Search

Purposes Propylene is an important olefin raw material, and the removal of propane impurities in it is very important in actual production. Metal-organic frameworks (MOFs) have great prospects for the separation and purification of propane/propylene. Among them, propane-selective adsorbents can be used to obtain high-purity propylene products in one step, which has extremely high industrial value. MIL-126(Fe) has great potential for preferential adsorption of alkanes becaused of the abundant low-polarity benzene rings that provide dense electronegativity binding sites. Methods MIL-126(Fe) was synthesized through solvothermal method. Findings The stability, C3H8/C3H6 adsorption, and separation properties of MIL-126(Fe) were studied. The results showed that MIL-126(Fe) had excellent stability. The adsorption capacity of C3H8 at 298 K and 1 bar was 185.37 cm3/g, which was higher than that of most propane-selective adsorption MOFs. The IAST selectivity for C3H8/C3H6 mixture was 1.44 at 0.1 bar and 1.23 at 1 bar. It is showed that MIL-126(Fe) had reverse adsorption on propane-propylene mixture, and its propylene recovery potential was 19.71 cm3/g, which was close to the highest level of domestic and international researches. Conclusions The results of gas breakthrough experiments showed that MIL-126(Fe) has great potential for industrial application in one-step production of high-purity propylene.

The arc stability and droplet transfer phenomenon in welding process were analyzed with the help of a high-speed camera system, and the correlation mechanism was explored of arc voltage-arc physical phenomenon-weld morphology and microstructure-mechanical properties of joints in MIG welding of 4 mm-thick 304 stainless steel. The results show that when the voltage is 20.6 V, the welding arc heat distribution is uniform, and the droplet transfer form is a stable and continuous short-circuit transfer. The macroscopic shape of weld is good, and the microstructure is vermicular ferrite. The welded joint has high strength and plasticity. When the voltage drops to 16.6 V, the arc length becomes shorter, and the droplet has been short-circuited before it grows up. Heat conduction is slow, and undercut defects and grooves appear on the upper surface of weld. Part of lathy ferrite appears in the microstructure of weld. When the voltage increases to 24.6 V, the arc energy diverges severely, and the stability and continuity of droplet transfer decrease. Irregular fish scales appear on the surface of weld. Insufficient penetration appears on the back of weld. More lathy ferrite is formed in the lower layer of weld. When the voltage is lower and higher, the strength and plasticity of welded joint are reduced.