Modeling of a Fluidized Bed Membrane Reactor for the Steam Reforming of Methane:  Advantages of Oxygen Addition for Favorable Hydrogen Production

Abstract

A bubbling fluidized bed membrane reactor for steam reforming of methane is mathematically investigated, with the permselective Pd membranes removing hydrogen from the reaction system to enhance the methane conversion. Oxygen fed into the reaction system can decrease the endothermicity of the overall reaction by the combustion of methane, thereby reducing the need of external firing. Operation at low feed steam−carbon ratios is also possible with the steam required for the reforming reaction being provided as a product from the combustion reactions, although problems related to coking also need to be addressed at very low ones. A drop in the reactor temperature at the inlet of the reactor itself due to the high endothermicity and fast kinetics of the steam reforming reactions does not strongly support the idea of a higher feed temperature favoring the reaction conversion. Thereafter, in situ generation of heat by the combustion reactions is a more effective means to give better reactor performance, and a higher feed temperature can be used to supplement this performance. However, since higher oxygen−methane ratios also tend to consume more of the methane itself, this cannot be increased much and an optimum value exists with respect to the favorable production of pure hydrogen from the reactor permeate side.

Membrane assisted fluidized bed reactors: Potentials and hurdles

“…Ethane dehydrogenation -Propane dehydrogenation -Cyclohexane dehydrogenation -Ethylbenzene dehydrogenation Abdalla and Elnashaie, 1995 Water-gas shift reaction -Methane steam reforming Abba et al, 2003;Adris et al, 1991Adris et al, , 1994aAdris and Grace, 1997;Chen et al, 2003a,b,c;Elnashaie, 2004a,b, 2005a,b,c;Gobina, 2000;Grace et al, 2001;Patil et al, 2005;Prasad and Elnashaie, 2002;Rakib and Alhumaizi, 2005 Methane partial oxidation to synthesis gas Mleczko et al, 1996;Ostrowski et al, 1998aOstrowski et al, ,b, 1999 Selectivity enhancement Oxidative coupling of methane -Partial oxidation of ethane to ethene Ahchieva et al, 2005 Ethylene epoxidation -Partial oxidation of propane to propene Alonso et al, 2005 Partial oxidation of propane to acrolein -Partial oxidation of butane to maleic anhydride Alonso et al, 2001 Partial oxidation of butene to methacrolene -Partial oxidation of methanol to formaldehyde Deshmukh et al, 2005a,b,c CO hydrogenation to hydrocarbons -Oxidative dehydrogenation of ethylbenzene - 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 Year Number of publications Our paper is based on a database search for the years 1965-2005 with the software SciFinder Scholar (2004) and with keywords "Fluidized beds and membranes". The obtained number of publications per year is plotted for the past 15 years in Fig.…”

“…The use of hydrogen separation membranes along with lime resulted in the complete conversion of methane with a high yield of hydrogen. Recently, Rakib and Alhumaizi (2005) discussed the advantages of oxygen addition for hydrogen production via the steam reforming of methane. Abashar (2004) used modelling tools to simulate the coupling of steam and dry (CO 2 ) reforming of methane in a catalytic fluidized bed membrane reactor.…”

“…It was concluded that with appropriate combinations of key operating parameters such as the methane-to-oxygen ratio, feed temperature and reactor temperature, the reactor can be operated autothermally. Recently, Rakib and Alhumaizi (2005) mathematically investigated a bubbling fluidized bed membrane reactor for autothermal steam reforming of methane with permselective Pd membranes. The oxygen fed into the reaction system could decrease the endothermicity of the overall reaction by combustion of methane, thereby reducing the need of external firing.…”

“…The model was shown to give excellent agreement with their experimental data. This model was later extended by Islam (1997), Roy (1998) and Rakib and Alhumaizi (2005) for autothermal steam reforming where oxygen was introduced to the fluidized bed with perm-selective membranes and to account for the significantly enhanced permeation of the hydrogen through the coated and more permeable membrane tubes. Subsequently, Grace et al (2001) used the equilibrium approach to model the MAFBR for steam reforming of methane with oxygen addition.…”

Simulation of autothermal reforming in a staged‐separation membrane reactor for pure hydrogen production

“…One option is to employ fluidized-beds to augment mass and heat transfer (Chen, 2002;Abba et al, 2003;Chen and Elnashaie, 2004;Boyd et al, 2005;Grace et al, 2005;Patil et al, 2005Patil et al, , 2006Patil et al, , 2007Rakib and Alhumaizi, 2005;Abashar et al, 2007;Deshmukh et al, 2007). Another is to introduce membrane separation.…”