Continuous Synthesis Of Vitamin D₃ By Gas-liquid Segmented Flow Technology

Vitamin D3 is an essential fat soluble vitamin,which is closely related to human health.High efficient synthesis of vitamin D3 is the difficulty,and the key lies in its photochemical reaction process.At present,microfluidic technology can achieve a more uniform photon distribution in the reactor owing to the characteristic size of its reactor only in the scope of micrometer and millimeter.It is a powerful means of strengthening the photochemical process.However,the preparation of vitamin D3 by microfluidic technology is mostly carried out in homogeneous system.The mixing is only driven by molecular diffusion for laminar flow in microchannels,which still leads to the problem of excessive illumination.By introducing the inert gas(nitrogen)into the homogeneous system,we can change the homogeneous system into the heterogeneous system.In gas-liquid segmented flow,recirculation motion will appear in the liquid slug under the interface force and axial velocity gradient,which can effectively enhances the mixing performance of the reaction system.At the same time,the two-step photoisomerization of 7-dehydrocholesterol can be carried out with the aid of microfluidic technology.With the initial concentration of 7-DHC at 5 g/L,the gas-liquid ratio was adjusted to 7/3,and the apparent liquid phase flow rate was adjusted 0.13 m/s feeding.By adjusting different tube lengths,the photochemical conversion rate in the first step was between 70-80%,and that in the second step was about 75%.Compared photochemical reaction with homogeneous system,the photon efficiency is increased about 3 times.As a result,78%conversion of 7-dehydrocholesterol can be achieved giving a 40%yield and 51%selectivity of Previtamin D3.And heating the previtamin D3 at 100℃,35%yield and 45%selectivity of vitamin D3 were obtained,which is higher than the reported in the literature(32%yield).Furthermore,we have increased the initial reactant concentration to 10 g/L and the size of the reaction tube to 1mm,which can produce 15.4g of vitamin D3 per day.This approach enhances productivity about 3-4 times compared with the current technology based vitamin D3 synthesis.