| As one of the necessities of our life,the diversity and quality of fruits and vegetables have been paid more and more attention.Because of the influence of natural conditions,seasonal and regional characteristics of fruits and vegetables are very important,it can't meet people's needs most of the time.In order to maintain the freshness,as well as excellent food quality of fruits and vegetables,researchers from domestic and international begin to study the preservation of fruits and vegetables.In our markets,the traditional physical methods are still widely used,but they can't offer good preservation effect.As a new and efficient method of preservation,controlled atmosphere storage technology has a great development and popularization value.The principle of controlled atmosphere equipment which is widely used in the market is pressure swing adsorption,but there are too many valves in the equipment and they will make a lot of noise when it runs.If we use membrane equipment to separate gas,we can solve these two problems effectively.What's more,it is necessary to use this kind of technology because it will use less energy,take less land and on the other hand,it is easy to install.The purpose of this project is to design a set of controlled atmosphere storage for the preservation of mango using hollow fiber membrane as the adjustment device.In order to get the optimal parameters of equipment operation,we designed a mathematical model for membrane gas transfer process of equilibrium state and non-equilibrium state,the distribution of gas pressure in the membrane was also calculated.According to the calculation results of the three parts,the optimum parameters of equipment operation and the membrane area of the required hollow fiber membrane were obtained.Through the study on coating process of polyethersulfone(PES)hollow fiber membrane,we used Sylgard 184 silicone rubber as coating material and decided the coating conditions for higher gas flux and better gas separation coefficient:the coating concentration is 3%,the coating time is 5s.We also analyzed the effect of PES support membrane,coating solution concentration and coating time on the results of gas separation.Then the small scale coating experiments were enlarged and we designed and machined the equipment used for large-scale coating.We also explored the preparation conditions for making large quantities of silicone rubber(PDMS),and we used it to carry out large-scale coating experiment.At last,we obtained the PES/PDMS hollow fiber composite membrane:separation coefficient of O2/N2 is beyond 2,separation coefficient of CO2/N2 is beyond 10,and the permeance of CO2 is between 450 and 600 GPU.Finally,we used the prepared PES/PDMS composite membrane to make a hollow fiber membrane module,analyzed the problems during the process and made solutions to solve these problems.Gas separation performance test was used to get the parameters of the module,and the result is:selectivity of O2/N2 is 1.82,selectivity of CO2/N2 is 9.29,which can reach about 88%separation effect of the single fiber.Gas flux of CO2 can obtain 64%coating effect of the single fiber.The results show that the hollow fiber membrane module prepared by our method is in accordance with the requirements of mango controlled atmosphere storage. |
PDF Full Text Request