Separation And Purification Process Of Green Refrigerant R290 In A Structured Fixed Bed

Environmental issues such as ozone depletion and global climate changes have become increasingly worse since 1990 s, and slowing down the ozone depletion as well as the greenhouse effect is one of the important environmental protection tasks. A large number of refrigerants available in the market contain halogen, which can contribute a lot to the ozone depletion and/or global warming. Recently, seeking halogen-free refrigerants has attracted much attention, and one of ideal alternatives is hydrocarbons. R290(propane of high purity, normally the volume fraction is higher than 99.5%), is not only environmentally-friendly but also has higher cooling efficiency. Thus, the method for refining green R290 refrigerant by using relatively inexpensive liquefied petroleum gas(LPG) as raw materials is a front subject with both theoretical significance and huge potential economic benefits. Fixed bed adsorption has been widely used for separation and purification of light hydrocarbons due to its easy operation and large capacity. However, it also has some drawbacks such as large pressure drop and low efficiency of mass transfer. Therefore, the development and application of novel materials, which can lower bed resistance and enhance mass transfer rate, have been recognized as an important research with engineering value. In this paper, microfibrous entrapped activated carbon was prepared and characterized, and the adsorption behavior of hydrocarbon components in LPG as well as 104 ppm methane in air in both traditional fixed bed and structured fixed bed based on microfibrous entrapped activated carbon composites were investigated, exploring the separation and purification process of green refrigerant R290 in the structured fixed bed.Firstly, the breakthrough curves of methane, ethane, propane, isobutane and nbutane from LPG in fixed bed filled separately by the zeolite 4A, 5A, 13 X, NaY and granular activated carbon were investigated. Adsorption dynamics of propane, isobutane and n-butane from LPG through granular activated carbon fixed bed were studied. Yoon-Nelson model and Length of unused bed(LUB) equation were used to analyze the breakthrough curves. The results show that methane and ethane could not be efficiently separated and removed from LPG in all adsorbers; all adsorbents except 5A zeolite are able to separate isobutane and n-butane from LPG, among which fixed bed packed with granular activated carbon show the largest adsorption capacity and the least LUB value; All correlation coefficients in fitted equations exceeded 0.98, indicating a good agreement with the experimental data.Secondly, microfibrous entrapped activated carbon composites were prepared by wet layup papermaking and sintering process, using stainless steel fibers, coniferous wood fibers and activated carbon particles(150-200 μm) as raw materials. Prepared composites were characterized by SEM and specific surface area and porosity analyzer. The structured fixed bed was designed by filling microfibrous entrapped activated carbon composites at the outlet of granular activated carbon fixed bed, and the adsorption dynamics of propane, isobutane and n-butane from LPG were studied. YoonNelson model and LUB equation were used to analyze the breakthrough curves. The results show that sintered-locked composites have specific three dimensional network with large voidage, entrapping granular activated carbon very well; parameters of pore structure of activated carbon changed slightly after being sintered. Compared with traditional fixed bed, the slope of breakthrough curves in structured fix bed was bigger, and the larger filling ratio of microfibrous entrapped activated carbon, the greater slope of the breakthrough curves. Breakthrough curves of the same adsorbate at different bed heights of structured fixed bed exhibited similar "S" shape; Raising flow rate can also increase the slope of breakthrough curves of propane, isobutane and n-butane adsorption in a structured fixed bed.; Yoon-Nelson model can be used to predict adsorption rate constant KYN and 50% breakthrough time t0.5 of propane, isobutane and n-butane adsorption in the structured fixed bed.Finally, adsorption dynamics of 104 ppm methane in air in both activated carbon particles fixed bed and structured fixed bed were investigated. Yoon-Nelson model and LUB equation were used to analyze breakthrough curves. The results show that the influence of bed height and flow rate for methane adsorption behavior is similar to that for multi-components alkane adsorption from LPG. Structured fixed bed has enhanced mass transfer characteristics, with 19%-32% bed utilization increase. Yoon-Nelson model can be also used to predict adsorption rate constant KYN and 50% breakthrough time t0.5 of fixed bed adsorption of 104 ppm methane in air in the structured fixed bed.