Dense and thin 13X membranes on porous α-Al2O3 tubes: preparation, structure and deep purification of oxygenated compounds from gaseous olefin flow

Abstract

The low contact efficiency, large mass transfer resistance and high operational cost of traditional 13X molecular sieve particle adsorbents (MSPs) have greatly limited their application in deep purification of trace oxygenated compounds from gaseous olefins. Herein, we successfully fabricated dense and thin 13X molecular sieve membranes on a porous α-Al₂O₃ tube (MSCMs) by a combination of 3-aminopropyl triethoxy silane (APTES) surface modification and vacuum pre-coating sol technology for purifying the above impurities. By a solid–solution transformation process, 13X molecular sieve membranes on MSCMs that were continuous and integral without any cracks, pinholes or other defects, and mainly composed of 1–1.5 μm regular 13X crystals with a thickness of 5–6 μm have been achieved. The purification performance of the MSPs, non-APTES functionalized MSCMs (nMSCMs) and MSCMs was evaluated by dynamic adsorption of N₂ or C₂H₄ feed flow containing dimethyl ether, methanol and propanal impurities at room temperature. The results demonstrated that both the nMSCMs and MSCMs could deeply purify the trace amounts of the three oxygenated compounds to below 1 × 10⁻⁶ (mol mol⁻¹) from gaseous olefins at an initial concentration of 20 × 10⁻⁶ (mol mol⁻¹), exhibiting much more excellent purification performance than that of MSPs. In particular, the breakthrough times of MSCMs for dimethyl ether, methanol and propanal were 7 h, 32 h and 51 h in a N₂ system, and 12.1 h, 53 h and 90 h in a C₂H₄ system. The cumulative adsorption amounts of MSCMs for dimethyl ether, methanol and propanal were 12.108 mg g⁻¹, 35.812 mg g⁻¹ and 103.129 mg g⁻¹ in a N₂ system, and 25.88 mg g⁻¹, 94.19 mg g⁻¹ and 256.26 mg g⁻¹ in a C₂H₄ system, respectively. The regeneration experiment also indicated that the MSCMs had a more stable structure and a longer lifetime. The excellent purification performance of MSCMs could be attributed to the continuous 13X molecular sieve layers without non-adsorption interfacial voids. Hence, the MSCMs have great potential for future industrial application of trace oxygenated compound removal from gaseous olefins.