Life cycle assessment of vitamin D₃ synthesis: from batch to photo-high p,T

Abstract

Purpose: Novel process windows allow the development of faster, flexible, and greener processes. Therefore, novel process windows were applied to develop a greener process for the synthesis of vitamin D₃. In this study the environmental impacts of several batch pathways to obtain vitamin D₃ are benchmarked against the continuous microflow process, where novel process windows such as high temperature and pressure were applied. To evaluate the environmental impact of these processes, life cycle assessments were conducted. Methods: A new process concept was developed to optimize and simplify the synthesis of crystalline vitamin D₃. This process was conducted in microflow by combining UV photoirradiation and high-p,T (photo-high-p,T) processing. Microreactors allow a high photon flux and enable the harsh conditions, respectively. The process was coupled with an integrated continuous crystallization, and its feasibility has been proven and reported before. The potential environmental impacts were assessed from a cradle-to-gate perspective. Both processes, continuous and batch, were modeled in Aspen Plus using foreground data from the experimental continuous setup, and background data from different patents. The assessment was performed in the software Umberto NXL LCA using the ReCiPe Midpoint 2008 method. Results and discussion: The continuous process has a significantly lower environmental impact than the batch processes. This lower impact is largely due to the fact that fewer amounts of material, particularly solvents, are used. Moreover, the continuous process is faster and has fewer steps, i.e., process-simplified. Among the industrial processes, the synthesis conducted in isopropanol has the lowest environmental impact, although, even in this case, the impact is between 20 and 30 times higher—depending on the conditions—compared with the continuous process. When the batch process is conducted in benzene, the worst environmental impact is obtained. Finally, recycle of the solvent for the best batch case was assessed. This improved the batch process to make it comparable with the continuous process. Conclusions: The continuous production of vitamin D₃ leads to an interesting alternative to the industrial process. Continuous manufacturing of vitamin D₃ is faster, requires fewer steps, and uses less solvents compared with the industrial synthesis. However, although the environmental impact of this continuous process is already lower than that of the batch processes, the continuous process can still benefit from further optimization, particularly the introduction of a recycle loops for the solvents methyl tert-butyl ether and acetonitrile.