Study and Design of a Heat-integrated Hybrid Pervaporation-Distillation Process
Advancing the chemical engineering fundamentals
Distillation, Absorption & Extraction - III (T2-10c)
Keywords: hybrid process, heat integration, pervaporation, distillation, azeotropic mixtures
The separation of homogenous azeotropic mixtures is a common problem in the chemical industry. High energy consuming techniques like extractive distillation, azeotrope distillation, pressure swing distillation or liquid-liquid extraction are the primarily used in practice. Hybrid-Pervaporation-Distillation processes have been intensely studied in the last decade and considered like a serious alternative to the existing techniques. The saving in energy costs and the need of no additional substance in the procedure are the major benefits of it. In the present paper, a newly developed system and membrane configuration are presented, a mathematical model is described and finally the advantages of the new heat-integrated flow-sheet are demonstrated. In the study, this new process and membrane module design yields not only to a reduction in the energy consumption but also to a decrease in the necessary membrane area, what means a smaller operation and investment costs.
The basis of the heat-integration concept, is to utilize part of the distillate vapor stream going out of the distillation column like a heating medium in the membrane module. The vapor condensates partially and energy is released into the pervaporation module. The homogeneous azeotropic binary mixture of acetonitrile-water is taken as an example.
Without internal heat support, the temperature along the module decreases significantly, and a heat exchanger is needed before the next pervaporation step. In the new system, there is no need of external energy support. Another benefit is that the heat transfer is realized directly in the membrane therefore, the temperature decrease along the module is minor. Its consequence is that the permeat flux rises and the membrane area drops.
To analyze the process a model is needed. The dynamic column model described in Repke et al. (2006) is used. On the basis of the pervaporation thermodynamic approach proposed by Wijmans and Baker (1993), a PDE model for the membrane has been developed in gPROMS. In it the temperature dependence of the permeability coefficient is defined like an Arrhenius function.
The influence of the heat integration in the Pervaporation process is analyzed for a fixed membrane area of 0.44 and with a permeat pressure of 3mbar. As a result, a small energy support (2.4 MJ/hr) benefits the pervaporation procedure by increasing the molar fraction of acetonitrile at the exit up to 30% and the permeation flux till 73%; what reduces the required membrane area (for a constant purity in the exit product). This energy can be obtained by the condensation process of the distillate.
For the validation of the built model and for the identification of process parameters and membrane module properties a new laboratory plant is built. With this plant different kinds of modules will be analyzed with or without a coupling to a high pressure distillation plant (see Klein 2006). In the presentation, this new concept will be described and its feasibility proved.
Project sponsored by EFRE (request number-10134788)
References
[Repke 2006] Repke, J.-U.; Forner, F.; Klein, A. Separation of Homogeneous Azeotropic Mixtures by Pressure Swing Distillation – Analysis of the Operation Performance. Chem. Eng. Techn. 28, 2006
[Klein 2006] A. Klein, J.-U. Repke, M. T. del Pozo Gómez, G. Wozny. AJChE Annual Meeting 2006, San Francisco, California ,409 Separation Design.
[Wijmans 1993] Wijmans, J.G. and R.W. Baker, 1993, Journal of Membrane Science, vol. 79: A simple predictive treatment of the permeation process in pervaporation, 101-113
Presented Tuesday 18, 09:05 to 09:25, in session Distillation, Absorption & Extraction - III (T2-10c).
