Preparation Of UVB-Band Luminescent Materials And Their Application In The Synthesis Of Vitamin D₃ By Microfluidic Technology

Vitamin D3 has important physiological functions,mainly regulating calcium and phosphorus metabolism in the body to maintain the stability of calcium and phosphorus in the blood,and is an essential endogenous synthetic hormone for the human body.At present,the market demand for vitamin D3 in China is large,but its production efficiency is low and energy consumption is high.Therefore,it is very important to develop an efficient and low energy consumption production process for vitamin D3.Firstly,this paper presents a technique to prepare controlled photoluminescent substrates to facilitate the photochemical microfluidic synthesis of vitamin D3.The method of preparing the photoluminescent substrates by dip-coating was optimized and theirs emssion behavior were systematically investigated.The substrates were successfully used to enhance the UVB emission of an 8 W low-pressure mercury lamp,which increased its emission intensity by about 11 times.Using this new light source,the productivity of a single photochemical microreactor set was increased to 1.83 kg·a-1,which is 42%higher than that of a conventional light source(100 W medium-pressure mercury lamp),and the production energy consumption was reduced by not using any cooling equipment.The whole process is simple and feasible,and has great potential to replace the conventional medium and high pressure mercury lamp for UVB radiation photochemical reaction.Secondly,the production process of vitamin D3 synthesis by microfluidic technology was systematically studied.It was found experimentally that the reaction was limited by mass transfer.We enhanced the internal mixing of the reaction system by introducing nitrogen,in an experimental manner with gas-liquid slug flow,which enhanced mass transfer,reduced the yield of by-products and increased the yield of vitamin D3.The photochemical synthesis reaction of vitamin D3 was carried out in a microchannel with an inner diameter of 0.5 mm,and the gas-liquid ratio was adjusted to 6/4.Controlled photochemical first step residence time of 60 s,photochemical second step residence time of 120 s,fed at a flow rate of 0.05 m/s.When the concentration of 7-dehydrocholesterol was 5 g/L,the yield of final photochemical product previtamin D3 was 43.8%,the selectivity of previtamin D3 was 54%,and the yield of side-products as 15%.Finally,the thermochemistry process was explored.When the thermochemical temperature is 110℃,it can ensure a faster reaction rate and avoid side reactions.The final vitamin D3 yield was 38%,and the selectivity was 47%.