using light instead of heat, thereby providing an energy efficient pathway for the regeneration of DAC sorbents.

Recovery of dilute (bio-based) volatile fatty acids by adsorption with magnetic hyperthermal swing desorption

Adsorption followed by stepwise desorption to concentrate volatile fatty acids (VFAs) from very dilute aqueous streams is challenging and only a limited amount of VFAs can be collected at high concentration using N2-stripping. Here, we describe the preparation and use of superparamagnetic porous adsorbents to recover much larger fractions of VFAs in highly concentrated form from dilute aqueous streams than with the state-of-the-art N2-stripping technique. Our system is based on poly(divinylbenzene) (PDVB) impregnated with superparamagnetic magnetite nanoparticles (MNPs) synthesized by coprecipitation and functionalized with oleic acid (OA). The OA grafted MNPs (OA-MNPs) were embedded in the matrix of the polymer during suspension polymerization. The porous particles had an average size of 222 ± 40 µm with a surface area of 496 ± 10 m2/g and contained 11 ± 1 wt% MNPs with an average core size of 10 nm. VFAs adsorption from a dilute aqueous solution (containing 0.25 wt% of each acid) reached a saturation capacity of 43 g carboxylic acid per kg adsorbent,. The two-stage desorption was started with alternating magnetic field (AMF) heating at 25 mT and 52 kHz, followed by a hot N2 stripping stage removed 90 ± 9% of the water that had physically filled the pores during adsorption, and only 11 ± 2% of the loaded VFAs. Subsequently, 89 ± 3% of the VFAs were recovered almost water free using hot N2 stripping. Compared to sorbent regeneration and vapor fractionation by nitrogen stripping with a temperature gradient only, this new approach offers a much sharper acid fractionation from water, facilitating large energy savings in downstream operations.

Thermodynamic analysis of a sorption-enhanced gasification process of municipal solid waste, integrated with concentrated solar power and thermal energy storage systems for co-generation of power and hydrogen

A system of coupled CO2 capture and gasification has led to a new concept entitled sorption-enhanced gasification (SEG) which can increase H2 concentration in the syngas composition. This study proposed a novel configuration of the SEG system comprising concentrated solar power and thermal energy storage systems. Calcium looping (CaL) is utilized as the CO2 capture process. Unlike conventional SEG systems in which calcination heat demand is supplied by an oxy-combustion process, this study considers a heliostat field to provide heat for sorbent regeneration. The solar and thermal energy storage systems are simulated dynamically to achieve accurate results. A steam Rankine cycle is also designed to recover the released heat sources through the SEG system. The overall system performance is explored through energy and exergy analyses. Based on the results, the proposed system managed to produce 0.58 kg/s pure hydrogen in addition to 13.96 MW of net electrical power. Meanwhile, CO2 is captured from syngas composition with capturing efficiency of 95%. The energy analysis shows cold gas efficiency and the annual total energy efficiency of 87.76 and 70.74%, respectively. Based on exergy analysis results, the carbonator reactor exhibits the highest permeance compared to the gasifier and calciner reactors, with an exergy efficiency of 88.74%. Parametric study results show an increase in the cold gas efficiency, hydrogen production rate, and electrical energy efficiency with enhancing steam-to-biomass ratio. An increase in CO2 capture efficiency also improves both the electrical energy efficiency and H2 concentration of the syngas composition. CO2 capture efficiency and S/B ratio are inversely related to the exergy efficiency of the system.

Detailed study on the regeneration of CoS2 loaded porous carbon for elemental mercury removal from flue gas

Metal sulfides are promising sorbents in elemental mercury (Hg0) removal from flue gas, but they need to be regenerated during Hg0 removal cycle. Developing an effective regeneration method and elucidating the associated mechanisms hold significant importance in reducing operating costs for Hg0 removal by metal sulfides. This paper reported a CoS2 loaded porous carbon for Hg0 capture and investigated the regeneration of the deactivated sorbent using elemental sulfur for the first time. The elemental sulfur can fully recover the Hg0 capture ability of the hybrid sorbent, and display the same regeneration stability during five Hg0 removal cycle in comparison with toxic H2S. The regained activity of the sorbent in Hg0 capture depends mainly on the regeneration of S22− sites. The regenerated sorbent contains higher amount of S22− sites than the fresh sample, but less Co3+ and Sn2−(n >2) sites. Particularly, elemental sulfur is more effective in recovering S22− sites than H2S. The particle size of CoS2 on carbon decreases obviously during the Hg0 adsorption and regeneration, but cannot be restored by elemental sulfur and H2S. This work provides a detailed insight into the deactivation of metal sulfides for Hg0 removal, and will help the design of sorbent regeneration method for practical gaseous Hg0 capture.

Magnetic-Induced Swing Adsorption over Iron Oxide/13X: Effects of Particle Size and Oxide Phase on Sorbent Regeneration in Ethylene/Ethane Separation

Magnetic induction has emerged as a viable method for regeneration of sorbents during separation processes. In this work, we investigated the efficacy of magnetic sorbents comprising iron oxide and zeolite 13X in ethylene/ethane separation via a magnetic induction process. The electromagnetic properties of the sorbents were tuned by varying the iron oxide (Fe2O3) particle size (30 nm, 100 nm, 5 μm) and iron oxide phase structure (FeO, Fe2O3, Fe3O4) at 20 wt % loading. The effects of these parameters on adsorption capacity, selectivity, and desorption rates were systematically investigated. The microporosity and surface area of magnetic sorbents were reduced by increasing the particle size of Fe2O3 from 30 nm to 5 μm. The results indicated that regardless of iron oxide particle size or phase structure, the C2H4/C2H6 selectivity ranges between 2.44 and 2.65 for all the magnetic sorbents. The specific heat absorption rate (SAR) was increased by ∼60% upon increasing the magnetic field intensity from 21.4 to 31.4 mT when the particle size increased from 30 nm to 5 μm. Fe3O4 was found to outperform the other phases by exhibiting 91.3 and 93.3% higher SAR than Fe2O3 and FeO at 31.4 mT, respectively, owing to its unique lattice structure with dual ion states (Fe2+ and Fe3+). Fe3O4/13X exhibited an ethylene desorption rate of 0.41 mmol/g·min at 21.4 mT, which was 58.5% faster than that under conventional thermal heating. Additionally, the sorbent was found to be highly durable, maintaining its adsorption and desorption capabilities over five consecutive cycles in the magnetic induction swing adsorption (MISA) process, conducted at 25 °C and 1 bar during adsorption and at 31.4 mT during desorption. These results indicate the potential of Fe3O4/13X as an effective magnetic sorbent in the MISA process. This study builds on our previous proof-of-concept work on the potential of magnetic sorbents as stimuli-responsive materials for light olefin/paraffin separation.

Integrated CO2 capture and utilisation: A promising step contributing to carbon neutrality

The release of CO2 into the atmosphere is problematic; however, it is an abundant, renewable, and inexpensive carbon resource. In the past, the environmental problems caused by excessive CO2 emissions, such as global warming and ocean acidification, have become increasingly severe. Carbon capture and utilisation (CCU) has drawn intensive interest due to its capacity to sequester CO2 and utilise it as a carbon source to produce high-value chemicals and fuels. However, state-of-the-art CCU exhibits poor economics and technological complexity due to extensive energy input, a multiple reactor configuration, and sorbent transfer between reactors for sorbent regeneration. Integrated CO2 capture and utilisation (ICCU) directly utilises CO2-containing exhaust gas and in situ upgrades them into valuable products in a highly intensified process, representing a more direct and promising path for CO2 emission control. A series of high-performance dual functional materials (DFMs) composed of catalytic and adsorbent sites have succeeded in various ICCU applications. In this account, we first briefly introduced the research background of ICCU technology and the motivation for developing various ICCU applications. Furthermore, we conducted a detailed description of ICCU technology from three aspects: ICCU-methanation, ICCU-dry reforming methane (DRM) and ICCU-reverse water gas shift reaction (RWGS). In particular, we have investigated the optimal adsorption and catalytic sites for specific reaction characteristics and have solved the problem of temperature matching between the adsorption and catalytic sites. In addition, The mechanism underlying ICCU technology has been explored, and the effect of interfering components on catalytic performance in real plant flue gases for future applications has also been analysed. Significantly, the catalyst stability was effectively improved by investigating the causes of catalyst deactivation. Finally, although the technology of in situ CO2 capture and conversion is still in its preliminary stages, we can see that current research results already indicate promising prospects. In-situ capture and conversion of CO2 into high-value-added chemical feedstock will be a very attractive application for reducing greenhouse gases in the atmosphere and recycling carbon resources. We are also committed to promoting the industrialisation and large-scale production of ICCU technology.

Multi-scale dynamic modeling and techno-economic optimization of a CO2 capture process using microencapsulated carbon sorbents in a moving bed contactors

A detailed 1-D non-isothermal model of moving beds for micro-encapsulated carbon sorbents (MECS) is developed in this study with sodium bicarbonate as the encapsulated sorbent. A rigorous capsule model is also developed and integrated with the bulk phase model leading to a multi-scale reactor model. A heat exchanger embedded in the regenerator is considered to provide the heat required for sorbent regeneration along with the heat input from direct steam. A new correlation for the heat transfer coefficient for heat exchange between the embedded heat exchanger and the moving solids is used. A plant-wide model of the capture system is developed with the absorbers, regenerators, heat recovery systems and the balance of the plant. Several sensitivity studies are conducted evaluating the impact of operating and design variables. An economic model of the process is developed. Key design and operating variables are optimized for minimizing Equivalent Annual Operating Cost (EAOC). Optimal EAOC of the moving bed reactor using MECS with encapsulated sodium carbonate is found to be about 8% better compared to the traditional MEA-based CO2 capture for similar extent of heat recovery. For +50% uncertainty in the capital costs of the moving beds, the moving bed technology using MECS studied here is found to result in about 3% higher EAOC than MEA while for -50% uncertainty in capital cost of moving beds, EAOC for the moving bed process is found to be about 19% lower than the MEA-based capture. Finally, the impact of part load operation on the economics of the capture system is evaluated.

Avoiding Interferences in Advance: Cyclodextrin Polymers to Enhance Selectivity in Extraction of Organic Micropollutants for Carbon Isotope Analysis

Compound-specific isotope analysis (CSIA) of organic water contaminants can provide important information about their sources and fate in the environment. Analyte enrichment from water remains nonetheless a critical yet inevitable step before measurement. Commercially available solid-phase extraction (SPE) sorbents are inherently nonselective leading to co-extraction of concurrent dissolved organic matter (DOM) and in turn to analytical interferences, especially for low-occurring contaminants. Here, we (i) increased extraction selectivity by synthesizing cyclodextrin polymers (α-, β-, γ-CDP) as SPE sorbents, (ii) assessed their applicability to carbon isotope analysis for a selection of pesticides, and (iii) compared them with commonly used commercial sorbents. Extraction with β-CDP significantly reduced backgrounds in gas chromatography-isotope ratio mass spectrometry (GC-IRMS) and enhanced sensitivity by a factor of 7.5, which was further confirmed by lower carbon-normalized CDOM/Canalyte ratios in corresponding extracts as derived from dissolved organic carbon (DOC) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. Gibbs free energies of adsorption demonstrated weak competition between DOM and analyte on the three CDPs. No isotopic fractionation (Δδ13C within ± 0.3‰) was observed for the investigated pesticides after using β-CDP as an SPE sorbent covering a range of concentrations (5-500 μg L-1), flow velocities (5-40 cm min-1), and sorbent regeneration (up to six times). The present study highlights the benefit of selecting innovative extraction sorbents to avoid interferences in advance. This strategy in combination with existing cleanup approaches offers new prospects for CSIA at field concentrations of tens to hundreds of nanograms per liter.

Calcium-Based Sorbent Carbonation at Low Temperature via Reactive Milling under CO2

The carbonation behavior of calcium-containing sorbents, CaO and Ca(OH)2, was investigated under pressurized CO2 at nominal room temperature. The carbonation reaction was mechanically driven via reactive ball milling. The carbonation rate was determined by monitoring the CO2 pressure inside the sealed milling jar. Two different versions of CaO were fabricated as starting materials. The addition of citric acid in CaO synthesis resulted in a significant increase in sorbent surface area, bringing up the conversion of CO2 from 18% to 41% after 3 h of reactive milling. The hydroxide formation from these two oxides closed the surface area gap. Nevertheless, we found that hydroxides had a higher initial carbonation rate and greater final CO2 uptake than their oxide counterparts. However, the formation of byproduct water limited the further carbonation of Ca(OH)2. When we added a controlled amount of water to the CaO-containing milling jar, the highest carbonation rate and most extensive CO2 uptake were attained due to the in situ formation of reactive Ca(OH)2 nanoparticles. We saw CaCO3 X-ray diffraction peaks only when Ca(OH)2 was involved in this low-temperature carbonation, indicating that the grain growth of CaCO3 is easier on the Ca(OH)2 surface than on the CaO surface. We used the Friedman isoconversional method to calculate the effective activation energy of decarbonation for the high surface area CaO sorbent milled with water. The average effective activation energy was found to be about 72 kJ mol−1, and its magnitude started to decrease significantly from 50% sorbent regeneration. The drastic change of the effective activation energy during decarbonation suggests that CaCO3, formed at nominal room temperature by reactive milling under pressurized CO2, should undergo a more drastic morphology change than the typical thermally carbonated CaCO3.

Optimization of Lead and Diclofenac Removal from Aqueous Media Using a Composite Sorbent of Silica Core and Polyelectrolyte Coacervate Shell.

The modification of inorganic surfaces with weak cationic polyelectrolytes by direct deposition through precipitation is a fast approach to generating composites with high numbers of functional groups. The core/shell composites present very good sorption capacity for heavy metal ions and negatively charged organic molecules from aqueous media. The sorbed amount of lead ions, used as a model for priority pollutants such as heavy metals, and diclofenac sodium salt, as an organic contaminant model for emerging pollutants, depended strongly on the organic content of the composite and less on the nature of contaminants, due to the different retention mechanisms (complexation vs. electrostatics/hydrophobics). Two experimental approaches were considered: (i) simultaneous adsorption of the two pollutants from a binary mixture and (ii) the sequential retention of each pollutant from monocomponent solutions. The simultaneous adsorption also considered process optimization by using the central composite design methodology to study the univariate effects of contact time and initial solution acidity with the purpose of enabling further practical applications in water/wastewater treatment. Sorbent regeneration after multiple sorption-desorption cycles was also investigated to assess its feasibility. Based on different non-linear regressions, the fitting of four isotherms (Langmuir, Freundlich, Hill, and Redlich-Peterson models) and three kinetics models (pseudo-first order (PFO), pseudo-second order (PSO), and two-compartment first order (TC)) has been carried out. The best agreement with experiments was found for the Langmuir isotherm and the PFO kinetic model. Silica/polyelectrolytes with a high number of functional groups may be considered efficient and versatile sorbents that can be used in wastewater treatment processes.

Computational particle fluid dynamics 3D simulation of the sorption-enhanced steam methane reforming process in a dual fluidized bed of bifunctional sorbent-catalyst particles

Sorption enhanced steam methane reforming (SE-SMR) is an efficient hydrogen production technology that combines steam methane reforming with CO2 capture. Reactions are shifted over their thermodynamic limits and hydrogen yield is enhanced, in more favorable thermodynamic conditions. Bifunctional sorbent-catalyst particles have been developed to assure stability over multiple cycles and to make the endothermic methane reforming and the exothermic CO2 capture completely integrated. Moreover, handling one granular material simplifies system management, reduces bed inventory and avoids the problem of segregation in case of two separated materials. The continuous and simultaneous operation of the process in a dual fluidized bed reactor (DFB), which combines a reformer and a calciner, for sorbent regeneration through high temperature calcination, increases productivity and allows a greater optimization.Aim of this work is the 3D simulation of the SE-SMR process in a DFB reactor, by the Computational Particle Fluid Dynamics (CPFD) method of the Barracuda VR® software. The simulation results in terms of solid flow, pressure balance and particles segregation are reported. A post-processing routine has been written to characterize bubbles in the two fluidized beds. The effects of bed inventory, superficial velocity and steam to methane ratio on hydrogen purity and methane conversion are discussed in the paper.

High-Temperature Syngas Desulfurization and Particulate Filtration by ZnO/Ceramic Filters.

Combustible gas (e.g., gasification syngas) cleaning at high temperatures can obtain further gains in energy efficiency for power generation and importantly leads to a simplified process and lower cost as a commercially viable source of clean energy. Thus, a feasibility study for high-temperature desulfurization (HTDS) and additional high-temperature particulate filtration (HTPF) of a raw syngas using ZnO sorbent-dispersed Raney CuO (ZnO/R-CuO) and ceramic filter (ZnO/CF) has been carried out. By synchrotron X-ray absorption near-edge structure (XANES) spectroscopy, mainly Zn(II) and Cu(II) are found in the ZnO/R-CuO sorbents. Both ZnO and R-CuO in the sorbents are involved in HTDS (1% H2S) at 873 K to form ZnS, Cu2S, and a small amount of CuS and reach relatively high HTDS efficiencies (82-90%). In addition, regeneration of the sulfurized sorbent by oxidation with O2 at 873 K (HTRG) for 1 h can restore ZnO and CuO for continuous and repetitive HTDS-HTRG cycles. To facilitate the HTDS engineering applications by the ZnO/R-CuO sorbents, their reaction rate constant (8.35 × 104 cm3/g/min) and activation energy (114.8 kJ/mol) at 873 K have also been determined. Furthermore, the ZnO/CF sorbent/filter can perform HTDS and additional HTPF at 873 K with very high particulate removal efficiencies (>98%). This demonstrates the feasibility for hot-syngas cleaning with a much better energy efficiency and lesser cost for cleaner power generation.

Is sorption technology fit for the removal of persistent and mobile organic contaminants from water?

Persistent, Mobile, and Toxic (PMT) and very persistent and very mobile (vPvM) substances are a growing threat to water security and safety. Many of these substances are distinctively different from other more traditional contaminants in terms of their charge, polarity, and aromaticity. This results in distinctively different sorption affinities towards traditional sorbents such as activated carbon. Additionally, an increasing awareness on the environmental impact and carbon footprint of sorption technologies puts some of the more energy-intensive practices in water treatment into question. Commonly used approaches may thus need to be readjusted to become fit for purpose to remove some of the more challenging PMT and vPvM substances, including for example short chained per- and polyfluoroalkyl substances (PFAS). We here critically review the interactions that drive sorption of organic compounds to activated carbon and related sorbent materials and identify opportunities and limitations of tailoring activated carbon for PMT and vPvM removal. Other less traditional sorbent materials, including ion exchange resins, modified cyclodextrins, zeolites and metal-organic frameworks are then discussed for potential alternative or complementary use in water treatment scenarios. Sorbent regeneration approaches are evaluated in terms of their potential, considering reusability, potential for on-site regeneration, and potential for local production. In this context, we also discuss the benefits of coupling sorption to destructive technologies or to other separation technologies. Finally, we sketch out possible future trends in the evolution of sorption technologies for PMT and vPvM removal from water.

Thermodynamic analysis of a waste heat utilization based efficient liquefaction and low-temperature adsorption carbon capture hybrid system

Cryogenic CO2 capture can obtain high-pressure and pure CO2, but existing methods are inefficient as they usually discharge the waste heat of refrigeration. Therefore, a new hybrid system is proposed to recycle the waste cooling, heat, and uncondensable CO2 of liquefaction CO2 capture into low-temperature adsorption CO2 capture. This enhances the overall energy efficiency and the CO2 recovery rate over existing cryogenic CO2 capture without external input. Moreover, it enables practical sub-zero temperature CO2 adsorption while lowering the desorption temperature to 70 °C. This system is analyzed by coupling the liquefaction CO2 capture and low-temperature adsorption CO2 capture thermodynamic models, whose heat and cooling needs are compared to that available by a vapor compression cycle. Results show that for 10% mol. CO2 flue gas, the proposed system is optimal at −53 °C and 5 MPa to yield a 2nd law efficiency of 9%, a CO2 recovery rate of 80%, and specific energy consumption of under 1.65 MJ/(kg of CO2). As the cooling demand is typically twice the heat needed for sorbent regeneration, a vapor compression cycle designed to meet the former can naturally meet the latter. Ultimately, the new hybrid system represents a new carbon capture technology with better potential to achieve carbon neutrality via waste heat utilization.

High-temperature sulfur capture by a Mn-Mo sorbent: An investigation of regeneration conditions and SO2 formation and prevention

The regeneration performance of a solid sorbent (alumina-supported 15Mn8Mo) for sulfur capture at high temperature has been studied. The regeneration of the sulfided sorbent was performed by oxidizing at different temperatures (400 – 800 °C) and O2concentrations (0.21 – 21 %). Temperature had a larger impact on the regeneration thanO2concentration. An unwanted side reaction during sulfur capture is SO2formation. Two pathways to SO2formation were identified, either via sulfate formation and decomposition or via oxidation of H2S. A new regeneration method which avoids SO2formation and achieves low residual H2S level in the gas phase involves adding an extra H2pre-reduction step between the regular O2-regeneration and the subsequent sorption step, i.e., a O2– H2regeneration. The stability of the sorbent was verified by 10 repeated sorption/regeneration cycles, with the sorbent regenerated either via the oxidative method or the new O2– H2regeneration method.

Process Simulations of High-Purity and Renewable Clean H2 Production by Sorption Enhanced Steam Reforming of Biogas

Renewable clean H2 has a very promising potential for the decarbonization of energy systems. Sorption enhanced steam reforming (SESR) is a novel process that combines the steam reforming reaction and the simultaneous CO2 removal by a solid sorbent, such as CaO, which significantly enhances hydrogen generation, enabling high-purity H2 production. The CO2 sorption reaction (carbonation) is exothermic, but the sorbent regeneration by calcination is highly endothermic, which requires extra energy. Biogas is one of the available carbon-neutral renewable H2 production sources. It can be especially relevant for the energy integration of the SESR process since, due to the exothermic sorption reaction, the CO2 contained in the biogas provides extra heat to the system, which can help to balance the energy requirements of the process. This work studies different process configurations for the energy integration of the SESR process of biogas for high-purity renewable H2 production: (1) SESR with sorbent regeneration using a portion of the produced H2 (SESR+REG_H2), (2) SESR with sorbent regeneration using biogas (SESR+REG_BG), and (3) SESR with sorbent regeneration using biogas and adding a pressure swing adsorption (PSA) unit for hydrogen purification (SESR+REG_BG+PSA). When using biogas as fuel (Cases 2 and 3), these configurations were studied using air and oxy-fuel combustion atmospheres in the sorbent regeneration step, resulting in five case studies. A thermodynamic approach for process modeling can provide the optimal process operating conditions and configurations that maximize the energy efficiency of the process, which are the basis for subsequent optimization of the process at the practical level needed to scale up this technology. For this purpose, process simulations were performed using a steady-state plant model developed in Aspen Plus, incorporating a complex heat exchanger network (HEN) to optimize heat integration. A comprehensive parametric study assessed the effects of biogas composition, temperature, pressure, and steam to methane (S/CH4) ratio on the process performance represented by the selected key performance indicators, i.e., H2 purity, H2 yield, CH4 conversion, cold gas efficiency (CGE), net efficiency (NE), fuel consumption for the sorbent regeneration step, and CO2 capture efficiency. H2 with a purity of 98.5 vol % and a CGE of 75.7% with zero carbon emissions can be achieved. When adding a PSA unit, nearly 100% H2 purity and CO2 capture efficiency were achieved with a CGE of 77.3%. The use of oxy-fuel combustion during regeneration lowered the net efficiency of the process by 2.3% points (since it requires an air separation unit) but allowed the process to achieve negative carbon emissions.

Rational fabrication of completely amorphous chitosan-formyl-sucrose sorbents with excellent durability and regenerability for high-throughput dye removal

We have developed chitosan-formyl-sucrose sorbents with densely charged groups and ultra-low polymer chain density via a room-temperature one-step approach for industrial adaptations. This sorbent reaches theoretic sorption and maximum desorption capacities with extremely high concentration factors suitable for fast continuous dye removal. We focus on the development of affordable cleaning technology. Such a technology must have high cleaning capacity and durable reusability. Via sorption of three reactive dyes, Reactive Blue 19, Reactive Black 5, and Reactive Red 120, the sorbent we report provided a dyestuff sorption capacity of as high as 7 g/g, 99% of its theoretical sorption value, due to its densely charged groups and complete accessibility. This sorbent also exhibited a 99% desorption efficiency even when the eluate concentrated 19 times the initial dye solution due to the adjustable charged groups and ultra-low polymer chain density, therefore, minimal van der Waals attractions to the dyes. Formyl-sucrose endows the sorbents with desirable mechanical properties and excellent water stability for high-speed continuous wastewater cleaning and sorbent regeneration readily adaptable to cost-effective industrializations.

Solar-driven calcium looping system for carbon capture in cement plants: Process modelling and energy analysis

The cement industry produces around 6–7% of the global anthropogenic CO2 emissions. This sector, therefore, needs to be decarbonized to meet the international goals on greenhouse gas emissions. In a cement plant, however, around 60% of the CO2 emissions are hard-to-abate because they come from the calcination of the raw materials. Carbon capture is thus needed to perform deep decarbonization of the cement production process. Among all the carbon capture technologies proposed in the literature, Calcium looping (CaL) is one of the most promising ones. This work analyses on novel solar-driven CaL process for carbon capture in a cement plant. In the system proposed, the energy required for the CO2 sorbent regeneration is fully supplied by a heliostat field. The performances of the overall system were evaluated through detailed process modelling and energy analyses. Primary energy consumption and CO2 emissions (sum of both direct process emissions and indirect emissions due to electricity consumption) were assessed considering different grid electricity mixes and integration levels (IL) between the carbon capture system and the clinker kiln. We estimate that the integration of a solar-driven CaL in a cement plant could be able to reduce over 90% of the plant CO2 emissions. Furthermore, this solution could potentially decrease the plant fuel consumption thanks to the reuse of the exhausted sorbent in the production process. On the other hand, a large heliostat field will be required to feed energy to the CaL process. Both the carbon intensity of the grid electricity mix and the IL impact on the system energy and carbon balance, as shown by the obtained values for the specific primary energy consumption for CO2 avoided (SPECCA) index. Obtained SPECCA indexes vary between a maximum of 2.17 MJ/kgCO2, obtained for an IL of 20% and grid electricity produced entirely from renewables, and a minimum of 0.57 MJ/kgCO2, estimated for an IL of 80% and grid electricity produced from state-of-the-art pulverized coal.