Abstract
AbstractIn this work, we explore the capabilities of an NLP optimization model to determine the viability of facilitated transport membrane processes intended to replace traditional distillation currently employed for propane/propylene separation. An NLP optimization model for multistage membrane processes has been formulated, introducing the mathematical description of the facilitated transport mechanisms in the PVDF‐HFP/BMImBF4/AgBF4 membranes previously developed by our research group. For the first time, a simultaneous optimization of the process and the membrane material (i.e., carrier concentration) has been performed, thanks to the implementation of the governing equations for the fixed site and mobile carrier mechanisms. Once the model is solved in GAMS it returns the optimal membrane area, carrier loading and permeate pressure of each stage based on Net Present Value Cost (NPVC) minimization. Different process flow sheets were evaluated and the results show prominent reductions on NPVC for facilitated transport multistage processes when compared to distillation.
Highlights
Propane/propylene gaseous mixtures resulting from fluid catalytic cracking and steam cracking are commonly separated using high pressure or cryogenic distillation, which is associated to major energy and capital consumptions.[1]
In this work, we explore the capabilities of an NLP optimization model to determine the viability of facilitated transport membrane processes intended to replace traditional distillation currently employed for propane/propylene separation
The Net Present Value Cost (NPVC) of both multistage processes will be compared with the NPVC of the reference distillation column
Summary
Propane/propylene gaseous mixtures resulting from fluid catalytic cracking and steam cracking are commonly separated using high pressure or cryogenic distillation, which is associated to major energy and capital consumptions.[1] Through the last years, process intensification by means of membrane technology has emerged as a promising alternative to large, expensive and energy-intensive distillation units.[2] Many membrane materials have been reported for olefin/paraffin separation, including polymers,[3,4,5] and more complex materials, such as carbon molecular sieves (CMSs),[6,7,8,9] zeolitic imidazolate frameworks (ZIFs)[10,11,12,13,14] or facilitated transport membranes.[15,16] Among these, facilitated transport membranes can surpass the permeabilityselectivity trade-off of polymeric membranes thanks to the reversible reaction between the olefin and a carrier cation, typically silver, which is added to the membrane composition.[17,18] Facilitated transport membranes have been synthesized following different approaches, from supported liquid membranes (SLM)[19,20] to supported ionic liquid membranes (SILM)[21] that replace organic solvents with non-volatile room temperature ionic liquids (RTILs)[22] in order to avoid solvent losses through evaporation.[23] Recently, composite facilitated transport membranes prepared by solvent casting of a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) polymeric solution containing the ionic liquid and the silver salt have been reported.[24] In these dense membranes, which feature a combination of fixed site and mobile carrier transport mechanisms,[25] selectivities up to 150 and propylene permeabilities higher than 1000 Barrer have been achieved that avoid the issues of supported liquid membranes
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