Sorption-enhanced Process Research Articles

Capture and catalytic conversion of CO2 from marine and offshore applications – A review

Abstract This contribution examines recent advances in modeling fluid dynamics and capture/conversion of CO2 from marine and offshore applications in packed-bed columns/trickle-bed reactors subjected to static inclination, externally-induced rolling and heaving motions. Breaking the axial symmetry of the two-phase flow once the packed bed system is tilted results in a significant decrease in process performance, the extent of which is determined by the magnitude of the tilt and the column/reactor diameter. Only the conversion of CO2 from marine engine emissions on-board large cargo ships via catalytic cycloaddition of CO2 to styrene oxide in multiphase large-diameter trickle-bed reactors increases slightly with increasing reactor inclination. Under the externally induced column/reactor oscillations, CO2 capture/conversion performance shifts toward the steady-state solution of the vertical column/reactor as the asymmetry between the two inclined positions decreases. Oscillating (between two inclined symmetrical positions) and heaving packed-bed columns/trickle-bed reactors generate an oscillating performance around the steady-state solution of the vertical static position, which is driven by the amplitude and period of the angular and heaving motions via the continuous evolution of the intensity of the reverse secondary flow and by the magnitude of the reactor/column diameter. The catalytic conversion of CO2 captured from marine emissions via an integrated process coupling reverse water-gas shift reaction and methanol synthesis in a fixed-bed reactors network system shows a remarkable enhancement with the addition of H2O adsorbent to the reaction systems in the sorption-enhanced process periods.

A Cold Flow Model of Interconnected Slurry Bubble Columns for Sorption-Enhanced Fischer–Tropsch Synthesis

For technical application with continuous operation of sorption-enhanced (SE) reactions, e.g., Fischer–Tropsch, a special reactor concept is required. SE processes are promising due to the negative effects of water on conversion and catalyst. The reactor concept of two interconnected slurry bubble columns combines the reaction with in situ water removal in the first, and sorbent regeneration in the second column with continuous exchange of slurry between the two. The liquid circulation rate (LCR) between the columns is studied in a cold flow model, measured by an ultrasonic sensor. The effects of different operating and geometric parameters, e.g., superficial gas velocity, liquid level and tube diameter on gas holdup and LCR are discussed and modelled via artificial intelligence methods, i.e., extremely randomized trees and neural networks. It was found that the LCR strongly depends on the gas holdup. The maximum of 4.28 L min−1 was reached with the highest exit, widest tube and highest superficial gas velocity of 0.15 m s−1. The influence of liquid level above the exit was marginal but water quality has to be considered. Both models offer predictions of the LCR with errors < 6%. With an extension of the models, particle circulation can be studied in the future.

Intensification of CO2 hydrogenation by in-situ water removal using hybrid catalyst-adsorbent materials: Effect of preparation method and operating conditions on the RWGS reaction as a case study

Intensifying CO2 hydrogenation reactions by in-situ water removal via hydrophilic adsorbents alongside the catalyst is an innovative approach that can drastically improve the performance of conventional processes whose yields are restricted by thermodynamics. Here, the sorption-enhanced (SE) reverse water–gas shift (RWGS) reaction was explored as a case study since it represents the starting point of all CO2 hydrogenation processes. Hybrid materials containing both catalyst (Cu/UGSO) and hydrophilic adsorbent (13X zeolite) were conceived to investigate for the first time (i) the effect of preparation method (with major impact on physicochemical properties and performance) and (ii) main operating parameters affecting greatly the yields (temperature and catalyst/adsorbent ratio). A comparison between mechanically mixed catalyst-adsorbent and bifunctional materials (containing active metal, catalytic support, and adsorbent within the same particle) revealed that Cu presence decreased the adsorptive ability of bifunctional materials, due to the decrease of specific surface area and zeolite acidity. In contrast, mechanical mixtures allowed to fully preserve the assets of both adsorbent and catalyst, to significantly intensify the reaction. The catalyst-adsorbent mixture obtained by wet mixing offered the best results by minimizing the average distance between catalytic and adsorption sites. 250 °C was found optimum for a significant reaction rate and a non-negligible water adsorption capacity of 13X zeolite. The reaction thermodynamic barrier was found to be crossed for catalyst/adsorbent mass ratio lower than 1, the intensification leading to a significant increase in CO2 conversion. The findings of this work are crucial for implementing this type of intensified process, which pushes the limits dictated by thermodynamic equilibrium, and provide information of high interest to guide future research on all SE processes of CO2 valorization via catalytic hydrogenation.

Process modelling and feasibility study of sorption-enhanced methanol synthesis

A sorption-enhanced process for hydrogenation of CO2 to methanol was designed and investigated by mathematical modelling and techno-economic analysis. The modelling methodology combined dynamic modelling of the cyclic reactor operation with pseudo-steady state modelling of the overall process. With continuous adsorption of water in the sorption-enhanced process, highly pure methanol (>99%) was produced without downstream distillation. The dynamic reactor cycle was designed and optimized to maximize the methanol production rate. The cycle and the process were modelled in two reactor configurations: adiabatic and isothermal. Under the default cost assumptions for the raw materials (CO2 50 €/t, hydrogen 3000 €/t) the adiabatic configuration was found more competitive in terms of the overall methanol production cost, at 1085 €/t compared to 1255 €/t for the isothermal case. The cost estimate for the adiabatic case was found comparable to a reference process representing conventional CO2 hydrogenation to methanol (1089 €/t). In addition to the methanol process, the developed modeling method has potential in the design of other sorption-enhanced processes.

Hydrogen Production with In Situ CO2 Capture at High and Medium Temperatures Using Solid Sorbents

Hydrogen is a versatile vector for heat and power, mobility, and stationary applications. Steam methane reforming and coal gasification have been, until now, the main technologies for H2 production, and in the shorter term may remain due to the current costs of green H2. To minimize the carbon footprint of these technologies, the capture of CO2 emitted is a priority. The in situ capture of CO2 during the reforming and gasification processes, or even during the syngas upgrade by water–gas shift (WGS) reaction, is especially profitable since it contributes to an additional production of H2. This includes biomass gasification processes, where CO2 capture can also contribute to negative emissions. In the sorption-enhanced processes, the WGS reaction and the CO2 capture occur simultaneously, the selection of suitable CO2 sorbents, i.e., with high activity and stability, being a crucial aspect for their success. This review identifies and describes the solid sorbents with more potential for in situ CO2 capture at high and medium temperatures, i.e., Ca- or alkali-based sorbents, and Mg-based sorbents, respectively. The effects of temperature, steam and pressure on sorbents’ performance and H2 production during the sorption-enhanced processes are discussed, as well as the influence of catalyst–sorbent arrangement, i.e., hybrid/mixed or sequential configuration.

Experimental Characterization and Energy Performance Assessment of a Sorption-Enhanced Steam–Methane Reforming System

The production of blue hydrogen through sorption-enhanced processes has emerged as a suitable option to reduce greenhouse gas emissions. Sorption-enhanced steam–methane reforming (SESMR) is a process intensification of highly endothermic steam–methane reforming (SMR), ensured by in situ carbon capture through a solid sorbent, making hydrogen production efficient and more environmentally sustainable. In this study, a comprehensive energy model of SESMR was developed to carry out a detailed energy characterization of the process, with the aim of filling a current knowledge gap in the literature. The model was applied to a bench-scale multicycle SESMR/sorbent regeneration test to provide an energy insight into the process. Besides the experimental advantages of higher hydrogen concentration (90 mol% dry basis, 70 mol% wet basis) and performance of CO2 capture, the developed energy model demonstrated that SESMR allows for substantially complete energy self-sufficiency through the process. In comparison to SMR with the same process conditions (650 °C, 1 atm) performed in the same experimental rig, SESMR improved the energy efficiency by about 10%, further reducing energy needs.

Hydrogen production through chemical looping and sorption-enhanced reforming of olive mill wastewater: Thermodynamic and energy efficiency analysis

A thermodynamic study was performed aiming to compare the performance of different reactor configurations, namely traditional (TR), sorption-enhanced (SER), chemical looping (CLR) and chemical-looping sorption-enhanced reforming (SE-CLR) for the steam reforming of olive mill wastewater (OMW), a byproduct of olive oil production, to produce green hydrogen. This analysis was accompanied by an energy balance in order to maximize energy efficiency and achieve autothermal operating conditions. The parameters assessed in the thermodynamic study were temperature (250–900 °C) and steam-to-carbon molar ratio (0.15–3.0), but also, for the sorption-enhanced process, the ratio between the CO2 sorbent and the OMW (0–8.0), and for the chemical looping process the ratio between the oxygen carrier and the OMW (0–6.0). The SER showed higher hydrogen yield for the range of conditions tested than both the traditional and chemical looping reformers, with a hydrogen purity above 99%. By combining sorption-enhanced with chemical looping reforming, an H2 purity above 99% and a yield higher than that for chemical looping by itself were observed. For the CLR and SE-CLR configurations, a system in which the energy released is higher than the required was achieved by varying the amount of oxygen carrier, enabling operating under autothermal conditions. A pinch analysis was performed for the CLR and the SE-CLR to quantify the possible heat integration in a realistic system. It was found that CLR can be 71% self-sufficient, whilst SE-CLR can be 55% self-sufficient.

Determination of Kinetic and Diffusion Parameters Needed to Predict the Behavior of CaO-Based CO2 Sorbent and Sorbent-Catalyst Materials

For about 10 years, this research group has developed and utilized a particle grain model (PGM), to simulate CO2-capture carried out by CaO-based porous particles. Chemical kinetics and diffusion parameters were either taken from literature studies or fixed by fitting experimental sorption data. As recently observed, this procedure was not fully satisfactory and revealed systematic, minor discrepancies between PGM numerical results and experimental data when predicting sorbents behavior during the initial chemically controlled regime of carbonation. This work deals with the experimental determination of kinetic and diffusion parameters, utilized in the PGM, by means of straightforward thermogravimetric analysis (TGA) tests on small samples of materials to be evaluated for CO2 sorption and sorption-enhanced processes. To validate this procedure, the carbonation of two Ni–CaO–mayenite combined sorbent-catalyst materials (CSCMs) was studied in TGA. The experimental data so obtained were used to infer carbona...

Modeling and optimization of the cyclic steady state operation of adsorptive reactors

Abstract Adsorptive reactors (AR), in which an adsorptive functionality is incorporated into the catalytic reactors, offer enhanced performance over their conventional counterparts due to the effective manipulation of concentration and temperature profiles. The operation of these attractive reactors is, however, inherently unsteady state, complicating the design and operation of such sorption-enhanced processes. In order to capture, comprehend and capitalize upon the rich dynamic texture of adsorptive reactors, it is necessary to employ cyclic steady state algorithms describing the entire reaction-adsorption/desorption cycle. The stability of this cyclic steady state is of great importance for the design and operation of adsorptive reactors. In this paper, the cyclic steady state of previously proposed novel adsorptive reactor designs has been calculated and then optimized to give maximum space–time yields. The results obtained revealed unambiguously that an improvement potential of up to multifold level could be attained under the optimized cyclic steady state conditions. This additional improvement resulted from the reduction of the regeneration time well below the reaction-adsorption time, which means, in turn, more space–time yield.

Overcoming the equilibrium barriers of CO2 hydrogenation to methanol via water sorption: A thermodynamic analysis

In this work, a detailed thermodynamic analysis and simulation of an intensified process for CO2 hydrogenation to methanol with in-situ water sorption is presented. The study focused on the effect of different operating parameters, such as temperature, pressure, H2/CO2 molar ratio and adsorbent volume capacity, on the reactor performance with the aim to define the optimum operating window. The analysis was also performed for the conventional process as benchmark. The continuous removal of H2O shifts the thermodynamic equilibrium and drives the reactions of CO2 to completion under the entire investigated parameter range. In temperatures and pressures of interest for practical application (220°C–270°C and 50–70bar), the methanol yield is up to 130% higher in the sorption-enhanced process compared to direct hydrogenation. The only negative aspect was the decrease of CH3OH selectivity in favor of CO production. Despite this, the benefits of water sorption are indisputable and overcome the slight decrease in selectivity. The simulation of the complete process, including gas recycle, showed that with in-situ water removal 15% higher methanol productivity can be attained, with very high once-through CO2 conversion and CH3OH yield and very low gas recycle. This has important implications on the economics of the process, as it decreases the size of the reactor and the auxiliary equipment and practically eliminates the need for downstream methanol-water separation via distillation, leading to substantial process intensification and reduction of capital and operating costs.

Overview on Pressure Swing Adsorption (PSA) as CO2 Capture Technology: State-of-the-Art, Limits and Potentials

This paper provides an insight on state-of-the-art, limits and potentials of pressure swing adsorption (PSA) as CO2 capture technology into power plants. To get a complete picture both post- and pre-combustion cases are considered. The expertise developed with modeling and simulation of PSA processes in power plants stressed the need of a holistic approach to the analysis. The different domains which determine the viability of the technology are taken into account, together with their mutual influence. Accordingly, adsorbent materials characteristics, process configurations and integration strategies are investigated and discussed, in order to provide a general evaluation. In post-combustion applications, PSA has been widely assessed with regard to adsorbent materials and processes. The integration into power plant does not entail significant issues, with a good potential for retrofitting old plants. An excessively large footprint of the separation unit has been reported, which seems to question the feasibility of PSA. In pre-combustion applications, prospects for improving adsorbent materials and processes are noticed. Good potential for PSA is envisaged whit hot gas separation processes, especially with sorption-enhanced processes. Furthermore, the complexity of the arrangements in pre-combustion cases may open room for interesting alternative system configurations, like power and H2 coproduction layouts.

Kinetics and reactor modeling for CaO sorption-enhanced high-temperature water–gas shift (SE–WGS) reaction for hydrogen production

Hydrogen, an important energy carrier of the future, produces no pollution and has a high content of energy. It is formed as a direct product of the water–gas shift (WGS) reaction, which occurs in various processes for the production of hydrogen, ammonia, methanol and different hydrocarbons, and is also a side reaction during the steam reforming of hydrocarbons and Fisher–Tropsch synthesis. Since it is an equilibrium reaction, it may be intensified by the selective removal of the products, which can lead to higher yields and energy savings. In this study, carbon dioxide was removed through chemisorption on CaO particles. In the first part, the WGS reaction kinetics were obtained on an industrial iron-chromium catalyst in a packed-bed reactor. In the second part, the CO2 chemisorption kinetics on CaO sorbent particles were examined, simultaneously with the WGS reaction. A modified dynamic shrinking-core model was used to describe the carbonation reaction, which accounted for the non-ideal core shrinkage. With the introduction of a sorbent conversion-dependent effective diffusion coefficient, the model perfectly reproduced the obtained experimental results. Valuable insight into the sorption-enhanced process was obtained with the full concentration profiles of the species involved (CO, H2O, CO2, H2) in time and space, as well as the conversion of the sorbent particles, also in the radial dimension. The developed model was used to simulate a cyclic sorption-enhanced water–gas shift operation in a revolver-type manner which allows for continuous sorbent regeneration and a much higher-than-equilibrium hydrogen production for various operational parameters. The significance of the model lies in the precise replication of the experimental results and its applicability to the vast area of the newly-emerged industrial sorption-enhanced technologies.

Autothermal reforming of impure glycerol for H2 production: Thermodynamic study including in situ CO2 and/or H2 separation

In the present work, thermodynamics was applied to study the autothermal reforming (ATR) of impure glycerol (mixture of glycerol and methanol) to generate pure hydrogen. The equilibrium compositions were calculated using the Gibbs free energy minimization method and simulations were performed in a wide range of conditions of pressure (1–20 atm), temperature (600–1000 K), oxygen to glycerol feed molar ratio (0.0–3.0), and water to glycerol feed molar ratio (3–12). The effect of in situ CO2 and/or H2 removal was investigated as well, in the perspective of reaction/separation process integration in a hybrid multifunctional reactor. Whatever the composition of the glycerol fed, the in situ separation of H2 and CO2 in ATR process maximizes the hydrogen yield and completely eliminates methane, carbon monoxide and carbon dioxide formation. At 700 K, it is possible to improve the H2 yield, with respect to the traditional reactor, up to 186% when CO2 removal is considered, up to 152% when only H2 removal is implemented, and by 195% when both H2 and CO2 removal are considered in the hybrid reactor.From the investigation of the energetically neutral conditions, it was found that in the sorption-enhanced process, with or without in situ H2 separation, no partial oxidation reactions are needed to provide the required heat to maintain the isothermal reformer at the desired temperature, and consequently the yield of hydrogen can be improved up to 6.93, which is close to the stoichiometric theoretical value of 7.

CO2 Sorption-Enhanced Processes by Hydrotalcite-Like Compounds at Different Temperature Levels

Abstract The aim of this work is to identify solid sorbents for CO2 capture for coal and biomass syngas conditioning and cleaning by means of a sorption-enhanced reaction process. Hydrotalcite-like compounds (HTlcs) were synthesized with and without K2CO3 impregnation. Samples were characterized by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) porosimetry after synthesis and after capture tests, respectively. Sorption and desorption tests were performed in a fluidized bed reactor, under cyclic conditions, at two different temperature levels: 350/450°C and 600/700°C. At low temperature only the Mg–Al HTlcs K promoted samples showed stability and sorption capacity comparable with literature values. On the other hand, results at high temperature indicate that the mixed Mg-Ca-Al HTlcs samples exhibit the best behavior with the highest sorption capacity (1.7 mmolCO2/g) almost stable over 5 sorption/regeneration cycles; furthermore, addition of steam allowed increasing their reactivity by 70% compared to the dry value. This type of sorbent could be a promising candidate to prepare a bifunctional sorbent–catalyst for sorption-enhanced processes, taking place directly in the fluidized bed gasifier, or downstream the reactor for adjustment of gas composition before further conversion in gaseous energy carriers.

Performance of a hybrid system sorbent–catalyst–membrane for CO2 capture and H2 production under pre-combustion operating conditions

This paper presents experimental results obtained for different approaches used for the simultaneous capture of CO2 and production of H2 under precombustion conditions. A novel hybrid system adsorbent–catalyst–membrane has been designed at Ciemat which combines a sorption enhanced WGS process (which consists of a mixture of adsorbent and catalyst) with a hydrogen selective membrane. First, the individual performance of the membrane and the binary adsorbent–catalyst system is evaluated in terms of H2 permeability, carbon monoxide conversion and CO2 capture and best operating conditions are determined for both approaches. The crucial role of temperature and steam on the overall performance of the system is especially discussed. Finally, first experimental results obtained for the hybrid adsorbent–catalyst–membrane system are presented and the advantages and challenges of adding a H2 selective membrane to the sorption-enhanced process are analysed.

Incorporating IGCC and CaO sorption-enhanced process for power generation with CO2 capture

Integrated gasification combined cycle (IGCC) is a power generation technology to convert solid fuels into electricity. IGCC with CCS is regarded as a promising option to mitigate CO2 emission. In this paper, the CaO sorption-enhanced process is incorporated downstream with coal gasification to produce a hydrogen-rich stream for electricity production and CO2 separation. A WGS-absorber substitutes the high- and low-temperature water–gas shift reactors and desulfurization units in conventional IGCC–CCS to produce a hydrogen-rich stream, which is sent onto a gas turbine. CaO is used as the sorbent to enhance hydrogen production and for CO2 capture. Regeneration of CaO is completed via calcination in a regenerator vessel. The IGCC with CaO sorption-enhanced process is modeled and simulated using Aspen Plus software. Two commercial available gasification technologies, Shell and Texaco, are integrated with the sorption-enhanced process. The results showed IGCC with CaO sorption-enhanced process has a satisfactory system performance. Even though the net electricity efficiency is not as high as expected, just around 30–33%, the system has a high CO2 capture efficiency ∼97% and low pollutant emissions. Moreover, compared with conventional IGCC–CCS, the schematic diagram of the IGCC–CCS process is simplified. Parameters that affect the plant performance are analyzed in the sensitive analysis, including WGS-absorber temperature, H2O/CO ratio, pressure, etc. Some challenges to the system are also discussed.

Process configuration options for handling incomplete fuel conversion in CO2 capture: Case study on natural gas-fired CLC

“Innovative reactors” (based on chemical looping, membrane separation or sorption-enhanced processes) in power processes for CO2 capture appear to behave in such a way that some unconverted fuel could remain in the captured CO2-rich stream. This has the double drawback of adding impurities to the CO2 and of reducing the efficiency of the power cycle from which the CO2 was captured. The purpose of this paper is to illustrate the implications of some options for handling fractions of unconverted fuel in a captured CO2-rich stream. The selected case study is a chemical looping combustion (CLC) reactor integrated in a gas turbine cycle. Different process layouts are presented for the CO2 processing to reduce the amount of fuel components in the CO2, and process simulations are performed for fuel conversion rates in the range of 90–100%. Three different assumptions for the composition of the unconverted fuel were investigated (mixture of hydrocarbons, methane only, mixture of H2 and CO). Also the impact of the presence of fuel-derived N2 in the CO2 was investigated. Three different process solutions were studied for handling of the unconverted fuel: Separation of non-condensable gases in a distillation column, either for recirculation to the CLC reactor (fuel recovery method C) or for combustion in a duct burner (fuel recovery method C/B), or final oxidation of the unconverted fuel with oxygen from a cryogenic ASU (fuel recovery method O). Generally speaking, recovery of unconverted fuel for recirculation to the CLC reduction reactor through the use of a distillation column could have the double benefit of increasing the cycle efficiency and reducing the amount of impurities in the compressed CO2. It is however difficult to quantify the efficiency improvement, since it cannot be determined with the applied CLC reactor model how the reactor would respond to the introduction of a recirculation stream. The presence of H2 in the CO2 as well as the presence of N2 (or other inerts) in the fuel are found to be issues that merit further investigation. Also increasing rates of unconverted fuel in the CO2 due to oxygen carrier degradation could be an issue that merits further attention for CLC.

96/03350 - Technology for removing carbon dioxide from power plant flue gas by the physical adsorption method

This paper provides an insight on state-of-the-art, limits and potentials of pressure swing adsorption (PSA) as CO2 capture technology into power plants. To get a complete picture both post- and pre-combustion cases are considered. The expertise developed with modeling and simulation of PSA processes in power plants stressed the need of a holistic approach to the analysis. The different domains which determine the viability of the technology are taken into account, together with their mutual influence. Accordingly, adsorbent materials characteristics, process configurations and integration strategies are investigated and discussed, in order to provide a general evaluation. In post-combustion applications, PSA has been widely assessed with regard to adsorbent materials and processes. The integration into power plant does not entail significant issues, with a good potential for retrofitting old plants. An excessively large footprint of the separation unit has been reported, which seems to question the feasibility of PSA. In pre-combustion applications, prospects for improving adsorbent materials and processes are noticed. Good potential for PSA is envisaged whit hot gas separation processes, especially with sorption-enhanced processes. Furthermore, the complexity of the arrangements in pre-combustion cases may open room for interesting alternative system configurations, like power and H2 coproduction layouts.