| Sesame and walnut are one of the main oilseed crops in China.They are widely planted in China,rich in nutrients,and play an important role in food,medical and health care.In this paper,the author designed a new continuous subcritical CO2 extraction and isobaric or depressurization separation process flow,based on which,the optimal process conditions of sesame and walnut in the new extraction process were explored,and the response surface method was used to further optimize them,and then the subcritical CO2 extraction and isobaric or depressurization separation extraction kinetic model under the optimal process conditions was established,Finally,the energy consumption in the new process flow is studied and analyzed based on the enthalpy change principle.First,aiming at the defects of the current supercritical or subcritical fluid extraction process,a new method of continuous extraction of subcritical fluid with stepwise pressure rise and fall based on valve switching is designed.The continuous extraction of the system is realized by controlling the opening and closing of the corresponding valve and the pressure self-balance of the extractor;on the basis of the continuous extraction subsystem and in cooperation with other subsystems,a process flow of continuous subcritical CO2 extraction and isobaric or depressurization separation,which can be used as a reference for industrial production,has been realized.The new process has the obvious advantages of low energy consumption and operation cost,continuous extraction,high degree of automation,and provides reliable support for the industrial promotion of the new technology.Then,the single-factor method was used to carry out the process test of subcritical CO2 extraction and isobaric or depressurization separation of sesame oil and walnut oil,and the effects of extraction pressure,separation temperature and the motor frequency of CO2 circulating pump which reflects the CO2 flow index on the extraction rate of the two oils were investigated respectively.The results showed that the optimal process conditions of subcritical fluid extraction and isobaric or depressurization separation of sesame oil were:extraction pressure 23 MPa,separation temperature 65℃,CO2 circulating pump motor frequency 15 Hz;the optimum process conditions for subcritical fluid extraction and isobaric or depressurization separation of walnut oil are as follows:extraction pressure 23MPa.separation temperature 65℃,CO2 circulating pump motor frequency 12.5Hz,and the feasibility of the new process of subcritical CO2 extraction and isobaric separation is verified by experiments.On the basis of single-factor experiments,the Box-behnken response surface was further used to optimize the extraction process conditions of walnut oil.The results showed that the order of the influence of each factor on the extraction rate was:separation temperature>extraction pressure>motor frequency of CO2 circulating pump.The validation experiment showed that the prediction results were reliable.Finally,the quadratic multiple regression equation of walnut oil extraction rate versus extraction pressure,separation temperature and motor frequency of CO2 circulating pump was obtained,the comprehensive effects of three factors and their interactions on the extraction rate of walnut oil were described in detail.Based on the extraction rate-time curve of sesame and walnut under the optimal process conditions,the extraction kinetics model was established.The results showed that both the empirical model and the differential mass conservation model could better reflect and predict the relationship between the extraction rate and time under a fixed process condition,but the relevant parameters in the empirical model did not reflect the change of the extraction mechanism,the relevant parameters in the differential mass conservation model can reflect the change of the extraction mechanism to a certain extent.By analyzing the cyclic change process of the extraction fluid in the process of subcritical or supercritical CO2 extraction using two different separation methods,namely isobaric separation and depressurization separation,the low energy consumption advantages of subcritical CO2 extraction and isobaric or depressurization separation technologies are analyzed and verified fundamentally and in theory;based on the principle of enthalpy change,the input of external energy in the whole extraction process is analyzed,the relationship between extraction energy consumption and enthalpy value is calculated according to the enthalpy change at each key node,and the energy consumption ratio between the two different separation methods of subcritical CO2 extraction,and between the subcritical CO2 extraction and isobaric or depressurization separation and the traditional supercritical CO2 extraction and depressurization separation is calculated and compared in detail,further explain the significant advantages of the new flow of subcritical CO2 extraction and isobaric or depressurization separation technologies in energy consumption. |
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