On the simultaneous effect of temperature, pressure, water content and space–time on acrylic acid production from propane

An attractive route for producing acrylic acid is the direct partial oxidation of propane for which, MoVTeNb-based mixed oxides have exhibited promising results. In this work, formal design of experiments (DOE) is applied to investigate the simultaneous impact of four key independent reaction variables (factors): temperature (613–693 K), pressure (4–55 kPa–g), space–time (55–167 gcath/mole) and water content in the feed (0–20 mole%) on the performance of a MoVTeNb-based catalyst to produce acrylic acid from propane. Catalytic experiments are performed in a lab-scale fixed-bed reactor feeding a gaseous mixture containing propane, oxygen, nitrogen and water. DOEs results are analyzed by combining graphical (main effects and interaction plots) and statistical tools (ANOVA, regression analysis as well as surface responses). Most of the factors accounted for in the DOEs have a linear effect on propane conversion and a quadratic effect on acrylic acid selectivity; binary interaction between factors is common for acrylic acid selectivity. Water addition to the reaction mixture is essential to improve acrylic acid selectivity. Regression models predict that adding 18 mole% of water to the feed maximizes acrylic acid selectivity when operating at moderate levels of temperature (648 K) and pressure (10 kPa-g). Also, operation at high severity in pressure, medium severity in space–time and low-medium severity in temperature increases further acrylic acid selectivity.