Optimisation of the higher pressure of pressure-swing distillation of a maximum azeotropic mixture

The pressure-swing distillation separation of a maximum azeotropic mixture, water-ethylenediamine, is simulated and optimised. In contrast to our previous works, the top pressure of the high-pressure column (HPC) is considered as an optimisation variable. The total annual cost (TAC) is minimised first without heat integration (NHI), then different energy demand reduction options are applied and optimised: partial (PHI) and full (FHI) heat integration and vapour recompression (VRC) heat pumps. For heat pumps, working fluid flow rate is optimised to minimise the work and thus the compressor costs. Environmental impacts are also considered by calculating CO2 emissions and Eco-indicator 99 (EI99) values. The application of HI does not significantly change the pressure optimum. The lowest TAC is obtained by the optimal PHI, which decreases TAC by 16% compared to the optimal NHI process. Applying VRC is uneconomical, but very favourable environmentally: CO2 emissions and EI99 are reduced by 44 and 95%, respectively

Contribució a l’estudi de la integració energètica de sistemes de rectificació per variació de pressió

Treballs Finals de Màster d'Enginyeria Química, Facultat de Química, Universitat de Barcelona. Curs: 2021-2022. Tutors: Jordi Bonet, Victor MansoSeparation processes of mixtures are one of the most important operations in the chemical industry due to the need of product purification or components recovery. Distillation is a widespread method of purification for liquid mixtures. The basis of this process is the selective boiling and condensation of the components. When it concerns an azeotropic mixture, the separation is limited to the azeotropic composition, so from this point it is impossible to continue with the purification and an alternative method must be used. Pressure swing distillation (PSD) process is an enhanced distillation method to break the azeotrope of azeotropic mixtures which are pressure sensitives. Heat integrated pressure swing distillation (HIPSD) is an improvement to overcome the high operating costs generated in the PSD process exchanging heat between hot and cold streams of the process in order to minimise the external energy requirements. In this project, the mixture to be separated is composed of methyl acetate (MetAc) and methanol (MeOH). This mixture is obtained in the synthesis of polyvinyl alcohol (PVA), and the purification of the components is useful as MeOH is a raw material for the PVA process, and to sell / use MetAc as a solvent in production processes such as glue or paint production. The PSD process is designed according to heuristic rules for distillation, and using Aspen Plus as simulation software. The process consists of two columns. MeOH is obtained in the first one (operating at 1 atm) and MetAc is obtained in the second one (operating at 10 atm), both by bottoms and with a 99.45 % of purity. Once the design is done, partial and full HIPSD are studied to achieve energy costs savings. This is done by means of Aspen Energy Analyzer complement, included in Aspen Plus. Since this is the first time using this tool in the department, the designs are also developed by a traditional method (Temperature-Interval) to compare the results and see how it works. For the partial HIPSD the feasible heat exchange between the first column reboiler and the second column condenser is performed, but the heat duties are not equal, hence an auxiliary reboiler is needed. The energy costs savings achieved are 37.47 %. For the full HIPSD, the PSD process is modified to equalise the heat duties, so that an auxiliary reboiler is not needed, and to minimise the second column reboiler heat requirements. The energy costs savings for this case are 46.27 %