Application of a Microreactor in the Oxidative Dehydrogenation of Propane to Propylene on Calcium Hydroxyapatite and Magnesium ortho-Vanadate Doped and Undoped with Palladium

Abstract

IntroductionPropylene mainly obtained by naphtha cracking is an important raw material for the petrochemical industry. Since the demand of propylene derivatives has recently exceeded that of ethylene, a lack of propylene is a concern for the middle to long term (Suwa, 2004). Therefore, the development of another technology for the production of propylene is desired. The oxidative dehydrogenation of propane on solid catalysts is one of the most attractive reactions for the production of propylene. In our laboratory, calcium hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 ; CaHAp) and palladium-doped magnesium ortho-vanadate (Mg 3 V 2 O 8 doped with Pd; PdMgVO) have shown relatively greater catalytic activity for the oxidative dehydrogenation of propane to propylene, while magnesium ortho-vanadate (MgVO) itself has shown rather low activity (Sugiyama et al., 2008a(Sugiyama et al., , 2008b. Although Pd-MgVO in particular has shown great catalytic activity during the oxidative dehydrogenation of propane, a deep oxidation of propylene to CO and CO 2 (COx) could not be avoided when using a typical fixed-bed continuous-flow reactor. Therefore, a different reactor system for the suppression of deep oxidation had to be developed.In the present study, a microreactor under steadystate operation was employed to suppress the deep oxidation of propylene to COx as an enhancement of the selectivity to propylene. As a catalyst, CaHAp, Pd-MgVO and MgVO were employed. We also examined the effect of unsteady-state operation, defined by heating (on) and cooling (off) of the power supply, on oxidative dehydrogenation. Furthermore, the catalytic activity of the microreactor was compared with a typical fixed-bed contin- A microreactor was employed for the oxidative dehydrogenation of propane to propylene in order to suppress a deep oxidation of the resultant propylene to CO and CO 2 . Magnesium ortho-vanadate, doped and undoped with palladium, and calcium hydroxyapatite, were used as catalysts while the reaction temperature was controlled by steady-and unsteady-state conditions. The enhancement of the selectivity to propylene was the most advantageous effect from using the microreactor, and it occurred when calcium hydroxyapatite was used under an unsteady-state. For example, the selectivity to propylene was 0 and 73.0% using a fixed-bed continuous-flow reactor and the microreactor, respectively, under almost identical propane conversion of 3.1 and 3.2%, respectively. The advantageous effect was also achieved, although to a lesser degree, when magnesium ortho-vanadate was used undoped with palladium under both steady-and unsteady-state conditions. However these advantageous effects of the microreactor were not observed with magnesium ortho-vanadate doped with palladium. With regard to the selectivity to propylene, the redox nature of the catalysts seemed to influence the performance of the microreactor. Application of a Microreactor in the Oxidative 575

Excess CO2 Reductions during CH3COOH Formation from CH4 and CO2 under Periodic Operation: Downhill Side Reactions in an Uphill Target Reaction under Unsteady Conditions

“…In order to address such thermodynamic issues, it has been reported that periodic operation [12][13][14][16][17][18][19][20][21][22][23][24][25] allowing non-equilibrium conditions can overcome the thermodynamic limitations. [12][13][14][16][17][18][19][20] Periodic operation leading to unsteady conditions, which is out of equilibrium, allows to break a target reaction into plural steps (i. e., reaction splitting) [26] with a solo reactor, and thereby the thermodynamic requirement for the target reaction will be split into multiple steps.…”