Sorption-enhanced Membrane Reactor Research Articles

Investigating the effects of operating parameters on the performance of sorption-enhanced membrane reactor for ethanol steam reforming reaction using computational fluid dynamics method

In this study, the performance of a sorption-enhanced membrane reactor (SEMR) was examined using a Pd-Ag membrane during ethanol steam reforming (ESR). During this study, simultaneous ESR and CO2 adsorption concept was adopted and computational fluids dynamic (CFD) method (two-dimensional model) was developed to evaluate the SEMR performance during ESR reaction. The employed CFD model for the present study provided information about the molar fractions and pressures of components to analyze driving forces under unsteady state condition. Regarding validation, the experimental data related to the membrane reactor (MR) during ESR reaction showed good agreement with modeling outcomes and the application of adsorption reaction improved MR performance. The SEMR performance was investigated after model validation, and during this step, SEMR and MR were compared. Moreover, the effects of main operating parameters, such as gas hour space velocity (GHSV), reaction pressure, and temperature, were studied to compare the SEMR and MR performance during C2H5OH conversion and hydrogen recovery. CFD modeling results showed that SEMR had better performance and increased the ethanol conversion about 20% (SEMR: 70% and MR: 59%) by temperature enhancement at low pressures compared with the conventional membrane reactor. The relative error between numerical and experimental data obtained was 3% in this study.

Olive mill wastewater valorization through steam reforming using hybrid multifunctional reactors for high-purity H2 production

The main purpose of this study was to assess the benefits of different hybrid multifunctional reactors (sorption-enhanced reactor (SER), membrane reactor (MR) and sorption-enhanced membrane reactor (SEMR)) comparatively to a traditional reactor (TR) for H2 production through the steam reforming of olive oil mill wastewater (OMWSR). In all reactor configurations, an in-house prepared Ni-Ru/Ce-SiO2 catalyst was used, combined in the SERs with a potassium-promoted hydrotalcite-based sorbent to capture CO2. Additionally, in the MR and SEMR configurations, a commercial Pd-Ag membrane was utilized to separate H2 from the reaction medium.It was verified an increase in both the H2 production and catalyst stability using the SER (during the pre-breakthrough of CO2) in comparison with the TR. However, a higher enhancement of the H2 yield was observed using the SEMR (again during the pre–breakthrough period), which was less pronounced after the saturation of the sorbent (i.e., in the MR), due to the effect of the H2-selective membrane only. Furthermore, pure H2 can be obtained in the permeate side of the membrane reactors (in the absence of sweep gas).It was also demonstrated that the use of such multifunctional reactors (and particularly the SEMR) in the steam reforming of real olive mill effluents allows reducing drastically the pollutant load of these streams, while economically valorizing this waste with the production of green H2.

Comparative techno-economic analysis for steam methane reforming in a sorption-enhanced membrane reactor: Simultaneous H2 production and CO2 capture

Hydrogen (H2) is currently receiving significant attention as a sustainable energy carrier. Steam methane reforming (SMR) accounts for approximately 50% of H2 production methods worldwide. However, SMR is concern because of the prodigious carbon dioxide (CO2) emissions that have resulted in a global climate emergency. CO2 emissions remain, although some efforts have been made in a membrane reactor (MR) coupled with membranes to improve the H2 yield. A sorption-enhanced membrane reactor (SEMR) has been proposed as a next-generation process for simultaneous H2 production and CO2 capture. In this study, the thermodynamic and economic evaluation of SEMR were implemented using a process simulation, an itemized cost estimation, a sensitivity analysis (SA), and an uncertainty analysis (UA). The thermodynamic analysis results revealed that unit H2 production costs of 4.53, 1.98, and 3.04 $ kgH2−1 were obtained at 773 K for a conventional packed-bed reactor (PBR), a MR, and a SEMR, respectively. The SA results identified PSA as the most critical economic parameter for a unit H2 production cost for a PBR, whereas natural gas is determined to be the most influential parameter for a MR and a SEMR. The UA results from a Monte-Carlo simulation provided a broad range of unit H2 production costs, with 4.26–5.44 $ kgH2−1 for a PBR, 1.61–2.94 $ kgH2−1 for a MR, and 2.83–4.19 $ kgH2−1 for an SEMR. This indicates that using a SEMR for next-generation H2 production and CO2 capture is beneficial.

Comparative numerical analysis for an efficient hydrogen production via a steam methane reforming with a packed-bed reactor, a membrane reactor, and a sorption-enhanced membrane reactor

Following the adoption of the Paris Agreement, H2 has come to be considered a promising alternative energy carrier owing to its eco-friendly characteristics. However, H2 is mostly obtained via carbon-based production methods, which account for approximately 96% of the global H2 yield and emit CO2 as a by-product. A membrane reactor (MR) was introduced to produce H2 more efficiently via a positive chemical equilibrium shift, according to Le Chatelier’s principle. CaO was employed as a CO2 adsorbent in an MR to form a sorption-enhanced membrane reactor (SEMR), in which the additional CO2 removal enhanced the equilibrium shift. Additionally, the direction of sweep gas through the membrane with respect to that of the reactants, i.e., co-current or counter-current flow, was found to affect the performance of the reactors.In this study, numerical simulations based on chemical reaction kinetics were carried out to investigate the effects of the employment of H2 separation membrane and/or CO2 adsorbent as well as those of co-current and counter-current flows. Based on the numerical simulation results, H2 yield rates of 0.00143, 0.00145, 0.00127, 0.00121, and 0.00852 mol s−1 were achieved using the SEMR with counter-current flow, SEMR with co-current flow, MR with counter-current flow, MR with co-current flow, and a packed-bed reactor, respectively. This showed that an SEMR can be used to not only enhance H2 production but also achieve this in an environment-friendly manner.

From sorption-enhanced reactor to sorption-enhanced membrane reactor: A step towards H2 production optimization through glycerol steam reforming

The main goal of this work is to access the benefits of using a sorption-enhanced membrane reactor (SEMR) comparatively to a sorption-enhanced reactor (SER) and a traditional reactor (TR) for H2 production through glycerol steam reforming (GSR). A SER, where a potassium-promoted hydrotalcite-like material (K-MG30) was used to capture the CO2 produced during GSR on an alumina supported Rh catalyst, was tested. An enhancement of the H2 production was observed not only during the pre- and breakthrough of CO2 but also during the post-breakthrough as compared to the conventional TR. While the initial enhancement was mostly due to CO2 sorption and affected more directly the water-gas shift (WGS) reaction, the observed catalytic activity of K-MG30 towards glycerol decomposition and mainly WGS reaction was responsible for the improved performance during post-breakthrough. Still, considerably higher H2 purity was obtained in the first moments. Ultimately, a much significant improvement in terms of H2 production was observed in the SEMR, where a Pd-Ag membrane separated selectively the hydrogen from the other gases. An increment of the maximum H2 yield in the pre- and breakthrough regions from 1.6 up to 3.6 mol∙molfedglycerol-1 was obtained. The simultaneous removal of both H2 and CO2 significantly benefited the WGS reaction. Consequently, only H2 was obtained in the gas phase of the retentate stream during the pre-breakthrough period. Moreover, ultra-pure H2 was obtained in the permeate side of the dense Pd-Ag membrane, meaning that if the SEMR is continuously operated in the pre-breakthrough region, pure H2 would continuously be obtained in both retentate and permeate streams.

Hydrogen production through steam reforming of bio-oils derived from biomass pyrolysis: Thermodynamic analysis including in situ CO2 and/or H2 separation

A thermodynamic analysis based on the minimization of the Gibbs free energy method was performed in order to study the steam reforming of real bio-oils (obtained from biomass fast pyrolysis) from different sources. For comparison purposes, four types of reactors were used, namely: traditional reactor (TR), membrane reactor (MR) with H2 separation, sorption-enhanced reactor (SER) with CO2 sorption, and sorption-enhanced membrane reactor (SEMR) with both H2 and CO2 separation. The CO2 capture was studied varying the sorbent (CaO) to feed molar ratio (SFR) while the effect of the H2 removal was assessed with the use of a removal fraction (fH2) of 0 to 0.8 (typical recoveries for an H2-selective membrane).The simulated results obtained for the TR showed a good agreement with those reported in literature experimental works at similar operation conditions. The optimum conditions for the production of hydrogen were obtained in the SEMR in which it was possible to obtain 99% of the maximum theoretical yield for spruce bio-oil and 97% of the maximum yield for wheat bio-oil. Furthermore, this reactor configuration minimizes CH4, H2, CO, CO2 and coke yields. In addition, the effect of pressure in a range of 1 to 10 bar was also assessed for the reactor configurations with H2 removal. It was shown that the increase of pressure decreases H2 yield; nevertheless, this can be offset by moderately increasing the WFR.

COx free hydrogen production through water-gas shift reaction in different hybrid multifunctional reactors

High-purity H2 production from the water-gas shift (WGS) reaction was assessed. Since the WGS is limited by the equilibrium, different reactor types that allow to extract one or more products from the reaction medium, namely membrane reactor (MR; for H2 separation), sorption-enhanced reactor (SER; for CO2 capture) and sorption-enhanced membrane reactor (SEMR; for simultaneous CO2 and H2 removal), were used and compared with fixed-bed traditional reactor (TR). Experimental results were obtained with commercial materials, namely WGS Cu-based catalyst and K-doped hydrotalcite for CO2 capture. Additionally, in the MR and SEMR, a self-supported Pd-Ag membrane for separating H2 selectively from the reaction zone was used.Experimental tests were performed at different temperatures and pressures, and the results obtained were compared with those predicted by theoretical simulations at the thermodynamic equilibrium. Moreover, in the case of SER, different methods for the hydrotalcite regeneration and the evaluation of its working sorption capacity under cycling conditions were also assessed. Not all sorbed CO2 can be desorbed under dry conditions (pure nitrogen purging stream); however, if steam is used during the regeneration step, all sites can be effectively regenerated, allowing to have a stable working sorption capacity. Concerning the performance of the different hybrid reactors tested, i.e. MR, SER and SEMR, it was found that all are able of overcoming the TR limitations, with performances reaching conversion above the equilibrium for the feed composition. Nonetheless, only the SER and SEMR configurations allow to obtain high-purity H2 in all reactor exiting streams under the operating conditions herein assessed.

Computational fluid dynamic simulation of a sorption-enhanced palladium membrane reactor for enhancing hydrogen production from methane steam reforming

To understand the reaction process of methane steam reforming in a sorption enhanced membrane reactor (SEMR), a computational fluid dynamic (CFD) model was developed to simulate the methane (CH4) steam reforming in a palladium-based membrane reactor using a Ni-based catalyst and Na2ZrO3 CO2 sorbent. The CFD model gained the insight of details in the reactor which could not be obtained by experiment. With the detailed information, this model detected the difference of reaction kinetics and fluid dynamic conditions in a SEMR and a traditional membrane reactor (MR). The comparison suggests that sorption-enhanced membrane reactor not only decreases CO2 fraction, but also improves hydrogen (H2) production by increasing reaction rates, CH4 conversion and H2 yield. The poisoning effect of carbon monoxide (CO) on the palladium membrane can also be minimized by reduced CO fraction as a result of in-situ CO2 capture.

CFD analysis of a hybrid sorption-enhanced membrane reactor for hydrogen production during WGS reaction

The main aim of this work is a comprehensive study on a new Hybrid Sorption-Enhanced Membrane Reactor (HSE-MR) concept, in which a Pd-Ag membrane during water gas shift (WGS) reaction was applied. This purpose was performed by integrating both the WGS and CO2 absorption reactions. To avoid the high experimental test costs, for evaluating the HSE-MR performance during WGS reaction, a 2D model based on Computational Fluid Dynamic (CFD) method was developed. The proposed CFD model provides the local information of pressure and component molar fractions for the driving force analysis at unsteady state conditions. The validation of the HSE-MR during WGS reaction was carried out by experimental data and a good agreement between modeling results and experimental data was found. After model validation, the performance of the HSE-MR has been compared with that obtained by both a Pd-Ag MR and a Sorption-Enhanced Reactor (SER). Moreover, the effects of some significant operating parameters, such as reaction temperature, reaction pressure and gas hour space velocity (GHSV), on the performance of the HSE-MR were studied in terms of CO conversion and hydrogen recovery in compared with both MR and SER. The CFD results show that HSE-MR, during WGS reaction, presents better performance with respect to MR and SER. As a special consequence, CFD simulation results also show that the increasing of operating parameters has a positive effects on the HSE-MR performance during WGS reaction.

Steam reforming of olive oil mill wastewater with in situ hydrogen and carbon dioxide separation – Thermodynamic analysis

A thermodynamic analysis of the steam reforming reaction of olive oil mill wastewater (OMW) with in situ carbon dioxide (CO2) and hydrogen (H2) simultaneous removal was performed. The idea behind is the integration of the reformer with a H2-selective membrane and a CO2-sorbent in a hybrid multifunctional reactor. The simulations were performed at different temperatures (300–500°C), pressures (1–11bar), removal fractions of H2 (0–0.8), removal fractions of CO2 (0–0.99) and also for different water contents in the feed (20–92wt.%). The results were compared in terms of performance reached for the different reactor configurations: traditional reactor (TR), membrane reactor (MR) with H2 separation, sorption-enhanced reactor (SER) with CO2 capture and sorption-enhanced membrane reactor (SEMR). For the SEMR, the optimum operation conditions were determined. An H2 yield very close to the stoichiometric value of 13.54 was obtained at 1bar, 500°C, water content in the feed of 60–92wt.% (steam-to-carbon feed ratio, SCFR=2.1–16.0), fCO2=0.99 and fH2=0.80. The H2 yield obtained in such optimum conditions corresponds to an enhancement of 141% comparatively to the TR. Moreover, under these operation conditions there is no significant production of CO2, CO, CH4 and coke.

Enhancing the low temperature water–gas shift reaction through a hybrid sorption-enhanced membrane reactor for high-purity hydrogen production

The low temperature water–gas-shift reaction (LT-WGS) has been assessed by means of a hybrid sorption-enhanced membrane reactor (HSEMR) that combines both CO2 and H2 removal from the reaction zone. The performance of this reactor has been compared with that obtained by (i) a traditional and (ii) a sorption-enhanced (only CO2 is removed) reactor operating in the same operational conditions. Cu/ZnO–Al2O3 and K2CO3-promoted hydrotalcite materials have been used as a catalyst and CO2 sorbent, respectively. A self-supported Pd–Ag membrane tube has been used in order to selectively separate the H2. The CO2 sorption capacity, in the presence and absence of water vapour, of the potassium-promoted hydrotalcite has been determined by means of breakthrough experiments. The presence of water vapour enhanced the sorption capacity of the hydrotalcite in the experimental conditions used. Concerning the performance of the HSERM, results clearly show that when both CO2 and H2 are removed from the reaction zone, the hydrogen production through the reversible LT-WGS reaction is enhanced compared to either a traditional or a sorption-enhanced reactor, allowing overcoming equilibrium limitations and obtain a pure H2 stream.

Thermodynamic analysis of Glycerol Steam Reforming for hydrogen production with in situ hydrogen and carbon dioxide separation

A thermodynamic study of Glycerol Steam Reforming (GSR) for hydrogen production with in situ carbon dioxide and hydrogen (reaction products) simultaneous removal was performed. The sorption-enhanced membrane reactor (SEMR) was divided into multiple sub-Gibbs reactors and the Gibbs free energy minimization method was employed. The effects of temperature (600–800 K), molar water-to-glycerol feed ratio (WGFR) (3–9), pressure (1–5 atm) and fraction of hydrogen and carbon dioxide removal (f, 0–0.99) on the GSR process were target of investigation. A hydrogen yield (total moles of hydrogen produced/mole of reacted glycerol) very close to the stoichiometric value of 7 was obtained at 700 K, WGFR of 9, 1 atm and for fCO2=0.99 and fH2=0.80. This corresponds to an enhancement of 217%, 47% and 22% in terms of hydrogen yield comparatively to the traditional reactor (TR), sorption-enhanced reactor (SER) with carbon dioxide capture (fCO2=0.99) and membrane reactor (MR) with hydrogen separation (fH2=0.80), respectively. In terms of coke, its formation was only observed under WGFRs below the stoichiometric value of 3.

Studies on water–gas-shift enhanced by adsorption and membrane permeation

A new sorption enhanced membrane reactor (SEMR), consisting of a packed adsorbent-catalyst bed (10% CuO/CeO2 catalyst and a hydrotalcite-derived Mg–Al mixed oxide) around a tubular Pd/Ag hollow fibre membrane, has been proposed to obtain high purity H2 and simultaneous capture of CO2 during the water gas shift reaction. For comparison purposes, catalytic activity tests were carried out at atmospheric pressure and operating temperatures between 100°C and 550°C in three different catalytic reactors: (1) a fixed-bed reactor (FBR), (2) a sorption enhanced reactor (SER) and (2) a new SEMR. In all cases, the feed mixture Ar/CO/H2O ratio was 11/1/0.75 with a space velocity of 22L/gh. The performance of the FBR was used as a reference to compare with the results obtained from the SER and SEMR. The H2 yield at 350°C using the SER was 80%, which is 33% higher than that obtained in the traditional FBR and 18% higher than the corresponding thermodynamic equilibrium. However, due to the high CO/H2O ratio (R>1), undesirable side-reactions such as C deposition become important at temperatures higher than 400°C. A similar behaviour was observed using the SEMR, however in this case, a high purity COx free H2 production was obtained. This preliminary study shows relevant data obtained using a SER and the new SEMR, which allows for the better understanding and design of multifunctional catalytic reactors.