Post-Combustion CO

Simulation results in the literature suggest that Vacuum Swing Adsorption (VSA) processes using physisorbents might largely outperform the current state-of-the-art post-combustion CO2 capture technologies based on amine solvents in terms of energy consumption. Most studies consider the zeolite NaX as adsorbent. NaX has a very strong affinity for CO2 but is difficult to regenerate and very sensitive to the presence of water in the flue gas. By tuning the polarity of the adsorbent, it might be possible to find a better compromise between adsorption capacity, regenerability and sensitivity to H2O. In the present contribution, we therefore screen the performance of a series of zeolites as physisorbents in a VSA process for CO2 capture. The adsorbents are tested by breakthrough experiments of a dry and wet model flue gas, in once-through and cyclic operation. The most interesting material, zeolite EMC-1, is selected for numerical simulations of a full VSA cycle, in comparison with zeolite NaX. Both solids satisfy the performance targets in terms of recovery (> 90%) and purity of CO2 (> 95%) but the very low pressure required for regeneration of the adsorbents will be a serious handicap for the deployment of this technology on a large scale

Design of a Pressure Swing Adsorption Process for Postcombustion CO₂ Capture

The adsorption processes for postcombustion CO₂ capture are usually based on a temperature or vacuum swing (TSA or VSA). In the present contribution an alternative concept is presented, which is based on the regeneration of the solid sorbent (an immobilized amine) by a purge gas, low pressure vapor, under almost isothermal conditions. Because of the close to isothermal operation, the process consumes significantly less thermal and mechanical energy than conventional TSA and VSA processes, respectively. We present a rough design of such an isothermal concentration swing process based on a simplified, analytical model of a 2-step PSA (pressure swing adsorption) process. The analytical model allows a definition of the range of operating conditions that lead to the best compromise between energy consumption and productivity (size and number of the adsorbers). Moreover, it is possible to define the equilibrium and mass transfer properties of the ideal solid sorbent. The feasibility of the concentration swing process was finally validated by numerical simulations of a full PSA cycle under adiabatic conditions

Intensification of Paraxylene Production using a Simulated Moving Bed Reactor

Multifunctional reactors, which combine a reaction step and a separation step in one single unit, constitute an important advance in design of sustainable processes to save energy and reduce environmental impact. They allow reductions of recycle flows and size units in order to have more safety and less expansive processes. This paper deals with separation by adsorption and reaction coupled in a Simulated Moving Bed reactor (SMBR) for paraxylene (PX) production. In the current industrial process, the major part of the separation step comes from a recycle flow where the C8 aromatics are isomerized. The SMBR, by decreasing this recycle stream, may reduce the energy needed to treat and convert the raffinate into a rich PX stream. As separation takes place in the liquid phase, the first part of this paper establishes the feasibility of liquid phase isomerization of xylene. Tests in a fixed bed reactor validate the use of a HZSM-5 zeolite catalyst. Paradiethylbenzene (paraDEB), the classical desorbent used in xylene separation, isomerizes into orthodiethylbenzene and metadiethylbenzene so it is replaced by toluene. Experimental data permit one to estimate the parameters used in a simple analytical model implemented in a classical True Moving Bed model. This TMBR model permits to find the various operating regimes of such a SMBR. The conditions found allow a 40% reduction of the recycle flow without any productivity loss. With this lower recycle flow, a reduction of investment and operating costs is expected on the global PX production process thanks to the SMBR process

Intensification of Paraxylene Production using a Simulated Moving Bed Reactor Intensification de la production de paraxylène à l’aide du lit mobile simulé réactif

Multifunctional reactors, which combine a reaction step and a separation step in one single unit, constitute an important advance in design of sustainable processes to save energy and reduce environmental impact. They allow reductions of recycle flows and size units in order to have more safety and less expansive processes. This paper deals with separation by adsorption and reaction coupled in a Simulated Moving Bed reactor (SMBR) for paraxylene (PX) production. In the current industrial process, the major part of the separation step comes from a recycle flow where the C8 aromatics are isomerized. The SMBR, by decreasing this recycle stream, may reduce the energy needed to treat and convert the raffinate into a rich PX stream. As separation takes place in the liquid phase, the first part of this paper establishes the feasibility of liquid phase isomerization of xylene. Tests in a fixed bed reactor validate the use of a HZSM-5 zeolite catalyst. Paradiethylbenzene (paraDEB), the classical desorbent used in xylene separation, isomerizes into orthodiethylbenzene and metadiethylbenzene so it is replaced by toluene. Experimental data permit one to estimate the parameters used in a simple analytical model implemented in a classical True Moving Bed model. This TMBR model permits to find the various operating regimes of such a SMBR. The conditions found allow a 40% reduction of the recycle flow without any productivity loss. With this lower recycle flow, a reduction of investment and operating costs is expected on the global PX production process thanks to the SMBR process. Les réacteurs multifonctionnels, qui associent une étape de séparation et une étape de réaction dans une seule et même unité, constituent un axe de développement important dans le domaine de l’écoconception des procédés afin de réduire les coûts énergétiques et environnementaux. Ils permettent de réduire, voire d’éliminer, les flux de recyclage et la taille des unités afin d’obtenir des procédés moins coûteux et plus sûrs. Cet article présente l’étude d’un réacteur multifonctionnel couplant une réaction d’isomérisation et une séparation par adsorption : le Lit Mobile Simulé Réactif (LMSR). Ce procédé est appliqué à la séparation réactive des xylènes. Le procédé actuel permet de produire du paraxylène (PX) pur (à plus de 99,7 %) à partir d’un mélange d’isomères grâce à une étape de séparation par Lit Mobile Simulé (LMS) et une étape d’isomérisation en phase gaz. La majeure partie de l’alimentation du LMS provient du recyclage des isomères du paraxylène qui sont transformés dans le réacteur. La séparation réactive, en intégrant l’isomérisation dans le LMS, devrait permettre de réduire ce flux de recyclage et les utilités associées. La séparation des xylènes s’effectuant en phase liquide, la première étape de cette étude a donc été de vérifier la faisabilité de la réaction en phase liquide. Ces tests ont permis de valider l’utilisation de la zéolithe HZSM-5 comme catalyseur de la réaction et du toluène comme désorbant pour la séparation (à la place du paradiéthylbenzène, plus classiquement utilisé, mais qui s’isomérise au contact de ce catalyseur). Les données expérimentales ont permis d’estimer des paramètres cinétiques pour un modèle d’isomérisation en phase liquide des xylènes. Ce modèle a été ajouté à un modèle de séparation par Lit Mobile Vrai (LMV) pour obtenir un simulateur de Lit Mobile Vrai Réactif (LMVR). Grâce à ce simulateur de LMVR, les conditions de fonctionnement du procédé LMSR ont pu être déterminées. Ces conditions de fonctionnement montrent qu’il est possible de réduire le flux de recyclage de plus de 40 % tout en conservant la même productivité. Une étude comparative des deux schémas de production de PX dans leur globalité permet d’espérer une réduction des coûts d’investissement et des coûts opératoires grâce au procédé LMSR

Post-Combustion CO 2

Simulation results in the literature suggest that Vacuum Swing Adsorption (VSA) processes using physisorbents might largely outperform the current state-of-the-art post-combustion CO2 capture technologies based on amine solvents in terms of energy consumption. Most studies consider the zeolite NaX as adsorbent. NaX has a very strong affinity for CO2 but is difficult to regenerate and very sensitive to the presence of water in the flue gas. By tuning the polarity of the adsorbent, it might be possible to find a better compromise between adsorption capacity, regenerability and sensitivity to H2O. In the present contribution, we therefore screen the performance of a series of zeolites as physisorbents in a VSA process for CO2 capture. The adsorbents are tested by breakthrough experiments of a dry and wet model flue gas, in once-through and cyclic operation. The most interesting material, zeolite EMC-1, is selected for numerical simulations of a full VSA cycle, in comparison with zeolite NaX. Both solids satisfy the performance targets in terms of recovery (> 90%) and purity of CO2 (> 95%) but the very low pressure required for regeneration of the adsorbents will be a serious handicap for the deployment of this technology on a large scale

Physicochemical properties and electrochemical behavior of Ebonex/Pt-based materials

Physicochem. properties and electrochem. behavior of Ebonex/Pt-based electrodes obtained with the use of a combined electrochem. method by electrodeposition of a thin platinum layer on substoichiometric titanium oxides (Ebonex) followed by heat treatment are studied. Phase compn. is found to depend substantially on the temp. of the electrode treatment. At temps. above 230°, a titanium-dioxide-hollandite phase is formed and facilitates thermal diffusion of platinum deep into the substrate. A previously unknown titanium-oxygen phase (310°) that affects the electrochem. behavior of the electrodes is discovered. Ebonex/Pt-based materials are n-type semiconductors, the flat band potentials and the no. of charge carriers of which are detd. by the formation conditions