Research On MEMS Micro Chromatography Column For Separating Light Hydrocarbons

With the increasing demand for real-time online testing in the fields of energy survey,drug separation,environmental testing,etc.,traditional commercial gas chromatography（GC）are gradually unable to meet the above-mentioned online needs due to factors such as high energy consumption,large volume,and long testing time.Therefore,real-time detection,short-detection time,low-energy consumption,and portable micro gas chromatography system have become one of the important researches.Aiming at the application in energy survey and the detection of hydrocarbon components in natural gas,this paper studies a series of micro GC columns used in the rapid separation system of light hydrocarbons with high resolution.Among them,the two main principles for the separation of light hydrocarbons are explored:one is based on that alumina series were used to separate light hydrocarbons by the instantaneous dipole moment when alkanes are separated;another is based on that different molecular diameters of light hydrocarbons.This article mainly includes the following two contents:（1）On the basis of MEMS technology,the main structure of the micro GC column is processed by semiconductor technology,then the aluminum sol with the gel core of Al₂O₃·n H₂O is coated by physical method on the inner of the micro GC column.After removing the moisture in the aluminum sol at high temperature,the separation test of light hydrocarbons and heavy hydrocarbons is carried out.The results show that the micro GC column can effectively complete the separation of light hydrocarbons.The separation of resolution between methane and ethane is improved by 225%compared with previous studies^[45].The physical coating of aluminum sol with a high viscosity always has certain limitations in stability and success rate of the column fabrication.Therefore,based on the condensation reaction of silanol groups,the hydrolysis and condensation of Tetraethyl Orthosilicate was used to connect the highly adsorbableγ-Al₂O₃with the silanol groups inside the micro GC column,forming a chemical bond is conducive to thermal stability.In the separation of alkanes C1-C6,the results show that the six components of C1-C6 can be separated.（2）The separation principle of molecular sieve is to create a suitable pore size,and separate molecules with different molecular diameters at different rates of entering the pore size.Firstly,an metal organic frameworks（MOFs）ZIF-8 with a window size of 0.34 nm was synthesized by hydrothermal method using zinc nitrate and dimethylimidazole as raw materials and constructed on the inner of the micro GC column as the stationary phase by dynamic coating.By testing the separation efficiency of alkanes C1-C4 at different flow rates,the resolution at the optimal flow rate is 2.23,which meets the requirements of the Chinese Pharmacopoeia for the resolution of substances qualitative and quantitative analysis to be greater than 1.5.However,for propane and butane,the molecular diameter is larger than the window size of the stationary phase,resulting in low peaks and low column efficiency.Therefore,a UIO-66 with a window size of 0.84 nm was added to form a combined two windows-molecular sieve with ZIF-8.The mixed components of alkanes C1-C6are separated as a whole and the results show that the micro GC column coated with this mixed stationary phase can baseline separation of alkanes C1-C6.The resolution of methane and ethane has reached 3.07,which is increased by 174%^[45];In addition,the peak height and separation efficiency of propane and butane have been improved under the temperature program,and the theoretical plate number of butanes has reached 10408 plates.