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Crystallization is one of the most widely applied separation processes in the chemical industry and the interest to combine membrane operations and crystallization has increased recently. Membrane crystallization (MCr) is emerging as a promising technique with some important advantages with respect to traditional crystallization processes: well-controlled nucleation and growth kinetics, fast crystallization rates and reduced induction time, membrane surface promoting heterogeneous nucleation and control of supersaturation level and rate. In a membrane crystallizer a hydrophobic membrane matrix acts as a selective gate for solvent evaporation and allows to modulate the final degree and the rate for the generation of the supersaturation. Therefore, the possibility to act on the trans-membrane flow rate allows to control and address the final properties of the crystals produced both in terms of structure (polymorphism) and morphology (habit, shape, size, and size distribution). In this work molecular simulations have been performed to give insights on the experimental results. The NaCl crystallization process at a PVDF and PP membrane interface was performed by using molecular dynamics simulations. The simulation have been developed for predicting variations in the crystalline form in function of cross velocity. REFERENCES Macedonio F. and Drioli E. (2010) "Hydrophobic membranes for salts recovery from desalination plants", Desalination and Water Treatment 18(1-3), 224-234 Drioli E., Di Profio G., Curcio E. (2015) "Membrane-Assisted Crystallization Technology" World Scientific

Rigid polymer membranes are recently regarded as state of the art materials for gas separation processes, due to their high permeability and selectivity [1]. Among these, thermally-rearranged polybenzoxazoles (TR-PBOs) have shown outstanding molecular and ionic transport and separation performance, beyond the limits of conventional polymers [?1-4]. Adsorption and diffusion in thermally rearranged polybenzoxazole (TR-PBO) polymer membranes are simulated in single-gas and in CO2/N2 binary mixture focusing at 35 °C and at relative gas concentration corresponding to a fugacity of 5 bar. For this purpose, molecular dynamics simulations are used in a synergistic pairing with Gran Canonical Monte Carlo approach (GCMC) and Ideal Adsorption Solution Theory (IAST). GCMC simulations are compared with IAST simulations to obtain adsorption isotherms in mixtures. The number of molecules present in the polymer matrix is estimated using GCMC. Molecular dynamics simulations are performed, calculating the Maxwell-Stefan diffusion coefficients. As main results, the evaluated diffusion coefficients of CO2 and N2 are in a satisfactory agreement with the values estimated using available permeability experimental data. CO2 diffusivity calculated in mixture conditions is found to be the same as that in single-gas ones, whereas the N2 diffusivity is slightly higher. These differences are explained in terms of the effect of both the mutual gas diffusion and the competing occupancy of the available free space occupied by the CO2 molecules in mixture.

Many environmental challenges of modern society are related to sustainable energy consumption. In particular, the need to reduce the atmospheric CO2 emissions from the combustion of fossil fuels is one of the main driving forces pushing research to find alternative and effective solutions not only to reduce the emissions, but also to separate and capture the emitted CO2. Membrane technology has become very competitive, much more than the traditional separation methods, such as adsorption, cryogenic separations, distillation, etc., since offers improved performance at lower cost with increased energy efficiency and lower environmental impact [1-3]. The successful development of highly permeable and selective membranes makes a membrane-based process a viable alternative for carbon dioxide capture and storage from flue gas. The classical simulation study at molecular level by using molecular dynamic simulations (MD) can powerfully support experimental studies about morphological and transport behaviour of such systems [4,5]. In the present work MD method has been applied for a detailed investigation of gas molecules transport through TRPBO membranes both in single gas state (CO2 and N2) and in binary gas mixture (CO2:N2) at high trans-membrane pressure difference (5 bar). The results revealed that the CO2 permeability under the mixed-gas condition remained the same as the single gas, while the permeability of other gas decreased, thus leading to a favored increase in selectivity. The theoretical data, along with the experimental results [6], give further information about the microscopic structure and atomistic interactions between gases, thus resulting in a reciprocal validation and useful correlations between MD and experimental analysis.

A well-known method for improving the diffusivity-selectivity, as well as the diffusion coefficient of gas molecules in polymer membranes, involves an increase in free volume that combine with the stiffness of the main chains. Among these, thermally-rearranged polybenzoxazoles (TR-PBOs) have shown outstanding molecular and ionic transport and separation performance, beyond the limits of conventional polymers [?1-4]. Adsorption and diffusion in thermally rearranged polybenzoxazole (TR-PBO) polymer membranes are simulated in single-gas and in CO2/N2 binary mixture focusing at 35 °C and at relative gas concentration corresponding to a fugacity of 5 bar. For this purpose, molecular dynamics simulations are used in a synergistic pairing with Gran Canonical Monte-Carlo approach (GCMC) and Ideal Adsorption Solution Theory (IAST). GCMC simulations are compared with IAST simulations to obtain adsorption isotherms in mixtures. The number of molecules present in the polymer matrix is estimated using GCMC. Molecular dynamics simulations are performed, calculating the Maxwell-Stefan diffusion coefficients. As main results, the evaluated diffusion coefficients of CO2 and N2 are in a satisfactory agreement with the values estimated using available permeability experimental data. CO2 diffusivity calculated in mixture conditions is found to be the same as that in single-gas ones, whereas the N2 diffusivity is slightly higher. These differences are explained in terms of the effect of both the mutual gas diffusion and the competing occupancy of the available free space occupied by the CO2 molecules in mixture. References [1]H.B. Park, C.H. Jung, Y.M. Lee, A.J. Hill, S.J. Pas, S.T. Mudie, E. Van Wagner, B.D. Freeman, D.J. Cookson, Polymers with cavities tuned for fast selective transport of small molecules and ions, Science 318 (2007) 254-258 [2]S.Kim, Y.M. Lee, Rigid and microporous polymers for gas separation membranes, Progress Polym. Sci. 43 (2015) 1-32 [3]C.H. Park, E. Tocci, S. Kim, A. Kumar, Y.M. Lee, E. Drioli, A Simulation Study on OH-Containing Polyimide (HPI) and Thermally Rearranged Polybenzoxazoles (TR-PBO): Relationship between Gas Transport Properties and Free Volume Morphology, J. Phys Chem. B 118 (2014) 2746-2757. [4]C.H. Park, E. Tocci, Y.M. Lee, E. Drioli, Thermal treatment effect on the structure and property change between hydroxy-containing polyimides (HPIs) and thermally rearranged polybenzoxazole (TR-PBO), J. Phys. Chem. B 116 (2012) 12864-12877.

Atomistic molecular modelling techniques have confirmed to be a very useful tool for the investigation of the structure and dynamics of dense amorphous membrane polymers and of transport processes in these materials [1]. In recent years, polymers of intrinsic microporosity (PIMs) are emerging materials characterized by high free volume above 20% [2] and they will be promising materials for making organic membranes suitable for gas separation. In this paper, we study polymer of intrinsic microporosity (PIMs), in particular, the Amine-PIM-1 that contains four nitrile groups randomly spaced (functionalization percentage of 85%). In adsorption experiments, the novel amine-PIM-1 showed higher CO2 uptake and higher CO2/N2 sorption selectivity than the parent polymer, with very evident dual-mode sorption behaviour [3]. Simulation of polymeric models is not trivial due to the difficulty in packing the polymeric chains in the correct configurations in order to obtain realistic results from the simulation. Here we will explain the polymeric matrix construction and the results obtained for the CO2/N2 separation [4]. We focus on the comparison between experimental and theoretical single gas-adsorption isotherms of several small molecular gases such N2, CO2 and CH4 by using Grand Canonical Mont Carlo (GCMC) method. Acknowledgements The work leading to these results has received funding from the European Union's Seventh Framework Program (FP7/2007-2013) under grant agreement n° 608490, project M4CO2. This work was further supported by the CNR/FCT Italian/Portuguese bilateral project 2015-2016 "Advanced studies of the transport properties and gas separation by Polymers of Intrinsic Microporosity (PIMs) and Ionic Liquid Gel Membranes via novel methods" [1]D. Hofmann, L. Fritz et al.; Macromol. Theory Simul., 2000, 9, 293-327. [2]D. Fritsch, P.M. Budd et al.; Macromolecules 2010, 43, 6075-6084. [3]C. R. Mason, J. C. Jansen et al.; Macromolecules 2014, 47, 1021-1029. [4]E. Tocci, P. Pullumbi; Molecular Simulation 2006, 32,145-154.

Fresh water scarcity has emerged as a big challenge of current era. Desalination of seawater has long been utilized to produce fresh water suitable for human consumption and irrigation in areas of water scarcity, and its use is becoming more widespread across the globe. Currently, the major desalination technologies are based on membrane separation via reverse osmosis (RO). High pressure, and thus significant energy, is required to force water through the membranes. The use of semipermeable membranes containing carbon nanotubes (CNTs) that form continuous pores has been suggested as a way to reduce the cost of desalination via reverse osmosis. Example membranes containing aligned CNTs have been fabricated, but obtaining only the very narrow pores that are able to block the passage of ions while allowing a rapid flow of water remains a challenge and previous computational studies have focused on idealized single-walled nanotubes. We use non-equilibrium molecular dynamics (NEMD) simulations of pressure induced flow of water and aqueous salt solutions through multi-walled CNTs (MWCNT) with the aim of investigating the effect of additional walls on the performance of CNT based membranes. For NEMD simulations, we apply a fixed force on a water salt solution having a defined length to obtain a hydrostatic pressure difference. Simulations on CNT with different number of walls incorporated into membranes have been conducted with a hydrostatic pressure difference in order to determine the ion rejection and water flux.