Discrimination of methanol desorption resistance relative to the reaction steps in presence of supercritical n-hexane

•Methanol yields in supercritical n-hexane were much larger than in n-paraffin.•Methanol desorption resistance is gradually reduced with the increasing of n-hexane pressure.•In supercritical n-hexane, a low methanol concentration on the catalyst surface, which is beneficial to methanol synthesis.

To experimentally study the effect of supercritical fluid on product desorption, methanol synthesis from CO/CO2/H2 over the Cu/ZnO/Al2O3 catalyst was conducted in the solvents of liquid paraffin, supercritical n-hexane, and their mixture. For the catalyst size of 0.15 mm at which the internal mass transfer resistance was negligible, methanol yields of 10% in n-paraffin and 18% in supercritical n-hexane were obtained respectively. From the conversion rates of CO2 at different n-hexane pressures, the resistance ratio of CO2 hydrogenation to methanol desorption was obtained to vary from 1:2.85 to 1:0.75 when n-hexane partial pressure was increased from 0 to 4.0 MPa. Furthermore, the resistance ratio of the consecutive steps of water–gas shift reaction (WGSR), CO2 hydrogenation and methanol desorption were then evaluated with respect to CO as the reactant. It shows the resistance ratio of the three steps varies from 0.77:1:2.82 to 0.75:1:0.75 when n-hexane partial pressure was increased from 0 to 4.0 MPa.