Development of a Membrane-Assisted Fluidized Bed Reactor. 2. Experimental Demonstration and Modeling for the Partial Oxidation of Methanol

Abstract

A small laboratory-scale membrane-assisted fluidized bed reactor (MAFBR) was constructed in order to experimentally demonstrate the reactor concept for the partial oxidation of methanol to formaldehyde. Methanol conversion and product selectivities were measured at various overall fluidization velocities, reactor temperatures, methanol and oxygen overall feed concentrations, ratios of gas fed via membranes relative to gas fed via the bottom distributor, and aspect ratios of the fluidized bed. High methanol conversions and high selectivities to formaldehyde were achieved with safe reactor operation (isothermal reactor conditions) at very high methanol inlet concentrations, much higher than currently employed in industrial processes. It was experimentally demonstrated that with distributive feeding of oxygen in a MAFBR the overall formaldehyde yield and throughput could be increased without a pronounced and undesirable conversion of formaldehyde to carbon monoxide. Furthermore, a one-dimensional two-phase phenomenological reactor model has been developed with which the experimentally observed conversion and selectivity as a function of the operating conditions could be well described.

Autothermal Reforming of Methane with Integrated CO2 Capture in a Novel Fluidized Bed Membrane Reactor. Part 2 Comparison of Reactor Configurations

“…In this one-dimensional model the fluidized bed is divided into a number of ideally-mixed reactors (CSTRs), with the same number of CSTRs for the bubble and emulsion phase where the size of the CSTR is related to the local bubble size. Based on this model, a one-dimensional two-phase model for a membrane-assisted fluidised bed reactor has been developed by Deshmukh et al [2,3]. Similar types of models have been used by the groups of Grace and Elnashaie and their co-workers [4][5][6].…”

“…The gas extracted from the emulsion phase is subsequently instantaneously replenished via exchange from the bubble phase (to maintain the emulsion phase at minimum fluidization conditions) (following [2,3]). …”

“…Empirical correlations for the mass transfer coefficients and fluidization properties of the fluidized beds have been taken from [2,3] and are summarized in Table 3. Although these correlations were originally obtained for beds without internals, it is assumed that the fluidized bed reactor with membranes can be reasonably well described with these equations.…”

“…By means of simulations and experimental validation, Deshmukh and co-workers have shown that the axial gas phase back-mixing in the emulsion phase is strongly reduced because of the presence of and permeation through the membranes. Typically, insertion of the membranes enhances bubble break-up, resulting in improved bubble-to-emulsion phase mass transfer [2,3].…”

Alternative Reaction Engineering Concepts in Partial Oxidations on Oxidic Catalysts

“…The alternative device, a distributive feeding of oxygen into a fluidised bed via inert membranes, has recently been investigated in the partial oxidation of methanol (86). The experimental results are interpreted with the aid of a two-phase model accounting for permeation through the membranes.…”