(22c) Process Intensification of Enzyme Catalysed Transesterification of Geraniol in the Spinning Mesh Disc Reactor

In recent years, chemical industries have begun to move towards more sustainable processes and practices to meet environmental regulations. Global political and pandemic events have exposed the inability of industrial processes to respond effectively to changes in demand, highlighting the importance of localised and resilient manufacturing. Reactor technologies that have shown potential for achieving process intensification through flexible, resource and energy efficient manufacturing are fast gaining commercial attention over traditional batch reactors. The spinning mesh disc reactor (SMDR) is one such process intensification technology that uses centrifugal force to drive reaction fluid over a mesh-supported catalyst on a rotating disc [1, 2]. The SMDR is modular, flexible and scalable and has shown be 50% more resource efficient compared to traditional batch reactors through improved productivity and re-usability of expensive catalysts like enzymes [3, 4]. In this study, we have demonstrated the potential of the SMDR for intensification of enzymatic structural modification of terpene alcohols into terpene esters.

The lipase-catalysed production of geranyl acetate was first investigated in batch, using both free lipase and lipase immobilised on woollen cloth. The synthesis pathway chosen was transesterification using vinyl acetate in ethyl acetate solvent. Using a design of experiments approach, significant variables affecting the reaction were investigated. Of the variables studied, temperature and molar ratio were determined to be the most impactful, with catalyst content and use of immobilisation being much less significant. Further batch experiments were also performed to investigate other parameters such as stirring speed, acyl donor concentration and substrate concentration. Stirring speed was observed to be significant for free lipase from 225 to 400 RPM, but insignificant for those same ranges for immobilised lipase. Acyl donor concentration was seen to be directly proportional with reaction rate for the range studied (0.1 to 0.4M of vinyl acetate with 0.1M of geraniol). The effects of increasing substrate concentrations were also investigated, with both constant and increasing catalyst concentrations. For free lipase, reaction rates were observed to increase from 0.01 Mh^-1 to 0.07Mh^-1 with increasing catalyst concentration (w/w of initial substrate concentration), demonstrating a synergistic relationship between catalyst content and substrate concentration. This synergy was not seen however for immobilised lipase.

The optimum reaction conditions were identified using design of experiments in batch and a maximum reaction conversion of 80% was observed at 40^oC at the end of 24 hours. The reaction was then scaled-up in the SMDR and a reaction conversion of 60% was obtained at 350 RPM and 3 ml s^-1 in 5 hours. Further, the catalyst loading in the reactor was increased by simply adding more cloths on the surface of the disc and a 5% increase in the reaction conversion was observed with the addition of two cloths. The lipase cloth was re-used for up to three cycles and 83% of the original activity was retained, demonstrating the robustness of this catalyst for organic reactions.

To the best of the authors’ knowledge, this is the first example of scale-up of production of terpene esters in rotating disc reactors. We are currently working towards further optimising the SMDR to improve the reaction productivity for pilot scale operations.

References

[1] X. Feng, D. A. Patterson, M. Balaban, G. Fauconnier and E. A. C. Emanuelsson, Chem. Eng. J., 2013, 221, 407-417.

[2] P. Shivaprasad, M. D. Jones, D. A. Patterson and E. A. C. Emanuelsson, Chemical Engineering and Processing: Process Intensification, 2017, 122, 550-559.

[3] E. A. C. Emanuelsson, A. Charles and P. Shivaprasad, Sustainability, 2021, 13, 6944.

[4] P. Shivaprasad, M. D. Jones, D. A. Patterson and E. A. C. Emanuelsson, Chemical Engineering and Processing-Process Intensification, 2018, 132, 56-64.