Papers by Stefano Brandani
Adsorption, 2017
The formulation of a thermodynamic framework for mixtures based on absolute, excess or net adsorp... more The formulation of a thermodynamic framework for mixtures based on absolute, excess or net adsorption is discussed and the qualitative dependence with pressure and fugacity is used to highlight a practical issue that arises when extending the formulations to mixtures and to the Ideal Adsorbed Solution Theory (IAST). Two important conclusions are derived: the correct fundamental thermodynamic variable is the absolute adsorbed amount; there is only one possible definition of the ideal adsorbed solution and whichever starting point is used the same final IAST equations are obtained, contrary to what has been reported in the literature.
Industrial & Engineering Chemistry Research, 2016
The key challenge in postcombustion capture from gas-fired power plants is related to the low CO ... more The key challenge in postcombustion capture from gas-fired power plants is related to the low CO 2 concentration in the flue gas (4−8% by volume). This means that conventional amine processes will result in a relatively high energy penalty, whereas novel adsorbents and adsorption processes have the potential to improve the efficiency of separation. High-selectivity adsorbents are required to achieve relatively high CO 2 uptake at low partial pressures, which means that the separation process should be based on either very strong physisorption or chemisorption with thermal regeneration. From the process point of view, the main challenge is to develop efficient separation processes with rapid thermal cycles. In this report we present a detailed overview of the methodology behind the development of novel materials and processes as part of the "Adsorption Materials and Processes for Gas-fired power plants" (AMPGas) project. Examples from a wide variety of materials tested are presented, and the design of an innovative bench-scale 12-column rotary wheel adsorber system is discussed. The strategy to design, characterize, and test novel materials (zeolites, amine-containing MOFs, amine-based silicas, amine-based activated carbons, and carbon nanotubes), specifically designed for CO 2 capture from dilute streams is presented.
Chemical Engineering & Technology, 2016
The mass balance for a zero length column (ZLC) system leads to a very simple check which can be ... more The mass balance for a zero length column (ZLC) system leads to a very simple check which can be used to ensure internal consistency of the experimental curves. This is based on reporting experiments run at different flow rates on a c/c 0 vs. Ft plot, where F is the volumetric flow rate. The proposed method is applied to two different sets of results from the literature and can be used to identify that in one case the data are inconsistent. The results lead to an important recommendation: any future contribution reporting ZLC curves should include the c/c 0 vs. Ft plot which can confirm the internal consistency of the results and indicate if the experiments are carried out under equilibrium or kinetic control.
International Journal of Greenhouse Gas Control, 2016
The impact of humidity and flue gas impurities on PIM-1 membrane performance for post combustion ... more The impact of humidity and flue gas impurities on PIM-1 membrane performance for post combustion capture, i.e. CO2 permeability and CO2/N2 selectivity, is investigated in this study. The presence of humidity in the feed stream induces a decrease in the permeability coefficients of both CO2 and N2, from 7010 Barrer (dry state) to 4135 Barrer (%RH=50%) and 360 Barrer (dry state) to 250 Barrer (%RH=50%) respectively. PIM-1 shows also a high water permeability (58800 Barrer) which increases with the relative humidity of the feed. The interaction with flue gas contaminants (NOx, SOx, Water) leads to a dramatic decrease of the membrane performance even after short exposure and FTIR analysis confirmed modifications of the chemical structure of PIM-1 caused by the acid environment. These results indicate that test with flue gases have to be considered for all novel materials proposed for carbon capture applications since the decrease in membrane permeability in presence of water and other impurities has to be taken into account during the design of the separation process.
Computers & Chemical Engineering, 2016
An equilibrium theory simulator (Esim) for the simulation of cyclic adsorption processes is prese... more An equilibrium theory simulator (Esim) for the simulation of cyclic adsorption processes is presented. The equations are solved with a Godunov upwind flux scheme that does not require either the evaluation of characteristics or shock equations or the imposition of a numerical entropy condition to track shocks. Esim is able to simulate non-trace and non-isothermal adsorption systems with any adsorption isotherm. Esim has been validated against gPROMS based simulations that use the full set of governing equations (including mass and heat transfer resistances and axial dispersion) carried out under conditions close to the limits where equilibrium theory is valid. Esim enables the establishment of bounds for the optimal performance of an equilibrium driven separation and requires only the measurement of adsorption isotherms.
Faraday Discuss., 2016
The zero length column (ZLC) technique is used to investigate the stability of Mg- and Ni-CPO-27 ... more The zero length column (ZLC) technique is used to investigate the stability of Mg- and Ni-CPO-27 metal–organic framework (MOF) crystals in the presence of water and humid flue gas. The design of the ZLC enables the stability test to be conducted over a considerably shorter time period and with lower gas consumption than other conventional techniques. A key advantage over other experimental methods for testing the stability of adsorbents is the fact that the ZLC allows us to quantify the amount adsorbed of every component present in the gas mixture. The developed protocol is based on a two-stage stability test. The samples were first exposed to a humid carbon dioxide and helium mixture in order to study the effect of water on the carbon dioxide adsorption capacity of the samples. In the second stage the samples were exposed to a flue gas mixture containing water. From the preliminary water stability test, the Ni-sample exhibited the highest tolerance to the presence of water, retaini...
Adsorption, 2016
The definitions of absolute, excess and net adsorption in microporous materials are used to ident... more The definitions of absolute, excess and net adsorption in microporous materials are used to identify the correct limits at zero and infinite pressure. Absolute adsorption is shown to be the fundamental thermodynamic property and methods to determine the solid density that includes the micropore volume are discussed. A simple means to define when it is necessary to distinguish between the three definitions at low pressure is presented. To highlight the practical implications of the analysis the case of adsorption of helium is considered in detail and a combination of experiments and molecular simulations is used to clarify how to interpret adsorption measurements for weakly adsorbed components.
International Journal of Greenhouse Gas Control, 2015
In 2005, the IPCC SRCCS recognized the large potential for developing and scaling up a wide range... more In 2005, the IPCC SRCCS recognized the large potential for developing and scaling up a wide range of emerging CO 2 capture technologies that promised to deliver lower energy penalties and cost. These included new energy conversion technologies such as chemical looping and novel capture systems based on the use of solid sorbents or membrane-based separation systems. In the last 10 years, a substantial body of scientific and technical literature on these topics has been produced from a large number of R&D projects worldwide, trying to demonstrate these concepts at increasing pilot scales, test and model the performance of key components at bench scale, investigate and develop improved functional materials, optimize the full process schemes with a view to a wide range of industrial applications, and to carry out more rigorous cost studies etc. This paper presents a general and critical review of the state of the art of these emerging CO 2 capture technologies paying special attention to specific process routes that have undergone a substantial increase in Technical Readiness Level towards the large scales required by any CO 2 capture system. 1. Introduction One important message from the IPCC SR on CCS (2005) was that a range of CO 2 capture technologies were already mature and ready for large scale demonstration, because gas separation processes were already operating in a mature industrial market, at scales close to those required by CCS. However, there was still scope for large reductions in capture costs by optimizing these mature gas separation technologies and other enabling components in the full CO 2 capture systems. Several reviews in this Special Issue are devoted to analysing the recent advances of the classic "postcombustion", "precombustion" or "oxyfuel combustion" CO 2 capture systems. The IPCC SR also noted that there was also potential for emerging CO 2 capture systems to compete with their more mature counterparts by offering lower capture cost and efficiency penalties. This review is only concerned with this second category of emerging CO 2 capture processes. Separation process Application TRL* Comments 2005 2015 Absorption Physical Industry 9 9 Commercial technology for the separation of H 2 /CO 2 mixtures from syngas (<3 Mt CO /y). Pre-combustion 8 8 Most components are TRL 9, but hydrogen-based power generation is less mature. Chemical Industry 9 9 Commercial technology in refineries and for the natural gas sweetening. Post-combustion 7 8 Demonstrated at a capture rate of 1 Mt CO 2 /y in the Boundary Dam CCS project. Cryogenics Air separation Industry 9 Commercial technology for oxygen production (<4000t O2/d). Oxy-combustion 5 7 Combustion island has been demonstrated up to MW th. CO 2 antisublimation Post-combustion 3 3 High temperature solid looping Chemical looping Oxy-combustion 3 6 Demonstrated at 1 MW th pilot plant using hard coal and ilmenite as oxygen carrier Pre-combustion 2 3 Calcium looping Post-combustion 2 6 Demonstrated at a scale of > 1 MW th using oxyfuel combustion-calcination Pre-combustion 2 2 Challenging sorbent regeneration at high pressure and temperature Solid sorbents Adsorption Industry 9 9 Commercial technology for natural gas sweetening and H 2 production (i.e. Port Arthur CCS project) Pre-combustion 8 8 Most components are TRL 9, but hydrogen based power generation is less mature. Post-combustion 2 5 CO 2 capture from flue gases by VPSA <2 t CO 2 /d. Oxy-combustion 6 6 VPSA is commercial for oxygen production, but at low capacity (<500t O 2 /d) Low T G/S reactions Post-combustion 4 6 Initial results from a 10 MW e fluidized bed pilot Pre-combustion 3 5 Sorption enhanced water gas shift (SWEGS) Membranes Polymeric membranes Industrial 9 9 Commercial technology for natural gas sweetening (i.e. Sleipner CCS project) Post-combustion 3 5 Demonstrated at a capture rate of 1t CO 2 /d using polymeric membranes. Other membranes Pre-combustion 3 3 Oxy-combustion 4 5 Oxygen production using Ion transport membranes (5 t O 2 /d) *Technology readiness level (TRL): 1) basic principles observed, 2) technology concept formulated (basic process 3 design), 3) experimental proof of concept (pilot testing of key components at small bench scale), 4) technology 4 validated in lab (continuous operated pilots at lab scale < 50 kWth), 5) technology validated in relevant environment 5 (pilots operated at industrially relevant conditions at 0.05-1 MWth), 6) technology demonstrated in relevant 6 environment (steady states at industrially relevant environments: pilots in the MWth range), 7) system prototype 7 demonstration in operational environment (industrial pilots operating at over 10 MWth), 8) system complete and 8 Air Reactor Cu2O + ½O2 => CuO Fuel Reactor CuO => Cu 2 O + ½O 2 C + O2 => CO2 MeO (+ Me) Me (+ MeO) N 2 , O 2 CO 2 , H 2 O Fuel Air CuO exothermic w. CH 4 Melting point 1085°C for Cu CLOU CuO/Cu 2 O Comprehensive studies of oxygen carriers (Adanez et al., 2004, Johansson, 2007) normally indicate a major difference in reactivity between the various oxides, Table 3. However, most reactivity comparisons are focused on CH 4. In general, the reactivity is significantly higher using H 2 and CO than when using CH 4 and may be rather high for cheaper materials showing low reactivity with CH 4. Reactivity may significantly increase with reaction temperature, especially in the case of low reactivity materials and CH 4. On the other hand, the reactivity of iron and manganese materials with CO and H 2 may be high even at lower temperatures and the same applies to nickel materials with CH 4. Although the highly reactive Ni materials have been operated at much lower temperatures, CLC carbonator
Energy Procedia, 2013
Ca-looping is one of the most promising processes for CO 2 capture in short to medium term plants... more Ca-looping is one of the most promising processes for CO 2 capture in short to medium term plants, which can be applied for both post-combustion and pre-combustion layouts. The recent successful operations of MW-scale pilot plants are leading to an increased interest in this technology. In addition, the particularly advantageous applicability in cement plants, the main industrial contributors to CO 2 emissions worldwide, can further lead to a forthcoming development of the technology. Quite a large amount of scientific papers on reactors and process modeling has been published in the recent years and more studies are expected to be published in the future. According to the experience of the authors in this field and on the basis of a literature review, suggestions and modeling needs for next works are provided in this paper.
International Journal of Hydrogen Energy, 2019
Small-scale steam methane reforming units produce more than 12 % of all the CO2-equivalent emissi... more Small-scale steam methane reforming units produce more than 12 % of all the CO2-equivalent emissions from hydrogen production and, unlike large-scale units, are usually not integrated with other processes. In this article, the authors examine the hitherto under-explored potential to utilise the excess heat available in the small-scale steam methane reforming process for partial carbon dioxide capture. Reforming temperature has been identified as a critical operating parameter to affect the amount of excess heat available in the steam methane reforming process. Calculations suggest that reforming the natural gas at 850 °C, rather than 750 °C, increases the amount of excess heat available by about 28.4 % (at 180 °C) while, sacrificing about 1.62 % and 1.09 % in the thermal and exergetic efficiency of the process, respectively. Preliminary calculations suggest that this heat could potentially be utilised for partial carbon capture from reformer flue gas, via structured adsorbents, in a compact capture unit. The reforming temperature can be adjusted in order to regulate the amount of excess heat, and thus the carbon capture rate.
Adsorption
Batch adsorption experiments are carried out by adding a known amount of adsorbent to a liquid so... more Batch adsorption experiments are carried out by adding a known amount of adsorbent to a liquid solution at a known initial concentration and following the evolution in time of the concentration of the adsorbate. This is a very common method to obtain equilibrium and kinetic information in liquid systems, but in most cases kinetic results are analysed on the basis of empirical models. Two phenomenological models based on macropore diffusion in beads and shrinking core kinetics are used to generate data that are then interpreted with the widely used unconstrained linear regression methods. The results show that for both cases R2 values close to unity are obtained leading to the incorrect interpretation of the mechanism of mass transport. It is recommended that batch adsorption experiments should be analysed using phenomenological models to obtain physical parameters that are applicable to other systems and to reduce the experiments required to characterise fully the kinetics of adsorp...
Adsorption
The availability of commercial gravimetric and volumetric systems for the measurement of adsorpti... more The availability of commercial gravimetric and volumetric systems for the measurement of adsorption equilibrium has seen also a growth of the use of these instruments to measure adsorption kinetics. A review of publications from the past 20 years has been used to assess common practice in 180 cases. There are worrying trends observed, such as lack of information on the actual conditions used in the experiment and the fact that the analysis of the data is often based on models that do not apply to the experimental systems used. To provide guidance to users of these techniques this contribution is divided into two parts: a discussion of the appropriate models to describe diffusion in porous materials is presented for different gravimetric and volumetric systems, followed by a structured discussion of the main trends in common practice uncovered reviewing a large number of recent publications. We conclude with recommendations for best practice to avoid incorrect interpretation of these...
Adsorption
In this study we present a new methodology for correcting experimental Zero Length Column data, t... more In this study we present a new methodology for correcting experimental Zero Length Column data, to account for contributions to the measured signal arising from extra-column volumes and the detector. The methodology considers the experimental setup as a series of mixing volumes with diffusive pockets whose contributions to the overall measured signal can be accurately described by simple model functions. The composite effect of the individual contributions is subsequently described through the method of convolution. It is shown that the model parameters are closely related to the physical characteristics of the setup components and as such they remain valid over a range of process conditions. The methodology is firstly validated through fitting to experimental experiments without adsorbent present. The inverse procedure of deconvolution can in turn be applied to experimental data with adsorbent, to yield corrected data which can readily be modelled using standard tools for equilibri...
Adsorption
Adsorbents exhibiting non type I adsorption behaviour are becoming increasingly more important in... more Adsorbents exhibiting non type I adsorption behaviour are becoming increasingly more important in industrial applications, such as drying and gas separation. The ability to model these processes is essential in process optimisation and intensification, but requires an accurate description of the adsorption isotherms under a range of conditions. Here we describe how the Rigid Adsorbent Lattice Fluid is capable of a priori predictions both type I and type V adsorption behaviour in silicalite-1. The predictions are consistent with experimental observations for aliphatic (type I) and polar (type V) molecules in this hydrophobic material. Type V behaviour is related to molecular clustering and the paper discusses the model parameters governing the presence/absence of this behaviour in the predicted isotherms. It is found that both the solid porosity and the adsorbate interaction energy/energy density are deciding factors for the isotherm shape. Importantly, the model, whilst thermodynami...
MRS Energy & Sustainability
Detailed report on MOFs for CO 2 adsorption on the basis of ligands employed, OMSs, and structure... more Detailed report on MOFs for CO 2 adsorption on the basis of ligands employed, OMSs, and structures. Systematic report on the highand low-pressure CO 2 capture. Report on the mechanism of CO 2 capture. A review on the promising field of MOF-based carbon capture and storage is presented. We discuss here the main features of MOFs applicable for CO 2 capture and separation, the linker functionalization role, and the most important CO 2-binding sites as also the most efficient and significant technologies, and a systematic report on the high-and low-pressure CO 2 capture.
Adsorption
The zero length column technique has been developed over the past 30 years as a versatile experim... more The zero length column technique has been developed over the past 30 years as a versatile experimental method to measure adsorption equilibrium and kinetics. In this review we discuss in detail the theory that forms the basis for the technique in order to understand how to design and operate efficiently a system. Experimental checks that should be performed to ensure the correct interpretation of the dynamic response are presented and examples are used to identify how to avoid major errors in determining diffusion time constants. The review concludes with an overview of all experimental studies available in the literature to date and a set of recommendations that should help improve the standard in the reported equilibrium and kinetic properties.
Adsorption
To match the dynamics of a linear driving force model and the diffusion equation is of great prac... more To match the dynamics of a linear driving force model and the diffusion equation is of great practical importance in the design and optimization of adsorption separation processes. A frequency response analysis is applied to show that it is not possible to arrive at an equivalence based on a single parameter. Using this as the basis, a universal equivalence for the linear problem is constructed and closed form analytical expressions for the two parameters are derived for the sphere and slab geometries. The two parameters represent the increased effective mass transfer coefficient and a reduction in the active volume of the particle, both corresponding to the internal concentration profiles of the diffusion equation at cyclic steady state.
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Papers by Stefano Brandani