Improvement of Cyclohexane Recovery Unit in a Polyethylene Plant: Process Optimization and Economic Evaluation

Steven Oyalemi, Otaraku, I. Jonathan, Akuma A. Oji

Cyclohexane Recovery; Process Optimization; Polyethylene Production; Solvent Recycling; Aspen HYSYS Simulation; Heat Integration.

This study presents a comprehensive approach to improving Cyclohexane recovery in a polyethylene production plant through process optimization and equipment modification. The current solvent recovery system, which utilizes three shell-and-tube heat exchangers in series, achieves only 83% recovery efficiency, leading to significant economic losses and environmental concerns. Cyclohexane is an indispensable solvent in the solution phase polymerization process critical for the manufacturing of diverse polyethylene products, including high-density (HDPE), low-density (LDPE), and linear low-density polyethylene (LLDPE). Despite its pivotal role, industrial operations frequently encounter substantial challenges in achieving comprehensive solvent recovery, leading to considerable economic penalties and an escalation in overall production costs. This comprehensive study undertakes an in-depth investigation into advanced methodologies aimed at enhancing cyclohexane recovery within an established polyethylene production facility. The research employs sophisticated process simulation techniques, specifically utilizing Aspen HYSYS, to model and analyze proposed modifications to the existing solvent recovery unit. A central focus is placed on assessing the impact of integrating a new condenser, referred to as a “chiller,” and meticulously examining how variations in operating temperatures influence both solvent recovery efficiency and the energy duty required by the chiller.

The empirical findings from the simulation rigorously demonstrate a pronounced inverse correlation between decreasing operating temperature and an increase in the volume of cyclohexane recovered. Concomitantly, this enhanced recovery at lower temperatures is directly linked to a significant rise in the energy duty demanded by the chiller. While the initial capital investment associated with the installation of these chillers is substantial, estimated at approximately $746,900.735, the projected economic analysis reveals a highly favorable and short payback period of approximately 1.57 years. This rapid return on investment strongly underscores the economic viability and strategic benefits of implementing such process enhancements. Ultimately, this study furnishes a detailed blueprint of simulated optimal operating conditions for superior cyclohexane recovery, thereby offering invaluable practical insights and a robust framework for the design, development, and optimized operation of future and existing polyethylene manufacturing facilities.

[1] Aspen Technology. (2012). Aspen HYSYS User Guide. Burlington, MA: Aspen Technology Inc.
[2] Baeyer, A. (1870). Ueber die Reduction aromatischer Kohlenwasserstoffe durch Jodphosphonium. Annalen der Chemie und Pharmacie, 155, 266–281.
[3] Bates, F. S., & Fredrickson, G. H. (2014). Block Copolymer Thermodynamics: Theory and Experiment. Annual Review of Physical Chemistry, 41, 525–557.
[4] Campbell, M. L. (2011). Cyclohexane. Ullmann’s Encyclopedia of Industrial Chemistry.
[5] Chanda, M. (2013). Introduction to Polymer Science and Chemistry (2nd ed.). CRC Press.
[6] Chremos, A., Nikoubashman, A., & Panagiotopoulos, A. (2014). Flory-Huggins parameter, from binary mixtures of Lennard-Jones particles to block copolymer melts. Journal of Chemical Physics.
[7] Eisenbach, C. D., & Heinemann, T. (1995). Thermoplastic graft copolymer elastomers with chain-folding or bifurcated side chains. Macromolecular Chemistry and Physics, 196(8), 2669–2686.
[8] Zhang, F. F., van Rijnman, T., Kim, J. S., & Cheng, A. (2008). On Present Methods of Hydrogenation of Aromatic Compounds, 1945 to Present Day. Lunds Tekniska Högskola.
[9] Gazit, O., Khalfin, R., Cohen, Y., & Tannenbaum, R. (2009). Self-assembled diblock copolymer ”nanoreactors” as catalysts for metal nanoparticle synthesis. Journal of Physical Chemistry C, 113, 576–583.
[10] Hadjichristidis, N., Pispas, S., & Floudas, G. (2003). Block Copolymers: Synthetic Strategies, Physical Properties, and Applications. Wiley.
[11] Hamley, I. W. (1998). The Physics of Block Copolymers. Oxford University Press.
[12] Hamley, I. W. (2004). Developments in Block Copolymer Science and Technology. Wiley.
[13] Mayer, J., Urban, S., Habrylo, S., Holderna, K., Natkaniec, I., Würflinger, A., & Zajac, W. (1991). Neutron Scattering Studies of C6H12 and C6D12 Cyclohexane under High Pressure. Physica Status Solidi (b), 166(2), 381.
[14] McNaught, A. D., & Wilkinson, A. (1996). Glossary of basic terms in polymer science (IUPAC Recommendations 1996). Pure and Applied Chemistry, 68, 2287–2311.
[15] Prince, D. M. (1995). Temperature Calibration of Differential Scanning Calorimeters. Journal of Thermal Analysis, 45(6), 1285–1296.
[16] Warnhoff, E. W. (1996). The Curiously Intertwined Histories of Benzene and Cyclohexane. Journal of Chemical Education, 73(6), 494.
[17] Musser, M. T. (2005). Cyclohexanol and Cyclohexanone. Ullmann’s Encyclopedia of Industrial Chemistry. Wiley-VCH.