The catalytic oxidation of n-butane to maleic anhydride using a membrane reactor
Catalytic oxidation of n-butane is important in an attempt towards developing economical and environmentally friendly processes for production of maleic anhydride. Methods of preparation of both the vanadium-phosphorus-oxides (VPO) catalyst and an inorganic composite membrane as well as the performance of the membrane obtained have been investigated in this work. The procedure used in the preparation of vanadium-phosphorus-oxides (VPO) catalyst was similar to that described by Katsumoto and Marquis (1979), while a dip coating method was used for preparation of a silica coated y-A^Os membrane from the outside, and the membrane prepared then was tested for permeance using nitrogen and air. The kinetics of the selective oxidation of n-butane to maleic anhydride has been studied over vanadium-phosphorus-oxides (VPO) catalyst in a differential glass reactor in the temperature range of 380 - 480°C and at atmospheric pressure. Apart from maleic anhydride (MA), the other detectable products were carbon monoxide (CO), carbon dioxide (CO2), and air (HhO). Kinetic measurements demonstrated the production of maleic anhydride, carbon monoxide, and carbon dioxide as initial products of the reaction at low n-butane conversion. Under conditions of a large excess of oxygen, the reaction model was represented according to a scheme of three parallel formation reactions. The activation energies for maleic anhydride (MA), carbon monoxide (CO), and carbon dioxide (CO2) production are 61.1 kJ/gmol, 56.1 kJ/gmol, and 70.9 kJ/gmol, respectively. These values of the activation energies are in the same range as those obtained from previous differential reactor studies. The oxidation of n-butane to maleic anhydride also has been compared by using fixedbed and membrane reactors with the same VPO catalyst. The effects of operating conditions on the conversion of n-butane, the selectivity to maleic anhydride, and the yield of maleic anhydride have been studied in detail. A simulation study on the use of fixed-bed and membrane reactors for oxidation of n-butane to maleic anhydride has also been undertaken. The results of a mathematical simulation study were compared with the experimental results. The membrane reactor offers several advantages over the fixed-bed reactor for selective oxidation of n-butane to maleic anhydride. The membrane reactor provides a wider operating range particularly with respect to inlet gas composition. Furthermore, they are inherently safer since n-butane and oxygen feeds can be separated by the membrane. The higher butane concentrations and controlled addition of oxygen along the reactor length by means of a membrane lead to higher product rates. A comparative study of butane oxidation to maleic anhydride in conventional fixed-bed and a membrane reactor show that using a membrane reactor gives a better selectivity and yield of maleic anhydride than the conventional fixed-bed reactor. From the simulation study, the mathematical models for both the fixed-bed and membrane reactors are in good agreement with the experimental results, except for the mathematical model for the fixed-bed reactor when considering the variation of the oxygen/n-butane ratio. For the membrane reactor, both feed n-butane concentration and oxygen/butane ratio are shown to be not sensitive parameters for the mathematical model, while temperature is a key parameter.