Continuous Production of Dimethyl Ether from Methane and Carbon Dioxide

The dry reforming of CH4 (with CO2) at 800 degrees C under 1 MPa to synthesis gas and the synthesis of dimethyl ether (DME) from synthesis gas were combined. A Ni/(MgO)(3)center dot Al2O3 catalyst derived from Mg3Ni3Al2(OH)(16)CO3 center dot xH(2)O hydrotalcite precursor showed a CH4 conversion of 85.4% after 5 min on stream for the dry reforming. The CH4 conversion decreased to 70.1% after 15 h on stream because the carbonaceous deposit formed during the reaction covered the active sites of Ni/(MgO)(3)center dot Al2O3 catalyst. The deactivated Ni/(MgO)(3)center dot Al2O3 catalyst was refreshed by calcining in air at 800 degrees C and subsequently reducing in H-2. A mechanical mixed catalyst containing Cu/(ZnO)(3)center dot Al2O3 and Cs2.5H0.5PW12O40 (denoted as Cu/(ZnO)(3)center dot Al2O3 + Cs2.5) was used for the DME synthesis from syngas. Cu/(ZnO)(3)center dot Al2O3 + Cs2.5 showed a CO conversion of 38.5% and a DME selectivity of 63.8% at 260 degrees C under 1 MPa. A stable activity of Cu/(ZnO)(3)center dot Al2O3 + Cs2.5 had been maintained over 30 h in the DME synthesis. A two-stage process was designed for the DME synthesis from CH4 and CO2. Two fixed-bed reactors filled with Ni/(MgO)(3)center dot Al2O3 were connected in parallel (switching between reaction and refresh) for the CH4 dry reforming. A fixed-bed reactor filled with Cu/(ZnO)(3)center dot Al2O3 + Cs2.5 was connected in series with the two reactors filled with Ni/(MgO)(3)center dot Al2O3 to produce DME. The conversion of CH4 was kept at above 80% and the yield of DME was kept at above 20% after 30 h on stream for the DME synthesis from CH4 and CO2. [GRAPHICS]