Design and Economic Analysis of Membrane Crystallization Processes

Design and economic analysis of processes for the crystallization of adipic acid are studied. Two membrane-based process alternatives, reverse osmosis (RO) and porous hydrophobic membranes, are considered, as well as a conventional multi-effect vacuum evaporation crystallization process. For each of these alternatives, a small-scale batch process (2×10⁵ kg/yr) and a large-scale continuous process (2×10⁷ kg/yr) are designed and a detailed economic analysis is performed. For the batch processes, the seeding policy and optimization of the evaporation rate trajectory are considered. The batch reverse osmosis process is similar to one described by Kuhn et al. (2009). Unlike the situation when using RO membranes, when porous hydrophobic membranes are used for the separation it is necessary to supply the enthalpy of vaporization of the water. However this energy is supplied at a relatively low temperature; it could be provided by waste heat if waste heat is available (Drioli et al., 2015). Therefore, in the economic analysis two scenarios are considered: one in which low-grade waste heat is available at no cost, and one in which no such heat is available.

The results show that when low-grade waste heat is not available, the RO membrane process has the lowest cost because, although pumping costs are significant, these costs are more than offset by the energy that is saved because the enthalpy of vaporization of the water does not need to be provided. When low-grade waste heat is available at no cost, a conventional single-effect vacuum evaporation process has the lowest cost because the low-grade waste heat can also be applied to power the evaporation in the conventional process and the conventional process does not incur the capital cost for the membranes.

References

Drioli, Enrico, Aamer Ali, Francesca Macedonio, Membrane Distillation: Recent Development and Perspectives. Desalination 2015, 356, 56-84

Kuhn, Jelan, Richard Lakerveld, Herman J. M. Kramer, Johan Grievink, Peter J. Jansens, Characterization and Dynamic Optimization of Membrane-Assisted Crystallization of Adipic Acid. IECR 2009, 48, 5360-5369