Search

The aim of this work was to evaluate the performance of three different supported amine sorbents in a 6‐step vacuum swing adsorption (VSA) cycle through process simulation and optimization for a representative post‐combustion CO2 capture system. Detailed process optimization revealed that all the adsorbents were able to achieve the desired purity‐recovery targets. The best performing adsorbent in terms of productivity was Lewatit with a productivity of 0.48 mol m−3 ads s−1. All the adsorbents exhibited similar minimum specific energy value of around 1 MJ kg−1 on an electric basis. [ABSTRACT FROM AUTHOR]

Steam adsorption enhanced reaction processes are a promising process intensification for many types of reactions, where water is formed as a byproduct. To assess the potential of these processes, adequate models are required that accurately describe water adsorption, particularly under the desired elevated temperatures and pressures. In this work, an adsorption isotherm is presented for H2O adsorption at 200–350 °C and 0.05–4.5 bar partial pressure on molecular sieve (LTA) 3A. The isotherm has been developed on the basis of experimental data obtained from a thermogravimetric analysis and integrated breakthrough curves. The experimental data at lower steam partial pressures can be described with a Generalized Statistical Thermodynamic Adsorption (GSTA) isotherm, whereas at higher steam partial pressures the experimental data can be adequately captured by capillary condensation. Based on the characteristics of the adsorbent particles, a linear driving force relation has been derived for the adsorption mass transfer rate and the apparent micropore diffusivity is determined. The isotherm and mass transport model presented here prove to be adequate for modelling and improved evaluation of steam adsorption enhanced reaction processes. [ABSTRACT FROM AUTHOR]

• Steam separation enhancement promising process intensification for CO 2 utilization. • Reactive steam permeation processes require hydrothermal stability, permselectivity. • Reactive steam adsorption processes require high working capacity, heat management. • Progress in process development requires combination of theory and experiments. Enhancement by steam separation is a promising process intensification for many types of reactions in which water is formed as a byproduct. For this, two main technologies are reactive vapor permeation (membrane technology) and reactive adsorption. Both can achieve significant conversion enhancement of equilibrium limited reactions by in situ removal of the by-product steam, while additionally it may help protecting catalysts from steam-induced deactivation. In general, reactive permeation or reactive adsorption would be preferable for distinctly different process conditions and requirements. However, although some advantages of reactive steam separation are readily apparent from a theoretical, thermodynamic point of view, the developments in several research lines make clear that the feasibility of in situ steam removal should be addressed case specifically and not only from a theoretical point of view. This includes the hydrothermal stability of the membranes and their permselectivity for reactive steam permeation, whereas high-temperature working capacities and heat management are crucial aspects for reactive steam adsorption. Together, these developments can accelerate further discovery, innovation and the rollout of steam separation enhanced reaction processes. [ABSTRACT FROM AUTHOR]

Abstract Acidic γ-Al 2 O 3 is an active catalyst for the dehydration of methanol to dimethyl ether (DME). However, the produced steam reduces the activity. In this work, the influence of the exposure of γ-Al 2 O 3 to steam on the catalytic activity for methanol dehydration has been determined. At 250 °C and increasing stream partial pressure the conversion of γ-Al 2 O 3 into γ-AlO(OH) is observed at a p(H 2 O) of 13–14 bar. As a consequence, the catalytic activity decreases, reducing the rate of methanol dehydration to around 25%. However, this conversion is reversible and under reaction conditions γ-AlO(OH) converts back to γ-Al 2 O 3 , recovering its catalytic activity. Graphical abstract Unlabelled Image Highlights • High pressure steam deactivates γ-Al 2 O 3 for the dehydration of methanol. • At 250 °C and from 14 bar steam upward γ-Al 2 O 3 is converted to γ-AlO(OH). • Conversion of γ-Al 2 O 3 to γ-AlO(OH) reduces its catalytic activity. • Under reaction conditions γ-AlO(OH) converts to γ-Al 2 O 3 restoring catalytic activity. [ABSTRACT FROM AUTHOR]

Palladium membranes are being developed for the separation of hydrogen from syngas in industrial applications. However, syngas constituents carbon monoxide, carbon dioxide, and steam are known to adsorb at the membrane surface and inhibit the permeation of hydrogen. The current study combines an experimental study and modelling approach in order to investigate and quantify the inhibition effects. Experiments have been performed with a 2.8 μm thick palladium membrane (surface area 174 cm 2 ) on a tubular alumina support, including systematic variation of the concentrations of carbon monoxide, carbon dioxide, and steam at 22 bar total pressure and 350–450 °C. Carbon monoxide and steam inhibit hydrogen permeation. No significant effect has been found for carbon dioxide, except indirectly by carbon monoxide produced in situ from carbon dioxide. A constriction resistance model has been derived, explicitly relating the decrease in surface coverage by adsorbed hydrogen to the ensuing decrease in transmembrane flux. Very high surface coverages by inhibiting species θ i > 0.995 are predicted. The results highlight that inhibition effects are greatly reduced at high hydrogen partial pressures due to competitive adsorption. Due to the lateral diffusion of permeating hydrogen atoms in the metallic membrane, the thickness of the palladium membrane strongly determines the extent to which surface coverage by non-hydrogen species causes a decrease in hydrogen transmembrane flux. Depending on the operating conditions, membranes are predicted to have an optimal minimum thickness below which an increased intrinsic permeance is offset by an increased impact of inhibition. [ABSTRACT FROM AUTHOR]

Sorption-enhanced water–gas shift (SEWGS) combines the water–gas shift reaction with in situ adsorption of CO 2 on potassium-promoted hydrotalcite (K-HTC) and thereby allows production of hot, high pressure H 2 from syngas in a single unit operation. SEWGS is a cyclic process, that comprises high pressure adsorption and rinse, pressure equalisation, and low pressure purge. Here, results are presented of a SEWGS cycle design study, based on recently developed expressions for the interaction of CO 2 and H 2 O with K-HTC. It is shown that during the cycle, steam adsorbs in the rinse step and desorbs during the subsequent reduction in pressure, thereby improving the CO 2 purity in the column and thus enhancing the efficiency of the rinse. A parameter study based on numerical simulations shows that the carbon capture ratio depends mainly on the purge steam to carbon feed ratio, whereas the CO 2 product purity depends mainly on the rinse steam to carbon feed ratio. An optimisation yields a SEWGS cycle that consumes significantly less steam than cycle designs previously reported in the literature. [ABSTRACT FROM AUTHOR]

Highlights: [•] We measured breakthrough curves for and adsorption at 400°C, up to 24bar. [•] Surface adsorption occurs at specific sites for or up to 5bar. [•] and adsorb competitively in nanopores at higher partial pressures. [•] Adsorption isotherm and sorption kinetics have been validated with a reactor model. [ABSTRACT FROM AUTHOR]

Abstract: Two main routes for small-scale diesel steam reforming exist: low-temperature pre-reforming followed by well-established methane steam reforming on the one hand and direct steam reforming on the other hand. Tests with commercial catalysts and commercially obtained diesel fuels are presented for both processes. The fuels contained up to 6.5ppmw sulphur and up to 4.5vol.% of biomass-derived fatty acid methyl ester (FAME). Pre-reforming sulphur-free diesel at around 475°C has been tested with a commercial nickel catalyst for 118h without observing catalyst deactivation, at steam-to-carbon ratios as low as 2.6. Direct steam reforming at temperatures up to 800°C has been tested with a commercial precious metal catalyst for a total of 1190h with two catalyst batches at steam-to-carbon ratios as low as 2.5. Deactivation was neither observed with lower steam-to-carbon ratios nor for increasing sulphur concentration. The importance of good fuel evaporation and mixing for correct testing of catalysts is illustrated. Diesel containing biodiesel components resulted in poor spray quality, hence poor mixing and evaporation upstream, eventually causing decreasing catalyst performance. The feasibility of direct high temperature steam reforming of commercial low-sulphur diesel has been demonstrated. [Copyright &y& Elsevier]

Kinetics of the water–gas shift reaction over a FeCr-based catalyst is measured with high and low extremes for CO2 and H2 content and containing 11–35 ppmv of H2S, relevant for separation-enhanced water–gas shift in IGCC. Kinetics is well described by a power rate law. H2S negatively affects the reaction rate. Comparison with literature shows a more elaborate kinetic model is better suited to fully capture kinetics from sulphur-free to high-sulphur. [ABSTRACT FROM AUTHOR]

A one-dimensional reactor model has been developed to describe the performance of a sorption-enhanced steam-methane reforming and water−gas shift reactor. In part I of this paper, the model is verified using the analytical solution for the breakthrough curve and validated using the results of laboratory-scale CO2sorption-only experiments. Langmuir and Freundlich isotherms are fitted to an experimentally derived adsorption isotherm, while a linear driving force model is used to describe the sorption kinetics. The breakthrough profile is accurately described using the Freundlich isotherm. This holds also when the purge flow or duration of the desorption step are decreased, provided the mass transfer coefficient is changed accordingly during the desorption step. A sensitivity analysis shows that the breakthrough profile is sensitive to the adopted isotherm model and its parameters. The molecular diffusion coefficient affects the slope of the breakthrough curve, while particle size and heat of adsorption show hardly any effect. In part II, the model will be applied to laboratory-scale sorption-enhanced steam-methane reforming experiments. [ABSTRACT FROM AUTHOR]

In this paper, the reactor model introduced in part I will be verified using the results of an analytical solution for the increase of CH4conversion over the bed and validated using the results of sorption-enhanced steam-methane reforming laboratory-scale experiments. An experimentally derived rate equation for the steam-methane reforming reaction is used, a literature rate equation for the water−gas shift reaction. An overview of modeling work on the sorption-enhanced reaction process for steam-methane reforming performed by other groups is presented. The CH4and CO2profiles obtained from laboratory-scale experiments are quite satisfactorily described using a Freundlich isotherm. A sensitivity analysis shows that both the CH4and CO2profiles are sensitive to the adopted isotherm model and its parameters. In addition to that, the CH4and CO2profiles are sensitive to the diffusion coefficient. Neither profile is sensitive to the particle size or the heat of adsorption. [ABSTRACT FROM AUTHOR]

The transition towards a CO2 neutral industry is currently spurring many new developments regarding processes for the conversion of CO2, or CO2-rich streams, into platform molecules such as methanol and dimethyl ether (DME). New processes give rise to new separation challenges, as well as novel opportunities for joint optimization of reaction and separation. In this context, the separation of CO2 and DME can be performed very efficiently using the newly developed concept of stripping enhanced distillation (SED). SED is a distillation process that utilizes an additional stripping component (clearing gas) to promote the separation in the column. SED benefits from the utilization of the feedstock components as a clearing gas that can afterwards be recycled back to the conversion unit with the vapor distillate. Strongly improving the separation performance in the column, this approach also removes the need for external stripping mediums and, in addition, this recycling approach may significantly reduce the demand on the conversion unit upstream of SED. The benefits of using SED are demonstrated for two different processes for DME synthesis: (i) CO2–DME separation after the sorption enhanced DME synthesis (SEDMES) process, using hydrogen as clearing gas, and (ii) CO2–DME separation after direct DME synthesis via dry reforming (DIDR), using methane as a clearing gas. For the different cases, it is shown that, with minimal adaptations, the energy consumption for distillation is reduced by 20–30%, while product losses are minimized at the same time. [ABSTRACT FROM AUTHOR]

Sorption enhanced dimethyl ether synthesis (SEDMES) is a novel DME production route from CO2-rich feedstocks. In situ water removal by adsorption results in high single-pass conversions, thereby circumventing the disadvantages of conventional routes, such as low carbon efficiency, energy intensive downstream separation and large recycling. The first-time demonstration of pressure swing regeneration with 80% single-pass carbon selectivity to DME allows for an enormous increase in productivity. Already a factor four increase compared to temperature swing regeneration is achieved, unlocking the potential of SEDMES as a carbon utilisation technology. [ABSTRACT FROM AUTHOR]

Sorption-enhanced reverse water–gas shift (SE-RWGS, here designated as 'COMAX') was studied with bifunctional reactive sorbents. First proof-of-concept is presented of the successful design of a multifunctional reactive sorbent, which combines CO2 activation and water adsorption functionalities in an integrated reactive sorbent, i.e. the active phase is loaded on the carrier that provides surface area for dispersion of the active (Pt, Cu) phase as well as H2O sorption capacity. Near complete selectivity to CO was achieved from atmospheric pressure up to at least 29 bar, i.e. the highest pressure studied in the experimental campaign. This selectivity was obtained with stoichiometric and excess quantities of hydrogen in the (RWGS) COMAX feed, the latter in view of the potential use of syngas mixtures. The newly developed bifunctional material bears important additional advantage for scaling up of the COMAX process, because it avoids the mixing of catalyst and adsorbent materials that differ in properties such as hardness. Evidently, the key parameter for optimizing the COMAX process is the working adsorption capacity of the system and (multi-column) cycle design. Improving the capacity can be done by optimizing the reactive adsorption conditions and by optimizing the regeneration method. [ABSTRACT FROM AUTHOR]

• Biomass, waste and CO 2 are suitable carbon sources for DME production. • New carbon sources require the development of new DME production processes. • Sorption Enhanced DME Synthesis (SEDMES) result in higher DME productivities. Renewable dimethyl ether (DME) is expected to contribute to the decarbonization of several sectors, including domestic heat supply and transport. The shift of the carbon source used for the production of DME from fossil to renewable, such as biomass, waste or captured CO 2 , entails an industrial challenge in terms of reactors, operation regimes, catalysts and product purification, with strong technical and economic repercussions. In this work, we review the latest developments on this topic, focusing on the direct synthesis of DME, and especial attention has been paid to the separation-enhanced technologies for DME production, including the Sorption Enhanced DME Synthesis (SEDMES). We address other aspects that are often neglected, such as the impact of heat and mass transfer phenomena, which become increasingly relevant in processes in which several reaction and sorption stages occur in the same reactor. We also include a techno-economic section that gives insight in the feasibility of several renewable DME production processes. Finally, we review the most recently deployed installations for renewable DME production, at commercial or pilot scale, as a model of the near-future of the DME industry. [ABSTRACT FROM AUTHOR]

A combined experimental and modeling study was performed to evaluate the relation between sorbent characteristics and process performance for solid sorption postcombustion CO2 capture. A pulverized coal (PC) and a natural gas combined cycle (NGCC) power plant were considered, addressing CO2 and H2O sorption. The measured isotherms for PEI/silica sorbent were implemented in an equilibrium-based flow sheeting model. The PC regeneration heat demand is 3.9 GJ/ton CO2 captured. This is lower than that of the NGCC and, though a direct comparison is not valid, similar to a literature MEA case. Solid sorption systems hold the promise to be energetically superior to MEA: a 2-fold increase in CO2 adsorption capacity (to 4.4 mmol/g) yields a regeneration heat demand of 3.3 GJ/ton, even when accompanied by a similar increase in H2O adsorption capacity. [ABSTRACT FROM AUTHOR]

Steel production is a main source of CO2 emissions globally. These emissions must be drastically reduced to meet climate change mitigation goals. STEPWISE is a Sorption Enhanced Reactive Process (SERP) technology that converts steel works arising gases to H2 with simultaneous CO2 capture. The main energy requirements of the process are the high- and low-pressure steam quantities that are needed to rinse and regenerate the adsorbent. In this simulation study, the separation performance of STEPWISE is evaluated over a range of steam and feed pressure inputs by searching those design points where CO2 recovery and purity percentages are equalized. This method is used to facilitate the comparison of different operating regimes. Results highlight the importance of the rinse to purge ratio (R/P) as a design variable. A higher R/P ratio is demonstrated to maintain CO2 recovery and purity of ~95.5%, while total steam consumption and feed carbon loading are reduced by 27% and 20%, respectively. This is achieved without changing other parameters, like cycle time. Additionally, it is demonstrated that the CO2 capture performance can be maintained for varying feed pressure values by tuning the feed carbon loading. Future studies are recommended to focus on the expected role of the feed gas steam content on these findings. [ABSTRACT FROM AUTHOR]

The synthesis of methanol from biomass-derived syngas can be challenging because of the high CO2 content in the bio-syngas, resulting in lower kinetics and higher catalyst deactivation. This work explores the in situ pre-treatment of a CO2-rich syngas with a CO2/CO ratio equal to 1.9 through the reverse-water gas shift reaction with the aim of adjusting this ratio to a more favorable one for the synthesis of methanol with Cu-based catalysts. Both reactions take place in two catalytic beds placed in the same reactor, thus intensifying the methanol process. The water produced during syngas conditioning is removed by means of a sorbent zeolite to prevent the methanol catalyst deactivation and to shift the equilibrium towards the methanol formation. The combination of the CO2 shifting and the water sorption strategies lead to higher productivities of the catalytic bed and, under certain reaction conditions, to higher methanol productions. [ABSTRACT FROM AUTHOR]

• Model analysis of fixed bed reactor for Sorption Enhanced DiMethyl Ether Synthesis. • Model validation with experimental data from bench scale reactor. • SEDMES ensures high CO x conversion and DME selectivity for any CO/CO 2 feed ratio. • Larger diameter tubes than in conventional direct DME synthesis can be adopted in SEDMES. Sorption Enhanced DiMethyl Ether Synthesis (SEDMES) is a promising option to overcome thermodynamic limitations of conventional DME production processes. In this work a 2D + 1D heterogeneous dynamic model of the reaction/adsorption step in a tube of an externally cooled multitubular fixed bed SEDMES reactor is developed in order to investigate the effect of design and operating parameters on thermal behavior and DME yield performances of the reactor. The model is validated by comparison with experimental results from a bench scale unit, including the dynamics of the outlet composition and the temperature trajectories in different points along the axial coordinate. Simulations with the validated model address the effect of the CO/CO 2 ratio in the feed. The results confirm that, thanks to the effective in-situ H 2 O removal, the DME yield performances (65–70% in this work) of SEDMES are poorly sensitive on the CO/CO 2 ratio. Accordingly, on increasing the CO 2 content in the feed, SEDMES provides larger advantages with respect to conventional DME direct synthesis. Calculations of maximum temperatures achieved along the axial coordinate show that catalyst thermal stress in the hottest inlet zone of the SEDMES reactor slightly increases with the CO content in the feed due to faster kinetics of the DME production reactions. However, thanks to the dilution effect provided by the adsorption material, maximum bed temperature keeps ∼ 20–30 K below the catalyst stability limit reported in the literature (573 K). Accordingly, larger tube diameters (up to 46.6 mm) than in conventional reactors for the direct synthesis of DME can be adopted with less than 2% loss in DME yield. [ABSTRACT FROM AUTHOR]